A forming aid for ZnO varistor chips, ZnO varistor chips, and a preparation method for ZnO varistor chips

Abstract

The present invention provides a forming aid for ZnO varistor chips and a preparation method for ZnO varistor chips. The forming aid comprises trimethylolpropane oleate 0.1-0.5% by mass fraction, an emulsifier 0.05-0.1%, and deionized water 99.4-99.85%. By virtue of the lubricating and wetting physical properties of trimethylolpropane oleate, the present invention can reduce the friction between particles and the wall surface of a metal mold during the forming process of ZnO resistor chips, reduce the stress release during the demolding of the formed resistor chips, and avoid the occurrence of cracking phenomena after sintering of ZnO formed resistor chips or annular crack phenomena during grinding. At the same time, the addition of an emulsifier can reduce the surface tension within the system of the forming aid, rendering it with certain stability. Using the above-mentioned forming aid to prepare ZnO varistor chips can effectively solve the defects in the forming process of ZnO resistor chips, reduce quality losses, and improve the forming quality.

Description

Technical Field

[0001] The present invention belongs to the field of varistor ceramics, and particularly relates to a forming aid for ZnO varistor chips, a ZnO varistor chip, and a preparation method of a ZnO varistor chip. Background Art

[0002] A metal oxide arrester (MOA) is a protective electrical appliance used to limit overvoltage, and is usually connected in parallel with the protected equipment between the system and the ground. As the core component of a metal oxide arrester, the performance of a ZnO varistor chip is directly related to the performance of the arrester. Therefore, improving the quality and stability of ZnO varistor chips is a key step in enhancing the performance of arresters.

[0003] With the continuous development of the preparation process of ZnO varistor chips, higher requirements are put forward for the chip forming process. Since the surface of the granulated material in the preparation process of ZnO varistor chips has no lubricity, the forming friction resistance is large, and the strength of the powder particles is too high, resulting in difficulty in crushing the granulated material particles and easy formation of high porosity in the sintered ceramic body. To solve this problem, a forming aid (i.e., lubricant) with lubricating properties is usually added to the granulated material to reduce the friction resistance during its forming.

[0004] However, the ZnO ceramic system is generally composed of various oxide particles, with certain complexity and particularity, manifested in: the lubricating ability of a lubricant for oxide particles with different properties and between particles and the metal mold wall surface is different; the sharp corners of oxide particles are difficult to be effectively covered by the lubricant; it is not suitable to use solid particle lubricants that are insoluble in water or have poor diffusion ability to avoid forming pores; the foaming property of the lubricant; the damage of the lubricant to adhesiveness, etc. Therefore, there are not many lubricants that can be applied to the above ZnO ceramic system. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a forming aid for ZnO varistor chips, a ZnO varistor chip, and a preparation method of a ZnO varistor chip. The forming aid can be uniformly sprayed on the granulated material in combination with a water-containing machine, and after the aging is completed, forming is carried out, which solves the defects in the forming of ZnO varistor chips and can also reduce the pressure of the forming press to make the process more stable.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a forming aid for ZnO varistor chips, which, by mass fraction, includes 0.1 - 0.5% of trimethylolpropane oleate, 0.05 - 0.1% of emulsifier, and 99.4 - 99.85% of deionized water.

[0008] Preferably, the molding aid comprises trimethylolpropane oleate in an amount of 0.15-0.3% by mass fraction, an emulsifier in an amount of 0.05-0.08% by mass fraction, and deionized water in an amount of 99.62-99.8% by mass fraction.

[0009] Preferably, the emulsifier is selected from ODEA emulsifiers.

[0010] In a second aspect, the present invention provides a ZnO varistor chip, which is prepared by mixing the above-mentioned molding aid with a ZnO varistor granulating material.

[0011] Preferably, the mass percentage water content of the material obtained by mixing the molding aid with the ZnO varistor granulating material is 1.4-1.6%.

