JPH0586407A - Production of magnetic metallic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To provide the magnetic metallic powder which has adequate magnetic characteristics suitable for high-performance magnetic recording and excellent dispersibility at the time of prepn. of a coating material and is extremely adequate for producing a high-density magnetic recording medium of high output decreased in the noises occurring in particle-like noises. CONSTITUTION:This process for production of the magnetic metallic powder for magnetic recording consists in settling an aq. soln. of an aluminum salt and ferric salt, an aq. alkaline soln. and aluminum hydrous ferric oxide in the suspension of the particles of a hydrous iron oxide base body, then subjecting the surfaces of the base body particles to a heating treatment at 10 to 13 pH and 40 to 120 deg.C to form an aluminum-contg. alpha-iron oxyhydroxide layer. A boron compd. is further added at need to the soln. and the surfaces of the base body particles are subjected to the heating treatment at 600 to 900 deg.C in a non-reducing atmosphere then to reduction by heating.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【発明の技術分野】本発明は、磁気記録用に好適な鉄系
金属磁性粉末の製造方法に関する。TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing an iron-based metal magnetic powder suitable for magnetic recording.

【０００２】[0002]

【発明の技術的背景とその問題点】磁気記録用媒体は、
近年その記録密度を向上させ、より小型のもの、より高
性能なものに改善しようとする指向が一段と強まってき
ている。これにともない、磁気記録用磁性粉末として、
酸化鉄系磁性粉末に比べて、飽和磁化及び保磁力が大き
い鉄または鉄系金属磁性粉末（以下、金属磁性粉末とい
う）が注目されている。金属磁性粉末は、デジタルオー
ディオテープや８ｍｍビデオテープなどへの実用が図ら
れつつあるが、近時さらに高画質ビデオテープ、高記録
密度ディスクなど、高性能記録媒体への適用が一層期待
されている。TECHNICAL BACKGROUND OF THE INVENTION AND PROBLEMS THEREOF
In recent years, there has been an increasing tendency to improve the recording density and to improve the recording density to a smaller size and a higher performance. Along with this, as magnetic powder for magnetic recording,
Attention has been paid to iron or iron-based metal magnetic powder (hereinafter referred to as metal magnetic powder), which has a larger saturation magnetization and coercive force than iron oxide-based magnetic powder. The magnetic metal powder is being put to practical use in digital audio tapes, 8mm video tapes, etc., but is expected to be applied to high-performance recording media such as high-quality video tapes and high-density disks recently. ..

【０００３】近年、高性能磁気記録用金属磁性粉末とし
て、これがたとえば針状粒子の場合、通常、長軸が約
０．５μｍ、さらには０．３μｍ以下の微細で焼結のな
いものが要求されており、なかんづく粒子性ノイズ低減
による高出力化をはかるために、一層超微細粉が要求さ
れており、このために、針状粒子を形成する結晶子の大
きさ（以下Ｌｃという）を小さくすることが、針状形骸
粒子を小さくすることと共に一層重要となってきてい
る。さらにこのような超微細粉を磁性塗料としたときの
分散性、その塗膜での配向性、充填性、表面平滑性など
の一層優れたものが希求されている。しかして、磁性粉
は一般に、微細なものにすればするほど、分散性や充填
性などが損なわれ易い。従って、鉄系金属磁性粉末の分
散性や充填性などを損なうことなく微細化をはかるに
は、まず出発原料の含水酸化鉄や酸化鉄は、その粒子が
微細であって、かつ良好な粒度分布のものが所望されて
いる。しかしながら、前記出発原料はそれが微細なもの
であればあるほど目的物への還元過程で、粒子内焼結に
より針状形状が変化したり、粒子間焼結により架橋や粒
子の粗大化を起こしたりして、目的物の磁気特性に著し
く悪影響を与える。In recent years, as magnetic metal powders for high-performance magnetic recording, when these are, for example, acicular particles, fine particles having a major axis of about 0.5 μm, and even 0.3 μm or less, which are fine and non-sintering, are required. In order to achieve higher output by reducing particle noise, in particular, ultrafine powder is required, and for this reason, the size of the crystallite forming the acicular particles (hereinafter referred to as Lc) is reduced. This is becoming more important along with making needle-shaped body particles smaller. Further, there is a demand for further excellent dispersibility when such an ultrafine powder is used as a magnetic coating, orientation in the coating film, filling property, surface smoothness, and the like. However, in general, the finer the magnetic powder, the more easily the dispersibility and filling properties are impaired. Therefore, in order to achieve fineness without impairing the dispersibility and filling properties of the iron-based metal magnetic powder, first of all, the iron oxide hydroxide or iron oxide as the starting material has fine particles and has a good particle size distribution. Are desired. However, the finer the starting material, the more it is reduced in the process of reduction to the desired product, and the needle-like shape is changed by intra-particle sintering, or the inter-particle sintering causes cross-linking or coarsening of particles. In that case, the magnetic properties of the target object are significantly adversely affected.

【０００４】従来から、これらの問題点を解決するた
め、種々の対策が提案されている。通常、含水酸化鉄ま
たは酸化鉄の粒子表面に、種々の形状保持剤を被着した
り、あるいは混合付着したりした後、加熱還元処理する
方法が行われている。前記形状保持剤としては、たとえ
ば、ケイ素化合物を用いる方法、アルミニウム化合物を
用いる方法、アルミニウム化合物とケイ素化合物を併用
する方法のほか、ホウ素化合物を用いる方法（特公昭５
４−４２８３２，特公昭５９−３２８８１，特公昭５９
−１９９６４，特公平１−２２９６８，特開昭５７−１
０６５２６，特開昭５８−４８６１１，特開昭５８−４
８６１２，特開昭５９−５６０３，特開昭６１−８８５
０５，特開昭６１−１７４３０４，特開昭６４−８４６
０１，特開昭５６−１２７７１０，特開昭５８−１７６
９０２，特開昭６３−１４０００５など）も提案されて
いる。しかしながら、これらの方法は、粒子形状の崩れ
や粒子間焼結などをある程度改善し得るものの、反面前
記還元反応の進行が阻害され易かったり処理条件によっ
て被着あるいは付着される処理量がバラツキ易かった
り、被覆層が不均一になり易かったりして得られる金属
磁性粉末の磁気特性の変動が避けられなかったり、する
など、解決を要する問題点が少なくない。Conventionally, various measures have been proposed in order to solve these problems. In general, a method of applying various shape-retaining agents or admixing them onto the surface of iron oxide hydroxide or iron oxide particles and then performing heat reduction treatment is performed. As the shape-retaining agent, for example, a method using a silicon compound, a method using an aluminum compound, a method using both an aluminum compound and a silicon compound, and a method using a boron compound (Japanese Patent Publication No.
4-42832, JP59-32881, JP59
-19964, Japanese Examined Patent Publication No. 1-22968, JP-A-57-1
06526, JP-A-58-48611, and JP-A-58-4
8612, JP-A-59-5603, JP-A-61-885
05, JP-A-61-174304, JP-A-64-846
01, JP-A-56-127710, JP-A-58-176
902, JP-A-63-140005, etc.) have also been proposed. However, although these methods can improve the collapse of the particle shape and the sintering between particles to some extent, on the other hand, the progress of the reduction reaction is likely to be hindered or the treatment amount deposited or adhered due to the treatment conditions may easily vary. However, there are many problems that need to be solved, such as that the coating layer is likely to be non-uniform and fluctuations in the magnetic properties of the metal magnetic powder obtained cannot be avoided.

