JP3833861B2 - Method for producing oxide magnetic body - Google Patents

Description

【００６１】
本発明で用いる分散剤は粉砕によるメカノケミカル反応で、その構造が変化する可能性がある。
【００６２】
さらに例えば加水分解反応などにより、本発明で用いる分散剤と同一の有機化合物を生成するような化合物、例えばエステルなどを添加することによっても本発明の目的を達成できる可能性もある。
【００６３】
なお、分散剤は２種以上を併用してもよい。このときに併用する分散剤は本発明の範囲に限定されない。
【００６４】
分散剤の添加量は、酸化物磁性体粒子である仮焼体粒子に対し、好ましくは０．０５〜５．０重量％、より好ましくは０．１〜３．０重量％、さらに好ましくは０．３〜２．０重量％、最も好ましくは０．５〜１．５重量％である。分散剤が少なすぎると配向度の向上が不十分となる。一方、分散剤が多すぎると、成形体や焼結体にクラックが発生しやすくなる。
【００６５】
分散剤の添加時期は特に限定されず、乾式粗粉砕時に添加してもよく、湿式粉砕時の粉砕用スラリー調製の際に添加してもよく、一部を乾式粗粉砕の際に添加し、残部を湿式粉砕の際に添加してもよい。あるいは、湿式粉砕後に撹拌などによって添加してもよい。いずれの場合でも、成形用スラリー中に分散剤が存在することになるので、本発明の効果は実現する。ただし、粉砕時に、特に乾式粗粉砕時に添加するほうが、配向度向上効果は高くなる。なお、分散剤を複数回に分けて添加する場合には、合計添加量が前記した好ましい範囲となるように各回の添加量を設定すればよい。
【００６６】
成形工程後、成形体を大気中または窒素中において１００〜５００℃の温度で熱処理して、添加した分散剤を十分に分解除去する。次いで焼結工程において、成形体を例えば大気中で好ましくは１１５０〜１２５０℃、より好ましくは１１６０〜１２２０℃の温度で０．５〜３時間程度焼結して、異方性フェライト磁石を得る。
【００６７】
なお、本発明による方法で作製した成形体をクラッシャー等を用いて解砕し、ふるい等により平均粒径が１００〜７００μm程度となるように分級して磁場配向顆粒を得、これを乾式磁場成形した後、焼結することにより焼結磁石を得てもよい。
【００６８】
以上では、異方性焼結フェライト磁石の製造に本発明を適用する場合について説明したが、例えば針状フェライト粒子などを用いた軟磁性フェライト焼結体等の他の酸化物磁性体の製造に適用する場合でも、上記説明に準じて分散剤を添加することにより、成形用スラリー中の酸化物磁性体粒子の分散性が良好となり、その結果、高配向度の酸化物磁性体が得られる。
【００６９】
本発明の方法により作成された焼結フェライト磁石を使用することにより、一般に次に述べるような効果が得られ、優れた応用製品を得ることができる。すなわち、従来のフェライト製品と同一形状であれば、磁石から発生する磁束密度を増やすことができるため、モータであれば高トルク化等を実現でき、スピーカーやヘッドホーンであれば磁気回路の強化により、リニアリティーのよい音質が得られるなど応用製品の高性能化に寄与できる。また、従来と同じ機能でよいとすれば、磁石の大きさ（厚み）を小さく（薄く）でき、小型軽量化（薄型化）に寄与できる。
【００７０】
本発明の方法により作製された焼結フェライト磁石は所定の形状に加工され、下記に示すような幅広い用途に使用される。
【００７１】
例えば、フュエールポンプ用、パワーウインド用、ＡＢＳ用、ファン用、ワイパ用、パワーステアリング用、アクティブサスペンション用、スタータ用、ドアロック用、電動ミラー用等の自動車用モータ；ＦＤＤスピンドル用、ＶＴＲキャプスタン用、ＶＴＲ回転ヘッド用、ＶＴＲリール用、ＶＴＲローディング用、ＶＴＲカメラキャプスタン用、ＶＴＲカメラ回転ヘッド用、ＶＴＲカメラズーム用、ＶＴＲカメラフォーカス用、ラジカセ等キャプスタン用、ＣＤ，ＬＤ，ＭＤスピンドル用、ＣＤ，ＬＤ，ＭＤローディング用、ＣＤ，ＬＤ光ピックアップ用等のＯＡ、ＡＶ機器用モータ；エアコンコンプレッサー用、冷蔵コンプレッサー用、電動工具駆動用、扇風機用、電子レンジファン用、電子レンジプレート回転用、ミキサ駆動用、ドライヤーファン用、シェーバー駆動用、電動歯ブラシ用等の家電機器用モータ；ロボット軸、関節駆動用、ロボット主駆動用、工作機器テーブル駆動用、工作機器ベルト駆動用等のＦＡ機器用モータ；その他、オートバイ用発電器、スピーカ・ヘッドホン用マグネット、マグネトロン管、ＭＲＩ用磁場発生装置、ＣＤ−ＲＯＭ用クランパ、ディストリビュータ用センサ、ＡＢＳ用センサ、燃料・オイルレベルセンサ、マグネットラッチ等に好適に使用される。
【００７２】
【実施例】
以下、本発明を実施例によりさらに詳細に説明する。
実施例１
目標組成を
Ｓｒ_0.9Ｌａ_0.1Ｚｎ_0.1Ｆｅ_11.9Ｏ₁₉
とし、出発原料としては以下のものを用いた。
【００７３】
Ｆｅ₂Ｏ₃粉末 (不純物として、Ｍｎ，Ｃｒ，Ｓｉ，Ｃｌを含む)
ＳｒＣＯ₃粉末 (不純物として、Ｂａ，Ｃａを含む)
ＺｎＯ粉末
Ｌａ₂Ｏ₃粉末
また、添加物として、ＳｉＯ₂粉末、ＣａＣＯ₃粉末を目標組成に対し、それぞれ０．２重量％、０．１５重量％となるように添加した。
【００７４】
上記出発原料および添加物を湿式アトライターで粉砕後、乾燥・整粒し、これを空気中において１２３０℃で３時間焼成し、顆粒状の仮焼体を得た。
【００７５】
得られた仮焼体の磁気特性を試料振動式磁力計（ＶＳＭ）で測定した結果、飽和磁化σsは７２emu/g、保磁力ＨcJは４．４kOeであった。
【００７６】
この仮焼体にＳｉＯ₂を０．４重量％、ＣａＣＯ₃を１．０５重量％添加した後、振動ミルにより乾式粗粉砕した。このときに粉砕による歪みが導入され、仮焼体粒子のＨcJは１．７kOeに低下していた。
【００７７】
次いで、分散媒として水を、分散剤としてソルビトールを用い、これらと上記仮焼体粒子とを混合して粉砕用スラリーを調製した。仮焼体粒子に対するソルビトールの添加量を、表１に示す。粉砕用スラリー中の固形分濃度は、３４重量％とした。
【００７８】
この粉砕用スラリーを用いて、ボールミル中で湿式粉砕を４０時間行った。湿式粉砕後の比表面積は、８．５m²/g（平均粒径０．５μm）であった。湿式粉砕後のスラリーの上澄み液のｐＨを、表１に示す。
【００７９】
湿式粉砕後、粉砕用スラリーを遠心分離して、スラリー中の仮焼体粒子の濃度が７５重量％となるように調整し、成形用スラリーとした。この成形用スラリーから水を除去しながら圧縮成形を行った。この成
形は１サイクル１．５minで行い、圧縮方向に約１０kOe の磁場を印加しながら行った。得られた成形体は、直径３０mm、高さ１８mmの円柱状であった。表１に金型からの離型不良に由来する成形体クラックの発生頻度を示した。
【００８０】
