A low-temperature-curable high-pressure-resistant conductive paste and a preparation method thereof

Abstract

This invention relates to the field of conductive paste technology, specifically to a low-temperature curable high-voltage conductive paste and its preparation method. The paste is composed of epoxy-modified resin, silver powder, auxiliary conductive materials, interface modifiers, and curing agents. The epoxy-modified resin is prepared by hydrolysis and condensation to form a hyperbranched structure and grafting epoxy groups. The auxiliary conductive materials are optimized through pyrrole polymerization and proton acid doping. In the preparation process, the silver powder is first ball-milled into flakes, then mixed with the epoxy-modified resin and functional additives, and then formed after high-speed shear dispersion, three-roll milling, and vacuum degassing. This paste can cure rapidly at relatively low temperatures, possessing low volume resistivity, excellent high-voltage stability, and strong substrate adhesion, preventing damage to heat-sensitive substrates. It is suitable for flexible electronics, high-voltage circuits, and other fields, with broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of conductive paste technology, and in particular to a low-temperature curable high-voltage conductive paste and its preparation method. Background Technology

[0002] Conductive pastes are core functional materials in electronic devices, flexible circuits, and new energy equipment. Their curing temperature, conductivity, high-voltage stability, and interfacial adhesion directly affect the reliability and lifespan of end products. As electronic devices evolve towards lighter weight, greater flexibility, and higher precision, the demand for low-temperature curing of conductive pastes is becoming increasingly urgent. Traditional conductive pastes often rely on high temperatures for resin cross-linking and curing, which not only consumes a lot of energy but also easily leads to deformation, aging, or even damage to heat-sensitive substrates such as PI films and flexible substrates, limiting their application in emerging fields like flexible electronics. Simultaneously, high-voltage conditions (such as power devices and high-voltage circuits) place higher demands on the high-voltage resistance of the paste, requiring it to maintain conductivity stability under specific high-voltage environments to avoid structural failure due to electric field impacts.

[0003] In existing technologies, some solutions for achieving low-temperature curing involve reducing the resin crosslinking density or using highly active curing agents. However, this often results in decreased mechanical strength and deterioration of high-pressure resistance of the cured product. Regarding conductivity optimization, increasing the amount of conductive fillers such as silver powder is often used to improve conductivity. However, excessive filler content leads to poor slurry dispersibility and weakened interfacial bonding, thus affecting adhesion and processing performance. Furthermore, while the application of auxiliary conductive materials (such as polypyrrole and polyaniline) can supplement the conductive pathway, unmodified conductive materials are prone to agglomeration and have poor interfacial compatibility with the resin matrix, making it difficult to form a stable synergistic conductive system. Simultaneously, the migration problem of silver ions under high-voltage electric fields has not been effectively solved, easily leading to local defects in the conductive network and reducing the high-pressure stability of the slurry.

[0004] In summary, existing conductive pastes have not yet formed an integrated solution that simultaneously satisfies the requirements of "low-temperature rapid curing, low volume resistivity, excellent high-voltage resistance, and strong substrate adhesion." Therefore, developing a conductive paste that achieves synergistic improvement in multiple properties through resin structure modification, functional optimization of auxiliary conductive materials, morphological control of conductive fillers, and the synergistic effect of functional additives has significant practical application value and industry significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a low-temperature curable high-voltage conductive paste and its preparation method.

[0006] To achieve the above objectives, the present invention provides a low-temperature curable high-voltage conductive paste, comprising the following raw materials in parts by weight: epoxy modified resin: 30-40 parts, silver powder: 45-90 parts, auxiliary conductive material: 0.5-1 part, interface modifier: 1-3 parts, curing agent: 1-2 parts, anti-migration agent: 0.1-0.3 parts, thixotropic agent: 0.3-0.7 parts;

[0007] The preparation method of the epoxy modified resin includes the following steps:

[0008] (1) In a reaction vessel equipped with a reflux condenser, side-hydrogen-containing silicone oil and phenyltrimethoxysilane were added to ethanol and stirred for 10-20 min. The pH of the system was adjusted to 3-4 with dilute hydrochloric acid, the temperature was raised to 60-70℃, and the reaction was carried out for 4-8 h. After cooling to room temperature, the mixture was filtered. The filtrate was distilled under vacuum at 80-100℃ to remove ethanol, water, and the byproduct methanol, to obtain hyperbranched phenyl side-hydrogen-containing polysiloxane. The chemical reaction process is illustrated below:

[0009] ;

[0010] In this step, the side-hydrogen-containing silicone oil and phenyltrimethoxysilane are dispersed in ethanol, and the pH is adjusted to 3-4 with dilute hydrochloric acid to provide a weakly acidic hydrolysis environment for the methoxy groups attached to Si, so that the methoxy groups on the two raw material molecules are simultaneously hydrolyzed to generate silanol groups (-Si-OH). The silanol groups have high reactivity and spontaneously undergo dehydration condensation to form Si-O-Si bonds. The side-hydrogen-containing silicone oil acts as a branching arm, and the three silanol sites of phenyltrimethoxysilane act as growth sites for the branching arm. The condensation forms a hyperbranched structure, and finally, a hyperbranched phenyl side-hydrogen-containing polysiloxane with Si-H active sites is obtained, which lays the foundation for subsequent grafting of epoxy groups.

