JPH0320816B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for manufacturing a perpendicular magnetic recording medium,
More specifically, the present invention relates to a method for manufacturing a perpendicular magnetic recording medium, in which a perpendicular magnetic recording medium comprising a soft magnetic layer comprising a NiFe alloy film and a Co-based alloy film is formed on a flexible organic polymer substrate. [Prior Art] In recent years, perpendicular magnetic recording media have been proposed as a magnetic recording system with excellent high-density recording characteristics. This method is published in Japanese Patent Publication No. 58-91 and Publication No. 58-10764.
As is known from the above publication, a recording medium in which the axis of easy magnetization is perpendicular to the film surface is used, and recording is performed so that the residual magnetization is oriented perpendicular to the film surface, so that the signal can be recorded at high density. Indeed, the demagnetizing field inside the medium is reduced, and excellent recording and reproduction can be performed.
A Co-based alloy thin film (particularly a CoCr alloy thin film) is known as a recording medium suitable for this method. In particular, a perpendicular magnetic recording medium in which a soft magnetic layer such as a permalloy alloy is provided on the base of a Co-based alloy thin film, as proposed in Japanese Patent Publication No. 58-91, can improve recording efficiency and provide a large reproduction output. It is attracting attention because of its ability to By the way, in the above-mentioned perpendicular magnetic recording medium,
When a soft magnetic layer and a recording layer are formed by sputtering on a substrate made of an organic polymer film such as polyethylene terephthalate (PET), which is inexpensive and has excellent mechanical properties, the surface becomes rough. At the same time, there is a problem in that the magnetic properties of the soft magnetic layer deteriorate, making it impossible to obtain desired recording and reproduction characteristics. [Object of the present invention] The present invention was made in order to solve such problems, and it is an object of the present invention to provide a method for manufacturing a perpendicular magnetic recording medium using a substrate made of an organic polymer and free from such problems. [Configuration and effects of the present invention] The above-mentioned objects are achieved by the present invention as described below.
That is, the present invention manufactures a perpendicular magnetic recording medium having a soft magnetic layer made of an alloy film mainly composed of Ni and Fe and a recording layer made of a Co-based alloy film on both sides of a flexible organic polymer substrate. In this method, the soft magnetic layer is formed on both sides of the substrate at a substrate temperature of 120° C. or lower, and then the recording layer is formed at a substrate temperature of a predetermined temperature or higher. be. The above-mentioned present invention was made as follows. In a perpendicular magnetic recording medium (hereinafter referred to as a dual-layer film medium) having a soft magnetic layer and a recording layer on a substrate, which is the object of the present invention, in order to achieve high-density recording and to obtain a practical reproduction output, recording It is necessary that the coercive force in the direction perpendicular to the film surface of the Co-based alloy film of the layer has an appropriate value (approximately 500±150 Oe (Oersted)). In order to obtain a Co-based alloy film that satisfies this requirement, the substrate temperature must be maintained at a certain temperature or higher during film formation. For example, when the Co-based alloy film is a CoCr alloy film, the vertical coercive force Hcv and the substrate temperature T when it is formed by sputtering have a relationship as shown in Figure 1. Therefore, in order to obtain a coercive force Hcv of 350 Oe or more, the substrate temperature T needs to be a high temperature of 140° C. or more. Note that the substrate temperature T in FIG. 1 is the surface temperature of the can for transferring the substrate. As a result of various studies, the present inventors found that the reason for the roughening of the surface of a two-layer film medium using an organic polymer substrate and the deterioration of the soft magnetic properties of the soft magnetic layer is as described above. The present invention was achieved by discovering that the cause is that volatile components contained in the substrate are deposited on the substrate surface during the formation of the recording layer at high temperatures. Below, we will discuss this point as a soft magnetic layer on a PET substrate.
The Ni Fe Mo alloy film will be explained in detail based on an example of a two-layer film medium in which a Co Cr alloy film is formed as a recording layer by a sputtering method. Figure 2 shows a Ni Fe Mo alloy with a thickness of 0.44 μm.
Figure 3 shows the relationship between the substrate temperature T and the coercive force Hch in the in-plane direction during the formation of the soft magnetic layer of the above-mentioned two-layer media. The relationship with playback output Ep is shown. Note that the measurement conditions for recording and reproducing characteristics are shown in Table 1. The head used was an auxiliary magnetic pole excitation type vertical head disclosed in Japanese Patent Publication No. 1982-91. Furthermore, Table 2 shows the properties of the CoCr alloy thin film (Cr: 20% by weight), which is the recording layer formed on the soft magnetic layer.

