JPH028372B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and in a magnetic recording medium using metal magnetic powder containing Fe as a main component,
In the magnetic layer of the magnetic recording medium, the average particle diameter is 1 to 1.
By containing 2 to 15% by weight of inorganic particles with a Mohs hardness of 6.5 or higher and having a diameter of 2 μm and sharp edges on the particle surface, it is possible to magnetically record and reproduce magnetic tapes, etc. It is possible to eliminate the phenomenon of coloring of the surface of the magnetic head when it is attached to a device and run it, and the magnetic layer surface is smooth, there is little dropout, etc., and furthermore, the magnetic recording medium has good magnetic properties such as maximum magnetic flux density. The purpose is to provide. Traditionally, γ-
Oxides such as Fe ₂ O ₃ have been mainly used, but
Magnetic recording media using these oxide magnetic powders are
Because of their low coercive force and low magnetic flux density, they are not suitable for high-density recording, and recently metal-based magnetic powders such as Fe have come to be used. This is because the coercive force and magnetic flux density of metal magnetic powder such as Fe are larger than those of oxide magnetic powder, and as a result, it is suitable for high-density recording. However, when metal magnetic powder is used instead of oxide as the magnetic powder, various problems arise if the other compositions of the magnetic recording medium are the same as in the case of oxide magnetic powder. In other words, the magnetization of the metal magnetic powder particles themselves is larger than that of oxide magnetic powder, and it is difficult to disperse in magnetic paint. Therefore, if you try to improve the dispersibility, the metal magnetic powder particles will break easily, and as a result, the magnetic properties will deteriorate. cause deterioration. In addition, in the case of oxide magnetic powder, the hardness is high, so it is difficult to cause scratches, but the hardness of metal magnetic powder is low, so the coating film strength is weak and it is easily scratched. Therefore, such magnetic recording media are required to improve the bonding strength of the coating film and to prevent the coating film from peeling off or powder falling off when rubbed by a magnetic head, etc., and clogging the magnetic head. For this reason, abrasives are added. In particular, in the case of metal magnetic powder, a larger amount is added as an essential component of the magnetic recording medium than in the case of oxide magnetic powder. It is desirable that the particle size of this abrasive be as small as possible in view of the smoothness of the surface of the magnetic tape, and for example, a particle size of about 0.3 to 0.5 μm is used. Further, it is said that it is preferable that the particle shape of this abrasive is spherical because it is easy to uniformly disperse it in the magnetic particles. However, when a magnetic tape using such an abrasive material is mounted on a tape recorder or the like and run, the surface of the magnetic head, which is the contact surface with the magnetic tape, becomes colored, for example, yellowish brown or bluish-purple. In some cases, a brown coating phenomenon was found where the color changed to dark purple. The colored matter that adheres to the surface of the magnetic head does not dissolve in any organic solvent, and its composition is unknown even by analytical means such as X-ray microanalysis or microausier analysis, and the cause of its occurrence is unknown. It was unclear. When a magnetic head with this brown coating phenomenon is compared with a magnetic head without the brown coating phenomenon, its performance does not deteriorate significantly, but due to the coloring of the magnetic head,
The user becomes worried that the performance has deteriorated, and furthermore, the appearance becomes bad and the commercial value decreases. It has been noticed that this brown coating phenomenon appears conspicuously when metal magnetic powder is used as the magnetic powder of the magnetic tape and a metal material such as a sendust alloy is used as the constituent material of the magnetic head. For example, γ-Fe ₂ O ₃ or
In the case of magnetic tapes made using oxide magnetic powder such as CrO ₂ , the surface of the magnetic head does not change color and no brown coating phenomenon is observed even if Sendust alloy is used as the component material of the magnetic head. Contrary to this, only the magnetic powder is replaced with metal magnetic powder,
The other composition in the magnetic layer is that when a magnetic tape made using the same composition as the magnetic powder of γ-Fe ₂ O ₃ is used for a magnetic head made of Sendust alloy, etc., the surface of the magnetic head is The color changed significantly and a brown coating phenomenon was observed. Table 1 shows the results of experiments on this situation. The contents of Table 1 are the results of experiments using commonly used abrasives in the form of particles, and the purpose of the present invention is to eliminate this brown coating phenomenon in magnetic tapes. Next, we will discuss experimental examples using various abrasives on this magnetic tape. In this series of examples, crushed particles with sharp edges were used to solve the brown coating phenomenon.

[Table] For example, approximately 100 parts by weight of acicular magnetic powder mainly composed of iron as metal magnetic powder, approximately 20 parts by weight of binder, approximately 290 parts by weight of solvents such as toluene, methyl ethyl ketone, and methyl isobutyl ketone, and approximately 200 parts by weight of dispersant. 2 parts by weight, about 2 parts by weight of a lubricant, and about 2 parts by weight of abrasive material.
A relatively spherical shape of 0.3μm (hereinafter simply referred to as μ)
When a magnetic tape made by coating a polyester film with a magnetic paint containing about 5 to 15 parts by weight of Cr ₂ O ₃ is attached to a tape recorder with a magnetic head made from a sendust alloy and run. The surface of the magnetic head was discolored and a brown coating phenomenon was observed. In addition, as an abrasive material, relatively spherical Al ₂ O ₃ with a particle size of about 0.5μ is used instead of the above example.
A similar brown coating phenomenon was also observed in the case of magnetic tape made using heavy weight parts. In addition, as an abrasive, a mixture of dichromium trioxide (hereinafter sometimes referred to as Cr ₂ O ₃ ) and Al ₂ O ₃ , such as the above
The brown coating phenomenon was also observed in the case of a magnetic tape made using about 10 parts by weight of Al ₂ O ₃ and about 10 parts by weight of the above-mentioned Cr ₂ O ₃ . Table 2 shows a summary of the above examples.

