JP2004005932A - Powder for lower layer of coating type magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain iron oxide powder capable of improving a variety of properties required by powder for a lower layer of a magnetic recording medium with a multilayered structure having durability adaptive to high record density, particularly, tape surface smoothness and tape strength. <P>SOLUTION: This powder for a lower layer of a coating type magnetic recording medium is composed of flat needle-like iron oxide particles, the average long axial length of which is 20-200 nm, wherein a long axis and a short axis cross section cut in the direction of a right angle have a longer width and a shorter width and the short axis aspect ratio of the long axis to the short axis is almost uniformly >1.3 in the direction of the long axis, and a specific surface area by a BET is 30-100 m<SP>2</SP>/g. The powder for a lower layer desirably contains P by 0.1-5.0 wt% and further contains R (R is one or two rare earth elements or more including Y) by 0.1-10 at.% in an atomic ratio percentage (at.%) of R/Fe. <P>COPYRIGHT: (C)2004,JPO

Description

【００６０】
表１の結果から，次のことがわかる。
【００６１】
（１）短軸断面比が異なる実施例１（短軸断面比＝１．４５）と比較例１（短軸断面比＝１）を対比すると明らかなように，短軸断面比の大きい実施例１の方が，表面粗度が小さく平滑な塗膜を作製でき，さらにテープ耐久性でも傷幅が小さく摺動パス回数も多くなり，テープの耐久性も向上する。すなわち，短軸断面比が大きい平針状の酸化鉄粉末では，これを塗料化して塗布するさいに粒子が重なって幅広の面ができ易くなるので，表面が平滑になると考えられる。また平針状であると，支持体面と垂直方向の成分が少なく且つテープ面内方向に密に配向されるので表面平滑性に加えてテープ強度も向上するものと考えられる。
【００６２】
（２）実施例１の平針状酸化鉄粉末で作製された塗膜は，比較例１のものに比べてカレンダー前後の表面粗度の変化が大きい。このため，この下層の上に上層である磁性層を形成した際に，カレンダー処理をおこなうと，カレンダーのかかりやすい下層となる。すなわち，より平滑な塗膜の形成が可能となり，重層磁気記録媒体用下層として好適である。
【００６３】
（３）Ｐを含有した平針状酸化鉄である実施例２のものは，Ｐを含有しない実施例１のものよりも表面平滑性がさらに向上している。また，Ｐを含有することで粉体ｐＨが４．６となり，脂肪酸吸着量（ＳｔＡ．）が低い。その結果，塗膜成分である潤滑剤（脂肪酸）の本来の役割を阻害しなくなったためと考えられるが，実施例１のものよりテープ耐久性が向上している。
【００６４】
（４）実施例２〜４は，オキシ水酸化鉄の製造条件を変化させることによって，短軸断面比を変化させたものであるが，平針状酸化鉄の短軸断面比が増加すればするほど，表面平滑性が向上し，かつテープ耐久性も向上することがわかる。
【００６５】
（５）Ｐに加えてさらにＹを含有する実施例５のものは，例えば実施例４のものと対比しても，平針状酸化鉄（ヘマタイト）の短軸断面比がさらに増加している。その結果，表面平滑性はさらに向上し，テープ耐久性もさらに向上している。したがって，テープ表面平滑性およびテープ耐久性の向上に寄与する平針状酸化鉄（ヘマタイト）を得るには，Ｐを含有していることが好ましく，さらにＰに加えてＲ（Ｙを含む）も含有していることが一層好ましい。
【００６６】
〔実施例６〕
本例は，実施例５で得られた下層用粉末を非磁性層とし，下記の金属磁性粉末を磁性層とした重層構造の磁気テープを作成して，電磁変換特性とテープ耐久性などの評価を行ったものである。
【００６７】
非磁性層の塗料は，実施例５の下層用粉末８５重量部に対し，下記の成分を下記の割合で配合し，ニーダーおよびサンドグラインダーを用いて，混練，分散を行った。
〔非磁性塗料の組成〕
実施例１の下層用粉末（α−Ｆｅ_２Ｏ_３）８５重量部
カーボンブラック　　　　　　　　　２０重量部
アルミナ　　　　　　　　　　　　　　３重量部
塩化ビニル樹脂（ＭＲ１１０）　　　１５重量部
ポリウレタン樹脂（ＵＲ８２００）　１５重量部
メチルエチルケトン　　　　　　　１９０重量部
シクロヘキサノン　　　　　　　　　８０重量部
トルエン　　　　　　　　　　　　１１０重量部
【００６８】
磁性層の塗料は，下記の金属磁性粉末１００重量部に対し，下記の成分を下記の割合で配合し，ニーダーおよびサンドグラインダーを用いて，混練，分散を行った。
〔金属磁性粉末〕
長軸長：８０ｎｍ
ＢＥＴ：６１ｍ^２／ｇ
Ｄｘ　：１５０オングストローム
Ｈｃ　：２４００（Ｏｅ）
σｓ　：１２７ｅｍｕ／ｇ
〔磁性塗料の組成〕
前掲の金属磁性粉末　　　　　　１００重量部
カーボンブラック　　　　　　　　　５重量部
アルミナ　　　　　　　　　　　　　３重量部
塩化ビニル樹脂（ＭＲ１１０）　　１５重量部
ポリウレタン樹脂（ＵＲ８２００）１５重量部
ステアリン酸　　　　　　　　　　　１重量部
アセチルアセトン　　　　　　　　　１重量部
メチルエチルケトン　　　　　　１９０重量部
シクロヘキサノン　　　　　　　　８０重量部
トルエン　　　　　　　　　　　１１０重量部
【００６９】
これらの塗料をアラミド支持体からなるベースフイルム上にそれぞれ，非磁性層厚（下層厚）２．０μｍ，磁性層厚が０．２０μｍの目標厚みとなるように塗布し，磁性層が湿潤状態にあるうちに，磁場をかけて配向させ，乾燥，カレンダーを行って磁気テープを作製した。
【００７０】
得られた磁気テープについて既述の方法で表面平滑性（粗度）およびテープ耐久性（鋼球摺動のパス回数）の試験を行うと共に電磁変換特性（Ｃ／Ｎおよび出力）を測定した。Ｃ／Ｎ比の測定は，記録ヘッドをドラムテスターに取り付けて，デジタル信号を記録波長０．３５μｍで記録した。そのさい，ＭＲヘッドを使用し，再生信号を測定し，ノイズは変調ノイズを測定し，後記比較例２の出力，Ｃ／Ｎを０ｄＢとしてその相対値で表示した。それらの結果を表２に示した。
【００７１】
〔実施例７〕
下層用粉末として前記の実施例１で得られたものを使用した以外は，実施例６を繰り返した。得られた磁気テープの表面平滑性（粗度），テープ耐久性（鋼球摺動のパス回数）および電磁変換特性を表２に示した。
【００７２】
〔比較例２〕
下層用粉末として前記の比較例１で得られたものを使用した以外は，実施例６を繰り返した。得られた磁気テープの表面平滑性（粗度），テープ耐久性（鋼球摺動のパス回数）および電磁変換特性を表２に示した。
【００７３】
【表２】

【００７４】
表２の結果から次のことがわかる。
まず，実施例６〜７と比較例２を対比すると明らかなように，本発明に従う下層用粉末は，重層構造にしたときのテープ表面平滑性が極めて良好であり，その結果，高い出力と高いＣ／Ｎを示し，高密度記録媒体として好適なものである。また磁気テープの耐久性にも優れており，ヘッドとの摺動に対しても優れた耐久性を示す。
【００７５】
また，実施例６と実施例７を対比すると明らかなように，ＰとＹを含有する断面比の高い平針状の下層用粉末（実施例５のもの）は，重層構造にしたときのテープ表面平滑性が一層良好となり，その結果，一層高い出力と高いＣ／Ｎを示し且つ一層優れた耐久性を示す。
【００７６】
〔実施例８〕
水酸化第二鉄の沈殿を含む懸濁液を３５℃に保持した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００７７】
〔実施例９〕
水酸化第二鉄の沈殿を含む懸濁液を７０℃に保持した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００７８】
〔比較例３〕
水酸化第二鉄の沈殿を含む懸濁液を２５℃に保持した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００７９】
〔比較例４〕
水酸化第二鉄の沈殿を含む懸濁液を８０℃に保持した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８０】
〔実施例１０〕
