JP2001357501A - Recording and reproducing method for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording and reproducing method excellent in noise, output and C/N characteristics of a magnetic recording medium in a short wavelength region and excellent in durability and frictional coefficient. SOLUTION: In the recording and reproducing method for the magnetic recording medium provided with a magnetic layer at least including a ferromagnetic metal powder, abrasives and carbon black on a substrate, data is recorded with the recording density of 106-108 nm3 bit volume Vbit on the magnetic recording medium in which the ferromagnetic powder has 30-100 nm average major axis length and 5×102-2.1×104 nm3 particle volume Vmp, the abrasives have 10-120 nm average particle size and 5×102-9×105 nm3 particle volume Vab, the carbon black has 5-60 nm average particle size and 6.5×101 to 1.1×105 nm3 particle volume Vc and specified relational formulae are simultaneously satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording / reproducing a magnetic recording medium such as a magnetic tape and a magnetic disk, and more particularly to a method for applying a magnetic paint mainly composed of a ferromagnetic metal powder and a binder on a support to form a magnetic layer. Related to the recording / reproducing method of the coating type magnetic recording medium in which is formed the noise, the output and the C in the short wavelength region.
The present invention relates to a recording / reproducing method having excellent / N, excellent characteristics, and excellent durability and friction coefficient. The invention also relates to a recording / reproducing method suitable for a magnetoresistive (MR) head, which has low noise, high output, running performance, and excellent friction coefficient.

[0002]

2. Description of the Related Art Magnetic recording technology requires that a medium can be used repeatedly, that signals can be easily digitized, and that a system can be constructed in combination with peripheral devices.
Video, audio, video, audio, etc.
It has been widely used in various fields including computer applications. In order to respond to demands such as miniaturization of equipment, improvement of the quality of recording / reproducing signals, prolongation of recording, and increase of recording capacity, recording density, reliability, and durability of recording media are further increased. Improvement has always been desired.

In recent years, with the spread of office computers such as minicomputers and personal computers,
As an external storage medium, magnetic tapes (so-called backup tapes) for storing computer information have been actively studied. When a magnetic recording medium for such a purpose is put to practical use, an improvement in recording capacity is strongly demanded, particularly in conjunction with a reduction in the size of a computer, an increase in information processing capacity, and an increase in the capacity of a hard disk to be mounted. In addition, the magnetic recording medium is a replaceable medium, the magnetic recording medium can be used under a wide range of environmental conditions (especially temperature and humidity conditions that are highly fluctuating, etc.) due to the expanding use environment, the reliability of data storage, and the high speed The reliability of performance such as stable recording and reading of data in a number of times of traveling by repeated use of the data is required more than ever.

In general, a magnetic recording medium has a configuration in which a magnetic layer is provided on a support made of a flexible material such as a synthetic resin. In order to achieve a large recording capacity (volume recording capacity) as described above, the magnetic layer itself is required to reduce the size of the magnetic powder, improve its dispersibility, or make the magnetic layer thinner. It is said that increasing the surface recording density is an effective method. In order to maintain good sensitivity (in particular, output in a high frequency range), the magnetic layer is smooth, and usually has a center plane average surface roughness of 1.0 to 3.0.
It is preferable to provide an underlayer between the support and the magnetic layer in order to achieve this smoothing, or to prevent turbulence and a decrease in runnability. In many cases, a back layer is usually provided on the opposite surface. Above all, the improvement of the recording density is an effective means of reducing the bit volume of the magnetic layer. To reduce the bit volume, it is necessary to reduce the size of the ferromagnetic powder, but the size is reduced. Therefore, there is a problem that the dispersibility is reduced, the surface properties of the magnetic layer are reduced, the output and C / N are reduced, and the signal error is increased. On the other hand, usually, the running durability of the magnetic recording medium is secured by adding a non-magnetic powder such as an abrasive or carbon black to the magnetic layer. And the signal error due to the miniaturization of the bit volume is
It has been considered that the size of the non-magnetic powder may have an effect, but it is possible to record on a magnetic recording medium at a high recording density in a specific range and reproduce at a high C / N while ensuring running durability. It is desired to specify the size range of the non-magnetic powder as described above.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a recording / reproducing method which is excellent in noise, output, C / N, durability and friction coefficient of a magnetic recording medium in a short wavelength region. is there.

[0006]

According to the present invention, there is provided a method for recording / reproducing a magnetic recording medium in which a magnetic layer containing at least a ferromagnetic metal powder, an abrasive and carbon black is provided on a support. With an axial length of 30-100 nm,
And the particle volume Vmp is 5 × 10 ^{2 to} 2.1 × 10 ⁴ nm ³ , the abrasive has an average particle diameter of 10 to 120 nm, and the particle volume Vab is 5 × 10 ^{2 to} 9 × 10 ⁵ nm ³ . The carbon black has an average particle diameter of ^{5 to} 60 nm and a particle volume Vc of 6.5 × 10 ^{1 to} 1.1 × 10 ⁵ nm ³ ,
In addition, the magnetic recording medium satisfying the following relational expressions (1), (2) and (3) simultaneously has a bit volume Vbit of 10 ⁶ to 10 ⁸ nm ^3.
And a recording / reproducing method for a magnetic recording medium characterized by recording at a recording density in the range of 0.0005 ≧ Vmp / Vbit ≧ 0.000005 (1) 200 ≧ Vab / Vmp ≧ 0.1 (2) 10 ≧ Vc / Vmp ≧ 0.03 (3)

In the present invention, the following embodiments are preferred. The coercive force Hc of the ferromagnetic metal powder is 0.94 × 10 ⁵ A / m
~ 2.86 × 10 ⁵ A / m (1200 to 3600O
e) and the saturation magnetization σs is 80 to 180 A · m ² / kg
Recording / reproducing method for a magnetic recording medium. A method for recording / reproducing a magnetic recording medium, wherein the ferromagnetic metal powder is Co / Fe and contains 5 to 50 atomic% of Co. A substantially nonmagnetic lower layer and a magnetic layer are provided on the support in this order, and the coercive force of the magnetic layer is 9.4 × 10 ⁴ A / m
(1200 Oe) or more, the product Φm of the saturation magnetic flux density of the magnetic layer and the thickness of the magnetic layer is 5 to 300 (mT · μm), and the surface roughness of the magnetic layer is a center plane average by 3D-MIRAU method. A recording / reproducing method for a magnetic recording medium, wherein a surface roughness is 1.0 to 3.0 nm.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present specification, the average major axis length and the average particle diameter mean the average of the major axis length and the equivalent circle diameter of primary particles. The primary particles are one independent powder without aggregation.

In the present specification, the sizes of various powders such as ferromagnetic metal powders, abrasives, and carbon black (hereinafter referred to as "powder sizes") can be obtained from high-resolution transmission electron micrographs. . That is, the powder size is
When the shape of the powder is needle-shaped, spindle-shaped, column-shaped (however, the height is larger than the maximum major axis of the bottom surface), the length of the major axis constituting the powder, that is, the major axis length, is represented by When the shape of the body is plate-shaped or column-shaped (however, the thickness or height is smaller than the maximum major axis of the plate or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface, and the shape of the powder is spherical or polyhedral. If the major axis of the powder cannot be specified based on the shape, the unspecified shape, or the like, the shape is represented by a circle equivalent diameter. The equivalent circle diameter is determined by a circular projection method.

