JP2796058B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium capable of high-density recording. 2. Description of the Related Art A magnetic recording medium is formed on a surface of a supporting base made of, for example, polyethylene terephthalate (PET) resin.
It is manufactured by applying a magnetic paint in which a predetermined magnetic powder is dispersed in a resin binder such as vinyl chloride or vinyl acetate together with a dispersant such as stearic acid to form a layer of the magnetic powder. At this time, conventionally, magnetic recording and reproduction have been performed using γ-
In general, a magnetic powder composed of needle-like crystals such as Fe ₂ O ₃ and CrO ₂ is oriented in the longitudinal direction of the recording medium in the longitudinal direction of the recording medium and the residual magnetization in the longitudinal direction of the recording medium is used. However, this recording / reproducing method has a disadvantage that the demagnetizing field in the magnetic recording medium tends to increase as the recording density increases, and recording / reproducing particularly in a short wavelength region deteriorates. In order to perform high-density recording by overcoming this demagnetizing field, it is necessary to increase the coercive force of the recording medium and make the magnetic recording layer thinner. However, at present, it is difficult to increase the coercive force of the magnetic recording layer, and reducing the thickness of the magnetic recording layer is not preferable because it causes problems such as deterioration of characteristics of a reproduced signal. As a result, it is difficult to increase the density of the magnetic recording by the conventional method in which the needle-shaped magnetic powder is oriented in the longitudinal direction in the plane and the residual magnetization in the direction is used. Therefore, a method has been proposed in which residual magnetization in a direction perpendicular to the surface of a magnetic recording medium is used. In such a perpendicular magnetization recording method, it is necessary that the magnetic powder used has an easy axis of magnetization in a direction perpendicular to the surface of the recording medium. At present, the following recording media have been proposed. [0005] One is that a Co-Cr alloy film is formed on the surface of a supporting base by sputtering. But,
In the case of this recording medium, when the Co-Cr alloy film and the magnetic head slide, the wear of both the recording medium and the magnetic head becomes remarkable, and the recording medium itself is inferior in flexibility and difficult to handle. Furthermore, it has drawbacks such as low productivity in manufacturing, and is difficult to be put to practical use. [0006] In view of the above,
The present inventors have proposed a perpendicular magnetization type recording medium using hexagonal ferrite powder having hexagonal uniaxial crystal magnetic anisotropy (see JP-A-56-61101). When observed microscopically, the magnetic powder used here has a hexagonal plane, a hexagonal columnar body or a hexagonal plate-like body having a certain thickness, and has an easy axis of magnetization in a direction perpendicular to the hexagonal plane. [0007] A magnetic recording medium using this magnetic powder can perform a much higher-density recording than the conventional one. However, recently, with the increase in the amount of information, there has been a strong demand for the development of a magnetic recording medium that enables higher density recording. An object of the present invention is to provide a further improved magnetic recording medium capable of recording at a higher density than the magnetic recording medium proposed by the present inventors. The present inventors have conducted detailed studies on the shape of magnetic powder having hexagonal uniaxial crystal magnetic anisotropy in order to achieve the above object. It has been found that when the hexagonal columnar body or hexagonal plate-like body constituting the above has a predetermined size and shape, it is possible to achieve more excellent high-density recording, and the magnetic recording medium of the present invention has been developed. That is, the magnetic recording medium of the present invention is a magnetic recording medium comprising a support base and a layer of magnetic powder applied to the surface of the base, wherein the magnetic powder has uniaxial crystal magnetic anisotropy. Consisting of hexagonal crystals, particle size 0.01-0.09μ
