Composition for preparing bonded magnet, bonded magnet and preparation method and regeneration method of bonded magnet

Abstract

The invention relates to a bonded magnet, and the bonded magnet comprises magnetic powder and a binder. The binder comprises a vitreous body-like polymer; the content of the magnetic powder in the bonded magnet is 96 to 98 percent by weight, and the content of the bonding agent is 0.88 to 2.17 percent by weight. The bonded magnet prepared by the method provided by the invention has a dynamic cross-linked network structure, and the exchangeable dynamic covalent bonds forming the structure inside the magnet can be subjected to a dynamic cross-linking reaction of cross-linking, unlinking and re-cross-linking under specific conditions, so that the surfaces of the magnet are mutually bonded after the magnet is crushed, thereby realizing the re-forming of the magnet; therefore, the bonded magnet provided by the invention has extremely high recycling rate, and meanwhile, the magnet after being crushed and reformed for multiple times can still keep the forming density of the original magnet and still has relatively high magnetic performance and mechanical performance.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the field of bonded magnets, and particularly relates to a composition for preparing a bonded magnet, a bonded magnet and a preparation method and a regeneration method thereof. BACKGROUND

[0002] Due to the scarcity of rare earth resources, the demand for recycling of rare earth magnets is increasingly valued. Bonded magnets prepared by using thermosetting resins as binders are widely used rare earth bonded magnets at present. For example, compression magnets prepared by using epoxy resins as binders have high magnetic powder filling ratio, high product strength, good high-temperature stability of the magnets, and simple preparation process. However, the thermosetting resins are once-formed and difficult to recycle after cross-linking and curing. Although compression magnets prepared by using thermoplastic resins as binders can be recycled and reprocessed, the thermoplastic resins have low thermal deformation temperature and poor stability during compression molding at high temperature, so they are rarely used in practice. SUMMARY

[0003] The purpose of the present application is to provide a composition for preparing a bonded magnet, a bonded magnet and a preparation method and a regeneration method thereof. The method provided by the present application can prepare a bonded magnet with excellent recyclability. The magnet can maintain high magnetic performance and mechanical performance after crushing and regeneration.

[0004] To achieve the above-mentioned purpose, the present application provides a bonded magnet, wherein the bonded magnet comprises magnetic powders and a binder; the binder comprises a glass-like polymer;

[0005] The content of the magnetic powders in the bonded magnet is 96-98 wt%, and the content of the binder is 0.89-2.17 wt%.

[0006] Optionally, the glass-like polymer is a temperature-responsive glass-like polymer; the dynamic cross-linking temperature of the glass-like polymer is 85-177℃; and the linear thermal expansion coefficient of the bonded magnet above the dynamic cross-linking temperature increases with the increase of temperature.

[0007] Preferably, the glass-like polymer is selected from one or more of an ester exchange type glass-like polymer, an ether exchange type glass-like polymer, an alkylization-anti-alkylization type glass-like polymer, an anti-carbonation type glass-like polymer, a hydroxyl-urethane bond exchange type glass-like polymer, a urethane bond-urethane bond exchange type glass-like polymer, a disulfide bond exchange type glass-like polymer, a silanol exchange type glass-like polymer, an olefin metathesis type glass-like polymer, an imine exchange type glass-like polymer, and an acylhydrazone bond exchange type glass-like polymer.

[0008] Optionally, the polymer precursor of the vitreous-like polymer is selected from one or more of thermoset resin, thermoplastic resin, thermoplastic elastomer and rubber.

[0009] Preferably, the polymer precursor is selected from one or more of polyimide, polyamide, polyester, polyether, polyformaldehyde, polycarbonate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybutylene terephthalate, polystyrene, poly(4-vinylpyridine), polylactic acid, chitosan, cellulose and its derivative compounds, polyurethane, thermoplastic polyester elastomer, acrylate copolymer, epoxy resin, phenolic resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyether ether ketone, natural rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, ternary ethylene-propylene rubber, cis-butyl rubber, silicone rubber, fluororubber, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-polystyrene copolymer and styrene-butadiene-styrene copolymer.

[0010] The magnetic powder is selected from NdFeB magnetic powder, SmFeN magnetic powder, NdFeN magnetic powder, SmCo magnetic powder, ferrite powder, AlNiCo magnetic powder, FeCo magnetic powder, FeSiAl magnetic powder and FeSi magnetic powder.

[0011] The second aspect of the present application provides a composition for preparing a bonded magnet, wherein the composition comprises magnetic powder, polymer precursor, cross-linking agent and catalyst; the catalyst can catalyze the cross-linking reaction of the cross-linking agent and the polymer precursor, and the cross-linking reaction forms a dynamic cross-linking network structure.

[0012] Optionally, the magnetic powder is selected from NdFeB magnetic powder, SmFeN magnetic powder, NdFeN magnetic powder, SmCo magnetic powder, ferrite powder, AlNiCo magnetic powder, FeCo magnetic powder, FeSiAl magnetic powder and FeSi magnetic powder; the particle size of the magnetic powder is 2-150 μm.

[0013] The polymer precursor is selected from one or more of polyimide, polyamide, polyester, polyether, polyformaldehyde, polycarbonate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybutylene terephthalate, polystyrene, poly(4-vinylpyridine), polylactic acid, chitosan, cellulose and its derivative compounds, polyurethane, thermoplastic polyester elastomer, acrylate copolymer, epoxy resin, phenolic resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyether ether ketone, natural rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, ternary ethylene-propylene rubber, cis-butyl rubber, silicone rubber, fluororubber, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-polystyrene copolymer and styrene-butadiene-styrene copolymer.

