JPS62204427A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the closeness of texture of an image and the resolution without deteriorating the linear audio characteristic by providing the first magnetic layer having an axis easy for magnetization in the in-plane direction on a carrier, and furnishing the second coat-type magnetic layer consisting essentially of hexagonal ferrite magnetic powder on the first magnetic layer in about 0.01-0.7mum thickness. CONSTITUTION:The first magnetic paint consisting essentially of Co coated gamma-Fe2O3, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and polyurethane is prepared. Besides, the second magnetic paint consisting essentially of hexagonal barium ferrite magnetic powder, a vinyl chloride-vinyl acetate copolymer, and polyurethane is prepared. The first magnetic material is coated on a nonmagnetic carrier of polyethylene terephthalate film, etc., in 4-7mum thickness to form the first magnetic layer, and the second magnetic paint is coated on the first magnetic layer in 0.01-0.7mum thickness to form the second magnetic layer. Subsequently, the material is slit, for example, in 1/2 inch width to obtain the magnetic recording medium of a magnetic tape for a video, etc.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks.

[Prior art and its problems]

1;j Since then, from the viewpoint of high-density recording, for example, in magnetic tape, γ-FezO, C
A coated first magnetic layer 8 with a thickness of 5 to 7 μm having an easy axis of magnetic f in the in-plane direction of rO2, Co deposited, Fe, O, and cap is provided, and on this first magnetic Jffl. A magnetic recording medium was proposed in which a coated second magnetic layer with a thickness of 1 to 5 μm mainly composed of barium ferrite magnetic powder was provided (Japanese Unexamined Patent Application Publication No. 1983-1992).
No. 119610). Although such a magnetic recording medium certainly has the great advantage of improving recording characteristics in a short wavelength region, it has the disadvantage that linear audio characteristics are not so good. c+fF, Akira's Disclosure] As a result of research into why the above-mentioned magnetic recording media do not have good linear audio characteristics, the present inventor has discovered 7.
- Fe2J, CrO2, Co coated - Fe2O, etc. on the first magnetic layer having a magnetic easy axis in the in-plane direction Barium ferrite magnetic It was discovered that there was a problem with the J-blindness of the second magnetic layer of the coated type, and when the thickness of the second magnetic layer of the coated type was about 0.01 to 0.7 μmo, the linear We have discovered that the audio characteristics have been significantly improved, and that even with the coating-type second magnetic layer 35.V, the high-density recording characteristics hardly deteriorate, and we have achieved the present invention. In other words, it is a two-layer magnetic recording medium consisting of a first magnetic layer having an axis of easy magnetization in the in-plane direction and a coated second magnetic layer mainly composed of hexagonal ferrite magnetic powder. As research progresses, it has become clear that, for example, when recording with current home video tape recorders, the video signal is only recorded to a level slightly below the surface due to its short wavelength. It has been found that linear audio signals are thought to be recorded in the almost thin layer of the magnetic layer because of their long wavelengths.In other words, the video signal is recorded in the upper layer of the magnetic layer, and the linear audio signal is recorded in the lower layer. It is safe to assume that the signals are recorded separately.A magnetic layer with an axis of easy magnetization in the in-plane direction has no problem with its linear audio characteristics, and is a hexagonal crystal system. It is known that ferrite magnetic powder has excellent properties in terms of short wavelength (1). Therefore, based on this knowledge, we have developed a magnetic layer with an axis of easy magnetization in the in-plane direction and a hexagonal system. In a two-layer magnetic recording medium consisting of a coated magnetic layer containing ferrite magnetic decay 1 as a main component, the first magnetic layer (] rc4') is composed of a magnetic layer containing an easy axis of magnetization in the in-plane direction. However, if the second magnetic layer (upper layer) is composed of a coated magnetic layer mainly composed of hexagonal ferrite magnetic powder, and if the thickness of this second magnetic layer is made as thick as possible, linear audio We thought that the characteristics would be improved. Based on this idea, we varied the thickness of the second coated magnetic N and investigated how this would affect the linear audio characteristics. In other words, the normal audio operation recording bias current of current home video tape recorders is the value at which the maximum output when recording and playing back the I K It z signal is lowered by 0.5 d [l]. The optimum bias current is used. In a conventionally proposed magnetic recording medium, that is, a coating-type second magnetic layer containing hexagonal barium ferrite I magnetic powder as a main component and having a J7 value of about 1 to 5 μIn, It was found that there was a large deviation from the above setting conditions, for example, the thickness of the second magnetic layer of this coating type was 1.
The optimum operating bias current deviates by 15% at 5 μm, and the thickness of the coated second magnetic layer is 0.80 μm.
However, it was found that the deviation was as much as 11%, and the distortion rate was large at 4.2% and 3.2%, respectively. Furthermore, the MOL was significantly reduced at -3.0 dB and -1.0 dB, respectively, and the linear audio characteristics were This is very bad. However, the thickness of the second magnetic layer of this coating type was set to 0.65.
When it comes to μ river, the deviation of the optimal operating bias current is 4.2%.
In addition, the distortion rate was as low as 2.4%, and the drop in MOL was significantly reduced to -0.2dB, and the linear audio characteristics were significantly improved. Furthermore, even if the thickness of the coated second magnetic layer is made extremely thin, short wavelength recording in the video area is possible. In other words, there was almost no adverse effect on high-density recording.

