Metal particles, method for preparing the same, and use thereof

Abstract

The present invention provides metal particles having holes distributed in the center, high sphericity, low shrinkage ratio, and small crystal grains inside the particles. The method for preparing the metal particles includes introducing spherical or nearly spherical metal seed crystals to prepare a polyol-seed crystal system, thereby enabling the particle size and sphericity of the metal particles to be controlled during the reduction process, and quickly and stably reducing the metal particles in a metal oxide or metal salt solution containing a metal source in the seed crystals, ensuring that the morphology of the formed metal particles is spherical or nearly spherical, and the particle size of the metal particles is adjusted by the number and size of the spherical nano metal seed crystals introduced. The metal particles are used in conductive adhesives for solar cells or semiconductors.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and specifically relates to metal particles, a method for preparing the same, and uses thereof.

Background Art

[0002] Compositions or dispersions containing fine metal particles are useful in fields such as flat panel displays (FPDs), solar cells, wiring formation for radio frequency identification technology (RFID), embedded wiring into fine channels and vias, coloring materials for painting cars and ships, medical, diagnostic, and biochemical substance adsorption carriers in the biotechnology field, catalysts, flexible printed circuits, capacitors, and the like. With the development of current and future optoelectronic technology industries, electronic devices are becoming miniaturized and have higher performance, which has led to higher requirements for performance indicators such as the sphericity, dispersibility, and particle size of fine metal nanoparticles.

[0003] In the prior art, methods for preparing metal particles include physical methods and chemical methods. Physical methods include atomization methods, vapor evaporation methods, grinding methods, etc., and chemical methods mainly include sol-gel methods, liquid phase reduction methods, physical vapor deposition (PVD) methods, hydrothermal methods, chemical vapor deposition (CVD) methods, precipitation methods, plasma methods, etc. Since physical methods have problems such as high cost and low yield, currently, like the method for preparing metal particles in Patent Document 1: Chinese Patent CN104128616A, a chemical liquid phase reduction method, that is, a method of reducing a salt solution or oxide containing a metal to a metal by a chemical reaction, is widely used.

[0004] However, although the metal particles required in current production are generally spherical, the proportion of particles of the desired shape in the total number of particles in the sample is very small. Among the metal particles, there are many particles of other shapes such as sheet, hexagonal, triangular, cubic shapes, etc. There are many problems existing therein, and there are also samples with large particle sizes and wide size distributions, and their applications in the microelectronics field are limited.

[0005] Prior art patent document 2: Chinese Patent CN105436517B discloses a preparation method for inductively producing metal powder using nano-seed crystals. However, even when adding metal seed crystals, the surface roughness of the metal powder is large, the irregularity is large, and metal powder with an angular polygonal appearance is obtained.

Prior art documents

Patent documents

[0006]

Patent document 1

Patent document 2

Summary of the invention

Problems to be solved by the invention

[0007] The object of the present invention is to overcome the drawbacks of the prior art and provide metal particles, a manufacturing method thereof, and applications.

Means for solving the problems

[0008] To achieve the above object, the present invention adopts the following technical means.

[0009] In a first aspect, the present invention provides metal particles, wherein holes are distributed at the center inside the metal particles, and the distribution pattern of the holes at the center inside the metal particles is form a, which is a plurality of holes uniformly distributed at the center of the metal particles, form b, which is a plurality of holes concentratedly distributed at the center of the metal particles, form c, which is a plurality of holes dispersedly distributed at the center of the metal particles, and form d, which is an annular hole surrounding the center of the metal particles, and provides metal particles that are one of these forms.

[0010] As a preferred embodiment of the method for preparing the metal particles of the present invention, the pore diameter of the pores is at least one of the following types: Type a: The pore diameter of the pores uniformly distributed around the center of the metal particles is 0.1 nm to 50 nm, preferably 5 nm to 50 nm, and more preferably 9 nm to 30 nm. Type b: The pore diameter of the pores concentrated around the center of the metal particles is 0.1 nm to 80 nm, preferably 2 nm to 80 nm, and more preferably 2.5 nm to 60 nm. Type c: The pore diameter of the pores dispersed around the center of the metal particles is 1 nm to 60 nm, preferably 10 nm to 60 nm, and more preferably 14 nm to 45 nm. Type d: The diameter of the annular pores is not more than half of the diameter of the metal particles, preferably 0.1 μm to 1 μm, and more preferably 0.2 μm to 0.5 μm.

[0011] As a preferred embodiment of the metal particles of the present invention, the metal is at least one of gold, silver, copper, and nickel. As a preferred embodiment of the metal particles of the present invention, the grain size of the crystal grains of the metal particles is 10 nm to 80 nm, and the sphericity of the metal particles is 0.6 to 1, preferably 0.8 to 0.95.

[0012] In a second aspect, the present invention provides Step (1) of dispersing spherical or substantially spherical nanometal species crystals in a polyol mixture to prepare a polyol - seed crystal system; Step (2) of adding the polyol - seed crystal system to a dispersion liquid, and then adding an oxidizing liquid and a reducing liquid containing a metal oxide or a metal salt containing a metal source in the seed crystals, and stirring to react; Step (3) of adding a flocculant, precipitating and separating to obtain metal particles, and provides a method for preparing metal particles.

