Method for preparing electronic paste for multilayer ceramic capacitor electrodes

Abstract

The present invention discloses a method and device for preparing electronic slurry for multilayer ceramic capacitor electrodes with uniform particle size distribution, high yield and production efficiency, and good continuity of the slurry layer after sintering and film formation. The method for preparing electronic slurry for multilayer ceramic capacitor electrodes specifically includes the following preparation steps: (1) ultrasonic emulsification dispersion; (2) grinding dispersion; (3) centrifugal classification; (4) filtration; (5) stirring replacement; and (6) distillation concentration. The device used in the preparation method includes an ultrasonic emulsification kettle, a grinder, a rotary vibrating screen, a centrifuge, a filter, a stirring kettle, and an evaporation concentration device connected by a pipeline. A peristaltic pump is installed on the pipeline connecting the ultrasonic emulsification kettle and the grinder, and a peristaltic pump is installed on the pipeline connecting the rotary vibrating screen and the centrifuge. The evaporation concentration device includes a heating kettle, a condenser, a storage tank, and a vacuum pump connected by pipelines in sequence. The outer layer of the ultrasonic emulsification kettle is provided with a jacket.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano powder classification and slurry preparation, and in particular relates to a method and a device for preparing electronic slurry for multilayer ceramic capacitor electrodes. Background Art

[0002] In the multilayer ceramic capacitor industry, chip-type multilayer ceramic capacitors (MLCCs) are composed of three parts: inner electrodes, ceramic layers, and terminal electrodes. The dielectric material and the inner electrodes are stacked in a staggered manner, then sintered at high temperature to form a structure, and then a metal layer is sealed at both ends of the chip to obtain a structure similar to a monolithic body. Therefore, MLCC is often called a "monolithic capacitor."

[0003] Multilayer ceramic capacitors (MLCCs), also known as chip capacitors, multilayer capacitors, and stacked capacitors, are characterized by their small size, high capacitance, low loss at high frequencies, suitability for mass production, low price, and high stability. The capacitance of an MLCC is directly proportional to the overlap area of ​​the internal electrodes, the number of dielectric ceramic layers, and the relative dielectric constant of the dielectric ceramic material used, and inversely proportional to the thickness of the single dielectric layer. There are two main methods for increasing capacitance within a given volume: reducing dielectric thickness (the lower the dielectric thickness, the higher the capacitance of the MLCC); increasing the number of layers within the MLCC (the greater the number of layers, the higher the capacitance).

[0004] The electrode materials of chip multilayer ceramic capacitors (MLCCs) mainly include metal materials such as palladium, silver, platinum, nickel, iron, and copper. Due to the limited resources and high prices of precious metal materials such as palladium, silver, and platinum, the manufacturing cost of chip multilayer ceramic capacitors (MLCCs) is greatly increased and their application areas are restricted. Iron requires a series of complex process measures to solve its oxidation and diffusion problems, which increases production costs. The electromigration rate of nickel electrodes is lower than that of precious metal electrodes. Nickel has good corrosion and heat resistance and relatively low resistivity. The corresponding MLCC manufacturing process and products are highly stable and have become one of the most widely used MLCC electrode materials. Although copper paste has problems such as easy oxidation, fast shrinkage, and high electromigration rate, these shortcomings have been gradually overcome with process improvements. Copper has the advantages of being cheaper than nickel, having lower resistivity, lower sintering temperature, lower overall manufacturing cost, being more environmentally friendly, and having a longer lifespan for finished MLCCs. Therefore, in recent years, base metals such as nickel and copper have been commonly used as electrode materials for chip multilayer ceramic capacitors (MLCCs). With technological advancements and the development of the electronics industry, electronic devices are increasingly moving towards miniaturization, high capacity, high reliability, and low cost. MLCC products, which are thin, lightweight, and compact, are becoming increasingly packaged and versatile. Many leading manufacturers are vying to develop high-capacity MLCCs, which offer significant profit margins. Consequently, higher requirements are being placed on the electrode materials used in capacitors, resulting in smaller metal particles and a more uniform particle size distribution.

