JP4660945B2 - Method for producing electrical steel sheet with insulating coating - Google Patents
Method for producing electrical steel sheet with insulating coating Download PDFInfo
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- JP4660945B2 JP4660945B2 JP2001076093A JP2001076093A JP4660945B2 JP 4660945 B2 JP4660945 B2 JP 4660945B2 JP 2001076093 A JP2001076093 A JP 2001076093A JP 2001076093 A JP2001076093 A JP 2001076093A JP 4660945 B2 JP4660945 B2 JP 4660945B2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/147—Alloys characterised by their composition
- H01F1/14766—Fe-Si based alloys
- H01F1/14775—Fe-Si based alloys in the form of sheets
- H01F1/14783—Fe-Si based alloys in the form of sheets with insulating coating
Description
【０００１】
【発明の属する技術分野】
本発明は、電磁鋼板にクロムを実質的に含有しない酸性の水系塗液を塗布焼付して絶縁被膜を形成する、絶縁被膜付き電磁鋼板の製造方法であって、外観に優れ、かつ、歪み取り焼鈍をすることができる電磁鋼板を得ることができる電磁鋼板の製造方法に関する。
【０００２】
【従来の技術】
モータ、変圧器等に使用される電磁鋼板の絶縁被膜には、層間抵抗だけでなく、加工成形時および保管時の利便さの観点から、種々の特性が要求される。また、電磁鋼板には、磁気特性を向上させるため、打抜加工後に歪取り焼鈍が行われる場合が多く、この場合には歪取り焼鈍の温度（一般には、７５０〜８５０℃程度）に耐えられるものである必要がある。このように、電磁鋼板は多様な用途に用いられるため、用途に応じて種々の絶縁被膜を有する電磁鋼板の開発が行われている。
【０００３】
絶縁被膜は、（１）溶接性、耐熱性を重視し、歪取り焼鈍に耐えられる無機質被膜、（２）打抜性、溶接性の両立を目指し歪取り焼鈍に耐えられる、樹脂を含有する半有機質被膜、（３）特殊用途に用いられ、歪取り焼鈍をすることができない有機質被膜の３種に大別される。このうち、汎用品として歪取り焼純に耐えられるのは（１）および（２）の無機質を含む被膜であり、特に、（２）の半有機質被膜である、有機樹脂を含有するクロム酸塩系絶縁被膜は、１コート１ベークの製造で、（１）の無機系絶縁被膜と比べて打抜性を格段に向上させることができるので、広く利用されている。
例えば、特公昭６０−３６４７６号公報には、少なくとも１種の２価金属を含む重クロム酸塩系水溶液に、該水溶液中のＣｒＯ3 １００重量部に対し有機樹脂として酢酸ビニル／ベオバ比が９０／１０〜４０／６０の比率になる樹脂エマルションを樹脂固形分で５〜１２０重量部および有機還元剤を１０〜６０重量部の割合で配合した処理液を生地鉄板の表面に塗布し、常法による焼き付け工程を経て被膜を得ることを特徴とする電磁鋼板の絶縁被膜形成法が記載されている。
【０００４】
これに対し、昨今においては、環境意識が高まる傾向にあり、電磁鋼板の製造工程または需要家においてクロム化合物がより少ない絶縁被膜またはクロム化合物を全く含まない絶縁被膜が望まれてきている。例えば、クロム化合物を含まず、打ち抜き性が良好な絶縁被膜として、樹脂およびシリカを含有するものが提案されている（特開平１０−３４８１２号公報等）。
【０００５】
【発明が解決しようとする課題】
しかし、このクロム化合物を実質的に含有しない水系塗液、例えば、樹脂および無機コロイドを成分とする水系塗液を電磁鋼板に塗布焼付した場合、水系塗液が酸性であると、鋼板のＦｅ成分が溶出して不透明な被膜部分が発生し、外観および被膜状態が劣ったものになることがあるという問題があった。特に、被膜厚みが薄い絶縁被膜を得る場合に、問題となることが多かった。一方で、水系塗液に含有される樹脂や無機物質の性質から、酸性の水系塗液を使用することに対する要望は多い。
【０００６】
