JP4021979B2 - Unidirectional electrical steel sheet having an insulating coating with a large tensioning effect and method for forming the insulating coating - Google Patents
Unidirectional electrical steel sheet having an insulating coating with a large tensioning effect and method for forming the insulating coating Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、鋼板に大きな張力を付与しうる皮膜を形成させたことにより鉄損が低減された一方向性電磁鋼板とその製造方法に関するものである。
【０００２】
【従来の技術】
一方向性電磁鋼板は（１１０）〔００１〕を主方位とする結晶組織を有し、磁気鉄芯材料として多用されており、特にエネルギーロスを少なくするために鉄損の少ない材料が求められている。ところで、５％以下の珪素を含有する鉄合金は結晶磁気異方性が大きいゆえ、外部張力を付与すると磁区の細分化が起こり、鉄損の主要素である渦電流損失を低下させることができる。従って、５％以下の珪素を含有する一方向性珪素鋼板の鉄損の低減には鋼板に張力を付与することが有効である。
【０００３】
一方向性電磁鋼板において、仕上げ焼鈍工程で鋼板表面の酸化物と焼鈍分離剤とが反応して生成するフォルステライトを主体とする皮膜（以下仕上焼鈍皮膜と称する）は、鋼板に与える張力が大きく、鉄損低減に効果がある。更に、特開昭４８−３９３３８号公報で開示されたコロイド状シリカと燐酸塩を主体とするコーティング液を焼き付けることによって絶縁皮膜を形成する方法は、鋼板に対して張力付与の効果が大きく、鉄損低減に有効である。このため、仕上げ焼鈍工程で生じた皮膜を残したうえで張力付与型の絶縁コーティングを施すことが一般的な一方向性電磁鋼板の製造方法となっている。
【０００４】
一方、最近、フォルステライト系皮膜と地鉄の乱れた界面構造が、鉄損に対する皮膜張力効果をある程度相殺していることが明らかになってきた。そこで、例えば、特開昭４９−９６９２０号公報や特開平４−１３１３２６号公報に開示されているように、仕上げ焼鈍工程で生ずるフォルステライト質皮膜を除いたり、更に鏡面化仕上げを行った後、張力皮膜を改めて付与することにより更なる鉄損低減を試みる技術が開発された。
【０００５】
仕上焼鈍皮膜が存在する場合、仕上焼鈍皮膜を除いた場合、および更に鏡面化を行った場合のいずれの場合においても、皮膜張力を付与することにより鉄損は低下する。そこで、絶縁被膜のさらなる高張力化の試みがなされてきた。
特開平６−２４８４６５号公報に示されているように、α−アルミナ皮膜は鋼板に対する付与張力が大きく、一方向性電磁鋼板の張力付与型絶縁被膜として期待できる。α−アルミナを形成するためのコーティング原料としては、特にベーマイト構造を有するアルミナ水和物を水溶液中に分散させたベーマイトゾル（アルミナゾルとも称される）がある。これは造膜性が良好であり、コーティング剤として使いやすいことの理由による。また一般に、コーティング原料として安価なコロイド状の水和物を用い、金属表面に塗布し焼き付ける方法は、複雑な設備を必要とせず、工業的に有利である。
【０００６】
ところが、ベーマイトに限らず、ギブサイト等のアルミナ水和物を出発物質としてα−アルミナを得ようとした場合、１２００℃以上での高温の加熱処理を要すると言われている。一方向性電磁鋼板の絶縁被膜形成工程は、生産性を考慮して連続ラインが用いられており、前述のような高い焼付温度では鋼板の軟化が著しく、現実性的ではない。従って、ベーマイト等のコロイド状のアルミナ水和物を用いて一方向性電磁鋼板にα−アルミナ皮膜からなる絶縁被膜を形成しようとするならば、ベーマイトのα−アルミナ化温度を１０００℃以下にする技術が必要となる。
【０００７】
最近、ベーマイトにα−アルミナを種子として添加すると、ベーマイトのγ−アルミナを経由したα−アルミナへの変態温度が低下できることが報告されている（M.Kumagai and G.L.Messing:J.Am.Ceram.Soc., vol68,p500(1985))。しかしながら、同報告においてもα化温度は１０００℃をうわまわっている。現在までのところ、ベーマイトから１０００℃以下の加熱温度でα−アルミナを得る方法は報告されていない。
【０００８】
【発明が解決しようとする課題】
本発明は、鋼板への付与張力の大きいα−アルミナ質絶縁被膜付与を１０００℃以下の焼付温度で可能にすることにより、鉄損の低い一方向性電磁鋼板を安価に製造する技術を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明では、ベーマイトゾルを一方向性電磁鋼板の表面に塗布し、α−アルミナ皮膜を形成するにあたり、１０００℃以下の加熱温度でのα−アルミナ化を達成するために、ベーマイトゾルを粉砕処理すること、あるいは、さらにこのゾルにα−アルミナ（以下、最終生成物であるα−アルミナと区別するために、種子用α−アルミナと称する）添加を行うことを特徴とするものであり、その要旨は以下のとおりである。
