JPH0466051B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a magnetic recording medium having a ferromagnetic metal thin film on a support, and more particularly to a method for manufacturing a durable magnetic recording medium by coating a lubricant solution on the ferromagnetic metal thin film. . Structure of conventional examples and their problems In conventional magnetic recording media, magnetic fine particles such as magnetic iron oxide fine particles and magnetic alloy fine particles are formed on a support as a magnetic recording layer along with a binder and additives added as necessary. Coated magnetic recording media, which are made by applying a homogeneously dispersed paint and drying it, have been widely used. However, in recent years, there has been a demand for higher density magnetic recording, and so-called metal thin film magnetic recording layers using obliquely deposited Co-Ni-O films or perpendicularly magnetized films such as Co-Cr are used as magnetic recording layers. Recording media are attracting attention, research, and active development. It has become clear that these metal thin film type magnetic recording media have superior electromagnetic conversion characteristics, but on the other hand, they are inferior in practical durability, and it has been found that improvements are necessary. This problem of poor durability is due to the fact that, unlike coating-type magnetic recording media that use conventional binders, metal thin-film magnetic recording media change the surface material to metal or its oxides, etc. The synergistic effect of smoothing the surface of the magnetic recording medium in order to reduce spacing loss during wavelength recording and reproduction has enabled the transport system, cylinder, and magnetic head that make up the equipment that actually uses metal thin film magnetic recording media. The frictional resistance between the recording medium and the like increases and the running performance worsens, which not only causes deterioration in image quality but also causes the ferromagnetic metal thin film to peel off and even completely lose its function as a magnetic recording medium. Therefore, it can be said that improving the frictional resistance of the ferromagnetic metal thin film so that it does not become large is an important problem for practical use. Therefore, many studies have been conducted to solve this problem, but it is said that the most effective solution at present is to apply a lubricant on the ferromagnetic metal thin film. Lubricant application methods can be divided into wet methods and dry methods. Either method can initially reduce the frictional resistance on the surface of the lubricant, but if the magnetic recording medium is used for repeated recording. When used in a regenerator, the effect of the lubricant gradually fades and the coefficient of friction gradually increases.
At present, the ferromagnetic metal thin film is scratched in the short time it takes to reproduce a still image, making it insufficient in terms of durability to be practical as a magnetic recording medium. On the other hand, attempts have been made to solve the problem by improving the moisturizing and lubricant material itself, and proposals have been made that focus on the melting point of the material, and proposals that hope for a composite effect by mixing multiple types of materials or applying multiple layers. The reality is that they cannot satisfy a wide range of use environments in terms of performance, and that they do not have sufficient practical durability. OBJECTS OF THE INVENTION An object of the present invention is to provide a method for manufacturing a ferromagnetic metal thin film magnetic recording medium having excellent running properties and wear resistance. Structure of the Invention The present invention provides a magnetic recording method in which, when applying a lubricant solution onto a ferromagnetic metal thin film provided on a support, an electric field is applied in the thickness direction of the ferromagnetic metal thin film, and then the lubricant solution is dried. Regarding the method of manufacturing the medium, the magnetic recording medium manufactured by this method can almost suppress an increase in the coefficient of friction even when used repeatedly, and can improve running performance and wear resistance. Supports that can be used in the present invention include polyethylene terephthalate, polyethylene naphthalate,
Supports such as aromatic polyamide and polyimide are preferred. In the present invention, the ferromagnetic metal thin film serving as the magnetic recording layer includes Co, Fe, Co-Ni, Co-Fe, Co-
B, In-plane magnetized films such as Co-Pt, Co-Cu, Co-Cr, Co-V, Co-Cr, Co-Ti, Co-W, Co-V,
Co−Mo, Co−Sm, Co−Ru, Co−Mn, Co−
Examples include perpendicularly magnetized films such as Ni-Cr and Co-Cr-Rh, and it is clear that the thickness of thin films of these metals and the composition in the case of alloys are well known to those skilled in the art and can be arbitrarily selected. The method for forming the ferromagnetic metal thin film in the magnetic recording medium of the present invention includes known vacuum deposition methods, sputtering methods, CVD methods, ion beam deposition methods, electroplating methods, electroless plating methods, and arbitrary methods. can be used. Note that the ferromagnetic metal thin film can also be applied directly onto the support. Alternatively, it is also possible to apply a known base layer in advance and apply it thereon. The lubricant to be applied on the ferromagnetic metal thin film according to the present invention is not particularly limited, and any conventionally known lubricants such as fatty acids, esters of fatty acids, mineral oils, animal and vegetable oils, silicone oils, higher alcohols,
There are fluorocarbons, etc., and these can be used alone or in the form of a mixture. When applying the above lubricant onto the ferromagnetic metal thin film, it is used as a solution dissolved in a suitable solvent such as acetone, methyl ethyl ketone, cyclohexanone, methanol, propanol, ethyl acetate, hexane, carbon tetrachloride, etc. do. The coating method that can be used to apply the above-mentioned lubricant solution to the ferromagnetic metal thin film is not particularly limited, and includes, for example, an air doctor coater, a blade coater, a rod coater, a squeeze coater, a reverse roll coater, a kiss coater, and a gravure coater. Any method such as a roll coater can be used. According to the present invention, when applying the lubricant solution onto the ferromagnetic metal thin film, an electric field is applied in the thickness direction of the ferromagnetic metal thin film. The electric field may be direct current, alternating current, or high frequency, and a high frequency electric field is particularly preferred. The strength of the applied electric field is related to the thickness of the ferromagnetic metal thin film and the maximum value of the applied voltage. For example, when the thickness of the ferromagnetic metal thin film is Tocm and the maximum value of the applied voltage is Vo volts, the electric field strength expressed as Vo/To (volts/cm) is from 5×10 ⁶ to 1×10 ⁹ is the preferred range. If it is less than 5×10 ⁶ , it becomes unstable, and if it exceeds 1×10 ⁹ , pinholes may occur in the ferromagnetic metal thin film due to current concentration, which is not preferable. DESCRIPTION OF EMBODIMENTS FIG. 1 is an explanatory diagram showing a specific example of implementing the method of the present invention. In FIG. 1, reference numeral 1 denotes a magnetic recording medium consisting of a support having a ferromagnetic metal thin film layer, and is conveyed in the direction of the arrow. Ferromagnetic metal thin film layer on the recording medium 1 (not particularly shown)
is fed so as to come into contact with the applicator roll 2. A metal touch roll 3 is brought into contact with the back surface of the magnetic recording medium 1 to form a pair with the applicator roll 2 and to press the magnetic recording medium 1 against the applicator roll 2. The applicator roll 2 and the touch roll 3 are connected to a power source 4 so that an electric field is generated in the thickness direction of the ferromagnetic metal thin film of the magnetic recording medium. The applicator roll 2 is partially immersed in the lubricant solution 5 in the container 8, and as it rotates in the direction of the arrow, the solution 5 adheres to the surface of the applicator roll 2 and is carried. This solution 5 is carried by a metal ring roll 6 in an appropriate amount and rotates, and comes into contact with the magnetic recording medium 1 and is applied thereto. 7 is a cleaning doctor. The magnetic recording medium coated with the lubricant solution then enters a drying device (not shown) and is dried. The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.
In addition, in the comparative example, coating was performed under the same conditions as each example without applying an electric field. Example 1 A polyethylene terephthalate film support with a thickness of 9 μm was made with a diameter of 1 m in which a medium at 70°C was circulated.
While winding the drum along a cylindrical drum at a speed of 20 m/min, heating electron beams were heated at 70 KW for Co and 38 KW for Cr using a dual evaporation source.
A Co--Cr perpendicular magnetization film having a Cr content of 20% by weight was formed with a thickness of 0.2 μm. The degree of vacuum at this time was 1×10 ^-6 torr. The film support on which the ferromagnetic metal thin film was formed was taken out into the atmosphere, and
After a day, the following lubricant solutions were applied so that each lubricant coating film had a thickness of 50 Å after drying. Myristic acid, stearic acid or octyl behenate was used as a lubricant, and n-
Hexane was used.