The average powder size of the powder is an arithmetic mean of the above powder sizes, and is obtained by measuring about 500 powders as described above. The average needle ratio of the powder is determined by measuring the length of the minor axis of the powder (the maximum length in the direction perpendicular to the major axis), that is, the minor axis length in the above measurement, and determining the (length) of each powder. (Axis length / short axis length). Here, the minor axis length, in the case of the definition of the powder size, the length of the minor axis constituting the powder, in the same case, each refers to the thickness to height, in the case of, Since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.

When the shape of the powder is specific, for example, in the case of the definition of the powder size, the average powder size is referred to as the average major axis length. The arithmetic mean of (maximum major axis / thickness to height) is called an average plate-like ratio. In the case of the same definition, the average powder size is called the average particle diameter. In the present invention, Vmp is a value obtained by spheroidal approximation based on the average major axis length and the average needle ratio, and Vab and Vc are values obtained by spherical approximation based on the average particle diameter. Vbit refers to a value obtained by the following equation. Vbit = recording track pitch × recording bit length × recording depth = where recording track pitch × λ ^2/8, λ: recording wavelength, recording bit length: lambda / 2, the recording depth:
λ / 4 In the present invention, Vbit is 10 ⁶ to 10 ⁸ nm ³ , preferably 2
The magnetic recording medium is recorded at a recording density in a range from × 10 ^{6 to} 9 × 10 ⁷ nm ³ . λ is usually 50 to 400 nm,
It is preferably in the range of 100 to 300 nm, and the recording track pitch is 400 to 7000 nm, preferably 10 to
It is in the range of 00 to 5000 nm.

In the recording / reproducing method for a magnetic recording medium according to the present invention, the ferromagnetic powder has an average major axis length of 30 to 100 nm, preferably 35 to 100 nm, and a particle volume Vmp of 5 ×.
10 ^{2 to} 2.1 × 10 ⁴ nm ³ , preferably 9 × 10 ² to
1.5 × 10 ⁴ nm ³ , and the abrasive has an average particle diameter of 10
～120Nm, preferably 10 to 100 nm, and particle volume Vab is ^{5 × 10 2 ~9 × 10 5} nm 3, preferably ^{5.2 × 10 2 ~5.2 × 10 5} nm 3, carbon black Average particle size is 5 to 60 nm, preferably 8 to
55 nm and the particle volume Vc is 6.5 × 10 ¹ to 1.
1 × 10 ⁵ nm ³ , preferably 2.7 × 10 ^{2 to} 8.7 ×
10 ⁴ nm ³ .

Further, the present invention provides the following relational expressions (1) to (1).
(3) must be satisfied. 0.0005 ≧ Vmp / Vbit ≧ 0.000005 (1)
200 ≧ Vab / Vmp ≧ 0.1 (2) 10 ≧ Vc / Vmp ≧ 0.03 (3) And their preferable ranges are as follows (1a) to (3)
As in a). 0.0003 ≧ Vmp / Vbit ≧ 0.000005 (1a) 100 ≧ Vab / Vmp ≧ 0.1 (2a) 6 ≧ Vc / Vmp ≧ 0.03 (3a)

According to the present invention, the size of each of the ferromagnetic metal powder, the abrasive and the carbon black contained in the magnetic layer is set to Vbit.
Is set so as to satisfy the relationship with the recording density in the range of 10 ⁶ to 10 ⁸ nm ³ , so that even when the recording density is as high as in the same range, the noise, output, C / N are excellent, and The durability of the recording medium can be ensured.

Hereinafter, the present invention will be described in detail. The magnetic recording medium suitable for the present invention will be described.

[Magnetic Layer] The magnetic layer may be a single layer or may be composed of two or more layers. In the latter case, the relative positions of the layers may be adjacent to each other depending on the purpose or the magnetic layer may be interposed between them. Layers other than the above may be interposed, and a known layer configuration can be adopted. In the present invention, the thickness of the magnetic layer means the dry thickness of the uppermost magnetic layer in the case of a multilayer.

Examples of the magnetic layer composed of multiple layers include ferromagnetic iron oxide, ferromagnetic cobalt-modified iron oxide, CrO ₂ powder,
Examples include a combination of a magnetic layer in which a ferromagnetic metal powder selected from hexagonal ferrite powder and various ferromagnetic metal powders is dispersed in a binder. In this case, even with the same type of ferromagnetic metal powder, magnetic layers containing ferromagnetic metal powders having different element compositions, powder sizes, and the like can be combined. Further, as the magnetic recording medium, a medium in which a substantially nonmagnetic lower layer and a magnetic layer are provided in this order on a support is preferable. Hereinafter, the magnetic layer is an upper layer or an upper magnetic layer,
The lower layer may be referred to as a non-magnetic layer.

The coercive force of the magnetic layer is preferably 9.4 × 10 ⁴ A / m from the viewpoint of securing a high output of the magnetic recording medium.
(1200 Oe) or more, and more preferably 1.43.
× 10 ⁵ A / m to 2.79 × 10 ⁵ A / m (1800 to 3
500 Oe). The product Φm of the saturation magnetic flux density of the magnetic layer and the thickness of the magnetic layer is preferably from 5 to 300 (mT · μm), more preferably from 10 to 270 (mT · μm) from the viewpoint of overwriting and noise. is there.

The magnetic recording medium in which the lower layer and the magnetic layer are provided on a support is coated on the lower layer, and then the upper layer is simultaneously or sequentially coated while the lower layer is in a wet state.
/ W) or a wet-on-dry method (W / D) in which an upper magnetic layer is provided after the lower layer is dried. From the viewpoint of production yield, simultaneous or sequential wet coating is preferred. Since the upper layer and the lower layer can be formed simultaneously by simultaneous or sequential wet application (W / W), a surface treatment step such as a calendering step can be effectively utilized, and the surface roughness of the upper magnetic layer can be improved even with an ultrathin layer.

(Ferromagnetic Metal Powder) The ferromagnetic metal powder used for the magnetic layer is preferably a ferromagnetic metal powder containing α-Fe as a main component. The ferromagnetic metal powder contains Al, Si, Ca, Mg, Ti, Cr, Cu, Y, S
n, Sb, Ba, W, La, Ce, Pr, Nd, P, C
It may contain atoms such as o, Mn, Zn, Ni, Sr, and B. In particular, Al, Ca, Mg, Y, Ba, L
a, Nd, Sm, Co, Ni at least one of α-F
It is preferable to include other than e. Co is particularly preferable when alloying with Fe increases the saturation magnetization and improves the demagnetization. The content of Co is preferably 5 to 50 atomic%, more preferably 10 to 40 atomic% with respect to Fe,
More preferably, it is 15 atomic% to 35 atomic%. The content of the rare earth element such as Y is preferably 1.5 atomic% to 12 atomic%, more preferably 3 atomic% to 10 atomic%, and still more preferably 4 atomic% to 9 atomic%. Al is preferably 1.5 atomic% to 12 atomic%, more preferably 3 atomic%.
10 at%, more preferably 4 at% to 9 at%. Rare earths including Y and Al function as a sintering inhibitor, and a higher sintering preventing effect can be obtained by using them in combination. These ferromagnetic metal powders may be treated in advance with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion before dispersion. In particular,
JP-B-44-14090, JP-B-45-18372
No., JP-B-47-22062, JP-B-47-2251
No. 3, JP-B-46-28466, JP-B-46-387
No. 55, JP-B-47-4286, JP-B-47-124
No. 22, JP-B-47-17284, JP-B-47-18
No. 509, JP-B-47-18573, JP-B-39-1
No. 0307, JP-B-46-39639, U.S. Pat.
No. 026215, No. 3031341, No. 310019
No. 4, No. 3242005, No. 3389014 and the like.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. A ferromagnetic metal powder obtained by a known production method can be used, and the following method can be used. Reduce sintering-containing iron oxide hydroxide and iron oxide with a reducing gas such as hydrogen to reduce Fe
Alternatively, a method of obtaining Fe—Co particles or the like, a method of reducing with a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, a method of thermally decomposing a metal carbonyl compound, or a method of adding borohydride to an aqueous solution of a ferromagnetic metal There are a method of reducing by adding a reducing agent such as sodium, hypophosphite or hydrazine, and a method of evaporating a metal in a low-pressure inert gas to obtain a powder. The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment. The method of reducing oxidized iron oxide and iron oxide with a reducing gas such as hydrogen and forming an oxide film on the surface by controlling the partial pressure, temperature and time of the oxygen-containing gas and the inert gas has a small amount of demagnetization. preferable.

