JPH0442729B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method of manufacturing a magnetic recording medium that achieves high-density magnetic recording in the consumer field such as magnetic recording and video recording, and the industrial field such as information recording in computers. Conventional Structures and Their Problems In recent years, metal thin film magnetic recording media without binders have become essential to achieving high density recording, and their development is actively progressing in various fields. Currently, the closest level to practical use is vapor deposition in oxygen.
It is an in-plane magnetized film made of a Co-Ni alloy thin film.
Although Co--Cr-based perpendicular magnetization films are considered promising for achieving even higher density, evaluation of these media from the viewpoint of durability in a practical environment is far from satisfactory. A simple example is to store these media at 65℃ and 95%
After leaving it in an RH environment for one month, a thin film is formed.
This is the point where Bs (saturation magnetic flux density) decreases by 10 to 50%. In order to improve such performance, studies have been made on alloy components, overcoats, etc., and many proposals have been made from various fields, but at present no definitive method has been found. OBJECTS OF THE INVENTION An object of the present invention is to provide a method for manufacturing a magnetic recording medium based on a vapor deposition method that can significantly improve the durability of the ferromagnetic thin film itself. Structure of the Invention The method for manufacturing a magnetic recording medium of the present invention involves directing ferromagnetic vapor toward a polymer substrate in a vacuum atmosphere to form a ferromagnetic thin film layer on the polymer substrate, at a deposition rate of 1000 Å/min. sec or more and the pressure of the vacuum atmosphere is 10 ^-6 Pascal or less to obtain a medium with improved durability. The balance between evaporation rate and degree of vacuum can be seen from the large changes in durability seen in the drawings summarizing the results of many experiments, including the experimental examples described below. Deposition rate is 1000Å/
If the deposition rate is slower than sec, the degree of vacuum will increase and production quality will become unstable. Therefore, it is preferable to select a deposition rate of 1000 Å/sec or more. In addition, regarding the degree of vacuum, if it is 10 ^-6 Pa or less, Bs when left for one month in an environment of 65℃ and 95%RH
Since the rate of change in is less than 2% and can be ignored, 10 ^-6
It can be seen that it is preferable to control the temperature below Pa. The reason why these criticalities occur is not clear, but
This is thought to be because the occurrence of rust is different from that in pulp, and in thin films, it is highly dependent on defects, so non-linear changes become a problem as a result. As the polymer substrate, a polyester substrate, a polyamide substrate, a polyimide substrate, etc. are used, and prior to the vapor deposition of the present invention, pretreatment such as glow treatment or ion bombardment treatment can be performed. Ferromagnetic materials include Fe, Co, Ni, Fe-Co,
Co−Ni, Fe−Co−Ni, Co−Cu, Co−Au, Co
-V, Co-Ru, Co-Cr, Co-Sm, Co-Pt,
Mn-Bi, Mn-Al, etc. are used, but the electron beam heating method is most suitable for thermal evaporation of these materials. Vapor deposition methods include simple electron beam evaporation, as well as
Ionization vapor deposition, electric field vapor deposition, etc. can also be used. A pressure of 10 ^-6 Pa or less can be achieved by a combination of an oil diffusion pump and a liquid nitrogen trap, or by a cryopump, ion pump, etc. 10 ^-6
Of course, it is also possible to maintain the pressure at Pa or lower and to use it in conjunction with introducing a gas from the outside so that the maximum partial pressure is, for example, oxygen. The deposition rate is 100 Å/sec, based on the assumption that it will be used for mass production of magnetic tapes, magnetic disks, etc.
Although it can be freely selected in the range of ~10,000 Å/sec, it can be said that 1,000 Å/sec or more is preferable in the present invention. Description of Examples Hereinafter, the manufacturing method of the present invention will be explained based on specific experimental examples. A polymer substrate winding system is placed around a rotating can with a diameter of 50 cm in a rectangular stainless steel vacuum container with an internal volume of 4 ^m3 that can be baked, and an electron beam evaporation source is placed 20 cm directly below the rotating can. An exhaust system with an exhaust speed of 70,000/sec was installed. Additionally, an ionization vacuum gauge was installed near the deposition site to enable pressure measurements. [Experimental example 1] The evaporation source was equipped with Co82% and Ni18%, and the incident angle was 47°.
Using the above method, a Co-Ni thin film of 0.06 μm to 0.22 μm was deposited at a thickness of 2000 Å on a polyethylene terephthalate substrate (9.5 μm thick) as a polymer substrate using the oblique evaporation method.
sec to obtain a magnetic recording medium. At this time, the pressure was divided into two cases: one with residual gas, and one where oxygen with a purity of 99.99% was forcibly introduced to reach the maximum partial pressure of oxygen. As a comparative example, values obtained by performing vapor deposition at 5×10 ⁻⁶ Pa and 1×10 ⁻⁵ Pa are shown as representative values, but other results are as shown as ranges in the drawings. The sample numbers and pressure conditions during production are as shown in Table 1.

