JP3986043B2 - Powder magnetic core and manufacturing method thereof - Google Patents

Description

【０００８】
請求項４〜６は以上の圧粉磁心の製法で、次のような構成特徴からなる。
（請求項４）粒子径が１０〜２００μｍの鉄粉、又は該鉄粉の表面に燐酸化合物被膜を表面に施した鉄粉に、前記した（請求項１または２に挙げた）何れかの結合用樹脂の粉末を質量比で０．１５〜１質量％混合し、この混合粉を圧縮成形すると共に加熱処理する。
（請求項５）粒子径が１０〜２００μｍの鉄粉、又は該鉄粉の表面に燐酸化合物被膜を施した鉄粉に、前記した（請求項１または２に挙げた）何れかの結合用樹脂を有機溶剤に溶融した液を混合したのち乾燥して、結合用樹脂の含有量が質量比で０．１５〜１質量％である樹脂被覆鉄粉とし、この樹脂被覆鉄粉を圧縮成形すると共に加熱処理する。
（請求項６）以上の製造方法において、第１段階として、前記した（請求項１または２に挙げた）何れかの結合用樹脂を有機溶剤に溶解した液を混合したのち乾燥して、前記樹脂の含有量が質量比で、０．３質量％以下である樹脂被覆鉄粉とする。第２段階として、前記樹脂被覆鉄粉に前記結合用樹脂粉末の何れかを添加して前記樹脂の全量を質量比で０．１５〜１％とし、この混合粉を圧縮成形すると共に加熱処理する。
【０００９】
（請求項７と８）以上の製造方法において、前記結合用樹脂粉末は粒度１〜１５０μｍのものが好ましいこと、前記混合粉又は樹脂被覆粉末の圧縮成形は常温下でもよいが、前記結合用樹脂が溶融しない温度に加熱した状態で行うことができることを確認したものである。
【００１０】
また、請求項８以降は前記加熱処理条件等の細部構成である。即ち、請求項８〜１０では、圧縮成形の形態として、第１に樹脂溶融しない温度以下で加熱する態様、第２に加熱しないで成形した圧粉体を樹脂溶融しない温度以下で加熱する態様、第３に樹脂溶融する温度下で加熱する態様、何れであってもよいことを特定した。請求項１１では、前記請求項４〜６の加熱処理について、大気中、不活性ガス中、減圧中の何れかにおいて、結合用樹脂の少なくとも１種が溶融する温度で加熱する態様を特定した。これは例えば、ＰＰＳでは２５０〜４００℃、熱可塑性ＰＩでは３００〜４５０℃に加熱することである。請求項１２では、加熱した状態で圧縮成形を行い、離型された熱い圧粉体を大気中、不活性ガス中、減圧中の何れかにおいて、前記結合用樹脂の少なくとも１種が溶融する温度で加熱処理する態様、つまり加熱圧粉成形と圧粉体の加熱処理を連続して行うことを特定した。請求項１３では、圧縮成形と共に加熱処理した圧粉磁心を、温度１５０〜３２０℃で加熱して安定化熱処理を施す態様を特定した。
【００１１】
【発明の実施の形態】
次に、以上の発明を実施の形態及び実施例により明らかにする。この説明では、まず、発明対象の磁性粉末、結合用樹脂及びその含有量、磁性粉末と樹脂の混合、圧縮成形、加熱処理、安定化熱処理について順に詳述する。その後、試験の代表的なものを実施例に挙げ利点を明らかにする。
【００１２】
（１．磁性粉末）
対象の鉄粉はアトマイズ法、還元法等の各種製法による鉄粉を適用することができる。鉄粉の粒度は、要求される磁束密度及び使用される周波数領域により選択される。粒子径は一般に粉末冶金で使用される２００μｍ以下を使用することができるが、圧縮性を考慮すると１５０μｍ以下である。鉄粉の粒子径が小さいほど過電流損失が小さくなり、高周波特性が向上するため、粒子径は１００μｍ以下とすることがより好ましい。細かい粒子については特に限定しなくてもよいが、細かな粒子が多い粒度分布は、粉末圧縮性及び粉末流動性が悪くなり、高密度な圧粉磁心が得られないため粒子径１０μｍ以上の粉末とすることが好ましい。
【００１３】
燐酸化合物被膜を表面に施した鉄粉は、その被膜が絶縁層として作用し、鉄粉粒子間の過電流発生を抑制する効果があり、結合用樹脂の存在によって、過電流の発生を抑制する効果がさらに高くなり、より高周波特性が向上する。被膜用燐酸化合物は、燐酸鉄、燐酸マンガン、燐酸亜鉛、リン酸カルシウム等が好適である。また、燐酸酸化合物被膜を表面に施した鉄粉の市販品でも差し支えない。この例としては、ヘガネス社製の鉄粉（商品名：Permite、或いはSomaloy）等が挙げられる。
【００１４】
（２．結合樹脂）
結合用樹脂としては、耐熱性に優れるＰＰＳ、熱可塑性ＰＩもよい特性を示し好適である。圧粉磁心の使用される温度が１８０℃を越えるような環境であり、長時間にわたって使用されると、圧粉磁心の形状、寸法に経時変化を生じたり、見掛けの絶縁性能が低下する虞がある。その理由は、前者は圧縮成形時に生じる複雑な残留応力があるものと考えられること、後者は高温環境により、磁性粉末間の絶縁樹脂の厚さが減少する可能性が考えられる。このような虞には、前記ＰＰＳ又は熱可塑性ＰＩに、これらよりガラス転移点が高い樹脂（上記表１の非熱可塑性ポリイミド、つまり実施例の熱硬化性ポリイミド）を混合すると、特性が改善される。これは、磁性粒子（鉄粒子）間の樹脂が、熱特性が異なる複合状態であるため、使用中の変形や移動を生じ難くしているものと考えられる。ガラス転移点が高い樹脂の含有量は、主体となるＰＰＳ又は熱可塑性ＰＩの量を超えない範囲とされる。ＰＰＳに熱可塑性ＰＩを混合することも、この技術思想と同じことである。
【００１５】
（３．結合樹脂の含有量）
結合用樹脂の含有量は、全質量の０．１５〜１質量％の範囲が好適である。０．１５質量％未満では、磁性粉末の粒子が結合及び絶縁する効果が少なく、圧粉磁心の強度が不十分となり、磁性粉末間の絶縁性が悪いものとなる。また、結合用樹脂の含有量が１質量％を越えると、圧粉磁心の強度及び絶縁性が高いものとなる反面、圧粉磁心に占める磁性粒子の占有率が低くなり、磁性粒子の密度が低いものとなるため、高い磁束密度及び透磁率が得られなくなる。
【００１６】
透磁率との関係において、５０Ｈｚ程度の低周波数領域では樹脂の含有量が多いものほど低くなる。５ｋＨｚ程度の高い周波数の領域では、樹脂を含まないものは低周波領域における透磁率よりはるかに低い値を示し、これに比べて、樹脂含有量が０．３質量％近傍で透磁率が最大値を示して低周波における透磁率とほぼ同じ値となる。樹脂含有量がさらに増加すると、低周波の場合の透磁率と同様に、次第に低下していき、樹脂含有量が１質量％を越えると、樹脂を含まない場合の透磁率より低くなる。このような樹脂量と透磁率の関係からも、結合用樹脂の含有量は、０．１５〜１質量％が最適となる。樹脂含有量は、０．３質量％近傍が特に好ましい。また、密度は７．３５ｇ／ｃｍ^３ 以上であることが望ましい。
