A flexible neodymium-iron-boron magnet, a preparation method and application thereof

Abstract

The present disclosure relates to the technical field of magnetic materials, in particular to a flexible neodymium-iron-boron magnet and a preparation method and application thereof; the flexible neodymium-iron-boron magnet comprises the following components in parts by weight: 80-100 parts by weight of first microparticles, 8-20 parts by weight of rubber, 0.25-2 parts by weight of antioxidant, 0.1-2 parts by weight of plasticizer, 0.1-1 parts by weight of friction aid, 0.5-2 parts by weight of reinforcing agent, 0.05-0.2 parts by weight of vulcanizing agent and 0.05-0.2 parts by weight of accelerator; wherein the first microparticles comprise modified neodymium-iron-boron magnetic powder and a polymer coating coated on the surface of the modified neodymium-iron-boron magnetic powder; and the rubber comprises ethylene-propylene-diene rubber. The present disclosure provides a flexible neodymium-iron-boron magnet with excellent mechanical properties, good interface bonding capacity and not easy to oxidize during the preparation process and a preparation method thereof.

Description

Technical Field

[0001] This disclosure relates to the field of magnetic materials technology, and in particular to a flexible neodymium iron boron magnet, its preparation method, and its application. Background Technology

[0002] Flexible neodymium iron boron (NdFeB) magnets are a new type of bonded permanent magnet material that has developed rapidly in recent decades. They maintain the high remanence, high coercivity, and high energy product of NdFeB permanent magnets by using rubber, thermoplastic elastomers, or other flexible polymers as a bonding carrier, giving the magnets properties such as flexibility, stamping, winding, and one-piece molding. Compared to traditional sintered magnets, flexible magnets can be fabricated into thinner structures without expensive secondary processing, showing great potential in fields such as micromotors, mobile phone vibration motors, hard drive spindle motors, sensors, wearable devices, smart packaging, and lightweight aerospace components.

[0003] As electronic products evolve towards miniaturization, thinning, and high performance, the market has presented unprecedented challenges to the thickness and shape of magnets: on the one hand, it requires that the magnet thickness be reduced to below 0.5 mm while still maintaining high magnetic performance; on the other hand, it requires that it not shed powder or break under repeated bending, twisting, or impact loads. However, the existing technology mainly has the following bottlenecks: (1) When the thickness is reduced, the volume fraction of magnetic powder must be increased to more than 85% to maintain the magnetic flux density, but high filling causes the rubber matrix to be unable to form a continuous network, and the toughness and tear resistance decrease sharply. (2) The surface polarity of NdFeB hard magnetic particles is large, and the compatibility with most non-polar rubbers is poor. Conventional coupling agent systems cannot take into account both high filling and strong interfacial bonding, resulting in easy shedding of magnetic powder. (3) At conventional mixing temperatures (150℃-180℃), the NdFeB phase is easily oxidized, resulting in an increase in irreversible magnetic loss and a decrease in coercivity.

[0004] Therefore, there is an urgent need to design a flexible NdFeB magnet with excellent mechanical properties, good interfacial bonding ability, and resistance to oxidation during the preparation process, as well as its preparation method. Summary of the Invention

[0005] This disclosure provides a flexible neodymium iron boron magnet, its preparation method, and its application, in order to address the shortcomings of related technologies.

[0006] According to a first aspect of the present disclosure, a flexible neodymium iron boron magnet is provided, the flexible neodymium iron boron magnet comprising the following components in parts by weight:

[0007] 80-100 parts by weight of the first microparticle, 8-20 parts by weight of rubber, 0.25-2 parts by weight of antioxidant, 0.1-2 parts by weight of plasticizer, 0.1-1 parts by weight of friction aid, 0.5-2 parts by weight of reinforcing agent, 0.05-0.2 parts by weight of vulcanizing agent and 0.05-0.2 parts by weight of accelerator;

[0008] The first microparticle comprises modified neodymium iron boron magnetic powder and a polymer coating applied to the surface of the modified neodymium iron boron magnetic powder; the rubber comprises ethylene propylene diene monomer (EPDM) rubber.

[0009] In one aspect of the embodiments of this disclosure, the rubber further comprises one or more combinations of butadiene rubber, styrene-butadiene rubber, natural rubber, chloroprene rubber, and nitrile rubber.

[0010] In one aspect of the embodiments of this disclosure, the antioxidant is selected from p-phenylenediamine antioxidants, aromatic amine antioxidants, hindered phenolic antioxidants, or thioester antioxidants.

