A bonded ferrite magnetic powder for calender molding, a method for producing the same, and use thereof

Abstract

The application provides a kind of adhesive ferrite magnetic powder for calendering and its preparation method and application, and relates to the technical field of ferrite material. Specifically, the preparation method comprises the following steps: mixing strontium carbonate, strontium chloride and iron red thoroughly, balling and obtaining material balls; dividing the material balls into first material balls and second material balls, and independently sintering and grinding the two, to obtain fine material balls with an average particle size of 0.2-0.4 microns and coarse material balls with an average particle size of 1.6-2.0 microns; mixing the fine material balls and coarse material balls in a mass ratio of 10-30:1, drying, then sequentially annealing and surface treating, and finally drying, crushing to obtain adhesive ferrite magnetic powder; the reagent for surface treatment comprises acetylene surfactant. The preparation method is simple and easy to operate, and the magnetic material prepared from the magnetic powder has very high remanence and intrinsic coercivity of the magnet, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of ferrite materials technology, and more specifically, to a bonded ferrite magnetic powder for calendering, its preparation method, and its application. Background Technology

[0002] In the field of bonded ferrite materials, calendered flexible magnets have been widely used in micromotors due to their high cost-effectiveness and high production efficiency. To adapt to the trend of miniaturization and increased efficiency in electronic appliances, higher requirements are placed on calendered magnets: First, to increase the torque of micromotors, calendered magnets need to provide higher air gap magnetic field strength, which requires higher remanence. Second, since magnets used in micromotors are mostly flat strips with a large demagnetization factor, and to increase the service life of micromotors and broaden their application areas, preventing demagnetization during frequent start-stop processes and under high and low temperature environments, magnets need to have higher intrinsic coercivity.

[0003] In calendered and bonded ferrite magnets, ferrite powder accounts for approximately 90% of the mass, and the properties of the powder directly affect the remanence and intrinsic coercivity of the magnet. Two representative current processes are provided below:

[0004] Chinese patent CN113690007A, entitled "A Rolled Permanent Magnet Ferrite Powder and its Rubber Products," discloses that the permanent magnet ferrite powder contains the metallic elements M, La, Fe, and Zn, where M is at least one of Sr and Ba, and its chemical formula can be expressed as M. 1- x La x Fe 2n-z Zn z Wherein, 0.01≤x≤0.30, 5.00≤n≤6.50, 0.5≤x / z≤1.70. The cumulative proportion of magnetic powder with a particle size distribution ≤3.0μm, Q3≥70.0%; and / or, the particle shape is plate-like, wherein the proportion of particles with a particle size-to-thickness ratio D / H between 2.0 and 4.0 is greater than 50%; by controlling the composition of ferrite magnetic powder, a magnetic powder with a suitable particle size-to-thickness ratio and excellent saturation magnetization is obtained. However, the technical drawback of this patent is that it requires the addition of rare earth metal lanthanum and strict control of powder particle size, resulting in high cost and weak industrial feasibility. Due to the proportion of certain plate-like magnetic powder being greater than 50%, the remanence index of its rolled magnet is 2832Gs, but its intrinsic coercivity index is low (3182Oe), which is lower than the level of 3890Oe of the prior art.

[0005] Chinese patent CN107399964A, entitled "A Method for Preparing Bonded Ferrite Magnetic Powder," describes a method that involves mixing a strontium-containing compound and / or a barium-containing compound with iron oxide to obtain a mixture. This mixture is then sintered to obtain a sintered material. The sintered material is ground and sieved to obtain coarse powder. This coarse powder is then finely ground into a slurry to obtain fine powder. An alcohol amine mixture is added to the fine powder and mixed thoroughly to obtain ferrite magnetic powder. Finally, the obtained ferrite magnetic powder is annealed to obtain bonded ferrite magnetic powder. This invention shortens the process route (eliminating the need for acid washing), has lower requirements for raw material purity (especially chlorine content), allows for a wider range of raw material sources, and reduces the difficulty of process control, significantly saving costs. Simultaneously, the resulting bonded ferrite magnetic powder exhibits high performance, with a remanent magnetic flux density as high as 273 mT, intrinsic coercivity as high as 310 kA / m, and maximum energy product as high as 13.8 kJ / m. 3 However, the technical drawback of this patent is that it requires secondary ball milling to add elements such as lanthanum and zinc, and the remanence index of the magnet is low (273mT), which is lower than the level of 283mT in the prior art.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a method for preparing bonded ferrite magnetic powder for calendering. The process is simple and easy to implement, suitable for mass production, and the magnetic material obtained by the magnetic powder of this invention has both high remanence and intrinsic coercivity.

