JP2005019594A - Ferrite core and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite core having excellent heat and shock resistant properties and therefore is prevented from cracking at the time of soldering, and to provide its manufacturing method. <P>SOLUTION: The ferrite core consists of an aggregate of ferrite granules. The maximum height Ry of the ferrite core surface defined by JIS B0601 is 15 μm or less, more preferably 12 μm or less, and specifically preferably 10 μm or less, and the width of a grain boundary space between the ferrite granules is 20 μm or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４１】
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潰れ性、耐崩壊性、成形体強度、焼結体密度、焼結体強度および耐熱衝撃性に影響を及ぼす。
【００４２】
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。
【００４３】
全体の平均鹸化度が８８モル％未満の所謂、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傾向にある。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傾向にある。また、水への溶解性が悪く、スラリー調整が困難となる傾向にある。
【００４４】
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る傾向にある。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傾向にある。
【００４５】
本発明においてバインダー成分として用いる前記のポリビニルアルコールの添加量は、仮焼物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添加量が０．４質量部未満の場合、フェライト原料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。
【００４６】
本発明において使用でき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。
【００４７】
〔他の添加物に関して〕
本発明において、フェライト顆粒を造粒する際に、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。
【００４８】
［造粒］
本発明では、これらの各成分を用いて、従来公知の造粒方法により、フェライト顆粒へと造粒する。この際の造粒は、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、前述のフェライト粒子、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整し、このようにして調整したスラリーをスプレードライヤー等で噴霧乾燥することにより、フェライト成形用顆粒が作製される。
【００４９】
あるいは、フェライト粒子、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適用することによってフェライト成形用顆粒が作製される。
【００５０】
このようにして造粒された顆粒の形状、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されるが、噴霧乾燥により造粒されたフェライト顆粒は、通常４０〜２５０μｍ、好ましくは６０〜２００μｍ、より好ましくは８０〜１５０μｍの粒径を持つ球形である。また、オシレーティング押出しにより造粒された顆粒は、通常８０〜５００μｍ、好ましくは１００〜３００μｍ、より好ましくは１２５〜２００μｍの粒径である。
【００５１】
［フェライト顆粒の平均粒径］
本発明においては、フェライト顆粒の好ましい平均粒径は、４０〜１５０μｍの範囲であり、２００μｍ以上の粗大顆粒の含有率は５質量％以下であり、２０μｍ以下の微細顆粒の含有率は５質量％以下であることが好ましい。また、顆粒は、球形顆粒にすることが好ましい。
【００５２】
フェライト顆粒の平均粒径が４０μｍ以上であれば、流動性および金型への充填性が優れており、フェライトコアの寸法および質量ばらつきを小さく抑えることが可能となる。また、金型への微粉付着（スティッキング）を抑制することが可能となる。また、平均粒径が１５０μｍ以下であれば、このフェライト顆粒からフェライト成形体を成形した際に顆粒粒界が少なく、成形不良の発生率を低く抑えることが可能となる。従って、このフェライト成形体を焼成して得られたフェライトコアは顆粒粒界に起因する欠陥が少ないため、耐熱衝撃性の高いものとなる。
【００５３】
［成形および焼成］
造粒されたフェライト顆粒は、各種圧縮成形法、たとえば片押し法、両押し法、フローティング・ダイ法、ウィズドロアル法などにより、所定形状に成形され、予備成形体となる。プレス機としては、機械プレス、油圧プレス、サーボプレスなど大きさや形状および数量によって適宜選択される。
予備成形体を形成するための成形圧力は、特に限定されないが、好ましくは２００ＭＰａ以上、さらに好ましくは３００ＭＰａ以上である。成形圧力が小さすぎると、顆粒粒界の粒界隙間幅または粒界隙間深さが大きくなる傾向にあり、耐熱衝撃特性が低下する傾向にある。
【００５４】
所定形状に成形された予備成形体は、次に、焼成され、フェライトコア、あるいはフェライトコアの一部（組み合わされることによりフェライトコアになる場合もある）となる。焼成温度は、フェライトの成分によって異なるが、一般的には、１０００〜１３００℃の温度である。
【００５５】
本実施形態では、このようにして得られた焼成後のフェライトコアの表面は、ＪＩＳ Ｂ０６０１で定義される最大高さＲｙが１５μｍ以下で、フェライト顆粒相互間の粒界隙間４の幅Ｗが２０μｍ以下である。そのため、本実施形態のフェライトコアでは、半田付けの際に、ひび割れが発生しない、耐熱衝撃性に優れたフェライトコアを得ることができる。
