JP6346412B2 - Soft magnetic powder, core and manufacturing method thereof - Google Patents

Description

  The present invention relates to a soft magnetic powder used for a core such as a smoothing choke coil, a core using the soft magnetic powder, and a manufacturing method thereof.

  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 core of the choke coil used therein is required to have a small characteristic change even at a large current. Specifically, a 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 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, the alloy powder is mixed with a low melting glass and a binder resin, and the mixture is compression-molded at room temperature or high temperature. A heat treatment is performed on the obtained molded body. In addition, since low-melting glass has a problem of high cost, instead of low-melting glass, as shown in Patent Document 1, the use of primary aluminum phosphate as an insulating film improves the insulation performance. As shown in the proposed proposal and Patent Document 2, attempts have been made to obtain high insulation and magnetic flux density by using a phosphate or phosphate compound containing aluminum. However, all of these prior arts focus on improving the insulation performance, and are not intended to improve the core strength.

JP 2003-272911 A JP 2005-113258 A

The primary aluminum phosphate used in the invention of Patent Document 1 is a water-soluble acidic phosphate represented by the formula of Al ₂ O ₃ .3P ₂ O ₅ .6H ₂ O. The curing bond is developed by reaction, dehydration condensation by heating, crystal transition by high temperature heating, or the like. On the other hand, it has a very high hygroscopic property and exhibits a rapid reaction with ambient water vapor even at room temperature, making it difficult to handle. Sex is difficult. Further, if the hardness of the soft magnetic powder is high, the anchor effect between the powders during compression molding becomes weak, the strength of the compact is reduced, and the core is damaged.

  In the invention described in Patent Document 2, a phosphoric acid compound and a metal compound are mixed and added to a soft magnetic powder, and a chemical conversion reaction is caused on the surface of the soft magnetic powder, whereby adhesion of the chemical film on the surface of the metal powder is achieved. However, if the mixing of the phosphoric acid compound and the metal compound is not properly controlled, the chemical reaction on the surface of the soft magnetic powder becomes insufficient, and the initial effect cannot be obtained. Further, free phosphoric acid remains unreacted in the phosphate or phosphoric acid compound, and such residual free phosphoric acid has a problem that causes the powder to be hygroscopic.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and an object thereof is to provide a dust core having high mechanical strength and excellent soft magnetic properties.

In the soft magnetic powder of the present invention, one or both of 0.25 to 2.0 wt% of aluminum tripolyphosphate or aluminum metaphosphate is mixed with the soft magnetic powder, and the aluminum tripolyphosphate or metallin is mixed around the soft magnetic powder. One or both coatings of aluminum oxide are formed, and the soft magnetic powder has a powder hardness of 100 MPa or more .

As one or both of the aluminum tripolyphosphate and aluminum metaphosphate , as a hardening accelerator, Al ₂ O ₃ , SiO ₂ , MgO, Mg (OH) ₂ , CaO, Ca (OH) ₂ , asbestos, talc, fly ash At least one kind can also be added.

  The core using the soft magnetic powder as described above and a method for manufacturing such a core are also one embodiment of the present invention.

  According to the present invention, a soft magnetic powder having no hygroscopic property at room temperature and easy to handle can be obtained by using a condensed metal phosphate obtained by heating and dehydrating and condensing a metal phosphate compound as a binder. Can do. The cost of the condensed metal phosphate is lower in each stage as compared with the low melting point glass, and there is an advantage that the cost competitiveness of the product is high. The condensed metal phosphate is generally used as a rust preventive agent, and is effective for rust prevention of the dust core, and does not cause an event of worsening hysteresis loss as in a low melting glass.

The graph which shows the relationship between the addition amount of the condensed phosphoric acid metal salt with respect to soft-magnetic powder, and the crushing strength of the obtained powder magnetic core.

(1) Soft magnetic powder As the soft magnetic powder, pure iron powder, sendust (Fe-Si-Al alloy) powder, Fe-Si alloy powder, amorphous soft magnetic powder, or the like can be used. Examples of the amorphous 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, 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. Glass 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 soft magnetic powder is preferably 30 to 100 μm. The crystallization start temperature of the soft magnetic powder is usually about 450 ° C. The soft 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.

  The soft magnetic powder preferably has a powder hardness (pressure required for displacement of 10%) of 100 MPa or more. For example, since the powder hardness of the amorphous alloy is 700 MPa, the powder hardness of the Fe-6.5Si alloy is 390 MPa, and the powder hardness of the FeSiAl alloy is 100 MPa, these alloys are suitable for the present invention. However, the present invention can also be applied to pure iron powder having a powder hardness of about 30 MPa.

