WO2023173627A1

WO2023173627A1 - Spherical silver powder and preparation method therefor, and conductive paste

Info

Publication number: WO2023173627A1
Application number: PCT/CN2022/103623
Authority: WO
Inventors: 夏孝天; 廖云红
Original assignee: 江苏连银新材料有限公司
Priority date: 2022-03-15
Filing date: 2022-07-04
Publication date: 2023-09-21
Also published as: CN114619039A; CN114619039B

Abstract

A preparation method for spherical silver powder, comprising: performing a reduction reaction: performing a reduction reaction on inorganic silver salt, a reducing agent, an organic silver colloid and a dispersion liquid comprising a dispersing agent; and wrapping silver powder: adding a wrapping agent into the solution subjected to the reduction reaction, so as to obtain spherical silver powder. Also provided is silver powder, wherein the D50 of the silver powder is 0.5-2.0 μm, and the specific surface area of the silver powder is 0.2-1.0 m²/g. Further provided is a conductive paste comprising the silver powder. The silver powder prepared by means of the method is stable in key indexes such as particle size distribution and specific surface area; by adjusting the dosage of organic silver, the key indexes such as particle size distribution and specific surface area of the silver powder can be flexibly adjusted, so that the diversification of a silver powder product is achieved.

Description

A kind of spherical silver powder and its preparation method and conductive paste

Technical field

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

Background technique

In the current silver powder manufacturing process, the commonly used technical solutions are generally: using silver nitrate or its complex as a silver precursor, and reducing it by adding a certain reducing agent to obtain silver powder. The reducing agent used generally uses vitamin C, and a large amount of dispersing agent is used. Polyvinylpyrrolidone (PVP).

The production cost of silver powder produced by the above-mentioned process technology is high, wastewater treatment is extremely difficult, and it is also very difficult to control performance indicators such as morphology, particle size, and microstructure, and it is highly uncontrollable.

The main defects of silver powder products prepared under currently common techniques are:

(1)Higher production costs

At present, a high-vibration spherical silver powder is widely used in front-side silver paste in the photovoltaic industry in China. The amount of dispersant PVP is as high as 22% to 50% of the silver powder output, and this cost accounts for about 20% to 30% of the material cost.

(2) Wastewater treatment is difficult and costly

PVP, which is used in large quantities, all enters the wastewater after completing the dispersion of the silver powder production process. In the evaporation stage of wastewater treatment, high-concentration PVP wastewater has extremely high viscosity. If the evaporation rate is too high, it will completely block the system and cause system paralysis. For the sake of system safety, the current evaporation rate can only be set to 80%, and the other 20%. % of the evaporated concentrated residue must be processed through the incineration system. The wastewater treatment cost per kilogram of silver powder is generally around 30 yuan.

(3) Stability in product performance

Key indicators such as particle size distribution and specific surface area of existing silver powder have large fluctuations between different batches, which seriously affects the performance indicators of downstream silver paste (glue) products and affects their stability;

(4) Product adjustability

Mainly manifested in the regulation of key indicators such as particle size distribution and specific surface area. With the development of the market, different customers' demands for silver paste (glue) performance continue to be refined, and the differentiation is getting bigger and bigger. The demand for differentiated performance of silver paste (glue) puts forward the differentiated demand for silver powder. However, the existing silver powder production technology has shortcomings in controllability, and most of them are partially replaced through doping, which seriously restricts the degree of satisfaction of silver powder in terms of differentiation requirements.

(5) Control of product microstructure

Most silver powders currently on the market have a single microstructure and lack diversification. The microstructure of silver powder affects the activity of silver powder and directly affects the sintering performance of silver paste. The lack of diversification of silver powder has seriously restricted the applicable window of silver powder and cannot meet the needs of different silver paste systems for silver powder activity at different sintering temperatures.

Contents of the invention

In order to solve the problems of high production cost of silver powder, poor performance stability, poor adjustability, single microstructure and difficulty in treating production wastewater in the existing technology, this application aims to provide a preparation method of spherical silver powder. During the reduction stage of silver powder, , using an organic silver colloid as a reduction aid, successfully prepared spherical silver powder with stable performance. This application also provides a spherical silver powder prepared by the above method and a conductive paste containing the spherical silver powder.

The specific technical solutions of this application are as follows:

1. A method for preparing spherical silver powder, characterized in that it includes the following steps:

Reduction reaction: reduction reaction of inorganic silver salt, reducing agent, organic silver colloid and dispersion containing dispersant;

Coating silver powder: Add coating agent to the solution after the reduction reaction to obtain spherical silver powder.

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

Dissolve the inorganic silver salt solid in water or dilute the inorganic silver salt solution with water to obtain an oxidation solution;

Dissolve the reducing agent in water to obtain a reducing liquid;

Add the dispersant to water to obtain a dispersion;

Add organic silver colloid to the dispersion to obtain organic silver colloid dispersion;

The oxidizing liquid, the reducing liquid and the organic silver colloidal dispersion are mixed to cause a reduction reaction.

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

Add the dispersant to water to obtain a dispersion;

A reducing agent and organic silver colloid are added to the dispersion liquid, and then an oxidizing liquid is added to cause a reduction reaction.

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

Dissolve the reducing agent in water to obtain a reducing liquid;

Add the dispersant to water to obtain a dispersion;

Add inorganic silver salt and organic silver colloid to the dispersion liquid, and then add the reducing liquid to cause a reduction reaction.

5. The preparation method according to any one of items 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 0.2 mol/ L, preferably 0.01～0.05mol/L;

Preferably, the organic silver colloid particles are silver dipyridine nitrate particles, silver tetrapyridine nitrate particles, silver dipyridine sulfate particles, silver tetrapyridine sulfate particles, silver citrate particles or silver oxalate particles, preferably nitric acid. Silver dipyridine particles or silver tetrapyridine nitrate particles;

Preferably, within at least 10 days after preparing the organic silver colloid, the viscosity of the organic silver colloid is maintained at 5 to 30 Pa·s, preferably 10 to 20 Pa·s;

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, and the part in contact with the bottom of the container is the bottom of the organic silver colloid, within at least 10 days after storage At any time, 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%;

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

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

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

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

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

6. The preparation method according to any one of items 1 to 5, characterized in that the dispersant is a non-ionic polymer compound, preferably the dispersant is selected from polyvinylpyrrolidone, gelatin or gum arabic. One kind, two kinds or three kinds, more preferably the dispersing agent is polyvinylpyrrolidone.