[0012] In a third aspect, the present invention provides a method for preparing the above-mentioned ZnO varistor chip, comprising the following steps:

[0013] Spray the molding aid on the ZnO varistor granulating material, and then obtain the ZnO varistor chip through aging, molding, debinding, sintering, grinding, spraying aluminum, and painting.

[0014] Preferably, the mass percentage water content of the material obtained by spraying the molding aid on the ZnO varistor granulating material is 1.4-1.6%.

[0015] Preferably, the aging time is 10-15 h.

[0016] Preferably, the molding pressure is 600-750 KN.

[0017] Preferably, the debinding temperature is 110-500 °C.

[0018] Preferably, the sintering temperature is 400-1200 °C.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The present invention provides a forming aid for ZnO varistor chips, which, by mass fraction, comprises 0.1 - 0.5% of trimethylolpropane oleate, 0.05 - 0.1% of an emulsifier, and 99.4 - 99.85% of deionized water. By virtue of the lubricating and wetting physical properties of trimethylolpropane oleate, the present invention can effectively improve the lubricating ability between oxide particles and the metal mold wall surface during the forming process of ZnO resistor chips, reduce the frictional force, thereby avoiding the cracking phenomenon of ZnO resistor chips after forming and sintering and the annular crack phenomenon after grinding. Meanwhile, the addition of the emulsifier can reduce the surface tension within the system of the forming aid, ensure the dispersibility of trimethylolpropane oleate, and render the system of the forming aid with a certain stability. In addition, all substances in the forming aid do not contain harmful substances, are environmentally friendly, reliable, and safe to use, and the process method of the forming aid is simple with high production efficiency. After all components are mixed together, they can be used after being stirred evenly.

[0021] The present invention uses a system composed of trimethylolpropane oleate, an emulsifier, and deionized water in a specific ratio as a forming aid for the preparation of ZnO varistor chips. After testing, compared with ZnO varistor chips without the addition of a forming aid or ZnO varistor chips with glycerol and water added as a forming aid, the rejection rate after sintering and the rejection rate after grinding of the present invention are 0, indicating that the forming aid provided by the present invention well solves the defects in the forming of ZnO resistor chips. Brief Description of the Drawings

[0022] Figure 1 SEM image of the cross-section of the ZnO varistor chip obtained in Example 1 at 100 μm;

[0023] Figure 2 SEM image of the cross-section of the ZnO varistor chip obtained in Example 2 at 100 μm;

[0024] Figure 3 SEM image of the cross-section of the ZnO varistor chip obtained in Comparative Example 3 at 100 μm. Detailed Description of the Invention

[0025] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] In view of the problems in the prior art that the surface of the granulated material in the preparation process of ZnO resistor chips has no lubricity and the forming friction resistance is large, the present invention provides a forming aid for ZnO varistor chips. By mass fraction, it includes trimethylolpropane oleate 0.1 - 0.5%, which can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%, etc.; emulsifier 0.05 - 0.1%, which can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09% or 0.1%, etc.; deionized water 99.4 - 99.85%, which can be 99.4%, 99.5%, 99.6%, 99.7%, 99.8% or 99.85%, etc.

[0027] In the present invention, the above-listed point values only serve as examples and are not limited thereto. Other point values within the numerical range are equally applicable. To avoid complexity, they will not be elaborated one by one here.

[0028] Preferably, by mass fraction, the forming aid of the present invention includes trimethylolpropane oleate 0.15 - 0.3%, emulsifier 0.05 - 0.08%, and deionized water 99.62 - 99.8%.

[0029] The present invention has no particular limitation on the sources of the trimethylolpropane oleate and the emulsifier, and general commercially available products can be used. Among them, the emulsifier is preferably selected from ODEA emulsifier. It should be noted that in the present invention, the emulsifier is specifically selected as ODEA emulsifier. When the emulsifier is selected as tallow amine polyoxyethylene ether or polyoxyethylene stearate, oil-water separation occurs, and the oleate cannot be evenly sprayed on the granulated material, resulting in instability in the subsequent process.

