JPH04337521A - Magnetic powder for magnetic recording medium and magnetic recording medium formed by using the powder - Google Patents

Abstract

PURPOSE:To obtain the high-density magnetic recording medium which is low in noise and has high S/N by applying magnetic powder consisting of hexagonal ferrite contg. Mg and/or Al respectively at specific ratios on a base body. CONSTITUTION:This magnetic recording medium is formed by applying the magnetic powder on the base body. The magnetic powder consists of the hexagonal ferrite expressed by formula I. In the formula I, A denotes the element selected from Ba, Sr, Ca, and Pb; MI denotes the element selected from Co, Ni, Cu, Mn, and Zn; MII denotes the element selected from Ti, Nb, Sn, Zr, V, Cr, Mo, Ge, and W. The grain size distribution of the magnetic power can be narrowed by incorporating 0.002 to 0.01wt.% Mg and/or 0.03 to 0.3wt.% Al therein. The high-density magnetic recording medium which is low in noise and has the high S/N is thus obtd.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder suitable for high-density magnetic recording and a magnetic recording medium using the same.

0003

[Prior Art] A coated magnetic recording medium consists of a base made of polyethylene terephthalate or the like, and a magnetic layer formed by applying a magnetic paint containing magnetic powder and a resin binder as main components onto the base. There is.

Conventionally, magnetic powders used in such magnetic recording media include, for example, γ-Fe2 03 , C
o Deposited γ-Fe2 03 , Co-doped γ-Fe2 0
Examples include acicular magnetic powders such as 3, Cr02, or metal Fe, and magnetic recording has been performed using magnetization in the longitudinal direction of the coated surface of these magnetic powders.

[0005] However, when attempting to improve the recording density in a magnetic recording method using magnetization in the longitudinal direction of the plane, a problem arises in that the demagnetizing field within the medium increases in the high frequency range, resulting in a decrease in recording and reproducing output. was there. Therefore, there was a limit to the improvement in recording density.

Therefore, in order to significantly improve the magnetic recording density, a perpendicular magnetic recording system has been proposed that uses magnetization in a direction perpendicular to the coated surface of 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 by vacuum evaporation or sputtering 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, as a magnetic recording medium that does not have such problems and is suitable for perpendicular magnetic recording, a magnetic recording medium that is mainly composed of hexagonal ferrite powder and a resin binder, which tend to orient the axis of easy magnetization in a direction perpendicular to the substrate, is proposed. Coating type magnetic recording media, in which a magnetic paint is coated on a substrate, are being researched and developed. Examples of hexagonal ferrite powder used in coated magnetic recording media include M-type barium ferrite, which is represented by the chemical formula BaFe12O19, and BaMe2Fe16O27 (
W-type barium ferrite represented by (Me represents a substitutional metal element), those containing both M-type ferrite and spinel ferrite, and hexagonal ferrites in which some of these atoms are replaced with other elements. can be given.

[0009] As methods for producing the above-mentioned hexagonal ferrite powder, there are generally coprecipitation methods, hydrothermal synthesis methods, glass crystallization methods, etc. Among them, the glass crystallization method is
This method is known as a preferred method for obtaining hexagonal ferrite with good dispersibility.

[0010] This glass crystallization method involves heating and melting a raw material mixture containing a hexagonal ferrite basic component, a substitution component for controlling coercive force, and a glass-forming component/modifying component, and rapidly cooling the resulting melt. The process consists of four steps: producing an amorphous body, then subjecting the amorphous body to heat treatment to precipitate hexagonal ferrite, and then extracting this.

[0011]

[Problems to be Solved by the Invention] However, the hexagonal ferrite powder obtained by the above-mentioned glass crystallization method has a drawback that its particle size distribution is wide. When the particle size distribution of magnetic powder is wide, particles with a large particle size will increase the noise of the manufactured magnetic recording medium, and particles with an extremely small particle size will make the medium magnetically unstable.
Both have an undesirable effect on the magnetic properties of the medium. Therefore, in order to obtain a high-density magnetic recording medium with low noise and a high S/N ratio, it was necessary to narrow the particle size distribution of the hexagonal ferrite magnetic powder, which is the main component of the magnetic paint. .

