JP2825263B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium, and more particularly, to an electromagnetic conversion characteristic, a head polishing property at the time of sliding contact between a head and a medium, and a medium. The present invention relates to a magnetic recording medium for high-density recording with improved durability and the like.

(Prior art) In a coating type magnetic recording medium used for audio, video, floppy disk, computer tape, etc., it is possible to prevent the magnetic layer from being damaged at the time of sliding contact with the magnetic head and the medium, and to prevent foreign matter on the magnetic head. Al ₂ O ₃ , Cr ₂ O ₃ ,
Abrasives such as α-Fe ₂ O ₃ , SiC, and TiO ₂ have been added.

Further, in recent years, in a magnetic recording medium, since a large amount of information has to be recorded, higher recording density and accompanying improvement in reliability have been required. By the way, what is important in increasing the density of a magnetic recording medium is to reduce the spacing between a magnetic head and a magnetic layer. As the recording density of a magnetic recording medium increases, the surface properties of the medium need to be improved. I have.

For this reason, strict characteristics are required for the abrasive added to the magnetic layer, and if the type, particle size and amount are not properly selected,
This not only causes damage to the magnetic head, increases the wear amount of the magnetic head, deposits foreign matter on the surface of the magnetic head, lowers the durability of the medium, etc., but also increases the medium noise and deteriorates the electromagnetic conversion characteristics. .

In order to solve the above-mentioned problems, methods such as using an abrasive having a small particle size or using an abrasive subjected to a surface treatment (Japanese Patent Application Laid-Open Nos. 62-250518 and 62-285228,
JP-A-63-74118 and JP-A-63-98828) have been studied.

(Problems to be Solved by the Invention) However, high-density recording is required. In particular, high-quality VTR tapes and digital audio (VTR tapes) using magnetic powder having a small particle diameter such as an average particle diameter of 0.03 to 0.08 μm are required. Below, DA
When the above-mentioned abrasive is used for tapes for T), large-capacity floppy disks, and the like, the dispersion state is poor, so that the medium noise increases, and in addition, the wear of the magnetic head increases, and the foreign matter on the surface of the magnetic head increases. And the durability of the medium was reduced, and it was impossible to obtain a sufficient effect.
In other words, when a conventional abrasive is used in a conventional dispersed state in a magnetic recording medium using a small-diameter magnetic powder having an average particle size of 0.03 to 0.08 μm as the magnetic powder, the medium noise increases and the electromagnetic conversion characteristics increase. However, there has been a serious problem in practical use as described above, for example, causing deterioration of the device.

The present invention has been made in order to solve such a conventional problem, and has a sufficient magnetic property in a high-density magnetic recording medium using a magnetic powder having an average particle diameter of 0.03 to 0.08 μm as a magnetic powder. An object of the present invention is to provide a magnetic recording medium having a head polishing property and excellent in medium durability, electromagnetic conversion characteristics, and the like.

According to the present invention, there is provided a magnetic recording medium comprising a ferromagnetic fine powder dispersed in a resin binder and a magnetic layer coated on a non-magnetic support. The ferromagnetic fine powder dispersed and contained in the magnetic layer has an average particle size of 0.03 to 0.08 μm, and the magnetic layer has an average particle size of 0.05 to 0.60 μm, and an average secondary particle on the surface and inside of the magnetic layer. The above object can be attained by dispersing an abrasive having a diameter of 0.70 μm or less in the range of 0.5 to 10 parts by weight per 100 parts by weight of the ferromagnetic fine powder.

In the present invention, the average secondary particle size of the abrasive is the aggregate diameter formed by the abrasive particles when the abrasive particles are dispersed in the magnetic layer. It does not depend on the dispersion conditions, and is determined by the dispersion state of the abrasive before addition.

In the present invention, ferromagnetic powder having an average particle size of 0.03 to 0.08 μm is used. If the average particle size of the magnetic powder is less than 0.03 μm, the saturation magnetization of the ferromagnetic powder decreases and high density recording is performed. It cannot function sufficiently as a medium. On the other hand, when the thickness exceeds 0.08 μm, the medium noise increases remarkably and cannot be used as a high-density recording medium.

