Composite dispersing agent for zinc oxide varistor paste and use method of composite dispersing agent

Abstract

The invention relates to a composite dispersant for zinc oxide varistor paste and a use method thereof. The composite dispersing agent comprises a dispersing agent A and a dispersing agent B; the dispersing agent A comprises a component u, a component v and a component w, the component u is ammonium polyacrylate with the average molecular weight of 1000-3000, the component v is ammonium polyacrylate with the average molecular weight of 5000-8000, and the component w is ammonium citrate; the dispersing agent B comprises one or more of amino-terminated polyacrylamide, carboxyl-terminated polyacrylamide, polyoxyethylene ether phosphate and a silane coupling agent. The composite dispersing agent comprises an anionic dispersing agent A and a chelating dispersing agent B, the anionic dispersing agent A and the chelating dispersing agent B are not mixed to form the composite dispersing agent, the chelating dispersing agent B is used for dispersing trace functional oxides, and the anionic dispersing agent A is used for dispersing main body zinc oxide. By adopting the composite dispersing agent and cooperating with a pretreatment process, the dispersion uniformity of the trace functional oxide in the main body zinc oxide can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of zinc oxide varistor ceramic materials, in particular to a composite dispersant for zinc oxide varistor slurry and a use method thereof. BACKGROUND

[0002] Zinc oxide varistor is a kind of semiconductor ceramic element with excellent nonlinear volt-ampere characteristics, which is widely used in surge protection, overvoltage protection and circuit stabilization fields. The electrical performance of zinc oxide varistor directly determines the safety and reliability of electronic power systems. The typical zinc oxide varistor formula mainly consists of zinc oxide (ZnO) as the main component, and a variety of trace functional metal oxides such as bismuth oxide (Bi2O3), antimony oxide (Sb2O3), cobalt oxide (Co2O3), manganese oxide (MnO2) and the like. Although the content of these functional metal oxide additives is small (usually each accounts for 0.5%-3% of the total powder mass), they play a crucial role in forming a uniform grain boundary layer, controlling the microstructure, and ultimately obtaining the desired nonlinear coefficient (α), leakage current and current-carrying capacity.

[0003] In the prior art, the preparation of zinc oxide varistor usually adopts a wet ball milling process of ceramic powder to prepare a uniform and stable slurry for subsequent granulation or tape casting. The zinc oxide varistor ceramic slurry is generally composed of more than 95% zinc oxide powder and about not more than 5% other functional oxides (such as bismuth oxide, antimony oxide, etc.) powder, and a core index that determines the final performance of the varistor is the uniformity of the dispersion of these functional oxide powders in the zinc oxide powder. The more uniform the dispersion of these functional oxide powders in the zinc oxide powder slurry, the less the agglomeration, and the better the electrical performance of the prepared zinc oxide varistor. However, this process faces a long-standing technical problem: the uneven dispersion of different powder components in the slurry, especially the trace functional powders.

[0004] Specifically, since zinc oxide is the main component, accounting for more than 90%, and the specific gravity, particle size and surface potential of functional additives such as bismuth oxide and antimony oxide differ significantly from those of zinc oxide, they are prone to self-agglomeration or heterogeneous flocculation with the main particles in the slurry system due to van der Waals forces. For example, bismuth oxide powder is prone to form soft agglomerates in the liquid phase, while the dispersibility of antimony oxide is poor. This uneven dispersion leads to a series of serious defects:

[0005] (1) Microcomponent segregation: During the drying of the slurry and the subsequent sintering process, trace components cannot be uniformly distributed at the zinc oxide grain boundaries, causing local component excess or deficiency, forming "hot spots" or areas of weak electrical performance.

[0006] (2) Poor density of sintered body: Aggregates may become the source of pores or the core of abnormal grain growth during sintering, resulting in a decrease in the density of ceramic body and uneven microstructure.

[0007] (3) Deterioration of electrical performance and poor consistency: The above-mentioned defects in microstructure directly manifest as unstable nonlinear characteristics of varistor products, increased leakage current, decreased surge resistance, and large performance dispersion between batches, making it difficult to improve yield.

