JPH0619829B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD AND OBJECT The present invention relates to a magnetic recording medium using magnetic powder having hexagonal uniaxial anisotropy as magnetic powder, and a magnetic recording medium suitable for high density magnetic recording. The purpose is to provide.

[Background technology]

Generally, a magnetic recording medium has γ-Fe ₂ O ₃ and Co-containing γ-.
Magnetic properties have been improved by orienting needle-shaped magnetic powders such as Fe ₂ O ₃ and CrO _{2 in} the longitudinal direction of a horizontal magnetic layer, and further improved recording density to achieve high-density recording. In order to be suitable, it has been practiced to use magnetic powders with a very small particle size.

However, since the magnetic anisotropy of this kind of needle-shaped magnetic powder is based on the shape magnetic anisotropy, when an external magnetic field is applied to this needle-shaped magnetic powder, the magnetic powder is oriented in the binder in the direction of the shape magnetic anisotropy. Rotate so that the direction of the external magnetic field is parallel to
The needle-like magnetic powder is oriented so that the needle-like direction and the direction of the external magnetic field, that is, the orientation magnetic field are parallel to each other. However, when the particle diameter of the magnetic powder used becomes smaller, the gap between the magnetic powders becomes narrower and Since the powder particles are easily aggregated and the shape magnetic anisotropy energy of the acicular magnetic powder is reduced, the interaction with the external magnetic field is also reduced, and it is difficult to orient in the magnetic field direction. There is a drawback that the orientation in the inside becomes worse and the squareness becomes smaller.

[Outline of Invention]

As a result of various studies from this point of view, the present invention is based on magnetocrystalline anisotropy, and if a magnetic powder having a hexagonal uniaxial anisotropy particle size of 0.03 to 0.10 μ is used. , This type of magnetic powder has the advantage that the interaction between particles is extremely small and high orientation is exhibited even if the particle size is small, as compared with the magnetic powder based on the shape magnetic anisotropy, and It was found that a magnetic recording medium suitable for high-density recording can be obtained because the surface smoothness of the magnetic layer can be made sufficiently smooth even if it is oriented in the longitudinal direction of the magnetic layer. Characterized in that a hexagonal uniaxially anisotropic magnetic powder having a particle size of 0.03 to 0.10μ is contained in the magnetic layer, and the squareness of the magnetic layer in the longitudinal direction is 0.6 or more. Is.

In addition, this type of hexagonal magnetic powder particles is originally subjected to vertical magnetic field orientation so that the thin plate surface is parallel to the magnetic surface or mechanical orientation by utilizing its thin plate shape. Attempts have been made to improve the output in the short wavelength region by utilizing the perpendicular magnetization component of the magnetic recording medium. In such a vertically aligned magnetic recording medium, a high output in the short wavelength region is obtained. However, there is a big problem that the output is low in the long wavelength region, but there is a fatal problem that compatibility is not obtained because the reproduction output waveform is different from the longitudinal recording currently used for all magnetic recording media. there were. Therefore, in order to solve such a problem, the present invention completely changes the way of thinking from the conventional way of thinking like this,
It is said that thin plate-shaped particles are oriented so that the longitudinal direction of the magnetic recording medium is the easy magnetization direction, and this longitudinal direction can significantly improve the output in the long wavelength range while maintaining the output in the short wavelength range. It was made by discovering a fact that could not have been predicted in the past.

It is not clear why the output is significantly improved in such a wide frequency range, but the hexagonal magnetic powder particles have strong uniaxial anisotropy, so that the magnetization transition region during magnetic recording and reproduction is narrowed. Longitudinal orientation gives a higher rectangular shape in the longitudinal direction than that using conventional acicular magnetic powder, and because the particles are finer, the surface of the magnetic layer is even more than when acicular magnetic powder is longitudinally oriented. It is considered that this is because the smoothness is improved.

In this way, the present invention achieves high squareness and excellent surface smoothness by completely changing the idea from the conventional idea of vertically orienting thin plate-shaped hexagonal grains and by orienting longitudinally. It has achieved excellent high-density recording characteristics.

The magnetic powder having a hexagonal uniaxial anisotropy used in the present invention is a magnetic powder having a hexagonal crystal structure, such as Mn-Bi alloy magnetic powder, barium ferrite magnetic powder and metallic cobalt magnetic powder. Is used as the preferred one. This kind of magnetic powder having such a hexagonal crystal structure is generally in the shape of a thin plate, the easy magnetization direction is perpendicular to the thin plate surface, and has a large crystal magnetic anisotropy. For this reason, the interaction between particles is extremely small, and even if the particle diameter becomes small, high orientation is exhibited, and if this is oriented in the magnetic layer so that its easy axis of magnetization is in the longitudinal direction, good orientation is achieved. Improved rectangular shape in the longitudinal direction,
A magnetic recording medium suitable for high density recording can be obtained.

