KR20050095764A - Process for producing oxide magnetic material based permanent magnet - Google Patents

Abstract

A process for producing an oxide magnetic material based permanent magnet, comprising a binder addition step of adding a binder and a molding auxiliary to raw material powder containing an oxide magnetic material and mixing the same; a moisture regulation step of regulating the moisture of the resultant molding mixture containing the raw material powder, binder and molding auxiliary; an in-magnetic-field dry molding step of charging the molding mixture after moisture regulation into a metal mold and pressing the mold in an applied magnetic field so as to align the easy magnetization directions of the oxide magnetic material powder; and a firing step of firing the thus molded item, wherein the binder added in the binder addition step is a fatty acid ester wax, while the molding auxiliary added in the binder addition step is a stearic acid salt having such a property that it is melted at 90°C or below in relation to the fatty acid ester wax as the binder (90°C melting characteristic). By this process, at low cost, there can be obtained an oxide magnetic material based permanent magnet of enhanced alignment and sintered body density excelling in magnetic characteristics.

Description

Process for producing permanent magnets based on oxide magnetic materials {PROCESS FOR PRODUCING OXIDE MAGNETIC MATERIAL BASED PERMANENT MAGNET}

The present invention relates to a method for producing an oxide magnetic material permanent magnet, and more particularly, to a method for producing an oxide magnetic material permanent magnet molded by a so-called dry molding method.

Magneto-plumbite anisotropic oxide permanent magnets such as Sr ferrite and Ba ferrite are molded in a magnetic field and then sintered. Molding in a magnetic field is roughly classified into a dry molding method and a wet molding method according to the method. In the wet molding method, since the permanent magnetic material particles easily rotate, the orientation of the magnetic material becomes good, and good magnetic properties are obtained. However, productivity needs to worsen because it is necessary to discharge the dispersion medium to the outside of the molding space (outside of the mold cavity) during the press molding. In addition, the mold structure becomes large, and the equipment cost also increases.

On the other hand, the dry molding method is a method in which a dry permanent magnet material is filled in a molding space (cavity) and molded in a magnetic field. Therefore, the orientation of the magnetic material is not as good as that of the wet molding method, but the productivity is high, and the device cost is extremely low.

In the dry forming method, a binder is contained in the permanent magnet material filled in the mold. As the ideal characteristic required for the binder, the adhesion of the material particles is excellent, and the material particles are not inhibited from magnetically aligned in the biaxial direction for magnetization. As a reason for the poor orientation, (1) the magnetic interference of the material particles, that is, the adhesion between the material particles and the binder is so strong that the particles are magnetically aligned in the biaxial direction for magnetization, ( 2) friction during molding, i.e., contact friction between particles, and friction between the particles and the mold, so that pressure transfer due to pressurization is insufficient, resulting in low moldability. have. In order to improve such deterioration of orientation, in the dry forming method, an attempt has been made to select a binder that does not magnetically inhibit low friction and add it to the permanent magnet material.

That is, paraffin wax, stearic acid, camphor etc. are used as a binder contained in a magnetic material at the time of shaping | molding by the dry molding method.

However, paraffin wax and stearic acid have excellent adhesion but are so strong that they tend to inhibit the material particles from magnetically aligning in the biaxial direction for magnetization. In addition, camphor is effective as an adhesive during molding in application of a magnetic field, but since it sublimes, the mixing ratio with ferrite powder changes with the passage of time. As a result, there is a drawback that the molding operation is hindered or the strength of the molded body is reduced.

In order to solve this problem, using a metal salt of stearic acid (as metal (M), M = Ca, Ba, Sr, Pb) as a binder of the dry magnetic field-forming ferrite magnet powder (JP-A 47-21197 (Japanese Patent Application Laid-Open No. 60-22484) and the use of magnesium stearate have been proposed.

However, since the binder of the metal salt of stearic acid is difficult to be uniformly deposited on the surface of individual particles, the amount of the binder added must be increased. As a result, the amount of carbon in the magnet after sintering increases, leading to a decrease in magnetic properties, or a weak form holding force, which causes cracks in the fired body after firing.

