JPH0136164B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic disks. Structures of conventional examples and their problems Polyester films are made of iron, cobalt, nickel, alloys containing these as main components, or thin films of their oxides using vacuum deposition methods such as vacuum evaporation, sputtering, and ion plating. ,
Ferromagnetic thin-film magnetic recording media formed on polymer film substrates such as polyimide films can dramatically improve recording density compared to conventional coating-type magnetic recording media. In order to achieve this, it is necessary to smooth the surface of the magnetic recording medium to reduce spacing loss as much as possible. However, if the surface is made too flat, it will cause problems in head touching and running surface. In order to further improve the magnetic tape recording density in rotating head video tape recorder systems that have become popular in the general market in recent years, it is necessary to apply ferromagnetic thin film magnetic recording media. Practical performance requirements for magnetic recording media include good head touch and head abrasion resistance, resistance to head clogging, and contact areas with rotating head cylinders, tape guide posts, audio fixed heads, etc. The objective is to achieve stable running performance (low friction, good wear resistance) in The surface properties of ferromagnetic thin film magnetic recording media depend almost entirely on the surface shape of the plastic film substrate, since the magnetic layer thickness is very small, about 0.1 to 0.5 μm. Therefore, many proposals have been made regarding the surface properties of films. An example is Japanese Patent Application Laid-open No. 116115/1983,
They are described in JP-A-53-128683, JP-A-54-94574, JP-A-56-10455, JP-A-56-16937, and the like. In all of these examples, the surface shape is roughened relatively finely and uniformly, for example, by forming wrinkle-like protrusions, wavy, earthworm-like, or granular protrusions, thereby improving head touch and running properties. This is an attempt to improve all at once. However, whereas the video rotary head has a narrow contact width of several hundred microns or less and a relative speed of several meters/second with the magnetic tape, the friction of the magnetic tape running system is slow (a few centimeters/second). /sec) Since it is a large-area contact, it is necessary to provide the same running performance with respect to the other partners (that is, the friction coefficient speed dependence is small), but in each of the above examples,
In general, the speed dependence of the friction coefficient is relatively large;
Therefore, during actual driving, it is easy to cause squealing,
The problem was that the envelope characteristics tended to become unstable. OBJECTS OF THE INVENTION It is an object of the present invention to provide a thin metal film type magnetic recording medium that has a small dependence of friction coefficient on speed, excellent running stability, and good envelope characteristics. Structure of the Invention The metal thin film type magnetic recording medium according to the present invention includes ultrafine particles with a diameter of 100 Å or less on at least a portion of the surface of a nonmagnetic substrate that is smooth or has wrinkle-like, earthworm-like, or granular projections on the surface that contributes to travel. After providing a thin layer of resin containing 5% or more and having a thickness of 1000 Å or less and a surface unevenness interval of 300 Å or less, a thin magnetic metal layer is formed by vacuum oblique deposition in an oxygen atmosphere at an incident angle of 20° or more. It is characterized by DESCRIPTION OF EMBODIMENTS FIGS. 1 to 3 are cross-sectional views in the thickness direction of typical magnetic recording media obtained by the manufacturing method according to the embodiments of the present invention. In the figure, 1, 1', 1'' are non-magnetic substrates, 2, 2', 2'' are non-magnetic underlayers having fine irregularities on the surface formed on the non-magnetic substrates,
3, 3', and 3'' are ferromagnetic metal thin films formed on the nonmagnetic underlayer by oblique vapor deposition in an oxygen atmosphere. In the diagram, Q ₁ to _{Q 3} are the main incident angles of oblique vapor deposition;
The arrow indicates the direction of incidence, and d ₁ to _{d 3} indicate the diameters of the microprotrusions formed on the surface of the ferromagnetic metal thin film in the planar direction. Note that this diameter can be measured by observation using a scanning electron microscope. Fig. 1 shows a case in which microprotrusion aggregates 3 are formed on the entire surface of a smooth nonmagnetic substrate 1, and Fig. 2 shows a case in which microprotrusion aggregates 3 are formed on the entire surface of a nonmagnetic substrate 1' whose surface is finely roughened. When the body 3' is formed, FIG. 3 shows that a bulge of the nonmagnetic underlayer 2'' is formed in a part of the smooth nonmagnetic substrate 1'', and a microprotrusion aggregate 3'' is formed only in that part. In the example shown in this figure, it is the 3'' portion that contributes to the actual running. Figure 4 shows a method for forming a ferromagnetic metal thin film on a long non-magnetic substrate by continuous oblique evaporation, in which 4 is a vacuum vessel, 5 is a non-magnetic substrate, 6 is
7 is the unwinding part, 7 is the winding part, 8 is a drum rotating in the direction a, 9 is an evaporation container, 10 is an evaporation source made of a ferromagnetic metal melt, and 8 is the incidence of evaporated vapor on the non-magnetic substrate. This is a mask that regulates the lower limit of the corner. θ represents the general angle of incidence, and θmin represents the minimum angle of incidence, that is, the main angle of incidence. When a ferromagnetic metal thin film is formed on a substrate by vacuum evaporation, the ferromagnetic metal vapor ejected from the evaporation source adheres to the substrate, then moves on the substrate and is fixed at an appropriate location. As a result, ferromagnetic metal crystals are formed. When oxygen gas is present in a vacuum, a portion of the ferromagnetic metal vapor adhering to the substrate reacts with oxygen early in the process of moving over the substrate, so that its movement is significantly restricted. Therefore, in oblique vapor deposition in an oxygen atmosphere, it is expected that a vapor deposited film will be formed having a surface in which the fine irregularities on the substrate surface are emphasized. As a result of the studies conducted by the present inventors, the above-mentioned expected effect appears when the spacing between the unevenness on the substrate surface is very small, that is, about 300 Å or less, and the surface shape obtained due to this effect is It has become clear that this significantly contributes to driving performance. 1 to 3 schematically illustrate this effect. Note that if the distance between the unevenness on the substrate surface is 300 Å or more, a slight disturbance will occur in the envelope of the signal reproduction output. Here, Table 1 shows a comparison with the conventional case regarding the spacing between the concave and convex portions. However, the difference between the present invention and the conventional example is not simply the spacing between the recesses, but the effects of the present invention are based on synergistic effects with other conditions.