[0008] To address the aforementioned dispersion issues, the industry commonly employs the technique of adding anionic dispersants (such as ammonium polyacrylate and polycarboxylates). These are typically added at the initial stage of slurry preparation, along with zinc oxide powder, functional oxide powder, adhesives, deionized water, and other slurry components. After stirring and dispersion, the next spray granulation process is carried out. Adding dispersants during the preparation of zinc oxide varistor slurries can improve the overall dispersibility of the slurry, reduce powder agglomeration, and enhance slurry flowability. However, the mechanism of anionic dispersants relies on forming an electric double layer on the powder surface, thereby preventing powder agglomeration through electrostatic repulsion. This dispersion mechanism is highly sensitive to parameters such as ion concentration and pH value in the system, with a very narrow suitable window. Furthermore, achieving a good electric double layer formation on the surface of functional oxides (comprising no more than 10%) within a zinc oxide powder composition of over 90%, while maintaining the overall ion concentration and pH value within a suitable range, presents significant challenges. If the amount of dispersant added is too small, the surface of the relatively small amount of functional zinc oxide powder will not have enough dispersant adsorbed, affecting the dispersion effect. If the amount of dispersant added is too large, the excess dispersant will increase the ion concentration of the system, change the pH value of the system, and thus compress the electric double layer thickness of the powder surface, which will also affect the dispersion. In other words, when the proportion of functional oxides is much smaller than that of zinc oxide powder, it is theoretically difficult to achieve the optimal dispersion state of the dispersant adsorbed on the surfaces of both, which is difficult to achieve with traditional anionic dispersants and their application methods. In addition, the dispersant of a single system usually only has good affinity for a certain type of powder surface, and it is difficult to simultaneously take into account the zinc oxide bulk and a variety of trace additive powders with different properties. The surface states of zinc oxide and other functional oxides are different, and it is difficult for a single type of dispersant to have a good dispersion effect on zinc oxide powder and other functional oxide powders at the same time. For example, the zeta potential of zinc oxide and antimony oxide varies greatly with pH value. Under the pH environment where the zeta potential of zinc oxide is suitable, the zeta potential of antimony oxide is not well improved, and sometimes it may even worsen. This "one-sided" dispersion effect cannot fundamentally solve the problem of the synergistic and stable dispersion requirements of multi-component, wide-particle-size powder systems, especially for trace amounts of key functional phase powders. Therefore, the long-term stability and uniformity of the slurry cannot be effectively guaranteed, becoming one of the bottlenecks restricting the manufacturing of high-performance, highly consistent zinc oxide varistors.

[0009] Currently, the innovative research and development of dispersants mainly focuses on the following three technical routes:

[0010] 1) Synthesize novel and highly efficient dispersant molecules to enhance the dispersing effect by increasing the steric hindrance of the dispersant itself. For example, CN118221853 A describes a zinc oxide dispersant and its preparation method, which generates polycarboxylic acid macromonomers of different molecular weights by adjusting the content of initiator and chain transfer agent, thereby increasing the steric hindrance of the oxide arms by adsorption on the zinc oxide surface. However, technologies similar to this patent are not only technically challenging, but also still cannot solve the problem of uniformly dispersing various powders with different surface properties and significantly different contents in zinc oxide varistor slurry.

