JPS61123020A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having good C/N in a high-frequency region and good dispersibility of a magnetic paint by incorporating a small amt. of hexagonal ferrite magnetic powder into a large amt. of needle- like ferromagnetic powder and using such powder mixture. CONSTITUTION:The magnetic recording medium which contains the magnetic powder having >=70emu/g satd. magnetization and the hexagonal ferrite magnetic powder having the axis of easy magnetization in the c-axis direction and having <=600 oersted coercive force, >=5 aspectratio and <=0.2mum particle size in the magnetic layer and in which the hexagonal ferrite magnetic powder is incorporated at <=5pts.wt. by 100pts.wt. the magnetic powder is formed. The vertically magnetizable component of the hexagonal ferrite magnetic powder is effectively utilized, by which the reproduced output in a high-frequency region is improved and the recording medium is made adaptable to high-denisty recording. The horizontally magnetizable component of the needle-like magnetic powder is effectively utilized, by which the reproduced output in a low-frequency region is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium such as a magnetic tape such as an audio tape or a video tape, or a magnetic disk such as a floppy disk or a hard disk. .

[Prior art and its problems]

Conventionally, magnetic recording media have been produced by coating an all-magnetic powder coating with acicular r-Fes magnetic powder on a non-magnetic substrate, and then oriented the magnetization in the in-plane longitudinal direction by an orientation process such as mechanical orientation or magnetic field orientation. The main type is the so-called horizontal magnetic recording method.

However, this type of horizontal magnetic recording type magnetic recording medium is
If the recording signal has a short wavelength, the self-demagnetizing effect increases and the reproduction output decreases, so it is not suitable for high-density recording.

Therefore, as a solution to these drawbacks, a so-called perpendicular magnetic recording type magnetic recording medium has been proposed9.
For example, ferromagnetic powder and hexagonal ferrite magnetic powder, especially hexagonal ferrite powder with an average particle size of 0.2 μm or less.
A magnetic recording medium has been proposed in which 100 parts by weight of ferromagnetic powder with a saturation magnetization of 70 emu/g or more and an average particle diameter larger than the average particle diameter of the hexagonal thread ferrite powder are dispersed in a resin binder (Unexamined Japanese Patent Publication No. No. 58-203625).

In other words, the technical idea of this proposal is that simply using ferromagnetic powder and hexagonal ferrite magnetic powder will result in a decrease in magnetic properties due to poor fractional properties of the magnetic paint. It is stated that if this configuration is adopted, the dispersibility of the magnetic coating material will be improved, and thus a magnetic recording medium with good magnetic properties can be obtained.

However, the inventor of the present invention has found that the proposed magnetic recording medium is not fully satisfactory for high-density recording.

[Disclosure of the invention]

The present inventor has been conducting research on magnetic recording media that can obtain large playback output using ring-shaped ferrite magnetic heads that are currently incorporated in recording and playback devices, and can also handle high-density recording. , saturation magnetization 70em
magnetic powder of u/g or more, has an axis of easy magnetization in the C-axis direction, has a coercive force of 600 Oe or more, and has a plate ratio of 5.
In the following, a magnetic layer includes a hexagonal 8-thread ferrite magnetic powder having a particle size of 0.2 μm or less, and the magnetic powder 100
A magnetic recording medium in which the ratio of the hexagonal ferrite magnetic powder to parts by weight is 5 parts by weight or less is capable of obtaining a large reproduction output with a ring-type ferrite magnetic head, and is also suitable for high-density recording. I found out that it is.

In other words, by mixing the hexagonal ferrite magnetic powder used in daily life with a large amount of acicular ferromagnetic powder, the perpendicular magnetization component of the hexagonal ferrite magnetic powder can be effectively used, improving the reproduction output in the high frequency range. However, it becomes compatible with high-density recording, and the horizontal magnetization component of the acicular ferromagnetic powder can be effectively used, improving the reproduction output in the low frequency region.

In order to perform recording and reproduction with good S/N especially in the high frequency range, for example, barium ferrite magnetic powder, strontium ferrite magnetic powder, calcium ferrite magnetic powder, lead ferrite magnetic powder, or substituted barium ferrite magnetic powder is used. It is desirable that the average particle diameter of the hexagonal ferrite magnetic powder is about 0.2 μm or less, more preferably about 0.05 μm or more and less than 0.2 μm.

In addition, in order to improve the reproduction output in the high frequency range, it is necessary to strengthen the perpendicular magnetization component of the hexagonal ferrite magnetic powder, and from this aspect the coercive force of the hexagonal ferrite magnetic powder is approximately 600 oersted or more. , even more preferably about 600 to 1000 oersteds. In other words, by doing so, high-density recording and high output are possible.

