JPS59129935A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve low frequency and high frequency recording and reproducing by forming successively a layer wherein magnetic powder having uniaxial anisotropy is oriented in a horizontal direction and a layer which is of a plate shape and contains barrium ferrite magnetic powder having the axis of easy magnetization perpendicular to the plate surface oriented perpendicularly to the magnetic layer on a base material. CONSTITUTION:A coated magnetic layer contg. magnetic powder such as gamma- Fe2O3, Co-contg. gamma-Fe2O3 or the like having uniaxial anisotropy is formed on a base material by orienting the magnetic powder in a horizontal direction. A magnetic layer wherein barrium ferrite magnetic powder, expressed by BaO. 6Fe2O3 or a hexagonal system plate substd. in a part of Ba and Fe with Ti, Cr, Co, etc. having the axis of easy magnetization perpendicular to the plate surface is oriented in the axis of easy magnetization in the direction perpendicular to the magnetic layer is formed on said layer. The thickness of the upper magnetic layer is made thinner than the lower magnetic layer. A medium which yields a substantial output in a low frequency range as well and is excellent in both low frequency and high frequency recording and reproducing is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having a two-layer magnetic layer structure, and its purpose is to provide high output in low frequency and high frequency bands and to be able to perform both long-wavelength recording and high-density recording well. The objective is to provide a magnetic recording medium that can perform

Generally, the magnetic properties of magnetic recording media such as magnetic tapes are improved by orienting the acicular magnetic powder in the magnetic layer in the longitudinal direction. Although these devices can provide high output in the low frequency band, they have a limit in density recording, and it is extremely difficult to record in the short wavelength region where the recording wavelength is 1°θμ or less.

Therefore, in recent years, as a magnetic recording medium suitable for high-density recording, barium ferrite magnetic powder, which is plate-shaped and has an axis of easy magnetization perpendicular to the substrate, has been used. A magnetic recording medium that is oriented perpendicular to the magnetic layer has been proposed, but this type of magnetic recording medium has the drawback that although it can obtain high output in the high frequency band, it cannot obtain high output in the low frequency band. There is.

In view of the current situation, the inventors conducted 441 (results of various studies) and found that the magnetic layer formed on the substrate has a two-layer structure, and the first magnetic layer, which is the lower layer, contains magnetic powder having 111111 anisotropy. The second magnetic layer serving as the upper layer contains barium ferrite magnetic powder that is plate-shaped and has an axis of easy magnetization perpendicular to the direction, so that the direction of easy magnetization is magnetic. When the orientation is perpendicular to the layer, the output in the low frequency band is sufficiently improved by the first magnetic layer in the lower layer, and the output in the high frequency band is sufficiently improved by the second magnetic layer in the upper layer. It was discovered that a magnetic recording medium capable of performing improved long-frequency recording and high-density recording could be obtained, and the present invention was completed.

In this invention, the second magnetic layer, which is the upper layer, is in the form of a plate made of 60,000-crystalline thread and has an axis of easy magnetization perpendicular to the plane of the plate, in order to effectively utilize the perpendicular magnetization component suitable for high-density recording. It is preferable to use a barium ferrite magnetic powder having the chemical formula B, and to orient the barium ferrite magnetic powder so that the direction of easy magnetization thereof is perpendicular to the magnetic layer.
In addition to what is represented by a0.6 Fe 203, some of Ba and Fe in this chemical formula are TiXCr-, C0XZn
Any barium ferrite magnetic powder substituted with a metal such as 5 Ins Mn5CuXGes Nb is preferably used. In addition, the barium ferrite magnetic powder used preferably has a particle size of 0.3μ or less, and if such fine particles are used in the form of a plate, the perpendicular magnetization component is fully utilized, and the surface of the magnetic layer is The smoothness is improved, noise is sufficiently reduced, and high-density recording can be performed satisfactorily.