[0011] 2) Composite dispersants are obtained by combining high and low molecular weight dispersants or by compounding different types of dispersants. For example, CN102059072 A describes a high- and low-molecular-weight composite dispersant, its preparation method, and its application. By controlling the reaction conditions, a mixed molecular weight dispersant with a mass ratio of low-molecular-weight dispersant to high-molecular-weight dispersant of 1000:375-450 is synthesized in one step, thereby improving the dispersing ability of the dispersant. CN103130510A describes a composite dispersant for building ceramics and its application. A novel composite dispersant for building ceramics is obtained by compounding different types of dispersants such as sodium polyacrylate, sodium tripolyphosphate, sodium hexametaphosphate, and organosilicon-modified sodium phosphate. Although these different dispersant compounding technologies can solve the problem of oxide dispersion with different surface properties, they are currently mainly aimed at the dispersion of powders in traditional industries such as building ceramics and fly ash. These dispersants do not need to consider the residual problem of dispersant elements in the final product. Zinc oxide varistors have very high requirements for the content of impurity atoms, and the concentration of elements designed for non-electronic ceramic formulations (such as sodium atoms) must be very low. Therefore, this type of composite dispersant is difficult to apply in the field of electronic ceramics. When this type of composite dispersant is used in the field of electronic ceramics, the impurity elements introduced by the dispersant are not fully volatilized during the sintering process with zinc oxide because they are embedded in the zinc oxide ceramic body, resulting in incomplete removal of impurity atoms.

[0012] 3) Pre-treatment processes such as pre-dispersion and pre-sintering can improve the dispersion of trace components in the main components. For example, CN102126852B describes a method for preparing zinc oxide varistor ceramics, which uses pre-sintering-pulverization between functional oxide powders and between functional oxides and zinc oxide to improve the dispersion uniformity of trace functional oxides in zinc oxide. While the pre-sintering-pulverization pre-treatment technology improves the dispersion of functional oxides in the main zinc oxide to some extent, the problem of uneven dispersion of various oxides still exists in the pre-dispersion stage, and the pre-treatment does not fundamentally solve this problem. Summary of the Invention

[0013] This application addresses the problem of uneven dispersion effect of existing dispersants by providing a composite dispersant for zinc oxide varistor slurry with high dispersion and low residue; in addition, this application also provides a method for using the composite dispersant for zinc oxide varistor slurry.

[0014] In a first aspect, this application provides a composite dispersant for zinc oxide varistor paste, comprising dispersant A and dispersant B; wherein:

[0015] Dispersant A comprises three components: u, v, and w. Component u is ammonium polyacrylate with an average molecular weight of 1000-3000, component v is ammonium polyacrylate with an average molecular weight of 5000-8000, and component w is ammonium citrate.

[0016] Dispersant B includes one or more of the following: amino-terminated polyacrylamide, carboxyl-terminated polyacrylamide, polyoxyethylene ether phosphate, and silane coupling agents.

[0017] In dispersant A, components u and v are 50% aqueous solutions, and component w is a powder.

[0018] Optionally, the mass ratio of the three components in dispersant A is u:v:w = 1~3:10:0.3~1.

[0019] Optionally, the total molar concentration of dispersant A is 20-50%.

[0020] Optionally, dispersant B can be prepared as an aqueous solution or ethanol solution with a concentration of 20-50% for use.

[0021] Secondly, this application provides a method for using a composite dispersant in zinc oxide varistor slurry to prepare zinc oxide varistors, the method comprising the following steps:

[0022] S1. Prepare dispersant A by mixing and stirring a 50% aqueous solution of ammonium polyacrylate with a molecular weight of 1000-3000 and a 50% aqueous solution of ammonium polyacrylate with a molecular weight of 5000-8000, along with ammonium citrate powder, in a mass ratio of 1-3:10:0.3-1. After the ammonium citrate is completely dissolved, continue stirring to obtain dispersant A.

[0023] S2, prepare dispersant B by adding one or more of the following: amino-terminated polyacrylamide, carboxyl-terminated polyacrylamide, polyoxyethylene ether phosphate, and silane coupling agent to deionized water and stirring to dissolve them.

[0024] S3, Functional oxide powder pretreatment: The functional oxide, dispersant B and deionized water are put into a ball mill jar for the first ball milling according to the proportion. Then, 1 to 3 times the amount of zinc oxide powder is added and the powder is ball milled for the second time. After filtering out the ball mill beads, the powder is spray dried. The dried powder is then placed in a muffle furnace for heating and thermal diffusion. After natural cooling, the powder is pulverized by air jet to obtain the pretreated functional oxide powder.

