CN114619039B

CN114619039B - Spherical silver powder, preparation method thereof and conductive paste

Info

Publication number: CN114619039B
Application number: CN202210254707.XA
Authority: CN
Inventors: 夏孝天; 廖云红
Original assignee: Jiangsu Lianyin New Material Co ltd
Current assignee: Jiangsu Lianyin New Material Co ltd
Priority date: 2022-03-15
Filing date: 2022-03-15
Publication date: 2023-01-31
Anticipated expiration: 2042-03-15
Also published as: CN114619039A; WO2023173627A1

Abstract

The application discloses a method for preparing spherical silver powder, which comprises the following steps: reduction reaction: carrying out reduction reaction on inorganic silver salt, a reducing agent, organic silver colloid and dispersing liquid containing a dispersing agent; wrapping silver powder: and adding a wrapping agent into the solution after the reduction reaction to obtain the spherical silver powder. Also provides a silver powder, the D50 of the silver powder is 0.5-2.0 mu m, and the specific surface area of the silver powder is 0.2-1.0 m ² (ii) in terms of/g. Also provides a conductive paste containing the silver powder. The silver powder prepared by the method keeps stable on key indexes such as particle size distribution, specific surface area and the like, and can flexibly adjust the key indexes such as particle size distribution, specific surface area and the like of the silver powder by adjusting the using amount of the organic silver, so that the aim of diversification of the silver powder product is fulfilled.

Description

Spherical silver powder, preparation method thereof and conductive paste

Technical Field

The application relates to the technical field of new electronic materials. Specifically, the application relates to spherical silver powder, a preparation method thereof and conductive paste.

Background

The common technical schemes of the existing silver powder manufacturing process are as follows: silver nitrate or a complex thereof is used as a silver precursor, silver powder is obtained by adding a certain reducing agent for reduction, the used reducing agent generally adopts vitamin C, and a large amount of polyvinylpyrrolidone (PVP) is used as a dispersing agent.

The silver powder produced by the process technology has high production cost, great difficulty in wastewater treatment, great difficulty in controlling the performance indexes such as morphology, particle size, microstructure and the like, and strong uncontrollable property.

The defects of the silver powder product prepared by the prior common technology are mainly as follows:

(1) The production cost is higher

At present, the high-tap spherical silver powder widely applied to front silver paste in the photovoltaic industry at home has the dispersant PVP consumption as high as 22-50% of the silver powder yield, and the cost accounts for about 20-30% of the material cost.

(2) High difficulty and high cost in wastewater treatment

The PVP used in large quantity completely enters the wastewater after the dispersion effect of the silver powder production link is finished. In the evaporation stage of wastewater treatment, the viscosity of high-concentration PVP wastewater is extremely high, if the evaporation rate is too high, a system is completely blocked, and system paralysis is caused, for system safety, the current evaporation rate can only be set to 80%, and the other 20% of evaporated thick slag needs to be treated by an incineration system. The cost of treating the waste water of each kilogram of silver powder is about 30 yuan.

(3) Product property stabilization

The existing silver powder has large fluctuation among different batches on key indexes such as particle size distribution, specific surface area and the like, the performance index of a downstream silver paste (adhesive) product is seriously influenced, and the stability of the silver paste (adhesive) product is influenced;

(4) Adjustability of product

Mainly expressed in the regulation and control of key indexes such as particle size distribution, specific surface area and the like. With the development of the market, the requirements of different customers on the performance of the silver paste (adhesive) are continuously refined, and the difference is larger and larger. The requirement of silver paste (glue) performance differentiation puts forward the differentiation requirement of silver powder. However, the defects of the existing silver powder production technology in the aspect of adjustability are mostly replaced partially by doping, and the satisfaction degree of the silver powder in the aspect of differentiation requirements is severely limited.

(5) Control of product microstructure

Most of silver powder on the market at present has single microstructure and is lack of diversification. The microstructure of the silver powder influences the activity of the silver powder and directly influences the sintering performance of the silver paste. The lack of diversification of the silver powder seriously restricts the applicable window of the silver powder, and the requirements of different silver paste systems on the activity of the silver powder at different sintering temperatures cannot be met.

Disclosure of Invention

In order to solve the problems of high production cost, poor performance stability, poor adjustability, single microstructure, high difficulty in treatment of production wastewater and the like of the silver powder in the prior art, the application aims to provide the preparation method of the spherical silver powder. The application also provides the spherical silver powder prepared by the method and conductive paste containing the spherical silver powder.

The specific technical scheme of the application is as follows:

1. the preparation method of the spherical silver powder is characterized by comprising the following steps:

reduction reaction: carrying out reduction reaction on inorganic silver salt, a reducing agent, organic silver colloid and dispersing liquid containing a dispersing agent;

wrapping silver powder: and adding a wrapping agent into the solution after the reduction reaction to obtain the spherical silver powder.

2. The production method according to item 1, characterized in that the reduction reaction step includes:

dissolving inorganic silver salt solid in water or diluting inorganic silver salt solution with water to obtain oxidation liquid;

dissolving a reducing agent in water to obtain a reducing solution;

adding a dispersing agent into water to obtain a dispersion liquid;

adding organic silver colloid into the dispersion liquid to obtain organic silver colloid dispersion liquid;

and mixing the oxidizing solution, the reducing solution and the organic silver colloid dispersion solution to perform a reduction reaction.

3. The production method according to item 1, characterized in that the reduction reaction step includes:

adding a dispersing agent into water to obtain a dispersion liquid;

and adding a reducing agent and an organic silver colloid into the dispersion liquid, and then adding an oxidizing liquid to perform a reduction reaction.

4. The production method according to item 1, characterized in that the reduction reaction step includes:

dissolving a reducing agent in water to obtain a reducing solution;

adding a dispersing agent into water to obtain a dispersion liquid;

and adding inorganic silver salt and organic silver colloid into the dispersion liquid, and then adding a reducing liquid to perform a reduction reaction.

5. The production method according to any one of claims 1 to 4, characterized in that the organic silver colloid contains organic silver colloid particles and a stabilizer, wherein the silver content in the organic silver colloid is 0.01 to 0.2mol/L, preferably 0.01 to 0.05mol/L;

preferably, the organic silver colloidal particles are silver bipyridyl nitrate particles, silver tetrapyridyl nitrate particles, silver bipyridyl sulfate particles, silver tetrapyridyl sulfate particles, silver citrate particles or silver oxalate particles, preferably silver bipyridyl nitrate particles or silver tetrapyridyl nitrate particles;

preferably, the viscosity of the organic silver colloid is maintained at 5 to 30 pas, preferably 10 to 20 pas, for at least 10 days after the preparation of the organic silver colloid;

preferably, the prepared organic silver colloid is stored in a container, wherein the part in contact with the air is the upper surface of the organic silver colloid, the part in contact with the bottom of the container is the bottom of the organic silver colloid, and the absolute value of the viscosity change rate of the bottom of the organic silver colloid relative to the upper surface of the organic silver colloid is less than 10% at any time within at least 10 days after the storage;

preferably, after the organic silver colloid is stored for at least 10 days, the absolute value of the viscosity change rate of the same position of the organic silver colloid is less than 10%;

preferably, the specific gravity of the organic silver colloid is 1.0-1.3 g/mL;

preferably, the mass of the organic silver colloid is 0.01-0.5%, preferably 0.1-0.5% of the mass of the silver ions in the inorganic silver salt;

preferably, the content of the stabilizer in the organic silver colloid is 20-150 g/L, preferably 40-130 g/L;

preferably, the stabilizer is a non-ionic polymer compound, preferably, the stabilizer is one or two or three selected from gelatin, gum arabic and polyvinylpyrrolidone, and more preferably, the stabilizer is polyvinylpyrrolidone.

