JP2005222598A - Magnetic tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a magnetic tape using ultrafine particle magnetic powder and having excellent high recording density characteristics and satisfactory durability. <P>SOLUTION: In the magnetic tape wherein a magnetic layer comprising magnetic powder constituted of iron as a main component is formed on one surface of a non-magnetic substrate via an undercoat layer comprising non-magnetic powder and a back coat layer comprising non-magnetic powder is formed on the other surface, the magnetic powder constituted of iron as the main component has ≥5 nm and <60 nm of average particle diameter, Y and Zr are contained in the magnetic layer, and contents of these elements by ESCA analysis are represented by that Y/Fe is 40 to 140at% and Zr/Fe is 2 to 15at%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a coating type magnetic tape excellent in high recording density characteristics and durability.

Magnetic tape has various uses such as audio tape, video tape, and computer tape. Especially in the field of data backup tape, recording capacity of 200 GB or more per volume is accompanied by the increase in capacity of a hard disk to be backed up. Has been commercialized. In the future, large-capacity backup tapes exceeding 1 TB have been proposed, and it is essential to increase the recording density.

When manufacturing magnetic tapes corresponding to such high recording density, in order to cope with the short wavelength of the recording signal, the magnetic powder is made finer, the film is densely packed, and the coating is smoothed. Advanced techniques relating to thinning of the magnetic layer are used.

Also, in order to increase the recording density, the recording signal has been shortened and the track pitch has been narrowed, and a system that also uses a servo track has been introduced so that the reproducing head can accurately trace the track. doing.

Due to the thinning of the magnetic layer and the narrowing of the track pitch, high sensitivity of the magnetic head has been required. Recently, a magnetoresistive (MR) type reproducing head has been used. This type of head is often used in recent computer drives, and is usually used in combination with a recording head (magnetic induction type). For this reason, the design of the magnetic coating layer is preferably matched to the conventional head due to the difference in material and shape.

As the magnetic powder becomes finer, the prevention of sintering during the production of the magnetic powder and the improvement of the durability of the magnetic coating film have been further studied. As the magnetic layer is made thinner, it is necessary to study inorganic and organic powder particles added to the magnetic layer.

As the magnetic powder, a metal magnetic powder capable of obtaining a high coercive force and a high magnetization amount is used, but in order to prevent sintering and improve corrosion resistance, rare earth elements are used in addition to Al and Si (for example, And Patent Documents 1 to 4).

In order to improve the durability of the magnetic coating film, inorganic particles having a Mohs hardness of 4 or more have been added, but in recent years, from zirconia beads, which is a dispersion medium for dispersing fine magnetic powder, It has been proposed to use wear powder to improve durability and to add Zr-containing fine powder (for example, Patent Documents 5 to 8).

JP-A-8-102046 JP 2000-11354 A JP 2003-119503 A JP 2003-296915 A Japanese Patent No. 2628186 JP 2000-215439 A JP 2001-222812 A JP 2003-59031 A

However, in these conventional techniques, sufficient durability could not be obtained for a magnetic tape using an ultrafine magnetic powder having an average particle diameter of less than 60 nm.

In light of such circumstances, an object of the present invention is to provide a magnetic tape that uses ultrafine magnetic powder and has excellent high recording density characteristics and good durability.

As a result of intensive studies to achieve the above object, the inventors have formed a magnetic layer on one surface of a nonmagnetic support through an undercoat layer, and formed a backcoat layer on the other surface. In the tape, a magnetic powder containing iron as a main constituent element is used as a magnetic powder to be included in the magnetic layer, and the magnetic powder has ultrafine particles having a particle diameter of less than 60 nm, while a rare earth is contained in the magnetic layer containing the magnetic powder. When Zr derived from the wear powder of zirconia beads is included together with the element Y, and the content of these elements on the surface of the magnetic layer is within a specific range with respect to the iron constituting the magnetic powder. In addition, the inventors have found that a magnetic tape excellent in high recording density characteristics and excellent in durability can be obtained, and has completed the present invention.

In the present invention, a magnetic layer containing magnetic powder containing iron as a main constituent element is formed on one surface of a nonmagnetic support through an undercoat layer containing nonmagnetic powder, and the nonmagnetic powder is formed on the other surface. In the magnetic tape in which the backcoat layer containing is formed, the average particle size of the magnetic powder containing iron as a main constituent element is 5 nm or more and less than 60 nm, and Y and Zr are contained in the magnetic layer. The content of these elements by ESCA analysis is Y / Fe = 40 to 140 at% and Zr / Fe = 2 to 15 at%.

The present invention also relates to a magnetic tape having the above-described configuration in which the magnetic powder containing iron as a main constituent element includes Y as one of constituent elements other than iron, and the magnetic powder containing iron as the main constituent element is a ferromagnetic iron-based metal magnetic powder. Alternatively, the magnetic tape having the above-described configuration, which is an iron nitride-based magnetic powder, and the magnetic layer having the Zr-containing powder as particles having a particle diameter of less than 50 nm as the wear powder of zirconia beads in the magnetic layer. The magnetic tape of the said structure which is contained La and the content by ESCA analysis of this element is La / Fe = 1-30at%.

As described above, according to the present invention, the content of Y and Zr in the surface portion of the magnetic layer is set to Y / Fe = 40 to 140 at% and Zr / Fe = 2 to 15 at%, so that the average particle diameter is less than 60 nm. Even a magnetic tape using ultrafine magnetic powder containing iron as a main constituent element can provide a magnetic tape having excellent high recording density characteristics and good durability.

In order to cope with the recent increase in recording density, as described above, an ultrafine magnetic powder is used for the magnetic layer, and an MR type head is used for the reproducing head.

In order to prevent sintering during firing and reduction or to impart corrosion resistance to the magnetic powder containing iron as a main constituent element, a rare earth element typified by Y is deposited on the surface. The amount of rare earth element deposited and the uniformity of the thickness of the deposited film not only affect the sinterability and corrosion resistance, but also affect the durability of the magnetic coating film and the head wear resistance.

In particular, the MR type head has a unique design in which the MR element portion is slightly recessed in consideration of the head life because the MR element used is softer than the conventional induction type head. Yes. On the contrary, there is a problem that a powder falling component adheres from the magnetic tape at the time of use and causes a decrease in output.

As a result of detailed analysis of the tape adhering matter to the MR element portion, the present inventors have found that rare earth elements and Zr are contained in addition to iron (Fe). Therefore, as a result of examining various element configurations on the surface of the magnetic tape, it was found that the head contamination was reduced and the running durability was improved when the following mode was adopted.

Here, the elemental composition on the surface of the magnetic tape does not necessarily match the elemental composition of the entire magnetic layer. The present inventors have found for the first time that the elemental composition on the surface of the magnetic layer has a correlation with head contamination. The elemental analysis on the surface of the tape is preferably quantified by ESCA which can know the elemental structure at a depth of several tens of inches from the surface.

That is, the content of Y and Zr by this ESCA analysis is preferably Y / Fe = 40 to 140 at%, more preferably Y / Fe = 60 to 110 at%, and Y / Fe = 70 to 100 at%. % Is most preferred. Further, Zr / Fe = 2 to 15 at% is preferable, Zr / Fe = 3 to 13 at% is more preferable, and Zr / Fe = 4 to 11 at% is most preferable.

If the value of Y / Fe by ESCA analysis is less than 40 at%, the abrasiveness of the surface of the magnetic coating film may be reduced, or the amount of head contamination increases and the running durability decreases. On the other hand, if the value of Y / Fe exceeds 140 at%, the polishing property of the magnetic coating film surface becomes too large, and the head life is shortened, or the saturation magnetization amount of the magnetic powder is reduced and the output is lowered. .

