JPH0315249B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium having a magnetic metal deposited film made of a ferromagnetic metal such as Co or Ni or an alloy thereof. Conventionally, magnetic recording media formed on a base with this type of magnetic metal vapor deposited film have been known to be suitable for high-density magnetic recording, and in order to put them into practical use, there have been a number of issues in terms of electromagnetic conversion characteristics and durability characteristics. Various improvements are being considered. One of the factors that governs the electromagnetic conversion characteristics of a deposited magnetic metal film is a magnetization reversal region, ie, a domain, which occurs when the deposited film is demagnetized. This magnetic domain is generally thought to depend on coercive force, and in fact, gases such as nitrogen and oxygen are introduced during vacuum evaporation to intervene between the deposited metal particles, and the evaporation rate is also selected. By reducing the size of the deposited particles by
When the interaction between deposited particles is reduced to increase the coercive force, the magnetic domain becomes smaller and favorable results can be obtained in terms of electromagnetic conversion characteristics. Therefore, if the presence of magnetic domains can be reduced to the extent that they are virtually invisible by increasing the coercive force, it should be possible to obtain even better electromagnetic conversion characteristics, but there are limits to such minimization of magnetic domains. There is.
This will be explained using drawings. First, in Figures 6A and 6B, Co metal was deposited on a polyester film base using a conventional method to a thickness of about 900 Å.
These are electron micrographs showing the surface of a deposited film magnified 7500 times when a deposited film with a thickness of approximately 1000 oersted was formed. Figure A is a photograph taken using the defocus method, that is, the image was observed by shifting the focus, and Figure B The figure is a photograph taken using the positive focus method and observing the same screen in focus. Here, to explain the defocus method using the principle diagram shown in FIG. 8, in the demagnetized magnetic film 21 formed on the base 20, the magnetization direction is reversed within the minimum unit magnetic domain 22, and therefore the magnetic film The electron beam 23 of the electron microscope irradiated from above 21 is bent by the reversed magnetization (○ and × in the figure) 24, and on the domain wall 25, the electron beam 23 is irradiated from above.
Blank space 26 or electron beam 23 that does not pass through
A concentrated area 27 is formed in which the magnetic flux is concentrated, and this is exposed as white or black, and a striped pattern is observed as a magnetic domain. On the other hand, since the positive focus method focuses on the surface position of the magnetic film, blanks or black areas such as those described above are not exposed. If a striped pattern that cannot be seen in the positive focus method appears in the defocus method, this indicates the presence of magnetic domains. From the above viewpoint, when comparing FIG. 6A and FIG. 6B, a striped pattern clearly indicating the presence of magnetic domains is observed in FIG. 6A obtained by the defocus method. That is, even though the coercive force of the deposited film is as high as about 1000 oersted, there are magnetic domains of considerable size. Next, FIGS. 7A and 7B are electron micrographs taken by the same defocus method and positive focus method of the surface of the deposited film when the coercive force of the deposited film is further increased to about 1400 oersteds. In this case, the magnetic domains are smaller than in the case of FIG. 6, and although miniaturization due to increased coercive force is recognized, the presence of magnetic domains is still obvious. As described above, the inventors believe that there is a limit to reducing the size of magnetic domains by increasing coercive force, and it is impossible to expect a significant improvement in electromagnetic conversion characteristics. We have continued to conduct intensive studies to find new means that can improve the properties. In this study process, when a magnetic vapor deposited film having a width of at least 100 Å in the recording direction and three or more partition walls that alleviate magnetic interaction within 10 μm was formed on the base, the magnetic domains of the vapor deposited film was found to be significantly smaller. FIGS. 3A and 3B are electron micrographs of a deposited film having the above structure observed by the defocus method and the positive focus method, respectively, similarly to FIGS. 6A and B and FIGS. 7A and B described above. As is clear from a comparison of FIGS. 3A and 3B, the striped pattern described above is hardly observed, and it is clear that most of the magnetic domains have disappeared. The coercive force of the magnetic film shown in this figure is approximately 1000 Oersteds, which is lower than the coercive force of the magnetic film shown in FIG. 7, which is approximately 1400 Oersteds. Despite this, the disappearance of magnetic domains is something that could never be predicted conventionally. Based on the above findings, the inventors conducted further studies and found that in order to improve the adhesion of the deposited film, the resin coating provided on the base was particularly