Preparation method of multilayer piezoelectric ceramic

Abstract

The invention relates to the technical field of piezoelectric ceramic forming, in particular to a preparation method of multilayer piezoelectric ceramic, which comprises the following steps: preparing slurry which comprises the following materials in percentage by mass: 50-80% of ceramic powder, 5-12% of acrylate latex, 1-2% of ammonium polyacrylate, 0.8-1.5% of sodium alginate and the balance of alcohol-water solvent, carrying out ball milling to obtain tape casting slurry, carrying out tape casting to obtain a single-layer blank film, carrying out gelation treatment, printing inner electrode slurry, drying, laminating, plastic discharging and sintering to obtain the multilayer piezoelectric ceramic; the preparation method comprises the following steps: carrying out tape casting on benzene-free system slurry to obtain a single-layer blank film, printing electrode slurry on one surface of the single-layer blank film, and carrying out lamination molding to obtain the multilayer piezoelectric ceramic containing the inner electrode; the thickness of a single-layer blank film is smaller than 10 microns, the bonding strength between the blank films is high, and the obtained multilayer piezoelectric ceramic has good piezoelectric performance.

Description

Technical Field

[0001] The invention relates to the technical field of piezoelectric ceramic forming, and in particular to a method for preparing a multilayer piezoelectric ceramic. Background Art

[0002] Piezoelectric ceramic devices are solid-state actuator micro-actuators made using the inverse piezoelectric effect. They are widely used in high-tech fields such as precision optics, micro-machines, microelectronics, and computer applications. These application scenarios require piezoelectric ceramic devices to have small size, low driving voltage, large displacement, and integration. In the prior art, adhesives are usually used to bond piezoelectric ceramic monoliths to form multilayer piezoelectric ceramic micro-actuators. However, due to the limitation of the thickness of the monolithic ceramic diaphragm, the development of the device towards miniaturization and integration is affected. In addition, the adhesive in the device causes the device to produce large creep under the action of the electric field, which is not conducive to the precise control of the displacement. In particular, when the device is under the action of a high electric field for a long time or after repeated use, the adhesive is easy to fall off from the ceramic sheet, causing the device performance to deteriorate, or even the device to break, shortening the service life of the device and bringing great inconvenience to the application.

[0003] In the prior art, the tape casting method is usually used to prepare ceramic green blanks. The tape casting process is a method of forming a thin film of ceramic green blank on a continuously moving film belt by controlling the fluidity of the slurry. The completion of tape casting requires multiple steps such as slurry preparation, tape casting, drying, and cutting. Each step is crucial. In the early slurry preparation process of tape casting, powders and organic additives have a great influence on the quality of ceramic green blanks. Generally speaking, the tape casting equipment is mainly composed of a tape casting mouth, a drying area, a carrier film, etc. The tape casting mouth is composed of a slurry tank and a scraper, etc. There is a certain gap size between the scraper and the carrier film, and the scraper blade must be kept smooth and tidy. The drying area is a key part of the tape casting equipment, and its main function is to dry the tape casting raw tape to obtain a certain strength and toughness. The carrier film is generally a polymer material coated with silicone oil. When the tape casting starts, the carrier film needs to keep a uniform linear motion, and cannot bend or fold, and does not adhere to the tape casting raw tape after it is dried. When the carrier film starts to move, the slurry will naturally flow out from the gap of the scraper due to its own gravity and the drag force of the carrier film and form a cast green tape. There is a certain gap size between the scraper and the carrier film, so that the thickness of the cast film flowing out can be controlled. Then the flowing green tape moves to the drying area together with the carrier film. The solvent will evaporate in the drying area and form a dry green sheet with a certain strength under the influence of additives such as binders and plasticizers.

[0004] However, during the preparation process of traditional multilayer piezoelectric ceramics, the thickness of a single layer is greatly affected by the slurry, resulting in a single layer thickness usually above 20 μm. Thicker ceramic sheets are difficult to polarize, thus affecting the piezoelectric properties of the ceramics. Summary of the invention

[0005] In order to solve the above technical problems, a method for preparing a multilayer piezoelectric ceramic is provided. The present invention adopts benzene-free system slurry casting to obtain a single-layer green film, prints electrode slurry on one side of the single-layer green film, and stacks the films to obtain a multilayer piezoelectric ceramic containing an internal electrode; the thickness of the single-layer green film is less than 10 microns, the bonding strength between the layers of the green film is high, and the obtained multilayer piezoelectric ceramic has good piezoelectric performance.

