Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Patent
1993-06-23
1996-02-27
Resan, Stevan A.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
428325, 428480, 428694SL, 428694SG, 428900, 523181, G11B 500
Patent
active
054947391
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film. More specifically, it relates to a biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film useful as a base film for a magnetic recording medium which permits recording for a long period of time and permits high-density recording.
TECHNICAL BACKGROUND
From former years, a polyethylene terephthalate film (PET film) is used widely as a base film for magnetic tapes. In recent years, magnetic tapes are being increasingly required to enable high-density recording for downsizing and for achieving high-quality images. Further, it is also required to decrease the thickness of magnetic tapes, as is typically required of 8-mm video tapes. For these reasons, the magnetic layer-side surface of a magnetic tape is required to be smoothest possible, and the thickness of a magnetic tape is required to be smallest possible.
Due to this, a base film is also required to have a flatter surface and a smaller thickness. However, a PET film used as a base film of conventional home VTR magnetic tapes has a rough surface, and many of PET films fails to satisfy the above-required properties for practical use.
For applying a PET film to a base film for a magnetic tape which permits high-density recording, it is basically required to extremely decrease the surface roughness. However, when the surface roughness is decreased, generally, the lubricity between film surfaces deteriorates, and further, air entrapped between film surfaces is hardly or poorly released, which makes it very difficult to take up the film on a roll. This difficulty also increases as the PET film thickness decreases.
Moreover, as the film thickness decreases, the film is required to have a higher Young's modulus in order to retain the film strength.
A PET film having a high Young's modulus can be obtained by increasing the stretch ratio. However, a film treated at a high stretch ratio generally has a high shrinkage, and a magnetic tape formed therefrom is poor in dimensional stability.
Further, in producing a magnetic tape, a magnetic layer is formed on the surface of a PET film treated at a high stretch ratio, and its surface is treated for smoothing it. Then, the magnetic tape is taken up in the form of a roll, and the magnetic layer of the rolled magnetic tape is thermoset. In the heat treatment for this thermosetting, the smoothly finished magnetic surface and the base film surface are frictionally and tightly contacted to each other due to heat shrinkage. Therefore, a phenomenon that the finished smooth magnetic surface is roughened (phenomenon of imprinting film surface roughness) is amplified, and the electromagnetic characteristics are deteriorated.
For overcoming the above defects of a PET film, Japanese Laid-open Patent Publication No. 62-164,733 (164,733/1987) proposes a biaxially oriented PET film for magnetic recording, which is formed from a polyester containing 0.1 to 0.5% by weight of inert solid particles having an average particle diameter of 0.03 to 0.3 .mu.m as small-sized particles, and 0.001 to 0.05% by weight of inert solid particles having an average particle diameter of 0.2 to 0.8 .mu.m as large-sized particles, a size difference between the large-sized particles and the small-sized particles being at least 0.15 .mu.m in average particle diameter, and which has a surface roughness Ra of 0.003 to 0.012 .mu.m, a Young's modulus of at least 650 kg/mm.sup.2 in the longitudinal (machine) direction, and a heat shrinkage of 0.06% or less when heat treated under no load at 70.degree. C. for 1 hour.
On the other hand, polyethylene-2,6-naphthalenedicarboxylate is available as a polyester which is excellent in heat resistance and strength, and it inherently has properties for giving an excellent base film for a magnetic recording medium. And, it has been proposed to use the above polymer for forming a base film for a magnetic recording medium, as will be described below.
For example, Japanese Laid-open Patent Publicatio
REFERENCES:
patent: 4804736 (1989-02-01), Utsumi
patent: 4833019 (1989-05-01), Suwarnasarn
patent: 4861674 (1989-08-01), Inaba et al.
patent: 5051292 (1991-09-01), Katoh et al.
Chuujou Takao
Hosoi Masahiro
Kobayashi Ieyasu
Saeki Yasuhiro
Resan Stevan A.
Teijin Limited
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