JP7428069B2 - Manufacturing method of bonded magnet - Google Patents

Description

The present invention relates to a method for manufacturing a bonded magnet.

Bonded magnets are made by mixing magnetic powder with a binder and solidifying it, and they can be manufactured into complex shapes more easily than sintered magnetic powder, and they require high temperatures (sintering) during manufacturing. It has the characteristics that it does not require heating to a temperature of around 1000°C (for a magnet) and that it is less likely to crack or chip.

Conventional bonded magnets often use resins such as phenol resins and epoxy resins as binders. However, while automobile motors, for example, reach temperatures of 150 to 180 degrees Celsius during use, bonded magnets with binders such as phenolic resin or epoxy resin do not have heat resistance at such temperatures. It cannot be used as a motor magnet. Therefore, in the bonded magnet described in Patent Document 1, polyphenylene sulfide (PPS) resin is used as the binder. Since PPS has a melting point of about 280° C., bonded magnets using PPS resin as a binder have heat resistance in the temperature range when used in automobile motors.

Japanese Patent Application Publication No. 2017-212308

When producing a bonded magnet using PPS resin as a binder, the PPS resin is heated and melted and then molded. However, when PPS resin is heated to such temperatures, it gradually decomposes and generates toxic gas consisting of molecules containing sulfur atoms. Therefore, this bonded magnet has low safety during manufacture.

The problem to be solved by the present invention is to provide a method that can safely produce a bonded magnet that has heat resistance at temperatures of 150 to 180°C, which is required for applications such as automobile motors.

A method for manufacturing a bonded magnet according to the present invention, which has been made to solve the above problems, includes:
Production of a bonded magnet material by mixing magnet powder and an aggregate of cellulose nanofibers containing water, or by mixing magnet powder, an aggregate of cellulose nanofibers, and water. process and
The preform is formed by accommodating the bonded magnet material in a cavity of a mold and applying a first pressure to the bonded magnet material with a piston having a gap of a predetermined size between it and the inner surface of the cavity. A preformed body production process to be produced;
a relaxation step of releasing the application of the first pressure and leaving it for a predetermined time;
After the relaxation step, the method is characterized by including a molded body manufacturing step of manufacturing a molded body by applying a second pressure equal to or higher than the first pressure to the preformed body using the piston.

A bonded magnet manufactured by the method according to the present invention contains magnet powder and a binder made of cellulose nano fiber (hereinafter referred to as "CNF") that binds the particles of the magnet powder to each other. Here, CNF is a fiber made of cellulose, and can be produced by finely disentangling a material containing cellulose such as wood pulp. The aggregate of CNF produced by such a method is usually in a state containing water (hereinafter, an aggregate of CNF containing water is referred to as "cellulose nanofiber-water mixture", and further abbreviated as "CNF-water mixture"). Although it is sold as a "water mixture"), development of dried CNF from which water has been separated is also underway. CNF has at least heat resistance at temperatures below 200°C, which is higher than the 150 to 180°C required for applications such as automobile motors.

In the method for manufacturing a bonded magnet according to the present invention, a bonded magnet material prepared by mixing magnet powder and a CNF-water mixture, or by mixing magnet powder, an aggregate of CNF, and water is placed in a mold. A preform is produced by placing the bonded magnet material in a cavity and applying a first pressure to the bonded magnet material with a piston. Here, the piston has a gap of a predetermined size between it and the inner surface of the cavity. Pressure is defined as the force applied by the piston to the magnetic material divided by the area of the piston in contact with the magnetic material. The predetermined size may be, for example, a value smaller than the particle size of most of the particles (for example, 95% or more of all particles) contained in the magnet powder, or an average value or median value of the particle size. Can be done.

By applying this first pressure, a portion of the water contained in the bonded magnet material passes through the gap and is discharged out of the mold. As a result, water is removed from the bonded magnet material, the CNF solidifies, and the bonded magnet material becomes a preform. However, due to the internal friction of the bonded magnet material, the vicinity of the piston becomes a high-density area where the density of magnet powder and CNF is higher than other areas (there is less water), and the preform has an internally uneven density. It is in a state. In addition, in the preform production process, some CNF is discharged out of the mold together with water, but most of the CNF is sandwiched between particles of magnet powder and remains inside the preform without being discharged. remain.

