High-dispersity polyvinylpyrrolidone for silver powder and preparation method thereof

Abstract

The invention relates to the technical field of chemical synthesis, in particular to high-dispersity PVP (polyvinyl pyrrolidone) for silver powder and a preparation method thereof.The preparation method comprises the steps that water, a catalyst, ammonia water and part of N-vinyl pyrrolidone monomers are mixed, deoxygenized and heated, and then hydrogen peroxide is added to initiate polymerization; after polymerizing for a period of time, adding the residual N-vinyl pyrrolidone monomer to continuously react; and at the later stage of polymerization, supplementing the initiator, preserving heat, continuing the reaction until the conversion rate exceeds 99.9%, cooling to obtain a PVP polymer solution, and drying the PVP polymer solution to obtain the high-dispersity polyvinylpyrrolidone for the silver powder. The prepared product is good in performance, and qualified silver powder can be prepared under the condition that the use amount is reduced by 60%; the prepared product is better in performance, the use amount of PVP can be reduced, the cost of raw materials for silver powder production is reduced, meanwhile, the amount of PVP entering waste water after silver powder washing and the use amount of water are reduced, and the waste water treatment cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, and particularly relates to a high-dispersibility polyvinylpyrrolidone for silver powder and a preparation method thereof. BACKGROUND

[0002] Polyvinylpyrrolidone, abbreviated as PVP, is a water-soluble polymer, has good dispersibility and safety, and is widely used in new energy, medicine, textile printing and dyeing, washing, personal care and other industries. With the development of the solar cell industry and the electronic industry, the demand for conductive silver powder has surged. As a key raw material for silver powder production, PVP plays a role in dispersion and stabilization in the growth process of silver powder particles, controls the particle size and morphology of silver powder, and therefore its dispersibility has a huge impact on the preparation of silver powder. However, the performance of PVP products on the market varies greatly, and the performance of products from the same company also fluctuates greatly, resulting in a low product pass rate, which has caused the downstream silver powder enterprises to be in an awkward situation of testing each batch of PVP products before placing orders. At the same time, in the process of silver powder production, PVP needs to be washed away after the growth of silver powder. PVP is the main source of high COD value of silver powder wastewater, and high-dispersibility PVP can effectively reduce the amount of PVP added, reduce production costs and wastewater treatment costs, and has great significance for the healthy development of the silver powder industry.

[0003] Studies have shown that PVP is adsorbed on the metal particles by the interaction of the oxygen atom and the nitrogen atom on the pyrrolidone structure (Journal of Molecular Structure 935 (2009) 32-38; Colloids Interfaces 2023, 7, 66), therefore, a higher molecular weight of PVP means that the polymer has more adsorption points with the metal particles, and therefore can more efficiently stabilize and disperse the silver powder. However, the higher the molecular weight of PVP, the stronger the adsorption force, making it more difficult to clean in the later stage, which hinders its popularization and application. Experiments have shown that a very small amount of high-molecular-weight PVP can keep the silver powder system stable, but too low an amount of PVP makes part of the surface of the silver powder not covered by PVP, and the strong adsorption force limits the migration, making the newly formed surface of the growing silver powder unable to be coated in time, resulting in anisotropy of the silver powder and damaging the performance of the silver powder. A simple low-molecular-weight PVP has fewer adsorption points and is prone to desorption and migration, resulting in poor stability of the silver powder, and often requires doubling the amount to obtain ideal stability. Selecting a moderate molecular weight, such as the current mainstream K30, although it balances stability and mobility, its narrow molecular weight distribution makes neither outstanding, and at the same time, the fluctuation in production leads to unstable molecular weight distribution, which seriously affects the stability of product performance.

