Lead-free and barium-free glass powder for PTC (Positive Temperature Coefficient) thermistor paste and preparation method thereof

Abstract

The invention discloses lead-free and barium-free glass powder for PTC (Positive Temperature Coefficient) thermistor paste and a preparation method of the lead-free and barium-free glass powder, and relates to the technical field of electronic functional materials. According to the lead-free and barium-free glass powder for the PTC thermistor paste, CaO-B2O3-SiO2-Al2O3 is taken as a matrix, and Na2O, TiO2, K2O, Li2O, MgO and SrO are added to regulate and control the glass powder; the preparation method comprises the following steps: weighing the raw materials and uniformly mixing to obtain a mixture; the mixture is subjected to high-temperature smelting and heat preservation, a homogenized glass melt is obtained, the homogenized glass melt is poured into water to be subjected to water quenching, and a glass material is obtained; drying and crushing the glass material to obtain glass fragments; carrying out ball milling on the glass fragments to obtain glass powder slurry; and carrying out solid-liquid separation on the glass powder slurry to obtain solid glass powder, and drying and screening the solid glass powder to obtain the lead-free and barium-free glass powder for the PTC thermistor slurry. The glass powder provided by the invention can enhance the combination of conductive particles and the compactness of a film layer, significantly improve the tight combination between the resistive film layer and a 96% Al2O3 substrate, and improve the reliability of PTC thermistor paste.

Description

Technical Field

[0001] This invention relates to a lead-free and barium-free glass powder for PTC thermistor paste and its preparation method, belonging to the field of electronic functional materials technology. Background Technology

[0002] With the rapid development of electronic technology, the advancements in the electrification and intelligentization of communications, food processing, medical devices, transportation, and home appliances, and the urgent need for temperature control, the market demand for thermistors has increased significantly, and their application areas are expanding. PTC thermistors, or Positive Temperature Coefficient thermistors, are widely used in aerospace, communication base stations, automotive electronics, high-end instruments, energy storage terminals, medical equipment, and home appliances due to their resistance-temperature characteristics, volt-ampere characteristics, and current-time characteristics.

[0003] Currently, PTC thermistor paste mainly consists of ruthenium powder and its ruthenium salts, glass powder, and an organic carrier. The performance of the glass powder directly determines the density of the resistive film layer after sintering and the good bonding between the film layer and the substrate. The glass powder in PTC thermistor paste requires a suitable melting temperature, good fluidity, and appropriate surface tension and viscosity to promote the formation of a complete conductive network. Secondly, the glass powder in PTC thermistor paste needs good mechanical strength and chemical corrosion resistance to extend the service life of the resistive paste.

[0004] Traditional PTC thermistor pastes use glass powders containing large amounts of lead. Lead is highly stable, lowers the transition temperature of the glass powder, and enhances its bonding with ceramic substrates. However, lead is a heavy metal and can seriously affect human health. When barium is added to glass powder, it can react with titanium in the raw materials to form barium titanate, providing the PTC effect. However, barium is highly toxic and sensitive to the sintering atmosphere during preparation, increasing the difficulty of preparing barium-containing glass powders. Therefore, the preparation of lead-free and barium-free glass powders is a future trend, but adjusting the elemental composition to replace the roles of lead and barium in the glass powder remains a challenge. To meet environmental protection requirements, lead-free and barium-free glass powders have become a research focus. Among them, the CaO-B2O3-SiO2-Al2O3 system has received widespread attention due to its low raw material cost, wide availability, and environmental friendliness.

