JPH11144932A - Method for forming insulating film of dust core magnetic powder and mixing device used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent attachment of magnetic powder to the inner wall of a mixing container by using a non-metal material for the mixing container in which an insulating film forming processing solution and magnetic powder are put. SOLUTION: A polyethylene container is used as a mixing container 10, and the gap between a housing section 5 and the mixing container 10 is caused to be about 10 cm, so that the mixing container vertically moves only about 10 cm to receive shock and vibration. As an insulating film forming processing solution, a solution prepared by dissolving phosphoric acid, boric acid and MgO as a metal oxide and adding a surface active agent and an anti-corrosive agent is used. Atomized spherical iron powder to which this insulating film forming processing solution is added is injected into the mixing container 10 and is rotationally mixed. For the mixing container, resin materials of polypropylene, polyethylene terephthalate, nylon and vinyl chloride are more preferred, in addition to polyethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a powder magnetic core,
Especially for high frequency transformers, reactors, thyristor valves,
The present invention relates to a method for forming an insulating coating of magnetic powder suitable for a method for producing a high frequency dust core such as a noise filter and a choke coil, and a mixing apparatus used for the method.

[0002]

2. Description of the Related Art A magnetic core used in a high-frequency coil of this type has a low iron loss, a high magnetic flux density, and a magnetic characteristic in a high frequency range (1 to 10 MHz).
Is not required to decrease. The iron loss includes an eddy current loss, which is closely related to the specific resistance of the magnetic core, and a hysteresis loss, which is affected by distortion in the iron powder resulting from the manufacturing process of the iron powder and the subsequent process history. The iron loss W can be expressed by the sum of the eddy current loss and the hysteresis loss as in the following equation 1. In Equation 1, f is the frequency, Bm is the exciting magnetic flux density, ρ is the specific resistance, t is the thickness of the material, k ₁ , k ₂
Is a coefficient.

[0003]

[Formula 1] W = (k ₁ Bm ² t ² / ρ) f ² + k ₂ Bm
^1.6 f

According to Equation 1, the eddy current loss increases in proportion to the square of the frequency. To improve the characteristics at high frequencies, the eddy current loss must be reduced. In order to reduce the eddy current loss, it is necessary to confine the eddy current to a small area. The effect is high if the magnetic powder is formed by compression and a dust core having a configuration in which individual magnetic powder particles are insulated. In this case, even if the dust core is insufficiently insulated, the eddy current loss increases. When the insulating coating is thickened, the ratio of the magnetic powder in the magnetic core decreases, and the magnetic flux density decreases. If this magnetic flux density is improved by increasing the density of the dust core, compression molding under high pressure is inevitable, distortion during molding is inevitable, hysteresis loss increases, and iron loss increases. Therefore, in manufacturing a dust core, it is important to increase the specific resistance of the core without lowering the density. For that it is thin,
In addition, it is essential to completely cover the powder with an insulating film having good insulating properties.

Regarding the above-mentioned insulating coating of magnetic powder, as a conventional method of forming a thin insulating coating on magnetic powder, phosphate conversion is known as disclosed in JP-A-63-70504 and JP-A-6-260319. It is known that an insulating film is formed using a treatment liquid, and there is one described in Japanese Patent Application No. 8-133239 previously developed by the present applicant. This development technology is to improve the phosphate chemical conversion treatment solution and to add a surfactant to the treatment solution when the insulating powder is formed by chemical reaction by contacting the magnetic powder with a reactive insulation film formation treatment solution. By lowering the surface tension and improving the wettability between the treatment liquid and the magnetic powder, a high-quality insulating film can be formed thinner and more uniformly on the surface of the magnetic powder.

[0006]

However, when a surfactant is contained in the above-mentioned insulating film forming treatment liquid, a V-type mixer commonly used for powder mixing is used, as shown in FIG.
As shown in (b) and (d), in the V-shaped mixing container 20 rotated up and down via the pivot 21, the magnetic powder adheres to the inner wall of the mixing container 20 so that normal coating cannot be performed. There is a problem that it becomes difficult to control the mixing of the components, and the formed insulating film becomes non-uniform. This problem, for example,
A similar tendency occurs in a mixer such as a double cone blender used for mixing powder and liquid. In addition, when using a conventional stirrer, the powder sandwiched between the stirrer and the container was crushed by pressure to forcibly stir with the stirrer. The insulating film is peeled off or the specific resistance is reduced.

