JPH06223359A - Magnetic recording medium - Google Patents

Abstract

(57) [Summary] [Structure] Coercive force of 1400 Oe or more and particle size of 0.12μ.
A magnetic recording medium having a magnetic layer composed of a needle-shaped cobalt-coated iron oxide having a particle size of m or less and a binder. [Effect] High-density recording is possible, durability and corrosion resistance are excellent, and the manufacturing cost is significantly low.

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, and more particularly to a coating type magnetic recording medium such as a magnetic disk, a magnetic tape or a magnetic sheet.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is
It is obtained by coating a magnetic coating material, which is made by dispersing magnetic powder in a binder and an organic solvent, on a substrate such as polyester and drying it. Especially for high-quality video tapes, large-capacity floppy disks, etc. Metal particles are used as the powder. The reason is that the magnetic energy can be calculated by the coercive force (Hc) × residual magnetic flux density (Br),
This is because Hc is high and the saturation magnetization (σs) is large, so that Br is high and high magnetic energy can be expected. However, in metal particles, (1) magnetic particles are chemically unstable and easily rusted (2) magnetic particles have a large magnetization, and particles are easily aggregated in the coating liquid, making it difficult to disperse (3) Since the particles easily aggregate, there are problems such as high noise level, and these problems have not been sufficiently solved.

Further, in order to perform high density recording, it is necessary to reduce the particle size of the magnetic powder. Because S / N
Is S / N∝ (1 / Vp) ^1/2 [where Vp is the volume of the particles], and it is necessary to reduce the particle size in order to obtain high S / N. However, as the particles become smaller, σs becomes extremely low in the case of metal powder. This is because of thermal fluctuation due to the increase in specific surface area. Further, if the particle size is reduced, the corrosion resistance deteriorates, so that it is necessary to further oxidize the surface of the metal particles in order to maintain the corrosion resistance, and as a result, σs decreases. As described above, when the surface of the metal powder is oxidized to improve the corrosion resistance, σs generally becomes 125 (emu / g) or less.

Further, when high-density recording is performed, the recording wavelength inevitably becomes short, which is an obstacle to the metal powder. For example, even when performing high-density recording with a recording wavelength of 0.7 μm or less, it is preferable that the particle size of the magnetic powder used in the magnetic recording medium is as small as possible, and it should be 0.2 μm or less, as described above. Yes, and particularly preferably 0.12 μm or less. However, when the particle size of the metal powder is 0.12 μm or less, σs decreases to about 110 (emu / g), which makes it impossible to cope with high density.

As described above, the high density recording using the metal powder still has a problem, and further improvement is demanded in terms of cost. Moreover, high density recording has not been sufficiently achieved with magnetic powders other than metal powders.

[0006]

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have used acicular cobalt-coated iron oxide having a high coercive force and a very fine particle size as the magnetic powder. By doing so, it was found that a magnetic recording medium capable of high-density recording, excellent in durability, and significantly lower in manufacturing cost than metal powder can be obtained, and the present invention has been completed.

That is, the present invention provides a magnetic recording medium having a magnetic layer, which has a coercive force of 1400 Oe or more and a particle size of 0.12 μm or less and is composed of acicular iron oxide coated with cobalt and a binder, on a substrate. To do.

In the present invention, needle-shaped cobalt-coated iron oxide having a coercive force of 1400 Oe or more and a particle size of 0.12 μm or less is used as the magnetic powder. Here, the particle size is 0.12μ
“M or less” means that the average major axis length is 0.12 μm or less. The cobalt-coated iron oxide is mainly Co-γ
-Fe ₂ O ₃ , Co-γ-Fe ₃ O ₄ , Co-γ-FeO _x (x is 1.33 to 1.
50) is used. If the coercive force of the cobalt-deposited iron oxide is not less than 1400 Oe, high magnetic energy cannot be obtained in the final product. Also, if the particle size of the iron oxide coated with cobalt is not more than 0.12 μm, high density recording and high S / N cannot be achieved. Also, in order to obtain higher energy,
The saturation magnetization of cobalt-coated iron oxide is preferably 72 emu / g or more, and in order to obtain high density and high σs, the acicular ratio has a short axis length:
The major axis length = 1: 5 to 1:10 is preferable. Usually, the cobalt-coated iron oxide according to the present invention is mixed in the magnetic coating material for forming the magnetic layer in an amount of about 20 to 40% by weight.

