A bend-resistant and sulfide-resistant conductive silver paste for flexible keyboards and its preparation method

Abstract

This invention relates to a bend-resistant and sulfide-resistant conductive silver paste for flexible keyboards and its preparation method. The conductive silver paste is composed of the following components by weight percentage: 40-65% modified metallic silver powder, 30-40% organic carrier, 1-2% organic additives, and 10-30% organic solvent. The preparation method includes the following steps: core-shell structure construction and surface treatment of the silver powder, formulation of the organic carrier, and mixing and grinding of the components. Compared with the prior art, this invention has advantages such as excellent conductivity, good bend resistance, and superior sulfide resistance.

Description

Technical Field

[0001] This invention relates to the field of electronic paste technology, and in particular to a bend-resistant and sulfide-resistant conductive silver paste for flexible keyboards and its preparation method. Background Technology

[0002] Conductive silver paste, as a key electronic material, is widely used in flexible printed circuits, touch screens, keyboard switches, and other fields. Among these, flexible keyboards are experiencing increasing market demand due to their thinness, flexibility, and adaptability. This places stringent requirements on the conductive silver paste used: on the one hand, the paste layer needs to withstand the repeated bending stress from tens of millions of keystrokes while maintaining extremely high flexibility and fatigue resistance; on the other hand, silver, as a reactive metal, readily reacts with sulfides in the environment to form non-conductive silver sulfide, leading to a sharp increase in circuit resistance and even failure—a problem known as "sulfidation." Therefore, excellent resistance to sulfidation is essential.

[0003] However, existing technologies often struggle to simultaneously address both aspects. For instance, patent application CN113972045A discloses a method for preparing sulfide-resistant thick-film wafer resistors, which improves stability by adding inorganic anti-sulfide agents such as molybdenum and indium to the paste and employing a high-temperature sintering process. However, this method is unsuitable for flexible substrates such as PET due to the high-temperature process; furthermore, the introduction of a large amount of rigid inorganic material significantly reduces the flexibility of the film layer, resulting in its bending resistance failing to meet the requirements of flexible keyboards. Patent application CN105702323A discloses a flexible and stretchable conductive paste that constructs a bendable conductive network using elastic resin and flake silver powder. However, this type of technology, in pursuit of flexibility, has a high organic content and a more porous film structure, lacking effective anti-sulfide protection for silver materials, making the circuitry prone to failure due to sulfide reactions in sulfur-containing environments.

[0004] Patent application CN119811741A discloses a conductive silver paste and its preparation method. This technology uses anti-sulfur silver powder, resin, curing agent, solvent, and additives to prepare the conductive silver paste. However, the curing agent used in this technology is an aromatic curing agent, and the resulting polymer has poor flexibility. This causes micro-cracks to easily form at the edges of the circuits after repeated bending of the paste on a flexible keyboard for more than 50,000 times, resulting in a sudden increase in resistance (ΔR / R0 > 10%), which cannot meet the bending resistance requirements of the "foldable" level (≥100,000 times, ΔR / R0 < 10%). Patent application CN118737522A discloses a conductive silver paste and its preparation method. This technology uses mixed silver powder, organic binder resin, curing agent, nano titanium dioxide powder, lead-free glass powder, organic solvent, and various additives to prepare the conductive silver paste. However, this technology only considers how to reduce the resistance and improve the adhesion of the conductive silver paste, without considering how to reduce the sulfidation risk of the conductive silver paste.

[0005] Therefore, existing technical solutions have limitations in performance and are mismatched with application scenarios. Simply combining anti-sulfurization agents and flexible resins often leads to mutual weakening of performance due to incompatibility between components. For example, anti-sulfurization agents may damage the integrity of the conductive network, or toughening resins may provide penetration channels for sulfur corrosion. There is an urgent need in this field for an innovative conductive silver paste that, under low-temperature curing conditions, can synergistically, rather than compromisingly, unify the two major properties of bending resistance and anti-sulfurization through novel material and structural design to meet the stringent application challenges of flexible keyboards. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a bend-resistant and sulfide-resistant conductive silver paste for flexible keyboards and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions: A bend-resistant and sulfide-resistant conductive silver paste for flexible keyboards, comprising the following components by weight percentage: 40-65% modified metallic silver powder; 30-40% organic carrier; 1-2% organic additives; and 10-30% organic solvent.

