JPS60131626A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which excels in the durability by forming a magnetic layer containing spherical (a) iron oxide. CONSTITUTION:A spherical particle has a smaller surface area than a cubic particle per particle and therefore has better fluidity to attain easily a state apporoximate to a filling performance with highest density. Furthermore the spherical particle has a small apparent bulk as well as an extremely small amount of liquid absorption. Owing to these features, the spherical particles are dispersed quite easily into a magnetic coating material and also have a small amount of abosorption of a binder in the magnetic layer. This reduces the fragility and the surface deterioration of the magnetic layer and improves the surface smoothness and the durability with high density for the magnetic layer. The average grain size of the spherical (a) iron oxide is preferably set at about 0.3- 1.5mu. If the grain size of the iron oxideis too small, the size of the gain is similar to that of the magnetic powder to deteriorate the effect of reinforcement of a film. While in case the grain size is too large, the surface smoothness is sometimes deteriorated. The amount of the spherical iron oxide is set preferably at 0.5-6wt% to the magnetic layer.

Description

【発明の詳細な説明】 産業上の利用分野 本発明は磁気テープやフロッピーディスクなどに用いる
ことができる磁気記録媒体に関する。DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium that can be used for magnetic tapes, floppy disks, and the like.

従来例の構成とその問題点 磁気記録媒体は通常ポリエステルフィルムなどの支持体
上に、磁性塗料を塗布して作られる。磁気記録媒体は磁
気ヘッドと摺接させて用いるため高度の耐摩耗性が要求
される。このため磁性層中にα酸化鉄、アルミナ、酸化
クロムなどの硬質非磁性微粒子を塗膜強化剤として混入
する方法が知られている。しかしながら従来のこのよう
な硬質微粒子は、粒状あるいは立方状を呈すものが多か
ったため、かさ高く、吸液量が大きかった。このためこ
のようなかさ高い硬質微粒子の混入は、磁性層の表面平
滑性を低下したり、磁性層を硬くて脆いものにし、ベー
スフィルムとの接着性を悪くするなどの・傾向をもたら
すので、その混入量には制約が多く、塗膜強化にも限界
があった。Conventional Structure and Problems Magnetic recording media are usually made by coating a magnetic paint on a support such as a polyester film. Since magnetic recording media are used in sliding contact with magnetic heads, they are required to have a high degree of wear resistance. For this reason, a method is known in which hard non-magnetic fine particles such as α-iron oxide, alumina, chromium oxide, etc. are mixed into the magnetic layer as a coating film strengthening agent. However, conventional hard fine particles often have a granular or cubic shape, are bulky, and absorb a large amount of liquid. Therefore, the inclusion of such bulky hard particles tends to reduce the surface smoothness of the magnetic layer, make the magnetic layer hard and brittle, and impair its adhesion to the base film. There were many restrictions on the amount of mixing, and there were also limits to the strength of the coating film.

発明の目的 本発明の目的は耐久性にとむすぐれた磁気記録媒体を提
供することである。OBJECTS OF THE INVENTION An object of the present invention is to provide a magnetic recording medium with excellent durability.

発明の構成 前記目的を達成するために、↑発明の磁気記録媒体は、
球状を呈するα酸化鉄が含まれてなる磁性層を有するも
のである。Structure of the Invention In order to achieve the above object, the magnetic recording medium of the invention has the following features:
It has a magnetic layer containing spherical α-iron oxide.

実施例の説明 従来塗膜の耐摩耗性を増すための塗膜強化剤として用い
られるα酸化鉄としては、粒子形状が立方竺を呈するも
のが多かった。このような粒子は水酸化第一鉄の懸濁液
を空気や酸化剤の導入により湿式酸化することにより生
成する立方状マグネタイトを取出し、酸素の存在下で赤
熱することにより得られる。他方球状を呈するα酸化鉄
は、上記の過程において、水酸化第一鉄の湿式酸化の際
の反応温度９時間、　ｐＨなどを特殊な条件にすること
により得られるが、本発明はこの球状α酸化鉄を塗膜強
化剤として導入することを骨子と−する。Description of Examples Conventionally, α-iron oxide used as a coating film strengthening agent to increase the abrasion resistance of coating films has often had a cubic grain shape. Such particles can be obtained by wet-oxidizing a suspension of ferrous hydroxide by introducing air or an oxidizing agent, extracting cubic magnetite, and heating it to red heat in the presence of oxygen. On the other hand, spherical α-iron oxide can be obtained by subjecting ferrous hydroxide to wet oxidation under special conditions such as reaction temperature and pH for 9 hours in the above process. The main idea is to introduce iron oxide as a coating film strengthening agent.

