A method for manufacturing a curved substrate direct printing type ceramic heating element

Abstract

The application discloses a preparation method of a curved surface substrate direct printing type ceramic heating body and belongs to the technical field of ceramic electric heating element processing. The preparation method uses a completely high-temperature sintered alumina or ZTA ceramic round rod as a processing substrate, polishes, cleans and activates the processing substrate after pretreatment, adopts a curved surface pad printing process to form a 5-20-micron-thick film conductive electrode in a special-shaped area at the end of the substrate, and then prepares a 50-300-micron high-precision heating line on the ceramic curved surface through a piezoelectric inkjet direct printing process and is formed after low-temperature segmented curing at 120-200 DEG C. The preparation method discards the traditional plane printing secondary bonding process, eliminates the bonding and composite interface, simplifies the process flow, improves the bonding strength of the line and the substrate, has strong conductive reliability of the end thick film electrode, has no cold and hot cycle delamination risk, can support the assembly of embedded brazing electrodes, is suitable for efficient mass production of ceramic heating bodies of various specifications.

Description

Technical Field

[0001] This invention belongs to the field of precision machining technology of ceramic heating elements, specifically relating to a method for preparing a ceramic heating element with direct printing on a curved substrate. This heating element can be widely used in household heating appliances, industrial precision heating equipment, constant temperature control instruments and other scenarios. Background Technology

[0002] Ceramic heating elements, with their superior insulation properties, rapid heating, high temperature resistance, strong thermal stability, and long service life, are currently the core consumables in the field of electric heating elements and are widely used in various civilian and industrial heating equipment. At present, the mainstream process for preparing curved ceramic heating elements in the industry is the planar casting and printing composite process. Its core technical solution is as follows: first, prepare ceramic casting green sheets; then, use screen printing to print complete heating circuits on the flat surface of the green sheet; after low-temperature drying and shaping, manually wrap and attach the casting sheet carrying the circuit to the outer wall of the ceramic cylindrical green sheet; finally, use tooling to fix it and send the whole assembly into a high-temperature sintering furnace to achieve co-firing and composite molding of the green body and the circuit.

[0003] The above method can mass-produce conventional cylindrical ceramic heating rods, meeting the basic temperature control and heating requirements of low-end heating products. The molding process is mature and the entry cost is low. However, after long-term industrial production and operational reliability verification, this inherent process has unavoidable structural defects, which seriously restrict the performance upgrade and application expansion of high-end ceramic heating elements.

[0004] Firstly, the interface defects are prominent, resulting in high thermal resistance and a tendency for delamination. During the bonding process between the cast sheet and the curved surface of the ceramic rod, air is easily trapped in the gap between the curved surfaces. After sintering, these air bubbles remain permanently at the composite interface, significantly increasing the interfacial thermal resistance and leading to uneven heat conduction and large surface temperature differences in the heating element. Simultaneously, the heating circuit and the ceramic substrate are bonded together using the cast layer, resulting in extremely low interfacial bonding strength. After prolonged operation under hot and cold cycles, the bonding interface is prone to peeling, delamination, and circuit detachment, significantly shortening the product's lifespan.

[0005] Secondly, its adaptability to curved surfaces is extremely poor, limiting its application scenarios. The flexibility of the cast film itself is limited, and it can only adapt to regular standard cylindrical curved surfaces. It cannot be fitted and shaped at all for irregular ceramic substrates with openings, grooves, and steps, large curvature irregular arc surfaces, and ceramic inner wall circuit processing scenarios. The product design freedom is extremely low, making it difficult to adapt to diversified and customized heating needs.

[0006] Third, the production process is cumbersome and inefficient. Traditional processes involve multiple steps, such as casting, flat screen printing, sheet cutting, curved surface lamination, tooling fixation, and high-temperature co-firing. These steps are redundant and complicated, with many intermediate transfers and manual adjustments. This not only occupies a large amount of production equipment and space but also significantly lengthens the production cycle and increases production and labor costs.

[0007] Fourth, the reliability of electrode connections is insufficient. The end electrodes of the traditional process rely on the overlap of the conductive layer at the edge of the cast film to form the electrode. The conductive layer is extremely thin and is prone to overheating and burning under high current and high power conditions. This makes it impossible to meet the assembly requirements of embedded brazed electrodes and is difficult to adapt to the usage standards of high-end high-power heating equipment.

[0008] Existing technologies include some improvements, such as direct screen printing on the surface of sintered ceramic substrates to avoid some defects associated with tape casting. However, screen printing relies on custom-made screens, resulting in high screen production costs and low changeover efficiency for small-batch, multi-specification products. Furthermore, the precision of screen printing is limited, with the minimum line width only exceeding 300μm, making it unsuitable for precision temperature control scenarios. More importantly, the screen squeegee cannot adapt to structures with varying heights, such as end openings or steps, preventing the electrode contacts from being thickened and thus failing to address the core issues of unstable and easily failed connections on complex curved surfaces. Summary of the Invention

[0009] This invention addresses many technical defects in existing curved ceramic heating element manufacturing processes, aiming to overcome problems such as residual interface bubbles, high thermal resistance, low bonding strength between the substrate and circuit, easy delamination during hot and cold cycles, and insufficient conductivity stability of the end electrodes caused by traditional planar casting printing bonding sintering processes.

