JP2004299977A - Method of manufacturing ferrite granule, ferrite formed body, ferrite sintered compact and electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a ferrite granule by which ferrite sintered compact free from surface defect is obtained. <P>SOLUTION: The method of manufacturing the ferrite granule is performed by spraying the water dispersion of metallic soap to make liquid drops having 10-100 μm mist diameter on the granulated ferrite granule. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３１】
バインダーであるポリビニルアルコールは、一次粒子の結合剤、すなわち、フェライト粉末とフェライト粉末との結合剤として機能し、フェライト顆粒の低圧つぶれ性、耐崩壊性、成形体強度および焼結体強度に影響を及ぼす。特に、ポリビニルアルコールの平均鹸化度は、成形体の成形性に影響を及ぼす。
【００３２】
本発明におけるポリビニルアルコールの平均鹸化度〔ｍ／（ｎ＋ｍ）〕は、バインダーとしてのポリビニルアルコール全体として、好ましくは８８〜９８モル％、より好ましくは９３〜９７モル％である。このような範囲の鹸化度のＰＶＡを中間鹸化ポリビニルアルコールと称する。
【００３３】
全体の平均鹸化度が８８モル％未満のいわゆる部分鹸化ポリビニルアルコールでは、顆粒の低圧つぶれ性は良好なものの、耐崩壊性および耐スティッキング性が悪い。また水への溶解性が良好でスラリー調製が簡単で噴霧造粒に適するが、オシレーティング押出造粒時には金網に材料が付着して連続整粒が困難となる。逆に、全体の平均鹸化度が９８モル％以上の所謂完全鹸化ポリビニルアルコールでは、耐崩壊性は良好であるが、造粒したフェライト顆粒が比較的に硬くなるため低圧つぶれ性が悪くなる。また、水への溶解性が悪く、スラリー調製が困難となる。
【００３４】
また、ポリビニルアルコールの平均重合度（ｍ＋ｎ）は、好ましくは５００〜１７００、より好ましくは８００〜１５００である。平均重合度が５００未満では、顆粒の低圧つぶれ性は良好なものの、耐崩壊性が悪く、成形体強度が低くなってくる。逆に、平均重合度が１７００を超えると、顆粒の耐崩壊性および成形体強度は比較的良好であるが、硬くなるため低圧つぶれ性が悪化し、顆粒粒界による欠陥が発生しやすくなる。
【００３５】
バインダーとして好ましく用いられる前記ポリビニルアルコールの含有量は、仮焼物の粉砕物としてのフェライト粉末１００質量部に対して０．４〜１．２質量部が好ましく、特に０．６〜０．８質量部の範囲が好ましい。ポリビニルアルコールの含有量が０．４質量部未満の場合、フェライト粉末の仮焼物を造粒できなくなる場合もある。逆に１．２質量部を超えると、フェライト顆粒が硬くなりすぎ、つぶれが悪くなることにより、顆粒粒界を多く残し成形不良を発生させる場合もある。また、同様に容量欠損が増加する傾向にある。
【００３６】
本発明において好ましく使用されるポリビニルアルコールは、全体として前記の所定の平均鹸化度、重合度を有していれば特に制限されず、また未変性のものであっても、たとえばアルキルビニルエーテル、ヒドロキシビニルエーテル、酢酸アリル、アミド、ビニルシラン、エチレン等により変性されていてもよい。
【００３７】
フェライト顆粒への造粒は、従来公知の噴霧乾燥造粒法またはオシレーティング押出し造粒法により行うことができる。具体的には、前述のフェライト粉末、バインダーおよび所望に応じて各種添加剤を水に分散させたスラリーを調製し、この調製されたスラリーを噴霧乾燥装置（スプレードライヤー）等で噴霧乾燥することによって、あるいはフェライト粉末、バインダーおよび所望に応じて各種添加剤を攪拌造粒機にて混合造粒して造粒粉を作製し、この造粒粉をオシレーティング造粒機により押出し造粒と乾燥を繰り返して適用することで、フェライト顆粒が作製される。
【００３８】
スプレードライヤーに使用されるアトマイザー（霧化器）は、従来、噴霧乾燥機に使用されるアトマイザであれば特に限定されず、例えば、二流体ノズル、ディスク方式のアトマイザを採用することが可能である。中でも、ディスク式のアトマイザを用いると、粒径の制御が容易であり、また得られた顆粒の粒度分布を狭くできる点で好ましい。この粒径は、ディスクの直径、アトマイザの回転数に依存して制御されるが、後述するように、好ましくは平均粒径１５０μｍ以下の球形顆粒を得るためには、例えばディスクの直径は８０ｍｍ〜１２５ｍｍで、アトマイザの回転数を３０００ｒｐｍ〜１００００ｒｐｍの範囲で調整するのが好ましい。
【００３９】
造粒されたフェライト顆粒の平均粒径は、造粒方法や、目的とする成形体の形状等に依存して適宜選択することができる。通常は、平均粒径が小さすぎると、流動性および金型への充填性が悪くなり、成形体の寸法および単重量のばらつきが大きくなる傾向にある。また、金型への微粉付着（スティッキング）が発生しやすくなる傾向にある。逆に、平均粒径が大きすぎると、顆粒粒界を多く残し、成形不良の発生率が増加する傾向にある。さらに、成形体の寸法および単重量のばらつきも大きくなる傾向にある。
【００４０】
本発明では、特に、電子部品の益々の小型化、薄型化、軽量化などの要請に応えるために、噴霧乾燥により造粒された場合には、フェライト顆粒の平均粒径が、１５０μｍ以下（より好ましくは１２５μｍ以下）となるように、造粒条件などを調整することが好ましい。平均粒径の下限は、好ましくは３０μｍ、より好ましくは６０μｍ程度である。オシレーティング押出しにより造粒された場合には、フェライト顆粒の平均粒径が、３００μｍ以下（より好ましくは２５０μｍ以下）となるように、造粒条件などを調整することが好ましい。平均粒径の下限は、好ましくは１５０μｍ、より好ましくは２００μｍ程度である。
【００４１】
フェライト顆粒の形状は、流動性などを考慮して、球形であることが好ましい。
【００４２】
なお、フェライト顆粒への造粒に際し、上記フェライト粉末およびバインダーの他に、所望に応じて本発明の目的・効果が損なわれない範囲で従来公知の各種添加物を含有させることができる。このような添加物の例として、ポリカルボン酸塩、縮合ナフタレンスルホン酸等の分散剤、グリセリン、グリコール類、トリオール類等の可塑剤、ワックス等の滑剤、ポリエーテル系、ウレタン変性ポリエーテル系、ポリアクリル酸系、変性アクリル酸系有機高分子等の有機系高分子凝集剤、硫酸アルミニウム、塩化アルミニウム、硝酸アルミニウム等の無機系凝集剤等が挙げられる。
【００４３】
（２）次に、造粒後のフェライト顆粒に、金属石鹸の水分散物を噴霧する。ここでの水分散物には、少量であれば、アルコールが含まれていても良い。つまり、本発明でいう水分散物には、純粋な水分散物の他に、水−アルコール系分散物をも含む。
【００４４】
本発明では、特に、造粒後のフェライト顆粒に対して、金属石鹸の水分散物を、スプレーノズルを用いて、ミスト径１０〜１００μｍ（好ましくは１０〜５０μｍ）の液滴で噴霧する点に特徴がある。この方法で噴霧すると、フェライト顆粒の表面には、金属石鹸の凝集物が生成されにくくなる。その結果、得られるフェライト顆粒は、造粒後のフェライト顆粒の表面に金属石鹸が均一に被覆されて構成される。
【００４５】
ミスト径が１００μｍを超えると、後述する転動流動層内でフェライト顆粒同士が付着し易くなり、凝集物が発生する。また、より小さい１０μｍ未満のミスト径を得ようとすると、スプレーノズルの圧縮空気量が高くなり、今度は容器内でフェライト顆粒の破壊が発生する。
【００４６】
本発明では、スプレーノズルでの圧縮空気量を調整することにより、金属石鹸の水分散物のミスト径を任意に調整することができる。金属石鹸の水分散物のミスト径を上記範囲とするには、スプレーノズルでの圧縮空気量を、好ましくは１０〜２００ＮＬ／ｍｉｎ、より好ましくは２０〜１００ＮＬ／ｍｉｎ程度に調整する。
【００４７】
本発明では、平均粒径が、好ましくは０．１〜９μｍ、より好ましくは０．５〜３μｍの金属石鹸を用いる。金属石鹸の平均粒径が大きすぎると、上述したミスト径の水分散物を噴霧することができない。
【００４８】
本発明では、金属石鹸として、好ましくはステアリン酸亜鉛またはステアリン酸マグネシウムを用いる。
【００４９】
金属石鹸の水分散物の噴霧量は、該水分散物中の金属石鹸が、造粒後のフェライト顆粒中のフェライト粉末１００質量部に対して、好ましくは０．０１〜０．１質量部、より好ましくは０．０１５〜０．０５質量部となる量である。この量で噴霧することで、凝集物の生成防止に一層寄与しうる。
【００５０】
本発明では、好ましくは２０〜７０質量部、より好ましくは３０〜５０質量部の金属石鹸を含有する水分散物を用いる。
【００５１】
以下に、本発明方法を実現可能な噴霧装置の一例を説明する。
【００５２】
図１〜２に示すように、本実施形態で用いる噴霧装置２は、円筒型の装置本体３と、該装置本体３の中央付近に内部に配置された転動流動層４と、前記装置本体３の内部で、かつ該転動流動層４の上方に配置された微粒子除去層６とを、有する。
【００５３】
転動流動層４には、フェライト顆粒Ｃを貯留可能な受け部４２を持つ水平回転自在なローター４４と、該受け部４２に貯留されたフェライト顆粒Ｃに対して、金属石鹸の水分散物を噴霧可能な二流体ノズル（スプレーノズルの一例）４６が設置してある。この二流体ノズル４６は、金属石鹸の水分散物の噴霧量を微調整自在とすることができ、しかも金属石鹸の水分散物を霧化自在に噴霧する。