[0005] This invention combines the characteristics of calcium borosilicate glass powder and, through the addition of Na2O, TiO2, K2O, Li2O, MgO, and SrO, designs and synergistically modifies the traditional CaO-B2O3-SiO2-Al2O3 glass powder system. This results in the development of a glass powder with excellent matching coefficient of thermal expansion, good sintering characteristics, and strong interfacial bonding, which is of great significance for meeting the development needs of high-reliability and environmentally friendly PTC thermistor pastes. Summary of the Invention

[0006] To address the problems of lead- and barium-containing glass powders used in current PTC thermistor pastes, such as mismatched thermal expansion coefficients with the conductive phase and insulating substrate, and insufficient wettability of the conductive phase at high temperatures, this invention provides a lead- and barium-free glass powder for PTC thermistor pastes and its preparation method. This effectively increases the coating and fixation of conductive particles during sintering, improves the density of the resistive film layer, significantly enhances the tight bonding between the resistive film layer and the 96% Al2O3 substrate, improves the high reliability of the PTC thermistor paste, and has a low manufacturing cost, thus solving the problem of poor performance of lead- and barium-free glass powders used in PTC thermistor pastes.

[0007] One objective of this invention is to provide a lead-free and barium-free glass powder for PTC thermistor paste. The glass powder uses CaO-B2O3-SiO2-Al2O3 as a matrix, and adds Na2O, TiO2, K2O, Li2O, MgO and SrO to regulate the glass powder composition. The composition of the glass powder, by mass percentage, includes: 10-25% CaO, 15-30% B2O3, 20-35% SiO2, 10-20% Al2O3, 5-10% Na2O, 3-5% TiO2, 1-5% K2O, 1-5% Li2O, 1-5% MgO, and 1-3% SrO.

[0008] The second objective of this invention is to provide a method for preparing lead-free and barium-free glass powder for PTC thermistor paste, specifically including the following steps: (1) Weigh each raw material according to the proportion and mix them evenly (preferably using a mixer to mix for 1 hour) to obtain a mixture.

[0009] (2) The mixture is smelted at high temperature and kept at a constant temperature to obtain a homogenized glass melt. The homogenized glass melt is then quenched in water to obtain glass material.

[0010] (3) Dry the glass material and then crush it to obtain glass fragments.

[0011] (4) The glass fragments are ball-milled to obtain glass powder slurry.

[0012] (5) The glass powder slurry is subjected to solid-liquid separation (preferably centrifuged at 6500 rpm for 6 min) to obtain solid glass powder. The obtained solid glass powder is dried and sieved to obtain lead-free and barium-free glass powder for PTC thermistor slurry.

[0013] Preferably, the conditions for high-temperature melting in step (2) are: melting at 1350~1500℃ for 2~4h, stirring the mixture 2~5 times during the melting process; and the heat preservation time is 1~3h.

[0014] Preferably, the drying conditions in step (3) are: drying at 80~120℃ for 24 hours.

[0015] Preferably, the ball milling conditions in step (4) are as follows: the grinding balls, glass fragments and dispersant are mixed in a volume ratio of (4.5~5.5):(1.8~2.2):(0.9~1.1) and ball milled for 15~20 hours.

[0016] More preferably, in step (4), the grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls; the dispersant is anhydrous ethanol.

[0017] Preferably, the drying conditions in step (5) are: drying at 60~80℃ for 18~24h; the lead-free and barium-free glass powder for PTC thermistor slurry is sieved through a 400-mesh sieve and the lead-free and barium-free glass powder for PTC thermistor slurry that passes through the 400-mesh sieve is collected.

[0018] Mechanism of the invention: Traditional CaO-B2O3-SiO2-Al2O3 system glass powder has high chemical stability and mechanical strength, but the melting temperature is high, the fluidity is poor, the coefficient of thermal expansion is difficult to control, and the sintering activity is insufficient. This invention improves the traditional CaO-B2O3-SiO2-Al2O3 glass powder system by introducing Na2O, TiO2, K2O, Li2O, MgO, and SrO. Through the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the glass powder undergoes network modification and fluxing, significantly reducing its melting temperature and high-temperature viscosity. This enhances its sintering activity, promotes densification, and improves bubble removal capabilities. Simultaneously, the metal oxides introduced in this invention synergistically regulate the glass network structure, enabling flexible control of the coefficient of thermal expansion, better matching it with encapsulation materials, optimizing interfacial bonding performance, and simultaneously enhancing the chemical stability, mechanical strength, and anti-crystallization ability of the glass. Ultimately, this achieves multi-faceted optimization of the glass powder's melting characteristics, thermal expansion behavior, interfacial bonding, and structural stability.

