A high-protection composite coating on the surface of a bonded NdFeB magnet and its preparation method

Abstract

The present invention discloses a high-protection composite coating for the surface of a bonded NdFeB magnet and a preparation method thereof, belonging to the technical field of magnet surface protection. The composite coating is sprayed with a ZnCOF / Al-EPB coating liquid; the preparation method comprises the following steps: pre-treating the surface of the bonded NdFeB magnet to prepare a substrate; spraying the ZnCOF / Al-EPB coating liquid onto the substrate surface using an air spray process, and then curing it at 200-250°C to obtain a ZnCOF / Al-EPB composite coating. The composite coating can significantly reduce the degree of corrosion of the bonded NdFeB magnet and has little effect on the magnetic properties of the bonded NdFeB magnet.

Description

Technical Field

[0001] The invention belongs to the technical field of magnet surface protection, and particularly relates to a high-protection composite coating on the surface of a bonded NdFeB magnet and a preparation method thereof. Background Art

[0002] As a special composite material, bonded neodymium iron boron (NdFeB) magnets have advantages such as easy mass production and easy manufacturing of complex shapes. They also have advantages such as low density, stable magnetic properties, and multi-polarized magnetization. Bonded NdFeB material is a NdFeB bonded material obtained by uniformly mixing processed NdFeB quenching powder with resin, plastic or other low-melting-point metal binders and then pressing, extruding or injection molding. The magnetic phase that makes up the bonded NdFeB magnet is a relatively complete structure of Nd2Fe 14 B grains have a structure closer to a single phase, with a complete grain structure and smooth grain boundaries, and are generally not easily corroded. However, their metastable Nd-rich grain boundaries and Laves phases are extremely susceptible to corrosion in a humid environment.

[0003] Patent document CN114582618A provides a nanoparticle-doped composite coating and its preparation method. This coating forms a nano-phosphating layer on the surface of a sintered NdFeB magnet, then applies an organic resin layer to the phosphating layer via cathodic electrophoresis. After curing, the resulting composite anti-corrosion coating is obtained. However, organic resins are brittle after curing and generate significant internal stress during the curing process, potentially affecting the coating's uniformity and adhesion. Therefore, a highly protective composite coating for bonded NdFeB magnets and its preparation method are urgently needed to address these issues. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a highly protective composite coating on the surface of a bonded NdFeB magnet to solve the problem of poor corrosion resistance of existing bonded NdFeB magnets.

[0005] A second object of the present invention is to provide a method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] In the first aspect, a high-protection composite coating on the surface of a bonded NdFeB magnet is sprayed with a ZnCOF / Al-EPB coating liquid;

[0008] The composite coating has a thickness of 25-35 μm.

[0009] Furthermore, the preparation method of the ZnCOF / Al-EPB coating liquid comprises the following steps:

[0010] S1. Zn(NO3)26H2O (zinc nitrate hexahydrate) and H3BTC (pyromellitic acid) were added to anhydrous ethanol, mixed well, and reacted at 90-110°C for 8-10 hours. The mixture was naturally cooled to room temperature (25-30°C). Al powder was then added, stirred for 1-2 hours, and vacuum dried to obtain a zinc metal organic framework aluminum composite material, designated as ZnMOF / Al.

[0011] S2. The ZnMOF / Al was placed in a nitrogen atmosphere and heated to 600-800°C at a constant rate for 3-4 hours to obtain a zinc metal organic framework aluminum carbon-based composite material, designated as ZnCOF / Al.

[0012] S3. PBa (bisphenol A type benzoxazine) and a silicone-containing epoxy resin were added to dichloromethane and ultrasonically mixed to obtain a benzoxazine-blended epoxy resin, recorded as EPB. ZnCOF / Al was then added and stirred for 3-6 hours to obtain a ZnCOF / Al-EPB coating solution.

[0013] Furthermore, the molar ratio of Zn(NO3)26H2O, H3BTC and Al powder in S1 is 1:0.4-0.6:0.5-0.7.