(2) Condensed phosphate metal salt As the condensed phosphate metal salt, aluminum tripolyphosphate and aluminum metaphosphate obtained by aging and dehydrating primary aluminum phosphate are suitable. In addition, condensed calcium phosphate and condensed magnesium phosphate have the same effect.

  The amount of the condensed metal phosphate added to the soft magnetic powder is preferably 0.25 to 2.0 wt%. When the addition amount is 0.25 wt% or more, an effect of increasing the strength of the manufactured core can be obtained. However, when the addition amount exceeds 2.0 wt%, the density of the core decreases and the strength also decreases.

(3) Cure Accelerator At least of Al ₂ O ₃ , SiO ₂ , MgO, Mg (OH) ₂ , CaO, Ca (OH) ₂ , asbestos, talc, fly ash as a cure accelerator in the condensed phosphate metal salt One kind can also be added. The curing accelerator is preferably 10 to 30 wt% with respect to the condensed phosphate metal salt. If it is 10% or less, the effect as a curing agent is small, and if it exceeds 30% by weight, the formation of a film of condensed metal phosphate on the surface of the soft magnetic powder is hindered.

(4) Binder Resin The binder resin is added to the mixed powder of soft magnetic powder and condensed phosphate metal salt. As a binder resin, when a mixture of a soft magnetic powder and a condensed metal phosphate is pressed at room temperature, a molded body that is densified to a certain degree is obtained, and an excessive force is exerted on the molded body. Unless it is added, a resin that is viscous enough to maintain a predetermined shape is used.

  Examples include silicone resins and waxes. As the silicone resin, methylphenyl silicone resin is preferable. An appropriate amount of methylphenyl silicone resin added is 0.75 to 2.0 wt% with respect to the soft 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. The addition amount of the PVA (polyvinyl alcohol) aqueous solution (12% aqueous solution) is an appropriate amount of 0.5 to 3.0 wt% with respect to the soft magnetic powder.

(5) Lubricating resin 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 addition amount of the lubricating resin is preferably about 0.1 wt% to 1.0 wt% with respect to the soft magnetic powder, and is generally about 0.5 wt%.

(6) Manufacturing method The core manufacturing method of the present embodiment includes the following steps.
(A) A step of mixing the soft magnetic powder and the condensed metal phosphate.
(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) Mixing step of condensed phosphate metal salt In the mixing step, for example, 0.25 to 2.0 wt% of condensed phosphate metal salt is added to soft magnetic powder having an average particle size of 30 to 100 μm. And mix. For example, the above mixture is mixed for about 2 hours using a V-type mixer. The timing of adding the condensed phosphoric acid metal salt does not necessarily need to be this step, and in the step (b) of adding the binding resin, it can be added and mixed together with the lubricant. However, the film formation on the surface of the soft magnetic powder is more effectively performed by mixing the condensed phosphate metal salt in the previous step.

(B) Binder resin addition step With respect to the mixture of the soft magnetic powder and the condensed metal phosphate, 0.75 to 2.0 wt% of the binder resin with respect to the soft magnetic powder, and 0.1 to Add 1.0 wt% of a lubricious resin and mix. It is also possible to simultaneously perform the mixing of the condensed phosphate metal salt (a) and the binding 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.

  In the case of amorphous soft magnetic alloy 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 below the crystallization temperature of the soft magnetic powder. On the other hand, if the heat treatment temperature is increased too much, the crystallization of the soft magnetic powder proceeds, the magnetic permeability decreases, and the iron loss (hysteresis) increases. Therefore, maintaining a temperature of 400 ° C. to 440 ° C. is effective for suppressing an increase in iron loss. In the case of Sendust alloy or Fe—Si alloy, it is preferable to perform heat treatment at a temperature of 600 to 750 ° C.

  The soft magnetic powder of the present invention is not necessarily used only for the dust core. For example, the core can be formed by injection molding or transfer molding of the soft magnetic powder of the present invention and a predetermined resin. In that case, the filling ratio of the soft magnetic metal powder to the resin is preferably 55 to 95% by weight. As the resin, a resin excellent in dimensional stability after molding, for example, an epoxy resin or a phenol resin is preferable for a thermosetting resin, and a polyether sulfone is preferable for a thermoplastic resin. When the filling rate of the soft magnetic metal powder is low, there is a problem that the magnetic performance is lowered. On the other hand, when the filling is high to 95 wt% or more, the filling amount of the binder is reduced and the strength of the core is lowered.

