VOC-free water-soluble environmentally-friendly flux and preparation method thereof

Abstract

This invention relates to a VOC-free, water-soluble, environmentally friendly flux and its preparation method, belonging to the field of flux technology. The raw material components include: polyethylene glycol-maleic anhydride graft copolymer, fumaric acid, zinc citrate nanoparticles, nonionic surfactant, water-soluble cationic chitosan quaternary ammonium salt, pH buffer, and deionized water. The polyethylene glycol-maleic anhydride graft copolymer forms an amphiphilic molecular framework, reducing the surface tension of the solution by adjusting the grafting rate. Stability is enhanced by intermolecular hydrogen bonding of fumaric acid. The use of triethanolamine lactate pH buffer and water-soluble cationic chitosan quaternary ammonium salt film-forming agent increases the flux's stability during the welding process and forms a protective film after welding. This invention contains no VOCs, eliminating harmful volatile substances during the welding process, thus reducing environmental pollution, lowering health risks to operators, and reducing VOC emissions in the welding process, achieving environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of flux technology and relates to a VOC-free, water-soluble, environmentally friendly flux and its preparation method. Background Technology

[0002] Fluxes aid and promote the welding process, while also providing protection and preventing oxidation. Rosin resin fluxes are among the most common. Rosin resin fluxes are popular due to their superior wetting and insulating properties. They promote solder flow and wetting by reducing the surface tension of the solder, thus forming a strong weld joint. However, these traditional fluxes typically contain volatile organic compounds (VOCs), which release harmful gases during the welding process, adversely affecting the environment and the health of operators. Furthermore, rosin resin leaves residues after welding. These residues can degrade electrical properties in high-temperature and humid environments, often requiring additional cleaning steps. This not only increases production costs but also creates environmental pressure.

[0003] With increasing environmental awareness and increasingly stringent regulations, water-soluble fluxes have emerged as an alternative. Water-soluble fluxes are typically composed of water-soluble organic acids, polymers, and other additives, and their non-toxic and harmless characteristics make them ideal for green manufacturing. Water-soluble fluxes are easy to clean after use, reducing post-soldering residues and environmental impact. Furthermore, they do not release VOCs during the soldering process, thus reducing health threats to operators. Due to these advantages, water-soluble fluxes are increasingly used in the manufacture of various electronic products, especially in fields requiring high reliability and stringent environmental regulations, such as consumer electronics, automotive electronics, and medical devices.

[0004] With the continuous development of welding technology, no-clean fluxes have become widely used. A major advantage of no-clean fluxes is that they eliminate the need for cleaning, reducing additional operations and costs in the production process. However, problems with no-clean fluxes have also gradually emerged, particularly the risk of excessive residues. This may affect electrical performance and even negatively impact the long-term stability of components. Especially in high-frequency or high-temperature operating environments, residues may lead to reduced conductivity, thereby affecting the overall performance of the product.

[0005] Despite the significant advantages of water-soluble fluxes in terms of environmental friendliness and safety, they still face some challenges in practical applications. Firstly, the wetting and flow properties of water-soluble fluxes are generally inferior to traditional rosin-based fluxes, potentially leading to reduced solder joint reliability. Furthermore, the thermal stability of water-soluble fluxes under high-temperature soldering conditions needs further improvement to ensure they do not decompose or fail during the soldering process. Summary of the Invention

[0006] To address the issues of poor wetting properties in water-based fluxes and excessive residues in no-clean fluxes, this invention proposes an innovative approach to improve flux performance through molecular structure modification. By modifying the molecular structure of water-soluble organic acids and polymers, this invention significantly enhances the wettability and flowability of the flux, thereby effectively improving soldering results. Furthermore, the modified flux forms a more uniform and stable protective film after soldering, reducing residue formation and ensuring that post-soldering residues remain within safe limits.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a VOC-free water-soluble environmentally friendly flux, the raw material components of which include: 15-25 parts by weight of polyethylene glycol-maleic anhydride graft copolymer, 2-5 parts by weight of fumaric acid, 0.5-4 parts by weight of zinc citrate nanoparticles, 0.5-1 parts by weight of nonionic surfactant, 0.7-1 parts by weight of water-soluble cationic chitosan quaternary ammonium salt, 2-4 parts by weight of pH buffer, and 50-70 parts by weight of deionized water.

[0008] As a preferred embodiment of the present invention, the nonionic surfactant is any one of polyvinyl alcohol, polysorbate-20, and sorbitol monooleate.

