A single-component water-based NdFeB magnet anticorrosion coating and preparation method thereof

Abstract

The present invention provides a single-component water-based NdFeB magnet anticorrosion coating, wherein the raw material formula comprises, by weight, 200-400 parts of water-based epoxy resin, 200-400 parts of water-based silica sol, 50-100 parts of amino resin, 10-20 parts of imidazole latent curing agent, and 100-200 parts of water-based color paste. The present invention combines the advantages of imidazole latent curing agent and amino resin, can reduce the usage of imidazole latent curing agent, and at the same time increase the crosslinking density of epoxy coating, improve the density of epoxy coating, and enhance the HAST (highly accelerated temperature and humidity stress) resistance and corrosion resistance of epoxy resin.

Description

Technical Field

[0001] The invention relates to the technical field of magnet anticorrosion, and in particular to a single-component water-based NdFeB magnet anticorrosion coating and a preparation method thereof. Background Art

[0002] NdFeB magnets have extremely high magnetic energy product and coercive force, and have been widely used in modern industry. They have become an indispensable key core material in the fields of electronic information, new energy vehicles, wind power generation, and medical care. NdFeB magnets contain active metal neodymium elements and the corrosion potential difference between multiple phases in the alloy is large, so they are very easy to corrode and peel off in warm and humid air environments.

[0003] Improving the corrosion resistance of NdFeB magnetic materials and improving their surface protection technology have become the key to breaking through the engineering application of rare earth permanent magnet materials. Plating coatings on the surface of magnets for protection has become the mainstream application technology for the corrosion protection of NdFeB magnets. Electroplating metal and alloy coatings have the problem of heavy metal ion pollution. With the continuous strengthening of environmental protection constraints, electroplating technology has also been greatly restricted. In recent years, a few companies have begun to pay attention to the application of EVERLUBE coatings and "spray black epoxy" technology in the corrosion protection of high-end NdFeB magnets, but these two have toxic VOC emissions, which also limits their use. Therefore, for the corrosion protection application of NdFeB magnets, the application of water-based anti-corrosion coatings has become a trend, but the coating properties and coating performance of water-based anti-corrosion coatings are still research issues that need to be solved urgently.

[0004] Water-based epoxy resin is a resin with excellent performance, excellent dielectric properties, mechanical properties, bonding properties and corrosion resistance, small curing shrinkage and thermal expansion coefficient. The resin uses water as solvent and contains no or very little organic small molecule solvents, which effectively reduces the impact on the environment and the probability of occupational diseases.

[0005] At present, most waterborne epoxy coatings are two-component room temperature curing types, in which the curing agent used is generally an active curing agent, which has a short construction time and is not suitable for the continuous construction requirements of automatic spraying of NdFeB magnets. Therefore, single-component waterborne epoxy coatings have attracted attention in the field of NdFeB magnet coatings. The key to the development of single-component waterborne epoxy coatings lies in the curing agent, which is mostly an amino resin curing agent or a latent curing agent. For example, a patent application with publication number CN119019911A discloses a water-based anti-corrosion coating for permanent magnet substrates such as cerium iron boron and neodymium iron boron. The coating comprises the following components in percentage by mass: 25-50% water-based epoxy resin, 2-15% water-based phenolic resin, 3-10% methyl etherified amino resin, 1-5% zinc strontium phosphate, 3-10% film-forming aid, 0.1-1% environmentally friendly metal catalyst, 0.5-3% adhesion promoter, 0.1-2% pH adjuster, 0.1-2% dispersant, 5-10% pigment, 0.1-0.5% defoamer, 1-3% matting powder, and water; wherein the methyl etherified amino resin is used as a curing agent.

[0006] The coating with amino resin as curing agent has good coating performance. The formed coating has a smooth appearance and excellent corrosion resistance, but it is not resistant to boiling water and HAST (highly accelerated temperature and humidity stress) tests, which are the key performance indicators of NdFeB magnet coatings.

[0007] The epoxy resin / imidazole system can obtain a cured product with high crosslinking degree and high corrosion resistance, and can withstand HAST (Highly Accelerated Temperature and Humidity Stress) test. For example, the patent application with publication number CN113881294A discloses a coating, a NdFeB magnet, and its preparation method and application, wherein the coating contains a resin and a curing agent, wherein the resin is selected from at least one of a water-based thermoplastic resin, a water-based thermosetting resin or a hot melt filling resin, and the water-based thermosetting resin is selected from at least one of a water-based epoxy resin and hydroxy acrylic acid; the curing agent is selected from at least one of imidazole, an epoxy resin adduct of imidazole or an epoxy resin adduct of polyamine, preferably 2-methylimidazole.