[0008] Furthermore, the modified metallic silver powder is a composite of flake silver powder and core-shell structured flake silver powder, which is obtained by surface treatment, wherein the core-shell structured flake silver powder and the flake silver powder are in a mass ratio of (30~5):(70~95).

[0009] Preferably, the tap density of the flake silver powder is 2.0-4.0 g / cm³. 3 The loose bulk density is 0.8-1.2 g / cm³. 3 The average particle size is 1-5 μm and the thickness is 0.1-1 μm.

[0010] Furthermore, the preparation method of the core-shell structured sheet silver powder includes the following steps: using sheet silver powder as a base, dispersing it in ethanol, reacting it with a tin source precursor and a precipitant under weakly alkaline conditions (pH 7-9) at 40-60°C and with the dispersant polyvinylpyrrolidone, and slowly stirring for 2-4 hours, a tin dioxide shell layer with a thickness of 5-20 nm is formed on the surface of the sheet silver powder; after the obtained reaction solution is allowed to stand and age for 12-24 hours, it is centrifuged, washed, vacuum dried at 70-90°C, and then calcined at a high temperature of 400-500°C for 1-2 hours to obtain a core-shell structured sheet silver powder with a silver core-tin dioxide shell layer structure.

[0011] Wherein, the tin source precursor is tin tetrachloride or stannate, and the molar ratio of the tin source precursor to the flake silver powder is (0.03-0.15):1; The precipitant is an ammonia-ethanol mixed solution or a urea aqueous solution, and the amount used is such that the pH value of the reaction solution is stably maintained at 7-9. The dispersant is polyvinylpyrrolidone, and the amount of dispersant used is 0.5% to 3.0% of the mass of silver powder.

[0012] Furthermore, the preparation method of the modified metallic silver powder includes the following steps: mixing core-shell structured flake silver powder and flake silver powder at a mass ratio of (30~5):(70~95), placing them in an ethanol solution of coupling agent, and stirring at 50~80℃ for 1~4h; the resulting product is filtered and dried to obtain modified metallic silver powder.

[0013] Furthermore, the coupling agent is one of bis-(γ-triethoxysilylpropyl)-polyether or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

[0014] The organic carrier is prepared by the following method: dissolving a polymer resin in isophorone and divalent ester, stirring at 70~80℃ until completely dissolved, cooling and filtering to obtain the organic carrier; the mass ratio of polymer resin, divalent ester and isophorone is (5~10):(5~10):(25~35).

[0015] Furthermore, the polymer resin is one or more of polyurethane resin, flexible epoxy resin, and acrylate elastomer, preferably polyurethane resin.

[0016] Furthermore, the organic additives include one or more of curing agents, thixotropic agents, and toughening agents.

[0017] Further, the curing agent is one of hexamethylene diisocyanate trimer or isophorone diisocyanate trimer; the thixotropic agent is one of quaternary ammonium salt modified organobentonite or polyamide wax; the toughening agent is a polyester-type or polyether-type thermoplastic polyurethane elastomer, preferably a polyester-type or polyether-type thermoplastic polyurethane elastomer, such as polyester-type thermoplastic polyurethane elastomer Desmopan 5377 A and polyether-type thermoplastic polyurethane elastomer Desmopan 3095 A, etc. In a further preferred embodiment, the organic additive is a mixture of polyurea and thermoplastic polyurethane elastomer in a mass ratio of 1:(0.1~1); Furthermore, the organic solvent is one or more of divalent esters, isophorone, diethylene glycol butyl ether acetate, and propylene glycol methyl ether acetate.