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

8. According to the preparation method described in item 2 or 3, the concentration of silver ions in the oxidation solution is 0.2 to 2 mol/L.

9. The preparation method according to any one of items 1 to 8, characterized in that the reducing agent is selected from one, two or three types 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 3:1.

10. The preparation method according to any one of items 1 to 9, characterized in that in the step of wrapping the silver powder, a coating agent is added to the solution after the reduction reaction, stirred, left to stratify, and after solid-liquid separation. Obtain spherical silver powder;

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

Preferably, the coating agent is added to the solution after the reduction reaction, stirred for 1 to 1.5 hours, and allowed to stand for separation;

Preferably, the coating agent is added to the solution after the reduction reaction, stirred at 200 to 500 rpm, and allowed to stand for separation.

11. The preparation method according to any one of items 1 to 10, characterized in that the mass of the dispersant does not exceed 10% of the mass of silver ions in the inorganic silver salt, preferably 2% to 8%;

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

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

Preferably, the D10 of the silver powder is 0.6-1.2 μm;

Preferably, the D90 of the silver powder is 1.5-2.5 μm;

Preferably, the D100 of the silver powder is 2.2-4.5 μm;

Preferably, the tap density of the silver powder is 5.5-6.6g/cm ³ ;

Preferably, the silver powder has a burning loss of 0.2% to 0.9% at 540°C.

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

14. A conductive paste, characterized in that it contains spherical silver powder prepared by the preparation method according to any one of items 1 to 11 or spherical silver powder according to item 12.

Effect of the invention

The preparation method of this application uses an organic silver colloid as a reduction aid in the reduction reaction stage of silver powder to prepare a low-cost and high-performance spherical silver powder, which successfully solves the following problems:

(1) Reduce the proportion of dispersant dosage and silver powder production from 24% to 50% to less than 8%. Correspondingly, the material cost of PVP in silver powder production is reduced from 20% to 30% to less than 5%.

(2) The difficulty and cost of wastewater treatment are greatly reduced. In this application, due to the significant reduction of the amount of dispersant, the evaporation rate of wastewater during the wastewater treatment process is increased from 80% to 97%, and the wastewater treatment cost per kilogram of silver powder is reduced to 10 Yuan or less;

(3) The prepared silver powder product has stable performance, and the parameters of the silver powder have been successfully controlled through the following methods:

Stabilizing the dosage of organic silver colloid keeps the silver powder stable in key indicators such as particle size distribution and specific surface area;

By adjusting the amount of organic silver colloid, key indicators such as silver powder particle size distribution and specific surface area can be conveniently and flexibly adjusted, achieving the goal of diversifying silver powder product models;

By adjusting the size of organic silver colloidal particles, the microstructure of silver powder can be affected.

Description of the drawings

Figures 1A and 1B are respectively 6.8mm×1.50k and 6.8mm×10.0k scanning electron microscope images of the silver powder (L1-6) in Example 1 of the present application.

Figures 2A and 2B are respectively 5.7mm×5.00k and 5.7mm×10.0k scanning electron microscope images of the silver powder (L1-2) in Example 2 of the present application.

Detailed ways

This application will be described in detail below. Although specific embodiments of the present application are shown below, it should be understood that the present application may be implemented in various forms and should not be limited to the embodiments set forth here. Rather, these embodiments are provided to provide a more thorough understanding of the present application, and to fully convey the scope of the present application to those skilled in the art.

It should be noted that the words "include" or "include" mentioned throughout the description and claims are open-ended terms, and therefore should be interpreted as "include but not limited to". The following descriptions of the description are preferred embodiments for implementing the present application. However, the descriptions are for the purpose of general principles of the description and are not intended to limit the scope of the present application. The scope of protection of this application shall be determined by the appended claims.

On the one hand, this application provides a method for preparing spherical silver powder, which includes the following steps:

The preparation method of spherical silver powder of the present application causes a reduction reaction between organic silver salt, reducing agent, and reduction aid organic silver colloid and a dispersion liquid containing a dispersant, so that the silver powder is reduced and precipitated, thereby obtaining microscopic and macroscopic silver powder with high efficiency and low cost. Silver powder with highly controllable and stable properties.

In a specific embodiment, the preparation method of the present application, the reduction reaction step includes:

Dissolve the reducing agent in water to obtain a reducing liquid;

Add the dispersant to water to obtain a dispersion;

In the above-mentioned specific embodiment, the preparation method of the present application adds organic silver colloidal dispersion liquid to the reaction kettle, and then adds the oxidizing liquid and the reducing liquid in order to cause a reduction reaction. The order of the oxidizing liquid and the reducing liquid is not limited. In an optional embodiment, the preparation method of the present application adds organic silver colloidal dispersion liquid and reducing liquid to the reaction kettle, mixes them evenly, and then adds the oxidizing liquid to cause a reduction reaction. In an optional embodiment, the preparation method of the present application adds the organic silver colloidal dispersion liquid and the oxidizing liquid to the reaction kettle, mixes them evenly, and then adds the reducing liquid to cause a reduction reaction.

Add the dispersant to water to obtain a dispersion;

In the above specific embodiment, the preparation method of the present application, the silver ion concentration in the oxidation solution is 0.2~2mol/L, for example, it can be 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. Further preferably, the volume of the reducing liquid is 0.3 to 1 times the volume of the oxidizing liquid, for example, it can be 0.3 times, 0.4 times, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, etc.

