Submicron flaky silver powder and preparation method thereof

Abstract

The present invention belongs to the technical field of metal powders, and specifically relates to a submicron flaky silver powder and a preparation method thereof. The preparation method of the present invention comprises adding a protective agent solution to a silver precursor solution, adding an acidic solution to adjust the pH value to 0.5-6 after mixing, and then adding a reducing agent solution to perform a nucleation reaction to obtain a nucleation system; adding an alkaline solution to the nucleation system to adjust the pH value to 7-13, and continuing to grow to obtain a silver powder dispersion; and post-treating the silver powder dispersion to obtain a submicron flaky silver powder. The preparation method designed by the present invention uses a selective reaction solvent to regulate the concentration of each reaction raw material, the reaction temperature and the reaction time, so as to control the stability of nucleation and the uniformity of the growth rate, thereby obtaining a silver powder with uniform particle size distribution and good crystal form.

Description

Technical Field

[0001] The invention belongs to the technical field of metal powders, and in particular relates to submicron flaky silver powder and a preparation method thereof. Background Art

[0002] Micro-nano silver powder is a functional raw material widely used in the electronics industry. It has excellent catalytic properties, magnetic properties, electrical properties, etc. It is the most widely used and largest amount of precious metal powder in the electronics industry. For example, it is used to make electronic pastes, conductive coatings, electromagnetic shielding materials, conductive inks, conductive plastics, conductive ceramics, etc. It is a key material for the production of various electronic components.

[0003] At present, the preparation methods of micro-nano silver powder are divided into physical methods and chemical methods. The silver powder prepared by physical methods has complex process and poor performance. Therefore, chemical methods are mainly used to prepare micro-nano silver powder, among which chemical reduction method, electrolysis method and sol-gel method are commonly used. Among them, chemical reduction method is the most commonly used method for preparing micro-nano silver powder. It has simple equipment, low production cost, and controllable product performance and good repeatability.

[0004] However, when preparing flaky silver powder by the existing chemical reduction method, not only is the post-processing complicated, but the morphology of the silver powder is also difficult to control, and there may also be problems such as uneven distribution of the silver powder particle size. Summary of the invention

[0005] The technical purpose of the present invention is to at least solve the problems that when preparing flaky silver powder by the existing chemical reduction method, not only the post-processing is complicated, but also the morphology of the silver powder is difficult to control, and there may also be problems such as uneven distribution of the silver powder particle size.

[0006] This purpose is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing submicron flaky silver powder, the method comprising the following preparation steps:

[0008] 1) taking a silver precursor, a reducing agent and a protective agent and dispersing them in a solvent to form a silver precursor solution, a reducing agent solution and a protective agent solution respectively;

[0009] The molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:(0.5-4):(1-4); the molar ratio here also refers to the molar ratio of substances.

[0010] 2) adding the protective agent solution to the silver precursor solution, mixing well, adding an acidic solution to adjust the pH value to 0.5-6, and then adding the reducing agent solution to perform a nucleation reaction to obtain a nucleation system;

[0011] 3) adding an alkaline solution to the nucleation system to adjust the pH value to 7-13, and continuing to grow to obtain a silver powder dispersion;

[0012] 4) Post-treating the silver powder dispersion to obtain submicron flaky silver powder.

[0013] In some embodiments of the present invention, the molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:(0.5-1):(1-2).

[0014] In some embodiments of the present invention, in step 1), the solvent is a mixed solvent of deionized water and polyol, and the mass ratio of deionized water to polyol in the mixed solvent is (0.5-4):1, preferably (1-2):1. The solvent is beneficial to controlling the stability of the nucleation reaction and is beneficial to generating flaky powders with a polyhedral structure.

[0015] In some embodiments of the present invention, the deionized water includes any one of pure water and ultrapure water, and the polyol includes any one of ethylene glycol and glycerol.

[0016] In some embodiments of the present invention, in step 1), the molar concentration ratio of the silver precursor solution, the reducing agent solution and the protective agent solution is (0.2-8): (0.02-2): (0.2-4), preferably (0.4-4): (0.04-1): (0.4-2), and the molar concentration unit is mol / L.

[0017] In some embodiments of the present invention, the silver precursor is any one of silver nitrate and silver acetate;

[0018] The protective agent is one or two or more of PVA, PVP, sorbitol, sodium citrate, gelatin, gum arabic, BTA, PEG, and SDBS; wherein the protective agent plays a role in controlling the particle morphology and plays an important role in the nucleation process.

