A method for preparing anisotropic bonded magnets with high orientation

Abstract

A method for preparing a highly oriented anisotropic bonded magnet belongs to the field of magnetic material preparation technology. The preparation method is as follows: First, a binder is dissolved in a solvent to form a homogeneous and stable solution. Then, surface-pretreated anisotropic magnetic powder is added to the solution. Next, the magnetic powder / binder solution is placed in a ball mill jar for ball milling to refine the powder, ensuring uniform dispersion and achieving better calendering orientation anisotropy. Finally, an extractant is added while vacuum filtering the ball-milled suspension, causing the magnetic powder / binder composite to precipitate as a pre-oriented precipitate. The precipitate is crushed, sieved, and then calendered. During calendering, the pre-oriented magnetic powder / binder composite undergoes further mechanical orientation, thereby preparing an anisotropic bonded magnet with a higher degree of orientation.

Description

Technical Field

[0001] This invention relates to the field of magnetic material preparation technology, and in particular to a method for preparing a highly oriented flexible anisotropic bonded magnet. Background Technology

[0002] Flexible anisotropic bonded magnets are anisotropic composite permanent magnet materials made by uniformly mixing high-performance anisotropic permanent magnet powder with binders (resins) and other additives in a certain proportion, and then using a calendering process. This type of flexible anisotropic bonded permanent magnet material possesses high magnetic and mechanical properties and is easily processed into complex-shaped devices such as flexible bonded magnetic plates, magnetic strips, and magnetic rings, thus meeting various requirements.

[0003] Currently, the most common high-performance bonded magnets on the market are bonded NdFeB magnets. The magnetic energy product of isotropic bonded NdFeB magnetic powder is typically 12-18 MGOe, and the magnetic energy product of isotropic bonded NdFeB magnets made from isotropic bonded NdFeB magnetic powder is typically 8-12 MGOe, with a magnet-to-powder magnetic energy product ratio of approximately 67%. The magnetic energy product of anisotropic bonded NdFeB magnetic powder is typically 30-40 MGOe, and the maximum magnetic energy product of anisotropic bonded NdFeB magnets made from anisotropic bonded NdFeB magnetic powder can reach 20 MGOe, with a magnet-to-powder magnetic energy product ratio of approximately 50%. By comparing the energy product ratio of anisotropic and isotropic bonded magnets, it can be found that the energy product ratio of anisotropic bonded magnets is 10-20% lower than that of isotropic bonded magnets. This is mainly because when using anisotropic bonded magnetic powder to prepare magnets, each particle of the anisotropic powder cannot achieve a sufficiently high degree of orientation, thus failing to achieve high magnetic properties. Isotropic bonded magnets, on the other hand, do not have this orientation problem. Therefore, improving the orientation degree of the magnet, and thus its magnetic properties, is currently an important solution for improving the magnetic properties of anisotropic bonded magnets.

[0004] Patent document CN200610089368.5 describes a magnetically oriented anisotropic calendered bonded magnet and its preparation method. The method involves granulating the material and then magnetically oriented rolling the granulated material on a magnetic calender. The main innovation of this method is the addition of electromagnets to the rollers of a traditional calender to generate an orientation magnetic field. As the material passes through the rollers, it is oriented under the influence of the magnetic field, thus creating anisotropic magnets. However, due to the extremely high coercivity of NdFeB magnetic powder, the required external orientation magnetic field strength is very high, which is difficult to achieve with calendering equipment. Furthermore, this method of adding a magnetic field inside the calender rollers does not produce ideal orientation results.

[0005] Publication No. CN101800106 describes a two-step process for preparing highly oriented flexible anisotropic bonded magnets using a thermal magnetic field orientation process that separates calendering and orientation. This method involves heating the calendered flexible bonded magnet at a specific temperature for a certain time, then immediately placing it in a magnetic field for thermal magnetic field orientation to obtain a highly oriented flexible anisotropic bonded magnet. However, during the thermal magnetic field orientation, the magnetic powder particles rotate, causing damage to the surface flatness of the magnet. Therefore, the oriented magnet must undergo a second flattening calendering process, which further damages the orientation degree and affects the magnetic properties of the magnet.

