Pre-coating type water-based soldering flux applied to photovoltaic solder strip welding and preparation method of pre-coating type water-based soldering flux

Abstract

The invention discloses a pre-coating type water-based soldering flux applied to photovoltaic solder strip welding and a preparation method of the pre-coating type water-based soldering flux. The pre-coating type water-based soldering flux is used for solving the technical problems that in the prior art, the wetting diffusion performance and the surface insulation resistance of a soldering flux need to be further improved, and a copper plate is prone to being corroded by the soldering flux. The flux comprises the following components in parts by weight: 3-5 parts of water-based polyester, 15-20 parts of a film-forming agent, 3-4 parts of organic acid, 0.6-0.8 part of a surfactant, 100 parts of deionized water and a pH regulator. The flux is prepared by preparing the film-forming agent from composite rosin, polyethylene glycol and glycerol and then combining the film-forming agent with carboxyl-modified water-based polyester, the organic acid and the surfactant. The wetting expansion performance, the surface insulation resistance and the electrochemical migration resistance are effectively improved, corrosion to a copper plate material is reduced, and the welding quality of the photovoltaic welding strip is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic welding, and in particular to a pre-coated water-based soldering flux used for photovoltaic ribbon welding and a preparation method thereof. Background Art

[0002] As an important part of the new energy field, the photovoltaic industry has developed rapidly in recent years. Photovoltaic welding ribbons are key components of photovoltaic modules. The welding quality and efficiency are directly related to the performance and conversion efficiency of photovoltaic cells. Photovoltaic modules are usually welded with tin-coated copper strips. Before welding, the tin-coated copper strips need to be soaked in flux and then dried to form a flux layer on the tin-coated copper strips to reduce defects such as cold solder joints and leaking solder joints that may occur during the welding process, and to improve the reliability and stability of the welded joints. This method results in the welding efficiency of photovoltaic modules that needs to be further improved.

[0003] The prior art, an invention patent with publication number CN114406524A, discloses a water-based pre-coating flux, which comprises the following components, in mass percentage: 8-15% organic acid, 2-5% organic amine, 5-8% film former, 0-5% cosolvent, 0.3-1.0% surfactant, 0.1-0.5% antioxidant, and the rest is water; it uses water as a carrier, and the entire manufacturing process has no VOC emissions, no waste liquid and waste residue generated, and can meet the production requirements of safety and environmental protection. At the same time, the pre-coated photovoltaic solder strip prepared by the water-based pre-coating flux can completely decompose the active agent by heat during welding, and there is almost no residual substance, so it has higher cleanliness and is more suitable for use with new high-speed string welding machines.

[0004] However, the traditional pre-coated flux uses polyethylene glycol or water-based rosin as a film-forming agent, which is prepared by combining a film-forming agent with an organic acid, an organic amine, and a surfactant. The flux has poor film expansion and wettability, and it is difficult to form a uniform flux film layer on the photovoltaic module. In order to avoid unnecessary short circuits or leakage with other metal parts during welding, the usual flux needs to have a certain surface resistance to ensure the reliability of the welding quality; however, the single polyethylene glycol or water-based rosin has limited improvement on the insulation resistance of the material's flux layer, and it is easy to cause short circuits or leakage during welding. In addition, the traditional flux is highly acidic and is also prone to corrode the copper plate of the photovoltaic module, affecting the welding quality.

[0005] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a pre-coated water-based flux used for photovoltaic ribbon welding and a preparation method thereof, so as to solve the technical problems in the prior art that the wetting and diffusion performance of the flux, the surface insulation resistance needs to be further improved, the flux easily causes corrosion to the copper plate, and the welding quality needs to be further improved.

[0007] The purpose of the present invention can be achieved by the following technical scheme: a pre-coated water-based flux used for photovoltaic ribbon welding, the pre-coated water-based flux comprising the following components in parts by weight: 3-5 parts of aqueous polyester, 15-20 parts of film-forming agent, 3-4 parts of organic acid, 0.6-0.8 parts of surfactant, 100 parts of deionized water and pH regulator, the pH of the pre-coated water-based flux is 4.2-4.8.

[0008] Furthermore, the organic acid is composed of salicylic acid, D,L-malic acid and maleic acid in a weight ratio of 2:5:1; the surfactant is composed of Span-20, Tween-80 and sodium dodecyl sulfate in a weight ratio of 3:2:1; and the pH regulator is 10-20wt% ammonia water.