成形体の磁気的配向度（Ｉr／Ｉs）は成形体の密度にも影響されるため、正確な評価ができない。このため、成形体の平坦な金型面に対しＸ線回折による測定を行い、現れたピークの面指数と強度とから成形体の結晶学的な配向度（Ｘ線配向度）を求めた。結果を表１に示す。成形体のＸ線配向度は、焼結体の磁気的配向度の値をかなりの程度支配する。なお、本明細書では、Ｘ線配向度としてΣＩ（００Ｌ）／ΣＩ（ｈｋＬ）を用いる。（００Ｌ）は、（００４）や（００６）等のｃ面を総称する表示であり、ΣＩ（００Ｌ）は（００Ｌ）面のすべてのピーク強度の合計である。また、（ｈｋＬ）は、検出されたすべてのピークを表し、ΣＩ（ｈｋＬ）はそれらの強度の合計である。したがってΣＩ（００Ｌ）／ΣＩ（ｈｋＬ）は、ｃ面配向の程度を表す。
【００８１】
次に、各成形体を空気中で１２００℃で１時間焼成した。なお、成形体を焼成する際に、ソルビトールを除去するためにあらかじめ空気中において１００〜３６０℃で十分に脱脂した。得られた焼結体の残留磁束密度Ｂr、保磁力ＨcJ、配向度Ｉr／Ｉs、角形比Ｈk／ＨcJおよび焼結密度を測定した。結果を表２に示す。なお、Ｈkは磁気ヒステリシスループの第２象限において磁束密度が残留磁束密度の９０％になるときの外部磁界強度である。Ｈkが低いと高エネルギー積が得られない。Ｈk／ＨcJは磁石性能の指標となるものであり、磁気ヒステリシスループの第２象限における角張りの度合いを表す。
実施例２
適量のアンモニア水を加えて粉砕時のｐＨを調整したほかは実施例１と同様にして、成形体および焼結体を得た。この成形体および焼結体について、実施例１と同様な測定を行った。結果を表１および表２に示す。
比較例１
ソルビトールのかわりにグルコン酸を添加したほかは実施例１と同様にして、成形体および焼結体を得た。表１のグルコン酸の添加量はソルビトールと重量％ベースでは異なっているがモル数では同一である。この成形体および焼結体について、実施例１と同様な測定を行った。結果を表１および表２に示す。
比較例２
適量のアンモニア水を加えて粉砕時のｐＨを調整したほかは比較例１と同様にして、成形体および焼結体を得た。この成形体および焼結体について、実施例１と同様な測定を行った。結果を表１および表２に示す。
比較例３
ソルビトールを添加しなかったほかは実施例１と同様にして、成形体および焼結体を得た。この成形体および焼結体について、実施例１と同様な測定を行った。結果を表１および表２に示す。
比較例４
適量のアンモニア水を加えて粉砕時のｐＨを調整したほかは比較例３と同様にして、成形体および焼結体を得た。この成形体および焼結体について、実施例１と同様な測定を行った。結果を表１および表２に示す。
【００８２】
【表１】

【００８３】
【表２】

【００８４】
表１から、ソルビトール添加によってもグルコン酸と同様に成形体のＸ線配向度が向上することがわかる。また、グルコン酸添加時の配向度がｐＨに依存するのに対し、ソルビトール添加ではｐＨ依存性が小さく安定した配向度が得られることがわかる。
【００８５】
また、離型クラックの発生頻度はグルコン酸と比較してソルビトールのほうが低く、分散剤としてソルビトールを用いた場合には成形性に与える影響が小さいことがわかる。グルコン酸を添加した場合でも成形速度をより遅くすることによって離型クラックなどの成形不良は回避できるが、この場合生産性は低下する。
【００８６】
実施例１〜２、比較例１〜４で使用した成形用スラリーを１０００℃で１時間熱処理したものについて、ＳｉＯ₂およびＣａＯの各含有量を測定した。結果を表３に示す。グルコン酸を添加した場合にはＣａＯ量の減少が認められた。特にｐＨが高い場合にはよりＣａＯ量の減少が多くなり、またＳｉＯ₂量も減少した。比較例２において保磁力ＨcJが低下しているのはこれらの添加物の流出による組成ずれが原因である。ソルビトールを添加した場合にはこのような問題は起こらない。なお、グルコン酸のカルシウム塩を用いる場合にはこのような添加物の減少は抑制される。
【００８７】
【表３】

【００８８】
また、分散剤としてソルビトールに替えてマンニトールを用いた場合にも実施例１〜２と全く同様の結果が得られた。
実施例３〜実施例９、比較例５〜比較例１１
目標組成を
Ｓｒ_0.8Ｌａ_0.2Ｃｏ_0.2Ｆｅ_11.8Ｏ₁₉
とし、出発原料としては以下のものを用いた。
【００８９】
Ｆｅ₂Ｏ₃粉末 (不純物として、Ｍｎ，Ｃｒ，Ｓｉ，Ｃｌを含む)
ＳｒＣＯ₃粉末 (不純物として、Ｂａ，Ｃａを含む)
酸化コバルト粉末
Ｌａ₂Ｏ₃粉末
また、添加物として、ＳｉＯ₂粉末、ＣａＣＯ₃粉末を目標組成に対し、それぞれ０．２重量％、０．１５重量％となるように添加した。
【００９０】
上記出発原料および添加物を湿式アトライターで粉砕後、乾燥・整粒し、これを空気中において１２００℃で３時間焼成し、顆粒状の仮焼体を得た。この仮焼体を振動ミルにより乾式粗粉砕した。
【００９１】
次いで、分散媒として水を、分散剤として表４に示した化合物を用い、これらと上記仮焼体粒子、仮焼体に対し０．４重量％のＳｉＯ₂、１．２５重量％のＣａＣＯ₃とを混合して粉砕用スラリーを調製した。仮焼体粒子に対する各分散剤の添加量を、表４に示す。なお、グルコン酸カルシウムは一水和物を用い、また、添加量はグルコン酸イオン換算の値を示してある。粉砕用スラリー中の固形分濃度は、３４重量％とした。
【００９２】
表４に示す分散剤を用いたほかは実施例１と同様にして、成形体を得た。これらの成形体について実施例１と同様な測定を行った。結果を表４に示す。
【００９３】
【表４】

【００９４】
表４から、炭素数ｎが３以下であるエチレングリコールＨＯＣＨ₂ＣＨ₂ＯＨ、グリセリンＣＨ₂（ＯＨ）ＣＨ（ＯＨ）ＣＨ₂ＯＨは配向度向上が不十分であり、本発明の対象外である。
【００９５】
表４からソルビトールの添加量を広い範囲で変更した場合でも、高配向の成形体が得られることがわかる。また、ソルビトール添加ではグルコン酸カルシウム添加の場合と比較して離型クラック発生頻度が低いことがわかる。
【００９６】
また、比較例７のグルコン酸カルシウム添加の成形体を急速に乾燥させるとクラックが発生したが、実施例３〜９のソルビトール添加の成形体ではこのようなクラック発生は認められなかった。
【００９７】
上記成形体を焼成したところ、それぞれ成形体配向度に対応した磁気的配向度、残留磁束密度が得られた。なおソルビトールの添加量を５．５重量％とすると焼結体にクラックが発生した。
【００９８】
以上の実施例の結果から、本発明の効果が明らかである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an oxide magnetic material such as an anisotropic ferrite magnet and an oxide magnetic material obtained thereby.
[0002]
[Prior art]
