【発明の詳細な説明】[Detailed description of the invention]
本発明は、磁気記録用媒体の製造方法に係り、
更に詳しくは、磁性塗膜における、配向性を向上
させ、高密度磁気記録に適した媒体を製造する方
法に関する。
磁気記録は、これまで、VTR、オーデイオ、
やデイジタルなどの記録に広く用いられてきた
が、それらの記録方式は、記録媒体の面内方向の
磁化を用いるものである。しかるに近年、磁気記
録の高密度化が推し進められてきた結果、上記の
ような、媒体面内の磁化を用いる記録において
は、記録最小単位の寸法が小さくなるに従がつ
て、媒体内の減磁作用が増加するため、高密度化
には限界が生じることが明らかとなつてきた。
これに対し、記録媒体の垂直方向の磁化を用い
て記録する方式を採用すれば、高密度化にともな
つて、上記減磁場が逆に小さくなるため、本質的
に高密度記録が可能となる。
しかして磁性塗料を支持体に塗布して、上記、
垂直磁化記録用媒体を作製する場合においては、
下記の点を考慮せねばならない。
まず磁性塗料中の磁性粒子の大きさは、記録最
短波長あるいは、ビツト長以下であることが要求
されるが、垂直磁化記録が、従来の面内記録に対
して、そのメリツトがより明らかとなるのは、こ
れら記録最小単位がサブミクロンの領域であるこ
とから、上記磁性粒子の大きさは、サブミクロン
以下の微粒であることが望まれる。
ところで一般に、このような微小寸法の磁性粒
子は、単磁区構造、即ち、微小な磁石となるた
め、お互いに磁気的に結合しやすく、１つには、
バインダー中への均一な分散状態を得るよう、と
くに注意を払う必要がある。
さらには又、均一な分散がなされ、所望の磁性
塗料が得られた場合に、このような磁性塗料を、
支持体面上に塗布して、垂直配向させる場合にお
いて下記の如き不都合が生ずる。
即ち、第１図の如く、NS極の対向する磁極１
間に、磁性塗料２を塗布した支持体３を、磁場方
向４と直交する方向に走行させて、磁性粒子５を
垂直配向させた後外部磁場を切るか、あるいは、
媒体を磁場外にとり出した場合、第２図の如く、
塗膜２の両面に磁極６が残存し、それによつて、
上記配向磁場と反対方向に、反磁場が生ずる。こ
の反磁場方向と角度をなす磁性粒子は、面内方向
へのトルクを受けるはずであるから、バインダー
中で、粒子の回転が許される状態では、配向磁場
除去後の配向性が著しく減少する。
本発明は、上記の欠点をなくするためになされ
たものであつて、磁場配向を行つた後、その方向
の磁場を保持した状態にて、バインダーの粘度を
高め換言すれば乾燥を施し、微粒子の回転を阻止
して、配向性を高めんとするものである。
本発明者らはこの方法を用いることによつて、
磁性微粒子の垂直配向性などを、著しく向上させ
ることができた。以下に具体例をもつて本発明を
説明する。
まず、バリウム塩、鉄塩、コバルト塩、チタン
塩を含む水溶液にアルカリを滴下し、共沈物を得
た後、アルカリ除去を行い、加熱して、Co―Ti
置換のバリウムフエライト微粒子を得た。これら
は、結晶粒径0.1μｍ以下で板状性をもち、又この
粉体の磁気特性は飽和磁化60emv／ｇ、抗磁力
1000（oe）であつた。次に表１の組成の磁性塗料
を作製して、25μｍ厚のポリエチレンテレフタレ
ートフイルムにロールコートした。
The present invention relates to a method for manufacturing a magnetic recording medium,
More specifically, the present invention relates to a method of improving the orientation of a magnetic coating film and producing a medium suitable for high-density magnetic recording. Until now, magnetic recording has been used in VTR, audio,
These recording methods use magnetization in the plane of the recording medium. However, as a result of recent efforts to increase the density of magnetic recording, in recording using magnetization within the plane of the medium, as described above, as the dimensions of the minimum recording unit become smaller, demagnetization within the medium increases. It has become clear that there is a limit to higher densities due to increased effects. On the other hand, if a recording method using perpendicular magnetization of the recording medium is adopted, the above demagnetizing field will become smaller as the density increases, essentially making high-density recording possible. . Then, by applying magnetic paint to the support, the above-mentioned
When producing a perpendicular magnetization recording medium,
The following points must be considered. First, the size of the magnetic particles in the magnetic paint must be smaller than the shortest recording wavelength or bit length, but the advantages of perpendicular magnetization recording over conventional in-plane recording will become clearer. This is because these minimum recording units are in the submicron range, so the size of the magnetic particles is preferably submicron or smaller. By the way, in general, such minute-sized magnetic particles have a single domain structure, that is, they form minute magnets, so they are likely to be magnetically coupled to each other.