[0010] The core innovation of this invention lies in its dual-process composite printing system: firstly, a curved surface pad printing technology for localized thick-film forming, utilizing the adaptive bonding characteristics of a flexible silicone pad printing head to adapt to irregularly shaped areas with height differences of 0.3~2mm at the ends, creating electrode contacts with high thickness, high conductivity, and high adhesion, providing a reliable electrical interface for the heating circuit; secondly, piezoelectric inkjet direct printing of precision circuits on curved surfaces, eliminating the need for customized screens and allowing direct forming of high-precision conformal heating circuits on sintered ceramic curved surfaces. This invention achieves a seamless integration of the heating circuit and the ceramic substrate through sintered substrate pretreatment and integrated curved surface direct printing, overcoming the structural limitations of traditional processes.

[0011] This invention abandons the traditional secondary bonding process and uses a fully high-temperature sintered ceramic curved surface substrate as the processing base. It adopts a composite printing scheme that combines curved surface pad printing and piezoelectric inkjet direct printing to directly form high-reliability electrode contacts and high-precision heating circuits on the ceramic curved surface. This can completely eliminate the adhesive composite interface, simplify the production process, and simultaneously improve the structural strength and thermal conductivity uniformity of the heating element. It also enables stable assembly of embedded brazed electrodes, which can meet the needs of high-end precision heating equipment.

[0012] The specific technical solution is as follows: A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Preparation of ceramic rod blanks, wherein the blank material is alumina or ZTA ceramic, and the blank is a cylindrical matrix with openings, grooves or stepped areas at the ends for forming electrode contacts; S2 substrate surface pretreatment: The outer surface of the blank is mechanically polished to make the surface roughness Ra≤0.8μm. After polishing, ultrasonic cleaning is used to remove surface dust and oil stains to obtain a clean and flat activated substrate. S3 Curved surface pad printing for conductive connection points at the ends: Using a silicone pad printing head and conductive paste, the ends of ceramic rods are coated with curved surface pad printing to form thick film conductive electrode contacts with a thickness of 5~20μm. After pad printing, the contacts are pre-baked at 80~100℃ for 5~10min to set the shape. S4 Piezoelectric Inkjet Direct Printing of Precision Heating Circuit on Curved Surface: It adopts a 3-axis or 4-axis motion platform equipped with an industrial piezoelectric printhead to directly print the heating circuit on the polished ceramic curved surface with conductive ink. The line width is controlled at 50~300μm, and the motion platform adjusts the distance between the printhead and the curved surface in real time. S5 Low-Temperature Curing and Drying: Two-stage temperature-controlled drying, first pre-drying at 80~100℃ for 5~10 minutes to set the circuit, then curing at 120~200℃ for 30~60 minutes to remove the slurry solvent and organic adhesive, thereby forming a continuous and stable conductive network. S6 conducts electrical performance tests, and qualified products are selectively coated with insulating protective glaze or functional coating.

[0013] Furthermore, the surface roughness of mechanically polished components in S2 is 0.4~0.6μm. Under these conditions, both substrate flatness and slurry adhesion are considered, effectively improving circuit uniformity and bonding strength, and meeting the long-term operating requirements of high-power, high-stability heating elements.

[0014] Furthermore, the S2 substrate surface pretreatment also includes at least one of the following auxiliary treatments: plasma cleaning to enhance the chemical activity of the substrate surface, and laser roughening treatment to construct a surface micro-anchoring structure; through the auxiliary treatments, the wettability and mechanical bonding force between the conductive ink and the ceramic substrate are improved, reducing the risk of circuit detachment and debonding during thermal cycling.

[0015] Furthermore, the curved surface transfer printing described in S3 involves single or multiple stacked transfer printing processes to fill irregularly shaped areas with a height difference of 0.3~2mm at the ceramic end, forming electrode contacts. Under these conditions, it is possible to ensure that the electrode forming is dense and defect-free, effectively reducing electrode contact resistance and significantly improving the conductivity reliability and current carrying capacity of the end electrical connection.

[0016] Furthermore, in S3, the curved surface pad printing process involves two stacking operations, resulting in a conductive electrode contact thickness of 10-12 μm. Under these conditions, the current-carrying capacity of the electrode can be balanced with the processing efficiency, avoiding the defects of insufficient current carrying capacity and easy melting at high power when the electrode is too thin, as well as the reduced adhesion and easy detachment of the electrode when it is too thick.

[0017] Furthermore, the industrial piezoelectric printhead mentioned in S4 is selected from any one of Dimatix, Konica, or Epson PrecisionCore industrial printheads, and the conductive ink is a silver-containing conductive ink with a viscosity of 8~15 cP, a surface tension of 28~35 mN / m, and a solid particle size of <100 nm.

[0018] Furthermore, the S4 piezoelectric inkjet printer employs multiple scanning printing, which improves the overall thickness and conductivity uniformity of the heating circuit by stacking multiple layers of circuits, reduces the overall resistance of the circuit, reduces heat loss under high power conditions, and improves heating efficiency and operating stability.

[0019] Furthermore, the sintering temperature of the S1 ceramic rod blank is 1650~1700℃, and the holding time is 2~3h. These sintering parameters can ensure that the ceramic matrix is ​​dense and non-porous, has high structural strength and excellent thermal stability, and provides a stable and reliable substrate support for subsequent high-precision printing processing of curved surfaces.

