High-performance high-fluidity magnetic particles for injection molding and a method for preparing the same

Abstract

The application discloses a kind of high-performance high fluidity magnetic particles for injection molding and a preparation method thereof, and relates to the technical field of bonded magnetic composite materials.The preparation steps include the following:S1. Anisotropic samarium iron-nitrogen magnetic powder is mixed with isotropic samarium iron-nitrogen magnetic powder to obtain a mixed magnetic powder;S2. Under stirring conditions, ethanol, ethylenediaminetetraacetic acid, phosphate ester coupling agent and antioxidant are added to the mixed magnetic powder, which is stirred and dispersed uniformly, and then dried to obtain pretreated magnetic powder;S3. The mixed material composed of pretreated magnetic powder, silane coupling agent, nylon, diacetyl epoxy vegetable oil glyceride, oleic acid amide and cerium stearate is added to an extrusion granulator, and the magnetic particles for injection molding are obtained by extrusion granulation under nitrogen conditions.The magnetic particles for injection molding prepared by the method have high fluidity, can meet the demand for injection molding of complex shapes, have stable mechanical properties, and have oxidation resistance, which ensures long-term stable magnetic properties of the magnetic particles and reduces magnetic attenuation during use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bonded magnetic composites, in particular to a kind of high-performance high-fluidity magnetic particles for injection molding and preparation method thereof. BACKGROUND

[0002] With the development of electronic appliances and household appliances, the requirements for micro motor rotor accessories are becoming higher and higher. The traditional magnet sintering method is difficult to meet the requirements of manufacturing fine parts, while the method of preparing magnets by injection molding has obvious advantages. Through injection molding, complex micro parts can be manufactured, and high production efficiency is achieved. This method can meet the requirements of new micro motor rotor production, and high-performance magnetic composites occupy a large share in the raw material market of magnetic devices for small household appliances and micro motors.

[0003] At present, anisotropic samarium-iron-nitrogen magnetic powder is mainly used for injection molding of samarium-iron-nitrogen magnets, which has a fine particle size, D50 is about 1-3 μm, and has high remanence and coercivity after orientation. However, due to the fine magnetic powder, the flowability of the magnetic particles made of nylon is poor, and the performance is reduced due to easy oxidation during processing. In addition, the plasticizer used for injection molding of magnets has the risk of environmental pollution, increasing the environmental protection investment of enterprises.

[0004] In the prior art, patent document CN111667967A discloses a high-fluidity samarium-iron-nitrogen flexible bonded permanent magnet for injection molding and a preparation method thereof. The invention improves the plasticizing degree and magnetic properties of samarium-iron-nitrogen magnetic powder by optimizing the plasticizer system and internal mixer process, and improves the molding efficiency and quality of the permanent magnet. However, the invention has the problem of poor melt flowability and temperature resistance in the plasticizer system. Patent document CN117174421A discloses a high-performance magnetic composite and a preparation method thereof. The invention significantly improves the flowability, slightly improves the magnetic properties and mechanical properties by adding inorganic lubricant. However, the invention still has the problem of poor magnet manufacturing precision and production efficiency in the optimization of injection molding process parameters. Therefore, there is an urgent need for an injection molding magnetic material with high coercivity and high flowability to be applied in the field of magnetic devices such as small household appliances and micro motors. SUMMARY

[0005] One of the purposes of the present application is to provide a preparation method of high-performance high-fluidity magnetic particles for injection molding to solve the problem of poor performance of magnetic particles for injection molding.

[0006] The second purpose of the present application is to provide a high-performance high-fluidity magnetic particle for injection molding prepared by the preparation method.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] The first aspect is a preparation method of high-performance high-fluidity magnetic particles for injection molding, comprising the following steps:

[0009] S1. Mixing powders: uniformly mix anisotropic samarium iron nitride magnetic powder and isotropic samarium iron nitride magnetic powder to obtain mixed magnetic powder;

[0010] S2. Pretreatment: under stirring conditions, add ethanol, ethylenediaminetetraacetic acid (EDTA), phosphate ester coupling agent and antioxidant to the mixed magnetic powder, uniformly stir and disperse, and dry to obtain pretreated magnetic powder;

[0011] S3. Extrusion granulation: add a mixture composed of pretreated magnetic powder, silane coupling agent, nylon, diacetyl epoxy vegetable oil glyceride, oleic acid amide and cerous stearate to an extrusion granulator, and extrude and granulate under nitrogen to obtain magnetic particles for injection molding.

