Method for improving surface tension of galvanized neodymium iron boron permanent magnet

Abstract

The invention belongs to the technical field of permanent magnet materials, and relates to a method for improving the surface tension of a galvanized neodymium-iron-boron permanent magnet. According to the protective agent disclosed by the invention, the solid epoxy resin emulsion modified by acrylic acid and polyether amine is used as a core film forming substance, so that an organic film layer with high crosslinking density and high mechanical strength is formed, and the corrosion resistance is also remarkably improved; the nano silica sol constructs a glass-like inorganic network rich in Si-O bonds in the film forming process, so that the surface polarity and tension are greatly enhanced; carboxymethyl cellulose has high hydrophilicity and a molecular bridging effect, silica sol particles are effectively anchored, and the uniformity and durability of a film layer are improved; hexamethylenetetramine is used as a cross-linking accelerant, so that the compactness of the membrane structure is further enhanced; the compound corrosion inhibitor benzotriazole and triethanolamine have a synergistic effect, the compound corrosion inhibitor benzotriazole inhibits oxidation corrosion of a zinc coating before film forming, and the compound corrosion inhibitor triethanolamine has the functions of pH buffering, corrosion inhibition and auxiliary curing, so that the stability of the treating fluid and the film forming quality are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet materials technology, and relates to a method for improving the surface tension of galvanized neodymium iron boron permanent magnets. Background Technology

[0002] Sintered NdFeB magnets are currently the permanent magnet material with the highest magnetic energy product. Renowned as the "King of Magnets" for their superior overall magnetic properties, they are widely used in fields with extremely high requirements for hard magnetic materials, such as maglev trains, high-performance motors, electroacoustic equipment (e.g., speakers and headphones), wind power generation, new energy vehicle drive systems, and various precision instruments. However, despite their excellent magnetic properties, NdFeB magnets face a significant drawback in practical applications—poor corrosion resistance. Because their main components include the rare earth element neodymium and the reactive metal iron, they are highly susceptible to oxidation and corrosion in humid or saline environments, severely impacting their service life and performance stability.

[0003] Therefore, industrial applications typically require surface protection treatments, with common methods including electroplating with metal layers (such as zinc, nickel, and copper) and applying organic or inorganic coatings. Among these, electroplating with zinc is widely used due to its low cost, mature technology, and certain anti-corrosion effect. However, while this surface treatment improves corrosion resistance, it also brings new challenges: in many applications, neodymium iron boron magnets need to be assembled with other components using adhesives, such as in audio units or micro-motors. This places specific requirements on the wettability and adhesion of the magnet surface, requiring a surface tension of at least 36 mN / m to ensure the adhesive can spread sufficiently and form a strong bond.

[0004] However, magnets treated with electroplating zinc usually require passivation to further enhance their corrosion resistance. The passivation process forms a dense but smooth passivation film on the surface, which, while improving corrosion resistance, significantly reduces surface energy. Experiments show that the surface tension of passivated magnets in a dry state is often below 36 mN / m, and this surface tension continues to decrease with prolonged storage time, leading to subsequent bonding failures or insufficient bonding strength. This contradiction highlights the importance of achieving a balance between corrosion resistance and bonding performance in the surface treatment process of NdFeB magnets, and has become one of the key technical challenges urgently needing to be solved in the fields of materials engineering and surface science.

[0005] Chinese patent application document (CN119252636A) discloses a neodymium iron boron magnet containing a sealing film, its preparation method and application. It treats zinc-plated and passivated neodymium iron boron magnets with a sealing agent, which improves the salt spray resistance test. However, due to the large number of non-polar groups in the protective film, the improvement and stability of the magnet's surface tension is insufficient, thus failing to provide a guarantee for the adhesion during magnet assembly. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention aims to provide a method for improving the surface tension of galvanized NdFeB permanent magnets, thereby enabling the NdFeB permanent magnets to achieve high and stable surface tension and good salt spray resistance.