[0019] The reducing agent is at least one of formaldehyde, ascorbic acid, potassium tartrate, hydrazine hydrate, hydrazine carbonate and glucose.

[0020] In some embodiments of the present invention, the reaction temperature of step 2) and step 3) is 10 to 60° C., preferably 15 to 50° C., and the reaction time of step 2) is lower than the reaction time of step 3);

[0021] Specifically, the reaction time of step 2) is ≤10 min, preferably 2 to 6 min;

[0022] The reaction time of step 3) is ≤120 min, preferably 60 to 100 min.

[0023] In some embodiments of the present invention, in step 2), the acidic solution comprises an aqueous solution of any one of nitric acid and acetic acid, and the concentration of the acidic solution is 0.02 to 0.5 mol / L;

[0024] In step 3), the alkaline solution comprises an aqueous solution of any one of sodium hydroxide and ammonia water, and the concentration of the alkaline solution is 0.02 to 3 mol / L.

[0025] In some embodiments of the present invention, in step 4), the post-treatment includes centrifugal separation, washing and drying, the washing includes washing 3 to 4 times with one or two or three of ethanol, acetone or deionized water, and the drying is vacuum drying, and the vacuum drying includes controlling the temperature at 40 to 90°C and drying for 1 to 6 hours.

[0026] In a second aspect, the present invention provides a submicron flaky silver powder, which is prepared by the method described in the first aspect.

[0027] In some embodiments of the present invention, the silver powder comprises flakes having a polyhedral crystal form, and the flakes account for more than 90 wt %; wherein the D50 of the flakes is 0.3 to 1 μm, and the thickness of the flakes is 50 to 200 nm;

[0028] The tap density of the silver powder is 4.0 to 6.0 g / cm 3 .

[0029] Wherein, the flaky powder with a polyhedral structure comprises flaky powder with regular or irregular hexagonal shape.

[0030] Therefore, the present invention produces silver powder with a polyhedral crystal form, and the particle size distribution of the silver powder is uniform.

[0031] In a third aspect, the present invention provides the silver powder prepared by the method described in the first aspect or the silver powder described in the second aspect as a raw material for conductive silver paste.

[0032] The beneficial effects of the technical solution disclosed in the present invention are mainly reflected in the following:

[0033] 1. The preparation method provided by the present invention uses a selective reaction solvent and regulates the concentration, dosage, reaction temperature and reaction time of each reaction raw material, thereby better controlling the stability of the nucleation reaction and the uniformity of the growth rate, and obtaining a silver powder with uniform particle size distribution and a polyhedral crystal form.

[0034] 2. The preparation method provided by the present invention is not complicated in post-processing for preparing silver powder and is suitable for large-scale industrial production.

[0035] 3. The silver powder provided by the present invention comprises flaky powder with a polyhedral structure, wherein the flaky powder with a polyhedral structure accounts for more than 90wt%, and the powder can be used as a raw material for conductive silver paste. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference numerals are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0037] Figure 1 The microscopic morphology of the silver powder prepared according to Example 1 of the present invention is schematically shown.

[0038] Figure 2 The microscopic morphology of the silver powder prepared according to Example 1 of the present invention is schematically shown.

[0039] Figure 3 The microscopic morphology of the silver powder prepared according to Example 5 of the present invention is schematically shown.

[0040] Figure 4 The microscopic morphology of the silver powder prepared according to Example 5 of the present invention is schematically shown.

[0041] Figure 5 The microscopic morphology of the silver powder prepared according to Example 6 of the present invention is schematically shown.

[0042] Figure 6 The microscopic morphology of the silver powder prepared according to Example 6 of the present invention is schematically shown.

[0043] Figure 7 The microscopic morphology of the silver powder prepared according to Example 11 of the present invention is schematically shown.

[0044] Figure 8 The microscopic morphology of the silver powder prepared according to Example 12 of the present invention is schematically shown. DETAILED DESCRIPTION

[0045] Chemical name and English abbreviation:

[0046] Polyvinyl alcohol: PVA; polyvinyl pyrrolidone: PVP; phenyltriazole: BTA; polyethylene glycol: PEG; sodium dodecylbenzene sulfonate: SDBS.

[0047] In the prior art, when a chemical reduction method is used to prepare flaky silver powder, not only is the post-processing complicated, but the morphology of the silver powder is also difficult to control, and there may also be a problem of uneven distribution of the silver powder particle size.

