JPS5923505A - Magnetic powder - Google Patents

Abstract

PURPOSE:To obtain magnetic material suitable for a high-density magnetic recording medium superior in the squareness ratio, orientation and electromagnetic conversion property by a method wherein a silica-alumina coprecipitate is deposited on the surface of magnetic iron oxide powder to improve dispersity into a resin bonding agent. CONSTITUTION:A circular gamma-Fe2O3 is dispersed into a NaOH aqueous solution to obtain slurry, and cobalt sulfate aqueous solution and ferrous sulfate aqueous solution are added thereto while blowing N2 gas. After sufficient agitation at the room temperature, the slurry is filtered and washed to obtain a wet cake of magnetized iron oxide containing cobalt which is then dispersed into water. Subsequently, the slurry is heated up to 45 deg.C while blowing N2 gas, and then sodium aluminate aqueous solution and ortho-sodium slicate aqueous solution are added thereto under agitation. Next, dilute sulfic acid is added thereto to neutralize the pH value to 7.5 and it then undergoes maturation while agitating. In this way, high dispersity is applied to the magnetic powder, thereby resulting in powder suitable for a magnetic recording medium material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic powder useful as a material for magnetic recording media.

Magnetic recording media such as magnetic tape are usually made by coating a polyester film with a magnetic paint containing magnetic powder dispersed in a binder. As the magnetic powder used in the manufacture of this magnetic recording medium, acicular magnetic iron oxide such as γ-Fe2O3 or a fine powder of the acicular magnetic iron oxide containing a cobalt compound is often used. In particular, the cobalt-containing magnetic iron oxide has a high coercive force and excellent sensitivity in a high frequency range, and its use has increased in recent years as the density of magnetic recording media has increased.

However, in the manufacture of magnetic recording media, these magnetic powders do not wet enough with the binder medium or cause magnetic aggregation between the particles, making it difficult to disperse them uniformly in the binder resin. Deterioration of the magnetic properties of the medium is likely to occur.

In particular, when using a binder whose main component is a polyurethane resin, which has recently become popular, the above-mentioned tendency is particularly noticeable and a solution to this problem is desired even more.

The present invention aims to provide a magnetic powder capable of solving the above-mentioned problems. Specifically, the present invention provides a magnetic powder characterized in that it has a silica-alumina coprecipitate on the surface of magnetic iron oxide powder. It is.

In the present invention, the magnetic iron oxide powder used is γ
-Fe2O3, Fe3O4, Bertolide compound (Fe
Cobalt or cobalt and other metal compounds are deposited on the particle surface of acicular acid ratio iron such as Ox1.33 < Some of them are doped with cobalt or cobalt and other gold compounds.

In the present invention, the silica-alumina coprecipitate present on the surface of the magnetic iron oxide powder refers to a hydrated aluminum silicate or a composite hydrated oxide of aluminum and silicon. They may be applied in the form of a continuous film on the surface of the magnetic iron oxide powder, or they may be applied in part or in whole in the form of a discontinuous film. The molar ratio of Al2O3:SiO2 in the silica-alumina co-precipitate may be in various ranges, but it is particularly desirable that the molar ratio is in the range of 1:2 to 1:4.

The amount of the silica-alumina coprecipitate deposited is 0.05 to 10% as SiO2 based on the weight of the magnetic iron oxide powder.
% desirably 0.1 to 2%, and 0.1 to 2% as Al2O3.
0.03 to 9%, preferably 0.1 to 1.7%. If the amount of the coating is less than the above range, the desired dispersibility effect may not be obtained, and the squareness ratio, orientation, etc. may not be sufficiently improved. On the other hand, if the amount of coating is too large, it may be difficult to expect any improvement in the above-mentioned properties, and further, magnetoelectric properties such as coercive force, saturation magnetization, and saturation magnetic flux density may be impaired, which is undesirable.