When the ferromagnetic metal powder of the magnetic layer is represented by the specific surface area (S _BET ) by the BET method, it is usually 40 to 80 m ² / g.
And preferably 45 to 70 m ² / g. 40m ²
If it is less than / g, noise increases, and if it is more than 80 m ² / g, it is difficult to obtain a smooth surface, which is not preferable. The crystallite size of the ferromagnetic metal powder is usually 30 to 180 °, preferably 35 to 170 °, more preferably 40 to 170 °. The average needle ratio (average of (major axis length / minor axis length)) of the ferromagnetic metal powder is preferably 3 to 15, and more preferably 3 to 10
Is preferred. The saturation magnetization s of the magnetic metal powder is usually 80
１８０180 A · m ² / kg, preferably 100 to 1
60 A · m ² / kg, more preferably 110 to 160
It is A · m ² / kg. The coercive force of the ferromagnetic metal powder is 0.
94 × 10 ⁵ A / m to 2.86 × 10 ⁵ A / m (1200
~ 3600 Oe), preferably 1700 Oersted ~
3500 Oersted (1.35 × 10 ⁵ A / m to 2.
79 × 10 ⁵ A / m), more preferably 1800 Oersted to 3000 Oersted (1.4).
3 × 10 ⁵ A / m to 2.39 × 10 ⁵ A / m).

The water content of the ferromagnetic metal powder is 0.1 to 2 mass
% Is preferable. Ferromagnetic gold depending on the type of binder
The moisture content of the genus powder is preferably optimized. Ferromagnetic metal
The pH of the powder is optimized by the combination with the binder used.
Preferably. The range is 6-12, but is preferred.
Or 7 to 11. SA (Stear) of ferromagnetic metal powder
(Phosphoric acid) adsorption amount (scale of basic point on the surface) is 1 to 15μ
mol / m^Two, Preferably 2 to 10 μmol / m^TwoAnd more
Preferably 3 to 8 μmol / m^TwoIt is. Stearin
When using ferromagnetic metal powder with a large amount of acid adsorption,
Magnetic recording media by surface modification with organic substances
Preferably. Soluble Na,
Ca, Fe, Ni, Sr, NH_Four, SO_Four, Cl, N
O_Two, NO_ThreeAnd other inorganic ions. these
Is preferably essentially absent. The sum of each ion is 30
If it is about 0 ppm or less, it does not affect the characteristics. Ma
In addition, it is preferable that the ferromagnetic metal powder has few vacancies.
The value is 20% by volume or less, more preferably 5% by volume or less.
is there. SFD (switching-field) of ferromagnetic metal powder itself
distribution) is preferably small, ferromagnetic metal powder
Needs to be reduced. Tape SFD
If it is small, the magnetization reversal is sharp and the peak shift is small.
This is suitable for high-density digital magnetic recording. Hc distribution
In order to reduce the
Monodisperse αFe to improve tight particle size distribution _TwoO_Threeuse
To prevent sintering between particles.

(Carbon Black of Magnetic Layer) As the carbon black used for the magnetic layer, furnace black for rubber, thermal for rubber, black for color, conductive carbon black, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 4
00ml / 100g, pH 2-10, water content 0.1
Preferably, the tap density is 0.1 to 1 g / ml. Specific examples of carbon black used for the magnetic layer include BLACKPEARLS manufactured by Cabot.
2000, 1300, 1000, 900, 905, 8
00, 700, VULCAN XC-72, manufactured by Asahi Carbon, # 80, # 60, # 55, # 50, # 35, manufactured by Mitsubishi Chemical, # 2400B, # 2300, # 900, # 100
0, # 30, # 40, # 10B, manufactured by Columbian Carbon, CONDUCTEX SC, RAVEN 150,
50, 40, 15, RAVEN-MT-P, manufactured by Akzo Corporation, Ketjen Black EC, and the like. Carbon black may be used after being surface-treated with a dispersant or grafted with a resin, or may be used with a part of the surface being graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks alone,
Or they can be used in combination. When carbon black is used, the amount is 0.1 to 30 based on the magnetic material.
Usually, it can be used in mass%. Carbon black has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength, and differs depending on the carbon black used. Therefore, these carbon blacks are different in type, amount and combination between the upper magnetic layer and the non-magnetic layer, and can be used according to the purpose based on the characteristics shown above, such as powder size, oil absorption, conductivity, and pH. Of course, it is possible to use them properly, and rather, it should be optimized in each layer.
The carbon black that can be used in the magnetic layer can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

(Abrasive) As the abrasive used for the magnetic layer, α-alumina, β-alumina having an α conversion of 90% or more, fine-particle diamond, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, Known materials mainly having a Mohs hardness of 6 or more such as corundum, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. Further, a composite of these abrasives (a surface of which is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the main component is 9
If it is 0% by mass or more, the effect is not changed. The size of these abrasives is as described above, but in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different sizes as needed, or to use a single abrasive to broaden the size distribution to achieve the same effect. Tap density is 0.3 to 1.5 g / ml, water content is 0.1 to 5% by mass, pH is 2 to 11, and specific surface area is 1 to 4.
0 m ² / g is preferred.

The shape of the abrasive is as described above.
In some cases, needles or the like are used in combination, and those having a corner in a part of the shape are preferable because of high abrasiveness. Specifically, AKP-10, AKP-15, AKP-20, A
KP-30, AKP-50, HIT-20, HIT-3
0, HIT-50, HIT-60A, HIT-50G,
HIT-70, HIT-80, HIT-82, HIT-
100, Reynolds ERC-DBM, HP-DB
M, HPS-DBM, WA1000 manufactured by Fujimi Abrasives Co., Ltd.
0, Uemura Kogyo UB20, Nippon Kagaku Kogyo G-5,
Chromex U2, Chromex U1, T made by Toda Kogyo
F100, TF140, Beta Random Ultra Fine manufactured by Ibiden, B-3 manufactured by Showa Mining Co., Ltd., and the like. These abrasives can be added to the lower layer as needed. By controlling the surface shape by adding it to the lower layer,
For example, the projecting state of the abrasive can be controlled. The particle size and amount of the abrasive added to the magnetic layer and the lower layer should of course be set to optimal values.