[0007] One objective of this invention can be achieved through the following technical solutions: A method for improving the surface tension of galvanized NdFeB permanent magnets, the method comprising the following steps: after the passivated galvanized NdFeB magnets are washed with water, they are then subjected to ultrasonic activation treatment, then immersed in an aqueous solution containing 0.5-1.5wt% protective agent, and finally dried and irradiated with ultraviolet light; The protective agent comprises the following raw materials in parts by weight: 15-20 parts of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt%, 20-25 parts of nano silica sol, 1.5-2.5 parts of carboxymethyl cellulose, 1-2 parts of hexamethylenetetramine, 1.5-3.5 parts of corrosion inhibitor, 0.5-1 part of coupling agent, and 50-60 parts of water.

[0008] This invention utilizes the synergistic effect of multiple components to construct a functional protective film on the surface of a zinc-plated NdFeB permanent magnet, exhibiting high surface tension, excellent adhesion, good corrosion resistance, and long-term stability. An acrylic acid and polyetheramine-modified solid epoxy resin emulsion with a solid content of 30%–50 wt% forms a high-molecular cross-linked film on the magnet surface, exhibiting high mechanical strength and excellent salt spray resistance. During the film formation process, the nano-silica sol releases abundant silicon-oxygen (Si-O) network structures, forming a dense, glass-like surface that significantly enhances surface polarity and surface tension. Carboxymethyl cellulose not only possesses excellent hydrophilicity and high surface energy properties but also acts as a "bridge" to effectively anchor the nano-silica sol particles onto its polymer chains, thereby enhancing the uniformity and long-term stability of the composite film. Hexamethylenetetramine increases the cross-linking density between components during film formation, strengthening the film structure.

[0009] Ultrasonic activation treatment, through its unique cavitation effect, microjets, and high-frequency vibration, significantly optimizes the physicochemical state of the galvanized surface before the magnet is immersed in the protective agent, thereby greatly promoting the uniform adsorption and effective penetration of the protective agent components. Firstly, the activated surface is clean and free of contaminants, exposing abundant active sites, which facilitates the formation of strong interfacial bonds through chemical bonding of coupling agents and other components. Secondly, enhanced hydrophilicity makes it easier for acrylic-epoxy resin emulsions and nano-silica sols in the aqueous system to wet and spread, avoiding cratering or agglomeration. Simultaneously, the micron / nano-scale uniform rough structure induced by ultrasound increases the specific surface area, providing anchoring points for polymers such as carboxymethyl cellulose and guiding the directional deposition of nano-silica sol particles to build a dense network. Furthermore, the increased surface energy promotes more uniform dispersion and adsorption of corrosion inhibitor molecules in the active areas, maximizing protective efficacy. This invention, by performing ultrasonic activation before immersion, lays a crucial foundation for the synergistic film formation of multiphase protective agents during the subsequent static placement process, ensuring a uniform and dense coating, thereby increasing the surface tension of the neodymium iron boron permanent magnet after galvanizing.

[0010] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, the preparation of the acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt% includes the following steps: S1. Epoxy resin is added to ethylene glycol butyl ether and heated, and then polyetheramine is added and the temperature is increased in a gradient to obtain polyetheramine modified solid epoxy resin. S2. Mix polyetheramine-modified solid epoxy resin and polymerization inhibitor, then add acrylic acid, ethyl acrylate and catalyst and stir to react to obtain acrylic acid and polyetheramine-modified solid epoxy resin. S3. Emulsify the acrylic acid and polyetheramine modified solid epoxy resin with water to obtain an acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt%.

[0011] Preferably, in step S1, epoxy resin is added to ethylene glycol butyl ether and heated to 100-120°C;

[0012] Preferably, in step S1, the gradient heating includes: holding at 100-120℃ for 0.5-1.5h, heating to 125-135℃ and holding for 0.5-1.5h, heating to 140-145℃ and holding for 0.5-1.5h, and heating to 150-155℃ and holding for 1h.

[0013] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, in step S1, the mass ratio of epoxy resin, ethylene glycol butyl ether and polyetheramine is 100:(20-40):(10-20).

[0014] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, in step S2, the mass ratio of polyetheramine modified solid epoxy resin, polymerization inhibitor, acrylic acid, ethyl acrylate and catalyst is 100:(2-5):(10-20):(10-20):(1-2).

