JP2004342171A - Method of manufacturing magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a magnetic recording medium which can effectively remove a ferromagnetic powder hardly fixed to the surface of a magnetic layer and also the binder components of an organic substance oozing out to the surface of the magnetic layer to prevent the wear and clogging of a magnetic head. <P>SOLUTION: A 1st process is carried out for making the surface treatment of the magnetic layer 13 by using a 1st abrasive tape having a Mohs scale equal to or lower than the Mohs scale of an abrasive included in the magnetic layer 13 and the size of ≥2,000 mesh, ≤4,000 mesh, and after this 1st process is carried out, a 2nd process is carried out for making the surface treatment of the magnetic layer 13 by using a 2nd abrasive tape having a Mohs scale equal to or higher than the Mohs scale of the abrasive included in the magnetic layer 13 and the size of ≥8,000 mesh. The ferromagnetic powder is removed by the 1st abrasive tape, and the binder components are removed by the 2nd abrasive tape. The use of the 2nd abrasive tape having non-parallel recessed linear parts on the surface with respect to a tape edge is preferable. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５０】
（実施例２）
表１に示したように、第１の研磨テープとして、日本ミクロコーティング製研磨テープＧＣ３０００（研磨剤ＳｉＯ_２ ：研磨剤サイズ３０００メッシュ：モース硬度６）を用いた表面処理を２回行い、第２の研磨テープとして、日本ミクロコーティング製研磨テープＤ１００００（研磨剤ダイヤモンド：研磨剤サイズ１００００メッシュ：モース硬度１０：べナールセル現象により形成された凹条部有）を用いた表面処理を１回行ったことを除き、実施例１と同様にして磁気記録媒体を作製した。
【００５１】
（実施例３）
表１に示したように、第１の研磨テープとして、日本ミクロコーティング製研磨テープＧＣ４０００（研磨剤ＳｉＯ_２ ：研磨剤サイズ４０００メッシュ：モース硬度６）を用いた表面処理を３回行い、第２の研磨テープとして、日本ミクロコーティング製研磨テープＷＡ８０００（研磨剤Ａｌ_２ Ｏ_３ ：研磨剤サイズ８０００メッシュ：モース硬度９：べナールセル現象により形成された凹条部有）を用いた表面処理を２回行ったことを除き、実施例１と同様にして磁気記録媒体を作製した。
【００５２】
（実施例４）
表１に示したように、第１の研磨テープとして、日本ミクロコーティング製研磨テープＷＡ２０００（研磨剤Ａｌ_２ Ｏ_３ ：研磨剤サイズ２０００メッシュ：モース硬度９）を用いた表面処理を１回行い、第２の研磨テープとして、日本ミクロコーティング製研磨テープＤ８０００（研磨剤ダイヤモンド：研磨剤サイズ８０００メッシュ：モース硬度１０：べナールセル現象により形成された凹条部有）を用いた表面処理を１回行ったことを除き、実施例１と同様にして磁気記録媒体を作製した。
【００５３】
（実施例５）
表１に示したように、第１の研磨テープとして、日本ミクロコーティング製研磨テープＷＡ３０００（研磨剤Ａｌ_２ Ｏ_３ ：研磨剤サイズ３０００メッシュ：モース硬度９）を用いたことを除き、実施例１と同様にして磁気記録媒体を作製した。
【００５４】
（比較例１）
比較例１として、表１に示したように、第１の研磨テープに、日本ミクロコーティング製研磨テープＧＣ６０００（研磨剤ＳｉＯ_２ ：研磨剤サイズ６０００メッシュ：モース硬度６）を用いたことを除き、実施例１と同様にして磁気記録媒体を作製した。すなわち、実施例１よりも第１の研磨テープにおける研磨剤の大きさを小さくした。
【００５５】
（比較例２）
比較例２として、表１に示したように、第１の研磨テープに、日本ミクロコーティング製研磨テープＤ３０００（研磨剤ダイヤモンド：研磨剤サイズ３０００メッシュ：モース硬度１０）を用いたことを除き、実施例２と同様にして磁気記録媒体を作製した。すなわち、実施例２よりも第１の研磨テープにおける研磨剤のモース硬度を大きくし、磁性層１３に含まれる研磨剤のモース硬度９よりも大きくした。
【００５６】
（比較例３）
比較例３として、表１に示したように、第２の研磨テープに、日本ミクロコーティング製研磨テープＷＡ６０００（研磨剤Ａｌ_２ Ｏ_３ ：研磨剤サイズ６０００メッシュ：モース硬度９：凹条部無）を用いたことを除き、実施例３と同様にして磁気記録媒体を作製した。すなわち、実施例３よりも第１の研磨テープにおける研磨剤の大きさを大きくし、かつ凹条部をなくした。
【００５７】
（比較例４）
比較例４として、表１に示したように、第２の研磨テープに、日本ミクロコーティング製研磨テープＫ８０００（研磨剤Ｃｒ_２ Ｏ_３ ：研磨剤サイズ８０００メッシュ：モース硬度８：べナールセル現象により形成された凹条部有）を用いたことを除き、実施例４と同様にして磁気記録媒体を作製した。すなわち、実施例４よりも第２の研磨テープにおける研磨剤のモース硬度を小さくし、磁性層１３に含まれる研磨剤のモース硬度９よりも小さくした。
【００５８】
（比較例５）
比較例５として、表１に示したように、第１の研磨テープに、日本ミクロコーティング製研磨テープＷＡ１０００（研磨剤Ａｌ_２ Ｏ_３ ：研磨剤サイズ１０００メッシュ：モース硬度９）を用いたことを除き、実施例５と同様にして磁気記録媒体を作製した。すなわち、実施例５よりも第１の研磨テープにおける研磨剤の大きさを大きくした。
【００５９】
（評価）
