JP2610445B2 - Method for producing soft magnetic hexagonal ferrite - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a soft magnetic powder, and more particularly to a method for producing a plate-like particle-shaped hexagonal soft magnetic ferrite powder having an easy axis of magnetization in a direction other than the C axis. The magnetic powder of the present invention can be widely used for magnetic shielding materials having a large magnetic shielding effect against a magnetic field in a specific direction, and for other uses of soft magnetic materials.

(Prior art and its problems) Soft magnetic powders are widely used for magnetic shielding and other uses. The conditions required for such a soft magnetic material are that the saturation magnetization is large and the magnetic permeability is high. For example, in the case of a magnetic shield material, in order for the magnetic field to be blocked by the magnetic shield material, the magnetic shield material is formed in a sheet or film shape, and a magnetic flux in a direction perpendicular to the surface is blocked and a magnetic flux in an in-plane direction. It is necessary that the axis of easy magnetization is oriented in the in-plane direction so that is induced. A magnetic powder that meets such conditions is a magnetic particle that develops in a plate shape, has a large saturation magnetization, and has an easy axis of magnetization in a plate-like in-plane direction. This is dispersed in an organic binder and applied in the form of a paint to the required location of the magnetic shield, or is applied to an appropriate flexible support to form a shield plate, or is press-formed, rolled, or the like. Various applications are possible, such as molding with a mold while applying an orientation magnetic field.

Various proposals have been made as a method for producing a plate-shaped or flat-shaped magnetic powder having a high magnetic permeability. For example, JP-A-58-59
No. 268 describes producing a flat powder by pulverizing an alloy having high magnetic permeability such as Sendust. Also JP
No. 59-201493 describes that a soft magnetic amorphous alloy is pulverized to produce flat powder.

However, these metal powders are easily oxidized and must be manufactured in a non-oxidizing atmosphere or in a vacuum, which increases the manufacturing cost. Further, when applied to a magnetic shielding material or the like, the oxidation resistance of the product is low. Another disadvantage of metal powders is that it is not easy to grind the material into a flat powder. For this reason, the flat powder must be used in a rather coarse particle form, so that it is difficult to make a paint, and if pulverization is advanced to make the paint easy, the flat shape can no longer be maintained and the granular shape cannot be maintained. When formed into a sheet or film by coating, the magnetic flux is induced also in the direction perpendicular to the sheet surface, and the magnetic flux in the in-plane direction is reduced.

On the other hand, soft magnetic oxides such as magnetic ferrite have high oxidation resistance and do not require the use of a non-oxidizing atmosphere during the manufacturing process. However, the saturation magnetization is lower than the metal material, or it is granulated when crushed,
There are drawbacks such as difficulty in obtaining flat particle-shaped powder, and no excellent oxide magnetic powder that can be used for applications such as magnetic shielding materials has been provided.

For example, Mn-Zn ferrite, which is spinel ferrite, has high saturation magnetization, low magnetic anisotropy, and high magnetic permeability, so a high shielding effect is expected.However, since it is a cubic crystal, it is a single crystal. It was difficult to obtain plate-like particles of Although plate-like particles of other crystals are obtained, the magnetic shielding effect is low.

On the other hand, it is known that hexagonal magnetic ferrite having a large magnetic anisotropy in the C-axis direction can develop a plate-like particle shape, and there are an aqueous solution method, an autoclave method, a glass crystal method and the like. Flux method used in the
No. 49030, JP-B-57-21518, JP-B-58-20890, JP-A-59-146944, JP-A-60-90829). However, since this is a magnetoplumbite type ferrite, unlike a soft magnetic material, it is a hard magnetic material, and the electromagnetic characteristics intended by the present invention cannot be obtained. A hexagonal ferrite similar to a W-type ferrite (defined later) having magnetic anisotropy in a direction other than the C axis, which is a hexagonal ferrite targeted by the present invention, is different from the method of the present invention. Aqueous solution method (JP-A-59-174530) or pulverization method (JP-A-59-1745).
No. 31, JP-A-60-11232). However, the magnetic powder thus obtained has a large magnetic anisotropy, and it is not only a soft magnetic material but a hard magnetic material, and it is necessary to prepare the particle shape and particle size necessary for obtaining excellent soft magnetic characteristics. Is difficult. This is because the magnetic powder of the hard magnetic material needs to be single magnetic domain particles and is intended to produce particles of 1 μm or less (the same applies to magnetic recording materials).