なお、本発明は、上述した実施形態に限定されるものではなく、本発明の範囲内で種々に改変することができる。
【００５６】
【実施例】
以下、本発明を、さらに詳細な実施例に基づき説明するが、本発明は、これら実施例に限定されない。
【００５７】
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。
【００５８】
次いで、この混合物を、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。
【００５９】
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、ＢＥＴ値が３．０ｍ^２／ｇの仮焼物粉砕粉を得た後、平均鹸化度９３モル％、平均重合度１２００のポリビニルアルコールを、仮焼物１００質量部に対して、０．８質量部添加し、スプレードライヤーで噴霧造粒乾燥することにより、平均粒径１００μｍのＮｉ−Ｃｕ−Ｚｎフェライト顆粒を得た。
【００６０】
この顆粒を、２９４ＭＰａ（３０００ｋｇｆ／ｃｍ^２）の圧力でプレス成形し、長さ１４ｍｍ、幅１４ｍｍ、高さ２ｍｍのブロック成形体を得た。得られた成形体の密度は、３．２９ｇ／ｃｍ^３であった。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。
【００６１】
得られた焼結体の密度は５．１６ｇ／ｃｍ^３であった。この焼結体の表面を、ＫＥＹＥＮＣＥ社製「超深度形状測定顕微鏡」を用いて、ＪＩＳ Ｂ０６０１で定義される最大高さＲｙと、顆粒粒界４の大きさ（幅Ｗの最大）を測定した。最大高さＲｙは７μｍ、顆粒粒界の大きさは８μｍであった。
【００６２】
このフェライト焼結体の端面を、４４０℃の半田浴に５秒間浸漬し、耐熱衝撃性の評価を行った。その結果、試料３０個中、１個もひび割れの発生がなかった。結果を表１に示す。また、この実施例１の試料を半田浴に浸漬する前の端面を、顕微鏡写真で撮影した結果を図２に示す。さらに、この実施例１の試料を半田浴に浸漬した後の端面を、顕微鏡写真で撮影した結果を図３に示す。
【００６３】
【表１】

【００６４】
比較例１
仮焼物１００質量部に対して、バインダーの添加量を２．０質量部にする以外は、実施例１と同様にして、フェライトコアの試料を作製し、実施例１と同様な試験を行った。結果を表１に示す。
【００６５】
また、この比較例１の試料を半田浴に浸漬する前の端面を、顕微鏡写真で撮影した結果を図４に示す。図４に示すように、図２に示す実施例１に比べて、粒界隙間の幅が広いことが確認できた。さらに、この比較例１の試料を半田浴に浸漬した後の端面を、顕微鏡写真で撮影した結果を図５に示す。図５に示すように、ひび割れが観察された。
【００６６】
実施例２〜５
バインダーの鹸化度、重合度、添加量、成形圧力を、表１に示すように変化させた以外は、実施例１と同様にして、フェライトコアの試料を作製し、実施例１と同様な試験を行った。結果を表１に示す。
【００６７】
比較例２および３
バインダーの鹸化度、重合度、添加量、成形圧力を、表１に示すように変化させた以外は、実施例１と同様にして、フェライトコアの試料を作製し、実施例１と同様な試験を行った。結果を表１に示す。なお、比較例３の試料を半田浴に浸漬する前の端面を、顕微鏡写真で撮影した結果を図５に示す。図５に示すように、図２に示す実施例１に比べて、粒界隙間の幅が広いことが確認できた。
【００６８】
評価
表１に示すように、比較例１および３では、最大高さＲｙが１５μｍを越えており、耐熱衝撃試験によりひび割れが多数発生することが確認された。また、実施例１〜５では、最大高さＲｙが１５μｍ以下、さらに好ましくは１２μｍ以下、特に好ましくは１０μｍ以下であることから、耐熱衝撃試験でも、ほとんど、ひび割れが発生しないことが確認された。
【００６９】
なお、比較例２では、最大高さＲｙが１５μｍであったが、顆粒の粒界隙間の幅Ｗが２１μｍと、２０μｍよりも大きく、そのために、耐熱衝撃試験によりひび割れが生じた試料の個数が、３０個中の１８個であった。
【００７０】
また、表１に示す結果から、粒界隙間の幅の最大値は、好ましくは２０μｍ以下、さらに好ましくは１５μｍ以下、特に好ましくは１２μｍ以下であることが確認できた。
【００７１】
さらに、表１に示す結果から、ポリビニルアルコールの平均鹸化度〔ｍ／（ｎ＋ｍ）〕は、好ましくは８８〜９８モル％、より好ましくは９３〜９７モル％であることが確認できた。さらにまた、その平均重合度は、５００〜１７００、より好ましくは８００〜１５００であることが確認できた。さらに、ポリビニルアルコールの添加量は、仮焼物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ことが確認できた。さらに、表１に示す結果から、成形圧力は、２００ＭＰａ以上が好ましいことも確認できた。
【００７２】
【発明の効果】
以上説明してきたように、本発明によれば、半田付けの際に、ひび割れが発生しない、耐熱衝撃性に優れたフェライトコアおよびその製造方法を提供することができる。
【図面の簡単な説明】
【図１】図１はフェライトコアの表面におけるフェライト顆粒および粒界を示す概略図である。
【図２】図２は本発明の実施例に係るフェライトコアの表面状態を示す顕微鏡写真である。
【図３】図３は半田浴浸漬後の本発明の実施例に係るフェライトコアの表面状体を示す顕微鏡写真である。
【図４】図４は本発明の比較例に係るフェライトコアの表面状態を示す顕微鏡写真である。
【図５】図５は半田浴浸漬後の本発明の比較例に係るフェライトコアの表面状体を示す顕微鏡写真である。
【図６】図６は本発明の比較例に係るフェライトコアの表面状態を示す顕微鏡写真である。
【符号の説明】
２… フェライト顆粒
４… 粒界隙間
１０… フェライトコア[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ferrite core that is a sintered product of a ferrite molded body obtained by a dry pressure molding method and a manufacturing method thereof, and more particularly to a ferrite core excellent in thermal shock resistance and a manufacturing method thereof.
[0002]
[Prior art]
