Method for producing high-dispersion nano-silver powder for low-temperature sintering silver paste

Abstract

The application relates to the technical field of metal powder processing, in particular to a production method of high-dispersion nano silver powder for low-temperature sintering silver paste, which comprises the following steps: adding a reducing agent solution and a dispersant solution into a silver nitrate solution to separate out crystal seeds, and adding the crystal seeds into the dispersant solution to obtain a crystal seed dispersant solution; adding the crystal seed dispersant solution into the silver nitrate solution, then dropping the reducing agent solution, and stirring at the same time, adjusting the actual remaining time of the later stage of a liquid phase reduction reaction in real time, obtaining a liquid phase reduction solution after the reaction is completed; removing supernatant after flocculation and precipitation of the liquid phase reduction solution after the reaction is completed, then sequentially performing deionized water cleaning, cooling and drying, and polishing treatment, and finally preparing the nano silver powder. The application aims to accurately adjust the actual remaining time of the later stage of the liquid phase reduction reaction, and improve the dispersion and particle size distribution uniformity of the subsequently prepared nano silver powder.

Description

Technical Field

[0001] This application relates to the field of metal powder processing technology, specifically to a method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste. Background Technology

[0002] Nano silver powder refers to silver powder with silver particles at the nanometer scale. It possesses excellent electrical and thermal conductivity, as well as antibacterial properties, and can be used as a conductive filler in the printed electronics industry to prepare conductive silver paste for screen printing. Currently, the main production methods for nano silver powder are chemical reduction and mechanical spheroidization. Among these, chemical reduction is generally used to produce nano silver powder due to its advantages such as low energy consumption, good dispersibility, and strong controllability. However, in the chemical reduction process, the reaction time has a significant impact on the particle size and morphology of nano silver powder. By optimizing the reaction time, the dispersibility of nano silver powder can be effectively improved, making it suitable for low-temperature sintering silver paste and exhibiting better sintering activity.

[0003] In existing processes, highly dispersed silver nanoparticles are mainly produced using liquid-phase reduction. The reaction time is typically determined experimentally by varying the reaction time to avoid affecting the dispersibility and particle size uniformity of the silver nanoparticles due to excessively long or short reaction times. However, this method of determining the reaction time solely through experimentation does not fully consider the actual reaction variations during the silver ion reduction process. This makes it impossible to accurately adjust the reaction time in the liquid-phase reduction reaction, which can easily affect the dispersibility and particle size uniformity of the silver nanoparticles. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste, thereby resolving the existing issues.

[0005] The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste in this application adopts the following technical solution:

[0006] One embodiment of this application provides a method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste, the method comprising the following steps:

[0007] (1) Add the reducing agent solution and the dispersant solution to the silver nitrate solution, stir to obtain the crystal nucleus solution, separate the crystal seeds by centrifugation, and add the separated crystal seeds to the dispersant solution to obtain the crystal seed dispersant solution;

[0008] (2) Add the seed dispersant solution to the silver nitrate solution, then add the reducing agent solution dropwise while stirring, and carry out the liquid-phase reduction reaction. After the reaction is completed, the liquid-phase reduced solution is obtained.

[0009] Among these measures, the reaction time in the liquid-phase reduction reaction is analyzed and adjusted in real time.

[0010] Step 1: Collect absorbance data of the reaction solution during the liquid-phase reduction reaction;

[0011] Step 2: Analyze the singular value difference variation characteristics of each row in the matrix composed of absorbance sequences at each acquisition time and its neighboring acquisition times, as well as the mean slope of the fitted straight line with a value greater than zero in each column, to determine the order variability characteristic value at each acquisition time.

[0012] Step 3: Correct the order variability eigenvalues ​​by using the correlation between the absorbance sequence at each acquisition time and the sequence formed by the slopes of the fitted straight lines of all columns, and determine the order variability confidence level at each acquisition time.

[0013] Step 4: Use the difference mean of the confidence levels of the step change in the early stage of the liquid-phase reduction reaction to calculate the remaining settling time in the later stage of the liquid-phase reduction reaction;

[0014] (3) After the reaction is completed, the liquid phase reduction solution is flocculated and precipitated, and the supernatant is removed. Then, the solution is washed with deionized water, cooled and dried, and polished to prepare nano silver powder.

