JPH01251423A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the mechanical strength of a magnetic recording layer and to enhance the durability thereof by dispersing carbon whiskers into the recording layer. CONSTITUTION:The magnetic recording layer contg. magnetic powder (A) and resin binder is formed on the above medium and the carbon whiskers (B) are dispersed in the recording layer. The whiskers having the minor axis and major axis in a desired range are usable in the component B at a prescribed ratio (e.g.: 0.5-15pts.wt. per 100pts.wt. component A). The uniaxially anisotropic hexagonal ferrite powder expressed by the formula, etc., are usable for the component A. In the formula, A denotes >=1 kinds among Ba, Sr, Pb, and Ca and (n) denotes 5-6. The compd. in which a part of Fe is substd. with Ti, Co, Zn, In, etc., is usable as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium with excellent electromagnetic properties and durability.

(Prior Art) Tape-shaped or disk-shaped magnetic recording media used in various fields such as audio, video, and computer applications consist of magnetic powder on a support base made of polyethylene terephthalate or the like. It is known that a magnetic layer, that is, a recording layer, is formed by uniformly applying a magnetic paint consisting of a resin binder, a dispersion medium, and various additives. The magnetic layer in such a magnetic recording medium is required not only to have excellent electromagnetic properties but also to have durability against destruction due to friction with the magnetic head.

For this reason, conventionally, Al2O3 powder, 5j02
It has been attempted to improve the strength of the coating film by dispersing inorganic fillers such as powder and Cr203 powder. These inorganic fillers have generally been powders that have a nearly spherical shape and have a size equivalent to the thickness of the magnetic layer.

Incidentally, in recent years, there has been a demand for higher recording density in magnetic recording media, and the particle size of magnetic powder tends to become finer. For this reason, it has become necessary to make the inorganic filler added to the magnetic paint into fine particles. However, by making the inorganic filler into fine particles in this way, the reinforcing effect of the coating film is impaired, and there is a problem of decreased durability due to insufficient coating film strength. In addition, in order to obtain sufficient coating strength with finely divided inorganic fillers, the amount added must be considerably increased, and in this case, the ratio of magnetic powder in the magnetic layer decreases, resulting in electromagnetic properties. or deteriorate.

To solve this problem, in order to achieve high-density recording, magnetic powders such as hexagonal ferrite powders that have a plate-like crystal structure and whose axis of easy magnetization is perpendicular to the plate surface are used. This is particularly noticeable in perpendicular magnetization type recording media that use magnetization in a direction perpendicular to the surface of the recording medium.

This is because the magnetic powder used is fine particles with a particle size of 0.2 μm or less.

For these reasons, instead of spherical inorganic fillers, silicon carbide or silicon nitride whiskers are dispersed in the magnetic layer.
A method for efficiently obtaining the reinforcing effect of the magnetic layer has been proposed (Japanese Patent Application Laid-open No. 80620/1983).

(Problem to be solved by the invention) However, since silicon carbide and silicon nitride cannot be expected to have much electrical conductivity, it is necessary to separately add a conductive substance such as carbon to ensure the electrical conductivity of the coating film. Sign. In this case, the addition of the conductive substance lowers the ratio of magnetic powder in the magnetic layer, similarly to the addition of the spherical inorganic filler described above, resulting in a decline in electromagnetic properties, particularly output properties. Furthermore, the silicon carbide whiskers and silicon nitride whiskers themselves have almost no lubricity, so if these whiskers exist on the surface of the magnetic layer, problems such as an increase in the coefficient of friction and wear on the head surface will occur. .

The present invention has been made to address the problems of the prior art, and even when using fine magnetic powder, the magnetic recording layer can be improved without impairing the electromagnetic properties and lubricity of the magnetic recording layer. The object of the present invention is to provide a magnetic recording medium with increased durability by improving the mechanical strength of the magnetic recording medium.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a magnetic recording medium in which a magnetic recording layer containing at least a magnetic powder and a resin binder is formed on a support substrate. It is characterized by carbon whiskers dispersed in the recording layer.

The carbon whiskers used in the present invention vary depending on the type and particle size of the magnetic powder used, but the short axis is approximately in the range of 0.01μI11 to 0.2μm, and the long axis is 0.
．． It is preferable to use one having a size in the range of 5 μm to 20 μm.

The amount of carbon whiskers added is preferably in the range of 0.5 to 15 parts by weight per 100 parts by weight of the magnetic powder in the magnetic recording medium. The amount of carbon whisker added is 0.5
If it is less than 15 parts by weight, not only will it not be possible to expect much of an effect on improving durability, but also sufficient conductivity will not be ensured.If it is added in excess of 15 parts by weight, not only will no further effect be expected, but the ratio of magnetic powder will be too high. and the electromagnetic properties deteriorate.

As the magnetic powder in the present invention, acicular iron oxide powders such as γ-Fe203 and Co-γ-Pe203, and metal powders such as CrO2 and Fe-Co may be used, but in particular, for example, general formula % formula %) ( In the formula, A represents at least one element selected from Ba, Sr, and PbSCa, and n represents a number from 5 to 6. However, a part of Fe is Ti5CoSZnSIn, Mn5C
uSGe, Nb.

One or two metals such as Zr, V, AI, Sn, etc.
More than one species may be substituted. ) is suitable when using a uniaxially anisotropic hexagonal ferrite powder. These hexagonal ferrite powders have a coercive force (
ie) adjusted to a range of 2000 e to 40000 e is preferable as a magnetic powder for a perpendicular magnetization type magnetic recording medium capable of high-density recording, and its shape has a particle size in a range of 0.005 μm to 0.3 μm. and the plate ratio is 1 to 1
A range of 5 is preferred.

