JPS59144043A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having high sensitivity with every frequency band by forming the 1st magnetic layer containing iron nitride magnetic powder with coercive force set within a specific range on a substrate and then the 2nd magnetic layer containing the iron oxide magnetic powder containing Co with the coercive force set equal to or higher than the 1st layer on the 1st magnetic layer. CONSTITUTION:The 1st magnetic layer containing the iron nitride magnetic powder with 600-1,300 Oe coercive force is formed on a substrate. Then the 2nd magnetic layer containing the iron oxide magnetic powder containing Co and the coercive force set equal to or higher than the 1st magnetic layer. In this case, the equal level includes a case where the coercive force of the 1st layer is higher by 30 Oe than the 2nd layer, and the higher level includes a case where the upper layer has a little higher level of coercive force than the lower layer. The thickness ratio is set within a 1:1-1:10 range between both layers. Thus it is possible to obtain a magnetic recording medium which has no slump of output with an intermediate frequency band and high sensitivity over a wide range of frequency bands with a low level of noises.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having a two-layer magnetic layer structure, and the object thereof is to provide a magnetic recording medium with good frequency characteristics and sensitivity in the entire frequency band without sagging in the frequency characteristics. It is about providing.

It has long been known that in magnetic recording media with a two-layer magnetic layer structure, sensitivity and frequency characteristics in low and high frequency bands can be improved by lowering the coercive force of the lower layer and increasing the coercive force of the upper layer. There is. This type of magnetic recording medium usually involves coating a substrate such as a polyester film with a magnetic paint containing magnetic powder with a relatively low coercive force, drying it to form a lower magnetic layer, and then coating the base with a magnetic paint containing a magnetic powder with a relatively low coercive force. Apply magnetic paint containing magnetic powder with relatively high coercive force on top,
It is made by drying, and the magnetic powders used in both the upper and lower magnetic layers include cobalt-containing iron oxide magnetic powders with different coercive forces.

However, in this type of conventional magnetic recording medium, cobalt-containing iron oxide magnetic powders with different coercive forces are used in both the upper and lower magnetic layers, and the coercive force of the upper magnetic layer is higher than that of the lower magnetic layer. Although this improves sensitivity and frequency characteristics in low and high frequency bands,
There is a problem in that a sagging phenomenon occurs in the frequency characteristics, resulting in a decrease in the frequency characteristics in the middle range.

The inventors conducted various studies in view of the current situation, and found that iron nitride magnetic powder was used as the magnetic powder in the lower magnetic layer, the coercive force of the lower magnetic layer was set to 600 to 1300 oersteds, and the upper magnetic layer If cobalt-containing iron oxide magnetic powder is used to make the coercive force of the upper magnetic layer equal to or higher than the coercive force of the lower magnetic layer, sagging occurs in the frequency characteristics and the frequency characteristics in the middle range decrease. Good frequency characteristics and sensitivity can be obtained in all frequency bands.
□I discovered this and came up with this invention.

In this invention, the iron nitride magnetic powder used in the lower magnetic layer is a fine powder obtained by heat-treating fine metallic iron particles in a mixed gas atmosphere of ammonia and hydrogen, and is more effective than cobalt-containing iron oxide magnetic powder. Therefore, iron nitride magnetic powder with large saturation magnetization is used as the magnetic powder for the lower magnetic layer, and cobalt-containing iron oxide magnetic powder is used as the magnetic powder for the upper magnetic layer. By making the coercive force of the upper magnetic layer equal to or higher than that of the lower magnetic layer, good frequency characteristics and sensitivity can be obtained in all frequency bands without causing sagging in the frequency characteristics. As such iron nitride magnetic powder, those containing nickel or silicon are also suitably used.

In addition, in order to sufficiently reduce noise and obtain sufficient output in the high frequency band, the cobalt-containing iron oxide magnetic powder used in the upper magnetic layer is replaced by the iron nitride magnetic powder used in the lower magnetic layer. It is preferable to use a fine powder with a larger specific surface area, and examples of such cobalt-containing iron oxide magnetic powder include CO-containing rFe2O3 powder, C
Any conventionally known cobalt-containing iron oxide magnetic powder such as o-containing Fe50 winter powder is preferably used.

The coercive force of both the upper and lower magnetic layers is determined by the magnetic force of the lower layer in order to improve the sensitivity and frequency characteristics in low and high frequency bands, and to prevent sagging in the frequency characteristics and deterioration of the frequency characteristics in the middle range. The coercive force of the layer is 600-13
It is preferable that the coercive force of the upper magnetic layer is equal to or higher than that of the lower magnetic layer. If the coercive forces of both the upper and lower magnetic layers are the same, the coercive force of the lower magnetic layer may be slightly higher than the coercive force of the upper magnetic layer, and the coercive force of the lower magnetic layer may be approximately 30 microns for the same range. This also includes cases where the coercive force is higher than the coercive force of the upper magnetic layer.