【００１７】
（４．磁性粉末と結合用樹脂の混合）
結合用樹脂は、磁性粉粒子間を絶縁し、過電流の発生を抑制する。燐酸化合物被膜を施した鉄粉は、粉末圧縮成形の際に剥離や脱落によって、燐酸化合物による絶縁が破られる虞があるが、結合用樹脂の存在によって保護され、より過電流の発生を抑制することができる。
【００１８】
結合用樹脂は粉末の形で混合することができる。その際は、磁性粉末の粒度分布と同等又は細かめとすると、混合状態が良好になり、耐熱性も向上する。磁性粉末間の絶縁性を向上させるためには、６０μｍ以下の粒度とすることが好ましい。また、結合用樹脂に、ｎ−メチル−２−ピロリドン等の極性が強い有機溶剤を添加して低粘度化させておき、流動層式又は撹拌混合式のコーティング装置を用いて、鉄粉に必要な量のコーティングを行ったのち、乾燥する方法も好ましい。
【００１９】
また、有機溶剤を含む結合用樹脂を、前記した場合より少ない樹脂量でコーティングしたのち乾燥して、樹脂被覆粉末を作り、この樹脂被覆粉末に結合用樹脂の粉末を混合する方法としてもよい。有機溶剤を含む結合用樹脂を用いて得られる樹脂被膜は、絶縁性能がより優れたものとなる。樹脂の膜厚は、２０ｎｍ以上であると過電流の発生が少なくなる。膜厚２０ｎｍの樹脂被膜を得るには、おおよそ樹脂量０．１５質量％程度となる樹脂溶液が混合される。一方、樹脂膜厚が２００ｎｍを越えると、粉末の圧縮性が悪くなり、その結果、磁気特性の不十分な圧粉磁心になる。樹脂を被覆した磁性粉末に、追加で結合用樹脂粉末を混合すると、被覆樹脂が保護され、より優れた磁性特性が得られる。
【００２０】
（５．圧縮成形）
樹脂被覆磁性粉末は金型を用いて圧縮成形される。圧縮成形のとき、圧縮性向上や圧粉体抜き出し摩擦の低減のために、金型面に粉末冶金で通常用いられるステアリン酸亜鉛やエチレンビスステアロアマイド等の成形潤滑剤粉末を静電塗布等により予め塗布しておくことが望ましい。また、より高い密度に成形するには、結合用樹脂が溶融しない温度に加熱した状態で行う態様、混合粉や樹脂被膜鉄粉を加熱しない状態で１次圧縮成形した後、結合用樹脂が溶融しない温度に加熱した状態で２次圧縮成形を行う態様、更に結合用樹脂が軟化する温度から溶融する温度まで加熱した状態で圧縮形成を行う態様で行うことである。なお、成形後処理としては、成形したのち、常温まで冷却して、以降に述べる加熱処理を行う方法としてもよいが、成形したのち、成形体が熱いままで加熱処理へ移行する方法とすれば熱エネルギーと冷却時間を省くことができるので、合理的である。
【００２１】
（６．加熱処理）
加熱処理は、結合用樹脂を溶融させ、さらに結合用樹脂の結晶化による樹脂特性の安定化を図る工程である。加熱温度、加熱時間は使用する樹脂の種類により選定される。温度は、樹脂の融点から樹脂が熱劣化しない範囲であり、ＰＰＳでは２５０〜４００℃、熱可塑性ＰＩでは３００〜４５０℃とされる。加熱時間は一般的に約０．５〜１時間程度である。
【００２２】
加熱時の雰囲気は大気中で行うことができる。但し、大気中の酸素の存在は、樹脂の強度低下、機械的特性の低下を生じる虞が考えられる。これは、酸素の存在によって、樹脂の重合反応が進行し、ガス状の縮合物が発生しやすくなり、樹脂内に気泡として残存することも起こり得るからである。そのため、より好ましくは、大気中での加熱に先立ち、窒素ガス等の不活性ガス雰囲気中で加熱される。また、減圧された雰囲気中で加熱すると、雰囲気の酸素量が減少すると共に、ガス状の縮合物をより樹脂から放出させることができる。これら雰囲気は、適宜組み合わせることができる。加熱処理の冷却過程では、温度３２０〜１５０℃程度の領域において時間をかけて冷却すると、以下に述べる安定化熱処理を兼ねることができる。
【００２３】
（７．安定化熱処理）
安定化熱処理を行うと、結合用樹脂の特性を安定化し、圧粉磁心を高い温度で使用したとき、経時変化を生じ難いものとすることができる。この場合、前記加熱処理を行い、一旦、冷却したのち、１５０〜３２０℃程度で１〜２時間程度加熱される。また、前記加熱処理の冷却過程で、３２０〜１５０℃程度の温度領域で１〜２時間保持する方法によることができる。
【００２４】
【実施例】
次に、本発明の実施例と比較例により、発明構成及び利点を明らかにする。
（１）準備した粉末は次の(1)〜(8)の８種類である。
(1)．アトマイズ鉄粉：これは「ヘガネス社製、品番：ＡＢＣ１００．３０，」粒度が１５０μｍ以下のものである（以下、純鉄粉と記す）。
(2)．燐酸被膜処理アトマイズ鉄粉：これは「ヘガネス社製、品番：Somaloy500、」粒度が１５０μｍ以下のものである（以下、被膜形成鉄粉と記す）。
(3)．熱可塑性ポリアミド樹脂（以下、ポリアミドと記す）入り燐酸被膜処理アトマイズ鉄粉：これは「ヘガネス社製の市販粉末」、燐酸被膜処理アトマイズ鉄粉(Somaloy500）に熱可塑性ポリアミドを０．６質量％混合したものである。
(4)．ＰＰＳ粉末：これは「大日本インキ製」粒度が１５０μｍ以下（−１５０μｍ）のもの、６０μｍ以下（−６０μｍ）のものである（以下、ＰＰＳと記す）。
(5)．熱可塑性ポリイミド粉末：これは「三井化学製」、粒度が１５０μｍ以下（−１５０μｍ）のものと、及び６０μｍ以下（−６０μｍ）のものである（以下、熱可塑性ＰＩと記す）。
(6)．熱硬化性ポリイミド粉末：これは「ローランヌ製」、粒度が１５０μｍ以下（−１５０μｍ）のものである（以下、熱硬化性ＰＩと記す）。
(7)．熱硬化性フェノール樹脂粉末：これは「大日本インキ製」、粒度が１５０μｍ以下（−１５０μｍ）のものである（以下、フェノールと記す）。
(8)．ステアリン酸亜鉛粉：これは一般に使用されている成形型用潤滑剤である。
【００２５】
（２）「実施例１」樹脂の含有量と圧粉磁心の実効透磁率
前記被膜処理鉄粉にＰＰＳ（−１５０μｍ）を所定量（全質量％で、０％、０．１５％、０．３％、０．４５％、０．６％、０．７５％、１．０％、１．２％となるよう）混合し、ステアリン酸亜鉛粉を塗布した金型を用い、混合粉を成形圧力１４７０ＭＰａでリング形状（φ１０×φ２３×５ｍｍ）に圧縮成形した。成形体は、空気中で温度３２０℃で１時間加熱したのち、温度２４０℃で１時間加熱して、冷却することにより圧粉磁心を得た。なお、ＰＰＳを含まないものは純圧粉体である。
【００２６】
実効透磁率は、Ｂ−Ｈアナライザーにより測定した。周波数は、５０Ｈｚ及び５０００Ｈｚで、印加磁束密度は１Ｔ（テスラー）である。実効透磁率の測定結果は図１の通りである。即ち、５０Ｈｚにおける実効透磁率は、樹脂含有量の増加に対してほぼ直線的に低下している。一方、５０００Ｈｚにおける実効透磁率は、ＰＰＳを含まないものは低く、ＰＰＳ含有量が０．３質量％近傍で最大値となり、それ以上のＰＰＳ含有量では、緩やかに低下しており、ＰＰＳ含有量が１質量％のとき、ＰＰＳを含まない圧粉磁心の値とほぼ同じになっている。なお、樹脂がＰＰＳの例を挙げたが、他の樹脂粉末の場合でも同様な傾向となる。
