JPS6194231A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the reproduction output, traveling performance and light shielding property and to enable high density recording by forming a magnetic layer contg. chromium dioxide. CONSTITUTION:Chromium dioxide is incorporated into the magnetic layer of a magnetic recording medium contg. magnetic powder of hexagonal ferrite to improve the light shielding property, durability and traveling performance and to prevent well the clogging of a magnetic head. Unlike carbon, black chromium dioxide reduces hardly the dispersibility, magnetic characteristics and S/N. The preferred average particle size of the chromium dioxide is about 0.1-0.5mum. The average particle size of the magnetic powder of hexagonal ferrite is preferably regulated to <=about 0.2mum so as to carry out recording and reproduction in high S/N especially in a high frequency region. The amount of the chromium dioxide is about 0.5-50pts.wt. per 100pts.wt. magnetic powder of hexagonal ferrite. The resulting magnetic recording medium has high reproduction output, traveling performance and light shielding property and can be adapted to high density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic tape for video or audio, or a magnetic disk such as a floppy disk.

[Prior art and its problems]

Magnetic recording media using hexagonal ferrite magnetic powder have been extensively researched and a number of proposals have been made to ensure that they are compatible with high-density recording.

In video magnetic tapes, floppy disks, etc. that use such hexagonal ferrite magnetic powder, carbon black with high light absorbance is contained in the magnetic layer due to the requirement for light-shielding properties. , the present inventor found that a magnetic paint containing carbon black and hexagonal ferrite magnetic powder has poor dispersibility, that is, the macrogonal ferrite magnetic powder is a plate-like powder and the magnetic cohesive force between the particles is large. Therefore, not only is it difficult to fractionate compared to acicular magnetic powder, but also the dispersibility of magnetic paint containing both is extremely poor due to the action of carbon black.
Therefore, it was noticed that the electromagnetic conversion characteristics deteriorated. Also, since carbon black is a non-magnetic material,
The reproduction output decreases accordingly.

Furthermore, in magnetic tapes for video and the like, an abrasive is added to the magnetic layer from the viewpoint of durability, running performance, and prevention of clogging of the magnetic head.

However, in order for the abrasive to efficiently develop its polishing effect, the average particle size of the abrasive is required to be approximately 0.3 μm or more. If an abrasive is contained in the magnetic layer containing crystalline ferrite magnetic powder, this abrasive becomes a source of noise, causing S/
It has also been found that N decreases.

[Disclosure of the invention]

The present inventor has discovered that in a magnetic recording medium using hexagonal ferrite magnetic powder, chromium dioxide (Cr0=) is present in the magnetic layer.
By adding carbon black, it is possible not only to effectively improve the above-mentioned light shielding properties, durability, runnability, and prevention of clogging of the magnetic head, but also to reduce the dispersibility that occurs when carbon black is used. It has been found that it is possible to provide a magnetic recording medium that has fewer drawbacks such as deterioration of magnetic properties and deterioration of S/N.

In other words, chromium dioxide has a higher degree of blackness than CO-coated iron oxide, so adding chromium dioxide is a good idea! l
l It can solve the problem of light-shielding properties, and in this case, the deterioration of dispersibility and therefore the deterioration of magnetic properties does not occur as in the case of carbon black, and since it is not a non-magnetic material, the problem of deterioration of reproduction output does not occur. In addition, since chromium dioxide has an abrasive effect, adding chromium dioxide is effective in improving durability, running performance, and preventing clogging of magnetic heads.Moreover, if a nonmagnetic abrasive is added at this time, The decrease in S/N that occurs in this case is not so much of a problem.

In addition, in coated magnetic recording media, it is thought that the magnetic powder particles are single-domain particles, and the smaller the particle size of the magnetic powder, the smaller the noise, but if it is too small, it will have a negative effect on the dispersibility of the magnetic paint. Therefore, the average particle size of chromium dioxide is preferably about 0.1 to 0.5 μm.