平針状α−ＦｅＯＯＨにＰの被着処理を施した後，イットリウム水溶液を添加しなかった以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８１】
〔実施例１１〕
平針状α−ＦｅＯＯＨにＰの被着処理を施した後，Ｆｅに対するＹの原子比百分率（Ｙ／Ｆｅ）が０．１８ａｔ．％となる量のイットリウム水溶液を添加した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８２】
〔実施例１２〕
平針状α−ＦｅＯＯＨにＰの被着処理を施した後，Ｆｅに対するＹの原子比百分率（Ｙ／Ｆｅ）が８．１８ａｔ．％となる量のイットリウム水溶液を添加した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８３】
〔比較例５〕
平針状α−ＦｅＯＯＨにＰの被着処理を施した後，Ｆｅに対するＹの原子比百分率（Ｙ／Ｆｅ）が４．５４ａｔ．％となる量のイットリウム水溶液を添加した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８４】
〔実施例１３〕
平針状α−ＦｅＯＯＨを生成させた後，これを含む懸濁液に，α−ＦｅＯＯＨに対しＰが０．２８ｗｔ％となる量のリン酸水溶液を攪拌下で添加した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８５】
〔実施例１４〕
平針状α−ＦｅＯＯＨを生成させた後，これを含む懸濁液に，α−ＦｅＯＯＨに対しＰが６．４３ｗｔ％となる量のリン酸水溶液を攪拌下で添加した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８６】
〔比較例６〕
平針状α−ＦｅＯＯＨを生成させた後，これを含む懸濁液に，α−ＦｅＯＯＨに対しＰが７．８６ｗｔ％となる量のリン酸水溶液を攪拌下で添加した以外は，実施例２を繰り返した。得られた平針状酸化鉄粉末の諸特性を実施例１と同様にして評価し，その結果を表３に示した。
【００８７】
【表３】

【００８８】
表３の結果から（表１も参照），次のことが明らかである。
（１）酸化鉄（ヘマタイト）の粒子径（平均長軸長）の影響を見ると，例えば比較例３，実施例８，実施例５，実施例９，比較例４の順に粒子径が大きくなり，それに伴って軸比も変化していが，粒子径が非常に小さい比較例３（長軸長＝１５ｎｍ）では樹脂への分散が困難となってテープ化が不可能である。他方，粒子径が大きい比較例４（長軸長＝２５０ｎｍ）では，軸比および短軸断面比も大きくなっているが，表面平滑性が損なわれる結果となっている。したがって，粒子径（平均長軸長）は，２０ｎｍ〜２００ｎｍの範囲が好適であることがわかる。
【００８９】
（２）酸化鉄（ヘマタイト）中のイットリウムの含有量の影響を見ると，例えば実施例１０，実施例１１，実施例５，比較例５の順にイットリウム含有量が高くなっているが，イットリウムが必要以上に多い比較例５では，比表面積が高くなって樹脂への分散性が劣るようになり，このために表面平滑性が損なわれる結果となっている。したがって，イットリウム含有量としても良好な表面平滑性を維持するには適切な範囲（Ｙ／Ｆｅの原子比百分率で０．１〜１０　ａｔ．％）が存在することがわかる。
【００９０】
（３）酸化鉄（ヘマタイト）中のリン含有量に影響について見ると，例えば実施例１３，実施例５，実施例１４，比較例６の順にリン含有量が高くなっているが，リン含有量が多すぎる比較例６では，塗料粘度が高くなって分散性が悪くなり，表面平滑性が損なわれる結果となっている。他方，リン含有量が減るにつれてステアリン酸吸着量が増え，潤滑材の作用が低下してテープ耐久性の傷幅が増加するようになる。すなわち，テープ耐久性の向上にはリンが有効に作用するが，あまり多すぎても表面平滑性が損なわれるので，リン含有量には好適な含有量の範囲（０．１〜５．０ｗｔ％）が存在することがわかる。
【００９１】
【発明の効果】
以上説明したように，本発明によると，重層構造の塗布型磁気記録媒体における下層用粉末に粉末に要求される諸特性，とくにテープの表面平滑性とテープ強度を向上させることができる平針状酸化鉄粉末が得られる。したがって，本発明の平針状酸化鉄粉末を重層構造の塗布型磁気記録媒体の下層用粉末として用いることにより，高記録密度に適した耐久性のある記録媒体を得ることができる。
【図面の簡単な説明】
【図１】本発明の平針状粒子の形状を説明するための概念図である。
【図２】本発明の平針状粒子の短軸断面の他の形状例を示す図である。
【図３】本発明の平針状粒子の短軸断面の他の形状例を示す図である。
【図４】本発明の平針状粒子の短軸断面の他の形状例を示す図である。
【図５】本発明の平針状粒子の短軸断面の他の形状例を示す図である。
【図６】実施例５で得られた下層用粉末の一つの粒子を，試料台の傾斜角度を変えて写した電子顕微鏡写真（ＴＥＭ像）を対比したものである。
【符号の説明】
１　平針状粒子
２　短軸断面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lower layer powder used for a coating type magnetic recording medium having a multilayer structure, and a magnetic recording medium using the same.
[0002]
[Prior art]
A non-magnetic layer (lower layer) in which a non-magnetic powder is dispersed in a resin is provided between a base layer and a magnetic layer in which a magnetic powder is dispersed in a resin. Magnetic tapes) are known. With such a multilayer structure, the electromagnetic conversion characteristics of the magnetic recording medium are improved, and a higher recording density can be achieved. In addition, the durability of the tape is improved, and the reliability is also improved. In the specification of the present application, “lower layer powder” means a powder for forming a nonmagnetic layer (lower layer) of such a coating type recording medium having a multilayer structure.
[0003]
The recent increase in the amount of information has never stopped, and accordingly, the recording medium has been required to further increase the recording capacity and improve the reliability. As a result, there is a demand for improvement of various characteristics in the lower layer powder of the coating type magnetic recording medium having a multilayer structure. The basic characteristics required for the lower layer powder include that a lower layer having a smoother surface can be formed when applied to the base film, and that the strength of the lower layer coating film is high.
[0004]
If the surface of the lower layer is smooth, the magnetic layer applied thereon becomes smoother, which can result in a magnetic recording medium having excellent electromagnetic conversion characteristics and leads to higher density. In addition, as the tape capacity increases, the tape thickness becomes thinner, and dimensional stability is important for higher density. For this purpose, it is desired to increase the strength of the lower layer. Increases the strength of the device, leading to improved reliability.
