JPS5960737A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a stable electromagnetic conversion characteristic by passing repeatedly a magnetic recording medium through the inside of a magnetic field wherein a magnetic field in a different direction is generated and the magnetic field intensity has a space ditribution and subjecting the same to a cooling treatment in the magnetic field from a specific temp. or above to around a room temp. CONSTITUTION:Fe3O4 contg. Co and Cu respectivly at 4wt% in the entire metallic element is used as a target, and a thin film of Fe3O3 having about 3,000Angstrom thickness and contg. Co and Cu is formed on a heat resistant high polymer film substrate by sputtering at 600W sputtering power and 8X10<-3>Torr sputtering pressure in gaseous argon. The film is oxidized for one hour at 260 deg.C whereby a thin film of iron oxide consisting essentially of the intermediate compsn. of Fe3O4-gamma-Fe2O3 is obtd. A floppy disc 6 cut from such thin film is once heated to 200 deg.C and is passed through the space between magnets 2 and 3 and is slowly cooled to 50 deg.C at 10 deg.C/min speed while the disc is rotated at 6rpm rotating speed. The high effect of an improvement in a magnetic characteristic and a reduction in a demagnetization characteristic under pressure by half is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a magnetic recording medium used for magnetic tapes, magnetic disks, and the like.

Improving the recording density in magnetic recording devices is a constant trend in this field, and in order to achieve this, it is essential to make the magnetic recording medium thinner and thinner.

Conventionally, a so-called coating medium in which a mixture of iron oxide fine particles and a binder is coated on a substrate has been widely used. These recording media include magnetic tape for audio, magnetic tape for VTRs, magnetic tape for computers, flexible magnetic disks, and rigid magnetic disks. Attempts are being made to increase the recording density by increasing the coercive force of the medium.

However, it is extremely difficult to achieve uniform recording and reproducing characteristics with a thickness of several thousand Å or less in coated media. Tapes and plated tapes have been proposed. However, such metal thin films are susceptible to damage and abrasion of the film surface due to contact with a hard head such as ferrite, and are susceptible to corrosion, and as the film becomes thinner, From the viewpoint of reliability, the interval is θ.

In order to solve this problem, we developed an oxide magnetic thin film with good wear resistance, corrosion resistance, or r-Fe203 or γ-1 (an intermediate composition between 'e203 and Fe50), or mainly Fe3O3. component, and in order to obtain a high coercive force (11), O
.

Cobalt-containing iron oxide magnetic thin films are attracting attention. However, depending on the degree of oxidation and the content of Kobal 1, such l-containing iron oxide magnetic thin films for edges may show large pressure demagnetization, and the reproduction output may decrease due to contact with the magnetic head, resulting in stable electromagnetic stability. It was not possible to obtain conversion characteristics. Further, depending on the shape conditions of the magnetic recording medium or the properties of the substrate, sufficient magnetic properties may not be achieved.

In order to solve these problems, a method has been proposed in which a cobalt-containing iron oxide magnetic thin film is heated and then cooled in a static magnetic field. When this cooling treatment in a magnetic field is applied, the heating demagnetization characteristics and magnetostatic characteristics are significantly improved, and unlike when the same treatment is applied to cobalt-containing iron oxide fine particles, there is no stabilization. It had the advantage of being extremely stable over a long period of time even without treatment.

However, when this method is applied to, for example, a magnetic tape medium, a solenoid coil is generally used in order to generate a static magnetic field of high strength along the length of the tape. However, in order to obtain a sufficiently strong static magnetic field, a coil that can flow a large current, a power supply, and a cooling mechanism to suppress the rise in coil temperature due to Joule heat are required, which requires extremely expensive and large-scale equipment. Ru. Furthermore, when this method is applied to a magnetic disk medium, it is not easy to generate a static magnetic field in the circumferential direction.

The purpose of the present invention is to solve various problems in performing such cooling treatment in a magnetic field. A method for manufacturing a recording medium is provided.

That is, the method for manufacturing a magnetic recording medium according to the present invention involves repeatedly passing a magnetic recording medium through a magnetic field containing magnetic fields in different directions and having a wall-to-wall distribution of magnetic field strength for 1n, and determining the magnetization state of the magnetic recording medium. The time the magnetic recording medium is held in a certain direction is longer than the time it is held in a different direction, and at the same time the same magnetic recording medium is cooled in a magnetic field from a temperature of 80°C or higher to near room temperature. It is characterized by including a step of applying.

