JPS649246B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for producing cobalt-containing magnetic iron oxide. A tape manufactured using iron oxide powder derived from iron oxide obtained by the method of the present invention has good magnetic properties such as coercive force, squareness ratio, orientation, and sharp coercive force distribution. It is known that magnetic iron oxide with high coercive force can be obtained by coating magnetic iron oxide with a cobalt compound, but in recent years there has been a demand for products with even higher magnetic properties, and improvements in the manufacturing method have been required. There is. The biggest drawback of magnetic iron oxide coated with a cobalt compound is that it has a wide coercive force distribution. The inventors believed that the cause of this was the non-uniformity of the coating, and after conducting various studies to make the coating uniform, neutralized the cobalt salt very close to the surface of the magnetic iron oxide particles, while neutralizing the cobalt salt far from the particles. When we tried a method that did not allow extra cobalt compounds to exist in the area, we found that
It has been found that a material with high degree of magnetic properties can be obtained. That is, in the present invention, magnetic iron oxide particles are suspended in an aqueous metal salt solution containing at least a cobalt salt, and the suspended slurry is supplied in the form of droplets of 1 mm or less into an aqueous alkaline solution. This is a method for producing cobalt-containing magnetic iron oxide, which is characterized in that a metal compound containing at least a cobalt compound is deposited on the surface. In the method of the present invention, magnetic iron oxide is first suspended in an aqueous metal salt solution containing at least a cobalt salt. The magnetic iron oxides used include γ-Fe ₂ O ₃ ,
Examples include bertolide compounds obtained by partially reducing Fe ₃ O ₄ or γ-Fe ₂ O ₃ in a reducing gas such as hydrogen. As the cobalt salt, inorganic or organic acid salts of cobalt, such as cobalt sulfate, cobalt chloride, and cobalt acetate, are used. Examples of metal salts other than cobalt include ferrous salts, manganese salts, zinc salts, etc., such as ferrous sulfate, manganous sulfate, zinc sulfate, ferrous chloride, manganous chloride, and zinc chloride. Can be mentioned. The slurry concentration of this suspension is usually 20-200
g/, preferably 50 to 100 g/.
The ratio of cobalt salts and metal salts other than cobalt to 100 parts by weight of iron oxide in the suspension cannot be absolutely specified, but it is usually 1 to 10 parts by weight when cobalt salt is used alone; When combining iron salts, 1 to 10 parts by weight of the former and 1 to 20 parts by weight of the latter
It is preferable to use parts by weight. In addition, when cobalt salts and ferrous salts are further combined with manganous salts, zinc salts, etc., 1 to 20 parts by weight of each can be added to the above-mentioned predetermined proportions. In this method, contrary to the usual operation, this suspension is added to an alkaline aqueous solution to cause a neutralization reaction.
As the alkali, hydroxides, oxides, or carbonates of alkali metals or alkaline earth metals are used, and specific examples include sodium hydroxide, potassium hydroxide, sodium oxide, and calcium carbide. It will be done. The alkali in the alkaline aqueous solution is usually used in an amount greater than the chemical equivalent to neutralize the metal salt such as cobalt, and the aqueous solution is prepared by dissolving a desired amount of the alkali in water. The suspension is supplied into the alkaline aqueous solution in a finely divided state. By such means, the metal salt in the suspension rapidly reacts with the alkali, and the reaction occurs only in the very vicinity of the surface of the magnetic iron oxide particles, resulting in the formation of a metal compound precipitate. It is presumed that the particles are well adhered to the surface of the particles. Therefore, the suspension is introduced in such a finely divided state that the neutralization reaction is completed immediately upon entering the alkaline aqueous solution. Specific methods for supplying the suspension include, for example, using a spray, rotating disk, shower, etc. to supply droplets from above the surface of the alkaline aqueous solution, or supplying droplets into the alkaline aqueous solution through many small nozzles or small holes. There are methods that introduce a trickle, or methods that combine them with a rotating disk, a stirrer, etc. In any case, it is supplied in droplets or trickles of about 1 mm or less. Industrially, it is desirable to supply it as droplets of 0.5 mm or less, preferably 0.05 mm or less, using a spray method. When the suspension is fed into an aqueous alkaline solution in this manner, the cobalt salt or other metal salt in the suspension comes into contact with the alkali and forms metal compounds such as hydroxides, oxides, and oxyhydroxides. , changes into carbonate, etc., and is deposited on the surface of iron oxide. Incidentally, magnetic iron oxide coated with cobalt and ferrous iron has been known for a long time, but in the usual method, it is best to first perform a cobalt treatment and then a ferrous treatment, and both are combined. There was a drawback that it was difficult to obtain desired results when treated simultaneously. However, in the method of the present invention, cobalt salt and ferrous salt are treated simultaneously to obtain magnetic iron oxide having sufficiently good magnetic properties. The reaction solution obtained in this way is subjected to conventional filtration, water washing, and drying, and is further subjected to conventional heat treatment, such as heat treatment at a temperature of 150 to 300 ° C. in a non-oxidizing atmosphere or an oxidizing atmosphere. A cobalt-containing magnetic iron oxide powder is obtained. In the method of the present invention, when a ferrous salt is used, the above heat treatment is preferably carried out in a non-oxidizing atmosphere. The reason why the magnetic properties of the cobalt-containing magnetic iron oxide obtained in the method of the present invention are improved is not fully clear, but it is presumed to be due to the following factors. Conventionally proposed methods include (a) dispersing magnetic iron oxide in a metal salt aqueous solution and adding an alkaline aqueous solution to this dispersion, and (b) adding an alkaline aqueous solution to the metal salt aqueous solution and adding magnetic There are two methods: adding iron oxide, and (iii) dispersing magnetic iron oxide in an alkaline aqueous solution in advance and adding a metal salt aqueous solution to this dispersion. It is presumed that because the objects are not necessarily in close proximity to each other, there are some areas where the adhesion is sufficient and others where it is insufficient, making it difficult to achieve uniform adhesion. On the other hand, in the method of the present invention, magnetic iron oxide is suspended in an aqueous metal salt solution, and this suspension is supplied into an aqueous alkaline solution in a finely divided state. The metal compound deposited on the iron oxide particles is immediately deposited on the magnetic iron oxide particles that are present in close proximity to the iron oxide particles, and because there is no extra metal compound separated from the iron oxide particles, almost uniform deposition is possible. It is inferred that this uniform adhesion led to the improvement of the magnetic properties of magnetic iron oxide. The present invention will be explained below with reference to Examples and Comparative Examples. Example 1 γ-Fe ₂ O ₃ into 9.2 g/aqueous cobalt acid solution
(Hc: 410 Oe, axial ratio: 1:7) was added to a concentration of 100 g/ml and stirred to prepare a suspension (referred to as suspension A). Separately, 4.7 g/aqueous sodium hydroxide solution was prepared (referred to as alkaline aqueous solution A). Put the alkali aqueous solution A15 into the reaction container,
The suspension A10, which had been heated to 90° C. with stirring and preheated to 90° C., was sprayed from above the liquid surface through a halo cone spray nozzle over a period of 2 hours. Suspension A was supplied into the alkaline aqueous solution as droplets with a size of about 25 μm. After the supply was completed, the reaction solution was held at 90°C for 3 hours. After filtering the reaction solution, washing with water, and drying (60℃, 24 hours), the coercive force of the dried product was measured using the usual method.
It was 580 Oersted. This dried product was treated at 200°C for 1 hour in a nitrogen stream,
After cooling, cobalt-containing magnetic iron oxide powder A (Co/iron oxide; 3.5%) was obtained. Comparative Example 1 Put the aqueous alkaline solution A15 into a reaction container,
The temperature was raised to 90°C, and the suspension A10, which had been preheated to 90°C, was supplied into the suspension for 2 minutes from a supply pipe having a diameter of 1 mm. The suspension was fed into the alkaline solution in droplets around 4 mm in size. After supplying the reaction solution,
It was held at 90°C for 3 hours. This reaction solution was treated in the same manner as in Example 1 to obtain a dried product. The coercive force of this material was 510 oersted. Further, heat treatment was performed in the same manner as in Example 1 to obtain cobalt-containing magnetic iron oxide powder B (Co/iron oxide; 3.4%). Comparative Example 2 Put suspension A into a reaction container and add alkaline aqueous solution A.
A dried product was obtained in the same manner as in Comparative Example 1, except that the material was sprayed and supplied. The coercive force of this thing is 515
It was Elsted. Furthermore, cobalt-containing magnetic iron oxide powder C (Co/iron oxide; 3.5%) was obtained in the same manner as in the previous example. The respective powders A to C obtained in Example 1 and Comparative Examples 1 and 2 were blended according to the following blending ratios and sufficiently kneaded to produce magnetic paints. (1) Cobalt-containing magnetic iron oxide powder 100 parts by weight (2) Vinyl chloride-vinyl acetate copolymer resin 15 parts by weight (3) Polyurethane resin 10 parts by weight (4) Lauric acid 0.8 parts by weight (5) Paraffin 0.4 parts by weight (6) ) Toluene/MIBK mixed solvent 130 parts by weight Each magnetic paint was applied to a polyethylene film using the usual method, oriented, dried,
A magnetic recording medium having a film thickness of 8μ was obtained. The coercive force (Hc), squareness ratio (Bγ/Bm) and orientation (OR) of these magnetic recording bodies were measured by conventional methods, and the results shown in Table 1 were obtained.

