JP2004178718A - Magnetic recording medium and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high density magnetic recording medium having an output and an S/N for coping with a large capacity. <P>SOLUTION: An average particle diameter of magnetic powder is in the range of 10 to 65nm, and the thickness of a magnetic layer is in the range of 0.01 to 0.15μm, and the magnetic paint used for forming the magnetic layer is manufactured at least through a process in which the magnetic powder is made wet by mixing at least a solvent by a high speed mixer, and a process in which the wetted magnetic powder is mixed with a resin liquid (including a case of only a solvent) at a transfer part of a continuous type two-shaft kneading machine, and then transferred to the kneading part. <P>COPYRIGHT: (C)2004,JPO

Description

【００６５】
Ｒａ： 磁性層表面の中心線平均表面粗さＲａ
Ｓ／Ｎ： 出力対ノイズ
【００６６】
表１を見ると明らかなように、本発明の実施例１〜６に係るコンピュータ用テープ（磁気記録媒体）は、比較例１〜４に係るコンピュータ用テープに比べて、電磁変換特性に優れている。特にＭＲヘッド（磁気抵抗効果型素子を利用した再生ヘッド）を使用した場合の再生出力や、出力対ノイズ（Ｓ／Ｎ）比が高いこともわかる。
【００６７】
【発明の効果】
以上のように本発明によれば、高い再生出力およびＳ／Ｎ等を有する電磁変換特性に優れた磁気記録媒体が得られる。これにより、例えば１ＴＢに迫り、越える大容量に対応できるコンピュータ等用のバックアップテープを実現することができる。
【図面の簡単な説明】
【図１】本発明に使用する連続式２軸混練機の構成図である。
【符号の説明】
１ 湿潤磁性粉末供給ユニット
２ 樹脂液注入ユニット
３、４、５ 希釈溶剤注入ユニット
６ 塗料排出口
７ 回転軸
８ スクリュー
９ パドル
１０、１１ バレルの搬送部位
１２、１３、１４、１５ バレルの混練部位
１６、１７ バレルの混練希釈部位
１８、１９、２０ バレルの希釈部位[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a coating type magnetic recording medium excellent in high recording density characteristics and a method for manufacturing the same.
[0002]
[Prior art]
Magnetic tapes have various uses, such as audio tapes, video tapes, and computer tapes. In the field of data backup tapes, in particular, with the increase in the capacity of the hard disk to be backed up, 10 to 100 GB per roll is required. Products with a recording capacity have been commercialized. Further, a large-capacity backup tape approaching 1 TB has been proposed in the future, and it is indispensable to increase its recording density.
[0003]
In order to cope with such a high recording density, when manufacturing a magnetic tape, it is necessary to use a magnetic powder with fine particles and improved magnetic properties, a further filling property of the magnetic powder, an improvement in dispersibility, Further, as the recording becomes shorter in wavelength, the thickness of the magnetic layer needs to be reduced in order to reduce the demagnetization due to the demagnetizing field during recording and reproduction.
[0004]
In order to improve the magnetic properties of the magnetic powder, it is desirable to increase the residual magnetization of the magnetic layer to increase the output. For this reason, the use of ferromagnetic alloy powder instead of conventional oxide magnetic powder or Co-containing iron oxide magnetic powder as the magnetic powder is becoming mainstream. For example, a ferromagnetic alloy having a coercive force of 120 kA / m (1500 Oe) or more is used. Alloy powders have also been proposed (reference patents: JP-A-5-234064, JP-A-6-25702, JP-A-6-139553).
[0005]
In order to improve the magnetic properties of the magnetic layer, it is effective to increase the filling of the ferromagnetic powder and improve the dispersibility. As means for increasing the filling of the ferromagnetic powder, a method of kneading the magnetic coating component while applying a high shearing force in a high solid content state state, for example, as disclosed in Patent Documents 1 to 3 A method using a continuous twin-screw kneader has been proposed.
[0006]
[Patent Document 1]
JP-A-6-338055 (pages 2-4)
[Patent Document 2]
JP-A-10-308022 (pages 2-4)
[Patent Document 3]
JP-A-7-14158 (pages 2-4, FIG. 1)
[0007]
[Problems to be solved by the invention]
However, in producing a high-density magnetic recording medium (corresponding to a large capacity approaching or exceeding 1 TB, for example), according to the above-mentioned conventionally known technique, the surface energy of the present invention having an average particle diameter in the range of 10 to 65 nm is used. However, it was difficult to sufficiently disperse ultrafine magnetic powder having high magnetic cohesion force, and high packing could not be achieved. As a result, a stable thin magnetic layer having excellent magnetic properties and excellent smoothness cannot be formed, and the output and the output-to-noise ratio (S / N) cannot be satisfied. .
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a high-density magnetic recording medium having an output and an S / N ratio corresponding to a large capacity approaching or exceeding 1 TB. The purpose is.
[0009]
[Means for Solving the Problems]
The present invention provides an undercoat layer containing a nonmagnetic powder and a binder resin on one surface of a nonmagnetic support, and a magnetic powder and a binder resin on the undercoat layer. A magnetic recording medium having a magnetic layer containing a non-magnetic powder and a back coat layer containing a binder resin on the other surface of the non-magnetic support is characterized by the following constitution.