【００５４】
微粒子除去層６は、フェライト顆粒への造粒の際に造粒しきれずに残存した一次フェライト微粒子を除去する作用を司る。この微粒子除去層６は、たとえば、バグフィルターあるいは、好ましくはバグフィルターの代わりに取り付けたメッシュクロス、好ましくは目開き７５μｍ以下のメッシュクロスなどで構成され、例えば粒径１０μｍ以下の微粒子を除去することができる。
【００５５】
本実施形態では、このような噴霧装置２の内部にフェライト顆粒Ｃを導入する。導入方法は、特に限定されない。
【００５６】
次に、導入されたフェライト顆粒Ｃを、好ましくは２０〜５０℃の加温下で、装置２の下方に設置された給気部７から給気を行いながら、ローター４４を回転させる。これにより、ローター４４の受け部４２に貯留されたフェライト顆粒Ｃを流動させる。すると、フェライト顆粒Ｃは、ローター４４の回転に伴う遠心力により、ローター４４上を径方向に転動する。次に、フェライト顆粒Ｃは、給気部７からの給気により、装置２上方に吹き上げられ、装置２の内径面に沿って上昇しながら流動し、やがて、処理容器の中心付近に向かって落下する。この際に、給気部７からの給気量を調整することによって、粒径が小さい、すなわち軽い微粒子は上方に移動し、微粒子除去層６に導入されて除去される（風力分級）。このように分級を行うことで、金型を用いたその後の成形工程で、金型にこれらの微粒子が付着・残存して生じるスティッキングを効果的に防止でき、成形不良を軽減できる。
【００５７】
次に、一次フェライト微粒子が除去されたフェライト顆粒を、該フェライト顆粒が凝集または破壊しないような、金属石鹸の水分散物の噴霧量、金属石鹸の水分散物の噴霧速度、転動流動層４内温度および流動条件で、転動流動させながら、該フェライト顆粒に金属石鹸の水分散物を二流体ノズル４６から噴霧する。これにより、ミスト径１０〜１００μｍの液滴で、金属石鹸の水分散物が噴霧される。フェライト顆粒の表面には、金属石鹸の凝集物が生成されにくくなる結果、造粒後のフェライト顆粒の表面に金属石鹸が均一に被覆される。
【００５８】
一次フェライト微粒子が除去されたフェライト顆粒が凝集または破壊しないような、金属石鹸の水分散物の噴霧量、金属石鹸の水分散物の噴霧速度、転動流動層４内温度および流動条件は、処理すべきフェライト顆粒自体の性状（造粒方法、粒径、密度等）、フェライト顆粒に含まれるフェライト粉末の種類、その平均粒径、バインダーの種類、その含有量等に依存し適宜選択される。
【００５９】
転動流動の際には、装置内温度を、好ましくは２０〜５０℃、より好ましくは３０〜４０℃に設定する。転動流動の際の装置内温度が２０℃未満であると、フェライト顆粒同士が凝集・造粒してしまうので好ましくなく、逆に５０℃を超えると、フェライト顆粒の表面近傍に、水分散物中の水分が充分に浸透する前に、水分が蒸発し乾燥してしまい、金属石鹸が均一に被覆されないおそれがある。
【００６０】
次に、表面に金属石鹸が均一に被覆されたフェライト顆粒を乾燥させる。乾燥の際には、装置内温度を、好ましくは５０〜８０℃、より好ましくは６５〜７５℃に設定する。乾燥時の装置内温度が５０℃未満であると、フェライト顆粒同士が凝集・造粒してしまうので好ましくなく、逆に８０℃を超えると、水分が急激に蒸発して、フェライト顆粒の表面に金属石鹸が均一に被覆されないおそれがある。乾燥時間は、使用設備やその容量、フェライト顆粒への金属石鹸の付着状態や、乾燥温度等の周囲環境に依存して適宜選択されるが、例えば導入量が２０ｋｇの装置においては３０秒〜１０分、好ましくは１〜３分である。
【００６１】
次に、乾燥後のフェライト顆粒の粒径を均一にするため、シフター等の整粒手段（図示省略）により所定の粒度分布となるように整粒するのが好ましい。
【００６２】
なお、以上の説明では、予め造粒されたフェライト顆粒について説明したが、フェライト顆粒は、図１に示す噴霧装置２内で造粒した後に、そのままの状態で、金属石鹸の水分散物を噴霧することも可能である。
【００６３】
フェライト成形体および焼結体
このようにして得られた、表面に金属石鹸が均一に被覆された乾燥後のフェライト顆粒は成形に供され、フェライト成形体とされる。
【００６４】
フェライト顆粒の成形方法としては、たとえば、乾式成形、湿式成形、押出成形などが挙げられるが、本実施形態では、フェライト顆粒を、金型に充填して圧縮加圧（プレス）することにより行う乾式加圧成形法を用いることが好ましい。成形体の形状は、特に限定されず、たとえばトロイダル（Ｔｏｒｏｉｄａｌ）形状などが挙げられる。
【００６５】
得られたフェライト成形体は、本焼成に供され、フェライト焼結体が形成される。本焼成は、多くの空隙を含んでいる成形体の粉体粒子間に、融点以下の温度で粉体が凝着する焼結を起こさせ、緻密な焼結体を得るために行われる。本焼成に用いる炉としては、バッチ式、プッシャー式、台車式などが挙げられる。焼成温度は、好ましくは９００〜１３００℃である。焼成温度があまりに低いと焼成不足になる傾向がある。焼成時間は、通常１〜３時間程度である。本焼成は、大気中で行ってもよく、大気中よりも酸素分圧が高い雰囲気で行っても良い。
【００６６】
得られたフェライト焼結体は、ノート型パソコン、ＰＤＡ等の情報端末や携帯電話、ＰＨＳ等の移動式電話あるいはこれらの周辺機器等の携帯を前提にした電子部品、テレビ、ステレオ等の比較的大型の家電製品等の種々の電子部品のコア材として使用される。
【００６７】
以上、本発明の実施形態について説明してきたが、本発明はこうした実施形態に何等限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々なる態様で実施し得ることは勿論である。
【００６８】
【実施例】
次に、本発明の実施の形態をより具体化した実施例を挙げ、本発明をさらに詳細に説明する。ただし、本発明はこれらの実施例のみに限定されるものではない。
【００６９】
フェライト顆粒の作製
実施例１〜９
まず、Ｎｉ−Ｃｕ−Ｚｎ系フェライト粉末（フェライト粉末）６６質量部と、水３３質量部と、平均鹸化度９３モル％および重合度１３００のポリビニルアルコール（バインダー）１質量部と、ポリカルボン酸アンモニウム塩（分散剤）０．３質量部とを、湿式粉砕混合機で混合してフェライトスラリーを調製した。
【００７０】
次に、調製されたスラリーを、スプレードライヤーを用いて噴霧造粒して平均粒径１００μｍの球形フェライト顆粒を得た。
【００７１】
得られたフェライト顆粒２０ｋｇを図１に示す転動流動層４を有する噴霧装置２に導入して、層内圧力を−４００ｍｍＡｑに保持して、加熱しながらロータ回転数２４０ｒｐｍ、一次エア量５５Ｌ／分で空気を吹き込みながら顆粒を転動流動させ、二流体ノズル（スプレーノズル）４６を用いて、流量６０ｃｃ／分で、１６分間、総量９６０ｃｃの表１に示す金属石鹸の水分散物を、前記フェライト顆粒に噴霧した。
【００７２】
次に、給気温度６７℃、給気風量２ｍ^３ ／分で熱風を吹き込みながら転動流動をさらに続行して、フェライト顆粒の乾燥を２分間行い、乾燥終了後、装置からフェライト顆粒を排出して、顆粒表面が金属石鹸で均一に被覆された乾式加圧成形用のフェライト顆粒を作製した。
【００７３】
比較例１
金属石鹸の水分散物を噴霧しなかった以外は、実施例１と同様にしてフェライト顆粒を得た。
【００７４】
比較例２
金属石鹸の水分散物を噴霧する代わりに、金属石鹸（一次粒子の平均粒径３μｍ）の粉末を固形のまま、顆粒に対して０．０３質量％添加して、フェライト顆粒を得た。
【００７５】
参考例１
造粒後のフェライト顆粒に含まれるフェライト粉末１００質量部に対して、金属石鹸の量が０．１５質量部となるような量の金属石鹸の水分散物を噴霧した以外は、実施例１と同様にして、フェライト顆粒を得た。
【００７６】
比較例３
造粒後のフェライト顆粒に含まれるフェライト粉末１００質量部に対して、金属石鹸の量が０．０３質量部となるような量の金属石鹸の水分散物を、ミスト径１５０μｍの液滴で噴霧した以外は、実施例１と同様にして、フェライト顆粒を得た。
【００７７】
比較例４
造粒後のフェライト顆粒に含まれるフェライト粉末１００質量部に対して、金属石鹸の量が０．２質量部となるような量の金属石鹸（一次粒子の平均粒径３μｍ）の水分散物を、ミスト径１５０μｍの液滴で噴霧した以外は、実施例１と同様にして、フェライト顆粒を得た。
【００７８】
【表１】

【００７９】
フェライト顆粒の評価
得られたそれぞれのフェライト顆粒の表面を顕微鏡で観察し、金属石鹸の凝集物の発生状態を評価した。結果を表２に示す。
【００８０】
フェライト成形体（１）の作製および評価
また、それぞれのフェライト顆粒０．５ｇを直径６ｍｍの金型に充填し、成形圧力９８ＭＰａ、２９４ＭＰａ、４９０ＭＰａの間で変化させ、乾式加圧成形することにより、直径６ｍｍ、長さ５．０ｍｍ〜５．５ｍｍの円柱状のフェライト成形体を作製した。
【００８１】
そして、成形圧力４９０ＭＰａで成形されたフェライト成形体を金型内から排出する際の抜き圧を測定した。結果を表２に示す。
【００８２】
また、得られたフェライト成形体について、成形圧力２９４ＭＰａでの成形体密度を測定した。成形体密度の測定は、成形体を切断し、水銀ポロシメータを用いて算出した。結果を表２に示す。
【００８３】
また、このフェライト成形体を２０万個連続成形した。連続成形後のフェライト材料の金型への付着（スティッキング）の様子を目視により観察し、２０万個連続成形後も金型にフェライト材料の付着が観察されなかったものを◎で、１０万個連続成形時点で金型へのフェライト材料の付着が観察されたものを△で、１万個程度でフェライト材料の付着が起こり連続成形不能であったものを×で、評価した。結果を表２に示す。
【００８４】
また、実施例１〜２および比較例１〜２でのサンプルに関し、成形圧力と成形体密度との関係を図３に、成形圧力と抜き圧（成形体を金型から脱型するために必要な圧力）との関係を図４に示した。