【０００５】[0005]

【発明の目的】本発明は、前記問題点を一掃して、工業
的有利に磁気記録用金属磁性粉末を製造できる方法を提
供することを目的とするものである。SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above problems and to provide a method capable of industrially producing a magnetic metal powder for magnetic recording industrially.

【０００６】[0006]

【発明の概要】本発明者等は、前記の問題点を解決する
ために種々検討した結果、アルミニウム化合物が金属磁
性粉末の表面に存在すると磁性塗料としたときの分散性
がよく、さらに還元時にα−Ｆｅ結晶子の成長が抑制さ
れ、Ｌｃの小さな金属磁性粉末が得られ易い反面、単に
アルミニウム化合物を含水酸化鉄粒子の表面にアルミニ
ウムの含水酸化物として被着する方法では、アルミニウ
ム被着層が不均一になり易く、還元時に金属磁性粉末粒
子の表面から偏析したり剥離し易いことなどの知見を得
た。これらの知見に基づき、アルミニウム化合物の被着
方法に関してさらに検討を進めた結果、（１）含水酸化
鉄基体粒子の懸濁液にアルミニウム塩と第二鉄塩との水
溶液とアルカリ水溶液とを添加して、きわめて微細なア
ルミニウム含有水酸化第二鉄を沈澱させ、次いで特定ｐ
Ｈ及び特定温度で加熱処理することにより、該基体粒子
表面にきわめて均一なアルミニウム含有α−オキシ水酸
化鉄層が形成され、さらに、このものを非還元性雰囲気
下に特定温度で加熱処理することにより表面にアルミニ
ウムが均一にドープしたきわめて緻密なヘマタイト粒子
となり、さらに、該ヘマタイト粒子を還元することによ
り、粒子形状の崩れや粒子間焼結が抑制されかつＬｃが
小さく緻密な金属磁性粉末が得られ、この金属磁性粉末
は磁気特性、特に保磁力、角形比、配向比、飽和磁束密
度、反転磁界分布、さらに耐酸化性に優れ、高記録密度
用磁気記録媒体に極めて好適なものとなること、及び、
（２）前記、非還元性雰囲気下での加熱処理をホウ素化
合物の存在下におこなうことにより、表面にアルミニウ
ムが均一にドープした一層緻密なヘマタイト粒子とな
り、さらに、このものを還元することにより、Ｌｃがよ
り小さく緻密な金属磁性粉末が得られるとの知見を得て
本発明を完成したものである。SUMMARY OF THE INVENTION The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, when an aluminum compound is present on the surface of a metal magnetic powder, the dispersibility in a magnetic coating is good, and further, during reduction, While the growth of α-Fe crystallites is suppressed and a metal magnetic powder having a small Lc is easily obtained, in the method of simply depositing an aluminum compound on the surface of hydrous iron oxide particles as a hydroxide of aluminum, an aluminum coating layer It has been found that the particle size is likely to be non-uniform, and that the metal magnetic powder particles are easily segregated or peeled off from the surface during reduction. Based on these findings, as a result of further study on the deposition method of the aluminum compound, (1) an aqueous solution of an aluminum salt and a ferric salt and an alkaline aqueous solution were added to a suspension of iron oxide hydroxide-containing base particles. Precipitate very fine aluminium-containing ferric hydroxide, then
By heat-treating at H and a specific temperature, a very uniform aluminum-containing α-iron oxyhydroxide layer is formed on the surface of the base particles, and further heat-treating this at a specific temperature in a non-reducing atmosphere. To form extremely dense hematite particles whose surface is uniformly doped with aluminum, and further, by reducing the hematite particles, collapse of the particle shape and interparticle sintering are suppressed, and Lc is small and a dense metal magnetic powder is obtained. This magnetic metal powder has excellent magnetic properties, particularly coercive force, squareness ratio, orientation ratio, saturation magnetic flux density, reversal magnetic field distribution, and oxidation resistance, and is extremely suitable for magnetic recording media for high recording density. ,as well as,
(2) By performing the heat treatment under a non-reducing atmosphere in the presence of a boron compound, more dense hematite particles in which aluminum is uniformly doped on the surface are formed, and further, by reducing this, The present invention has been completed based on the finding that a dense metal magnetic powder having a smaller Lc can be obtained.

【０００７】[0007]