本発明は、上述した問題点を解決すべくなされたものである。即ち、本発明は、クロム化合物を実質的に含有しない、樹脂および無機コロイドを成分とする酸性の水系塗液を電磁鋼板に塗布焼付し薄膜の絶縁被膜を形成させた場合においても、Ｆｅの溶出が抑制され外観および被膜状態が良好なものとなる、絶縁被膜付き電磁鋼板の製造方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明者は、塗液がクロム化合物を含有する場合には、塗液が酸性であってもクロムが不動態皮膜を生成するためＦｅ溶出が起こりにくいが、塗液がクロム化合物を実質的に含有しない場合には、そのような効果がないためＦｅ溶出が起こるのだと考えた。また、電磁鋼板の場合は、通常の表面処理鋼板のように防錆のためのメッキ等が施されないため、Ｆｅ溶出を抑えて良好な被膜を得ることは難しい。そして、上記問題は、被膜厚みが薄い絶縁被膜を得る場合において、塗布から焼付までの時間が長いときや、製鉄所で汎用されているコークスガスを燃料として直火で塗布焼付するときなどに、特に顕著となることが分かった。
【０００８】
更に、本発明者は、酸性の水系塗液を用いて被膜厚みが薄い絶縁被膜を得る場合に生じる上記問題を解決すべく、鋭意研究した。その結果、装置上の都合等のため、塗布から焼付までの時間が長いときには、塗液と鋼板との反応時間が長くなり酸化が進みやすいこと、および、コークスガス焼付した場合には、コークスガスを燃焼したときに発生するＳＯ2 ガス等により酸化が進みやすいことを見出した。そして、本発明者は、これらの二つの酸化機構においては、本質的には同等のことが起きていると考えた。即ち、絶縁被膜が薄い場合には塗液中の酸素のやり取りが多く、酸化反応がより進みやすくなっているものと考えた。
そして、本発明者は、水系塗液の固形分濃度を特定範囲とすることにより、上記酸化反応を抑制することができることを見出し、本発明を完成した。
【０００９】
即ち、本発明は、電磁鋼板に樹脂および無機成分を含有するｐＨ２〜７の水系塗液を塗布焼付し、被膜焼付量が２ｇ／ｍ2 以下でありクロム含有量が０〜１質量％である絶縁被膜を形成する、絶縁被膜付き電磁鋼板の製造方法であって、該水系塗液の固形分濃度が１０〜３０質量％であることを特徴とする絶縁被膜付き電磁鋼板の製造方法を提供する。
【００１０】
前記水系塗液が、ｐＨ３〜６であるのが好ましい。
【００１１】
前記樹脂が水性樹脂として供給されるのが好ましく、また、前記無機成分が無機コロイドとして供給されるのが好ましい。
【００１２】
【発明の実施の形態】
以下、本発明について詳細に説明する。
本発明においては、出発素材として電磁鋼板（電気鉄板）が用いられる。本発明に用いられる電磁鋼板は、特に限定されない。
【００１３】
本発明に用いられる水系塗液は、樹脂および無機物質を含有し、かつ、ｐＨ２〜７である。
【００１４】
本発明に用いられる水系塗液は、溶媒として水を含有する塗液である。したがって、水以外に他の溶媒を含有していてもよい。
本発明に用いられる水系塗液の態様は、特に限定されず、例えば、エマルション（乳濁液）、ディスパージョン、水溶液が挙げられる。
【００１５】
本発明に用いられる水系塗液に含有される樹脂は、特に限定されないが、例えば、アクリル樹脂、アルキド樹脂、ポリオレフィン樹脂、スチレン樹脂、酢酸ビニル樹脂、エポキシ樹脂、フェノール樹脂、ウレタン樹脂、メラミン樹脂が挙げられる。これらは単独で用いてもよく、２種以上を併用してもよい。樹脂は、ガラス転移点が３０〜１５０℃であるものが好ましい。
樹脂は、塗液の分散性の点から、水性樹脂で供給されるのが好ましい。水性樹脂は、エマルション、ディスパージョン、水溶性の形態をとることができる。粒子の形状、粒子径、乳化剤、保護コロイド、電荷等は、特に限定されず、樹脂および用途に応じて、選択することができる。
【００１６】
また、本発明に用いられる水系塗液に含有される無機成分は、特に限定されないが、例えば、シリカ、アルミナ、酸化チタン、酸化アンチモンが挙げられる。これらは単独で用いてもよく、２種以上を併用してもよい。
無機成分は、無機コロイドとして水系塗液に供給されるのが好ましい。例えば、コロイダルシリカ、アルミナゾル、酸化チタンゾルが挙げられる。
【００１７】
上述した無機成分の中でも、シリカが好ましい。特に、酸性の水系塗液中でのコロイド安定性に優れる点で、アルミナ処理シリカ（シリカ表面にアルミナをコーティングしたもの）および／またはアルミナ含有シリカが好ましい。
【００１８】
なお、本発明に用いられる水系塗液は、後述するようにクロム含有量が０〜１質量％である絶縁被膜を形成するために用いられるので、クロム化合物を実質的に含有しないものである。
また、本発明に用いられる水系塗液は、被膜の性能を一層向上させるなどのために、防錆剤等の添加剤を含有することができる。添加剤を含有する場合、歪取り焼鈍後の性能を確保するために、塗液中の無機物質の合計量が、塗液中の固形分１００質量部に対し、３〜３００質量部であるのが好ましい。
【００１９】
本発明に用いられる水系塗液は、ｐＨ２以上であり、かつ、ｐＨ７以下である。上記範囲において、上述した鋼板のＦｅ成分が溶出し、外観および被膜状態が劣るという問題が生じるからである。また、この問題は、水系塗液がｐＨ６以下の場合に起こりやすいので、本発明は、水系塗液がｐＨ６以下である場合に好適に用いられる。水系塗液がｐＨ３以上であると、分散性が特に優れたものとなるので好ましい。
