JP3812831B2 - Ferrite core manufacturing method and ferrite core - Google Patents

Description

【００３７】
バインダー成分であるＰＶＡは、一次粒子の結合剤、すなわち、原料粉末同士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ＰＶＡの平均鹸化度は成形性に影響を及ぼす。
【００３８】
（ＰＶＡの平均鹸化度）
本発明におけるＰＶＡの平均鹸化度〔ｍ／（ｎ＋ｍ）〕（ｍ、ｎの意味は化１参照）は、バインダー成分としてのＰＶＡ全体として、好ましくは８８〜９７モル％、である。このような範囲の鹸化度のＰＶＡを中間鹸化ＰＶＡと称する。
【００３９】
全体の平均鹸化度が８８モル％未満のいわゆる部分鹸化ＰＶＡ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整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９７モル％を超えるいわゆる完全鹸化ＰＶＡ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に低圧つぶれ性が悪くなる。また、水への溶解性が悪く、スラリー調整が困難となる。
【００４０】
（ＰＶＡの重合度）
また、ＰＶＡ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であるが、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。
【００４１】
（ＰＶＡの添加量）
本発明において、バインダー成分として用いるＰＶＡの添加量は、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。ＰＶＡの添加量が０．４質量部未満の場合、フェライト粉末を造粒できなくなる場合がある。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がある。また、同様に容量欠損が増加する傾向にある。
【００４２】
（使用可能なＰＶＡの種類）
本発明において使用できるＰＶＡは、全体として前記所定の平均鹸化度、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、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。
【００４３】
（造粒のための添加物）
本発明において、フェライト顆粒を造粒するため、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添加することができる。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、ステアリン酸（塩）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。
【００４４】
（フェライトコアの焼成温度、時間）
本発明により製造されるフェライトコアは、例えばＮｉ−Ｃｕ−Ｚｎ系フェライトでは、酸化性雰囲気中、通常は空気中で焼成すればよい。焼成温度（保持温度）は、通常、８００〜１２５０℃、焼成時間（保持時間）は、通常、１〜６時間とすればよい。
【００４５】
（焼結体密度）
本発明により製造されるフェライトコアは、例えばＮｉ−Ｃｕ−Ｚｎ系フェライトでは、焼結体密度として、５．１ｇ／ｃｍ^３以上、特に５．１５〜５．３０ｇ／ｃｍ^３程度の高い値が得られる。
【００４６】
（抗折強度）
本発明のフェライトコアは、粗大粒子の少ないフェライト粉末（一次粒子）と顆粒粒界に起因する内部欠陥が少ないことにより、抗折強度を格段に向上させることができる。具体的には、前記Ｎｉ−Ｃｕ−Ｚｎ系フェライトコアにおいて、ＪＩＳ Ｒ１６０１に規定される３点式測定法において、抗折強度で１１７．６ＭＰａ（１２ｋｇｆ／ｍｍ^２）以上、特に１８０〜２６４ＭＰａ（１５〜２２ｋｇｆ／ｍｍ^２）程度が得られる。
【００４７】
このような抗折強度を有することにより、特に肉薄のコアや、肉薄部分を有するコアのハンドリング時、または加工時、あるいは樹脂モールド時等におけるクラックの発生や、チッピング等を防止することができ、品質を著しく向上させることができる。
【００４８】
（具体的なコア形状）
本発明を適用するのに特に好適なコア形状は、例えば図２（Ａ）に示すような鍔部を有しない円柱状のコアや、図２（Ｂ）に示すように胴部と鍔部とを有するコア、あるいは図２（Ｃ）に示すように、鍔部が大きく胴部が短いコア等に有効である。これらのコアは、これに巻線その他の導電部材を巻回してインダクタやノイズ抑制部材としている。
【００４９】
また、図３（Ａ）および（Ｂ）に示すように、板状や箱状に形成されたフェライトコアにおいても有効である。このような板状や箱状のフェライトコアは、主にパワーインダクタやコイルの部材として用いられる。
【００５０】
これらの形状のコアは、図２（Ａ）、（Ｂ）に示すコアの胴部の直径ａが２ｍｍ以下、特に１．５ｍｍ以下、図２（Ｃ）に示す鍔部の厚みｂが１ｍｍ以下、特に０．７ｍｍ以下、図３（Ａ）に示す板状コアや図３（Ｂ）に示す箱状の場合にはその厚みｃが１ｍｍ以下、特に０．７ｍｍ以下のもので特に有効である。このような形状のコアを、本発明の方法によって製造することで、抗折強度に優れ、容易に破損しないコアが得られる。
【００５１】
【実施例】
次に実施例および比較例により本発明を説明する。
【００５２】
（実施例１）Ｆｅ_２Ｏ_３：４９モル％、ＮｉＯ：２２モル％、ＣｕＯ：９モル％、ＺｎＯ：２０モル％の比率となるようにこれらの酸化物を秤量し、湿式メディア攪拌型粉砕機を用いて４時間湿式混合した。この湿式混合には、分散媒として純水を用いた。
【００５３】
次いで、混合物をスプレードライヤーにより乾燥し、９００℃で２時間仮焼してＮｉ−Ｃｕ−Ｚｎフェライトの仮焼物を得た。
【００５４】
この仮焼物を湿式メディア攪拌型粉砕機で８時間粉砕し、体積平均粒子径Ｄ１０が０．６μｍ、Ｄ５０が１．０μｍ、Ｄ９０が１．９μｍ、１０μｍを超える粉末の質量％が０、ＢＥＴ値が３．２ｍ^２／ｇのフェライト粉末を得た。
【００５５】