[0011] (2) Under nitrogen protection, hyperbranched phenyl-containing polysiloxane was added to a reaction vessel equipped with a reflux condenser. With stirring, the temperature was raised to 80-90℃ and held for 20-40 min. The temperature was then lowered to 50-60℃, and then isopropanol chloroplatinic acid solution was added. 2-((allyloxy)methoxy)methyl ethylene oxide was added dropwise over 50-90 min. After the addition was complete, the temperature was raised to 80-90℃ and the reaction was allowed to proceed for 4-6 h to obtain epoxy-modified resin. The chemical reaction process is illustrated below:

[0012] ;

[0013] The core mechanism of this step is "selective hydrosilylation reaction catalyzed by Pt". The added 2-((allyloxy)methoxy)methyl ethylene oxide undergoes a hydrosilylation reaction between the carbon-carbon double bonds in its molecule and the Si-H bonds of the hyperbranched polysiloxane under Pt catalysis. This reaction is highly selective, targeting only the carbon-carbon double bonds and Si-H bonds, without damaging the epoxy groups in the molecule. By controlling the reaction temperature and time, the addition reaction is ensured to be complete, ultimately grafting epoxy groups onto the branch ends of the hyperbranched polysiloxane, forming an epoxy-modified resin that combines a hyperbranched structure, epoxy active groups, and benzene rings.

[0014] The preparation method of the auxiliary conductive material is as follows:

[0015] Polyvinylpyrrolidone K30 and FeCl3·6H2O were added to an ethanol / water mixture and stirred for 20-30 min. Then, pyrrole and (1H-pyrrole-3-yl)methylamine were added, and the reaction was carried out at room temperature for 3-5 h. After filtration, the obtained solid was washed, freeze-dried, and ground into powder to obtain an auxiliary conductive material. The chemical reaction process is illustrated below:

[0016] ;

[0017] In this step, FeCl3·6H2O acts as two main functions: first, as an oxidant, causing pyrrole to lose electrons at the 2 and 5 carbon atoms of the pyrrole ring in (1H-pyrrole-3-yl)methylamine to form cationic free radicals. These free radicals then polymerize through carbon-carbon coupling and disproportionation reactions to form a polypyrrole backbone. The conjugated structure of alternating single and double carbon bonds in the backbone is the basis for electrical conductivity. Second, it acts as a protonic acid dopant, providing chloride ions (Cl... - Undoped polypyrrole has poor conductivity due to the restricted electron movement in its conjugated structure. However, after chloride ions are inserted into the conjugated structure, the original conjugated π bonds are transformed into large delocalized π bonds, and free-moving holes are formed. The delocalization of the holes and the synergistic effect of electrons significantly enhance the electron mobility on the conjugated chain, greatly improving the conductivity of polypyrrole. The amino group of (1H-pyrrole-3-yl)methylamine does not participate in the main chain polymerization, but is only grafted as a side group onto the nitrogen atom of the pyrrole ring in the polypyrrole main chain. This does not destroy the conjugated structure, but can also improve the interfacial compatibility of polypyrrole with epoxy modified resin and flake silver powder through hydrogen bonding. At the same time, it can inhibit the agglomeration of polypyrrole particles by means of steric hindrance. Finally, after washing, freeze-drying and grinding, an auxiliary conductive material with both high conductivity and good dispersibility is obtained.

[0018] Preferably, the D50 particle size of the silver powder is ≤1μm.

[0019] Preferably, the interface modifier refers to the silane coupling agent KH-550.

[0020] Preferably, the curing agent refers to polyetheramine D2000.

[0021] Preferably, the anti-migration agent refers to benzotriazole.

[0022] Preferably, the thixotropic agent refers to polyamide wax.

[0023] Preferably, in (1), the hydrogen-containing silicone oil has H%=0.365% and average Mn=3000.

[0024] Preferably, in (1), the side-containing hydrogen silicone oil, phenyltrimethoxysilane and ethanol are in a weight ratio of 4-6:1:5-10.

[0025] Preferably, the concentration of dilute hydrochloric acid in (1) is 0.1-1 mol / L.

[0026] Preferably, in (2), the hyperbranched phenyl-containing hydrogen polysiloxane, isopropanol chloroplatinate solution and 2-((allyloxy)methoxy)methyl ethylene oxide are in a weight ratio of 1:0.005-0.01:0.2-0.4.

[0027] Preferably, the Pt content in the isopropanol chloroplatinate solution in (2) is 5000 ppm.

[0028] Preferably, in the preparation method of the auxiliary conductive material, the polyvinylpyrrolidone K30, FeCl3·6H2O, ethanol / water mixed solution, pyrrole and (1H-pyrrole-3-yl)methylamine are in a weight ratio of 0.8-1:8-12:80-120:1:0.05-0.2.

[0029] Preferably, in the preparation method of the auxiliary conductive material, the volume ratio of ethanol to water in the ethanol / water mixed solution is 7:3.

[0030] Furthermore, the present invention also provides a method for preparing a low-temperature curable high-voltage conductive paste, comprising the following steps:

[0031] S1. Silver powder, anhydrous ethanol, and stearic acid are loaded into the grinding jar of a vertical planetary ball mill. The rotation speed is set to 1000-2000 r / min, and the ball milling is carried out for 6-9 hours. The product after ball milling is washed and dried to obtain flake silver powder.

[0032] S2. Add epoxy modified resin to a mixing tank, heat to 40-60℃ and stir for 10-20 min; after cooling to room temperature, add interface modifier, anti-migration agent and thixotropic agent in sequence, and stir for 20-40 min; then add flake silver powder and stir for 0.5-1.5 h; finally add auxiliary conductive material and curing agent, and disperse by high-speed shearing at 1000-1500 r / min for 10-30 min; grind three times in sequence with roller gaps of 20μm, 10μm and 5μm using a three-roll mill, and then vacuum degas for 10-30 min to obtain a low-temperature curable high-voltage conductive slurry.

[0033] Preferably, the silver powder, anhydrous ethanol and stearic acid in S1 are in a weight ratio of 1:1-3:0.008-0.012.

