High-weather-resistance low-temperature silver paste and preparation method thereof

Abstract

The invention discloses high-weather-resistance low-temperature silver paste and a preparation method thereof. The coating comprises the following components in parts by weight: 5-10 parts of fluorocarbon resin, 25-40 parts of an organic solvent, 0.5-2 parts of a latent curing agent, 1-4 parts of a functional aid and 50-70 parts of modified silver powder, wherein the fluorocarbon resin is soluble fluorocarbon resin; the organic solvent is an ester solvent with the boiling point of 180-230 DEG C; and the latent curing agent is a blocked isocyanate curing agent. The invention has the advantages of corrosion resistance, water vapor resistance, chemical resistance and long-term stability; the silver paste has hydrophobic, antifouling, anti-adhesion and anti-scratch effects, and the weather resistance of the silver paste is further improved; according to the low-temperature silver paste, the surface of the silver powder is coated with the fluorosilane coupling agent, corrosion of external factors such as water vapor to the silver powder is blocked through fluorine groups, reduction of the conductivity and pulverization of a film layer in the long-term use process are avoided, and therefore the low-temperature silver paste with high conductivity and high weather resistance is formed.

Description

Technical Field

[0001] The present invention relates to a slurry production and preparation technology, and in particular to a high-weather-resistant low-temperature silver slurry and a preparation method thereof. Background Art

[0002] With the development of the electronics and electronic materials industries, the conductive silver paste industry has received widespread attention and has experienced significant growth in China. Among conductive silver pastes, low-temperature silver pastes, due to their excellent properties of high conductivity, high flexibility, and low-temperature curing (typically below 200°C), have been gradually applied to various fields such as touch screens, membrane switches, RFID cards, and notebook keyboard circuits. They form conductive circuits or structures on printed substrates. Mass production has been achieved and the technology is undergoing continuous advancement.

[0003] Low-temperature silver paste is composed of polymer resin, organic solvent, silver powder and functional additives, wherein the polymer resin is usually a compound of one or more of polyester resin, polyurethane resin, epoxy resin and chlorovinyl resin. Low-temperature silver paste is susceptible to erosion by external factors such as water vapor, oxygen, ultraviolet light, heat and cold, sweat, etc. in a long-term working environment. Even if a curing agent is used for cross-linking, the polymer resin is still prone to aging and deterioration, resulting in reduced adhesion to the substrate and silver powder, causing problems such as decreased adhesion, increased resistance and yellowing of the film layer. In order to achieve the printing of fine conductive circuits, the particle size of the silver powder in the low-temperature silver paste is often micron-submicron level, with a large specific surface area, resulting in an increase in its adsorption of water vapor and oxidizing gases, and being corroded faster in harsh environments, which reduces the conductivity of the low-temperature silver paste and causes instability in the performance of electronic devices. Therefore, improving the weather resistance of existing low-temperature silver paste is still a technical problem that needs to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a highly weather-resistant silver paste having good conductivity and printability, as well as excellent weather resistance, and can effectively resist corrosion in harsh environments such as water vapor, salt spray, and boiling water, and a preparation method thereof.

[0005] In order to solve the above technical problems, the high weather resistance and low temperature silver paste of the present invention comprises the following components in parts by weight: Fluorocarbon resin: 5-10 parts Organic solvent: 25-40 parts Latent curing agent: 0.5-2 parts Functional additive: 1-4 parts Modified silver powder: 50-70 parts; The fluorocarbon resin adopts a soluble fluorocarbon resin; the organic solvent adopts an ester solvent with a boiling point of 180 to 230° C.; and the latent curing agent is a blocked isocyanate curing agent.

[0006] The fluorocarbon resin is tetrafluoroethylene-alkyl vinyl ester copolymer resin.

[0007] The organic solvent is a combination of one or more of ethylene glycol butyl ether acetate, dimethyl glutarate, dimethyl adipate, diethylene glycol ethyl ether acetate and DBE.