【００１０】
（１）仕上焼鈍後の一方向性電磁鋼板表面にα−アルミナ化温度が１０００℃以下のベーマイトゾルから形成された絶縁被膜を有することを特徴とする張力付与効果の大きい絶縁被膜を有する一方向性電磁鋼板。
（２）仕上焼鈍後の一方向性電磁鋼板に、１０分以上の粉砕処理を施したベーマイトゾル、もしくは１０分以上の粉砕処理を施した微粉ベーマイト粉を水に分散したゾルを塗布し、７５０℃以上の温度で焼き付けることを特徴とする一方向性電磁鋼板の絶縁被膜形成方法。
【００１１】
（３）仕上焼鈍済後の一方向性電磁鋼板に、平均粒径０．５μｍ以下のα−アルミナが添加され、かつ１０分以上の粉砕処理が施されたベーマイトゾルもしくは１０分以上の粉砕処理が施された微粉ベーマイト粉を水に分散したゾルを塗布し、７５０℃以上の温度で焼き付けることを特徴とする一方向性電磁鋼板の絶縁被膜形成方法。
【００１２】
（４）粉砕処理をボールミルもしくはコロイドミルによって行うことを特徴とする上記（２）または（３）記載の一方向性電磁鋼板の絶縁被膜形成方法。
（５）ベーマイトに対するα−アルミナの添加量が５０重量％以下であることを特徴とする上記（３）または（４）記載の一方向性電磁鋼板の絶縁被膜形成方法。
【００１３】
（６）仕上焼鈍済みの一方向性電磁鋼板が、仕上焼鈍で生ずる無機鉱物質皮膜を除去したもの、仕上焼鈍で生ずる無機鉱物質皮膜を除去した後鋼板表面を鏡面化したもの、仕上げ焼鈍工程での無機鉱物質皮膜の形成を意図的に阻害したもの、或いは仕上げ焼鈍工程での無機鉱物質皮膜の形成を意図的に阻害し鋼板表面を鏡面化したものであることを特徴とする上記（２），（３），（４）または（５）記載の一方向性電磁鋼板の絶縁被膜形成方法。
【００１４】
【発明の実施の形態】
本発明は、ベーマイト微粉末またはベーマイトゾルに対して粉砕処理を施すことによってα−アルミナ化温度が１０００℃以下になること、および粉砕処理に種子用アルミナを添加することによりさらに著しくα化温度を低下できるとの知見に基づいている。
【００１５】
ベーマイトゾルに種子用α−アルミナ（平均粒径０．１μｍ）を添加量を変えて分散させ、ボールミルによる粉砕処理を３０分間行い、これを乾燥してゲル化させた後、各種温度まで加熱した。それぞれの試料につき冷却後Ｘ線回析を行い、α−アルミナ化温度を調べた。ここで言うα化温度は、原料物質のα−アルミナへの変態がほぼ１００％完了する温度である。
【００１６】
図１はこの実験結果を整理したものである。種子用α−アルミナを添加せず、かつ粉砕処理をしない場合のα化温度は１１００℃であり、種子用α−アルミナの添加によりα化温度が低下するが、１０００℃以下にはならない。これに対し、粉砕処理を施した場合には、種子用α−アルミナの添加を添加せずとも１０００℃でα化している。また、種子用α−アルミナを添加すればα化温度をさらに低下させることができ、５０％の添加では７５０℃付近まで下がっている。
【００１７】
以上の事実より、ベーマイトゾルを粉砕処理した後一方向性電磁鋼板に塗布した場合には、１０００℃以下の加熱処理によりα−アルミナ皮膜からなる絶縁被膜が施せることがわかる。また、これに種子用α−アルミナを添加して塗布した場合には、更に低い加熱温度でこれが実現できることになる。
アルミナ水和物のボールミル粉砕時にアルミナボールを用いて処理を行うと、アルミナボールの磨砕粉が発生し、これによってアルミナ水和物のα化温度が低下することが報告されている（吉澤友一、齋藤文良：J.Ceram.Soc.,Jpn., vol104,p867(1996)) 。本発明者らは、ベーマイトのα化温度の低減に関する粉砕処理効果は、このアルミナボールの磨砕粉による効果とは異なると考えている。これは、α化温度の低下を達成するに十分な量のアルミナ粉を、アルミナボールの磨砕効果によって得るためには、数時間ないし数十時間の処理が必要であり、これに対し、図１のような効果はせいぜい数十分の処理で得られるからである。図１から、仮に粉砕効果によって１１００℃から１０００℃にα化温度を下げるためには、約２０％の種子用α−アルミナを添加しなければならないことになるが、僅か３０分のボールミル粉砕により、２０％のα−アルミナ磨砕粉が生成するとは考え難い。
【００１８】
従って、３０分の粉砕処理によるα化温度の劇的低減は理由を別に求めなければならない。本発明者らは、現在のところこれを以下のように推定している。ベーマイトゾル中において、ベーマイト粒子は二次凝集している可能性がある。粉砕処理により二次凝集がほぐれ、ベーマイト粒子の分散性が向上し、これがα化温度低下の原因と考えられる。
【００１９】
図１からわかるように、粉砕処理によって種子用α−アルミナ添加のα化温度低下効果は増大している。これは、ベーマイト粒子の二次凝集がほぐされたことにより、種子用α−アルミナとの混合が均一化された結果と解釈している。いずれにしても、ベーマイトの粉砕処理は、単にそれ自体α化温度低下に効果を発揮するのみならず、種子用α−アルミナの効果を促進することにもなっているといえる。
【００２０】
