JP5916638B2 - Manufacturing method of dust core - Google Patents

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 powder magnetic core made from an amorphous soft magnetic alloy (amorphous soft magnetic alloy) powder has excellent DC superposition characteristics and low loss characteristics.

  In order to obtain a powder magnetic core using these amorphous soft magnetic alloy powders (hereinafter referred to as alloy powders), the alloy powder is mixed with a low melting point glass and a binder resin and then compression molded, followed by heat treatment. I do. As the binder resin, for example, a methylphenyl silicone resin is used. In the method of Patent Document 1, a two-layer film of a silane coupling agent and a silicone resin is formed on the outer periphery of the soft magnetic powder and then molded. In the method of Patent Document 2, low melting point glass and methylphenyl silicone resin are added to the alloy powder and molded.

Japanese Patent No. 4908546 Japanese Patent No. 5030441

  At the time of molding the dust core, the alloy powder needs to be filled evenly into each part of the mold smoothly and without gaps. The characteristic when the alloy powder is filled in the mold is generally called “flowability”. It is necessary to improve the flowability of the alloy powder in order to suppress variations such as direct current superposition characteristics and low loss characteristics of the molded powder magnetic core. That is, when the flowability of the alloy powder is poor, the density of the molded powder magnetic core becomes non-uniform, resulting in variation in characteristics.

  In the method of Patent Document 1, since the silane coupling agent and the silicone resin are formed in two layers around the alloy powder, the flowability is not improved despite the addition of the silane coupling agent. In the method of Patent Document 2, when only methylphenyl silicone resin is used, the flowability of the powder is poor, and the density variation at the time of molding becomes large in the mechanical press device. In the hydraulic press device, the molded powder magnetic core The variation in the height becomes large.

  An object of the present invention is to provide a dust core that improves flowability when filling an alloy powder into a mold and suppresses variations such as direct current superposition characteristics and low loss characteristics, and a method for manufacturing the same.

In the present invention, the amorphous soft magnetic alloy powder is mixed with glass powder having a softening point lower than the crystallization temperature of the amorphous soft magnetic alloy, and a silane coupling agent is added to the mixture. In the method for producing a powder magnetic core, in which a heat-resistant resin is mixed, pressure-molded, and then heat-treated at a temperature lower than the crystallization temperature of the amorphous soft magnetic alloy,
The amount of the silane coupling agent added to the binder resin is 0.25% to less than 1.0% with respect to the binder resin.

  In the present invention, it is preferable to use a methylphenyl silicone resin as the binder resin. In mixing the amorphous soft magnetic alloy powder and the low melting point glass, a lubricating resin can be added. The dust core obtained by the above manufacturing method is also an embodiment of the present invention.

  According to the present invention, the addition amount of the silane coupling agent is 0.25% to less than 1.0% with respect to the binder resin, so that the standard deviation of the density of the molded dust core, the magnetic It is possible to obtain a dust core that exhibits excellent performance in both characteristics and strength.

The graph which shows the relationship between the addition amount of the silane coupling agent in an Example, and the standard deviation of a density. The graph which shows the relationship between the addition amount of a silane coupling agent in an Example, and a density. The graph which shows the relationship between the addition amount of the silane coupling agent and magnetic permeability in an Example. The graph which shows the relationship between the addition amount of the silane coupling agent in an Example, and crushing strength.

The manufacturing method of the powder magnetic core of the present embodiment includes the following steps.
(1) A step of mixing amorphous soft magnetic alloy powder and low melting point glass.
(2) A step of adding a binder resin to the mixture obtained in the mixing step.
(3) A molding step for producing a molded body by pressurizing the mixture that has undergone the binder resin addition step.
(4) A heat treatment step for heating the molded body obtained by the molding step.

Hereinafter, each step will be described in detail.
(1) Mixing step In the mixing step, for example, 0.5 wt% phosphoric low-melting glass and 0.5 wt% lubricating resin are added to an alloy powder having an average particle size of 30 to 100 μm. These are mixed for 2 hours using a V-type mixer. As the alloy powder, Fe-based alloy powder is used. In this Fe-based alloy powder, the Si component is 6.7%, the B component is 2.5%, the Cr component is 2.5%, the C component is 0.75%, and the remaining component is Fe.

  In addition, FeBPN (N is one or more elements selected from Cu, Ag, Au, Pt, and Pd) can be used as the alloy powder. As the alloy 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 alloy powder is desirably a metallic glass having a glass transition temperature Tg lower than the crystallization temperature Tx and exhibiting a supercooled liquid region. This is because the core loss can be suppressed because the magnetocrystalline anisotropy is suppressed by using metallic glass.

