JPS6048885B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and an object thereof is to provide a magnetic recording medium with excellent magnetic properties and erasing properties.

Magnetic recording media are usually made by applying magnetic powder together with a binder resin onto a substrate such as a polyester film.The magnetic powder used at this time has excellent magnetic properties, high sensitivity, and A device that can provide various excellent electromagnetic conversion characteristics such as a high S/N ratio and excellent frequency characteristics is desired.

As a material that satisfies such requirements, γ-Fe2O3
Cobalt-containing iron oxide ferromagnetic powder obtained by dissolving cobalt atoms in the crystal lattice of iron oxide ferromagnetic powder such as powder has been proposed. However, in γ-Fe, cobalt atoms are dissolved in solid solution.

O. The powder is usually made from α-iron oxyhydroxide powder obtained by mixing an aqueous ferrous salt solution and an aqueous alkaline solution (by air oxidation at a temperature of 30 to 60°C, which is further oxidized after being heated and reduced). However, in such a method, α-iron oxyhydroxide powder with a large axial ratio and a non-uniform particle size distribution is obtained. Although the axial ratio of the magnetic powder increases, the particle size distribution is relatively uneven and it is difficult to obtain fine particles.As a result, cobalt atoms are dissolved in the crystal lattice of this γ-Fe.O. powder. The resulting cobalt-containing iron oxide ferromagnetic powder had problems such as insufficient magnetic properties for practical use and good erasing properties.The inventors conducted various studies in view of these circumstances. , γ-Fe2O before solid solution with cobalt atoms.

In producing ferromagnetic powder, an aqueous solution containing trivalent iron ions is added to an equivalent or more alkaline aqueous solution at a temperature of 30°C or less, reacted to produce ferric hydroxide, and heated at 100°C. After aging for at least 1 minute, usually at room temperature for at least 3 gin, the α-
After producing iron oxyhydroxide powder, filtering and drying, the produced powder is heated and reduced, and further oxidized to produce γ-Fe. O. When made into powder, γ-Fe is fine, has a small axial ratio, and has a uniform particle size distribution. O3 ferromagnetic powder is obtained, and by dissolving cobalt ions in the γ-Fe2O3 ferromagnetic powder particles, the particle size is adjusted to a major axis diameter of 300 nm or less, an axial ratio of 5 or less, and a coercive force of 39.8 KA/m or more. A cobalt-containing iron oxide ferromagnetic powder with a uniform distribution can be obtained, and when a magnetic recording medium is manufactured using this powder, a magnetic recording medium with a large square shape, excellent magnetic properties, and excellent erasing characteristics and transfer characteristics can be obtained. He discovered this and came up with this invention. The cobalt-containing iron oxide ferromagnetic powder used in this invention is preferably fine with a major axis diameter of 300 nm or less, an axial ratio of 5 or less, and a uniform particle size distribution, and a coercive force of 39.8 KA/m or more. If the particle size distribution is uneven, the square shape will be small and the coercive force distribution will be wide, resulting in poor erasing characteristics.
Sufficient magnetic properties cannot be obtained below 9.8 KA/m.

Suitable examples include a long axis diameter of 100 to 300 nm, a short axis diameter of 30 to 60 nm, an axial ratio of 1.5 to 5, and a coercive force of 39.8.
Cobalt-containing iron oxide magnetic powder having a KA/m or more is preferably used.

The magnetic recording medium of the present invention can be produced by a conventional method, for example, the above-mentioned cobalt-containing iron oxide ferromagnetic powder, binder resin, organic solvent, and other necessary ingredients are placed on a substrate such as a polyester film. The magnetic paint containing the above may be applied by any coating means such as a roll coater and dried.

As the binder resin used here, three conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, polyurethane resin, and nitrocellulose are widely used.

The organic solvent may be appropriately selected from commonly used organic solvents such as toluene, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, and ethyl acetate, and these may be used alone or in a mixture of two or more. .

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

Next, embodiments of the invention will be described.

Example 1 A ferric chloride aqueous solution in which 10 moles of ferric chloride (FeCl3.6H20) was dissolved in water 301 and a sodium hydroxide aqueous solution in which 60 moles of sodium hydroxide were dissolved in water 60e were prepared, and the mixture was heated at a temperature of 10°C. An aqueous ferric chloride solution was added to an aqueous sodium hydroxide solution to obtain a brown precipitate.

After aging this at room temperature for 1 hour, this suspension was placed in an autoclave and subjected to a hydrothermal reaction at 180° C. for 1 hour. After the reaction was completed, the yellow precipitate produced was washed with water, filtered, and dried to obtain α-iron oxyhydroxide powder. Next, the obtained α-iron oxyhydroxide powder was heated in air at a temperature of 600°C for 1 hour.
By heating for a time to produce α-Fe2O3 powder, this α-Fe2O3 powder is produced.
800 da of Fe2O3 powder was spread on a quartz board, placed in a tubular electric furnace, hydrogen gas was passed through at a rate of 51/min, and reduced at 300°C to obtain FeO.

A powder was obtained, which was further oxidized in air at a temperature of 250°C to obtain γ-Fe. A powder was obtained. Next, this γ-Fe.

O. Cobalt chloride (COCl.6H) powder 800 da
20) Cobalt chloride aqueous solution 21 in which 0.8 mol was dissolved
Complexing agent aqueous solution 2 in which 0.3 mol of sodium citrate and 0.15 mol of sodium tartrate were dissolved
A hydrothermal reaction was carried out at a temperature of 200° C. for 3 hours. Cobalt-containing γ-Fe produced after completion of the reaction. O. The powder is filtered, washed with water, dried, and then placed in air at a temperature of 2
The mixture was heated and oxidized at 00° C. for 3 hours to obtain cobalt-containing iron oxide ferromagnetic powder. The obtained cobalt-containing iron oxide ferromagnetic powder has a major axis diameter of 200 nm) a minor axis diameter of 50 nm) an axial ratio of 4,
Specific surface area by BET method is 24.5g/y) Coercive force is 6
5.3KA/m) Saturation magnetization (σs) is 9.06×10-
°Wb-m/K9, squareness ratio (σr/σs) was 0.78, and the cobalt atom content was 5.9%. Cobalt-containing γ-Fe thus obtained.

