JP2004063006A - Magnetic recording medium and manufacturing method for magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the electromagnetic conversion characteristic and durability by suppressing addition of carbon black to a minimum and making it low electric resistance, in a magnetic recording medium provided with a magnetic layer including magnetic powder. <P>SOLUTION: Magnetic powder comprises magnetite coated with cobalt or includes cobalt, quantity of cobalt coated to or included in the magnetic powder is 1.0 to 5.0 atm% with Co/Fe conversion, specific surface area by a BET method of the magnetic powder is 25 to 35m<SP>2</SP>/g, absorption quantity of bonding agent included in the magnetic layer for pigment including magnetic powder is 2.0 to 3.0 mg/m<SP>2</SP>for specific surface area of pigment including magnetic powder, the existence ratio of bonding agent in a magnetic coating film is 90 volume % or more at the surface layer of the magnetic coating film (binder layers 13a, 13b), and it is 70 volume % or less at depth 5nm or more ( magnetic coating film 12a, 12b) from the surface layer of the magnetic coating film. <P>COPYRIGHT: (C)2004,JPO

Description

【００４９】
調製した磁性塗料を押し出しコートにより厚さが１５．０μｍのポリエチレンテレフタレートフィルム上に３．０μｍの厚みでコーティングした後、磁性層とは反対側に取り付けた３０００ガウスのマグネットユニットを通過し、配向、乾燥、カレンダー処理、硬化の工程を経て得られたフィルムを１／２インチに裁断したビデオテープを作製した。以下、表１を参照しながら実施形態例、比較例の詳細を説明する。
【００５０】
尚本発明における磁性粉の比表面積を規定しているＢＥＴ法とは、実験的に決定されるパラメータとしての単分子層吸着量と、吸着質の分子断面積とを組み合わせて表面積を算出する方法である。
【００５１】
実施形態例−１
特許請求の範囲のＣｏ−マグネタイト磁性粉末、ポリウレタン結合剤、ニトロセルロース結合剤を用い磁性塗料を調製後、マグネットユニットを用いてビデオテープを作製した。
【００５２】
実施形態例−２
特許請求の範囲のＣｏ−マグネタイト磁性粉末、ポリウレタン結合剤、ニトロセルロース結合剤、カーボンブラック１重量部を用い磁性塗料を調製後、マグネットユニットを用いてビデオテープを作製した。
【００５３】
実施形態例−３
特許請求の範囲のＣｏ−マグネタイト磁性粉末、ポリウレタン結合剤、ニトロセルロース結合剤、カーボンブラック２重量部を用い磁性塗料を調製後、マグネットユニットを用いてビデオテープを作製した。
【００５４】
比較例−１
特許請求の範囲のＣｏ−マグネタイト磁性粉末、ポリウレタン結合剤、ニトロセルロース結合剤、カーボンブラック３重量部を用い磁性塗料を調製後、マグネットユニットを用いてビデオテープを作製した。
【００５５】
比較例−２
特許請求の範囲に記載した磁性粉末の請求範囲外の磁性粉末（表−１参照）を用いたこと以外は、実施形態例−３同様の手法にてビデオテープを作製した。
【００５６】
比較例−３
特許請求の範囲に記載した磁性粉末の請求範囲外の磁性粉末（表−１参照）を用いたこと以外は、実施形態例−３同様の手法にてビデオテープを作製した。
【００５７】
比較例−４
特許請求の範囲に記載したポリエステルポリウレタン結合剤の請求範囲外のポリエステルポリウレタン結合剤を用いたこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００５８】
比較例−５
特許請求の範囲に記載したポリエステルポリウレタン結合剤の請求範囲外のポリエステルポリウレタン結合剤を用いたこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００５９】
比較例−６
特許請求の範囲に記載したニトロセルロース結合剤の請求範囲外のニトロセルロース結合剤を用いたこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００６０】
比較例−７
特許請求の範囲に記載したニトロセルロース結合剤の請求範囲外のニトロセルロース結合剤を用いたこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００６１】
比較例−８
特許請求の範囲に記載したカーボンブラックの請求範囲外のカーボンブラックを用いたこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００６２】
比較例−９
特許請求の範囲に記載したカーボンブラックの請求範囲外のカーボンブラックを用いたこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００６３】
比較例−１０
マグネットユニットによる磁性粉末の引き寄せを行わないこと以外は、実施形態例−３と同様の手法にてビデオテープを作製した。
【００６４】
上記工程を経て作製した実施形態例及び比較例のビデオテープについて下記の測定を行った。各測定は次の通りである。
【００６５】
・結合剤吸着量
作製した塗料を遠心分離機にて分離した後、その上澄液をＧＰＣ法（高速液体クロマトグラフィ〔Ｗａｔｅｒ社製　：　Ｍｏｄｅｌ１５００　／　検出器　：　Ｓｈｏｄｅｘ　ＲＩ　ＳＥ−６１〕、カラム〔Ｓｏｕｄｅｘ　ＫＦ８０４　＋ＫＦ８０３＋ＫＦ８０２＋ＫＦ８０１〕を用いて結合剤存在量を測定した。溶液中の理論量と存在量から顔料への結合剤吸着量を差算出した。