[0030] The present invention also provides a ZnO varistor chip, which is prepared by mixing the above-mentioned forming aid with ZnO resistor chip granulated material. Through exploration in the present invention, if the mass percentage moisture content of the material after mixing the forming aid with ZnO resistor chip granulated material is lower than 1.4%, the formed resistor chips are prone to cracking. If it is higher than 1.6%, the granulated material is prone to sticking to the mold during forming, increasing the forming difficulty. Therefore, preferably, the mass percentage moisture content of the material after mixing the forming aid with ZnO resistor chip granulated material in the present invention is 1.4 - 1.6%, and more preferably is 1.5%.

[0031] The present invention also provides a preparation method of the above ZnO varistor chip, including the following steps:

[0032] Spray the forming aid on the ZnO resistor chip granulated material, and then obtain the ZnO varistor chip through aging, forming, debinding, sintering, grinding, spraying aluminum, and painting.

[0033] According to the present invention, first, a forming aid is sprayed on the ZnO varistor granulation material. The forming aid can be prepared according to the proportion range in the above technical solution, specifically: trimethylolpropane oleate, an emulsifier, and deionized water are mixed according to the above mass percentages, and then the mixed solution is stirred evenly to obtain the forming aid. The ZnO varistor granulation material is preferably obtained by spray-drying a slurry obtained by mixing the raw materials of the ZnO varistor with water. The slurry can be subjected to drying, pulverization, sieving, or ball milling treatments as needed. Among them, the raw materials of the ZnO varistor, by mass fraction, include 90-95% of the main component zinc oxide, and the rest include 1-4% of bismuth oxide, 1-4% of antimony oxide, 1-2% of cobalt oxide, 0.1-1% of nickel oxide, 0.1-0.5% of manganese oxide, etc.

[0034] Since using the forming aid by spray granulation means will have a pungent smell, the present invention adopts a more convenient method. Preferably, the obtained mixed solution of the forming aid is added to a water-containing machine for spraying and water-containing, and the forming aid is evenly sprayed on the ZnO varistor granulation material by the water-containing machine. Then, the granulation material is aged. After the aging is completed, the granulation material is subjected to subsequent manufacturing processes such as forming, debinding, sintering, grinding, spraying aluminum, and painting, and finally, a ZnO varistor chip can be obtained. The present invention has no special restrictions on the above-mentioned aging, forming, debinding, sintering, grinding, spraying aluminum, and painting technical means, and can be carried out according to the conventional technical means well-known to those skilled in the art.

[0035] In some embodiments of the present invention, preferably, after spraying and water-containing, the moisture content of the obtained granulation material is tested. Preferably, the mass percentage moisture content of the obtained material being 1.4-1.6% is qualified, and then aging is carried out. The aging time is preferably 10-15 h, more preferably 12 h. After the aging is completed, billet-making powder can be obtained. According to the present invention, the obtained billet-making powder is pressed into a formed body, and the forming pressure is preferably 600-750 KN, more preferably 650-700 KN.

[0036] After obtaining the formed green body, according to the present invention, it is subjected to debinding treatment to remove the organic matter in the green body, and the temperature of the debinding treatment is 110 - 280°C. In some embodiments of the present invention, the debinding treatment includes R1 - R9 temperature zones, and the corresponding temperatures are 110 - 120°C, 170 - 180°C, 190 - 200°C, 220 - 230°C, 260 - 270°C, 280 - 290°C, 340 - 350°C, 380 - 390°C, 270 - 280°C respectively. In some embodiments of the present invention, after the debinding treatment is completed, a sintering treatment is carried out. The sintering treatment includes R1 - R11 temperature zones, and the corresponding temperatures are 400 - 410°C, 500 - 510°C, 520 - 530°C, 650 - 660°C, 750 - 760°C, 90 - 950°C, 950 - 1000°C, 1030 - 1130°C, 1030 - 1130°C, 960 - 1060°C, 800 - 900°C respectively. Then, the obtained ZnO resistor chip green body is ground, painted, and aluminized to obtain the finished ZnO resistor chip.