[0034] Preferably, the working mechanism of the low-temperature curable high-voltage conductive paste of the present invention is explained as follows:

[0035] The low-temperature curing characteristics of this invention stem from the synergistic effect of the hyperbranched structure of the epoxy-modified resin and the curing agent. The epoxy-modified resin has a hyperbranched structure, which provides the system with ample free volume, significantly reducing the degree of molecular chain entanglement. This allows for uniform exposure of the epoxy groups grafted onto the branch ends, enabling efficient contact with the amine groups of polyetheramine D2000 without high-temperature driving. A specific ring-opening crosslinking reaction occurs between the epoxy groups and the amine groups, which can be initiated under mild conditions. The multi-terminal epoxy groups provided by the hyperbranched structure offer sufficient sites for the crosslinking reaction, ensuring rapid and complete reaction. Simultaneously, the flexibility and free volume characteristics of the hyperbranched structure allow the epoxy groups and amine groups to maintain good reactivity at low temperatures, ultimately forming a stable crosslinked network and achieving low-temperature curing of the slurry.

[0036] The core of the high-pressure resistance lies in the structural characteristics of the epoxy-modified resin matrix and the synergistic stabilizing effect of its components. The hyperbranched structure of the epoxy-modified resin forms a dense, defect-free cross-linked network after curing. Combined with the process of removing solvents and byproducts by vacuum distillation during preparation, this effectively reduces micro-voids within the system. These voids can lead to localized electric field concentration under high pressure, potentially causing loosening of the conductive network or matrix damage. The dense network, on the other hand, can uniformly disperse electric field stress, preventing localized overload. Simultaneously, the benzene rings introduced into the resin molecules are high-dielectric rigid groups. Their synergistic effect with the high-bond-energy Si-O bonds of the polysiloxane backbone significantly enhances the structural stability of the resin matrix, enabling it to withstand mechanical and electric field impacts under high-pressure conditions and preventing matrix cracking or deformation. In addition, the anti-migration agent benzotriazole can inhibit the migration and aggregation of silver ions under the action of high voltage electric field, and prevent local breaks or defects in the conductive network due to the migration of silver ions; the auxiliary conductive material forms chemical bonds with the resin epoxy group through the side group amino group, which reduces the interfacial gap between the conductive component and the resin matrix, further avoiding the problem of electric field concentration at the gap, and ultimately ensuring that the slurry maintains stable conductivity and structural integrity under the target high voltage environment.

[0037] Finally, the high conductivity of the slurry relies on a synergistic system of "flaky silver powder dominating the conductive network, auxiliary conductive materials supplementing the conductive pathway, and chemical bonding stabilizing the interface." After ball milling, the silver powder forms a flake-like morphology, significantly increasing its specific surface area and creating a two-dimensional structure. This structure easily overlaps with each other in the slurry to form a continuous three-dimensional conductive network, providing the main channel for electron transport. The auxiliary conductive material has a conjugated structure with alternating carbon-carbon single and double bonds in its main chain. After being doped with ferric chloride protonic acid, chloride ions are embedded in the conjugated system to form large delocalized π bonds and freely moving holes, greatly improving its conductivity. Crucially, the amino groups grafted onto the side groups of the auxiliary conductive material not only enhance the interfacial compatibility with the resin and silver powder through hydrogen bonding but also undergo ring-opening crosslinking reactions with the epoxy groups of the epoxy-modified resin, chemically bonding the auxiliary conductive material into the resin matrix and preventing the polypyrrole from migrating or agglomerating in the slurry. Simultaneously, this amino group does not disrupt the conjugated structure of the polypyrrole main chain, ensuring that its conductivity remains unaffected. In addition, the silane coupling agent KH-550 further optimizes the compatibility between the conductive components and the resin matrix, inhibits the agglomeration of silver powder, and ensures that the conductive components are uniformly dispersed, ultimately constructing a highly efficient and stable conductive system.

[0038] The beneficial effects of this invention are:

[0039] 1. This invention utilizes a hyperbranched epoxy-modified resin prepared through molecular design. With ample free volume and a multi-terminal epoxy group structure, it significantly reduces molecular chain entanglement, enabling efficient ring-opening crosslinking reactions between epoxy groups and curing agent amine groups at mild temperatures, achieving curing without the need for high temperatures. This characteristic not only reduces energy consumption but also prevents deformation, aging, or damage to heat-sensitive substrates such as PI films and flexible substrates due to high temperatures. Furthermore, the cured crosslinked network is dense and complete, balancing low-temperature curing with mechanical strength, thus expanding the application scenarios of conductive pastes in emerging fields such as flexible electronics.

[0040] 2. The dense, defect-free cross-linked network formed after the epoxy-modified resin in this invention, combined with the synergistic effect of the high-dielectric rigidity groups of the benzene ring in the molecule and the high-bond-energy Si-O bonds of the polysiloxane backbone, can effectively disperse the stress of the high-voltage electric field and avoid structural failure caused by electric field concentration in the gaps. The anti-migration agent can inhibit the migration and aggregation of silver ions under high voltage, and assist the conductive material in forming chemical bonds with the resin through amino groups, eliminating interfacial gaps and further improving electric field stability. Ultimately, the slurry can maintain structural integrity and conductive stability for a long time under high-voltage conditions, and will not be damaged, discharged, or have its conductivity degraded due to electric field impact.

