JP4236431B2 - Method for forming insulating film on grain-oriented electrical steel sheet - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、鋼板に対する付与張力が大きく方向性電磁鋼板の鉄損低減に有効に作用するほう酸アルミニウム皮膜を絶縁皮膜として形成する方法に関する。
【０００２】
【従来の技術】
方向性電磁鋼板は（１１０）［００１］方位を主方位とする結晶組織を有し、通常２質量％以上のＳｉを含有する鋼板であり、磁気鉄心材料として多用されており、特にエネルギーロスが少ない鉄損の低い材料が求められている。Ｓｉ含有量が５％以下である場合、その磁気異方性の故に、鋼板に張力を付与することにより鉄損が低減するという性質がある。鋼板に半永久的に張力を付与するためには、鋼板表面に地鉄より熱膨張係数の小さい皮膜を高温で形成することが有効である。方向性電磁鋼板の仕上げ焼鈍工程に通常自然に形成されるＭｇ2ＳｉＯ4もしくはＭｇ2ＳｉＯ4とＭｇＡｌ2Ｏ4を主体とする仕焼鈍皮膜は、焼鈍後の冷却によって鋼板に対して０．５ｋｇｆ／ｍｍ2程度の張力を付与しており、ある程度の鉄損低減効果を有するが、その効果は十分ではない。このため仕上げ焼鈍後の方向性電磁鋼板の絶縁性を高めるために形成する絶縁皮膜によってさらに張力を付与する努力がなされている。例えば、特許文献１に開示された、コロイド状シリカと燐酸塩を主体とする塗布液を焼き付けて得られる絶縁被膜は、さらに０．５ｋｇｆ／ｍｍ2程度の張力を付与することができ、現行の市販の方向性電磁鋼板に広く用いられている。
【０００３】
本発明者らは、方向性電磁鋼板の鉄損値に対する付与張力の影響を調査したところ、仕上げ焼鈍皮膜＋上記絶縁皮膜で得られる付与張力は未だ不十分であり、より付与張力の大なる絶縁皮膜が形成できるならば、方向性電磁鋼板の鉄損値はさらに低減しうることが判明した。そこで、本発明者らは新規なる絶縁被膜の開発に着手し、極めて付与張力の大きい絶縁被膜として、特許文献２、特許文献３等において、アルミナゾルとほう酸を混合した塗布液を塗布、焼き付けることによって得られるほう酸アルミニウム被膜（ＡｌｘＢｙＯ１．５（ｘ−ｙ））を提案してきた。この絶縁皮膜は従来の絶縁皮膜の１．５〜２倍程度の皮膜張力を与える。
【０００４】
しかしながら、本皮膜の開発を進めて行く過程で、用いるべきアルミナゾルの性状によって得られる皮膜張力や造膜性、塗布液の安定性が異なることがわかった。例えば、結晶性の低いアルミナゾルはほう酸との反応性が良好であるため高い皮膜張力を得ることができる一方、ほう酸と混合した後に時間とともに粘度が増大し、最終的にゲル化すると言う性質を有する。一方、結晶性の良好なベーマイト的なアルミナゾルは、ほう酸との混合の後の粘度安定性に優れる一方で、ほう酸との反応性が劣り得られる皮膜張力が不足する。
【０００５】
【特許文献１】
特開昭４８−３９３３８号公報
【特許文献２】
特開平６−６５７５４号公報
【特許文献３】
特開平６−６５７５５号公報
【０００６】
【発明が解決しようとする課題】
本発明は、方向性電磁鋼板にほう酸アルミニウム質の絶縁皮膜を形成するに際し、得られる皮膜張力を低下させることなしに、塗布液の粘度安定性等を確保する方法を提供するものである。
【０００７】
【課題を解決するための手段】
本発明は上記課題を解決するためになされたもので、その要旨は次のとおりである。
【０００８】
（１）アルミナゾルとほう酸をＡｌ：Ｂのモル比で１：１〜５：１の範囲で混合し、これを仕上げ焼鈍済みの方向性電磁鋼板に塗布し、５００℃以上で焼き付けてほう酸アルミニウムからなる絶縁皮膜を形成させるに際し、アルミナゾルとして、１００℃乾燥後のＸ線回折測定におけるベーマイト（０２０）回折線の半価幅が３度以上のものを用い、かつアルミナゾルに硝酸を添加し、その硝酸の添加量が、Ａｌ2Ｏ3に対するＨＮＯ3の質量比で５％以上８０％以下であることを特徴とする方向性電磁鋼板の絶縁皮膜形成方法。
【０００９】
（２）アルミナゾルとほう酸をＡｌ：Ｂのモル比で１：１〜５：１の範囲で混合し、これを仕上げ焼鈍済みの方向性電磁鋼板に塗布し、５００℃以上で焼き付けてほう酸アルミニウムからなる絶縁皮膜を形成させるに際し、１００℃乾燥後のＸ線回折測定におけるベーマイト（０２０）回折線の半価幅が３度以上のアルミナゾルを全アルミナゾルに対するＡｌ2Ｏ3分質量割合で５０％以上、および１００℃乾燥後のＸ線回折測定におけるベーマイト（０２０）回折線の半価幅が３度未満のアルミナゾルをＡｌ2Ｏ3源全体に対する質量割合で５０％未満として混合し、さらに硝酸を添加し、その硝酸の添加量が、１００℃乾燥後のＸ線回折測定におけるベーマイト（０２０）回折線の半価幅が３度以上のアルミナゾルから計算されるＡｌ2Ｏ3に対するＨＮＯ3の質量比で５％以上８０％以下であることを特徴とする方向性電磁鋼板の絶縁皮膜形成方法。
【００１０】
（３）Ｍｇ2ＳｉＯ4もしくはＭｇ2ＳｉＯ4とＭｇＡｌ2Ｏ4を主体とする仕上げ焼鈍皮膜を有する方向性電磁鋼板に、ほう酸とアルミナゾルからなる混合液を塗布焼き付けることを特徴とする（１）または（２）記載の方向性電磁鋼板の絶縁皮膜形成方法。
【００１１】
（４）Ｍｇ2ＳｉＯ4もしくはＭｇ2ＳｉＯ4とＭｇＡｌ2Ｏ4を主体とする仕上げ焼鈍皮膜を有する方向性電磁鋼板に、燐酸塩とコロイダルシリカを主体とする塗布液を塗布した後、乾燥もしくは焼き付けた上でほう酸とアルミナゾルからなる混合液を塗布焼き付けることを特徴とする（１）または（２）記載の方向性電磁鋼板の絶縁皮膜形成方法。
【００１２】
（５）仕上げ焼鈍皮膜を除去あるいは意図的に形成させなかった方向性電磁鋼板に、０．００１μｍ以上のＳｉＯ2皮膜を形成した後、ほう酸とアルミナゾルからなる混合液を塗布焼き付けることを特徴とする（１）または（２）記載の方向性電磁鋼板の絶縁皮膜形成方法。
【００１３】
