A method for preparing a thermistor substrate by a water-based gel method and the thermistor substrate

Abstract

The present invention provides a method for preparing a thermistor substrate by a water-based gel method and a thermistor substrate. The method includes the following steps: 1) Mix ceramic powder, sintering aids, water, dispersant, organic monomer and crosslinking agent evenly to obtain a slurry; 2) Add a catalyst and an initiator to the slurry, pour it into a mold, initiate a polymerization reaction to form a shape, and demold to obtain a green ceramic body; 3) Cut the green ceramic body and sinter it to obtain the thermistor substrate. By adding an organic monomer and a crosslinking agent externally, a polymer network structure is formed through a polymerization reaction, enabling in-situ curing and shaping of ceramic powder. The operation is simple, the stability is good, it is green and environmentally friendly, and it can be mass-produced; then a thermistor substrate is prepared through processes such as cutting and sintering. The ceramic substrate of the present invention has high flatness, low roughness, flexible size adjustment, simple process steps, low equipment investment, environmental friendliness, and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of resistor substrates, and particularly to a method for preparing a thermistor substrate by a water-based gel method and a thermistor substrate. Background Art

[0002] In the prior art, thermistors are mainly prepared by a granulated powder pressing and forming process. This process has low production efficiency and high production cost, and the target product is related to the mold size and the press tonnage. Since the mold size is fixed, the size of the obtained thermistor product is also fixed. If the size of the thermistor product needs to be adjusted, it can only be achieved by replacing the mold. The larger the product size, the larger the required press tonnage and the higher the price. These factors will cause a substantial increase in production cost and limit its application in production to a certain extent.

[0003] The Chinese patent document discloses "Processing Technology of Patch-Type Ceramic Thermistor Substrate", with the publication number CN113773072A. The processing technology of this invention includes the following steps: A. Raw material preparation; B. Mixing; C. Pressing into a blank; D. Sintering; E. Grinding; F. Dielectric strength test; The patch-type ceramic thermistor substrate of the present invention has relatively high strength and good dielectric strength performance, and its stability is relatively high; Multiple different temperatures are used for sintering the blank, and the sintering and forming stability is high, which has high practical value. However, the process of this invention still relies on specific molds and presses, with large equipment investment and high costs, which is not conducive to large-scale industrial production. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for preparing a thermistor substrate by a water-based gel method and a thermistor substrate, which are used to solve the problems of large equipment investment, high cost and unfavorable large-scale industrial production in the prior art when using a granulated powder pressing and forming process.

[0005] To achieve the above object and other related objects, the present invention is obtained by including the following technical solutions.

[0006] The present invention provides a method for preparing a thermistor substrate by a water-based gel method, including the following steps:

[0007] 1) Mix ceramic powder, sintering aid, water, dispersant, organic monomer and crosslinking agent evenly to obtain a slurry;

[0008] 2) Add a catalyst and an initiator to the slurry, pour it into a mold, initiate a polymerization reaction to form, and demold to obtain a ceramic green body;

[0009] 3) Cut the ceramic green body and perform sintering to obtain the thermistor substrate.

[0010] Preferably, the ceramic powder includes a main material and additives. Based on the total weight of the ceramic powder, the main material includes the following components in weight percentages: 50-80 wt% of BaCO 3 and 10-35 wt% of TiO 2 ; the additives include the following components in weight percentages: 0-10 wt% of SrCO 3 , 0-10 wt% of PbO, 0-5 wt% of Y 2 O 3 , 0-5 wt% of Nb 2 O 5 , 0-5 wt% of Sb 2 O 3 , 0-5 wt% of La 2 O 3 , 0-5 wt% of Bi 2 O 3 , 0-5 wt% of MnCO 3 and 0-5 wt% of CuO.

[0011] Preferably, based on the total weight of the ceramic powder, the sintering aid includes the following components in weight percentages: 0-5 wt% of Al 2 O 3 , 0-5 wt% of SiO 2 and 0-10 wt% of CaCO 3 .

