A coating for protecting NdFeB magnetic materials and its preparation method and application

Abstract

The invention discloses a coating for protecting NdFeB magnetic materials, which comprises, by weight, 20-50 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-10 parts of pigment, 10-20 parts of filler, 2-3 parts of auxiliary agent, 1-2 parts of dispersant, 1-3 parts of silane coupling agent, and 30-50 parts of solvent. The coating uses a specific amount of silicone resin as the main resin and is combined with a silane coupling agent to form a bonding layer of an organic matrix-silane coupling agent-inorganic matrix on the surface of the NdFeB magnetic material, so that the coating has stronger adhesion on the surface of the NdFeB magnetic material, and improves the corrosion resistance of the NdFeB magnet; and the use process of the coating does not generate pollutants, reducing the harm to the environment and operators.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of a coating for protecting NdFeB magnetic materials, and in particular to a coating for protecting NdFeB magnetic materials, a preparation method thereof and an application thereof. Background Art

[0002] Neodymium magnet, also known as NdFeB magnet, is a tetragonal crystal formed by neodymium, iron and boron (Nd2Fe14B). In 1982, Sagawa Masato of Sumitomo Special Metals discovered neodymium magnet. The magnetic energy product (BHmax) of this magnet is greater than that of samarium cobalt magnet, and it was the material with the largest magnetic energy product in the world at that time. Later, Sumitomo Special Metals successfully developed the powder metallurgy process, and General Motors successfully developed the melt-spinning process, which can produce neodymium iron boron magnets. This magnet is the permanent magnet with the second highest magnetic property after the absolute zero holmium magnet, and it is also the most commonly used rare earth magnet. Neodymium iron boron magnets are widely used in electronic products, such as hard disks, mobile phones, headphones, and battery-powered tools.

[0003] However, NdFeB magnets are very active and can be easily corroded, leading to rust, powdering or loss of magnetism, which greatly limits the service life and application areas of NdFeB magnets. In order to avoid corrosion damage, the surface of the permanent magnet material needs to be protected during use, such as electroplating with gold, nickel, zinc, tin, and spraying epoxy resin on the surface.

[0004] At present, the corrosion resistance of NdFeB magnetic materials is mainly improved by electroplating the surface or applying conventional coatings. Although the electroplating layer isolates the contact between the NdFeB magnetic materials and the external environment to a certain extent, improving the corrosion resistance of the NdFeB magnetic materials, due to the limitations of the electroplating process, the electroplating layer has more or less pores, and the external environment can contact the NdFeB magnetic materials through these pores, thereby corroding the NdFeB magnetic materials; in addition, the electroplating process consumes a lot of energy, the process is complicated, and a large amount of wastewater is generated. The wastewater contains heavy metals, which is extremely harmful to the environment and operators. At the same time, the coatings used for the protection of NdFeB magnetic materials in the prior art cannot fully meet the requirements in terms of protection, hardness and resistance, and the thickness is relatively thick.

[0005] Therefore, how to design a coating for protecting NdFeB magnetic materials to overcome the defects in the above-mentioned prior art is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0006] One object of the present invention is to provide a coating for protecting NdFeB magnetic materials, wherein the protective layer formed by the coating has moderate thickness, strong adhesion, excellent corrosion resistance and PCT resistance, and a hardness of more than 4H.

[0007] The second object of the present invention is to provide a method for preparing the coating for protecting NdFeB magnetic materials.

[0008] The third object of the present invention is to provide the application of the above-mentioned coating for protecting NdFeB magnetic materials.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A coating for protecting NdFeB magnetic materials comprises, by weight, 20-50 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-10 parts of pigment, 10-20 parts of filler, 2-3 parts of auxiliary agent, 1-2 parts of dispersant, 1-3 parts of silane coupling agent and 30-50 parts of solvent.

[0011] Optionally, the silicone resin is a high-solid branched hydroxyl-containing polyester silicone resin with a solid content ≥90%, a Tg value >40° C., a non-volatile hydroxyl value ≥200 mg KOH / g, and a non-volatile acid value <9 mg KOH / g.

[0012] Optionally, the silane coupling agent is selected from one or more of vinyltriethoxysilane, vinyltrimethoxysilane or vinyltri(β-methoxyethoxy)silane.

[0013] Optionally, the blocked isocyanate includes blocked water-based isocyanate and / or blocked solvent-based isocyanate.

[0014] Optionally, the auxiliary agent includes a leveling agent and / or a defoaming agent.