(Object of the Invention) An object of the present invention is to provide a method for producing a hexagonal magnetic powder composed of plate-like or flat particles having an easy axis of magnetization in a direction other than the C axis.

Another object of the present invention is to provide the above oxide magnetic powder which can be used for a magnetic shield material having good oxidation resistance and other soft magnetic materials.

(Summary of the Invention) In the present invention, the composition is (AO) _a (Me _1-x Co _x O) _b (Fe _2-y D _y
O ₃ ) At least one type of _c- type magnetic oxide (where A is Ba, S
At least one of alkaline earth metals such as r, and Me is divalent F
e, Ni, Zn, Mn, Cu, Cd, Mg, and at least one of (Fe ³⁺ + Li ¹⁺ ) / 2, and D is trivalent Al, Mn, Cr, Ga, (Co ²⁺ +
Ti ⁴⁺ ) / 2, x represents the amount of substitution of Me, and y represents the amount of substitution of Fe). Ten
The present invention provides a method for producing a soft magnetic hexagonal ferrite having a magnetic easy axis in a direction other than the C-axis composed of plate-like particles by heat-treating at 00 to 1400 ° C., cooling, and then removing the flux by dissolving in water.

According to this method, a soft magnetic magnetic powder composed of plate-like particles having an average diameter of 1 to 100 μm, an average thickness of 0.01 to 10 μm, and an average diameter / average thickness ratio of 5 or more can be easily obtained.

This magnetic powder is mixed with a binder such as synthetic resin or rubber to make a magnetic paint, applied in a sheet shape, or molded while applying a magnetic field in a specific direction, etc. Products can be manufactured. For example, in the case of a magnetic shielding material, the transmission of magnetic flux in a direction perpendicular to the sealing surface is extremely reduced, and a significant advantage is obtained in that most of the magnetic flux is guided in the in-plane direction.

(Structure and Function of the Invention) As described above, the present invention uses the flux method. This method is well known, so please refer to the references cited above if necessary. However, it should be emphasized again that it is not known at all that the flux method can be applied to the production of a hexagonal soft magnetic ferrite having an axis of easy magnetization in a direction other than the C axis, which is a target product of the present invention. In the first place, there has been almost no application of a magnetic material of the W type or the same type as that produced in the present invention because of its low magnetic properties. However, according to the present invention, it has been discovered for the first time that hexagonal magnetic powder in the form of plate-like particles has extremely excellent properties in applications such as magnetic shielding materials. That is, not only is the method of the present invention novel, but the magnetic powder produced is also novel.

About Magnetic Material The magnetic material produced by the method of the present invention is a hexagonal soft magnetic powder having an easy axis of magnetization in a direction other than the C axis. Hexagonal magnetic materials of this type include Y-type, Z-type, and W-type ferroxplanar-type ferrites.
O) _a (Me _1-x Co _x O) _b (Fe _2-y D _y O ₃ ) _c W type is (AO) (Me _1-x Co _x O) ₂ (Fe _{2−y DyO 3} ) ₈ (preferably x is 0.35 or more and y is 0.5 or less), and Y type is (AO)
₂ (Me _1-x Co _x O) ₂ (Fe _2-y D _y O ₃ ) ₆ (x is 0 to 1, y is
0.5 or less) and Z type is (AO) ₃ (Me _1-x Co _x O) ₂ (Fe _2-y D _y O
₃ ) ₁₂ (X is 0.25-1 and y is 0.5 or less). (Where A is at least one of alkaline earth metals such as Ba and Sr, Me
Are divalent Fe, Ni, Zn, Mn, Cu, Cd, Mg, and (Fe ³⁺ + Li
^{1 +} ) / 2, D is trivalent Al, Mn, Cr, Ga,
It is at least one of (Co ²⁺ + Ti ⁴⁺ ) / 2. ). If the above conditions of x and y are satisfied, soft magnetism is obtained,
Further, soft magnetism is not impaired even in a mixed state of Y-type, Z-type and W-type. In addition, a crystal phase other than Y-type, Z-type and W-type may coexist in the material. In this case, the S type, that is, (Me _1-x Co _x O) (Fe _2−y D _y O ₃ ) is cubic, and plate-like particles are difficult to obtain, but is a phase exhibiting soft magnetism and 20 wt% or less. In this case, the soft magnetism of the material is not significantly impaired. Also Fe
_2-y D _y O ₃ is generally a non-magnetic phase, and softens the soft magnetism. However, if it is 10 wt% or less, the soft magnetism of the entire material is not significantly impaired. However, the M type, ie, (AO) (Fe _2-y D
_y O ₃ ) ₆ is hexagonal, but since it is a phase exhibiting hard magnetism in which the C axis becomes the axis of easy magnetization, coexistence greatly impairs the soft magnetism of the entire material, so it is suppressed to 3 wt% or less. There is a need to. Summarizing the above results, (AO) _a (Me
Assuming that the composition range in which _1-x Co _x O) _b (Fe _{2 -y Dy} O ₃ ) _c can obtain the desired soft magnetism is a + b + c = 100, as shown in FIG. c) is I (5, 40, 55), II (3
0, 15, 55), III (25, 5, 70), and IV (5, 15, 80). The magnetic material Y type can develop an easy axis of magnetization in a direction other than the C axis without containing Co, but the W type and the Z type can be developed in a direction other than the C axis if they do not contain at least Co. The easy axis cannot be developed. Since the magnetic powder having the above composition is an oxide, it is thermally stable before and after processing into a soft magnetic magnetic article such as a magnetic shielding material, and has good oxidation resistance. In addition, the above magnetic powder contains expensive cobalt but remains in a small amount, and the cost of raw materials is low because inexpensive iron oxide occupies about 80%, and the hexagonal ferrite is low in cost because it can be produced in air. Cost.

