JP2001068314A - Magnetic powder and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium which exhibits excellent weathering resistance and low electric resistance. SOLUTION: In a magnetic layer 4, the surface of metal magnetic powder is mechanochemically covered with carbon black. Thereby oxidation on the surface of the metal magnetic powder can be prevented. Since the surface of metal magnetic powder is mechanochemically covered with the carbon black whose electric conductivity is high, electric resistance is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder and a coating type magnetic recording medium containing the magnetic powder in a magnetic layer.

[0002]

2. Description of the Related Art A so-called coating type magnetic recording medium, in which a magnetic layer formed by applying a magnetic coating material in which a magnetic powder is dispersed and mixed with a binder together with an additive on a non-magnetic support, is formed.
Widely used as video tapes, audio tapes, magnetic disks, and the like.

[0003] In such a coating type magnetic recording medium, fine magnetic powder is used in order to increase the average number of magnetic powder per unit volume of the magnetic layer for the purpose of high density recording.

[0004] In a coating type magnetic recording medium, high-density recording is progressing by using a short recording wavelength. For this reason, in order to realize high-density recording in a coating type magnetic recording medium, it is required to improve electromagnetic conversion characteristics for a short recording wavelength.

However, as the recording wavelength becomes shorter, the output of the magnetic recording medium decreases. Therefore, in order to obtain a high output from the magnetic recording medium, it is required that the magnetic powder contained in the magnetic layer has a large saturation magnetization and a high coercive force.

In view of the above, in place of the conventionally used oxide magnetic powder, in recent years, a metal magnetic powder mainly containing Fe and having a high coercive force and a large saturation magnetization has been used.

In particular, the finely divided metal magnetic powder has a higher saturation magnetization σ _S than the oxide magnetic powder.
Therefore, a magnetic recording medium containing finely divided metal magnetic powder in the magnetic layer can obtain a high output.

[0008]

When metal magnetic powder is used for the magnetic layer, magnetic interaction acts between adjacent metal magnetic powders. Such magnetic interaction causes noise when reproducing a magnetic recording medium. Therefore, the magnetic recording medium has a problem that even if the output is improved by using a metal magnetic powder exhibiting a high saturation magnetization, the noise is increased and the S / N is reduced.

Further, the metal magnetic powder is liable to be oxidized by reacting with moisture and oxygen components in the atmosphere. In particular, since the metal magnetic powder becomes finer, the surface area increases, so that the metal magnetic powder is more easily oxidized. For this reason, the magnetic recording medium in which the magnetic layer contains the metal magnetic powder has a problem that the metal magnetic powder is oxidized and the weather resistance is poor.

[0010] Furthermore, when the surface of the metal magnetic powder is oxidized, the electric resistance on the surface increases. For this reason, in a magnetic recording medium, when the magnetic layer contains a metal magnetic powder having an oxide film on the surface, the magnetic layer has high electric resistance and is easily charged. Therefore, the magnetic recording medium includes a magnetic layer that is easily charged, so that dust or the like is adsorbed,
There has been a problem that sticking occurs when a plurality of sheets are stacked.

The present invention has been devised in view of such conventional problems, and exhibits high saturation magnetization, reliably prevents oxidation of the surface, and exhibits low electric resistance. It is intended to provide a magnetic powder. Another object of the present invention is to provide a magnetic recording medium using this magnetic powder, in which noise is reduced, S / N is excellent, weather resistance is excellent, and electric resistance is reduced.

[0012]

The magnetic powder according to the present invention which has achieved the above-mentioned object is characterized in that the particle surface of the metal magnetic powder is mechanochemically coated with carbon black.

In the magnetic powder according to the present invention configured as described above, the particle surface of the metal magnetic powder is mechanochemically coated with carbon black. Thereby, oxidation on the surface of the metal magnetic powder can be prevented. Further, the magnetic powder is made of carbon black having high electric conductivity and the particle surface of the metal magnetic powder is mechanochemically coated, so that the electric resistance is low.

A magnetic recording medium according to the present invention is a magnetic recording medium comprising at least a non-magnetic support and a magnetic layer formed by applying a magnetic paint obtained by dispersing a magnetic powder in a binder. Is characterized in that the particle surface of the metal magnetic powder is mechanochemically coated with carbon black.

In the magnetic recording medium according to the present invention configured as described above, the magnetic powder is obtained by coating the surface of the metal magnetic powder with non-magnetic carbon black in a mechanochemical manner. Will be adjacent to each other. Thereby, the magnetic interaction between the adjacent magnetic powders is reduced.