Examples of the ferromagnetic powder having an average particle size of 0.03 to 0.08 μm used in the present invention include γ-Fe ₂ O ₃ , Co-coated γ-Fe ₂ O ₃ ,
Needles such as O ₂ , metal powder with high coercive force suitable for high-density recording, magnetic powder with flat axis such as hexagonal ferromagnetic metal powder and hexagonal ferrite powder and having an easy axis of magnetization perpendicular to the plane of the flat plate And various kinds of magnetic powders. Among these, hexagonal ferrite powder is particularly suitable in the present invention. The hexagonal ferromagnetic metal powder includes fine powder of a metal that forms a hexagonal crystal by itself, such as Co, Co—Cr, Co—Al, and Mn—Al. As the hexagonal ferrite powder, a general formula: AO · n (Fe ₂ O ₃ ) (where A is any one selected from the group consisting of Ba, Sr, Pb, and Ca)
Represents a kind of element, n represents a number of 5 to 6, and part of Fe is replaced with a transition metal such as Ti, Co, Zn, In, Mn, Cu, Ge, Nb, Sn, etc. Good. The hexagonal ferrite represented by ()) is preferable, and among them, Ba ferrite is preferable. Such fine powder of hexagonal ferrite is a hexagonal plate-like single crystal, and its easy axis of magnetization is in a direction perpendicular to the plate surface,
For example, it can be produced by a glass crystallization method (see JP-A-56-67904 and JP-A-56-155022).

In the present invention, the above-mentioned hexagonal system magnetic powder is mainly used as the magnetic powder, but acicular and granular ferromagnetic metal powders and ferromagnetic ferrite powders can be used in combination.

The magnetic recording medium of the present invention is based on a high-density recording medium such as a high-quality VTR tape, a DAT tape, and a large-capacity floppy disk. Particle size is 0.05 ~ 0.60μm
An abrasive having an average secondary particle size of 0.70 μm or less on the surface and inside of the magnetic layer is dispersed and contained in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder. That is,
When the average secondary particle diameter of the abrasive exceeds 0.70 μm on the surface and inside of the magnetic layer, the increase in medium noise becomes remarkable,
It does not satisfy the requirements as a high-density recording medium. Further, when the average particle size of the abrasive is less than 0.05 μm, it is extremely difficult to control the dispersion during pretreatment of the abrasive or during the production of a master batch, and the average secondary particle size on the surface and inside the magnetic layer is 0.70 μm. μm, the increase in medium noise becomes remarkable. On the other hand, when the average particle size exceeds 0.60 μm, with the increase in the average particle size, it becomes easy to control the dispersion state of the abrasive particles on the surface and inside the magnetic layer,
Although it is possible to disperse the abrasive almost alone, the average secondary particle size also exceeds the above 0.70 μm, and the increase of the medium noise becomes remarkable.

If the amount of the abrasive added to the magnetic layer is less than 0.5 part by weight based on 100 parts by weight of the magnetic powder, the head is not sufficiently polished at the time of sliding contact between the magnetic head and the medium. Deterioration of the electromagnetic conversion characteristics occurs due to the deposition of foreign matter on the surface and a decrease in the reproduction output. On the other hand, when the amount exceeds 10 parts by weight, the amount of wear of the head during sliding contact between the magnetic head and the medium becomes excessive, or the head is likely to be damaged. As abrasives that can be used, for example, fine powder having an old Mohs hardness of 6 or more, such as alumina, chromium oxide, α-iron oxide, silicon carbide, titanium oxide, cerium oxide, corundum, and artificial diamond, is generally used. Among them, alumina, particularly, alumina having a square shape is most suitable in the present invention.

A magnetic recording medium according to the present invention is characterized in that a pre-dispersed abrasive masterbatch is added to a coating system containing the ferromagnetic powder, a resin binder, a solvent, and various additives, and then dispersed. It is obtained by a method in which a magnetic layer is formed by applying an orientation treatment, a drying treatment, and the like after coating on the magnetic recording medium, and a magnetic recording medium is manufactured.