[0005]
In general, in order to satisfy these required properties, the non-magnetic powder for the lower layer has properties such as excellent dispersibility at the stage of coating, high strength of the particles themselves, and high adhesiveness to the resin. When a coating film is formed using such a nonmagnetic powder, a smooth and high-strength lower layer can be formed.
[0006]
Conventionally, as a nonmagnetic powder for forming the lower layer, spherical titanium oxide powder or acicular iron oxide powder has been mainly used. Examples of such a multilayered magnetic recording medium having a lower layer include those described in JP-A-63-187418 and JP-A-4-167225.
[0007]
Further, Japanese Patent Application Laid-Open Nos. 6-60362, 6-139553, 6-215360, 7-192248, and 9-170003 disclose such a multilayer structure. In the magnetic recording medium described above, characteristic values are shown when needle-like iron oxide or the like is used as the nonmagnetic powder forming the lower layer.
[0008]
[Problems to be solved by the invention]
Spherical titanium oxide, which has been used as the lower layer powder, had insufficient strength when taped compared to needle-like ones. As for the needle-shaped iron oxide, since it is in the form of a needle, when a coating film containing the dispersed iron is formed, the smoothness is improved due to a decrease in the vertical component of the coating film surface. Interaction (entanglement) between the particles leads to an increase in the strength of the coating film. However, needle-like iron oxide requires a firing process at a high temperature in the process of obtaining it, so interparticle firing is required. Knots are formed and the needle-like property is liable to collapse. Therefore, as a lower layer powder that can meet the demands for further tape properties (surface smoothness, coating film strength), the current needle-like iron oxide powder cannot be said to be sufficient.
[0009]
The present invention is intended to solve such a problem and to satisfy various properties required for a lower layer powder in a coating type magnetic recording medium having a multilayer structure, and in particular, to improve the surface smoothness and coating strength of a tape. It is an object of the present invention to obtain iron oxide powder for use, and further to obtain a recording medium having a multilayer structure with high capacity and high reliability.
[0010]
[Means for Solving the Problems]
According to the present invention, an average major axis length is 20 to 200 nm, and a minor axis section cut in a direction perpendicular to the major axis has a longer width and a shorter width. Consisting of flat needle-like iron oxide particles having a ratio substantially greater than 1.3 in the major axis direction, and having a specific surface area of 30 to 100 m by the BET method. ² / G of a coating-type magnetic recording medium having a thickness of 0.1 g / g. The lower layer powder according to the present invention preferably has a powder pH of 7 or less. The lower layer powder according to the present invention contains 0.1 to 5.0 wt% of P, and contains R (R is one or more of rare earth elements including Y) in the atomic ratio of R / Fe (%). %) at 0.1 to 10 at. %contains. By using this lower layer powder, it is possible to obtain a magnetic recording medium having excellent surface smoothness and durability suitable for increasing the recording density.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention provides a lower layer powder for forming a nonmagnetic layer of a coating type magnetic recording medium having a multilayer structure, which has an average major axis length of 20 to 200 nm and a specific surface area of 30 to 100 m by the BET method. ² / G, powder having a powder needle pH of preferably 7 or less is used. The flat needle-like powder for the lower layer is obtained by using a flat needle-like iron oxyhydroxide as a precursor material, desirably surface-treating it with a phosphorus compound or a phosphorus compound and a rare earth metal compound, and then firing. can get. The conventional needle-like iron oxide has insufficient dispersibility, and insufficient particle arrangement and interaction (entanglement) during coating, resulting in insufficient tape surface smoothness and film strength. Although insufficient, according to the present invention, the surface smoothness of the tape is further improved by changing its shape to flat needle-like iron oxide and by suppressing sintering between particles, and the coating film strength is improved. Was also found to improve further.
[0012]
Here, the term “flat needle shape” refers to the ratio of the length in the longitudinal direction (long axis length) to the maximum length in the short direction orthogonal to it (short axis length) (ratio of long axis / short axis, ie, axis). Ratio) is preferably 2 or more, and the short-axis cross section cut in the direction perpendicular to the long axis has a long width and a short width, and the short-axis cross-section ratio of the long width and the short width is It means a flat needle-like shape which is substantially uniformly larger than 1.3, preferably 1.4 or more, and more preferably 1.5 or more in the major axis direction.
[0013]
FIG. 1 schematically shows the flat needle shape. As shown in the figure, in the needle-shaped body 1 having a maximum length L (long axis length) in the longitudinal direction and a maximum length S (short axis length) in the short direction orthogonal thereto, cut in a direction perpendicular to the long axis. The short axis section 2 is the long width W _L And short width W _S It has a flat shape with. For example, the width is W _L And the thickness is W _S Has a shape similar to a flat plate (strip shape). However, the flat shape of the short-axis cross section 2 is not limited to a rectangle, but various shapes such as a capsule shape as shown in FIG. 2, an elliptical shape as shown in FIG. 3, a polygonal shape as shown in FIG. 4, and a deformed circular shape as shown in FIG. May be any shape, where necessary _L / W _S (This is referred to as “short-axis cross-sectional ratio” in the present specification) is greater than 1.3 uniformly (meaning that it is not twisted) in the long-axis direction. , Preferably 1.4 or more, more preferably 1.5 or more. Further, the flat needle-like iron oxide particles of the present invention have almost no branches.
[0014]
To measure the short-axis cross-sectional ratio of flat needle-shaped particles, when taking an electron micrograph, multiple samples of the same sample are taken while tilting the sample stage, and the maximum short width and maximum width are measured for each tilt angle. The minor axis cross-sectional ratio can be obtained using the inclination angle and the measured value. This is measured for 100 particles and calculated as an average value.
[0015]
The flat-needle-shaped iron oxide powder according to the present invention can be obtained by producing a flat-needle-shaped iron oxyhydroxide powder and then appropriately firing the powder. First, a method for producing a flat needle-like iron oxyhydroxide powder will be described.
[0016]
(Method for producing flat needle iron oxyhydroxide)
In order to obtain iron oxide powder for the lower layer, a method of calcining needle-like iron oxyhydroxide is adopted, and as a method of obtaining iron oxyhydroxide for this purpose, typically,
(1) A suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution is passed through an oxygen-containing gas at a pH of 11 or more and a temperature of 80 ° C. or less. A method of performing an oxidation reaction to produce iron oxyhydroxide,
(2) a method in which an oxygen-containing gas is passed through a suspension obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali carbonate to cause an oxidation reaction to generate iron oxyhydroxide;
There is.
[0017]
However, iron oxyhydroxides obtained by these methods generally have a small short-axis cross-sectional ratio, and are unlikely to be particles having a stable short-axis cross-sectional ratio as intended by the present invention. However, it is possible to obtain iron oxyhydroxide particles having a short-axis cross-sectional ratio exceeding 1.3 by the method (1) depending on the adjustment of the conditions.
[0018]
In order to obtain iron oxyhydroxide having a larger short-axis cross-sectional ratio, the following method (3) is preferable.
(3) A suspension containing a ferric hydroxide colloid obtained by adding 1.0 to 3.5 equivalents of an alkali hydroxide aqueous solution to iron to an aqueous ferric salt solution is formed at 10 to 90 ° C. After aging for 2 to 20 hours, it is hydrolyzed to produce iron oxyhydroxide powder.
