JPH0283219A - Production of cobalt-containing ferromagnetic iron oxide powder - Google Patents

Abstract

PURPOSE:To improve adsorption characteristics of lubricants, etc., on magnetic powder and obtain a magnetic iron oxide powder well balanced in magnetic and physical characteristics by forming a silicon compound layer on the surface of a Co-containing ferromagnetic iron oxide and heat-treating the resultant substance. CONSTITUTION:A water-soluble silicon compound (e.g., sodium orthosilicate) and, as necessary, further a water-soluble compound containing at least one element selected from Al, P, Ti, V, Mn, Ni and Zn are added to a slurry prepared by dispersing a Co-containing ferromagnetic iron oxide in an aqueous medium, neutralized and precipitated with an acid or alkali to form compound layers thereof on the particle surfaces of the iron oxide. The applied amount is 0.01-5wt.%, desirably 0.02-2wt.% expressed in terms of the respective elements based on the Co-oontaining iron oxide. The obtained slurry is then heat-treated at >=60 deg.C, normally 60-150 deg.C, desirably 80-140 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing cobalt-containing ferromagnetic iron oxide powder having excellent magnetic properties and useful as a material for magnetic recording media.

[Conventional technology]

As technology advances in audio, video, computers, word processing, etc., higher quality recording materials are required for these magnetic recording media. Cobalt-containing ferromagnetic iron oxide powder is no exception, and in addition to magnetic properties such as coercive force and reversal magnetic field distribution, in recent years, magnetic paint manufacturing has been concerned with dispersibility, stability over time, and even the physical properties of magnetic tapes. It is also desired that lubricants and resins that are sometimes used have excellent adsorption properties to magnetic powder.

Techniques for increasing the coercive force of magnetic powder or improving the dispersibility of magnetic powder in the magnetic layer of a magnetic recording medium include (1) co-precipitation of silica-alumina on the surface of ferromagnetic iron oxide powder; Magnetic powder containing substances (JP-A-59-
23505), (2) By immersing and treating cobalt-containing ferromagnetic iron oxide powder, which is formed by forming an iron oxide layer containing cobalt on the surface of ferromagnetic iron oxide powder, in a solution containing a silicon compound. A method of attaching a silicon compound to the surface of cobalt-containing ferromagnetic iron oxide powder and heating it in an oxidizing atmosphere (Japanese Patent Publication No. 62-17364) Ferromagnetic powder to which alkaline metal oxides and/or hydroxides are attached (Japanese Patent Publication No. 62-50889),
(4) Method of depositing manganese and/or vanadium compounds on the surface of cobalt-containing iron oxide (Japanese Unexamined Patent Publication No. 59-14
7414), (5) Method of depositing a zinc compound on the surface of cobalt-containing iron oxide (JP-A-59-159502)
, (6) Method of coating the surface of cobalt-containing iron oxide with calcium-silicon co-precipitate (Japanese Patent Application Laid-Open No. 63-45129)
and so on.

[Problem that the invention seeks to solve]

However, although the method (1) improves the dispersibility, the adsorption properties of the lubricant and resin to the magnetic powder, which are involved in the physical properties of the magnetic tape, are still insufficient, and the method (2) does not improve the retention. Although the magnetic force is high, the dispersibility,
The adsorption properties described above cannot be satisfied, and the method (3) has drawbacks such as insufficient dispersibility and adsorption properties. Furthermore, although methods (4) and (5) improve coercive force and dispersibility, it is difficult to improve reversal magnetic field distribution, adsorption characteristics, etc., and method (6) improves coercive force and reversal magnetic field. Although the distribution is improved, there are drawbacks such as insufficient adsorption properties.

As described above, in the prior art, even if a magnetic tape with high coercive force or good dispersibility is obtained, there is a problem in that the physical properties of the magnetic tape cannot be satisfied even when it is used. In recent years, as audio and video tapes have become more sophisticated, magnetic tapes are required to have excellent dispersibility as well as excellent physical properties when manufactured. A cobalt-containing ferromagnetic iron oxide powder is highly desired.