なお、図１に示した実験においては粉砕処理時間が３０分間であったが、α−アルミナ化温度の粉砕処理時間依存性を調査したところ、１０分以上の粉砕処理で図１に示したものとほぼ同じ効果が発揮されることがわかった。
次に本発明の実施形態を述べる。
本発明において対象とする一方向性電磁鋼板は、公知の方法によって製造されたものなら、いずれのものでも良い。すなわち、一方向性電磁鋼板は（１１０）〔００１〕を主方位とする結晶組織を有するがゆえに、鋼板への付与張力によって鉄損値が低下させ得る電磁鋼板すべてに効果を発揮するものと考えている。通常の一方向性電磁鋼板はＳｉを含有するため脱炭焼鈍工程でＳｉＯ2 を主体とするサブスケールが生成し、仕上焼鈍（コイル焼鈍）での鋼板の焼付を防止するためにＭｇＯを主体とする焼鈍分離剤を塗布した後に仕上焼鈍を行うために、仕上焼鈍でＳｉＯ2 とＭｇＯが反応して生ずるフォルステライトを主体とする焼鈍皮膜が形成されている。しかしながら、本発明は、例えば、特開昭６４−６２４１７号公報に開示されている焼鈍分離剤に塩化物を加えることにより仕上焼鈍皮膜の生成を抑制した一方向性電磁鋼板、特開平７−５４１５５号公報に開示されている焼鈍分離剤にＢｉの塩化物を添加することによって仕上焼鈍皮膜の形成を防止しかつ鋼板表面を鏡面化した一方向性電磁鋼板、特開平５−１９５０６２号公報に開示されている焼鈍分離剤としてアルミナ等の不活性酸化物を用い仕上焼鈍雰囲気を制御することにより仕上焼鈍皮膜の形成を防止しかつ鋼板表面を鏡面化した一方向性電磁鋼板、あるいは特開平８−３６４８号公報に開示されているアルカリ金属酸化物を含有するアルミナを焼鈍分離剤として用いることにより仕上焼鈍皮膜の形成を防止しかつ鋼板表面を鏡面化した一方向性電磁鋼板等、仕上焼鈍皮膜のない或いは更に鏡面化した一方向性電磁鋼板にも適用できる。仕上焼鈍皮膜が無い一方向性電磁鋼板に張力付与型の絶縁被膜を直接形成した場合には焼付後の被膜の密着性が悪いが、特開平６−１８４７６２号公報に開示されているように、絶縁被膜を形成するに先立ち鋼板表面にＳｉＯ2 膜を形成させる方法を採用することによって密着性を改善できる。
【００２１】
また、更に表面が鏡面化された一方向性電磁鋼板に、本発明による張力付与型絶縁皮膜形成と、特開昭５７−２２５２号公報や特開昭５９−２５５９２８号公報等に開示されているレーザー照射処理やプラズマ照射、特開昭６１−１１７２１８等に開示されている鋼板表面への歯形ロールによる溝形成、特公平３−６９９６８号公報等に開示されているエッチングによる溝形成、特開昭６１−７５５０６等に開示されているレーザー照射による溝形成等の、いわゆる磁区細分化処理技術と組み合わせることにより、極めて鉄損の低い一方向性電磁鋼板が製造できる。
【００２２】
本発明において用いるベーマイトゾルは、市販品（場合によりアルミナゾルとも称される）を用いても良く、また、例えば、各種アルミニウム塩、アルミニウムアルコキシドの加水分解等の公知の方法で合成しても良い。また、ＶｉｓｔａＣｈｅｍｉｃａｌ社から販売されているベーマイト微粉末、商品名：ＣａｔａｐａｌあるいはＤｉｓｐａｌは、希酸もしくは水に容易に分散し、ベーマイトゾルを作成することができる。
【００２３】
粉砕処理には、公知の粉砕機、例えばボールミル、コロイドミル等を利用できる。粉砕は乾式、溶媒を用いた湿式のいずれでも良い。たとえば、Ｖｉｓｔａ Ｃｈｅｍｉｃａｌ社から販売されている上記ＣａｔａｐａｌあるいはＤｉｓｐａｌのように、溶媒に分散するとコロイド状になるベーマイト微粉末は、乾式で粉砕処理を行った後水に懸濁しても良いし、また、粉砕処理前に水に懸濁し湿式で粉砕処理を行ってもかまわない。いずれの粉砕処理手段を用いた場合でも、処理時間１０分以上で効果が発揮される。
【００２４】
特に、低いα化温度を必要とする場合は、種子用α−アルミナを添加する。種子用α−アルミナはなるべく粒子の細かいものが望ましく、平均粒径０．５μｍ以上では効果が殆どない。このような目的に適した市販のα−アルミナとして、住友化学工業（株）製商品名：ＡＫＰ−５０があげられる。種子用α−アルミナ添加量はα化温度との対応で決めることができるが、ベーマイトに対して５０重量％以下とする。その理由は、５０％を越えて添加しても添加量に見合う効果が無く非経済であるばかりでなく、ベーマイトの有する良好な造膜性を損ねるからである。
【００２５】
種子用α−アルミナは粉砕処理の後で添加しても良いが、粉砕処理の前に添加した方がベーマイトゾルとの混合が均一になり好ましい。
また、以下のような工夫をすることにより、種子用α−アルミナを意図的に添加することなしに、極めて低いα化温度を得ることができる。すなわち、ミル媒体（ボールミルの場合はボール、コロイドミルの場合は砥石）にα−アルミナ製のものを採用し、処理時間を数ないし数十時間確保する。この場合にはベーマイトの粉砕処理と、ミル媒体の磨砕による種子用α−アルミナ添加が、同一工程で行われることになる。
【００２６】
以上のように粉砕処理を施したベーマイトゾルもしくは水に分散した微粉ベーマイト粉末を一方向性電磁鋼板に塗布し、７５０℃以上の加熱温度で焼き付ける。７５０℃以下の焼付温度では皮膜がα−アルミナ化しない。塗布方法としては公知のロールコート法、噴霧法、浸漬法等、いずれでも良い。