[0018] This invention also provides a method for preparing an anti-bending and anti-sulfurization conductive silver paste for flexible keyboards, which is prepared according to the following steps: (1) Prepare materials according to the following components and weight percentages: Modified metallic silver powder 40-65%, organic carrier 30-40%, organic additives 1-2%, organic solvent 10-30%; (2) Preparation of carrier: Weigh the polymer resin and organic solvent, heat them to 70~80℃ and keep the temperature constant. After the polymer resin is completely dissolved, filter it on a 300-400 mesh to remove impurities, and then obtain the organic carrier. (3) Production of conductive silver paste: First, add the weighed organic additives to the organic carrier and stir evenly. Then, continue to weigh the modified metallic silver powder and mix it thoroughly. The resulting mixed paste is ground in a three-roll mill until the fineness reaches below 15μm to obtain the conductive silver paste.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) Core-shell structure design to construct a physical barrier against sulfide and optimize the conductive pathway This invention innovatively employs a core-shell structured silver powder with a tin dioxide shell. Its working principle lies in the fact that the tin dioxide shell acts as an inert physical barrier, effectively preventing the diffusion and reaction of sulfides to the silver core, significantly improving the material's resistance to sulfidation. Simultaneously, surface treatment technology modifies the silver powder, enhancing its interfacial compatibility with the organic carrier and optimizing the contact network between conductive particles, ensuring good dispersion and electron transport efficiency even at high silver content.

[0020] (2) Surface treatment enhances bending adaptability and stabilizes the conductive network By surface-modifying core-shell and flake silver powders, a stable coupling layer is formed on the silver powder surface. The mechanism of this layer is to enhance the interfacial bonding strength and stress matching between the silver powder and the flexible resin system. When the conductive film layer is bent, it can effectively disperse and buffer interfacial stress, inhibiting the generation and propagation of cracks in the conductive network. Simultaneously, the stable interfacial bonding ensures a strong bond between the anti-sulfurization layer and the flexible substrate, preventing the separation of functional layers and performance degradation.

[0021] (3) The system works together to achieve a balance between bending resistance and sulfurization resistance. This invention constructs a synergistic mechanism at the material structure level by combining the chemical protection of the core-shell structure with the interface enhancement of surface treatment, supplemented by a matched flexible resin and toughening agent system. Its core lies in the fact that the core-shell structure provides intrinsic sulfur resistance, the surface treatment strengthens interfacial stress transfer and bonding stability, and the flexible carrier ensures overall deformation adaptability. This design effectively solves the problem of the mutual constraint between sulfur resistance and flexibility in traditional technologies, enabling the conductive silver paste to achieve a synergistic improvement in repeated bending resistance and long-term sulfur resistance stability while maintaining excellent conductivity. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0023] To verify that the present invention has good resistance to sulfurization and bending, experiments were conducted through the following examples. It should be noted that all raw materials mentioned in the present invention are commercially available, and the methods and instruments used are common in the field.

[0024] Comparative Example 1 (1) Prepare 100g of material according to the following composition and mass: Ordinary flake silver powder (unprocessed) 58g; Organic carrier (thermoplastic polyurethane resin) 34g; Curing agent (isocyanate) 0.5g; 1.5g of organic additives; 6g of organic solvent; The flake silver powder used is silver micro powder #1: tap density 3.5 g / cm³. 3 Loose packing density 1.5 g / cm³ 3 The average particle size D50 is 2.5 μm. The organic additives used are 1g polyurea and 0.5g polyester thermoplastic polyurethane elastomer, and in this embodiment, Desmopan 5377 A is used. The organic solvents used were 4g propylene glycol methyl ether acetate and 2g diethylene glycol butyl ether; (2) Preparation of organic carrier: Dissolve 6g of thermoplastic polyurethane resin in 28g of isophorone, stir at 75°C until completely dissolved, cool and filter to obtain organic carrier; (3) Preparation of conductive silver paste: Add organic additives and organic solvents to the organic carrier, stir evenly, add ordinary flake silver powder, pre-disperse and grind to a fineness of about 15μm by a three-roll mill to obtain conductive silver paste.

