JPH03199301A - Magnetic metallic powder and production thereof and magnetic recording medium - Google Patents

Abstract

PURPOSE:To develop the magnetic metallic iron powder for magnetic recording media having excellent magnetic characteristics by subjecting the suspension of Fe(OH)2 to two stages of oxidation treatments in a specific oxidative atmosphere and subjecting the resulted alpha-FeOOH to dry reduction. CONSTITUTION:While the suspension of the Fe(OH)2 is kept at 15 to 40 deg.C, the suspension is stirred in the atmosphere of 15 to 40vol.% O2 concn. and is thereby subjected to primary oxidation in a range of 10 to 50% oxidation rate. Gaseous N2 contg. O2 at 0.5 to 15vol.% ratio is brought into reaction at 40 to 60 deg.C and is thereby subjected to secondary oxidation to obtain the alpha-iron oxyhydroxide (alpha-FeOOH). The thin film of Al2O3 and SiO2 is formed for the purpose of preventing sintering on the surface of the iron oxyhydroxide obtd. by filtering the above-mentioned alpha-iron oxyhydroxide and thereafter, the oxide is calcined to form Fe2O3 which is then subjected to the dry reduction in a reducing gas contg. H2, CO, etc. The resulted powder reduced iron is kneaded with a binder and the mixture is applied on a polyethylene terephthalate film, etc., and is subjected to the orientation of magnetic particles in a magnetic flux, by which the iron powder for magnetic recording media having a small inversion magnetization rate distribution (SFD) and excellent magnetic characteristics is produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a metal magnetic powder that can be used in coated magnetic recording media such as audio tapes, 8mm VTR tapes, magnetic camera disks, and DAT tapes. be.

[Prior Art] In recent years, there has been a strong need for higher performance in recording media, and high-density recording, high output characteristics, and lower noise levels are required. The characteristics of magnetic powder that satisfies these requirements are that it is fine, has a large surface area, and has excellent acicularity, and has high saturation magnetization and the desired optimal coercive force. However, when the magnetic powder is made into a tape, the squareness ratio (Rs) is large,
It is important that 5FD (flip magnetic susceptibility distribution) is small.

- The metal magnetic powder in the film is α-iron oxyhydroxide (α-F
e00H) or iron oxide as H2.

It is produced by reduction with a reducing gas such as Co, but in the past, in order to reduce the SFD of magnetic powder, the starting material α
- It has been proposed to narrow the particle size distribution of metal magnetic powder by making the shape of iron oxyhydroxide uniform and preventing the powder from sintering and deforming during reduction (for example, JP-A-52-1398
No. 58, JP-A-57-23002, JP-A-Sho 5
9-57917, etc.).

However, since it is very difficult to make the metal magnetic powder uniform in shape, there is a limit to reducing the SFD using the above method.

In addition, when applying metal magnetic powder, in order to increase the residual magnetic flux density and Rs of the applied material and to reduce SFD, the metal magnetic powder is oriented in the longitudinal direction by a magnet after application. It is impossible to perfectly align the axis of easy magnetization of metal magnetic powder in the longitudinal direction, and therefore, even in a coated material obtained by coating uniform magnetic powder with the shape described above, the distribution of coercive force is widened. There was a problem with putting it away.

[Problems to be Solved by the Invention] An object of the present invention is to provide a metal magnetic powder that has a small SFD and excellent magnetic properties when applied, and a method for producing the same.

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors discovered a metal magnetic powder whose coercive force has a small dependence on angle, and completed the present invention. . That is, the present invention provides a metal magnetic powder that is used by coating, and the specific coercive force with respect to the orientation direction of the coated material obtained by coating the powder is applied at all angles in the range of o'' to ±50'' within the coated surface. It is a metal magnetic powder with a value of 90% or more and a value of 0% at ±90@.

The small angular dependence of coercive force here means that when the magnetization reversal mechanism is normally in coherent mode, the coercive force when the axis of easy magnetization is inclined by θ° with respect to the magnetic field direction is He (θ0), which is the same as the magnetic field. If the coercive force in the direction He (0')-A is Hc
(45°) - A/2 and H in fanning mode
If e (0')=A', then Hc (45'):1. I
It is said that the angle dependence of the coercive force is smaller in the fanning mode than in the coherent mode, and the coercive force does not change even if the angle between the axis of easy magnetization and the magnetic field direction changes. It's a small thing.

In addition, the specific coercive force in the present invention is measured when a metal magnetic powder is applied as a magnetic paint to a polyester film, etc., oriented by an external magnetic field, etc., and a magnetic field is applied at an angle of 00 within the coating surface with respect to the orientation direction. By measuring the coercive force Hc (θ″) with a vibrating sample magnetometer, it can be determined from the following equation.