【００２７】
以上のことから、発明の樹脂含有量に関し、樹脂含有量の少ない領域では、実効透磁率の平均変化率が大きいので、樹脂含有量は０．１５質量％以上とした。樹脂含有量の多い側では、樹脂を含まない圧粉磁心の実効透磁率より低くならない１．０質量％以下の樹脂含有量とした。
【００２８】
（３）「実施例２」純鉄粉を用いた樹脂の種類と圧粉磁心の耐熱性
前記純鉄粉に各樹脂粉末を所定量添加し、Ｖ型混合機で混合した。樹脂粉末の混合割合は表２に示す通りである。ＰＰＳ及び熱可塑性ＰＩは粒度が−１５０μｍのものを用いた。
【表２】

【００２９】
各混合粉は、成形圧力１４７０ＭＰａで円柱（φ２３×５ｍｍ）及び円筒形状（φ１０×φ２３×１０ｍｍ）に圧縮成形した。成形では、金型の内壁面に予めステアリン酸亜鉛を静電塗布しておき、混合粉を充填及び圧粉した。成形体の加熱処理温度は、樹脂がＰＰＳを含むもの、及び熱可塑性ＰＩを含むものは３２０℃、フェノールを含むものは１５０℃とし、窒素ガス雰囲気中でそれぞれ１時間加熱した。安定化熱処理は、樹脂がＰＰＳ及び熱可塑性ＰＩを含むものについて行い、大気中で、２４０℃で１時間加熱した。
【００３０】
円柱形状（φ２３×５ｍｍ）の各試料は、５×２３×５ｍｍの角柱形状に切削加工し、絶縁性能評価に供した。絶縁性能評価は、温度２００℃の恒温層中で、１００時間加熱したのち、四端子法（試料両端に直流電流を流し、その間に２端子を接して電気抵抗を測定）による見掛け固有抵抗値を測定し、加熱する前の値に対する低下率で評価した。また、円筒形状（φ１０×φ２３×１０ｍｍ）の各試料については圧環強度値を測定した。圧環強度は室温及び温度２００℃において、圧縮速度毎分０．５ｍｍで圧縮して破壊するまでの最大荷重である。表３に見掛け固有抵抗、室温及び２００℃の圧環強度の測定結果を示した。
【表３】

【００３１】
（評価）見掛け固有抵抗は、樹脂の含有量の増加によって一次関数的に上昇する。樹脂含有量が０．１５質量％と１質量％では見掛け固有抵抗が異なるが、圧粉磁心の用途によってそれぞれ実用できるものである。樹脂の種類による加熱前後の見掛け固有抵抗をみると、ＰＰＳを含むもの（試料Ａ１〜Ａ３）は樹脂含有量が変わっても加熱前後の変化量がほぼ同じで、低下率（変化率）では樹脂含有量が多いほど少なくなっている。熱可塑性ＰＩを含むもの（試料Ａ４）でも同じなっている。ＰＰＳに熱硬化性ＰＩを含むもの（試料Ａ５）、及び熱可塑性ＰＩに熱硬化性ＰＩを含むもの（試料Ａ６）は、見掛け固有抵抗の変化量は、ＰＰＳのものより少なくなっている。これらに比べて、フェノールを含むもの（試料Ａ７）は、加熱前の見掛け固有抵抗はＰＰＳ等を含むものより高いが、加熱後の変化量がきわめて多く、加熱後の見掛け固有抵抗が著しく低いものとなっている。
【００３２】
圧環強度は樹脂含有量が多いほど低くなる。室温と２００℃との差は、ＰＰＳを含むもの（試料Ａ１〜Ａ３）及び熱可塑性ＰＩを含むもの（試料Ａ４）共にほぼ同じであるが、フェノールを含むもの（試料Ａ７）は、室温の強度も低いが、２００℃における強度が著しく低いものとなっている。
【００３３】
（４）「実施例３」被膜形成鉄粉を用いた樹脂の種類と圧粉磁心の耐熱性
前記被膜形成鉄粉に、表４に示す各樹脂を所定量添加した混合粉を作製した。なお、試料Ｂ１６のポリアミドは上記した燐酸被膜処理アトマイズ鉄粉(Soｍaloy500）にポリアミドを０．６質量％混合した市販粉末である。試料Ｂ１３は、ＰＰＳに有機溶剤としてｎ−メチル−２−ピロリドンを添加した液を被膜形成鉄粉に加えて混合し、乾燥してＰＰＳ含有量が０．１５質量％で被覆された磁性粉末としたのち、更にＰＰＳを混合してＰＰＳ含有量を０．６質量％とした混合粉である。それ以外の混合粉は、被膜形成鉄粉に樹脂の粉末を添加し、Ｖ型混合機で混合した。試料Ｂ１４〜１６は比較例である。各混合粉は、前記実施例２と同様な条件で円柱（φ２３×５ｍｍ）及び円筒形状（φ１０×φ２３×１０ｍｍ）に圧縮成形した。
【００３４】
成形体の加熱処理温度は、樹脂がＰＰＳ及び熱可塑性ＰＩを含むものは３２０℃、熱硬化性ＰＩを含むものは２００℃、フェノールを含むものは１５０℃、ポリアミドを含むものは２７５℃とし、窒素ガス雰囲気中でそれぞれ１時間加熱した。なお、試料Ｂ１２については空気中で行った。安定化熱処理は、樹脂がＰＰＳ及び熱可塑性ＰＩを含むものについて行い、温度２４０℃で１時間加熱した。
【００３５】
【表４】

【００３６】
前記実施例２と同様な方法で、温度２００℃で１００時間加熱したのちの見掛け固有抵抗値と、室温及び温度２００℃における圧環強度を測定した。測定結果は表５のと通りである。
【００３７】
【表５】

【００３８】
（評価）見掛け固有抵抗は、純鉄粉を用いた圧粉磁心より高い。燐酸化合物被膜があるだけ、鉄粉粒子の絶縁がよくなっていることが分かる。樹脂の含有量の増加によって一次関数的に上昇することは、純鉄粉のものと同様である。樹脂の種類による加熱前後の見掛け固有抵抗をみると、ＰＰＳを含むものは樹脂含有量に係わらず、変化量がほぼ同じであり、低下率（変化率）では樹脂含有量が多いほど少なくなる。また、粒度が−１５０μｍのＰＰＳ、このＰＰＳと熱可塑性ＰＩ又は熱硬化性ＰＩとの混合物のもの、粒度が−１５０μｍの熱可塑性ＰＩ及びこの熱可塑性ＰＩと熱硬化性ＰＩとの混合のものは、ほぼ同じ特性を示すが、細部的にはＰＰＳ又は熱可塑性ＰＩに熱硬化性ＰＩが混ざっているものが、加熱による見掛け固有抵抗の低下が少ない。
【００３９】
ＰＰＳも熱可塑性ＰＩも添加した粉末の粒度を−６０μｍとしたものは、加熱前後ともに粒度−１５０μｍのものより高くなっている。試料Ｂ１３のＰＰＳを湿式混合して被覆し、ＰＰＳを混合したものは、粉末で混合したものより、僅かに見掛け固有抵抗が高い。試料Ｂ１３の加熱処理を空気中で行ったものは、加熱による見掛け固有抵抗の低下が大きいが、窒素ガス中加熱より高い値を示している。これらに比べて、フェノールを含むもの（試料Ｂ１５）及びポリアミドのもの（試料Ｂ１６）は、初期値が低く、加熱した低下量が大きくなっている。また、熱硬化性ＰＩだけを含むもの（試料Ｂ１６）では、加熱による低下量は少ないが、低い値を示している。
【００４０】