[Table] As a result of various studies, it was discovered that this brown coating phenomenon is closely related to the degree of wear of the magnetic head, and therefore
As a result of further research on the abrasive composition, we found that the abrasive material has an average particle size of approximately 1 to 2 μm, especially an average particle size of approximately 1 to 2 μm, and many sharp edges are formed on the particle surface. Furthermore, they have discovered that by using a predetermined amount of inorganic particles whose particle shape has an aspect ratio of about 1 and a Mohs hardness of about 6.5 or more, the brown coating phenomenon does not occur. Examples of the magnetic recording medium according to the present invention will be described below. Example 1 Extended magnetic powder mainly composed of iron (acicular ratio is about 7~
11. After first mixing about 100 parts by weight (average particle size is about 0.3 to 0.4 μ), about 350 parts by weight of a mixed solvent of methyl ethyl ketone, methyl isobutyl ketone and toluene, and about 2 parts by weight of a dispersant, the mixture was mixed in a ball mill. about 20 parts by weight of a magnetic recording binder such as vinyl alcohol-containing vinyl chloride-vinyl acetate copolymer or polyurethane elastomer, about 2 parts by weight of a lubricant,
and about 2 Al ₂ O ³ with an average particle size of about 1.0μ as an abrasive.
Add parts by weight and fully disperse to make magnetic paint. The Al ₂ O ₃ used in the production of this magnetic paint is so-called crushed particles, which are made by mechanically crushing molten alumina using a crusher, etc., and then passing through a sieving and classification process to classify it by size. A large number of sharp edge portions were formed, and the aspect ratio of the particles was approximately 1. Then, this magnetic paint is coated on a polyester base film, subjected to calendering treatment to form a magnetic layer with a thickness of about 3 to 4 μm, and slit to a width of about 3.81 mm to produce a magnetic tape. Example 2 The same procedure as in Example 1 was carried out except that about 2 to 5 parts by weight of Al ₂ O ₃ with an average particle size of about 2 μ was used in place of the Al ₂ O ₃ with an average particle size of about 1 μ used in Example 1. to make magnetic recording media. Note that the particle shape of Al ₂ O ₃ of this example is almost the same as that of Al ₂ O ₃ of Example 1. Example 3 A magnetic recording medium is produced in the same manner as in Example 1 except that about 6 parts by weight of Cr ₂ O ₃ having an average particle size of about 1 μm is used instead of Al ₂ O ₃ used in Example 1. Note that the particle shape of Cr ₂ O ₃ in this example is almost the same as that of Al ₂ O ₃ in Example 1. Example 4 In place of Al ₂ o ₃ used in Example 1, about 5 parts by weight of silicon oxide (hereinafter referred to as SiO ₂ , sometimes referred to as SiO ₂ ) having an average particle size of about 1 μm was used to produce Example 1. A magnetic recording medium is made in the same manner. Incidentally, the particle shape of SiO ₂ of this example is almost the same as that of Al ₂ O ₃ of Example 1. Example 5 A magnetic recording medium is produced in the same manner as in Example 1 except that about 5 parts by weight of silicon carbide having an average particle size of about 1 μm is used instead of Al ₂ O ₃ used in Example 1. Note that silicon carbide in this example is also Al ₂ O ₃ in Example 1.
and their particle shapes are almost the same. Example 6 A magnetic recording medium is produced in the same manner as in Example 1 except that about 5 parts by weight of boron carbide having an average grain size of about 1 μm is used instead of Al ₂ O ₃ used in Example 1. Note that boron carbide in this example is also Al ₂ O ₃ in Example 1.
and their particle shapes are almost the same. Comparative Example 1 A magnetic recording medium is produced in the same manner as in Example 1 using about 1 part by weight of Al ₂ O ₃ having an average particle size of about 1.0 μm. Note that the Al ₂ O ₃ of this comparative example is also the same as that of Example 1.
The particle shape of Al 2 O 3 is almost the same as that of Al ₂ O ₃ . Comparative Example 2 Approximately 1 Al ₂ O ₃ with an average particle size of 2.0μ used in Example 2
A magnetic recording medium is prepared in the same manner as in Example 1 using the weight parts. Note that the particle shape of Al ₂ O ₃ of this comparative example is almost the same as that of Al ₂ O ₃ of Example 1. Note that the particle shape of Cr ₂ O ₃ in this example is almost the same as that of Al ₂ O ₃ in Example 1. In addition, inorganic particles with an average particle size of about 1μ,
Approximately 30% below 1μ, approximately 30% between 1 and 1.5μ, approximately 24% between 1.5 and 2μ, approximately 10% between 2 and 2.5μ, approximately 2% between 2.5 and 3μ,
Approximately 4% of particles are 3μ or more, and for those with an average grain size of approximately 2μ, approximately 21% are 1.5μ or less, 25% are 1.5 to 2μ, 20% are 2 to 25μ, and 2.5 to 3μ. Approximately 16%, 3~
3.5μ is about 8%, 3.5 to 4μ is about 4%, 4μ or more is about 6
%. These magnetic tapes made in Examples 1 to 6 and Comparative Examples 1 and 2 above were attached to a magnetic recording/reproducing device using a magnetic head made of a Sendust alloy material.
A repeated running test was carried out for about one day and a night, and it was investigated whether or not colored matter was formed on the surface of the magnetic head. As a result, the average particle diameter in Comparative Examples 1 and 2 was
Brown coating phenomenon occurs or is slightly observed in the magnetic tapes in which the addition amount of Al ₂ O ₃ of 1.0μ and 2.0μ is about 1 part by weight, and the Al _{2 O 3} with an average particle size of 1.0μ in Example 1 is observed. A magnetic tape in which the amount of O ₃ added is about 2 parts by weight or more and the amount of Al ₂ O ₃ added with an average particle size of 2.0 μ in Example 2 is 2 to 5 parts by weight.
In the case of the weight part magnetic tape, almost no brown coating phenomenon was observed. Tables 3 and 4 summarize the above examples. It is clearly seen from Table 3 that when sharp-edged abrasive particles are used, the state of occurrence of brown coating changes depending on the particle size and amount added. Table 4 shows that abrasives other than Al ₂ O ₃ are also effective in preventing the occurrence of brown coating.