[0009] As a preferred embodiment of the present invention, the polyethylene glycol-maleic anhydride graft copolymer is used as an active carrier. When the grafting rate is controlled at 35-45%, the surface tension of the solution is reduced, and the content of carboxylic acid groups and the flexibility of the molecular chain are balanced. During welding, the ester bond breaks at a temperature above 280°C, generating CO2 and H2O that escape.

[0010] As a preferred technical solution of the present invention, the preparation method of the polyethylene glycol-maleic anhydride graft copolymer includes the following steps: under nitrogen protection, polyethylene glycol is heated and melted, maleic anhydride and 0.8-1.2wt% catalyst p-toluenesulfonic acid are added dropwise and stirred at 80-85℃ for 5-6 hours until the acid value reaches 120-140mgKOH / g.

[0011] As a preferred embodiment of the present invention, the molar ratio of polyethylene glycol to maleic anhydride is 1:1.1-1.3.

[0012] As a preferred embodiment of the present invention, the zinc citrate nanoparticles are prepared by a microemulsion method, with a particle size of 50-80 nm. The preparation method is as follows: hexadecyltrimethylammonium bromide, n-butanol, and cyclohexane are mixed in a mass ratio of 1:2-4:5-7 to form a microemulsion. A 0.05-0.2 mol / L zinc nitrate solution and a 0.05-0.2 mol / L sodium citrate solution are added dropwise to the microemulsion at a volume ratio of 5-10%. The mixture is ultrasonically emulsified for 10-20 min to generate zinc citrate precipitate. The nanoparticles are obtained by centrifugation, washing, and vacuum drying.

[0013] As a preferred embodiment of the present invention, the pH buffer is triethanolamine lactate, which prevents excessive ionization of carboxylic acid groups and dissociation of hydrogen bond networks.

[0014] Furthermore, the preparation method of the VOC-free water-soluble environmentally friendly flux includes the following steps:

[0015] (1) Add fumaric acid to deionized water, add polyethylene glycol-maleic anhydride graft copolymer and ultrasonically disperse at 50-60℃, stir for 1-2h to form a dynamic hydrogen bond network complex.

[0016] (2) After adding zinc citrate nanoparticles to the complex and ultrasonically treating it, nonionic surfactant, water-soluble cationic chitosan quaternary ammonium salt and pH buffer were added in sequence to adjust the pH to 6.8-7.0.

[0017] The beneficial effects of this invention are:

[0018] (1) The present invention uses water-soluble cationic chitosan quaternary ammonium salt and polyethylene glycol-maleic anhydride graft copolymer, which does not contain volatile organic compounds (VOCs). There are no harmful volatile substances during the welding process, which not only reduces environmental pollution, but also reduces the health risks to operators, reduces VOC emissions in the soldering process, and achieves the effect of environmental protection.

[0019] (2) By adjusting the grafting rate (35-45%), the content of carboxylic acid groups and the flexibility of molecular chains are balanced to ensure that the welding decomposition products escape in the form of small molecules; by binding fumaric acid with hydrogen bonds, the surface tension of the solution is reduced, the stability is improved, and low-temperature deactivation is avoided; through the thermal stability of nanoparticles and the fluidity of graft copolymer, the flux exhibits excellent thermal stability during high-temperature welding, avoiding flux decomposition or performance degradation during welding.

[0020] (3) This invention employs triethanolamine lactate pH buffer and water-soluble cationic chitosan quaternary ammonium salt film-forming agent. By optimizing their component ratio and preparation method, the stability of the flux during the welding process is ensured, and a protective film is formed after welding. This protective film can effectively prevent surface oxidation and contamination after welding, and improve the quality and stability of the weld joint. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0022] The sources of the raw materials involved in the following examples and comparative examples are as follows: the polyethylene glycol was purchased from Guangzhou Zhongwan New Materials Co., Ltd.; the water-soluble cationic chitosan quaternary ammonium salt was purchased from Dongying Tianhua Biological Additives Business Department; the polyvinylpyrrolidone was purchased from Boai Xinkaiyuan Medical Technology Group Co., Ltd.; and the fumaric acid was purchased from Fadoli Biotechnology Co., Ltd.

[0023] Example 1

[0024] For the soldering setup of electronic components, PEG-600 polyethylene glycol was selected, and fumaric acid was pre-micronized to reduce the particle size to less than 5 μm.