ItHe(θ")-11c(90'))/1Hc(
0°) - He (90°) + 1
represents the coercive force in the direction perpendicular to the orientation direction.

As described above, the metal magnetic powder of the present invention has a small angular dependence of coercive force, so the SFD is small and the magnetic properties when applied are excellent.

The method for producing the metal magnetic powder of the present invention will be described below.

The metal magnetic powder of the present invention is produced by primary oxidizing a suspension containing ferrous hydroxide in an atmosphere with a temperature of 15 to 40°C and an oxygen concentration of 15 to 40% by volume until an oxidation rate of 10 to 50% is obtained. It can be produced by dry reducing α-iron oxyhydroxide obtained by secondary oxidation in an atmosphere with a temperature of 40 to 60° C. and an oxygen concentration of 0.5 to 15% by volume.

Examples of suspensions containing ferrous hydroxide used in the above method include ferrous chloride and ferrous sulfate.

It can be obtained from an aqueous solution containing a mixture of a ferrous salt such as ferrous nitrate and an alkali hydroxide such as sodium hydroxide or potassium hydroxide. In this suspension are nickel, cobalt, chromium, calcium and zinc.

One or more metals such as manganese can be added as modifiers. Note that the amount of crystal modifier added is preferably 2.0% by weight or less based on iron. If the amount of the crystal modifier exceeds the above range, the angular dependence of the obtained metal magnetic powder may not be reduced.

Moreover, when obtaining ferrous hydroxide, ferrous hydroxide having a high acicular ratio can be obtained by performing crystallization at a temperature of 40° C. or lower in a non-oxidizing atmosphere. At this time,
By increasing the acicular ratio of ferrous hydroxide, the magnetic properties of the produced metal magnetic powder are improved.

Next, the suspension containing the above ferrous hydroxide is oxidized, and α
- iron oxyhydroxide is obtained, the oxidation reaction being carried out in two steps. Further, this oxidation can be carried out in an oxidizing gas atmosphere while stirring the suspension. The primary oxidation of the above oxidation reaction is carried out at a temperature of 15 to 40°C, an oxygen concentration of 15
The oxidation is carried out in an atmosphere of ~40% by volume until the oxidation rate reaches 10~50%. Due to this oxidation, the α
- Iron oxyhydroxide is produced. After further primary oxidation, the temperature was increased to 40
Secondary oxidation is carried out at ~60°C in an atmosphere with an oxygen concentration of 0.5 to 15% by volume, but this oxidation suppresses new nucleation of α-oxyiron hydroxide and removes the already generated α-oxyhydroxide. Iron oxide crystals grow. By performing the oxidation reaction in two stages as described above, the acicular ratio of α-iron oxyhydroxide can be increased. Note that -blown oxidation is performed at an oxidation rate of 1
If the concentration is less than 0%, the resulting α-iron oxyhydroxide crystals may become too large;
If the process is completed in excess of 20%, the acicular ratio of the obtained α-iron oxyhydroxide will become small.

Thereafter, the obtained α-iron oxyhydroxide is subjected to dry reduction to obtain the metal magnetic powder of the present invention.

This dry reduction is carried out, for example, by α-
This can be done by surface-treating iron oxyhydroxide with an aluminum compound, silicon compound, etc. to prevent sintering, dehydrating and firing it to form ferric oxide, and then reducing it in a reducing gas atmosphere. can. Dehydration at this time.

Although the firing may be performed in the air, it is preferable to perform the firing in a nitrogen atmosphere since this can prevent the powder from losing its shape. Furthermore, when dehydrating and firing in a nitrogen atmosphere, it is preferable to perform the dehydration and baking at a temperature of 500 to 750°C.
If the temperature is lower than 500°C, the powder may lose its shape, and if the temperature is higher than 750°C, the powder may be sintered. Further, gases used in the reduction include hydrogen gas, -carbon oxide gas, etc., and although not particularly limited, hydrogen gas is preferably used. When reduction is performed using hydrogen gas, sintering between powders, deformation of powder, etc. can be suppressed by adjusting the reduction temperature, hydrogen gas supply amount, etc. so that the reduction time is 5 to 15 hours. The above conditions are usually a reduction temperature of 350 to 550°C and a hydrogen gas supply amount of 3 to 2 ONffl per 1 kg of ferric oxide.
/ This is achieved by taking time.

Although the metal magnetic powder of the present invention can be obtained by the above method,
Since the powder may ignite in the air immediately after reduction, it is preferable to form a thin oxide film on the powder surface before taking it out into the air. This can be done by contacting with.

Further, the metal magnetic powder of the present invention is kneaded with a binder and used as a magnetic coating, and a magnetic recording medium can be obtained by coating this on a non-magnetic support.