The present invention was made to solve the above-mentioned difficulties in hexagonal ferrite powder produced by glass crystallization, and its purpose is to provide hexagonal ferrite powder with a narrow particle size distribution. Further, it is an object of the present invention to provide a high-density magnetic recording medium having low noise and a high S/N ratio.

[Configuration of the invention]

[0014]

[Means for Solving the Problems] The magnetic powder for magnetic recording media of the present invention has the general formula AO・n(Fe12-x-yMI x MIIy O
18-α) 0.8≦n≦2.0 0.55≦x≦2.7 0.0≦y<2.0 0.0≦α≦1.0 (In the formula, A is Ba, Sr, Ca , and Pb, and MI represents Co, Ni
, Cu, Mn, and Zn, and MII represents Ti, Nb, Sn, Zr,
0.002 to 0.01 wt% of Mg and/or 0.03 to 0.01 wt% of Mg and/or 0.03 to It is characterized by containing 0.3 wt% of Al.

The hexagonal ferrite powder of the present invention has a particle size of 0.
．． 01 to 0.3 μm is preferable. This is because if the particle size is within this range, sufficient recording and reproduction can be carried out in the region of recording wavelengths of 1 μm or less, which makes it clear that the perpendicular magnetic recording method is more effective than the longitudinal magnetic recording method.

The coercive force of the hexagonal ferrite powder of the present invention is preferably in the range of 200 to 2,000 Oe. If it is larger than 2,000 Oe, the head magnetic field will be saturated during recording, and if it is smaller than 200 Oe, it will be impossible to hold the recording signal, both of which are undesirable. In order to control the coercive force within this range, in the magnetic powder of the present invention, some of the constituent atoms of Ba ferrite or Sr ferrite are replaced with specific other atoms. Furthermore, in the above general formula, n , x , y ,
By setting and α within the above range, the coercive force can be controlled within the range of 200 to 2,000 Oe,
In addition, temperature changes in coercive force are reduced, and a decrease in saturation magnetization is also prevented.

In the present invention, Mg and/or Al
When the content is within the above range, magnetic powder with a narrow particle size distribution and uniform particle size can be obtained. Mg and/or Al
If the content is less than the above range, the effect of narrowing the particle size distribution will not appear much, and if it is more than the above range, it will cause a decrease in the saturation magnetization of the obtained magnetic powder.
Both are undesirable.

The method for obtaining the magnetic powder of the present invention described above will be explained below.

First, the raw materials will be specifically described. The basic components of hexagonal ferrite are BaO, SrO, CaO,
and one or more oxides selected from PbO and Fe2O3, and the substitution components for coercive force control are CoO, NiO, CuO, ZnO, TiO2, Nb2
O5, SnO2, ZrO2, V2 O5
, CrO2 , MoO2 , MoO, GeO2
and WO2.

Glass forming components/modifying components generally include BaO, SrO, CaO, PbO, Li2O, Na
2 O, K2 O, B2 O3, SiO2, etc. are used, but other materials may be used as long as they are effective in making the melt amorphous by rapid cooling and are not incorporated into the hexagonal ferrite. It's okay. Here, the sum of the basic components of the hexagonal ferrite and the substituted components for coercive force control is preferably in the range of 30 to 60 mol%. 3
When it is less than 0 mol%, the particle size becomes too large than the desired range, and when it is more than 60 mol%, it becomes difficult to extract hexagonal ferrite from the heat-treated material. Note that each of the above raw material components is displayed as an oxide, but in the process of heating and melting the raw material mixture, other forms of compounds such as various salts may be used as long as they can be converted into the above oxides. can do.

As the Mg and/or Al source, fine metal powders or compounds of these metals may be used.