[0014] The cross-linking agent is selected from one or more of the following: a multi-functional halogenated hydrocarbon or a compound with active hydrogen; preferably, the cross-linking agent is selected from one or more of the following: a dihalogenated hydrocarbon, a polyhalogenated hydrocarbon, diethylamine, triethylamine, a polyamine and its derivative compound, 1,4-dibutanol, isopentyl glycol, pentaerythritol, glycerol, a polyol and its derivative compound, a dihydric phenol, a polyhydric phenol, a dihydric thiol, a polyhydric thiol, an amide, a diurea, a polyurea, a diisocyanate, a polyisocyanate, maleic anhydride and its derivative compound, a phthalate and its derivative compound, oxalic acid, a diacid, a polyacid and its derivative compound, polytetrahydrofuran, polyethylene glycol, polyvinyl alcohol, a macromolecular dihydric alcohol, a telechelic polyhydric alcohol polymer, a telechelic linear polymer containing a hydroxyl group, a mercapto group, an amino group, a carboxyl group, an epoxy group, a formate group or an acetate group, a star polymer and a hyperbranched polymer;

[0015] The catalyst is selected from one or more of the following: an organic zinc salt; preferably, the catalyst is selected from one or more of the following: zinc acetate, triazabicyclodecene, triphenylphosphine and stannous octoate;

[0016] The content of the magnetic powder in the composition is 96-98 wt%, the content of the polymer precursor is 0.88-2.17 wt%, the content of the cross-linking agent is 0.22-0.55 wt%, and the content of the catalyst is 0.3-0.5 wt%.

[0017] Optionally, the composition further comprises a coupling agent and a release agent;

[0018] The coupling agent is selected from one or more of the following: a siloxane coupling agent, a titanate coupling agent, an aluminate coupling agent, a phosphate coupling agent and an organic iron coupling agent;

[0019] The release agent is selected from one or more of the following: an organosilicon, an organofluorine, a natural wax, a synthetic wax, molybdenum disulfide, a fatty wax and a polyester film;

[0020] The content of the coupling agent in the composition is 0.28-0.30 wt%, and the content of the release agent is 0.30-0.50 wt%.

[0021] The third aspect of the present application provides a method for preparing a bonded magnet using the composition according to the second aspect of the present application, wherein the method comprises:

[0022] S1, mixing the magnetic powder, the polymer precursor, the cross-linking agent and the catalyst to obtain a granular mixture;

[0023] S2, performing a molding process on the granular mixture to obtain a green body, and then performing a solidification process on the green body.

[0024] Optionally, the method further comprises: adding a solvent and stirring in the mixing of step S1, and heating to remove the solvent during the stirring, to obtain the granular mixture; the heating temperature is 10-50℃ higher than the boiling point of the solvent, preferably 10-20℃ higher, and the time is 3-4h;

[0025] The solvent is selected from one or more of deionized water, methanol, ethanol, isopropanol, n-butanol, isobutanol, tert-amyl alcohol, diethyl ether, acetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl isobutyl ketone, tetrahydrofuran, chloroform, n-pentane, cyclopentane, cyclohexane, n-hexane, n-heptane, n-octane, N,N-dimethylformamide, N,N-dimethylacetamide, pyridine, benzene, toluene, xylene, isobutyl acetate, n-butyl acetate, sec-butyl acetate, ethyl acetate, isopropyl acetate, and n-propyl acetate;

[0026] Alternatively, the method further comprises: under heating conditions, feeding the magnetic powders, polymer precursors, cross-linking agents, and catalysts into an open mill for mixing and processing, to obtain the granular mixture;

[0027] The surface of the double rollers of the open mill is provided with a groove or protrusion structure.

[0028] Optionally, the method further comprises: before step S1, pre-treating the magnetic powders using a coupling agent;

[0029] In step S1, the granular mixture further comprises adding a release agent;

[0030] In step S2, the forming processing adopts compression molding or calender molding;

[0031] The pressure of the forming processing is 5-10MPa, and the temperature is 25-100℃;

[0032] The temperature of the solidification processing is 80-200℃, and the time is 2-24h.

[0033] The fourth aspect of the present application provides a bonded magnet prepared by the method of the third aspect of the present application.

[0034] The fifth aspect of the present application provides a method for regenerating a bonded magnet, wherein the method comprises: after the dynamic covalent bonds inside the bonded magnet undergo chain scission at 85-177℃, then performing a thermoreversible reaction of re-crosslinking to obtain a regenerated bonded magnet.

[0035] By the technical scheme, the polymeric system capable of forming a dynamic covalent crosslinking network is used as the binder for bonding the magnet, so that the bonded magnet provided by the application has a dynamic crosslinking network structure, the exchangeable dynamic covalent bonds formed in the magnet have a dynamic crosslinking-unlinking-relinking reaction under specific conditions, the surfaces of the magnets are bonded to each other after being broken, so that the magnets are reformed, and the regenerated bonded magnet is obtained, therefore, the bonded magnet provided by the application has a very high recycling rate, has reversible processability and is not fused, meanwhile, the magnet after being broken and reformed for multiple times still has the forming density of the original magnet and still has high magnetic performance and mechanical performance. Further, the solution blending or melt blending is used to effectively mix the high filling ratio of the magnetic powder and the binder, wherein, the solution blending is to add a solvent and remove the solvent by heating in the stirring process, so that the flowability of the granular mixture with high viscosity is effectively improved in the rapid removal process of the solvent, so that the high filling ratio of the magnetic powder and the high molecular weight binder are effectively mixed uniformly, and the melt blending is to use the open mill with the double rollers provided with the groove or protrusion structure to mix the magnetic powder and the binder at high temperature, so that the high filling ratio of the magnetic powder and the rubber or other insoluble high molecular binder are fully mixed uniformly.

[0036] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, and are used together with the following specific embodiments to explain the application, but do not constitute a limitation on the application. In the drawings:

[0038] Figure 1 The thermal deformation behavior of the bonded magnet prepared for the inventive example 1 and the bonded magnet prepared for the comparative example 1.

[0039] Figure 2 The thermal deformation behavior of the bonded magnet prepared for the inventive example 12 and the bonded magnet prepared for the comparative example 1.