[0010]
The magnetic powder has an average particle diameter in the range of 10 to 65 nm and a thickness of the magnetic layer in the range of 0.01 to 0.15 μm. In forming the magnetic layer, at least a step of wetting the magnetic powder containing at least a solvent in a high-speed stirring mixer and a step of transporting the wetted magnetic powder at a transfer site of a continuous twin-screw kneader. After being mixed with a resin liquid (including the case of using only a solvent), and then sent to a kneading site. Further, the addition amount of the resin liquid to be added at the transport site in the continuous twin-screw kneader is in the range of 0 to 15 parts by weight with respect to 100 parts by weight of the magnetic powder in the resin solid content, and with a high-speed stirring mixer. It is preferable that the total amount of the resin solid content to be added and the resin solid content to be added at the transport site is 2 to 25 parts by weight. With such a configuration, it is possible to achieve both high filling and ultra-smoothness in the thin magnetic layer, and as a result, a magnetic recording medium having excellent electromagnetic conversion characteristics (output, S / N) is obtained. It is.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, in order to obtain high resolution, the thickness of the magnetic layer is preferably in the range of 0.01 to 0.15 μm, and more preferably in the range of 0.05 to 0.12 μm. This range is preferable because if the thickness of the magnetic layer is less than 0.01 μm, a sufficient output cannot be obtained or the thickness unevenness becomes large and noise becomes large. When the thickness of the magnetic layer exceeds 0.15 μm, the resolution decreases and the short-wavelength recording characteristics deteriorate.
[0012]
In order to improve the output characteristics and S / N characteristics of the magnetic recording medium, the average particle size of the magnetic powder contained in the magnetic layer is preferably in the range of 10 to 65 nm, more preferably in the range of 15 to 50 nm. . This range is preferable because if the average particle diameter is less than 10 nm, the surface energy of the particles becomes large and dispersion becomes difficult, and if the average particle diameter exceeds 65 nm, noise increases. As the magnetic powder, ferromagnetic iron-based metal magnetic powder, iron nitride magnetic powder, plate-like hexagonal Ba-ferrite magnetic powder and the like are preferable.
[0013]
The ferromagnetic iron-based metal magnetic powder may contain a transition metal such as Mn 2, Zn 2, Ni 2, Cu 2 or Co as an alloy. Among them, Co 2 and Ni are preferable, and Co 2 is particularly preferable because the saturation magnetization can be improved most. The amount of the above-mentioned transition metal element is preferably 5 to 50 at%, more preferably 10 to 30 at%, based on iron. Further, at least one rare earth element selected from yttrium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium and the like may be contained. Among them, neodymium and samarium, terbium, and yttrium are preferable because a high coercive force can be obtained. The amount of the rare earth element is from 0.2 to 20 atomic%, preferably from 0.3 to 15 atomic%, more preferably from 0.5 to 10 atomic%, based on iron.
[0014]
The ferromagnetic iron-based metal magnetic powder may contain boron. By containing boron, ultrafine particles in the form of particles or ellipse having an average particle diameter of 50 nm or less can be obtained. The amount of boron is 0.5 to 30 atomic%, preferably 1 to 25 atomic%, more preferably 2 to 20 atomic%, based on iron in the whole magnetic powder. The above-mentioned both atomic percentages are values measured by fluorescent X-ray analysis (reference patent: JP-A-2001-181754).
[0015]
As the iron nitride magnetic powder, known powders can be used, and in addition to acicular shapes, irregular shapes such as spheres and cubes can be used. With respect to the particle size and specific surface area, in order to meet the required characteristics as a magnetic powder for magnetic recording, it is necessary to set the manufacturing conditions of the magnetic powder to be limited (refer to Japanese Patent Application Laid-Open No. 2000-27731). .
[0016]
Coercive force of the ferromagnetic iron-based metal magnetic powder and the iron nitride magnetic powder is preferably 80~320kA / m, saturation magnetization ^{is, 80~200A · m 2 / kg (} 80~200emu / g) are preferable, 100 ^{180A · m 2 / kg (100~180emu} / g) is more preferable.
[0017]
The average particle diameter of the ferromagnetic iron-based metal magnetic powder and the iron nitride magnetic powder is preferably from 10 to 65 nm, more preferably from 15 to 50 nm. This range is preferable because, when the average particle diameter is less than 10 nm, the coercive force is reduced, or the surface energy of the particles is increased, so that it is difficult to disperse in the paint, or when the average particle diameter is larger than 65 nm. This is because the particle noise based on the particle size increases. Further, BET specific surface area of the ferromagnetic powder is preferably at least ^35m 2 / g, more preferably at least ^{40 m} 2 / g, or most preferably ^50m 2 / g. Usually, it is 100 m ² / g or less.
[0018]
Coercive force of the hexagonal Ba- ferrite magnetic powder is preferably 120~320kA / m, saturation magnetization ^{is, 40~70A · m 2 / kg (} 40~70emu / g) are preferable. The magnetic properties of these ferromagnetic powders refer to values measured with an external magnetic field of 1273.3 kA / m (16 kOe) using a sample vibrating magnetometer. Further, the particle size (the size in the plate surface direction) is preferably 10 to 50 nm, more preferably 10 to 30 nm, and still more preferably 10 to 20 nm. If the particle size is less than 10 nm, the surface energy of the particles increases, making it difficult to disperse the particles in the coating. If the particle size exceeds 50 nm, the particle noise based on the particle size increases. The above average particle diameter was obtained by actually measuring the maximum diameter of each particle (long axis diameter for acicular powder, plate diameter for platy powder) from a photograph taken with a transmission electron microscope (TEM). It is obtained from the average value. Further, the plate ratio (plate diameter / plate thickness) is preferably 2 to 10, more preferably 2 to 5, and even more preferably 2 to 4. The BET specific surface area of the hexagonal Ba-ferrite magnetic powder is preferably from 1 to 100 m ² / g.
