Magnet and preparation method and application thereof

Abstract

The invention discloses a magnet and a preparation method and application thereof. The preparation method comprises the following steps: mixing magnetic powder, organic silicon resin, an organic solvent and phosphoric acid, performing ball milling, and performing tape casting and drying on slurry obtained by ball milling to obtain the magnet. The preparation method has the advantages that the low-temperature curing characteristic of the easy-to-cure resin is utilized, and the easy-to-cure resin is matched with the phosphoric acid, the organic solvent and the ball milling, tape casting and drying process, so that the magnet is quickly dried and formed, and the problem that the coercive force is reduced due to traditional high-temperature processing is avoided.

Description

Technical Field

[0001] The present invention relates to the field of magnets, and relates to a magnet, a preparation method thereof, and an application thereof. Background Art

[0002] Samarium iron nitride magnets are one of the most promising applications. However, due to the properties of samarium iron nitride magnets themselves, they cannot be made into sintered magnets. Currently, the main application field is in injection-molded magnets. The prepared magnetic powder is mixed with nylon and other materials to form pellet materials, and then injection-molded into devices with the required shape and properties.

[0003] However, during the granulation and injection molding processes, the magnetic powder needs to undergo a high temperature of 200 - 300 °C. Although practitioners have tried many methods to protect the magnetic powder, it is still difficult to avoid the decline of the magnetic properties of the magnetic powder, especially the coercivity, during the high-temperature process. CN 113053608 A provides a rare-earth iron nitride-based magnetic powder with excellent heat resistance and magnetic properties and a preparation method thereof. The magnetic powder is treated by methods such as phosphoric acid coating and resin binder. However, the process adopted in this patent is a high-temperature forming process, which will cause the magnetic powder to oxidize, and the coercivity still drops by about 30%.

[0004] CN 110246685 A discloses a preparation method of a samarium iron nitride thin film. The invention first prepares a samarium iron thin film by using an ionic liquid pulse electrodeposition method under a magnetic field; then anneals and hydrogenates the samarium iron thin film in a heat treatment furnace; and finally nitriding is carried out by introducing high-purity nitrogen gas to obtain a samarium iron nitride thin film. The invention utilizes the process conditions of magnetic field, ionic liquid, and pulse electrodeposition to enable Sm 3+ and Fe 2+ to co-deposit to form a samarium iron thin film; the nanosized samarium iron thin film provides favorable conditions for nitriding through annealing and hydrogenation, obtaining a samarium iron nitride thin film with a higher nitrogen content, and this thin film has a higher magnetic energy product and excellent magnetic anisotropy. However, the thin film preparation technology used in this method is an ionic liquid pulse electrodeposition method, which has a high cost and is not conducive to mass production. Moreover, the raw materials adopt the co-deposition of Sm 3+ and Fe 2+ with a complex method and is not easy to operate.

[0005] CN 111383834 A provides a bonded magnet with excellent magnetic properties and a manufacturing method thereof. It relates to a manufacturing method of a bonded magnet, which includes: a first compression process of magnetically orienting and compressing magnetic powder with an average particle size of 10 μm or less to obtain a first formed body; a second compression process of contacting the first formed body with a thermosetting resin with a viscosity of 200 mPa·S or less and then compressing to obtain a second formed body; and a heat treatment process of heat-treating the second formed body. However, this method uses a thermosetting resin for compression and requires heat treatment, which will reduce the magnetic properties of the magnet.

[0006] Although the mechanism of the decrease in coercivity during high temperature is still unclear, the inventors found that if the temperature can be lowered, the performance degradation will be significantly reduced.

[0007] Therefore, providing a method for preparing a magnet that avoids the use of high temperatures and thereby retains the excellent properties of the material to a greater extent is a technical problem that needs to be solved urgently. Summary of the invention

[0008] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a magnet and its preparation method and application. The present invention provides a method for processing magnets without high temperature, avoiding the decrease of magnetic properties caused by high temperature and retaining the excellent properties of the material, especially the coercive force, to the maximum extent.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing a magnet, the method comprising the following steps:

[0011] The magnetic powder, silicone resin, organic solvent and phosphoric acid are mixed and ball-milled, and the slurry obtained by ball milling is cast and dried to obtain the magnet.

