JP2014229839A - Powder-compact magnetic core, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a powder-compact magnetic core which delivers an excellent performance in view of any of the standard deviation of the density, the magnetic property and the hardness; and a method for manufacturing such a powder-compact magnetic core.SOLUTION: A method for manufacturing a powder-compact magnetic core comprises the steps of: mixing powder of a magnetic material, powder of glass having a transition point lower than a crystallization temperature of the magnetic material powder, and a binding resin together; press-compacting the resultant mixture at a room temperature; and performing a heat treatment on the resultant compact at a temperature lower than the crystallization temperature of the magnetic material powder in a non-reducing atmosphere. The difference between the transition point of the glass powder, and the crystallization temperature of the magnetic material is 50°C or more. The difference between a crystallization temperature of the glass and the crystallization temperature of the magnetic material powder is 50°C or less. The quantity of the mixed glass is in a range of 0.5-5 wt% of that of the magnetic material powder. It is preferable to decide the quantity of the mixed glass according to the magnetic permeability of the powder-compact magnetic core to be manufactured. Further, it is preferable that the glass powder has a particle diameter of 0.5-5 μm. In mixing the magnetic material powder and the glass powder, a lubricative resin may be added thereto.

Description

  The present invention relates to a dust core used for a smoothing choke coil or the like and a method for manufacturing the same.

  A choke coil is used to smooth the output waveform of a switching power supply or the like. As various electronic devices become more sophisticated and multifunctional, the choke coil magnetic core used therein is required to have a small characteristic change even at a large current. Specifically, a magnetic core having excellent direct current superposition characteristics and low loss characteristics is required. Conventionally, ferrite cores and dust cores have been used as this type of magnetic core. Among these, a dust core made of amorphous soft magnetic powder (amorphous soft magnetic powder) has excellent DC superposition characteristics and low loss characteristics.

  In order to obtain a powder magnetic core using these amorphous soft magnetic powders (hereinafter referred to as soft magnetic powders), the soft magnetic powder is mixed with a low-melting glass and a binder resin and the mixture is mixed at room temperature or After compression molding at a high temperature, the obtained molded body is subjected to heat treatment. In the method of Patent Document 1, a molded body is produced by forming a mold and soft magnetic powder at a high temperature during molding. In the method of Patent Document 2, a soft magnetic powder is mixed with a low-melting glass and a binder resin to produce a molded body at room temperature.

Japanese Patent Laid-Open No. 10-212503 JP 2001-73062 A

  However, Patent Documents 1 and 2 do not describe in detail the physical properties of glass and the effects based thereon. The magnetic properties of the produced dust core are also evaluated only for magnetic permeability, and no iron loss is described. In these prior arts, it was not possible to obtain a dust core with low loss and high strength.

  The present invention provides a powder magnetic core in which a magnetic powder and a glass powder having a transition point lower than the crystallization temperature of the magnetic powder are mixed, and the transition point of the glass powder is the crystallization of the magnetic powder. The glass powder has a difference of 50 ° C. or more, and the crystallization temperature of the glass powder has a difference of 50 ° C. or less with the crystallization temperature of the magnetic powder.

  In the present invention, the magnetic powder may be an amorphous soft magnetic powder. The mixing amount of the glass is in the range of 0.5 wt% to 5 wt% of the magnetic powder, and the mixing amount of the glass can be determined according to the permeability of the dust core to be manufactured. The particle size of the glass powder mixed with the magnetic powder can be set to 0.5 μm to 5 μm. In addition, a binder resin can be mixed together with the magnetic powder and the glass powder, and the binder resin can be a methylphenyl silicone resin. In mixing the magnetic powder and the glass powder, a lubricating resin may be added.