[0009] Furthermore, the preparation method of the water-based polyester is as follows: under the protection of inert gas, suberic acid, citric acid, trimethylolpropane and a catalyst are added to a high-pressure reactor filled with deionized water and stirred in a closed manner, the temperature of the reaction system is increased to 225-235°C, the reaction is kept warm for 6-8 hours, the temperature of the reaction system is reduced to 160-180°C, 2-(2,5-dioxytetrahydrofuran-3-yl)acetic acid is added to the reaction system, the reaction is kept warm for 80-120 minutes, the temperature of the reaction system is reduced to room temperature, and the water-based polyester is obtained by post-treatment.

[0010] The synthetic reaction mechanism of waterborne polyester is:

[0011] In the reaction process, monobutyltin oxide is used as an esterification catalyst, suberic acid, citric acid and trimethylolpropane are used as reaction raw materials, and the carboxyl groups and hydroxyl groups on the molecules undergo esterification reaction under high temperature environment to generate polyester. By controlling the reaction dosage ratio, a large number of hydroxyl groups remain on the polyester. Under high temperature environment, the anhydride ring on the 2-(2,5-dioxotetrahydrofuran-3-yl)acetic acid molecule undergoes ring-opening condensation with the residual hydroxyl groups on the polyester to form ester bonds. A large number of carboxyl groups are modified on the polyester molecules to prepare water-based polyester.

[0012] Furthermore, the amount ratio of suberic acid, citric acid, trimethylolpropane and 2-(2,5-dioxotetrahydrofuran-3-yl)acetic acid is 2mol:1mol:3mol:1.5mol, the amount ratio of suberic acid, catalyst and deionized water is 5g:0.2g:50mL, the catalyst is monobutyltin oxide, and the post-treatment includes: after the reaction is completed, suction filtration, transferring the filtrate to a rotary evaporator with a water bath temperature of 80-90°C, deionized water is evaporated under reduced pressure, ethyl acetate is added to the reaction system, stirring until the system is dissolved, petroleum ether is added to the reaction system, a large amount of solid is precipitated, suction filtration, transferring the filter cake to a drying oven with a temperature of 55-65°C, and vacuum drying to constant weight to obtain water-based polyester.

[0013] Further, the film-forming agent is obtained by processing the following steps:

[0014] A1. Add modified rosin and cocamidopropyl betaine to toluene and stir. Raise the temperature of the reaction system to 60-70°C. Add a catalyst to the reaction system and keep the reaction warm for 2.5-3.5h. Post-treat to obtain composite rosin.

[0015] The synthetic reaction mechanism of composite rosin is:

[0016] During the reaction, the epoxy groups on the modified rosin molecules undergo ring-opening condensation with the hydroxyl groups or imino groups on the cocamidopropyl betaine molecules, and chemical bonds are formed between the cocamidopropyl betaine and the rosin resin molecules to prepare the composite rosin.

[0017] A2. Add polyethylene glycol and glycerol into deionized water and stir. Raise the temperature of the reaction system to 70-80°C and increase the stirring speed to 900-1000r / min. Add the composite rosin solution to the reaction system and stir and disperse for 30-50min. Post-treat to obtain a film-forming agent with a solid content of 35-40wt%.

[0018] Further, in step A1, the amount ratio of the modified rosin, cocamidopropyl betaine, toluene and catalyst is 3g:2g:30mL:0.05g, the catalyst is triethylamine, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, petroleum ether is added to the reaction system, stirred for 20-30min, filtered, the filter cake is washed with petroleum ether 3 times and then dried, the filter cake is transferred to a drying oven at a temperature of 60-70°C, and vacuum dried to constant weight to obtain Composite rosin; in step A2, the amount ratio of the polyethylene glycol, glycerol, deionized water and composite rosin solution is 3g:1g:20mL:10mL, the composite rosin solution is composed of composite rosin and ethanol in an amount ratio of 2g:5mL, and the post-treatment comprises: after the reaction is completed, lowering the temperature of the reaction system to 45°C, distilling under reduced pressure until no liquid drips out, raising the temperature of the reaction system to 70°C, distilling off part of the solvent under reduced pressure, and obtaining a film-forming agent with a solid content of 35-40wt%.