[0005] The MLCC electrode slurry preparation process involves first grading the raw metal powder to remove excessive particles, then filtering to further remove agglomerated powder clumps and particles. The electronic slurry is then formulated, and the electrode slurry is printed onto a ceramic diaphragm. After drying, a clear, complete dielectric diaphragm is obtained. Currently, domestic metal powder suppliers can only provide primary metal powder raw materials. These metal powders have a wide particle size distribution, many large particles, and severe agglomeration, making them unsuitable for direct application in the MLCC field. The metal powders require further grading to remove excessive particles, then are formulated into an electrode slurry, printed onto a ceramic diaphragm, and fired. Because the quality of the metal powder electrode slurry directly determines the performance of the capacitor, improving the metal powder particle size distribution, enhancing the metal powder quality, and preparing ultrafine metal powder electronic slurry are key to reducing capacitor size, increasing capacitance, and enhancing the competitiveness of the MLCC market. Summary of the Invention

[0006] In response to the problems raised in the background technology, the present invention studies and designs a method and apparatus for preparing electronic paste for multilayer ceramic capacitor electrodes, the purpose of which is to provide a method and apparatus for preparing electronic paste for multilayer ceramic capacitor electrodes with uniform particle size distribution, high yield and production efficiency, and good continuity of the paste layer after sintering and film formation.

[0007] The technical solution of the present invention:

[0008] A method for preparing an electronic paste for multilayer ceramic capacitor electrodes, comprising the following steps:

[0009] (1) Ultrasonic emulsification dispersion

[0010] Adding organic solvent into ultrasonic emulsification kettle, stirring, adding ultrafine metal powder to prepare metal slurry, then adding thickener, ultrasonic emulsification and dispersion to prepare mixed electronic slurry;

[0011] (2) Grinding and dispersion

[0012] The slurry after ultrasonic emulsification and dispersion in step (1) is sent to a grinder for grinding and dispersion and then sieved to form a homogeneous emulsion;

[0013] (3) Centrifugal classification

[0014] The slurry after screening in step (2) is sent to a centrifuge for centrifugal classification to remove particles exceeding the standard and obtain an electronic slurry with uniform particle size distribution;

[0015] (4) Filtering

[0016] The electronic slurry after centrifugal classification in step (3) is sent to a filter to remove foreign matter and powder clumps;

[0017] (5) Stirring and replacement

[0018] The electronic slurry after filtering in step (4) is added to a stirred tank after solid-liquid separation by sedimentation, and ethanol solvent is added for replacement to reduce the carbon content;

[0019] (6) Distillation and concentration

[0020] The electronic paste after replacement in step (5) is added with an electronic solvent and then sent to an evaporation concentration device for concentration to obtain an electronic paste for multilayer ceramic capacitor electrodes.

[0021] Preferably, the ultrafine metal powder in step (1) is prepared by a PVD method, and its specific surface area equivalent particle size is 30~250nm, the ultrafine metal powder is one of nickel and copper, the organic solvent is at least one of ethanol, ethylene glycol, propanol, n-butanol, glycerol, and acetone, the thickener is lignin or ethyl cellulose (EC), and its molecular weight is 100~2000, the ultrasonic emulsification temperature is 10~25℃, the emulsification dispersion time is 0.5~3h, and the prepared mixed electronic slurry has a viscosity of 5~45cps and a solid content of 5~35wt%.

[0022] Further preferably, in step (1), the ultrasonic emulsification temperature is 12-15° C., the viscosity of the prepared mixed electronic slurry is 10-25 cps, and the solid content is 7-25 wt %; the ultrafine metal powder is nickel powder, and the oxygen content of the nickel powder is 10,000-55,000 ppm.

[0023] Preferably, in step (2), the grinder uses 0.1-2 mm zirconium beads, the grinder speed is 300-3000 r / min, the grinding temperature is 5-45° C., the grinding time is 1.5-3 h, and the screen is 100-1000 mesh.

[0024] Preferably, the electronic slurry after screening in step (3) is sent to a tubular centrifuge for classification through a peristaltic pump, the drum speed of the tubular centrifuge is 5000~30000 r / min, the separation factor is 15000~20000, and the electronic slurry after centrifugal classification has a DMax of 0.2~0.7μm according to the PSD test.

[0025] Further preferably, the drum speed of the tubular centrifuge in step (3) is 10,000-25,000 r / min.

[0026] Preferably, the electronic slurry after centrifugal classification in step (4) is sent to a filter for filtration through a peristaltic pump, and the pore size of the filter element is 0.2-2 μm.

[0027] Preferably, the electronic slurry filtered in step (5) is added to a stirred tank, solid-liquid separated by sedimentation, and the concentration is controlled at 30-80%, and ethanol solvent is added with a concentration of 15-50%. After stirring for 0.5-3 hours, solid-liquid separation is carried out by sedimentation, and the supernatant is removed, and ethanol solvent is added for replacement until the carbon content of the slurry is ≤2% and the slurry viscosity drops below 20 cps.