[0014] Furthermore, the uniform heating rate in S2 is 6-8°C / min.

[0015] Furthermore, the usage ratio of PBa, silicone-containing epoxy resin and dichloromethane in S3 is 0.4-0.6 g: 1 g: 12-14 mL.

[0016] Furthermore, the amount of ZnCOF / Al in S3 is 70-80% of the total amount of PBa and the silicone-containing epoxy resin.

[0017] In a second aspect, a method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet comprises the following steps:

[0018] Step 1: pre-treating the surface of the bonded NdFeB magnet as a substrate;

[0019] Step 2: Use air spraying process to spray the ZnCOF / Al-EPB coating liquid on the surface of the substrate, and then cure it at 200-250° C. to obtain a composite coating, which is recorded as ZnCOF / Al-EPB layer.

[0020] Furthermore, the pretreatment method in step 1 is specifically to perform chamfer polishing and ultrasonic water washing on the bonded NdFeB magnet in sequence, drying at 45-65° C., and naturally cooling to room temperature.

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

[0022] 1. The high-protection composite coating on the surface of the bonded NdFeB magnet provided by the present invention is sprayed by ZnCOF / Al-EPB coating liquid. The composite coating can significantly reduce the corrosion degree of the bonded NdFeB magnet and has little effect on the magnetic properties of the bonded NdFeB magnet.

[0023] 2. The present invention utilizes a composite system of ZnCOF / Al and EPB resin. Because the zinc metal organic framework aluminum carbon-based composite material has a unique pore structure, the excellent permeability of the EPB resin further fills the carbonized pore structure, making the potential corrosion path of the ZnCOF / Al-EPB layer more tortuous. ZnCOF / Al acts as the anode protecting the cathode. The corrosive medium first reacts with the Zn and Al to form an oxide film, which is continuously consumed and regenerated during contact with the corrosive medium, slowing the corrosion process. Furthermore, the carbon skeleton structure and EPB resin enhance the surface hydrophobicity of the coating, better shielding it from moisture and effectively improving the coating's chemical corrosion resistance.

[0024] 3. A spherical zinc metal-organic framework (ZnMOF / Al) with abundant voids and a large specific surface area is prepared through hydrothermal synthesis. This ZnMOF / Al, then composited with aluminum powder, forms a carbonized skeleton structure upon sintering. The Zn and Al elements are evenly distributed throughout the carbonized skeleton, making it resistant to high temperatures and corrosion from acidic and alkaline solutions. ZnCOF / Al exhibits excellent chemical stability. Because Zn and Al have negative potentials in the electrochemical system, electron loss is likely to occur. In corrosive environments, the carbon-based ZnCOF / Al acts as a sacrificial anode and is oxidized, further chemically reacting to form a protective film that protects the substrate. During the corrosion process, ZnCOF / Al not only blocks the corrosive medium from invading the substrate but also reacts with it, resulting in its substantial consumption, slowing the corrosion process to a certain extent.

[0025] 4. Bisphenol A-type benzoxazine is introduced into the silicone-containing epoxy resin system. The oxazine ring in the bisphenol A-type benzoxazine structure undergoes a ring-opening reaction to generate hydroxyl groups. This hydroxyl group acts as a catalyst and curing initiator for the silicone-containing epoxy resin, further catalyzing the ring-opening of the silicone-containing epoxy resin, thereby forming a Si-O-Si cross-linked network structure and improving the hydrophobicity of the coating surface. The dual-polymer network structure synergistically improves the density of the coating with ZnCOF / Al, thereby significantly improving the hydrophobicity of the coating and preventing the penetration of corrosive media such as H and O. On the other hand, during the blending process of the siloxane structure in the siloxane-containing epoxy resin and bisphenol A-type benzoxazine, it may react with moisture and hydrolyze to form silanol (-Si-OH), which further reacts with the hydroxyl groups on the surface of the substrate to form a Si-O-Fe covalent bond at the interface between the coating and the substrate, resulting in strong adhesion between the substrate and the coating; in addition, the excess silanol generated by the siloxane structure during the system reaction can undergo a condensation reaction to form a Si-O-Si cross-linked network, making the composite coating and the substrate more tightly adhered. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] Figure 1 It is a schematic diagram of the process flow of preparing the ZnCOF / Al-EPB coating solution in the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] See also Figure 1 A method for preparing a ZnCOF / Al-EPB coating solution comprises the following steps:

