A high-temperature resistance paste for microcrystalline glass heating plate, a preparation method thereof and a sintering process

Abstract

The application provides a high-temperature resistance paste for microcrystalline glass heating plate, a preparation method and a sintering process, and the resistance paste comprises, by mass percentage, 45-75% of silver powder, 1-5% of palladium powder, 5-30% of composite glass powder, 18-20% of an organic carrier, wherein the composite glass powder comprises component A and component B at a mass ratio of 1-3:1, the component B is silicon powder, and the component A comprises, by mass percentage, 30-45% of silicon oxide, 8-15% of boric acid, 15-18% of magnesium oxide, 10-15% of aluminum oxide, 5-10% of bismuth oxide, 0.1-3% of sodium carbonate and 0.1-1% of lithium oxide. The resistance paste has good compatibility with the high-temperature conductor paste for microcrystalline glass, and the joint part will not be disconnected and cracked due to the too thick film thickness, the joint part will not be failed due to current impact, and the long-term service life of the microcrystalline glass heating plate is not affected.

Description

Technical Field

[0001] This invention relates to the field of resistive paste technology, and in particular, to a high-temperature resistive paste for microcrystalline glass heating plates, its preparation method, and sintering process. Background Technology

[0002] Microcrystalline glass boasts high strength, light weight, high insulation, excellent weather resistance and durability, and good corrosion resistance. In particular, it features a smooth surface, low coefficient of thermal expansion, and strong resistance to thermal shock. Utilizing these characteristics, thick-film resistors are fabricated on the surface of microcrystalline glass using a thick-film process. These resistors offer unparalleled advantages such as fast thermal response, small size, environmental friendliness, energy efficiency, and hygiene, and are widely used in applications such as health-preserving kettles, barbecue grills, medical devices, and industrial electrical appliances, experiencing rapid market growth.

[0003] Thick-film resistor pastes are mainly composed of metal powder, a glass binder phase, and an organic carrier, with small amounts of additives to improve the thermal stability and resistance temperature characteristics of thick-film resistors. Depending on the sintering process and operating temperature, resistor pastes are classified into high-temperature resistor pastes and medium-temperature resistor pastes. High-temperature resistor pastes typically have a peak sintering temperature of 800 to 850℃, and a long-term operating temperature that can reach 450℃ or higher; the softening point of their glass phase generally needs to reach above 750℃. Medium-temperature resistor pastes, on the other hand, typically have a sintering temperature of 550 to 600℃, and their operating temperature generally cannot exceed 300℃.

[0004] The main difference between high-temperature and medium-temperature resistance pastes lies in the glass phase. The higher the softening point of the glass phase, the higher its temperature resistance. Because thick-film resistors consist of uniformly distributed metal powders such as silver and palladium and glass powder, the resistance value depends on the conductive network formed by the shrinkage of the glass powder after high-temperature sintering, where the metal particles are "tightened." Due to the high melting point of the metals, the bonding phase formed by the glass powder after sintering softens at high temperatures, bonding the resistor body to the substrate and simultaneously binding the metal powder together to form a bulk material. As long as the structure of the conductive network does not change due to the low softening temperature of the glass phase at the operating temperature, the resistance value of the thick-film resistor will not shift. However, the thermal stress inherent between the thick-film resistor and the microcrystalline substrate at the operating temperature can lead to thermal expansion mismatch, causing microcracks between the thick-film resistor and the microcrystalline substrate to propagate continuously, resulting in a continuous increase in resistance.