[0006] Therefore, it is an urgent problem to develop a process that can obtain highly oriented anisotropic bonded magnets without applying a high-energy magnetic field for orientation during or after calendering, and to prepare high-performance, flexible anisotropic bonded magnets with a high degree of orientation with simple process. Summary of the Invention

[0007] This invention provides a method for preparing highly oriented anisotropic bonded magnets without applying a high-energy magnetic field for orientation during or after calendering. This avoids the complex, cumbersome, and energy-intensive production process caused by high-energy magnetic field orientation and fully leverages the advantages of simple and continuous production in calendering.

[0008] The objective of this invention is achieved through the following steps:

[0009] Step (1) Preparation of magnetic powder / binder suspension:

[0010] Add the binder to the solution and stir at a suitable temperature to ensure that the binder is completely dissolved in the solution. Then, add the surface-pretreated anisotropic magnetic powder to the solution.

[0011] The adhesive is a polymer material, and its components are any one of polyurethane elastomer (TPU), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butene-styrene block copolymer (SEBS), and chlorinated polyethylene (CPE).

[0012] The binder is added at a ratio of 1-20% of the magnetic powder mass.

[0013] The solution is a benign solvent corresponding to the selected adhesive. When the adhesive resin is TPU, the solution is preferably N,N-dimethylformamide; when the adhesive resin is EVA, the solution is preferably toluene; when the adhesive resin is SEBS, the solution is preferably tetrahydrofuran; and when the adhesive resin is CPE, the solution is preferably xylene.

[0014] In the method for preparing the magnetic powder / binder suspension, preferably, the mixture is stirred at 80°C for 6-8 hours to ensure that the binder is fully dissolved in the solution.

[0015] The anisotropic magnetic powder is preferably calendered anisotropic magnetic powder or a mixture of calendered anisotropic magnetic powder and anisotropic magnetic powder A; the calendered anisotropic magnetic powder A is selected from calendered anisotropic Nd-Fe-B magnetic powder and calendered anisotropic Sm-Co magnetic powder, and the anisotropic magnetic powder A is selected from anisotropic Sm-Fe-N magnetic powder and anisotropic Nd-Fe-N magnetic powder; when a mixture of magnetic powders is used, the anisotropic Sm-Fe-N and Nd-Fe-N magnetic powders are 1-20 wt% of the calendered anisotropic magnetic powder.

[0016] The surface pretreatment step involves dissolving the surface pretreatment agent in an acetone solution, then adding magnetic powder and stirring to achieve uniform distribution. Next, the mixture is dried in a vacuum drying oven to remove the solvent, ultimately obtaining surface-pretreated magnetic powder. During the surface treatment process, some groups of the coupling agent molecule react with the hydroxyl groups on the surface of the magnetic powder to form chemical bonds. Then, in the later stage when it interacts with the binder, another part of the groups reacts with the binder to form physical entanglement, organically combining the magnetic powder and the binder, and increasing the bonding force between the two.

[0017] The surface pretreatment agent is preferably one or a mixture of two of silane coupling agents and titanate coupling agents, and its mass is 0.5-1.0 wt% of the magnetic powder.

[0018] Step (2) Ball milling of magnetic powder / binder suspension:

[0019] The magnetic powder / binder suspension obtained in step (1) is placed in a ball mill jar for ball milling and refining.

[0020] The specific steps of ball milling are as follows: To prevent the magnetic powder from oxidizing during the ball milling process, a magnetic powder / binder suspension is added to the ball milling jar in a vacuum glove box. The ball milling media are agate beads or zirconia beads. After sealing, the jar is taken out of the vacuum glove box for ball milling. The ball milling time is 1-6 hours, and the aspect ratio (D / H) of the ball-milled magnetic powder is 3.0-4.0.