  Moreover, this invention also makes the manufacturing method which manufactures the above powder magnetic cores as one aspect | mode. In the production method of the present invention, a magnetic powder and a glass powder having a transition point lower than the crystallization temperature of the magnetic powder are mixed and pressed, and then at a temperature lower than the crystallization temperature of the magnetic powder. In the method of manufacturing a powder magnetic core for performing a heat treatment, the transition point of the glass powder has a difference of 50 ° C. or more from the crystallization temperature of the magnetic powder, and the crystallization temperature of the glass powder is the magnetic substance It has a difference from the crystallization temperature of the powder to 50 ° C. or less. The pressure molding may be performed at 5 ° C. to 80 ° C., and the heat treatment may be performed in a non-reducing atmosphere.

  In order to reduce the loss (core loss) of the dust core, eddy current loss may be mainly reduced. According to the present invention, low melting point glass and binder resin are mixed with magnetic powder, and the periphery of the magnetic powder is coated with glass, thereby reducing eddy current loss, low loss, high magnetic permeability, and direct current. It is possible to provide a dust core having excellent superposition characteristics and high strength. In particular, in the present invention, the heat treatment temperature for the molded body is 50 ° C. or more away from the transition point of the glass powder, and within the difference of 50 ° C. or less from the crystallization temperature of the glass powder. It is possible to improve the strength of the molded body after the heat treatment by utilizing the fluidity.

The graph which shows the deviation of the crystallization temperature of the soft-magnetic powder in an Example, and the transition point and crystallization temperature of glass. The graph which shows the relationship between the heat processing temperature and magnetic permeability in an Example. The graph which shows the relationship between the heat processing temperature and core loss in an Example. The graph which shows the direct current | flow superimposition characteristic in an Example. The photograph of the state of the glass powder before the heat processing in an Example. The photograph of the state of the glass powder after the heat processing in an Example. The graph which shows the result of the crushing strength after the heat processing in an Example.

(1) Magnetic powder As the magnetic powder, pure iron powder or amorphous soft magnetic powder (hereinafter simply referred to as “soft magnetic powder”).
) Can be used. Examples of the soft magnetic powder include Fe-based (Fe-Si-B-Cr-based) alloy atomized powder and pulverized powder. For example, as an Fe-based alloy powder, a Si component of 6.7%, a B component of 2.5%, a Cr component of 2.5%, a C component of 0.75%, and the remaining component of Fe can be used. .

  In addition, FeBPN (N is one or more elements selected from Cu, Ag, Au, Pt, and Pd) can be used as the soft magnetic powder. As the soft magnetic powder, those produced by a water atomizing method, a gas atomizing method, or a water / gas atomizing method can be used, and those by a water atomizing method are particularly preferable. The reason is that the water atomization method is rapidly cooled at the time of atomization, so that it is difficult to crystallize.

  The average particle size of the magnetic powder is preferably 30 to 100 μm. The crystallization start temperature of the magnetic powder is usually about 450 ° C. The magnetic powder is preferably a metallic glass having a glass transition temperature Tg lower than the crystallization temperature Tx and showing a supercooled liquid region. This is because the core loss can be suppressed because the magnetocrystalline anisotropy is suppressed by using metallic glass. Magnetostriction is large and magnetic permeability is easily affected by external stress.

(2) Glass As the glass, bismuth-based, phosphoric acid-based, alkali-based, or vanadium-based low-melting glass is used. In addition, a glass having a softening point equal to or lower than the crystallization temperature of the magnetic powder can be used. By using a glass whose softening point is equal to or lower than the crystallization temperature of the magnetic powder, even when the glass is heated to a temperature at which the glass is softened, it is possible to prevent a reduction in magnetic properties due to the crystallization of the magnetic powder.