In addition, in order to improve the dispersibility and magnetic properties of the magnetic paint containing both hexagonal ferrite magnetic powder and acicular ferromagnetic powder, the plate ratio of the hexagonal ferrite magnetic powder is approximately 5 or less. , more preferably about 1 or more and less than 5, and the content of the hexagonal ferrite magnetic powder is about 5 parts by weight or less, even more preferably about 5 parts by weight or less based on 100 parts by weight of the acicular ferromagnetic powder. Desirably, the amount is about 0.1 parts by weight or more and less than 5 parts by weight.

Further, examples of magnetic powders having a saturation magnetization of about 70 emu/g or more include r-Peach, Oo-coated r-FesOs
, Fe504, OrO-rich, re or alloy powders, etc., have acicular (acicularity ratio is preferably about 5 to 15) ferromagnetic powders, and the saturation magnetization of such magnetic powders is about 70 emu.
/g or more, the reproduction output in the low frequency region will decrease.

[Example 1] Hexagonal barium ferrite magnetic powder (saturation magnetization Ms approximately 5
4emu/g, coercive force HC approx. 6300e, average particle size approx.
, isμm, plate-like ratio 3.5) 4 parts by weight, CO-containing γ-
FesOs magnetic powder (Ms approx. 75 emu/g, Hc approx. 6
300e.

Average particle size: about 0.2 μm, needle-like ratio: 100 parts by weight, vinyl chloride-vinyl alcohol copolymer: 15 parts by weight,
15 parts by weight of polyurethane elastomer, 1 part by weight of lecithin, 7 parts by weight of carbon black, 3 parts by weight of oleic acid,
A magnetic paint is prepared by mixing and dispersing a mixture of 300 parts by weight of a mixed solvent of equal amounts of toluene and methyl ethyl ketone in a sand mill for a predetermined period of time.

Then, 15 parts by weight of polyisocyanate (Coronate L1 Japan Polyurethane [)] was added to this magnetic paint, and this was applied to a polyester film, dried, calendered, and slit into 1-inch widths to be used as magnetic tape for video. A floppy disk was constructed by punching out a 25-inch diameter piece.

[Example 2] Hexagonal substituted barium ferrite magnetic powder (Ms approx. 54
emu/g, Hc approx. 6800e, average grain size 0.12μm, plate ratio approx. 4.5) Triple attachment part, strong 6Ii iron powder (Ms approx. 125emu/g, TLC approx. 13000e
, average grain size 0.2 μm, acicular specificity 10) 100 parts by weight, 15 parts by weight of nitrocellulose, 20 parts by weight of polyurethane elastomer, 2 parts by weight of lecithin, 4 parts by weight of carbon black, 4 parts by weight of oleic acid, A magnetic paint was prepared by mixing and dispersing a mixture of equal amounts of methyl ethyl ketone and methyl imbutyl ketone in a solvent of 340 tbsp for a predetermined time using a sand mill, and a magnetic tape for video and a 70 tb disk were constructed in the same manner as in Example 1. .

[Example 3] Hexagonal barium ferrite magnetic powder (Ms approximately 54 emu
/g, H (approximately 6200e, average grain size 0.18 μm, plate ratio approximately 3.5) 4 parts by weight, Fete<magnetic powder (Ms approximately 8
2emu/g, IIc approx. 6200e, average grain madness 0.2
μm1 acicular ratio approx. to) 1oo fl[, vinyl chloride-
A mixture of 13 parts by weight of vinyl alcohol copolymer, 17 parts by weight of polyurethane elastomer, 1 part by weight of lecithin, 5 parts by weight of carbon black, 3 parts by weight of oleic acid, and 30011 parts by weight of a mixed solvent of toluene and methyl isobutyl ketone. A magnetic paint was prepared by mixing and dispersing the mixture for a predetermined time using a land mill, and a video magnetic tape and a floppy disk were constructed in the same manner as in Example 1.

[Example 4] Barium ferrite magnetic powder (Ms approx. 54
emu/g, IlcHe approx. 7000e even grain madness 0.1
0 μtn, plate ratio approx. 4.5) 4.5 type needle, Or Os
uf magnetic powder Ms approx. 70 emu/g, I (c approx. 6500
e, 0.21 Jm, acicular ratio 10) 100
Juinabe, 15 parts of vinyl chloride-vinyl acetate copolymer,
18 parts by weight of polyurethane elastomer, 1 part by weight of lecithin, 7.5 parts by weight of carbon black, 3 parts by weight of oleic acid, 3 parts of a mixed solvent of equal amounts of toluene and methyl ethyl ketone.
A magnetic coating material was prepared by mixing and dispersing 00 parts by weight of the mixture in a sand mill for a predetermined period of time, and a video magnetic tape and a floppy disk were constructed in the same manner as in Example 1.

[Comparative Example 1] A video magnetic tape and a floppy disk were constructed in the same manner as in Example 1 except that 8 parts by weight of hexagonal barium ferrite magnetic powder was used.