[0021] Step (3) Preparation of pre-oriented precipitate:

[0022] The suspension after ball milling in step (2) was vacuum filtered while ethanol extractant was continuously and uniformly added to the suspension. Because ethanol extractant is miscible with the solution but poorly miscible or even immiscible with the magnetic powder / binder composite, the magnetic powder / binder composite precipitated out. The precipitate was then filtered and vacuum filtered 4-6 times using ethanol extractant; the precipitate was then dried in a vacuum drying oven to obtain a pre-oriented precipitate; the specific orientation principle is as follows... Figure 1 As shown, during vacuum filtration, under the influence of pressure difference and gravity, the magnetic powder particles gradually descend and accumulate in layers on the filter membrane surface, forming a pre-oriented structure, such as... Figure 2 As shown.

[0023] The vacuum filtration of the suspension preferably uses a microporous filter membrane with a pore size of 0.22 μm.

[0024] The vacuum drying temperature is 40-80℃.

[0025] Step (4) Anisotropic bonded magnet calendering:

[0026] The precipitate dried in step (3) is crushed and sieved. Then, the crushed particles are mixed evenly with one or more of the plasticizer and lubricant as processing aids and then calendered to obtain a magnetic flux sheet with a thickness of 0.1-4 mm.

[0027] The mass of the processing aid is 0.1-5% of the mass of the magnetic powder / binder mixture.

[0028] Compared with existing technologies, the most significant features of this invention are: ① The magnetic powder in the solution is refined during the ball milling process, allowing the magnetic powder to be uniformly dispersed in the solution and achieving better calendering orientation anisotropy; ② The magnetic powder / binder mixture prepared by vacuum filtration avoids the risk of reduced magnetic properties caused by oxidation of the magnetic powder during conventional mixing and granulation; ③ The magnetic powder undergoes pre-orientation during vacuum filtration, and subsequently, during calendering, the pre-oriented magnetic powder / binder composite undergoes further mechanical orientation, thereby effectively improving its orientation effect and greatly enhancing its magnetic properties. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the orientation principle of vacuum filtration.

[0030] Figure 2 To form a pre-oriented surface layered stacking pattern. Detailed Implementation

[0031] Comparative Example 1

[0032] In this embodiment, 95 parts of anisotropic NdFeB magnetic powder, 4 parts of TPU binder, and 1 part of stearic acid processing aid were used. The anisotropic NdFeB magnetic powder was first ball-milled for 2 hours. The ball-milled powder was then surface-treated with a silane coupling agent KH550, with the surface treatment agent accounting for 0.5 wt% of the magnetic powder. The surface-treated NdFeB magnetic powder, TPU binder, and stearic acid processing aid were then mixed and granulated using a Banbury mixer at a mixing temperature of 150-170℃. The mixture was then calendered to obtain products with a thickness of 0.1-4 mm at a calendering temperature of 150-170℃. The properties of the final magnet are shown in the table below.

[0033] Table 1:

[0034] DOA (%) <![CDATA[B r (kG)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 61％ 5.63 14.88 6.88

[0035] in,

[0036] In the table, DOA represents the orientation degree of the magnet;

[0037] B in the table r Represents the remanence of a magnet;

[0038] H in the table cj This represents the intrinsic coercivity of a magnet;

[0039] (BH) in the table max Represents the maximum magnetic energy product of a magnet;

[0040] Example 1

[0041] In this embodiment, the anisotropic NdFeB magnetic powder surface-treated with silane coupling agent KH550 was used, comprising 95 parts, TPU binder 4 parts, and stearic acid processing aid 1 part, wherein the surface treatment agent was 0.5 wt% of the magnetic powder. First, the 4 parts of dried TPU were dissolved in dimethylformamide and stirred at 80°C for 4 hours. Then, 95 parts of calendered and oriented anisotropic NdFeB magnetic powder were added to the TPU solution. The NdFeB / TPU dispersion was then continuously ball-milled for 2 hours, resulting in refined NdFeB magnetic powder that was uniformly distributed in the TPU solution. The ball-milled mixture was then vacuum-filtered, while ethanol extractant was continuously and uniformly added to the suspension, resulting in the formation of a pre-oriented NdFeB / TPU precipitate. The precipitate was repeatedly filtered and vacuum-filtered with ethanol, and then placed in a vacuum drying oven at 60°C until its mass remained unchanged. The dried precipitate was crushed and passed through a 5-mesh standard sieve, then calendered to obtain products with a thickness of 0.1-4 mm at a calendering temperature of 150-170℃. The properties of the final magnets are shown in the table below. By comparing Example 1 and Comparative Example 1, it can be found that the magnets after pre-orientation treatment have a 33% higher degree of orientation and a 53% higher magnetic energy product compared to the magnets without pre-orientation treatment.