【００２７】
【実施例】
以下、本発明を実施例により説明するが、本発明はこれら実施例に限定されるものではない。
なお、実施例における種子用α−アルミナの添加量は、ベーマイトに対する重量％換算である。したがって、ベーマイトゾルの場合、ゾル乾燥重量に対する重量％となる。
〔実施例１〕
ベーマイトゾル（日産化学社製商品名：ＡＳ−５２０）に、一部のゾルには種子用α−アルミナ（住友化学工業（株）製商品名：ＡＫＰ−５０）を添加した後、ボールミルもしくはコロイドミルにより湿式で粉砕処理を施した。比較例として粉砕処理を施さないものも用意した。これを仕上焼鈍済みの３％のＳｉを含有する一方向性電磁鋼板（板厚０．２３mm、フォルステライトを主体とする仕上焼鈍皮膜付き）に塗布し、所定の温度で焼き付けた。焼付後の膜厚はすべて２μｍである。なお、その後一部の試料について、特開昭５７−２２５２号公報に開示されているレーザー照射もしくは特開昭６１−１１７２１８号公報等に開示されている鋼板表面への歯形ロールによる溝形成によって、磁区細分化処理を施した。ただし、溝形成による場合は、溝形成を絶縁被膜形成前に行った。絶縁被膜の比較例としてコロイダルシリカと燐酸塩からなる従来の絶縁被膜（焼付後膜厚２μｍ）を施した。処理条件と磁気特性（Ｂ８：８００Ａ／ｍにおける磁束密度、Ｗ１７／５０：５０Ｈｚ，１．７Ｔにおける鉄損値）評価結果を表１に示す。
【００２８】
【表１】
表１に示すように、従来の絶縁皮膜を施したＮｏ．１の一方向性電磁鋼板では付与張力が低く、０．８Ｗ／kgを下回る鉄損値を得ることは困難である。また、ベーマイトゾルを用いた場合の中で、粉砕処理を施さないベーマイトゾルを１０００℃以下で焼き付けたＮｏ．２およびＮｏ．３では、絶縁被膜による付与張力が無いためと思われるが、従来の絶縁被膜を施した場合よりもむしろ大きな鉄損値を与えてしまう。これに対し、本発明の粉砕処理を施したベーマイトゾルを用いたＮｏ．４〜８では、０．８Ｗ／kg以下の鉄損値が得られ、かつこれが１０００℃以下の焼付温度で実現されている。これは鋼板に対する付与張力の大きい絶縁被膜が得られた結果であると解釈できる。種子用α−アルミナを添加したＮｏ．５〜８の場合には、特に低い焼付温度で効果が得られている。また、Ｎｏ．８は、本発明による絶縁被膜形成技術を、磁区細分化処理と組み合わせて一方向性電磁鋼板に適用することにより、極めて鉄損の低いが得られている。
〔実施例２〕
微粉ベーマイト粉末（Ｖｉｓｔａ Ｃｈｅｍｉｃａｌ社製商品名：Ｄｉｓｐａｌ）に、種子用α−アルミナ（住友化学工業（株）製商品名：ＡＫＰ−５０）を添加した後、ボールミルもしくはコロイドミルにより湿式若しくは乾式粉砕処理を施し、乾式粉砕の場合にはその後に水に分散させてコロイド液を作成した。これを、特開平８−３６４８号公報に開示されているアルカリ金属酸化物を含有するアルミナを焼鈍分離剤として用いることにより仕上焼鈍皮膜の形成を防止しかつ鋼板表面を鏡面化した一方向性電磁鋼板（板厚０．２３mm）に塗布し、所定の温度で焼き付けた。焼付後の膜厚はすべて２μｍである。なお、いずれのコーティング液を焼き付けるに際しても、特開平６−１８４７６２号公報に開示されている方法によって、絶縁被膜を形成するに先立ち鋼板表面にＳｉＯ2 膜を形成させ、皮膜密着性を確保した。その後、特開昭５７−２２５２号公報に開示されているレーザー照射もしくは特開昭６１−１１７２１８号公報等に開示されている鋼板表面への歯形ロールによる溝形成によって、磁区細分化処理を施した。ただし、溝形成による場合は、溝形成は絶縁被膜形成前に行った。絶縁被膜の比較例としてコロイダルシリカと燐酸塩からなる従来の絶縁被膜（焼付後膜厚２μｍ）を施した。処理条件と磁気特性（Ｂ８：８００Ａ／ｍにおける磁束密度、Ｗ１７／５０：５０Ｈｚ，１．７Ｔにおける鉄損値）評価結果を表２に示す。
【００３０】
【表２】
一般に表面を鏡面化した一方向性電磁鋼板に張力付与型の絶縁被膜を形成し、さらに磁区細分化処理を施すことにより、良好な良好な鉄損値を得ることができるが、このときに本発明による絶縁被膜形成技術を適用するならば、Ｎｏ．２〜６のように０．７Ｗ／kgをはるかに下回る極めて鉄損の低い一方向性電磁鋼板が得られることがわかる。
【００３２】
【発明の効果】
以上述べてきたように、本発明による絶縁被膜を一方向性電磁鋼板に適用することにより、鋼板に対する付与張力の大きい絶縁被膜を形成することができ、これによって鉄損の低い一方向性電磁鋼板が製造でき、その工業的効果は大きい。
【図面の簡単な説明】
【図１】ベーマイトのα−アルミナ化温度に及ぼすベーマイトに対する粉砕処理および種子用α−アルミナ添加効果を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a unidirectional electrical steel sheet in which iron loss is reduced by forming a film capable of imparting a large tension to the steel sheet, and a method for manufacturing the same.