[0015] Preferably, the polymerization inhibitor is N,N-dimethylbenzylamine.

[0016] Preferably, the catalyst is p-methoxyphenol.

[0017] This invention utilizes a solid epoxy resin emulsion modified with acrylic acid and polyetheramine at a solid content of 30-50 wt%, exhibiting unique advantages as a protective agent to improve the surface tension of galvanized NdFeB permanent magnets. Firstly, this modified emulsion enhances water solubility through self-emulsification, eliminating the need for additional small-molecule emulsifiers. This not only improves water solubility but also enhances storage stability, preventing separation or sedimentation during long-term storage and ensuring consistent and reliable performance. Secondly, regarding curing performance, the unsaturated double bonds introduced by acrylic acid endow the resin with photocuring and free radical polymerization capabilities. Compared to traditional thermosetting epoxy resins, it exhibits a faster curing speed, completing the curing process in a short time and significantly improving production efficiency. Furthermore, free radical polymerization can be carried out at room temperature, reducing energy consumption and lowering production costs. The three-dimensional network structure formed by acrylic acid modification significantly improves the crosslinking density of the resin, making it more resistant to chemicals such as acids, alkalis, and organic solvents. This ensures stability and durability in harsh environments. Regarding adhesion, the modified resin contains multiple polar groups that interact strongly with the material surface, effectively enhancing adhesion to the substrate and preventing peeling. Emulsifying the emulsion with water to a solid content range of 30-50% ensures thorough emulsification while maintaining good storage stability, avoiding incomplete emulsification caused by excessively high solid content. This optimized acrylic acid and polyetheramine modified solid epoxy resin emulsion demonstrates superior performance in improving the surface treatment effect of NdFeB magnets, providing a solid guarantee for the manufacture of high-performance permanent magnet devices.

[0018] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, the nano-silica sol has a pH of 6.8-7.2 and a silica content of 25-35 wt%, wherein the average particle size of the silica particles is 10-30 nm.

[0019] In the aforementioned method for improving the surface tension of galvanized NdFeB permanent magnets, the corrosion inhibitor is benzotriazole and triethanolamine in a mass ratio of 1:(1-4). This invention uses benzotriazole and triethanolamine as corrosion inhibitors. The former can form a protective adsorption film on the surface of the galvanized layer, effectively inhibiting oxidative corrosion before film formation. The latter not only has corrosion inhibition function but also forms a pH buffer system with components such as acrylic acid in the system, maintaining the stability of the treatment solution. Furthermore, it acts as an auxiliary curing agent for epoxy resin in the film-forming reaction, further optimizing the film performance.

[0020] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, the coupling agent is at least one of silane coupling agents and titanate coupling agents.

[0021] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, the preparation method of the protective agent includes the following steps: S1. Prepare the above-mentioned raw materials; S2. Mix water and carboxymethyl cellulose evenly, then let stand. Add nano silica sol, hexamethylenetetramine, acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50wt%, coupling agent and corrosion inhibitor in sequence and stir evenly to obtain a protective agent.

[0022] In the above-mentioned method for improving the surface tension of galvanized NdFeB permanent magnets, the ultrasonic activation treatment temperature is 20-40℃ and the time is 1-2 min.

[0023] In the above-mentioned method for improving the surface tension of galvanized neodymium iron boron permanent magnets, the ultraviolet light wavelength is 315-400nm and the irradiation time is 5-10min.

[0024] This invention utilizes ultraviolet light to effectively oxidize trace organic pollutants or non-polar groups remaining on the surface of magnets, transforming them into oxygen-containing polar functional groups. This significantly enhances surface free energy and wettability, macroscopically manifested as increased surface tension. Secondly, ultraviolet light can also activate photosensitive or photocatalyst reactive groups in the acrylic-epoxy resin emulsion and coupling agent in the protective agent, promoting free radical polymerization or cationic crosslinking reactions. This accelerates the curing of the protective film and the densification of its network structure. This photoinduced crosslinking not only shortens the film-forming time but also significantly improves the coating's hardness, water resistance, and corrosion resistance, enabling the protective film to maintain high surface tension while possessing excellent long-term protective performance.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention provides a protective agent for improving the surface tension of galvanized NdFeB permanent magnets, effectively solving the key technical bottleneck that the traditional galvanizing passivation process leads to a decrease in the surface tension of the magnet, making it difficult to meet the requirements of subsequent bonding processes (such as a surface tension of ≥36 mN / m). This protective agent, through the scientific formulation of various functional components, constructs a composite functional film on the magnet surface that combines high surface tension, excellent adhesion, good salt spray resistance, and long-term stability.