（６）前記ＳｉＯ2皮膜の形成方法が、方向性電磁鋼板の弱酸化性雰囲気中での焼鈍、もしくは方向性電磁鋼板へのドライコーティングのいずれかであることを特徴とする（５）記載の方向性電磁鋼板の絶縁皮膜形成方法。
【００１４】
【発明の実施の形態】
アルミナゾルとは、アルミナ水和物の微粒子から成るコロイドであり、コロイドの組成は形式的にＡｌ2Ｏ3・ｘＨ2Ｏで表される。アルミナゾルの製法は各種存在し、各製造法や製造条件によってコロイド粒子の結晶性は様々に変化する。アルミナゾルコロイド粒子の結晶性の比較的良好なものは、図１に示すように、乾燥ゲルのＸ線回折パターンのピークの幅が狭く、かつ各回折ピークはγ−ＡｌＯＯＨ（ベーマイト、Ａｌ2Ｏ3・Ｈ2Ｏ）的の回折パターンに一致する。結晶性の低下とともに各回折ピークの幅は広がり、殆どピークの認められない場合もある。従って、Ｘ線回折のピーク幅はアルミナゾル中のコロイド粒子の結晶性の評価に適している。また、結晶性良好なものはＡｌ2Ｏ3・ｘＨ2Ｏで表現した場合のｘの値が１〜２程度にあり、結晶性の低下とともにｘの値が増大する。これは結晶性の低下とともにコロイド粒子に結合する水が増えるからであると考えられる。一般に１００℃程度の乾燥では結晶水は解放されない。
【００１５】
本発明者らは、ほう酸との反応性が良好で高い皮膜張力が得られる一方で、ほう酸との混合の後の粘度安定性に劣る、結晶性の低いアルミナゾルの改良方法を検討した。各種の添加物を試みたところ、硝酸を添加することが有効であることが判明した。すなわち、アルミナゾルに対し硝酸を添加したうえで所定の量のほう酸を混合したところ、硝酸添加量の増大とともに粘度安定性が改善されることを発見した。
【００１６】
図２は、本発明者らが得たアルミナゾルとほう酸混合液の粘度の経時変化に及ぼす硝酸添加の影響である。図２における数値はＡｌ2Ｏ3に対するＨＮＯ3の質量比である。硝酸無添加の場合は作液直後から直ちに粘度上昇が始まる。３％添加した場合には、粘度上昇の傾きはやや抑制されるが、やはり作液直後から粘度上昇が始まる。これに対し、５％の硝酸を添加した場合には、粘度が一定値に維持される時間域が出現する。その後、硝酸添加の増大とともにこの粘度が一定値にとどまる時間域が大きくなることがわかる。
【００１７】
塗布液の粘度変化は塗布量の制御を困難にし、粘度上昇は塗布模様の原因となる。したがって塗布液の粘度は低位安定していなければならない。図２に示したように、アルミナゾルにＡｌ2Ｏ3に対し質量比で５％のＨＮＯ3を添加することにより塗布液の粘度が一定値を示す時間域が生じ、塗布操業が可能となることがわかる。この時間域は硝酸添加の増大とともに長くなり、より操業が容易になる。
【００１８】
低結晶性アルミナゾルとほう酸との混合液の粘度が硝酸添加により安定化する理由は定かではない。透過電子顕微鏡観察によれば、硝酸を添加してもアルミナゾル中のコロイドの粒子形状には変化がないことから、添加された硝酸ないし硝酸イオンはコロイド粒子表面に吸着された形で存在しているものと考えられる。吸着した硝酸ないし硝酸イオンがコロイド粒子とほう酸との反応を防止し、安定化がはかられているものと推測される。
【００１９】
次に、アルミナゾルの結晶性と得られる皮膜張力の関係について述べる。本発明では結晶性の指標として、１００℃乾燥後のＸ線回折におけるベーマイト（０２０）回折線の半価幅を採用する。図３に本発明における回折線半価幅の定義を示した。図１に示したように、ベーマイト（０２０）回折線は、最も強い反射強度を与える回折線であり、格子間隔で約０．６ｎｍ付近にあり、ＣｕＫα線を用いた場合には回折角２θ＝１４度付近となる。
【００２０】
各種アルミナゾルを用意してほう酸と混合し（Ａｌ：Ｂ＝２：１（モル比））、鋼板に塗布し８５０℃で焼き付けて得られる皮膜張力を測定した結果を図４に示す。図４を得る実験にあたっては、１００℃乾燥後のＸ線回折におけるベーマイト（０２０）回折線の半価幅が３度以上のアルミナゾルを用いた場合には、ＨＮＯ3／Ａｌ2Ｏ3質量比で１０％の硝酸を添加することによりほう酸添加後の粘度を安定化させた。ベーマイト（０２０）回折線の半価幅が３度以上のアルミナゾルを用いた場合には高い皮膜張力が得られる。従って、皮膜張力の観点からは、アルミナゾルとして１００℃乾燥後のＸ線回折におけるベーマイト（０２０）回折線の半価幅が３度以上のものを用いるべきであることがわかる。また、そのようなアルミナゾルを用いた場合に生ずる塗布液粘度の不安定性は硝酸添加によって回避できる。
【００２１】
皮膜張力と粘度安定性の観点からは、上述のように低結晶性アルミナゾルを用いるべきであるが、低結晶性アルミナゾルには造膜性が低いという欠点がある。特に乾燥速度が速い場合には皮膜が剥離しやすくなることがある。この問題は乾燥速度を制御しやすい設備ではあまり問題にならないが、そうでない場合には考慮しなければならないことである。
【００２２】
低結晶性アルミナゾルを用いた場合の造膜性劣化は、低結晶性アルミナゾルに結晶性良好なアルミナゾルを混合することにより改善できる。結晶性良好なアルミナゾルを併用することは皮膜張力の低下をもたらすことは明らかである。そこで、低結晶性アルミナゾルと結晶性良好なアルミナゾルを混合して用いた場合の皮膜張力を調査した。
【００２３】
図５はその結果である。横軸は低結晶性アルミナゾルの全アルミナゾル（低結晶性アルミナゾル＋結晶性良好なアルミナゾル）に対する比率であり、Ａｌ2Ｏ3分換算の質量比である。図５では低結晶性アルミナゾルとして１００℃乾燥後のＸ線回折における回折線が明瞭に認められなかったもの（無定型）のものを用い、結晶性良好なアルミナゾルとしては１００℃乾燥後のＸ線回折におけるベーマイト（０２０）回折線の半価幅が１°のものを用いた。ほう酸とアルミナゾルの混合比はモル比でＡｌ：Ｂ＝２：１である。また、アルミナゾルを混合するに先立ち、低結晶性アルミナゾルにはＨＮＯ3／Ａｌ2Ｏ3質量比で１０％の硝酸を添加することにより、ほう酸添加後の粘度を安定化させた。図５より、低結晶性アルミナゾルの混合率が全アルミナゾルに対しＡｌ2Ｏ3換算で５０％以上であれば、顕著な張力劣化が無く、従来皮膜に比較して高い皮膜張力を発揮できることがわかる。
