JPS59121122A - Powder of granular magnetite having high coercive force and its preparation - Google Patents

Abstract

PURPOSE:To obtain powder of granular magnetite having high coercive force, by applying inner stress to the granular magnetite synthesized from a Fe<2+>-containing aqueous solution by impact and grinding, thereby imparting a strain anisotropy to the magnetite. CONSTITUTION:A granular magnetite (FeOx.Fe2O3; 0<x<=1) having a coercive force of <=120 Oe is prepared from an aqueous solution containing Fe<2+> by wet synthesis, etc. The granular magnetite is applied with internal stress by the impact and grinding force using a vibration mill or rotary mill, and a magnetite particle having an coercive force of >=130 Oe and imparted with strain anisotropy can be prepared. A powder of granular magnetite having high coercive force and suitable as a magnetic recording medium can be prepared by this process without adding foreign metals.

Description

Detailed Description of the Invention The present invention relates to granular magnetite having a high coercive force, particularly 1300e or more (L construction, F820g, where O<X≦1,
Hereinafter, it will simply be referred to as granular magnetite. ) Particulate powder and its manufacturing method.

The high coercive force granular magnetite particle powder in the present invention is
Primarily magnetic recording media that are magnetically isotropic, especially
Used for floppy disks.

In recent years, with the spread of office computers, word processors, etc., floppy disks have been widely used as magnetic recording media for inputting and outputting information. A floppy disk is a magnetically isotropic magnetic recording medium made by housing a disk made of a polyester base in the form of a sheet and coated with magnetic particles for magnetic recording on one or both sides in a vinyl chloride jacket. .

Nowadays, as magnetic recording and reproducing devices such as office computers and word processors become smaller and lighter, there is an increasing need for high-performance floppy disks, which are magnetic recording media.

That is, high recording density characteristics, high output characteristics, and stability of reproduction output are required.

The properties of magnetic particles for magnetic recording suitable for satisfying the above requirements for floppy disks include having a high coercive force Hc, a large saturation magnetization and magnetic stability, and being magnetically isotropic. It has a particle form.

As is well known, the magnitude of the coercive force of magnetic particles for magnetic recording is determined by shape anisotropy, crystal anisotropy, strain anisotropy,
or depend on their interaction.

Currently, the main types of magnetic particles used for magnetic recording are acicular magnetite particles or acicular maghemite particles, which have magnetic anisotropy due to the shape anisotropy of the acicular particles. This was an attempt to obtain high coercive force by utilizing .

These are generally made by reacting an aqueous ferrous salt solution with an aqueous alkaline solution and oxidizing the needle-like goethite particles (usually called a "wet reaction") in a reducing gas such as hydrogen. Thermal reduction is performed at °C to obtain acicular magnetite particles, or this is then heated at 200 °C in air.
It is obtained by heating and oxidizing it at 300°C to 300°C to obtain acicular maghemite particles. These particle powders are
A high coercive force is obtained by making maximum use of the shape anisotropy derived from the shape.

The above-mentioned acicular crystal magnetite particles or acicular crystal maghemite particles generally have a coercive force of 3000θ or more, and in terms of coercive force, they have the high recording density characteristics and high output currently required for floppy disks. Although it is suitable as a magnetic particle powder for obtaining properties, it has been pointed out that it has a drawback in that the reproduction output fluctuates due to the highly magnetically anisotropic particle morphology.

That is, the reproduction output fluctuations are detailed as follows.

When a floppy disk is manufactured using magnetic particle powder exhibiting an acicular shape, the relative positional relationship between the magnetic head and the magnetic recording disk due to the structure causes the disk to rotate and displace by 900 degrees. The main output changes at t. This is described, for example, in Japanese Patent Publication No. 55-39049 as follows.

``Magnetic recording material created by orienting needle-shaped magnetic material is
If a recording method is adopted in which the disc or sheet has a spiral, concentric, or arcuate recording locus (track), there are extremely disadvantageous drawbacks. ”
In other words, [the spiral, concentric, and arcuate recording and reproducing characteristics of magnetic sheets produced by the conventional method of forcibly orienting needle-like particles in the direction of the magnetic field and then drying and solidifying the magnetic paint are in the scanning direction of the magnetic head. varies greatly depending on ”
It is as stated.

As a method for reducing the above-mentioned reproduction output fluctuations that occur when using magnetic particle powder exhibiting an acicular shape, there is a method of applying a disturbing magnetic field and applying acicular magnetic particles in random directions. (Japanese Patent Publication No. 55-59049) (1) A method of suppressing the orientation of acicular magnetic particles in the coating direction by employing a gravure roll coating method. (Unexamined Japanese Patent Publication No. 54-3300
Publication No. 7) etc. have been disclosed.

The present inventors believe that if granular iron oxide, which is magnetically isotropic, is used, the resulting magnetic coating film will also be magnetically isotropic, without the need for the complicated coating method described above. It was thought that if used in a floppy disk, there would be no fluctuation in the playback output in the recording and playback characteristics.

Generally, granular magnetite particles are well known as granular iron oxide that is magnetically isotropic.

