Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1997-11-26
2002-10-08
Copenheaver, Blaine (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S403000, C428S407000, C428S480000, C428S690000, C428S690000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06461726
ABSTRACT:
This invention relates to a laminate film and, more specifically, to a laminate film suitable for use as a magnetic recording medium, particularly a high-density magnetic recording medium, having excellent electromagnetic conversion characteristics and durability and few drop-outs.
BACKGROUND OF THE INVENTION
In recent years, remarkable progress has been made in high-density magnetic recording, as exemplified by the development and implementation of a ferromagnetic metal thin film magnetic recording medium in which a ferromagnetic metal thin film is formed on a non-magnetic base film by a physical deposition method such as vacuum vapor deposition or sputtering, or a plating method, and a thin layer coated magnetic recording medium in which a needle-shaped magnetic powder such as a metal powder or iron oxide powder is coated on a film to a thickness of not larger than 2 &mgr;m.
Known examples of the former include a Co deposited tape (see JP-A 54-147010) (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and a vertical magnetic recording medium composed of Co—Cr alloy (see JP-A 52-134706). Known examples of the latter include an extremely thin layer coated medium for high-density magnetic recording (see “Technical Report MR 94-78” (1995-02) issued by the Institute of Electronics and Communication Engineering of Japan).
Since a coated magnetic recording medium of the prior art, i.e. a magnetic recording medium, in which a mixture of magnetic powders and an organic polymer binder is coated on a non-magnetic base film, has a low recording density and a long recording wavelength, the thickness of its magnetic layer is as large as about 2 &mgr;m or more. On the other hand, a metal thin film formed by thin film forming means such as vacuum vapor deposition, sputtering or ion plating has a thickness as extremely small as 0.2 &mgr;m or less. In the case of an extremely thin layer coated medium, a coated magnetic layer is as extremely thin as 0.13 &mgr;m though a non-magnetic primary coat layer is provided.
In the above high-density magnetic recording media, the surface condition of the non-magnetic base film has a great influence on the surface characteristics of the magnetic recording layer. Particularly, in the case of a metal thin film magnetic recording medium, the surface condition of the non-magnetic base film appears directly as an uneven surface of the magnetic recording layer, which causes noise in a reproduction signal. Therefore, it is desirable that the surface of the non-magnetic base film be as smooth as possible.
Further, in the case of a deposited metal thin film magnetic recording medium, the durability of a metal thin film surface is an important factor when the medium is actually used. In the case of a coated magnetic recording medium in which magnetic powders are mixed into an organic polymer binder and the resulting mixture is coated onto the base film, the durability of the magnetic surface can be improved by mixing hard fine particles such as aluminum oxide into the binder. However, in the case of a deposited metal thin film magnetic recording medium, this measure cannot be taken, and it is extremely difficult to maintain stable durability.
As means for solving this problem, there have been proposed (1) a method for forming a discontinuous surface film by applying a specific coating to the surface of a film (see JP-B 3-80410 (the term “JP-B” as used herein means an “examined patent publication”), JP-A 60-180839, JP-A 60-180838, JP-A 60-180837, JP-A 56-16937 and JP-A 58-68223) and (2) a method for forming a continuous surface film having fine protrusions (see JP-A 5-194772 and JP-A 5-210833).
However, it is difficult to maintain sufficient durability with a discontinuous surface film alone. Also when a continuous surface film having fine protrusions is to be formed by inert fine particles, it is difficult to uniformly disperse the inert fine particles into a surface film and coarse protrusions are liable to produce by agglomerated particles, thereby deteriorating electromagnetic conversion characteristics. Thus, films produced by the above proposals still have a problem in that the quality of a magnetic tape is unstable. Further, the agglomerated particles are scraped off by their contact with a guide roll in the film formation step more easily than monodisperse particles, adhered to and accumulated on the base film thereby to produce protrusions, which causes a drop out when a magnetic tape is formed therefrom.
Generally speaking, inorganic particles are excellent in the cleaning properties of a magnetic head because they are hard and difficult to be deformed, are rarely changed in shape by heat in the tape processing step due to its high heat resistance and hence, provide excellent durability to a tape. However, they have poor affinity with a polymer and are apt to fall off. On the other hand, organic particles have lower hardness than inorganic particles though they have excellent affinity with a polymer, and the electromagnetic conversion characteristics of a tape degrade along with repeated running of the tape because all the particles undergo deformation by heat and mechanical friction.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a laminate film which eliminates the above defects of the prior art, has excellent abrasion resistance in the film formation step and excellent electromagnetic conversion characteristics, resistance to drop-out and running durability when it is used as a base film for a deposited metal thin film magnetic recording medium or an extremely thin layer coated magnetic recording medium, for example.
It is another object of the present invention to provide a magnetic recording medium which comprises the above laminate film of the present invention as a base film and is excellent in electromagnetic conversion characteristics, resistance to drop out and running durability.
Other objects and advantages of the present invention are apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention can be attained by a laminate film:
(A) which comprises a film consisting of a single layer or a plurality of layers of a thermoplastic resin, and a first coated film layer present on at least one surface of the film, the first coated film layer containing a binder resin and an organic filler,
(B) which satisfies the following expressions (1) and (2) at the same time when it is heated at 200° C. for 120 minutes:
0≦(
Ra
1
−Ra
2
)/
Ra
1
<0.4 (1)
0.1
<Ra
2
<7 (2)
wherein Ra
1
is an average roughness of root mean square (nm), measured by an atomic force microscope, of an exposed surface of the first coated film layer before the heat treatment and Ra
2
is an average roughness of root mean square (nm), measured by the atomic force microscope, of the exposed surface of the first coated film layer after the heat treatment, and
(C) in which protrusions with two or more interference fringes which can be observed when two films are superposed in such a manner that their first coated film layers come in contact with each other and exposed to light from a sodium lamp are present on the surface of each film at a density of 100 per 100 cm
2
at the most.
DETAILED DESCRIPTION OF THE INVENTION
In the laminate film of the present invention, the thermoplastic resin for the single layer or the plurality of layers of the film is, for example, a polyester resin, polyamide resin, polyimide resin, polyether resin, polycarbonate resin, polyvinyl resin, polyolefin resin or the like. Out of these, the thermoplastic resin is preferably a polyester resin, more preferably an aromatic polyester. The thermoplastic resin preferably has a melting point of at least 210° C.
Preferred examples of the aromatic polyester include polyethylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthale
Handa Makoto
Osawa Toshifumi
Tojo Mitsuo
Copenheaver Blaine
Kruer Kevin R
Teijin Limited
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