Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-12-19
2002-10-22
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S480000, C428S674000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06468627
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a polyester film and, more particularly, to a polyester film suitable as a base film for a ferromagnetic metal thin film type magnetic recording medium for recording digital data, such as a digital video cassette tape, and the like.
A consumer digital videotape commercialized in 1995 is formed by, for example, providing a metal magnetic thin film of Co on a base film through vacuum evaporation and by coating a surface thereof with a diamond-like carbon film. This videotape has good durability while having a further smoothed surface property in comparison with the ME (metal evaporated) tape for the Hi8.
Base films used for the videotape are, for example, as follows: (1) a polyester film formed by a polyester film, a discontinuous coating adhered to at least one side of the film, and a fine particle present in the coating and on a surface of the coating (e.g., JP-B-62-30105); (2) a co-extruded film formed by laminating a layer A made of a thermoplastic resin and a layer B made of a thermoplastic resin containing a fine particle (e.g., JP-B-1-26338); (3) a smooth polyester film in which a coating layer is formed mainly from a lubricant on a non-magnetic surface-side surface (e.g., JP-A-57-195321). The base films have further reduced roughness of a metal magnetic film-formed surface, compared with the base films for the Hi8 ME tape.
However, the magnetic recording tapes produced by using these base films have drawbacks, such as poor handling characteristics, great variations in the surface undulation of the tape magnetic surface, increased dropouts (DOs) due to the effects of foreign materials that deposit on a cooling can during a vacuum evaporation process, etc.
As a polyester film for a magnetic recording medium that overcomes the aforementioned problems, and that forms a magnetic recording tape with good electromagnetic conversion property, and that has good handling characteristic and is suitable for mass production, JP-A-10-172127 discloses a polyester film for a magnetic recording medium wherein the SRa value of a side surface A of the polyester film is 2 nm to 4 nm, and the SRz value thereof is 10 nm to 40 nm, and the SRa value of the other side surface B is 5 nm to 15 nm, and the SRz value thereof is 50 nm to 250 nm, and the outer side of the surface B is not provided with a lubricating layer formed by application, and the number of projections as high as or higher than 540 nm is 2 to 20 (100 cm
2
), and wherein a ferromagnetic metal thin film is provided on the outer side of the surface A for use.
Consumer digital videotapes presently enjoy great popularity, and it is demanded that more consumer digital videotapes be put on the market. Therefore, in order to allow production of a greater quantity of digital videotapes through a single vapor deposition process, the base film length has been increased, from the conventional lengths of 10,000 m or less to lengths of 12,000 m or greater, and to lengths of 15,000 m or greater.
Along with such situational changes, it has become evident that if a base film roll having a winding length exceeding 10,000 m is formed by winding a base film disclosed in the aforementioned JP-A-10-172127, and is used to produce consumer digital videotapes, digital videotapes produced from a base film in a winding core portion close to the bobbin of the film roll have poor electromagnetic conversion property and therefore dropouts increase.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a polyester film for a magnetic recording medium that allows production of digital videotapes with good electromagnetic conversion property and reduced dropouts from any portion of the entire length of the film rolled, that is, the entire length from a winding core portion to a surface portion of the film roll, even if the film length of the roll exceeds 10,000 m.
To achieve this and other objects, the invention is constructed as follows.
A polyester film for a magnetic recording medium, comprising at least a polyester layer A and a polyester layer B laminated, wherein a center-line surface average roughness (SRa value) of a layer A-side surface of the film is 2 nm to 4 nm, and a ten-point average surface roughness (SRz value) of the layer A-side surface is 10 nm to 40 nm, and the layer B contains a fine particle &agr; whose average particle size is at least 50 nm and less than 250 nm, and a fine particle &bgr; whose average particle size is at least 250 nm and less than 500 nm, and a content of the fine particle &agr; in the layer B is 0.1 wt. % to 1 wt. %, and a content of the fine particle &bgr; in the layer B is 0.01 wt. % to 0.1 wt. %. A magnetic recording tape is formed by providing a ferromagnetic metal thin film on a layer A-side surface of the polyester film.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A polyester film in accordance with the invention is formed by laminating at least a polyester layer A and a polyester layer B. The polyester film in accordance with the invention is provided with a ferromagnetic metal thin film formed on a layer A-side surface, and is used as a magnetic recording medium.
The polyester in the invention may be a polyester that forms a high-strength film through molecular orientation. The polyester is preferably a polyethylene terephthalate or a polyethylene-2, 6-naphthalate. If at least 80% of the components of the polyester is ethylene terephthalate or ethylene naphthalate, other components may also be copolymerized. Examples of the polyester copolymer components other than ethylene terephthalate and ethylene naphthalate include diol components, such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, 1,4-cyclohexane dimethanol, etc., dicarboxylic acid components, such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, etc., multifunctional dicarboxylic acid components, such as trimellitic acid, pyromellitic acid, etc., p-oxyethoxybenzoic acid, etc.
The polyester may further contain at least one of alkali metal salt derivatives of sulfonic acids that are not reactive with polyester, polyalkylene glycols that are substantially insoluble in polyester, etc., in an amount that is not greater than about 5 wt. %.
The center-line surface average roughness (SRa value) of the layer A-side surface of the polyester film in accordance with the invention is 2 nm to 4 nm and, preferably, 2 nm to 3 nm. The ten-point average surface roughness of the layer A-side surface (SRz value) is 10 nm to 40 nm and, preferably, 20 nm to 40 nm.
If the SRa value is less than 2 nm, the ferromagnetic metal thin film formed on the surface A by vacuum evaporation becomes excessively smooth so that the ferromagnetic metal thin film of the videotape is abraded by a video head during the recording and reproduction in a digital video recorder. Thus, the SRa value less than 2 nm is not preferable. If the SRa value is greater than 4 nm, the ferromagnetic metal thin film becomes excessively rough so that the output characteristics of the videotape deteriorate. Thus, the SRa value exceeding 4 nm is not preferable.
If the SRz value is less than 10 nm, the ferromagnetic metal thin film becomes excessively smooth so that the durability of the videotape is decreased by recording and reproduction being repeated many times in a digital videotape recorder. Thus, the SRz value less than 10 nm is not preferable. If the SRz value is greater than 40 nm, the ferromagnetic metal thin film becomes excessively rough so that the number of small videotape DOs increases. Thus, the SRz value exceeding 40 nm is not preferable.
It is preferable that the layer A-side surface of the polyester film be provided with a coating layer formed from an organic compound containing 0.5 wt. % to 12 wt. % of a fine particle having an average particle size of 5 nm to 30 nm. As the fine particle, silica, calcium carbonate, alumina, polyacrylic acid spherical particles and polystyrene spherical particles may be preferably used. T
Morimoto Tsutomu
Okamoto Katsuya
Ono Masaaki
Tsuzuki Toshihiro
Kubovcik & Kubovcik
Resan Stevan A.
Toray Industries Inc.
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