Also, if the Zr / Fe value by ESCA analysis is less than 2 at%, the effect of reinforcing the magnetic coating film by the Zr-containing powder, which is the abrasion powder from the zirconia beads, may be reduced, or the amount of head dirt increases and the running Durability decreases. On the other hand, when the value of Zr / Fe exceeds 15 at%, the ratio of the magnetic powder in the coating film becomes relatively small, and the output decreases.

The particle size of the Zr-containing powder that is a wear powder from zirconia beads is preferably less than 50 nm, and more preferably 5 to 30 nm. The particle diameter is preferably within this range. When the particle diameter is 50 nm or more, the orientation of the magnetic powder particles having an axial ratio of 2 or more tends to be disturbed in the magnetic coating film. This is because when the granular magnetic material is less than 2, the filling properties of the magnetic particles tend to decrease.

In addition, when the particle diameter of the magnetic powder containing iron as a main constituent element is small, the present inventors desirably further include La in the magnetic layer, and the content of the above element by ESCA analysis is particularly preferable. It has been found that when La / Fe = 1-30 at%, more preferably when La / Fe = 5-20 at%, the amount of head contamination is further reduced.

If the La / Fe value by ESCA analysis is less than 1 at%, such an effect of La cannot be obtained. If the La / Fe value exceeds 30 at%, the abrasiveness of the magnetic coating film surface becomes too large and the head life is shortened. The effect of La increases as the magnetic powder becomes finer.

The value of Y / Fe by the above-mentioned ESCA analysis depends on the selection of the amount of Y to be deposited (contained) on the magnetic powder, the dispersion method of the magnetic paint, the dispersion conditions, and the addition of Y ₂ O ₃ fine powder. It can be controlled by the presence / absence and selection of the addition amount.

In addition, the Zr / Fe value and the particle size of the Zr-containing powder by the above ESCA analysis should be controlled by the selection of the dispersion method of the magnetic paint using zirconia beads and the dispersion conditions (particularly the particle size of zirconia beads). Can do.

Furthermore, the value of La / Fe by the above-mentioned ESCA analysis is determined by the selection of the amount of La deposited (contained) on the magnetic powder, the dispersion method of the magnetic paint, the dispersion conditions, and the addition of the La ₂ O ₃ fine powder. It can be controlled by the presence / absence and selection of the addition amount.

Here, the above findings of the present inventors will be described in more detail in comparison with Patent Documents 1 to 7 which are conventional techniques.

First, Patent Documents 1 to 4 disclose magnetic recording media using magnetic powder containing rare earth elements such as Y. The purpose of including rare earth elements in the magnetic powder is to control the shape of the magnetic powder, to prevent sintering during firing and reduction, to form a thin and dense oxide film, etc., to improve the SFD of the magnetic recording medium, to reduce noise, Corrosion resistance is added. These patent documents each disclose a preferable addition amount range of rare earth elements to be included in the magnetic powder, and propose a magnetic powder excellent in recording characteristics and corrosion resistance. However, there is no indication about the amount of rare earth element component on the surface of the magnetic layer of the magnetic recording medium obtained.

The present invention uses a magnetic powder containing a rare earth element as in Patent Documents 1 to 4 above, but the powder from the magnetic tape that adheres to the MR head surface when it is run by a recording / reproducing apparatus using an MR head. In order to reduce the amount of the falling component, the amount of Y / Fe on the surface of the magnetic layer is defined, which is clearly different from Patent Documents 1 to 4.

Patent Document 5 discloses a method for producing a magnetic coating using zirconia beads having a surface roughness of 1.5 S or less at the maximum height Rmax. However, it is not mentioned at all that the Zr-containing powder is mixed into the magnetic layer as the wear powder of the beads during the production, and the amount of Zr / Fe on the surface of the magnetic layer derived from this influences the contamination on the MR head surface. .

Further, Patent Document 6 discloses a magnetic recording medium having a Zr / Fe weight ratio of 0.01 to 2% as measured by fluorescent X-ray measurement of a magnetic layer. The value obtained by this measurement method indicates the elemental composition of the entire coating film, and is different from the elemental composition on the surface of the magnetic layer of the present invention. Further, when the Zr / Fe weight ratio shown in this document is converted into an atomic ratio, it becomes Zr / Fe = 0.006 to 1.2 at%, which is different from the Zr / Fe = 2 to 15 at% range of the present invention. .

Patent Document 7 discloses that the magnetic layer contains zirconia powder having an average primary particle size of 0.005 to 0.2 μm. However, it is not a wear powder from zirconia beads but a zirconia powder separately added, and there is no description about the amount of Zr / Fe on the surface of the magnetic layer, which is different from the present invention.

Patent Document 8 discloses a magnetic recording medium in which the intensity ratio of Zr to Fe is 0.001 to 0.1 when the magnetic layer is measured by fluorescent X-rays. It is presumed that there is a part overlapping with the present invention as the value of / Fe. However, the above measurement is the elemental composition of the entire magnetic layer, and does not necessarily indicate the elemental composition on the surface of the magnetic layer.

Further, the average particle size of the Zr-containing powder contained as the wear powder is preferably in the range of 0.01 to 1.0 μm, and more preferably in the range of 0.1 to 0.8 μm. Further, there is no description about the particle size of the Zr-containing powder contained in the magnetic layer of the magnetic recording medium, and it is not clear whether it is within the preferred range. In addition, in the examples, there is only data on magnetic recording media using barium ferrite magnetic powder, and no magnetic tape using magnetic powder containing iron as a main constituent element is shown.

Further, in this document, the zirconia beads used when dispersing the magnetic paint have a particle diameter of 1 mm. According to the study by the present inventors, such zirconia beads have a large wear powder size as described later. It becomes too much, and a favorable result is not obtained.

Next, with respect to the magnetic tape of the present invention having the above characteristics, a method for preparing a magnetic paint for forming the magnetic layer will be described in detail.

In the method for preparing a magnetic coating material, it is desirable to provide a mixing step, a kneading step and a dilution step before the dispersing step. Among these steps, in the mixing step, as a pre-step of the kneading step, the magnetic powder granules are crushed with a high-speed stirring mixer, and subsequently, phosphoric acid-based or sulfonic acid-based using a high-speed stirring mixer It is mixed with an organic acid or the like or a binder resin to perform surface treatment of the magnetic powder or mixing with the binder resin.

The high-speed stirring mixers mentioned above include gas blow-up type stirrers using rolling fluid effects such as Hosokawa Micron's Agromaster, Cyclomix and Mechano-Fusion Systems manufactured by the company, and axial mixers manufactured by Matsuyama Heavy Industries, Ltd. A rotary mixer, a Henschel mixer manufactured by Mitsui Mining Co., etc. can be used.

Next, in the kneading step, kneading is usually carried out by a continuous biaxial kneader in a state where the solid content concentration is 80 to 85% by weight and the ratio of the binder resin to the magnetic powder is 17 to 30% by weight. is there. In the dilution step, as a subsequent step of the above kneading step, kneading dilution is performed by adding at least one binder resin solution and / or solvent using a continuous twin-screw kneader or other diluting device. It is.

The continuous twin-screw kneader includes KEX-30, KEX-40, KEX-50, KEX-65, KEX-80 manufactured by Kurimoto Steel Works, TEX30α, TEX44α, TEX65α, TEX77α manufactured by Nippon Steel Works, TEX90α or the like can be used.

After passing through such a pre-process, it is used for the dispersion process. Although this dispersion | distribution process is as touching previously, solid content concentration before dispersion | distribution is 30 to 50 weight%, and a coating-material viscosity is 0.5 to 5.0 Pa.s (500 to 5,000 cP). preferable. In this dispersion step, a so-called media agitation type disperser typified by a sand mill is used, and dense and hard zirconia beads having a large specific gravity are used as the dispersion medium.