[0019]
According to the method (3), as described in Japanese Patent Application Laid-Open No. H10-34047 of the same applicant, the short-axis cross-sectional ratio becomes larger than 1.3, preferably 1.4 or more. In some cases, iron oxyhydroxide of 1.5 or more can be stably obtained. By appropriately baking this flat needle-like iron oxyhydroxide, the flat needle-like iron oxide particle powder (hematite) according to the present invention can be obtained. Proper firing means preventing sintering during firing. For this purpose, it is preferable to coat the phosphorus compound with flat needle-shaped iron oxyhydroxide. The compound of the element (including Y) is preferably coated on the flat needle-like iron oxyhydroxide.
[0020]
(Sintering prevention treatment when firing flat needle-like iron oxyhydroxide)
When sintering iron oxyhydroxide into iron oxide, sintering usually occurs between the particles or the shape of the particles themselves is distorted. As a method for improving this point, it has been conventionally known to include a sintering inhibitor represented by Al or Si in iron oxyhydroxide or to coat the surface of the iron oxyhydroxide. It was found that a sufficient effect could not be obtained when trying to obtain flat needle-like iron oxide from iron oxyhydroxide.
[0021]
In the present invention, a method of coating a flat needle-like iron oxyhydroxide with a phosphorus compound or a phosphorus compound and a rare earth element (including Y) compound is employed. In order to coat these compounds on the flat needle-shaped iron oxyhydroxide, when the method (3) is carried out, a solution in which the iron oxyhydroxide after the hydrolysis reaction is dispersed and suspended, or the liquid (1) In the case of carrying out the above method, all the liquids in which the iron oxyhydroxide is dispersed and suspended after the completion of the oxidation reaction are vigorously stirred, and a phosphorus-containing aqueous solution having a specified concentration is added thereto. For a predetermined time. Thereafter, a prescribed amount of a sulfuric acid aqueous solution of a rare earth element (including Y) can be added. In the latter case as well, it is preferable to carry out vigorous stirring and to lengthen the stirring time after the addition, which can promote uniform deposition.
[0022]
As an alternative method, iron oxide oxyhydroxide prepared in advance may be added to pure water, and the mixture may be stirred to prepare a suspension. In this case, since the liquid shows near neutrality, hydroxide may not be formed when the rare earth element compound is applied, and the application may not be possible. In such a case, it is preferable to add a suitable alkali to the solution and treat the suspension on the alkaline side.
[0023]
The obtained phosphorus compound and the iron oxyhydroxide coated with the rare earth element compound are filtered from the liquid, washed with water and dried. In the washing with water, the filtrate is sufficiently washed off until the filtrate becomes almost neutral. Is good. Since the amount of phosphorus to be deposited is limited, undeposited phosphorus is likely to coexist. If the removal of undeposited phosphorus is insufficient even by washing with water, the surface can be smoothed when taped. This is because it leads to a decrease in sex.
[0024]
Examples of the phosphorus compound that can be used include phosphoric acid, metaphosphoric acid, diphosphoric acid, phosphates such as ammonium phosphate and ammonium dihydrogen phosphate. Regardless of the phosphorus compound used, the content of phosphorus is preferably in the range of 0.1 to 5.0 wt% as the content of elemental phosphorus in iron oxide. If the content is less than 0.1 wt%, the effect of preventing sintering by the phosphorus coating becomes insufficient, so that the lower layer does not have excellent surface smoothness, and sufficient coating film strength cannot be obtained. On the other hand, if the phosphorus content exceeds 5.0 wt%, the effect of preventing sintering is sufficient, but the iron oxide powder has a high specific surface area and tends to cause poor dispersion when it is made into a coating and dispersed, so that it cannot be used as a lower layer powder. In addition to being appropriate, there is a phosphorus compound released when the film is formed, and this free phosphorus compound becomes a part of the coating film composition and adversely affects the coating film. Not very good.
[0025]
The rare earth element that can be used is not particularly limited, and any element can be used to confirm the effect of the present invention. However, when Y and La are used, the synergistic effect of the effect of preventing sintering with P increases. , Y and La are suitable. The content of the rare earth element in the iron oxide is 0.1 to 10 at.% In terms of atomic ratio of R / Fe (at.%). %. 0.1 at. %, The effect of R coating to prevent sintering becomes insufficient, so that the lower layer does not have excellent surface smoothness, and sufficient coating film strength cannot be obtained. On the other hand, 10 at. %, The coated iron oxyhydroxide particles are apt to agglomerate, and sintering is likely to occur during the subsequent firing, which is not preferable.
[0026]
After obtaining the flat needle-like iron oxyhydroxide whose surface is coated with the phosphorus compound and the rare earth element compound in this way, by firing this, a flat needle-like iron oxide powder can be obtained. The firing treatment may be performed at 300 to 900 ° C, preferably 400 to 700 ° C, in the atmosphere. The treatment time may be about 10 to 60 minutes, and if too long, sintering proceeds. In this baking treatment, it is necessary to pay attention to the water vapor that stays in the inside. It is advisable to adjust the atmosphere to lower it. Then, when the predetermined process is completed, it is taken out at normal temperature of the atmosphere and cooled, so that flat needle-like iron oxide powder can be obtained. The iron oxide powder thus obtained inherits the flat needle shape of iron oxyhydroxide and has a flat needle shape.
[0027]
Regarding the sintering temperature, iron oxyhydroxide coated with a compound of P or R can be sintered at a lower temperature than a conventional solid solution containing a sintering inhibitor such as Al. For this reason, it is easy to maintain the flat needle shape of iron oxyhydroxide to iron oxide. Conventionally, there has been an attempt to improve the sintering prevention effect by dissolving Al and the like in the interior of the iron oxyhydroxide, which is a precursor of iron oxide, but other elements are dissolved in the interior. Then, the dehydration temperature at which iron oxyhydroxide turns into iron oxide tends to shift to a higher temperature side, and firing at a higher temperature is required. In the iron oxyhydroxide coated on the surface with a P or R compound according to the present invention, the dehydration reaction proceeds from a low temperature range, so that the firing temperature can be set low. As a result, sintering between particles can be suppressed and A flat needle shape can be maintained.
[0028]
If other elements (for example, Al and Si) coexist in the liquid at the time of the production of iron oxyhydroxide, these other elements act as a growth inhibitor of the iron oxyhydroxide, and the iron oxyhydroxide having a deformed shape is formed. However, according to the present invention, it is not necessary to coexist such other elements when producing flat needle-like iron oxyhydroxide. Therefore, the iron oxyhydroxide easily grows two-dimensionally in the major axis direction and the width direction (when the major axis direction is X and the minor axis direction is Y, Z, the X and Y directions dominantly grow). This is advantageous in obtaining particles having a high short-axis cross-sectional ratio, and is therefore advantageous in obtaining flat needle-like iron oxide particles according to the present invention. However, applying the sintering inhibitor such as Al to the surface of the flat needle-like iron oxyhydroxide after the formation of the flat needle-like iron oxyhydroxide does not impair the effect of the present invention. Therefore, the flat needle-like iron oxide powder according to the present invention can be obtained by calcining the surface of the flat needle-like iron oxyhydroxide particles having the Al compound adhered thereto.
[0029]
The iron oxide powder thus obtained has good dispersion with respect to the resin component for forming the lower layer since sintering is prevented. In addition, since each particle has a flat needle shape, the particles are likely to overlap with each other during the application of the tape to form a wide surface, so that the surface is smooth and the component in the direction perpendicular to the base film surface is small. In addition, since the tapes are densely oriented in the in-plane direction of the tape, there is an effect of improving the tape strength in addition to improving the surface smoothness. Further, since P and R present on the surface of the flat needle-like iron oxide particles modify the surface characteristics of the iron oxide particles to improve the dispersibility in the resin and the adhesion to the resin, the coating film is also used in this respect. Contributes to improving strength.