【００２４】
本発明による方向性電磁鋼板の絶縁皮膜形成方法は、アルミナゾルとほう酸との混合液を、仕上げ焼鈍（二次再結晶焼鈍）が完了した方向性電磁鋼板に塗布し焼き付けてほう酸アルミニウムからなる絶縁皮膜を形成するにあたり、アルミナゾルとして結晶性の低いものを主体として用い、かつ硝酸を添加することに特徴を有する。結晶性の低いアルミナゾルとは、１００℃で乾燥した場合のＸ線回折におけるベーマイト（０２０）回折線の半価幅が３度以上のアルミナゾルである。３度以上の半価幅を有するアルミナゾルは、ほとんど（０２０）回折線が認められないいわゆる無定形ないし非晶質アルミナゾルを含め、ほう酸と混合して焼き付けることにより、高い皮膜張力を鋼板に付与することができる。
【００２５】
低結晶性アルミナゾルとほう酸との混合液の粘度安定性を確保するために、硝酸を添加する必要がある。硝酸の添加量は、低結晶性アルミナゾルに対し質量比ＨＮＯ3／Ａｌ2Ｏ3で５％以上、８０％以下とする。５％未満では粘度安定性の効果が十分でない。一方、多量の硝酸添加は作業環境を悪化させるばかりでなく、８０％を越えるとアルミナゾルの粘度安定性が再び悪化する。したがって、硝酸の添加量は８０％以下が適当である。
【００２６】
アルミナゾルとして低結晶性アルミナゾルのみを採用した場合、乾燥条件によっては乾燥後の造膜性が劣化し、剥離しやすくなる場合がある。そのような場合には低結晶性アルミナゾルと結晶性良好なアルミナゾルとを併用することにより造膜性が改善できる。ここで結晶性良好なアルミナゾルとは、１００℃で乾燥した場合のＸ線回折におけるベーマイト（０２０）回折線の半価幅が３度未満のアルミナゾルである。高い皮膜張力を維持するためには、結晶性良好なアルミナゾルの添加量は、全アルミナゾルに対しＡｌ2Ｏ3質量換算で５０％未満にする必要がある。
【００２７】
結晶性良好なアルミナゾルと低結晶性アルミナゾルを混合して用いた場合でも、塗布液粘度安定化のためには硝酸添加を必要とする。この場合の硝酸の添加量は、低結晶性アルミナゾルに対して計量される。すなわち低結晶性アルミナゾルに対し質量比ＨＮＯ3／Ａｌ2Ｏ3で５％以上、８０％以下とする。
【００２８】
塗布液中のアルミナゾルとほう酸の混合比は、Ａｌ：Ｂのモル比で１：１〜５：１の範囲とする。この範囲外では得られる皮膜張力が著しく低下し、特にほう酸が過剰の場合には未反応のＢ2Ｏ3が生成し、耐水性等が劣化する。
【００２９】
本発明の塗布液には、上記アルミナゾルとほう酸に、必要に応じ他の添加物を加えても良い。例えば、酸化珪素前駆体化合物、遷移金属化合物、アルカリあるいはアルカリ金属化合物、希土類元素化合物、無機酸、有機酸，アンモニア等を必要量添加することができる。
【００３０】
上記塗布液を５質量％以下のＳｉを含有する仕上げ焼鈍済みの方向性電磁鋼板に、ロールコート法、デップ法、スプレー法、あるいは電気泳動法など、公知の手段により塗布する。塗布法は特に限定されず、液性状等に応じて最適な方法を選択すればよい。
【００３１】
本発明でいう仕上げ焼鈍済みの方向性電磁鋼板には、１）一般的に公知の製造法、すなわち、ＭｇＯを主体とする焼鈍分離剤を塗布して仕上げ焼鈍を行うことによって生ずるＭｇ2ＳｉＯ4もしくはＭｇ2ＳｉＯ4とＭｇＡｌ2Ｏ4を主体とする仕焼鈍皮膜を有するものと、２）これら仕上げ焼鈍皮膜のない方向性電磁鋼板の２種類があり、本発明はいずれの方向性電磁鋼板にも適用できる。２）の方向性電磁鋼板の製造方法としては、（ａ）ＭｇＯ焼鈍分離剤中に仕上げ焼鈍皮膜形成を阻害する添加物を含有させたり（特開平０５−２９９２２８号公報）、（ｂ）ＭｇＯに代えてＡｌ2Ｏ3等、不活性な酸化物等を主体とする焼鈍分離剤として用いることにより意図的に仕上げ焼鈍皮膜を形成させない方法、（ｃ）通常の仕上げ焼鈍を行った後に仕上げ焼鈍皮膜を酸洗等で除去する方法がある。（ｂ）の方法では、焼鈍分離剤中のアルカリ金属元素濃度を制御することにより仕上げ焼鈍皮膜がないばかりでなく表面が平滑である方向性電磁鋼板が得られる（特開平８−３６４８号公報）。また、（ｃ）の製造法を採用した後、化学研磨、電解研磨によって（ｂ）と同様の表面が平滑な方向性電磁鋼板が得られる。本発明の絶縁皮膜は、特に表面が平滑な方向性電磁鋼板の鉄損値を著しく低減させることに効果的である。
【００３２】
一般的な製造法によって製造した、すなわち仕上げ焼鈍皮膜を有する方向性電磁鋼板の場合、Ｍｇ2ＳｉＯ4もしくはＭｇ2ＳｉＯ4とＭｇＡｌ2Ｏ4を主体とする仕焼鈍皮膜が形成されており、その上に直接本発明の塗布液を塗布焼き付けても特段問題はないが、本発明の塗布液を焼き付ける前に、燐酸塩とコロイダルシリカを主体とする従来の絶縁皮膜をあらかじめ形成すると、極めて耐食性の高い絶縁皮膜となる。
【００３３】
仕上げ焼鈍皮膜の無い方向性電磁鋼板に本発明の塗布液を適用する場合には、０．００１μｍ以上の膜厚を有するＳｉＯ2の膜をあらかじめ形成させる（特開平０６−１８４７６２号公報）ことによって、鋼板と絶縁皮膜との間の良好な密着性を得ることができる。ＳｉＯ2膜の形成方法には、方向性電磁鋼板の弱酸化性雰囲気中焼鈍によりＳｉＯ2外部酸化膜を形成する方法や、ＣＶＤやＰＶＤ等のドライコーティングによりＳｉＯ2膜を形成する方法があるが、ＳｉＯ2膜の形成手段はこれらの手段に限定されない。
【００３４】
いずれの方向性電磁鋼板においても、レーザー照射による点列状の局所歪み導入や溝形成等の、いわゆる磁区制御と併用すれば、本発明の絶縁皮膜による高い付与張力により、極めて低い鉄損値を有する方向性電磁鋼板が得られる。
【００３５】