[0019]
In general, at the time of producing a magnetic paint for a magnetic recording medium, at least a kneader, a kneading step of kneading the magnetic paint components with a continuous kneader, a dispersion step using a fine media rotating dispersion device such as a sand mill, and, if necessary, Before and after these steps, a mixing step is provided.
[0020]
In the present invention, a coating method using a high-speed stirring mixer as a pre-kneading step and a kneading step using a continuous twin-screw kneader are applied. This is preferable because the filling property of the magnetic powder in the magnetic layer can be improved to the maximum and a high remanent magnetization can be obtained.
[0021]
The reason why the high-speed stirring mixer is used is to coat the resin to single particles to perform a uniform surface treatment, and to concomitantly improve the transportability of the wet magnetic powder. A wet magnetic powder using a high-speed stirring mixer is composed of a magnetic powder, a resin, a solvent and other additional components. The mixing step using a high-speed stirring mixer can be performed by a known method (for example, Japanese Patent Application Laid-Open Nos. 7-14149 and 2002-275504).
[0022]
As for the high-speed stirring mixer, in the present invention, for example, a gas blow-up stirrer utilizing the rolling and flowing effect such as an agromaster manufactured by Hosokawa Micron, a cyclomix or mechanofusion system manufactured by the company, an axial manufactured by Matsuyama Heavy Industries, Ltd. A rotary mixer such as a mixer, a Henschel mixer manufactured by Mitsui Mining Co., and the like can be used.
[0023]
Prior art using a continuous twin-screw kneader includes Patent Documents 1 to 3. In Patent Literature 1 and Patent Literature 2, in order to obtain a highly filled magnetic coating film, consolidation kneading is performed at a high solid content concentration, and a dilution step for sending to a final sand mill dispersion step is performed in a continuous twin-screw kneader. It is disclosed that the steps are performed step by step. This is because the kneaded material subjected to consolidation kneading at a high solid content concentration does not disperse even in the sand milling process unless it is properly diluted, leaving hard aggregates. As described above, the technology disclosed in these documents relates to a technology relating to a dilution site next to a kneading site in a continuous twin-screw kneader. Is completely different from the technique of adding. Further, in these documents, a magnetic powder having a specific surface area of 45 m ² / g is used, and the ultrafine magnetic powder having an average particle diameter in the range of 10 to 65 nm targeted by the present invention (the specific surface area is approximately This technique is intended for magnetic powders having a particle diameter much larger than 60 m ² / g), and is insufficient for highly filling and highly dispersing the ultrafine magnetic powder as in the present invention. Patent Document 3 discloses a continuous twin-screw kneader having a configuration in which a magnetic powder inlet and a resin liquid inlet are provided in a transport unit (screw part). Although similar in constitution, in this document, high-speed stirring mixing in which the magnetic powder contains at least a solvent and is wet before entering the kneading step of the continuous twin-screw kneader, which is an essential component of the present invention, is performed. The machine process is not a constituent element of the invention. For this reason, it is inevitable that the material supply section of the continuous twin-screw kneader requires an inlet for charging the magnetic powder and the resin liquid. The buffering action of the resin liquid at the kneading portion, which is an object of the present invention, which will be described later, does not work. In addition, since there is no high-speed stirring mixer step in which the magnetic powder is wetted with at least a solvent before entering the kneading step, the present invention is directed to ultrafine magnetic powder having an average particle diameter in the range of 10 to 65 nm. However, kneading cannot be performed sufficiently, and it is difficult to provide a high-density magnetic recording medium aimed at by the present invention, which is different from the present invention.
[0024]
FIG. 1 shows the configuration of a continuous twin-screw kneader used in producing a magnetic paint in the present invention. The continuous twin-screw kneader includes a wet magnetic powder supply unit 1, a resin liquid injection unit 2, diluting solvent injection units 3 to 5, a paint outlet 6, a rotating shaft 7, a screw 8, a paddle 9 And barrels 10 to 20. Of these, the portion where the barrels 10 to 11 are arranged is the transport site, the portion where the barrels 12 to 15 are arranged is the kneading site, the portion where the barrels 16 to 17 are arranged is the kneading dilution site, and the portion where the barrels 18 to 20 are arranged is the dilution site. Part.
[0025]
In the present invention, for the continuous twin-screw kneader, for example, KEX-30, KEX-40, KEX-50, KEX-65, KEX-80 manufactured by Kurimoto Iron Works, TEX30αII, TEX44αII, TEX65αII manufactured by Japan Steel Works, Ltd. , TEX77αII, TEX90αII, etc. can be used.
[0026]
As described above, in order to obtain a magnetic recording medium with high resolution and high S / N, the average particle size of the magnetic powder is preferably in the range of 10 nm to 65 nm, but a high-speed stirring mixer and a continuous twin-screw kneader are preferred. However, in the conventional paint production process using the above, the performance of the magnetic powder could not be sufficiently exhibited, and the resolution and S / N of the obtained medium were conversely reduced. The reason is that the magnetic powder in the present invention is fine particles, so even if the magnetic powder is mixed in advance with a high-speed stirring mixer, the resin is not coated even to single particles, and the magnetic powder is in a state of being aggregated. When a high shearing force is applied suddenly at the kneading site of the continuous twin-screw kneading machine, which is the next step, the magnetic powder not coated with the resin is further agglomerated. This is because these aggregates cannot be dispersed even in the subsequent dispersing step using a fine media rotating dispersing device such as a sand mill.