[0008] The method for preparing the bonded ferrite magnetic powder for calendering includes the following steps:

[0009] (a) Strontium carbonate, strontium chloride and iron oxide are thoroughly mixed, and pelletized to obtain pellets;

[0010] (b) The pellets are divided into first pellets and second pellets, and the first pellets and the second pellets are sintered and ground independently to obtain fine pellets with an average particle size of 0.2μm to 0.4μm and coarse pellets with an average particle size of 1.6μm to 2.0μm.

[0011] (c) The fine granules and coarse granules are mixed in a mass ratio of 10% to 30%:1, dried, and then subjected to annealing and surface treatment in sequence. After drying and crushing, the bonded ferrite magnetic powder is obtained. The surface treatment reagents include acetylene surfactants.

[0012] The second objective of this invention is to provide a bonded ferrite magnetic powder, which is prepared by the aforementioned method for preparing bonded ferrite magnetic powder for calendering.

[0013] A third objective of this invention is to provide a ferrite material prepared using the aforementioned bonded ferrite magnetic powder.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) The present invention combines iron oxide red and strontium carbonate with a low molar ratio and a low temperature sintering process to produce ferrite particles that are micro-flaky, which is beneficial for mechanical orientation on the rolls of a rolling mill.

[0016] (2) The present invention uses two independent sintering and grinding processes to obtain flaky granular materials of different particle sizes and mixes them to improve the compressibility of magnetic powder; under the same magnetic powder and binder volume ratio, more magnetic powder can be filled than conventional processes; while ensuring mechanical properties, the mass ratio of magnetic powder in the magnet is increased (it can reach more than 91%, while the existing technology level is generally less than 90%), thereby improving the performance of the magnet.

[0017] (3) The present invention contains a certain proportion of low-temperature pre-calcined fine powder, which can effectively improve the intrinsic coercivity of the ferrite magnetic powder as a whole, thereby making the intrinsic coercivity index of the magnet exceed the current process level.

[0018] (4) The present invention uses a specific surface treatment reagent to treat the ferrite magnetic powder, which increases the dispersion of the powder in the binder during the subsequent mixing process, which is beneficial to the rolling and orientation of the magnetic powder, thereby improving the performance of the magnet. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0020] It is difficult to obtain ferrite magnetic powder with both high remanence and high intrinsic coercivity in existing technologies. Regarding the remanence of magnets, since calendered magnets mainly rely on the rolling force of the calender rolls for mechanical orientation to ensure remanence, two requirements are necessary: ​​First, the ferrite magnetic powder must have a high flake shape. Under the rolling force of the rolls, the easy magnetization axes of the flake-shaped magnetic powder align in the same direction, thus giving the magnet high remanence. Second, the ferrite magnetic powder must have a high compressibility density to achieve a smaller volume percentage of the same mass percentage of magnetic powder in the binder, thereby further increasing the mass ratio of magnetic powder to binder and improving remanence while maintaining the mechanical properties of the magnet.

[0021] However, the current technical problem is that after improving the sheet shape of the magnetic powder, during the compression process, the sheet-like magnetic powder will form a "bridging" state, resulting in gaps between the magnetic powder particles. This leads to a decrease in compression density, which in turn reduces the volume ratio of the magnetic powder in the magnet, thus reducing the magnetic properties. This creates a contradictory relationship between improving the sheet shape and compression density of the magnetic powder.

[0022] Regarding the intrinsic coercivity of magnets, due to the shearing and friction between materials during the mixing and molding process of magnetic powder and binder, the intrinsic coercivity of magnets will be lost to a certain extent. Under certain magnet molding process conditions, the level of intrinsic coercivity of magnets is positively related to the intrinsic coercivity of magnetic powder.