[0028] Preferably, in step (6), the electronic solvent is one of DHTA, terpineol, propylene glycol, n-butanol, and sec-butanol. After the electronic solvent is added, the concentration of the electronic slurry is 30-80 wt%. The electronic slurry is distilled and concentrated under vacuum, the absolute pressure in the heating concentration kettle is 10-100 KPa, the slurry temperature in the heating concentration kettle is controlled at 50-100°C, the alcohol solvent is removed by vacuum evaporation, the solvent residue is ≤5%, the solid content of the electronic slurry is 50-75%, and the metal content is 55-75%.

[0029] Further preferably, in step (6), the absolute pressure in the heating and concentrating kettle is 20-80 KPa, the temperature of the slurry in the heating and concentrating kettle is controlled at 50-80°C, the residual solvent content is ≤1.5%, the solid content of the electronic slurry is 55-75%, and the metal content is 60-70%.

[0030] A device used in the method for preparing electronic slurry for multilayer ceramic capacitors as described above comprises, in sequence, an ultrasonic emulsification kettle, a grinder, a rotary vibrating screen, a centrifuge, a filter, a stirring kettle, and an evaporation concentration device connected by pipelines. A peristaltic pump is installed on the pipeline connecting the ultrasonic emulsification kettle and the grinder, and a peristaltic pump is installed on the pipeline connecting the rotary vibrating screen and the centrifuge.

[0031] Preferably, the evaporation and concentration device includes a heating kettle, a condenser, a storage tank, and a vacuum pump which are sequentially connected through pipelines, and the condenser can recover and reuse the evaporated ethanol vapor.

[0032] Preferably, the outer layer of the ultrasonic emulsification kettle is provided with a jacket to cool and control the emulsification temperature of the slurry in the ultrasonic emulsification kettle.

[0033] Beneficial effects of the present invention: 1) The present invention uses ultrafine metal powder with an average particle size of 50-150nm measured by BET to prepare the slurry. The powder particle size is small, and the fine metal powder particles have good sintering performance, which can improve the density of the sintered film and the number of stacking layers inside the MLCC. The more stacking layers, the higher the capacitance; 2) The metal powder prepared by the PVD method has high sphericity (MLCC Electrode slurry requires that the metal powder used to make the conductive phase must be round, evenly distributed, and have a certain specific surface area. Spherical particles have good packing properties, high mechanical strength, and can make the sintered film structure more dense. 3) Spherical metal powder with uniform particle size in the electrode slurry can ensure the uniformity of the conductive slurry and ensure good contact between the metal particles after sintering; 3) Nickel oxide powder with an oxygen content of 10,000-55,000 ppm is used to prepare the slurry. Nickel oxide has a high melting point (1984°C), which can prevent the metal powder from melting when sintering simultaneously with the ceramic dielectric, maintaining the continuity of the metal slurry layer after sintering. 4) Tube The slurry is graded by a centrifuge, and the slurry is fed from the center of the bottom of the drum, eliminating the short-circuit problem of conventional grading equipment. The drum speed is 5000~30000r / min, and the separation factor is in the range of 15000~20000. The grading accuracy is improved, the slurry has fewer large particles, and the overflow Dmax after classification is less than 500nm. The particle size distribution is uniform, which can prevent the occasional large particles in the powder from penetrating the dielectric layer and causing structural defects without lamination; 5) Ethyl cellulose thickener is added to the graded slurry, and the slurry viscosity is 10~15cps. The powder forms a suspension, which reduces the sedimentation rate of the powder particles, improves the yield, and has high production efficiency; 6) The organic carrier of the electrode slurry is composed of a variety of organic solvents, whose function is to ensure the quality of electrode slurry printing. DHTA, terpineol, etc. are selected as slurry solvents with a boiling point of ≥200℃. The slurry preparation process is not easy to agglomerate or agglomerate. The slurry layer has good continuity after sintering and forming a film. The electrode and dielectric layer are tightly combined to avoid stratification or electrode cracking problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an electron microscope image of the nickel powder of Example 3 before step (3);

[0035] Figure 2 This is an electron microscope image of the nickel powder of Example 3 after step (3);

[0036] Figure 3 This is an electron microscope image of the nickel powder of Example 3 before step (4);

[0037] Figure 4 This is an electron microscope image of the nickel powder in Example 3 after step (6);

[0038] Figure 5 Schematic diagram of the structure of the preparation device of the present invention.