【発明の構成】すなわち、本発明は以下のとおりであ
る。 （１）含水酸化鉄基体粒子の懸濁液に、アルミニウム塩
と第二鉄塩との水溶液及びアルカリ水溶液とを添加して
アルミニウム含有水酸化第二鉄を沈澱させ、次いでｐＨ
１０〜１３、４０〜１２０℃で加熱処理して該基体粒子
表面にアルミニウム含有α−オキシ水酸化鉄層を形成さ
せ、しかる後このものを非還元性雰囲気下６００〜９０
０℃で加熱処理した後加熱還元処理することを特徴とす
る磁気記録用金属磁性粉末の製造方法。 （２）含水酸化鉄基体粒子の懸濁液に、アルミニウム塩
と第二鉄塩との水溶液及びアルカリ水溶液とを添加して
アルミニウム含有水酸化第二鉄を沈澱させ、次いでｐＨ
１０〜１３、４０〜１２０℃で加熱処理して該基体粒子
表面にアルミニウム含有α−オキシ水酸化鉄層を形成さ
せ、さらにこのものにホウ素化合物を添加した後、非還
元性雰囲気下６００〜９００℃で加熱処理し、しかる後
加熱還元処理することを特徴とする磁気記録用金属磁性
粉末の製造方法。 （３）アルミニウム塩の添加量が、含水酸化鉄基体粒子
に対しＡｌ／Ｆｅとして０．０５〜０．１５（原子重量
比）であり、かつ添加する第二鉄塩量に対してＡｌ／Ｆ
ｅ³⁺として０．１〜１．５（原子重量比）であることを
特徴とする前（１）項または前（２）項の磁気記録用金
属磁性粉末の製造方法。 （４）含水酸化鉄基体粒子が比表面積６０ｍ² ／ｇ以上
の針状ゲーサイトであることを特徴とする前（１）項ま
たは前（２）項の磁気記録用金属磁性粉末の製造方法。That is, the present invention is as follows. (1) An aqueous solution of an aluminum salt and a ferric salt and an alkaline aqueous solution are added to a suspension of iron oxide hydroxide-containing base particles to precipitate aluminum-containing ferric hydroxide, and then pH
Heat treatment is carried out at 10 to 13, 40 to 120 ° C. to form an aluminum-containing α-iron oxyhydroxide layer on the surface of the base particles, and then this is subjected to 600 to 90 in a non-reducing atmosphere.
A method for producing a metal magnetic powder for magnetic recording, comprising performing a heat treatment at 0 ° C. and then a heat reduction treatment. (2) An aqueous solution of an aluminum salt and a ferric salt and an alkaline aqueous solution are added to a suspension of iron oxide hydroxide-containing base particles to precipitate aluminum-containing ferric hydroxide, and then the pH is adjusted.
After heat treatment at 10 to 13 and 40 to 120 ° C., an aluminum-containing α-iron oxyhydroxide layer is formed on the surface of the substrate particles, and a boron compound is further added to this, and then 600 to 900 in a non-reducing atmosphere. A method for producing a metal magnetic powder for magnetic recording, which comprises heat-treating at ℃ and then heat-reducing. (3) The amount of aluminum salt added is 0.05 to 0.15 (atomic weight ratio) as Al / Fe with respect to the iron oxide hydroxide base particles, and Al / F with respect to the amount of ferric iron added.
e ³⁺ is 0.1 to 1.5 (atomic weight ratio), the method for producing the metallic magnetic powder for magnetic recording according to the above (1) or (2). (4) The method for producing a magnetic metal powder for magnetic recording according to item (1) or (2), wherein the iron oxide hydroxide base particles are acicular goethite having a specific surface area of 60 m ² / g or more.

【０００８】本発明において、基体粒子としての含水酸
化鉄には種々のものがある。含水酸化鉄の代表的なもの
としてオキシ水酸化鉄があり、たとえばα−ＦｅＯＯ
Ｈ、β−ＦｅＯＯＨ、γ−ＦｅＯＯＨなどを挙げ得る。
なお、前記の含水酸化鉄の粒子形状は、代表的には針状
であるが、それ以外の種々の形状のものが使用できる。
たとえば紡錘状、米粒状、棒状、平板状、サイコロ状な
どである。これら基体粒子の中、とくに望ましいのは針
状α−ＦｅＯＯＨ及びγ−ＦｅＯＯＨである。また基体
粒子は、その比表面積が６０ｍ² ／ｇ以上、とくに望ま
しくは７０ｍ² ／ｇ以上のように微細なものが好適であ
る。In the present invention, there are various iron oxide hydroxides as the base particles. A typical iron oxide hydroxide is iron oxyhydroxide, for example, α-FeOO.
H, β-FeOOH, γ-FeOOH and the like may be mentioned.
The particle shape of the above-mentioned iron oxide hydroxide is typically needle-like, but various other shapes can be used.
For example, it is spindle-shaped, rice grain-shaped, rod-shaped, flat-plate-shaped or dice-shaped. Among these substrate particles, needle-shaped α-FeOOH and γ-FeOOH are particularly desirable. The base particles are preferably fine particles having a specific surface area of 60 m ² / g or more, particularly preferably 70 m ² / g or more.

