JP5263654B2 - Method for forming silica coating of soft magnetic powder for dust core and method for producing dust core - Google Patents
Method for forming silica coating of soft magnetic powder for dust core and method for producing dust core Download PDFInfo
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本発明は、デジタル情報機器などに用いられるパワーチョークやトランス、リアクトル、回転機などの電気電子部品の磁性コアとして用いた際、高強度で良好な電気絶縁性を有しかつ低損失である、圧粉磁心用のＦｅを主成分とする軟磁性粉末とその製造方法に関する。 The present invention has high strength and good electrical insulation and low loss when used as a magnetic core of electrical and electronic parts such as power chokes, transformers, reactors, and rotating machines used in digital information equipment and the like. The present invention relates to a soft magnetic powder mainly composed of Fe for a dust core and a manufacturing method thereof.
近年、デジタル情報機器の高周波化、大電流化に伴い、軟磁性金属粉末を用いたインダクタやノイズ対策部品が注目されている。特に１０−１００ｋＨｚ帯域で駆動電流が１０−１００Ａで使用される部品の用途が拡大している。また回転機コアやトランスコアなどの電気部品分野においても高密度化および小型化が求められている。このため、これらの電気電子部品に使用される軟磁性金属圧粉磁心、特に中高周波領域において優れた磁気的特性を有する軟磁性圧粉磁心の開発が進められている。軟磁性金属粉末を用いて作製される圧粉磁心は、従来から使用されていたフェライト磁心よりも高い飽和磁束密度を有しているため電子部品の小型化および大電流化に対しては有利である。 In recent years, with the increase in frequency and current of digital information devices, inductors using soft magnetic metal powder and noise countermeasure components have been attracting attention. In particular, the application of parts used at a drive current of 10-100 A in the 10-100 kHz band is expanding. Further, in the field of electrical components such as a rotating machine core and a transformer core, higher density and smaller size are required. For this reason, the development of soft magnetic metal dust cores used in these electric and electronic parts, particularly soft magnetic powder magnetic cores having excellent magnetic properties in the mid-high frequency region, is underway. A dust core made of soft magnetic metal powder has a higher saturation magnetic flux density than a ferrite core that has been used so far, which is advantageous for downsizing electronic components and increasing current. is there.
しかし、軟磁性金属粉末による圧粉磁心はフェライトと比較して電気抵抗率が低いため渦電流損失が大きいという欠点もある。それ故に、金属系圧粉磁心をコアとして用いた場合フェライトコアと比較して、特に数１０ｋＨｚ以上の中高周波域での損失が大きくなる。またコアの発熱による温度上昇の問題もあり、電子部品としての実用化が困難であった。この問題を解決するため、金属粉末に微細な酸化物等の絶縁粉末を混合することで金属粉末間を高抵抗化し、渦電流損失を低減する方法が提案されている。（特許文献１） However, the powder magnetic core made of soft magnetic metal powder has a drawback that the eddy current loss is large because the electrical resistivity is lower than that of ferrite. Therefore, when a metal-based powder magnetic core is used as a core, the loss particularly in the middle and high frequency range of several tens of kHz or more is greater than that of a ferrite core. In addition, there was a problem of temperature rise due to heat generation of the core, and it was difficult to put it into practical use as an electronic component. In order to solve this problem, a method has been proposed in which an insulating powder such as a fine oxide is mixed with the metal powder to increase resistance between the metal powders and reduce eddy current loss. (Patent Document 1)
鉄損は一般にヒステリシス損失と渦電流損失の和で表されることから、コア全体の損失を低減するためには渦電流損失のみならず、ヒステリシス損失をも抑制する必要がある。そのためには、磁性粉末の保磁力を出来るだけ小さくすることが必要である。軟磁性粉末の保磁力は、磁界を印加した際の磁壁移動の容易さを反映したものであり、粒界や不純物介在物、圧粉磁心の成形時に生じた塑性変形による歪み、転位などがこれを妨げる要因となる。このため低ヒステリシス損失のコアを得るためには、Ｆｅ系の軟磁性粉末においては本来低保磁力の粉末を低圧で成形し、７００℃以上、好ましくは９００℃以上の高温において歪取り焼鈍を行うことが望まれる。 Since iron loss is generally represented by the sum of hysteresis loss and eddy current loss, it is necessary to suppress not only eddy current loss but also hysteresis loss in order to reduce the loss of the entire core. For that purpose, it is necessary to make the coercive force of the magnetic powder as small as possible. The coercive force of soft magnetic powder reflects the ease of domain wall movement when a magnetic field is applied, and this includes distortion, dislocation, etc. caused by plastic deformation that occurs during the formation of grain boundaries, impurity inclusions, and dust cores. It becomes a factor to prevent. For this reason, in order to obtain a core with low hysteresis loss, an Fe-based soft magnetic powder is originally formed with a low coercive force powder at low pressure and subjected to strain relief annealing at a high temperature of 700 ° C. or higher, preferably 900 ° C. or higher. It is desirable.