[0019] The beneficial effects of this invention are: (1) This invention optimizes the thermal expansion coefficient, sintering performance, and interfacial bonding of traditional CaO-B2O3-SiO2-Al2O3 glass powder by adding Na2O, TiO2, K2O, Li2O, MgO, and SrO to the CaO-B2O3-SiO2-Al2O3 system, thereby achieving the preparation of lead-free and barium-free glass powder. This glass powder has an average particle size of less than 4 μm, exhibits high density, and its raw material cost is significantly lower than that of the ZnO and Bi2O3 systems. This glass powder is applied to the square resistance R of a thermistor paste prepared with RuO2-CuO as the conductive phase. S It reaches 100Ω / □, and the temperature coefficient of resistance (TCR) reaches 2200ppm / ℃.

[0020] (2) Due to the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the thermal expansion coefficient of the glass powder prepared in this invention matches that of the conductive phase and the 96% insulating substrate, effectively increasing the density of the resistive film layer and improving the tight bonding between the resistive film layer and the substrate. This promotes the contact between conductive particles to form a complete conductive network, resulting in excellent long-term storage stability at room temperature and high-temperature storage stability. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the glass powder prepared in Example 1 of the present invention applied to a PTC thermistor slurry.

[0022] Figure 2 The image shows a cross-sectional scanning electron microscope image of the resistive film layer and the insulating substrate formed by applying the glass powder prepared in Example 1 of this invention to a PTC thermistor paste. Detailed Implementation

[0023] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. In the embodiments and comparative examples of this invention, unless otherwise specified, all chemical reagents used were commercially available analytical grade reagents.

[0024] Example 1 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 13% CaO, 22% B2O3, 33% SiO2, 10% Al2O3, 6% Na2O, 3% TiO2, 4% K2O, 3% Li2O, 3% MgO, and 3% SrO.

[0025] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1400℃ for 2 hours and kept at that temperature for 2 hours (the mixture is stirred 5 times during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0026] (3) Dry the glass material at 80°C for 24 hours, then crush it to obtain glass fragments.

[0027] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 5:2:1 and placed in an agate ball milling jar for 16 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0028] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 80°C for 24 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the sieve through the 400-mesh sieve is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0029] The glass powder prepared in this embodiment for the PTC thermistor paste has an average particle size of 3.87 μm. This glass powder is added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. Scanning electron microscope images are shown below. Figure 1 As shown, the thermistor paste exhibits a multi-morphological, multi-size, and uniformly distributed microstructure, which facilitates subsequent film formation and performance improvement of the PTC thermistor paste. This enables the construction of a conductive network and temperature sensitivity control, providing microstructural support for the resistance-temperature characteristics of the PTC thermistor. Cross-sectional scanning electron microscope images of the resistive film layer formed by this thermistor paste and the insulating substrate are shown below. Figure 2 As shown, by Figure 2 The resistive film layer exhibits a dense surface morphology, and the conductive particles form a complete conductive network under the action of glass powder. This results in a PTC thermistor with a relatively high sheet resistance (R0). SThe resistance reaches 100 Ω / □, and the temperature coefficient of resistance (TCR) reaches 2200 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate decreases to 1.24%, and after storage at 150℃ for 240 h, the resistance change rate decreases to 3.43%. The PTC thermistor paste prepared in this embodiment uses lead-free and barium-free glass powder. Through the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the glass network structure is adjusted, achieving flexible control of the coefficient of thermal expansion. This allows for better matching with the encapsulation material, optimizes the interfacial bonding performance, and realizes the preparation of a material with excellent long-term storage stability, high resistance, and high positive TCR.