[0030] S1. Zn(NO3)26H2O and H3BTC were added to anhydrous ethanol, mixed uniformly, and reacted at 90-110°C for 8-10 hours. The mixture was cooled to room temperature, and Al powder was added. The mixture was stirred for 1-2 hours and then dried under vacuum to obtain a zinc metal organic framework aluminum composite material, designated as ZnMOF / Al. The molar ratio of Zn(NO3)26H2O, H3BTC, and Al powder was 1:0.4-0.6:0.5-0.7.

[0031] S2. The ZnMOF / Al was placed in a nitrogen atmosphere and heated to 600-800°C at a rate of 6-8°C / min and calcined for 3-4 hours to obtain a zinc metal organic framework aluminum carbon-based composite material, designated as ZnCOF / Al.

[0032] S3. PBa and a silicone-containing epoxy resin are added to dichloromethane and ultrasonically mixed to obtain a benzoxazine-blended epoxy resin, recorded as EPB. ZnCOF / Al in an amount of 70-80% of the total amount of PBa and the silicone-containing epoxy resin is then added and stirred for 3-6 hours to obtain a ZnCOF / Al-EPB coating liquid; the amount ratio of PBa, silicone-containing epoxy resin and dichloromethane is 0.4-0.6g:1g:12-14mL.

[0033] A method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet comprises the following steps:

[0034] Step 1: chamfering and polishing the bonded NdFeB magnet using a double-end grinder and a rotary roller grinder to an R angle of 0.2, washing it with water in an ultrasonic cleaner for two stages, drying it at 45-65°C, and cooling it naturally to room temperature to obtain a substrate;

[0035] Step 2: Use air spraying process to spray the ZnCOF / Al-EPB coating liquid on the surface of the substrate, and then cure it at 200-250° C. to obtain a composite coating, recorded as ZnCOF / Al-EPB layer, with a thickness of 25-35 μm.

[0036] Example 1

[0037] See also Figure 1 A method for preparing a ZnCOF / Al-EPB coating solution comprises the following steps:

[0038] S1. 1 mol Zn(NO3)26H2O and 0.5 mol H3BTC were added to anhydrous ethanol, mixed, and reacted at 100°C for 9 h. The mixture was cooled to room temperature, and 0.6 mol Al powder was added. The mixture was stirred at 200 rpm for 1.5 h, and then vacuum dried to obtain a zinc metal organic framework aluminum composite material, designated as ZnMOF / Al.

[0039] S2. The ZnMOF / Al was placed in a nitrogen atmosphere and heated to 700°C at a rate of 7°C / min and calcined for 3.5 h to obtain a zinc metal organic framework aluminum carbon-based composite material, denoted as ZnCOF / Al.

[0040] S3. PBa and KH560 were added to dichloromethane and ultrasonically mixed to obtain a benzoxazine-blended epoxy resin, designated as EPB. ZnCOF / Al was then added in an amount equivalent to 75% of the total amount of PBa and KH560. The mixture was stirred at 150 rpm for 4 h to obtain a ZnCOF / Al-EPB coating solution. The ratio of PBa, KH560, and dichloromethane was 0.5 g:1 g:14 mL.