The inventor of the present invention thought that it would be possible to use a permanent magnet instead of a solenoid coil, and as a result of intensive study, it was found that even when a magnetic field with a different direction is applied, the magnetization state of the magnetic recording medium remains unchanged during the cooling time. The inventors have discovered that cooling treatment in a magnetic field is sufficiently effective when there is a clear difference between a certain time in the direction and a time in the opposite direction, and this has led to the present invention.

The significance of the present invention will be explained in detail below using specific examples. In the following, the magnetic properties were measured using a vibrating sample magnetometer.
It was measured by applying a magnetic field of KOeo-p, and the amount of pressure demagnetization was measured by magnetizing the sample in one direction in a static magnetic field of 3KOe, and then applying a magnetic field of 1.000 kg/cJ perpendicular to the sample surface. Pressure is applied for 10 seconds, and the decrease in residual magnetization before and after that is shown as a percentage ratio of the value before pressurization.

Example 1 Fe1O, which contains 4% Co and 4% O out of all metal elements, was used as a target, and sputtered in argon gas on a 150 mm square heat-resistant polymer film substrate at a power of 600 W and a sputtering pressure of 8 0. "Approximately 300 OA of Co by sputtering at Torr.

A Cu-containing Fe3O4 thin film was formed. This is 2.60℃
.

Oxidized in air for 1 hour to produce Fe, O,-r-Fe, 0.
An iron oxide thin film containing the intermediate composition as a main component was obtained. The obtained sample has an inner diameter of approximately 28.5 milJ and an outer diameter of 133 mil.
J's 51/4 inch large floppy disk (1-A)
I cut it out.

On the other hand, a pair of Co-rare earth magnets (10 x 10 x 50 mm, magnetized in the short side direction) with a residual magnetic flux density of about 9,700 G were arranged as shown in Figure 1.2. Figure 1 is a plan view, FIG. 2 is a side view when viewed from the direction of arrow 5 in FIG. 1.

In the figure, 1&i floppy disk, 2 and 3 are magnets, and 4 is the rotating shaft of the floppy disk.The magnets 2 and 3 were arranged with a gap of 5 mm as shown in FIG. 2, with the same magnetic poles facing each other. Figure 3A shows the measured and plotted in-plane magnetic field component (H+t) on a plane passing exactly through the center of the magnet gap along the direction of arrow 5 in Figure 1. However, the positive direction of the magnetic field is the rotational direction 6 of the floppy disk in FIG. By experiencing such a distributed magnetic field once per rotation, the magnetization at each point on the Flora Bi disk maintains a positive residual magnetization except when a magnetic field in the negative direction is applied. Of course, when a magnetic field in the negative direction is applied, there is magnetization in the negative direction, but this is for about 1/7 to 1/33 of the time required for one rotation.

After heating the floppy disk 1-A with rice to 200° C., the disk was slowly cooled down to 50° C. at a rate of 10° C./min while rotating through the gap at a rotation speed of 6 rpm to obtain sample 1-B. When the magnetic properties 1 and pressure demagnetization properties of disks 1-A and 1-B were measured, as shown in Table 1, s,
Significant effects such as improvement in s* and halving of pressure demagnetization characteristics were observed.

Table 1 Sample salt HCS S* Pressure demagnetization 1-A
9000e O,680,55-25%1-B
930 0.71 0.61 -13% Example Using the same Co-rare earth magnet as in Example 1, the 4th.
As shown in Figure 5 (4 magnets are placed).

At this time, the distribution of in-plane time (Hll) on a plane passing through the center of the magnet gap along the direction BB' in FIG. 4 was as shown in FIG.

The same floppy disk 1-A as in Example 1 was once inserted into the 210
After heating to ℃, Sample 2-B was cooled to room temperature at a rate of 20℃/min while rotating at 12 rpm through a gap made up of four magnets as shown in Figure 5.
I got it. When its magnetic properties and pressure demagnetization properties were measured, as shown in Table 2, it was found that the magnetic properties and pressure demagnetization properties were improved to the same extent as in Example 1.