Currently, hexagonal Sr ferrite and Ba ferrite are used as oxide permanent magnet materials. In these magnets, anisotropy by pressing in a magnetic field is widely performed in order to improve magnet characteristics. One of the magnet characteristics is residual magnetic flux density (Br). Factors that greatly affect the residual magnetic flux density Br have the following relationship. In addition, the saturation magnetization (σs) per unit weight in the following formula is a value unique to a substance.
[0003]
Formula Br∝ (saturation magnetization per unit weight) x (density) x (degree of orientation)
Therefore, in order to manufacture an anisotropic sintered ferrite magnet having a high Br, it is very important to increase the sintered density and the degree of orientation. In order to obtain a high degree of orientation, so-called wet molding, in which a slurry in which ferrite particles are dispersed in water, is conventionally performed. On the other hand, in order to obtain a large coercive force, it is necessary to reduce the ferrite particle size to a single domain critical diameter of 1 μm or less and to make it a single domain, but such particles are generally used even when a wet molding method is used. However, there is a problem that the degree of orientation decreases. As a cause of this, in addition to the fact that submicron particles generally tend to aggregate, (1) an increase in magnetic cohesion due to the formation of a single magnetic domain, (2) a decrease in torque that the particles tend to move in the direction of the magnetic field, (3) Increase in frictional force due to increase in the specific surface area of the particles.
[0004]
In order to solve this problem, the present inventors have found that the magnetic cohesive force can be reduced by introducing grinding distortion into the submicron ferrite particles to temporarily reduce the coercive force of the particles. (JP-A-6-53064).
[0005]
Furthermore, by using an organic solvent such as toluene or xylene instead of water, and adding a surfactant such as oleic acid, even if submicron-sized ferrite particles are used, the maximum is about 98%. It has been found that a high degree of magnetic orientation can be obtained (also JP-A-6-53064). However, since this method uses an organic solvent, it has an adverse effect on the human body and the environment, and in order to solve this problem, a large facility such as a recovery device is required, which increases the cost.
[0006]
In this specification, the degree of magnetic orientation is the ratio (Ir / Is) of residual magnetization (Ir) to saturation magnetization (Is).
[0007]
On the other hand, in order to improve the degree of orientation in the wet magnetic field forming method using water, conventionally, for example, a polymer dispersant represented by polycarboxylic acid (salt) is added and adsorbed on the surface of the magnetic particles. Attempts have been made to disperse particles and improve the degree of orientation by the effects of steric hindrance and electrical repulsion (Japanese Patent Laid-Open No. 6-112030). However, the obtained orientation degree and residual magnetic flux density Br are not high.