In a specific embodiment, the preparation method of the present application involves mixing the oxidizing liquid, the reducing liquid and the organic silver colloid dispersion to undergo a reduction reaction, or adding a reducing agent and organic silver colloid to the dispersion. When adding the oxidizing solution to cause a reduction reaction, the speed of adding the oxidizing solution is 25-50L/min, for example, it can be 25L/min, 27L/min, 30L/min, 32L/min, 35L/min, 38L/min, 40L/min , 43L/min, 45L/min, 48L/min, 50L/min, etc. The grain growth mechanism of the silver powder reduction reaction is as follows: crystal nuclei are formed first, and the crystal nuclei grow in a specific direction due to the influence of the reaction environment. As the reaction time passes, the grown crystal nuclei will gradually agglomerate between particles. The feeding speed is fast, the reaction time is shortened, and the probability of grain agglomeration is greatly reduced, so the dispersion is improved.

Dissolve the reducing agent in water to obtain a reducing liquid;

Add the dispersant to water to obtain a dispersion;

In a specific embodiment, the preparation method of the present application involves mixing the oxidizing liquid, the reducing liquid and the organic silver colloid dispersion to undergo a reduction reaction, or adding silver salt and organic silver colloid to the dispersion. When adding the reducing solution to cause the reduction reaction, the speed of adding the reducing solution is 25~50L/min, for example, it can be 25L/min, 27L/min, 30L/min, 32L/min, 35L/min, 38L/min, 40L/min , 43L/min, 45L/min, 48L/min, 50L/min, etc. The feeding speed is fast, the reaction time is shortened, and the probability of grain agglomeration is greatly reduced, so the dispersion is improved.

In a specific embodiment of the preparation method of the present application, 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 0.2 mol/L, preferably 0.01 to 0.05 mol. /L, for example, it can 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, etc.

The method for measuring the silver content in the organic silver colloid of this application is:

(1) Take about 50g of organic silver colloid W1 (accurate to 0.001g), place it in a 60°C oven, and dry it for 2 hours; then raise the temperature to 105°C and dry it for 1 hour;

(2) Move the above sample into the muffle furnace, burn it at 540°C for 1 hour, and take out the constant weight;

(3) Accurately weigh the sample weight W2 in step (2) (accurate to 0.001g);

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

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

(6) Use a fully automatic potentiometric titrator to titrate the silver content in the silver nitrate solution prepared with W3, and measure the value C1 (g/L);

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

(8) Calculate the molar concentration of silver based on the specific gravity of organic silver colloid.

In a specific embodiment of the preparation method of the present application, the organic silver colloidal particles are silver dipyridine nitrate particles, silver tetrapyridine nitrate particles, silver dipyridine sulfate particles, silver tetrapyridine sulfate particles, citric acid Silver particles or silver oxalate particles are preferably silver dipyridine nitrate particles, silver tetrapyridine nitrate particles, silver dipyridine sulfate particles or silver tetrapyridine sulfate particles, and more preferably silver dipyridine nitrate particles or tetrapyridine nitrate particles. Silver particles. The organic silver colloid particles formed by the complexation of two or four molecules of pyridine groups with one silver ion can make the organic silver colloid more stable.

In a specific embodiment, the preparation method of the present application, the organic silver colloid is prepared at any time within at least 10 days, preferably at least 15 days, more preferably at least 20 days, using a rotational viscometer at 25°C, The viscosity measured at 10 rpm is 5 to 30 Pa·s, preferably 10 to 20 Pa·s, for example, it can be 5 Pa·s, 8 Pa·s, 10 Pa·s, 12 Pa·s, 15 Pa·s, 18 Pa·s, 20 Pa·s , 23Pa·s, 25Pa·s, 27Pa·s, 30Pa·s, etc., wherein at least 10 days can be, for example, 10 days, 15 days, 20 days, 25 days, 30 days, etc. By controlling the viscosity of organic silver colloidal within this range, higher colloidal stability and activity can be obtained, which will provide guarantee for controlling the performance of silver powder. However, too high stability requires more stabilizers to maintain, and colloidal stability Excessive dosage will affect the particle size of silver powder, so the viscosity of organic silver colloid needs to be controlled within an appropriate range. In a specific embodiment, the specific gravity of the organic silver colloid obtained by the preparation method of the present application is 1.0-1.3g/mL, for example, it can be 1.0g/mL, 1.05g/mL, 1.1g/mL, 1.15g/mL, 1.2g/mL, 1.25g/mL, 1.3g/mL, etc.

In a specific embodiment, according to the preparation method of the present application, the viscosity of the organic silver colloid is maintained at 5 to 30 Pa·s for at least 10 days, preferably at least 15 days, and more preferably at least 20 days after preparation, preferably 10 to 30 Pa·s. 20 Pa·s; the prepared organic silver colloid is stored in a container, where the part in contact with the air is the upper surface of the organic silver colloid, and the part in contact with the bottom of the container is the bottom of the organic silver colloid. After storage, at least 10 At any time within a day, preferably at least 15 days, and more preferably at least 20 days, 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%, for example, it can be 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%, etc., the smaller the value, the more stable the organic silver colloid is, wherein at least 10 days can be, for example, 10 days, 15 days, 20 days, 25 days, 30 days, etc.

In a specific embodiment, according to the preparation method of the present application, the viscosity of the organic silver colloid is maintained at 5 to 30 Pa·s, preferably 10 to 20 Pa within 10 days, preferably at least 15 days, and more preferably at least 20 days after preparation. ·s; 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, and the part in contact with the bottom of the container is the bottom of the organic silver colloid, within at least 10 days after storage , preferably within at least 15 days, more preferably at any time within at least 20 days, 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%, for example, it can be 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%, etc., at least 10 days can be, for example, 10 days, 15 days, 20 days, 25 days, 30 days, etc., preferably at least 15 days, more preferably at least 20 days; the organic silver colloid After storage for at least 10 days, preferably at least 15 days, more preferably at least 20 days, the absolute value of the viscosity change rate of the organic silver colloid at the same position is less than 10%, for example, it can be 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%, etc., the smaller the value, the more stable the organic silver colloid is, and at least 10 days can be, for example, 10 days, 15 days, 20 days, 25 days, 30 days, etc.

In a specific embodiment, in the preparation method of the present application, the mass of the organic silver colloid is 0.01% to 0.5% of the mass of silver ions in the inorganic silver salt, preferably 0.1% to 0.5%, for example, it can be 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%, etc.