[0027]
Therefore, the present inventors have conducted intensive studies on a manufacturing method in which fine particles having an average particle diameter in the range of 10 to 65 nm are highly filled in order to maximize the magnetic energy and are highly dispersed. In obtaining the magnetic paint, the magnetic paint components are mixed at least with a high-speed stirring mixer, and the obtained wet magnetic powder is kneaded from the resin liquid injection unit 2 in a continuous twin-screw kneader at a stage before the kneading is started. At a certain transport site, a resin liquid containing a resin solid content of 0 to 15 parts by weight, more preferably 2.0 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder is added to form a kneaded paste, whereby the agglomeration described above is obtained. No phenomenon occurred, and high dispersion and high filling by high shearing force were found to be possible. This mechanism is considered as follows. When the resin liquid is added at the transport site, the wet magnetic powder is wrapped by the resin liquid added at the transport site, and even when a high shear force is applied in this state, the wet magnetic powder wraps around the wet magnetic powder. Since the resin liquid acts as a buffer, local energy is not directly applied to the magnetic powder. It is presumed that this prevents the magnetic powder from aggregating with each other, and the magnetic powder gradually becomes highly dispersed and filled in a state of being wrapped in the resin liquid. If the resin solid content in the resin liquid exceeds 15 parts by weight, the output will decrease because the ratio of the magnetic powder in the magnetic layer becomes relatively small. In addition, the resin liquid added at the transport site is preferably a polyurethane resin liquid, and the solid content concentration of the resin liquid is preferably 0 to 40% by weight.
[0028]
Next, the components of the magnetic recording medium of the present invention will be described in more detail.
<Non-magnetic support>
The thickness of the nonmagnetic support varies depending on the application, but preferably the thickness is 2.0 to 7.0 μm. It is more preferably from 2.5 to 5.0 μm, most preferably from 3.0 to 4.0 μm. When the non-magnetic support having a thickness in this range is used, if the thickness is less than 2.0 μm, it is difficult to form a film, and the tape strength is reduced. If the thickness exceeds 7.0 μm, the total thickness of the tape is increased. This is because the recording capacity per hit becomes smaller.
[0029]
The longitudinal Young's modulus of the non-magnetic support used in the present invention is preferably 6.8 GPa (700 kg / mm ² ) or more, more preferably 8.8 GPa (900 kg / mm ² ) or more. The reason why the non-magnetic support preferably has a Young's modulus in the longitudinal direction of 6.8 GPa (700 kg / mm ² ) or more is that when the Young's modulus in the longitudinal direction is less than 6.8 GPa (700 kg / mm ² ), the tape running becomes unstable. That's why. In the helical scan type, the specific ratio of Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.60 to 0.80. The ratio of the Young's modulus in the longitudinal direction / the Young's modulus in the width direction is more preferably in the range of 0.65 to 0.75. The specific range of the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.60 to 0.80. The mechanism is unknown at present if the Young's modulus is less than 0.60 or exceeds 0.80. This is because the output variation (flatness) between the entry side and the exit side of the track of the magnetic head becomes large. This variation becomes minimum when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.70. Further, in the linear recording type, the ratio of the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.70 to 1.30, although the reason is not clear. Resin films satisfying such characteristics include a biaxially stretched polyethylene terephthalate film, a polyethylene naphthalate film, an aromatic polyamide film, and an aromatic polyimide film.
[0030]
<Undercoat layer>
The thickness of the undercoat layer is preferably in the range of 0.2 to 2.2 μm. This range is preferable because if it is less than 0.2, the supply of the lubricant to the magnetic layer becomes insufficient, and the effect of smoothing the magnetic layer becomes small.
[0031]
Carbon black is added to the undercoat layer to improve conductivity, and iron oxide is added to control the rigidity of the tape. The undercoat layer contains 15 to 35% by weight of carbon black having an average particle diameter of 10 to 100 nm based on the weight of all inorganic powders in the undercoat layer, and has an average major axis diameter of 0.05 to 0.20 μm, It is preferable to contain 35 to 83% by weight of nonmagnetic iron oxide having a short axis diameter of 5 to 200 nm, because the thickness unevenness of the magnetic layer formed on a wet-on-wet and dried by far-infrared radiation is reduced. . The nonmagnetic iron oxide is usually acicular, but when granular or amorphous nonmagnetic iron oxide is used, iron oxide having an average particle diameter of 5 to 200 nm is preferable.
[0032]
It is preferable to add carbon black or nonmagnetic iron oxide to the undercoat layer. As carbon black (CB) to be added to the undercoat layer, acetylene black, furnace black, thermal black and the like can be used. Those having an average particle diameter of 5 to 200 nm are used, and those having an average particle diameter of 10 to 100 nm are preferred. This range is preferable because, since the carbon black has a structure, it is difficult to disperse CB when the average particle diameter is 10 nm or less, and the smoothness is deteriorated when the average particle diameter is 100 nm or more. The amount of CB to be added varies depending on the particle diameter of CB, but is preferably 15 to 35% by weight based on the weight of the entire inorganic powder in the undercoat layer. This range is preferable because the effect of improving conductivity is poor when the amount is less than 15% by weight, and the effect is saturated when the amount exceeds 35% by weight. It is more preferable to use CB having a particle size of 15 to 80 nm by 15 to 35% by weight, and it is more preferable to use CB having a particle size of 20 to 50 nm by 20 to 30% by weight. By adding carbon black having such a particle diameter and amount, the electric resistance is reduced, the occurrence of electrostatic noise and the unevenness of tape running are reduced, and the thickness unevenness of the magnetic layer dried by far infrared rays is also reduced.