本発明の塗布液を塗布した方向性電磁鋼板は、５００℃〜１２００℃で焼付を行う。５００℃未満の場合、アルミナ水和物の脱水が不十分であり、ほう酸アルミニウムが形成し難い。また、１２００℃以上の焼付温度は、特に大きな不都合はないものの、経済的ではない。より好ましくは７００〜１２００℃であり、この温度範囲ではほう酸アルミニウムの形成が容易に進行し、高い皮膜張力が得られる。焼付の雰囲気は、一般的には限定されないが、仕上げ焼鈍皮膜がない方向性電磁鋼板に適用する場合には、絶縁皮膜と鋼板との間の界面の酸化を防止するために、非酸化性雰囲気ないし水素を含有する雰囲気を採用することが望ましい。
【００３６】
【実施例】
（実施例１）
表１に示すように、結晶性の異なる各種アルミナゾルとほう酸を混合し、一部については硝酸を添加した塗布液を準備した。通常の製造法により製造した仕上げ焼鈍皮膜を有する板厚０．２３ｍｍの方向性電磁鋼板を用意し、表１の塗布液を片面あたり５ｇ／ｍ2塗布し、８５０℃で３０秒間焼き付けた。塗布液中のＡｌ：Ｂのモル比は２：１である。その際の塗布液の安定性、絶縁皮膜形成後の磁気特性と絶縁皮膜張力を表１に示した。皮膜張力は片面を保護しつつアルカリにより絶縁皮膜を除去した場合の鋼板のそりから算出した。
【００３７】
表１に示したように、乾燥後の（０２０）回折線半価幅が３度以上のアルミナゾルを用いた場合には、そうでない場合に比較して得られる皮膜張力が大きく、鉄損値のより低い方向性電磁鋼板となっている。またこのようなアルミナゾルは５％以上８０％以下の硝酸添加によって塗布作業が安定的に行えるようになる。
【００３８】
【表１】
（実施例２）
通常の製造法により製造した仕上げ焼鈍皮膜を有する板厚０．２３ｍｍの方向性電磁鋼板を用意し、ほう酸とアルミナゾルからなる塗布液を４ｇ／ｍ2塗布して８５０℃で６０秒焼き付けた。ほう酸とアルミナゾルからなる塗布液は、表２に示すように、結晶性良好なアルミナゾル（（０２０）半価幅＝１度）と低結晶性アルミナゾル（（０２０）半価幅＝５．２度）を各種の割合で混合したものを用いた。また、硝酸添加を行った場合と、そうでない場合の比較も行った。
【００４０】
得られた結果を表２に示す。アルミナゾルとして低結晶性アルミナゾルを５０％以上混合した塗布液は、硝酸を添加しない場合にはゲル化起こるが、これは５％以上８０以下の硝酸添加によって回避されている。また、アルミナゾルとして低結晶性アルミナゾルを５０％以上混合した塗布液は、高い皮膜張力が得られ、方向性電磁鋼板の鉄損を低くなる結果を与えている。
【００４１】
【表２】
（実施例３）
通常の製造法により製造した仕上げ焼鈍皮膜を有する板厚０．２３ｍｍの方向性電磁鋼板を用意し、これに従来のコロイダルシリカと燐酸塩を主体とするコーティング液を４ｇ／ｍ2塗布し８５０℃で６０秒焼き付けたもの、および、コロイダルシリカと燐酸塩を主体とするコーティング液を１ｇ／ｍ2塗布し６００℃で３０秒焼き付け、続いてほう酸とアルミナゾルからなる塗布液を４ｇ／ｍ2塗布して８５０℃で６０秒焼き付けたものを試作した。ほう酸とアルミナゾルからなる塗布液は、表３に示すように、結晶性良好なアルミナゾル（（０２０）半価幅＝１度）と低結晶性アルミナゾル（（０２０）半価幅＝５．２度）を各種の割合で混合し、かつ硝酸を添加したものを用いた。
【００４３】
得られた方向性電磁鋼板の磁気特性、絶縁皮膜張力、耐錆性を調査した。耐錆性は、５０℃、５％食塩水を５時間噴霧した後の発生の有無により判定した。結果を表３に示す。コロイダルシリカと燐酸塩を主体とする従来のコーティング液を薄く形成した後に本発明のコーティング液を焼き付けた方向性電磁鋼板は、従来のコーティング液のみを用いた方向性電磁鋼板に劣らない耐食性を有し、かつ、鉄損が著しく改善されている。
【００４４】
【表３】
（実施例４）
特開平８−３６４８号公報に従って仕上げ焼鈍を行った板厚０．２２ｍｍの仕上げ焼鈍皮膜が無く、かつ表面が平滑である方向性電磁鋼板を用意した。溝付歯車ロールによりこれに深さ２０μｍ、幅１００μｍの溝を５ｍｍ間隔で圧延方向にほぼ垂直の方向に形成した。その後、還元性雰囲気中の焼鈍もしくはドライコーティングにより鋼板表面に１０ｎｍの厚さでＳｉＯ2膜を形成した。これに従来のコロイダルシリカと燐酸塩を主体とするコーティング液を５ｇ／ｍ2塗布し８５０℃で６０秒焼き付けたもの、およびほう酸とアルミナゾルからなる塗布液を５ｇ／ｍ2塗布して８５０℃で６０秒焼き付けたものを用意した。アルミナゾルには乾燥後の（０２０）回折線半価幅が６度以上の無定型のアルミナゾルを用い、Ａｌ2Ｏ3に対し質量で３０％のＨＮＯ3を添加した。得られた方向性電磁鋼板の磁気特性、絶縁皮膜張力を調査した。表４に示すように、低結晶性アルミナゾルとほう酸からなる塗布液は、従来のコロイダルシリカと燐酸塩を主体とする塗布液に比較して、得られる皮膜張力が大きく、その結果極めて低い鉄損値を与えている。
【００４６】
【表４】
【発明の効果】
本発明によって、従来の絶縁皮膜に比較して格段に大きい張力を方向性電磁鋼板に付与することができるほう酸アルミニウム質の絶縁皮膜を、粘度変化の少ない塗布液を用いて形成することができ、方向性電磁鋼板の鉄損を著しく改善できる。
【図面の簡単な説明】
【図１】 １００℃で乾燥したアルミナゾルのＸ線回折パターンを示す図。（ＣｕＫα線使用。）
【図２】 アルミナゾルとほう酸混合液の粘度の経時変化に及ぼす硝酸添加の影響を示す図。
【図３】 Ｘ線回折線の半価幅の定義を示す図。
【図４】 アルミナゾルの結晶性と皮膜張力の関係を示す図。
【図５】 全アルミナゾル中の低結晶性アルミナゾル配合比率と皮膜張力の関係を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming an aluminum borate film as an insulating film that has a large applied tension to a steel sheet and effectively acts to reduce iron loss of a grain-oriented electrical steel sheet.