The above-mentioned coercive force according to the present invention is 1400 Oe.
The needle-shaped cobalt-adhered iron oxide particles having a particle size of 0.12 μm or less have not been used in the conventional production of magnetic recording media, and have a smaller particle size than ordinary cobalt-coated iron oxide particles. Nevertheless, it has a very high coercive force. If the cobalt-coated iron oxide has such characteristics, Co
Any of a -doped type, a Co-adsorption type, a surface Co layer generation type and the like can be used, and the amount of cobalt deposited is not particularly limited.

The magnetic recording medium of the present invention includes a cobalt-coated iron oxide of the cobalt-coated iron oxide according to the present invention as described above, a magnetic metal powder usually used in a magnetic recording medium,
For example, Fe, Fe-Co alloy, Fe-Ni-Co alloy, Co-Ni alloy,
It is also possible to use a small amount of powder such as Co-Ni-P alloy and Fe-Ni-Zn alloy.

Further, as the binder of the magnetic paint according to the present invention, a urethane resin, particularly a polyurethane resin containing a polar group such as SO ₃ Na group, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer is used. Polymers, vinyl chloride-copolymers such as vinyl chloride-acrylonitrile copolymers, especially vinyl chloride copolymers containing polar groups such as SO ₃ Na groups, butadiene-acrylonitrile copolymers,
Polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenol resin, epoxy resin, urea resin, melamine Resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol / high molecular weight diol / isocyanate, and these And the like. Normal,
The binder is mixed in the magnetic paint in an amount of about 3.0 to 10.0% by weight.

As the organic solvent, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, benzene, toluene, xylene, dimethyl sulfoxide, tetrahydrofuran, dioxane, etc., which are suitable for dissolving the binder resin used, are particularly limited. It is used alone or as a mixture of two or more kinds without being used. Usually, the organic solvent is mixed in the magnetic coating material in an amount of about 20 to 80% by weight.

In addition, various additives that are usually used, such as a dispersant, an abrasive and a lubricant, may be appropriately added and used in the magnetic paint. As the dispersant, lecithin,
Nonionic surfactants, anionic surfactants, cationic surfactants and the like can be used. As an abrasive, α-
Alumina, fused alumina, silicon carbide, chromium oxide (Cr ₂
O ₃ ), corundum, diamond, etc. average particle size 0.05 ~
Fine powder of 0.5 μ can be used, and usually 0.5 to 100 parts by weight is added to 100 parts by weight of the binder as described above. Examples of lubricants include silicone oils such as various polysiloxanes, graphite, inorganic powders such as molybdenum disulfide, fine plastic powders such as polyethylene and polytetrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters, and fluorocarbons. And the like are added in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the binder as described above.

The base material used in the magnetic recording medium of the present invention is a synthetic resin (eg, polyester, polyamide,
Examples thereof include polyolefins, cellulose derivatives), non-magnetic metals, glass, ceramics, papers, etc., and their forms are used in films, tapes, sheets, cards, disks and the like.

The thickness of the magnetic layer of the magnetic recording medium of the present invention is
It is about 0.3 to 5 μm. Further, the magnetic recording medium of the present invention may have a back coat layer, a protective layer, an undercoat layer, a lubricating layer, etc. formed, and in this case, it is formed by a usual method using a usual material.

[0016]

The present invention will be further described in the following examples, but the present invention is not limited to these examples.

Example 1 Needle-shaped and having an average major axis length of 0.10 μm and an average minor axis length of 0.010 μm
, S = 75 emu / g Co-γ-Fe ₂ O ₃ powder [coercive force (H
c) = 1400 (Oe), axial ratio = 1:10 (minor axis length: major axis length, the same applies hereinafter)], and each of the components shown below was used to form a paint in a sand mill. <Magnetic paint component> -Co-γ-Fe ₂ O ₃ powder 24.6% by weight-Vinyl chloride resin 1.9% by weight-Polyurethane resin 2.8% by weight-Isocyanate 0.7% by weight-Al ₂ O ₃ (particle size 0.15 μm) 3.0 % By weight-fatty acid ester 0.8% by weight-toluene 29.8% by weight-methyl ethyl ketone 29.8% by weight-cyclohexanone 6.6% by weight.