[0015] Preferably, the mass ratio of solute in the reducing agent solution, dispersant solution, and silver nitrate solution is (0.2-0.4):(0.1-0.2):1.

[0016] Preferably, the reducing agent solution is one of sodium borohydride or ascorbic acid, and the dispersant solution is one of gelatin, gum arabic, or polyvinylpyrrolidone (PVP).

[0017] Preferably, the method for determining the order-variable eigenvalue is as follows:

[0018] Analyze the mean of the singular value absolute differences of all rows in the matrix;

[0019] Analyze the mean slope of the fitted lines in all columns of the matrix that are greater than zero;

[0020] The order-variable eigenvalues ​​are positively correlated with the two means, respectively.

[0021] Preferably, before analyzing the mean of the absolute differences of the singular values ​​of all rows in the matrix, the singular values ​​of all rows are first normalized to their maximum values.

[0022] Preferably, before using the correlation degree to correct the order variability eigenvalue, the correlation degree is first normalized to correct the order variability eigenvalue to a range of (0,1) times it, thereby obtaining the order variability confidence level.

[0023] Preferably, before calculating the differential mean of the confidence level of the first stage of the liquid-phase reduction reaction, the confidence level of the first stage of the reaction is first normalized to control the range of the calculated differential mean between (0,1).

[0024] Preferably, the method for calculating the remaining adjustment time in the later stage of the liquid-phase reduction reaction is as follows:

[0025]

[0026] In the formula, This refers to the remaining adjustment time in the later stages of the liquid-phase reduction reaction. This represents the actual remaining time in the later stages of the liquid-phase reduction reaction. The maximum value of the preset adjustable time is C, which is the third mean value in the early stage of the liquid phase reduction reaction. The third mean value is the differential mean value.

[0027] Preferably, the initial stage refers to the first 30 minutes of the liquid-phase reduction reaction, and the actual remaining time in the later stage is the difference between the preset reaction time of the liquid-phase reduction reaction and the time used in the initial stage.

[0028] Preferably, the flocculation and precipitation are achieved by adding a flocculant to the liquid-phase reduction solution after the reaction is completed. The flocculant is a mixture of one amine and one acid from the following: octylamine, dodecylamine, hexadecylamine, stearic acid, ricinoleic acid, and lac acid.

[0029] This application has at least the following beneficial effects:

[0030] (1) This application measures the difference in singularity between different row vectors by performing SVD singular value decomposition on the absorption spectrum matrix, which more clearly reflects the characteristics of the characteristic peak changes in the absorption spectrum of the reaction solution in a short time. Combined with the trend of absorbance change with reaction time, it more accurately measures the step change characteristics in the generation process of nano-silver particles in the reaction solution, which is beneficial to avoid the problem of excessive reaction time in the subsequent liquid phase reduction reaction.

[0031] (2) By accurately measuring the reliability of the step transformation changes during the generation of silver nanoparticles, this application can more reliably highlight the significance of the step transformation changes during the generation of silver nanoparticles, which is conducive to improving the accuracy of adjusting the reaction time in the liquid phase reduction reaction, thereby avoiding the problem of the reaction time being too long or too short during the liquid phase reduction reaction.

[0032] (3) This application uses the difference in the change of confidence of intermediate denaturation in the early stage of liquid phase reduction reaction to accurately analyze and measure the actual reaction change characteristics in the reduction reaction of silver ions, and then accurately adjusts the actual remaining time in the later stage of liquid phase reduction reaction, thereby avoiding the problem of the reaction time of liquid phase reduction being too long or too short, and improving the dispersibility and particle size distribution uniformity of the subsequently prepared nano silver powder. Attached Figure Description

[0033] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart of a method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste provided in this application;

[0035] Figure 2 The flowchart provided in this application outlines the steps for real-time analysis and adjustment of reaction time in liquid-phase reduction reactions. Detailed Implementation

[0036] To further illustrate the technical means and effects adopted by this application to achieve the intended purpose of the invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of the method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to this application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0038] The following description, in conjunction with the accompanying drawings, details the specific scheme of the method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste provided in this application.