[0008]
In addition, the problem that the orientation deteriorates when the particle size is reduced is not limited to the case of manufacturing a ferrite magnet. For example, in the case where other oxide magnetic particles such as acicular soft magnetic ferrite are magnetically oriented. It is the same.
[0009]
In addition, the present inventors improve the magnetic field orientation during wet molding using water, which is advantageous in terms of environment and cost, by adding a dispersant represented by gluconic acid or its neutralized salt or its lactone. A method has been proposed (Japanese Patent Application No. 10-525449). However, in this method, although the degree of orientation is very high, the formability at the time of wet magnetic field molding is lowered, and the productivity may be adversely affected.
[0010]
[Problems to be solved by the invention]
The object of the present invention is to achieve high orientation by improving the magnetic field orientation during wet molding using water, which is advantageous in terms of environment and cost, in the production process of oxide magnetic materials such as anisotropic ferrite magnets. It is to obtain an oxide magnetic material having a high degree of productivity at the same time.
[0011]
  Such purposes are as follows (1) to (7This is achieved by the present invention.
  (1)The average particle size is 1 μm or lessA method for producing an oxide magnetic body comprising a forming step of wet forming a forming slurry containing magnetic oxide particles and water in a magnetic field to obtain a formed body,
  Formula C_n(OH)_nH_{n + 2}The manufacturing method of the oxide magnetic body using the slurry for shaping | molding which added the dispersing agent which consists of 1 type or 2 types of sorbitol and mannitol which are polyhydric alcohol represented by (n = 6).
  (2) The method for producing an oxide magnetic material according to (1), further including a wet pulverization step of pulverizing the oxide magnetic particles before the molding step.
  (3) The method for producing an oxide magnetic body according to (2) above, wherein at least a part of the dispersant is added in the wet pulverization step.
  (4) The method for producing an oxide magnetic material according to (2) or (3), further including a dry coarse pulverization step of pulverizing the oxide magnetic particles before the wet pulverization step.
  (5) The method for producing an oxide magnetic body according to (4) above, wherein at least a part of the dispersant is added in the dry coarse pulverization step.
  (6) The method for producing an oxide magnetic material according to any one of (1) to (5), wherein an addition amount of the dispersant is 0.05 to 5.0% by weight with respect to the oxide magnetic particles.
  (7(1) to (1) to obtain a sintered body by firing the molded body.6) Oxide magnetic body production method.
[0026]
The present inventors have found a method for improving the degree of orientation by adding a compound having a strongly hydrophilic group such as gluconic acid (Japanese Patent Application No. 10-525449). However, the addition of hydroxycarboxylic acids represented by gluconic acid or its neutralized salt or its lactone as a dispersant greatly improves the degree of orientation, but the moldability during molding in a magnetic field tends to deteriorate, and the molding time is prolonged. In some cases, time was reduced and the molding yield decreased. Further, when these dispersants are used, cracks are likely to occur when the molded body is dried, and it is necessary to appropriately set the drying conditions of the molded body. On the other hand, sorbose and the like do not have a problem such as a decrease in moldability, but the degree of orientation is not as great as that of hydroxycarboxylic acids such as gluconic acid.
[0027]
Furthermore, when a compound that shows acidity in an aqueous solution such as gluconic acid is used as a dispersant, it is necessary to adjust the pH by adding a basic compound or using a neutralized salt of the compound. That is, there is a problem that the orientation degree is easily affected by pH, and the dispersant reacts with an additive such as a magnetic oxide or calcium carbonate. In contrast, since the dispersant used in the present invention does not have an acidic group such as a carboxyl group, such a problem does not occur.
[0028]
As a result of examining various compounds, the present inventors have found that, for example, addition of a polyhydric alcohol such as sorbitol can achieve both a high degree of orientation and good moldability. In this case, cracks in the molded body tend to hardly occur.
[0029]
Furthermore, the dispersant such as sorbitol used in the present invention is relatively inexpensive and advantageous in terms of production cost.
[0030]
As described above, an oxide magnetic body having a high degree of orientation can be produced at low cost by using the dispersant of the present invention.
[0031]
Most of the conventionally used polymer dispersants are artificially synthesized, are difficult to biodegrade and have a problem of drainage treatment, but many of the dispersants used in the present invention exist in nature, There is also an advantage that it is safe for the human body and the environment and can be decomposed by microorganisms.
[0032]
Among the dispersants used in the present invention, substances having a particularly high effect of improving the degree of orientation are sorbitol and mannitol. Sorbitol and mannitol have the same molecular formula and are in the relationship of optical isomers having different steric structures only. Other optical isomers are considered to show the same effect as sorbitol.
[0033]
Specifically, the degree of magnetic orientation when submicron ferrite particles are wet-pulverized and shaped using water as a dispersion medium and sintered is 93 to 94% when no dispersant is added, When a polycarboxylic acid type compound that has been widely used as a dispersant is used, it is about 94%, but when sorbitol is used as a dispersant, it becomes 95 to 97%, and gluconic acid was used. The degree of orientation is the same as in the case. When an organic solvent (xylene) is used as a dispersion medium and oleic acid is used as a dispersant, the degree of magnetic orientation is 97 to 98%. It can be seen that a degree of magnetic orientation close to that used can be obtained.
[0034]
As a secondary component in the ferrite magnet manufacturing process, SiO₂And CaCO_ThreeIn the case where hydroxycarboxylic acid such as gluconic acid or its lactone is used as a dispersant, SiO in the molding slurry preparation process and wet molding process is used.₂And CaCO_ThreeMay be leaked. Moreover, in addition to hydroxycarboxylic acid and its lactone, when a basic compound is added for pH adjustment and pH is raised, the outflow amount becomes larger.
