JPH0387002A - Manufacture of magnetic powder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain magnetic powder having narrow grain size distribution, and to improve signal to noise ratio by mixing specific amounts of compounds of individual elements forming a hexagonal ferrite represented by a specific formula and specific amounts so other specific compounds, melting the mixture, and quickly cooling it. CONSTITUTION:Compounds of elements for forming a hexagonal ferrite represented by a general formula, and R2O2 (R: at least one type selected from Li, Na, k, Rb, Cs), AO) and B2O3 as the other components are so mixed that the compounds of R, A and B satisfy the relation:1.0<B2O3/(AO+R2O)<1.5, 0.0<AO<1.0 by mol ratio; the mixture is then melted; and quickly cooled to be brought into an amorphous state. Then, It is heat-treated, and hexagonal ferrite is extracted. Thus, magnetic powder having narrow grain size distribution is obtained, noise due to magnetic powder having large grain size is reduced, and its recording density and signal to noise ratio are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing magnetic powder mainly used in the construction of high-density perpendicular magnetic recording media.

(Prior Art) A coating type magnetic recording medium is composed of a base made of, for example, polyethylene terephthalate, and a magnetic layer whose main components are ferrite and binder resin, which are deposited on the base surface.

Conventionally, ferrite used in magnetic recording media is
7-Fo 2O ] + Co 7-Fe 2O3
, Co-doped 7-PC2O3, Cr02. metal PC
Acicular ferrite is used, and magnetic recording is performed by a method that uses magnetization in the in-plane longitudinal direction.

However, in magnetic recording media that use magnetization in the in-plane longitudinal direction, when attempting to improve recording and reproduction in the high frequency range, the demagnetizing field within the recording medium increases, making it impossible to improve the recording density that much. There's a problem.

In recent years, in order to significantly improve magnetic recording density, a perpendicular magnetic recording system has been proposed that uses magnetization in a direction perpendicular to the base of a magnetic recording medium. A magnetic recording medium using this method is suitable for high-density recording because it does not suffer from demagnetization field problems even in high frequency ranges.

As a magnetic recording medium suitable for such a perpendicular magnetic recording system, one in which a Co--Cr alloy or the like is deposited on a substrate surface by a vacuum evaporation method or a sputtering method has been proposed. However, this type of magnetic recording medium has problems in terms of environmental stability, running durability, productivity, etc. On the other hand, magnetic recording media that have solved these problems include hexagonal ferrites whose axis of easy magnetization is easily oriented in one direction perpendicular to the substrate surface, such as M-type BaFeI2O4 and W-type BaMe2re1.
6027 (Me is a substituted metal element) A hexagonal ferrite in which some of the atoms are substituted with other elements has been coated on the substrate surface.

One method for manufacturing hexagonal ferrite for such coated magnetic recording media is to use an elemental compound that forms hexagonal ferrite and an elemental compound that forms glass as another component. A glass crystallization method is known in which the hexagonal ferrite is precipitated by mixing and melting the amorphous material, followed by rapid cooling and heat treatment to precipitate the hexagonal ferrite, which is then washed and then extracted. . In this glass crystallization method, B2O. and AO (A is Ba, Sr, Ca.

and at least one element selected from pb),
It is known to use . Furthermore, it is also known to use sodium borate as a raw material for forming glass.

(Problems to be Solved by the Invention) However, in the conventional glass crystallization method described above, the elements forming the glass are B2O3 and AO (A is Ba,
At least one selected from Sr, Ca, and pb
Hexagonal ferrite manufactured using hexagonal ferrite (seed elements) has a wide particle size distribution, and has the problem of large noise caused by large particles, and low S/N characteristics of the magnetic recording medium made of it. be. Furthermore, when sodium borate is used, non-uniform melting tends to occur and the atomic distribution in the amorphous body tends to be biased, resulting in a wide particle size distribution of the obtained hexagonal ferrite, and S of recording medium?
There is a problem that the N characteristic is low.

The present invention was made in order to solve the above-mentioned problems when obtaining a magnetic recording medium having high recording density and high S/N characteristics. The purpose of this invention is to provide a manufacturing method that can be used.

[Structure of the Invention] (Means for Solving the Problems) Hexagonal ferrite used in magnetic recording media has a recording wavelength of 1 μm or less, in which perpendicular magnetization recording is more significant than in-plane recording. In order to perform sufficient recording◆reproduction, the particle size should be 0. It is desirable that the particles have a diameter of 1 to 0.3 μm and have uniform particle sizes in order to ensure a high S/N ratio. Further, if the coercive force of the hexagonal ferrite is too high, the head magnetic field will be saturated during recording, and if it is too low, it will be impossible to hold the recording signal, so it is preferable to have a coercive force of 200 to 2000 Oersted. Therefore, the hexagonal ferrite according to the present invention may be one in which some of the constituent atoms of barium ferrite or strontium ferrite are replaced with specific other atoms to control the coercive force.