[0006] In order to achieve the above objectives, the present invention is implemented by the following technical solutions:

[0007] A method for preparing a multilayer piezoelectric ceramic comprises the following steps:

[0008] S1. Preparation of tape casting slurry;

[0009] S11, material preparation: including the following materials in 100% by mass percentage, ceramic powder 50-80%, acrylate latex 5-12%, ammonium polyacrylate 1-2%, sodium alginate 0.8-1.5%, and the balance is alcohol-water solvent;

[0010] S12, slurry preparation: ball milling the ceramic powder and part of the alcohol-water solvent, then adding ammonium polyacrylate to adjust the pH to alkaline, and continue ball milling to obtain solution A; at the same time, the acrylic latex, sodium alginate, and the remaining part of the alcohol-water solvent are stirred and mixed to form solution B; after mixing solution A and solution B, ball milling is performed for a second time, and vacuum degassing is performed to obtain a casting slurry;

[0011] S2, tape casting to obtain a single-layer green film: the tape casting slurry is allowed to enter the slurry tank of the tape casting machine and flow out from the tape casting port of the tape casting machine, the distance between the scraper and the carrier film is controlled, and the tape casting slurry is formed into a tape casting green tape under the uniform linear motion of the carrier film, and then enters the drying area of ​​the tape casting machine for pre-drying to form a green film;

[0012] Put the pre-film into a calcium ion aqueous solution for gelation, and after drying, peel it off from the carrier film to obtain a single-layer film, and cut it;

[0013] S3, screen printing the inner electrode slurry on one surface of the plurality of single-layer green films, drying, laminating, and sintering to obtain a multilayer piezoelectric ceramic.

[0014] Furthermore, the D50 particle size of the acrylic latex is between 200-500nm, and the acrylic latex is selected from one of pure acrylic latex, styrene-acrylate latex, and vinyl acetate-acrylate latex; the solid mass fraction of the acrylic latex is at least 50wt%. Pure acrylic latex has a low glass transition temperature but a high cost, and although benzo latex has a high glass transition temperature, the film-forming temperature can be reduced by adding a plasticizer. It should be noted that there is a difference between latex and emulsion. Emulsion is droplets dispersed in water, while latex is solid colloid particles dispersed in water, and latex is obtained by emulsion polymerization.

[0015] Furthermore, the D50 particle size of the ceramic powder is less than 1 micron, and the ceramic powder is one of PZT piezoelectric ceramic powder, KNN piezoelectric ceramic powder, and BNT piezoelectric ceramic powder. The powder has a small particle size and high sintering density, and the particle size of the ceramic powder after grinding is less than 0.3 μm.

[0016] Furthermore, the number average molecular weight of the ammonium polyacrylate is less than 8000 g / mol; the alcohol-water solvent is a combination of one or more of methanol, ethanol, propanol, butanol and water, and the proportion of water in the solvent is at least 50wt%; the calcium ion aqueous solution is a calcium chloride aqueous solution, and its mass fraction is 0.8-1.5%.

[0017] Furthermore, the alkaline pH value is 9-10. Ammonium polyacrylate ionizes in water to produce polyacrylate and ammonium ions, and can be basically completely ionized at a pH value of 9-10. The polyacrylate is adsorbed on the surface of the ceramic particles to provide the particles with sufficient charge. At the same time, the molecular chain of the small molecular weight polyacrylic acid can be fully extended to produce electrostatic repulsion and steric hindrance effects, which has a better dispersion effect; the extension of the polymer chain increases with the increase of pH value, making the steric hindrance effect more sufficient. Therefore, the pH is adjusted to alkaline. On the one hand, ammonium polyacrylate can produce electrostatic repulsion and steric hindrance on ceramic powder under alkaline conditions, so that the ceramic powder has better suspension stability. On the other hand, the alkalinity can make the latex particles added later have better dispersion stability.