[0002]
[Prior art]
A grain-oriented electrical steel sheet is a steel sheet having a crystal structure with the (110) [001] orientation as the main orientation and usually containing 2% by mass or more of Si, and is often used as a magnetic core material. There is a need for materials with low iron loss. When the Si content is 5% or less, due to the magnetic anisotropy, there is a property that iron loss is reduced by applying tension to the steel sheet. In order to apply a semi-permanent tension to the steel sheet, it is effective to form a film having a smaller thermal expansion coefficient than that of the ground iron at a high temperature on the steel sheet surface. A finish annealing film mainly composed of Mg 2 SiO 4 or Mg 2 SiO 4 and MgAl 2 O 4 that is naturally formed in the finish annealing process of grain-oriented electrical steel sheets is 0.5 kgf to the steel sheet by cooling after annealing. Although a tension of about / mm 2 is applied and has a certain iron loss reducing effect, the effect is not sufficient. For this reason, efforts are made to further apply tension by an insulating film formed in order to enhance the insulation of the grain-oriented electrical steel sheet after finish annealing. For example, the insulating coating obtained by baking a coating liquid mainly composed of colloidal silica and phosphate disclosed in
[0003]
The present inventors investigated the influence of the applied tension on the iron loss value of the grain-oriented electrical steel sheet. As a result, the applied tension obtained by the finish annealed film + the above insulating film is still insufficient, and the insulation having a higher applied tension. It was found that if the film can be formed, the iron loss value of the grain-oriented electrical steel sheet can be further reduced. Therefore, the present inventors have started the development of a new insulating coating, and by applying and baking a coating solution in which alumina sol and boric acid are mixed in
[0004]
However, in the process of developing this film, it was found that the film tension, film-forming property, and coating solution stability obtained differ depending on the properties of the alumina sol to be used. For example, alumina sol with low crystallinity has good reactivity with boric acid, so that high film tension can be obtained. On the other hand, after mixing with boric acid, the viscosity increases with time and finally gels. . On the other hand, boehmite-like alumina sol with good crystallinity is excellent in viscosity stability after mixing with boric acid, but lacks the film tension that can cause poor reactivity with boric acid.
[0005]
[Patent Document 1]
JP 48-39338 A [Patent Document 2]
JP-A-6-65754 [Patent Document 3]
JP-A-6-65555 [0006]
[Problems to be solved by the invention]
The present invention provides a method for ensuring the viscosity stability of a coating solution without lowering the resulting film tension when forming an insulating film made of aluminum borate on a grain-oriented electrical steel sheet.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and the gist thereof is as follows.
[0008]
(1) Alumina sol and boric acid are mixed at a molar ratio of Al: B in the range of 1: 1 to 5: 1, and this is applied to a finish-oriented grain-oriented electrical steel sheet and baked at 500 ° C. or higher from aluminum borate. In forming an insulating film, an alumina sol having a half width of boehmite (020) diffraction line of 3 degrees or more in X-ray diffraction measurement after drying at 100 ° C. is added, and nitric acid is added to the alumina sol, The method for forming an insulating film on grain-oriented electrical steel sheet, wherein the added amount of HNO 3 is 5% to 80% by mass ratio of HNO 3 to Al 2 O 3 .
[0009]
(2) Alumina sol and boric acid are mixed at a molar ratio of Al: B in the range of 1: 1 to 5: 1, and this is applied to a finish-oriented grain-oriented electrical steel sheet and baked at 500 ° C. or higher from aluminum borate. When forming an insulating film, an alumina sol having a half-width of boehmite (020) diffraction line of 3 degrees or more in X-ray diffraction measurement after drying at 100 ° C. is 50% or more by mass ratio of Al 2 O 3 to the total alumina sol, And alumina sol having a half width of boehmite (020) diffraction line of less than 3 degrees in the X-ray diffraction measurement after drying at 100 ° C. is mixed at a mass ratio of less than 50% with respect to the entire Al 2 O 3 source, and nitric acid is added The amount of nitric acid added is Al 2 O calculated from alumina sol in which the half width of boehmite (020) diffraction line in X-ray diffraction measurement after drying at 100 ° C. is 3 degrees or more. A method for forming an insulating film on grain-oriented electrical steel sheets, wherein the mass ratio of HNO 3 to 3 is 5% or more and 80% or less.
[0010]
(3) A directional magnetic steel sheet having a finish annealed film mainly composed of Mg 2 SiO 4 or Mg 2 SiO 4 and MgAl 2 O 4 is coated and baked with a mixed solution of boric acid and alumina sol (1) Or the insulating film formation method of the grain-oriented electrical steel sheet as described in (2).
[0011]
(4) After applying a coating solution mainly composed of phosphate and colloidal silica to a grain oriented electrical steel sheet having a finish annealed film mainly composed of Mg 2 SiO 4 or Mg 2 SiO 4 and MgAl 2 O 4 , it is dried or The method for forming an insulating film on a grain-oriented electrical steel sheet according to (1) or (2), wherein the mixed liquid comprising boric acid and alumina sol is applied and baked after baking.
