Conductive silver paste for geothermal film and preparation method thereof

Abstract

The present invention relates to a geothermal film conductive silver paste and a preparation method thereof, comprising the following components in parts by weight: 35-45 parts nanometer aqueous silver powder; 10-15 parts ultrafine graphene powder; 0.5-1 part Triton X-100; 30-35 parts aqueous polyurethane resin emulsion; 2-5 parts deionized water; 2-5 parts isopropyl alcohol; 0.2-0.5 parts adhesion promoter; 0.5-1 part dibutyl phthalate; 1-1.5 parts ethyl acetate; 0.2-0.5 parts hydrophilic silica; and 0.1-0.5 parts silicone defoamer. The silver paste product is obtained by carrier configuration, silver powder pretreatment, batching, high-speed dispersion, three-roll grinding, filtration, finished product testing, homogenous stirring, and canning. Compared with the prior art, the present invention can obtain a geothermal film conductive silver paste with stable resistance, fast heating rate, uniform heat generation, and strong adhesion.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic materials and relates to a geothermal film conductive silver paste and a preparation method thereof. Background Art

[0002] Conductive printing ink, commonly known as paste ink, is a paste made by dispersing conductive materials (gold, silver, copper, and carbon) in a binder. It exhibits a certain degree of conductivity and can be used to print conductive dots or circuits. Metallic and carbon-based conductive inks have reached practical use and are used in printed circuits, electrodes, electroplating substrates, keyboard contacts, printed resistors, and other materials.

[0003] Conductive inks consist of conductive fillers, binders, solvents, and additives. Silver and copper powders, which have the highest conductivity, are used as conductive fillers, though gold powder, graphite, carbon black (specialized conductive carbon black is now available), carbon fiber, and nickel powder are sometimes used. Synthetic resins used as binders include epoxy resins, alkyd resins, acrylic resins, polyurethane resins, melamine formaldehyde resins, phenolic resins, and vinyl chloride-vinyl acetate copolymers. The solvent used is an environmentally friendly, mid-boiling-range solvent specifically designed for screen inks, with a boiling point between 120°C and 230°C. Additives such as dispersants, lubricants, and coupling agents are added as needed. Required properties for conductive inks include conductivity (antistatic properties), adhesion, printability, hardness, and solvent resistance. Thick-film colorants are used for integrated circuits, capacitors, and electrodes, while resin-based inks are used for printed circuits, diaphragm switches, and antistatic packaging.

[0004] According to the ink formula design principles, conductive ink consists of four parts: binder resin, conductive filler, solvent and additives. In order to achieve the required performance, the materials used in each part need to be selected.

[0005] With rising economic levels and adjustments to the energy mix, fuel-fired boiler centralized heating systems are increasingly exposed to shortcomings, necessitating reforms to traditional heating systems and mechanisms. Geothermal membrane heating, however, meets people's evolving needs for a better indoor environment and is currently recognized both domestically and internationally as the most ideal heating method. Electricity is a clean energy source, reducing emissions of pollutants such as sulfur dioxide. China is currently vigorously promoting energy conservation and emission reduction, and is also promoting the use of electric heating. Durex membranes are currently widely used in villas, residential buildings, rural self-built houses, schools, hospitals, supermarkets, and other public buildings, as well as in rural urbanization and road snow melting. Geothermal membrane radiant heating, a heating method that converts electricity into thermal energy, offers advantages such as high energy efficiency, high thermal comfort, no generation of environmentally harmful gases, convenient household metering, a long service life, and health benefits. These advantages have led to the widespread development and application of this heating method.

[0006] Geothermal films can be divided into metal geothermal films, inorganic geothermal films and organic geothermal films. Although inorganic geothermal films have the advantages of long life, low cost and high temperature resistance, they are rigid materials and cannot meet the current requirements of being light, small, thin and flexible. Organic heating geothermal films are made by printing and hot pressing special conductive ink and metal current-carrying strips between two layers of insulating polyester film. Therefore, organic heating geothermal films have the following advantages: (1) High efficiency and energy saving. Geothermal film radiant heating can be controlled by layers, households and rooms, and users can adjust according to actual conditions. (2) Human perception is comfortable and hygienic. The heat dissipation surface of geothermal film radiant heating is a whole, the horizontal temperature in the room is uniform, and the vertical temperature gradually decreases from bottom to top; radiation is mainly for heat dissipation, and it is not easy to cause convection of dirty air. (3) Intelligent control: It meets the needs of modern people for smart homes and the Internet of Things. (4) Space saving. Compared with traditional water heating, it occupies less space, has low investment, and low operating and management costs. (4) Long service life. Geothermal film radiant heating is buried underground, with good stability and corrosion resistance. (5) The manufacturing process is simple. Organic geothermal film is generally made by screen printing or roll printing, which is simple and low-pollution.

[0007] The heating mechanism of the heating film is resistance heating, in which the conductive ink is equivalent to the resistor, so the heating performance of the heating film depends on the performance of the conductive ink. Figure 1 As shown, it includes EVA film 1, graphene heating carbon paste 2, copper foil 3, silver paste 4 and surface PET 5. Existing geothermal film electrodes generally use screen printing technology to apply the geothermal film conductive silver paste to flexible substrates such as PET or PI film according to the printed pattern. Traditional conductive silver paste belongs to an oily system, which has poor compatibility with the water-based graphene in the heating layer, and can easily cause cracking of the graphene layer, large fluctuations in resistance, resulting in uneven heating and other undesirable phenomena. Therefore, it is very necessary to develop a geothermal film conductive silver paste that has good compatibility with the water-based graphene heating layer. Geothermal film conductive silver paste silver-based conductive ink is composed of silver powder, water-based polyurethane resin and solvent as basic raw materials.