In addition, in order to sufficiently improve the output in the low frequency band and perform long wavelength recording, the first magnetic layer, which is the lower layer, uses magnetic powder with -axis anisotropy, and It is preferable to orient the layer in the horizontal direction, and examples of magnetic powder having such -axis anisotropy include γ-
Fe2o3 powder, Fe3O4 powder, Co-containing -Fe2
o3 powder, Co-containing Fe3O4 powder, CrO2 powder,
Fe powder, Co powder, Fe-Ni powder, etc. are preferably used.

The thickness of both the upper and lower magnetic layers is preferably such that the upper magnetic layer is thinner than the lower magnetic layer; if the upper magnetic layer is made too thick, sufficient output cannot be obtained in the low frequency band.

The first magnetic layer is formed according to a conventional method. For example, a magnetic paint containing a magnetic powder having -axis anisotropy, a binder resin, an organic solvent, and other additives is coated on a substrate such as a polyester film. is applied by any coating means such as a roll coater, subjected to horizontal orientation treatment, and dried.

The second magnetic layer is made of a magnetic paint containing barium ferrite magnetic powder, a binder resin, an organic solvent, and other additives, which is plate-shaped and has an axis of easy magnetization perpendicular to the surface.
Coating the barium ferrite magnetic powder onto the first magnetic layer using any coating means such as a roll coater, and performing a vertical orientation treatment so that the direction of easy magnetization of the barium ferrite magnetic powder is perpendicular to the magnetic layer; Formed by drying.

The binder resins used in both the upper and lower magnetic layers include conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, polyurethane resins, cellulose resins, and isocyanate compounds. is widely used.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethyl formamide, etc. are used alone or in combination of two or more.

Additionally, various additives commonly used in magnetic paints, such as dispersants, lubricants, abrasives, antistatic agents, etc., may be optionally used.

Next, embodiments of the invention will be described.

Example 1 <Magnetic paint for lower layer made by W11> Uniaxial anisotropic Co-containing γ-F e 203 8007
8 ut part magnetic powder (particle size (long axis) 0.4μ, axial ratio (long axis/short axis) 8, coercive force 1250 oersted) Nitrocellulose H1/2 80 1/(
Takelac E-551 (manufactured by Shikasei Co., Ltd., nitrocellulose) Takelac E-551 (manufactured by Kogyo Co., Ltd., 90 (manufactured by Kogyo Co., Ltd., urethane prepolymer) Coronate L (manufactured by Nippon Polyurethane Co., Ltd. 30 (manufactured by Nashisha Co., Ltd., trifunctional low molecular weight isocyanate compound) Methyl isobutyl ketone 700 Toluene 700 This composition was mixed and dispersed in a ball mill for about 90 hours to prepare a magnetic paint for the lower layer. ' Preparation of magnetic paint for upper layer> Barium ferrite magnetic powder 750 parts (particle diameter (major axis) 0°3μ, thickness 0.03μ, coercive force 1350 oersted) VAGH (manufactured by U, C, C, USA, chloride) 125 〃Vinyl-vinyl acetate-vinyl alcohol copolymer) Pandex]' -5250100// (manufactured by Daih Hon Ink Co., Ltd., urethane elastomer) Coro*-) L (Nippon polyurethane) 25 〃manufactured by a certain company, trifunctional low molecular weight Ht isocyanate Compounds) n-Butyl stearate 15 Methyl ethyl ketone 600 Toluene 600 This composition was mixed and dispersed in a ball mill for about 90 hours to prepare a magnetic paint for the lower layer.

<Manufacture of double layered magnetic tape> The above-mentioned magnetic paint for the lower layer is applied onto a polyester base film of 11 mm and 1.2 μm, and an opposing magnetic field is applied to the surface of the base film to perform a horizontal orientation treatment. Dry-C
A first magnetic layer was formed as a lower layer with a dry thickness of 3°0μ. Next, the above-mentioned magnetic paint for the upper layer is applied on top of this magnetic layer, and a magnetic field is applied in a direction perpendicular to the base film using an N-S magnet, subjected to vertical orientation treatment, and dried to obtain a dry thickness. A second magnetic layer was formed as an upper layer with a thickness of 1.0 μm. Thereafter, it was cut to a predetermined width to produce a double layer magnetic tape. The longitudinal coercive force of the first magnetic layer of the obtained double-layer magnetic tape was 1270 Oersteds, the longitudinal coercive force of the entire tape was 1100 Oersteds, and the perpendicular coercive force was 900 Oersteds.

