JPH04221427A - Manufacture of magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention uses Fe4 as a magnetic material.
The present invention relates to a method of manufacturing a magnetic storage medium using N.

0002

BACKGROUND OF THE INVENTION Acicular ferrite (γ-Fe2 O3) has conventionally been used as a powder magnetic material used in magnetic storage media. However, the saturation magnetization of ferrite is at most 70 to 7
It has a coercive force of about 5 emu/g and a coercive force of about 0.3 kOe,
This is insufficient for applications requiring high-density recording such as high-performance audio tapes and VTRs. For this reason, various magnetic materials having higher saturation magnetization and higher coercive force have been developed.

[0003] One such material is metal Fe, which has been put into practical use to some extent. However, metal Fe
Since it is extremely easily oxidized, even when used as a magnetic storage medium, the saturation magnetization decreases to about half that of pure iron due to oxidation, resulting in a problem that the output decreases.

[0004] Fe is a material that eliminates these drawbacks.
4N is attracting attention (Japanese Patent Application Laid-Open No. 59-11532). Since Fe4N has dense α-Fe2O3 formed on its surface, it has much better oxidation resistance than Fe, and also maintains sufficient saturation magnetization and coercive force. Fe4N
A powder containing particles having the above structure is formed by nitriding Fe particles.

However, when nitriding acicular iron particles, the acicular particles aggregate, making it difficult to maintain their acicular shape. When the magnetic particles of a magnetic recording medium become non-acicular like this, it becomes impossible to obtain the desired magnetic properties.
Application to magnetic recording media becomes difficult. This invention was made in view of the above circumstances, and has excellent oxidation resistance,
Moreover, it is an object of the present invention to provide a magnetic storage medium with good magnetic properties.

[0006]

[Means and effects for solving the problems] A magnetic storage medium according to the present invention reduces acicular goethite particles to form acicular iron particle powder, and disperses the iron particle powder by floating and fluidizing it. The present invention is characterized in that the powder is nitrided to form Fe4N while the powder is being heated, and the particle powder in which Fe4N is formed is applied to a substrate.

[0007] The present invention provides a method for producing a magnetic recording medium that can maintain the final shape of the Fe4N powder particles in an acicular shape when Fe4N is used as a magnetic recording medium.

Fe4N used in the present invention corresponds to the γ' phase in the phase diagram of the iron-nitrogen system shown in FIG. Fe4N has a perovskite crystal lattice in which nitrogen atoms are located at the body center of the fcc phase of iron. This phase is stable even at room temperature and is a ferromagnetic material with Tc=488°C. The saturation magnetization at room temperature is 195 emu/g, which is slightly lower than that of pure iron, and the surface contains dense α-Fe2.
Since O3 is formed, the oxide layer on the surface is thinner and the saturation magnetization decreases less than that of Fe, where Fe3 O4 is formed on the surface. Furthermore, the coercive force is relatively high. Therefore, by arranging the longitudinal directions of the acicular particles, the squareness ratio of the hysteresis curve in the magnetic field-magnetization (magnetic flux density) curve can be improved, making it suitable as a magnetic recording medium.

[0009] Moreover, Fe4N has a dense α
- Due to the presence of Fe2O3, the oxidation resistance is much better than that of Fe. Furthermore, metal nitrides generally have higher hardness than metals, and Fe4N also has higher hardness than Fe. Therefore, it is possible to prevent head burn-in, which is a problem with magnetic storage media using magnetic metal materials. A magnetic storage medium using such Fe4N can be manufactured as follows.

First, acicular goethite (α
-FeOOH) powder to obtain iron powder. The method of reduction at this time is not particularly limited as long as goethite is reduced and iron powder in the form of acicular particles can be obtained. An example is hydrogen reduction.

[0011] Next, the thus formed acicular particle iron powder is subjected to a nitriding treatment to form Fe4N. By this nitriding treatment, almost the entire iron powder particles are converted into Fe4N
Although it is preferable that Fe4N be formed partially, it is also possible. Moreover, if the outer peripheral part of the particles is made of Fe4N, it is effective from the viewpoint of oxidation resistance. There are various nitriding methods, but gas nitriding and ion nitriding are preferred.

[0012] This nitriding treatment is carried out while the iron particles are suspended and dispersed. Specifically, when using the gas nitriding method, iron powder is charged into a reaction vessel, and while the inside of the vessel is heated to about 500°C using an external heater, NH3 gas is added from below the vessel. , H2 gas, etc. are introduced to make the iron powder float and flow while nitriding treatment is performed. In addition, when using the ion nitriding method, the interior of the reaction vessel is kept in a high vacuum, and N2 gas as a reaction gas is introduced from the bottom of the vessel to flow the iron powder, while nitriding is performed by glow discharge. Perform processing. At this time, the nitriding conditions are appropriately set so that the produced iron nitride will surely be mainly composed of Fe4N. By performing the nitriding treatment in this manner, agglomeration of the powder particles can be avoided and the acicular particle shape can be maintained. Therefore, Fe4N, which has conventionally been difficult to use in practice despite having magnetic properties suitable for magnetic storage media, has been unable to maintain its acicular particles due to agglomeration during nitriding. , it becomes possible to apply it as a magnetic storage medium.