[0025] Comparative Example 2 (1) Prepare 100g of material according to the following composition and mass: Core-shell structured sheet-like silver powder (untreated with silane) 18g; Ordinary flake silver powder (untreated with silane) 40g; Organic carrier (thermoplastic polyurethane resin) 34g; Curing agent (isocyanate) 0.5g; 1.5g of organic additives; 6g of organic solvent; The flake silver powder used is silver micro powder #1: tap density 3.5 g / cm³. 3 Loose packing density 1.5 g / cm³ 3 The average particle size D50 is 2.5 μm. The organic additives used are 1g of polyurea and 0.5g of thermoplastic polyurethane elastomer; The organic solvents used were 4g propylene glycol methyl ether acetate and 2g diethylene glycol butyl ether; (2) Preparation of core-shell structured sheet silver powder: 100g of sheet silver powder (tap density 3.2g / cm³) was prepared. 3 A silver powder suspension was obtained by dispersing 0.1 mol of tin tetrachloride in 100 mL of ethanol and adding 1 g of polyvinylpyrrolidone. The tin tetrachloride solution was then slowly added dropwise to the silver powder suspension over 2 hours while stirring in a 50°C water bath. After another 2 hours of reaction, the mixture was allowed to stand for 12 hours. After centrifugation and washing, the powder was vacuum dried at 80°C and calcined at 450°C for 1 hour to obtain core-shell flake silver powder (shell thickness approximately 10 nm).

[0026] (3) Preparation of organic carrier: Dissolve 6g of thermoplastic polyurethane resin in 28g of isophorone, stir at 75°C until completely dissolved, cool and filter to obtain organic carrier; (4) Preparation of conductive silver paste: Add organic additives and organic solvents to the organic carrier, stir evenly, add ordinary flake silver powder and core-shell structure flake silver powder, pre-disperse, and grind to a fineness of about 15μm by a three-roll mill to obtain conductive silver paste.

[0027] Comparative Example 3 (1) Prepare 100g of material according to the following composition and mass: Ordinary flake silver powder (silane treated) 58g; Organic carrier (thermoplastic polyurethane resin) 34g; Curing agent (isocyanate) 0.5g; 1.5g of organic additives; 6g of organic solvent; The flake silver powder used is silver micro powder #1: tap density 3.5 g / cm³. 3 Loose packing density 1.5 g / cm³ 3 The average particle size D50 is 2.5 μm. The organic additives used are 1g of polyurea and 0.5g of thermoplastic polyurethane elastomer; The organic solvents used were 4g propylene glycol methyl ether acetate and 2g diethylene glycol butyl ether; (2) Treatment of flake silver powder: Ordinary flake silver powder was treated with 1.5wt% silane coupling agent KH550 ethanol solution at 25℃ for 30 minutes, filtered, washed and filtered twice with ethanol, and dried at 60℃ for 4 hours to obtain modified silver powder.

[0028] (3) Preparation of organic carrier: Dissolve 6g of thermoplastic polyurethane resin in 28g of isophorone, stir at 75°C until completely dissolved, cool and filter to obtain organic carrier; (4) Preparation of conductive silver paste: Add organic additives and organic solvents to the organic carrier, stir evenly, add ordinary flake silver powder (treated with silane), pre-disperse, and then grind to a fineness of about 15μm by a three-roll mill to obtain conductive silver paste.

[0029] Example 1 (1) Prepare 100g of material according to the following composition and mass: Core-shell structured sheet-like silver powder (silane treated) 18g; Ordinary flake silver powder (silane treated) 40g; Organic carrier (thermoplastic polyurethane resin) 34g; Curing agent (isocyanate) 0.5g; 1.5g of organic additives; 6g of organic solvent; The flake silver powder used is silver micro powder #1: tap density 3.5 g / cm³. 3 Loose packing density 1.5 g / cm³ 3 The average particle size D50 is 2.5 μm. The organic additives used are 1g of polyurea and 0.5g of thermoplastic polyurethane elastomer; The organic solvents used were 4g propylene glycol methyl ether acetate and 2g diethylene glycol butyl ether; Preparation of core-shell structured sheet-like silver powder: The method is the same as step (2) of Comparative Example 2.