このフェライト粉末と分散媒および平均鹸化度９３モル％、平均重合度１３００のＰＶＡを、フェライト粉末１００重量部に対してＰＶＡが０．７質量部となるように含有させてスラリーとし、噴霧造粒機でその入口温度１８０℃、出口温度８０℃として乾燥することにより、Ｎｉ−Ｃｕ−Ｚｎフェライト顆粒を得た。この顆粒の平均粒径は９０μｍであり、１５０μｍを超える顆粒の質量％は０であった。
【００５６】
この顆粒を、２４５ＭＰａ（２５ｋｇｆ／ｍｍ^２）の圧力でプレス成形し、長さ５５ｍｍ、幅１２ｍｍ、高さ５ｍｍの直方体状のブロック成形体を得た。この成形体を、焼成温度１０４０℃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。得られた焼結体の密度は５．２３ｇ／ｃｍ^３であった。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。測定の結果、１７１．５ＭＰａ（１７．５ｋｇｆ／ｍｍ ^２ ）の高い抗折強度が得られた（表１、表２の実施例１参照）。
【００５７】
（実施例２〜実施例１０）
表１には実施例１以外に、実施例２〜１０として、フェライト粉末の体積平均粒径Ｄ１０、Ｄ５０、Ｄ９０およびＢＥＴ値（粒度分布）と、ＰＶＡの鹸化度、重合度、添加量と、噴霧造粒機における入口温度、出口温度とを、本発明の範囲で種々に変化させた例を示し、また、その結果、顆粒として、平均粒径と粗大粒子含有量（１５０μｍを超える粒子の質量％）が本発明の範囲内となるようにしたものを、比較例と共に示す。また、表２は実施例と比較例の焼結体密度と抗折強度とハンドリング性（二重丸印はハンドリング性が優、丸印は良、三角印はあまりよくないことを示す。）を示す。各比較例は下記の点で本発明の範囲から逸脱している。
【００５８】
（比較例１）
比較例１はフェライト粉末の粒度分布が広く（Ｄ１０＞０．７μｍ、Ｄ５０≧１．４μｍ、Ｄ９０≧５．０μｍ）、かつ平均粒径が大きく（１０μｍ以上の質量％が１３．３％）、ＢＥＴ値≦２．１ｍ ^２ ／ｇのもの、すなわち本発明の範囲を逸脱し、かつＰＶＡ、噴霧条件は本発明の範囲内とした場合の例である。
【００５９】
（比較例２）
比較例２はＤ５０≧１．４μｍ、Ｄ９０≧５．０μｍでしかも１０μｍの質量％≧０．５質量％であって、ＢＥＴ値≦２．１ｍ ^２ ／ｇである点、すなわち平均粒径が大きく、また、粒度分布が広い点において本発明の範囲を逸脱した例である。
【００６０】
（比較例３）
ＰＶＡの鹸化度＞９７モル％とした点のみが本発明の範囲を逸脱した例である。
【００６１】
（比較例４）
ＰＶＡの鹸化度＜８８モル％とした点のみが本発明の範囲を逸脱した例である。
【００６２】
（比較例５）
比較例２のフェライト粉末を用い、さらにＰＶＡの鹸化度＞９７モル％、重合度＞１７００、ＰＶＡの添加量＞１．２質量部とした点で本発明の範囲を逸脱した例である。
【００６３】
（比較例６）
比較例１のフェライト粉末を用い、さらに顆粒製造において、顆粒の平均粒径が１６０μｍ（＞１００μｍ）で、１５０μｍを超える顆粒の含有量＞５質量％である点において本発明の範囲を逸脱した例である。
【００６４】
（比較例７）
比較例２のフェライト粉末を用い、さらに噴霧造粒機の入口温度＞２３０℃、出口温度＞１２５℃、顆粒の平均粒径＞１００μｍであり、１５０μｍを超える顆粒の含有量＞５質量％である点において、本発明の範囲を逸脱した例である。
【００６５】
（比較例８）
比較例２のフェライト粉末を用い、また、ＰＶＡの鹸化度＞９７モル％、重合度＞１７００、その添加量＞１．２質量部、噴霧造粒機の入口温度＞２３０℃、出口温度＞１２５℃、顆粒の平均粒径＞１００μｍであり、さらに１５０μｍを超える顆粒の含有量＞５質量％である点において、本発明の範囲を逸脱した例である。
【００６６】
〔粒度分布の比較〕
図４は実施例１と比較例１のフェライト粉末の粒度分布を比較して示す図であり、本発明による場合の粒度分布曲線は尖鋭であり、従来品に比較して狭い粒度分布を有することを示す。
【００６７】
≪評価≫
（抗折強度）
表２から分かるように、実施例１〜１０においては、抗折強度で１２３．５ＭＰａ（１２．６ｋｇｆ／ｍｍ^２）以上、特に１８０〜２６４ＭＰａ（１５〜２２ｋｇｆ／ｍｍ^２）程度が得られる。一方、比較例１〜１０においては、抗折強度は実施例による場合の最低値よりも低くなる。
【００６８】
（焼結体密度）
実施例１〜１０の場合、焼結体密度は５．１７〜５．２８ｇ／ｃｍ^３という高い値が得られる。一方、比較例による場合には、比較例４による場合以外はすべて焼結体密度は５．１０以下になる。比較例４の場合は、焼結体密度は本発明による場合のレベルに達しているが、しかし前述のように高い抗折強度が得られず、その上ハンドリング性が悪くなる。すなわち前述のように、ＰＶＡの鹸化度が８８モル％未満になると、耐崩壊性および耐スティッキング性が悪くなり、操作性が悪くなる。
【００６９】
（薄型コアの強度評価）
実施例１、実施例５、比較例１、比較例４で得られたＮｉ−Ｃｕ−Ｚｎフェライト顆粒を図５（Ａ）に示す直径Ｄ＝８ｍｍ、高さｈ＝１．０ｍｍの円柱コアに形成した。この成形体をダイヤモンドホイルにより切削加工して図５（Ｂ）に示すような鍔部厚みｔ＝０．３ｍｍ、深さｓ＝１．７ｍｍのコイル巻回用溝６ａを有する薄型のドラム型コアを作製し、さらに１０４０℃で焼成を行って焼結体（コア）６を得た。
【００７０】
【表１】

【００７１】
【表２】

【００７２】
そして図５（Ｃ）に示すようにコア６を台７上にセットしてチャック具９により水平方向にチャックし、このコア６の上方の鍔部６ｂを、鍔部端部から中心に至る距離Ｗ＝０．７ｍｍの点を加圧し、破壊に至る強度（Ｎ）を測定した。その測定結果を表３に示す。表３に示す結果から明らかなように、本発明により得られたコアは高い強度を示す。
【００７３】
【表３】

【００７４】
本発明は特に図２（Ａ）、（Ｂ）に示すような直径ａ、ｂが２ｍｍ以下のコアや、図３（Ａ）、（Ｂ）に示すような厚さｃが１ｍｍ以下の板状コアまたは板状部を有するコアや、図２（Ｃ）に示すような厚さｔが１ｍｍ以下の鍔部を有するコアに好適に適用される。
【００７５】
【発明の効果】
本発明によれば、フェライト粉末（一次粒子）の体積平均粒径とその粒度分布を所定範囲に設定し、さらに好ましくは噴霧造粒機の入口温度、出口温度や顆粒の平均粒径を所定範囲に設定することにより、すなわち特殊な物質を添加して特性の劣化を来たすことなく、高い焼結体密度および強度のフェライトコアを得ることができる。
【図面の簡単な説明】
【図１】本発明によるフェライトコアの製造方法において顆粒製造に用いられる噴霧造粒機の一例を示す構成図である。