In addition, as a method of preliminary dispersion of the abrasive masterbatch, a method of obtaining a masterbatch (slurry) by subjecting an abrasive having an average particle size of 0.05 to 0.60 μm to a surface treatment in an organic solvent and then ultrasonically dispersing the abrasive, A masterbatch (paste) can be obtained by adding a small amount of resin and a solvent and then performing ball mill dispersion to obtain a masterbatch (paste). However, the dispersing condition is that the average secondary particle size when formed into a master batch is 0.70 μm.
It is necessary to:

In the present invention, the mixing ratio of the ferromagnetic powder and the binder (binder) is such that the binder is 6 to 5 parts per 100 parts by weight of the magnetic powder.
It is selected in the range of about 0 parts by weight. If the amount of the binder is too large, the recording density of the magnetic tape decreases, while if the amount is too small, undesired situations such as a decrease in the strength of the magnetic layer, a decrease in durability, and powder falling occur. Also, as required in the magnetic paint, with respect to 100 parts by weight of the magnetic powder, 10 parts by weight or less of a dispersant, 10 parts by weight or less of a lubricant, 50 parts by weight or less of a hardener, and 10 parts by weight of an antistatic agent.
You may add less than weight part etc. Examples of the dispersant that can be used here include lecithin, phosphate ester, and polyaminoamide compound, and examples of the lubricant include higher fatty acids and fatty acid esters. And an antistatic agent such as conductive carbon.

In the present invention, examples of the nonmagnetic support on which the magnetic layer is formed by coating include a polyamide film and a polyester film. Thus, when applying a magnetic paint to a non-magnetic support, there is no problem if a magnetic recording medium is produced without passing through a magnetic field, but depending on the required recording and reproduction characteristics, When applying the magnetic paint, apply a magnetic field in any direction, such as a direction perpendicular or parallel to the non-magnetic substrate, to orient it, or pass it through a magnetic field that causes a reversal of the magnetic field at a specific frequency. Tapes can also be made. In particular, it is preferable to perform vertical alignment that provides a preferable vertical alignment rate for the perpendicular recording method, because the toughness of the magnetic layer increases and the toughness of the entire magnetic tape increases.

(Function) In the magnetic recording medium of the present invention, a magnetic layer provided on a nonmagnetic support and having a ferromagnetic powder having an average particle size of 0.03 to 0.08 μm dispersed in a resin binder has an average particle size of 0.05 to 0.60 μm. And the average secondary particle size on the surface and inside of the magnetic layer is 0.70
μm or less abrasive is added to 0.5 part
Contains up to 10 parts by weight. The average particle size of the abrasive dispersed and contained in the magnetic layer, the average secondary particle size in the state of being dispersed and contained in the magnetic layer, and the dispersion content as described above are selected and set, so that the conventional high particle size can be obtained. Compared with the magnetic recording medium for recording density, the polishing characteristics of the magnetic head are remarkably improved, and the medium noise is also remarkably reduced. For this reason, the electromagnetic conversion characteristics and the durability of the medium are good.

(Example) Hereinafter, an example of the present invention will be described.

Examples 1 to 8 A magnetic tape was prepared by dispersing and applying under the same conditions paints of the same composition except that an abrasive masterbatch having a different preparation method from the components was used. The conversion characteristics were compared.

 First, a magnetic paint having the following composition was prepared.

Magnetic coating composition Ba ferrite magnetic powder (part of Fe is replaced by Co and Zn, produced by glass crystallization method, average particle size 0.06μm, plate ratio 3.
9, coercive force 1100Oe, saturation magnetization 60emu / g, specific surface area by BET method 40m ² / g) 100 parts by weight vinyl chloride / vinyl acetate / vinyl alcohol copolymer (UCC VAGH) 6 〃 polyurethane resin (Morton) CA-118) 10 カ ー ボ ン Carbon (average particle size 0.03 μm) 1 〃 Phosphate ester surfactant 1 〃 Palmitic acid 1 ブ チ ル Butyl palmitate 1 ト ル エ ン Toluene 50 メ チ ル Methyl ethyl ketone 50 シ ク ロ Cyclohexanone 50 をDisperse well in a bead mill,
At 2/3 of the total dispersion time, a separately prepared abrasive master batch was added, and the remaining dispersion was performed. The abrasive masterbatch was preliminarily dispersed as follows.

A masterbatch (slurry, hereinafter abbreviated as S) obtained by subjecting abrasive particles to surface treatment with a Si coupling agent in an organic solvent having a solid content of 30% and ultrasonically dispersing 12 parts by weight per 100 parts by weight of abrasive particles A masterbatch (paste, hereinafter abbreviated as P) obtained by adding a polyurethane resin, kneading, diluting to a solid content of 60% and dispersing in a ball mill, obtained by the type of abrasive used, average particle size, dispersion conditions and dispersion. The average secondary particle size is shown in Table 1. The shapes of Examples 1, 2, 3, 5, 7 and Comparative Examples 1, 2, 4, and 5 are all square, and Examples 4, 6, 8 and Comparative Example 3 are all spherical. is there.