[0012] Further, in S1, the anisotropic samarium iron nitride magnetic powder is 90-99 parts by weight, and the isotropic samarium iron nitride magnetic powder is 1-10 parts by weight.

[0013] Further, in S1, the particle size distribution D50 of the anisotropic samarium iron nitride magnetic powder is 1-3 μm, the remanence Br is ≥11 kGs, and the coercivity Hcj is ≥9000 Oe.

[0014] Further, in S1, the particle size distribution D50 of the isotropic samarium iron nitride magnetic powder is 8-10 μm, the remanence Br is ≥6.5 kGs, and the coercivity Hcj is ≥12000 Oe.

[0015] Further, in S2, the mixed magnetic powder is 100 parts by weight, the ethanol is 100 parts by weight, the ethylenediaminetetraacetic acid is 0.3-1 part by weight, the phosphate ester coupling agent is 0.3-0.6 part by weight, and the antioxidant is 0.5-1 part by weight.

[0016] Further, in S2, the antioxidant is a phenolic antioxidant, including antioxidant 1010.

[0017] Further, in S2, the stirring speed is 10-20 r / min, and the stirring time is 10-20 min.

[0018] Further, in S2, the drying temperature is 40-60℃, and the drying time is 5-8 h.

[0019] Further, in S3, the pretreated magnetic powder is 100 parts by weight, the silane coupling agent is 0.3-0.6 parts by weight, the nylon is 5-15 parts, the diacetyl epoxy vegetable oil glyceride is 0.5-1 part, the oleic acid amide is 0.3-1 part, and the cerous stearate is 0.3-1 part.

[0020] Further, in S3, the nylon is any one of nylon 6, nylon 66, and nylon 12; and the silane coupling agent is any one of KH550, KH560, and KH570.

[0021] Further, in S3, the temperature of the extrusion section of the extrusion granulator is divided into three sections, and the temperature from the feeding port to the discharge port is 210-230 DEG C, 230-250 DEG C, and 250-270 DEG C in sequence.

[0022] In the second aspect, the high-performance and high-fluidity magnetic particle for injection molding is prepared by the preparation method of the first aspect.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] 1. The present application provides a preparation method of a high-performance and high-fluidity magnetic particle for injection molding, which is prepared by synergizing anisotropic and isotropic samarium iron nitrogen magnetic powder, taking into account high remanence, high coercivity, and uniformity of magnetic performance, avoiding the performance short board of a single magnetic powder, and performing EDTA surface functionalization-dual coupling agent matrix interface engineering-internal and external lubrication cross-linking multi-scale design preparation process on the magnetic powder to avoid the risk of reduction of coercivity and performance of traditional injection molding magnetic particles due to oxidation during the processing process. The present application is simple and effective, suitable for industrialized continuous production, and effectively improves the fluidity and processing performance of the magnetic powder for injection molding.

[0025] 2. The injection molding magnetic particle prepared by the preparation method of the present application has high fluidity, can meet the complex shape injection molding demand, has stable mechanical properties, and has oxidation resistance, which ensures that the magnetic particle has long-term stable magnetic performance and reduces the magnetic decay during use. The remanence of the particle can reach 7000Gs, the intrinsic coercivity can reach 8000 Oe, the magnetic energy product is higher than 10MGOe, and the fluidity is better than 260g / 10min. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a preparation process flow diagram of the high-performance and high-fluidity magnetic particle for injection molding of the present application. DETAILED DESCRIPTION

[0027] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments.

[0028] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0029] It should be understood that the size of the sequence number of each process in various embodiments of the present application does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0030] The weight of the related components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the embodiment description of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass mentioned in the embodiment description of the present application can be μg, mg, g, kg and other mass units commonly known in the chemical field.