[0033]
In addition, as the nonmagnetic iron oxide to be added to the undercoat layer, in the case of a needle shape, those having an average major axis diameter of 0.05 to 0.20 μm and an average minor axis diameter of 5 to 200 nm are preferable, and are granular or amorphous. In this case, the average particle size is preferably 5 to 200 nm. Note that a needle-like material is more preferable because the orientation of the magnetic layer is improved. The addition amount is preferably from 35 to 83% by weight based on the weight of all the inorganic powders in the undercoat layer. The average particle diameter in this range (short axis diameter in the case of needle shape) is preferable. If the average particle diameter is less than 5 nm, uniform dispersion is difficult, and if it exceeds 200 nm, unevenness at the interface between the undercoat layer and the magnetic layer increases. That's why. The addition amount in this range is preferable because if it is less than 35% by weight, the effect of improving the coating film strength is small, and if it exceeds 83% by weight, the coating film strength decreases. Further, as a result of examining the Young's modulus of the coating layer composed of the undercoat layer and the magnetic layer, the Young's modulus of the coating layer also has an optimum range, and the Young's modulus of the coating layer is in the longitudinal direction and the width direction of the nonmagnetic support. When the average value of the Young's modulus is in the range of 40 to 200%, the durability of the tape is large, the touch between the tape and the head is improved, and the variation in output from the entry side to the exit side of the track of the magnetic head (flat) Ness) was found to be small. A range of 50 to 150% is more preferable, and a range of 60 to 120% is still more preferable. This range is preferable because if it is less than 40%, the durability of the coating film becomes small, and if it exceeds 200%, the touch between the tape and the head becomes poor. The Young's modulus of the coating layer composed of the undercoat layer and the magnetic layer is controlled by a control method based on calendar conditions.
[0034]
Further, the Young's modulus of the undercoat layer is preferably 80 to 99% of the Young's modulus of the magnetic layer. The reason why the Young's modulus of the undercoat layer is preferably lower than that of the magnetic layer is that the undercoat layer acts as a kind of cushion.
[0035]
<Lubricant>
Lubricants having different roles are used for the coating layer composed of the undercoat layer and the magnetic layer. When the undercoat layer contains 0.5 to 4.0% by weight of higher fatty acid and 0.2 to 3.0% by weight of higher fatty acid ester with respect to the whole powder, friction with the head is obtained. This is preferable because the coefficient becomes small. When the higher fatty acid is added in this range, the effect of reducing the coefficient of friction is small at less than 0.5% by weight, and when it exceeds 4.0% by weight, the undercoat layer is plasticized and the toughness is lost. Further, it is preferable that the ester of higher fatty acid in this range is added. When the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and when the amount exceeds 3.0% by weight, the amount of transfer to the magnetic layer is too large. This causes side effects such as sticking of the head.
[0036]
When the magnetic layer contains 0.5 to 3.0% by weight of a fatty acid amide and 0.2 to 3.0% by weight of an ester of a higher fatty acid with respect to the ferromagnetic powder, friction when the tape runs is reduced. This is preferable because the coefficient becomes small. When the fatty acid amide in this range is preferable, if it is less than 0.5% by weight, direct contact at the head / magnetic layer interface easily occurs, and the effect of preventing seizure is small. If it exceeds 3.0% by weight, it bleeds out and drops. Out and other defects occur. Amides such as palmitic acid and stearic acid can be used as the fatty acid amide. Further, the reason why the ester of higher fatty acid in the above range is preferably added is that if less than 0.2% by weight, the effect of lowering the friction coefficient is small, and if it exceeds 3.0% by weight, there are side effects such as sticking to the head. Note that this does not exclude mutual movement between the lubricant of the magnetic layer and the lubricant of the undercoat layer.
[0037]
<Magnetic layer>
As the binder resin used for the magnetic layer (the same applies to the undercoat layer), vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer Resin, at least one selected from cellulosic resins such as vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, nitrocellulose resin, and polyurethane resin Is mentioned. Among them, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Examples of the polyurethane resin include a polyester polyurethane resin, a polyether polyurethane resin, a polyether polyester polyurethane resin, a polycarbonate polyurethane resin, and a polyester polycarbonate polyurethane resin.
[0038]
-COOH as a functional _{group, -SO 3 M, -OSO 3 M} , -P = O (OM) 3, -O-P = O (OM) 2 [M represents a hydrogen atom, an alkali metal base or an amine salt], - OH, -NR'R ", -N ⁺ R '" R ""R'"" [R ', R ", R'", R "", R '"'' Is a hydrogen or hydrocarbon group], and a resin such as a urethane resin comprising a polymer having an epoxy group is used. The reason for using such a resin is to improve the dispersibility of the magnetic powder and the like as described above. When used in combination of two or more resins are preferably match the polarity of the functional groups, among them the combination of each other -SO 3 _M group.
[0039]
These resins are used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of the ferromagnetic powder. In particular, it is most preferable to use 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin in combination.