[Table] Example 4 γ-Fe ₂ O ₃ (Hc;
410Oe, axial ratio: 1:7) was added to give a concentration of 100g/, and stirred to prepare a suspension (referred to as suspension B). Separately, 11.3g/aqueous sodium hydroxide solution was prepared. (referred to as aqueous alkaline solution B). In the same manner as in Example 1, the suspension B was sprayed into the alkaline aqueous solution B for 2 hours, dried (coercive force was 590 oersted), and then cobalt-containing magnetic iron oxide powder D (Co/iron oxide; 3.2%) was obtained. Example 3 The temperature when spraying suspension B into aqueous alkaline solution B and the holding temperature after spraying were set at room temperature (27°C).
Cobalt-containing magnetic iron oxide powder E (Co/iron oxide; 3.1%) was obtained in the same manner as in Examples 1 and 2 except that the powder was dried (retention force was 570 oersted). Comparative Example 3 Put the alkali aqueous solution B15 into a reaction container,
The suspension B10 was supplied into the solution from a supply tube having a diameter of 1 mm for 2 minutes at room temperature (the droplet size was approximately 4 mm). In the same manner as in Examples 1 to 3, cobalt-containing magnetic iron oxide powder F (Co/iron oxide; 3.2%) was obtained through drying (coercive force: 560 oersted). Comparative Example 4 Put suspension B into a reaction container and add alkaline aqueous solution B.
Cobalt-containing magnetic iron oxide powder G (Co/iron oxide; 3.2%) was obtained in the same manner as in Example 3 except that the powder was dried (retention force was 528 oersted). Magnetic recording bodies were prepared in the same manner as in Example 1 using the powders D to G obtained in Examples 2 and 3 and Comparative Examples 3 and 4, and the coercive force (Hc) and square shape were determined by a conventional method. The ratio (Bγ/Bm) and orientation (OR) were measured, and the results shown in Table 2 were obtained.