[0011] In one aspect of this disclosure, the plasticizer is selected from one or more combinations of diisononyl cyclohexane 1,2-dicarboxylate, dioctyl adipate, dioctyl sebacate, diisononyl cyclohexane 1,2-dicarboxylate, plasticizer TP-95, plasticizer TP-90B, coumarone resin, chlorinated paraffin, and triphenyl phosphate.

[0012] In one aspect of this disclosure, the friction aid is selected from calcium carbonate, melamine, molybdenum disulfide, natural graphite, and expanded graphite.

[0013] In one aspect of this disclosure, the reinforcing agent is selected from carbon black, glass fiber, aramid fiber, polyethylene fiber, polyester fiber, cellulose nanofibers, or carbon fiber.

[0014] In one aspect of this disclosure, the vulcanizing agent is selected from sulfur, phenolic resin, p-benzoquinone dioxime, or triethylenetetramine.

[0015] In one aspect of the embodiments of this disclosure, the accelerator is selected from one or more combinations of thiazole accelerators, guanidine accelerators, sulfenamide accelerators, and thiuram accelerators.

[0016] In one aspect of this disclosure, the flexible neodymium iron boron magnet comprises the following components in parts by weight:

[0017] 90-100 parts by weight of the first microparticles, 10-15 parts by weight of rubber, 0.25-0.5 parts by weight of antioxidant, 0.1-0.2 parts by weight of plasticizer, 0.2-0.25 parts by weight of friction aid, 0.5-0.75 parts by weight of reinforcing agent, 0.05-0.1 parts by weight of vulcanizing agent, and 0.05-0.1 parts by weight of accelerator;

[0018] The rubber includes EPDM rubber, natural rubber, and butadiene rubber.

[0019] In one aspect of the embodiments of this disclosure, the modified NdFeB magnetic powder is NdFeB magnetic powder modified with a silane coupling agent; the polymer coating is a rosin-based magnetic polymer coating.

[0020] In one aspect of this disclosure, the rosin-based magnetic polymer coating further comprises dysprosium oxide.

[0021] According to a second aspect of the present disclosure, a method for preparing the aforementioned flexible neodymium iron boron magnet is provided, the method comprising the following steps:

[0022] Step 1: Provide neodymium iron boron magnetic powder; modify the neodymium iron boron magnetic powder with a silane coupling agent to obtain modified neodymium iron boron magnetic powder;

[0023] Step 2: Prepare the rosin-based magnetic polymer coating on the surface of the modified NdFeB magnetic powder to obtain the first microparticles;

[0024] Step 3: The first microparticles obtained in Step 2 are mixed with rubber and vulcanized to obtain a flexible neodymium iron boron magnet.

[0025] In one aspect of this disclosure, step 1 includes:

[0026] Step 1-1: Provide neodymium iron boron magnetic powder; disperse the neodymium iron boron magnetic powder in a first organic solvent;

[0027] Steps 1-2: Add silane coupling agent and adjust the pH to 5.0-5.5; then raise the temperature to 75℃-90℃ and react for 3-6 hours;

[0028] Steps 1-3: After centrifugation, washing and drying, the modified NdFeB magnetic powder is obtained.

[0029] In one aspect of this disclosure, step 2 includes:

[0030] Step 2-1: Under nitrogen protection, heat and melt rosin, then add modified neodymium iron boron magnetic powder, ferric chloride and dysprosium chloride; then add unsaturated acid and heat to react at 125℃-155℃ for 2-5 hours.

[0031] Step 2-2: Lower the temperature to 70℃-80℃, remove the nitrogen protection, add 2-carboxyethyl acrylate and hydroxyethyl methacrylate, and continue the reaction for 2-6 hours;

[0032] Steps 2-3: The modified NdFeB magnetic powder after the reaction is separated by an external magnetic field, and the first microparticle is obtained after washing.

[0033] In one aspect of the embodiments of this disclosure, the rosin is selected from any one of resin rosin, wood rosin, and oil rosin, preferably resin rosin, which is selected from Masson rosin, wetland rosin, Simao rosin, or South Asian rosin.

[0034] In one aspect of the embodiments of this disclosure, the unsaturated acid is selected from fumaric acid, acrylic acid, maleic acid, maleic anhydride, itaconic acid, or citraconic acid.

