Plastic and nonmetallic article shaping or treating: processes – Carbonizing to form article – Agglomeration or accretion
Patent
1990-09-10
1993-02-23
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Carbonizing to form article
Agglomeration or accretion
264211, 264216, 528275, 528276, 528286, 528287, 528293, 528295, 528308, B29C 4126
Patent
active
051887746
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an aromatic polyester film and a process for producing the film. More particularly, the present invention relates to a process for producing an aromatic polyester film having no surface defect and a uniform thickness, at a high productivity, by allowing a molten film of an aromatic polyester to adhere onto a rotating cooling drum to cool the molten film, as well as to such an aromatic polyester film.
BACKGROUND ART
Thermoplastic polyesters typified by poly(ethylene terephthalate) have excellent physical and chemical properties and accordingly are in wide use in film fields such as magnetic tape application, electrical insulation application, condenser application, photography application, packaging application and the like.
Polyester films are usually produced by extruding a film-like melt from an extruder die, rapidly cooling the melt on the surface of a rotating cooling drum, then biaxially stretching the resulting film to lengthwise and crosswise directions. In this case, in order to obtain a film having no surface defect and a thickness of high uniformity, it is necessary to increase the adhesion between the film-like melt and the surface of the rotating cooling drum. As the method for increasing the adhesion, there is known a method in which a wire-shaped electrode is provided between the extruder die and the surface of the rotating cooling drum to deposit electrostatic charges on the surface of the film-like melt and thereby the film-like melt is allowed to adhere to the surface of the cooling drum and is cooled rapidly under this condition (the method is hereinafter referred to as electrostatic casting method) (reference is made to Japanese Patent Publication No. 6142/1962).
Even in this electrostatic casting method, however, as the circumferential speed of the rotating cooling drum is made faster to increase the productivity of film, the strength of the adhesion of the film-like melt onto the surface of the cooling drum is reduced, inviting the formation of pinner bubbles on the film surface and reducing the uniformity of film thickness.
In film formation, particularly the formation of a monoaxially or biaxially stretched film, higher productivity and resultant reduced production cost is an important task, together with higher film quality. To achieve it, employing a faster circumferential speed of the rotating cooling drum and thereby increasing a speed of film formation is most effective. In the electrostatic casting method, when the circumferential speed of the rotating cooling drum is made faster, the amount of electrostatic charges applied per unit area of the surface of film-like melt becomes smaller, and thereby the adhesion between film-like melt and drum surface is reduced, which invites formation of pinner bubbles on film surface and reduction in uniformity of film thickness. Hence, in order to increase the adhesion, there can be taken a means for increasing the amount of electrostatic charges deposited on the film-like melt surface by increasing the voltage applied to the above-mentioned electrode. Application of too high a voltage to the electrode gives rise, in some cases, to arcing between the electrode and the rotating cooling drum, breakage of the film-like melt on the cooling drum surface and damaging of the cooling drum surface. Thus, increase of the voltage applied to the electrode to higher than a certain level is virtually impossible and the conventional electrostatic casting method has a limitation for obtaining a uniform film by increasing the speed of film formation.
To produce a polyester film having a uniform thickness and no surface defect at a high efficiency by overcoming such a limitation of the electrostatic casting method and using a higher film formation speed, Japanese Patent Publication No. 40231/1978 proposes incorporation into a polymer an alkali metal, an alkaline earth metal or a compound thereof in an amount of 0.005-1% by weight, preferably 0.07-0.3% by weight, to allow the resulting molten polymer to have
REFERENCES:
patent: 3732183 (1973-05-01), Popp et al.
patent: 4478772 (1984-10-01), Takagi et al.
patent: 4604453 (1986-08-01), Kuze et al.
patent: 4851504 (1989-07-01), Suzuki et al.
Ichihashi Tetsuo
Kurihara Hideshi
Nitta Shozo
Sanenobu Kazuyuki
Takagi Norio
Teijin Limited
Tentoni Leo B.
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