[0025] S4. The pretreated functional oxide powder, the remaining zinc oxide powder, dispersant A, deionized water and adhesive are put into a ball mill jar in proportion and ball milled for the third time. After filtering out the ball mill beads, spray granulation is performed.

[0026] S5. After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheets are obtained.

[0027] Optionally, the functional oxide in step S3 is one or more of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide.

[0028] Optionally, in step S3, the first ball milling lasts 48 hours, the second ball milling lasts 24 hours, and the muffle furnace is heated to 900℃ for thermal diffusion for 3-5 hours.

[0029] Optionally, in step S3, some zinc oxide is added as a carrier during the pretreatment of functional oxide powder, with an addition ratio of 1:1 to 1:3.

[0030] Optionally, in step S4, the third ball milling lasts 24 hours.

[0031] The beneficial effects of this application are as follows: The composite dispersant of this application comprises two dispersants, anionic dispersant A and chelating dispersant B, rather than a mixture of two dispersants. Chelating dispersant B is used to disperse trace amounts of functional oxides, while anionic dispersant A is used to disperse the main zinc oxide. Combined with a pretreatment process, this improves the uniformity of dispersion of trace functional oxides within the main zinc oxide. Furthermore, by using this composite dispersant, in the functional oxide pretreatment process, dispersants containing silicon or boron can be used as components of dispersant B. By introducing doping elements such as silicon and boron during predisposition, the dual purpose of doping and dispersion can be achieved. Detailed Implementation

[0032] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to specific embodiments.

[0033] This application provides a composite dispersant for zinc oxide varistor slurry, comprising dispersant A and dispersant B.

[0034] Dispersant A comprises three components: u, v, and w. Component u is ammonium polyacrylate with an average molecular weight of 1000–3000, component v is ammonium polyacrylate with an average molecular weight of 5000–8000, and component w is ammonium citrate. Components u and v are each a 50% aqueous solution, while component w is a powder. The mass ratio of the three components is u:v:w = 1–3:10:0.3–1. The total molar concentration of dispersant A is 20–50%.

[0035] Dispersant B includes one or more of the following: amino-terminated polyacrylamide, carboxyl-terminated polyacrylamide, polyoxyethylene ether phosphate, and silane coupling agents. Dispersant B is prepared as an aqueous solution or ethanol solution with a concentration of 20–50% before use.

[0036] Dispersant A is an anionic dispersant used to disperse the main zinc oxide in the zinc oxide varistor material; dispersant B is a chelating dispersant used to disperse trace amounts of functional oxides in the zinc oxide varistor material. Dispersant A and dispersant B are two separate dispersants, not a mixture of two dispersants. The combination of these two dispersants improves the uniformity of dispersion of trace functional oxides within the main zinc oxide.

[0037] The composite dispersant of this application consists of two main components: an anionic dispersant component A, which disperses most zinc oxide powder, and a nonionic anchoring dispersant component B, which disperses functional oxides. The method of use involves first adding dispersant component B during the grinding and mixing process of the functional oxides. After grinding and mixing, zinc oxide (1-3 times the amount of functional oxides) is added and simply stirred to ensure the already dispersed functional oxide powder is evenly distributed around the subsequently added zinc oxide. Then, spray drying, low-temperature pre-sintering (600-900℃), and air jet milling are performed to obtain a "pre-synthesized powder." Due to the low-temperature sintering, the functional oxides and some zinc oxide powders have bonded together into a strong precursor compound through atomic diffusion during the pre-sintering process, making it possible to disperse trace components with this zinc oxide serving as a carrier.

[0038] The following describes, with reference to specific embodiments, a method for preparing zinc oxide varistors using the composite dispersant for zinc oxide varistor slurry of this application.