ところが、微細な絶縁粉末を混合する方法では８００℃以上の高温で熱処理すると、絶縁物のわずかな隙間から金属粉末間が接触し導通が生じて電気抵抗率が低下するため、高温での熱処理を行うことができず、結晶粒径を大きくしたり、加工歪を完全に除去することが出来ないため、ヒステリシス損失を十分に低減させることができないという課題がある。 However, in the method of mixing fine insulating powder, if heat treatment is performed at a high temperature of 800 ° C. or higher, the metal powder comes into contact through a small gap between the insulators and conduction is caused to decrease the electrical resistivity. There is a problem that the hysteresis loss cannot be sufficiently reduced because the crystal grain size cannot be increased and the processing strain cannot be completely removed.
他には、例えば特許文献２に記載されるリン酸塩等の絶縁物や、非特許文献１などに紹介されるＭｇＯ等の酸化物で、金属粉末の表面全体を絶縁物で被覆することで高抵抗化し渦電流損失を低減する方法が提案されている。しかし、８００℃以上の高温で熱処理すると、これらの絶縁被覆は磁性粉末と反応したり、熱分解等を起こすことにより変質破壊し絶縁性が劣化するために、全体のコア損失を十分に低減させることができないという課題がある。 In addition, for example, an insulator such as phosphate described in Patent Document 2 or an oxide such as MgO introduced in Non-Patent Document 1 is used to coat the entire surface of the metal powder with an insulator. A method for reducing the eddy current loss by increasing the resistance has been proposed. However, when heat treatment is performed at a high temperature of 800 ° C. or higher, these insulating coatings react with the magnetic powder or undergo thermal degradation or the like, resulting in alteration destruction and deterioration of insulation, thereby sufficiently reducing the overall core loss. There is a problem that it cannot be done.
従って、本発明の目的は、高電気抵抗でかつ、高温熱処理が可能である圧粉磁心用軟磁性粉末のシリカ被覆形成方法、および圧粉磁心の製造方法を提供することである。 Accordingly, an object of the present invention is to provide a method for forming a silica coating of a soft magnetic powder for a dust core and a method for producing a dust core, which has high electrical resistance and can be heat-treated at a high temperature.
本発明者らは、絶縁性酸化物であるシリカを軟磁性粉末表面全体に特定の膜厚で付着させ上記目的が達成できることに加え、防錆性も付与されることを見出し、本発明に至った。 The present inventors have found that silica, which is an insulating oxide, is adhered to the entire surface of the soft magnetic powder with a specific film thickness, and that the above object can be achieved, and that rust prevention is also imparted, leading to the present invention. It was.
即ち、本発明はＦｅを主成分とする軟磁性粉末の表面に、テトラエトキシシラン、有機溶剤、アルカリ、及び水を含む加水分解溶液によってシリカ皮膜を形成する圧粉磁心用軟磁性粉末のシリカ皮膜形成方法であって、前記テトラエトキシシランの濃度が前記加水分解溶液全体に対して０．２３ｍｏｌ／Ｌ以上１．０２ｍｏｌ／Ｌ以下であり、かつ水濃度がモル比でテトラエトキシシラン濃度の２２倍以上２９倍以下のものを使用し、前記加水分解溶液は、ｐＨが９．４から１０．８の範囲であることを特徴とする。
That is, the present invention is a silica film of a soft magnetic powder for a powder magnetic core in which a silica film is formed on a surface of a soft magnetic powder containing Fe as a main component by a hydrolysis solution containing tetraethoxysilane, an organic solvent, an alkali, and water. The tetraethoxysilane concentration is 0.23 mol / L or more and 1.02 mol / L or less with respect to the whole hydrolysis solution, and the water concentration is a tetraethoxysilane concentration in a molar ratio. use a 22 times 29 times or less, the hydrolysis solution, wherein the pH is in the range of 9.4 10.8.