To the paint obtained by the above method, 3 parts by weight of a polyfunctional isocyanate (manufactured by Nippon Polyurethane Co., Coronate L) is added as a binder curing agent, and the mixture is uniformly stirred and then filtered. The paint thus prepared was coated with a 0.5 μm-thick back coat for antistatic on the back surface,
μm polyethylene terephthalate film on the other side of the coating with a gravure coater, smoothing, vertical alignment, drying, smoothing treatment with a calendar and cured,
Raw magnetic tapes each having a magnetic layer having a thickness of 3 μm were produced. These stocks were slit into 3.81 mm width and then wound into a cassette to obtain a magnetic tape sample whose characteristics could be measured using a DAT cassette deck.

Comparative Example 1 As a magnetic powder, an average particle size of 0.02 μm (plate ratio 3.2, coercive force 8
50 Oe, saturation magnetization 45 emu / g, specific surface area by BET method 48 m ² /
g), and a magnetic tape sample was prepared under the same conditions as in the example except that the abrasive master batch shown in Table 1 was used, and various characteristics were measured.

Comparative Example 2 As a magnetic powder, an average particle size of 0.1 μm (plate ratio 4.2, coercive force 99)
0 Oe, saturation magnetization 61 emu / g, specific surface area by BET method 35 m ² /
g), and a magnetic tape sample was prepared under the same conditions as in the example except that the abrasive master batch shown in Table 1 was used, and various characteristics were measured.

Comparative Example 3 A magnetic tape sample was prepared under the same conditions as in the example except that the abrasive master batch shown in Table 1 was used as the abrasive, and various characteristics were measured.

Comparative Example 4 A magnetic tape sample was prepared under the same conditions as in the example except that the abrasive master batch shown in Table 1 was used as the abrasive, and various characteristics were measured.

Comparative Example 5 A magnetic tape sample was prepared under the same conditions as in the example except that the abrasive master batch shown in Table 1 was used as the abrasive, and various characteristics were measured.

Examples 1 to 8 and Comparative Example 1 obtained as described above, respectively.
Table 2 shows the characteristics and measurement results of each of the tape samples Nos. 1 to 5. The reference values of the measurement results of the RF output (the higher the better) and the noise level... N level (abbreviated as the lower level) (the lower the better), the comparative example 5 is shown as ± 0 dB. In Table 2, the secondary particle size indicates the average secondary particle size of the abrasive in the magnetic layer, and the head wear amount indicates the average value of the wear amounts of both the A and B heads during continuous running for 200 hours. The surface condition indicated the damaged state of the head during this running.

[Effects of the Invention] As described above, according to the magnetic recording medium of the present invention, a magnetic layer in which a ferromagnetic fine powder having an average particle size of 0.03 to 0.08 µm is dispersed in a resin binder is formed on a nonmagnetic support. In the coated magnetic recording medium, the magnetic layer has an average particle size of 0.05.
Abrasive powder having a mean secondary particle size of 0.70 μm or less on the surface and inside of the magnetic layer,
By containing 0.5 to 10 parts by weight with respect to parts by weight, the polishing performance of the magnetic head is improved, the head wear amount is optimized, and the head surface is kept clean.
Medium noise is reduced, and electromagnetic conversion characteristics required for high-density recording are improved.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-143429 (JP, A) JP-A-62-134827 (JP, A) JP-A-62-16242 (JP, A) JP-A 61-143 104427 (JP, A) JP-A-64-66816 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/708 G11B 5/706 G11B 5/84

Claims (3)

(57) [Claims] 1. A magnetic recording medium comprising: a nonmagnetic support; and a magnetic layer formed by dispersing a ferromagnetic fine powder coated on the surface of the nonmagnetic support in a resin binder. The ferromagnetic fine powder has an average particle size of 0.03 to 0.08 μm, and the magnetic layer has an average particle size of 0.05 to 0.60 μm.
And an abrasive material having an average secondary particle size of 0.70 μm or less on the surface and inside of the magnetic layer dispersed and contained in the range of 0.5 to 10 parts by weight per 100 parts by weight of the ferromagnetic powder. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the ferromagnetic fine powder is a hexagonal ferrite powder. 3. A magnetic recording medium according to claim 1, wherein the abrasive is rectangular alumina.