JPH051966B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing magnetic powder for magnetic recording,
More specifically, the present invention relates to a method for easily and reproducibly producing hexagonal ferrite magnetic powder consisting of fine particles suitable for use in high-density magnetic recording media. (Prior Art) In recent years, increasing the density of magnetic recording has been actively studied, and a perpendicular magnetic recording method that records a magnetic field in the thickness direction of a magnetic recording medium such as a tape has been attracting attention. In such a perpendicular magnetic recording system, the magnetic material used must have an axis of easy magnetization in a direction perpendicular to the surface of the recording medium. Ferrite with hexagonal uniaxial magnetization anisotropy, such as Ba ferrite (BaFe ₁₂ O ₁₉ ), is a hexagonal plate-shaped crystal with an axis of easy magnetization perpendicular to the plate surface, and has a perpendicular magnetic field. It satisfies the above requirements as a magnetic material for recording. In addition to this, the magnetic material has a moderate coercive force (Hc, usually 200
In relation to these characteristics, the average particle diameter of the powder is
It needs to be 0.35 μm or less. Since Ba ferrite has a high coercive force of 5000 Oe or more, it cannot be used as it is, and a method has been proposed to reduce the coercive force by substituting a part of Fe with Co and Ti (for example, JP-A No. 56-149328 No. Publication, JP-A-59-
175707, etc.). (Problems to be solved by the invention) In these methods, divalent Co ions and tetravalent Ti
It is necessary to use equal molar amounts of ions. The reason for this is that if the metal elements replacing Fe are not always combined so that the average ion valence is trivalent, divalent iron ions will exist, and different metal elements containing divalent iron, such as magnetite, will exist. Tokukai Sho says it's because crystals form easily.
56-149328. For this reason,
When replacing a portion of Fe with Co and Ti, it is said that tetravalent Ti ions must be used in place of divalent Co ions. By the way, TiCl ₄ or TiO ₂ is usually an easily available tetravalent Ti ion raw material. Therefore, in any of the known methods of substituting a part of Fe with Co and Ti, TiCl ₄ or TiO ₂ is used. TiCl ₄ is used in both cases of production by coprecipitation method or hydrothermal method as in the present invention. By the way, commercially available TiCl ₄ is in liquid form, and when it comes into contact with air even in small amounts, it produces dense white smoke, and when it tries to dissolve in water at room temperature, it is easily hydrolyzed and produces white smoke. However, it produces poorly soluble oxychlorides and hydroxides. For this reason, when TiCl ₄ is used in the coprecipitation method or the hydrothermal method, it is not only difficult to handle, but also special equipment is required to dissolve it in water. Due to the unavoidable production of substances, a uniform solution is not obtained, resulting in large variations in product performance such as magnetic properties and average particle size. (Means for Solving the Problems) The present inventors have conducted intensive studies to develop an industrially easy manufacturing method for hexagonal ferrite that does not have these conventional drawbacks. Contrary to the common sense that trivalent Ti, which easily becomes an aqueous solution at room temperature, magnetic powder with the desired performance can be easily and reproducibly obtained, and tetravalent Ti can be used to When using trivalent Ti, excellent magnetic properties cannot be obtained unless the amounts of Co and Ti are the same molar amount, but when trivalent Ti is used, Co
and that a magnetic powder having excellent magnetic properties can be obtained even if the amounts of Ti are not the same molar amount, that a magnetic powder that has a larger saturation magnetization than when using tetravalent Ti is obtained, and further the present invention The present invention was completed based on the discovery that coprecipitation or hydrothermal reactions can be carried out at a pH value lower than that of an aqueous solution, which has traditionally been considered preferable in the field of technology, and that the amount of alkali used can be reduced. That is, the main object of the present invention is to create a hexagonal ferrite magnetic powder suitable for perpendicular magnetic recording that contains Co and Ti and has excellent magnetic properties by using trivalent Ti, which is easy to handle. The purpose of this invention is to provide a method for manufacturing the same. The object of the present invention is at least (1) trivalent
8 to 11.8 moles of Fe ions, 0.1 mole of divalent Co ions
~2.0 moles, 0.1 to 2.0 moles of trivalent Ti ions, and
(2) 1 selected from the group consisting of Ba, Sr, Ca and Pb
0.8 species or two or more divalent metal element ions
Add an alkaline aqueous solution to an aqueous solution containing ~3.0 mol until the pH reaches 5.0 or higher to form a precipitate, then heat-treat the separated and dried precipitate, or
Alternatively, this can be achieved by heat treating an aqueous solution containing precipitate. In the present invention, trivalent Fe ions, divalent Co
The object of the present invention is achieved only when the molar ratio of at least one divalent element ion selected from Ba, Sr, Ca and Pb and trivalent Ti ion is within the above range. If even one ion is outside the above usage range, the main characteristic values desired for magnetic powder for perpendicular magnetic recording, namely coercive force 400 to 1500 Oe, saturation magnetization 45 emu/g or more, and average particle size 0.01 to It is not possible to obtain magnetic powder that satisfies 0.3 μm at the same time. In the present invention, the amounts of divalent Co ions and trivalent Ti ions used to replace a portion of Fe do not always have to be the same molar amount, unlike the case of tetravalent Ti ions. , can be appropriately selected independently within the scope of the present invention according to the required magnetic properties. In the present invention, trivalent Fe ions, divalent Co
As the ions and divalent metal element ions mentioned above, aqueous solutions of chlorides, nitrates, sulfates, and organic acid salts such as oxalates and acetates of these metals are usually used. In the present invention, an aqueous solution of TiCl ₃ is usually used as the trivalent Ti ion. In the method of the present invention, first, each ion source compound is dissolved in water to form an aqueous solution so that each metal element ion has the above-mentioned molar amount. Next, an alkaline aqueous solution is added to this aqueous solution to form a precipitate. The alkaline component used in the alkaline aqueous solution may be any water-soluble one, and examples thereof include alkali metal hydroxides, carbonates, ammonia, ammonium carbonate, and the like. For example, NaOH, Na ₂ CO ₃ ,
_NaHCO3 , KOH _{, K2CO3} , _NH4OH , ( _NH4 ) ₂
