JPH11102517A - Manufacture of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of mechanical characteristics and corrosion resistance due to presence of hydrogen as impurities by controlling the partial pressure of hydrogen and steam in a vacuum vessel at the time of evaporation within specified ranges when a metallic thin-film type magnetic layer is formed by an evaporation method in the vacuum vessel. SOLUTION: A feed roll 12 and a wind-up roll 14 for making a base film 11 travel on a can roll 13 in a vacuum chamber 16 are arranged, and the heating pretreatment of the vacuum chamber 16 is conducted and water adsorbed onto an interior wall is removed. Total pressure is adjusted in approximately 5×10<-6> Torr, a magnetic material 18 in a crucible 15 is irradiated with electron beams by an electron gun 19, and the magnetic material 18 is dissolved and an evaporation atmosphere is obtained. The partial pressure of hydrogen and steam is controlled so as to be kept within a range of 1×10<-7> -5×10<-6> Torr after the vapor of the magnetic material 18 is stabilized. Accordingly, a magnetic layer, in which corrosion resistance and mechanical characteristics are improved, can be formed onto the base film 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a magnetic recording medium. More specifically, the present invention relates to a method for producing a magnetic recording medium having improved corrosion resistance and mechanical properties.

[0002]

2. Description of the Related Art A magnetic recording medium represented by a video tape, a floppy disk or the like is conventionally manufactured by forming a magnetic layer by a coating method. However, in recent years, as the demand for high-density recording on a magnetic recording medium has increased, it has become difficult to respond to a magnetic layer formed by a coating method. Therefore, recently, a magnetic recording medium having a metal thin film type magnetic layer, which is filled with a magnetic material at a high density, has attracted attention. Above all, the vacuum deposition method is becoming mainstream as a method of forming such a metal thin film type magnetic layer because the apparatus is simpler and stable film formation is possible as compared with other methods.

[0003] By the way, the vacuum deposition method is performed under a vacuum as the name implies, but it is difficult to obtain a complete vacuum, and the presence of some impurities is inevitable. However, for example, if hydrogen is present as an impurity, it easily penetrates into the metal when in contact with a high-energy metal vapor stream, resulting in embrittlement known as hydrogen embrittlement. It is also known that, as the time elapses over a long period of time, it reacts with oxygen in the metal to adversely affect corrosion resistance.

[0004] As another example, if carbon is present as an impurity, it is also incorporated into the metal when it comes into contact with the metal vapor stream, deteriorating its mechanical properties like hydrogen, and in some cases, its magnetic properties. Also reduce. Therefore, when forming a film by dissolving a metallic magnetic material by a vacuum deposition method to generate a vapor thereof and attaching it to a support, even if a perfect vacuum is impossible, it is as high as possible so as not to cause such problems. It is desired to achieve a degree of vacuum.

[0005]

As described above, it is desirable to increase the degree of vacuum in the container for vapor deposition as much as possible, that is, to exhaust impurities as much as possible. However, the higher the ultimate vacuum degree is set, the larger the vacuum exhaust device becomes. This imposes a considerable burden on capital investment. Further, in actual operation, there is a problem that even if a vacuum exhaust device capable of achieving a high degree of vacuum is installed, a necessary high vacuum cannot be obtained due to time constraints.

On the other hand, as can be understood from the fact that an oxidizing gas is introduced to oxidize a magnetic layer in vacuum deposition, not all substances have to be necessarily removed from a vacuum vessel. Further, it is considered that an inert gas such as argon may be present as long as it does not hinder the flight of the metal vapor. However, in the past, the pressure in the vacuum vessel was controlled by the degree of vacuum based on the total pressure, and sufficient attention was not paid to the concentrations of individual substances and impurities. However, if it is possible to determine the allowable range of each impurity and control it together with the total pressure, it is extremely useful when performing vacuum deposition.
Therefore, an object of the present invention is to provide a method for suitably controlling the pressure in a vacuum vessel from such a viewpoint.

[0007]

Means for Solving the Problems The present inventors have individually studied impurities present in a vacuum vessel, particularly from the viewpoint of whether or not the properties of a magnetic recording medium are adversely affected. As a result, in the vacuum chamber,
The present inventors have found that by manufacturing a magnetic recording medium while controlling the partial pressure of a gas containing a specific impurity, it is possible to particularly improve corrosion resistance and mechanical characteristics, and have accomplished the present invention.