In a specific embodiment, in the preparation method of the present application, the organic silver colloid also contains a stabilizer, and the organic silver colloid particles are evenly dispersed in the microscopic colloidal structure constructed by the stabilizer. Due to the protection of the microscopic colloidal structure, the organic silver colloid is protected. The agglomeration between silver colloid particles plays a very good blocking role and effectively prevents organic silver from losing activity due to oxidation when exposed to air, thereby preparing highly stable organic silver colloid. The content of the stabilizer is 20 to 150g/L, preferably 40 to 130g/L. The stabilizer is a non-ionic polymer compound, and preferably the stabilizer is selected from the group consisting of gelatin, gum arabic and polyvinylpyrrolidone. One kind, two kinds or three kinds, more preferably the stabilizer is polyvinylpyrrolidone.

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

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

In a specific embodiment, the preparation method of the present application uses a reducing agent to reduce and precipitate silver. As the reducing agent, one or more of vitamin C, formaldehyde, hydrazine hydrate, amine compounds and glucose can be selected. ; Preferably, the reducing agent is selected from one, two or three types of vitamin C, formaldehyde and hydrazine hydrate. Using the above reducing agent, silver powder with stable particle size distribution can be obtained. In order to improve the reaction yield of silver, the molar ratio of silver in the reducing agent and the inorganic silver salt is 0.43 to 3:1, for example, it can be 0.43:1, 0.45:1, 1:1, 1.5:1, 2: 1, 2.5:1, 3:1, etc.

In a specific embodiment of the preparation method of the present application, the coating agent is attached to the surface of the silver powder. The coating agent has two functions: it provides a guarantee for the stability of the dispersion performance of the silver powder product during storage; This ensures that the organic components in the slurry, including solvents, carriers, etc., form a whole quickly and uniformly. The coating agent is not particularly limited. For example, it can be any one of stearic acid, sodium stearate or palmitic acid. kind.

In a specific embodiment, in the preparation method of the present application, in the step of coating silver powder, a coating agent is added to the solution after the reduction reaction, stirred, left to stand for layering, and spherical silver powder is obtained after solid-liquid separation. In a preferred In the embodiment, the above-mentioned stirring speed is 200-500 rpm, and the stirring time is 1-1.5 h, etc.

In a specific embodiment, in the preparation method of the present application, the mass of the dispersant does not exceed 10% of the mass of silver ions in the inorganic silver salt, and is preferably 2% to 8% of the mass of silver ions in the inorganic silver salt. For example, it is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. The greater the amount of dispersant, the smaller the degree of agglomeration between silver powder particles will be, but Excessively high dispersant dosage will bring great difficulty to the subsequent cleaning of silver powder and related wastewater treatment, so the dosage of dispersant that meets the basic requirements of silver powder dispersion performance is very important; the quality of the coating agent is the inorganic The mass of silver ions in the silver salt is 0.5% to 1.5%, preferably 0.5% to 1.0%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

In a specific embodiment, the preparation method of the present application is to add each reaction liquid, such as: oxidizing liquid, reducing liquid, organic silver colloid dispersion liquid, the liquid obtained by adding reducing agent and organic silver colloid to the dispersion liquid, or to the dispersion liquid. The temperature of the liquid obtained after adding inorganic silver salt and organic silver colloid is controlled at 15-40°C for later use. For example, it can be 15°C, 18°C, 20°C, 23°C, 25°C, 28°C, 30°C, 33°C. ℃, 35℃, 37℃, 40℃, etc.

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

If necessary, the preparation method of the present application may also include a cleaning step of silver powder. Since the silver powder obtained through the above-mentioned reduction reaction and silver powder coating contains impurities, cleaning is required.

As a cleaning solvent used for the above-mentioned cleaning, pure water is preferred. The above-mentioned recovery and cleaning methods are not particularly limited and can be appropriately selected according to the purpose. Examples thereof include decantation and press filtration.

If necessary, the preparation method of the present application may also include a step of drying the silver powder. The silver powder obtained after solid-liquid separation or the cleaned silver powder contains moisture and needs to be removed before use. As a method for removing the above-mentioned moisture, vacuum drying is preferred. The drying temperature is preferably 100°C or lower.

On the other hand, the present application also provides a spherical silver powder, the D50 of the silver powder is 0.2-2.0 μm, preferably 0.9-1.6 μm, for example, it can be 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.5 μm, 1.7 μm, 1.9 μm, 2.0 μm, etc., the specific surface area of the silver powder is 0.2 to 1.0 m ² /g, preferably 0.3 to 0.7 m ² /g, and more It is preferably 0.25 to 0.4m ² /g, for example, it can 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, 0.5 m ² /g, 0.6m ² /g, 0.7m ² /g, 0.8m ² /g, ^{0.9m 2} /g, 1.0m ² /g, etc. The specific surface area of this application was measured with reference to GB/T1774-1995 - "Superfine Silver Powder Standard".

The spherical shape in this application refers to a silver powder whose particle shape is spherical or approximately spherical when observed under a scanning electron microscope (SEM), and the sphericity of 100 particles is 1.5 or less. The sphericity refers to the silver powder obtained through the SEM photo. When observing particles, the ratio of the longest diameter to the shortest diameter.

The measurement method of D50 is the cumulative 50% particle size in the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring method.

The specific surface area of the silver powder in this application is the BET specific surface area. The measurement method is: BET static method, and the measurement equipment is: Japanese Horiba 9603SA. When the specific surface area is too high, such as higher than 1.0m ² /g, the viscosity of the prepared slurry will increase sharply, which will have a fatal impact on the printing performance of the slurry. On the other hand, when the specific surface area is too low, such as higher than 0.2m ² /g, the viscosity of the prepared slurry will be very low, the printing line shape of the slurry cannot be maintained, and collapse will occur, seriously affecting the electrical properties of the slurry.

In a specific embodiment, the D10 of the silver powder of the present application is 0.6-1.2 μm, for example, it can be 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, etc. D10 in this application means that 10% of particles have a particle size smaller than this value.