[0018] Further, the parameters of the first ball milling are: the grinding beads are selected from small zirconia balls of Φ0.03-0.6 mm and large zirconia balls of Φ1-8 mm in a mass ratio of 3-5:1, and the planetary ball milling is performed at a speed of 100-400 rpm for 2-8 hours according to the mass ratio of ceramic powder to grinding beads;

[0019] The parameters of the secondary ball milling are as follows: the grinding beads are small zirconium oxide balls with a diameter of 0.03-0.6 mm, and the mass ratio of ceramic powder to grinding beads is 1:3-5, and the planetary ball milling is performed at a rotation speed of 100-400 rpm for 0.5-3 hours.

[0020] Furthermore, the drying temperature of the drying zone is 25-60°C; the movement speed of the carrier film is 1-4cm / s; the distance between the scraper and the carrier film is less than 30 microns, and the slurry shrinks in the thickness direction after drying, so the film thickness can be controlled within the required range.

[0021] Furthermore, the plastic is preformed by hot pressing and then pre-sintered in a muffle furnace;

[0022] The hot pressing molding is to first perform hot pressing at 2-10MPa and 180-250℃ for 0.5-2h, so that the multi-layer ceramic sheets are bonded. During the hot pressing, it is necessary to exhaust and remove the small molecule gas decomposed at high temperature; the pre-sintering process is to first pre-sinter at 300-350℃ for 2-5h, and then pre-sinter at 600-800℃ for 2-5h, with a heating rate not exceeding 5℃ / min. The subsequent sintering is the sintering procedure of conventional ceramics, which is no different from the conventional one. After sintering, it also includes polarization treatment of the multi-layer ceramic sheets.

[0023] Beneficial technical effects:

[0024] The present invention obtains a single-layer blank film by tape casting, and then prints an internal electrode slurry on the single-layer blank film, performs lamination, plastic removal, and sintering to obtain a multilayer piezoelectric ceramic; the slurry used in the tape casting is mainly made of acrylic latex and is supplemented with sodium alginate. The acrylic latex is a non-crosslinked film-forming agent, and pre-drying after tape casting provides a certain strength and toughness to the blank film. The blank film is then treated with calcium ions, and the sodium alginate in the blank film is rapidly gelled and cross-linked under the action of calcium ions. The acrylic latex and the sodium alginate cooperate with each other to make the obtained single-layer blank film have good strength and toughness, so that the thin blank film and the carrier film can be smoothly separated without breaking, and the film has good flexibility, uniformity, and a strength of 3.7 g / cm or more. 3 The density of membrane bands;

[0025] In addition, sodium alginate has a good thickening and viscosity-increasing effect on the slurry system with acrylic latex as the binder. The subsequent lamination and plasticization only require a small pressure to preform. The density of the ceramic after sintering is greater than or equal to 7.8g / cm 3 The grains are fully grown and have good strength. They can be fully polarized under 2000V / mm polarization conditions and give full play to their piezoelectric properties.

[0026] By optimizing the slurry formula and preparation process, the problems of cracking, uneven distribution and substandard density of single-layer green film were solved, and a single-layer green film with high flexibility, uniformity and density and a thickness of less than 10 microns was obtained. Multiple layers of thinner green films can be stacked to obtain multilayer piezoelectric ceramics with smaller volumes, which are also easier to fully polarize, thereby obtaining higher piezoelectric performance. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Unless otherwise specifically stated, the numerical value set forth in these embodiments does not limit the scope of the present invention. The technology and method known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology and method should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0029] The experimental methods in the following examples without specifying specific conditions are usually measured in accordance with national standards; if there is no corresponding national standard, the method is carried out in accordance with the general standard requirements or general methods.

[0030] The following case uses PZT ceramic powder as an example.

[0031] Each of the following cases was tested 10 times in parallel and the data were averaged.

