JPS59167854A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the recording characteristic within a high density range by including metallic magnetic powder having a prescribed characteristic into a magnetic layer and applying orientation so as to attain >=1,000 gauss of vertical residual magnetic flux density. CONSTITUTION:As the metallic magnetic powder, powder having uniaxial anisotropy, needle shape and <=0.4mu of grain diameter is used. When the grain diameter is larger than 0.4mu, the surface smoothness of a magnetic tape is deteriorated and a short wavelength output is deteriorated. The powder like this is coated on the base by an optional means such as roll coater or gravure coating together with a binder resin and the base is dried while being orientated vertically by using a rod magnet with a magnetic field in vertical direction to the base. Then, the vertical residual mangetic flux density of the magnetic layer thus obtained is taken as >=1,000 gauss.

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 particularly suitable for high-density recording.

In general, magnetic recording media such as magnetic tape have improved magnetic properties by orienting acicular magnetic powder in the magnetic layer in the longitudinal direction of the magnetic tape, and when high performance is required, Metal magnetic powder is used, which has a much higher coercive force than iron oxide magnetic powder and the like, and allows high-density recording to be performed relatively well.

However, in the case where the acicular magnetic powder is oriented in the longitudinal direction, even if metal magnetic powder with a high coercive force is used, there is a limit to the improvement in recording density because magnetization is used in the longitudinal direction. As the signal recording density increases, the demagnetizing field within the magnetic recording medium increases, causing attenuation and rotation of residual magnetization, making it difficult to detect recorded signals. Therefore, conventional magnetic recording media, even those using metal magnetic powder, have problems such as not being able to perform high-density recording sufficiently and not being able to perform short-wavelength recording with a recording wavelength of 1 μm or less.

In view of the above circumstances, the inventor conducted various studies and found that
As the magnetic powder contained in the magnetic layer, an acicular magnetic metal powder having -axis anisotropy and a particle size of 0.4 μ or less is used,
When the magnetic layer containing this metal magnetic powder is oriented so that the residual magnetic flux density in the perpendicular direction is 1000 Gauss or more, the perpendicular magnetization of the magnetic layer becomes sufficiently good and the recording characteristics in the high density range are sufficiently improved. However, it was discovered that a magnetic recording medium capable of sufficiently performing short wavelength recording with a recording wavelength of 1 μm or less can be obtained, and the present invention was completed.

The metal magnetic powder used in this invention is preferably a metal magnetic powder that has -axis anisotropy, is acicular and has a particle size of 0.4 μ or less, and has a particle size larger than 0.4 μ. The surface smoothness of the magnetic tape deteriorates, and the short wavelength output decreases.

It is acicular with such -axis anisotropy and has a particle size of 0.4μ.
The following metal magnetic powders are coated on a substrate with a binder resin etc. by any means such as a roll coater or gravure coating, and then applied in a vertical direction using a magnetic field perpendicular to the substrate using a bar magnet, horse-shaped magnet, etc. Dry while orienting to
It is preferable that the residual magnetic flux density in the vertical direction of the obtained magnetic layer is 1000 Gauss or more, and if the residual magnetic flux density in the vertical direction is smaller than 1000 Gauss, a sufficiently high output cannot be obtained in the short wavelength region.

In this way, the metal magnetic powder is coated on the substrate in a vertically oriented manner along with a binder resin, an organic solvent, and other necessary components, and dried to form a magnetic layer, and the vertical residual of the magnetic layer is removed. When the magnetic flux density is 1000 Gauss or more, perpendicular magnetization becomes sufficiently good, recording characteristics in a high density range are improved, and a magnetic recording medium capable of sufficiently performing short wavelength recording with a recording wavelength of 1 μm or less can be obtained.

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

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

In addition, process additives normally 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 The metal magnetic powder used was an acicular powder having -axis anisotropy, a particle size of 0.4μ, and an axial ratio of 10.
) is 1120 oersted, and the saturation magnetization (σS) is 14
Using metal iron magnetic powder with 0 emu/g- and square shape (σr/σS) of 0.49, 750 parts by weight of Fe magnetic powder VAGH
(Manufactured by U, C, C, USA, salt 125 vinylide-vinyl acetate-vinyl alcohol copolymer) Bandex T5250 (Oguchi 100 manufactured by Hon Ink Co., Ltd., urethane elastomer) Coronate L (Nippon Polyurethane 25 Ink Co., Ltd.) Made by
Trifunctional low molecular weight isocyanate compound) n-butyl stearate 15〃Methyl isobutyl ketone 600〃Toluene
A magnetic coating material was prepared by mixing and dispersing a composition having a composition of 600% in a ball mill for 3 days. This magnetic paint was applied with a gravure roll onto a polyester base film with a thickness of 12 μm, the paint was temporarily retained by applying a magnetic field to smooth the paint film, and then the paint was run through opposing magnetic fields of different polarities. The magnetic layer was subjected to vertical alignment treatment and dried to form a magnetic layer having a dry thickness of 3 μm. Next, the formed magnetic layer was subjected to surface treatment, and then cut to a predetermined width to produce a magnetic tape.

Example 2 In Example 1, in place of the metal iron magnetic powder used in Example 1, a coercive force (Hc
) 1070 oersted, saturation magnetization (σS) 140
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of uniaxially anisotropic metal iron magnetic powder having an acicular shape of emu/g and a square shape (σr/σs) of 0.49 was used.

Example 3 In Example 1, instead of the metal magnetic powder used in Example 1, a particle size of 0.25μ, an axial ratio of 7, and a coercive force (Hc) were used.
1300 oersted, saturation magnetization (σS) 135em
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of metal iron magnetic powder having acicular uniaxial anisotropy of u/g and square shape (σr/σs) of 0.4'l was used.

Comparative Example 1 Using the same metal iron magnetic powder as used in Example 1,
A magnetic tape was produced in the same manner as in Example 1, except that instead of applying the magnetic powder in a non-oriented manner in Example 1, the coating was applied with a gravure roll and then a plastic sheet was brought into contact with the coating to smooth the surface.

Comparative Example 2 Using the same metal iron magnetic powder as used in Example 1,
Instead of the orientation treatment of the magnetic powder in Example 1, the orientation treatment was performed by applying a 3000 Gauss opposing magnetic field in the longitudinal direction of the base film using a pair of bar magnets placed on both the front and back surfaces of the base film. A magnetic tape was made in the same manner as in Example 1.

For the magnetic tapes obtained in each example and each comparative example, longitudinal coercive force (Hc), residual magnetic flux density (Br)
, maximum magnetic flux density (Bs), square shape (Br/Bs) and perpendicular coercive force (Hc), residual magnetic flux density (Br) and square shape (Br/Bs) were measured, and the orientation ratio (vertical corner shape) was measured. The shape/longitudinal square shape) was measured. The maximum output levels (M, O, L) at various recording wavelengths were also measured.

The table below shows the results.

As is clear from the above table, the magnetic tapes obtained by the present invention (Examples 1 to 3) are different from the conventional magnetic tapes (Comparative Examples 1 to 2).
), they all have a larger coercive force in the vertical direction, a larger residual magnetic flux density, a larger square shape, and a thicker orientation ratio. It can be seen that the magnetic recording medium produced by the present invention has good perpendicular magnetization and is excellent in high-density recording.

Claims (1)

[Claims] 1. A magnetic layer contains acicular magnetic metal powder with a -axis anisotropy and a particle size of 0.4μ or less, and is oriented so that the residual magnetic flux density in the vertical direction is 1000 Gauss or more. magnetic recording medium