[0013] The present invention uses spherical or substantially spherical nano metal particles as seed crystals, and disperses the spherical or substantially spherical nano metal seed crystals in a polyol, that is, a polyol-seed crystal system that coats the seed crystals with the polyol and disperses the seed crystals is adopted. After adding the polyol-seed crystal system to the dispersion liquid, alcohol-water substitution occurs, and a uniform nanobubble coating layer composed of spherical and / or elliptical nanobubbles is formed on the surface of the seed crystals. When an oxidizing solution and a reducing solution are added and reacted, crystal grains are reductively precipitated on the surface by the induction of the seed crystals, the nanobubbles are compressed and the nanobubbles burst, generating an extremely strong shock wave, causing lattice rupture during the growth process of the metal crystals, forming cavities. Since the sizes of the seed crystals are different and the sizes and numbers of the coated nanobubbles are also different, cavities with different sizes and shapes are formed in the central region during the growth process of the metal crystals, and the ratio of metal particles having different types of cavities is related to the particle size distribution of the spherical nano metal seed crystals.

[0014] Also, in the present invention, spherical or substantially spherical nano metal particles are used as seed crystals. By crystallization, fine crystal grains are formed so as to surround the periphery of the seed crystals. During the process of inducing the growth of the crystal grains, the two-dimensional effect of the generated crystal interface becomes more uniform, and metal particles with smaller crystal grains and higher sphericity are formed. The spherical or substantially spherical seed crystals have a uniform grain boundary binding force, so the reaction is rapidly accelerated, the cavitation effect formed during the reaction is promoted, pores are formed in the central region inside the metal particles during the reaction, the shrinkage rate of the crystal grains of the metal particles becomes more uniform, and the shrinkage rate increases. In addition, the polyol-seed crystal system of the present invention promotes the generation of bubbles during the reaction, and there is an affinity effect of the same solvent between the polyol and the dispersion liquid, so the dispersion of the seed crystals is further promoted. The dispersion liquid disperses the generated metal particles and prevents the aggregation of the metal particles during the reaction.

[0015] As a preferred embodiment of the method for preparing the metal particles of the present invention, the metal is at least one of gold, silver, copper, and nickel.

[0016] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (1), the particle size of the seed crystal is 1 nm to 100 nm. Preferably, the particle size of the seed crystal is 1 nm to 70 nm. More preferably, the particle size of the seed crystal is 5 nm to 40 nm.

[0017] When using seed crystals with such a particle size, since there are many air valves in the reaction solution, a cavitation effect occurs in the crystallization process of the metal particles in the reaction, pores are formed inside the metal particles, and due to the cavitation effect in the reaction process, with the increase within the limited range of the particle size of the seed crystal, large air valves are formed inside the metal particles by the air valves in the reaction solution, and pores are formed.

[0018] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (1), the polyol occupies 15% to 95% by volume of the polyol mixture. Preferably, the polyol occupies 50% to 85% by volume, and the balance is at least one of esters, ethers, ketones, ether esters, hydrocarbons, amines, pyrrolidones, dispersants and / or surfactants, preferably at least one of polyvinylpyrrolidone, octylamine, and tweens.

[0019] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (1), the polyol is at least one of pentaerythritol, ethylene glycol, 1,2 - propylene glycol, 1,4 - butanediol, 1,6 - hexylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol, and glycerin.

[0020] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the stirring speed is 5 rpm to 1000 rpm. Preferably, the stirring speed is 50 rpm to 500 rpm.

[0021] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the content of the metal species crystal is 0.0001% by mass to 0.01% by mass of the metal in the oxidation solution. Preferably, the content of the metal species crystal is 0.0002% by mass to 0.001% by mass of the metal in the oxidation solution.

[0022] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the temperature of the reaction is 10 to 90 °C. Preferably, the temperature of the reaction is 20 to 40 °C.

[0023] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the pH value of the oxidation solution is 2.5 to 8.5. Preferably, the pH value of the oxidation solution is 5 to 7.5.

[0024] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the reducing solution contains at least one of reducing agents such as hydrazines, amines, organic acids, alcohols, aldehydes, hydrides, transition metal salts, pyrrolidones, and hydroxylamines.

[0025] Preferably, the hydrazines are at least one of hydrazine, hydrazine hydrate, phenylhydrazine, and hydrazine sulfate; the amines are at least one of dimethylaminoethanol, triethylamine, octylamine, and dimethylaminoborane; the organic acids are at least one of citrate, ascorbic acid and its salts, tartrate, gallic acid and its salts, malate, malonic acid and its salts, and formic acid; the alcohols are at least one of methanol, ethanol, isopropanol, ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; the hydrides are at least one of sodium borohydride, lithium borohydride, lithium triethylborohydride, lithium aluminum hydride, diisobutylaluminum hydride, tributyltin hydride, lithium tri-sec-butylborohydride, potassium tri-sec-butylborohydride, zinc borohydride, and sodium acetoxyborohydride; the transition metal salts are iron sulfate and / or tin sulfate; the pyrrolidones are at least one of polyvinylpyrrolidone, 1-vinylpyrrolidone, N-vinylpyrrolidone, and methylpyrrolidone; and the hydroxylamines are hydroxylamine sulfate and / or hydroxylamine nitrate.

