JPH0572014B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a metal thin film type magnetic recording medium, and particularly to a method for reproducibly producing a medium having excellent C/N characteristics in a short wavelength region. Structures of Conventional Examples and Their Problems In recent years, media with a ferromagnetic thin film as a magnetic recording layer have attracted attention as media suitable for high-density recording, and some have been put to practical use in audio applications. Efforts are being made in various fields to put metal thin film magnetic recording media into practical use for video applications, but tapes made using the known oblique evaporation method produce large noise due to non-uniformity of magnetism, and although they have high sensitivity, However, as a result, there is a problem that the C/N is low, and the present inventors have already proposed a method to improve the problem by a combination of introducing oxygen into a vacuum atmosphere and modified oblique evaporation. did.
(Japanese Patent Publication No. 57-29770) Although improvements in productivity and C/N can be expected with this method, stability in long lengths and reproducibility between lots were not sufficient. OBJECTS OF THE INVENTION It is to provide a method for manufacturing a metal thin film type magnetic recording medium with improved long-length stability and lot-to-lot reproducibility. Structure of the Invention When a ferromagnetic layer is formed by vapor deposition on a substrate moving along a rotating support in a vacuum atmosphere with a maximum partial pressure of oxidizing gas, the evaporation of the ferromagnetic material is caused by a focused electron beam. The gist of this method is to carry out impact heating and to exhaust air mainly from the vicinity of the scanning part of the electron beam and the part where the ferromagnetic material is deposited on the base material. If the focused electron beam used to heat and evaporate a ferromagnetic material is an electron beam with a large current, the beam tends to diverge due to the repulsive force between the electrons. However, by introducing an inert gas into the high-current electron beam,
Using the gas focusing method, in which inert gas ions generated by the interaction between inert gas and electrons attract electrons and reduce the repulsive force between electrons, it is possible to prevent the divergence of large current electron beams and can be focused. Therefore, the gas focusing method is most suitable for focusing a large current electron beam, and as a result, the input power density can be increased and large amounts of high melting point materials such as Co can be evaporated. This is because, industrially, the source of thermionic electrons is composed of high-temperature tungsten, so if oxygen is used for gas focusing, the tungsten is often rapidly oxidized and damaged, making it impractical. However, this inert gas flows into the ferromagnetic thin film formation atmosphere and interferes with the oxygen effect. In other words, the magnetic domains that have become extremely fine due to the oxygen effect are locally generated into large magnetic domains due to the influence of inert gas such as argon, which increases noise in the short wavelength range and reduces the reproducibility between lots. It becomes a source of deterioration. The best practical way to eliminate this cause is to focus the scanning part of the electron beam (this is an essential component in obtaining uniform film thickness and magnetic properties on a wide substrate) from the vicinity. It is to exhaust the air. The meaning of main exhaust here is that in winding deposition, the deposition area and the winding area are generally separated into two parts and evacuated separately, or an auxiliary exhaust system is often prepared for glow treatment. However, it refers to an exhaust system that exhausts the deposition atmosphere at the maximum exhaust speed.
Even if two exhaust systems are provided in the deposition chamber, the exhaust system that has the higher exhaust speed is called the main exhaust system. Another effect of the main evacuation method described above is that when the surface of the ferromagnetic metal particles is partially oxidized by introducing an oxidizing gas such as oxygen into the vacuum chamber, the heat that the base material receives during vapor deposition is used to oxidize the base material. This is an effect in which the temperature rises and gases such as water vapor released from the base material are exhausted to such an extent that the inconvenience of interfering with oxygen can be ignored. Therefore, it can be said that a configuration in which the above-mentioned main exhaust is performed from near the scanning part of the electron beam and the part where the substrate receives the ferromagnetic material deposition is most excellent. DESCRIPTION OF EMBODIMENTS FIG. 1 is a block diagram of the main parts of an apparatus used to carry out the present invention. The base material 1 is configured to move from the feed shaft 3 to the wind-up shaft 4 along the circumferential surface of the rotary can 2. Known elements of the winding system that are essential for winding deposition but are not directly related to the present invention are simplified and omitted. The ferromagnetic material 6 held in the evaporation source container 5 is heated by an accelerated electron beam 7. A piercing type electron gun is used as the electron source 8, and a variable leak valve 9 is adjusted to introduce gas from the outside for gas focusing. The gas-focused electron beam 7 passes through the scanning coil 1
The scanning magnetic field generated by the ferromagnetic material 6 is scanned in the width direction of the base material, and the evaporation distribution of the ferromagnetic material 6 is controlled, and the required magnetic properties including the film thickness are adjusted to be uniform in the width direction of the base material. Ru. The main exhaust system 11 exhausts the inside of the vacuum chamber 12, and is configured near the part of the substrate where the ferromagnetic material is deposited, and as close to the part where the electron beam is scanned as structurally permitted. is desirable. As a result, as schematically shown, the gas 13 for gas focusing, the unnecessary gas 14 coming from the base material, etc. are effectively exhausted, and are introduced into the vacuum chamber by adjusting the viaable leak valve 15, e.g. The effect of oxidizing gas such as oxygen on the ferromagnetic deposited film can be obtained with good reproducibility. 16 is a mask that limits the angle of incidence in order to adjust the magnetic properties. As a comparative example, a case was taken up in which the exhaust system 17 was disposed directly below the rotating support at the center position in the width direction of the substrate of the vacuum chamber (indicated by a broken line). [Example 1] Vapor deposition was carried out on a polyethylene terephthalate base material with a width of 50 cm, a length of 4000 m, and a thickness of 10 μm under the conditions shown in Table 1 using the apparatus whose main part configuration is shown in the figure to obtain a magnetic recording medium. . The comparative example is a case where the above-mentioned exhaust system position is used. The angle of incidence was 45°, and the surface temperature of the rotating support was controlled at 5±0.5°C. In addition, the thickness of polyethylene terephthalate was 8 μm.
to 25 μm, and the other conditions were Sample 2.
A magnetic recording medium was obtained under these conditions. Regarding the type of base material, in addition to polyethylene terephthalate, the present invention was also carried out using polyamide and polyimide in the same manner as described above. For magnetic materials, Co, CoNi alloys,
Focusing on CoNiCr alloys, CoAg, CoFe,
Tests were also conducted for CoSi, CoPt, etc. [Example 2] In the system of Example 1, the present invention and a comparative example were examined in the case where the length of the base material was tripled to 12000 m.