Next, the manufacturing process of the magnetic powder of the present invention will be specifically explained. Predetermined amounts of the basic component of the hexagonal ferrite and the glass-forming component/modifying component described above are weighed and thoroughly mixed, and further Mg and/or Al are added to form a raw material mixture. Thereafter, glass crystallization is performed according to a conventional method. That is, the raw material mixture is heated and melted at about 1,250 to 1,500°C in a platinum crucible, for example. Next, this melt is dropped, for example, between twin rolls and rapidly cooled to form an amorphous material. The obtained amorphous body has 650 to 1,
Heat treatment is performed at approximately 000°C. Then, components related to glass are removed by acid treatment and water washing, and then dried to obtain the hexagonal ferrite powder of the present invention. Note that in order to obtain the magnetic powder of the present invention, it is necessary that Mg and/or Al be present at the stage when the raw material mixture is melted, but this is not the case for the method of adding the Mg and/or Al source. .

Furthermore, a magnetic recording medium using the hexagonal ferrite powder of the present invention obtained by the above manufacturing method is as follows:
It is manufactured as follows according to conventional methods. That is,
The above-mentioned hexagonal ferrite powder is sufficiently kneaded and dispersed with a resin binder etc. to form a paint, and then applied onto a substrate. In some cases, after performing orientation treatment in a direction perpendicular to the substrate, drying, It can be obtained through calendering, curing, etc. The resin binder used is not particularly limited, and various conventionally used thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. Furthermore, the magnetic layer using the magnetic powder of the present invention may contain, as necessary, an abrasive such as aluminum oxide or chromium oxide, and a lubricant such as various fatty acids, fatty acid esters, or silicone oil. . Further, as the substrate, various substrates such as a stirrable substrate such as polyethylene terephthalate and a non-magnetic metal substrate can be used.

[0024]

[Operation] In the hexagonal ferrite powder of the present invention, 0
．． 002 to 0.01 wt% Mg and/or 0.01 wt%.
By containing 0.03 to 0.3 wt% of Al, the particle size distribution is narrowed. In order to contain the above amounts of Mg and/or Al in the hexagonal ferrite powder, it is necessary to combine the hexagonal ferrite basic component, a replacement component for coercive force control, and a glass-forming component during the production process using the glass crystallization method. When melting the raw material mixture containing the modifying component, these Mg
and/or Al may be added.

Further, the magnetic recording medium according to the present invention uses the above-mentioned hexagonal ferrite having a narrow particle size distribution, and reduces noise caused by particles having a large particle size, and reduces noise caused by particles having a small particle size. Magnetic instability caused by particles is eliminated, and high recording density and high S/N ratio are achieved.

[0026]

EXAMPLES The present invention will be explained in detail below based on examples.

Example 1 First, in order to produce hexagonal Ba ferrite powder, which is an example of the present invention, raw materials having the composition shown in Example 1 in Table 1 were mixed with a basic ferrite component and a substitute component for coercive force control. and Mg was added as a trace additive to obtain a raw material mixture 1. Furthermore, Table 1
Each item of ferrite component in MI, x, MII,
y, n and α are the symbols shown in the general formula according to the invention.

This raw material mixture 1 was placed in a platinum crucible and melted at 1,400°C, then dropped into twin rolls and rapidly cooled to obtain an amorphous body. Next, this amorphous body was heated at 800℃ to 5
Heat treatment was performed for several hours to precipitate hexagonal ferrite. Then, the heat-treated material was washed with 10% acetic acid and then further washed with water to obtain magnetic powder of Example 1 of the present invention.

Obtained hexagonal Ba ferrite magnetic powder 1
The various characteristics are shown in Table 2. In addition, the magnetic properties are
Measurements were made using a vibrating sample magnetization measuring device with a maximum magnetic field of 10 kOe. In addition, the shape is 4 in the transmission electron micrograph.
00 particles were investigated. The particle size distribution was investigated by determining the geometric standard deviation since the particle distribution follows a lognormal distribution.

Example 2 The raw material having the composition shown in Example 2 in Table 1 was prepared so that the sum of the amounts of the ferrite basic component and the replacement component for coercive force control was 40 m
Weigh it so that it is ol%, and add A as a trace additive.
1 was added to obtain a raw material mixture 2. Hereinafter, magnetic powder of Example 2 of the present invention was manufactured from this raw material mixture 2 through the same steps as in Example 1.

Obtained hexagonal Ba ferrite magnetic powder 2
The various properties of the sample are shown in Table 2 as in Example 1.

