Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-08-05
2001-03-20
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S213000, C428S215000, C428S339000, C428S323000, C428S327000, C428S328000, C428S329000, C428S330000, C428S331000, C428S480000, C428S690000, C428S690000, C428S910000
Reexamination Certificate
active
06203883
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field
The present invention relates to a biaxially oriented laminated polyester film for magnetic recording medium. More particularly, it relates to a biaxially oriented laminated polyester film for magnetic recording medium, having excellent windability, abrasion resistance and durability in transportation as well as electromagnetic conversion characteristics, producible at a low production cost, and useful especially as a base film of a magnetic recording medium for a high-speed duplicator.
2. Background Arts
Biaxially oriented polyester films represented by polyethylene terephthalate film are being widely used as a base film of a magnetic recording medium such as a magnetic tape owing to their excellent physical and chemical properties.
The growth of the production of tapes recorded with information such as cinema picture is remarkable recently among various uses of magnetic tapes. The production of recorded tapes was carried out formerly by duplicating from a master VTR (video tape recorder) to several thousands of VTRs at a high speed, however, a new duplication technology has been developed recently which comprises the superposition of a blank magnetic tape to a mirror master tape recorded with the above information and the application of a magnetic field and heat to transfer the information to the blank tape. The duplication speed of the method is extremely high. Accordingly, the required characteristics for the magnetic tape are varied, and various new required characteristics have been developed for the base film of the tape for the high-speed duplication use. For example, the tape is required to have improved windability in the form of a magnetic tape in the high-speed winding, close contact to the master tape, smoothness of the film surface to improve the electromagnetic conversion characteristics and abrasion resistance with a guide tape contacting with the tape in duplication.
The conventional base film of magnetic recording medium is incorporated with inert particles having large diameter to improve the windability by improving the air-squeezing performance. The addition of a large amount of such inert particles having large diameter to a base film forms protrusions on the surface of the magnetic layer by the particles, and the transfer of the profile of the protrusions formed by the large-diameter inert particle to the magnetic layer surface in the case of winding the tape in overlapped state to remarkably deteriorate the surface properties of the magnetic layer of the magnetic tape. There are other problems such as the abrasion of the coarse inert particles by contacting with the guide roll to generate white powder and cause drop-out defects.
The environment against the abrasion resistance and transport durability of magnetic tapes tends to be severe owing to e.g. the use of roughly surface-finished cassette half and guide pin or the use of a plastic guide pin to reduce the cost of a magnetic recording and playing apparatus such as VTR, add the improvement for meeting the requirements is still more keenly desired.
DISCLOSURE OF THE INVENTION
As a result of vigorous investigation for achieving the new characteristics required as a base film of a magnetic tape for the aforementioned high-speed duplicator, i.e. the improvement on the windability at a high speed, the smoothness of the film surface and the abrasion resistance, etc., and for solving the problems to improve the abrasion resistance and the transportation durability so as to be usable even on an inferior cassette half, guide pin, etc., the inventors of the present invention have found that the above problems can be solved by using a laminated polyester film, adding three specific kinds of particles to the outermost layer constituting at least one of the surfaces and selecting the ratio of the thickness of the outermost layer to the diameter of the particle having the largest average particle diameter to be fallen within a specific range and that a biaxially oriented laminated polyester film having extremely excellent total performance and producible at a low cost can be produced by this process.
The object of the present invention is to provide a biaxially oriented laminated polyester film for a magnetic recording medium having excellent windability, abrasion resistance, transportation durability and electromagnetic conversion characteristics, producible at a low cost and useful as a base film of a magnetic recording medium for high-speed duplicators.
The other objects and advantages of the present invention will become clear from the following explanations.
The object of the present invention is achieved by a biaxially oriented laminated polyester film for magnetic recording medium comprising a biaxially oriented polyester film having a polyester layer A containing fine particles laminated to at least one surface of a polyester layer B and characterized in that the fine particles in the polyester layer A are composed of 0.001 to 0.03% by weight of crosslinked polymer particles (a) having an average particle diameter (da) of 0.9 to 1.6 &mgr;m, 0.1 to 0.8% by weight of inert particles (b) having an average particle diameter (db) of 0.4 to 0.8 &mgr;m and 0.05 to 1.0% by weight of inert inorganic particles (c) having an average particle diameter (dc) of 0.01 to 0.3 &mgr;m and a Mohs hardness of 7 or above and that the ratio of the thickness TA (&mgr;m) of the polyester layer A to the average particle diameter da (&mgr;m) of the crosslinked polymer particles (a) TA/da is from 0.4 to 2.0.
REFERENCES:
patent: 5336079 (1994-08-01), Okazaki et al.
patent: 5458964 (1995-10-01), Okazaki
patent: 5516574 (1996-05-01), Ogawa et al.
patent: 06313052 (1994-08-01), None
Ogawa Tatsuya
Watanabe Hideaki
Chen Vivian
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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