JPS6257577B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field of the invention] The present invention relates to a method for producing magnetic powder for magnetic recording,
More specifically, it is a fine powder suitable for high-density magnetic recording, does not cause agglomeration during the drying process during manufacturing, has excellent dispersibility when preparing magnetic paint, and reduces tape noise. The present invention relates to a method for producing magnetic powder that is capable of producing magnetic powder. [Technical background of the invention and its problems] Conventionally, during magnetic recording and reproduction, residual magnetization in the in-plane longitudinal direction of the recording medium is used, but in this method using this in-plane longitudinal direction, the high density of recording There are limits to what can be done. That is, in a recording/reproducing system using residual magnetization in the in-plane longitudinal direction, there is a property that the demagnetizing field within the magnetic recording medium increases as the recording density increases. In order to overcome this demagnetizing field and perform high-density recording, it is necessary to increase the coercive force of the recording medium (recording layer) and at the same time to make this recording medium layer thinner. However, if the coercive force of the recording medium layer is increased, the corresponding magnetic head must also be increased in magnetic flux density, which is difficult to expect at present. Further, making the recording medium layer thinner causes a problem of lowering the output of the reproduced signal. For this reason, in order to meet the demand for higher density magnetic recording, a method has been proposed that uses residual magnetization in the direction perpendicular to the plane of the recording medium layer, instead of the conventional method that uses residual magnetization in the longitudinal direction of the recording medium. ing. The magnetic powder used in this perpendicular magnetization recording method is
It is necessary to have an axis of easy magnetization in a direction perpendicular to the surface of the magnetic recording medium. As such magnetic powder, hexagonal ferrite magnetic powder, which has a particle shape of a hexagonal plate and has an axis of easy magnetization perpendicular to the plane of the plate, is attracting attention. _For example, _BaFe12O19 . However, BaFe ₁₂ O ₁₉ magnetic powder has a coercive force (IHc) of 5000 Oe or more, which is too high for magnetic recording, so some of the Fe is replaced with Co etc. to increase the IHc to 200 Oe, which is appropriate for magnetic recording. It is used after being reduced to ~2000Oe. As a result of many studies, the following formula: (AFe ₁₂ −x
−yCoxMyO ₁₉ ) (wherein A represents at least one element selected from the group of Ba, Sr, and Ca; M is
Represents at least one element selected from the group of Ti, Zn, Nb, V, Sb, Ta, Ni, Mn, In; x,
A cobalt-substituted hexagonal ferrite magnetic powder having a composition represented by the formula (y represents a number from 0.5 to 1.1) is known. This Co-substituted hexagonal ferrite magnetic powder is produced as follows. That is, an aqueous solution containing the stoichiometrically required amounts of ions of each element necessary to constitute the above composition is brought into contact with an alkaline solution with a pH of 9 or higher, and if necessary, an autoclave treatment is performed to prepare the precursor. Produces body precipitate. Although this precursor has the desired composition, it is not crystalline and does not have the magnetic properties of magnetic powder. This precursor is then thoroughly washed and then frozen. Thereafter, this is naturally thawed, dried on, for example, a hot plate, and then heat-treated in a temperature range of 600 to 1000°C to crystallize it to obtain magnetic powder with desired characteristics. By the way, when this Co-substituted hexagonal ferrite is used for magnetic recording media, especially high-density magnetic recording media, its grain size is 0.3 μm or less and its grain size distribution is narrow, and the size and shape of individual grains are small. It is strongly desired that the following be completed. Note that the particle size here refers to the length of the diagonal line on the plate surface of the hexagonal flat plate of the ferrite powder. However, in the case of the above-mentioned manufacturing method, when the precipitate is thawed and then dried, the individual particles agglomerate, and these agglomerates are baked and solidified in the next heat treatment step, resulting in particles with a particle size of 0.5 μm or more. The phenomenon of turning into magnetic powder occurs. When a magnetic paint is prepared using such magnetic powder together with a solvent, a dispersant, a binder, etc., and this magnetic paint is applied onto a support such as a polyester film, the magnetic powder is absorbed into the magnetic paint. Due to poor dispersion, a uniform recording medium layer cannot be obtained, and as a result,
The table noise becomes louder. [Object of the invention] The present invention does not cause the above-mentioned inconveniences, has a fine structure,
The object of the present invention is to provide a method for producing Co-substituted hexagonal ferrite magnetic powder that has good dispersibility and is therefore suitable for high-density perpendicular magnetization recording. [Summary of the Invention] In order to achieve the above object, the present inventors have made sufficient studies on the conventional manufacturing process, and found that the thawing process is performed using a certain kind of solvent instead of natural thawing. They discovered that the agglomeration phenomenon in the next drying step was eliminated and fine magnetic powder could be obtained, and the method of the present invention was completed. That is, the method of the present invention involves adding an aqueous solution containing ions of each element necessary to constitute hexagonal barium ferrite or partially substituted barium ferrite.
A step of contacting with an alkaline solution having a pH of 9 or more to produce a precipitate (Step 1); A step of washing and then freezing the precipitate (Step 2); A step of thawing the frozen form of the precipitate (Step 3);
and a step of drying the thawed precipitate and then heating it to crystallize it (step 4), wherein the thawing step is performed using a water-soluble organic solvent. It is characterized by being The barium ferrite targeted by the method of the present invention has the following formula: AFe ₁₂ −x−yCoxMyO ₁₉ (where A is
Represents at least one element selected from the group of Ba, Sr, Ca, and M is Ti, Zn, Nb, V, Sb, Ta,
The composition preferably represents at least one element selected from the group of Ni, Mn, and In; x and y each represent a number from 0.5 to 1.1. First, in step 1, the aqueous solution containing ions is
It is prepared by dissolving water-soluble salts of each element necessary to constitute the above-mentioned composition in water. For example, for Fe and Co, their respective chlorides, sulfates, nitrates,
Ba, Sr, Ca, etc. are salts such as chlorides. At this time, the ion concentration of each element is not unique because it is determined in relation to the stoichiometrically necessary amount in the target composition. Further, examples of the alkaline solution include sodium hydroxide, potassium hydroxide, and aqueous ammonia. All of these alkaline solutions must have a pH of 9 or higher; if the pH is lower than 9, a precursor precipitate having the desired composition cannot be obtained in step 1. The aqueous solution and the alkaline solution may be brought into contact with each other by dropping the former into the latter, or dropping the latter into the former. At this time, it may be added dropwise while stirring. Further, at this time, autoclave treatment may be performed as in the conventional method. In this way, a precursor precipitate is obtained. This precipitate is a coprecipitate of each element and has the same composition as the target composition. However, it is not crystalline and does not retain the magnetic properties of magnetic powder. Next, in step 2, the obtained precipitate is washed and then frozen. Wash thoroughly with normal water. If cleaning is not sufficient, alkali and the like remain and cause aggregation. Freezing can be carried out according to conventional methods. For example, liquid nitrogen is used. Step 3, ie, the thawing step, is the most distinctive feature of the present invention. In the method of the present invention, thawing is not carried out naturally, but using a water-soluble organic solvent. The organic solvent used may be any organic solvent as long as it is soluble in water, but it is particularly preferable to use an organic solvent that is soluble in water at room temperature in an amount of 20% by weight or more. For example, methyl alcohol, ethyl alcohol, iso-propyl alcohol, n-propyl alcohol, tert-butyl alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, 1,2-propylene oxide, 1,4-dioxane, trioxane, tetrahydrofuran, tetrahydrofurfuryl alcohol, Examples include pyran, methylal, acetone, methylacetone, methyl ethyl ketone, acetonylacetone, diacetonyl alcohol, and methyl formate. Among these, methyl alcohol, ethyl alcohol, and acetone are particularly preferred. Further, these organic solvents may be used alone or in an appropriate mixture of two or more. Thawing is carried out by introducing the frozen precipitate obtained in step 2 into the organic solvent. After thawing, the suspension of the organic solvent and the precipitate is filtered to obtain a precipitate cake, which is then dried and then heat-treated at a predetermined temperature to crystallize it. Drying may be natural drying in the air or hot air drying using an air bath. In addition, heat treatment is carried out in the air for 600~
It can be carried out in a temperature range of 900℃. [Embodiment of the invention] FeCl ₃ 6H ₂ O containing 126.5 g of F ³⁺ _e ions
Aqueous solution 1.5, containing 33.6g B ²⁺ _a ion
BaCl ₂ 2H ₂ O aqueous solution 0.5, CoCl ₂ 6H ₂ O aqueous solution 0.25 containing 12.0 g C ²⁺ _p ions, 9.8 g T
0.25% of TiCl ₄ aqueous solution containing ⁴⁺ _i ions was mixed. Add this mixed aqueous solution to 1.2 kg of sodium hydroxide.
was added to alkaline solution 3 while stirring, and the whole was reacted in an autoclave at 150°C for 45 minutes. After repeatedly washing the obtained precipitate with pure water, the precipitate was collected by filtration and frozen with liquid nitrogen. This frozen body was thawed. Thawing was carried out in four ways: natural thawing, thawing using ethyl alcohol, thawing using acetone, and thawing using a mixture of equal amounts of ethyl alcohol and acetone. After filtering, the resulting cakes were dried on a hot plate at 200°C, and then heated in air at 900°C.
Heat treated at ℃. The bulk specific gravity (g/cc) of the four types of magnetic powder obtained was measured, and the appearance was observed with the naked eye. In addition, magnetic tapes are manufactured using conventional methods using these magnetic powders,
The noise of these tapes was measured. The above results are summarized in the table.

