KR101113529B1 - Method for producing sintered magnet - Google Patents

Abstract

Wet grinding the magnetic powder in the presence of a surfactant, drying the wet pulverized magnetic powder 20 to obtain the magnetic powder 20 to which the surfactant is attached, and the dried magnetic powder 20 as a binder A method for producing a sintered magnet, comprising: a step of forming a pellet by heating and kneading with a resin; a step of melting the pellet and injection molding in a mold applied with a magnetic field to obtain a preform; and a step of firing the preform.

Description

Manufacturing method of sintered magnet {METHOD FOR PRODUCING SINTERED MAGNET}

The present invention relates to a method for producing a sintered magnet, and more particularly, to a method for manufacturing a sintered magnet capable of producing a sintered magnet having excellent magnetic properties with high productivity.

As a manufacturing method of a sintered magnet, the dry molding method (for example, Unexamined-Japanese-Patent No. 2004-296849) and the wet molding method (for example, Japanese Unexamined-Japanese-Patent No. 3833861) are known. In the dry molding method, the preform is calcined after applying the magnetic field to form the preform while pressurizing the dry magnetic powder. In the wet molding method, a preform is calcined after applying a magnetic field to remove a liquid component by forming a slurry containing a magnetic powder to remove a liquid component and forming a preform.

The dry molding method has the advantage that the time required for the molding process is short because the dry magnetic powder is press-molded in the mold, but it is difficult to improve the orientation ratio of the magnetic powder by the magnetic field during molding, and as a result, The magnetic properties are inferior to the sintered magnets obtained by the wet molding method. In addition, in the wet molding method, the magnetic powder tends to be oriented by the magnetic field during molding, but the magnetic properties of the sintered magnet are good, but there is a problem that the molding takes a long time because the pressing is performed while removing the liquid component.

On the other hand, as disclosed in Japanese Patent No. 3229435, a method of injecting and molding a kneading pellet containing magnetic powder and binder resin into a mold to which a magnetic field is applied is also proposed. However, in the method of injection molding in the mold to which the magnetic field is applied, however, when the kneading pellet is formed, in particular, the magnetic powder of fine particle size tends to aggregate and is unevenly distributed, and the magnetic field orientation of the magnetic powder in subsequent injection molding is There are problems such as poorly performed.

This invention is made | formed in view of such a real situation, The objective is to provide the manufacturing method of the sintered magnet which can manufacture the sintered magnet which is excellent in a magnetic characteristic with high productivity.

In order to achieve the above object, a method of manufacturing a sintered magnet according to the present invention, the process of wet grinding the magnetic powder in the presence of a surfactant, and the magnetic powder to which the surfactant is attached by drying the wet powdered magnetic powder Obtaining a preform, by heating and kneading the dried magnetic powder together with a binder resin to form pellets, melting the pellets and injection molding in a mold to which a magnetic field is applied to obtain a preform, and the preform It has a process to bake.

The said surfactant may be added directly to the magnetic powder before wet grinding, and may be added to the slurry for performing wet grinding.

According to the present invention, the binder resin is reliably entered between the particles of the magnetic powder by the surfactant being interposed between the particles of the magnetic powder and the binder resin. Therefore, even when the magnetic powder is heated and kneaded together with the binder resin and pelletized, the dispersed state of the magnetic powder is maintained well, and the magnetic powder is uniformly dispersed and flows in correspondence with the magnetic field in the mold of injection molding, so that the magnetic field orientation is good. Is done. Therefore, the orientation degree of the sintered magnet finally obtained improves.

In addition, according to the present invention, since the binder resin becomes a preform in a state interposed between the magnetic powder particles, a preform in which the magnetic powder is uniformly dispersed can be obtained, and the magnetism of the sintered magnet obtained by firing the preform is Characteristics become uniform.

Further, according to the present invention, by using the binder resin melted during injection molding as a conveying medium, the magnetic powder is conveyed inside the mold while preventing aggregation of the magnetic powder particles and preventing adhesion of the particles to the conveying path contact surface. can do.

In addition, it is not necessary to remove a conveyance medium at the time of orientation of the magnetic powder by the magnetic field in a metal mold | die. For this reason, according to this invention, not only can a magnetic cavity be filled uniformly in a narrow cavity, but also the time required for one shot is short, and it is excellent in productivity. Moreover, in the method of this invention, not only a clogging arises in the flow path for removing a conveying medium, but a problem, such as a degassing process, does not arise either. As a result, it becomes possible to manufacture a relatively thin sintered magnet with high productivity.