[0008] The functional auxiliary agent is a combination of a silane coupling agent and polytetrafluoroethylene wax powder.

[0009] The silane coupling agent is a combination of one or more of silane coupling agent KH171, silane coupling agent KH172, silane coupling agent KH560, silane coupling agent KH570 and silane coupling agent KH792.

[0010] The modified silver powder is micron-sized silver powder that has been modified by coating with a fluorosilane coupling agent.

[0011] The micron-sized silver powder is a combination of micron-sized flaky silver powder and micron-sized spherical silver powder. In terms of weight ratio, the ratio of micron-sized flaky silver powder to micron-sized spherical silver powder in the modified silver powder is 2-5:1.

[0012] The micron-sized flaky silver powder has a particle size of 3.0 to 5.0 μm and a tap density of 1.5 to 2.5 g / cm 3 The micron-sized spherical silver powder has a particle size of 1.0 to 1.5 μm and a tap density of 3.0 to 4.0 g / cm 3 .

[0013] The latent curing agent is a blocked isocyanate curing agent with a deblocking temperature of 80 to 120°C.

[0014] The fluorosilane coupling agent is one of perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane and trifluoropropylmethyldimethoxysilane.

[0015] A method for preparing a high-weather-resistant low-temperature silver paste comprises the following steps: (1) Silver powder coating modification: The fluorosilane coupling agent is dissolved in isopropyl alcohol and mixed uniformly to prepare a 2%wt fluorosilane coupling agent isopropyl alcohol solution; micron-sized silver powder and the fluorosilane coupling agent isopropyl alcohol solution are weighed in a weight ratio of 4:1, and dispersed and mixed at a speed of 800-1200 rpm for 30-60 minutes; after the dispersion is completed, the mixture is dried at 60-80°C for 4-6 hours, and the dried silver powder is crushed to a particle size of no more than 5.0 μm using a jet mill to eliminate the agglomeration of the silver powder during drying, thereby obtaining a modified silver powder; (2) Preparation of organic carrier: Weigh the fluorocarbon resin and organic solvent according to the weight ratio, mix and stir at 60-90°C until they are evenly dissolved and dispersed, with a stirring speed of 400-700 rpm. After dissolution, use a 400-mesh filter to remove impurities and cool to room temperature for use; (3) Preparation of silver paste matrix: The organic carrier, latent curing agent and functional additive prepared in step (2) are weighed according to the weight ratio, and mixed evenly in a planetary disperser at a dispersion speed of 1000 to 1500 rpm for 30 to 90 minutes to obtain a silver paste matrix; (4) Preparation of low-temperature silver paste: The silver paste matrix and modified silver powder prepared in step (3) are weighed according to the weight ratio, mixed evenly in a planetary disperser at a dispersion speed of 1000 to 1500 rpm for 30 to 90 min, and then placed in a three-roll grinder for grinding until the fineness is less than 5 μm to obtain the high weather resistance low-temperature silver paste.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a solvent-soluble fluorocarbon resin as the binding phase of the low-temperature silver paste, and utilizes the characteristics of the fluorocarbon resin, such as stable chemical bonds, stable molecular structure, hydrophobicity and stain resistance, to avoid the performance degradation caused by corrosion and aging of commonly used polymer resins, so that the low-temperature silver paste of the present invention has the characteristics of corrosion resistance, water vapor resistance, chemical resistance and long-term stability; polytetrafluoroethylene wax powder is used as a functional auxiliary component, which not only has a thickening and thixotropic function, but also forms a protective layer after the silver paste is dried and solidified, and has the effects of hydrophobicity, stain resistance, anti-adhesion and scratch resistance. Further improve the weather resistance of silver paste; use low-density, high-filling flaky silver powder as the main conductive filler, spherical silver powder fills the gaps between the flaky silver powder to form a dense conductive network, and the silver powder is treated and modified with a fluorosilane coupling agent to improve its compatibility and dispersibility in the fluorocarbon resin matrix. The fluorosilane coupling agent coats the surface of the silver powder, and the fluorine group blocks the erosion of the silver powder by external factors such as water vapor, avoiding the decrease in conductivity and powdering of the film during long-term use, thereby forming a low-temperature silver paste with high conductivity and high weather resistance. DETAILED DESCRIPTION