Further, the surface of the metal magnetic powder is hardly oxidized because it is mechanochemically coated with carbon black. Therefore, in the magnetic recording medium, the oxidation of the magnetic layer is reliably prevented.

Further, the magnetic layer has a low electric resistance because the surface of the particles of the metal magnetic powder contains a magnetic powder which is mechanochemically coated with carbon black having high electric conductivity.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the magnetic powder and the magnetic recording medium according to the present invention will be described.

The magnetic powder to which the present invention is applied is composed of a metal magnetic powder and carbon black, and the particle surface of the metal magnetic powder is mechanochemically coated with carbon black.

As the metal magnetic powder, any conventionally known metal magnetic powder can be used. Further, it is preferable that the magnetic powder is Fe-based metal magnetic powder.

Examples of the Fe-based metal magnetic powder include Fe powder, Fe—Co alloy powder, Fe—Al alloy powder, and Fe powder.
-Al-Ni alloy powder, Fe-Al-Zn alloy powder, F
e-Al-Co alloy powder, Fe-Al-Ca alloy powder,
Fe-Ni alloy powder, Fe-Ni-Al alloy powder, Fe
-Ni-Co alloy powder, Fe-Ni-Si-Al-Mn
Alloy powder, Fe-Ni-Si-Al-Zn alloy powder, F
e-Al-Si alloy powder, Fe-Ni-Zn alloy powder,
Fe-Ni-Mn alloy powder, Fe-Ni-Si alloy powder, Fe-Mn-Zn alloy powder, Fe-Co-Ni-P
Metal powders such as alloy powders, iron nitride, and iron carbide can be used.

The metal magnetic powder may contain an additive element or oxide for the purpose of oxidation stability, sintering prevention, shape stability and the like. As these additional elements and oxides,
For example, Al, Y, Si, Ca, La and the like, and oxides thereof, α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ , Fe ₃ O _{4 and the} like can be mentioned.

The size of the metal magnetic powder is preferably fine particles. Specifically, the major axis length of the metal magnetic powder is preferably 0.01 to 1.0 μm.

As the carbon black, any of the production methods can be used, and specific examples include furnace black, thermal black, acetylene black, channel black, lamp black and the like. These carbon blacks may be used alone or in combination.

The carbon black may be subjected to a surface treatment with a dispersant or the like, graphitized with a resin, or a part of the surface graphitized.

Here, it is preferable that the carbon black is mechanochemically coated in the range of 0.5% by weight to 50% by weight based on the metal magnetic powder.

It is to be noted that mechanochemical is a phenomenon in which when a stress exceeding a certain criticality is applied to a solid, the vicinity of the action point is locally brought into a high-energy state, the arrangement of atoms and molecules is disturbed, and the physical properties are changed. It is. Using this phenomenon, carbon black is treated to coat the metal magnetic powder with carbon black.

When coating the metal magnetic powder with carbon black, the structure of carbon black is mechanochemically crushed to obtain graphite crystallites.
Then, the obtained graphite crystallites are coated on the metal magnetic powder.

When performing this coating treatment, for example, a high-speed airflow impact device (trade name: Hybridizer manufactured by Nara Machinery Co., Ltd.) is used.

On the other hand, the magnetic recording medium 1 to which the present invention is applied
As shown in FIG. 1, a non-magnetic support 2, a non-magnetic layer 3 formed on the non-magnetic support 2,
And a magnetic layer 4 containing the magnetic powder described above.

The present invention is not limited to the structure described above, but may be applied to a magnetic recording medium comprising a non-magnetic support and a magnetic layer formed on the non-magnetic support. Further, as the magnetic recording medium, a back coat layer for improving the running property of the magnetic recording medium, and preventing charge and transfer is provided on the surface opposite to the surface on which the magnetic layer is provided on the non-magnetic support. May be provided.

In the magnetic recording medium 1, as the non-magnetic support 2, any one used in a usual coating type magnetic recording medium can be used. Specifically, polyethers such as polyethylene terephthalate, polyethylene, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, cellulose derivatives such as cellulose butyrate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, polycarbonate, In addition to plastics such as polyimide and polyamide-imide, light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass are exemplified.

When a rigid substrate such as an Al alloy plate or a glass plate is used for the nonmagnetic support 2, an oxide film such as alumite treatment or a Ni-P film is formed on the surface of the substrate. The surface may be hardened.