[0004] Therefore, there is an urgent need for a high-dispersibility polyvinylpyrrolidone for silver powder and a preparation method thereof to solve the above technical problems. SUMMARY

[0005] The present application aims to overcome the problems of low performance and unstable quality of PVP for silver powder industry, and provides a high-dispersibility polyvinylpyrrolidone for silver powder and a preparation method thereof. The method has a simple process, and the prepared polyvinylpyrrolidone has a wide molecular weight distribution and excellent dispersing capacity for silver powder.

[0006] The specific scheme is as follows: A preparation method of a high-dispersibility polyvinylpyrrolidone for silver powder, comprising the following steps: S1, mixing water, a catalyst, ammonia water, and part of N-vinylpyrrolidone monomers to remove oxygen, adding hydrogen peroxide to initiate polymerization after heating; S2, after a period of polymerization, adding the remaining N-vinylpyrrolidone monomers to continue the reaction; S3, adding an initiator in the late stage of polymerization to continue the reaction until the conversion rate exceeds 99.9%, cooling to obtain a PVP polymer solution, and drying the solution to obtain a high-dispersibility polyvinylpyrrolidone for silver powder.

[0007] Specifically, the method comprises the following steps: S1, mixing water, a catalyst, ammonia water, and N-vinylpyrrolidone monomers to remove oxygen, adding hydrogen peroxide to initiate polymerization after heating to a certain temperature; S2, when the polymerization reaches a certain time, adding the remaining N-vinylpyrrolidone monomers to the system to continue the reaction, and adding ammonia water to control the pH at about 7 during the reaction; S3, adding an initiator in the late stage of polymerization to continue the reaction until the conversion rate exceeds 99.9%, cooling to obtain a PVP polymer solution, and drying the solution to obtain a high-dispersibility polyvinylpyrrolidone for silver powder.

[0008] Preferably, in step S1, the catalyst is a multivalent metal ion; and the amount of the catalyst used is 1-1000 ppm of the total reaction mass.

[0009] Further preferably, in step S1, the catalyst is a multivalent metal ion such as iron ion and copper ion; and the amount of the catalyst used is 5-100 ppm of the total reaction mass.

[0010] Specifically, the amount of the catalyst used is calculated based on the metal ion used.

[0011] Preferably, in step S1, the amount of ammonia water used is 0.1-1% of the total reaction mass based on the active ingredient.

[0012] Specifically, the active ingredient of the ammonia water refers to monohydrate of ammonia in the ammonia water (NH3·H2O).

[0013] Preferably, in the step S1, the content of the N-vinyl pyrrolidone monomer is 1-40% of the total mass of the reactants.

[0014] Further preferably, in the step S1, the content of the N-vinyl pyrrolidone monomer is 5-20% of the total mass of the reactants.

[0015] Preferably, in the step S1, the heating temperature is 30-100℃.

[0016] Further preferably, in the step S1, the heating temperature is 60-80℃.

[0017] Preferably, in the step S2, the polymerization time is 15-180 minutes.

[0018] Further preferably, in the step S2, the polymerization time is 30-90 minutes.

[0019] Preferably, in the step S2, the added N-vinyl pyrrolidone monomer is 50-99% of the total amount of the N-vinyl pyrrolidone monomer.

[0020] Further preferably, in the step S2, the added N-vinyl pyrrolidone monomer is 70-90% of the total amount of the N-vinyl pyrrolidone monomer.

[0021] The total amount of the N-vinyl pyrrolidone monomer refers to the total mass of the N-vinyl pyrrolidone monomer used in the steps S1 and S2.

[0022] Preferably, in the step S2, the N-vinyl pyrrolidone monomer is added completely in 10-120 minutes.

[0023] Further preferably, in the step S2, the N-vinyl pyrrolidone monomer is added completely in 20-60 minutes.

[0024] Preferably, in the step S3, the initiator is a free radical initiator.

[0025] Preferably, the free radical initiator is at least one of peroxide initiators, azo initiators, redox initiators, etc.

[0026] Preferably, the free radical initiator is a water-soluble free radical initiator; further preferably, the free radical initiator is hydrogen peroxide.