[0023] However, the current technical problem is that in order to improve the coercivity of magnetic powder, the method of refining the grains is often used, that is, to refine the ferrite magnetic powder particles by long-term grinding. However, this treatment method increases the specific surface area of ​​the magnetic powder, which leads to a decrease in the compressive density of the magnetic powder. This is reflected in the magnet surface as an increase in hardness, making it difficult to mix and form, making it difficult to orient the magnetic powder, and making it impossible to achieve high remanence.

[0024] The present invention achieves the above-mentioned technical problems through the following specific embodiments: a method for preparing bonded ferrite magnetic powder for calendering, comprising the following steps:

[0025] (a) Strontium carbonate, strontium chloride, and iron oxide are thoroughly mixed, pelletized, and then pelletized to obtain granules; (b) The granules are divided into first granules and second granules, and the first and second granules are sintered and ground independently to obtain fine granules with an average particle size of 0.2 μm to 0.4 μm and coarse granules with an average particle size of 1.6 μm to 2.0 μm; (c) The fine granules and the coarse granules are mixed in a mass ratio of 10% to 30%:1, dried, and then annealed and surface treated sequentially. After drying and crushing, bonded ferrite magnetic powder is obtained; the surface treatment reagents include acetylene surfactants.

[0026] In a preferred embodiment, the molar ratio of the iron oxide red to the strontium carbonate is 4 to 7:1; in an optional embodiment, the molar ratio of the iron oxide red to the strontium carbonate includes, but is not limited to, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, and 7:1.

[0027] In a preferred embodiment, the mass ratio of strontium chloride to iron oxide red is 2.5% to 5.5%; in an optional embodiment, the mass ratio of strontium chloride to iron oxide red includes, but is not limited to, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, and 5.5%.

[0028] In a preferred embodiment, the strontium carbonate, the strontium chloride, and the iron oxide are all of industrial grade purity, i.e., the purity of all three is ≥98.5%.

[0029] In a preferred embodiment, the sintering temperature of the first material ball is 900℃~970℃, and the sintering time of the first material ball is 1h~3h; the fine-grained material ball is obtained after the first material ball is sintered and ground; in an optional embodiment, the sintering temperature of the first material ball includes, but is not limited to, 900, 910, 920, 930, 940, 950, 960, 970 (℃), and the sintering time of the first material ball includes, but is not limited to, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.4, 2.5, 2.8, 3 (h).

[0030] In a preferred embodiment, the sintering temperature of the second material ball is 1000℃~1150℃, and the sintering time of the second material ball is 1h~3h; the coarse material ball is obtained after the second material ball is sintered and ground; in an optional embodiment, the sintering temperature of the second material ball includes, but is not limited to, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1100, 1110, 1120, 1130, 1140, 1150 (℃), and the sintering time of the second material ball includes, but is not limited to, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.4, 2.5, 2.8, 3 (h).

[0031] In one preferred embodiment, the annealing process includes the following steps: placing the mixture of the coarse granules and the fine granules in an environment with a temperature of 950℃~980℃ for 1h~3h, and then air-cooling it to room temperature; in another preferred embodiment, the standing time is 1.5h.

[0032] In a preferred embodiment, the surface treatment reagent includes acetylene ethanol and / or acetylene ethylene glycol. This invention employs a specific type of surface treatment reagent to treat the magnetic powder, which can improve the dispersibility of the magnetic powder in the binder during subsequent preparation. During the mixing and calendering process of the magnetic powder and binder, it facilitates the mechanical orientation of the sheet-like magnetic powder during calendering, reduces damage caused by mutual compression and friction of the powder during mixing and calendering, and reduces the loss of intrinsic coercivity of the powder during mixing, thereby improving the intrinsic coercivity of the magnet to a certain extent.

[0033] As a more preferred embodiment, the surface treatment reagent is PD-201 (brand name) manufactured by Nissin Chemical Industries, Ltd. PD-201 contains acetylene glycol, which is a wetting surfactant; it is characterized by providing wetting while also having an antifoaming effect, and is tasteless, odorless, has good water resistance, and low water absorption.

