JPH08185623A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To ensure satisfactory dispersibility and to provide a magnetic recording medium having satisfactory electromagnetic transducing characteristics and still durability. CONSTITUTION: Magnetic powder used in a magnetic layer is iron nitride powder having 160-210emu/g saturation magnetization σs , 1,500-2,500Oe coercive force, an acicularity ratio of 5-15 and 0.05-0.15μm major axis size. One kind of surfactant or a mixture of surfactants selected from among carboxylate, sulfonate, nitric ester and phosphoric ester surfactants, betaine type, ether type, ether ester type and ester type surfactants, a nitrogen-contg. surfactant and modified products of them and phosphoric ester and/or lecithin are added to the magnetic powder by 0.2-5wt.%.

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,
In particular, the present invention relates to a coating type magnetic recording medium that realizes high electromagnetic conversion characteristics and good reliability.

[0002]

2. Description of the Related Art In order to increase the recording density of a magnetic recording medium, the magnetic characteristics are being improved. Therefore, it is well known that it is effective to use magnetic powder having high magnetic properties in order to improve the magnetic properties of the coating film of the medium.

However, magnetic powders having high magnetic properties, especially those having a high saturation magnetization σ _s , have a strong magnetic attraction between the magnetic powders and the dispersibility of the magnetic powders during the preparation of the magnetic coating is poor. Advancement of dispersion contributes to improvement of magnetic characteristics, improvement of reproduction output, and reduction of noise level. Further, resin is more adsorbed on the surface of the magnetic powder in the manufacturing process so that mechanical strength is increased and reliability is improved. It will be done. From the above, improving the dispersibility of magnetic powder having high magnetic characteristics improves both electromagnetic conversion characteristics and reliability, but it is not yet sufficient.

[0004]

The present invention has been made in view of the above problems, and provides a magnetic recording medium which realizes high electromagnetic conversion characteristics and good reliability, and is provided on a film-shaped support. A magnetic recording medium formed by applying a magnetic layer to the magnetic layer, the magnetic powder used in the magnetic layer is iron nitride, and the saturation magnetization σ _s is 160 to 210 emu / g,
Holding power Hc is 1500-2500 Oe, needle ratio is 5-1
5. The major axis length is 0.05 ~ 0.15μm, and carboxylate, sulfonate, nitrate ester salt, phosphate ester salt, betaine type, ether type, ether ester type as a surfactant in the magnetic layer. , Ester type, nitrogen-containing type and modified products thereof, phosphoric acid ester, lecithin of 1 to 2 kinds with respect to magnetic powder 0.2
By adding ~ 5% (part by weight), a magnetic recording medium having high electromagnetic conversion characteristics and good reliability was realized.

[0005]

The present invention relates to a coating type magnetic recording medium, which uses iron nitride magnetic powder in a magnetic layer and adds a surfactant to achieve high electromagnetic conversion characteristics and good reliability and storage stability. To do.

That is, it is effective to use fine magnetic powder having high magnetic characteristics in order to realize high electromagnetic conversion characteristics.

In the present invention, it is effective to use, as the above-mentioned iron nitride-based magnetic powder as the magnetic powder having high magnetic properties, the one represented by the chemical formula <1>, which is larger than the widely used metal magnetic powder. It shows a high saturation magnetization,
It was effective in realizing good magnetic properties.

[0008]

Embedded image

Regarding the composition of the magnetic powder, the saturation magnetization σ _s
Is 160 to 210 emu / g, holding power Hc 1500 to 25
00 Oe, acicular ratio 5 to 15, major axis length 0.05 to 0.
By setting the thickness to 15 μm, high magnetic properties and good chemical stability were obtained.

Regarding the saturation magnetization amount σ _s of the magnetic powder, when the saturation magnetization amount σ _s is 160 emu / g or less, the saturation magnetic flux density Bm of the magnetic layer after mediumization is not sufficient to satisfy the electromagnetic conversion characteristics. Didn't arrive. If the magnetic powder has good chemical stability, the saturation magnetization σ _s is 21
A magnetic powder of 0 emu / g or more could not be produced.

If the acicular ratio of the magnetic powder is less than 5, the orientation will be poor, the squareness ratio after mediumization will be low, and good electromagnetic conversion characteristics cannot be realized, and the acicular ratio will be 15.
If it exceeds, the magnetic properties and electromagnetic conversion properties after being made into media become poor. It is presumed that the cause of this is that it is difficult to disperse the magnetic powder in terms of shape and that the magnetic powder is destroyed.

