JPH0581656A - Magnetic disk - Google Patents

Abstract

PURPOSE:To provide a coating type magnetic disk capable of high density recording and having excellent electromagnetic transducing characteristics and durability. CONSTITUTION:A first magnetic layer 4 having 2.5mum thickness and contg. magnetic powder of acicular gamma-Fe2O3 having an axis of easy magnetization oriented in an intrasurface direction and 270Oe coercive force is formed on the surface of a nonmagnetic substrate 3. A second magnetic layer 5 having 0.4mum thickness and contg. magnetic metal powder having 1,500Oe coercive force is formed on the first magnetic layer 4. A third magnetic layer 6 having 0.1mum thickness and contg. magnetic powder of Co doped gamma-Fe2O3 having 800Oe coercive force, plural axes of easy magnetization and crystal magnetic anisotropy is formed on the second magnetic layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk having a magnetic layer formed by coating a surface of a non-magnetic substrate with a magnetic coating material containing magnetic powder.

[0002]

2. Description of the Related Art For magnetic disks such as floppy disks and hard disks, high density recording has been advanced in response to a demand for larger capacity. As a result, in the coating type magnetic disk, as shown in FIG. 2, the magnetic powder in the magnetic layer 2 having a thickness of 3 μm and containing the metal magnetic powder on the surface of the non-magnetic substrate 1 was made finer and highly filled. The electromagnetic conversion characteristics have been improved.

Further, in order to achieve high density recording, the thickness of the magnetic layer 2 has been reduced to further improve the smoothness of the surface of the magnetic layer. Further, performing high-density recording means shortening the wavelength of a recording signal. In this case, in digital recording, adjacent signals interfere with each other, resulting in an increase in peak shift, a decrease in resolution and output, and electromagnetic conversion. The characteristic deteriorated. In order to improve the deterioration of the electromagnetic conversion characteristics, a means of increasing the coercive force (Hc) of the magnetic layer 2 has been taken. However, in this case, since the overwrite characteristic tends to deteriorate in the single-gap magnetic head, the characteristics have been improved by further reducing the thickness of the magnetic layer 2.

[0004]

However, when the thickness of the magnetic layer is reduced, there is a problem that defects are likely to occur in the magnetic layer due to contact and friction with the magnetic head or slider, and durability is deteriorated.

It is an object of the present invention to solve the above problems and provide a magnetic disk capable of high density recording and excellent in electromagnetic conversion characteristics and durability.

[0006]

To achieve the above object, the magnetic disk of the present invention has a coercive force of 250 to 800 O with the easy axis of magnetization oriented in the in-plane direction on the surface of the non-magnetic substrate.
The first magnetic layer containing the magnetic powder of e and having a film thickness of 1.0 to 4.0 μm is provided, and the coercive force with the easy axis of magnetization oriented in the in-plane direction is 900 on the first magnetic layer. A second magnetic layer containing a magnetic powder of ˜2000 Oe and having a film thickness of 0.2 to 0.4 μm is provided, and a coercive force with the easy axis of magnetization oriented in the thickness direction is 800 on the second magnetic layer. ˜2000 Oe crystal magnetic anisotropy magnetic powder is contained and the film thickness is 0.1˜0.3.
The third magnetic layer having a thickness of μm is provided.

[0007]

According to the above structure, the magnetic powder in the first and second magnetic layers has an easy axis of magnetization in the plane. On the other hand, the easy axis of magnetization of the third magnetic layer is oriented in the thickness direction of the magnetic layer. Here, by increasing the coercive force of the second and third magnetic layers and thinning them, it is possible to suppress deterioration of resolution and peak shift during high density recording. Furthermore, the total coating film thickness including the first, second and third magnetic layers is set to a thickness that is necessary and sufficient for durability.

By setting the coercive force and the maximum magnetic flux density of the first magnetic layer to be low, the electromagnetic conversion characteristics are secured by the effect of the second magnetic layer without deteriorating the overwrite characteristics.

When the linear recording density increases, the output decreases due to the interference between adjacent signals, but by providing the third magnetic layer, the magnetic flux in the coating film effectively reaches the magnetic layer surface. Guided to suppress the decrease in output.

[0010]

EXAMPLES Examples will be described below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the magnetic disk of the present invention. In the case of a floppy disk, a polyethylene terephthalate film is generally used for the nonmagnetic substrate 3. In the case of a hard disk, the non-magnetic substrate 3 is
Aluminum, glass, polycarbonate, etc. are used. The first magnetic layer 4, the second magnetic layer 5 and the third magnetic layer 6 are composed of magnetic powder, abrasive, carbon black, lubricant, binder resin and the like. As an abrasive,
A fine powder of alumina, chromium oxide, α-iron oxide or the like is used. A plurality of combinations of fatty acids and fatty acid esters are used for the lubricant. As the binder resin, a system in which a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, nitrocellulose, a polyurethane resin, and a polyester resin are appropriately combined is used, and a low-molecular weight isocyanate compound is used as a curing agent if necessary. These materials are made into a coating material by using a dispersing machine such as a pressure kneader, a planetary mixer, a ball mill, a sand mill, and a pebble mill together with a mixed solvent in which methyl ethyl ketone, toluene, cyclohexanone, etc. are combined, and the produced magnetic coating material of the non-magnetic substrate 3 is formed. A magnetic disk is formed by coating, drying and curing on both sides.