[0027] The application also includes the high-dispersibility polyvinyl pyrrolidone for silver powder prepared by the above preparation method.

[0028] The present application mixes water, N-vinyl pyrrolidone monomer (NVP), catalyst, ammonia, heats to the specified temperature after oxygen removal, then adds hydrogen peroxide to initiate polymerization, adds a certain amount of NVP at a certain stage of the reaction to adjust the molecular weight and molecular weight distribution of the polymer, adds initiator to reduce residual monomer after the polymerization is basically completed, and the obtained PVP solution is dried by spray drying to obtain a yield of more than 99.9%. The process of the present application is simple, the prepared PVP has a wide molecular weight distribution, and the problem of unstable product performance is overcome, and the prepared product has excellent dispersing ability for silver powder.

[0029] Principle of action: The present application increases the molecular weight distribution of the currently mainstream PVP K30 through process optimization, and a small amount of high molecular weight PVP produced thereby can efficiently stabilize silver powder particles, and the small molecular weight PVP introduced can timely fill the newly generated surface blank in the growth process of the silver powder due to its good migration ability, not only effectively solving the problem of silver powder anisotropy, but also unexpectedly solving the problem of high molecular weight PVP cleaning difficulty, and the synergistic effect of the two is much better than the current product. The present application finds that the PDI of the PVP prepared under normal conditions is about 3-4 when the K value is about 30, and as the PDI increases, the performance of the PVP significantly improves, and when the PDI reaches about 6, the dispersing ability changes little with the increase, and at the same time, too high PDI leads to too high molecular weight of the high molecular weight part of the polymer, so that the washing residue has an increasing trend, affecting the subsequent use of the silver powder.

[0030] In order to prepare PVP with a mixture of high molecular weight and small molecular weight, there are two schemes: one is to directly synthesize PVP with a wide molecular weight distribution, and the other is to mix two PVPs with different molecular weights. The experimental results of the present application show that the former has a simpler overall preparation process, lower cost, and more balanced molecular weight distribution of the prepared product, and better dispersing effect.

[0031] The present application adopts hydrogen peroxide initiation system to synthesize PVP, adopts hydrogen peroxide as initiator, the main reason is that hydrogen peroxide not only plays the role of initiator in the polymerization process, but also plays the role of transfer agent, because hydrogen peroxide decomposes rapidly with polymerization, the concentration will decrease, so that the molecular weight of the produced polymer appears low first and then high with reaction time, that is, small molecular weight PVP is generated in the initial stage, high molecular weight PVP is generated in the middle stage of polymerization, which is different from the traditional free radical polymerization (Pharmaceutical Chemistry Journal 16, 292-295 (1982).), at the same time, the molecular weight of the polymer is proportional to the monomer concentration, therefore, the effect can be amplified by controlling the monomer concentration in the two stages, that is, the monomer concentration is controlled to further reduce the molecular weight in the initial stage of polymerization to generate smaller molecular weight, and the monomer concentration is increased to further increase the molecular weight in the middle stage of generating higher molecular weight, so that the product with wider molecular weight distribution than the PVP produced by the prior art is prepared, the method is simple and effective, and the molecular weight distribution of the prepared polymer is strong.

[0032] The present application studies and finds that the molecular weight and molecular weight distribution of PVP affect its performance in the process of preparing silver powder: the higher the molecular weight of PVP, the stronger the dispersing force, but too high molecular weight makes it difficult to be washed out from the product. PVP mixed with small molecular weight PVP, that is, PVP with wider molecular weight distribution, overcomes the washing problem in the later stage while retaining high dispersing force. In order to prepare PVP with high molecular weight distribution in one step, the principle that hydrogen peroxide initiates polymerization and terminates polymerization in the process of NVP polymerization with hydrogen peroxide and the relationship that the molecular weight of the polymer is proportional to the monomer concentration are used, the monomer concentration is controlled to further reduce the molecular weight in the initial stage of polymerization to generate smaller molecular weight, and the monomer concentration is increased to further increase the molecular weight in the stage of generating higher molecular weight, so that the product with wider molecular weight distribution than the PVP produced by the prior art is prepared.