【００２０】
本発明においては、本発明に用いられる水系塗液が、固形分濃度が１０〜３０質量％であることを特徴とする。ここで、「固形分濃度」とは、塗液から水、有機溶媒等の塗布焼付時に揮発する成分を除いたものの質量の塗液全体の質量に対する割合である。
水系塗液の固形分濃度が１０質量％以上であると、Ｆｅの溶出を抑制することができ、外観および被膜状態に優れた絶縁被膜が得られ、しかも焼付後の被膜厚みの均一性もさほど劣化しない。
一方、水系塗液の固形分濃度が高すぎると、粘性が増加して泡立ちやすくなったり、沈殿が生じやすくなったりするという問題があり、また、外観および被膜状態、ならびに、焼付後の被膜厚みの均一性も劣化する。水系塗液の固形分濃度が３０質量％以下であると、このような問題が生じない。
【００２１】
本発明の絶縁被膜付き電磁鋼板の製造方法においては、電磁鋼板に上述したような水系塗液を塗布焼付し、被膜焼付量が２ｇ／ｍ2 以下でありクロム含有量が０〜１質量％である絶縁被膜を形成する。
【００２２】
本発明においては、塗布焼付の前に、鋼板に対して前処理を行うことができる。鋼板に対する前処理は行ってもよく、行わなくてもよい。鋼板に対する前処理は、特に限定されず、例えば、アルカリ等を用いた脱脂処理；塩酸、硫酸、リン酸等を用いた酸洗処理が好適に挙げられる。
【００２３】
未処理の鋼板、または、上述したような前処理を行った鋼板に対して、塗布焼付を行う。
本発明において、塗布焼付の方法は特に限定されず、工業的に一般に用いられる塗布方法および焼付方法を用いることができる。塗布方法は、例えば、ロールコーター法、フローコーター法、スプレー法、ナイフコーター法が挙げられる。焼付方法は、例えば、熱風式、赤外式、誘導加熱式の焼付方法が挙げられる。
【００２４】
本発明においては、被膜焼付量は２ｇ／ｍ2 以下である。被膜焼付量が２ｇ／ｍ2 以下となる程度に被膜厚みが薄い場合に、Ｆｅ溶出により外観および被膜状態が悪くなりやすいからである。また、被膜焼付量が２ｇ／ｍ2 を超えると、被膜の密着性が低下し、また、高温乾燥時にふくれが発生するなど塗装性が低下する場合がある。被膜焼付量は、１．８ｇ／ｍ2 以下であるのが好ましい。
また、被膜焼付量は０．０５ｇ／ｍ2 以上であるのが好ましい。付着量が０．０５ｇ／ｍ2 未満であると、被膜厚みが不均一になって地鉄が露出しやすく、スティッキング性および沸騰水蒸気曝露性が不足する場合がある。被膜焼付量は、０．１ｇ／ｍ2 以上であるのがより好ましい。
【００２５】
本発明により得られる絶縁被膜は、クロム含有量が０〜１質量％である。ここで、「クロム含有量」は、絶縁被膜中に含まれる六価クロム化合物のＣｒ換算での絶縁被膜全体に対する質量比である。
クロム含有量が多い場合には、Ｆｅ溶出により外観および被膜状態が劣ったものになるという問題がないが、クロム含有量が多すぎると、電磁鋼板の製造工程等において環境に対する負荷が多くなる。本発明は、実質的にクロム化合物を含有しない絶縁被膜、即ち、クロム化合物を全く含有しないか、または、クロム化合物をわずかに含有するかのいずれかの絶縁被膜を製造する場合におけるＦｅ溶出により生じる外観および被膜状態の問題を解決すべくなされたものであり、クロム含有量を上記範囲とした。したがって、本発明においては、絶縁被膜におけるクロムは、任意成分であり、全く含有していなくてもよく、１質量％以下の濃度で含有していてもよい。
【００２６】
本発明の絶縁被膜付き電磁鋼板の製造方法によれば、得られる絶縁被膜の外観および被膜状態が優れたものとなる。
上述したように、クロム化合物を実質的に含有しない酸性の水系塗液を電磁鋼板に塗布焼付し、被膜厚みが薄い絶縁被膜を得ようとする場合、鋼板のＦｅ成分が溶出して不透明な被膜部分が発生し、外観および被膜状態が劣ったものになることがあるという問題があった。特に、塗布から焼付までの時間が長いとき、および、コークスガス直火で焼き付けたときにこの問題は顕著であった。これは、クロム化合物を実質的に含有しない酸性の水系塗液においては、クロムの不動態効果が発揮されないため、鋼板のＦｅが溶出しやすいからである。
【００２７】
従来、被膜厚み２ｇ／ｍ2 以下程度の薄い絶縁被膜を塗布焼付する場合には、塗布ロール等と鋼板との接触焼付きを防ぎ、被膜厚みの均一性を確保するため、塗液の固形分濃度を数質量％程度にしていた。
本発明者は、Ｆｅの溶出反応を抑制する方法を鋭意研究した結果、意外にも水系塗液の固形分濃度がＦｅ溶出反応に及ぼす影響が甚大であることを知見し、本発明に至ったのである。即ち、本発明においては、水系塗液の固形分濃度を１０質量％以上にすることにより、Ｆｅの溶出を抑制し、外観および被膜状態を優れたものとし、更に、焼付後の被膜厚みの均一性も確保したのである。
本発明において、固形分濃度が１０質量％以上の水系塗液を用いた場合にＦｅの溶出が抑制されるメカニズムは、Ｆｅ溶出反応、即ち、錆の発生に必要な水分量が少なくなるためと考えられる。逆に、固形分濃度が低く水分量が多い場合は、水と接触している時間、即ち、水との反応時間が長くなるため、Ｆｅ溶出反応自体が速く進行するのだと考えられる。
