JPS58199434A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To perform high-density recording, by specifying the relation between the triaxial anisotropic component of anisotropic energy, and coercive force and saturated magnetism. CONSTITUTION:The temperature dependency of coercive force is nearly equal to that of the triaxial anisotropic component of anisotropic energy obtained by measuring the magnetic torque of a magnetic recording medium in a surface and performing Fourier expansion. The equation holds the relation among the triaxial anisotropic component (Kco) of anisotropic energy found by measuring the magnetic troque in the surface 0 deg.C and performing Fourier expansion, and coercive force (Hco) and saturated magnetism (Iso) at 0 deg.C, the triaxial anisotropic component (kc100) of anisotropic energy found by measuring the magnetic, torque at 100 deg.C in the surface and performing Fourier expansion coercive force (Hc100) and saturated magnetism (Is100) at 100 deg.C. Consequently, vertical magnetism is improved and high-density recording is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and an object thereof is to provide a magnetic recording medium suitable for high-density recording.

Magnetic recording media are usually made by applying magnetic powder together with a binder resin onto a substrate such as a polyester film to form a magnetic layer. Magnetic properties are improved by orienting the material.

However, since the acicular magnetic powder is oriented in the longitudinal direction, there is a limit to the improvement in recording density because it uses magnetization in the longitudinal direction, and as the signal recording density is increased, the As the demagnetizing field increases, residual magnetization attenuates, making it difficult to detect recorded signals. - On the other hand, it has been reported that in ultra-high-density recording, not only the magnetization in the longitudinal direction of the magnetic tape but also the magnetization component in the direction perpendicular to the magnetic layer surface acts effectively. Attempts have been made to use cobalt-containing iron oxide magnetic powder as a recording element without longitudinally oriented magnetic recording media suitable for magnetic recording systems.
The cobalt-containing iron oxide magnetic powder, which has not been commonly used in the past, was used as a recording material by Ishikawa, but it was easy to use, and the perpendicular magnetization force was still zero.

However, short wavelength recording of 1μ or less is better.
6. High-density recording cannot be performed well. □゛.

The inventors were deeply moved and conducted various studies.
As a result, in conventional magnetic recording media, the temperature dependence of the coercive force is determined by measuring the magnetic torque of the magnetic recording medium in the plane and expanding the anisotropy' energy by two [axial anisotropy]. Temperature dependence of the component or exhibits the same tendency, and the temperature dependence and anisotropy of the coercive force - Nergini's biaxial anisotropic component temperature-preservation is good. □ 5. Although it is not possible to obtain a relationship suitable for height and density recording, it is possible to measure the magnetic torque of a magnetic recording medium in the plane of the temperature of coercive force and use Fourier If the anisotropic energy obtained by the expansion almost matches the temperature dependence of the triaxial anisotropic component, the perpendicular magnetization will be sufficiently good and short wavelength recording with a recording wavelength of 1 μm or less will be possible. It was discovered that a magnetic recording medium suitable for high-density recording could be obtained, leading to the present invention.

In order to make the temperature better, the temperature dependence of the coercive force almost matches the temperature dependence of the triaxial anisotropic component of the anisotropic energy of the magnetic recording medium, and the magnetic torque is measured in the plane at a temperature of θ°C and then Fourier The ball axis anisotropy component (Kco) of the anisotropic energy obtained by expansion and the coercive force (H
co) and ttjt” sum magnetization (llso) and temperature 10
The anisotropy obtained from the Fourie expansion by measuring the magnetic torque in the plane at 0°C - Ne'Bougie's triaxial anisotropy component (
Kcloo), and temperature ↓7 at 00℃
′□.

The coercive force (, Hc 1'o, o) and q saturation magnetism, (I
slooo) is preferably in the relationship expressed by the formula % formula %. If the temperature dependence of the coercive force does not match the temperature dependence of the ball axis anisotropy component outside this range, the vertical Magnetization is not good enough, and high-density recording cannot be performed well.

As described above, the magnetic recording medium of the present invention has a temperature dependence of coercive force that can be measured by measuring the magnetic torque of the magnetic recording medium in-plane.
- It is preferable that the anisotropic energy obtained by the Rie expansion has a relationship that approximately corresponds to the temperature dependence of the triaxial anisotropic component. Therefore, as the magnetic powder used in this invention, it is preferable that It is preferable that the relationship expressed by the above formula can be maintained. Spoon with many anisotropic components (long axis/
Acicular cobalt-containing iron oxide magnetic powder with a short axis of 3 to 15 is preferably used, and has a coercive force of 600 to L-50.
0 Oersted is preferably used.
1.・・ ・ ・゛・1 ・The magnetic recording medium of the present invention can be manufactured using such magnetic powder according to a conventional method. For example, 1. A magnetic paint is prepared by mixing and dispersing the above-mentioned cobalt-containing iron oxide magnetic powder with a binder resin, an organic solvent, and other additives, and this magnetic paint is applied onto a substrate such as a polyester film using a roll coater or other suitable method. It can be applied using the following application means and dried. .

・As the binder resin used here, conventionally widely used binder resins such as vinyl chloride→vinyl acetate copolymer, polyvinyl butyral, polyurethane resin, cellulose resin, and isocyanate compound are widely used6'
, ,=Also, as an organic solvent, toluene, methylisobutylene/I/ton (methyl ethyl ton), cyclohexanoyl, tetrahydrofuran,
Conventionally widely used organic solvents such as ethyl acetate can be used alone or in combination of two or more.

Incidentally, various additives commonly used in magnetic paints, such as dispersants, lubricants, abrasives, antistatic agents, etc., may be optionally added.