[Table] Example 2 A cylindrical drum with a diameter of 1 m in which a medium at 200°C was circulated was held insulated, and an aromatic polyamide film support with a thickness of 7 μm was held along the cylindrical drum.
While winding at 30m/min, using a dual evaporation source,
Heating electron beam 74KW for Co, respectively
Cr was controlled to 40KW, and a Co-Cr perpendicular magnetization film with a Cr content of 19% by weight was formed to a thickness of 0.2 μm. Prior to vapor deposition, the inside of the vacuum chamber was heated to 2×10 ^-7
The reactor was evacuated to a pressure of 2×10 ⁻⁶ Torr, oxygen was introduced, and deposition was performed at 2×10 −6 Torr. Note that a high frequency of 13.56MHz was applied to the drum. The film support on which the ferromagnetic metal thin film was formed was taken out into the atmosphere, and one day later, the following lubricant solution was applied so that the thickness of each lubricant coating film after drying was 50 Å. Myristic acid or butyl stearate was used as the lubricant, n-hexane was used as the solvent, and the application speed was
The speed was 70m/min. 100KHz, voltage as electric field condition
The voltage was 1200V, and the electric field strength was 6×10 ⁷ V/cm. Each magnetic recording medium thus obtained was heated to 25°C and 80%
Figure 2 shows the change in friction coefficient against stainless steel (0.1S) after repeated running at RH. Example 3 A polyethylene terephthalate film support with a thickness of 9.5 μm was heated to a diameter of 1 m in which a medium at 70°C was circulated.
While winding along a cylindrical drum at 70 m/min, the angle of incidence was 30° in an oxygen atmosphere of 1 × 10 ^-5 Torr.
As described above, an alloy containing 80% by weight of Co and 20% by weight of Ni was deposited to a thickness of 0.12 μm by electron beam evaporation. The film support on which the ferromagnetic metal thin film was formed was taken out into the atmosphere, and after one day, a stearic acid solution dissolved in n-hexane was used as the lubricant solution, so that the thickness of the lubricant coated film after drying was 50 Å. It was applied to. The coating speed was kept constant at 100 m/min, and the electric field conditions were varied.