The magnetic powder of the present invention has very good dispersibility in a binder resin, and has excellent squareness ratio, orientation, and electromagnetic conversion characteristics in magnetic recording media. In particular, for materials such as cobalt-containing iron oxide magnetic powder that are difficult to uniformly disperse in a binder resin, a high degree of dispersibility can be achieved by applying the silica-alumina coprecipitate coating treatment of the present invention. It can be applied as a magnetic material for high-density magnetic recording media.

In the present invention, the cobalt-containing iron oxide magnetic powder used in the production of magnetic powder is obtained by depositing cobalt or cobalt and other metal compounds on the surface of acicular magnetic iron oxide base particles such as γ.Fe2O3. Alternatively, the iron oxide particles may be doped. Examples of the other metal compounds include ferrous, manganese, zinc, chromium, and nickel, but it is more advantageous to deposit a ferrous compound together with a cobalt compound. When depositing the above-mentioned cobalt or cobalt and other metal compounds, in the case of cobalt alone, it is usually 0.5 to 10% as Co, and for example, based on the weight basis of the total Fe amount of the base acid ratio iron particles. When depositing a combination of a cobalt compound and a ferrous compound, it is appropriate that the former be 0.5 to 10% as Co, and the latter as Fe2+ be 1 to 20%. In addition, when doping with a cobalt compound, co-precipitation with the cobalt compound is performed during the production of acicular hydrated iron oxide such as goethite, or heat treatment is performed on the cobalt compound-adhered product at a temperature of about 200° C. or higher. You can do it by doing this. As for the doping amount,
0 as Co with respect to the weight basis of the total Fe amount of iron oxide particles
．． Approximately 5 to 10% is appropriate.

In the present invention, various methods can be used to deposit the silica-alumina coprecipitate on the surface of the magnetic iron oxide powder. For example, an aqueous slurry of magnetic iron oxide powder may be formed, and to this slurry water-soluble compounds of silicon and aluminum may be added in parallel or in any order, or both water-soluble compounds may be mixed in advance. This can be done by adding a fine coprecipitate.

This slurry is then neutralized and aged if necessary. In this case, the temperature during treatment is usually below the boiling point, preferably 3.
The temperature is 0 to 70°C. Note that the atmosphere during the treatment may be non-oxidizing or oxidizing, but a non-oxidizing atmosphere is more desirable.

The water-soluble compounds of silicon include, for example, salts of orthosilicic acid and metasilicic acid such as sodium, potassium, and cobalt, and the water-soluble compounds of aluminum include, for example, sodium or potassium aluminate, aluminum sulfate, and aluminum chloride. Each can be used.

In addition, in the present invention, when applying a silica-alumina co-precipitate to a cobalt-containing magnetic iron oxide powder obtained by coating cobalt or cobalt and other metal ratios on acicular magnetic iron oxide, Before its deposition treatment or (
and) The effects of the present invention may be made more desirable by performing heat treatment later. This heat treatment can be carried out by various methods. For example, a wet cake obtained by filtering and washing a slurry coated with cobalt or cobalt and other metal compounds is heated at 60 to 250°C in the presence of water vapor, and then
A silica-alumina coprecipitate is deposited, or a silica-alumina coprecipitate is deposited on a deposit of cobalt or cobalt and other metal compounds, and the resulting wet cake is similarly heat-treated. You can

The present invention will be further explained below by giving Examples and Comparative Examples.

Example 1. Acicular γ-Fe2O3 [coercive force (Hc): 4050e, specific surface performance: 31m2/g, axial ratio (L/W): 10/1] 1
00g was dispersed in a 1 mol/l NaON aqueous solution to obtain 1
While blowing N2 gas into the slurry, 59 ml of a 1 mol/l cobalt sulfate aqueous solution and 125 ml of a 1 mol/l ferrous sulfate aqueous solution were added to the slurry at room temperature (3.0 g/l).
The mixture was stirred at 0° C. for 5 hours. This slurry is then filtered,
Wet cake of cobalt-containing magnetic iron oxide obtained by washing with water 23
Disperse 0g in water to make a 100g/l slurry, and add N
This slurry was heated to 45°C while blowing 2 gases, and a sodium aluminate aqueous solution (Al2O3
/Na2O molar ratio 0.75, 50g/ as Al2O3
l) 3.6 ml, followed by aqueous sodium orthosilicate solution (SiO2/Na2O molar ratio 0.5, Si
6.4 ml of 50 g/l as O2 was added (0.32% as SiO2 and A
0.18% as l2O3), then dilute sulfuric acid was added to the slurry to neutralize it to pH 7.5, followed by stirring and aging for 30 minutes.

