JP2001344738A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium suitable as a magnetic tape which is excellent in electromagnetic conversion characteristics and traveling durability, highly reliable when data are recorded and read out, excellent in preservation characteristics under moist and hot environments and can be advantageously used particularly for recording digital data even when the surface roughness of a magnetic layer is made so small as to be 1.0-3.0 nm for increasing short-wavelength output and the whole medium and a back layer are made comparatively thin. SOLUTION: This magnetic recording medium has a nonmagnetic layer and the ferromagnetic powder-containing magnetic layer formed on a support in this order. The nonmagnetic layer contains carbon black treated with a compound having an amino group at the end.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and, more particularly, to a coating type in which a magnetic coating mainly composed of a ferromagnetic metal powder and a binder is coated on a non-magnetic support to form a magnetic layer. And a magnetic recording medium having excellent output, C / N, and dropout characteristics in a short wavelength region.

[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 the 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 and reducing the total thickness of the magnetic recording medium are effective methods. In order to maintain good sensitivity (especially output in a high frequency range), the magnetic layer is smooth,
The center plane average surface roughness is preferably 1.0 to 3.0 nm, but in order to achieve this smoothness, an underlayer may be provided between the support and the magnetic layer, the winding may be disturbed, and the running property may decrease. In order to prevent this, a back layer is usually provided on the surface of the support opposite to the magnetic layer in many cases. In particular, when the total thickness is reduced, the self-supporting property and strength of the magnetic tape are also reduced. Therefore, the provision of the back layer is necessary to maintain good running durability against repeated use. However, as described above, with the thinning of the magnetic tape,
The thickness of the back layer also needs to be relatively thin.

A magnetic recording medium in which the total thickness of the magnetic recording medium and the thickness of the back layer are relatively thin is disclosed in, for example,
-215350. And as a specific example of the magnetic tape described in this publication,
The total thickness of the magnetic tape is 10 μm, and the thickness of the back layer is 0.5
μm or the total thickness is 9.5μ
m, an embodiment in which the layer thickness of the back layer is 0.5 μm. In the back layer in these embodiments, in the former embodiment, relatively fine carbon black is used alone in order to provide antistatic properties and stable running properties, and in the latter embodiment, relatively fine carbon black is used. There are two types of carbon black used, i.e., carbon black in the form of particles and carbon black in the form of relatively coarse particles.

On the other hand, in order to obtain a high surface smoothness of the back layer, a reduction in the coefficient of friction with respect to the guide pins, and a good running stability, fine carbon black and coarse carbon black are contained in the back layer. And a magnetic tape containing finely divided calcium carbonate (JP-A-2-7223). Further, it is described that an inorganic powder (for example, α-iron oxide or the like) may be further added to the back layer.

The present inventors have proposed that the total thickness of the magnetic tape is 10 μm.
m and the thickness of the back layer is 0.2 to 0.8 μm.
The use of a magnetic recording medium with an extremely small thickness of m as an external recording medium for digital data was studied. As a result, it has been found that the magnetic tape described in JP-A-6-215350 cannot provide satisfactory performance. That is, because the strength of the medium itself is insufficient due to the thinning of the magnetic recording medium, especially when the humidity and temperature are high or low, the friction coefficient of the magnetic layer increases, the dropout increases, and the output also increases. A problem has arisen that it tends to decrease. This is considered to be due to the fact that the carbon black is likely to fall off the magnetic layer during repeated running.

Accordingly, a method of treating the surface of carbon black using fluorine gas has been devised (Chemistry, Vol. 46, No. 9).
No., 1991). According to this method, carbon particles having excellent dispersibility can be obtained by ionizing the carbon particle surface with fluorine gas on the particle surface. However, the ionization of the carbon particle surface has a problem in performance stability during storage in a powder state, and has a disadvantage that it is unstable with respect to pH and temperature changes in the dispersion system. The use of the carbon black thus prepared as a magnetic paint and a magnetic recording medium were still insufficient.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the surface roughness of a magnetic layer to 1.0 to improve short-wavelength output.
Even when the thickness is as small as 3.0 nm and the overall thickness and the thickness of the back layer are relatively small, the electromagnetic conversion characteristics and running durability are excellent, the reliability for data recording and reading is high, and the heat and humidity is high. An object of the present invention is to provide a magnetic recording medium which has excellent storage characteristics and is particularly suitable as a magnetic tape which can be advantageously used for digital data recording.

[0010]

According to the present invention, a magnetic recording medium having the following structure is provided, and the above object is achieved. 1. In a magnetic recording medium in which a non-magnetic layer and a magnetic layer containing ferromagnetic powder are provided in this order on a support, the non-magnetic layer contains carbon black treated with a compound having an amino group at the terminal. A magnetic recording medium characterized by the above-mentioned. 2. 2. The magnetic recording medium according to the above item 1, wherein the compound having an amino group at the terminal is at least one selected from the amine group represented by the following general formula (1). Formula _{(1) H 2 N- (CH} 2) n-NR 1 R 2 in the formula; R _1, R ₂ are each independently, a carbon number 1 to 1
It is a linear or branched alkyl group which may have a substituent of 8. However, R ₁ and R ₂ may be combined to form a heterocyclic group which may have a substituent. n is 1
Represents an integer of ~ 18. 3. 3. The magnetic recording medium according to 1 or 2, wherein the carbon black has an average particle diameter in a range of 5 to 20 nm. 4. The non-magnetic layer contains a metal oxide having an average powder size of 10 to 300 nm, and its content is the mass ratio with the carbon black (metal oxide / carbon black).
The magnetic recording medium according to any one of the above items 1 to 3, wherein the magnetic recording medium has a ratio of 95/5 to 60/40. 5. The non-magnetic layer is a layer formed by separately dispersing the metal oxide and the carbon black, preparing a coating material containing these, and applying the coating to a non-magnetic support. 5. The magnetic recording medium according to any one of 4. 6. (1) The thickness of the magnetic layer is 0.01 to 0.5 μm, and the surface roughness is 1.0 to 3.0 nm as a center plane average surface roughness by a 3D-MIRAU method.
6. The magnetic recording medium according to any one of items 1 to 5, 7. The coercive force of the magnetic layer is 1.35 × 10 ⁵ A / m (170
0 Oe) or more, and the product of the saturation magnetic flux density of the magnetic layer and the thickness of the magnetic layer is 5 to 300 (mT · μm). 8. The carbon black contained in the nonmagnetic layer has an average particle diameter of 5 to 15 nm and a specific surface area of 200 to 800 m ² /
g, a DBP oil absorption of 50 to 120 ml / 100 g, a volatile content of 5 to 15% by weight, and a dispersion treatment with a compound having a terminal amino group. The magnetic recording medium according to the above.

In the present specification, the average particle diameter means the average of the circle-equivalent diameters of primary particles. Primary particles are independent single particles without agglomeration, and the powder shape is spherical,
It means that the long axis constituting the powder cannot be specified from the shape, such as a polyhedral shape or an unspecified shape. The equivalent circle diameter means a value obtained by a circular projection method. The same applies to the average particle diameter of carbon black.