[0031] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present application.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0033] The embodiment of the present application provides a preparation method of a high-performance high-fluidity magnetic particle for injection molding, specifically comprising the following steps:

[0034] S1. Powder mixing: uniformly mix anisotropic samarium iron nitride magnetic powder and isotropic samarium iron nitride magnetic powder to obtain mixed magnetic powder;

[0035] S2. Pretreatment: under stirring conditions, add ethanol, ethylenediaminetetraacetic acid (EDTA), phosphate ester coupling agent and antioxidant to the mixed magnetic powder, stir and disperse uniformly, and dry to obtain pretreated magnetic powder;

[0036] S3. Extrusion granulation: add a mixture composed of pretreated magnetic powder, silane coupling agent, nylon, diacetyl epoxy vegetable oil glyceride, oleic acid amide and cerous stearate to an extrusion granulator, and under nitrogen condition, extrusion granulation is performed to obtain magnetic particles for injection molding.

[0037] The anisotropic samarium iron nitride magnetic powder has high magnetic crystal anisotropy, and the atomic arrangement direction is consistent, which can provide excellent magnetic properties (core magnetic property source) such as high remanence (Br) and high coercivity (Hcj); while the magnetic domain orientation of the isotropic samarium iron nitride magnetic powder is random, although the magnetic property is slightly lower, the particle shape is more regular, the bulk density is more uniform, and the flowability is better.

[0038] EDTA coordinates with Sm / Fe ions through carboxyl / amine groups, forming a nanoscale chelate layer, inhibiting the oxidation of magnetic powder, and reducing the decay of magnetic properties. At the same time, the chelate layer provides active anchor sites for subsequent coupling agents.

[0039] During the pretreatment stage, the phosphonate coupling agent's magnetic powder-philic end (phosphonic group) is bonded to the EDTA chelate layer, and the oil-philic end (long-chain alkyl) reduces the surface energy of the magnetic powder, reduces agglomeration, and is compatible with subsequent organic matrices such as nylon, reducing interface defects between the magnetic powder and the matrix through "inorganic-organic interface bridging"; during the extrusion stage, the silane coupling agent reacts with the nylon molecular chain to form a "magnetic powder-silane-nylon" transition layer, reducing the interface friction coefficient, forming a double interface modification with the phosphonate coupling agent, and reducing the interface stress to reduce viscosity.

[0040] Nylon, as a high molecular carrier, encapsulates the magnetic powder through extrusion melting, giving the material the plasticity and mechanical strength required for injection molding. Diacetyl epoxidized vegetable oil glyceride acts as a plasticizer, with the epoxy group opening and reacting with the terminal amine group of nylon to form flexible branches, which are inserted between nylon molecular chains to reduce intermolecular forces, forming a lightly cross-linked network that reduces melt viscosity and improves flowability.

[0041] Oleamide acts as an external lubricant, reducing friction between the magnetic powder and the nylon molecules, while migrating to the surface of the melt to improve the lubricity of the melt and the equipment, reducing adhesion to the screw / mold;

[0042] Cerium stearate acts as an internal lubricant, with rare earth metal ions (Ce 3+ ) capturing free radicals (nylon carbonyl groups) to form coordination, enhancing oxidation resistance; the stearic acid segment further enhances lubrication, and the three work together to ensure high flowability under high magnetic powder filling. At the same time, cerium stearate decomposes into CeO2 nanoparticles during extrusion through temperature control, pinning at the magnetic powder / nylon interface to inhibit crack propagation.

[0043] In a specific implementation case, in S1, the anisotropic samarium-iron-nitrogen magnetic powder is 90-99 parts by weight, and the isotropic samarium-iron-nitrogen magnetic powder is 1-10 parts by weight.

[0044] When mixed, through the particle grading effect: the anisotropic magnetic powder serves as the "magnetic performance skeleton" to ensure overall magnetic performance, and the isotropic magnetic powder fills the gaps to form a "main magnetic phase + auxiliary magnetic phase" composite structure. This reduces the "magnetic performance blind area" caused by single magnetic powder agglomeration, while improving the bulk density and dispersibility of the powder, providing a uniform powder base for subsequent pretreatment and extrusion processing.