[0012] Preferably, based on the total weight of the ceramic powder, the addition amount of water is 15-20 wt%.

[0013] Preferably, the dispersant is ammonium polyacrylate. Based on the total weight of the ceramic powder, the addition amount of the dispersant is 0.5-5 wt%.

[0014] Preferably, based on the total weight of the ceramic powder, the organic monomer is acrylamide, and the addition amount of the organic monomer is 0.01-5 wt%.

[0015] Preferably, in step 2), the catalyst is selected from one or more of tetramethylethylenediamine, cuprous chloride, 2,2-bipyridine, and ethylenediamine;

[0016] Preferably, in step 2), the initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium persulfate. Preferably, in step 2), based on the total weight of the slurry, the addition amounts of the catalyst and the initiator are both 0.01-0.2 wt%.

[0017] Preferably, before molding, the temperature is controlled ≤ 35°C.

[0018] Preferably, in step 3), the sintering temperature is 1200-1400 °C and the sintering time is 0.5-4 h.

[0019] The present invention also provides a thermistor substrate prepared by the method described in any one of the above.

[0020] As described above, the method for preparing a thermistor substrate by the aqueous gel method and the thermistor substrate of the present invention have the following beneficial effects: by adding an organic monomer and a crosslinking agent, a polymer network structure is formed through a polymerization reaction based on the aqueous gel method, enabling in-situ curing and shaping of ceramic powder, with advantages such as a simple production method, good stability, environmental friendliness, and suitability for large-scale production; then, the required thermistor substrate is prepared through cutting and sintering processes; the ceramic substrate prepared by the present invention has high flatness, low roughness, flexible size adjustment, simple process steps, low equipment investment, environmental friendliness, and is suitable for industrial production. Specific Embodiments

[0021] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] It should be noted that the process equipment or devices not specifically noted in the following examples are all conventional equipment or devices in the art.

[0023] Before further describing the specific embodiments of the present invention, it should be understood that the protection scope of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present invention are for describing specific embodiments and not for limiting the protection scope of the present invention. The test methods without specific conditions noted in the following examples are generally carried out under conventional conditions or according to the conditions recommended by each manufacturer.

[0024] When the embodiments give a numerical range, it should be understood that unless otherwise specified in the present invention, any value between the two endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, equipment, and materials used in the embodiments, according to the knowledge of those skilled in the art of this technology and the description of the present invention, any methods, equipment, and materials similar or equivalent to those described in the embodiments of the present invention can also be used to implement the present invention.

[0025] The embodiment of the present application provides a specific method for preparing a thermistor substrate by a water-based gel method, including the following steps:

[0026] 1) Mix ceramic powder, sintering aid, water, dispersant, organic monomer and cross-linking agent evenly to obtain a slurry;

[0027] 2) Add a catalyst and an initiator to the slurry, pour it into a mold, initiate a polymerization reaction to form a shape, and demold to obtain a green ceramic body;

[0028] 3) Cut the green ceramic body and sinter it to obtain the thermistor substrate.

[0029] Currently, in the prior art, there are relevant reports on preparing thermistor substrates by the tape casting method. It mainly uses dissolving ceramic powder in an organic solvent and volatilizing the organic solvent to form a thermistor substrate. This method is easy to obtain a stable thermistor substrate; however, this method requires a large amount of organic solvents, which is harmful to the environment and not conducive to large-scale industrial production. In the above technical solution of the present application, by adding an organic monomer and a cross-linking agent externally, a polymer network structure is formed through a polymerization reaction based on the water-based gel method, enabling the in-situ curing and shaping of ceramic powder, which has the advantages of simple manufacturing method, good stability, environmental friendliness, and large-scale production; then, the required thermistor substrate is prepared through processes such as cutting and sintering. The ceramic substrate prepared by the present invention has high flatness, low roughness, flexible size adjustment, simple process steps, low equipment investment, environmental friendliness, and is suitable for industrial production.