Manufacturing Method The powder having a flat or plate-like particle shape of the present invention is manufactured by a special manufacturing method. The desired particle shape cannot be obtained in the pulverization process using a conventionally known pulverizer. For example, conventionally known pulverizers include a stamp mill, a dry ball mill, a wet ball mill, an attritor, a vibration mill, a rod mill, an impact mill, a disk mill,
Although there are crusher rolls, etc., these pulverization methods cannot obtain fine flat particles, only granular particles can be obtained, and soft magnetic products such as magnetic shield materials manufactured from them can be used. It is close to anisotropy, and sufficient magnetic properties cannot be expected.

The present invention is a method for producing a magnetic powder by a flux method. Regarding the application of this method, a proposal has been made by the present applicant regarding cubic ferrite (Japanese Patent Application Laid-Open No. 60-1985).
No. 89902, Japanese Patent Application No. 58-199206, Japanese Patent Application No. 59-197377,
JP-A-60-91699). Hexagonal ferrites for magnets are known from JP-B-55-49030, JP-B-57-21518, and JP-A-60-90829. However, the flux method has never been applied to the production of ferrite having a magnetic easy axis different from the C axis which is a soft magnetic material suitable for the present invention, that is, ferroxplanar. A, D, Me,
Co, Fe oxides, hydroxides, carbonates and the like are selected.
The water-soluble salt used as the flux is one of sulfates such as K ₂ SO ₄ and Na ₂ SO ₄ , one kind of chloride such as KCl, or a combination of two or more kinds for controlling the melting point. Flux mixture is 20-70mo based on the total amount including flux
l% is suitable, more preferably 35-55 mol%. After mixing the raw material and the flux, charge this mixture into a crucible such as alumina and 1000 to 1400 ° C according to the composition
And heat treatment at an appropriate temperature. The heat treatment temperature depends on the composition, 1000 ° C or higher for Y-type ferrite, and for Z-type and W-type.
1200 ° C or higher is appropriate. These temperatures must of course be higher than the melting point of the flux. The heat treatment time is usually set between 30 minutes and 3 hours. After the heat treatment, the mixture is cooled to room temperature, the flux is dissolved in water or hot water and separated, and after dehydration and drying, a soft magnetic hexagonal ferrite composed of the desired flat particles, ie, plate-like particles, is obtained. The obtained powder is mixed with a resin and a solvent to prepare a paint, which is applied to a plastic substrate or the like to be used as a magnetic shield material, or other natural or magnetic or mechanical orientation operation is performed. Various uses such as performing a molding operation are possible.