[0026] As a preferred embodiment of the method for preparing the metal particles of the present invention, in step (2), taking the metal mass in the oxidation solution as 1 equivalent, the addition amount of the reducing agent is 0.1 to 7 equivalents. Preferably, the addition amount of the reducing agent is 1 to 5 equivalents.

[0027] If the addition amount of the reducing agent is less than 0.1, un-reduced metal may remain. If it exceeds 7, the reaction is too fast, the aggregated particles increase, and as a result, the particle size becomes non-uniform.

[0028] As a preferred embodiment of the method for preparing the metal particles of the present invention, in step (2), the addition amount of the dispersant is 0.1 to 5 times the mass of the metal oxide or metal salt in the oxidation solution.

[0029] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the dispersion liquid contains at least one of dispersants and / or surfactants such as organic acids, esters, ethers, ketones, ether esters, alcohols, hydrocarbons, amines, pyrrolidones.

[0030] Preferably, the dispersant is at least one of fatty acid salts, α-sulfo fatty acid ester salts, alkylbenzene sulfonate salts, linear alkylbenzene sulfonate salts, alkyl sulfates, alkyl ether sulfate ester salts, triethanol alkyl sulfate, fatty acid ethanolamide, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, sorbitol, sorbitan, alkyltrimethylammonium salts, dialkyldimethylammonium chloride, alkylpyridine chloride, alkyl carboxy betaine, sulfobetaine, lecithin, formaldehyde condensates of naphthalene sulfonate salts, polystyrene sulfonate salts, polyacrylate salts, copolymer salts of vinyl compounds and carboxylic acid monomers, carboxymethyl cellulose, polyvinyl alcohol, partial alkyl esters of polyacrylic acid and / or polyalkylene polyamines, polyethyleneimine and / or aminoalkyl methacrylate copolymers, polyvinylpyrrolidone, 1-vinylpyrrolidone, N-vinylpyrrolidone, methylpyrrolidone.

[0031] The dispersant is at least one of polyvinylpyrrolidone, octylamine, ethanol, polyethylene glycol, Tween, glycerol, maleic acid.

[0032] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (2), the oxidation liquid and / or the reduction liquid may be added to the dispersion liquid by pumping with a pump, pumping with compressed air or injection, the addition flow rate of the oxidation liquid and / or the reduction liquid is 1 mL / min to 1500 L / min, and the stirring speed is 50 rpm to 500 rpm.

[0033] Compared with the prior art, the flow rate range is significantly widened, the stirring reaction speed is fast, the reaction conditions are also broadened, the output is increased, and mass production is made possible.

[0034] As a preferred embodiment of the method for preparing the metal particles of the present invention, in the step (3), the aggregating agent is a fatty acid and / or a carboxylic acid compound.

[0035] Preferably, the fatty acids are at least one saturated fatty acid among caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, or at least one unsaturated fatty acid among oleic acid, linoleic acid, linolenic acid, arachidonic acid and salts thereof, and the carboxylic acid compound is at least one of a compound having a carbon-carbon double bond (such as sorbic acid), a dihydroxy compound (such as adipic acid), and a dicarboxy compound.

[0036] By adding an aggregating agent after the reaction to aggregate the nanoparticles, the charge potential (ζ-potential) at the bonding surface between the particles and the particles is changed, and then, it is precipitated and separated to obtain the nano metal particles.

[0037] In a third aspect, the present invention is the use of the above metal particles in a conductive adhesive for a solar cell and / or a semiconductor.

Advantages of the Invention

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows. The metal particles of the present invention have a high sphericity, pores are distributed in the center of the particles, and the shrinkage rate is Large , and the crystal grains inside the particles are small (10 nm to 80 nm), so they are applicable to HJT (heterojunction cell) silver paste and can be applied to fields such as perc SP and step-by-step printing. For example, when metal particles with a high shrinkage ratio are applied to screen printing of a solar cell panel, when the electrodes on the surface of the solar cell panel are sintered at a high temperature, the line width becomes narrow, and the conversion efficiency is improved by 0.05% to 0.1%.

[0039] The method for preparing metal particles of the present invention is to introduce spherical or substantially spherical metal species crystals to prepare a polyol-metal crystal system, so that the particle size and sphericity of the metal particles can be controlled during the reduction process, quickly and stably reduce the metal particles in the metal oxide or metal salt solution containing the metal source in the seed crystal, ensure that the morphology of the formed metal particles is spherical or substantially spherical, and the particle size of the metal particles is adjusted by the number and size of the introduced spherical nano metal species crystals.