[0020] Furthermore, the S5 low-temperature curing process is conducted at temperatures below the phase transition temperature of the ceramic matrix, with a curing temperature of 150~160℃ and a curing time of 40~50 minutes. Under these conditions, the nano-conductive particles can be fully sintered and overlapped, resulting in optimal conductive network density and strong resistance stability over long-term use.

[0021] This invention also protects a direct-printed ceramic heating element on a curved substrate, which is prepared using the aforementioned method.

[0022] Furthermore, the ceramic heating element undergoes more than 500 cycles of hot and cold cycling without delamination, peeling, or open circuit failure. Its overall resistance at room temperature remains stable at 8.5~13Ω, its electrode contact resistance is ≤0.3Ω, and it shows no breakdown in a 1000V withstand voltage test.

[0023] Beneficial effects First, this invention uses a fully sintered ceramic substrate as the direct printing base, eliminating the redundant processes of traditional methods such as casting sheet preparation, thin sheet cutting, curved surface lamination, tooling fixation, and co-firing. This simplifies the overall process. Traditional methods require two separate processing systems for both green body sintering and casting sheet forming, resulting in cumbersome process connections and significant equipment investment. This invention retains only a single sintering process for the ceramic substrate, with subsequent printing and curing processes highly integrated. This significantly reduces intermediate transfer and manual adjustment steps, effectively shortening the production cycle, lowering equipment and labor costs, and significantly improving production efficiency.

[0024] Secondly, this invention directly prints conductive circuitry onto the polished curved surface of the ceramic, eliminating the need for an organic adhesive layer and a casting composite interface between the heating circuit and the ceramic substrate. This achieves a truly interface-free, integrated bond, significantly improving the bonding strength between the circuitry and the substrate compared to traditional processes. During the curing process, the conductive paste directly wets the activated ceramic surface, and the metal particles form a mechanical anchor and molecular-level interface bond with the ceramic substrate. There is no layered sandwich structure, preventing interface peeling, bubble debonding, or other defects under long-term thermal cycling. Simultaneously, it completely eliminates the additional thermal resistance caused by the air layer at the traditional composite interface, allowing heat to be uniformly conducted and diffused along the ceramic substrate, greatly improving the temperature uniformity and heating stability of the heating element across its entire surface.

[0025] Furthermore, this invention employs a composite printing scheme combining curved surface pad printing and piezoelectric inkjet printing, significantly expanding the range of curved surfaces that the ceramic heating element can adapt to. The curved surface pad printing process can precisely fill areas with height differences of 0.3~2mm, such as end openings, steps, and grooves, forming thick-film electrodes with complete structures and excellent conductivity. The piezoelectric inkjet printing, relying on a multi-axis adaptive motion platform, can follow the curved surface contour to print irregular heating trajectories such as spirals, variable linewidths, and segmented curves. This process is suitable for standard cylindrical ceramic rods as well as processing large-curvature arcs and irregular irregular curved surfaces. It also supports printing circuitry on the inner wall of ceramics, effectively supporting the implementation of embedded brazing electrode assembly schemes, completely overcoming the application limitations of traditional tape-bonding processes, which can only adapt to simple cylindrical curved surfaces.

[0026] Furthermore, the piezoelectric inkjet direct printing process used in this invention eliminates the need for customized screen printing stencils. The equipment can quickly switch between different heating circuit design drawings without changing tooling molds, making it adaptable to the production needs of small batches, multiple specifications, and customized heating elements, demonstrating extremely strong flexible production capabilities. Simultaneously, the minimum linewidth of inkjet-printed lines can reach 50μm, compared to the traditional screen printing minimum linewidth of 300μm, resulting in several times improved line accuracy and enabling high-density, zoned, independently temperature-controlled precision circuit layouts. Moreover, the conductive ink particles used in piezoelectric inkjet printing have high utilization rates, eliminating ink waste and significantly improving material utilization compared to traditional screen printing, effectively reducing raw material loss costs.

[0027] Furthermore, this invention utilizes curved surface pad printing to form 5-20μm thick conductive electrode contacts. The electrode thickness is significantly greater than that of traditional cast sheet electrodes, resulting in a substantial increase in current carrying capacity. This makes the electrodes less prone to overheating, oxidation, and melting under high power and high current conditions. Simultaneously, the thick-film electrode seamlessly connects to the inkjet precision heating circuitry, ensuring a tight and stable electrical connection with extremely low contact resistance. This completely solves the problems of loose connections, poor contact, and easy circuit breaks associated with traditional electrodes, significantly improving the service life and operational stability of high-power heating equipment.

[0028] Finally, the overall curing temperature of this invention is controlled within a low-temperature range of 120~200℃, far below the sintering phase transformation temperature of alumina and ZTA ceramics. This ensures that the processing does not cause thermal damage to the formed ceramic matrix, effectively avoiding problems such as matrix cracking, deformation, and performance degradation, resulting in a significant improvement in finished product yield. Simultaneously, the matrix pretreatment stage allows for flexible selection of plasma activation and laser micro-roughening auxiliary processes based on product power and application scenarios, precisely adapting to product production with different adhesion and stability requirements, demonstrating extremely strong process adaptability and versatility.

[0029] In summary, the preparation method provided by this invention has the combined advantages of high production efficiency, long product lifespan, high design freedom, low processing cost, and good working condition stability, and has extremely high industrialization and promotion value. Detailed Implementation

[0030] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. In the following embodiments, unless otherwise explicitly stated, "%" refers to weight percentage.