得られた実施例１〜５および比較例１〜５の磁気記録媒体について、磁性層の表面の結合剤成分量を計測した。その結果を表２に示す。磁性層の表面の結合材成分量は、磁気記録媒体の表面から１０ｎｍまでの情報を得ることができる分析方法であるＸ線光電子分光分析（ＥＳＣＡ；Ｅｌｅｃｔｒｏｎ Ｓｐｅｃｔｒｏｓｃｏｐｙ ｆｏｒ Ｃｈｅｍｉｃａｌ Ａｎａｌｙｓｉｓ ）により、Ｃｌ−２ｐスペクトルとＦｅ−２ｐ（３／２）スペクトルとの積分強度比、および、Ｃ−１ＳスペクトルとＦｅ−２ｐ（３／２）スペクトルとの積分強度比として測定した。
【００６０】
【表２】

【００６１】
なお、ＥＳＣＡ測定の具体的な条件の一例としては、Ｘ線強度：８ｋＶ−２００Ｗ、Ｘ線アノード種類：モノクロメータＡｌ、測定Ｘ線：ＡｌＫα線、測定時間：１０分以内を挙げることができる。このような測定に使用する具体的な装置としては、アルバック・ファイ社製のＥＳＣＡ３２００型を使用することができる。
【００６２】
また、スリットされた磁気記録媒体を、カセットに組み込み、信頼性およびドロップアウト特性を測定した。その結果も表２に併せて示す。ここで「信頼性」とは、バージンテープを記録１パスおよび再生１パスさせる操作を、次々とかけ換えて行い、ヘッドクロッグが生じるまでの時間により測定した。表２には、ヘッドクロッグが生じるまでの時間が４０ｈ以上であった場合を良、４０ｈよりも短かった場合を不良として示した。ドロップアウト特性は、信頼性評価時にドロップアウトカウンターを用いて３μｓ相当の記録抜けの個数をカウントすることにより行った。ドロップアウト特性の判断基準は、記録抜けの個数が１分間に５０個以下の場合に良とした。
【００６３】
表２に示したように、実施例１〜実施例５によれば、信頼性についてもドロップアウト特性についても共に良好な結果を得られた。これに対して比較例１および比較例２では、ドロップアウト特性を改善することができなかった。これは、比較例１では第１の研磨テープにおける研磨剤の大きさが小さいので磁性層の表面にある極端に大きな突起を十分に除去することができなかったためと考えられる。また、比較例２では、第１の研磨テープにおける研磨剤のモース硬度が磁性層に含まれる研磨剤のモース硬度よりも大きいので、磁性層の表面にキズをつけてしまったためと考えられる。
【００６４】
更に、比較例３および比較例４では信頼性を改善することができなかった。これは、比較例３では、第２の研磨テープにおける研磨剤の大きさが大きく、かつ凹条部もないので、ブレードに似た表面有機物捕獲効果の働きがなかったためと考えられる。また、比較例４では、第２の研磨テープにおける研磨剤のモース硬度が磁性層に含まれる研磨剤のモース硬度よりも小さいので、研磨テープの磨耗が急速に進み、表面処理効果が得られなくなったためと考えられる。その結果、比較例３および比較例４では、ＥＳＣＡによるＣｌ／ＦｅまたはＣ／Ｆｅの減少が見られなくなり、結果的に表層有機物リッチとなり、ヘッドクロッグが生じてしまったものと考えられる。
【００６５】
加えて、比較例５ではドロップアウト特性を改善することができなかった。これは、第１の研磨テープにおける研磨剤の大きさが大きいので、磁性層に対して、研磨テープが粗すぎて突起あるいは強磁性粉末を除去する効果もないばかりか、傷も発生してしまったためと考えられる。
【００６６】
なお、第１の研磨テープを用いた表面処理のみを行った場合、および第２の研磨テープを用いた表面処理のみを行った場合は、磁気記録媒体の走行が不可能となり特性の評価を行えなかった。
【００６７】
すなわち、第１の研磨テープを用いた表面処理と、第２の研磨テープを用いた表面処理とを行い、第１の研磨テープにおける研磨剤の大きさを２０００メッシュ以上４０００メッシュ以下、モース硬度を磁性層に含まれる研磨剤のモース硬度以下とし、第２の研磨テープにおける研磨剤の大きさを８０００メッシュ以上、モース硬度を磁性層に含まれる研磨剤のモース硬度以上とし、凹条部を設けるようにすれば、信頼性およびドロップアウト特性を改善できることが分かった。
【００６８】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は上記実施の形態および実施例に限定されるものではなく、種々変形が可能である。例えば、上記実施の形態および実施例では、磁気記録媒体の構成を具体的に挙げて説明したが、上記実施の形態において説明した全ての層を備える必要はなく、また、他の層を更に備えていてもよい。また、上記実施の形態では磁性層１３が単層構造である場合について説明したが、磁性層１３は積層構造としてもよく、この場合、積層数は何層でもよい。
【００６９】
また、上記実施の形態および実施例で説明した成膜方法や成膜条件は、他の成膜方法や成膜条件に変更することも可能である。
【００７０】
【発明の効果】
以上説明したように本発明の磁気記録媒体の製造方法によれば、モース硬度が磁性層に含まれる研磨剤のモース硬度以下であり、かつ大きさが２０００メッシュ以上４０００メッシュ以下の研磨剤を含む第１の研磨テープを用いて磁性層を表面処理する第１の工程と、この第１の工程を行ったのち、モース硬度が磁性層に含まれる研磨剤のモース硬度以上であり、かつ大きさが８０００メッシュ以上の研磨剤を含む第２の研磨テープを用いて磁性層を表面処理する第２の工程とを含むようにしたので、磁性層の表面に存在する固定不十分な強磁性粉末、および乾燥過程で磁性層の表面に染み出した樹脂ないし有機物などの結合剤成分を、第１の研磨テープおよび第２の研磨テープの組合せにより効果的に除去することができる。よって、磁気記録媒体の走行中に強磁性粉末が磁性層から脱離して磁気ヘッドに付着するいわゆるパウダーと呼ばれる汚れ、あるいは結合剤成分が磁気ヘッドに付着するいわゆるウィスカーと呼ばれる汚れが確実に防止され、ドロップアウトあるいはヘッドの目詰まりを防ぎ、優れた信頼性を実現することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る磁気記録媒体の製造方法を工程順に表す断面図である。
【図２】本発明の一実施の形態に係る磁気記録媒体の製造方法に用いられる表面処理装置の構成を表す斜視図である。
【図３】図２に示した表面処理装置の動作を説明するための斜視図である。
【符号の説明】
１０…積層テープ、１１…非磁性支持体、１２…下地層、１２Ａ…下地塗布層、１３…磁性層、１３Ａ…磁性塗布層、１４…バックコート層、１００…表面処理装置、１１０…バックアップローラ、１２０…研磨テープ、１３０…研摩テープ保持部、１３１…基台、１３２…巻出し側リール、１３３…巻取り側リール、１３４…ガイドローラ、１３５…スライド板、θ…抱き角[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a magnetic recording medium having a magnetic layer, and more particularly to a method of manufacturing a magnetic recording medium including a step of subjecting a magnetic layer to a surface treatment with a polishing tape.