In the next relaxation step, the application of the first pressure is released. By leaving the preform in this state for a predetermined period of time, water in the interior of the preform other than the high density portion permeates into the high density portion, thereby homogenizing the density inside the preform.

Note that during this relaxation process, it is preferable to eliminate the clogging of the gap by removing deposits containing CNF and small-sized magnet powder that have adhered to the inner surface of the cavity and the surface of the piston.

Thereafter, by applying a second pressure to the preformed body using the piston, water contained in the preformed body is discharged out of the mold through the gap, thereby producing a molded body. This reduces the amount of water remaining in the preform, and as the water is removed, the CNF further hardens, increasing the density of the preform as a whole, resulting in a molded body. This suppresses the occurrence of cracks and cracks in the molded body. Furthermore, since the density is higher than that of the preform, the magnetic properties can be improved.

As described above, by the method according to the present invention, a bonded magnet including a binder made of CNF and having heat resistance at temperatures of 150 to 180° C. can be safely manufactured without generating toxic gas.

In addition, in recent years, it has become a problem that plastics contained in waste materials remain for a long period of time without being decomposed, which adversely affects the environment. While conventional bonded magnets use plastics such as phenol resin, epoxy resin, and PPS resin as binders, bonded magnets manufactured by the method of the present invention use CNF as a non-plastic material. It is possible to suppress the negative impact on the environment during disposal.

In the method for manufacturing a bonded magnet according to the present invention, if the mass ratio of water in the bonded magnet material is too low, it will be difficult to mix CNF and magnet powder, while if it is too high, the shape of the molded object will become too soft. becomes difficult to hold. Taking these points into consideration, in the present invention, the water content in the bonded magnet material is preferably 2 to 28% by mass.

Additionally, if the amount of CNF relative to water is too large, a mixture of CNF and water with high viscosity will be formed between the particles of magnet powder when producing a bonded magnet material, making it difficult to mix the mixture with magnet powder. On the other hand, if the amount is too small, it becomes difficult to maintain the shape of the molded article. Therefore, it is desirable that the content of CNF to the total of CNF and water is 5 to 15% by mass.

It is desirable that the second pressure be higher than the first pressure. Thereby, the molded body can be molded more reliably and the density can be increased.

The magnet powder includes an RFeB-based magnet whose main constituent elements are rare earth elements (referred to as "R"), iron (Fe), and boron (B) (in particular, an NdFeB-based magnet whose main constituent elements are neodymium (Nd) as R). SmFeN magnet powder whose main constituent elements are samarium (Sm), iron and nitrogen (N), SmCo magnet powder whose main constituent elements are samarium and cobalt (Co), etc. be able to. In particular, SmFeN magnet powder has higher corrosion resistance to water than RFeB magnet powder, so it can be suitably used.

In the method for manufacturing a bonded magnet according to the present invention, it is preferable to further perform a drying step of drying the molded body after the molded body production step. Thereby, water remaining in the binder can be removed and the density of the molded body can be increased.

According to the present invention, it is possible to safely produce a bonded magnet that has heat resistance at temperatures of 200° C. or lower, which is higher than the 150 to 180° C. required for applications such as automobile motors.

1 is a schematic diagram showing an embodiment ((a) to (h)) of a method for manufacturing a bonded magnet according to the present invention and an example ((i)) of a structure of a manufactured bonded magnet. Photographs taken from above (a-1) and from the side (a-2) of the bonded magnet manufactured by the method of this embodiment, and from above (b-1) and from the side (b-1) of the bonded magnet manufactured by the method of the comparative example. Photo taken from side (b-2).

An embodiment of a method for manufacturing a bonded magnet according to the present invention will be described with reference to FIGS. 1 and 2.

FIGS. 1(a) to (h) show the overall flow of the bonded magnet manufacturing method of this embodiment, and FIG. 1(i) shows the configuration of an example of a bonded magnet 20 manufactured by the method of this embodiment. .

In the bonded magnet manufacturing method of this embodiment, first, a bonded magnet material 13 is manufactured by mixing magnet powder 11, CNF 121, and water 122 as described below (FIGS. 1(a) to (c): bonded magnet material production process). Here, we will show an example using a commercially available cellulose nanofiber-water mixture (CNF-water mixture) 12 (same (b)) in which CNF 121 and water 122 are mixed in advance, but in a state in which CNF 121 and water 122 are separated. It may be mixed with the magnet powder 11.