なお球に近い多面体は球と類似の挙動を示すことは当然
であり、以下とのような多面体を含めて球状と表現する
。It goes without saying that polyhedra that are close to spheres behave similarly to spheres, and the following polyhedra are also expressed as spherical.

球状粒子は立方状や粒子にくらべ、１粒子当りの表面積
が小さく、粒子としての流動性が良好で、最密充填に近
づ竺やす“ため・見掛？嵩が小さく・吸液量も、著しく
小さいという特長がある。このため、磁性塗料中に混入
する場合にも極めて分散しやすい。まだ磁性層中におい
ても結合剤の吸収量が少いために、磁性層を脆くしたり
、その表面性を損うことが少なく、表面平滑性がすぐれ
、緻密で耐久性にとむ磁性層が形成される。Spherical particles have a smaller surface area per particle than cubic particles, have good fluidity as particles, and are close to close-packed, making them easier to sag, have a smaller apparent bulk, and have a lower amount of liquid absorption. It has the characteristic of being extremely small.For this reason, it is extremely easy to disperse when mixed into magnetic paint.However, since the amount of binder absorbed in the magnetic layer is small, it may make the magnetic layer brittle or cause its surface roughness. A magnetic layer with excellent surface smoothness, denseness, and durability is formed.

本発明に用いる球状α酸化鉄の平均粒径は０．３〜１．
６μ程度が好ましい。粒径過小の場合は磁性粉と類似の
サイズとなるため塗膜強化の効果がうすれ、捷た粒径過
大の場合は表面平滑性に悪影響添加量過少の場合には塗
膜強化の効果が少く、また添加量過大の場合には、磁性
層の脆さや表面平滑性に悪影響が出たり、ヘット１摩耗
を過大にするおそれがあるからである。The average particle size of the spherical alpha iron oxide used in the present invention is 0.3 to 1.
Approximately 6μ is preferable. If the particle size is too small, it will be similar in size to magnetic powder, so the effect of strengthening the coating will be diminished, and if the particle size is too large, it will have a negative effect on surface smoothness.If the amount added is too small, the effect of strengthening the coating will be reduced. Moreover, if the amount added is too large, there is a risk that the brittleness and surface smoothness of the magnetic layer will be adversely affected and the wear of the head 1 will be excessive.

以下さらに本発明の具体的な実施例について説明する。Specific examples of the present invention will be further described below.

（実施例１） 水酸化第一鉄の湿式空気酸化法により得られた球状マグ
ネタイトを空気中にて６００℃に加熱してα酸化鉄（α
へマタイト）としだ。この球状α酸化鉄の平均粒径は０
．６μ、吸液量はｏ、１ｅｒｎＱ／ｙであった。(Example 1) Spheroidal magnetite obtained by a wet air oxidation method of ferrous hydroxide was heated to 600°C in air to obtain α iron oxide (α
Hematite) Toshida. The average particle size of this spherical α-iron oxide is 0
．． 6μ, and the amount of liquid absorbed was o, 1ernQ/y.

次にγ−酸化鉄（長軸０．４μｍ、軸比８）６２０部（
重量部、以下同じ）球状α酸化鉄（上記）２０部、カー
ホンブラック（ＣＳ　Ｘ　１５０Ａ−２゜キャボット社
製）３５部、ポリウレタ、ｙ（Ｎ−２３０４゜日本ポリ
ウレタン製）１１０部、塩ビー酢ビーポリビニルアルコ
ール共重合物（■ＡＧＨ−ＵＣＣ社製）１２５部、ステ
アリン酸１０部、流動パラフィン３０部、レシチン（大
豆製）４部、硬化剤（コロネートＬ１日本ポリウレタン
製）４６部。Next, 620 parts of γ-iron oxide (long axis 0.4 μm, axial ratio 8) (
Parts by weight (same below) 20 parts of spherical alpha iron oxide (above), 35 parts of carphone black (CS 125 parts of acetic acid bee polyvinyl alcohol copolymer (manufactured by AGH-UCC), 10 parts of stearic acid, 30 parts of liquid paraffin, 4 parts of lecithin (made from soybeans), and 46 parts of hardening agent (Coronate L1 manufactured by Nippon Polyurethane).