[0013] In view of magnetic properties, it is preferable to adjust the starting materials, nitriding conditions, etc. so that the finally formed Fe4N particles have an aspect ratio in the range of 6 to 9. After the nitriding process is completed in this way, the particles are dispersed in a binder to create a magnetic paint, which is applied onto a substrate to obtain a magnetic storage medium.

As mentioned above, Fe4N has good oxidation resistance and good magnetic properties as a magnetic storage medium, so by using Fe4N, it has excellent oxidation resistance and magnetic properties. However, a good magnetic storage medium can be obtained.

[0015] Note that fine powder with a length of about 10 μm or less in the longitudinal direction is scattered above the reaction area in the container during the above-mentioned floating flow, making it difficult to form a uniform fluidized bed. becomes. Therefore, in this case, it is effective to provide a magnetic field generating means such as an electromagnet around the upper part of the container, apply a magnetic field to the powder, sweep the powder particles, and prevent the powder particles from scattering. As for the mode of applying the magnetic field at this time, it is preferable that a plurality of electromagnets are arranged in parallel along the vertical direction, and alternating current is applied to the electromagnets in sequence while changing the phase. The strength of the magnetic field at this time needs to be appropriately adjusted depending on the speed of the gas to be supplied.

[0016] In addition to applying such a magnetic field, by applying vibration to the reaction vessel, the powder particles can be transported downward, and scattering of the powder particles can be more effectively prevented. Furthermore, it is also possible to further provide a magnetic field applying means at the lower part of the reaction vessel, and to apply the magnetic field thereby to prevent powder particles from falling from the reaction site within the reaction vessel.

[0017]

[Embodiments] Examples of the present invention will be described below.

First, acicular goethite was reduced with hydrogen to obtain acicular iron. The aspect ratio of this acicular iron was about 9, and the average particle length was about 0.3 μm. Next, needle iron is charged into the container, and NH3 gas and H2 are poured from below.
The nitriding was carried out while forming a fluidized bed. At this time, nitriding is carried out using NH3 /H2 in a ratio of 90/10 to 50/50.
The temperature was set at 80 to 450℃, and after treatment 1
It was collected in 0-30 minutes. In addition, in this process,
The proportion of gas was varied depending on the processing temperature. As a result of this treatment, acicular particle powder of Fe4N was obtained. An example of the magnetic field-magnetic flux density curve of this acicular particle powder is shown in FIG. As shown in this figure, it was confirmed that a good squareness ratio of the hysteresis curve was obtained. In addition, for those treated at 300°C with NH3 /H2 set to 80/20, the residual magnetic flux density was 2300 to 6000 Gauss,
It was confirmed that the coercive force was 1,000 to 2,000 Oe, and that it had good characteristics as a magnetic storage medium.

Next, a magnetic storage medium coated with such iron nitride powder and a conventional magnetic storage medium made of a magnetite film were maintained in an environment of a temperature of 60° C. and a humidity of 99% to test their environmental resistance. In this test, these storage media were removed every week and their residual magnetic flux densities were measured. The results are shown in FIG. As is clear from this figure, the saturation magnetic flux density of the storage medium using acicular iron nitride powder does not decrease much even after 4 weeks, whereas the saturation magnetic flux density of the conventional storage medium decreases significantly within 1 week. It was confirmed that this decreases.

[0020]

[Effects of the Invention] According to the present invention, since acicular Fe4N particles can be used as magnetic powder in a magnetic storage medium, a magnetic storage medium with excellent oxidation resistance and good magnetic properties can be obtained. .

[Brief explanation of the drawing]

FIG. 1: Phase diagram of the iron-nitrogen system.

FIG. 2 is a diagram showing a hysteresis curve of a magnetic field-magnetic flux density curve.

FIG. 3 is a diagram showing changes in saturation magnetic flux density over time.

Claims (3)

[Claims] [Claim 1] Acicular goethite particles are reduced to form acicular iron particle powder, and while the iron particle powder is suspended and flowed and dispersed, the powder is nitrided to form Fe4N. , a method for manufacturing a magnetic storage medium, comprising applying the Fe4N formed particle powder to a substrate. 2. The magnetic storage medium according to claim 1, wherein the floating flow of the iron powder is performed by charging the iron powder into a container and introducing a fluid from below the container. 3. A method for manufacturing a magnetic storage medium, wherein the floating flow of the iron powder is performed while applying a magnetic field to the iron powder.