[0030] Preparation of modified metallic silver powder: 16g of core-shell structured flake silver powder obtained in step (2) was mixed with 42g of ordinary flake silver powder, and an equal mass of ethanol solution containing 1.5wt% silane coupling agent KH550 was added. The mixture was stirred at 50°C for 1h, filtered, and then washed and filtered twice with ethanol. Finally, the mixture was dried at 60°C for 4h to obtain modified silver powder.

[0031] (4) Preparation of organic carrier: Dissolve 6g of thermoplastic polyurethane resin in 6g of divalent ester and 28g of isophorone, stir at 75°C until completely dissolved, filter through a 300-400 mesh screen to remove impurities, and obtain organic carrier. (5) Preparation of conductive silver paste: Add 1.5g of organic additive and 10g of organic solvent to 34g of organic carrier obtained in step (4), stir evenly, heat to 70~80℃ and keep the temperature constant. After the polymer resin is completely dissolved, add 65g of modified metallic silver powder obtained in step (3), pre-disperse and grind to a fineness of about 15μm by a three-roll mill to obtain conductive silver paste. Test method: Initial sheet resistance test: Using a four-probe tester, at least 5 points are measured at different locations in the conductive circuit of each sample, and the average value is taken as the initial sheet resistance value of the sample.

[0032] Resistance to sulfurization test: The test shall be conducted in accordance with the reference standard JESD22-A110 or the industry-standard high temperature and high humidity sulfurization test.

[0033] Bending resistance test: The test shall be conducted in accordance with the standard ASTM F1841 or IEC 60068-2-21.

[0034] The silver pastes prepared in the above four embodiments were screen-printed onto PET films and cured at 130°C for 15 minutes to form conductive circuits. Performance tests were then conducted, and the results are shown in Table 1 below. Table 1. Test results of comparative and example cases.

[0035] As shown in Table 1, the bending resistance of the conductive circuit gradually increases from Comparative Example 1 to Example 1, indicating that the bending resistance of the conductive silver paste and resin is effectively improved after silane treatment and the use of core-shell structured flake silver powder composite treatment. Comparative Examples 1 and 3, and Comparative Example 2 and Example 1 show that after silane treatment, the core-shell structure can effectively resist sulfidation, improving the sulfidation resistance of the silver powder and thus effectively enhancing the sulfidation resistance of the conductive silver paste. In summary, the synergistic effect of silane treatment and the use of core-shell structured flake silver powder composite treatment enables the conductive silver paste prepared in this invention to achieve a synergistic balance between bending resistance and sulfidation resistance.

[0036] Example 2 Prepare 100g of material according to the components and mass given in Example 1.

[0037] (1) Preparation of core-shell structured sheet-like silver powder: 100g of flake silver powder (tap density 3.5 g / cm³) 3 Silver powder (D50 = 2.5 μm) was dispersed in 400 mL of anhydrous ethanol to obtain a silver powder suspension.

[0038] Dissolve 0.1 mol of tin tetrachloride in 100 mL of ethanol, and add 1 g of polyvinylpyrrolidone to obtain a tin tetrachloride solution.

[0039] Under stirring in a 50°C water bath, tin tetrachloride solution and 60 ml of ammonia-ethanol solution (pH=8, where ammonia accounts for 50% v / v) were simultaneously and slowly added dropwise to the silver powder suspension over 2 hours. After continuing the reaction for another 2 hours, the mixture was allowed to stand for 12 hours. After centrifugation and washing, the powder was vacuum dried at 80°C and calcined at 450°C for 1 hour to obtain core-shell flake silver powder (shell thickness approximately 10 nm).