As the magnet powder 11 (FIG. 1(a)), RFeB magnet powder, SmFeN magnet powder, SmCo magnet powder, etc. can be used. Among these, SmFeN magnet powder is superior in that it is difficult to oxidize and does not require the use of Co, which is more expensive than Fe. The method for producing the magnet powder 11 is the same as the method used to produce conventional bonded magnets, so the explanation will be omitted.

CNF-water mixture 12 (FIG. 1(b)) is sold by Sugino Machine Co., Ltd. under the trade name "BiNFi-s" (registered trademark). The content of CNF121 in the CNF-water mixture 12 (the proportion of CNF in the mass of the CNF-water mixture 12) is preferably within the range of 5 to 25% by mass. If this content exceeds 25% by mass, the viscosity of the CNF-water mixture 12 becomes too high, making it difficult to mix the magnet powder 11 and the CNF-water mixture 12. Furthermore, if this content is less than 5% by mass, the viscosity of the CNF-water mixture 12 becomes too low, making it difficult to mold it. For example, the above-mentioned "BiNFi-s" is sold as a standard product with a CNF content of 5% by mass and 10% by mass, and these can be used as the CNF-water mixture 12 of the present embodiment. Furthermore, by heating, freezing, or centrifugally concentrating standard products and separating a portion of the water, a CNF-water mixture 12 having a higher CNF content than those of these standard products can be obtained.

By mixing the magnet powder 11 prepared as described above and the CNF-water mixture 12 (FIG. 1(b)), a bonded magnet material 13 is obtained (FIG. 1(c)). At that time, the magnet powder 11 and the CNF-water mixture 12 are mixed so that the mass ratio of the water 122 to the mass of the bonded magnet material 13 (water content of the bonded magnet material 13) is within the range of 2 to 28% by mass. It is desirable to adjust the mass. If this ratio is too low, it will be difficult to mix the magnet powder 11 and CNF 121, while if this ratio is too high, molding will be difficult.

Next, after filling a mold 141 with the bonded magnet material 13, a first pressure is applied to the bonded magnet material 13 with a piston (punch) 142 using a press machine (not shown) (see FIG. 1(d)), the preform 15 is produced (preform production step). At that time, a gap 143 of a predetermined size is provided between the cavity of the mold 141 and the piston 142. The size of the gap 143 can be set, for example, to a value smaller than the particle size of 95% or more of the particles contained in the magnet powder, or to the average value or median value of the particle sizes. The first pressure can be, for example, 1.0 to 2.2 GPa (approximately 10 to 22 tonf/cm ² ), but is not limited to these ranges.

By applying the first pressure, a portion of the water 122 contained in the bonded magnet material 13 passes through the gap 143 and is discharged out of the mold 141, thereby obtaining the preform 15. At this time, since the gap 143 is set as described above, the particles of the magnet powder 11 will not leak out of the mold 141 through the gap 143, except for some particles with small particle sizes. do not have. Further, since the CNF 121 is sandwiched between the particles of the magnet powder 11, it hardly leaks out of the mold 141 through the gap. Inside the preform 15, a high-density portion is formed near the piston 142 where there is less water 122 and the density of the magnet powder 11 and CNF 121 is higher than in other locations, and the density is non-uniform.

Subsequently, the first pressure is released and left for a predetermined period of time (for example, several seconds to several minutes) (FIG. 1(e): relaxation step). There is no need to remove the preform 15 from the cavity of the mold 141 after this first pressure is released. When the first pressure is released, water in the parts other than the high-density part penetrates into the high-density part inside the preform 15, and the density becomes homogenized. However, the moment the first pressure is released, cracks 151 or cracks may occur in the preform 15. This is because liquid water is generally difficult to compress (low compressibility), so when a high pressure of 1.0 to 2.2 GPa is applied as in this embodiment, the powder (magnetic powder 11 and CNF 121) and water 122 This is because there is a difference in the amount of expansion between the two.

Note that during the relaxation process, it is preferable to remove deposits that have adhered to the inner surface of the cavity of the mold 141 and the surface of the piston 142. This deposit includes water discharged from the bonded magnet material 13, smaller particles of the magnet powder 11, or a portion of the CNF 121. By removing such deposits, clogging of the gap 143 can be prevented.

