Zinc oxide resistor disc and preparation method and application thereof

Abstract

The invention belongs to the technical field of high-voltage electric appliance material preparation, and particularly relates to a zinc oxide resistor disc and a preparation method and application thereof. The preparation method comprises the following steps: (1) pre-sintering zinc oxide powder; (2) mixing the zinc oxide powder obtained in the step (1), an auxiliary agent and a dispersion liquid, and carrying out ball milling to obtain slurry; the particle size D50 of the slurry is 0.8-1.2 [mu] m, and the dispersity is greater than or equal to 95%; (3) performing spray drying and granulation on the slurry to obtain granulation powder; (4) carrying out molding and first sintering on the granulated powder to obtain a resistor disc semi-finished product; the first sintering adopts sectional sintering; and (5) forming an electrode layer on at least one surface of the resistor disc semi-finished product by adopting a vacuum sputtering and / or electrophoretic deposition process, and performing secondary sintering and annealing. The contact resistance of the zinc oxide resistor disc is less than or equal to 5m omega; and after 1000 hours of aging in a 85 DEG C + 85% RH environment, the leakage current increase is less than or equal to 2 [mu] A, and the performance degradation rate is less than or equal to 5%.

Description

Technical Field

[0001] This invention belongs to the field of high voltage electrical material preparation technology, and particularly relates to a zinc oxide resistor sheet, its preparation method and application. Background Technology

[0002] As a core component for overvoltage protection in high-voltage power systems, the performance of zinc oxide resistors depends on the microstructure of "ZnO grains-grain boundaries" and must meet the following requirements: varistor voltage fluctuation ≤ ±5%, leakage current ≤ 10μA at 25℃ (at 1.05 times the varistor voltage), and lightning current carrying capacity ≥ 60kA for 4 / 10μs.

[0003] The existing zinc oxide resistor manufacturing process faces the following industrialization bottlenecks: 1) Uneven raw material dispersion leads to performance fluctuations: Traditional dry ball milling or single-stage wet ball milling cannot solve the problem of dopant aggregation such as Bi2O3 and Sb2O3, resulting in varistor voltage fluctuations of ±8% or more and batch pass rates ≤90%. 2) Uncontrolled sintering process affects microstructure: Intermittent kiln constant temperature sintering is prone to low-temperature sintering leading to incomplete decomposition of organic matter and high-temperature sintering leading to abnormal grain growth (≥15μm), resulting in leakage current ≥20μA and current capacity ≤45kA, which cannot meet the performance requirements of zinc oxide resistors. 3) High electrode preparation cost and poor adhesion: The silver paste printing-high-temperature sintering process uses ≥5g / piece of silver, accounting for 30% of the cost, leading to increased costs. At the same time, the difference in thermal expansion coefficient between the silver layer and the ceramic substrate is large, resulting in adhesion ≤3MPa, which is prone to peeling off during long-term operation. 4) Insufficient industrial adaptability: Existing processes focus on small-batch preparation in the laboratory (≤100 pieces per batch), molding relies on manual dry pressing (bulk density fluctuation ±3%), and the sintering cycle is ≥24h / batch, which cannot meet the needs of large-scale mass production. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a zinc oxide resistor sheet, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a method for preparing a zinc oxide resistor sheet, comprising the following steps: (1) Pre-sintering of zinc oxide powder; (2) The zinc oxide powder, additives and dispersion obtained in step (1) are mixed and ball-milled to obtain a slurry; the median particle size D50 of the slurry is 0.8μm-1.2μm and the dispersibility is ≥95%; (3) The slurry is spray-dried and granulated to obtain granulated powder; (4) The granulated powder is shaped and sintered for the first time to obtain a resistor sheet semi-finished product; the first sintering adopts segmented sintering; (5) An electrode layer is formed on at least one surface of the resistor sheet semi-finished product by vacuum sputtering and / or electrophoretic deposition process, followed by a second sintering and annealing.

[0006] For example, the particle size D50 of the slurry is 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm or within any two of the above values.

[0007] As an optional implementation, in step (1), the pre-sintering temperature is 850℃-900℃ and the time is 1.5h-2h; Preferably, the specific steps of the pre-sintering include: heating to 850℃-900℃ at a heating rate of 8℃ / min-10℃ / min and then holding at that temperature for 1.5h-2h.

[0008] For example, the pre-sintering temperature is 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, or within any two of the above values.

[0009] As an optional implementation, step (2) satisfies at least one of (1)-(4): (1) The additives include at least one of Cr2O3, SiO2, Bi2O3, Sb2O3, CoO, MnO, and Al2O3; Preferably, the additives include Cr2O3, SiO2, Bi2O3, Sb2O3, CoO, MnO, and Al2O3; More preferably, based on 100wt% of the total mass percentage of the zinc oxide powder and additives, the content of Bi2O3 is 1.5wt%-3.0wt%, the content of Sb2O3 is 1.0wt%-2.0wt%, the content of CoO is 0.5wt%-1.0wt%, the content of MnO is 0.3wt%-0.8wt%, the content of Cr2O3 is 0.2wt%-0.5wt%, the content of SiO2 is 0.1wt%-0.3wt%, and the content of Al2O3 is 0.05wt%-0.15wt%. (2) The dispersion is a dispersion containing TiO2; Preferably, the dispersion comprises TiO2 particles coated with organosilane; More preferably, the median particle size D50 of the organosilane-coated TiO2 particles is 20nm-50nm; (3) The ratio of the total mass of the zinc oxide powder and the additive to the mass of the organosilane-coated TiO2 in the dispersion is (10-15):1; for example, the mass ratio is 10:1, 11:1, 12:1, 13:1, 14:1, 15:1 or within any two of the above ratios. (4) The ball mill includes a primary ball mill and a secondary ball mill; Preferably, the parameters of the primary ball mill include: using a planetary ball mill, a ball-to-material ratio of 4-5:1, a rotation speed of 200-250 rpm, and a time of 5-6 hours; Preferably, the parameters of the secondary ball milling include: ultrasonic ball milling, ball milling ratio of 2-3:1, rotation speed of 150rpm-250rpm, ultrasonic power of 400W-450W, and time of 1h-1.5h.