[0040] Figure 3 The schematic diagram of the shape of the protrusion structure on the surface of the double rollers in the open mill used for the inventive example 12.

[0041] Figure 4 The schematic diagram of the shape of the protrusion structure on the surface of the double rollers in the open mill used for another embodiment of the application.

[0042] Figure 5 The schematic diagram of the shape of the protrusion structure on the surface of the double rollers in the open mill used for another embodiment of the application. DETAILED DESCRIPTION

[0043] The specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0044] A bonded magnet, wherein the bonded magnet comprises magnetic powders and a bonding agent; the bonding agent comprises a vitrimer material;

[0045] The content of the magnetic powders in the bonded magnet is 96-98wt%, and the content of the bonding agent is 0.88-2.17wt%.

[0046] The bonded magnet provided by the present disclosure comprises a vitrimer material, i.e. a dynamic cross-linking network structure, which enables the dynamic cross-linking reaction of the exchangeable dynamic covalent bonds in the above structure under certain conditions, so that the surfaces of the magnets are bonded to each other after being broken, thereby realizing the reshaping of the magnets and obtaining regenerated bonded magnets. Therefore, the bonded magnet provided by the present disclosure has a very high recyclability, and the magnets after being broken and reshaped for multiple times still maintain the forming density of the original magnets and have high magnetic properties and mechanical properties.

[0047] In a preferred embodiment, the density of the bonded magnet is 3.9-7.0g / cm 3 , the residual magnetism of the bonded magnet is 3100-7800Gs, the intrinsic coercive force is 2500-12000Oe, and the maximum magnetic energy product is 1.92-13.55MGOe.

[0048] In a specific embodiment, the vitrimer material is a temperature-responsive vitrimer material; the dynamic cross-linking temperature of the vitrimer material is 85-177℃; and the linear thermal expansion coefficient of the bonded magnet above the dynamic cross-linking temperature increases with the increase of temperature. In the above embodiment, when a proper stimulus is applied to the magnet, for example, the magnet is placed at a specific temperature, the dynamic covalent bonds in the temperature-responsive vitrimer material contained in the magnet will undergo dynamic exchange, i.e. the dynamic cross-linking reaction of unzipping-relinking, to realize the topological rearrangement of the cross-linking network, so that the magnet provided by the present disclosure has a very high recyclability, can be processed and reshaped at a specific temperature, and the magnet after being broken and reshaped for multiple times still has high magnetic properties and mechanical properties. In other embodiments of the present disclosure, the vitrimer material can also be selected from one or more of a light-responsive vitrimer material, a pH-responsive vitrimer material, a solvent-responsive vitrimer material, and a humidity-responsive vitrimer material.

[0049] In a specific embodiment, the glassy polymer is selected from one or more of an ester-exchanged glassy polymer, an ether-exchanged glassy polymer, an alkylated-dealkylated glassy polymer, a decarbonated glassy polymer, a hydroxyl-urethane bond-exchanged glassy polymer, an urethane bond-urethane bond-exchanged glassy polymer, a disulfide bond-exchanged glassy polymer, a silanol-exchanged glassy polymer, an olefin metathesis glassy polymer, an imine-exchanged glassy polymer, and an acylhydrazone bond-exchanged glassy polymer.

[0050] The ester exchange type vitreous polymer refers to a vitreous polymer that can be dynamically cross-linked through an ester exchange reaction at a dynamic cross-linking temperature. The meanings of other types of vitreous polymers are similar and will not be repeated here.

[0051] In a further embodiment, the reaction process of the dynamic cross-linking reaction of the transesterified glass-like polymer is as shown in formula (1):

[0052]

[0053] The reaction process of the ester exchange reaction of epoxy glass polymer is shown in formula (2):

[0054]

[0055] The reaction process of the dynamic cross-linking reaction of the ether exchange type glassy polymer is shown in formula (3):

[0056]

[0057] The reaction process of the dynamic cross-linking reaction of the alkylation-dealkylation type glassy polymer is shown in formula (4):

[0058]

[0059] The reaction process of the dynamic cross-linking reaction of the reverse-carbonated glass-like polymer is shown in formula (5):

[0060]

[0061] The reaction process of the dynamic cross-linking reaction of the hydroxyl-urethane bond exchange type glassy polymer is shown in formula (6):

[0062]

[0063] The reaction process of the dynamic crosslinking reaction of the urethane bond-urethane bond exchange type glassy polymer is shown in formula (7):

[0064]

[0065] The reaction process of the disulfide exchange type vitrimer undergoing dynamic crosslinking reaction is shown in formula (8):

[0066]

[0067] The reaction process of the silanol exchange type vitrimer undergoing dynamic crosslinking reaction is shown in formula (9):

[0068]

[0069] The reaction process of the olefin metathesis type vitrimer undergoing dynamic crosslinking reaction is shown in formula (10):

[0070]

[0071] The reaction process of the imine exchange type vitrimer undergoing dynamic crosslinking reaction is shown in formula (11):

[0072]

[0073] The reaction process of the acylhydrazone bond exchange type vitrimer undergoing dynamic crosslinking reaction is shown in formula (12):

[0074]

[0075] It can be understood that the above reaction processes are exemplary and do not limit the vitrimer.

[0076] In one specific embodiment, the polymer precursor of the vitrimer is selected from one or more of thermosetting resins, thermoplastic resins, thermoplastic elastomers and rubbers.