[0039] One embodiment of this application provides a method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste.

[0040] Specifically, the following method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste is provided; please refer to [link / reference]. Figure 1 The method includes the following steps:

[0041] (1) Add the reducing agent solution and the dispersant solution to the silver nitrate solution, stir to obtain the crystal nucleus solution, place the crystal nucleus solution in a centrifuge, separate the crystal seeds by centrifuging, add the separated crystal seeds to the dispersant solution to obtain the crystal seed dispersant solution.

[0042] In this embodiment, the mass ratio of solutes in the reducing agent solution, dispersant solution, and silver nitrate solution is 0.2:0.1:1, the centrifuge speed is 10000 r / min, and the centrifugation time is 12 min; the reducing agent solution is sodium borohydride, and the dispersant solution is gelatin.

[0043] (2) Add the seed dispersant solution to the silver nitrate solution, then add the reducing agent solution dropwise while stirring at the same time to carry out the liquid phase reduction reaction. After the reaction is completed, the liquid phase reduced solution is obtained.

[0044] In this embodiment, the stirring speed is 250 r / min, the dropping speed is 80 ml / min, the reaction temperature is 40°C, and the preset reaction time is 60 min.

[0045] This application specifically addresses the real-time analysis and adjustment of reaction time in liquid-phase reduction reactions. (See attached document for details.) Figure 2 Specifically:

[0046] Step 1: Collect absorbance data of the reaction solution during the liquid-phase reduction reaction.

[0047] In order to fully explore the actual reaction changes during the reduction reaction of silver ions and thus more accurately adjust the reaction time parameters in the chemical reduction reaction, this application uses a UV-3600Plus spectrophotometer to collect absorbance data of the reaction solution in the liquid-phase reduction reaction. The wavelength scanning range is 200-500nm, the acquisition time interval is 10s, and the acquisition time is the first 30 minutes of the liquid-phase reduction reaction, that is, the early stage of the liquid-phase reduction reaction is the spectral acquisition time. The absorbance data of each acquisition time in the wavelength scanning range are arranged in order of increasing wavelength to obtain the absorbance sequence of each acquisition time in the first 30 minutes of the liquid-phase reduction reaction.

[0048] Step 2: Analyze the singular value difference variation characteristics of each row in the matrix composed of absorbance sequences at each acquisition time and its neighboring acquisition times, as well as the mean slope of the fitted straight line with a value greater than zero in each column, to determine the order variability characteristic value at each acquisition time.

[0049] Because of the free electron movement on the surface of the silver nanoparticles generated during the liquid-phase reduction reaction, characteristic peaks will appear in the absorption spectrum of the reaction solution. Therefore, in order to avoid affecting the dispersibility and particle size uniformity of the silver nanoparticles, it is necessary to analyze the actual reaction characteristics of the silver ion reduction process based on the absorption spectrum of the reaction solution, so as to accurately adjust the reaction time in the liquid-phase reduction reaction and avoid the problem of the reaction time being too long or too short.

[0050] In order to accurately analyze the changes in characteristic peaks of the absorption spectrum during the formation of nano-silver, this application analyzes the mean of the singular absolute differences of all rows in the matrix.

[0051] Specifically, the K acquisition times that are closest to each acquisition time interval are denoted as the K nearest acquisition times for each acquisition time, where K is 10.

[0052] The absorbance sequences of each acquisition time and its K neighboring acquisition times are then sorted in chronological order to obtain the absorption spectrum matrix for each acquisition time, reflecting the continuous changes in the absorption spectrum over a short local time.

[0053] Furthermore, the absorption spectrum matrix at each acquisition time is used as the input of the Singular Value Decomposition (SVD) algorithm to obtain the singular values ​​of all row vectors in the absorption spectrum matrix.