[0040] (2) Preparation of modified metallic silver powder: 30g of core-shell structured flake silver powder obtained in step (1) is mixed with 70g of ordinary flake silver powder, and an equal mass of ethanol solution containing 1.5wt% silane coupling agent KH550 is added. The mixture is treated at 60℃ for 2 hours, filtered and dried to obtain modified metallic silver powder.

[0041] (3) Preparation of organic carrier: Weigh 6g of thermoplastic polyurethane resin and dissolve it in 28g of isophorone. Stir at 75°C until completely dissolved, cool and filter to obtain organic carrier. (4) Preparation of conductive silver paste: 2g of organic additive (a mixture of 1g hexamethylene diisocyanate trimer and 1g polyamide wax) and organic solvent (30g diethylene glycol butyl ether acetate) are added to 34g of organic carrier obtained in step (3). After stirring evenly, 65g of modified metallic silver powder prepared in step (2) is added. After pre-dispersion, it is ground to a fineness of about 15μm by a three-roll mill to obtain conductive silver paste.

[0042] Example 3 Prepare 100g of material according to the components and mass given in Example 1.

[0043] (1) Preparation of core-shell structured sheet-like silver powder: 100g of flake silver powder (tap density 3.2 g / cm³) 3 Silver powder (D50 = 2.5 μm) was dispersed in 400 mL of anhydrous ethanol to obtain a silver powder suspension.

[0044] Dissolve 0.1 mol of tin tetrachloride in 100 mL of ethanol, and add 1 g of polyvinylpyrrolidone to obtain a tin tetrachloride solution.

[0045] Under stirring in a 50°C water bath, tin tetrachloride solution and 60 ml of ammonia-ethanol solution (pH=8, where ammonia accounts for 50% v / v) were simultaneously and slowly added dropwise to the silver powder suspension over 2 hours. After continuing the reaction for another 2 hours, the mixture was allowed to stand for 12 hours. After centrifugation and washing, the powder was vacuum dried at 80°C and calcined at 450°C for 1 hour to obtain core-shell flake silver powder (shell thickness approximately 10 nm).

[0046] (2) Preparation of modified metallic silver powder: 5g of core-shell structured flake silver powder obtained in step (1) is mixed with 95g of ordinary flake silver powder, and an equal mass of ethanol solution containing 1.5wt% silane coupling agent KH550 is added. The mixture is treated at 60℃ for 2 hours, filtered and dried to obtain modified metallic silver powder.

[0047] (3) Preparation of organic carrier: Weigh 6g of thermoplastic polyurethane resin and dissolve it in 28g of isophorone. Stir at 75°C until completely dissolved, cool and filter to obtain organic carrier. (4) Preparation of conductive silver paste: Add 1g of organic additive (1g of hexamethylene diisocyanate trimer in this embodiment) and organic solvent (10g of diethylene glycol butyl ether acetate in this embodiment) to 34g of organic carrier obtained in step (3). After stirring evenly, add 40g of modified metallic silver powder obtained in step (2). After pre-dispersing, grind it to a fineness of about 15μm by a three-roll mill to obtain conductive silver paste.

[0048] The properties of the conductive silver pastes obtained in Examples 2-3 were tested using the same method as in Example 1, as follows: Table 2 Test Results of Examples 2-3

[0049] As can be seen from Table 2: A comparison of Examples 2 (65% modified metallic silver powder) and 3 (40% modified metallic silver powder) suggests that, with an increase in the total amount of silver powder, a denser and more continuous conductive network is formed in the slurry system while maintaining a reasonable core-shell structure silver powder ratio. This means that a higher silver powder content results in a higher proportion of silver cores physically protected by a tin dioxide shell per unit volume, thereby effectively improving the overall anti-sulfurization performance. Furthermore, increasing the core-shell structure silver powder ratio within a specific range (e.g., 5%-30%) can further enhance the shell coverage and barrier effect, strengthening the ability to block sulfur diffusion.