[0033] Overall, the PVP prepared in the present application has simple process, good product performance and good quality stability.

[0034] The beneficial effects of the present application are: (1) The product prepared by the present application has good performance, and qualified silver powder can also be prepared at a reduced dosage of 60%; (2) The product prepared by the present application has good stability, overcomes the problem of low product qualification rate and the need to pick batches in the industry, and ensures that the performance of the product produced in each batch is qualified; (3) The product prepared by the present application has better performance, which can reduce the amount of PVP used, not only reduces the cost of raw materials for silver powder production, but also reduces the amount of PVP in waste water after silver powder washing and the amount of water used, greatly reducing the cost of waste water treatment. DETAILED DESCRIPTION

[0035] The present application will be further described in the following detailed examples, which illustrate the present application by way of example and are not meant to be limiting thereof.

[0036] The concentration of the ammonia water used in the following examples and comparative examples is 30%.

[0037] Example 1 A method for preparing a high dispersibility polyvinylpyrrolidone for silver powder, comprising the following steps: 2700 g of water and 600 g of NVP, 18 ppm of iron ions and 8 ml of ammonia water were mixed to remove oxygen, and then heated to 70 degrees. 20 g of hydrogen peroxide was added to initiate polymerization. After 30 minutes of reaction, the remaining 700 g of NVP was added at a uniform speed within half an hour. 10 g of hydrogen peroxide was added after 30 minutes of continuous reaction, and the pH was adjusted to 7 with ammonia water. The reaction was continued with incubation, and 2 g of hydrogen peroxide was added every two hours. The pH of the system was adjusted to 7 with ammonia water every half hour. When the residual monomer was less than 100 ppm, the reaction was terminated by cooling. The obtained PVP polymerization solution was dried by spray drying to obtain a powder sample with a K value of about 30.

[0038] Example 2 A method for preparing a high dispersibility polyvinylpyrrolidone for silver powder, comprising the following steps: 2700 g of water and 500 g of NVP, 20 ppm of copper ions and 10 ml of ammonia water were mixed to remove oxygen, and then heated to 70 degrees. 25 g of hydrogen peroxide was added to initiate polymerization. After 40 minutes of reaction, the remaining 800 g of NVP was added at a uniform speed within 20 minutes. 10 g of hydrogen peroxide was added after 30 minutes of continuous reaction, and the pH was adjusted to 7 with ammonia water. The reaction was continued with incubation, and 2 g of hydrogen peroxide was added every two hours. The pH of the system was adjusted to 7 with ammonia water every half hour. When the residual monomer was less than 100 ppm, the reaction was terminated by cooling. The obtained PVP polymerization solution was dried by spray drying to obtain a powder sample with a K value of about 30.

[0039] Example 3 A method for preparing a high dispersibility polyvinylpyrrolidone for silver powder, comprising the following steps: 2700 g of water and 500 g of NVP, 18 ppm of iron ions and 8 ml of ammonia water were mixed to remove oxygen, and then heated to 70 degrees. 20 g of hydrogen peroxide was added to initiate polymerization. After 30 minutes of reaction, the remaining 700 g of NVP was added at a uniform speed within half an hour. 10 g of hydrogen peroxide was added after 30 minutes of continuous reaction, and the pH was adjusted to 7 with ammonia water. The reaction was continued with incubation, and 2 g of hydrogen peroxide was added every two hours. The pH of the system was adjusted to 7 with ammonia water every half hour. When the residual monomer was less than 100 ppm, the reaction was terminated by cooling. The obtained PVP polymerization solution was dried by spray drying to obtain a powder sample with a K value of about 30.