[0019] Further, the modified rosin is processed by the following steps:

[0020] B1, add rosin resin to toluene, stir at room temperature until the rosin resin is dissolved, add catalyst to the reaction system, lower the temperature of the reaction system to 18-22 ° C, add epichlorohydrin dropwise to the reaction system, and after the addition is complete, increase the temperature of the reaction system to 70-80 ° C at a heating rate of 1-3 ° C / min, keep the temperature for 6-8 hours, and post-treat to obtain a modified rosin precursor;

[0021] B2. Add the modified rosin precursor into the sodium hydroxide solution and stir. Raise the temperature of the reaction system to 35-45°C. Keep stirring for 5-7 hours. Post-treat to obtain the modified rosin.

[0022] The synthetic reaction formula of modified rosin is:

[0023]

[0024] The synthetic reaction mechanism of modified rosin is:

[0025] In the reaction process, the carboxyl group on the rosin resin molecule and the epoxy group on the epichlorohydrin molecule are used as active reaction groups. Under the condition of a catalyst, the carboxyl group and the epoxy group undergo ring-opening condensation to form 1-chloro-2-propanol modification on the rosin resin molecule to prepare a modified rosin precursor. The 1-chloro-2-propanol modification modified on the modified rosin precursor molecule undergoes cyclization under alkaline conditions to form an epoxy group to prepare a modified rosin.

[0026] Further, in step B1, the amount ratio of the rosin resin, toluene, catalyst and epichlorohydrin is 5g:15mL:0.1g:3g, the catalyst is diisopropylamine, and the post-treatment includes: after the reaction is completed, the reaction system is kept at 70-80°C, and low-boiling substances are evaporated under reduced pressure to obtain a modified rosin precursor; in step B2, the amount ratio of the modified rosin precursor and the sodium hydroxide solution is 1g:5-7mL, and the concentration of the sodium hydroxide solution is 9-10mol / L, and the post-treatment includes: after the reaction is completed, hydrochloric acid is added dropwise to the reaction system, the pH of the system is adjusted to 7, suction filtering, the filter cake is washed with purified water 3 times and then the card is drawn, the filter cake is transferred to a drying oven at a temperature of 60-70°C, and vacuum dried to constant weight to obtain modified rosin.

[0027] The invention discloses a method for preparing a pre-coated water-based flux for photovoltaic ribbon welding. The method comprises the following steps: adding water-based polyester, a film-forming agent, an organic acid and a surfactant into deionized water and stirring the mixture. The stirring speed is set to 900-1000 r / min, and the mixture is stirred at room temperature for 90-120 min. A pH adjusting agent is added into the reaction system to adjust the pH of the system to 4.2-4.8, and the mixture is stirred for 60-80 min to obtain the pre-coated water-based flux.

[0028] The present invention has the following beneficial effects:

[0029] 1. The present invention is to modify rosin resin and compound it with cocamidopropyl betaine to prepare the composite rosin resin. Cocamidopropyl betaine is an amphoteric surfactant, which reduces the surface tension of the composite rosin and helps the composite rosin resin to be dispersed in the water-based soldering flux. At the same time, the molecular chain of the rosin resin is relatively long and has a certain fluidity, which helps the uniform distribution of the soldering flux on the welding surface. In addition, functional groups such as carboxyl in the composite rosin resin molecule can form hydrogen bonds or chemical bonds with the metal surface, thereby enhancing the adhesion between the soldering flux and the metal surface. The composite rosin resin is compounded with polyethylene glycol and glycerol to further improve the expansion rate and wettability of the water-based soldering flux. The good film-forming property of polyethylene glycol and the hydrophilicity of glycerol cooperate with the composite rosin to enhance the stability and continuity of the film of the water-based soldering flux after film formation, so that the molecules in the film are more closely arranged, and a dense and stable protective layer is formed on the metal surface to prevent the penetration of ions and water molecules, inhibit corrosion, and improve the insulation resistance of the soldering flux coating and reduce the risk of electrochemical migration.

[0030] 2. The present invention uses suberic acid, citric acid and trimethylolpropane as reaction raw materials to prepare polyester with molecules cross-linked and entangled with each other, and then modifies a large number of carboxyl groups on it, thereby improving the hydrophilicity of the water-based polyester and reducing the surface tension of the water-based polyester, making it easier to wet the metal surface. The carboxyl groups in the molecules can form hydrogen bonds or chemical bonds with oxides or hydroxides on the metal surface, thereby enhancing the adhesion between the flux and the metal surface, cooperating with the film-forming agent, and further improving the overall performance of the flux.

