Preparation and application methods of neodymium-iron-boron magnet water-based anticorrosive paint

Abstract

The invention relates to the technical field of coatings, and aims to provide a preparation method and a use method of a neodymium-iron-boron magnet water-based anticorrosive coating. Comprising the following steps: mixing bisphenol A epoxy resin, n-butyl alcohol and ethylene glycol monobutyl ether, and mixing methacrylic acid, butyl acrylate, styrene and an initiator; mixing the two mixed solutions drop by drop, and reacting to obtain water-based acrylic acid modified epoxy resin; the preparation method comprises the following steps: uniformly mixing organic siloxane, deionized water and propylene glycol monomethyl ether, and reacting to obtain water-based silica sol; uniformly mixing the water-based acrylic modified epoxy resin, the water-based silica sol, the ether solvent, the ultra-fine filler, the curing agent, the carbon black color paste and the deionized water, adding the deionized water, uniformly stirring, and filtering to obtain the water-based anticorrosive coating. The product is high in environmental protection property and small in influence on the environment; the method is simple and efficient to use, easy to operate, low in energy consumption requirement and suitable for large-scale industrial production; and the compactness and the corrosion medium infiltration resistance of the coating are remarkably improved, and the coating has excellent corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings, and relates to a preparation and application technology of a water-based anticorrosive coating for a neodymium iron boron magnet. BACKGROUND

[0002] The neodymium iron boron magnet has superior magnetic properties and is widely used in many fields such as wind power generation, automobile motor and medical equipment, and also plays an important role in the increasingly developed electric vehicle field. However, the neodymium iron boron magnet has a multi-phase structure, and the potential difference between the phases is large, especially the chemical activity of the grain boundary rare earth-rich phase is high; therefore, it is easy to be corroded in a high-temperature and high-humidity environment or in contact with a corrosive medium, which leads to a decrease in performance and seriously limits the application of the neodymium iron boron magnet in fields requiring the magnet to have corrosion resistance.

[0003] At present, the mainstream neodymium iron boron anticorrosion technology mainly adopts electroplating technology, but due to environmental protection reasons, the production capacity of the neodymium iron boron anticorrosion treatment is greatly limited, and it is difficult to meet the demand of the rapidly growing downstream application. Moreover, with the continuous improvement of the reliability and durability of the downstream permanent magnet motor products, higher requirements are put forward for the anticorrosion performance of the neodymium iron boron magnet, and the traditional electroplating technology has been unable to meet the requirements. Existing public research results propose to use a coating spraying process to replace the electroplating process. However, the anticorrosive coating used in the current spraying process is mostly solvent-based, which has a strong odor and is toxic, limiting the green and sustainable development of the neodymium iron boron anticorrosion technology. Environmentally friendly water-based anticorrosive coating has become the focus of the industry, but the water-based coating usually has the disadvantage of weak water vapor permeation resistance, resulting in a much lower anticorrosion performance than the solvent-based coating.

[0004] In summary, it is urgent to develop a water-based coating with high permeation resistance and anticorrosion capacity to meet the application requirements of the neodymium iron boron magnet industry. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies in the prior art and provide a preparation and use method of a water-based anticorrosive coating for a neodymium iron boron magnet.

[0006] To solve the above technical problems, the solution provided by the present application is:

[0007] A preparation method of a water-based anticorrosive coating for a neodymium iron boron magnet is provided, comprising the following steps:

[0008] (1) Take bisphenol A type epoxy resin, n-butanol and ethylene glycol monobutyl ether according to mass fractions of 80-120:8-12:10-20, mix and dissolve under heating and stirring conditions to obtain a mixed solution A;

[0009] Take methacrylic acid, butyl acrylate, styrene and initiator BPO according to mass fractions of 8-12:15-25:3-8:1-5, mix uniformly to obtain a mixed solution B;

[0010] Mixture B was added dropwise to mixture A. After the addition was complete, the mixture was reacted at 110°C with stirring for 5 hours. After the reaction was completed, the temperature was lowered to 60°C, and an appropriate amount of triethanolamine was added to adjust the pH to 3-5. Stirring was continued and an appropriate amount of water was added to obtain waterborne acrylic modified epoxy resin.

[0011] (2) Take organosiloxane, deionized water and propylene glycol methyl ether in a mass ratio of 20-30:1-10:30-50, mix them and stir evenly; add an appropriate amount of triethanolamine to adjust the pH to 7.5-8.5, stir and react for 3-20 hours under a water bath at 50-80℃ to obtain waterborne silica sol.