【００８５】
フェライト成形体（２）の作製および評価
また、実施例１と比較例２のフェライト顆粒に関し、それぞれの顆粒の充填量を０．５ｇから１．０ｇに変更し、かつ上記と同様の金型を用いて、成形圧力２９４ＭＰａで乾式加圧成形することにより、直径６ｍｍ、長さ１０．５ｍｍのフェライト成形体を作製した。このフェライト成形体の圧力が伝わり易い上部と、比較的に圧力が伝わり難い成形体の中間部の成形体表面の顆粒粒界（潰れ状態）と成形体密度の比較を行った。実施例１のフェライト成形体の上部側面および中間部側面の顕微鏡写真を図５および６に、比較例２のフェライト成形体の上部側面および中間部側面の顕微鏡写真を図７および８に示した。また、成形体密度の測定は、上述と同様の方法で行った。
【００８６】
フェライト成形体（３）およびフェライト焼結体（１）の作製および評価
また、それぞれのフェライト顆粒１．０ｇを、２４５ＭＰａの圧力で乾式加圧成形し、長さ５５ｍｍ、幅１２ｍｍ、高さ５ｍｍの直方体状のブロック成形体を得た。
【００８７】
得られたブロック成形体を、焼成温度１０６０℃で２時間保つことにより焼成し、Ｎｉ−Ｃｕ−Ｚｎフェライト焼結体を得た。
【００８８】
このフェライト焼結体の抗折強度を、加重試験機（アイコーエンジニアリング社製）を用いてＪＩＳ−Ｒ１６０１に規定されている方法を用いて測定した。結果を表２に示す。
【００８９】
フェライト焼結体（２）の作製および評価
次に、得られたフェライト成形体（１）を、焼成温度１０６０℃で２時間保つことにより焼成し、Ｎｉ−Ｃｕ−Ｚｎフェライト焼結体を得た。
【００９０】
得られたそれぞれのフェライト焼結体の表面を顕微鏡で観察し、穴やヒビの発生状態を評価した。結果を表２に示す。代表的な実施例１のフェライト焼結体表面の顕微鏡写真を図９に、比較例２のフェライト焼結体表面の顕微鏡写真を図１０に、比較例４のフェライト焼結体表面の顕微鏡写真を図１１に示す。
【００９１】
また、得られたそれぞれのフェライト焼結体について、成形圧力２９４ＭＰａで成形体を成形した場合の焼結体密度を測定した。焼結体密度の測定は、上述と同様の方法で行った。結果を表２に示す。
【００９２】
【表２】

【００９３】
表２に示すように、実施例の成形体サンプルでは、比較例３〜４の成形体サンプルと比較して、フェライト顆粒の表面に、金属石鹸の凝集物が発生していないことが確認できた。なお、ここでの凝集物は、ＳＥＭで２００倍の視野１ｍｍ×１ｍｍの観察により、３０μｍ以上の凝集物の存在の有無を基準に判断した。
【００９４】
表２および図３〜４に示すように、実施例の成形体サンプルでは、比較例１〜４および参考例１の成形体サンプルと比較して、抜き圧が低く、かつ低い成形圧力で高い成形体密度が得られることが確認できた。なお、ここでは、抜き圧が３０ｋｇｆ以下の場合に良好と判断し、成形体密度が上部および中間部の平均で３．２８ｇ／ｃｍ^３ 以上の場合に良好と判断した。
【００９５】
表２に示すように、実施例の成形体サンプルでは、比較例４および参考例１の成形体サンプルと比較して、金型へのスティッキングが観察されず、良好な耐スティッキング性を有することが確認された。
【００９６】
図５〜８に示すように、密度測定の結果、実施例１の成形体サンプルは、上部の成形体密度が３．３５ｇ／ｃｍ^３ 、中間部の成形体密度が３．３０ｇ／ｃｍ^３ とほとんど差が無かったのに対し、比較例２の成形体サンプルは、上部が３．２８ｇ／ｃｍ^３ 、中間部が３．１０ｇ／ｃｍ^３ と成形体密度に大きな差が有り、中間部は顆粒粒界が多く見られた。なお、ここでは、成形体サンプルの上部と中間部との密度差が、０．１０ｇ／ｃｍ^３ 以内である場合に良好と判断した。
【００９７】
表２に示すように、抗折強度測定の結果、実施例の焼結体サンプルは、いずれも１５〜１８ｋｇｆ／ｍｍ^２ の高い抗折強度が得られた。これに対し、比較例の焼結体サンプルでは、１２ｋｇｆ／ｍｍ^２ と低い抗折強度しか得られないことが確認できた。なお、ここでは、焼結体サンプルの抗折強度が、１５ｋｇｆ／ｍｍ^２ 以上である場合に良好と判断した。
【００９８】
図９〜１１にも示すように、実施例のいずれの焼結体サンプルも、顆粒時に金属石鹸が表面に均一に噴霧されていたため、焼成時の有機物分解による穴やヒビの発生が見られず、表面の欠陥の無いことが確認できた。これに対し、比較例の焼結体サンプルでは、顆粒時に金属石鹸の凝集物がフェライト成形体内に点在していたため、焼結体表面に有機物の分解による穴が多く見られ、外観不良を生じることが確認できた。
【００９９】
表２に示すように、実施例の焼結体サンプルでは、比較例の焼結体サンプルと比較して、高い焼結体密度が得られることが確認できた。なお、ここでは、焼結体密度が５．１５ｇ／ｃｍ^３ 以上の場合に良好と判断した。
【０１００】
以上の考察により、比較例および参考例の各サンプルと比較して、実施例の各サンプルの優位性が確認できた。
【０１０１】
【発明の効果】
以上説明してきたように、本発明によれば、表面欠陥のないフェライト焼結体を得ることが可能なフェライト顆粒の製造方法と、該方法により製造されたフェライト顆粒を乾式加圧成形してなるフェライト成形体と、該成形体を焼成してなるフェライト焼結体と、該焼結体を有する電子部品とを、提供することができる。
【図面の簡単な説明】
【図１】図１は本発明方法を実現可能な噴霧装置の一例を示す断面図である。
【図２】図２は図１の噴霧装置に含まれる転動流動層の要部を示す一部破断断面図である。
【図３】図３は、実施例１〜２と比較例１〜２のフェライト成形体の成形圧力と成形体密度との関係を示すグラフである。
【図４】図４は、実施例１〜２と比較例１〜２のフェライト成形体の成形圧力と抜き圧との関係を示すグラフである。
【図５】図５は実施例１のフェライト成形体の上部側面の顕微鏡写真である。
【図６】図６は実施例１のフェライト成形体の中間部側面の顕微鏡写真である。
【図７】図７は比較例２のフェライト成形体の上部側面の顕微鏡写真である。
【図８】図８は比較例２のフェライト成形体の中間部側面の顕微鏡写真である。
【図９】図９は実施例１のフェライト焼結体表面の顕微鏡写真である。
【図１０】図１０は比較例２のフェライト焼結体表面の顕微鏡写真である。
【図１１】図１１は比較例５のフェライト焼結体表面の顕微鏡写真である。
【符号の説明】
２… 噴霧装置
３… 装置本体
４… 転動流動層
４２… 受け部
４４… 円形ローター
４６… 二流体ノズル（スプレーノズル）
６… 微粒子除去層
７… 給気部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for producing ferrite granules suitably used for dry pressure molding, a ferrite molded article obtained by dry-pressing the ferrite granules produced by the method, and firing the ferrite molded article. And an electronic component having the ferrite sintered body.
[0002]
[Prior art]
Soft magnetic ferrite is widely used for various electronic components. This soft magnetic ferrite is generally composed of a ferrite sintered body obtained by molding ferrite granules containing ferrite powder and a binder into various shapes according to the purpose to obtain a ferrite molded body, and firing this. I have.
[0003]
As a method for molding ferrite granules, casting, injection molding, dry pressure molding and the like are known. Above all, dry press molding is generally used because it is easy to apply it to various shapes from small to large or to a complicated shape.
[0004]
When molding ferrite compacts by dry-pressure molding, a liquid must be used during granulation of ferrite granules to prevent the ferrite powder from adhering to the mold and uneven density and defects from occurring. Or a solid lubricant after granulation is added or mixed (see Patent Documents 1 and 2).
[0005]
However, none of the techniques of Patent Documents 1 and 2 can uniformly coat the surface of ferrite granules after granulation with a lubricant, and as a result, adhesion of ferrite powder to a mold or molding Various inconveniences such as non-uniform body density have occurred.