〔Effect of the invention〕

As is clear from the above explanation, the Co-substituted hexagonal ferrite magnetic powder produced by the method of the present invention has no agglomerates compared to those produced by the conventional method, as seen in the bulk density data. It is fine and has excellent dispersibility when applied to tape manufacturing, and does not cause tape noise, making it suitable as a magnetic powder for high-density perpendicular magnetization recording.

Claims (1)

[Scope of Claims] 1. A step of contacting an aqueous solution containing ions of each element required to constitute hexagonal barium ferrite or partially substituted barium ferrite with an alkaline solution having a pH of 9 or higher to form a precipitate; A method for producing magnetic powder for magnetic recording comprising: washing the precipitate and then freezing it; thawing the frozen precipitate; and drying the thawed precipitate and then heat-treating it to crystallize it. . A method for producing magnetic powder for magnetic recording, characterized in that the thawing step is carried out using a water-soluble organic solvent. 2 The barium ferrite has the following formula: AFe ₁₂ −x−yCoxMyO ₁₉ (wherein A represents at least one element selected from the group of Ba, Sr, and Ca; M represents Ti, Zn,
represents at least one element selected from the group of Nb, V, Sb, Ta, Ni, Mn, and In; x and y each represent a number from 0.5 to 1.1). A method for producing magnetic powder for magnetic recording according to claim 1.