[0037] After testing, compared with the ZnO varistor chips without adding a forming aid or the ZnO varistor chips adding glycerol and water as forming aids, the rejection rate after sintering and the rejection rate after grinding of the present invention are 0, indicating that the forming aid provided by the present invention well solves the defects in the forming of ZnO resistor chips.

[0038] In order to further illustrate the present invention, the following detailed description is given through the following examples. The experimental raw materials used in the following examples of the present invention are all general commercially available products. For example, trimethylolpropane oleate is purchased from Shandong Fushun New Material Technology Co., Ltd. In the following examples or comparative examples, the temperature of the debinding includes: R1 - R9 temperature zones, and the corresponding temperatures are 110°C, 170°C, 190°C, 220°C, 260°C, 280°C, 340°C, 380°C, 270°C respectively. The temperature of the sintering includes: R1 - R11 temperature zones, and the corresponding temperatures are 400°C, 500°C, 520°C, 650°C, 750°C, 90 - 950°C, 950 - 1000°C, 1030 - 1130°C, 1030 - 1130°C, 960 - 1060°C, 800 - 900°C respectively.

[0039] Example 1

[0040] The present invention provides a ZnO varistor chip, and its preparation method is as follows:

[0041] S1: Prepare an aqueous solution of the forming aid according to the following mass percentage ratio: trimethylolpropane oleate 0.15%, emulsifier 0.05%, deionized water 99.8% (the effective components are trimethylolpropane oleate 0.15% and emulsifier 0.05%, and the total is 0.2%);

[0042] S2: Add the obtained aqueous solution of the forming aid to a water-containing machine for spraying to make it water-containing. After the granulated material (90% zinc oxide, 4% bismuth oxide, 2.5% antimony oxide, 2% cobalt oxide, 1% nickel oxide, 0.5% manganese oxide) is water-containing, measure the water content. After the water content meets the process requirements (the water content is 1.4 - 1.6%), age the granulated material for 12 h. After the aging is completed, perform subsequent manufacturing processes such as forming, debinding, sintering, and grinding on the granulated material, and finally obtain a ZnO varistor chip of the selected D45 specification.

[0043] Observe the ZnO varistor chips of 5 batches obtained by the method of Example 1 (the defective products after sintering refer to the resistor chips with delamination observed after sintering; the defective products after grinding refer to the resistor chips with delamination defects on the end face after grinding). The results are shown in Table 1:

[0044] Table 1

[0045] Batch number Forming pressure / KN Scrap rate after sintering Scrap rate after grinding 1 667 0％ 0％ 2 674 0％ 0％ 3 683 0％ 0％ 4 685 0％ 0％ 5 675 0％ 0％ Average 677 0％ 0％

[0046] Taking the ZnO varistor chip obtained with the above batch number as an example, perform SEM characterization on it, and the results are as Figure 1 (SEM image of the cross-section of the ZnO varistor chip after forming at 100 μm) shown. It can be seen that the defects of the ZnO varistor chip after forming are significantly reduced, and the crushing situation of the granulated material particles is significantly improved.

[0047] Example 2

[0048] The present invention provides a ZnO varistor chip, and its preparation method is as follows:

[0049] S1: Prepare an aqueous solution of the forming aid according to the following mass percentage ratio: trimethylolpropane oleate 0.3%, emulsifier 0.05%, deionized water 99.65% (the active ingredients are trimethylolpropane oleate 0.3% and emulsifier 0.05%, and the total is 0.35%);

[0050] S2: Add the prepared aqueous solution of the forming aid to a water-containing machine for spraying to make it water-containing. After the granulated material (95% zinc oxide, 1% bismuth oxide, 2.8% antimony oxide, 1% cobalt oxide, 0.1% nickel oxide, 0.1% manganese oxide) is water-containing, measure the water content. After the water content meets the process requirements (the water content is 1.4 - 1.6%), age the granulated material for 12 h. After the aging is completed, perform subsequent manufacturing processes such as forming, debinding, sintering, and grinding on the granulated material, and finally obtain a ZnO varistor chip of the selected D45 specification.