[0006]
On the other hand, there has been proposed a technique of spraying water containing zinc stearate as a lubricant onto the ferrite granules while stirring and mixing the ferrite granules containing the ferrite powder and the binder, while stirring and mixing the ferrite granules. Patent Document 3).
[0007]
However, in the technique of Patent Document 3, zinc stearate is sprayed in a relatively large amount of 0.2% by weight with respect to the ferrite granules after the granulation. Therefore, an aggregate of zinc stearate is easily generated on the surface of the ferrite granules. As a result, the surface of the ferrite granules after granulation may not be uniformly coated. Not only this, but also on the surface of a ferrite sintered body obtained by firing a ferrite molded body formed using the granules, decomposition of organic substances at the time of firing, which is considered to be caused by the aggregate of zinc stearate. In some cases, a hole was generated along with the above, and a surface defect was sometimes caused on the sintered body.
[0008]
[Patent Document 1] Japanese Patent Application Laid-Open No. 10-94726
[Patent Document 2] JP-A-2001-19558
[Patent Document 3] JP-A-8-151272
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing ferrite granules capable of obtaining a ferrite sintered body having no surface defects, a ferrite molded body obtained by dry-press molding the ferrite granules produced by the method, An object of the present invention is to provide a ferrite sintered body obtained by firing a body, and an electronic component having the sintered body.
[0009]
Means and action for solving the problem
In order to achieve the above object, according to the present invention, an aqueous dispersion of metal soap is sprayed on ferrite granules after granulation using a spray nozzle as droplets having a mist diameter of 10 to 100 μm. A manufacturing method is provided.
[0010]
In the technique of Patent Document 3, as described above, the spray amount of zinc stearate on ferrite granules after granulation is as large as 0.2% by weight. The fact that the spray amount is large is usually considered to mean that zinc stearate having a relatively large average particle diameter is sprayed with a relatively large mist diameter. The present inventors hypothesized that the size of the mist diameter might be related to the formation of aggregates on the surface of the ferrite granules after granulation, and as a result of verifying this, Reached.
[0011]
According to the present invention, the aqueous dispersion of the metal soap is sprayed onto the ferrite granules after granulation with droplets having a mist diameter in a specific range. In order to set the mist diameter to a specific range, the average particle diameter of the metal soap used is usually specified naturally. In the present invention, since atomization is performed with droplets having a mist diameter of 10 to 100 μm, aggregates of metal soap are less likely to be generated on the surface of the ferrite granules. As a result, the surface of the ferrite granules after granulation is uniformly coated with the metal soap. A ferrite sintered body obtained by baking a ferrite molded body formed using ferrite granules having a metal soap uniformly coated on the surface without generation of agglomerates is formed on the surface of the ferrite sintered body. The generation of holes due to the decomposition of organic substances at the time of firing, which is considered to be caused by the above, is effectively prevented, and no surface defects are generated in the sintered body. That is, according to the present invention, a method for producing ferrite granules capable of obtaining a ferrite sintered body having no surface defects can be provided.
[0012]
Preferably, a metal soap having an average particle size of 0.1 to 9 μm is used.
[0013]
Preferably, an aqueous dispersion of the metal soap is sprayed in such an amount that the amount of the metal soap becomes 0.01 to 0.1 part by mass with respect to 100 parts by mass of the ferrite powder contained in the ferrite granules after granulation. . By setting the amount of the metal soap in this range, it is possible to further contribute to prevention of generation of aggregates.