The slurry coated with the silica-alumina co-precipitate in this way was filtered and washed, and the resulting wet cake was placed in an autoclave with water in a separate container, and replaced with N2.
After sealing, it was heat-treated at 130° C. for 6 hours in the presence of steam.

The magnetic powder (A) of the present invention was then dried at 60°C for 8 hours.
I got it.

Example 2. In Example 1, the amounts of the sodium orthosilicate aqueous solution and the sodium aluminate aqueous solution were determined based on the weight of iron oxide, the former being 0.64% as SiO2, and the latter being A
The magnetic powder (B) of the present invention was obtained in the same manner as in Example 1 except that the l2O3 content was changed to 0.36%.

Example 3. In Example 1, the wet cake of cobalt-containing iron oxide was treated in the same manner as in Example 1, except that the silica-alumina co-precipitate was applied after the steam heat treatment. , magnetic powder (C) of the present invention was obtained.

Example 4. Except that γ-Fe2O3 powder having a coercive force (He) of 341, a specific surface area of 31 m2/g, and an axial ratio (L/W) of 10:4 was used as the magnetic iron oxide powder used in Example 1. was treated in the same manner as in Example 1 to obtain magnetic powder (D) of the present invention.

Comparative example 1. In Example 1, magnetic powder (E) was prepared in the same manner as in Example 1 except that the sodium orthosilicate aqueous solution and the sodium aluminate aqueous solution were not added.
I got it.

Comparative example 2. A magnetic powder (F) was obtained in the same manner as in Example 1 except that the aqueous sodium orthosilicate solution was not added.

Comparative example 3. A magnetic powder (G) was obtained in the same manner as in Example 1 except that the aqueous sodium aluminate solution was not added.

Comparative example 4. In Example 4, magnetic powder (H) was prepared in the same manner as in Example 4 except that the sodium orthosilicate aqueous solution and the sodium aluminate aqueous solution were not added.
I got it.

Magnetic powders obtained in Examples 1 to 4 and Comparative Examples 1 to 4 (
For A) to (H), coercive force (He),
After measuring the saturation magnetization current (δs), a magnetic paint was prepared according to the blending ratio shown below, and this paint was applied onto a polyester film by a conventional method, oriented and dried to form a magnetic coating film with a magnetic coating thickness of about 6μ. I made a tape.

Magnetic powder 24 parts by weight Polyurethane resin 5 PVC-vinyl acetate copolymer
1.2 Dispersant 0.5
〃Mixed solvent toluene/MEK 69.3 〃Measure the coercive force (He), squareness ratio (Br/Bm), orientation (OR), and switching field distribution (SFD) of each obtained magnetic tape by the usual method The results are shown in Table 1.

Note that the squareness ratio, orientation, and reversal magnetic field distribution are indicators of dispersibility, and the higher the value of the former two, and the lower the value of the latter, the better the dispersibility.

As is clear from the results in Table 1, the magnetic powder of the present invention has improved dispersibility compared to each comparative example, and the magnetic properties of the tape are good. It can be seen that it is. In addition, as in Example 3, when applying the silica-alumina co-precipitate to the cobalt-containing magnetic iron oxide, heat treatment is applied to the cobalt-containing magnetic iron oxide in advance, which improves not only dispersibility but also retention. It can be seen that the magnetic force can also be improved.

Patent applicant: Ishihara Sangyo Co., Ltd.

Claims (1)

[Claims] A magnetic powder characterized by having a silica-alumina co-precipitate on the surface of the magnetic iron oxide powder.