JPS59144037A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which excels in wear resistance, durability and electromagnetic conversion characteristics with no deterioration in characteristics of the iron oxide magnetic powder containing Co, by mixing the iron nitride magnetic powder into a magnetic layer together with the iron oxide magnetic powder containing Co. CONSTITUTION:The magnetic powder is obtained by mixing the iron nitride magnetic powder which is finer and harder than the iron oxide magnetic powder containing Co into said iron oxide magnetic powder in 1-50wt%. This magnetic powder is dispersed into the binder resin to obtain a magnetic layer, and this magnetic layer is formed on a substrate. The iron nitride magnetic powder has a larger amount of saturated magnetization than the iron oxide magnetic powder containing Co. Thus such a magnetic recording medium excels in electromagnetic conversion characteristics, wear resistance, surface smoothness, traveling stability and durability respectively and with a low level of AC noises.

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 that has excellent electromagnetic conversion characteristics and excellent durability.

In general, magnetic recording media, which are made by coating a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components on a substrate such as a polyester film, come into violent sliding contact with magnetic heads, etc. during recording and playback. The magnetic layer is easily abraded, so a material with excellent durability and little abrasion is required.

In order to meet these demands, it has been conventionally practiced to mix α-Fe203 powder, which has a large particle size among non-magnetic powders with high hardness such as Cr2O5 powder and Al2O5 powder, into the magnetic layer. The abrasion resistance of the magnetic layer is improved by mixing agents.

However, since all of these solid additives are non-magnetic powders, when the amount added to the magnetic layer increases, the amount of magnetic powder decreases relatively, and the saturation magnetic flux density of the magnetic recording medium decreases, causing the electromagnetic conversion characteristics to deteriorate. There are disadvantages such as deterioration, which is particularly noticeable when trying to obtain a magnetic recording medium with good electromagnetic conversion characteristics using magnetic powder with relatively good magnetic properties, such as cobalt-containing iron oxide magnetic powder. .

The inventors conducted various studies in view of the current situation, and found that the iron nitride magnetic powder was used as a solid additive to reinforce the magnetic layer, and it was incorporated into the magnetic layer containing the cobalt-containing iron oxide magnetic powder. Since the solid additive used is iron nitride magnetic powder rather than non-magnetic powder, the electromagnetic conversion characteristics will not deteriorate, and the wear resistance of the magnetic layer will be sufficiently improved to improve durability and electromagnetic conversion. It was discovered that a magnetic recording medium with excellent characteristics could be obtained, and the present invention was completed.

The iron nitride magnetic powder used in this invention is a fine powder obtained by heating fine metal iron particles in a mixed gas atmosphere of ammonia and hydrogen, and has a higher saturation magnetization than cobalt-containing iron oxide magnetic powder. is large, much finer and harder, and therefore, when this iron nitride magnetic powder is included in a magnetic layer containing cobalt-containing iron oxide magnetic powder, the reinforcing effect of the magnetic layer can be fully exerted without deteriorating the electromagnetic conversion characteristics. This improves wear resistance and also reduces noise. The effect of such iron nitride magnetic powder as a solid additive is exhibited when it is contained in the magnetic layer in an amount of 1% by weight or more based on the cobalt-containing iron oxide magnetic powder, and the effect becomes more pronounced as the content increases. However, if it exceeds 50% by weight, it may adversely affect electromagnetic conversion characteristics such as deterioration of erasing characteristics, so it is preferably contained in the magnetic layer within the range of 1 to 50% by weight. As such iron nitride magnetic powder, those containing nickel or silicon are also suitably used.

Further, as the cobalt-containing iron oxide magnetic powder used in this invention, Co-containing -Fe20. Any of the conventionally known cobalt-containing iron oxide magnetic powders such as magnetic powder, Co-containing Fe 504m powder, and the like are preferably used.

The magnetic recording medium of the present invention can be manufactured by conventional methods, such as mixing and dispersing metal iron nitride magnetic powder with cobalt-containing iron oxide magnetic powder, binder resin, organic solvent, etc. to form a magnetic paint. 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, dimethyl formamide, etc. may be used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, a dispersant, a lubricant, an antistatic agent, etc. may be optionally added.