[0005] Because the main components of thick-film resistive pastes, whether silver powder, palladium powder, or the glass binder phase, have a much higher coefficient of thermal expansion than those of microcrystalline glass plates, and the higher the sintering temperature, the more prone they are to bulging or cracking defects. Therefore, the higher the sintering temperature, the higher the operating temperature, and the greater the difficulty in developing resistive pastes. Microcrystalline heating plates are generally used as barbecue grills or health pots, requiring an operating temperature of 400℃ and stable power output during long-term operation. Currently, commercially available microcrystalline heating plates, whether using antimony tin oxide nanofilms or high-temperature carbon paste "graphene" films, cannot reliably meet the high operating temperature requirements. Therefore, there is an urgent need to develop high-temperature thick-film resistive pastes with operating temperatures exceeding 400℃ to address the high-temperature application needs of microcrystalline heating plates. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature resistance paste for microcrystalline glass heating plates, so as to solve the technical problem of thermal expansion mismatch between thick film resistance paste and microcrystalline glass plates during high-temperature sintering, and overcome problems such as bulging, cracking and increased resistance value during long-term high-temperature service.

[0007] To achieve the above objectives, the present invention provides a high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage: silver powder: 45-75%; palladium powder: 1-5%; composite glass powder: 5-30%; and organic carrier: 18-20%.

[0008] The composite glass powder comprises component A and component B in a mass ratio of 1 to 3:1;

[0009] Component B is silicon micropowder or similar substances with high melting point properties, such as alumina, titanium dioxide, zirconium oxide, silicon carbide, etc.; Component A, by mass percentage, includes silicon dioxide: 30-45%; boric acid: 8-15%; magnesium oxide: 15-18%; alumina: 10-15%; bismuth oxide: 5-10%; sodium carbonate: 0.01-3%; and lithium oxide: 0.01-1%.

[0010] Furthermore, the silver powder has an average particle size of 2–3 micrometers, a D99 of no more than 6 micrometers, a tap density of 5.0–6.5 g / ml, and a specific surface area of ​​0.4–0.7 m². 2 / g; the palladium powder is ultrafine palladium powder with an average particle size of 0.25-0.3 micrometers and is pure black.

[0011] Furthermore, the silicon micropowder is composed of silicon dioxide with a purity of 99.9%, an average particle size of 0.5–1 micrometer, and a maximum particle size not exceeding 2 micrometers. Alternatively, similar substances with high melting point characteristics, such as alumina, titanium dioxide, zirconium oxide, and silicon carbide, also have similar effects and properties.

[0012] Furthermore, the coefficient of thermal expansion of the composite glass powder is 3.5 to 5*10. -6 / K, softening point is 750~780℃.

[0013] Furthermore, the organic carrier comprises, by mass percentage, 25-35% decyl alcohol ester, 20-30% butyl carbitol, 10-20% butyl carbitol acetate, 3-6% γ-butyrolactone, 1-5% Span 85, and 2-6% ethyl cellulose std45; each component is boiled at 80°C for 4-6 hours to form a uniform and transparent organic solvent, which is then filtered through a 300-mesh polyester screen.

[0014] Furthermore, the viscosity of the resistive slurry is between 140 and 180 Pa·s, and the fineness is no greater than 15 micrometers.

[0015] This invention also provides a method for preparing the above-mentioned high-temperature resistance paste for a microcrystalline glass heating plate, comprising the following steps:

[0016] 1) First, mix component A of the composite glass powder evenly using a mixer. Then, using a platinum crucible, melt the mixture in a high-temperature melting furnace. Hold the temperature at 300℃ for 15 minutes, then raise the temperature to 900℃ and hold for 15 minutes. Finally, raise the temperature to 1500℃ and hold for 1 hour. Water quench the mixture.

[0017] 4) After mixing component A and component B in a certain proportion, the mixture is ball-milled to obtain a composite glass powder with a low coefficient of thermal expansion and a high softening point.

[0018] 5) Mix the composite glass powder, silver powder, palladium powder and organic carrier evenly according to the proportion, and roll it 4 to 6 times with a three-roll mill to make its fineness less than 15 micrometers. By adjusting the ratio of solid phase and liquid phase, a high-temperature resistance paste for microcrystalline glass heating plates with a viscosity of 140 to 180 Pa·s suitable for printing is obtained.

[0019] The present invention also provides a sintering process for a high-temperature resistive paste for a microcrystalline glass heating plate, wherein the above-mentioned high-temperature resistive paste for a microcrystalline glass heating plate is printed on the surface of a microcrystalline glass heating substrate, and then dried and sintered in sequence to obtain a resistive film for a microcrystalline glass heating plate.