m, the ratio of particle size to thickness is 2.3 to 15, and the tapping filling ratio of the magnetic powder is 15% or more. The material of the support substrate used in the magnetic recording medium of the present invention may be any material as long as it is conventionally used. Various resin sheets. The magnetic powder used has a hexagonal uniaxial crystal anisotropy, for example, a Co alloy containing Co or Fe or Ni; an MnBi; an alloy; a MnAl alloy; an alloy of various rare earths (R) and Co RCo ₅ , R ₂ Co ₁₇ ;
Hexagonal ferrite containing Ba, Sr, Pb, Ca, or the like;
i, Ni, Mn, Cu, Zn, In, Ga, Nb, Z
Substituted hexagonal ferrite substituted with at least one element selected from the group consisting of r, V, and Al can be given. Of these magnetic powders, substitutional hexagonal ferrite is suitable for use in the present invention. Also, the coercive force is 200-2000 O
Magnetic powder in the range of e is useful for high density recording. Each magnetic powder has a particle size of 0.01 to 0.09 μm
, Preferably 0.03 to 0.09 μm, the ratio of particle size to thickness is 2.3
-15, preferably 2.8-5. Here, the particle diameter means the maximum value of the distance between the corner vertices on the hexagonal surface of the hexagonal columnar body or hexagonal plate-like body,
The thickness refers to the height or thickness of the column or plate. If the particle size is less than 0.01 μm, the saturation magnetization (σg emu / g) is not sufficiently large. The generated noise is large and unsuitable. When the ratio between the particle diameter and the thickness is smaller than 2.3, the output during recording / reproduction becomes low, and it cannot be said that high-density recording could be achieved. Conversely, if the ratio exceeds 15, the shape of the magnetic powder becomes extremely thin, and the thickness of the magnetic powder becomes at most about 200 Å, and the saturation magnetization which greatly contributes to the reproduction output decreases. Further, when a magnetic paint is prepared by dispersing the magnetic powder before resin bonding, the magnetic powder is thin and easily broken. The tapping filling rate is a value obtained by dropping a long cylindrical container containing powder from a certain height (4 cm) and dividing the weight of the powder at that time by the volume occupied by the powder. Further, the value divided by the true specific gravity of the powder is expressed as a percentage. A large tapping filling rate means that the powder has good filling properties. For example, it means that the powder has a uniform shape, small gaps between the powders, and a particle size distribution. Is equivalent to being sharp. In a coating type magnetic recording medium, magnetic powder is uniformly dispersed in a binder, and this is applied to the surface of a supporting substrate. A magnetic powder having a large tapping filling rate is useful because it has a high filling density even in a magnetic recording medium and can increase the magnetization related to the output among the electromagnetic conversion characteristics. When the filling rate is less than 15%, strong agglomeration of the magnetic powder is recognized, and the S / N of the obtained magnetic recording medium becomes low. When the filling rate is greater than 15%,
Since the individual magnetic powders are well separated, the S / N of the obtained magnetic recording medium increases. The magnetic powder according to the present invention is disclosed, for example, in
-67904 or JP-A-56904
The magnetic powder prepared by using a method such as the coprecipitation method disclosed in JP-160328-A can be obtained by measuring and evaluating the tapping filling ratio and selecting. The recording medium of the present invention can be easily adjusted by dispersing the above-mentioned magnetic powder in a known resin binder together with a dispersant to form a magnetic paint, and applying the magnetic paint to the surface of a supporting substrate. it can. At this time, it is effective to apply a predetermined magnetic field after applying the magnetic paint, because the orientation of the magnetic powder can be enhanced. EXAMPLES Example 1 Nine types of Co—Ti-substituted Ba ferrite powder having the specifications shown in Table 1 were prepared. In the table, samples 3 to 8 are magnetic powders according to the present invention, and samples 1, 2 and 9 are comparative examples. [Table 1] Using these, a magnetic paint having the following composition was prepared, and 1 μm was prepared.