[0002]
[Prior art]
Unidirectional electrical steel sheets have a crystal structure with (110) [001] as the main orientation and are frequently used as magnetic iron core materials. In particular, a material with low iron loss is required to reduce energy loss. Yes. By the way, since an iron alloy containing 5% or less of silicon has a large magnetocrystalline anisotropy, when an external tension is applied, magnetic domains are subdivided, and eddy current loss, which is a main element of iron loss, can be reduced. . Therefore, it is effective to apply tension to the steel sheet to reduce the iron loss of the unidirectional silicon steel sheet containing 5% or less of silicon.
[0003]
In unidirectional electrical steel sheets, forsterite-based coatings (hereinafter referred to as finish annealing coatings) produced by the reaction of oxides on the steel sheet surface and the annealing separator in the final annealing process have a large tension on the steel plates. , Effective in reducing iron loss. Furthermore, the method of forming an insulating film by baking a coating liquid mainly composed of colloidal silica and phosphate disclosed in Japanese Patent Application Laid-Open No. 48-39338 has a great effect of imparting tension to a steel sheet. It is effective for reducing loss. For this reason, it is a general method for producing a unidirectional electrical steel sheet to leave a film produced in the finish annealing step and then apply a tension-imparting type insulating coating.
[0004]
On the other hand, recently, it has been clarified that the disordered interface structure between the forsterite film and the ground iron offset the effect of the film tension on the iron loss to some extent. Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 49-96920 and Japanese Patent Application Laid-Open No. 4-131326, after removing the forsterite film generated in the finish annealing step, and further performing a mirror finish, Technology has been developed to further reduce iron loss by applying a tensile film anew.
[0005]
In any case where a finish annealed film is present, when the finish annealed film is removed, and when mirror finishing is further performed, the iron loss is reduced by applying the film tension. Thus, attempts have been made to further increase the tension of the insulating coating.
As disclosed in JP-A-6-248465, the α-alumina film has a large applied tension to the steel sheet, and can be expected as a tension-applying insulating film for the unidirectional electrical steel sheet. As a coating raw material for forming α-alumina, there is boehmite sol (also referred to as alumina sol) in which alumina hydrate having a boehmite structure is dispersed in an aqueous solution. This is because the film-forming property is good and it is easy to use as a coating agent. In general, a method of using an inexpensive colloidal hydrate as a coating material and applying and baking it on a metal surface does not require complicated equipment and is industrially advantageous.
[0006]
However, it is said that heat treatment at a high temperature of 1200 ° C. or higher is required when α-alumina is obtained using not only boehmite but also alumina hydrate such as gibbsite as a starting material. In the insulating film forming step of the unidirectional electrical steel sheet, a continuous line is used in consideration of productivity, and the steel sheet is extremely softened at a high baking temperature as described above, which is not realistic. Therefore, if an insulating coating composed of an α-alumina coating is to be formed on a unidirectional electrical steel sheet using colloidal alumina hydrate such as boehmite, the α-aluminization temperature of boehmite is set to 1000 ° C. or lower. Technology is required.
[0007]
Recently, it has been reported that the transformation temperature of boehmite to α-alumina via γ-alumina can be reduced by adding α-alumina as seeds to boehmite (M. Kumagai and GLMessing: J. Am. Ceram. Soc ., vol68, p500 (1985)). However, in this report, the pregelatinization temperature is about 1000 ° C. To date, no method for obtaining α-alumina from boehmite at a heating temperature of 1000 ° C. or less has been reported.
[0008]
[Problems to be solved by the invention]
The present invention provides a technique for inexpensively producing a unidirectional electrical steel sheet with low iron loss by enabling application of an α-alumina insulating coating having a high applied tension to a steel sheet at a baking temperature of 1000 ° C. or less. For the purpose.
[0009]
[Means for Solving the Problems]
In the present invention, boehmite sol is applied to the surface of a unidirectional electrical steel sheet to form an α-alumina film. In order to achieve α-aluminization at a heating temperature of 1000 ° C. or less, the boehmite sol is pulverized. Or further adding α-alumina (hereinafter referred to as α-alumina for seeds in order to distinguish from α-alumina as a final product) to the sol, The summary is as follows.
[0010]
(1) Unidirectional with an insulating film having a large tension-imparting effect, characterized by having an insulating film formed from boehmite sol having an α-aluminization temperature of 1000 ° C. or less on the surface of the unidirectional electrical steel sheet after finish annealing. Electrical steel sheet.
(2) Apply a boehmite sol that has been pulverized for 10 minutes or more or a sol in which fine boehmite powder that has been pulverized for 10 minutes or more is dispersed in water to a unidirectional electrical steel sheet after finish annealing; An insulating film forming method for a unidirectional electrical steel sheet, characterized by baking at a temperature of ℃ or higher.
[0011]
(3) Boehmite sol in which α-alumina having an average particle size of 0.5 μm or less is added to the unidirectional electrical steel sheet after finish annealing and pulverization for 10 minutes or more, or pulverization for 10 minutes or more A method for forming an insulating coating on a unidirectional electrical steel sheet, wherein a sol obtained by dispersing finely boehmite powder with water dispersed in water is applied and baked at a temperature of 750 ° C. or higher.