[0040]
It is desirable to use a thermosetting cross-linking agent that bonds to a functional group or the like contained in the resin and cross-links with these resins. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are generally used in a proportion of 10 to 50 parts by weight based on 100 parts by weight of the resin. More preferably, it is 15 to 35 parts by weight.
[0041]
Conventionally known abrasives can be added to the magnetic layer. Examples of these abrasives include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, Artificial diamonds, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride, etc., mainly having a Mohs hardness of 6 or more are used alone or in combination. Among them, alumina has high hardness and a small amount is added. The amount is particularly preferable because the head cleaning effect is excellent. As the particle diameter of the abrasive, in a magnetic layer as thin as 0.01 to 0.1 μm, it is usually preferable to set the average particle diameter to 0.002 to 0.15 μm, and the average particle diameter to 0.005 to 0.10 μm Is more preferred. The addition amount is preferably 5 to 20% by weight based on the ferromagnetic powder. More preferably, it is 8 to 18% by weight.
[0042]
Further, conventionally known carbon black (CB) can be added to the magnetic layer of the present invention for the purpose of improving conductivity and surface lubricity. Examples of these carbon blacks include acetylene black, furnace black, and thermal black. Black or the like can be used. Those having an average particle diameter of 5 to 200 nm are used, and those having an average particle diameter of 10 to 100 nm are preferred. This range is preferable because when the average particle diameter is 5 nm or less, dispersion of carbon black is difficult, and when the average particle diameter is 200 nm or more, it is necessary to add a large amount of carbon black, and in any case, the surface becomes rough and the output decreases. It is because it causes. The addition amount is preferably 0.2 to 5% by weight based on the ferromagnetic powder. More preferably, it is 0.5 to 4% by weight.
[0043]
<Back coat layer>
A back coat layer is provided on the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the nonmagnetic support constituting the magnetic recording medium of the present invention for the purpose of improving running properties and the like. Can be. The thickness of the back coat layer is preferably from 0.2 to 0.8 μm. The reason why this range is good is that if the thickness is less than 0.2 μm, the effect of improving the running property is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the storage capacity per roll becomes small. As carbon black (CB), acetylene black, furnace black, thermal black, and the like can be used. Usually, small particle size carbon black and large particle size carbon black are used. As the small particle size carbon black, those having an average particle diameter of 5 to 200 nm are used, and those having an average particle diameter of 10 to 100 nm are more preferable. This range is more preferable because when the average particle diameter is 10 nm or less, dispersion of carbon black is difficult, and when the average particle diameter is 100 nm or more, it is necessary to add a large amount of carbon black, and in any case, the surface is rough. This is because it causes set-off (emboss) to the magnetic layer. If a large particle size carbon black having an average particle size of 300 to 400 nm is used in an amount of 5 to 15% by weight of the small particle size carbon black as the large particle size carbon black, the surface is not roughened, and the effect of improving the running property is increased. The total added amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight, more preferably 70 to 95% by weight, based on the total weight of the inorganic powder in the back coat layer. The surface roughness Ra is preferably from 3 to 8 nm, more preferably from 4 to 7 nm.
[0044]
Further, it is preferable to add iron oxide having an average particle diameter of 0.05 to 0.6 μm to the back coat layer, and more preferably 0.08 to 0.5 μm, for the purpose of improving the strength. The addition amount is preferably from 2 to 40% by weight, more preferably from 5 to 30% by weight, based on the total weight of the inorganic powder in the back coat layer. Further, when alumina having an average particle diameter of 0.1 to 0.6 μm is added in an amount of 0.5 to 5% by weight based on the total weight of the inorganic powder in the back coat layer, the strength of the back coat layer is further improved.
[0045]
As the binder resin used for the back coat layer, the same binder resin used for the magnetic layer and the undercoat layer described above can be used. Among them, a cellulose resin and a polyurethane resin are used in order to reduce the friction coefficient and improve the running property. It is preferable to use a composite resin in combination. The content of the binder is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight based on 100 parts by weight of the total amount of the carbon black and the inorganic nonmagnetic powder. And more preferably 70 to 110 parts by weight. The reason why the above range is preferable is that when the amount is less than 50 parts by weight, the strength of the back coat layer is insufficient, and when it exceeds 120 parts by weight, the friction coefficient tends to be high. It is preferable to use 30 to 70 parts by weight of the cellulose resin and 20 to 50 parts by weight of the polyurethane resin. In order to further cure the binder, it is preferable to use a crosslinking agent such as a polyisocyanate compound.
[0046]
For the back coat layer, the same crosslinking agent as that used for the magnetic layer and the undercoat layer described above is used. The amount of the crosslinking agent is usually 10 to 50 parts by weight, preferably 10 to 35 parts by weight, more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder. The above range is preferable because the coating strength of the back coat layer tends to be weak when the content is less than 10 parts by weight, and the dynamic friction coefficient against SUS increases when the content exceeds 35 parts by weight.
[0047]
<Others>
For example, if the above-described magnetic recording medium (magnetic tape) is wound around one reel, and this is housed in a case main body to produce a magnetic tape cartridge, the capacity per one roll is large and the MR reproducing head is used. It is possible to realize a magnetic tape cartridge having a high reproduction output and a high S / N ratio and suitable as a backup tape for a computer or a hard disk drive.
[0048]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. The parts in Examples and Comparative Examples are parts by weight.