[0042] Table 2:

[0043] DOA (%) <![CDATA[B r (kG)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 81％ 7.00 14.87 10.52

[0044] Comparative Example 2

[0045] In this embodiment, 95 parts of anisotropic magnetic powder, 4 parts of TPU binder, and 1 part of stearic acid processing aid were used. The anisotropic magnetic powder included 93 parts of calendered oriented anisotropic NdFeB magnetic powder and 2 parts of anisotropic SmFeN magnetic powder mixed powder. The NdFeN / SmFeN magnetic powder was first ball-milled for 1 hour. The ball-milled powder was then surface-treated with a silane coupling agent KH550, with the surface treatment agent weighing 0.5 wt% of the magnetic powder. The surface-treated NdFeN / SmFeN mixed magnetic powder, TPU binder, and stearic acid processing aid were mixed and granulated using a Banbury mixer at a mixing temperature of 60-80℃. Then, the mixture was calendered to obtain products with a thickness of 0.1-4 mm at a calendering temperature of 60-80℃. The properties of the final magnet are shown in the table below.

[0046] Table 3:

[0047] DOA (%) <![CDATA[B r (kG)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 67％ 5.77 14.70 7.28

[0048] Example 2

[0049] In this embodiment, the surface-treated anisotropic composite magnetic powder used is 95 parts, the binder CPE is 4 parts, and the processing aid stearic acid is 1 part. The anisotropic magnetic powder comprises a mixture of 93 parts calendered oriented anisotropic NdFeB magnetic powder and 2 parts anisotropic SmFeN magnetic powder, with the surface treatment agent weighing 0.5 wt% of the magnetic powder. First, 4 parts of CPE are dissolved in xylene and stirred at 80°C for 6 hours. Then, 95 parts of the surface-treated anisotropic composite magnetic powder are added to the CPE solution. The NdFeN / SmFeN / CPE dispersion is then continuously ball-milled for 1 hour, resulting in refined magnetic powder that is uniformly distributed in the CPE solution. The ball-milled mixture was vacuum filtered while ethanol extract was continuously and uniformly added to the suspension, resulting in the formation of pre-oriented NdFeN / SmFeN / CPE precipitate. The precipitate was then repeatedly filtered and vacuum-filtered with ethanol, and finally dried in a vacuum drying oven at 60°C until its mass remained unchanged. The dried precipitate was crushed and passed through a 5-mesh standard sieve, and then calendered to obtain products with a thickness of 0.1-4 mm at a calendering temperature of 60-80°C. The properties of the final magnets are shown in the table below. Comparison of Example 2 and Comparative Example 2 shows that the pre-oriented magnet exhibited a 28% increase in orientation degree and a 74% increase in magnetic energy product compared to the un-pre-oriented magnet.

[0050] Table 4:

[0051] DOA (%) <![CDATA[B r (kG)]]> <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> 86％ 7.77 14.71 12.70

[0052] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a highly oriented anisotropic bonded magnet, characterized in that, Includes the following steps: Step (1) Preparation of magnetic powder / binder suspension: Add the binder to the solution and stir at a suitable temperature to ensure that the binder is completely dissolved in the solution. Then add the surface-pretreated anisotropic magnetic powder to the solution. The adhesive is a polymer material, and its components are any one of polyurethane elastomer (TPU), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butene-styrene block copolymer (SEBS), and chlorinated polyethylene (CPE). Step (2) Ball milling of magnetic powder / binder suspension: The magnetic powder / binder suspension obtained in step (1) was placed in a ball mill jar for ball milling and refining. The specific steps of ball milling are as follows: To prevent the magnetic powder from oxidizing during the ball milling process, a magnetic powder / binder suspension is added to the ball milling jar in a vacuum glove box. The ball milling media are agate beads or zirconium oxide beads. After sealing, the jar is taken out of the vacuum glove box for ball milling. The ball milling time is 1-6 hours, and the aspect ratio (D / H) of the ball-milled magnetic powder is 3.0-4.