[0030]
As a result, the lower layer powder comprising the flat needle-like iron oxide particles according to the present invention simultaneously improves both the surface smoothness of the tape and the durability of the tape. Therefore, even when an extremely thin magnetic layer is applied thereon, This improves the surface smoothness of the magnetic layer and contributes to the improvement of the electromagnetic conversion characteristics, and it is possible to use a magnetic tape with sufficient strength even with a thinner tape. It is a very preferred underlayer powder.
[0031]
In addition, the lower layer powder is advantageous in that the powder pH can show a pH of 7 or less. A necessary property of the lower layer powder is powder pH. Since the pH change of the lower layer powder affects the adsorption behavior of the lower layer powder with the fatty acid in the resin, the lower layer powder preferably has a low powder pH, and the powder pH is preferably 7 or less. More specifically, fatty acids called lubricants are usually added to a coating material containing and dispersing a lower layer powder and a magnetic powder for producing a coating type magnetic recording medium. This lubricant serves to reduce the interference between the tape surface and the head in the form of a coating film, and improves the durability of the tape. Since fatty acids, which are acidic substances, are generally used as such lubricants, when the powder pH of the lower layer powder is on the alkaline side, the reaction with the acidic lubricant in the coating material will not occur. The reaction easily proceeds, and if this reaction occurs, the original lubricating action of the lubricant cannot be exhibited. For this reason, it is desirable that the lower layer powder has a surface property that does not cause adsorption to fatty acids. In practice, the lower layer powder should have a powder pH of 7 or less, preferably on the acidic side. .
[0032]
The powder for the lower layer according to the present invention has a powder pH of 7 or less when calcined iron oxyhydroxide coated with a phosphorus compound. Therefore, the effect of the lubricant is not degraded as described above, and it is also effective in improving the compatibility (compatibility) with the paint. In addition to the above-mentioned effect of preventing sintering, from this point, It was confirmed that the surface smoothness and running durability of the tape were improved. However, if the pH is too low, an undesirable effect on surrounding substances (for example, metal magnetic powder of the magnetic layer) is considered. Therefore, the pH is preferably 3 or more, preferably 4 or more. The preferred range of the powder pH is about 4 to 7. In the pH range of 3 to 7, the effect of corrosion on the metal magnetic powder in the magnetic layer does not appear.
[0033]
The lower layer powder composed of the flat needle-like iron oxide powder of the present invention has an average major axis length (average major axis length measured for 100 randomly selected particles in the field of view of a TEM photograph) of preferably 20 to 200 nm. Is 50 to 160 nm, more preferably 50 to 120 nm. Generally, as long as the average major axis length of the flat needle-like iron oxide particles is small, the tape surface can be smoothed when the tape is formed, as long as it can be dispersed in the coating material. Since the lower layer powder of the present invention is flat needle-shaped fine particles having an average major axis length in the above range and a minor axis cross-sectional ratio of 1.3 or more, it contributes to the surface smoothing of the tape. The axial ratio is preferably 2 to 10, preferably 3 to 8, and more preferably 4 to 8. By having a high axial ratio and a flat needle shape, it is easy to arrange the base film in parallel with the base film at the time of coating, which contributes to the smoothing of the surface of the tape and the strength of the tape. The specific surface area of the lower layer powder according to the present invention is 30 to 100 m by the BET method. ² / G, preferably 35-80 m ² / G, more preferably 35 to 70 m ² / G. If the specific surface area is higher than this value, poor dispersion in the paint occurs, and 30 m ² The ratio of less than / g is not preferable because it becomes a powder accompanied by aggregation and sintering.
[0034]
The lower layer powder according to the present invention can further have the following powder characteristics in addition to the above, and can also have tape characteristics when taped.
[0035]
[Stearic acid adsorption amount]: 0.1 to 3.0 mg / m ² , Preferably 0.1 to 2.0 mg / m ² , More preferably 0.1 to 1.5 mg / m ² It is. The smaller the stearic acid adsorption, the smaller the amount of lubricant (fatty acid) adsorbed when the lower layer powder is dispersed in the paint. The smaller the stearic acid adsorption, the more adversely the lubricant is affected. Since it is not provided, the effect of the durability of the tape by the lubricant can be maintained.
[0036]
[Resin adsorption amount (MR)]: 0.1 to 3 mg / m ² , Preferably 0.5 to 3 mg / m ² , More preferably 1-3 mg / m ² It is. A high resin adsorption (MR) indicates good adhesion to the resin, and also improves the strength of the coating film. Therefore, the higher the resin adsorption amount, the better.
[0037]
[Resin adsorption amount (UR)]: 0.1 to 4 mg / m ² , Preferably 1.0 to 4 mg / m ² , More preferably 2 to 4 mg / m ² It is. For the same reason as the above-mentioned resin adsorption amount (MR), the resin adsorption amount (UR) is preferably higher.
[0038]
[Surface roughness of tape]: The roughness after calendering is 200 Å or less, preferably 150 Å or less. The change rate before and after the calendar is 50% or more. The larger the change rate before and after the calender, the better the moldability of the lower layer when the layers are stacked, which leads to an improvement in the surface smoothness of the magnetic layer. Therefore, the larger the change rate of the calender in the lower layer, the better.
[0039]
[Steel ball sliding of tape: scratch width]: 190 μm or less, preferably 170 μm or less, more preferably 150 μm or less. The smaller the scratch width, the stronger the coating.
[0040]
[Steel ball sliding of tape: running durability]: 600 pass or more, preferably 900 pass or more, more preferably 1500 pass or more. The running durability is affected not only by the strength of the coating but also by the action of the lubricant in the coating. The coating film should be stable against as many sliding movements as possible.
[0041]
When the lower layer is formed using the flat needle-like iron oxide powder according to the present invention in the magnetic recording medium having the multilayer structure, the following are exemplified as the magnetic powder, the coating composition, and the base film constituting the upper magnetic layer. it can.
As the magnetic powder constituting the magnetic layer,
Co: over 5 to 50 at. %,
Al: 0.1 to 50 at. %,
Rare earth element (including Y): 0.1 to 30 at. %,
Group 1a element of the periodic table (Li, Na, K, etc.): 0.05% by weight or less,
Group 2a element of the periodic table (Mg, Ca, Sr, Ba, etc.): 0.1% by weight or less,
Iron-containing ferromagnetic powder containing
Average long axis length: 10 to 200 nm,
Specific surface area is 30-150m by BET method ² / G,
X-ray crystal grain size (Dx): 50 to 200 angstroms,
Needle-shaped ferromagnetic powder having the shape of
Coercive force (Hc): 1000-3000 Oe,
Saturation magnetization (σs): 10 to 200 emu / g
Magnetic powder having the following magnetic properties.
[0043]
Base films for forming a multilayered magnetic recording medium include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone aramid, and fragrance. Resin films such as aromatic polyamides.