[0007] The applicants of the present application have studied the above problems, and as a result, the conventional mixer used for the green compact is usually a metal mixing container. As a result, the inventors of the present invention have found that the increase in wettability not only with the magnetic powder but also with the metal mixing container has led to the completion of the present invention.

[0008]

In order to solve the above-mentioned problems, the method of the present invention comprises mixing a phosphate conversion treatment solution, an insulating film forming treatment solution containing at least a surfactant, and a magnetic powder with the magnetic powder. In the method for forming an insulating film of a magnetic powder for a dust core, the method comprises using a non-metallic material for a mixing container for containing the insulating film forming treatment liquid and the magnetic powder. Further, in the method of the present invention, in the method of forming an insulating film, a non-metallic material is used for a mixing container in which the treatment liquid for forming an insulating film and the magnetic powder are mixed, and the mixing is performed while applying an impact vibration to the mixing container with rotation. preferable.

In the present invention described above, the V-type mixer or the like frequently used for powder mixing is usually a stainless steel mixing container, and as described above, the insulating film forming treatment solution containing a surfactant and the When the powder is charged, the surfactant improves the wettability with the magnetic powder and the mixing vessel together with the magnetic powder, and the mechanism whereby the insulating powder formed by the adhesion of the magnetic powder to the inner wall of the mixing vessel becomes non-uniform accordingly. It was elucidated and completed. That is, in the present invention, by using a nonmetallic material for the mixing container, the wettability to the insulating film forming treatment liquid is reduced, and the adhesion of the magnetic powder to the inner wall of the mixing container is prevented. In this case, it is conceivable to apply a resin coating such as Teflon on the surface of the metal mixing container,
Such a coating method is disadvantageous in terms of investment in equipment and equipment, and has a long-term durability problem such as peeling of a coating film.

As the non-metallic material for the mixing vessel to be used, a resin material having low wettability with the above-mentioned insulating film forming treatment liquid is preferable. Still, there is a possibility that some spontaneous adhesion may occur. For this reason, as a mixing mode, it is desirable to mix the mixing container while applying impact vibration, and to force the attached magnetic powder to fall by the impact collision. By doing so, it is possible to always maintain a uniform coating action on the magnetic powder surface of the insulating coating forming treatment liquid in the mixing vessel,
A high-quality insulating film can be formed thinner and more evenly. After mixing, drying is the same as in the past. In addition, since the mixing container receives the above-described impact vibration, resin materials such as polyethylene, polypropylene, polyethylene terephthalate, nylon, and vinyl chloride are more preferable in consideration of wet resistance and impact resistance. When using ceramics, ceramics, etc., care must be taken when selecting ceramics and ceramics because they may be broken by impact vibration.

Further, the apparatus of the present invention has a mixing container for containing an insulating film forming treatment liquid and magnetic powder, and the mixing device for forming an insulating film of magnetic powder mixed by rotating the mixing container. On the other hand, it has at least a rotating body rotated via a pivot, and a storage portion provided on the rotating body to hold the mixing container, and the insulating coating forming treatment liquid and the magnetic powder in the mixing container. , Which is rotatably moved to the top and bottom through the rotating body and mixed, and at the same time, the periodic impact vibration deviating from the trajectory of the rotational movement is given to the mixing container so that the magnetic powder attached to the inner wall of the mixing container can be dropped. It is. With this device structure, the above-described method of the present invention can be reliably performed, and can be relatively easily realized by the constituent members and the driving mechanism as in the following embodiments.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following embodiments, a typical example of the mixing apparatus of the present invention will be described, and then the method of the present invention will be described in detail along with examples. The mixing apparatus shown in FIGS. 1 to 4 has been devised for carrying out the method of the present invention, and FIG. 1 shows the configuration of the apparatus viewed from the side and from above. FIG. 2 shows an example of a storage section for a mixing container provided in the apparatus, FIG. 3 shows another example of the impact vibration mechanism, and FIG. 4 shows an example of the mixing container.