Soft magnetic ferrite is widely used in various electronic parts. Such a soft magnetic ferrite can generally be obtained as follows. That is, first, a plurality of oxides constituting ferrite are mixed and calcined, and the calcined product is pulverized into powder, and a granule is prepared by adding a binder to the ferrite powder and granulating. Next, the granule is molded into various shapes according to the purpose to form a preform, and the preform can be sintered to obtain a ferrite core.
[0003]
Ferrite cores obtained in this way are, for example, information terminals such as notebook personal computers and PDAs, mobile phones such as mobile phones and PHS, or electronic components on the premise of carrying such peripheral devices, televisions and stereos. It is used for various electronic parts such as relatively large home appliances. As these electronic components become smaller, thinner and lighter, ferrite sintered bodies used in these electronic components tend to be increasingly smaller, thinner and lighter. Therefore, there is a demand for a ferrite that is smaller or thin and has high durability.
[0004]
By the way, a winding is applied to a ferrite core such as a drum-type core, and both ends of the winding are drawn out to one or more end faces of the core and wound around lead pins installed in advance on the end faces. Then, by immersing this end face in the molten solder, the winding is fixed to the lead pin, and this portion becomes an external electrode.
[0005]
The solder dipping method thus performed is an extremely effective means for automating the soldering and external electrode formation. However, in order to increase the efficiency of work, recently, a solder bath having a high temperature of 420 ° C. or higher has been used, and cracks have occurred in the core due to thermal stress due to local rapid thermal expansion, resulting in a defective rate. It is becoming a problem.
[0006]
In particular, high frequency ferrite cores containing nickel, such as Ni—Zn, Ni—Cu—Zn, and Ni—Cu—Zn—Mg ferrites, are a serious problem.
[0007]
In Patent Document 1 below, Bi—Zn-based ferrite contains Bi as a secondary component.₂O₃, SiO₂, Cr₂O₃It has been proposed to improve thermal shock resistance by adding a stress relaxation layer at the grain boundaries.
[0008]
However, in the method described in this document, in order to improve the thermal shock resistance, it is necessary to add an additive as a subcomponent, and the thermal shock resistance is somewhat improved, but at the time of soldering, It has not yet been possible to prevent the core from cracking.
[0009]
Further, as described in Patent Document 2 below, it is proposed to improve the thermal shock resistance by firing the molded body after coating the surface of the ferrite molded body with a slurry having the same composition as the core. Has been.
[0010]
However, in the method disclosed in this document, there is a possibility that the coating layer may be peeled off at the time of firing, and this method is not practical, and even this method has not yet prevented cracking of the core during soldering.