[0010] As an optional implementation, the granulated powder has a flowability ≥20s / 100mL and a bulk density of 1.2g / cm³. 3 -1.4g / cm 3 ; And / or, the mass percentage of particles with a mesh size of 40-60 mesh in the granulated powder is ≥95 wt%; And / or, the inlet temperature of the spray dryer is 200℃-220℃, and the outlet temperature is 80℃-90℃.

[0011] As an optional implementation, the molding pressure is 25MPa-30MPa, and the time is 8min-10min; And / or, the rough blank obtained after molding is dried at 100℃-120℃ for 2h-3h to obtain a green body; preferably, the density of the green body is ≥3.2g / cm³. 3 .

[0012] As an optional implementation, in step (5), the ZnO grain size in the resistor sheet semi-finished product is 5μm-8μm, and the thickness of the grain boundary layer is 10nm-15nm. And / or, the specific steps of the segmented sintering include: heating from room temperature to 300-350℃ at a heating rate of 8-10℃ / min and holding for 15-20 min; heating to 600-650℃ at a heating rate of 3-5℃ / min and holding for 30-35 min; heating to 1100-1150℃ at a heating rate of 2-3℃ / min and holding for 35-40 min; heating to 1150-1180℃ at a heating rate of 1-1.2℃ / min and holding for 60-80 min; cooling to 600-800℃ at a cooling rate of 4-5℃ / min and holding for 25-30 min; and finally cooling to room temperature in the furnace.

[0013] As an optional implementation, the electrode layer includes a first film layer and a second film layer; Preferably, the thickness of the first film layer is 50nm-80nm; Preferably, the thickness of the second film layer is 5 μm-8 μm; Preferably, the material of the electrode layer includes at least one of silver and aluminum.

[0014] As an optional implementation, the heating rate of the second sintering is no higher than 10℃ / min, the temperature is 250℃-300℃, and the time is 1h-1.5h; And / or, the annealing heating rate is not higher than 20℃ / min, the temperature is 280℃-300℃, and the time is 1h-1.5h.

[0015] Secondly, the present invention provides a zinc oxide resistor sheet prepared by the above-described preparation method.

[0016] Secondly, the present invention provides a zinc oxide resistor sheet prepared by the above-mentioned preparation method or the application of the above-mentioned zinc oxide resistor sheet in surge arresters and / or surge protectors.

[0017] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: 1. This invention provides a method for preparing zinc oxide resistor sheets, which includes the following steps: (1) pre-sintering zinc oxide powder; (2) mixing the zinc oxide powder, additives, and dispersion obtained in step (1), ball milling to obtain a slurry; the particle size D50 of the slurry is 0.8μm-1.2μm, and the dispersion is ≥95%; (3) spray drying and granulation of the slurry to obtain granulated powder; (4) molding and first sintering of the granulated powder to obtain a resistor sheet semi-finished product; the first sintering adopts segmented sintering; (5) forming an electrode layer on at least one surface of the resistor sheet semi-finished product using vacuum sputtering and / or electrophoretic deposition processes, followed by a second sintering and annealing. This invention pre-sintersects zinc oxide powder to eliminate zinc oxide agglomeration, and when mixed with additives and dispersion, improves the dispersion uniformity and stability, improves the agglomeration of existing dopants, reduces the varistor voltage fluctuation of the finished resistor sheet, and improves the stability of batch qualification rate. After ball milling, the slurry particle size D50 is controlled to be 0.8μm-1.2μm, which helps reduce performance fluctuations during the preparation of the resistor sheet. Segmented sintering allows for control of the resistor sheet density, zinc oxide grains, and grain boundary layer, reducing impurity phases (e.g., Bi2O3-Sb2O3), lowering leakage current, and increasing current carrying capacity, thus meeting the performance requirements of zinc oxide resistor sheets. Furthermore, segmented sintering also helps reduce energy consumption and cost, with energy consumption reduced by approximately 20%. Using vacuum sputtering and / or electrophoretic deposition processes to form an electrode layer on at least one surface of the resistor sheet semi-finished product can improve the adhesion between the electrode layer and the resistor sheet, reducing the risk of detachment during long-term operation. This invention uses vacuum sputtering and / or electrophoretic deposition processes to form the electrode layer, which can reduce the amount of silver used in the electrode material; compared to the traditional 5g / sheet, this invention can reduce it to 1.5g / sheet, thus lowering raw material costs. The zinc oxide resistive sheet of this invention has an electrode adhesion of ≥5MPa and a contact resistance of ≤5mΩ; after aging for 1000h at 85℃+85% RH, the leakage current increase is ≤2μA and the performance degradation rate is ≤5%. Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0019] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0020] In a first aspect, embodiments of the present invention provide a method for preparing a zinc oxide resistor sheet, comprising the following steps: (1) Pre-sintering of zinc oxide powder; (2) The zinc oxide powder, additives and dispersion obtained in step (1) are mixed and ball-milled to obtain a slurry; the median particle size D50 of the slurry is 0.8μm-1.2μm and the dispersibility is ≥95%; (3) The slurry is spray-dried and granulated to obtain granulated powder; (4) The granulated powder is shaped and sintered for the first time to obtain a resistor sheet semi-finished product; the first sintering adopts segmented sintering; (5) An electrode layer is formed on at least one surface of the resistor sheet semi-finished product by vacuum sputtering and / or electrophoretic deposition process, followed by a second sintering and annealing.