[0012]
(4) The method for forming an insulating film on a unidirectional electrical steel sheet according to the above (2) or (3), wherein the pulverization is performed by a ball mill or a colloid mill.
(5) The method for forming an insulating film on a unidirectional electrical steel sheet according to the above (3) or (4), wherein the amount of α-alumina added to boehmite is 50% by weight or less.
[0013]
(6) Finished annealed unidirectional electrical steel sheet from which the inorganic mineral film produced by finish annealing has been removed, the surface of the steel sheet mirrored after removing the inorganic mineral film produced by finish annealing, finish annealing process Intentionally inhibiting the formation of an inorganic mineral film in the above, or intentionally inhibiting the formation of an inorganic mineral film in the final annealing step and mirroring the steel sheet surface 2), (3), (4) or (5) The method for forming an insulating coating on a unidirectional electrical steel sheet.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, by subjecting boehmite fine powder or boehmite sol to pulverization treatment, the α-alumination temperature becomes 1000 ° C. or less, and by adding seed alumina to the pulverization treatment, the α-alumination temperature is further remarkably increased. Based on the knowledge that it can be reduced.
[0015]
Α-alumina for seeds (average particle size: 0.1 μm) was dispersed in boehmite sol while changing the amount added, pulverized by a ball mill for 30 minutes, dried and gelled, and then heated to various temperatures. . Each sample was cooled and then subjected to X-ray diffraction to examine the α-alumination temperature. The pregelatinization temperature here is a temperature at which the transformation of the raw material into α-alumina is almost 100% complete.
[0016]
FIG. 1 summarizes the results of this experiment. In the case where α-alumina for seeds is not added and the pulverization treatment is not performed, the α-ization temperature is 1100 ° C., and the addition of α-alumina for seeds reduces the α-ization temperature, but does not become 1000 ° C. or less. On the other hand, when the pulverization treatment is performed, it is α-ized at 1000 ° C. without adding α-alumina for seeds. Moreover, if α-alumina for seeds is added, the pregelatinization temperature can be further lowered, and if added at 50%, the temperature is lowered to around 750 ° C.
[0017]
From the above facts, it can be seen that when the boehmite sol is pulverized and then applied to a unidirectional electrical steel sheet, an insulating film made of an α-alumina film can be applied by a heat treatment at 1000 ° C. or lower. In addition, when α-alumina for seeds is added and applied thereto, this can be realized at a lower heating temperature.
It has been reported that treatment with alumina balls during ball milling of alumina hydrate generates alumina ball pulverized powder, which reduces the pregelatinization temperature of alumina hydrate (Yoshizawa friend) I. Fumiyoshi Saito: J. Ceram. Soc., Jpn., Vol104, p867 (1996)). The present inventors believe that the pulverization effect relating to the reduction of boehmite pregelatinization temperature is different from the effect obtained by grinding the alumina balls. This is because several hours to several tens of hours of treatment are required to obtain a sufficient amount of alumina powder by the grinding effect of alumina balls to achieve a decrease in the pregelatinization temperature. This is because an effect such as 1 can be obtained at most by several tens of minutes. From FIG. 1, it is necessary to add about 20% α-alumina for seeds in order to lower the pregelatinization temperature from 1100 ° C. to 1000 ° C. due to the pulverization effect. 20% α-alumina ground powder is unlikely to be produced.
[0018]
Therefore, the reason for the dramatic reduction in the pregelatinization temperature by the 30 minutes of pulverization must be obtained separately. The present inventors currently estimate this as follows. In the boehmite sol, boehmite particles may be secondary agglomerated. The secondary agglomeration is loosened by the pulverization treatment, and the dispersibility of the boehmite particles is improved, which is considered to be the cause of the decrease in the alpha conversion temperature.
[0019]
As can be seen from FIG. 1, the effect of lowering the alpha conversion temperature by adding α-alumina for seeds is increased by the pulverization treatment. This is interpreted as a result of uniforming the mixing with the α-alumina for seeds by loosening the secondary aggregation of the boehmite particles. In any case, it can be said that the boehmite pulverization process is not only effective in lowering the pregelatinization temperature itself, but also promotes the effect of α-alumina for seeds.
[0020]
In the experiment shown in FIG. 1, the pulverization time was 30 minutes, but when the dependency of the α-alumination temperature on the pulverization time was investigated, the pulverization treatment for 10 minutes or more showed the result shown in FIG. It was found that almost the same effect is exhibited.
Next, embodiments of the present invention will be described.