The shape of the nonmagnetic support 2 is not particularly limited, and may be any shape such as a tape shape, a disk shape, and a card shape.

The non-magnetic layer 3 is formed by applying a non-magnetic paint comprising at least a non-magnetic powder and a binder on the non-magnetic support 2. As the non-magnetic powder, a known non-magnetic powder conventionally used, for example, α-Fe
₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , α-FeOOH, CaO,
SiO ₂ or the like can be used. As the binder to be contained in the non-magnetic paint, a conventionally known binder such as a vinyl chloride resin can be used.

The magnetic layer 4 is formed by applying a magnetic paint comprising at least a magnetic powder and a binder on the non-magnetic layer 3. As the magnetic powder contained in the magnetic paint, the above-mentioned magnetic powder is used. As the binder, any binder used in a usual coating type magnetic recording medium can be used. Specific examples include polyvinyl copolymer resins, polyester polyurethane resins, polycarbonate polyurethane resins, nitrocellulose resins, and mixtures of these resins.

Further, additives such as a lubricant, an abrasive, an antistatic agent and the like may be added to the magnetic paint as needed. As these additives, any conventionally known additives can be used.

The non-magnetic paint and the magnetic paint are prepared by kneading and dispersing the above-mentioned components together with a solvent.

As the solvent used in the kneading and dispersion,
Methyl ethyl ketone, toluene, butyl acetate, cyclohexanone, etc., which are used for adjusting ordinary non-magnetic paints and magnetic paints, can be used.

The method of kneading and dispersing is not particularly limited as long as it is a method used for adjusting ordinary non-magnetic paints and magnetic paints, and the order of addition of each component can be appropriately set. For adjusting the non-magnetic paint and the magnetic paint, a usual kneader, for example, a continuous twin-screw kneader (extruder), a co-kneader, a pressure kneader and the like can be mentioned. In addition, as a dilution and dispersion machine,
A vertical sand mill, a horizontal sand mill, a spike mill, a pearl mill, a double cylinder pearl mill, and the like can be given.

In forming the non-magnetic layer 3 and the magnetic layer 4, a non-magnetic paint and a magnetic paint are applied on the non-magnetic support 2 in this order. At this time, a so-called wet-on-coating method in which the non-magnetic paint and the magnetic paint are applied one by one and dried.
A dry method may be used, or a so-called wet-on-wet method in which a magnetic paint is applied over a non-magnetic paint in a wet state. When coating is performed by a wet-on-wet method, a die coater is mainly used as a coating device.

When a magnetic layer is formed by applying a magnetic paint on a non-magnetic support, gravure coating,
Conventionally known coating methods such as extrusion coating, air doctor coating, and reverse roll coating can be used.

According to the above-described method, at least the magnetic layer 3 is formed on the non-magnetic support 2, an orientation treatment is performed, and the wet magnetic coating film is dried. The magnetic recording medium 1 is manufactured by performing processing and slitting or punching into a desired shape.
The magnetic recording medium 1 is slit into a desired width in the case of a tape medium, for example.

In the magnetic recording medium 1 thus manufactured, the magnetic powder is a metal magnetic powder whose surface is mechanochemically coated with carbon black as described above. In this magnetic powder, the surface of the metal magnetic powder is covered with carbon black,
Protected against external moisture and oxygen. For this reason, the surface of the metal magnetic powder is less likely to be oxidized, so that the magnetic powder has excellent weather resistance.

In other words, on the surface of the metal magnetic powder,
It becomes difficult to form an oxide film. Since the oxide film has low electric conductivity, the electric resistance of the surface of the metal magnetic powder increases. However, in the above-described magnetic powder, an oxide film is hardly formed on the surface of the metal magnetic powder, so that the electric resistance can be suppressed low.

Here, it is preferable that the carbon black is mechanochemically coated in a range of 0.5% by weight to 50% by weight based on the metal magnetic powder. By coating the carbon black mechanochemically in the range of 0.5% by weight to 50% by weight with respect to the metal magnetic powder, the weather resistance is surely improved. If the amount of carbon black applied is less than 0.5% by weight with respect to the metal magnetic powder, it may not be possible to sufficiently achieve the above-described improvement in weather resistance and reduction in electric resistance. If the amount of carbon black applied is more than 50% by weight of the metal magnetic powder, the saturation magnetization s of the metal magnetic powder may be too small.