[0048] In order to solve the above technical problems, the present invention provides a submicron flaky silver powder and a preparation method thereof. The preparation method designed by the present invention uses a selective reaction solvent to regulate the concentration, dosage, reaction temperature and reaction time of each reaction raw material to control the stability of nucleation and the uniformity of growth rate, thereby obtaining a silver powder with uniform particle size distribution and a polyhedral crystal form.

[0049] The first aspect of the present invention to achieve the above technical effects is to provide a method for preparing submicron flaky silver powder, the method comprising the following preparation steps:

[0050] 1) taking a silver precursor, a reducing agent and a protective agent and dissolving them in a solvent to form a silver precursor solution, a reducing agent solution and a protective agent solution respectively;

[0051] Wherein, the molar ratio between the silver precursor, the reducing agent and the protecting agent is 1:(0.5-4):(1-4);

[0052] 2) adding the protective agent solution to the silver precursor solution, mixing well, adding an acidic solution to adjust the pH value to 0.5-6, and then adding the reducing agent solution to perform a nucleation reaction to obtain a nucleation system;

[0053] 3) adding an alkaline solution to the nucleation system to adjust the pH value to 7-13, and continuing to grow to obtain a silver powder dispersion;

[0054] 4) Post-treating the silver powder dispersion to obtain submicron flaky silver powder.

[0055] Exemplarily, the molar ratio of the silver precursor to the reducing agent is any one of 1:0.5, 1:0.8, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or any ratio within the range.

[0056] Exemplarily, the molar ratio of the silver precursor to the protective agent is any one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or any ratio within a range of values.

[0057] In some embodiments, the molar ratio of the silver precursor, the reducing agent, and the protecting agent is 1:(0.5-1):(1-2).

[0058] Exemplarily, the molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:0.75:1.5.

[0059] Exemplarily, the molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:0.5:1.5.

[0060] Exemplarily, the molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:0.75:1.

[0061] Exemplarily, the molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:0.5:1.

[0062] Exemplarily, the molar ratio of the silver precursor, the reducing agent and the protecting agent is 1:1:1.

[0063] Illustratively, in step 2), the pH value is adjusted to any one of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.2, 4.5, 4.8, 5.0, 5.2, 5.5, 5.8, 6.0 or any ratio of the range value.

[0064] Exemplarily, in step 3), the pH value is adjusted to any one of 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13 or any ratio of the range value.

[0065] In some embodiments, the solvent is a mixed solvent of deionized water and polyol, and the mass ratio of deionized water to polyol in the mixed solvent is (0.5-4):1.

[0066] In some embodiments, the mass ratio of deionized water to polyol in the mixed solvent is preferably (1-2):1.

[0067] Exemplarily, the mass ratio between deionized water and polyol in the mixed solvent is any one of 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or any ratio within the range.

[0068] In some embodiments, the deionized water includes any one of pure water and ultrapure water, and the polyol includes any one of ethylene glycol and glycerol. When glycerol is selected as the polyol, due to the high viscosity of glycerol, the amount of deionized water used in preparing the solvent is relatively large.

[0069] In some embodiments, in step 1), the molar concentration ratio between the silver precursor solution, the reducing agent solution and the protective agent solution is:

[0070] (0.2~8):(0.02~2):(0.2~4). And the solution can be prepared at room temperature.

[0071] In some embodiments, the molar concentration ratio of the silver precursor solution, the reducing agent solution and the protecting agent solution is preferably (0.4-4):(0.04-1):(0.4-2), and the molar concentration unit is mol / L.

[0072] Exemplarily, the molar concentration ratio between the silver precursor solution, the reducing agent solution and the protective agent solution is:

[0073] Any one of 0.2:1:1, 0.5:1:1, 1:1:1, 1.5:1:1, 2:1:1, 2.5:1:1, 3:1:1, 3.5:1:1, 4:1:1, 4.5:1:1, 5:1:1, 5.5:1:1, 6:1:1, 6.5:1:1, 7:1:1, 7.5:1:1, 8:1:1 or any ratio in the range value.

[0074] In some embodiments, the silver precursor is any one of silver nitrate and silver acetate;

[0075] The protective agent is one or two or more of PVA, PVP, sorbitol, sodium citrate, gelatin, gum arabic, BTA, PEG, and SDBS;

[0076] The reducing agent is at least one of formaldehyde, ascorbic acid, potassium tartrate, hydrazine hydrate, hydrazine carbonate and glucose.