[0020] Furthermore, the peak sintering temperature is 800–850℃, the peak holding time is 5–10 min, the entire sintering cycle is approximately 30–60 minutes, and the sintered film thickness is 12–18 micrometers.

[0021] Furthermore, 200-250 mesh stainless steel composite mesh is used for printing.

[0022] The present invention has the following beneficial effects:

[0023] 1. This invention provides a high-temperature resistive paste for microcrystalline glass heating plates, comprising, by mass percentage: 45-75% silver powder; 1-5% palladium powder; 5-30% composite glass powder; and 18-20% organic carrier. The composite glass powder comprises component A and component B in a mass ratio of 1-3:1. Component B is silicon micropowder. Component A, by mass percentage: 30-45% silicon oxide; 8-15% boric acid; 15-18% magnesium oxide; 10-15% aluminum oxide; 5-10% bismuth oxide; 0.01-3% sodium carbonate; and 0.01-1% lithium oxide. The silver powder has an average particle size of 2-3 micrometers, a D99 not exceeding 6 micrometers, a tap density of 5.0-6.5 g / ml, and a specific surface area of ​​0.4-0.7 m². 2 / g; the palladium powder is ultrafine palladium powder with an average particle size of 0.25-0.3 micrometers and is pure black. The composite glass powder has a coefficient of thermal expansion of 3.5-5*10-6 / K and a softening point of 750-780℃.

[0024] Silver and palladium powders serve as the functional phases in the resistive paste, acting as conductors. A higher palladium content results in a lower temperature coefficient of resistance. A higher proportion of functional phases leads to a lower sheet resistance of the resistive paste. Glass powder acts as a binder phase, mixing with the functional phases to form conductive chains and bonding firmly to the microcrystalline glass plate during high-temperature sintering. A higher glass powder content results in a higher sheet resistance and stronger adhesion of the resistive paste. Using glass powder with a low coefficient of thermal expansion is to match the low thermal expansion of the microcrystalline glass, preventing defects such as cracking during sintering. Adding high-melting-point silica powder prevents the glass powder from flowing too quickly during softening and acting as a "pinning" agent, further achieving thermal expansion matching with the microcrystalline glass and preventing bubbling during high-temperature sintering. The organic carrier allows the functional and binder phases to form a fluid with properties suitable for screen printing within the organic carrier (a mixture of resin and solvent), which completely evaporates during high-temperature sintering. Generally speaking, the higher the resin content in an organic carrier, the greater its viscosity. Conversely, the higher the proportion of the same organic carrier in the slurry, the lower its viscosity.

[0025] 2. The present invention provides a high-temperature resistive paste for a microcrystalline glass heating plate, and at the same time develops a resistive paste glass bonding phase with a high softening point and a low coefficient of thermal expansion. The high-temperature resistive paste made with this glass phase is well matched with the microcrystalline glass substrate. The resistive paste cannot be scraped off with a utility knife, has high strength and hardness, and is free of bubbles and cracks.

[0026] 3. The high-temperature resistance paste for microcrystalline glass heating plates provided by this invention is applied to microcrystalline glass. It adopts a peak sintering temperature of 850℃ and a peak holding time of 5-10 minutes. It has good thermal expansion matching, does not fail after multiple sintering cycles, does not blister or crack, has strong adhesion, and cannot be scraped off with a utility knife. Under thermal shock (at the same power of 1000W, it is continuously powered on for 30 seconds, the working temperature reaches 400℃ and is held for 5 minutes, then the power is cut off and the substrate is cooled to room temperature for 10 minutes, and the cycle test is repeated 1000 times), the resistance value change rate is less than 5%, which is excellent and meets the requirements of the application.