[0017] The highly weather-resistant low-temperature silver paste and the preparation method thereof of the present invention will be further described in detail below in conjunction with specific embodiments. Example 1

[0018] The high weather resistance low temperature silver paste of this embodiment comprises the following components in parts by weight: Fluorocarbon resin: 5-10 parts Organic solvent: 25-40 parts Latent curing agent: 0.5-2 parts Functional additive: 1-4 parts Modified silver powder: 50-70 parts; Among them, fluorocarbon resin uses tetrafluoroethylene-alkyl vinyl ester copolymer resin; fluorocarbon resin has a unique CF chemical bond and molecular structure. The high bond energy of the CF chemical bond (487KJ / mol) makes it extremely chemically stable; the F atom wraps the CC bond main chain in a three-dimensional helical structure, which has a "shielding" effect on the carbon chain skeleton, ensuring the tightness of the molecular structure and preventing the penetration and destruction of the molecular structure by external substances such as gas and liquid; at the same time, fluorocarbon resin has low surface energy and is hydrophobic and stain-resistant; but commonly used fluorocarbon resins have poor solubility and use conventional Organic solvents are difficult to dissolve and cannot be prepared into slurries. For example, polytetrafluoroethylene (PTFE) is almost insoluble in any solvent, and polyvinylidene fluoride (PVDF) can only be dissolved in highly polar solvents such as DMF, DMAC, and NMP. These solvents are highly toxic and do not meet environmental protection requirements. The tetrafluoroethylene-alkyl vinyl ester copolymer resin used in this embodiment has the basic structure of a fluorocarbon resin, and the alkyl vinyl ester groups it contains make it solvent-soluble. The hydroxyl groups contained in the side chains can cross-link with the curing agent to further improve the density, stability, and mechanical properties of the film layer.

[0019] The organic solvent is a combination of one or more of ethylene glycol butyl ether acetate, dimethyl glutarate, dimethyl adipate, diethylene glycol ethyl ether acetate and DBE; the present invention uses an ester solvent with a boiling point of 180 to 230°C, which not only ensures the resin solubility, silver paste printability and dryability, but also takes into account environmental protection requirements with low toxicity and low odor; the latent curing agent is a blocked isocyanate curing agent with an unblocking temperature of 80 to 120°C; the blocked isocyanate in the present invention can undergo a cross-linking reaction with the hydroxyl group of the side chain of the tetrafluoroethylene-alkyl vinyl ester copolymer resin above the unblocking temperature, thereby increasing the cross-linking density of the resin and improving the density of the silver paste film layer.

[0020] The functional additive is a combination of a silane coupling agent and polytetrafluoroethylene wax powder. The silane coupling agent improves the adhesion between the silver paste film layer and the substrate. The polytetrafluoroethylene wax powder acts as a thickening and thixotropic agent. When dispersed in the silver paste, it increases the viscosity of the silver paste, regulates the flow state, and prevents silver powder sedimentation. During the drying and curing process, the polytetrafluoroethylene wax powder migrates to the surface of the silver paste film layer, forming a polytetrafluoroethylene protective layer, enhancing the silver paste film layer's resistance to water vapor, corrosion, stains, and chemicals. Preferably, the silane coupling agent can be a combination of one or more of the commercially available silane coupling agents KH171, KH172, KH560, KH570, and KH792.