[Table] Non-magnetic substrates used in the present invention include polyester films made of polyethylene terephthalate or copolymers or mixtures thereof, polyester films made of polyethylene naphthalate or copolymers or mixtures thereof, polyesterimide, polyimide-based materials such as polyimide, etc. Films, aromatic polyamide films, etc., which have particularly excellent surface smoothness, are suitable. Taking polyester film as an example, it has good smoothness with almost no microprotrusions made of polymerization residues or the height of the microprotrusions is several hundred Å or less, the wrinkle-like, worm-like, etc. These include those on which uniform fine protrusions such as granules are formed on the surface, and the surface roughness is several hundred Å or less. Although a non-magnetic underlayer, which will be described later, is formed on the surface of these materials, uniform fine protrusions such as wrinkle-like, earthworm-like, granular, etc. mentioned above are formed on the surface without forming a separate underlayer. In this case, by adding a large number of ultrafine particles with a diameter of 100 Å or less to the surface forming material, the fine protrusions themselves may have the properties of a non-magnetic underlayer, which will be described later. The magnetic recording medium obtained by the manufacturing method of the present invention is characterized by a surface composed of aggregates of microprotrusions with an average diameter of 20 to 300 Å developed by oblique vapor deposition in an oxygen atmosphere. This is obtained when the surface of the substrate has a similar shape with gentler irregularities. Even if you try to examine this type of shape in advance before vapor deposition, it is difficult to confirm it with a scanning electron microscope with a normal magnification of about 100,000 or so, and it is difficult to confirm it with a high-resolution electron microscope with a magnification of 100,000 or more. It is only to the extent that it becomes clear. Moreover, even if the normal incidence angle is close to 90°, it is not possible to obtain a microprotrusion aggregate that is effective in the present invention, and even if vapor deposition is performed on a surface with such a shape at an angle of incidence close to 90°, it is impossible to obtain a microprotrusion aggregate that is effective in the present invention. In vapor deposition, it is not possible to obtain the remarkable unevenness enlarging effect that can be obtained by oblique vapor deposition in an oxygen atmosphere. This is clear, for example, from the results of measuring the coefficient of dynamic friction of the magnetic surface, which will be described later. As a non-magnetic underlayer, a thin layer of resin (with a thickness of 1000 Å or less, more preferably 10 to 50 Å) containing 5% or more, more preferably 10 to 50% by weight of ultrafine particles with a diameter of 100 Å or less, more preferably 10 to 90 Å, is used. 500
Å) is suitable, for example, by smoothing a resin solution (resin concentration 1 to 100 ppm) in which ultrafine particles are dispersed.
Alternatively, it can be obtained by coating the surface of a substrate having wrinkle-like, worm-like, or granular projections. Examples of ultrafine particles with a diameter of 100 Å or less include hydrolysis of organometallic compounds, hydrolysis of metal halides, decomposition by acids and alkalis,
Oxides and hydroxides of aluminum, silicon, magnesium, titanium, zinc, iron, etc., which are obtained by reduction of salt solutions, evaporation in gas, agglomeration and crystallization of organic compounds and polymer compounds, etc. ,
Fine particles of metals such as gold, silver, copper, nickel, iron, etc., or fine particles of organic compounds and polymer compounds can be used. Furthermore, when fine particles with an average diameter of 100 Å are used, the average diameter of microprotrusions in the plane direction on the surface of the underlayer is 200 Å due to secondary aggregation of the particles.
It will be about 300 Å. The nonmagnetic underlayer may be provided over the entire surface of the substrate as shown in FIGS. 1 and 2, or may be provided partially as shown in FIG. In the latter case, it is desirable that the underlayer regions exist over 10% or more of the entire surface at intervals of at least 20 μm or less. Such a state can be obtained, for example, by adding a small amount of silicone oil to the coating liquid when forming the base layer. In any case, it is necessary to have the microprotrusion aggregates present in the protruding portions of the magnetic layer, that is, in the portions that contribute to travel. Regarding vacuum evaporation in an oxygen atmosphere,
56-23208, Special Publication 57-23931, Special Publication 57-29770,
Although described in JP-A-56-15014, JP-A-57-37719, etc., the effect of the present invention is that the above-mentioned main angle of incidence is