[0031] The following testing methods are included: 1. Thermal cycling reliability test: Referring to the industry standard JB / T4088-2022 "Daily Use Tubular Electric Heating Elements", the test was conducted using a high and low temperature cycling test chamber. The single cycle procedure was as follows: the temperature was raised from room temperature to 200℃ and held for 10 minutes, then naturally cooled to room temperature and left to stand for 10 minutes, which was recorded as one thermal cycle. After the cycle was completed, the sample was observed to see if there were any faults such as delamination, peeling, wire detachment, or open circuit, and the number of valid cycles was counted.

[0032] 2. Conductivity test: Using a high-precision digital milliohm meter, under constant temperature and humidity conditions of 25℃ and 50%, the overall resistance of the heating element and the contact resistance between the electrodes and the circuit are tested. Each sample is tested 5 times and the average value is taken. The smaller the resistance value and the smaller the fluctuation range, the better the conductivity and the uniformity of the circuit.

[0033] 3. Adhesion test: Referring to GB / T9286-1998 "Cross-cut test of paint and varnish film", a cross-cut tester is used to perform a cross-cut test on the product surface, observe the detachment of the lines, and determine the bonding strength between the substrate and the conductive lines.

[0034] 4. Insulation performance test: A withstand voltage tester is used to apply a 1000V AC voltage for 1 minute to test the insulation breakdown of the sample and determine the insulation safety of the product.

[0035] The conductive pastes and conductive inks used in the following examples and comparative examples are all industrial-grade raw materials; the conductive paste is a tungsten-containing paste. As an example, the composition of the conductive paste is as follows: 78% solid powder in total, including: 62% tungsten powder W (D50 0.8–1.2μm), 14% molybdenum powder Mo (D50 1.0–1.5μm), 1.8% alumina micro powder Al2O3 (96%, matching green shrinkage), and 0.2% manganese dioxide MnO2 (interface wetting, enhancing adhesion); 22% organic carrier in total, including: 3.2% ethyl cellulose EC (bonding resin), 14.5% terpineol (main solvent), 3.5% diethylene glycol butyl ether (slow drying, anti-clogging mesh), 0.6% oleic acid (dispersion / anti-settling), and 0.2% silane coupling agent (powder wetting). The conductive ink is a commercially available ink. Any conductive ink that meets the requirements of viscosity 8~15cP, surface tension 28~35mN / m, and solid particle size <100nm is acceptable. For example, you can purchase the monomer silver conductive ink from Yurui Chemical. The insulating protective glaze is a commercially available silicone high-temperature resistant insulating varnish, such as the high-temperature resistant varnish from Guangzhou Kaige Coatings Co., Ltd.

[0036] In this invention, ZTA ceramic refers to zirconia-toughened alumina ceramic, which is a composite ceramic material with alumina as the matrix and toughening achieved through zirconia phase transformation. It is a commercially available material.

[0037] Example 1 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Alumina ceramic cylindrical blanks with a diameter of 10 mm and a 1 mm deep perforated step structure at the end were prepared by extrusion molding. The blanks were then sent into a high-temperature sintering furnace at 1650℃ and held for 2 hours to obtain a dense, non-porous, and structurally stable alumina ceramic cylindrical blank matrix.

[0038] S2 substrate surface pretreatment: The outer surface of the sintered ceramic rod is mechanically polished to control the surface roughness Ra=0.8μm; after polishing, it is immersed in anhydrous ethanol for ultrasonic cleaning for 15min to thoroughly remove surface polishing dust, oil and impurities; then plasma cleaning is performed for 5min to improve the surface activity of the ceramic substrate and enhance the wettability of subsequent slurry.

[0039] S3 curved surface pad printing for conductive connection points at the ends: A flexible silicone pad printing head is used in conjunction with a highly conductive paste to perform a single curved surface pad printing on the irregularly shaped area of ​​the opening step at the end of the ceramic rod, forming a uniform thick film conductive electrode contact with a thickness of 5μm; after the pad printing is completed, it is sent to an oven and pre-baked at 80℃ for 10 minutes to set the shape, preventing the subsequent inkjet process from smearing the electrode and damaging the contact structure.

[0040] S4 Piezoelectric Inkjet Direct Printing of Precision Heating Circuit on Curved Surface: It adopts a 3-axis motion platform equipped with a Dimatix industrial piezoelectric printhead and uses single-cell silver conductive ink; the printhead moves at a constant speed along the spiral trajectory of the ceramic cylindrical curved surface with the three-axis platform, directly printing a precision heating circuit with a line width of 50μm. A complete and continuous circuit can be formed in a single scan, without any breaks or offsets.

[0041] S5 Low-Temperature Curing and Drying: It adopts a segmented temperature-controlled curing mode. First, it is pre-baked at 80℃ for 10 minutes to complete the initial shaping of the circuit. Then, it is heated to 120℃ for main curing for 60 minutes to completely evaporate the solvent and organic binder inside the ink, so as to promote the full sintering and overlapping of the nano-silver particles and form a continuous and stable conductive network. The curing temperature throughout the process should be far lower than the phase transformation temperature of alumina ceramics, so that the substrate is free from cracking, deformation and performance degradation.

[0042] S6 Finished Product Inspection and Protection: After the sample has cooled to room temperature naturally, resistance, withstand voltage insulation, adhesion, and thermal cycling performance tests are conducted to screen qualified products; a layer of insulating protective glaze is uniformly coated on the outer surface of the finished product to improve the product's insulation protection and oxidation resistance.

