Aqueous dispersions of polytetrafluoroethylene having a low amount of fluorinated surfactant

US7041728B2 · kind B2 · utility

Assignee

• 3M INNOVATIVE PROPERTIES COMPANY · US

Inventors

• Tilman C. Zipplies · Burghausen, DE
• Klaus Hintzer · Woodbury, US
• Michael C. Dadalas · Eggenfelden, DE
• Gernot Loehr · Altötting, DE

Key dates

• Filing date: Oct 12, 2004
• Grant date: May 9, 2006
• Expiry date: Oct 12, 2024

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C08L71/02
• WIPO field: Macromolecular chemistry, polymers
• WIPO sector: Chemistry

Abstract

The present invention provides a method of making an aqueous dispersion of non-melt processible polytetrafluoroethylene, the method comprising:(a) an aqueous emulsion polymerization of an amount of tetrafluoroethylene to produce a final amount of polytetrafluoroethylene solids and optionally up to 1% by weight based on the amount of tetrafluoroethylene of a perfluorinated comonomer, wherein said aqueous emulsion polymerization is initiated with a free radical initiator and the polymerization is carried out in the presence of a fluorinated surfactant, and wherein before completing the feeding of said amount of tetrafluoroethylene but after feeding at least 80% by weight of said amount of tetrafluoroethylene, free radicals capable of introducing ionic end groups or precursors thereof in the polytetrafluoroethylene polymer are caused to be formed at a rate that without counter measures would cause an increase in the polymerization rate of at least 20%;(b) reducing the amount of fluorinated surfactant in the thus obtained aqueous dispersion to an amount of not more than 200 ppm, preferably not more than 100 ppm and more preferably not more than 50 ppm based on the amount of polytetrafl…