JPS59144041A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To eliminate a slump of frequency characteristics and to improve the sensitivity with reduction of noises by forming a lower magnetic layer containing metallic magnetic powder with the coercive force set within a specific range and an upper magnetic layer containing iron nitride magnetic powder with the coercive force set equal to or higher than that of the lower layer on a supporter. CONSTITUTION:The 1st magnetic layer containing the metallic magnetic powder having 600-1,300 Oe coercive force is formed on a supporter of a polyester film, etc. Then the 2nd magnetic layer containing the iron nitride magnetic powder having the coercive force set equal to or higher than the 1st layer is formed on the 1st magnetic layer. The ratio of thickness is preferably set within a (1:1)- (1:10) range between both magnetic layers. The characteristics of a low-frequency band are not improved if the upper magnetic layer is too much thicker than the lower layer, while the characteristics of a high-frequency band are not satisfactory if the upper layer is too much thinner than the lower layer with unsatisfactory reduction of noises. In such a way, the excellent characteristics can be secured over a wide range of frequencies for a magnetic recording medium.

Description

[Detailed Description of the Invention] The present invention relates to a magnetic recording medium having a two-layer magnetic layer structure, and its purpose is to have no sagging in frequency characteristics, good frequency characteristics and sensitivity in the entire frequency band, and low noise. The purpose of this invention is to provide a magnetic recording medium.

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. It is also known that sensitivity and frequency characteristics can be further improved by using metal magnetic powder with a large amount of saturation magnetization as the magnetic powder in these magnetic layers, and such magnetic recording media are usually made of polyester film. A magnetic paint containing a metal magnetic powder with a relatively low coercive force is first applied onto a substrate, such as a metal powder, and dried to form a lower magnetic layer.Then, a magnetic paint containing a metal magnetic powder with a relatively high coercive force is coated on the lower magnetic layer. Apply magnetic paint containing
It is made by drying to form an upper magnetic layer.

However, in this type of conventional magnetic recording medium, by making the coercive force of the upper magnetic layer higher than that of the lower magnetic layer, the sensitivity and frequency characteristics in low frequency and high frequency bands are improved, but the frequency characteristics are The problem is that a sagging phenomenon occurs, and the frequency characteristics in the midrange gradually deteriorate.

On the other hand, when metal magnetic powder with a relatively small specific surface area is used in a single magnetic layer, a large residual magnetic flux density can be obtained, resulting in excellent electromagnetic conversion characteristics such as increased sensitivity and output. Unlike a magnetic recording medium with a two-layered magnetic layer structure, the frequency characteristics in the middle range do not deteriorate, but noise cannot be sufficiently reduced.

As a result of various studies in view of the current situation, the inventors used metal magnetic powder as the magnetic powder of the lower magnetic layer, and set the coercive force of the lower magnetic layer to 600 to 1300 oersteds, and the upper magnetic layer. When iron nitride magnetic powder is used as the magnetic powder, and the coercive force of the upper magnetic layer is made equal to or higher than the coercive force of the lower magnetic layer, sagging occurs in the frequency characteristics, causing the frequency characteristics in the mid-range to deteriorate. It was discovered that good frequency characteristics and sensitivity can be obtained in all frequency bands without any deterioration, and noise can also be sufficiently reduced, leading to the invention.

In this invention, the iron nitride magnetic powder used in the upper magnetic layer is a fine powder obtained by heat-treating fine metal iron particles in a mixed gas atmosphere of ammonia and hydrogen, and is far more effective than metal magnetic powder. It has a large surface area, is fine, and has a coercive force equivalent to that of metal magnetic powder. Therefore, this fine iron nitride magnetic powder with high coercive force is used as the magnetic powder in the upper magnetic layer, and metal magnetic powder is used as the magnetic powder in the lower magnetic layer, and the coercive force of the upper magnetic layer is lowered by the coercive force of the lower layer. If the coercive force is equal to or higher than that of the magnetic layer, the smoothness of the surface of the magnetic layer will be good, noise will be sufficiently reduced, and there will be no sagging in the frequency characteristics, resulting in good frequency characteristics and sensitivity in all frequency bands. is obtained. As such iron nitride magnetic powder, those containing nickel or silicon are also preferably used.