Required conditions of the powder Most of the magnetic powder produced by the method of the present invention,
Probably, about 80% or more of the total amount is composed of flat particles, has good orientation due to its shape, and has excellent characteristics as a soft magnetic material such as a magnetic shield. For example, the better the plate shape, the higher the magnetic shielding effect is obtained. The ferrite of the present invention, which is a hexagonal crystal, has a good plate-like property, and has an average diameter (the average particle diameter as viewed from the plane direction, and the diameter when the total weight becomes 50% from the smaller particle shape.) 1~100μm is known are) d as D _50, the average thickness t of the particle 0.01~10μ
m, an average diameter and an average thickness ratio d / t of 5 or more can be manufactured by adjusting the conditions, and the axis of easy magnetization such as a magnetic shielding effect is in a direction close to the plate surface direction of the particles. Magnetic properties can be exhibited effectively. In particular, the average diameter d is 5 to 50 μm, the average thickness t of the particles is 0.01 to 2 μm, and the average diameter to average thickness ratio d / t is 10 or more. Magnetic properties are improved.

In a magnetic sheet formed using such flat particles, the plate surface tends to be arranged in parallel to the coated surface, and if a magnetic orientation method is used at the time of coating, the ease of plane-parallel magnetization can be further enhanced.

When the average diameter of the particles is smaller than 1 μm, not only is it difficult to orient the particles, but also high soft magnetic characteristics cannot be obtained. However, powder smaller than 1 μm is 10
% Does not significantly reduce the magnetic shielding effect. On the other hand, if the average diameter is larger than 100 μm, it becomes difficult to mix with a resin binder to form a coating, and it becomes difficult to form a film, and even if it is formed, uneven magnetic properties occur. When the average thickness of the particles is smaller than 0.01 μm, it becomes difficult to obtain a plate-like shape, and the same applies when the average thickness is larger than 10 μm. If the average diameter / average thickness ratio is smaller than 5, the magnetic properties are degraded.

The soft magnetic material contains the magnetic particles of the present invention and, as a resin component, synthetic resins such as epoxy, polyester, acrylic, urethane, phenol, melamine, silicon, and synthetic rubber, and an additive such as a suitable solvent and some dispersant. Mix to obtain paint. Alternatively, it is formed into a film shape, a sheet shape, a bulk shape, or any other shape by an extrusion molding method, an injection molding method, or the like.
At that time, natural orientation action (in the case of film or sheet),
A molded product that is easily magnetized in a desired direction by performing mechanical orientation such as magnetic orientation, rolling, and pressing.

The magnetic properties evaluated in the examples of the present invention are the initial magnetic permeability μi, which is a typical property of soft magnetism, and the evaluation method will be briefly described here.

A ring-shaped (for example, an outer diameter of 20 mm and an inner diameter of 10 mm) sample was cut out from the soft magnetic molded product obtained by the above method, and a copper wire (about 0.3 mm in diameter) was wound around the coil N = 20 to 50 times. The inductance L at both ends is measured at a frequency f = 1 to 100 KHz,
Based on JIS C 2561, the initial magnetic permeability μi is determined by the following equation.

Where A is the average sectional area, l is the average magnetic path length, and μo
Is the vacuum permeability.

 Next, examples of the present invention will be described.

Examples and Comparative Examples For each of the five compositions shown in Table 1, plate-like particles prepared by the flux method of the present invention (samples of Examples
) And a powder composed of granular particles by a conventional pulverization method (a sample according to a comparative example and represented by B) were prepared, and the initial magnetic permeability after molding was compared.

In the case of flux method, mol of each raw material according to the above mixing ratio
Assuming that the sum of the numbers is 1, a sulfate corresponding to 0.8 mol was mixed as a flux. The flux is 1-
A, the case of 2-A, 5-A K 2 SO 4 alone, 3-A, 4-A
Here, a 1: 1 mixture of K ₂ SO ₄ and Na ₂ SO ₄ was used. For example, 1-
In the case of A, BaCO ₃ 5.05mol%, ZnO 4.04mol%, CoO 6.06
mol%, Fe ₂ O ₃ 40.4 mol%, and K ₂ SO ₄ 44.45 mol%. The raw material and the flux were mixed by a dry stirrer and placed in an alumina crucible. This mixture weighs about
It was 200 g. This crucible was placed in an electric furnace, heat-treated in air at the temperature shown in Table 1 for 1 hour, and cooled to room temperature. Then crush it with an iron mortar with a force that does not impair the plate shape, put it in about 1000 ml in a beaker, about 80 ° C hot water,
Stir to dissolve the flux. This dissolution is repeated 3 to 4 times until the amount of flux becomes almost nonexistent, and after dehydration by excessive drying, it is dried in a dryer at 100 to 150 ° C to obtain about 100 g of soft magnetic hexagonal ferrite. Was.