For reference, in the conventional wet method, it is necessary to remove the solvent as a conveying medium at the time of pressurizing the magnetic powder in a specific magnetic field, and it was not easy to remove the solvent smoothly. For this reason, not only a crack is easy to generate | occur | produce in a molded object, but the time required for one shot is long, and there exists a problem that productivity is remarkably bad.

In addition, in the conventional dry method, it is necessary to degas the air or nitrogen as a conveying medium during the pressurization treatment of the magnetic powder in a specific magnetic field, which not only makes the processing complicated, but also pressurizes the dry magnetic powder in the mold. Magnetic powder particles tend to be compression molded while aggregated. For this reason, even if a magnetic field is applied to the mold, friction between the agglomerated magnetic powder particles or the binding force between the particles tends to cause the particles to easily be shaped with their respective axes of easy magnetization.

In the present invention, the magnetic powder is a ferrite powder, the average particle diameter of the magnetic powder after drying is preferably in the range of 0.03 to 0.7㎛. According to the present invention, even if the ferrite powder having an average particle diameter of 0.7 µm or less can be suppressed from aggregation of the ferrite powder before molding, the magnetic field can be molded in a state where the ferrite powder is uniformly dispersed in the cavity of the mold. For this reason, a ferrite magnet having high magnetic characteristics can be manufactured.

And as the surfactant is not particularly limited, but preferably includes a polyhydric alcohol, and more preferably sorbitol, and at least one of mannitol represented by the general formula _{C n (OH) n H n} + 2. By using these surfactant, the effect of this invention is improved.

The surfactant is preferably contained 0.05 to 5 parts by weight based on 100 parts by weight of the magnetic powder. By containing surfactant in such a range, the effect of this invention improves.

In the case where there are a plurality of steps of wet milling the magnetic powder, the magnetic powder may be wet milled in the presence of the surfactant in the last step of wet milling. The magnetic powder obtained as the final result of the grinding process is dispersed in the solvent for wet grinding, whereby the agglomeration of the powder particles is released and a solvent interposed between the particles induces the surfactant between the magnetic particles. For this reason, even if the magnetic powder after drying re-aggregates, surfactant will enter between magnetic powder particles. As a result, it is thought that the reaggregated granules (assembly of magnetic powder particles) contribute to the decomposition of the magnetic powder particles in a subsequent step (kneading or molding), thereby improving the degree of orientation.

The method of the present invention has a step of dry coarsely pulverizing the magnetic powder before the process of wet pulverization without adding a surfactant during wet milling, and the surfactant is further added in a process of dry coarsely crushing. desirable.

In the case of performing dry coarse grinding prior to wet milling, if a surfactant is added during dry coarse grinding, the wet milling can be started from the surface of the surfactant adhering to the surface of the coarsely ground particles. For this reason, in wet grinding, surfactant is easy to interpose evenly between magnetic particles, and orientation degree can be improved.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated based on embodiment shown in drawing.

First, the magnetic field injection molding apparatus 2 shown in FIG. 1 will be described. As shown in FIG. 1, the magnetic field injection molding apparatus 2 is a cavity containing an extruder 6 having a hopper 4 into which the pellets 10 are introduced and a melt of the pellets 10 extruded from the extruder 6. It has the metal mold | die 8 for shaping | molding in 12. This magnetic field injection molding apparatus is a molding apparatus using CIM (Ceramic Injection Molding) molding.

In the manufacturing method of the sintered magnet which concerns on this embodiment, the raw material powder of magnetic powder is prepared first. Although it does not specifically limit as a raw material powder of a magnetic powder, Ferrite is used, Especially hexagonal ferrites, such as a magnettoplumbite type M phase and a W phase, are used preferably.

The ferrite of the same, in particular, MO? NFe ₂ O ₃ is preferably a (M is preferably 1 or more, n = 4.5 to 6.5 of Sr and Ba). Such ferrite may further contain rare earth elements, Ca, Pb, Si, Al, Ga, Sn, Zn, In, Co, Ni, Ti, Cr, Mn, Cu, Ge, Nb, Zr and the like.