[0008] Conductive silver paste for geothermal films is typically printed onto flexible materials such as polymer films. The heating rate requirements are very strict, typically reaching 60°C within 3 minutes. This requires the conductive layer to have low sheet resistance and resistance stability. Because geothermal films release heat as a whole, high requirements for heat dissipation uniformity are also in place. For example, on a standard 50cm*25cm sheet, ten irregularly spaced points must be tested, and the temperature deviation must be within ±0.5°C.

[0009] In addition to meeting the above conditions, the requirements for product environmental protection, service life, printing accuracy, coating hardness, and coating resistance are becoming increasingly higher. At present, ordinary low-temperature conductive silver paste only has the requirements of conductivity and adhesion, and cannot meet all of the above requirements. It has the defects of unstable resistance, slow heating speed, uneven heating temperature, and poor adhesion. Summary of the Invention

[0010] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a geothermal film conductive silver paste with stable resistance, fast heating rate, uniform heating and strong adhesion and a preparation method thereof.

[0011] The purpose of the present invention can be achieved by the following technical solution: A geothermal film conductive silver paste comprises the following components in parts by weight:

[0012]

[0013] Furthermore, the nano water-based silver powder is prepared by the following method:

[0014] (1) Weigh an appropriate amount of silver nitrate, dissolve it in deionized water to prepare a silver nitrate solution, and preheat it in a 50°C water bath for 30 minutes. Then weigh sodium hypophosphite, sodium hexametaphosphate, and PVP, mix them, and dissolve them in deionized water. Stir until they are completely dissolved to obtain a silver ion solution.

[0015] (2) adding the silver ion solution prepared in step (1) to the reducing solution at a rate of 20 to 30 drops per minute, stirring at high speed for 30 minutes after the addition is completed, to obtain a brown nanosilver sol;

[0016] (3) The prepared nanosilver sol was stirred at high speed and placed in an ultrasonic field, stirred continuously, and a pH regulator was added dropwise. After the addition was completed, ultrasonication and stirring were continued for 30 minutes. After standing, vacuum filtration was performed. The filtered nanosilver powder was soaked in a passivating agent for 30 minutes, vacuum filtered again, and finally washed three times with anhydrous ethanol and dried completely in a vacuum drying oven to obtain nano water-based silver powder with an average particle size of 35 nm to 50 nm.

[0017] The nano water-based silver powder prepared by the above method can form a dense point coating and is not easy to agglomerate. While being covered with a heating carbon paste, it provides excellent conductive properties. Since the coating is dense, it is not easy for the carbon paste to infiltrate or become air permeable, and has excellent weather resistance and antioxidant properties.

[0018] Furthermore, the mass ratio of silver nitrate, sodium hypophosphite, sodium hexametaphosphate and PVP in step (1) is 1:1-3:1-3:1-3.

[0019] Furthermore, the volume ratio of the reducing solution in step (2) to the silver ion solution is 1:1; and the reducing solution is 1.0 mol / L sulfuric acid.

[0020] Furthermore, in step (2), the pH adjusting agent is sodium hydroxide solution, which adjusts the pH value of the nanosilver sol to 6-7;

[0021] The passivating agent is a commercially available trivalent chromium aluminum passivating agent solution.

[0022] Furthermore, the particle size of the ultrafine graphene powder is 10-100 nm.

[0023] Furthermore, the aqueous polyurethane resin emulsion is prepared by the following method:

[0024] (1) Weigh 50-100 parts of acrylic monomer, 30-50 parts of polyester polyol, 30-50 parts of dimethylol propionic acid (DMPA), 10-20 parts of isophorone diisocyanate (IPDI), 3-5 parts of hexamethylene diisocyanate (HDI), 3-5 parts of azobisisobutyl cyanide (AIBN), 10-20 parts of glycerol, 10-20 parts of butanediol, and 3-5 parts of N,N-dimethylethanolamine (DMEA) by weight;

[0025] (2) Add polyester polyol to the reactor, heat it to 100 ° C, remove water under reduced pressure for 1 hour, cool it down after removing water, add IPDI and HDI mixture, stir it evenly, heat it to 90 ° C, keep it warm for 2 hours, add DMPA and propylene glycol, stir and react for 2 hours, then add butanediol, keep it warm to the end of the reaction, cool it to room temperature, add acrylic monomer to the reactor and stir evenly, add DMEA to neutralize and react for 0.5 hours, finally heat the above dispersion to 70 ° C, add AIBN solution evenly dropwise into the reaction system, add it dropwise for 2 hours, continue to keep it warm for 2 hours after completion, cool it to room temperature after the reaction, and finally obtain waterborne polyurethane resin.

[0026] Since the waterborne polyurethane resin emulsion is a (AB)n type block linear link, the groups it contains are very polar and easily form elastic cross-linking points, so the tear strength and bending resistance of this type of resin will be stronger, and when external force is applied, the rearrangement of the molecular chain will be easier to achieve. The large molecular chain polyester polyurethane is selected as the adhesive phase because it has more polar groups (hydroxyl, ether bond, amino bond, ester bond and carbonyl group), which can form hydrogen bonds to increase the surface electrostatic attraction and intermolecular force, and can show high adhesion with organic flexible substrates. In addition, the waterborne polyurethane resin emulsion can well match the current mainstream water-based heating carbon paste, has little effect on resistance after drying, and has good heating adaptability.