Table 2 Sample salt Hc S 8* Pressure demagnetization 1-A 9000c O, 680, 55-25
Satoru 2-B 900 0.70 0.60
-16% In this example, the magnetization at each point of the disk and the disk once turns in the positive direction due to the positive magnetic field (811) when passing through the above gap, but then reverses to the negative direction and maintains that state. . That is, as in Example 1, residual magnetization in the negative direction is maintained for most of the time during one rotation.

Example 3 A floppy disk 3-A using an iron oxide thin film whose main component is an intermediate composition of Fe304-γFe2O3 containing 5 weight percent Oo and 4 weight percent Cu is produced by the same process as the floppy disk 1-A in Example 1.
I got it.

On the other hand, using the same Co-rare earth magnet as in Example 1, a set of four magnets M1, as shown in FIG. 7.8, was arranged on the disk surface as shown in FIG.

Also, magnets M2M3 with the same configuration. M, were arranged as shown in FIG. 7 depending on the case. The distribution of the in-plane magnetic field (Hlt) on a plane passing through the center of the magnet gap along the direction 00' in FIG. 7 of the magnet M was as shown in FIG.

After the floppy disk 3-A was once heated to 200 DEG C., some of the magnets M1 to M4 were arranged as shown in FIG. 7 and cooled in a magnetic field at a cooling rate of 20 DEG C./min. The set of magnets used for samples 3-B1 to 3-B4 obtained in this way, magnetic customization, and measurement results of demagnetization are as follows.
The third sample compared to sample 3-A which was not cooled in a magnetic field.
Shown in the table.

Table 3 San 7) Shina Usui Regnet He' S
S*7 Duqiu Mirage 3-A -7200e O
,630,57-19%3-BI M,
930 0.70 0.75-14%B2
M,,M, 930 0.72 0.
73-10%B3 M,,M,,M3950 0.
76 0.86-8.7%B4 M, , M2. M,
, M, 960 0.76 0.90-BE% As shown in the table above, when the set of magnets is 3 or 4,
Further improvements were observed in both magnetism and pressure demagnetization.

Comparative Example Co, Ou with a thickness of 4,000× was deposited on a heat-resistant polymer film substrate by sputtering a Fe504 target containing 3% Co and 4% O out of all metal elements in argon gas. Contains FeHO
4 thin film was formed, and this was oxidized in the air at 260° C. for 1 hour to obtain an iron oxide thin film whose main component was Fe304-γ-Fe20g intermediate composition. Width 1 from the obtained sun file
2.56 mm (1/2 inch) Qi 70-shaped sample (
R-1) was cut out.

On the other hand, using the same permanent magnet as used in Examples 1 to 3,
As shown in Figure 0, 10 pairs of magnets with the same type of magnetic poles facing each other were arranged along one direction at regular intervals, and a temperature gradient from 200°C to 50°C was applied over this range. Also the first
As shown in Figure 1, 11 pairs of magnets are arranged so that the polarity changes alternately, giving a temperature gradient of 200°C to 50°C over the same range. The gap between these magnet pairs was adjusted as shown in the figure (the tape sample 9 was sent at a speed of 2w from the high temperature side to the low temperature side, and cooling treatment was performed in a magnetic field to obtain samples R-2 and R-3, respectively. When the magnetic properties and the amount of demagnetization under pressure were measured, no difference was observed between sample r't-i which was not cooled in a magnetic field.

The reason for this is that the in-plane magnetic field H in the gap due to the magnet arrangement in Figure 10.11 has a periodic distribution that is symmetrical in the positive and negative directions as shown in Figure 12.13, and the tape sample passing through it has a periodic distribution that is symmetrical in the positive and negative directions. The magnetization is thought to be due to the fact that the magnetization states in both the positive and negative directions occur at approximately the same rate.

Example 4 An alumite film was formed on the surface of an aluminum alloy by sputtering in argon gas using Fe3O4 as a target containing 2 and 3 weight percent of Co and Cu, respectively, among all metal elements. Approximately 2,000 on the disk board
A Fe3O4 film containing Co and O was formed. This was oxidized in the air at 275°C for 1 hour to obtain an iron oxide thin film medium disk 4A'2 containing γ-Fe2O3 as a main component.