【図２】（Ａ）〜（Ｃ）はそれぞれ本発明による製造されるフェライトコアの例を示す斜視図である。
【図３】（Ａ）、（Ｂ）はそれぞれ本発明による製造されるフェライトコアの他の例を示す斜視図である。
【図４】本発明の実施例と比較例の粒度分布を対比して示す図である。
【図５】（Ａ）は本発明の製造方法を適用するコアの加工前の素材を示す斜視図、（Ｂ）は加工後の形状を示す斜視図、（Ｃ）はその強度試験装置を説明する側面図である。
【符号の説明】
１：チャンバー、２：アトマイザ、３：フェライトスラリー、４：バルブ、５：出口、６：コア、６ａ：溝、６ｂ：鍔部、７：台、９：チャック具[0001]
[Technical field to which the invention belongs]
  The present invention relates to a high-strength ferrite core and a method for manufacturing the same.
[0002]
[Prior art]
  Soft magnetic ferrite is widely used in various electronic components. Such soft magnetic ferrite is generally calcined after mixing oxides constituting ferrite, and the calcined product is pulverized into powder, and a granule is obtained by adding a binder to the ferrite powder (primary particles) and granulating. It is obtained by producing and molding the granules into various shapes according to the purpose, and sintering the molded body thus molded.
[0003]
  The ferrite sintered body (ferrite core) thus obtained is an electronic device on the premise of portable information terminals such as notebook computers, PDAs and other information terminals, mobile phones, mobile phones such as PHS, and peripheral devices thereof. Are used for electronic parts such as relatively large home appliances such as televisions and stereos. Ferrite sintered bodies used for these tend to be increasingly smaller, thinner and lighter. For this reason, ferrite sintered bodies are required to maintain high strength even if they are small and thin.
[0004]
  That is, for example, a ferrite core used for an inductor or a noise absorbing member has a thin body, a thin flange, or a thin plate-like part, the core will be damaged during handling or winding. It becomes easy. Moreover, even if it does not lead to breakage, a crack is generated, and there is a risk that moisture, a treatment liquid used in a specific process, or the like may enter and the characteristics and reliability may be greatly impaired.
[0005]
  In order to increase the strength of the ferrite sintered body, in Patent Document 1, in Ni—Zn-based ferrite, 0.1 to 10.0 parts by weight of ZrO with respect to 100 parts by weight of the main component.₂In which ferrite having an average crystal grain size of 1 to 18 μm is disclosed.
[0006]
  Further, in Patent Document 2, in order to provide an oxide magnetic body that does not cause cracks in a molded body, a slurry mixed with a predetermined amount of binder at a granulation temperature of 280 ± 10 ° C. during spray granulation by an atomizer. It is described that water is further added to the granulated powder prepared by spray-drying to prepare a powder (granule) in which the moisture content is adjusted to a range of 0.6% ± 0.1%. In this case, it is described that the granule is centered on a particle size of 100 to 150 μm.