[0041] 3. In this invention, the flake-like morphology of silver powder formed by ball milling significantly increases the specific surface area, facilitating the formation of continuous three-dimensional conductive main channels. The polypyrrole backbone of the auxiliary conductive material, after protonic acid doping, forms large delocalized π bonds and free holes, significantly enhancing conductivity. Simultaneously, the amino groups on the side groups of the auxiliary conductive material are uniformly dispersed in the gaps between the silver powder particles through chemical bonding and hydrogen bonding, forming supplementary electron tunneling paths to compensate for minor breaks in the main channels, constructing a synergistic conductive system of "main channel + supplementary path." This system not only significantly reduces volume resistivity but also inhibits the aggregation of conductive components, ensuring uniformity and long-term effectiveness of conductivity.

[0042] 4. In this invention, the amino groups of the interface modifier chemically bond with the epoxy groups of the resin and the hydroxyl groups of the substrate. The multi-terminal structure of the hyperbranched resin increases the contact area and interaction with the substrate. The amino groups of the conductive auxiliary material tightly bind with the resin through cross-linking reactions and simultaneously form hydrogen bonds with the silver powder, eliminating interfacial gaps between the conductive components and the substrate. These multiple effects synergistically inhibit coating peeling and component agglomeration, resulting in a strong bond between the slurry and the substrate, achieving a high level of adhesion. Furthermore, the addition of a thixotropic agent optimizes the rheological properties of the slurry. Combined with three-roll milling and vacuum degassing processes, this improves the processing and molding effect, ensuring a smooth and dense coating after curing.

[0043] 5. This invention achieves an integrated improvement in low-temperature curing, high conductivity, high voltage resistance, strong adhesion, and good processing performance through resin structure modification, functional design of auxiliary conductive materials, morphology control of conductive fillers, and synergistic formulation of functional additives. This solves the pain point of multiple properties being mutually restrictive in existing technologies. The slurry can be prepared without complex processes, has mild curing conditions, and is suitable for different substrates and processing scenarios. It can be widely used in electronic devices, flexible circuits, high-voltage power devices, and other fields, demonstrating significant practical application value and industry promotion potential. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0045] Preparation Example 1: The specific preparation method of epoxy modified resin includes the following steps:

[0046] (1) In a reaction vessel equipped with a reflux condenser, 400g of side-hydrogenated silicone oil (H%=0.365%, averageMn=3000) and 100g of phenyltrimethoxysilane were added to 500g of ethanol and stirred for 10min. The pH of the system was adjusted to 3-4 with dilute hydrochloric acid with a concentration of 0.1mol / L. The temperature was raised to 60℃ and the reaction was carried out for 4h. After cooling to room temperature, the mixture was filtered. The filtrate was distilled under vacuum at 80℃ to remove ethanol, water and byproduct methanol to obtain hyperbranched phenyl side-hydrogenated polysiloxane.

[0047] (2) Under nitrogen protection, 400g of hyperbranched phenyl-containing polysiloxane was added to a reaction vessel equipped with a reflux condenser. The mixture was stirred, heated to 80°C, kept at that temperature for 20min, cooled to 50°C, and then 2g of isopropanol chloroplatinate solution (Pt content: 5000ppm) was added. 80g of 2-((allyloxy)methoxy)methyl ethylene oxide was added dropwise over a period of 50min. After the addition was complete, the temperature was raised to 80°C and the reaction was carried out for 4h to obtain epoxy modified resin.

[0048] Preparation Example 2: The specific preparation method of epoxy modified resin includes the following steps:

[0049] (1) In a reaction vessel equipped with a reflux condenser, 500g of side-hydrogen-containing silicone oil (H%=0.365%, averageMn=3000) and 100g of phenyltrimethoxysilane were added to 800g of ethanol and stirred for 15min. The pH of the system was adjusted to 3-4 with dilute hydrochloric acid with a concentration of 0.5mol / L. The temperature was raised to 65℃ and the reaction was carried out for 6h. After cooling to room temperature, the mixture was filtered. The filtrate was distilled under vacuum at 90℃ to remove ethanol, water and byproduct methanol to obtain hyperbranched phenyl side-hydrogen-containing polysiloxane.

[0050] (2) Under nitrogen protection, 500g of hyperbranched phenyl-containing polysiloxane was added to a reaction vessel equipped with a reflux condenser. The mixture was stirred, heated to 85°C, kept at that temperature for 30 min, cooled to 55°C, and then 4g of isopropanol chloroplatinate solution (Pt content: 5000ppm) was added. 150g of 2-((allyloxy)methoxy)methyl ethylene oxide was added dropwise over a period of 75 min. After the addition was complete, the temperature was raised to 85°C and the reaction was carried out for 5 h to obtain epoxy modified resin.

[0051] Preparation Example 3: The specific preparation method of epoxy modified resin includes the following steps:

[0052] (1) In a reaction vessel equipped with a reflux condenser, 600g of side-hydrogenated silicone oil (H%=0.365%, averageMn=3000) and 100g of phenyltrimethoxysilane were added to 1kg of ethanol and stirred for 20min. The pH of the system was adjusted to 3-4 with 1mol / L dilute hydrochloric acid, the temperature was raised to 70℃, and the reaction was carried out for 8h. After cooling to room temperature, the mixture was filtered. The filtrate was distilled under vacuum at 100℃ to remove ethanol, water and byproduct methanol to obtain hyperbranched phenyl side-hydrogenated polysiloxane.

[0053] (2) Under nitrogen protection, 600g of hyperbranched phenyl-containing polysiloxane was added to a reaction vessel equipped with a reflux condenser. Under stirring, the temperature was raised to 90℃ and kept at that temperature for 40min. The temperature was then lowered to 60℃ and 6g of isopropanol chloroplatinate solution (Pt content: 5000ppm) was added. 240g of 2-((allyloxy)methoxy)methyl ethylene oxide was added dropwise over a period of 90min. After the addition was complete, the temperature was raised to 90℃ and the reaction was carried out for 6h to obtain epoxy modified resin.