Brief Description of the Drawings

[0040]

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Embodiments for Carrying Out the Invention

[0041] To better explain the object, technical means, and advantages of the present invention, the present invention will be further described below with reference to specific examples. Those skilled in the art should understand that the specific examples described in this specification are only used to explain the present invention and do not limit the present invention. Unless otherwise specified, all the test methods used in the examples are ordinary methods. Unless otherwise specified, the materials, reagents, etc. used are available as commercial products. The metal particles are also simply referred to as "particles", generally handled in a powder state, and are also called "metal particle powder" or simply "powder". The D50 is the particle diameter when the cumulative particle size distribution rate of one sample reaches 50%. Example 1 (1) Preparation of oxidation solution 100 g of silver nitrate solid or an equivalent amount of silver nitrate liquid was dissolved in 250 mL of deionized water, the pH was adjusted to 5, and the solution was kept at 20°C. (2) Preparation of reduction solution 50 g of vitamin C was added to 250 mL of deionized water to prepare a reduction solution, and the solution was kept at 20°C. (3) Preparation of dispersion solution 20 g of PVP was added to 300 mL of deionized water and dissolved to prepare a dispersion solution, which was stirred well and the solution was kept at 20°C. (4) Preparation of polyol-seed crystal system Spherical nano silver seed crystals were dispersed in 80% by volume of glycerin (the remaining amount is PVP). The particle diameter of the spherical nano silver seed crystals is 5 nm to 40 nm, and the mass of the spherical nano silver seed crystals is 0.001% of the mass of silver in the silver nitrate-containing solution. The solution was kept at 20°C, and the seed crystals magnified by an electron microscope are shown in Fig. 1 (200K×) and Fig. 2 (40K×). (5) Preparation of metal particles The dispersion solution was sent to the reaction kettle using a metering pump, and the polyol-seed crystal system was put into the reaction kettle. Then, the oxidation solution and the reduction solution were sent to the reaction kettle simultaneously (flow rate: 38 mL / Min), and a reduction reaction was carried out at a stirring speed of 50 rpm. After the reaction was completed, 0.031 g of stearic acid was added as a flocculant, and the precipitate was separated to obtain silver particle powder. As shown in Fig. 3, as a result of observing the silver particles magnified 20K× under an electron microscope, the sphericity of the obtained silver particles was high. As shown in Fig. 4, as a result of observing the silver particles magnified 30K× under an electron microscope, the silver particles had a D50 of about 400 nm and a high sphericity. When calculated according to the principle of the GB / T37406-2019 method, the average value of the sphericity was 0.89. Regarding the obtained silver particle sample, as a result of detection by XRD (X-ray diffractometer model: Shimadzu XRD-6100, Japan), as shown in Figure 5, the measured value was 20561, the peak value was high, the obtained silver particles had a consistent crystal form, indicating that the peaks were sharp, and it was shown that the particle size of the obtained silver grains was uniform and the distribution was concentrated. Example 2

[0042] (1) Preparation of oxidation solution 100 g of silver nitrate solid or an equivalent amount of silver nitrate liquid was dissolved in 250 mL of deionized water, the pH was adjusted to 6.5, and the solution was kept warm at 30°C. (2) Preparation of reduction solution 20 g of hydrazine hydrate was added to 250 mL of deionized water to prepare a reduction solution, and the solution was kept warm at 30°C. (3) Preparation of dispersion solution 20 g of octylamine was added to 300 mL of deionized water and dissolved to prepare a dispersion solution, which was stirred thoroughly, and the solution was kept warm at 30°C. (4) Preparation of polyol-seed crystal system Spherical nano silver seed crystals were dispersed in 65% by volume of glycerin (the remaining amount was PVP). The particle size of the spherical nano silver seed crystals was 5 nm to 40 nm, and the mass of the spherical nano silver seed crystals was 0.0005% of the mass of silver in the silver nitrate-containing solution. The solution was kept warm at 30°C, and the seed crystals magnified by an electron microscope are shown in Figure 1 (200K×) and Figure 2 (40K×). (5) Preparation of metal particles The dispersion solution was sent to the reaction kettle using a metering pump, the polyol-seed crystal system was put into the reaction kettle, and then the oxidation solution and the reduction solution were sent to the reaction kettle simultaneously (flow rate: 38 mL / Min). The reduction reaction was carried out at a stirring speed of 50 rpm. After the reaction was completed, 0.05 g of oleic acid was added as a flocculant, and precipitation and separation were carried out to obtain silver particle powder. As a result of observing the silver particle sample under an electron microscope at a magnification of 10K×, as shown in Figure 6, the obtained silver particles had a high sphericity, with rounded edges. As a result of calculating according to the principle of the GB / T37406-2019 method, the sphericity was 0.92. The size of the internal crystal grains was 10 to 80 nanometers. Compared with Example 1, the amount of the added seed crystals decreased, and the particle size of the obtained silver particles also increased, with D50 being about 600 nm. A method of cutting silver particles with gallium ions was adopted, and the cross-section of the obtained silver particles was observed with an electron microscope. Three silver particles were randomly selected and their cross-sections were observed. When the sample was dispersed on carbon paste and measured in ultra-high vacuum, as shown in Figure 7, there were many pores inside the silver particles, and the pores were uniformly distributed in the center of the silver particles, with the pore size being 9 to 29 nm. Since the spherical or substantially spherical seed crystals have a uniform grain boundary binding force, the catalytic reaction is rapidly accelerated. As a result, a cavitation effect occurs during the reaction process, and pores are formed in the metal particles. The silver particles with a large number of pores uniformly distributed in the center of the silver particles have a high shrinkage ratio of TMA metal, and these silver particles were useful in many technical fields such as HIT silver paste, perc SP, and step printing. Example 3