[0034] It should be noted that the surface treatment reagents used in this invention should have good dispersibility or water solubility in water to facilitate production operations.

[0035] In a preferred embodiment, the surface treatment is performed simultaneously with pickling, comprising the following steps: immersing the mixture after the annealing treatment in a solvent, wherein the solvent includes a surface treatment reagent, hydrochloric acid, and water;

[0036] In a more preferred embodiment, the pH of the solvent is 6 to 7.

[0037] In a more preferred embodiment, the mass concentration of hydrochloric acid in the solvent is 1.5% to 3%, and the mass concentration of the surface treatment reagent in the solvent is 1.5% to 3%.

[0038] Example 1

[0039] (1) Manufacturing of fine powder

[0040] Iron oxide and strontium carbonate were weighed according to a molar ratio of 5.5:1, and strontium chloride (4% by weight of iron oxide) was also weighed. After being mixed evenly, an appropriate amount of water was added, and the mixture was passed through a pelletizer to obtain pellets with a diameter of 5-10 mm. The pellets were then dried in an oven at 130°C, sintered in an electric furnace at 920°C for 2 hours, crushed by a jaw crusher, and then ball-milled for 8 hours using a JM-2L wet ball mill. After drying, fine powder with an average particle size of 0.2 micrometers was obtained.

[0041] (2) Coarse powder manufacturing

[0042] The pellets obtained in step (1) were dried in an oven at 130 degrees Celsius. The dried pellets were then sintered in an electric furnace at 1100 degrees Celsius for 2 hours and ball-milled in a JM-2L wet ball mill for 2 hours. After drying, coarse powder with an average particle size of 2.0 micrometers was obtained.

[0043] (3) Magnetic powder manufacturing

[0044] After mixing 10 wt.% fine powder and 90 wt.% coarse powder evenly, the mixture is placed in an electric furnace at a temperature of 950℃~980℃ for annealing. Then, it is pickled and surface treated with a 2% hydrochloric acid aqueous solution and a 2% dispersant PD-201 aqueous solution to maintain its pH value at 6~7. Finally, it is crushed and used as the final product, magnetic powder.

[0045] (4) Manufacturing of bonded ferrite

[0046] 91 parts by weight of mixed magnetic powder, 5.0 parts by weight of binder chlorinated polyethylene, 0.5 parts by weight of lubricant stearic acid, 0.5 parts by weight of titanate coupling agent, and 3.0 parts by weight of plasticizer epoxidized soybean oil were mixed evenly and then kneaded evenly in a mixer at 120-130 degrees Celsius. The evenly mixed material was pressed into sheet-like plates with a thickness of 2.0-3.0 mm on the rolls of a calender at a roll temperature of 80-90 degrees Celsius. The plates were then pressed into sheet-like magnets with a thickness of 1.9-2.1 mm on the rolls of a calender at a roll temperature of 30-40 degrees Celsius. The magnetic properties were tested and the values ​​were recorded.

[0047] Example 2

[0048] It is basically the same as Example 1, except that in step (3), 30 wt.% of fine powder and 70 wt.% of coarse powder are mixed evenly.

[0049] Example 3

[0050] The process is basically the same as in Example 1, except that in step (1), the dried pellets are sintered in an electric furnace at 950 degrees Celsius for 2 hours, then crushed by a jaw crusher, and then ball-milled in a JM-2L wet ball mill for 6 hours to obtain fine powder with an average particle size of 0.4 micrometers. In step (2), the dried pellets are sintered in an electric furnace at 1050 degrees Celsius for 2 hours, and then ball-milled in a JM-2L wet ball mill for 3 hours to obtain coarse powder with an average particle size of 1.6 micrometers.

[0051] Example 4

[0052] It is basically the same as Example 3, except that in step (3), 30 wt.% of fine powder and 70 wt.% of coarse powder are mixed evenly.

[0053] Example 5

[0054] The process is basically the same as in Example 1, except that in step (2), the dried pellets are sintered in an electric furnace at 1050 degrees Celsius for 2 hours and then ball-milled in a JM-2L wet ball mill for 3 hours to obtain coarse powder with an average particle size of 1.6 micrometers.