The present invention solves the problems of the prior art, and provides a cobalt-containing magnetic tape that has excellent magnetic properties and dispersibility, and has excellent physical properties of a magnetic tape with improved adsorption properties of lubricants and resins to magnetic powder. An object of the present invention is to provide a method for producing 6fi iron oxide powder.

[Means for solving problems]

Aluminum on the surface of cobalt-containing ferromagnetic iron oxide particles,
Coating with compounds containing elements such as silicon, phosphorus, titanium, vanadium, manganese, nickel, and zinc improves the temporal stability, dispersibility, and lubricant adsorption properties of magnetic powder, but on the other hand, it Magnetic force, reversal magnetic field distribution,
A problem arises in that the amount of saturation magnetization decreases. However, when heated in a medium such as water at a temperature of 60°C or higher after the coating treatment, the coercive force, reversal magnetic field distribution, and saturation magnetization (2) are improved without adversely affecting the above-mentioned improvement effects, and various magnetic properties are improved. , a cobalt-containing ferromagnetic iron oxide powder with well-balanced physical properties is obtained.

The present invention was completed based on such knowledge.

That is, the present invention provides a silicon compound layer or a silicon compound and aluminum, phosphorus, titanium, vanadium,
A cobalt-containing ferromagnetic material characterized by forming a compound layer containing at least one element selected from the group of manganese, nickel, and zinc, and then heat-treating the slurry at a temperature of 60° C. or higher. This is a method for producing iron oxide powder.

In obtaining the knowledge related to the present invention, the present inventors discovered silicon, aluminum, nickel, calcium, titanium, vanadium, manganese, nickel, zinc,
After conducting intensive studies on compounds such as phosphorus, we found that
Regarding silicon, as described in the specification of Japanese Patent Application No. 63-29543 (by the same person as the applicant of this patent), silicon either does not substantially bring about the effect of improving magnetic properties, or does not significantly improve the effect. Although the results are poor, it has been found that desired effects can be obtained in improving the adsorption properties of lubricants.

Furthermore, from among the elements described in Japanese Patent Application No. 10375/1982, a compound containing a silicon compound and at least one element selected from the group of aluminum, phosphorus, titanium, vanadium, manganese, nickel, and zinc; It has been found that even more excellent effects can be obtained by coating cobalt-containing ferromagnetic iron oxide and then heating the iron oxide in an aqueous medium at a temperature of 60° C. or higher.

In the present invention, compounds such as silicon, phosphorus, titanium, nickel, vanadium, manganese, zinc, and aluminum present on the particle surface of cobalt-containing ferromagnetic iron oxide are hydrated hydroxides, hydrated oxides, and the like. These are hydroxides or oxides such as hydrated oxyhydroxides, which are intermediate between the following.

The coating amount of the compound is 0.0 in terms of each element on a weight basis with respect to the cobalt-containing ferromagnetic iron oxide serving as the nucleus crystal.
It is 1 to 5%, preferably 0.02 to 2%. In particular, when coating a plurality of compounds, the content should be such that the content falls within the above range in terms of elements. If the coating amount is too less than the above range, it will be difficult to obtain the desired dispersibility, physical properties and stability over time.

Furthermore, if the amount of coating is too large than the above range, magnetic properties such as coercive force, saturation magnetization, and reversal magnetic field distribution will be impaired, which is not desirable.

The cobalt-containing ferromagnetic iron oxide used in the present invention includes a cobalt compound or a cobalt compound and other metal compounds such as T-Pe, 0. , pe, 0. , bertolide compound (FeOx 1.33 < x < 1.5
), or doped into the iron oxide particles. Examples of the other metal compounds include compounds such as ferrous, manganese, zinc, lithium, and nickel, but it is more advantageous to deposit a ferrous compound together with a cobalt compound. The doping and deposition of the cobalt compound or the cobalt compound and other metal compounds may be carried out according to a conventional method.