[0035] In one aspect of this disclosure, step 3 includes:

[0036] Step 3-1: Rubber and the first microparticles are placed in a twin-screw mixer for extrusion, drying, and granulation; the product of step 3-1 is obtained; wherein, an electromagnetic field of 2.0-6.0T is applied outside the twin-screw mixer;

[0037] Step 3-2: The product obtained in Step 3-1 is subjected to hot-press vulcanization to obtain the flexible NdFeB magnet.

[0038] In one aspect of this disclosure, step 3 includes:

[0039] Step 3-1: Add rubber to a twin-screw mixer, then add the first microparticle, reinforcing agent, antioxidant, plasticizer, and friction aid in sequence, and perform extrusion, drying, and granulation; to obtain the product of Step 3-1; wherein, an electromagnetic field of 2.0-6.0T is applied to the twin-screw mixer; the blending extrusion temperature of the twin-screw mixer is: Zone 1 130℃-140℃, Zone 2 140℃-150℃, Zone 3 150℃-160℃, Zone 4 160℃-170℃, Zone 5 170℃-180℃, the die head temperature is 130℃-160℃, and the screw speed is 180-220r / min;

[0040] Step 3-2: Mix the product obtained in step 3-1 with a vulcanizing agent and an accelerator, and then perform hot-press vulcanization to obtain the flexible NdFeB magnet; wherein the hot-press vulcanization temperature is 130℃-160℃, the pressure is selected from 0.8-1.5MPa, and the vulcanization time is selected from 20-25min.

[0041] In one aspect of this disclosure, the first organic solution is water and any one of ethanol, methanol, n-butanol or isopropanol.

[0042] In one aspect of the embodiments of this disclosure, in the preparation method, the rubber comprises ethylene propylene diene monomer (EPDM) rubber, and also comprises one or more combinations of butadiene rubber, styrene-butadiene rubber, natural rubber, chloroprene rubber, and nitrile rubber; preferably, it is a combination of EPDM rubber, natural rubber, and butadiene rubber.

[0043] In one aspect of the embodiments of this disclosure, in the preparation method, the antioxidant is selected from p-phenylenediamine antioxidants, aromatic amine antioxidants, hindered phenolic antioxidants, or thioester antioxidants; preferably N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-disec-octyl-p-phenylenediamine, N-phenyl-α-naphthylamine, or N-phenyl-β-naphthylamine. N,N'-Diphenyl-p-phenylenediamine, 2,6-di-tert-butyl-4-methylphenol, 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, distearate thiodipropionate, dilaurate thiodipropionate, 2,2'-thiobis(4-methyl-6-tert-butylphenol).

[0044] In one aspect of the embodiments of this disclosure, in the preparation method, the plasticizer is selected from one or more combinations of diisononyl cyclohexane 1,2-dicarboxylate, dioctyl adipate, dioctyl sebacate, diisononyl cyclohexane 1,2-dicarboxylate, plasticizer TP-95, plasticizer TP-90B, coumarone resin, chlorinated paraffin, and triphenyl phosphate; preferably dioctyl adipate, plasticizer TP-95, or plasticizer TP-90B.

[0045] In one aspect of the present disclosure, in the preparation method, the friction aid is selected from calcium carbonate, melamine, molybdenum disulfide, natural graphite, and expanded graphite; preferably calcium carbonate or natural graphite.

[0046] In one aspect of the present disclosure, in the preparation method, the reinforcing agent is selected from carbon black, glass fiber, aramid fiber, polyethylene fiber, polyester fiber, cellulose nanofibers or carbon fiber; preferably carbon black, aramid fiber or polyester fiber.

[0047] In one aspect of the embodiments of this disclosure, in the preparation method, the vulcanizing agent is selected from sulfur, phenolic resin, p-benzoquinone dioxime or triethylenetetramine; preferably sulfur.

[0048] In one aspect of the embodiments of this disclosure, in the preparation method, the accelerator is selected from one or more combinations of thiazole accelerators, guanidine accelerators, sulfenamide accelerators, and thiuram accelerators; preferably N-tert-butyl-2-benzothiazolium sulfenamide, 2,2'-dibenzothiazolium disulfide, N-tert-butyl-bis(2-benzothiazolium)sulfenimide, N-cyclohexyl-2-benzothiazolium sulfenamide, N-cyclohexyl-2-benzothiazolium sulfenamide, or diphenylguanidine.

[0049] According to a third aspect of the present disclosure, the aforementioned flexible NdFeB magnet and / or the flexible NdFeB magnet prepared according to the aforementioned method are provided for application in the fields of 3C products, automobiles, drones, and aerospace products.