[0027] 4. The high-temperature resistive paste for microcrystalline glass heating plates provided by this invention has a temperature coefficient of resistance of 300ppm / C to 3000ppm / C, a sheet resistance of 10 milliohms / square to 300 milliohms / square, and a maximum operating temperature of over 400°C. After 1000 hours of long-term testing, the power attenuation is less than 5%. Furthermore, the high-temperature resistive paste for microcrystalline glass provided by this invention exhibits good compatibility with high-temperature conductive paste for microcrystalline glass. At the overlap, there will be no open circuit or cracking due to excessive film thickness, and the overlap will not fail due to current surges, thus not affecting the long-term service life of the microcrystalline glass heating plate.

[0028] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0029] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 This is a photograph of the resistive slurry obtained in Example 2 of the present invention after sintering;

[0031] Figure 2 This is a photo of the resistive slurry prepared in Comparative Example 1 after sintering.

[0032] Figure 3 This is a photo of the resistive slurry prepared in Comparative Example 2 after sintering.

[0033] Figure 4 This is a photo of the resistive slurry prepared in Comparative Example 3 after sintering. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0035] Example 1

[0036] A high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage, 72% silver powder (spherical silver powder, average particle size 1.8 micrometers, tap density 6.5 g / ml, specific surface area 0.42 m²). 2 / g); Ultrafine palladium powder: 3%; Composite glass powder: 5%; Organic carrier: 20%.

[0037] The coefficient of thermal expansion of the composite glass powder is 3.5 to 5*10. -6 / K, with a softening point of 750–780℃, comprises component A and component B in a mass ratio of 2:1.

[0038] Component B is silicon micro powder, and component A, by mass percentage, includes silicon oxide: 30-45%; boric acid: 8-15%; magnesium oxide: 15-18%; aluminum oxide: 10-15%; bismuth oxide: 5-10%; sodium carbonate: 0.01-3%; and lithium oxide: 0.01-1%.

[0039] The organic carrier, by mass percentage, comprises: 25-35% decyl alcohol ester, 20-30% butyl carbitol, 10-20% butyl carbitol acetate, 3-6% γ-butyrolactone, 1-5% Span 85, and 2-6% ethyl cellulose std45. Each component is boiled at 80°C for 4-6 hours to form a uniform and transparent organic solvent, which is then filtered through a 300-mesh polyester screen.

[0040] The specific preparation method is as follows:

[0041] 1) First, mix component A in the composite glass powder evenly with a mixer, use a platinum crucible, melt it in a high-temperature melting furnace, hold at 300℃ for 15 minutes, raise the temperature to 900℃, hold for 15 minutes, raise the temperature to 1500℃, hold for 1 hour, and then quench in water.

[0042] 2) After mixing component A and component B in a certain proportion, the mixture is ball-milled to obtain a glass-ceramic composite glass powder with a low coefficient of thermal expansion and a high softening point.

[0043] 3) Mix the composite glass powder, silver powder, palladium powder and organic carrier evenly according to the proportion, and roll it 4 to 6 times with a three-roll mill to make its fineness less than 15 micrometers. By adjusting the ratio of solid phase and liquid phase, a high-temperature resistance paste for microcrystalline glass heating plates with a viscosity of 140 to 180 Pa·s suitable for printing is obtained.

[0044] The resistive slurry prepared in this embodiment has a viscosity of 178 Pa·s and a fineness of less than 10 micrometers.

[0045] Example 2

[0046] A high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage, 52.8% silver powder (spherical silver powder, average particle size 1.8 micrometers, tap density 6.5 g / ml, specific surface area 0.42 m²). 2 / g); Ultrafine palladium powder: 2.2%; Composite glass powder: 25%; Organic carrier: 20%.

[0047] The coefficient of thermal expansion of the composite glass powder is 3.5 to 5*10. -6 / K, with a softening point of 750–780℃, comprises component A and component B in a mass ratio of 2:1.

[0048] Component B is silicon micro powder, and component A, by mass percentage, includes silicon oxide: 30-45%; boric acid: 8-15%; magnesium oxide: 15-18%; aluminum oxide: 10-15%; bismuth oxide: 5-10%; sodium carbonate: 0.01-3%; and lithium oxide: 0.01-1%.