【００６６】
・電気抵抗
サンプルサイズを１／２インチ×１／２インチとし、デジタルマルチメーター（松下電気産業社製）により測定した（２３℃、３０％ＲＨ条件下）。
【００６７】
・ドロップアウト
ＶＴＲ−ＡＧ６２００（松下電気産業社製）を用い、ＶＴＲドロップアウトカウンター（ＳＨＩＢＡＳＯＫＵ社製）により、−１６ｄＢ、３μｓｅｃ以上の信号欠陥個数を測定した。
【００６８】
・Ｘ−ＭＡ解析
作製したテープを日立製−２３８０ＮにてＳＥＭ観察し、ＨＯＲＩＢＡ製ＥＭＡＸ−５７７０Ｗにて処理電圧５〜３０ｋＶとして、塗膜表面から深さ５０Åまでの表面元素分析を行ない、ＦｅとＣについて定量を行なった。その元素存在量から原材料の体積を算出した。
【００６９】
・静磁気特性
作製したテープを、東英株式会社製室温専用超高度振動試料型磁力計（ＶＳＭ−Ｐ１０−１５ａｕｔｏ）を用い、２０℃５０％ＲＨの条件で測定した。
【００７０】
・塗膜厚
ＴＥＳＡ社製Ｍｏｄｕｌｅユニット４０３、３７２を用いて、磁気記録媒体の全厚を測定した後、非磁性支持体の厚みを差し引いて算出した。測定の誤差を考え３点測定し平均を塗膜厚とした。
【００７１】
・電磁変換特性
ＲＦ−ＯＵＴビデオ出力
ＶＴＲ　ＡＧ−６２００（松下電気産業社製）を用いてビデオ信号を記録し、比較例１の再生レベルを基準テープとし、これを０ｄＢとした時の相対値で表す。
【００７２】
Ｙ−Ｓ／ＮビデオＳ／Ｎ
ビデオ信号のＳ／Ｎ比を、上記基準テーを０ｄＢとした時の相対値で表す。
【００７３】
Ｃ−ＯＵＴクロマ出力
クロマ出力を記録再生し、その出力レベルを上記基準テープを０ｄＢとした時の相対値で表す。
【００７４】
Ｃ−Ｓ／ＮクロマＳ／Ｎ
クロマ信号のＳ／Ｎ比を、上記基準テープを０ｄＢとした時の相対値で表す。
【００７５】
・スチル特性
ＶＴＲ　ＡＧ６２００（松下電気産業社製）を用いて、再生中の一時停止状態での塗膜耐久性を確認。各々の耐久時間を以下の評価基準にて表した。
二重丸：耐久時間６００分以上
○：耐久時間３００分以上、６００分以下
△：耐久時間１２０分以上、３００分以下
▲：耐久時間　６０分以上、１２０分以下
×：耐久時間　６０分未満。
【００７６】
・ヘッドクロッグ特性
ＶＴＲ−ＡＧ６２００（松下電気産業社製）を用いて、再生走行中の粉落ちの影響によるヘッドギャップの目詰まり状態を評価。各々のヘッド状態を以下の評価基準にて表した。
二重丸：目詰まり、粉落ち全く無し
○：目詰まり、粉落ち若干有り
△：目詰まり、粉落ちは見られるが記録再生に問題無し
▲：目詰まり、粉落ちによりヘッドクロッグが発生するが短時間で回復
×：目詰まり、粉落ちによりヘッドクロッグが発生し記録再生が不可能。
【００７７】
上記各測定の結果は次の表２のとおりである。
【００７８】
【表２】

【００７９】
上記表１、表２によれば、実施形態例１〜３及び比較例１にてカーボンブラックの添加量の確認を行った結果、添加量が２重量部以上、すなわち実施形態例３および比較例１では、磁性粉末の充填が低下し、電磁変換特性の悪化が生じることがわかる。
【００８０】
実施形態例３及び比較例２〜３では用いる磁性粉末の変更を行った。比較例２では、磁性粉末粒径が小さいため高分散が難しく、充填性の低下から、電磁変換特性の悪化が生じる。比較例３では磁性粉末粒径が大きく充填性、角形比も良好であるが、ノイズ成分増大のため電磁変換特性の悪化が生じる。
【００８１】
また、結合剤の吸着量は、磁性粉末粒径が大きくなるほど、即ち磁性粉末の比表面積が小さくなるほど、結合剤の吸着性が向上し電気抵抗の増大が生じる。電気抵抗の増大により、ドロップアウトの増加、走行耐久性の悪化が生じる。
【００８２】
実施形態例３及び比較例４〜５では、用いるポリエステルポリウレタン結合剤の変更を行った。比較例４では、分子量が小さいため高分散が容易であるが、磁性塗膜の強度低下から、ドロップアウト、走行耐久性の悪化が生じる。比較例５では、分子量が大き過ぎるために、高分散を得るのが困難であり、電磁変換特性の悪化が生じる。
【００８３】
また、結合剤の分子量が小さいと、磁性粉末への吸着量向上から電気抵抗の増大が生じ、逆に分子量が大きいと、磁性粉末への吸着量低下から、電気抵抗は改善される。
【００８４】
実施形態例３及び比較例６〜７では、用いるニトロセルロース結合剤の変更を行った。結果は前述のポリエステルポリウレタン結合剤と同様で分子量の変化により、ドロップアウト、走行耐久性、電磁変換特性、電気抵抗の変化が生じた。
【００８５】
実施形態例３及び比較例８〜９では、用いるカーボンブラックの変更を行った。比較例８では、超微粒子カーボンブラックであるため、磁性粉末の充填性を妨げずに高電磁変換特性が得られるが、電気抵抗が増大する。比較例９では、粗大粒子カーボンブラックであるため、磁性粉末の充填性が低下し、電磁変換特性が悪化するが、電気抵抗の改善が生じる。
【００８６】
実施形態例３と比較例１０の相違点は、テープ作製工程のマグネットユニットの使用の有無である。比較例１０では、マグネットユニットを使用せずにテープを作製しているため、磁性塗膜中の成分は全て均一である。しかし、結合剤の磁性粉末への吸着性が良好でない組成であるため、磁性粉末と記録／再生ヘッドとの接触が生じ、磁性粉末の欠落が発生する。これに対しマグネットユニットを用いた場合、磁性塗膜表層に結合剤が多く存在するため、磁性粉末の欠落を防止できる。
【００８７】
上記の結果から、結合剤の磁性粉末への吸着量を２．０〜３．０ｍｇ／ｍ^２にすることで、電気抵抗が低く、カーボンブラックの少添加、磁性粉末の高充填が可能となり、電磁変換特性に優れた磁気記録媒体の供給が可能となる。また、マグネットユニットを用いることで、結合剤の磁性粉末への吸着性が良好でない組成であっても、高耐久性を得ることが可能となる。
【００８８】
【発明の効果】
（１）以上のように、請求項１〜１２に記載の発明によれば、電気抵抗が低く、カーボンブラックの少添加、磁性粉末の高充填が可能となり、電磁変換特性および走行耐久性に優れた磁気記録媒体の供給が可能となる。
（２）また請求項２、１１、１２に記載の発明によれば、磁性塗膜表層に未吸着状態の結合剤が多く存在することになり、磁性粉末と記録／再生ヘッドの接触が妨げられ、磁性粉末の脱落を防止することができる。これによって高耐久性を得ることができる。
（３）また請求項１３に記載の発明によれば、磁性塗膜表層に未吸着状態の結合剤を多く存在させることができる。このため本発明の方法により製造された磁気記録媒体は、磁性粉末と記録／再生ヘッドの接触が妨げられ、磁性粉末の脱落を防止することができる。
【図面の簡単な説明】
【図１】本発明の実施形態例を表し、（ａ）は磁性層を単層塗膜により形成した磁気記録媒体の断面図、（ｂ）は磁性層を２層塗膜により形成した磁気記録媒体の断面図。