[0077] In some embodiments, the reaction temperature of step 2) and step 3) is 10-60° C., preferably 15-50° C., and the reaction time of step 2) is lower than the reaction time of step 3);

[0078] Specifically, the reaction time of step 2) is ≤10 min, preferably 2 to 6 min;

[0079] The reaction time of step 3) is ≤120 min, preferably 60 to 100 min.

[0080] In some embodiments, in step 2), the acidic solution comprises an aqueous solution of any one of nitric acid and acetic acid, and the concentration of the acidic solution is 0.02-0.5 mol / L.

[0081] In some embodiments, in step 3), the alkaline solution comprises an aqueous solution of any one of sodium hydroxide and ammonia water, and the concentration of the alkaline solution is 0.02 to 3 mol / L.

[0082] In some embodiments, in step 4), the post-treatment includes centrifugal separation, washing and drying, the washing includes washing 3 to 4 times with one, two or three of ethanol, acetone or deionized water, the drying is vacuum drying, and the vacuum drying includes controlling the temperature at 40 to 90°C and drying for 1 to 6 hours.

[0083] The second aspect of the present invention to achieve the above technical effects is to provide a submicron flaky silver powder, which is prepared by the method described in the first aspect.

[0084] In some embodiments, the silver powder comprises flakes having a polyhedral crystal form, and the flakes account for more than 90 wt %; wherein the D50 of the flakes is 0.3 to 1 μm, and the thickness of the flakes is 50 to 200 nm;

[0085] The tap density of the silver powder is 4.0 to 6.0 g / cm 3 .

[0086] In a third aspect, the present invention provides the silver powder prepared by the method described in the first aspect or the silver powder described in the second aspect as a raw material for conductive silver paste.

[0087] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. Among them, the chemical reagents, chemical raw materials, etc. used in the following embodiments are all for laboratory use, and their purity levels are laboratory grade, and the selection of each reagent and raw material is not limited by manufacturer or model.

[0088] Example 1

[0089] Disclosed is a method for preparing submicron flaky silver powder, which comprises the following preparation steps:

[0090] 1) Ultrapure water and glycerol were mixed in a mass ratio of 1:1 as a solvent, and 0.2 L of 2 mol / L silver nitrate solution, 1.5 L of 0.2 mol / L ascorbic acid solution, and 1 L of 0.6 mol / L PVP solution were prepared at room temperature;

[0091] 2) At room temperature, add the PVP solution to the silver nitrate solution, stir and mix, add 0.2 mol / L nitric acid aqueous solution to the mixture, and adjust the pH value of the system to 2.8; then add ascorbic acid solution, control the reaction temperature to 35°C, and perform nucleation reaction for 6 minutes;

[0092] 3) adding 2 mol / L sodium hydroxide aqueous solution to the reaction product of step 2), adjusting the pH value of the system to 11, maintaining the reaction temperature at 35° C., and reacting for 1 h to obtain a silver powder dispersion;

[0093] 4) centrifuging the silver powder dispersion to obtain silver colloid, and washing the silver colloid with ethanol

[0094] 3 times, washed once with ultrapure water, and then vacuum dried at 55 °C for 3 h to obtain flaky silver powder.

[0095] Example 2 to Example 14

[0096] Disclosed is a method for preparing submicron flaky silver powder, wherein the concentration and dosage of each raw material and the control of the reaction system are shown in Table 1 below;

[0097] Table 1 List of silver powder preparation process parameters provided in Examples 2 to 14

[0098]

[0099]

[0100] The silver powder dispersions obtained in Examples 1 to 14 were centrifuged, washed and dried to obtain silver powder, and the particle size distribution and tap density of the silver powder are shown in Table 2 below:

[0101] Table 2 Particle size distribution and tap density list

[0102]

[0103]

[0104] The testing method of the tap density described in Table 2 meets GB / T 5162-2021, and the thickness of the flaky silver powder is the distance between two opposite polygonal planes of the same flaky powder in the microscopic morphology.

[0105] Combined with the above Figure 1 and Figure 2 It can be seen that the silver powder prepared by the present invention comprises a typical flake structure with a polyhedral crystal form, wherein the polyhedral crystal form comprises regular or irregular flakes with hexagons, combined with Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 It can be seen that the particle size distribution and thickness of the silver powder are within the protection scope of the claims of the present invention.