[0008] The application period of epoxy resin / imidazole system is very short, and it is generally necessary to chemically or physically modify it to seal the activity and improve the storage stability at room temperature. In recent years, there have been endless studies on chemical modification to extend the incubation period of imidazole curing agents, but the amount of such curing agents added needs to be well controlled. Too much will lead to suspended structures, thereby reducing the overall performance of the coating. At the same time, micropores and microcracks are prone to appear in the curing process of epoxy coatings, making their corrosion resistance fail to meet the requirements, limiting their large-scale use. Summary of the invention

[0009] Based on the above technical problems existing in the prior art, the present invention provides a one-component water-based NdFeB magnet anti-corrosion coating and a preparation method thereof, which improves the applicability of the curing agent while reasonably controlling the amount of the curing agent added, thereby enhancing the HAST (highly accelerated temperature and humidity stress) resistance and corrosion resistance of the epoxy resin.

[0010] The present invention provides a single-component water-based NdFeB magnet anticorrosive coating, wherein the raw material formula comprises, by weight, 200-400 parts of water-based epoxy resin, 200-400 parts of water-based silica sol, 50-100 parts of amino resin, 10-20 parts of imidazole latent curing agent and 100-200 parts of water-based color paste.

[0011] Preferably, the raw material formula comprises, by weight: 400 parts of water-based epoxy resin, 400 parts of water-based silica sol, 50 parts of amino resin, 10 parts of imidazole latent curing agent, and 100 parts of water-based color paste.

[0012] Preferably, the waterborne epoxy resin is a bisphenol A epoxy resin with an epoxy equivalent of 500-1000 g / eq, a viscosity of 1000-10000 cP, and a solid content of 50 wt%-55 wt%, and has moderate flexibility, hardness, viscosity and crosslinking density, and has good corrosion resistance and coating performance.

[0013] Preferably, the aqueous silica sol is obtained by mixing aqueous granular silica sol, methyltriethoxysilane and acetic acid aqueous solution, wherein the mass ratio of aqueous granular silica sol, methyltriethoxysilane and acetic acid aqueous solution is 1:1:0.1, the mass percentage of acetic acid in the acetic acid aqueous solution is 10%, and the obtained aqueous silica sol contains both aqueous granular silica sol and polymer aqueous silica sol. The aqueous granular silica sol can fill the micropores in the epoxy resin coating, and the polymer aqueous silica sol can increase the crosslinking degree of the epoxy resin, thereby making the epoxy resin coating have a stronger shielding ability.

[0014] Preferably, the amino resin is at least one of CYMEL 303, CYMEL 385, CYMEL 327 and CYMEL 350. The amino resin can easily react with polymers having primary hydroxyl groups, secondary hydroxyl groups, carboxyl groups or amide groups, and cross-link with the epoxy resin through chemical reaction to form a three-dimensional network structure, thereby improving the hardness and corrosion resistance of the epoxy resin.

[0015] Preferably, the imidazole latent curing agent is a curing agent obtained by chemically grafting an imidazole curing agent with hexamethylene diisocyanate, butyl glycidyl ether or acrylonitrile to obtain latent performance. Further, the imidazole curing agent is preferably 2-ethyl-4-methylimidazole, 2-phenylimidazole or 2-methylimidazole. More preferably, the imidazole latent curing agent is 2-methylimidazole grafted with hexamethylene diisocyanate.

[0016] Imidazole latent curing agent is obtained by chemical grafting reaction using the reactivity of nitrogen atoms at positions 1 and 3 on the imidazole ring of imidazole curing agent. The groups grafted onto the imidazole ring form steric hindrance to the active points (nitrogen atoms at positions 1 and 3) on the imidazole ring, thereby sealing and reducing the reactivity of the active points. At room temperature, imidazole latent curing agent has a long application period in epoxy resin and can extend the use time of epoxy resin.

[0017] Preferably, the water-based color paste is prepared by mixing pigment, inorganic filler and deionized water in a mass ratio of 1:1:2, and then sand-milling the mixture to obtain a slurry, wherein the particle size of the slurry is controlled within 20 μm; the pigment is one of rutile, titanium yellow, black iron oxide, cobalt blue or aluminum silver powder; the inorganic filler is at least one of quartz powder, alumina and mica.