[Lower Layer (Non-Magnetic Layer)] Next, the details of the lower layer which is a non-magnetic layer will be described. The lower layer is not particularly limited as long as it is at least substantially non-magnetic, and is preferably composed of a non-magnetic powder and a binder. The lower layer is such that a magnetic powder can be used as long as it is substantially non-magnetic. That the lower layer is substantially non-magnetic means that the lower layer is allowed to have magnetism as long as the electromagnetic conversion characteristics of the upper layer are not substantially reduced.

The non-magnetic powder used for the lower layer of the magnetic recording medium can be selected from, for example, inorganic compounds such as metal oxides, hydrated metal oxides, metal carbonates, metal nitrides, and metal carbides. Examples of the inorganic compound include α-alumina, β-alumina, and γ having an α conversion of 90% or more.
-Alumina, θ-alumina, silicon carbide, chromium oxide,
Cerium oxide, α-iron oxide, goethite, silicon nitride, titanium dioxide, silicon dioxide, tin oxide, magnesium oxide, zirconium oxide, zinc oxide, barium sulfate, and the like are used alone or in combination. Particularly preferred is
Due to the small particle size distribution and many means for imparting functions,
Titanium dioxide, zinc oxide, α-iron oxide, goethite, barium sulfate, more preferably titanium dioxide,
α-iron oxide and goethite. α-iron oxide is used to heat and dehydrate magnetic iron oxide and metal raw materials with uniform particle sizes.
It is preferable to reduce the number of vacancies by performing a hole treatment and to perform a surface treatment as necessary. Normally, titanium dioxide has photocatalytic properties, so when exposed to light, radicals are generated and a binder,
There is a concern of reacting with lubricants. For this reason, it is preferable that titanium dioxide is made into solid solution of 1 to 10% by mass of Al, Fe or the like to lower the photocatalytic property. Further, the surface is Al and / or
Alternatively, it is preferable to reduce the catalytic action by treating with a Si compound.

The average powder size of these nonmagnetic powders is 5 to 5.
The thickness is preferably 1000 nm, but if necessary, nonmagnetic powders having different average powder sizes may be combined, or even a single nonmagnetic powder may have the same effect by widening the powder size distribution. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle diameter is preferably in the range of 10 to 150 nm. When the nonmagnetic powder is a needle-shaped metal oxide, the average major axis length is preferably 10 to 300 nm. Preferably, 10 to 200
nm is more preferred.

The tap density is usually 0.3 to 1.5 g / m
1, preferably 0.4 to 1.3 g / ml. The water content of the nonmagnetic powder is usually 0.2 to 5% by mass, preferably 0.3 to 3% by mass, and more preferably 0.3 to 1.5% by mass. The pH of the nonmagnetic powder is usually from 3 to 12, but the pH is particularly preferably from 5.5 to 11. The specific surface area of the non-magnetic powder is usually 1 to 100 m ² / g, preferably 5 to 80 m ² / g, more preferably 10 to 80 m ² / g.
It is. The crystallite size of the non-magnetic powder is 40-1000Å
Is preferable, and 40 to 800 ° is more preferable. DBP
The oil absorption using (dibutyl phthalate) is usually 5 to 1
00ml / 100g, preferably 10-80ml / 10
0 g, more preferably 20 to 60 ml / 100 g. The specific gravity is usually 1.5 to 7, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The adsorption amount of SA (stearic acid) of non-magnetic powder is usually
1 to 20 μmol / m ² , preferably ² to 15 μmol
/ M ² , more preferably 3 to 8 μmol / m ² .
When a non-magnetic powder having a large stearic acid adsorption amount is used, it is preferable to prepare a magnetic recording medium by surface modification with an organic substance which strongly adsorbs to the surface.

The surface of these non-magnetic powders is made of Al, M
g, Si, Ti, Zr, Sn, Sb, Zn, Y compound
Surface treatment is preferred. Especially preferred for dispersibility
Is Al _TwoO_Three, SiO_Two, TiO_Two, ZrO_Two, MgO and
And their hydrated oxides, more preferably A
l_TwoO_Three, SiO_Two, ZrO_TwoAnd with these hydrated oxides
is there. These may be used in combination or alone
It can also be used. Tables coprecipitated according to purpose
A surface treatment layer may be used.
After that, the surface layer is coated with silica, or
The reverse method can be adopted. Also, the surface treatment layer
Depending on the purpose, a porous layer may be used.
Is generally preferred.

Specific examples of the non-magnetic powder used for the lower layer include Nanotite manufactured by Showa Denko and HIT- manufactured by Sumitomo Chemical.
100, HIT-82, α-iron oxide DPN- manufactured by Toda Kogyo
250BX, DPN-245, DPN-270BX, D
PN-550BX, DPN-550RX, DBN-65
0RX, DAN-850RX, Titanium oxide T made by Ishihara Sangyo
TO-51B, TTO-55A, TTO-55B, TT
O-55C, TTO-55S, TTO-55D, SN-
100, titanium industrial STT-4D, STT
-30D, STT-30, STT-65C, α-iron oxide α-40, Teica titanium oxide MT-100S, MT-
100T, MT-150W, MT-500B, MT-6
00B, MT-100F, MT-500HD, FINEX-25, BF-1, BF-10, BF-2 manufactured by Sakai Chemical
0, ST-M, Dowa Mining iron oxide DEFIC-Y, DE
FIC-R, Nippon Aerosil AS2BM, TiO ₂ P
25, Ube Industries 100A, 500A, and those obtained by firing the same.

The lower layer contains carbon black as described above. The content of carbon black is preferably 1 to 50 parts by mass, more preferably 5 parts by mass with respect to 100 parts by mass of the nonmagnetic powder (not including carbon black).
-30 parts by mass. Further, the mass ratio of the nonmagnetic powder to the carbon black (nonmagnetic powder / carbon black) is preferably from 95/5 to 60/40,
More preferably, it is 90/10 to 70/30.

Further, an organic powder can be added to the lower layer according to the purpose. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. As the production method, those described in JP-A-62-18564 and JP-A-60-255827 can be used.

With respect to the binder resin (type and amount) of the lower layer, the amounts and types of the lubricant, dispersant and additives, the solvent, and the dispersing method, known techniques for the magnetic layer can be applied.

[Binder] As the binder which can be used for forming the magnetic layer, the non-magnetic layer formed as required, and the back layer, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used. A mixture is used. As the thermoplastic resin, the glass transition temperature is -100 to 150C, and the number average molecular weight is usually 1,000 to 200,000, preferably 1
0.00-100,000, degree of polymerization about 50-1000
Of the degree. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

As the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin , A mixture of a polyester resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in JP-A-62-256219.
In more detail. The above resins can be used alone or in combination, but preferred are vinyl chloride resins, vinyl chloride vinyl acetate copolymers, vinyl chloride vinyl acetate vinyl alcohol copolymers, and vinyl chloride vinyl acetate maleic anhydride copolymers. And a combination of at least one of these and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known materials such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. Among them, a polyurethane resin containing a short-chain diol having a cyclic structure and having a molecular weight of less than 500 and a long-chain polyether diol having a molecular weight of 500 to 5,000 as a diol component is preferable.

The short-chain diol having a cyclic structure and having a molecular weight of less than 500 (hereinafter also referred to simply as “short-chain diol”) includes aromatic and alicyclic diols and ethylene oxide or propylene oxide adducts thereof. Those that can be selected from are preferred.