The present invention has been accomplished as a method for manufacturing such particles, and has the general formula (%), where A: at least an IFfl element selected from Ba+Sr, Ca, and pb, M: Co, T1
1n, NI, Cu, Zn, Nb, Zr, V, Ta, AI
, Cr, Sb, II[', Mo, W, Ir, Sn,
and a compound of each element forming a hexagonal ferrite such as at least one element selected from Mg and other components, R2O (R: Ll, Na,
at least -gI) selected from Rb, C8), AO
and B2O3 in molar ratio 1.0 <8 2O 3 / (AO + R2O)
< 1.50.0 <R2O < 1.0, the compounds R, A, and B are mixed and melted, rapidly cooled to become amorphous, and then this amorphous body is This is a method for producing magnetic powder for magnetic recording media, in which a heat treatment is performed to precipitate hexagonal ferrite, and a washing treatment is performed to extract the hexagonal ferrite.

Here, M is used to control the coercive force of the hexagonal ferrite, but if the substitution ff1X is smaller than 0.02, the coercive force becomes too large, and if it exceeds 0.24, the coercive force becomes small. It's too much and I don't like it.

In addition, the molar ratio of other components is B2O3/(AO
+R2O)≦1.0,
Particle size distribution is not narrow enough. On the other hand, B 2O3 /
When (AO+R2O)≧1.5, α-Pe2O3 is generated.

In the case of AO5R2O, however, the amorphous body severely absorbs moisture and carbon dioxide, making it difficult to stably produce hexagonal ferrite. Furthermore, even if the amorphous material is stored in a good condition and is prevented from absorbing moisture or carbon dioxide, the melting point of the amorphous material decreases, making it easier for sintering of the ferrite particles to occur. The mold ratio becomes low.

(Function) In the method for producing magnetic powder for magnetic recording media according to the present invention, a compound of each element forming hexagonal ferrite and other components are used in a molar ratio of 1. Q<B2O3ha^O+R2O) <1.5 and 0.0 <R2O
/AO < 1.0 by mixing and melting each compound of R, A, and B, and crystallizing the amorphous material by rapid cooling, so it is possible to obtain magnetic powder with a narrow particle size distribution. I can do it. In other words, when used in the production of media, it is possible to obtain hexagonal ferrite that can be highly filled in the media, and the media produced using this are free from noise caused by large particle size magnetic powder. Reduced recording density and high S/N
characteristics can be realized. Moreover, since compounds of each essential component are used as raw materials instead of using compounds synthesized in advance with two or more elements such as R28407, it can be melted with good uniformity and is amorphous with no bias in atomic distribution. An amorphous material with good properties can be obtained.

(Example) The present invention will be explained in detail below using examples.

Ba ferrite was selected as the target magnetic powder, and the substitution element for coercive force control was a combination of CO and TI ions so that the substitution mX-0,14, n = [i, 0
We tried the following composition. Other ingredients include B
% Ba and Na compounds were used. The ferrite component was 40flO1%.

Examples 1 to 6 and Comparative Examples 1a to 6a Raw material components to become Ba ferrite and other components were the first
Mix the carbonates of each element in the proportions shown in the table,
After melting at 1400° C., the material was rapidly cooled and rolled using twin rolls to obtain an amorphous material. The amorphous body obtained above was heat-treated at 800°C for 5 hours to precipitate hexagonal ferrite, and then washed with acetic acid and pure water, extracted, and dried to obtain magnetic powder. Obtained.

1st (a) Table B 2O3 / (BaO+Na2O) Na2O
/BaO Example 1 1.05 0.
52 1.1
0.5 Comparative Example 1a O,00,0 2a O,00,5 3a O,90,5 Magnetic powder with an average particle size of 50 to BOr+m was obtained with the above composition. (Left below) 1st (b) Table B 2 0 3 / (BaO+Na2 0 )
Na2 0 /BaO Example 3 1.1
0.24t,i
o, s5 1.25
0.56 1.
4 0.5 Comparative Example 4a
Magnetic powder with an average particle size of 65 to 75 rv was obtained with a composition of 1.3 0.0 or more.