[0007]
  Patent Document 3 discloses a method for producing a raw material (granule) for a powder molded body for the purpose of reducing the wear of a mold by reducing a molding load for obtaining a predetermined molded body density. The ferrite powder has a particle size distribution range in which the frequency of the powder having a particle size of 1 μm or less is 20% or less, the frequency of the powder having a particle size of 10 μm or less is 4% or less, and the average particle size is 2 to 3 μm. It describes that granules are produced with 0.5 to 15 parts by weight of water-soluble binder and 10 to 20 parts by weight of water based on 100 parts by weight of powder.
[0008]
[Patent Document 1]
  JP-A-8-157253 (paragraphs 40 and 42, Table 1)
[Patent Document 2]
  JP-A-4-137704 ((2) upper left column, lines 9-15, (2) lower left column, lines 7-11)
[Patent Document 3]
  JP-A-6-263514 (paragraphs 16 and 18)
[0009]
[Problems to be solved by the invention]
  As described in Patent Document 1, ZrO₂Is added to this ZrO₂There is a problem in that the permeability decreases with the increase in the amount of addition, and the core characteristics deteriorate.
[0010]
  Moreover, in the thing of patent document 2, 3, there exists a problem that it is difficult to obtain a high sintered compact density and it is difficult to obtain high intensity | strength.
[0011]
  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a ferrite core manufacturing method and a ferrite core capable of obtaining a sintered body density and strength without causing deterioration of characteristics.
[0012]
[Means for Solving the Problems]
  In the present invention, in order to produce a high sintered body density, first, the average particle size and particle size distribution of ferrite powder (primary particles) were examined. And the volume average particle diameter is D10, D50, D90 (these values are 10%, 50%, 90% of the total particle, respectively.For up toIt is a particle size, D50 is a value that approximates the average particle size, and the values of D10, D50, and D90 as a whole mean the particle size distribution. ) Is in a predetermined range described later, that is, it is preferable in terms of increasing the strength and density of the sintered body that the particle size and particle size distribution are in the predetermined ranges described below.
[0013]
  Further, the surface area of the powder is related to the average particle size and the particle size distribution, and the particle size distribution is unknown only by the average particle size, and it is necessary to refer to the values such as D10 and D90. In addition, the particle size distribution affects the surface area of the entire powder, and even if the average particle size is the same, if the surface area is large, there are few particles with a particle size close to the average particle size, and many particles with a small particle size. This is the case. Therefore, when discussing the particle size of the ferrite powder, it is necessary to consider the surface area. In the present invention, it is found that it is preferable in terms of increasing the strength and density of the sintered body that the volume average particle diameter is within a predetermined range, the surface area is within a predetermined range, and the particle size is as uniform as possible. It is a thing.
[0014]
  Such strength is obtained in relation to the degree of polymerization of polyvinyl alcohol as a binder, the average degree of saponification, and the amount added.
[0015]
  In addition, the present invention not only examines the volume average particle size and particle size distribution of the primary particles and the composition of the binder, but also provides granulation temperature in the production of the granules in order to obtain the ease of granulation and a suitable average particle size. By examining the above, the grain boundary (gap between the particles) is eliminated, and the density and strength of the sintered body are improved. That is, the object of the present invention is the following (1) to(5)Is achieved.
[0016]
  (1)Volume average particle diameters D10, D50 and D90 are 0.4 μm ≦ D10 ≦ 0.7 μm, 0.8 μm ≦ D50 <1.4 μm, 1.5 μm ≦ D90 <5.0 μm, respectively, and the surface area is 2.1 m. ² / G <BET value ≦ 4.5m ² / GAnd particles having a size of 10 μm or more are 0.5% by mass.Less thanFerrite powder and an average saponification degree of 88 to97Polyvinyl alcohol having a mol% and an average polymerization degree of 500 to 1700Use
  The addition amount of the polyvinyl alcohol is 0.4 to 1.2 parts by weight with respect to 100 parts by weight of the ferrite powder, and a slurry is prepared.
  By spraying the slurry in the chamber with the inlet temperature of the spray granulator being 160 to 230 ° C. and the outlet temperature being 65 to 125 ° C., the average particle size is 40 to 100 μm and the particle size is Granulating a granule having a content of granules of 150 μm or more of 5% by mass or less,
  A method for producing a ferrite core, wherein the granule is molded and then fired to obtain a ferrite core.
[0017]
  (2)(1) A slurry is prepared by further adding a dispersion medium to the ferrite powder and polyvinyl alcohol.Ferrite core manufacturing method.
[0018]
  (3)(1)Or (2)A ferrite core obtained by the production method described in 1.
[0019]
  (4)The ferrite core is made of Ni-Zn based ferrite(3)The ferrite core described in 1.
[0020]
  (5)The inductor or the noise suppression element is configured by winding a winding or a conductor equivalent thereto.(3) or (4)The ferrite core described in 1.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
  (Manufacturing process of ferrite core)
  As the ferrite raw material powder, oxide powders, which are raw material powders for producing ferrite, are weighed and mixed, and calcined. Next, the calcined product is pulverized so as to have a predetermined average particle size and particle size distribution. As an example, a slurry containing the pulverized ferrite powder, a dispersion medium and a binder (polyvinyl alcohol) is used, and the temperature and flow rate are adjusted using a spray granulator so that the average particle diameter of the granules is within a predetermined range. Granulate to fit. After forming this granule, it is fired to obtain a ferrite core.