[0039] Among them: 1. Pipeline, 2. Ultrasonic emulsification kettle, 2-1, Jacket, 3. Grinder, 4. Rotary vibrating screen, 5. Centrifuge, 6. Filter, 7. Stirring kettle, 8. Peristaltic pump, 9. Heating kettle, 10. Condenser, 11. Storage tank, 12. Vacuum pump. DETAILED DESCRIPTION

[0040] The following embodiments will further illustrate the present invention with reference to the accompanying drawings.

[0041] like Figure 5 As shown, a device used in a method for preparing an electronic slurry for multilayer ceramic capacitor electrodes includes, in sequence, an ultrasonic emulsification kettle 2, a grinder 3, a rotary vibrating screen 4, a centrifuge 5, a filter 6, a stirring kettle 7, and an evaporation concentration device connected through a pipe 1. A peristaltic pump 8 is installed on the pipe 1 connecting the ultrasonic emulsification kettle 2 and the grinder 3, and a peristaltic pump 8 is installed on the pipe 1 connecting the rotary vibrating screen 4 and the centrifuge 5.

[0042] The evaporation concentration device includes a heating kettle 9, a condenser 10, a storage tank 11, and a vacuum pump 12 which are sequentially connected through a pipeline 1.

[0043] The outer layer of the ultrasonic emulsification kettle 2 is provided with a jacket 2 - 1 to cool and control the emulsification temperature of the slurry in the ultrasonic emulsification kettle 2 .

[0044] Among them, the ultrasonic emulsification kettle 2 model is LEGEE-WZLG22116, the grinder 3 model is DBM7L, the rotary vibrating screen 4 model is ZSΦ500-1, the centrifuge 5 model is GQ105RS, the filter 6 model is cobetter19-187-1, the stirring kettle 7 model is LEGEE-WZLG230411, the peristaltic pump 8 model is WG6005, the heating kettle 9 model is XHSG-100L, and the vacuum pump 12 model is 2XZ-2. The models not mentioned in the above device structures are also prior art.

[0045] Example 1 (refer to Figure 5 )

[0046] 1. Prepare ultrafine nickel powder by PVD method and measure its equivalent particle size by BET to be 225 nm. Add propanol to an ultrasonic emulsification kettle and stir. Then add ultrafine nickel powder and ethyl cellulose (molecular weight 148). Ultrasonic emulsification and dispersion are carried out at 12°C for 3 hours. Emulsify uniformly and adjust the emulsion slurry to a viscosity of 5.5 cps and a solid content of 5.3 wt%.

[0047] 2. The emulsified and dispersed electronic slurry is fed into a grinder through a peristaltic pump for grinding and dispersion. The grinder uses 1.8mm zirconium beads, the grinding temperature is 6.5°C, and it is ground at 2850r / min for 2.75h. It is then sieved through a 100-mesh rotary vibrating sieve to form a uniform homogeneous emulsion.

[0048] 3. The screened electronic slurry is sent to a tubular centrifuge for classification through a peristaltic pump. The centrifuge speed is adjusted by frequency conversion. The centrifuge drum rotates at a high speed of 5000r / min, with a separation factor of 15000. Excessive particles are removed, and a nickel powder slurry with uniform particle size distribution is obtained after overflow. The maximum particle size DMax of the slurry is 0.68μm according to PSD test.

[0049] 4. The graded nickel powder slurry is sent to the filter through a peristaltic pump for filtration. The slurry is filtered through a 1.5μm pore size filter element to remove foreign matter and powder clumps.

[0050] 5. The filtered slurry is separated into solid and liquid by sedimentation, and the concentration is controlled at 35%. Ethanol solvent is added to the stirred tank at a concentration of 45%. After stirring for 0.5 hours, solid and liquid are separated by sedimentation. The supernatant is removed and ethanol solvent is added again. The mixture is stirred and replaced. This is repeated three times until the carbon content of the slurry is ≤2% and the viscosity of the slurry is ≤20cps.

[0051] 6. Add DHTA to the replaced nickel powder slurry to prepare an electronic slurry with a concentration of 30wt% and send it into a heating concentration kettle for distillation and concentration under vacuum. The pressure in the heating kettle is pumped to 90Kpa by a vacuum pump. The slurry temperature in the kettle is controlled at 90℃ for evaporation. The ethanol vapor is condensed by a condenser and collected in a storage tank. After concentration, a nickel powder slurry for ceramic capacitor electrodes with a solid content of 70~73% and a metal content of 65~70% is obtained.

