Patent ID: 7294668

Claim:
Aqueous non-melt processible polytetrafluoroethylene dispersion comprising non-melt processible polytetrafluoroethylene particles in an amount of 30 to 70% by weight and an amount of non-ionic surfactant between 2 and 15% by weight based on the weight of polytetrafluoroethylene solids, wherein the dispersion is free of fluorinated surfactant or contains fluorinated surfactant in amounts of not more than 200 ppm based on the amount of polytetrafluoroethylene solids and wherein at least part of said non-melt processible polytetrafluoroethylene particles comprise an effective amount of ionic end groups in the polytetrafluoroethylene polymer chains such that an aqueous dispersion thereof having the following composition: (a) 58% by weight of the non-melt processible polytetrafluoroethylene particles having said effective amount of ionic end groups; (b) an amount of 5% by weight based on the total weight of solids, of non-ionic surfactant consisting of polyethylene glycol mono [4-(1,1,3,3-tetramethylbutyl)phenyl]ether having an average of 9-10 ethylene oxide groups; (c) less than 100 ppm of fluorinated surfactant; and (d) a conductivity of at least 500 μS/cm, has a shear stability of at least 3 minutes when the average particle diameter of said polytetrafluoroethylene particles is 150 nm or more, or shear stability of at least 4 minutes when the particle size is less than 150 nm and wherein the shear stability is measured by stirring 150 g of said aqueous dispersion with 2 g of xylol at a temperature of 20° C. and a stirring rate of 8000 rpm.