In the specification of the present application, various powder sizes (hereinafter referred to as carbon black and ferromagnetic powder)
"Powder size" is determined from a high-resolution transmission electron micrograph. That is, when the powder shape is needle-like, spindle-like, column-like (however, the height is larger than the maximum major axis of the bottom surface) or the like, the length of the major axis constituting the powder, ie, the length of the powder, When the shape of the powder is plate-like or column-shaped (however, the thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface. When the shape of the body is spherical, polyhedral, unspecified, or the like, and the major axis of the powder cannot be specified from the shape, the shape is represented by a circle equivalent diameter.

The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by measuring about 500 powders as described above. The average acicular ratio of the powder is determined by measuring the length of the minor axis of the powder in the above measurement, that is, the minor axis length, and calculating the (major axis length / minor axis length) of each powder.
Means the arithmetic mean of the values of 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 ratio. In the case of the same definition, the average powder size is called the average particle diameter.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with respect to a magnetic recording medium. In the magnetic recording medium of the present invention, a nonmagnetic layer and a magnetic layer containing ferromagnetic powder are provided on a nonmagnetic support in this order. The nonmagnetic layer contains carbon black treated with a compound having an amino group at the terminal. Hereinafter, layers constituting the magnetic recording medium of the present invention,
The components and the like contained in the layer will be described.

[Carbon black contained in nonmagnetic layer] The carbon black contained in the nonmagnetic layer preferably has an average particle diameter of 5 to 20 nm, more preferably 5 to 1 nm.
8 nm. There is no particular restriction on the type or production history, and various types such as commercially available oil furnace black, gas furnace black, and channel black can be used. Also, ozone treatment that is usually performed,
Carbon black subjected to plasma treatment and liquid phase oxidation treatment may be used. It is very difficult to disperse the carbon black in the fine particles, but if the carbon black is treated using a compound having an amino group at a terminal as a dispersant, the ultrafine carbon black having an average particle diameter of 5 to 20 nm can be obtained. Can also improve dispersibility. However, when the average particle diameter is less than 5 nm or more than 20 nm, the effect of improving the smoothness of the surface of the non-magnetic layer and thus the surface of the magnetic layer tends to be small.

In general, functional groups such as a carboxyl group (—COOH), a phenolic hydroxyl group (—OH), and a quinone group are formed on the particle surface of carbon black during the production process. One of the methods for determining the functional group is a volatile component. One of the methods of quantifying functional groups and polar group-containing atomic groups of carbon black is a volatile component. The carbon black used in the present invention has a volatile content of preferably 5 to 15% by weight, more preferably 6 to 13% by weight. When the volatile content is 5% by weight or more, the number of adsorption or reaction sites of the dispersant is large, and a sufficient dispersing effect can be obtained. On the other hand, there is no particular problem when carbon black having a volatile content of more than 15% by weight is used, but no remarkable improvement in the dispersion effect is observed. The ratio of each functional group and the atomic group containing a polar group is not particularly limited, but the ratio of the carboxyl group is preferably large. Particularly preferred carbon black used for the nonmagnetic layer has an average particle diameter of 5 to 15 nm and a specific surface area of 20.
0-800m ² / g, DBP oil absorption 50-120cc
/ 100 g, a carbon black having a volatile content of 5 to 15% by mass.

As a compound having an amino group at a terminal, which is a dispersant used for the treatment of carbon black, a compound represented by the following general formula (1) can be preferably exemplified. Formula (1) H ₂ N— (CH ₂ ) n —NR ₁ R ₂ The compound represented by the above formula (1) is an amino compound having a primary amino group, and these amino groups are those of carbon black. Among the surface functional groups, it adsorbs to the carboxyl group and the phenolic hydroxyl group showing acidity by the acid-base interaction. Further, the primary amino group is, besides the acid-base interaction, a carbonyl group of the quinone skeleton and a Schiff base (>)
C = N−). With such an effect, a high dispersing effect can be obtained by using the compound represented by the general formula (1).

R ₁ and R ₂ in the general formula (1) are each independently a straight-chain or branched-chain alkyl group which may have a substituent having 1 to 18 carbon atoms. Examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a hexyl group, an octyl group, a nonyl group, a decyl group, a lauryl group, and a stearyl group. In the general formula (1), R ₁ and R ₂ are taken together to form a heterocyclic group which may have a substituent, preferably a 5- or 6-membered heterocyclic group. You may. The hetero atom constituting the heterocyclic group may include other nitrogen atoms, oxygen atoms and the like in addition to the nitrogen atom to which R ₁ and R ₂ are bonded. Examples of the heterocyclic group include a pyrrolidinyl group, a piperidino group, and a morpholino group. These alkyl groups and heterocyclic groups include an alkyl group having 1 to 4 carbon atoms (eg, a methyl group or an ethyl group), an alkoxy group having 1 to 4 carbon atoms (eg, a methoxy group), a hydroxy group, a sulfo group, and a carboxy group. May be substituted with a substituent selected from the group consisting of In the general formula (1),-
(CH ₂₎ groups represented by n- is preferably n is 1-4. Further, R ₁ and R ₂ are particularly preferably an alkyl group having 1 to 4 carbon atoms. Specific examples of the compound represented by the general formula (1) include, for example, N, N-dimethylaminoethylamine, N, N-dimethylaminopropylamine, N, N-dimethylaminobutylamine, N, N-
Diethylaminoethylamine, N, N-diethylaminopropylamine, N, N-diethylaminobutylamine, N, N-dipropylaminobutylamine, N, N-
Diisopropylaminopropylamine, N, N-dibutylaminoethylamine, N, N-dibutylaminopropylamine, N, N-dibutylaminobutylamine,
N-diisobutylaminopropylamine, N, N-diethylaminohexylamine, N, N-methyl-laurylaminopropylamine, N, N-dioctylaminoethylamine, N, N-distearylaminobutylamine,
And the following No. Examples include, but are not limited to, the compounds shown in 1-10. These can be used alone or in combination of two or more.

[0020]

Embedded image

Among these compounds, N, N-dimethylaminoethylamine, N, N
N-dimethylaminopropylamine, N, N-dimethylaminobutylamine, N, N-diethylaminoethylamine, N, N-diethylaminopropylamine, N, N
-Diethylaminobutylamine, N, N-dipropylaminobutylamine, N, N-diisopropylaminopropylamine, N, N-dibutylaminoethylamine,
N, N-dibutylaminopropylamine, N, N-dibutylaminobutylamine and N, N-diisobutylaminopropylamine can be particularly preferably used.

The amount of the compound having an amino group at the terminal, which is a dispersant, is based on 100 parts by mass of carbon black
Usually, it is preferably 0.1 to 100 parts by mass, more preferably 1 to 100 parts by mass. The amount of the dispersant added is 0.01
If the amount is less than mmol, the dispersing effect of carbon black is small, which is not preferable. Also, when the amount of the dispersant added is more than 10 mmol / g, no remarkable improvement in the dispersing effect is observed. The solvent used in the step of dispersing carbon black is not particularly limited as long as it dissolves the dispersant, and water, an organic solvent, and a mixture thereof are used. The treatment with a carbon black dispersant is usually performed when preparing a coating liquid for forming a non-magnetic layer, but a treatment previously performed with the above dispersant can also be used for preparing the coating liquid. The processing method will be described later together with the description of the method for manufacturing the magnetic recording medium of the present invention.