Any one-way electrical steel sheet may be used as long as it is manufactured by a known method. That is, since the unidirectional electrical steel sheet has a crystal structure with (110) [001] as the main orientation, it is considered that the unidirectional electrical steel sheet is effective for all electrical steel sheets whose iron loss value can be reduced by the tension applied to the steel sheet. ing. Since normal unidirectional electrical steel sheets contain Si, a subscale mainly composed of SiO 2 is generated in the decarburization annealing process, and MgO is mainly used to prevent steel sheet seizure during finish annealing (coil annealing). In order to perform finish annealing after applying the annealing separator, an annealing film mainly composed of forsterite formed by reaction of SiO 2 and MgO is formed in the finish annealing. However, the present invention relates to, for example, a unidirectional electrical steel sheet that suppresses the formation of a finish annealed film by adding chloride to the annealing separator disclosed in JP-A-64-62417, JP-A-7-54155. No. 5-195062 discloses a unidirectional electrical steel sheet in which the finish annealing film is prevented from forming by adding Bi chloride to the annealing separator disclosed in Japanese Patent Publication No. 5-195062. A unidirectional electrical steel sheet in which a finish annealing film is prevented by controlling the finish annealing atmosphere by using an inert oxide such as alumina as an annealing separator, and the steel sheet surface is mirror-finished, or Japanese Patent Laid-Open No. 8- The use of alumina containing an alkali metal oxide disclosed in Japanese Patent No. 3648 as an annealing separator prevents the formation of a finish annealing film and mirrors the surface of the steel sheet. Such phased-oriented electrical steel sheet, can be applied to no finish annealing film or even mirror-finished and the grain-oriented electrical steel sheet. When a tension-imparting type insulating coating is directly formed on a unidirectional electrical steel sheet having no finish annealing coating, the adhesion of the coating after baking is poor, but as disclosed in JP-A-6-184762, Adhesion can be improved by adopting a method of forming a SiO 2 film on the surface of the steel sheet prior to forming the insulating coating.
[0021]
Further, a tension-imparting type insulating film is formed on a unidirectional electrical steel sheet having a mirror-finished surface and disclosed in Japanese Patent Application Laid-Open Nos. 57-2252 and 59-255928. Laser irradiation treatment or plasma irradiation, groove formation by a tooth profile roll on the surface of a steel sheet disclosed in JP-A-61-117218, etc., groove formation by etching as disclosed in JP-B-3-69968, etc. A unidirectional electrical steel sheet with extremely low iron loss can be manufactured by combining with a so-called magnetic domain refinement processing technique such as groove formation by laser irradiation disclosed in 61-75506.
[0022]
The boehmite sol used in the present invention may be a commercially available product (sometimes referred to as alumina sol) or may be synthesized by a known method such as hydrolysis of various aluminum salts or aluminum alkoxides. Further, boehmite fine powder, trade name: Catapal or Dispal, sold by Vista Chemical Co., can be easily dispersed in dilute acid or water to form a boehmite sol.
[0023]
For the pulverization treatment, a known pulverizer such as a ball mill or a colloid mill can be used. The pulverization may be either dry or wet using a solvent. For example, the boehmite fine powder that becomes colloidal when dispersed in a solvent, such as the above Catapal or Dispal sold by Vista Chemical, may be suspended in water after being pulverized in a dry process. It may be suspended in water and pulverized in a wet manner before pulverization. Regardless of which pulverization means is used, the effect is exhibited in a processing time of 10 minutes or more.
[0024]
In particular, when a low pregelatinization temperature is required, α-alumina for seeds is added. The α-alumina for seeds is desirably as fine as possible, and there is almost no effect when the average particle size is 0.5 μm or more. As a commercially available α-alumina suitable for such purpose, trade name: AKP-50 manufactured by Sumitomo Chemical Co., Ltd. can be mentioned. The amount of α-alumina added for seeds can be determined depending on the pregelatinization temperature, but is 50% by weight or less based on boehmite. The reason is that adding over 50% is not only uneconomical and has an effect commensurate with the amount added, but also deteriorates the good film forming property of boehmite.
[0025]
The seed α-alumina may be added after the pulverization treatment, but it is preferable to add it before the pulverization treatment because the mixing with the boehmite sol becomes uniform.
Further, by devising the following, it is possible to obtain a very low α-izing temperature without intentionally adding α-alumina for seeds. That is, α-alumina is used for the mill medium (ball in the case of a ball mill, and grindstone in the case of a colloid mill), and the processing time is secured for several to several tens of hours. In this case, the boehmite grinding treatment and the addition of α-alumina for seeds by grinding of the mill medium are performed in the same step.
[0026]
The boehmite sol that has been pulverized as described above or fine boehmite powder dispersed in water is applied to a unidirectional electrical steel sheet and baked at a heating temperature of 750 ° C. or higher. The coating does not become α-alumina at a baking temperature of 750 ° C. or lower. As a coating method, any known roll coating method, spraying method, dipping method, etc. may be used.
[0027]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
In addition, the addition amount of the seed α-alumina in the examples is in terms of% by weight with respect to boehmite. Therefore, in the case of boehmite sol, it becomes weight% with respect to sol dry weight.
[Example 1]
After adding α-alumina for seeds (trade name: AKP-50, manufactured by Sumitomo Chemical Co., Ltd.) to some sols to boehmite sol (trade name: AS-520, manufactured by Nissan Chemical Co., Ltd.), ball mill or colloid The mill was wet crushed by a mill. The thing which does not give a grinding process as a comparative example was also prepared. This was applied to a unidirectional electrical steel sheet (finish thickness 0.23 mm, with a finish annealing film mainly composed of forsterite) containing 3% Si that had been subjected to finish annealing, and baked at a predetermined temperature. The film thickness after baking is 2 μm. In addition, about some samples after that, by the laser irradiation disclosed in Japanese Patent Laid-Open No. 57-2252 or the groove formation by a tooth profile roll on the steel sheet surface disclosed in Japanese Patent Laid-Open No. 61-117218, etc. Magnetic domain refinement treatment was applied. However, in the case of groove formation, the groove was formed before the formation of the insulating coating. As a comparative example of the insulating coating, a conventional insulating coating made of colloidal silica and phosphate (film thickness after baking: 2 μm) was applied. Table 1 shows the evaluation results of processing conditions and magnetic characteristics (B8: magnetic flux density at 800 A / m, W17 / 50: 50 Hz, iron loss value at 1.7 T).