In addition, in order to obtain sufficient output in the low frequency band, the metal magnetic powder used in the lower magnetic layer is preferably one with a relatively small specific surface area and good orientation.
Examples of such metal magnetic powders include metal powders such as iron, cobalt, and nickel, or alloy powders thereof, and iron containing AI, C', Mn-, S+-,
An alloy powder containing an element such as Zn is preferably used.

The coercivity of both the upper and lower magnetic layers is determined by the coercive 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 mid-range. The coercive force of the magnetic layer is 600-1
300 oersted, and the coercive force of the upper magnetic layer is preferably equal to or higher than that of the lower magnetic layer. If the coercive forces of 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. This also includes cases where the coercive force is higher than that 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 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 metal magnetic powder, a binder resin, an organic solvent, and other additives is coated on a substrate such as a polyester film using a conventional method. A magnetic paint containing iron nitride magnetic powder, a binder resin, an organic solvent, and other additives is applied on the lower magnetic layer by conventional means. , and then dry to form an upper magnetic layer.

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.

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.

In addition, various additives commonly used in magnetic paints,
For example, a dispersant, hot water agent, abrasive, antistatic agent, etc. may be optionally added and used.

Next, embodiments of the invention will be described.

Example 1 <Preparation of magnetic paint for lower layer> α-Fe magnetic powder (coercive force 890, 100 parts by weight Oersted, saturation magnetization amount 138 emu 7g, specific surface area by SB ET method 21.Onf/g) VAGH (US t+, C, Co., Ltd., salt 10 vinylide-vinyl acetate-vinyl alcohol copolymer) Bandex T-5201 (Dainippon Ink Co., Ltd., urethane elastomer) Corone) L (Nippon Polyurethane 3 Kogyo Co., Ltd., Trifunctional 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> Iron nitride magnetic powder (coercive force 880 mm, 100 parts by weight Rusted, saturation magnetization 118 emu 7 g, specific surface area 32.5 by BET method)
M/g) VAGH14〃Takelac E-551T (21) 6〃Yakuhin Kogyo Co., Ltd., urethane prepolymer) Coronate 2〃Myristic acid 2〃Silicone oil
0.3〃Carbon Black 2
A-Fe203 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.

Example 2 In the composition of the magnetic paint for the lower layer in Example 1, the coercive force was 890 oersted, the saturation magnetization was 138 emu, and 7 g.
, α of specific surface area 21.0rrr/g by BET method
-In place of the Fe magnetic powder, the same amount of α-Fe magnetic powder with a coercive force of 1220 oersted, a saturation magnetization of 139 emu 7 g, and a specific surface area of 24.8 rrr/g by the BET method was used, and in the composition of the upper layer magnetic paint, Instead of iron nitride magnetic powder with a magnetic force of 880 Oersted, a saturation magnetization of 118 emu/g, and a specific surface area of 32.5 rrr/g by the BET method, a coercive force of 1200 Oersted and a saturation magnetization of 116
emu 7g, specific surface area 38.7r by BET method
The same amount of iron nitride magnetic powder of d/g was used, and the thickness of the lower magnetic layer was varied from 3.5 μm to 2.0 μm.
The thickness of the upper magnetic layer was changed from 2.0μ to 1.5μ.
A double layer magnetic tape was produced in the same manner as in Example 1 except that the thickness was changed to 5μ.