[0011]
[Patent Document 1] JP-A-11-35369
[Patent Document 2] JP-A-11-204360.
[0012]
[Problems to be solved by the invention]
The present invention has been made in view of such a situation, and an object of the present invention is to provide a ferrite core excellent in thermal shock resistance that does not generate cracks during soldering and a method for manufacturing the same.
[0013]
[Means for Solving the Problems]
As a result of various studies to solve the above-mentioned problems, the present inventor has controlled the grain boundary gap of the ferrite core generated at the grain boundary in the dry pressure molding method with a certain size in the production of ferrite. As a result, it has been found that a ferrite core excellent in thermal shock resistance can be obtained, and the present invention has been completed.
[0014]
That is, the ferrite core according to the first aspect of the present invention is
It is composed of an aggregate of ferrite granules and has a surface having a maximum height Ry defined by JIS B0601 of 15 μm or less, more preferably 12 μm or less, and particularly preferably 10 μm or less.
[0015]
The ferrite core according to the second aspect of the present invention is:
It is composed of aggregates of ferrite granules, and the maximum height Ry defined by JIS B0601 is 15 μm or less, more preferably 12 μm or less, particularly preferably 10 μm or less, and the width of the intergranular gap between the ferrite granules is 20 μm or less. , Preferably 15 μm or less, particularly preferably 12 μm or less.
[0016]
Preferably, the depth of the intergranular gap between the ferrite granules is 15 μm or less, more preferably 12 μm or less, and particularly preferably 10 μm or less.
[0017]
The maximum height Ry defined in JIS B0601 qualitatively means the maximum depth of the intergranular gap between ferrite granules at the reference length on the surface of the ferrite core. If the depth and / or width of the grain boundary gap is increased, the core is cracked by thermal stress due to local rapid thermal expansion caused by soldering, and the defect rate tends to increase.
[0018]
In the present invention, on the surface of the ferrite core, by setting the maximum height Ry (depth and / or width of the intergranular gap of the ferrite granule at the reference length) within a predetermined value, during soldering, A ferrite core excellent in thermal shock resistance that does not crack can be obtained.
[0019]
Preferably, the ferrite granule has an average particle size of 40 to 150 μm. In this case, the content of the ferrite granule having a particle size of 200 μm or more is preferably 5% by mass or less, and the content of the ferrite granule having a particle size of 20 μm or less is 5% by mass or less.
[0020]
In the present invention, it is easy to reduce the depth and / or width of the intergranular gap of the ferrite granule by using the ferrite granule having a predetermined particle diameter range in which the particle diameters are uniform.
[0021]
The method for producing a ferrite core according to the present invention is as follows.
A method for producing a ferrite core according to any one of the above,
Granulating ferrite granules using a slurry containing polyvinyl alcohol having an average degree of saponification of 88 to 98 mol% and an average degree of polymerization of 500 to 1700;
Forming a predetermined shape by applying pressure to the ferrite granules, and forming a preform,
Firing the preform.
[0022]
With partially saponified polyvinyl alcohol having an average degree of saponification of less than 88 mol%, the low-pressure crushability of the granules is good, but the disintegration resistance and sticking resistance tend to be poor. Moreover, although the solubility in water is good and the slurry adjustment is simple and suitable for spray granulation, the material adheres to the wire mesh at the time of oscillating extrusion granulation, and it tends to be difficult to perform continuous granulation.
[0023]
Fully saponified polyvinyl alcohol having an average degree of saponification of 98 mol% or more has good disintegration resistance, but the granulated ferrite granule becomes relatively hard and tends to deteriorate the low-pressure crushing property. Further, the solubility in water is poor, and the slurry adjustment tends to be difficult. Therefore, the average saponification degree is preferably within the above-mentioned range.
[0024]
The average degree of polymerization (m + n) of polyvinyl alcohol is preferably 500 to 1700, more preferably 800 to 1500. When the average degree of polymerization is less than 500, although the low-pressure crushability of the granules is good, the disintegration resistance is poor and the strength of the molded product tends to be low. On the contrary, when the average degree of polymerization exceeds 1700, the granules have relatively good disintegration resistance and strength of the molded product, but since they become hard, the low-pressure crushing property deteriorates and defects due to the grain boundaries occur. It becomes easy.
[0025]
Preferably, the polyvinyl alcohol is contained in the slurry in a proportion of 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 granules. It is. When the addition amount of polyvinyl alcohol is less than 0.4 parts by mass, the calcined product of the ferrite raw material 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 many granule boundaries may be left and a molding defect may occur. Similarly, capacity deficiencies tend to increase.