[0043] In this embodiment, the polishing process yields a surface roughness of Ra=0.8μm, which provides sufficient adhesion for the slurry. The plasma activation process ensures that the conductive slurry fully wets the ceramic substrate surface, balancing processing efficiency and adhesion stability. The 5μm single-layer pad printing electrode meets the conductivity requirements of conventional low-power heating elements, and the electrode is thin and uniformly formed. The 120℃ low-temperature curing process completely removes organic impurities, leaving no residual contaminants and preventing aging and failure of the circuit over long-term use. The 50μm ultra-fine inkjet circuit enables a high-density, refined heating layout with higher temperature control accuracy.

[0044] Performance testing showed that the sample in this embodiment had an average resistance of 12.8Ω at room temperature, a contact resistance of only 0.3Ω between the electrode and the circuit, and a resistance fluctuation error of ≤0.2Ω, demonstrating excellent conductivity uniformity. After 500 cycles of thermal cycling, the sample showed no delamination, peeling, or circuit detachment, with a resistance fluctuation of less than 5%, indicating excellent conductivity stability. Furthermore, the circuit detached completely during the cross-cut adhesion test, and the adhesion between the substrate and the circuit fully met the standards. The insulation withstand voltage was 1000V / 1min without breakdown, demonstrating good overall safety in use.

[0045] Example 2 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: ZTA ceramic round rod blanks with a diameter of 12 mm and a 1.2 mm deep opening step structure at the end were prepared by hot pressing casting process; the blanks were sent into a high-temperature sintering furnace at 1700℃ and held for 2.5 h to obtain a dense and high-toughness ZTA ceramic matrix.

[0046] S2 substrate surface pretreatment: The outer surface of the ceramic substrate is mechanically polished to control the surface roughness Ra=0.6μm; after polishing, it is ultrasonically cleaned with pure water for 20min to remove surface oil and dust impurities; plasma cleaning for 8min is performed in sequence to improve surface activity and laser micro-roughening treatment to form a micro-anchoring structure on the ceramic surface, which greatly enhances the bonding force of conductive paste.

[0047] S3 curved surface pad printing for conductive connection points at the ends: A flexible silicone pad printing head is used in conjunction with conductive paste to perform two superimposed curved surface pad printings on the end opening step area to form a thick film conductive electrode contact with a total thickness of 12μm; after the pad printing is completed, it is pre-baked at 90℃ for 8 minutes to set the shape and ensure that the electrode structure is flat and dense.

[0048] S4 Piezoelectric Inkjet Direct Printing of Precision Heating Circuit on Curved Surface: It adopts a 4-axis motion platform equipped with Konica industrial piezoelectric printheads and matches single-cell silver conductive ink; relying on the curved surface adaptive adjustment capability of the four-axis platform, the heating circuit is printed along the ceramic curved surface in a segmented variable line width trajectory with a line width of 180μm. The thickness and conductivity uniformity of the line are improved by scanning twice.

[0049] S5 Low-Temperature Curing and Drying: Segmented temperature control treatment, 90℃ pre-baking for 8 minutes to set the circuit shape, 160℃ main curing for 45 minutes, the nano copper particles are fully sintered and overlapped to form a low-resistance, high-stability conductive network.

[0050] S6 Finished Product Inspection and Protection: After cooling, various performance tests are completed. As in Example 1, qualified products are coated with insulating protective glaze to complete the finished product preparation.

[0051] In this embodiment, the dual pretreatment of laser micro-roughening and plasma activation achieves a combination of chemical wetting and mechanical anchoring, resulting in good adhesion of the circuit. The four-axis motion platform can adapt to slightly irregular curved surfaces, resulting in good product adaptability and heat generation uniformity.

[0052] The performance test results of the finished product show that the average resistance of the sample at room temperature is 10.2Ω, the electrode contact resistance is 0.15Ω, the resistance fluctuation is ≤0.1Ω, and the conductivity is excellent. After 800 consecutive thermal cycles, the resistance fluctuation is only 2.8%, with no delamination, no open circuit, no oxidation failure, and no breakdown phenomenon in the insulation withstand voltage test. It has both conductivity, structural stability and safety performance.

[0053] Example 3 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Alumina ceramic cylindrical blanks with a diameter of 15 mm and a 2 mm deep pre-reserved perforated stepped structure at the end were prepared by extrusion molding. The blanks were then fed into a high-temperature sintering furnace at 1680℃ and held for 3 hours to obtain a high-density, high-stability high-power adaptable ceramic matrix.

[0054] S2 substrate surface pretreatment: The substrate surface is finely mechanically polished to control the surface roughness Ra=0.4μm; after polishing, it is ultrasonically cleaned with anhydrous ethanol for 20min to thoroughly remove microscopic dust impurities; and then plasma cleaning is completed for 10min to maximize the chemical activity of the ceramic surface.

[0055] S3 curved surface pad printing end conductive connection point: A silicone pad printing head is used with conductive paste to form an ultra-thick film conductive electrode contact with a total thickness of 20μm through three-layer pad printing; after pad printing, it is pre-baked at 100℃ for 5 minutes for rapid shaping, which improves processing efficiency.

[0056] S4 Piezoelectric Inkjet Direct Printing Precision Heating Circuit on Curved Surface: It adopts a 4-axis motion platform equipped with Epson PrecisionCore piezoelectric printhead and selects single-component silver conductive ink; it prints a 300μm wide heating circuit along the spiral trajectory of the ceramic curved surface, and the circuit is thickened by three scans to meet the high power heating requirements.