This becomes noticeable when the angle is 20° or more, more preferably 30° or more, the resulting film thickness is 400 Å or more, and the oxygen content (atomic ratio of oxygen to ferromagnetic metal) is 3% or more. As described above, the effects of the present invention can be explained as follows in comparison with the prior art. FIGS. 6a to 6c show a comparison of each case. The feature of the present invention is that it is obliquely deposited on the surface shape of the substrate shown in Table 1 in an oxygen atmosphere at an incident angle of 20° or more. Estimating the mechanism in this case, at the beginning of oblique vapor deposition, a part with a high incidence angle that is perpendicular to or close to the vapor incidence angle on the surface (a part with a high incidence angle within the surface because there are minute irregularities)
A nucleus is first formed. Due to the presence of oxygen, the deposited metal is partially oxidized, its movement or migration on the substrate after deposition is suppressed, and limited selective crystal growth occurs. As a result, unevenness is formed on the surface of the deposited magnetic layer in a shape that emphasizes the fine unevenness of the substrate (FIG. 6a). Even in an oxygen atmosphere, the shape becomes difficult to emphasize in vertical evaporation at an incident angle of 20° or less, as shown in Figure 6b. Furthermore, in the absence of oxygen, the shape becomes difficult to be emphasized due to the migration effect even in oblique deposition as shown in FIG. 6c. In carrying out the present invention, various lubricant-containing layers, rust preventive agent-containing layers, etc. may be provided on the surface of the magnetic layer or the back surface of the non-magnetic substrate. Next, a more specific example will be explained. Surface roughness Rmax=approximately 250Å at a thickness of 12μm,
A silica colloid (hydrolysis product of alkoxysilane) with an average particle size of 80 Å is coated on the surface of a long polyester film having wavy projections with an interval of approximately 2 μm.
A solution containing 10 ppm and 30 ppm of copolymerized polyester resin was applied and dried. This was placed along the circumferential surface of the cylindrical drum, and 0.3% oxygen gas was pumped in at a vacuum level of 5×10 ^-5 Torr.
A CoNi alloy (Ni content: 20 wt%) melted by electron beam heating was continuously deposited to form an oxygen-containing CoNi ferromagnetic thin film with a thickness of 1000 Å on the film. At this time, by changing the position of the incident angle limiting mask, four types of samples with main incident angles of 30°, 20°, 10°, and 0° were obtained. These samples were designated as A, B, C, and D, respectively. For comparison, the original film without silica colloid treatment was also deposited in the same manner as above at a main incident angle of 30°. This product was designated as sample E. moreover,
An experiment was also carried out under the manufacturing conditions of sample A in which oxygen was not introduced, and this sample was designated as F. The average amount of oxygen in the films of samples A to F was A to E≈10% and F<1% in atomic ratio to CoNi (0/Co+Ni×100). By scanning electron microscopy, it was confirmed that microprotrusion aggregates with an average diameter of 200 Å were formed on the entire surface of Samples A and B. However, in Samples C, D, and F, only traces of the roots of the microprotrusion aggregates were barely recognized, and in Sample E, no traces of the roots were observed. These samples were cut to a predetermined width to make magnetic tape, and the envelope characteristics were observed on a prototype deck.
The speed dependence of the coefficient of friction was measured by winding the rod around a 5 mmφ stainless steel round rod at an angle of 180 degrees and running it. The envelopes were good in the following order. Best A・B>E・C・F>D In addition, Fig. 5 shows the speed codependency of the friction coefficient. Effects of the Invention The magnetic recording medium produced by the manufacturing method of the present invention has a small speed dependence of the coefficient of friction, excellent running stability,
It has good envelope characteristics and is expected to have a head cleaning effect due to the aggregate of fine protrusions, so its practical value is very high.

[Brief explanation of drawings]

1, 2, and 3 are sectional views of a magnetic recording medium according to an embodiment of the present invention, FIG. 4 is a sectional view of a continuous oblique evaporation apparatus, and FIG. 5 is a sectional view of a magnetic recording medium according to an embodiment of the present invention. FIG. 6, which is a diagram showing the speed dependence of the friction coefficient of the recording medium, is an explanatory diagram showing the state of the deposited film that is formed. 1...Nonmagnetic substrate, 2...Underlayer, 3...Ferromagnetic metal thin film.

Claims (1)

[Claims] 1. A non-magnetic substrate with a smooth surface or with wrinkle-like, earthworm-like, or granular protrusions on the surface, at least in the portion contributing to running, with a thickness of 1000 Å or less containing 5% or more of ultrafine particles with a diameter of 100 Å or less. A thin metal film type magnetic recording medium characterized in that a thin layer of resin is formed with a spacing of 300 Å or less, and then a thin magnetic metal layer is formed at an incident angle of 20° or more by vacuum oblique evaporation in an oxygen atmosphere. Production method.