JPH043325A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the output characteristic by providing a multilayered constitution magnetic layer on the other face of a nonmagnetic supporting body whose one face a back coat layer is formed and including magnetic powder having a required form in the uppermost magnetic layer and setting the magnetic layer thickness to a specific value and prescribing coercive force relations between upper and lower magnetic layers. CONSTITUTION:Magnetic powder having a plate form is included in the uppermost layer of the multilayered lamination magnetic layer and the thickness of the magnetic layer is set to 0.1 to 0.5mum, and the coercive force of the lower magnetic layer is made weaker than that of the upper magnetic layer. Thus, a magnetic recording medium is obtained which has the output characteristic improved to have a short wavelength output higher than that for the use of a shombohedral iron oxide and have the same long wavelength output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media used in video equipment and the like that require high-density recording, and in particular to magnetic recording media that are used in conventional acicular iron oxide tapes. This is a magnetic recording medium that emphasizes compatibility with the conventional acicular iron oxide tape, shows equivalent output in the long wavelength region, and has better characteristics in the short wavelength region than conventional acicular iron oxide tapes.

BACKGROUND OF THE INVENTION Magnetic recording has traditionally been developed using a longitudinal magnetic recording method that uses in-plane magnetization of a magnetic recording medium. Most of the magnetic tapes currently in use use this longitudinal recording method.

Currently, the magnetic materials constituting the medium are acicular iron oxide and metal magnetic powder, and in order to increase the strength of the coating and polish the magnetic head, alumina, chromium dioxide,
Titanium Mide and other abrasives are added, carbon is added to lower electrical resistance and improve runnability, and lubricant is added to improve runnability and durability, and these materials are uniformly mixed in an organic binder. It is well known that magnetic films can be obtained by dispersion. These prior disclosed techniques include, for example, Japanese Patent Publication No. 60-47650, Japanese Patent Application Publication No. 60160018, Japanese Patent Application Publication No. 61-115237, and Japanese Patent Application Publication No. 63-1989.
There are publications such as No. 166011. Regarding the back coat layer, many prior art techniques have been disclosed with the main purpose being to ensure runnability in VTRs and prevent static electricity. For example, JP-A-5
7212622 Publication 1 JP-A-57-208637, JP-A-58-200426, JP-A-59-9
There is a publication No. 2436.

Gravure coating, applicator coating, etc. are generally well known methods for forming magnetic coatings on non-magnetic substrates, but recently, multilayer coating technology has been developed, for example, in Japanese Patent Laid-Open No. 6
It is disclosed in 2-257263 and the like.

In terms of output, tapes using metal magnetic powder are
Because the magnetic powder has a large saturation magnetization, it is more advantageous than tapes using acicular iron oxide. However, metal magnetic powder is highly reactive if left as it is, and its characteristics deteriorate as a result of environmental changes. For this purpose, a protective layer is provided on the surface of the magnetic powder. By the way, 5-VHS video decks have become popular these days, but the magnetic tape used for them is different from the conventional VHS video deck.
Acicular iron oxide, which has been used in HS tape, is used. However, in order to improve the CN ratio, attempts have been made to make the magnetic powder particles finer and to increase the coercive force. 5VH3 maintains backward compatibility, and tapes recorded on conventional VHS decks can be played back on 5-VHS decks. This backward compatibility means that there is no major confusion for users, and 5-V
It is moving to H3. It is considered that the existence of backward compatible tapes with better characteristics has greatly contributed to this.

As in the example above, the backward compatibility of next-generation VTR decks with current models seems to be a very important factor for users, and we would like to pay attention to the development of magnetic tapes that enable backward compatibility of VTRs. I have paid.

On the other hand, a perpendicular magnetic recording system which is excellent in principle has been proposed in order to dramatically increase the recording density. For example, the literature includes Nikkei Electronics, August 7, 1978, 2100-111 by Iwasaki.

As a means of achieving high-density recording using this perpendicular recording method, it was published in Japanese Unexamined Patent Application Publication No. 6 (1983) to use orthogonal ferrite fine powder.
It is disclosed in Japanese Patent Application Laid-open No. 0-149205 and Japanese Patent Application Laid-Open No. 149106-1983.

It has been reported that barium ferrite magnetic powder, which is a fine hexagonal ferrite powder, utilizes the principle of perpendicular magnetic recording to obtain good output and C/N ratio in short wavelength recording. For example, the literature includes Toshiba Review by Yokoyama et al. (vol. 40, 13).
No.) has a pH of 11 to 1114.