[0054] Furthermore, the singular values ​​of all row vectors in the absorption spectrum matrix are normalized to their maximum values. The sequence of normalized singular values ​​of all row vectors arranged in the order of rows is denoted as the local singularity sequence at each acquisition time. The mean of the absolute values ​​of all first-order differences in the local singularity sequence is denoted as the first mean at each acquisition time. The larger the first mean, the greater the difference in singularity between different row vectors. This more clearly reflects the characteristics of the characteristic peak changes in the absorption spectrum of the reaction solution in a short local time. It indicates that the reduction reaction of the nano-silver particles is more intense at this time. It is necessary to avoid the problem of excessively long reaction time in the liquid phase reduction reaction. The SVD singular value decomposition algorithm is a well-known technique, and the specific process will not be described in detail.

[0055] Meanwhile, since different column vectors in the absorption spectrum matrix represent the changes in absorbance at different wavelengths with reaction time, if the absorbance at some wavelengths changes more significantly with reaction time, it indicates that the absorption peak characteristics generated by the nano-silver particles in the reaction solution are more significant, which can accelerate the liquid-phase reduction reaction. It is necessary to avoid the problem of excessively long reaction time during the liquid-phase reduction reaction.

[0056] Therefore, this application analyzes the mean slope of the fitted straight line in all columns of the matrix that are greater than zero.

[0057] Specifically, each column vector in the absorption spectrum matrix at each acquisition time is used as the input of the linear least squares method. The fitting slope of each column vector in the absorption spectrum matrix at each acquisition time is obtained by the linear least squares method. The mean of all fitting slopes greater than 0 is calculated and recorded as the second mean at each acquisition time. The larger the second mean, the greater the trend of absorbance of some wavelengths with reaction time. It can reflect the more significant absorption peak characteristics generated by the nano silver particles in the reaction solution at this time. It is necessary to avoid the problem of excessively long reaction time in the liquid phase reduction reaction.

[0058] Based on the above analysis, this application determines the order variability feature value at each acquisition time based on the two means obtained above, wherein the order variability feature value is positively correlated with the two means respectively.

[0059] It is understandable that a positive correlation means that the dependent variable increases as the independent variable increases, and the dependent variable decreases as the independent variable decreases. This is determined by the actual application and is not subject to any special restrictions in this application.

[0060] Specifically, the order-variance eigenvalue at the t-th acquisition time is calculated. :

[0061]

[0062] In the formula, Let be the first mean value at the t-th sampling time. It is the second mean at the t-th sampling time.

[0063] Calculation principle: The first mean is calculated by the difference in the change of singular values ​​of the absorption spectrum in a local short time, which can reflect the intensity of the reduction reaction of the formation of silver nanoparticles. The second mean is calculated by the change trend of absorbance at different wavelengths with reaction time, which can reflect the significance of the absorption peak characteristics when the silver nanoparticles are formed. Both can reflect the step change of the reduction reaction process of silver nanoparticles. Therefore, the step change characteristic value is measured based on the prior knowledge of the first mean and the second characteristic value.

[0064] Among them, due to the first mean The calculation result is a value in the range of (0,1). If the first mean is directly used... Compared with the second mean Multiplying these values ​​would reduce the accuracy of measuring the eigenvalues ​​of order-variable characteristics, so 1 is multiplied by the first mean in the formula. The sum is used as a product factor to avoid the product factor being less than 1, which would affect the accuracy of measuring the order-variable eigenvalues.

[0065] The step transformation characteristic value reflects the step transformation characteristics during the generation of silver nanoparticles in the reaction solution. The larger the step transformation characteristic value, the faster the step transformation of the generation reaction process of silver nanoparticles in the reaction solution, and the more it can improve the generation rate of silver nanoparticles. It is necessary to avoid the problem of excessively long reaction time during the liquid phase reduction reaction.

[0066] Step 3: Correct the order variability eigenvalues ​​by using the correlation between the absorbance sequence at each acquisition time and the slope of the fitted straight line of all columns, and determine the order variability confidence level at each acquisition time.

[0067] Because the absorption spectrum of the reaction solution in the liquid-phase reduction reaction is easily affected by noise from the external environment or the operation process, the reliability of the step transformation changes during the generation of silver nanoparticles is low, which affects the accuracy of subsequent control and adjustment of the reaction time parameters in the liquid-phase reduction reaction.