The zirconia beads are preferably those obtained by isostatic pressing at room temperature (CIP method) or isostatic pressing at high temperature (HIP method). Among them, zirconia beads by the HIP method are particularly preferable because the beads are not easily broken even when strong dispersion is performed with a sand mill or the like, which is close to the theoretical density, and wear is uniformly generated. Further, the crushing strength of zirconia beads is preferably high because it is necessary to uniformly wear beads having a small particle diameter. From this viewpoint, crushing strength is usually 15 to 60 kgf, particularly 20 to 50 kgf. It is preferable.

Zirconia materials include Y ₂ O ₃ —ZrO ₂ , CaO—ZrO ₂ , MgO—ZrO ₂ , stabilized zirconia (FSZ), and fine tetragonal crystals precipitated in cubic crystals of zirconia. Partially stabilized zirconia (PSZ) and zirconia reinforced ceramics (ZTC) in which tetragonal zirconia is dispersed with alumina, silicon nitride or the like are effective.

Examples of such commercially available zirconia beads include “Traceram” manufactured by Toray Industries, Inc. and “Zirconia Ball” manufactured by Nippon Chemical Ceramics Co., Ltd.

The zirconia beads preferably have a particle size of 0.05 to 0.5 mm, and more preferably 0.3 mm or less. The smaller the particle size of the zirconia beads, the larger the bead surface area. Therefore, the dispersion to the ultrafine magnetic powder is efficiently performed, and the particle size of the wear powder from the zirconia beads is preferably reduced.

In addition, when the particle diameter of the zirconia beads exceeds 0.5 mm, the size of the wear powder tends to increase. Therefore, it is preferable to adjust appropriately so as not to exceed the preferable range of the present invention. In order to improve the dispersion efficiency, the dispersion by the sand mill may be performed in combination with a sand mill filled with zirconia beads having different particle diameters.

In such a dispersion step, in order to set the Zr / Fe atomic ratio (at%) on the surface of the magnetic layer by the ESCA analysis to a value within a preferable range, stirring of the sand mill in the primary dispersion step using the zirconia beads as a dispersion medium. It is desirable to appropriately adjust the peripheral speed of the shaft in the range of 7 to 10 m / sec, the residence time of the magnetic paint in the range of 20 to 90 minutes, and the bead filling rate in the range of 60 to 85 vol% (apparent volume ratio). .

In the above dispersion step, the dispersion condition also affects the value of the Y / Fe atomic ratio (at%) of the magnetic layer surface by the ESCA analysis described above, and this value tends to decrease when the dispersion condition is hard. Therefore, it is preferable to prepare appropriately.

Further, an ultrasonic dispersion step may be provided during and / or after the sand mill dispersion step. By providing the ultrasonic dispersion step, the fluidity of the paint is improved and the uniformity of the thickness of the coating film is improved, which is preferable. The ultrasonic disperser preferably has a residence time of 0.1 to 10 seconds. A conventionally well-known thing can be used for an ultrasonic disperser.

In the present invention, the magnetic powder used for the preparation of the magnetic coating is a magnetic powder mainly composed of iron, and as a typical one, a ferromagnetic iron-based metal magnetic powder or an iron nitride-based magnetic powder is preferable. Used.

The average particle size of such magnetic powder is preferably in the range of 5 nm or more and less than 60 nm, and more preferably in the range of 10 to 40 nm. This range is preferable because when the average particle size is less than 5 nm, the surface energy of the particles becomes large and dispersion becomes difficult, and when the average particle size is 60 nm or more, noise increases.

The average particle diameter is obtained by measuring the maximum diameter of each particle (major axis diameter for needle-like powder) from a photograph taken with a transmission electron microscope (TEM) and calculating an average value of 100 particles.

The ferromagnetic iron-based metal magnetic powder may contain transition metals such as Mn, Zn, Ni, Cu, and Co as an alloy. Among these, Co and Ni are preferable, and Co is particularly preferable because it can improve saturation magnetization most. As a quantity of said transition metal element, it is preferable to set it as 5-50 at% with respect to iron, and it is more preferable to set it as 10-30 at%.

In order to prevent sintering, at least one rare earth element selected from yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium and the like may be included. Among these, when yttrium, cerium, neodymium, samarium, and terbium are used, the shape is favorably maintained, and a uniform ceramic layer is formed on the surface of the magnetic powder, which is preferable.

The amount of these rare earth elements is 0.2 to 25 atomic%, preferably 0.3 to 20 atomic%, and more preferably 0.5 to 15 atomic% with respect to iron. In the present invention, since Y (yttrium) is contained in the magnetic layer, it is desirable to contain yttrium in the magnetic powder within the above range. However, instead of or including Y in the magnetic powder, a powder made of an oxide of yttrium or the like may be added to the magnetic layer.

Known iron nitride magnetic powders can be used. The shape can be an indefinite shape such as a spherical shape or a cubic shape in addition to a needle shape. Regarding the particle diameter and specific surface area, in order to clear the required characteristics as a magnetic powder for magnetic recording, it is necessary to use limited production conditions for the magnetic powder (see Japanese Patent Application Laid-Open No. 2000-277311).

Such ferromagnetic iron-based metal magnetic powder and iron nitride-based magnetic powder may be used after being surface-treated with Al, Si, P, Y, Zr or an oxide thereof.

The coercive force of these magnetic powders is preferably 80 to 320 kA / m, and the saturation magnetization is preferably 80 to 200 A · m ² / kg (80 to 200 emu / g), and 100 to 180 A · m ² / kg (100 ~ 180 emu / g) is more preferred. These magnetic characteristics are measured values in an external magnetic field of 273.3 kA / m (16 kOe) with a sample vibration type magnetometer.

Further, BET specific surface area of these magnetic powders is preferably at least 35m ² / g, more preferably at least 40 m ² / g, most preferably at least 50 m ² / g. Usually, it should be 100 m ² / g or less.

In the present invention, the binder resin used for the preparation of the above magnetic coating material includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol. A polyurethane resin, at least one selected from a copolymer resin, a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and a cellulose resin such as nitrocellulose; And a combination of these.

Among these binder resins, 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 polyester polyurethane resin, polyether polyurethane resin, polyether polyester polyurethane resin, polycarbonate polyurethane resin, polyester polycarbonate polyurethane resin, and the like.

Such a binder resin has —COOH, —SO ₃ M, —OSO ₃ M, —P═O (OM) ₃ , —O—P═O (OM) ₂ [in these formulas, M Represents a hydrogen atom, an alkali metal base or an amine salt], —OH, —NR ¹ R ² , —N ⁺ R ³ R ⁴ R ⁵ [in these formulas, R ¹ , R ² , R ³ , R ⁴ , R ⁵ represents hydrogen or a hydrocarbon group], and those having an epoxy group are preferably used.

This is because the use of such a binder resin improves the dispersibility of magnetic powder and the like. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

These binder resins are usually used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the magnetic powder. In particular, when a vinyl chloride resin and a polyurethane resin are used in combination, it is 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 addition to these binder resins, it is preferable to use a thermosetting crosslinking agent that is bonded to a functional group contained in the binder resin and crosslinked.

Examples of such crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 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 such as are preferably used.

These crosslinking agents are usually used in a proportion of 1 to 30 parts by weight with respect to 100 parts by weight of the binder resin. More preferably, it is 5 to 20 parts by weight.

In addition, when a magnetic layer is formed on the undercoat layer by wet-on-wet, a certain amount of polyisocyanate is diffused and supplied from the undercoat paint. It is crosslinked to some extent.

Further, instead of the thermosetting binder resin described above, a radiation curable resin may be used. As the radiation curable resin, those obtained by modifying the thermosetting resin with acrylic to have a radiation-sensitive double bond, acrylic monomers, and acrylic oligomers are used.