[0030] In a specific embodiment, the ceramic powder includes a main material and an additive. Based on the total weight of the ceramic powder, the main material includes the following components in weight percentage: 50 - 80 wt% of BaCO 3 and 10 - 35 wt% of TiO 2 ; the additive includes the following components in weight percentage: 0 - 10 wt% of SrCO 3 , 0 - 10 wt% of PbO, 0 - 5 wt% of Y 2 O 3 , 0 - 5 wt% of Nb 2 O 5 , 0 - 5 wt% of Sb 2 O 3 , 0 - 5 wt% of La 2 O 3 , 0 - 5 wt% of Bi 2 O 3 , 0 - 5 wt% of MnCO 3 and 0 - 5 wt% of CuO.

[0031] In a more specific embodiment, the ceramic powder includes a main material and additives. Based on the total weight of the ceramic powder, the main material includes components with the following weight percentages: 50-65 wt% of BaCO 3 and 20-30 wt% of TiO 2 ; The additives include components with the following weight percentages: 1-10 wt% of SrCO 3 , 1-10 wt% of PbO, 1-2 wt% of Y 2 O 3 , 1-4 wt% of Nb 2 O 5 , 1-3 wt% of Sb 2 O 3 , 1-3 wt% of La 2 O 3 , 1-2 wt% of Bi 2 O 3 , 1-2.5 wt% of MnCO 3 and 1-3.5 wt% of CuO.

[0032] In the above technical solution of the present application, SrCO 3 and PbO are used as peak-shifting agents in the system. When neither of them is added, the Curie temperature Tc of the prepared thermistor is 120 °C; by adding SrCO 3 , the Curie temperature Tc of the thermistor can be reduced below 120 °C. The more SrCO 3 is added, the smaller Tc is; on the contrary, for PbO, the more is added, the higher Tc is. The appropriate addition of Y 2 O 3 , Nb 2 O 5 , Sb 2 O 3 , La 2 O 3 and Nb 2 O 5 can enable the thermistor to obtain a good PTC effect.

[0033] In a specific embodiment, based on the total weight of the ceramic powder, the sintering aid includes components with the following weight percentages: 0-5 wt% of Al 2 O 3 , 0-5 wt% of SiO 2 and 0-10 wt% of CaCO 3 . The sintering aid can form a liquid phase during solid-phase sintering, reduce the sintering temperature, save energy and reduce consumption, and reduce production costs.

[0034] In a more specific embodiment, based on the total weight of the ceramic powder, the sintering aid comprises the following components in weight percentages: 0.5 to 1.5 wt% of Al 2 O 3 , 0.5 to 1 wt% of SiO 2 and 4 to 7 wt% of CaCO 3 .

[0035] In a specific embodiment, based on the total weight of the ceramic powder, the addition amount of water is 16 to 18 wt%.

[0036] In a specific embodiment, the dispersant is ammonium polyacrylate. Based on the total weight of the ceramic powder, the addition amount of the dispersant is 0.05 to 5 wt%, such as specifically 0.05 to 0.1 wt%, 0.1 to 1 wt%, 1 to 2 wt%, 2 to 3 wt%, 3 to 4 wt%, 4 to 5 wt%.

[0037] In a specific embodiment, based on the total weight of the ceramic powder, the organic monomer is acrylamide, and the addition amount of the organic monomer is 0.01 to 5 wt%, such as specifically 0.01 to 2 wt%, 2 to 3 wt%, 3 to 4 wt%, 4 to 5 wt%.

[0038] In a specific embodiment, in step 1), the pH of the slurry is 9 to 10, and the purpose is to maintain the stability of the slurry system. Ammonia water can be used to adjust the pH value of the slurry.

[0039] In a specific embodiment, in step 1), the slurry is degassed.

[0040] In a more specific embodiment, the slurry is degassed by vacuum stirring: the vacuum degree is -0.095 ± 0.002 Mpa, the stirring speed is 140 to 160 RPM, and the vacuum pumping time is 20 to 30 min. During the degassing process, the temperature of the slurry needs to be controlled below 35 °C to avoid premature gelation due to excessive temperature.