[0002]
[Prior art]
A magnetic recording medium such as a magnetic recording tape or a magnetic disk is used in a magnetic recording / reproducing device as a peripheral device such as an audio device, a video device, and a computer device. As the magnetic recording medium, there are a coating type and a thin film type. Of these, the coating type is obtained by using a ferromagnetic powder such as iron or iron oxide, a binder and various additives in an organic solvent. The magnetic recording layer is formed by applying, drying, smoothing and curing the dispersed and kneaded magnetic paint on a non-magnetic support.
[0003]
In these various magnetic recording media, in recent years, higher image quality, longer time, digital recording, and the like have been developed, and higher electromagnetic recording characteristics as well as higher density recording are required.
[0004]
In order to realize excellent electromagnetic conversion characteristics, it is very important not only to make the tape surface smooth, but also to make the thickness of the magnetic layer thin and uniform. As one of the techniques, a method has been proposed in which a lower layer made of a non-magnetic paint is provided on a non-magnetic support, and an upper layer made of a magnetic paint is applied while the lower layer is not dried, and a magnetic layer is provided ( For example, see Patent Document 1.)
[0005]
However, depending on the method of smoothing the tape surface or reducing the thickness of the magnetic layer, there is a problem that a magnetic head is stained and electromagnetic conversion characteristics are deteriorated.
[0006]
Magnetic head contamination causes clogging of the video head (head clog). For example, the reliability is poor when the virgin tape is used in a mode in which the virgin tape is recorded and reproduced (only in two passes) and is successively changed (for example, at the time of dubbing). is there. The dirt mainly composed of the binder component is that the component in the binder of the magnetic recording medium floats near the surface of the magnetic layer and adheres to the magnetic head due to sliding contact between the magnetic recording medium and the magnetic head.
[0007]
In terms of running durability, in the case of a one-reel type linear running tape, the head mount becomes dirty due to a long shuttle running, and the contents of the soil are mainly made of ferromagnetic powder called so-called powder. Soil and binder components, so-called whiskers, are roughly classified into main soil. The dirt mainly composed of ferromagnetic powder is such that particulate components such as insufficiently fixed ferromagnetic powder present on the surface of the magnetic layer of the magnetic recording medium are detached during running of the magnetic recording medium and adhere to the magnetic head. In addition, such insufficiently fixed granular components on the surface of the magnetic layer increase the surface roughness of the magnetic layer and cause abrasion of the surface of the magnetic head.
[0008]
In order to obtain good reliability and running durability, a nitrocellulose resin having a polymerization degree of 30 to 50 is added to the binder of the magnetic paint at a ratio of 2 to 8 parts by weight based on 100 parts by weight of the magnetic powder. Although a method has been proposed (see, for example, Patent Document 2), there is a problem that the addition of a nitrocellulose resin causes a thickening of a magnetic paint and makes it difficult to thin a magnetic layer.
[0009]
Similarly, in order to obtain good reliability and running durability, a method has been proposed in which an abrasive and a lubricant are added to the magnetic layer to remove dirt on the magnetic head during running. Increasing the height increases the wear of the head, and conversely, decreasing the abrasion reduces the function of cleaning the deposits that cause dirt and clogging of the head. Therefore, there is a limit in keeping the head wear low and preventing head clogging and dirt only by adding the abrasive.
[0010]
Therefore, in order to solve these problems, a surface treatment of cleaning or polishing the surface of the magnetic recording medium with a nonwoven fabric or a polishing tape has been performed. For example, Patent Literature 3 discloses a technology in which a magnetic layer of a magnetic recording medium is subjected to a surface smoothing process using a calender, and then the surface of the magnetic layer is polished with a polishing tape. The surface treatment using such a polishing tape can easily obtain a high effect in a short time as compared with the blade treatment.
[0011]
Further, Patent Document 4 proposes that the polishing tape and the magnetic recording medium are brought into non-parallel sliding contact with each other so that the effect of the surface treatment is further enhanced.
[0012]
[Patent Document 1]
Japanese Patent Publication No. 6-93297
[Patent Document 2]
JP-A-5-334654
[Patent Document 3]
JP-A-63-259830
[Patent Document 4]
JP 2000-90433 A
[0013]
[Problems to be solved by the invention]
However, most of the surface treatment techniques disclosed so far are effective mainly for soiling with ferromagnetic powder, and insufficient for soiling with a binder component.
[0014]
The present invention has been made in view of such a problem, and an object thereof is to provide a magnetic head capable of effectively removing not only a ferromagnetic powder but also a binder component and suppressing the occurrence of wear and clogging of a magnetic head. An object of the present invention is to provide a method for manufacturing a recording medium.
[0015]
[Means for Solving the Problems]
The method for producing a magnetic recording medium according to the present invention is for producing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder and an abrasive, and has a Mohs hardness of Mohs of the abrasive contained in the magnetic layer. A first step of surface-treating the magnetic layer using a first polishing tape containing an abrasive having a hardness of not more than 2,000 mesh and not more than 4000 mesh, and after performing the first step, A second step of surface-treating the magnetic layer using a second polishing tape having an Mohs hardness equal to or higher than the Mohs hardness of the abrasive contained in the magnetic layer and having a size of 8000 mesh or more. It is a thing.