[0044]
As a magnetic paint for forming the magnetic layer (upper layer),
100 parts by weight of metal magnetic powder
5 parts by weight carbon black
Alumina 3 parts by weight
15 parts by weight of vinyl chloride resin (MR110)
15 parts by weight of polyurethane resin (UR8200)
1 part by weight of stearic acid
1 part by weight of acetylacetone
190 parts by weight of methyl ethyl ketone
80 parts by weight of cyclohexanone
110 parts by weight of toluene
And a magnetic paint having a composition consisting of
[0045]
As a non-magnetic paint for forming a non-magnetic layer (lower layer),
Flat needle-shaped non-magnetic powder α-Fe ₂ O ₃ 85 parts by weight
20 parts by weight of carbon black
Alumina 3 parts by weight
15 parts by weight of vinyl chloride resin (MR110)
15 parts by weight of polyurethane resin (UR8200)
190 parts by weight of methyl ethyl ketone
80 parts by weight of cyclohexanone
110 parts by weight of toluene
A non-magnetic paint having a composition consisting of
[0046]
In any of the paints, each material is blended in such a ratio as to achieve the above composition, and can be adjusted to a coating solution by kneading and dispersing using a kneader and a sand grinder. After application to a thickness, while the magnetic layer is in a wet state, a magnetic field is applied to orient the magnetic layer, followed by drying and calendering to produce a magnetic tape. By forming a non-magnetic layer using the ferromagnetic powder, base film, and coating composition exemplified above and using the flat needle-like lower layer powder according to the present invention, high-density recording, which is not available in the prior art, is achieved. And a high-performance magnetic recording medium suitable for a computer.
[0047]
【Example】
Hereinafter, typical examples of the present invention will be described. Before that, measurement of characteristic values in each example will be described.
[0048]
-Average major axis length, average minor axis length, and axis ratio: The average of the values measured for 100 particles randomly extracted from an electron micrograph of 174,000 times was taken.
・ Short axis cross-section ratio: When taking an electron micrograph, multiple samples of the same sample are taken while tilting the sample stage, and the maximum short width and maximum width are measured for 20 particles while referring to the tilt angle. , The average maximum width was divided by the average maximum short width. For reference, FIG. 6 shows an electron micrograph (TEM image) of the lower layer powder obtained in Example 5 described later. In FIG. 6, the same particle (particle in the center of the photograph indicated by a leader line) was observed when the inclination angle of the sample stage was -60 degrees in the upper TEM image and the inclination angle of the sample stage was +30 degrees in the lower TEM image. By the way, when the same particle is viewed at a different angle (90 degrees), the short-axis width is 18.5 nm for the former and 35.2 nm for the latter, so that the short-axis cross-sectional ratio of this particle is 35.2. /18.5=1.9 is calculated.
-Specific surface area: measured by the BET method.
-Powder pH: Measured according to JIS K5101.
-Stearic acid adsorption amount: After dispersing the sample powder in a 2% solution of stearic acid (solvent is MEK), the sample powder is settled by a centrifugal separator, and the concentration of the supernatant is determined to obtain the adsorption amount per specific surface area. Calculated.
-Resin adsorption amount (MR): Calculated in the same manner as the stearic acid adsorption amount using a 1% solution of vinyl chloride resin (MR-110) (solvents are MEK and toluene).
-Resin adsorption amount (UR): A 2% solution of polyurethane resin (UR-8200) (solvents: MEK, toluene and MIBK) was used and calculated in the same manner as the stearic acid adsorption amount.
[0049]
Regarding the evaluation of the coating film viscosity and the tape, the obtained iron oxide powder was formed into a coating under the following coating conditions, and the lower layer tape was prepared under the following conditions.
[0050]
・ Coating conditions
Iron oxide powder 100 parts by weight
20 parts by weight of PVC resin
165 parts by weight of methyl ethyl ketone
Cyclohexanone 65 parts by weight
165 parts by weight of toluene
1 part by weight of stearic acid
1 part by weight of acetylacetone
Each of the materials was blended so as to have the following component composition, and the mixture was dispersed in a centrifugal ball mill for 1 hour. A coating was obtained by using an applicator on a polyethylene terephthalate base film. A non-magnetic lower layer (lower layer tape) was formed by coating so that the target thickness was about 3 μm.
[0051]
Paint viscosity: The viscosity of the dispersion paint was measured using a viscometer (R110 type) manufactured by Toki Sangyo Co., Ltd.
・ Surface smoothness (surface roughness): The surface roughness (Ra) of the lower tape before calendering and the surface roughness after calendering using a three-dimensional fine shape measuring device (ET-30HK) manufactured by Kosaka Laboratory Co., Ltd. The degree (Ra) was measured.
Calender change rate: Calculated as 100 × (surface roughness before calender-surface roughness after calender) / (surface roughness before calender). The larger the calender change rate, the more easily the calendering occurs when the magnetic layer is formed on the lower layer and calendered. That is, the smoother the tape surface can be formed as the calendar change rate increases.
Surface smoothness (gloss): The gloss of the lower tape was measured at an angle of 60 degrees using a gloss meter.
・ Film strength (Steel ball sliding): Affix to glass plate with lower tape applied side up, place glass plate on a horizontal surface, and place stainless steel ball of 5mm diameter on tape applied surface And apply a load of 5 g in the vertical direction. From this state, the glass plate is reciprocated 300 times horizontally at a constant speed of 2320 mm / min and one way at 20 mm. After this operation, the scratches left on the tape surface by the SUS steel ball were observed with an optical microscope, and the scratch width was measured. Also, the number of passes until the tape was peeled was measured, and this was defined as the number of slides.
-Running durability (steel ball sliding): In the above-mentioned steel ball sliding, the number of times of sliding until the coating film peels off is measured.
[0052]
[Example 1]
0.5 mol of Fe ³⁺ Fe solution ³⁺ Was added while stirring at a liquid temperature of 10 ° C. to produce a precipitate of ferric hydroxide. Thereafter, the suspension containing the precipitate was kept at 45 ° C. and aged for 10 hours to produce α-FeOOH in the form of flat needles. Then, to the suspension containing the flat needle-like α-FeOOH, an aqueous solution of sodium aluminate in an amount such that Al becomes 1.0 wt% with respect to α-FeOOH is added with stirring, and the pH is adjusted to 9 or less to obtain the flat needle-like α-FeOOH. The particles were subjected to an Al deposition treatment. Thereafter, the suspension was filtered, washed with water and dried in a usual manner, and calcined at 650 ° C. to obtain flat needle-like iron oxide.
[0053]
The composition of the components obtained by chemical analysis of the obtained flat needle-like iron oxide powder, the properties of this powder measured as described above, and the measurement results of the tape properties of the lower layer tape using this powder are shown. The results are shown in Table 1.
[0054]
[Example 2]
0.5 mol of Fe ³⁺ Fe solution ³⁺ Was added while stirring at a liquid temperature of 10 ° C. to produce a precipitate of ferric hydroxide. Thereafter, the suspension containing the precipitate was kept at 45 ° C. and aged for 10 hours to produce α-FeOOH in the form of flat needles. Next, to the suspension containing the flat needle-like α-FeOOH, an aqueous phosphoric acid solution is added with stirring so that the amount of P becomes 2.0 wt% with respect to α-FeOOH, and the flat needle-like α-FeOOH is subjected to P deposition treatment. Was given. Thereafter, the suspension was filtered, washed with water and dried in a usual manner, and calcined at 650 ° C. to obtain flat needle-like iron oxide. Various characteristics of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0055]
[Example 3]
Example 2 was repeated except that the suspension containing the ferric hydroxide precipitate was kept at 50 ° C. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0056]
[Example 4]
Add sodium hydroxide to Fe ³⁺ Example 2 was repeated except that the suspension containing 1.3 eq. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0057]
[Example 5]
0.5 mol of Fe ³⁺ Fe solution ³⁺ 1.3 equivalents of an aqueous sodium hydroxide solution was added thereto while stirring at a liquid temperature of 10 ° C. to produce a precipitate of ferric hydroxide. Thereafter, the suspension containing the precipitate was kept at 55 ° C. and aged for 10 hours to produce flat needle-like α-FeOOH. Next, to the suspension containing the flat needle-like α-FeOOH, an aqueous phosphoric acid solution in an amount such that P becomes 2.0 wt% with respect to α-FeOOH is added with stirring, and P is applied to the flat needle-like α-FeOOH. Was given. Thereafter, the atomic ratio of Y to Fe of α-FeOOH (Y / Fe) was further increased to 1.0 at. % Yttrium aqueous solution was added to adjust the pH to 9 or less, and the flat needle-like α-FeOOH was subjected to Y deposition treatment. Thereafter, the suspension was filtered, washed with water and dried in a usual manner, and calcined at 650 ° C. to obtain flat needle-like iron oxide. Various characteristics of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 1.