【図２】本発明の実施形態例で用いる塗布システムの一例を示す構成図。
【図３】従来の磁気記録媒体を表し、（ａ）は磁性層を単層塗膜により形成した磁気記録媒体の断面図、（ｂ）は磁性層を２層塗膜により形成した磁気記録媒体の断面図。
【符号の説明】
１１…ベースフィルム、１２ａ，１２ｂ…磁性塗膜、１３ａ，１３ｂ…バインダー層、２１…押し出しコート装置、２２…マグネットユニット、２３…配向機、２４…ドライヤーシステム、２５…磁気テープ。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to various magnetic recording media such as a video tape, an audio tape, a floppy disk, and a data storage.
[0002]
[Prior art]
In order to improve the potential conversion characteristics of magnetic recording media for video tapes and audio tapes as recording wavelengths have become shorter and higher in density in recent years for VTRs, etc. The surface of the coating film is made mirror-finished and the magnetic particles are made finer.
[0003]
For example, in a coating-type magnetic recording medium, various polar groups are introduced into a binder or various kneaders are used in a dispersion process in order to make ultrafine magnetic powders in a highly dispersed state.
[0004]
Further, the structure of the magnetic recording medium may be changed from a conventional magnetic single layer structure as shown in FIG. 3A to a two-layer structure of a magnetic layer and a magnetic layer as shown in FIG. Various structures such as a two-layer structure of a nonmagnetic layer and the like have been used depending on purposes. In FIG. 3, 1 is a base film, and 2, 2 _U and 2 _L are magnetic coating films.
[0005]
As a technique for improving various characteristics of the magnetic recording medium, it is effective to increase the filling of the magnetic powder and improve the dispersibility of the magnetic coating film.
[0006]
In order to increase the filling of the magnetic powder, it is effective to minimize the addition amount of other raw materials such as a binder, a pigment, an abrasive, a dispersant, a lubricant, and a curing agent. Particularly, carbon black added for the purpose of reducing electric resistance is generally added in an amount of 1 to 10 parts by weight, and this reduction in the amount of added carbon black is effective for increasing the filling of magnetic powder. .
[0007]
[Problems to be solved by the invention]
However, when the addition amount of carbon black is reduced, the conductivity of the magnetic layer is reduced and the electric resistance is increased. Therefore, sticking to the recording / reproducing head when the magnetic recording medium is running, running noise is increased, and dust due to static electricity is increased. An increase in dropout due to adhesion occurs.
[0008]
Therefore, there is a need for a magnetic recording medium that is required at the moment, in which the amount of added carbon black is reduced as much as possible and the magnetic recording medium has low electric resistance.
[0009]
According to the present invention, a magnetic recording medium to which a minimum necessary amount of carbon black is added and which has low electric resistance and high electromagnetic conversion characteristics / high durability is supplied.
