Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-07-11
2003-01-07
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S212000, C428S409000, C428S480000, C428S690000, C428S690000
Reexamination Certificate
active
06503599
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a biaxially oriented polyester film for magnetic recording media and to a magnetic recording medium. More specifically, it relates to a biaxially oriented polyester film suitable for use as a base film for ferromagnetic metal thin film magnetic recording media which can record a large volume of digital data for a long time, such as a digital video cassette tape and a data storage tape and to a magnetic recording medium.
A digital video cassette tape (DVC tape) for general consumers which was implemented in 1995 comprises a base film which is more flat than a base film for Hi8ME tapes to provide greater magnetic force than Hi8ME tapes, a Co metal magnetic thin film and not Co/Ni alloy metal thin film formed on the base film and a diamond-like carbon film formed on the surface of the magnetic thin film to provide high running durability.
This base film comprises, for example, a polyester film and a discontinuous film which is essentially composed of a polymer blend closely bonded to at least one side of the above film and fine particles having a particle diameter of 50 to 500 Å. A polyester film containing a water-soluble polyester copolymer and having fine protrusions formed on the surface by the fine particles is used as the discontinuous film (for example, JP-B 63-57238) (the term “JP-B” as used herein means an “examined Japanese patent publication”) and the metal magnetic film forming surface thereof has smaller roughness than that of a base film for Hi8ME tapes The base film must have a small thickness of less than 7 &mgr;m.
However, this very thin and flat base film is difficult to be handled in film formation and deposition steps. For instance, as the surface of the film is heated in the deposition step of a metal thin film layer, the deformation of the film by heat is prevented by closely contacting the surface of the film to a cooling drum. If the above line speed is accelerated, a conventional base film for magnetic recording media is not fully cooled on the surface of the drum, thereby causing a heat yielding phenomenon and the breakage of the film in the worst case. Even if the film is not broken, the base film is wrinkled, resulting in nonuniform deposition. Even when the obtained magnetic tape has excellent initial output, the output of the tape after long-term storage or after repeated running tends to lower. When the conventional base film is used as a base film for long-time recording video tapes, the edges of a tape are damaged during recording and reproduction, whereby the flatness of the tape is apt to become unsatisfactory.
It is an object of the present invention to provide a biaxially oriented polyester film for magnetic recording media which has excellent handling properties provides a magnetic tape having excellent output after storage or repeated running and prevents the edges of the tape from being damaged.
It is another object of the present invention to provide a polyester film for magnetic recording media which has sufficient slipperiness to enable the acceleration of the line speed and sufficient adhesion to a cooling drum at the time of deposition to prevent a heat yielding phenomenon and is free from a reduction in output caused by shape transfer to the surface of a magnetic layer in the production process of a metal thin film magnetic recording medium.
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 biaxially oriented polyester film for magnetic recording media which has (1) a Young's modulus in a machine direction of 5.0 GPa or less and a Young's modulus in a direction perpendicular to the above machine direction of 8.0 GPa or more, (2) a surface roughness on one side of 0.3 to 1.5 nm when measured for a measurement area of 246.6×187.5 &mgr;m and 0.1 to 3.0 nm when measured for a measurement area of 2.5×1.9 mm and a surface roughness on the other side of 0.6 to 2.5 nm when measured for a measurement area of 246.6×187.5 &mgr;m and 0.1 to 5.0 nm when measured for a measurement area of 2.5×1.9 mm, and (3) a heat shrinkage factor in a machine direction when heated at 105° C. for 30 minutes of 0 to 1.5% and when heated at 150° C. for 30 minutes of 2.0 to 5.0% and a heat shrinkage factor in a direction perpendicular to the machine direction when heated at 105° C. for 30 minutes of 0.5 to 3.0% and when heated at 150° C. for 30 minutes of 6.0 to 11.0%.
Secondly, the above objects and advantages of the present invention are attained by a magnetic recording medium comprising the above biaxially oriented polyester film of the present invention and a magnetic layer formed on one side of the polyester film.
The present invention will be described in detail hereinafter.
The polyester which is the material of the biaxially oriented polyester film of the present invention is preferably an aromatic polyester for forming a high-strength film through molecular orientation. The aromatic polyester may be either a homopolyester or a copolyester. The homopolyester is preferably polyethylene terephthalate or polyethylene-2,6-naphthalene dicarboxylate. The copolyester may be a copolyester comprising ethylene terephthalate or ethylene-2,6-naphthalene dicarboxylate as the main recurring unit and a third component in an amount of 20 mol % or less, preferably 10 mol % or less based on the total of all the recurring units. Examples of the third component include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol and 1,4-cyclohexane dimethanol, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid and 5-sodium sulfoisophthalic acid, polycarboxylic acid components such as trimellitic acid and pyromellitic acid, and p-oxyethoxybenzoic acid.
The above polyester may contain a film formation modifier (for example, alkali metal salt compound, quaternary phosphonium sulfonate compound, etc.), thermal stabilizer (for example, phosphoric acid, phosphorous acid, derivative thereof, etc.), antioxidant (for example, hindered phenol-based compound, etc.) and other additives as required in limits that do not impair the object of the present invention.
The intrinsic viscosity of the above polyester (measured at 25° C. in orthochlorophenol by an Ostwald's viscometer) is preferably 0.4 to 0.9.
The biaxially oriented polyester film of the present invention has a Young's modulus in a machine direction of 5.0 GPa or less, preferably 4.8 GPa or less and a Young's modulus in a direction perpendicular to the machine direction of 8.0 GPa or more, preferably 9.0 GPa or more. The Young's modulus in the machine direction is more preferably 3 GPa or more and the Young's modulus in a direction perpendicular to the machine direction is more preferably 18 GPa or less. When the Young's modulus in the machine direction is larger than 5.0 GPa and a digital magnetic tape is formed from the polyester film, a sound generated by beating the tape by the rotating head of a digital video recorder resonates disadvantageously. When the Young's modulus in the direction perpendicular to the machine direction is smaller than 8.0 GPa, the obtained magnetic tape does not contact the head properly, resulting in an output reduction.
The biaxially oriented polyester film of the present invention has the following surface characteristics.
The surface roughness of one side (to be referred to as “side A” hereinafter) of the biaxially oriented polyester film is 0.3 to 1.5 nm when measured for a measurement area of 246.6×187.5 &mgr;m (to be referred to as “WRa(25)A” hereinafter) and 0.1 to 3.0 nm when measured for a measurement area of 2.5×1.9 mm (to be referred to as “WRa(2.5)A” hereinafter) and the surface roughness of the other side (to be referred to as “side B” hereinafter) is 0.6 to 2
Osawa Toshifumi
Tojo Mitsuo
Bernatz Kevin M
Teijin Limited
Thibodeau Paul
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