[0021] This invention pre-sintersects zinc oxide powder to eliminate zinc oxide agglomeration. When mixed with additives and dispersions, this improves dispersion uniformity and stability, mitigates existing dopant agglomeration, reduces varistor voltage fluctuations in finished resistor sheets, and enhances batch yield stability. Ball milling controls the slurry particle size (D50) to 0.8 μm-1.2 μm, which helps reduce performance fluctuations during resistor sheet preparation. Segmented sintering allows for control of resistor sheet density, zinc oxide grain size, and grain boundary layers, reducing impurity phases (e.g., Bi₂O₃-Sb₂O₃), lowering leakage current, and increasing current carrying capacity, thus meeting the performance requirements of zinc oxide resistor sheets. Furthermore, segmented sintering reduces energy consumption and cost, with energy consumption reduced by approximately 20%. Vacuum sputtering and / or electrophoretic deposition processes are used to form an electrode layer on at least one surface of the resistor sheet semi-finished product, improving adhesion between the electrode layer and the resistor sheet and reducing the risk of detachment during long-term operation. This invention employs vacuum sputtering and / or electrophoretic deposition processes to form the electrode layer, which reduces the amount of silver used in the electrode material. Compared to the traditional 5g / piece, this invention reduces the amount to 1.5g / piece, thus lowering raw material costs. The zinc oxide resistor sheet of this invention exhibits electrode adhesion ≥5MPa and contact resistance ≤5mΩ; after aging at 85℃+85% RH for 1000h, the leakage current increase is ≤2μA, and the performance degradation rate is ≤5%.

[0022] The zinc oxide resistor sheet prepared by the method of this invention achieves a performance breakthrough in the first aspect. The resistor sheet prepared by this invention has a varistor voltage fluctuation of ≤±3%, leakage current of ≤8μA, 4 / 10μs current capacity of ≥70kA, and residual voltage ratio of ≤1.77. Compared with the resistor sheet prepared by the traditional process, which has a varistor voltage fluctuation of ±8%, leakage current of ≥20μA, 4 / 10μs current capacity of ≤45kA, and residual voltage ratio of ≥1.9, the resistor sheet prepared by this invention has higher performance and meets the requirements of ultra-high voltage equipment of AC 1000kV and DC ±800kV and above. Secondly, the preparation method of this invention can be used with continuous equipment, shortening the production cycle to 12 hours per batch, which significantly improves production efficiency compared to the traditional 24-hour cycle. Furthermore, it is well-suited to existing industrial equipment, meeting the needs of large-scale mass production. With a daily production capacity of 15,000 pieces, and a raw material utilization rate of no less than 98% compared to the traditional method, this invention significantly improves raw material utilization. In preparing the electrode layer, this invention reduces the amount of silver used in the electrode material, further reducing costs. Thirdly, the batch pass rate of the resistor sheet obtained by the preparation method of this invention is ≥98%, improving upon the traditional process where the batch pass rate is ≤90%. Under conditions of 85℃ and 85%RH, after 1000 hours of aging, the leakage current increase is ≤2μA, and the performance degradation rate is ≤5%. The resistor sheet prepared by this invention exhibits less performance degradation and higher stability, improving upon the traditional process where the change rate is ≥10%.

[0023] As an optional implementation, in step (1), the pre-sintering temperature is 850℃-900℃ and the time is 1.5h-2h; Preferably, the specific steps of the pre-sintering include: heating to 850℃-900℃ at a heating rate of 8℃ / min-10℃ / min and then holding at that temperature for 1.5h-2h. This invention pre-sintersulates the raw material zinc oxide, which helps improve the dispersion uniformity in subsequent operations such as ball milling and reduces agglomeration.

[0024] As an optional implementation, the additive includes at least one of Cr2O3, SiO2, Bi2O3, Sb2O3, CoO, MnO, and Al2O3; optionally, the additive includes Cr2O3, SiO2, Bi2O3, Sb2O3, CoO, MnO, and Al2O3; exemplaryly, the mass ratio of Bi2O3, Sb2O3, CoO, MnO, Cr2O3, SiO2, and Al2O3 may be, but is not limited to, (1.5-3):(1-2):(0.5-1.0):(0.3-0.8):(0.2-0.5):(0.1-0.3):(0.05-0.15).

[0025] As an optional implementation, when the additives include multiple components, all additives are first mixed to form an additive mixture. For example, the mixing process includes primary mixing and secondary mixing. Primary mixing may be, but is not limited to, a rotation speed of 500 rpm for 1 minute; secondary mixing may be, but is not limited to, a rotation speed of 1500 rpm for 10 minutes. After mixing all additives, the elemental content deviation is detected using X-ray fluorescence spectrometry (XRF) and is ≤±0.05%.

[0026] As an optional implementation, based on a total mass percentage (100 wt%) of the zinc oxide powder and additives, the content of Bi₂O₃ is 1.5 wt%-3.0 wt%, the content of Sb₂O₃ is 1.0 wt%-2.0 wt%, the content of CoO is 0.5 wt%-1.0 wt%, the content of MnO is 0.3 wt%-0.8 wt%, the content of Cr₂O₃ is 0.2 wt%-0.5 wt%, the content of SiO₂ is 0.1 wt%-0.3 wt%, the content of Al₂O₃ is 0.05 wt%-0.15 wt%, and the balance is zinc oxide powder.

[0027] As an optional implementation, the dispersion is a TiO2-containing dispersion; preferably, the dispersion comprises TiO2 particles coated with an organosilane; in some embodiments, the median particle size D50 of the organosilane-coated TiO2 particles is 20nm-50nm, and the organosilane includes KH-550. In some embodiments, the preparation method of organosilane-coated TiO2 particles includes: mixing TiO2 and water at a solid-liquid ratio of 1:5, adding KH-550, and obtaining a dispersion by stirring and ultrasonic dispersion, wherein the amount of KH-550 added is 1wt%-2wt% of TiO2. Optionally, the dispersion degree is ≥95%.