[0027] The present invention also provides a method for preparing a geothermal film conductive silver paste, comprising the following steps:

[0028] (1) Carrier preparation: Pour the weighed aqueous polyurethane emulsion, deionized water (the amount added is 30-60% of the total mass of deionized water), isopropyl alcohol, and silicone defoamer into a constant temperature dissolution kettle according to the formula ratio, then control the stirring speed of the constant temperature dissolution kettle at 800-1000 rpm / min, the temperature at 20-30°C, and stir at high speed for 2-4 hours;

[0029] (2) Silver powder pretreatment: Ethyl acetate (30-60% of the total mass of ethyl acetate) is added to the aqueous nano-silver powder, stirred evenly, allowed to stand, filtered, and dried. Then, ultrafine graphene powder and ethyl acetate are added to the drying silver powder, stirred evenly, allowed to stand, filtered, and dried to obtain a dried aqueous nano-silver powder and graphene powder mixture;

[0030] (3) Preparation of silver paste: The carrier obtained in step (1) is added to the mixture obtained in step (2), and then deionized water, Triton X-100, an adhesion promoter, dibutyl phthalate, and hydrophilic silica are added, and the mixture is stirred at high speed. The resulting mixed slurry is poured into a horizontal sand mill for dispersion, and then cyclically ground on a three-roll mill and vacuum filtered to obtain the product.

[0031] The high-speed stirring step (3) is to move the material barrel to the high-speed stirrer platform after weighing, then turn on the high-speed stirrer switch, lower the stirring head to 2 cm from the bottom of the barrel, turn on the frequency converter switch to 35 Hz, set the timing and stir continuously for 10 minutes, and finally observe that the ink is a silver-gray slurry as a whole and there are no silver powder particles, which means it is evenly dispersed.

[0032] The sanding medium of the horizontal sand mill described in step (3) is zirconia beads with a diameter of 1.2mm-1.4mm, a rotation speed of 800r / min, and a sanding time of 15-20min.

[0033] The three-roll mill described in step (3) is subjected to three cycles of grinding. After each pass of the ink, the high-speed dispersion step is repeated. The gap between the fast roller and the middle roller in the three-roll mill is then gradually controlled. The roller gap is controlled to 0.25mm-0.30mm for the first pass of grinding the low-temperature conductive ink, 0.20-0.25mm for the second pass, and 0.15-0.20mm for the third pass. During the adjustment of the roller gap, the uniformity of the discharge is observed. After the three passes of grinding, a process inspection is performed. Only when the detected fineness is less than or equal to 8μm can the next step be carried out.

[0034] The vacuum filtration process simulates a customer's use of a screen printing screen with a specific mesh size. Its primary function is to separate large impurities generated during the grinding process. This equipment uses a high-power vacuum pump connected to a stainless steel chamber, within which a stainless steel material barrel is placed. Finally, a 300-mesh stainless steel screen is installed above the chamber as needed. To use, first turn on the vacuum pump. Then, continuously pour the dispersed geothermal film conductive silver paste onto the stainless steel screen, using a rubber scraper to continuously smooth the paste and rapidly filter it into the built-in stainless steel material barrel. At this point, one of the geothermal film conductive silver pastes in the barrel is a semi-finished product awaiting inspection, and inspectors test it according to company standards. Only when the test value meets the standard can the next step be performed.

[0035] The homogenizing step uses a homogenizer, which primarily removes bubbles from the conductive ink and prevents silver powder from settling. The homogenized conductive ink is very fine and uniform. Set the vacuum to 0.10-0.15 MPa, then place the canned conductive silver paste into the homogenizer and stir for 3-5 minutes. After homogenization, the conductive silver paste is ready for immediate packaging.

[0036] The present invention adopts water-based nano silver powder as the main solid phase, which can match the adhesion, conductivity and electrode penetration performance of the water-based graphene carbon paste heating layer. Using graphene powder as the auxiliary conductive phase can further enhance the conductivity of the conductive ink and the adhesion of the graphene heating layer; using water-based polyurethane resin as the main adhesive phase can achieve short-term low-temperature curing, and provide intentional adhesion on metals and flexible films, and have a certain degree of bending resistance and flexibility. The use of water-based system solvents can not only meet the EU ROSH and WEEE environmental protection requirements, but also achieve rapid curing to prevent the occurrence of local expansion of graphics after printing; using silicone as a defoaming agent can effectively increase the lubricity and printability of the conductive ink. Using a self-made vacuum filter can effectively simulate the client's screen printing effect and filter out impurities generated during the production of the conductive ink; using a homogenizer can effectively degas the conductive ink and further fully mix the raw materials to achieve higher fineness and uniformity.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Using water-based nano silver powder as the main solid phase can match the adhesion, conductivity and electrode penetration performance of the water-based graphene carbon paste heating layer. Using graphene powder as the auxiliary conductive phase can further enhance the conductivity of the conductive ink and the adhesion of the graphene heating layer; using water-based polyurethane resin as the main adhesive phase can achieve short-term low-temperature curing, and provide intentional adhesion on metal and flexible films, and have certain bending resistance and certain flexibility. Using water-based system solvents can not only meet the environmental protection requirements of the EU ROSH and WEEE, but also achieve rapid curing and prevent the local expansion of the graphics after printing; using silicone as a defoaming agent can effectively increase the lubricity and printability of the conductive ink. Using a vacuum filter can effectively simulate the screen printing effect of the client and filter out impurities generated during the production of the conductive ink; using a homogenizer can effectively degas the conductive ink and further fully mix the raw materials to achieve higher fineness and uniformity.