[Table] Effects of the invention Each sample of Examples 1 and 2 described above was fixed.
Friction against any of the following: SVS post (surface roughness 0.1S), fixed BN coated SVS post (surface roughness 0.1S), fixed hard chrome plating SVS post (surface roughness 0.1S), or rotating cylinder of a commercially available VHS deck. The coefficient was measured. At this time, each sample was wound 180° around each post or cylinder, and the tension was kept constant at 20g across an 8mm width (in the case of cylinders, the winding side was 20g), and the tension was fixed at 20g for 100 passes, 300 passes, and 600 passes. Table 3 below shows the changes in the coefficient of friction as relative values when each initial value is set to 1.0. The environment was kept constant at 30°C and 90% RH.

[Table] Samples 1-A to 1-E and 3- according to the present invention
The initial dynamic friction coefficients of samples A to 3-E and the comparative example were almost the same, but the change in the friction coefficient after each pass was very large in the comparative example, and the sample stopped running after 300 passes. On the other hand, it is clear from the data in Table 3 and the data in FIG. 2 that the samples of the present invention showed very small changes and had excellent durability. From the above results, the metal thin film magnetic recording medium manufactured by the method of the present invention has significantly improved wear resistance and runnability, and these effects are sustained over a long period of time even under high temperature and high humidity, making it extremely durable. It can be seen that a magnetic recording medium with high properties can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a specific example of implementing the method of the present invention, and FIG. 2 is a diagram showing changes in the coefficient of friction in Example 2. 1 is a magnetic recording medium, 2 is an applicator roll, 3 is a tatsuchi roll, 4 is a power source, 5 is a lubricant solution, 6 is a metering roll, 7 is a cleaning roll, and 8 is a container.

Claims (1)

[Claims] 1. When applying a lubricant solution onto a ferromagnetic metal thin film provided on a support, an electric field is applied in the thickness direction of the ferromagnetic metal thin film to apply the lubricant solution, and then drying is performed. A method for manufacturing a magnetic recording medium. 2. The method according to claim 1, wherein the electric field is applied as a direct current, alternating current, or high frequency. 3. The method according to claim 1 or 2, wherein the electric field has a strength of 5×10 ⁶ to 1×10 ⁹ volts/cm.