Examples of the short-chain diol include bisphenol A, hydrogenated bisphenol A, bisphenol S, hydrogenated bisphenol S, bisphenol P, hydrogenated bisphenol P, cyclohexanedimethanol, cyclohexanediol, and hydroquinone. Among these, preferred are bisphenol A, hydrogenated bisphenol A and their ethylene oxide adducts and propylene oxide adducts.
More preferred is hydrogenated bisphenol A. The content of the short-chain diol in the polyurethane resin is preferably 1
5 to 40% by mass.

The long-chain polyether diol having a molecular weight of 500 to 5,000 (hereinafter also referred to simply as “long-chain diol”) is preferably a propylene oxide adduct of bisphenol A, an ethylene oxide adduct of bisphenol A, Examples include an ethylene oxide adduct of bisphenol A and a propylene oxide adduct of hydrogenated bisphenol A.

Further, a dimer acid which is a dimer of an unsaturated aliphatic carboxylic acid having 18 carbon atoms is formed, and then a dimer diol obtained by hydrogenating and reducing an unsaturated bond and a carboxylic acid and further purifying by distillation. Polyurethanes comprising polyisocyanates are also preferred. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and _{durability, -COOM, -SO 3 M, -OSO} 3 M, -
P = O (OM) ₂ , —OP = O (OM) ₂ , where M is a hydrogen atom or an alkali metal, OH, NR ₂ ,
N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, SH, CN,
It is preferable to use one obtained by introducing at least one or more polar groups selected from the group by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders include VAGH, VYHH, VMCH and VA manufactured by Union Carbide.
GF, VAGD, VROH, VYES, VYNC, VM
CC, XYHL, XYSG, PKHH, PKHJ, PK
HC, PKFE, Nissin Chemical Industries, MPR-TA, MP
R-TA5, MPR-TAL, MPR-TSN, MPR
-TMF, MPR-TS, MPR-TM, MPR-TA
O, Electrochemical 1000W, DX80, DX81, DX
82, DX83, 100FD, ZEON MR-10
4, MR-105, MR110, MR100, MR55
5, 400X-110A, Nipporan N2301, N2302, N2304 made by Nippon Polyurethane, Pandex T-5105, T-R3080, T-5 made by Dainippon Ink.
201, Barnock D-400, D-210-80, Crisbon 6109, 7209, Toyobo Byron UR8
200, UR8300, UR-8700, RV530,
RV280, manufactured by Dainichi Seika, Diferamine 4020, 5
020, 5100, 5300, 9020, 9022, 7
020, Mitsubishi Chemical Corporation, MX5004, Sanyo Chemical Sanpuren SP-150, Asahi Kasei Saran F310, F210
And so on.

The binder used in the nonmagnetic layer and the magnetic layer of the magnetic recording medium is used in an amount of 5 to 50% by mass, preferably 10 to 30% by mass, based on the nonmagnetic inorganic powder or the ferromagnetic metal powder. Can be 5 to 30% by mass when using a vinyl chloride resin, 2 when using a polyurethane resin.
-20% by mass and the polyisocyanate is preferably used in combination of 2-20% by mass,
For example, if head corrosion occurs due to a slight amount of dechlorination, it is also possible to use only polyurethane or only polyurethane and isocyanate. When using polyurethane, the glass transition temperature is -50 to 150 ° C, preferably 0 to 100 ° C, the breaking elongation is 100 to 2000%,
The breaking stress is 0.05 to 10 kg / mm ² (0.49 to 98 MP
a), the yield point is 0.05 to 10 kg / mm ² (0.49 to 98
MPa) is preferred.

Since the magnetic recording medium preferably has a multilayer structure,
Binder amount, vinyl chloride resin, polyurethane resin, polyisocyanate or the amount of other resins in the binder, molecular weight of each resin forming each layer, polar group weight,
Alternatively, it is of course possible to change the above-mentioned physical properties of the resin in each layer as needed, but rather it should be optimized in each layer, and a known technique relating to a multilayer magnetic layer can be applied. For example, when changing the amount of binder in each layer,
It is effective to increase the amount of binder in the magnetic layer to reduce scratches on the surface of the magnetic layer, and in order to improve head touch with the head, the amount of binder in the nonmagnetic layer is increased to increase flexibility. Can be made.

The isocyanate which can be used for the magnetic layer, non-magnetic layer, back layer and the like includes tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, Isocyanates such as o-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, products of these isocyanates and polyalcohol, and polyisocyanates formed by condensation of isocyanates can be used. . Commercially available trade names of these isocyanates include those manufactured by Nippon Polyurethane, Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MT.
L, Takeda Pharmaceutical, Takenate D-102, Takenate D
-110N, Takenate D-200, Takenate D-2
02, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc., and these may be used alone or in combination of two or more for each layer utilizing the difference in curing reactivity. Can be.

[Additives] As additives used in the magnetic layer, the non-magnetic layer and the like, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate And its alkali metal salts, alkyl sulfates and its alkali metal salts, polyphenyl ether, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various silane couplings Agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (may contain unsaturated bonds or may be branched) No), and their metal salts (Li, N
a, K, Cu, etc.) or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched) , Carbon number 1
2 to 22 alkoxy alcohols (which may contain an unsaturated bond or may be branched), and have 10 to 2 carbon atoms
4 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and any of mono-, di-, tri-, tetra-, penta-, and hexa-hydric alcohols having 2 to 12 carbon atoms Mono- or di-fatty acid esters or tri-fatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, containing 8 or more carbon atoms, which may contain unsaturated bonds or may be branched. And -22 fatty acid amides and aliphatic amines having 8-22 carbon atoms.

Specific examples of these fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and isostearic acid. No. Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, and 2-octyldodecyl palmitate. 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, oleyl alcohol, stearyl Alcohol, lauryl alcohol, and the like. Nonionic surfactants such as alkylene oxides, glycerin, glycidols, alkylphenol ethylene oxide adducts, etc., cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums Or a cationic surfactant such as a sulfonium, a carboxylic acid, a sulfonic acid,
Also used are anionic surfactants containing acidic groups such as phosphoric acid, sulfate ester groups and phosphate ester groups, amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and alkyl betaines. it can. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 100%
It is not pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably at most 30% by mass, more preferably at most 10% by mass.

Each of these lubricants and surfactants has a different physical action, and the type, amount, and combination ratio of the lubricant that produces a synergistic effect should be optimally determined according to the purpose. Things. To control bleeding to the surface by using fatty acids having different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface by using esters having different boiling points, melting points and polarities, and to adjust the amount of surfactant However, the lubrication effect can be improved by increasing the amount of the lubricant added in the intermediate layer, and it is a matter of course that the present invention is not limited to only the examples shown here. Generally, the total amount of lubricant is relative to magnetic or non-magnetic powder,
It is selected in the range of 0.1 to 50% by mass, preferably 2 to 25% by mass.

In addition, all or a part of the additives are
It may be added in any step of the production of magnetic and non-magnetic paint, for example, when mixing with a magnetic material before the kneading step,
When added in a kneading process with a magnetic substance, a binder and a solvent,
There are a case where it is added in the dispersion step, a case where it is added after the dispersion, and a case where it is added just before the application. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after slitting. Known organic solvents can be used, and for example, the solvents described in JP-A-6-68453 can be used.