[0051] Observe the ZnO varistor chips of 5 batches obtained by the method of Example 2. The results are shown in Table 2 below:

[0052] Table 2

[0053] Batch number Forming pressure / KN Scrap rate after sintering Scrap rate after grinding 1 682 0％ 0％ 2 684 0％ 0％ 3 676 0％ 0％ 4 688 0％ 0％ 5 679 0％ 0％ Average 681 0％ 0％

[0054] Taking the ZnO varistor chip obtained with the above batch number 1 as an example, SEM characterization was carried out on it, and the results are as Figure 2 (SEM image of the cross-section of the ZnO varistor chip after molding at 100 μm) shown. It can be seen that the defects of the ZnO varistor chip after molding are significantly reduced, and the crushing of the granulated material particles is significantly improved.

[0055] Comparative Example 1

[0056] The present invention provides a ZnO varistor chip, and its preparation method is as follows:

[0057] S1: Prepare an aqueous solution of a molding aid according to the following mass percentage ratio: glycerol 0.2%, deionized water 99.8% (the active ingredient is glycerol 0.2%);

[0058] S2: Add the prepared aqueous solution of the molding aid to a water-containing machine for spraying and water-containing. After the granulated material (zinc oxide 90%, bismuth oxide 4%, antimony oxide 2.5%, cobalt oxide 2%, nickel oxide 1%, manganese oxide 0.5%) is water-containing, measure the water content. After the water content meets the process requirements (the water content is 1.4 - 1.6%), the granulated material is aged for 12 h. After the aging is completed, the granulated material is subjected to subsequent manufacturing processes such as molding, debinding, sintering, and grinding to finally obtain a ZnO varistor chip of the selected D45 specification.

[0059] The results of observing 5 batches of ZnO varistor chips obtained by the method of Comparative Example 1 are shown in Table 3 below:

[0060] Table 3

[0061]

[0062]

[0063] Comparative Example 2

[0064] The present invention provides a ZnO varistor chip, and its preparation method is as follows:

[0065] S1: Prepare an aqueous solution of a molding aid according to the following mass percentage ratio: glycerol 0.5%, deionized water 99.5% (the active ingredient is glycerol 0.5%);

[0066] S2: Add the prepared aqueous solution of the forming aid to the water-containing machine for spraying to make the granulated material (90% zinc oxide, 4% bismuth oxide, 2.5% antimony oxide, 2% cobalt oxide, 1% nickel oxide, 0.5% manganese oxide) contain water. After the water content is completed, measure the water content. After the water content meets the process requirements (the water content is 1.4 - 1.6%), age the granulated material for 12 h. After aging, carry out subsequent manufacturing processes such as forming, debinding, sintering, and grinding of the granulated material, and finally obtain a ZnO varistor chip of specification D45.

[0067] The results of 5 batches of ZnO varistor chips obtained by the method of Comparative Example 2 are shown in Table 4 below:

[0068] Table 4

[0069] Batch number Forming pressure / KN Scrap rate after sintering Scrap rate after grinding 1 667 0％ 0.23％ 2 674 0％ 0.17％ 3 683 0％ 0.11％ 4 685 0％ 0.32％ 5 675 0％ 0.33％ Average 677 0％ 0.23％

[0070] Comparative Example 3

[0071] The present invention provides a ZnO varistor chip. Compared with Example 1, the difference is that the aqueous solution of the forming aid is not sprayed on the granulated material, and the other parameters and steps are the same as those in Example 1.