[0016]
In the method for manufacturing a magnetic recording medium according to the present invention, in the first step, the Moth hardness of the abrasive contained in the magnetic layer is equal to or less than the Mohs hardness and the size includes an abrasive having a size of 2,000 mesh or more and 4000 mesh or less. The surface of the magnetic layer is treated using the polishing tape of No. 1 to remove insufficiently fixed ferromagnetic powder present on the surface of the magnetic layer. After the first step is performed, in the second step, a second polishing step is performed in which the Mohs' hardness is equal to or higher than the Mohs hardness of the abrasive contained in the magnetic layer and the abrasive has a size of 8000 mesh or more. The magnetic layer is surface-treated using a tape, and the binder component floating on the surface of the magnetic layer is removed.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 shows a method of manufacturing a magnetic recording tape as a magnetic recording medium according to an embodiment of the present invention. First, as shown in FIG. 1A, for example, a nonmagnetic support 11 as a base film is prepared. The non-magnetic support 11 is not particularly limited. For example, a polyester film made of polyethylene terephthalate or polyethylene-2,6-naphthalate or an aramid film can be used. It is desirable that the thickness of the nonmagnetic support 11 be, for example, about 3.0 μm to 15.0 μm.
[0019]
Next, the non-magnetic inorganic particles are mixed and dispersed, for example, in an amount of about 250% to 1300% by weight with respect to the binder, and the obtained dispersion is dispersed in an organic solvent to prepare a base layer paint. By applying the underlayer coating material to the nonmagnetic support 11, the undercoat layer 12A is formed as shown in FIG.
[0020]
The non-magnetic inorganic particles are not particularly limited. For example, carbon black, aluminum oxide, chromium oxide, silicon carbide, titanium oxide, silicon oxide, calcium carbonate, α-iron oxide, kaolin, graphite, mica, titanium carbide or calcium phosphate Can be used. The shape of the non-magnetic inorganic particles may be spherical, needle-like or plate-like. Considering the smoothness of the undercoating layer 12A, the size of the non-magnetic inorganic particles is, for example, a long axis length of 0.2 μm or less in the case of a needle, a particle size of 0.2 μm or less in the case of a sphere, and a plate shape. In this case, the diameter of the plate is preferably set to, for example, 0.2 μm or less.
[0021]
As the binder, any resin material used in a usual coating type magnetic recording medium can be used, and the kind thereof is not particularly limited. Typical examples of the binder include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-vinylidene chloride copolymer. Copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride, vinylidene chloride -Acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, polyvinyl acetal, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, phenol Shi resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, or urea - formaldehyde resins.
[0022]
Among them, at least a part of -SO ₃ M group (M represents an alkali metal such as Na or K or an alkyl group), -SO ₄ At least one of an M group (M represents an alkali metal such as Na or K or an alkyl group), a carboxylate group, an amino acid group, an aminosulfonic acid group, a phosphone group, a phosphine group, and an amino group are introduced. It is desirable that it is.
[0023]
As the organic solvent, for example, ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, or organic chlorine compound solvents can be used depending on the type of the binder.
[0024]
In kneading and dispersing the constituent materials of the underlayer coating, various kneaders can be used. Examples of the kneading machine include an extruder, a sand mill, a dyno mill, a pressure kneader, a continuous kneader, a dissolver, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a side grinder, a high-speed impeller disperser, a high-speed stone mill, and a high-speed mill. Examples include an impact mill, a disperser, a high-speed mixer, a homogenizer, and an ultrasonic disperser.
[0025]
There is no particular limitation on the method of applying the underlayer paint, and a known method can be employed. For example, die coating, gravure coating, knife coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calender coating, skies coating, kiss coating Extrusion coaters of the fanning coating method or the extrusion method can be used.
[0026]
Subsequently, about 10 to 30 parts by weight of a binder is blended with 100 parts by weight of the ferromagnetic powder, and about 5 to 20 parts by weight of an abrasive is further blended and dispersed. The liquid is dispersed in an organic solvent to prepare a magnetic layer coating. This magnetic layer coating material is applied onto the undercoating layer 12A while the undercoating layer 12A is still dry, thereby providing the magnetic coating layer 13A as shown in FIG. 1A.
[0027]
As the ferromagnetic powder, any conventionally known ferromagnetic powder can be used, and it may be an oxide magnetic powder or a metal magnetic powder. As the oxide magnetic powder, for example, γ-diiron trioxide (γ-Fe ₂ O ₃ ), Γ-Fe doped with cobalt (Co) ₂ O ₃ , Triiron tetroxide (Fe ₃ O ₄ ), Fe with cobalt added ₃ O ₄ , Γ-Fe coated with cobalt ₂ O ₃ , Co-coated Fe ₃ O ₄ Or chromium oxide (CrO ₂ ) Is used. Examples of the metal magnetic powder include iron, cobalt, nickel, iron-cobalt alloy, iron-nickel alloy, iron-cobalt-nickel alloy, cobalt-nickel alloy, iron-cobalt-boron alloy, and iron-cobalt-chromium-boron alloy. , A manganese-bismuth alloy, a manganese-aluminum alloy, or an iron-cobalt-vanadium alloy is used, and a metal component such as aluminum, silicon, titanium, chromium, manganese, copper, zinc, etc. for the purpose of further improving these various characteristics. A material to which a rare earth element containing yttrium or yttrium is added may be used. Further, for example, Fe ₅ C ₂ And the like can also be used. As the binder, the same binder as that of the base coating layer 12A can be used. As the abrasive, for example, an inorganic powder such as an aluminum oxide powder having a Mohs hardness of about 8 to 9 is preferably used.