[0015] Optionally, the dispersant is selected from one or more of sodium pyrophosphate, sodium polyacrylate or carboxylates.

[0016] Optionally, the solvent is one or more of ketone compounds, alcohol compounds and ester compounds.

[0017] A method for preparing the coating for protecting NdFeB magnetic materials as described above comprises the following steps:

[0018] Add 1-10 parts of pigment, 10-20 parts of filler, 20-30 parts of solvent, 10-25 parts of silicone resin and 1-2 parts of dispersant into a grinder and grind for 0.3-1h; then add 10-20 parts of solvent, 10-25 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-3 parts of silane coupling agent and 2-3 parts of auxiliary agent, put into a stirred reactor and continue stirring for 1-2h to obtain the product.

[0019] An application of the coating as described above for protecting NdFeB magnetic materials, the application comprising the following process: firstly, degreasing, derusting and sealing the NdFeB magnets; performing phosphating treatment; then spraying the coating as described above on the phosphated NdFeB magnets, curing the coating, and completing the surface anti-corrosion treatment of the NdFeB magnets.

[0020] Optionally, the curing temperature is 200-250° C., and the curing time is 30-50 min.

[0021] The beneficial effects of the present invention are as follows:

[0022] The invention provides a coating for protecting NdFeB magnetic materials. The coating uses a specific amount of organic silicon resin as a main resin and is combined with a silane coupling agent to form a bonding layer of an organic matrix-silane coupling agent-inorganic matrix on the surface of the NdFeB magnetic material, so that the coating has stronger adhesion on the surface of the NdFeB magnetic material. The formed coating has a thickness of 12-25um, salt spray resistance of more than 720h, PCT test of more than 500h, coating adhesion of more than 0 level, and coating hardness of more than 4H, thereby improving the corrosion resistance of the NdFeB magnetic material. Moreover, the use process of the coating does not generate pollutants, thereby reducing the harm to the environment and operators. DETAILED DESCRIPTION

[0023] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described in detail below in conjunction with specific implementation methods. Those skilled in the art should understand that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0024] In the case of illustrating and explaining the purpose of the present invention through the following embodiments, the components of the composition are explained in parts by weight as a general standard. Unless otherwise specified, for the sake of simplicity, the "parts" described in the embodiments of the present invention have the same meaning as parts by weight.

[0025] The present invention provides a coating for protecting NdFeB magnetic materials. In a preferred embodiment, the coating comprises, by weight: 20-50 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-10 parts of pigment, 10-20 parts of filler, 2-3 parts of auxiliary agent, 1-2 parts of dispersant, 1-3 parts of silane coupling agent and 30-50 parts of solvent.

[0026] The coating for protecting NdFeB magnetic materials in the present invention uses silicone resin as the main resin, and the added portion is 20-50 portions. If it is less than 20 portions, the main film-forming substance is too little, which will deteriorate the various properties of the paint film. If it is more than 50 portions, the cross-linking density will be too low, resulting in poor adhesion, recoatability, metal bonding and other properties, which cannot meet the requirements. Preferably, the Tg value of the silicone resin is greater than 40°C, the hydroxyl value of the non-volatile matter is ≥200mg KOH / g, and the acid value of the non-volatile matter is <9mg KOH / g. It is used in combination with a blocked isocyanate curing reaction, especially in combination with a silane coupling agent, to achieve high hardness and various high chemical resistance properties.

[0027] A possible implementation is that the organosilicon resin is a polyorganosiloxane, and the polyorganosiloxane in the present invention has a highly cross-linked three-dimensional network structure. A possible preparation method of polyorganosiloxane includes dissolving a mixture of methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane or methylphenyldichlorosilane in an organic solvent such as toluene, hydrolyzing at a relatively low temperature to obtain an acidic hydrolyzate, in which the acidic hydrolyzate is a mixture of cyclic, linear and cross-linked polymers, and usually contains a considerable amount of hydroxyl groups; removing the acid in the acidic hydrolyzate, and further condensing the primary polymer in air by thermal oxidation or under a catalyst to obtain. Of course, those skilled in the art may also adopt other methods to prepare polyorganosiloxane, and the present invention is not limited here.