In particular, in the present invention, as glass, the transition point is about 50 ° C. lower than the crystallization start temperature of the magnetic powder, and the difference between the crystallization temperature of the magnetic powder and the crystallization temperature of the glass is 50 ° C. or less. Use something. This is because the difference between the glass transition point and the heat treatment temperature is large, the softening of the glass proceeds and the viscosity of the glass decreases, and the crystallization temperature of the glass is close to the crystallization temperature of the magnetic powder. This is because the fluidity is increased, the fluidity of the magnetic powder is easily increased, and the coating property of the magnetic powder is increased. Mechanical strength can be increased by filling the gaps between the magnetic powders with glass. In addition, it is preferable that the magnetic powder has a low thermal expansion coefficient so that a compressive stress is not applied to the magnetic powder. Furthermore, generally, glass has a property of increasing strength by increasing the temperature, but in the present invention, since magnetic powder is used, temperature is limited. Examples of the glass suitable for the present invention include bismuth-based glass (Bi ₂ O ₃ .B ₂ O ₃ ).

  The mixing amount of the glass is set according to the desired magnetic permeability. However, if the amount of glass mixed with the magnetic powder is small, the coating between the magnetic powders is not sufficient, and eddy current loss increases. When the mixing amount of glass is large, the magnetic permeability of the magnetic powder is reduced and the magnetic powders are aggregated, so that sufficient magnetic properties cannot be secured. For example, from the range of about 0.5 wt% to 5 wt% of the magnetic powder, the glass mixing amount is determined in accordance with the desired magnetic permeability.

  Glass is mixed with the magnetic powder as a powder. The particle size (D50 / average particle size) of the glass powder is preferably 5 μm or less, particularly preferably 0.5 to 1.5 μm. When the particle size of the glass powder exceeds 5 μm, the transition point increases and the viscosity does not decrease.

(3) Binder Resin The binder resin is added to the mixed powder of magnetic powder and glass powder. As a binder resin, when a mixture of magnetic powder and glass powder is pressurized at room temperature, a compact that has been densified to some extent is obtained, and as long as no excessive force is applied to the compact. A resin having a viscosity capable of maintaining a predetermined shape is used.

  Examples include silicone resins and waxes. As the silicone resin, methylphenyl silicone resin is preferable. An appropriate amount of the methylphenyl silicone resin added is 0.75 to 2.0 wt% with respect to the magnetic powder. If it is less than this, the strength of the molded product will be insufficient and cracks will occur. If it is more than this, there arises a problem that the maximum magnetic flux density is decreased due to the decrease in density and the magnetic characteristics are decreased due to an increase in hysteresis loss.

  As other binder resin, an acrylic acid copolymer resin (EAA) emulsion can be used. The addition amount of the acrylic acid copolymer resin (EAA) emulsion to be mixed is 0.5 to 2.0 wt% with respect to the alloy powder, and the drying temperature and drying time in that case are 80 ° C. to 150 ° C. for 2 hours. is there. Instead of the acrylic acid copolymer resin (EAA) emulsion, an aqueous PVA (polyvinyl alcohol) solution (12% aqueous solution) may be used. An appropriate amount of PVA (polyvinyl alcohol) aqueous solution (12% aqueous solution) is 0.5 to 3.0 wt% with respect to the magnetic powder.

(4) Lubricating resin As the lubricating resin, stearic acid and its metal salt, and waxes such as ethylene bisstearamide can be used. By mixing these, it is possible to improve the sliding between the powders, so that the density during mixing can be improved and the molding density can be increased. Furthermore, it is possible to reduce the punching pressure of the upper punch during molding and to prevent the vertical stripes on the core wall surface from being generated due to the contact between the mold and the powder. The addition amount of the lubricating resin is preferably about 0.1 wt% to 1.0 wt% with respect to the magnetic powder, and is generally about 0.5 wt%.

(5) Manufacturing method The manufacturing method of the powder magnetic core of this embodiment has the following steps.
(A) A step of mixing magnetic powder and low-melting glass.
(B) A step of adding a binder resin to the mixture obtained in the mixing step.
(C) A molding step for producing a molded body by pressurizing the mixture that has undergone the binder resin addition step.
(D) A heat treatment step for heating the molded body obtained by the molding step.

Hereinafter, each step will be described in detail.
(A) Glass mixing step In the mixing step, for example, 0.5 wt% to 5 wt% glass powder is added to and mixed with the magnetic powder having an average particle size of 30 to 100 µm. For example, the above mixture is mixed for about 2 hours using a V-type mixer.