Regarding multilayer tapes using plate-shaped magnetic powder, for example, Japanese Patent Application Laid-Open No. 60-212815, Japanese Patent Application Laid-Open No. 60-212
Although disclosed in Japanese Patent No. 818, the actual situation is that even with this method, the output during long wavelength recording and reproduction is still not sufficient.

Problems to be Solved by the Invention As explained above, magnetic recording media using hexagonal ferrite magnetic powder and conventional magnetic recording media multilayered using macrogonal ferrite magnetic powder shown in the literature have short-term problems. Although the output in the wavelength range exceeds the output of 5VHS tape, it is said that sufficient output cannot be obtained in the long wavelength range!
I! It had S.

Means for Solving the Problems In order to solve the above problems, the magnetic recording medium of the present invention includes:
In a magnetic recording medium in which a magnetic layer is formed on one side of a non-magnetic substrate and a back coat layer is formed on the opposite side, the magnetic layer has a multilayer structure of at least two layers, and the uppermost magnetic layer is The magnetic layer contains magnetic powder having a plate-like shape, the thickness of the magnetic layer is 0.1 to 0.5 μm, and the coercive force of the lower magnetic layer is smaller than the coercive force of the upper magnetic layer. It is prepared.

Function The magnetic recording medium of the present invention has the above-described structure, and while the output is compensated by the lower magnetic layer in the long wavelength region, it takes advantage of the characteristics of the magnetic recording medium using plate-shaped magnetic powder in the short wavelength region, and 5V on the wavelength side) (to obtain a magnetic recording medium that maintains the output of the S tape and exceeds the output of the 5-VHS tape in the short wavelength region.

EXAMPLES Below, the magnetic recording medium of the present invention will be explained with reference to the drawings. FIG. 1 is an enlarged sectional view of the main part of the magnetic recording medium of the present invention. In FIG. 1, 1 represents a nonmagnetic substrate, 2 represents an upper magnetic layer containing plate-shaped magnetic powder, 3 represents a lower magnetic layer, and 4 represents a back coat layer.

The magnetic powder used in the examples will be explained below.

(Magnetic powder A used in the upper magnetic layer of Examples 1 to 3) A magnetic powder in which a magnetoplumbite type structure and an excessive spinel type structure are mixed, and in the elements constituting the powder,
Fe (iron)/Ba (barium) ratio is 15. Average particle size: 0.06 μm Average particle size/average thickness: 5 Powder coercive force: 8000e Saturation magnetization: 61 emu/g specific surface area
40m"7g (Magnetic powder B used in the upper magnetic layer of Examples 4 to 6) Hexagonal ferrite having a magnetoplumbite structure represented by BaO.6 (Fe203) coated with spinel type ferrite. Average grain size. Diameter: 0.07 μm Average particle size/average thickness: 5 Powder coercive force: 8200e Saturation magnetization: 63 e m u / g Nitrogen adsorption amount: 38 mz/g (Magnetic powder C used in the upper magnetic layer of Examples 7 to 9) B a F e ro
, hc OO,? T i 0.70+q Average particle size 0.05 μm Average particle size/average thickness 3 Powder coercive force 8000e Saturation magnetization 57 emu/g specific surface area
A magnetic paint was prepared using 35 m''/g of the above magnetic powder using a pressurized knife and then dispersed using a vertical sand mill.The composition of the paint is shown below.

・Magnetic powder ・Old...100 parts by weight・
Vinyl chloride polymer...9 parts by weight Polyurethane...9 parts by weight Carbon...3 parts by weight Alumina Old...101!1
Parts: Lubricant: 5 parts by weight, solvent, toluene, old bow: 5 parts by weight, methyl ethyl ketone: 150 parts by weight, methyl phthalate ketone: 150 parts by weight, cyclohexanone.・-150 parts by weight ・Curing agent
The magnetic paint for the 6-weight lower layer had the same paint composition as above, and the powder properties of the magnetic material were as follows.

Average major axis length 0.25μm Average acicular ratio
8 Powder coercive force 6000e Saturation magnetization 74 e m u / g Specific surface area 30 m 2 /g The coating material was prepared in the same manner as the coating for the upper magnetic layer described above.

Using the paint obtained as above, coat the lower layer with a film thickness of 2
．． After coating 5 μm, the upper layer was coated with a film thickness of 0.10.3.0.
Three types of 5 μm coating were applied. The non-magnetic substrate has a thickness of 14μ.
A polyethylene terephthalate film of m.m was used. After coating and before the coating film dried, a longitudinal magnetic field orientation treatment using a permanent magnet was performed.