[0010]
[Means for Solving the Problems]
As described above, in order to obtain a magnetic recording medium having excellent electromagnetic conversion characteristics, it is effective to highly fill a magnetic powder and make a coating film mirror-finished. The reduction of other additives is most effective for increasing the filling of the magnetic powder, but the amount of carbon black added is determined by the electric resistance of the magnetic recording medium.
[0011]
In the coating type magnetic recording medium, the magnetic powder is dispersed in a binder and a solvent, so that the surface of the magnetic powder is covered with the binder. This coating cuts off the conductivity in the magnetic coating film, thereby increasing the electric resistance.
[0012]
The adsorption of the binder is determined by the surface characteristics of the magnetic powder, the polar group of the binder, and the dispersant to be added. It is very effective in preventing powder falling off.
[0013]
The addition of carbon black is effective for the purpose of reducing the high electric resistance, and a magnetic recording medium having a good adsorption state, that is, a magnetic recording medium having a high electric resistance, requires a large amount of carbon black to be added.
[0014]
Addition of a large amount of carbon black hinders high filling of the magnetic powder, leading to a decrease in electromagnetic conversion characteristics.
[0015]
In the present invention, by controlling the amount of the binder adsorbed on the pigment containing the magnetic powder to a certain amount, the conductivity of the magnetic powder is maintained and the electric resistance is reduced.
[0016]
As described above, when the adsorption amount of the binder decreases, the magnetic powder may fall off while the magnetic recording medium is running in the VTR. However, the presence of the binder in a non-adsorbed state prevents the contact between the magnetic powder and the recording / reproducing head, thereby preventing the magnetic powder from falling off.
[0017]
Since the contact between the recording / reproducing head and the magnetic powder occurs only on the surface layer of the magnetic coating film, it is ideal that a large amount of unadsorbed binder is present on the surface layer as shown in FIG. FIG. 1A shows a cross-sectional configuration of a magnetic recording medium in which a magnetic layer is formed by a single-layer coating, and FIG. 1B shows a cross-sectional configuration of a magnetic recording medium in which a magnetic layer is formed by a two-layer coating. I have.
[0018]
In FIG. 1, 11 is a base film (non-magnetic support), 12a and 12b are magnetic coating films, and 13a and 13b are binder layers containing a non-adsorbed binder.
[0019]
Therefore, a magnetic recording medium having low electric resistance and excellent running durability can be obtained by reducing the amount of the binder adsorbed on the magnetic powder and by allowing a large amount of the unadsorbed binder to exist in the surface layer of the coating film.
[0020]
Further, it is possible to reduce the electric resistance by controlling the amount of adsorption of the binder to the magnetic powder, and it is possible to eliminate or reduce the amount of carbon black to be added. In addition, the reduction of additives other than the magnetic powder enables high filling of the magnetic powder.
[0021]
In the present invention, for example, an apparatus shown in FIG. 2 (an apparatus described in JP-A-10-151396) is used in order to easily control the ratio of the magnetic powder and the binder in the surface layer of the coating film.
[0022]
The apparatus shown in FIG. 2 is constituted by a general single-layer coating system, in which a magnetic paint is applied to a base film 11 as a magnetic recording medium sent from a reel, that is, a non-magnetic support by an extrusion coater 21 and immediately thereafter. Then, it passes through the magnet unit 22 provided on the side opposite to the magnetic paint application surface, that is, on the non-magnetic support side.
[0023]
The magnet unit 22 is a magnet unit having a plate-like structure in which permanent magnets of S pole and N pole are alternately stacked in a predetermined direction in the running direction of the nonmagnetic support, and attracts magnetic powder on the surface layer of the coating film.
[0024]
Next, the medium that has passed through the magnet unit 22 is subjected to a magnetic field orientation treatment by an orientation machine 23, and then subjected to processes such as drying, calendering, and curing by a drier system 24 to become a magnetic tape 25, which is wound around a reel. .
[0025]
When the magnetic paint passes through the magnet unit 22, only the magnetic powder in the paint is attracted to the non-magnetic support, and a large amount of binder not adsorbed by the pigment containing the magnetic powder is present on the surface layer of the coating film.
[0026]
However, if the thickness of the binder layer is unnecessarily large, a space is created between the magnetic powder of the magnetic recording medium and the recording / reproducing head, causing deterioration of the electromagnetic conversion characteristics.
[0027]
The required thickness of the binder layer varies depending on the recording wavelength of each format, but in the present invention, it is verified in the VHS format.
[0028]
From the above theory, it is possible to obtain a magnetic recording medium with high filling of magnetic powder, low electric resistance, and excellent running durability.
[0029]
In the magnetic recording medium according to the present invention, the solvent used for adjusting the non-magnetic support, the abrasive mixed in the magnetic layer, or the magnetic paint can be any conventionally known one, and is not limited at all. .
[0030]
As the magnetic powder used in the present invention, a ferromagnetic alloy containing Co-modified magnetite Fe or Ni or Co as a main component (75% or more) can be used. These ferromagnetic powders include Al, I, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Se, Te, Ba, Ni, Ta, W , Re, Au, Hg, Pd, Bi, La, Ce, P, Mn, Zn, Co, Sr, B, and the like.