Regarding the pulverization method, the raw materials were mixed in a wet ball mill according to the compounding ratio shown in Table 1, and put in an alumina crucible.
Heat treated under the same conditions as the flux method, lightly disintegrate with an iron mortar, and place it in an iron ball mill with an inner diameter of about 10 cm and a depth of about 15 cm.
The material was put together with 400 g of 400 g of a hard sphere having a diameter of 12 mm, sealed, and rotated for 20 hours to pulverize the material to obtain a granular powder.

Each powder thus obtained and the chloroprene rubber
Formed with rolling rolls to have a volume ratio of 1: 1, thickness 3 mm,
A ring sample having an outer diameter of 20 mm and an inner diameter of 10 mm was cut out, wound with 25 turns, and the inductance L was measured with an LCR meter at a frequency f = 100 KHz to measure the initial magnetic permeability.

Table 2 shows the average diameter d, average thickness t of the powder particles of each sample,
The ratio d / t (granular particles have only an average diameter) and initial permeability are shown.

It was found that the soft magnetic powder having a plate-like particle shape as compared with the co-granular shape of each sample can obtain about twice the initial permeability after being combined with a resin or the like.

[Brief description of the drawings]

FIG. 1 is a ternary composition diagram showing the composition of a soft magnetic material having an easy axis of magnetization in a direction other than the C-axis produced by the method of the present invention.

Claims (5)

(57) [Claims] The composition is (AO) _a (Me _1-x Co _x O) _b (Fe _2-y D _y
O ₃ ) At least one type of _c- type magnetic oxide (where A is Ba, S
At least one of alkaline earth metals such as r, and Me is divalent F
e, Ni, Zn, Mn, Cu, Cd, Mg, and at least one of (Fe ³⁺ + Li ¹⁺ ) / 2, and D is trivalent Al, Mn, Cr, Ga, (Co ²⁺ +
Ti ⁴⁺ ) / 2, x represents the amount of substitution of Me, and y represents the amount of substitution of Fe). Ten
A method for producing a soft magnetic hexagonal ferrite having an axis of easy magnetization in a direction other than the C-axis made of plate-like particles, comprising heat-treating at 00 to 1400 ° C., cooling and then removing the flux by dissolving in water. 2. The method according to claim 1, wherein the magnetic oxide is (AO) (Me _1-x Co _x O) ₂ (Fe _{2 -y} D _y O ₃ ) ₈ (x is from 0.35 to
1, y is 0.5 or less), (AO) ₂ (Me _1-x Co _x O) ₂ (Fe _2-y D
_y O _{3) 6} (x is 0 to 1, y is 0.5 or less), and (AO)
₃ (Me _1-x Co _x O) ₂ (Fe _2-y D _y O ₃ ) ₁₂ (X is 0.25 to 1, y
Is 0.5 or less). (However, A is at least one of alkaline earth metals such as Ba and Sr, Me is divalent Fe, Ni, Zn, Mn, Cu, C
At least one of d, Mg, and (Fe ³⁺ + Li ¹⁺ ) / 2, and D is at least one of trivalent Al, Mn, Cr, Ga, and (Co ²⁺ + Ti ⁴⁺ ) / 2. ). 3. The plate-like particles have an average diameter of 1 to 100 μm,
2. The method according to claim 1, wherein the average thickness is 0.01 to 10 [mu] m, and the average diameter / average thickness ratio is 5 or more. 4. A flux comprising a sulfate such as K ₂ SO ₄ or Na ₂ SO ₄ ,
3. The method according to claim 1 or 2, wherein the flux is 20 to 70 mol% based on the total amount of the flux and the raw material oxide. 5. The method according to claim 1, wherein the raw material oxide has a composition (AO) _a (Me _1-x Co
_x O) _b (Fe _2−y D _y O ₃ ) _c has a composition that produces a magnetic oxide (where a + b + c = 100, as shown in FIG. 1, the composition points (a, b, c) is I (5,40,5)
5), II (30, 15, 55), III (25, 5, 70), IV (5,
15. The manufacturing method according to item 1, wherein the area is a range surrounded by four points (15, 80).