[0077] In further embodiments, the polymer precursor is selected from one or more of polyimide, polyamide, polyester, polyether, polyformaldehyde, polycarbonate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybutylene terephthalate, polystyrene, poly(4-vinylpyridine), polylactic acid, chitosan, cellulose and its derivatives, polyurethane, thermoplastic polyester elastomer, acrylate copolymer, epoxy resin, phenolic resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyether ether ketone, natural rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, cis-butyl rubber, silicone rubber, fluororubber, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer and styrene-butadiene-styrene copolymer. Preferably, the polymer precursor is selected from one or more of epoxy resin, phenolic resin, polymethyl methacrylate, polybutylene terephthalate, polycarbonate, polyamide, poly(4-vinylpyridine), polyurethane, thermoplastic polyester elastomer, nitrile rubber and ethylene-propylene-diene rubber. In the above embodiments, the use of the preferred polymer precursor can further enhance the mechanical properties such as tensile strength and bending strength of the prepared magnet, and can provide the magnet with more excellent processability.

[0078] In a specific embodiment, the magnetic powder is selected from NdFeB magnetic powder, SmFeN magnetic powder, NdFeN magnetic powder, SmCo magnetic powder, ferrite powder, AlNiCo magnetic powder, FeCo magnetic powder, FeSiAl magnetic powder and FeSi magnetic powder. Preferably, the magnetic powder is selected from NdFeB magnetic powder, SmFeN magnetic powder, NdFeN magnetic powder, ferrite powder and SmCo magnetic powder.

[0079] In a second aspect, the present disclosure provides a composition for preparing a bonded magnet, wherein the composition comprises magnetic powder, polymer precursor, crosslinking agent and catalyst; the catalyst can catalyze the crosslinking reaction of the crosslinking agent and the polymer precursor, and the crosslinking reaction forms a dynamic crosslinking network structure.

[0080] In the composition provided by the present disclosure, the crosslinking agent can undergo a crosslinking and curing reaction with the polymer precursor under catalytic conditions, which on one hand can form a molecular network structure to enhance the mechanical properties of the prepared magnet, and on the other hand can provide a dynamic crosslinking structure for the bonded magnet, so that the magnet can undergo a thermal reversible reaction of crosslinking-unlinking-re-crosslinking under specific conditions, thereby ensuring the magnetic properties and mechanical properties of the magnet while providing the magnet with excellent regeneration ability.

[0081] In one embodiment, the magnetic powders are selected from the group consisting of NdFeB powders, SmFeN powders, NdFeN powders, SmCo powders, ferrite powders, AlNiCo powders, FeCo powders, FeSiAl powders and FeSi powders, preferably NdFeB powders, SmFeN powders, NdFeN powders, ferrite powders and SmCo powders.

[0082] In a further embodiment, the magnetic powders have a particle size of 2-150 μm, preferably 40-70 μm. In the above embodiment, the use of magnetic powders with a preferred particle size range can further improve the compactness and maximum energy product of the bonded magnets prepared.

[0083] The polymer precursor is selected from one or more of the group consisting of polyimide, polyamide, polyester, polyether, polyformaldehyde, polycarbonate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybutylene terephthalate, polystyrene, poly(4-vinylpyridine), polylactic acid, chitosan, cellulose and its derivatives, polyurethane, thermoplastic polyester elastomer, acrylate copolymer, epoxy resin, phenolic resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyether ether ketone, natural rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, cis-butadiene rubber, silicone rubber, fluororubber, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer and styrene-butadiene-styrene copolymer. Preferably, the polymer precursor is selected from one or more of the group consisting of epoxy resin, phenolic resin, polymethyl methacrylate, polybutylene terephthalate, polycarbonate, polyamide, poly(4-vinylpyridine), polyurethane, thermoplastic polyester elastomer, nitrile rubber and ethylene-propylene-diene rubber. In the above embodiment, the use of the preferred polymer precursor can further enhance the mechanical properties such as tensile strength and bending strength of the magnets prepared, and can provide the magnets with more excellent processability.

[0084] In one embodiment, the cross-linking agent is selected from one or more of a multi-functional halogenated hydrocarbon or a compound with active hydrogen; preferably, the cross-linking agent is selected from one or more of a dihalogenated hydrocarbon, a polyhalogenated hydrocarbon, diethylamine, triethylamine, a polyamine and a derivative compound thereof, 1,4-dibutanol, isopentyl glycol, pentaerythritol, glycerol, a polyol and a derivative compound thereof, a di-phenol, a poly-phenol, a di-mercaptan, a poly-mercaptan, an amide, a di-urea, a poly-urea, a di-isocyanate, a poly-isocyanate, maleic anhydride and a derivative compound thereof, a phthalate and a derivative compound thereof, oxalic acid, a di-acid, a poly-acid and a derivative compound thereof, polytetrahydrofuran, polyethylene glycol, polyvinyl alcohol, a macro-molecular diol, a telechelic polyol polymer, a telechelic linear polymer comprising a hydroxyl, a thiol, an amino, a carboxyl, an epoxy, a formate or an acetate group, a star polymer and a hyperbranched polymer; more preferably, the cross-linking agent is selected from one or more of glycerol, polyvinyl alcohol, diethylamine, triethylamine, pentaerythritol and 1,4-dibromo-butane. In the above embodiment, the use of the preferred cross-linking agent can further increase the functional groups within the magnet, and make the dynamic cross-linking reaction more complete, thereby making the magnet have more excellent recyclability.

[0085] In one embodiment, the catalyst is selected from one or more of an organic zinc salt; preferably, the catalyst is selected from one or more of zinc acetate, triazabicyclodecene, triphenylphosphine and stannous octoate.

[0086] In one embodiment, the content of the magnetic powder in the composition is 96-98 wt%, the content of the polymer precursor is 0.88-2.17 wt%, the content of the cross-linking agent is 0.22-0.55 wt%, and the content of the catalyst is 0.3-0.5 wt%.

[0087] In one embodiment, the composition further comprises a coupling agent and a release agent. In the above embodiment, the use of the coupling agent for coating treatment on the surface of the magnetic powder can further improve the oxidation resistance of the magnetic powder, improve the compatibility between the binder and the magnetic powder, isolate the binder from the surface of the magnetic powder, and at the same time, can also improve the bonding strength between the surface of the magnetic powder and the polymer precursor. The addition of the release agent can reduce or prevent the adhesion of solid or liquid film on the surface of the magnet, prevent the adhesion of the magnetic powder, the binder and the like to the surface of the equipment, and provide lubricity of the material.