Particular care must be taken to obtain a uniform dispersion in the binder. Furthermore, if uniform dispersion is achieved and a desired magnetic paint is obtained, such a magnetic paint may be
When coating on a support surface and vertically aligning, the following disadvantages occur. That is, as shown in Figure 1, the magnetic pole 1 opposite the NS pole
In the meantime, the support 3 coated with the magnetic paint 2 is run in a direction perpendicular to the magnetic field direction 4 to orient the magnetic particles 5 perpendicularly, and then the external magnetic field is turned off, or
When the medium is taken out of the magnetic field, as shown in Figure 2,
The magnetic poles 6 remain on both sides of the coating film 2, thereby
A demagnetizing field is generated in the opposite direction to the orienting magnetic field. Since the magnetic particles forming an angle with the direction of the demagnetizing field are expected to receive a torque in the in-plane direction, when the particles are allowed to rotate in the binder, the orientation after the orienting magnetic field is removed is significantly reduced. The present invention has been made to eliminate the above-mentioned drawbacks, and after performing magnetic field orientation, the viscosity of the binder is increased while maintaining the magnetic field in that direction, in other words, drying is performed, and fine particles are The purpose is to prevent rotation of the material and improve orientation. By using this method, the present inventors
We were able to significantly improve the vertical orientation of magnetic particles. The present invention will be explained below using specific examples. First, an alkali is added dropwise to an aqueous solution containing barium salt, iron salt, cobalt salt, and titanium salt to obtain a coprecipitate, and then the alkali is removed and heated to produce a Co-Ti
Substituted barium ferrite fine particles were obtained. These have a crystal grain size of 0.1 μm or less and plate-like properties, and the magnetic properties of this powder are a saturation magnetization of 60 emv/g and a coercive force.
It was 1000 (oe). Next, a magnetic paint having the composition shown in Table 1 was prepared and roll coated onto a 25 μm thick polyethylene terephthalate film.