[0031] 3. The present invention forms a more complex surfactant system by the interaction of the hydrophilic groups and hydrophobic groups of Span-20, Tween-80 and sodium dodecyl sulfate in the solution, thereby reducing the surface tension of the solution, promoting the uniform dispersion of the components in the water-based soldering flux, making it easier for the soldering flux to spread and wet on the metal surface, and improving the expansion rate and wettability of the soldering flux. The salicylic acid in the organic acid has a cleaning effect, which can remove oxides, dirt, grease and other impurities on the welding surface, and is helpful for the spreading of the soldering flux on the welding surface. D, L-malic acid and maleic acid (Maleic acid) as an activator can improve the activation performance of the flux and promote the fusion of welding materials and substrate materials. In addition, organic acids such as salicylic acid can form complexes with metal ions, thereby slowing down the migration speed of ions. The pH of the water-based flux is conditioned by ammonia water, the ion content in the flux is controlled, and the dispersibility of the flux molecules in the aqueous solution is improved. At the same time, the surface tension of the flux is reduced, making it easier to wet the metal surface. At the same time, by adjusting the pH of the flux, the strong acidity of the flux is avoided. Corrosion to the copper plate material is reduced. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The polyethylene glycol in this application is polyethylene glycol 2000.

[0034] Example 1

[0035] This embodiment provides a method for preparing a pre-coated water-based soldering flux for photovoltaic ribbon welding, comprising the following steps:

[0036] S1. Preparation of modified rosin

[0037] Weigh: 50g of rosin resin and 150mL of toluene are added to a three-necked flask and stirred. Stir at room temperature until the rosin resin is dissolved. Add 1g of diisopropylamine to the three-necked flask. Lower the temperature of the three-necked flask to 18°C. Add 30g of epichlorohydrin dropwise to the three-necked flask. After the addition is complete, the reaction system is heated to 70°C at a heating rate of 1°C / min. Keep the temperature for 6h. Keep the three-necked flask at 70°C and evaporate the low-boiling substances under reduced pressure to obtain a modified rosin precursor.

[0038] Weigh: 50 g of modified rosin precursor and 250 mL of 9 mol / L sodium hydroxide solution are added into a three-necked flask and stirred. The temperature of the three-necked flask is raised to 35°C, and the mixture is kept warm and stirred for 5 hours. Hydrochloric acid is added dropwise into the three-necked flask to adjust the pH of the system to 7. The filter cake is filtered and washed with purified water for 3 times. The filter cake is transferred to a drying oven at 60°C and vacuum dried to constant weight to obtain modified rosin.

[0039] S2. Preparation of film-forming agent

[0040] Weigh: 30 g of modified rosin, 20 g of cocamidopropyl betaine and 300 mL of toluene, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 60°C, add 0.5 g of triethylamine into the three-necked flask, keep warm for 2.5 h, lower the temperature of the three-necked flask to room temperature, add 1000 mL of petroleum ether into the reaction system, stir for 20 min, filter, wash the filter cake with petroleum ether 3 times and then drain, transfer the filter cake into a drying oven at 60°C, and vacuum dry to constant weight to obtain composite rosin;

[0041] Add the composite rosin and anhydrous ethanol in a ratio of 2 g:5 mL into a three-necked flask and stir. Raise the temperature of the three-necked flask to 65°C and stir until the system is dissolved to obtain a composite rosin solution.

[0042] Weigh: 30g of polyethylene glycol, 10g of propylene glycol, and 200mL of deionized water, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 70°C, increase the stirring speed to 900r / min, add 100mL of the composite rosin solution into the three-necked flask, stir and disperse for 30min, lower the temperature of the three-necked flask to 45°C, and distill under reduced pressure until no liquid drips out, raise the temperature of the three-necked flask to 70°C, and distill off part of the solvent under reduced pressure to obtain a film-forming agent with a solid content of 35wt%.