The mixing device shown in FIG. 1 is rotated via a motor 4 in a state in which a rotating body 2 is held on an apparatus frame 1 via a pivot 3, and a plurality of mixing vessels are mounted on the rotating body 2. Is provided with a storage unit 5. The device frame 1 is formed into a three-dimensional structure constituted by substantially rectangular parallelepiped sides by upper and lower frames 1a and 1b and four vertical frames 1c provided between the upper and lower frames 1a and 1b. Bearings 6 are fixed to opposing sides of the upper frame 1a, respectively. The pivot 3 is pivotally supported by the bearings 6 and is disposed substantially horizontally. A sprocket 7 is mounted on a part of the pivot 3. This sprocket 7
Is connected to a drive unit of the motor 4 mounted on the lower frame 1b by a chain 8, and is rotated via the chain 8. The rotating body 2 is fixed to a position substantially at the center of the pivot 3, and is driven in conjunction with the rotation of the pivot 3. The rotating body 2 has a plurality of storage portions 5 protruding from one side surface. Each of these storage sections 5 is provided in a storage space corresponding to the mixing vessel 10 and has a band 9 for preventing the stored mixing vessel 10 from falling out.

In the above-described mixing apparatus, the drive of the motor 4 is transmitted to the pivot 3 via the chain 8 and the sprocket 7 to rotate the rotating body 2, and the mixing held in each of the storage sections 5 with the rotation. In this configuration, the container 10 is sequentially rotated up and down. Further, in this structure, as illustrated in FIG. 2A, the mixing container 10 is held by each of the storage sections 5 via the band 9 and rotated. In this case, the mixing container 10 corresponds to FIG.
It may be formed to have a size that can be stored in the space of the storage part 5 without a gap like the container of reference numeral 10a of (a), but by forming the vertical dimension and the like small like the container of reference numeral 10b in FIG. Preferably. In this case, in the process of turning upside down, at the upper position, as shown in the figure, it moves to the inner surface (the surface on the center side of the rotating body 2) inside the storage portion 5, and conversely, at the lower position, the storage portion 5 moves. 5 to an outer surface (a surface on the outer peripheral side of the rotating body 2). Each of these movements occurs periodically in the process of rotating the rotating body 2 in the vertical direction, acts as an impact vibration on the mixing container 10b, and becomes a drop force of the magnetic powder attached to the inner wall of the mixing container 10b.

Such a dropping action of the magnetic powder can be made larger based on the basic structure described above, or can be deformed so that a mixing action can be obtained at the same time. Mixing container 1
If you want to increase the impact force applied to zero, see FIG.
As illustrated in (b), the storage unit 5 is
When the length of “a” is relatively large, the moving distance of the mixing container 10 in the storage portion 5a is sufficiently ensured, the impact force due to its own weight is increased, and the magnetic powder attached to the inner wall of the mixing container 10 is more reliably removed. Can fall. As an example of the structure accompanied by the mixing action, one of a spiral ((non-linear)) guide groove and a projection which are fitted to each other is formed on the inner wall of the storage portion 5a and the outer surface of the mixing container 10, respectively. Container 10 is storage section 5
A configuration in which the mixing container 10 moves up and down along the guide groove while rotating in a torsional motion when moving in the area a may be considered.

Further, as another example of a structure for applying impact vibration to the mixing vessel 10, it is also possible to use a cam means as shown in FIG. FIGS. 3A and 3B are schematic configuration diagrams viewed from the apparatus side and one end. In this device, FIG.
The rotating body 2 is mounted on the pivot 3. This rotating body 2 is in a state where the corresponding ends of the pivot 3 are fitted into the guide grooves 12 provided in the vertical frames 11 b on both sides, respectively.
It is held movably up and down via the pivot 3 and the guide groove 12. A column 13 is provided upright from the horizontal frame 11a between the rotating body 2 and one vertical frame 11b, and the vertical frame 11b and the column 13 have a drive shaft 1 mounted thereon.
4 is rotatably supported. The drive shaft 14 has a cam 15 mounted on a shaft between the vertical frame 11b and the column 13, and a pulley 16 mounted on a shaft end. They are connected by a belt 17 and are rotated via the belt 17. Therefore, the feature of this device is that the drive of the motor 4 is transmitted to the drive shaft 14 via the belt 17 and the pulley 16, and the drive shaft 14 rotates together with the cam 15. In this rotation process, the cam 15 is in contact with the pivot 3, and the contact force of the cam 15 at this time is such that the mixing container 1 held in the storage portion 5 by rotating the pivot 3
At the same time as rotating the axis 0 to the top and bottom, the pivot 3 is moved upward along the guide groove 12 and acts as an impact vibration deviating from the rotation trajectory of the rotating body 2 to drop the magnetic powder attached to the inner wall of the container. Functions similarly to the structure of FIG.