[0052] Example 2 (refer to Figure 5 )

[0053] 1. Prepare ultrafine nickel powder by PVD method and measure its equivalent particle size by BET to be 36 nm. Add ethanol to an ultrasonic emulsification kettle and stir. Then add ultrafine nickel powder and ethyl cellulose (molecular weight 1848). Ultrasonic emulsification and dispersion are carried out at 25°C for 3 hours. Emulsify uniformly and adjust the emulsion slurry to a viscosity of 45 cps and a solid content of 35 wt%.

[0054] 2. The emulsified and dispersed electronic slurry is fed into a grinder through a peristaltic pump for grinding and dispersion. The grinder uses 0.1mm zirconium beads, the grinding temperature is 43°C, and it is ground at 325r / min for 1.5h. It is then sieved through a 1000-mesh rotary vibrating sieve to form a uniform homogeneous emulsion.

[0055] 3. The screened electronic slurry is sent to a tubular centrifuge for classification through a peristaltic pump. The centrifuge speed is adjusted by frequency conversion. The centrifuge drum rotates at a high speed of 30,000 r / min and the separation factor is 20,000 to remove particles exceeding the standard. After overflow, a nickel powder slurry with uniform particle size distribution is obtained. The maximum particle size DMax of the slurry is 0.22 μm according to the PSD test.

[0056] 4. The graded nickel powder slurry is sent to the filter through a peristaltic pump for filtration. The slurry is filtered through a 0.25 μm pore size filter element to remove foreign matter and powder clumps.

[0057] 5. The filtered slurry is separated into solid and liquid by sedimentation, and the concentration is controlled at 35%. Ethanol solvent is added to the stirred tank at a concentration of 18%. After stirring for 3 hours, solid and liquid separation is carried out by sedimentation. The supernatant is removed, and ethanol solvent is added again. Stirring and replacement is carried out until the carbon content of the slurry is ≤2% and the slurry viscosity is ≤20cps;

[0058] 6. Add terpineol to the replaced nickel powder slurry to prepare an electronic slurry with a concentration of 55wt% and send it into a heating concentration kettle for distillation and concentration under vacuum. The pressure in the heating kettle is pumped to 10Kpa by a vacuum pump. The slurry temperature in the kettle is controlled at 50°C for evaporation. The ethanol vapor is condensed by a condenser and collected in a storage tank. After concentration, a nickel powder slurry for ceramic capacitor electrodes with a solid content of 61~63% and a metal content of 62% is obtained.

[0059] Example 3 (refer to Figure 5 )

[0060] 1. Ultrafine nickel powder was prepared by PVD method and the equivalent particle size of the powder was 125 nm as measured by BET. n-Butanol was added to an ultrasonic emulsification kettle and stirred. Ultrafine nickel powder and lignin (molecular weight 1650) were added. Ultrasonic emulsification and dispersion were carried out at 15°C for 0.5 h. The emulsification was uniform and the emulsion slurry was adjusted to a viscosity of 23 cps and a solid content of 18 wt%.

[0061] 2. The emulsified and dispersed electronic slurry is fed into a grinder through a peristaltic pump for grinding and dispersion. The grinder uses 0.5mm zirconium beads, the grinding temperature is 25°C, and it is ground at 1200r / min for 2h. It is then sieved through a 400-mesh rotary vibrating sieve to form a uniform homogeneous emulsion.

[0062] 3. The screened electronic slurry is sent to a tubular centrifuge for classification through a peristaltic pump. The centrifuge speed is adjusted by frequency conversion. The centrifuge drum rotates at a high speed of 20,000 r / min, with a separation factor of 18,000. Excessive particles are removed, and a nickel powder slurry with uniform particle size distribution is obtained after overflow. The maximum particle size DMax of the slurry is 0.5 μm according to PSD test.

[0063] 4. The graded nickel powder slurry is sent to the filter through a peristaltic pump for filtration. The slurry is filtered through a 0.75 μm pore size filter element to remove foreign matter and powder clumps.

[0064] 5. The filtered slurry is separated into solid and liquid by sedimentation, and the concentration is controlled at 80%. Ethanol solvent is added to the stirred tank at a concentration of 50%. After stirring for 1.5 hours, solid and liquid are separated by sedimentation. The supernatant is removed and ethanol solvent is added again. The mixture is stirred and replaced. This process is repeated twice until the carbon content of the slurry is ≤2% and the viscosity of the slurry is ≤20cps.

[0065] 6. Add propylene glycol to the replaced nickel powder slurry to prepare an electronic slurry with a concentration of 30wt%, and send it into a heating and concentrating kettle for distillation and concentration under vacuum. The pressure in the heating kettle is pumped to 50Kpa by a vacuum pump. The slurry temperature in the kettle is controlled at 100℃ for evaporation. The ethanol vapor is condensed by a condenser and collected in a storage tank. After concentration, a nickel powder slurry for ceramic capacitor electrodes with a solid content of 70~72% and a metal content of 68~71% is obtained.