[Comparative Example 2] The same procedure as in Example 2 was carried out except that 25 parts by weight of the hexagonal substituted barium ferrite magnetic powder was used to construct a video magnetic tape and a floppy disk.

[Comparative Example 3] In Example 1, Ms about 54 emu/g, He about 6
The same procedure was carried out using hexagonal barium ferrite magnetic powder of 300e, average grain size of 0.15 μm, and platelet ratio of about 6 to construct a video magnetic tape and a floppy disk.

[Comparative Example 4] In Example 2, Ms about 54 emu/g, He about 6
The same procedure was carried out using hexagonal substituted barium ferrite magnetic powder of 800e, average grain size of 0.12 μm, and platelet ratio of about 9 to construct video magnetic tapes and floppy disks.

[Comparative Example 5] A video magnetic tape and a floppy disk were constructed in the same manner as in Example 2 without using the hexagonal substituted barium ferrite magnetic powder.

[Comparative Example 6] In Example 3, Ms about 54 emu/g,
A video magnetic tape and a floppy disk were constructed in the same manner using hexagonal barium ferrite magnetic powder having a He of about 5750e, an average grain size of 0.18 μm, and a platelet ratio of about 3.5.

[Comparative Example 7] In Example 4, Ms about 54 emu/g, Ilc about 700 Qe, average grain deviation 0.28 μm, plate ratio about 4.5
A video magnetic tape and a floppy disk were constructed in the same manner using hexagonal substituted barium ferrite magnetic powder.

[Comparative Example 8] In Example 2, Ms about 54 emu/g, He about 5
A video magnetic tape and a floppy disk were constructed in the same manner using barium ferrite magnetic powder using a hexagonal device with an average grain size of 0.40 μm and a plate ratio of about 4.5.

〔Characteristic〕

Dispersion time of magnetic paints prepared in the above examples and comparative examples -
The relationship between the maximum magnetic flux density is shown in the drawing.

According to this, it can be seen that the dispersibility of the magnetic paint used in the magnetic layer structure of the magnetic recording medium of the present invention is good. In other words, by reducing the amount of hexagonal thread ferrite magnetic powder added, that is, 5 parts by weight or less per 100 parts by weight of ferromagnetic powder, the dispersibility is improved and the magnetic properties are improved.

The maximum magnetic flux density Bm was measured at an applied magnetic field of 2 KOe using samples prepared by applying a magnetic paint to a polyester film with a blade at each dispersion time.

Also, when measuring the color S/N of video magnetic tape,
3.5 dB in Example 1, 3.5 dB in Example 2
．． 6dB, while that of Comparative Example 3 is 0.5dB.
B, Comparative Example 4 -1.0 dB, etc.
It can be seen that the color S/N is greatly influenced by the plate ratio, and is good when the plate ratio of the hexagonal ferrite magnetic powder is 5 or less.

Same color 8/N is HR-220 manufactured by Victor Japan.
It was measured at 0.

In addition, the video modulation noise was measured as shown in the table. Similarly, the carrier output is expressed by the reproduction output level when a 5 MHz single signal is recorded and reproduced, and 0/N is expressed by the ratio of the noise level at a frequency 1 MHz away from the carrier and the carrier output.

According to this table, those containing hexagonal ferrite magnetic powder with an average grain size of 0.2 μm or less and a coercive force of 600 Oe or more improve carrier output level, reduce noise level, and improve O/N. It can be seen that this is an excellent magnetic recording medium.

Also, when measuring the 2F output and modulation of the floppy disk, the 2F output power of Example 1 was 340 m
Vp-p, modulation is 2%, 2F output is 350 mVp-p and modulation is 3 in Example 2, whereas 2F output is 3 in Comparative Example 3.
00 mVp-p, modulation is 6chi, and the 2F output in Comparative Example 5 is 280mVp-p.

The modulation was 8%, and from this point of view it can be seen that the material containing hexagonal ferrite magnetic powder with a plate ratio of about 5 or less is good. - [Effects] It has good OA in a high frequency range such as 5 MHz, and since the magnetic paint has good dispersibility, the time required for dispersion is short and it can be done at low cost.

[Brief explanation of drawings]

The drawing is an explanatory diagram of the characteristics of a magnetic recording medium.

Claims (1)

[Claims] A magnetic powder with a saturation magnetization of 70 emu/g or more, a hexagonal ferrite having an easy axis of magnetization in the c-axis direction, a coercive force of 600 Oe or more, a plate ratio of 5 or less, and a particle size of 0.2 μm or less. 1. A magnetic recording medium comprising a magnetic powder in a magnetic layer, wherein the hexagonal ferrite magnetic powder is contained in a ratio of 5 parts by weight or less to 100 parts by weight of the magnetic powder.