[0057] S5 Low-Temperature Curing and Drying: First, pre-bake at 100℃ for 5 minutes to set the shape, then cure at 200℃ for 30 minutes to quickly complete the sintering and molding of nano-silver particles, completely volatilize the organic components, and make the conductive network dense and stable.

[0058] S6 Finished Product Inspection and Protection: After cooling, electrical performance and reliability tests are completed. As in Example 1, qualified products are coated with insulating protective glaze to obtain high-power ceramic heating element finished products.

[0059] In this embodiment, the 20μm ultra-thick film electrode contacts have extremely strong current carrying capacity and can withstand large current impacts, eliminating electrode ablation and melting problems under high power conditions; the 200℃ high temperature rapid curing can significantly shorten production time and improve mass production efficiency; the 300μm wide circuit can effectively reduce circuit resistance and improve heating power and thermal conductivity.

[0060] The performance test results of the finished product show that the average resistance of the sample at room temperature is 8.5Ω, the electrode contact resistance is 0.1Ω, and the conductivity loss is extremely low. After 1000 consecutive hot and cold cycles, the resistance fluctuation is only 3.5%, and no structural failure occurs. It can be used in high-end high-power heating equipment.

[0061] Example 4 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Alumina ceramic rods with a diameter of 10 mm were prepared by extrusion molding, with a 1 mm opening step reserved at the end. The rods were sintered at 1650℃ for 2 hours to obtain a dense sintered matrix.

[0062] S2 substrate surface pretreatment: The substrate surface is polished to Ra=0.6μm, ultrasonically cleaned with ethanol for 15min, and plasma cleaned for 5min to complete the activation treatment.

[0063] S3 curved surface pad printing end conductive connection point: A silicone pad printing head is used with conductive paste to form a 12μm thick electrode by pad printing twice, and it is pre-baked at 90℃ for 8 minutes to set the shape.

[0064] S4 Piezoelectric Inkjet Direct Printing Precision Heating Circuit for Curved Surfaces: It adopts a three-axis motion platform equipped with a Dimatix piezoelectric printhead, uses single-cell silver conductive ink, and prints a 180μm spiral heating circuit in a single scan; the three-axis platform can be adapted to standard regular cylindrical curved surfaces.

[0065] S5 Low-Temperature Curing and Drying: First, pre-dry at 90℃ for 8 minutes, then main cure at 160℃ for 45 minutes to complete the conductive network formation.

[0066] S6 Finished Product Inspection and Protection: Same as in Example 1, after passing the performance test, an insulating protective glaze is applied to obtain the finished product.

[0067] The sample was tested and found to have an average resistance of 10.5Ω at room temperature. After 700 cycles of hot and cold cycling, there was no delamination or open circuit failure, and the performance remained stable.

[0068] Example 5 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 ceramic matrix forming and high-temperature sintering: ZTA ceramic rods with a diameter of 12mm were prepared by hot pressing and casting process, with a 1.2mm opening step reserved at the end. The rods were sintered at 1700℃ for 2.5h to obtain a dense sintered matrix.

[0069] S2 substrate surface pretreatment: The substrate surface is polished to Ra=0.6μm, ultrasonically cleaned with pure water for 20min, and plasma cleaned for 8min to complete the activation treatment, omitting the laser micro-roughening process.

[0070] S3 curved surface pad printing end conductive connection point: A silicone pad printing head is used with conductive paste to form a 12μm thick electrode by pad printing twice, and it is pre-baked at 90℃ for 8 minutes to set the shape.

[0071] S4 Piezoelectric Inkjet Direct Printing Precision Heating Circuit for Curved Surfaces: It adopts a four-axis motion platform equipped with a Konica piezoelectric printhead, uses single-component silver conductive ink, and performs two scans to thicken and form a 180μm spiral heating circuit; the four-axis platform can adapt to standard regular cylindrical curved surfaces, ensuring the printing accuracy of curved surfaces.

[0072] S5 Low-Temperature Curing and Drying: First, pre-dry at 90℃ for 8 minutes, then main cure at 160℃ for 45 minutes to complete the conductive network formation.

[0073] S6 Finished Product Inspection and Protection: After passing the performance test, an insulating protective glaze is applied to obtain the finished product.

[0074] Testing revealed that this embodiment lacked the mechanical anchoring effect brought about by laser micro-roughening, resulting in a slight decrease in the physical bonding strength between the circuit and the substrate. The average resistance of the sample at room temperature was 10.6Ω. After 600 cycles of thermal cycling, a slight debonding trend was observed in some circuits, and the resistance fluctuation increased to 6.2%. The conductivity uniformity and structural stability were lower than those of Example 2, but the overall performance could meet the needs of conventional low- to mid-range heating products.

[0075] Example 6 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Alumina ceramic rods with a diameter of 12 mm were prepared by extrusion molding without any additional openings or steps. The rods were sintered at 1680℃ for 2.5 h to obtain a dense sintered matrix.

[0076] S2 substrate surface pretreatment: The substrate surface is polished to Ra=0.6μm, and a full set of pretreatment processes including conventional ultrasonic cleaning, plasma cleaning and activation, and laser micro-roughening are completed to ensure the cleanliness and bonding activity of the substrate surface.