加水分解反応の触媒として、アンモニア、または有機塩基の中から選ばれる少なくとも１種類以上が含まれることが好ましい。 As a catalyst of pressurized water decomposition reaction, it is preferably contained at least one or more selected from ammonia or organic bases.
これらのシリカ皮膜形成方法により作製した軟磁性粉末を圧粉磁心とする場合、圧縮成形中、もしくは圧縮成形後に７００℃〜１１００℃で熱処理を行うことで、圧粉磁心の機械的強度を高くすることができる。 When the soft magnetic powder produced by these silica film forming methods is used as a powder magnetic core, the mechanical strength of the powder magnetic core is increased by performing heat treatment at 700 ° C. to 1100 ° C. during or after compression molding. be able to.
以下に本発明のシリカ皮膜製造方法を具体的に説明する。本発明は圧粉磁心用途としてＦｅを主成分とする軟磁性粉末の表面に、テトラエトキシシランと水を所定の濃度範囲に調整した溶液を用いることによって絶縁性酸化物のシリカ皮膜を形成させるための製造方法である。
テトラエトキシシランは別名正珪酸四エチルと呼ばれるものであり、その化学式はＳｉ（ＯＣ２Ｈ５）４である。ＴＥＯＳと称されることもある。
The silica film production method of the present invention will be specifically described below. In order to form a silica film of an insulating oxide by using a solution in which tetraethoxysilane and water are adjusted to a predetermined concentration range on the surface of a soft magnetic powder containing Fe as a main component for use as a dust core in the present invention. It is a manufacturing method.
Tetraethoxysilane is also known as orthotetraethyl silicate, and its chemical formula is Si (OC 2 H 5 ) 4. Sometimes referred to as TEOS.
本発明のシリカ皮膜製造方法はアルコキシド溶液を加水分解させることによる。この溶液とは、シリカの原料となるアルコキシドであるテトラエトキシシラン、アルカリ及び水をＩＰＡ、エタノールなどのアルコールに溶解させたものである。用いるテトラエトキシシランには特に制限はなく、試薬、工業用など一般に用いられているもので良い。
加水分解反応に使用される他のアルコキシドとしては、メトキシドＳｉ（ＯＣＨ３）４、エトキシドＳｉ（ＯＣ２Ｈ５）４、プロポキシドＳｉ（Ｏ・ｎ−、ｉ−Ｃ３Ｈ７）４などがあるが、コスト面を考慮するとテトラエトキシシランが最適である。
The silica film production method of the present invention is based on hydrolyzing an alkoxide solution. This solution is obtained by dissolving tetraethoxysilane, alkali, and water, which are alkoxides that are raw materials for silica, in an alcohol such as IPA and ethanol. There is no restriction | limiting in particular in the tetraethoxysilane to be used, What is generally used, such as a reagent and industrial use, may be used.
Other alkoxides used in the hydrolysis reaction include methoxide Si (OCH 3 ) 4, ethoxide Si (OC 2 H 5 ) 4, propoxide Si (O · n-, i-C 3 H 7 ) 4 and the like. However, considering the cost, tetraethoxysilane is optimal.
シリカを生成させるだけであればテトラエトキシシランの濃度はいくらであっても構わないが、本発明の目的を達成するような軟磁性粉末表面全体を均一に被覆させるためには本発明の濃度範囲が要求される。テトラエトキシシラン濃度が０．２ｍｏｌ／Ｌより小さい場合、濃度が低すぎてシリカ源の絶対量が少ないため軟磁性粉末全体を覆うほどの皮膜が生成しにくい。また、反応速度が小さくなり時間がかかるので効率がよくない。テトラエトキシシラン濃度が１．１ｍｏｌ／Ｌより大きい場合、反応速度が大きくなり過ぎて軟磁性粉末表面に生成する皮膜以外に単独でシリカ球を生成し、軟磁性粉末表面皮膜としてのシリカ生成効率は低下する。さらにシリカ球を除去する作業が必要になり作業効率もよくない。
加水分解を促進させるために添加する水濃度は、理論的にはモル比でテトラエトキシシラン濃度の２倍以上存在すればよいが、水濃度が２０倍より小さい場合、加水分解の反応速度が小さいため目的の膜厚を得るまでに非常に時間がかかり、３０倍より大きい場合は加水分解速度が過剰になり、シリカが軟磁性粉末の表面に生成せず、単独で球をなす量が多くなるため、いずれも効率が良くない。
したがって、効率良く目的のシリカ皮膜を得るために用いる加水分解溶液の濃度としては、テトラエトキシシランの濃度が加水分解溶液全体に対して０．２ｍｏｌ／Ｌ以上１．１ｍｏｌ／Ｌ以下であり、かつ水濃度がテトラエトキシシラン濃度の２０倍以上３０倍以下であることが好ましい。
Any concentration of tetraethoxysilane may be used as long as silica is generated. However, in order to uniformly coat the entire surface of the soft magnetic powder so as to achieve the object of the present invention, the concentration range of the present invention is used. Is required. When the tetraethoxysilane concentration is less than 0.2 mol / L, the concentration is too low and the absolute amount of the silica source is small, so that it is difficult to form a film that covers the entire soft magnetic powder. In addition, the reaction rate is low and it takes time, so the efficiency is not good. When the tetraethoxysilane concentration is greater than 1.1 mol / L, the reaction rate becomes too high and silica spheres are generated independently of the film formed on the surface of the soft magnetic powder. descend. Furthermore, work for removing the silica spheres is required, and work efficiency is not good.