[0043] (1) Preparation of oxidation solution 100 g of silver nitrate solid or an equivalent amount of silver nitrate liquid was dissolved in 250 mL of deionized water, the pH was adjusted to 6.8, and the solution was kept warm at 40 °C. (2) Preparation of reduction solution 12 g of sodium borohydride was added to 200 mL of deionized water with a pH value greater than 10 to prepare a reduction solution, and the solution was kept warm at 40 °C. (3) Preparation of dispersion solution 20 g of Tween was added to 300 mL of deionized water and dissolved to prepare a dispersion solution, which was stirred well and the solution was kept warm at 30 °C. (4) Preparation of polyol-seed crystal system Disperse spherical nano silver seed crystals in 65% by volume of ethylene glycol (the remaining amount is PVP). The particle size of the spherical nano silver seed crystals is 10 nm to 40 nm, and the mass of the spherical nano silver seed crystals is 0.00025% of the mass of silver in the silver nitrate-containing solution. Keep the solution at 40 °C. The seed crystals are ACS1044 spherical nano silver particles. (5) Preparation of Metal Particles Use a metering pump to send the dispersion liquid to the reaction kettle, put the polyol-seed crystal system into the reaction kettle, and then send the oxidation liquid and the reduction liquid to the reaction kettle (flow rate: 38 mL / Min). Carry out the reduction reaction at a stirring speed of 350 rpm. After the reaction is completed, add 0.03 g of adipic acid as a flocculant, precipitate and separate to obtain silver particle powder. As a result of observing the silver particle sample magnified 10K× under an electron microscope, as shown in Figure 8, the sphericity of the obtained silver particles is high. Calculated according to the principle of the GB / T37406-2019 method, the sphericity is 0.88. Compared with Example 2, the number of added seed crystals was reduced by half, the particle size of the obtained silver particles increased, and D50 was about 1.2 μm. Adopt a method of cutting silver particles with gallium ions, observe the cross section of the obtained silver particles with an electron microscope, randomly select three silver particles and observe their cross sections. When the sample was dispersed on the carbon paste and measured in ultra-high vacuum, as shown in Figure 9, there were a small number of pores inside the silver particles, and the pores were concentrated and distributed at the center of the silver particles. The size of the pores was 2.5 to 60 nm. The TMA metal shrinkage ratio of such silver particles is slightly larger than that of the pores in Example 2, and is lower than that of the silver particles uniformly distributed at the center of the particles. Example 4

[0044] (1) Preparation of Oxidation Liquid Dissolve 250 kg of silver nitrate solid or an equivalent amount of silver nitrate liquid in 650 L of deionized water, adjust the pH to 6.5, and keep the solution at 20 °C. (2) Preparation of Reduction Liquid Add 150 kg of ascorbic acid to 250 L of deionized water to prepare a reduction liquid, and keep the solution at 20 °C. (3) Preparation of Dispersion Liquid 60 kg of polyethylene glycol was added to 700 L of deionized water and dissolved to prepare a dispersion, which was stirred thoroughly and the solution was kept at 20 °C. (4) Preparation of polyol - seed crystal system Spherical nano - silver seed crystals were dispersed in 50% by volume of 1,2 - propylene glycol (the remaining amount was PVP). The particle size of the spherical nano - silver seed crystals was 10 nm to 40 nm, and the mass of the spherical nano - silver seed crystals was 0.0002% of the mass of silver in the silver nitrate - containing solution. The solution was kept at 20 °C, and the seed crystals were ACS1044 spherical nano - silver particles. (5) Preparation of metal particles The dispersion was sent to the reaction kettle using a metering pump, and the polyol - seed crystal system was put into the reaction kettle. Then, the oxidation liquid and the reduction liquid were sent to the reaction kettle (flow rate: 40 L / Min to 60 L / Min), and a reduction reaction was carried out at a stirring speed of 100 rpm to 200 rpm. After the reaction was completed, 0.08 kg of caprylic acid was added as a flocculant, and the precipitate was separated to obtain silver particle powder. The silver particle sample was observed under an electron microscope at a magnification of 10K×. As shown in Figure 10, the sphericity of the obtained silver particles was high. Calculated according to the principle of the GB / T37406 - 2019 method, the sphericity was 0.87. The D50 of the obtained silver particles was about 1.45 μm. A method of cutting silver particles with gallium ions was adopted. The cross - section of the obtained silver particles was observed with an electron microscope. Three silver particles were randomly selected and their cross - sections were observed. The sample was dispersed on a carbon paste and measured under ultra - high vacuum. As shown in Figure 11, a small number of large pores and fine pores were dispersed and distributed inside the silver particles. The pores were concentrated and distributed at the center of the silver particles, and the size of the pores was 14 - 45 nm. Example 5