[0055] Example 6

[0056] It is basically the same as Example 5, except that in step (3), 30 wt.% of fine powder and 70 wt.% of coarse powder are mixed evenly.

[0057] Example 7

[0058] The process is basically the same as in Example 1, except that in step (1), the dried pellets are sintered in an electric furnace at 950 degrees Celsius for 2 hours, then crushed by a jaw crusher, and then ball-milled for 6 hours by a JM-2L wet ball mill to obtain fine powder with an average particle size of 0.4 micrometers.

[0059] Example 8

[0060] It is basically the same as Example 7, except that in step (3), 30 wt.% of fine powder and 70 wt.% of coarse powder are mixed evenly.

[0061] Comparative Example 1

[0062] It is basically the same as Example 1, except that the dispersant PD-201 was not used in step (3).

[0063] Comparative Example 2

[0064] It is basically the same as Example 1, except that in step (3), 0 wt.% fine powder and 100 wt.% coarse powder are mixed evenly.

[0065] Comparative Example 3

[0066] It is basically the same as Example 1, except that in step (3), 40 wt.% of fine powder and 60 wt.% of coarse powder are mixed evenly.

[0067] The test results of the magnetic and mechanical properties of the magnets prepared in the above embodiments and comparative examples are shown in Tables 1 and 2 below.

[0068] Table 1

[0069]

[0070] Table 2

[0071]

[0072]

[0073] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for producing a bonded ferrite magnetic powder for calender molding, characterized by comprising the steps of: The preparation method comprises the following steps: ​ (a) mixing strontium carbonate, strontium chloride and iron red thoroughly, performing balling treatment and obtaining material balls; (b) dividing the material balls into first material balls and second material balls, independently performing sintering and grinding treatment on the first material balls and the second material balls, and obtaining fine material balls with an average particle size of 0.2 μm to 0.4 μm and coarse material balls with an average particle size of 1.6 μm to 2.0 μm; (c) mixing the fine material balls and the coarse material balls according to a mass ratio of 10% to 30%:1, performing annealing treatment and surface treatment in sequence after drying, and then performing drying and crushing to obtain bonded ferrite magnetic powder; the reagent for surface treatment comprises an acetylene surfactant, and the reagent for surface treatment comprises acetylene alcohol and / or acetylene glycol.

2. The method of producing a bonded iron oxide magnetic powder for calender molding according to claim 1, characterized by, The molar ratio of the iron red to the strontium carbonate is 4 to 7:1; And / or, the mass ratio of the strontium chloride to the iron red is 2.5% to 5.5%.

3. The method of producing a bonded iron oxide magnetic powder for calender molding according to claim 1, characterized by, The sintering temperature of the first material balls is 900°C to 970°C, and the sintering time of the first material balls is 1h to 3h; The first material balls are subjected to sintering and grinding treatment to obtain the fine material balls.

4. The method of producing a bonded iron oxide magnetic powder for calender molding according to claim 1, characterized by, The sintering temperature of the second material balls is 1000°C to 1150°C, and the sintering time of the second material balls is 1h to 3h; The second material balls are subjected to sintering and grinding treatment to obtain the coarse material balls.

5. The method of producing a bonded iron oxide magnetic powder for calender molding according to claim 1, characterized by, The annealing treatment comprises the following steps: After the mixed material of the coarse material balls and the fine material balls is placed in an environment with a temperature of 950°C to 980°C for 1h to 3h, air cooling is performed to room temperature.

6. The method of producing a bonded iron oxide magnetic powder for calender molding according to claim 1, characterized by, The surface treatment is performed simultaneously with pickling treatment, which comprises the following steps: The mixed material after the annealing treatment is soaked in a solvent, and the solvent comprises a surface treatment reagent, hydrochloric acid and water; The pH of the solvent is 6 to 7.

7. The method of producing a bonded iron oxide magnetic powder for calender molding according to claim 6, characterized in that, The mass concentration of hydrochloric acid in the solvent is 1.5% to 3%, and the mass concentration of the surface treatment reagent in the solvent is 1.5% to 3%.

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