[0028]
If necessary, a dispersant such as lecithin, an antistatic agent such as carbon black, or a rust preventive may be added to the base coating layer 12A and the magnetic coating layer 13A. As the dispersant, antistatic agent and rust preventive, any conventionally known materials can be used, and there is no particular limitation. Further, known lubricants may be added, for example, fatty acids and fatty acid esters are used.
[0029]
Further, an inorganic pigment may be blended in the base coating layer 12A and the magnetic coating layer 13A. As the inorganic pigment, for example, aluminum oxide, chromium oxide, silicon oxide, titanium oxide, silicon carbide, calcium carbonate, α-iron oxide, kaolin, graphite, mica, or titanium carbide can be used.
[0030]
Further, a curable resin can be added to the base coating layer 12A and the magnetic coating layer 13A in order to improve durability. Specifically, a thermosetting resin represented by a polyisocyanate compound or a polyepoxy compound or an electron beam-reactive curable resin can be used. These may be used alone or in combination of two or more.
[0031]
After the formation of the magnetic coating layer 13A, the magnetic coating layer 13A in an undried state is subjected to a magnetic field orientation treatment, and a surface smoothing treatment is performed by calendering using a super calendar roll or the like. . It is preferable that the temperature at that time is usually, for example, 50 ° C. to 250 ° C., the linear pressure is, for example, 50 kg / cm to 400 kg / cm, and the coating speed is, for example, 20 m / min to 600 m / min.
[0032]
After performing a surface smoothing process, a hardening process is performed to form the underlayer 12 and the magnetic layer 13 as shown in FIG. 1B. Note that burnishing or blade treatment may be performed as necessary. The thickness of the magnetic layer 13 is preferably, for example, 0.1 μm to 4.0 μm, and more preferably 0.01 μm to 2.5 μm.
[0033]
Subsequently, as shown in FIG. 1 (C), a back coat layer 14 is formed by applying a carbon black paint on the back surface of the non-magnetic support 11, and slit to a 3/4 inch width to form a laminated tape. It is assumed to be 10. The back coat layer 14 is provided for the purpose of improving the running properties of the magnetic recording medium, preventing static charge and preventing transfer, and is formed by adding a binder and various known additives for the back coat layer. As the binder of the back coat layer 14, the same binder as that of the underlayer 12 and the magnetic layer 13 can be used.
[0034]
After slitting, the magnetic layer 13 is subjected to a surface treatment with a polishing tape. FIG. 2 shows a surface treatment apparatus used for this surface treatment. In the surface treatment apparatus 100, a backup roller 110 that holds the laminated tape 10 and a polishing tape holding unit 130 that holds a polishing tape 120 are arranged to face each other. The backup roller 110 has a smooth peripheral surface for running the laminated tape 10. The polishing tape 120 has, for example, a polishing layer containing an abrasive and a binder. The polishing tape holding unit 130 has a configuration in which an unwinding reel 132, a winding reel 133, and a pair of guide rollers 134 are provided on a base 131. The base 131 is attached to the slide plate 135, and is movable in the direction of arrow A by a cylinder (not shown) provided on the slide plate 135. The polishing tape 120 is wound between the take-out reel 132 and the take-up reel 133, and is pulled out toward the backup roller 110 by a pair of guide rollers 134.
[0035]
In the surface treatment apparatus 100, as shown in FIG. 3, the polishing tape holding unit 130 is moved in the direction of arrow A, that is, toward the backup roller 110, and the polishing tape 120 between the pair of guide rollers 134 is wound around the backup roller 110. To a predetermined holding angle θ with respect to the laminated tape 10. Then, by rotating the backup roller 110 in the direction indicated by the arrow B, the laminated tape 10 is caused to travel in the direction indicated by the arrow C, and the unwind-side reel 132, the take-up reel 133, and a pair of guide rollers 134 are rotated. This causes the polishing tape 120 to run in the direction of arrow D. Thus, the surface treatment of the magnetic layer 13 is performed by bringing the laminated tape 10 into sliding contact with the polishing tape 120.
[0036]
Here, in the present embodiment, the cause of dropout and clogging of the head (head clog), which is the most fatal problem in running durability, is caused by insufficient fixing existing on the surface of the magnetic layer 13. Focusing on being roughly classified into ferromagnetic powder and binder components such as organic substances precipitated and unevenly distributed on the surface of the magnetic layer 13, the surface treatment is performed several times using two types of polishing tapes 120. ing.
[0037]
First, a first step of surface-treating the magnetic layer 13 using a first polishing tape whose Mohs hardness is equal to or less than the Mohs hardness of the abrasive contained in the magnetic layer 13 and whose size is 2,000 mesh or more and 4000 mesh or less. After the first step, the Mohs hardness is equal to or greater than the Mohs hardness of the abrasive contained in the magnetic layer 13 and the size of the magnetic layer 13 is determined using a second polishing tape having a size of 8000 mesh or more. Is performed in a second step. The first polishing tape is suitable for removing ferromagnetic powder, and the second polishing tape is suitable for removing binder components. As described above, by selecting and combining the first polishing tape and the second polishing tape according to the object to be removed, more effective surface treatment can be performed, and the dropout characteristics and running durability can be improved.
[0038]
Further, as the second polishing tape, it is preferable to use, for example, a tape having a concave portion which is not parallel to the tape edge on the surface. This is because such a recessed portion comes into contact with the magnetic layer 13 as if it were a blade, and the binder component can be effectively removed. Further, as disclosed in the above-mentioned Patent Document 4, it is not necessary to make the sliding direction of the polishing tape and the magnetic recording medium non-parallel with each other, and the sliding direction of the polishing tape and the magnetic recording medium is changed. This is because, even if parallel, the concave stripes do not become parallel to the magnetic recording medium, so that good surface treatment can be performed. Further, since the recessed portion can collect abrasion powder generated at the time of polishing, it is possible to perform a high-grade polishing finish of a quality that does not cause so-called shiranuke. In addition, the non-parallel ridges that are not parallel to the tape edge may be straight lines provided so as to intersect the tape edge at an angle greater than 0 ° and less than 180 °, or a curved shape. Means the one provided in
[0039]
Above all, as the second polishing tape, it is preferable to use, for example, a tape having a concave portion forming a hexagonal image. This is because a higher effect can be obtained. In addition, this concave ridge portion is formed by, for example, a Benard cell phenomenon that occurs in a resin coating film when a resin coating film made of a coating agent containing an inorganic component is applied to form a polishing layer. At the corners of the hexagonal image, spot-shaped concave portions may be formed, and these spot-shaped concave portions also collect wear powder generated during polishing, like the concave ridge portions. be able to.