[0021] The modified silver powder is a micron-sized silver powder coated with a fluorosilane coupling agent and modified. The micron-sized silver powder is a combination of micron-sized flaky silver powder and micron-sized spherical silver powder. Preferably, the ratio of micron-sized flaky silver powder to micron-sized spherical silver powder in the modified silver powder is 2-5:1 by weight. The particle size of the micron-sized flaky silver powder is 3.0-5.0 μm, and the tap density is 1.5-2.5 g / cm 3 The particle size of micron-sized spherical silver powder is 1.0-1.5 μm, and the tap density is 3.0-4.0 g / cm 3 ; Preferably, the fluorosilane coupling agent is one of perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane and trifluoropropylmethyldimethoxysilane. Example 2

[0022] The high weather resistance low temperature silver paste of this embodiment is prepared by the following steps: (1) Silver powder coating modification: Perfluorooctyltrimethoxysilane was dissolved in isopropanol and mixed evenly to prepare a 2% wt perfluorooctyltrimethoxysilane isopropanol solution; 71.4 parts by weight of micron-sized flaky silver powder (particle size 3.0-5.0 μm, tap density 2.0 g / cm 3 ), 28.6 parts of micron-sized spherical silver powder (particle size 1.0-1.5 μm, tap density 3.5 g / cm 3 ) and 25 parts of perfluorooctyltrimethoxysilane isopropanol solution were dispersed and mixed at a speed of 1000 rpm for 45 minutes; after dispersion, the silver powder was dried at 70°C for 5 hours, and the dried silver powder was crushed to a particle size of no more than 5 μm using a jet mill to eliminate the agglomeration of the silver powder during drying, thereby obtaining modified silver powder.

[0023] (2) Preparation of organic carrier: Weigh 6 parts of tetrafluoroethylene-alkyl vinyl ester copolymer resin and 24 parts of DBE by weight, mix and stir at 80°C until uniformly dissolved and dispersed, with a stirring speed of 500 rpm. After dissolution, use a 400-mesh filter to remove impurities and cool to room temperature for use.

[0024] (3) Preparation of silver paste matrix: 30 parts by weight of the organic carrier prepared in step (2), 0.6 parts of blocked isocyanate curing agent (deblocking temperature 90°C), 1 part of silane coupling agent KH560 and 1 part of polytetrafluoroethylene wax powder were weighed and mixed uniformly in a planetary disperser at a dispersion speed of 1200 rpm for 60 min to obtain a silver paste matrix.

[0025] (4) Preparation of low-temperature silver paste: 32.6 parts of the silver paste matrix prepared in step (3) and 67.4 parts of the modified silver powder prepared in step (1) were weighed and mixed evenly in a planetary disperser at a dispersion speed of 1200 rpm for 60 min. The mixture was then placed in a three-roll mill for grinding until the fineness was less than 5 μm to obtain the high weather resistance and low temperature silver paste of the present invention. Example 3

[0026] The high weather resistance low temperature silver paste of this embodiment is prepared by the following steps: (1) Silver powder coating modification: Perfluorooctyl triethoxysilane was dissolved in isopropanol and mixed evenly to prepare a 2% wt perfluorooctyl triethoxysilane isopropanol solution; 75 parts by weight of micron-sized flaky silver powder (particle size 3.0-5.0 μm, tap density 2.0 g / cm 3 ), 25 parts of micron-sized spherical silver powder (particle size 1.0-1.5 μm, tap density 3.5 g / cm 3 ) and 25 parts of perfluorooctyltriethoxysilane isopropanol solution were dispersed and mixed at a speed of 1000 rpm for 45 minutes; after the dispersion was completed, the silver powder was dried at 70°C for 5 hours, and the dried silver powder was crushed to a particle size of no more than 5μm using a jet mill to eliminate the agglomeration of the silver powder during drying, thereby obtaining modified silver powder.

[0027] (2) Preparation of organic carrier: Weigh 7 parts of tetrafluoroethylene-alkyl vinyl ester copolymer resin and 28 parts of dimethyl adipate by weight, mix and stir at 80°C until uniformly dissolved and dispersed, with a stirring speed of 500 rpm. After dissolution, use a 400-mesh filter to remove impurities and cool to room temperature for use.