[0012] (3) Take the water-based acrylic modified epoxy resin obtained in step (1), the water-based silica sol obtained in step (2), the ether solvent, the ultrafine filler, the curing agent, the carbon black paste and the deionized water according to the mass ratio of 30-40: 20-30: 5-10: 2-6: 8-12: 1-4: 10-20, mix them and stir evenly; add 10% of the mass of deionized water to the mixture, stir evenly and filter to obtain the water-based anti-corrosion coating for neodymium iron boron magnets.

[0013] As a preferred embodiment of the present invention, in step (1), the heating temperature is 100°C; after adding triethanolamine to adjust the pH value, stirring is continued for 30 minutes; the amount of water added is controlled so that the solid content of the waterborne acrylic modified epoxy resin is 35%.

[0014] As a preferred embodiment of the present invention, in step (2), the mixing and stirring time of organosiloxane, deionized water and propylene glycol methyl ether is 30 min; in step (3), the stirring time for both times is 30 min, and filtration is performed using a 300 mesh filter cloth.

[0015] As a preferred embodiment of the present invention, the organosiloxane is at least one of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and γ-(2,3-epoxypropoxy)propylmethyldiethoxysilane.

[0016] As a preferred embodiment of the present invention, the ether solvent is at least one of propylene glycol methyl ether, dipropylene glycol methyl ether, or dipropylene glycol butyl ether.

[0017] As a preferred embodiment of the present invention, the ultrafine filler is calcium ion exchange type silica particles, and its average particle size is at least one of 1 micrometer, 3 micrometer, and 6 micrometer.

[0018] As a preferred embodiment of the present invention, the curing agent is a mixture of amino resin and dimer polyamide, wherein the mass ratio of the two is 1:1 to 2:3.

[0019] The present invention further provides a method for using the water-based anti-corrosion coating for NdFeB magnets prepared by the aforementioned method, comprising: firstly pre-treating the NdFeB magnets, including: chamfering, pickling, two ultrasonic water washings, alcohol washing, and drying; then, firstly spraying the anti-corrosion coating onto one side of the NdFeB magnets, followed by heat curing and cooling to room temperature; then, flipping the NdFeB magnets over and spraying them a second time, followed by heat curing to obtain NdFeB magnets coated with the anti-corrosion coating.

[0020] As a preferred embodiment of the present invention, the pickling treatment refers to soaking the magnet in a 3%–5% (v / v) dilute nitric acid aqueous solution for 10–30 seconds; the two ultrasonic water washes refer to immersing the neodymium iron boron magnet in deionized water for ultrasonic treatment for 50–70 seconds, then replacing the deionized water and ultrasonically treating it again for 30–40 seconds; the alcohol wash refers to soaking the magnet in 95%–100% (v / v) ethanol for 10–20 seconds, then wiping it dry with degreased cotton gauze; the drying treatment refers to baking at 130–140°C for 20–30 minutes; and the thermosetting treatment refers to baking in an oven at 140–160°C for 15–30 minutes.

[0021] Description of the invention principle:

[0022] 1. This invention modifies epoxy resin by grafting acrylic acid, retaining some epoxy groups in the coating system to react with dimer polyamide; the hydroxyl groups generated after ring opening can further combine with amino resin and aqueous silica sol to form a three-dimensional cross-linked network. This approach can improve the overall density of the coating film and further improve salt spray performance. Furthermore, the combination of the acrylic acid structure and polyamide gives the coating superior weather resistance compared to traditional epoxy coatings.

[0023] 2. This invention introduces calcium ion-exchange silica in the form of ultrafine fillers. Calcium ions exchange hydrogen ions on the paint film and substrate, thereby neutralizing acidic substances in the coating and maintaining a high pH value. This method inhibits corrosion while simultaneously forming a protective layer with the metal oxide film, protecting the NdFeB magnet substrate and extending its service life while reducing corrosion.

[0024] 3. This invention utilizes the surface hydroxyl groups rich in water-based silica sol to form chemical bonds with calcium ion-exchange silica and acrylic acid grafted modified epoxy resin during the curing process, thereby improving the dispersibility and interfacial bonding strength of the calcium ion-exchange silica anti-rust functional filler and ensuring the density of the coating after adding the functional filler.

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

[0026] 1. Compared with traditional solvent-based coatings using xylene, methyl ethyl ketone, etc., the water-based coating provided by this invention has the characteristics of high environmental friendliness and low environmental impact. Furthermore, the preparation technology is simple, efficient, and easy to operate, with low energy consumption requirements, making it suitable for large-scale industrial production.

[0027] 2. Compared with existing electroplating processes, the method of using water-based coatings provided by this invention avoids the problem of heavy metal ion pollution.

[0028] 3. The water-based coating provided by the present invention can significantly improve the density of the coating and its resistance to the penetration of corrosive media, and the resulting coating has excellent anti-corrosion performance. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments can enable those skilled in the art to have a more comprehensive understanding of the present invention, but do not limit the present invention in any way.