[0088] In a further embodiment, the coupling agent is selected from one or more of a siloxane coupling agent, a titanate coupling agent, an aluminate coupling agent, a phosphate coupling agent and an organic iron coupling agent, preferably one or more of a siloxane coupling agent, a titanate coupling agent, an aluminate coupling agent and a phosphate coupling agent;

[0089] The release agent is selected from one or more of organosilicon, organofluorine, natural wax, synthetic wax, metal stearate, molybdenum disulfide and fat wax; preferably one or more of silicone oil, silicone rubber, silicone ester, silicone emulsifier, natural wax, synthetic wax, zinc stearate, calcium stearate, molybdenum disulfide, montan wax, carnauba wax, palm wax, paraffin wax, Fischer-Tropsch wax and polyester film; more preferably one or more of zinc stearate, silicone oil, paraffin wax and palm wax.

[0090] The content of the coupling agent in the composition is 0.28-0.30 wt%, and the content of the release agent is 0.3-0.5 wt%.

[0091] The third aspect of the present disclosure provides a method for preparing bonded magnets using the composition of the second aspect of the present disclosure, wherein the method comprises:

[0092] S1, mixing magnetic powder, polymer precursor, crosslinking agent and catalyst to obtain a granular mixture;

[0093] S2, performing a molding process on the granular mixture to obtain a green body, and then performing a curing process on the green body.

[0094] The bonded magnet prepared by the method has a dynamic crosslinking network structure. The exchangeable dynamic covalent bonds of the above structure formed inside the magnet can undergo a dynamic crosslinking-unwinding-re-crosslinking reaction under certain conditions, so that the surfaces of the magnet are adhered to each other after being broken, thereby realizing the reforming of the magnet and obtaining a regenerated bonded magnet. Therefore, the bonded magnet provided by the present disclosure has a very high recyclability. At the same time, the magnet after being broken and reformed for multiple times still maintains the molding density of the original magnet and still has high magnetic performance and mechanical performance.

[0095] In one specific embodiment, the method further comprises: adding a solvent and stirring in the mixing of step S1, and heating to remove the solvent during the stirring to obtain the granular mixture; the heating temperature is 10-50°C higher than the boiling point of the solvent, preferably 10-20°C higher; and the time is 3-4h; and the polymer precursor is selected from non-rubber polymer precursors. In the above embodiment, by adding a solvent and heating to remove the solvent during stirring, the solvent evaporation speed is accelerated, the flowability of the granular mixture with high viscosity is effectively improved during the rapid removal of the solvent, and the magnetic powder with high filling ratio and the binder with high molecular weight can be effectively mixed uniformly.

[0096] In one embodiment, the solvent is selected from one or more of deionized water, methanol, ethanol, isopropanol, n-butanol, isobutanol, t-amyl alcohol, diethyl ether, acetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl isobutyl ketone, tetrahydrofuran, chloroform, n-pentane, cyclopentane, cyclohexane, n-hexane, n-heptane, n-octane, N,N-dimethylformamide, N,N-dimethylacetamide, pyridine, benzene, toluene, xylene, isobutyl acetate, n-butyl acetate, sec-butyl acetate, ethyl acetate, isopropyl acetate, and n-propyl acetate. Preferably, the solvent is selected from one or more of tetrahydrofuran, acetone, and N,N-dimethylformamide.

[0097] In one embodiment, the method further comprises: under heating conditions, feeding the magnetic powder, the polymer binder, the cross-linking agent, and the catalyst into an open mill for mixing and processing to obtain the granular mixture; the polymer precursor is selected from a rubber-based polymer precursor; the surface of the double rollers of the open mill is provided with a groove or protrusion structure, and the gap between the double rollers is 1.5-2.0 mm. In the above embodiment, the open mill with the double rollers provided with the groove or protrusion structure is used to mix and process the magnetic powder and the binder under heating conditions. For the rubber-based polymer binder that is difficult to dissolve, the groove and protrusion structure can effectively improve the flowability of the mixture during the mixing and processing, so that the magnetic powder with a high filler ratio and the rubber-based polymer binder that is difficult to dissolve can be fully mixed and processed uniformly. The temperature of the heating conditions refers to a temperature at which the polymer binder is in a molten state or a softened state.

[0098] In one embodiment, before step S1, the magnetic powder is pretreated with a coupling agent; and in step S1, a release agent is further added to the granular mixture. In the above embodiment, the surface of the magnetic powder is coated with the coupling agent, which can further improve the oxidation resistance of the magnetic powder, improve the compatibility between the binder and the magnetic powder, isolate the binder from the surface of the magnetic powder, and improve the bonding strength between the surface of the magnetic powder and the polymer precursor. The addition of the release agent can reduce or prevent the adhesion of solid or liquid films on the surface of the magnet, prevent the adhesion of the magnetic powder, the binder, etc. to the surface of the equipment, and provide lubricity of the material.

[0099] In one embodiment, in step S2, the forming process is compression molding or calender molding.

[0100] The pressure of the forming process is 5-10 MPa, preferably 6-8 MPa, and the temperature is 25-100°C.

[0101] The temperature of the curing process is 80-200°C, preferably 100-160°C, and the time is 2-24 h, preferably 3-4 h.

[0102] The fourth aspect of the present disclosure provides a bonded magnet prepared by the method of the third aspect of the present disclosure.

[0103] In a fifth aspect, the present application provides a method for regenerating bonded magnets, wherein the method comprises: crushing the bonded magnets, and then performing a molding process on the crushed product, the molding process being performed at a temperature above the dynamic cross-linking temperature of the glass-like polymer.

[0104] The present application is further illustrated by the following examples without thereby limiting the present application.