(B) Binder resin addition step 0.75 to 2.0 wt% of the binder resin and 0.1 to 1.0 wt% of the magnetic powder with respect to the mixture of the magnetic powder and the glass powder. % Lubricating resin is added and further mixed. It is also possible to simultaneously mix the glass powder (a) and the binder resin and the lubricating resin (b).

  In the step of adding the binder resin, a silane coupling agent can also be added. When a silane coupling agent is used, the amount of the binder resin can be reduced. As the type of silane coupling agent having good compatibility, an amino silane coupling agent can be used, and γ-aminopropyltriethoxysilane is particularly preferable. The amount of the silane coupling agent added to the binder resin is preferably 0.25 wt% to 1.0 wt%. By adding a silane coupling agent in this range to the binder resin, the standard deviation of density of the molded dust core, magnetic characteristics, and strength characteristics can be improved.

(C) Molding step In the molding step, the mixture to which the binder resin has been added is filled into a mold and pressure-molded. In that case, the mold temperature is preferably room temperature, but may be in the range up to 80 ° C. That is, the normal temperature here means a range from 5 ° C. to 35 ° C., but may be a range from 5 ° C. to 80 ° C. The molding pressure is, for example, 1300 to 1700 MPa.

(D) Heat treatment step The heat treatment for the molded body is performed in a non-reducing atmosphere such as an air atmosphere. The non-reducing atmosphere may be in an inert gas atmosphere such as 100% nitrogen gas in addition to the air. For example, the molded body can be heated in the atmosphere at a temperature of 350 ° C. for 2 hours, and then switched to a nitrogen atmosphere and heated at 470 ° C. for 2 hours. Heat treatment in a non-reducing atmosphere prevents the glass from being reduced by hydrogen, prevents the coating film from deteriorating in insulation, and maintains the original glass properties without losing oxygen in the glass. Serves to coat the periphery of the powder.

  The heat treatment temperature is preferably 400 ° C. to 440 ° C., and the heating time is about 2 to 4 hours. The reason for maintaining such a temperature and heating time is to ensure the crushing strength required when the powder magnetic core is formed into a ring shape in a state of not higher than the crystallization temperature of the magnetic substance powder. On the other hand, if the heat treatment temperature is raised too much, the crystallization of the magnetic powder proceeds, the magnetic permeability decreases, and the iron loss (hysteresis loss) increases. Therefore, maintaining a temperature of 400 ° C. to 440 ° C. is effective for suppressing an increase in iron loss.

  Examples of the present invention will be described below with reference to Tables 1 to 3 and FIGS.

(1) Measurement items As measurement items, permeability and iron loss were measured by the following methods. The magnetic permeability was calculated from the inductance at 100 kHz and 0.5 V by applying a primary winding (10 turns) to each dust core produced and using an impedance analyzer.

  For iron loss, the primary winding (15 turns) and the secondary winding (3 turns) are applied to each dust core, and a BH analyzer (Iwatsu Measurement Co., Ltd .: SY-8232), which is a magnetic measurement device, is used. The iron loss was calculated under the conditions of a frequency of 100 kHz and a maximum magnetic flux density Bm = 0.05T. This calculation was performed by calculating the hysteresis loss coefficient and the eddy current loss coefficient of the iron loss frequency curve by the following method (1) to (3) by the least square method.

Pc = Kh × f + Ke × f ² (1)
Ph = Kh × f (2)
Pe = Ke × f ² (3)
Pc: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

  Regarding the strength, the crushing strength was measured according to JIS 2507.

(2) Sample preparation method The sample used for the characteristic comparison was prepared as follows.
Fe-Si-B Fe-based amorphous soft magnetic powder having an average grain size of 45 μm and a crystallization temperature of 450 ° C., 1.5 wt% of bismuth-based glass having various transition points and particle sizes, lithium stearate (lubricating Agent) is mixed with 0.3 wt%, organic binder (silicone resin) is mixed with 2.0 wt%, dried at 150 ° C., passed through a sieve with an opening of 850 μm, and lithium stearate (lubricant) is further added. A granulated powder was prepared by mixing 0.3 wt%.