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

  The mixing amount of the glass is set according to the desired magnetic permeability. However, if the amount of glass mixed with the alloy powder is small, the coating between the alloy powders becomes insufficient, and eddy current loss increases. When the mixing amount of the glass is large, the magnetic permeability of the alloy powder is lowered and the alloy 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 alloy powder, the glass mixing amount is determined in accordance with the desired magnetic permeability.

  Glass is mixed with the alloy powder as a powder. The glass powder preferably has a particle size (D50) of about 0.5 to 1.5 μm. When the particle size of the glass powder is about 5 μm, the softening point increases and the viscosity does not decrease.

  By adding a lubricating resin, the molding density can be increased. As the lubricating resin, stearic acid and metal salts thereof 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 amount of the lubricious resin added is preferably about 0.1 wt% to 1.0 wt%, and generally about 0.5 wt% with respect to the alloy powder.

(2) Binder resin addition step In the addition step, the binder resin added with the silane coupling agent is further mixed into the mixture that has undergone the mixing step. As the binder resin, a methylphenyl silicone resin is preferable. The addition amount of the silane coupling agent with respect to the binder resin is 0.25% to less than 1.0%. Outside this range, the desired performance cannot be exhibited in any one of the standard deviation, magnetic characteristics, and strength of the density of the molded powder magnetic core.

  When a methylphenyl silicone resin is used as the binder resin, the appropriate amount of methylphenyl silicone resin added is 0.75 to 2.0 wt% with respect to the alloy 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 a kind of the silane coupling agent having good compatibility with the methylphenyl silicone resin, an amino silane coupling agent can be used, and γ-aminopropyltriethoxysilane is particularly preferable.

  As another binder resin, an acrylic acid copolymer resin (EAA) emulsion can be used instead of the methylphenyl silicone resin. The addition amount of the acrylic acid copolymer resin (EAA) emulsion to be mixed is 2.0 wt% with respect to the alloy powder, and the drying temperature and drying time in that case are 150 ° C. for 2 hours.

  The acrylic acid copolymer resin (EAA) emulsion is a soap-free colloidal emulsion in which various crosslinking agents and various physical property-imparting agents are blended. An acrylic acid copolymer resin (EAA) emulsion forms a film having a cross-linked structure that is not redissolved in water and hardly absorbs moisture when water is evaporated by heat drying. This film is tacky and works optimally as a binder during molding.

  The addition amount of acrylic acid copolymer resin (EAA) emulsion is an appropriate amount of 0.5 to 2.0 wt% with respect to the alloy powder. If it is less than this, the strength of the molded body will be insufficient and cracks will occur. If it is more than 2.0 wt%, there arises a problem that the maximum magnetic flux density is lowered due to the density reduction and the magnetic characteristics are lowered due to the increase in hysteresis loss.

  Instead of the acrylic acid copolymer resin (EAA) emulsion, an aqueous PVA (polyvinyl alcohol) solution (12% aqueous solution) may be used. The addition amount of PVA (polyvinyl alcohol) aqueous solution (12% aqueous solution) is 0.5 to 3.0 wt% with respect to the alloy powder. When a PVA (polyvinyl alcohol) aqueous solution (12% aqueous solution) is used, if the amount is less than the appropriate amount, the strength of the molded body is insufficient and cracking occurs. On the other hand, when the amount is more than the appropriate amount, there arises a problem that the maximum magnetic flux density is lowered due to the density reduction and the magnetic characteristics are lowered due to the increase in hysteresis loss.

  By adding and mixing the binder resin to the alloy powder, the lubricating resin, and the low melting point glass, the mixing step and the adding step can be performed simultaneously.

(3) 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 25 ° C to 150 ° C. The molding pressure is, for example, 1300 to 1700 MPa.

(4) Heat treatment step In the heat treatment step, the compact obtained in the molding step is heated in a nitrogen atmosphere at a temperature of 450 to 470 ° C for 2 hours. The reason why the temperature of 450 ° C. is maintained is to secure the crushing strength required when the powder magnetic core is formed into a ring shape in a state below the crystallization temperature of the amorphous soft magnetic alloy powder. is there. On the other hand, when the heat treatment temperature is increased too much, crystallization of the alloy powder proceeds, the magnetic permeability decreases, and the iron loss (hysteresis) increases. Therefore, maintaining a temperature of 450 to 470 ° C. is effective for suppressing an increase in iron loss.

  The molded body can be heated in air at a temperature of 350 ° C. for 2 hours, and then switched to a nitrogen atmosphere and heated at 470 ° C. for 2 hours.

  The methylphenyl silicone resin is heated and dried at around 200 ° C. to act as a binder (binder) at the time of molding, and the methyl group directly bonded to the Si group is thermally decomposed at about 350 ° C. When methylphenyl silicone resin is used as the binder resin and stearic acid and its metal salt are used as the lubricating resin, thermal decomposition of the methylphenyl silicone resin occurs due to the catalytic effect of stearic acid and its metal salt. Increases speed.