[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 provided adjacent to each other depending on the purpose, or the magnetic layer may be provided 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. Hereinafter, the magnetic layer may be referred to as an upper layer or an upper magnetic layer, and the nonmagnetic layer may be referred to as an underlayer.

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 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 powder, magnetic layers containing ferromagnetic powders having different element compositions, powder sizes, and the like can be combined.

The coercive force of the magnetic layer is preferably 1.35 × 10 ⁵ A / A from the viewpoint of ensuring high output of the magnetic recording medium.
m (1700 Oe) or more, and more preferably 1.4
3 × 10 ⁵ A / m to 2.79 × 10 ⁵ A / m (1800 to
3500 Oe). Also, the product of the saturation magnetic flux density of the magnetic layer and the thickness of the magnetic layer, from the viewpoint of overwriting and noise,
The range is preferably from 5 to 300 (mT · μm), more preferably from 10 to 270 (mT · μm).

The magnetic recording medium of the present invention has an underlayer and a magnetic layer provided on a support. After the underlayer is coated, the upper layer is coated simultaneously or sequentially while the underlayer is in a wet state. It can also be prepared by a wet-on-wet method (W / W) or by a wet-on-dry method (W / D) in which an upper magnetic layer is provided after an underlayer is dried. From the viewpoint of production yield, simultaneous or sequential wet coating is preferred. In the present invention, the upper layer / underlayer can be simultaneously formed by simultaneous or sequential wet application (W / W), so that a surface treatment step such as a calendering step can be effectively utilized, and the surface roughness of the upper magnetic layer can be reduced even with an ultrathin layer. Can be improved.

(Ferromagnetic Powder) The ferromagnetic powder used in the magnetic layer is preferably a ferromagnetic metal powder or a hexagonal ferrite powder. As the ferromagnetic metal powder, a ferromagnetic metal powder containing α-Fe as a main component is preferable. Al, Si, Ca, Mg, T
i, Cr, Cu, Y, Sn, Sb, Ba, W, La, C
e, Pr, Nd, P, Co, Mn, Zn, Ni, Sr,
It may contain an atom such as B. In particular, Al, C
It is preferable that at least one of a, Mg, Y, Ba, La, Nd, Sm, Co, and Ni is contained in addition to α-Fe.
Co is particularly preferable when alloying with Fe increases the saturation magnetization and improves the demagnetization. The content of Co is preferably 1 to 40 atomic%, more preferably 15 to 35 atomic%, more preferably 20 to 35 atomic% with respect to Fe. The content of rare earth elements such as Y is preferably 1.5 atomic% to 12 atomic%, more preferably 3 atomic% to 10 atomic%, more preferably 4 atomic% to 9 atomic%.
Atomic%. Al is preferably 1.5 atomic% to 12 atomic%, more preferably 3 atomic% to 10 atomic%, and still more preferably 4 atomic% to 9 atomic%. 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 powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. Specifically, Japanese Patent Publication No. 44-14090
No., JP-B-45-18372, JP-B-47-2206
2, JP-B-47-22513, JP-B-46-284
No. 66, JP-B-46-38755, JP-B-47-42
No. 86, JP-B-47-12422, JP-B-47-17
No. 284, JP-B-47-18509, JP-B-47-1
8573, JP-B-39-10307, JP-B-46-
39639, U.S. Pat.
No. 1341, No. 3100194, No. 3242005
No. 3,389,014, 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 powder of the magnetic layer is expressed by the specific surface area (S _BET ) by the BET method, it is usually 40 to 80 m ² / g, preferably 45 to 70 m ² / g. 40m ² / g
Below, noise increases, and above 80 m ² / g, it is difficult to obtain a smooth surface, which is not preferable. The crystallite size of the ferromagnetic powder of the magnetic layer of the present invention is usually 80 to 180 °,
Preferably 100-170 °, more preferably 110
１６165 °. The average major axis length of ferromagnetic powder is usually
0.02 μm to 0.25 μm, preferably 0.02 μm to 0.25 μm.
3 μm to 0.15 μm, more preferably 0.0
It is 3 μm to 0.12 μm. The average needle ratio (average of (major axis length / minor axis length)) of the ferromagnetic powder is preferably 3 to 15,
Further, 3 to 10 is preferable. Saturation magnetization σs of the magnetic metal powder is usually 90~170A · m ² / kg, preferably 100~160A · m ² / kg, more preferably 110~160A · m ² / kg. The coercive force of the ferromagnetic metal powder is 1700 to 3500 Oe (1.35 × 10 ⁵ A / m to 2.79 × 10 ⁵ A / m).
m) is preferable, and more preferably 1800 Oersted to 3000 Oersted (1.43 × 10 ⁵ A / m to
2.39 × 10 ⁵ A / m).

The water content of the ferromagnetic metal powder is preferably 0.1 to 2% by mass. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. P of ferromagnetic powder
Preferably, H is optimized by the combination with the binder used. Its range is from 6 to 12, but preferably 7
~ 11. SA (stearic acid) of ferromagnetic metal powder
The amount of adsorption (a measure of basic points on the surface) is 1 to 15 μmol /
m ² , preferably ^{2 to} 10 μmol / m ² , more preferably 3 to 8 μmol / m ² . When a ferromagnetic metal 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. Ferromagnetic powder contains soluble Na, Ca, Fe,
It may contain inorganic ions such as Ni, Sr, NH ₄ , SO ₄ , Cl, NO ₂ , and NO ₃ . These are preferably essentially absent. If the total sum of each ion is about 300 ppm or less, the characteristics are not affected. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be acicular, rice grain, or spindle shape as long as the powder size and the magnetic characteristics described above are satisfied. SFD (switching-field di) of ferromagnetic powder itself
The distribution is preferably small, and the Hc of the ferromagnetic powder is preferably small.
The distribution needs to be small. If the SFD of the tape is small, the magnetization reversal is sharp and the peak shift is small,
It is suitable for high-density digital magnetic recording. In order to reduce the Hc distribution, monodisperse αFe ₂ O ₃ is used in the ferromagnetic metal powder to improve the particle size distribution of goethite.
There are methods such as preventing sintering between particles.