In particular, a ferrite having a hexagonal magneto plumbite-type (M-type) ferrite containing the following A, R, Fe, and M as constituent elements as a main phase is preferable. Provided that A is at least one element selected from Sr, Ba, Ca and Pb, R is at least one element selected from rare earth elements (including Y) and Bi, and M is Co and / or Zn to be. The composition ratio of the total amount of the metal elements of each of these A, R, Fe and M is based on the total amount of metal elements,

A: 1 to 13 atomic%,

R: 0.05 to 10 atomic%,

Fe: 80-95 atomic%,

M: 0.1-5 atomic%.

In this ferrite, the composition formula of ferrite in the case where R is present at the A site and M is present at the Fe site can be expressed as shown in Equation 1 below. On the other hand, x, y, z are values calculated from the above amounts.

A _{1- x} R _x (Fe _{12 - y} M _y ) _z O ₁₉ . Equation 1

In order to manufacture the raw material powder of such anisotropic ferrite, the oxide of a ferrite composition raw material or the compound which becomes an oxide by baking is mixed before baking, and then calcining is performed. The calcining may be performed in the air, for example, at 1000 to 1350 ° C. for 1 second to 10 hours, particularly when obtaining fine calcined powder of M-type Sr ferrite at 1000 to 1200 ° C. for 1 second to 3 hours.

Such calcined powder is composed of granular particles having a ferrite structure of a magneto plumbite type, and the average particle diameter of the primary particles is preferably 0.1 to 1 m, particularly 0.1 to 0.5 m. What is necessary is just to measure an average particle diameter with a scanning electron microscope (SEM), and the coefficient of variation CV is 80% or less, It is preferable that it is generally 10 to 70%. The saturation magnetization s is preferably 65 to 80 emu / g, in particular 65 to 71.5 emu / g in M-type Sr ferrite, and the coercive force HcJ is 2000 to 8000 Oe, in particular 4000 to 8000 Oe in M-type Sr ferrite.

In this embodiment, the calcined powder thus produced is dry coarsely pulverized as necessary and then wet pulverization is performed once or more.

In the dry coarse grinding process, grinding is usually performed until the BET specific surface area is about 2 to 10 times. It is preferable that the average particle diameter after grinding | pulverization is about 0.1-1 micrometer, and BET specific surface area is about 4-10 m <2> / g, and CV of a particle diameter is 80% or less, It is preferable to keep especially 10-70%. A grinding | pulverization means is not specifically limited, For example, a dry vibration mill, a dry attritor (medium stirring type mill), a dry ball mill, etc. can be used, It is especially preferable to use a dry vibration mill. What is necessary is just to determine grinding time suitably according to grinding | pulverization means.

Dry coarse grinding also has the effect of reducing the coercive force HcB by introducing crystal distortion into the plastic particles. Agglomeration of particles is suppressed by decreasing the coercive force, thereby improving dispersibility. In addition, the degree of orientation is also improved. Crystal distortion introduced into the particles is released in a subsequent sintering process to return to the original hard magnetism to become a permanent magnet.

After the dry coarse grinding, a slurry for grinding containing plasticizer particles and water is prepared, and wet grinding is performed using this. It is preferable that content of the plasticizer particle in a grinding | pulverization slurry is about 10 to 70 weight%. Although the grinding | pulverization means used for wet grinding | pulverization is not specifically limited, It is preferable to use a ball mill, an attritor, a vibration mill, etc. normally. What is necessary is just to determine grinding time suitably according to grinding | pulverization means.

In this embodiment, surfactant is added at the time of wet grinding. A surfactant it is preferred to use a polyhydric alcohol represented by the general formula _{C n (OH) n H n} + 2. The polyhydric alcohol has 4 or more carbon atoms, preferably 4 to 100, more preferably 4 to 30, still more preferably 4 to 20, most preferably 4 to 12 carbon atoms.

The general formula of the polyhydric alcohol is a formula when the skeleton is all chains and does not contain an unsaturated bond. The number of hydroxyl groups and hydrogen water in the polyhydric alcohol is at least somewhat smaller than the number represented by the general formula. The polyhydric alcohol may be saturated or may contain an unsaturated bond. Although a basic skeleton may be a chain or a ring, it is preferable that it is a chain. If the number of hydroxyl groups is at least 50% of the number of carbon atoms n, the effect of the present invention is realized. However, the number of hydroxyl groups is more preferable, and the number of hydroxyl groups and carbon number is most preferable.