[Experiment example 2]

When there are two evaporation sources, A is directly below the rotating can and B is the side where the polymer substrate enters along the rotating can (the distance between the centers of A and B is 11 cm), A The material on the side is fixed to 100% Co, the material on the B side is selected from one of three types: Cr, Sm, and V, and the dwell time of the electron beam is changed to increase the B component for each alloy component relative to the whole. 10% by weight%
A thin film with a thickness of 0.1 μm was formed on a polyamide substrate as a polymer substrate by oblique deposition at an incident angle of 50° or more at an average rate of 3000 Å/sec. The temperature of the rotating can was maintained at 250°C during the deposition. Before vapor deposition, the rotating can temperature was maintained at 300° C. for 4 hours, and care was taken to maintain the pressure conditions constant during vapor deposition for a long time. Common pressure conditions and sample numbers for Co-Cr, Co-Sm, and Co-V films are shown in Table 2. As a comparative example, 5×10 ^-6 Pa, 1×10 ^-5
Vapor deposition with Pa was performed.

[Experiment example 3]

Using two evaporation sources with the same positional relationship as in [Experimental Example 2], the A side was made to have a constant Co of 100%, and the B side was
Choose one from each of the three types: Cr, Ru, and W.
A perpendicularly magnetized film was obtained in the same manner as in [Experimental Example 3], except that only the masking method was changed, and vertical evaporation was performed (the incident angle was within ±6°). As a comparative example, using the high frequency bipolar sputtering method,
It was created on the same substrate with a thickness of 0.1 μm. carrier gas is
Two types were used: Ar and He, with a pressure condition of 10 ^-1 Pa and an electron beam evaporation method (pressure condition was 5×
10 ^-6 Pa, 1×10 ^-5 Pa). The pressure conditions are as shown in Table 3.

[Table] The thus obtained magnetic recording medium was cut to a width of 8 mm, wound on a reel to a length of 100 m, and changes in magnetic properties before and after storage in various environments were investigated. The saturation magnetic flux density Bs was calculated by measuring the film thickness and using a vibrating sample flux meter (VSM). The sample numbers used are those explained in the experimental examples, and the comparative examples are representative of those described in the experimental examples that yielded the best results. Table 4 shows the results of storage under environmental conditions of 60°C and 90% RH for 3 months.

【table】

[Table] In addition, the difference is even more obvious in the test results of 65℃ 96% for 1 month and 65℃ 95% for 3 months, and the durability of the product obtained by the manufacturing method of the present invention is extremely good. It is also possible to further improve the durability of the obtained magnetic layer by using an organic or inorganic overcoat, or by changing the thickness of the overcoat layer.
Combined with the fact that it is possible even with a thickness of about 100 Å, it has great industrial value. In addition, in the above embodiment, cooling of the polymer substrate,
Although the conveying means was a rotating can, it may also be a rotating belt or the like. Effects of the Invention As explained above, according to the method of manufacturing a magnetic recording medium of the present invention, by simply setting the deposition rate and the pressure of the vacuum atmosphere during formation within a predetermined range, it is possible to create a medium with improved durability compared to conventional media. This is something that can be obtained.

[Brief explanation of drawings]

The drawing is a diagram showing the relationship between the deposition rate, degree of vacuum, and environmental test results for the saturation magnetic flux density during the formation of a ferromagnetic thin film layer.

Claims (1)

[Claims] 1. When forming a ferromagnetic thin film layer on a polymer substrate by directing ferromagnetic vapor toward the polymer substrate in a vacuum atmosphere, the deposition rate is set to 1000 Å/sec or more, and the pressure of the vacuum atmosphere at the time of formation is A method for manufacturing a magnetic recording medium that reduces the temperature to 10 ^-6 Pascal or less.