[0054] Preparation Example 4: The specific preparation method of the auxiliary conductive material includes the following steps:

[0055] 8g of polyvinylpyrrolidone K30 and 80g of FeCl3·6H2O were added to 800g of ethanol / water mixed solution (ethanol to water volume ratio of 7:3), stirred for 20min, then 10g of pyrrole and 0.5g of (1H-pyrrole-3-yl)methylamine were added, and the reaction was carried out at room temperature for 3h. After filtration, the obtained solid was washed, freeze-dried, and ground into powder to obtain the auxiliary conductive material.

[0056] Preparation Example 5: The specific preparation method of the auxiliary conductive material includes the following steps:

[0057] 9g of polyvinylpyrrolidone K30 and 100g of FeCl3·6H2O were added to 1kg of ethanol / water mixed solution (ethanol to water volume ratio of 7:3) and stirred for 25min. Then, 10g of pyrrole and 1g of (1H-pyrrole-3-yl)methylamine were added and reacted at room temperature for 4h. After filtration, the obtained solid was washed, freeze-dried and ground into powder to obtain the auxiliary conductive material.

[0058] Preparation Example 6: A specific preparation method for auxiliary conductive materials, including the following steps:

[0059] 10g of polyvinylpyrrolidone K30 and 120g of FeCl3·6H2O were added to 1.2kg of ethanol / water mixed solution (ethanol to water volume ratio of 7:3) and stirred for 30min. Then, 10g of pyrrole and 2g of (1H-pyrrole-3-yl)methylamine were added and reacted at room temperature for 5h. After filtration, the obtained solid was washed, freeze-dried and ground into powder to obtain the auxiliary conductive material.

[0060] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 3 is that phenyltrimethoxysilane is replaced with trimethoxysilane.

[0061] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 3 is that 2-((allyloxy)methoxy)methyl ethylene oxide is replaced with allyl glycidyl ether.

[0062] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 3 is that step (1) is omitted, and the hyperbranched phenyl side-hydrogen polysiloxane in step (2) is replaced with side-hydrogen silicone oil.

[0063] Comparative Preparation Example 4: The difference between Comparative Preparation Example 4 and Preparation Example 3 is that 2g of (1H-pyrrole-3-yl)methylamine was not added.

[0064] Comparative Preparation Example 5: The difference between Comparative Preparation Example 5 and Preparation Example 3 is that FeCl3·6H2O is replaced with ammonium persulfate.

[0065] Example 1: A specific preparation method for a low-temperature curable high-voltage conductive paste, comprising the following steps:

[0066] S1. 450g of silver powder (D50 particle size ≤ 1μm), 450g of anhydrous ethanol and 3.6g of stearic acid were loaded into the ball milling jar of a vertical planetary ball mill. The speed was set to 1000r / min and the ball milling was carried out for 6 hours. The ball-milled product was washed and dried to obtain flake silver powder.

[0067] S2. Add 300g of the epoxy modified resin prepared according to Preparation Example 1 to a mixing tank, heat to 40℃ and stir for 10min; after cooling to room temperature, add 10g of KH-550, 1g of benzotriazole and 3g of polyamide wax in sequence, and stir for 20min; then add the flake silver powder obtained in S1 and stir for 0.5h; finally add 5g of the auxiliary conductive material prepared according to Preparation Example 4 and 10g of polyetheramine D2000, and disperse by high-speed shearing at 1000r / min for 10min; grind three times in sequence with roller gaps of 20μm, 10μm and 5μm using a three-roll mill, and then vacuum degas for 10min to obtain a low-temperature curable high-voltage conductive slurry.

[0068] Example 2: A specific preparation method for a low-temperature curable high-voltage conductive paste, comprising the following steps:

[0069] S1. 700g of silver powder (D50 particle size ≤1μm), 1.4kg of anhydrous ethanol and 7g of stearic acid were loaded into the ball mill jar of a vertical planetary ball mill. The speed was set to 1500r / min and the ball milling was carried out for 8 hours. The ball-milled product was washed and dried to obtain flake silver powder.

[0070] S2. Add 350g of the epoxy modified resin prepared according to Preparation Example 1 to a mixing tank, heat to 50℃ and stir for 15min; after cooling to room temperature, add 20g of KH-550, 2g of benzotriazole and 5g of polyamide wax in sequence, and stir for 30min; then add the flake silver powder obtained in S1 and stir for 1h; finally add 8g of the auxiliary conductive material prepared according to Preparation Example 5 and 15g of polyetheramine D2000, and disperse at high speed of 1200r / min for 20min; grind three times in sequence with roller gaps of 20μm, 10μm and 5μm using a three-roll mill, and vacuum degas for 20min to obtain a low-temperature curable high-voltage conductive slurry.

[0071] Example 3: A specific preparation method for a low-temperature curable high-voltage conductive paste, comprising the following steps:

[0072] S1. 900g of silver powder (D50 particle size ≤1μm), 2.7kg of anhydrous ethanol and 10.8g of stearic acid were loaded into the ball mill jar of a vertical planetary ball mill. The speed was set to 2000r / min and the ball milling was carried out for 9h. The ball milled product was washed and dried to obtain flake silver powder.

[0073] S2. Add 400g of the epoxy modified resin prepared according to Preparation Example 3 to a mixing tank, heat to 60℃ and stir for 20min; after cooling to room temperature, add 30g of KH-550, 3g of benzotriazole and 7g of polyamide wax in sequence, and stir for 40min; then add the flake silver powder obtained in S1 and stir for 1.5h; finally add 10g of the auxiliary conductive material prepared according to Preparation Example 6 and 20g of polyetheramine D2000, and disperse by high-speed shearing at 1500r / min for 30min; grind three times in sequence with roller gaps of 20μm, 10μm and 5μm using a three-roll mill, and then degas under vacuum for 30min to obtain a low-temperature curable high-voltage conductive slurry.