The water concentration added to promote the hydrolysis should theoretically be at least twice the tetraethoxysilane concentration by molar ratio, but when the water concentration is less than 20 times, the hydrolysis reaction rate is low. Therefore, it takes a very long time to obtain the desired film thickness. When the film thickness is larger than 30 times, the hydrolysis rate becomes excessive, silica is not formed on the surface of the soft magnetic powder, and the amount of spheres alone is increased. Therefore, neither is efficient.
Therefore, the concentration of the hydrolysis solution used to efficiently obtain the target silica film is such that the concentration of tetraethoxysilane is 0.2 mol / L or more and 1.1 mol / L or less with respect to the entire hydrolysis solution, and The water concentration is preferably 20 to 30 times the tetraethoxysilane concentration.
このような加水分解溶液はｐＨにより反応の形態と速度が変化する。加水分解溶液のｐＨは、ｐＨ７．０からｐＨ１１．０、より好ましくはｐＨ９．０からｐＨ１０．８であることが望ましい。ｐＨ７付近で最も反応速度が小さく、ｐＨ７よりも小さいか、もしくはｐＨ７よりも大きくなるにつれ反応速度は大きくなる。ｐＨ７未満では、軟磁性粉末から溶液中にＦｅの溶出が起こり好ましくないため、反応速度を大きくするためにはｐＨは大きい方が好ましい。一方で、ｐＨが大きくなるにつれて反応速度が過大になると、軟磁性粉末表面に皮膜が形成されるよりも、単独のシリカ球が多く生成するので、テトラエトキシシラン溶液のシリカ皮膜生成効率は低下する。 Such hydrolyzed solutions vary in reaction form and rate depending on pH. The pH of the hydrolysis solution is desirably pH 7.0 to pH 11.0, more preferably pH 9.0 to pH 10.8. The reaction rate is the lowest near pH 7, and the reaction rate increases as it is smaller than pH 7 or larger than pH 7. If the pH is less than 7, Fe is eluted from the soft magnetic powder into the solution, which is not preferable. Therefore, in order to increase the reaction rate, a higher pH is preferable. On the other hand, when the reaction rate becomes excessive as the pH increases, more silica spheres are formed than when a film is formed on the surface of the soft magnetic powder, so the silica film formation efficiency of the tetraethoxysilane solution decreases. .