In a specific embodiment, the D90 of the silver powder of the present application is 1.5-2.5 μm, for example, it can be 1.5 μm, 1.6 μm, 1.7 μm, 1.9 μm, 2.2 μm, 2.4 μm, 2.5 μm, etc. D90 in this application means that 90% of particles have a particle size smaller than this value.

In a specific embodiment, the D100 of the silver powder of the present application is 2.2-4.5 μm, for example, it can be 2.5 μm, 2.8 μm, 3.0 μm, 3.3 μm, 3.5 μm, 3.9 μm, etc. D100 in this application means that 100% of particles have a particle size smaller than this value.

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

If the particle size distribution of the silver powder is too large, the prepared silver paste will easily block the screen during printing and will be difficult to burn through during sintering, causing electrical performance problems. If the particle size distribution of the silver powder is too small, it will be difficult to disperse and easy to form agglomerates when preparing the silver paste. It is easy to block the screen during printing, and the silver paste is easy to burn out when sintering, causing electrical performance problems. In addition, it is preferable to use a silver powder with a narrow peak width of the particle size distribution and a uniform particle size with little variation.

In a specific embodiment, the tap density of the silver powder of the present application is 5.5-6.6g/cm ³ , preferably 6.1-6.6g/cm ³ , for example, it can be 5.5g/cm ³ , 5.6g/cm ³ , 5.7 g/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 etc. 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 will be high, making it difficult to increase the silver content of the silver paste, making it difficult to achieve the purpose of improving electrical properties by increasing the silver content. The tap density of silver powder in this application was measured with reference to GB/T 5162-2006.

In a specific embodiment, the burning loss of the silver powder of the present application at 540°C is 0.2% to 0.9%, preferably 0.25% to 0.6%, for example, it can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4% , 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc. Burning loss refers to: after burning at 540°C for 2 hours, the organic coating agent is completely decomposed. At this time, the measured weight loss of the silver powder (i.e., the burning loss value) is the content of the organic coating agent.

In a specific embodiment, the preparation method of the organic silver colloid of the present application includes the following steps:

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

Preparing an organic complexing solution: diluting the organic complexing agent with water to obtain the organic complexing solution;

Prepare a stabilizer solution: dissolve the stabilizer in water to obtain the stabilizer solution;

Preparing organic silver colloid: Mix the stabilizer solution, organic complex solution and silver precursor solution to cause a complexing reaction to obtain the organic silver colloid.

The preparation method of organic silver colloids in this application uses organic groups to complex with silver ions, and at the same time, stabilizers are used in the synthesis environment, so that the organic silver colloid particles generated by the complexation reaction are evenly dispersed in the microscopic colloidal structure constructed by the stabilizer. , due to the protection of the microscopic colloidal structure, it plays a good blocking role in the agglomeration of organic silver compound powders, and effectively prevents the loss of activity of organic silver due to oxidation due to exposure to air, thus preparing highly stable organic Silver colloid.

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

Pyridine is an organic compound, a six-membered heterocyclic compound containing a nitrogen heteroatom, which can be regarded as a CH in the benzene molecule replaced by N. The chemical properties of this type of heterocyclic compounds are as follows: electrophilic substitution reaction is difficult, nucleophilic substitution reaction is easy, oxidation reaction is difficult, and reduction reaction is easy. The stability is greatly improved in common application scenarios, especially in storage environments. A pyridine group is introduced into the anionic part of the organic silver compound, and the pyridine group is used to complex with silver ions, thereby obtaining an organic silver colloid with higher stability.

In a specific embodiment, in the preparation method of organic silver colloid of the present application, in the step of preparing the organic complex solution, the concentration of the organic complexing agent in the organic complex solution is 0.1 to 1 mol/L, preferably It is 0.2~0.6mol/L, for example, it can be 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, etc., to control the concentration of organic complexing agent in the organic complexing solution Within this range, organic silver colloids with better stability can be obtained. When the organic complexing agent is pyridine, the coordination number between silver and pyridine groups can be better controlled, and silver bipyridine has the best stability.

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

In a specific embodiment, in the preparation method of the organic silver colloid of the present application, in the step of preparing the silver precursor solution, the concentration of silver ions in the silver precursor solution is 0.05~0.5mol/L, preferably 0.08~0.3mol /L, for example, it can be 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. If the concentration of silver ions is too high, it is easy to produce precipitates with coarse particle sizes during the complexation process, which affects the activity and stability of the colloid. If the concentration is too low, the amount of colloid used in the actual application process will increase. By controlling the concentration of silver ions in the silver precursor solution within this range, the prepared organic silver colloid can have higher activity, better stability and a smaller dosage.

In a specific embodiment, in the preparation method of organic silver colloid of the present application, the stabilizer is a non-ionic polymer compound, which dissolves in the aqueous phase and builds a stable colloidal structure, for example, it can be selected from gelatin One, two or three of gum arabic and polyvinylpyrrolidone (PVP). Because PVP has high water solubility, it is more preferred that the stabilizer is polyvinylpyrrolidone.

In a specific embodiment, in the step of preparing the stabilizer solution, the stabilizer concentration in the stabilizer solution is 50-150g/L, preferably 50-135g/L, for example, it can be 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., put into the dosage solution The concentration of the stabilizer is controlled within the above range, so that the prepared organic silver colloid has better stability and a smaller dosage.

In a specific embodiment, in the preparation method of the organic silver colloid of the present application, in the step of preparing the stabilizer solution, the viscosity of the stabilizer solution measured at 25°C and 10 rpm using a rotational viscometer is 10 to 30 Pa. ·s, preferably 18 to 30 Pa·s, more preferably 20 to 25 Pa·s, for example, 10 Pa·s, 12 Pa·s, 14 Pa·s, 15 Pa·s, 18 Pa·s, 20 Pa·s, 22 Pa·s , 24Pa·s, 25Pa·s, 28Pa·s, 30Pa·s, etc., control the viscosity of the stabilizer solution within this range, so that the viscosity of the finally prepared organic silver colloid is controlled at 5-30Pa·s, and the viscosity is more stable and uniform , the organic silver colloidal particles generated by the complexation reaction are more evenly dispersed in the stabilizer.

