JPH06131654A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To maintain excellent electromagnetic transducing characteristics as well as to reduce surface electric resistance by using electric conductive powder prepd. by mixing spherical electric conductive powder with acicular electric conductive powder as an antistatic agent in a magnetic layer. CONSTITUTION:When a magnetic layer contg. a ferromagnetic substance and electric conductive powder dispersed in a binder is formed on at least one principal face of a substrate to obtain a magnetic recording medium, a mixture of spherical electric conductive powder with acicular electric conductive powder is used as the above-mentioned electric conductive powder. Since a smaller amt. of this mixture added ensures easier control of electric conductivity with no anisotropy as compared with simple electric conductive powder, the amt. of the ferromagnetic substance filled into the magnetic layer can be increased and the objective magnetic recording medium optimum for high density recording can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a magnetic layer formed on a support.

[0002]

2. Description of the Related Art Magnetic recording media are roughly classified into those formed by a coating technique and those formed by a vacuum technique according to their manufacturing methods. Among them, the magnetic recording medium using the coating technique is excellent in productivity and can be manufactured at low cost. Therefore, the magnetic recording medium represented by the magnetic tape or the floppy disk is mainly formed by using the coating technique. There is.

Such a magnetic recording medium is generally PET.
A (polyethylene terephthalate) film or other support is coated with a magnetic coating material in which magnetic powder is dispersed in a binder resin to form a magnetic layer.

[0004]

By the way, the conventional magnetic recording medium is intended to prevent foreign matter such as dust from being charged and attached due to charging on the surface of the magnetic layer caused by sliding between the magnetic layer and the magnetic head. The surface resistance of the magnetic layer is 10 ⁶ -10
⁹ Efforts were made to make it about Ω.

If the magnetic layer does not have a certain degree of conductivity, foreign matter such as dust easily adheres to the surface of the magnetic layer, which causes dropout. Also, the charging of the surface of the magnetic layer may cause noise during the discharging.

Therefore, as a method for reducing the surface resistance of the magnetic layer, conductive powder such as carbon black is mixed as an antistatic agent in the magnetic layer. However, since the spherical conductive powder such as carbon black ensures the conductivity of the magnetic layer only after being arranged in a chain,
It needs to be added sufficiently to the magnetic layer. However, the spherical conductive powder has a drawback that not only the reproduction output of the magnetic recording medium is lowered depending on the added amount but also the squareness ratio (residual magnetization / saturation magnetization) of the magnetic layer is deteriorated. It was

In particular, oxide ferromagnets typified by Balihum ferrite have extremely low electric conductivity, and
At the sacrifice of the reproduction output or the squareness ratio, there was no choice but to add a larger amount of antistatic agent than usual magnetic powder.

[0008] Further, conventionally, it has been reported that a high effect can be obtained by mixing and using two kinds of spherical conductive powders having different particle diameters, but it is still not sufficient. Therefore, conventionally, at least one of conductivity and electromagnetic conversion characteristics of the magnetic layer has to be sacrificed.

The present invention has been made in view of the above technical problems, and provides a magnetic recording medium having excellent conductivity while sufficiently maintaining the electromagnetic conversion characteristics of the magnetic recording medium. It is intended for.

[0010]

The present invention provides a magnetic recording medium in which a magnetic layer formed by dispersing a ferromagnetic material and a conductive powder in a binder is provided on at least one main surface of a support. The powder is characterized by including spherical conductive powder and acicular conductive powder.

The conductive powder is characterized in that it is selected from at least one of carbon black, metal oxides, inorganic fibers, and particles having a conductor coated on the surface of the powder. Further, it is characterized in that the ferromagnetic material is barium ferrite.

[0012]

The present inventors have conducted various studies to solve the above-mentioned technical problems, and as a result, use a conductive powder in which spherical conductive powder and acicular conductive powder are mixed as an antistatic agent in the magnetic layer. In particular, they have found that the surface electrical resistance can be reduced and excellent electromagnetic conversion characteristics can be maintained.

When the spherical conductive powder and the needle-shaped conductive powder are used in combination as described above, it is possible to control the conductivity without anisotropy with a smaller addition amount as compared with the conventional case where the conductive powder is used alone. It will be easy.

For this reason, it is possible to increase the filling amount of the ferromagnetic material in the magnetic layer, which makes it possible to obtain a magnetic recording medium most suitable for high density recording. Further, as the amount of conductive powder added is reduced, the dispersion state of the ferromagnetic material can be increased, and thereby an excellent squareness ratio can be obtained.

The amount of the conductive powder formed by mixing the spherical conductive powder and the needle-shaped conductive powder is 2 parts by weight or more with respect to 100 parts by weight of the magnetic layer in order to ensure excellent conductivity of the magnetic layer. Is good. If the amount of conductive powder added exceeds 4 parts by weight, electromagnetic conversion characteristics may deteriorate. Further, the mixing ratio of the spherical conductive powder and the acicular conductive powder is preferably in the range of 4: 6 to 7: 3.

Incidentally, the spherical conductive powder in the present invention is one in which each shape is substantially spherical and may have pores formed on the surface, such as carbon black,
Examples thereof include spherical rutile-type conductive TiO ₂ , fine particles of conductive SnO _2, fine particles of BaSO ₄ coated with SnO ₂ , and the like. Among them, carbon black is a preferable material for the present invention from the viewpoint of characteristics or its price. The average particle diameter of the spherical conductive powder is preferably 10 nm or more and 30 nm or less. This is because if the average particle diameter exceeds 30 nm, it becomes difficult to secure sufficient conductivity, and if it is smaller than 10 nm, the viscosity of the magnetic coating material increases.