(Examples) Hereinafter, the present invention will be explained with reference to Examples, but the present invention is not limited thereto.

Example 1 50 u of an aqueous solution containing 11 kg of caustic soda was added to 50 j2 of an aqueous solution containing 2.2 kg of ferric chloride under a nitrogen atmosphere]
The mixture was stirred at 8°C to obtain a suspension of ferrous hydroxide. Next, while maintaining the temperature at 18° C., air was passed through the reactor at a rate of 61 per minute for 45 minutes to complete the first half of the oxidation reaction. The oxidation rate at this time is 35
%Met. The air is then diluted with nitrogen to reduce the oxygen content to 4%.
This gas was passed through the reactor at a rate of 111 per minute for 10 hours to complete the second half of the oxidation reaction and obtain α-iron oxyhydroxide. The obtained α-iron oxyhydroxide was filtered and washed with water, and a film made of a silicon compound and an aluminum compound was formed using an aqueous solution of sodium silicate and an aqueous solution of sodium aluminate.

Thereafter, the obtained α-iron oxyhydroxide powder was dissolved in a nitrogen stream for 6 hours.
It was fired at 00°C for 3 hours to form ferric oxide.

Add 12 NTI of H2 gas to 1 kg of this ferric oxide! Magnetic iron powder was obtained through reduction at 450° C. for 10 hours.

Next, the surface of the iron powder was oxidized at 80°C in a nitrogen stream with an oxygen concentration of 0.2% to obtain ferromagnetic iron powder.
Parts by weight include 25 parts by weight of vinyl chloride-vinyl acetate copolymer, 1 part by weight of lecithin, and 100 ml of methyl ethyl ketone.
, cyclohexanone 100ml and toluene 100ml
were mixed for 6 hours using a sand grinder containing glass beads and dispersed to prepare a magnetic paint. This was applied onto a polyethylene terephthalate film, the magnetic particles were oriented in a magnetic flux, a magnetic tape was produced, and the specific coercive force and other magnetic properties of the resulting magnetic tape were measured using a vibrating sample magnetometer. .

The electromagnetic conversion characteristics were measured using an electromagnetic conversion characteristics measurement system (model: WV24AO) manufactured by Sibaku Corporation and an 8 mm video deck manufactured by Sony Corporation. The results are shown in FIG. 1 and Table 1.

Example 2 The same procedure as in Example 1 was carried out except that 25 g of N iCj22 was added to the ferric chloride aqueous solution. In this example, 1.1% by weight of Ni was contained relative to iron in the metal magnetic powder.

The results obtained under the same measurement conditions as in Example 1 are shown in FIG. 2 and Table 1.

Example 3 The same procedure as in Example 1 was carried out except that 15 g of Ca Ci2 was added to the ferric chloride aqueous solution. In this example, 0.5% by weight of Ca was contained relative to iron in the metal magnetic powder.

The results obtained under the same measurement conditions as in Example 1 are shown in FIG. 3 and Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that 130 g of N i Cfl□ was added to the ferric chloride aqueous solution. The metal magnetic powder contained 6.0% by weight of Ni based on iron.

The results obtained under the same measurement conditions as in Example 1 are shown in FIG. 4 and Table 1.

[Effects of the Invention] The metal magnetic powder of the present invention has a small SFD and a small angular dependence of coercive force, so that the rise of the hysteresis loop near the coercive force in the second quadrant becomes steep, and recording resolution is improved. , because the effective residual density is large,
This makes it suitable for short wavelength recording.

[Brief explanation of drawings]

1 to 3 are diagrams showing the relationship between the specific coercive force and the angle with respect to the orientation direction of coated articles coated with metal magnetic powders of Examples 1 to 3 of the present invention. FIG. 4 is a diagram showing the relationship between the specific coercive force and the angle with respect to the orientation direction of the coated product coated with the metal magnetic powder of Comparative Example 1.

Claims (3)

[Claims] (1) A metal magnetic powder used by coating, which has a specific coercive force of 90% in the coating surface at all angles in the range of 0° to ±50° with respect to the orientation direction of the coated material obtained by applying the powder.
% or more and 0% at ±90°. (2) A suspension containing ferrous hydroxide at a temperature of 15 to 40°C.
Oxidation rate 10-5 in an atmosphere with an oxygen concentration of 15-40% by volume
Primary oxidation is performed until it becomes 0%, then the temperature is 40-60℃,
The production of metal magnetic powder according to claim 1, characterized in that α-iron oxyhydroxide obtained by secondary oxidation in an atmosphere with an oxygen concentration of 0.5 to 15% by volume is subjected to dry reduction. Law. (3) A magnetic recording medium obtained by coating metal magnetic powder on a non-magnetic support, characterized in that the metal magnetic powder is the metal magnetic powder according to claim 1.