[0035]
On the other hand, when the polyhydric alcohol is used as a dispersant, SiO₂And CaCO_ThreeThere is also an advantage that the deterioration of characteristics such as a decrease in HcJ can be suppressed.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a specific configuration of the present invention will be described in detail.
[0037]
Although the present invention can be applied to the production of various oxide magnetic materials, a particularly remarkable effect can be obtained. Therefore, in the following description, a case where the present invention is applied to the production of an anisotropic ferrite magnet will be described as an example.
[0038]
The anisotropic ferrite magnet to which the present invention is applied is mainly hexagonal ferrite such as magnetoplumbite type M phase and W phase. As such a ferrite, particularly MO · nFe₂O_Three(M is preferably one or more of Sr and Ba, n = 4.5 to 6.5). Such ferrite further contains rare earth elements, Ca, Pb, Si, Al, Ga, Sn, Zn, In, Co, Ni, Ti, Cr, Mn, Cu, Ge, Nb, Zr, and the like. May be.
[0039]
More preferably, A represents at least one element selected from Sr, Ba, Ca and Pb, R represents at least one element selected from rare earth elements (including Y) and Bi, and Co and / Alternatively, when Zn is L, the total composition ratio of the metal elements of A, R, Fe and L is based on the total metal element amount.
A: 1 to 13 atomic%,
R: 0.05 to 10 atomic%,
Fe: 80 to 95 atomic%,
L: 0.1 to 5 atomic%
It is preferable to have hexagonal magnetoplumbite type (M type) ferrite in the main phase.
[0040]
In this case, it is assumed that R is present at the A site and L is present at the Fe site.
Formula I A_1-xR_x(Fe_12-yL_y)_zO₁₉
It is preferable to form a main phase represented by Note that x, y, and z are values calculated from the above amounts.
[0041]
Furthermore, preferably,
A: 3 to 11 atomic%,
R: 0.2-6 atomic%
Fe: 83 to 94 atomic%,
L: 0.3-4 atomic%,
Particularly preferably,
A: 3-9 atomic%,
R: 0.5-4 atomic%,
Fe: 86-93 atomic%,
L: 0.5-3 atomic%.
[0042]
In each of the above constituent elements, A is at least one element selected from Sr, Ba, Ca, and Pb, and preferably necessarily contains Sr. If A is too small, M-type ferrite will not form, or α-Fe₂O_ThreeEtc. The nonmagnetic phase increases. If A is too large, M-type ferrite will not form, or SrFeO_3-xEtc. The nonmagnetic phase increases. The ratio of Sr in A is preferably 51 atomic% or more, more preferably 70 atomic% or more, and further preferably 100 atomic%. If the ratio of Sr in A is too low, it becomes impossible to obtain both the saturation magnetization and the significant improvement in coercive force.
[0043]
R is at least one element selected from rare earth elements (including Y) and Bi. R preferably contains La, Pr, and Nd, and particularly preferably contains La. If R is too small, the solid solution amount of L will be small, and the effect will be difficult to obtain. When R is too large, nonmagnetic heterogeneous phases such as orthoferrite increase. The proportion of La in R is preferably 40 atomic% or more, more preferably 70 atomic% or more, and it is most preferable to use only La as R in order to improve saturation magnetization. This is because La is the largest when the solid solution limit amount for hexagonal M-type ferrite is compared. Therefore, if the ratio of La in R is too low, the solid solution amount of R cannot be increased. As a result, the solid solution amount of element L cannot be increased, and the effect becomes small. Further, if Bi is used in combination, the calcination temperature and the sintering temperature can be lowered, which is advantageous in production.
[0044]
The element L is Co and / or Zn, and it is particularly preferable that Co is necessarily contained. The ratio of Co in L is preferably 10 atomic% or more, more preferably 20 atomic% or more. If the Co ratio is too low, the coercive force will be insufficiently improved.
[0045]
In order to manufacture such an anisotropic ferrite sintered magnet, a raw material oxide of a ferrite composition or a compound that becomes an oxide by firing is mixed before calcining, and then calcined. The calcination may be performed in the air at, for example, 1000 to 1350 ° C. for 1 second to 10 hours, particularly when obtaining fine calcined powder of M-type Sr ferrite at 1000 to 1200 ° C. for 1 second to 3 hours. .
[0046]
Such calcined powder is substantially composed of granular particles having a magnetoplumbite-type ferrite structure, and the average primary particle size is 0.1 to 1 μm, particularly 0.1 to 0.5 μm. Preferably there is. The average particle diameter may be measured by a scanning electron microscope (SEM), and the coefficient of variation CV is preferably 80% or less, and generally 10 to 70%. The saturation magnetization [sigma] s is preferably 65 to 80 emu / g, particularly 65 to 71.5 emu / g for M-type Sr ferrite, and the coercive force HcJ is preferably 2000 to 8000 Oe, particularly 4000 to 8000 Oe for M-type Sr ferrite.
[0047]
In the present invention, wet molding is performed using a molding slurry containing oxide magnetic particles, water as a dispersion medium, and a dispersant. To increase the effect of the dispersant, the wet molding step It is preferable to provide a wet pulverization step before the step. Further, when calcined particles are used as the oxide magnetic particles, the calcined particles are generally granular, and therefore, for coarse pulverization or pulverization of the calcined particles, dry-type roughening is performed before the wet pulverization step. It is preferable to provide a grinding step. In addition, when oxide magnetic particles are produced by a coprecipitation method or a hydrothermal synthesis method, a dry coarse pulverization step is usually not provided, and a wet pulverization step is not essential, but in order to increase the degree of orientation. It is preferable to provide a wet grinding process. Below, the case where a calcined body particle is used as an oxide magnetic body particle and a dry-type coarse pulverization process and a wet pulverization process are provided is demonstrated.