Further, the thickness of both the upper and lower magnetic layers is preferably within the range of 1:1 to 1:1o in terms of the ratio of the upper magnetic layer thickness to the lower magnetic layer thickness. If the upper magnetic layer is too thick, the characteristics in the low frequency band will not be sufficiently good, and if it is too thin, the characteristics in the high frequency band will not be sufficiently good.
Noise also cannot be sufficiently reduced.

The formation of both the upper and lower magnetic layers can be carried out according to a conventional method. For example, first, a magnetic paint containing iron nitride magnetic powder, a binder resin, an organic solvent, and other additives is usually applied on a substrate such as a polyester film. A magnetic paint containing cobalt-containing iron oxide magnetic powder, a binder resin, an organic solvent and other additives is coated on the lower magnetic layer by a conventional method. The upper magnetic layer may be formed by coating and drying by any means.

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, cellulose resins, polyurethane resins, and isocyanate compounds. used.

In addition, as organic solvents, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, vinegar M
Polymer, tetrahydrofuran, dimethylformamide, etc. are used alone or in combination of two or more.

In addition, 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 <Preparation of magnetic paint for lower layer> Iron nitride magnetic powder (retentive cuff 30 pieces, 100 parts by weight Rusted, saturation magnetization amount 120 emu/g%, specific surface area 25.5 rrr/g by BET method) VAGH (U.S.A., C,C, Co., Ltd., salt 1) Vinyl oxide-vinyl acetate-vinyl alcohol copolymer) Bandesox T-5201 (Dainippon Ink Co., Ltd., urethane elastomer) Coronate Nippon Polyurethane 3 Kogyo Co., Ltd., 3 Functional low molecular weight isocyanate compound) Myristic acid 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 for the lower layer.

<Preparation of magnetic paint for upper layer> CO-containing 7 Fe2O3 magnetic 100 parts by weight powder (
Coercive force 670 oersted, saturation magnetization 73emu 7g, specific surface area 29M/g by BET method) VAGH14〃Takelac E-551T (Bu1) 6〃Yakuhin Kogyo Co., Ltd., urethane prepolymer) Coronated 2〃Myristic acid 2 〃Silicone oil
0.3〃Carbon black
2 α Fe2O3 powder 4 Toluene 92, Methyl isobutyl ketone 92 This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint for the upper layer.

<Manufacture of double-layer magnetic tape> After applying the above magnetic paint for the lower layer on a polyester base film with a thickness of about 12μ, drying, and performing surface treatment,
Further curing was performed at 60° C. for 24 hours to form a lower magnetic layer with a thickness of 3.5 μm.

Next, the above-mentioned upper layer magnetic paint is further applied on this magnetic layer, dried, and subjected to surface treatment to form a 2.0μ thick upper magnetic layer, which is then cut to a predetermined width to form a double layer magnetic tape. I made it.

Comparative Example 1 In the composition of the lower layer magnetic paint in Example 1, the coercive cuff was 30 oersted, the saturation magnetization was 120 emu/g,
Specific surface area 25.5n by BET method? /g of iron nitride magnetic powder, coercive force of 500 oersted, saturation magnetization of 76 emu 7g, specific surface area of 22 by BET method.
．． A double-layer magnetic tape was prepared in the same manner as in Example 1 except that the same amount of 5rrr/g Co-containing yFe203 magnetic powder was used.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that the formation of the upper magnetic layer was omitted and the thickness of the lower magnetic layer was changed from 3.5 μm to 5.5 μm.

Comparative Example 3 In Example 1, the formation of the lower magnetic layer was omitted, and the composition of the upper layer magnetic paint was Co-containing Fe2O3 with a coercive force of 670 oersted, a saturation magnetization of 73 emu/g, and a specific surface area of 29 rrr/g by the BET method. Instead of magnetic powder, coercive force 650 oersted, saturation magnetization 7
5emu/g, specific surface area 22.5rd by BET method
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of co-containing TFe203 magnetic powder of /g was used and the thickness of the upper magnetic layer was changed from 2.0 .mu.0 to 5.5 .mu.0.

For the magnetic tapes obtained in Examples and Comparative Examples, coercive force of both upper and lower magnetic layers, sensitivity at 315 Hz, 12
．． Frequency characteristics at 5KHz, 3151 (z and 2
The maximum output level at KHz, the saturated output level at 10 KHz and the AC noise were measured.

The table below shows the results.

As is clear from the above table, the double-layer magnetic tape obtained in Comparative Example 1 had a low maximum output level at 2 KHz and sagging in frequency characteristics, whereas the double-layer magnetic tape obtained in Example 1 The tape does not show any sagging like this,
Furthermore, the double-layer magnetic tape obtained in Example I has better frequency characteristics and sensitivity in all frequency bands and lower AC noise than the magnetic tapes obtained in each comparative example. It can be seen that the magnetic recording medium has no sag in its frequency characteristics, has good frequency characteristics and sensitivity in the entire frequency band, and has sufficiently reduced noise.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. Coercive force containing iron nitride magnetic powder on the substrate is 600~
A first magnetic layer of 1,300 oersted is formed, and a second magnetic layer containing cobalt-containing iron oxide magnetic powder and having a coercive force equal to or higher than that of the first magnetic layer is further layered thereon. magnetic recording media