[0058]
[Comparative Example 1]
Na ₂ CO ₃ And an aqueous solution containing 0.45 mol of NaOH were mixed. ²⁺ Was added and an aging treatment was carried out at 45 ° C. for 90 minutes, and then air was passed through the solution at 45 ° C. to obtain α-FeOOH (short-axis cross-sectional ratio ≒ 1). To the suspension containing α-FeOOH, an aqueous solution of sodium aluminate in which Al becomes 1.0 wt% with respect to α-FeOOH is added to adjust the pH to 9 or less, and the α-FeOOH particles are subjected to Al deposition treatment. gave. Thereafter, the suspension was filtered, washed with water and dried in a usual manner, and then calcined at 650 ° C. to obtain needle-like (but short-axis cross-sectional ratio ≒ 1) iron oxide. Various properties of the obtained iron oxide powder were evaluated in the same manner as in Example 1. The results are shown in Table 1.
[0059]
[Table 1]

[0060]
The following can be seen from the results in Table 1.
[0061]
(1) Examples in which the short-axis cross-sectional ratios are different from each other in Example 1 (short-axis cross-sectional ratio = 1.45) and Comparative Example 1 (short-axis cross-sectional ratio = 1) In the case of No. 1, a smooth coating film having a small surface roughness can be produced, and the tape durability is also small, the scratch width is small, the number of sliding passes is large, and the tape durability is also improved. That is, in the case of flat needle-shaped iron oxide powder having a large short-axis cross-sectional ratio, the particles are likely to be overlapped to form a wide surface when the powder is applied as a paint, and the surface is considered to be smooth. Further, it is considered that the flat needle shape reduces the component in the direction perpendicular to the support surface and is densely oriented in the tape surface direction, so that the tape strength is improved in addition to the surface smoothness.
[0062]
(2) The coating film made of the flat needle-like iron oxide powder of Example 1 has a larger change in surface roughness before and after the calender than that of Comparative Example 1. For this reason, when the upper magnetic layer is formed on the lower layer, if a calendering process is performed, the lower layer is likely to be calendered. That is, a smoother coating film can be formed, which is suitable as a lower layer for a multilayer magnetic recording medium.
[0063]
(3) The flat needle-shaped iron oxide of Example 2 which contains P has further improved surface smoothness than that of Example 1 which does not contain P. Further, by containing P, the powder pH becomes 4.6, and the fatty acid adsorption amount (StA.) Is low. As a result, it is considered that the original role of the lubricant (fatty acid) as a coating film component was not hindered, but the tape durability was improved as compared with that of Example 1.
[0064]
(4) In Examples 2 to 4, the short-axis cross-sectional ratio was changed by changing the production conditions of iron oxyhydroxide. It can be seen that the surface smoothness is improved and the tape durability is improved.
[0065]
(5) In Example 5, which further contains Y in addition to P, the minor axis cross-sectional ratio of flat needle-like iron oxide (hematite) is further increased even in comparison with, for example, Example 4. As a result, the surface smoothness is further improved, and the tape durability is further improved. Therefore, in order to obtain flat needle-like iron oxide (hematite) which contributes to the improvement of tape surface smoothness and tape durability, it is preferable that P is contained, and furthermore, R (including Y) is contained in addition to P. It is more preferable that
[0066]
[Example 6]
In this example, a magnetic tape having a multilayer structure in which the lower layer powder obtained in Example 5 was used as a nonmagnetic layer and the following metal magnetic powder was used as a magnetic layer was prepared, and the electromagnetic conversion characteristics and tape durability were evaluated. It was done.
[0067]
The coating material for the non-magnetic layer was prepared by mixing the following components with 85 parts by weight of the lower layer powder of Example 5 in the following ratio, and kneading and dispersing the mixture using a kneader and a sand grinder.
(Composition of non-magnetic paint)
Example 1 Powder for lower layer (α-Fe ₂ O ₃ ) 85 parts by weight
20 parts by weight of carbon black
Alumina 3 parts by weight
15 parts by weight of vinyl chloride resin (MR110)
15 parts by weight of polyurethane resin (UR8200)
190 parts by weight of methyl ethyl ketone
80 parts by weight of cyclohexanone
110 parts by weight of toluene
[0068]
The coating material for the magnetic layer was prepared by mixing the following components in the following ratio with respect to 100 parts by weight of the following metal magnetic powder, and kneading and dispersing using a kneader and a sand grinder.
(Metal magnetic powder)
Long axis length: 80 nm
BET: 61m ² / G
Dx: 150 angstroms
Hc: 2400 (Oe)
σs: 127 emu / g
(Composition of magnetic paint)
100 parts by weight of the above-mentioned metal magnetic powder
5 parts by weight carbon black
Alumina 3 parts by weight
15 parts by weight of vinyl chloride resin (MR110)
15 parts by weight of polyurethane resin (UR8200)
1 part by weight of stearic acid
1 part by weight of acetylacetone
190 parts by weight of methyl ethyl ketone
80 parts by weight of cyclohexanone
110 parts by weight of toluene
[0069]
These paints are applied on a base film composed of an aramid support so that the nonmagnetic layer thickness (lower layer thickness) is 2.0 μm and the magnetic layer thickness is 0.20 μm, respectively, so that the magnetic layer is wet. Meanwhile, a magnetic field was oriented by applying a magnetic field, dried and calendered to produce a magnetic tape.
[0070]
The obtained magnetic tape was tested for surface smoothness (roughness) and tape durability (the number of passes of steel ball sliding) and the electromagnetic conversion characteristics (C / N and output) were measured by the methods described above. The C / N ratio was measured by attaching a recording head to a drum tester and recording a digital signal at a recording wavelength of 0.35 μm. At that time, the reproduction signal was measured using an MR head, the modulation noise was measured for noise, and the output of Comparative Example 2 described later and C / N were set to 0 dB and displayed as relative values. Table 2 shows the results.
[0071]
[Example 7]
Example 6 was repeated except that the powder obtained in Example 1 was used as the lower layer powder. Table 2 shows the surface smoothness (roughness), tape durability (number of passes of steel ball sliding), and electromagnetic conversion characteristics of the obtained magnetic tape.
[0072]
[Comparative Example 2]
Example 6 was repeated except that the powder obtained in Comparative Example 1 was used as the lower layer powder. Table 2 shows the surface smoothness (roughness), tape durability (number of passes of steel ball sliding), and electromagnetic conversion characteristics of the obtained magnetic tape.