[0012] The method of the invention adopts easy-to-curable organic silicon resin and phosphoric acid to mix with magnetic powder, and ball milling is performed in an organic solvent. The organic silicon resin is used as a binder and has the characteristics of being curable at low temperature. During the drying process, dealcoholization condensation and curing are carried out under the catalysis of phosphoric acid, and the magnetic powder can be formed without heating. The organic solvent is used as the ball milling liquid to reduce oxidation of the magnetic powder during the crushing process. Moreover, phosphoric acid can also coat the magnetic powder to prevent oxidation. After ball milling, the slurry is cast and dried to obtain a high coercive force and high performance magnet.

[0013] The advantage of the preparation method of the present invention is that it utilizes the low-temperature curing characteristics of the easily curable resin in combination with phosphoric acid, organic solvents, and ball milling, casting and drying processes to quickly dry and shape the magnet, thereby avoiding the problem of reduced coercive force caused by traditional high-temperature processing.

[0014] The method of the invention has simple procedures, low cost, high preparation efficiency and is suitable for industrial production.

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0016] Preferably, the magnetic powder is samarium iron nitrogen magnetic powder.

[0017] During the high-temperature processing of samarium-iron-nitrogen magnetic powder, its properties, especially the coercivity, are significantly reduced. The root cause may be that when oxygen is present, the magnetic powder undergoes high-temperature oxidation, resulting in the decomposition of the magnetic powder and the formation of a soft magnetic phase and a non-magnetic phase. Since the soft magnetic phase has an extremely low coercivity and is easily magnetically conductive, it will cause a significant reduction in coercivity; and the non-magnetic phase does not contribute to the remanence, so the remanence will also decrease. By using the method of the present invention to form a magnet from the samarium-iron-nitrogen magnetic powder, the high-temperature processing process can be avoided, enabling the magnetic powder to be formed at a lower temperature to obtain a magnet with a certain shape and strength. Since there is no high-temperature process, the decline in magnetic properties, especially the coercivity, can be reduced.

[0018] The present invention does not limit the source of the magnetic powder, which can be commercially available conventional magnetic powder or magnetic powder prepared according to the methods disclosed in the prior art. Those skilled in the art can choose according to their needs.

[0019] Preferably, the D50 of the magnetic powder is 30 μm to 50 μm, such as 30 μm, 32 μm, 35 μm, 37 μm, 38 μm, 40 μm, 43 μm, 46 μm or 50 μm, etc.

[0020] Preferably, the silicone resin includes at least one of methyl silicone resin, methyl / phenyl silicone resin, or propyl / phenyl silicone resin.

[0021] Preferably, the dosage of the silicone resin is 2% to 10% of the weight of the magnetic powder, such as 2%, 3%, 3.5%, 4%, 5%, 6%, 6.5%, 7%, 8%, 9% or 10%, etc. If the dosage of the silicone resin is too small, it will cause inability to form, and the material will scatter during the drying process; if the dosage of the silicone resin is too large, it will cause a reduction in magnetic properties.

[0022] Preferably, the mass fraction of the phosphoric acid is 85%, and the dosage of the phosphoric acid is 1% to 5% of the weight of the magnetic powder, such as 1%, 2%, 3%, 4% or 5%, etc. It should be noted that here the dosage of the phosphoric acid is illustrated with the mass fraction of the phosphoric acid being 85%, but in the actual preparation process, the mass fraction of the phosphoric acid is not necessarily 85%, and the mass fraction can be changed. The dosage of the phosphoric acid defined in this scheme changes adaptively. For example, for the phosphoric acid with a mass fraction of 42.5%, the dosage of the phosphoric acid is 2% to 10% of the weight of the magnetic powder.

[0023] Preferably, the organic solvent is volatile and preferably includes at least one of absolute ethanol, acetone, isopropyl alcohol and methyl ethyl ketone, but is not limited to the above-listed types. The selection principle of the organic solvent is that it has very good volatility, so that the organic solvent can be completely volatilized under short-time and low-temperature conditions.

[0024] Preferably, the amount of the organic solvent is 0.5 to 1 times the weight of the magnetic powder, such as 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times or 1 time, etc. If the amount of the organic solvent is too small, a slurry cannot be formed and a blocking phenomenon occurs during the casting process; if the amount of the organic solvent is too large, the slurry will be too thin, resulting in a running material phenomenon, and it is not conducive to drying and forming.

