JPS63845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic recording medium using so-called perpendicular magnetization, in which recording is performed by magnetization in a direction substantially along the thickness direction of a magnetic recording layer. especially,
By type of tape, sheet, disk, etc.,
This invention relates to a method of manufacturing a so-called flexible magnetic disk.

Efforts to improve recording density have produced thin-film magnetic recording media with high coercive force, and recently, vapor-deposited metal thin-film magnetic tapes have come into practical use.

This is a recording medium that is said to achieve the highest recording density with longitudinal recording, but a perpendicular recording medium has been proposed as a medium that can compete with this medium, and research is progressing in various fields.

The configuration of a medium that has electromagnetic conversion characteristics closest to practical use known to date is what is called a double-sided flexible magnetic disk.

As the cross-sectional structure is shown in FIG. 1, this has permalloy layers 2 and 4 on both sides of a molded polymer substrate 1 made of polyester, polyamide, polyimide, etc.
This is a medium formed by stacking Co--Cr alloy layers 3 and 5.

This configuration was adopted to temporarily offset the deformation of the medium due to the essentially inescapable internal stress of the thin film, and the alloy layer formed on one surface is not required for recording and playback. However, there are high expectations for a method of manufacturing a disk having a magnetic recording layer on only one side, since it does not have any essential advantages and also from a manufacturing cost perspective.

The present invention can fully meet these industry demands, and a representative example of the cross-sectional structure of the target magnetic recording medium is as shown in FIG. Permalloy layer 7 with a thickness of 1.0μ, and on top of that a Co~ layer with a thickness of 0.3 to 1.0μ as a magnetic recording layer.
A Cr alloy layer is formed.

A third example of the apparatus for carrying out the present invention will be described below.
It is shown and explained in the figure.

A moving conveyance system for the polymer molded substrate 12 is provided inside the vacuum chamber 11, that is, a winding shaft 13, a winding shaft 14, a free roller 15, and a rotating drum 16. Of course, it goes without saying that the expander rollers, dancer rollers, etc. are devised each time depending on the control system of the conveyance system.

The inside of the vacuum chamber 11 is constantly evacuated by the evacuation device 17, and it is natural that gas is sometimes actively introduced from the outside to balance the pressure at a predetermined level. Although the figure schematically shows an example in which the alloy layer is formed by a so-called sputtering method, it is of course possible to use an electron beam evaporation method or other known physical vapor deposition method. Appropriate measures should be taken, such as using multiple numbers. Reference numeral 18 schematically shows a NiFe sputter source, and 19 schematically shows a Co-15wt% Cr sputter source, for example. The configuration of the sputter source may be a bipolar sputter system consisting of a known cathode and anode, or may be of other variations.

In any case, the use of high frequencies is common.
The present inventor has mainly used the high-frequency sputtering method, but this is because the important point of the present invention is in the post-process, and for forming the alloy layer, we have also confirmed the DC sputtering method and the electron beam evaporation method. Although this difference due to the film forming method had an influence on the conditions of the post-process, it was not essential and was a change within the adjustment range.

First, regarding the selection of the substrate, a biaxially stretched polyethylene terephthalate film, which is a so-called balanced type without anisotropy in orientation, was used.
Thickness ranges from 10μ to 60μ, average Young's modulus is 400
It was ~500Kg/ ^mm2 . In addition, the effects of the present invention were also confirmed for polyamide films of 6μ to 40μ and polyimide films of 45μ.

The width of the board is 550mm and 200mm, and the standard manufacturing length is 1000m.

First, the permalloy layer was formed by placing a target at a close distance of 9 cm along the circumferential side of a rotating drum (1 m in diameter). The target area is
Three sheets of 600 mm x 300 mm were used. High frequency is 13.56MHz
Then, argon gas was introduced, and the pressure was adjusted by a valve using a servo motor to 2×10 ^-2 to 3×10 ^-2 Torr.
was maintained within the range of

Prior to film formation, NiFe, Co-Cr at 20 m/min
Using a sputtering source, a polymer film substrate was surface treated with high frequency power of 90W to 120W.

The gas introduced at this time is a mixed gas of Ar and O ₂ .
The flow rate ratio of Ar and O ₂ was adjusted to a value of approximately 1:2.

The importance of this treatment, especially the importance of the presence of _O2 , is
This is a point that has a remarkable effect in ensuring durability of recording and reproduction, especially in a humid environment.

It goes without saying that the apparatus has a substantial configuration in which the NiFe film and the Co--Cr film are successively formed after performing the above-mentioned pre-treatment, but a detailed explanation will be omitted.

Standard film forming conditions are line speed 3m/
min, the input of high frequency power to NiFe is 450 ~
The high frequency power input to Co-Cr was 900W/target and 1600 to 1950W/target, and sufficient consideration was given to the surface quality of the rotating drum 16 and the coolant circulation path configuration to prevent overheating of the substrate.

As for the magnetic properties, the NiFe layer has a coercive force of 10 O¨e or less, and the saturation magnetization (Ms) is 500 to 700 G. The Co-Cr layer has a coercive force of 800 to 1000 O¨e in the direction perpendicular to the film surface, and the saturation magnetization (Ms). was 560 to 650G, and the film thickness was set to 0.4μ as a standard value.