[0068] Therefore, the fitting slopes of all column vectors in the absorption spectrum matrix at each acquisition time are sorted by column, and the sorted sequence is recorded as the rate of change characteristic sequence at each acquisition time, reflecting the change in absorbance trend of all wavelengths in a local short time.

[0069] Generally, the lower the positive correlation between the absorbance sequence and the rate of change characteristic sequence at a certain acquisition time, the greater the difference between the change of absorbance with wavelength in the reaction solution at that acquisition time and the change of absorbance trend with wavelength in a short local time. In this case, the greater the influence of external noise interference on the step transformation change during the generation of silver nanoparticles, the lower the reliability of the step transformation change during the generation of silver nanoparticles.

[0070] Therefore, based on the above analysis, this application uses the correlation between the absorbance sequence at each acquisition time and the sequence formed by the slope of the fitted straight line of all columns to correct the order variability characteristic value and determine the order variability confidence level.

[0071] Specifically, calculate the order variability confidence level at the t-th acquisition time. :

[0072]

[0073] In the formula, The correlation between the absorbance sequence and the rate of change feature sequence at the t-th acquisition time can be measured using either the Pearson correlation coefficient or covariance. In this embodiment, the Pearson correlation coefficient is used. for The normalization function maps the correlation to the range (0,1).

[0074] Calculation principle: The degree of correlation between absorbance sequence and rate of change characteristic sequence This demonstrates the positive correlation between characteristic peaks in the absorption spectrum and characteristic peaks formed locally over a short period of time. The stronger the positive correlation, the greater the correlation between the two peaks. The larger the value, the smaller the interference of false characteristic peaks in the absorption spectrum, and the more reliable the step transformation change during the generation of silver nanoparticles is. Therefore, the correlation between the absorbance sequence and the rate of change characteristic sequence is used to measure the confidence level of step transformation.

[0075] Among them, the order-variable eigenvalues This reflects the step-change characteristics during the formation of silver nanoparticles in the reaction solution. The formula uses the correlation between the absorbance sequence and the rate of change characteristic sequence. Eigenvalues ​​of order-variable Make corrections, pass After correction, to Control to (0, Within the range of ), thus more accurately measuring the confidence level of order variability.

[0076] The confidence level of step transformation reflects the credibility of the step transformation changes during the generation of silver nanoparticles. The higher the confidence level of step transformation, the more significant the step transformation changes during the generation of silver nanoparticles, and the faster the reaction process of generating silver nanoparticles. It is necessary to avoid the problem of excessively long reaction time during the liquid-phase reduction reaction.

[0077] Step 4: Use the difference mean of the confidence levels of the step change in the early stage of the liquid-phase reduction reaction to calculate the remaining settling time in the later stage of the liquid-phase reduction reaction.

[0078] Furthermore, this application utilizes the differential mean of the confidence levels of the step change in the early stage of the liquid-phase reduction reaction to calculate the remaining conditioning time in the later stage of the liquid-phase reduction reaction.

[0079] Specifically, the confidence scores of the order of change at all sampling times within the first 30 minutes of the liquid-phase reduction reaction are arranged in chronological order, and the maximum value of all elements in the arranged sequence is normalized. The sequence after the maximum value normalization is recorded as the order of change sequence in the early stage of the liquid-phase reduction reaction, which reflects the actual reaction change characteristics in the early stage of the liquid-phase reduction reaction. This is beneficial for accurately controlling and adjusting the reaction time parameters in the subsequent chemical reduction reaction.

[0080] Furthermore, the mean of all first-order differences in the sequence of phase changes during the early stage of the liquid-phase reduction reaction is calculated and denoted as the third mean during the early stage of the liquid-phase reduction reaction. The calculated value of the third mean is controlled within the range of (0,1).

[0081] If the third mean is positive and the larger the value, the faster the actual reaction process of the nano-silver powder in the early stage of the liquid-phase reduction reaction. Therefore, in order to avoid the problem of excessively long reaction time, the remaining reaction time should be shortened in the later stage of the liquid-phase reduction reaction. Conversely, if the third mean is negative and the smaller the value, the slower the actual reaction process of the nano-silver powder in the early stage of the liquid-phase reduction reaction. Therefore, in order to avoid the problem of excessively short reaction time, the remaining reaction time should be extended in the later stage of the liquid-phase reduction reaction.