[0040]
The number of times of the surface treatment in the first step and the second step may be one or more. In the case where the process is performed a plurality of times, it is preferable that the process is performed a plurality of times in the first process and then the second process is performed. However, the first process and the second process are sequentially repeated. It may be. Further, in this surface treatment step, before the first step, between the first step and the second step, or after the second step, surface treatment with another polishing tape is performed as necessary. Is also good. Thereby, the magnetic recording medium is completed.
[0041]
As described above, in the present embodiment, the Mohs hardness is equal to or less than the Mohs hardness of the abrasive contained in the magnetic layer, and the size is determined by using the first polishing tape including the abrasive having a size of 2,000 to 4,000 mesh. A first step of surface-treating the layer, and after performing the first step, including an abrasive having a Mohs hardness equal to or higher than the Mohs hardness of the abrasive contained in the magnetic layer and having a size of 8000 mesh or more. And a second step of surface-treating the magnetic layer using the second polishing tape, so that the insufficiently fixed ferromagnetic powder present on the surface of the magnetic layer 13 and the magnetic layer 13 A binder component such as a resin or an organic substance that has exuded on the surface can be effectively removed. Therefore, during the running of the magnetic recording medium 10, the so-called powder that the ferromagnetic powder detaches from the magnetic layer 13 and adheres to the magnetic head, or the so-called whisker that the binder component adheres to the magnetic head is surely removed. Thus, dropout or head clogging can be prevented, and excellent reliability can be achieved.
[0042]
【Example】
Further, specific examples of the present invention will be described.
[0043]
(Example 1)
The magnetic recording medium 10 was manufactured in the same manner as in the above embodiment. First, an underlayer coating was prepared, and the underlayer coating was applied to a nonmagnetic support 11 made of a polyethylene terephthalate film having a thickness of 8.0 μm to form an undercoat layer 12A. At this time, the underlayer paint was kneaded with a kneader using the following materials, diluted with a solvent, and then dispersed in a sand mill. ) Was added.
[0044]
Non-magnetic inorganic particles:
100 parts by weight of α-iron oxide (major axis length 0.15 μm)
Binder:
3.5 parts by weight of polyester-polyurethane (number-average molecular weight = 10000, polar group: containing sodium sulfonate 0.08 mmol / g, polyester main component: isophthalic acid, adipic acid-neopentyl glycol, ethylene glycol, urethanized isocyanate: Diphenylmethane diisocyanate)
6.5 parts by weight of vinyl chloride copolymer (average degree of polymerization = 305, polar group: containing potassium sulfate 0.08 mmol / g, other main substituents: containing epoxy 0.8 mmol / g, hydroxyl group 0.3 mmol) / G)
lubricant:
Isooctyl palmitate 1 part by weight
1 part by weight of stearic acid
solvent:
80 parts by weight of methyl ethyl ketone
80 parts by weight of toluene
40 parts by weight of cyclohexanone
[0045]
Subsequently, a magnetic layer coating material was prepared, and the base coating layer 12A was applied while it was not dried to form a magnetic coating layer 13A. At this time, the magnetic layer coating material was kneaded with a kneader using the following materials, diluted with a solvent, and then dispersed in a sand mill. Immediately before application, a polyisocyanate (Nippon Polyurethane curing agent “Coronate L (trade name)”) was used. ) Was added and prepared by passing through a homogenizer.
[0046]
Fine ferromagnetic powder:
100 parts by weight of iron-cobalt alloy (major axis length 0.15 μm)
Binder:
10 parts by weight of polyester-polyurethane (number-average molecular weight = 21000, polar group: containing sodium sulfonate 0.12 mmol / g, polyester main component: isophthalic acid-ethylene glycol, urethanized isocyanate: diphenylmethane diisocyanate)
10 parts by weight of vinyl chloride copolymer (average degree of polymerization = 200, polar group: containing potassium sulfate 0.08 mmol / g, other main substituents: containing epoxy 0.8 mmol / g, hydroxyl group 0.3 mmol / g) Contained)
Inorganic powder (abrasive):
10 parts by weight of aluminum oxide powder (alpha conversion = 85%, average particle size = 0.23 µm, Mohs hardness 9)
lubricant:
1 part by weight of butyl stearate
Stearyl amide 0.5 parts by weight
solvent:
20 parts by weight of methyl ethyl ketone
20 parts by weight of toluene
10 parts by weight of cyclohexanone
[0047]
Next, a magnetic field orientation treatment was performed, dried appropriately, wound up, calendered, and cured to form the underlayer 12 and the magnetic layer 13. Thereafter, a carbon black paint was applied to the back surface of the non-magnetic support 11 to form a back coat layer 14, which was slit to a ／ inch width.
[0048]
After slitting, surface treatment was performed as described in the above embodiment using the first polishing tape and the second polishing tape shown in Table 1. The processing conditions were a line speed of 300 m / min, a polishing tape holding angle of 120 °, a tension of 200 g, and a polishing tape feed speed of 20 mm / min. As a first polishing tape, a polishing tape GC2000 made by Nihon Micro Coating (abrasive SiO ₂ : Surface treatment using abrasive mesh 2000 mesh: Mohs hardness 6) was performed once, and as a second polishing tape, polishing tape WA10000 manufactured by Nippon Micro Coating (Abrasive A1203: Abrasive size 10000 mesh: Mohs hardness 9: Surface treatment using a concave stripe formed by the Benard cell phenomenon was performed twice. Thus, the magnetic recording medium of Example 1 was obtained.