[0027] 2. The protective agent of this invention uses a solid epoxy resin emulsion modified with acrylic acid and polyetheramine as the core film-forming material, which not only forms an organic film layer with high cross-linking density and high mechanical strength, but also significantly improves corrosion resistance. Nano-silica sol constructs a glassy inorganic network rich in Si-O bonds during the film formation process, greatly enhancing surface polarity and tension. Carboxymethyl cellulose has both high hydrophilicity and molecular bridging effect, effectively anchoring silica sol particles and improving the uniformity and durability of the film layer. Hexamethylenetetramine acts as a cross-linking promoter, further strengthening the compactness of the film structure. The combined corrosion inhibitors benzotriazole and triethanolamine work synergistically, with the former inhibiting the oxidation corrosion of the zinc plating layer before film formation, and the latter having both pH buffering, corrosion inhibition, and auxiliary curing functions, ensuring the stability of the treatment solution and the quality of film formation. Silane or titanate coupling agents significantly enhance the interfacial bonding force between the film layer and the metal substrate.

[0028] 3. The protective agent of this invention only needs to be diluted to a 0.5-1.5wt% aqueous solution. The treatment can be completed by simple soaking and drying. The process is simple, cost-controllable, and suitable for industrial application. The zinc-plated NdFeB magnets treated in this way have significantly improved surface tension and maintain a stable level above 36 mN / m for a long time. At the same time, the excellent corrosion resistance is verified by the neutral salt spray test. It fully meets the dual requirements of high-end manufacturing fields such as audio equipment and motors for magnet bonding reliability and environmental durability. It has significant technological progress and industrialization value. Attached Figure Description

[0029] Figure 1 This is a photograph of the zinc-plated neodymium iron boron magnet from Example 1, immersed in an aqueous solution of a protective agent. Detailed Implementation

[0030] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0031] The preparation of the zinc-plated NdFeB magnets in the following embodiments includes the following steps: The NdFeB permanent magnets are ground in a vibratory finishing machine to remove burrs, sharp edges, and surface oil, improve the appearance, and reduce the current concentration at the sharp edges of the magnet during electroplating, thus preventing ablation. Subsequently, a 3wt% nitric acid pickling is performed to effectively remove oxides and residual impurities, ensuring the cleanliness of the substrate. The cleaned magnets, along with the accompanying materials, are placed into an electroplating drum and undergo two activation and zinc plating steps: first, activation with 0.1% dilute sulfuric acid for 35 seconds to remove the micro-oxide film; then, zinc plating for 45 minutes in a zinc sulfate system (ZnSO4 400 g / L, H3BO3 30 g / L) to form a preliminary zinc layer. After a second activation with 0.1wt% hydrochloric acid, the magnets are transferred to a potassium chloride zinc plating system (KCl 180 g / L, ZnCl2 45 g / L, H3BO3 30 g / L) for further zinc plating for 40 minutes. After electroplating, the plating material is separated from the auxiliary material and then brightened in 8wt% nitric acid for 25 seconds to quickly dissolve surface dust and impurities and enhance the gloss of the plating layer. This is followed by a two-stage countercurrent pure water rinse to thoroughly remove any acid residue. Finally, the plating is passivated for 30 seconds in a tank containing 6wt% specialized passivation solution (D-109 trivalent blue-white passivating agent purchased from Dishi Chemical Co., Ltd.) to form a dense passivation film that enhances corrosion resistance. The plating is then rinsed again in a two-stage countercurrent water rinse to complete the pretreatment process.