[0028] As an optional implementation, the ratio of the total mass of the zinc oxide powder and additives to the mass of the organosilane-coated TiO2 in the dispersion is (10-15):1.

[0029] As an optional implementation, the ball mill includes a primary ball mill and a secondary ball mill; As an optional implementation, the parameters of the primary ball milling include: using a planetary ball mill, a ball-to-material ratio of 4-5:1, a rotation speed of 200rpm-250rpm, and a time of 5h-6h; the particle size D50 of the primary slurry obtained after primary ball milling is ≤1.5μm.

[0030] As an optional implementation, the parameters for the secondary ball milling include: ultrasonic ball milling, a ball-to-milling ratio of 2-3:1, a rotation speed of 150-250 rpm, an ultrasonic power of 400W-450W, and a time of 1-1.5 hours. The slurry obtained after primary and secondary ball milling has a particle size D50 of 0.8μm-1.2μm, a dispersity ≥95%, and a sedimentation rate ≤2%.

[0031] As an optional implementation, the primary dry powder after spray drying contains ≥90 wt% particles of 40-100 mesh. The primary dry powder after spray drying of this invention meets the above parameters, is fine, and has good particle size uniformity, which is beneficial to improving the consistency of the composition of the zinc oxide resistor sheet and enhancing its lightning protection capability.

[0032] As an optional implementation, the inlet temperature of the spray dryer is 200℃-220℃, and the outlet temperature is 80℃-90℃.

[0033] As an optional implementation, the granulated powder has a flowability ≥20s / 100mL and a bulk density of 1.2g / cm³. 3 -1.4g / cm 3 The present invention regulates the granulated powder to meet the above parameters, which is beneficial for subsequent molding.

[0034] As an optional implementation, the mass percentage of particles with a mesh size of 40-60 in the granulated powder is ≥95wt%.

[0035] As an optional implementation, the granulation process also includes the step of adding a binder. The binder may be, but is not limited to, PVA (degree of polymerization 1700), and the amount of binder used is the conventional amount used in the art, for example, 3 wt% of the primary dry powder. Optionally, the binder is an aqueous PVA solution with a concentration of 10-20 wt%.

[0036] As an optional implementation, the molding pressure is 25MPa-30MPa, and the time is 8min-10min; As an optional implementation, the rough blank obtained after molding is dried at 100℃-120℃ for 2h-3h to obtain a green body; preferably, the density of the green body is ≥3.2g / cm³. 3 The density of the billet was determined using the water displacement method.

[0037] As an optional implementation, in step (5), the ZnO grain size in the resistor sheet semi-finished product is 5μm-8μm, and the grain boundary layer is 10nm-15nm. Optionally, after segmented sintering, the density of the resistor sheet semi-finished product is ≥5.5g / cm³. 3 .

[0038] As an optional implementation, the specific steps of the segmented sintering include: 1) heating from room temperature to 300-350℃ at a heating rate of 8-10℃ / min and holding for 15-20 min; 2) heating to 600-650℃ at a heating rate of 3-5℃ / min and holding for 30-35 min; 3) heating to 1100-1150℃ at a heating rate of 2-3℃ / min and holding for 35-40 min; 4) heating to 1150-1180℃ at a heating rate of 1-1.2℃ / min and holding for 60-80 min; 5) cooling to 600-800℃ at a cooling rate of 4-5℃ / min and holding for 25-30 min; 6) finally cooling to room temperature in the furnace. Optionally, the segmented sintering is carried out in a nitrogen atmosphere with an oxygen content ≤0.5%. The segmented sintering process of this invention includes the above six steps: the first step removes moisture, the second step decomposes organic matter, the third step promotes grain nucleation, the fourth step achieves densification sintering, the fifth step stabilizes grain boundaries, and the sixth step eliminates internal stress. This sintering process controls the density of the resistor sheet, the zinc oxide grains and the grain boundary layer, reduces impurity phases (such as Bi2O3-Sb2O3), reduces leakage current, and increases current carrying capacity, which is beneficial to meeting the performance requirements of zinc oxide resistor sheets.

[0039] As an optional implementation, after obtaining the resistor sheet semi-finished product, a precision machining step is also included, including double-end face grinding, external cylindrical grinding and other operations, so that the dimensional accuracy of the resistor sheet semi-finished product is ±0.02mm and the surface roughness Ra≤0.8μm.

[0040] As an optional implementation, the electrode layer includes a first film layer and a second film layer; in some embodiments, the electrode layer has a first film layer disposed along a direction perpendicular to the annular plane of the zinc oxide resistor sheet, and the second film layer is disposed on the surface of the first film layer, and the materials of the first film layer and the second film layer can be the same or different.

[0041] As an optional implementation, the thickness of the first film layer is 50nm-80nm; in some embodiments, the first film layer is prepared by vacuum sputtering. This invention does not have special requirements for the parameters of vacuum sputtering and uses parameters known in the art. For example, the vacuum sputtering parameters are: vacuum degree ≤ 5 × 10⁻⁶. -4 Pa, argon flow rate 20 sccm, sputtering power 500-800W, time 10-20min.

[0042] As an optional implementation, the thickness of the second film layer is 5μm-8μm; in some embodiments, the second film layer is prepared by electrophoretic deposition. This invention does not have special requirements for the parameters of the electrophoretic deposition process and uses parameters known in the art. For example, the parameters for the electrophoretic deposition process are: electrophoretic solution pH 6.5-7.0, electrophoretic voltage 50-80V, and time 15-30min.

[0043] As an optional implementation, the electrode layer is made of at least one of silver and aluminum.

[0044] As an optional implementation, the heating rate of the second sintering is no higher than 10℃ / min, the temperature is 250℃-300℃, and the time is 1h-1.5h.