[0072] The results of 10 batches of ZnO varistor chips obtained by the method of Comparative Example 3 are shown in Table 5 below:

[0073] Table 5

[0074] Batch number Forming pressure / KN Scrap rate after sintering Scrap rate after grinding 1 687 0％ 0.90％ 2 685 0％ 1.34％ 3 688 0％ 2.00％ 4 682 0％ 1.43％ 5 685 0％ 4.44％ 6 691 0％ 3.00％ 7 689 0％ 1.52％ 8 688 0％ 2.07％ 9 682 0％ 2.32％ 10 684 0％ 5.08％ Average 686 0％ 2.41％

[0075] Taking the ZnO varistor chip obtained from Batch No. 1 above as an example, perform SEM characterization on it, and the results are as Figure 3 (SEM image of the cross-section of the ZnO varistor chip after forming at 100 μm) shown. It can be seen that there are obvious defects in the ZnO varistor chip after forming, and the crushing of the granulated material particles has not been improved.

[0076] From the data comparison of the above Examples 1 - 3 and Comparative Examples 1 - 2, it can be seen that for the ZnO varistor chips with glycerol and water added as the forming aid, although the rejection rate after sintering is 0, there is still a rejection rate after grinding. For the ZnO varistor chips with the forming aid provided by the present invention added, the rejection rate after sintering and the rejection rate after grinding are 0, indicating that the forming aid provided by the present invention well solves the defects in the forming of ZnO resistor chips.

[0077] From the data comparison of the above Examples 1 - 3 and Comparative Example 3, it can be seen that if the forming aid provided by the present invention is not added, for the finally prepared ZnO varistor chips, the rejection rate after grinding significantly increases, and from the comparison of the SEM images, the defects of the formed resistor chips significantly increase.

[0078] Verification

[0079] The present invention preferably adopts the forming aid made of 0.3% of trimethylolpropane oleate, 0.05% of emulsifier and 99.8% of deionized water in Example 2. The forming aid is used for spraying and moisturizing with a water-containing machine. After aging for 12 h, forming is carried out, followed by degumming, sintering and grinding. By observing the quality of ZnO resistor chips, it is found that there is an obvious improvement.

[0080] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present 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 present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A forming aid for ZnO varistor chips, characterized in that By mass fraction, it includes 0.1 - 0.5% of trimethylolpropane oleate, 0.05 - 0.1% of emulsifier, and 99.4 - 99.85% of deionized water; The emulsifier is selected from ODEA emulsifier.

2. The molding aid according to claim 1, characterized in that, The molding aid includes 0.15 - 0.3% of trimethylolpropane oleate, 0.05 - 0.08% of emulsifier, and 99.62 - 99.85% of deionized water by mass fraction.

3. A ZnO varistor chip, characterized in that, It is prepared by mixing the molding aid according to Claim 1 or 2 with ZnO resistor chip granulating material.

4. The ZnO varistor chip according to claim 3, characterized in that The mass percentage water content of the material after mixing the molding aid with ZnO resistor chip granulating material is 1.4 - 1.6%.

5. A method for preparing a ZnO varistor chip as described in claim 3 or 4, characterized in that, It includes the following steps: Spray the molding aid on the ZnO resistor chip granulating material, and then obtain ZnO varistor chips through aging, molding, debinding, sintering, grinding, spraying aluminum, and painting.

6. The preparation method according to claim 5, characterized in that, The mass percentage water content of the material obtained by spraying the molding aid on the ZnO resistor chip granulating material is 1.4 - 1.6%.

7. The preparation method according to claim 5, characterized in that, The aging time is 10 - 15h; The molding pressure is 600 - 750kN.

8. The preparation method according to claim 5, characterized in that, The debinding temperature is 110 - 500°C.

9. The preparation method according to claim 5, characterized in that, The sintering temperature is 400 - 1200°C.

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