[0048]
In the dry coarse pulverization step, pulverization is usually performed until the BET specific surface area is about 2 to 10 times. The average particle size after pulverization is about 0.1 to 1 μm, and the BET specific surface area is 4 to 10 m.²The CV of the particle size is preferably maintained at 80% or less, particularly 10 to 70%. The pulverizing means is not particularly limited, and for example, a dry vibration mill, a dry attritor (medium stirring mill), a dry ball mill, and the like can be used, and it is particularly preferable to use a dry vibration mill. What is necessary is just to determine a grinding | pulverization time suitably according to a grinding | pulverization means.
[0049]
Dry coarse pulverization also has the effect of reducing the coercive force HcB by introducing crystal distortion into the calcined particles. The decrease in coercive force suppresses particle aggregation and improves dispersibility. Also, the degree of orientation is improved. The crystal strain introduced into the particles is released in a subsequent sintering step, and thereby returns to the original hard magnetism and becomes a permanent magnet.
[0050]
In dry coarse pulverization, usually SiO₂And CaCO which becomes CaO by firing_ThreeAnd are added. SiO₂And CaCO_ThreeMay be partially added before calcination, in which case an improvement in properties is observed.
[0051]
After dry coarse pulverization, a slurry for pulverization containing calcined particles and water is prepared, and wet pulverization is performed using the slurry. The content of the calcined particles in the pulverizing slurry is preferably about 10 to 70% by weight. The pulverizing means used for wet pulverization is not particularly limited, but it is usually preferable to use a ball mill, an attritor, a vibration mill or the like. What is necessary is just to determine a grinding | pulverization time suitably according to a grinding | pulverization means.
[0052]
After the wet pulverization, the pulverization slurry is concentrated to prepare a molding slurry. Concentration may be performed by centrifugation or the like. The content of the calcined body particles in the molding slurry is preferably about 60 to 90% by weight.
[0053]
In the wet molding process, molding in a magnetic field is performed using a molding slurry. Molding pressure is 0.1-0.5ton / cm²The applied magnetic field may be about 5 to 15 kOe.
[0054]
In the present invention, a molding slurry to which a dispersant is added is used. The dispersant used in the present invention has the general formula C_n(OH)_nH_{n + 2}It is a polyhydric alcohol represented by.
[0055]
The polyhydric alcohol has 4 or more carbon atoms, preferably 4 to 100, more preferably 4 to 30, further preferably 4 to 20, and most preferably 4 to 12. When the carbon number n is 3 or less, the effect of the present invention is not realized.
[0056]
The general formula of the polyhydric alcohol is a formula when the skeleton is all a chain formula and does not contain an unsaturated bond. The number of hydroxyl groups and the number of hydrogen in the polyhydric alcohol may be slightly less than the number represented by the general formula. The polyhydric alcohol may be saturated or may contain an unsaturated bond, and the basic skeleton may be chain or cyclic, but is preferably chain. Moreover, if the number of hydroxyl groups is 50% or more of the carbon number n, the effect of the present invention is realized, but it is preferable that the number of hydroxyl groups is large, and it is most preferable that the number of hydroxyl groups and the number of carbons coincide.
[0057]
However, even if it is a polyhydric alcohol satisfying the above conditions, a compound having an enolic hydroxyl group that can be dissociated as an acid has already been filed by the present inventors, and is excluded in the present application.
[0058]
Specifically, the dispersant used in the present invention is preferably sorbitol or mannitol in which n = 6.
[0059]
The structure of the above preferred dispersant is shown below.
[0060]
[Chemical 1]

[0061]
The dispersant used in the present invention may change its structure due to a mechanochemical reaction caused by pulverization.
[0062]
Furthermore, the object of the present invention may also be achieved by adding a compound such as an ester that generates the same organic compound as the dispersant used in the present invention by, for example, a hydrolysis reaction.
[0063]
Two or more dispersants may be used in combination. The dispersant used at this time is not limited to the scope of the present invention.
[0064]
The addition amount of the dispersant is preferably 0.05 to 5.0% by weight, more preferably 0.1 to 3.0% by weight, and still more preferably 0% with respect to the calcined body particles which are oxide magnetic particles. .3 to 2.0% by weight, most preferably 0.5 to 1.5% by weight. When the amount of the dispersant is too small, the degree of orientation is not sufficiently improved. On the other hand, when there are too many dispersing agents, it will become easy to generate | occur | produce a crack in a molded object and a sintered compact.
[0065]
The addition timing of the dispersant is not particularly limited, may be added at the time of dry coarse pulverization, may be added at the time of slurry preparation for pulverization at the time of wet pulverization, a part is added at the time of dry coarse pulverization, The remainder may be added during wet grinding. Or you may add by stirring etc. after wet grinding. In any case, since the dispersant is present in the molding slurry, the effect of the present invention is realized. However, the effect of improving the degree of orientation is higher when added during pulverization, particularly during dry coarse pulverization. In addition, when adding a dispersing agent in multiple times, what is necessary is just to set the addition amount of each time so that a total addition amount may become the above-mentioned preferable range.
[0066]
After the molding step, the molded body is heat-treated at a temperature of 100 to 500 ° C. in the air or nitrogen to sufficiently decompose and remove the added dispersant. Next, in the sintering step, the molded body is sintered, for example, in the atmosphere, preferably at a temperature of 1150 to 1250 ° C., more preferably 1160 to 1220 ° C., for about 0.5 to 3 hours to obtain an anisotropic ferrite magnet.
[0067]
In addition, the molded body produced by the method according to the present invention is crushed using a crusher or the like, and classified by a sieve or the like so that the average particle diameter is about 100 to 700 μm to obtain magnetic field oriented granules, which are dry-type magnetic field molded Then, a sintered magnet may be obtained by sintering.
[0068]
In the above, the case where the present invention is applied to the production of an anisotropic sintered ferrite magnet has been described, but for example, the production of other oxide magnetic bodies such as a soft magnetic ferrite sintered body using acicular ferrite particles or the like. Even in the case of application, by adding a dispersant according to the above description, the dispersibility of the oxide magnetic particles in the molding slurry is improved, and as a result, a highly oriented oxide magnetic material is obtained.