【table】

[Table] Therefore, as a countermeasure against the occurrence of the brown coating phenomenon, inorganic particles with an average particle size of about 1 to 2 μm, especially particles with an average particle size of about 1 to 2 μm with many sharp edges formed on the particle surface, are recommended. It can be seen that it is effective to add about 2% by weight or more of inorganic particles to the magnetic powder. However, if too much inorganic particles are added, the magnetic properties of the magnetic recording medium will be significantly degraded. For example, Al ₂ O ₃ with an average particle size of about 1μ is mixed with 20% of magnetic powder.
If more than % by weight is added, the maximum magnetic flux density of the magnetic recording medium will decrease by 10% or more, and the magnetic properties will become unfavorable. Therefore, it is preferable that the amount of inorganic particles is about 20% by weight or less based on the magnetic powder. The upper limit of the amount of inorganic particles added is the same for particles other than Al ₂ O ₃ . Here, the relationship between the magnetic flux density change rate and the amount of Al ₂ O ₃ added will be shown using a diagram. Regarding the size of the inorganic particles, the larger the average particle size, the more effective it is against the brown coating phenomenon, but if the inorganic particles are too large, the surface smoothness of the magnetic recording medium will be lost and dropouts will occur. Therefore, the average particle size of the inorganic particles should not be too large, and preferably has an average particle size of about 1 to 2 μm as in the present invention. And, within this range, there was almost no dropout or the like. Furthermore, inorganic particles having a small Mohs' hardness have problems in terms of coating film strength, head clog, etc. From this point of view, it is preferable that the Mohs' hardness of the inorganic particles is about 6.5 or more. As such inorganic particles, the above-mentioned
In addition to Al ₂ O ₃ , etc., diamond, fused zircon,
These include garnet, jadeite, quartz, fused quartz (glass made of SiO ₂ ), orthoclase, etc. For reference, Table 5 shows the Mohs hardness of various inorganic particles.
Shown below.

【table】

[Table] As described above, the magnetic recording medium according to the present invention is a magnetic recording medium using metal magnetic powder containing Fe as a main component, and has an average particle diameter of 1 to 2 μm in the magnetic layer of the magnetic recording medium. The Mohs hardness is 6.5, with sharp edges formed on the particle surface.
2 to 15 inorganic particles to the metal magnetic powder
% by weight, so even if a magnetic head made of metal material is attached to a magnetic recording/reproducing device and run, the so-called brown coating phenomenon is unlikely to occur, and the running properties and magnetic properties of the magnetic recording medium are good. When the amount of inorganic particles added is about 2 to 15% by weight based on the magnetic powder, no brown coating phenomenon is observed, and the magnetic properties of the magnetic recording medium, such as runnability and saturation magnetic flux density, are also good. It has the following features.

[Brief explanation of drawings]

The figure is a graph showing the relationship between the amount of alumina added and the rate of change in magnetic flux density.

Claims (1)

[Claims] 1. In a magnetic recording medium using metal magnetic powder containing Fe as a main component, the magnetic layer of the magnetic recording medium has an average particle diameter of 1 to 2 μm and has sharp edges formed on the particle surface. A magnetic recording medium comprising 2 to 15% by weight of inorganic particles having a Mohs hardness of 6.5 or more based on the metal magnetic powder.