[0049] The organic carrier, by mass percentage, comprises: 25-35% decyl alcohol ester, 20-30% butyl carbitol, 10-20% butyl carbitol acetate, 3-6% γ-butyrolactone, 1-5% Span 85, and 2-6% ethyl cellulose std45. Each component is boiled at 80°C for 4-6 hours to form a uniform and transparent organic solvent, which is then filtered through a 300-mesh polyester screen.

[0050] The specific preparation method is the same as in Example 1. The obtained resistive slurry has a viscosity of 180 Pa·S and a fineness of less than 10 micrometers.

[0051] Example 3

[0052] A high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage, 49% silver powder (spherical silver powder, average particle size 1.8 micrometers, tap density 6.5 g / ml, specific surface area 0.42 m²). 2 / g); Ultrafine palladium powder: 5%; Composite glass powder: 25%; Organic carrier: 20%.

[0053] The coefficient of thermal expansion of the composite glass powder is 3.5 to 5*10. -6 / K, with a softening point of 750-780℃, includes component A and component B in a mass ratio of 2:1.

[0054] Component B is silicon micro powder, and component A, by mass percentage, includes silicon oxide: 30-45%; boric acid: 8-15%; magnesium oxide: 15-18%; aluminum oxide: 10-15%; bismuth oxide: 5-10%; sodium carbonate: 0.01-3%; and lithium oxide: 0.01-1%.

[0055] The organic carrier, by mass percentage, comprises: 25-35% decyl alcohol ester, 20-30% butyl carbitol, 10-20% butyl carbitol acetate, 3-6% γ-butyrolactone, 1-5% Span 85, and 2-6% ethyl cellulose std45. Each component is boiled at 80°C for 4-6 hours to form a uniform and transparent organic solvent, which is then filtered through a 300-mesh polyester screen.

[0056] The specific preparation method is the same as in Example 1. The obtained resistive slurry has a viscosity of 180 Pa·S and a fineness of less than 10 micrometers.

[0057] Example 4

[0058] A high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage, 45% silver powder (spherical silver powder, average particle size 1.8 micrometers, tap density 6.5 g / ml, specific surface area 0.42 m²). 2 / g); Ultrafine palladium powder: 5%; Composite glass powder: 30%; Organic carrier: 20%.

[0059] The coefficient of thermal expansion of the composite glass powder is 3.5 to 5*10. -6 The composite glass powder, with a softening point of 750–780°C, comprises components A and B in a 1:1 mass ratio. The specific components A and B in the composite glass powder, as well as the organic carrier, are the same as in Example 1. The resistive slurry prepared in this example has a viscosity of 178 Pa·s and a fineness of less than 10 micrometers.

[0060] Example 5

[0061] A high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage, 75% silver powder (spherical silver powder, average particle size 1.8 micrometers, tap density 6.5 g / ml, specific surface area 0.42 m²). 2 / g); Ultrafine palladium powder: 1%; Composite glass powder: 5%; Organic carrier: 19%.

[0062] The coefficient of thermal expansion of the composite glass powder is 3.5 to 5*10. -6 The composite glass powder, with a softening point of 750–780°C, comprises components A and B in a mass ratio of 3:1. The specific components A and B in the composite glass powder, as well as the organic carrier, are the same as in Example 1. The resistive slurry prepared in this example has a viscosity of 178 Pa·s and a fineness of less than 10 micrometers.

[0063] Comparative Example 1 (Silver powder is microcrystalline silver powder)

[0064] A high-temperature resistance paste for microcrystalline glass heating plates, comprising, by weight percentage, 52.8% silver powder (microcrystalline silver powder, average particle size 0.8 micrometers, tap density 3.17 g / ml, specific surface area 2.78 m²).2 / g); Ultrafine palladium powder: 2.2%; Composite glass powder: 25%; Organic carrier: 20%.

[0065] Comparative Example 1 is the same as Example 2 except for the silver powder used.

