Aqueous dispersions of polytetrafluoroethylene particles
The present invention provides an aqueous non-melt processible polytetrafluoroethylene dispersion comprising non-melt processible polytetrafluoroethylene particles in an amount between 30 and 70% by weight based on the total weight of the dispersion and one or more non-ionic surfactants and wherein at least a part of said non-melt processible polytetrafluoroethylene particles comprise polytetrafluoroethylene polymer chains having repeating units comprising ionic groups. The invention further provides a method for obtaining the dispersions.
1. A composition comprising an aqueous non-melt processible polytetrafluoroethylene dispersion containing non-melt processible polytetrafluoroethylene particles in an amount between 30 and 70% by weight based on the total weight of the dispersion and one or more non-ionic surfactants, wherein one or more the non-melt processible polytetrafluoroethylene particles comprise polytetrafluoroethylene polymer chains containing repeating units comprising ionic groups, and wherein the total amount of repeating units containing ionic groups is not more than 1% by weight based on the total weight of polytetrafluoroethylene particles comprising polytetrafluoroethylene polymer chains that contain repeating units comprising ionic groups.
2. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 1 wherein the ionic groups comprise carboxylic or sulfonic acid groups or salts thereof.
3. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 1 wherein the repeating units comprising ionic groups are derivable from a perfluorinated monomer having an ionic group or precursor thereof.
4. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 3 wherein the perfluorinated monomer corresponds to the general formula:
CF 2 ═CF—O—R f -Z
wherein R f represents a perfluoroalkylene group optionally interrupted by one or more oxygen atoms and Z represents a carboxylic acid group, a salt thereof or a precursor thereof, or a sulfonic acid group, a salt thereof or a precursor thereof.
5. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 1 wherein the repeating units containing an ionic group correspond to the general formula:
—CF 2 —CF—O—R f -G
wherein R f represents a perfluoroalkylene group optionally interrupted by one or more oxygen atoms and G represents a carboxylic acid group or a salt thereof or a sulfonic acid group or a salt thereof and wherein the open valences indicate the linkage of the repeating unit to other repeating units in the polymer chain.
6. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 1 wherein the amount of fluorinated surfactant in the dispersion is not more than 200 ppm based on the amount of fluoropolymer solids.
7. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 1 wherein the total amount of non-melt processible polytetrafluoroethylene particles is between 45 and 65% by weight and wherein the one or more non-ionic surfactants are present in a total amount of 2 to 15% by weight based on the total weight of polytetrafluoroethylene solids.
8. An aqueous non-melt processible polytetrafluoroethylene dispersion according to claim 1 wherein the non-melt processible polytetrafluoroethylene particles, characterized by polytetrafluoroethylene polymer chains containing repeating units comprising ionic groups, comprise at least 30% by weight of the total weight of non-melt-processible polytetrafluoroethylene particles.
9. A method comprising coating a substrate utilizing an aqueous non-melt processible polytetrafluoroethylene dispersion as defined in claim 1 .