[0025] A VOC-free, water-soluble, environmentally friendly flux, comprising the following raw material components: 20 parts by weight of polyethylene glycol-maleic anhydride graft copolymer, 4 parts by weight of fumaric acid, 2 parts by weight of zinc citrate nanoparticles, 0.7 parts by weight of nonionic surfactant, 0.8 parts by weight of water-soluble cationic chitosan quaternary ammonium salt, 3 parts by weight of pH buffer, and 60 parts by weight of deionized water.

[0026] The preparation method of the polyethylene glycol-maleic anhydride graft copolymer includes the following steps: under nitrogen protection, polyethylene glycol PEG-600 is heated and melted, maleic anhydride and 1wt% catalyst p-toluenesulfonic acid are added dropwise and stirred at 82°C for 5.5h until the acid value reaches 130mgKOH / g and the grafting rate is controlled at 40%.

[0027] The molar ratio of polyethylene glycol to maleic anhydride is 1:1.2.

[0028] The zinc citrate nanoparticles were prepared using a microemulsion method. The preparation method was as follows: hexadecyltrimethylammonium bromide, n-butanol, and cyclohexane were mixed in a mass ratio of 1:3:6 to form a microemulsion. 0.1 mol / L zinc nitrate solution and 0.1 mol / L sodium citrate solution were added dropwise to the microemulsion at a volume ratio of 8%. The mixture was ultrasonically emulsified for 15 min to generate zinc citrate precipitate. The precipitate was obtained by centrifugation, washing, and vacuum drying to obtain nanoparticles with a particle size of 60 nm.

[0029] The pH buffer is triethanolamine lactate.

[0030] The preparation method of the VOC-free water-soluble environmentally friendly flux includes the following steps:

[0031] (1) Add fumaric acid to deionized water, add polyethylene glycol-maleic anhydride graft copolymer and ultrasonically disperse at 55°C, then stir and complex for 1.5 h to form a complex.

[0032] (2) After adding zinc citrate nanoparticles to the complex and ultrasonically treating it, nonionic surfactant polyvinyl alcohol, water-soluble cationic chitosan quaternary ammonium salt and pH buffer were added in sequence to adjust the pH to 6.9.

[0033] (3) It is prepared by aging at 40℃ for 2 hours.

[0034] Example 2

[0035] In high-temperature and high-humidity environments (85℃ / 85%RH), hydrogen bonds may partially break, leading to the aggregation of active ingredients. Therefore, a small amount of polyvinylpyrrolidone is introduced into the formulation to stabilize the hydrogen bond network through π-π conjugation.

[0036] A VOC-free, water-soluble, environmentally friendly flux, comprising the following raw material components: 20 parts by weight of polyethylene glycol-maleic anhydride graft copolymer, 4 parts by weight of fumaric acid, 2 parts by weight of zinc citrate nanoparticles, 0.7 parts by weight of nonionic surfactant, 0.8 parts by weight of water-soluble cationic chitosan quaternary ammonium salt, 3 parts by weight of pH buffer, 60 parts by weight of deionized water, and 0.18 parts by weight of polyvinylpyrrolidone.

[0037] The preparation method of the polyethylene glycol-maleic anhydride graft copolymer includes the following steps: under nitrogen protection, polyethylene glycol PEG-600 is heated and melted, maleic anhydride and 1wt% catalyst p-toluenesulfonic acid are added dropwise and stirred at 82°C for 5.5h until the acid value reaches 130mgKOH / g and the grafting rate is controlled at 40%.

[0038] The molar ratio of polyethylene glycol to maleic anhydride is 1:1.2.

[0039] The zinc citrate nanoparticles were prepared using a microemulsion method. The preparation method was as follows: hexadecyltrimethylammonium bromide, n-butanol, and cyclohexane were mixed in a mass ratio of 1:3:6 to form a microemulsion. 0.1 mol / L zinc nitrate solution and 0.1 mol / L sodium citrate solution were added dropwise to the microemulsion at a volume ratio of 8%. The mixture was ultrasonically emulsified for 15 min to generate zinc citrate precipitate. The precipitate was obtained by centrifugation, washing, and vacuum drying to obtain nanoparticles with a particle size of 60 nm.

[0040] The pH buffer is triethanolamine lactate.