CO ₃ etc. are used, and in particular, a combination of hydroxide and carbonate is used. The magnetic properties and powder properties of magnetic powder also vary depending on the pH value of the aqueous solution during precipitate formation or hydrothermal synthesis reaction. Traditionally, this pH value is generally 10
It is said that 12 or more is preferred (for example, Japanese Patent Laid-Open No. 58-56303), and specifically, 13.0 or more is practiced. By the way, the amount of alkali required to adjust the pH value increases significantly when the pH value exceeds 13 (see Figure 1). For this reason, known methods require large amounts of alkaline components. In the present invention, the pH value at a liquid temperature of 25° C. may be 5 or more, preferably in the range of 5.5 to 13.0. This makes it possible to significantly reduce the amount of alkaline components used. This is not only economical, but also makes it easier to select the reactor material (especially in the case of hydrothermal synthesis reactors), eases handling because it is less harmful to the human body, and allows coprecipitation or Wastewater treatment in the washing process performed after the hydrothermal synthesis reaction becomes easier. This is an improvement over conventional manufacturing methods. In the present invention, the target hexagonal ferrite can be obtained by performing any of the following heat treatment methods after forming the precipitate. The first method is to prepare an aqueous solution containing precipitates, usually from 10 to
After aging with stirring at a constant temperature of 100°C for 10 minutes to 1 week, the precipitate is separated and washed with water. 700~ after drying this
Calcinate at 1100℃ to produce hexagonal ferrite. The second method is a method using hydrothermal synthesis.
In this method, an aqueous solution containing a precipitate obtained by adding an alkaline aqueous solution is poured into an autoclave, and after stirring at a temperature of usually 150 to 700°C for 10 minutes to one week,
The precipitate is separated, washed with water, and dried to produce hexagonal ferrite. In this method as well, it is desirable to further perform firing similar to the first method. Thus, according to the present invention, it is possible to obtain a magnetic powder for magnetic recording that has excellent reproducibility, is easy to handle, has a large saturation magnetization, and is economical compared to conventional methods. The present invention will be explained in more detail with reference to Examples below. The coercive force and saturation magnetization in the examples were measured by filling a glass test tube with an inner diameter of 5 mm and a length of 5 cm with the obtained magnetic powder, and using a DC magnetization characteristic measuring device at a maximum applied magnetic field of 3500 Oe. The average particle diameter was calculated by measuring the maximum diameter of 400 particles from a photograph taken with a transmission electron microscope and calculating the arithmetic average. X-ray diffraction was performed on all of the Examples and Comparative Examples listed here, and in all cases, the crystal phase of the magnetic powder was hexagonal ferrite having a magnetoplumpite structure. Furthermore, the empirical formula of the magnetic powder shown in the examples uses the molar composition at the time of raw material preparation. The representation of oxygen in the ferrite component has been omitted for the sake of brevity. Example 1 BaCl ₂ 2H ₂ O 0.55 mol, TiCl ₃ 0.375 mol,
CoCl ₂・6H ₂ O0.375 mol, and FeCl ₃・6H ₂ O5.25
Dissolve 10 moles in distilled water in this order, and add this to A.
It was made into a liquid. 17.5 moles of NaOH and 4.72 moles of Na ₂ CO ₃ were dissolved in distilled water at room temperature, and this was used as liquid B. After gradually adding liquid B to liquid A heated to 50℃,
Stirred at 50°C for 16 hours. The pH after stirring was 10.7. The coprecipitate thus obtained was separated, thoroughly washed with water, dried at 150°C, and fired in an electric furnace at 900°C for 2 hours. The Ba-ferrite thus obtained is
It is shown as Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 . This fine particle powder was plate-shaped with an average particle size of 0.11 μm, Hc was 900 Oe, and σs was 55 emu/g. In addition, when the experiment was repeated 5 times using exactly the same method, the average particle size was 0.10±0.01μm, and the Hc was 902±
20Oe and σs were 55.2±0.8emu/g. All of them show substantially the same characteristic values, and can be said to be a method with excellent repeatability. Comparative Example 1 Ba-ferrite was produced in exactly the same manner as in Example 1, except that TiCl ₄ was used instead of TiCl ₃ used in Example 1. Same as Example 1
When TiCl ₄ was added to distilled water at room temperature, it decomposed with intense white smoke, and the resulting solution A was cloudy, but
This was used as is. The thus obtained Ba-ferrite fine particle powder has a plate shape with an average particle size of 0.36 μm, and Hc is
1720 Oe, σs was 31 emu/g. In addition, when the experiment was repeated 5 times using exactly the same method, the average particle size was 0.52 ± 0.16 μm, and the Hc was 1630
±350Oe and σs were 27.4±5.1emu/g, and there were wide variations in the characteristic values. This is mainly
This is probably due to the use of TiCl ₄ . Comparative Example 2 TiCl ₄ used in Comparative Example 1 was dissolved in ice-cooled distilled water to form an aqueous solution, and this was used to prepare Comparative Example 1.
Ba-ferrite was produced in exactly the same manner.
In this case, white smoke as in Comparative Example 1 was not generated. The thus obtained Ba-ferrite fine particle powder has a plate shape with an average particle size of 0.23 μm, Hc of 436 Oe,
σs was 36 emu/g. Example 2 BaCl ₂ 2H ₂ O 0.66 mol, TiCl ₃ 0.3 mol,
0.3 mol of CoCl ₂ .6H ₂ O and 5.4 mol of FeCl ₃ .6H ₂ O were dissolved in 10 distilled water in this order, and this was used as Solution A. 17.5 moles of NaOH and 4.72 moles of Na ₂ CO ₃
No. 15 was dissolved in distilled water, and this was used as Solution B. 50℃
Add solution A and solution B heated to , into the autoclave.
After stirring at 450°C for 4 hours, it was cooled to room temperature. The pH at this time was 10.58. The precipitate thus obtained was thoroughly washed with water, dried at 150℃, and dried at 750℃.
The sample was heat-treated in an electric furnace for 8 hours. The Ba-ferrite thus obtained is represented by Ba _1.32 Fe _10.8 Co _0.6 Ti _0.6 . This fine particle powder had a plate shape with an average particle size of 0.18 μm, He content of 843 Oe, and σs of 49 emu/g. Comparative Example 3 Instead of TiCl ₃ used in Example 2, Comparative Example 2
Ba-ferrite was produced in exactly the same manner as in Example 2, except that the TiCl ₄ aqueous solution used in Example 2 was used. The thus obtained Ba-ferrite fine particle powder has a plate shape with an average particle size of 0.48 μm, Hc is 341 Oe, and σs is
It was 27 emu/g. Examples 3 to 12 According to Example 1, Ba-ferrite was prepared by varying the raw materials and composition ratios used. These results are summarized in Table 1.