However, since it is a thin plate and the easy magnetization direction is perpendicular to the thin plate surface, if this kind of magnetic powder is oriented in the longitudinal direction of the horizontal magnetic layer, the thin plate stands on the magnetic layer surface and the particle diameter of the magnetic powder becomes If is not small, the surface smoothness of the magnetic layer will deteriorate,
Good high density recording cannot be performed. Therefore, the particle size is 0.10μ
The following are preferably used, and the smaller the particle size, the better the surface smoothness of the magnetic layer. However, if the particle size is smaller than 0.03μ, it becomes difficult to disperse it in the paint, and as a result, the squareness is reduced, so the particle size is 0.03μm.
It is preferable to use a magnetic powder having a particle size within the range of 0.10 μ to 0.10 μ, and even if the magnetic powder of this kind has a very small particle diameter, it does not agglomerate between magnetic powders like needle-shaped magnetic powders. The surface smoothness of the magnetic layer is improved rather than the case where the acicular magnetic powder is used.

In addition, this type of hexagonal magnetic powder having uniaxial anisotropy generally has a high coercive force because of its high crystal magnetic anisotropy, and the magnetic anisotropy based on this crystal magnetic anisotropy is Generally, since the temperature change is large, the coercive force has a large temperature dependence, and it is difficult to use it for ordinary magnetic recording media. Therefore, as the magnetic powder having hexagonal uniaxial anisotropy used in the present invention, a magnetic powder having suitable coercive force and temperature dependence of coercive force adjusted by introducing appropriate metal ions is used. The coercive force is preferably in the range of 500 to 1500 Oersted, and the temperature dependence of the coercive force is the rate of change of the coercive force at temperatures of 20 ° C and 100 ° C [Hc (100 ° C) -Hc (20 ° C). ] / Hc (2
It is preferable to use those whose temperature is 0 ° C.) and within ± 10%.

Such a hexagonal magnetic powder having uniaxial anisotropy is
When the magnetic coating prepared using this is applied and dried to form the magnetic layer, it is preferable that the horizontal magnetic layer is oriented so that the squareness in the longitudinal direction is 0.6 or more. If the mold is smaller than 0.6, good high density recording cannot be performed.

Thus, the particle size used in the present invention is 0.03-0.10μ.
The hexagonal magnetic powder having uniaxial anisotropy has a large crystal magnetic anisotropy, so that the interaction between particles is extremely small, and even if the particle size becomes small, high orientation is exhibited. Is extremely small, so that even if it is oriented in the magnetic layer so that its easy axis of magnetization is in the longitudinal direction, the surface smoothness of the magnetic layer is not deteriorated, but rather improved. Therefore, if this kind of magnetic powder is contained in the magnetic layer and the axis of easy magnetization is oriented in the longitudinal direction so that the squareness in the longitudinal direction is 0.6 or more, good surface smoothness and high density are achieved. A magnetic recording medium suitable for recording can be obtained.

To produce the magnetic recording medium of the present invention may be carried out according to a conventional method, for example, a magnetic powder having a particle size of 0.03 to 0.10μ having uniaxial anisotropy in the hexagonal system, a binder resin,
A magnetic coating material is prepared by mixing and dispersing it with an organic solvent or the like, and this is coated on a substrate such as polyester film by any coating means such as a roll coater, and then subjected to magnetic field orientation treatment in the longitudinal direction of the magnetic layer. The magnetic powder may be oriented so that the squareness of the magnetic layer in the longitudinal direction is 0.6 or more, and dried.

As the binder resin used here, widely used binder resins such as vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, fibrin resin, polyurethane resin, polyester resin, and isocyanate compound are widely used. To be

As the organic solvent, conventionally used organic solvents such as toluene, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran and ethyl acetate may be used alone or in combination of two or more.

In addition, various additives that are usually used, such as a dispersant, a lubricant, an abrasive, and an antistatic agent, may be optionally added to the magnetic paint.

〔Example〕

 Next, an embodiment of the present invention will be described.

Example 1 1 mol of ferric chloride, 1/8 mol of barium chloride and 1/10 mol of cobalt chloride were dissolved in 1 of water, and this mixed solution was added to 1 caustic soda aqueous solution in which 5 mol of caustic soda was dissolved. It was stirred. The suspension is then left for 1 day and the precipitate is placed in an autoclave at 300 ° C.
It was made to react by heating for 4 hours. The reaction product was washed with water, dehydrated and dried, and then heat-treated in air at 800 ° C. for 2 hours to obtain barium ferrite magnetic powder. The obtained barium ferrite magnetic powder has a hexagonal plate shape, the particle size is 0.08 μ, the coercive force is 1220 Oersted, and the saturation magnetization is 54.5 emu.
/ G, the square type was 0.44.