[0105] Example 1

[0106] The composition used in the present example for preparing bonded magnets comprises, based on the total weight of the composition: 98 wt% of magnetic powders, 0.885 wt% of polymer precursor, 0.221 wt% of cross-linking agent, 0.3 wt% of catalyst, 0.294 wt% of coupling agent, and 0.3 wt% of release agent. The magnetic powders are selected from NdFeB 15-7, the particle size of the magnetic powders is 59.6 μm, the polymer precursor is bisphenol A type epoxy resin, the cross-linking agent is pyromellitic acid, the catalyst is zinc acetate, the coupling agent is siloxane type coupling agent, and the release agent is zinc stearate.

[0107] a. mixing the magnetic powders with the coupling agent to perform coating treatment, thereby obtaining magnetic powders coated with the coupling agent on the surface;

[0108] b. mixing the prepared polymer precursor, cross-linking agent, catalyst and release agent with 200 g of solvent, and then adding the magnetic powders in step a, thereby obtaining a mixture, which is sent into a mixer to perform stirring, and in the process of stirring, the mixture is heated to 66 °C, and after the solvent is completely volatilized, a granular mixture is obtained; wherein the solvent is tetrahydrofuran, and the stirring speed is 20-30 rpm;

[0109] c. sending the granular mixture in step b into a press to perform compression molding treatment, thereby obtaining a green compact. The molding treatment is performed at a pressure of 8 MPa, and the green compact is pressed for 10 min at room temperature;

[0110] d. placing the green compact in step c in an oven at 160 °C to perform curing treatment, and the curing time is 3 h, thereby obtaining a bonded magnet.

[0111] Examples 2-11

[0112] Examples 2-11 refer to the preparation method in Example 1, and the difference from Example 1 is that the bonded magnets are prepared according to the compositions, molding temperatures and curing temperatures listed in Table 1, and the rest of the process is the same as Example 1.

[0113] Example 12

[0114] The composition for preparing bonded magnets in the embodiment includes, based on the total weight of the composition, 96 wt% of magnetic powder, 2.17 wt% of polymer precursor, 0.542 wt% of crosslinking agent, 0.5 wt of catalyst, 0.288 wt% of coupling agent, and 0.5 wt% of release agent. The magnetic powder is selected from NdFeB 16-10, the polymer precursor is polyurethane, the crosslinking agent is triethylamine, the catalyst is stannous octoate, the coupling agent is a siloxane-based coupling agent, and the release agent is palm wax.

[0115] a. mixing the magnetic powder with the coupling agent to perform coating treatment, to obtain magnetic powder coated with the coupling agent on the surface;

[0116] b. feeding the magnetic powder, the polymer precursor, the crosslinking agent, and the catalyst in step a into an open mill at 100°C to perform mixing treatment, to obtain a granular mixture; the surface of the double rollers of the open mill is provided with groove or protrusion structure;

[0117] c. feeding the granular mixture in step b into a press to perform calendering molding treatment, to obtain a press blank. The gap between the double rollers is 1.5-2.0 mm;

[0118] d. placing the press blank in step c in an oven at 120°C to perform curing treatment, and the curing time is 4 h, to obtain a bonded magnet.

[0119] Examples 13-16 and 21-22

[0120] Examples 13-16 and 21-22 refer to the preparation method in Example 1, and the difference from Example 1 is that the bonded magnets are prepared according to the composition, molding temperature, and curing temperature listed in Table 1, and the rest of the process is the same as Example 1.

[0121] Examples 17-20

[0122] Examples 17-20 refer to the preparation method in Example 12, and the difference from Example 12 is that the bonded magnets are prepared according to the composition, molding temperature, and curing temperature listed in Table 1, and the rest of the process is the same as Example 12.

[0123] Comparative Example 1

[0124] The composition for preparing bonded magnets in the comparative example includes, based on the total weight of the composition, 98 wt% of magnetic powder, 1.085 wt% of binder, 0.121 wt% of crosslinking agent, 0.294 wt% of coupling agent, and 0.5 wt% of release agent. The magnetic powder is selected from NdFeB 15-7, the binder is bisphenol A type epoxy resin, the crosslinking agent is dicyandiamide, the coupling agent is a siloxane-based coupling agent, and the release agent is zinc stearate.

[0125] a. mixing the magnetic powder with a coupling agent to perform coating treatment, to obtain magnetic powder coated with the coupling agent on the surface;

[0126] b. dissolving the binder in 200 g of tetrahydrofuran and mixing with the magnetic powder in step a to obtain a mixture, and feeding the mixture into a mixer to perform stirring to obtain a granular mixture; wherein the stirring speed is 20-30 rpm, and the stirring time is 0.5 h;

[0127] c. feeding the granular mixture in step b into a press to perform compression molding treatment to obtain a green compact. The molding treatment pressure is 0.8 MPa, and the pressure is maintained for 10 min at room temperature;

[0128] d. placing the green compact in step c in an oven at 160℃ to perform curing treatment, and the curing time is 3 h, to obtain a bonded magnet.

[0129] Test Example

[0130] The bonded magnets of Examples 1-22 are tested in the following manner:

[0131] The magnetic properties of the original bonded magnet, the bonded magnet after recycling once, and the bonded magnet after recycling twice are tested by a demagnetization curve testing instrument (device model NIM-200C);

[0132] The recycling method is crushing treatment, and except for rubber and elastomer types which need to be frozen and crushed, the rest are crushed at room temperature. The recycled granular material is obtained after crushing treatment.

[0133] The heat distortion temperature and heat distortion behavior are tested by a thermal mechanical analyzer instrument (TMA);

[0134] The test method of high humidity and high temperature reduction includes: treating the bonded magnet in a high humidity oven at a temperature of 60℃ and a humidity of 90% for 72 h, and comparing the change in magnetic moment before and after treatment;

[0135] The tensile strength is tested by a universal tensile testing machine (device model CTM2100);

[0136] The results are shown in Tables 2, 3 and 4, and the heat distortion behavior results are shown in Figure 1 and Figure 2 .