[0030] I. Preparation method of water-based anti-corrosion coating for NdFeB magnets

[0031] (1) Add 80-120 parts by weight of bisphenol A epoxy resin, 8-12 parts by weight of n-butanol and 10-20 parts by weight of ethylene glycol monobutyl ether to a reaction vessel, heat to 100°C, stir to dissolve, and obtain mixture A. Prepare mixture B with 8-12 parts by weight of methacrylic acid, 15-25 parts by weight of butyl acrylate, 3-8 parts by weight of styrene and 1-5 parts by weight of initiator BPO. Add mixture B dropwise to mixture A, heat the solution after the addition to 110°C, stir and react for 5 hours, cool to 60°C after the reaction, add an appropriate amount of triethanolamine to adjust the pH to 3-5. Then continue stirring for 30 minutes, add water to prepare waterborne acrylic modified epoxy resin with a solid content of about 35%.

[0032] (2) Mix 20-30 parts by weight of at least one organosiloxane selected from γ-(2,3-epoxypropoxy)propyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and γ-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 1-10 parts by weight of deionized water, and 30-50 parts by weight of propylene glycol methyl ether. After stirring for 30 min, add an appropriate amount of triethanolamine to adjust the pH to 7.5-8.5. Stir and react for 3-20 h in a water bath at 50-80 °C to obtain an aqueous silica sol.

[0033] (3) Weigh the following raw materials by mass: 30-40 parts by mass of waterborne acrylic modified epoxy resin, 20-30 parts by mass of waterborne silica sol, 5-10 parts by mass of at least one ether solvent selected from propylene glycol methyl ether, dipropylene glycol methyl ether and dipropylene glycol butyl ether, 2-6 parts by mass of at least one ultrafine filler selected from silica particles with average particle sizes of approximately 1 micrometer, 3 micrometer and 6 micrometer respectively, 8-12 parts by mass of curing agent of a mixture of amino resin and dimer acid polyamide in a mass ratio of 1:1 to 2:3, 1-4 parts by mass of carbon black paste, and 10-20 parts by mass of deionized water; stir in a container for 30 minutes, mix the above raw materials evenly, add 10% by mass of deionized water, stir for 30 minutes, filter with a 300-mesh filter cloth to obtain a waterborne anti-corrosion coating for neodymium iron boron magnets.

[0034] (4) Application method of water-based anti-corrosion coating for neodymium iron boron magnets:

[0035] The neodymium iron boron magnets were subjected to chamfering, pickling, two ultrasonic water washes, alcohol washing, and drying in sequence. For pickling, a 3%–5% (v / v) dilute nitric acid aqueous solution was used as the pickling agent, and the magnets were immersed in deionized water for 50–70 seconds, then the deionized water was replaced, and the magnets were ultrasonically washed again for 30–40 seconds. For alcohol washing, a 95%–100% (v / v) ethanol solution was used as the alcohol washing agent, and the magnets were immersed for 10–20 seconds, then wiped dry with degreased cotton gauze. For drying, the magnets were baked at 130–140°C for 20–30 minutes.

[0036] The neodymium iron boron magnets are placed on a tray, and the coating is applied to the magnet surface for the first time, followed by heat curing. After the neodymium iron boron magnets cool to room temperature, they are flipped over so that the uncoated magnet surface faces upwards, and a second coating is applied. After heat curing, neodymium iron boron magnets with an anti-corrosion coating are obtained. During both heat curing processes, the magnets are baked in an oven at 140–160°C for 15–30 minutes.

[0037] This invention provides water-based anti-corrosion coatings for neodymium iron boron magnets through eight embodiments. The experimental equipment used in each embodiment is conventional chemical experimental equipment, and the reagents used, except for those specially prepared in this invention, are commercially available reagents.

[0038] II. Performance Testing of Anti-corrosion Coatings

[0039] 1. Test method for resistance to neutral salt spray:

[0040] According to the national standard GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", the NdFeB magnets coated with anti-corrosion coating obtained in each example were cleaned with deionized water or a neutral solvent (such as ethanol), air-dried naturally or dried at low temperature, and the sample number and test surface were marked, and the initial appearance was recorded. A 5%±0.5% sodium chloride solution was prepared and adjusted to pH 6.5~7.2 (25℃). Under the conditions of relative humidity ≥95% and temperature 35℃±2℃, the NdFeB magnets were continuously sprayed with a spray pressure of about 98 kPa and a salt spray deposition rate of 1.0~2.0 mL / (80 cm²·h) to test the resistance to neutral salt spray and impermeability.

[0041] 2. In accordance with the provisions of XBT903-2002, the performance of each comparison sample was tested by the Pressure Cooker Test (PCT).

[0042] The data for the coating performance test are shown at the end of Table 1.