圧環強度は、純鉄粉の場合と殆ど同じ水準で、樹脂含有量との関係及び２００℃に加熱したときの低下量共に同じ傾向を示している。圧環強度においては、樹脂粉末の粒度の影響、樹脂の湿式被覆、加熱処理の雰囲気中の違いに差は認められない。ＰＰＳ系及び熱可塑性ＰＩ系に比べて、フェノールを含むもの及びポリアミドのものは初期値が低く、加熱したときの低下量が大きいこと、及び熱硬化性ＰＩが加熱による低下量は少ないが、低い値を示していることは、見掛け固有抵抗の場合の序列と同じになっている。
【００４１】
【発明の効果】
以上説明したように、本願の各発明は、例えば、請求項１や２に特定されるごとく粒子径が１０〜２００μｍの鉄粉、又は該鉄粉の表面に燐酸化合物被膜を施した鉄粉に、ＰＰＳ樹脂及び熱硬化性ＰＩ、熱可塑性ＰＩ及び熱硬化性ＰＩ、ＰＰＳと熱可塑性ＰＩ及び熱硬化性ＰＩ、の何れかの混合物の形で、０．１５〜１質量％含むものとしたことで、透磁率が高く、特に高周波領域で使用される場合に優れた特性を示し、また、温度が高い環境で使用される場合でも、固有抵抗及び耐熱強度が高いものであるから、用いられる装置の性能及び小型化に寄与でき、圧粉磁心の適用範囲を拡大することができる。
【図面の簡単な説明】
【図１】燐酸化合物被覆鉄粉をＰＰＳ樹脂で結合した圧粉磁心の樹脂含有量と実効透磁率の関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention particularly relates to a dust core excellent in mold formability and soft magnetic properties and a method for producing the same.
[0002]
[Prior art]
With recent downsizing and higher density of electrical and electronic equipment, there is an increasing demand for high-frequency cores that are small in size and have high magnetic flux density, magnetic permeability and low iron loss for the core materials used in these devices. . Such a magnetic core material has a drawback that although a ferrite core is used, the saturation magnetic flux density is low. On the other hand, in a dust core in which an alloy powder such as Sendust or Permalloy is bonded with an insulating resin such as phenol resin or epoxy resin, eddy current loss can be suppressed even at 100 kHz or more. To a high degree, it is difficult to sufficiently satisfy the demand for miniaturization. Further, it is known that a dust core made of high-purity iron powder as a magnetic particle has a relatively high magnetic flux density for a motor core or a transformer core. This is, for example, a soft magnetic composite material (name: Soft Magnetic Composite: CMC) of Höganäs, which forms a phosphate-based ultra-thin insulating film on the surface of high-purity atomized iron powder or reduced iron powder, and is a binding resin Is a thermosetting phenol resin or thermoplastic polyamide resin (nylon), and is characterized by high magnetic flux density, high magnetic permeability, and low iron loss.
[0003]
[Problems to be solved by the invention]
The dust cores described above are inexpensive and promising for reducing the size of the core, but their mechanical strength is low, so cracking or chipping occurs when cutting or drilling. It tends to occur, and the mechanical strength tends to be remarkably lowered when used in an environment where the temperature is high. That is, this type of soft magnetic material is often used in high temperature environments in applications such as automobiles and industrial machinery, and maintains high magnetic properties in such environments and has no strength reduction or dimensional change. In addition, it has material strength that can withstand cutting and the like, and further cost reduction is required. Of course, the frequency used is relatively high, and high permeability is also desired.