[0066] Example 4 (refer to Figure 5 )

[0067] 1. Ultrafine copper powder was prepared by PVD method and the equivalent particle size of the powder was 180 nm as measured by BET. Acetone was added to an ultrasonic emulsification kettle and stirred. Ultrafine copper powder and lignin (molecular weight 509) were added. Ultrasonic emulsification and dispersion were carried out at 25°C for 1 hour. The emulsification was uniform and the emulsion slurry was adjusted to a viscosity of 12 cps and a solid content of 15 wt%.

[0068] 2. The emulsified and dispersed electronic slurry is fed into a grinder through a peristaltic pump for grinding and dispersion. The grinder uses 1mm zirconium beads, the grinding temperature is 35°C, and it is ground at 1000r / min for 2h. It is then sieved through a 200-mesh rotary vibrating sieve to form a uniform homogeneous emulsion.

[0069] 3. The screened electronic slurry is sent to a tubular centrifuge for classification through a peristaltic pump. The centrifuge speed is adjusted by frequency conversion. The centrifuge drum rotates at a high speed of 10,000 r / min, with a separation factor of 17,000. Excessive particles are removed, and a nickel powder slurry with uniform particle size distribution is obtained after overflow. The maximum particle size DMax of the slurry is 0.6 μm according to PSD test.

[0070] 4. The graded nickel powder slurry is sent to the filter through a peristaltic pump for filtration. The slurry is filtered through a 1μm pore size filter element to remove foreign matter and powder clumps;

[0071] 5. The filtered slurry is separated into solid and liquid by sedimentation, and the concentration is controlled at 50%. Ethanol solvent is added to the stirred tank at a concentration of 30%. After stirring for 2 hours, solid and liquid are separated by sedimentation. The supernatant is removed and ethanol solvent is added again. The mixture is stirred and replaced. This process is repeated twice until the carbon content of the slurry is ≤2% and the viscosity of the slurry is ≤20cps.

[0072] 6. Add n-butanol to the replaced copper powder slurry to prepare an electronic slurry with a concentration of 60wt% and send it into a heating concentration kettle for distillation and concentration under vacuum. The pressure in the heating kettle is pumped to 30Kpa by a vacuum pump. The slurry temperature in the kettle is controlled at 65°C for evaporation. The ethanol vapor is condensed by a condenser and collected in a storage tank. After concentration, a copper powder slurry for ceramic capacitor electrodes with a solid content of 71~74% and a metal content of 73% is obtained.

[0073] Example 5 (refer to Figure 5 )

[0074] 1. Prepare ultrafine copper powder by PVD method and measure its equivalent particle size by BET to be 53 nm. Add ethylene glycol to an ultrasonic emulsifier and stir. Then add ultrafine copper powder and lignin (molecular weight 1513.5). Ultrasonic emulsification and dispersion are carried out at 15°C for 2 hours. Emulsify uniformly and adjust the emulsion slurry to a viscosity of 30-40 cps and a solid content of 35 wt%.

[0075] 2. The emulsified and dispersed electronic slurry is fed into a grinder through a peristaltic pump for grinding and dispersion. The grinder uses 0.5mm zirconium beads, the grinding temperature is 45°C, and it is ground at 500r / min for 3h. It is then sieved through a 200-mesh rotary vibrating sieve to form a uniform homogeneous emulsion.

[0076] 3. The screened electronic slurry is sent to a tubular centrifuge for classification through a peristaltic pump. The centrifuge speed is adjusted by frequency conversion. The centrifuge drum rotates at a high speed of 20,000 r / min, with a separation factor of 18,000. Excessive particles are removed, and a nickel powder slurry with uniform particle size distribution is obtained after overflow. The maximum particle size DMax of the slurry is 0.35 μm according to PSD test.

[0077] 4. The graded nickel powder slurry is sent to the filter through a peristaltic pump for filtration. The slurry is filtered through a 0.65μm pore size filter element to remove foreign matter and powder clumps;

[0078] 5. The filtered slurry is separated into solid and liquid by sedimentation, and the concentration is controlled at 45%. Ethanol solvent is added to the stirred tank at a concentration of 30%. After stirring for 3 hours, solid and liquid are separated by sedimentation. The supernatant is removed and ethanol solvent is added again. The mixture is stirred and replaced. This process is repeated twice until the carbon content of the slurry is ≤2% and the viscosity of the slurry is ≤20cps.