[0043] Table 1. Example Data Table

[0044]

[0045]

[0046] 3. Comparison with existing anti-corrosion coatings:

[0047] The applicant tested the coating performance of products made using existing publicly available technologies (such as CN120137474A) or commercially available products using the same testing method. The results showed that the neutral salt spray resistance was usually 96~288 hours and the PCT performance was usually 96~264 hours, and there was a general need to further improve the resistance to water vapor penetration.

[0048] The coatings formed by the water-based anti-corrosion coatings in the various embodiments of the present invention have a neutral salt spray resistance performance comparable to that of the prior art under the same testing conditions, but their PCT performance is significantly better than that of the prior art.

[0049] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A method for preparing a waterborne anticorrosive coating for neodymium-iron-boron magnets, characterized by, The method comprises the following steps: (1) taking bisphenol A type epoxy resin, n-butanol and ethylene glycol monobutyl ether according to mass fraction 80-120:8-12:10-20, mixing and dissolving under heating and stirring to obtain a mixed solution A; taking methyl methacrylate, butyl acrylate, styrene and initiator BPO according to mass fraction 8-12:15-25:3-8:1-5, mixing uniformly to obtain a mixed solution B; adding the mixed solution B dropwise into the mixed solution A, and reacting at 110℃ under stirring for 5h after the dropwise addition is completed; after the reaction is completed, cooling to 60℃, adding appropriate amount of triethanolamine to adjust pH to 3-5, continuing to stir and adding appropriate amount of water to prepare a water-based acrylic modified epoxy resin; (2) taking organosiloxane, deionized water and propylene glycol methyl ether according to mass fraction 20-30:1-10:30-50, mixing and stirring uniformly; adding appropriate amount of triethanolamine to adjust pH to 7.5-8.5, and stirring and reacting under water bath at 50-80℃ for 3-20h to obtain a water-based silica sol; (3) taking the water-based acrylic modified epoxy resin prepared in step (1), the water-based silica sol prepared in step (2) and ether solvent, ultra-fine filler, curing agent, carbon black paste and deionized water according to mass fraction 30-40:20-30:5-10:2-6:8-12:1-4:10-20, mixing and stirring uniformly; adding deionized water with 10% of the mass of the mixture, stirring uniformly and then filtering to obtain a water-based anticorrosive coating for neodymium-iron-boron magnet.

2. The method of claim 1, wherein, In the step (1), the heating temperature is 100℃; after adjusting pH by adding triethanolamine, continuing to stir for 30min; and the water is added in an amount to control the solid content of the water-based acrylic modified epoxy resin to 35%.

3. The method of claim 1, wherein, In the step (2), the mixing and stirring time of the organosiloxane, deionized water and propylene glycol methyl ether is 30min; and in the step (3), the stirring time of each time is 30min, and the filtration is performed using 300-mesh filter cloth.

4. The method of claim 1, wherein, The organosiloxane is at least one of γ-(2,3-epoxypropoxy)propyl trimethoxysilane, β-(3,4-epoxycyclohexyl)ethyl triethoxysilane and γ-(2,3-epoxypropoxy)propyl methyldiethoxysilane.

5. The method of claim 1, wherein, The ether solvent is at least one of propylene glycol methyl ether, dipropylene glycol methyl ether or dipropylene glycol butyl ether.

6. The method of claim 1, wherein, The ultra-fine filler is calcium ion exchange type silicon dioxide particles, and the average particle size is at least one of 1 micron, 3 microns and 6 microns.

7. The method of claim 1, wherein, The curing agent is a mixture of amino resin and dimer acid polyamide, and the mass ratio of the two is 1:1-2:

3.

8. The use of the waterborne anticorrosive coating for neodymium-iron-boron magnets produced by the method according to any one of claims 1 to 7, characterized in that The method comprises: firstly, pretreating the neodymium-iron-boron magnet, including chamfering, pickling, twice ultrasonic water washing, alcohol washing and drying treatment; then, using the anticorrosive coating to spray the neodymium-iron-boron magnet on one side, cooling to room temperature after heat curing treatment; turning over the neodymium-iron-boron magnet to spray again, and obtaining the neodymium-iron-boron magnet coated with anticorrosive coating after heat curing treatment.

9. The method of claim 8, wherein, The pickling treatment refers to soaking 10-30s with 3%-5% dilute nitric acid solution as pickling agent; the twice ultrasonic water washing refers to ultrasonic treatment for 50-70s in deionized water, then replacing the deionized water and ultrasonic treatment for 30-40s; the alcohol washing refers to soaking 10-20s with 95%-100% ethanol as alcohol washing agent, and then wiping dry with degreasing cotton gauze; the drying treatment refers to baking at 130-140℃ for 20-30min; the heat curing treatment refers to baking in an oven at 140-160℃ for 15-30min.

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