That is, according to the first aspect of the present invention, there is provided a method for producing a magnetic recording medium by a vapor deposition method in a vacuum vessel, wherein the partial pressure of hydrogen and water vapor in the vacuum vessel during vapor deposition is reduced to 1 × 10 ^−. It is characterized in that it is controlled within the range of ^{7 to} 5 × 10 ⁻⁶ Torr. As described above, if hydrogen is present as an impurity during vacuum film formation, the mechanical properties and corrosion resistance of the magnetic recording medium are deteriorated due to hydrogen embrittlement. However, as in the present invention, the partial pressure of hydrogen and water vapor is reduced to 1 × 10 ^−7. By controlling to within the range of -5 × 10 ^-6 Torr, such effects can be minimized.

According to the second aspect of the present invention, the partial pressures of carbon monoxide and carbon dioxide are further controlled to 2 × 10 ⁻⁷ Torr or less. The lower the lower limit of these partial pressures is, the better, but what is actually obtained is on the order of 10 ^-8 Torr. According to this, it is possible to further substantially prevent a decrease in mechanical properties due to the incorporation of carbon.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, according to the present invention, when forming a film by vapor deposition, the partial pressure of hydrogen and water vapor is 1 × 10 ^{−7 to} 5 × 10 ⁻⁶ Torr in the vacuum chamber. Is controlled as follows. Preferably, the partial pressure of carbon monoxide and carbon dioxide is controlled to be 2 × 10 ⁻⁷ Torr or less. In order to achieve such partial pressures of hydrogen and water vapor, carbon monoxide and carbon dioxide, the total pressure in a vacuum vessel is generally 5 ×
It is necessary to keep it at about 10 ^-6 Torr or less. However, such control of the total pressure does not necessarily directly relate to the control of the above ranges for hydrogen, water vapor, carbon monoxide and carbon dioxide. It is necessary to control the total pressure so as to obtain the value of

The partial pressure of hydrogen and water vapor is 1 × 10 ^{-7 to} 5 ×
It is controlled within the range of 10 ^-6 Torr. In order to reduce the partial pressure to less than 1 × 10 ⁻⁷ , the exhaust system tends to be complicated and large, which is not advantageous in terms of cost and time. If the partial pressure is larger than 5 × 10 ⁻⁶ Torr, the mechanical properties and corrosion resistance of the obtained film tend to deteriorate. On the other hand, the partial pressures of carbon monoxide and carbon dioxide are controlled to be 2 × 10 ⁻⁷ Torr or less. When these partial pressures are higher than 2 × 10 ⁻⁷ Torr, the object of further improving the mechanical properties is hardly achieved.

According to the invention, the above-mentioned partial pressure has to be obtained during the deposition in a vacuum vessel. Generally, the vapor deposition operation is performed by evacuating the inside of the container and then generating a metal vapor by electron beam heating or the like to obtain a vapor deposition atmosphere, but the total pressure in the container rises rapidly with the generation of the metal vapor, and At the same time, the process follows that the partial pressures of hydrogen, water vapor, carbon monoxide and carbon dioxide increase. Then, the total pressure gradually recovers, and the partial pressure of the impurities also drops. The deposition is continued under the thus obtained stable vacuum state, and the "at the time of deposition" in which the partial pressure is controlled in the present invention is intended for such a stabilized state. This is, for example, based on time,
The time after 30 minutes after the generation of metal vapor can be regarded as “at the time of vapor deposition”. However, it is also acceptable to judge the time of vapor deposition according to other criteria. The measurement of the partial pressure can be performed by, for example, a quadrupole mass spectrometer connected to a vacuum vessel.

In the present invention, the partial pressures of hydrogen, water vapor, carbon monoxide and carbon dioxide are controlled, for example, by baking a vacuum vessel, purifying the metal pellets used, bombarding the base film, and controlling the gas introduced. Although it can depend on a number of factors, such as purification, the biggest controlling factor is having a suitable exhaust system. In general, a cryopump or the like is generally used as an evacuation device for a vacuum evaporation apparatus. However, these have a particularly low evacuation ability for hydrogen, and it is doubtful whether a required hydrogen partial pressure during evaporation can be achieved. When controlling the partial pressure by paying attention to individual gases as in the present invention, special considerations such as appropriately using in combination with other vacuum pumps, for example, powerful turbo molecular pumps, oil diffusion pumps, etc., are required. Often.

The method for manufacturing a magnetic recording medium of the present invention can be used mainly for forming a magnetic layer. This is performed, for example, by vacuum deposition using an electron beam. As the ferromagnetic metal material forming the magnetic layer, for example, a ferromagnetic metal such as Co, Ni, Fe, or Fe-Co, Fe-Ni, Co-Ni, Fe −Co
-Ni, Fe-Cu, Co-Cu, Co-Au, Co-Y, Co-La, Co-
Pr, Co-Gd, Co-Sm, Co-Pt, Ni-Cu, Mn-Bi, Mn-S
b, Mn-Al, Fe-Cr, Co-Cr, Ni-Cr, Fe-Co-Cr, Ni
-Co-Cr and other ferromagnetic alloys. In particular, at least one selected from ferromagnetic alloys containing iron, cobalt, and nickel as main components and nitrides thereof is preferable. In particular, in the present invention, it is desirable to use a raw material having a concentration of impurities of 300 ppm or less as a source of hydrogen or carbon. For example, cobalt pellets contain hydrogen and carbon monoxide as reducing gas, and it is desired that their concentrations be as low as possible.