Granular magnetite particles are obtained by a wet synthesis method in which IT'e2+ is synthesized from an aqueous solution.

The representative ones are as follows.

BPe (OH%) obtained by adding a basic substance (alkali)
An aqueous solution containing colloids with a pH of 10 or higher is heated to 60~jDD℃
temperature range and aerate oxidizing gas.
4-668) or by adding an alkali to an aqueous solution of ferrous salt to reduce the amount of Fe in the aqueous solution.
mo1% is suspended as an iron precipitate consisting of Fe2+, a suspension in which the total F♂+ concentration in the suspension is in the range of 1 to 2 mol/l is prepared, and then the temperature of this suspension is 6
Maintain the temperature at 0 to 90°C, aerate oxidizing gas with sufficient stirring, and continuously add alkali so that the pH of the suspension is always maintained in the range of 5 to O ( (Japanese Patent Publication No. 49-35520).

The granular magnetite particle powder obtained by the wet synthesis method as described above is magnetically isotropic and has a large saturation magnetization, but as a material for magnetic recording media, the coercive force is at most 120.
There were only about 0e.

On the other hand, Co-added magnetite particles exist as granular magnetite particles having a high coercive force. To obtain a coercive force of about 3000e, approximately 5wt% (Oo/
It is necessary to add Co in total he), and increasing the amount of CO added is effective in improving coercive force, but it is extremely unstable due to changes in magnetic properties over time, pressure, and temperature. It has been pointed out that it is unsuitable as a magnetic powder for floppy disks.

In view of the above, the present inventor has conducted various studies in order to obtain granular magnetite particles having a high coercive force without adding a different metal such as CO other than F'e.

Then, the present inventors synthesized granular magnetite from an aqueous solution containing Fe2+ (Fed/Frog, however, O
<X≦1) particles are used as a starting material, and high coercive force granular magnetite is given strain anisotropy by applying internal stress to the starting material using a vibration mill or a rotary mill (08 to I8・F, however, The present invention was completed by discovering that o<x≦1) particle powder could be obtained.

That is, the present invention provides granular magnetite (
Fed Engineering・F~03 However, granular magnetite with a coercive force of 1200e or less synthesized from an aqueous solution containing high coercive force granular magnetite particle powder consisting of o<x≦1) particles and Fez+) (Fed,・Fe, O, Granular magnetite with a coercive force of 1300e or more, which uses particles (O < ) (Fed.

・Fe, 03 However, O < state

As described above, granular magnetite particles synthesized from an aqueous solution containing Fe2+ by the conventional method have a low coercive force.

As a result of various studies on methods for improving the coercive force of granular magnetite particles without adding dissimilar metals other than Fe such as CO, the present inventor found that a coercive force synthesized from an aqueous solution containing F♂+ When granular magnetite (Seiko F, e203, O<X≦1) particles with a magnetic force of 1200e or less are used as a starting material and internal stress is applied to the starting material by impact and grinding, the starting material granular We have found that the coercive force of magnetite particles can be improved.

This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor.

Figure 1 shows the relationship between the coercive force of granular magnetite particles obtained by applying internal stress to granular magnetite particles synthesized from an aqueous solution containing III'♂+ using a vibration mill and the operating time of the vibration mill. It is a diagram.

In FIG. 1, curves A, 1 and 1 are obtained by using starting granular magnetite particles having BET specific surface areas of 4.5 g/g, 'a, +2 g/g and 15.6 g/g, respectively. This is the case.

As is clear from FIG. 1, as the operating time of the vibration mill increases, the coercive force of the starting granular magnetite particles tends to improve.

Although the theoretical elucidation of the phenomenon of improving the coercive force of the granular magnetite particles in the present invention is not yet clear, the inventor of the present invention thinks as follows.

As described above, the magnitude of the coercive force of magnetic particles for magnetic recording depends on any one of shape anisotropy, crystal anisotropy, and strain anisotropy, or the interaction thereof.

The present inventor studied the above-mentioned factors that cause an increase in coercive force, and found that the present invention relates to an increase in coercive force of granular magnetite particles that are magnetically isotropic, and that the present invention relates to an increase in coercive force of granular magnetite particles that are magnetically isotropic, and that the present invention relates to an increase in coercive force of granular magnetite particles that are magnetically isotropic Since no dissimilar metal is added to the granular magnetite particles, no crystal structure change occurs in the granular magnetite particles. Therefore, the coercive force improvement in the present invention is not due to shape anisotropy or crystal anisotropy, but is due to strain anisotropy. I think this is due to orientation.

The relationship between coercive force and strain anisotropy is generally expressed by the following formula (1): (1) In formula (1), if the internal stress σ increases or the saturation magnetization coefficient 8 decreases, then , the coercive force will improve.

In the present invention, since the saturation magnetization hole of the product granular magnetite particles is almost unchanged and constant compared to the saturation magnetization size S of the starting material granular magnetite particles,
It is thought that the coercive force of the granular magnetite particles improved due to the increase in internal stress.

That is, it is thought that the improvement in the coercive force of the granular magnetite particles in the present invention is due to strain anisotropy occurring in the granular magnetite particles by applying internal stress through impact and grinding.