[0049]
[Table 1]

[0050]
(Example 2)
As shown in Table 1, as the first polishing tape, a polishing tape GC3000 made by Nippon Micro Coating (polishing agent SiO ₂ : Surface treatment using an abrasive size 3000 mesh: Mohs hardness 6) was performed twice, and as a second abrasive tape, Nippon Micro Coating abrasive tape D10000 (Abrasive diamond: Abrasive size 10000 mesh: Mohs hardness 10: A magnetic recording medium was produced in the same manner as in Example 1 except that the surface treatment using the concave stripe formed by the Benard cell phenomenon was performed once.
[0051]
(Example 3)
As shown in Table 1, as the first polishing tape, Nippon Micro Coating polishing tape GC4000 (polishing agent SiO ₂ : Abrasive size 4000 mesh: Surface treatment using Mohs hardness 6) was performed three times, and as a second polishing tape, Nippon Micro Coating polishing tape WA8000 (Abrasive Al ₂ O ₃ : Abrasive size 8000 mesh: Mohs hardness 9: Concave stripes formed by Benard cell phenomenon) A magnetic recording medium was produced in the same manner as in Example 1 except that the surface treatment was performed twice. .
[0052]
(Example 4)
As shown in Table 1, as a first polishing tape, a polishing tape WA2000 manufactured by Nippon Micro Coating (abrasive Al ₂ O ₃ : Surface treatment using an abrasive size of 2000 mesh: Mohs hardness of 9) was performed once, and as a second polishing tape, Nippon Micro Coating polishing tape D8000 (Abrasive diamond: Abrasive size 8000 mesh: Mohs hardness: 10) A magnetic recording medium was produced in the same manner as in Example 1 except that the surface treatment using the concave stripe formed by the Benard cell phenomenon was performed once.
[0053]
(Example 5)
As shown in Table 1, as a first polishing tape, Nippon Micro Coating polishing tape WA3000 (abrasive Al ₂ O ₃ : Abrasive size 3000 mesh: Mohs hardness 9), except that a magnetic recording medium was produced in the same manner as in Example 1.
[0054]
(Comparative Example 1)
As Comparative Example 1, as shown in Table 1, a polishing tape GC6000 made by Nippon Micro Coating (abrasive SiO ₂ : Abrasive size 6000 mesh: Mohs hardness 6), except that a magnetic recording medium was produced in the same manner as in Example 1. That is, the size of the abrasive in the first polishing tape was smaller than that in Example 1.
[0055]
(Comparative Example 2)
Comparative Example 2 was carried out as shown in Table 1, except that as the first polishing tape, Nippon Micro Coating polishing tape D3000 (abrasive diamond: abrasive size 3000 mesh: Mohs hardness 10) was used as the first abrasive tape. A magnetic recording medium was manufactured in the same manner as in Example 2. That is, the Mohs hardness of the abrasive in the first polishing tape was made larger than that in Example 2, and was larger than the Mohs hardness 9 of the abrasive contained in the magnetic layer 13.
[0056]
(Comparative Example 3)
As Comparative Example 3, as shown in Table 1, as the second polishing tape, a polishing tape WA6000 made by Nippon Micro Coating (abrasive Al ₂ O ₃ : Abrasive size 6000 mesh: Mohs hardness 9: no concave streak) except that a magnetic recording medium was produced in the same manner as in Example 3. That is, the size of the abrasive in the first polishing tape was made larger than in Example 3, and the concave streak was eliminated.
[0057]
(Comparative Example 4)
As Comparative Example 4, as shown in Table 1, as the second polishing tape, a polishing tape K8000 manufactured by Nippon Micro Coating (abrasive Cr ₂ O ₃ : Abrasive size 8000 mesh: Mohs hardness 8: With concave streaks formed by Benard cell phenomenon), except that magnetic recording medium was produced in the same manner as in Example 4. That is, the Mohs hardness of the abrasive in the second polishing tape was smaller than that in Example 4, and was smaller than the Mohs hardness 9 of the abrasive contained in the magnetic layer 13.
[0058]
(Comparative Example 5)
As Comparative Example 5, as shown in Table 1, the first polishing tape was a polishing tape WA1000 (abrasive Al) manufactured by Nippon Micro Coating. ₂ O ₃ A magnetic recording medium was manufactured in the same manner as in Example 5, except that abrasive size: 1000 mesh: Mohs hardness 9) was used. That is, the size of the abrasive in the first polishing tape was made larger than in Example 5.
[0059]
(Evaluation)
With respect to the obtained magnetic recording media of Examples 1 to 5 and Comparative Examples 1 to 5, the amount of the binder component on the surface of the magnetic layer was measured. Table 2 shows the results. The amount of the binder component on the surface of the magnetic layer can be determined by X-ray photoelectron spectroscopy (ESCA), which is an analysis method capable of obtaining information of up to 10 nm from the surface of the magnetic recording medium, by a Cl-2p spectrum by ESCA (electron spectroscopy for chemical analysis). And the integrated intensity ratio of the Fe-1p (3/2) spectrum and the integrated intensity ratio of the C-1S spectrum and the Fe-2p (3/2) spectrum.
[0060]
[Table 2]

[0061]
In addition, as an example of specific conditions of ESCA measurement, X-ray intensity: 8 kV-200 W, X-ray anode type: Monochromator Al, X-ray measurement: AlKα ray, measurement time: within 10 minutes. As a specific device used for such a measurement, an ESCA3200 manufactured by ULVAC-PHI can be used.
[0062]
In addition, the slit magnetic recording medium was assembled in a cassette, and the reliability and dropout characteristics were measured. The results are also shown in Table 2. Here, the “reliability” was measured by measuring the time until head clog was generated by repeatedly performing operations of making the virgin tape perform one pass of recording and one pass of reproduction. In Table 2, the case where the time until the head clog occurs is 40 hours or more is shown as good, and the case where the time is shorter than 40 hours is shown as bad. The dropout characteristics were measured by counting the number of missing recordings corresponding to 3 μs using a dropout counter at the time of reliability evaluation. The criteria for judging the dropout characteristics were good when the number of missing recordings was 50 or less per minute.