[0066] The specific preparation method is the same as in Example 2. The obtained resistive slurry has a viscosity of 192 Pa·S and a fineness of less than 10 micrometers.

[0067] Comparative Example 2 (The composite glass powder only includes component A, excluding component B, silica powder)

[0068] A high-temperature resistance paste for microcrystalline glass heating plates, comprising, by weight percentage, 52.8% silver powder (microcrystalline silver powder, average particle size 0.8 micrometers, tap density 3.17 g / ml, specific surface area 2.78 m²). 2 / g); Ultrafine palladium powder: 2.2%; Composite glass powder: 25%; Organic carrier: 20%.

[0069] The glass powder is component A glass, which, by mass percentage, includes silicon dioxide: 30-45%; boric acid: 8-15%; magnesium oxide: 15-18%; aluminum oxide: 10-15%; bismuth oxide: 5-10%; sodium carbonate: 0.01-3%; and lithium oxide: 0.01-1%.

[0070] Comparative Example 2 is the same as Comparative Example 1 except that it uses a different composite glass powder.

[0071] The specific preparation method is the same as in Example 2. The obtained resistive slurry has a viscosity of 176 Pa·S and a fineness of less than 10 micrometers.

[0072] Comparative Example 3 (the glass powder is high-temperature calcium aluminum silicate glass powder)

[0073] A high-temperature resistive paste for microcrystalline glass heating plates, comprising, by weight percentage, 52.8% silver powder (spherical silver powder, average particle size 1.8 micrometers, tap density 6.5 g / ml, specific surface area 0.42 m²). 2 / g); Ultrafine palladium powder: 2.2%; Glass powder: 25%; Organic carrier: 20%.

[0074] The composite glass powder is a high-temperature calcium aluminum silicate glass powder with a coefficient of thermal expansion of 7.8*10. -6 The temperature is ℃, and the softening point is 750~760℃. The composition is: calcium oxide 32%; aluminum oxide 25%; silicon oxide 20%; boric acid 15%; barium oxide 3%; titanium oxide 3%; zirconium oxide 1%; strontium oxide 1%.

[0075] Comparative Example 3 is the same as Example 2 except that it uses a different composite glass powder.

[0076] The specific preparation method is the same as in Example 2. The obtained resistive slurry has a viscosity of 192 Pa·S and a fineness of less than 10 micrometers.

[0077] The resistance pastes prepared above exhibit significant viscosity variations due to differences in the specific surface area and addition ratio of various powders. This results in resistance layers of varying sintering thicknesses under the same printing and sintering conditions, potentially interfering with the rigor of the experiments. In this approach, different proportions of ethyl cellulose (STD45) in the organic carrier were adjusted to obtain organic carriers of varying viscosities. For resistance pastes containing powders with large specific surface areas, organic carriers with low ethyl cellulose content were used to achieve resistance pastes with similar viscosity and fineness. Since the organic carrier is largely removed during drying and evaporates during sintering, it is considered to have no impact on the experimental results.

[0078] The resistive pastes obtained in Examples 1-3 and Comparative Examples 1-3 were used to form resistive films using the same sintering process. Specifically, the resistive pastes were printed using the same 250-mesh stainless steel mesh with a wire diameter of 36 micrometers. The printed patterns were identical. The pastes were dried at 180°C for 12 minutes, and then held at a peak temperature of 850°C for 6 minutes. The same testing methods were used for each film. The resistance change rate test involved 1000 pulses under a 1000W power condition, followed by a 30-second continuous energization and 30-second cooling period. The resistance change rate ΔR was measured and calculated as (Rfinal - Rinitial) / Rinitial) * 100%.