Moreover, as a mixing method of a binder, the method of coating the binder of a gaseous state on the surface of particle | grains by heating or reduced pressure is mentioned. However, this method has a problem that the facility becomes large and the number of labors increases, and the cost reduction can not be achieved.

In addition, in order to improve moldability, improve fluidity, reduce friction during mold drawing, and the like, a molding aid is usually added to the binder.

Since such a molding aid serves as a source for generating carbide during sintering, lowers the sintering density and deteriorates the magnetic property (Br), it is desired to suppress the addition amount as much as possible.

However, in order to reduce the extraction pressure between the molded product and the metal mold and to ensure good moldability, the amount of the molding aid added must be increased to some extent.

Under the circumstances, the present invention has been invented, and its object is to use a novel molding aid that produces sufficient moldability with a small amount of addition when producing an oxide magnetic material-based permanent magnet using dry molding. The present invention provides an oxide magnetic material permanent magnet having excellent magnetic properties by improving the orientation and sintered compact density.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention provides the binder addition process of adding and mixing a binder and a shaping | molding adjuvant to the raw material powder containing an oxide magnetic material, and the moisture in the shaping | mixing mixture containing a raw material powder, a binder, and a shaping | molding aid. A moisture adjustment process for adjusting the moisture content, a dry molding process in a magnetic field in which a magnetization of the oxide magnetic material powder is matched by pressing the moisture-adjusted molding mixture into a mold and pressing in an applied magnetic field, and firing the molded body A method for producing an oxide magnetic material-based permanent magnet comprising a step, wherein the binder used in the binder addition step is a fatty acid ester wax, and the molding aid used in the binder addition step is a stearate and the fatty acid that is the binder. Dissolution at temperatures below 90 ° C in relation to ester waxes ) It is configured to occur have.

Moreover, as a preferable aspect of this invention, the said stearate is comprised as at least 1 chosen from calcium stearate, zinc stearate, magnesium stearate, and aluminum stearate.

Moreover, as a preferable aspect of this invention, the addition amount of the said stearate is comprised so that it may become 0.1 to 0.45 wt% of range.

Moreover, as a preferable aspect of this invention, the said fatty acid ester wax is comprised as plant lead.

Moreover, as a preferable aspect of this invention, it is comprised so that binder content in molding mixture may be 0.2 to 1.5 w%.

Best Mode for Carrying Out the Invention

Hereinafter, the manufacturing method of the oxide magnetic material permanent magnet of this invention is demonstrated in detail.

The method for producing an oxide magnetic material-based permanent magnet of the present invention includes a binder addition step of adding and mixing a binder to a raw material powder containing an oxide magnetic material, and a molding mixture containing the raw material powder and the binder as a main step. A moisture adjustment step of adding moisture and adjusting the moisture of the mixture, a dry molding step of a magnetic field in which the moisture-adjusted molding mixture is put into a mold and pressed in an applied magnetic field to facilitate magnetization of the oxide magnetic material powder; It is comprised including the baking process which bakes a molded object.

The raw material powder of the oxide magnetic material prepared before the binder addition step is usually produced in the following manner.

[Production of raw powder]

For example, barium ferrite is generally made of powders of iron oxide (Fe ₂ O ₃ ) and barium carbonate (BaCO ₃ ), and in strontium ferrite, iron oxide (Fe ₂ O ₃ ) and strontium carbonate (SrCO ₃ ) are generally used. ) Powder is used as the main raw material, and they are weighed so as to be a predetermined ingredient, and a predetermined additive is added and blended, and mixed in a ball mill or the like.

As the additive, for example, oxides such as Bi, As, B, Si, Ge, Na, Al, Cr, Ti, W, Mo, chlorides, and the like are used. Such additives are used to promote sintering or to prevent excessive growth of grains. This mixture is performed at a temperature of about 1000 ° C. By this plasticity, the carbon dioxide gas is decomposed and dissipated, and the combination of barium oxide and iron oxide or strontium oxide and iron oxide proceeds.