[0039] (2) The conductive silver paste of the geothermal film obtained by the present invention has stable resistance. When conducting high and low temperature cycle tests, its resistance loss does not exceed 1%, the heating speed is fast, and the temperature can be raised to above 50°C within 1 minute, the heating is uniform (10 points, the temperature difference does not exceed 0.2°C), and the adhesion is strong (5B when powered on at 5V voltage for 72h). BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the electric heating film. DETAILED DESCRIPTION

[0041] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0042] Among the various raw materials used in the present invention, except for nano water-based silver powder and water-based polyurethane resin emulsion which are homemade products, the other raw materials are commercially available products.

[0043] Examples 1 to 5

[0044] Nano water-based silver powder and water-based polyurethane resin emulsion are homemade products, and the preparation method is as follows:

[0045] Nano water-based silver powder is prepared by the following method:

[0046] (1) Weigh an appropriate amount of silver nitrate, dissolve it in deionized water to prepare a silver nitrate solution, and preheat it in a 50°C water bath for 30 minutes. Then weigh sodium hypophosphite, sodium hexametaphosphate, and PVP, mix them, and dissolve them in deionized water. Stir and completely dissolve them to obtain a silver ion solution; the mass ratio of the silver nitrate, sodium hypophosphite, sodium hexametaphosphate, and PVP is 1:2:2:2.

[0047] (2) adding the silver ion solution prepared in step (1) to the reducing solution at a rate of 20 to 30 drops per minute, stirring at high speed for 30 minutes after the addition is completed, to obtain a brown nanosilver sol; the volume ratio of the reducing solution to the silver ion solution is 1:1; and the reducing solution is 1.0 mol / L sulfuric acid.

[0048] (3) The prepared nanosilver sol is stirred at high speed and placed in an ultrasonic field, stirred continuously, and a pH regulator is added dropwise, wherein the pH regulator is a sodium hydroxide solution, and the pH value of the nanosilver sol is adjusted to 6-7; after the addition is completed, ultrasonication and stirring are continued for 30 minutes, and vacuum filtration is performed after standing. The filtered nanosilver powder is immersed in a passivating agent (trivalent chromium aluminum passivating agent solution) for 30 minutes, vacuum filtration is performed again, and finally, it is washed three times with anhydrous ethanol and dried completely in a vacuum drying oven to obtain nano water-based silver powder with an average particle size of 35nm to 50nm.

[0049] The aqueous polyurethane resin emulsion is prepared by the following method:

[0050] (1) Weigh 100 parts of acrylic monomer, 30 parts of polyester polyol, 30 parts of dimethylol propionic acid (DMPA), 10 parts of isophorone diisocyanate (IPDI), 3 parts of hexamethylene diisocyanate (HDI), 3 parts of azobisisobutyl cyanide (AIBN), 10 parts of glycerol, 10 parts of butanediol, and 3 parts of N,N-dimethylethanolamine (DMEA) by weight;

[0051] (2) Add polyester polyol to the reactor, heat it to 100 ° C, remove water under reduced pressure for 1 hour, cool it down after removing water, add IPDI and HDI mixture, stir it evenly, heat it to 90 ° C, keep it warm for 2 hours, add DMPA and propylene glycol, stir and react for 2 hours, then add butanediol, keep it warm to the end of the reaction, cool it to room temperature, add acrylic monomer to the reactor and stir evenly, add DMEA to neutralize and react for 0.5 hours, finally heat the above dispersion to 70 ° C, add AIBN solution evenly dropwise into the reaction system, add it dropwise for 2 hours, continue to keep it warm for 2 hours after completion, cool it to room temperature after the reaction, and finally obtain waterborne polyurethane resin.

[0052] A method for preparing conductive silver paste for geothermal film, wherein the components and ingredients are shown in Table 1. Methyl methacrylate and thermoplastic polycarbonate resin are used as the bonding phase:

[0053] Table 1

[0054] Material name Example 1 Example 2 Example 3 Example 4 Example 5 Water-based nanosilver powder 4.5 4.5 4.5 4.5 4.5 Ultrafine graphite powder 1.5 1.5 1.5 1.5 1.5 Triton X-100 0.1 0.1 0.1 0.1 0.1 Waterborne polyurethane resin emulsion 3.1 3.05 3.0 3.2 3.3 Deionized water 0.25 0.3 0.35 0.40 0.45 Isopropyl alcohol 0.3 0.3 0.3 0.3 0.3 Adhesion promoter 0.05 0.05 0.05 0.05 0.05 Dibutyl phthalate 0.05 0.05 0.05 0.05 0.05 Ethyl acetate 0.1 0.1 0.1 0.1 0.1 hydrophilic silica 0.02 0.02 0.02 0.02 0.02 Silicone defoamer 0.03 0.03 0.03 0.03 0.03

[0055] The actual production process of the above-mentioned geothermal film conductive silver paste is mainly divided into eight steps: carrier configuration, silver powder pretreatment, batching, high-speed dispersion, three-roller grinding, filtration, finished product testing, homogenous mixing, and canning, as follows:

[0056] 1. Carrier configuration: Pour the weighed water-based polyurethane emulsion, deionized water, isopropyl alcohol, and silicone defoamer into a constant temperature dissolution kettle according to the formula ratio. Then control the stirring speed of the constant temperature dissolution kettle at 9000 rpm / min, the temperature at 25°C, and stir at high speed for 3 hours.

[0057] 2. Silver powder pretreatment: Add ethyl acetate to aqueous nano-silver powder, stir with a magnetic stirrer, let it stand, filter and dry. Then, add ultrafine graphene powder and ethyl acetate to the drying silver powder, stir with a magnetic stirrer for 1 hour, let it stand, filter and dry.