[Layer Structure] The thickness structure of the magnetic recording medium is preferably 2.5 to 8 μm, more preferably 2.5 to 7.5 μm, particularly preferably 2. 5 to 7 μm. An undercoat layer for improving adhesion may be provided between the support and the nonmagnetic layer or the magnetic layer. The thickness of the undercoat layer is 0.01 to 0.5 µm, preferably 0.02 to 0.5 µm. Known undercoat layers can be used. The thickness of the magnetic layer is optimized depending on the saturation magnetization of the head to be used, the head gap length, and the band of the recording signal.
μm to 0.5 μm, more preferably 0.05 μm
m to 0.30 μm. The thickness of the lower nonmagnetic layer is preferably 0.3 to 2.5 μm, and more preferably 0.5 to 2.0 μm.

[Back Layer] The back layer will be described below in detail. The back layer basically has effects such as antistatic and curl correction. Also, the back layer contains carbon black as a filler with fine particles and excellent electrical conductivity,
Two types of carbon black having different average particle diameters may be contained, or an inorganic powder may be contained as necessary. For example, an inorganic powder having a Mohs hardness of 5 to 9 can be contained.

The carbon black generally contained in the back layer is a fine carbon black having an average particle diameter of 10 to 20 nm and a coarse carbon black having an average particle diameter of 50 to 300 nm, preferably 230 to 300 nm. . In general, the surface electric resistance of the back layer can be set low and the light transmittance can be set low by the addition of the fine carbon black as described above. Some magnetic recording devices use the light transmittance of the tape and use it for operation signals. In such a case, the addition of fine carbon black is particularly effective. In addition, the particulate carbon black generally has excellent lubricant retention, and contributes to a reduction in friction coefficient when used in combination with a lubricant. On the other hand, 50 to 300 nm, preferably 230 to 30
Coarse-particle carbon black having a thickness of 0 nm has a function as a solid lubricant, and also forms minute protrusions on the surface of the back layer to reduce the contact area, thereby contributing to a reduction in the coefficient of friction. Also, with only coarse-grained carbon black,
In a severe running system, the tape may easily fall off from the back layer due to the sliding of the tape, which may lead to an increase in the error ratio.

Specific products of the fine carbon black that can be used include the following. The values in parentheses indicate the average particle size. Raven
2000B (18 nm), RAVEN 1500B (17
nm) (above, manufactured by Columbia Carbon Co., Ltd.), BP800
(17 nm) (Cabot Corporation), PRINTNTEX9
0 (14 nm), PRINTEX 95 (15 nm), P
RINTEX85 (16 nm), PRINTEX75
(17 nm) (all manufactured by Degussa), # 3950 (16
nm) (manufactured by Mitsubishi Chemical Corporation). Examples of specific products of coarse-grained carbon black include thermal black (270 nm) (manufactured by Khancarb) and RAVEN M.
TP (275 nm) (manufactured by Columbia Carbon Co., Ltd.) can be mentioned. The carbon black of 50 to 200 nm can be selected from carbon black for rubber and carbon black for color.

The inorganic powder which can be added to the back layer preferably has an average powder size of 20 to 250.
and inorganic powders having a Mohs' hardness of 5 to 9 and more preferably 20 to 150 µm. As the inorganic powder, the same non-magnetic powders and abrasives used for the lower layer described above are used, among which α-iron oxide and α-iron oxide are used.
Alumina and the like are preferred.

The amount of the inorganic powder excluding carbon black added to the back layer is preferably in the range of 3 to 40 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the binder described later. Range.

Examples of the binder that can be used in the back layer include, in addition to the above-mentioned binders, fibrous resins (such as cellulose acetate butyrate, cellulose diacetate, cellulose propionate, and nitrocellulose).

The back layer is formed by dispersing the above components in a binder, and it is preferable to add a dispersant and a lubricant as other optional components. Examples of the dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid,
Oleic acid, elaidic acid, linoleic acid, linolenic acid,
C18-C18 fatty acids such as stearic acid (RC
OOH and R are an alkyl group or an alkenyl group having 11 to 17 carbon atoms), a metal soap of an alkali metal or an alkaline earth metal of the fatty acid, a fluorine-containing compound of the fatty acid ester, an amide of the fatty acid, Polyalkylene oxide alkyl phosphate, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl has 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, copper phthalocyanine, etc. can be used. it can. These may be used alone or in combination. Among the above, copper oleate, copper phthalocyanine, and barium sulfate are preferred. The dispersant is usually added in the range of 0.5 to 20 parts by mass based on 100 parts by mass of the binder resin.

As the lubricant, any lubricant conventionally used in magnetic recording media can be appropriately selected and used. In particular, fatty acids having 18 or more carbon atoms or fatty acid esters are preferable from the viewpoint of improving running properties. . The lubricant is usually added in the range of 1 to 5 parts by mass with respect to 100 parts by mass of the binder resin.

The back layer is provided on the side of the support opposite to the side on which the magnetic layer is provided according to a conventional method. That is, the above-mentioned components are dissolved in an appropriate organic solvent, and a coating solution is prepared by dispersing the components.
By drying, a back layer can be provided on the support. The back layer has a surface roughness Ra of 3D-M
The center plane average surface roughness by the IRAU method is preferably 1 to
It is in the range of 15 nm, more preferably 1 to 10 nm. This surface roughness is adjusted to the above range because the surface of the back layer is transferred to the surface of the magnetic layer while the tape is wound, affecting the reproduction output and affecting the coefficient of friction with the guide pole. Is preferred. In addition, this adjustment of the surface roughness Ra is usually performed by applying and forming a back layer.
In the surface treatment step using a calender, it is performed by adjusting the material of the calender roll to be used, its surface properties, pressure and the like. The back layer preferably has a thickness of 0.2 to
It is 0.8 μm, more preferably in the range of 0.2 to 0.7 μm.

[Support] The support used for the magnetic recording medium includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide and polysulfone. ,
Known films such as aromatic polyamide and polybenzoxazole can be used. A support having a glass transition temperature of 100 ° C. or higher is preferred, and a high-strength support such as polyethylene naphthalate or aramid is particularly preferred. If necessary, a laminated support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the base surface. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance.

As the support, TOPO- made by WYKO was used.
Center plane average surface roughness (S) measured by 3D MIRAU method
Ra) is usually 5.0 nm or less, preferably 3.0 nm.
Hereinafter, it is more preferable to use those having a thickness of 2.0 nm or less. These supports preferably have not only a small center plane average surface roughness but also no coarse projections of 0.5 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the support as required. Examples of these fillers include oxides and carbonates such as Ca, Si and Ti, and organic powders such as acrylic. The maximum height SRmax of the support is 1 μm or less, and the ten-point average roughness S
Rz is 0.5 μm or less, and peak height of the center plane is SRp 0.5 μm.
m, the center plane valley depth SRv is 0.5 μm or less, the center plane area ratio SSr is 10% or more, 90% or less, and the average wavelength Sλa.
Is preferably 5 μm or more and 300 μm or less. In order to obtain the desired electromagnetic conversion characteristics and durability, the surface projection distribution of these supports can be arbitrarily controlled by a filler. Each of the particles having a size of 0.01 μm to 1 μm has a size of 0 to 0.1 mm ^2. Control can be performed in a range of 2000 pieces.

The F-5 value of the support is preferably 5 to 50.
Kg / mm^Two(49-490MPa) and supported
The heat shrinkage of the body at 100 ° C for 30 minutes is preferably 3% or less.
Under, more preferably 1.5% or less, at 80 ° C. for 30 minutes
Has a heat shrinkage of preferably 1% or less, more preferably
0.5% or less. Breaking strength is 5-100Kg / mm
^Two(49-980 MPa), elastic modulus is 100-2000
Kg / mm^Two(980 to 19600 MPa) is preferable
No. Thermal expansion coefficient is 10^-Four-10^-8/ ° C, preferred
H10^-Five-10^-6/ ° C. Humidity expansion coefficient is 10^-Four
/ RH% or less, preferably 10^-Five/ RH% or less
is there. Supports these thermal, dimensional and mechanical strength properties
Approximately equal within 10% of each direction in the plane of the body
Is preferred.