[0045] In a specific implementation case, in S1, the anisotropic samarium-iron-nitrogen magnetic powder has a particle size distribution D50 of 1-3 μm, a remanence Br≥11 kGs, and a coercivity Hcj≥9000 Oe.

[0046] In one specific embodiment, in S1, the particle size distribution D50 of the isotropic samarium iron nitride magnetic powder is 8-10 μm, the remanence Br is ≥6.5 kGs, and the coercivity Hcj is ≥12000 Oe.

[0047] In one specific embodiment, in S2, the mixing magnetic powder is 100 parts, the ethanol is 100 parts, the ethylenediaminetetraacetic acid is 0.3-1 part, the phosphate ester coupling agent is 0.3-0.6 part, and the antioxidant is 0.5-1 part by weight. The amount of ethylenediaminetetraacetic acid is controlled to reduce the activity of the samarium iron nitride magnetic powder while avoiding the reduction of the remanence of the non-magnetic phase.

[0048] In one specific embodiment, in S2, the stirring speed is 10-20 r / min, and the stirring time is 10-20 min. Low-speed stirring achieves uniform dispersion, and the stirring time is short, which improves the production efficiency.

[0049] In one specific embodiment, in S2, the drying temperature is 40-60℃, and the drying time is 5-8 h.

[0050] In one specific embodiment, in S3, the pretreated magnetic powder is 100 parts, the silane coupling agent is 0.3-0.6 parts, the nylon is 5-15 parts, the diacetyl epoxidized vegetable oil glyceride is 0.5-1 part, the oleic acid amide is 0.3-1 part, and the cerous stearate is 0.3-1 part by weight. The samarium iron nitride solid phase is ≥85 wt %, the appropriate amount of silane coupling agent ensures complete coverage and avoids excessive amount leading to screw slipping and particle sticking; the addition of 0.5-1 part of diacetyl epoxidized vegetable oil glyceride is a safe amount for lubrication-oil separation; the amount of 0.3-1 part of internal and external lubricants is in the win-win interval of heat resistance-rheology, which has both demolding property and appearance quality.

[0051] In one specific embodiment, in S3, the extrusion section temperature of the extrusion granulator is divided into three sections, and the temperature from the feeding port to the discharge port is 210-230℃, 230-250℃, and 250-270℃, respectively. The mixture enters the double-screw extrusion granulator through the feeding bin, nitrogen is introduced into the granulator to prevent oxidation of the magnetic powder and nylon during high temperature, the extrusion section temperature is divided into three sections, and the temperature from the feeding port to the discharge port is 210-230℃, 230-250℃, and 250-270℃, respectively. With the rotation of the double screw, the temperature gradually increases as the material continuously moves forward; at the discharge port, the material is cut into magnetic particles with a diameter of about 3 mm and a length of about 5 mm by a rotary cutter, and then cooled to room temperature.

[0052] In the following examples and comparative examples, the antioxidant is selected as antioxidant 1010, the silane coupling agent is selected as KH-550, the nylon is selected as nylon 12, the isotropic samarium-iron-nitrogen magnetic powder has a particle size distribution D50 of 8-10 μm, a remanence Br≥6.5 kGs, and a coercivity Hcj≥12000 Oe; the anisotropic samarium-iron-nitrogen magnetic powder has a particle size distribution D50 of 1-3 μm, a remanence Br≥11 kGs, and a coercivity Hcj≥9000 Oe.

[0053] The following will be further illustrated with specific examples.