Example 3 In the composition of the magnetic paint for the lower layer in Example 2, the coercive force was 1220 oersted, and the saturation magnetization was 139 emu 7.
g % Specific surface area by BET method 24.8 rrr 7
g of α-Fe magnetic powder, coercive force 1170 oersted, saturation magnetization amount 140 e'mu 7 g, B E
Using the same amount of α-Fe magnetic powder with a specific surface area of 23.8rrf/g by the 'T method, in the composition of the upper layer magnetic paint,
Coercive force 1200 oersted, saturation magnetization 116 emu
7g, specific surface area by BET method: 38.7rrr
/g of iron nitride magnetic powder, coercive force 1160 oersted, saturation magnetization 117 emu 7g, B ET
A double-layer magnetic tape was prepared in the same manner as in Example 2, except that the same amount of iron nitride magnetic powder having a specific surface area of 34.1 rrr/g was used.

Comparative Example 1 11 In the composition of the magnetic paint for the upper layer in Example 1, the coercive force was 880 oersted, the saturation magnetization was 118 emu, and 7 g.
, Instead of the iron nitride magnetic powder with a specific surface area of 32.5rd/g by the BET method, the same amount of α-Fe magnetic powder with a specific surface area of 32.2nf/g by the SBET method with a coercive force of 990 oersted and a saturation magnetization of 130 emu 7g was used. A double layer magnetic tape was produced in the same manner as in Example 1 except that the following 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 A magnetic tape was produced in the same manner as in Example 1 except that the formation of the lower magnetic layer was omitted and the thickness of the upper magnetic layer was changed from 2.0 μm to 5.5 μm.

Comparative Example 4 In Example 1, the formation of the lower magnetic layer was omitted, and the composition of the upper layer magnetic paint was iron nitride magnetic powder with a coercive force of 880 oersted, a saturation magnetization of 118 emu of 7 g, and a specific surface area of 32.5 rd/g by the BET method. Instead, coercive force 650 oersted, saturation magnetization 75 emu/g, BE
Specific surface area 22.5n by T method? /g CO-containing -F
A magnetic tape was made in the same manner as in Example 1, except that the same amount of e203 magnetic powder was used and the thickness of the upper magnetic layer was changed from 2.0 μm to 5.5 μm.

Comparative Example 5 In the composition of the magnetic paint for the upper layer in Example 2, the coercive force was 1200 oersted, and the saturation magnetization was 116 emu 7.
g, instead of the iron nitride magnetic powder with a specific surface area of 38.7nr/g by the BET method, a coercive force of 131O oersted, a saturation magnetization amount of 133emu 7g, and a specific surface area of 38.7nr/g by the BET method. A double layer magnetic tape was prepared in the same manner as in Example 2 except that the same amount of α-Fe magnetic powder of Inf/g was used.

Comparative Example 6 A magnetic tape was produced in the same manner as in Example 2 except that the formation of the upper magnetic layer in Example 2 was omitted and the thickness of the lower magnetic layer was changed from 2.5 μm to 4.0 μm.

Comparative Example 7 A magnetic tape was produced in the same manner as in Example 2, except that the formation of the lower magnetic layer was omitted and the thickness of the upper magnetic layer was changed from 1.5 μm to 4.0 μm.

For the magnetic tapes obtained in each example and each comparative example, the coercive force, residual magnetic flux density, and rectangular shape (llr/
Bm), sensitivity at 315 Hz, 12.5KHz
The frequency response at 315 Hz and the maximum output level at 2 KHz, the saturated output level at l0KI (z) and the AC noise were measured.

The table below shows the results.

15 As is clear from the above table, the double-layer magnetic tapes obtained in Comparative Examples 1 and 5 had a low maximum output level at 2 Kl (z) (sagging in the frequency characteristics was observed, whereas Examples 1 to 5 The double-layer magnetic tape obtained in Example 3 did not show such sagging, and the double-layer magnetic tape obtained in Examples 1 to 3 had a higher overall frequency band than the magnetic tape obtained in each comparative example. The magnetic recording medium obtained by this invention has good frequency characteristics and sensitivity, and low AC noise. Therefore, the magnetic recording medium obtained by this invention has no sag in the frequency characteristics, has good frequency characteristics and sensitivity in the entire frequency band, and has sufficiently reduced noise. I understand that.

Patent applicant: Hitachi Maxell, Ltd. 221-

Claims (1)

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