加水分解溶液に、アルカリを添加して上述のｐＨ範囲に調整する。つまりアルカリは触媒として作用している。このアルカリとして水酸化ナトリウムなどのアルカリ金属水酸化物やアルカリ土類金属水酸化物のような金属元素を含むアルカリを用いると皮膜生成後に金属元素が残留し、後工程の熱処理時に軟磁性粉末への拡散が起こり保磁力の増大、つまりはコア損失の増大につながりうる。そこで、アンモニア、または有機塩基の中から選ばれる少なくとも１種類以上のものが含まれることが望ましい。これらのアルカリは加水分解反応後の粉末熱処理や圧粉磁心成形後の熱処理時に揮発、分解するので、磁気特性に悪影響を与えないため好ましい。有機塩基としては、ジエチルアミンやトリエチルアミンに代表されるような脂肪族アミンが一般的であるが、ピリジンのような複素環式化合物やグアニジンとその誘導体のような不飽和結合を持つものでも構わないし、尿素のように分解してアンモニアを生じるものでも構わない。 An alkali is added to the hydrolysis solution to adjust to the above pH range. That is, the alkali acts as a catalyst. If an alkali containing a metal element such as an alkali metal hydroxide such as sodium hydroxide or an alkaline earth metal hydroxide is used as the alkali, the metal element remains after the film is formed, and becomes a soft magnetic powder during the heat treatment in the subsequent process. Diffusion may occur, leading to an increase in coercive force, that is, an increase in core loss. Therefore, it is desirable that at least one selected from ammonia or an organic base is included. These alkalis are preferred because they do not adversely affect the magnetic properties because they volatilize and decompose during the powder heat treatment after the hydrolysis reaction and the heat treatment after the powder magnetic core molding. The organic base is generally an aliphatic amine represented by diethylamine or triethylamine, but may be a heterocyclic compound such as pyridine or an amide having an unsaturated bond such as guanidine and its derivative, What decomposes | disassembles like urea and produces ammonia may be used.
加水分解溶液に対して処理する軟磁性粉末の量は、攪拌できる量であらば、シリカ皮膜の形成量に影響を与えず同じ膜厚のシリカ皮膜が得られる。攪拌可能な粉末量は、粉末の大きさ、密度、形状等により異なるが、例えば、平均粒径８０μｍの球状粉末の場合、加水分解溶液１Ｌに対して３５０〜５５００ｇの範囲である。 If the amount of the soft magnetic powder to be treated with respect to the hydrolyzed solution is an amount that can be stirred, a silica film having the same film thickness can be obtained without affecting the formation amount of the silica film. The amount of powder that can be stirred varies depending on the size, density, shape, and the like of the powder.
このように形成されたシリカ皮膜が施された軟磁性粉末は大気中にて１２０℃程度の低温で熱処理を行うことが好ましい。熱処理により残存する有機溶剤と一部の水分が除去されるとともに、防錆性が付与される。 The soft magnetic powder having the silica film formed as described above is preferably heat-treated at a low temperature of about 120 ° C. in the atmosphere. The remaining organic solvent and part of the water are removed by the heat treatment, and rust prevention is imparted.
通常、このような加水分解によりシリカ皮膜を作製する場合は、７００〜１１００℃の加熱処理が必要になる。加水分解反応を終了させた時点ではまだシリカが完全に形成されておらず、軟磁性粉末の周りには水酸基やアルコキシ基が存在している。加熱処理することでこれらが脱水縮合しシロキサン架橋を形成する。圧粉工程、もしくは圧粉後に熱処理を行えば粉末間でこの架橋形成反応が起こり、圧粉磁心の強度が向上する。よって、７００〜１１００℃の加熱処理は圧縮成形中、若しくは圧縮成形後に行うことが好ましい。加熱温度は８００〜１０００℃がなお好ましい。 Usually, when producing a silica film by such hydrolysis, heat treatment at 700 to 1100 ° C. is required. At the time when the hydrolysis reaction is terminated, silica is not completely formed, and there are hydroxyl groups and alkoxy groups around the soft magnetic powder. These are dehydrated and condensed by heat treatment to form siloxane crosslinks. If heat treatment is performed after the dusting step or after the dusting, this cross-linking reaction occurs between the powders, and the strength of the dust core is improved. Therefore, the heat treatment at 700 to 1100 ° C. is preferably performed during compression molding or after compression molding. The heating temperature is still preferably 800 to 1000 ° C.
加水分解溶液と原料の軟磁性粉末を反応させる際の処理時間には上限はないが、反応が平衡に達するとそれ以上の付着効果がないし、生産性を考慮するとより短時間の方が好ましい。一方で処理時間が短すぎるとシリカ皮膜の付着が不十分になり好ましくない。したがって、処理時間は現実的には３０分から５時間の範囲が好ましい。 There is no upper limit for the treatment time when the hydrolyzed solution and the raw soft magnetic powder are reacted, but when the reaction reaches equilibrium, there is no further effect of adhesion, and a shorter time is preferable in consideration of productivity. On the other hand, if the treatment time is too short, the silica film is not sufficiently adhered, which is not preferable. Therefore, the treatment time is preferably in the range of 30 minutes to 5 hours in practice.