[0077] S3 curved surface pad printing end conductive connection point: using a silicone pad printing head with conductive paste, a single pad printing of an 8μm thick electrode is formed, and pre-baked at 90℃ for 8 minutes to set the shape.

[0078] S4 Piezoelectric Inkjet Direct Printing Precision Heating Circuit for Curved Surfaces: It adopts a four-axis motion platform equipped with a piezoelectric printhead, uses single-component silver conductive ink, and performs two scans to thicken and form a 180μm spiral heating circuit; the four-axis platform can accurately adapt to cylindrical curved surfaces to ensure the uniformity of the heating circuit formation.

[0079] S5 Low-Temperature Curing and Drying: Directly cure at 160℃ for 45 minutes to complete the formation of the conductive network.

[0080] S6 Finished Product Inspection and Protection: After passing the performance test, an insulating protective glaze is applied to obtain the finished product.

[0081] Testing revealed that the electrode thickness in this embodiment was reduced, resulting in a slight decrease in current carrying capacity compared to the double-layer stacked electrode. The average resistance of the sample at room temperature was 11.0 Ω. Under high-power conditions, the electrode exhibited slight heating. After 700 cycles of thermal cycling, slight oxidation marks appeared on the electrode edge, with a resistance fluctuation of 5.5%. This design is suitable for low-power, room-temperature stable operation scenarios.

[0082] Example 7 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 ceramic matrix forming and high-temperature sintering: 12mm diameter ZTA ceramic rods were prepared by hot die casting and sintered at 1700℃ to obtain a dense sintered matrix.

[0083] S2 substrate surface pretreatment: The substrate surface is polished to Ra=0.6μm, and then ultrasonic cleaning, plasma activation and laser micro-roughening are completed in sequence to improve the wettability and mechanical bonding performance of the substrate surface.

[0084] S3 curved surface pad printing end conductive connection point: A silicone pad printing head is used with conductive paste to form a 12μm thick electrode by pad printing twice, and it is pre-baked at 90℃ for 8 minutes to set the shape.

[0085] S4 Piezoelectric Inkjet Direct Printing Precision Heating Circuit for Curved Surfaces: It adopts a four-axis piezoelectric inkjet motion platform and selects single-component silver conductive ink to accurately print 180μm precision spiral heating circuits, which are suitable for cylindrical curved surface forming requirements.

[0086] S5 Low-Temperature Curing and Drying: First, pre-dry at 90℃ for 8 minutes, then main cure at 150℃ for 50 minutes to complete the conductive network formation.

[0087] S6 Finished Product Inspection and Protection: After passing the performance test, an insulating protective glaze is applied to obtain the finished product.

[0088] Testing revealed that the curing temperature of this embodiment was slightly lower, resulting in a slight decrease in the sintering saturation of the conductive metal particles and a slight decrease in the density of the conductive network. The average room temperature resistance of the sample was 10.8Ω, with a resistance fluctuation of 4.8%. After 650 cycles of thermal cycling, the circuit showed no detachment or open circuit, and its performance remained stable. The overall conductivity and reliability were slightly inferior to those of Example 2, but they still meet the requirements for use under normal operating conditions.

[0089] Example 8 A method for preparing a ceramic heating element directly printed on a curved substrate includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Alumina ceramic rods with a diameter of 10 mm were prepared by extrusion molding, with conventional structural dimensions reserved at the ends. The rods were sintered at 1650℃ for 2 hours to obtain a dense sintered matrix.

[0090] S2 substrate surface pretreatment: The substrate surface is polished to Ra=0.6μm, cleaned by ultrasonic cleaning with ethanol, and then laser micro-roughening is performed, omitting the plasma activation process.

[0091] S3 curved surface pad printing end conductive connection point: A silicone pad printing head is used with conductive paste to form a 12μm thick electrode by pad printing twice, and it is pre-baked at 90℃ for 8 minutes to set the shape.

[0092] S4 Piezoelectric Inkjet Direct Printing of Precision Heating Circuit on Curved Surfaces: It adopts a three-axis motion platform equipped with piezoelectric printheads and uses single-component silver conductive ink to print 180μm spiral heating circuits; the three-axis platform can be adapted to standard regular cylindrical curved surfaces to complete precision circuit printing.

[0093] S5 Low-Temperature Curing and Drying: Main curing at 160℃ for 45 minutes to complete the formation of the conductive network.

[0094] S6 Finished Product Inspection and Protection: After passing the performance test, a protective coating is applied to obtain the finished product.

[0095] This embodiment omits the plasma activation process. Upon testing, the surface chemical activity of the ceramic substrate is insufficient, the uniformity of conductive ink wetting decreases, and there are slight differences in the local density of the circuit. The average resistance of the sample at room temperature is 11.2Ω. After 550 cycles of hot and cold, slight signs of debonding appear in some areas, and the resistance fluctuates by 7.0%. The overall stability is lower than that of Example 2, but it is still significantly better than the comparative product of the traditional process.

[0096] Comparative Example 1 This comparative example uses existing traditional processes. The specific steps are as follows: prepare alumina ceramic casting green sheet, screen print heating circuit, cut and wrap it to fit the outer wall of the ceramic green sheet, fix it with tooling and co-fire it at 1650℃, and polish the lead-out electrode after cooling.

[0097] Performance test results show that the samples prepared by traditional processes have a large number of bubbles at the interface, extremely high interfacial thermal resistance, an average resistance of 18.5Ω at room temperature, a resistance fluctuation of 15.2%, and extremely poor conductivity uniformity; after only 300 cycles of hot and cold cycling, large-area delamination and peeling, and circuit detachment failures occur, resulting in premature product failure.