As surfactant used by this invention, sorbitol and mannitol whose n = 6 are specifically, preferable. The structure is shown below about the above-mentioned preferable surfactant.

The surfactant used in the present invention may change its structure by mechanochemical reaction due to pulverization. In addition, the object of the present invention may also be attained by adding a compound, for example, an ester or the like, to produce the same organic compound as the surfactant used in this embodiment by, for example, a hydrolysis reaction. . In addition, surfactant may use 2 or more types together. The surfactant used in this case is not limited to the illustrated range of the present invention.

The amount of the surfactant added is preferably 0.03 to 5 parts by weight, more preferably 0.03 to 3.0 parts by weight with respect to 100 parts by weight of the magnetic powder. When the amount of the surfactant added is too small, the improvement of the degree of orientation becomes insufficient. When the amount of the surfactant is too large, cracking tends to occur in the molded body or the sintered body.

The addition time of surfactant is not specifically limited, You may add at the time of dry coarse grinding, You may add at the time of preparation of the slurry for grinding in wet grinding, A part is added at dry coarse grinding, The remainder is added at the time of wet grinding. You may also Or you may add by wet etc. after wet grinding. In any case, since a surfactant exists in the pellet mentioned later, the effect of this invention is realized.

However, especially in the case of dry coarse grinding prior to wet grinding, the surfactant is preferably added in the step of dry coarse grinding, not during wet grinding. In the case of performing dry coarse grinding prior to wet grinding, when the surfactant is added during dry coarse grinding, the wet grinding can be started while the surfactant is attached to the surface of the coarsely ground particles. For this reason, in wet grinding, surfactant is easy to interpose evenly between magnetic particles, and orientation degree can be improved.

On the other hand, in the case where the surfactant is added in several stages, the addition amount of each stage may be set so that the total addition amount is within the above-mentioned preferred range, but it is preferable to add the surfactant during the final wet grinding among the various stages. The magnetic powder obtained as the final result of the grinding process is dispersed in the solvent for wet grinding, so that the powder particles are agglomerated and the solvent interposed between the particles induces the surfactant between the magnetic particles. For this reason, even if the magnetic powder after drying re-aggregates, surfactant will enter between magnetic powder particles. As a result, it is thought that the reaggregated granules (assembly of magnetic powder particles) contribute to the decomposition of the magnetic powder particles in a subsequent step (kneading or molding), and the degree of orientation can be improved.

After wet grinding, the magnetic powder is dried. Preferably drying temperature is 80-150 degreeC, More preferably, it is 100-120 degreeC. Moreover, drying time becomes like this. Preferably it is 60 to 600 minutes, More preferably, it is 300 to 600 minutes.

The average particle diameter of the magnetic powder particles after drying, Preferably it is in the range of 0.03-0.7 micrometer, More preferably, it exists in the range of 0.1-0.5 micrometer. The surfactant is attached to the magnetic powder after drying. It is confirmed by thermogravimetry-differential heat simultaneous analysis (TG-DTA) that a surfactant adheres to the magnetic powder after drying.

The magnetic powder after drying is kneaded together with a binder resin, waxes, lubricants, plasticizers, sublimable compounds, etc., and formed into pellets by a pelletizer or the like. Kneading is performed by kneader etc., for example. As a pelletizer, the twin screw single screw extruder is used, for example.

As the binder resin, a high molecular compound such as a thermoplastic resin is used. As the thermoplastic resin, for example, polyethylene, polypropylene, ethylene vinyl acetate copolymer, atactic polypropylene, acrylic polymer, polystyrene, polyacetal, etc. Is used.

As waxes, synthetic waxes such as paraffin wax, urethane wax and polyethylene glycol are used in addition to natural waxes such as carnauba wax, montan wax and beeswax.

As a lubricant, fatty acid ester etc. are used, for example, and a phthalic acid ester is used as a plasticizer.

The addition amount of the binder resin is preferably 5 to 20 parts by weight, the addition amount of the waxes is preferably 5 to 20 parts by weight, and the addition amount of the lubricant is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the magnetic powder. The amount of plasticizer added is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the binder resin.

When the pellets of this embodiment containing at least the magnetic powder and the binder resin were cut and the SEM photograph of the cut surface was observed, it was confirmed that the magnetic powder was uniformly dispersed in the matrix of the binder resin.

