JPS5928965B2 - pine tree - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an iron oxide magnetic powder containing cobalt atoms suitable as a recording element of a magnetic recording medium.

This type of magnetic powder has a higher coercive force than iron oxide magnetic powder, which is commonly used as a recording element in conventional magnetic recording media, so it has various advantages such as high-density recording and high sensitivity in the high frequency range. One of the methods for its production is a hydrothermal denaturation method already devised by the inventors, in which magnetic iron oxide powder is dissolved in a solution of a metal salt containing a cobalt salt and an oxycarboxylic acid or its salt. By dispersing the cobalt and subjecting it to a hydrothermal reaction under relatively mild reaction conditions of weak acidity to weak alkalinity, it is possible to obtain a product with high coercive force even with a lower content of cobalt atoms compared to other production methods. This ferromagnetic powder has the advantage that it has excellent dispersibility in a binder when forming a magnetic layer and can provide a magnetic recording medium with excellent sensitivity. However, since the ferromagnetic powder obtained by this method has cobalt uniformly dissolved in the powder particles, a magnetic recording tape using this as a recording element must be wound and stored at a relatively high temperature after recording. , the recording signal is immediately transferred to the opposing magnetic layer.

This tendency becomes more pronounced when the content of cobalt atoms is small. The present invention aims to provide a ferromagnetic powder that is resistant to demagnetization under heating or pressure conditions, and is therefore resistant to transfer, without losing the above-mentioned advantages. This is achieved by using cobalt-containing iron oxide powder, in which cobal is uniformly dissolved in powder particles, as a nucleation crystal, and then epitaxially growing a crystal mainly composed of iron-cobalt oxide on this nucleation crystal. It was discovered that something could be done.

The above-mentioned hydrothermal denaturation method is most suitable as a method for producing cobalt-containing iron oxide powder that uniformly dissolves cobalt, which is used as the nucleus crystals in this invention. Examples of carboxylic acids and their salts include citric acid, tartaric acid, malic acid, glycolic acid, lactic acid, and salts thereof. Metal salts containing cobalt salts include cobalt salts alone and in combination with manganese, Examples include salts such as zinc and nickel. The reaction temperature during the hydrothermal reaction may be about 120 to 200 QC, and the pH is preferably in the relatively mild range of weakly acidic to weakly alkaline, usually 6.0 to 13.0. The content of cobalt atoms (weight ratio relative to relaxation with iron atoms, same hereinafter) obtained by the above hydrothermal denaturation method is about 1
The iron oxide powder containing less than 0% by weight of cobalt is then used as a nucleus crystal to epitaxially grow a crystal mainly composed of iron-cobalt oxide.

Epitaxial growth may be carried out according to the method described in Japanese Patent Publication No. 49-49475, using a solution of an iron salt and a cobalt salt and, if necessary, another metal salt such as a zinc salt, and at least the above-mentioned iron salt and cobalt salt. is mixed with an alkaline solution at a concentration that precipitates, and the mixture and oxidation are carried out while blowing in an oxidizing gas, so that iron-cobalt oxide crystals are epitaxially grown on the core crystals. At this time, the oxidation temperature is room temperature ZO
Preferably, the temperature is higher than 0.degree. The drawing shows the transfer suppression effect due to epitaxial growth. In this drawing, acicular Fe3O4 is used as the raw material magnetic iron oxide powder.
Cobalt atom content and transfer in epitaxial crystal films using powder (recording a 1 kHz signal on the sample tape within one rotation of the reel at a specified bias current and an input level 10 dB higher than the specified input level; The difference in playback output level between the original signal and the most transcribed signal when recorded after rotation, repeated several times, and left at a temperature of 30°C for 24 hours is expressed in DB (the same applies below). It represents. As is clear from the figure, the content of cobalt atoms in the epitaxial crystal film is 8% by weight or more, and usually 12~12% by weight.
It can be seen that transfer can be sufficiently suppressed by setting the amount to 33% by weight.

However, if such an epitaxial crystal film is formed too thick, the coercive force will become higher than necessary and the dispersibility with respect to the binder will deteriorate, thereby impairing the original advantages of the hydrothermal denaturation method.

Therefore, the film thickness is preferably such that the total amount of cobalt atoms in the core crystals and the crystal film is about 12% by weight or less. The ferromagnetic powder of the present invention formed in this way usually has a coercive force of about 400 to 1300 oersteds, has good dispersibility in a binder, and is equivalent to or even better than the raw magnetic iron oxide powder. It has the excellent property of suppressing transfer as described above.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Acicular Fe3O4 magnetic powder (manufactured by Toda Kogyo Co., Ltd., trade name MRM-450B, coercive force: 420 oersted, transcription: 48.5 dB) 809 with a particle size of 0.5μ was mixed with cobalt chloride (COCl2.6H20) in 300 ml of water. The mixture was dispersed in an aqueous solution containing 3.79 and sodium tartrate 409, charged into an autoclave, and subjected to a hydrothermal reaction at 190°C for 3 hours.

When the precipitate formed after the reaction was completed was filtered, washed with water, and dried, a black cobalt-containing iron oxide powder with a cobalt atom content of 1.5% by weight was obtained. , the above powder is 5
It exhibited a coercive force of 80 oersted and had a diagonal shape that was almost the same as that of the raw material Fe3O4 magnetic powder.
e3O was more easily transferred than magnetic powder.

Next, the above cobalt-containing iron oxide powder is used as a core crystal, and an iron-cobalt oxide crystal is epitaxially grown on the core crystal by the following method.

That is, ferrous sulfate (FeSO4.6H20) 21.4
Aqueous solution containing 9 and cobalt chloride (COC'2.6H20
) 2.59 to prepare a metal 5 metal ion solution, add an aqueous solution containing NaOH4O9 to this solution so that the total water volume is 500 ml, and mix to form an iron-cobalt coprecipitate. Let it precipitate.

After that, the cobalt-containing iron oxide powder after hydrothermal modification 80
9 was added, and while stirring at 100 DEG C. for 3 hours, air was blown at a rate of 11 per minute to carry out an oxidation reaction to epitaxially grow iron-cobalt oxide crystals. The ferromagnetic powder of the present invention thus obtained has a cobalt content of 2% by weight of Cl in the epitaxial crystal film and 2% by weight in the entire powder.

It was 4% by weight.

The coercive force was 610 oersted, and the good dispersibility before epitaxial growth was not impaired at all. Moreover, the transfer is easier than the raw material Fe3Q magnetic powder 4
9.0 dB, indicating that the transcriptional suppression effect was sufficiently expressed. Example 2 Cobalt-containing iron oxide powders with different cobalt contents obtained in the same manner as in Example 1 (hydrothermal denaturation method) were used as nucleus crystals, and this powder, cobalt chloride cubes, and sulfuric acid A ferromagnetic powder was obtained in the same manner as in Example 1 except that the amount of iron used was changed.

The ratio of each component used and the characteristic values of the obtained ferromagnetic powder are as shown in the table below. As is clear from the table above, it can be seen that the epitaxial growth and transfer were sufficiently suppressed as in Example 1 above.

[Brief explanation of drawings]

The drawing is a characteristic diagram showing the relationship between the cobalt atom content and transfer of the epitaxial crystal film according to the present invention.

Claims (1)

[Claims] 1. A ferromagnetic powder for magnetic recording, in which a cobalt-containing iron oxide powder containing cobalt as a uniform solid solution is used as a core crystal, and crystals mainly composed of iron-cobalt oxide are epitaxially grown on the core crystal.