JPS60137829A - Production of magnetic powder - Google Patents

Abstract

PURPOSE:To produce a magnetic powder capable of forming an easily magnetizable axis in the coated film thickness direction only by coating, by coprecipitating hydroxides of iron and barium under specific conditions, and treating the resultant coprecipitates at a high temperature under a high pressure. CONSTITUTION:(i) An aqueous solution containing an iron salt, e.g. Fe(NO3)3. 9H2O and a barium salt, e.g. Ba(NO3)2 at 7.5-9.5 ratio between the iron ions and the barium ions is mixed with an aqueous solution of sodium hydroxide (at 1.1-3 ratio between the total nonmetallic ions in the iron and barium salts and the hydroxyl ions). (ii) The resultant suspension is then placed in an autoclave, kept at a temperature (T) expressed by the formula for >=1hr and naturally cooled to collect a solid material, which is then washed with water and dried to afford the aimed magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing magnetic powder used in magnetic recording media, particularly magnetic powder suitable for coated perpendicular recording media.

Conventional configurations and their problems In the field of magnetic recording, there is a constant need to increase the density of recorded information, and the perpendicular recording method, which in principle does not generate a rotating magnetization mode in the short wavelength region, has the ability to increase the density. Many people are considering this as one of the most promising ways to make it more concrete.

The media used for these are Co-Cr zCo-
0 and other so-called continuous films are mainly used, and the film forming methods include sputtering and PVD
For example, vacuum deposition), 'mX7, etc. are commonly used. However, these methods have drawbacks such as slow film formation speed and therefore unsuitability for mass production, and furthermore, it is difficult to obtain homogeneous properties over a large area. Moreover, there are many problems and inherent difficulties that must be solved, such as reliability problems due to use in sliding contact with a magnetic head, and problems with large noise caused by using cobalt, which has a high magnetostriction, as a main component. .

In contrast, attempts have been made to apply acicular γ-Fe2O3, which has achieved high reliability through years of experience, in an oriented manner in the thickness direction of the coating film using an oriented magnetic field. However, unlike in the case of conventional longitudinal media, the magnetic powder is piled up in the thickness direction due to the oriented magnetic field, and in extreme cases, there are areas where there is no magnetic powder in the coating film, and it is used as a recording medium. At present, it is not possible to obtain sufficient 4f surface properties.

Attempts to use magnetic powder having a granular shape have essentially resulted in the same results as those for commercial γ-Fe203 powder.

On the other hand, barium ferrite powder, which has a flat plate shape, is considered to be advantageous for orientation by an external magnetic field due to its shape, and has been tested by many people.

In the case of barium ferrite, however, the orientation caused by an external magnetic field is essentially the same as in the case of the acicular γ-F e203 powder, and the magnetic powder is piled up in the thickness direction to obtain a coating surface that can be used as a recording medium. is difficult.

These disturbances on the surface of the paint film are caused by the application of an external magnetic field to generate magnetic charges of the same sign on the surface of the paint film, and the resulting increase in static magnetic energy is attempted to be lowered by the movement of particles. It must be understood that this is inevitable with respect to the application of a magnetic field.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for producing magnetic powder that can orient the direction of easy magnetization in the thickness direction of the coating film only by coating without using an external magnetic field for orientation. be.

Structure of the Invention The present invention provides an aqueous solution containing iron ions and barium ions.
Barium comprising a first step of adding sodium hydroxide to coprecipitate iron and barium hydroxide, and a second step of maintaining the suspension obtained in the first step at high temperature and high pressure in a closed container. In the method for producing ferrite powder, the ratio of iron ions to barium ions is in the range of 7.5 to 95, and in the second step, the ratio of hydroxyl to all nonmetal ions constituting the iron salt and barium salt is The ion concentration ratio (R) is in the range of 1.1 to 3.0, and T"
340R7'·4+30 to -40 (° C.) is maintained at a set temperature for at least one hour or more. By using the magnetic powder of the present invention, excellent orientation in the thickness direction of the coated film can be achieved only by stress acting on the magnetic powder during coating without using an external magnetic field for orientation. Moreover, since no external orientation magnetic field is applied, the smoothness of the coating/removal 1n1 is not disturbed.

Examples of the invention The present invention will be explained below using examples.

Example 1 Ba(NO3)2 of 8172 and 101. Of's Fe
Dissolve (NOs)a.9H20 in 500 ml of water.

Separately, 42.3 f NaOH was dissolved in 300 m water, and both were mixed while stirring well. The obtained suspension was placed in an autoclave furnace and maintained at a temperature of 275° C. for about 4 hours, and then the furnace was turned off and allowed to cool naturally to synthesize magnetic powder. The size of the obtained magnetic powder is 6 in thickness.
00A and a diameter of 0.3μ. The obtained magnetic powder was thoroughly washed with water, dried, and subjected to examination of component phases using X-rays, magnetic measurement using VSM, BET measurement, and observation using electron microscopy.