The slurry of cobalt-containing ferromagnetic iron oxide obtained by deposition treatment or doping treatment can be used as it is, or after filtering the slurry, or after filtering and washing, or after filtering, washing, and drying. , dispersed in an aqueous medium and subjected to the next coating treatment with compounds such as silicon, aluminum, phosphorus, titanium, vanadium, manganese, nickel, and zinc.

The amount of deposition or doping is usually 0.5 to 10% as Go in the case of cobalt alone, based on the weight of all Fe of the base iron oxide particles, or, for example, in the case of a combination of a cobalt compound and a ferrous compound. In this case, the former is G.

0.5-10% as FeI2 and 1-20% as FeI2
% is appropriate.

In the present invention, first, a silicon compound layer or a silicon compound and a group of aluminum, phosphorus, titanium, vanadium, manganese, nickel, and zinc are formed on the surface of the cobalt-containing ferromagnetic iron oxide particles that have been tlked in an aqueous medium. and a compound containing at least one selected element. Even if only silicon compound is coated,
The desired effect can be obtained, but when coated with a compound consisting of a silicon compound and a compound containing at least one element selected from the group of aluminum, phosphorus, titanium, vanadium, manganese, nickel and zinc, even more The desired effect is achieved. Among these, it is particularly desirable to coat a silicon compound with an aluminum compound or a manganese compound from the viewpoint of various magnetic properties and separation properties.

Coating the compound can be done by various methods. For example, when coating a silicon compound,
A water-soluble silicon compound and an acid or alkali are added in parallel to a slurry in which cobalt-containing ferromagnetic iron oxide is dispersed in an aqueous medium to neutralize and precipitate the silicon compound, or a water-soluble silicon compound and an acid or alkali are added in parallel. are added in any order to neutralize and precipitate, or an acid or alkali is added to the slurry in advance and then the water-soluble silicon compound is added for neutralization and precipitate, or another system is added in advance. This can be carried out by neutralizing a water-soluble silicon compound to form a fine precipitate and adding it to the slurry. In addition, when coating a compound consisting of a silicon compound and a compound containing at least one element selected from the group of aluminum, phosphorus, titanium, vanadium, manganese, nickel and zinc, a cobalt-containing ferromagnetic acid is used in an aqueous medium. A water-soluble silicon compound, a water-soluble compound of at least one element selected from the group of aluminum, phosphorus, titanium, vanadium, manganese, nickel and zinc, and an acid or alkali are added to the slurry for 11 minutes in parallel. Alternatively, after adding an acid or alkali to the slurry in advance, a mixture of two or more water-soluble compounds may be added, or a mixture of two or more water-soluble compounds may be added separately in advance. This can be carried out by neutralizing the water-soluble compound in a system or in a mixed system and adding a fine precipitate or coprecipitate to the acid slurry.Also, cobalt-containing ferromagnetic iron oxide It can also be carried out by immersing it in a solution of the water-soluble compound.After neutralization, precipitation or immersion, it is desirable to ripen it in a slurry if necessary.The temperature during coating and aging is as follows:
Usually below the boiling point. Note that the pH of the slurry during aging is usually 7 to 9.5.

Examples of the water-soluble silicon compounds include salts of orthosilicic acid and metasilicic acid such as sodium, potassium, and cobalt; examples of the water-soluble phosphorus compounds include orthophosphoric acid and pyrophosphoric acid; examples of the water-soluble titanium compounds include:
Water-soluble compounds of vanadium include vanadyl sulfate, sodium vanadate, etc. Water-soluble compounds of aluminum include sodium or potassium aluminate, aluminum sulfate, aluminum chloride, etc., nickel, manganese, etc. As water-soluble compounds of zinc, sulfates, nitrates, chlorides, etc. of each can be used.