[0043] S3. Preparation of water-based polyester

[0044] Weigh: 34.8 g of suberic acid, 19.2 g of citric acid, 40.3 g of trimethylolpropane, 1.4 g of monobutyltin oxide and 348 mL of deionized water, add them into a nitrogen-protected autoclave and stir them in a closed manner, raise the temperature of the autoclave to 225°C, maintain the pressure at 0.15 MPa, and keep the temperature for 6 hours. Then, lower the temperature of the autoclave to 160°C, add 23.7 g of 2-(2,5-dioxytetrahydrofuran-3-yl)acetic acid to the reaction system, keep the temperature for 80 minutes, lower the temperature of the autoclave to room temperature, filter, transfer the filtrate to a rotary evaporator with a water bath temperature of 80°C, and remove the ionized water by evaporation under reduced pressure to obtain a crude water-based polyester;

[0045] Add the crude aqueous polyester and ethyl acetate into a three-necked flask and stir until the system is dissolved. Add petroleum ether to the reaction system, and a large amount of solid precipitates. Filter with suction, transfer the filter cake to a drying oven at a temperature of 55°C, and vacuum dry to constant weight to obtain aqueous polyester, wherein the amount ratio of the crude aqueous polyester, ethyl acetate and petroleum ether is 1g:3mL:10mL.

[0046] S4. Preparation of pre-coated water-based flux

[0047] salicylic acid, D,L-malic acid and maleic acid are uniformly mixed in a weight ratio of 2:5:1 to obtain an organic acid;

[0048] Span-20, Tween-80 and sodium dodecyl sulfate are mixed uniformly in a weight ratio of 3:2:1 to obtain a surfactant;

[0049] Weigh: 30g of water-based polyester, 150g of film-forming agent, 30g of organic acid, 6g of surfactant and 1000g of deionized water, add into a three-necked flask and stir, set the stirring speed to 900r / min, stir for 90min at room temperature, add 10wt% ammonia water into the three-necked flask, adjust the system pH to 4.2, stir for 60min, and obtain a pre-coated water-based flux.

[0050] Example 2

[0051] This embodiment provides a method for preparing a pre-coated water-based soldering flux for photovoltaic ribbon welding, comprising the following steps:

[0052] S1. Preparation of modified rosin

[0053] Weigh: 50g of rosin resin and 150mL of toluene are added to a three-necked flask and stirred. Stir at room temperature until the rosin resin is dissolved. Add 1g of diisopropylamine to the three-necked flask. Lower the temperature of the three-necked flask to 20°C. Add 30g of epichlorohydrin dropwise to the three-necked flask. After the addition is complete, the reaction system is heated to 75°C at a rate of 2°C / min. Keep the temperature for 7h. Keep the three-necked flask at 75°C and evaporate the low-boiling substances under reduced pressure to obtain a modified rosin precursor.

[0054] Weigh: 50 g of modified rosin precursor and 300 mL of 9.5 mol / L sodium hydroxide solution are added into a three-necked flask and stirred. The temperature of the three-necked flask is raised to 40°C, and the mixture is kept warm and stirred for 6 hours. Hydrochloric acid is added dropwise into the three-necked flask to adjust the pH value of the system to 7. The filter cake is washed with purified water for 3 times and then removed from the filter cake. The filter cake is transferred to a drying oven at a temperature of 65°C and vacuum dried to constant weight to obtain modified rosin.

[0055] S2. Preparation of film-forming agent

[0056] Weigh: 30 g of modified rosin, 20 g of cocamidopropyl betaine and 300 mL of toluene, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 65°C, add 0.5 g of triethylamine into the three-necked flask, keep warm for 3.0 h, lower the temperature of the three-necked flask to room temperature, add 1000 mL of petroleum ether into the reaction system, stir for 25 min, filter, wash the filter cake with petroleum ether 3 times and then drain, transfer the filter cake into a drying oven at 65°C, and vacuum dry to constant weight to obtain composite rosin;

[0057] Add the composite rosin and anhydrous ethanol in a ratio of 2 g:5 mL into a three-necked flask and stir. Raise the temperature of the three-necked flask to 70°C and stir until the system is dissolved to obtain a composite rosin solution.

[0058] Weigh: 30g of polyethylene glycol, 10g of propylene glycol, and 200mL of deionized water, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 75°C, increase the stirring speed to 950r / min, add 100mL of the composite rosin solution into the three-necked flask, stir and disperse for 40min, lower the temperature of the three-necked flask to 45°C, and distill under reduced pressure until no liquid drips out, raise the temperature of the three-necked flask to 70°C, and distill off part of the solvent under reduced pressure to obtain a film-forming agent with a solid content of 38wt%.