Examples of the organic solvent used in the preparation of the magnetic coating in the present invention include ketone solvents such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetates such as ethyl acetate and butyl acetate. System solvents and the like. These organic solvents are used alone or in combination, and further mixed with toluene.

In the present invention, as the additive used for the preparation of the magnetic coating material, a conventionally known abrasive can be used as required in addition to the lubricant and dispersant described later.

As this abrasive, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, nitriding Boron or the like having a Mohs hardness of 6 or more is mainly used alone or in combination. The particle size of these abrasives is usually preferably 10 to 200 nm as an average particle size.

In addition, conventionally known carbon black may be added to the magnetic coating material for the purpose of improving conductivity and surface lubricity, if necessary. As carbon black, acetylene black, furnace black, thermal black, and the like can be used. Those having an average particle diameter of 10 to 100 nm are preferred. This range is preferable because when the average particle size is less than 10 nm, it is difficult to disperse carbon black. When the average particle size exceeds 100 nm, it is necessary to add a large amount of carbon black. Because it becomes. If necessary, two or more carbon blacks having different average particle diameters may be used.

In the present invention, together with the above magnetic powder and binder resin, an organic solvent, the above additive components, etc. are used, and these are dispersed by the above-described method to prepare a magnetic paint. In accordance with the law, a magnetic layer is formed on one side of a non-magnetic support through an undercoat layer containing non-magnetic powder and dried to form a magnetic layer on the other side. A coat layer is formed, and a magnetic tape is manufactured through a required processing step.

Here, the thickness of the magnetic layer is preferably 0.01 μm or more and 0.15 μm or less. This range is preferable because if the output is less than 0.01 μm, it is difficult to apply a uniform magnetic layer, and if it exceeds 0.15 μm, the resolution of the short wavelength signal is deteriorated. is there. In order to further improve the short wavelength recording characteristics, the thickness of the magnetic layer is more preferably 0.01 to 0.1 μm, most preferably 0.02 to 0.06 μm.

The coercive force of the magnetic layer is preferably 80 to 320 kA / m, more preferably 100 to 300 kA / m, and still more preferably 120 to 280 kA / m. This range is preferable because if the recording wavelength is shorter than 80 kA / m, the output is reduced due to demagnetization, and if it exceeds 320 kA / m, recording by the magnetic head becomes difficult.

Next, (1) a nonmagnetic support and (2) an undercoat layer will be described as the constituent elements of the present invention. The magnetic layer and undercoat layer usually contain (3) a lubricant and (4) a dispersant, and these additives will also be described. Further, (5) the configuration of the backcoat layer will also be described.

(1) Nonmagnetic support Although the thickness of a nonmagnetic support changes with uses, it is usually preferable that it is 1.5-11 micrometers, it is more preferable that it is 2-7 micrometers, and it is 2-5 micrometers. Is most preferred. Thicknesses in this range are preferred when the thickness is less than 1.5 μm, film formation becomes difficult, and the tape strength decreases. When the thickness exceeds 11 μm, the total thickness of the tape increases, and the recording capacity per tape roll. This is because becomes smaller.

The longitudinal Young's modulus of the nonmagnetic support, preferably 5.8GPa (590kg / mm ²⁾ or more, 7.1GPa (720kg / mm ²⁾ or more is more preferable. The reason why the Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 5.8 GPa or more is that the tape running becomes unstable when the Young's modulus in the longitudinal direction is less than 5.8 GPa.

In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction is preferably in the range of 0.6 to 0.8, and more preferably in the range of 0.65 to 0.75. The Young's modulus in the longitudinal direction / Young's modulus in the width direction is good when the range is less than 0.6 or more than 0.8. The mechanism is currently unknown, but from the entrance side of the magnetic head track. This is because the output variation (flatness) between the output sides increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.7.

In the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.7 to 1.3, although the reason is not clear.

The temperature expansion coefficient in the width direction of the nonmagnetic support is preferably −10 to 10 × 10 ⁻⁶ , and the humidity expansion coefficient is preferably 0 to 10 × 10 ⁻⁶ . The reason why this range is preferred is that if it is outside this range, off-track occurs due to changes in temperature and humidity, and the error rate increases.

Examples of the non-magnetic support that satisfies the above characteristics include a biaxially stretched polyethylene terephthalate film, a polyethylene naphthalate film, an aromatic polyamide film, and an aromatic polyimide film.

(2) Undercoat layer The thickness of the undercoat layer is preferably 0.2 μm or more and 1.5 μm or less, more preferably 1 μm or less, and even more preferably 0.8 μm or less. The reason why this range is preferable is that when the thickness is less than 0.2 μm, the effect of reducing the thickness unevenness of the magnetic layer and the effect of improving the durability are reduced, and when it exceeds 1.5 μm, the total thickness of the magnetic tape becomes too thick. This is because the recording capacity per tape roll is reduced. As the binder resin (or crosslinking agent) used for the undercoat layer and the coating solvent for forming the undercoat layer, the same materials as those for the magnetic layer are used.

Nonmagnetic powders used for the undercoat layer include titanium oxide, iron oxide, and aluminum oxide. Iron oxide alone or a mixed system of iron oxide and aluminum oxide is preferable. The particle shape of the non-magnetic powder may be any of spherical, plate-like, needle-like and spindle-like, but in the case of needle-like and spindle-like, the major axis length is usually 20 to 200 nm and the minor axis length is 5 to 200 nm. Are preferred.

In many cases, non-magnetic powder is used as a main component, and if necessary, carbon black having a particle size of 0.01 to 0.1 μm and aluminum oxide having a particle size of 0.05 to 0.5 μm are supplementarily contained. In order to apply the undercoat layer smoothly and with little thickness unevenness, it is preferable to use non-magnetic particles and carbon black having a sharp particle size distribution.

It is preferable to add a nonmagnetic plate-like powder having an average particle diameter of 10 to 100 nm to the undercoat layer. As the component of the non-magnetic plate-like powder, rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used.

For the purpose of improving conductivity, a plate-like carbonaceous powder such as graphite having an average particle size of 10 to 100 nm or a plate-like ITO (indium tin composite oxide) powder having an average particle size of 10 to 100 nm is added. Also good. By adding the non-magnetic plate-like powder, film thickness uniformity, surface smoothness, rigidity, and dimensional stability are improved.

(3) Lubricant Although it does not exclude the mutual movement of the lubricant in the undercoat layer and the lubricant in the magnetic layer, generally, the undercoat layer has a content of 0. 0% relative to the total powder contained in the magnetic layer and the undercoat layer. It is preferable to contain 5 to 5% by weight of higher fatty acid and 0.2 to 3% by weight of higher fatty acid ester because the coefficient of friction with the head becomes small. The addition of higher fatty acids in the above range is preferable when the content is less than 0.5% by weight, and the effect of reducing the friction coefficient is small. When the content exceeds 5% by weight, the undercoat layer may be plasticized and the toughness may be lost. Because.

Further, the addition of higher fatty acid esters within the above range is preferable because if the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3% by weight, the amount transferred into the magnetic layer is too large. This is because side effects such as sticking to the head may occur.

As the higher fatty acid, a fatty acid having 10 or more carbon atoms is preferably used, and as the higher fatty acid ester, an ester of the above higher fatty acid is preferably used. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. These fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

The amount of fatty acid added to the magnetic layer is not particularly limited since the fatty acid is transferred between the undercoat layer and the magnetic layer, and the amount of fatty acid added to the magnetic layer and the undercoat layer may be the above amount. If a fatty acid is added to the undercoat layer, it is not always necessary to add a fatty acid to the magnetic layer.