By depriving B, the value of B and the value of Fe/Ba can be changed.

The upper limit of the synthesis temperature is 320°C due to the equipment, and it can be controlled within a range of ±5°C with respect to the set temperature.

Fe (NO3)3-9 From the analysis of the component phase of sample OI created by changing the orientation ratio of H2O and Ba(NO3)2, it was found that if there is too much iron, α・Fe2O3 will be mixed in, and conversely, iron will be mixed. If it is too small, unknown phases will be mixed in and the magnetic properties will deteriorate. From this, a suitable range of ye/Ba is determined to be 9.5≧Fe/Ba≧75.

The orientation of the coating film was determined by the method described below. That is, hysteresis curves were measured in two directions, one in the thickness direction of the coating film and the other in the plane of the coating film, and the value of was used as a standard for vertical alignment.

Example of the first magnetic paint (hereinafter referred to as "first magnetic paint") 30 parts of vinyl chloride/vinyl acetate-vinyl alcohol copolymer (manufactured by UAC V
AGH) Polyurethane 10 parts (Nilaporan N 2304 manufactured by Nippon Polyurethane Industries Co., Ltd.)
) Carbon 5 parts MEK (methyl-ethyl-ketone) 200 parts Toluene 130 parts Cyclohexanone 30 parts and a small amount of dispersant were added to make a magnetic paint.

Approximately 30 m/cm using a blade with a 50 μm gap
It was coated on a 75 μm thick polyester film at a transfer speed of 10 min. The thickness of the magnetic layer after drying was approximately 4 μm, and a sample of 6 an x 6 m+a was cut out from it, and the history curve was measured using a vibrating sample type magnetometer. P: 2
．． 04 Hc=8340e Ms=7, 64 X 10
It was emu. Moreover, the surface roughness was 0.12 μm.

Figure 1 shows the measurement results of samples obtained by varying the synthesis temperature (T) and H values on the T-R plane, with the P value in the center of the frame and the coercive force in the lower left. 103X'Ms on the top right
are shown respectively.

From this figure, the R value range and synthesis temperature range that exhibit good orientation are determined as shown in the claims. Also, from this figure, when R is fixed, there is a synthetic humidity that gives the best orientation.
It can be seen that the curve connecting the maximum values of the P values corresponding to each P value is well expressed by I'=340R■°4. It can be seen that the vertical orientation deteriorates as the value and/or synthesis temperature deviate from the desired range.

Second Magnetic Paint Example Example 1 Ba (No3)2 and Fe(NO3)3
・9H20 with other salts, namely B a cA2 and Fec,
Magnetic powder was synthesized in the same manner as in Example 1 except that 83.6 H20 was used.

The obtained powder was made into a magnetic paint in the same manner as in the first magnetic paint example, and magnetism was measured in the same manner. p = 2,
75 Hc=8040e Ms=8.14X ] 0
The surface roughness was 0.14 μm in emu.

Third magnetic paint example Butyral resin (Eslec BLS manufactured by Block Chemical) Polyester resin (Vylon 200 manufactured by Toyobo) Polyurethane resin (550A manufactured by Takeda Pharmaceutical Co., Ltd.) Nitrocellulose (5L-1 manufactured by Asahi Kasei Industries) 7/'!
J O nitrile butadiene copolymer (E1 Zeon N
1pol 1432J) Using epoxy resin (Epicoat manufactured by Shell Chemical Co., Ltd.), a magnetic paint was prepared in the same manner as the first magnetic paint, and the P value was measured. Shows high orientation/c
.

Effects of the invention - As is clear from the above explanation, the magnetic powder according to the present invention has a shape of 600λ in thickness and 0.3μ in diameter when made into a paint using a commonly used organic binder. Therefore, it exhibits good vertical alignment by coating alone, without the use of an external alignment magnetic field. Moreover, since no external alignment magnetic field is used, there is no disturbance of the coating film surface, and good surface smoothness can be obtained, making it highly practical as a perpendicular recording medium.

[Brief explanation of the drawing]

The figure shows the synthesis properties and magnetic properties of magnetic powder. #’7”!’7 f l Patent applicant: Matsushita Electric Industrial Co., Ltd. Representative Patent Attorney Isao Abe

Claims (1)

[Claims] A second step of adding sodium hydroxide to an aqueous solution containing iron ions and barium ions to coprecipitate iron and barium hydroxides, and a suspension obtained in the first step. and a second step of holding the powder at high temperature and high pressure in a closed container, wherein the ratio of iron ions to barium ions (Fe ions/barium ions) is in the range of 75 to 95, The concentration ratio of hydroxide ions to all nonmetal ions constituting the salt and barium salt (R = [hydroxide ions]/[total nonmetal ions]) is in the range of 11 to 30, and in the second step A method for producing magnetic powder for magnetic recording media, characterized by holding the temperature (T) at a temperature (T) that satisfies the following formula T=34OR+30°C to -40°C for at least 1 hour.