In this embodiment, such a pellet 10 is injection-molded in the metal mold | die 8 using the magnetic field injection molding apparatus 2 shown in FIG. Before injection into the mold 8, the mold 8 is closed to form a cavity 12 therein, and a magnetic field is applied to the mold 8. On the other hand, the pellet 10 is melted by heating to 160-230 degreeC, for example in the inside of the extruder 6, and is injected into the cavity 12 of the metal mold 8 by a screw. The temperature of the metal mold | die 8 is 20-80 degreeC. The magnetic field applied to the mold 8 may be about 5 to 15 kOe.

The pre-molded product after the magnetic field injection molding step is subjected to a heat treatment at a temperature of 300 to 600 ° C. in air or in nitrogen to perform a binder treatment. Subsequently, in the sintering step, the molded body is sintered in the air, for example, at a temperature of preferably 1100 to 1250 ° C, more preferably 1160 to 1220 ° C for about 0.2 to 3 hours to obtain an anisotropic ferrite magnet.

On the other hand, the molded article produced by the method according to the invention is pulverized by using a crusher (crusher) or the like, and classified by a sieve or the like so as to have an average particle diameter of about 100 to 700㎛ to obtain a magnetic field-oriented granules, and then dry magnetic field molding You may obtain a sintered magnet by sintering.

According to the manufacturing method of the sintered magnet which concerns on this embodiment, binder resin is reliably entered between the particle | grains of magnetic powder by surfactant interposed between the particle | grains of magnetic powder, and binder resin. For this reason, even if the magnetic powder is kneaded by heating and kneading together with the binder resin, the dispersed state of the magnetic powder is maintained well.

When magnetic field injection molding is performed using such pellets, as shown in FIGS. 2A and 2B, the magnetic powder 20 is uniformly dispersed and flows corresponding to the magnetic field in the mold, and the magnetic field orientation along the magnetic field direction X is satisfactorily. Is done. That is, in the method of this embodiment, unlike the wet-molding method, since the pressure which disperse | distributes magnetic field orientation does not act, orientation degree improves.

Therefore, the orientation degree of the sintered magnet finally obtained improves. In addition, the orientation degree of a magnet is ratio (Ir / Is) of residual magnetization Ir to saturation magnetization Is. The degree of orientation of the magnet is proportional to the degree of magnetic field orientation of the magnetic powder 20 in the preform after magnetic field injection molding shown in FIG. 2B.

In addition, in the method of this embodiment, since the binder resin becomes a preform in a state interposed between the magnetic powder particles, a preform in which the magnetic powder 20 is evenly dispersed can be obtained, and the preform is obtained by firing the preform. The magnetic properties of the sintered magnet are made uniform.

In the method of the present embodiment, in the case of injection molding, the molten binder resin is used as a carrier medium to transport the magnetic powder into the mold while preventing aggregation of the magnetic powder particles and preventing adhesion of the particles to the carrier path contact surface. can do.

In addition, it is not necessary to remove a conveyance medium at the time of orientation of the magnetic powder by the magnetic field in the metal mold | die 8 shown in FIG. For this reason, in the method of this embodiment, not only can a magnetic cavity be filled uniformly in the narrow cavity 12, but also the time required for one shot is short, and it is excellent in productivity. Moreover, in the method of this embodiment, not only a clogging arises in the flow path for removing a conveying medium, but a problem such as degassing treatment does not occur. As a result, it becomes possible to manufacture a relatively thin sintered magnet with high productivity.

Moreover, in the method of this embodiment, the magnetic powder obtained as a final result of a grinding | pulverization process is disperse | distributed in the solvent for wet grinding | pulverization, agglomeration of powder particle is loosened, and a solvent is interposed between particle | grains. By adhering the surfactant to the magnetic powder in this state, the surfactant enters between the magnetic powder particles even when the dried magnetic powder reaggregates. For this reason, the reaggregated granules (assembly of magnetic powder particles) are easily decomposed into magnetic powder particles in a subsequent step (kneading or molding).

In addition, the method of this embodiment is especially effective when producing a thin sintered magnet. In order to manufacture a thin sintered magnet, a thin preform may be produced. When the preform becomes thin, not only the binder removal process is easy but also the degree of freedom in the shape of molding by injection molding increases.

In addition, this invention is not limited to embodiment mentioned above, It can change variously within the scope of this invention.

Hereinafter, an Example demonstrates this invention further in detail.

