Nippon Ester Co., Ltd.

Atsuko Ueda

Tetsuo Matsumoto

Keizo Tsujimoto

Takayuki Imamura

A process for producing a polyester film is disclosed, which comprises melt-mixing from 3 to 12 parts by weight of a master polymer comprising a poly(alkylene terephthalate) which contains from 0.3 to 3 wt % inorganic lubricant and has an intrinsic viscosity of 0.5 or higher with from 97 to 88 parts by weight of a poly(alkylene terephthalate) containing no inorganic lubricant and having an intrinsic viscosity of 0.5 or higher, and forming the resulting mixture into a film by the electrostatic casting method. The master polymer is obtained by a process comprising adding to a poly(alkylene terephthalate) oligomer having an average degree of polymerization of 10 or lower an alkylene glycol slurry of an inorganic lubricant and specific amounts of a potassium compound and a phosphorus compound, depolymerizing the oligomer, subsequently adding specific amounts of antimony trioxide and germanium dioxide, and then effecting polycondensation. By this process, a polyester film having an excellent color tone can be produced with a high producibility and a high operation efficiency.

Process for producing polyester film

A flame resistant polyester produced by addition and copolymerization of a phosphorus compound represented by general formula (I) below as a diol component of the polyester in an amount of 500 ppm or more in terms of phosphorus atom content in the polyester, which polyester has alkylene terephthalate units as main repeating units and which has an intrinsic viscosity of not less than 0.5 measured at 20.degree. C. in a mixture of equal weight of phenol and tetrachloroethane: ##STR1## where E is --CH.sub.2 CH.sub.2 --, Ar is an aromatic group or an aromatic group substituted by a lower alkyl group or a halogen atom, and m and n denote, respectively, integers the sum of which is from 1 to 20.

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Aichi, Japan

Atsuko Ueda