JPS6093629A - Ferromagnetic iron oxide powder for magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To obtain vertically magnetized recording medium magnetic powder having proper coercive force and reduced in demagnetization due to heating by forming a coat consisting of Co-containing iron oxide containing Co at a specific rate to Fe uniformly to the surface of Co-containing iron oxide nuclear crystal. CONSTITUTION:The cost consisting of Co-containing iron oxide containing 15wt% or more Co to Fe is formed on the Co-containing iron oxide nuclear crystal containing 5wt% or less Co to Fe uniformly inside the iron oxide so as to be uniform thickness to obtain a magnetic layer. In the production of the magnetic powder, ions adjusted at the additional ratio of Fe ions to Co ions are precipitated into an alkaline solution so that Co/Fe is set to 5wt% or less at the composition of gamma-FeOOH and the gamma-FeOOH containing Co uniformly is dehydrated, deoxidized and then oxidized to obtain Co-containing gamma-Fe2O3. Then the Co-containing Fe2O3 is used for the nuclear crystal and a Co-containing iron oxide coat is formed on the surface of the nuclear crystal so that Co/Fe is set up to 15wt% or more, so that Co-containing iron oxide having optional coercive force can be obtained.

Description

Detailed Description of the Invention The present invention relates to ferromagnetic fermented iron powder for magnetic recording media, and provides high-density recording media having an isotropic magnetic anisotropic component and having excellent thermal stability of magnetic properties. The purpose is to provide something suitable for the.

Cobalt-doped iron oxide, in which cobalt is uniformly contained within the iron oxide, has isotropic magnetic anisotropy based on magnetocrystalline anisotropy, and can easily be made into powder with a coercive force of 400 to 20QQO. In recent years, it has been attracting attention as a magnetic powder for high-strength media that utilizes a perpendicular magnetization component. On the other hand, the magnetic properties of this magnetic powder are thermally unstable, and in particular, heating demagnetization is extremely large, so when the medium on which the signal is recorded is exposed to heat, it has the disadvantage of causing a decrease in output. There is. This thermal demagnetization is observed when the cobalt content relative to iron is 15% by weight or less, and is particularly noticeable when the cobalt content is in the range of 5 to 10% by weight. Therefore, in order to reduce thermal demagnetization, it is possible to increase the cobalt content to 15% by weight or more, or reduce it to 5% by weight or less, but the coercive force of cobalt-doped iron oxide depends on the cobalt content. Since it is almost proportional, when the cobalt content is 15wt% or more, the coercive force is 15000e.
On the other hand, if the cobalt content is 5% by weight or less, the coercive force decreases to 7000 e or less, making it impossible to obtain the coercive force of 700 to 15000 e required for a high-density magnetic recording medium. In this way, the amount of cobalt doping is a factor that directly affects both the coercive force and heating demagnetization of the particles, so adjusting the amount alone will not satisfy the coercive force range required for high-density recording media and Noh Ogawa was able to obtain particles that were less likely to be demagnetized by heating.

Therefore, the present inventors conducted various studies to obtain a magnetic powder for high-density recording media that utilizes a perpendicular magnetization component, which has an appropriate coercive force value, and has extremely low thermal demagnetization. They realized that the conventional technique of uniformly doping cobalt into particles could not produce the desired magnetic powder, and as a result of further investigation, they discovered that ■ In order to reduce heating demagnetization, cobalt ions should be oxidized. It is better to locate it near the surface of the particle than to locate it inside the iron; ■The amount of cobalt, which is a factor that affects coercive force, is not related to its position in the particle, but is the total amount contained in the particle. The present invention was based on the discovery that cobalt ions must be located inside the particles in order to generate a perpendicular magnetization component. Therefore, a coating of cobalt-containing iron oxide containing cobalt of 15 weight percent or more relative to iron is applied on a cobalt-containing iron oxide core crystal that uniformly contains cobalt within the iron oxide in an amount of 5% by weight or less relative to iron. The iron oxide magnetic powder formed with a uniform thickness not only has the above-mentioned appropriate coercive force, but also has low thermal demagnetization, making it a satisfactory magnetic powder for high-density recording media that utilize perpendicular magnetization components. It was found that it has the following characteristics. However, the overall coercive force of such magnetic powders can be adjusted by adjusting the overall cobalt content;
It has the characteristic that the strength of the perpendicular magnetization component can be adjusted by adjusting the ratio of the cobalt content in the core crystal to the cobalt content in the surface coating.