[0069]
By using the sintered ferrite magnet prepared by the method of the present invention, the following effects are generally obtained, and excellent applied products can be obtained. That is, if the shape is the same as that of a conventional ferrite product, the magnetic flux density generated from the magnet can be increased. Therefore, if the motor is used, higher torque can be achieved. If the speaker or headphone is used, the magnetic circuit is strengthened. In addition, it can contribute to higher performance of applied products, such as obtaining good sound quality with linearity. Moreover, if the same function as the conventional one is sufficient, the size (thickness) of the magnet can be reduced (thin), which can contribute to reduction in size and weight (thinning).
[0070]
The sintered ferrite magnet produced by the method of the present invention is processed into a predetermined shape and used for a wide range of applications as described below.
[0071]
For example, automotive motors for fuel pumps, power windows, ABSs, fans, wipers, power steering, active suspensions, starters, door locks, electric mirrors, etc .; for FDD spindles, VTR caps For stun, VTR rotary head, VTR reel, VTR loading, VTR camera capstan, VTR camera rotary head, VTR camera zoom, VTR camera focus, radio cassette cassette capstan, CD, LD, MD spindle OA, AV equipment motors for CD, LD, MD loading, CD, LD optical pickup, etc .; for air conditioner compressors, refrigeration compressors, electric tool drive, electric fan, microwave oven fan, microwave plate rotation For mixer drive Motors for household appliances such as yer fans, shaver drives, electric toothbrushes, etc .; motors for FA devices such as robot shafts, joint drives, robot main drives, machine tool table drives, machine tool belt drives, etc .; Generator, speaker / headphone magnet, magnetron tube, MRI magnetic field generator, CD-ROM clamper, distributor sensor, ABS sensor, fuel / oil level sensor, magnet latch, etc.
[0072]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
Target composition
Sr_0.9La_0.1Zn_0.1Fe_11.9O₁₉
The following materials were used as starting materials.
[0073]
Fe₂O_ThreePowder (including Mn, Cr, Si, Cl as impurities)
SrCO_ThreePowder (Contains Ba and Ca as impurities)
ZnO powder
La₂O_ThreePowder
As an additive, SiO₂Powder, CaCO_ThreeThe powder was added so as to be 0.2% by weight and 0.15% by weight, respectively, with respect to the target composition.
[0074]
The above starting materials and additives were pulverized with a wet attritor, dried and sized, and calcined in air at 1230 ° C. for 3 hours to obtain a granular calcined body.
[0075]
As a result of measuring the magnetic properties of the obtained calcined body with a sample vibration magnetometer (VSM), the saturation magnetization σs was 72 emu / g, and the coercive force HcJ was 4.4 kOe.
[0076]
This calcined body is made of SiO.₂0.4% by weight, CaCO_ThreeAfter adding 1.05% by weight, dry coarse pulverization was performed with a vibration mill. At this time, distortion due to pulverization was introduced, and the HcJ of the calcined particles was lowered to 1.7 kOe.
[0077]
Subsequently, water was used as a dispersion medium and sorbitol was used as a dispersant, and these and the calcined particles were mixed to prepare a slurry for pulverization. Table 1 shows the amount of sorbitol added to the calcined particles. The solid content concentration in the grinding slurry was 34% by weight.
[0078]
Using this slurry for grinding, wet grinding was performed in a ball mill for 40 hours. Specific surface area after wet grinding is 8.5m²/ g (average particle size 0.5 μm). The pH of the supernatant of the slurry after wet pulverization is shown in Table 1.
[0079]
After the wet pulverization, the pulverization slurry was centrifuged to adjust the concentration of the calcined particles in the slurry to 75% by weight, thereby forming a molding slurry. Compression molding was performed while removing water from the molding slurry. This
The shape was made in one cycle of 1.5 min while applying a magnetic field of about 10 kOe in the compression direction. The obtained molded body had a cylindrical shape with a diameter of 30 mm and a height of 18 mm. Table 1 shows the frequency of occurrence of molded body cracks resulting from defective release from the mold.
[0080]
Since the magnetic orientation degree (Ir / Is) of the molded body is also affected by the density of the molded body, it cannot be accurately evaluated. Therefore, X-ray diffraction measurement was performed on the flat mold surface of the molded body, and the crystallographic orientation degree (X-ray orientation degree) of the molded body was determined from the surface index and intensity of the peak that appeared. The results are shown in Table 1. The degree of X-ray orientation of the compact dominates the value of the magnetic orientation of the sintered body to a considerable extent. In the present specification, ΣI (00L) / ΣI (hkL) is used as the X-ray orientation degree. (00L) is a display that collectively refers to the c-plane such as (004) or (006), and ΣI (00L) is the sum of all peak intensities on the (00L) plane. Further, (hkL) represents all detected peaks, and ΣI (hkL) is the sum of their intensities. Therefore, ΣI (00L) / ΣI (hkL) represents the degree of c-plane orientation.
[0081]
Next, each compact was fired in air at 1200 ° C. for 1 hour. In addition, when baking a molded object, in order to remove sorbitol, it fully degreased at 100-360 degreeC in the air previously. The obtained sintered body was measured for residual magnetic flux density Br, coercive force HcJ, orientation degree Ir / Is, squareness ratio Hk / HcJ, and sintered density. The results are shown in Table 2. Hk is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop. If Hk is low, a high energy product cannot be obtained. Hk / HcJ is an index of magnet performance and represents the degree of angularity in the second quadrant of the magnetic hysteresis loop.