[0032] The following density is tested according to standard GB 2413-81, static bending strength is tested according to standard GB / T11387-2008, relative dielectric constant is tested according to standard GB 11310-89, longitudinal piezoelectric strain constant d 33 The test is carried out in accordance with the standard GB 11309-89. The resonant impedance is tested by an LCR tester. The capacitance C, loss D, resonant frequency Fr, resonant impedance Zr and insulation performance RPa of the multilayer piezoelectric ceramic material are tested in accordance with GB / T3389-2008.

[0033] Example 1

[0034] A method for preparing a multilayer piezoelectric ceramic comprises the following steps:

[0035] S1. Preparation of tape casting slurry;

[0036] S11, material preparation: including the following materials in 100% by mass percentage, 53% of PZT piezoelectric ceramic powder with a D50 particle size of less than 1 micron, 12% of styrene-acrylate latex (latex D50 particle size is between 200-500nm, solid phase mass fraction is 50wt%), 1% of ammonium polyacrylate with a number average molecular weight of 3000-5000g / mol, 1% of sodium alginate, and the balance is 33% of ethanol-water solvent (of which water accounts for 70wt%);

[0037] S12, slurry preparation:

[0038] The PZT ceramic powder was ball-milled with half the amount of ethanol-water solvent, and the parameters of the ball-milling were as follows: the grinding beads were selected to be Φ0.3 mm small zirconium oxide balls and Φ3 mm large zirconium oxide balls in a mass ratio of 3:1, and the planetary ball milling was performed at a speed of 350 rpm for 3 h according to the mass ratio of the PZT piezoelectric ceramic powder and the grinding beads; then, ammonium polyacrylate was added to adjust the pH to 9.5, and the ball milling was continued at 350 rpm for 1 h to obtain solution A;

[0039] At the same time, the acrylic latex, sodium alginate, and the remaining ethanol-water solvent are stirred and mixed to form a B solution;

[0040] Solution A and solution B were mixed and then subjected to secondary ball milling. The parameters of the secondary ball milling were as follows: small zirconia balls with a diameter of 0.05 mm were selected as grinding beads, and the mass ratio of PZT piezoelectric ceramic powder to grinding beads was 1:3. The planetary ball milling was performed at a speed of 360 rpm for 2 h (the particle size of the ceramic powder after grinding was less than 0.3 μm), and the casting slurry was obtained after vacuum degassing;

[0041] S2, tape casting to obtain a single-layer green film: the tape casting slurry is allowed to enter the slurry tank of the tape casting machine and flow out from the tape casting port of the tape casting machine, the distance between the scraper and the carrier film is controlled to be 20 microns, and the tape casting slurry is allowed to form a tape casting green tape on the carrier film under the condition that the carrier film moves linearly at a uniform speed of 1 cm / s, and then enters the drying area of ​​the tape casting machine and is pre-dried under hot air at 40° C. for half an hour to form a green film;

[0042] The pre-film is immersed in a 1% by mass calcium chloride aqueous solution for 30 seconds to generate rapid gelation and cross-linking, and then naturally dried at 25° C. for 3 hours, and then peeled off to obtain a single-layer film, which is then cut;

[0043] The single-layer film in this case can be separated from the carrier film smoothly without breaking, and has good flexibility and uniformity. The single-layer film has no cracks or holes, and the overall consistency is good. The thickness of the single-layer film in this case is 9.6 microns and the density is 3.75g / cm 3 , resonant impedance R = 6Ω, relative dielectric constant ε = 2488, longitudinal piezoelectric strain constant d 33=611pC / N, displacement in the range of 35-40μm;

[0044] S3, screen printing an internal electrode slurry on one surface of the plurality of single-layer green films, and after the internal electrode slurry is dried and solidified, stacking the films one side with the electrode slurry on top, arranging the films, and sintering at 900-1000° C. to obtain a multilayer piezoelectric ceramic;

[0045] The plastic removal is first hot pressing preforming, and then pre-sintering in a muffle furnace. The hot pressing preforming is to heat up to 250°C at a heating rate of 1°C / min, pressurize after reaching the temperature, and exhaust during the pressurization process until the pressure is increased to 2MPa and hot pressing is performed for 0.5h, so that the multilayer ceramic sheets are bonded; the pre-sintering process is to heat up to 350°C at a heating rate of 3°C / min, pre-sinter for 2h, and then heat up to 750°C and pre-sinter for 3h;

[0046] The piezoelectric properties of the multilayer piezoelectric ceramics were subsequently tested after polarization treatment, with the polarization treatment temperature being 120°C, the polarization time being 30 min, and the polarization electric field being 2000 V / mm.