(Hexagonal Ferrite Powder) Examples of the hexagonal ferrite include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and their various substituted substances, Co substituted substances, and the like. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite in which the particle surface is coated with spinel, and composite magnetoplumbite-type barium ferrite and strontium ferrite that further include a part of spinel phase. Other than predetermined atoms, Al, Si, S, Nb, S
n, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, A
g, Sn, Sb, Te, W, Re, Au, Bi, La,
Ce, Pr, Nd, P, Co, Mn, Zn, Ni, B,
It may contain atoms such as Ge and Nb. Generally, Co-Zn, Co-Ti, Co-Ti-Zr, Co-T
i-Zn, Ni-Ti-Zn, Nb-Zn-Co, Sn
A material to which an element such as Zn-Co, Sn-Co-Ti, or Nb-Zn is added can be used. Some raw materials and production methods contain specific impurities. The powder size is preferably a hexagonal plate diameter with an average plate diameter of 10 to 55 nm,
It is more preferably from 10 to 45 nm, particularly preferably from 10 to 40 nm.

In particular, when reproducing with a magnetoresistive head (MR head) in order to increase the track density, it is necessary to reduce noise, and the average plate diameter is preferably 45 nm or less.
If it is smaller than nm, stable magnetization cannot be expected due to thermal fluctuation. If it is larger than 55 nm, noise is high, and none of them is suitable for high-density magnetic recording. The plate ratio (plate diameter / plate thickness) is 1 to
15 is desirable. Preferably it is 1-7. If the plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area according to the BET method in this powder size range is 30 to ²⁰⁰ m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. The narrower the distribution of the particle plate diameter and plate thickness, the better.
Although it is difficult to make a numerical value, it can be compared by randomly measuring about 500 particles from a transmission electron microscope (TEM) photograph. The distribution is often not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average powder size = 0.1 to 1.5. In order to sharpen the powder size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving an ultrafine powder in an acid solution is also known. In the vitrification crystallization method, a more uniform powder is obtained by performing heat treatment a plurality of times and separating nucleation and growth.

The coercive force Hc measured with the magnetic powder is 500
~ 5000 Oersted (0.4 × 10 ⁵ A / m ~ 4 ×
It can be made up to about 10 ⁵ A / m). Higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. Hc can be controlled by powder size (plate diameter / plate thickness), kind and amount of contained element, substitution site of element, particle generation reaction condition and the like. Saturation magnetization σs is 30~70A · m ² / kg. σs tends to be smaller as the particles become finer. As the production method, there are a method of reducing the crystallization temperature or the heat treatment temperature time, a method of increasing the amount of the compound to be added, and a method of increasing the surface treatment amount. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment agent, an inorganic compound or an organic compound is used. Typical examples of the main compound include oxides or hydroxides of Si, Al, P and the like, various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% by mass based on the magnetic material. The pH of the magnetic material is also important for dispersion. Usually, the optimum value is about 4 to 12, depending on the dispersion medium and the polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.1 to 2.0% by mass is selected.

As a method for producing hexagonal ferrite, a metal oxide for replacing barium carbonate, iron oxide, and iron and boron oxide or the like as a glass-forming substance are mixed so as to have a desired ferrite composition, then melted, and quenched. Amorphous, then reheated, washed and pulverized to obtain barium ferrite crystal particles by vitrification crystallization method, barium ferrite composition metal salt solution is neutralized with alkali, and by-products are removed. Hydrothermal reaction method to obtain barium ferrite crystal particles by washing, drying and pulverizing after heating the liquid phase above
The barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain barium ferrite crystal particles. Do not choose.

(Carbon black of magnetic layer)
If desired, carbon black can be included. The carbon black used is furnace for rubber, thermal for rubber, black for color, conductive carbon black,
Acetylene black and the like can be used. Specific surface area is 5-500 m ² / g, DBP oil absorption is 10-400
ml / 100 g, average particle size is 5 nm to 300 nm, p
H is preferably 2 to 10, the water content is preferably 0.1 to 10% by mass, and the tap density is preferably 0.1 to 1 g / ml. Specific examples of the carbon black used for the magnetic layer include those manufactured by Cabot, BLACKPEARLS 2000, 1300,
1000, 900, 905, 800, 700, VULC
AN XC-72, made by Asahi Carbon, # 80, # 60, #
55, # 50, # 35, Mitsubishi Chemical, # 2400B, #
2300, # 900, # 1000, # 30, # 40, #
10B, made by Columbian Carbon, CONDUCTEX
SC, RAVEN 150, 50, 40, 15, RA
VEN-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. In particular, similarly to the case of carbon black contained in the nonmagnetic layer, a compound having an amino group at the terminal,
Particularly, carbon black which is treated with the compound represented by the general formula (1) and has an average particle diameter of 5 to 100 nm is preferable. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it can be usually used in an amount of 0.1 to 30% by mass of the magnetic substance. 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 used in the present invention have different types, amounts and combinations in the upper magnetic layer and the lower non-magnetic layer, and exhibit the above-mentioned properties such as powder size, oil absorption, conductivity, and pH. It is, of course, possible to use differently according to the purpose, but rather to optimize each layer. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

(Abrasives) The abrasives usable for the magnetic layer include α-alumina, β-alumina having an α conversion of 90% or more, fine-particle diamond, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum. Known materials having a Mohs hardness of 6 or more, such as 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 particle size of these abrasives is preferably from 0.01 to 1 μm, and in particular, the particle size distribution is preferably narrow in order to enhance the electromagnetic conversion characteristics. Further, in order to improve the durability, it is possible to combine abrasives having different particle diameters as needed, or to achieve the same effect by widening the particle diameter distribution by using a single abrasive.
Tap density 0.3-1.5 g / ml, water content 0.1
-5% by mass, pH 2-11, specific surface area 1-40m ²
/ G is preferred. The shape of the abrasive may be any of a needle shape, a spherical shape, and a dice shape. Specifically, AK manufactured by Sumitomo Chemical Co., Ltd.
P-10, AKP-15, AKP-20, AKP-3
0, AKP-50, HIT-20, HIT-30, HI
T-50, HIT-60A, HIT-50G, HIT-
70, HIT-80, HIT-82, HIT-100,
Reynolds ERC-DBM, HP-DBM, HPS
-DBM, WA10000 manufactured by Fujimi Abrasives, UB20 manufactured by Uemura Industries, G-5 manufactured by Nippon Kagaku Kogyo, Chromex U2, Chromex U1, TF100 manufactured by Toda Kogyo, T
F140, 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 underlayer as needed. By adding to the underlayer, the surface shape can be controlled, and the projected state of the abrasive can be controlled. These magnetic layers,
The particle size and amount of the abrasive added to the underlayer should of course be set to optimal values.

[Nonmagnetic Layer (Underlayer)] Next, the details of the underlayer which is a nonmagnetic layer will be described. The underlayer is not particularly limited as long as it is at least substantially nonmagnetic in a structure containing at least carbon black and a binder, and it is preferable to use a nonmagnetic powder other than carbon black in combination. In this specification, carbon black is not included when referring to non-magnetic powder. For the underlayer, magnetic powder can be used as long as it is substantially non-magnetic. The fact that the underlayer is substantially non-magnetic means that the underlayer 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 underlayer of the magnetic recording medium includes, for example, metal oxides, hydrated metal oxides,
It can be selected from inorganic compounds such as metal carbonates, metal nitrides and metal carbides. As the inorganic compound, for example, α-alumina, β-alumina having an α conversion of 90% or more,
γ-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,
Are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, α-iron oxide, goethite, and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and α- Iron oxide and goethite. α-iron oxide is
Heat dehydration of raw materials for magnetic iron oxide and metal with uniform particle size,
It is preferable to use an annealing treatment to reduce the number of pores and, if necessary, a surface treatment. Normally, titanium dioxide has a photocatalytic property, and when exposed to light, there is a concern that radicals are generated and react with binders and lubricants. For this reason, it is preferable that the titanium dioxide used in the present invention has a solid solution of 1 to 10% by mass of Al, Fe or the like to lower the photocatalytic properties.
Further, it is preferable to treat the surface with an Al and / or Si compound to reduce the catalytic action.