In the magnetic recording medium 1 described above, the magnetic layer 4 contains metal magnetic powder having a higher saturation magnetization σs than the oxide magnetic powder, so that the reproducing output is excellent. In particular, in the magnetic recording medium 1, since the above-described magnetic powder is used, the metal magnetic powder is adjacent to the magnetic layer 4 via non-magnetic carbon black coated on the surface. For this reason, in the magnetic recording medium 1, no magnetic interaction acts between the adjacent metal magnetic powders, and the noise component is greatly reduced. As described above, since the magnetic recording medium 1 uses the magnetic powder having the metal magnetic powder having the large saturation magnetization s and the noise is significantly reduced, the magnetic recording medium 1 exhibits excellent S / N.

Since the magnetic powder coats the surface of the metal magnetic powder with carbon black, the magnetic powder exhibits a lower saturation magnetization s as compared to the case where the metal magnetic powder is used alone. However, in the magnetic recording medium 1, the reduction in the noise component is greater than the reduction in the saturation magnetization s, and as a result, a high S / N is exhibited.

Further, in the magnetic recording medium 1, as described above, since the magnetic powder having excellent weather resistance is used for the magnetic layer 4, the magnetic layer 4 is prevented from being oxidized by external moisture and oxygen components. be able to. In other words, in the magnetic recording medium 1, the magnetic layer 4 is excellent in weather resistance, for example, excellent electromagnetic conversion over a long period of time without inconvenience such as a decrease in output even after long-term storage. Characteristics can be maintained.

Further, in the magnetic recording medium 1, since the surface of the metal magnetic powder is coated with the carbon black having high electric conductivity as described above, Electrical continuity can be achieved. In other words, in the magnetic recording medium 1, the electric resistance of the magnetic layer 4 is reduced by using the above-described magnetic powder. Therefore, in this magnetic recording medium 1,
The electrification of the magnetic layer 4 can be prevented. For this reason, the magnetic recording medium 1 is prevented from inconvenience such as dust and the like adhering to the magnetic layer 4 and sticking when a plurality of sheets are overlapped.

Here, it is preferable to use a magnetic powder in which carbon black is mechanochemically coated in a range of 0.5% by weight to 50% by weight based on the metal magnetic powder. Carbon black is added to the metal magnetic powder in an amount of 0.
By coating mechanochemically in the range of 5% by weight to 50% by weight, the magnetic recording medium 1 can reliably improve weather resistance and maintain a high reproduction output. When the amount of carbon black deposited is less than 0.5% by weight with respect to the metal magnetic powder, it is possible to sufficiently improve the weather resistance of the magnetic layer 4 and reduce the electric resistance of the magnetic layer 4 as described above. It may not be possible. When the amount of carbon black applied is more than 50% by weight with respect to the metal magnetic powder, the saturation magnetization σs of the metal magnetic powder becomes small, so that the magnetic recording medium 1 has a reduced output. There is a risk of becoming.

[0052]

EXAMPLES Hereinafter, a plurality of samples were prepared as specific examples and comparative examples of the present invention, and using these samples, the amount of carbon black coated on the metallic magnetic powder was examined. As a sample, a magnetic tape was manufactured.

<Experiment 1> In Experiment 1, magnetic tapes having a magnetic layer formed on a nonmagnetic support were prepared as Samples 1 to 11.

Sample 1 First, a magnetic powder was prepared which had been subjected to a coating treatment in which the particle surface of a metal magnetic powder was mechanochemically coated with carbon black. The magnetic properties of the magnetic powder are as follows.
In addition, as the metal magnetic powder, Fe-based metal acicular ferromagnetic powder (major axis length: 0.07 μm, σ _s = 130 emu /
g) was used.

Here, the coating amount of carbon black is expressed as a weight percentage (C) with respect to Fe, which is a main component of the metal magnetic powder.
/ Fe).

<Magnetic powder>-Carbon black coating amount (C / Fe) = 0.5% by weight-Saturation magnetization = 129 emu / g-Average particle size = 0.02 µm The magnetic properties were measured using a sample vibration magnetometer. Measured.

Next, according to the following composition, each component of the magnetic paint was measured, kneaded, and dispersed to prepare the magnetic paint.

<Magnetic paint composition>-Magnetic powder 100 parts by weight-Binder resin Polyvinyl chloride resin (manufactured by Zeon Corporation: MR-110) 10 parts by weight Polyester polyurethane (manufactured by Toyobo Co., Ltd .: UR-8200) 10 parts by weight-Polishing Agent: Al ₂ O ₃ 3 parts by weight Additive: stearic acid 1 part by weight Solvent: methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

The magnetic paint prepared as described above was coated on a non-magnetic support made of polyethylene terephthalate and dried to form a magnetic layer. Note that the thickness of the magnetic layer was 1.5 μm. This is cut into 8mm width,
A magnetic tape of Sample 1 having a magnetic layer formed on a non-magnetic support was obtained.

