JPH05217727A - Ferromagnetic metallic powder for magnetic record medium, and magnetic record medium - Google Patents

Abstract

PURPOSE:To pick out only the metallic powder excellent in dispersion property efficiently by making the difference between the surface potential at pH10 of metallic magnetic powder and the surface potential at pH7 an index. CONSTITUTION:In respect of the dispersion property of each metallic magnetic powder, the difference between the surface potential ZP10 at pH10 and the surface potential ZP7 at pH7 is determined as an index, and an object where the difference of surface potential is 30mV or more, that is, an object which fulfills the condition that ZP10-ZP7<=-30mV is selected as one which has favorable dispersion property, and it is used as magnetic powder for a magnetic record medium. That is, in the metallic magnetic powder, the dispersion property and the surface potential difference ZP10-ZP7 show nearly accurate proportional relation. Accordingly, the surface potential difference ZP1-ZP7 becomes the accurate index of dispersion property. Since such surface potential difference ZP10-ZP7 is made an index in selection when selecting metallic magnetic powder which has favorable dispersion property, it follows that only the metallic magnetic powder which has favorable dispersion property is selected, and the metallic magnetic powder which has favorable dispersion property is used efficiently.

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 in particular, a magnetic coating mainly composed of ferromagnetic powder or a binder is applied on a non-magnetic support to form a magnetic layer. The present invention relates to a so-called coating type magnetic recording medium.

[0002]

2. Description of the Related Art As a magnetic recording medium such as a magnetic tape or a magnetic disk, a magnetic paint prepared by mixing and dispersing a ferromagnetic powder, a resin binder, an organic solvent and various additives on a non-magnetic support. A so-called coating type magnetic recording medium in which a magnetic layer is formed by coating is widely used. In the field of magnetic recording, particularly in VTRs (video tape recorders) and the like, higher recording densities are required to achieve higher image quality and the like, and the above magnetic recording media also need to meet such demands. Instead of the iron oxide type magnetic powder which has been conventionally used as the magnetic powder, iron or a metal magnetic powder mainly composed of iron is used, or the magnetic powder is made finer.

By the way, in the coating type magnetic recording medium, the surface property of the magnetic layer must be excellent in order to obtain good electromagnetic conversion characteristics and improve the durability. It is important that the are highly dispersed in the binder.

However, the fine metal magnetic powder, that is, the metal magnetic powder having a large specific surface area has a large cohesive force, and it is difficult to uniformly disperse it in the magnetic paint. Therefore, in order to improve the dispersibility of the metal magnetic powder used in the magnetic recording medium, Al, S and
Treatments such as alloying with metals such as i, Ni, Co, Mn, Zn, Cr, modifying with organic low-molecular compounds having a surface-active effect, or depositing a dispersant on the particle surface by dry or wet methods. Is applied. Then, the metal magnetic powder thus treated is further evaluated for dispersibility, and one having particularly good dispersibility is selected and used as the magnetic powder for the magnetic recording medium.

Here, the quality of the dispersibility of the magnetic metal powder depends on
It is general that the equipotential point of the metal magnetic powder is measured using various pH standard solutions, and the measured equipotential point is used as an index for judgment. For example, in Japanese Examined Patent Publication No. 63-22367, a magnetic metal powder having an equipotential point of pH 7.5 or higher is used as a magnetic powder for a magnetic recording medium with good dispersibility.

[0006]

However, when the present inventors measured the dispersibility of the metal magnetic powder which was not selected by the evaluation selection method using the equipotential point as an index as described above, it was not selected. It was found that some of the magnetic metal powders also had good dispersibility. This means that the dispersibility of the metal magnetic powder is not accurately evaluated at the equipotential point, and the equipotential point is used as an index of dispersibility in order to efficiently obtain only the metal magnetic powder having good dispersibility. Indicates that it is inappropriate.

Therefore, the present invention has been proposed in view of such conventional circumstances, and has a good dispersibility and a ferromagnetic metal powder for a magnetic recording medium in which the metal magnetic powder can be used with high efficiency, and An object is to provide a magnetic recording medium.

[0008]

DISCLOSURE OF THE INVENTION As a result of intensive investigations by the present inventors to find out an index that can accurately reflect the dispersibility of a metal magnetic powder, the dispersibility of the metal magnetic powder is Surface potential Z at pH 10 rather than at equipotential point
It depends largely on the difference between the surface potential ZP _{pH =} 7 at P _{pH = 10} and pH 7, and the dispersibility of the metallic magnetic powder is accurately determined by using this surface potential difference ZP _{pH = 10} −ZP _{pH = 7} as an index. We have come to the knowledge that we can do it.