[0014]
Preferably, zinc stearate or magnesium stearate is used as the metal soap.
[0015]
Preferably, granulated ferrite granules having an average particle size of 150 μm or less are used. As a result, it is possible to suitably respond to recent demands for miniaturization and thinning of electronic components.
[0016]
Preferably, a spray device having a tumbling fluidized bed is used, and the ferrite granules introduced into the tumbling fluidized bed of the spray device are sprayed with an aqueous dispersion of a metallic soap such that the ferrite granules do not agglomerate or break. The ferrite granules are sprayed with the aqueous dispersion of the metal soap while being tumbled under the conditions of the amount, the spray speed of the aqueous dispersion of the metal soap, the temperature in the layer, and the flow conditions.
[0017]
Preferably, polyvinyl alcohol having an average degree of saponification of 88 to 98 mol% and an average degree of polymerization of 500 to 1700 is used as a binder contained in the ferrite granules after granulation.
[0018]
According to the present invention, there is provided a ferrite compact obtained by dry-pressing the ferrite granules produced by any of the methods described above.
[0019]
According to the present invention, there is provided a ferrite sintered body obtained by firing the ferrite molded body.
[0020]
According to the present invention, there is provided an electronic component having the ferrite sintered body.
[0021]
The electronic components are not particularly limited, but are compared with information terminals such as notebook personal computers and PDAs, mobile phones such as mobile phones, PHSs and the like, or mobile devices such as peripheral devices and the like, electronic components, TVs, stereos, etc. Various electronic components such as extremely large home appliances are exemplified.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. Here, FIG. 1 is a sectional view showing an example of a spraying device capable of realizing the method of the present invention, FIG. 2 is a partially cutaway sectional view showing a main part of a tumbling fluidized bed included in the spraying device of FIG. Is a graph showing the relationship between the molding pressure and the compact density of the ferrite compacts of Examples 1-2 and Comparative Examples 1-2, and FIG. 4 is a ferrite compact of Examples 1-2 and Comparative Examples 1-2. FIG. 5 is a micrograph of the upper side surface of the ferrite molded body of Example 1, FIG. 6 is a micrograph of the middle side surface of the ferrite molded body of Example 1, and FIG. 8 is a micrograph of the upper side surface of the ferrite molded body of Comparative Example 2, FIG. 8 is a micrograph of the intermediate part side surface of the ferrite molded body of Comparative Example 2, and FIG. 9 is a micrograph of the surface of the ferrite sintered body of Example 1. 10 is a micrograph of the surface of the ferrite sintered body of Comparative Example 2, and FIG. It is a micrograph of the ferrite sintered body surface of Example 5.
[0023]
Method for producing ferrite granules
The method for producing ferrite granules according to the present invention is characterized in that an aqueous dispersion of a metal soap is sprayed onto the ferrite granules after granulation using a spray nozzle as droplets having a mist diameter of 10 to 100 μm. Hereinafter, this will be described step by step.
[0024]
(1) First, ferrite granules are prepared.
[0025]
In this embodiment, the ferrite granules include a ferrite powder and a binder.
[0026]
The ferrite powder is not particularly limited, and may be appropriately selected depending on the application. This ferrite powder usually contains at least Fe₂O₃And preferably further contains at least one oxide selected from the group consisting of NiO, MnO, MgO, CuO and ZnO, and if necessary, as a subcomponent or an unavoidable impurity, Ca, Co, W, Metal oxides such as Bi, Si, B, and Zr may be included. In this embodiment, two or more ferrite powders may be mixed and used, without being limited to one type of ferrite powder. In the present embodiment, a typical example of the ferrite powder is Fe₂O₃, NiO, CuO and ZnO as main components.
[0027]
The particle size of the ferrite powder may be appropriately selected within the range conventionally used as a raw material of a ferrite sintered body as a final product, and is generally about 0.5 to 5 μm, preferably about 0.7 to 3 μm. .
[0028]
The binder used for granulating ferrite granules can be appropriately selected from binders conventionally used for granulating ferrite granules according to the purpose of use. Examples of such a binder include partially saponified polyvinyl alcohol and polyvinyl acetate, and homopolymers and copolymers of poly (meth) acrylic acid, methylcellulose, acrylamides, and the like. These binders can be used alone or as a mixture of two or more.
[0029]
In the present invention, it is particularly preferable that polyvinyl alcohol (PVA) represented by the following structural formula (I) is contained as a binder. By including a specific polyvinyl alcohol as a binder, the density and the transverse rupture strength of the sintered body can be improved by reducing defects due to grain boundaries and maintaining a high molded body strength. In addition, an expansion phenomenon after releasing, which is referred to as springback, can be suppressed, the occurrence of cracks in the molded body can be suppressed, and the burden on the mold can be reduced.
[0030]
Embedded image

[0031]
Polyvinyl alcohol as a binder functions as a binder for primary particles, that is, a binder between ferrite powder and ferrite powder, and affects the low-pressure crushing property of ferrite granules, the collapse resistance, the strength of the compact and the strength of the sintered body. Exert. In particular, the average degree of saponification of polyvinyl alcohol affects the moldability of a molded article.
[0032]
The average degree of saponification [m / (n + m)] of the polyvinyl alcohol in the present invention is preferably 88 to 98 mol%, more preferably 93 to 97 mol%, as a whole of the polyvinyl alcohol as the binder. PVA having a saponification degree in such a range is referred to as an intermediate saponified polyvinyl alcohol.
[0033]
In the case of a so-called partially saponified polyvinyl alcohol having an overall average saponification degree of less than 88 mol%, the granules have good low-pressure crushing properties, but have poor disintegration resistance and sticking resistance. In addition, it has good solubility in water and is easy to prepare a slurry, and is suitable for spray granulation. However, at the time of oscillating extrusion granulation, a material adheres to a wire mesh, making continuous granulation difficult. Conversely, so-called completely saponified polyvinyl alcohol having an overall degree of saponification of 98 mol% or more has good collapse resistance, but the granulated ferrite granules are relatively hard, resulting in poor low-pressure crushability. In addition, the solubility in water is poor, and it becomes difficult to prepare a slurry.
[0034]
The average degree of polymerization (m + n) of polyvinyl alcohol is preferably 500 to 1700, and more preferably 800 to 1500. If the average degree of polymerization is less than 500, the granules have good low-pressure crushing properties, but have poor collapse resistance and low molded article strength. Conversely, when the average degree of polymerization exceeds 1700, the disintegration resistance of the granules and the strength of the molded body are relatively good, but the granules become hard and the low-pressure crushing property is deteriorated, and defects due to the grain boundaries are likely to occur.
[0035]
The content of the polyvinyl alcohol preferably used as a binder is preferably 0.4 to 1.2 parts by mass, particularly preferably 0.6 to 0.8 parts by mass with respect to 100 parts by mass of ferrite powder as a pulverized calcined product. Is preferable. When the content of the polyvinyl alcohol is less than 0.4 parts by mass, the calcined product of the ferrite powder may not be able to be granulated in some cases. On the other hand, when it exceeds 1.2 parts by mass, the ferrite granules become too hard, and the crushing worsens, so that many granule grain boundaries are left and molding failure may occur. Similarly, the capacity loss tends to increase.
[0036]
The polyvinyl alcohol preferably used in the present invention is not particularly limited as long as it has the above-mentioned predetermined average saponification degree and polymerization degree as a whole, and even if it is unmodified, for example, alkyl vinyl ether, hydroxy vinyl ether , Allyl acetate, amide, vinylsilane, ethylene and the like.
[0037]
Granulation into ferrite granules can be performed by a conventionally known spray drying granulation method or oscillating extrusion granulation method. Specifically, a slurry is prepared by dispersing the above-mentioned ferrite powder, binder and various additives as desired in water, and the prepared slurry is spray-dried by a spray-drying device (spray drier) or the like. Alternatively, a ferrite powder, a binder and, if desired, various additives are mixed and granulated by a stirring granulator to produce a granulated powder, and the granulated powder is extruded by an oscillating granulator and granulated and dried. Repeated application produces ferrite granules.