The uniformity of the film thickness is as follows for a film with a width of 550 mm.
It was ±4% in the range of 500 mm, and in the case of a 200 mm wide film, it was ±3% in the range of 180 mm. In addition, the uniformity of each magnetic property is that the coercive force is ±18 for the NiFe layer.
%, ±2% for Co-Cr layer, ±6% for NiFe layer for Ms,
It was ±3% in the Co--Cr layer. Although the coercive force of the NiFe layer has large variations, this does not pose any problem in recording and reproducing, and as will be described later, the most closely related to the present invention is the uniformity of the film thickness. By selecting a substrate film, the limit of film thickness uniformity required to ensure dimensional stability and flatness of the recording medium is ±7%, and it has been extensively demonstrated that the present invention can be achieved within this range. We repeated the experiment to confirm.

The explanation so far has only mentioned the two-layer structure of NiFe and Co-Cr, but other combinations of soft magnetic layers and perpendicular magnetic layers are of course possible, and non-magnetic layers such as Al ₂ O ₃ , SiO, metal It is also possible to select one of these and add it to the configuration depending on the purpose, and this does not limit the present invention. In addition, coating method, plasma CVD method, plasma CVD method, etc.
It is also free to form by any known means such as sputtering. However, care must be taken to complete the above steps before heat treatment.

Next, we will explain the heat treatment process, which is one of the important points of the present invention.The purpose of this process is to flatten the recording medium, ensure durability, and in particular stabilize the adhesion strength between the polymer molded substrate and the thin film layer. The objective is to strengthen and strengthen the structure, ensure dimensional stability, and stabilize the properties of the perpendicular magnetic layer.

The first points to be considered as conditions for heat treatment are the thermophysical property values of the polymer molded substrate and the internal stress of each thin film formed on the polymer molded substrate, and their composite value. These can be suppressed by changing the shape of the composite, or by dissolving the polyester with a solvent, separating the NiFe-Co-Cr composite film from the polymer molded substrate, and measuring the internal stress. Good.

As a result, the internal stress varies depending on the manufacturing conditions, film thickness, and material of the film, but one step is processing for several hours at a temperature near the glass transition point of the polymer molded substrate. This treatment does not aim to complete planarization, but is adjusted with the second stage heat treatment described later, and therefore various combinations of temperature, time, and environment are possible.

However, the main point to be considered is to suppress the influence of external forces on the medium to be treated as much as possible during the first stage heat treatment. This requirement is 550
This is accomplished by rolling a 200 mm wide medium over 1000 m and storing it in an oven, for example.

The selection of time has a strong correlation with temperature, which is determined by the thermophysical properties of the polymer molded substrate.

To give a specific example of the range mentioned above, when normalized to an oxygen atmosphere and humidity of 60% RH, 70 to
2 to 12 hours at 80°C was sufficient.

This is not a limitation of the present invention, and tests were also conducted at 60° C. for one day to one week, and it was found that the objective was achieved in all cases.

The details are still under consideration, but as there is a barrier to accelerating with temperature down to the second level, it is preferable to reach the set conditions by increasing the heat capacity of the processing medium (the longer the length, the more care must be taken) ), several hours should be chosen.

The second stage of heat treatment is to complete the flattening of the medium, and after the first stage has corrected it to a nearly flat state,
Particularly in the case of long media, the flatness is detected online while moving along the heated roll (choose the atmosphere if necessary), and while changing the length of time the media is acting on the heated roll. Stress relaxation is performed to complete flattening.

The resulting wide, long media is then punched into the required disc shape. In order to continuously process a large amount of discs, a carrier sheet was used, the discs were stacked and conveyed, and the discs were punched out, and the punched discs were collected.

Of course, the punching process of the present invention includes, in a broad sense, cutting with laser light, as well as the modification of the carbide punching jig and the cooling of the medium.

According to the present invention, it is possible not only to mass-produce magnetic disks, but also to obtain a magnetic recording medium with extremely stable characteristics in actual use.

Conventional double-sided flexible disks have a NiFe layer,
Because the Young's modulus of the Co-Cr layer is large, controlling the film thickness necessary to achieve strict flatness is difficult as the area becomes larger, and the dimensions due to the difference in thermal expansion between the polymer molded substrate and the metal. As can be easily understood from the fact that there is a metal layer on both sides, the influence is greater than in the case of the present invention, which has a metal layer on only one side. Obtained in large quantities. The industrial value of the present invention is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional magnetic recording medium, FIG. 2 is a sectional view of a magnetic recording medium according to the present invention, and FIG. 3 is a schematic sectional view of an apparatus for carrying out the manufacturing method of the present invention. 6, 12... Polymer molded substrate, 8... Alloy film (alloy layer), 19... Alloy spatter source.

Claims (1)

[Claims] 1 After forming an alloy film having an axis of easy magnetization in the direction perpendicular to the film surface of at least one layer on only one side of a polymer molded substrate having a glass transition point Tg (°C), A first heat treatment step in which the material is heat treated in a roll shape at high temperature for a long time under no tension to minimize distortion at the interface between the alloy film and the polymer molded substrate; 1. A method of manufacturing a magnetic recording medium, which comprises punching a molded polymer substrate into a predetermined shape through a second heat treatment step of thermally shrinking and flattening the polymer molded substrate.