1st (c) Table B 2 0 3 /(BaO+Na2O)
Na2O /BaO Comparative Example 5a 1.6
0.5Ga 1.1
1.0 The magnetic properties of each hexagonal ferrite obtained above were measured using a sample vibrating magnetometer, and the shape was measured from photographs taken with a transmission electron microscope. The breadth and narrowness of the particle size distribution was investigated by determining the geometric standard deviation since the distribution of particles follows a lognormal distribution. The properties of the obtained particles are shown in Table 2. (White space below) Second (a) Table Example 2 Comparative example Coercive force (Oe) Saturation magnetization (eIllu/g) Square specific grain size (μlI grain size/thickness geometric standard deviation maximum grain size (μm) 60 57.0 0.50 54.7 3.3 1.39 47 95 58.5 0.49 60.5 3.4 1.37 56 50 58.0 0.50 49.9 2.9 1.55 H 2O 30 58,5 59,0 0,49 0,50 58,2 57,9 3,2 3,1 0,48 1,46 189180 (Margins below) 2nd (b) Table Examples Comparative Examples Coercive force ( Oe) Saturation magnetization (enu/g) Square specific grain size (μm) Grain size/thickness geometric standard deviation maximum grain size (μra) 70 59.0 0.48 67.8 3.7 1.43 9g 40 58 .5 0.48 64.8 245 98 30 58.5 0.47 69.0 4.1 1.41 93 00 60 56.0 54.0 0.46 0.48 73.7 65.0 5.0 5.7 643 1.50 218 22O (Left below) 2nd (c) Surface coercive force (Oe) Saturation magnetization (emu/g) Square specific grain size <μm> Grain size/thickness geometric standard deviation Maximum grain size (μm) Remarks Comparative Example a 80 45.0 0.41 5B 9.3 1.75 3B α-Fe 2 0 3 is produced a 2O 6i,0 0.33 With sintering (blank below) Then, A magnetic paint was prepared using the magnetic powder having the composition shown in Table 3.

Table 3 Ingredients Blend amount Hexagonal ferrite 100 parts by weight Sulfonated vinyl hydrochloride resin io Dispersant (lecithin) 3 Abrasive (Al2O2)
2 Lubricant (St^/5tBu)
2 Hardening agent (Coronate)
4 〃Methyl ethyl ketone 40〃Toluene 40〃Cyclohexanone 40/〆After thoroughly kneading these with a sand grinder to form a paint, it was applied onto a 9μ-thick polyethylene terephthalate film, dried, and then calendered and cured. A magnetic recording medium was obtained.

Table 4 shows the properties of the obtained magnetic powder and the properties of the magnetic recording medium.

Table 4 Particle size Geometric standard deviation Maximum particle size Nbu I K (ni)
(nm) (dB) Example 1
54.7 1.39 147 -1.22
00.5 1.37 156 -0.9 Comparative example 1a 49.9 1.55 186 +0
．． 52a 58.2 1.48 189
+0.13a 57.9 1.46 180
0.0 Example 3 67.1! 1.43
198 -0.34 64.8 1.45
198 -0.35 H,01,41193-0
,4 673,71,43216-0,1 Comparative example 4a [i5.0 1.50 22O
0.0 Comparative Example 5a 158 1.75
8366a 61.0 ... As is clear from Examples 1 to 6, other components include B
2O3, BaO and Na2O 1.0<B 2O
3/(13aO+Na2O) <1.5 or o, o <
By setting the composition such that Na2O/BaO<1.0, B 2O3 / (I3aO+Na 2O)
Ferrite with a narrower particle size distribution and a smaller maximum particle size was obtained than ferrite with approximately the same particle size when ≦1.0. Further, in Comparative Example 5a, α-Fe 2O3 was generated, and the saturation magnetization was as small as 45 (emu/g), the particle size was large, and the particle size distribution was wide. Furthermore, in Comparative Example 6a, the squareness ratio was 0 due to sintering. It was as low as .33. Compared to these comparative examples, in Examples 1 to 6, media with low noise were obtained because the particle size distribution of Fe and Light was narrower. That is, other components include I3. Using Da and Na compounds, and 1.0 <82O3 / (BaO + Na2O) <
1.5 and 0.0 < Na2O/ BaO < 1.0
A medium with high S/N can be obtained by hexagonal ferrite manufactured with a composition such that .

In addition, regardless of the ratio of ferrite and other components, other ferrites such as Sr ferrite instead of Ba ferrite, substitution elements other than Co-Ti ions, and R among other components, in compounds other than Na. A similar effect was obtained.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, magnetic powder with a narrow particle size distribution suitable for obtaining a magnetic recording medium having both high recording density and high S/N characteristics can be easily produced. It becomes possible to manufacture.

Claims (1)

[Claims] General formula AO・n(Fe_1_-_XM_X)_2O_35.0
≦n≦6.5 0.02≦X≦0.24 However, A: At least one element selected from Ba, Sr, Ca, and Pb M: Co, Ti, In, Ni,
Cu, Zn, Nb, Zr, V, Ta, Al, Cr, Sb
, Hf, Mo, W, Ir, Sn, and a compound of each element forming a hexagonal ferrite such as at least one element selected from Mg, and R_2O( R: Li, Na, K,
at least one selected from Rb, Cs), AO and B_2O_3 have a molar ratio of 1.0<B_2O_3/(AO+R_2O)<1.50
．． The compounds R, A, and B are mixed and melted so that 0<R_2O/AO<1.0, and then rapidly cooled to become amorphous. This amorphous body is then heat-treated to form a hexagonal shape. A method for producing magnetic powder for magnetic recording media, characterized by precipitating crystalline ferrite, performing a washing treatment, and extracting hexagonal ferrite.