[0073]
[Table 2]

[0074]
The following can be seen from the results in Table 2.
First, as is clear from comparison between Examples 6 and 7 and Comparative Example 2, the lower layer powder according to the present invention has a very good tape surface smoothness when a multilayer structure is formed, and as a result, a high output and a high output are obtained. C / N, which is suitable as a high-density recording medium. It also has excellent durability of magnetic tape and shows excellent durability against sliding with the head.
[0075]
As is clear from the comparison between Example 6 and Example 7, the flat needle-like lower layer powder containing P and Y having a high cross-sectional ratio (of Example 5) had a tape surface in a multilayer structure. Smoothness is better, resulting in higher output, higher C / N and better durability.
[0076]
Example 8
Example 2 was repeated except that the suspension containing the ferric hydroxide precipitate was kept at 35 ° C. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0077]
[Example 9]
Example 2 was repeated except that the suspension containing the ferric hydroxide precipitate was kept at 70 ° C. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0078]
[Comparative Example 3]
Example 2 was repeated except that the suspension containing the ferric hydroxide precipitate was kept at 25 ° C. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0079]
[Comparative Example 4]
Example 2 was repeated except that the suspension containing the ferric hydroxide precipitate was kept at 80 ° C. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0080]
[Example 10]
Example 2 was repeated except that the flat needle-like α-FeOOH was subjected to the P deposition treatment, and then no yttrium aqueous solution was added. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0081]
[Example 11]
After the flat needle-like α-FeOOH is subjected to the P deposition treatment, the atomic ratio of Y to Fe (Y / Fe) is 0.18 at. Example 2 was repeated, except that an amount of yttrium aqueous solution was added in an amount of 0.2%. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0082]
[Example 12]
After the flat needle-like α-FeOOH is subjected to the P deposition treatment, the atomic ratio of Y to Fe (Y / Fe) is 8.18 at. Example 2 was repeated, except that an amount of yttrium aqueous solution was added in an amount of 0.2%. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0083]
[Comparative Example 5]
After the flat needle-like α-FeOOH is subjected to the P deposition treatment, the atomic ratio of Y to Fe (Y / Fe) is 4.54 at. Example 2 was repeated, except that an amount of yttrium aqueous solution was added in an amount of 0.2%. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0084]
[Example 13]
Example 2 was repeated except that, after the flat needle-like α-FeOOH was formed, an aqueous phosphoric acid solution was added to the suspension containing the aqueous solution under stirring with an amount of 0.28 wt% of P based on α-FeOOH. Repeated. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0085]
[Example 14]
Example 2 was repeated except that, after the flat needle-like α-FeOOH was formed, an aqueous phosphoric acid solution was added to the suspension containing the aqueous solution under stirring so that the amount of P became 6.43 wt% based on α-FeOOH. Repeated. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0086]
[Comparative Example 6]
Example 2 was repeated except that, after the flat needle-like α-FeOOH was formed, an aqueous phosphoric acid solution was added to the suspension containing the same under stirring with an amount of a phosphoric acid aqueous solution in which P became 7.86 wt% based on α-FeOOH. Repeated. Various properties of the obtained flat needle-like iron oxide powder were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0087]
[Table 3]

[0088]
From the results in Table 3 (see also Table 1), the following is clear.
(1) Looking at the influence of the particle diameter (average major axis length) of iron oxide (hematite), for example, the particle diameter increases in the order of Comparative Example 3, Example 8, Example 5, Example 9, and Comparative Example 4. However, in Comparative Example 3 (major axis length = 15 nm) in which the particle diameter is very small, it is difficult to disperse the resin into a resin, and it is impossible to make a tape. On the other hand, in Comparative Example 4 having a large particle diameter (major axis length = 250 nm), the axial ratio and the minor axis cross-sectional ratio are also large, but the surface smoothness is impaired. Therefore, it is understood that the particle diameter (average major axis length) is preferably in the range of 20 nm to 200 nm.
[0089]
(2) Looking at the influence of the yttrium content in iron oxide (hematite), for example, the yttrium content increases in the order of Example 10, Example 11, Example 5, and Comparative Example 5, but the yttrium content increases. In Comparative Example 5 which is more than necessary, the specific surface area is increased and the dispersibility in the resin is deteriorated, and as a result, the surface smoothness is impaired. Therefore, it can be seen that there is an appropriate range (0.1 to 10 at.% In terms of atomic ratio of Y / Fe) for maintaining good surface smoothness even with the yttrium content.
[0090]
(3) Looking at the influence on the phosphorus content in iron oxide (hematite), for example, the phosphorus content increases in the order of Example 13, Example 5, Example 14, and Comparative Example 6, but the phosphorus content increases. In Comparative Example 6 in which the content was too high, the viscosity of the paint was increased, the dispersibility was deteriorated, and the surface smoothness was impaired. On the other hand, as the phosphorus content decreases, the amount of stearic acid adsorbed increases, the effect of the lubricant decreases, and the scratch width of the tape durability increases. That is, although phosphorus effectively acts to improve the tape durability, if it is too much, the surface smoothness is impaired. Therefore, the phosphorus content should be within a suitable range (0.1 to 5.0 wt%). ) Exists.
[0091]
【The invention's effect】
As described above, according to the present invention, the flat needle-like oxide which can improve the properties required for the powder for the lower layer in the coating type magnetic recording medium having a multilayer structure, particularly the surface smoothness and the tape strength of the tape can be improved. An iron powder is obtained. Therefore, by using the flat needle-like iron oxide powder of the present invention as a lower layer powder of a coating type magnetic recording medium having a multilayer structure, a durable recording medium suitable for high recording density can be obtained.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram for explaining the shape of flat needle-like particles of the present invention.
FIG. 2 is a view showing another example of the shape of the short needle cross section of the flat acicular particles of the present invention.
FIG. 3 is a view showing another example of the shape of the flat needle-shaped particle of the present invention in a short-axis cross section.
FIG. 4 is a view showing another example of the shape of the short axis cross section of the flat needle-like particles of the present invention.
FIG. 5 is a view showing another example of the shape of the flat needle-shaped particle of the present invention in a short-axis cross section.
FIG. 6 is a comparison of electron micrographs (TEM images) of one particle of the lower layer powder obtained in Example 5 taken while changing the inclination angle of the sample stage.
[Explanation of symbols]
1 flat needle-like particles
2 Short axis section

Claims (5)

The average major axis length is 20 to 200 nm, and the minor axis section cut in the direction perpendicular to the major axis has a longer width and a shorter width. Powder for a lower layer of a coating type magnetic recording medium comprising flat needle-like iron oxide particles almost uniformly larger than 1.3 and having a specific surface area of 30 to 100 m ² / g by a BET method. The powder for a lower layer of a coating type magnetic recording medium according to claim 1, wherein the powder pH is 7 or less. The powder for a lower layer of a coating type magnetic recording medium according to claim 1, which contains 0.1 to 5.0 wt% of P. 4. R (R is one or more kinds of rare earth elements including Y) is 0.1 to 10% at. The powder for a lower layer of the coating type magnetic recording medium according to claim 1, wherein In a coating type magnetic recording medium having a multilayer structure, a non-magnetic layer (lower layer) in which non-magnetic powder is dispersed in a resin is provided between a magnetic layer in which the magnetic powder is dispersed in a resin and a base film. 5. A coating type magnetic recording medium using the lower layer powder according to claim 1 as a magnetic powder.

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