[0004]
[Means for Solving the Problems]
As a result of repeated studies on how to solve the problems of the above-described conventional powder magnetic cores, the present inventors have solved the above problems by devising the selection, addition amount, resin powder, mixing mode, and the like of a binding resin. As a result, the present invention has been completed.
[0005]
The invention according to claims 1 and 2 is a powder magnetic core in which iron powder having a particle diameter of 10 to 200 μm or iron powder having a phosphoric acid compound coating on the surface of the iron powder is bonded with a resin. Is one of the following, and the resin content is 0.15 to 1% by mass of the total mass.
(Claim 1) A mixture of polyphenylene sulfide (hereinafter referred to as PPS) and thermosetting polyimide , or a mixture of thermoplastic polyimide (hereinafter referred to as thermoplastic PI) and thermosetting polyimide (Claim 2 ). Mixture of PPS with thermoplastic PI and thermosetting polyimide
A third aspect of the present invention is the method according to the first or second aspect, wherein the content of the thermosetting polyimide is less than half of the total content of the binding resin of 0.15 to 1% by mass.
Table 1 shows representative values of the glass transition temperatures (differential calorimetry, DSC: Differential Scanning Calorimetry) of each resin.
[0007]
[Table 1]

[0008]
The fourth to sixth aspects of the present invention are the above-described dust core manufacturing methods and have the following structural features.
(Claim 4 ) Any of the above-mentioned bonds (listed in claim 1 or 2 ) on iron powder having a particle diameter of 10 to 200 μm , or iron powder having a surface coated with a phosphoric acid compound coating. The resin powder is mixed at a mass ratio of 0.15 to 1% by mass, and the mixed powder is compression-molded and heat-treated.
(Claim 5 ) Any of the above binding resins (listed in claim 1 or 2 ) applied to iron powder having a particle diameter of 10 to 200 μm or iron powder having a phosphoric acid compound coating on the surface of the iron powder. After the liquid melted in an organic solvent is mixed and dried, a resin-coated iron powder having a binding resin content of 0.15 to 1% by mass is compression-molded. Heat treatment.
(Claim 6 ) In the above production method, as a first step, a liquid obtained by dissolving any of the binding resins described in (Claim 1 or 2 ) in an organic solvent is mixed and then dried, A resin-coated iron powder having a resin content by mass ratio of 0.3% by mass or less is used. As a second stage, any one of the resin powders for binding is added to the resin-coated iron powder so that the total amount of the resin is 0.15 to 1% by mass, and the mixed powder is compression-molded and heat-treated. .
[0009]
(Claims 7 and 8 ) In the above manufacturing method, the binder resin powder preferably has a particle size of 1 to 150 μm, and compression molding of the mixed powder or resin-coated powder may be performed at room temperature, but the binder resin It was confirmed that it can be carried out in a state heated to a temperature at which no melting occurs.
[0010]
Further, the eighth and subsequent aspects are detailed configurations such as the heat treatment conditions. That is, in claims 8 to 10 , as compression molding, firstly, an aspect of heating at a temperature not melting the resin, secondly, an aspect of heating the green compact molded without heating at a temperature not melting the resin, Thirdly, it was specified that the heating may be performed at a temperature at which the resin is melted. In Claim 11 , about the heat processing of the said Claims 4-6, the aspect heated at the temperature which at least 1 sort (s) of bonding resin fuse | melts in air | atmosphere, an inert gas, and pressure reduction was specified. This is, for example, heating to 250-400 ° C for PPS and 300-450 ° C for thermoplastic PI. According to claim 12, performs compression molded in a state of heated, in air demolded hot green compact in an inert gas, in either vacuo, at least one of said bonding resin melts temperature It was specified that the heat treatment in the above, that is, the heat compacting and the heat treatment of the green compact are performed continuously. In Claim 13 , the aspect which heats the powder magnetic core heat-processed with compression molding at the temperature of 150-320 degreeC, and performs stabilization heat processing was specified.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, the above invention will be clarified by embodiments and examples. In this description, first, the magnetic powder, the binding resin and the content thereof, mixing of the magnetic powder and the resin, compression molding, heat treatment, and stabilization heat treatment will be described in detail in order. Thereafter, representative examples of the tests are listed in the examples to clarify the advantages.
[0012]
(1. Magnetic powder)
As the target iron powder, iron powder produced by various manufacturing methods such as an atomizing method and a reduction method can be applied. The particle size of the iron powder is selected according to the required magnetic flux density and the frequency region used. The particle diameter can be 200 μm or less, which is generally used in powder metallurgy, but is 150 μm or less in consideration of compressibility. As the particle size of the iron powder is smaller, the overcurrent loss is reduced and the high frequency characteristics are improved. Therefore, the particle size is more preferably 100 μm or less. There is no particular limitation on the fine particles, but the particle size distribution with many fine particles deteriorates the powder compressibility and powder flowability, and a high-density powder magnetic core cannot be obtained. It is preferable that
[0013]
The iron powder with a phosphoric acid compound coating on its surface acts as an insulating layer and has the effect of suppressing overcurrent generation between the iron powder particles. The presence of a binding resin suppresses the generation of overcurrent. The effect is further enhanced and the high frequency characteristics are improved. The phosphate compound for coating is preferably iron phosphate, manganese phosphate, zinc phosphate, calcium phosphate or the like. Also, a commercial product of iron powder having a phosphoric acid compound coating on the surface may be used. Examples of this include iron powder (trade name: Permite or Somaloy) manufactured by Höganäs.
[0014]
(2. Binding resin)
As the bonding resin, PPS and thermoplastic PI, which are excellent in heat resistance, are preferable because they exhibit good characteristics. If the temperature at which the dust core is used exceeds 180 ° C and it is used for a long time, the shape and dimensions of the dust core may change over time, or the apparent insulation performance may be reduced. is there. The reason is that the former is considered to have a complex residual stress generated during compression molding, and the latter may be caused by a decrease in the thickness of the insulating resin between the magnetic powders due to a high temperature environment. In such a concern, when the PPS or thermoplastic PI is mixed with a resin having a glass transition point higher than these (non-thermoplastic polyimide in Table 1 above, that is, the thermosetting polyimide of the example) , the characteristics are improved. The This is thought to be because the resin between the magnetic particles (iron particles) is in a composite state with different thermal properties, so that deformation and movement during use are less likely to occur. The content of the resin having a high glass transition point is set so as not to exceed the amount of PPS or thermoplastic PI as a main component. Mixing thermoplastic PI with PPS is the same as this technical idea.
[0015]
(3. Content of binding resin)
The content of the binding resin is preferably in the range of 0.15 to 1% by mass of the total mass. If it is less than 0.15% by mass, the effect of bonding and insulating the particles of the magnetic powder is small, the strength of the powder magnetic core is insufficient, and the insulation between the magnetic powders is poor. On the other hand, if the content of the binding resin exceeds 1% by mass, the strength and insulation of the dust core become high, while the occupancy ratio of the magnetic particles in the dust core decreases, and the density of the magnetic particles decreases. Since it becomes low, a high magnetic flux density and magnetic permeability cannot be obtained.