The magnetic layer usually contains 0.5 to 3% by weight of fatty acid amide and 0.2 to 3% by weight of higher fatty acid ester with respect to the magnetic powder. Is preferable. As the fatty acid amide, a fatty acid amide having 10 or more carbon atoms such as palmitic acid and stearic acid can be used.

The addition of the fatty acid amide within the above range is preferable when the amount is less than 0.5% by weight, and direct contact at the head / magnetic layer interface is likely to occur, and the effect of preventing seizure is reduced. This is because there is a possibility that defects such as dropout may occur. The addition of higher fatty acid esters in the above range is preferably less than 0.2% by weight if the effect of reducing the friction coefficient is reduced, and if it exceeds 3% by weight, side effects such as sticking to the head may occur. Because there is.

(4) Dispersant The nonmagnetic powder, carbon black, or magnetic powder contained in the undercoat layer or magnetic layer may be surface-treated with a dispersant, or a coating for each layer may be produced together with the dispersant. These may be used alone or in combination. In any layer, the dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

As the dispersant, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearic acid, etc. Fatty acid [RCOOH (R is an alkyl group or alkenyl group having 11 to 17 carbon atoms)], metal soap composed of alkali metal or alkaline earth metal of the fatty acid, fluorine-containing compound of the fatty acid ester, amide of the fatty acid , Polyalkylene oxide alkyl phosphate ester, lecithin, trialkylpolyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonate, phosphate, copper Various known dispersants such as phthalocyanine, It can be used.

(5) Backcoat layer A backcoat layer is provided on the other surface of the nonmagnetic support (the surface opposite to the surface on which the magnetic layer is formed) for the purpose of improving running performance. If the backcoat layer is magnetic, the magnetic signal of the magnetic layer may be disturbed, and the backcoat layer is usually nonmagnetic.

The thickness of the back coat layer is preferably 0.2 to 0.8 μm. This range is preferable because if it 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 recording capacity per roll becomes small. The center line average surface roughness Ra of the backcoat layer is preferably 3 to 8 nm, and more preferably 4 to 7 nm.

The back coat layer contains carbon black as one type of nonmagnetic powder. As this carbon black, acetylene black, furnace black, thermal black, etc. can be used. Usually, it is desirable to use small particle size carbon black and large particle size carbon black. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 100% by weight, more preferably 70 to 100% by weight based on the weight of the inorganic powder. .

As the small particle size carbon black, those having an average particle size of 5 to 200 nm are used, and those having an average particle size of 10 to 100 nm are more preferable. This range is more preferable if the average particle size is less than 10 nm, it becomes difficult to disperse the carbon black, and if the average particle size exceeds 100 nm, it is necessary to add a large amount of carbon black. This is because it becomes rough and causes a setback (embossing) to the magnetic layer.

When the large particle diameter carbon black is 5 to 15% by weight of the small particle diameter carbon black and the large particle diameter carbon black having an average particle diameter of 200 to 400 nm is used, the surface is not roughened, and the effect of improving running performance is increased.

A nonmagnetic plate-like powder having an average particle size of 10 to 100 nm can be added to the backcoat layer for the purpose of improving strength, temperature / humidity dimensional stability, and the like. As the component of the nonmagnetic plate-like powder, in addition to aluminum oxide, rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used.

For the purpose of improving conductivity, a plate-like carbonaceous powder having an average particle size of 10 to 100 nm, a plate-like ITO powder having an average particle size of 10 to 100 nm, or the like may be added. Moreover, you may add the granular iron oxide powder whose average particle diameter is 0.1-0.6 micrometer as needed. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight, based on the weight of the total inorganic powder in the backcoat layer. Moreover, it is preferable to add alumina having an average particle size of 0.1 to 0.6 μm because durability is further improved.

For the back coat layer, the same resin as that for the magnetic layer can be used as the binder resin. Among these, in order to reduce the coefficient of friction and improve the runnability, it is preferable to use a cellulose resin and a polyurethane resin in combination.

The content of the binder resin is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight, with respect to 100 parts by weight of the total amount of carbon black and inorganic nonmagnetic powder. More preferably, it is 70-110 weight part. The above range is preferable because if the amount is less than 50 parts by weight, the strength of the backcoat layer is insufficient, and if it exceeds 120 parts by weight, the friction coefficient tends to increase. It is preferable to use 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin.

In the backcoat layer, it is preferable to use a crosslinking agent such as a polyisocyanate compound in order to cure the binder resin. As the crosslinking agent, the same one as in the magnetic layer can be used. The amount of the crosslinking agent is usually 10 to 50 parts by weight, preferably 10 to 35 parts by weight, and more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder resin. The above range is preferable because if less than 10 parts by weight, the coating strength of the backcoat layer tends to be weak, and if it exceeds 35 parts by weight, the dynamic friction coefficient against SUS increases.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these. In addition, the part in an Example and a comparative example shows a weight part. Moreover, the particle diameter (average particle diameter) in an Example and a comparative example shows a number average particle diameter.

<Undercoat paint component>
(1) Component Needle-like iron oxide powder (average particle size: 110 nm) 64 parts

Carbon black (average particle size: 25 nm) 24 parts

12 parts of alumina (average particle size: 80 nm)

Stearic acid 2.0 parts

8.8 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)

Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)

25 parts of cyclohexanone

40 parts of methyl ethyl ketone

Toluene 10 parts

(2) Component 1 part butyl stearate

70 parts of cyclohexanone

50 parts of methyl ethyl ketone

20 parts of toluene

(3) Component Polyisocyanate 1.4 parts

10 parts of cyclohexanone

15 parts of methyl ethyl ketone

Toluene 10 parts

<Magnetic paint component>
(1) Kneading process component Magnetic powder (Co—Fe—Al—Y) 100 parts [Co / Fe: 24 at%, Al / (Fe + Co): 4.7 wt%,
Y / (Fe + Co): 7.9 at%,
σs: 127 A · m ² / kg (127 emu / g),
Hc: 177.1 kA / m (2,225 Oe),
Average particle diameter: 45 nm, axial ratio: 4]

13 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)

Polyester polyurethane resin 4.5 parts (contained -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)

Alumina powder (average particle size: 80 nm) 8 parts

Carbon black (average particle size: 25 nm) 5 parts

2 parts of methyl acid phosphate

Tetrahydrofuran 20 parts

Methyl ethyl ketone 4.5 parts

4.5 parts of cyclohexanone

(2) Dilution process components Palmitic acid amide 1.5 parts

1 part of n-butyl stearate

125 parts of methyl ethyl ketone

125 parts of cyclohexanone

(3) Compounding process component Polyisocyanate 1.5 parts

65 parts of methyl ethyl ketone

64 parts of cyclohexanone

Among the above-mentioned undercoat paint components, (1) component is kneaded with a batch kneader, then (2) component is added and stirred, and then a sand mill [zirconia beads (particle diameter 0.5 mm), apparent volume 80% Filling, peripheral speed 8 m / s] and a residence time of 60 minutes for dispersion treatment, further adding component (3), stirring and filtering to obtain an undercoat paint (undercoat layer paint).

Apart from this, among the above-mentioned magnetic paint components, (1) kneading step components are mixed at high speed in advance, and the mixed powder is kneaded with a continuous biaxial kneader, and then (2) dilution step components Was added and diluted in at least two stages using a continuous twin-screw kneader to obtain a primary dispersion paint. This coating material was subjected to a dispersion treatment (residence time 50 minutes) with a sand mill (circumferential speed 8 m / s) filled with zirconia beads (particle diameter 0.5 mm) with an apparent volume of 80%. To this primary-dispersed paint, (3) ingredients of the blending step were further added, stirred and filtered to obtain a magnetic paint.