【table】

[Table] Half-width of surface rocking curve Until now, not much attention has been paid to the magnetic properties (Hc, etc.) of the soft magnetic layer, but as shown in Figures 2 and 3, the substrate temperature T during the formation of the soft magnetic layer It was found that there is a clear relationship between the coercive force Hch of the soft magnetic layer and the reproduction output Ep of the double-layer film medium. That is, in order to obtain a good reproduction output Ep, it is necessary to form a soft magnetic film at a low substrate temperature T while preventing precipitation of volatility from the substrate. Volatile matter from the substrate includes substances adsorbed on the surface of the substrate such as moisture, but especially in double-sided media such as floppy disks that have magnetic layers on both sides, volatile matter is precipitated from the PET film of the substrate and crystallized on the surface. The oligomers, which are mainly composed of trimers, roughen the surface and become a big problem. In our research on oligomer analysis using PET in vacuum, we found that oligomer precipitation and
It was found that crystallization mainly occurs at the heated surface, that is, the surface in contact with the high temperature can, and its behavior is different from that in the atmosphere. In other words, when producing a medium that has a magnetic layer on only one side of the substrate, oligomers do not precipitate on the magnetic layer side of the substrate (or even if they precipitate, they sublimate immediately), and the magnetic properties of the soft magnetic layer differ slightly. Although it only damages the surface and does not roughen the surface, in media with magnetic layers on both sides,
During sputter film formation of the recording layer, oligomers precipitate and crystallize on the opposite surface, causing the opposite surface to become rough, which poses a serious problem. Incidentally, the precipitation of such oligomers varies by about 10 to 20 degrees Celsius depending on the stretching ratio and heat setting temperature in biaxially stretched PET films, and although it is slightly less in polyethylene naphthalate, it appears at approximately 120 degrees Celsius or higher, and especially at 140 degrees Celsius. Above this, it becomes noticeable. In a medium in which oligomers are precipitated, there is a problem that not only is the output reduced due to spacing loss, but also the adhesion and durability between the substrate and the alloy film formed thereon are deteriorated. The present invention has been made based on the above-mentioned knowledge, and therefore, it is possible to create a good polymer substrate having a soft magnetic layer with a low coercive force and with unimpaired surface properties. It is clear that a bilayer media is obtained. Furthermore, as shown in FIG. 4, which is suitable for a floppy disk, a soft magnetic layer S and a recording layer R are provided on both sides of the substrate F.
In a double-sided double-layer film medium provided with a soft magnetic layer S
By forming the recording layer R on both sides, a double-sided double-layer film medium of a polymer substrate with good characteristics on both sides can be obtained. Note that in the present invention, the substrate temperature refers to the temperature of a contact surface with the substrate, such as a cooling can or a substrate holder that regulates the temperature of the substrate. Further, the substrate of the present invention is made of an organic polymer film. As the organic polymer, known ones such as polyester and polyimide can be used, but polyester whose main constituent is ethylene terephthalate or ethylene naphthalate is preferred because it is inexpensive and has excellent mechanical properties such as surface properties and dimensional stability. Note that the soft magnetic layer of the present invention is made of Ni Fe alloy or Ni
The so-called permalloy made of Fe Mo alloy is a typical example, but there are also other permalloys whose main components are Co, Fe,
Amorphous alloys containing Zr, Nb, Ta, W, B, Si, etc. may also be used. Recording layer contains 10 to 25 Cr
Co Cr alloy containing % by weight is representative, but other
Co Cr with Re, W, Mo, Ta, etc. added thereto, barium ferrite, etc. may also be used. The manufacturing method is preferably a sputtering method, but vapor deposition or ion plating may also be used. Further, an intermediate layer may be provided between the soft magnetic layer and the recording layer, a suitable protective layer may be provided on the recording layer, and an adhesive layer may be provided on the substrate.
In short, the present invention is applicable to any medium whose main components are a soft magnetic layer and a recording layer. Examples of the present invention will be described below along with comparative examples. First, a winding-type opposed target sputtering device used in the examples will be explained. This facing target sputtering device is based on the same principle as the facing target sputtering method known in Japanese Patent Application Laid-Open No. 58-158380, etc., and is capable of continuously manufacturing two-layer film media on both sides of a long substrate film. The structure shown in FIG. 5 is used to make this possible. In other words, 11 and 12 in the figure are temperature controllable cans, 13 is an unwinding roll,
14 is a take-up roll, 15 is a guide roll, 20 is a vacuum chamber, 21 is an argon gas introduction system, and 22 is an exhaust port. F is the substrate film, P ₁ to _{P 4} are
It is a facing target cathode with two 300 mmW x 150 mmL targets facing each other, and a shielding plate T prevents particles from scattering to unnecessary areas. P ₁ and P ₃ are alloy targets for the soft magnetic layer, and P ₂ and P ₄ are alloy targets for the recording layer. The opposed target sputtering method is well known as described above, and the accompanying equipment such as a vacuum pump, a target cooling water system, a power source for supplying power to the target, and a wiring system are not shown.