The plasticized material in this way is sufficiently crushed by a ball mill or the like. After grinding, you may add an additive further as needed.

Binder Addition Process

A binder is added and mixed to the raw material powder containing the oxide magnetic material prepared by the above-mentioned method. As a binder to add, it is good to emulsify fatty acid ester wax, especially the fatty acid ester wax of molecular weight 300-800. In the present invention, a fatty acid ester wax is used as the binder, and a salt forming aid composed of stearic acid having a predetermined physical property described later is further added.

Among the fatty acid ester waxes, in particular, plant lead (carnauba wax, candelilla, tree wax, duck cury, etc.) is preferable.

The amount of binder added is preferably 0.2 to 1.5 wt%, particularly 0.25 to 1.2 wt%, and more preferably 0.3 to 0.9 wt%. When the addition amount is too small, the effect as a binder is not expressed, and the form holding power is weakened. If the amount is too large, the density of the sintered compact may be reduced by carbonization of the organic material at the time of sintering, resulting in deterioration of magnetic properties such as Br.

In addition, in this binder addition process, the shaping | molding adjuvant predetermined in this application is added. That is, in the binder addition process of this invention, a stearate is used as a shaping | molding adjuvant, Moreover, this stearate dissolves at the temperature of 90 degrees C or less with respect to the fatty acid ester wax which is the said binder (it simply follows: 90 degreeC dissolution characteristics "is an essential requirement.

This 90 degreeC dissolution characteristic is defined by the following measuring procedures so that the presence or absence of the characteristic can be verified. That is, 10 ml of the base emulsion solution (trade name: Cellosol 524 (manufactured by Chukyo Yushi Co., Ltd.)) which is an emulsified fatty acid ester wax is heated to a solution of 90 ° C., and 1.5 g of stearate is added to the solution. (The solution temperature is kept at 90 ° C). Ordinary manual stirring is performed to determine whether or not the solution is dissolved at 90 ° C. When it melt | dissolves at 90 degreeC, it is determined as a stearate which has a 90 degreeC dissolution characteristic. Whether or not it is in a dissolved state can be judged sufficiently by the naked eye. When dissolved, the solution becomes an almost uniform solution. When undissolved, a powder of stearate remains in a floc form. The determination of the dissolved state is also possible by measuring the viscosity of the solution. When dissolved, the viscosity is significantly lowered (for example, 1 to 20 at ShearRate 8 / sec).

Examples of suitable stearates include calcium stearate, zinc stearate, magnesium stearate, aluminum stearate, and the like, which all need to satisfy the above 90 ° C dissolution characteristics.

In general, the stearates are prepared by (1) a wet metathesis method and (2) a dry direct method. Although various know-hows exist in the manufacturing method in order to provide 90 degreeC dissolution characteristics, it can be said that it is a manufacturing method suitable for obtaining what has the 90 degreeC dissolution characteristics of the manufacturing method of the former (1).

In addition, the general grade of stearate conventionally used in the technical field of this application has melting | fusing point near 120 degreeC (it does not have the 90 degreeC dissolution characteristic mentioned here), and these raise a binder solution about 120 degreeC, It has almost the ability to dissolve.

The stearate having a 90 ° C dissolution property in the present invention exhibits a sufficient effect by addition in a small amount so that the amount of addition thereof has not been conventionally proposed. That is, in the present invention, the stearate having a 90 ° C dissolution property is 0.1 to 0.45 wt%, preferably 0.1 to 0.4 wt%, more preferably 0.15 to 0.30. When the addition amount is too small, the effect of improving moldability, improving fluidity, reducing friction, and the like does not appear. On the contrary, when the addition amount is excessively large, the density of the sintered compact is deteriorated due to carbonization of organic materials during sintering, and the magnetic property Br is deteriorated. The problem arises.

In a binder addition process, when mixing the raw material powder containing a magnetic powder and a binder, the method of mixing in a liquid phase or a solid phase is taken. When a liquid binder is used, aggregation tends to occur, and the orientation of the magnetic powder tends to decrease. Moreover, when a solid binder is used, the problem that it is difficult to mix uniformly is discovered. At the time of mixing, the binder is sufficiently stirred using a mixer such as a Henschel mixer or a blender.