[0063]
As shown in Table 2, according to Examples 1 to 5, good results were obtained for both reliability and dropout characteristics. On the other hand, in Comparative Examples 1 and 2, the dropout characteristics could not be improved. This is presumably because in Comparative Example 1, the size of the abrasive in the first polishing tape was small, so that extremely large protrusions on the surface of the magnetic layer could not be sufficiently removed. Further, in Comparative Example 2, it is considered that the Mohs hardness of the abrasive in the first polishing tape was larger than the Mohs hardness of the abrasive contained in the magnetic layer, so that the surface of the magnetic layer was scratched.
[0064]
Furthermore, in Comparative Examples 3 and 4, the reliability could not be improved. This is probably because Comparative Example 3 did not have a surface organic substance capturing effect similar to that of a blade because the size of the abrasive in the second polishing tape was large and there were no concave ridges. In Comparative Example 4, since the Mohs hardness of the abrasive in the second polishing tape was smaller than the Mohs hardness of the abrasive contained in the magnetic layer, the wear of the polishing tape rapidly progressed, and the surface treatment effect could not be obtained. It is thought that it was. As a result, in Comparative Example 3 and Comparative Example 4, it is considered that Cl / Fe or C / Fe was not reduced by ESCA, and as a result, the surface layer became rich in organic substances, and head clogging occurred.
[0065]
In addition, in Comparative Example 5, the dropout characteristics could not be improved. This is because the size of the polishing agent in the first polishing tape is large, so that the polishing tape is too coarse for the magnetic layer and has no effect of removing protrusions or ferromagnetic powder, and also has scratches. it is conceivable that.
[0066]
When only the surface treatment using the first polishing tape and only the surface treatment using the second polishing tape were performed, the running of the magnetic recording medium became impossible, and the characteristics could be evaluated. Did not.
[0067]
That is, the surface treatment using the first polishing tape and the surface treatment using the second polishing tape are performed, and the size of the abrasive in the first polishing tape is 2000 to 4000 mesh, and the Mohs hardness is The Mohs hardness of the abrasive contained in the magnetic layer is not more than, the size of the abrasive in the second polishing tape is 8000 mesh or more, the Mohs hardness is not less than the Mohs hardness of the abrasive contained in the magnetic layer, and the concave portion is provided. By doing so, it has been found that reliability and dropout characteristics can be improved.
[0068]
As described above, the present invention has been described with reference to the embodiment and the example. However, the present invention is not limited to the above-described embodiment and example, and can be variously modified. For example, in the above-described embodiments and examples, the configuration of the magnetic recording medium has been specifically described. However, it is not necessary to include all the layers described in the above-described embodiments, and further includes other layers. May be. In the above embodiment, the case where the magnetic layer 13 has a single-layer structure has been described. However, the magnetic layer 13 may have a stacked structure, and in this case, the number of stacked layers may be any.
[0069]
Further, the film formation method and the film formation conditions described in the above embodiment and examples can be changed to other film formation methods and film formation conditions.
[0070]
【The invention's effect】
As described above, according to the method for manufacturing a magnetic recording medium of the present invention, the Mohs hardness is equal to or less than the Mohs hardness of the abrasive contained in the magnetic layer, and the abrasive includes the abrasive having a size of 2,000 to 4000 mesh. A first step of surface-treating the magnetic layer using the first polishing tape, and after performing the first step, the Mohs hardness is equal to or higher than the Mohs hardness of the abrasive contained in the magnetic layer, and And the second step of surface-treating the magnetic layer using a second polishing tape containing an abrasive of 8000 mesh or more, the insufficiently fixed ferromagnetic powder present on the surface of the magnetic layer, In addition, a binder component such as a resin or an organic substance that has exuded on the surface of the magnetic layer during the drying process can be effectively removed by a combination of the first polishing tape and the second polishing tape. Therefore, during the running of the magnetic recording medium, the so-called powder that the ferromagnetic powder detaches from the magnetic layer and adheres to the magnetic head, or the so-called whisker that the binder component adheres to the magnetic head is reliably prevented. , Dropout or clogging of the head can be prevented, and excellent reliability can be realized.
[Brief description of the drawings]
FIG. 1 is a sectional view illustrating a method of manufacturing a magnetic recording medium according to an embodiment of the present invention in the order of steps.
FIG. 2 is a perspective view illustrating a configuration of a surface treatment apparatus used in a method for manufacturing a magnetic recording medium according to one embodiment of the present invention.
FIG. 3 is a perspective view for explaining the operation of the surface treatment apparatus shown in FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Laminated tape, 11 ... Non-magnetic support, 12 ... Underlayer, 12A ... Undercoat layer, 13 ... Magnetic layer, 13A ... Magnetic coat layer, 14 ... Backcoat layer, 100 ... Surface treatment device, 110 ... Backup roller , 120: polishing tape, 130: polishing tape holder, 131: base, 132: unwinding reel, 133: winding reel, 134: guide roller, 135: slide plate, θ: angle

Claims (4)

A method for producing a magnetic recording medium having a magnetic layer containing a ferromagnetic powder, a binder, and an abrasive,
A first surface treatment of the magnetic layer using a first polishing tape having a Mohs hardness equal to or less than the Mohs hardness of the abrasive contained in the magnetic layer and having a size of 2,000 to 4,000 mesh; Process and
After performing the first step, the magnetic property is increased by using a second polishing tape having a Mohs hardness equal to or higher than the Mohs hardness of the abrasive contained in the magnetic layer and having a size of 8000 mesh or more. A second step of surface-treating the layer. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the second polishing tape has a concave portion on its surface that is not parallel to the tape edge. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein a tape having a concave portion forming a hexagonal image on the surface is used as the second polishing tape. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein a tape having a concave portion formed by Benard cell phenomenon on a surface is used as the second polishing tape.

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