[0039] Example 1

[0040] A method for using a composite dispersant in zinc oxide varistor paste for preparing zinc oxide varistors, the method comprising the following steps:

[0041] S1. Prepare dispersant A by mixing and stirring 50% aqueous solution of ammonium polyacrylate with a molecular weight of 1000 and 50% aqueous solution of ammonium polyacrylate with a molecular weight of 5000, as well as ammonium citrate powder, in a mass ratio of 1:10:1. After the ammonium citrate is completely dissolved, continue stirring for 1-2 minutes to obtain dispersant A.

[0042] S2, prepare dispersant B by adding amino-terminated polyacrylamide with a molecular weight of 10,000 to 15,000 and isomeric tridecyl alcohol polyoxyethylene ether phosphate to deionized water at a mass ratio of 1:10 and stirring to dissolve, thus preparing dispersant B with a concentration of 20%.

[0043] S3, Functional oxide powder pretreatment: 3% of the total powder content of a mixture of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide, dispersant B, deionized water, and grinding beads are placed in a ball mill jar at a mass ratio of 1:0.008:2:2.5 and ball milled for 48 hours. Then, the ball mill jar is opened, 1 part of zinc oxide is added, along with 2 parts of water and 2.5 parts of grinding beads. The ball milling is continued for a second time for 24 hours. After filtering out the grinding beads, the powder is spray-dried. The dried powder is then placed in a muffle furnace and heated to 900℃ for thermal diffusion for 5 hours. After natural cooling, it is then air-jet pulverized to obtain the pretreated functional oxide powder.

[0044] S4. The pretreated functional oxide powder, the remaining zinc oxide powder, dispersant A, deionized water and PVA binder are put into a ball mill jar at a mass ratio of 60:0.3:40:0.3 and ball milled for a third time for 24 hours. After filtering out the ball mill beads, the performance of slurry 1 is tested and spray granulation is performed.

[0045] S5. After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheet 1 is obtained, and various electrical properties are tested.

[0046] Example 2

[0047] A method for using a composite dispersant in zinc oxide varistor paste for preparing zinc oxide varistors, the method comprising the following steps:

[0048] S1. Prepare dispersant A by mixing and stirring 50% aqueous solution of ammonium polyacrylate with a molecular weight of 3000 and 50% aqueous solution of ammonium polyacrylate with a molecular weight of 8000, and ammonium citrate powder in a mass ratio of 3:10:0.3. After the ammonium citrate is completely dissolved, continue stirring for 1-2 minutes to obtain dispersant A.

[0049] S2, prepare dispersant B by adding amino-terminated polyacrylamide with a molecular weight of 10,000 to 15,000 and isomeric tridecyl alcohol polyoxyethylene ether phosphate to deionized water at a mass ratio of 1:10 and stirring to dissolve, thus preparing dispersant B with a concentration of 20%.

[0050] S3, Functional oxide powder pretreatment: 3% of the total powder content of a mixture of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide and nickel oxide, dispersant B, deionized water, and grinding beads are placed in a ball mill jar at a mass ratio of 1:0.008:2:2.5 and ball milled for 48 hours. Then, the ball mill jar is opened, 3 parts of zinc oxide are added, along with 6 parts of water and 7.5 parts of grinding beads. The ball milling is continued for a second time for 24 hours. After filtering out the grinding beads, the powder is spray-dried. The dried powder is then placed in a muffle furnace and heated to 900℃ for thermal diffusion for 5 hours. After natural cooling, it is then air-jet pulverized to obtain the pretreated functional oxide powder.

[0051] S4. The pretreated functional oxide powder, the remaining zinc oxide powder, dispersant A, deionized water and PVA binder are put into a ball mill jar at a mass ratio of 60:0.3:40:0.3 and ball milled for a third time for 24 hours. After filtering out the ball mill beads, the performance of slurry 2 is tested and spray granulation is performed.

[0052] S5. After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheet 2 is obtained, and various electrical properties are tested.