[0047] The thickness of the multilayer piezoelectric ceramics prepared in this case is 0.79 mm (100 layers are stacked, and the thickness of the inner electrode is about 1-2 μm) and the density is 7.857 g / cm 3 , static bending strength ≥100Mpa, capacitance C = 19.6nF, loss D = 0.9%, resonant frequency Fr = 364KHz, resonant impedance Zr = 13.16Ω, insulation (0.9V / 10s) RPa = 4.75GΩ.

[0048] Example 2

[0049] A method for preparing a multilayer piezoelectric ceramic comprises the following steps:

[0050] S1. Preparation of tape casting slurry;

[0051] S11, material preparation: including the following materials in 100% by mass percentage, 60% of PZT piezoelectric ceramic powder with a D50 particle size of less than 1 micron, 7% of styrene-acrylate latex (latex D50 particle size is between 200-500nm, solid phase mass fraction is 50wt%), 1.5% of ammonium polyacrylate with a number average molecular weight of 3000-5000g / mol, 1.5% of sodium alginate, and the balance is 30% of ethanol-water solvent (of which water accounts for 60wt%);

[0052] S12, slurry preparation:

[0053] The PZT ceramic powder was ball-milled with half the amount of ethanol-water solvent, and the parameters of the ball-milling were as follows: the grinding beads were selected to be Φ0.3 mm small zirconium oxide balls and Φ3 mm large zirconium oxide balls in a mass ratio of 4:1, and the planetary ball milling was performed at a speed of 250 rpm for 5 h according to the mass ratio of the PZT piezoelectric ceramic powder and the grinding beads; then, ammonium polyacrylate was added to adjust the pH to 10, and the ball milling was continued at 250 rpm for 2 h to obtain solution A;

[0054] At the same time, the acrylic latex, sodium alginate, and the remaining ethanol-water solvent are stirred and mixed to form a B solution;

[0055] Solution A and solution B were mixed and then subjected to secondary ball milling. The parameters of the secondary ball milling were as follows: small zirconia balls with a diameter of 0.03 mm were selected as grinding beads, and the mass ratio of PZT piezoelectric ceramic powder to grinding beads was 1:5. The planetary ball milling was performed at a speed of 250 rpm for 1 h (the particle size of the ceramic powder after grinding was less than 0.3 μm), and the casting slurry was obtained after vacuum degassing;

[0056] S2, tape casting to obtain a single-layer green film: the tape casting slurry is allowed to enter the slurry tank of the tape casting machine and flow out from the tape casting port of the tape casting machine, the distance between the scraper and the carrier film is controlled to be 12 microns, and the tape casting slurry is allowed to form a tape casting green tape on the carrier film under the condition that the carrier film moves linearly at a uniform speed of 3.3 cm / s, and then enters the drying area of ​​the tape casting machine and is pre-dried under hot air at 35° C. for half an hour to form a green film;

[0057] The pre-film is immersed in a 1.5% by mass calcium chloride aqueous solution for 20 seconds to generate rapid gelation and cross-linking, and then naturally dried at 25° C. for 4 hours to obtain a single-layer film, which is then cut;

[0058] The single-layer film in this case can be separated from the carrier film smoothly without breaking, and has good flexibility and uniformity. The single-layer film has no cracks or holes, and the overall consistency is good. The thickness of the single-layer film in this case is 6.4 microns and the density is 3.98g / cm 3 , resonant impedance R = 8Ω, relative dielectric constant ε = 2539, longitudinal piezoelectric strain constant d 33 =615pC / N, displacement in the range of 35-40μm;

[0059] S3, screen printing an internal electrode slurry on one surface of the plurality of single-layer green films, and after the internal electrode slurry is dried and solidified, stacking the films one side with the electrode slurry on top, arranging the films, and sintering at 900-1000° C. to obtain a multilayer piezoelectric ceramic;

[0060] The plastic removal is first hot-pressed preforming, and then pre-sintered in a muffle furnace. The hot-pressed preforming is heated to 220°C at a heating rate of 1°C / min, and pressurized after reaching the temperature. The pressurization process is vented until the pressure is increased to 3.5MPa and hot-pressed for 1h, so that the multi-layer ceramic sheets are bonded. The pre-sintering process is first heated to 320°C at a heating rate of 3°C / min and pre-sintered for 2h, and then heated to 700°C and pre-sintered for 3h.