CO-containing γ-Fe2O3 powder 8 volumes VAGH (manufactured by U.C.C., USA, vinyl chloride-vinyl acetate-vinyl alcohol copolymer) 11" Pandex T-5250 (Dainippon Ink Co., Ltd.) A magnetic paint was prepared by mixing and dispersing a composition consisting of 60 parts cyclohexanone and 60 parts toluene in a ball mill for 7 hours. was prepared.

This magnetic paint was applied onto a 12 μm thick polyester base film to a dry thickness of 4 μm, dried, and surface treated. After processing, the fabric was cut into the desired size to create magnetic tape. Example 2 In Example 1, the temperature when adding the ferric chloride aqueous solution to the sodium hydroxide aqueous solution was set to 0°C to obtain a brown precipitate, and this suspension was charged into an autoclave and heated for 180'
A hydrothermal reaction was carried out at C for 1 hour to obtain α-iron oxyhydroxide, but in the same manner as in Example 1, the major axis diameter was 120 nm) the minor axis diameter was 30 nm) the axial ratio was 4, and the specific surface area by BET method was 31. ．．
8d/y) cobalt-containing γ-Fe with a coercive force of 62.9 KA/m and a content of cobalt atoms of 5.90% by weight.

O. A powder is obtained, and this cobalt-containing γ-Fe is further obtained. O.
A magnetic tape was made in the same manner as in Example 1 using the powder. Example 3 In the process of obtaining cobalt-containing iron oxide powder in Example 2, the same procedure as in Example 2 was carried out except that the amount of cobalt chloride used was 1.1 mol, the major axis diameter was 120 nm) the minor axis diameter was 30 nm) Axial ratio 4, specific surface area 31.5g/y by BET method) coercive force 78.0KA/Rn, saturation magnetization (σs)
8.98×10-°Wb. m/K9, squareness ratio (σr/σ
s) 0.77 and the content of cobalt atoms 8. m wt % cobalt-containing γ-Fe.

O. A powder is obtained, and this cobalt-containing γ-Fe is further obtained. O3
A magnetic tape was made in the same manner as in Example 2 using the powder. Comparative Example Ferrous sulfate (FeSO.

・7H. 0) Prepare an aqueous solution of ferrous sulfate in which 10 mol of ferrous sulfate is dissolved in 401 water, and an aqueous sodium hydroxide solution in which 70 mol of sodium hydroxide is dissolved in 401 mol of water. An aqueous solution was added to obtain a pale green precipitate.

Next, this suspension was heated to 40°C in a constant temperature water bath, and air was blown into the suspension at a rate of 10 e/min to carry out an oxidation reaction for 6 hours to obtain a yellow precipitate, which was washed with water, filtered, and dried. Te α
- Iron oxyhydroxide powder was obtained. Next, this α-iron oxyhydroxide was heated and reduced in the same manner as in Example 1, and further oxidized to obtain γ-Fe2O3 powder, and then subjected to a cobalt atom solid solution treatment in the same manner as in Example 1 to form a cobalt-containing Iron oxide ferromagnetic powder was obtained. The obtained cobalt-containing iron oxide ferromagnetic powder has a long axis diameter of 200 nm, a short axis diameter of 30 nm), an axial ratio of 6.7, and a specific surface area of 47.9 d/9 by the BET method.
, coercive force is 51.7 KA/m) saturation magnetization (σs) is 7
．． 80×10-'Wb. m/K9, squareness ratio (σr/σs
) is 0.64 and the content of cobalt atoms is 5.89% by weight.
It was hot. Furthermore, this cobalt-containing γ-Fe. A magnetic tape was made in the same manner as in Example 1 using O3 powder. Regarding the magnetic tapes obtained in each example and comparative example, the coercive force in the longitudinal direction (Hc [/]), the squareness ratio (Br/
Br [/]), residual magnetic flux density (Br [']), coercive force in the direction perpendicular to the tape surface (Hc [earth]), square 5-type ratio (Br
/Br [earth]), residual magnetic flux density (Br [earth]), DCS
IN and ACSIN were measured and erasure properties were tested.

In the erase characteristic test, a 1 KHz signal was recorded on the magnetic tape with +B input, and the erase characteristics before and after erasure were erased with an erase current 20% higher than the erase current of 10 current, which makes the erase characteristic of the reference tape (BASFC4OlR) 65 dB. The difference between the reproduced output signals was measured and indicated by B. The table below shows the results. As is clear from the above table, the magnetic tapes produced by the present invention (Examples 1 to 3) are superior to the conventional magnetic S tape (comparative example) in coercive force, squareness ratio, The residual magnetic flux density, especially the squareness ratio in the direction perpendicular to the plane, also increases with DCSIN and ACS.
Since 'N is low, erasing is particularly easy. This shows that the magnetic recording medium obtained by the present invention has excellent magnetic properties and erasing properties.

Claims (1)

[Claims] 1 Cobalt atoms are dissolved in magnetic iron oxide powder particles with a major axis diameter of 300 nm or less, an axial ratio of 5 or less, and a coercive force of 3
A magnetic recording medium comprising cobalt-containing iron oxide ferromagnetic powder of 9.8 KA/m or more applied to a substrate together with a binder resin.