[0026]
Preferably, the pressure for forming the preform is 200 MPa or more. When the molding pressure is too small, the grain boundary gap width or the grain boundary gap depth of the grain boundary tends to increase, and the thermal shock resistance tends to deteriorate.
[0027]
In addition, in this invention, a ferrite core is a core material comprised with the ferrite sintered compact, and is used by the concept also including a part of core.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a schematic diagram showing ferrite granules and grain boundaries on the surface of a ferrite core.
[0029]
The specific overall shape of the ferrite core according to the present invention is not particularly limited as long as the winding is wound, and various shapes are conceivable. In the present invention, as shown in FIG. 1, the ferrite core 10 is composed of an aggregate of ferrite granules 2.
[0030]
A grain boundary gap 4 between ferrite granules is formed on the surface of the ferrite core 10. On the surface of the core 10, there are a plane in which the individual granules 2 are crushed by pressure and a grain boundary gap 4. If the surface roughness of the core 10 is measured by a measurement method defined in JIS B0601, and the maximum height Ry is obtained, in the present invention, the maximum height Ry is 15 μm or less, preferably 10 μm or less. Become.
[0031]
The maximum height Ry defined by this JIS is qualitatively shown in FIG. 1 between the ferrite granules at the reference length (measurement reference length defined by JIS) on the surface of the ferrite core 10. It means the maximum value of the depth D of the gap 4. That is, on the surface of the ferrite core 10 according to the present invention, the maximum value of the depth D of the grain boundary gap 4 is 15 μm or less, preferably 10 μm or less. At least in the soldered portion of the ferrite core 10, the maximum value of the depth D of the grain boundary gap 4 is 15 μm or less, preferably 10 μm or less.
[0032]
In this embodiment, the maximum value of the width W of the grain boundary gap 4 is preferably 20 μm or less, more preferably 15 μm or less, and particularly preferably 12 μm or less. At least at the soldering location in the ferrite core 10, the maximum value of the width W of the grain boundary gap 4 is preferably 20 μm or less, more preferably 15 μm or less, and particularly preferably 12 μm or less.
[0033]
In this embodiment, the average particle diameter of the ferrite granule 2 is 40 to 150 μm. In this case, the content of ferrite granules 2 having a particle size of 200 μm or more is preferably 5% by mass or less, and the content of ferrite granules 2 having a particle size of 20 μm or less is 5% by mass or less.
[0034]
In the present embodiment, by using the ferrite granule 2 having a predetermined particle diameter range in which the particle diameters are uniform in this way, it is easy to reduce the depth D and / or the width W of the intergranular gap 4 of the ferrite granule 2. Become.
[0035]
[Outline of Ferrite Core Manufacturing Process]
Next, a method for manufacturing the ferrite core 10 will be described.
First, as a 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 is prepared, and the temperature and flow rate are adjusted using a spray granulator so that the average particle diameter of the granules falls within a predetermined range. Grain. After forming this granule, it is fired to obtain a ferrite core.
[0036]
[Ferrite composition]
The raw material for producing the ferrite core of the present invention is appropriately selected depending on the intended use of the finally fired ferrite core, and is not particularly limited. For example, in order to manufacture Ni-Zn based ferrite or Ni-Zn-Cu based ferrite, for example, Fe₂O₃NiO, CuO, MnO, MgO, ZnO are the main components, and subcomponents are added as necessary. This raw material may contain metal oxides such as Co, W, Bi, Si, B, and Zr as inevitable impurities.
[0037]
[Crushing of calcined product of ferrite raw material powder]
In order to obtain a ferrite powder having a predetermined 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.
[0038]
[Binder component]
The binder used when granulating the ferrite granule in the present invention can be appropriately selected from binders conventionally used for granulating the ferrite granule according to the purpose of use. Examples of such binders include partially saponified products of polyvinyl alcohol and polyvinyl acetate, poly (meth) acrylic acid, methylcellulose, homopolymers and copolymers of acrylamides, and the like. These binders can be used alone or as a mixture of two or more.
[0039]
In the present invention, it is particularly preferable to contain polyvinyl alcohol (PVA) represented by the following structural formula as a binder. By including a specific polyvinyl alcohol as a binder, defects due to grain boundaries can be reduced, and high molded body density and strength can be maintained, and the density and thermal shock resistance of the sintered body can be improved. Can do. 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.