[Manufacturing Method of Magnetic Recording Medium]
Prepare paint for each layer, apply them on the support, dry,
It is manufactured by heating / curing treatment or calendering treatment as necessary. The step of producing the paint corresponding to each layer of the magnetic recording medium includes at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All raw materials such as a magnetic substance, a non-magnetic powder, a binder, carbon black, an abrasive, an antistatic agent, a lubricant, and a solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, the polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion, and a conventionally known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder.
When a kneader is used, all or a part of the magnetic substance or non-magnetic powder and the binder (30% by mass of the total binder)
The above is preferable) and 15 to 5 with respect to 100 parts of the magnetic material.
The kneading process is performed in the range of 00 parts. The details of these kneading processes are described in JP-A-1-106338 and JP-A-1-106338.
-79274. Glass beads can be used to disperse the magnetic layer solution and the non-magnetic layer solution, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and filling rate of these dispersion media are optimized and used. A well-known disperser can be used. A magnetic material, an abrasive, carbon black, and the like having different dispersion speeds can be separately dispersed in advance, mixed, and further finely dispersed as necessary to obtain a coating solution.

The preparation of the paint for forming the non-magnetic layer can be performed according to the preparation of the magnetic paint.

When applying a magnetic recording medium having a multilayer structure,
It is preferable to use the following method. First, a lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in the application of a magnetic paint, and the lower layer is wet in a wet state. JP-A-60-23817
No. 9, JP-A-2-265672, and a method of applying an upper layer using a support-pressing-type extrusion coating apparatus. Secondly, JP-A-63-88080, JP-A-2-17971, and JP-A-2-2656
No. 72, a method of applying upper and lower layers almost simultaneously by using a single coating head having two built-in coating liquid passage slits. A third method is to apply the upper and lower layers almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to the aggregation of the magnetic particles, Japanese Patent Application Laid-Open No.
It is desirable to apply shear to the coating liquid inside the coating head by a method disclosed in Japanese Patent Application Laid-Open No. 5174 or Japanese Patent Application Laid-Open No. 1-236968. Further, the viscosity of the coating liquid must satisfy the numerical range disclosed in Japanese Patent Application Laid-Open No. 3-8471.

In order to form a magnetic recording medium having the above-mentioned multilayer structure, the lower layer is coated and dried, and then a magnetic layer is formed thereon. Not something. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

A calendering roll is treated with a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll. The processing temperature is preferably 50 ° C. or higher, and more preferably 1 ° C.
It is 00 ° C or higher. The linear pressure is preferably 200 kg / c
m (196 kN / m) or more, more preferably 300 kN / m
g / cm (294 kN / m) or more.

The coefficient of friction of the magnetic recording medium with respect to the head is 0.5 or less, preferably 0.3 or less, in the temperature range of -10 ° C. to 40 ° C. and the humidity of 0% to 95%. 10 ⁴ -10 ¹² Ω / sq, and the charge potential is preferably within a range of −500 V to +500 V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 10 in each direction in the plane.
0 to 2000 kg / mm ² (980 to 19600 MP
a), the breaking strength is preferably 10 to 70 kg / mm
² (98 to 686 MPa), and the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm in each in-plane direction.
² (980-14700 MPa), residual elongation is preferably 0.5% or less, and heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less.
Or less, most preferably 0.1% or less. The glass transition temperature of the magnetic layer (the maximum point of the loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably from 50 ° C to 120 ° C, and that of the lower nonmagnetic layer is preferably from 0 ° C to 100 ° C. The loss modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ N / m ² , and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each direction in the plane of the medium. The residual solvent contained in the magnetic layer is preferably at most 100 mg / m ² , more preferably at most 10 mg / m ² . The porosity of the coating layer is preferably 3 for both the nonmagnetic layer and the magnetic layer.
0 vol% or less, more preferably 20 vol% or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose.

The center plane average surface roughness Ra of the magnetic layer measured by the 3D-MIRAU method is preferably 1.0 to 3.0 n.
m, more preferably 1.0 to 2.5 nm. The maximum height Rmax of the magnetic layer is 0.5 μm or less, and the ten-point average roughness Rz
Is 0.3 μm or less, the height Rp of the center plane is 0.3 μm or less, the depth Rv of the center plane is 0.3 μm or less, the center plane area ratio Sr is 20 to 80% or less, and the average wavelength λa is 5 to 300 μm.
The following is preferred. The surface protrusion of the magnetic layer is 0.01 μm to 1 μm.
It is possible to arbitrarily set the size of μm in the range of 0 to 2000, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the particles to be added to the magnetic layer, and the roll surface shape of the calendar treatment. Curl is ± 3
It is preferably within mm.

It is easily presumed that the physical properties of the magnetic recording medium can be changed depending on the purpose, for example, between the non-magnetic layer and the magnetic layer. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[0072]

EXAMPLES The novel features of the present invention will be specifically described in the following examples, but the present invention is not limited to these examples.

Example 1 Using the ferromagnetic metal powder shown in Table 1, the abrasive shown in Table 2, and the carbon black shown in Table 3, a magnetic layer contained in the combination shown in Table 4 was provided. In order to prepare a magnetic tape, the following composition for the magnetic layer and the composition for the non-magnetic layer were prepared. In the following prescriptions, all indications of “parts” indicate “parts by mass”. (Material of magnetic layer) Ferromagnetic metal powder (Type 1 in Table 1) 100 parts Binder resin Vinyl chloride copolymer 13 parts (contains 1 × 10 ^-4 eq / g of -SO ₃ K group, degree of polymerization) : 300) Polyurethane resin A 5 parts Diamond (Type 2 in Table 2, average particle diameter: 90 nm) 5.0 parts Carbon black (Type 1, average particle diameter: 53 nm in Table 3) 1.0 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts

(Composition of Nonmagnetic Layer) Acicular Hematite 80 parts (S _BET : 55 m ² / g, average major axis length: 0.12 μm, average needle ratio: 8, pH: 8.8, Al on the surface 20 parts of carbon black (average particle diameter: 17 nm, DBP oil absorption: 80 ml / 100 g, S _BET : 240 m ² / g, pH: 7.5) Binder resin Vinyl chloride 12 parts of copolymer (containing 1 × 10 ^-4 eq / g of -SO ₃ K group, degree of polymerization: 300) 5 parts of polyurethane resin A 1 part of butyl stearate 2.5 parts of stearic acid 1: 1 mixture of methyl ethyl ketone and cyclohexanone Solvent 200 parts Each of the above-mentioned composition for a magnetic layer and the composition for a non-magnetic layer was kneaded with a kneader, and then dispersed using a sand grinder. The polyisocyanate was added to the resulting dispersion in an amount of 5 parts for the coating solution for the non-magnetic layer and 6 parts for the coating solution for the magnetic layer.
20 parts of 1 mixed solvent was added, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a coating solution for a nonmagnetic layer and a magnetic layer.