[0045] (1) Preparation of oxidation liquid 150 g of silver nitrate solid or an equivalent amount of silver nitrate liquid was dissolved in 500 mL of deionized water, the pH was adjusted to 7.0, and the solution was kept at 40 °C. (2) Preparation of reduction liquid 85 g of gallic acid was added to 500 mL of deionized water to prepare a reduction liquid, and the solution was kept at 40 °C. (3) Preparation of the dispersion 35 g of glycerol was added to 350 mL of deionized water and dissolved to prepare a dispersion, which was stirred thoroughly and kept at 40 °C. (4) Preparation of the polyol-seed crystal system Spherical nano silver seed crystals were dispersed in 65 vol% ethylene glycol (the balance was PVP). The particle size of the spherical nano silver seed crystals was 5 nm to 50 nm, and the mass of the spherical nano silver seed crystals was 0.0004% of the mass of silver in the silver nitrate-containing solution. The solution was kept at 40 °C. (5) Preparation of metal particles The dispersion was sent to the reaction kettle using a metering pump, and the polyol-seed crystal system was put into the reaction kettle. Then, the oxidizing solution and the reducing solution were injected into the reaction kettle, and a reduction reaction was carried out at a stirring speed of 150 rpm to 350 rpm. After the reaction was completed, 0.015 g of oleic acid was added as a flocculant, and precipitation and separation were carried out to obtain silver particle powder. As a result of observing the silver particle sample under an electron microscope at a magnification of 20K×, as shown in Fig. 12, the sphericity of the obtained silver particles was high. When calculated according to the principle of the GB / T37406-2019 method, the sphericity was 0.86. The D50 of the obtained silver particles was about 800 nm. A method of cutting silver particles with gallium ions was adopted, and the cross section of the obtained silver particles was observed with an electron microscope. Three silver particles were randomly selected and their cross sections were observed. When the sample was dispersed on a carbon paste and measured under ultra-high vacuum, as shown in Fig. 13, there were annular pores at the center inside the silver particles. Regarding the size of the pores, the diameter was less than half of the diameter of the metal particles. In this example, the diameter of the annular pores was 0.39 μm. Since there are many air valves in the reaction solution, a cavitation effect occurs in the crystallization process of metal particles during the reaction process, and pores are formed inside the metal particles. Also, due to the cavitation effect during the reaction process, as the particle size of the seed crystals increases, a large air valve is formed inside the metal particles by the air valve in the reaction solution. In this example, spherical silver nano-seed crystals with a particle size of 5 nm to 50 nm are used. During the reaction process, on the surface of the small metal particles being formed, a part of the metal particles undergoes a two-stage reaction, and an annular pore is formed between the interface of the metal particles that have completed the first-stage reaction and the crystal grains formed by the second-stage reaction. Test Example

[0046] The silver particle powders prepared in Examples 1 to 5 were pressed onto a silver sheet, and a thermomechanical analyzer TMA (TA model in the United States: Q400) was used to detect the sintering shrinkage rate, and the results are shown in Fig. 14. Fig. 14 is a TMA detection chart of the silver particles prepared in Examples 1 to 5. a is the detection curve of the silver particles prepared in Example 1, b is the detection curve of the silver particles prepared in Example 3, c is the detection curve of the silver particles prepared in Example 4, d is the detection curve of the silver particles prepared in Example 2, and e is the detection curve of the silver particles prepared in Example 5. From the above, the silver particles prepared in Examples 2 and 5 have a shrinkage rate of about 13.7%. In Example 5, a special structure such as an annular pore is formed in the central region of the particles. Therefore, the sintering activity of the powder is improved by the formed annular pores, and it is also found to be advantageous for improving the diversification of requirements for the products of each formulation by the fine line printing design. The silver particles prepared in Example 1 have a shrinkage rate of about 9%, the silver particles prepared in Example 3 have a shrinkage rate of about 10%, and the silver particles prepared in Example 4 have a shrinkage rate of about 10.6%. Example 6

[0047] (1) Preparation of oxidation solution 80 g of copper oxide was dissolved in 600 mL of ammonium chloride, the pH was adjusted to 7.2, and the solution was kept at 20°C. (2) Preparation of reduction solution 30 g of hydrazine hydrate was added to 600 mL of deionized water to prepare a reduction solution, and the solution was kept at 20°C. (3) Preparation of dispersion solution 45 g of PVP was added to 500 mL of deionized water and dissolved to prepare a dispersion solution, which was stirred thoroughly, and the solution was kept at 20°C. (4) Preparation of polyol-seed crystal system Spherical nano copper seed crystals are dispersed in 85% by volume of glycerin (the balance is octylamine). The particle size of the spherical nano copper seed crystals is 5 nm to 10 nm, and the mass of the spherical nano copper seed crystals is 0.0005% of the mass of copper in the copper-containing solution. The solution is kept warm at 20 °C. The seed crystals are spherical nano copper particles with a particle size of 5 nm as shown in Figure 15. (5) Preparation of metal particles Using a metering pump, the dispersion is sent to a reaction kettle, and the polyol-seed crystal system is put into the reaction kettle. Then, the oxidation solution and the reduction solution are sent to the reaction kettle simultaneously (flow rate: 50 mL / Min), and a reduction reaction is carried out at a stirring speed of 200 rpm. After the reaction is completed, 0.03 g of capric acid is added as a flocculant, and precipitation and separation are carried out to obtain copper particle powder. Example 7