[0018] Preferably, the raw material formula also includes an auxiliary agent, and the auxiliary agent is 10 to 30 parts; the auxiliary agent is at least one of a co-solvent, a leveling agent, and a wetting agent.

[0019] Preferably, the cosolvent is at least one of dipropylene glycol methyl ether, dipropylene glycol butyl ether and dimethylethanolamine; the leveling agent is at least one of BYK333, TEGO410 and BYK381; and the wetting agent is at least one of TEGO4100, SURFYNOL420 and DOWSIL67.

[0020] The present invention also provides a method for preparing the above-mentioned single-component water-based NdFeB magnet anticorrosion coating, comprising the following steps: mixing and dispersing the components in the raw material formula evenly according to the formula amount to obtain the single-component water-based NdFeB magnet anticorrosion coating.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The epoxy group in the epoxy resin is ring-opened and polymerized by imidazole latent curing agent to cure the epoxy resin, but too much addition may cause performance degradation; amino resin can cross-link the hydroxyl functional groups of the epoxy resin, but the coating is obviously insufficient in HAST (highly accelerated temperature and humidity stress) test and does not meet the use requirements. The present invention combines the advantages of imidazole latent curing agent and amino resin, can reduce the amount of imidazole latent curing agent used, and at the same time increases the cross-linking density of the epoxy coating, improves the density of the epoxy coating, and enhances the HAST (highly accelerated temperature and humidity stress) resistance and corrosion resistance of the epoxy resin.

[0023] 2. The present invention utilizes the strong rigidity and bonding ability of silica sol to effectively improve the cracks and micropores that appear in the epoxy resin film-forming process, and improve the density, toughness, impact resistance and water resistance of the film.

[0024] 3. The present invention utilizes the property that imidazole latent curing agent does not react with epoxy resin at room temperature, solves the inconvenience of epoxy resin in storage and use, and optimizes the use process of epoxy material. DETAILED DESCRIPTION

[0025] Examples 1-5

[0026] The steps of the method for preparing the single-component water-based NdFeB magnet anticorrosion coating in Examples 1-5 are as follows:

[0027] 1. Preparation of aqueous silica sol:

[0028] Aqueous granular silica sol (50 wt %, 50 nm), methyltriethoxysilane and 10 wt % acetic acid aqueous solution were taken in a mixing barrel at a mass ratio of 1:1:0.1 and mixed evenly; then moved to a roller mixer and rolled for 7 hours to obtain aqueous silica sol.

[0029] 2. Preparation of water-based color paste:

[0030] Pigment, inorganic filler and deionized water are taken in a mass ratio of 1:1:2 and sand-milled to obtain a slurry which is a water-based color paste. The particle size of the slurry is controlled within 20 μm.

[0031] 3. Preparation of single-component water-based NdFeB magnet anti-corrosion coating:

[0032] According to the formula, bisphenol A epoxy resin (epoxy equivalent of 700-800 g / eq, viscosity of 5000-6000 cP, solid content of 52wt%-53wt%), aqueous silica sol, amino resin, 2-methylimidazole grafted with hexamethylene diisocyanate (preparation method refers to the literature: Synthesis and properties of imidazole-blocked diisocyanates [J]. Polymer International, 1999, 48 (7): 614-620.), aqueous color paste and additives were taken, stirred and dispersed for 2 hours to obtain a single-component water-based NdFeB magnet anti-corrosion coating.

[0033] The formulation amounts in Examples 1-5 are shown in Table 1 in parts by weight.

[0034] Comparative Example 1

[0035] The difference between Comparative Example 1 and Example 4 is that no aqueous silica sol is added.

[0036] Comparative Example 2

[0037] The difference between Comparative Example 2 and Example 4 is that 2-methylimidazole grafted with hexamethylene diisocyanate is not added.

[0038] Comparative Example 3

[0039] The difference between Comparative Example 3 and Example 4 is that no amino resin is added.

[0040] Table 1

[0041]

[0042]

[0043] Test Example 1

[0044] Neutral salt spray resistance test of coating.