[0016]
In relation to magnetic permeability, the lower the resin content, the lower the frequency in the low frequency range of about 50 Hz. In the high frequency region of about 5 kHz, those not containing resin show a value much lower than the magnetic permeability in the low frequency region. Compared with this, the maximum magnetic permeability is obtained when the resin content is around 0.3% by mass. It becomes substantially the same value as the magnetic permeability at low frequency. When the resin content further increases, the magnetic permeability gradually decreases as in the case of low frequency. When the resin content exceeds 1% by mass, the magnetic permeability becomes lower than that when no resin is contained. Also from such a relationship between the resin amount and the magnetic permeability, the content of the bonding resin is optimally 0.15 to 1% by mass. The resin content is particularly preferably around 0.3% by mass. The density is desirably 7.35 g / cm ³ or more.
[0017]
(4. Mixing of magnetic powder and binding resin)
The binding resin insulates the magnetic powder particles and suppresses the occurrence of overcurrent. Iron powder coated with a phosphoric acid compound film may be broken by insulation during the powder compression molding process due to peeling or dropping, but it is protected by the presence of a binding resin and suppresses overcurrent generation. be able to.
[0018]
The binding resin can be mixed in powder form. In that case, if the particle size distribution of the magnetic powder is equal to or finer, the mixed state becomes better and the heat resistance is improved. In order to improve the insulation between the magnetic powders, it is preferable to have a particle size of 60 μm or less. In addition, it is necessary for iron powder using a fluidized bed type or stirring and mixing type coating device by adding a low polarity organic solvent such as n-methyl-2-pyrrolidone to the binding resin to reduce the viscosity. A method of drying after applying an appropriate amount of coating is also preferred.
[0019]
Alternatively, a binding resin containing an organic solvent may be coated with a smaller amount of resin than described above, and then dried to form a resin-coated powder, and the resin-coated powder may be mixed with the binding resin powder. A resin film obtained by using a binding resin containing an organic solvent has better insulating performance. When the thickness of the resin is 20 nm or more, the occurrence of overcurrent is reduced. In order to obtain a resin film having a thickness of 20 nm, a resin solution having a resin amount of about 0.15% by mass is mixed. On the other hand, when the resin film thickness exceeds 200 nm, the compressibility of the powder is deteriorated, resulting in a dust core having insufficient magnetic properties. If the resin powder for binding is additionally mixed with the magnetic powder coated with the resin, the coating resin is protected and more excellent magnetic properties can be obtained.
[0020]
(5. Compression molding)
The resin-coated magnetic powder is compression molded using a mold. For compression molding, electrostatic coating of molding lubricant powders such as zinc stearate and ethylene bisstearamide, which are commonly used in powder metallurgy, on the mold surface, in order to improve compressibility and reduce the friction of green compact extraction It is desirable to apply in advance. Also, in order to mold to a higher density, an embodiment in which the bonding resin is heated to a temperature at which the bonding resin is not melted, primary compression molding is performed without heating the mixed powder and the resin-coated iron powder, and then the bonding resin is melted. The second compression molding is performed in a state of being heated to a temperature that is not, and the compression molding is performed in the state of being heated from the temperature at which the binding resin is softened to the temperature at which it is melted. As the post-molding treatment, after molding, it may be cooled to room temperature and subjected to the heat treatment described below, but after molding, if the molded body is still hot and the process proceeds to heat treatment It is reasonable because it saves heat energy and cooling time.
[0021]
(6. Heat treatment)
The heat treatment is a step of melting the bonding resin and further stabilizing the resin characteristics by crystallization of the bonding resin. The heating temperature and heating time are selected according to the type of resin used. The temperature ranges from the melting point of the resin so that the resin is not thermally deteriorated, and is 250 to 400 ° C. for PPS and 300 to 450 ° C. for thermoplastic PI. The heating time is generally about 0.5 to 1 hour.
[0022]
The atmosphere during heating can be performed in the air. However, the presence of oxygen in the atmosphere may cause a decrease in resin strength and mechanical properties. This is because, due to the presence of oxygen, the polymerization reaction of the resin proceeds, a gaseous condensate is likely to be generated, and it may remain as bubbles in the resin. Therefore, more preferably, heating is performed in an inert gas atmosphere such as nitrogen gas prior to heating in the air. In addition, when heating is performed in a reduced pressure atmosphere, the amount of oxygen in the atmosphere is reduced and more gaseous condensate can be released from the resin. These atmospheres can be combined as appropriate. In the cooling process of the heat treatment, if the cooling is performed in a region of about 320 to 150 ° C. over time, the stabilization heat treatment described below can be used.
[0023]
(7. Stabilization heat treatment)
When the stabilization heat treatment is performed, the characteristics of the binding resin are stabilized, and when the dust core is used at a high temperature, it is difficult to cause a change with time. In this case, after performing the heat treatment and once cooling, it is heated at about 150 to 320 ° C. for about 1 to 2 hours. Moreover, it can be based on the method of hold | maintaining for 1-2 hours in the temperature range of about 320-150 degreeC in the cooling process of the said heat processing.
[0024]
【Example】
Next, the configuration and advantages of the invention will be clarified by examples and comparative examples of the invention.
(1) The prepared powders are the following eight types (1) to (8).
(1). Atomized iron powder: This is “manufactured by Höganäs, product number: ABC100.30,” having a particle size of 150 μm or less (hereinafter referred to as pure iron powder).
(2). Phosphoric acid film-treated atomized iron powder: This is “Heganess Co., product number: Somaloy500,” having a particle size of 150 μm or less (hereinafter referred to as film-forming iron powder).
(3). Phosphoric acid coating treated atomized iron powder containing thermoplastic polyamide resin (hereinafter referred to as polyamide): This is "commercially available powder made by Höganäs", 0.6 mass% of thermoplastic polyamide mixed with phosphoric acid coating treated atomized iron powder (Somaloy500) It is a thing.
(Four). PPS powder: “Dainippon Ink” having a particle size of 150 μm or less (−150 μm) or 60 μm or less (−60 μm) (hereinafter referred to as PPS).
(Five). Thermoplastic polyimide powder: This is "Mitsui Chemicals," one having a particle size of 150 µm or less (-150 µm) and 60 µm or less (-60 µm) (hereinafter referred to as thermoplastic PI).
(6). Thermosetting polyimide powder: This is “Lauranne” and has a particle size of 150 μm or less (−150 μm) (hereinafter referred to as thermosetting PI).