[0040] Example 4 A method for preparing high dispersibility polyvinylpyrrolidone for silver powder, comprising the following steps: 2700 g of water and 500 g of NVP, 20 ppm of copper ions and 10 ml of ammonia were mixed to remove oxygen, and then heated to 70 degrees. 25 g of hydrogen peroxide was added to initiate polymerization. After 40 minutes of reaction, 550 g of NVP was added to the polymerization kettle. After 30 minutes, the remaining 250 g of NVP and 10 g of hydrogen peroxide were added, and the pH was adjusted to 7 with ammonia. The reaction was continued with heat preservation. Every two hours, 2 g of hydrogen peroxide was added. Every half hour, the pH of the system was adjusted to 7 with ammonia. When the residual monomer was less than 100 ppm, the reaction was terminated by cooling. The obtained PVP polymerization solution was dried by spraying powder to obtain a powder sample with a K value of about 30.

[0041] Example 5 A method for preparing high dispersibility polyvinylpyrrolidone for silver powder, comprising the following steps: 2700 g of water and 400 g of NVP, 20 ppm of copper ions and 10 ml of ammonia were mixed to remove oxygen, and then heated to 70 degrees. 30 g of hydrogen peroxide was added to initiate polymerization. After 60 minutes of reaction, 600 g of NVP was added to the polymerization kettle. After 30 minutes, the remaining 300 g of NVP and 15 g of hydrogen peroxide were added, and the pH was adjusted to 7 with ammonia. The reaction was continued with heat preservation. Every two hours, 2 g of hydrogen peroxide was added. Every half hour, the pH of the system was adjusted to 7 with ammonia. When the residual monomer was less than 100 ppm, the reaction was terminated by cooling. The obtained PVP polymerization solution was dried by spraying powder to obtain a powder sample with a K value of about 34.

[0042] Comparative Example 1 370 g of PVP K60 with high molecular weight and 630 g of K12 powder with lower molecular weight were mixed in a high-speed mixer to obtain a sample with a K value of about 30. K60 and K12 are commercially produced products, and the production process is more complex than K30. The production cost and selling price are also significantly higher than K30 on the market.

[0043] Comparative Example 2 1750 g of water, 500 g of NVP, 6 ml of ammonia and 20 ppm of copper ions were mixed to remove oxygen, and then heated to 70 degrees. 10 g of hydrogen peroxide was immediately added to initiate polymerization. After the initiation of polymerization, the system had a significant temperature rise and a drop. Then, 800 g of NVP and a solution containing 20 g of hydrogen peroxide were simultaneously added dropwise. After one hour of dropwise addition, ammonia was added to adjust the pH to about 7. The reaction was continued with heat preservation. During the reaction, 2 g of hydrogen peroxide was added every two hours, and ammonia was added every half hour to ensure that the pH of the system was near 7. When the residual monomer was less than 1000 ppm, the reaction was terminated by cooling. The obtained PVP solution was dried by spraying powder to obtain a sample with a K value of about 30.

[0044] Comparative Example 3 Mix 1750g water, 400g NVP, 6ml ammonia water and 18 ppm iron ions, deoxygenate and heat to 70 degrees, then add 8.5g hydrogen peroxide to initiate polymerization, after half an hour of reaction, add 450g monomer and 10g hydrogen peroxide, continue to react for half an hour, then add the remaining 450g monomer and 10g hydrogen peroxide, and supplement ammonia water to adjust the pH value to about 7, continue to react, supplement 2g hydrogen peroxide every two hours during the reaction, and supplement ammonia water every half hour to ensure that the pH value is near 7, and then take samples until the residual monomer is less than 1000 ppm, and then cool to end the reaction. The obtained PVP solution is dried by spray drying to obtain a sample with a K value of about 30.

[0045] Comparative Example 4 Commercially available silver powder with K30.

[0046] The molecular weight and molecular weight distribution are tested by GPC, using polyethylene oxide standard sample as reference, and the test results of the molecular weight and molecular weight distribution of each example and comparative example are shown in Table 1.