The undercoat paint is dried on a nonmagnetic support made of an aromatic polyamide film (thickness: 3.9 μm, MD = 11 GPa, MD / TD = 0.7, trade name “Mikutron” manufactured by Toray Industries, Inc.) The thickness after the calendering is applied to 0.9 μm, and the magnetic coating is applied on the undercoat layer so that the magnetic layer thickness after the magnetic field orientation treatment, drying and calendering treatment is 0.06 μm. A magnetic sheet was prepared by applying wet-on-wet with an extrusion type coater, followed by magnetic field orientation treatment and drying using a dryer and far infrared rays.

<Backcoat layer paint component>
80 parts of carbon black (average particle size: 25 nm)

Carbon black (average particle size: 350 nm) 10 parts

Nonmagnetic plate-like iron oxide powder (average particle size: 50 nm) 10 parts

45 parts of nitrocellulose

Polyurethane resin (containing -SO ₃ Na group) 30 parts

260 parts of cyclohexanone

260 parts of toluene

525 parts of methyl ethyl ketone

After the coating component for the back coat layer was dispersed in a sand mill [zirconia beads (particle diameter 0.5 mm), apparent volume 80% filling, peripheral speed 8 m / s] with a residence time of 45 minutes, 15 parts of polyisocyanate was added. The mixture was stirred and filtered to prepare a paint for the backcoat layer.

This back coat layer coating was applied to the opposite side of the magnetic layer of the magnetic sheet produced by the above method so that the thickness after drying and calendering was 0.5 μm and dried.

The magnetic sheet thus obtained was mirror-finished at a temperature of 100 ° C. and a linear pressure of 196 kN / m with a seven-stage calendar made of a metal roll, and the magnetic sheet was wound on a core at 70 ° C. for 72 hours. After aging, it was cut into 1/2 inch width.

A slit machine (an apparatus for cutting a magnetic tape original into a magnetic tape having a predetermined width) was used in which various constituent elements were improved as follows. A tension cut roller was provided in the web path from the unwinding raw fabric to the slit blade group, this tension cut roller was a suction type, and the suction part was a mesh suction in which a porous metal was embedded. A direct drive directly connected to a motor without a mechanism for transmitting power to the blade drive unit was used.

While running the cut tape at 200 m / min, the surface of the magnetic layer was subjected to post-processing such as lapping tape polishing, blade polishing, and surface wiping to produce a magnetic tape. At this time, K10000 was used for the wrapping tape, the carbide blade was used for the blade, and the trade name “Toresse” manufactured by Toray Industries, Inc. was used for wiping the surface.

Using the magnetic tape thus obtained, a servo signal was written on the backcoat layer with a servo writer for S-DLT, and then the length of four cottons with a short fiber diameter of 4 μm twisted on the backcoat layer The tape was run while contacting a velvet planted with 2.5 mm fibers to remove the burning residue at the time of servo signal writing, and it was incorporated into a cartridge to produce a computer tape.

In the magnetic coating component, the magnetic powder is Co—Fe—Al—Y [Co / Fe: 24 at%, Al / (Fe + Co): 9.7 wt%, Y / (Fe + Co): 12.8 at%, La / (Fe + Co ): 0.2 at%, σs: 92 A · m ² / kg (92 emu / g), Hc: 111.0 kA / m (1,395 Oe), average particle size: 30 nm, axial ratio: 3] In the same manner as in Example 1, a computer tape was produced.

In the magnetic coating component, the magnetic powder was synthesized as follows: iron nitride magnetic powder (Y-Fe-N) [σs: 135.2 Am ^{2 /} kg (135.2 emu / g), Hc: 226.9 kA / m (2,850 Oe), average particle diameter: 20 nm, axial ratio: 1.1] A computer tape was produced in the same manner as in Example 1.

<Synthesis of iron nitride magnetic powder>
41.9 moles of iron (II) sulfate heptahydrate and 97.4 moles of iron (III) nitrate nonahydrate were dissolved in 150 kg of water. Next, 376 moles of sodium hydroxide were dissolved in 150 kg of water. The aqueous solution of sodium hydroxide was added to the aqueous solution of the two types of iron salts and stirred for 20 minutes to generate magnetite particles. The magnetite particles were put in an autoclave, heated at 200 ° C. for 4 hours, hydrothermally treated, and washed with water. The obtained magnetite particles had a spherical or elliptical shape with a particle size of 25 nm.

1 kg of the magnetite particles were dispersed in 50 liters of water for 30 minutes using an ultrasonic disperser. To this dispersion, 250 g of yttrium nitrate was added and dissolved, and stirred for 30 minutes. Separately, 80 g of sodium hydroxide was dissolved in 10 liters of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour. By this treatment, yttrium hydroxide was deposited on the surface of the magnetite particles. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which yttrium hydroxide was deposited on the surface of magnetite particles.

The powder in which the yttrium hydroxide was deposited on the surface of the magnetite particles in this manner was heated and reduced at 450 ° C. for 2 hours in a steam flow to obtain an yttrium-iron magnetic powder. Next, the temperature was lowered to 150 ° C. over about 1 hour in a state where hydrogen gas was allowed to flow. When the temperature reached 150 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C. Thereafter, the temperature was lowered from 150 ° C. to 90 ° C. in a state of flowing ammonia gas, and the ammonia gas was changed to a mixed gas of oxygen and nitrogen at 90 ° C., and a stabilization treatment was performed for 2 hours. Next, the temperature was lowered from 90 ° C. to 40 ° C. in the state of flowing the mixed gas, and the mixture was held at 40 ° C. for about 10 hours, and then taken out into the air.

The thus obtained yttrium-iron nitride magnetic powder had a content of yttrium and nitrogen measured by fluorescent X-ray of 5.3 atomic% and 10.8 atomic%, respectively. Further, to obtain a profile indicating a Fe ₁₆ N ₂ phase by X-ray diffraction pattern. From this profile, a diffraction peak based on Fe ₁₆ N ₂ and a diffraction peak based on α-Fe are observed, and this yttrium-iron nitride magnetic powder is composed of a mixed phase of Fe ₁₆ N ₂ phase and α-Fe phase. I found myself standing.

Moreover, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was a substantially spherical particle and the average particle size was 20 nm. Furthermore, the specific surface area determined by the BET method was 53.2 m ² / g. The saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 135.2 Am ² / kg (135.2 emu / g), and the coercive force was 226.9 kA / m (2,850 Oe). It was. Further, after storage at 60 ° C. and 90% RH for 1 week, the saturation magnetization was measured in the same manner as described above. As a result, it was 118.2 A / m ² (118.2 emu / g). Was 87.4%.

In the same manner as in Example 1, except that the particle size of the zirconia beads was changed from 0.5 mm to 0.7 mm, and the apparent filling amount of the beads was changed from 80% to 85% in the dispersion treatment of the magnetic paint. Thus, a computer tape was produced.

Comparative Example 1
In the magnetic coating component, the magnetic powder is Co—Fe—Al—Y [Co / Fe: 24 at%, Al / (Fe + Co): 4.7 wt%, Y / (Fe + Co): 7.9 at%, σs: 112 A · m ^{2 /} kg (112 emu / g), Hc: 181.4 kA / m (2,280 Oe), average particle size: 60 nm, axial ratio: 5], and in the dispersion treatment of magnetic paint, particles of zirconia beads Example 1 except that the diameter was changed from 0.5 mm to 0.7 mm, the filling amount of beads was changed from 80% to 85% in apparent volume, and the residence time of sand mill dispersion was changed from 50 minutes to 80 minutes. Thus, a computer tape was produced.

Comparative Example 2
In the same manner as in Example 1, except that the amount of beads filled was changed from 80% to 75% in apparent volume and the residence time of sand mill dispersion was changed from 50 minutes to 40 minutes in the dispersion treatment of the magnetic paint. A tape was prepared.