Further, as another example of the structure for applying the impact vibration to the mixing container 10 described above, for example, the mixing container itself is formed in a three-pronged shape, and the center of the three-pronged shape is rotatably supported. In addition, it is conceivable that the mixing container itself can be periodically moved in a direction substantially intersecting with the rotation trajectory during the rotation process by a mechanism similar to the above-mentioned cam means.

On the other hand, the mixing container 10 is a resin molded article made of polyethylene or the like in consideration of wettability and impact resistance of the insulating film forming treatment liquid. The shape of the container is arbitrarily designed as long as the container body can be sealed by the lid member. In this case, as illustrated in FIGS. 4A and 4B, when the substantially conical cone portions 10c and 10d are formed on the bottom portion or the lid member of the container body, the insulating coating forming treatment liquid and the magnetic powder are mixed. The dispersion and collision of the cones 10c and 10d can also be expected to result in more uniform mixing.

[0019]

EXAMPLES The method for forming an insulating film of magnetic powder according to the present invention will be described below in detail with reference to examples. This embodiment is different from the mixing apparatus of the present invention shown in FIG. 1 in comparison with the mixing apparatus shown in FIG.
It is a case where it carried out on the following conditions using a mold mixer. As the mixing container 10 of the present invention, a commercially available polyethylene container (capacity: 10 liters) is used, and when impact vibration due to falling is applied (invention mixing mode 1), and when impact vibration is not applied (invention mixing). Form 2) -2
Used in one embodiment. In the former, the gap (gap) between the storage part 5 and the mixing container 10 shown in FIG.
The mixing vessel moves up and down by 10 cm and receives impact vibration.
The latter made the gap of 10 cm immovable with the spacer S interposed. Similarly, the mixing vessel 20 of the V-type mixer has a capacity of 10 liters (conventional mixing mode).

The solution for forming an insulating film is composed of 20 g of phosphoric acid, 4 g of boric acid, and 4 g of MgO as a metal oxide per liter of water.
It is dissolved, and EF-104 (manufactured by Tokemi Products) is used as a surfactant, and benzotriazole (0.04 mol) is added as a rust preventive. Then, a solution obtained by adding 50 ml of this insulating film forming treatment liquid to 1 kg of atomized spherical iron powder having an average particle diameter of 70 μm was prepared for testing. 10 kg of each of the above-prepared products was put into each of the mixing containers 10 and 20, and set in the mixing apparatus of the present invention and a V-type mixer. The driving conditions are both rotation speed 2
Mix for 20 minutes at 0 rpm. Then, it dried at 180 degreeC for 60 minutes using the warm air circulation type | mold high temperature tank, and the insulating treatment state of the iron powder surface was investigated.

Table 1 shows a list of the results of visually observing the presence or absence of adhesion of the powder in the mixing container after mixing the powder. Visual observation confirms the effectiveness of the non-metallic mixing container as shown in Table 1. When mixing while applying impact vibration, the adhesion of magnetic powder to the inner wall of the container is completely eliminated, and the ideal mixing form is obtained. Was also realized. In addition, the dispersion state of P as an element was examined by Auger analysis in order to check the coating state of the phosphate on the surface of the insulated iron powder after drying. As a result, in the insulated iron powder using the V-type mixer, a portion where P was concentrated and a portion where P was not present were clearly distinguished. On the other hand, P was uniformly detected in any of the insulated iron powders using the mixing apparatus of the present application, and it was confirmed that the insulating film was formed uniformly.

[0022]

[Table 1]

Next, the following test pieces of the dust core were prepared using the three types of magnetic powders for forming an insulating film prepared above. After adding 2% by weight of a polyimide resin as a binder and adding 0.1% by weight of lithium stearate as a molding lubricant, the mixture is filled into a mold, compression-molded at a pressure of 500 MPa, and then 60 mm × 10 mm × 10 mm. The test piece of the powder magnetic core was manufactured. 200 ° C for compression molding
And cured for 4 hours. Then, the specific resistance of each of these test pieces was measured, and the change in the specific resistance when stored in an atmosphere at 15 ° C. and a humidity of 90% for a maximum of 80 days was measured. Table 2 lists the results, and FIG. 6 is a graph.