The magnetic recording medium of the present invention is manufactured, for example, as follows.

That is, first, magnetic powder and carbon whiskers as described above are dispersed in a resin binder together with a dispersant such as lecithin to prepare a magnetic coating, and after coating this on the surface of a supporting substrate, an alignment treatment is performed. It can be easily prepared by drying or the like.

As the resin binder for producing the above-mentioned magnetic paint, it is possible to use various conventionally used and well-known resin binders, such as polyurethane resins, polyester resins, phenol resins, epoxy resins, Examples include vinyl chloride resin. In addition, various additives such as anionic and cationic surfactants, lubricants such as lauric acid, palmitic acid, and stearic acid, and abrasives such as alumina powder and chromium oxide powder are added to the magnetic paint. All can be used together.

In addition, as supporting substrates used in the present invention, various &1
It is possible to use various known materials used as bases for tapes, floppy disks, etc. For example, polyester film is used as a tape base, and polyester sheet or aluminum substrate is used as a floppy disk base. Ru.

(Function) In the magnetic recording medium of the present invention, carbon whiskers are dispersed in the magnetic recording layer, and the acicular structure of the carbon whiskers greatly improves the mechanical strength of the magnetic recording layer and improves durability. It is elevated. In addition, this carbon whisker can be used in place of carbon powder, which has traditionally been used to ensure conductivity, to ensure conductivity and durability without reducing the ratio of magnetic powder in the magnetic recording layer. It works both to improve.

Furthermore, since carbon whiskers themselves have lubricating properties, even if they exist on the surface of the magnetic recording layer, they do not increase the coefficient of friction and prevent the surface of the magnetic head from being abraded. You can

(Example) Next, examples of the present invention will be described.

Example Co-T I-substituted Ba ferrite powder 100 parts by weight (average particle size 0.08 μm, lie 7000e
) Salt-vinyl acetate copolymer resin 1071 Polyurethane resin IO//Carbon whisker 2 (Average short axis 0.05μ
m, average long axis 5μm) Alumina powder
4 (average particle size 0.3 μl + 1) Lecithin 3 Stearic acid o, t ll n-butyl stearate 0, 1 methyl ethyl ketone 80 cyclohexane
80 g) Iyl: /gQ // First, the carbon whiskers and alumina powder are removed from the above-mentioned composition and thoroughly kneaded with a sand grinder, and the carbon whiskers and alumina powder are added thereto. The magnetic paint was prepared by uniformly dispersing it. Next, after filtering this magnetic paint, 3 parts by weight of an isocyanate compound as a hardening agent was added and kneaded, and the thickness was 75 mm.
A magnetic recording medium was obtained by coating both sides of a μm polyethylene tereuterate film to a dry thickness of 2.5 μm, drying and curing, and further calendering to form a magnetic recording layer. .

The thus obtained magnetic recording medium was punched out into a disk shape with a diameter of 90+ nm to produce a magnetic disk, and a durability test and a surface resistance measurement were performed. In the durability test, the magnetic disk was loaded into a recording/reproducing device, and the magnetic head was brought into sliding contact with the pad at a pressure of 40 g/ci, and the durability test was evaluated based on the number of revolutions until the reproduction output reached 70% of the initial output. As a result, the magnetic disk showed good results in the durability test BXIO' times and the surface resistance of 1×10 6 Ω/hole.

On the other hand, for comparison with the present invention, a magnetic disk was manufactured under the same conditions as in the above example except that carbon whiskers were not added, and a durability test and surface resistance measurement were performed in the same manner as in the above example. The durability test was 4X 106 times and the surface resistance was 8XlO'2/
It was the mouth.

Furthermore, magnetic disks were manufactured under the same conditions as in the above examples except that the amount of carbon whiskers added was varied, and durability tests and surface resistance measurements were conducted in the same manner as in the above examples. The results are shown in FIG.

As is clear from the figure, adding carbon whiskers to the magnetic recording layer improves durability, lowers surface resistance, and improves conductivity. Also,
Carbon whiskers have a surface resistance of 1, which is required for practical purposes.
×108Ω/From the point of view of satisfying the mouth,
It was found that the effective range is 0.5 parts by weight or more per 100 parts by weight of magnetic powder, and by adding 0.5 parts by weight or more, durability can be ensured at LX 10' times, which is suitable for general practical use. Durability is obtained. In addition, these characteristics hardly change even if more than 15 parts by weight of carbon whiskers are added, and they settle down to almost constant values, and as the amount of carbon whiskers added increases, the magnetic powder in the magnetic recording layer It can be seen that the effective range is 15 parts by weight or less, since the proportion thereof decreases and the electromagnetic properties deteriorate.

[Effects of the Invention] As is clear from the above examples, the magnetic recording medium of the present invention improves the mechanical strength of the magnetic recording layer without impairing the electromagnetic properties or conductivity of the magnetic recording layer. This makes it possible to obtain excellent durability and to minimize the occurrence of increases in the coefficient of friction and wear of the magnetic head. Therefore, it is possible to provide a magnetic recording medium that exhibits excellent electromagnetic properties and helad touch while satisfying durability.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of carbon whiskers added to the magnetic powder in the magnetic recording layer and the durability and surface resistance in Examples of the present invention. Applicant Toshiba Corporation Representative Patent Attorney Sasa Suyama −

Claims (1)

[Claims] (1) A magnetic recording medium comprising a magnetic recording layer containing at least magnetic powder and a resin binder formed on a supporting substrate, characterized in that carbon whiskers are dispersed in the magnetic recording layer. recoding media.