Comparative Example 3
In the magnetic coating component, the magnetic powder is Co—Fe—Al—Y [Co / Fe: 24 at%, Al / (Fe + Co): 4.7 wt%, Y / (Fe + Co): 15.8 at%, σs: 121 A · m ^{2 /} kg (121 emu / g), Hc: 178.3 kA / m (2,240 Oe), average particle diameter: 45 nm, axial ratio: 4] A tape was prepared.

Comparative Example 4
A computer tape was produced in the same manner as in Example 1 except that the zirconia beads were changed to titania beads in the dispersion treatment of the magnetic paint.

Comparative Example 5
A computer tape was produced in the same manner as in Comparative Example 2 except that the residence time of the sand mill dispersion was changed from 80 minutes to 120 minutes in the dispersion treatment of the magnetic paint.

About each computer tape of said Examples 1-4 and Comparative Examples 1-5, by the following method, the elemental analysis of the magnetic layer surface and the particle diameter of a zirconia abrasion powder are measured, Furthermore, electromagnetic conversion characteristics (C, C / N), still durability, durability running property and head wear were measured. These results are shown in Table 1 (Examples 1 to 4) and Table 2 (Comparative Examples 1 to 5) together with the characteristics (size, Hc, σs) of the magnetic powder used in the magnetic layer.

<Elemental analysis>
The “ESCA LAB mark” manufactured by VG is used, the excitation X-ray source is MgKα, the acceleration voltage is 12 kV, and the current value is 10 mA. Y / Fe, Zr / Fe, La / Fe (at %).

<Particle size of zirconia wear powder>
Using a focused ion beam processing apparatus (FIB: “FB-2000A” manufactured by Hitachi, Ltd., acceleration voltage: 30 kv, processing ions: Ga), a thin film sample having a thickness of 1 to 1.5 μm in the longitudinal direction of the sample tape is prepared. Elemental mapping with STEM-EDS (STEM = device used: “HF-2210” manufactured by Hitachi, Ltd., imaging method: TEM mode, EDS = device used: “X-ray microanalysis system Vantage” manufactured by Noran Instruments) And confirm the location of the Zr particles, and transmit a transmission image at a magnification of 1 million with a TEM (“HF-2200” manufactured by Hitachi Prototype, acceleration voltage: 200 kv, photographing method: bright field). The average particle diameter obtained by photographing and measuring the maximum diameter of each particle from the obtained 10 particle images was taken as the particle diameter.

<Electromagnetic conversion characteristics (C, C / N)>
A drum tester was used to measure the electromagnetic conversion characteristics of the magnetic tape. The drum tester was equipped with an electromagnetic induction head (track width 25 μm, gap 0.2 μm) and an MR head (track width 8 μm). Recording was performed with the induction head, and reproduction was performed with the MR head. These electromagnetic induction type head and MR head are installed at different locations with respect to the rotating drum, and the two heads can be operated in the vertical direction so that tracking can be matched. An appropriate amount of the magnetic tape was drawn out from the state of being wound around the cartridge and discarded, and further 60 cm was cut out, further processed into a width of 4 mm, and wound around the outer periphery of the rotating drum.

As for output and noise, a rectangular wave was input to the recording current / current generator by a function generator, a signal having a wavelength of 0.2 μm was written, the output of the MR head was amplified by a preamplifier, and then read into a spectrum analyzer. The carrier value of 0.2 μm was set as the medium output C. Further, when a rectangular wave of 0.2 μm was written, an integrated value obtained by subtracting the output and system noise from the spectral component corresponding to the recording wavelength of 0.2 μm or more was used as the noise value N. Furthermore, the ratio of both was taken as C / N. Both C and C / N were determined relative to the value of the computer tape of Comparative Example 1.

<Still durability>
Still durability was evaluated using a drum tester in the same manner as described above. With the magnetic tape mounted as described above, a carrier signal of 0.9 μm is written by the same writing method, and the output is continuously measured with both heads being applied. Thereafter, the time when the initial output value dropped to 95% was defined as the still life.

<Durable running performance>
The error rate before running was obtained by recording and reproducing (recording wavelength 0.37 μm) in a test mode using an S-DLT drive improved so that a thin tape could be measured. In addition, the error rate after running the entire length and all the tracks for 300 hours in an environment of 25 ° C. and 55% RH was determined as the error rate after running.

<Head wear>
The amount of wear of the head was evaluated by the wear width when the magnetic tape was slidably contacted with the edge of the ferrite prism and reciprocated. It has been confirmed that this wear width has a correlation with the wear amount of MR-head, and it is known that there is no practical problem if it is 10 μm or less.

Measurement is performed by mounting an AlFeSil prism (a prism defined in ECMA-288 / AnnexH / H2) on a 1/2 inch-2 reel tester using a special jig, a winding angle of 164 °, and a traveling speed of 2.54 m / s. The travel was reciprocated by 180 m as the running tension 1N. The measurement environment was 23 ° C. and 50% RH. After traveling, the prisms were observed with an optical microscope, and the edge width was taken as the prism wear amount.

Table 1
┌──────────┬────┬────┬┬────┬────┐
│ │Example 1 │Example 2 │Example 3 │Example 4│
├──────────┼────┼────┼┼────┼────┤
│Magnetic powder size (μm) │ 45│ 30│ 20│ 45│
│ │ │ │ │ │
│Magnetic powder Hc (Oe) │2225│1395│2850│2225│
│ │ │ │ │ │
│Magnetic powder σs (emu) │ 127│ 92│ 135│ 127│
├──────────┼────┼────┼┼────┼────┤
│Y / Fe (at%) │ 65│ 95│ 52│ 45│
│ │ │ │ │ │
│Zr / Fe (at%) │ 3.7│ 9.8│ 4.3│ 12│
│ │ │ │ │ │
│La / Fe (at%) │-│ 14│-│-│
│ │ │ │ │ │
│Zirconia wear powder │ 22│ 25│ 20│ 54│
│ Average particle size (nm) │ │ │ │ │
├──────────┼────┼────┼┼────┼────┤
│C (dB) │ 1.0│-2.2│ 2.5│ 0.5│
│ │ │ │ │ │
│C / N (dB) │ 4.2│ 4.4│ 4.8│ 3.8│
│ │ │ │ │ │
│Still durability (minutes) │ 15│ 11│ 22│ 21│
│ │ │ │ │ │
│Initial error rate │ 3.5│ 3.3│ 2.8│ 4.4│
│ (× 10 ^-7 ) │ │ │ │ │
│ │ │ │ │ │
│ Error rate after driving │ 8.7 │ 11.5 │ 7.7 │ 13.2 │
│ (× 10 ^-7 ) │ │ │ │ │
│ │ │ │ │ │
│Square column wear (μm) │ 5│ 8│ 4│ 3│
└──────────┴────┴────┴┴────┴────┘

Table 2
┌──────────┬────┬────┬────┬────┬────┐
│ │Comparative Example 1 │Comparative Example 2 │Comparative Example 3 │Comparative Example 4 │Comparative Example 5│
├──────────┼────┼────┼────┼────┼────┤
│Magnetic powder size (μm) │ 60│ 45│ 45│ 45│ 45│
│ │ │ │ │ │ │
│ Magnetic powder Hc (Oe) │ 2280 │ 2225 │ 2240 │ 2225 │ 2225 │
│ │ │ │ │ │ │
│Magnetic powder σs (emu) │ 112│ 127│ 121│ 127│ 127│
├──────────┼────┼────┼────┼────┼────┤
│Y / Fe (at%) │ 30│ 33│ 144│ 88│ 43│
│ │ │ │ │ │ │
│Zr / Fe (at%) │ 17│ 13│ 10│ 0│ 20│
│ │ │ │ │ │ │
│La / Fe (at%) │-│-│-│-│-│
│ │ │ │ │ │ │
│Zirconia wear powder │ 58│ 45│ 28│-│ 45│
│ average particle size (nm) │ │ │ │ │ │
├──────────┼────┼────┼────┼────┼────┤
│C (dB) │ 0.0│ 0.7│ 0.5│ 0.2│-0.5│
│ │ │ │ │ │ │
│C / N (dB) │ 0.0│ 3.6│ 3.2│ 2.4│ 3.3│
│ │ │ │ │ │ │
│Still durability (minutes) │ 17│ 9│ 22│ 7│ 24│
│ │ │ │ │ │ │
│Initial error rate │11.3│ 4.6│ 5.1│ 7.3│ 5.5│
│ (× 10 ^-7 ) │ │ │ │ │ │
│ │ │ │ │ │ │
│Error rate after driving │ 125│ 142│12.4│ 54│10.3│
│ (× 10 ^-7 ) │ │ │ │ │ │
│ │ │ │ │ │ │
│Prism wear amount (μm) │ 2│ 3│ 13│ 7│ 3│
└──────────┴────┴────┴────┴────┴────┘

