Recording Medium and Method of Producing the Same

This invention relates to a recording medium and method of producing the same, and more particularly to formation of a protective layer on a recording layer of a recording medium such as magnetic tape, magnetic disc, magnetic card, opto-magnetic disc, optical disc, etc.

The conventional technology is explained by use of a magnetic recording medium as one example. Magnetic recording media are roughly classified into two types, i.e., coating type and deposition type.

The coating type magnetic recording medium is generally formed by the following method. A magnetic powder such as Fe.sub.2 O.sub.3 or .gamma.-Fe.sub.2 O.sub.3 having an additive of CO is mixed with polyvinyl butyral, toluene and methyl isobutyl ketone so that the mixed material becomes coating agent. Then, the coating agent is applied on a surface of a base of the recording medium at 4.about.5 .mu.m thickness. This method has an advantage in that production of the recording medium is easy, but has disadvantages in that performance is not sufficient for use in high density recording since there is a limit to reducing the size of magnetic powder.

In contrast, the deposition type has a better recording density than that of the coating type, but has problem in durability since magnetic metal layer is exposed on the surface of the recording medium. To solve this problem, an overcoating is applied on a deposition metal layer of 1000.about.2000 .ANG. which is formed by use of spattering method or of electron beam, and further, a smoothing agent is applied on the deposition metal layer. However, even this processing can not solve the problem perfectly. That is, sufficient durability can not be obtained. In addition, since overcoating and coating of the smoothing agent of a thinner and even thickness are difficult to carry out, a gap between a recording or reading magnetic head and a recording layer is widened so that it is not difficult to obtain sufficient high density recording performance.

Accordingly, a principal object of the invention is to provide a recording medium which is capable of providing high density recording performance, and to provide a method of producing such a recording medium.

These and other objects will be accomplished by a recording medium which comprises a base body of the recording medium, at least one recording layer formed on the base body, and at least one protective layer formed on the recording layer directly or indirectly through other material for protecting the recording layer. The protective layer is made from a mono-molecular film or mono-molecular cumulative film containing carbon and fluorine as major components and atoms for bonding. In a specific embodiment, a chemical substance of CF.sub.3 --(CF.sub.2)m--(CH.sub.2)n--SiCl.sub.3 (m, n: integer) is used to form a mono-molecular film or mono-molecular cumulative film. The recording and protection layers may be formed on both surfaces of the base body.

This invention has various advantages, among which are as follows:

(1) It may make possible to provide a recording medium which is capable of high density recording.

(2) It may be possible to provide a recording medium which has a very thin organic film of high density formed on a surface thereof without pin-holes with a uniform thickness. Therefore, in case that the recording medium is a magnetic recording medium as one example, the performance of a recording and reproducing magnetic head is improved and noise is reduced.

(3) It may be possible to provide a method of producing a recording medium in which a protective layer can be readily coated on a surface of a base of a recording medium by pin-hole free and uniform thickness. If it is processed by use of a surface active agent containing fluorine, smoothing can be applied on the surface of the organic film so that smoothing characteristic of the head, i.e., durability is improved.

While the novel features of the invention are set forth with particularity in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description in conjunction with the drawings.

FIG. 1 is a section view of a magnetic recording medium as a first embodiment of the invention;

FIG. 2 shows processes for producing the recording medium of the first embodiment;

FIG. 3 is a section view of a recording medium as a second embodiment;

FIG. 4 shows a machine for producing the recording medium; and

FIG. 5 is a section view of a magnetic recording medium as a third embodiment.

FIGS. 1 and 2 show a magnetic recording medium as a first embodiment of the invention. The magnetic recording medium 10, as shown in FIG. 1, is constructed as follows. That is, there is provided a disc plate 12 for magnetic recording use (base of recording medium). Magnetic recording layer 14 (e.g., magnetic metal or magnetic metal oxide such as Fe--Ni, Ni--C.sub.2, Fe.sub.2 O.sub.3) is formed on the disc plate 12 by use of spattering deposition method, etc. Thereafter, a silane surface active agent containing fluorine atoms is adsorbed on the magnetic recording layer 14 so that a mono-molecular polymeric protective film 16, which is formed by a silane surface active agent containing fluorine atoms, is formed.

For example, as the silane surface active agent 18, CF.sub.3 --(CF.sub.2)m--(CH.sub.2)n--SiCl.sub.3 (m, n: integer, the value of approximately 5.about.15 is the easiest to handle) is used as shown in FIG. 2. There is provided a solution of 80% n-hexane, 12% trichloro carbon and 8% chloroform which are dissolved by concentration of approximately 2.times.10.sup.-3 .about.5.0.times.10.sup.-2 Mol/l. Then the base of recording medium base 12 on which the magnetic recording layer 14 is formed is immersed in the above-stated solution.

As a result, bonding 20 of ##STR1## is formed between magnetic recording layer 14 and the silane surface active agent 18 since a natural oxide is formed on the metal surface of the magnetic recording layer 14, so that protective film 16 with high smoothing characteristics of a mono-molecular film, which is formed by a silane surface active agent containing fluorine atoms, is further formed up to the thickness of 20.about.30 .ANG. in a manner that fluorine atoms 22 are juktaposed as shown in FIG. 2.

Incidentally, the above-stated protective film 16 is applicable to an optical recording medium (e.g., optical disc), semiconductor devices, etc. as their protection film. Further, in case that, as material for chemical adsorption, derivatives of di-acetylene such as CF.sub.3 --(CF.sub.2)m--(CH.sub.2)n--C.tbd.C--C.tbd.C--(CH.sub.2)l--SiCl.sub.3 (n, m, l: integer) are used, a bridge can be formed upon irradiation of ultraviolet rays so that conductivity in the surface direction can be attained and a surface of the base can be prevented from being electrically charged.

Another embodiment of the invention is shown in FIG. 3. The first embodiment is of the recording medium wherein the recording layer is formed on only one surface of the medium, whereas the fourth embodiment is of the recording medium wherein the recording layer 14 and protection film 16 are formed on both surfaces of the base 12.

Another embodiment is shown in FIG. 4. In the case that the recording medium is a magnetic recording tape, a tape manufacturing machine shown in FIG. 4 may be used. An uncoated magnetic recording tape 44 which is supplied from supply drum 46 passes through first solution 48 for chemical absorption, first reaction solution 50, second reaction solution 52 and second solution 54 for chemical adsorption, respectively so that tape 56 having the recording layer and protection film is obtained and taken up by take-up drum 58. In FIG. 4, 60 denotes a capstan for forming a tape feed path.

In the above-stated embodiment, mono-molecular film containing fluorine is formed directly on a recording layer by chemical adsorption. However, it is possible to use another structure as shown in FIG. 5. That is, in FIG. 5, an intermediate layer 24, which is made by, for example, SiO.sub.2, Si.sub.3 N.sub.4, C or other metal oxide (e.g., MoO.sub.3, WO.sub.3) is first formed on recording layer 14 and, protection film 16 is formed on said intermediate layer 24 by chemical adsorption. In this case, durability is further improved.

While specific embodiments of the invention have been illustrated and described herein, it is realized that modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all modifications and changes as fall within the true spirit and scope of the invention.