Examples of the acid or alkali used to neutralize the water-soluble compound and precipitate it as the first layer include sulfuric acid, hydrochloric acid, nitric acid, etc., and sodium hydroxide, potassium hydroxide, potassium hydroxide, etc. for the latter.
Examples include sodium oxide, calcium carbonate, and ammonia.

In the present invention, the coated cobalt-containing ferromagnetic iron oxide is then heat treated in an aqueous slurry at a temperature of 60°C or higher. The reason why magnetic properties and adsorption properties are improved by heat treatment in an aqueous medium is not necessarily clear, but heat treatment makes the coating layer formed of the above-mentioned compounds more uniform and denser, and this improves the magnetic properties and adsorption properties. It is presumed that the effects of the invention can be obtained. Furthermore, it is considered that cobalt ferrite formation is promoted in the cobalt-containing ferromagnetic iron oxide and the coating layer on its surface, improving the coercive force as a magnetic property and avoiding a decrease in the amount of saturation magnetization. Furthermore, it is presumed that by increasing the uniformity and homogeneity of the coating layer, the high coercive force component and the low coercive force component decrease, and the reversal magnetic field distribution improves. This wet heat treatment is usually performed at a temperature of 60° to 150°.
"C1 is preferably carried out at 80° to 140°C. If the processing temperature is above the boiling point, use a pressurized container such as an autoclave. If the processing temperature is too low than the above range, the above-mentioned cobalt ferrite formation will not be promoted much. , the uniformity and homogenization of the coating layer is not satisfactory, and the coercive force and reversal t
ii) If the desired effect is not obtained in the magnetic and adsorption properties expressed by the field distribution and the amount of lubricant adsorbed, or if the values are too high, the magnetic iron oxide itself will change in quality and the l1lC properties expressed by the squareness ratio, orientation, etc. This is undesirable because the magnetic properties expressed by the distribution of the reversed magnetic field and the like are distorted.

Cobalt-containing ferromagnetic iron oxide that has undergone wet heat treatment is
After conventional filtration, water washing and drying, a ferromagnetic iron oxide with the desired properties is obtained, but it is further
Dry heat treatment at 00° C. may yield magnetic powder with improved coercive force and other magnetic properties.

〔Example〕

Next, the present invention will be explained using specific examples.

Example 1 Average major axis diameter 0.3 μm, average axial ratio 8, coercive force 3800e
Acicular 1-Fe, 0. 100g of powder in 1 liter of water! It was dispersed into a slurry. While blowing nitrogen gas into this slurry, 70 mff1 of a 0.85 mol/2 cobalt sulfate aqueous solution, 140 ffIQ of a 0.90 mol/2 ferrous sulfate aqueous solution, and 175 mff1 of a 10 mol/l sodium hydroxide aqueous solution were added to the slurry. After stirring for 5 hours, γ-F
e, O, was metamorphosed. The resulting slurry was filtered and washed with water, and the resulting wet cake was dispersed in water. After stirring in a nitrogen gas atmosphere, a sodium orthosilicate aqueous solution and a sodium aluminate aqueous solution were added to the cobalt-containing ferromagnetic iron oxide, respectively. 0.25% as Si,
It was added to 0.05% as ^2. Subsequently, the slurry was neutralized to a pH of 8. After stirring for about 1 hour and aging, the cough slurry was placed in an autoclave for 12 hours.
After heat treatment at 0''C for 3 hours, filtration, washing with water, and drying at 120C in a nitrogen atmosphere, the desired cobalt-containing ferromagnetic iron oxide powder (A) was obtained.

Example 2 In Example 1, the added amounts of the sodium orthosilicate aqueous solution and the sodium aluminate aqueous solution were adjusted to 50% to the cobalt-containing ferromagnetic iron oxide, respectively. The desired cobalt-containing ferromagnetic iron oxide powder (B) was obtained in the same manner as in Example 1 except that the Si content was 0.5% and the Si content was 0.1%.