Next, a second pressure is applied to the preform 15 in the cavity of the mold 141 by the piston 142 using a press machine (not shown) (FIG. 1(f)). (g)) is produced (molded body production process). As a result, the water contained in the preformed body 15 is discharged from the mold 141 through the gap 143, and the density of the whole becomes high, thereby forming the molded body 16. By increasing the density in this way, the magnetic properties can be made higher than that of the preformed body 15. Furthermore, when a second pressure is applied to the preformed body 15 in which cracks or cracks have occurred during preforming, the water 122 that has been homogenized within the preformed body 15 is further removed, the CNF 121 hardens, and the preformed body 15 is A molded body 16 in which generated cracks and cracks have been repaired is obtained.

A portion of the water contained in the bonded magnet material 13 still remains in the obtained molded body 16 to the extent that it does not affect the shape of the molded body 16. Therefore, in this embodiment, a step of evaporating water 122 from the molded body 16 is further performed (FIG. 1(h)). At that time, the molded body 16 may be left to stand while being maintained at room temperature, or the molded body 16 may be heated. When heating the molded body 16, it is desirable that the heating temperature be 200° C. or less so that the CNF 121 is not affected by the heat. Alternatively, the water 122 may be gradually evaporated by placing the molded body 16 in a vacuum (under reduced pressure) or in an inert gas, regardless of whether or not heating is performed.

Through the above operations, a bonded magnet 20 is obtained (FIG. 1(i)). The bonded magnet 20 includes particles 21 of magnetic powder and a binder 22 made of CNF that binds the particles 21 of the magnetic powder.

Next, the results of an experiment in which a bonded magnet was manufactured using the method of this embodiment will be shown. In this experiment, powder of SmFeN magnets (Examples 1 to 7, 9, and 10) or NdFeB magnets (Example 8) was used as the magnet powder 11. The method for producing the magnet powder 11 of the SmFeN magnet is as follows. First, an alloy containing each element except N is melted so that Sm: 19.30 mass%, Zr: 1.65 mass%, Co: 3.95 mass%, Al: 0.30 mass%, N: 3.29 mass%, and Fe: the balance. Then, the obtained molten metal was dropped onto a roll using a single-roll ultra-quenching device and quenched, thereby producing ribbon-shaped flake powder. This flake powder is ground with a pin mill and classified using a sieve with an opening of 150 μm. Thereafter, the magnet powder 11 of the SmFeN magnet was obtained by nitriding by heating in a gas containing molecules having nitrogen atoms (in this example, a mixed gas of ammonia and hydrogen). The method for producing the magnetic powder 11 of the NdFeB magnet is based on the fact that the composition of the raw material alloy is different (Nd: 24.8% by mass, Pr: 0.84% by mass, B: 0.92% by mass, Fe: the balance) and molecules having nitrogen atoms. The method for producing the magnet powder 11 of the SmFeN magnet is the same as that of the SmFeN magnet powder 11, except that heating in a gas containing SmFeN is not performed. The content of CNF in the CNF-water mixture 12 was 10% by mass. The moisture content in the bonded magnet material 13 was within the range of 2.0 to 23.2% by mass. The content of the magnet powder 11 in these bonded magnet materials 13 is 74.2 (when the water content is 23.2% by mass) to 97.8 (when the moisture content is 2.0% by mass) by mass.

In Examples 1 to 8, first pressure and second pressure having the magnitudes listed in Table 1 below were applied to bonded magnet materials 13 having various compositions listed in Table 1 below. In Examples 9 and 10, a pressure of 2.0 GPa was applied to the bonded magnet material 13 having the same composition as shown in Table 2 below for the number of times shown in the table. The first pressure corresponds to the first pressure, the second pressure corresponds to the second pressure, and the third and subsequent pressures are additionally applied pressures. Table 2 also shows Comparative Example 4 (described later) in which a pressure of 2.0 GPa was applied only once to the bonded magnet material 13 having the same composition as Examples 9 and 10, and Comparative Example 4 (described later) in which a pressure of 2.0 GPa was applied only once. The experimental results of Example 3, in which the voltage was applied twice, are shown in Table 1 in duplicate.

In addition, as Comparative Examples 1 to 4, bonded magnet materials 13 having the same composition as Examples 1 and 2 or Example 3 shown in Table 1 below were subjected to the pressure shown in Table 1 at 1 A bonded magnet was produced by applying the voltage only once.