6. The production method according to any one of items 1 to 5, wherein the dispersant is a nonionic polymer compound, preferably the dispersant is one or two or three selected from polyvinylpyrrolidone, gelatin, and gum arabic, and more preferably the dispersant is polyvinylpyrrolidone.

7. The production method according to any one of claims 1 to 6, characterized in that the inorganic silver salt is silver nitrate.

8. The production method according to item 2 or 3, wherein the concentration of silver ions in the oxidizing solution is 0.2 to 2mol/L.

9. The production method according to any one of claims 1 to 8, characterized in that the reducing agent is selected from one or two or three of vitamin C, formaldehyde and hydrazine hydrate;

preferably, the molar ratio of the reducing agent to the silver in the inorganic silver salt is 0.43 to 3.

10. The preparation method according to any one of items 1 to 9, characterized in that in the step of coating silver powder, a coating agent is added to the solution after the reduction reaction, stirring is carried out, standing and layering are carried out, and the spherical silver powder is obtained after solid-liquid separation;

preferably, the wrapping agent is selected from any one of stearic acid, sodium stearate or palmitic acid;

preferably, the wrapping agent is added into the solution after the reduction reaction, stirred for 1 to 1.5 hours, and kept stand for layering;

preferably, the coating agent is added into the solution after the reduction reaction, stirred at 200-500 rpm, and kept stand for layering.

11. The production method according to any one of claims 1 to 10, characterized in that the mass of the dispersant is not more than 10%, preferably 2% to 8%, of the mass of silver ions in the inorganic silver salt;

preferably, the mass of the coating agent is 0.5-1.5%, preferably 0.5-1% of the mass of the silver ions in the inorganic silver salt.

12. The spherical silver powder is characterized in that the D50 of the silver powder is 0.5-2.0 mu m, and the specific surface area of the silver powder is 0.2-1.0 m ² /g；

Preferably, the silver powder has a D10 of 0.6 to 1.2 μm;

preferably, the silver powder has a D90 of 1.5 to 2.5 μm;

preferably, the D100 of the silver powder is 2.2 to 4.5 μm;

preferably, the tap density of the silver powder is 5.5 to 6.6g/cm ³ ；

Preferably, the burning loss of the silver powder at 540 ℃ is 0.2-0.9%.

13. A spherical silver powder produced by the production method described in any one of items 1 to 11.

14. An electroconductive paste characterized by comprising the spherical silver powder produced by the production method described in any one of items 1 to 11 or the spherical silver powder described in item 12.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the preparation method, in the reduction reaction stage of the silver powder, an organic silver colloid is used as a reduction auxiliary agent to prepare the spherical silver powder with low cost and high performance, and the following problems are successfully solved:

(1) The proportion of the using amount of the dispersing agent to the yield of the silver powder is reduced from 24-50% to below 8%, and correspondingly, the material cost of PVP in the production of the silver powder is reduced from 20-30% to below 5%.

(2) The method greatly reduces the wastewater treatment difficulty and the treatment cost, and because the using amount of the dispersing agent is greatly reduced, the evaporation rate of wastewater in the wastewater treatment process is improved from 80% to 97%, and the wastewater treatment cost per kilogram of silver powder is reduced to below 10 yuan;

(3) The prepared silver powder has stable product performance, and the parameter indexes of the silver powder are successfully regulated and controlled by the following method:

the using amount of the organic silver colloid is stabilized, so that the silver powder is kept stable on key indexes such as particle size distribution, specific surface area and the like;

by adjusting the using amount of the organic silver colloid, key indexes such as particle size distribution, specific surface area and the like of the silver powder can be conveniently and flexibly adjusted, and the purpose of diversification of the types of the silver powder products is realized;

the microstructure of the silver powder can be influenced by adjusting the size of the organic silver colloid particles.

Drawings

FIGS. 1A and 1B are SEM images of 6.8mm × 1.50k and 6.8mm × 10.0k, respectively, of the silver powder (L1-6) of example 1 of the present application.

FIGS. 2A and 2B are SEM images of 5.7 mm. Times.5.00 k and 5.7 mm. Times.10.0 k, respectively, of the silver powder (L1-2) of example 2 of the present application.

Detailed Description

The present application is described in detail below. While specific embodiments of the present application are shown below, it should be understood that the present application may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

It should be noted that throughout the specification and claims, the terms "comprises" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to. The description which follows is a preferred embodiment of the application, however, the description is made for the purpose of illustrating the general principles of the application and is not intended to limit the scope of the application. The protection scope of the present application shall be subject to the definitions of the appended claims.

In one aspect, the present application provides a method for preparing spherical silver powder, comprising the steps of:

According to the preparation method of the spherical silver powder, the organic silver salt, the reducing agent, the reducing auxiliary agent, the organic silver colloid and the dispersing liquid containing the dispersing agent are subjected to reduction reaction, so that the silver powder is reduced and separated out, and the silver powder with high microcosmic and macroscopic properties and stable properties can be obtained at high efficiency and low cost.

In one embodiment, the reduction reaction step of the preparation method of the present application comprises:

dissolving inorganic silver salt solid in water or diluting inorganic silver salt solution with water to obtain oxidation solution;

dissolving a reducing agent in water to obtain a reducing solution;

adding a dispersing agent into water to obtain a dispersion liquid;

In the above embodiment, in the preparation method of the present application, the organic silver colloid dispersion liquid is added into the reaction kettle, and then the oxidizing solution and the reducing solution are sequentially added in sequence, so that the reduction reaction occurs, and the sequence of the oxidizing solution and the reducing solution is not limited. In an optional embodiment, in the preparation method, the organic silver colloid dispersion liquid and the reducing liquid are added into a reaction kettle, uniformly mixed, and then the oxidizing liquid is added to perform a reduction reaction. In an optional embodiment, in the preparation method, the organic silver colloid dispersion liquid and the oxidizing liquid are added into a reaction kettle, uniformly mixed, and then the reducing liquid is added to perform a reduction reaction.

adding a dispersing agent into water to obtain a dispersion liquid;

In the above embodiment, in the preparation method of the present application, the silver ion concentration in the oxidizing solution is 0.2 to 2mol/L, for example, 0.2mol/L, 0.4mol/L, 0.6mol/L, 0.8mol/L, 1mol/L, 1.2mol/L, 1.4mol/L, 1.6mol/L, 1.8mol/L, 2mol/L, etc. More preferably, the volume of the reducing solution is 0.3 to 1 time of the volume of the oxidizing solution, and may be, for example, 0.3 time, 0.4 time, 0.5 time, 0.6 time, 0.7 time, 0.8 time, 0.9 time, 1 time, or the like.

In a specific embodiment, in the preparation method of the present application, the oxidizing solution, the reducing solution and the organic silver colloid dispersion are mixed to perform a reduction reaction, or, after the reducing agent and the organic silver colloid are added to the dispersion, the oxidizing solution is added to perform a reduction reaction, at a rate of 25 to 50L/min, for example, 25L/min, 27L/min, 30L/min, 32L/min, 35L/min, 38L/min, 40L/min, 43L/min, 45L/min, 48L/min, 50L/min, and the like. The grain growth mechanism of the silver powder reduction reaction is as follows: the crystal nucleus is formed firstly, the crystal nucleus generates growth in a specific direction due to the influence of reaction environment, and the grown crystal nucleus gradually generates agglomeration among particles along with the reaction time. The feeding speed is high, the reaction time is shortened, and the agglomeration probability of crystal grains is greatly reduced, so that the dispersibility is improved.

dissolving a reducing agent in water to obtain a reducing solution;

adding a dispersing agent into water to obtain a dispersion liquid;

In a specific embodiment, in the preparation method of the present application, the oxidizing solution, the reducing solution and the organic silver colloid dispersion solution are mixed to perform a reduction reaction, or after the silver salt and the organic silver colloid are added to the dispersion solution, the reducing solution is added to perform a reduction reaction, the speed of adding the reducing solution is 25 to 50L/min, for example, 25L/min, 27L/min, 30L/min, 32L/min, 35L/min, 38L/min, 40L/min, 43L/min, 45L/min, 48L/min, 50L/min, and the like. The feeding speed is high, the reaction time is shortened, and the agglomeration probability of crystal grains is greatly reduced, so that the dispersibility is improved.