[0079] 6. Add sec-butanol to the replaced copper powder slurry to prepare an electronic slurry with a concentration of 50wt% and send it into a heating concentration kettle for distillation and concentration under vacuum. The pressure in the heating kettle is pumped to 20Kpa by a vacuum pump. The slurry temperature in the kettle is controlled at 80℃ for evaporation. The ethanol vapor is condensed by a condenser and collected in a storage tank. After concentration, a copper powder slurry for ceramic capacitor electrodes with a solid content of 71~74% and a metal content of 70% is obtained.

[0080] Example 6 (refer to Figure 5 )

[0081] 1. Prepare the ultrafine copper-nickel alloy powder by PVD method and measure the equivalent particle size of the powder by BET to be 240 nm. Add glycerol to an ultrasonic emulsification kettle and stir. Then add the ultrafine copper-nickel alloy powder and ethyl cellulose (molecular weight 1345). Ultrasonic emulsification and dispersion are carried out at 20°C for 1.5 hours. Emulsify uniformly and adjust the emulsion slurry to a viscosity of 40-45 cps and a solid content of 28 wt%.

[0082] 2. The emulsified and dispersed electronic slurry is fed into a grinder through a peristaltic pump for grinding and dispersion. The grinder uses 2mm zirconium beads, the grinding temperature is 40°C, and it is ground at 300r / min for 2h. It is then sieved through a 100-mesh rotary vibrating sieve to form a uniform homogeneous emulsion.

[0083] 3. The screened electronic slurry is sent to a tubular centrifuge for classification through a peristaltic pump. The centrifuge speed is adjusted by frequency conversion. The centrifuge drum rotates at a high speed of 25,000 r / min, with a separation factor of 18,000. Excessive particles are removed, and a nickel powder slurry with uniform particle size distribution is obtained after overflow. The maximum particle size DMax of the slurry is 0.7 μm according to PSD test.

[0084] 4. The graded nickel powder slurry is sent to the filter through a peristaltic pump and filtered through a 2μm pore filter to remove foreign matter and powder clumps;

[0085] 5. The filtered slurry is separated into solid and liquid by sedimentation, and the concentration is controlled at 55%. Ethanol solvent is added to the stirred tank at a concentration of 20%. After stirring for 3 hours, solid and liquid are separated by sedimentation. The supernatant is removed and ethanol solvent is added again. The mixture is stirred and replaced. This process is repeated twice until the carbon content of the slurry is ≤2% and the viscosity of the slurry is ≤20cps.

[0086] 6. Add DHTA to the replaced copper-nickel alloy powder slurry to prepare an electronic slurry with a concentration of 80wt%, and send it into a heating concentration kettle for distillation and concentration under vacuum. The pressure in the heating kettle is pumped to 10Kpa by a vacuum pump. The slurry temperature in the kettle is controlled at 90°C for evaporation. The ethanol vapor is condensed by a condenser and collected in a storage tank. After concentration, a copper-nickel alloy powder slurry for ceramic capacitor electrodes with a solid content of 50-64% and a metal content of 55-61% is obtained.

[0087] The process steps in Examples 1 to 6 refer to the above examples. The specific metal powder specifications, measurements, and the corresponding performance test results of the electronic paste for ceramic capacitor electrodes prepared therefrom are shown in Table 1:

[0088] Table 1 Performance test results of raw powder and electronic paste for MLCC electrodes prepared from it

[0089]

[0090] Depend on Figure 1 、 Figure 2 It can be seen that in Example 3, the particles in the slurry obtained after centrifugal classification are more evenly distributed, so that Dmax is controlled within the range of less than 0.5 μm.

[0091] Depend on Figure 3 、 Figure 4 It can be seen that in Example 3, foreign matter and powder clumps are basically removed after the slurry is filtered through the filter element.