The average particle size of these nonmagnetic powders is 5 to
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. Non-magnetic
The water content of the powder is usually 0.2 to 5% by mass, preferably
0.3-3% by mass, more preferably 0.3-1.5%
%. The pH of the non-magnetic powder is usually 3 to 12.
However, the pH is particularly preferably between 5.5 and 11. Non-magnetic powder
The specific surface area of the powder is usually 1 to 100 m^Two/ G, preferably
5-80m^Two/ G, more preferably 10 to 80 m^Two/ 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.
You. The specific gravity is usually 1.5 to 7, preferably 3 to 6.
You. The shape may be any of needle, sphere, polyhedron, and plate
No. The adsorption amount of SA (stearic acid) of non-magnetic powder is usually
1 to 20 μmol / m^Two, Preferably 2 to 15 μmol
/ M^Two, More preferably 3 to 8 μmol / m^TwoIt is.
When using non-magnetic powder with high stearic acid adsorption,
Surface modification with an organic substance that strongly adsorbs to the surface
It is preferable to create it. On the surface of these non-magnetic powders
Are Al, Mg, Si, Ti, Zr, Sn, Sb, Zn,
It is preferable to perform a surface treatment with a Y compound. Especially for dispersibility
Preferred is Al _TwoO_Three, SiO_Two, TiO_Two, ZrO_Two,
MgO and their hydrated oxides are more preferred.
What's new is Al_TwoO_Three, SiO_Two, ZrO_TwoAnd their inclusion
Hydroxide. These may be used in combination
However, they can be used alone. Also, depending on the purpose,
A precipitated surface treatment layer may be used.
If the surface layer is coated with silica after coating
The method may be used, or vice versa. Also, the table
The surface treatment layer may be a porous layer depending on the purpose,
Homogeneous and dense are generally preferred.

Specific examples of the non-magnetic powder used for the underlayer 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,
DPN-550BX, DPN-550RX, DBN-6
50RX, DAN-850RX, Titanium oxide TTO-51B, TTO-55A, TTO-55B, T made by Ishihara Sangyo
TO-55C, TTO-55S, TTO-55D, SN
-100, titanium industrial STT-4D, ST
T-30D, STT-30, STT-65C, α-iron oxide α-40, Titanium oxide MT-100S, MT manufactured by Teika
-100T, MT-150W, MT-500B, MT-
600B, 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 underlayer contains carbon black as described above. The content of carbon black is preferably in the range of 1 to 50 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the nonmagnetic powder. The mass ratio of nonmagnetic powder to carbon black (nonmagnetic powder / carbon black) is 95/5 to 60/40.
And more preferably 90/10 to 7
0/30.

Further, an organic powder can be added to the underlayer 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.

The binder resin (type and amount) of the underlayer, the lubricant
With respect to the amount, type, solvent, and dispersion method of the dispersant / additive, a known technique for the magnetic layer can be applied.

[Binder] As the binder used for the magnetic layer, the non-magnetic layer and the like of the magnetic recording medium of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof can be used. used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight (polystyrene conversion value by a GPC method) of 1,000 to 200,00.
0, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000. 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, and vinyl acetate. Polymers, copolymers, polyurethane resins, and various rubber-based resins each containing, as a structural unit, a polymer, vinyl ether, or the like. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, and an 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 detail in JP-A-62-256219. These resins can be used alone or in combination.

The structure of the polyurethane resin is polyester
Polyurethane, polyether polyurethane, polyether
Polyesterpolyurethane, polycarbonate-polycarbonate
Urethane, polyester polycarbonate-polyurethane,
Uses known materials such as polycaprolactone polyurethane
it can. For all of the binders shown here,
In order to obtain excellent dispersibility and durability, if necessary,
OM, -SO_ThreeM, -OSO_ThreeM, -P = O (OM)_Two, −
OP = O (OM)_Two, (Where M is a hydrogen atom or
Lucari metal), OH, NR_Two, N⁺R_Three(R is carbonized
Hydrogen group), epoxy group, SH, CN, etc.
Introduce at least one polar group by copolymerization or addition reaction
It is preferable to use those that have been used. Such a polar group
Quantity is 10 ^-1-10^-8Mol / g, preferably 10^-2
-10^-6Mol / g.

Specific examples of these binders used in the present invention include VAGH and VYH manufactured by Union Carbide.
H, VMCH, VAGF, VAGD, VROH, VYE
S, VYNC, VMCC, XYHL, XYSG, PKH
H, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries,
MPR-TA, MPR-TA5, MPR-TAL, MP
R-TSN, MPR-TMF, MPR-TS, MPR-
TM, MPR-TAO, Electrochemical 1000W, DX8
0, DX81, DX82, DX83, 100FD, ZEON MR-104, MR-105, MR110, M
R100, MR555, 400X-110A, Nipporan N2301, N2302, N23 made by Nippon Polyurethane
04, Dainippon Ink Pandex T-5105, T-
R3080, T-5201, Burnock D-400, D
-210-80, Chris Bon 6109, 7209, Toyobo Byron UR8200, UR8300, UR-87
00, RV530, RV280, manufactured by Dainichi Seika, diferamine 4020, 5020, 5100, 5300, 90
20,9022,7020, Mitsubishi Chemical, MX500
4, Sanyo Kasei sampler SP-150, Asahi Kasei Saran F310, F210 and the like.

The binder used for the non-magnetic layer and the magnetic layer of the present invention is usually 5 to 5 with respect to the non-magnetic powder or the magnetic substance.
It is used in the range of 0% by mass, preferably in the range of 10 to 30% by mass. 5-30 when using vinyl chloride resin
% By mass, 2 to 20% by mass in the case of using a polyurethane resin, and 2 to 20% by mass of the polyisocyanate. It is also possible to use only or only polyurethanes and isocyanates. In the present invention, when polyurethane is used, the glass transition temperature is usually -50 to 150.
° C, preferably 0 to 100 ° C, elongation at break of 100 to 20
00%, the breaking stress is 0.05 to 10 kg / mm ² (0.
49-98MPa), yield point 0.05-10Kg / m
m ² (0.49 to 98 MPa) is preferred.