[0137] As can be seen from Figure 1 , the linear thermal expansion coefficient of the bonded magnet prepared in Example 1 increases with increasing temperature above the dynamic crosslinking temperature (150℃). The linear thermal expansion coefficient of the bonded magnet prepared in Comparative Example 1 does not change with increasing temperature.

[0138] As can be seen from Figure 2It is known that the linear thermal expansion coefficient of the bonded magnet (vitrimer rubber magnet) prepared in Example 12 increases with increasing temperature above the dynamic crosslinking temperature (85°C). The linear thermal expansion coefficient of the bonded magnet (ordinary rubber magnet) prepared in Comparative Example 1 does not change with increasing temperature.

[0139] Table 1

[0140]

[0141]

[0142] Table 2 Performance data of the original bonded magnet

[0143]

[0144]

[0145] Table 3 Performance data of the bonded magnet after recycling once

[0146]

[0147]

[0148] Table 4 Performance data of the bonded magnet after recycling twice

[0149]

[0150] As can be seen from Tables 2-4, the adhesive used in the present application is the polymerization system 5 capable of forming a dynamic covalent crosslinking network, so that the bonded magnet provided by the present application has a dynamic crosslinking network structure, the exchangeable dynamic covalent bonds in the above structure formed in the magnet can undergo a dynamic crosslinking-unlinking-relinking reaction under certain conditions, so that the surfaces of the magnet are adhered to each other after being broken, thereby realizing the reshaping of the magnet, and obtaining a regenerated bonded magnet. As can be seen from Examples 1-22, the bonded magnet provided by the present application has a very high recyclability, has reversible processability and is not fused, and the original product can be broken and reshaped to achieve 100% regeneration. After recycling once, the bonded magnet has almost the same forming density as the original bonded magnet, the maximum magnetic energy product (BH)max-1 is 95-98% of the (BH)max of the original bonded magnet, the wet heat high reduction is almost unchanged, and the tensile strength is 90-98% of that of the original bonded magnet. After recycling twice, the bonded magnet still maintains the forming density of the original magnet, the maximum magnetic energy product (BH)max-2 is 89-91% of the (BH)max of the original bonded magnet, the wet heat high reduction is almost unchanged, and the tensile strength is 89-96% of that of the original bonded magnet. Therefore, the bonded magnet prepared by the method of the present application still maintains the forming density of the original magnet after being broken and reshaped for multiple times, and still has high magnetic and mechanical properties.

[0151] As can be seen from Examples 1-11, 13-16, 21 and 22, the solution blending or melt blending method can effectively mix the high filling ratio of magnetic powder and the adhesive. In the solution blending method, the solvent is added and heated during stirring to remove the solvent, so that the flowability of the high viscosity particle mixture is effectively improved during the rapid removal of the solvent, thereby effectively mixing the high filling ratio of magnetic powder and the high molecular weight adhesive, further improving the regeneration performance of the magnet, and making the bonded magnet have a very high recyclability, so that the broken and reshaped magnet still maintains the forming density and wet heat high reduction of the original magnet, and still has high magnetic and mechanical properties.

[0152] As can be seen from Examples 12, 17-20, the melt blending method uses a double-roller open mill provided with a groove or protrusion structure to mix the magnetic powder and the adhesive at high temperature, so that the high filling ratio of magnetic powder and the high molecular adhesive such as rubber which is difficult to dissolve are fully mixed and uniform, further improving the regeneration performance of the magnet, and making the bonded magnet have a very high recyclability, so that the broken and reshaped magnet still maintains the forming density and wet heat high reduction of the original magnet, and still has high magnetic and mechanical properties.

[0153] Compared with Examples 1-22, the adhesive used in Comparative Example 1 is a common epoxy resin, so that the bonded magnet prepared thereby does not have regeneration performance, and therefore cannot be reshaped after being broken for multiple times.

[0154] The preferred embodiments of the present application are described in detail above with reference to the drawings, but the present application is not limited to the specific details of the above-described embodiments. Various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0155] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again by the present application.

[0156] In addition, various different embodiments of the present application can also be combined in any appropriate manner, as long as they do not deviate from the idea of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A bonded magnet, wherein, The bonded magnet comprises magnetic powder and a binder; the binder comprises a vitrimer; The content of the magnetic powder in the bonded magnet is 96-98 wt%, and the content of the binder is 0.88-2.17 wt%; Preferably, the bonded magnet has a density of 3.9 to 7.0 g / cm3 3 , a residual magnetism of 3100 to 7800 Gs, an intrinsic coercive force of 2500 to 12000 Oe, and a maximum magnetic energy product of 1.92 to 13.55 MGOe.

2. The bonded magnet of claim 1, wherein, The vitrimer is a temperature-responsive vitrimer; the dynamic crosslinking temperature of the vitrimer is 85-177℃; the linear thermal expansion coefficient of the bonded magnet above the dynamic crosslinking temperature increases with the increase of temperature; Preferably, the vitrimer is selected from one or more of transesterification type vitrimer, ether exchange type vitrimer, alkylization-anti-alkylization type vitrimer, anti-carbonation type vitrimer, hydroxyl-urethane bond exchange type vitrimer, urethane bond-urethane bond exchange type vitrimer, disulfide bond exchange type vitrimer, silanol exchange type vitrimer, olefin metathesis type vitrimer, imine exchange type vitrimer and acylhydrazone bond exchange type vitrimer.

