JPS5828809A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having high coercive force, high magnetic flux density and high stability by as much as suppressing addition of the ferrous ion (Fe<2+>). CONSTITUTION:The needle-crystallized gamma-Fe2O3 etc. is sufficiently dispersed into the cobalt salt aqueous solution. This dispersive solution is mixed with a reducing agent such as the hydro-sulfite, boron sodium hydroxide, hydrazine, derivative of hydrazine and sodium hypophosphite etc. and the alkali solution in order to trigger the reducing reaction. Thereafter, this mixed solution is heated with a temperature of almost 100 deg.C or lower for the purpose of reaction. Thereby, the cobalt compound is deposited on the surface of corpuscules of needle- crystallized gamma-Fe2O3 etc. When reaction comes to the end, the deposited material is washed by water and it is collected as the magnetic powder by filtering and then dried up. The magnetic recording medium obtained thereby shows the characteristic that the coercive force at a temperature of 25 deg.C is 550 oersted or more, a ratio of the coercive forces at the temperatures of minus 190 deg.C and 25 deg.C is 1.8 or less, content of Fe<2+> included is 1.0wt% or less, orientation degree is 2.0 or higher.

Description

[Detailed description of the invention] The present invention relates to magnetic recording media.

A fundamental need for magnetic recording media is an increase in recording density. That is, the amount of information stored per unit area or unit volume is increased, which leads to miniaturization of the magnetic recording medium. However, using materials that have been used traditionally,
Attempting to miniaturize leads to a decrease in sensitivity and deterioration of frequency characteristics, so a material with higher performance, that is, one with a higher coercive magnetic flux density and easier to orient, is required.In addition to these points, high density A magnetic recording medium with a high coercive force is required for recording, but in consideration of harmony with the magnetic head, it is sufficient if the coercive force is 550 or more at normal temperature (25° C.).

Regarding the degree of orientation, the higher the degree, the better, but a value of at least 2.0 is desired.

Next, there is the issue of stability.

Even if magnetic properties such as coercive force have desirable values, if these properties are unstable and vary greatly depending on temperature, pressure, etc., it cannot be used practically as a magnetic recording medium.

Therefore, stable magnetic properties are one of the important properties of a magnetic recording medium. Therefore, among the magnetic properties, we take the coercive force and use it as an index to express its dependence on temperature.The coercive force Hc-
Coercive crab FIc25 at 196℃ and room temperature (25℃)
Look at the ratio Hc-196°C/Hc 25°C. Generally, the coercive force increases as the temperature decreases, so Hc-196℃/
The value of He25°C is greater than 1. Therefore, the larger this value is, the greater the temperature dependence is, and conversely, the smaller tl is, the smaller the dependence is. Therefore, it is desirable to have a magnetic recording medium with this index as small as possible from the viewpoint of temperature stability, and the value to be added to J:'6:Ji for practical use has a condition of 1.8 or less.

In order to increase the coercive force, there is a magnetic recording medium made by adding cobalt ions and ferrous ions (II''e2+) to iron monooxide, but in this case, if the amount of Fe2+ added is large, the coercive force On the other hand, the increase in magnetic properties becomes unstable, and other transfer and erasing effects deteriorate, or the binder is altered by the Fe needle, giving a shadow or V to the tape physical properties, which becomes a practical problem. There are various disadvantages such as the possibility that the addition of FC2+ [to other magnetic materials] has been considered as a practical range without problems.
．． It was found that the content must be 0% by weight or less.The conditions necessary for a magnetic recording medium can be summarized as follows.

■Hc25°C must be 550 oersted or more.

■Inc-196℃/lIC25℃ is 1.8 or less.

■The content of Ti''e2+ component is 1.0% by weight or less.

6- If we look at conventional magnetic recording media under these conditions, there is no one that satisfies all the conditions as shown in Table 1.

An example of a material that satisfies the high coercive force and high magnetic flux density conditions listed in Table 1 is a magnetic powder made by adding a small amount of cobalt to γ-Fe2O3 magnetic powder (cobalt-doped type γ
-Fe203), which was put into practical use for a time. However, the dependence of the magnetic properties on temperature and pressure is extremely large, and condition (2) is not satisfied. When used as a magnetic recording tape, it has drawbacks such as a large transfer effect, and is hardly used at present.

=4- As another example, the cobalt-doped γ-Fe20
There is a cobalt adsorption type γ-Fe203 that improves the drawbacks of No. 3. It has a structure in which acicular γ-Fe203 is used as a core, cobalt ions are adsorbed on its surface, and a surface layer made of a certain yuzu cobalt compound is formed.It has a high coercive force due to its surface anisotropy. It is something. This stabilizes the magnetic properties, improves the transfer effect, and increases the coercive force by increasing the adsorption amount of cobalt ions, but there is a limit to this, which is about 500 millimeters.

Magnetic powder made by adding ferrous ions (Fe2+) in addition to cobalt ions in order to increase the coercive force even higher has a higher coercive force, but on the other hand, as mentioned above, it worsens the transfer effect erasing effect. In addition to making the magnetic properties unstable, it also alters the quality of the binder, which has a negative effect on the overall properties.

In this way, conventional magnetic recording media have transfer effects, erasure effects,
It had various drawbacks in physical properties, stability, degree of orientation, etc.

On the other hand, the magnetic recording medium of the present invention not only has a high coercive force (■-IC25°C of 550 degrees or more), but also is easily oriented (degree of orientation 2.0 or higher) and -
Good stability against temperature (HC-196℃/
Hc value at 25°C is 1.6 to 1.7) Furthermore, since it contains only a small amount of Fe2+, which has a negative effect on the properties of the steel, (
1.0% by weight or less) The above-mentioned damage to physical properties has been improved compared to the conventional one. Table 2 shows a comparison with the conventional one.