[Table] Examples 13 to 18 Ba− represented by Ba _1.1 Fe _10.5 Co _0.75 Ti _0.75 was prepared in the same manner as in Example 1 except that the amounts of NaOH and Na ₂ CO ₃ used in the alkaline aqueous solution used were varied.
Ferrite was prepared. These results are summarized in Table 2.

[Table] Example 19 Sr-ferrite represented by Sr _1.1 Fe _10.5 Co _{0.75 Ti 0.75 was} prepared in the same manner as in Example 1 except that SrCl ₂ .6H ₂ O was used instead of BaCl ₂ .2H 2 O. Manufactured. This fine particle powder was plate-shaped with an average particle size of 0.12 μm, He was 923 Oe, and σs was 55 emu/g. Example 20 Instead of 0.55 mol of BaCl _{2.2H 2} O, BaCl ₂ .
Ba-Sr- represented by Ba _0.55 Sr _0.55 Fe _10.5 Co _0.75 Ti _0.75 was prepared in exactly the same manner as in Example 1, except that 0.275 mol each of _{2H 2 O} and SrCl 2.6H ₂ O was used.
Manufactured ferrite. This fine particle powder was plate-shaped with an average particle size of 0.11 μm, He was 911 Oe, and σs was 56 emu/g. Example 21 BaCl ₂ 2H ₂ O in Example 1 was replaced with CaCl ₂ or
Ca-ferrite and Pb-ferrite were produced in the same manner as in the example except that PbCl ₂ was used. The properties of these ferrites were comparable to Ba-ferrite.

[Brief explanation of the drawing]

FIG. 1 shows the change in pH value when coprecipitation was performed by changing the amount of NaOH used in Example 1.

Claims (1)

[Claims] 1 At least (1) 8 to 11.8 moles of trivalent Fe ions, 0.1 to 2.0 moles of divalent Co ions, 0.1 to 2.0 moles of trivalent Ti ions, and (2) Ba, Sr, Ca, and Pb. Adding an alkaline aqueous solution to an aqueous solution containing divalent ions of at least one metal element selected from 0.8 to 3 moles until the pH of the aqueous solution becomes 5.0 or more to produce a precipitate, and separating.
1. A method for producing hexagonal ferrite magnetic powder for magnetic recording, which comprises heat-treating a dried precipitate or heat-treating an aqueous solution containing the precipitate.