[0040]
[Chemical 1]

[0041]
Polyvinyl alcohol as a binder functions as a binder for primary particles, that is, a binder between ferrite powder and ferrite powder, and low-pressure crushability, collapse resistance, compact strength, sintered compact density, and sintered density of ferrite granules. Affects body strength and thermal shock resistance.
[0042]
The average saponification degree [m / (n + m)] of the polyvinyl alcohol in the present invention is preferably 88 to 98 mol%, more preferably 93 to 97 mol% as the whole polyvinyl alcohol as a binder. PVA having a saponification degree in such a range is referred to as intermediate saponified polyvinyl alcohol.
[0043]
In the so-called partially saponified polyvinyl alcohol having an overall average saponification degree of less than 88 mol%, the low-pressure crushing property of the granules is good, but the disintegration resistance and sticking resistance tend to be 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. On the contrary, the so-called fully saponified polyvinyl alcohol having an overall average saponification degree of 98 mol% or more has good disintegration resistance, but the granulated ferrite granules tend to be relatively hard, so that the low-pressure crushing property tends to deteriorate. It is in. Further, the solubility in water is poor, and the slurry adjustment tends to be difficult.
[0044]
The average degree of polymerization (m + n) of polyvinyl alcohol is preferably 500 to 1700, more preferably 800 to 1500. When the average degree of polymerization is less than 500, although the low-pressure crushability of the granules is good, the disintegration resistance is poor and the strength of the molded product tends to be 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 since they become hard, the low-pressure crushing property deteriorates and defects due to the grain boundaries tend to occur. It is in.
[0045]
In the present invention, the amount of the polyvinyl alcohol 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 calcined product. . When the addition amount of polyvinyl alcohol is less than 0.4 parts by mass, the calcined product of the ferrite raw material powder may not be granulated. On the other hand, if it exceeds 1.2 parts by mass, the ferrite granules become too hard and the crushing becomes worse, so that there are cases where many grain boundaries are left and defective molding occurs. Similarly, capacity deficiencies tend to increase.
[0046]
The polyvinyl alcohol that can be used in the present invention is not particularly limited as long as it has the aforementioned predetermined average saponification degree and polymerization degree as a whole, and even if it is unmodified, for example, alkyl vinyl ether, hydroxy vinyl ether, acetic acid It may be modified with allyl, amide, vinylsilane, ethylene or the like.
[0047]
[Regarding other additives]
In the present invention, when granulating ferrite granules, conventionally known various additives can be added as desired within a range that does not impair the objects and effects of the present invention. Examples of such additives include dispersants such as polycarboxylates and condensed naphthalene sulfonic acids; plasticizers such as glycerin, glycols, and triols; lubricants such as waxes; polyether-based, urethane-modified polyether-based, Examples thereof include organic polymer flocculants such as polyacrylic acid and modified acrylic acid organic polymers; inorganic flocculants such as aluminum sulfate, aluminum chloride, and aluminum nitrate.
[0048]
[Granulation]
In the present invention, these components are used to granulate into ferrite granules by a conventionally known granulation method. The granulation at this time can be performed by a conventionally known spray-drying granulation method or oscillating extrusion granulation method. Specifically, the ferrite particles are prepared by preparing a slurry in which the above-described ferrite particles, binder, and various additives as desired are dispersed in water, and spray-drying the slurry thus prepared with a spray dryer or the like. Granules are produced.
[0049]
Alternatively, ferrite particles, a binder, and various additives as required are mixed and granulated with a stirring granulator to produce a granulated powder, and this granulated powder is extruded and granulated with an oscillating granulator. By repeatedly applying, a granule for forming a ferrite is produced.
[0050]
The shape and particle size of the granules granulated in this way are appropriately selected depending on the granulation method, the shape of the target molded product, etc., but ferrite granules granulated by spray drying are usually It has a spherical shape with a particle size of 40 to 250 μm, preferably 60 to 200 μm, more preferably 80 to 150 μm. Moreover, the granule granulated by oscillating extrusion is 80-500 micrometers normally, Preferably it is 100-300 micrometers, More preferably, it is a particle size of 125-200 micrometers.
[0051]
[Average diameter of ferrite granules]
In the present invention, the preferred average particle size of the ferrite granules is in the range of 40 to 150 μm, the content of coarse granules of 200 μm or more is 5% by mass or less, and the content of fine granules of 20 μm or less is 5% by mass. The following is preferable. The granules are preferably spherical granules.