[0041] The preparation method of the VOC-free water-soluble environmentally friendly flux includes the following steps:

[0042] (1) Add fumaric acid to deionized water, add polyethylene glycol-maleic anhydride graft copolymer and polyvinylpyrrolidone, and ultrasonically disperse at 55°C. Stir and complex for 1.5 h to form a complex.

[0043] (2) After adding zinc citrate nanoparticles to the complex and ultrasonically treating it, nonionic surfactant polysorbate-20, water-soluble cationic chitosan quaternary ammonium salt, and pH buffer were added in sequence to adjust the pH to 6.9.

[0044] (3) It is prepared by aging at 40℃ for 2 hours.

[0045] Example 3

[0046] For soldering small, precision electronic components, extremely high soldering accuracy and good material dispersibility are required. Fumaric acid nanoparticles with a particle size of less than 200 nm were prepared using a ball milling method, with ethanol added as a co-solvent to promote dissolution.

[0047] A VOC-free, water-soluble, environmentally friendly flux, comprising the following raw material components: 20 parts by weight of polyethylene glycol-maleic anhydride graft copolymer, 4 parts by weight of fumaric acid, 2 parts by weight of zinc citrate nanoparticles, 0.7 parts by weight of nonionic surfactant, 0.8 parts by weight of water-soluble cationic chitosan quaternary ammonium salt, 3 parts by weight of pH buffer, 60 parts by weight of deionized water, and 1.8 parts by weight of anhydrous ethanol.

[0048] The preparation method of the polyethylene glycol-maleic anhydride graft copolymer includes the following steps: under nitrogen protection, polyethylene glycol PEG-600 is heated and melted, maleic anhydride and 1wt% catalyst p-toluenesulfonic acid are added dropwise and stirred at 82°C for 5.5h until the acid value reaches 130mgKOH / g and the grafting rate is controlled at 40%.

[0049] The molar ratio of polyethylene glycol to maleic anhydride is 1:1.2.

[0050] The zinc citrate nanoparticles were prepared using a microemulsion method. The preparation method was as follows: hexadecyltrimethylammonium bromide, n-butanol, and cyclohexane were mixed in a mass ratio of 1:3:6 to form a microemulsion. 0.1 mol / L zinc nitrate solution and 0.1 mol / L sodium citrate solution were added dropwise to the microemulsion at a volume ratio of 8%. The mixture was ultrasonically emulsified for 15 min to generate zinc citrate precipitate. The precipitate was obtained by centrifugation, washing, and vacuum drying to obtain nanoparticles with a particle size of 60 nm.

[0051] The pH buffer is triethanolamine lactate.

[0052] The preparation method of the VOC-free water-soluble environmentally friendly flux includes the following steps:

[0053] (1) Add anhydrous ethanol and fumaric acid to deionized water, add polyethylene glycol-maleic anhydride graft copolymer and ultrasonically disperse at 55°C, stir and complex for 1.5 h to form a complex.

[0054] (2) After adding zinc citrate nanoparticles to the complex and ultrasonically treating it, nonionic surfactant sorbitan monooleate, water-soluble cationic chitosan quaternary ammonium salt, and pH buffer were added in sequence to adjust the pH to 6.9.

[0055] (3) It is prepared by aging at 40℃ for 2 hours.

[0056] Comparative Example 1

[0057] Based on Example 1, the grafting rate of the polyethylene glycol-maleic anhydride graft copolymer was controlled at 20%, while the rest remained the same as in Example 1.

[0058] Comparative Example 2

[0059] Based on Example 1, the grafting rate of the polyethylene glycol-maleic anhydride graft copolymer was controlled at 50%, while the rest remained the same as in Example 1.

[0060] Comparative Example 3

[0061] Based on Example 1, polyethylene glycol-itaconic acid graft copolymer was used instead of polyethylene glycol-maleic anhydride graft copolymer, while the rest remained the same as in Example 1.

[0062] Comparative Example 4

[0063] Based on Example 1, the amount of fumaric acid added was changed to 8 parts by weight, while the rest remained the same as in Example 1.

[0064] Comparative Example 5

[0065] Based on Example 1, the amount of fumaric acid added was changed to 0.5 parts by weight, while the rest remained the same as in Example 1.

[0066] Performance testing:

[0067] The spread rate, residual rate, wetting time, copper mirror corrosion and insulation resistance of the samples in Examples 1-3 and Comparative Examples 1-5 were tested according to the SJ / T11273-2016 standard.