[0022]
  (Ferrite composition)
  The raw material for producing the ferrite core of the present invention is appropriately selected depending on the use of the finally sintered ferrite core sintered body, and is not particularly limited, but is not limited to Ni—Zn (Ni—Cu—Zn). For example, Fe for producing ferrite and Mn-Zn ferrite₂O₃NiO, MnO, CuO, ZnO as main components, and if necessary, metal oxides such as Co, W, Bi, Si, B, and Zr may be further included as subcomponents or inevitable impurities.
[0023]
  (Crushing the calcined product of ferrite raw material powder)
  In order to obtain a ferrite powder having a predetermined volume average particle size and particle size distribution, the calcined product is pulverized using a conventionally known means such as a ball mill, an attritor, or a wet media agitation type pulverizer. In this case, the pulverization method may be either a wet pulverization method or a dry pulverization method.
[0024]
  (Spray granulator for ferrite granule production)
  FIG. 1 shows a schematic configuration of a spray granulator used in the present invention. The spray granulator has a disk atomizer 2 for spraying a ferrite slurry 3 into a chamber 1. The ferrite slurry 3 sprayed into the chamber 1 evaporates in the air as a solvent or the like to become ferrite granules, accumulates in the vicinity of the outlet 5, and can be taken out from the chamber 1 by appropriately opening the valve 4.
[0025]
  Here, the inlet temperature indicates the temperature at which the ferrite slurry 3 is sprayed into the chamber 1. That is, it is the temperature of the atmosphere in the vicinity of the disc type atomizer 2. The outlet temperature indicates the ambient temperature near the outlet 5.
[0026]
  (Relationship between spray granulator inlet and outlet temperatures, low-pressure crushability, and core strength)
  In the method for producing a ferrite core of the present invention, the ferrite granule is granulated by the atomizer 2 in the range where the inlet temperature of the spray granulator is 160 to 230 ° C and the outlet temperature is 65 to 125 ° C. This granulation temperature condition affects the low-pressure crushability of the ferrite granule, and this low-pressure crushability affects the strength of the compact and the sintered body.
[0027]
  In spray granulation at a high temperature of 280 ° C. shown in Patent Document 2, the binder component also moves to the surface of the droplets as the solvent water evaporates due to rapid drying. A thick portion of the component is generated, and a non-uniform ferrite granule of the binder component is obtained. Since the granule obtained by this conventional technique has many binder components on the surface, the ferrite granule is hard and has a low pressure crushing property. Therefore, when this ferrite granule is molded, a ferrite molded body that leaves many grain boundaries, that is, internal defects. Thus, this grain boundary remains even after firing, resulting in a ferrite core with low strength.
[0028]
  Here, the grain boundary is a gap generated at the contact surface between the ferrite granules inside the ferrite compact. Here, if the ferrite granules are sufficiently adhered to each other inside the ferrite molded body, the grain boundary becomes small, and if the adhesion between the ferrite granules is poor, the grain boundary becomes large.
[0029]
  On the other hand, under the granulation temperature condition of the present invention, the migration and segregation of the binder component to the ferrite granule surface can be suppressed, and a ferrite granule having a relatively uniform distribution of the binder component in the granule can be obtained. Since this ferrite granule is moderately soft and excellent in low-pressure crushing properties, when a molded body or a sintered body is produced from the ferrite granule of the present invention, a ferrite having high strength with almost no grain boundary is obtained.
[0030]
  The inlet temperature in the spray granulator is determined by the temperature of hot air supplied, and the outlet temperature is determined by the inlet temperature, the flow rate of hot air, and the flow rate of slurry. The granulation temperature condition in the present invention is that the inlet temperature of the spray granulator is 160 to 230 ° C. (more preferably 170 to 210 ° C.) and the outlet temperature is 65 to 125 ° C. (more preferably 70 to 110 ° C.). Preferably there is. If the inlet temperature is lower than 230 ° C. and the outlet temperature is 125 ° C. or lower, it is possible to suppress the migration of the binder component to the ferrite granule surface, and the granules are soft and have good low-pressure crushing properties. Further, when the inlet temperature is 160 ° C. or higher and the outlet temperature is 65 ° C. or higher, the drying proceeds sufficiently to suppress aggregation of ferrite granules, and the granules contain little moisture and have low adhesion.
[0031]
  (About the atomizer to be used)
  The atomizer used for granulation of the ferrite granule of the present invention is not particularly limited as long as it is an atomizer conventionally used in a spray granulator, and for example, a two-fluid nozzle or disk type atomizer can be adopted. A disk type atomizer is particularly suitable in the present invention. This is because when a disk type atomizer is used, it is easy to control the particle diameter by the diameter of the disk and the rotational speed of the atomizer, and the particle size distribution of the obtained ferrite granules can be narrowed.
[0032]
  In the present invention, in order to obtain a suitable average particle diameter of ferrite granules described later, it is preferable that the diameter of the atomizer disk is 80 to 125 mm and the rotation speed of the atomizer is 3000 to 20000 rpm.
[0033]
  (Average particle size of ferrite granules)
  In the present invention, the preferable average particle size of the ferrite granules is in the range of 40 to 100 μm, and it is preferable to form spherical granules in which the content of coarse granules of 150 μm or more is 5% by mass or less.
[0034]
  If the average particle size of the ferrite granule is 40 μm or more, the fluidity and the filling property into the mold are excellent, and it becomes possible to suppress the size and mass variation of the ferrite core. Moreover, it becomes possible to suppress adhesion of fine powder (sticking) to the mold. Further, when the average particle size is 100 μm or less, there are few granule grain boundaries when a ferrite molded body is formed from this ferrite granule, and the occurrence rate of molding defects can be kept low. Therefore, the ferrite core obtained by firing this ferrite compact has a high strength because it has few internal defects due to the grain boundary.