[Table] Effects of the invention Table 1 shows the C/N values and reproducibility. The C/N value was calculated by setting the center frequency of the carrier to 5.5 MHz and measuring the noise at 5 MHz, since it is thought that the noise near the carrier reflects the non-uniformity of the magnetic properties. The standard tape has the highest C/N among the improved γ-Fe ₂ O ₃ coated tapes commercially available.
The best one was used. The relative speed between the tape and the head was 2 m/sec. Regarding reproducibility, the variation in C/N between 5 lots was compared under the same conditions. As is clear from Table 1, the product of the present invention is superior in both C/N and reproducibility. These effects were also confirmed in many of the above examples not shown in Table 1. In addition, the C/N obtained in Example 2 was almost the same as in Example 1, but when looking at reproducibility, the difference between the conventional example and the present invention was even wider, from 1 of Example-1. In the case corresponding to condition No. 5, it was ±1.5 dB, whereas in the comparative example (conditions equivalent to No. 6 and 7), it was ±4.6 dB and ±5.9 dB, respectively. It goes without saying that the present invention is not limited to the above-mentioned embodiments, and the equipment conditions used may be independent of the rotation can, for example, a rotating support made of an endless belt, and the basic requirements of the exhaust system. As long as it satisfies the following, the type does not matter. The present invention is extremely valuable in that it enables the supply of excellent media in large quantities to the field of magnetic recording, where wavelengths are increasingly becoming shorter in recent years.

[Brief explanation of drawings]

The figure is a diagram illustrating the main part of an example of a winding vapor deposition apparatus used to carry out the manufacturing method of the present invention. DESCRIPTION OF SYMBOLS 1... Base material, 2... Rotation can, 5... Evaporation source container, 6... Vapor deposition material, 7... Electron beam, 8...
...Electron source, 11...Exhaust system.

Claims (1)

[Claims] 1. In a method of depositing a ferromagnetic layer on a substrate moving along a rotating support in a vacuum atmosphere with maximum partial pressure of an oxidizing gas, The ferromagnetic material is evaporated by impact heating by the focused electron beam emitted by a gas focusing type bias electron gun equipped with an inert gas introducing means for introducing an inert gas into the passage through which the ferromagnetic material passes, and the focused electron beam A method for manufacturing a metal thin film type magnetic recording medium, characterized in that exhaust is mainly carried out from the vicinity of a scanning portion of an electron beam and a portion of the substrate where the ferromagnetic layer is deposited.