[0050] The technical solutions provided by the embodiments of this disclosure may include the following beneficial effects:

[0051] To address the problem that the high filler content of flexible NdFeB magnets prevents the rubber matrix from forming a continuous network, resulting in a sharp decline in toughness and tear resistance, this disclosure presents a rosin-based magnetic polymer coating on the surface of the flexible NdFeB magnet. The rosin-based magnetic polymer can soften synchronously with the rubber, enabling extrusion molding at lower temperatures to avoid thermal damage to the magnetic phase caused by high temperatures, and better retaining the orientation ability of the pulsed magnetic field. Furthermore, the rosin coating has good compatibility with the rubber matrix, which can significantly improve the mechanical properties of the flexible NdFeB magnet.

[0052] To address the problem that NdFeB phases are easily oxidized at conventional mixing temperatures, leading to increased irreversible magnetic loss and decreased coercivity, the rosin-based magnetic polymer coating prepared in this disclosure forms a dense, hydrophobic, and low-permeability glassy film on the surface of the magnetic powder, which can significantly reduce oxidation-induced demagnetization.

[0053] To address the issue that NdFeB hard magnetic particles have high polarity on their surface and poor compatibility with most non-polar rubbers, the rosin coating prepared in this disclosure has good compatibility with the rubber matrix. Furthermore, this disclosure uses a silane coupling agent to modify the surface of the NdFeB magnetic powder, thereby enabling it to have good compatibility with the rosin coating.

[0054] This disclosure also introduces Dy³⁺ into the rosin coating, which can achieve grain boundary diffusion during subsequent heat treatment, thereby improving coercivity.

[0055] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0057] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0058] In this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0059] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0060] Unless otherwise stated, the terms used in this disclosure have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this disclosure can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this disclosure).

[0061] The term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0062] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0063] In this disclosure, the neodymium iron boron magnetic powder used can be either homogeneous or heterogeneous neodymium iron boron magnetic powder; this disclosure is not limited thereto; homogeneous neodymium iron boron magnetic powder is used in the embodiments of this disclosure.

[0064] The present disclosure is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure.

[0065] Examples and comparative examples:

[0066] Example 1:

[0067] Example 1 includes the following steps:

[0068] 1. Preparation of modified NdFeB magnetic powder:

[0069] Weigh 93 parts by weight of neodymium iron boron magnetic powder (D50 value approximately 30 μm), mix 180 parts by weight of isopropanol and 70 parts by weight of water, add the neodymium iron boron magnetic powder to the mixture, start mechanical stirring, then add 30 parts by weight of silane coupling agent KH-550, add glacial acetic acid dropwise, and adjust the pH to 5.2; then raise the temperature to 80℃ and react for 5 hours; after centrifugation (2000 rpm, 4 min), washing (washing once with ethanol, then once with deionized water), and drying (drying at 60℃ to constant weight), the modified neodymium iron boron magnetic powder of Example 1 is obtained.

[0070] 2. Preparation of the first microparticle:

[0071] Under nitrogen protection, 85 parts by weight of rosin were heated and melted, and then the modified NdFeB magnetic powder prepared above, 15 parts by weight of ferric chloride and 2 parts by weight of dysprosium chloride were added; then 15 parts by weight of fumaric acid were added, and the mixture was heated to react at 135°C for 4 hours; the temperature was lowered to 80°C, the nitrogen protection was removed, and 10 parts by weight of 2-carboxyethyl acrylate and 12 parts by weight of hydroxyethyl methacrylate were added, and the reaction was continued for 3 hours; then the modified NdFeB magnetic powder after reaction was separated by an external magnetic field, and after washing, the first microparticle of Example 1 (weighed as 99 parts by weight) was obtained.

[0072] 3. Preparation of flexible NdFeB magnets:

[0073] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, the first microparticle, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [temperature missing]. The temperatures were as follows: Zone 1: 130℃-140℃; Zone 2: 140℃-150℃; Zone 3: 150℃-160℃; Zone 4: 160℃-170℃; Zone 5: 170℃-180℃; Die head temperature: 130℃-160℃; Screw speed: 200 r / min. The product was then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and subjected to hot-press vulcanization at 150℃, 1.2 MPa, and 25 min for 25 min. The flexible NdFeB magnet of Example 1 was obtained.