In the present invention, magnetic paints having different compositions are applied three times in order to form three magnetic layers. In FIG. 1, only the magnetic layer on one side is shown.

(Example 1) The first magnetic layer 4 shown in FIG. 1 was provided as follows.

Needle-shaped γ-Fe ₂ O ₃ magnetic powder (Hc: 270
Oe, σs: 74 emu / g, BET specific surface area: 30 m ² / g)
Was made into a coating material by dispersing for 3 hours with the following composition using a sand mill, and this was applied onto a non-magnetic substrate 3 (polyethylene terephthalate film) having a thickness of 62 μm to form the first magnetic layer 4.

Γ-Fe ₂ O ₃ 100 parts by weight carbon black 10 parts by weight PVC-vinyl acetate copolymer 15 parts by weight polyurethane resin 15 parts by weight oleyl oleate 7 parts by weight methyl ethyl ketone 100 parts by weight toluene 100 parts by weight cyclohexanone 30 parts by weight Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) 6 parts by weight Further, the second magnetic layer 5 shown in FIG. 1 was provided as follows. Metal magnetic powder (Hc: 1500 Oe, σs: 1
25 emu / g, BET specific surface area: 49 m ² / g) is dispersed in a sand mill with the following composition for 3 hours to form a paint, which is then applied on the first magnetic layer 4 to form a second coating.
The magnetic layer 5 was provided.

Metal magnetic powder 100 parts by weight Carbon black 3 parts by weight Alumina 7 parts by weight PVC-vinyl acetate copolymer 15 parts by weight Polyurethane resin 15 parts by weight Oleyl oleate 7 parts by weight Methyl ethyl ketone 120 parts by weight Toluene 120 parts by weight Cyclohexanone 40 parts by weight Parts Coronate L 6 parts by weight Further, the third magnetic layer 6 shown in FIG. 1 was provided as follows. Co-doped γ-Fe ₂ O ₃ magnetic powder (Hc: 800
Oe, σs: 76 emu / g, BET specific surface area: 48 m ² / g)
Was made into a paint by dispersing for 3 hours with the following composition using a sand mill, and this was applied onto the second magnetic layer 5 to form the third magnetic layer 6.

Co-doped-γ-Fe ₂ O ₃ 100 parts by weight carbon black 5 parts by weight alumina 5 parts by weight vinyl chloride-vinyl acetate copolymer 15 parts by weight polyurethane resin 15 parts by weight oleyl oleate 7 parts by weight methyl ethyl ketone 100 parts by weight toluene 100 parts by weight Cyclohexanone 30 parts by weight Coronate L 6 parts by weight The magnetic sheet thus obtained was calendered and punched into 3.5 inch disks. At this time, the coating thickness of each of the magnetic layers 4, 5 and 6 is 2.5 μm.
m, 0.4 μm, and 0.1 μm. In addition, the recording area of the disk is 10
After polishing for a second and hub attachment, the casing was used as a sample.

(Examples 2 to 7) The film thicknesses of the first, second and third magnetic layers shown in Example 1 were changed as shown in (Table 1), and Examples 2 to 4 respectively. And

Further, the magnetic powder of the first magnetic layer of Example 1 was replaced with Co-γ-Fe ₂ O ₃ magnetic powder (Hc: 750 Oe, σs: 7).
3 emu / g, BET specific surface area: 47 m ² / g), and the magnetic powder of the second magnetic layer of Example 5 and Example 1 was changed to Co.
-γ-Fe ₂ O ₃ (Hc: 920 Oe, σs: 72 emu / g,
The BET specific surface area was changed to 45 m ² / g) and the magnetic powder of the third magnetic layer of Example 6 and Example 1 was changed to hexagonal barium ferrite (Hc: 1200 Oe, σs: 55 emu /
g, BET specific surface area: 30 m ² / g) was changed to Example 7.

[0020]

[Table 1]

The magnetic sheet thus obtained was calendered and punched into 3.5 inch disks. In addition, the recording part of the disk 1
After polishing for 0 seconds, hub attachment was performed, and then the casing was used as a sample.