[0059] S3. Preparation of water-based polyester

[0060] Weigh: 34.8 g of suberic acid, 19.2 g of citric acid, 40.3 g of trimethylolpropane, 1.4 g of monobutyltin oxide and 348 mL of deionized water, add them into a nitrogen-protected autoclave and stir them in a closed manner, raise the temperature of the autoclave to 230°C, maintain the pressure at 0.20 MPa, and keep the temperature for 7 hours. Then, lower the temperature of the autoclave to 170°C, add 23.7 g of 2-(2,5-dioxytetrahydrofuran-3-yl)acetic acid to the reaction system, keep the temperature for 100 minutes, lower the temperature of the autoclave to room temperature, filter, transfer the filtrate to a rotary evaporator with a water bath temperature of 85°C, and remove the ionized water by evaporation under reduced pressure to obtain a crude water-based polyester;

[0061] Add the crude aqueous polyester and ethyl acetate into a three-necked flask and stir until the system is dissolved. Add petroleum ether to the reaction system, and a large amount of solid precipitates. Filter with suction, transfer the filter cake to a drying oven at a temperature of 60°C, and vacuum dry to constant weight to obtain aqueous polyester, wherein the amount ratio of the crude aqueous polyester, ethyl acetate and petroleum ether is 1g:3mL:10mL.

[0062] S4. Preparation of pre-coated water-based flux

[0063] salicylic acid, D,L-malic acid and maleic acid are uniformly mixed in a weight ratio of 2:5:1 to obtain an organic acid;

[0064] Span-20, Tween-80 and sodium dodecyl sulfate are mixed uniformly in a weight ratio of 3:2:1 to obtain a surfactant;

[0065] Weigh: 40g of water-based polyester, 175g of film-forming agent, 35g of organic acid, 7g of surfactant and 1000g of deionized water, add into a three-necked flask and stir, set the stirring speed to 950r / min, stir for 105min at room temperature, add 15wt% ammonia water into the three-necked flask, adjust the system pH to 4.5, stir for 70min, and obtain a pre-coated water-based flux.

[0066] Example 3

[0067] This embodiment provides a method for preparing a pre-coated water-based soldering flux for photovoltaic ribbon welding, comprising the following steps:

[0068] S1. Preparation of modified rosin

[0069] Weigh: 50g of rosin resin and 150mL of toluene are added to a three-necked flask and stirred. Stir at room temperature until the rosin resin is dissolved. Add 1g of diisopropylamine to the three-necked flask. The temperature of the three-necked flask is lowered to 22°C. 30g of epichlorohydrin is added dropwise to the three-necked flask. After the addition is complete, the reaction system is heated to 80°C at a heating rate of 3°C / min. The temperature is kept for 8h. The three-necked flask is kept at 80°C. Low-boiling substances are evaporated under reduced pressure to obtain a modified rosin precursor.

[0070] Weigh: 50 g of modified rosin precursor and 350 mL of 10 mol / L sodium hydroxide solution are added into a three-necked flask and stirred. The temperature of the three-necked flask is raised to 45°C, and the mixture is kept warm and stirred for 7 hours. Hydrochloric acid is added dropwise into the three-necked flask to adjust the pH of the system to 7, and the filter cake is filtered off after being washed three times with purified water. The filter cake is transferred to a drying oven at a temperature of 70°C and vacuum dried to constant weight to obtain modified rosin.

[0071] S2. Preparation of film-forming agent

[0072] Weigh: 30 g of modified rosin, 20 g of cocamidopropyl betaine and 300 mL of toluene, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 70°C, add 0.5 g of triethylamine into the three-necked flask, keep warm for 3.5 hours, lower the temperature of the three-necked flask to room temperature, add 1000 mL of petroleum ether into the reaction system, stir for 30 minutes, filter, wash the filter cake with petroleum ether 3 times and then drain, transfer the filter cake into a drying oven at a temperature of 70°C, and vacuum dry to constant weight to obtain composite rosin;

[0073] Add the composite rosin and anhydrous ethanol in a ratio of 2 g:5 mL into a three-necked flask and stir. Raise the temperature of the three-necked flask to 75°C and stir until the system is dissolved to obtain a composite rosin solution.