It is preferable that the method and the procedure of addition of the shaping | molding adjuvant which have the said predetermined physical property in this binder addition process are as follows. That is, it is preferable to add a shaping | molding adjuvant after mixing a binder and magnetic powder. This is because the presence of the molding aid around the mixed powder of the binder and the magnetic powder has a large effect of reducing friction, improving fluidity, and improving moldability. Moreover, even if it adds before binder addition or simultaneously with a binder, the same effect is acquired.

Moisture Control Process

In this moisture adjustment step, the moisture of the mixture is adjusted by adding or subtracting water to the molding mixture containing the raw material powder, the binder and the molding aid.

The moisture content of the molding mixture after mixing greatly affects moldability and magnetic properties. The amount of water is preferably 0.20 to 0.80 wt%, particularly 0.25 to 0.35 wt%. When the amount of water is less than 0.20 wt%, it becomes difficult to maintain the desired form during the molding of the next step. When the amount of water exceeds 0.80 wt%, agglomeration of the magnetic powder occurs, and the magnetic powder particles are prevented from being aligned in the axial direction easily magnetically, and the magnetic property (Br) is lowered. Moreover, there exists a tendency for the fall of a sinter density, a crack, and a pinhole to generate | occur | produce.

Moisture adjustment can be made into arbitrary amount of moisture by managing temperature and humidity. It is preferable to add water by adjusting the moisture by leaving it at room temperature or by fine water vapor (a few microns to several tens of microns) such as a constant temperature / humidity bath or nebraiza. For example, when the thing which becomes large in water particle with a nebulizer etc. is used, aggregation tends to occur and the tendency which disturbs the orientation at the time of shaping | molding arises.

It is preferable to provide a disintegration step for pulverizing the aggregate in the molding mixture after such a water adjustment step. By providing the disintegration step, for example, aggregates formed by drying can be removed (pulverized into fine particles). When agglomerates exist, when a magnetic field is applied in the dry molding process of the magnetic field mentioned later, an orientation becomes difficult and it becomes a cause of the fall of a magnetic characteristic. In addition, when this disintegration process is added after the said moisture adjustment process, it is preferable to make the amount of moisture in the mixture at the time of completion of the disintegration process into 0.20 to 0.80 wt%. The reason is the same as the reason described in the above-mentioned moisture adjustment process.

[Dry forming process in magnetic field]

The moisture-adjusted molding mixture is placed in a mold and pressed in an applied magnetic field. As a result, the magnetization of the raw material powder (magnetic powder particles) coincides with the direction, and the magnetic properties can be improved.

In the present invention, the molding mixture (input raw material) to be put into the mold of the dry molding process in the magnetic field has an abundance of 0.01 to 0.80 wt%, and preferably 0.01 to 0.8 µm or more of aggregates present in the molding mixture. It is preferable to be 0.78 wt%. When this value exceeds 0.80 wt%, the orientation becomes difficult when the magnetic field is applied in the dry molding step in the magnetic field, which tends to cause the deterioration of the magnetic properties. Although the lower limit may be 0, it is considered that 0.01 wt% is appropriate at the current technical level.

The existence ratio of the aggregate of 500 micrometers or more may be calculated | required by the following methods, for example. That is, what is necessary is just to hang a shaping | molding mixture on an automatic sieving machine, and give a vibration for 3 minutes, and then measure the ratio of the aggregate of 500 micrometers or more, and calculate the abundance ratio of the aggregate of 500 micrometers or more from the measured value.

Among the magnetic fields, the orientation magnetic field in the dry forming step is about 3 to 12 kOe (239 to 955 kA / m), and the molding pressure is about 0.1 to 5 ton / cm ² .

The molded article thus formed is usually fired by the firing step of the next step.