Furthermore, in order to perform recording and reproduction with good S/N especially in the high frequency range, hexagonal ferrite magnetic powder such as barium ferrite magnetic powder or substituted barium ferrite magnetic powder has an average particle size of about 0. The thickness is preferably 2 μm or less.

In addition, if the content of chromium dioxide is too low, the light shielding property and polishing effect will be weak, and if the content is too high, the wear of the magnetic head will increase.
Preferably, it is about 0.5 to 50 parts by weight, more preferably about 5 to 30 parts by weight.

〔Example〕

100 parts by weight of barium ferrite magnetic powder with coercive force Hc approx. 5500e, average particle size approx. 0.15 μm, Hc approx. 5300
e, about 5 chromium dioxide with an average particle size of about 0.1 to 0.7 μm
0 parts by weight or less, 30 parts by weight of a binder, 1 part by weight of a dispersant, 2 parts by weight of a lubricant, and 300 parts by weight of a solvent are thoroughly mixed and dispersed to prepare a magnetic paint.
Parts by weight were added, and the mixture was coated to a predetermined thickness on a polyethylene terephthalate film, and after calendering, it was slit to a predetermined width to form a video magnetic tape.

[Comparative Example 1] A video magnetic tape was constructed in the same manner as in the above example, but without adding chromium dioxide.

[Comparative Example 2] A video magnetic tape was constructed in the same manner as in the above Example except that 8 parts by weight of carbon black and 10 parts by weight of alumina were used in place of chromium dioxide.

〔Characteristic〕

When examining the light absorption coefficient α, magnetic head wear amount β, and dynamic friction coefficient μ at a wavelength of 800 nm for each of the above sides, the results are shown in the table.

As can be seen, both the light-shielding properties and running properties are improved, and it has been shown that the addition of chromium dioxide has an effect comparable to that of the addition of carbon black and alumina in terms of light-shielding properties and running properties.

Further, as shown in FIG. 1, the reproduced output characteristics are high, and the reproduction output of the device according to the present invention is high, and the decrease in the reproduced output is small even when repeated reproduction is performed. In other words, it can be seen that the method of adding chromium dioxide is significantly superior to the method of adding carbon black and alumina. It can also be seen that there is little clogging of the magnetic head. In short, comparative example 2
In Comparative Example 1, the dispersion of the magnetic paint was poor and the output decreased due to the addition of carbon black and alumina, whereas in Comparative Example 1, the output suddenly decreased after repeated regeneration. On the other hand, this defect is not observed in the case of the present example. As the amount of chromium dioxide added increases, the regeneration output improves.

Next, C/N is determined by the average particle size of the added chromium dioxide.
When examining how the chromium dioxide changes, the results are shown in Figure 2.As the average particle size of chromium dioxide increases, the C/N decreases, and the average particle size of chromium dioxide is approximately 0.5
A value smaller than μm is desirable.

Furthermore, when we examine the relationship between the playback output when recording a 5 MHz FM signal and the amount of chromium dioxide added, we find that the relationship between the amount of chromium dioxide added and the amount of chromium dioxide added is as shown in Figure 3. According to this, it is preferable to add more chromium dioxide. When running repeatedly for 100 hours under the conditions of , 40°C and 80% RH, as shown in Figure 3, as the amount of chromium dioxide added increases, the amount of wear on the magnetic head increases; therefore, chromium dioxide is macrogonal. Ferrite magnetic powder 100
It is preferably about 0.5 to 50 parts by weight, more preferably about 5 to 30 parts by weight.

〔effect〕

It has excellent reproduction output, runnability, light-shielding properties, etc., and can also be used for high-density recording.

[Brief explanation of drawings]

1 to 3 are graphs showing the characteristics of magnetic recording media. Rest 1 Trouble T 2 Figure 2 Lucky Riron Dining I (pm) 73rd

Claims (1)

[Claims] A magnetic recording medium using hexagonal ferrite magnetic powder, characterized in that the magnetic layer contains chromium dioxide.