【００２８】
【実施例】
以下に実施例を示して本発明を具体的に説明するが、本発明はこれらに限られるものではない。
１．絶縁被膜付き電磁鋼板の製造
（実施例１）
板厚０．５ｍｍ、幅１５０ｍｍ、長さ３００ｍｍの電磁鋼板をアルカリ脱脂した後、第１表に記載のエポキシ樹脂およびコロイダルシリカ（アルミナ処理シリカ）を含有する、固形分濃度が１０質量％のｐＨ４．０の塗液（固形分の質量比：エポキシ樹脂／コロイダルシリカ＝５０／５０）をロールコーターで塗布した。その後、到達板温２００℃となるようにプロパンガス直火焼付を行い、放冷して、エポキシ樹脂およびアルミナ処理シリカを含有する被膜を形成させ、絶縁被膜付き電磁鋼板を得た。
【００２９】
（実施例２〜１４および比較例１〜１４）
塗液成分（樹脂および無機成分）、塗液の固形分濃度、塗液のｐＨおよび被膜焼付量を第１表に示すようにした以外は、実施例１と同様の方法により、絶縁被膜付き電磁鋼板を得た。ただし、比較例２は、塗液の固形分濃度が高すぎ、均一に塗布することができなかった。また、比較例１３および１４は、塗液の分散状態が悪く、塗布することができなかった。
【００３０】
２．評価
（１）塗液の分散状態
用いた塗液の分散状態を目視により評価した。評価の結果は、第１表中に以下の記号で表した。
○：均一に分散していた
△：やや凝集しており、増粘した
×：凝集によりゲル化した
【００３１】
（２）被膜の密着性
セロハンテープを絶縁被膜付き電磁鋼板の被膜面に貼り付けた後、はがし、被膜がはく離するかどうかを目視観察し、塗膜の密着性を評価した。評価の結果は、第１表中に以下の記号で表した。
○：はく離しなかった
△：若干はく離した
×：はく離した
【００３２】
（３）外観・被膜状態
ロールコーターで塗布してから焼付を開始するまでの時間を１５秒、３０秒、６０秒と変化させて絶縁被膜付き電磁鋼板の製造を行い、Ｆｅ溶出による外観および被膜状態の悪化の有無を目視観察により評価した。評価の結果は、第１表中に以下の記号で表した。
○：良好（無色透明な被膜が得られた）
△：若干悪かった（不透明な部分や、変色が若干見られた）
×：悪かった（斑点状の不透明部分が多く見られ醜かった）
××：非常に悪かった（被膜全面が不透明であり、明らかに不良であった）
【００３３】
第１表から明らかなように、本発明の絶縁被膜付き電磁鋼板の製造方法（実施例１〜１４）は、いずれも得られた絶縁被膜付き電磁鋼板の外観および被膜状態に優れることが分かる。
これに対し、水系塗液の固形分濃度が低すぎる場合（比較例３〜７および１０〜１２）は、Ｆｅが溶出するため、外観および被膜状態に劣る。また、水系塗液の固形分濃度が高すぎる場合（比較例１および２）は、被膜の密着性に劣るか、または、均一に塗布することができないかである。
被膜焼付量が多すぎる場合は、被膜の密着性に劣る（比較例８および９）。
ｐＨが低すぎる場合（比較例１３および１４）は、塗液の分散状態が悪く、塗布することができない。
【００３４】
【表１】
【表２】
第１表中、絶縁被膜の欄の「エポキシ／シリカ」は、エポキシ樹脂／コロイダルシリカ＝５０／５０（固形分の質量比）の塗液を用いて得た被膜を意味し、「アクリル／シリカ」は、アクリル樹脂／コロイダルシリカ＝５０／５０（固形分の質量比）の塗液を用いて得た被膜を意味する。また、「被膜中クロム」の欄は、被膜が無機成分として更に重クロム酸マグネシウムを含有する場合のＣｒ換算の含有量を示す。
【００３７】
【発明の効果】
本究明の絶縁被膜付き電磁鋼板の製造方法によれば、クロム化合物を実質的に含有しない酸性の水系塗液を電磁鋼板に塗布焼付し薄膜の絶縁被膜を形成させた場合においても、外観および被膜状態に優れた電磁鋼板の絶縁被膜を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention is a method for producing an electrical steel sheet with an insulating coating, which forms an insulating coating by applying and baking an acidic aqueous coating solution substantially free of chromium on the electrical steel plate, having an excellent appearance, and removing distortion. The present invention relates to a method for manufacturing an electrical steel sheet capable of obtaining an electrical steel sheet that can be annealed.