Regarding the bonded magnets obtained in these Examples and Comparative Examples, the molding state, the density of the bonded magnet, and the magnetic properties at room temperature are shown in Tables 1 and 2 together with the material and pressure conditions described above. Here, the molding condition was visually checked and those with cracks and/or cracks were rated "x", and those with no cracks were rated "○". Regarding magnetic properties, residual magnetic flux density B _r , coercive force H _cJ , and maximum energy product (BH) _max were measured for samples with no cracks or cracks.

According to these experimental results, although bonded magnets were obtained in Comparative Examples 1 and 2 without any cracks or cracks, the applied pressure was small, so the density after drying was lower than in the Examples, and as a result, The residual magnetic flux density B _r and the maximum energy product (BH) _max become low. Moreover, in Comparative Examples 3 and 4, cracks and cracks occur in the obtained bonded magnets. FIG. 2(b) shows a photograph (b-1) taken from the top and a photograph (b-2) taken from the side of the bonded magnet manufactured in Comparative Example 4. From this photograph, it can be seen that in Comparative Example 4, cracks were generated in the bonded magnet.

On the other hand, all of Examples 1 to 7, 9, and 10, which were manufactured using the same type of (SmFeN-based) magnet powder 11 as Comparative Examples 1 to 4, had a higher residual magnetic flux density B _r than Comparative Examples 1 and 2. A bonded magnet with a high maximum energy product (BH) _max was obtained without any cracks or cracks. FIG. 2(a) shows a photograph (a-1) taken from the top of the bonded magnet produced in Example 2, and a photograph (a-2) taken from the side. In Example 2, after applying a pressure lower than the pressure applied to the bonded magnet material 13 in Comparative Example 4 (the pressure of Comparative Example 4) as a first pressure, the same pressure as that of Comparative Example 4 was applied to a second pressure. It was applied as pressure. From the photograph in FIG. 2(a), it can be seen that in Example 2, a bonded magnet was obtained without any cracks or cracks.

From the results of Examples 3, 9, and 10, the density after drying increases as the number of times pressure is applied increases, and the residual magnetic flux density B _r and the maximum energy product (BH) _max increase accordingly. Recognize.

In Example 8, NdFeB-based powder instead of SmFeN-based powder was used as the magnet powder 11, and a bonded magnet was obtained without any cracks or cracks as in Examples 1-7, 9, and 10. However, the magnetic properties of Examples 1 to 7, 9, and 10 using SmFeN-based magnet powder 11 are higher than that of Example 8.

11... Magnet powder 12... CNF (cellulose nanofiber)-water mixture 121... CNF (cellulose nanofiber)
122...Water 13...Bond magnet material 141...Mold (molding die)
142...Piston (punch)
143... Gap between mold cavity and piston 15... Preformed body 16... Molded body 20... Bonded magnet 21... Magnet powder particles 22... Binder

Claims (6)

Production of a bonded magnet material by mixing magnet powder and an aggregate of cellulose nanofibers containing water, or by mixing magnet powder, an aggregate of cellulose nanofibers, and water. process and
The preform is formed by accommodating the bonded magnet material in a cavity of a mold and applying a first pressure to the bonded magnet material with a piston having a gap of a predetermined size between it and the inner surface of the cavity. A preformed body production process to be produced;
a relaxation step of releasing the application of the first pressure and leaving it for a predetermined time;
After the relaxation step, a molded body manufacturing step is performed in which a molded body is manufactured by applying a second pressure equal to or higher than the first pressure to the preformed body using the piston. Production method. The method for manufacturing a bonded magnet according to claim 1, wherein the content of water in the bonded magnet material is 2 to 28% by mass. 3. The method for manufacturing a bonded magnet according to claim 1, wherein the content of the cellulose nanofibers is 5 to 15% by mass relative to the total of the cellulose nanofibers and the water. The method for manufacturing a bonded magnet according to any one of claims 1 to 3, wherein the second pressure is greater than the first pressure. 5. The method for manufacturing a bonded magnet according to claim 1, wherein the magnet powder is SmFeN magnet powder containing samarium, iron, and nitrogen as main constituent elements. The method for manufacturing a bonded magnet according to any one of claims 1 to 5, further comprising performing a drying step of drying the molded body after the molded body production step.

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