被覆対象のＦｅを主成分とする軟磁性粉末としては、例えば、Ｆｅ、Ｆｅ−Ｓｉ系、Ｆｅ−Ｓｉ−Ａｌ系、Ｆｅ−Ｎｉ系、Ｆｅ−Ｓｉ−Ｂ系、Ｆｅ基ナノ結晶、Ｆｅ基アモルファスなどの金属粉末であり、結晶を持つものでも非晶質の材料でもよい。Ｆｅ−Ｓｉ系粉末やＦｅ−Ｓｉ−Ａｌ系粉末であれば、Ｆｅ量は８５原子％以上が好ましく、９０原子％以上がさらに好ましい。Ｆｅ−Ｎｉ系粉末、Ｆｅ−Ｓｉ−Ｂ系粉末、Ｆｅ基ナノ結晶粉末、Ｆｅ基アモルファス粉末であれば、Ｆｅ量は５０原子％以上が好ましく、さらには６０原子％以上、さらには７０原子％以上が好ましい。 Examples of the soft magnetic powder mainly composed of Fe to be coated include Fe, Fe-Si, Fe-Si-Al, Fe-Ni, Fe-Si-B, Fe-based nanocrystal, and Fe-based A metal powder such as amorphous, which may be a crystal or an amorphous material. In the case of Fe—Si based powder or Fe—Si—Al based powder, the Fe content is preferably 85 atomic% or more, more preferably 90 atomic% or more. In the case of Fe-Ni-based powder, Fe-Si-B-based powder, Fe-based nanocrystal powder, and Fe-based amorphous powder, the amount of Fe is preferably 50 atomic% or more, more preferably 60 atomic% or more, and even 70 atomic%. The above is preferable.
軟磁性粉末の製造方法としては、ガスアトマイズ法、水アトマイズ法などの既知の方法を用いてもよいし、ロール急冷法などにて作製した合金薄帯の破片やそれらを粉砕したものを用いても構わない。また、軟磁性粉末の形状は、球状、偏平状、異形状などいずれの形状であっても本発明の効果が同様に得られる。また、軟磁性粉末の粒径に関わらず本発明は有効であるが、同じ組成であれば粒径が大きい方が一つの結晶粒を大きくして保磁力を減少させることができるため圧粉磁心にしたときにヒステリシス損失が小さくなり、全体としての圧粉磁心の損失を小さく出来る傾向がある。 As a method for producing the soft magnetic powder, a known method such as a gas atomization method or a water atomization method may be used, or a piece of alloy ribbon produced by a roll quenching method or a crushed one may be used. I do not care. In addition, the effect of the present invention can be obtained in the same manner regardless of the shape of the soft magnetic powder such as a spherical shape, a flat shape, or an irregular shape. Although the present invention is effective regardless of the particle size of the soft magnetic powder, if the particle size is the same, a larger particle size can increase the size of one crystal grain and reduce the coercive force, thereby reducing the dust core. When this is done, the hysteresis loss is reduced, and the loss of the powder magnetic core as a whole tends to be reduced.
（実施例１）
Ｆｅ−６．５％Ｓｉからなる組成で、平均粒径が８０μｍの軟磁性粉末５００ｇを、テトラエトキシシラン（関東化学製）１４ｇとＩＰＡ溶液の混合液１００ｍＬ、濃アンモニア水２ｍＬ、水３０ｇからなる室温２５℃の加水分解溶液に浸漬し、プロペラ攪拌機を用いて３時間攪拌した。その後、軟磁性粉末と加水分解溶液を分離し、軟磁性粉末を１２０℃で１時間熱処理してＩＰＡ溶液と水とを乾燥した。乾燥後の軟磁性粉末の酸素量を赤外線吸収法により測定し、原料粉末からの酸素量増加分が生成したシリカに因るものとし、ＳｉＯ２が生成したと仮定してシリカ生成量を算出した。赤外線吸収法の測定には堀場製作所製ＥＭＧＡ−５５０を使用した。
加えたテトラエトキシシランのＳｉ量に対する生成したシリカ皮膜のＳｉ量を変換効率として算出したところ、変換効率は８０．９％であった。
Example 1
500 g of soft magnetic powder having a composition of Fe-6.5% Si and an average particle size of 80 μm is composed of 14 g of tetraethoxysilane (manufactured by Kanto Chemical) and 100 mL of a mixed solution of IPA solution, 2 mL of concentrated ammonia water, and 30 g of water. It was immersed in a hydrolysis solution at room temperature of 25 ° C. and stirred for 3 hours using a propeller stirrer. Thereafter, the soft magnetic powder and the hydrolysis solution were separated, and the soft magnetic powder was heat treated at 120 ° C. for 1 hour to dry the IPA solution and water. The amount of oxygen in the soft magnetic powder after drying was measured by an infrared absorption method, and the amount of oxygen produced from the raw material powder was attributed to the produced silica, and the amount of silica produced was calculated assuming that SiO 2 was produced. EMGA-550 manufactured by HORIBA, Ltd. was used for the measurement of the infrared absorption method.