[0053] Example 3

[0054] A method for using a composite dispersant in zinc oxide varistor paste for preparing zinc oxide varistors, the method comprising the following steps:

[0055] S1. Prepare dispersant A by mixing and stirring 50% aqueous solution of ammonium polyacrylate with a molecular weight of 2000 and 50% aqueous solution of ammonium polyacrylate with a molecular weight of 6000, as well as ammonium citrate powder, in a mass ratio of 2:10:0.6. After the ammonium citrate is completely dissolved, continue stirring for 1-2 minutes to obtain dispersant A.

[0056] S2, prepare dispersant B by adding alkylphenol polyoxyethylene phosphate and silane coupling agent KH55 to anhydrous ethanol at a mass ratio of 5:1 and stirring to dissolve, thus preparing a 50% concentration dispersant B ethanol solution.

[0057] S3, Functional oxide powder pretreatment: 3% of the total powder content of a mixture of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide, dispersant B, deionized water, and grinding beads are placed in a ball mill jar at a mass ratio of 1:0.008:2:2.5 and ball milled for 48 hours. Then, the ball mill jar is opened, 1 part of zinc oxide is added, along with 2 parts of water and 2.5 parts of grinding beads. The ball milling is continued for a second time for 24 hours. After filtering out the grinding beads, the powder is spray-dried. The dried powder is then placed in a muffle furnace and heated to 900℃ for thermal diffusion for 5 hours. After natural cooling, it is then air-jet pulverized to obtain the pretreated functional oxide powder.

[0058] S4. The pretreated functional oxide powder, the remaining zinc oxide powder, dispersant A, deionized water and PVA binder are put into a ball mill jar at a mass ratio of 60:0.3:40:0.3 and ball milled for a third time for 24 hours. After filtering out the ball mill beads, the properties of slurry 3 are tested and spray granulation is performed.

[0059] S5. After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheet 3 is obtained, and various electrical properties are tested.

[0060] Comparative Example 1

[0061] A mixture of functional oxides (3% of the total powder content) consisting of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide, along with deionized water and grinding beads, was placed in a ball mill jar at a mass ratio of 1:2:2.5 and ball-milled for 72 hours. The grinding beads were then filtered out, dried, and pulverized. The pulverized functional oxides, along with 97% zinc oxide, commercial dispersant HDK698, deionized water, and PVA binder, were placed in a ball mill jar at a mass ratio of 60:0.3:40:0.3 and ball-milled for 24 hours. After filtering out the grinding beads, the slurry properties were tested, and then spray granulation was performed.

[0062] After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheets 4 are obtained, and various electrical properties are tested.

[0063] Comparative Example 2

[0064] To prepare dispersant A, mix and stir a 50% aqueous solution of ammonium polyacrylate with a molecular weight of 3000 and a 50% aqueous solution of ammonium polyacrylate with a molecular weight of 8000, along with ammonium citrate powder, at a mass ratio of 1:10:1. After the ammonium citrate is completely dissolved, continue stirring for 1-2 minutes to obtain dispersant A.

[0065] To prepare dispersant B, amino-terminated polyacrylamide with a molecular weight of 10,000 to 15,000 and isomeric tridecyl alcohol polyoxyethylene ether phosphate were added to deionized water at a mass ratio of 1:10 and stirred to dissolve, thus preparing dispersant B with a concentration of 20%.

[0066] A mixture of functional oxides (3% of the total powder content) consisting of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide, along with deionized water and grinding beads, was placed in a ball mill jar at a mass ratio of 1:2:2.5 and ball-milled for 72 hours. The grinding beads were then filtered out, spray-dried, and pulverized. The pulverized functional oxides, along with 97% zinc oxide, dispersant A, dispersant B, deionized water, and PVA binder, were placed in a ball mill jar at a mass ratio of 60:0.2:0.1:40:0.3 and ball-milled for 24 hours. After filtering out the grinding beads, the slurry properties were tested, and then spray-granulated.

[0067] After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheets 5 are obtained, and various electrical properties are tested.