Using the hexagonal barium ferrite magnetic powder thus obtained, 800 parts by weight of barium ferrite magnetic powder VAGH (manufactured by UCC, USA, 110 cc vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Pandex T- 5250 (Dainichi 70〃 Hon Ink Chemical Co., Ltd., urethane elastomer) Coronate L (Nippon Polyurethane 20〃 Kogyo Co., trifunctional low molecular weight isocyanate compound) Stearic acid-n-butyl 8〃 Methyl isobutyl ketone 504〃 Toluene 504 A magnetic coating material was prepared by mixing and dispersing the composition having the above composition in a ball mill for 48 hours. Apply this magnetic paint to a thickness of 12
It was coated on a polyester base film having a thickness of .mu. Then, the magnetic layer was surface-treated and then cut into a predetermined width to prepare a magnetic tape.

Example 2 In the synthesis of the barium ferrite magnetic powder in Example 1, the addition amount of ferric chloride was kept constant at 1 mol, and the addition amount of barium chloride was variously changed from 1/4 mol to 1/12 mol, Addition amount of cobalt chloride from 1/4 mol to 1
Particle diameters of 0.02μ to 0.2μ were synthesized in the same manner as in Example 1 except that the content was variously changed to / 20 mol, and a large number of magnetic tapes were prepared using these barium ferrite magnetic powders having different particle diameters. Made.

Comparative Example 1 In the composition of the magnetic coating material of Example 1, the barium ferrite magnetic powder was replaced with a particle size of 0.02 μ to 0.2 μ, an axial ratio of 3 to 10, and various particle sizes of γ−.
A large number of magnetic tapes were produced in the same manner as in Example 1 except that Fe ₂ O ₃ powder was used.

Comparative Example 2 The same as Example 1 except that a magnetic field was applied in the direction perpendicular to the polyester base film instead of applying the magnetic field in the running direction of the polyester base film to perform the alignment treatment in Example 1. I made a magnetic tape in the same way.

For the magnetic tapes obtained in Examples 1 and 2 and Comparative Example 1, the squareness and surface roughness in the tape longitudinal direction were measured. As for the surface roughness, the center line average roughness was measured at a cutoff of 0.08 mm using a stylus type surface roughness meter manufactured by Tokyo Seiki Co., Ltd. Further, with respect to the magnetic tapes obtained in Example 1 and Comparative Examples 1 and 2, the frequency dependence of reproduction output was examined by using a sendust head having a gap length of 0.2 μm.

FIG. 1 shows the relationship between the center line average roughness measured in this way and the particle size of the magnetic powder used. Graph A shows the magnetic tapes obtained in Examples 1 and 2. B shows the magnetic tape obtained in Comparative Example 1.

FIG. 2 shows the relationship between the rectangular shape in the longitudinal direction measured as described above and the particle size of the magnetic powder used. Graph A shows the magnetic tapes obtained in Examples 1 and 2. The graph B shows the magnetic tape obtained in Comparative Example 1.

Further, FIG. 3 shows the wavelength dependence of the output of the magnetic tapes of Example 1 and Comparative Examples 1 and 2, Graph A shows the magnetic tape obtained in Example 1, and Graph B shows the comparative example. The magnetic tape obtained in 1 is shown. Graph C shows the magnetic tape obtained in Comparative Example 2.

〔The invention's effect〕

As is clear from FIGS. 1 and 2, the particle size is 0.03
The magnetic tape obtained by using ~ 0.10μ barium ferride magnetic powder is far more rectangular in the longitudinal direction than the magnetic tape obtained by using needle-shaped γ-Fe ₂ O ₃ powder. The surface roughness is almost the same, and it becomes smaller as the particle size becomes smaller. Further, as is clear from FIG. 3, the magnetic tape obtained in Example 1 has a high output over a wide frequency range from low to high, as compared with the magnetic tapes obtained in Comparative Examples 1 and 2. Therefore, according to the present invention, a magnetic layer having a high longitudinal rectangularity and excellent surface smoothness is formed, and a high output is obtained over a wide frequency range from a low range to a high range. It can be seen that a magnetic recording medium suitable for density recording can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the center line average roughness of the magnetic tape obtained by the present invention and the particle diameter of the magnetic powder used, and FIG. 2 is a longitudinal rectangular shape of the magnetic tape obtained by the present invention. FIG. 3 is a diagram showing the relationship with the particle size of the magnetic powder used, and FIG. 3 is a diagram showing the frequency dependence of the reproduction output of the magnetic tape obtained by the present invention.

Claims (1)

[Claims] 1. A particle size of hexagonal system having uniaxial anisotropy is 0.
A magnetic recording medium, characterized in that a magnetic powder having a particle size of 03 to 0.10 μ is contained in the magnetic layer, and the squareness of the magnetic layer in the longitudinal direction is 0.6 or more.