As is clear from Table 2 and FIG. 6, the dust core test pieces prepared from the insulated iron powders obtained according to Inventive Mixtures 1 and 2 all show high specific resistance values,
Since the insulating film is formed uniformly, no rust occurs,
It can be seen that the specific resistance does not change even after storage for 80 days. Also, it can be seen that the application of the shock vibration enables the insulating film to be formed more uniformly, the initial specific resistance value and the change in the specific resistance value to be small, and the effect is higher. In contrast,
In the dust core test piece made from the insulated iron powder obtained by the V-type mixer, the insulating coating was not formed uniformly, and rust was generated from the portion without the insulating coating. The insulation film is destroyed by this and rust further progresses,
The specific resistance value has dropped sharply.

[0025]

[Table 2]

As described above, in the method of the present invention using the mixing vessel made of a nonmetallic material, the insulating coating is uniformly formed on the iron powder, and the dust core using the iron powder has a high specific resistance value. Even after a number of days, the specific resistance value does not change, and the quality can be greatly improved.

[0027]

As described above, according to the present invention, an insulating film forming treatment solution containing at least a phosphate chemical conversion treatment solution and a surfactant is mixed with a magnetic powder to form an insulating film on the surface of the magnetic powder. In the method of forming an insulating coating of a magnetic powder for a dust core, a non-metallic material is used for the mixing container to prevent the magnetic powder from adhering to the inner wall of the mixing container and to form a uniform insulating coating on the surface of the magnetic powder. And a dust core having high specific resistance can be obtained. Further, the mixing device of the present invention enables the method of the present invention to be reliably performed, and the device configuration can be realized relatively easily.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an example of a mixing apparatus of the present invention.

FIG. 2 is a configuration diagram showing a relationship and deformation between a storage section and a mixing container in the mixing apparatus.

FIG. 3 is a schematic configuration diagram showing another example of the shock vibration mechanism of the mixing device.

FIG. 4 is a view showing a modification of the mixing container.

FIG. 5 is a schematic diagram showing a mixing apparatus and a mixing mode used in an example of the method of the present invention.

FIG. 6 is a graph showing a result of examining a change in a specific resistance value with respect to a change in storage days for a dust core test piece manufactured from the example.

[Explanation of symbols]

 1 is an apparatus frame 2 is a rotating body 3 is a pivot 4 is a motor 5 is a storage unit 10 is a mixing container 14 is a drive shaft 15 is a cam

Claims (4)

[Claims] Insulating a magnetic powder for a dust core, wherein an insulating film forming treatment solution containing at least a phosphate chemical conversion treatment solution and a surfactant is mixed with a magnetic powder to form an insulating film on the surface of the magnetic powder. In the method for forming a coating film, a non-metallic material is used for a mixing container in which the treatment liquid for forming an insulating coating film and the magnetic powder are placed. 2. Insulation of a magnetic powder for a dust core, wherein an insulating film forming treatment solution containing at least a phosphate chemical conversion treatment solution and a surfactant is mixed with a magnetic powder to form an insulating film on the surface of the magnetic powder. In the method for forming a coating film, a non-metallic material is used for a mixing container in which the insulating film forming treatment liquid and the magnetic powder are placed, and mixing is performed while applying an impact vibration to the mixing container while rotating the mixing container. Method for forming an insulating film. 3. The method according to claim 1, wherein the non-metallic material is a resin material selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, nylon, and vinyl chloride. 4. A mixing device for forming an insulating coating of magnetic powder, which comprises a mixing container for storing an insulating coating forming treatment liquid and magnetic powder, wherein the mixing container is rotated to mix the magnetic powder. A rotating body to be rotated,
And at least a storage portion provided on the rotating body to hold the mixing container, and an insulating film forming treatment liquid and a magnetic powder in the mixing container,
At the same time as rotating and moving to the top and bottom through the rotating body to mix, the magnetic powder adhering to the inner wall of the mixing container can be dropped by applying a periodic shock vibration deviating from the trajectory of the rotation to the mixing container. A mixing apparatus for forming an insulating coating of magnetic powder, characterized by the following.