[0028] (3) Preparation of silver paste matrix: 35 parts of the organic carrier prepared in step (2), 0.7 parts of blocked isocyanate curing agent (deblocking temperature 90°C), 1 part of silane coupling agent KH560 and 1 part of polytetrafluoroethylene wax powder were weighed and mixed uniformly in a planetary disperser at a dispersion speed of 1200 rpm for 60 min to obtain a silver paste matrix.

[0029] (4) Preparation of low-temperature silver paste: 37.7 parts of the silver paste matrix prepared in step (3) and 62.3 parts of the modified silver powder prepared in step (1) were weighed and mixed evenly in a planetary disperser at a dispersion speed of 1200 rpm for 60 min. The mixture was then placed in a three-roll mill for grinding until the fineness was less than 5 μm to obtain the high weather resistance and low temperature silver paste of the present invention. Example 4

[0030] The high weather resistance low temperature silver paste of this embodiment is prepared by the following steps: (1) Silver powder coating modification: Perfluorodecyltrimethoxysilane was dissolved in isopropanol and mixed evenly to prepare a 2% wt perfluorodecyltrimethoxysilane isopropanol solution; 77.8 parts by weight of micron-sized flaky silver powder (particle size 3.0-5.0 μm, tap density 2.0 g / cm 3 )、22.2 parts of micron-sized spherical silver powder (particle size 1.0-1.5 μm, tap density 3.5 g / cm 3 ) and 25 parts of perfluorodecyltrimethoxysilane isopropanol solution were dispersed and mixed at a speed of 1000 rpm for 45 minutes; after dispersion, the silver powder was dried at 70°C for 5 hours, and the dried silver powder was crushed to a particle size of no more than 5.0 μm using a jet mill to eliminate the agglomeration of the silver powder during drying, thereby obtaining modified silver powder.

[0031] (2) Preparation of organic carrier: In parts by weight, 8 parts of tetrafluoroethylene-alkyl vinyl ester copolymer resin, 10.6 parts of ethylene glycol butyl ether acetate and 21.4 parts of DBE were weighed and mixed at 80°C and stirred until uniformly dissolved and dispersed. The stirring speed was 500 rpm. After dissolution, impurities were removed through a 400-mesh filter and cooled to room temperature for use.

[0032] (3) Preparation of silver paste matrix: 40 parts of the organic carrier prepared in step (2), 0.8 parts of blocked isocyanate curing agent (deblocking temperature 90°C), 1 part of silane coupling agent KH570 and 1.2 parts of polytetrafluoroethylene wax powder were weighed and mixed uniformly in a planetary disperser at a dispersion speed of 1200 rpm for 60 min to obtain a silver paste matrix.

[0033] (4) Preparation of low-temperature silver paste: 43 parts of the silver paste matrix prepared in step (3) and 57 parts of the modified silver powder prepared in step (1) were weighed and mixed uniformly in a planetary disperser at a dispersion speed of 1200 rpm for 45 min. The mixture was then placed in a three-roll mill for grinding until the fineness was less than 5 μm to obtain the high weather resistance and low temperature silver paste of the present invention. Example 5

[0034] A high weather resistance low temperature silver paste is prepared by the following steps: (1) Silver powder coating modification: Dissolve trifluoropropyltrimethoxysilane in isopropanol and mix evenly to prepare a 2%wt trifluoropropyltrimethoxysilane isopropanol solution; weigh 81.8 parts by weight of micron-sized flaky silver powder (particle size 3.0-5.0 μm, tap density 2.0 g / cm3 )、18.2 parts of micron-sized spherical silver powder (particle size 1.0-1.5 μm, tap density 3.5 g / cm 3 ) and 25 parts of trifluoropropyltrimethoxysilane isopropanol solution were dispersed and mixed at a rotation speed of 1000 rpm for 45 minutes; after dispersion, the silver powder was dried at 70°C for 5 hours, and the dried silver powder was crushed to a particle size of no more than 5.0 μm using a jet mill to eliminate the agglomeration of the silver powder during drying, thereby obtaining modified silver powder.