[0052]
If the average particle diameter 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 to be small. Moreover, it becomes possible to suppress fine powder adhesion (sticking) to the mold. Further, when the average particle size is 150 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 few defects due to the grain boundary, and therefore has high thermal shock resistance.
[0053]
[Molding and firing]
The granulated ferrite granule is molded into a predetermined shape by various compression molding methods, for example, a single pressing method, a double pressing method, a floating die method, a withdrawal method, etc., and becomes a preform. The press machine is appropriately selected depending on the size, shape, and quantity, such as a mechanical press, a hydraulic press, and a servo press.
The molding pressure for forming the preform is not particularly limited, but is preferably 200 MPa or more, more preferably 300 MPa or more. When the molding pressure is too small, the grain boundary gap width or the grain boundary gap depth of the grain boundary tends to increase, and the thermal shock resistance tends to deteriorate.
[0054]
The preform formed into a predetermined shape is then fired to become a ferrite core or a part of the ferrite core (which may be combined to become a ferrite core). The firing temperature varies depending on the ferrite component, but is generally 1000 to 1300 ° C.
[0055]
In the present embodiment, the surface of the ferrite core after firing thus obtained has a maximum height Ry defined by JIS B0601 of 15 μm or less, and the width W of the intergranular gap 4 between the ferrite granules is 20 μm. It is as follows. Therefore, in the ferrite core of the present embodiment, it is possible to obtain a ferrite core excellent in thermal shock resistance that does not crack during soldering.
The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.
[0056]
【Example】
Hereinafter, the present invention will be described based on further detailed examples, but the present invention is not limited to these examples.
[0057]
Example 1
Fe₂O₃: 49 mol%,
NiO: 22 mol%,
CuO: 9 mol%,
ZnO: 20 mol%,
These oxides were weighed so that the ratio was as follows, and wet-mixed for 4 hours using a wet media stirring type pulverizer. In this wet mixing, pure water was used as a dispersion medium.
[0058]
Next, this mixture was dried by a spray dryer and calcined at 900 ° C. for 2 hours to obtain a calcined product of Ni—Cu—Zn ferrite.
[0059]
This calcined product is pulverized for 8 hours with a wet media agitation type pulverizer, and the BET value is 3.0 m.²/ G of calcined calcined powder, 0.8 parts by mass of polyvinyl alcohol having an average saponification degree of 93 mol% and an average polymerization degree of 1200 parts by mass with respect to 100 parts by mass of the calcined substance, and sprayed with a spray dryer. The particles were dried to obtain Ni—Cu—Zn ferrite granules having an average particle size of 100 μm.
[0060]
This granule is 294 MPa (3000 kgf / cm²) To form a block molded body having a length of 14 mm, a width of 14 mm, and a height of 2 mm. The density of the obtained molded body was 3.29 g / cm.³Met. 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.
[0061]
The density of the obtained sintered body is 5.16 g / cm.³Met. The surface of the sintered body was measured for the maximum height Ry defined by JIS B0601 and the size of the grain boundary 4 (maximum of the width W) using an “ultra-deep shape measuring microscope” manufactured by KEYENCE. . The maximum height Ry was 7 μm, and the grain boundary size was 8 μm.
[0062]
The end face of this ferrite sintered body was immersed in a solder bath at 440 ° C. for 5 seconds to evaluate thermal shock resistance. As a result, no cracks were generated in 30 samples. The results are shown in Table 1. Moreover, the result of having photographed the end surface before immersing the sample of this Example 1 in a solder bath with a microscope picture is shown in FIG. Furthermore, the result of having photographed the end surface after immersing the sample of this Example 1 in a solder bath with the microscope picture is shown in FIG.
[0063]
[Table 1]

[0064]
Comparative Example 1
A ferrite core sample was prepared in the same manner as in Example 1 except that the amount of binder added was 2.0 parts by mass with respect to 100 parts by mass of the calcined product, and the same test as in Example 1 was performed. . The results are shown in Table 1.
[0065]
Moreover, the result of having image | photographed the end surface before immersing the sample of this comparative example 1 in a solder bath with a microscope picture is shown in FIG. As shown in FIG. 4, it was confirmed that the width of the grain boundary gap was wider than that of Example 1 shown in FIG. Furthermore, the result of having photographed the end surface after immersing the sample of this comparative example 1 in a solder bath with a microscope picture is shown in FIG. As shown in FIG. 5, cracks were observed.