  The thermally decomposed methylphenyl silicone resin remains on the surface of the alloy powder as a silica (SiO2) layer, which becomes a strong binder and insulating film. Therefore, after the molded body is heat-treated at 450 to 470 ° C. as described above, an insulating film mainly composed of a silica layer is formed around the alloy powder constituting the molded body.

(1) Manufacturing method of dust core An Fe-Si-B-Cr-C Fe-based amorphous soft magnetic alloy powder having an average particle size of 45 μm and a bismuth-based glass having a softening temperature of 360 ° C. and an average particle size of 1.1 μm Was mixed with 1.5 wt%, and lithium stearate as a lubricant was mixed with 0.3 wt%.

  Next, a silane coupling agent was added to the methylphenyl silicone resin at a ratio shown in Table 1 and mixed. The binder resin to which the silane coupling agent was added was added to a mixture of alloy powder and bismuth-based glass, mixed, and then dried at 150 ° C. for 2 hours. Thereafter, the dried mixture was passed through a sieve having an opening of 850 μm, and 0.3 wt% of lithium stearate as a lubricant was mixed with the powder that passed through the sieve to prepare a powder for filling.

The powder for filling was filled in a mold and pressed at a pressure of 1700 MPa to prepare a molded body, and further heated in an oxidizing atmosphere (in the air) at a temperature of 420 ° C. for 2 hours.
(2) Measuring method of iron loss Primary (15 turns) and secondary winding (3 turns) are applied to the dust core, and using a BH analyzer (Iwadori: SY-8232), frequency is 100 kHz, maximum magnetic flux density The iron loss Pcv was measured under the condition of Bm = 0.05T. Hysteresis loss and eddy current loss were calculated from iron loss. This calculation was performed by calculating the hysteresis loss coefficient and the eddy current loss coefficient by the least square method using the following three equations for the frequency curve of the iron loss.

Pc = Kh × f + Ke × f2
Ph = Kh × f
Pe = Ke × f2
Pc: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

(3) Evaluation of molding characteristics Dust core shape ... Toroidal shape with outer shape 16.55mm, inner diameter 11.00mm, height 15.00mm Molding conditions ... Molding speed 11 pieces / min, specified pressure 58 tons Variation data number ... 200 shots Crushing strength: measured according to JIS2507

(4) Measurement result (4-1) Evaluation of density characteristics As can be seen from Table 1 and FIG. 1, in Comparative Example 1 in which no silane coupling agent is added to the methylphenyl silicone resin, the standard deviation value of the density is It is large and it can be seen that the density varies in each part of the molded body. When the amount of the silane coupling agent added is 0.25% or more, the effect of suppressing variation in density is obtained. It can be seen that when the addition amount of the silane coupling agent exceeds 1%, the change in the standard deviation value of the density is small, and even if 1% or more is added, there is no effect.

(4-2) Evaluation of magnetic properties The density, amplitude magnetic permeability (μa), iron loss and strength in each comparative example and example are analyzed, as shown in Table 2, FIG. 2 and FIG. As is clear from these analysis results, the density and the amplitude magnetic permeability decrease as the addition amount of the silane coupling agent increases. It can be seen that the addition amount of the silane coupling agent capable of obtaining a preferable density and amplitude permeability as the dust core is 0.25 to 1.0% of the methylphenyl silicone resin.

(4-3) Evaluation of Strength Characteristics As can be seen from Table 2 and FIG. 4, in Comparative Example 1 where no silane coupling agent is added, the strength is reduced. Moreover, compared with Examples 1-3, the intensity | strength is falling in the comparative example 2 and the comparative example 3 which added 1% or more of silane coupling agents. This also shows that the addition amount of the silane coupling agent is preferably 0.25 to 1.0%.

Claims (3)

Amorphous soft magnetic alloy powder and glass powder whose softening point is lower than the crystallization temperature of the amorphous soft magnetic alloy are mixed, and a binder resin added with a silane coupling agent is mixed with the mixture. In the method of manufacturing a powder magnetic core, which is heat-treated at a temperature lower than the crystallization temperature of the amorphous soft magnetic alloy after being pressure-molded,
The method for producing a dust core, wherein an amount of the silane coupling agent added to the binder resin is 0.25% to less than 1.0% with respect to the binder resin. The method for producing a dust core according to claim 1, wherein the binder resin is a methylphenyl silicone resin. The method for producing a dust core according to claim 1 or 2, wherein a lubricating resin is added in mixing the amorphous soft magnetic alloy powder and the low melting point glass.