[0074] Example 2:

[0075] Example 2 includes the following steps:

[0076] 1. Preparation of modified NdFeB magnetic powder:

[0077] Weigh 93 parts by weight of neodymium iron boron magnetic powder (D50 value approximately 30 μm), mix 180 parts by weight of isopropanol and 70 parts by weight of water, add the neodymium iron boron magnetic powder to the mixture, start mechanical stirring, then add 30 parts by weight of silane coupling agent KH-560, add glacial acetic acid dropwise to adjust the pH to 5.2; then raise the temperature to 80℃ and react for 5 hours; after centrifugation (2000 rpm, 4 min), washing (washing once with ethanol, then once with deionized water), and drying (drying at 60℃ to constant weight), the modified neodymium iron boron magnetic powder of Example 2 is obtained.

[0078] 2. Preparation of the first microparticle:

[0079] Under nitrogen protection, 85 parts by weight of rosin were heated and melted, and then the modified NdFeB magnetic powder prepared above, 15 parts by weight of ferric chloride and 2 parts by weight of dysprosium chloride were added to it; then 15 parts by weight of fumaric acid were added, and the mixture was heated to react at 135°C for 4 hours; the temperature was lowered to 80°C, the nitrogen protection was removed, and 10 parts by weight of 2-carboxyethyl acrylate and 12 parts by weight of hydroxyethyl methacrylate were added, and the reaction was continued for 3 hours; then the modified NdFeB magnetic powder after reaction was separated by an external magnetic field, and after washing, the first microparticle of Example 2 was obtained.

[0080] 3. Preparation of flexible NdFeB magnets:

[0081] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, the first microparticle, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [temperature missing]. The temperatures were as follows: Zone 1: 130℃-140℃; Zone 2: 140℃-150℃; Zone 3: 150℃-160℃; Zone 4: 160℃-170℃; Zone 5: 170℃-180℃; Die head temperature: 130℃-160℃; Screw speed: 200 r / min. The product was then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and subjected to hot-press vulcanization at 150℃, 1.2 MPa, and 25 min for 25 min. This yielded the flexible NdFeB magnet of Example 2.

[0082] The difference between Example 2 and Example 1 is that Example 2 uses an equal mass of silane coupling agent KH560 instead of KH550 used in Example 1.

[0083] Example 3:

[0084] The steps in Example 3 are the same as those in Example 1, except that an equal mass of silane coupling agent KH792 is used instead of KH550 used in Example 1.

[0085] Example 4:

[0086] Example 4 includes the following steps:

[0087] 1. Preparation of modified NdFeB magnetic powder:

[0088] Weigh 93 parts by weight of neodymium iron boron magnetic powder (D50 value approximately 30 μm), mix 180 parts by weight of isopropanol and 70 parts by weight of water, add the neodymium iron boron magnetic powder to the mixture, start mechanical stirring, then add 30 parts by weight of silane coupling agent KH-550, add glacial acetic acid dropwise, and adjust the pH to 5.2; then raise the temperature to 80°C and react for 5 hours; after centrifugation (2000 rpm, 4 min), washing (washing once with ethanol, then once with deionized water), and drying (drying at 60°C to constant weight), the modified neodymium iron boron magnetic powder of Example 4 is obtained.

[0089] 2. Preparation of the first microparticle:

[0090] Under nitrogen protection, 85 parts by weight of rosin were heated and melted, and then the modified NdFeB magnetic powder prepared above, 15 parts by weight of ferric chloride and 2 parts by weight of dysprosium chloride were added; then 15 parts by weight of itaconic acid were added, and the mixture was heated to react at 135°C for 4 hours; the temperature was lowered to 80°C, the nitrogen protection was removed, and 10 parts by weight of 2-carboxyethyl acrylate and 12 parts by weight of hydroxyethyl methacrylate were added, and the reaction was continued for 3 hours; then the modified NdFeB magnetic powder after reaction was separated by an external magnetic field, and after washing, the first microparticle of Example 4 (weighed as 98 parts by weight) was obtained.

[0091] 3. Preparation of flexible NdFeB magnets:

[0092] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, the first microparticle, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [temperature missing]. The temperatures were as follows: Zone 1: 130℃-140℃; Zone 2: 140℃-150℃; Zone 3: 150℃-160℃; Zone 4: 160℃-170℃; Zone 5: 170℃-180℃; Die head temperature: 130℃-160℃; Screw speed: 200 r / min. The product was then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and subjected to hot-press vulcanization at 150℃, 1.2 MPa, and 25 min for 25 min. This yielded the flexible NdFeB magnet of Example 4.