[0028] The coating for protecting NdFeB magnetic materials provided by the present invention includes a silane coupling agent. Silane coupling agent, also known as silane treatment agent, is an organic silicon monomer having two or more different reactive groups in the molecule, which can chemically bond (couple) with organic materials and inorganic materials. The chemical formula of the silane coupling agent is: RSiX3. X represents a hydrolyzable functional group, which can undergo a coupling reaction with methoxy, ethoxy, cellosolve and inorganic materials (glass, metal, SiO2) and the like. R represents an organic functional group, which can undergo a coupling reaction with organic groups such as vinyl, ethoxy, methacrylic, amino, thiol and NdFeB magnets. In the present invention, the silane coupling agent can form a bonding layer of organic matrix-silane coupling agent-inorganic matrix between the organic and inorganic interfaces, thereby improving the adhesion of the coating on the surface of the NdFeB magnet. Preferably, the silane coupling agent of the present invention is selected from one or more of vinyltriethoxysilane, vinyltrimethoxysilane or vinyltri(β-methoxyethoxy)silane.

[0029] Blocked isocyanates can coexist stably with resins containing active groups (hydroxyl, carboxyl, amine, epoxy, etc.) for a long time. After the solvent evaporates, the -NCO group released by the blocked isocyanate after heat treatment can react with the hydroxyl, carboxyl, amino and other groups in the silicone resin and silane coupling agent to form crosslinks, which can significantly improve the adhesion, color stability and resistance to boiling and disinfection of the silicone resin. At the same time, aliphatic isocyanate crosslinkers have excellent yellowing resistance. A possible implementation is that the blocked isocyanate includes a blocked water-based isocyanate and / or a blocked solvent-based isocyanate.

[0030] In a possible implementation, the auxiliary agent includes one or more of a leveling agent and / or a defoaming agent.

[0031] Preferably, the leveling agent is selected from organic modified siloxane or fluorocarbon modified polyacrylic acid. The leveling agent can promote the coating to form a flat, smooth and uniform coating film during the curing film formation process; at the same time, it can effectively reduce the surface tension of the coating liquid, improve its leveling and uniformity; it can also improve the permeability of the coating liquid, reduce the possibility of spots and scars during spraying, increase coverage, and make the film formation uniform.

[0032] Preferably, the defoamer is selected from one or more of emulsified silicone oil, high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane. The defoamer is beneficial to inhibiting the generation of foam in the coating and preventing the formation of pores in the anticorrosive film.

[0033] The dispersant can change the surface properties of the pigment and filler in the organic coating, so that the coating is in a stable dispersed state. In a possible implementation, the dispersant is selected from one or more of sodium pyrophosphate, sodium polyacrylate or carboxylate.

[0034] Those skilled in the art can add suitable pigments to the coating according to needs, such as one or more of titanium dioxide, scarlet, phthalocyanine blue, permanent yellow, and carbon black.

[0035] In a possible implementation manner, the solvent is one or more of ketone compounds, alcohol compounds and ester compounds.

[0036] The preparation process of the protective coating for NdFeB magnetic materials in the present invention can be as follows: first, 1-10 parts of pigment, 10-20 parts of filler, 20-30 parts of solvent, 10-25 parts of silicone resin, and 1-2 parts of dispersant are added into a grinder and ground for 0.3-1h; then, 10-20 parts of solvent, 10-25 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-3 parts of silane coupling agent, and 2-3 parts of auxiliary agent are added into the ground liquid, and then the mixture is put into a stirred reactor and stirred continuously for 1-2h; after the stirring is completed, the coating for protecting NdFeB magnetic materials is obtained.

[0037] The present invention also provides the application of the above-mentioned coating for protecting NdFeB magnetic materials, including the following process: firstly, degreasing, derusting and sealing the NdFeB magnets; performing phosphating treatment; then spraying the above-mentioned coating on the phosphated NdFeB magnets, curing, and completing the surface anti-corrosion treatment of the NdFeB magnets.

[0038] In order to improve the anti-corrosion protection of the surface of the NdFeB magnet, the NdFeB magnet in the present invention is first degreased, derusted and phosphated before spraying the coating. A possible implementation is that the degreasing liquid used in the degreasing process includes solvent cleaning, acid cleaning agent cleaning, strong alkali solution cleaning, low alkaline cleaning agent cleaning, solvent emulsification cleaning, etc. The rust removal process includes two methods: chemical rust removal and mechanical rust removal. The phosphating liquid used in the phosphating process refers to a method in which an acidic solution containing dihydrogen phosphate is treated to produce a stable insoluble phosphate film layer on its surface by chemical reaction.

[0039] A possible implementation is that the curing temperature in the method for anti-corrosion treatment of the surface of the NdFeB magnet is 200-250° C. and the curing time is 30-50 min.

[0040] The technical solution of the present invention will be described below in conjunction with specific embodiments and comparative examples.