[0012]
(5) oriented electrical steel sheet did not finish annealing film removal or intentionally formed, after forming the above SiO 2 film 0.001 [mu] m, and wherein the baking coating a mixed solution comprising boric acid and alumina sol (1) The insulating film formation method of the grain-oriented electrical steel sheet according to (2).
[0013]
(6) The method for forming the SiO 2 film is any one of annealing of the grain-oriented electrical steel sheet in a weakly oxidizing atmosphere or dry coating on the grain-oriented electrical steel sheet. Insulating film forming method for grain-oriented electrical steel sheet.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Alumina sol is a colloid composed of fine particles of alumina hydrate, and the composition of the colloid is formally expressed as Al 2 O 3 .xH 2 O. There are various methods for producing alumina sol, and the crystallinity of colloidal particles varies depending on each production method and production conditions. As shown in FIG. 1, the alumina sol colloidal particles having relatively good crystallinity have a narrow peak width of the X-ray diffraction pattern of the dried gel, and each diffraction peak is γ-AlOOH (boehmite, Al 2 O 3 It matches the diffraction pattern of (H 2 O). As the crystallinity decreases, the width of each diffraction peak increases, and there are cases where almost no peak is observed. Therefore, the peak width of X-ray diffraction is suitable for evaluating the crystallinity of colloidal particles in alumina sol. Moreover, the value of x when expressed by Al 2 O 3 .xH 2 O is about 1-2 when the crystallinity is good, and the value of x increases as the crystallinity decreases. This is presumably because the amount of water bound to the colloidal particles increases with decreasing crystallinity. Generally, crystallization water is not released by drying at about 100 ° C.
[0015]
The inventors of the present invention have studied a method for improving an alumina sol having low crystallinity, which has good reactivity with boric acid and high film tension, but has poor viscosity stability after mixing with boric acid. When various additives were tried, it was found that adding nitric acid was effective. That is, when nitric acid was added to the alumina sol and a predetermined amount of boric acid was mixed, it was found that the viscosity stability was improved as the amount of nitric acid added increased.
[0016]
FIG. 2 shows the effect of nitric acid addition on the change over time in the viscosity of the alumina sol and boric acid mixture obtained by the present inventors. The numerical value in FIG. 2 is the mass ratio of HNO 3 to Al 2 O 3 . In the case of no addition of nitric acid, the viscosity starts to increase immediately after liquid preparation. When 3% is added, the slope of the viscosity increase is somewhat suppressed, but the viscosity increase starts immediately after the liquid preparation. On the other hand, when 5% nitric acid is added, a time range in which the viscosity is maintained at a constant value appears. Thereafter, it can be seen that as the addition of nitric acid increases, the time period in which this viscosity remains at a constant value increases.
[0017]
A change in the viscosity of the coating solution makes it difficult to control the coating amount, and an increase in viscosity causes a coating pattern. Therefore, the viscosity of the coating solution must be low and stable. As shown in FIG. 2, by adding 5% by weight of HNO 3 to Al 2 O 3 to alumina sol, a time range in which the viscosity of the coating solution shows a constant value is generated, and coating operation becomes possible. I understand. This time range becomes longer with increasing nitric acid addition, and operation becomes easier.
[0018]
The reason why the viscosity of the mixed liquid of low crystalline alumina sol and boric acid is stabilized by addition of nitric acid is not clear. According to the transmission electron microscope observation, even when nitric acid is added, the shape of the colloidal particles in the alumina sol does not change, so the added nitric acid or nitrate ions are adsorbed on the surface of the colloidal particles. It is considered a thing. The adsorbed nitric acid or nitrate ions prevent the reaction between the colloidal particles and boric acid, which is presumed to be stabilized.
[0019]
Next, the relationship between the crystallinity of alumina sol and the obtained film tension will be described. In the present invention, the half width of boehmite (020) diffraction line in X-ray diffraction after drying at 100 ° C. is adopted as an index of crystallinity. FIG. 3 shows the definition of the half-width of the diffraction line in the present invention. As shown in FIG. 1, the boehmite (020) diffraction line is the diffraction line that gives the strongest reflection intensity, and is in the vicinity of about 0.6 nm in the lattice spacing. When the CuKα line is used, the diffraction angle 2θ = Near 14 degrees.
[0020]
Various alumina sols are prepared and mixed with boric acid (Al: B = 2: 1 (molar ratio)), applied to a steel plate and baked at 850 ° C., and the film tension obtained is shown in FIG. In the experiment to obtain FIG. 4, in the case of using an alumina sol in which the half width of boehmite (020) diffraction line in X-ray diffraction after drying at 100 ° C. is 3 degrees or more, the mass ratio is HNO 3 / Al 2 O 3 . The viscosity after addition of boric acid was stabilized by adding 10% nitric acid. When an alumina sol having a half width of boehmite (020) diffraction line of 3 degrees or more is used, a high film tension can be obtained. Therefore, from the viewpoint of the film tension, it is understood that the alumina sol should have a half width of 3 degrees or more of boehmite (020) diffraction line in X-ray diffraction after drying at 100 ° C. Further, instability of the coating solution viscosity that occurs when such an alumina sol is used can be avoided by adding nitric acid.
[0021]
From the viewpoint of film tension and viscosity stability, a low crystalline alumina sol should be used as described above. However, the low crystalline alumina sol has a drawback of low film forming property. In particular, when the drying speed is high, the film may be easily peeled off. This problem is less of an issue with equipment that can easily control the drying rate, but must be considered otherwise.
[0022]
The deterioration of the film forming property when a low crystalline alumina sol is used can be improved by mixing an alumina sol with good crystallinity into the low crystalline alumina sol. It is clear that the use of an alumina sol with good crystallinity causes a decrease in film tension. Therefore, the film tension was investigated when a low crystalline alumina sol and an alumina sol with good crystallinity were mixed.
[0023]
FIG. 5 shows the result. The horizontal axis represents the ratio of the low crystalline alumina sol to the total alumina sol (low crystalline alumina sol + alumina sol with good crystallinity), which is a mass ratio in terms of Al 2 O 3 . In FIG. 5, a low crystalline alumina sol whose diffraction line in X-ray diffraction after drying at 100 ° C. was not clearly recognized (amorphous) was used, and an alumina sol with good crystallinity was X-ray after drying at 100 ° C. Boehmite (020) diffraction line having a half width of 1 ° in diffraction was used. The mixing ratio of boric acid and alumina sol is Al: B = 2: 1 in molar ratio. Prior to mixing the alumina sol, 10% nitric acid with a HNO 3 / Al 2 O 3 mass ratio was added to the low crystalline alumina sol to stabilize the viscosity after the addition of boric acid. From FIG. 5, it can be seen that when the mixing ratio of the low crystalline alumina sol is 50% or more in terms of Al 2 O 3 with respect to the total alumina sol, there is no significant deterioration in tension and a higher film tension can be exhibited compared to the conventional film. .