[Table] Furthermore, the results of measuring the anisotropic magnetic field distribution of the magnetic recording bodies using the magnetic iron oxide powders E and F by the method described below are shown in the figure. As is clear from this, magnetic iron oxide E produced by the method of the present invention
When F is used (indicated by the solid line), the coercive force distribution, especially on the high coercive force side, is less spread and has a sharper coercive force distribution than when F is used (indicated by the dotted line). It can be seen that it is. Measurement of anisotropic magnetic field distribution: Using a vibrating magnetometer (manufactured by Toei Kogyo, model VSM-3), apply a magnetic field of 10 kilooersted in the tape orientation direction, then return the magnetic field to O, and adjust the direction of the initial magnetic field. Measure the residual magnetization σγ ₁ in the perpendicular direction from .
Next, it is rotated 10 degrees from the initial magnetic field direction, a magnetic field of 100 oersted is applied, the magnetic field is returned to O, and σγ ₂ in a direction perpendicular to the initial magnetic field direction is measured again. In this way, the operation of applying a magnetic field in the 10° direction and measuring σγm in the direction perpendicular to the initial magnetic field direction is repeated at intervals of 100 oersteds up to 10 kilooersteds.
Subtract σγn−1 from each measured value of σγn to obtain Σ[σγ _o −
σγ _o-1 ]. Each σγ ₂ −σγ ₁ , σγ ₃ −σγ ₂ ,
σγ ₄ ―
σγ ₃ ,...σγ _o −σγ _o-1 divided by Σ[σγ _o −σγ _o-1 ],
This value is taken as the volume % of the particles whose magnetization is reversed by the corresponding applied magnetic field. Example 4 Fe ₃ O ₄ into 9.5 g/cobalt sulfate aqueous solution 10
(Hc: 430 Oe, axial ratio: 1:7) 1 kg was added and stirred to prepare a suspension, and separately 4.8 g/aqueous sodium hydroxide solution 15 was prepared. In the same manner as in Example 3, cobalt-containing magnetic iron oxide powder (Co/iron oxide; 3.5%) was obtained through drying (retention force: 555 oersted). Magnetic recording bodies were prepared in the same manner, and the magnetic properties of the obtained magnetic recording bodies were measured using a conventional method. OR) obtained a result of 1.9.

[Brief explanation of drawings]

The figure shows the distribution of coercive force in magnetic recording media using magnetic iron oxides E and F. The horizontal axis represents the magnetic field strength (kloersted), the vertical axis represents the particle volume (%), and the solid line represents E, The dotted line indicates the measured value of the magnetic recording medium using F.

Claims (1)

[Claims] 1. Magnetic iron oxide powder is suspended in a metal salt aqueous solution containing at least a cobalt salt, and the suspended slurry is
A method for producing cobalt-containing magnetic iron oxide, which comprises supplying the magnetic iron oxide particles in the form of droplets of mm or less into an alkaline aqueous solution, and depositing a metal compound containing at least a cobalt compound on the surface of the magnetic iron oxide particles.