[0032] The following examples illustrate the specific preparation of acrylic acid and polyetheramine modified solid epoxy resin emulsions with a solid content of 30-50 wt%, all following the steps described below, wherein the raw materials are prepared according to parts by mass: S1. Add 100 parts of E-12 epoxy resin to 30 parts of ethylene glycol butyl ether and heat to 120°C. Then add 15 parts of polyetheramine M3085 and keep at 120°C for 1 hour. Then raise the temperature to 130°C and keep at 1 hour. Then raise the temperature to 140°C and keep at 1 hour. Then raise the temperature to 150°C and keep at 1 hour to obtain polyetheramine modified solid epoxy resin. S2. Mix 100 parts of polyetheramine-modified solid epoxy resin and 3 parts of p-methoxyphenol, then add 15 parts of acrylic acid, 15 parts of ethyl acrylate and 1.5 parts of N,N-dimethylbenzylamine and stir for 8 hours to obtain acrylic acid and polyetheramine-modified solid epoxy resin. S3. Emulsify the acrylic acid and polyetheramine modified solid epoxy resin with water to obtain an acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt%.

[0033] The nano-silica sol was a neutral nano-silica sol purchased from Shandong Yinfeng Nanomaterials Co., Ltd. The nano-silica sol had a pH of 7.0 and a silica content of 30 wt%, with an average particle size of 18 nm for the silica particles.

[0034] The corrosion inhibitor is a mixture of benzotriazole and triethanolamine in a mass ratio of 1:2.

[0035] The coupling agent was JSC-1800M titanate coupling agent purchased from Hangzhou Jessica Chemical Co., Ltd.

[0036] The preparation method of the protective agent of the present invention will be further described in detail below through specific embodiments.

[0037] Example 1:

[0038] S1. Prepare the raw materials according to the following mass proportions: 18 parts of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 40wt%, 23 parts of nano silica sol, 2 parts of carboxymethyl cellulose, 1.5 parts of hexamethylenetetramine, 3 parts of corrosion inhibitor, 0.8 parts of coupling agent, and 55 parts of water.

[0039] S2. Slowly sprinkle water into carboxymethyl cellulose while stirring, stir evenly at 25°C, and then let stand for 18 hours until the solution is uniform, transparent and free of particles. Add nano silica sol and hexamethylenetetramine and stir for 30 minutes. Then add acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 35wt% and stir for 35 minutes. Finally, add coupling agent and corrosion inhibitor and stir for 25 minutes to obtain the protective agent.

[0040] S3. Wash 10 kg of passivated zinc-plated NdFeB magnets with water, then immerse them in a 30 L ultrasonic bath for ultrasonic treatment at 50 Hz for 2 minutes. Figure 1 The zinc-plated NdFeB magnet was immersed in 20L of an aqueous solution containing 1wt% protective agent at 30℃ for 3 minutes, and then air-dried before being irradiated under 365nm ultraviolet light for 8 minutes.

[0041] Example 2:

[0042] S1. Prepare the raw materials according to the following mass proportions: 15 parts of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 40wt%, 20 parts of nano silica sol, 1.5 parts of carboxymethyl cellulose, 1.0 part of hexamethylenetetramine, 1.5 parts of corrosion inhibitor, 0.5 parts of coupling agent, and 50 parts of water.

[0043] S2. Slowly sprinkle water into carboxymethyl cellulose while stirring, stir evenly at 25°C, and then let stand for 18 hours until the solution is uniform, transparent and free of particles. Add nano silica sol and hexamethylenetetramine and stir for 30 minutes. Then add acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30 wt% and stir for 35 minutes. Finally, add coupling agent and corrosion inhibitor and stir for 25 minutes to obtain the protective agent. S3. Wash 10kg of passivated zinc-plated NdFeB magnets with water, then immerse them in a 30L ultrasonic water bath for 2 minutes at 50Hz. Next, immerse the zinc-plated NdFeB magnets in a 20L aqueous solution containing 1wt% protective agent at 30℃ for 3 minutes. After air drying, irradiate them under 365nm ultraviolet light for 8 minutes.

