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AssigneeDaikin Kogyo Co., Ltd.
InventorsShun Koizumi, Shigeru Ichiba, Tetsuo Shimizu, Chuzo Okuno, Tosinori Kadowaki, Katsutoshi Yamamoto
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Polytetrafluoroethylene fine powders which have an average molecular weight of not less than 5,000,000, preferably not less than 5,500,000, an amorphous index of not more than 0.1, preferably not more than 0.09, a number average primary particle size of 0.1 to 0.4 micron, preferably 0.15 to 0.38 micron, and a sharp endothermic peak at a temperature between 343.degree. C. and 350.degree. C. on the melting diagram by a differential scanning calorimeter, said sharp peak having an endothermic ratio of not more than 0.3, preferably not more than 0.27, and a half value width of the endothermic peak of not more than 8 degrees, preferably not more than 6 degrees, and a process for producing the polytetrafluoroethylene fine powders. The polytetrafluoroethylene fine powders have an excellent stretchability and are useful for electric wire coating, small diameter tubes, large diameter tubes, sealing tapes and the like.
A polytetrafluoroethylene fine powder which has an average molecular weight of not less than 5,000,000, an amorphous index of not more than 0.1 and a sharp endothermic peak at a temperature between 343.degree. C. and 350.degree. C. on the melting diagram by a differential scanning calorimeter, said sharp peak having an endothermic ratio of not more than 0.3 and a half value width of the endothermic peak of not more than 8 degrees.
In a process for producing a polytetrafluoroethylene fine powder, which has an average molecular weight of not less than 5,000,000, an amorphous index of not more than 0.1 and a sharp endothermic peak at a temperature between 343.degree. C. and 350.degree. C. on the melting diagram by a differential scanning calorimeter, said sharp peak having an endothermic ratio of not more than 0.3 and a half value width of the endothermic peak of not more than 8 degrees, the polymerization reaction at a polymerization temperature of 55.degree. to 86.degree. C. using a water-soluble persulfate as the polymerization initiator in a concentration of 0.002% by weight or less, and changing the polymerization condition after the initiation of polymerization and after the polymer in an amount of at least 25% by weight of the final yield is produced but before at most 85% by weight of the final yield of the polymer is produced, said changing of the polymerization condition being carried out by adding either or both of an alkali and a radical scavenger to the polymerization system or by lowering the polymerization temperature 5.degree. to 30.degree. C. said alkali being added in such an amount that the polymerization system is kept on an alkaline side and said radical scavenger being added in an amount of about 2 to 5 times by weight of the amount of the polymerization initiator.
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