When the Si amount of the generated silica film with respect to the Si amount of the added tetraethoxysilane was calculated as the conversion efficiency, the conversion efficiency was 80.9%.
（実施例２）
実施例１に対してテトラアルコキシシランと水の量を変え、その他は同様にしてテトラアルコキシシランからシリカ皮膜への変換効率を求めた。表１に示すように、テトラエトキシシラン濃度が０．１２ｍｏｌ／Ｌの場合、変換効率が非常に低い。また、０．４７ｍｏｌ／Ｌまではテトラエトキシシラン濃度が増加するに従って、変換効率が向上しているが、本発明範囲を超えた１．１７ｍｏｌ／Ｌになると逆に変換効率が低下している。
(Example 2)
The conversion efficiency from the tetraalkoxysilane to the silica film was determined in the same manner as in Example 1 except that the amounts of tetraalkoxysilane and water were changed. As shown in Table 1, when the tetraethoxysilane concentration is 0.12 mol / L, the conversion efficiency is very low. Further, the conversion efficiency is improved as the tetraethoxysilane concentration is increased up to 0.47 mol / L, but the conversion efficiency is decreased when the concentration is 1.17 mol / L exceeding the range of the present invention.
（実施例３）
表１の、テトラエトキシシラン濃度が０．４７ｍｏｌ／ＬのＡ−３の試料と、テトラエトキシシラン濃度が０．６７ｍｏｌ／ＬのＡ−４〜６の試料の実験条件と水濃度が異なる以外はほぼ同様の条件で軟磁性粉末にシリカ被覆を形成し、水濃度により変換効率がどのように変化するのかを調べた。表２に示すように、水濃度がモル比で２０倍に満たないと、変換効率は４０％を下回っている。一方、水濃度がモル比で３０倍を超えると、水濃度が増加したにもかかわらず変換効率はむしろ低下する傾向にある。また、乾燥前の攪拌後の加水分解溶液を調べると、溶液中に軟磁性粉末に付着しないシリカ粒子が浮遊しており、反応速度が増加しても皮膜になる割合は減少していることが解った。
(Example 3)
Except that the experimental conditions and the water concentration of the sample A-3 having a tetraethoxysilane concentration of 0.47 mol / L and the samples A-4 to 6 having a tetraethoxysilane concentration of 0.67 mol / L in Table 1 are different. Under the same conditions, a silica coating was formed on the soft magnetic powder, and how the conversion efficiency changed depending on the water concentration was investigated. As shown in Table 2, the conversion efficiency is less than 40% when the water concentration is less than 20 times in terms of molar ratio. On the other hand, when the water concentration exceeds 30 times in terms of molar ratio, the conversion efficiency tends to decrease rather than increase in water concentration. In addition, when examining the hydrolyzed solution after stirring before drying, silica particles that do not adhere to the soft magnetic powder are floating in the solution, and the rate of forming a film decreases even when the reaction rate increases. I understand.