[0025] As a preferred technical solution of the method for preparing the magnet according to the present invention, in the preparation method, a dispersant is further included in the raw materials for mixing.

[0026] Preferably, the dispersant includes at least one of calcium gluconate, sorbitol, castor oil, zinc stearate, sodium pyrophosphate and alkylaryl phosphate.

[0027] Preferably, the amount of the dispersant is 0.5% to 3% of the weight of the magnetic powder, such as 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6% or 3%, etc.

[0028] Adding a dispersant during the ball milling process can make the magnetic powder more uniform, better distributed, not easily agglomerated, and is conducive to the improvement of performance.

[0029] Preferably, the ball milling time is 0.5 h to 12 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 7 h, 7.5 h, 8 h, 9 h, 10 h, 11 h or 12 h, etc.

[0030] Ball milling makes the materials mixed evenly on the one hand and makes the materials finer on the other hand. If the ball milling time is too short, the magnetic powder is too thick, and it is difficult to improve the coercivity of the magnetic powder, resulting in too low magnetic powder performance; if the ball milling time is too long, the magnetic powder is too fine and is extremely easy to oxidize during the drying process, thus reducing the performance.

[0031] Preferably, the particle size D50 of the slurry obtained after ball milling is 1.3 μm to 3.0 μm, such as 1.3 μm, 1.4 μm, 1.5 μm, 1.7 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.6 μm, 2.8 μm or 3 μm, etc.

[0032] Preferably, during the casting process, the slurry is stirred, and the stirring speed is 5 r / min to 15 r / min, such as 5 r / min, 6 r / min, 7 r / min, 8 r / min, 9 r / min, 10 r / min, 11 r / min, 12 r / min, 13 r / min, 14 r / min or 15 r / min, etc.

[0033] Preferably, the feeding speed of the casting is 0.5 m / min to 2 m / min, such as 0.5 m / min, 0.6 m / min, 0.8 m / min, 1 m / min, 1.2 m / min, 1.3 m / min, 1.5 m / min, 1.7 m / min or 2 m / min, etc.

[0034] Preferably, during the casting process, the blade gap is 100 μm to 300 μm, such as 100 μm, 125 μm, 140 μm, 150 μm, 155 μm, 165 μm, 170 μm, 180 μm, 200 μm, 210 μm, 220 μm, 240 μm, 260 μm, 280 μm, 290 μm or 300 μm, etc.

[0035] In the present invention, sheet-shaped magnets (magnetic sheets) with different thicknesses can be obtained by adjusting the feeding speed and the blade gap. By adjusting the above parameters, the film thickness of the magnetic sheet obtained by casting can be ensured to be uniform, and there is no obvious influence on the performance of the magnetic sheet. Therefore, it will not be elaborated here.

[0036] Preferably, the drying is air-blowing drying.

[0037] Preferably, the air inlet and outlet volume of the air-blowing drying is 0.1 m 3 / min - 0.5 m 3 / min, such as 0.1 m 3 / min, 0.2 m 3 / min, 0.3 m 3 / min, 0.4 m 3 / min or 0.5 m 3 / min, etc.

[0038] In the present invention, the drying method can adopt air-blowing drying without heating. During the drying process, the silicone resin is cured to form the magnet.

[0039] In the second aspect, the present invention provides a magnet prepared by the preparation method described in the first aspect.

[0040] Preferably, the magnet is a magnetic sheet, and the thickness of the magnetic sheet is 100 μm to 300 μm, such as 100 μm, 125 μm, 140 μm, 150 μm, 155 μm, 165 μm, 170 μm, 180 μm, 200 μm, 210 μm, 220 μm, 240 μm, 260 μm, 280 μm, 290 μm or 300 μm, etc.

[0041] Through the method of the present invention, high-performance thin-film magnets can be prepared, with a remanence Br of more than 3850 Gs, a coercivity Hcj of more than 6390 Oe, and a maximum magnetic energy product (BH)max of more than 3.6 MGOe.

[0042] In a third aspect, the present invention provides a use of the magnet as described in the second aspect, and the magnet is used in the fields of magnetic adsorption, packaging, display or sensors.