[ Firing process ]

The molded article formed in the dry molding step of the magnetic field is fired by this step. The baking temperature is preferably in the range of 1200 to 1260 ° C. When the firing temperature is lower than 1200 ° C, it is difficult to obtain a sufficient sintered density. On the other hand, when a baking temperature exceeds 1260 degreeC, abnormal grain growth will be easy to occur and it will become the tendency for iHc value to fall. The settling time for firing is about 0.5 to 4.0 hours. The minor component atmosphere may be in the air, but by firing while controlling the oxygen partial pressure, a magnet having a higher density and higher magnetic characteristics is obtained.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

100 parts by weight of Sr ferrite plastic powder, 0.5 parts by weight of SiO ₂ , and 1 part by weight of CaCO ₃ were wet pulverized using water so that the specific surface area of the plastic powder was 7.0 m ² / g. Subsequently, the slurry was dried to obtain an experimental raw material powder.

After adding the binder as shown in following Table 1 to the raw material powder obtained in this way, it mixed for 20 minutes at 90 degreeC using the Henschel mixer. After mixing, a molding aid as shown in Table 1 was added, followed by further mixing for 3 minutes.

Details of molding aid are as follows.

Sample 1 . The basic component is calcium stearate, and has 90 ° C dissolution characteristics (indicated by ○ in the table). It melt | dissolved in the base emulsion solution of 90 degreeC in about 3 minutes.

Sample 2 . The basic component is calcium stearate, and has 90 ° C dissolution characteristics (indicated by ○ in the table). It melt | dissolved in the base emulsion solution of 90 degreeC in about 3 minutes.

Sample 3 . The basic component is calcium stearate, and has 90 ° C dissolution characteristics (indicated by ○ in the table). It melt | dissolved in the base emulsion solution of 90 degreeC in about 4 minutes.

Sample 4 . The basic component is zinc stearate, and has 90 ° C dissolution characteristics (indicated by ○ in the table). It melt | dissolved in the base emulsion solution of 90 degreeC in about 5 minutes.

Sample 5 . The basic component is magnesium stearate, and has 90 ° C dissolution characteristics (indicated by ○ in the table). It melt | dissolved in the base emulsion solution of 90 degreeC in about 3 minutes.

Sample 6 . The basic component is aluminum stearate, and has 90 ° C dissolution characteristics (indicated by ○ in the table). It melt | dissolved in the base emulsion solution of 90 degreeC in about 6 minutes.

Comparative sample 1 . The basic ingredient is calcium stearate and does not have a 90 ° C dissolution property (indicated by × in the table). It does not melt | dissolve in a 90 degreeC base emulsion solution, a floc-shaped powder remains, and the viscosity of a solution also gradually increases. It is only dissolved by raising the temperature of the base emulsion solution to about 120 ° C.

Comparative sample 2 . The basic ingredient is calcium stearate and does not have a 90 ° C dissolution property (indicated by × in the table). It does not melt | dissolve in a 90 degreeC base emulsion solution, a floc-shaped powder remains, and the viscosity of a solution also gradually increases. It is only dissolved by raising the temperature of the base emulsion solution to about 110 ° C.

Next, the moisture content of the mixed powder mix | blended in the said procedure was adjusted so that it might become 0.30 wt% using the constant temperature and humidity tank.

Thereafter, this mixed powder was pulverized using an atomizer to obtain a permanent magnet material.

Subsequently, this permanent magnet material was dry-molded in a magnetic field of about 7.5 kOe. Molding pressure was 1 ton / cm ² . The obtained molded object was baked at 1240 ° C. for 1 hour in the air to obtain a magnet sample having a diameter of about 26 mm and a height of 10 mm.

The magnetic samples obtained in this way were evaluated for the magnetic properties of Br and iHc using a B-H tracer (Toe Kogyo Co., Ltd .: DC magnetization characteristic measuring apparatus TRF-5BH).

In addition, the density (dP) of the molded body and the density (df) of the sintered body were measured by the following method.

Density of Molded Product (dP)

The volume V was calculated | required from the actual dimension of the molded object, the weight W was measured, and it calculated by dividing the weight by volume. dP = W / V

Density of sintered body (df)

The density (df) of the sintered compact was computed based on the numerical value obtained using the Archimedes method.