In a specific embodiment, the preparation method of the present application, the organic silver colloid comprises organic silver colloid particles and a stabilizer, wherein the silver content in the organic silver colloid is 0.01 to 0.2mol/L, preferably 0.01 to 0.05mol/L, and for example, may be 0.01mol/L, 0.02mol/L, 0.03mol/L, 0.04mol/L, 0.05mol/L, 0.06mol/L, 0.07mol/L, 0.08mol/L, 0.09mol/L, 0.1mol/L, 0.12mol/L, 0.14mol/L, 0.16mol/L, 0.18mol/L, 0.2mol/L, and the like.

The method for measuring the silver content in the organic silver colloid comprises the following steps:

(1) Taking about 50g of organic silver colloid W1 (accurate to 0.001 g), placing in a 60 ℃ oven, and drying for 2 hours; then heating to 105 ℃, and drying for 1 hour;

(2) Transferring the sample into a muffle furnace, burning for 1 hour at 540 ℃, and taking out the sample with constant weight;

(3) Accurately weighing the sample weight W2 (accurately to 0.001 g) in the step (2);

(4) Weighing about 5g of sample W3 (accurate to 0.0001 g) from the W2 in the step (3);

(5) Dissolving a sample W3 in about 20mL of concentrated nitric acid (50%), and fixing the volume to 50mL;

(6) Titrating the silver content in the silver nitrate solution prepared by W3 by using a full-automatic potentiometric titrator to obtain a measured value C1 (g/L);

(7) The silver percentage content C (%) in the organic silver colloid was calculated according to the following formula:

(8) The molar concentration of silver was calculated from the specific gravity of the organic silver colloid.

In a specific embodiment, in the preparation method of the present application, the organic silver colloidal particles are bipyridyl silver nitrate particles, tetrapyridyl silver nitrate particles, bipyridyl silver sulfate particles, tetrapyridyl silver sulfate particles, silver citrate particles, or silver oxalate particles, preferably bipyridyl silver nitrate particles, tetrapyridyl silver nitrate particles, bipyridyl silver sulfate particles, or tetrapyridyl silver sulfate particles, and more preferably bipyridyl silver nitrate particles or tetrapyridyl silver nitrate particles. The organic silver colloid particles generated by complexing two molecules or four molecules of pyridine groups with one silver ion can ensure that the stability of the organic silver colloid is higher.

In one embodiment, the preparation method of the present application, the organic silver colloid has a viscosity of 5 to 30Pa · s, preferably 10 to 20Pa · s, and for example, may be 5Pa · s, 8Pa · s, 10Pa · s, 12Pa · s, 15Pa · s, 18Pa · s, 20Pa · s, 23Pa · s, 25Pa · s, 27Pa · s, 30Pa · s, or the like, measured at any time within at least 10 days, preferably within at least 15 days, more preferably within at least 20 days after the preparation, using a rotational viscometer at 25 ℃ and 10rpm, and wherein at least 10 days may be, for example, 10 days, 15 days, 20 days, 25 days, 30 days, or the like. The viscosity of the organic silver colloid is controlled within the range, so that higher colloid stability and activity can be obtained, the control effect on the performance of the silver powder is guaranteed, too high stability needs more stabilizers for maintenance, and too high colloid stability consumption can influence the particle size of the silver powder, so that the viscosity of the organic silver colloid needs to be controlled in a proper interval. In one embodiment, the specific gravity of the organic silver colloid obtained by the preparation method of the present application is 1.0 to 1.3g/mL, and may be, for example, 1.0g/mL, 1.05g/mL, 1.1g/mL, 1.15g/mL, 1.2g/mL, 1.25g/mL, 1.3g/mL, or the like.

In one embodiment, the preparation method of the present application, the viscosity of the organic silver colloid is maintained at 5 to 30Pa · s, preferably 10 to 20Pa · s, within at least 10 days, preferably within at least 15 days, more preferably within at least 20 days after the preparation; the prepared organic silver colloid is stored in a container, wherein the part in contact with the air is the upper surface of the organic silver colloid, the part in contact with the bottom of the container is the bottom of the organic silver colloid, and the absolute value of the viscosity change rate of the bottom of the organic silver colloid relative to the upper surface of the organic silver colloid is less than 10% at any time within at least 10 days, preferably within at least 15 days, more preferably within at least 20 days after storage, and may be, for example, 9.8%, 9.5%, 9%, 8%, 7.5%, 7%, 6.5%, 6%, 5.5%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5%, 0%, and the like, and the smaller value is, the more stable the organic silver colloid becomes, wherein, for example, 10 days, 15 days, 20 days, 25 days, 30 days, and the like may be performed for at least 10 days.

In one embodiment, the preparation method of the present application, the viscosity of the organic silver colloid is maintained at 5 to 30Pa · s, preferably 10 to 20Pa · s, within 10 days, preferably within at least 15 days, more preferably within at least 20 days after the preparation; the prepared organic silver colloid is stored in a container, wherein the part in contact with the air is the upper surface of the organic silver colloid, the part in contact with the bottom of the container is the bottom of the organic silver colloid, and the absolute value of the viscosity change rate of the bottom of the organic silver colloid relative to the upper surface of the organic silver colloid is less than 10% within at least 10 days, preferably within at least 15 days, more preferably within at least 20 days after storage, and can be, for example, 9.8%, 9.5%, 9%, 8%, 7.5%, 7%, 6.5%, 6%, 5.5%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5%, 0%, and the like, and at least 10 days can be, for example, 10 days, 15 days, 20 days, 25 days, 30 days, and the like, preferably at least 15 days, more preferably at least 20 days; after the organic silver colloid is stored for at least 10 days, preferably at least 15 days, and more preferably at least 20 days, the absolute value of the change rate of the viscosity of the same position of the organic silver colloid is less than 10%, and may be, for example, 9.8%, 9.5%, 9%, 8.5%, 8%, 7.5%, 7%, 6.5%, 6%, 5.5%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5%, 0%, and the like, and the smaller the value, the more stable the organic silver colloid is, and the smaller the value is, the longer the organic silver colloid is, and the longer the organic silver colloid is, for example, 10 days, 15 days, 20 days, 25 days, 30 days, and the like.

In one embodiment, in the preparation method of the present application, the mass of the organic silver colloid is 0.01% to 0.5%, preferably 0.1% to 0.5%, of the mass of the silver ions in the inorganic silver salt, and may be, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.12%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or the like.

In a specific embodiment, in the preparation method of the present application, the organic silver colloid further comprises a stabilizer, the organic silver colloid particles are uniformly dispersed in a microcolloidal framework constructed by the stabilizer, due to protection of the microcolloidal framework, a good blocking effect is provided for agglomeration among the organic silver colloid particles, and the organic silver is effectively prevented from losing activity due to oxidation when exposed in air, so that the high-stability organic silver colloid is prepared. The content of the stabilizer is 20-150 g/L, preferably 40-130 g/L, the stabilizer is a nonionic polymer compound, preferably the stabilizer is one or two or three selected from gelatin, gum arabic and polyvinylpyrrolidone, and more preferably the stabilizer is polyvinylpyrrolidone.