[0035] (2) Preparation of organic carrier: Weigh 9 parts of tetrafluoroethylene-alkyl vinyl ester copolymer resin, 12 parts of ethylene glycol butyl ether acetate, and 24 parts of diethylene glycol ethyl ether acetate in parts by weight, mix and stir at 80°C until uniformly dissolved and dispersed, with a stirring speed of 500 rpm. After dissolution, use a 400-mesh filter to remove impurities and cool to room temperature for use.

[0036] (3) Preparation of silver paste matrix: 45 parts of the organic carrier prepared in step (2), 0.9 parts of blocked isocyanate curing agent (deblocking temperature 90°C), 1 part of silane coupling agent KH570 and 1.4 parts of polytetrafluoroethylene wax powder were weighed in parts by weight and mixed evenly in a planetary disperser at a dispersion speed of 1200 rpm for 60 min to obtain a silver paste matrix.

[0037] (4) Preparation of low-temperature silver paste: 48.3 parts of the silver paste matrix prepared in step (3) and 51.7 parts of the modified silver powder prepared in step (1) were weighed and mixed uniformly in a planetary disperser at a dispersion speed of 1200 rpm for 45 min. The mixture was then placed in a three-roll mill for grinding until the fineness was less than 5 μm to obtain the high weather resistance and low temperature silver paste of the present invention.

[0038] Comparative Example 1 The method is basically the same as Example 1, except that the fluorocarbon resin is replaced with a saturated polyester resin commonly used in low-temperature silver paste on the market, and the other components and weight ratios remain unchanged.

[0039] Comparative Example 2 The method is basically the same as Example 1, except that polytetrafluoroethylene wax powder is not added, and the other components and weight ratios remain unchanged.

[0040] Comparative Example 3 The method is basically the same as Example 1, except that the micron-sized silver powder is not subjected to the fluorosilane coupling agent coating modification treatment, but is directly mixed and ground with the silver paste matrix to prepare a low-temperature silver paste, and the weight ratio remains unchanged.

[0041] Performance Testing The low-temperature silver paste prepared in Examples 2 to 5 of the present invention and Comparative Examples 1 to 3 was printed on a PET film by screen printing. The screen was 250 mesh and the thickness of the photosensitive adhesive was 15 μm. The curing temperature was 120°C and the curing time was 30 min. After curing, the square resistance was tested using a four-probe tester, and the adhesion was tested using the hundred-grid method. The low-temperature silver paste prepared in Examples 2 to 5 and Comparative Examples 1 to 3 after curing was subjected to constant temperature and humidity tests (85°C, 85% RH, 720h), salt spray resistance (5% NaCl solution, 35°C, 96h) and boiling water tests (80°C, 24h). After the test was completed, the square resistance and adhesion were tested using the same method. The test results are shown in Table 1: Table 1

[0042] It can be seen from the above test results that under conventional test conditions after curing, Examples 2 to 5 and Comparative Examples 1 to 3 all have good square resistance and adhesion. After constant temperature, salt spray and boiling water tests, the low-temperature silver paste prepared in Examples 2 to 5 showed excellent weather resistance, specifically manifested in a small change in square resistance and adhesion maintained at 5B. The conventional resin system used in Comparative Example 1 has insufficient environmental stability, the surface of the silver paste film layer in Comparative Example 2 lacks a protective layer, and the silver powder surface in Comparative Example 3 is not modified, resulting in a decrease in corrosion resistance, which is manifested in a decrease in adhesion and a significant increase in square resistance. In summary, the high weather resistance low-temperature silver paste prepared by the present invention can remain stable under harsh environments, overcomes the problem of performance degradation caused by corrosion in long-term use of existing silver paste, and has great practicality.

[0043] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A high weather resistance low temperature silver paste, characterized in that, In parts by weight, it comprises the following components: Fluorocarbon resin: 5-10 parts Organic solvent: 25-40 parts Latent curing agent: 0.5-2 parts Functional additives: 1-4 parts Modified silver powder: 50-70 parts; The fluorocarbon resin adopts a soluble fluorocarbon resin; the organic solvent adopts an ester solvent with a boiling point of 180 to 230° C.; and the latent curing agent is a blocked isocyanate curing agent.