[0054] Example 1

[0055] Please refer to Figure 1 The preparation process flowchart is shown in the figure. A preparation method of a high-performance high-fluidity magnetic particle for injection molding includes the following steps:

[0056] S1. Powder mixing: 95 parts of anisotropic samarium-iron-nitrogen magnetic powder and 5 parts of isotropic samarium-iron-nitrogen magnetic powder are weighed according to the weight fraction, and mixed uniformly to obtain mixed magnetic powder;

[0057] S2. Pretreatment: 100 parts of ethanol, 100 parts of mixed magnetic powder, 0.5 parts of EDTA, 0.4 parts of phosphate coupling agent, and 0.8 parts of antioxidant are sequentially added to the disperser under the condition of stirring speed of 15 r / min, and stirred for 15 min until uniformly dispersed, and dried at 50℃ for 6 h to obtain pretreated magnetic powder;

[0058] S3. Extrusion granulation: 100 parts of pretreated magnetic powder, 0.5 parts of silane coupling agent, 10 parts of nylon, 0.8 parts of diacetyl epoxidized vegetable oil glyceride, 0.5 parts of oleic acid amide, and 0.5 parts of cerous stearate are sequentially added in a high-speed powder mixer at a stirring speed of 200 r / min, and mixed uniformly to obtain a mixture;

[0059] The mixture is fed into a double-screw extrusion granulator through a feeding bin, nitrogen is introduced into the granulator to prevent oxidation of the magnetic powder and nylon during high-temperature process, the extrusion section temperature is divided into three sections, and the temperature from the feeding port to the discharge port is 220℃, 240℃, and 260℃ in sequence; with the rotation of the double screw, the temperature gradually increases in the process of continuously feeding the material forward; at the discharge port, the material is cut into magnetic particles with a diameter of about 3 mm and a length of about 5 mm by a rotary cutter, and cooled to room temperature.

[0060] Example 2

[0061] A preparation method of a high-performance high-fluidity magnetic particle for injection molding includes the following steps:

[0062] S1. Powder mixing: 95 parts of anisotropic samarium-iron-nitrogen magnetic powder and 5 parts of isotropic samarium-iron-nitrogen magnetic powder are weighed according to the weight fraction, and mixed uniformly to obtain mixed magnetic powder;

[0063] S2-S3: same as example 1.

[0064] Example 3

[0065] A preparation method of a high-performance high-fluidity magnetic particle for injection molding, comprising the following steps:

[0066] S1. Mix the powder: take 90 parts of anisotropic samarium iron nitride magnetic powder and 10 parts of isotropic samarium iron nitride magnetic powder by weight, mix uniformly to obtain mixed magnetic powder;

[0067] S2-S3: same as example 1.

[0068] Example 4

[0069] A preparation method of a high-performance high-fluidity magnetic particle for injection molding, comprising the following steps:

[0070] S1: same as example 1;

[0071] S2. Pretreatment: under the condition of stirring speed 15r / min, 100 parts of ethanol, 100 parts of mixed magnetic powder, 0.3 parts of EDTA, 0.4 parts of phosphate ester coupling agent and 0.8 parts of antioxidant are sequentially added into the disperser, stirring for 15min to uniformly disperse, drying at 50℃ for 6h to obtain pretreated magnetic powder;

[0072] S3: same as example 1.

[0073] Example 5

[0074] A preparation method of a high-performance high-fluidity magnetic particle for injection molding, comprising the following steps:

[0075] S1: same as example 1;

[0076] S2. Pretreatment: under the condition of stirring speed 15r / min, 100 parts of ethanol, 100 parts of mixed magnetic powder, 1 part of EDTA, 0.4 parts of phosphate ester coupling agent and 0.8 parts of antioxidant are sequentially added into the disperser, stirring for 15min to uniformly disperse, drying at 50℃ for 6h to obtain pretreated magnetic powder;

[0077] S3: same as example 1.

[0078] Example 6

[0079] A preparation method of a high-performance high-fluidity magnetic particle for injection molding, comprising the following steps:

[0080] S1-S2: same as example 1.

[0081] S3. Extrusion granulation: 100 parts of pretreated magnetic powder, 0.5 parts of silane coupling agent, 10 parts of nylon, 0.5 parts of diacetyl epoxidized vegetable oil glyceride, 0.5 parts of oleic acid amide and 0.5 parts of cerous stearate were added in a high-speed powder mixer in the order of weight fraction, and stirred and mixed uniformly at a rotation speed of 200 r / min to obtain a mixture;

[0082] The extrusion process of the mixture was consistent with that of Example 1.

