Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-07-03
2003-12-30
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S220000, C428S339000, C428S332000, C428S480000, C428S692100, C428S690000, C428S690000, C428S690000, C428S690000, C428S900000, C428S923000, C428S924000, C428S926000
Reexamination Certificate
active
06670030
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a biaxially oriented laminate polyester film for a magnetic recording medium. More specifically, it relates to a biaxially oriented laminate polyester film useful as a base film for a magnetic recording medium which is excellent in running durability and electromagnetic conversion characteristics and is almost free from drop-out. Further, the invention relates to a biaxially oriented laminate polyester film excellent in durability against deterioration under dry heat and controllability of precipitation of foreign matters.
PRIOR ART
In recent years, progress has been remarkably made toward higher-density magnetic recording media, as exemplified by the development and practical use of a thin metal film magnetic recording medium having a thin ferromagnetic metal film formed on a non-magnetic base film by a physical deposition method such as vacuum deposition, sputtering or the like or a plating method, and a thin layer coated magnetic recording medium having a layer having a thickness of 2 &mgr;m or less, the layer being formed from a needle-like magnetic powder such as a metal powder or an iron oxide powder.
As examples of the thin metal film magnetic recording medium, JP-A 54-147010 discloses a magnetic recording medium having a first thin Co-film magnetic layer coated on a non-magnetic base film and a second thin Co-film magnetic layer which has a larger thickness than the first thin Co-film magnetic layer and is formed on the first thin Co-film magnetic layer via a non-magnetic material layer. Further, JP-A 52-134706 discloses a vertical magnetic recording medium formed from a Co—Cr alloy.
As an example of the thin layer coated magnetic recording medium, “Technical Report MR 94-78” issued by the Institute of Electronics and Communication Engineers of Japan (1995-02) discloses a high-density magnetic recording on the basis of an extremely thin layer coated magnetic recording medium.
The conventional coated magnetic recording media (magnetic recording media produced by incorporating a magnetic powder in an organic polymer binder and coating the mixture on a non-magnetic base film) has a low recording density and uses a long recording wavelength, so that the thickness of their magnetic layer is as thick as about 2 &mgr;m or more. In contrast, a thin ferromagnetic metal film formed by thin film-forming means such as vapor deposition, sputtering or ion plating has a remarkably small thickness of as small as 0.2 &mgr;m or less. Further, concerning the extremely thin-layer coated media, some media having a thickness of 0.13 &mgr;m are provided and hence, have a very small thickness, although they have a non-magnetic underlying layer.
In the above high-density magnetic recording media, therefore, the surface condition of the non-magnetic base film has a great influence on the surface characteristics of the magnetic layer. In the thin metal film magnetic recording medium in particular, the surface condition of the non-magnetic base film develops directly into an unevenness of surface of a magnetic layer (magnetic recording layer).
Further, the thin metal film magnetic recording medium involves the running property of the surface of a thin metal film as one of serious problems in actual use. In the coated magnetic recording medium having a base film coated with a mixture of a magnetic powder incorporated in an organic polymer binder, the running property of the magnetic layer surface can be improved by dispersing a lubricant in the binder.
In the thin metal film magnetic recording medium, however, such measure cannot be taken, and it is very difficult to maintain the stable running property. Particularly, it has a problem that its running property is inferior under high-temperature and high-humidity conditions. Further, in this case, there is another drawback that a reduction in the output during its repeated use is larger than that of a coated magnetic recording medium.
On the other hand, from the viewpoint of the formation of a non-magnetic base film and handling properties such as transportation, winding-up and unwinding in processing steps, an extreme smoothness of the film surface causes slipperiness between films to be poor and causes a blocking phenomenon to take place, so that the roll formation thereof is deteriorated and that the yield of products decreases. As a consequence, the production cost thereof increases. In view of a production cost, therefore, the surface of the non-magnetic base film is as rough as possible.
As described above, the surface of the non-magnetic base film is required to be smooth from the viewpoint of electromagnetic conversion characteristics, whereas it is required to be rough from the viewpoint of handling properties and film costs.
For the production of a high-density magnetic recording medium of excellent qualities, it is required to satisfy the above two contradictory requirements at the same time.
JP-A 5-194772 discloses a polyester film for a magnetic recording medium, the polyester film having one surface coated with a primer layer of a continuous thin film for a magnetic layer, wherein the continuous thin film surface of the primer layer has (A) small protrusions which have a height of 13 nm or less and comprise particles having an average particle diameter of less than 0.06 &mgr;m as cores, (B) large protrusions which have a height of 30 nm or less and comprise particles having an average particle diameter of 0.06 &mgr;m or more as cores, and (C) fine protrusions formed solely of a resin forming the primer layer, the numbers of these protrusions satisfying the following expressions:
AN
≧1.0×10
6
(pieces/mm
2
)
BN
≧1.05×10
4
(pieces/mm
2
)
AN
≦−3.4×10
2
×BN
+13.6×10
6
(pieces/mm
2
)
CN
≦4.0×10
6
(pieces/mm
2
)
in which AN is the number (pieces/mm
2
) of the small protrusions, BN is the number (pieces/mm
2
) of the large protrusions and CN is the number (pieces/mm
2
) of the fine protrusions,
the continuous thin film formed solely of a resin forming the primer layer has a fine surface roughness, RaS, of 1.10 nm or less, and the continuous thin film has a surface roughness, Ra, of 1 to 10 nm.
JP-A 5-298670 discloses a polyester film for magnetic recording medium, the polyester film having one surface coated with a primer layer of a continuous thin film for a magnetic layer, wherein the continuous thin film surface of the primer layer has (A) small protrusions which have a height of 13 nm or less and comprise particles having an average particle diameter of less than 0.06 &mgr;m as cores, (B) large protrusions which have a height of 30 nm or less and comprise particles having an average particle diameter of 0.06 &mgr;m or more as cores, and (C) fine protrusions formed solely of a resin forming the primer layer and having the longest major diameter of 0.30 &mgr;m or less, the numbers of these protrusions satisfying the following expressions:
AN
≧1.0×10
6
(pieces/mm
2
)
BN
≧1.05×10
4
(pieces/mm
2
)
AN
≦−3.4×10
2
×BN
+13.6×10
6
(pieces/mm
2
)
1.0×10 (pieces/mm
2
)≦
CN
≦1.0×10
4
(pieces/mm
2
)
in which AN is the number (pieces/mm
2
)of the small protrusions, BN is the number (pieces/mm
2
) of the large protrusions and CN is the number (pieces/mm
2
) of the fine protrusions,
the continuous thin film formed solely of a resin forming the primer layer has a fine surface roughness, RaS, of 1.10 nm or less, the continuous thin film has a surface roughness, Ra, of 1 to 10 nm, and when the polyester film is continuously heated in air at 160° C. for 5 minutes, the continuous thin film can be controlled to show that the rate of deposition of polyester oligomer fine crystals on the film surface is 0.8% or less.
The above polyester film can attain a smoother base film on the magnetic layer surface side to some extent. However, particles contained in the base film on the magnetic layer surface side for improving the running durability perform insufficient dispe
Kameoka Akira
Kosuge Masahiko
Osawa Toshifumi
Tojo Mitsuo
Uchida Toshikazu
Ahmed Sheeba
Teijin Limited
Thibodeau Paul
LandOfFree
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