The magnetic recording medium of the present invention has at least two layers. Therefore, the amount of the binder, the vinyl chloride resin in the binder, polyurethane resin, polyisocyanate,
Alternatively, it is of course possible to change the amount of the other resin, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the physical properties of the resin described above with each layer as necessary. It should be optimized, and a known technique for a multilayer magnetic layer can be applied. For example, when the amount of the binder is changed in each layer, it is effective to increase the amount of the binder in the magnetic layer in order to reduce the abrasion on the surface of the magnetic layer. The amount of the binder in the magnetic layer can be increased to provide flexibility.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Use of isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can do. Commercially available trade names of these isocyanates include Nippon Polyurethane, Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR,
Millionate MTL, Takeda Pharmaceutical, Takenate D-10
2, Takenate D-110N, Takenate D-200,
Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N Desmodur HL, and the like. Can be used.

[Additives] The additives used in the magnetic layer, non-magnetic layer and the like of the present invention include a lubricating effect, an antistatic effect,
Those having a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone having polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester,
Polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenylether, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid , Aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, having 10 to 24 carbon atoms
Monobasic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts thereof (Li,
Na, K, Cu, etc.) or monovalent having 12 to 22 carbon atoms,
Dihydric, trivalent, tetravalent, pentavalent, hexahydric alcohols (which may contain an unsaturated bond or may be branched), alkoxy alcohols having 12 to 22 carbon atoms (including an unsaturated bond, It may be branched), having 10 to 10 carbon atoms
24 monobasic fatty acids (which may contain an unsaturated bond 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 used in the present invention has a different physical action, and the kind, amount, and combination ratio of the lubricant producing a synergistic effect depend on the purpose. It should be determined optimally. 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 To improve the application stability,
It is conceivable that the amount of the lubricant added is increased in the intermediate layer to improve the lubricating effect. Generally, the total amount of the lubricant is 0.1 to 50% by mass, preferably 2% by mass, based on the magnetic substance or nonmagnetic powder.
２５25% by mass.

Further, all or a part of the additives used in the present invention may be added at any step of the production of the magnetic and non-magnetic paints. For example, when the additives are mixed with the magnetic material before the kneading step, There are a case where it is added in a kneading step using a magnetic substance, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. 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 in the present invention.
No. 453 can be used.

[Layer Structure] In the thickness structure of the magnetic recording medium of the present invention, the support is preferably 2.5 to 8 μm, and more preferably 2.5 to 7.5 in order to increase the volume density.
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. Undercoat layer thickness 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 of the medium of the present invention is optimized depending on the saturation magnetization of the head used, the head gap length, and the band of the recording signal, but is preferably 0.01 μm to 0.5 μm, more preferably. Is 0.05 μm to 0.30 μm. The magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multilayer magnetic layer can be applied. The thickness of the nonmagnetic layer serving as the underlayer is preferably 0.3 to 2.
It is 5 μm, 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. The back layer may contain a modified carbonaceous powder. The back layer may contain fine particles of carbon black having excellent electrical conductivity as a filler, and may contain two types of carbon black having different average particle diameters, or may contain an inorganic powder if necessary.
For example, an inorganic powder having a Mohs hardness of 5 to 9 can be contained.

(Carbon Black of Back Layer) Carbon black generally contained in the back layer is composed of fine carbon black having an average particle diameter of 10 to 20 nm and an average particle diameter of 50 to 300 nm, preferably 230 to 300 nm.
m of coarse particle carbon black. 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, 50-300
nm, preferably 230 to 300 nm coarse particle carbon black has a function as a solid lubricant,
In addition, minute projections are formed on the surface of the back layer to reduce the contact area, thereby contributing to a reduction in the coefficient of friction. However, the coarse-grained carbon black has a disadvantage that in a severe running system, the tape slides easily to drop off from the back layer, leading to an increase in the error ratio.

Specific products of the particulate carbon black that can be used in the present invention include the following. The values in parentheses indicate the average particle size. R
AVEN2000B (18nm), RAVE1500
B (17 nm) (all manufactured by Columbia Carbon Co.), B
P800 (17 nm) (Cabot), PRINN
TEX90 (14 nm), PRINTEX95 (15n
m), PRINTEX85 (16 nm), PRINTE
X75 (17 nm) (all manufactured by Degussa), # 3950
(16 nm) (manufactured by Mitsubishi Chemical Corporation). Specific examples of commercial products of coarse particle carbon black include thermal black (270 nm) (manufactured by Khancarb) and RAVEN.
MTP (275 nm) (manufactured by Columbia Carbon Co., Ltd.) can be mentioned. Carbon black of 50 to 200 nm can be selected from carbon black for rubber and carbon black for color.

(Inorganic Powder of Back Layer) The inorganic powder that can be added to the back layer preferably has an average powder size of 20 to 250 nm, more preferably 20 to 250 nm.
An inorganic powder having a Mohs hardness of 5 to 9 and a Mohs hardness of 5 to 9 is exemplified. As the inorganic powder, the same non-magnetic powder or abrasive as used in the underlayer described above is used, and among them, α-iron oxide, α-alumina and the like are preferable.

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.

(Binder for Back Layer) Examples of the binder that can be used in the back layer include a thermoplastic resin, a thermosetting resin, a reactive resin, and a mixture thereof. Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride Copolymer, acrylate-styrene copolymer, methacrylate-acrylonitrile copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-styrene copolymer, polyvinyl fluoride, Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose resin (cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), styrene-butyl Diene copolymer, polyester resin, chlorovinyl ether - acrylic acid ester copolymer, an amino resin, and various rubber resins.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, and epoxy-polyamide. Resins and polyisocyanates can be mentioned.

(Arbitrary Components of Back Layer) The back layer according to the present invention is formed by dispersing the above components in a binder described later. It is preferable to add. Examples of the dispersant include 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and stearolic acid. Fatty acids (RCOOH,
R represents 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, or a polyalkylene. Oxide alkyl phosphates, lecithin, trialkyl polyolefin oxyquaternary ammonium salts (alkyl has 1 to 5 carbon atoms, olefins such as ethylene and propylene), sulfates, copper phthalocyanine, and the like can be used. These may be used alone or in combination. In the above, copper oleate,
Copper phthalocyanine and barium sulfate are preferred. The dispersant is usually 0.5 to 100 parts by mass of the binder resin.
It is added in the range of 20 parts by mass.

As the lubricant, any lubricant conventionally used for magnetic tapes can be appropriately selected and used. In the present invention, fatty acids having 18 or more carbon atoms or fatty acid esters are particularly useful in improving running properties. Is preferred. 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.

(Formation of back layer, physical properties, etc.)
According to a usual method, the support is provided on the side opposite to the side on which the magnetic layer is provided. That is, a back layer can be provided on a support by dissolving each of the above-mentioned components in an appropriate organic solvent, preparing a coating liquid in which the coating liquid is dispersed, and applying and drying the coating liquid according to a conventional coating method. . The back layer has a surface roughness Ra of preferably 1 to 15 nm, more preferably 1 to 10 nm as a center plane average surface roughness according to the 3D-MIRAU method. 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. The adjustment of the surface roughness Ra is usually performed by adjusting the material of the calender roll to be used, its surface properties, pressure and the like in the surface treatment step using a calender after the back layer is applied and formed. In the present invention, the back layer has a thickness of 0.2 to 0.8 μm, and more preferably 0.2 to 0.7 μm.