[0083] Example 7

[0084] A method for preparing a high-performance high-flow magnetic particle for injection molding, comprising the following steps:

[0085] S1-S2: consistent with Example 1.

[0086] S3. Extrusion granulation: 100 parts of pretreated magnetic powder, 0.5 parts of silane coupling agent, 10 parts of nylon, 1 part of diacetyl epoxidized vegetable oil glyceride, 0.5 parts of oleic acid amide and 0.5 parts of cerous stearate were added in a high-speed powder mixer in the order of weight fraction, and stirred and mixed uniformly at a rotation speed of 200 r / min to obtain a mixture;

[0087] The extrusion process of the mixture was consistent with that of Example 1.

[0088] Comparative Example 1

[0089] A method for preparing a magnetic particle for injection molding, comprising the following steps:

[0090] S1. 100 parts of anisotropic samarium iron nitride magnetic powder were weighed according to the weight fraction;

[0091] S2. Pretreatment: 100 parts of ethanol, 100 parts of anisotropic samarium iron nitride magnetic powder, 0.5 parts of EDTA, 0.4 parts of phosphate coupling agent and 0.8 parts of antioxidant were added in the order of weight fraction into a disperser under the condition of stirring rotation speed of 15 r / min, and stirred for 15 min until uniformly dispersed, and dried at 50℃ for 6h to obtain pretreated magnetic powder;

[0092] S3: consistent with Example 1.

[0093] Comparative Example 2

[0094] A method for preparing a magnetic particle for injection molding, comprising the following steps:

[0095] S1. Powder mixing: 85 parts of anisotropic samarium iron nitride magnetic powder and 15 parts of isotropic samarium iron nitride magnetic powder were mixed uniformly according to the weight fraction to obtain a mixed magnetic powder;

[0096] S2-S3: consistent with Example 1.

[0097] Comparative Example 3

[0098] A method for preparing magnetic particles for injection molding, comprising the following steps:

[0099] S1: consistent with Example 1;

[0100] S2. Pretreatment: under the condition of stirring speed 15 r / min, 100 parts of ethanol, 100 parts of mixed magnetic powder, 0.4 parts of phosphate coupling agent and 0.8 parts of antioxidant were added into the disperser in turn according to the weight fraction, stirred for 15 min to uniformly disperse, dried at 50℃ for 6h to obtain pretreated magnetic powder;

[0101] S3: consistent with Example 1.

[0102] Comparative Example 4

[0103] A method for preparing magnetic particles for injection molding, comprising the following steps:

[0104] S1-S2: consistent with Example 1;

[0105] S3. Extrusion granulation: 100 parts of pretreated magnetic powder, 0.5 parts of silane coupling agent, 10 parts of nylon, 0.5 parts of oleic acid amide and 0.5 parts of cerous stearate were added into the high-speed powder mixer in turn according to the weight fraction, stirred and mixed uniformly at the speed of 200 r / min, to obtain the mixture;

[0106] The extrusion process of the mixture is consistent with Example 1.

[0107] Comparative Example 5

[0108] A method for preparing magnetic particles for injection molding, comprising the following steps:

[0109] S1: consistent with Example 1;

[0110] S2. Pretreatment: under the condition of stirring speed 15 r / min, 100 parts of ethanol, 100 parts of mixed magnetic powder, 0.5 parts of EDTA and 0.8 parts of antioxidant were added into the disperser in turn according to the weight fraction, stirred for 15 min to uniformly disperse, dried at 50℃ for 6h to obtain pretreated magnetic powder;

[0111] S3: consistent with Example 1.

[0112] Comparative Example 6

[0113] A method for preparing magnetic particles for injection molding, comprising the following steps:

[0114] S1-S2: consistent with Example 1;

[0115] S3. Extrusion granulation: 100 parts of the pretreated magnetic powder, 10 parts of nylon, 0.8 parts of diacetyl epoxidized vegetable oil glyceride, 0.5 parts of oleic acid amide and 0.5 parts of cerous stearate were added in a high-speed powder mixer in the order of weight fraction, and stirred and mixed uniformly at a rotation speed of 200 r / min to obtain a mixture;

[0116] The extrusion process of the mixture was consistent with that of Example 1.