The blowing and grinding can be easily applied using a vibratory or rotary mill.

Next, various conditions for implementing the present invention will be described.

The starting material used in the present invention is granular magnetite particle powder obtained by the wet synthesis method described above.

In addition to the above-mentioned method, the wet synthesis method includes a well-known method using co-precipitation of ferrous ions Fe2+ and ferric ions Fe3+.

The coprecipitation reaction method uses a ferrous salt aqueous solution such as ferrous sulfate and a ferric salt aqueous solution such as ferric sulfate, and F♂+:F♂
A method of synthesizing granular magnetite particles by preparing a mixed iron aqueous solution with a ratio of 1:2, adding 1 equivalent or more of an alkaline aqueous solution such as NcLOH to the mixed iron aqueous solution, and heating and mixing at a temperature of 50 to 100 ° C. It is.

In the present invention, a well-known vibrating mill and rotary mill can be used as means for applying internal stress by impact and grinding.

Vibrating mills and rotary mills use 6 mediums of various sizes (steel balls, holes, and rads) in a horizontal cylinder that vibrates or rotates at low speed.
It is encapsulated at about 0 to 40%, and has an action mechanism of ``one blow caused by the fall of the medium lifted by the vibration or rotation of the cylinder'' and ``friction'' during the rolling of the medium.

It is thought that strain anisotropy is produced in the granular magnetite particles by applying internal stress through the effects of this "blow" and "friction".

The present invention configured as described above has the following effects.

That is, according to the present invention, it is possible to obtain magnetically isotropic granular magnetite particle powder having a high coercive force, especially 1300 s or more, so that recording density characteristics without fluctuation in reproduction output, which is currently most required, can be obtained. It can be used as a magnetically isotropic magnetic recording medium with excellent output characteristics, especially as an SL powder for floppy disks.

Furthermore, in the production of magnetic paint, the granular magnetite particles obtained by the present invention can be applied to the surface of the material disk without applying a disturbing magnetic field or using the conventional technology of complex coating means such as a gravure roll. By simply coating it, it is possible to obtain a magnetically isotropic magnetic recording medium with stable reproduction output without affecting the structural relative positional relationship between the magnetic head and the magnetic recording disk.

The present invention will now be explained by way of examples.

In addition, the specific surface area of the particles in the above experimental examples and the following examples was measured by the BET method, and magnetic measurements were performed using Toei Kogyo P-1 models V, S, and M, and external Measurement was performed with a magnetic field of 10 KOe.

Production of starting materials> Starting materials A, B, and O having various properties were produced by a wet synthesis method in which an oxidation reaction was performed at a pH of 10 or higher using an aqueous solution containing Fe2+.

The initial characteristics of starting materials A, B, and C are shown in Table 1. 12.7”J’ as a medium
Using a vibrating mill containing 7 kg of steel balls,
Starting material A 500 f was sealed in the pot and the pot was operated for 5 minutes at a motor speed of 1 (Son rpm).

The specific surface area of the obtained granular magnetite particle powder is 2.0
〆/g, and the magnetic properties were a coercive force of 2610e and a saturation magnetization of f3f3.5 @mu/y.

Example 2 Shiba 9 Granular magnetite particle powder was obtained in the same manner as in Example 1, except that the type of starting material, the type of processing equipment, and the operating time were varied.

Table 1 shows the properties of the obtained granular magnetite particles.

Example 10 Pot internal volume 500m1. Using a ball mill with 12.4"y steel balls 1.5 kliF as the medium, the starting material B 70'7 was enclosed in the pot and the pot was operated at a rotational speed of 75 rpm for 120 minutes.

The specific surface area of the obtained granular magnetite F particle powder is 4.6
The magnetic properties and coercive force are 2500e.

Saturation magnetization87. ．． It was 2 emu/g.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the coercive force of granular magnetite particles obtained by applying internal stress to granular magnetite particles synthesized from an aqueous solution containing Fe2+ using a vibration mill and the operating time of the vibration mill. Patent Applicant Toda Kogyo Co., Ltd. Figure 1 ⑍ Meeting or Time (Now) Procedural Amendment (Voluntary) 1. Display of the case 1982 Patent No. 11 No. 232186 2, Name of the invention 3, Person making the amendment Relationship to the case Patent applicant No. 7/4, Yokoyo Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture, " Detailed Description of the Invention Column" 5. Contents of the Amendment 1) The words "various in size and small" in the third line of page 14' of the specification will be deleted. 2) "3 minutes" on line 6 of page 1 of the statement will be corrected to "10 minutes."that's all

Claims (1)

[Claims] 1) Granular magnetite 0niji FQ2 imparted with strain anisotropy by applying internal stress by impact and grinding.
03 High coercive force granular magnetite particle powder consisting of particles where o<x≦1. 2) Granular magnetite with a coercive force of 1200e or less synthesized from an aqueous solution containing Fθ2+) (?eO,・F~
However, O <
Granular magnetite of 300e or more (Tomuri ~ o, however, 'L
A method for producing a high coercive force granular magnetite particle powder, characterized in that O<X≦1) particles are obtained.