If the major axis length of the magnetic powder is less than 0.05, it is difficult to improve the magnetic properties,
Also, dispersion became difficult, and as a result, the magnetic properties of the magnetic layer after being made into a medium were low. When the major axis length exceeds 0.15 μm, the reproduction output and the C / N ratio when the short wavelength signal is recorded / reproduced.
Became lower.

The holding power Hc of the magnetic powder is 1500
If it is Oe or less, the reproduction output at the time of recording / reproduction of the short wavelength signal is low, and if it is 2500 Oe or more, the reproduction output at the time of recording / reproduction of the long wavelength signal is low, which further deteriorates the erasing rate.

It has been found that the dispersibility is remarkably improved by adding a surfactant to the magnetic layer when a magnetic coating material is prepared by using the above magnetic powder to prepare a magnetic layer of a medium. . As a result, a magnetic recording medium with improved electromagnetic conversion characteristics, mechanical strength and reliability was realized.

As the surfactant, carboxylate, sulfonate, nitrate ester salt, phosphate ester salt, betaine type, ether type, ether ester type,
Ester type, nitrogen-containing type and their modified products,
It was effective to add 0.2 to 5% (parts by weight) of the phosphate and lecithin to the magnetic powder.

Specific examples of the magnetic recording medium according to the present invention will be described below. The magnetic paint was prepared with the following composition.

Magnetic powder 100 parts by weight Polyvinyl butyral (Sekisui Chemical's S-REC B-BX1) 10 parts by weight Polyurethane (TOYOBO UR8300) 10 parts by weight α-alumina 2 parts by weight Carbon black 2 parts by weight Surfactant 1 X parts by weight Interface Activator 2 Y parts by weight Palmitic acid (Coronate L manufactured by Nippon Polyurethane) 2 parts by weight Isocyanate 3 parts by weight Cyclohexanone 100 parts by weight Methyl ethyl ketone 100 parts by weight The above mixture was mixed and dispersed by a sand mill. The amounts of the magnetic powder and the surfactant used here are shown in Table 1, Table 2 and Table 3
And Table 4 respectively.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

The glossiness of the magnetic paints of Examples 1 to 19 and Comparative Examples 1 to 7 thus obtained during dispersion were measured, and the results are shown in Table 5.

[0023]

[Table 5]

Further, the dispersed paint is applied on a polyester film having a thickness of 10 μm and slit to a width of 1/2 inch to prepare a tape for D-3 format, which is D-3VT.
R (Matsushita, AJ-D350) is used to measure the reproduction output by inputting a 40 MHz sine wave signal, and the still resistance is the same VTR in an environment of 20 ° C and a humidity of 10%. The measurement was carried out in Table 1 and the results are shown in Table 6.

[0025]

[Table 6]

From the above-mentioned evaluation, it is understood that Examples 1 to 16 have high gloss during dispersion, high reproduction output, and extremely excellent still resistance.

On the other hand, in Comparative Examples 1 and 4, the glossiness during dispersion is low, the reproduction output is low, and the still resistance is poor. In Comparative Examples 2 and 3, the glossiness during dispersion is high and the reproduction output is also high, but still resistance is extremely poor. In Comparative Examples 5 and 6, metal magnetic powder was used and a surfactant was added, but the improvement in gloss during dispersion was small and the reproduction output was also low.

From the above, it is possible to greatly improve the dispersibility by adding the above-mentioned amount of the surface active agent using the iron nitride magnetic powder, and to obtain good reproduction output and still resistance. I was able to.

[0029]

The magnetic recording medium according to the present invention, which has been described in detail above, has an effect that the dispersibility is improved by the surfactant and the electromagnetic conversion characteristics and the still resistance are realized.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a film-shaped support coated with a magnetic layer, wherein the magnetic powder used in the magnetic layer is iron nitride and the saturation magnetization σ _s is 160-.
210emu / g, coercive force Hc is 1500-2500O
e, acicular ratio 5 to 15, major axis length 0.05 to 0.15μ
m is a carboxylate, sulfonate, nitrate ester salt, phosphate ester salt, betaine type, ether type, ether ester type, ester type, nitrogen-containing type and / or one of these modified surfactants.
A magnetic recording medium, characterized in that 0.2 to 5% (parts by weight) of the seed or mixture and / or phosphate ester and lecithin are added to the magnetic powder.