roughened, and a ferromagnetic metal or alloy This led to the completion of this invention after discovering that when vacuum-deposited from an oblique direction, the magnetic domains of the deposited film become significantly smaller, resulting in extremely good results in terms of electromagnetic conversion characteristics. be. 1 and 2 are cross-sectional views showing an example of the magnetic recording medium of the present invention obtained by the above method, in which 1 is a base, 2 is a roughened resin coating formed on the base 1, and 3 is the above-mentioned A magnetic film made of a ferromagnetic metal or alloy that is diagonally vacuum-deposited on the coating 2. This magnetic film 3 has a large number of voids 4 and alleviates the interaction between the evaporation part 5 and each evaporation part 5, 5. It is composed of a partition wall 6 consisting of a gap. That is, when a ferromagnetic metal or alloy is vacuum-deposited on the roughened resin coating 2 in an oblique direction, that is, with an incident angle α relative to the base 1 surface, the deposited portion 5 grows at an angle β smaller than the incident angle α. However, at this time, a gap 4 having a minute width (usually 20 to 30 Å) is formed depending on the amount of nitrogen or oxygen present in the vacuum system or the deposition rate. The structure itself of this vapor deposition section 5 is essentially unchanged from the conventional one. On the other hand, when vacuum evaporation is performed with an incident angle α, the protrusions 7 present in the roughened resin coating 2 cast shadows on the back side of the protrusions 7, making it impossible for the evaporated metal or alloy to reach the undeposited area. A partition wall 6 consisting of the portion, that is, the gap is formed. The partition walls 6 usually have a width of 100 Å or more, particularly preferably 100 to 1000 Å, and the number of partition walls is 3 or more, preferably 3 to 100, within 10 μm. This is largely different from the deposited film structure, and it has been discovered that this makes it possible to minimize the magnetic domain, which was previously impossible to predict. As described above, according to the present invention, the film structure of the magnetic film can be made to have a structure different from the conventional one, and thereby the magnetic domain can be made extremely small, so that the electromagnetic conversion characteristics can be greatly improved. . Moreover, the roughened resin coating increases the adhesion strength between the magnetic film and the base, resulting in the effect of greatly improving the durability of this type of magnetic recording medium. In this invention, the average thickness of the roughened resin coating is usually about 1μ or less, and the formation of such a coating is generally performed using carboxyl groups, hydroxyl groups, sulfone groups, etc. that have an affinity for the base surface as the resin. Items with functional groups, such as vinyl chloride
This is done by using a vinyl acetate copolymer, butyral resin, etc., dissolving it in a relatively low boiling point solvent such as methyl ethyl ketone, tetrahydrofuran, or ethyl acetate, applying it to the base surface, and then heating and drying it relatively quickly. It will be done. The degree of surface roughening can be set arbitrarily depending mainly on the type of low boiling point solvent used and heating drying conditions, but the suitable degree of surface roughening for forming the partition walls described above is as follows. As shown in FIG. 4, the height h of the protrusion 7 is 40 Å from the average roughness center M.
The number of such protrusions 7 is preferably 3 or more, preferably 3 to 100 within 10μ.
If the above-mentioned height is too low or the number is too small, effective partition walls will not be formed and good results will not be obtained in minimizing or eliminating magnetic domains. On the other hand, if the height is too high or the number of partitions is too large, problems similar to those described above will occur, or conversely, there will be too many partition walls, which will inevitably reduce the reproduction output, which is not preferable. It is sufficient that the partition walls are formed so as to intersect with the recording direction, but they may also have a lattice pattern such as a triangular lattice, a square lattice, a pentagonal lattice, or a hexagonal lattice, or a dot shape. Therefore, the roughened resin coating for providing this partition wall is
It is sufficient that the rough surface is formed so as to correspond to the above. However, in general, when a roughened coating is formed by the method described above, the surface usually has a roughened surface having ridges in a lattice pattern. Any means can be used to perform vacuum deposition on the roughened resin film in an oblique direction. For example, as shown in FIG. 5, in a vacuum system 9 equipped with a vacuum pump 8,
The ferromagnetic metal or alloy 12 in the hearth 11 is evaporated by a heating source 13 such as an electron beam to a base 1 surface provided with a roughened resin coating that travels through a cylindrical rotating can 10 and is heated to a vacuum. The shield plate 14 may be provided so that the evaporated metal or alloy reaches the surface of the base at an incident angle α during vapor deposition. The incident angle α at this time varies depending on the degree of roughness of the resin coating, but is generally 10 to 80 degrees.