【０００９】本発明方法においては、まず含水酸化鉄基
体粒子の懸濁液に、アルミニウム塩と第二鉄塩との水溶
液及びアルカリ水溶液とを添加して水酸化アルミニウム
と水酸化第二鉄の微細な共沈物を生成させる。アルミニ
ウム塩としては、たとえば、塩化アルミニウム、硫酸ア
ルミニウム、硝酸アルミニウムなどを挙げることがで
き、第二鉄塩としては、たとえば塩化第二鉄、硫酸第二
鉄、硝酸第二鉄などを挙げることができる。また、アル
カリ剤としては、たとえば水酸化ナトリウム、水酸化カ
リウム、アンモニア水などを挙げることができる。アル
ミニウム塩の添加量は、基体粒子に対してＡｌ／Ｆｅと
して０．０５〜０．１５（原子重量比）でかつ添加する
第二鉄塩量に対して、Ａｌ／Ｆｅ³⁺として０．１〜１．
５（原子重量比）である。添加するアルカリ剤の量はア
ルミニウム塩と第二鉄塩とのほぼ中和当量であり懸濁液
のｐＨが７〜８を示すまでアルカリ剤を添加する。な
お、この際の懸濁液の温度は、望ましくは４０℃以下に
保持する。次いで前記のようにして得られた水酸化アル
ミニウムと水酸化第二鉄の共沈物を含有する含水酸化鉄
基体粒子の懸濁液に、さらにアルカリ剤を添加して懸濁
液のｐＨ１０〜１３に調整した後４０〜１２０℃で常圧
または加圧下で１〜１２時間加熱処理して、基体粒子表
面上に均一にアルミニウムが固溶したα−オキシ水酸化
鉄層を形成させる。前記中和時の処理温度が、余り高す
ぎると微細な水酸化アルミニウムと水酸化第二鉄共沈物
が得られず而後の加熱処理でのいわゆるゲーサイト化反
応が進みにくく、また中和処理時のｐＨが余り高すぎる
と水酸化アルミニウムと水酸化第二鉄とが別々に沈澱し
易く、その後の加熱処理で基体粒子表面上に形成される
α−オキシ水酸化鉄層へアルミニウムの固溶が不均一に
なる。次に加熱処理時のｐＨが前記範囲より高すぎると
α−オキシ水酸化鉄層へのアルミニウムの固溶が難し
く、またｐＨが前記範囲より低すぎると前記共沈物のゲ
ーサイト化反応が進まず、さらに加熱処理の温度が前記
範囲より高すぎると、新たにゲーサイト粒子が別相に生
成したりするなど、アルミニウム固溶α−オキシ水酸化
鉄層の生長が不均一になり易い。また温度が前記範囲よ
り低すぎると該共沈物のゲーサイト化反応の進行が損な
われ易かったりする。添加するアルミニウム塩の量は、
基体粒子の大きさに応じ前記範囲内で選択し得るが、ア
ルミニウム量が少なすぎると所望効果がもたらされず、
また前記範囲より多すぎるとアルミニウム固溶α−オキ
シ水酸化鉄層の生長が阻害され易くなる。In the method of the present invention, first, an aqueous solution of an aluminum salt and a ferric salt and an alkaline aqueous solution are added to a suspension of iron oxide hydroxide-containing base particles to prepare a fine powder of aluminum hydroxide and ferric hydroxide. Co-precipitate. Examples of the aluminum salt include aluminum chloride, aluminum sulfate, and aluminum nitrate. Examples of the ferric salt include ferric chloride, ferric sulfate, and ferric nitrate. .. Examples of the alkaline agent include sodium hydroxide, potassium hydroxide, aqueous ammonia and the like. The amount of aluminum salt added is 0.05 to 0.15 (atomic weight ratio) as Al / Fe with respect to the base particles, and 0.1 as Al / Fe ^{3+ with} respect to the amount of ferric salt added. ~ 1.
5 (atomic weight ratio). The amount of the alkaline agent to be added is approximately the neutralization equivalent of the aluminum salt and the ferric salt, and the alkaline agent is added until the pH of the suspension shows 7-8. The temperature of the suspension at this time is desirably maintained at 40 ° C or lower. Then, an alkaline agent is further added to the suspension of the iron oxide hydroxide-containing particles containing the coprecipitate of aluminum hydroxide and ferric hydroxide obtained as described above, and the pH of the suspension is adjusted to 10 to 13 After that, heat treatment is performed at 40 to 120 ° C. under normal pressure or under pressure for 1 to 12 hours to form an α-iron oxyhydroxide layer in which aluminum is uniformly solid-dissolved on the surface of the base particles. If the treatment temperature during the neutralization is too high, a fine aluminum hydroxide and ferric hydroxide coprecipitate cannot be obtained, and the so-called goethite reaction in the subsequent heat treatment is difficult to proceed, and the neutralization treatment If the pH at this time is too high, aluminum hydroxide and ferric hydroxide tend to precipitate separately, and aluminum is solid-dissolved in the α-iron oxyhydroxide layer formed on the surface of the substrate particles by the subsequent heat treatment. Becomes uneven. Next, if the pH during the heat treatment is higher than the above range, it is difficult to form a solid solution of aluminum in the α-iron oxyhydroxide layer, and if the pH is lower than the above range, the goethite reaction of the coprecipitate proceeds. First, if the temperature of the heat treatment is higher than the above range, the growth of the aluminum solid solution α-iron oxyhydroxide layer is likely to be nonuniform, such as new generation of goethite particles in a separate phase. If the temperature is lower than the above range, the progress of the goethite reaction of the coprecipitate may be easily impaired. The amount of aluminum salt added is
It can be selected within the above range depending on the size of the base particles, but if the amount of aluminum is too small, the desired effect is not brought about,
On the other hand, if the amount exceeds the above range, the growth of the aluminum solid solution α-iron oxyhydroxide layer tends to be inhibited.

【００１０】次に前記のようにして得られた粒子表面に
アルミニウム固溶α−オキシ水酸化層を有する基体粒子
はろ過、洗浄、乾燥した後、非還元性雰囲気において６
００〜９００℃で加熱処理して粒子表層部に均一にアル
ミニウムがドープした緻密なヘマタイト粒子とする。こ
の加熱処理により、粒子全体が焼きしまって緻密にな
り、また還元時の焼結や粒子形状の崩れを一層抑制する
ことができ、さらにＬｃの小さなメタル粉を得ることが
できる。焼成温度が高きに過ぎるとヘマタイトの段階で
粒子内及び粒子間焼結による針状性の悪化や粗大化が生
じて好ましくない。また焼成温度が低きに過ぎるとヘマ
タイト粒子内に空孔が多く残り、そのものが緻密な結晶
でないため、引続く還元工程での形状劣化が大きく、所
望の効果が得られない。さらに本発明においては、上記
非還元性雰囲気での加熱処理をホウ素化合物の存在下で
行うことにより、ヘマタイト粒子の焼結や粒子形状の崩
れはより一層抑制され、還元時の焼結や粒子形状の崩れ
をより一層抑制することができ、さらによりＬｃの小さ
な金属磁性粉を得ることができる。ホウ素化合物として
は、たとえば、ホウ酸、酸化ホウ素、ホウ酸アンモニウ
ム、ホウ酸亜鉛、ホウ酸マグネシウム、ホウ酸マンガ
ン、ホウ酸ニッケルなど挙げることができるが、とりわ
けホウ酸を使用することが好ましい。ホウ素化合物の添
加処理は、種々の方法によって行うことができるが、た
とえば、水酸化アルミニウムと水酸化第二鉄の共沈物を
含有してなる基体粒子懸濁液を、前記のように加熱処理
した後の湿ケーキに、ホウ素化合物を添加湿練した後蒸
発乾固したり、あるいは前記湿ケーキの乾燥状物にホウ
素化化合物を混合したりもしくは混合粉砕処理したりし
て行うことができる。ホウ素化合物の添加量は、ホウ素
と鉄との重量比で、通常０．１／１００〜５／１００、
好ましくは０．３／１００〜３／１００である。添加量
が前記範囲より少なきに過ぎると所望の効果がもたらさ
れず、また多きに過ぎると飽和磁化が低下するなど好ま
しくない。前記ホウ素化合物を添加処理した後、次いで
前記と同様にして非還元性雰囲気において６００〜９０
０℃で加熱処理して、粒子表層部にアルミニウムが均一
にドープした緻密なヘマタイト粒子とする。Next, the base particles having an aluminum solid solution α-oxyhydroxide layer on the surface of the particles obtained as described above are filtered, washed and dried, and then subjected to 6 in a non-reducing atmosphere.
Heat treatment is performed at 00 to 900 ° C. to obtain dense hematite particles in which the surface layer of the particles is uniformly doped with aluminum. By this heat treatment, the whole particles are burnt and become dense, and further, sintering at the time of reduction and the collapse of the particle shape can be further suppressed, and a metal powder having a small Lc can be obtained. If the firing temperature is too high, the acicularity is deteriorated and coarsened due to intra-particle and inter-particle sintering at the stage of hematite, which is not preferable. On the other hand, if the firing temperature is too low, many pores remain in the hematite particles, and since the crystals themselves are not dense crystals, the shape deterioration in the subsequent reduction step is large and the desired effect cannot be obtained. Further, in the present invention, by performing the heat treatment in the presence of the boron compound in the non-reducing atmosphere, the sintering of the hematite particles and the collapse of the particle shape are further suppressed, and the sintering and particle shape at the time of reduction are performed. Can be further suppressed, and a metal magnetic powder having a smaller Lc can be obtained. Examples of the boron compound include boric acid, boron oxide, ammonium borate, zinc borate, magnesium borate, manganese borate, nickel borate, and the like, but boric acid is particularly preferably used. The addition treatment of the boron compound can be carried out by various methods. For example, a substrate particle suspension containing a coprecipitate of aluminum hydroxide and ferric hydroxide is heated as described above. It can be carried out by adding a boron compound to the wet cake after the kneading and kneading and then evaporating to dryness, or by mixing the dried product of the wet cake with the borated compound or by mixing and grinding. The amount of the boron compound added is usually 0.1 / 100 to 5/100 in terms of the weight ratio of boron and iron,
It is preferably 0.3 / 100 to 3/100. If the amount added is less than the above range, the desired effect will not be obtained, and if it is too large, the saturation magnetization will decrease, such being undesirable. After the addition treatment of the boron compound, 600 to 90 in a non-reducing atmosphere in the same manner as described above.
Heat treatment is performed at 0 ° C. to obtain dense hematite particles in which the surface layer of the particles is uniformly doped with aluminum.