[0068] The performance comparison list of the paste and resistor sheet in the above embodiments and comparative examples is as follows:

[0069] Table 1 Comparison of Slurry Performance

[0070]

[0071] Table 2 Comparison of Basic Electrical Properties of Varistors

[0072] Resistance disc H / mm U 1mA / kV]]> U 0.1mA / kV]]> U 5kA / kV]]> [EV / mm -1 ]] U 5kA / U 1mA ]]> α 1 12.41 2.9 2.72 4.97 233.7 1.71 35.93 2 12.39 2.87 2.66 4.93 231.6 1.72 30.30 3 12.42 2.86 2.65 4.84 230.3 1.69 30.19 4 12.44 3.06 2.8 5.35 246.0 1.75 25.93 5 12.38 2.82 2.61 4.8 227.8 1.70 29.75

[0073] As can be seen from the comparison table of slurry performance, the particle size (D10 / D50 / D90) of Example 1 (slurry 1) and Example 2 (slurry 2) is smaller than that of Comparative Example 1 (slurry 4), and the nonlinear coefficient and pressure ratio of the resistive sheet are significantly improved, which fully demonstrates the effectiveness of the composite dispersant and its application method disclosed in this application.

[0074] This application addresses the problems of poor dispersion and instability of commonly used single-type anionic dispersants in existing zinc oxide varistors. It proposes to use a variety of anionic dispersants with different molecular weights and side functional groups to form dispersant A, thereby ensuring the dispersion effect of zinc oxide powder, which accounts for the majority of the slurry composition.

[0075] To address the issue of varying surface properties between different trace oxides and zinc oxide, a method is proposed using chelated nonionic dispersants (Dispersant B) added pre-processed during the grinding and mixing of functional oxides. This allows the dispersants to adhere firmly to the newly formed surfaces of the functional oxide powders through chelation and covalent bonding during the breakup and formation of new surfaces. This improves grinding efficiency, increases the adsorption capacity of the dispersants on the functional oxide powder surface, and reduces the re-agglomeration of the powder after grinding. Furthermore, because the dispersant uses an anchoring adsorption mechanism, it is less affected by changes in the system environment compared to electrostatic adsorption, making it less prone to desorption from the powder surface. This ensures the dispersion of the functional oxides in the varistor slurry later. The later-added Dispersant A also ensures the dispersion of most of the zinc oxide powder.

[0076] To address the problem of large differences in the content of functional oxides and zinc oxide, and the difficulty in uniformly distributing trace components in the main components, this application adopts a pretreatment process of grinding, spray drying, thermal diffusion, and pulverizing the functional oxides and a portion of the zinc oxide. This allows the trace functional oxides and a portion of the zinc oxide to undergo thermal diffusion with each other at a temperature of 900°C, thereby firmly "binding" the trace functional oxides to the portion of the zinc oxide and improving the dispersion in the entire zinc oxide system in the later stages.

[0077] In addition, in the above-mentioned pretreatment processes of dispersion, thermal diffusion, and high-temperature impurity removal, for dispersants with high anchoring effects but relatively difficult decomposition, such as ammonium, phosphate, and amide groups, impurity elements such as nitrogen and phosphorus in powder form are easier to remove. Furthermore, through reasonable design, functional elements such as aluminum, silicon, and boron that need to be doped can be introduced simultaneously using silane coupling agents, aluminate coupling agents, etc., thereby improving the dispersion effect while simultaneously achieving functional doping.

[0078] This application significantly improves the uniformity of the distribution of functional oxides such as bismuth oxide and antimony oxide, which have different surface properties from zinc oxide, in the main zinc oxide powder by separately adding anionic and chelating dispersants and using a pretreatment process of grinding-spray drying-thermal diffusion-pulverization. Furthermore, the pretreatment process can enhance the dispersion uniformity of functional oxide powders by introducing coupling agents such as aluminates, titanates, borates, and silanes, while introducing dopants such as aluminum, titanium, boron, and silicon to further improve the electrical performance of the zinc oxide varistor.