[0047] Table 1

[0048] The PVP obtained from Examples 1-5 and Comparative Examples 1-4 is used for silver powder preparation, and the specific application process is as follows: “Normal amount” application: accurately weigh 6.336g ascorbic acid, and configure it into a 46.3g solution; accurately weigh 10.200g silver nitrate to make a 75g solution; configure PVP into a 20% solid content solution, take 13.320g and put it into a 250ml beaker, and add the prepared ascorbic acid solution into the mixture for 5 minutes, then quickly add the silver nitrate solution into the mixed solution at a speed of 30ml / min under stirring, the system quickly reacts to generate silver powder, and the color quickly turns into brown after quickly turning black, and then slowly turns lighter, after the addition is completed, the system is stable for 30 seconds, then a dropper is inserted into the bottom to take samples, and the particle size is measured by a particle size instrument, and the finer the particle size of the obtained silver powder under the same PVP addition amount indicates that the dispersing force of the PVP is stronger. The silver powder is precipitated, filtered, washed with water three times, and then dried, and the sample is tested by TGA to determine the PVP residue.

[0049] “20% reduction” application: compared with the “normal amount” application, the difference is that the mass of PVP used in this application is 80% of that in the “normal amount” application.

[0050] “40% reduction” application: compared with the “normal amount” application, the difference is that the mass of PVP used in this application is 60% of that in the “normal amount” application.

[0051] "60% reduction" application: different from the "normal amount" application, the mass of PVP used in the application is 40% of the "normal amount" application.

[0052] The application results of each embodiment and comparative example in the preparation of silver powder are shown in Table 2.

[0053] Table 2

[0054] Compared with the preparation method in the prior art, the product obtained by the synthesis of the application has a wider molecular weight distribution, stronger dispersing capacity for silver powder, finer particle size of the prepared silver powder, and can significantly reduce the amount of PVP.

[0055] The embodiments of the application have been described above, and the above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0056] The technical solutions of the application are not limited to the above specific embodiments, and any technical modification made according to the technical solutions of the application falls within the protection scope of the application.

Claims

1. A method for producing a high-dispersibility polyvinylpyrrolidone for silver powder, characterized by, The method comprises the following steps: S1, mixing water, a catalyst, ammonia, and part of N-vinyl pyrrolidone monomer to remove oxygen, and then adding hydrogen peroxide to initiate polymerization after heating; S2, after polymerization for a period of time, the remaining N-vinyl pyrrolidone monomer is added for continuous reaction; S3, the initiator is added in the later stage of polymerization for continuous reaction until the conversion rate is more than 99.9%, and then the temperature is lowered to obtain a PVP polymer solution, and the solution is dried to obtain the silver powder use high-dispersibility polyvinyl pyrrolidone.

2. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein: In the step S1, the catalyst is a multivalent metal ion; and the amount of the catalyst used is 1-1000 ppm of the total amount of the reactants.

3. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein the process is characterized by: In the step S1, the amount of ammonia used is 0.1-1% of the total amount of the reactants in terms of active ingredients.

4. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein the process is characterized by: In the step S1, the content of the N-vinyl pyrrolidone monomer is 1-40% of the total amount of the reactants.

5. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein the process is characterized by: In the step S1, the heating temperature is 30-100℃.

6. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein: In the step S2, the polymerization time is 15-180 minutes.

7. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein the process is characterized by: In the step S2, the N-vinyl pyrrolidone monomer added is 50-99% of the total amount of the N-vinyl pyrrolidone monomer.

8. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein the process is characterized by: In the step S2, the N-vinyl pyrrolidone monomer is added completely in 10-120 minutes.

9. The process for the preparation of high dispersibility polyvinyl pyrrolidone for silver powder as claimed in claim 1, wherein the process is characterized by: In the step S3, the initiator is a free radical initiator.

10. The silver powder use high-dispersibility polyvinyl pyrrolidone prepared by the preparation method in any one of claims 1-9.

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