The electromagnetic conversion characteristics and continuous durability test of these samples were measured by FDD. The specifications of the FDD for measurement are a head gap length of 0.3 μm, a track density of 542 TPI, 1f of 0.5 MHz, and 2f of 1 MHz.
Outermost recording wavelength: 1f is 4.96 μm, 2f is 2.48
.mu.m, innermost recording wavelength: 1f is 2.90 .mu.m, 2f is 1.45 .mu.m, and the disc rotation speed is 600 rpm.

The evaluation results of the electromagnetic conversion characteristics and durability of the sample are shown in (Table 2). The electromagnetic output characteristics of head output, resolution, peak shift and overwrite in Table 2 are shown as relative values with the value of Example 1 as 100. The durability was evaluated at room temperature and normal humidity, and the initial head output was 70%.
% When the output decreases to 10%, and
The relative value was set to 0.

[0024]

[Table 2]

The head output is 2 in the innermost track.
This is a reproduction output when the f signal is recorded, and the resolution is a head output ratio at the time of recording the 2f signal and the 1f signal on the same track. Overwrite represents the size of the unerased portion of the 1f signal when the 1f signal is recorded on the outermost track and the 2f signal is overwritten thereon.

It can be seen that there is no great difference between the electromagnetic conversion characteristics and durability in Examples 1 to 7. On the other hand, in the conventional example, the thickness of the magnetic layer is 3 μm, which is the same as that of the example, but the durability is poor and the electromagnetic conversion characteristics are greatly deteriorated. this is,
It is presumed that the magnetization recorded by the magnetic head forms a closed loop of magnetic flux in the coating film due to the large thickness of the magnetic layer, and the magnetic field is unlikely to reach the surface of the magnetic coating film. Also, 1f
Since the signal is written deeper in the magnetic layer than the 2f signal, both resolution and overwrite characteristics are deteriorated.

[0027] As the magnetic powder contained in the third magnetic layer, other Co ferrite Co doped-gamma-Fe ₂ O ₃ used here as having a plurality of easy magnetization axis, include magnetite, As a material having a single easy axis of magnetization, barium ferrite, strontium ferrite, metallic cobalt particles, and the like can be expected to have similar effects. Further, in the case of using the magnetic powder having a single easy axis of magnetization, the effect is further improved if the easy axis of magnetization is oriented perpendicular to the coating film at the time of forming the coating film.

[0028]

As described above, the magnetic disk of the present invention is
On the surface of the non-magnetic substrate, the easy axis of magnetization is oriented in the plane, and the first magnetic layer having a low coercive force and maximum magnetic flux density is provided to suppress the deterioration of the overwrite characteristics. A second magnetic layer having an in-plane easy magnetization axis and a high coercive force and a small thickness, and having the easy magnetization axis oriented in the thickness direction and having a small thickness on the second magnetic layer; By providing the thin third magnetic layer, it is possible to suppress deterioration of resolution and peak shift at the time of high-density recording and also ensure durability.

[Brief description of drawings]

FIG. 1 is a sectional view of a magnetic disk according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional magnetic disk.

[Explanation of symbols]

 3 Nonmagnetic Substrate 4 First Magnetic Layer 5 Second Magnetic Layer 6 Third Magnetic Layer

Claims (2)

[Claims] 1. A first magnetic material containing magnetic powder having a coercive force of 250 to 800 Oe and having a film thickness of 1.0 to 4.0 .mu.m, in which the easy axis of magnetization is oriented in the in-plane direction, on the surface of a non-magnetic substrate. A second layer having a layer and containing magnetic powder having a coercive force of 900 to 2000 Oe and having a coercive force oriented in the in-plane direction on the first magnetic layer and having a film thickness of 0.2 to 0.4 μm. Providing a magnetic layer,
A third magnetic layer having an easy axis of magnetization in the thickness direction, a magnetic powder of crystalline magnetic anisotropy of coercive force of 800 to 2000 Oe, and a film thickness of 0.1 to 0.3 μm on the second magnetic layer. A magnetic disk provided with the magnetic layer of. 2. Needle-shaped γ-Fe ₂ O _{3 on} the surface of a non-magnetic substrate
The coercive force of which the easy axis is oriented in the in-plane direction of
Contains magnetic powder of 0 to 300 Oe and has a film thickness of 1.0 to
A first magnetic layer having a thickness of 4.0 μm is provided, and a coercive force of metal magnetic powder is 1300 to 1700 on the first magnetic layer.
A second magnetic layer containing Oe magnetic powder and having a thickness of 0.2 to 0.4 μm is provided, and a coercive force of Co-doped γ-Fe ₂ O ₃ of 800 is provided on the second magnetic layer. ~ 1000 Oe
And a third magnetic layer containing a magnetic powder of crystalline magnetic anisotropy having a plurality of easy magnetization axes and having a film thickness of 0.1 to 0.3 μm.