[0074] Comparative Example 1: The difference between Comparative Example 1 and Example 3 is that the epoxy modified resin prepared according to Preparation Example 2 is replaced with the epoxy modified resin prepared according to Comparative Preparation Example 1.

[0075] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that the epoxy modified resin prepared according to Preparation Example 2 is replaced with the epoxy modified resin prepared according to Comparative Preparation Example 2.

[0076] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that the epoxy modified resin prepared according to Preparation Example 2 is replaced with the epoxy modified resin prepared according to Comparative Preparation Example 3.

[0077] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that the auxiliary conductive material prepared according to Preparation Example 5 is replaced with the auxiliary conductive material prepared according to Comparative Preparation Example 4.

[0078] Comparative Example 5: The difference between Comparative Example 5 and Example 3 is that the auxiliary conductive material prepared according to Preparation Example 5 is replaced with the auxiliary conductive material prepared according to Comparative Preparation Example 5.

[0079] Comparative Example 6: The difference between Comparative Example 6 and Example 3 is that step S1 is omitted and the flake silver powder in step S2 is replaced with silver powder.

[0080] Performance testing:

[0081] According to the corresponding testing standards, the conductive pastes prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests. The test items included the temperature required for the conductive paste to cure in 30 minutes, the pressure resistance of the conductive paste, the volume resistivity, the surface hardness of the cured conductive paste, and the adhesion grade of the conductive paste to the PI substrate. The experimental results are shown in Table 1. The adhesion grade was tested using the cross-cut test according to GB / T 9286-1998. Rating standards: 6B grade (no peeling), 5B grade (no peeling at the grid edge), 4B grade (peeling area ≤5%), 3B grade (5%-15%), 2B grade (15%-35%), 1B grade (35%-65%), 0B grade (≥65%).

[0082] Table 1 Performance Test Results

[0083]

[0084] Performance Analysis:

[0085] As can be seen from the experimental data in Table 1, Examples 1-3 all exhibited excellent overall performance. This is because the hyperbranched structure of the epoxy modified resin provides sufficient reaction sites and free volume, the protonic acid-doped auxiliary conductive material constructs an efficient supplementary conductive path, the flake silver powder forms a continuous conductive network, and the synergistic effect of functional additives such as interface modifiers and anti-migration agents achieves a combination of low-temperature curing, high conductivity, high voltage resistance, and strong adhesion. Among them, Example 3 showed the best overall performance.

[0086] In Example 3, the epoxy-modified resin underwent a highly branched hyperbranched phenyl-containing hydrogen polysiloxane through the complete hydrolytic condensation of side-hydrogen-containing silicone oil and phenyltrimethoxysilane. This hyperbranched resin was then grafted with a large number of epoxy groups via a Pt-catalyzed hydrosilylation reaction. The hyperbranched structure provides the molecule with ample free volume, significantly reducing chain entanglement and allowing the epoxy groups to be uniformly exposed and rapidly contact the amine groups of polyetheramine D2000. The multi-terminal epoxy groups undergo a specific ring-opening crosslinking reaction with the amine groups, resulting in dense and highly reactive reaction sites. Curing can be completed within 30 minutes without high temperatures, and the curing is more thorough. Simultaneously, the higher amount of silver powder further densifies the crosslinking network through physical filling, indirectly improving curing efficiency and keeping the curing temperature within a reasonable range.

[0087] In Example 3, the hyperbranched structure of the epoxy-modified resin, after curing, forms a dense, defect-free three-dimensional cross-linked network. Combined with the vacuum distillation process used to remove solvents and byproducts during preparation, this eliminates micro-voids within the system, preventing the electric field from concentrating at these voids under high voltage. The benzene ring introduced into the resin molecule acts as a high-dielectric rigid group, synergistically interacting with the high-bond-energy Si-O bonds of the polysiloxane backbone to enhance the structural stability and resistance to electric field impacts of the resin matrix. Furthermore, the anti-migration agent benzotriazole inhibits the migration and aggregation of silver ions under high-voltage electric fields through adsorption, preventing localized defects in the conductive network. The amino groups on the side groups of the auxiliary conductive material form chemical bonds with the epoxy groups of the resin, eliminating interfacial gaps between the conductive components and the matrix, further preventing electric field concentration and ensuring the slurry maintains structural and conductive stability under high-voltage conditions.

[0088] Silver powder is ball-milled to form a flake-like morphology, significantly increasing the specific surface area. In Example 3, a continuous three-dimensional conductive network is formed at high dosages, providing an efficient main channel for electron transport. The polypyrrole backbone of the auxiliary conductive material is provided with Cl- by FeCl3·6H2O. - After protonic acid doping, the conjugated π bond is transformed into a large delocalized π bond, forming a large number of freely moving holes, which greatly improves its conductivity. At the same time, the amino group of (1H-pyrrole-3-yl)methylamine is grafted onto the polypyrrole backbone. Through chemical bonding and hydrogen bonding with the epoxy group of the resin, the auxiliary conductive material is uniformly dispersed in the gaps between the silver powder, forming an electron tunneling supplementary path, making up for the small discontinuities in the silver powder network, and constructing a synergistic conductive system of "main channel + supplementary path", which significantly reduces the volume resistivity.

