JPH04353620A - Magnetic recording medium and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium wherein a flat output level from a low-frequency region to a high-frequency region can be obtained while it is provided with a magnetic layer whose coercive force Hc is high. CONSTITUTION:The surface roughness of a magnetic layer 2 formed on a base film 1 composed of a high-polymer resin film is set at 0.08mum or higher. For this purpose, a filler whose particle size is coarse is added to a magnetic paint used to form the magnetic layer 2. When the surface of the magnetic layer is made rough, a spacing loss generated between a magnetic head and the magnetic film is increased, and a sensitivity characteristic especially in a high- frequency region is suppressed.

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic tape in which a magnetic layer is formed on a base film made of a polymeric resin film. 2. Description of the Related Art The concept of the cross-sectional structure of such a magnetic recording medium is shown in FIG. That is, the magnetic recording medium is formed by forming a magnetic layer 2 on the surface of a base film 1 made of a film such as polyethylene terephthalate film (PET). Such a magnetic recording medium is manufactured by applying a thin layer of magnetic paint to the surface of the base film 1 and drying and curing it to form a magnetic layer 2. Magnetic paint is generally made by dispersing magnetic powder such as γ-Fe2O3 in a binder component dissolved in an organic solvent. Such magnetic recording media, in which magnetic recording is performed by the magnetization of the magnetic powder, are used, for example. It is cut into thin slits and used as a magnetic tape. For example, in a magnetic tape cassette, this magnetic tape is wound around a reel hub. For example, recording on audio magnetic tape,
The frequency band of the reproduced signal is 30Hz to 20KHz
Covers a wide range of areas. The output obtained in response to a certain input is generally referred to as "sensitivity," but in order to faithfully record and reproduce the original sound using audio magnetic tape, it is necessary to It is desirable that the sensitivity be flat and unbiased across frequencies. in particular,
In the case of audio magnetic tapes, it is said that it is desirable that the sensitivity deviation be about 1 to 2 dB or less when a specified recording level of -20 dB is input. In the case of audio magnetic tapes, in order to obtain such characteristics, the holding force Hc of the magnetic powder dispersed in the magnetic paint is appropriately adjusted to improve the sensitivity characteristics in the high frequency range. It is. For example, the coercive force Hc of the magnetic layer at the normal position is 300 to 400 Oe, and the coercive force Hc of the magnetic layer at the high position is 600 to 700 Oe.
Oe, the coercive force Hc of the magnetic layer at the metal position is 11
It is assumed to be 50 to 1250 Oe. In addition, in today's magnetic recording media, in order to meet the demands for high-density recording, the particles of magnetic powder forming the magnetic layer 2 have become much finer than in the past, and the surface roughness of the magnetic layer 2 has become much finer. Ra is approximately 0.0
It is about 3 μm. [Problems to be Solved by the Invention] However, when the magnetic layer 2 is formed using magnetic powder having a high coercive force Hc, the output level of the magnetic recording medium changes flat from the low frequency side, and the output level changes from the low frequency side to the high frequency region. There is a tendency for the output level to rise rapidly and then drop sharply. For example, Figure 2
shows the relationship between the output level and frequency obtained when a specified recording level of -20 dB is input, where the solid line represents the coercive force Hc of the magnetic layer 2 when the coercive force Hc of the magnetic layer 2 is 300 Oe, and the broken line represents the coercive force Hc of the magnetic layer 2. is 700 Oe. As described above, in a magnetic recording medium in which the magnetic layer 2 is formed using magnetic powder having a high coercive force Hc, the output in the high frequency range increases, but flat characteristics cannot be obtained from the low frequency range to the high frequency range. An object of the present invention is to provide a magnetic recording medium that can obtain a flat output level from a low frequency to a high frequency range, and a method for manufacturing the same. [Problems to be Solved by the Invention] That is, the gist of the means adopted in the present invention in order to solve the above problems is to form a magnetic layer 2 on a base film 1 made of a polymer resin film. The present invention is a magnetic recording medium characterized in that the surface roughness of the magnetic layer 2 is 0.08 μm or more. Furthermore, in the method for manufacturing a magnetic recording medium in which a magnetic coating is applied on a base film 1 made of a polymeric resin film and cured to form a magnetic layer 2, a filler with a coarse particle size is added to the magnetic coating. By this, the surface roughness of the magnetic layer 2 is reduced to 0.08 μm.
This is a method of manufacturing a magnetic recording medium characterized by the above adjustment. [Operation] When recording a magnetic signal on the magnetic layer of a magnetic recording medium and reproducing it, a magnetic head comes into contact with the surface of the magnetic layer. At this time, the magnetic layer and the magnetic head contact each other. If air gaps exist between them and there is insufficient contact, the output level will be reduced. This decrease in output level is generally called "spacing loss," and this spacing loss tends to increase in the high frequency region. Therefore, in the present invention, this spacing loss is actively utilized and magnetic powder with a high coercive force Hc is used.