Next, the above magnetic paint was applied onto a polyethylene terephthalate film having a thickness of 10 μm by the direct gravure method so that the thickness after drying was 2.9 μm. Next, a coating material containing carbon as a main component was applied to the back surface so that the thickness after drying was 0.5 μm, and dried. This film is cut into a tape with a width of 8 mm, placed in an 8 mm cassette case, a commercially available 8 mm VTR device is connected to the noise meter, and Y-SN and C-SN (AM, PM) are measured (recording wavelength
0.7 μm), commercially available reference tape (Sony Corporation)
It is displayed in dB as compared with (made by). The durability and corrosion resistance were also measured. Still durability was measured as the durability and used as a guide. The still durability was measured as a still state for 1 hour with the above apparatus, and the decrease in output was measured. The corrosion resistance was determined by measuring the decrease rate (ΔBs) of the saturation magnetic flux density after leaving the above magnetic tape for 1 week at 60 ° C. and 90% RH. The results are shown in Table 1.

Example 2 In Example 1, σ s = 78 emu / g, average major axis length = 0.12
Needle-like Co-γ-Fe with μm, axial ratio = 1: 5, Hc = 1450 (Oe)
_A magnetic tape was manufactured in the same manner as in Example 1 except that ₂ O ₃ powder was used, and the same test was performed. The results are shown in Table 1.

Example 3 In Example 1, σ s = 72 emu / g, average major axis length = 0.08
Needle-like Co-γ-Fe with μm, axial ratio = 1: 8, Hc = 1500 (Oe)
_A magnetic tape was manufactured in the same manner as in Example 1 except that ₂ O ₃ powder was used, and the same test was performed. The results are shown in Table 1.

Comparative Example 1 In Example 1, σs = 68 emu / g, average major axis length = 0.19.
Needle-like Co-γ-Fe with μm, axial ratio = 1: 10, Hc = 1400 (Oe)
_A magnetic tape was manufactured in the same manner as in Example 1 except that ₂ O ₃ powder was used, and the same test was performed. The results are shown in Table 1.

Comparative Example 2 In Example 1, σ s = 74 emu / g, average major axis length = 0.11
Needle-like Co-γ-Fe with μm, axial ratio = 1: 4, Hc = 1350 (Oe)
_A magnetic tape was manufactured in the same manner as in Example 1 except that ₂ O ₃ powder was used, and the same test was performed. The results are shown in Table 1.

Comparative Example 3 In Example 1, σ s = 98 emu / g, average major axis length = 0.12
A magnetic tape was produced in the same manner as in Example 1 except that acicular metal particles having a particle size of μm, an axial ratio of 1: 8, and Hc of 1500 (Oe) were used, and the same test was conducted. The results are shown in Table 1.

[0024]

[Table 1]

Example 4 The magnetic coating material obtained in Example 1 was randomly oriented on a PET (polyethylene terephthalate) film having a thickness of 75 μm and applied so that the dry coating film had a thickness of 2.0 μm.
After that, it was punched out into a disk and put into a shell to make a 3.5 inch floppy disk. The electromagnetic conversion characteristics of this floppy disk were evaluated, and the results are shown in Table 2.

Comparative Example 4 Using the magnetic coating material obtained in Comparative Example 3, a floppy disk was prepared in the same manner as in Example 4, and its electromagnetic conversion characteristics were evaluated. The results are shown in Table 2.

Comparative Example 5 In Comparative Example 3, Hc = 1300 (O
e), a magnetic coating material was prepared using hexagonal plate-shaped Ba ferrite particles having a particle size of 0.05 μm, and a floppy disk was prepared in the same manner as in Example 4 and its electromagnetic conversion characteristics were evaluated. The results are shown in Table 2.

[0028]

[Table 2]

Here, as practically required standards, 10 kBPI is 10 μV / μm or more, O / W is −28.0 dB or less,
The demagnetization rate is 40% or less, and all the magnetic recording media of the present invention clear this.

Front Page Continuation (72) Inventor Katsumi Sasaki 2606 Akabane, Kaigai-cho, Haga-gun, Tochigi Kao Corporation

Claims (2)

[Claims] 1. A coercive force of 1400 Oe or more and a grain size of 0.12.
A magnetic recording medium having, on a substrate, a magnetic layer composed of a needle-shaped cobalt-coated iron oxide having a particle size of not more than μm and a binder. 2. The saturation magnetization of the cobalt-coated iron oxide is 72.
emu / g or more, and the acicular ratio is minor axis length: major axis length = 1: 5
The magnetic recording medium according to claim 1, wherein the range is 1:10.