0. Step (3) Preparation of pre-oriented precipitate: The suspension after ball milling in step (2) was vacuum filtered, and ethanol extract was continuously and uniformly added to the suspension. Since ethanol extract is miscible with the solution, but miscible or even immiscible with the magnetic powder / binder complex, the magnetic powder / binder complex precipitates out to form a precipitate. The precipitate was filtered and vacuum filtered 4-6 times using ethanol extract. The precipitate obtained by extraction was then placed in a vacuum drying oven for drying to obtain a pre-oriented precipitate. During vacuum filtration, under the action of pressure difference and gravity, the magnetic powder particles gradually descended and formed a layered stack on the filter membrane surface to form a pre-oriented precipitate. Step (4) Anisotropic bonded magnet calendering: The precipitate dried in step (3) is crushed and sieved. Then, the crushed particles are mixed evenly with one or more of the plasticizer and lubricant as processing aids and calendered to obtain a magnetic flux sheet with a thickness of 0.1-4 mm.

2. The method for preparing a highly oriented anisotropic bonded magnet according to claim 1, characterized in that, in, The proportion of the binder added in step (1) is 1-20% of the mass of the magnetic powder.

3. The method for preparing a highly oriented anisotropic bonded magnet according to claim 1, characterized in that, in, The solution described in step (1) is a benign solvent corresponding to the selected adhesive. When the adhesive resin is TPU, the solution is N,N-dimethylformamide; when the adhesive resin is EVA, the solution is toluene; when the adhesive resin is SEBS, the solution is tetrahydrofuran; when the adhesive resin is CPE, the solution is xylene. In the preparation method of the magnetic powder / binder suspension, the mixture is stirred at 80°C for 6-8 hours to ensure that the binder is fully dissolved in the solution.

4. A method for preparing a highly oriented anisotropic bonded magnet according to claim 1, characterized in that, in, The anisotropic magnetic powder mentioned in step (1) is calendered anisotropic magnetic powder or a mixture of calendered anisotropic magnetic powder and anisotropic magnetic powder A; the calendered anisotropic magnetic powder A is selected from calendered anisotropic Nd-Fe-B magnetic powder and calendered anisotropic Sm-Co magnetic powder, and the anisotropic magnetic powder A is selected from anisotropic Sm-Fe-N magnetic powder and anisotropic Nd-Fe-N magnetic powder; when a mixture of magnetic powders is used, the anisotropic Sm-Fe-N and Nd-Fe-N magnetic powders are 1-20 wt% of the calendered anisotropic magnetic powder.

5. A method for preparing a highly oriented anisotropic bonded magnet according to claim 1, characterized in that, in, The surface pretreatment step (1) is as follows: the surface pretreatment agent is dissolved in acetone solution, and then magnetic powder is added and stirred to achieve uniform distribution; next, the mixture is placed in a vacuum drying oven to dry to remove the solvent, and finally the surface pretreated magnetic powder is obtained. During the surface treatment process, some groups of the coupling agent molecule react with the hydroxyl groups on the surface of the magnetic powder to form chemical bonds; then, when it reacts with the binder in the later stage, another part of the groups react with the binder to form physical entanglement, organically combining the magnetic powder and the binder, and increasing the bonding force between the two. The surface pretreatment agent is one or a mixture of two of the following: silane coupling agent and titanate coupling agent, and its mass is 0.5-1.0 wt% of the magnetic powder.

6. A method for preparing a highly oriented anisotropic bonded magnet according to claim 1, characterized in that, in, In step (3), the vacuum filtration of the suspension is performed using a microporous filter membrane with a pore size of 0.22 μm. The drying temperature is 40-80℃.

7. A method for preparing a highly oriented anisotropic bonded magnet according to claim 1, characterized in that, in, In step (4), the mass of the processing aid is 0.1-5% of the mass of the magnetic powder / binder mixture.

8. A highly oriented anisotropic bonded magnet prepared according to any one of claims 1-7.

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