  A molded body was produced from this at a normal temperature and a pressure of 1700 MPa, and heat-treated at 400 ° C., 420 ° C., 440 ° C., 460 ° C., and 480 ° C. for 2 hours in the air atmosphere.

  As described above, the mixing amount of the glass here defines the coating amount on the soft magnetic powder, and is not limited to 1.5 wt%. As described above, if the glass mixing amount is small, the coating onto the soft magnetic powder becomes insufficient, resulting in an increase in eddy current loss. In addition to a decrease in the magnetic permeability of the magnetic powder, there is a possibility that the soft magnetic powders may be aggregated, so that sufficient magnetic properties cannot be ensured. What is necessary is just to determine the mixing amount of glass according to a desired magnetic permeability.

(3) Measurement results Table 1 and FIG. 1 show the glass powder used. Each glass powder used had a different transition point, crystallization temperature, particle size (D50), and linear expansion coefficient. Table 1 shows numerical values of these numerical values and the crystallization temperature of the used soft magnetic powder, and the glass transition point and crystallization temperature. FIG. 1 shows the graph of the divergence.

  The magnetic properties (permeability and core loss) when using each glass material are shown in FIG. 2, Table 3, and FIG. In addition, the comparative example X described in these shows an example of a dust core in which glass is not mixed. From FIG. 2 showing the magnetic permeability, Comparative Example X (none), Comparative Example 1 (A material) using glass, Example 1 (D material), and Example 2 (E material) are 400 to 460. It can be seen that a high magnetic permeability of 50 or more at ° C. and the change is small. Moreover, although the comparative example 3 (C material) has the same degree of change as these four examples, it shows a lower magnetic permeability than these. It turns out that the comparative example 2 (B material) has shown the low magnetic permeability further.

Table 2 shows data of core loss with respect to each heat treatment temperature in each glass material, and FIG. 3 is a graph of this. The core loss indicates the total core loss because it is difficult to separate the hysteresis loss and the eddy current loss.

  From FIG. 3, compared with Comparative Examples 1-3, Examples 1 and 2 show that the core loss is reduced at 420 ° C. to 440 ° C., and that the insulating coating made of glass functions sufficiently. In both the comparative example and the example, a decrease in magnetic permeability and an increase in core loss were confirmed at 460 ° C. and 480 ° C. compared to 400 ° C. to 440 ° C. This is because the soft magnetic powder is crystallized at 460 ° C. and 480 ° C.

  In Examples 1 and 2, it is not possible to confirm particularly a decrease in magnetic permeability and an increase in core loss due to the heat treatment below the crystallization temperature of the soft magnetic powder.

  On the other hand, in Comparative Example 2, the transition point is 337 ° C. and there is a deviation from the heat treatment temperature of 50 ° C. or more, but the glass crystallization temperature is different from the heat treatment temperature by more than 50 ° C. Therefore, only a part of the glass is melted, so that the density does not increase as shown in Table 3, and the direct current superposition characteristics are also lowered as shown in FIG. In Comparative Example 3, the density is increased to the same extent as in Examples 1 and 2, but the core loss is large. This is presumably because the glass crystallization temperature is significantly different from the heat treatment temperature, so that the viscosity is relatively high and the film is not thin and uniform. That is, the apparent density is high and it is inferred that the glass is melted, but the coating state of the glass itself is uneven, and it is considered that the unevenness appears in the core loss.

  In Comparative Example 2 in which the glass transition point deviates by 50 ° C. or more from the heat treatment temperature of the soft magnetic powder, although the glass transition point deviates from the heat treatment temperature by 50 ° C. or more, the particle size is 5.0 μm, etc. Therefore, the crystallization temperature is high. Therefore, even if the glass transition point and the heat treatment temperature are greatly deviated, the fluidity is not improved and the thickness of the coating is increased. This is also inferred from the density in Table 3 and the DC superposition characteristics in FIG.