In a specific embodiment, in the preparation method of the present application, the dispersant is a nonionic polymer compound, preferably the dispersant is selected from one or two or three of polyvinylpyrrolidone, gelatin or gum arabic, and more preferably the dispersant is polyvinylpyrrolidone.

In one embodiment, in the preparation method of the present application, the inorganic silver salt used in the reduction reaction is a silver salt solution or a silver salt crystal. Preferably, the inorganic silver salt is silver nitrate, the silver nitrate is the inorganic salt with the best water solubility, the cost is low, the market supply is sufficient, and the performance is stable.

In a specific embodiment, the preparation method of the application, silver is reduced and separated out by using a reducing agent, and the reducing agent can be one or more than two selected from vitamin C, formaldehyde, hydrazine hydrate, amine compounds and glucose; preferably, the reducing agent is one or two or three selected from the group consisting of vitamin C, formaldehyde and hydrazine hydrate, and the silver powder having a stable particle size distribution can be obtained using the reducing agent. In order to improve the reaction yield of silver, the molar ratio of the reducing agent to silver in the inorganic silver salt is 0.43 to 3, and for example, can be 0.43.

In one embodiment, in the preparation method of the present application, the encapsulant is attached to the surface of the silver powder, and the encapsulant has two functions: the silver powder coating agent is not particularly limited, and can be any one of stearic acid, sodium stearate or palmitic acid.

In a specific embodiment, in the step of coating the silver powder, the coating agent is added into the solution after the reduction reaction, and the mixture is stirred, kept stand for layering, and subjected to solid-liquid separation to obtain the spherical silver powder, wherein in a preferred embodiment, the stirring speed is 200-500 rpm, the stirring time is 1-1.5 h, and the like.

In a specific embodiment, in the preparation method of the present application, the mass of the dispersant is not more than 10% of the mass of the silver ions in the inorganic silver salt, preferably 2% to 8% of the mass of the silver ions in the inorganic silver salt, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., and the larger the dispersant is used, the smaller the agglomeration degree between the silver powder particles will be, but the too high dispersant is used, which will bring great difficulty to the subsequent cleaning of the silver powder and the treatment of the related wastewater, so the dispersant used amount meeting the basic requirement of the dispersibility of the silver powder is important; the mass of the coating agent is 0.5% to 1.5%, preferably 0.5% to 1.0%, of the mass of the silver ions in the inorganic silver salt, and may be, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or the like.

In one embodiment, the preparation method of the present application comprises the steps of mixing each reaction solution, such as: the temperature of the oxidizing solution, the reducing solution, the organic silver colloid dispersion solution, the solution obtained by adding the reducing agent and the organic silver colloid to the dispersion solution, or the solution obtained by adding the inorganic silver salt and the organic silver colloid to the dispersion solution is controlled to 15 to 40 ℃ for use, and may be, for example, 15 ℃, 18 ℃, 20 ℃, 23 ℃, 25 ℃, 28 ℃, 30 ℃, 33 ℃, 35 ℃, 37 ℃, 40 ℃ or the like.

In a specific embodiment, in the preparation method of the present application, the water is deionized water.

The production method of the present application may further include a step of washing the silver powder, as necessary, since impurities are contained in the silver powder obtained through the above-mentioned reduction reaction and silver powder coating, washing is necessary.

As the cleaning solvent used for the above cleaning, pure water is preferable. The recovery and washing method is not particularly limited, and may be appropriately selected according to the purpose, and examples thereof include decantation, pressure filtration and the like.

The production method of the present application may further include a step of drying the silver powder, and the silver powder obtained after solid-liquid separation or the silver powder after washing contains water, which needs to be removed before use. The method of removing the water is preferably vacuum drying. The drying temperature is preferably 100 ℃ or lower.

On the other hand, the present application also provides a spherical silver powder having a D50 of 0.2 to 2.0. Mu.m, preferably 0.9 to 1.6. Mu.m, and for example, may be 0.2. Mu.m, 0.4. Mu.m, 0.6. Mu.m, 0.8. Mu.m, 0.9. Mu.m, 1.0. Mu.m, 1.1. Mu.m, 1.2. Mu.m, 1.3. Mu.m, 1.5. Mu.m, 1.7. Mu.m, 1.9. Mu.m, 2.0. Mu.m, etc., and a specific surface area of 0.2 to 1.0m ² A ratio of 0.3 to 0.7 m/g is preferred ² A ratio of 0.25 to 0.4 m/g is more preferable ² Per g, for example, may be 0.2m ² /g、0.25m ² /g、0.3m ² /g、0.35m ² /g、0.4m ² /g、0.45m ² /g、0.5m ² /g、0.6m ² /g、0.7m ² /g、0.8m ² /g、0.9m ² /g、1.0m ² And/g, etc. The specific surface area of the silver powder is determined by reference to GB/T1774-1995-Standard for ultrafine silver powder.

The spherical shape in the present application means that the particle shape is spherical or nearly spherical when the silver powder is observed under a Scanning Electron Microscope (SEM), and the sphericity of 100 particles is 1.5 or less, wherein the sphericity means the ratio of the longest diameter to the shortest diameter when the particles are observed by SEM photograph.

The D50 determination method comprises the following steps: cumulative 50% particle diameter in volume-based particle diameter distribution measured by laser diffraction particle size distribution measurement.

The specific surface area of the silver powder is BET specific surface area, and the determination method comprises the following steps: the BET static method comprises the following measurement equipment: horiba 9603SA, japan. When the specific surface area is too high, e.g. above 1.0m ² At/g, the viscosity of the formulated paste will rise sharply, with a fatal effect on the printing properties of the paste. On the other hand, when the specific surface area is too low, e.g., higher than 0.2m ² At/g, the viscosity of the formulated paste will be very low, the paste printing line shape cannot be maintained, collapse occurs, and the electrical properties of the paste are seriously affected.

In one embodiment, the silver powders of the present application have a D10 of 0.6 to 1.2. Mu.m, and may be, for example, 0.6. Mu.m, 0.7. Mu.m, 0.8. Mu.m, 0.9. Mu.m, 1.0. Mu.m, 1.1. Mu.m, 1.2. Mu.m, and the like. D10 in the present application means that 10% of the particles having a particle size smaller than this value are present.

In one embodiment, the silver powder of the present application has a D90 of 1.5 to 2.5. Mu.m, and may be, for example, 1.5. Mu.m, 1.6. Mu.m, 1.7. Mu.m, 1.9. Mu.m, 2.2. Mu.m, 2.4. Mu.m, 2.5. Mu.m, or the like. D90 in the present application means that 90% of the particles having a particle size smaller than this value are present.

In one embodiment, the silver powders of the present application have a D100 of 2.2 to 4.5. Mu.m, and may be, for example, 2.5. Mu.m, 2.8. Mu.m, 3.0. Mu.m, 3.3. Mu.m, 3.5. Mu.m, 3.9. Mu.m, and the like. D100 in the present application means that particles having a particle size of less than this value account for 100%.

The measurement methods of D10, D90 and D100 in the present application are the same as the measurement method of D50.

If the particle size distribution of the silver powder is too large, the prepared silver paste is easy to block the screen during printing and difficult to burn through during sintering, and the electrical property problem is generated. Further, silver powder having a narrow peak width of particle size distribution and uniform and less variation in particle size is preferable.