The saturation residual magnetic flux density of the first magnetic layer was 2100 Gauss, and the saturation residual magnetic flux density of the entire tape was 2050 Gauss. Furthermore, the square shape of the first magnetic layer in the longitudinal direction is 0.81
The squareness of the entire tape in the longitudinal direction was 0.72, and the squareness in the vertical direction was 0.60°.

Example 2 In the composition of the magnetic paint for the lower layer in Example 1, instead of the -axis anisotropic Co-containing γ-Fe203 magnetic powder, the particle size (long axis) was 0.3μ and the axial ratio (long axis/short axis) 10, Coercive force 1
The same amount of uniaxially anisotropic metal iron magnetic powder of 400 oersteds was used, and in the composition of the upper layer magnetic coating, barium ferrite magnetic powder with a particle size (major axis) of 0.3μ, thickness of 0.03μ, and coercive force of 1350 oersteds was used. Instead of, particle size (
A double-layer magnetic tape was prepared in the same manner as in Example 1, except that the same amount of barium ferrite magnetic powder having a major axis) of 0.2 μm, a thickness of 0°02 μm, and a coercive force of 1450 oersted was used.

The coercive force in the longitudinal direction of the first magnetic layer of the obtained double-layer magnetic tape was 1450 Oersteds, the coercive force in the longitudinal direction of the entire tape was 1250 Oersteds, and the coercive force in the perpendicular direction was 950 Oersteds. The saturation residual magnetic flux density of the first magnetic layer was 2800 Gauss, and the saturation residual magnetic flux density of the entire tape was 2550 Gauss. Further, the squareness of the first magnetic layer in the longitudinal direction was 0680, the squareness of the entire tape in the longitudinal direction was 0°72, and the squareness in the vertical direction was 0.58.

Comparative Example 1 In Example 1, the structure of the upper second magnetic layer was omitted,
A magnetic tape was produced in the same manner as in Example 1 except that the thickness of the lower first magnetic layer was changed from 3.0 μm to 4.0 μm. The longitudinal coercive force of the obtained magnetic tape was 1270
Ersted, the saturation residual magnetic flux density is 2100 Gauss,
The squareness in the longitudinal direction was 0.81.

Comparative Example 2 In Example 1, the formation of the lower first magnetic layer was omitted,
The thickness of the upper second magnetic layer 19a is 1.0μ to 4.0μ.
A magnetic tape was made in the same manner as in Example 1 except that the following was changed. The vertical coercive force of the obtained magnetic tape is 1
It was 380 Oersted, the saturation residual magnetic east density was 1900 Gauss, and the vertical square shape was O, SO.

The maximum output level (M.0°L) at various recording wavelengths for the magnetic tapes obtained in each example and each comparative example.
was measured.

The table below shows the results.

As is clear from the above table, the magnetic tapes obtained by the present invention (Examples 1 and 2) have a higher maximum output level than the conventional magnetic tapes (Comparative Examples 1 and 2) in all frequency bands; It can be seen from the above that the magnetic recording medium obtained according to the present invention can obtain high output in all frequency bands, and can perform both long wavelength recording and high density recording well.

Claims (1)

[Claims] 1. Form a first magnetic layer containing magnetic powder having -axis anisotropy and oriented in the horizontal direction on the substrate, and then form a plate-shaped magnetic layer that is easily magnetized in the direction perpendicular to the surface. A second layer containing barium ferrite magnetic powder having an axis and oriented so that the direction of easy magnetization is perpendicular to the magnetic layer.
A magnetic recording medium characterized by having a multilayered magnetic layer of