[0117] The weight fractions of the raw materials used in each step of the above Examples 1-7 and Comparative Examples 1-6 are shown in Table 1.

[0118] Table 1

[0119]

[0120] The magnetic particles prepared in Examples 1-7 and Comparative Examples 1-6 were tested for performance:

[0121] (1) The test method for magnetic properties refers to GB / T 18880-2012 to test the residual magnetization (Br), coercivity (Hcj) and maximum magnetic energy product ((BH)max);

[0122] (2) The test method for fluidity refers to GB / T 3682 melt flow rate (MFR) test method;

[0123] (3) The test method for long-term stability refers to preparing a micro-motor rotor from the magnetic particles, running at 80℃ for 1000h, stopping every 250h to test, recording Br1, Hcj1 measured at 750h and Br2, Hcj2 measured at 1000h, calculating ΔBr = (Br1 - Br2) / Br1; ΔHcj = (Hcj1 - Hcj2) / Hcj1; and calculating the ΔBr / ΔHcj result and recording.

[0124] The test results are shown in Table 2.

[0125] Table 2

[0126]

[0127] From Table 2, it can be seen that:

[0128] Comparing Examples 1, 2 and 3 with Comparative Examples 1 and 2, as the addition ratio of isotropic powder increases from 0 parts to 15 parts, the residual magnetization of the magnetic particles gradually decreases, the coercivity gradually increases, and the fluidity gradually increases. This is because, compared with anisotropic powder, isotropic powder has lower residual magnetization and higher coercivity, and the particle size of isotropic powder is coarser, so less nylon is needed for coating the magnetic powder, and the flowability of the magnetic particles after granulation is higher.

[0129] Comparative Example 1, 4, 5 and Comparative Example 3, with the increase of the content of ethylenediaminetetraacetic acid, the remanence of the magnetic particles slightly decreases, the coercivity gradually increases, and the fluidity slightly improves. Ethylenediaminetetraacetic acid mainly reacts with iron in the magnetic powder, reducing the activity of the magnetic powder and reducing the oxidation of the magnetic powder at high temperature during the granulation process, thereby reducing the coercivity reduction during this process. However, since it is a non-magnetic phase, the remanence slightly decreases.

[0130] Comparative Example 1, 6, 7 and Comparative Example 4, the role of diacetyl epoxidized vegetable oil glycerol plasticizer is to reduce the friction between the nylon macromolecular chains, making the molecular chains more easily slide and rotate, and the plasticity of the material is enhanced. The molecular chain of nylon macromolecular material is usually in the form of a long chain, and the molecules are attracted to each other through van der Waals force, hydrogen bond, etc., forming a relatively tight aggregation structure, resulting in hard and brittle material, lacking of elasticity. The plasticizer is a small molecule compound with polar groups, and the polar part can interact with the polar groups of the macromolecular chain, and the non-polar part inserts between the macromolecular chains, thereby weakening the attraction between the macromolecular chains. Reduce the melt viscosity of the material, so that it is more easily molded by injection molding, extrusion and other processes. Therefore, the increase of the plasticizer greatly improves the fluidity of the magnetic particles.

[0131] And because the plasticizer reduces the viscosity of the nylon, it softens at a lower temperature and coats the magnetic powder, reducing the oxidation of the magnetic powder during high-temperature processing, and the remanence and coercivity of the magnetic powder will be improved. Moreover, the magnetic powder in the magnetic particles has a higher degree of orientation during sample preparation, and the remanence is further increased, so adding plasticizer within a certain range can improve the remanence and coercivity of the magnetic particles, and also improve the fluidity of the magnetic particles, with multiple benefits. However, too much plasticizer will reduce the proportion of the magnetic phase, resulting in a decrease in remanence.

[0132] Comparative Example 1 and Comparative Example 5, 6, the phosphate ester coupling agent and the silane coupling agent form a double interface modification, reducing the interfacial stress while achieving synergistic viscosity reduction.