[0031]
The binder used in the present invention comprises a polyester polyurethane resin obtained by a reaction between a polyester polyol and a polyfunctional isocyanate. The polyester polyurethane resin has a weight average molecular weight Mw of 40,000 to 50,000 and a glass transition point of 40 to 50. C. and 0.01 to 1.0 mmol / g of an alkylphosphine group as a polar group.
[0032]
The binder used in the present invention is composed of nitrocellulose, has a weight average molecular weight Mw of 10,000 to 60000, and contains a carboxyl group of 0.02 mmol / g.
[0033]
The carbon black used in the present invention is an acidic carbon having an average particle diameter of 20 to 50 nm, a pH of 2 to 5, and an addition amount of 0 to 2 parts by weight based on the magnetic powder.
[0034]
Examples of the curing agent include an aromatic polyisocyanate and an aliphatic polyisocyanate, and an active hydrogenated product thereof is preferable. As the aromatic polyisocyanate, toluene diisocyanate (TDI), 1,3-xylene diisocyanate, 1,4-xylene anisate, 4,4-diphenylmethane diisocyanate, p-phenyl diisocyanate, m-phenyl diisocyanate, 1,5-naphthyl Examples include diisocyanate. Examples of the aliphatic polyisocyanate include hexanemethylene diisocyanate and cyclohexane diisocyanate. Examples of active hydrogen compounds that form adducts with these include ethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane, and glycerin, and have an average molecular weight of 100 to Those having a range of 5000 are preferred.
[0035]
As the material of the nonmagnetic support used in the present invention, those generally used for magnetic recording media can be used, such as polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyethylene, polyolefins such as polypropylene, and cellulose triacetate. , Cellulose derivatives such as cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamideimide, other plastics, metals such as aluminum and copper, aluminum alloys, and titanium alloys And other light metals, ceramics, single crystal silicon, and the like.
[0036]
As the lubricant used in the present invention, silicone oil, fatty acid-modified silicone, fluorine-containing silicone, or other fluorine-based lubricant, polyolefin, polyglycol, alkyl phosphate and metal salt, polyphenyl ether, having 12 to 24 carbon atoms Alcohols (which may or may not contain the respective unsaturations), higher fatty acids and fatty acid esters having 12 to 24 carbon atoms (which may or may not contain the respective unsaturations), alkyls Amine-based lubricants such as carboxylic acid amine salts and fluorinated alkylcarboxylic acid amine salts can be used.
[0037]
Specific examples of higher fatty acids and fatty acid esters include lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid, linoleic acid, and octyl stearate. Isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate, butyl stearate, heptyl stearate and the like. The lubricant may be mixed with a plurality of lubricants.
[0038]
Examples of the abrasive used in the present invention include α-alumina, β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, diamond, silica, garnet, garnet, and nitride. Known materials having a Mohs' hardness of 6 or more containing silicon, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium oxide, or the like as a main component can be used alone or in combination.
[0039]
The average particle size of these abrasives is preferably from 0.01 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used with a broad particle size distribution.
[0040]
As a solvent for adjusting the magnetic paint of the present invention, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketone solvents such as cyclohexanenon, methyl acetate, butyl acetate, ethyl lactate, ester solvents such as ethyl acetate monoethyl ether, Glycol ether solvents such as glycol monoethyl ether and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; and chlorine-containing solvents such as methylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene. No. In addition, other conventionally known organic solvents can be used.
[0041]
As a method for preparing the magnetic paint of the present invention, any known method can be used. For example, a roll mill, a ball mill, a sand mill, a high-speed stone mill, a basket mill, a disper, a homomixer, a kneader, a continuous kneader, an extruder, a homogenizer, an ultrasonic disperser, and the like can be used. When preparing the magnetic paint, the magnetic particles and other additive particles may be separately dispersed and then mixed.
[0042]
In the application of the magnetic paint, a pretreatment such as a corona discharge treatment or an electron beam irradiation treatment may be performed on the undercoat layer such as an adhesive layer or the nonmagnetic support before directly applying to the nonmagnetic support.
[0043]
Although a back coat layer made of carbon or a non-magnetic paint may be provided on the opposite side of the magnetic layer, it is not provided in the present invention because it is a verification in the VHS format in the present invention.
[0044]
As a method of coating on the non-magnetic support of the present invention, an experiment is performed by extrusion coating, but if the coating line passes a magnet immediately after coating, an air doctor coat, a blade coat, a rod coat, Examples of the method include an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a gravure coat, a transfer roll coat, and a cast coat, and other methods are also possible.
[0045]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiment of the present invention, the magnetic paint is adjusted according to the composition table in Table 1 and passed through the magnet unit 22 shown in FIG. It was confirmed.
[0046]
Hereinafter, specific experimental examples will be described in order to clarify the effects of the present invention. In the experimental examples, “parts” represents “parts by weight”.
[0047]
A paint for forming a magnetic layer was prepared according to the composition shown in Table 1. After kneading the magnetic coating composition in Table 1 with a continuous kneader, the mixture was dispersed using a sand mill, 4 parts of polyisocyanate and 1 part of myristic acid were added, and the mixture was filtered through a filter having an average diameter of 1 μm to prepare a magnetic coating. .
[0048]
[Table 1]

[0049]
After coating the prepared magnetic paint with a thickness of 3.0 μm on a polyethylene terephthalate film having a thickness of 15.0 μm by extrusion coating, it passed through a 3000 Gauss magnet unit attached on the side opposite to the magnetic layer, and was oriented, A video tape was prepared by cutting the film obtained through the steps of drying, calendering and curing into 1/2 inch. Hereinafter, the embodiment and the comparative example will be described in detail with reference to Table 1.