[0074] Weigh: 30g of polyethylene glycol, 10g of propylene glycol, and 200mL of deionized water, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 80°C, increase the stirring speed to 1000r / min, add 100mL of the composite rosin solution into the three-necked flask, stir and disperse for 50min, lower the temperature of the three-necked flask to 45°C, and distill under reduced pressure until no liquid drips out, raise the temperature of the three-necked flask to 70°C, and distill off part of the solvent under reduced pressure to obtain a film-forming agent with a solid content of 40wt%.

[0075] S3. Preparation of water-based polyester

[0076] Weigh: 34.8 g of suberic acid, 19.2 g of citric acid, 40.3 g of trimethylolpropane, 1.4 g of monobutyltin oxide and 348 mL of deionized water, add them into a nitrogen-protected autoclave and stir them in a closed manner, raise the temperature of the autoclave to 235°C, maintain the pressure at 0.25 MPa, and keep the temperature for 8 hours. Then, lower the temperature of the autoclave to 180°C, add 23.7 g of 2-(2,5-dioxytetrahydrofuran-3-yl)acetic acid to the reaction system, keep the temperature for 120 minutes, lower the temperature of the autoclave to room temperature, filter, transfer the filtrate to a rotary evaporator with a water bath temperature of 90°C, and remove the ionized water by evaporation under reduced pressure to obtain a crude water-based polyester;

[0077] Add the crude aqueous polyester and ethyl acetate into a three-necked flask and stir until the system is dissolved. Add petroleum ether to the reaction system, and a large amount of solid precipitates. Filter with suction, transfer the filter cake to a drying oven at a temperature of 65°C, and vacuum dry to constant weight to obtain aqueous polyester, wherein the amount ratio of the crude aqueous polyester, ethyl acetate and petroleum ether is 1g:3mL:10mL.

[0078] S4. Preparation of pre-coated water-based flux

[0079] salicylic acid, D,L-malic acid and maleic acid are uniformly mixed in a weight ratio of 2:5:1 to obtain an organic acid;

[0080] Span-20, Tween-80 and sodium dodecyl sulfate are mixed uniformly in a weight ratio of 3:2:1 to obtain a surfactant;

[0081] Weigh: 50g of water-based polyester, 200g of film-forming agent, 40g of organic acid, 8g of surfactant and 1000g of deionized water, add into a three-necked flask and stir, set the stirring speed to 1000r / min, stir for 120min at room temperature, add 20wt% ammonia water into the three-necked flask, adjust the system pH to 4.8, stir for 80min, and obtain a pre-coated water-based flux.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 3 is that the rosin resin in step S1 is used to replace the composite rosin in step S2.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 3 is that step S3 is omitted and no water-based polyester is added in step S4.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 3 is that the pH of the pre-coated water-based flux prepared in step S4 is adjusted by ammonia water.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Example 3 is that sodium dodecyl sulfate is not added to the surfactant in step S4.

[0090] Performance Test:

[0091] The expansion rate, wetting time, surface insulation resistance, electrochemical migration phenomenon, and copper plate corrosion phenomenon of the pre-coated water-based flux prepared in Examples 1-3 and Comparative Examples 1-4 were measured with reference to the standard SJ / T 11273-2016 "No-clean liquid flux". The specific test results are shown in Table 1 below.

[0092] Table 1-Performance test data of the sample

[0093]

[0094]

[0095] Data Analysis:

[0096] Comparative analysis of the data in Table 1 above shows that the expansion rate of the pre-coated water-based flux prepared by the present invention reaches 85.6%, the wetting time is reduced to 1.76s, and the surface insulation resistance is increased to 1.65×10 12 Ω, and there is no corrosion to the copper plate, no obvious electrochemical migration, and all performance test data are better than the comparative example; the present invention is to modify the rosin resin by cocamidopropyl betaine to prepare a composite rosin, and then blend the composite rosin with polyethylene glycol and glycerol to prepare a film-forming agent, and combine the film-forming agent with a carboxyl-modified water-based polyester, an organic acid, and a surfactant, which not only effectively improves the wetting and spreading performance of the pre-coated water-based flux, but also improves its surface insulation resistance and electrochemical migration resistance, reduces the corrosion of the copper plate material, and improves the welding quality of the photovoltaic welding strip.

[0097] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A pre-coated water-based flux for photovoltaic ribbon welding, characterized in that: The pre-coating water-based soldering flux comprises the following components by weight: 3-5 parts of water-based polyester, 15-20 parts of film former, 3-4 parts of organic acid, 0.6-0.8 parts of surfactant, 100 parts of deionized water and pH regulator, and the pH of the pre-coating water-based soldering flux is 4.2-4.