In forming the magnetic layer by vacuum deposition, it is preferable to improve the durability by introducing an oxidizing gas and forming an oxide on the surface of the magnetic layer. And raise the concentration of the impurity gas contained in it, especially the
It is preferable that the content be less than ppm. The magnetic layer is formed of one layer or two or more layers. To cope with high-frequency recording, it is advantageous to have many layers, but it is considered that 2 to 5 layers are appropriate as a practical range. . The thickness of the magnetic layer is not particularly limited, but is preferably 50 to 500 nm,
Particularly, a practical range is preferably from 80 to 300 nm.

In the method for producing a magnetic recording medium of the present invention, a magnetic recording medium is generally obtained by forming a magnetic layer on a support.
Conventionally known ones can be used. For example, in the case of a plastic film, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonate; polyvinyl chloride; And aromatic polyamides. However, PET is preferred in terms of price. Such a support is usually wound in a roll and placed in a chamber adjacent to a vacuum vessel for vapor deposition, and introduced into the vacuum vessel through a slit provided in a wall separating the chamber and the vacuum vessel. In this case, it is preferable to perform a known treatment such as bombarding in the above-mentioned chamber so that the support does not carry impurities.

The method for producing a magnetic recording medium of the present invention can also be used to form a back coat layer on the surface of the support opposite to the magnetic layer by vapor deposition. Such a back coat layer may be formed by e-beam evaporation of a metal such as Cu, Ni, or Al, or a metalloid such as Si or Ge, and simultaneously or afterward performing oxidation, nitridation, or carbonization. it can. In this case, by controlling the partial pressures of hydrogen and water vapor, furthermore, carbon monoxide and carbon dioxide according to the present invention, the resulting back coat layer can be made excellent in corrosion resistance and mechanical properties. The thickness of the back coat layer is not particularly limited, and is appropriately determined depending on the material and the purpose of use. But the thickness is generally 500nm
The following is preferred.

The magnetic recording medium manufactured according to the present invention can be provided with a protective layer, a lubricating layer, and the like as needed. For example, the protective layer can be formed by depositing a high-hardness material such as diamond-like carbon on the magnetic layer and / or on the back coat layer using a CVD method or the like. The lubricating layer can be formed by applying or spraying a fluorine-based lubricant represented by perfluoropolyether on the outermost layer of the magnetic recording medium.

FIG. 1 shows a specific example of a vacuum deposition apparatus used in the present invention. Here, a vacuum chamber 16 connected to a vacuum exhaust device (not shown), a can roll 13 provided in the vacuum chamber 16, and a support on the can roll 13
An unwind roll 12 and a take-up roll 14 for running the 11 are appropriately arranged.

In order to carry out the manufacturing method of the present invention, first, for example, a pre-heating treatment (baking treatment) of the vacuum chamber 16 is performed.
To remove the water adsorbed on the inner wall. After that, the total pressure was increased to 5 × 10 by cryopump / turbo molecular pump, etc.
Adjust to about ^-6 Torr, and place an electron gun on the magnetic material 18 in the crucible 15
An electron beam is irradiated from 19 to melt the magnetic material 18 to make a vapor deposition atmosphere. After the vapor of the magnetic material 18 is stabilized, that is, for example, 30 minutes after the start of melting, the partial pressures of hydrogen and water vapor are in the range of 1 × 10 ^{−7 to} 5 × 10 ⁻⁶ Torr, and carbon monoxide and carbon dioxide Control is performed so that the partial pressure of carbon is 2 × 10 ⁻⁷ Torr or less. The partial pressure of the impurity gas such as hydrogen is measured by a quadrupole mass spectrometer 17 connected to a vacuum chamber 16.

In this case, the partial pressure is controlled by using, for example, an oil diffusion pump or the like as a vacuum evacuation device, selecting the purity of the magnetic material 18, and moving the support 11 into the vacuum chamber 16. This also includes a bombardment process that can be performed before, selection of the purity of the oxidizing gas introduced from the gas introduction pipe 20, and the like. By controlling the partial pressure in a predetermined range in this manner, a magnetic layer having improved corrosion resistance and mechanical properties is formed on the support.