[0045] As an optional implementation, the annealing heating rate is no higher than 20℃ / min, the temperature is 280℃-300℃, and the time is 1h-1.5h.

[0046] As an optional implementation, the method further includes the step of coating an insulating layer on at least one surface perpendicular to the thickness direction of the zinc oxide resistor sheet; optionally, the insulating layer is selected from conventional materials in the art; as an example, the raw material for the insulating layer includes coatings, such as epoxy resin.

[0047] In some embodiments, the thickness of the insulating layer is 50-80 μm.

[0048] Secondly, the present invention provides a zinc oxide resistor sheet prepared by the above method.

[0049] The zinc oxide resistor sheet provided by this invention meets the requirements of Table 1 after being tested according to DL / T 815-2021.

[0050] Table 1 Performance Requirements of Zinc Oxide Resistance Sheets

[0051] Note: Pass rate ≥ 98%.

[0052] Thirdly, the present invention provides the application of the zinc oxide resistive sheet prepared by the above method in surge arresters and / or surge protectors.

[0053] The following embodiments and comparative examples use the following equipment: Rotary kiln (Φ1.2m×6m, 310S stainless steel, lined with high-alumina refractory bricks, kiln body filling rate ≤30%), equipped with automatic temperature control system (accuracy ±5℃), frequency conversion drive (0.5-1r / min), cyclone separator + bag filter exhaust gas treatment unit.

[0054] GHJ-500 Double Helix High-Speed ​​Mixer (500L capacity, 15kW motor, 1500rpm), equipped with a ±0.1kg precision weighing system and a -80Pa negative pressure dust collection hood.

[0055] SB-500DY Ultrasonic Disperser (500W, 20kHz).

[0056] Mastersizer 3000 laser particle size analyzer (detection range: 0.01-3000μm).

[0057] XQM-200 planetary ball mill (200L tank, 30kW motor, 0-500rpm).

[0058] VOS-100 ultrasonic ball mill (400W, 20kHz, 100L tank).

[0059] LPG-500 centrifugal spray dryer (3.2m diameter tower, 8m height, 200mm atomizing disc, 18000rpm), equipped with a 0.8MPa steam-heated hot air furnace, a cyclone separator with ≥98% separation efficiency, and a bag filter.

[0060] GY-60 twin-roll tablet press (200mm roller diameter, 300mm roller width, 0-20MPa, 0-30rpm).

[0061] PC-100 crusher (10L chamber, 1000rpm), 40-60 mesh vibrating screen (amplitude 2mm, 45Hz).

[0062] 50L adhesive preparation tank with 50℃ heating.

[0063] The mold used for isostatic pressing is a nitrile rubber elastic mold (Shore hardness 70±5A, temperature resistance -40-120℃), inner diameter Φ50mm×30mm (according to specifications), 3-5mm wall thickness, and 1mm diameter vent hole.

[0064] GYJ-100 continuous isostatic press (0-60MPa, 0-5MPa / min pressurization) and CT-C drying kiln (5m³, room temperature - 200℃, 2m / s hot air circulation).

[0065] 30m long tunnel kiln (divided into 6 zones: zone 1 2m, zone 2 3m, zone 3 6m, zone 4 6m, zone 5 5m, cooling zone 2m), electric heating (zones 1-4) + water cooling (zone 5), corundum roller conveyor (80mm diameter, adjustable speed), nitrogen protection system (oxygen content ≤1%).

[0066] SMD-80 CNC double-end face grinder (Φ20-100mm grinding range, ±0.01mm accuracy), 120# diamond grinding wheel (3000rpm), 5% emulsion coolant system (10L / min, 5μm filter).

[0067] M1080 CNC centerless grinder (Φ20-100mm range, ±0.01mm accuracy), 150# grinding wheel (4000rpm), 200rpm guide wheel, -100Pa negative pressure dust collection (dust ≤0.5mg / m³). JGP-500 Continuous Vacuum Sputtering Machine (500L chamber, 5×10) -4 (Pa ultimate vacuum), Φ150mm×5mm pure silver target (99.99%), 20sccm argon gas, 80mm sputtering distance.

[0068] 200L stainless steel electrophoresis tank (electrode spacing 500mm).

[0069] TSL-300 tunnel sintering furnace (3m long, room temperature - 500℃, 5℃ / min heating rate) SX-100 box-type annealing furnace (100L, room temperature - 500℃, heating rate 3℃ / min) DISK-50 electrostatic spraying machine (1.5mm spray gun, 200mm distance, 60kV voltage).

[0070] GH-200 Curing Oven (room temperature - 200℃, temperature rise 10℃ / min) The raw materials used in the following examples and comparative examples are all commercially available.

[0071] Example 1 This embodiment provides a method for preparing a zinc oxide resistor sheet, including the following steps: (1) Prepare raw materials: 1) Using a screw conveyor to feed zinc oxide powder at a uniform speed, the powder is transported to the rotary kiln. The temperature is increased from room temperature to 880℃ at a rate of 10℃ / min, held for 2 hours, and then allowed to cool naturally to 300℃ before being cooled by a 500m cold air system. 3 Cool to room temperature ( / h), pass through a 200-mesh vibrating screen (vibrating screen amplitude 3mm, 50Hz), and place the sieved powder in a silo for later use.

[0072] 2) Weigh out 2.0 kg of Bi2O3, 1.5 kg of Sb2O3, 0.8 kg of CoO, 0.5 kg of MnO, 0.3 kg of Cr2O3, 0.2 kg of SiO2, and 0.1 kg of Al2O3 respectively, and mix them in a double-helix high-speed mixer. Stir at 500 rpm for 1 min, and then stir at 1500 rpm for 10 min to obtain the additive mixture. The element content deviation was detected by X-ray fluorescence spectrometry (XRF) and was ≤ ±0.05%. Unqualified batches were remixed.