[0061] The piezoelectric properties of the multilayer piezoelectric ceramics were subsequently tested after polarization treatment, with the polarization treatment temperature being 120°C, the polarization time being 30 min, and the polarization electric field being 2000 V / mm.

[0062] The thickness of the multilayer piezoelectric ceramics prepared in this case is 0.58 mm (100 layers are stacked, and the thickness of the inner electrode is about 1-2 μm) and the density is 7.872 g / cm 3 , static bending strength ≥100Mpa, capacitance C = 20.4nF, loss D = 1.0%, resonant frequency Fr = 366KHz, resonant impedance Zr = 11.02Ω, insulation (0.9V / 10s) RPa = 3.19GΩ.

[0063] Example 3

[0064] A method for preparing a multilayer piezoelectric ceramic comprises the following steps:

[0065] S1. Preparation of tape casting slurry;

[0066] S11, material preparation: including the following materials in 100% by mass percentage, 70% of PZT piezoelectric ceramic powder with a D50 particle size of less than 1 micron, 7.5% of styrene-acrylate latex (latex D50 particle size is between 200-500nm, solid phase mass fraction is 50wt%), 1.2% of ammonium polyacrylate with a number average molecular weight of 3000-5000g / mol, 1.3% of sodium alginate, and the balance is 20% of ethanol-water solvent (of which water accounts for 50wt%);

[0067] S12, slurry preparation:

[0068] The PZT ceramic powder was ball-milled with half the amount of ethanol-water solvent, and the parameters of the ball-milling were as follows: the grinding beads were selected to be Φ0.3 mm small zirconium oxide balls and Φ3 mm large zirconium oxide balls in a mass ratio of 5:1, and the PZT piezoelectric ceramic powder and the grinding beads were planetarily ball-milled at a speed of 360 rpm for 2 h; then ammonium polyacrylate was added to adjust the pH to 9.5, and the ball-milling was continued at 360 rpm for 2 h to obtain solution A;

[0069] At the same time, the acrylic latex, sodium alginate, and the remaining ethanol-water solvent are stirred and mixed to form a B solution;

[0070] Solution A and solution B were mixed and then subjected to secondary ball milling. The parameters of the secondary ball milling were as follows: small zirconia balls with a diameter of 0.03 mm were selected as grinding beads, and the mass ratio of PZT piezoelectric ceramic powder to grinding beads was 1:4. The planetary ball milling was performed at a speed of 360 rpm for 2 h (the particle size of the ceramic powder after grinding was less than 0.3 μm), and the casting slurry was obtained after vacuum degassing;

[0071] S2, tape casting to obtain a single-layer green film: the tape casting slurry is allowed to enter the slurry tank of the tape casting machine and flow out from the tape casting port of the tape casting machine, the distance between the scraper and the carrier film is controlled to be 10 microns, and the tape casting slurry is allowed to form a tape casting green tape on the carrier film under the condition that the carrier film moves linearly at a uniform speed of 3.3 cm / s, and then enters the drying area of ​​the tape casting machine and is pre-dried under hot air at 35° C. for half an hour to form a green film;

[0072] The pre-film is immersed in a calcium chloride aqueous solution with a mass fraction of 1.3% for 20 seconds to generate rapid gelation and cross-linking, and then naturally dried at 25° C. for 5 hours, and then the single-layer film can be peeled off and cut;