In one embodiment, the silver powder of the present application has a tap density of 5.5 to 6.6g/cm ³ Preferably 6.1 to 6.6g/cm ³ For example, it may be 5.5g/cm ³ 、5.6g/cm ³ 、5.7g/cm ³ 、5.8g/cm ³ 、6.0g/cm ³ 、6.1g/cm ³ 、6.2g/cm ³ 、6.3g/cm ³ 、6.5g/cm ³ 、6.6g/cm ³ And the like. Tap density refers to the mass per unit volume measured after the powder in the container is tapped under specified conditions. If the tap density is too low, the viscosity of the prepared silver paste is too high, the silver content of the silver paste is difficult to improve, and the purpose of improving the electrical property by improving the silver content is difficult to achieve. The tap density of the silver powder is measured by referring to GB/T5162-2006.

In one embodiment, the silver powder of the present application has a burnout at 540 ℃ of 0.2% to 0.9%, preferably 0.25% to 0.6%, and may be, for example, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or the like. The burning loss refers to: and (3) burning at 540 ℃ for 2 hours to completely decompose the organic coating agent, wherein the weight loss (namely the burning loss value) of the silver powder is the content of the organic coating agent.

In one embodiment, the method of preparing the organosilver colloid of the present application comprises the steps of:

preparing a silver precursor solution: dissolving inorganic silver salt solid in water to obtain the silver precursor solution;

preparing an organic complex solution: diluting an organic complexing agent with water to obtain an organic complexing solution;

preparing a stabilizer solution: dissolving a stabilizer in water to obtain a stabilizer solution;

preparing organic silver colloid: and mixing the stabilizer solution, the organic complexing solution and the silver precursor solution to perform a complexing reaction to obtain the organic silver colloid.

The preparation method of the organic silver colloid adopts the organic group to be complexed with the silver ions, and simultaneously adopts the stabilizer in the synthetic environment, so that organic silver colloid particles generated by the complexing reaction are uniformly dispersed in a microcosmic colloid framework constructed by the stabilizer, and due to the protection of the microcosmic colloid framework, the fine separation effect is played on the agglomeration between organic silver compound powder, and the situation that the organic silver loses activity due to the oxidation when exposed in the air is effectively avoided, so that the high-stability organic silver colloid is prepared.

In one embodiment, the organic complexing agent is selected from one of pyridine, citric acid and salts thereof, oxalic acid and salts thereof, and is preferably pyridine.

Pyridine is an organic compound, is a six-membered heterocyclic compound containing one nitrogen heteroatom, and can be regarded as one CH in a benzene molecule substituted by N. The heterocyclic compound has the chemical properties of difficult electrophilic substitution reaction, easy nucleophilic substitution reaction, difficult oxidation reaction and easy reduction reaction. The stability is greatly increased in common application scenarios, especially in storage environments. Pyridine groups are introduced into the anion part of the organic silver compound, and the pyridine groups are adopted to be complexed with silver ions, so that the organic silver colloid with higher stability is obtained.

In one embodiment, in the step of preparing the organic silver colloid, the concentration of the organic complexing agent in the organic complexing solution is 0.1 to 1mol/L, preferably 0.2 to 0.6mol/L, and may be, for example, 0.1mol/L, 0.12mol/L, 0.15mol/L, 0.17mol/L, 0.2mol/L, 0.22mol/L, 0.24mol/L, 0.26mol/L, 0.3mol/L, 0.35mol/L, 0.4mol/L, 0.45mol/L, 0.5mol/L, 0.55mol/L, 0.6mol/L, or the like, and the concentration of the organic complexing agent in the organic complexing solution is controlled in this range, thereby obtaining an organic silver colloid having high stability. When the organic complexing agent is pyridine, the coordination number between silver and a pyridine group can be better controlled, and the silver bipyridyl has the best stability.

In one embodiment, in the method for preparing an organic silver colloid of the present application, in the step of preparing a silver precursor solution, the inorganic silver salt is silver nitrate or silver sulfate, preferably silver nitrate. The silver nitrate is inorganic salt with best water solubility, the cost is low, the market supply is sufficient, and the performance is stable, so that the organic silver colloid with good stability can be finally obtained.

In one embodiment, in the step of preparing the silver precursor solution, the silver ion concentration in the silver precursor solution is 0.05 to 0.5mol/L, preferably 0.08 to 0.3mol/L, for example, 0.05mol/L, 0.1mol/L, 0.15mol/L, 0.2mol/L, 0.25mol/L, 0.3mol/L, 0.35mol/L, 0.4mol/L, 0.45mol/L, 0.5mol/L, etc., and the silver ion concentration is too high, so that precipitates with large particle size are easily generated during the complexing process, which affects the activity and stability of the colloid, and the concentration is too low, so that the amount of the colloid used in the actual application process is increased. The concentration of silver ions in the silver precursor solution is controlled within the range, so that the prepared organic silver colloid has high activity, good stability and small dosage.

In one embodiment, in the method for preparing an organic silver colloid of the present application, the stabilizer is a non-ionic polymer compound, which is dissolved in an aqueous phase and constitutes a stable colloid structure, and may be selected from one or two or three of gelatin, acacia and polyvinylpyrrolidone (PVP), for example, and it is more preferable that the stabilizer is polyvinylpyrrolidone because PVP has high water solubility.

In one embodiment, in the step of preparing the stabilizer solution, the concentration of the stabilizer in the stabilizer solution is 50 to 150g/L, preferably 50 to 135g/L, for example, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 133g/L, 135g/L, 140g/L, 150g/L, etc., and the concentration of the stabilizer in the stabilizer solution is controlled within the above range, so that the prepared organic silver colloid has good stability and small dosage.

In one embodiment, in the method for preparing an organic silver colloid according to the present application, in the step of preparing a stabilizer solution, the viscosity of the stabilizer solution measured at 25 ℃ and 10rpm using a rotational viscometer is 10 to 30Pa · s, preferably 18 to 30Pa · s, more preferably 20 to 25Pa · s, and may be, for example, 10Pa · s, 12Pa · s, 14Pa · s, 15Pa · s, 18Pa · s, 20Pa · s, 22Pa · s, 24Pa · s, 25Pa · s, 28Pa · s, 30Pa · s, or the like, and the viscosity of the stabilizer solution is controlled within this range, so that the finally prepared organic silver colloid has a viscosity of 5 to 30Pa · s, and the viscosity is more stable and uniform, and organic silver colloid particles generated by a complexation reaction are more uniformly dispersed in the stabilizer.

In one embodiment, in the preparation method of the organic silver colloid of the present application, the molar ratio of the organic complexing agent to the silver in the inorganic silver salt solid is 2 to 4, and for example, can be 2. The mass of the stabilizer is 20 to 50 times, preferably 30 to 45 times, for example, 20 times, 22 times, 24 times, 26 times, 28 times, 30 times, 32 times, 34 times, 36 times, 38 times, 40 times, 42 times, 44 times, 46 times, 48 times, 50 times, etc., of the mass of the inorganic silver salt solid, and the organic silver colloid can be sufficiently encapsulated.

In a specific embodiment, in the preparation method of the organic silver colloid, in the step of preparing the organic silver colloid, the stabilizer solution and the organic complexing solution are mixed, and then the silver precursor solution is slowly added to perform a complexing reaction, so as to obtain the organic silver colloid; or, mixing the stabilizer solution and the silver precursor solution, and slowly adding the organic complexing solution to perform a complexing reaction to obtain the organic silver colloid.