[0073] 3) Add TiO2 and water to a 100L stainless steel tank at a solid-liquid ratio of 1:5, add KH550 (1% of TiO2), stir at 500rpm for 30min, then ultrasonically disperse in an ultrasonic disperser for 30min. The particle size D50 is measured to be 30nm by a laser particle size analyzer, and the dispersion is ≥95%. The resulting dispersion is placed in a sealed storage tank with a 100rpm stirrer for later use. If the particle size and dispersion requirements are not met, the mixture needs to be remixed.

[0074] (2) Take 94.6 kg of ZnO obtained in step 1), the above-mentioned additive mixture and 59.5 kg of dispersion (approximately 10 kg of TiO2 coated with KH550), place them in a planetary ball mill, use zirconia grinding balls (density 6.0 g / cm³, 5 mm: 8 mm: 10 mm = 3: 5: 2, ball-to-material ratio 4: 1), grind at 250 rpm for 5 h, stop for 5 min every 1 h (tank temperature ≤ 50℃, if the temperature exceeds the limit, extend the stop to 10 min), and obtain a first-grade slurry. Take a sample and determine the particle size D50 of the first-grade slurry ≤ 1.5 μm.

[0075] The above-mentioned primary slurry was placed in an ultrasonic ball mill, a dispersion liquid was added, the ball-to-material ratio was 2:1, and ultrasonically ball milled at 150 rpm and 400 W for 1 hour to obtain a slurry. 20 ml of the slurry was taken and the particle size was measured using a laser particle size analyzer. The particle size was D50 of 1 μm, the dispersion was ≥95%, and the sedimentation rate was ≤2%.

[0076] (3) Preheat the spray dryer. The inlet temperature of the spray dryer is 210℃ and the outlet temperature is 85℃. Use a peristaltic pump to send the above slurry to the spray dryer for drying. After receiving the material, put it into the silo to obtain primary dry powder. Take 100g of sample and use a halogen moisture analyzer (105℃, 30min) to measure the moisture content ≤1% and the particle size ratio ≥90wt% through a 40-100 mesh sieve. If it is not qualified, re-dry it.

[0077] The above-mentioned primary dry powder and the PVA aqueous solution (PVA degree of polymerization 1700, PVA aqueous solution concentration 10wt%) were mixed at a mass ratio of 100:3. The mixture was stirred for 15 minutes using a twin-screw mixer, and then pressed using a two-roll press at a pressure of 10 MPa, a speed of 15 rpm, and a roller surface temperature of 40-45°C until a thickness of 3-5 mm and a density of 1.6-1.8 g / cm³ were achieved. 3 The powder is then crushed in a crusher and passed through a 40-60 mesh sieve. Coarse particles on the sieve are re-crushed, and fine powder passing through the sieve is remixed to obtain 40-60 mesh granulated powder. Flowability is measured using a Hall effect flowmeter, and loose bulk density is measured using the volumetric method. The granulated powder has a flowability ≥20s / 100mL, a loose bulk density of 1.2-1.4g / cm³, and the mass percentage of 40-60 mesh particles in the granulated powder is ≥95wt%. The silo is sealed.

[0078] (4) Place the above granulated powder in a mold, then pressurize it to 25 MPa at 2 MPa / min, hold the pressure for 8 min, and then depressurize it at a rate of 5 MPa / min. Remove the mold and demold the green body to obtain a rough green body. Place the rough green body at 120℃ and dry it for 2 h to obtain a qualified green body with a density ≥3.2 g / cm³ and a density fluctuation ≤±1%. Use a vernier caliper to test the size deviation of the green body ≤0.2 mm. Use a 5 MHz ultrasonic flaw detector to test the green body for pores ≥0.5 mm and internal defects.

[0079] The green body was placed in a long tunnel kiln for segmented continuous sintering under a nitrogen atmosphere with an oxygen content ≤0.5%. The sintering process included: 1) heating from room temperature to 300℃ at a heating rate of 8℃ / min and holding for 20min, with the green body conveying speed at 6m / h during this stage; 2) heating to 600℃ at a heating rate of 3℃ / min and holding for 30min, with the green body conveying speed at 6m / h during this stage; 3) heating to 1100℃ at a heating rate of 2℃ / min. 4) After heating to 1160℃ at a rate of 1℃ / min, hold for 40 minutes, with a billet conveying speed of 9 m / h during this stage; 5) Then heat to 1160℃ at a rate of 1℃ / min and hold for 60 minutes, with a billet conveying speed of 6 m / h during this stage; 6) Cool to 600℃ using water cooling at a rate of 4℃ / min and hold for 25 minutes, with a billet conveying speed of 12 m / h during this stage; 7) Finally, cool to room temperature in the furnace, with a billet conveying speed of 4 m / h during this stage, obtaining a semi-finished resistor sheet. The density was measured using the water displacement method and was ≥5.5 g / cm³. 3 Observation under a 500x metallographic microscope showed that the ZnO grain size was 5-8 μm and the grain boundary layer was 10-15 nm. XRD analysis showed that the main phase ZnO contained a small amount of Bi2O3-Sb2O3 composite phase.

[0080] The resistor sheet semi-finished product is precision machined using a CNC double-end face grinder and a CNC centerless grinder to achieve a dimensional accuracy of ±0.02mm and a surface roughness Ra≤0.8μm.

[0081] (5) Place the semi-finished resistor sheet in a vacuum sputtering machine for silver plating, and evacuate to a vacuum level of 5×10. -4 Argon gas was passed through at a flow rate of 20 sccm, sputtering power of 600 W, time of 15 min, and the water-cooled target material temperature was controlled to ≤80℃. A first film layer with a thickness of 60 nm was formed on both surfaces of the resistor sheet semi-finished product. The thickness was measured using a film thickness gauge, and the film layer was tested with a cross-cut tester (1 mm × 1 mm) and found to be free of peeling.