[0073] The single-layer film in this case can be separated from the carrier film smoothly without breaking, and has good flexibility and uniformity. The single-layer film has no cracks or holes, and the overall consistency is good. The thickness of the single-layer film in this case is 4.8 microns and the density is 3.84g / cm 3 , resonant impedance R = 9Ω, relative dielectric constant ε = 2350, longitudinal piezoelectric strain constant d 33 =601pC / N, displacement in the range of 35-40μm;

[0074] S3, screen printing an internal electrode slurry on one surface of the plurality of single-layer green films, and after the internal electrode slurry is dried and solidified, stacking the films one side with the electrode slurry on top, arranging the films, and sintering at 900-1000° C. to obtain a multilayer piezoelectric ceramic;

[0075] The plastic removal is first hot pressing preforming, and then pre-sintering in a muffle furnace. The hot pressing preforming is to heat up to 250°C at a heating rate of 1°C / min, pressurize after reaching the temperature, and exhaust during the pressurization process until the pressure is increased to 4.5MPa and hot pressing is performed for 0.5h, so that the multilayer ceramic sheets are bonded; the pre-sintering process is to heat up to 350°C at a heating rate of 2°C / min, pre-sinter for 3h, and then heat up to 650°C and pre-sinter for 3h;

[0076] The piezoelectric properties of the multilayer piezoelectric ceramics were subsequently tested after polarization treatment, with the polarization treatment temperature being 120°C, the polarization time being 30 min, and the polarization electric field being 2000 V / mm.

[0077] The thickness of the multilayer piezoelectric ceramics prepared in this case is 0.47 mm (100 layers are stacked, and the thickness of the inner electrode is about 1-2 μm) and the density is 7.887 g / cm 3 , static bending strength ≥100Mpa, capacitance C = 22.9nF, loss D = 1.1%, resonant frequency Fr = 369KHz, resonant impedance Zr = 9.80Ω, insulation RPa = 2.04GΩ.

[0078] Comparative Example 1

[0079] The preparation process of the multilayer piezoelectric ceramics in this case is the same as that in Example 3, except that sodium alginate is not added to the S1 slurry and the S2 does not need to be immersed in a calcium chloride solution, but is directly dried in the drying area of ​​the casting machine under hot air at 30°C for 5 hours to form a single-layer green film. The single-layer green film in this case can be separated from the carrier film smoothly, but the single-layer green film has a few cracks and holes.

[0080] The static bending strength of the multilayer piezoelectric ceramic in this case is at least 20% lower than that of Example 3, and the piezoelectric constant d of the single-layer green film is 33 Compared with Example 3, it decreases by at least 10%.

[0081] Comparative Example 2

[0082] The preparation process of the multilayer piezoelectric ceramics in this case is the same as that in Example 3, except that the gel was not immersed in a calcium chloride solution in S2, but was directly dried in the drying area of ​​the casting machine under hot air at 30°C for 5 hours to form a single-layer green film. The single-layer green film in this case can be separated from the carrier film smoothly, and the single-layer green film has a few cracks but no holes.

[0083] The static bending strength of the multilayer piezoelectric ceramic in this case is at least 10% lower than that of Example 3, and the piezoelectric constant d of the single-layer green film is 33 Compared with Example 3, it decreases by at least 6%.

[0084] Comparative Example 3

[0085] The preparation process of multilayer piezoelectric ceramics in this case is as follows:

[0086] The tape casting slurry contains the following materials by mass: 53% PZT ceramic powder, 20.5% PVB solution (the mass fraction of the solution is 53%, and the solvent in the solution is anhydrous ethanol), 6% xylene, 4% ethyl acetate, 3% n-propanol, and 12% anhydrous ethanol;

[0087] Slurry preparation: add anhydrous ethanol, polyvinyl butyral solution, xylene, ethyl acetate, and n-propanol into a ball mill, add Φ8 mm zirconium oxide balls as grinding beads (material-ball ratio 1:2), and ball mill at 100 rpm for 0.5 hours; then add PZT ceramic powder and polyether polyol and continue ball milling for 20 hours to obtain a casting slurry;

[0088] Subsequently, the casting slurry enters the slurry tank of the casting machine and flows out from the casting port of the casting machine. The distance between the scraper and the carrier film is controlled to be 20 microns. When the carrier film moves in a uniform straight line at a rate of 1 cm / s, the casting slurry forms a casting green tape on the carrier film, and then enters the drying area of ​​the casting machine and is dried under hot air at 35°C for 5 minutes to form a single-layer green film. Although the forming is fast, due to the thin green film, the separation process of the single-layer green film and the carrier film in this case produces fragmentation due to the influence of cracks and holes. This may be caused by uneven ball milling dispersion and insufficient bonding strength and toughness of the bonding system to the ceramic powder.