[0079] The specific experimental results are shown in Table 1:

[0080] Table 1:

[0081]

[0082] As shown in Table 1, Examples 1 to 3 are preferred solutions. Using silver powder with high tap density and low specific surface area results in less shrinkage during high-temperature sintering, effectively preventing blistering. The use of low-thermal-expansion glass powder combined with silicon micropowder further reduces the coefficient of thermal expansion. Furthermore, the silicon micropowder, being a high-melting-point material with a low coefficient of thermal expansion, acts as a "pinning" agent to control the flow of softened glass powder during high-temperature sintering, reducing thermal stress caused by excessive dissolution of the microcrystalline glass surface and minimizing microcrack formation. Because of its smooth, flat, and crack-free surface and strong adhesion, the resistivity changes within 5% after repeated thermal shocks, meeting the application requirements at a working temperature of 400℃. The results of Examples 4 and 5 are the same as those of Example 1 and will not be repeated here.

[0083] A comparison of Examples 1 and 2 shows that increasing the content of composite glass powder can increase the sheet resistance of the resistive paste. However, as the content of composite glass powder increases, the resistance to thermal shock does not increase. This is because the increased glass powder content increases the stress on the surface of the microcrystalline board, increasing the probability of microcracks. Therefore, in circuit design, prioritizing resistive pastes with lower sheet resistance can achieve better operational stability.

[0084] A comparison of Examples 2 and 3 revealed that increasing the palladium powder content can reduce the temperature coefficient of resistance. Simultaneously, due to the poor conductivity of palladium powder, the sheet resistance is significantly improved, while its resistance to thermal shock remains largely unchanged. Based on this principle, a series of resistance pastes with varying temperature coefficients of resistance can be developed.

[0085] A comparison of Example 2 and Comparative Example 1 revealed that, with all other components identical, using different silver powders yielded different application results. The resistive paste prepared with silver powder having a smaller particle size and a larger specific surface area was prone to surface detachment. This is because a larger specific surface area of ​​the silver powder results in greater shrinkage during sintering, making it more susceptible to stress concentration in the resistive circuit, leading to partial detachment and a sharp decline in resistance to current surges.

[0086] By comparing Comparative Example 2 with Comparative Example 1, it was found that when all other components were exactly the same, the detachment phenomenon was more obvious when only low-expansion glass component A was used. This is because without the "pinning" effect of high-melting-point silica microparticles, stress is more easily concentrated, resulting in more obvious detachment and relatively poor resistance to current impact.

[0087] By comparing Example 2 and Comparative Example 3, it was found that Comparative Example 3 used microcrystalline silver powder with high specific surface area and small particle size to match high thermal expansion glass. However, it could not be matched with microcrystalline glass, resulting in many appearance defects on the surface and failing to meet application requirements.

[0088] also, Figure 1 The figure shows the surface state of the resistive paste obtained in Example 2 of the present invention after sintering. As can be seen from the figure, the resistive paste obtained by the present invention has a smooth and flat surface after sintering. Figure 2 , Figure 3 , Figure 4 The images show the surface states of the resistive slurries prepared in Comparative Examples 1, 2, and 3 after sintering, and all of them have obvious surface defects.

[0089] Based on the above embodiments and comparative examples, it is evident that spherical silver powder with large particle size, high tap, and low specific surface area is more suitable as a conductive functional phase in microcrystalline thick-film resistors due to its lower shrinkage rate during high-temperature sintering. Adding high-melting-point powders with a "pinning" effect, such as silicon micropowder, helps reduce the flow of low-thermal-expansion glass powder during sintering, thus achieving similar low-shrinkage characteristics. This helps reduce appearance defects in the microcrystalline glass thick-film resistor and improves its resistance to current surges. Such high-melting-point powders include, but are not limited to, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and silicon carbide. It is also required that these powders have small particle sizes and uniform particle size distribution to avoid causing open circuits or other effects on the thick-film resistor. Microcrystalline thick-film resistors with lower glass powder content have better current-carrying capacity.