[0058] 3. Ingredients: A Mettler BBA211 electronic scale was used as a weighing tool, along with a recording component. The operator could add the corresponding raw materials according to the displayed value, with an accuracy of one ten-thousandth. The order of weighing ingredients was as follows: add the carrier prepared in step 1 → add the dried aqueous nanosilver powder and graphene powder mixture → add deionized water → add the remaining additives. Because the amount of additives added was relatively small, a JY20002 electronic scale was used.

[0059] 4. High-speed dispersion: After weighing, move the material barrel to the high-speed mixer platform, then turn on the high-speed mixer switch, lower the stirring head to 2 cm from the bottom of the barrel, turn on the frequency converter switch to 35 Hz, set the timer and stir continuously for 10 minutes. Finally, observe that the ink is a silver-gray slurry without silver powder particles, which means it is evenly dispersed.

[0060] Pour the high-speed dispersed mixed slurry into a horizontal sand mill for dispersion. The sand milling medium is zirconium oxide beads with a diameter of 1.2mm-1.4mm. The speed is adjusted to 800r / min. The sand milling time is 15-20min.

[0061] 5. Three-roller grinding: Three cycles of grinding are required on a three-roller mill. After each pass of the ink, the high-speed dispersion step must be repeated. The gap between the fast and middle rollers of the three-roller mill is then gradually controlled. For the first pass of grinding low-temperature conductive ink, the gap is controlled between 0.25mm and 0.30mm. For the second pass, the gap is controlled between 0.20mm and 0.25mm. For the third pass, the gap is controlled between 0.15mm and 0.20mm. While adjusting the gap, the uniformity of the discharge should be observed. After three passes of grinding, a process inspection is performed. Only when the fineness is less than or equal to 8μm can the next step be carried out.

[0062] 6. Vacuum Filtration: This simulates the mesh size of a customer's screen printing screen. Its primary function is to separate large impurities generated during the grinding process. This equipment, designed and manufactured in-house, utilizes a high-power vacuum pump connected to a stainless steel chamber, within which a stainless steel material barrel is placed. Finally, a 300-mesh stainless steel screen is installed above the chamber as needed. To use it, first turn on the vacuum pump. Then, pour the dispersed geothermal film conductive silver paste onto the stainless steel screen, using a rubber scraper to continuously smooth the paste and rapidly filter it into the internal stainless steel material barrel. At this point, the geothermal film conductive silver paste in the barrel is the semi-finished product awaiting inspection.

[0063] 7. Finished product testing: The inspector will test the product according to the company's standards. The next step can only be carried out after the test value meets the standard.

[0064] 8. Homogenization and Canning: The homogenization step uses a homogenizer. Its main function is to remove bubbles from the conductive ink and prevent the silver powder from settling. The homogenized conductive ink is very fine and uniform. When using, set the vacuum level to 0.10-0.15 MPa. Place the canned geothermal film conductive silver paste into the homogenizer and stir for 3-5 minutes. After homogenization, the geothermal film conductive silver paste can be shipped directly to the warehouse for filling.

[0065] The properties of the obtained geothermal film conductive silver paste are shown in Table 2.

[0066] Table 2

[0067]

[0068] Example 6

[0069] Nano water-based silver powder is prepared by the following method:

[0070] (1) Weigh an appropriate amount of silver nitrate, dissolve it in deionized water to prepare a silver nitrate solution, and preheat it in a 50°C water bath for 30 minutes. Then weigh sodium hypophosphite, sodium hexametaphosphate, and PVP, mix them, and dissolve them in deionized water. Stir and completely dissolve them to obtain a silver ion solution; the mass ratio of the silver nitrate, sodium hypophosphite, sodium hexametaphosphate, and PVP is 1:1:1:1.

[0071] (2) adding the silver ion solution prepared in step (1) to the reducing solution at a rate of 20 to 30 drops per minute, stirring at high speed for 30 minutes after the addition is completed, to obtain a brown nanosilver sol; the volume ratio of the reducing solution to the silver ion solution is 1:1; and the reducing solution is 1.0 mol / L sulfuric acid.

[0072] (3) The prepared nanosilver sol is stirred at high speed and placed in an ultrasonic field, stirred continuously, and a pH regulator is added dropwise, wherein the pH regulator is a sodium hydroxide solution, and the pH value of the nanosilver sol is adjusted to 6-7; after the addition is completed, ultrasonication and stirring are continued for 30 minutes, and vacuum filtration is performed after standing. The filtered nanosilver powder is immersed in a passivating agent (trivalent chromium aluminum passivating agent solution) for 30 minutes, vacuum filtration is performed again, and finally, it is washed three times with anhydrous ethanol and dried completely in a vacuum drying oven to obtain nano water-based silver powder with an average particle size of 35nm to 50nm.

[0073] The aqueous polyurethane resin emulsion is prepared by the following method:

[0074] (1) Weigh 50 parts of acrylic monomer, 50 parts of polyester polyol, 50 parts of dimethylol propionic acid (DMPA), 20 parts of isophorone diisocyanate (IPDI), 5 parts of hexamethylene diisocyanate (HDI), 5 parts of azobisisobutyl cyanide (AIBN), 20 parts of glycerol, 20 parts of butanediol, and 5 parts of N,N-dimethylethanolamine (DMEA) by weight;

[0075] (2) Add polyester polyol to the reactor, heat it to 100 ° C, remove water under reduced pressure for 1 hour, cool it down after removing water, add IPDI and HDI mixture, stir it evenly, heat it to 90 ° C, keep it warm for 2 hours, add DMPA and propylene glycol, stir and react for 2 hours, then add butanediol, keep it warm to the end of the reaction, cool it to room temperature, add acrylic monomer to the reactor and stir evenly, add DMEA to neutralize and react for 0.5 hours, finally heat the above dispersion to 70 ° C, add AIBN solution evenly dropwise into the reaction system, add it dropwise for 2 hours, continue to keep it warm for 2 hours after completion, cool it to room temperature after the reaction, and finally obtain waterborne polyurethane resin.