[0093] The difference between Example 4 and Example 1 is that Example 4 uses itaconic acid of equal mass instead of fumaric acid used in Example 1.

[0094] Example 5:

[0095] The steps in Example 5 are the same as those in Example 1, except that an equal mass of acrylic acid is used instead of the fumaric acid used in Example 1.

[0096] Example 6:

[0097] The steps in Example 6 are the same as those in Example 1, except that maleic acid of equal mass is used instead of fumaric acid used in Example 1.

[0098] Example 7:

[0099] Example 7 includes the following steps:

[0100] 1. Preparation of modified NdFeB magnetic powder:

[0101] Weigh 93 parts by weight of neodymium iron boron magnetic powder (D50 value approximately 30 μm), mix 180 parts by weight of isopropanol and 70 parts by weight of water, add the neodymium iron boron magnetic powder to the mixture, start mechanical stirring, then add 30 parts by weight of silane coupling agent KH-550, add glacial acetic acid dropwise, and adjust the pH to 5.2; then raise the temperature to 80℃ and react for 5 hours; after centrifugation (2000 rpm, 4 min), washing (washing once with ethanol, then once with deionized water), and drying (drying at 60℃ to constant weight), the modified neodymium iron boron magnetic powder of Example 1 is obtained.

[0102] 2. Preparation of the first microparticle:

[0103] Under nitrogen protection, 85 parts by weight of rosin were heated and melted, and then the modified NdFeB magnetic powder prepared above, 15 parts by weight of ferric chloride and 2 parts by weight of dysprosium chloride were added to it; then 15 parts by weight of fumaric acid were added, and the mixture was heated to react at 135°C for 4 hours; the temperature was lowered to 80°C, the nitrogen protection was removed, and the reaction continued for 3 hours; then the modified NdFeB magnetic powder after reaction was separated by an external magnetic field, and after washing, the first microparticle of Example 7 (weighed as 99 parts by weight) was obtained.

[0104] 3. Preparation of flexible NdFeB magnets:

[0105] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, the first microparticle, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [temperature missing]. The temperatures were as follows: Zone 1: 130℃-140℃; Zone 2: 140℃-150℃; Zone 3: 150℃-160℃; Zone 4: 160℃-170℃; Zone 5: 170℃-180℃; Die head temperature: 130℃-160℃; Screw speed: 200 r / min. The product was then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and subjected to hot-press vulcanization at 150℃, 1.2 MPa, and 25 min for 25 min. This yielded the flexible NdFeB magnet of Example 7.

[0106] The difference between Example 7 and Example 1 is that 2-carboxyethyl acrylate and hydroxyethyl methacrylate were not used.

[0107] Comparative Example 1:

[0108] Comparative Example 1 includes the following steps:

[0109] 1. Preparation of the first microparticle:

[0110] Under nitrogen protection, 85 parts by weight of rosin were heated and melted, and then 93 parts by weight of neodymium iron boron magnetic powder (D50 value of approximately 30 μm), 15 parts by weight of ferric chloride, and 2 parts by weight of dysprosium chloride were added; then 15 parts by weight of fumaric acid were added, and the mixture was heated to react at 135°C for 4 hours; the temperature was lowered to 80°C, the nitrogen protection was removed, and 10 parts by weight of 2-carboxyethyl acrylate and 12 parts by weight of hydroxyethyl methacrylate were added, and the reaction was continued for 3 hours; then the modified neodymium iron boron magnetic powder was separated by an external magnetic field, and after washing, the first microparticle of Comparative Example 1 (weighed as 95 parts by weight) was obtained.

[0111] 2. Preparation of flexible NdFeB magnets:

[0112] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, the first microparticle, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [temperature missing]. The temperature ranges are as follows: Zone 1: 130℃-140℃, Zone 2: 140℃-150℃, Zone 3: 150℃-160℃, Zone 4: 160℃-170℃, Zone 5: 170℃-180℃, die head temperature: 130℃-160℃, screw speed: 200 r / min. The product is then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and hot-pressed at 150℃, 1.2 MPa, and 25 min for 25 min to obtain the flexible NdFeB magnet of Comparative Example 1.

[0113] The main difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include the step of modifying neodymium iron boron magnetic powder.