[Example 1] First, 100 parts by weight of Co-deposited γ-Fe20* (coercive force 630 oersted), 15 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer, polyurethane 201
1 m part of i, 6 parts of plasticizer, 1 part of 2 parts of dispersant, 70 parts by weight of methyl isobutyl ketone, 60 parts by weight of methyl ethyl ketone
A first magnetic paint is prepared by thoroughly cross-dispersing a mixture of parts by weight and 60 ffi parts of toluene. In addition, hexagonal barium ferrite magnetic powder (coercive force 620
100 parts by weight of vinyl chloride-vinyl acetate copolymer, 20 parts by weight of polyurethane, 41 parts by weight of plasticizer. 1 part of dispersant 41iJ, 1 part of lubricant, 52 parts of Cr2O, 7 parts of methyl isobutyl ketone
0 parts by weight, 60 parts by weight of methyl ethyl ketone, 6 parts by weight of toluene
A second magnetic paint is prepared by thoroughly cross-dispersing 0 parts by weight of the mixture. Then, a first magnetic paint is applied to a thickness of 4 to 7 μm, for example, 4.0 μm, on a non-magnetic support such as a polyethylene terephthalate film to form a first magnetic layer, and the first magnetic coating On top of the layer, apply 0.01 of the second magnetic paint.
~0.7) A second magnetic layer is formed by coating to a thickness of, for example, 0.85 μm. The first magnetic layer is subjected to magnetic field orientation treatment or mechanical orientation treatment so that the acicular magnetic powder is oriented in the longitudinal direction. Then, the ribs on which the coated first magnetic layer and the coated second magnetic layer were formed on the support as described above are slit into a width of, for example, 172 inches, and the magnetic tape used for magnetic tape such as video tape is slitted. Obtain a recording medium. [Ratio Example 1] A magnetic recording medium was obtained in exactly the same manner as in Example 1111 except that the thickness of the coated second magnetic layer was set to 0.80 μm.

[Comparative Example 2] In Example 1, the thickness of the coated second magnetic layer was changed to 1.
A magnetic recording medium is obtained in exactly the same manner except that 57zs is used.

【Characteristic】

Regarding the magnetic recording media obtained between the above, the deviation of the optimum operating bias, the strain rate, and the maximum output level at 3% strain (M
OL) is as shown in the table. As will be seen from now on, the magnetic recording medium of this example has extremely small deviation and low strain rate, and furthermore, the M O
L is also small and there is no problem in practical use, and the linear audio characteristics are good. However, the magnetic recording media of 11SI112 examples have sharply large deviations, large distortion rates, and even MOL etc. It has become noticeably louder, and the linear audio characteristics have significantly deteriorated. Although the thickness of the coated second magnetic layer in the magnetic recording medium of this example is about half or less than that of Comparative Example 2, its high-density characteristics are almost unaffected. Met. Further, in this example, the first magnetic layer is formed on the support by coating, but the same effect can be obtained by forming it by sputtering, for example.

【effect】

The magnetic recording medium according to the present invention includes a first magnetic layer having an axis of easy magnetization in the in-plane direction on a support, and a magnetic layer containing hexagonal ferrite l-magnetic powder as a main component on the first magnetic layer. Since the coating-type second magnetic layer of 0.7 μm is provided to the thickness of approximately 0.01 μm, it is possible to improve the fineness of the picture drum and the degree of resolution without impairing the linear audio characteristics. It has characteristics.

Claims (1)

[Claims] A first magnetic layer having an axis of easy magnetization in the in-plane direction is provided on the support, and a layer of about 0.01 to 0.7 μm thick containing hexagonal ferrite magnetic powder as a main component is disposed on the first magnetic layer. 1. A magnetic recording medium comprising a coating-type second magnetic layer.