Example 1
≪Undercoat paint ingredients≫
(1)
-68 parts of iron oxide powder (average particle diameter: 0.11 x 0.02 m)-8 parts of alumina (alpha conversion: 50%, average particle diameter: 0.07 m)-24 parts of carbon black (particle diameter: 25 nm) - 2 parts vinyl chloride copolymer 8.8 parts of stearic acid (containing _-SO 3 Na group: 0.7 × 10 ^{- 4} equivalents / g)
・ 4.4 parts of polyester polyurethane resin (Tg: 40 ° C., containing —SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
-1 part of butyl stearate-70 parts of cyclohexanone-50 parts of methyl ethyl ketone-20 parts of toluene (3)
1.4 parts of polyisocyanate 10 parts of cyclohexanone 15 parts of methyl ethyl ketone 10 parts of toluene
≪Magnetic paint ingredients≫
(1) Kneading and dilution process / ferromagnetic iron-based metal powder (magnetic powder)
(Co / Fe: 24 at%,
Y / (Fe + Co): 7.9 at%,
Al / (Fe + Co): 4.7 wt%,
σs: 120 A · m ² / kg (120 emu / g),
Hc: 175 kA / m (2190 Oe),
(pH: 9.5, average particle diameter: 60 nm)
・ Vinyl chloride-hydroxypropyl acrylate copolymer (PVC)
(Containing _-SO 3 Na group: 0.7 × 10 ^{- 4} equivalents / g)
・ Polyester polyurethane resin (PU)
(Contains -SO ₃ Na group: 1.0 × 10 ⁻⁴ eq / g)
・ Α-alumina (average particle size: 0.07 μm) (alumina)
・ Carbon black (CB)
(Average particle diameter: 75 nm, DBP oil absorption: 72 cc / 100 g)
・ Methyl acid phosphate (MAP)
・ Palmitic acid amide (PA)
・ N-butyl stearate (SB)
・ Tetrahydrofuran ・ Cyclohexanone ・ Methyl ethyl ketone ・ Toluene (2) compounding process ・ Polyisocyanate (PI)
・ Cyclohexanone [0050]
After kneading (1) in a batch type kneader in the above-mentioned undercoat paint component, (2) was added, and the mixture was stirred, followed by dispersion treatment with a sand mill with a residence time of 60 minutes, and (3) was added thereto, followed by stirring and filtration. After that, a paint for an undercoat layer was obtained.
[0051]
Separately, a predetermined amount of the above-mentioned magnetic paint component (1) is previously stirred and mixed at a high speed, and the mixed powder is kneaded by a continuous twin-screw kneader, and the residence time is set to 45 minutes by a sand mill. The resultant was dispersed, and the magnetic coating component (2) was added thereto. The mixture was stirred and filtered to obtain a magnetic coating.
[0052]
Table 1 shows the specific composition.
Mixing and wetting treatment is performed at a blade peripheral speed of 20 m / s for 30 minutes by a Henschel mixer manufactured by Mitsui Mining with the stirring composition shown in Table 1. The obtained wet magnetic powder is put into a continuous twin-screw kneader from the wet magnetic powder supply unit 1, and 5 parts (30% solution) of the polyester polyurethane resin solution is injected from the resin liquid injection unit 2 connected to the transport site. Knead. Hereinafter, the solvent was continuously injected from the injection units 3 to 5 and kneaded and diluted to obtain a paste having a solid content of 50 parts. Then, after adding palmitic acid amide and n-butyl stearate to dilute to a solid concentration of 35 parts, the mixture was dispersed in a sand mill with a residence time of 45 minutes, and the magnetic coating component (2) was added thereto. Paint.
[0053]
The above undercoat paint is coated on a non-magnetic support (base film) composed of an aromatic polyamide film (thickness: 3.9 μm, MD = 11 GPa, MD / TD = 0.70, trade name: MICRON, manufactured by Toray) The magnetic coating is applied so that the thickness after drying and calendering becomes 1.1 μm, and the magnetic coating is magnetically oriented on this undercoating layer, and the thickness of the magnetic layer after drying and calendering is 0.13 μm. Was applied wet-on-wet, and after a magnetic field orientation treatment, dried using a dryer and far-infrared rays to obtain a magnetic sheet. In the magnetic field orientation treatment, an NN counter magnet (5 kG) was installed before the dryer, and two NN counter magnets (5 kG) were placed at intervals of 50 cm from 75 cm in front of the finger erosion and drying position of the coating film in the dryer. We set up and went. The coating speed was 100 m / min.
[0054]
塗料 Paint component for back coat layer≫
・ 80 parts of carbon black (average particle diameter: 25 nm) ・ 10 parts of carbon black (average particle diameter: 370 nm) ・ 10 parts of iron oxide (average particle diameter: 0.4 μm) ・ 45 parts of nitrocellulose ・ Polyurethane resin (SO ₃ Na) 30 parts cyclohexanone 260 parts Methyl ethyl ketone 525 parts Toluene 260 parts After the above-mentioned coating composition for a backcoat layer is dispersed in a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate is added to prepare a coating for a backcoat layer. After filtration, the magnetic sheet prepared above was coated on the opposite side of the magnetic layer so as to have a thickness of 0.5 μm after drying and calendering, and dried.
[0055]
The magnetic sheet thus obtained was subjected to mirror finishing at a temperature of 100 ° C. and a linear pressure of 196 kN / m using a seven-stage calender made of metal rolls. After aging for a time, it was cut into a 1/2 inch width, and the magnetic layer surface was subjected to post-processing such as lapping tape polishing, blade polishing and surface wiping while running at 200 m / min to produce a magnetic tape. At this time, K10000 was used for the wrapping tape, a carbide blade was used for the blade, and Toraysee (trade name) manufactured by Toray was used for wiping the surface, and the treatment was performed with a running tension of 30 g. The magnetic tape obtained as described above was assembled in a cartridge to produce a computer tape.