As is clear from the results of Table 1 above, each computer tape of Examples 1 to 4 of the present invention has a good C / N, a small initial error rate, and a small increase in error rate after running. It can be seen that the still durability is good.

On the other hand, as is clear from the results of Table 2 above, the computer tapes of Comparative Examples 1 to 5 do not satisfy the configuration of the present invention, so the C / N, the initial error rate, and the error after running. It can be seen that either the rate or still durability is poor, or the head wear (the amount of prism wear) is too large to be suitable for practical use.

Next, the critical significance of each numerical value in the configuration of the present invention will be described in more detail with reference to FIGS. FIG. 1 shows the basic form of Example 1 and changes the particle diameter of the magnetic powder (however, when the particle diameter is 20 nm, the spherical powder of Example 3 is used). And the relationship with still durability.

From FIG. 1, the still durability shows a slightly small value when a needle-shaped magnetic powder having a magnetic powder size of 45 nm is used, and when a spherical magnetic powder having a magnetic powder size of 20 nm is used. It can be seen that a good value is exhibited regardless of the size of the magnetic powder, except that a slightly high value is exhibited. Further, it can be seen that C / N tends to increase as the magnetic powder size decreases, and in particular, it becomes a low value when it is 60 nm or more.

From the above tendency, it can be seen that the average particle size of the magnetic powder is preferably less than 60 nm. In addition, when the average particle diameter is less than 5 nm, the preferable numerical range of the average particle diameter of the magnetic powder in the present invention is 5 nm or more and less than 60 nm, considering that the surface energy of the particles becomes large and dispersion becomes difficult. It is thought that.

FIG. 2 shows that the Y / Fe amount on the surface of the magnetic layer is changed by changing the paint dispersion condition with Example 1 as a basic form (however, the Y / Fe amount of 144 at% is the magnetic powder shown in Comparative Example 3). This shows the relationship between the Y / Fe amount on the surface of the magnetic layer, the error rate after running, and the amount of prismatic wear.

From FIG. 2, the prism wear amount tends to increase as the Y / Fe value on the surface of the magnetic layer increases. In particular, when the Y / Fe value exceeds 140 at%, the prism wear amount exceeds 10 μm. In practice, head wear becomes a problem. Further, the error rate after traveling tends to increase when the value of Y / Fe is smaller than 60 at%, and rapidly increases when the value is less than 40 at%. Considering the above, it is considered that the preferable range of the Y / Fe value in the present invention is 40 to 140 at%.

FIG. 3 shows that the Zr / Fe amount on the surface of the magnetic layer was changed by changing the paint dispersion condition based on Example 1 (however, a Zr / Fe value of 0 is a titania having a particle diameter of 0.5 mm). This was obtained by dispersing the paint under the same conditions as in Example 1 using beads), showing the relationship between the amount of Zr / Fe on the surface of this magnetic layer and C and still durability.

From FIG. 3, the still durability tends to become better when the value of Zr / Fe on the surface of the magnetic layer is increased, and when it is less than 2 at%, less than 10 minutes, practical problems begin to appear. If it exceeds 15 at%, the effect is saturated. Further, C tends to increase as the Zr / Fe value on the magnetic layer surface decreases, but 0 indicates that the magnetic paint is dispersed using titania beads. Is slightly worse, C decreases in reverse. Considering the above, it is considered that the preferable range of the value of Zr / Fe is 2 to 15 at%.

FIG. 4 shows the relationship between the particle size of the zirconia wear powder in the magnetic layer and C by changing the paint dispersion condition by changing the particle diameter of the zirconia wear powder in the magnetic layer based on Example 1 as a basic form. It is shown.

From FIG. 4, the highest C is obtained when the particle diameter of the zirconia wear powder in the magnetic layer is about 20 to 30 nm. When the particle size of the zirconia wear powder is 50 nm or more, the orientation of the magnetic powder is deteriorated, or C is lowered, and the particle size of the zirconia wear powder is reduced (the dispersion condition of the paint is weakened) C is slightly lowered because of insufficient dispersion. Considering the above, it is considered that the preferable range of the particle diameter of the zirconia wear powder is less than 50 nm, and the more preferable range is 5 to 30 nm.

FIG. 5 shows that the La / Fe amount on the surface of the magnetic layer was changed by changing the La / Fe amount of the magnetic powder based on Example 2, and the La / Fe amount on the surface of the magnetic layer, the still durability, and the prisms. It shows the relationship with the amount of wear.

FIG. 5 shows that the still durability tends to increase as the La / Fe value on the surface of the magnetic layer increases. However, when the La / Fe value on the surface of the magnetic layer increases, the amount of prism wear also increases. When the value of La / Fe exceeds 30 at%, the amount of prism wear exceeds 10 μm, and the practical head wear amount is a problem. become. On the other hand, when the La / Fe value is less than 2 at%, the still durability is greatly lowered. Considering the above, it is considered that the preferable range of the value of La / Fe is 1 to 30 at%.

It is a characteristic view which shows the relationship between the particle diameter of the magnetic powder contained in the magnetic layer, C / N, and still durability. It is a characteristic view which shows the relationship between Y / Fe on the surface of a magnetic layer, the error rate after driving | running | working, and the amount of prism wear. It is a characteristic view which shows the relationship between Zr / Fe of a magnetic layer surface, C (output), and still durability. It is a characteristic view which shows the relationship between the particle diameter of zirconia abrasion powder in a magnetic layer, and C (output). It is a characteristic view which shows the relationship between La / Fe on the surface of a magnetic layer, still durability, and prism wear.

Claims (5)

A magnetic layer containing magnetic powder containing iron as a main constituent element is formed on one surface of the nonmagnetic support through an undercoat layer containing nonmagnetic powder, and a backcoat containing nonmagnetic powder is formed on the other surface. In the magnetic tape in which the layer is formed, the average particle size of the magnetic powder containing iron as a main constituent element is 5 nm or more and less than 60 nm, and the magnetic layer contains Y and Zr. Content by ESCA analysis is Y / Fe = 40-140at%, Zr / Fe = 2-15at%, The magnetic tape characterized by the above-mentioned.
The magnetic tape according to claim 1, wherein the magnetic powder containing iron as a main constituent element contains Y as one of constituent elements other than iron.
The magnetic tape according to claim 1, wherein the magnetic powder containing iron as a main constituent element is a ferromagnetic iron-based metal magnetic powder or an iron nitride-based magnetic powder.
The magnetic tape according to any one of claims 1 to 3, wherein the magnetic layer contains a Zr-containing powder as particles having a particle diameter of less than 50 nm as a wear powder of zirconia beads.
The magnetic tape according to any one of claims 1 to 4, wherein La is contained in the magnetic layer, and the content of this element by ESCA analysis is La / Fe = 1 to 30 at%.

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