[0041] The information of the materials used in the embodiments and comparative examples is as follows:

[0042] Silicone resin: SILIKOTOP_E_901, purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0043] Blocked isocyanate: DESMODUR BL3175A, purchased from Covestro Polymers (China) Co., Ltd.

[0044] Silane coupling agent: WD055, purchased from Foshan Gaoming Tongde Chemical Co., Ltd.

[0045] Dispersants: -DISPERSANT-161, purchased from BYK-Chemie GmbH

[0046] Example

[0047] Example 1

[0048] Step 1: First, add 2 parts of carbon black pigment, 10 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 30 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin, and 1 part of dispersant into a grinder and grind for 0.5h; Step 2: Add 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin, 5 parts of blocked isocyanate, 1 part of silane coupling agent, and additives (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0049] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0050] Example 2

[0051] Step 1: First, add 2 parts of carbon black pigment, 15 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 25 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 15 parts of silicone resin, and 1.5 parts of dispersant into a grinder and grind for 0.5h; Step 2: Add 15 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin, 10 parts of blocked isocyanate, 1.5 parts of silane coupling agent, and additives (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour; Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0052] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0053] Example 3

[0054] Step 1: First, add 3 parts of carbon black pigment, 15 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 25 parts of silicone resin, and 1.5 parts of dispersant into a grinder and grind for 0.5 hours; Step 2: Add 15 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 15 parts of silicone resin, 10 parts of blocked isocyanate, 2 parts of silane coupling agent, and additives (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 2.5 parts are put into a stirred reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0055] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0056] Example 4

[0057] Step 1: First, add 0.5 parts of carbon black pigment, 9.5 parts of titanium white pigment, 20 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 25 parts of silicone resin, and 2 parts of dispersant into a grinder and grind for 0.5h; Step 2: Add 10 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 25 parts of silicone resin, 15 parts of blocked isocyanate, 3 parts of silane coupling agent, and additives (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 2 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0058] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0059] Comparative Example

[0060] Comparative Example 1

[0061] Step 1: First, add 2 parts of carbon black pigment, 10 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 30 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin, and 1 part of dispersant into a grinder and grind for 0.5h; Step 2: Add 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 5 parts of silicone resin, 5 parts of blocked isocyanate, 1 part of silane coupling agent, and auxiliary agent (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0062] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0063] Comparative Example 2

[0064] Step 1: First, add 2 parts of carbon black pigment, 10 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 30 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 5 parts of silicone resin, and 1 part of dispersant into a grinder and grind for 0.5h; Step 2: Add 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 5 parts of silicone resin, 5 parts of blocked isocyanate, 1 part of silane coupling agent, and auxiliary agent (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0065] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0066] Comparative Example 3

[0067] Step 1: First, add 2 parts of carbon black pigment, 10 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 30 parts of silicone resin, and 1 part of dispersant into a grinder and grind for 0.5h; Step 2: Add 10 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 30 parts of silicone resin, 5 parts of blocked isocyanate, 1 part of silane coupling agent, and auxiliary agent (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0068] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0069] Comparative Example 4

[0070] Step 1: First, add 2 parts of carbon black pigment, 10 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 30 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin, and 1 part of dispersant into a grinder and grind for 0.5h; Step 2: Add 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin, 5 parts of blocked isocyanate, 0 parts of silane coupling agent, and additives (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0071] The Tg of the silicone resin is 45° C., and the hydroxyl value is 200 mg KOH / g.

[0072] Comparative Example 5

[0073] Step 1: First, add 2 parts of carbon black pigment, 10 parts of filler (talcum powder: aluminum tripolyphosphate: silicon powder: precipitated barium sulfate = 4:6:1:10), 30 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin KR-242A, and 1 part of dispersant into a grinder and grind for 0.5 hours; Step 2: Add 20 parts of solvent (butyl acetate: propylene glycol methyl ether acetate: xylene: n-butanol = 17:2:2.5:0.5), 10 parts of silicone resin KR-242A, 5 parts of blocked isocyanate, 1 part of silane coupling agent, and auxiliary agent (DISPARLON 6901-20X: DISPARLON 4200-20:OTSN=1:0.5:1) 3 parts are put into a stirring reactor and stirred for 1 hour. Step 3: After the stirring is completed, a coating for protecting NdFeB magnetic materials is obtained.

[0074] The Tg of silicone resin KR-242A is 20° C. and the hydroxyl value is 200 mg KOH / g.