【００１１】前記加熱処理によって得られた焼成物は、
次いで還元して本発明の目的物が得られる。この還元
は、公知の種々の方法が適用できる。通常、還元性ガス
としてたとえば水素を使用し３５０〜６００℃で処理す
ることによって鉄酸化物の実質的に全部を金属に還元で
きる。このように還元して得られた金属磁性粉末は、通
常大気中への取り出しにあたっては種々の公知の方法を
用い安定化させる。たとえば、トルエン等の有機溶媒中
に浸漬後、ゆっくりトルエンを蒸発させ安定化する方
法、トルエン等の液相または気相中に含酸素ガスを通気
して安定化する方法、さらには種々の化合物による酸化
抑制の皮膜形成処理と上記方法とを併用する方法などが
ある。このようにして得られた本発明の磁気記録用金属
磁性粉末は後記するとおり飽和磁化、保磁力などの磁気
特性、耐酸化性に優れさらに磁性塗料とした時の分散性
に優れたものである。なお本発明において、（１）含水
酸化鉄基体粒子の形状調節剤として主に作用する、たと
えばリン、カルシウム、マグネシウム、スズ、亜鉛な
ど、また（２）還元工程で還元促進剤として主に作用す
る、たとえば、ニッケル、銅、コバルトなどの金属イオ
ンを適宣使用することができる。The fired product obtained by the heat treatment is
Then, the product is reduced to obtain the object of the present invention. For this reduction, various known methods can be applied. In general, hydrogen is used as a reducing gas, for example, and hydrogen can be treated at 350 to 600 ° C. to reduce substantially all of the iron oxides to metals. The metal magnetic powder obtained by such reduction is usually stabilized by various known methods when taken out into the atmosphere. For example, after immersion in an organic solvent such as toluene, a method of slowly evaporating and stabilizing toluene, a method of aerating and stabilizing an oxygen-containing gas in a liquid phase or a gas phase of toluene, and various compounds are used. There is a method in which a film forming treatment for suppressing oxidation and the above method are used in combination. The metal magnetic powder for magnetic recording of the present invention thus obtained is excellent in magnetic properties such as saturation magnetization, coercive force and the like, as well as in oxidation resistance as described later, and is also excellent in dispersibility when used as a magnetic paint. .. In the present invention, (1) mainly acts as a shape-modifying agent for iron oxide hydroxide-containing base particles, for example, phosphorus, calcium, magnesium, tin, zinc, etc., and (2) acts mainly as a reduction accelerator in the reduction step. For example, metal ions such as nickel, copper and cobalt can be appropriately used.

【００１２】[0012]

