Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-08-16
2001-12-18
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, C428S323000, C428S343000, C428S344000, C428S480000, C428S690000, C428S690000, C428S910000, C525S437000, C525S444000
Reexamination Certificate
active
06331344
ABSTRACT:
TECHNICAL FIELD
This invention is directed to biaxially oriented polyester films.
BACKGROUND ART
As biaxially oriented polyester films, a biaxially oriented laminated polyester film is known (for instance, U.S. Pat. Nos. 5,069,962 and 5,626,942). There is also known a biaxially oriented polypropylene terephthalate film (Japanese Unexamined Patent Publication No. 9-175055 for example).
Such a commonly known, biaxially oriented polyester film when in use for magnetic recording media affords improved electromagnetic conversion characteristics, but leaves the problem that polymer particles become escaped due to insufficient wear resistance of the polymer surface, eventually inviting particle dusting. Upon application to magnetic tapes, this type of polyester film involves the lack of signals which would result from particle dusting. In magnetic recording media of a higher density, a need exists for those physical characteristics that could prevent polymer particles from escaping out of the corresponding polyester film. In order to solve these problems, a principal object of the present invention is to provide a biaxially oriented polyester film which, in particular, is excellent in wear resistance and free from oligomer separation.
DISCLOSURE OF THE INVENTION
The biaxially oriented polyester film according to the present invention is so constituted as to have at least one film layer disposed, which film layer is composed predominantly of polypropylene terephthalate. A first embodiment of the polyester film lies in such having a heat shrinkage of 0.8% or below after standing at 80° C. for 30 minutes. A second embodiment of the polyester film lies in such having on at least one surface a surface roughness Ra of 5-120 nm, a 10-point average roughness Rz/Ra of 12 or below and a protrusion-to-protrusion spacing Sm of 15 &mgr;m or below.
BEST MODE OF CARRYING OUT THE INVENTION
To gain high resistance to wear and freedom from oligomer separation, the polypropylene terephthalate (hereinafter called PPT) for use in the present invention is derived preferably by polymerization of 1,3-propanediol with terephthalic acid, or a methyl ester derivative or the like thereof. A blend of two or more different polymers or a copolymer is also suitably useful so long as it has no adverse effects on achieving the object of the invention.
The PPT-predominated film layer used herein is one in which a PPT component is contained in an amount of more than 50% by weight.
The PPT-predominated film layer (hereinafter called the layer A where relevant) may be incorporated with an inorganic particle material such as of aluminum silicate, calcium carbonate, alumina, silica, calcium phosphate, titanium oxide or the like, or with an organic particle material so that the film layer is made resistant to wear. The average particle diameter of such particle material is in the range of 0.01-2.0 &mgr;m, preferably of 0.02-1.5 &mgr;m, more preferably of 0.02-1.0 &mgr;m. Further, the relative standard deviation of this particle diameter is preferably 0.5 or below, more preferably 0.3 or below, most preferably 0.2 or below. The content of that particle material is in the range of 0.01-3% by weight, preferably of 0.02-2% by weight, more preferably of 0.05-1% by weight. The layer A may be incorporated with various additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and the like in conventional amounts, provided that the object of the invention is not adversely affected.
The biaxially oriented polyester film provided by the present invention may be a single-layered film formed solely of the above-mentioned PPT-predominated film layer.
In the case where the biaxially oriented polyester film provided by the present invention is of a laminated structure in which two or more layers are superposed one on another, at least one of the constituent film layers should be formed of the PPT-predominated film layer described above. Though not particularly restricted, the other film layer or layers may preferably be formed of polyethylene terephthalate (hereinafter called PET), poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) and the like. A blend of two or more different polymers or a copolymer may be used unless the object of the invention is adversely affected. These film layers can be incorporated with the same inorganic or organic particle material as noted above in connection with the layer A. Such additives as an antioxidant, a heat stabilizer, an ultraviolet absorber and the like may also be added in conventional amounts unless the object of the invention is adversely affected.
According to the first embodiment of the present invention, a biaxially oriented polyester film should have a heat shrinkage of 0.8% or below after standing for 30 minutes at 80° C. so as to prevent signals from getting lacked when in use for magnetic recording media. The heat shrinkage is preferably 0.6% or below, more preferably 0.4% or below.
The thickness of the layer A is not particularly restricted.
Desirably, however, it may be set to be in the range of 0.01-3.0 &mgr;m, preferably of 0.02-2.0 &mgr;m, more preferably of 0.03-1.0 &mgr;m, in respect of the increase in wear resistance and the preclusion of oligomer separation.
No particular restriction is imposed upon the relationship between the thickness t of the layer A and the average particle diameter d of the particle material contained in the layer A. However, the wear resistance can noticeably be improved in the case of 0.2 d≦t≦10 d, preferably of 0.3 d≦t≦5 d, more preferably of 0.5 d≦t≦3 d. When two or more layers A are used and when two such layers are disposed for example as the outermost front and back surfaces of the finished film, those equations should preferably be satisfied.
According to the second embodiment of the present invention, a biaxially oriented polyester film should have on at least one surface a surface roughness Ra of 5-120 nm, a 10-point average roughness Rz/Ra of 12 or below and a protrusion-to-protrusion spacing Sm of 12 &mgr;m. With wear resistance in view, the surface roughness Ra is preferably in the range of 5-50 nm, especially of 10-30 nm, the 10-point average roughness Rz/Ra is preferably 10 or below, and the protrusion-to-protrusion spacing Sm is preferably 12 &mgr;m or below. The lower limit of Rz/Ra is not particularly restrictive which, however, is 4 or above for practical film production, and the lower limit of Sm is not particularly restrictive which, however, is in the order of 3 for practical film production.
Also in the second embodiment, it is desired that the relationship between the thickness t of the layer A and the average particle diameter d of the particle material contained in the layer A be observed in the same ranges as specified above in connection with the first embodiment.
In the present invention, a further embodiment is included which is designed to simultaneously comply with the requirements of the first and second embodiments. In addition and more advantageously, each of the first and second embodiments should meet the following requirements.
To increase wear resistance, to render oligomer separation free and to define surface profiling effectively, each of the biaxially oriented polyester films according to the present invention is preferably brought into a multi-layered structure in which at least two or more film layers are placed in superposed relation to one another. The crystallization parameter &Dgr;Tcg of an outermost layer-constituting polymer should be preferably lower than 60° C., more preferably lower than 50° C., especially lower than 40° C., in view of wear resistance and dimensional stability. The crystallization parameter &Dgr;Tcg is defined by the difference between the cold crystallization temperature during the course of temperature rise and the glass transition temperature. The smaller difference, the speed of polymer crystallization becomes higher with consequent arrival at a specific range of thermal shrinkage after standing for 30 minutes at 80° C. that falls within the scope
Kubota Akira
Nakajima Shozi
Nakamori Yukari
Okazaki Iwao
Shirakawa Yuri
Birch & Stewart Kolasch & Birch, LLP
Chen Vivian
Toray Industries Inc.
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