Example 3 A raw material having the composition shown in Example 3 in Table 1 was used in an amount where the sum of the amounts of the ferrite basic component and the replacement component for coercive force control was 40 m
ol%, and further added M as a trace additive.
A raw material mixture 3 was obtained by adding g and Al. Hereinafter, magnetic powder of Example 3 of the present invention was produced from this raw material mixture 3 through the same steps as Examples 1 and 2.

Obtained hexagonal Ba ferrite magnetic powder 3
The various properties of the sample are shown in Table 2 as in Example 1.

Comparative Example Magnetic powder was produced in the same manner as in Example 1, except that no trace additives were added, and this was used as a comparative example of the present invention. The various properties of the magnetic powder of the obtained comparative example are also shown in Table 2 as in Examples 1-3.

[0035]

[Table 1]

[0036]

[Table 2]

As is clear from Table 2, according to the present invention, hexagonal ferrite magnetic powder with a narrow particle size distribution can be obtained.

Next, for the magnetic powders of Examples 1 to 3 and Comparative Example, the influence of the width of the particle size distribution on the magnetic properties of magnetic recording media produced using the magnetic powders was investigated.

In producing the magnetic recording medium, each magnetic powder was used to prepare magnetic paints having the following compositions.

Magnetic powder
100 parts by weight sulfonated vinyl hydrochloride resin
10 parts by weight Dispersant (lecithin)
3 parts by weight Abrasive (Al2 03
)
2 parts by weight Lubricant (stearic acid/butyl stearate) 2 parts by weight Curing agent (Coronate L, trade name) 4 parts by weight Methyl ethyl ketone
40 parts by weight
toluene
40 parts by weight cyclohexanone
In preparing the 40 parts by weight magnetic paint, the above raw materials were sufficiently kneaded with a sand grinder to form a paint, which was then applied onto a 9 μm thick polyethylene terephthalate film and dried. After that, it was subjected to calendar treatment and cured. This was cut into 1/2 inch width to obtain magnetic recording media Examples 1 to 3 and a comparative example. Note that the sample number of the magnetic powder corresponds to the sample number of the medium.

To evaluate the characteristics of these magnetic recording media, noise and S/N ratio were measured. Table 3 shows the measurement results. The magnetic head used at this time was a ring-type ferrite head with a gap width of 0.3 μm and a track width of 3.
5 μm, relative speed between head and tape is 3.75 m/
sec, and the recording wavelength was 5 MHz.

[0042]

[Table 3]

As is clear from Table 3, the magnetic powder of the present invention provides an excellent magnetic recording medium with low noise and high S/N ratio.

In the present invention, the sum of the amounts of the basic components and substituted components of the hexagonal ferrite is not limited to the amounts in this example. Furthermore, in these Examples, the present invention was implemented on Ba ferrite, but S
For other hexagonal ferrites such as r-ferrite,
The present invention can be similarly applied to elements other than those in the examples as replacement elements, or to glass components other than those in the examples.

[0045]

[Effects of the Invention] As explained above, the hexagonal ferrite powder of the present invention can narrow the particle size distribution by containing Mg and/or Al. Therefore, by using the hexagonal ferrite powder of the present invention, an excellent high-density magnetic recording medium having low noise and a high S/N ratio can be obtained.

Claims (2)

[Claims] [Claim 1] General formula AO・n(Fe12-x-yMI x MIIy O
18-α) 0.8≦n≦2.0 0.55≦x≦2.7 0.0≦y<2.0 0.0≦α≦1.0 (In the formula, A is Ba, Sr, Ca , and Pb, and MI represents Co, Ni
, Cu, Mn, and Zn, and MII represents Ti, Nb, Sn, Zr,
0.002 to 0.01 wt% of Mg and/or 0.03 to 0.01 wt% of Mg and/or 0.03 to A magnetic powder for magnetic recording media, characterized by containing 0.3 wt% of Al. 2. A magnetic recording medium comprising magnetic powder coated on a substrate, wherein the magnetic powder is
A magnetic recording medium comprising the magnetic powder for a magnetic recording medium as described above.