[0030] Example 2 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 15% CaO, 22% B2O3, 33% SiO2, 10% Al2O3, 6% Na2O, 3% TiO2, 4% K2O, 2% Li2O, 3% MgO, and 2% SrO.

[0031] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1350°C for 4 hours and kept at that temperature for 3 hours (the mixture is stirred 4 times during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0032] (3) Dry the glass material at 90°C for 24 hours, then crush it to obtain glass fragments.

[0033] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 5.5:1.8:0.9 and placed in an agate ball milling jar for 15 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0034] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 60°C for 20 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the 400-mesh sieve was collected, which is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0035] The lead-free and barium-free glass powder used in this embodiment for PTC thermistor paste has an average particle size of 3.54 μm. This glass powder is added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. S The resistance reached 110 Ω / □, and the temperature coefficient of resistance (TCR) reached 2150 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate was 1.47%, and after storage at 150℃ for 240 h, the resistance change rate was 3.64%. The PTC thermistor paste prepared in this embodiment utilizes lead-free and barium-free glass powder. Through the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the glass network structure is adjusted, achieving flexible control of the thermal expansion coefficient. This allows for better matching with the encapsulation material, optimizes interfacial bonding performance, and realizes the preparation of a material with excellent long-term storage stability, high resistance, and high positive TCR.

[0036] Example 3 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 12% CaO, 15% B2O3, 33% SiO2, 15% Al2O3, 6% Na2O, 3% TiO2, 5% K2O, 5% Li2O, 5% MgO, and 1% SrO.

[0037] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1500℃ for 3 hours and kept at that temperature for 1 hour (the mixture is stirred 3 times during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0038] (3) Dry the glass material at 100°C for 24 hours, then crush it to obtain glass fragments.

[0039] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 4.5:2.2:1.1 and placed in an agate ball milling jar for 20 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0040] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 70°C for 22 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the 400-mesh sieve was collected, which is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0041] The lead-free and barium-free glass powder prepared in this embodiment for PTC thermistor paste has an average particle size of 3.47 μm. This glass powder is added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. S The resistance reached 115 Ω / □, and the temperature coefficient of resistance (TCR) reached 2110 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate decreased to 1.86%, and after storage at 150℃ for 240 h, the resistance change rate decreased to 3.71%. The PTC thermistor paste prepared in this embodiment uses lead-free and barium-free glass powder. Through the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the glass network structure is adjusted, achieving flexible control of the coefficient of thermal expansion. This allows for better matching with the encapsulation material, optimizes the interfacial bonding performance, and realizes the preparation of a material with excellent long-term storage stability, high resistance, and high positive TCR.

[0042] Example 4 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 25% CaO, 15% B2O3, 35% SiO2, 10% Al2O3, 5% Na2O, 5% TiO2, 1% K2O, 1% Li2O, 1% MgO, and 2% SrO.

[0043] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1400℃ for 2 hours and kept at that temperature for 2 hours (the mixture is stirred 5 times during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0044] (3) Dry the glass material at 120°C for 18 hours, then crush it to obtain glass fragments.

[0045] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 5:2:1 and placed in an agate ball milling jar for 16 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0046] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 80°C for 18 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the 400-mesh sieve was collected, which is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0047] The glass powder prepared in this embodiment for the PTC thermistor paste has an average particle size of 3.78 μm. This glass powder is added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. S The resistance reached 112 Ω / □, and the temperature coefficient of resistance (TCR) reached 2167 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate was 1.77%, and after storage at 150℃ for 240 h, the resistance change rate was 3.63%. The PTC thermistor paste prepared in this embodiment utilizes lead-free and barium-free glass powder. Through the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the glass network structure is adjusted, achieving flexible control of the coefficient of thermal expansion. This allows for better matching with the encapsulation material, optimizes interfacial bonding performance, and realizes the preparation of a material with excellent long-term storage stability, high resistance, and high positive TCR.

