Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-12-21
2004-03-30
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S212000, C428S323000, C428S336000, C428S480000, C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06713155
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium and a base film for the same. More specifically, it relates to a magnetic recording medium which has excellent electromagnetic conversion characteristics and a small reduction in output when it is repeatedly used and a base film for the same.
DESCRIPTION OF THE PRIOR ART
Remarkable progress has recently been made to increase the density of a magnetic recording medium, and the development and implementation of a ferromagnetic metal thin film magnetic recording medium comprising a ferromagnetic metal thin film formed on a non-magnetic base film by a physical deposition method such as vacuum deposition or sputtering, or plating are now underway. For example, there are known a Co-deposited tape (JP-A 54-147010) (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and a Co—Cr alloy vertical magnetic recording medium (JP-A 52-134706).
As conventional coated magnetic recording media (magnetic recording media comprising a magnetic layer formed on a non-magnetic base film by mixing magnetic powders with an organic polymer binder and applying the resulting mixture) have a low recording density and a long recording wavelength, the magnetic layer has a large thickness of about 2 &mgr;m or more. In contrast to this, a metal thin film formed by thin film forming means such as vacuum deposition, sputtering or ion plating has a very small thickness of 0.2 &mgr;m or less.
Therefore, in the above high-density magnetic recording medium, the surface state of a non-magnetic base film has a great influence upon the surface properties of a magnetic recording layer. That is, the surface state of the non-magnetic base film appears as the unevenness of the surface of the magnetic recording layer directly which causes noise in recording and reproduction signals. Therefore, the surface of the non-magnetic base film is desirably as smooth as possible.
On the other hand, from the viewpoints of handling properties such as conveyance, scratching, winding-off and winding-up in the formation of a non-magnetic base film and the film formation process, if the surface of the film is too smooth, slipperiness between films degrades, resulting in a reduction in product yield and an increase in production cost. Therefore, the surface of the non-magnetic base film is preferably as rough as possible from the viewpoint of production cost.
Thus, 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 viewpoints of handling properties and production cost.
Further, in the case of a metal thin film magnetic recording medium, a treatment called “ion bombardment” that the surface of a base film is activated by ions is made before a metal thin film is formed in order to improve adhesion between the metal thin film and the base film.
Since high-temperature heat is applied to the front side of the film when this metal thin film is formed, the rear side of the film is cooled to prevent the fusion of the base film or deterioration in the physical properties such as mechanical properties of the film. To cool the rear side of the film, the base film is often wound round a drum-like cooling material. At this point, both ends of the base film are masked to prevent the formation of a metal thin film on the surface of the drum.
Accordingly, a portion whose surface is activated by ion bombardment and devoid of a metal thin film is continuously existent at both ends of a sample roll subjected to the above deposition step in a longitudinal direction. When the film is rolled, this portion is contacted to the opposite side of the film at a high pressure, there by readily causing blocking. To produce a metal thin film magnetic recording medium, after a metal thin film is deposited, aback coat layer and optionally a top coat layer are formed. If the above blocking occurs in the step of processing these layers, the base film will be readily broken or wrinkled with the result of a great reduction in yield.
To solve the above problem, JP-A 9-207290 and JP-A 9-226063 propose a laminated film consisting of a layer A and a layer B whose surface is rougher than the surface of the layer A. However,this method cannot suppress a reduction in output at the time of repeated use and the occurrence of the above blocking though electromagnetic conversion characteristics, handling properties and winding properties can be balanced to a certain extent.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polyester base film for magnetic recording media, which overcomes the above defect of the prior art and has excellent electromagnetic conversion characteristics, a small reduction in output at the time of repeated use and high running durability.
It is another object of the present invention to provide a laminated thermoplastic resin base film for magnetic recording media, which overcomes the above defect of the prior art, has excellent anti-block properties, winding properties and processability and gives a metal deposition thin film magnetic recording medium having excellent electromagnetic conversion characteristics.
It is still another object of the present invention to provide a magnetic recording medium which comprises a magnetic layer on the above base film of the present invention and has excellent characteristic properties such as electromagnetic conversion characteristics.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a polyester base film for magnetic recording medium (may be referred to as “first base film of the present invention” hereinafter), which comprises a polyester film containing first inert fine particles having an average particle diameter of primary particles of 30 to 120 nm and a volume shape coefficient of 0.1 to &pgr;/6 and having a density of protrusions derived from the first inert fine particles on the surface of the film of 5,000 to 50,000/mm
2
and an agglomeration rate of the first inert fine particles forming the protrusions on the surface of the film of 4 to 20%.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a laminated thermoplastic resin base film for magnetic recording medium (may be referred to as “second base film of the present invention” hereinafter), consisting of a first thermoplastic resin layer having a surface roughness WRa of the exposed surface of 0.1 to 4 nm and a second thermoplastic resin layer which contains 0.001 to 5 wt % of third inert fine particles having an average particle diameter of primary particles of 0.1 to 2.0 &mgr;m and 0.001 to 10 wt % of an ester wax of an aliphatic monocarboxylic acid having 8 or more carbon atoms and a polyhydric alcohol and which has a water contact angle with the exposed surface of 70 to 90°, the first thermoplastic resin layer and the second thermoplastic resin layer being laminated together.
Thirdly, the above objects and advantages of the present invention are attained by a magnetic recording medium comprising either one of the first base film and the second base film of the present invention as a base film and a magnetic layer formed on the base film
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A description is first given of the first base film of the present invention.
The polyester used in the present invention is an aliphatic, alicyclic or aromatic polyester. Out of these, an aromatic polyester is particularly preferred.
Examples of the aromatic polyester include polyethylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate. Out of these, polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are preferred.
Handa Makoto
Murooka Hirofumi
Osawa Toshifumi
Kiliman Leszek
Teijin Limited
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