[0041] In a specific embodiment, in step 2), the catalyst is selected from one or more of tetramethylethylenediamine, cuprous chloride, 2,2-bipyridine, and ethylenediamine. The above catalysts are green, non-toxic, and efficient, and the catalytic mechanism is to catalyze the initiator to generate free radicals and accelerate the formation of gel in the system.

[0042] In a specific embodiment, in step 2), the initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium persulfate; using the above inorganic peroxides as initiators has the characteristics of being green, non-toxic, and efficient.

[0043] In a specific embodiment, in step 2), based on the total weight of the slurry, the addition amounts of the catalyst and the initiator are both 0.01 - 0.2 wt%.

[0044] In a specific embodiment, before molding, the temperature is controlled to be ≤ 35°C to avoid premature polymerization reaction and premature gelation caused by too high system temperature.

[0045] In a specific embodiment, in step 3), the sintering temperature is 1200 - 1400°C, such as specifically 1200 - 1300°C, 1300 - 1325°C, 1325 - 1350°C, 1350 - 1400°C.

[0046] In a specific embodiment, in step 3), the sintering time is 0.5 - 4 h, such as specifically 0.5 - 2 h, 2 - 2.5 h, 2.5 - 3.5 h, 3.5 - 4 h.

[0047] In a specific embodiment, in step 1), ball milling is used for mixing: the ball stones are made of zirconia, the ball-to-material ratio is (1 - 1.5):1, and the ball milling time is 8 - 32 h; the ceramic powder is added in batches.

[0048] In a more specific embodiment, the batch addition is carried out according to the mass ratio (1.5 - 2):(1.5 - 2):1, and the addition is carried out in three batches, with an addition interval time of 2 - 2.5 h.

[0049] The present invention also provides a thermistor substrate prepared by the method as described in any one of the above.

[0050] In a specific embodiment, the density of the thermistor substrate is ≥ 5.1 g / cm 3 。

[0051] In a specific embodiment, the Curie temperature of the thermistor substrate is 60 - 160°C.

[0052] In a specific embodiment, the resistivity range of the thermistor substrate is 1 - 1000 Ω*mm.

[0053] In a more specific embodiment, the density of the thermistor substrate is 5.1 g / cm 3 , the Curie temperature is 120°C, and the resistivity is 600 Ω*mm.

[0054] In a more specific embodiment, the density of the thermistor substrate is 5.2 g / cm 3 , the Curie temperature is 160°C, and the resistivity is 40 Ω*mm.

[0055] In a more specific embodiment, the density of the thermistor substrate is 5.15 g / cm 3 , the Curie temperature is 80 °C, and the resistivity is 6 Ω·mm.

[0056] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0057] Example 1

[0058] In this embodiment, the ceramic powder includes a main material and additives. Based on the total weight of the ceramic powder, the main material includes the following components by weight percentage: 55 wt% of BaCO 3 and 28 wt% of TiO 2 ; the additives include the following components by weight percentage: 7.5 wt% of SrCO 3 , 1 wt% of Y 2 O 3 , 0.5 wt% of Sb 2 O 3 , 1 wt% of MnCO 3 Based on the total weight of the ceramic powder, the sintering aid includes the following components by weight percentage: 0.5 wt% of Al 2 O 3 , 0.5 wt% of SiO 2 and 6 wt% of CaCO 3 .

[0059] Based on the total weight of the ceramic powder: the addition amount of water is 17 wt%; the dispersant is ammonium polyacrylate, and the addition amount of the dispersant is 2 wt%; the organic monomer is acrylamide, and the addition amount of the organic monomer is 4 wt%; the crosslinking agent is N-N methylene bisacrylamide, and the addition amount of the crosslinking agent is 8 wt% of the total weight of the organic monomer.