[0068] VOC test: Take 100g of each of the materials from Examples 1-3 and Comparative Examples 1-5 and spread them evenly in a 1m3 environmental release chamber for 3 days (23℃, 50% humidity). Adsorb benzene hydrocarbons using Tenax tubes and detect them using ATD-GC-MS.

[0069]

[0070] By comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that when the grafting rate of polyethylene glycol-maleic anhydride graft copolymer is 20%, the density of carboxylic acid groups may be insufficient, the hydrogen bond network may be loose, the surface tension may increase, the wettability may deteriorate, and the spread rate may decrease. When the grafting rate is 50%, the molecular chain is too rigid, the hydrogen bond breaking is insufficient at high temperature, and the residual rate increases to 0.52%.

[0071] Comparative Example 3 shows that replacing grafted polyethylene glycol with itaconic acid results in a larger intercarboxylic acid spacing, a lower hydrogen bonding energy, an increased surface tension, and a 0.89% increase in residual rate.

[0072] Comparative Examples 1-3 and 4-5 show that excessive addition of fumaric acid may lead to an overly dense hydrogen bond network, excessive acid release at high temperatures, increased corrosion risk, and a residual rate of up to 0.75%. When insufficient addition is made, the release of active acid is insufficient, the oxide removal capacity decreases, and the wetting time is extended to 2.1 seconds.

[0073] The VOC emissions of ordinary rosin flux range from 500 to 3000 μg / m³. 3 The flux prepared in the examples has a VOC content of 4-17 μg / m³. 3 .

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A VOC-free, water-soluble, environmentally friendly flux, characterized in that: The flux raw material composition includes: 15-25 parts by weight of polyethylene glycol-maleic anhydride graft copolymer, 2-5 parts by weight of fumaric acid, 0.5-4 parts by weight of zinc citrate nanoparticles, 0.5-1 parts by weight of nonionic surfactant, 0.7-1 parts by weight of water-soluble cationic chitosan quaternary ammonium salt, 2-4 parts by weight of pH buffer, and 50-70 parts by weight of deionized water.

2. The VOC-free, water-soluble, environmentally friendly flux according to claim 1, characterized in that: The nonionic surfactant is any one of polyvinyl alcohol, polysorbate-20, and sorbitol monooleate.

3. The VOC-free, water-soluble, environmentally friendly flux according to claim 1, characterized in that: The grafting rate of the polyethylene glycol-maleic anhydride graft copolymer is 35-45%.

4. The VOC-free, water-soluble, environmentally friendly flux according to claim 1, characterized in that: The preparation method of the polyethylene glycol-maleic anhydride graft copolymer includes the following steps: under an inert atmosphere, polyethylene glycol is heated and melted, and maleic anhydride and the catalyst p-toluenesulfonic acid are added dropwise and stirred until the acid value reaches 120-140 mgKOH / g.

5. The VOC-free, water-soluble, environmentally friendly flux according to claim 1, characterized in that: The zinc citrate nanoparticles have a particle size of 50-80 nm.

6. The VOC-free, water-soluble, environmentally friendly flux according to claim 1, characterized in that: The method for preparing the zinc citrate nanoparticles is as follows: hexadecyltrimethylammonium bromide, n-butanol, and cyclohexane are mixed to form a microemulsion, zinc nitrate solution and sodium citrate solution are added dropwise to the microemulsion, ultrasonic emulsification is performed to generate zinc citrate precipitate, and vacuum drying is performed to obtain nanoparticles.

7. The VOC-free, water-soluble, environmentally friendly flux according to claim 6, characterized in that: The mass ratio of hexadecyltrimethylammonium bromide, n-butanol, cyclohexane, zinc nitrate, and sodium citrate is 0.8-1.2:2.5-3.5:5-7:1.5-2:2-2.

5.

8. The VOC-free, water-soluble, environmentally friendly flux according to claim 1, characterized in that: The pH buffer is triethanolamine lactate.

9. A method for preparing a VOC-free, water-soluble, environmentally friendly flux as described in any one of claims 1-8, characterized in that: Includes the following steps: (1) Add fumaric acid to deionized water and add polyethylene glycol-maleic anhydride graft copolymer to form a complex by hydrogen bonding. (2) After adding zinc citrate nanoparticles to the complex and ultrasonically treating it, nonionic surfactant, water-soluble cationic chitosan quaternary ammonium salt and pH buffer were added in sequence to adjust the pH to 6.8-7.0.

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