（実施例４）
表１の、テトラエトキシシラン濃度が０．６７ｍｏｌ／Ｌで、水濃度がモル比で２５倍のＡ−５の試料の実験条件と、ｐＨが異なる以外はほぼ同様の条件で変換効率がどのように変化するのかを調べた。表３に示すように、ｐＨが７．０を下まわると、軟磁性粉末に錆が発生した。圧粉磁心の飽和磁束密度が低下し、磁心強度が大きく低下する要因となるので錆が発生した軟磁性粉末は使用に耐えない。ｐＨ７以上では軟磁性粉末が錆びることなくシリカ皮膜を形成できるが、変換効率を考慮するとｐＨ９以上が好ましい。ｐＨが１１．０を超えると変換効率が低下した。このとき乾燥前の攪拌後の加水分解溶液を調べると、溶液中に軟磁性粉末に付着しないシリカ粒子が浮遊しており、加水分解速度が大きくなりすぎることで、皮膜の生成効率が落ちていることが解った。
Example 4
What is the conversion efficiency under the same conditions as in Table 1 except that the experimental conditions of the A-5 sample with a tetraethoxysilane concentration of 0.67 mol / L and a water concentration of 25 times the molar ratio are different from the pH? We investigated whether it changed to. As shown in Table 3, when the pH fell below 7.0, rust was generated in the soft magnetic powder. Since the saturation magnetic flux density of the dust core is reduced and the strength of the magnetic core is greatly reduced, the soft magnetic powder with rust cannot be used. When the pH is 7 or more, the silica film can be formed without rusting the soft magnetic powder, but considering the conversion efficiency, the pH is preferably 9 or more. Conversion efficiency fell when pH exceeded 11.0. At this time, when examining the hydrolyzed solution after stirring before drying, silica particles that do not adhere to the soft magnetic powder are floating in the solution, and the rate of hydrolysis becomes too high, resulting in a decrease in film formation efficiency. I understood that.
（実施例５）
実施例１で得られた軟磁性粉末を用いて圧粉磁心を作製した。軟磁性粉末に対して、バインダーとしてアモルファスシリカ１．５重量部、アクリル樹脂１．５重量部、ステアリン酸亜鉛０．３重量部を混合した。
この混合粉末を外径Φ１４ｍｍ、内径Φ８ｍｍ、高さ５ｍｍのトロイダル状コアに成形した。成形圧は１．２ＧＰａ（１２ｔｏｎ／ｃｍ２）とした。成形時に導入される歪みを除去するため、窒素気流中８００℃で２時間熱処理を行った。
得られたリング試料のプレス面に銀ペーストを塗布し、岩崎通信機社製デジタルマルチメータＶＯＡＣ７５２１を用いて２端子法にて測定し、シリカの膜厚と電気抵抗率の関係を図１に示した。本発明の製造方法により０．２μｍ以上の厚さのシリカ皮膜を作製することで１０６Ωｍ以上の高い電気抵抗率が得られた。
(Example 5)
A dust core was prepared using the soft magnetic powder obtained in Example 1. As a binder, 1.5 parts by weight of amorphous silica, 1.5 parts by weight of acrylic resin, and 0.3 parts by weight of zinc stearate were mixed with the soft magnetic powder.
This mixed powder was formed into a toroidal core having an outer diameter of 14 mm, an inner diameter of 8 mm, and a height of 5 mm. The molding pressure was 1.2 GPa (12 ton / cm 2 ). In order to remove distortion introduced during molding, heat treatment was performed at 800 ° C. for 2 hours in a nitrogen stream.
A silver paste is applied to the pressed surface of the obtained ring sample and measured by a two-terminal method using a digital multimeter VOAC7521 manufactured by Iwasaki Tsushinki Co., Ltd., and the relationship between the silica film thickness and electrical resistivity is shown in FIG. It was. By producing a silica film having a thickness of 0.2 μm or more by the production method of the present invention, a high electrical resistivity of 10 6 Ωm or more was obtained.
アルカリとして、有機塩基（ジエチルアミン、トリエチルアミン、グアニジン）を用いて実施例１と同様に軟磁性粉末にシリカ皮膜を形成した。比較として、水酸化ナトリウム水溶液を用いて同様に実験を行った。それぞれのシリカ皮膜形成が施された軟磁性粉末と何も処理を施していない軟磁性粉末を窒素中８００℃で熱処理し、東英工業製ＶＳＭ−５−２０にて最大印加磁界２０ｋＯｅで測定した粉末の保磁力を比較した。表４にその結果を示す。 As an alkali, an organic base (diethylamine, triethylamine, guanidine) was used to form a silica film on the soft magnetic powder in the same manner as in Example 1. For comparison, an experiment was similarly performed using an aqueous sodium hydroxide solution. Each of the soft magnetic powders with silica film formation and the untreated soft magnetic powders were heat-treated at 800 ° C. in nitrogen and measured with a maximum applied magnetic field of 20 kOe with VSM-5-20 manufactured by Toei Kogyo. The coercivity of the powders was compared. Table 4 shows the results.
Claims (3)
A soft magnetic powder on which a silica film is formed by the method for forming a silica film according to claim 1 or 2 is prepared, and the soft magnetic powder is compression-molded, and during or after the compression molding, 700 ° C to 1100 A method for producing a dust core, wherein the heat treatment is performed at a temperature of ° C.
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