[0041] Example 2

[0042] See also Figure 1 A method for preparing a ZnCOF / Al-EPB coating solution comprises the following steps:

[0043] S1. 1 mol Zn(NO3)26H2O and 0.4 mol H3BTC were added to anhydrous ethanol, mixed, and reacted at 100°C for 9 h. The mixture was cooled to room temperature, and 0.5 mol Al powder was added. The mixture was stirred at 200 rpm for 1.5 h, and then vacuum dried to obtain a zinc metal organic framework aluminum composite material, designated as ZnMOF / Al.

[0044] S2. The ZnMOF / Al was placed in a nitrogen atmosphere and heated to 700°C at a rate of 7°C / min and calcined for 3.5 h to obtain a zinc metal organic framework aluminum carbon-based composite material, denoted as ZnCOF / Al.

[0045] S3. PBa and KH560 were added to dichloromethane and ultrasonically mixed to obtain a benzoxazine-blended epoxy resin, designated as EPB. ZnCOF / Al was then added in an amount equivalent to 70% of the total amount of PBa and KH560. The mixture was stirred at 150 rpm for 4 h to obtain a ZnCOF / Al-EPB coating solution. The ratio of PBa, KH560, and dichloromethane was 0.4 g:1 g:14 mL.

[0046] Example 3

[0047] See also Figure 1 A method for preparing a ZnCOF / Al-EPB coating solution comprises the following steps:

[0048] S1. 1 mol Zn(NO3)26H2O and 0.6 mol H3BTC were added to anhydrous ethanol, mixed, and reacted at 100°C for 9 h. The mixture was cooled to room temperature, and 0.7 mol Al powder was added. The mixture was stirred at 200 rpm for 1.5 h, and then vacuum dried to obtain a zinc metal organic framework aluminum composite material, designated as ZnMOF / Al.

[0049] S2. The ZnMOF / Al was placed in a nitrogen atmosphere and heated to 700°C at a rate of 7°C / min and calcined for 3.5 h to obtain a zinc metal organic framework aluminum carbon-based composite material, denoted as ZnCOF / Al.

[0050] S3. PBa and KH560 were added to dichloromethane and ultrasonically mixed to obtain a benzoxazine-blended epoxy resin, designated as EPB. ZnCOF / Al was then added in an amount equal to 80% of the total amount of PBa and KH560. The mixture was stirred at 150 rpm for 4 h to obtain a ZnCOF / Al-EPB coating solution. The ratio of PBa, KH560, and dichloromethane was 0.6 g:1 g:14 mL.

[0051] Example 4

[0052] A method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet comprises the following steps:

[0053] Step 1: chamfering and polishing the bonded NdFeB magnet using a double-end grinder and a rotary roller grinder to an R angle of 0.2, washing it with water in an ultrasonic cleaner for two stages, drying it at 50°C, and cooling it naturally to room temperature to obtain a substrate;

[0054] Step 2: The ZnCOF / Al-EPB coating liquid prepared in Example 1 was sprayed onto the substrate surface using an air spraying process, and then cured at 220° C. The resulting composite coating, referred to as the ZnCOF / Al-EPB layer, had a thickness of 30 μm.

[0055] Example 5

[0056] A method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet is different from Example 4 in that the ZnCOF / Al-EPB coating liquid prepared in Example 2 is used for substrate spraying in step 2, and the remaining steps and parameters remain the same.

[0057] Example 6

[0058] A method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet is different from Example 4 in that in step 2, the ZnCOF / Al-EPB coating liquid prepared in Example 3 is used for substrate spraying, and the remaining steps and parameters remain the same.

[0059] Comparative Example 1

[0060] A method for preparing a ZnCOF / Al-EP coating liquid comprises the following steps:

[0061] S1 and S2 are the same as in Example 1;

[0062] S3. KH560 was added to dichloromethane and ultrasonically mixed. Then, ZnCOF / Al in an amount of 75% of the total amount of KH560 was added and stirred at 150 rpm for 4 h to obtain a ZnCOF / Al-EP coating solution; the amount ratio of KH560 to dichloromethane was 1 g:14 mL.