  FIG. 5 and FIG. 6 show photographs of the state of each glass material before and after the heat treatment. FIG. 5 shows a state before the heat treatment, and FIG. 6 shows a state after the heat treatment. The amount of each glass powder was 5 cc. The heat treatment conditions were a heat treatment temperature of 450 ° C., a heat treatment time of 2 hours, and an atmosphere of air. In Comparative Examples 1 to 3 and Examples 1 and 2 photographed, the glass transition point deviates from the heat treatment temperature by 50 ° C. or more, but from FIG. 6, the comparison with the glass crystallization temperature is large. It can be seen that Examples 1 and 2 are not dissolved, and Comparative Example 3 and Examples 1 and 2 with relatively small divergence are dissolved. Since Comparative Example 2 has a large particle size, it is considered that the crystallization temperature is high. In Comparative Example 1, although the particle size is smaller than that in Comparative Example 2, the higher crystallization temperature is considered to be due to the glass composition.

FIG. 7 shows a graph of the core strength when the heat treatment temperature is 440 ° C. From FIG. 7, it can be confirmed that the smaller the difference between the heat treatment temperature and the glass crystallization temperature, the greater the strength. As described above, this is presumed that the strength is increased because the glass is sufficiently melted. If the magnetic properties are ignored, it can be easily understood from the fact that all glasses have the same tendency.

Claims (14)

In a powder magnetic core obtained by mixing magnetic powder and glass powder having a transition point lower than the crystallization temperature of the magnetic powder,
The transition point of the glass powder has a difference of 50 ° C. or more from the crystallization temperature of the magnetic powder,
The dust core according to claim 1, wherein a crystallization temperature of the glass powder has a difference of 50 ° C. or less from a crystallization temperature of the magnetic powder.   2. The dust core according to claim 1, wherein the magnetic powder is an amorphous soft magnetic powder.   The dust core according to claim 1 or 2, wherein a mixing amount of the glass powder is in a range of 0.5 wt% to 5 wt% of the magnetic powder.   4. The dust core according to claim 1, wherein a particle size of the glass powder is 0.5 μm to 5 μm.   The dust core according to any one of claims 1 to 4, wherein a binder resin is mixed in addition to the magnetic powder and the glass powder.   The dust core according to claim 5, wherein the binder resin is a methylphenyl silicone resin. Magnetic powder and glass powder having a transition point lower than the crystallization temperature of the magnetic powder are mixed, pressed, and then heat treated at a temperature lower than the crystallization temperature of the magnetic powder. In the manufacturing method,
The transition point of the glass powder has a difference of 50 ° C. or more from the crystallization temperature of the magnetic powder, and the crystallization temperature of the glass powder is a difference of 50 ° C. or less from the crystallization temperature of the magnetic powder. A method for producing a powder magnetic core, comprising:   The method of manufacturing a dust core according to claim 7, wherein the magnetic powder is an amorphous soft magnetic powder.   The method for manufacturing a dust core according to claim 7 or 8, wherein the pressure molding is performed at 5 to 80 ° C.   The method for manufacturing a dust core according to any one of claims 7 to 9, wherein the heat treatment is performed in a non-reducing atmosphere.   The mixing amount of the glass powder is in the range of 0.5 wt% to 5 wt% of the magnetic powder, and the mixing amount of the glass powder is determined in accordance with the permeability of the dust core to be manufactured. The manufacturing method of the powder magnetic core of any one of Claims 7-10.   The method for producing a dust core according to any one of claims 7 to 11, wherein a particle diameter of the glass powder is 0.5 µm to 5 µm.   The method for producing a dust core according to any one of claims 7 to 12, wherein a binder resin is added when mixing the magnetic powder and the glass powder.   The method for producing a dust core according to any one of claims 7 to 13, wherein a lubricating resin is added in mixing the magnetic powder and the glass powder.