[0089] In Example 3, the multi-terminal epoxy groups of the hyperbranched epoxy-modified resin are fully cross-linked with the curing agent, forming a high-density cross-linked network that restricts the mobility of molecular chains. Simultaneously, the benzene rings in the resin molecules enhance molecular rigidity through conjugation, while the Si-O bonds in the polysiloxane backbone provide excellent mechanical support. The higher amount of silver powder further enhances the mechanical strength of the cured product through particle filling. The flake-like silver powder has a tight interface with the resin matrix, making it less prone to slippage or deformation under external forces, collectively contributing to the high surface hardness of the cured product.

[0090] Finally, in Example 3, the amino groups of the interface modifier silane coupling agent KH-550 react chemically with the epoxy groups of the resin and the hydroxyl groups on the surface of the PI substrate to form chemical bonds, enhancing the interfacial interaction between the resin and the substrate. The amino groups of the auxiliary conductive material's side groups undergo ring-opening crosslinking reactions with the epoxy groups of the resin, and simultaneously form hydrogen bonds with the silver powder surface, ensuring a tight bond between the conductive components and the resin matrix, preventing interfacial delamination. The multi-terminal structure of the hyperbranched resin further increases the contact area and interaction with the substrate. The synergistic effect of multiple chemical bonds and physical adsorption results in extremely high bonding strength between the slurry and the PI substrate, achieving the highest level of adhesion.

[0091] Comparative Example 1 replaced phenyltrimethoxysilane with trimethoxysilane, which lacked the benzene ring functional group. Although trimethoxysilane contains three hydrolyzable methoxy groups, the lack of a benzene ring in the branched structure increased the degree of resin molecular chain entanglement, reduced epoxy group exposure, decreased curing reactivity, increased curing temperature, and resulted in incomplete curing. Without the rigid support of the benzene ring, the dielectric strength and structural stability of the resin matrix decreased, and the compressive strength decreased. Hyperbranched entanglement led to a reduction in interfacial bonding sites with the substrate and conductive components, resulting in a decrease in adhesion level. The interfacial compatibility of the conductive network decreased slightly, and the volume resistivity and surface hardness also deteriorated accordingly.

[0092] In Comparative Example 2, 2-((allyloxy)methoxy)methyl ethylene oxide was replaced with allyl glycidyl ether. The latter lacks the "-OCH2CH2O-" flexible segment, which leads to a decrease in the interfacial compatibility of the epoxy modified resin. This further results in a decrease in crosslinking density, an increase in curing temperature, a decrease in the structural density and mechanical strength of the cured product, and a decrease in surface hardness. The crosslinking network is loose and the interfacial gaps are increased, making it easy for the electric field to concentrate under high voltage, resulting in a decrease in withstand voltage strength. The deterioration of interfacial compatibility leads to uneven dispersion of conductive components, weakens the synergistic effect between the silver powder network and the auxiliary conductive material, increases the volume resistivity, and reduces adhesion due to insufficient interfacial bonding.

[0093] Comparative Example 3 omitted the hyperbranching preparation step and directly grafted epoxy groups onto side-containing hydrogen silicone oil, lacking a hyperbranched structure. The linear side-containing hydrogen silicone oil molecular chains were severely entangled, with low and uneven epoxy group grafting density, resulting in a significant decrease in contact efficiency with amine groups. Higher temperatures were required to break the chain entanglement and complete curing, leading to a significant increase in curing temperature. The lack of a hyperbranched structure resulted in a loose linear cross-linked network after resin curing, with numerous voids, severe electric field concentration, and a significant reduction in compressive strength. The low cross-linking density and lack of rigid support from benzene rings significantly reduced surface hardness. The linear resin had very few interfacial bonding sites with the conductive components and substrate, reducing adhesion. Poor interfacial compatibility led to silver powder agglomeration, uneven dispersion of auxiliary conductive materials, impaired conductive network continuity, and a significant increase in volume resistivity.

[0094] Comparative Example 4 did not contain (1H-pyrrole-3-yl)methylamine, and the polypyrrole backbone of the auxiliary conductive material lacked amino grafting. Without the interfacial effect of amino groups, the polypyrrole particles easily agglomerate due to van der Waals forces, failing to disperse uniformly in the resin and silver powder system. This leads to broken conductive pathways and a significant increase in volume resistivity. Agglomerated polypyrrole particles form localized defects in the system, causing the electric field to concentrate at these defects under high voltage, resulting in decreased withstand voltage. The lack of chemical bonding between amino groups and resin epoxy groups weakens the interfacial adhesion between the auxiliary conductive material and the matrix. Simultaneously, the interfacial compatibility between the silver powder and resin deteriorates due to the absence of hydrogen-bonded bridging effects from amino groups, leading to a significant reduction in adhesion grade. Agglomerated particles also affect the density of the cross-linked network, slightly decreasing surface hardness.

[0095] In Comparative Example 5, FeCl3·6H2O was replaced with ammonium persulfate. Ammonium persulfate could only act as an oxidant to initiate pyrrole polymerization and could not provide the small-sized anions required for protic acid doping. In the undoped polypyrrole conjugated structure, electron movement was restricted, resulting in poor conductivity. It could not form an effective supplementary conductive pathway and relied solely on the silver powder network for conduction, leading to a significant increase in volume resistivity. Although ammonium persulfate did not affect the hyperbranched structure and curing reaction of the resin, nor did it alter the interfacial bonding between the auxiliary conductive material and the matrix, resulting in no significant changes in curing temperature, surface hardness, compressive strength, and adhesion, the lack of synergistic conductivity from the auxiliary conductive material led to a significant deterioration in conductivity.

