Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-08-06
2001-02-20
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S143000, C428S147000, C428S213000, C428S220000, C428S323000, C428S327000, C428S338000, C428S480000, C428S690000, C428S900000, C428S910000, C528S298000, C524S425000, C524S430000
Reexamination Certificate
active
06190753
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a biaxially oriented polyester film for magnetic recording medium. More particularly, it relates to a biaxially oriented polyester film having thin film thickness, excellent dimensional stability and small dimensional change in the direction of width (transversal direction) especially under a load in the direction of the length of the film (machine direction) and useful as a base film for a magnetic recording medium generating little error in magnetic recording and reproduction, especially for a digital data storage tape.
BACKGROUND ARTS
Polyester films are widely used in the fields of magnetic recording medium, electrical insulation material, packaging material, etc., owing to the excellent thermal and mechanical properties.
The development of a magnetic recording medium of digital recording system is recently in progress to enable the recording and reproduction of picture and sound in improved quality compared with conventional analog recording system. The recent progress of the medium for the digital recording system aims at high capacity, high recording density, long recording time and compact-sized cassette as well as high picture quality and sound quality and the requirement on the properties of the base film is increasing according to the improvement of the above qualities.
It is necessary to decease the thickness of a magnetic tape and, accordingly, the thickness of a base film for prolonging the recording time and reducing the cassette size. However, the rigidity of a tape decreases with decreasing thickness of a magnetic tape to deteriorate the contact of the tape with a magnetic head in recording and reproduction, which makes difficult to get high picture quality and sound quality.
The track pitch is selected to be extremely narrow especially in the data-storage use adopting a linear track system such as QIC (Quarter Inch Cartridge) and DLT (Digital Liner Tape) for getting high capacity and high density. The narrow track pitch produces a problem of error by the shift of track caused by the dimensional change in the transversal direction of the tape.
These dimensional changes are supposed to be caused by the changes in the temperature and humidity in the use of the magnetic tape and the variation of tape width induced by the variation of the transport tension of the tape inherent to the recent compact-sized drive. The extent of the influence of each factor is not yet clear to produce a problem in the case of increasing the capacity and density of a magnetic tape.
DISCLOSURE OF THE INVENTION
An object of this invention is to solve the above problems and provide a biaxially oriented polyester film having thin thickness and excellent dimensional stability, exhibiting small dimensional change in the direction of width (transversal direction) especially under a load applied in the direction of the film length (machine direction), and useful as a base of a magnetic recording medium having low error rate in magnetic recording and reproduction.
Another object of this invention is to provide a biaxially oriented polyester film useful as a base of a magnetic recording medium which is less liable to generate error rate caused by track shift and has improved output characteristics in a linear-track digital data storage use.
The object of this invention can be achieved by a biaxially oriented polyester film for magnetic recording medium having a thickness of less than 7 &mgr;m and satisfying the formula
1
≤
P
-
(
α
t
+
α
h
)
10
≤
10
wherein &agr;t (×10
−6
/° C.) is the thermal expansion coefficient of the film in transversal direction, &agr;h (×10
−6
/%RH) is the humidity expansion coefficient in transversal direction and P (ppm/g) is the transversal shrinkage of the film under the load (grams) applied to the film in machine direction.
REFERENCES:
patent: 5006589 (1991-04-01), Sakamoto et al.
patent: 5051292 (1991-09-01), Katoh et al.
patent: 5252388 (1993-10-01), Murooka et al.
patent: 5415930 (1995-05-01), Etchu et al.
patent: 5439738 (1995-08-01), Chujo et al.
patent: 5665454 (1997-09-01), Hosol et al.
patent: 5958553 (1999-09-01), Hosol et al.
patent: 5958568 (1999-09-01), Mizutani et al.
patent: 6068909 (2000-05-01), Koseki et al.
patent: 3-93024 (1991-04-01), None
patent: 5-212787 (1993-08-01), None
patent: 6-46450 (1994-02-01), None
patent: 7-223288 (1995-08-01), None
International Search Report.
Koseki Masafumi
Watanabe Hideaki
Acquah Samuel A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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