# US 5,705,601 A · Process for producing polyester film > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,601 A - Document ID: US5705601A - Status: Granted - Kind: A - Application number: 08/650,902 - Filed: 1996-05-17 - Granted: 1998-01-06 - Earliest claimed: 1996-05-17 - Assignees: Nippon Ester Co., Ltd. - Inventors: Atsuko Ueda; Tetsuo Matsumoto - Web page: https://patentgrep.com/patent/US5705601A ## CPC - C08G 63/85: Germanium, tin, lead, arsenic, antimony, bismuth, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or compounds thereof {(C08G63/823 takes precedence)} - C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS ## Abstract 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. ## Claims ### Claim 1 A process for producing a master polymer for film production which comprises: 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, a potassium compound, and a phosphorus compound, the addition amounts of the potassium compound and the phosphorus compound satisfying the following expressions (1) to (3): depolymerizing the oligomer; adding antimony trioxide and germanium dioxide in respective amounts satisfying the following expressions (4) to (6); and then effecting polycondensation, ##EQU3## wherein a, b, c, and d are the molar amounts of the potassium compound, phosphorus compound, antimony trioxide, and germanium dioxide, respectively, per mol of the terephthalic acid component constituting the oligomer. ### Claim 2 (depends on 1) The process for producing a master polymer for film production as claimed in claim 1, wherein the poly(alkylene terephthalate) oligomer is a poly(ethylene terephthalate) oligomer and the alkylene glycol is ethylene glycol. ### Claim 3 (depends on 1) The process for producing a master polymer for film production as claimed in claim 1, wherein the inorganic lubricant is silica. ### Claim 4 (depends on 1) The process for producing a master polymer for film production as claimed in claim 1, wherein the potassium compound is potassium acetate. ### Claim 5 (depends on 1) The process for producing a master polymer for film production as claimed in claim 1, wherein the phosphorus compound is triethyl phosphate. ### Claim 6 (depends on 1) The process for producing a master polymer for film production as claimed in claim 1, wherein the depolymerization is conducted for at least 30 minutes under an increased pressure at a temperature of 260.degree. C. or higher. ### Claim 7 (depends on 1, 2, 3, 4, 5, 6) The process for producing a master polymer for film production as claimed in any one of claims 1 to 6, wherein the master polymer has an intrinsic viscosity of 0.5 or higher. ### Claim 8 (depends on 1) The process for producing a master polymer for film production as claimed in claim 1, wherein the content of the inorganic lubricant in the master polymer is from 0.3 to 3% by weight. ### Claim 9 (depends on 1) A process for producing a polyester film which comprises: melt-mixing (a) from 3 to 12 parts by weight of the master polymer obtained by the process of claim 1, which comprises a poly(alkylene terephthalate), and which contains from 0.3 to 3 wt % inorganic lubricant and has an intrinsic viscosity of 0.5 or higher with (b) from 97 to 88 parts by weight of a poly(alkylene terephthalate) which contains no inorganic lubricant and has an intrinsic viscosity of 0.5 or higher; and forming the resulting mixture into a film by the electrostatic casting method. ### Claim 10 (depends on 9) The process for producing a polyester film as claimed in claim 9, wherein the poly(alkylene terephthalate) is poly(ethylene terephthalate). ### Claim 11 (depends on 9) The process for producing a polyester film as claimed in claim 9, wherein the inorganic lubricant is silica. ### Claim 12 (depends on 9) The process for producing a polyester film as claimed in claim 9, wherein the potassium compound is potassium acetate. ### Claim 13 (depends on 9) The process for producing a polyester film as claimed in claim 9, wherein the phosphorus compound is triethyl phosphate.