[0038]
The atomizer (atomizer) used for the spray drier is not particularly limited as long as it is an atomizer conventionally used for a spray drier. For example, a two-fluid nozzle or a disk type atomizer can be adopted. . Among them, the use of a disk atomizer is preferable in that the particle size can be easily controlled and the particle size distribution of the obtained granules can be narrowed. The particle size is controlled depending on the diameter of the disk and the number of revolutions of the atomizer. As will be described later, preferably, in order to obtain spherical granules having an average particle size of 150 μm or less, the diameter of the disk is, for example, 80 mm to It is preferable to adjust the rotation speed of the atomizer in a range of 3000 rpm to 10000 rpm at 125 mm.
[0039]
The average particle size of the granulated ferrite granules can be appropriately selected depending on the granulation method, the shape of the target compact, and the like. Usually, when the average particle size is too small, the fluidity and the filling property to the mold are deteriorated, and the variation in the size and single weight of the molded body tends to be large. In addition, there is a tendency that the adhesion of fine powder (sticking) to the mold tends to occur. Conversely, if the average particle size is too large, a large number of grain boundaries remain, and the incidence of molding defects tends to increase. Further, the variation in the size and unit weight of the molded body tends to increase.
[0040]
In the present invention, in particular, in order to respond to the demands for increasingly smaller, thinner, and lighter electronic components, when granulated by spray drying, the average particle size of the ferrite granules is 150 μm or less (more than It is preferable to adjust the granulation conditions and the like so that the particle size is 125 μm or less. The lower limit of the average particle size is preferably about 30 μm, and more preferably about 60 μm. When granulated by oscillating extrusion, it is preferable to adjust the granulation conditions and the like such that the average particle size of the ferrite granules is 300 μm or less (more preferably, 250 μm or less). The lower limit of the average particle size is preferably about 150 μm, and more preferably about 200 μm.
[0041]
The shape of the ferrite granules is preferably spherical in consideration of fluidity and the like.
[0042]
When granulating the ferrite granules, conventionally known various additives can be contained as required, in addition to the ferrite powder and the binder, as long as the objects and effects of the present invention are not impaired. Examples of such additives include polycarboxylates, dispersants such as condensed naphthalenesulfonic acid, glycerin, glycols, plasticizers such as triols, lubricants such as waxes, polyethers, urethane-modified polyethers, Examples include organic polymer coagulants such as polyacrylic acid-based and modified acrylic acid-based organic polymers, and inorganic coagulants such as aluminum sulfate, aluminum chloride, and aluminum nitrate.
[0043]
(2) Next, an aqueous dispersion of metal soap is sprayed on the ferrite granules after granulation. The water dispersion here may contain an alcohol if the amount is small. That is, the aqueous dispersion in the present invention includes a water-alcohol-based dispersion in addition to a pure aqueous dispersion.
[0044]
In the present invention, in particular, an aqueous dispersion of metal soap is sprayed on ferrite granules after granulation in the form of droplets having a mist diameter of 10 to 100 μm (preferably 10 to 50 μm) using a spray nozzle. There are features. Spraying by this method makes it difficult for aggregates of metal soap to be formed on the surface of the ferrite granules. As a result, the obtained ferrite granules are constituted by uniformly coating the surface of the ferrite granules after granulation with the metal soap.
[0045]
When the mist diameter exceeds 100 μm, the ferrite granules easily adhere to each other in the tumbling fluidized bed described later, and aggregates are generated. Further, when an attempt is made to obtain a smaller mist diameter of less than 10 μm, the amount of compressed air of the spray nozzle increases, and this time, the ferrite granules are broken in the container.
[0046]
In the present invention, the mist diameter of the aqueous dispersion of the metal soap can be arbitrarily adjusted by adjusting the amount of compressed air at the spray nozzle. In order to make the mist diameter of the aqueous dispersion of metal soap within the above range, the amount of compressed air at the spray nozzle is adjusted to preferably about 10 to 200 NL / min, more preferably about 20 to 100 NL / min.
[0047]
In the present invention, a metal soap having an average particle size of preferably 0.1 to 9 μm, more preferably 0.5 to 3 μm is used. If the average particle size of the metal soap is too large, the water dispersion having the above-mentioned mist size cannot be sprayed.
[0048]
In the present invention, zinc stearate or magnesium stearate is preferably used as the metal soap.
[0049]
The spray amount of the aqueous dispersion of the metal soap, the metal soap in the aqueous dispersion is preferably 0.01 to 0.1 parts by mass, based on 100 parts by mass of the ferrite powder in the ferrite granules after granulation. More preferably, the amount is 0.015 to 0.05 parts by mass. Spraying in this amount can further contribute to preventing generation of aggregates.
[0050]
In the present invention, an aqueous dispersion containing preferably 20 to 70 parts by mass, more preferably 30 to 50 parts by mass of metal soap is used.
[0051]
Hereinafter, an example of a spray device that can realize the method of the present invention will be described.
[0052]
As shown in FIGS. 1 and 2, a spraying device 2 used in the present embodiment includes a cylindrical device main body 3, a tumbling fluidized bed 4 disposed inside a center of the device main body 3, and the device main body 3. 3 and a fine particle removal layer 6 disposed above the tumbling fluidized bed 4.
[0053]
In the tumbling fluidized bed 4, a horizontally rotatable rotor 44 having a receiving portion 42 in which ferrite granules C can be stored, and an aqueous dispersion of a metallic soap is added to the ferrite granules C stored in the receiving portion 42. A sprayable two-fluid nozzle (an example of a spray nozzle) 46 is provided. The two-fluid nozzle 46 can finely adjust the spray amount of the water dispersion of the metal soap, and sprays the water dispersion of the metal soap so as to be atomized.
[0054]
The fine particle removing layer 6 functions to remove the primary ferrite fine particles remaining without being completely granulated during granulation into ferrite granules. The fine particle removal layer 6 is made of, for example, a bag filter or, preferably, a mesh cloth attached in place of the bag filter, preferably a mesh cloth having a mesh size of 75 μm or less. Can be.
[0055]
In the present embodiment, the ferrite granules C are introduced into such a spraying device 2. The method of introduction is not particularly limited.
[0056]
Next, the rotor 44 is rotated while the introduced ferrite granules C are supplied with air from a supply unit 7 provided below the apparatus 2 under heating at preferably 20 to 50 ° C. Thereby, the ferrite granules C stored in the receiving portion 42 of the rotor 44 are caused to flow. Then, the ferrite granules C roll on the rotor 44 in the radial direction due to the centrifugal force accompanying the rotation of the rotor 44. Next, the ferrite granules C are blown up above the apparatus 2 by the air supply from the air supply section 7, flow while rising along the inner diameter surface of the apparatus 2, and eventually fall near the center of the processing container. I do. At this time, by adjusting the amount of air supplied from the air supply unit 7, fine particles having a small particle size, that is, light particles, move upward, are introduced into the fine particle removal layer 6, and are removed (wind classification). By performing the classification in this manner, in the subsequent molding process using the mold, sticking caused by the adhesion and remaining of these fine particles to the mold can be effectively prevented, and molding defects can be reduced.
[0057]
Next, the spray amount of the aqueous dispersion of the metal soap, the spray speed of the aqueous dispersion of the metal soap, An aqueous dispersion of metal soap is sprayed from the two-fluid nozzle 46 onto the ferrite granules while rolling and flowing at an internal temperature and flow conditions. Thus, the aqueous dispersion of the metal soap is sprayed as droplets having a mist diameter of 10 to 100 μm. Aggregates of metal soap are less likely to be formed on the surface of the ferrite granule, so that the surface of the ferrite granule after granulation is uniformly coated with the metal soap.
[0058]
The spray amount of the aqueous dispersion of the metal soap, the spray speed of the aqueous dispersion of the metal soap, the temperature in the tumbling fluidized bed 4 and the flow conditions are set so that the ferrite granules from which the primary ferrite fine particles have been removed do not agglomerate or break. It is appropriately selected depending on the properties (granulation method, particle size, density, etc.) of the ferrite granules to be used, the type of ferrite powder contained in the ferrite granules, the average particle size, the type of binder, the content thereof, and the like.