[0079] The foregoing has provided a sufficiently detailed and specific description of this application. Those skilled in the art should understand that the descriptions in the embodiments are merely exemplary, and all changes made without departing from the true spirit and scope of this application should fall within the protection scope of this application. The scope of protection claimed in this application is defined by the claims, and not by the above descriptions in the embodiments.

Claims

1. A composite dispersant for zinc oxide varistor slurry, characterized in that, The composite dispersant for the zinc oxide varistor slurry includes dispersant A and dispersant B; wherein: The dispersant A comprises three components: u, v, and w. Component u is ammonium polyacrylate with an average molecular weight of 1000-3000, component v is ammonium polyacrylate with an average molecular weight of 5000-8000, and component w is ammonium citrate. The dispersant B includes one or more of the following: amino-terminated polyacrylamide, carboxyl-terminated polyacrylamide, polyoxyethylene ether phosphate, and silane coupling agent.

2. The composite dispersant for zinc oxide varistor slurry according to claim 1, characterized in that, In the dispersant A, components u and v are 50% aqueous solutions, and component w is a powder.

3. The composite dispersant for zinc oxide varistor slurry according to claim 2, characterized in that, The mass ratio of the three components in the dispersant A is u:v:w = 1~3:10:0.3~1.

4. The composite dispersant for zinc oxide varistor slurry according to claim 3, characterized in that, The total molar concentration of dispersant A is 20-50%.

5. The composite dispersant for zinc oxide varistor slurry according to claim 1, characterized in that, The dispersant B is prepared as an aqueous solution or ethanol solution with a concentration of 20-50% when used.

6. A method of using the composite dispersant for zinc oxide varistor slurry as described in any one of claims 1-5, for preparing zinc oxide varistors, characterized in that, The method includes the following steps: S1. Prepare dispersant A by mixing and stirring a 50% aqueous solution of ammonium polyacrylate with a molecular weight of 1000-3000 and a 50% aqueous solution of ammonium polyacrylate with a molecular weight of 5000-8000, along with ammonium citrate powder, in a mass ratio of 1-3:10:0.3-1. After the ammonium citrate is completely dissolved, continue stirring to obtain dispersant A. S2, prepare dispersant B by adding one or more of the following: amino-terminated polyacrylamide, carboxyl-terminated polyacrylamide, polyoxyethylene ether phosphate, and silane coupling agent to deionized water and stirring to dissolve them. S3, Functional oxide powder pretreatment: The functional oxide, dispersant B and deionized water are put into a ball mill jar for the first ball milling according to the proportion. Then, 1 to 3 times the amount of zinc oxide powder is added and the powder is ball milled for the second time. After filtering out the ball mill beads, the powder is spray dried. The dried powder is then placed in a muffle furnace for heating and thermal diffusion. After natural cooling, the powder is pulverized by air jet to obtain the pretreated functional oxide powder. S4. The pretreated functional oxide powder, the remaining zinc oxide powder, dispersant A, deionized water and adhesive are put into a ball mill jar in proportion and ball milled for the third time. After filtering out the ball mill beads, spray granulation is performed. S5. After the spray-generated particles undergo the conventional aging, pressing, debinding, sintering, grinding, post-treatment, and aluminum spraying processes required for the preparation of varistors, zinc oxide varistor ceramic sheets are obtained.

7. The method of using the composite dispersant for zinc oxide varistor slurry according to claim 6, characterized in that, The functional oxide in step S3 is one or more of bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide.

8. The method of using the composite dispersant for zinc oxide varistor slurry according to claim 6, characterized in that, In step S3, the first ball milling lasts 48 hours, the second ball milling lasts 24 hours, and the muffle furnace is heated to 900℃ for thermal diffusion for 3-5 hours.

9. The method of using the composite dispersant for zinc oxide varistor slurry according to claim 6, characterized in that, In step S3, zinc oxide is added as a carrier during the pretreatment of functional oxide powder, with an addition ratio of 1:1 to 1:

3.

10. The method of using the composite dispersant for zinc oxide varistor slurry according to claim 6, characterized in that, In step S4, the third ball milling lasts for 24 hours.

Images