8.

2. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 1, characterized in that: The organic acid is composed of salicylic acid, D,L-malic acid and maleic acid in a weight ratio of 2:5:1; the surfactant is composed of Span-20, Tween-80 and sodium dodecyl sulfate in a weight ratio of 3:2:1; and the pH regulator is 10-20wt% ammonia water.

3. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 1, characterized in that: The preparation method of the water-based polyester comprises the following steps: under the protection of inert gas, suberic acid, citric acid, trimethylolpropane and a catalyst are added to a high-pressure reactor filled with deionized water and stirred in a closed manner, the temperature of the reaction system is increased to 225-235° C., the reaction is carried out by heat preservation for 6-8 hours, the temperature of the reaction system is reduced to 160-180° C., 2-(2,5-dioxytetrahydrofuran-3-yl)acetic acid is added to the reaction system, the reaction is carried out by heat preservation for 80-120 minutes, the temperature of the reaction system is reduced to room temperature, sodium hydroxide solution is added to the reaction system, the pH of the system is adjusted to 7.5-8.5, and post-treatment is performed to obtain the water-based polyester.

4. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 3, characterized in that: The usage ratio of suberic acid, citric acid, trimethylolpropane and 2-(2,5-dioxotetrahydrofuran-3-yl)acetic acid is 2 mol:1 mol:3 mol:1.5 mol, the usage ratio of suberic acid, catalyst and deionized water is 5 g:0.2 g:50 mL, and the catalyst is monobutyl tin oxide.

5. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 1, characterized in that: The film-forming agent is obtained by processing the following steps: A1. Add modified rosin and cocamidopropyl betaine to toluene and stir. Raise the temperature of the reaction system to 60-70°C. Add a catalyst to the reaction system and keep the reaction warm for 2.5-3.5h. Post-treat to obtain composite rosin. A2. Add polyethylene glycol and glycerol into deionized water and stir. Raise the temperature of the reaction system to 70-80°C and increase the stirring speed to 900-1000r / min. Add the composite rosin solution to the reaction system and stir and disperse for 30-50min. Post-treat to obtain a film-forming agent with a solid content of 35-40wt%.

6. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 5, characterized in that: In step A1, the amount ratio of the modified rosin, cocamidopropyl betaine, toluene and the catalyst is 3g:2g:30mL:0.05g, and the catalyst is triethylamine; in step A2, the amount ratio of the polyethylene glycol, glycerol, deionized water and the composite rosin solution is 3g:1g:20mL:10mL, and the composite rosin solution is composed of composite rosin and ethanol in an amount ratio of 2g:5mL.

7. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 5, characterized in that: Modified rosin is obtained by the following steps: B1, add rosin resin to toluene, stir at room temperature until the rosin resin is dissolved, add catalyst to the reaction system, lower the temperature of the reaction system to 18-22 ° C, add epichlorohydrin dropwise to the reaction system, and after the addition is complete, increase the temperature of the reaction system to 70-80 ° C at a heating rate of 1-3 ° C / min, keep the temperature for 6-8 hours, and post-treat to obtain a modified rosin precursor; B2. Add the modified rosin precursor into the sodium hydroxide solution and stir. Raise the temperature of the reaction system to 35-45°C. Keep stirring for 5-7 hours. Post-treat to obtain the modified rosin.

8. The pre-coated water-based flux for photovoltaic ribbon welding according to claim 7, characterized in that: In step B1, the dosage ratio of the rosin resin, toluene, catalyst and epichlorohydrin is 5g:15mL:0.1g:3g, and the catalyst is diisopropylamine; in step B2, the dosage ratio of the modified rosin precursor and the sodium hydroxide solution is 1g:5-7mL, and the concentration of the sodium hydroxide solution is 9-10mol / L.

9. A method for preparing a pre-coated water-based soldering flux for photovoltaic ribbon welding, using the pre-coated water-based soldering flux for photovoltaic ribbon welding as described in any one of claims 1 to 8, characterized in that: Add water-based polyester, film-forming agent, organic acid and surfactant into deionized water and stir. Set the stirring speed to 900-1000 r / min and stir for 90-120 min at room temperature. Add pH adjuster to the reaction system and adjust the pH of the system to 4.2-4.

8. Stir for 60-80 min to obtain a pre-coated water-based flux.

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