3. The bonded magnet of claim 1, wherein, The polymer precursor of the vitrimer is selected from one or more of thermosetting resin, thermoplastic resin, thermoplastic elastomer and rubber; Preferably, the polymer precursor is selected from one or more of polyimide, polyamide, polyester, polyether, polyformaldehyde, polycarbonate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybutylene terephthalate, polystyrene, poly(4-vinylpyridine), polylactic acid, chitosan, cellulose and its derivative compounds, polyurethane, thermoplastic polyester elastomer, acrylate copolymer, epoxy resin, phenolic resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyether ether ketone, natural rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, ternary ethylene-propylene rubber, cis-butyl rubber, silicone rubber, fluororubber, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-polystyrene copolymer and styrene-butadiene-styrene copolymer; The magnetic powder is selected from NdFeB magnetic powder, SmFeN magnetic powder, NdFeN magnetic powder, SmCo magnetic powder, ferrite powder, AlNiCo magnetic powder, FeCo magnetic powder, FeSiAl magnetic powder and FeSi magnetic powder.

4. A composition for making bonded magnets, wherein, The composition comprises magnetic powder, polymer precursor, crosslinking agent and catalyst; the catalyst can catalyze the crosslinking reaction of the crosslinking agent and the polymer precursor, and the crosslinking reaction forms a dynamic crosslinking network structure.

5. The composition of claim 4, wherein, The magnetic powder is selected from NdFeB magnetic powder, SmFeN magnetic powder, NdFeN magnetic powder, SmCo magnetic powder, ferrite powder, AlNiCo magnetic powder, FeCo magnetic powder, FeSiAl magnetic powder and FeSi magnetic powder; the particle size of the magnetic powder is 2-150 μm; The polymer precursor is selected from one or more of polyimide, polyamide, polyester, polyether, polyformaldehyde, polycarbonate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybutylene terephthalate, polystyrene, poly(4-vinylpyridine), polylactic acid, chitosan, cellulose and its derivative compounds, polyurethane, thermoplastic polyester elastomer, acrylate copolymer, epoxy resin, phenolic resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyether ether ketone, natural rubber, nitrile rubber, butyl rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, cis-butyl rubber, silicone rubber, fluororubber, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer and styrene-butadiene-styrene copolymer; The crosslinking agent is selected from one or more of multifunctional halogenated hydrocarbon or active hydrogen compound; preferably, the crosslinking agent is selected from one or more of dihalogenated hydrocarbon, polyhalogenated hydrocarbon, diethylamine, triethylamine, polyamine and its derivative compounds, 1,4-dibutanol, isopentyl glycol, pentaerythritol, glycerol, polyol and its derivative compounds, dihydric phenol, polyhydric phenol, dihydric thiol, polyhydric thiol, amide, diurea, polyurea, diisocyanate, polyisocyanate, maleic anhydride and its derivative compounds, phthalate and its derivative compounds, oxalic acid, diacid, polyacid and its derivative compounds, polytetrahydrofuran, polyethylene glycol, polyvinyl alcohol, macromolecular diol, telechelic polyol polymer, telechelic linear polymer containing hydroxyl, mercapto, amino, carboxyl, epoxy, formate or acetate, star polymer and hyperbranched polymer; The catalyst is selected from one or more of organic zinc salt; preferably, the catalyst is selected from one or more of zinc acetate, triazabicyclodecene, triphenylphosphine and stannous octoate; The content of the magnetic powder in the composition is 96-98wt%, the content of the polymer precursor is 0.88-2.17wt%, the content of the crosslinking agent is 0.22-0.55wt%, and the content of the catalyst is 0.3-0.5wt%.

6. The composition of claim 4, wherein, The composition further comprises a coupling agent and a release agent; The coupling agent is selected from one or more of siloxane coupling agent, titanate coupling agent, aluminate coupling agent, phosphate coupling agent and organic iron coupling agent; The release agent is selected from one or more of organosilicon, organofluorine, natural wax, synthetic wax, molybdenum disulfide, lipid wax and polyester film; The content of the coupling agent in the composition is 0.28-0.30wt%, and the content of the release agent is 0.30-0.50wt%.

7. A method of making bonded magnets using the composition of any of claims 4-6, wherein, The method comprises: S1, mixing the magnetic powder, the polymer precursor, the crosslinking agent and the catalyst to obtain a granular mixture; S2, performing a forming treatment on the granular mixture to obtain a compact, and then performing a curing treatment on the compact.

8. The method of claim 7, wherein, The method further comprises adding a solvent and stirring in the mixing of step S1, and heating to remove the solvent during the stirring to obtain the granular mixture; the heating temperature is 10-50°C higher than the boiling point of the solvent, preferably 10-20°C higher, and the time is 3-4h; The solvent is selected from one or more of deionized water, methanol, ethanol, isopropanol, n-butanol, isobutanol, t-amyl alcohol, diethyl ether, acetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl isobutyl ketone, tetrahydrofuran, chloroform, n-pentane, cyclopentane, cyclohexane, n-hexane, n-heptane, n-octane, N,N-dimethylformamide, N,N-dimethylacetamide, pyridine, benzene, toluene, xylene, isobutyl acetate, n-butyl acetate, sec-butyl acetate, ethyl acetate, isopropyl acetate and n-propyl acetate; Alternatively, the method further comprises feeding the magnetic powders, polymer precursors, cross-linking agents and catalysts into an open mill for mixing and processing under heating to obtain the granular mixture; The surface of the double rollers of the open mill is provided with a groove or protrusion structure.

9. The method of claim 7, wherein, The method further comprises, before step S1, pre-treating the magnetic powders with a coupling agent; In step S1, a release agent is further added to the granular mixture; In step S2, the forming processing is compression forming or calendering forming; The pressure of the forming processing is 5-10MPa, and the temperature is 25-100°C; The temperature of the curing processing is 80-200°C, and the time is 2-24h.

10. A bonded magnet prepared by the method of any one of claims 7-9.

11. The method of regenerating bonded magnets as claimed in any one of claims 1 to 3 and claim 10, wherein, The regeneration method comprises crushing the bonded magnet, and then performing forming processing on the crushed product, wherein the temperature of the forming processing is above the dynamic cross-linking temperature of the glass-like polymer.

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