In a specific embodiment, in the preparation method of the organic silver colloid of the present application, the speed of slowly adding the silver precursor solution or slowly adding the organic complex solution is 0.01 to 1L/min, preferably 0.05 to 0.5L/min, and for example, may be 0.01L/min, 0.05L/min, 0.1L/min, 0.2L/min, 0.3L/min, 0.4L/min, 0.5L/min, 0.6L/min, 0.7L/min, 0.8L/min, 0.9L/min, 1L/min, etc., and the slow adding speed is controlled to enable the complex reaction to be more thorough; and after the complexing reaction, carrying out vacuum pumping treatment, preferably carrying out vacuum pumping treatment under low-speed stirring to obtain the organic silver colloid, wherein the vacuum pumping treatment can fully remove air mixed in the preparation process of the organic silver colloid so as to further ensure the stability of the organic silver colloid.

In one embodiment, in the method for preparing organic silver colloid of the present application, the steps of preparing silver precursor solution, preparing organic complex solution, preparing stabilizer solution and preparing organic silver colloid are all performed at 10-30 ℃, for example, 10 ℃, 12 ℃, 14 ℃, 16 ℃, 18 ℃, 20 ℃, 22 ℃, 24 ℃, 26 ℃, 28 ℃, 30 ℃ and the like; the water is deionized water.

In still another aspect, the present application also provides a spherical silver powder prepared by any one of the aforementioned preparation methods.

In still another aspect, the present application also provides an electroconductive paste comprising any one of the spherical silver powders described above or the spherical silver powder obtained by any one of the preparation methods described above.

In one embodiment, the conductive paste further includes a glass frit, an organic solvent, and a vehicle.

Examples

The materials used in the assays and the methods of the assays are generally and/or specifically described herein, and in the examples that follow, the reagents or instruments used are conventional reagents or instruments that are commercially available when the reagents or instruments are indicated as being available from the sources.

Silver nitrate solid: purity: not less than 99.8%, and cortex Oriental Heterophyllae;

PVP: pharmaceutical grade, basf;

sodium stearate: AR grade, shanghai national drug;

organic silver colloid: the method is self-made in a laboratory.

Examples 1 to 1

The organic silver colloid of this example was prepared as follows:

preparing a silver precursor solution: adding 48g of silver nitrate solid into a mixing tank, adding deionized water, and stirring to dissolve the silver nitrate solid into a clear and transparent solution to obtain 1.5L of silver precursor solution;

preparing an organic complexing solution: adding 67g of pyridine liquid into a proportioning tank, diluting with deionized water, and uniformly stirring to obtain 1.5L of organic complex solution;

preparing a stabilizer solution: adding 2000g of PVP into a stirring tank, adding deionized water, stirring and dissolving to obtain a clear transparent solution, and obtaining 15L of stabilizer solution, wherein the viscosity of the stabilizer solution is 25 pas measured by using a rotary viscometer at 25 ℃ and 10 rpm;

preparing organic silver colloid: and mixing the stabilizer solution and the organic complexing solution in a stirring tank, adding the silver precursor solution after uniformly stirring, adding for 2 hours, controlling the temperature to be 15 ℃, stirring at a low speed of 20rpm after the reaction is finished, standing for 1 hour, sealing the stirring tank, and vacuumizing under the low-speed stirring of 20rpm to obtain the bipyridyl silver nitrate organic silver colloid or the bipyridyl silver nitrate organic silver colloid mixed with the tetrapyridyl silver nitrate with uniform color.

Examples 1 to 2

The organic silver colloid of this example was prepared as follows:

preparing a silver precursor solution: adding 60g of silver nitrate solid into a mixing tank, adding deionized water, and stirring to dissolve the silver nitrate solid into a clear and transparent solution to obtain 1.5L of silver precursor solution;

preparing an organic complexing solution: adding 83.8g of pyridine liquid into a material preparing tank, diluting with deionized water, and uniformly stirring to obtain 1.5L of organic complex solution;

preparing organic silver colloid: and (2) mixing the stabilizer solution and the silver precursor solution in a stirring tank, adding the organic complexing solution after uniformly stirring, adding for 3 hours, controlling the temperature to be 20 ℃, stirring at a low speed of 20rpm after the reaction is finished, standing for 2 hours, sealing the stirring tank, and vacuumizing under the low-speed stirring of 20rpm to obtain the bipyridyl silver nitrate organic silver colloid or the bipyridyl silver nitrate organic silver colloid mixed with the tetrapyridyl silver nitrate with uniform color.

Examples 1 to 3

The organic silver colloid of this example was prepared as follows:

preparing an organic complex solution: adding 67g of pyridine liquid into a proportioning tank, diluting with deionized water, and uniformly stirring to obtain 1.5L of organic complex solution;

preparing a stabilizer solution: adding 1000g of gelatin into a stirring tank, adding deionized water, stirring and dissolving to obtain a clear transparent solution, and obtaining 20L of stabilizer solution, wherein the viscosity of the stabilizer solution is 30 Pa.s when the viscosity of the stabilizer solution is measured by using a rotary viscometer at 25 ℃ and 10 rpm;

Examples 1 to 4

The organic silver colloid of this example was prepared as follows:

preparing an organic complex solution: adding 83.8g of pyridine liquid into a material preparing tank, diluting with deionized water, and uniformly stirring to obtain 1.5L of organic complex solution;

preparing a stabilizer solution: adding 1000g of gelatin into a stirring tank, adding deionized water, stirring and dissolving to obtain a clear transparent solution, and obtaining 20L of stabilizer solution, wherein the viscosity of the stabilizer solution is 30Pa s measured by using a rotary viscometer at 25 ℃ and 10 rpm;

preparing organic silver colloid: and mixing the stabilizer solution and the silver precursor solution in a stirring tank, adding the organic complexing solution after uniformly stirring, adding for 3 hours, controlling the temperature to be 20 ℃, stirring at a low speed of 20rpm after the reaction is finished, standing for 2 hours, sealing the stirring tank, and vacuumizing under the low-speed stirring of 20rpm to obtain the bipyridyl silver nitrate organic silver colloid or the bipyridyl silver nitrate organic silver colloid mixed with the tetrapyridyl silver nitrate with uniform color.

Examples 1 to 5

The organic silver colloid of this example was prepared as follows:

silver precursor solution: adding 48g of silver nitrate solid into a mixing tank, adding deionized water, and stirring to dissolve the silver nitrate solid into a clear and transparent solution to obtain 1.5L of silver precursor solution;

preparing an organic complexing solution: adding 110g of citric acid crystals into a mixing tank, diluting with deionized water, and uniformly stirring to obtain a clear and transparent solution, thereby obtaining 1.5L of an organic complexing solution;

preparing a stabilizer solution: 2000g of PVP and deionized water were added to a stirred tank and dissolved by stirring to give a clear, transparent solution, giving 15L of stabilizer solution having a viscosity of 25 pas measured at 25 ℃ and 10rpm using a rotary viscometer.

Preparing organic silver colloid: and mixing the organic complexing solution and the stabilizer solution in a stirring tank, uniformly stirring, then adding the silver precursor solution, adding for 2 hours, controlling the temperature to be 15 ℃, stirring at a low speed of 20rpm after the reaction is finished, standing for 1 hour, sealing the stirring tank, and vacuumizing under the low speed stirring of 20rpm to obtain the organic silver colloid with uniform color.

Examples 1 to 6

The organic silver colloid of this example was prepared as follows:

preparing a stabilizer solution: adding 750g of PVP into a stirring tank, adding deionized water, stirring and dissolving to obtain a clear transparent solution, and obtaining 15L of stabilizer solution, wherein the viscosity of the stabilizer solution is 10Pa s measured at 25 ℃ and 10rpm by using a rotary viscometer;

Examples 1 to 7

The organic silver colloid of this example was prepared according to the following procedure:

preparing a stabilizer solution: adding 1350g of PVP into a stirring tank, adding deionized water, stirring and dissolving to obtain a clear transparent solution, and obtaining 15L of stabilizer solution, wherein the viscosity of the stabilizer solution is 15Pa s measured at 25 ℃ and 10rpm by using a rotary viscometer;

The raw materials and parameters for examples 1-1 to 1-7 are listed in table 1:

TABLE 1

The organic silver colloid products prepared in examples 1-1 to 1-7 were examined, and the parameters of the respective products are shown in table 2 below.