Example 3 In Example 1, the slurry after completion of coating aging was heated to 90°C.
The desired cobalt-containing ferromagnetic iron oxide powder (C) was obtained in the same manner as in Example 1 except that the powder was heat-treated for 3 hours.

Example 4 Same as in Example 1, except that an aqueous manganese sulfate solution was added to the cobalt-containing ferromagnetic iron oxide so that the amount of Mn was 0.05% by weight in place of the aqueous sodium aluminate solution. The desired cobalt-containing ferromagnetic iron oxide powder (D) was obtained.

Example 5 Same as in Example 1 except that orthophosphoric acid aqueous solution was added to the cobalt-containing ferromagnetic iron oxide so that the amount of P was 0.05% based on the weight of the cobalt-containing ferromagnetic iron oxide. The desired cobalt-containing ferromagnetic iron oxide powder (E) was obtained.

Example 6 The desired cobalt-containing ferromagnetic iron oxide powder (F) was obtained in the same manner as in Example 1 except that the sodium aluminate aqueous solution was not added.

Comparative Example 1 A cobalt-containing ferromagnetic iron oxide powder (G) was obtained in the same manner as in Example 1 except that the wet heat treatment was not performed after coating and aging.

Comparative Example 2 A cobalt-containing ferromagnetic iron oxide powder (H) was obtained in the same manner as in Example 2, except that the wet heat treatment was not performed after coating and aging.

Comparative Example 3 The y-Pe, O, coated and metamorphosed with cobalt and ferrous compounds before being coated with silicon and aluminum compounds in Example 1 was used as cobalt-containing ferromagnetic iron oxide powder (1). .

Samples (A) to (A) obtained in the above Examples and Comparative Examples
Regarding 1), a magnetic paint was prepared according to the formulation shown below, and this paint was applied onto a polyester film, oriented, and dried to produce a magnetic tape having a magnetic coating film about 9 μm thick. For each magnetic tape obtained, the coercive force (Ilc) and reversal magnetic field distribution (
SFD) was measured.

Compounding composition of magnetic paint) Cobalt-containing ferromagnetic iron oxide powder 100.0 parts by weight Polyurethane resin 11.2 parts by weight Vinyl chloride-vinyl acetate copolymer resin 11.2 Surfactant (phosphate ester) 4.0 〃Methyl ethyl ketone 94.9 〃Cyclohexanone
37.8 Toluene
104.8 Furthermore, in order to investigate the adsorption properties of the lubricant used in the production of magnetic tape, the amount of fatty acids (
The adsorption amount of myristic acid) was measured.

(Method for measuring adsorption amount of myristic acid) 5 g of the obtained cobalt-containing ferromagnetic iron oxide powder, 50 mj of methyl ethyl ketone, 50 mj of toluene, and 0.2 g of myristic acid were mixed, and after shaking in a paint shaker for 30 minutes, The supernatant liquid was collected by centrifugation, and myristic acid (■) was quantitatively analyzed.The amount of myristic acid adsorbed on the cobalt-containing ferromagnetic iron oxide powder was calculated from the added myristic acid (■) and the analysis amount.

The results obtained as described above are shown in Table 1.

In general, the smaller the amount of lubricant adsorbed, the better the lubrication effect on the tape surface.

Table [Effects of the Invention] As shown in Table 1, the cobalt-containing ferromagnetic iron oxide powder obtained by the present invention has excellent magnetic properties such as coercive force and reversal magnetic field distribution, and is also excellent in adsorption properties. It is well-balanced.

hand

Claims (1)

[Claims] Contains a silicon compound layer or a silicon compound and at least one element selected from the group of aluminum, phosphorus, titanium, vanadium, manganese, nickel, and zinc on the surface of cobalt-containing ferromagnetic iron oxide particles dispersed in an aqueous medium. 1. A method for producing a cobalt-containing ferromagnetic iron oxide powder, which comprises forming a compound layer comprising a compound and subsequently heat-treating the slurry at a temperature of 60° C. or higher.