After drying the coating film, it was calendered (temperature: 80°C). Thereafter, a curing treatment was performed for 20 hours, and a hack coat layer having a thickness of 0.7 μm was applied. Examples 1 to 3 were prepared in the order of magnetic layers using the above-mentioned magnetic powder A and having upper layer thicknesses of 0.1 and 0.30.5 μm. Similarly, Examples 4 to 6 are given in the order of magnetic layers using magnetic powder B with an upper layer thickness of 0.1, 0.3° and 0.5 μm, and magnetic layers using magnetic powder C with an upper layer thickness of 0.1, 0.3° and 0.5 μm. 0
．． Examples 7 to 9 were given in the order of 1, 0, 3, and 0.5 μm.

The back coat paint was prepared by dispersing it in a ball mill with the composition shown below.

-Carbon black powder -Polyurethane resin -Vinyl chloride resin -Nitrocellulose -Lubricant...100 parts by weight...30 parts by weight...15 parts by weight... 35 parts by weight 3 parts by weight Methyl ethyl ketone 300 parts by weight Toluene 3001
1 part cyclohexanone 300
Part by weight/hardening agent...2
0 parts by weight Comparative Examples 1 to 3 each used the magnetic paint for the upper layer of Example 1.4.7 to form a single magnetic layer with a thickness of 2.9 μm.
A sample was obtained by forming and subsequent processing in the same manner as in the example. In addition, as Comparative Examples 4 to 6, Examples 1 and 4 were used, respectively.
．． Using paint No. 7, a sample was prepared with an upper magnetic layer thickness of 0.7 μm and a lower magnetic layer thickness of 2.2 μm. Comparative Example 7 was a commercially available tape for our type 5-VH3.

The electromagnetic conversion characteristics of Examples and Comparative Examples were measured using a commercially available 5VHS deck (equipped with a ferrite head). The measurement frequencies are 100 KHz and 7 MHz. The output shows the optimum record of Comparative Example 7 as a current value, and shows the relative value with the output of Comparative Example set to 0 deciher (Table 1).

(Margins below) Table 1 As is clear from Table 1, the magnetic recording medium of the present invention has 5
- It is determined that it is backward compatible with VHS tapes.

As described above, the magnetic recording medium of the present invention has better short wavelength output than the conventional acicular iron oxide tape, and shows equivalent output at long wavelength with an upper layer thickness of 0.1 to 0.5 μm. A magnetic recording medium can be obtained.

Effects of the Invention As described above, the magnetic recording medium of the present invention has a multilayer structure including at least two magnetic recording layers, the upper magnetic layer contains magnetic powder having a plate-like shape, and the magnetic layer has a thickness. 0.1
~0.5 μm, and by making the coercive force of the lower magnetic layer smaller than the coercive force of the upper magnetic layer, it has better short wavelength output than conventional acicular iron oxide tape, and has the same output as long wavelength output. The magnetic recording medium shown can be manufactured. This makes it possible to create a new VTR with even higher performance while taking into account compatibility with conventional VTR decks, making it an extremely useful invention in industry.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a magnetic recording medium in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Nonmagnetic substrate, 2...Upper magnetic layer, 3...Lower magnetic layer, 4...Nink coat layer. Name of agent: Patent attorney Shigetaka Awano (1 figure)

Claims (4)

[Claims] (1) In a magnetic recording medium in which a magnetic layer is formed on one side of a non-magnetic substrate and a back coat layer is formed on the opposite side, the magnetic layer has a multilayer structure of at least two layers, and the uppermost layer The magnetic layer contains magnetic powder having a plate-like shape, the thickness of the magnetic layer is 0.1 to 0.5 μm, and the coercive force of the lower magnetic layer is smaller than the coercive force of the upper magnetic layer. A magnetic recording medium characterized by: (2) The plate-shaped magnetic powder is a magnetic powder with a magnetoplumbite type structure and an excessive spinel type structure, and the elements constituting the powder include Fe (iron)/
2. The magnetic recording medium according to claim 1, wherein the magnetic powder has a Ba (barium) ratio of greater than 12. (3) The plate-shaped magnetic powder is MO・nFe_2
A magnetic powder made by coating hexagonal ferrite with a magnetoplumbite structure represented by O_3 (where M is one element selected from Ba, Pb, and Br, and n is 5 to 6) and spinel ferrite. The magnetic recording medium according to claim 1, characterized in that: (4) Magnetic powder having a plate-like shape is MFe_(_1_2_-_x_)A_xO_1_9 (where M is one or more elements selected from Ba, Br, and Pb, and A is In, Zn-Ge, and Zn- Nb, Zn-V,
Either Co-Ti or Co-Ge, and
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a composition as follows: each represents a number from 1 to 2.5.