[0044] Example 3:

[0045] S1. Prepare the raw materials according to the following mass proportions: 20 parts of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 40wt%, 25 parts of nano silica sol, 2.5 parts of carboxymethyl cellulose, 2.0 parts of hexamethylenetetramine, 3.5 parts of corrosion inhibitor, 1.0 part of coupling agent, and 60 parts of water.

[0046] S2. Slowly sprinkle water into carboxymethyl cellulose while stirring, stir evenly at 25°C, and then let stand for 18 hours until the solution is uniform, transparent and free of particles. Add nano silica sol and hexamethylenetetramine and stir for 30 minutes. Then add acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 50 wt% and stir for 35 minutes. Finally, add coupling agent and corrosion inhibitor and stir for 25 minutes to obtain the protective agent. S3. Wash 10kg of passivated zinc-plated NdFeB magnets with water, then immerse them in a 30L ultrasonic water bath for 2 minutes at 50Hz. Next, immerse the zinc-plated NdFeB magnets in a 20L aqueous solution containing 1wt% protective agent at 30℃ for 3 minutes. After air drying, irradiate them under 365nm ultraviolet light for 8 minutes.

[0047] Example 4:

[0048] The only difference from Example 1 is that the corrosion inhibitor is benzotriazole.

[0049] Example 5:

[0050] The only difference from Example 1 is that the corrosion inhibitor is only triethanolamine.

[0051] Comparative Example 1: The only difference from Example 1 is that the raw materials did not contain a solid epoxy resin emulsion modified with acrylic acid and polyetheramine with a solid content of 40wt%.

[0052] Comparative Example 2: The only difference from Example 1 is that the amount of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 40wt% added to the raw materials is 5 parts.

[0053] Comparative Example 3: The only difference from Example 1 is that the amount of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 40wt% added to the raw materials is 30 parts.

[0054] Comparative Example 4: The only difference from Example 1 is that no nano-silica sol was added to the raw materials.

[0055] Comparative Example 5: The only difference from Example 1 is that the amount of nano-silica sol added to the raw materials is 10 parts.

[0056] Comparative Example 6: The only difference from Example 1 is that the amount of nano-silica sol added to the raw materials is 35 parts.

[0057] Comparative Example 7: The only difference from Example 1 is that hexamethylenetetramine was not added to the raw materials.

[0058] Comparative Example 8: The only difference from Example 1 is that the amount of hexamethylenetetramine added to the raw materials is 10 parts.

[0059] Comparative Example 9: The only difference from Example 1 is that the amount of hexamethylenetetramine added to the raw materials is 0.1 parts.

[0060] Comparative Example 10: The difference from Example 1 is that the solid epoxy resin emulsion is only a polyetheramine-modified solid epoxy resin emulsion with a solid content of 40 wt%. 100 parts of E-12 epoxy resin are added to 30 parts of ethylene glycol butyl ether and heated to 120°C. Then, 15 parts of polyetheramine M3085 are added and kept at 120°C for 1 hour. The temperature is then raised to 130°C and kept for 1 hour, raised to 140°C and kept for 1 hour, and raised to 150°C and kept for 1 hour to obtain a polyetheramine-modified solid epoxy resin. Water is added for emulsification to obtain a polyetheramine-modified solid epoxy resin emulsion with a solid content of 40 wt%.

[0061] Comparative Example 11: The only difference from Example 1 is that no ultrasonic treatment was performed.

[0062] Comparative Example 12: The only difference from Example 1 is that no ultraviolet light irradiation was performed.

[0063] Comparative Example 13: The only difference from Example 1 is that the zinc-plated NdFeB magnet was not protected after passivation.

[0064] Comparative Example 14: The only difference from Example 1 is that after passivation, it is protected with YC-520 anti-tempering sealant; YC-520 anti-tempering sealant is produced by Meiguang Environmental Technology (Chongqing) Co., Ltd. It is suitable for sealing trivalent blue-white, trivalent yellow, polychrome and trivalent black after passivation. It can also be used for sealing hexavalent yellow, polychrome and olive green after passivation, as well as sealing zinc-nickel and chromium plating.