In a specific embodiment, in the preparation method of 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 4:1, for example, it can be 2:1, 2.2 :1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, etc., in this application, by controlling the organic complexation The molar ratio of the agent to the silver in the inorganic silver salt solid is such that an excess of organic complexing agent is added to ensure that the inorganic silver salt is fully complexed. The mass of the stabilizer is 20 to 50 times the solid mass of the inorganic silver salt, preferably 30 to 45 times, for example, it can be 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., which can ensure that the organic silver colloid is fully wrapped.

In a specific embodiment, in the preparation method of the organic silver colloid of the present application, in the step of preparing the organic silver colloid, the stabilizer solution and the organic complex solution are mixed, and then the silver precursor solution is slowly added , a complexation reaction occurs, and the organic silver colloid is obtained; or, the stabilizer solution and the silver precursor solution are mixed, and then the organic complexation solution is slowly added, and a complexation reaction occurs, and the organic silver colloid is obtained. colloid.

In a specific embodiment, in the preparation method of organic silver colloid of the present application, the speed of slowly adding the silver precursor solution or slowly adding the organic complex solution is 0.01~1L/min, preferably 0.05~0.5L /min, for example, it can 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., controlling the slow addition speed can make the complexation reaction more thorough; after the complexation reaction, vacuum treatment is performed, preferably under low-speed stirring. , the organic silver colloid is obtained, and the vacuum treatment can fully remove the air mixed in the organic silver colloid during the preparation process to further ensure the stability of the organic silver colloid.

In a specific embodiment, in the preparation method of the organic silver colloid of the present application, the steps of preparing the silver precursor solution, the step of preparing the organic complex solution, the step of preparing the stabilizer solution, and the step of preparing the organic silver colloid are all performed at 10 to 30°C. The temperature may be 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, etc.; the water is deionized water.

On the other hand, the present application also provides a spherical silver powder prepared by any of the aforementioned preparation methods.

In another aspect, the present application also provides a conductive paste containing any of the aforementioned spherical silver powders or spherical silver powders prepared by any of the aforementioned preparation methods.

In a specific embodiment, the conductive slurry further includes glass powder, organic solvent and carrier.

Example

This application provides a general and/or specific description of the materials and test methods used in the test. In the following examples, when the sources of the reagents or instruments used are indicated, they are all conventional reagents or instruments that are commercially available.

Silver nitrate solid: Purity: ≥99.8%, Tongbai, Henan;

PVP: pharmaceutical grade, BASF;

Sodium stearate: AR grade, Shanghai Sinopharm;

Organic silver colloid: homemade in the laboratory.

Example 1-1

Prepare the organic silver colloid of this example according to the following steps:

Prepare the silver precursor solution: add 48g of solid silver nitrate in the batching tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 1.5L of silver precursor solution;

Prepare the organic complex solution: add 67g of pyridine liquid into the batching tank, dilute it with deionized water, and stir evenly to obtain 1.5L of organic complex solution;

Prepare the stabilizer solution: add 2000g of PVP in the stirring tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 15L of stabilizer solution. The stabilizer solution is measured using a rotational viscometer at 25°C and 10rpm. The viscosity is 25Pa·s;

Preparation of organic silver colloid: Mix the stabilizer solution and the organic complex solution in a stirring tank. After stirring evenly, add the silver precursor solution. The adding time is 2 hours. The temperature is controlled to 15°C. After the reaction is completed, stir at a low speed of 20 rpm and let stand. Leave for 1 hour, seal the stirring tank, and perform vacuum treatment with low-speed stirring at 20 rpm to obtain uniform color dipyridine silver nitrate organic silver colloid or dipyridine silver nitrate organic silver colloid mixed with tetrapyridine silver nitrate.

Example 1-2

Prepare the silver precursor solution: add 60g of solid silver nitrate in the batching tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 1.5L of silver precursor solution;

Prepare the organic complex solution: add 83.8g of pyridine liquid into the batching tank, dilute it with deionized water, and stir evenly to obtain 1.5L of organic complex solution;

Preparation of organic silver colloid: Mix the stabilizer solution and silver precursor solution in a stirring tank. After stirring evenly, add the organic complex solution. The adding time is 3 hours. The temperature is controlled to 20°C. After the reaction is completed, stir at a low speed of 20 rpm and let stand. Leave for 2 hours, seal the stirring tank, and perform vacuum treatment with low-speed stirring at 20 rpm to obtain uniform color dipyridine silver nitrate organic silver colloid or dipyridine silver nitrate organic silver colloid mixed with tetrapyridine silver nitrate.

Example 1-3

Prepare the stabilizer solution: add 1000g of gelatin in the stirring tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 20L of stabilizer solution. The stabilizer solution is measured using a rotational viscometer at 25°C and 10rpm. The viscosity is 30Pa·s;

Examples 1-4

Prepare the stabilizer solution: add 1000g of gelatin in the mixing tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 20L of stabilizer solution. The stabilizer solution is measured using a rotational viscometer at 25°C and 10rpm. The viscosity is 30Pa·s;

Examples 1-5

Silver precursor solution: Add 48g of solid silver nitrate into the batching tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 1.5L of silver precursor solution;

Prepare organic complex solution: add 110g citric acid crystals into the batching tank, dilute with deionized water, stir evenly to form a clear and transparent solution, and obtain 1.5L organic complex solution;

Prepare the stabilizer solution: Add 2000g of PVP and deionized water to the stirring tank, stir and dissolve into a clear and transparent solution, and obtain 15L of stabilizer solution. The viscosity of the stabilizer solution is measured using a rotary viscometer at 25°C and 10 rpm. is 25Pa·s.

Preparation of organic silver colloid: Mix the organic complex solution and the stabilizer solution in a stirring tank. After stirring evenly, add the silver precursor solution. The adding time is 2 hours. The temperature is controlled to 15°C. After the reaction is completed, stir at a low speed of 20 rpm and let stand. Leave for 1 hour, seal the mixing tank, and perform vacuum treatment with low-speed stirring at 20 rpm to obtain organic silver colloid with uniform color.