[0063] Comparative Example 2

[0064] A method for preparing a ZnCOF / Al-EB coating solution comprises the following steps:

[0065] S1 and S2 are the same as in Example 1;

[0066] S3. PBa was added to dichloromethane and ultrasonically mixed. Then, ZnCOF / Al in an amount of 75% of the total amount of PBa was added and stirred at 150 rpm for 4 h to obtain a ZnCOF / Al-EB coating solution; the amount ratio of PBa to dichloromethane was 1 g:14 mL.

[0067] Comparative Example 3

[0068] A method for preparing a Zn / Al-EPB coating liquid comprises the following steps:

[0069] PBa and KH560 were added to dichloromethane and ultrasonically mixed to obtain a benzoxazine-blended epoxy resin, recorded as EPB. Zn powder and Al powder (the molar ratio of Zn powder to Al powder was 1:0.6) in an amount of 75% of the total amount of PBa and KH560 were then added, and stirred at 150 rpm for 4 hours to obtain a Zn / Al-EPB coating liquid; the amount ratio of PBa, KH560 and dichloromethane was 0.5 g:1 g:14 mL.

[0070] Comparative Example 4

[0071] A method for preparing a Zn / Al-EP coating liquid comprises the following steps:

[0072] KH560 was added to dichloromethane and ultrasonically mixed. Zn powder and Al powder (the molar ratio of Zn powder to Al powder was 1:0.6) in an amount of 75% of the total amount of KH560 were then added. The mixture was stirred at 150 rpm for 4 h to obtain a Zn / Al-EP coating liquid. The dosage ratio of KH560 to dichloromethane was 1 g:14 mL.

[0073] Comparative Example 5

[0074] A method for preparing a protective composite coating on the surface of a bonded NdFeB magnet is different from that of Example 4 in that the ZnCOF / Al-EP coating liquid prepared in Comparative Example 1 is used to spray the substrate in step 2, and the remaining steps and parameters remain the same.

[0075] Comparative Example 6

[0076] A method for preparing a protective composite coating on the surface of a bonded NdFeB magnet is different from that of Example 4 in that the ZnCOF / Al-EB coating liquid prepared in Comparative Example 2 is used to spray the substrate in step 2, and the remaining steps and parameters remain the same.

[0077] Comparative Example 7

[0078] A method for preparing a protective composite coating on the surface of a bonded NdFeB magnet is different from that of Example 4 in that the Zn / Al-EPB coating liquid prepared in Comparative Example 3 is used to spray the substrate in step 2, and the remaining steps and parameters remain the same.

[0079] Comparative Example 8

[0080] A method for preparing a protective composite coating on the surface of a bonded NdFeB magnet is different from that of Example 4 in that the Zn / Al-EP coating liquid prepared in Comparative Example 4 is used to spray the substrate in step 2, and the remaining steps and parameters remain the same.

[0081] The performance of the composite coatings prepared on the surfaces of the bonded NdFeB magnets in Examples 4 to 6 and Comparative Examples 5 to 8 was tested:

[0082] (1) Neutral Salt Spray Test (NSS): Conducted in a continuous spray test. Test conditions are: spray chamber temperature 35°C ± 2°C, test solvent 5% ± 1% NaCl solution (mass fraction), saturated pressure barrel temperature 48°C, atomizing compressed air 98kPa, salt spray deposition 1.0-2.0 / 80cm 2 h. The pH of the collected salt spray solution should be between 6.5 and 7.2. The sample should be suspended. The placement angle will affect the test results. The sample surface should be tilted at a 20°±5° angle in the salt spray chamber. Observe the corrosion state of the test sample at regular intervals throughout the test. The test period ends when the first visible corrosion product appears on the test sample. This time is the neutral salt spray resistance time for the sample.