[0065] Comparative Example 15: The only difference from Example 1 is that the aqueous solution in step S3 contains 10 wt% of a protective agent; Excessive concentration of protective agent will cause the magnet surface to adsorb too much functional component, forming an excessively thick and uneven wet film. During the subsequent water discharge and drying process, the water evaporation rate and the migration of components in the film will be out of balance, resulting in local solute enrichment, which will produce water stains, mottled and striped appearance defects, seriously affecting the visual consistency and commercial value of the electroplated layer.

[0066] The permanent magnet materials of the examples and comparative examples were subjected to the following performance tests:

[0067] (1) Stability of NdFeB zinc plating surface tension treatment agent The NdFeB zinc plating surface tension treatment agent was stored at room temperature in a sealed container for three months, and its state was observed. The evaluation results were as follows: I indicates no change at all; II indicates a small amount of particles or precipitates, but the passivation solution was evenly dispersed after shaking; III indicates a large number of particles that were extremely difficult to redisperse; and IV indicates that the passivation solution gelled.

[0068] (2) Surface tension Using a test pen with different surface tension (such as the German Arcotest corona pen), draw a line on one side of the sample and observe the liquid contraction at the drawn line. If the liquid contracts into droplets or lines within 5 seconds, it is considered unqualified; otherwise, it is considered qualified. The maximum acceptable surface tension value is determined. The surface tension pen used in this invention has a surface tension of 30-60 mN / m. Samples with a surface tension greater than 60 mN / m may be considered as having a surface tension of 60 mN / m.

[0069] (3) Neutral salt spray test Referring to the national standard GB / T 10125, the treated galvanized NdFeB samples were continuously sprayed with water for 24, 72, and 144 ppm, respectively. Samples were removed within the corresponding time periods, rinsed with clean water, and the surface of the galvanized sheet was lightly brushed with a soft brush. The appearance of "white rust" was observed, and the area of ​​"white rust" was calculated using the cross-cut method. Evaluation grades are: I indicates white rust area less than 5%, II indicates white rust area 5%-10%, III indicates white rust area 10%-20%, and IV indicates white rust area 20%-50%.

[0070] Table 1: Performance test results of galvanized NdFeB magnets after treatment with the treatment solutions prepared in Examples 1-5 and Comparative Examples 1-14

[0071] The results above show that in Example 4, the lack of triethanolamine weakened the synergistic protective effect of the passivation film, resulting in a decrease in the protective capability of the magnet. In Example 5, the lack of benzotriazole weakened the synergistic protective effect of the passivation film, resulting in a decrease in the protective capability of the magnet. In Comparative Example 1, because the raw materials did not contain a solid epoxy resin emulsion modified with acrylic acid and polyetheramine with a solid content of 40%, the film-forming mechanical strength was poor, the film was weak and easily detached, resulting in poor protective capability. At the same time, the film detachment affected the surface tension. Comparative Example 2 is similar to Comparative Example 1, with slightly better performance. Comparative Example 3 shows enhanced mechanical strength and protective properties after film formation, but reduced surface polar substances and decreased surface tension. Comparative Example 4, lacking the main material for improving surface tension, shows a significant decrease in surface tension, a reduction in silica-like substances in the protective film, increased film permeability, and a decrease in protective ability. Comparative Example 5, with less of the main material for improving surface tension, shows a decrease in surface tension, a reduction in silica-like substances in the protective film, increased film permeability, and a decrease in protective ability. Comparative Example 6, with excessive addition of the main material for improving surface tension, shows a decrease in resin-like substances in the protective film, resulting in decreased mechanical strength and protective ability, but better improvement in surface tension. In addition, excessive addition of silica sol affected the stability of the solution; in Comparative Example 7, the absence of hexamethylenetetramine resulted in a decrease in the mechanical strength and protective ability of the protective film, while also causing pH changes and affecting solution stability; in Comparative Example 8, the excessive addition of hexamethylenetetramine led to excess hexamethylenetetramine becoming an impurity, further reducing the mechanical strength and protective ability of the protective film; the situation in Comparative Example 9 was similar to that of Comparative Example 7; in Comparative Example 10, due to the lack of acrylic acid modification, the protective film was difficult to cure, resulting in poor mechanical strength and protective ability, and the low proportion of polar groups in the resin affected surface tension and protective properties. In Comparative Example 11, the lack of ultrasonic treatment resulted in an incomplete or uneven protective film on the magnet surface, affecting protective properties and surface tension; in Comparative Example 12, the lack of ultraviolet irradiation resulted in low polarity and low mechanical strength of the protective film on the magnet surface, leading to a decrease in surface tension and reduced protective ability; Comparative Example 13 was in a state without any protective agent treatment, representing the conventional situation where no additional measures were taken to improve protective properties and surface characteristics.