[Support] The support used in the magnetic recording medium of the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide and polyamide imide. And known films such as polysulfone, aromatic polyamide, and polybenzoxazole. Glass transition temperature is 10
A support having a temperature of 0 ° C. or higher is preferable.
It is particularly preferable to use a high-strength support such as aramide or aramid. 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 have a corona discharge treatment, a plasma treatment,
An easy adhesion treatment, heat treatment, dust removal treatment, or the like may be performed.

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] The magnetic recording medium of the present invention is manufactured by preparing paints for the respective layers, applying them to a support, drying them and, if necessary, subjecting them to a heat / curing treatment or a calendering treatment. Is done. 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. Magnetic material used in the present invention, non-magnetic powder, binder, carbon black, abrasive,
All raw materials such as 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, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, 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 the non-magnetic powder and the binder (however, 3/3 of the total binder) is used.
0 mass% or more) and kneading treatment in the range of 15 to 500 parts with respect to 100 parts of the magnetic material. For details of these kneading processes, see JP-A-1-106338,
It is described in JP-A-1-79274. Also,
Glass beads can be used to disperse the magnetic layer liquid and the non-magnetic layer liquid, 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.

In the preparation of the coating for forming the nonmagnetic layer, the step of dispersing carbon black is carried out in the presence of the above-mentioned dispersant. This dispersion treatment step may be performed in the presence of a known solvent, and may be performed by adding other components contained in the nonmagnetic layer. Further, it is preferable that the metal oxide as the nonmagnetic powder contained in the nonmagnetic layer is subjected to a dispersion treatment separately from the carbon black, and then mixed to prepare a coating solution.

When applying a magnetic recording medium having a multilayer structure in the present invention, it is preferable to use the following method. First, an undercoat layer is first applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like generally used in the application of a magnetic paint, and the undercoat layer is in a wet state while the base layer is in a wet state. Gazette and JP 6
0-238179 and JP-A-2-265672 discloses a method of applying an upper layer using a support-pressing-type extrusion coating apparatus. Second, JP-A-63-
JP-A-80080, JP-A-2-17971, and JP-A-2-265672, in which the upper base layer is applied almost simultaneously by using a single coating head having two coating liquid passage slits. Third, JP-A-2-
This is a method of applying the upper base layer almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in Japanese Patent No. 174965. Incidentally, in order to prevent a decrease in the electromagnetic conversion characteristics and the like of the magnetic recording medium due to the aggregation of the magnetic particles, Japanese Patent Application Laid-Open No. Sho 62-95174 and Japanese Patent Application Laid-Open No.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in Japanese Patent Application Publication No. 968-968.
Further, regarding the viscosity of the coating solution, see JP-A-3-8471.
It is necessary to satisfy the numerical range disclosed in Japanese Patent Application Laid-Open Publication No. H10-26095. In order to form the structure of the present invention, it is of course possible to use a sequential multi-layer coating in which a magnetic layer is provided thereon after coating and drying a base layer, and the effect of the present invention is not lost. 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 of the present invention with respect to the head is 0.5 or less, preferably 0.3 or less in a temperature range of -10 ° C. to 40 ° C. and a humidity of 0% to 95%. A magnetic surface of 10 ⁴ to 10 ¹² Ω / sq
The charge potential is preferably within a range from -500 V to +500 V. The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 kg / mm ² (980 to 1960 M) in each direction in the plane.
Pa), 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 ² in each in-plane direction.
80 to 14700 MPa), and the residual elongation is preferably 0.
The heat shrinkage at any temperature of 5% or less and 100 ° C or less is preferably 1% or less, more preferably 0.5% or less,
Most preferably, it is 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 30% by volume or less, more preferably 20% by volume or less, for both the nonmagnetic layer and the magnetic layer. 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 non-magnetic layer and the magnetic layer of the magnetic recording medium of the present invention can be changed according to the purpose. 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.

[0076]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not construed as being limited to these examples. Table 1 shows the types and characteristics of the carbon blacks used in Examples and Comparative Examples.

[0077]

[Table 1]

Example 1 <Coating Composition for Magnetic Layer> 100 parts of ferromagnetic metal fine powder (Co / Fe = 30 atomic%, Al / Fe = 8 atomic%, Y / Fe = 6 atomic%, Hc: 1. 87 × 10 ⁵ A / m (2350 Oe), specific surface area: 55 m ² / g, σs: 140 Am ² / kg, crystallite size: 140 °, average major axis length: 0.068 μm, average needle ratio: 6,・ Surface oxide film thickness: 25 mm) ・ 12 parts of vinyl chloride polymer MR110 (manufactured by Zeon Corporation) ・ 4 parts of polyurethane resin UR8200 (manufactured by Toyobo) ・ 5 parts of α-alumina (average particle diameter: 0.15 μm) ・ 5 parts of carbon black 5 parts ・ Phenylphosphonic acid 3 parts ・ Butylstearate 5 parts ・ Stearic acid 6 parts ・ Methylethylketone 180 parts ・ Cyclohexanone 180 parts

<Non-magnetic layer coating composition> Non-magnetic powder α-Fe ₂ O ₃ 80 parts Average major axis length: 0.12 μm, BET specific surface area: 50 m ² / g pH: 9, Aluminum in surface layer Compound (1% by mass as Al ₂ O ₃ ) 7 parts of α-alumina (average particle diameter: 0.15 μm) 20 parts of carbon black (A in Table 1) 20 parts of vinyl chloride polymer MR110 (manufactured by Zeon Corporation) 12 parts ・ Polyurethane resin UR8200 (manufactured by Toyobo) 5 parts ・ Phenylphosphonic acid 2 parts ・ Dispersant (see Table 2) 2 parts ・ Butylstearate 6 parts ・ Stearic acid 5 parts ・ Methyl ethyl ketone / cyclohexanone (7/3 mixed solvent) ) 250 copies

<Coating liquid composition (1) for forming back layer> 100 parts of fine carbon black powder (BP-800, manufactured by Cabot Corporation, average particle diameter: 17 nm) 10 parts of coarse carbon black powder (Karncarb Co., Ltd.) , Thermal black, average particle diameter: 270 nm)-α-alumina 15 parts (Sumitomo Chemical Co., Ltd., HIT60A, average particle diameter: 0.17 µm, Mohs hardness: 9)-Nitrocellulose 120 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 ・ Toluene 800 parts

The above coating material for the magnetic layer was kneaded with a powder, polyvinyl chloride, phenylphosphonic acid and 50% of the prescribed amount of each solvent with a kneader, and the polyurethane resin and the remaining components were added to the mixture, followed by sand grinder. Was dispersed. To the resulting dispersion, 14 parts of polyisocyanate was added, 30 parts of cyclohexanone was further added, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare a coating solution for forming a magnetic layer.