The ferromagnetic metal powder for a magnetic recording medium of the present invention has been completed on the basis of such findings, and is made of a ferromagnetic metal material or a ferromagnetic alloy material and has a pH of 10
Surface potential at ZP _{pH = 10} , surface potential at _pH 7 at ZP
_{When pH = 7} , ZP _{pH = 10} −ZP _{pH = 7} ≦ −30 mV
It is characterized by satisfying the following condition. Furthermore, the specific surface area is 50 m ² / g or less.

Further, the magnetic recording medium of the present invention is a magnetic recording medium comprising a non-magnetic support and a magnetic layer comprising a magnetic powder and a binder as a main component, wherein the magnetic powder has a pH value.
When the surface potential at ₁₀ is ZP _{pH = 10} and the surface potential at _{pH 7} is ZP _{pH = 7} , ZP _{pH = 10} −ZP _{pH = 7} ≦ −30
The ferromagnetic metal powder satisfies the condition of mV.

Further, the specific surface area of the magnetic powder is 50 m ²
/ G or less.

The magnetic metal powder made of a ferromagnetic metal material or a ferromagnetic alloy material is, for example, Al, Si, Ni, C.
The surface property is controlled by alloying with o, Mn, Zn, Cr or the like, by modifying with a low molecular weight organic compound having a surface activating effect, or by applying a dispersant to the surface by dry or wet method. In order to select only the magnetic powder having a higher degree of dispersibility among the metal magnetic powders whose surface properties are controlled in this way, the dispersibility of each metal magnetic powder is determined by It is important to make judgments using an index that accurately reflects diversification.

Therefore, in the present invention, the dispersibility of each magnetic metal powder is determined by _adjusting the surface potential ZP _{pH = 10} and pH 7 at _{pH 10.}
The difference between the surface potential ZP _{pH = 7} and the surface potential ZP _{pH = 7} is set as an index, and the surface potential difference is 30 mV or more, that is, ZP _{pH = 10} −Z.
Those satisfying the condition of P _{pH = 7} ≦ −30 mV are selected as those having good dispersibility and used as the magnetic powder for the magnetic recording medium.

That is, in the metallic magnetic powder, the dispersibility and the surface potential difference ZP _{pH = 10-} ZP _{pH = 7} show a nearly accurate proportional relationship. Therefore, the surface potential difference ZP _{pH = 10}
-ZP _{pH = 7} is an accurate indicator of dispersibility. In the present invention,
In selecting a metal magnetic powder having good dispersibility, since such a surface potential difference ZP _{pH = 10-} ZP _{pH = 7} is used as a selection index, only a metal magnetic powder having good dispersibility can be selected without exception. Therefore, the metal magnetic powder having good dispersibility can be efficiently used.

As the material constituting the above-mentioned ferromagnetic metal powder, a ferromagnetic metal material such as Fe, Co, Ni, or F is used.
e-Co, Fe-Ni, Fe-Co-Ni, Co-N
i, Fe-Mn-Zn, Fe-Ni-Zn, Fe-Co
-Ni-Cr, Fe-Co-Ni-P, Fe-Co-
Fe such as B, Fe-Co-Cr-B, Fe-Co-V,
Examples include various ferromagnetic alloy materials containing Co and Ni as main components.

The specific surface area of the ferromagnetic metal powder is preferably 30 m ² / g or more, more preferably 40 m ² / g or more in view of high density recording, but it is uniformly dispersed in the binder. Therefore, it is preferably 50 m ² / g or less.

In the present invention, the ferromagnetic metal particles for a magnetic recording medium can be kneaded with a resin binder or an organic solvent to prepare a magnetic paint, and this magnetic paint is applied onto a non-magnetic support. As a result, a magnetic recording medium can be obtained. In this case, as a resin binder, an organic solvent, and various additives,
Any of those used for ordinary magnetic recording media can be used, and the compounding ratio and the like are set in accordance with those for ordinary magnetic recording media.

[0018]

In the present invention, when selecting the metal magnetic powder to be used as the magnetic powder for the magnetic recording medium, the metal magnetic powder having a surface potential difference ZP _{pH = 10-} ZP _{pH = 7 of} -30 mV or less has good dispersibility. Evaluate and select. In metal magnetic powder, dispersibility and surface potential difference ZP _{pH = 10} -ZP
_{pH = 7} shows an almost exact proportional relationship. Therefore, when the surface potential difference ZP _{pH = 10} −ZP _{pH = 7} is used as an index, the dispersibility of the metal magnetic powder is accurately evaluated, and only the magnetic powder having good dispersibility is used without fail as the magnetic powder for the magnetic recording medium. The Rukoto.