[0060] The catalyst is tetramethylethylenediamine; the initiator is ammonium persulfate; based on the total weight of the slurry, the addition amounts of the catalyst and the initiator are both 0.1 wt%;

[0061] This embodiment provides a method for preparing a thermistor substrate by a water-based gel method, including the following steps:

[0062] 1) According to the above ratios, put the ceramic powder, sintering aid, water, dispersant, organic monomer and crosslinking agent into a ball mill for ball milling. The ball stones are made of zirconia, and the ball-to-material ratio is taken as 1.5:1. The ball milling time is 20 h. Among them, the powder is added in three portions according to the mass ratio of 2:2:1, with an interval of 2 h between each addition. After mixing evenly, adjust the pH value with ammonia water to obtain a slurry with a pH of 10; Carry out vacuum stirring on the ball-milled slurry to remove the gas in the slurry as much as possible; The vacuum degree is -0.095 ± 0.002 Mpa, the stirring speed is 150 RPM, and the vacuum pumping time is 30 min. It is necessary to control the slurry temperature below 35 °C to prevent premature gelation due to excessive temperature;

[0063] 2) Add a catalyst (concentration 50%) and an initiator (concentration 5%) to the slurry, control the ambient temperature ≤ 35 °C, pour it into a mold, and form it by self-initiated polymerization reaction. Demold to obtain a green ceramic body, and place it on a flat and breathable wire mesh sieve to dry naturally;

[0064] 3) Cut the dried green ceramic body (diameter 3 mm, thickness 1.5 mm), and then sinter it at 1350 °C for 4 h to obtain the thermistor substrate.

[0065] Examples 2 - 5

[0066] Examples 2 - 5 are different from Example 1 in that the ratio of raw material components in the ceramic powder is different, and some process parameters are different. For details, refer to Table 1, and the rest of the processes are exactly the same.

[0067] Test the performance of the thermistor substrates prepared in Examples 1 - 5. The test methods are as follows:

[0068] The density is measured according to the principle of Archimedes' drainage method:

[0069] First, place the fired thermistor substrate in boiling water for 6 h to open the internal pores, then take out the sample and weigh its floating weight, wet weight, and dry weight respectively. Finally, calculate the density according to the formula listed below: ρ = m 1 *m liquid / m 3 -m 2 In the formula, m1 is the dry weight of the sample; m 3 is the saturated wet weight of the ceramic sample; m 2 is the floating weight of the sample in the test liquid. The m liquid selected is deionized water with a specific gravity of 1 g / cm 3 .

[0070] Room temperature resistance test conditions: Ta = 25 ± 0.5 °C, test voltage ≤ 1.5 V DC .

[0071] Under normal temperature conditions, after standing for 1 - 2 hours, then measure its normal temperature resistance value within the test temperature range.

[0072] Electrodes were plated on the surfaces of the thermistor substrates prepared in Examples 1 to 5 to prepare thermistors, and their properties were tested:

[0073] Curie temperature: the temperature point corresponding to 2*R25

[0074] Curie temperature experiment:

[0075] (1) The thermistors were connected in series and soldered onto the PCB board, and leads were led out at both ends of each thermistor;

[0076] (2) The thermistors were placed inside the oven, and the lead-out ends were placed outside the oven;

[0077] (3) The temperature of the chamber was raised to 1 °C below the lower limit of the Curie temperature and maintained for 30 min, and the resistance of the thermistor was measured with a multimeter;

[0078] (4) The temperature of the chamber was raised to the upper limit of the Curie temperature and maintained for 30 min, and the resistance of the thermistor was measured with a multimeter;

[0079] (5) It was judged whether twice the initial resistance value was within the resistance values measured at the upper and lower limit temperatures;

[0080] Note: The influence of air flow should be minimized during the experiment.

[0081] Maximum withstand voltage test

[0082] Before the test, the resistance of the thermistor was measured. First, a 220 V AC voltage was applied across the thermistor at room temperature for 3 s, then the voltage was raised to its maximum withstand voltage value and maintained for 30 s. There should be no breakdown or arc. After that, the voltage was disconnected, and the resistance of the thermistor was measured after 3 hours of recovery. The change in resistance was within 5%.