[0043] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The method of the present invention uses an easily curable silicone resin and phosphoric acid to be mixed with magnetic powder and ball-milled in an organic solvent. The silicone resin, as a binder, has the characteristic of being curable at low temperature and undergoes de-alcohol condensation curing catalyzed by phosphoric acid during the drying process, and can be formed without heating; using an organic solvent as the ball-milling liquid can reduce the oxidation of magnetic powder during the crushing process; moreover, phosphoric acid can also coat the magnetic powder to prevent oxidation. After the ball-milled slurry is cast and dried, a high-coercivity and high-performance magnet can be obtained.

[0046] (2) The method of the present invention has simple processes, low cost, high preparation efficiency, and is suitable for industrial production. Specific Embodiments

[0047] The technical solutions of the present invention will be further described below through specific embodiments.

[0048] Example 1

[0049] This example provides a method for preparing a magnet, including the following steps:

[0050] 1. Weighing and formulating

[0051] Weigh 100 parts by weight of samarium-iron-nitrogen magnetic powder, 5 parts by weight of silicone resin (alkoxy methyl silicone resin), 3 parts by weight of phosphoric acid (orthophosphoric acid with a mass fraction of 85%), 80 parts by weight of isopropyl alcohol, and 2 parts by weight of sorbitol.

[0052] 2. Ball-milling

[0053] Add the weighed materials into a ball mill and ball-mill for 5 h. During the ball-milling process, stirring and mixing are carried out evenly and grinding makes the particles finer. The particle size D50 of the ball-milled slurry is 2.05 μm.

[0054] 3. Casting

[0055] The slurry after ball milling is used for tape casting. During the treatment process, the stirring speed of the feeding system is 5 r / min, and the slurry is ensured to be uniform during tape casting through stirring. The feeding speed of the tape casting treatment is 0.5 m / min, and the blade gap of the tape casting treatment is 200 μm.

[0056] 4. Drying

[0057] After tape casting is completed, drying is carried out to obtain the magnet. Among them, the drying process uses air-blowing drying, and the air inlet and outlet volume is 0.25 m 3 / min. During the drying process, the silicone resin is cured to form the magnet.

[0058] Example 2

[0059] This example provides a method for preparing a magnet. The difference from Example 1 is that the silicone resin is adjusted to 2 parts by weight, and the rest is the same as Example 1.

[0060] Example 3

[0061] This example provides a method for preparing a magnet. The difference from Example 1 is that the silicone resin is adjusted to 10 parts by weight, and the rest is the same as Example 1.

[0062] Example 4

[0063] This example provides a method for preparing a magnet. The difference from Example 1 is that the phosphoric acid is adjusted to 1 part by weight, and the rest is the same as Example 1.

[0064] Example 5

[0065] This example provides a method for preparing a magnet. The difference from Example 1 is that the phosphoric acid is adjusted to 5 parts by weight, and the rest is the same as Example 1.

[0066] Example 6

[0067] This example provides a method for preparing a magnet. The difference from Example 1 is that the isopropanol is adjusted to 50 parts by weight, and the rest is the same as Example 1.

[0068] Example 7

[0069] This example provides a method for preparing a magnet. The difference from Example 1 is that the isopropanol is adjusted to 100 parts by weight, and the rest is the same as Example 1.

[0070] Example 8

[0071] This example provides a method for preparing a magnet. The difference from Example 1 is that except that the ball milling time is adjusted to 0.5 h, the rest is the same as Example 1.

[0072] Example 9

[0073] This embodiment provides a method for preparing a magnet. The difference from Embodiment 1 is that except that the ball milling time is adjusted to 12 h, the rest is the same as Embodiment 1.

[0074] Embodiment 10

[0075] This embodiment provides a method for preparing a magnet, including the following steps:

[0076] 1. Weigh the ingredients

[0077] Weigh 100 parts by weight of samarium-iron-nitrogen magnetic powder, 7 parts by weight of silicone resin (alkoxyphenyl oligomer), 4 parts by weight of phosphoric acid (orthophosphoric acid with a mass fraction of 85%), 85 parts by weight of absolute ethanol, and 1.5 parts by weight of calcium gluconate.