ＭＥＫ１６００部、トルエンａｏｏ部、シクロヘキサノ
ン６００部からなる磁性塗料を調整し、厚さ７６μｍの
ポリエステルフブルム上に塗布、乾燥、カレンダリング
、加熱硬化２表面研摩したのち外径７２論の円板状に打
抜き試験試料とした。A magnetic paint consisting of 1,600 parts of MEK, AOO parts of toluene, and 600 parts of cyclohexanone was prepared, applied onto a polyester fabric with a thickness of 76 μm, dried, calendered, heated, hardened, and polished.After surface polishing, it was shaped into a disc with an outer diameter of 72 mm. This was used as a punching test sample.

このようにして作られた試料の表面平滑性を示す光沢度
（日本電色工業製光沢計）は１３８を示した。次にこの
試料をヘッド圧を３倍（４ｓｙ）にしたドライバー（３
００ｒｐｍ）にかけ、加速耐久試験を行なったところ、
出力が初期値の７０％に低下するのに３５０時間を要し
た。The glossiness (gloss meter manufactured by Nippon Denshoku Kogyo), which indicates the surface smoothness of the sample thus prepared, was 138. Next, use this sample with a driver (3
00 rpm) and conducted an accelerated durability test.
It took 350 hours for the output to drop to 70% of the initial value.

（実施例２） 実施例１において、球状α酸化鉄の混入量が磁性層中に
１重量％および４重量％になるように加減した試料を作
製し、同様の試験を行・た。ｉ果を実施例１（Ｄ＆ｉ果
とあ！′１て第′表に示した・（比較例１） 実施例１およ□び２において球状のα酸化鉄のかわりに
、立方状のα酸化鉄（平均粒径０．６μ、吸液量０．２
５ｍ１１／ｙ　）を用いて同様の試験を行っ九結果を第
１表にあわせて示しだ。(Example 2) In Example 1, samples were prepared in which the amount of spherical α-iron oxide mixed in the magnetic layer was adjusted to 1% by weight and 4% by weight, and the same tests were conducted. Example 1 (Comparative Example 1) In Examples 1 and 2, cubic α-iron oxide was used instead of spherical α-iron oxide. Iron (average particle size 0.6 μ, liquid absorption 0.2
A similar test was conducted using 5m11/y) and the results are shown in Table 1.

第　１　表 発明の効果 本発□明においては、塗膜強化剤として、球状のａｉ化
鉄を磁性層に混入することを特長とする□ものであるが
、球状α酸化鉄は前記のように従来用いられて来た粒状
或は立方状の粒子形状を有する塗膜強化用非磁性無機粉
末にくらべ、平均粒径同一であっても吸液量が小さいた
め、磁性層に混入しても結合剤の吸収量が少く、緻密性
１表面平滑性、基材との接着性にすぐれた磁性層が形成
される。Table 1 Effects of the Invention The present invention is characterized in that spherical iron oxide is mixed into the magnetic layer as a coating film strengthening agent. Compared to conventionally used non-magnetic inorganic powders for coating reinforcement that have granular or cubic particle shapes, even if the average particle size is the same, the amount of liquid absorbed is smaller, so even if mixed into the magnetic layer, it will not bind. A magnetic layer is formed that absorbs a small amount of agent and has excellent density, surface smoothness, and adhesion to the base material.

以上のように本発明の磁気記録媒体は表面光沢度と再生
出力が大きく、しかも耐久性にとんだすぐれたものであ
る。As described above, the magnetic recording medium of the present invention has high surface gloss and high reproduction output, and has excellent durability.

Claims (1)

【特許請求の範囲】[Claims] 球状を呈するα酸化鉄が含まれてなる磁性層を有する磁
気記録媒体。A magnetic recording medium having a magnetic layer containing spherical α-iron oxide.