[0090] This invention provides a high-temperature resistive paste for microcrystalline glass heating plates. Through the synergistic effect of its components, its temperature coefficient of resistance ranges from 300ppm / °C to 3000ppm / °C, its sheet resistance ranges from 10 milliohms / square to 300 milliohms / square, and its maximum operating temperature can reach over 400°C. After 1000 hours of long-term testing, the power attenuation is less than 5%. Furthermore, this high-temperature resistive paste for microcrystalline glass exhibits good compatibility with high-temperature conductive pastes for microcrystalline glass. At the overlap, excessive film thickness will not cause open circuits or cracks, and the overlap will not fail due to current surges, thus not affecting the long-term service life of the microcrystalline glass heating plate.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-temperature resistance paste for microcrystalline glass heating plates, characterized in that, By weight percentage, it includes silver powder: 45-75%; palladium powder: 1-5%; composite glass powder: 5-30%; and organic carrier: 18-20%. The composite glass powder comprises component A and component B in a mass ratio of 1 to 3:1; Component B is silica powder; component A, by mass percentage, comprises: silicon dioxide: 30-45%; boric acid: 8-15%; magnesium oxide: 15-18%. Alumina: 10-15%; Bismuth oxide: 5-10%; Sodium carbonate: 0.01-3%; Lithium oxide: 0.01-1%; The silver powder has an average particle size of 2-3 micrometers, a tap density of 5.0-6.5 g / ml, and a specific surface area of ​​0.4-0.7 m². 2 / g; the palladium powder is ultrafine palladium powder with an average particle size of 0.25~0.3 micrometers; The coefficient of thermal expansion of the composite glass powder is 3.5~5. 10 -6 / K, softening point is 750~780℃.

2. The high-temperature resistance paste for a microcrystalline glass heating plate according to claim 1, characterized in that, The silicon micropowder is composed of silicon dioxide with a purity of 99.9%, an average particle size of 0.5 to 1 micrometer, and a maximum particle size of no more than 2 micrometers.

3. The high-temperature resistance paste for a microcrystalline glass heating plate according to claim 1, characterized in that, The organic carrier comprises, by mass percentage, 25-35% decyl alcohol ester, 20-30% butyl carbitol, 10-20% butyl carbitol acetate, 3-6% γ-butyrolactone, 1-5% Span 85, and 2-6% ethyl cellulose std45. Each component is boiled at 80°C for 4-6 hours to form a uniform and transparent organic solvent, which is then filtered through a 300-mesh polyester screen.

4. A high-temperature resistance paste for a microcrystalline glass heating plate according to any one of claims 1 to 3, characterized in that, The viscosity of the resistive slurry is 140~180 Pa·s, and the fineness is no more than 15 micrometers.

5. A method for preparing a high-temperature resistance paste for a microcrystalline glass heating plate according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) First, mix component A of the composite glass powder evenly using a mixer. Then, using a platinum crucible, melt the mixture in a high-temperature melting furnace. Hold the temperature at 300℃ for 15 minutes, then raise the temperature to 900℃ and hold for 15 minutes. Finally, raise the temperature to 1500℃ and hold for 1 hour. Water quench the mixture. 2) After mixing component A and component B in a certain proportion, the mixture is ball-milled to obtain a composite glass powder with a low coefficient of thermal expansion and a high softening point. The composite glass powder, silver powder, palladium powder and organic carrier are mixed evenly according to the proportion, and rolled 4 to 6 times with a three-roll mill to make its fineness less than 15 micrometers. By adjusting the ratio of solid phase and liquid phase, a high-temperature resistance paste for microcrystalline glass heating plates with a viscosity of 140 to 180 Pa·s is obtained.

6. A sintering process for a high-temperature resistance paste for a microcrystalline glass heating plate, characterized in that, A high-temperature resistive paste as described in any one of claims 1-4 is printed onto the surface of a microcrystalline glass heating substrate, and then dried and sintered sequentially to obtain a resistive film for a microcrystalline glass heating plate.

7. The sintering process of high-temperature resistance paste for microcrystalline glass heating plates according to claim 6, characterized in that, The peak sintering temperature is 800~850℃, the peak holding time is 5~10min, the entire sintering cycle is 30~60min, and the sintered film thickness is 12~18 micrometers.

8. The sintering process of high-temperature resistance paste for a microcrystalline glass heating plate according to claim 6, characterized in that, Printing is done using a 200-250 mesh stainless steel composite screen.

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