[0083] (2) Self-corrosion potential (E corr ) Test: Electrochemical experiments were performed using a standard three-electrode system. The sample to be tested served as the working electrode, the Pt electrode served as the counter electrode, the saturated calomel electrode served as the reference electrode, and a 3.5% NaCl solution served as the corrosive medium. The initial voltage was -1.4 V, the final voltage was 0.2 V, and the scan rate was 0.005 V·s. -1 According to the potential value and current density value, the potential corresponding to the intersection of the cathode curve and the anodic curve in the potentiodynamic polarization curve is the self-corrosion potential.

[0084] (3) Static contact angle test: The test is performed using a water contact angle meter.

[0085] (IV) Coating adhesion test: Adopt ASTM D3359 Method B and GB-T9286-1998 and scanning electron microscope test, and determine the adhesion level according to GB adhesion standard.

[0086] (V) Magnetic flux loss (ΔФ / %) test: The NIM-200C magnetic property tester was used to test the magnetic properties of bare bonded NdFeB magnets and surface treated magnets to compare the magnetic flux loss.

[0087] The test results are shown in Table 1.

[0088] Table 1

[0089]

[0090] The test results indicate that the metal-organic framework (MOF) structure introduced into the ZnAl coating and further composited with a bisphenol A benzoxazine-silicone-containing epoxy resin dual-polymer network structure utilizes the resin's leveling properties to improve the coating's hydrophobicity while simultaneously penetrating and filling carbonized pores, thereby effectively enhancing the coating's corrosion resistance. Furthermore, the composite layer has virtually no effect on the magnetic properties of the bonded NdFeB magnet.

[0091] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0092] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high-protection composite coating on the surface of a bonded NdFeB magnet, characterized in that: Sprayed with ZnCOF / Al-EPB coating liquid; The composite coating has a thickness of 25-35 μm; The preparation method of the ZnCOF / Al-EPB coating liquid comprises the following steps: S1. Zn(NO3)26H2O and H3BTC were added to anhydrous ethanol, mixed well, and reacted at 90-110°C for 8-10 hours. The mixture was cooled to room temperature, and Al powder was added. The mixture was stirred for 1-2 hours and then dried under vacuum to obtain ZnMOF / Al. S2. Place ZnMOF / Al in a nitrogen atmosphere, uniformly heat to 600-800°C, and calcine for 3-4 hours to obtain ZnCOF / Al; S3. Add bisphenol A-type benzoxazine and KH560 to dichloromethane, mix them evenly by ultrasonication to obtain EPB, then add ZnCOF / Al and stir for 3-6 hours to obtain ZnCOF / Al-EPB coating solution.

2. The high-protection composite coating on the surface of a bonded NdFeB magnet according to claim 1, characterized in that: The molar ratio of Zn(NO3)26H2O, H3BTC and Al powder in S1 is 1:0.4-0.6:0.5-0.

7.

3. The high-protection composite coating on the surface of a bonded NdFeB magnet according to claim 1, characterized in that: The uniform heating rate in S2 is 6-8°C / min.

4. The high-protection composite coating on the surface of a bonded NdFeB magnet according to claim 1, characterized in that: The usage ratio of bisphenol A benzoxazine, KH560 and dichloromethane in S3 is 0.4-0.6 g: 1 g: 12-14 mL.

5. The high-protection composite coating on the surface of a bonded NdFeB magnet according to claim 1, characterized in that: The amount of ZnCOF / Al in S3 is 70-80% of the total amount of bisphenol A benzoxazine and KH560.

6. A method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet as claimed in claim 1, characterized in that: The following steps are involved: Step 1: pre-treating the surface of the bonded NdFeB magnet as a substrate; Step 2: spray the ZnCOF / Al-EPB coating liquid onto the surface of the substrate using an air spraying process, and then cure it at 200-250° C. to obtain a ZnCOF / Al-EPB composite coating.

7. The method for preparing a high-protection composite coating on the surface of a bonded NdFeB magnet according to claim 6, characterized in that: The pretreatment method in step 1 is specifically to perform chamfer polishing, ultrasonic water washing, drying at 45-65° C., and naturally cooling to room temperature on the bonded NdFeB magnet.

Images