[0114] Comparative Example 2:

[0115] Comparative Example 2 includes the following steps:

[0116] 1. Preparation of modified NdFeB magnetic powder:

[0117] Weigh 93 parts by weight of neodymium iron boron magnetic powder (D50 value approximately 30 μm), mix 180 parts by weight of isopropanol and 70 parts by weight of water, add the neodymium iron boron magnetic powder to the mixture, start mechanical stirring, then add 30 parts by weight of silane coupling agent KH-550, add glacial acetic acid dropwise to adjust the pH to 5.2; then raise the temperature to 80℃ and react for 5 h; after the reaction, centrifuge (2000 rpm, 4 min), wash (wash once with ethanol, then wash once with deionized water), and dry (dry at 60℃ to constant weight) to obtain the modified neodymium iron boron magnetic powder of Comparative Example 2.

[0118] 2. Preparation of flexible NdFeB magnets:

[0119] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, modified neodymium iron boron magnetic powder, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [not specified]. The temperatures were as follows: Zone 1: 130℃-140℃, Zone 2: 140℃-150℃, Zone 3: 150℃-160℃, Zone 4: 160℃-170℃, Zone 5: 170℃-180℃, Die head temperature: 130℃-160℃, Screw speed: 200 r / min. The product was then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and subjected to hot-press vulcanization at 150℃, 1.2 MPa, and 25 min for 25 min, resulting in the flexible NdFeB magnet of Comparative Example 2.

[0120] Mechanical property testing:

[0121] The products of Examples 1-6 and Comparative Examples 1-2 were cut into samples of 5*2*0.5 (cm) respectively, and their elongation at break, tensile strength and elastic modulus were tested respectively. The values ​​are shown in Table 1:

[0122] Table 1

[0123]

[0124] As can be seen, the use of silane coupling agent can improve the interfacial compatibility between NdFeB magnetic powder and rosin-based coating layer, thereby improving the overall interfacial compatibility. The mechanical properties of Example 6 are further improved compared with Examples 1-5. This is because Example 6 uses maleic acid, while the rubber systems of the examples and comparative examples use cis-butadiene rubber. During the mixing process, the residues of maleic acid can undergo free radical substitution reaction with the allyl hydrogen on the cis-butadiene rubber main chain, thereby further improving the mechanical properties. The mechanical properties of Example 7 are significantly reduced compared with Examples 1-6. This is because 2-carboxyethyl acrylate has carboxyl and acrylic acid double bonds, and hydroxyethyl methacrylate has hydroxyl and methacrylic acid double bonds. They can (1) copolymerize with the rosin-unsaturated acid skeleton under free radical initiation to form a carboxyl-hydroxyl-double bond three-dimensional cross-linked network, making the coating layer dense and improving the mechanical properties. (2) They can cross-link with the NdFeB magnetic powder modified by silane coupling agent, thereby improving the mechanical properties.

[0125] Example 8:

[0126] Example 8 includes the following steps:

[0127] 1. Preparation of modified NdFeB magnetic powder:

[0128] Weigh 93 parts by weight of neodymium iron boron magnetic powder (D50 value approximately 30 μm), mix 180 parts by weight of isopropanol and 70 parts by weight of water, add the neodymium iron boron magnetic powder to the mixture, start mechanical stirring, then add 30 parts by weight of silane coupling agent KH-550, add glacial acetic acid dropwise to adjust the pH to 5.2; then raise the temperature to 80°C and react for 5 hours; after centrifugation (2000 rpm, 4 min), washing (washing once with ethanol, then once with deionized water), and drying (drying at 60°C to constant weight), the modified neodymium iron boron magnetic powder of Example 8 is obtained.

[0129] 2. Preparation of the first microparticle:

[0130] Under nitrogen protection, 85 parts by weight of rosin were heated and melted, and then the modified NdFeB magnetic powder prepared above and 17 parts by weight of ferric chloride were added to it; then 15 parts by weight of maleic acid were added, and the mixture was heated to react at 135°C for 4 hours; the temperature was lowered to 80°C, the nitrogen protection was removed, and 10 parts by weight of 2-carboxyethyl acrylate and 12 parts by weight of hydroxyethyl methacrylate were added, and the reaction was continued for 3 hours; then the modified NdFeB magnetic powder after reaction was separated by an external magnetic field, and after washing, the first microparticle of Example 8 (weighed as 99 parts by weight) was obtained.