[0076] A geothermal film conductive silver paste comprising the following components in parts by weight:

[0077]

[0078]

[0079] The conductive silver paste of geothermal film is prepared by the following method:

[0080] (1) Carrier preparation: Pour the weighed aqueous polyurethane emulsion, deionized water (the amount added is 30% of the total mass of deionized water), isopropyl alcohol, and silicone defoamer into a constant temperature dissolution kettle according to the formula ratio. Then, control the stirring speed of the constant temperature dissolution kettle at 800 rpm / min and the temperature at 30°C, and stir at high speed for 4 hours;

[0081] (2) Silver powder pretreatment: Ethyl acetate (30% of the total mass of ethyl acetate) was added to the aqueous nano-silver powder, stirred evenly, allowed to stand, filtered, and dried. Then, ultrafine graphene powder and ethyl acetate were added to the drying silver powder, stirred evenly, allowed to stand, filtered, and dried to obtain a dried aqueous nano-silver powder and graphene powder mixture;

[0082] (3) Preparation of silver paste: Add the carrier obtained in step (1) to the mixture obtained in step (2), and then add deionized water, Triton X-100, adhesion promoter, dibutyl phthalate, and hydrophilic silica. After weighing, move the material barrel to the high-speed mixer platform, then turn on the high-speed mixer switch, lower the stirring head to 2 cm from the bottom of the barrel, turn on the frequency converter switch to 35 Hz, set the timer and stir continuously for 10 minutes. Finally, observe that the ink is a silver-gray slurry without silver powder particles, which means it is uniformly dispersed.

[0083] (4) The mixed slurry obtained by high-speed stirring is poured into a horizontal sand mill for dispersion. The sand milling medium of the horizontal sand mill is zirconia beads with a diameter of 1.2 mm, a rotation speed of 800 r / min, and a sand milling time of 20 min.

[0084] (5) Then, the ink is cyclically ground on a three-roll mill. The three-roll mill is cyclically ground three times. After each rolling, the ink needs to be dispersed again at a high speed. Then, the gap between the fast roller and the middle roller in the three-roll mill is continuously and gradually controlled. The roller gap of the first grinding low-temperature conductive ink is controlled at 0.25mm-0.30mm, the second roller gap is controlled at 0.20-0.25mm, and the third roller gap is controlled at 0.15-0.20mm. In the process of adjusting the roller gap, the uniformity of the discharge should also be observed. After three grindings, the process is tested. When the fineness is less than or equal to 8μm, the next step can be carried out.

[0085] (6) Vacuum filtration, simulating the customer's use of a mesh screen printing screen for vacuum filtration, its main function is to separate large particles of impurities generated during the grinding process. This type of equipment uses a high-power vacuum pump connected to a stainless steel cavity, a stainless steel material barrel is placed in the stainless steel cavity, and finally a 300-mesh stainless steel net is installed above the stainless steel cavity as needed. When in use, first turn on the vacuum pump switch, then continuously pour the dispersed geothermal film conductive silver paste on the stainless steel net, and use a rubber scraper to continuously flatten the silver paste so that it is quickly filtered into the built-in stainless steel material barrel. At this time, a geothermal film conductive silver paste in the material barrel is a semi-finished product to be inspected, and the inspector inspects it according to the company standard. The next step can be carried out only after the test value reaches the standard.

[0086] (7) The homogenization step uses a homogenizer. Its main function for the conductive ink is to degas and prevent the silver powder from settling. The conductive ink after homogenization will be very fine and uniform. When using, set the vacuum degree to 0.10Mpa, and then put the canned geothermal film conductive silver paste into the homogenizer and stir for 5 minutes. After homogenization, the geothermal film conductive silver paste can be directly shipped out for filling.

[0087] Example 7

[0088] Nano water-based silver powder is prepared by the following method:

[0089] (1) Weigh an appropriate amount of silver nitrate, dissolve it in deionized water to prepare a silver nitrate solution, and preheat it in a 50°C water bath for 30 minutes. Then weigh sodium hypophosphite, sodium hexametaphosphate, and PVP, mix them, and dissolve them in deionized water. Stir and completely dissolve them to obtain a silver ion solution; the mass ratio of the silver nitrate, sodium hypophosphite, sodium hexametaphosphate, and PVP is 1:3:3:3.

[0090] (2) adding the silver ion solution prepared in step (1) to the reducing solution at a rate of 20 to 30 drops per minute, stirring at high speed for 30 minutes after the addition is completed, to obtain a brown nanosilver sol; the volume ratio of the reducing solution to the silver ion solution is 1:1; and the reducing solution is 1.0 mol / L sulfuric acid.

[0091] (3) The prepared nanosilver sol is stirred at high speed and placed in an ultrasonic field, stirred continuously, and a pH regulator is added dropwise, wherein the pH regulator is a sodium hydroxide solution, and the pH value of the nanosilver sol is adjusted to 6-7; after the addition is completed, ultrasonication and stirring are continued for 30 minutes, and vacuum filtration is performed after standing. The filtered nanosilver powder is immersed in a passivating agent (trivalent chromium aluminum passivating agent solution) for 30 minutes, vacuum filtration is performed again, and finally, it is washed three times with anhydrous ethanol and dried completely in a vacuum drying oven to obtain nano water-based silver powder with an average particle size of 35nm to 50nm.