[0096] Comparative Example 6 omits the ball milling step and uses the original silver powder directly. The silver powder retains its original morphology, resulting in a small specific surface area and irregular shape, low overlap efficiency, and an inability to form a continuous, dense three-dimensional conductive network, leading to a decrease in the conductivity of the main channels. The contact area between the original silver powder and the resin matrix is ​​much smaller than that of the flake silver powder, weakening the interfacial bonding force and causing a decrease in adhesion. The discontinuity of the silver powder network makes it easy for the electric field to concentrate at the gaps under high voltage. Simultaneously, the lack of physical filling effect from the flake silver powder results in slightly insufficient density of the cross-linked network and a slight decrease in pressure resistance. The defects in the main conductive channels cannot be completely compensated for by auxiliary conductive materials, leading to an increase in volume resistivity. The mechanical support of the silver powder for the cured network is weakened, and the surface hardness also decreases slightly.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low temperature curable high pressure resistant conductive paste, characterized in that, The raw materials include the following parts by weight: epoxy modified resin: 30-40 parts, silver powder: 45-90 parts, auxiliary conductive material: 0.5-1 part, interface modifier: 1-3 parts, curing agent: 1-2 parts, anti-migration agent: 0.1-0.3 parts, thixotropic agent: 0.3-0.7 parts; The epoxy-modified resin is obtained by grafting 2-((allyloxy)methoxy)methyl ethylene oxide onto a side-containing hydrogen silicone oil and phenyltrimethoxysilane after a condensation reaction; its preparation method includes the following steps: (1) In a reaction vessel equipped with a reflux condenser, side-hydrogenated silicone oil and phenyltrimethoxysilane were added to ethanol. Under stirring, the pH of the system was adjusted to 3-4 with dilute hydrochloric acid, the temperature was raised to 60-70℃, and the reaction was carried out for 4-8 hours. After cooling to room temperature, the mixture was filtered. The filtrate was distilled under vacuum to remove ethanol, water and byproduct methanol to obtain hyperbranched phenyl side-hydrogenated polysiloxane. (2) Under nitrogen protection, hyperbranched phenyl-containing polysiloxane was added to a reaction vessel equipped with a reflux condenser. Under stirring, the temperature was raised to 80-90℃ and kept at that temperature for 20-40 min. The temperature was then lowered to 50-60℃ and chloroplatinic acid isopropanol solution was added. 2-((allyloxy)methoxy)methyl ethylene oxide was added dropwise. After the addition was complete, the temperature was raised to 80-90℃ and the reaction was carried out for 4-6 h to obtain epoxy modified resin. The auxiliary conductive material is obtained from ferric chloride hexahydrate, pyrrole oxide and (1H-pyrrole-3-yl)methylamine.

2. The low-temperature curable high-voltage conductive paste according to claim 1, characterized in that, The D50 particle size of the silver powder is ≤1μm.

3. The low-temperature curable high-voltage conductive paste according to claim 1, characterized in that, The interface modifier refers to silane coupling agent KH-550; the curing agent refers to polyetheramine D2000; the anti-migration agent refers to benzotriazole; and the thixotropic agent refers to polyamide wax.

4. The low-temperature curable high-voltage conductive paste according to claim 1, characterized in that, The method for preparing the conductive auxiliary material includes the following steps: Polyvinylpyrrolidone K30 and FeCl3·6H2O were added to an ethanol / water mixed solution, followed by the addition of pyrrole and (1H-pyrrole-3-yl)methylamine. The reaction was carried out at room temperature for 3-5 hours. After filtration, the resulting solid was washed, freeze-dried, and then ground into powder to obtain an auxiliary conductive material.

5. The low-temperature curable high-voltage conductive paste according to claim 1, characterized in that, In (1), the side-containing hydrogen silicone oil has H%=0.365% and average Mn=3000; the side-containing hydrogen silicone oil, phenyltrimethoxysilane and ethanol are in a weight ratio of 4-6:1:5-10; the concentration of dilute hydrochloric acid is 0.1-1mol / L.

6. The low-temperature curable high-voltage conductive paste according to claim 1, characterized in that, In (2), the hyperbranched phenyl-containing polysiloxane, isopropanol chloroplatinate solution and 2-((allyloxy)methoxy)methyl ethylene oxide are in a weight ratio of 1:0.005-0.01:0.2-0.4; the Pt content in the isopropanol chloroplatinate solution is 5000 ppm.

7. The low-temperature curable high-voltage conductive paste according to claim 4, characterized in that, In the preparation method of the auxiliary conductive material, polyvinylpyrrolidone K30, FeCl3·6H2O, ethanol / water mixed solution, pyrrole and (1H-pyrrole-3-yl)methylamine are in a weight ratio of 0.8-1:8-12:80-120:1:0.05-0.2; the volume ratio of ethanol to water in the ethanol / water mixed solution is 7:

3.

8. The method for preparing the low-temperature curable high-voltage conductive paste according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Silver powder, anhydrous ethanol, and stearic acid are loaded into the grinding jar of a vertical planetary ball mill. The rotation speed is set to 1000-2000 r / min, and the ball milling is carried out for 6-9 hours. The product after ball milling is washed and dried to obtain flake silver powder. S2. Add the epoxy modified resin to the mixing tank, heat to 40-60℃ and stir for 10-20 min; after cooling to room temperature, add the interface modifier, anti-migration agent and thixotropic agent in sequence, and stir for 20-40 min; then add the flake silver powder and stir for 0.5-1.5 h; finally add the auxiliary conductive material and curing agent, and disperse by high-speed shearing at 1000-1500 r / min for 10-30 min; After being ground three times in sequence with roller gaps of 20μm, 10μm and 5μm using a three-roll mill, and then vacuum degassed for 10-30 minutes, a high-voltage conductive slurry that can be cured at low temperature is obtained.

9. The method for preparing the low-temperature curable high-voltage conductive paste according to claim 8, characterized in that, In S1, the silver powder, anhydrous ethanol, and stearic acid are in a weight ratio of 1:1-3:0.008-0.012.

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