[0133] In summary, the application effectively improves the flowability and processing performance of the magnetic particles by adding a small amount of isotropic samarium iron-nitrogen magnetic powder. Since the isotropic samarium iron-nitrogen magnetic powder has a coarse particle size (D50 is about 10 μm), high coercivity and is not easy to oxidize, it can significantly improve the flowability of the magnetic particles and effectively solve the problem of the reduction of coercivity and performance caused by easy oxidation of the traditional injection molding magnetic particles in the processing process. The use of ethylenediaminetetraacetic acid combined with the magnetic powder reduces the activity of the magnetic powder and improves the oxidation resistance of the magnetic powder. In the high-temperature granulation process, the performance decreases less. The plasticizer diacetyl epoxidized vegetable oil glyceride is used as an environmentally friendly plasticizer, which has excellent heat resistance and aging resistance and can significantly improve the high-temperature oxidation resistance of nylon plastic. The prepared injection molding magnetic particles have excellent magnetic performance and flowability, and have good oxidation resistance, so that they maintain good magnetic stability in the application process, thereby meeting the use in various working conditions.

[0134] It should be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0135] The above disclosure is only a few specific embodiments of the application, but the embodiments of the application are not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the application.

Claims

1. A method for preparing high-performance, high-flowability magnetic particles for injection molding, characterized in that, Includes the following steps: S1. Mix anisotropic samarium iron nitrogen magnetic powder and isotropic samarium iron nitrogen magnetic powder evenly to obtain mixed magnetic powder; S2. Under stirring conditions, ethanol, ethylenediaminetetraacetic acid, phosphate coupling agent and antioxidant are added to the mixed magnetic powder, stirred and dispersed evenly, and dried to obtain pretreated magnetic powder; S3. A mixture consisting of pretreated magnetic powder, silane coupling agent, nylon, diacetyl epoxy vegetable oil glycerol ester, oleamide and cerium stearate is added to an extruder and granulated under nitrogen conditions to obtain magnetic particles for injection molding. In S1, by weight, there are 90-99 parts of anisotropic samarium iron nitrogen magnetic powder and 1-10 parts of isotropic samarium iron nitrogen magnetic powder; In S2, by weight, there are 100 parts of mixed magnetic powder, 100 parts of ethanol, 0.3-1 parts of ethylenediaminetetraacetic acid, 0.3-0.6 parts of phosphate coupling agent, and 0.5-1 parts of antioxidant; In S3, by weight, there are 100 parts of pretreated magnetic powder, 0.3-0.6 parts of silane coupling agent, 5-15 parts of nylon, 0.5-1 parts of diacetylepoxy vegetable oil glyceride, 0.3-1 parts of oleamide, and 0.3-1 parts of cerium stearate.

2. The method for preparing high-performance, high-flowability magnetic particles for injection molding according to claim 1, characterized in that, In S1, the particle size distribution D50 of the anisotropic samarium iron nitrogen magnetic powder is 1-3 μm, the remanence Br≥11kGs, and the coercivity Hcj≥9000Oe.

3. The method for preparing high-performance, high-flowability magnetic particles for injection molding according to claim 1, characterized in that, In S1, the particle size distribution D50 of the isotropic samarium iron nitrogen magnetic powder is 8-10 μm, the remanence Br≥6.5 kGs, and the coercivity Hcj≥12000Oe.

4. The method for preparing high-performance, high-flowability magnetic particles for injection molding according to claim 1, characterized in that, In S2, the stirring speed is 10-20 r / min and the stirring time is 10-20 min.

5. The method for preparing high-performance, high-flowability magnetic particles for injection molding according to claim 1, characterized in that, In S2, the drying temperature is 40-60℃ and the drying time is 5-8h.

6. The method for preparing high-performance, high-flowability magnetic particles for injection molding according to claim 1, characterized in that, In S3, the temperature of the extrusion section of the extrusion granulator is divided into three sections, with the temperatures from the feed port to the discharge port being 210-230℃, 230-250℃, and 250-270℃ respectively.

7. A high-performance, high-flowability magnetic particle for injection molding, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

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