[0083] The test results are shown in Table 1:

[0084] Table 1. Formulation table of ceramic powders in Examples 1 - 5 and test results of thermistors

[0085]

[0086] In Table 1, PTC log(R250 / R25) represents the logarithm of the resistance of the PTC thermistor sample at 250 °C divided by the resistance of the same sample at 25 °C.

[0087] In summary, the present invention forms a polymer network structure through a polymerization reaction based on the aqueous gel method by adding an organic monomer and a crosslinking agent, enabling in-situ curing and shaping of ceramic powder. It has the advantages of simple manufacturing method, good stability, environmental friendliness, and large-scale production. Then, the required thermistor substrate is prepared through processes such as cutting and sintering. The ceramic substrate prepared by the present invention has high flatness, low roughness, flexible size adjustment, simple process steps, low equipment investment, environmental friendliness, and is suitable for industrial production. Therefore, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0088] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a thermistor substrate by a water-based gel method, characterized in that, it comprises the following steps: 1) Mix the ceramic powder, sintering aid, water, dispersant, organic monomer, and crosslinking agent evenly to obtain a slurry; the ceramic powder includes a main material and an additive. Based on the total weight of the ceramic powder, the main material includes the following components in weight percentage: 50-65 wt% of BaCO 3 and 20-30 wt% of TiO 2 ; the additive includes the following components in weight percentage: 1-10 wt% of SrCO 3 , 1-10 wt% of PbO, 1-2 wt% of Y 2 O 3 , 1-4 wt% of Nb 2 O 5 , 1-3 wt% of Sb 2 O 3 , 1-3 wt% of La 2 O 3 , 1-2 wt% of Bi 2 O 3 , 1-2.5 wt% of MnCO 3 and 1-3.5 wt% of CuO; based on the total weight of the ceramic powder, the sintering aid includes the following components in weight percentage: 0.5-1.5 wt% of Al 2 O 3 , 0.5-1 wt% of SiO 2 and 4-7 wt% of CaCO 3 ; based on the total weight of the ceramic powder, the addition amount of water is 15-20 wt%; the dispersant is ammonium polyacrylate; the addition amount of the dispersant is 0.5-5 wt%; the organic monomer is acrylamide, and the addition amount of the organic monomer is 0.01-5 wt%; the crosslinking agent is N-N methylene bisacrylamide, and the addition amount of the crosslinking agent is 5-10 wt% of the total weight of the organic monomer; the pH of the slurry is 9-10; 2) Add a catalyst and an initiator to the slurry, pour it into a mold, initiate a polymerization reaction to form a shape, and demold to obtain a green ceramic body; 3) Cut the green ceramic body and sinter it to obtain the thermistor substrate.

2. The method according to claim 1, characterized in that: In step 1), the slurry is degassed.

3. The method according to claim 1, characterized in that: In step 2), the catalyst is selected from one or more of tetramethylethylenediamine, cuprous chloride, 2,2-bipyridine, and ethylenediamine; and / or, the initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium persulfate.

4. The method according to claim 1, characterized in that: In step 2), based on the total weight of the slurry, the addition amounts of the catalyst and the initiator are both 0.01 - 0.2 wt%; and / or, before forming, the temperature is controlled ≤ 35°C; In step 3), the sintering temperature is 1200 - 1400°C; and / or, the sintering time is 0.5 - 4 h.

5. The method according to claim 1, characterized in that: In step 1), mixing is carried out by ball milling: the ball stones are made of zirconia, the ball-to-material ratio is (1 - 1.5):1; the ball milling time is 8 - 32 h; the ceramic powder is added in batches.

6. A thermistor substrate prepared by the method according to any one of claims 1 - 5.

7. The thermistor substrate according to claim 6, characterized in that: The density of the thermistor substrate ≥ 5.1 g / cm 3 ; and / or, the Curie temperature of the thermistor substrate is 60 - 160°C; and / or, the resistivity range of the thermistor substrate is 1 - 1000 Ω*mm.

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