(7). Thermosetting phenol resin powder: This is “Dainippon Ink”, whose particle size is 150 μm or less (−150 μm) (hereinafter referred to as phenol).
(8). Zinc stearate powder: This is a commonly used mold lubricant.
[0025]
(2) “Example 1” Resin content and effective magnetic permeability of dust core A predetermined amount of PPS (−150 μm) is added to the coated iron powder (total mass%, 0%, 0.15%,. 3%, 0.45 %, 0.6 %, 0.75 %, 1.0%, 1.2%), and mixed powder is molded using a die coated with zinc stearate powder It was compression molded into a ring shape (φ10 × φ23 × 5 mm) at a pressure of 1470 MPa. The compact was heated in air at a temperature of 320 ° C. for 1 hour, then heated at a temperature of 240 ° C. for 1 hour and cooled to obtain a dust core. In addition, what does not contain PPS is a pure green compact.
[0026]
The effective magnetic permeability was measured with a BH analyzer. The frequencies are 50 Hz and 5000 Hz, and the applied magnetic flux density is 1 T (Tessler). The measurement result of the effective magnetic permeability is as shown in FIG. That is, the effective permeability at 50 Hz decreases almost linearly with an increase in resin content. On the other hand, the effective permeability at 5000 Hz is low for those that do not contain PPS, the PPS content reaches its maximum value in the vicinity of 0.3% by mass, and gradually decreases at PPS content higher than that. Is 1 mass%, it is almost the same as the value of the dust core not containing PPS. In addition, although the example whose resin is PPS was given, it becomes the same tendency also in the case of other resin powder.
[0027]
From the above, regarding the resin content of the invention, in the region where the resin content is small, the average change rate of the effective magnetic permeability is large, so the resin content is set to 0.15% by mass or more. On the side where the resin content is large, the resin content is 1.0% by mass or less which does not become lower than the effective magnetic permeability of the dust core not containing the resin.
[0028]
(3) “Example 2” Resin type using pure iron powder and heat resistance of dust core A predetermined amount of each resin powder was added to the pure iron powder and mixed with a V-type mixer. The mixing ratio of the resin powder is as shown in Table 2. PPS and thermoplastic PI having a particle size of −150 μm were used.
[Table 2]

[0029]
Each mixed powder was compression-molded into a cylindrical shape (φ23 × 5 mm) and a cylindrical shape (φ10 × φ23 × 10 mm) at a molding pressure of 1470 MPa. In molding, zinc stearate was electrostatically applied in advance to the inner wall surface of the mold, and the mixed powder was filled and compacted. The heat treatment temperature of the molded body was 320 ° C. for resins containing PPS and those containing thermoplastic PI, and 150 ° C. for those containing phenol, and each was heated in a nitrogen gas atmosphere for 1 hour. Stabilization heat treatment was performed for the resin containing PPS and thermoplastic PI, and heating was performed at 240 ° C. for 1 hour in the air.
[0030]
Each sample having a cylindrical shape (φ23 × 5 mm) was cut into a prismatic shape of 5 × 23 × 5 mm and subjected to evaluation of insulation performance. Insulation performance evaluation is based on an apparent specific resistance value measured by a four-terminal method (a direct current is applied to both ends of the sample and two terminals are in contact with each other to measure electric resistance) after heating in a constant temperature layer at a temperature of 200 ° C. for 100 hours. It measured and evaluated with the decreasing rate with respect to the value before heating. In addition, the crushing strength value was measured for each sample having a cylindrical shape (φ10 × φ23 × 10 mm). The crushing strength is the maximum load until compression and breaking at room temperature and a temperature of 200 ° C. at a compression speed of 0.5 mm / min. Table 3 shows the measurement results of apparent specific resistance, room temperature and crushing strength at 200 ° C.
[Table 3]

[0031]
(Evaluation) The apparent specific resistance increases linearly as the resin content increases. Although the apparent specific resistance differs when the resin content is 0.15% by mass and 1% by mass, it can be practically used depending on the application of the dust core. Looking at the apparent specific resistance before and after heating depending on the type of resin, samples containing PPS (samples A1 to A3) have almost the same amount of change before and after heating even if the resin content changes, and the rate of change (rate of change) is resin. The higher the content, the lower. The same is true for the sample containing thermoplastic PI (sample A4). The amount of change in the apparent specific resistance of the sample containing the thermosetting PI in PPS (sample A5) and the sample containing the thermosetting PI in the thermoplastic PI (sample A6) is smaller than that of the PPS. Compared with these, those containing phenol (sample A7) have higher apparent specific resistance before heating than those containing PPS, etc., but the amount of change after heating is extremely large, and apparent specific resistance after heating is extremely low. It has become.
[0032]
The crushing strength decreases as the resin content increases. The difference between room temperature and 200 ° C. is almost the same for both those containing PPS (samples A1 to A3) and those containing thermoplastic PI (sample A4), but those containing phenol (sample A7) are stronger at room temperature. However, the strength at 200 ° C. is remarkably low.
[0033]
(4) “Example 3” Type of resin using film-forming iron powder and heat resistance of dust core A mixed powder was prepared by adding a predetermined amount of each resin shown in Table 4 to the film-forming iron powder. The polyamide of sample B16 is a commercial powder obtained by mixing 0.6% by mass of polyamide with the above-described phosphoric acid film-treated atomized iron powder (Somaloy 500). Sample B13 was prepared by adding a liquid obtained by adding n-methyl-2-pyrrolidone as an organic solvent to PPS to the film-forming iron powder, mixing it, drying it, and coating the magnetic powder with a PPS content of 0.15% by mass. After that, PPS is further mixed to make the PPS content 0.6% by mass. For the other mixed powders, resin powder was added to the film-forming iron powder and mixed with a V-type mixer. Samples B14 to 16 are comparative examples. Each mixed powder was compression-molded into a cylindrical shape (φ23 × 5 mm) and a cylindrical shape (φ10 × φ23 × 10 mm) under the same conditions as in Example 2.
[0034]
The heat treatment temperature of the molded body is 320 ° C. when the resin contains PPS and thermoplastic PI, 200 ° C. containing thermosetting PI, 150 ° C. containing phenol, and 275 ° C. containing polyamide. Each was heated in a nitrogen gas atmosphere for 1 hour. Note that Sample B12 was performed in air. The stabilization heat treatment was performed on the resin containing PPS and thermoplastic PI, and heated at a temperature of 240 ° C. for 1 hour.
[0035]
[Table 4]

[0036]
In the same manner as in Example 2, the apparent specific resistance value after heating at a temperature of 200 ° C. for 100 hours and the crushing strength at a room temperature and a temperature of 200 ° C. were measured. The measurement results are as shown in Table 5.