First Example

The target composition _{La 0 .4 Ca 0 .2 Sr 0} .4 Co 0 .3 Fe by _{11 .3} O _19, and the starting material was used as the following. Fe ₂ O ₃ powder (containing Mn, Cr, Si, Cl as impurities), SrCO ₃ powder (containing Ba, Ca as impurities), La (OH) ₃ powder, CaCO ₃ powder, CO ₃ O ₄ powder Was prepared to be the target composition. The starting materials and additives were pulverized with a wet attritor, dried and granulated, and calcined at 1230 ° C. for 3 hours in air to obtain granular plastic bodies.

This plastic body was dry coarsely pulverized by vibration milling. Subsequently, 0.5 parts by weight of sorbitol, 0.6 parts by weight of SiO ₂ and 1.4 parts by weight of CaC0 ₃ were added using water as a dispersion medium and sorbitol as a dispersing agent, and 100 parts by weight of plasticizer particles. Sieve particles were mixed to prepare a slurry for grinding. Wet grinding was performed for 40 hours in a ball mill using this slurry for grinding. The specific surface area after wet grinding was 8.5 m 2 / g (average particle size 0.5 µm).

After wet grinding, the plastic particles (magnetic powder) were dried at 100 ° C. for 10 hours. It was 0.3 micrometer when the average particle diameter of the plasticizer particle after drying was examined by SEM.

The magnetic powder after drying was kneaded with a kneader together with a binder resin, waxes, lubricants, plasticizers, sublimable compounds and the like, and pelletized with a pelletizer. Kneading was performed at 150 degreeC and the conditions of 2 hours.

POM (polyacetal) was used as binder resin, paraffin wax was used as wax, fatty acid ester was used as a lubricant, and phthalic acid ester was used as a plasticizer.

The amount of the binder resin added is 7.5 parts by weight based on 100 parts by weight of the magnetic powder, the amount of the wax added is 7.5 parts by weight, and the amount of the lubricant added is preferably 0.5 parts by weight. The addition amount of the plasticizer was preferably 1 part by weight based on 100 parts by weight of the binder resin.

When the pellets of this example containing at least the magnetic powder and the binder resin were cut and the SEM photograph of the cut surface was observed, it was confirmed that the magnetic powder was uniformly dispersed in the matrix of the binder resin. The SEM photograph of the pellet cross section before magnetic field injection molding obtained by the method which concerns on a present Example is shown in FIG. It was confirmed that the white contrast portion shown in FIG. 3 was a magnetic powder and uniformly dispersed.

Next, the pellet 10 is injection-molded in the metal mold | die 8 using the magnetic field injection molding apparatus 2 shown in FIG. Before injection into the mold 8, the mold 8 is closed to form a cavity 12 therein, and a magnetic field is applied to the mold 8. On the other hand, the pellets 10 were melted by, for example, 160 ° C inside the extruder 6 and injected into the cavity 12 of the mold 8 by a screw. The temperature of the metal mold | die 8 was 40 degreeC. The thickness of the preform after a magnetic field injection molding process was 2 mm, and the arc-shaped flat plate was shape | molded.

Since the magnetic orientation degree (Ir / Is) of a molded object is also influenced by the density of a molded object, accurate evaluation cannot be made. For this reason, the measurement by X-ray diffraction of the molded object was performed with respect to the flat metal mold | die surface, and the crystallographic orientation (X-ray orientation degree) of the molded object was calculated | required from the surface index and intensity of the peak which appeared.

The X-ray orientation of the molded body dominantly controls the value of the magnetic orientation of the sintered body. In this specification, ΣI (00L) / ∑I (hkL) was used as the X-ray orientation. (00L) is a generic term for c planes such as (004) and (006), and? I (00L) is the sum of all peak intensities of the (00L) plane. In addition, (hkL) represents all the detected peaks, and? I (hkL) is the sum of these intensities. Thus,? I (00L) / ∑I (hkL) represents the degree of c-plane orientation. ΣI (00L) / ∑I (hkL) in this example was 0.58.

Next, the preform after this magnetic field injection molding process was heat-treated at the temperature of 500 degreeC in air for 48 hours, and the binder removal process was performed. Subsequently, in the sintering step, the molded body was sintered for example at a temperature of 1160 ° C. in the air for 0.4 hour to obtain a sintered ferrite magnet.