[0066]
Examples 2-5
A ferrite core sample was prepared in the same manner as in Example 1 except that the saponification degree, polymerization degree, addition amount, and molding pressure of the binder were changed as shown in Table 1, and the same test as in Example 1 was performed. Went. The results are shown in Table 1.
[0067]
Comparative Examples 2 and 3
A ferrite core sample was prepared in the same manner as in Example 1 except that the saponification degree, polymerization degree, addition amount, and molding pressure of the binder were changed as shown in Table 1, and the same test as in Example 1 was performed. Went. The results are shown in Table 1. In addition, the result of having image | photographed the end surface before immersing the sample of the comparative example 3 in a solder bath with a microscope picture is shown in FIG. As shown in FIG. 5, it was confirmed that the width of the grain boundary gap was wider than that of Example 1 shown in FIG.
[0068]
Evaluation
As shown in Table 1, in Comparative Examples 1 and 3, the maximum height Ry exceeded 15 μm, and it was confirmed by the thermal shock test that many cracks were generated. Moreover, in Examples 1-5, since the maximum height Ry is 15 micrometers or less, More preferably, it is 12 micrometers or less, Most preferably, it is 10 micrometers or less, Therefore In the thermal shock test, it was confirmed that a crack hardly generate | occur | produces.
[0069]
In Comparative Example 2, the maximum height Ry was 15 μm, but the width W of the grain boundary gap of the granule was 21 μm, which was larger than 20 μm. Therefore, the number of samples in which cracking occurred in the thermal shock test was , 18 out of 30.
[0070]
From the results shown in Table 1, it was confirmed that the maximum value of the width of the grain boundary gap was preferably 20 μm or less, more preferably 15 μm or less, and particularly preferably 12 μm or less.
[0071]
Furthermore, from the results shown in Table 1, it was confirmed that the average saponification degree [m / (n + m)] of polyvinyl alcohol was preferably 88 to 98 mol%, more preferably 93 to 97 mol%. Furthermore, it has confirmed that the average degree of polymerization was 500-1700, More preferably, it was 800-1500. Furthermore, it was confirmed that the addition amount of polyvinyl alcohol 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 calcined product. Furthermore, from the results shown in Table 1, it was confirmed that the molding pressure was preferably 200 MPa or more.
[0072]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a ferrite core excellent in thermal shock resistance that does not generate cracks during soldering and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing ferrite granules and grain boundaries on the surface of a ferrite core.
FIG. 2 is a photomicrograph showing the surface state of a ferrite core according to an example of the present invention.
FIG. 3 is a photomicrograph showing the surface of a ferrite core according to an example of the present invention after immersion in a solder bath.
FIG. 4 is a photomicrograph showing the surface state of a ferrite core according to a comparative example of the present invention.
FIG. 5 is a photomicrograph showing the surface of a ferrite core according to a comparative example of the present invention after immersion in a solder bath.
FIG. 6 is a photomicrograph showing the surface state of a ferrite core according to a comparative example of the present invention.
[Explanation of symbols]
2 ... Ferrite granules
4 ... Grain boundary gap
10 ... Ferrite core

Claims (8)

A ferrite core comprising an aggregate of ferrite granules and having a surface having a maximum height Ry defined by JIS B0601 of 15 μm or less. A ferrite core comprising an aggregate of ferrite granules, wherein the maximum height Ry defined by JIS B0601 is 15 μm or less, and the width of the intergranular gap between the ferrite granules is 20 μm or less. The ferrite core according to claim 2, wherein a depth of a grain boundary gap of the ferrite granule is 15 µm or less. The ferrite core according to any one of claims 1 to 3, wherein the ferrite granules have an average particle size of 40 to 150 µm. The content of the ferrite granule having a particle size of 200 μm or more is 5% by mass or less, and the content of the ferrite granule having a particle size of 20 μm or less is 5% by mass or less. Ferrite core. A method for producing a ferrite core according to any one of claims 1 to 5,
Granulating ferrite granules using a slurry containing polyvinyl alcohol having an average degree of saponification of 88 to 98 mol% and an average degree of polymerization of 500 to 1700;
Forming a predetermined shape by applying pressure to the ferrite granules, and forming a preform,
And a step of firing the preform. The said polyvinyl alcohol is a manufacturing method of the ferrite core of Claim 6 contained in the said slurry in the ratio of 0.4-1.2 mass parts with respect to 100 mass parts of the said ferrite granule. The method for manufacturing a ferrite core according to claim 6 or 7, wherein a pressure for forming the preform is 200 MPa or more.

Images