[0035]
  (binder)
  In the present invention, when ferrite granules are granulated, it is preferable to add polyvinyl alcohol (PVA) represented by the following structural formula 1 as a binder in the slurry. By adding a specific PVA as a binder, there are few defects due to the grain boundary, and a high molded body strength can be maintained, whereby the density and bending strength of the sintered body can be improved. Moreover, the expansion phenomenon after mold release called a spring back can be suppressed, generation | occurrence | production of the crack of a molded object can be suppressed, and the burden to a metal mold | die can also be reduced.
[0036]
[Chemical 1]

[0037]
  PVA as a binder component functions as a binder for primary particles, that is, a binder for raw material powders, and affects the low-pressure crushing property, collapse resistance, compact strength, and sintered strength of ferrite granules. In particular, the average degree of saponification of PVA affects the moldability.
[0038]
  (Average saponification degree of PVA)
  The average degree of saponification [m / (n + m)] of PVA in the present invention (m and n means the chemical formula 1) is preferably from 88 to the whole PVA as a binder component.97 mol%,. PVA having a saponification degree in such a range is referred to as intermediate saponified PVA.
[0039]
  In the so-called partially saponified PVA having an overall average saponification degree of less than 88 mol%, the low-pressure crushability of the granules is good, but the disintegration resistance and sticking resistance are poor. In addition, the solubility in water is good and the slurry adjustment is easy and suitable for spray granulation. However, during oscillating extrusion granulation, the material adheres to the wire mesh, making continuous granulation difficult. Conversely, the overall average saponification degree is97So-called fully saponified PVA exceeding mol% has good collapse resistance, but the granulated ferrite granules become relatively hard, so that the low-pressure crushing property is deteriorated. Moreover, the solubility to water is bad and slurry adjustment becomes difficult.
[0040]
  (Polymerization degree of PVA)
  Moreover, the average degree of polymerization (m + n) of PVA is preferably 500 to 1700, more preferably 800 to 1500. When the average degree of polymerization is less than 500, the low-pressure crushing properties of the granules are good, but the disintegration resistance is poor, and the strength of the molded product becomes low. On the other hand, when the average degree of polymerization exceeds 1700, the granules have relatively good disintegration resistance and strength of the molded product, but become hard, so that the low-pressure crushing property is deteriorated and defects due to the grain boundaries are likely to occur.
[0041]
  (PVA addition amount)
  In the present invention, the addition amount of PVA used as the binder component 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 the ferrite powder. If the amount of PVA added is less than 0.4 parts by mass, the ferrite powder may not be granulated. On the other hand, if it exceeds 1.2 parts by mass, the ferrite granule becomes too hard and the crushing becomes worse, so that a large number of granule grain boundaries are left and molding defects may occur. Similarly, capacity deficiencies tend to increase.
[0042]
  (Types of PVA that can be used)
  The PVA that can be used in the present invention is not particularly limited as long as it has the predetermined average saponification degree and polymerization degree as a whole, and even if it is unmodified, alkyl vinyl ether, hydroxy vinyl ether, allyl acetate, It may be modified with amide, vinyl silane, ethylene or the like.
[0043]
  (Additive for granulation)
  In the present invention, since the ferrite granule is granulated, conventionally known various additives can be added as long as the purpose and effect of the present invention are not impaired. Examples of such additives include dispersants such as polycarboxylates, condensed naphthalene sulfonic acids, plasticizers such as glycerin, glycols and triols, waxes, lubricants such as stearic acid (salts), polyethers, Examples thereof include organic polymer flocculants such as urethane-modified polyether-based, polyacrylic acid-based, and modified acrylic acid-based organic polymers, and inorganic flocculants such as aluminum sulfate, aluminum chloride, and aluminum nitrate.
[0044]
  (Burning temperature and time of ferrite core)
  The ferrite core produced according to the present invention may be fired in an oxidizing atmosphere, usually in air, for example, in the case of Ni—Cu—Zn ferrite. The firing temperature (holding temperature) is usually 800 to 1250 ° C., and the firing time (holding time) is usually 1 to 6 hours.
[0045]
  (Sintered body density)
  The ferrite core produced according to the present invention is, for example, Ni-Cu-Zn-based ferrite with a sintered body density of 5.1 g / cm.³Above, especially 5.15-5.30 g / cm³A high value is obtained.
[0046]
  (Folding strength)
  The ferrite core of the present invention can remarkably improve the bending strength because the ferrite powder (primary particles) with few coarse particles and few internal defects due to the grain boundary. Specifically, in the Ni-Cu-Zn ferrite core, the bending strength is 117.6 MPa (12 kgf / mm) in the three-point measurement method defined in JIS R1601.²) Above, especially 180-264 MPa (15-22 kgf / mm²) Degree is obtained.
[0047]
  By having such a bending strength, it is possible to prevent the occurrence of cracks, chipping, etc. particularly during handling of the core having a thin core or a thin portion, during processing, or during resin molding, The quality can be significantly improved.
[0048]
  (Specific core shape)
  The core shape particularly suitable for applying the present invention is, for example, a cylindrical core having no flange as shown in FIG. 2 (A), or a trunk and a flange as shown in FIG. 2 (B). As shown in FIG. 2 (C), it is effective for a core having a long core and a short trunk. These cores are wound around a coil or other conductive member to form an inductor or a noise suppression member.