2. The high weather resistance low temperature silver paste according to claim 1, characterized in that: The fluorocarbon resin is tetrafluoroethylene-alkyl vinyl ester copolymer resin.

3. The high weather resistance low temperature silver paste according to claim 1 or 2, characterized in that: The organic solvent is a combination of one or more of ethylene glycol butyl ether acetate, dimethyl glutarate, dimethyl adipate, diethylene glycol ethyl ether acetate and DBE.

4. The high weather resistance low temperature silver paste according to claim 3, characterized in that: The functional auxiliary agent is a combination of a silane coupling agent and polytetrafluoroethylene wax powder.

5. The high weather resistance low temperature silver paste according to claim 4, characterized in that: The silane coupling agent is a combination of one or more of silane coupling agent KH171, silane coupling agent KH172, silane coupling agent KH560, silane coupling agent KH570 and silane coupling agent KH792.

6. The high weather resistance low temperature silver paste according to claim 1, 2, 4 or 5, characterized in that: The modified silver powder is micron-sized silver powder that has been modified by coating with a fluorosilane coupling agent.

7. The high weather resistance and low temperature silver paste according to claim 6, characterized in that: The micron-sized silver powder is a combination of micron-sized flaky silver powder and micron-sized spherical silver powder. In terms of weight ratio, the ratio of micron-sized flaky silver powder to micron-sized spherical silver powder in the modified silver powder is 2-5: 1； The high weather resistance and low temperature silver paste according to claim 6 is characterized in that the particle size of the micron-sized flaky silver powder is 3.0 to 5.0 μm, and the tap density is 1.5 to 2.5 g / cm 3 The micron-sized spherical silver powder has a particle size of 1.0 to 1.5 μm and a tap density of 3.0 to 4.0 g / cm 3 .

8. The high weather resistance low temperature silver paste according to claim 1, characterized in that: The latent curing agent is a blocked isocyanate curing agent with a deblocking temperature of 80 to 120°C.

9. The high weather resistance and low temperature silver paste according to claim 6, characterized in that: The fluorosilane coupling agent is one of perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane and trifluoropropylmethyldimethoxysilane.

10. A method for preparing a high weather resistance low temperature silver paste, characterized in that: The following steps are involved: (1) Silver powder coating modification: The fluorosilane coupling agent is dissolved in isopropyl alcohol and mixed uniformly to prepare a 2%wt fluorosilane coupling agent isopropyl alcohol solution; micron-sized silver powder and the fluorosilane coupling agent isopropyl alcohol solution are weighed in a weight ratio of 4:1, and dispersed and mixed at a speed of 800-1200 rpm for 30-60 minutes; after the dispersion is completed, the mixture is dried at 60-80°C for 4-6 hours, and the dried silver powder is crushed to a particle size of no more than 5.0 μm using a jet mill to eliminate the agglomeration of the silver powder during drying, thereby obtaining a modified silver powder; (2) Preparation of organic carrier: Weigh the fluorocarbon resin and organic solvent according to the weight ratio, mix and stir at 60-90°C until they are evenly dissolved and dispersed, with a stirring speed of 400-700 rpm. After dissolution, use a 400-mesh filter to remove impurities and cool to room temperature for use; (3) Preparation of silver paste matrix: The organic carrier, latent curing agent and functional additive prepared in step (2) are weighed according to the weight ratio, and mixed evenly in a planetary disperser at a dispersion speed of 1000 to 1500 rpm for 30 to 90 minutes to obtain a silver paste matrix; (4) Preparation of low-temperature silver paste: The silver paste matrix and modified silver powder prepared in step (3) are weighed according to the weight ratio, mixed evenly in a planetary disperser at a dispersion speed of 1000 to 1500 rpm for 30 to 90 min, and then placed in a three-roll grinder for grinding until the fineness is less than 5 μm to obtain the high weather resistance low-temperature silver paste.

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