[0050]
In the present invention, the BET method that defines the specific surface area of the magnetic powder is a method of calculating the surface area by combining the monolayer adsorption amount as a parameter determined experimentally and the molecular cross-sectional area of the adsorbate. It is.
[0051]
Embodiment example-1
After preparing a magnetic paint using the Co-magnetite magnetic powder, polyurethane binder, and nitrocellulose binder described in the claims, a video tape was produced using a magnet unit.
[0052]
Embodiment example-2
After preparing a magnetic paint using the Co-magnetite magnetic powder, polyurethane binder, nitrocellulose binder and 1 part by weight of carbon black described in the claims, a video tape was produced using a magnet unit.
[0053]
Embodiment example-3
After preparing a magnetic paint using the Co-magnetite magnetic powder described in the claims, a polyurethane binder, a nitrocellulose binder, and 2 parts by weight of carbon black, a video tape was produced using a magnet unit.
[0054]
Comparative Example-1
After preparing a magnetic paint using the Co-magnetite magnetic powder, polyurethane binder, nitrocellulose binder, and 3 parts by weight of carbon black, a video tape was produced using a magnet unit.
[0055]
Comparative Example-2
A video tape was produced in the same manner as in Embodiment Example 3, except that a magnetic powder outside the scope of the magnetic powder described in the claims (see Table 1) was used.
[0056]
Comparative Example-3
A video tape was produced in the same manner as in Embodiment Example 3, except that a magnetic powder outside the scope of the magnetic powder described in the claims (see Table 1) was used.
[0057]
Comparative Example-4
A video tape was produced in the same manner as in Embodiment Example 3, except that a polyester polyurethane binder outside the scope of the polyester polyurethane binder described in the claims was used.
[0058]
Comparative Example-5
A video tape was produced in the same manner as in Embodiment Example 3, except that a polyester polyurethane binder outside the scope of the polyester polyurethane binder described in the claims was used.
[0059]
Comparative Example-6
A video tape was produced in the same manner as in Embodiment Example 3, except that a nitrocellulose binder outside the scope of the nitrocellulose binder described in the claims was used.
[0060]
Comparative Example-7
A video tape was produced in the same manner as in Embodiment Example 3, except that a nitrocellulose binder outside the scope of the nitrocellulose binder described in the claims was used.
[0061]
Comparative Example-8
A video tape was produced in the same manner as in Embodiment Example 3, except that carbon black outside the scope of the carbon black described in the claims was used.
[0062]
Comparative Example-9
A video tape was produced in the same manner as in Embodiment Example 3, except that carbon black outside the scope of the carbon black described in the claims was used.
[0063]
Comparative Example-10
A video tape was manufactured in the same manner as in Embodiment 3 except that the magnetic powder was not attracted by the magnet unit.
[0064]
The following measurements were performed on the video tapes of the embodiment and the comparative example manufactured through the above steps. Each measurement is as follows.
[0065]
-Binder adsorption amount After the prepared coating material was separated by a centrifugal separator, the supernatant was subjected to GPC (high performance liquid chromatography [Water: Model 1500 / detector: Shodex RI SE-61], column [Soudex KF804]. + KF803 + KF802 + KF801], and the difference between the theoretical amount and the amount present in the solution and the amount of the binder adsorbed on the pigment was calculated.
[0066]
-The electrical resistance sample size was set to × inch × １ ／ inch, and measured with a digital multimeter (manufactured by Matsushita Electric Industrial Co., Ltd.) (under conditions of 23 ° C. and 30% RH).
[0067]
Using a dropout VTR-AG6200 (manufactured by Matsushita Electric Industrial Co., Ltd.), a VTR dropout counter (manufactured by SHIBASOKU) measured the number of signal defects of -16 dB, 3 μsec or more.
[0068]
X-MA analysis The prepared tape was observed by SEM with Hitachi-2380N, and the processing voltage was 5-30 kV with HORIBA EMAX-5770W, and the surface element analysis from the coating film surface to a depth of 50 ° was performed. C was quantified. The volume of the raw material was calculated from the element abundance.
[0069]
The magnetostatic properties of the tape were measured using a super-high-vibration sample magnetometer (VSM-P10-15auto) manufactured by Toei Co., Ltd. at room temperature under the conditions of 20 ° C. and 50% RH.
[0070]
-Film thickness The total thickness of the magnetic recording medium was measured using the Module units 403 and 372 manufactured by TESA, and then the thickness was calculated by subtracting the thickness of the nonmagnetic support. Considering measurement errors, three points were measured and the average was taken as the coating thickness.
[0071]
Electromagnetic conversion characteristics RF-OUT video output A video signal was recorded using VTR AG-6200 (manufactured by Matsushita Electric Industrial Co., Ltd.), and the reproduction level of Comparative Example 1 was used as a reference tape, and the relative value when this was set to 0 dB Represent.
[0072]
YS / N Video S / N
The S / N ratio of the video signal is represented by a relative value when the above-mentioned reference table is set to 0 dB.
[0073]
C-OUT Chroma Output Chroma output is recorded and reproduced, and its output level is represented by a relative value when the reference tape is set to 0 dB.