[0002]
[Prior art]
Various properties are required for insulating coatings of electrical steel sheets used for motors, transformers and the like from the viewpoint of convenience during processing and storage as well as interlayer resistance. Further, in order to improve magnetic properties, electromagnetic steel sheets are often subjected to strain relief annealing after punching, and in this case, they can withstand the temperature of strain relief annealing (generally about 750 to 850 ° C.). It needs to be a thing. As described above, electrical steel sheets are used for various applications, and therefore, electrical steel sheets having various insulating coatings have been developed according to the applications.
[0003]
The insulating coating is (1) an inorganic coating that emphasizes weldability and heat resistance and can withstand strain relief annealing, and (2) a semi-resin containing resin that can withstand strain relief annealing to achieve both punchability and weldability. Organic coatings (3) There are three types of organic coatings that are used for special purposes and cannot be strain-annealed. Among these, a general-purpose product that can withstand strain-relief pure is a coating containing an inorganic substance of (1) and (2), and in particular, a chromate containing an organic resin, which is a semi-organic coating of (2). The system insulating film is widely used since it can be significantly improved in punching performance as compared with the inorganic insulating film of (1) in the production of one coat and one bake.
For example, in Japanese Patent Publication No. 60-36476, a dichromate aqueous solution containing at least one divalent metal has a vinyl acetate / veova ratio of 90 as an organic resin with respect to 100 parts by weight of CrO 3 in the aqueous solution. A processing solution in which a resin emulsion having a ratio of / 10 to 40/60 is blended in a ratio of 5 to 120 parts by weight of a resin solid content and an organic reducing agent in a ratio of 10 to 60 parts by weight is applied to the surface of the dough iron plate. A method for forming an insulating coating on an electrical steel sheet, characterized in that a coating is obtained through a baking step according to the above, is described.
[0004]
On the other hand, in recent years, environmental consciousness tends to increase, and an insulating coating containing less chromium compound or an insulating coating containing no chromium compound has been desired in the manufacturing process or consumers of electrical steel sheets. For example, an insulating coating that does not contain a chromium compound and has good punchability has been proposed that contains a resin and silica (Japanese Patent Laid-Open No. 10-34812, etc.).
[0005]
[Problems to be solved by the invention]
However, when an aqueous coating liquid that does not substantially contain this chromium compound, for example, an aqueous coating liquid containing resin and inorganic colloid as a component is applied and baked on an electromagnetic steel sheet, the Fe component of the steel sheet is said to be acidic. Elution occurs to produce an opaque coating portion, which may cause the appearance and the coating state to be inferior. In particular, when an insulating coating having a thin coating thickness is obtained, there are many problems. On the other hand, due to the nature of the resin and inorganic substances contained in the aqueous coating liquid, there is a great demand for using an acidic aqueous coating liquid.
[0006]
The present invention has been made to solve the above-described problems. In other words, the present invention is effective in elution of Fe even when an acidic aqueous coating solution containing substantially no chromium compound and containing resin and inorganic colloid is applied and baked on a magnetic steel sheet to form a thin insulating film. An object of the present invention is to provide a method for producing an electrical steel sheet with an insulating coating, in which the appearance and the coating state are improved.
[0007]
[Means for Solving the Problems]
When the coating liquid contains a chromium compound, the present inventor does not easily cause Fe elution because chromium forms a passive film even if the coating liquid is acidic, but the coating liquid substantially contains the chromium compound. When not contained, it was thought that Fe elution occurred because there was no such effect. Moreover, in the case of an electromagnetic steel sheet, unlike a normal surface-treated steel sheet, plating for rust prevention or the like is not performed, and thus it is difficult to obtain a good coating by suppressing Fe elution. And, when the above-mentioned problem is to obtain an insulating coating with a thin coating thickness, when the time from application to baking is long, or when applying and baking with a direct fire as a coke gas widely used in steelworks, etc. It turned out to be particularly remarkable.
[0008]
Furthermore, the present inventor has intensively studied in order to solve the above-described problems that occur when an insulating coating having a thin coating thickness is obtained using an acidic aqueous coating solution. As a result, due to the convenience of the equipment, when the time from application to baking is long, the reaction time between the coating liquid and the steel plate becomes long, and oxidation tends to proceed, and in the case of coke gas baking, coke gas It has been found that oxidation is likely to proceed due to SO 2 gas generated when the gas is burned. The present inventor thought that essentially the same thing occurred in these two oxidation mechanisms. That is, it was considered that when the insulating coating was thin, there was much exchange of oxygen in the coating solution, and the oxidation reaction was easier to proceed.
And this inventor discovered that the said oxidation reaction could be suppressed by making solid content concentration of aqueous | water-based coating liquid into a specific range, and completed this invention.
[0009]
That is, in the present invention, an aqueous steel sheet containing a resin and an inorganic component and having a pH of 2 to 7 is applied and baked on a magnetic steel sheet, the film baking amount is 2 g / m 2 or less, and the chromium content is 0 to 1% by mass. Provided is a method for producing an electrical steel sheet with an insulating coating, which forms an insulating coating, wherein the solid content concentration of the aqueous coating liquid is 10 to 30% by mass. .