[0131] 3. Preparation of flexible NdFeB magnets:

[0132] Four parts by weight of EPDM rubber, three parts by weight of natural rubber, and four parts by weight of butadiene rubber were added sequentially to a twin-screw mixer. Then, the first microparticle, 0.5 parts by weight of reinforcing agent (carbon black N234), 0.35 parts by weight of antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.1 parts by weight of plasticizer (plasticizer TP-95), and 0.25 parts by weight of friction aid (calcium carbonate) were added sequentially. The mixture was then extruded, dried, and granulated to obtain the product. A 3.0T electromagnetic field was applied externally to the twin-screw mixer. The blending extrusion temperature of the twin-screw mixer was [temperature missing]. The temperatures were as follows: Zone 1: 130℃-140℃; Zone 2: 140℃-150℃; Zone 3: 150℃-160℃; Zone 4: 160℃-170℃; Zone 5: 170℃-180℃; Die head temperature: 130℃-160℃; Screw speed: 200 r / min. The product was then mixed with 0.1 parts by weight of a vulcanizing agent (sulfur) and 0.1 parts by weight of an accelerator (N-tert-butyl-2-benzothiazolyl sulfenamide), and subjected to hot-press vulcanization at 150℃, 1.2 MPa, and 25 min for 25 min. This yielded the flexible NdFeB magnet of Example 8.

[0133] The difference between Example 8 and Example 6 is that dysprosium chloride was not added in Example 8.

[0134] Magnetic property testing: The intrinsic coercivity and maximum magnetic product energy of Examples 6, 7, and 8 were tested respectively, and the results are shown in Table 2:

[0135] Table 2

[0136]

[0137] As can be seen, the introduction of dysprosium can achieve a certain degree of grain boundary diffusion on the surface of neodymium iron boron magnets, thereby improving intrinsic coercivity. Furthermore, it can be seen that the magnetic properties of Example 7 are inferior to those of Example 6. This is because 2-carboxyethyl acrylate and hydroxyethyl methacrylate can coordinate with rare earth ions (e.g., Dy³⁺) to form magnetic complexes, which is beneficial for the grain boundary diffusion of rare earth ions in subsequent processing.

[0138] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A method of making a flexible neodymium-iron-boron magnet, characterized by, The flexible Nd-Fe-B magnet comprises the following components by weight: 80-100 parts of first microparticles, 8-20 parts of rubber, 0.25-2 parts of antioxidant, 0.1-2 parts of plasticizer, 0.1-1 part of friction aid, 0.5-2 parts of reinforcing agent, 0.05-0.2 parts of vulcanizing agent, and 0.05-0.2 parts of accelerator; wherein the first microparticles comprise modified Nd-Fe-B magnetic powder and a polymer coating coated on the surface of the modified Nd-Fe-B magnetic powder; and the rubber comprises ethylene-propylene-diene rubber. The method comprises the following steps: Step 1: providing Nd-Fe-B magnetic powder; modifying the Nd-Fe-B magnetic powder with a silane coupling agent to obtain modified Nd-Fe-B magnetic powder; Step 2: under nitrogen protection, heating and melting rosin, then adding the modified Nd-Fe-B magnetic powder, iron chloride and dysprosium chloride to it; then adding unsaturated acid and heating to react at 125-155°C for 2-5h; reducing the temperature to 70-80°C, removing the nitrogen protection, adding 2-carboxyethyl acrylate and hydroxyethyl methacrylate, and continuing to react for 2-6h; separating the modified Nd-Fe-B magnetic powder after reaction by an external magnetic field, and obtaining first microparticles after washing; Step 3: mixing and vulcanizing the first microparticles prepared in step 2 with rubber to obtain a flexible Nd-Fe-B magnet.

2. The method of claim 1, wherein, Step 1 comprises: Step 1-1: providing Nd-Fe-B magnetic powder; dispersing the Nd-Fe-B magnetic powder in a first organic solvent; Step 1-2: adding a silane coupling agent and adjusting the pH value to 5.0-5.5; then increasing the temperature to 75-90°C and reacting for 3-6h; Step 1-3: centrifuging, washing and drying the product after reaction to obtain the modified Nd-Fe-B magnetic powder.

3. The method of claim 1, wherein, Step 3 comprises: Step 3-1: placing rubber and first microparticles in a twin-screw extruder for extrusion, drying and granulation; obtaining the product of step 3-1; wherein an electromagnetic field of 2.0-6.0T is applied outside the twin-screw extruder; Step 3-2: hot-pressing and vulcanizing the product obtained in step 3-1 to obtain the flexible Nd-Fe-B magnet.

4. Application of the flexible Nd-Fe-B magnet prepared by the method of any one of claims 1-3 in the fields of 3C, automobiles, drones, aerospace and aviation products.

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