[0075] The coatings in Examples 1-5 and Comparative Examples 1-5 were applied to protect NdFeB magnetic materials, and the performance test results are shown in the following table:

[0076] Table 1 Properties of coatings in Examples 1-5 and Comparative Examples 1-5

[0077] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 hardness 4H-5H 4H-5H 4H-5H 4H-5H 3H 4H-5H HB 2H 2H TG value 106 106 106 106 90 106 ＜10 100 50 Heat resistance pass pass pass pass Not passed Not passed Not passed Not passed Not passed Thermal Cycle Test pass pass pass pass Not passed Not passed Not passed Not passed Not passed ATF resistance pass pass pass pass pass Not passed Not passed Not passed pass Rust resistance ≥480h ≥480h ≥480h ≥480h ＜240h ＜240h ＜240h ＜240h ＜240h Moisture resistance pass pass pass pass Not passed Not passed Not passed Not passed Not passed Metal bonding ≥12MPa ≥12MPa ≥12MPa ≥12MPa <10MPa <10MPa <10MPa <10MPa <10MPa Edge banding performance qualified qualified qualified qualified qualified qualified Failure qualified qualified PCT ≥1000h ≥1000h ≥1000h ≥1000h ＜96h ＜96h ＜96h ＜96h ＜96h Boiling water resistance pass pass pass pass Not passed Not passed Not passed Not passed Not passed Acid resistance pass pass pass pass Not passed Not passed Not passed Not passed Not passed Alkali resistance pass pass pass pass Not passed Not passed Not passed Not passed Not passed

[0078] According to the measured data in the table above, if the silicone resin is the main resin and the content is less than 20 parts, the main film-forming substance is too little, which will deteriorate the performance of the paint film. If the content is more than 50 parts, the cross-linking density will be too high, resulting in poor adhesion, recoatability, metal bonding and other properties that fail to meet the requirements. For silicone resin, if the TG value is lower than 40°C, the performance will not meet the requirements. The most important thing is to add silane coupling agent to achieve high hardness and various high chemical resistance properties.

[0079] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A coating for protecting NdFeB magnetic materials, characterized in that: In parts by weight, it includes: 20-50 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-10 parts of pigment, 10-20 parts of filler, 2-3 parts of additives, 1-2 parts of dispersant, 1-3 parts of silane coupling agent, and 30-50 parts of solvent; The silicone resin is a high-solid branched hydroxyl polyester silicone resin with a solid content of ≥90%, a Tg value of >40°C, a non-volatile hydroxyl value of ≥200 mg KOH / g, and a non-volatile acid value of <9 mg KOH / g.

2. The coating for protecting NdFeB magnetic materials according to claim 1, characterized in that: The silane coupling agent is selected from one or more of vinyl triethoxy silane, vinyl trimethoxy silane or vinyl tri (β-methoxyethoxy) silane.

3. The coating for protecting NdFeB magnetic materials according to claim 1, characterized in that: The blocked isocyanate includes blocked water-based isocyanate and / or blocked solvent-based isocyanate.

4. The coating for protecting NdFeB magnetic materials according to claim 1, characterized in that: The auxiliary agent includes a leveling agent and / or a defoaming agent.

5. The coating for protecting NdFeB magnetic materials according to claim 1, characterized in that: The dispersant is selected from one or more of sodium pyrophosphate and carboxylates.

6. The coating for protecting NdFeB magnetic materials according to claim 1, characterized in that: The solvent is one or more of ketone compounds, alcohol compounds and ester compounds.

7. A method for preparing a coating for protecting NdFeB magnetic materials as claimed in any one of claims 1 to 6, characterized in that: The steps include: Add 1-10 parts of pigment, 10-20 parts of filler, 20-30 parts of solvent, 10-25 parts of silicone resin and 1-2 parts of dispersant into a grinder and grind for 0.3-1h; then add 10-20 parts of solvent, 10-25 parts of silicone resin, 5-15 parts of blocked isocyanate, 1-3 parts of silane coupling agent and 2-3 parts of auxiliary agent, put into a stirred reactor and continue stirring for 1-2h to obtain the product.

8. An application of a coating for protecting NdFeB magnetic materials as claimed in any one of claims 1 to 6, characterized in that: The application includes the following process: firstly, degreasing, derusting and sealing the NdFeB magnetic material; performing phosphating treatment; then spraying the phosphated NdFeB magnetic material with the coating as described in any one of claims 1 to 6, and curing it to complete the surface anti-corrosion treatment of the NdFeB magnetic material.

9. The use according to claim 8, characterized in that: The curing temperature is 200-250° C., and the curing time is 30-50 minutes.