[0074]
CS / N chroma S / N
The S / N ratio of the chroma signal is represented by a relative value when the reference tape is set to 0 dB.
[0075]
・ Still characteristics Using a VTR AG6200 (manufactured by Matsushita Electric Industrial Co., Ltd.), the durability of the coating film in a pause state during reproduction was confirmed. Each endurance time was represented by the following evaluation criteria.
Double circle: durable time 600 minutes or more ：: durable time 300 minutes or more and 600 minutes or less △: durable time 120 minutes or more and 300 minutes or less ：: durable time 60 minutes or more and 120 minutes or less X: durable time less than 60 minutes.
[0076]
-Head clog characteristics Using a VTR-AG6200 (manufactured by Matsushita Electric Industrial Co., Ltd.), the clogging state of the head gap due to the effect of powder drop during regeneration running was evaluated. Each head state was represented by the following evaluation criteria.
Double circle: No clogging, no powder dropping ○: Some clogging, powder dropping slightly △: Clogging, powder dropping is observed but no problem in recording / reproduction ▲: Head clog is generated due to clogging and powder dropping Recovery in a short time x: Clogging and powder drop-out cause head clogging, making recording and reproduction impossible.
[0077]
The results of the above measurements are shown in Table 2 below.
[0078]
[Table 2]

[0079]
According to Tables 1 and 2, as a result of confirming the addition amount of carbon black in Embodiment Examples 1 to 3 and Comparative Example 1, the addition amount was 2 parts by weight or more, that is, Embodiment Example 3 and Comparative Example In the case of No. 1, it can be seen that the filling of the magnetic powder decreases and the electromagnetic conversion characteristics deteriorate.
[0080]
In Embodiment 3 and Comparative Examples 2 and 3, the magnetic powder used was changed. In Comparative Example 2, high dispersion is difficult due to the small particle size of the magnetic powder, and the electromagnetic conversion characteristics are deteriorated due to a decrease in filling property. In Comparative Example 3, although the magnetic powder particle size was large and the filling property and the squareness ratio were good, the electromagnetic conversion characteristics deteriorated due to an increase in the noise component.
[0081]
As for the amount of binder adsorbed, as the particle diameter of the magnetic powder becomes larger, that is, as the specific surface area of the magnetic powder becomes smaller, the adsorbability of the binder is improved and the electric resistance is increased. An increase in electric resistance causes an increase in dropout and a deterioration in running durability.
[0082]
In Embodiment Example 3 and Comparative Examples 4 and 5, the polyester polyurethane binder used was changed. In Comparative Example 4, high dispersion is easy because the molecular weight is small, but dropout and deterioration in running durability occur due to a decrease in the strength of the magnetic coating film. In Comparative Example 5, it is difficult to obtain high dispersion because the molecular weight is too large, and the electromagnetic conversion characteristics are deteriorated.
[0083]
On the other hand, when the molecular weight of the binder is small, the electric resistance is increased due to the increase in the amount of adsorption to the magnetic powder. Conversely, when the molecular weight is large, the electric resistance is improved due to the decrease in the amount of adsorption to the magnetic powder.
[0084]
In Embodiment Example 3 and Comparative Examples 6 and 7, the nitrocellulose binder used was changed. The results were the same as those of the above-mentioned polyester polyurethane binder, and a change in molecular weight resulted in a change in dropout, running durability, electromagnetic conversion characteristics, and electric resistance.
[0085]
In Embodiment 3 and Comparative Examples 8 and 9, the carbon black used was changed. In Comparative Example 8, since it is ultrafine carbon black, high electromagnetic conversion characteristics can be obtained without hindering the filling property of the magnetic powder, but the electric resistance increases. In Comparative Example 9, since the carbon black is coarse particles, the filling property of the magnetic powder is reduced and the electromagnetic conversion characteristics are deteriorated, but the electric resistance is improved.
[0086]
The difference between the third embodiment and the comparative example 10 is whether or not a magnet unit is used in the tape manufacturing process. In Comparative Example 10, since the tape was produced without using the magnet unit, all the components in the magnetic coating film were uniform. However, since the binder has a composition that does not have good adsorbability to the magnetic powder, the magnetic powder comes into contact with the recording / reproducing head, and the magnetic powder is lost. On the other hand, when a magnet unit is used, a large amount of a binder is present in the surface layer of the magnetic coating film, so that the magnetic powder can be prevented from being lost.
[0087]
From the above results, by setting the amount of binder adsorbed on the magnetic powder to 2.0 to 3.0 mg / m ² , the electric resistance is low, the addition of carbon black is small, and the magnetic powder can be highly filled. It is possible to supply a magnetic recording medium having excellent electromagnetic conversion characteristics. Further, by using the magnet unit, it is possible to obtain high durability even if the composition has a poor adsorption property of the binder to the magnetic powder.
[0088]
【The invention's effect】
(1) As described above, according to the first to twelfth aspects of the present invention, low electric resistance, low addition of carbon black and high filling of magnetic powder are possible, and excellent electromagnetic conversion characteristics and running durability are obtained. The magnetic recording medium can be supplied.
(2) According to the second, eleventh and twelfth aspects of the present invention, a large amount of the binder in a non-adsorbed state exists in the surface layer of the magnetic coating film, so that contact between the magnetic powder and the recording / reproducing head is prevented. In addition, the magnetic powder can be prevented from falling off. Thereby, high durability can be obtained.