[0049]
  Further, as shown in FIGS. 3A and 3B, it is also effective in a ferrite core formed in a plate shape or a box shape. Such a plate-like or box-like ferrite core is mainly used as a member of a power inductor or a coil.
[0050]
  The cores of these shapes have a core diameter a shown in FIGS. 2A and 2B of 2 mm or less, particularly 1.5 mm or less, and a collar thickness b shown in FIG. 2C of 1 mm or less. Particularly, in the case of a plate core shown in FIG. 3A or a box shape shown in FIG. 3B, the thickness c is 1 mm or less, particularly 0.7 mm or less, particularly 0.7 mm or less. . By manufacturing the core having such a shape by the method of the present invention, a core having excellent bending strength and not easily broken can be obtained.
[0051]
【Example】
  Next, the present invention will be described with reference to examples and comparative examples.
[0052]
  Example 1 Fe₂O₃: 49 mol%, NiO: 22 mol%, CuO: 9 mol%, ZnO: Weighed these oxides so as to have a ratio of 20 mol%, and wet-mixed them for 4 hours using a wet media stirring type pulverizer. . In this wet mixing, pure water was used as a dispersion medium.
[0053]
  Next, the mixture was dried with a spray dryer and calcined at 900 ° C. for 2 hours to obtain a calcined product of Ni—Cu—Zn ferrite.
[0054]
  This calcined product was pulverized for 8 hours with a wet media agitation type pulverizer. The volume average particle diameter D10 was 0.6 μm, D50 was 1.0 μm, D90 was 1.9 μm, and the mass% of the powder exceeding 10 μm was 0, BET value Is 3.2m²/ G ferrite powder was obtained.
[0055]
  This ferrite powder, a dispersion medium, and PVA having an average saponification degree of 93 mol% and an average polymerization degree of 1300 are added to 100 parts by weight of ferrite powder so that PVA is 0.7 parts by mass to form a slurry, and spray granulation Ni-Cu-Zn ferrite granules were obtained by drying at an inlet temperature of 180 ° C and an outlet temperature of 80 ° C. The average particle size of the granules was 90 μm, and the mass% of the granules exceeding 150 μm was 0.
[0056]
  This granule is 245 MPa (25 kgf / mm²) To obtain a rectangular block-shaped molded body having a length of 55 mm, a width of 12 mm, and a height of 5 mm. This molded body was fired by maintaining it at a firing temperature of 1040 ° C. for 2 hours to obtain a Ni—Cu—Zn ferrite sintered body. The density of the obtained sintered body is 5.23 g / cm.³Met. The bending strength of this ferrite sintered body was measured using a method specified in JIS R1601 using a load tester (manufactured by Aiko Engineering Co., Ltd.). As a result of the measurement,171.5 MPa (17.5 kgf / mm ² )A high bending strength was obtained (see Example 1 in Tables 1 and 2).
[0057]
  (Example 2 to Example10)
  In Table 1, in addition to Example 1, Example 210The volume average particle diameters D10, D50, D90 and BET values (particle size distribution) of the ferrite powder, the saponification degree, the polymerization degree, the addition amount of the PVA, the inlet temperature and the outlet temperature in the spray granulator are as follows. As a result, the average particle size and the coarse particle content (mass% of particles exceeding 150 μm) are within the scope of the present invention. It shows with a comparative example. Table 2 shows the sintered body density, bending strength, and handling properties of the examples and comparative examples (double circles indicate that handling is excellent, circles are good, and triangles are not very good). Show. Each comparative example deviates from the scope of the present invention in the following points.
[0058]
  (Comparative Example 1)
  Comparative Example 1 has a wide particle size distribution of ferrite powder (D10> 0.7 μm,D50 ≧ 1.4μm, D90 ≧ 5.0μm) And a large average particle size (mass% of 10 μm or more is 13.3%), BET value≦ 2.1m ² / GIn other words, the PVA and spraying conditions are within the scope of the present invention.
[0059]
  (Comparative Example 2)
  Comparative Example 2D50 ≧ 1.4μm,D90 ≧ 5.0μmMoreover, 10% by mass≧0.5% by mass, BET value≦ 2.1m ² / GThis is an example that deviates from the scope of the present invention in that the average particle size is large and the particle size distribution is wide.
[0060]
  (Comparative Example 3)
  Saponification degree of PVA>97 mol%Only these points are examples that deviate from the scope of the present invention.
[0061]
  (Comparative Example 4)
  Only the point where the degree of saponification of PVA is <88 mol% is an example that deviates from the scope of the present invention.
[0062]
  (Comparative Example 5)
  Using the ferrite powder of Comparative Example 2, and further, the degree of saponification of PVA>97This is an example that deviates from the scope of the present invention in terms of mol%, degree of polymerization> 1700, and addition amount of PVA> 1.2 parts by mass.
[0063]
  (Comparative Example 6)
  An example deviating from the scope of the present invention in that the ferrite powder of Comparative Example 1 was used, and in the production of granules, the average particle size of the granules was 160 μm (> 100 μm) and the content of granules exceeding 150 μm was> 5% by mass. It is.
[0064]
  (Comparative Example 7)
  Using the ferrite powder of Comparative Example 2, the spray granulator inlet temperature> 230 ° C., outlet temperature> 125 ° C., granule average particle size> 100 μm, and granule content> 150% by mass This is an example that deviates from the scope of the present invention.