Samples 2 to 10 A magnetic layer was formed on a nonmagnetic support in the same manner as in Sample 1, except that the magnetic powders were prepared at the weight ratios shown in Table 1 with respect to the metal magnetic powder. Was formed on the magnetic tape.

Sample 11 A magnetic tape having a magnetic layer formed on a non-magnetic support was prepared in the same manner as in Sample 1, except that a magnetic metal powder not coated with carbon black was used as the magnetic powder. .

<Experiment 2> Next, in Experiment 2, a magnetic tape comprising a non-magnetic support, a non-magnetic layer formed on the non-magnetic support, and a magnetic layer formed on the non-magnetic layer was used. , Samples 12 to 22.

Sample 12 A magnetic powder was prepared in which the surface of the metal magnetic powder was mechanochemically coated with carbon black. The magnetic properties of the magnetic powder are as follows. In addition, as the metal magnetic powder, Fe-based metal needle-shaped ferromagnetic powder (major axis length: 0.07
μm, σ _s = 130 emu / g).

<Magnetic powder>-Carbon black coating amount (C / Fe) = 0.5% by weight-Saturation magnetization = 129 emu / g-Average particle size = 0.02 µm The magnetic properties were measured using a sample vibration magnetometer. Measured.

Next, according to the following composition, each component of the magnetic paint was measured, kneaded and dispersed to prepare the magnetic paint.

<Magnetic coating composition>-Magnetic powder 100 parts by weight-Binder resin Polyvinyl chloride resin (manufactured by Zeon Corporation: MR-110) 10 parts by weight Polyester polyurethane (manufactured by Toyobo Co., Ltd .: UR-8200) 10 parts by weight-Polishing Agent: Al ₂ O ₃ 3 parts by weight Additive: stearic acid 1 part by weight Solvent: methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

Next, each component of the non-magnetic paint was weighed, kneaded and dispersed according to the following composition to prepare the non-magnetic paint.

<Non-magnetic coating composition> ・ 100 parts by weight of iron oxide powder ・ Binder resin: 20 parts by weight of polyvinyl chloride resin ・ Antistatic agent: 10 parts by weight of carbon (average particle size = 0.03 μm) ・ Additive: stearin Acid 2 parts by weight Solvent: methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight

The non-magnetic coating material and the magnetic coating material prepared as described above are applied on a non-magnetic support made of polyethylene terephthalate by wet coating using a die coater, and then dried to form a non-magnetic support. A magnetic recording medium including a non-magnetic layer formed on a non-magnetic support and a magnetic layer formed on the non-magnetic layer was manufactured. The thickness of the magnetic layer was 0.3 μm, and the thickness of the non-magnetic layer was 1.5 μm. This was cut into a width of 8 mm to obtain a magnetic tape of Sample 12.

Samples 13 to 21 Magnetic tapes were prepared in the same manner as in Sample 12, except that the magnetic powders were used at the weight ratios shown in Table 2 with respect to the metal magnetic powder.

Sample 22 Sample 12 was prepared except that a magnetic metal powder not coated with carbon black was used as the magnetic powder.
In the same manner as in the above, a magnetic tape was produced.

Samples 1 to 22 produced as described above
, The electromagnetic conversion characteristics, weather resistance and electric resistance were evaluated. The evaluation methods are described below.

<Electromagnetic Conversion Characteristics> Using samples 1 to 22, a relative speed of 3.8 m / s and a frequency of 7.6 were applied to a magnetic tape.
Output when a signal of MHz (0.5 μm) is recorded;
The noise of 7.6 ± 1.0 MHz was measured, and the ratio between the output and the noise was evaluated as S / N.

The measurement data was a relative value when the measured value obtained with the sample 11 in the experiment 1 and the measured value obtained with the sample 22 in the experiment 2 were 0 dB.

<Weather resistance> The magnetic tape was stored for one week in an environment of a temperature of 60 ° C. and a humidity of 90%, and the saturation magnetization σ _S of the magnetic tape was measured before and after storage, and the deterioration of the saturation magnetization σ _S was expressed as a percentage. _It was evaluated as _S deterioration.