(3) According to the invention of claim 13, a large amount of the binder in a non-adsorbed state can be present in the surface layer of the magnetic coating film. Therefore, in the magnetic recording medium manufactured by the method of the present invention, the contact between the magnetic powder and the recording / reproducing head is prevented, and the magnetic powder can be prevented from falling off.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention, in which (a) is a cross-sectional view of a magnetic recording medium in which a magnetic layer is formed by a single-layer coating film, and (b) is magnetic recording in which a magnetic layer is formed by a two-layer coating film. Sectional drawing of a medium.
FIG. 2 is a configuration diagram showing an example of a coating system used in an embodiment of the present invention.
3A and 3B show a conventional magnetic recording medium, in which FIG. 3A is a cross-sectional view of a magnetic recording medium in which a magnetic layer is formed by a single-layer coating film, and FIG. 3B is a magnetic recording medium in which a magnetic layer is formed by a two-layer coating film; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Base film, 12a, 12b ... Magnetic coating film, 13a, 13b ... Binder layer, 21 ... Extrusion coating device, 22 ... Magnet unit, 23 ... Orienting machine, 24 ... Dryer system, 25 ... Magnetic tape.

Claims (13)

In a magnetic recording medium having a magnetic layer containing magnetic powder,
The magnetic powder is made of magnetite deposited or contained in cobalt, the amount of cobalt deposited or contained in the magnetic powder is 1.0 to 5.0 atm% in terms of Co / Fe, and The specific surface area by the BET method is 25 to 35 m ² / g, and the amount of the binder contained in the magnetic layer adsorbed on the pigment containing the magnetic powder is 2.0 to the specific surface area of the pigment containing the magnetic powder. A magnetic recording medium characterized in that the amount is from 3.0 to 3.0 mg / m ² . The raw material composition of the magnetic layer is not uniform, and the ratio of the binder and additives such as carbon black in the magnetic coating film is 90% by volume or more in the magnetic coating surface layer with respect to the magnetic powder. 2. The magnetic recording medium according to claim 1, wherein the depth is 5 nm or more and 70% by volume or less from the surface layer of the coating film. 2. The magnetic recording medium according to claim 1, wherein the binder contained in the magnetic layer comprises 14 to 16% by weight of a polyester polyurethane resin and 4 to 6% by weight of nitrocellulose based on magnetic powder. The magnetic recording medium according to claim 2, wherein the binder contained in the magnetic layer comprises 14 to 16% by weight of a polyester polyurethane resin and 4 to 6% by weight of nitrocellulose based on magnetic powder. The binder contained in the magnetic layer is made of a polyester polyurethane resin obtained by a reaction between a polyester polyol and a polyfunctional isocyanate. The polyester polyurethane resin has a weight average molecular weight Mw of 40,000 to 50,000 and a glass transition point of 40. 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a temperature of from about 50 ° C. to about 0.1 mmol / g to 1.0 mmol / g as a polar group. The binder contained in the magnetic layer is made of a polyester polyurethane resin obtained by a reaction between a polyester polyol and a polyfunctional isocyanate. The polyester polyurethane resin has a weight average molecular weight Mw of 40,000 to 50,000 and a glass transition point of 40. 3. The magnetic recording medium according to claim 2, wherein the magnetic recording medium has a temperature of from about 50 ° C. to about 0.1 mmol / g to 1.0 mmol / g as a polar group. 2. The binder according to claim 1, wherein the binder contained in the magnetic layer is made of nitrocellulose, has a weight average molecular weight Mw of 10,000 to 60,000, and contains a carboxyl group of 0.02 mmol / g. Magnetic recording medium. 3. The binder according to claim 2, wherein the binder contained in the magnetic layer is made of nitrocellulose, has a weight average molecular weight Mw of 10,000 to 60,000, and contains a carboxyl group of 0.02 mmol / g. Magnetic recording medium. The carbon black contained in the magnetic layer is an acidic carbon having an average particle diameter of 20 to 50 nm, a pH of 2 to 5, and an addition amount of 0 to 2 parts by weight based on the magnetic powder. 2. The magnetic recording medium according to claim 1, wherein: The carbon black contained in the magnetic layer is an acidic carbon having an average particle diameter of 20 to 50 nm, a pH of 2 to 5, and an addition amount of 0 to 2 parts by weight based on the magnetic powder. The magnetic recording medium according to claim 2, wherein The magnetic layer according to claim 1, wherein the magnetic layer is formed on a non-magnetic support, and is manufactured by performing a step of attracting magnetic powder in the magnetic layer by a magnet from the non-magnetic support side. recoding media. The magnetic layer according to claim 2, wherein the magnetic layer is formed on a non-magnetic support, and is subjected to a step of attracting magnetic powder in the magnetic layer by a magnet from the non-magnetic support side. recoding media. A method for producing a magnetic recording medium having a magnetic layer containing magnetic powder on a non-magnetic support,
By performing a step of attracting magnetic powder in the magnetic layer by a magnet from the non-magnetic support side,
The proportion of the binder and additives such as carbon black in the magnetic layer is 90% by volume or more in the magnetic coating surface layer with respect to the magnetic powder, and 70% by volume at a depth of 5 nm or more from the magnetic coating surface layer. A method for manufacturing a magnetic recording medium, wherein the method is controlled as follows.

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