[0082] The semi-finished resistor sheet containing the first film layer is then placed in an electrophoresis tank containing electrophoresis solution. The temperature is controlled at 25±2℃ using a water bath, and electrophoresis is performed at 60V for 20 minutes to form a second film layer with a thickness of 5μm on the surfaces of the two first film layers. After removal, the film is ultrasonically cleaned with ethanol for 5 minutes and dried at 80℃ for 20 minutes. The electrophoresis solution consists of ethanol and water in a volume ratio of 7:3, and also includes 15wt% silver powder (particle size 0.5-1μm) and 0.5wt% sodium dodecylbenzenesulfonate. The pH of the electrophoresis solution is adjusted to 6.5-7 using acetic acid.

[0083] The resistive sheet semi-finished product containing the first and second film layers was placed in a tunnel sintering furnace and heated from room temperature to 250°C at a heating rate of 5°C / min, and then held at that temperature for 1 hour to obtain the finished product. The performance of the finished product was tested using an adhesion tester with a test parameter of 10N and a cross-cut test method. The adhesion was 5.75MPa. The contact resistance was measured to be 4.7mΩ using the four-probe method.

[0084] The finished product is placed in an annealing furnace and heated to 280°C at a heating rate of 3°C / min. It is then held at this temperature for 1.5 hours and cooled in the furnace to below 100°C. After that, it is taken out and allowed to cool naturally to obtain zinc oxide resistance sheets.

[0085] (6) E-44 epoxy resin and 650# polyamide were mixed at a mass ratio of 10:3 and diluted with xylene to obtain a coating. The xylene content in the coating was about 20wt%. After the Forecast-4 cup test, the viscosity at 25℃ was 20-25s.

[0086] The above coating was applied to the side of the zinc oxide resistor sheet (the side is the direction perpendicular to the thickness of the zinc oxide resistor sheet) to form a coating with a thickness of 50 μm, and then cured at 120°C for 30 min and allowed to cool naturally.

[0087] Example 2 This embodiment provides a method for preparing a zinc oxide resistor sheet, which is basically the same as that in Embodiment 1, with the main differences as follows: Adjusting the amount of raw materials, the raw materials in this embodiment include 95.57 kg of ZnO, 1.8 kg of Bi2O3, 1.2 kg of Sb2O3, 0.6 kg of CoO, 0.4 kg of MnO, 0.2 kg of Cr2O3, 0.15 kg of SiO2, and 0.08 kg of Al2O3. The amount of KH550-coated TiO2 is 10 kg (median particle size D50 is 25 nm).

[0088] The sintering time in step 4) of the segmented sintering in Example 1 is changed. In this example, the sintering time in step 4) of the segmented sintering is 70 min.

[0089] The voltage and time of electrophoresis in Example 1 were changed. In this example, the electrophoresis voltage was 55V and the time was 25min.

[0090] Example 3 This embodiment provides a method for preparing a zinc oxide resistor sheet, which is basically the same as that in Embodiment 1, with the main differences as follows: The specific steps of the segmented sintering in this embodiment include: heating from room temperature to 400°C at a heating rate of 5°C / min and holding for 20 min; heating to 600°C at a heating rate of 3°C / min and holding for 30 min; heating to 1400°C at a heating rate of 2°C / min and holding for 40 min; heating to 1600°C at a heating rate of 1°C / min and holding for 60 min; cooling to 600°C at a cooling rate of 4°C / min and holding for 25 min; and finally cooling to room temperature in the furnace.

[0091] Comparative Example 1 This comparative example provides a method for preparing a zinc oxide resistor sheet, which is basically the same as that in Example 1, with the main differences as follows: Adjust the ball milling process. In step (2) of this comparative example, zinc oxide, additive mixture and dispersion are mixed and ball milled at 200 rpm for 8 hours to obtain slurry with a particle size D50 of 3 μm.

[0092] To adjust the segmented sintering process, this comparative example uses an intermittent furnace for sintering, heating from room temperature to 1150℃ at a heating rate of 8℃ / min and holding at that temperature for 3 hours without nitrogen protection.

[0093] The electrode layer preparation process was adjusted. In this comparative example, silver electrode layers were formed on both surfaces of the resistor sheet by printing silver paste, and then sintered at 850℃ for 1 hour. Each zinc oxide resistor sheet contained 5g of silver.

[0094] Compared to Example 1, the production cost of this comparative example is 40% higher.

[0095] Comparative Example 2 This comparative example provides a method for preparing a zinc oxide resistor sheet, which is basically the same as that in Example 1, with the main differences as follows: Adjust the ball milling process. In step (2) of this comparative example, zinc oxide, additive mixture and dispersion are mixed and ball milled at 200 rpm for 8 hours to obtain slurry with a particle size D50 of 3 μm.

[0096] Test case This test case provides performance tests for the zinc oxide resistance sheets in various embodiments and comparative examples, as detailed below: The varistor voltage, leakage current, 4 / 10μs current capacity, and residual voltage ratio were all tested for the electrical performance of the zinc oxide resistor according to the DL / T 815-2021 standard.

[0097] Leakage current test method after 1000h aging: Place the resistor in the aging test chamber and run it for 1000h at DC 1mA voltage and 45℃. Then test the leakage current according to the above standard.

[0098] Table 2 Test Results

[0099] Based on the test results of the above embodiments and comparative examples, for example, in Example 1 and Comparative Example 2, the D50 of the slurry formed by mixing zinc oxide powder, additives and dispersion of the present invention is 0.8μm-1.2μm, which is beneficial to reduce the performance fluctuations that occur during the preparation of the resistor sheet. The varistor voltage fluctuation is ≤±3%, the leakage current is ≤8μA, the 4 / 10μs current capacity is ≥70kA, the residual voltage ratio is ≤1.77, and the current capacity does not decrease after 3 tests.