Claims

1. A method for preparing an electronic paste for multilayer ceramic capacitor electrodes, characterized in that: The specific preparation steps include: (1) Ultrasonic emulsification dispersion Adding organic solvent into ultrasonic emulsification kettle, stirring, adding ultrafine metal powder to prepare metal slurry, then adding thickener, ultrasonic emulsification and dispersion to prepare mixed electronic slurry; (2) Grinding and dispersion The slurry after ultrasonic emulsification and dispersion in step (1) is fed into a grinder for grinding and dispersion and then sieved to form a homogeneous emulsion; (3) Centrifugal classification The slurry after screening in step (2) is sent to a centrifuge for centrifugal classification to remove particles exceeding the standard and obtain an electronic slurry with uniform particle size distribution; (4) Filtering The electronic slurry after centrifugal classification in step (3) is sent to a filter to remove foreign matter and powder clumps; (5) Stirring and replacement The electronic slurry filtered in step (4) is added to a stirred tank after solid-liquid separation by sedimentation, and ethanol solvent is added for replacement to reduce the carbon content; (6) Distillation and concentration The electronic paste after replacement in step (5) is added with an electronic solvent and then sent to an evaporation concentration device for concentration to obtain an electronic paste for multilayer ceramic capacitor electrodes; Wherein, the ultrafine metal powder in the step (1) is prepared by a PVD method, and its specific surface area equivalent particle size is 30~250nm, the ultrafine metal powder is one of nickel and copper, the organic solvent is at least one of ethanol, ethylene glycol, propanol, n-butanol, glycerol, and acetone, the thickener is lignin or ethyl cellulose (EC), and its molecular weight is 100~2000, the ultrasonic emulsification temperature is 10~25℃, the emulsification dispersion time is 0.5~3h, and the prepared mixed electronic slurry has a viscosity of 5~45cps and a solid content of 5~35wt%.

2. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: In the step (1), the ultrasonic emulsification temperature is 12-15° C., the viscosity of the prepared mixed electronic slurry is 10-25 cps, and the solid content is 7-25 wt %. The ultrafine metal powder is nickel powder, and the oxygen content of the nickel powder is 10,000-55,000 ppm.

3. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: In the step (2), the grinding machine uses 0.1-2 mm zirconium beads, the grinding machine speed is 300-3000 r / min, the grinding temperature is 5-45 ° C, the grinding time is 1.5-3 h, and the screen is 100-1000 mesh.

4. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: The electronic slurry after screening in step (3) is sent to a tubular centrifuge for classification through a peristaltic pump. The drum speed of the tubular centrifuge is 5000~30000 r / min, and the separation factor is 15000~20000. After centrifugal classification, the electronic slurry is tested by PSD and the DMax is 0.2~0.7μm.

5. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: The electronic slurry after centrifugal classification in step (4) is sent to a filter for filtration through a peristaltic pump, and the pore size of the filter element is 0.2-2 μm.

6. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: The electronic slurry filtered in step (5) is added to a stirred tank, and solid-liquid separation is carried out by sedimentation, and the concentration is controlled at 30-80%. Ethanol solvent is added, and the concentration is adjusted to 15-50%. After stirring for 0.5-3 hours, solid-liquid separation is carried out by sedimentation, and the supernatant is removed. Ethanol solvent is then added for replacement until the carbon content of the slurry is ≤2% and the slurry viscosity is reduced to below 20 cps.

7. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: In step (6), the electronic solvent is one of DHTA, terpineol, propylene glycol, n-butanol, and sec-butanol. After the electronic solvent is added, the electronic slurry concentration is 30-80 wt%. The electronic slurry is distilled and concentrated under vacuum. The absolute pressure in the heating concentration kettle is 10-100 KPa. The slurry temperature in the heating concentration kettle is controlled at 50-100°C. The alcohol solvent is removed by vacuum evaporation. The solvent residue is ≤5%. The solid content of the electronic slurry is 50-75%, and the metal content is 55-75%.

8. The method for preparing an electronic paste for multilayer ceramic capacitor electrodes according to claim 1, wherein: In the step (6), the absolute pressure in the heating and concentrating kettle is 20-80 KPa, the temperature of the slurry in the heating and concentrating kettle is controlled at 50-80°C, the residual solvent content is ≤1.5%, the solid content of the electronic slurry is 55-75%, and the metal content is 60-70%.

9. An apparatus for use in the method for preparing an electronic paste for a multilayer ceramic capacitor according to claim 1, characterized in that: The invention comprises an ultrasonic emulsification kettle, a grinder, a rotary vibrating screen, a centrifuge, a filter, a stirring kettle and an evaporation concentration device which are connected through pipelines. A peristaltic pump is installed on the pipeline connecting the ultrasonic emulsification kettle and the grinder, and a peristaltic pump is installed on the pipeline connecting the rotary vibrating screen and the centrifuge.

10. The apparatus used in the method for preparing electronic paste for multilayer ceramic capacitors according to claim 9, wherein: The evaporation and concentration device comprises a heating kettle, a condenser, a storage tank, and a vacuum pump which are sequentially connected through pipelines. The condenser can recover and reuse evaporated ethanol vapor.

Images