[0019]

EXAMPLES Preferred examples of the present invention will be described based on experimental results. A magnetic coating composition having the composition shown below was put into a ball meal and dispersed and mixed for 24 hours to prepare a magnetic coating composition. Magnetic coating composition Ferromagnetic metal powder 100 parts by weight Vinyl chloride resin 10 parts by weight Thermoplastic polyurethane resin 10 parts by weight Carbon fine powder 3 parts by weight Alumina fine powder 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

Then, the prepared magnetic paint is applied to a thickness of 11 μm.
A magnetic tape (magnetic tape 1 to magnetic tape 3, comparative tape 1, comparative tape 2) was prepared by coating and drying the above polyester film so that the dry thickness would be 3.5 μm.

The surface potential difference ZP _{pH = 10} −ZP _{pH = 7 of} the ferromagnetic metal powder used in each magnetic tape, the dispersiveness G (gross) 45 ° saturation magnetization σ _s , the coercive force Hc and the specific surface area SSA are shown in Table 1. As shown. Further, FIG. 1 shows the relationship between the surface potential difference ZP _{pH = 10} −ZP _{pH = 7} and the dispersibility G45 °.

The surface potentials ZP _{pH = 10} and ZP _{pH = 7} are
It was measured under the following conditions immediately before the dispersibility measurement. Measurement method: Electrophoresis measurement Applied voltage: 100 V pH standard solution: KNO ₃ 0.01 mol / l Metal powder amount: 500 mg / l

[0023]

[Table 1]

First, as can be seen from FIG. 1, in the ferromagnetic metal powder, the dispersibility and the surface potential difference ZP _{pH = 10} −ZP.
_{pH = 7} shows an almost accurate proportional relationship. Therefore, from this fact, the surface potential difference ZP _{pH = 10} −ZP _{pH = 7} is suitable as an index of dispersibility, and from FIG.
It was found that by selecting one having P _{pH = 10} −ZP _{pH = 7 of} −30 mV or less, one having good dispersibility can be obtained.

Further, as can be seen from Table 1, the metallic magnetic powder having a surface potential difference ZP _{pH = 10-} ZP _{pH = 7 of} -30 mV or less has excellent dispersibility and maintains magnetic properties at practical values. It was found that it is suitable as a magnetic powder for magnetic recording media.

[0026]

As is apparent from the above description, in the present invention, when the metal magnetic powder used as the magnetic powder for the magnetic recording medium is selected, the surface potential difference ZP is selected.
_{pH = 10} −ZP Since _{pH = 7} is selected to be −30 mV or less, only the magnetic metal powder having good dispersibility can be efficiently used.

Therefore, according to the present invention, the magnetic powder is uniformly dispersed in the magnetic layer, the electromagnetic conversion characteristics and the durability are excellent, the magnetic powder is used efficiently, and the productivity is high. It is possible to obtain

[Brief description of drawings]

FIG. 1 Surface potential difference ZP _{pH = 10} −Z of ferromagnetic metal powder
It is a characteristic view which shows the relationship between P _{pH = 7} and dispersibility.

Claims (4)

[Claims] 1. A ferromagnetic metal material or a ferromagnetic alloy material, wherein when the surface potential at _{pH 10} is ZP _{pH = 10} and the surface potential at _{pH 7} is ZP _{pH = 7} , ZP _{pH = 10} −ZP _{pH = 7} ≦ −30 mV, which is a ferromagnetic metal powder for magnetic recording media. 2. The ferromagnetic metal powder for a magnetic recording medium according to claim 1, which has a specific surface area of 50 m ² / g or less. 3. A magnetic recording medium comprising a non-magnetic support and a magnetic layer comprising a magnetic powder and a binder as a main component, wherein the magnetic powder has a surface potential at _{pH 10} of ZP _{pH = 10} , p.
When the surface potential at H7 is ZP _{pH = 7} , ZP _{pH = 10}
A magnetic recording medium characterized by being a ferromagnetic metal powder satisfying the condition of -ZP _{pH =} 7≤ _- 30 mV. 4. The magnetic recording medium according to claim 3, wherein the specific surface area of the magnetic powder is 50 m ² / g or less.