For the coating for the non-magnetic layer, all of the non-magnetic powder and α-alumina, 8 parts of polyvinyl chloride, 2 parts of phenylphosphonic acid, 70 parts of methyl ethyl ketone, and 30 parts of cyclohexanone are kneaded with a kneader, and then the polyurethane is mixed. 3 parts of the resin, 21 parts of methyl ethyl ketone and 9 parts of cyclohexanone were added and dispersed by a sand grinder to obtain a dispersion (a) for a nonmagnetic layer. About the coating material for the non-magnetic layer, after kneading all of carbon black, the remainder of polyvinyl chloride, all of the dispersant (Table 2) and 70 parts of methyl ethyl ketone and 30 parts of cyclohexanone, the remaining polyurethane resin and 14 parts of methyl ethyl ketone were kneaded. Cyclohexanone 6
The mixture was dispersed by a sand grinder to obtain a dispersion (b) for a nonmagnetic layer. The obtained dispersion liquid (a) and dispersion liquid (b) were mixed with a prescribed amount in a disper and then dispersed by a sand grinder. 15 parts of polyisocyanate and 30 parts of cyclohexanone were added to the obtained dispersion,
Filtration using a filter having an average pore size of 1 μm,
A coating solution for forming a non-magnetic layer was prepared.

<Preparation of magnetic tape> Non-magnetic layer obtained
The thickness of the lower layer after drying the coating solution for application becomes 1.7 μm
And immediately thereafter, apply the coating liquid of the magnetic paint 1 thereon.
A thickness of 5.5 such that the thickness of the magnetic layer is 0.20 μm.
on aramid base with μm and average surface roughness of 2nm
At the same time, both layers are still wet
4.8 x 10 ^FiveA / m (6000 Oe) magnetic force
4.8 × 10 with cobalt magnet^FiveA / m (6000O
e) Orientation and drying were carried out by a solenoid having a magnetic force.
Thereafter, the coating solution (1) for forming a back layer was applied to a thickness of 0.4 μm.
It applied so that it might become. Composed of metal rolls only
150m / mi / min at a temperature of 95 ° C with a 7-stage calendar
n. And heat-treated. Then obtained
The coated material is slit to a width of 3.8 mm, and the surface of the magnetic layer is polished.
After processing, incorporate it into a DDS cartridge and
Pull (magnetic tape) was used. The magnetic characteristics of the obtained magnetic layer
Performance, Ra of magnetic layer and back layer, and 4.7 MHz reproduction
Output, C / N, coefficient of friction at 23 ° C, 60% RH
Measured by the method.

(1) Magnetic properties (Hc, SQ, Bm) Using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.), Hm: 8 ×
It was measured at 10 ⁵ A / m (10 kOe). Bm is a magnetic moment and a magnetic moment per unit volume of the magnetic recording medium. SQ refers to squareness ratio. (2) Center plane average surface roughness (Ra): 3D-MIRAU
Surface roughness (Ra) Ra value of an area of about 250 × 250 μm was measured by MIRAU method using TOPO3D manufactured by WYKO. 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) 4.7 MHz reproduction output A single frequency signal of 4.7 MHz was recorded at the optimum recording current by a DDS drive, and the reproduction output was measured. The output value was shown as a relative value with the reproduction output of Comparative Example 1 being 0 dB.

(4) A 4.7 MHz C / N DDS drive records a 4.7 MHz single frequency signal at the optimum recording current, and averages the reproduced output and the noise level ± 1 MHz away from 4.7 MHz. Calculated. The C / N of Comparative Example 1 was shown as a relative value with 0 dB. (5) The friction coefficient (μ value) of the first pass and the friction coefficient (μ) of the 100 th pass on the magnetic layer surface in an environment of 23 ° C. and 60% RH.
(N value) The magnetic layer surface of the magnetic tape is brought into contact with the guide pole of the magnetic layer surface touch used in the DDS drive, a load of 20 g (T1) is applied, and tension (14 mm / sec.) Is applied. T2) was applied, and the friction coefficient μ (N) of the magnetic layer surface with respect to the guide pole was determined from T2 / T1. The measurement was repeated up to 100 passes, and the friction coefficient μ1 of the first pass and the friction coefficient μ100 of the 100th pass were obtained. (6) Surface Electric Resistance of Magnetic Layer Surface Under 23 ° C. and 60% RH Environment The surface electric resistance of the magnetic layer surface was measured. Surface Electric Resistance Measurement Value of Example—Surface Electric Resistance Measurement Value of Comparative Example 1 (2 × 10
⁹ Ω / sq). Example: measured value-When the measured value of the comparative example was + 0.5 × 10 ¹ Ω / sq or more, ×, -0.5 × 1
The case where the value is larger than 0 ¹ Ω / sq and smaller than + 0.5 × 10 ¹ Ω / sq is Δ, and the case where it is larger than −0.5 × 10 ² Ω / sq and −0.5 × 10 ¹
場合 / sq or less was evaluated as ○, and -0.5 × 10 ² Ω / sq or less as ◎.

Examples 2 to 6 Magnetic recording media were prepared in the same manner as in Example 1 except that the types of carbon black and dispersant in the nonmagnetic layer were changed to those shown in Table 2.

Comparative Example 1 A magnetic recording medium was prepared in the same manner as in Example 1, except that # 950 manufactured by Mitsubishi Chemical Corporation was used instead of the carbon black of the nonmagnetic layer in Example 1, and no dispersant was added. .

Comparative Example 2 Instead of carbon black in the non-magnetic layer of Comparative Example 1, CO
A magnetic recording medium was prepared in the same manner as in Comparative Example 1 except that CONDUVCTEX SC URTLA manufactured by LOMBIAN Chem. Was used.

The above contents and results are shown in Tables 2 and 3.

[0090]

[Table 2]

[0091]

[Table 3]

From Tables 2 and 3, it can be seen that the magnetic layer has a smaller surface roughness (Ra), a smoother output,
Excellent in C / N. Further, the values of the initial running friction coefficient are the same, the change in the friction coefficient during repeated running is a small value stably, and the conductivity is improved.

[0093]

According to the magnetic recording medium of the present invention, the surface roughness of the magnetic layer is adjusted to 1.0 to 3.0 n in order to improve the short wavelength output.
m, the overall thickness and the thickness of the back layer are relatively thin, even when formed with excellent electromagnetic conversion characteristics and running durability, high reliability in data recording and reading, and wet heat storage characteristics. And is particularly suitable as a magnetic tape that can be advantageously used for digital data recording.

Continued on front page F term (reference) 4J038 CA021 CC021 CD021 CD081 CE021 CE051 CE071 CF03 CG031 CG071 CG141 CG161 DA011 DA061 DA141 DA161 DB001 DD001 DG001 DL001 HA026 HA066 HA166 KA08 KA14 MA13 MA14 NA17 NA22 PB04 FA08

Claims (1)

[Claims] 1. A magnetic recording medium in which a nonmagnetic layer and a magnetic layer containing ferromagnetic powder are provided in this order on a support, wherein the nonmagnetic layer is treated with a compound having an amino group at the terminal. A magnetic recording medium containing black.