Claims

1. A bend-resistant and sulfide-resistant conductive silver paste for flexible keyboards, characterized in that, The conductive silver paste comprises the following components by weight percentage: 40-65% modified metallic silver powder; 30-40% organic carrier; 1-2% organic additives; and 10-30% organic solvent.

2. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 1, characterized in that, The modified metallic silver powder is a composite of flake silver powder and core-shell structured flake silver powder, which is obtained by surface treatment, wherein the core-shell structured flake silver powder and flake silver powder are in a mass ratio of (30~5):(70~95).

3. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 2, characterized in that, The core-shell structured sheet silver powder is prepared by the following method: using sheet silver powder as a base, it is dispersed in ethanol, and reacted with tin source precursor and precipitant under weakly alkaline conditions at 40-60°C and with the action of a dispersant. After slow stirring for 2-4 hours, a tin dioxide shell layer with a thickness of 5-20 nm is formed on the surface of the sheet silver powder. After the resulting reaction solution is allowed to stand and age, it is centrifuged, washed, vacuum dried, and calcined to obtain a core-shell structured sheet silver powder with a silver core-tin dioxide shell layer.

4. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 3, characterized in that, The tin source precursor is tin tetrachloride or stannate, and the molar ratio of the tin source precursor to the flake silver powder is (0.03-0.15):1; The precipitant is an ammonia-ethanol mixed solution or a urea aqueous solution, and the amount used is such that the pH value of the reaction solution is stably maintained at 7-9. The dispersant is polyvinylpyrrolidone, and the amount of dispersant used is 0.5% to 3.0% of the mass of silver powder.

5. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 2, characterized in that, The modified metallic silver powder is prepared by the following method: core-shell structured lamellar silver powder and lamellar silver powder are mixed in a certain proportion and then placed in an ethanol solution of coupling agent and stirred; after treatment, the mixture is filtered and dried to obtain the modified metallic silver powder.

6. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 5, characterized in that, The coupling agent is one of bis-(γ-triethoxysilylpropyl)-polyether or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

7. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 1, characterized in that, The organic carrier is prepared by the following method: dissolving a polymer resin in isophorone and divalent ester, stirring at 70~80℃ until completely dissolved, cooling and filtering to obtain the organic carrier; The polymer resin is one or more of polyurethane resin, flexible epoxy resin, and acrylate elastomer; The mass ratio of the polymer resin, divalent ester and isophorone is (5~10):(5~10):(25~35).

8. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 1, characterized in that, The organic additives include one or more of curing agents, thixotropic agents, and toughening agents; The organic solvent is one or more of divalent esters, isophorone, diethylene glycol butyl ether acetate, and propylene glycol methyl ether acetate.

9. The anti-bending and anti-sulfurization conductive silver paste for flexible keyboards according to claim 8, characterized in that, The curing agent is one of hexamethylene diisocyanate trimer or isophorone diisocyanate trimer; the thixotropic agent is one of quaternary ammonium salt modified organic bentonite or polyamide wax; and the toughening agent is polyester-type or polyether-type thermoplastic polyurethane elastomer.

10. A method for preparing an anti-bending and anti-sulfurization conductive silver paste for a flexible keyboard as described in any one of claims 1 to 9, characterized in that, Prepare according to the following steps: (1) Prepare materials according to the following components and weight percentages: Modified metallic silver powder 40-65%, organic carrier 30-40%, organic additives 1-2%, organic solvent 10-30%; (2) Preparation of carrier: Weigh the polymer resin and organic solvent, heat them to 70~80℃ and keep the temperature constant. After the polymer resin is completely dissolved, filter it on the mesh to remove impurities, and then obtain the organic carrier. (3) Production of conductive silver paste: First, add organic additives to the organic carrier obtained in step (2), stir evenly, then add modified metallic silver powder and mix thoroughly. Grind the resulting mixed paste to obtain the conductive silver paste.

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