The residual magnetic flux density Br, coercive force HcJ, orientation degree Ir / Is, square ratio Hk / HcJ, and sintered density of the obtained sintered ferrite magnet were measured. Hk, on the other hand, is the external magnetic field strength when the magnetic flux density becomes 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop. If Hk is low, high energy products cannot be obtained. Hk / HcJ is an index of magnet performance and indicates the degree of protrusion in the second quadrant of the magnetic hysteresis loop.

The residual magnet density Br of the obtained sintered ferrite magnet was 4600 G, the coercive force HcJ was 4900 Oe, the orientation degree Ir / Is was 97.2%, the square ratio Hk / HcJ was 93.0%, and the sintered density was 5.1 g / cm 3.

2nd Example

In the same manner as in Example 1, except that mannitol was used instead of sorbitol as a surfactant, a preform was molded and a sintered ferrite magnet was produced. The X-ray orientation degree ΣI (00L) / ∑I (hkL) of the obtained preform was 0.57.

The residual magnetic flux density Br of the obtained sintered ferrite magnet was 4590 G, the coercive force HcJ was 4900 Oe, the orientation degree Ir / Is was 97.1%, the square ratio Hk / HcJ was 92.8%, and the sintered density was 5.1 g / cm 3.

The third Example

Except having changed the addition amount of surfactant as shown in following Table 1, the preform was shape | molded similarly to Example 1, and the sintered ferrite magnet was produced.

X-ray orientation degree ∑I (00L) / ∑I (hkL), residual magnetic flux density Br, coercive force HcJ, orientation degree Ir / Is, squareness Hk / HcJ, sinter density and crack incidence of the obtained preform, Shown in

As shown in Table 1, by adding the surfactant within the range of 0.03 to 5 parts by weight, more preferably 0.03 to 3 parts by weight with respect to 100 parts by weight of the magnetic powder, it can be confirmed that there are less cracks and the magnetic properties are improved. there was. In addition, the crack incidence rate was computed by preparing five samples produced on the same conditions, and dividing the number of the sample in which the crack was observed visually by the number of all the samples.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing of the principal part of the magnetic field injection molding machine used for the manufacturing method of the sintered magnet which concerns on one Embodiment of this invention.

2A is a schematic diagram showing a state of magnetic powder before magnetic field injection molding.

It is a schematic diagram which shows the orientation state of the magnetic powder after magnetic field injection molding.

3 is a cross-sectional SEM photograph of pellets before magnetic field injection molding.

Claims (9)

Wet grinding the magnetic powder in the presence of a surfactant, Drying the wet-pulverized magnetic powder to obtain a magnetic powder having the surfactant attached thereto; Heating and kneading the dried magnetic powder together with a binder resin to form pellets, Melting the pellets and injection molding in a mold to which a magnetic field is applied to obtain a preform; The manufacturing method of the sintered magnet which has a process of baking the said preform. The method of claim 1, The said magnetic powder is a ferrite powder, The manufacturing method of the sintered magnet whose average particle diameter of the said magnetic powder after drying exists in the range of 0.03-0.7 micrometer. The method according to claim 1 or 2, Method for producing a sintered magnet wherein the surfactant comprises at least one of sorbitol and mannitol. The method according to claim 1 or 2, The surfactant is a method for producing a sintered magnet containing 0.05 to 5 parts by weight based on 100 parts by weight of the magnetic powder. The method according to claim 1 or 2, In the case where there are a plurality of steps of wet grinding the magnetic powder, a method of manufacturing a sintered magnet in which wet grinding of the magnetic powder in the presence of the surfactant in the last wet grinding step. The method according to claim 1 or 2, A method of producing a sintered magnet, which has a step of dry coarsely pulverizing the magnetic powder before the process of wet pulverization, wherein the surfactant is added in a process of dry coarsely crushing. A sintered magnet according to claim 1 or 2, wherein the binder comprises at least one selected from the group consisting of polyethylene, polypropylene, ethylene vinyl acetate copolymer, atactic polypropylene, acrylic polymer, polystyrene and polyacetal. Way. The method for producing a sintered magnet according to claim 1 or 2, wherein the dried magnetic powder is kneaded with the binder resin and a plasticizer to form the pellets. The manufacturing method of the sintered magnet of Claim 8 whose addition amount of the said plasticizer is 0.1-5 weight part with respect to 100 weight part of said binder resins.

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