Next, embodiments of the invention will be described.

Example I Co-containing-Fe20. Magnetic powder (coercive force 69 weight part force 650 oersted, saturation magnetization 75 emu/l, specific surface area 22.5 m'/g by BET method) Iron nitride magnetic powder (coercive cuff 60 e/l, saturation magnetization 122 emu/g) g, specific surface area by BET method: 28.9 WI/liter) VAGH (manufactured by U, C, C, USA, chloride 14 # vinyl-acetate-vinyl alcohol copolymer) Takelac E-551T (Takeda Pharmaceutical Co., Ltd. 6) manufactured by J Company , urethane prepolymer) L (manufactured by Nippon Polyurethane 2 Ltd., trifunctional low molecular weight isocyanate compound) Myristic acid 2 parts by weight Silicone oil 0.3 Toluene 92 Methyl isobutyl ketone 92 This composition A magnetic paint was prepared by mixing and dispersing the mixture in a ball mill for 72 hours. This magnetic paint was applied onto a polyester film having a thickness of about 12 .mu.m to a dry thickness of about 5.5 .mu.m, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, c.

The procedure was the same as in Example 1, except that the amount of the rFe20s magnetic powder used was changed from 99 parts by weight to 90 parts by weight, and the amount of iron nitride magnetic powder was changed from 1 part by weight to 10 parts by weight. and made magnetic tape.

Example 3 In the composition of the magnetic paint in Example 1, c.

Magnetic production was carried out in the same manner as in Example 1, except that the amount of r-Fe205 magnetic powder used was changed from 99 parts by weight to 60 parts by weight, and the amount of iron nitride magnetic powder was changed from 1 part by weight to 40 parts by weight. I made a tape.

Comparative Example 1 In the composition of the magnetic paint in Example IK, the amount of CO-containing -Fe203 magnetic powder used was changed from 99 parts by weight to 10 parts by weight.
A magnetic tape was produced in the same manner as in Example 1, except that the iron nitride magnetic powder was changed to 0 parts by weight and the iron nitride magnetic powder was omitted.

Comparative Example 2 In the composition of the magnetic paint in Example 1, CO-containing r
- A magnetic tape was produced in the same manner as in Example 1, except that the amount of Fe205 magnetic powder used was changed from 99 parts by weight to 30 parts by weight, and the amount of iron nitride magnetic powder used was changed from 1 part by weight to 70 parts by weight. Ta.

For the magnetic tapes obtained in each example and each comparative example, sensitivity at 315 Hz, frequency characteristics at 12.5 KHz, AC noise, and erasing characteristics were measured, and durability was tested. A durability test was conducted on the obtained magnetic tape in 4.
The output fluctuation was measured after running 100 times while in sliding contact with a magnetic head at a running speed of 76 cm/sec, and was expressed as a standard deviation value.

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained in Examples 1 to 3 have higher sensitivity and frequency characteristics, lower AC noise, and better durability than the magnetic tapes obtained in Comparative Example 1. The erasing properties are better than that of the magnetic tape obtained in Comparative Example 2, and this shows that the magnetic recording medium obtained by this invention has excellent electromagnetic conversion properties, excellent durability, and sufficiently reduced noise. I understand that.

In addition, Figure 1 is a graph showing the relationship between the proportion of iron nitride magnetic powder in the total magnetic powder of magnetic tapes obtained in each example and each comparative example, and the output fluctuation and erasing characteristics after 100 runs. As shown in graphs A and B, it is clear from these graphs that in order to improve both durability and erasing characteristics, the proportion of iron nitride magnetic powder in the total magnetic powder should be increased from 1 to 50% by weight. It can be seen that it is preferable to keep it within the range.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of iron nitride magnetic powder in the total magnetic powder of the magnetic tape obtained according to the present invention, and the output fluctuation and erasing characteristics after 100 runs. Patent applicant: Hitachi Maxell, Ltd. Figure 1: Percentage of iron nitride magnetic powder in total magnetic powder (wt%)

Claims (1)

[Claims] 1. A magnetic recording medium characterized by containing iron nitride magnetic powder in a magnetic layer containing cobalt-containing iron oxide magnetic powder