[0082] Therefore, the remaining settling time in the later stage of the liquid-phase reduction reaction needs to be calculated. :

[0083]

[0084] In the formula, This represents the actual remaining time in the later stages of the liquid-phase reduction reaction. The maximum value of the preset adjustable time is 14-15 min, and the value in this embodiment is 15 min. C is the third mean value in the early stage of the liquid phase reduction reaction, and the third mean value is the difference mean value.

[0085] Therefore, by analyzing the actual reaction characteristics in the early stage of the liquid-phase reduction reaction, the actual remaining time in the later stage of the liquid-phase reduction reaction can be adjusted to avoid the problem of the reaction time being too long or too short, thereby improving the dispersibility and particle size uniformity of the subsequently prepared silver nanoparticles. Therefore, the remaining adjustment time... As the remaining reaction time in the later stage of the liquid-phase reduction reaction, the liquid-phase reduced solution is obtained after the reaction is completed.

[0086] (3) After the reaction is completed, the liquid phase reduction solution is flocculated and precipitated, and the supernatant is removed. Then, the solution is washed with deionized water, cooled and dried, and polished to prepare nano silver powder.

[0087] By adjusting the reaction time of the liquid-phase reduction reaction to avoid problems such as excessively long or short reaction times, a liquid-phase reduced solution is obtained after the reaction. The following process steps are then used to complete the production of highly dispersed nano-silver powder:

[0088] Flocculant was added to the liquid-phase reduction solution after the reaction was completed, and the mixture was stirred for 10 minutes. After sufficient flocculation and precipitation, the supernatant was removed. Then, the mixture was successively washed with deionized water, cooled and dried, and polished to prepare nano-silver powder. Nano-silver powder has the characteristics of high dispersion and can be sintered at low temperature of 180℃, and the sintered layer is dense. Therefore, it can be used in the field of low-temperature sintered silver paste, such as solar photovoltaic cathode silver paste and nano-sintered silver paste.

[0089] The flocculant is a mixture of one amine and one acid from the following: octylamine, dodecylamine, hexadecylamine, stearic acid, ricinoleic acid, and lac acid.

[0090] Thus, the invention of a method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste was completed.

[0091] Example 2

[0092] Based on Example 1, in step (1) of producing highly dispersed nano-silver powder using liquid-phase reduction method in this example, the mass ratio of solute in the reducing agent solution, dispersant solution, and silver nitrate solution is 0.4:0.2:1, the centrifuge speed is 20000 r / min, and the centrifugation time is 10 min; the reducing agent solution is sodium borohydride, and the dispersant solution is gum arabic.

[0093] In step (2) of producing highly dispersed nano-silver powder using the liquid-phase reduction method in this embodiment, the stirring speed is 300 r / min, the dropping speed is 120 ml / min, the reaction temperature is 60°C, and the preset reaction time is 60 min.

[0094] In step (3) of producing highly dispersed nano-silver powder using the liquid-phase reduction method in this embodiment, the flocculant is added to the liquid-phase reduction solution after the reaction is completed and stirred for 15 minutes.

[0095] Apart from the above settings, the other steps are the same as all the methods in Example 1, and will not be described in detail here.

[0096] Example 3

[0097] Based on Example 1, in step (1) of producing highly dispersed nano-silver powder using the liquid-phase reduction method in this example, the mass ratio of solutes in the reducing agent solution, dispersant solution, and silver nitrate solution is 0.3:0.15:1, the centrifuge speed is 15000 r / min, and the centrifugation time is 15 min; the reducing agent solution is one of ascorbic acid, and the dispersant solution is polyvinylpyrrolidone (PVP).

[0098] In step (2) of producing highly dispersed nano-silver powder using the liquid-phase reduction method in this embodiment, the stirring speed is 275 r / min, the dropping speed is 100 ml / min, the reaction temperature is 50 °C, and the preset reaction time is 60 min.