[0059]
At the time of tumbling flow, the temperature in the apparatus is set to preferably 20 to 50 ° C, more preferably 30 to 40 ° C. If the temperature in the apparatus during the tumbling flow is less than 20 ° C., the ferrite granules are not preferably aggregated or granulated. If the temperature exceeds 50 ° C., on the other hand, the water dispersion is formed near the surface of the ferrite granules. Before the water contained therein sufficiently penetrates, the water is evaporated and dried, and the metal soap may not be uniformly coated.
[0060]
Next, the ferrite granules whose surfaces are uniformly coated with metal soap are dried. At the time of drying, the temperature in the apparatus is set to preferably 50 to 80C, more preferably 65 to 75C. If the temperature in the apparatus during drying is lower than 50 ° C, the ferrite granules are undesirably agglomerated and granulated. If the temperature exceeds 80 ° C, on the other hand, the water rapidly evaporates, and the surface of the ferrite granules is evaporated. The metal soap may not be uniformly coated. The drying time is appropriately selected depending on the equipment used, its capacity, the state of adhesion of the metal soap to the ferrite granules, and the surrounding environment such as the drying temperature. Minutes, preferably 1 to 3 minutes.
[0061]
Next, in order to make the particle size of the ferrite granules after drying uniform, it is preferable that the particles be sized by a sizing means such as a shifter (not shown) so as to have a predetermined particle size distribution.
[0062]
In the above description, ferrite granules that have been granulated in advance have been described. However, after ferrite granules are granulated in the spraying device 2 shown in FIG. 1, an aqueous dispersion of metal soap is sprayed as it is. It is also possible.
[0063]
Ferrite compact and sintered compact
The dried ferrite granules having the surface uniformly coated with metal soap obtained in this way are subjected to molding to obtain a ferrite molded body.
[0064]
Examples of the method of forming the ferrite granules include dry molding, wet molding, and extrusion molding. In the present embodiment, the ferrite granules are filled in a mold and compressed and pressed (pressed). It is preferable to use a pressure molding method. The shape of the molded body is not particularly limited, and examples thereof include a toroidal shape.
[0065]
The obtained ferrite molded body is subjected to main firing to form a ferrite sintered body. The main firing is performed in order to cause sintering in which the powder adheres at a temperature equal to or lower than the melting point between the powder particles of the compact including many voids, and to obtain a dense sintered body. Examples of the furnace used for the main firing include a batch type, a pusher type, and a cart type. The firing temperature is preferably 900 to 1300 ° C. If the firing temperature is too low, the firing tends to be insufficient. The firing time is usually about 1 to 3 hours. The main baking may be performed in the air, or may be performed in an atmosphere having a higher oxygen partial pressure than the air.
[0066]
The obtained ferrite sintered body can be used for information terminals such as notebook personal computers and PDAs, mobile phones, mobile phones such as PHSs, or portable electronic devices such as peripheral devices, televisions, stereos and the like. It is used as a core material for various electronic components such as large home appliances.
[0067]
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments at all, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. .
[0068]
【Example】
Next, the present invention will be described in more detail with reference to examples which embody the embodiments of the present invention. However, the present invention is not limited to only these examples.
[0069]
Production of ferrite granules
Examples 1 to 9
First, 66 parts by mass of a Ni—Cu—Zn ferrite powder (ferrite powder), 33 parts by mass of water, 1 part by mass of polyvinyl alcohol (binder) having an average saponification degree of 93 mol% and a polymerization degree of 1300, and ammonium polycarboxylate A ferrite slurry was prepared by mixing 0.3 parts by mass of a salt (dispersant) with a wet pulverizer.
[0070]
Next, the prepared slurry was spray-granulated using a spray dryer to obtain spherical ferrite granules having an average particle size of 100 μm.
[0071]
20 kg of the obtained ferrite granules are introduced into the spraying apparatus 2 having the tumbling fluidized bed 4 shown in FIG. 1, the pressure in the bed is kept at −400 mmAq, the rotor is rotated at 240 rpm, the primary air amount is 55 L / The granules are tumbled and flown while blowing air in each minute, and an aqueous dispersion of the metal soap shown in Table 1 having a total amount of 960 cc for 16 minutes at a flow rate of 60 cc / min using the two-fluid nozzle (spray nozzle) 46 Sprayed on ferrite granules.
[0072]
Next, supply air temperature 67 ° C, supply air volume 2m³The tumbling flow is further continued while blowing hot air at a rate of / min., And the ferrite granules are dried for 2 minutes. After the drying is completed, the ferrite granules are discharged from the apparatus, and the granule surface is uniformly coated with a metallic soap. Ferrite granules for pressure molding were prepared.
[0073]
Comparative Example 1
Ferrite granules were obtained in the same manner as in Example 1, except that the aqueous dispersion of the metal soap was not sprayed.
[0074]
Comparative Example 2
Instead of spraying the aqueous dispersion of the metal soap, 0.03% by mass of the powder of the metal soap (average primary particle diameter: 3 μm) was added to the granules in a solid state to obtain ferrite granules.
[0075]
Reference Example 1
Example 1 was repeated except that an aqueous dispersion of the metal soap was sprayed in such an amount that the amount of the metal soap was 0.15 part by mass with respect to 100 parts by mass of the ferrite powder contained in the ferrite granules after granulation. Similarly, ferrite granules were obtained.
[0076]
Comparative Example 3
An aqueous dispersion of metal soap in an amount such that the amount of metal soap is 0.03 parts by mass is sprayed as droplets having a mist diameter of 150 μm with respect to 100 parts by mass of ferrite powder contained in the ferrite granules after granulation. Except having done, it carried out similarly to Example 1, and obtained the ferrite granule.
[0077]
Comparative Example 4
With respect to 100 parts by mass of ferrite powder contained in the ferrite granules after granulation, an aqueous dispersion of metal soap (average particle size of primary particles: 3 μm) in an amount such that the amount of metal soap is 0.2 part by mass. Ferrite granules were obtained in the same manner as in Example 1, except that the mist was sprayed with droplets having a mist diameter of 150 μm.
[0078]
[Table 1]

[0079]
Evaluation of ferrite granules
The surface of each of the obtained ferrite granules was observed with a microscope, and the state of generation of metal soap aggregates was evaluated. Table 2 shows the results.
[0080]
Preparation and evaluation of ferrite compact (1)
In addition, 0.5 g of each ferrite granule is filled in a mold having a diameter of 6 mm, the molding pressure is changed between 98 MPa, 294 MPa, and 490 MPa, and dry pressing is performed to obtain a diameter of 6 mm and a length of 5.0 mm to 5 mm. A ferrite molded body having a columnar shape of 0.5 mm was produced.
[0081]
Then, the pressure at which the ferrite molded body molded at a molding pressure of 490 MPa was discharged from the mold was measured. Table 2 shows the results.
[0082]
Further, with respect to the obtained ferrite molded body, the molded body density at a molding pressure of 294 MPa was measured. The measurement of the compact density was performed by cutting the compact and using a mercury porosimeter. Table 2 shows the results.
[0083]
Also, 200,000 ferrite molded bodies were continuously molded. The state of adhesion (sticking) of the ferrite material to the mold after continuous molding was visually observed. When the adherence of the ferrite material to the mold was observed at the time of the continuous molding, it was evaluated as △, and when the adherence of the ferrite material occurred in about 10,000 pieces and continuous molding was impossible, the evaluation was evaluated as x. Table 2 shows the results.
[0084]
FIG. 3 shows the relationship between the molding pressure and the compact density with respect to the samples of Examples 1 and 2 and Comparative Examples 1 and 2, and FIG. 4 is shown in FIG.
[0085]
Preparation and evaluation of ferrite molding (2)
Further, with respect to the ferrite granules of Example 1 and Comparative Example 2, the filling amount of each granule was changed from 0.5 g to 1.0 g, and dry pressing was performed at a molding pressure of 294 MPa using the same mold as above. By molding, a ferrite molded body having a diameter of 6 mm and a length of 10.5 mm was produced. A comparison was made between the density of the compact and the grain boundary (crushed state) on the surface of the compact in the upper part where the pressure of the ferrite compact is easily transmitted, and the middle part of the compact where the pressure is relatively difficult to transmit. FIGS. 5 and 6 show micrographs of the upper side surface and the intermediate side surface of the ferrite molded body of Example 1, and FIGS. 7 and 8 show microscopic photographs of the upper side surface and the intermediate side surface of the ferrite molded body of Comparative Example 2. The measurement of the density of the compact was performed in the same manner as described above.