[0089] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a multilayer piezoelectric ceramic, characterized in that: The steps include: S1. Preparation of tape casting slurry; S11, material preparation: including the following materials in 100% by mass percentage, ceramic powder 50-80%, acrylate latex 5-12%, ammonium polyacrylate 1-2%, sodium alginate 0.8-1.5%, and the balance is alcohol-water solvent; S12, slurry preparation: ball milling the ceramic powder and part of the alcohol-water solvent, then adding ammonium polyacrylate to adjust the pH to alkaline, and continuing ball milling to obtain solution A; At the same time, the acrylic latex, sodium alginate, and the remaining alcohol-water solvent are stirred and mixed to form a B solution; The A solution and the B solution are mixed and then ball-milled for a second time, and then vacuum-defoamed to obtain a casting slurry; S2, tape casting to obtain a single-layer green film: the tape casting slurry is allowed to enter the slurry tank of the tape casting machine and flow out from the tape casting port of the tape casting machine, the distance between the scraper and the carrier film is controlled, and the tape casting slurry is formed into a tape casting green tape under the uniform linear motion of the carrier film, and then enters the drying area of ​​the tape casting machine for pre-drying to form a green film; Put the pre-film into a calcium ion aqueous solution for gelation, and after drying, peel it off from the carrier film to obtain a single-layer film, and cut it; S3, screen printing the inner electrode slurry on one surface of the plurality of single-layer green films, drying, laminating, and sintering to obtain a multilayer piezoelectric ceramic.

2. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The D50 particle size of the acrylic latex is between 200-500 nm, and the acrylic latex is selected from one of pure acrylic latex, styrene-acrylate latex, and vinyl acetate-acrylate latex; the solid phase mass fraction of the acrylic latex is at least 50wt%.

3. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The D50 particle size of the ceramic powder is less than 1 micron, and the ceramic powder is one of PZT piezoelectric ceramic powder, KNN piezoelectric ceramic powder and BNT piezoelectric ceramic powder.

4. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The number average molecular weight of the ammonium polyacrylate is less than 8000 g / mol; The alcohol-water solvent is a combination of one or more of methanol, ethanol, propanol, butanol and water, and the proportion of water in the solvent is at least 50wt%; The calcium ion aqueous solution is a calcium chloride aqueous solution with a mass fraction of 0.8-1.5%.

5. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The alkaline pH value is 9-10.

6. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The parameters of the first ball milling are: the grinding beads are selected from small zirconia balls of Φ0.03-0.6 mm and large zirconia balls of Φ1-8 mm in a mass ratio of 3-5:1, and the planetary ball milling is performed at a speed of 100-400 rpm for 2-8 hours according to the mass ratio of ceramic powder to grinding beads; The parameters of the secondary ball milling are as follows: the grinding beads are small zirconium oxide balls with a diameter of 0.03-0.6 mm, and the mass ratio of ceramic powder to grinding beads is 1:3-5, and the planetary ball milling is performed at a rotation speed of 100-400 rpm for 0.5-3 hours.

7. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The drying temperature in the drying zone is 25-60°C; The movement speed of the carrier film is 1-4 cm / s; The distance between the doctor blade and the carrier film is less than 30 micrometers.

8. The method for preparing a multilayer piezoelectric ceramic according to claim 1, characterized in that: The plastic is preformed by hot pressing first and then pre-sintered in a muffle furnace; The hot pressing molding is first performed at 2-10MPa and 180-250°C for 0.5-2h; The pre-sintering process is to pre-sinter at 300-350° C. for 2-5 hours, and then pre-sinter at 600-800° C. for 2-5 hours, with a heating rate not exceeding 5° C. / min.