Further, a description of the sputtering effect will also be omitted. With the above configuration, a two-layer film medium is created as follows. That is, the substrate film F is fed out from a film roll set on the unwinding roll 13 and wound onto the take-up roll 14. If targets P ₁ , P ₂ , P ₃ , and P ₄ are all operated during this time, a double-sided double-layer film medium can be obtained in one operation. Alternatively, after forming a soft magnetic layer by operating only P ₁ and P ₃ , it is also possible to form a recording layer by operating only P ₂ and P ₄ while rewinding to form a double-sided double-layer film medium. . In this way, double-sided double-layer film media can be produced in various ways. [Example] Using the above-mentioned facing target type sputtering apparatus shown in FIG.
Ni Fe Mo (Ni: 79, Fe: 16, Mo: 5wt%)
A double-sided double-layer film medium having an alloy thin film and a Co Cr (Cr: 20 wt%) alloy thin film of approximately 0.44 μm on both sides was prepared. Opposing targets P ₁ and P ₃ are opposed targets with two Ni Fe Mo alloy targets (330 mm x 150 mm), P ₂ and P ₄ are opposed targets with two Co Cr alloy targets (330 mm x 150 mm), as follows. Created as follows. That is, the substrate film F is unwound from the roll 13.
Cans 11 and 12 kept at 90℃ while being fed out
Argon gas pressure is 0.5 Pa and average deposition rate is 0.3 μm/min for opposing targets P ₁ and P ₃ while the top is being fed.
Sputtering was performed to form a Ni Fe Mo alloy thin film on both sides, and the film was wound onto a take-up roll 14. After that, cans 11 and 12 are kept at 150℃, all rolls are reversed, and argon gas pressure is applied to opposing targets P ₂ and P ₄ .
A CoCr alloy thin film was formed on the NiFeMo alloy thin film by sputtering at 0.5 Pa and an average deposition rate of 0.3 μm/min, and the film was wound around an unwinding roll 13 to produce a double-sided double-layer film medium. Slit the above media into 0.3 inch width Table-1
I checked the playback output under the following conditions, and the 2KFRPI output on both front and back sides was 165 to 215μVo-p, and the 45KFRPI output was 55 to 215μVo-p.
It was 60 μVo-p, which was good. [Comparative Example] The same PET film used in the example was used as the substrate film F, and the substrate film F was fed out from the unwinding roll 13 while passing through the cans 11 and 12 kept at 140°C and wound on the take-up roll 14. During this time, all of the opposing targets P ₁ to _{P 4} were operated to perform sputtering, and a double-sided double-layer film medium consisting of a Co Cr alloy thin film and a Ni Fe Mo alloy thin film was produced on both sides of the substrate film F at once. Although no oligomer precipitation or crystallization was observed on the surface prepared by Can 11, the recording/reproducing output was lowered by about 4 dB compared to the example. Oligomers were abundant on the surface prepared with Can 12, and the recording/reproducing output was reduced by more than 8 dB.Furthermore, the adhesion between the alloy thin film and the substrate film was poor, and the durability of the medium against repeated recording/reproducing was extremely poor.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between substrate temperature T and coercive force Hcv measured in the vertical direction of a recording layer made of a CoCr alloy, and Figure 2 is a graph showing the relationship between substrate temperature T and coercivity of a soft magnetic layer made of a Ni Fe Mo alloy. Graph showing the relationship with magnetic force Hch, Figure 3 shows the coercive force Hch of the soft magnetic layer and reproduction output
FIG. 4 is a cross-sectional view showing the structure of a perpendicular magnetic recording medium, and FIG. 5 is a schematic structural diagram of a winding continuous facing target sputtering apparatus. F is the substrate, S is the soft magnetic layer, R is the recording layer, 11,
12 is a can, P ₁ to _{P 4} are opposing target cathodes,
20 is a vacuum chamber, 21 is an argon gas introduction part, 22
is an exhaust port.

Claims (1)

[Claims] 1. A perpendicular magnetic recording medium in which a soft magnetic layer made of an alloy film mainly composed of Ni and Fe and a recording layer made of a Co-based alloy film are formed on both sides of a flexible organic polymer substrate. Manufacturing a perpendicular magnetic recording medium, characterized in that the soft magnetic layer is formed on both sides of the substrate at a substrate temperature of 120° C. or lower, and then the recording layer is formed at a substrate temperature of a predetermined temperature or higher. Method. 2. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the substrate is made of polyester whose main component is ethylene terephthalate or ethylene naphthalate.