The temperature is particularly preferably 30 to 70 degrees. In addition to the above-mentioned Co metal, materials for forming the magnetic film according to the present invention include Fe, Ni metals, alloys thereof, or combinations of these metals with Cu, Zn, Mn, Cr, and Al.
Alloys with other metals such as When these materials are formed on a base having a roughened resin coating according to the present invention, the coercive force of the magnetic film is usually 300 oersted or more, but it gives even better results in electromagnetic conversion characteristics. From the viewpoint of achieving good results in high-density recording, preferably 500~
It is best to set it at 2500 Oersted. The base may be made of paper or metal, in addition to a plastic film such as polyester film, and its shape may be appropriately selected as required, such as tape, disk, or card. Next, examples of the present invention will be described and explained more specifically. Example A 5% by weight solution of butyral resin in methyl ethyl ketone was gravure coated on a polyester base film approximately 10 μm thick at room temperature and dried by heating at 120° C. for 30 seconds. The formed barrier film had an average film thickness of 0.5 μm, and had protrusions having a hexagonal lattice pattern with each side of about 1 μm and a height of 500 to 1000 Å. The polyester base film on which the above resin coating was formed was set in a vacuum system as shown in Fig. 5, and Co metal was vacuum evaporated from an oblique direction at an incident angle of 70 degrees to a thickness of about 800 Å and a coercive force of about 1000. An Oersted magnetic film was formed. The details of the vapor deposition conditions are as follows. Cylindrical rotating can; diameter 300mm Heating source: Electron beam gun Hearth: Oxygen-free copper (water cooling) Distance from hearth: 300mm Atmosphere: Oxygen/argon = 1/10, approximately 1 x 10 ^-4 Torr film Running speed: approximately 1 m/min This vapor deposition product was cut into a predetermined width to obtain a magnetic tape of the present invention. When the presence of magnetic domains in this tape was observed using electron micrographs taken by the defocus method and the positive focus method, the presence of magnetic domains was hardly recognized, as in the case of FIG. 3. Next, this tape was assembled into a cartridge, loaded into a video tape recorder, and the electromagnetic conversion characteristics and steel characteristics were examined, and the results were as shown in the following table. Note that Comparative Examples 1 and 2 in the table refer to coercive forces of approximately
These are test results for magnetic tapes of 1400 oersted (Comparative Example 1) and about 1000 oersted (Comparative Example 2). Electromagnetic conversion characteristics are based on Comparative Example 2 (0)
It is shown as a relative value.

【table】

[Table] As is clear from the above table, the magnetic tape of the present invention has significantly improved electromagnetic conversion characteristics as compared to conventional magnetic tapes, and is also significantly superior in durability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the magnetic recording medium of the present invention, FIG. 2 is an enlarged sectional view of the portion shown in FIG. 1, and FIG. FIG. 3B is an electron micrograph taken using a defocus method of the film surface. FIG. 3B is an electron micrograph taken using a positive focus method of the magnetic film surface of a magnetic recording medium used for explaining the present invention. FIG. FIG. 5 is an explanatory diagram showing an example of the vacuum evaporation method according to the present invention, and FIG. 6A and FIG. 6B and 7B are electron micrographs of the magnetic film surface of a magnetic recording medium different from the present invention, respectively, taken using a positive focusing method. FIG. 8 is an electron micrograph taken using a defocus method. It is a principle diagram of a microscope. 1...Base, 2...Roughened resin coating, 3...
Magnetic film, 6... Partition wall, 7... Protrusion, 12... Ferromagnetic metal or alloy, h... Height of protrusion, M...
...average roughness center.

Claims (1)

[Claims] 1. A roughened resin film is formed on a base, and a magnetic film made of a ferromagnetic metal or alloy is provided on the base by vacuum deposition from an oblique direction, and this magnetic film has a rough surface at least in the recording direction. has a width of 100 Å or more and
1. A magnetic recording medium characterized by having three or more partition walls within 10μ for relaxing magnetic interaction. 2 The roughened resin coating has a height of 40 Å or more and 10 μ from the center of average roughness in at least the recording direction.
The magnetic recording medium according to claim 1, having three or more protrusions within the range of 3 or more. 3 The roughened resin coating has a height of 40 Å or more from the center of average roughness in the recording direction and a height of 10 μ
3. The magnetic recording medium according to claim 2, having three or more protrusions within the range of 3 or more.