[0099] In step (3) of producing highly dispersed nano-silver powder using the liquid-phase reduction method in this embodiment, the flocculant is added to the liquid-phase reduction solution after the reaction is completed and stirred for 12 minutes.

[0100] Apart from the above settings, the other steps are the same as all the methods in Example 1, and will not be described in detail here.

[0101] The above technical features constitute the preferred embodiment of this application, which has strong adaptability and the best implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for producing highly dispersed nanosilver powder for low-temperature sintering of silver paste, characterized in that, The method comprises the following steps: (1) adding a reducing agent solution and a dispersant solution into a silver nitrate solution, obtaining a crystal nucleus solution after stirring, separating the crystal nucleus through a centrifuge, adding the separated crystal nucleus into the dispersant solution, and obtaining a crystal nucleus dispersant solution; (2) adding the crystal nucleus dispersant solution into the silver nitrate solution, then adding the reducing agent solution dropwise, and stirring simultaneously to perform a liquid phase reduction reaction, and obtaining a liquid phase reduction solution after the reaction; wherein, the reaction time in the liquid phase reduction reaction is analyzed and adjusted in real time: Step 1: collecting absorbance data of the reaction solution in the liquid phase reduction reaction; Step 2: analyzing singular value differential change characteristics of each row in a matrix composed of absorbance sequences at each collection time and adjacent collection times, and analyzing a fitting straight line slope average of each column greater than zero to determine a step change characteristic value at each collection time; the step change characteristic value is determined by analyzing an average of singular value absolute differentials of all rows in the matrix, and analyzing an average of fitting straight line slopes greater than zero in all columns in the matrix; the step change characteristic value is positively correlated with the two averages respectively; Step 3: correcting the step change characteristic value by using a correlation degree of an absorbance sequence at each collection time and a sequence of fitting straight line slopes of all columns to determine a step change confidence at each collection time; Step 4: calculating a remaining adjustment time in a later period of the liquid phase reduction reaction by using a differential average of the step change confidence in an early period of the liquid phase reduction reaction; (3) removing supernatant after flocculation and precipitation of the liquid phase reduction solution after the reaction, then sequentially performing deionized water cleaning, cooling and drying, and polishing to prepare the nano silver powder.

2. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 1, characterized in that, The mass ratio of solutes in the reducing agent solution, the dispersant solution and the silver nitrate solution is (0.2-0.4):(0.1-0.2):

1.

3. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 1, characterized in that, The reducing agent solution is one of sodium borohydride or ascorbic acid, and the dispersant solution is one of gelatin, gum arabic or polyvinylpyrrolidone (PVP).

4. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 1, characterized in that, Before analyzing the average of singular value absolute differentials of all rows in the matrix, the singular values of all rows are normalized to the maximum value.

5. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 1, characterized in that, Before correcting the step change characteristic value by using the correlation degree, the correlation degree is normalized to correct the step change characteristic value to a range of (0, 1) to obtain the step change confidence.

6. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 1, characterized in that, Before calculating the differential average of the step change confidence in the early period of the liquid phase reduction reaction, the step change confidence in the early period is normalized to the maximum value to control the value range of the calculated differential average to (0, 1).

7. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 6, characterized in that, The calculation method of the remaining adjustment time in the later period of the liquid phase reduction reaction is: In the formula, is the remaining adjustment time in the later stage of the liquid phase reduction reaction, is the actual remaining time in the later stage of the liquid phase reduction reaction, is the maximum value of the preset adjustable time, C is the third average value in the early stage of the liquid phase reduction reaction, and the third average value is the difference average value.

8. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 7, characterized in that, The early period is the first 30 minutes of the liquid phase reduction reaction, and the actual remaining time in the later period is a difference between a preset reaction time of the liquid phase reduction reaction and a time used in the early period.

9. The method for producing highly dispersed nano-silver powder for low-temperature sintering silver paste according to claim 1, wherein The flocculation and precipitation is achieved by adding a flocculating agent into the liquid phase reduction solution after the reaction, and the flocculating agent is a mixture of one amine and one acid from octylamine, dodecylamine, hexadecylamine, stearic acid, ricinoleic acid and urushi acid.

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