[0024]
An insulating film forming method for a grain-oriented electrical steel sheet according to the present invention is a method of applying a mixed solution of alumina sol and boric acid to a grain-oriented electrical steel sheet that has been subjected to finish annealing (secondary recrystallization annealing) and baking it. Is characterized by using mainly an alumina sol with low crystallinity and adding nitric acid. An alumina sol having low crystallinity is an alumina sol in which the half width of boehmite (020) diffraction line in X-ray diffraction when dried at 100 ° C. is 3 degrees or more. Alumina sol having a half width of 3 degrees or more, including so-called amorphous or amorphous alumina sol in which almost no (020) diffraction line is observed, is mixed with boric acid and baked to impart high film tension to the steel sheet. be able to.
[0025]
In order to ensure the viscosity stability of the mixed solution of the low crystalline alumina sol and boric acid, it is necessary to add nitric acid. The amount of nitric acid added is 5% or more and 80% or less in a mass ratio of HNO 3 / Al 2 O 3 with respect to the low crystalline alumina sol. If it is less than 5%, the effect of viscosity stability is not sufficient. On the other hand, addition of a large amount of nitric acid not only deteriorates the working environment, but if it exceeds 80%, the viscosity stability of the alumina sol deteriorates again. Therefore, an appropriate amount of nitric acid is 80% or less.
[0026]
When only the low crystalline alumina sol is employed as the alumina sol, the film-forming property after drying may be deteriorated depending on the drying conditions, and may be easily peeled off. In such a case, the film forming property can be improved by using a low crystalline alumina sol in combination with an alumina sol having good crystallinity. Here, the alumina sol with good crystallinity is an alumina sol in which the half width of boehmite (020) diffraction line in X-ray diffraction when dried at 100 ° C. is less than 3 degrees. In order to maintain a high film tension, the amount of alumina sol with good crystallinity needs to be less than 50% in terms of Al 2 O 3 mass with respect to the total alumina sol.
[0027]
Even when a mixture of an alumina sol with good crystallinity and a low crystallinity alumina sol is used, nitric acid must be added to stabilize the viscosity of the coating solution. The amount of nitric acid added in this case is measured with respect to the low crystalline alumina sol. That is, the mass ratio of HNO 3 / Al 2 O 3 is 5% or more and 80% or less with respect to the low crystalline alumina sol.
[0028]
The mixing ratio of alumina sol and boric acid in the coating solution is in the range of 1: 1 to 5: 1 in terms of a molar ratio of Al: B. Outside this range, the resulting film tension is remarkably reduced. In particular, when boric acid is excessive, unreacted B 2 O 3 is formed, and the water resistance and the like deteriorate.
[0029]
In the coating solution of the present invention, other additives may be added to the alumina sol and boric acid as necessary. For example, a necessary amount of silicon oxide precursor compound, transition metal compound, alkali or alkali metal compound, rare earth element compound, inorganic acid, organic acid, ammonia, or the like can be added.
[0030]
The above coating solution is applied to a finish annealed grain-oriented electrical steel sheet containing 5% by mass or less of Si by a known means such as a roll coating method, a dipping method, a spray method, or an electrophoresis method. The coating method is not particularly limited, and an optimal method may be selected according to the liquid properties and the like.
[0031]
In the grain-oriented electrical steel sheet that has been subjected to finish annealing in the present invention, 1) Mg 2 SiO 4 produced by applying a generally known manufacturing method, that is, annealing by applying an annealing separator mainly composed of MgO. Alternatively, there are two types, one having a finish annealing film mainly composed of Mg 2 SiO 4 and MgAl 2 O 4 , and 2) a directional electrical steel sheet without these finish annealing films. Is also applicable. As a method for producing a grain-oriented electrical steel sheet 2), (a) an additive that inhibits the formation of a finish annealing film is contained in the MgO annealing separator (Japanese Patent Laid-Open No. 05-299228), or (b) MgO Instead, a method that does not intentionally form a finish annealed film by using it as an annealing separator mainly composed of an inert oxide such as Al 2 O 3 , (c) a finish annealed film after performing a normal finish anneal Can be removed by pickling. In the method (b), a grain-oriented electrical steel sheet having not only a finish annealing film but also a smooth surface can be obtained by controlling the alkali metal element concentration in the annealing separator (Japanese Patent Laid-Open No. 8-3648). . Further, after adopting the production method (c), a grain-oriented electrical steel sheet having a smooth surface similar to (b) can be obtained by chemical polishing and electrolytic polishing. The insulating film of the present invention is particularly effective for significantly reducing the iron loss value of a grain-oriented electrical steel sheet having a smooth surface.
[0032]
In the case of a grain-oriented electrical steel sheet manufactured by a general manufacturing method, that is, having a finish annealed film, a finish annealed film mainly composed of Mg 2 SiO 4 or Mg 2 SiO 4 and MgAl 2 O 4 is formed. There is no particular problem if the coating liquid of the present invention is directly applied and baked on the surface, but if a conventional insulating film mainly composed of phosphate and colloidal silica is formed in advance before baking the coating liquid of the present invention, it is extremely corrosion resistant. High insulation film.
[0033]
When the coating liquid of the present invention is applied to a grain-oriented electrical steel sheet having no finish annealing film, a SiO 2 film having a thickness of 0.001 μm or more is formed in advance (Japanese Patent Laid-Open No. 06-184762). Good adhesion between the steel sheet and the insulating film can be obtained. As a method for forming the SiO 2 film, there are a method of forming a SiO 2 external oxide film by annealing a grain-oriented electrical steel sheet in a weakly oxidizing atmosphere, and a method of forming a SiO 2 film by dry coating such as CVD or PVD. The means for forming the SiO 2 film is not limited to these means.
[0034]
In any grain-oriented electrical steel sheet, when used in combination with so-called magnetic domain control, such as the introduction of local strain in the form of a point sequence by laser irradiation or groove formation, the iron coating has a very low iron loss value due to the high tension applied by the insulating film of the present invention. A grain-oriented electrical steel sheet is obtained.