[0065]
  (Comparative Example 8)
  Using the ferrite powder of Comparative Example 2, and the degree of saponification of PVA>97Granules with mol%, degree of polymerization> 1700, addition amount> 1.2 parts by mass, spray granulator inlet temperature> 230 ° C., outlet temperature> 125 ° C., average particle size> 100 μm, and more than 150 μm This is an example that deviates from the scope of the present invention in that the content of> 5% by mass.
[0066]
  [Comparison of particle size distribution]
  FIG. 4 is a diagram comparing the particle size distributions of the ferrite powders of Example 1 and Comparative Example 1, and the particle size distribution curve in the case of the present invention is sharp and has a narrow particle size distribution compared to the conventional product. Indicates.
[0067]
  ≪Evaluation≫
  (Folding strength)
  As can be seen from Table 2, Examples 1 to10In the bending strength123.5MPa (12.6kgf / mm²) Above, especially 180-264 MPa (15-22 kgf / mm²) Degree is obtained. Meanwhile, Comparative Examples 1 to10In this case, the bending strength is lower than the minimum value in the case of the embodiment.
[0068]
  (Sintered body density)
  Example 110In the case of5.17~ 5.28 g / cm³High value is obtained. On the other hand, in the case of the comparative example, the sintered body density is 5.10 or less except in the case of the comparative example 4. In the case of Comparative Example 4, the sintered body density has reached the level of the case according to the present invention, but as described above, a high bending strength cannot be obtained, and the handling property is deteriorated. That is, as described above, the saponification degree of PVA is 88 mol%.Less thanWhen it becomes, disintegration resistance and sticking resistance will worsen, and operativity will worsen.
[0069]
  (Strength evaluation of thin core)
  The Ni—Cu—Zn ferrite granules obtained in Example 1, Example 5, Comparative Example 1 and Comparative Example 4 were formed into a cylindrical core having a diameter D = 8 mm and a height h = 1.0 mm shown in FIG. Formed. A thin drum core having a coil winding groove 6a having a flange thickness t = 0.3 mm and a depth s = 1.7 mm as shown in FIG. Was further fired at 1040 ° C. to obtain a sintered body (core) 6.
[0070]
[Table 1]

[0071]
[Table 2]

[0072]
  Then, as shown in FIG. 5C, the core 6 is set on the base 7 and chucked in the horizontal direction by the chucking tool 9, and the collar 6b above the core 6 is a distance from the collar end to the center. A point at W = 0.7 mm was pressurized, and the strength (N) leading to breakage was measured. The measurement results are shown in Table 3. As is apparent from the results shown in Table 3, the core obtained by the present invention exhibits high strength.
[0073]
[Table 3]

[0074]
  In particular, the present invention is a core having diameters a and b of 2 mm or less as shown in FIGS. 2A and 2B, or a plate shape having a thickness c of 1 mm or less as shown in FIGS. The present invention is preferably applied to a core having a core or a plate-like portion, or a core having a collar portion having a thickness t of 1 mm or less as shown in FIG.
[0075]
【The invention's effect】
  According to the present invention, the volume average particle size of the ferrite powder (primary particles) and the particle size distribution thereof are set within a predetermined range, and more preferably, the inlet temperature, the outlet temperature of the spray granulator and the average particle size of the granules are within a predetermined range. In other words, a ferrite core having a high sintered body density and strength can be obtained without deteriorating characteristics by adding a special substance.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a spray granulator used for granule production in a method for producing a ferrite core according to the present invention.
FIGS. 2A to 2C are perspective views showing examples of ferrite cores manufactured according to the present invention, respectively.
3A and 3B are perspective views showing another example of a ferrite core manufactured according to the present invention, respectively.
FIG. 4 is a diagram showing a comparison of particle size distributions of an example of the present invention and a comparative example.
5A is a perspective view showing a material before processing a core to which the manufacturing method of the present invention is applied, FIG. 5B is a perspective view showing a shape after processing, and FIG. FIG.
[Explanation of symbols]
1: chamber, 2: atomizer, 3: ferrite slurry, 4: valve, 5: outlet, 6: core, 6a: groove, 6b: collar, 7: stand, 9: chuck

Claims (5)

Volume average particle diameters D10, D50, D90 are 0.4 μm ≦ D10 ≦ 0.7 μm, 0.8 μm ≦ D50 <1.4 μm, 1.5 μm ≦ D90 <5.0 μm, respectively, and the surface area is 2.1 m ² / Ferrite powder in which g <BET value ≦ 4.5 m ² / g and particles of 10 μm or more are less than 0.5% by mass and an average degree of saponification of 88 to 97 mol% and an average degree of polymerization of 500 to 1700 using,
The addition amount of the polyvinyl alcohol is 0.4 to 1.2 parts by weight with respect to 100 parts by weight of the ferrite powder, and a slurry is prepared.
By spraying the slurry in the chamber with the inlet temperature of the spray granulator being 160 to 230 ° C. and the outlet temperature being 65 to 125 ° C., the average particle size is 40 to 100 μm and the particle size is Granulating a granule having a content of granules of 150 μm or more of 5% by mass or less,
A method for producing a ferrite core, wherein the granule is molded and then fired to obtain a ferrite core. The method for producing a ferrite core according to claim 1, wherein a slurry is further prepared by adding a dispersion medium to the ferrite powder and polyvinyl alcohol . A ferrite core obtained by the production method according to claim 1 . The ferrite core according to claim 3 , wherein the ferrite core is made of Ni-Zn ferrite. 5. The ferrite core according to claim 3 , wherein an inductor or a noise suppression element is formed by winding a winding or a conductor equivalent thereto. 6.

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