【実施例】【Example】

実施例１ 基体粒子として、比表面積（ＢＥＴ法）９０ｍ² ／ｇ、
平均長軸径０．１８μｍ、軸比９の針状α−オキシ水酸
化鉄粉末１０５０ｇを水３５リットルに懸濁させ、攪拌
下にＡｌとして２０ｇ／ｌの塩化アルミウム水溶液１９
８０ｍｌ〔Ａｌ／Ｆｅ（原子重量比）：０．１２５〕と
Ｆｅ³⁺として４０ｇ／ｌの硝酸第二鉄水溶液４５７０ｍ
ｌ〔Ａｌ／Ｆｅ³⁺（原子重量比）：０．４５〕とを添加
した。この懸濁液を攪拌下、３０℃に保持しながら５Ｎ
の苛性ソーダ水溶液をｐＨが７．０となるまで添加し、
水酸化第二鉄と水酸化アルミニウムの共沈物を沈澱させ
た。次いで前記共沈物を含有した基体粒子懸濁液中にさ
らに５Ｎの苛性ソーダ水溶液をｐＨが１２にになるまで
添加した後、８０℃に昇温し、６時間加熱処理した。し
かる後ろ過、水洗、乾燥して、アルミニウムが固溶した
α−オキシ水酸化鉄層を粒子表面に有するα−オキシ水
酸化鉄を得た。前記のようにして得られた粒子表面にア
ルミニウムが固溶したα−オキシ水酸化鉄に、水酸化ニ
ッケルを被着処理し（Ｎｉ／Ｆｅ：１重量％）、このも
のを成型後、マッフル炉で大気中６６０℃で２時間加熱
処理した。しかる後、この加熱処理物を堅型反応器に入
れ、水素気流下（１０リットル／分）、４５０℃で排出
ガスの露点が−５０℃になるまで還元反応を行った。得
られた還元物は窒素気流下で冷却後トルエン中に浸漬
し、ついでトルエンを室温で徐々に蒸発させ、目的の金
属磁性粉末を得た（試料Ａ）。Example 1 As the substrate particles, a specific surface area (BET method) of 90 m ² / g,
1050 g of needle-shaped α-iron oxyhydroxide powder having an average major axis diameter of 0.18 μm and an axial ratio of 9 was suspended in 35 liters of water, and 20 g / l of aluminum chloride aqueous solution as Al was stirred under stirring.
80 ml [Al / Fe (atomic weight ratio): 0.125] and 40 g / l ferric nitrate aqueous solution 4570 m as Fe ³⁺
1 [Al / Fe ³⁺ (atomic weight ratio): 0.45] was added. The suspension was stirred and kept at 30 ° C. while maintaining
Of caustic soda solution was added until the pH reached 7.0,
A coprecipitate of ferric hydroxide and aluminum hydroxide was precipitated. Next, a 5N caustic soda aqueous solution was further added to the substrate particle suspension containing the coprecipitate until the pH reached 12, then the temperature was raised to 80 ° C., and heat treatment was performed for 6 hours. Then, the mixture was filtered, washed with water, and dried to obtain α-iron oxyhydroxide having an α-iron oxyhydroxide layer on the surface of which aluminum was dissolved. The α-iron oxyhydroxide obtained by solid-solving aluminum on the surface of the particles obtained as described above is coated with nickel hydroxide (Ni / Fe: 1% by weight), and after molding this, a muffle furnace is used. And heat-treated in the atmosphere at 660 ° C. for 2 hours. Then, this heat-treated product was put into a rigid reactor and subjected to a reduction reaction under a hydrogen stream (10 l / min) at 450 ° C until the dew point of the exhaust gas reached -50 ° C. The obtained reduced product was cooled under a nitrogen stream, immersed in toluene, and then the toluene was gradually evaporated at room temperature to obtain a target metal magnetic powder (Sample A).

【００１３】実施例２ 実施例１で得たアルミニウムが固溶したオキシ水酸化鉄
層を粒子表面に有するα−オキシ水酸化鉄に、水酸化ニ
ッケルを被着処理した（Ｎｉ／Ｆｅ：１重量％）ものの
乾燥物１００ｇとホウ酸３．３ｇをピンミル（日本精機
製）を用いて１パスすることにより粉砕混合処理を行っ
た。該粉砕混合物を成形後、マッフル炉で大気中７２０
℃で２時間加熱処理し、しかる後、この加熱処理物を実
施例１の場合と同様に処理して、目的の金属磁性粉末を
得た（試料Ｂ）。Example 2 Nickel hydroxide was applied to the α-iron oxyhydroxide having the iron oxyhydroxide layer in which aluminum was solid-solved on the surface of the particles obtained in Example 1 (Ni / Fe: 1 weight). %) And 100 g of the dried product and 3.3 g of boric acid were passed through a pin mill (manufactured by Nippon Seiki Co., Ltd.) for 1 pass to carry out a crushing and mixing treatment. After molding the crushed mixture, it is heated in a muffle furnace at 720 in the atmosphere.
This was heat-treated at 2 ° C. for 2 hours, and then this heat-treated product was treated in the same manner as in Example 1 to obtain the target metal magnetic powder (Sample B).

【００１４】実施例３ 基本粒子として、比表面積（ＢＥＴ法）９０ｍ² ／ｇ、
平均長軸径０．１８μｍ、軸比９の針状α−オキシ水酸
化鉄粉末１０５０ｇを水３５リットルに懸濁させ、攪拌
下に、Ａｌとして２０ｇ／ｌの塩化アルミニウム水溶液
１６７０ｍｌ〔Ａｌ／Ｆｅ（原子重量比）：０．１〕と
Ｆｅ³⁺として４０ｇ／ｌの硝酸第二鉄水溶液１５２０ｍ
ｌ〔Ａｌ／Ｆｅ³⁺（原子重量比）；１．１４〕を添加し
た。この懸濁液を攪拌下、３０℃に保持しながら５Ｎの
苛性ソーダ水溶液をｐＨが７となるまで添加し水酸化第
二鉄と水酸化アルミニウムの共沈物を沈澱させた。次い
でこの懸濁液中にさらに５Ｎ苛性ソーダ水溶液をｐＨが
１２になるまで添加した後、６０℃に昇温し、５時間加
熱処理した。しかる後ろ過、水洗、乾燥し、アルミニウ
ムが固溶したα−オキシ水酸化鉄層を粒子表面に有する
α−オキシ水酸化鉄を得た。前記のようにして得られた
粒子表面にアルミニウムが固溶したα−オキシ水酸化鉄
に、還元促進剤として水酸化ニッケルを被着処理した
（Ｎｉ／Ｆｅ：１重量％）ものの乾燥物１００ｇとホウ
酸５ｇとをピンミルを用いて１パスすることにより粉砕
混合処理を行った。該粉砕混合物を成形後、マッフル炉
で大気中６８０℃で２時間加熱処理し、しかる後この加
熱処理物を実施例１の場合と同様に処理して、目的の金
属磁性粉末を得た（試料Ｃ）。Example 3 As the basic particles, a specific surface area (BET method) of 90 m ² / g,
1050 g of acicular α-iron oxyhydroxide powder having an average major axis diameter of 0.18 μm and an axial ratio of 9 was suspended in 35 liters of water, and, with stirring, 1670 ml of an aluminum chloride aqueous solution of 20 g / l as Al [Al / Fe ( (Atomic weight ratio): 0.1] and ¹⁵ g of ferric nitrate aqueous solution of 40 g / l as Fe ³⁺
1 [Al / Fe ³⁺ (atomic weight ratio); 1.14] was added. While maintaining the suspension at 30 ° C. with stirring, a 5N aqueous solution of sodium hydroxide was added until the pH reached 7, to precipitate a coprecipitate of ferric hydroxide and aluminum hydroxide. Next, a 5N caustic soda aqueous solution was further added to this suspension until the pH reached 12, and then the temperature was raised to 60 ° C. and heat treatment was performed for 5 hours. After that, it was filtered, washed with water, and dried to obtain α-iron oxyhydroxide having an α-iron oxyhydroxide layer in which aluminum was solid-dissolved on the particle surface. 100 g of a dried product of α-iron oxyhydroxide obtained by solid-solving aluminum on the surface of the particles obtained as described above, to which nickel hydroxide was applied as a reduction accelerator (Ni / Fe: 1% by weight) Grinding and mixing treatment was carried out by making 1 pass with 5 g of boric acid using a pin mill. After molding the pulverized mixture, the mixture was heat-treated in a muffle furnace at 680 ° C. for 2 hours in the atmosphere, and then this heat-treated product was treated in the same manner as in Example 1 to obtain a target metal magnetic powder (sample C).