[0098] Comparative Example 2 This comparative example refers to Example 2, retaining the piezoelectric inkjet direct printing circuit, eliminating the curved surface pad printing thick film electrode process, and directly using inkjet printing to form the corresponding end electrodes. The remaining processes are the same as in Example 2.

[0099] Test results show that the inkjet-molded electrode is only 2~3μm thick, has extremely low current carrying capacity, an average room temperature resistance of 16.8Ω, a contact resistance of 3.5Ω, and severe conductivity loss. The electrode burns out after only 200 cycles of hot and cold cycling, the electrode molding in the end opening area is incomplete, the product defect rate exceeds 40%, the reliability and practicality are extremely poor, and it cannot meet the requirements for long-term stable use in industrial applications.

[0100] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0101] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0102] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a direct-printed ceramic heating element on a curved substrate, characterized in that, Includes the following steps: S1 Ceramic Matrix Forming and High-Temperature Sintering: Preparation of ceramic rod blanks, wherein the blank material is alumina or ZTA ceramic, and the blank is a cylindrical matrix with openings, grooves or stepped areas at the ends for forming electrode contacts; S2 substrate surface pretreatment: The outer surface of the blank is mechanically polished to make the surface roughness Ra≤0.8μm. After polishing, ultrasonic cleaning is used to remove surface dust and oil stains to obtain a clean and flat activated substrate. S3 Curved surface pad printing for conductive connection points at the ends: Using a silicone pad printing head and conductive paste, the ends of ceramic rods are coated with curved surface pad printing to form thick film conductive electrode contacts with a thickness of 5~20μm. After pad printing, the contacts are pre-baked at 80~100℃ for 5~10min to set the shape. S4 Piezoelectric Inkjet Direct Printing of Precision Heating Circuit on Curved Surface: It adopts a 3-axis or 4-axis motion platform equipped with an industrial piezoelectric printhead to directly print the heating circuit on the polished ceramic curved surface with conductive ink. The line width is controlled at 50~300μm, and the motion platform adjusts the distance between the printhead and the curved surface in real time. S5 Low-Temperature Curing and Drying: Two-stage temperature-controlled drying, first pre-drying at 80~100℃ for 5~10 minutes to set the circuit shape, and then curing at 120~200℃ for 30~60 minutes to remove the slurry solvent and organic adhesive, thereby forming a continuous and stable conductive network. S6 conducts electrical performance tests, and qualified products are selectively coated with insulating protective glaze or functional coating.

2. The method for preparing a direct-printed ceramic heating element on a curved substrate according to claim 1, characterized in that, The surface roughness of mechanically polished S2 is 0.4~0.6μm.

3. The method for preparing a direct-printed ceramic heating element on a curved substrate according to claim 2, characterized in that, The S2 substrate surface pretreatment also includes at least one of the following auxiliary treatments: plasma cleaning to enhance the chemical activity of the substrate surface, and laser roughening treatment to construct a surface micro-anchoring structure; through the auxiliary treatments, the wettability and mechanical bonding force between the conductive ink and the ceramic substrate are improved, reducing the risk of circuit detachment and debonding during thermal cycling.

4. The method for preparing a curved substrate direct-printed ceramic heating element according to any one of claims 1-3, characterized in that, The curved surface transfer printing described in S3 is a single or multiple stacked transfer printing process to fill irregularly shaped areas with a height difference of 0.3~2mm at the ceramic end, forming electrode contacts.

5. The method for preparing a direct-printed ceramic heating element on a curved substrate according to claim 4, characterized in that, The curved surface transfer printing described in S3 involves two transfer printing stacks, and the thickness of the formed conductive electrode contact is 10-12 μm.

6. The method for preparing a direct-printed ceramic heating element on a curved substrate according to claim 1, characterized in that, The industrial piezoelectric printhead mentioned in S4 is selected from any one of Dimatix, Konica, or Epson PrecisionCore industrial printheads. The conductive ink is a silver-containing conductive ink with a viscosity of 8~15cP, a surface tension of 28~35mN / m, and a solid particle size of <100nm.

7. The method for preparing a direct-printed ceramic heating element on a curved substrate according to claim 1 or 6, characterized in that, S4 piezoelectric inkjet printing uses multiple scanning printing, which improves the overall thickness and conductivity uniformity of the heating circuit by stacking multiple layers of circuits, reduces the overall resistance of the circuit, reduces heat loss under high power conditions, and improves heating efficiency and operating stability.

8. The method for preparing a direct-printed ceramic heating element on a curved substrate according to claim 1, characterized in that, The sintering temperature of S1 ceramic rod blank is 1650~1700℃, and the holding time is 2~3h; the temperature of S5 low-temperature curing is lower than the phase transformation temperature of the ceramic matrix throughout the process, the curing temperature is 150~160℃, and the curing time is 40~50min.

9. A type of ceramic heating element directly printed on a curved substrate, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The direct-printed ceramic heating element on a curved substrate according to claim 9, characterized in that, The ceramic heating element has undergone more than 500 cycles of hot and cold cycling without delamination, peeling, or open circuit failure. Its overall resistance at room temperature is stable at 8.5~13Ω, the electrode contact resistance is ≤0.3Ω, and it shows no breakdown in a 1000V withstand voltage test.