[0045] The test method refers to the neutral salt spray (NSS) test method in the national standard GB / T 10125-2021 "Artificial atmosphere corrosion test salt spray test". The test results are shown in Table 1. The anti-corrosion coatings prepared in Examples 1-5 and Comparative Example 2 have a longer neutral salt spray resistance time and better corrosion resistance. The anti-corrosion coatings without the addition of aqueous silica sol or amino resin have poor corrosion resistance.

[0046] Test Example 2

[0047] Highly accelerated humidity and temperature stress (HAST) test of coatings.

[0048] The test method refers to the test method of high-voltage accelerated aging test in Section 7.3.3 of the national standard GB / T 40793-2021 "Sintered NdFeB Surface Coating", and detects the time when the coating begins to show corrosion phenomena such as bulging, cracking or rust under this test condition. The test results are shown in Table 1. The coatings formed by the anti-corrosion coatings prepared in Examples 1-5, Comparative Examples 1 and Comparative Examples 3 and coated on NdFeB magnets have a longer life under high temperature, high humidity and high pressure conditions, while Comparative Example 2, which does not add 2-methylimidazole grafted with hexamethylene diisocyanate, has a shorter tolerance time in the HAST test and the difference is obvious.

[0049] In summary, the anti-corrosion coating containing aqueous silica sol, imidazole latent curing agent and amino resin prepared by the method of the present invention has better HAST (highly accelerated temperature and humidity stress) resistance and corrosion resistance, and the anti-corrosion coating prepared in Example 4 has the best comprehensive performance.

Claims

1. A single-component water-based NdFeB magnet anticorrosion coating, characterized in that: The raw material formula, calculated by weight, includes: 200-400 parts of water-based epoxy resin, 200-400 parts of water-based silica sol, 50-100 parts of amino resin, 10-20 parts of imidazole latent curing agent, and 100-200 parts of water-based color paste.

2. The one-component water-based NdFeB magnet anticorrosion coating according to claim 1, characterized in that: The waterborne epoxy resin is a bisphenol A type epoxy resin with an epoxy equivalent of 500-1000 g / eq, a viscosity of 1000-10000 cP, and a solid content of 50 wt%-55 wt%.

3. The one-component water-based NdFeB magnet anticorrosion coating according to claim 1, characterized in that: The aqueous silica sol is obtained by mixing aqueous granular silica sol, methyltriethoxysilane and acetic acid aqueous solution, wherein the mass ratio of aqueous granular silica sol, methyltriethoxysilane and acetic acid aqueous solution is 1:1:0.1, and the mass percentage of acetic acid in the acetic acid aqueous solution is 10%.

4. The one-component water-based NdFeB magnet anticorrosion coating according to claim 1, characterized in that: The amino resin is at least one of CYMEL 303, CYMEL 385, CYMEL 327 and CYMEL 350.

5. The one-component water-based NdFeB magnet anticorrosion coating according to claim 1, characterized in that: The imidazole latent curing agent is a curing agent obtained by chemically grafting an imidazole curing agent with hexamethylene diisocyanate, butyl glycidyl ether or acrylonitrile to obtain latent properties.

6. The one-component water-based NdFeB magnet anticorrosion coating according to claim 1, characterized in that: The water-based color paste is prepared by mixing pigment, inorganic filler and deionized water in a mass ratio of 1:1:2, and then sand-milling to obtain a slurry, wherein the particle size of the slurry is controlled within 20 μm; the pigment is one of rutile, titanium yellow, black iron oxide, cobalt blue or aluminum silver powder; the inorganic filler is at least one of quartz powder, alumina and mica.

7. The one-component water-based NdFeB magnet anticorrosion coating according to claim 1, characterized in that: The raw material formula also includes an auxiliary agent, and the auxiliary agent is 10 to 30 parts; The auxiliary agent is at least one of a cosolvent, a leveling agent and a wetting agent.

8. The one-component water-based NdFeB magnet anticorrosion coating according to claim 7, characterized in that: The cosolvent is at least one of dipropylene glycol methyl ether, dipropylene glycol butyl ether and dimethylethanolamine; The leveling agent is at least one of BYK333, TEGO410 and BYK381; The wetting agent is at least one of TEGO4100, SURFYNOL420 and DOWSIL67.

9. The method for preparing the one-component water-based NdFeB magnet anticorrosion coating according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: mixing and dispersing the components in the raw material formula evenly according to the formula amount to obtain the single-component water-based NdFeB magnet anticorrosion coating.

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