[0010]
The aqueous coating liquid preferably has a pH of 3 to 6.
[0011]
The resin is preferably supplied as an aqueous resin, and the inorganic component is preferably supplied as an inorganic colloid.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
In the present invention, an electromagnetic steel plate (electric iron plate) is used as a starting material. The electrical steel sheet used in the present invention is not particularly limited.
[0013]
The aqueous coating liquid used in the present invention contains a resin and an inorganic substance, and has a pH of 2 to 7.
[0014]
The aqueous coating liquid used in the present invention is a coating liquid containing water as a solvent. Therefore, other solvents may be contained in addition to water.
The aspect of the aqueous coating liquid used in the present invention is not particularly limited, and examples thereof include emulsions (emulsions), dispersions, and aqueous solutions.
[0015]
The resin contained in the aqueous coating liquid used in the present invention is not particularly limited. For example, acrylic resin, alkyd resin, polyolefin resin, styrene resin, vinyl acetate resin, epoxy resin, phenol resin, urethane resin, and melamine resin can be used. Can be mentioned. These may be used alone or in combination of two or more. The resin preferably has a glass transition point of 30 to 150 ° C.
The resin is preferably supplied as an aqueous resin from the viewpoint of dispersibility of the coating liquid. The aqueous resin can take an emulsion, dispersion, or water-soluble form. The shape, particle diameter, emulsifier, protective colloid, charge and the like of the particles are not particularly limited, and can be selected according to the resin and application.
[0016]
Moreover, the inorganic component contained in the water-based coating liquid used in the present invention is not particularly limited, and examples thereof include silica, alumina, titanium oxide, and antimony oxide. These may be used alone or in combination of two or more.
The inorganic component is preferably supplied to the aqueous coating liquid as an inorganic colloid. Examples thereof include colloidal silica, alumina sol, and titanium oxide sol.
[0017]
Among the inorganic components described above, silica is preferable. In particular, alumina-treated silica (silica surface coated with alumina) and / or alumina-containing silica is preferable because it is excellent in colloidal stability in an acidic aqueous coating solution.
[0018]
In addition, since the aqueous coating liquid used for this invention is used in order to form the insulating film whose chromium content is 0-1 mass% so that it may mention later, it does not contain a chromium compound substantially.
Moreover, the aqueous coating liquid used in the present invention can contain additives such as a rust preventive agent in order to further improve the performance of the coating film. When the additive is contained, in order to ensure the performance after strain relief annealing, the total amount of inorganic substances in the coating liquid is 3 to 300 parts by mass with respect to 100 parts by mass of the solid content in the coating liquid. Is preferred.
[0019]
The aqueous coating liquid used in the present invention has a pH of 2 or more and a pH of 7 or less. This is because, within the above range, the Fe component of the steel sheet described above is eluted, resulting in a problem of poor appearance and coating state. Moreover, since this problem is likely to occur when the aqueous coating liquid is pH 6 or lower, the present invention is suitably used when the aqueous coating liquid is pH 6 or lower. It is preferable for the aqueous coating liquid to have a pH of 3 or higher because the dispersibility is particularly excellent.
[0020]
In the present invention, the aqueous coating liquid used in the present invention has a solid content concentration of 10 to 30% by mass. Here, the “solid content concentration” is the ratio of the mass of the coating liquid excluding components that volatilize during coating and baking such as water and organic solvent to the total mass of the coating liquid.
When the solid content concentration of the aqueous coating liquid is 10% by mass or more, the elution of Fe can be suppressed, an insulating film excellent in appearance and film state can be obtained, and the uniformity of the film thickness after baking is also great. Does not deteriorate.
On the other hand, if the solid content concentration of the aqueous coating solution is too high, there is a problem that the viscosity increases and foaming is likely to occur, or precipitation is likely to occur. Also, the appearance and coating state, and the coating thickness after baking The uniformity of the is also degraded. Such a problem does not occur when the solid content concentration of the aqueous coating liquid is 30% by mass or less.
[0021]
In the method for producing an electrical steel sheet with an insulating coating according to the present invention, the above-described aqueous coating liquid is applied and baked onto the electrical steel sheet, the coating baking amount is 2 g / m 2 or less, and the chromium content is 0 to 1% by mass. An insulating film is formed.
[0022]
In the present invention, the pretreatment can be performed on the steel plate before the application baking. The pretreatment for the steel plate may or may not be performed. The pretreatment for the steel sheet is not particularly limited, and preferred examples include degreasing treatment using an alkali or the like; pickling treatment using hydrochloric acid, sulfuric acid, phosphoric acid, or the like.
[0023]
Application baking is performed on an untreated steel plate or a steel plate that has been pretreated as described above.
In the present invention, the coating and baking method is not particularly limited, and a coating method and a baking method generally used industrially can be used. Examples of the coating method include a roll coater method, a flow coater method, a spray method, and a knife coater method. Examples of the baking method include a hot air type, an infrared type, and an induction heating type baking method.