[0048] Example 5 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 10% CaO, 30% B2O3, 20% SiO2, 20% Al2O3, 10% Na2O, 4% TiO2, 1% K2O, 1% Li2O, 1% MgO, and 3% SrO.

[0049] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1400℃ for 2 hours and kept at that temperature for 2 hours (the mixture is stirred twice during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0050] (3) Dry the glass material at 80°C for 24 hours, then crush it to obtain glass fragments.

[0051] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 5:2:1 and placed in an agate ball milling jar for 16 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0052] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 80°C for 24 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the sieve through the 400-mesh sieve is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0053] The glass powder prepared in this embodiment for the PTC thermistor paste has an average particle size of 3.89 μm. This glass powder is added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. S The resistance reached 123 Ω / □, and the temperature coefficient of resistance (TCR) reached 2079 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate was 1.91%, and after storage at 150℃ for 240 h, the resistance change rate was 3.68%. The PTC thermistor paste prepared in this embodiment utilizes lead-free and barium-free glass powder. Through the synergistic effect of Na2O, TiO2, K2O, Li2O, MgO, and SrO on the CaO-B2O3-SiO2-Al2O3 system, the glass network structure is adjusted, achieving flexible control of the coefficient of thermal expansion. This allows for better matching with the encapsulation material, optimizes interfacial bonding performance, and realizes the preparation of a material with excellent long-term storage stability, high resistance, and high positive TCR.

[0054] Comparative Example 1 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 13% CaO, 22% B2O3, 36% SiO2, 10% Al2O3, 6% Na2O, 4% K2O, 3% Li2O, 3% MgO, and 3% SrO.

[0055] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1400℃ for 2 hours and kept at that temperature for 2 hours (the mixture is stirred 5 times during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0056] (3) Dry the glass material at 80°C for 24 hours, then crush it to obtain glass fragments.

[0057] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 5:2:1 and placed in an agate ball milling jar for 16 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0058] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 80°C for 24 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the sieve through the 400-mesh sieve is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0059] The lead-free and barium-free glass powder prepared in this comparative example for PTC thermistor paste has an average particle size of 3.67 μm. This glass powder was added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. S The resistance reached 118 Ω / □, and the temperature coefficient of resistance (TCR) reached 2121 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate was 2.14%, and after storage at 150℃ for 240 h, the resistance change rate decreased to 3.78%. Due to the absence of Ti, the network structure of the glass powder became loose, resulting in poor stability and mechanical strength of the prepared PTC thermistor slurry.

[0060] Comparative Example 2 A method for preparing lead-free and barium-free glass powder for PTC thermistor paste specifically includes the following steps: (1) Weigh each raw material according to the proportion and mix them with a mixer for 1 hour to obtain a uniform mixture. The composition of each raw material by mass percentage includes: 13% CaO, 22% B2O3, 36% SiO2, 10% Al2O3, 6% Na2O, 3% TiO2, 4% K2O, 3% Li2O, and 3% MgO.

[0061] (2) The mixture is loaded into an alumina crucible and placed in a muffle furnace at 1400℃ for 2 hours and kept at that temperature for 2 hours (the mixture is stirred 5 times during the melting process to ensure uniform melting) to obtain a homogenized glass melt. The homogenized glass melt is then quickly poured into deionized water for water quenching to obtain glass material.

[0062] (3) Dry the glass material at 80°C for 24 hours, then crush it to obtain glass fragments.

[0063] (4) The grinding balls, glass fragments and anhydrous ethanol are mixed in a volume ratio of 5:2:1 and placed in an agate ball milling jar for 16 hours of room temperature ball milling to obtain glass powder slurry. The grinding balls are mixed in a volume ratio of 3:5:2 for large, medium and small grinding balls.