After filtration with a m-filter, it was applied on a PET film. Magnetic powder 100 parts by weight, vinyl chloride-vinyl acetate copolymer 10 parts by weight, polyurethane 10 parts by weight, lecithin 4 parts by weight, methyl isobutyl ketone 93 parts by weight,
93 parts by weight of toluene and 3 parts by weight of Coronate L (trade name, manufactured by Nippon Polyurethane Co., polyisocyanate compound). Next, the vertical direction of the PET film surface is
The magnetic powder was magnetically oriented by applying a magnetic field of 00 Oe, dried, and calendered to smooth the surface. This is 1 /
The specimen was cut into a width of 2 inches. After performing magnetic recording on these test pieces, the reproduction output was measured to examine the tape characteristics. The magnetic head used at this time was a ring type ferrite head with a gap width of 0.3 μm and a track width of 35 μm, and the relative speed between the head and the tape was 3.75 m / sec. The recording frequency was 4 MHz. The results are shown in FIG. As is apparent from FIG. 1, when the ratio between the particle diameter and the thickness is smaller than 2.3, the reproduction output is small and rapidly changes, and becomes unstable. However, when the ratio is larger than 2.3, the reproduction output becomes larger. In addition, the change becomes small and the change is stabilized. However, when it exceeds 15, the reproduction output decreases with a decrease in σg of the magnetic powder, and the usefulness as a magnetic recording medium is lacking. Example 2 Five types of Co-Ti substituted Ba ferrite powder having the specifications shown in the table were prepared. [Table 2] In the table, samples 3 to 5 are magnetic powders according to the present invention, and samples 1 and 2 are comparative examples. Vinyl chloride was added to 100 parts by weight of the magnetic powder.
A magnetic paint was prepared using 10 parts by weight of a vinyl acetate copolymer, 10 parts by weight of polyurethane, 4 parts by weight of lecithin, 93 parts by weight of methyl isobutyl ketone, 93 parts by weight of toluene, and 3 parts by weight of coronate L. Then, each paint was applied on a polyethylene terephthalate film, and a magnetic field of 4000 Oe was applied vertically to the film, followed by drying and calendering to make the surface smooth. This was cut into 1/2 inch widths to obtain test pieces. After magnetic recording was performed on these test pieces, the reproduction output was measured to examine the tape characteristics. The magnetic head used at this time was a ring type ferrite head having a gap width of 0.3 μm and a track width of 35 μm, a relative speed between the head and the tape of 3.75 m / sec, and a recording frequency of 4 MHz.
The results are shown in FIG. As is apparent from FIG. 2, when the tapping filling ratio is 15% or less, the ratio of the reproduction output to the noise and the S / N are small. On the other hand, when it is 15% or more, the S / N is large and stable. The magnetic recording medium of the present invention is capable of high-density recording, has a large reproduction output, and can be manufactured using the conventional coating method as it is, so that it is industrially useful.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the particle size / thickness of magnetic particles, that is, the plate ratio, and the reproduction output in a magnetic tape specimen manufactured in Example 1. FIG. 2 is a graph showing the tapping filling rate and S / F in Example 2.
FIG.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Tatsumi Maeda               1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa               Toshiba Research Institute, Inc. (72) Inventor Masahiro Fukasawa               1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa               Toshiba Research Institute, Inc. (72) Inventor Riki Nomura               1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa               Toshiba Research Institute, Inc.                (56) References JP-A-56-67904 (JP, A)                 JP-A-56-160328 (JP, A)

Claims (1)

(57) [Claims] A supporting substrate, a magnetic recording medium comprising a base body layer of magnetic powder coated on the surface of the magnetic powder, hexagonal Fe having uniaxial magnetocrystalline anisotropy
It is made of light crystals, has a particle size of 0.01 to 0.09 μm, a ratio of the particle size to the thickness of 2.3 to 15, and has a tapping filling ratio of the magnetic powder of 15% or more. Magnetic recording medium. 2. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder has a coercive force of 200 to 2000 Oersteds. 3. 3. The magnetic recording medium according to claim 1, wherein said magnetic powder is a substituted hexagonal ferrite powder. 4. The substitution type hexagonal ferrite, cobalt, titanium, nickel, manganese, a part of the iron of the hexagonal ferrite,
4. The magnetic recording medium according to claim 3, wherein the magnetic recording medium is substituted with at least one element selected from the group consisting of copper, zinc, indium, gallium, niobium, zirconium, vanadium, and aluminum.