[0037]
[Table 5]

[0038]
(Evaluation) Apparent specific resistance is higher than that of a dust core using pure iron powder. It can be seen that the insulation of the iron powder particles is improved by the presence of the phosphoric acid compound coating. The increase in a linear function due to the increase in the resin content is the same as that of pure iron powder. Looking at the apparent specific resistance before and after heating depending on the type of resin, the amount of change for PPS-containing materials is almost the same regardless of the resin content, and the decrease rate (change rate) decreases as the resin content increases. In addition, PPS having a particle size of −150 μm, a mixture of this PPS and thermoplastic PI or thermosetting PI, a thermoplastic PI having a particle size of −150 μm, and a mixture of this thermoplastic PI and thermosetting PI Although exhibiting almost the same characteristics, in detail, a material in which thermosetting PI is mixed with PPS or thermoplastic PI has a small decrease in apparent specific resistance due to heating.
[0039]
When the particle size of the powder to which PPS and thermoplastic PI are added is -60 μm, the particle size is higher than that of the particle size of −150 μm before and after heating. The sample B13 wet-mixed and coated with PPS and mixed with PPS has a slightly higher apparent resistivity than that mixed with powder. Sample B13 subjected to heat treatment in the air has a large decrease in apparent specific resistance due to heating, but shows a higher value than heating in nitrogen gas. Compared to these, those containing phenol (sample B15) and polyamide (sample B16) have a low initial value and a large amount of decrease in heating. In addition, the sample containing only the thermosetting PI (sample B16) shows a low value although the amount of decrease due to heating is small.
[0040]
The crushing strength is almost the same level as in the case of pure iron powder, and the relationship with the resin content and the decrease amount when heated to 200 ° C. show the same tendency. In the crushing strength, there is no difference in the influence of the particle size of the resin powder, the wet coating of the resin, or the difference in the atmosphere of the heat treatment. Compared with PPS and thermoplastic PI systems, those containing phenol and polyamides have a low initial value, a large amount of decrease when heated, and thermosetting PI is less decreased by heating, but low The value is the same as the rank in the case of apparent resistivity.
[0041]
【The invention's effect】
As described above, the invention of the present patent application, for example, claim 1 or iron powder having a particle size as specified 10~200μm to 2, or iron powder subjected to the phosphate compound film on the surface of the iron powder And 0.15 to 1% by mass in the form of a mixture of PPS resin and thermosetting PI, thermoplastic PI and thermosetting PI, PPS and thermoplastic PI and thermosetting PI . Because of its high magnetic permeability, it exhibits excellent characteristics especially when used in a high frequency region, and even when used in a high temperature environment, it has a high specific resistance and heat resistance, so it is used. It can contribute to the performance and miniaturization of the device, and can expand the application range of the dust core.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the resin content and the effective magnetic permeability of a dust core obtained by binding phosphoric acid compound-coated iron powder with a PPS resin.

Claims (13)

In a powder magnetic core in which iron powder having a particle diameter of 10 to 200 μm or iron powder having a phosphoric acid compound coating on the surface of the iron powder is bonded with a resin,
The binding resin for polyphenylene sulfide (hereinafter, PPS hereinafter) mixture of and thermosetting polyimide, or is either a mixture of a thermoplastic polyimide and a thermosetting polyimide, 0 resin content of the total mass. A dust core having a content of 15 to 1% by mass. In a powder magnetic core in which iron powder having a particle diameter of 10 to 200 μm or iron powder having a phosphoric acid compound coating on the surface of the iron powder is bonded with a resin,
The bonding resin is a mixture of polyphenylene sulfide (hereinafter referred to as PPS), a thermoplastic polyimide and a thermosetting polyimide, and the resin content is 0.15 to 1% by mass of the total mass. Dust magnetic core.  3. The dust core according to claim 1, wherein a content of the thermosetting polyimide is half or less of a total content of the binding resin of 0.15 to 1% by mass. The binding resin powder according to any one of (1) to (3) below is added to the iron powder having a particle diameter of 10 to 200 μm, or the iron powder having a phosphoric acid compound coating on the surface of the iron powder in a mass ratio of 0. A method for producing a powder magnetic core, comprising mixing 15 to 1% by mass, compression-molding the mixed powder, and heat-treating the mixed powder.
(1) Mixture of polyphenylene sulfide (hereinafter referred to as PPS) and thermosetting polyimide (2) Mixture of thermoplastic polyimide and thermosetting polyimide (3) The PPS and the thermoplastic polyimide and thermosetting polyimide blend The binding resin powder according to any one of (1) to (3) according to claim 4, wherein the iron powder has a particle diameter of 10 to 200 µm, or the iron powder having a surface coated with a phosphoric acid compound coating. After mixing the liquid which melt | dissolved in the organic solvent and drying, it is set as the resin coating iron powder whose resin content is 0.15-1 mass% by mass ratio,
A method for producing a dust core, wherein the resin-coated iron powder is compression-molded and heat-treated. The binding resin powder according to any one of (1) to (3) according to claim 4, wherein the iron powder has a particle diameter of 10 to 200 µm, or the iron powder having a surface coated with a phosphoric acid compound coating. After mixing the liquid dissolved in the organic solvent and drying, the resin content is 0.3% by mass or less in resin ratio,
One of the resin powders for binding is added to the resin-coated iron powder so that the total amount of the resin is 0.15 to 1% by mass, and the mixed powder is compression-molded and heat-treated. A method for manufacturing a dust core.  The method for producing a dust core according to claim 4 or 6, wherein the bonding resin powder has a particle size of 1 to 150 µm.  The method for producing a dust core according to any one of claims 4 to 7, wherein the compression molding of the mixed powder or the resin-coated iron powder is performed in a state where the powder is heated to a temperature at which the binding resin does not melt.  The compression molding of the mixed powder or the resin-coated iron powder is performed by performing the primary compression molding without heating, and then performing the secondary compression molding with heating to a temperature at which the binding resin does not melt. The manufacturing method of the powder magnetic core in any one of.  The method for producing a powder magnetic core according to any one of claims 7 to 10, wherein the compression molding of the mixed powder or the resin-coated iron powder is performed in a state of being heated to a temperature at which the binding resin is softened or melted.  The powder magnetic core according to any one of claims 4 to 6, wherein the heat treatment is performed at a temperature at which at least one of the binding resins melts in the atmosphere, in an inert gas, or under reduced pressure. Production method.  The compression molding is performed in a heated state, and the released hot green compact is heat-treated at a temperature at which at least one of the binding resins melts in the air, in an inert gas, or under reduced pressure. Item 11. A method for producing a dust core according to any one of Items 8 to 10.  The manufacturing method of the powder magnetic core in any one of Claim 4 to 12 which performs the stabilization heat processing which heats the powder magnetic core heat-processed with the said compression molding at the temperature of 150-320 degreeC.

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