Example 2
A compact and a sintered body were obtained in the same manner as in Example 1 except that an appropriate amount of aqueous ammonia was added to adjust the pH during pulverization. The molded body and the sintered body were measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Comparative Example 1
Molded bodies and sintered bodies were obtained in the same manner as in Example 1 except that gluconic acid was added instead of sorbitol. The addition amount of gluconic acid in Table 1 is different from sorbitol on a weight percent basis, but is the same in terms of the number of moles. The molded body and the sintered body were measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Comparative Example 2
A compact and a sintered body were obtained in the same manner as in Comparative Example 1 except that an appropriate amount of aqueous ammonia was added to adjust the pH during pulverization. The molded body and the sintered body were measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Comparative Example 3
A molded body and a sintered body were obtained in the same manner as in Example 1 except that sorbitol was not added. The molded body and the sintered body were measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Comparative Example 4
A compact and a sintered body were obtained in the same manner as in Comparative Example 3, except that an appropriate amount of aqueous ammonia was added to adjust the pH during pulverization. The molded body and the sintered body were measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.
[0082]
[Table 1]

[0083]
[Table 2]

[0084]
From Table 1, it can be seen that the X-ray orientation degree of the molded body is improved by adding sorbitol as well as gluconic acid. It can also be seen that the degree of orientation when gluconic acid is added depends on the pH, whereas the addition of sorbitol has a small degree of pH dependence and a stable degree of orientation can be obtained.
[0085]
In addition, it is understood that the occurrence frequency of the release crack is lower in sorbitol than in gluconic acid, and when sorbitol is used as a dispersant, the influence on moldability is small. Even when gluconic acid is added, molding defects such as a release crack can be avoided by lowering the molding speed, but in this case, productivity is lowered.
[0086]
About what heat-processed the slurry for shaping | molding used in Examples 1-2 and Comparative Examples 1-4 at 1000 degreeC for 1 hour, SiO₂And each content of CaO was measured. The results are shown in Table 3. When gluconic acid was added, a decrease in the amount of CaO was observed. In particular, when the pH is high, the amount of CaO decreases more, and SiO₂The amount also decreased. In Comparative Example 2, the coercive force HcJ is decreased due to the composition shift due to the outflow of these additives. Such a problem does not occur when sorbitol is added. In addition, when using the calcium salt of gluconic acid, the reduction | decrease of such an additive is suppressed.
[0087]
[Table 3]

[0088]
Moreover, when mannitol was used instead of sorbitol as a dispersant, the same results as in Examples 1 and 2 were obtained.
Example 3 to Example 9, Comparative Example 5 to Comparative Example 11
Target composition
Sr_0.8La_0.2Co_0.2Fe_11.8O₁₉
The following materials were used as starting materials.
[0089]
Fe₂O_ThreePowder (including Mn, Cr, Si, Cl as impurities)
SrCO_ThreePowder (Contains Ba and Ca as impurities)
Cobalt oxide powder
La₂O_ThreePowder
As an additive, SiO₂Powder, CaCO_ThreeThe powder was added so as to be 0.2% by weight and 0.15% by weight, respectively, with respect to the target composition.
[0090]
The starting materials and additives were pulverized with a wet attritor, dried and sized, and calcined in air at 1200 ° C. for 3 hours to obtain a granular calcined body. This calcined body was dry crushed by a vibration mill.
[0091]
Next, water was used as a dispersion medium, and the compounds shown in Table 4 were used as a dispersant.₂1.25 wt% CaCO_ThreeWere mixed to prepare a pulverizing slurry. Table 4 shows the amount of each dispersant added to the calcined particles. In addition, the calcium gluconate uses a monohydrate, and the addition amount has shown the value of gluconate ion conversion. The solid content concentration in the grinding slurry was 34% by weight.
[0092]
A molded body was obtained in the same manner as in Example 1 except that the dispersant shown in Table 4 was used. These molded bodies were measured in the same manner as in Example 1. The results are shown in Table 4.
[0093]
[Table 4]

[0094]
From Table 4, ethylene glycol HOCH whose carbon number n is 3 or less₂CH₂OH, glycerin CH₂(OH) CH (OH) CH₂OH is insufficient in improving the degree of orientation and is out of the scope of the present invention.
[0095]
It can be seen from Table 4 that a highly oriented molded product can be obtained even when the amount of sorbitol added is changed within a wide range. Moreover, it turns out that a release crack generation frequency is low compared with the case of calcium gluconate addition with sorbitol addition.
[0096]
Moreover, when the calcium gluconate-added molded product of Comparative Example 7 was rapidly dried, cracks were generated, but such cracks were not observed in the sorbitol-added molded products of Examples 3-9.
[0097]
When the molded body was fired, a magnetic orientation degree and a residual magnetic flux density corresponding to the molded body orientation degree were obtained. When the amount of sorbitol added was 5.5% by weight, cracks occurred in the sintered body.
[0098]
The effects of the present invention are apparent from the results of the above examples.

Claims (7)

A method for producing an oxide magnetic body having a forming step of obtaining a formed body by wet-forming a forming slurry containing oxide magnetic body particles having an average particle diameter of 1 μm or less and water in a magnetic field,
Oxide using a slurry for molding to which a dispersant composed of one or two of sorbitol and mannitol, which is a polyhydric alcohol represented by the general formula C _n (OH) _n H _{n + 2} (n = 6) A method for producing a magnetic material.   The method for producing an oxide magnetic body according to claim 1, further comprising a wet pulverization step of pulverizing the oxide magnetic particles before the forming step.   The method for producing an oxide magnetic body according to claim 2, wherein at least a part of the dispersant is added in the wet pulverization step.   4. The method for producing an oxide magnetic material according to claim 2, further comprising a dry coarse pulverization step of pulverizing the oxide magnetic particles before the wet pulverization step.   The method for producing an oxide magnetic body according to claim 4, wherein at least a part of the dispersant is added in the dry coarse pulverization step.   The method for producing an oxide magnetic material according to any one of claims 1 to 5, wherein an addition amount of the dispersant is 0.05 to 5.0 wt% with respect to the oxide magnetic particles. The manufacturing method of the oxide magnetic body of Claims 1-6 which obtains a sintered compact by baking the said molded object.