[0086]
Preparation and evaluation of ferrite compact (3) and sintered ferrite (1)
Further, 1.0 g of each ferrite granule was dry-press molded under a pressure of 245 MPa to obtain a rectangular parallelepiped block molded body having a length of 55 mm, a width of 12 mm and a height of 5 mm.
[0087]
The obtained block molded body was fired at a firing temperature of 1060 ° C. for 2 hours to obtain a Ni—Cu—Zn ferrite sintered body.
[0088]
The bending strength of the ferrite sintered body was measured using a load tester (manufactured by Aiko Engineering Co., Ltd.) according to the method specified in JIS-R1601. Table 2 shows the results.
[0089]
Preparation and evaluation of ferrite sintered body (2)
Next, the obtained ferrite molded body (1) was fired at a firing temperature of 1060 ° C. for 2 hours to obtain a Ni—Cu—Zn ferrite sintered body.
[0090]
The surface of each of the obtained ferrite sintered bodies was observed with a microscope, and the state of occurrence of holes and cracks was evaluated. Table 2 shows the results. FIG. 9 shows a micrograph of the surface of the ferrite sintered body of the representative example 1, FIG. 10 shows a micrograph of the surface of the ferrite sintered body of Comparative Example 2, and FIG. As shown in FIG.
[0091]
Further, for each of the obtained ferrite sintered bodies, the density of the sintered bodies when the molded bodies were molded at a molding pressure of 294 MPa was measured. The measurement of the sintered body density was performed in the same manner as described above. Table 2 shows the results.
[0092]
[Table 2]

[0093]
As shown in Table 2, in the molded body sample of the example, compared to the molded body samples of Comparative Examples 3 and 4, it was confirmed that no aggregate of metal soap was generated on the surface of the ferrite granules. . In addition, the aggregate here was determined by observing the presence or absence of an aggregate of 30 μm or more by observing the field of view 1 mm × 1 mm with a SEM at a magnification of 200 times.
[0094]
As shown in Table 2 and FIGS. 3 and 4, in the molded body samples of the examples, compared with the molded body samples of Comparative Examples 1 to 4 and Reference Example 1, the punching pressure was low and the molding was high at a low molding pressure. It was confirmed that body density was obtained. In this case, it is judged to be good when the withdrawal pressure is 30 kgf or less, and the density of the molded body is 3.28 g / cm on average in the upper part and the middle part.³It was judged to be good in the above cases.
[0095]
As shown in Table 2, in the molded article sample of the example, compared to the molded article samples of Comparative Example 4 and Reference Example 1, sticking to the mold was not observed, and the molded article sample had good sticking resistance. confirmed.
[0096]
As shown in FIGS. 5 to 8, as a result of the density measurement, the molded article sample of Example 1 had an upper molded article density of 3.35 g / cm.³, The density of the compact in the middle part is 3.30 g / cm³And the molded article sample of Comparative Example 2 had an upper part of 3.28 g / cm.³3.10 g / cm in the middle part³And the density of the compact were large, and many grain boundaries were found in the middle part. Here, the difference in density between the upper part and the middle part of the molded product sample was 0.10 g / cm.³It was judged to be good when it was within.
[0097]
As shown in Table 2, as a result of the transverse rupture strength measurement, the sintered body samples of Examples were all 15 to 18 kgf / mm²High bending strength was obtained. On the other hand, in the sintered body sample of the comparative example, 12 kgf / mm²It was confirmed that only low bending strength was obtained. Here, the bending strength of the sintered body sample was 15 kgf / mm.²It was judged to be good when it was above.
[0098]
As shown in FIGS. 9 to 11, in all of the sintered body samples of the examples, since the metal soap was uniformly sprayed on the surface during granulation, generation of holes and cracks due to decomposition of organic substances during firing was not observed. It was confirmed that there were no surface defects. In contrast, in the sintered body sample of the comparative example, aggregates of metal soap were scattered in the ferrite molded body at the time of granulation, so that many holes due to decomposition of organic substances were found on the surface of the sintered body, resulting in poor appearance. That was confirmed.
[0099]
As shown in Table 2, it was confirmed that a higher sintered body density was obtained in the sintered body sample of the example than in the sintered body sample of the comparative example. Here, the sintered body density is 5.15 g / cm.³It was judged to be good in the above cases.
[0100]
From the above consideration, the superiority of each sample of the example was confirmed as compared with each sample of the comparative example and the reference example.
[0101]
【The invention's effect】
As described above, according to the present invention, a method for producing a ferrite granule capable of obtaining a ferrite sintered body having no surface defects, and a method of dry-press molding the ferrite granule produced by the method. A ferrite molded body, a ferrite sintered body obtained by firing the molded body, and an electronic component having the sintered body can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a spraying device capable of realizing the method of the present invention.
FIG. 2 is a partially cutaway sectional view showing a main part of a tumbling fluidized bed included in the spray device of FIG.
FIG. 3 is a graph showing the relationship between the molding pressure and the compact density of the ferrite compacts of Examples 1 and 2 and Comparative Examples 1 and 2.
FIG. 4 is a graph showing the relationship between the molding pressure and the removal pressure of the ferrite molded bodies of Examples 1 and 2 and Comparative Examples 1 and 2.
FIG. 5 is a photomicrograph of the upper side surface of the ferrite molded body of Example 1.
FIG. 6 is a photomicrograph of a side surface of an intermediate part of the ferrite molded body of Example 1.
FIG. 7 is a photomicrograph of the upper side surface of the ferrite compact of Comparative Example 2.
FIG. 8 is a photomicrograph of a side surface of an intermediate part of a ferrite molded body of Comparative Example 2.
FIG. 9 is a photomicrograph of the surface of the ferrite sintered body of Example 1.
FIG. 10 is a photomicrograph of the surface of the ferrite sintered body of Comparative Example 2.
FIG. 11 is a micrograph of the surface of a ferrite sintered body of Comparative Example 5.
[Explanation of symbols]
2. Spray device
3. The device body
4. Rolling fluidized bed
42 ... Receiving part
44… Circular rotor
46 ... Two-fluid nozzle (spray nozzle)
6 ... Particle removal layer
7 ... Air supply unit

Claims (10)

A method for producing ferrite granules, which comprises spraying an aqueous dispersion of metal soap as droplets having a mist diameter of 10 to 100 μm onto the granulated ferrite granules using a spray nozzle. The method for producing ferrite granules according to claim 1, wherein a metal soap having an average particle size of 0.1 to 9 µm is used. Spraying an aqueous dispersion of metal soap in an amount such that the amount of metal soap is 0.01 to 0.1 part by mass with respect to 100 parts by mass of ferrite powder contained in the ferrite granules after granulation. 3. The method for producing ferrite granules according to 1 or 2. The method for producing ferrite granules according to any one of claims 1 to 3, wherein zinc stearate or magnesium stearate is used as the metal soap. The method for producing ferrite granules according to any one of claims 1 to 4, wherein granulated ferrite granules having an average particle size of 150 µm or less are used. Using a spraying device having a tumbling fluidized bed, the ferrite granules introduced into the tumbling fluidized bed of the spraying device, such that the ferrite granules do not agglomerate or break, the spray amount of an aqueous dispersion of metal soap, metal The ferrite granule according to any one of claims 1 to 5, wherein the ferrite granule is sprayed with an aqueous dispersion of a metal soap while being tumbled at a spray speed of an aqueous dispersion of soap, a temperature in a bed, and flow conditions. Manufacturing method. The ferrite granules according to any one of claims 1 to 6, wherein polyvinyl alcohol having an average degree of saponification of 88 to 98 mol% and an average degree of polymerization of 500 to 1700 is used as a binder contained in the ferrite granules after granulation. Method. A ferrite molded article obtained by dry-press molding ferrite granules produced by the method according to claim 1. A ferrite sintered body obtained by firing the ferrite molded body according to claim 8. An electronic component comprising the ferrite sintered body according to claim 9.

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