JPS59144034A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium containing a magnetic layer of high sensitivity and high durability with a low level of noises, by mixing metallic magnetic powder and iron nitride magnetic powder and making use of a fact that the iron nitride magnetic powder is fine and has the coercive force equivalent to the metallic magnetic powder with high hardness. CONSTITUTION:The iron nitride magnetic fine powder is obtained by giving thermal treatment to the metallic magnetic fine powder in an atmosphere of mixture gas of NH3 and H2. Such iron nitride magnetic powder is mixed with the metallic magnetic powder within a mixing ratio range of (98:2)-(50:50) in terms of weight %.A magnetic coating material containing this mixture powder together with the binder resin, an organic solvent, etc. is coated and dried on a supporter film to form a magnetic layer. Thus the smoothness and the wear resistance are improved for the surface of the magnetic layer. In addition, the durability is improved without deteriorating the output and with a low level of AC noises for a magnetic recording medium.

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 having a magnetic layer with a low noise level, excellent electromagnetic conversion characteristics, and excellent durability. be.

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating.
When high performance is required, metal magnetic powders such as iron and cobalt are used.

However, these metal magnetic powders have higher coercive force and residual magnetic flux density than oxide-based basic powders, and therefore can produce high output levels, especially in high frequency bands. The problem is that it is not possible to achieve good smoothness and sufficiently reduce noise. In addition, the magnetic layer formed using these metal magnetic powders does not have sufficient wear resistance, so it is not possible to improve the wear resistance of the magnetic layer by mixing fillers such as valve handles. However, since the filler in the valve handle is made of non-magnetic powder, there are drawbacks such as a reduction in output even though wear resistance can be improved.

The inventors conducted various studies in view of the current situation, and found that if iron nitride magnetic powder is used together with metal magnetic powder and contained in the magnetic layer, the iron nitride magnetic powder used in combination is more effective than metal magnetic powder. Because it is fine, has the same coercive force, and is hard, it can improve the surface smoothness of the magnetic layer and sufficiently reduce noise, and also acts as a filler, increasing magnetic properties without reducing output. It was discovered that the abrasion resistance of the layer can be sufficiently improved, and a magnetic recording medium with low noise level, excellent electromagnetic conversion characteristics, and excellent durability can be obtained, and this invention has been completed.

The iron nitride magnetic powder used in this invention is a fine powder obtained by heat-treating metal iron fine particles in a mixed gas atmosphere of ammonia and hydrogen, and has the same coercive force as metal iron magnetic powder. A much finer product can be obtained than powder. Therefore, if this iron nitride magnetic powder is used together with metal iron magnetic powder or other metal magnetic powder, the surface smoothness of the magnetic layer can be improved and noise can be sufficiently reduced. In addition, iron nitride magnetic powder obtained by nitriding metal iron fine particles is harder than metal iron magnetic powder and other metal magnetic powders, so when used together with metal magnetic powder, it also acts as a filler and reduces output. The wear resistance of the magnetic layer is improved without causing damage. As iron nitride magnetic powder such as nickel, those containing nickel or silicon are also preferably used, and have a coercive force of 500
~1300 oersted, specific surface area 30 by BET method
Those with rrl/9 or more are preferably used.

In addition, as the metal magnetic powder used in this invention, powders of iron, cobalt, nickel, etc. alone or alloys, and metal magnetic powders in which iron contains elements such as Als Crs Mn, 5isZn, etc. are preferable. A coercive force in the range of 500 to 1300 oersteds is preferably used.

The mixing ratio of the metal magnetic powder and the iron nitride magnetic powder is preferably within the range of 98:2 to 50:50 in weight ratio of the metal magnetic powder to the iron nitride magnetic powder. The desired effect may not be obtained, and if the amount is too large, the saturation magnetization amount of the iron nitride magnetic powder is small, so there is a risk that the sensitivity will decrease.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, a mixed powder of metal magnetic powder and iron nitride magnetic powder is mixed and dispersed with a binder resin, an organic solvent, etc., and a magnetic paint is applied. The magnetic coating material may be prepared, coated on a substrate such as a polyester film using any coating means such as a roll coater, and dried.

As the binder resin used here, conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, polyurethane resins, and isocyanate compounds are widely used.

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

Six, various additives commonly 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 α-Fe magnetic powder (coercive force 1220, 98 parts by weight Oersted, saturation magnetization 139 emu/l, specific surface area 24.8 m'/g by BET method) Iron nitride magnetic powder (coercive force 1200 2 Oersted, specific surface area 24.8 m'/g by BET method) Saturation magnetization: 116 emu/9, specific surface area by BET method: 3 g, 7 tri10) Medicine 6 (manufactured by Kogyo Co., Ltd., urethane prepolymer) Conquaternate Nippon Polyurethane 2 (manufactured by Kogyo Co., Ltd., trifunctional low molecular weight isocyanate compound) Myristic acid 2 (Silicone oil 0.3) Carbon black 2 (Toluene)
92 Methyl isobutyl ketone 92 This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint. This magnetic paint was applied onto a polyester film with a thickness of about 10 μm to a dry thickness of 4.0 μm, dried, surface treated, and then cut into a predetermined width to produce a magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, the amount of α-Fe magnetic powder used was changed from 98 parts by weight to 80 parts by weight,
A magnetic tape was produced in the same manner as in Example 1 except that the amount of iron nitride magnetic powder used was changed from 2 parts by weight to 20 parts by weight.

Example 3 In the composition of the magnetic paint in Example IK, α-Fe
A magnetic tape was produced in the same manner as in Example 1, except that the amount of magnetic powder used was changed from 98 parts by weight to 60 parts by weight, and the amount of iron nitride magnetic powder used was changed from 2 parts by weight to 40 parts by weight.

Comparative Example 1 In the composition of the magnetic paint in Example 1, the amount of α-Fe magnetic powder used was changed from 98 parts by weight to 40 parts by weight,
A magnetic tape was produced in the same manner as in Example 1 except that the amount of iron nitride magnetic powder used was changed from 2 parts by weight to 60 parts by weight.

Comparative Example 2 Magnetic paint was produced in the same manner as in Example 1, except that in the composition of the magnetic paint in Example IK, the amount of α-Fe magnetic powder used was changed from 98 parts by weight to 100 parts by weight, and the iron nitride magnetic powder was omitted. I made a tape.

Comparative Example 3 A magnetic tape was produced in the same manner as in Comparative Example 2, except that 4 parts by weight of Bengara was newly added to the composition of the magnetic paint in Comparative Example 2.

For the magnetic tapes obtained in each example and each comparative example, sensitivity at 315) Tz, frequency characteristics at 12.5 KHz, and AC noise were measured, and durability was tested. Durability test
/sec sliding contact with the magnetic head from 1 to 1
Run the tape back and forth 00 times and observe the surface condition after running, and if there are no visible scratches on the tape surface (◎
), cases in which the scratches were visually discernible but had no problem in terms of characteristics were evaluated as (O), and cases in which the scratches were visually discernable but had problems in terms of characteristics were evaluated as (Δ).

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained in Examples 1 to 3 have lower AC noise, higher sensitivity and frequency characteristics, and are more durable than the magnetic tapes obtained in Comparative Examples 1 to 3. This clearly shows that the magnetic recording medium obtained by the present invention has a low noise level, excellent electromagnetic conversion characteristics, and excellent durability.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. Magnetic recording medium having a magnetic layer containing metal magnetic powder and iron nitride magnetic powder