[0035]
The grain-oriented electrical steel sheet coated with the coating liquid of the present invention is baked at 500 ° C to 1200 ° C. When the temperature is less than 500 ° C., the dehydration of the alumina hydrate is insufficient and aluminum borate is difficult to form. A baking temperature of 1200 ° C. or higher is not economical, although there is no particular disadvantage. More preferably, it is 700-1200 degreeC, and formation of aluminum borate advances easily in this temperature range, and high film tension is obtained. In general, the baking atmosphere is not limited, but when applied to a grain-oriented electrical steel sheet without a finish annealed film, a non-oxidizing atmosphere is used to prevent oxidation at the interface between the insulating film and the steel sheet. It is desirable to employ an atmosphere containing hydrogen.
[0036]
【Example】
Example 1
As shown in Table 1, various alumina sols having different crystallinity and boric acid were mixed, and a coating solution to which nitric acid was added was prepared in part. A 0.23 mm-thick grain-oriented electrical steel sheet having a finish annealed film manufactured by a normal manufacturing method was prepared, and the coating solution shown in Table 1 was applied at 5 g / m 2 per side and baked at 850 ° C. for 30 seconds. The molar ratio of Al: B in the coating solution is 2: 1. Table 1 shows the stability of the coating liquid, the magnetic properties after the formation of the insulating film, and the insulating film tension. The film tension was calculated from the warpage of the steel sheet when the insulating film was removed with alkali while protecting one side.
[0037]
As shown in Table 1, when an alumina sol having a half-width of (020) diffraction line after drying of 3 degrees or more is used, the film tension obtained is larger than that in the other case, and the iron loss value is It is a lower grain-oriented electrical steel sheet. Such alumina sol can be stably applied by adding nitric acid in an amount of 5% to 80%.
[0038]
[Table 1]
(Example 2)
A 0.23 mm-thick grain-oriented electrical steel sheet having a finish annealed film manufactured by a normal manufacturing method was prepared, and a coating solution composed of boric acid and alumina sol was applied at 4 g / m 2 and baked at 850 ° C. for 60 seconds. As shown in Table 2, the coating solution composed of boric acid and alumina sol has good crystallinity alumina sol ((020) half-value width = 1 degree) and low-crystalline alumina sol ((020) half-value width = 5.2 degrees). Were mixed at various ratios. In addition, a comparison was made between the case where nitric acid was added and the case where nitric acid was not added.
[0040]
The obtained results are shown in Table 2. A coating solution in which 50% or more of a low crystalline alumina sol is mixed as an alumina sol causes gelation when nitric acid is not added, but this is avoided by adding 5% or more and 80 or less nitric acid. Moreover, the coating liquid which mixed 50% or more of low crystalline alumina sol as an alumina sol has obtained the result that the high film | membrane tension | tensile_strength is obtained and the iron loss of a grain-oriented electrical steel sheet becomes low.
[0041]
[Table 2]
(Example 3)
A 0.23 mm-thick grain-oriented electrical steel sheet having a finish annealed film manufactured by a normal manufacturing method is prepared, and a conventional coating liquid mainly composed of colloidal silica and phosphate is applied at 4 g / m 2 to 850 ° C. 1 g / m 2 of a coating solution mainly composed of colloidal silica and phosphate, and then baked at 600 ° C. for 30 seconds, followed by 4 g / m 2 of a coating solution composed of boric acid and alumina sol. And then baked at 850 ° C. for 60 seconds. As shown in Table 3, the coating solution composed of boric acid and alumina sol has good crystallinity alumina sol ((020) half-value width = 1 degree) and low-crystalline alumina sol ((020) half-value width = 5.2 degrees). Were mixed at various ratios, and nitric acid was added.
[0043]
The magnetic properties, insulating film tension, and rust resistance of the obtained grain-oriented electrical steel sheet were investigated. Rust resistance was determined by the presence or absence of occurrence after spraying 5% saline at 50 ° C. for 5 hours. The results are shown in Table 3. The grain-oriented electrical steel sheet obtained by baking the coating liquid of the present invention after thinly forming a conventional coating liquid mainly composed of colloidal silica and phosphate has corrosion resistance comparable to that of the conventional grain-oriented electrical steel sheet using only the coating liquid. In addition, the iron loss is remarkably improved.
[0044]
[Table 3]
(Example 4)
A grain-oriented electrical steel sheet without a finish annealing film having a thickness of 0.22 mm, which has been subjected to finish annealing in accordance with JP-A-8-3648, and having a smooth surface was prepared. Grooves having a depth of 20 μm and a width of 100 μm were formed on the grooved gear roll at intervals of 5 mm in a direction substantially perpendicular to the rolling direction. Thereafter, an SiO 2 film having a thickness of 10 nm was formed on the surface of the steel sheet by annealing or dry coating in a reducing atmosphere. A conventional coating liquid mainly composed of colloidal silica and phosphate was applied at 5 g / m 2 and baked at 850 ° C. for 60 seconds, and a coating liquid composed of boric acid and alumina sol was applied at 5 g / m 2 at 850 ° C. What was baked for 60 seconds was prepared. As the alumina sol, amorphous alumina sol having a half-width of (020) diffraction line after drying of 6 degrees or more was used, and 30% by mass of HNO 3 was added to Al 2 O 3 . The magnetic properties and insulating film tension of the obtained grain-oriented electrical steel sheet were investigated. As shown in Table 4, the coating liquid composed of low crystalline alumina sol and boric acid has a higher film tension than the conventional coating liquid mainly composed of colloidal silica and phosphate, and as a result, extremely low iron loss. Giving value.
[0046]
[Table 4]
【The invention's effect】
According to the present invention, it is possible to form an aluminum borate-based insulating film capable of imparting a significantly larger tension to a grain-oriented electrical steel sheet compared to a conventional insulating film, using a coating liquid with little viscosity change, The iron loss of grain-oriented electrical steel sheets can be significantly improved.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of alumina sol dried at 100 ° C. FIG. (Uses CuKα rays.)
FIG. 2 is a graph showing the influence of nitric acid addition on the change over time in the viscosity of an alumina sol and boric acid mixed solution.
FIG. 3 is a view showing a definition of a half width of an X-ray diffraction line.
FIG. 4 is a graph showing the relationship between crystallinity of alumina sol and film tension.
FIG. 5 is a graph showing the relationship between the blending ratio of low crystalline alumina sol in all alumina sols and film tension.
Claims (6)
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| JP6863473B2 (en) * | 2018-07-31 | 2021-04-21 | Ｊｆｅスチール株式会社 | Insulation coating treatment liquid, grain-oriented electrical steel sheet with insulation coating and its manufacturing method |
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| JP3172025B2 (en) * | 1994-01-13 | 2001-06-04 | 新日本製鐵株式会社 | Method for forming insulating film on unidirectional silicon steel sheet with good adhesion |
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