While improving the frequency characteristics, the output level in the high frequency region is suppressed by spacing loss, and flat characteristics are obtained over the entire frequency region. Therefore, in the magnetic recording medium of the present invention, the surface of the magnetic layer is roughened to a surface roughness Ra of 0.08 μm or more, and the sensitivity characteristics in the high frequency region are improved by taking advantage of the increase in spacing loss caused by the roughness. suppress. moreover,
In the magnetic recording medium according to the present invention, the surface of the magnetic layer is roughened by adding a coarse filler component dispersed in the magnetic paint, so the surface of the magnetic layer is roughened while maintaining fine particles of magnetic powder. can do. Thereby, the required surface roughness can be obtained without degrading the magnetic properties of the magnetic layer. [Embodiments] Next, specific embodiments of the present invention will be described in detail. (Example 1) γFe2O3 (holding force Hc=700Oe)
100g, vinyl chloride 9g, polyurethane 9g,
A magnetic paint was prepared by kneading 1 g of Al2O3 (average particle size: 0.4 μm), 4 g of SiO2 (average particle size: 1.5 μm) as a filler, 100 g of methyl ethyl ketone, and 80 g of toluene. This magnetic paint was applied to a thickness of 5 μm on a polyethylene terephthalate film using a gravure roll coater. Next, this coating film was oriented in a magnetic field, dried, and then calendered to obtain an original magnetic tape. This original magnetic tape was slit into thin pieces using a slitter to produce a magnetic tape. and,
This magnetic tape was wound around a pair of reel hubs and assembled into a magnetic tape cassette. The holding force Hc of the obtained magnetic tape was 72
0 Oe, and the surface roughness Ra of the magnetic layer side of the magnetic tape is
As a result of measuring with a probe type surface roughness meter, it was 0.10 μm. Furthermore, this magnetic tape has a -20 dB difference to the frequency.
The sensitivity was determined by inputting a signal with a level of , and measuring the output difference in that frequency band. This sensitivity measurement was performed at 1KHz.
, 3.15 KHz, 12.5 KHz, and 16 KHz, and the results are shown in the sample No. 1 column of Table 1. (Example 2) In the above Example 1, the average particle size of SiO2 added to the magnetic paint as a filler was
A magnetic tape was produced in the same manner as in Example 1 except that the thickness was changed from 1.5 μm to 2.0 μm. The coercive force Hc of the magnetic film of this magnetic tape is 720 Oe, and the surface roughness Ra is 0.
．． It was 17 μm. In addition, the sensitivity at each frequency was measured in the same manner as in Example 1, and the results are shown in the column for sample No. 2 in Table 1. (Example 3) In Example 1, SiO2 (average particle size 1.
A magnetic tape was produced in the same manner as in Example 1, except that CaCO3 (average particle size: 1.0 μm) was used instead of CaCO3 (average particle size: 1.0 μm). The coercive force Hc of the magnetic film of this magnetic tape is 720
Oe and surface roughness Ra were 0.08 μm. In addition, the sensitivity at each frequency was measured in the same manner as in Example 1, and the results are shown in the column for sample No. 3 in Table 1. (Comparative Example) A magnetic tape was manufactured in the same manner as in Example 1 except that SiO2 was not added as a filler to the magnetic coating material. The holding force Hc of this magnetic tape is 720 Oe, and the surface roughness R
a was 0.03 μm. In addition, the sensitivity at each frequency was measured in the same manner as in Example 1, and the results are shown in Table 1.
It is shown in the column of sample No. 4. [Table 1] ──────────────────────
────────── Sample No. Filler particle size Holding force Hc Surface roughness Each frequency (KH
Sensitivity at (μm) (Oe
) (μm) 1 3.15 1
2.5 16 ────────────────
────────────────────
1 1.5 720
0.10 0.0 0.0
0.1 0.1 2
2.0 720 0.1
7 0.0 -0.2 -0.5
-1.5 3 1.0
720 0.08 0
．． 0 +0.3 +0.5 +1.3
4 0.4 720
0.03 0.0 0.
0 +1.0 +2.1 ────────
──────────────────────────
As is clear from the above examples and comparative examples, even if the holding force Hc is as high as 720 Oe,
In the example of the present invention, compared to the comparative example, 3.15KHz
It can be seen that the sensitivity in the above high frequency range is suppressed, and a generally flat sensitivity characteristic is obtained from the low frequency side to the high frequency side. [0016] As explained above, the magnetic recording medium according to the present invention is a magnetic recording medium that can obtain a flat output level from low frequency to high frequency range while having a magnetic layer with high coercive force Hc. There are advantages that the manufacturing method can provide.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a magnetic recording medium.

FIG. 2 is a graph showing an example of the relationship between frequency and output level.

[Explanation of symbols]

1 Base film 2 Magnetic layer

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic layer (2) formed on a base film (1) made of a polymeric resin film, wherein the surface roughness of the magnetic layer (2) is 0.0.
A magnetic recording medium characterized in that it has a diameter of 0.08 μm or more. 2. A method for manufacturing a magnetic recording medium, which comprises applying a magnetic paint onto a base film (1) made of a polymeric resin film and curing it to form a magnetic layer (2).
A method for manufacturing a magnetic recording medium, characterized in that the surface roughness of the magnetic layer (2) is adjusted to 0.08 μm or more by adding a filler with a coarse particle size to the magnetic coating material.