[0056]
Examples 2 to 4:
Computer tapes of Examples 2 to 4 were produced in the same manner as in Example 1 except that the production composition of the magnetic paint was changed to the conditions shown in Table 1.
[0057]
Example 5:
A computer tape of Example 5 was produced in the same manner as in Example 1, except that the production composition of the magnetic paint was changed to the conditions shown in Table 1 and the magnetic powder was changed to the following conditions.
・ Ferromagnetic iron-based metal powder (magnetic powder)
(Co / Fe: 24 at%,
Y / (Fe + Co): 12.7 at%,
Al / (Fe + Co): 4.7 wt%,
σs: 116 A · m ² / kg (116 emu / g),
Hc: 170 kA / m (2130 Oe),
(pH: 9.5, average particle diameter: 45 nm)
[0058]
Example 6:
A computer tape of Example 6 was produced in the same manner as in Example 1 except that the production composition of the magnetic paint was changed to the conditions shown in Table 1 and the magnetic powder was changed to the following conditions.
・ Ne-Fe-B based metal magnetic powder (magnetic powder)
(Nd / Fe: 2.4 at%,
B / Fe: 9.1 at%,
σs: 132 A · m ² / kg (132 emu / g),
Hc = 192 kA / m (2400 Oe),
(Average particle diameter: 25 nm)
[0059]
Comparative Examples 1-3
Computer tapes of Comparative Examples 1 to 3 were produced in the same manner as in Example 1 except that the production composition of the magnetic paint was changed to the conditions shown in Table 1.
[0060]
Comparative Example 4:
A computer tape of Comparative Example 4 was produced in the same manner as in Example 1 except that the production composition of the magnetic paint was changed to the conditions shown in Table 1. In Comparative Example 4, high-speed stirring and mixing were performed at a blade peripheral speed of 20 m / s for 10 minutes without a solvent.
[0061]
The evaluation was performed as follows.
<Surface roughness of magnetic layer>
Scan Length was measured at 5.0 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer New View 5000 manufactured by ZYGO. The measurement visual field is 350 μm × 260 μm. The center line average surface roughness of the magnetic layer was determined as Ra.
[0062]
<Playback output and output versus noise>
The reproduction output and output-to-noise (S / N) were determined by recording (recording wavelength 0.37 μm) and reproducing using an LTO drive modified for a thin tape. The reproduction output and the output-to-noise were represented by relative values (dB) with respect to the tape of Comparative Example 1.
[0063]
<Resolution>
Using the LTO modified drive described above, the reproduction output at the recording wavelength of 0.37 μm was taken as the HF output, the reproduction output at the recording wavelength of 1.48 μm was taken as the LF output, and the ratio of these (HF output / LF output) was taken as the resolution. The measured values were expressed as relative values (%) based on the tape of Comparative Example 1.
Table 1 shows the above results.
[0064]
[Table 1]

[0065]
Ra: center line average surface roughness Ra of the magnetic layer surface
S / N: output versus noise
As is clear from Table 1, the computer tapes (magnetic recording media) according to Examples 1 to 6 of the present invention have better electromagnetic conversion characteristics than the computer tapes according to Comparative Examples 1 to 4. I have. In particular, it can be seen that the reproduction output and the output-to-noise (S / N) ratio are high when an MR head (reproduction head using a magnetoresistive element) is used.
[0067]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a magnetic recording medium having high reproduction output, S / N, etc., and excellent in electromagnetic conversion characteristics. This makes it possible to realize a backup tape for a computer or the like that can handle a large capacity approaching, for example, 1 TB.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a continuous twin-screw kneader used in the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 Wet magnetic powder supply unit 2 Resin liquid injection units 3, 4, 5 Diluent solvent injection unit 6 Paint outlet 7 Rotary shaft 8 Screw 9 Paddles 10, 11 Barrel transfer parts 12, 13, 14, 15 Barrel kneading parts 16 , 17 barrel kneading dilution site 18, 19, 20 barrel dilution site

Claims (2)

On one surface of the nonmagnetic support, an undercoat layer containing a nonmagnetic powder and a binder resin, a magnetic layer containing a magnetic powder and a binder resin on the undercoat layer, and the other of the nonmagnetic support A magnetic recording medium having a back coat layer containing a non-magnetic powder and a binder resin on a surface thereof, wherein the average particle diameter of the magnetic powder is in the range of 10 to 65 nm, and the thickness of the magnetic layer is 0.01 The magnetic coating used for forming the magnetic layer is at least a step in which the magnetic powder is wetted with at least a solvent in a high-speed stirring mixer; And a method of mixing with a resin liquid (including the case of only a solvent) at a transport portion of a twin-screw kneading machine and then sending the mixed solution to a kneading portion, and a method of manufacturing the same. . The addition amount of the resin liquid to be added at the transfer site in the continuous twin-screw kneader is in the range of 0 to 15 parts by weight based on 100 parts by weight of the magnetic powder in terms of resin solid content, and is added by a high-speed stirring mixer. 2. The magnetic recording medium according to claim 1, wherein the total amount of the solid resin to be added and the solid resin to be added at the transport site is 2 to 25 parts by weight.

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