The method for evaluating the activity of the organic silver colloid comprises the following steps: the organic silver colloid product is applied to a silver nitrate reduction system, and the lower the using amount of colloid under the condition of obtaining silver powder particles with the same particle size, the higher the activity.

The evaluation criteria for the stability of the organic silver colloid were: according to the satisfaction degree of the production continuity of the silver powder, at any time within 10 days after the organic silver colloid is prepared, the absolute value of the viscosity change rate of the bottom of the organic silver colloid relative to the upper surface of the organic silver colloid is required to be less than 10%, and after the organic silver colloid is stored for 10 days, the absolute value of the viscosity change rate of the same position of the organic silver colloid is required to be less than 10%.

TABLE 2

From the data in table 2 above:

the organic silver colloid with better performance can be obtained in the examples 1-1 to 1-4 and 1-7;

in terms of stability, in example 5, sedimentation occurs after 10 days of storage, and meanwhile, the activity is greatly reduced;

examples 1-1 to 1-4, examples 1-6 and 1-7 had close stability;

examples 1-1 to 1-4 are higher in activity than examples 1-6 and examples 1-7;

as a result of the evaluation of stability and activity in combination, examples 1-1 and 1-2 are superior to examples 1-3 and 1-4, examples 1-3 and 1-4 are superior to examples 1-6 and 1-7, and examples 1-6 and 1-7 are superior to examples 1-5.

The spherical silver powders of example 2-1 to example 2-7 were prepared using the organic silver colloid prepared in example 1-1.

Example 2-1

(1) Preparing an oxidizing solution: adding 40kg of silver nitrate solid into a 300L batching tank A, adding 320L of deionized water, dissolving and uniformly stirring, and heating to 30 ℃ for later use;

(2) Preparing a reducing solution: adding 20kg of vitamin C into a 300L dosing tank B, adding 380L of deionized water, dissolving and stirring uniformly, and heating to 30 ℃ for later use;

(3) Preparing a dispersion liquid: adding 2kg of PVP into a 1000L reaction kettle, adding 400L of deionized water and 50g of organic silver colloid, dissolving and uniformly stirring, and heating to 30 ℃ for later use;

(4) Reduction reaction: opening a stirrer of the reaction kettle, and adding the prepared oxidizing solution and the prepared reducing solution into the reaction kettle in sequence according to a set flow rate and a set sequence by using a metering pump, wherein the adding speed of the oxidizing solution and the reducing solution is 50L/min, and the stirring speed is controlled to be 200rpm;

(5) Silver powder wrapping: after the reduction reaction is finished, adding sodium stearate into the reaction kettle, wherein the adding amount is 0.5-1.5% of the mass of silver ions in the initially charged silver nitrate, stirring at a high speed for 1-1.5 h, and then standing for layering, wherein the stirring speed is 400rpm; and obtaining the spherical silver powder with different particle size ranges after solid-liquid separation.

Examples 2 to 2

(1) Preparing an oxidizing solution: adding 40kg of silver nitrate into a 300L dosing tank A, adding 320L of deionized water, dissolving and stirring uniformly, and heating to 30 ℃ for later use;

(2) Preparing a reaction base solution: adding 2kg of PVP into a 1000L reaction kettle, adding 450L of deionized water, dissolving, then adding 20kg of vitamin C, and stirring for dissolving; finally, adding 50g of organic silver colloid, uniformly stirring, and heating to 30 ℃ for later use;

(3) Reduction reaction: opening a stirrer of the reaction kettle, and adding the prepared oxidizing solution into the reaction kettle by using a metering pump according to a set flow rate, wherein the adding speed of the oxidizing solution is 50L/min, and the stirring speed is 200rpm;

(4) Silver powder wrapping: after the reduction reaction is finished, adding sodium stearate into the reaction kettle, wherein the adding amount is 0.5-1.5% of the mass of silver ions in the initially charged silver nitrate, stirring at a high speed for 1-1.5 h, standing for layering, and stirring at a speed of 400rpm; and obtaining the spherical silver powder with different particle size ranges after solid-liquid separation.

Examples 2 to 3

(1) Preparing a reducing solution: adding 20kg of vitamin C into a 300L dosing tank B, adding 380L of deionized water, dissolving and stirring uniformly, and heating to 30 ℃ for later use;

(2) Preparing a reaction base solution: adding 2kg of PVP into a 1000L reaction kettle, adding 450L of deionized water, adding 40kg of silver nitrate after dissolving, and stirring to dissolve; finally, adding 50g of organic silver colloid, uniformly stirring, adjusting the pH value to 7-8 by using ammonia water, and heating to 30 ℃ for later use;

(3) Reduction reaction: opening a stirrer of the reaction kettle, and adding the prepared reducing liquid into the reaction kettle by using a metering pump according to a set flow, wherein the adding speed of the reducing liquid is 50L/min, and the stirring speed is 200rpm;

(4) Silver powder wrapping: after the reduction reaction is finished, adding sodium stearate into the reaction kettle, wherein the adding amount is 0.5-1.5% of the mass of silver ions in the initially charged silver nitrate, stirring at a high speed for 1-1.5 h, standing for layering, and the stirring speed is 400rpm; and obtaining the spherical silver powder with different particle size ranges after solid-liquid separation.

Examples 2 to 4

(3) Preparing a dispersion liquid: adding 2kg of PVP into a 1000L reaction kettle, adding 400L of deionized water and 200g of organic silver colloid, dissolving and uniformly stirring, and heating to 30 ℃ for later use;

Examples 2 to 5

(3) Preparing a dispersion liquid: adding 2kg of PVP into a 1000L reaction kettle, adding 400L of deionized water and 0.4g of organic silver colloid, dissolving and uniformly stirring, and heating to 30 ℃ for later use;

(4) Reduction reaction: opening a stirrer of the reaction kettle, and adding the prepared oxidizing solution and the prepared reducing solution into the reaction kettle in sequence according to a set flow and a set sequence by using a metering pump, wherein the adding speed of the oxidizing solution and the reducing solution is 50L/min, and the stirring speed is controlled to be 200rpm;

Examples 2 to 6

(3) Preparing a dispersion liquid: adding 0.8kg of PVP into a 1000L reaction kettle, adding 400L of deionized water and 50g of organic silver colloid, dissolving and uniformly stirring, and heating to 30 ℃ for later use;

Comparative example 2-1

(3) Preparing a dispersion liquid: adding 2kg of PVP into a 1000L reaction kettle, adding 400L of deionized water, dissolving and uniformly stirring, and heating to 30 ℃ for later use;

The raw materials and the amounts of the raw materials used in the respective examples and comparative examples are listed in table 3 below.