[0092] The aqueous polyurethane resin emulsion is prepared by the following method:

[0093] (1) Weigh 80 parts of acrylic monomer, 40 parts of polyester polyol, 40 parts of dimethylol propionic acid (DMPA), 15 parts of isophorone diisocyanate (IPDI), 4 parts of hexamethylene diisocyanate (HDI), 4 parts of azobisisobutyl cyanide (AIBN), 15 parts of glycerol, 15 parts of butanediol, and 4 parts of N,N-dimethylethanolamine (DMEA) by weight;

[0094] (2) Add polyester polyol to the reactor, heat it to 100 ° C, remove water under reduced pressure for 1 hour, cool it down after removing water, add IPDI and HDI mixture, stir it evenly, heat it to 90 ° C, keep it warm for 2 hours, add DMPA and propylene glycol, stir and react for 2 hours, then add butanediol, keep it warm to the end of the reaction, cool it to room temperature, add acrylic monomer to the reactor and stir evenly, add DMEA to neutralize and react for 0.5 hours, finally heat the above dispersion to 70 ° C, add AIBN solution evenly dropwise into the reaction system, add it dropwise for 2 hours, continue to keep it warm for 2 hours after completion, cool it to room temperature after the reaction, and finally obtain waterborne polyurethane resin.

[0095] A geothermal film conductive silver paste comprising the following components in parts by weight:

[0096]

[0097] The conductive silver paste of geothermal film is prepared by the following method:

[0098] (1) Carrier preparation: Pour the weighed aqueous polyurethane emulsion, deionized water (the amount added is 60% of the total mass of deionized water), isopropyl alcohol, and silicone defoamer into a constant temperature dissolution kettle according to the formula ratio. Then, control the stirring speed of the constant temperature dissolution kettle at 1000 rpm / min and the temperature at 20°C, and stir at high speed for 2 h;

[0099] (2) Silver powder pretreatment: Ethyl acetate (the amount added is 60% of the total mass of ethyl acetate) is added to the aqueous nano-silver powder, stirred evenly, allowed to stand, filtered and dried, and then ultrafine graphene powder and ethyl acetate are added to the drying silver powder, stirred evenly, allowed to stand, filtered and dried to obtain a dried aqueous nano-silver powder and graphene powder mixture;

[0100] (3) Preparation of silver paste: Add the carrier obtained in step (1) to the mixture obtained in step (2), and then add deionized water, Triton X-100, adhesion promoter, dibutyl phthalate, and hydrophilic silica. After weighing, move the material barrel to the high-speed mixer platform, then turn on the high-speed mixer switch, lower the stirring head to 2 cm from the bottom of the barrel, turn on the frequency converter switch to 35 Hz, set the timer and stir continuously for 10 minutes. Finally, observe that the ink is a silver-gray slurry without silver powder particles, which means it is uniformly dispersed.

[0101] (4) The mixed slurry obtained by high-speed stirring is poured into a horizontal sand mill for dispersion. The sand milling medium of the horizontal sand mill is zirconia beads with a diameter of 1.4 mm, a rotation speed of 800 r / min, and a sand milling time of 15 min.

[0102] (5) Then, the ink is cyclically ground on a three-roll mill. The three-roll mill is cyclically ground three times. After each rolling, the ink needs to be dispersed again at a high speed. Then, the gap between the fast roller and the middle roller in the three-roll mill is continuously and gradually controlled. The roller gap of the first grinding low-temperature conductive ink is controlled at 0.25mm-0.30mm, the second roller gap is controlled at 0.20-0.25mm, and the third roller gap is controlled at 0.15-0.20mm. In the process of adjusting the roller gap, the uniformity of the discharge should also be observed. After three grindings, the process is tested. When the fineness is less than or equal to 8μm, the next step can be carried out.

[0103] (6) Vacuum filtration, simulating the customer's use of a mesh screen printing screen for vacuum filtration, its main function is to separate large particles of impurities generated during the grinding process. This type of equipment uses a high-power vacuum pump connected to a stainless steel cavity, a stainless steel material barrel is placed in the stainless steel cavity, and finally a 300-mesh stainless steel net is installed above the stainless steel cavity as needed. When in use, first turn on the vacuum pump switch, then continuously pour the dispersed geothermal film conductive silver paste on the stainless steel net, and use a rubber scraper to continuously flatten the silver paste so that it is quickly filtered into the built-in stainless steel material barrel. At this time, a geothermal film conductive silver paste in the material barrel is a semi-finished product to be inspected, and the inspector inspects it according to the company standard. The next step can be carried out only after the test value reaches the standard.

[0104] (7) The homogenization step uses a homogenizer. Its main function for the conductive ink is to degas and prevent the silver powder from settling. The conductive ink after homogenization will be very fine and uniform. When using, set the vacuum degree to 0.15Mpa, and then put the geothermal film conductive silver paste that has been canned into the homogenizer and stir for 3 minutes. The geothermal film conductive silver paste after homogenization can be directly shipped out for filling.