The above polyurethane resin A was synthesized as follows. Hydrogenated bisphenol A, a propylene oxide adduct of bisphenol A (molecular weight 700), polypropylene glycol (molecular weight 400) and bis (2-hydroxyethyl) sulfoisophthalate were placed in a vessel equipped with a reflux condenser and a stirrer and purged with nitrogen in advance. Was dissolved in a mixed solvent containing cyclohexanone and dimethylacetamide at a molar ratio of 50:50 at a molar ratio of 24: 14: 10: 2, respectively, and dissolved at 60 ° C. under a nitrogen stream. As a catalyst, 60 ppm was added to the total amount of raw materials using di-n-dibutyltin dilaurate. MDI (4,4
-Diphenylmethane didiisocyanate) was added in an equimolar amount to the total amount of the diols, and the mixture was heated and reacted at 90 ° C. for 6 hours to contain 4.0 mmol / g of ether groups and 8 × 10 ⁻⁵ equivalents / g of —SO ₃ Na groups With Mw 45000 introduced, Mn
25,000 polyurethane resins A were obtained.

Preparation of Coating Liquid for Forming Back Layer Fine Particle Carbon Black Powder 100 parts (Cabot, BP-800, average particle diameter: 17 nm) Coarse Particle Carbon Black Powder 10 parts (Karncarb, Thermal Black, average) Particle size: 270 nm) Calcium carbonate 80 parts (Shiraishi Kogyo Co., Ltd., white luster O, average particle size: 40 nm) α-iron oxide 15 parts (Toda Kogyo Co., Ltd., TF100, average particle size: 110 nm, Mohs hardness: 5.5) Nitrocellulose resin 140 parts Polyurethane resin 15 parts Polyisocyanate 40 parts Polyester resin 5 parts Dispersant: Copper oleate 5 parts Copper phthalocyanine derivative 5 parts Barium sulfate 5 parts Methyl ethyl ketone 2200 parts Butyl acetate 300 parts Toluene 600 parts Each of the above After kneading the components with a continuous kneader, Mills were dispersed using. The obtained dispersion was filtered using a filter having an average pore size of 1 μm to prepare a coating solution for a back layer.

The obtained coating solution for forming a non-magnetic layer is further coated with a magnetic coating solution immediately thereon, so that the thickness of the lower layer after drying becomes 1.7 μm, and the thickness of the magnetic layer becomes 0.20 μm. The center plane average surface roughness is 5.5 μm and
nm aramid base, and 4.8 × 10 ⁵ A / m while both layers are still wet.
The samarium-cobalt magnet having a magnetic force of (6000 Oe) was oriented by homopolar opposition and the solenoid was oriented by a solenoid having a magnetic force of 6000 Oe, and dried. Thereafter, a coating solution for forming a back layer was applied so as to have a thickness of 0.4 μm. A seven-stage calender composed of only metal rolls at a temperature of 95 ° C and a speed of 150 m / min. Process with
Heat treatment was applied. Next, the obtained coating material was 3.8 mm.
After slitting to a width and subjecting the magnetic layer to a surface polishing treatment,
Sample built into DS cartridge (magnetic tape)
And

Examples 2 to 16 and Comparative Examples 1 to 6
Among the magnetic layer compositions, the ferromagnetic metal powders shown in Table 1, the abrasives shown in Table 2, and the types of carbon black shown in Table 3 are shown in Table 4. A multilayer tape was prepared in the same manner as in Example 1, except that the combination was used.

The magnetic properties of the magnetic layer of each of the obtained samples,
The Ra of the magnetic layer and the back layer were measured. Furthermore, the reproduction output of 1/2 Tb, C / N, and the friction coefficient at 23 ° C. and 60% were measured. (1) Magnetic properties: Measured using a vibration sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at Hm 8 × 10 ⁵ A / m (10 kOe). (2) Center plane average surface roughness (Ra): 3D-MIRAU
Surface roughness (Ra): using a TOPO3D manufactured by WYKO Co., using an MIRAU method with an R of about 250 × 250 μm.
a was measured. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by light interference. (3) Output Using a drum tester, the relative speed of the laminated head (head gap 0.1 μm, track pitch 3.0 μm, saturation magnetic flux density 1.3 Tesla) was set to 10.2 m / sec, The optimum recording current was determined from the input / output characteristics of / 2Tb (λ = 125 nm), a signal was recorded with this current, and the reproduction output characteristics were measured. 1 measured using a drum tester
Table 5 shows the output characteristics of / 2Tb. The output value was shown as a relative value for each recording density, with the reproduction output of Comparative Example 1 having different recording densities being 0 dB. (4) C / N 1/2 Tb output measured using a drum tester and C
Table 5 shows the / N characteristics. 1 / 2Tb playback output and 1/2
A noise level separated by ± 1 MHz from Tb was averaged and calculated. The C / N of Comparative Example 1 having different recording densities is shown as a relative value for each recording density assuming that the C / N is 0 dB. (5) Friction coefficient (μ value) of the first pass of the magnetic layer surface under the environment of 23 ° C. and 60% RH, and friction coefficient of the 100th pass The tape was passed at a 180 ° angle to sus420J of 4 mmφ, and the load was 10 g and the speed per second. After sliding at 18 mm, the friction coefficient was determined based on Euler's equation. μ = (1 / π) ln (T2 / 10) T2: sliding resistance value (g)

[0080]

[Table 1]

[0081]

[Table 2]

[0082]

[Table 3]

[0083]

[Table 4]

[0084]

[Table 5]

In the above table, for example, “9.9E + 03” in the column of Vmp in Table 1 means “9.9 × 10 ³ ”.
That is, E of “9.9E + 03” indicates 10 and +03 indicates an index. The same applies to other descriptions. Tables 4 and 5 show that the examples of the present invention have low surface roughness and good C / N. However, the ferromagnetic metal powder of the comparative example,
When an abrasive and carbon black were used, the surface roughness was large, the C / N was low, and this was not good. With the improvement of recording density, more suitable for miniaturization of Bit volume,
It is presumed that the use of the ferromagnetic metal powder, the abrasive and the carbon black resulted in low surface roughness and good C / N. The magnetic recording medium using this has a high C
/ N is excellent.

[0086]

According to the present invention, the use of a combination of a ferromagnetic metal powder, an abrasive and carbon black having characteristics more suitable for miniaturizing the bit volume results in low surface roughness and good C / N. The present invention is also suitable for an MR head mounting system.

Claims (1)

[Claims] (1) at least a ferromagnetic metal powder on a support;
In the recording / reproducing method for a magnetic recording medium provided with a magnetic layer containing an abrasive and carbon black, the ferromagnetic powder has an average major axis length of 30 to 100 nm and a particle volume Vmp of 5 × 1.
0 ^{2 to} 2.1 × 10 ⁴ nm ³ , and the abrasive has an average particle size of 10 to 120 nm and a particle volume Vab of 5 × 10 ² to
9 × 10 ⁵ nm ³ , and carbon black has an average particle diameter of ^{5 to} 60 nm and a particle volume Vc of 6.5 × 10 ^1.
To 1.1 a × 10 ⁵ nm ^3, and the following relational expressions (1) and (2), the range bit volume Vbit a magnetic recording medium which satisfies (3) at the same time is 10 ⁶ to 10 ⁸ nm ³ A recording / reproducing method for a magnetic recording medium, wherein recording is performed at a recording density. 0.0005 ≧ Vmp / Vbit ≧ 0.000005 (1) 200 ≧ Vab / Vmp ≧ 0.1 (2) 10 ≧ Vc / Vmp ≧ 0.03 (3)