Various methods can be used to produce such magnetic powder, but the method described below is the most preferred from the viewpoint of efficient use of the cobalt float added, economy, productivity, etc. That is, first, when synthesizing alpha iron oxyhydroxide (α-FeOOH), the ratio of the amount of iron ions to cobalt ions added was adjusted to 11K- so that the content of cobalt to iron was 5% by weight or less. ion and cobalt ion are co-precipitated in an alkaline solution, and u
By carrying out a thermal reaction, α-ys00H uniformly containing cobalt &C is dehydrated, reduced, and magnetized to produce cobalt-containing T-Fe.

03. This cobalt-containing T k' e 204
, has isotropic outgoing anisotropy and contributes to the perpendicular magnetization component of the magnetic recording medium. Since the cobalt-containing T Fe, O, C, "balt content is as small as 5% by weight or less, the coercive force is usually less than 70002, and it is difficult to obtain a coercive force higher than this. Therefore, next, Cobalt-containing T-Fe
, O, as a nucleus crystal, and by forming a cobalt-containing iron oxide coating on the surface of which the content of cobalt is 15% or more per iron, cobalt-containing iron oxide with an arbitrary coercive force can be produced. can be obtained. 700~
In order to obtain a coercive force of 1 soooe, it is sufficient to adjust the total amount of cobalt added to 5 to 15% by weight. Since the cobalt-containing iron oxide formed on the surface has a cobalt content of 15% by weight or more, heating demagnetization is extremely small as described below. The present invention will be explained in detail below with reference to Examples.

Example 1 (1) Production of Nucleic Crystals Into 20 g of an aqueous sodium hydroxide solution with a concentration of 5 mol/l, while stirring at room temperature, ferrous sulfate with a concentration of mol/l and 20 d of an aqueous cobalt sulfate solution with a concentration of 0.03% WE. is added and reacted to co-precipitate ferrous hydroxide and cobalt hydroxide.

Next, while keeping this suspension at 50°C, 301/
Air was blown into the mixture at a rate of 1 minute and the mixture was stirred for 8 hours to obtain cobalt-containing α-FeOOH powder. This cobalt-containing α-? After dissolving eOOH in water and drying, in air at 500℃
The cobalt-containing α-1.,0. I got it. Using an electric furnace, this cobalt-containing α-Pa, O, was reduced for 3 hours at 550°C in a 1 m″/hr water-purple airflow to obtain cobalt-containing Fe, 04, and further in air.
Cobalt-containing T-Fe2C% by oxidation at 50°C for 1 hour
It was used as a nuclear crystal. This copal) containing T-Fe.

The 03 nucleus had a major axis diameter of o, spmc, and an axial ratio (major axis diameter/minor axis diameter) of 8. The cobalt content (00/F・) was 6.6% by weight, the coercive force was 6900θ, the saturation magnetization was 72.0 m−4, and the square shape was o, 71. This cobalt-containing T-Fe20. 1000 g of nuclear crystals were dispersed in water at 10 eK, 75 g of cobalt sulfate and 220 g of ferrous sulfate were added thereto, mixed and dissolved, and then an aqueous solution of caustic soda 51 in which caustic soda 12009 was dissolved was added and reacted at 45°C for 8 hours to obtain a solution containing 00. Coating with iron oxide was performed. The iron oxide obtained after washing with water, filtration, and drying had a major axis diameter of 0.3 pIIL, an axial ratio of 8, a coercive force of 8100 es, a saturation magnetization of 76.2 e=u7, and a square shape of 0.70.

Example 2 Same as Example 1 except that the amount of cobalt sulfate added during α-7600 synthesis was changed from 0.03%/1 to 0.02% lL/l in the manufacturing process of the nucleus crystals of Example 1. By a similar method, T-IFe, O, and nuclear crystals containing cobalt content of 2.4% by weight, coercive force of 5850 s, saturation magnetization of 722 e, t /9, square shape o, and 67 cores were obtained. I got it. This cobalt-containing T-Fe20. Using the nuclear crystals, the amount of cobalt sulfate added in the OOo-containing iron oxide coating step was changed from 759 to 1209 VC, the amount of ferrous sulfate added was changed from 2209 to 350 g, and the amount of caustic soda was changed to 120 g in Example 1.
The final result was coercive force of 81,508% and saturation magnetization of 76.4 in the same manner as in Example 1 except for changing from 0g to 1300g.
Iron oxide of 0#-zoq1 square shape 0.65 was obtained.