[0024]
In the present invention, the film baking amount is 2 g / m 2 or less. This is because, when the coating thickness is so thin that the coating baking amount is 2 g / m 2 or less, the appearance and coating state are likely to deteriorate due to Fe elution. On the other hand, if the coating baking amount exceeds 2 g / m 2 , the adhesion of the coating is lowered, and the paintability may be lowered, for example, blistering occurs at high temperature drying. The film baking amount is preferably 1.8 g / m 2 or less.
Moreover, it is preferable that the film baking amount is 0.05 g / m 2 or more. When the adhesion amount is less than 0.05 g / m 2 , the coating thickness becomes non-uniform, and the base iron is likely to be exposed, and sticking property and boiling water vapor exposure property may be insufficient. The film baking amount is more preferably 0.1 g / m 2 or more.
[0025]
The insulating coating obtained by the present invention has a chromium content of 0 to 1% by mass. Here, the “chromium content” is a mass ratio of the hexavalent chromium compound contained in the insulating coating to the entire insulating coating in terms of Cr.
When the chromium content is high, there is no problem that the appearance and the coating state are inferior due to Fe elution, but when the chromium content is too high, the load on the environment increases in the manufacturing process of the electromagnetic steel sheet. The present invention arises from Fe elution in the production of an insulating coating that is substantially free of chromium compounds, i.e., either contains no chromium compounds or contains little chromium compounds. The present invention was made to solve the problems of appearance and coating state, and the chromium content was within the above range. Therefore, in the present invention, chromium in the insulating coating is an optional component and may not be contained at all, and may be contained at a concentration of 1% by mass or less.
[0026]
According to the method for manufacturing an electrical steel sheet with an insulating coating of the present invention, the appearance and the coating state of the resulting insulating coating are excellent.
As described above, when an acidic aqueous coating solution substantially free of a chromium compound is applied and baked on a magnetic steel sheet to obtain an insulating film with a thin film thickness, the Fe component of the steel sheet is eluted and an opaque film There existed a problem that a part generate | occur | produced and an external appearance and a film state may become inferior. In particular, this problem was remarkable when the time from application to baking was long and when baking was performed with coke gas direct flame. This is because, in an acidic water-based coating liquid that does not substantially contain a chromium compound, the passive effect of chromium is not exerted, so that Fe of the steel sheet is likely to be eluted.
[0027]
Conventionally, when a thin insulating film having a coating thickness of 2 g / m 2 or less is applied and baked, in order to prevent contact baking between the coating roll and the steel sheet and to ensure the uniformity of the coating thickness, The concentration was about several mass%.
As a result of diligent research on a method for suppressing the elution reaction of Fe, the present inventor has unexpectedly found that the influence of the solid content concentration of the aqueous coating liquid on the Fe elution reaction is enormous, and led to the present invention. It is. That is, in the present invention, by making the solid content concentration of the aqueous coating liquid 10% by mass or more, the elution of Fe is suppressed, the appearance and the coating state are excellent, and the coating thickness after baking is uniform. The sex was also secured.
In the present invention, when an aqueous coating liquid having a solid content concentration of 10% by mass or more is used, the mechanism for suppressing the elution of Fe is that the amount of water necessary for Fe elution reaction, that is, the generation of rust is reduced. Conceivable. On the contrary, when the solid content concentration is low and the water content is large, the time of contact with water, that is, the reaction time with water becomes longer, so the Fe elution reaction itself is considered to proceed faster.
[0028]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
1. Production of electrical steel sheet with insulation coating (Example 1)
PH 4 with a solid content concentration of 10% by mass containing an epoxy resin and colloidal silica (alumina-treated silica) listed in Table 1 after alkaline degreasing of a steel sheet having a thickness of 0.5 mm, a width of 150 mm, and a length of 300 mm 0.0 coating liquid (mass ratio of solid content: epoxy resin / colloidal silica = 50/50) was applied with a roll coater. Thereafter, propane gas direct baking was performed so that the ultimate plate temperature was 200 ° C., and the film was allowed to cool to form a film containing an epoxy resin and alumina-treated silica, thereby obtaining an electrical steel sheet with an insulating film.
[0029]
(Examples 2-14 and Comparative Examples 1-14)
An electromagnetic wave with an insulating coating is produced in the same manner as in Example 1 except that the coating liquid components (resin and inorganic components), the solid content concentration of the coating liquid, the pH of the coating liquid, and the coating baking amount are as shown in Table 1. A steel plate was obtained. However, in Comparative Example 2, the solid content concentration of the coating liquid was too high and could not be applied uniformly. In Comparative Examples 13 and 14, the dispersion state of the coating liquid was poor and could not be applied.
[0030]
2. Evaluation (1) Dispersion state of coating liquid The dispersion state of the coating liquid used was evaluated visually. The results of the evaluation are represented by the following symbols in Table 1.
○: Uniformly dispersed Δ: Slightly aggregated and thickened ×: Gelled by aggregation [0031]
(2) Film adhesion The cellophane tape was affixed to the film surface of the electrical steel sheet with an insulation film, and then peeled off. The film was visually observed to determine whether the film peeled, and the adhesion of the film was evaluated. The results of the evaluation are represented by the following symbols in Table 1.