[0106] Therefore, the silver powder prepared by the present invention can be used as a raw material for conductive silver paste and has good application prospects.

[0107] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and / or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0108] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for preparing submicron flaky silver powder, characterized in that: The method comprises the following preparation steps: 1) taking a silver precursor, a reducing agent and a protective agent and dispersing them into a solvent to form a silver precursor solution, a reducing agent solution and a protective agent solution respectively; the solvent is a mixed solvent of deionized water and a polyol; the mass ratio of the deionized water to the polyol in the mixed solvent is (0.5-4):1; wherein the molar ratio of the silver precursor, the reducing agent and the protective agent is 1:(0.5-4):(1-4); 2) adding the protective agent solution to the silver precursor solution, mixing well, adding an acidic solution to adjust the pH value to 0.5-6, and then adding the reducing agent solution to perform a nucleation reaction to obtain a nucleation system; 3) adding an alkaline solution to the nucleation system to adjust the pH value to 7-13, and continuing to grow to obtain a silver powder dispersion; 4) post-treating the silver powder dispersion to obtain submicron flaky silver powder; The silver powder comprises flakes with a polyhedral crystal form, and the flakes account for more than 90wt%; wherein the D50 of the flakes is 0.3-1μm; and the thickness of the flakes is 50-200nm; The tap density of the silver powder is 4.0 to 6.0 g / cm 3 .

2. The preparation method according to claim 1, characterized in that: The mass ratio of deionized water to polyol in the mixed solvent is (1-2):

1.

3. The preparation method according to any one of claims 1 to 2, characterized in that The deionized water includes any one of pure water and ultrapure water, and the polyol includes any one of ethylene glycol and glycerol.

4. The preparation method according to any one of claims 1 to 2, characterized in that In step 1), the molar concentration ratio of the silver precursor solution, the reducing agent solution and the protecting agent solution is (0.2-8): (0.02-2): (0.2-4), and the molar concentration unit is mol / L.

5. The preparation method according to claim 4, characterized in that: The molar concentration ratio of the silver precursor solution, the reducing agent solution and the protecting agent solution is (0.4-4): (0.04-1): (0.4-2).

6. The preparation method according to any one of claims 1 to 2, characterized in that: The silver precursor is any one of silver nitrate and silver acetate; The protective agent is one or more of PVA, PVP, sorbitol, sodium citrate, gelatin, gum arabic, BTA, PEG, and SDBS; The reducing agent is at least one of formaldehyde, ascorbic acid, potassium tartrate, hydrazine hydrate, hydrazine carbonate and glucose.

7. The preparation method according to any one of claims 1 to 2, characterized in that: The reaction temperature of step 2) and step 3) is 10-60° C., and the reaction time of step 2) is lower than the reaction time of step 3); Specifically, the reaction time of step 2) is ≤10min; The reaction time of step 3) is ≤120min.

8. The preparation method according to claim 7, characterized in that: The reaction temperature of step 2) and step 3) is 15-50°C; and / or; The reaction time of step 2) is 2 to 6 minutes; and / or; The reaction time of step 3) is 60 to 100 minutes.

9. The preparation method according to any one of claims 1 to 2, characterized in that: In step 2), the acidic solution comprises an aqueous solution of any one of nitric acid and acetic acid, and the concentration of the acidic solution is 0.02 to 0.5 mol / L; In step 3), the alkaline solution comprises an aqueous solution of any one of sodium hydroxide and ammonia water, and the concentration of the alkaline solution is 0.02 to 3 mol / L.

10. The preparation method according to any one of claims 1 to 2, characterized in that: In step 4), the post-treatment includes centrifugal separation, washing and drying, the washing includes washing 3 to 4 times with one or two or three of ethanol, acetone or deionized water, the drying is vacuum drying, and the vacuum drying includes controlling the temperature at 40 to 90° C. and drying for 1 to 6 hours.

11. A submicron flaky silver powder, characterized in that: The silver powder is obtained by the method according to any one of claims 1 to 10.

12. The silver powder according to claim 11, characterized in that The silver powder comprises flakes with a polyhedral crystal form, and the flakes account for more than 90wt%; wherein the D50 of the flakes is 0.3-1μm, and the thickness of the flakes is 50-200nm; The tap density of the silver powder is 4.0 to 6.0 g / cm 3 .

Images