Comparative Example 1 In the nucleus crystal production process of Example 1, cobalt-containing α-F
The amount of sulfate cogluto added during eOOH synthesis was set to 0.0.
The same method as in Example 1 was used except that 5e/11 was changed to 0.45M, and the cobalt content was 5.1% by weight. The coercive force was 81008, the saturation magnetization was 722e-, s/9, and the square shape was 0. A cobalt-containing T-Fll,O, of .71 was obtained, and the subsequent steps were omitted.

Comparative Example 2 In the nucleus crystal manufacturing process of Example 1, cobalt-containing α-'
During PgOOH synthesis, only α-Felon was synthesized by reacting without adding cobalt sulfate, and through the same process as in Example 1, the major axis diameter was 0.35/'', the axial ratio was 8, and the coercive force was 5700. A T-Fe, O, powder with a saturation magnetization of 721 smu/9 and a square shape of 0.44 was obtained. This T-Fe
, O, in the 00 iron oxide coating step of Example 1, the amount of cobalt sulfate added was increased from 752 to 24 o 9
Coercive force 8150e, saturation magnetization 7
6.11e-arm, square 0.51 iron oxide was obtained.

Composition 00-containing iron oxide powder 750 parts by weight VAGH125 - Vandex T-5250100, using the iron oxide powders obtained in Examples 1 and 2 and Comparative Examples 1 and 2, and having the following composition.

Coronate L 25.

n-butyl stearate 15 . . . methyl r-butyl ketone 600 -.

A magnetic paint was prepared by mixing and dispersing 60 ott parts of toluene for 3 days. This magnetic paint was applied onto a polyester base film having a thickness of 12/I to a dry thickness of 4 fi, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape. For these magnetic tapes, the coercive force in the longitudinal direction, the saturation magnetic flux density, the rectangular shape, the coercive force in the direction perpendicular to the magnetic layer surface, and the rectangular shape were measured, and the results are shown in the table below. Also, the recording wavelength is 0,
The maximum output level CM, 01, U,) and heating demagnetization in 8 voices were measured. For heating demagnetization, after saturated magnetizing the tape and measuring the saturated residual magnetization Bar at that time,
This tape was held at 60°C for 2 hours, the residual magnetization Br was measured again at room temperature, and the amount of decrease in residual magnetization (Bs
r-Br)/Bar. The table below shows the results.

Further, the square shape in the vertical direction is a value obtained after correcting the influence of the demagnetizing field by plotting it on a hysteresis curve, assuming that the demagnetizing field coefficient is 4.

As is clear from Table 1, the magnetic tape obtained by the present invention is 0.8μ shorter than the conventional tape (Ratio 1 Example 2) K using magnetic powder with uniaxial orientation. The tape has large lengths, M, O, and L, and thermal demagnetization is small compared to the conventional tape using cobalt-containing T-Fe, O (Comparative Example 1).

From this, by using the magnetic powder obtained in the present invention, a high-density medium that undergoes less thermal demagnetization can be obtained.

Applicant: Hitachi Maxell, Ltd. Atsushi Nagai

Claims (2)

[Claims] (1) On the surface of cobalt-containing iron oxide core crystals containing 5% by weight or less of cobalt based on iron, 15% by weight based on iron
A ferromagnetic iron oxide powder for a magnetic recording medium, characterized in that a coating made of cobalt-containing iron oxide containing cobal as described above is integrally formed. (2) Cobalt-containing iron oxyhydroxide containing 5 JijL% or less of cobalt based on iron is produced, and this is thermally reduced and oxidized to produce iron oxide core crystals containing 5 wt% or less of cobalt. , this core crystal is heat-treated in an alkaline solution containing yJ" ion and this Fe" (00 of 15 weight% or more with respect to ion), so that the content of cobalt relative to iron is 15% by weight on the surface of the powder particles. A method for preparing ferromagnetic iron oxide powder for magnetic recording media, characterized in that the above cobalt-containing iron oxide coating is formed.