Further, the acicular conductive powder in the present invention refers to one having a ratio of the short axis to the long axis of greater than 5, for example, aluminum borate whiskers (9Al ₂ O ₃ .2B).
₂ O ₃ ), ZnO having conductivity, needle-shaped rutile conductive TiO ₂ , kalim titanate whiskers (K ₂ O.
8 TiO ₂ carbon fiber) and the like. And, as the average particle diameter (long axis) of this spherical conductive powder,
It is better to set it to 0.2 μm or more and 0.8 μm or less. This is because if the average particle size exceeds 0.8 μm, the dispersed state of the magnetic paint becomes unstable, and if it is less than 0.2 μm, sufficient conductivity cannot be obtained unless the addition amount is significantly increased.

Further, as the ferromagnetic material in the present invention,
Well-known γ-Fe ₂ O ₃ and Co deposited γ-F
It is possible to use e ₂ O ₃ , Fe-Al powder, Fe-Ni powder, hexagonal ferrite powder, or the like. In particular, since the hexagonal ferrite powder has an easy axis of magnetization in the direction perpendicular to the plate surface, it is easy to manufacture a magnetic recording medium having a large perpendicular angle, and it is optimal for achieving high density recording. Among them, even if barium ferrite, which has low conductivity and was difficult to reduce the surface resistance of the magnetic layer, is used as the ferromagnetic material, according to the present invention, it is possible to reduce the surface resistance of the magnetic layer with a small addition amount. Therefore, it is possible to secure the excellent reproduction output of barium ferrite.

[0019]

EXAMPLES The present invention will be described below with reference to examples and comparative examples. (Coating composition) Co-Ti substituted barium ferrite particles (average diameter 0.04 μm, coercive force 750 Oe) 100 parts by weight Dispersant (phosphate ester) 2 parts by weight Nitrocellulose 4 parts by weight Polyurethane resin (molecular weight 50000) 11 parts by weight α -Alumina (average diameter 0.3 μm) 6 parts by weight Lubricant (fatty acid ester) 5 parts by weight The above-mentioned magnetic paint was mixed with and dispersed in the two types of conductive powders shown in Table 1, filtered, and then a polyisocyanate curing agent. Was added to prepare a magnetic paint.

Then, after being coated on a polyester base film having a thickness of 75 μm so as to have a dry film thickness of 2.0 μm, it was heated and pressed by a super calendar to prepare a magnetic recording medium.

This magnetic recording medium was heat-treated to harden the magnetic coating film, then punched out into a 3.5-inch disk shape, and a metal center core was placed in the central portion and stored in a hard jacket to obtain 3.5. I used an inch floppy disk.

[0022]

[Table 1]

With respect to the 3.5-inch floppy disks of Examples and Comparative Examples thus obtained, the surface resistance, reproduction output and durability of the magnetic layer were measured, and the results are shown in Table 2.

The surface resistance of the magnetic layer was measured in the state where the magnetic recording medium was punched into a disk, and the reproduction output,
The durability was measured with a 3.5-inch floppy disk. The reproduction output uses a MIG (Metal-In-Gap) head with a gap length of 0.4 μm and a track width of 35 μm.
The optimum current at a recording density of 35 FRPI was used to evaluate the number of revolutions at 300 rpm and the track at the innermost track of 79 tracks. Durability is J
70% of initial output on track 12 specified by IS
5 ℃, humidity 1 with reference to the time when the output drops
0% low temperature and low humidity, 60 ° C temperature and 90% high temperature
It was evaluated under the environment where the high humidity condition changes every 24 hours.

[0025]

[Table 2]

As described above, by using the spherical conductive powder and the needle-shaped conductive powder together as the conductive powder added to the magnetic layer, excellent conductivity can be imparted to the magnetic layer. It has become possible to secure excellent durability and secure good electrical characteristics. In each of the above-mentioned Examples and Comparative Examples, barium ferrite was used as the ferromagnetic material, but conventionally known magnetic powder can also be appropriately used.

Further, in the above-mentioned embodiment, a magnetic recording medium having a magnetic layer thickness of 2 μm is shown as an example. Generally, the conductivity of the magnetic layer sharply decreases as the thickness of the magnetic layer decreases, but according to the present invention, good results were confirmed even for a thin film magnetic layer of 1 μm or less.

Further, in each of the above-mentioned embodiments, the magnetic layer is directly arranged on the polyester base film, but the magnetic layer may be provided via an adhesive layer or a conductive layer. The magnetic layer itself may have a single-layer structure or a multilayer structure, and it is particularly effective to adopt the structure of the present invention for the magnetic layer arranged on the magnetic head side.

[0029]

As described in detail above, according to the present invention, it is possible to provide a magnetic recording medium which ensures excellent conductivity while sufficiently maintaining the electromagnetic conversion characteristics of the magnetic recording medium. According to the present invention, it is possible not only to ensure high durability but also to obtain magnetic characteristics most suitable for high-density recording because of the electromagnetic conversion characteristics and the conductivity ensured as described above. Therefore,
The present invention is most suitable for a large capacity magnetic disk.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuichi Fukai 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Stock Company Toshiba Horikawa-cho Factory

Claims (3)

[Claims] 1. A magnetic recording medium in which a magnetic layer comprising a ferromagnetic material and conductive powder dispersed in a binder is provided on at least one main surface of a support, wherein the conductive powder is spherical conductive powder. A magnetic recording medium comprising: and a needle-shaped conductive powder. 2. The magnetic recording according to claim 1, wherein the conductive powder is selected from at least one of carbon black, metal oxides, inorganic fibers, and particles having a conductor coated on the surface of the powder. Medium. 3. A magnetic recording medium, wherein the ferromagnetic material according to claim 1 is barium ferrite.