【００１５】比較例１ 実施例１において、大気中での加熱処理を行わなかった
ことのほかは同例の場合と同様に処理して金属磁性粉末
を得た（試料Ｄ）。Comparative Example 1 Metal magnetic powder was obtained by the same procedure as in Example 1 except that the heat treatment was not performed in the atmosphere (Sample D).

【００１６】比較例２ 実施例２において、大気中での加熱処理を行わなかった
ことのほかは同例の場合と同様にして金属磁性粉末を得
た。（試料Ｅ）。Comparative Example 2 A magnetic metal powder was obtained in the same manner as in Example 2, except that the heat treatment in the atmosphere was not carried out. (Sample E).

【００１７】比較例３ 基本粒子として、比表面積（ＢＥＴ法）９０ｍ² ／ｇ、
平均長軸径０．１８μｍ、軸比９の針状α−オキシ水酸
化鉄粉末２１０ｇを水７リットルに懸濁させ、攪拌下
に、Ａｌとして２０ｇ／ｌの塩化アルミニウム水溶液４
９０ｍｌ〔Ａｌ／Ｆｅ（原子重量比）：０．１５４〕と
Ｆｅ²⁺として３０ｇ／ｌの硫酸第一鉄水溶液２１７０ｍ
ｌ〔Ａｌ／Ｆｅ²⁺（原子重量比）：０．３１１〕とを添
加した。この懸濁液を攪拌下、５０℃に保持しながら２
Ｎの苛性ソーダ水溶液を２２９０ｍｌ添加した後、空気
を吹き込みながら５時間酸化反応を行った。しかる後こ
の懸濁液をろ過水洗乾燥し、アルミニウム含有α−オキ
シ水酸化鉄を得た。前記のアルミニウム含有α−オキシ
水酸化鉄に還元促進剤として水酸化ニッケルを被着処理
した（Ｎｉ／Ｆｅ：１重量％）ものの乾燥物１００ｇと
ホウ酸５ｇとをピンミルを用いて１パスすることにより
粉砕混合処理を行った。該混合粉末を成形後、マッフル
炉で大気中７００℃で２時間加熱処理し、しかる後、こ
の加熱処理物を実施例１の場合と同様に処理して、金属
磁性粉末を得た（試料Ｆ）。Comparative Example 3 As the basic particles, a specific surface area (BET method) of 90 m ² / g,
210 g of acicular α-iron oxyhydroxide powder having an average major axis diameter of 0.18 μm and an axial ratio of 9 was suspended in 7 liters of water, and 20 g / l of aluminum chloride aqueous solution as Al was stirred under stirring.
90 ml [Al / Fe (atomic weight ratio): 0.154] and 2170 m of ferrous sulfate aqueous solution of 30 g / l as Fe ²⁺
1 [Al / Fe ²⁺ (atomic weight ratio): 0.311] was added. This suspension is stirred and kept at 50 ° C for 2
After adding 2290 ml of a caustic soda aqueous solution of N, an oxidation reaction was carried out for 5 hours while blowing air. Thereafter, this suspension was filtered, washed with water and dried to obtain aluminum-containing α-iron oxyhydroxide. 100 g of a dried product of the aluminum-containing α-iron oxyhydroxide coated with nickel hydroxide as a reduction promoter (Ni / Fe: 1% by weight) and 5 g of boric acid are passed through a pin mill using a pin mill. The pulverization and mixing process was carried out. After molding the mixed powder, the mixture was heat-treated in a muffle furnace at 700 ° C. for 2 hours in the atmosphere, and then this heat-treated product was treated in the same manner as in Example 1 to obtain a metal magnetic powder (Sample F). ).

【００１８】前記の実施例及び比較例で得られた各金属
磁性粉末試料について、常法により保磁力（Ｈｃ：０
ｅ）、飽和磁化（σｓ：ｅｍｕ／ｇ）角形比（Ｒｓ）を
測定した。また粉末Ｘ線回析によりα−Ｆｅ（１１０
面）の回析ピークの半値巾を測定し、下記Ｓｃｈｅｒｒ
ｅｒ式（式１）からＬｃを求めた。また酸化安定性を評
価するために各金属磁性粉末試料を、温度６０℃、相対
湿度８０％の環境下で１週間放置して、σｓについて促
進経時変化を測定し、飽和磁化の劣化率Δσｓ（％）を
次記（式２）によって求めた。次にこれらの試料を下記
の塗料組成で混合分散して磁性塗料を調製した。The coercive force (Hc: 0) of each metal magnetic powder sample obtained in the above-mentioned Examples and Comparative Examples was determined by a conventional method.
e) and the saturation magnetization (σs: emu / g) squareness ratio (Rs) were measured. In addition, α-Fe (110
Surface) and the full width at half maximum of the diffraction peak of
Lc was calculated from the er formula (Formula 1). Further, in order to evaluate the oxidation stability, each metal magnetic powder sample was allowed to stand for 1 week in an environment of a temperature of 60 ° C. and a relative humidity of 80%, and the accelerated aging change of σs was measured to determine the deterioration rate Δσs of the saturation magnetization. %) Was calculated according to the following (formula 2). Next, these samples were mixed and dispersed with the following coating composition to prepare a magnetic coating.