Examples 1-6

Prepare the stabilizer solution: add 750g of PVP in the stirring tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 15L of stabilizer solution. The stabilizer solution is measured using a rotational viscometer at 25°C and 10 rpm. The viscosity is 10Pa·s;

Example 1-7

Prepare silver precursor solution: add 48g of solid silver nitrate in the batching tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 1.5L of silver precursor solution;

Prepare the stabilizer solution: add 1350g of PVP in the mixing tank, add deionized water, stir and dissolve into a clear and transparent solution, and obtain 15L of stabilizer solution. The stabilizer solution is measured using a rotational viscometer at 25°C and 10rpm. The viscosity is 15Pa·s;

The raw materials and parameters of 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 tested. The parameters of each product are as shown in Table 2 below.

Among them, the evaluation method of organic silver colloid activity is as follows: apply organic silver colloid products to the silver nitrate reduction system. When obtaining silver powder particles of the same particle size, the smaller the amount of colloid used, the higher the activity.

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

Table 2

According to the data in Table 2 above, we can know:

Examples 1-1 to 1-4 and 1-7 can all obtain organic silver colloids with better performance;

In terms of stability, Example 5 settled after being stored for 10 days, and the activity also decreased significantly;

The stabilities of Examples 1-1 to 1-4, Examples 1-6 and 1-7 are close;

In terms of activity, Examples 1-1 to 1-4 are higher than Examples 1-6 and 1-7;

Comprehensive evaluation of stability and activity shows that Example 1-1 and Example 1-2 are better than Example 1-3 and Example 1-4, and Examples 1-3 and 1-4 are better than Examples 1-6 and 1 -7, Embodiments 1-6 and 1-7 are better than Embodiment 1-5.

The organic silver colloid prepared in Example 1-1 was used to prepare the spherical silver powder of Examples 2-1 to 2-7.

Example 2-1

(1) Prepare oxidation solution: Add 40kg of silver nitrate solid into 300L batching tank A, add 320L of deionized water, dissolve and stir evenly, then heat to 30°C for later use;

(2) Prepare reducing solution: Add 20kg of vitamin C into 300L batching tank B, add 380L of deionized water, dissolve and stir evenly, then heat to 30°C for later use;

(3) Prepare dispersion: add 2kg of PVP into a 1000L reaction kettle, add 400L of deionized water and 50g of organic silver colloid, dissolve and stir evenly, then heat to 30°C for later use;

(4) Reduction reaction: Open the stirrer of the reaction kettle, use a metering pump to add the prepared oxidizing liquid and reducing liquid to the reactor in sequence according to the set flow rate and order. The adding speed of the oxidizing liquid and reducing liquid is 50L/ min, the stirring speed is controlled to 200rpm;

(5) Silver powder coating: After the reduction reaction is completed, add sodium stearate into the reaction kettle in an amount of 0.5% to 1.5% of the mass of silver ions in the initial silver nitrate. Stir at high speed for 1 to 1.5 hours and then let stand for stratification. , the stirring speed is 400rpm; after solid-liquid separation, spherical silver powders with various particle size ranges are obtained.

Example 2-2

(1) Prepare oxidation solution: Add 40kg of silver nitrate into 300L batching tank A, add 320L of deionized water, dissolve and stir evenly, then heat to 30°C for later use;

(2) Prepare the reaction bottom solution: add 2kg of PVP into a 1000L reaction kettle, add 450L of deionized water, add 20kg of vitamin C after dissolving, stir and dissolve; finally add 50g of organic silver colloid, stir evenly, and heat to 30℃ for later use;

(3) Reduction reaction: Open the stirrer of the reaction kettle, use a metering pump to add the prepared oxidation liquid into the reaction kettle according to the set flow rate, the oxidation liquid addition speed is 50L/min, and the stirring speed is 200rpm;

(4) Silver powder coating: After the reduction reaction is completed, add sodium stearate into the reaction kettle in an amount of 0.5% to 1.5% of the mass of silver ions in the initial silver nitrate. Stir at high speed for 1 to 1.5 hours and then let stand for separation. layer, the stirring speed is 400 rpm; after solid-liquid separation, spherical silver powders with various particle size ranges are obtained.

Example 2-3

(1) Prepare reducing solution: Add 20kg of vitamin C into 300L batching tank B, add 380L of deionized water, dissolve and stir evenly, then heat to 30°C for later use;

(2) Prepare the reaction bottom solution: add 2kg of PVP to a 1000L reaction kettle, add 450L of deionized water, add 40kg of silver nitrate after dissolution, stir and dissolve; finally add 50g of organic silver colloid, stir evenly and adjust with ammonia water Adjust pH to 7~8, heat to 30℃ and set aside;

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

Example 2-4

(3) Prepare dispersion: add 2kg of PVP into a 1000L reaction kettle, add 400L of deionized water and 200g of organic silver colloid, dissolve and stir evenly, then heat to 30°C for later use;

Example 2-5

(3) Prepare dispersion: add 2kg of PVP into a 1000L reaction kettle, add 400L of deionized water and 0.4g of organic silver colloid, dissolve and stir evenly, then heat to 30°C for later use;

Example 2-6

(3) Prepare dispersion: add 0.8kg of PVP into a 1000L reaction kettle, add 400L of deionized water and 50g of organic silver colloid, dissolve and stir evenly, then heat to 30°C for later use;

Comparative example 2-1

(3) Prepare dispersion: add 2kg of PVP into a 1000L reaction kettle, add 400L of deionized water, dissolve and stir evenly, then heat to 30°C for later use;

The raw materials and amounts of raw materials used in each example and comparative example are listed in Table 3 below.

table 3

The spherical silver powder products of each embodiment and comparative example were tested. The parameters of each product are as shown in Table 4 below:

Table 4

The performance of silver powder is mainly reflected in its applicability. Silver powder with better performance often has stronger applicability and shows good performance under different customer systems. Among the many characterization indicators of silver powder, the particle size distribution range represents the concentration of the silver powder particle size. The narrower the particle size distribution range, the stronger the applicability of the silver powder; the width of the particle size distribution range can be determined by the difference between D100 and D10. V (V=D100-D10) to judge: the smaller the difference, the narrower the particle size distribution width, and vice versa. In the silver powder production industry, it is generally believed that when the difference is less than 4 μm, especially less than 3 μm, the silver powder particle size distribution width is narrow; conversely, when the difference is greater than 4 μm, especially greater than 5 μm, the silver powder particle size distribution width is large. The specific surface area and tap density are related to the printing performance of the prepared silver paste. A suitable specific surface area and a higher tap density provide guarantee for the printing performance of the silver paste. In addition, a higher tap density also ensures the printing performance of the silver paste. Linear shape and higher electrical performance are guaranteed. The appropriate burning loss value at 540°C ensures the dispersion and stability of the prepared slurry.

