Concentrated fluoropolymer dispersions
View Patent ↗An aqueous dispersion composition of about 30 to about 70 weight % non-melt-processible fluoropolymer particles having a standard specific gravity (SSG) of less than 2.225 and about 2 to about 11 weight % surfactant based on the weight of said fluoropolymer comprising a compound or mixture of compounds of the formula: R(OCH 2 CH 2 ) n OH wherein R is a branched alkyl, branched alkenyl, cycloalkyl, or cycloalkenyl hydrocarbon group having 8-18 carbon atoms and n is an average value of 5 to 18. The fluoropolymer particles of the dispersion comprise a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene. Preferably, the aqueous dispersion composition comprises about 45 to about 65 weight % non-melt-processible fluoropolymer particles.
1. An aqueous dispersion comprising:
about 30 to about 70 weight % non-melt-processible fluoropolymer particles having a Standard Specific Gravity (SSG) of less than about 2.225, said fluoropolymer particles comprising a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene; and
about 2 to about 11 weight % surfactant based on the weight of said fluoropolymer comprising a compound or mixture of compounds of the formula:
R(OCH 2 CH 2 ) n OH
wherein R is a branched alkyl, branched alkenyl, cycloalkyl, or cycloalkenyl hydrocarbon group having 8-18 carbon atoms and n is an average value of 5 to 18.
2. The aqueous dispersion of claim 1 comprising about 3 to about 11 weight % of said surfactant based on the weight of said fluoropolymer.
3. The aqueous dispersion of claim 1 comprising from about 45 to about 65 weight % non-melt processible fluoropolymer.
4. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene of said core is greater than about 1.2×10 10 Pa·s.
5. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene of said core is greater than about 1.3×10 10 Pa·s.
6. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene of said core is greater than about 1.5×10 10 Pa·s.
7. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene or modified polytetrafluoroethylene of said shell is greater than about 9×10 9 Pa·s and less than the average melt viscosity of polytetrafluoroethylene of said core.
8. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene or modified polytetrafluoroethylene of said shell is at least 0.1×10 10 Pa·s less than the average melt creep viscosity of polytetrafluoroethylene of said core.
9. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene or modified polytetrafluoroethylene of said shell is at least 0.2×10 10 Pa·s less than the average melt creep viscosity of polytetrafluoroethylene of said core.
10. The aqueous dispersion of claim 1 wherein the average melt creep viscosity of the polytetrafluoroethylene or modified polytetrafluoroethylene of said shell is about 9×10 9 Pa·s to about 1.3×10 10 Pa·s.
11. The aqueous dispersion of claim 1 wherein said shell comprises about 5 to about 30% by weight of said fluoropolymer particles.
12. The aqueous dispersion of claim 1 having a cloud point of about 50° C. to about 85° C.
13. The aqueous dispersion of claim 1 having a cloud point of about 59° C. to about 70° C.
14. The aqueous dispersion of claim 1 wherein said surfactant containing 0-20 weight % water is a stable liquid at room temperature.
15. The aqueous dispersion of claim 1 wherein said surfactant containing 0-15 weight % water is a stable liquid at room temperature.
16. The aqueous dispersion of claim 1 wherein the molecular weight of the polytetrafluoroethylene or modified polytetrafluoroethylene in the shell is sufficiently low that said dispersion at about 60 weight % fluoropolymer and at about 6 weight % surfactant has a gel time greater than about 700 seconds.
17. The aqueous dispersion of claim 1 wherein the molecular weight of the polytetrafluoroethylene or modified polytetrafluoroethylene in the shell is sufficiently low that said dispersion at about 60 weight % fluoropolymer and at about 6 weight % surfactant has a gel time greater than about 800 seconds.
18. The aqueous dispersion of claim 1 wherein the molecular weight of the polytetrafluoroethylene or modified polytetrafluoroethylene in the shell is sufficiently low that said dispersion at about 60 weight % fluoropolymer and at about 6 weight % surfactant has a gel time greater than about 1000 seconds.
19. The aqueous dispersion of claim 1 wherein the molecular weight of the polytetrafluoroethylene or modified polytetrafluoroethylene in the shell is sufficiently low that said dispersion at about 60 weight % fluoropolymer and at about 6 weight % surfactant has a gel time greater than about 1200 seconds.
20. The aqueous dispersion of claim 1 wherein the shell is polytetrafluoroethylene.
21. The aqueous dispersion of claim 1 wherein the fluoropolymer is fibrillating.
22. The aqueous dispersion of claim 1 wherein said fluoropolymer has a melt creep viscosity of greater than about 1.4×10 10 Pa·s.
23. A coating composition of the aqueous dispersion of claim 1 .
24. A coating composition in the form of a baked layer of an aqueous dispersion comprising:
about 30 to about 70 weight % non-melt-processible fluoropolymer particles having a Standard Specific Gravity (SSG) of less than about 2.225, said fluoropolymer particles comprising a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene; and
about 2 to about 11 weight % surfactant based on the weight of said fluoropolymer comprising a compound or mixture of compounds of the formula:
R(OCH 2 CH 2 ) n OH
wherein R is a branched alkyl, branched alkenyl, cycloalkyl, or cycloalkenyl hydrocarbon group having 8-18 carbon atoms and n is an average value of 5 to 18.
25. A substrate coated with the composition of claim 24 .
26. The substrate of claim 25 wherein the substrate is metal.
27. The substrate of claim 25 wherein the substrate is glass fabric.
28. A self-supporting film cast from an aqueous dispersion comprising:
about 30 to about 70 weight % non-melt-processible fluoropolymer particles having a Standard Specific Gravity (SSG) of less than about 2.225, said fluoropolymer particles comprising a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene; and
about 2 to about 11 weight % surfactant based on the weight of said fluoropolymer comprising a compound or mixture of compounds of the formula:
R(OCH 2 CH 2 ) n OH
wherein R is a branched alkyl, branched alkenyl, cycloalkyl, or cycloalkenyl hydrocarbon group having 8-18 carbon atoms and n is an average value of 5 to 18.