【００１９】 [0019]

【００２０】次いで、前記磁性塗料をポリエステルフィ
ルム上に、乾燥膜厚１０μｍとなるように塗布し、配向
処理後乾燥して磁気テープを作成し、常法により保持力
（Ｈｃ：Ｏｅ）、飽和磁化（σｓ：ｅｍｕ／ｇ）、飽和
磁束密度（Ｂｍ：Ｇａｕｓｓ）、角形比（Ｒｓ、Ｓ
Ｑ）、配向比（ＯＲ）、反転磁界分布（ＳＦＤ）、光沢
（６０°−６０°）を測定した。さらに光沢計により磁
気テープの光沢（６０°−６０°）を測定した。これら
の結果を表１及び表２に示す。Next, the above magnetic coating material is applied onto a polyester film so that the dry film thickness is 10 μm, and after orientation treatment, dried to prepare a magnetic tape, and a coercive force (Hc: Oe) and saturation magnetization are prepared by a conventional method. (Σs: emu / g), saturation magnetic flux density (Bm: Gauss), squareness ratio (Rs, S
Q), orientation ratio (OR), switching field distribution (SFD), and gloss (60 ° -60 °) were measured. Further, the gloss (60 ° -60 °) of the magnetic tape was measured with a gloss meter. The results are shown in Tables 1 and 2.

【００２１】（式１） λ＝１．５４１７８Å（Ｃｕ Ｋα） β＝α−Ｆｅ（１１０）の半値巾（ラジアン） θ＝α−Ｆｅ（１１０）のブラッグ角(Equation 1) λ = 1.54178Å (Cu Kα) β = α-Fe (110) full width at half maximum (radian) θ = α-Fe (110) Bragg angle

【００２２】（式２） （式中、σｓ⁰ は経時前のσｓであり、σｓ´は経時後
のσｓである。）(Equation 2) (In the formula, σs ⁰ is σs before aging, and σs ′ is σs after aging.)

【００２３】[0023]

【表１】 [Table 1]

【００２４】[0024]

【表２】 [Table 2]

【００２５】[0025]

【発明の効果】本発明方法により、比較的簡潔な工程処
理操作によって、従来の被着処理にみられるような不具
合を惹起することなく、粒子内及び相互の焼結や粒子形
状崩れが抑制されるとともに、Ｌｃの小さな金属磁性粉
末が得られ、このものは磁気記録媒体における分散性が
良好であり、角型比、配向比などの優れた特性を有する
とともに、粒子性ノイズに起因するノイズを低下でき、
高密度記録用に一層好適な微細な金属磁性粉末を効率良
く製造方することができ、甚だ工業的に有利な方法であ
る。According to the method of the present invention, it is possible to suppress the sintering of particles and mutual deformation of particles and the collapse of the shape of particles by a relatively simple process operation without causing the inconveniences of the conventional adhesion processing. In addition, a metal magnetic powder having a small Lc can be obtained, which has good dispersibility in a magnetic recording medium, has excellent characteristics such as squareness ratio and orientation ratio, and can reduce noise caused by particle noise. Can be lowered,
This is a very industrially advantageous method because it is possible to efficiently produce a fine metal magnetic powder more suitable for high-density recording.

Claims (4)

【特許請求の範囲】[Claims] 【請求項１】含水酸化鉄基体粒子の懸濁液に、アルミニ
ウム塩と第二鉄塩との水溶液及びアルカリ水溶液とを添
加してアルミニウム含有水酸化第二鉄を沈澱させ、次い
でｐＨ１０〜１３、４０〜１２０℃で加熱処理して該基
体粒子表面にアルミニウム含有α−オキシ水酸化鉄層を
形成させ、しかる後このものを非還元性雰囲気下６００
〜９００℃で加熱処理した後加熱還元処理することを特
徴とする磁気記録用金属磁性粉末の製造方法。1. An aluminum-containing ferric hydroxide is precipitated by adding an aqueous solution of an aluminum salt and a ferric salt and an alkaline aqueous solution to a suspension of iron oxide hydroxide-containing base particles, and then pH 10 to 13, It is heat-treated at 40 to 120 ° C. to form an aluminum-containing α-iron oxyhydroxide layer on the surface of the substrate particles, and then this is subjected to 600 ° C. in a non-reducing atmosphere.
A method for producing a metal magnetic powder for magnetic recording, which comprises performing a heat treatment at ˜900 ° C. and then a heat reduction treatment. 【請求項２】含水酸化鉄基体粒子の懸濁液に、アルミニ
ウム塩と第二鉄塩との水溶液及びアルカリ水溶液とを添
加してアルミニウム含有水酸化第二鉄を沈澱させ、次い
でｐＨ１０〜１３、４０〜１２０℃で加熱処理して該基
体粒子表面にアルミニウム含有α−オキシ水酸化鉄層を
形成させ、さらにこのものにホウ素化合物を添加した
後、非還元性雰囲気下６００〜９００℃で加熱処理し、
しかる後加熱還元処理することを特徴とする磁気記録用
金属磁性粉末の製造方法。2. An aluminum-containing ferric hydroxide is precipitated by adding an aqueous solution of an aluminum salt and a ferric salt and an aqueous alkaline solution to a suspension of iron oxide hydroxide-containing base particles, and then pH 10 to 13, After heat treatment at 40 to 120 ° C. to form an aluminum-containing α-iron oxyhydroxide layer on the surface of the base particles, and further adding a boron compound to this, heat treatment at 600 to 900 ° C. in a non-reducing atmosphere. Then
A method for producing a metal magnetic powder for magnetic recording, which is characterized by performing a heating reduction treatment thereafter. 【請求項３】アルミニウム塩の添加量が、含水酸化鉄基
体粒子に対しＡｌ／Ｆｅとして０．０５〜０．１５（原
子重量比）であり、かつ添加する第２鉄塩量に対してＡ
ｌ／Ｆｅ³⁺として０．１〜１．５（原子重量比）である
ことを特徴とする請求項１または２記載の磁気記録用金
属磁性粉末の製造方法。3. The amount of aluminum salt added is 0.05 to 0.15 (atomic weight ratio) as Al / Fe relative to the iron oxide hydroxide base particles, and A is added to the amount of ferric iron added.
The method for producing a metal magnetic powder for magnetic recording according to claim 1 or 2, wherein l / Fe ³⁺ is 0.1 to 1.5 (atomic weight ratio). 【請求項４】含水酸化鉄基体粒子が比表面積６０ｍ² ／
ｇ以上の針状ゲーサイトであることを特徴とする請求項
１または２記載の磁気記録用金属磁性粉末の製造方法。4. The iron oxide hydroxide base particles have a specific surface area of 60 m ² /
3. The method for producing a magnetic metal powder for magnetic recording according to claim 1 or 2, which is acicular goethite of g or more.