Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Patent
1991-05-23
1993-10-26
Thibodeau, Paul J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
264 22, 4251748E, 428323, 428327, 428330, 428480, B32B 2736, B29C 4788, G11B 5704, B29K 6700
Patent
active
052564711
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a composite polyester film and particularly to a composite polyester film having excellent electrostatic impression casting property and thermal stability.
2. Background Art
Polyester such as polyethylene terephthalate and the like is excellent in mechanical characteristics, thermal resistance, weather-proof and electrical insulation properties. Polyester has been broadly used as film and for molding articles.
Preferable film forming productivity, uniform thickness and excellent transparency have been needed for polyester film. Normally, polyester film is produced by quenching a melt-extruded polyester sheet with a rotating quenching drum or the like. The polyester sheet is, however, difficult to adhere to the surface of the quenching drum so that uniform film is not readily obtained. There have been proposed a variety of methods of improving the adherence of polyester sheet. For instance, there has been proposed a method in which a polyester sheet is made adherent to a quenching drum by forming an electrode between an extrusion die and the quenching drum, and subsequently applying a high voltage to unsolidified polyester sheet in order to adhere the polyester sheet to the quenching drum (hereinafter referred to as an electrostatic impression casting method) (Japanese Patent Publication No.37-6142). When the film forming rate is increased, this electrostatic impression casting method causes a problem of decreasing adherence between the sheet and the quenching drum.
In order to solve such a problem, there has been proposed a method of decreasing the specific resistance of the polyester by adding metal compounds to the polyester (Japanese Patent Application Laid-Open Specifications Nos. 53-34894, 57-190040 etc.). The film containing such compound has a uniform thickness but has decreased thermal stability. The decrease of thermal stability results in the formation of coarse protrusions derived from polymer gel formed by thermal degradation and the metal compounds. There arises a problem of increasing defects (fish eyes) on the surface of the film after stretching. Furthermore, these coarse protrusions cause a problem of decreasing insulation breakdown voltage for use of the polyester in capacitors.
On the other hand, in order to improve the slipperiness of polyester film, there have been proposed numerous methods of adding inorganic particles to the polyester. In these methods, not only the electrostatic impression casting property but also uniformity of the protrusions formed on the film surface by inorganic particles are insufficient (Japanese Patent Application Laid-Open Specification No. 59-171623 etc.).
The inventors have found that the electrostatic impression casting property is influenced by the quantity of metal present in the region of the surface of the melt polyester sheet which is in contact with the rotating quenching drum, which through extensive research, has led to the present invention.
The object of the invention is to provide a composite polyester film having excellent electrostatic impression casting property as well as thermal stability, which comprises: a main layer and a sublayer.
Another object of the invention is to provide a composite polyester film having excellent uniformity of thickness, transparency, and fewer fish eyes resulting from polymer gel formed by thermal degradation.
Another object of the invention is to provide a composite polyester film having excellent smoothness and suitable slipperiness and a specified amount of inactive particles contained in the polyester of a sublayer.
A further object of the invention is to provide a composite polyester film in which numerous protrusions, when numerous inactive particles are contained in the polyester of the sublayer, are formed on the film surface, so as to afford the film excellent smoothness and electromagnetic transfer characteristic .
DISCLOSURE OF THE INVENTION
Accordingly, the object of the invention is attained by providing a composite polyester film compris
REFERENCES:
patent: 3900653 (1975-08-01), Riboulet et al.
patent: 4111625 (1978-09-01), Remmington et al.
patent: 4198458 (1980-04-01), Mitsuishi et al.
patent: 4255516 (1981-03-01), Katoh et al.
patent: 4478772 (1984-10-01), Takagi et al.
patent: 4990400 (1991-04-01), Endo et al.
Morita Tohru
Nagahama Akihiko
Ono Masaaki
Ueda Toshiaki
Miller Austin R.
Nakarani D. S.
Thibodeau Paul J.
Toray Industries Inc.
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