[0078] 2. Ball milling

[0079] Add the weighed materials into a ball mill and ball mill for 3 h. During the ball milling process, stirring and mixing are carried out evenly and grinding makes the particles finer. The particle size D50 of the slurry after ball milling is 2.39 μm.

[0080] 3. Casting

[0081] Use the slurry after ball milling for casting. During the process, the stirring speed of the feeding system is 10 r / min. Through stirring, the slurry is ensured to be uniform during casting. The feeding speed of the casting process is 1 m / min, and the blade gap of the casting process is 240 μm.

[0082] 4. Drying

[0083] After casting is completed, drying is carried out to obtain a magnet. Among them, the drying process uses hot air drying, and the air inlet and outlet volume is 0.3 m 3 / min. During the drying process, the silicone resin is cured to form the magnet.

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing a magnet. The difference from Embodiment 1 is that hot air drying at 100 °C is replaced, and the rest is the same as Embodiment 1.

[0086] Performance test:

[0087] Prepare the magnets of Embodiments 1 to 10 and Comparative Example 1 into standard cylinders with φ10*10, test the magnetic properties, and the data of the remanence Br, coercivity Hcj, and maximum magnetic energy product (BH)max are shown in Table 1.

[0088] Table 1

[0089]

[0090]

[0091] As can be seen from Table 1, the magnets prepared by the preparation method of the present invention have excellent properties and high coercivity. However, D1 uses heating for drying, resulting in a decrease in magnetic properties, especially coercivity. By comparing Example 1 with Examples 2-3, it can be seen that there is an optimal range for the dosage of silicone resin.

[0092] The applicant declares that the present invention uses the above examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a magnet, characterized in that, the preparation method comprises the following steps: Mixing magnetic powder, silicone resin, organic solvent and phosphoric acid and ball milling, casting and drying the slurry obtained by ball milling to obtain the magnet.

2. The method for preparing a magnet according to claim 1, characterized in that, the magnetic powder is samarium-iron-nitrogen magnetic powder; Preferably, the particle size D50 of the magnetic powder is 30 μm to 50 μm.

3. The method for preparing a magnetic sheet according to claim 1, characterized in that, the silicone resin includes at least one of methyl silicone resin, methyl / phenyl silicone resin, or propyl / phenyl silicone resin; Preferably, the dosage of the silicone resin is 2% to 10% of the weight of the magnetic powder.

4. The method for preparing a magnet according to any one of claims 1-3, characterized in that, the mass fraction of the phosphoric acid is 85%, and the dosage of the phosphoric acid is 1% to 5% of the weight of the magnetic powder.

5. The method for preparing a magnet according to any one of claims 1-4, characterized in that, the organic solvent is volatile and preferably includes at least one of anhydrous ethanol, acetone, isopropanol and methyl ethyl ketone; Preferably, the dosage of the organic solvent is 0.5 times to 1 times the weight of the magnetic powder.

6. The method for preparing a magnet according to any one of claims 1-5, characterized in that, in the preparation method, a dispersant is further included in the raw materials for mixing; Preferably, the dispersant includes at least one of calcium gluconate, sorbitol, castor oil, zinc stearate, sodium pyrophosphate and alkylaryl phosphate; Preferably, the dosage of the dispersant is 0.5% to 3% of the weight of the magnetic powder.

7. The method for preparing a magnet according to any one of claims 1-6, characterized in that, the ball milling time is 0.5 h to 12 h; Preferably, the particle size D50 of the slurry obtained after ball milling is 1.3 μm to 3.0 μm.

8. The method for preparing a magnet according to any one of claims 1-7, characterized in that, during the casting process, the slurry is stirred, and the stirring speed is 5 r / min to 15 r / min; Preferably, the feeding speed of the casting is 0.5 m / min to 2 m / min; Preferably, during the casting process, the blade gap is 100 μm to 300 μm; Preferably, the drying is air-blowing drying; Preferably, the air inflow and outflow volume of the air-blowing drying is 0.1 m 3 / min - 0.5 m 3 / min.

9. A magnet prepared by the preparation method according to any one of claims 1-8; Preferably, the magnet is a magnetic sheet, and the thickness of the magnetic sheet is 100 μm to 300 μm.

10. The use of a magnet as described in claim 9, characterized in that, the magnet is used in the fields of magnetic adsorption, packaging, display or sensors.

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