TABLE 3

The spherical silver powder products of the examples and the comparative examples were tested, and the parameters of the products are shown in the following table 4:

TABLE 4

The good and bad performance of the silver powder is mainly reflected by the applicability of the silver powder, and the better the performance of the silver powder is, the stronger the applicability is, and the silver powder shows good performance under different client systems. Among various characterization indexes of the silver powder, the particle size distribution range characterizes the concentration of the particle size of the silver powder, and the narrower the particle size distribution range is, the stronger the applicability of the silver powder is; the width of the particle size distribution range can be judged by the difference V between D100 and D10 (V = D100-D10): the smaller the difference, the narrower the width of the particle size distribution, and vice versa. In the silver powder production industry, the particle size distribution width of the silver powder is generally considered to be narrow when the difference value is less than 4 micrometers, particularly less than 3 micrometers; on the contrary, when the difference is more than 4 μm, particularly more than 5 μm, the silver powder has a large particle size distribution width. The specific surface area and the tap density are related to the printing performance of the prepared silver paste, the suitable specific surface area and the higher tap density provide guarantee for the printing performance of the silver paste, and in addition, the higher tap density simultaneously provides guarantee for the line type and the higher electrical performance of the silver paste. The appropriate burnout value at 540 ℃ ensures the dispersing performance and the stability of the prepared slurry.

As can be seen from Table 4, the silver powders of examples 2-1 and 2-2 are the most excellent in the properties, the silver powders of examples 2-6 are the more excellent in the properties, the silver powders of examples 2-3 to 2-5 are the most excellent in the properties, and the silver powder of comparative example 2-1 is the worst.

The foregoing is illustrative of the preferred embodiments of the present application and is not to be construed as limiting thereof, since other modifications and equivalents of the disclosed embodiments may be devised by those skilled in the art. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application still belong to the protection scope of the technical solution of the present application.

Claims

reduction reaction: carrying out reduction reaction on an inorganic silver salt, a reducing agent, an organic silver colloid and a dispersing solution containing a dispersing agent;

wrapping silver powder: adding a wrapping agent into the solution after the reduction reaction to obtain spherical silver powder;

the organic silver colloid comprises organic silver colloid particles and a stabilizer, wherein the content of silver in the organic silver colloid is 0.01 to 0.2mol/L;

the organic silver colloid particles are silver bipyridyl nitrate particles, silver tetrapyridyl nitrate particles, silver bipyridyl sulfate particles, silver tetrapyridyl sulfate particles, silver citrate particles or silver oxalate particles.

2. The method of claim 1, wherein the reduction step comprises:

dissolving a reducing agent in water to obtain a reducing solution;

adding a dispersing agent into water to obtain a dispersion liquid;

3. The method of claim 1, wherein the reduction step comprises:

adding a dispersing agent into water to obtain a dispersion liquid;

4. The method of claim 1, wherein the reduction step comprises:

dissolving a reducing agent in water to obtain a reducing solution;

adding a dispersing agent into water to obtain a dispersion liquid;

5. The method according to any one of claims 1 to 4, wherein the silver content in the organic silver colloid is 0.01 to 0.05mol/L.

6. The method according to any one of claims 1 to 4, wherein the organic silver colloidal particles are silver bipyridyl nitrate particles or silver tetrapyridyl nitrate particles.

7. The method according to any one of claims 1 to 4, wherein the viscosity of the organic silver colloid is maintained within 5 to 30Pa-s for at least 10 days after the organic silver colloid is produced.

8. The method according to any one of claims 1 to 4, wherein the viscosity of the organic silver colloid is maintained within a range from 10 to 20Pa-s for at least 10 days after the organic silver colloid is prepared.

9. The production method according to any one of claims 1 to 4, wherein the produced organic silver colloid is stored in a container, wherein a part in contact with air is an upper surface of the organic silver colloid, a part in contact with a bottom of the container is a bottom of the organic silver colloid, and an absolute value of a viscosity change rate of the bottom of the organic silver colloid relative to the upper surface of the organic silver colloid is less than 10% at any time within at least 10 days after the storage.

10. The method according to any one of claims 1 to 4, wherein the absolute value of the viscosity change rate of the organic silver colloid at the same position is less than 10% after the organic silver colloid is stored for at least 10 days.

11. The method according to any one of claims 1 to 4, wherein the specific gravity of the organic silver colloid is 1.0 to 1.3g/mL.

12. The preparation method according to any one of claims 1 to 4, wherein the mass of the organic silver colloid is 0.01 to 0.5 percent of the mass of the silver ions in the inorganic silver salt.

13. The preparation method according to any one of claims 1 to 4, wherein the mass of the organic silver colloid is 0.1 to 0.5 percent of the mass of the silver ions in the inorganic silver salt.

14. The production method according to any one of claims 1 to 4, wherein the content of the stabilizer in the organic silver colloid is 20 to 150g/L.

15. The preparation method according to any one of claims 1 to 4, wherein the content of the stabilizer in the organic silver colloid is 40 to 130g/L.

16. The production method according to any one of claims 1 to 4, wherein the stabilizer is a nonionic polymer compound.

17. The method according to any one of claims 1 to 4, wherein the stabilizer is selected from one or two or three of gelatin, gum arabic and polyvinylpyrrolidone.

18. The method according to any one of claims 1 to 4, wherein the stabilizer is polyvinylpyrrolidone.

19. The method according to any one of claims 1 to 4, wherein the dispersant is a nonionic polymer compound.

20. The preparation method according to any one of claims 1 to 4, wherein the dispersant is selected from one or two or three of polyvinylpyrrolidone, gelatin and gum arabic.

21. The production method according to any one of claims 1 to 4, wherein the dispersant is polyvinylpyrrolidone.

22. The method according to any one of claims 1 to 4, wherein the inorganic silver salt is silver nitrate.

23. The method according to claim 2 or 3, wherein the concentration of silver ions in the oxidizing solution is 0.2 to 2mol/L.

24. The preparation method according to any one of claims 1 to 4, wherein the reducing agent is one or two or three selected from vitamin C, formaldehyde and hydrazine hydrate.

25. The production method according to any one of claims 1 to 4, wherein the molar ratio of the reducing agent to silver in the inorganic silver salt is 0.43 to 3.

26. The preparation method according to any one of claims 1 to 4, wherein in the step of coating the silver powder, a coating agent is added into the solution after the reduction reaction, stirring is carried out, standing and layering are carried out, and the spherical silver powder is obtained after solid-liquid separation.

27. The method according to any one of claims 1 to 4, wherein the coating agent is selected from any one of stearic acid, sodium stearate, and palmitic acid.

28. The preparation method according to claim 26, wherein the coating agent is added to the solution after the reduction reaction, stirred for 1 to 1.5 hours, and allowed to stand for layering.

29. The method according to claim 26, wherein the coating agent is added to the solution after the reduction reaction, stirred at 200 to 500rpm, and allowed to stand for layering.

30. The production method according to any one of claims 1 to 4, wherein the mass of the dispersant is not more than 10% of the mass of the silver ions in the inorganic silver salt.

31. The preparation method according to any one of claims 1 to 4, wherein the mass of the dispersing agent is 2 to 8 percent of the mass of silver ions in the inorganic silver salt.

32. The preparation method according to any one of claims 1 to 4, wherein the mass of the wrapping agent is 0.5 to 1.5% of the mass of silver ions in the inorganic silver salt.

33. The preparation method according to any one of claims 1 to 4, wherein the mass of the wrapping agent is 0.5 to 1% of the mass of silver ions in the inorganic silver salt.

34. Spherical silver powder prepared by the preparation method according to any one of claims 1 to 33, wherein the silver powder has a D50 of 0.5 to 2.0 μm and a specific surface area of 0.2 to 1.0m ² /g；

The D10 of the silver powder is 0.6 to 1.2 mu m;

the D90 of the silver powder is 1.5 to 2.5 mu m;

the D100 of the silver powder is 2.2 to 4.5 mu m;

the tap density of the silver powder is 5.5 to 6.6g/cm ³ ；

The burning loss of the silver powder at 540 ℃ is 0.2% -0.9%.

35. An electroconductive paste comprising the spherical silver powder according to claim 34.