[0048] (1) Preparation of oxidation solution 50 g of nickel sulfate is dissolved in 1600 mL of water, the pH is adjusted to 6.5, and the solution is kept warm at 35 °C. (2) Preparation of reduction solution 60 g of hydroxylamine sulfate is added to 1300 mL of deionized water to prepare a reduction solution, and the solution is kept warm at 35 °C. (3) Preparation of dispersion 50 g of sodium alkylbenzene sulfonate is added to 300 mL of deionized water and dissolved to prepare a dispersion, which is stirred thoroughly, and the solution is kept warm at 35 °C. (4) Preparation of polyol-seed crystal system Spherical nano nickel seed crystals are dispersed in 80% by volume of diethylene glycol (the balance is octylamine). The particle size of the spherical nano nickel seed crystals is 5 nm to 20 nm, and the mass of the spherical nano nickel seed crystals is 0.0001% of the mass of nickel in the nickel-containing solution. The solution is kept warm at 35 °C. The seed crystals are spherical nano nickel particles. (5) Preparation of metal particles Using a metering pump, the dispersion liquid was sent to the reaction kettle, and the polyol-seed crystal system was put into the reaction kettle. Then, the oxidation liquid and the reduction liquid were sent to the reaction kettle (flow rate: 30 mL / Min), and the reduction reaction was carried out at a stirring speed of 500 rpm. After the reaction was completed, 0.095 g of linoleic acid was added as a flocculant, and the mixture was precipitated and separated to obtain nickel particle powder. Example 8

[0049] (1) Preparation of oxidation liquid A HAuCl4 tetrachloroauric acid solution with a concentration of 24 mmol / L was prepared, and the solution was kept warm at 110 - 130 °C. (2) Preparation of reduction liquid 15 ml of ethylene glycol was used as the reduction liquid, and the solution was kept warm at 110 - 130 °C. (3) Preparation of dispersion liquid Polyvinylpyrrolidone and polyethylene glycol were used as a double dispersant system, and the mass ratio of PVP to PEG was 1:9 - 3:7. The solution was kept warm at 110 - 130 °C. (4) Preparation of polyol-seed crystal system Spherical nanogold seed crystals were dispersed in 85% by volume of glycerin (the remaining amount was PVP). The particle size of the spherical nanogold seed crystals was 5 nm - 50 nm, and the mass of the spherical nanogold seed crystals was 0.0001% of the mass of gold in the tetrachloroauric acid-containing solution. The seed crystals are shown in Figure 16. (5) Preparation of metal particles The temperature of the constant-temperature reaction and the temperature of the oil bath kettle were set at 110 - 130 °C. The dispersion liquid was added to the reaction vessel, and then, while stirring, the polyol-seed crystal system was added. Then, 15 ml of ethylene glycol was added, and 10 ml of a 24 mmol / L HAuCl4 oxidation liquid was added dropwise to the reaction vessel batchwise using a dropper. The constant-temperature reaction was carried out sufficiently, cooled to room temperature, 0.0003 g of a flocculant was added, and the mixture was precipitated and separated to obtain gold particle powder. Comparative Example 1

[0050] (1) Preparation of oxidation liquid 100 g of silver nitrate solid or an equivalent amount of silver nitrate liquid was dissolved in 250 mL of deionized water, the pH was adjusted to 7.5, and the solution was kept warm at 30 °C. (2) Preparation of reduction liquid 50 g of vitamin C was added to 250 mL of deionized water to prepare a reducing solution, and the solution was kept warm at 29°C. (3) Preparation of the dispersion 20 g of PVP was added to 250 mL of deionized water and dissolved to prepare a dispersion, which was stirred thoroughly. Seed crystals (40 nm - 50 nm) of silver nanoparticles having a regular shape were added, and the mass of the added silver nano-seed crystals was 0.001% of the mass of silver in the silver nitrate solution. The solution was kept warm at 30°C. As shown in Figure 17, the seed crystals are G5 silver nanoparticles. (4) Preparation of metal particles The dispersion was sent to the reaction kettle using a metering pump, and then the oxidizing solution and the reducing solution were sent to the reaction kettle (flow rate: 50 mL / Min). A reduction reaction was carried out at a stirring speed of 300 rpm. After the reaction was completed, 0.30 g of oleic acid was added as a coagulant, and the mixture was precipitated and separated to obtain silver particle powder. As a result of observing the silver particles under an electron microscope at a magnification of 10K×, as shown in Figure 18, the D50 of the obtained silver particles was 1.2 μm - 1.5 μm. The prepared silver particle powder was pressed onto a silver sheet, and the sintering shrinkage rate was detected by a thermomechanical analyzer TMA (TA model: Q400, USA). Since the center of this particle has a solid structure and less heat loss, as shown in Figure 19, the shrinkage ratio was 4.694%. Comparative Example 2