○: not peeled △: peeled slightly ×: peeled [0032]
(3) Appearance / coating state The time from coating with a roll coater to the start of baking is changed to 15 seconds, 30 seconds, and 60 seconds to produce an insulating steel sheet with an insulating coating. The presence or absence of state deterioration was evaluated by visual observation. The results of the evaluation are represented by the following symbols in Table 1.
○: Good (colorless and transparent film was obtained)
Δ: Slightly bad (opaque parts and slight discoloration were observed)
×: Bad (a lot of speckled opaque parts were seen and ugly)
Xx: It was very bad (the whole surface of the film was opaque and was clearly poor)
[0033]
As is apparent from Table 1, it can be seen that the method for producing an electrical steel sheet with an insulating coating of the present invention (Examples 1 to 14) is excellent in the appearance and the coating state of the electrical steel sheet with an insulating coating obtained.
On the other hand, when the solid content concentration of the aqueous coating liquid is too low (Comparative Examples 3 to 7 and 10 to 12), since Fe is eluted, the appearance and the coating state are inferior. Moreover, when the solid content concentration of an aqueous coating liquid is too high (Comparative Examples 1 and 2), it is inferior to the adhesiveness of a film, or cannot be applied uniformly.
When there is too much film baking amount, it is inferior to the adhesiveness of a film (Comparative Examples 8 and 9).
When pH is too low (Comparative Examples 13 and 14), the dispersion state of the coating liquid is poor and cannot be applied.
[0034]
[Table 1]
[Table 2]
In Table 1, “epoxy / silica” in the column of insulating coating means a coating obtained using a coating solution of epoxy resin / colloidal silica = 50/50 (mass ratio of solid content), and “acrylic / silica”. "Means a coating obtained using a coating liquid of acrylic resin / colloidal silica = 50/50 (mass ratio of solid content). The column “Chromium in coating” indicates the content in terms of Cr when the coating further contains magnesium dichromate as an inorganic component.
[0037]
【The invention's effect】
According to the method for producing an electrical steel sheet with an insulating coating of the present study, even when an acidic aqueous coating liquid that does not substantially contain a chromium compound is applied and baked on the electrical steel sheet, the appearance and the coating are formed. It is possible to obtain an insulating coating film of an electromagnetic steel sheet excellent in state.
Claims (3)
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| JP2001076093A JP4660945B2 (en) | 2001-03-16 | 2001-03-16 | Method for producing electrical steel sheet with insulating coating |
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| JP2001076093A JP4660945B2 (en) | 2001-03-16 | 2001-03-16 | Method for producing electrical steel sheet with insulating coating |
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0578855A (en) * | 1991-09-25 | 1993-03-30 | Nisshin Steel Co Ltd | Composition for forming magnetic steel sheet insulating film and method therefor |
| JPH07268641A (en) * | 1994-03-31 | 1995-10-17 | Kawasaki Steel Corp | Silicon steel sheet with electrically insulating coating film excellent in corrosion resistance |
| JPH09263951A (en) * | 1996-03-29 | 1997-10-07 | Nippon Steel Corp | Production of low core loss grain oriented silicon steel sheet |
| JPH09323066A (en) * | 1996-06-07 | 1997-12-16 | Kawasaki Steel Corp | Silicon steel sheet capable of stress relief annealing and provided with insulating coating film excellent in resistance to corrosion and solvent and formation of the insulating coating film |
| JPH1036976A (en) * | 1996-07-24 | 1998-02-10 | Kawasaki Steel Corp | Silicon steel sheet with insulating coating film producible by low temperature baking, capable of stress relieving annealing and good in solvent resistance |
| JPH11350157A (en) * | 1998-06-09 | 1999-12-21 | Toyobo Co Ltd | Surface treating agent free from chromium and surface treated metal material |
-
2001
- 2001-03-16 JP JP2001076093A patent/JP4660945B2/en not_active Expired - Lifetime
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0578855A (en) * | 1991-09-25 | 1993-03-30 | Nisshin Steel Co Ltd | Composition for forming magnetic steel sheet insulating film and method therefor |
| JPH07268641A (en) * | 1994-03-31 | 1995-10-17 | Kawasaki Steel Corp | Silicon steel sheet with electrically insulating coating film excellent in corrosion resistance |
| JPH09263951A (en) * | 1996-03-29 | 1997-10-07 | Nippon Steel Corp | Production of low core loss grain oriented silicon steel sheet |
| JPH09323066A (en) * | 1996-06-07 | 1997-12-16 | Kawasaki Steel Corp | Silicon steel sheet capable of stress relief annealing and provided with insulating coating film excellent in resistance to corrosion and solvent and formation of the insulating coating film |
| JPH1036976A (en) * | 1996-07-24 | 1998-02-10 | Kawasaki Steel Corp | Silicon steel sheet with insulating coating film producible by low temperature baking, capable of stress relieving annealing and good in solvent resistance |
| JPH11350157A (en) * | 1998-06-09 | 1999-12-21 | Toyobo Co Ltd | Surface treating agent free from chromium and surface treated metal material |
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| JP2002275640A (en) | 2002-09-25 |
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