  Examples of the present invention will be described below with reference to Tables 1 to 5 and FIG.

(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.

  0 to 4% of a condensed phosphate metal salt in which 25 wt% of magnesium oxide, which is a hardening accelerator, is blended with an amorphous soft magnetic alloy powder having a hardness of 700 MPa and an average grain size of 50 μm with respect to aluminum dihydrogen phosphate. Then, 2.0 wt% of methylphenyl silicone resin is mixed with the mixed powder, heat-dried at 180 ° C. for 2 hours, and further mixed with 0.3 w% of lithium stearate as a lubricant. Granule powder was produced.

  A compact was prepared from this at a normal pressure and a pressure of 1500 MPa, and a heat treatment was performed in an air atmosphere at a temperature of 410 ° C. for 120 minutes to prepare a dust core.

(3) Measurement results Table 1 and FIG. 1 show the crushing strength of the dust core produced.

  As can be seen from Table 1 and FIG. 1, the strength is increased and the effect is obtained when the addition amount of the condensed phosphate metal salt and its curing agent is 0.25 wt% or more, but when the addition amount exceeds 2.0 wt%, Density decreases and strength also decreases.

(4) Fe-6.5Si alloy powder 0.5 wt% of aluminum dihydrogen phosphate + magnesium oxide is mixed with Fe-6.5Si alloy powder having a hardness of 390 MPa and an average particle diameter of 20 μm. Then, 1.8 wt% of methylphenyl-based silicone resin was mixed, heat-dried at 180 ° C. for 2 hours, and 0.6 mass% of zinc stearate as a lubricant was further mixed.

This was pressure-molded at a pressure of 1500 MPa at room temperature to produce a ring-shaped molded body having an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 5 mm. Furthermore, this molded body was heat-treated at 700 ° C. for 120 minutes in a nitrogen atmosphere (N ₂ ) to produce a dust core.

As can be seen from this example, the strength increases by adding aluminum dihydrogen tripolyphosphate and magnesium oxide as a hardening accelerator.

(5) Pure iron and sendust As soft magnetic powder, pure iron with a hardness of 30 MPa and sendust (FeSiAl) with a hardness of 100 MPa were used to produce a dust core under the same conditions as described above. Table 3 shows the relationship between these binder addition amounts, three-point bending strength, and iron loss.

  No. in Table 3 As can be seen from A1 to A3, with pure iron having a hardness of 30 MPa, the effect cannot be obtained. In Sendust having a hardness of 100 MPa, low melting point glass powder increases hysteresis loss as in B2. As can be seen from B3 and B4, the strength is higher when aluminum dihydrogen tripolyphosphate is added to Sendust. When C2 and C3 are compared, the strength of a product obtained by adding aluminum dihydrogen tripolyphosphate and magnesium oxide as its hardener to Sendust increases.

Claims (7)

One or both of 0.25 to 2.0 wt% of aluminum tripolyphosphate or aluminum metaphosphate is mixed with the soft magnetic powder, and the aluminum tripolyphosphate or aluminum metaphosphate is mixed around the soft magnetic powder. A soft magnetic powder, wherein one or both coatings are formed, and the soft magnetic powder has a powder hardness of 100 MPa or more . The soft magnetic powder according to claim 1, wherein one or both of the tripolyphosphate aluminum or aluminum metaphosphate, as a curing accelerator, wherein the basic substance is added. Claim 2, wherein the basic _{substance, Al 2 O 3, SiO 2} , MgO, Mg (OH) 2, CaO, Ca (OH) 2, asbestos, talc, characterized in that at least one of fly ash Soft magnetic powder according to 1. The core comprised by shape | molding the soft-magnetic powder of any one of the said Claims 1-3. After mixing one or both of 0.25 to 2.0 wt% of aluminum tripolyphosphate or aluminum metaphosphate with respect to the soft magnetic powder, the soft magnetic powder is molded into a predetermined shape, and the powder hardness of the soft magnetic powder Is 100 MPa or more, The manufacturing method of the core characterized by the above-mentioned . As one or both of the aluminum tripolyphosphate and aluminum metaphosphate, as a hardening accelerator, Al ₂ O ₃ , SiO ₂ , MgO, Mg (OH) ₂ , CaO, Ca (OH) ₂ , asbestos, talc, fly ash 6. The core manufacturing method according to claim 5 , wherein at least one kind is added. A core manufactured by the method according to claim 5 or 6 .