Example 1 Particle size (long axis) 0.15μ, axial ratio (long axis/short axis) 8.r
-100 of Fe, 03 powder and 1.0 of water. After dispersing in OIt, this was mixed with cobal sulfate) 380F and ferrous sulfate 11
30F and mix and dissolve, then add caustic soda 130F.
A caustic soda aqueous solution 51 in which 0 g of sodium hydroxide was dissolved was added and reacted at 45° C. for 8 hours. After the reaction was completed, it was washed with water, filtered and dried, and then heated and oxidized in the air at 450° C. for ≦ hours to obtain cobalt solid-dissolved iron oxide magnetic powder. The obtained cobalt solid solution iron oxide magnetic powder is a triaxially anisotropic acicular powder with a particle size (long axis) of 0.2μ, an axial ratio (long axis/short axis) of β, and a cobalt content of 5.7 weight range, coercive force (Hc) is 11
It was 00 Oersted.

Using the thus obtained cobalt solid solution iron oxide magnetic powder, Co solid solution r -Fe, O, powder 750 parts by weight VAGH (manufactured by U.C., U.S.A., chloride 125
Vinyl-vinyl acetate-vinyl alcohol copolymer) Bandex T-5250 (Dai 100, manufactured by Nippon Ink Co., Ltd., urethane elastomer) Coronae) L (manufactured by Nippon Polyurethane 25 Weight Division Co., Ltd., trifunctional low molecular weight isocyanate compound) Stearic acid -n-butyl 15 〃Methyl isobutyl ketone 600 〃Toluene
A magnetic coating material was prepared by mixing and dispersing a composition having a composition of .

This magnetic paint was applied onto a 12 μm thick polyester base film to a dry thickness of 3 μm, dried, surface treated, and then cut into a predetermined width of 6 to form a magnetic tape.

Example 2 In Example 1, the amount of cobalt sulfate used was 38 of
to 28.51, and the amount of iron used in the sulfuric acid clause was changed to 113.
The procedure was the same as in Example 1, except that the amount of caustic soda was changed from 0f to 85of, and the amount of caustic soda was changed from 1.300f to 975I, and the particle size (8 major axis) was 0.18μ,
An acicular, triaxially anisotropic cobalt solid solution iron oxide magnetic powder with an axial ratio (major axis/minor axis) of 8, a cobalt content of 4.6% by weight, and a coercive force (Hc) of 950 oersted was obtained. A magnetic tape was produced in the same manner as in Example 1, except that the same amount of the cobalt solid-solubilized iron oxide magnetic powder obtained in Example 1 was used in place of the Co-solid-solubilized r-Fe20B powder in the magnetic paint.

Example 3 In Example 1, the particle size (long axis) of the starting material was 0.15μ.
, axial ratio (long axis/short axis) of r Fe20B powder of 8, particle size (long axis) of 0.4 μm axial ratio (long axis/short axis) of 1
The same procedure as in Example 1 was carried out except that the same amount of γ-Fe, 03 powder was used as the starting material, and the particle size (long axis) was 0.42μ.
, axial ratio (major axis/minor axis) 10, cobalt content 5.7% by weight, coercive force (Hc) ios Ørsted needle-like example 1
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of CO solid solution -Fe and 03 powder in the magnetic paint was used in place of the powder.

Comparative Example 1 The same procedure as in Example 1 was carried out except that cobalt sulfate and ferrous sulfate were added to the dispersion aqueous solution of rFe, 03 powder, and the heat treatment in air after adding and reacting with caustic soda was omitted. In the same manner as in Example 1, the particle size (major axis) containing cobalt in the surface layer was 0.2μ, the axial ratio (major axis/minor axis) was 8, the cobalt content was 5.7% by weight, and the coercive force (He) was 1100. A cobalt-containing iron oxide magnetic powder having an acicular shape and uniaxial anisotropy was obtained, and the cobalt-containing iron oxide magnetic powder thus obtained was further added to the Co solid solution of the magnetic paint in Example 1 - Fe, 03 powder. A magnetic tape was produced in the same manner as in Example 1, except that the same amount was used instead of .

Regarding the magnetic tapes obtained in each example and comparative example,
The magnetic torque is measured in the plane at a temperature of θ℃, and this is Fourier expanded to obtain the triaxial anisotropic component of the anisotropic energy (Kco).
was determined, and the coercive force (HCO) and saturation magnetization (Iso) at a temperature of θ°C were measured. In addition, the magnetic torque was measured in the plane at a temperature of 100°C, and this was expanded into 7-liers to obtain the triaxial anisotropic component (Kcloo) of the anisotropic energy, and the coercive force (Hcloo) at a temperature of 100°C was obtained. and saturation magnetization (l
51oo) was measured. Next, these measured values were substituted into the formula % formula % to obtain the numerical value. Also, the recording wavelength is 0.75
The maximum output level at μ was measured.

The table below shows the results.

As is clear from the above table, the magnetic tapes obtained according to the present invention (Examples 1 to 3) have a short wavelength of 0.75μ compared to the conventional magnetic tape (Comparative Example 1). The maximum output level is high, which indicates that the magnetic recording medium obtained by the present invention is suitable for high-density recording.

Patent applicant: Hitachi Maxell, Ltd. 1゛41″ α's

Claims (1)

[Claims] 1. Anisotropy determined by measuring magnetic torque in the plane at a temperature of θ°C and performing 7-lier expansion in a magnetic recording medium in which magnetic powder is coated on a substrate together with a binder. The three-ring anisotropic component of energy (Kco) and the coercive force at a temperature of 0°C (
Hco), saturation magnetization (Iso), and temperature 100°C
The triaxial anisotropic component of the anisotropic energy (Kcl
A magnetic recording medium characterized in that the coercive force (Hctao) and saturation magnetization (Isloo) at a temperature of 100° C. have a relationship expressed by Formula 1 % □ ′