[0051] (1) Preparation of the oxidizing solution 100 g of silver nitrate solid or an equivalent amount of silver nitrate liquid was dissolved in 250 mL of deionized water, the pH was adjusted to 7.0, and the solution was kept warm at 30°C. (2) Preparation of the reducing solution 50 g of vitamin C was added to 250 mL of deionized water to prepare a reducing solution, and the solution was kept warm at 30°C. (3) Preparation of the dispersion Dissolve 20 g of PVP in 300 mL of deionized water to prepare a dispersion, stir well, add seed crystals (40 nm - 50 nm) of silver nanoparticles having an irregular shape, and the mass of the added silver nano-seed crystals is 0.0005% of the mass of silver in the silver nitrate solution. Keep the solution at 30 °C. As shown in Fig. 17, the seed crystals are silver nano-seed crystal particles, with poor sphericity, sharp edges, and irregular shapes. (4) Preparation of metal particles Use a metering pump to send the dispersion into the reaction kettle, and then send the oxidation solution and the reduction solution into the reaction kettle (flow rate: 50 mL / Min), and carry out a reduction reaction at a stirring speed of 300 rpm. After the reaction is completed, add 0.033 g of linoleic acid as a flocculant, precipitate and separate to obtain silver particle powder. As a result of observing the silver particle sample under an electron microscope at a magnification of 10K×, as shown in Fig. 20, the obtained silver particles have a D50 of 2.0 μm - 2.5 μm, poor sphericity, sharp edges, and irregular shapes. Comparative Example 3

[0052] Silver particles were prepared using the method in Patent Document 2: Chinese Patent CN105436517B. For the prepared silver particles, detection was carried out by XRD (X-ray diffractometer model: Shimadzu XRD-6100, Japan). As shown in Fig. 21, the measured value was 15046, the peak value was low, indicating that the obtained silver particles did not have a consistent crystal form, and also indicating that the peak top was not sharp and the particle size of the obtained silver particles was non-uniform.

[0053] It should be noted that the above-described embodiments are merely used to explain the technical means of the present invention and are not intended to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art can modify or equivalently replace the technical means of the present invention without departing from the essence and scope of the technical means of the present invention.

Claims

1. A method for preparing metal particles, comprising: Step (1) of dispersing spherical or substantially spherical nano metal species crystals in a polyol mixture to prepare a polyol - seed crystal system; Step (2) of adding the polyol - seed crystal system to a dispersion liquid, and then adding an oxidation liquid and a reduction liquid containing a metal oxide or a metal salt containing a metal source in the seed crystal, and stirring and reacting them; Step (3) of adding a flocculant, precipitating and separating to obtain metal particles. In step (1), the polyol accounts for 15% to 95% by volume of the polyol mixture; The remainder of the polyol mixture is at least one of dispersants and / or surfactants such as esters, ethers, ketones, ether esters, hydrocarbons, amines, pyrrolidones; A method for preparing metal particles, characterized in that.

2. The metal is at least one of gold, silver, copper, and nickel. The method for preparing metal particles according to Claim 1.

3. In step (1), the particle diameter of the seed crystal is 1 nm to 100 nm. The method for preparing metal particles according to Claim 1.

4. In step (1), the polyol is at least one of pentaerythritol, ethylene glycol, 1,2 - propylene glycol, 1,4 - butanediol, 1,6 - hexylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol, and glycerin. The method for preparing metal particles according to Claim 1.

5. In step (1), the polyol accounts for 50% to 85% by volume of the polyol mixture. The method for preparing metal particles according to Claim 1.

6. In step (2), the content of the metal species crystals is 0.0001% to 0.01% by mass of the metal in the oxidation liquid. The method for preparing metal particles according to Claim 1.

7. In step (2), the reduction liquid contains at least one of reducing agents such as hydrazines, amines, organic acids, alcohols, aldehydes, hydrides, transition metal salts, pyrrolidones, and hydroxylamines. The method for preparing metal particles according to Claim 1.

8. In step (2), the dispersion liquid contains at least one of dispersants and / or surfactants such as organic acids, esters, ethers, ketones, ether esters, alcohols, hydrocarbons, amines, and pyrrolidones. The method for preparing metal particles according to Claim 1.

9. The dispersant is at least one of fatty acid salts, α-sulfo fatty acid ester salts, alkylbenzene sulfonate salts, linear alkylbenzene sulfonate salts, alkyl sulfates, alkyl ether sulfate ester salts, triethanol alkyl sulfate, fatty acid ethanolamides, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, sorbitol, sorbitan, alkyltrimethylammonium salts, dialkyldimethylammonium chlorides, alkylpyridinium chlorides, alkyl carboxybetaines, sulfobetaines, lecithin, formaldehyde condensates of naphthalene sulfonate salts, polystyrene sulfonate salts, polyacrylate salts, copolymer salts of vinyl compounds and carboxylic acid monomers, carboxymethyl cellulose, polyvinyl alcohol, partial alkyl esters of polyacrylic acid and / or polyalkylene polyamines, polyethyleneimine and / or aminoalkyl methacrylate copolymers, polyvinylpyrrolidone, 1-vinylpyrrolidone, N-vinylpyrrolidone, methylpyrrolidone. The method for preparing metal particles according to Claim 8.

10. The dispersant is at least one of polyvinylpyrrolidone, octylamine, ethanol, polyethylene glycol, Tween, glycerol, maleic acid. The method for preparing metal particles according to Claim 8.

11. In step (3), the flocculant is fatty acids and / or carboxylic acid compounds, the fatty acids are at least one saturated fatty acid of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, or at least one unsaturated fatty acid of oleic acid, linoleic acid, linolenic acid, arachidonic acid and its salts, the carboxylic acid compounds are at least one of compounds having a carbon-carbon double bond, dihydroxy compounds, dicarboxy compounds. The method for preparing metal particles according to Claim 1.

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