It can be seen from Table 4 that the performance of the silver powder of Examples 2-1 and 2-2 is the best, the performance of the silver powder of Example 2-6 is better, the performance of the silver powder of Examples 2-3 to 2-5 is average, and the performance of Comparative Example 2 -1 silver powder is the worst.

The above are only preferred embodiments of the present application, and are not intended to limit the present application in other forms. Any skilled person familiar with the art may make changes or modifications to equivalent changes using the technical contents disclosed above. Example. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application still fall within the protection scope of the technical solution of the present application.

Claims

A method for preparing spherical silver powder, characterized in that it includes the following steps:

Reduction reaction: reduction reaction of inorganic silver salt, reducing agent, organic silver colloid and dispersion containing dispersant;

Coating silver powder: Add coating agent to the solution after the reduction reaction to obtain spherical silver powder.
The preparation method according to claim 1, characterized in that the reduction reaction step includes:

Dissolve the inorganic silver salt solid in water or dilute the inorganic silver salt solution with water to obtain an oxidation solution;

Dissolve the reducing agent in water to obtain a reducing liquid;

Add the dispersant to water to obtain a dispersion;

Add organic silver colloid to the dispersion to obtain organic silver colloid dispersion;

The oxidizing solution, the reducing solution and the organic silver colloidal dispersion are mixed to cause a reduction reaction.
The preparation method according to claim 1, characterized in that the reduction reaction step includes:

Dissolve the inorganic silver salt solid in water or dilute the inorganic silver salt solution with water to obtain an oxidation solution;

Add the dispersant to water to obtain a dispersion;

A reducing agent and organic silver colloid are added to the dispersion liquid, and then an oxidizing liquid is added to cause a reduction reaction.
The preparation method according to claim 1, characterized in that the reduction reaction step includes:

Dissolve the reducing agent in water to obtain a reducing liquid;

Add the dispersant to water to obtain a dispersion;

Add inorganic silver salt and organic silver colloid to the dispersion liquid, and then add the reducing liquid to cause a reduction reaction.
The preparation method according to any one of claims 1 to 4, wherein 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 0.2 mol/L. , preferably 0.01～0.05mol/L;

Preferably, the organic silver colloid particles are silver dipyridine nitrate particles, silver tetrapyridine nitrate particles, silver dipyridine sulfate particles, silver tetrapyridine sulfate particles, silver citrate particles or silver oxalate particles, preferably nitric acid. Silver dipyridine particles or silver tetrapyridine nitrate particles;

Preferably, within at least 10 days after preparing the organic silver colloid, the viscosity of the organic silver colloid is maintained at 5 to 30 Pa·s, preferably 10 to 20 Pa·s;

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, and the part in contact with the bottom of the container is the bottom of the organic silver colloid, within at least 10 days after storage At any time, 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%;

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

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

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

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

Preferably, the stabilizer is a non-ionic polymer compound, preferably the stabilizer is selected from one, two or three types of gelatin, gum arabic and polyvinylpyrrolidone, and more preferably the stabilizer is polyethylene. Pyrrolidone.
The preparation method according to any one of claims 1 to 5, characterized in that the dispersant is a non-ionic polymer compound, preferably the dispersant is selected from one of polyvinylpyrrolidone, gelatin or gum arabic. One or two or three kinds, more preferably the dispersant is polyvinylpyrrolidone.
The preparation method according to any one of claims 1 to 6, characterized in that the inorganic silver salt is silver nitrate.
According to the preparation method of claim 2 or 3, the concentration of silver ions in the oxidation solution is 0.2-2 mol/L.
The preparation method according to any one of claims 1 to 8, characterized in that the reducing agent is selected from one, two or three types 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 3:1.
The preparation method according to any one of claims 1 to 9, characterized in that, in the step of wrapping the silver powder, a coating agent is added to the solution after the reduction reaction, stirred, left to stand for layering, and solid-liquid separation is obtained. Spherical silver powder;

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

Preferably, the coating agent is added to the solution after the reduction reaction, stirred for 1 to 1.5 hours, and allowed to stand for separation;

Preferably, the coating agent is added to the solution after the reduction reaction, stirred at 200 to 500 rpm, and allowed to stand for separation.
The preparation method according to any one of claims 1 to 10, characterized in that the mass of the dispersant does not exceed 10% of the mass of silver ions in the inorganic silver salt, preferably 2% to 8%;

Preferably, the mass of the coating agent is 0.5% to 1.5% of the mass of silver ions in the inorganic silver salt, preferably 0.5% to 1%.
A spherical silver powder, characterized in that the D50 of the silver powder is 0.5 to 2.0 μm, and the specific surface area of the silver powder is 0.2 to 1.0 m 2 /g;

Preferably, the D10 of the silver powder is 0.6-1.2 μm;

Preferably, the D90 of the silver powder is 1.5-2.5 μm;

Preferably, the D100 of the silver powder is 2.2-4.5 μm;

Preferably, the tap density of the silver powder is 5.5-6.6g/cm 3 ;

Preferably, the silver powder has a burning loss of 0.2% to 0.9% at 540°C.
A spherical silver powder prepared by the preparation method according to any one of claims 1 to 11.
A conductive paste, characterized in that it contains spherical silver powder prepared by the preparation method according to any one of claims 1 to 11 or spherical silver powder according to claim 12.