[0105] Table 3

[0106]

[0107]

Claims

1. A geothermal film conductive silver paste, characterized in that: It comprises the following components in parts by weight: Nano water-based silver powder 35~45; Ultrafine graphene powder 10~15; Triton X-100 0.5~1; Waterborne polyurethane resin emulsion 30~35; Deionized water 2~5; Isopropyl alcohol 2~5; Adhesion promoter 0.2~0.5; Dibutyl phthalate 0.5~1; Ethyl acetate 1~1.5; Hydrophilic silica 0.2~0.5; Silicone defoamer 0.1~0.5; The nano water-based silver powder is prepared by the following method: (1) Weigh an appropriate amount of silver nitrate, dissolve it in deionized water to prepare a silver nitrate solution, and preheat it in a 50°C water bath for 30 minutes. Then weigh sodium hypophosphite, sodium hexametaphosphate, and PVP, mix them, and dissolve them in deionized water. Stir until they are completely dissolved to obtain a silver ion solution. (2) adding the silver ion solution prepared in step (1) to the reducing solution at a rate of 20 to 30 drops per minute, stirring at high speed for 30 minutes after the addition is completed, to obtain a brown nanosilver sol; (3) The prepared nanosilver sol was stirred at high speed and placed in an ultrasonic field, stirred continuously, and a pH regulator was added dropwise. After the addition was completed, ultrasonication and stirring were continued for 30 minutes. After standing, vacuum filtration was performed. The filtered nanosilver powder was soaked in a passivating agent for 30 minutes, vacuum filtered again, and finally washed three times with anhydrous ethanol. The obtained nanosilver powder had an average particle size of 35nm~50nm.

2. The geothermal film conductive silver paste according to claim 1, characterized in that: The mass ratio of silver nitrate, sodium hypophosphite, sodium hexametaphosphate and PVP in step (1) is 1:1~3:1~3:1~3.

3. The geothermal film conductive silver paste according to claim 1, characterized in that: The volume ratio of the reducing solution to the silver ion solution in step (2) is 1:1; the reducing solution is 1.0 mol / L sulfuric acid.

4. The geothermal film conductive silver paste according to claim 1, characterized in that: Step (2) The pH regulator is sodium hydroxide solution, which adjusts the pH value of the nanosilver sol to 6-7; The passivating agent is a commercially available trivalent chromium aluminum passivating agent solution.

5. The geothermal film conductive silver paste according to claim 1, characterized in that: The particle size of the ultrafine graphene powder is 10-100 nm.

6. The geothermal film conductive silver paste according to claim 1, characterized in that: The aqueous polyurethane resin emulsion is prepared by the following method: (1) Weigh 50-100 parts of acrylic monomer, 30-50 parts of polyester polyol, 30-50 parts of dimethylol propionic acid (DMPA), 10-20 parts of isophorone diisocyanate (IPDI), 3-5 parts of hexamethylene diisocyanate (HDI), 3-5 parts of azobisisobutyl cyanide (AIBN), 10-20 parts of glycerol, 10-20 parts of butanediol, and 3-5 parts of N,N-dimethylethanolamine (DMEA) by weight; (2) Add polyester polyol to the reactor, heat it to 100 °C, remove water under reduced pressure for 1 hour, cool it down after removing water, add IPDI and HDI mixture, stir it evenly, heat it to 90 °C, keep it warm for 2 hours, add DMPA and propylene glycol, stir it for 2 hours, then add butanediol, keep it warm to the end of the reaction, cool it to room temperature, add acrylic monomer to the reactor and stir it evenly, add DMEA to neutralize and react for 0.5 hours, finally heat the above dispersion to 70 °C, add AIBN solution evenly dropwise into the reaction system, add it dropwise for 2 hours, keep it warm for 2 hours after completion, cool it to room temperature after the reaction, and finally obtain waterborne polyurethane resin.

7. A method for preparing a geothermal film conductive silver paste according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Carrier configuration: Pour the weighed waterborne polyurethane resin emulsion, deionized water, isopropyl alcohol, and silicone defoamer into a constant temperature dissolution kettle according to the formula ratio. Then, control the stirring speed of the constant temperature dissolution kettle at 800-1000 rpm / min, the temperature at 20-30°C, and stir at high speed for 2-4 hours. (2) Silver powder pretreatment: Ethyl acetate is added to the aqueous nano-silver powder, stirred evenly, allowed to stand, filtered and dried, and then ultrafine graphene powder and ethyl acetate are added to the drying silver powder, stirred evenly, allowed to stand, filtered and dried to obtain a dried aqueous nano-silver powder and graphene powder mixture; (3) Preparation of silver paste: The carrier obtained in step (1) is added to the mixture obtained in step (2), and then deionized water, Triton X-100, adhesion promoter, dibutyl phthalate, and hydrophilic silica are added, and stirred at high speed. The resulting mixed slurry is poured into a horizontal sand mill for dispersion, and then cyclically ground on a three-roll mill and vacuum filtered to obtain the product.

8. The method for preparing conductive silver paste for geothermal film according to claim 7, characterized in that: The sanding medium of the horizontal sand mill described in step (3) is zirconia beads with a diameter of 1.2 mm to 1.4 mm, a rotation speed of 800 r / min, and a sanding time of 15 to 20 min.

9. The method for preparing conductive silver paste for geothermal film according to claim 7, characterized in that: The three-roll mill described in step (3) is cyclically ground three times. After each rolling of the ink, the high-speed dispersion step needs to be performed again. Then, the gap between the fast roller and the middle roller in the three-roll mill is continuously and gradually controlled. The roller gap of the first grinding of the low-temperature conductive ink is controlled at 0.25mm-0.30mm, the roller gap of the second grinding is controlled at 0.20-0.25mm, and the roller gap of the third grinding is controlled at 0.15-0.20mm.

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