Table 2 Next, the method for manufacturing the 41k (magnetic recording medium) according to the present invention is described.The present invention can add ferrous ions (Fe2-1-), which are recognized to have an effect on magnetic recording media. Takeo succeeded in printing a magnetic recording medium with high coercivity, high magnetic flux density, and stability.

That is, acicular γ-Fe20x, etc. are sufficiently dispersed in an aqueous cobalt salt solution, and this dispersion is mixed with hydrogenated sulfite, hydrogenated borosulfur, hydrazine, hydrazine derivatives, hypophosphorous acid, triuno, etc. A reducing agent and an alkaline solution are mixed to cause a reduction reaction, and then this solution is mixed with t 10
Acicular γ-1i'a2 is heated and reacted at a temperature below 0°C.
After the completion of the 0 reaction in which a cobalt compound is precipitated on the surface of the particles such as 03, the 1 & 2 powder is collected by washing with water and filtration and dried.

In this case, in order to reduce the uniformity of the reduction reaction, a complexing agent was conventionally added before the addition of the reducing agent, but this did not contribute to the larger coercive force, but rather reduced the It was found that by weakening the action of the complexing agent, the increase in coercive force was considerably smaller than in the case without the complexing agent. (
(described later with reference to comparative examples) Therefore, in the present invention, it is important not to add a complexing agent.

In addition, in the present invention, changing the amount of cobalt salt,
Do not add the reducing agent later than the alkali! :1 or alkaline concentration: 1 By changing the amount of reducing agent and heating time, the coercive force of the magnetic powder obtained can be changed.

Examples are shown below.

Practical hIi Example 1 Cobalt sulfate 142 is dissolved in 1 t of water, and γ-1i is added to it.
'820310Of was added and dispersed for 20 minutes using a homomixer. Next, 400 yt of 6N caustic soda solution
E and a reducing agent (hydrozalphi) 2 Of) were added to this dispersion and allowed to react for 20 minutes. This was further heated at 100° C. for 2 hours to cause a reaction. After the reaction was completed, the magnetic powder was collected by washing with water and filtration, and was dried at 70° C. for 8 hours. The magnetic properties of the magnetic powder obtained by this method were compared with the magnetic powder produced when only the addition of core iron oxide and reducing agent (nohedrozulfite) was omitted, as shown in Table 3. Table 3 Example 2 141 parts of cobalt sulfate and 1 part of water. γ- in a solution dissolved in t
Fe2O31009 was dispersed, 400 me of 6N caustic soda solution and 52 ml of reducing agent (hydrozulfite) were added to this dispersion, and the mixture was heated at 100°C with stirring.
The mixture was heated to react for 3 hours.

After completion of the reaction, the magnetic powder was collected by washing with water, filtered, and dried at 70°C for 12 hours. The magnetic properties of the obtained magnetic powder were compared with those of the core, and are shown in Table 4. Therefore, in Example 2, when dispersing γ-Fe2us in a cobalt sulfate solution, a complexing agent (potassium tartrate, sodium 15y) was added, and the subsequent operations were performed in exactly the same manner as in Example 2. The magnetic properties of the magnetic powder obtained by this method are shown in Table 5 together with Example 2 and the core.

Table 5 Example 3 A magnetic powder was obtained in the same manner as in Example 1, except that the reducing agent was 22 H1 borohydride thorium and the drying time was 12 hours. Table 6 shows the magnetic properties of the magnetic powder obtained by this method in comparison with that of the core.

11- Table 6 Example 4 Example 1 except that the reducing agent was replaced with 3 tnl of hydrazine
Magnetic powder was obtained in the same manner as in Table 7. The magnetic properties of the magnetic powder obtained by this method are shown in Table 7 in comparison with the core C1 -,12- Table 7 Example 5 (1) Cobalt sulfate 142 γ in a solution dissolved in 1 t of water.
-Disperse Feze3100 y and add 6N to this dispersion.
400 g of a caustic soda solution and 25 g of a reducing agent (hydrosulfide) were added to the mixture, and a reduction reaction was carried out with stirring. Next, heat the solution to 100℃ while stirring.
The mixture was heated to react for 4 hours. After the reaction was completed, the mixture was washed with water, collected by filtration, and dried at 70° C. for 12 hours to obtain a magnetic powder.

(2) In (1), the heating time at 100°C was changed to 2 hours to obtain magnetic powder.

(3) In (2), the timing of adding hydrosulfide was delayed from the addition of caustic soda.

The magnetic properties of the magnetic powder obtained by the above method are shown in Table 8 in comparison with those of the core.

As is clear from the Examples in Table 8 and above, the products of the present invention have a high coercive force, a high magnetic flux density, and an excellent squareness ratio.

Next, the characteristics of the magnetic tape coated with the magnetic powder described above were determined in the ninth section.
Shown in the table.

Table 9: As is clear from this table, the magnetic recording medium according to the present invention]
, ITc 25℃+Hc '96℃/H, IC25℃,
Both the degree of orientation and the content of Fe2+ meet the requirements for intercropping, and due to its high coercivity, high magnetic flux density, stability, and ease of orientation, it is extremely useful as a high-density recording medium. It is.

15- 35-

Claims (1)

[Claims] Coercive force value at 25°C is 550 or more
Magnetism in which the ratio of the coercive force value at -196°C to the coercive force value at 25°C is 1.8 or less, the Fe2+ component contained is 1.0% by weight or less, and the degree of orientation is 2.0 or more. recoding media