【表】
磁性塗料塗布後のフイルムを第３図の如く、磁
場方向とフイルム面が直角となるように、磁場中
を走行させて、垂直配向させた。なお第３図より
明らかなように、磁場配向の工程において、ポー
ルピース１を断熱材７で２分して、前半では、粘
度の低い状態で磁場配向を行ない、また後半で
は、塗膜に温風８をふきつけることにより、その
塗膜を磁場下で乾燥させた。このようにして得ら
れた磁気テープにカレンダー処理を施して磁気記
録用媒体を得た。なお配向磁場の大きさは、
1000，2000，3000（oe）の３種類とした。
［比較例］
フイルム上に、実施例と全く同様にして作製し
た磁性塗料を塗布した後、直ちに磁場中にて配向
処理を施した。その直後に、試料をそのままの状
態に保持したまま電磁石の電流を切り磁場ゼロの
状態でフイルム上の塗料を温風吹付けにより乾燥
した。その後カレンダー処理を施すことにより磁
気記録媒体を得た。
上記によつて得たそれぞれの試料についてＸ線
回析の測定を行い。Baフエライトの（008）面か
らの強度と（110）面からの強度を求めて、それ
らの比から垂直配向度を求めた。その結果を表２
に示す。この方法で求めた垂直配向度はほぼ反磁
場補正を行つた場合の媒体の磁化曲線における角
形比とほぼ一致する。[Table] As shown in FIG. 3, the film coated with the magnetic paint was run in a magnetic field so that the direction of the magnetic field and the film surface were perpendicular to each other, and the film was oriented vertically. As is clear from Fig. 3, in the process of magnetic field orientation, the pole piece 1 is divided into two by the heat insulating material 7, and in the first half, the magnetic field orientation is performed in a state of low viscosity, and in the second half, the coating film is heated. The coating was dried under a magnetic field by blowing with Air 8. The magnetic tape thus obtained was calendered to obtain a magnetic recording medium. The magnitude of the orientation magnetic field is
There were three types: 1000, 2000, and 3000 (oe). [Comparative Example] A magnetic paint prepared in exactly the same manner as in the example was applied onto a film, and then immediately subjected to an orientation treatment in a magnetic field. Immediately thereafter, the electromagnetic current was turned off while the sample remained as it was, and the paint on the film was dried by blowing hot air in a state of zero magnetic field. Thereafter, a magnetic recording medium was obtained by calendering. X-ray diffraction measurements were performed on each sample obtained as described above. The intensity from the (008) plane and the intensity from the (110) plane of Ba ferrite were determined, and the degree of vertical orientation was determined from their ratio. Table 2 shows the results.
Shown below. The degree of perpendicular orientation determined by this method almost matches the squareness ratio of the magnetization curve of the medium when demagnetizing field correction is performed.
【表】
表２から、本発明法によつて得られた媒体の垂
直配向度は磁場強度依存性はあるものの、配向後
磁場をかけない状態で乾燥させた場合に比べその
配向度は大幅に改善されていることがわかる。
なお上記具体例においては、乾燥時の磁場の大
きさを、配向時のそれと同一としたが、塗料の粘
度、磁性粉の性状等により、配向時と乾燥時の磁
場の大きさは、異なつてもかまわない。さらに
は、本発明のように板状粒子などを垂直配向させ
る場合においては、磁場配向の後に、ロール配向
を施してもよく、このような場合には塗膜を完全
に乾燥させずに、乾燥後の粘度を、適宜、制御し
てもよい。さらには、又、本発明法は、上記のよ
うな微粒子を面内方向に配向させる場合でも、分
散の不均一性に基づく、反磁場が局所的に生ずる
場合などは有効である。[Table] From Table 2, although the degree of vertical orientation of the media obtained by the method of the present invention is dependent on the magnetic field strength, the degree of orientation is significantly greater than when drying without applying a magnetic field after orientation. You can see that it has been improved. In the above specific example, the magnitude of the magnetic field during drying was the same as that during orientation, but the magnitude of the magnetic field during orientation and drying may differ depending on the viscosity of the paint, the properties of the magnetic powder, etc. I don't mind. Furthermore, when plate-like particles are vertically aligned as in the present invention, roll orientation may be performed after magnetic field orientation. The subsequent viscosity may be controlled as appropriate. Furthermore, the method of the present invention is effective even when fine particles are oriented in the in-plane direction as described above, when a demagnetizing field is generated locally due to non-uniformity of dispersion.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は、磁場による磁性粒子の垂直配向を説
明するための説明図、第２図は、配向磁場除去後
における塗膜内の磁気的状態を示す説明図、第３
図は、本発明法による、磁場中乾燥の実施態様を
示す説明図である。
Fig. 1 is an explanatory diagram for explaining the vertical alignment of magnetic particles due to a magnetic field, Fig. 2 is an explanatory diagram showing the magnetic state within the coating after the orientation magnetic field is removed, and Fig.
The figure is an explanatory diagram showing an embodiment of drying in a magnetic field according to the method of the present invention.