JPH071538B2 - Magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium that can be used for audio tapes, video tapes, magnetic disks and the like.

2. Description of the Related Art In recent years, particularly for video tapes, efforts for higher output and lower noise have been vigorously made. Among these, the residual magnetic flux density Br and the coercive force Hc of the magnetic recording medium are pointed out as the dominant factors for the output. Therefore, the alloy magnetic powder having a saturation magnetization and coercive force about twice that of the oxide magnetic powder is very useful for high output. The alloy magnetic powder-based magnetic recording medium is the optimum Br / H based on the magnetic recording theory.
c is almost the same as the oxide system. On the other hand, Br is about double, and theoretically the output can be doubled, that is, about 6 dB can be improved. As these prior arts, for example, JP-A-57-143733 is known.

Problems to be Solved by the Invention However, since the alloy magnetic powder has a large magnetic moment, agglomeration of the magnetic powders easily occurs and the dispersibility is poor. Modulation noise generated when a signal is recorded / reproduced on / from a magnetic recording medium largely depends on the degree of dispersion of magnetic powder.
Therefore, although the alloy magnetic powder type magnetic recording medium having a poor dispersity shows an improvement of about 6 dB in the output as compared with the oxide type, the modulation noise also increases almost in proportion to it and the signal noise increases. No significant improvement in noise ratio.

In view of the above problems, the present invention provides a high output, low noise alloy magnetic powder magnetic recording medium.

Means for Solving the Problems In order to solve the above problems, the present invention provides a magnetic recording medium in which a magnetic coating material containing an alloy magnetic powder is applied on a non-magnetic support and subjected to orientation treatment. The maximum squareness ratio Br / B in the in-plane horizontal direction of the magnetic recording medium measured with the above maximum magnetic field
Br / Bm in the direction with m and orientation ratio Br / Br '(remanent magnetic flux density in the direction having the maximum squareness ratio in the horizontal direction / remanent magnetic flux density in the direction 90 ° different from the direction in the horizontal plane) are 0. <(Br / B
It has been found that modulation noise can be significantly reduced by creating a magnetic layer dispersed so as to satisfy r ′) · (1-Br / Bm) <0.370.

Action Conventional methods for evaluating the degree of dispersion include excess rate of the magnetic coating material, surface smoothness of the magnetic layer after coating, and magnetic characteristics. Here, the magnetic property means the squareness ratio Br / Bm or the orientation ratio B.
r / Br ', which has been used independently as a measure of the degree of orientation of magnetic powder, that is, the degree of dispersion.

As a result of diligent study of the relationship between the modulation noise, that is, the degree of dispersion and the magnetic characteristics, the inventors of the present invention found that the square ratio and the orientation ratio are not individual values, but the product of these two (Br / Br It was clarified that ′) · (1-Br / Bm) is a very good indicator of the degree of dispersion.

Further, it was found that the modulation noise was remarkably reduced by creating an alloy magnetic powder type magnetic recording medium dispersed so that (Br / Br '). (1-Br / Bm) <0.370. The above formula was established by experimentally determining the relationship between the squareness ratio Br / Bm and the orientation ratio Br / Br 'that determine the allowable upper limit of noise.

Example As magnetic alloy powder used in the present invention, metallic iron, Fe-
Co, Fe-Ni, Co-Ni, Fe-Ni-Cr, Fe-Co-B, Fe-Co-Cr-
Examples include B. As the binder, polyurethane resin, vinyl chloride resin, nitrocellulose, nitrocellulose derivative, polyester resin, butyral resin, phenoxy resin, or a mixture thereof can be used. As the dispersant, lecithin or higher fatty acids such as oleic acid and palmitic acid can be used. Α- as an abrasive
Alumina, α-Fe ₂ O ₃ , chromium oxide, etc. are used. As an antistatic agent, conductive carbon such as Ketchin Black EC may be added.