In addition, the extraction pressure at the time of taking out a molded object from a metal mold | die, and the crack generation rate which may arise at the time of taking out a molded object from a metal mold | die were evaluated based on the following criteria. In general, when the extraction pressure is high, the crack generation rate tends to be high.

Extraction pressure (Kg / cm ² )

Molding (φ15.4 mm x 5 mm) for the extraction pressure test is carried out (molding pressure is 1 ton / cm ² ), and then the extraction pressure when the molded product is removed from the mold is measured using a strength tester (Instron). MODEL-4550). Extraction speed was 100 mm / min.

Crack incidence

It was visually checked whether or not cracks that could occur when the molded product was taken out of the mold were generated. Crack generation is usually confirmed at the bottom part of the molding, and an umbrella-like crack occurs from the bottom peripheral edge to the inside. The bottom part of the molded part is the part which is taken out last from the mold, and is the point where cracks are most likely to occur because the stress is relieved momentarily and suddenly expands in volume.

The number of measurement samples was 50 pieces.

The results are shown in Table 1 below.

In addition, the criterion which should be made clear of each measurement item of this invention in Table 1 is that the extraction pressure is 0.120 (Kg / cm ² ) or less, the crack incidence is 0/50, and the density (dp) of the molded body is 2.880. (Mg / m ³ ) or more, the density of the sintered body (df) is 4.910 (Mg / m ³ ) or more, the sintered body strength is 16.0 (Kgf / mm ² ) or more, Br is 3800 (G) or more, and iHc is 3000 (Oe) or more.

The effect of this invention is clear from the said result. That is, the present invention provides a binder addition step of adding and mixing a binder and a molding aid to a raw material powder containing an oxide magnetic material, and a moisture adjustment for adjusting the moisture in the molding mixture containing the raw material powder, the binder and the molding aid. And a step of forming the moisture-adjusted molding mixture into a mold and pressing in an applied magnetic field to dry the forming process in a magnetic field where the magnetization of the oxide magnetic material powder is aligned, and a firing step of firing the molded body. A method for producing an oxide magnetic material permanent magnet, wherein the binder used in the binder addition step is a fatty acid ester wax, and the molding aid used in the binder addition step is a stearate and a fatty acid ester wax as the binder. It is configured to have the property of dissolving at a temperature below 90 ℃ (90 ℃ dissolution property) As a result, an oxide magnetic material permanent magnet having excellent magnetic properties can be obtained by improving the orientation and the density of the sintered body while achieving a low cost.

The present invention can be used at the time of manufacturing an oxide magnetic material permanent magnet.

Claims (5)

A binder addition step of adding and mixing a binder and a molding aid to a raw material powder containing an oxide magnetic material, A water adjustment step of adjusting the water in the molding mixture containing the raw material powder, the binder and the molding aid; A dry molding process in a magnetic field in which the moisture-adjusted molding mixture is placed in a mold and pressed in an applied magnetic field to match the direction of magnetization of the oxide magnetic material powder; A method of manufacturing an oxide magnetic material-based permanent magnet comprising a firing step of firing a molded body, The binder used in the binder addition step is a fatty acid ester wax, The molding aid used in the binder addition step is a stearate, and has an oxide magnetic material which has a property of dissolving at a temperature of 90 ° C. or lower in relation to a fatty acid ester wax which is the binder (90 ° C. dissolution property). Method of manufacturing permanent magnets. The method of claim 1, wherein the stearate is at least one selected from calcium stearate, zinc stearate, magnesium stearate, and aluminum stearate. The method of manufacturing an oxide magnetic material-based permanent magnet according to claim 1, wherein the amount of the stearate added is 0.1 to 0.45 wt%. The method of claim 1, wherein the fatty acid ester wax is vegetable lead. The method for producing an oxide magnetic material-based permanent magnet according to claim 1, wherein the binder content in the molding mixture is 0.2 to 1.5 wt%.