[0072] The embodiments herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0073] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0074] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for increasing the surface tension of galvanized NdFeB permanent magnets, characterized in that, The method includes the following steps: after the passivated zinc-plated neodymium iron boron magnet is washed with water, it is then subjected to ultrasonic activation treatment, then immersed in an aqueous solution containing 0.5-1.5wt% protective agent, and finally dried and irradiated with ultraviolet light. The protective agent comprises the following raw materials in parts by weight: 15-20 parts of acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt%, 20-25 parts of nano silica sol, 1.5-2.5 parts of carboxymethyl cellulose, 1-2 parts of hexamethylenetetramine, 1.5-3.5 parts of corrosion inhibitor, 0.5-1 part of coupling agent, and 50-60 parts of water.

2. The method for improving the surface tension of galvanized NdFeB permanent magnets according to claim 1, characterized in that, The preparation of the acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt% includes the following steps: S1. Epoxy resin is added to ethylene glycol butyl ether and heated, and then polyetheramine is added and the temperature is increased in a gradient to obtain polyetheramine modified solid epoxy resin. S2. Mix polyetheramine-modified solid epoxy resin and polymerization inhibitor, then add acrylic acid, ethyl acrylate and catalyst and stir to react to obtain acrylic acid and polyetheramine-modified solid epoxy resin. S3. Emulsify the acrylic acid and polyetheramine modified solid epoxy resin with water to obtain an acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50 wt%.

3. The method for improving the surface tension of galvanized NdFeB permanent magnets according to claim 2, characterized in that, In step S1, the mass ratio of epoxy resin, ethylene glycol butyl ether, and polyetheramine is 100:(20-40):(10-20).

4. The method for improving the surface tension of galvanized NdFeB permanent magnets according to claim 2, characterized in that, In step S2, the mass ratio of polyetheramine modified solid epoxy resin, polymerization inhibitor, acrylic acid, ethyl acrylate and catalyst is 100:(2-5):(10-20):(10-20):(1-2).

5. The method for improving the surface tension of a galvanized NdFeB permanent magnet according to claim 1, characterized in that, The nano-silica sol has a pH of 6.8-7.2 and a silica content of 25-35 wt%, with the silica particles having an average particle size of 10-30 nm.

6. The method for improving the surface tension of a galvanized NdFeB permanent magnet according to claim 1, characterized in that, The corrosion inhibitor is benzotriazole and triethanolamine in a mass ratio of 1:(1-4).

7. The method for improving the surface tension of a galvanized NdFeB permanent magnet according to claim 1, characterized in that, The coupling agent is at least one of silane coupling agents and titanate coupling agents.

8. A method for improving the surface tension of a galvanized NdFeB permanent magnet according to claim 1, characterized in that, The preparation method of the protective agent includes the following steps: S1. Prepare the raw materials as described in claim 1; S2. Mix water and carboxymethyl cellulose evenly, then let stand. Add nano silica sol, hexamethylenetetramine, acrylic acid and polyetheramine modified solid epoxy resin emulsion with a solid content of 30-50wt%, coupling agent and corrosion inhibitor in sequence and stir evenly to obtain a protective agent.

9. A method for improving the surface tension of a galvanized NdFeB permanent magnet according to claim 1, characterized in that, The ultrasonic activation treatment temperature is 20-40℃, and the time is 1-5 minutes.

10. A method for improving the surface tension of a galvanized NdFeB permanent magnet according to claim 1, characterized in that, The ultraviolet light wavelength is 315-400nm, and the irradiation time is 5-10min.

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