Various kneading machines are used for kneading and dispersing the magnetic paint. For example, three roll mill, agitator mill, ball mill, pebble mill, sand grinder, high speed impeller disperser, high speed stone mill Henschel mixer,
High-speed impact mill, disper, attritor, kneader,
A high speed mixer, a homogenizer co-ball mill, an ultrasonic disperser, etc. may be used alone or in combination.

The present invention will be described in more detail below.

(Example 1) Ferromagnetic metallic iron powder The above composition was kneaded and dispersed in a ball mill for 48 hours. Next, 4 parts of Coronate L (polyisocyanate, trade name of Nippon Polyurethane Co., Ltd.) is added, and the mixture is passed through a filter having an average pore size of 1 μm. It is applied on a polyethylene terephthalate film with a thickness of 10 μm, oriented, dried, calendered, and then cured. Further, a back coat layer containing carbon black as a main component was provided on polyethylene terephthalate on the side opposite to the magnetic layer to obtain a magnetic tape.

(Comparative Example 1) A magnetic tape was obtained in the same manner as in Example 1, except that the kneading and dispersing time by the ball mill was 96 hours.

(Example 2) Fe-Cr-Ni alloy magnetic powder Composition ratio 90: 2: 8 The composition was kneaded with an attritor for 5 hours and then mixed and dispersed in a sand mill for 2 hours to obtain a magnetic coating material. After that, 6 parts of Desmodur L (trade name of polyisocyanate manufactured by Bayer) was added, and the mixture was stirred with a disper, and then the average pore diameter was 1
Pass with a μm filter. This is applied onto polyethylene terephthalate with a thickness of 10 μm, oriented, dried, calendered and then cured. Further, a back coat layer containing carbon black and calcium carbonate as main components was provided on polyethylene terephthalate on the side opposite to the magnetic layer to obtain a magnetic tape.

(Example 2) In Example 2, the magnetic powder was replaced with a Fe-Cr-Ni alloy. A magnetic tape was obtained in the same manner except that

For each magnetic tape obtained, the magnetic properties when measured under the condition of maximum magnetic field of 5 KOe, and the surface roughness Ra (arithmetic mean of deviation from the center line of surface roughness) measured by Tallysurf manufactured by Rank Taylor Hobson The results are shown in Table 1.

Further, the magnetic tape was cut into 1/2 inch width, wound around a cassette half, and C / N and modulation noise Nm were measured.
The results are also shown in Table 1.

In the figure, the modulation noise in Examples 1 and 2 and Comparative Examples 1 and 2 and (Br / B
r ′) · (1-Br / Bm) is shown. C / N is at 5 MHz, and modulation noise Nm is the average value of modulation noise from 1 MHz to 4.5 MHz. The VHS video tape recorder (Matsushita Electric Industrial Co., Ltd.) with a recording / playback head changed to Sendust alloy was used for the video deck for recording / playback characteristics measurement.
Manufactured by NV-8800) was used. As standard tape, National Video Tape Super HG120 (Matsushita Electric Industrial Co., Ltd.)
Manufactured by NV-T120HG) and its C / N was set to 0 dB.

EFFECTS OF THE INVENTION The present invention has a lower modulation noise Nm in the examples in which (Br / Br ′) · (1-Br / Bm) is 0.370 or less, as is clear from the comparative examples corresponding to the examples. C / N is improving.

From the above, the effect of the present invention on noise reduction and C / N improvement is clear.

[Brief description of drawings]

The figure shows the relationship between the modulation noise Nm and (Br / Br '). Multidot. (1-Br / Bm) in the examples and comparative examples of the present invention.

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic coating material containing an alloy magnetic powder is applied on a non-magnetic support and subjected to orientation treatment, wherein the magnetic recording medium is measured in a maximum magnetic field of 5 KOe or more in the in-plane horizontal direction. And Br / Bm in the direction with the maximum squareness ratio of Br / Bm, and the orientation ratio Br / Br '(residual magnetic flux density in the direction with the maximum squareness ratio in the horizontal direction / 90 ° with the above direction in the horizontal plane). A residual magnetic flux density in different directions) satisfies the following expression 0 <(Br / Br ') · (1-Br / Bm) <0.370.