This disk 4-A was used in Example 3 using four sets of magnets Ml 2M22M51M4 (Fig. 7).
A similar cooling treatment in a magnetic field was performed from 0° C. to room temperature at a cooling rate of 20° C./min to obtain disk 4-B. When we evaluated the recording and playback characteristics of these two types of disks, we found that the output and recording density characteristics of disks 4 and 4 increased in line with the improvements in magnetostatic characteristics.
- It was clearly recognized in H. Also, the disk 4-B is suitable for the amount of demagnetization caused by multiple contact start/stop tests or by strongly rubbing the media surface with gauze, etc.
An improvement was observed.

This shows that the cooling process in a magnetic field according to the present invention is effective regardless of the substrate of the medium.

In the above embodiments, the maximum cooling temperature in a magnetic field and the cooling rate were set to 200°C or higher and 10 to b, respectively, but the effects of the present invention are not limited to these, and even at temperatures of 80°C or higher and 200°C/min, respectively. The same is true.

As described above, according to the method of manufacturing a magnetic recording medium according to the present invention, cooling treatment in a magnetic field can be performed using a simple device using permanent magnets, regardless of the shape of the medium such as tape or disk. This makes it possible to manufacture magnetic recording media with excellent performance and reliability.

[Brief explanation of drawings]

Figure 2 is a partial side view of Figure 1, Figure 3 is a diagram showing the distribution of in-plane magnetic field components due to the magnet pair in Figures 1 and 2, and Figure 4 is the floppy disk surface in the combination of four magnets. Fig. 5 is a partial side view of Fig. 4, Fig. 6 is a diagram showing the distribution of in-plane magnetic field components due to the four magnets in Fig. 4.5, and Fig. 7 is a plan view showing the above arrangement. A plan view showing another arrangement of four magnets on the floppy disk surface, FIG. 8 is a partial side view of FIG. 7, and FIG. 9 is an in-plane view of the four magnets of No. FIG. 10 is a diagram showing the distribution of magnetic field components. FIG. 10 is a diagram showing a magnet arrangement for a tape-shaped sample in a comparative example. FIG. 11 is a diagram showing another magnet arrangement in the same comparative example. 12.1
FIG. 3 is a diagram showing the tape in-plane magnetic field distribution (for one period) in the magnet arrangement shown in FIG. 10.11. In the figure, 1...floppy disk, 2, 3...
・Magnet, 4...Floppy disk rotating shaft, 5
... Side view line of sight, 6... Floppy disk rotation direction, 7.8... Magnet, 9... Tape 3rd
Figure (KOe) Figure 6 Figure 1O Figure # 1112 aq Tower IO Figure 1I

Claims (4)

[Claims] (1) A magnetic recording medium is repeatedly passed through a magnetic field that includes magnetic fields in different directions and has a spatial distribution of magnetic field strength, and the time period during which the magnetization state of the magnetic recording medium is maintained in a certain direction is difficult. A magnetic recording medium comprising the step of cooling the magnetic recording medium in a magnetic field from a temperature of 80° C. or higher to the vicinity of the first part of the chamber at the same time. Method of manufacturing media. (2) The magnetic recording medium is Co and other gold 1d (including elemental additives, Fe50. film or Fe50. and r-F
Intermediate composition with e2o3 j1α or γ-Fe2O3
A method for manufacturing a magnetic recording medium according to claim 1, which is a film. (3) At least two pairs of permanent magnets generate an in-plane component magnetic field along the radial direction at one or more locations on the disk-shaped magnetic recording medium, and the disk-shaped medium is moved through the same magnetic field. A method for manufacturing a magnetic recording medium according to claims 1 and 2, wherein the magnetic recording medium is repeatedly passed through the medium. (4) A plurality of pairs of upper and lower permanent magnets into which the medium is inserted are arranged along the longitudinal direction so as to generate an in-plane magnetic field in the longitudinal direction of the magnetic tape-like magnetic recording medium, and the area where the magnet pairs exist is A temperature gradient is created from one end to the other, and the medium is passed through this range continuously to perform cooling treatment in a magnetic field. A method for manufacturing a magnetic recording medium according to claims 1 and 2.