FIG. 2 exemplarily shows details of the evacuation system not shown in FIG. In this example, two cryopumps, two turbo molecular pumps and two oil diffusion pumps, and a mechanical booster pump and a rotary pump suitable for these are provided in the vacuum chamber. However, the type and combination of pumps used can be appropriately selected within the scope of the present invention.
For example, roughing is a rotary pump and a mechanical booster pump, in the cryopump Once turned 10 ^-4 Torr table,
And so on.

[0023]

【Example】

Examples 1 to 4 and Comparative Examples 1 to 4 <Production Method> A magnetic layer was formed using a vacuum evaporation apparatus as shown in FIG. The volume of the vacuum chamber is 700 liters.
Cryopump 2 with a pumping capacity of 00 liter / second
And two turbo-molecular pumps having a pumping capacity of 2000 l / s, and two oil diffusion pumps having a pumping capacity of 2000 l / s, and a mechanical booster pump and a rotary pump suitable for each pump. Prior to the vapor deposition, the moisture adsorbed on the inner wall of the vacuum chamber was blown off by heat treatment (baking).

A 4.5 μm thick polyamide film was used as a support, and 99.9% pure metal cobalt was used as a magnetic material. The support was bombarded before entering the vacuum chamber. In order to experimentally control the partial pressures of hydrogen and water vapor, water vapor was introduced into the vacuum chamber using argon as a carrier gas. Similarly, in order to control the partial pressures of carbon monoxide and carbon dioxide, carbon was contained in metallic cobalt as required. The partial pressure of each impurity gas was measured using a partial pressure gauge connected to a vacuum chamber (QIG-066, manufactured by Anelva).
The measurement was carried out 30 minutes after the generation of the cobalt vapor by using. The partial pressures of hydrogen and water vapor, carbon monoxide, and carbon dioxide in Examples 1 to 4 and Comparative Examples 1 to 4 were controlled as shown in Table 1, respectively.

The maximum incident angle and the minimum incident angle of the deposited atoms were 90 ° and 60 °, respectively, the deposition rate was 100 nm / sec, and the thickness of the magnetic layer was 180 nm. After forming the magnetic layer, a back coat layer and a lubricating layer were formed on the obtained raw material, slit to a width of 6.35 mm, and loaded on a DVC cassette to produce a magnetic recording medium.

[0026]

[Table 1]

<Evaluation> The samples obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated for mechanical properties and corrosion resistance.

The mechanical properties were evaluated by performing a scratch strength test. A scanning scratch tester for thin film evaluation (SST-101 manufactured by Shimadzu Corporation) was used as a test apparatus, and a diamond stylus having a tip diameter of 10 μm was run on the sample surface while slightly vibrating with an amplitude of 50 μm, and the load was gradually increased. The minimum load at which the film was broken was taken as a measure of the mechanical strength of the film surface. For corrosion resistance, 60 ° C, relative humidity
The evaluation was made based on the change (%) in the magnetostatic property Bs (saturated magnetic flux density) after exposure for one week in a 90% environment. Table 2 shows the above results.

[0029]

[Table 2]

[0030]

As is clear from Table 2, the partial pressures of hydrogen and water vapor are reduced by 1 × 10 ^{−7 to} 5 × 10 5 by the production method of the present invention.
^{When the} pressure is controlled in the range of ^-6 Torr, the corrosion resistance and the mechanical properties are improved, and the mechanical properties are further improved by setting the partial pressures of carbon monoxide and carbon dioxide to 2 × 10 ^-7 Torr or less. Can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a vacuum evaporation apparatus that can be used for carrying out the manufacturing method of the present invention.

FIG. 2 is a schematic view illustrating an example of a vacuum evaporation apparatus that can be used for carrying out the manufacturing method of the present invention, with respect to details of an exhaust system.

[Explanation of symbols]

 11 Base film 12 Unwind roll 13 Can roll 14 Take-up roll 15 Crucible 16 Inner wall of vacuum chamber 17 Quadrupole mass spectrometer 18 Magnetic material 19 Electron gun 20 Gas inlet tube

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Hirohide Mizunoya 2606 Akabane, Kaimachi, Haga-gun, Tochigi Pref.

Claims (2)

[Claims] 1. A method for producing a magnetic recording medium by a vapor deposition method in a vacuum vessel, wherein a partial pressure of hydrogen and water vapor in the vessel at the time of vapor deposition is 1 × 10 ^{−7 to} 5 × 10 ⁻⁶ Torr. A method for manufacturing a magnetic recording medium, characterized in that the magnetic recording medium is controlled within a range. 2. The method according to claim 1, further comprising controlling a partial pressure of carbon monoxide and carbon dioxide in said container to 2 × 10 ⁻⁷ Torr or less at the time of vapor deposition.