<Electrical Resistance> The electric resistance of the magnetic layer was measured using a bipolar surface electric resistance measuring instrument (manufactured by YHP: HIGHRESIS).
TANCE METER).

The results of the above property evaluation and the weight ratio of the coating amount of carbon black to the metal magnetic powder are shown in Table 1.
And Table 2 below.

[0078]

[Table 1]

[0079]

[Table 2]

As can be seen from Tables 1 and 2, Samples 1 to 3 each containing a magnetic powder in which the particle surface of a metal magnetic powder was mechanochemically coated with carbon black in a magnetic layer.
10 and samples 12 to 21 were found to have significantly reduced noise, excellent weather resistance, and low electrical resistance.

On the other hand, as shown in Samples 11 and 22, when metal magnetic powder not coated with carbon black was contained in the magnetic layer as magnetic powder, noise reduction was not observed. Poor weather resistance and high electrical resistance.

As shown in Samples 8 and 19, when the weight ratio of the coating amount of carbon black to the metal magnetic powder was 0.2% by weight, the coating amount of carbon black was insufficient. In addition, noise reduction is not so much observed, weather resistance is not so much improved, and electric resistance is not so much reduced.

On the other hand, as shown in Samples 9, 10, 20, and 21, when the weight ratio of the coating amount of carbon black to the metal magnetic powder was set to 50% by weight or more, the coating amount of non-magnetic carbon black , The saturation magnetization σ _S becomes too low. Therefore, the magnetic tape cannot obtain a sufficient output.

From the above, it was found that the weight ratio of the coating amount of carbon black to the magnetic metal powder was preferably in the range of 0.5% by weight to 50% by weight.

[0085]

As is clear from the above description, in the magnetic powder according to the present invention, the particle surface of the metal magnetic powder is mechanochemically coated with carbon black.
Oxidation on the surface of the metal magnetic powder can be prevented. Thereby, it becomes a magnetic powder excellent in weather resistance.

The magnetic powder is made of carbon black having a high electric conductivity and the surface of the metal magnetic powder is mechanochemically coated, so that the electric resistance is low.

In the magnetic recording medium according to the present invention, the magnetic powder contained in the magnetic layer is mechanochemically coated with nonmagnetic carbon black on the particle surface of the metallic magnetic powder. Will be adjacent. For this reason, in the magnetic recording medium, the magnetic interaction between adjacent magnetic particles is reduced.

Since the surface of the metal magnetic powder is mechanochemically coated with carbon black, it is hardly oxidized. Therefore, in the magnetic recording medium, the oxidation of the magnetic layer is reliably prevented, and the magnetic layer has excellent weather resistance.

Further, the magnetic layer contains a magnetic powder in which the particle surface of the metal magnetic powder is mechanochemically coated with carbon black having high electric conductivity. Therefore, in the magnetic recording medium, the electric resistance of the magnetic layer is low.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetic recording medium to which the present invention is applied.

[Explanation of symbols]

1 magnetic recording medium, 2 non-magnetic support, 3 non-magnetic layer,
4 Magnetic layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 7/12 C09D 7/12 Z 201/00 201/00 G11B 5/712 G11B 5/712 F term (reference) ) 4J037 AA02 AA04 CA02 CA03 DD12 EE03 EE29 FF11 FF22 4J038 BA081 DG111 DG121 HA026 HA066 HA076 HA316 KA07 KA15 KA20 NA03 NA17 NA22 PB11 4K018 BA13 BC16 BC28 BD02 5D006 BA04 BA07 BA08 EA01 FA02 FA08 A

Claims (6)

[Claims] 1. A magnetic powder, wherein the particle surface of the metal magnetic powder is mechanochemically coated with carbon black. 2. The magnetic powder according to claim 1, wherein the carbon black is coated in a range of 0.5% by weight to 50% by weight based on the metal magnetic powder. 3. The magnetic powder according to claim 1, wherein the metal magnetic powder is an Fe-based metal magnetic powder. 4. A magnetic recording medium comprising at least a non-magnetic support and a magnetic layer formed by applying a magnetic paint obtained by dispersing a magnetic powder in a binder, wherein the magnetic powder comprises particles of a metal magnetic powder. A magnetic recording medium, the surface of which is mechanochemically coated with carbon black. 5. The magnetic recording medium according to claim 4, wherein said carbon black is coated in a range of 0.5% by weight to 50% by weight based on said metal magnetic powder. 6. The magnetic recording medium according to claim 4, wherein the metal magnetic powder is an Fe-based metal magnetic powder.