[0100] As can be seen from Comparative Examples 1 and 2, the present invention controls factors such as segmented sintering and electrode layer preparation processes, which is beneficial to reduce costs, reduce residual pressure ratio, and increase current capacity.

[0101] As can be seen from Examples 1 and 3, the segmented sintering controlled by the present invention meets the requirements of the present invention, which is beneficial to further reduce the residual voltage ratio of the resistor sheet (≤1.7), and can also improve the current carrying capacity and reduce leakage current.

[0102] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0103] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a zinc oxide resistor sheet, characterized in that, Includes the following steps: (1) Pre-sintering of zinc oxide powder; (2) The zinc oxide powder, additives and dispersion obtained in step (1) are mixed and ball-milled to obtain a slurry; the median particle size D50 of the slurry is 0.8μm-1.2μm and the dispersibility is ≥95%; (3) The slurry is spray-dried and granulated to obtain granulated powder; (4) The granulated powder is shaped and sintered for the first time to obtain a resistor sheet semi-finished product; the first sintering adopts segmented sintering; (5) An electrode layer is formed on at least one surface of the resistor sheet semi-finished product by vacuum sputtering and / or electrophoretic deposition process, followed by a second sintering and annealing.

2. The preparation method according to claim 1, characterized in that, In step (1), the pre-sintering temperature is 850℃-900℃ and the time is 1.5h-2h; Preferably, the specific steps of the pre-sintering include: heating to 850℃-900℃ at a heating rate of 8℃ / min-10℃ / min and then holding at that temperature for 1.5h-2h.

3. The preparation method according to claim 1 or 2, characterized in that, Step (2) satisfies at least one of (1)-(4): (1) The additives include at least one of Cr2O3, SiO2, Bi2O3, Sb2O3, CoO, MnO, and Al2O3; Preferably, the additives include Cr2O3, SiO2, Bi2O3, Sb2O3, CoO, MnO, and Al2O3; More preferably, based on 100wt% of the total mass percentage of the zinc oxide powder and additives, the content of Bi2O3 is 1.5wt%-3.0wt%, the content of Sb2O3 is 1.0wt%-2.0wt%, the content of CoO is 0.5wt%-1.0wt%, the content of MnO is 0.3wt%-0.8wt%, the content of Cr2O3 is 0.2wt%-0.5wt%, the content of SiO2 is 0.1wt%-0.3wt%, and the content of Al2O3 is 0.05wt%-0.15wt%. (2) The dispersion is a dispersion containing TiO2; Preferably, the dispersion comprises TiO2 particles coated with organosilane; More preferably, the median particle size D50 of the organosilane-coated TiO2 particles is 20nm-50nm; (3) The ratio of the total mass of the zinc oxide powder and the additives to the mass of the organosilane-coated TiO2 in the dispersion is (10-15):1; (4) The ball mill includes a primary ball mill and a secondary ball mill; Preferably, the parameters of the primary ball mill include: using a planetary ball mill, a ball-to-material ratio of 4-5:1, a rotation speed of 200-250 rpm, and a time of 5-6 hours; Preferably, the parameters of the secondary ball milling include: ultrasonic ball milling, ball milling ratio of 2-3:1, rotation speed of 150rpm-250rpm, ultrasonic power of 400W-450W, and time of 1h-1.5h.

4. The preparation method according to any one of claims 1-3, characterized in that, The granulated powder has a flowability ≥20s / 100mL and a loose packing density of 1.2g / cm³. 3 -1.4g / cm 3 ; And / or, the mass percentage of particles with a mesh size of 40-60 mesh in the granulated powder is ≥95 wt%; And / or, the inlet temperature of the spray dryer is 200℃-220℃, and the outlet temperature is 80℃-90℃.

5. The preparation method according to any one of claims 1-4, characterized in that, The molding pressure is 25MPa-30MPa, and the time is 8min-10min; And / or, the rough blank obtained after molding is dried at 100℃-120℃ for 2h-3h to obtain a green body; preferably, the density of the green body is ≥3.2g / cm³. 3 .

6. The preparation method according to any one of claims 1-5, characterized in that, In step (5), the ZnO grains in the resistor sheet semi-finished product have a grain size of 5μm-8μm and a grain boundary layer thickness of 10nm-15nm. And / or, the specific steps of the segmented sintering include: heating from room temperature to 300-350℃ at a heating rate of 8-10℃ / min and holding for 15-20 min; heating to 600-650℃ at a heating rate of 3-5℃ / min and holding for 30-35 min; heating to 1100-1150℃ at a heating rate of 2-3℃ / min and holding for 35-40 min; heating to 1150-1180℃ at a heating rate of 1-1.2℃ / min and holding for 60-80 min; cooling to 600-800℃ at a cooling rate of 4-5℃ / min and holding for 25-30 min; and finally cooling to room temperature in the furnace.

7. The preparation method according to any one of claims 1-6, characterized in that, The electrode layer includes a first film layer and a second film layer; Preferably, the thickness of the first film layer is 50nm-80nm; Preferably, the thickness of the second film layer is 5 μm-8 μm; Preferably, the material of the electrode layer includes at least one of silver and aluminum.

8. The preparation method according to any one of claims 1-7, characterized in that, The heating rate of the second sintering is no higher than 10℃ / min, the temperature is 250℃-300℃, and the time is 1h-1.5h; And / or, the annealing heating rate is not higher than 20℃ / min, the temperature is 280℃-300℃, and the time is 1h-1.5h.

9. The zinc oxide resistor sheet prepared by the preparation method according to any one of claims 1-8.

10. The application of the zinc oxide resistor sheet prepared by the preparation method according to any one of claims 1-8 or the zinc oxide resistor sheet according to claim 9 in surge arresters and / or surge protectors.

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