[0028]
[Table 1]
As shown in Table 1, the conventional insulation film No. With one unidirectional electrical steel sheet, the applied tension is low, and it is difficult to obtain an iron loss value lower than 0.8 W / kg. In addition, in the case where boehmite sol was used, No. obtained by baking boehmite sol not subjected to pulverization treatment at 1000 ° C. or lower. 2 and no. No. 3 is considered to be because there is no applied tension due to the insulating coating, but gives a larger iron loss value than when the conventional insulating coating is applied. On the other hand, No. using the boehmite sol which performed the grinding | pulverization process of this invention. In 4 to 8, an iron loss value of 0.8 W / kg or less is obtained, and this is realized at a baking temperature of 1000 ° C. or less. This can be interpreted as a result of obtaining an insulating film having a large applied tension to the steel sheet. No. to which α-alumina for seeds was added. In the case of 5-8, the effect is acquired at especially low baking temperature. No. No. 8 is obtained by applying the insulating film forming technique according to the present invention to the unidirectional electrical steel sheet in combination with the magnetic domain fragmentation treatment, so that the iron loss is extremely low.
[Example 2]
After adding alpha-alumina for seeds (trade name: AKP-50 manufactured by Sumitomo Chemical Co., Ltd.) to fine boehmite powder (trade name: Dispal manufactured by Vista Chemical), wet or dry pulverization treatment with a ball mill or a colloid mill In the case of dry pulverization, it was then dispersed in water to prepare a colloidal solution. By using alumina containing an alkali metal oxide disclosed in JP-A-8-3648 as an annealing separator, the formation of a finish annealed film is prevented and the steel sheet surface is mirror-finished. It was applied to a steel plate (plate thickness 0.23 mm) and baked at a predetermined temperature. The film thickness after baking is 2 μm. When any of the coating liquids was baked, a SiO 2 film was formed on the surface of the steel plate prior to forming the insulating film by the method disclosed in Japanese Patent Application Laid-Open No. 6-184762 to ensure film adhesion. Thereafter, magnetic domain subdivision treatment was performed by laser irradiation disclosed in Japanese Patent Laid-Open No. 57-2252 or groove formation by a tooth profile roll on a steel sheet surface disclosed in Japanese Patent Laid-Open No. 61-117218. . However, in the case of groove formation, the groove formation was performed before the formation of the insulating coating. As a comparative example of the insulating coating, a conventional insulating coating made of colloidal silica and phosphate (film thickness after baking: 2 μm) was applied. Table 2 shows the evaluation results of the processing conditions and magnetic characteristics (B8: magnetic flux density at 800 A / m, W17 / 50: 50 Hz, iron loss value at 1.7 T).
[0030]
[Table 2]
In general, a good iron loss value can be obtained by forming a tension-imparting type insulation coating on a unidirectional electrical steel sheet with a mirror-finished surface and further subjecting it to a magnetic domain subdivision treatment. If the insulating film forming technology according to the invention is applied, the It can be seen that a unidirectional electrical steel sheet having an extremely low iron loss that is much lower than 0.7 W / kg is obtained as in 2-6.
[0032]
【The invention's effect】
As described above, by applying the insulating coating according to the present invention to a unidirectional electrical steel sheet, it is possible to form an insulating coating with a high applied tension to the steel sheet, thereby reducing the unidirectional electrical steel sheet with low iron loss. Can be manufactured, and its industrial effect is great.
[Brief description of the drawings]
FIG. 1 is a graph showing the effects of pulverization treatment on boehmite and addition of α-alumina for seeds on the α-alumination temperature of boehmite.
Claims (6)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29111797A JP4021979B2 (en) | 1997-10-23 | 1997-10-23 | Unidirectional electrical steel sheet having an insulating coating with a large tensioning effect and method for forming the insulating coating |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29111797A JP4021979B2 (en) | 1997-10-23 | 1997-10-23 | Unidirectional electrical steel sheet having an insulating coating with a large tensioning effect and method for forming the insulating coating |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11126712A JPH11126712A (en) | 1999-05-11 |
| JP4021979B2 true JP4021979B2 (en) | 2007-12-12 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP29111797A Expired - Fee Related JP4021979B2 (en) | 1997-10-23 | 1997-10-23 | Unidirectional electrical steel sheet having an insulating coating with a large tensioning effect and method for forming the insulating coating |
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| Country | Link |
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| JP (1) | JP4021979B2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100457834C (en) * | 2005-06-21 | 2009-02-04 | 中国科学院合肥物质科学研究院 | Alumina insulating coating and preparation method thereof |
| KR100828951B1 (en) | 2006-10-31 | 2008-05-13 | 한국과학기술연구원 | Fabrication method of metal substrate coated with alumina carrier |
| CN112639037A (en) * | 2018-09-03 | 2021-04-09 | 住友精化株式会社 | Coating material for partial discharge resistance, insulating coating film for partial discharge resistance, electric wire, and rotating electrical machine |
| EP3848424A4 (en) * | 2018-09-03 | 2022-06-08 | Sumitomo Seika Chemicals Co., Ltd. | Coating material for partial-discharge resistance, insulating coating film for partial-discharge resistance, electrical wire, and dynamo-electric machine |
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1997
- 1997-10-23 JP JP29111797A patent/JP4021979B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH11126712A (en) | 1999-05-11 |
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