[0064] (5) The glass powder slurry was centrifuged at 6500 rpm for 6 min to obtain solid glass powder. The obtained solid glass powder was dried at 80°C for 24 h in an electric heating blower. After that, it was screened through a 400-mesh sieve. The solid glass powder that passed through the sieve through the 400-mesh sieve is the lead-free and barium-free glass powder for PTC thermistor slurry.

[0065] The lead-free and barium-free glass powder prepared in this comparative example for PTC thermistor paste has an average particle size of 3.94 μm. This glass powder was added to a thermistor paste with RuO2-CuO as the conductive phase to prepare a PTC thermistor for temperature control and overheat protection. S The resistance reached 128 Ω / □, and the temperature coefficient of resistance (TCR) reached 2134 ppm / ℃. After storage at 25℃ for 1000 h, the resistance change rate was 2.21%, and after storage at 150℃ for 240 h, the resistance change rate decreased to 3.76%. Due to the absence of Sr, the thermal expansion coefficient of the glass powder was difficult to match with the 96% Al2O3 substrate, resulting in poor bonding between the resistive film layer and the Al2O3 substrate. Secondly, the lack of Sr resulted in poor wettability of the glass powder to the metallic conductive phase and ceramic, hindering the uniform distribution of the resistive paste during sintering and thus affecting the stability of the resistive paste.

[0066] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A lead-free and barium-free glass powder for PTC thermistor paste, characterized in that, The glass powder uses CaO-B2O3-SiO2-Al2O3 as the matrix, and adds Na2O, TiO2, K2O, Li2O, MgO and SrO to regulate the glass powder composition. The composition of the glass powder, by mass percentage, includes: 10-25% CaO, 15-30% B2O3, 20-35% SiO2, 10-20% Al2O3, 5-10% Na2O, 3-5% TiO2, 1-5% K2O, 1-5% Li2O, 1-5% MgO, and 1-3% SrO.

2. The method for preparing lead-free and barium-free glass powder for PTC thermistor paste according to claim 1, characterized in that, Specifically, the following steps are included: (1) Weigh each raw material according to the proportion and mix them evenly to obtain a mixture; (2) The mixture is smelted at high temperature and kept at a constant temperature to obtain a homogenized glass melt. The homogenized glass melt is then quenched in water to obtain glass material. (3) Dry the glass material and then crush it to obtain glass fragments; (4) The glass fragments are ball-milled to obtain glass powder slurry; (5) Solid-liquid separation is performed on the glass powder slurry to obtain solid glass powder. The obtained solid glass powder is dried and sieved to obtain lead-free and barium-free glass powder for PTC thermistor slurry.

3. The method for preparing lead-free and barium-free glass powder for PTC thermistor paste according to claim 2, characterized in that, The conditions for high-temperature melting in step (2) are: melting at 1350~1500℃ for 2~4 hours, stirring the mixture 2~5 times during the melting process; and the heat preservation time is 1~3 hours.

4. The method for preparing lead-free and barium-free glass powder for PTC thermistor paste according to claim 2, characterized in that, The drying conditions in step (3) are: drying at 80~120℃ for 24 hours.

5. The method for preparing lead-free and barium-free glass powder for PTC thermistor paste according to claim 2, characterized in that, The ball milling conditions in step (4) are as follows: the grinding balls, glass fragments and dispersant are mixed in a volume ratio of (4.5~5.5):(1.8~2.2):(0.9~1.1) and ball milled for 15~20 hours.

6. The method for preparing lead-free and barium-free glass powder for PTC thermistor paste according to claim 2, characterized in that, The drying conditions in step (5) are: drying at 60~80℃ for 18~24h; the lead-free and barium-free glass powder for PTC thermistor slurry is sieved through a 400-mesh sieve and the lead-free and barium-free glass powder for PTC thermistor slurry that passes through the 400-mesh sieve is collected.

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