Process for preparing aqueous fluoropolymer dispersions and the concentrated aqueous fluoropolymer dispersions produced by such process

Example 1

[0070] Four samples of PTFE dispersions containing 19.3 wt. % of PTFE, 754 ppm of APFO (3907 ppm of APFO based on the weight of PTFE), and having a pH of 3.5 were processed as follows: [0071] 1. The raw latex was stabilized with 18 wt. % of Triton X-100. 0.1 wt. % of NH4OH (30 wt. % aqueous solution) was added to adjust the pH. [0072] 2. It was then transferred into a lab Thermal Concentrator, which was connected to a circulating temperature control bath with maximum temperature set at 83° C. [0073] 3. The dispersion was slowly heated up from room temperature with no agitation. [0074] 4. Heating continued until temperature reached about 75° C. [0075] 5. The temperature was maintained between 75 and 80° C. until phase separation was complete. [0076] 6. The concentrated latex contained 66.9 wt. % of PTFE, 2.6 wt. % Triton X-100 and 450 ppm of APFO (673 ppm of APFO based on the weight of PTFE). The APFO reduction from 3907 to 450 ppm (based on PTFE) was 83% after one cycle of thermal concentration. [0077] 7. The supernatant was drained into a separate container for future recycling. [0078] 8. The concentrated latex was diluted to 33 wt. % PTFE with purified water and re-concentrated according to step 1 to 7 as shown above except that the total surfactant was reduced to 10 wt. %. NH4OH were added to adjust the pH. [0079] 9. The concentrated latex contained 63.5 wt. % PTFE, 3.1 wt. % Triton X-100 and 209 ppm (329 ppm by weight of PTFE). The APFO reduction from 673 to 329 ppm (based on PTFE) was 51 % on the second cycle of thermal concentration. [0080] 10. The latex was diluted to 33 wt. % PTFE with purified water and re-concentrated for the 3rd time as described above. [0081] 11. The concentrated latex contained 65.9 wt. % PTFE, 5.1 wt. % Triton X-100 and 127 ppm (193 ppm by weight of PTFE). The APFO reduction from 329 to 193 ppm was 41% on the 3rd cycle of thermal concentration. The overall APFO reduction from 3907 to 193 ppm (based on PTFE) was about 95%. [0082] 12. The concentrated latex was used for coating application.

Example 2

[0083] An aqueous dispersion of PTFE with trace commoner PPVE containing 18.8 wt. % by weight of modified PTFE, 210 ppm of APFO (1117 ppm of APFO based on the weight of PTFE), and having a pH of 3.5 was processed as follows: [0084] 1. The raw latex was stabilized with 18 wt. % of Newcol 1308 FA(90). NH4OH (30 wt. % aqueous solution) was added to adjust the pH. [0085] 2. It was then transferred into a lab Thermal Concentrator, which was connected to a circulating temperature control bath with maximum temperature set at 54° C. [0086] 3. The dispersion was slowly heated up from room temperature with no agitation. [0087] 4. Heating continued until temperature reached about 50° C. [0088] 5. The temperature was maintained between 50 and 52° C. until phase separation was complete. [0089] 6. The concentrated latex contained 64.3 wt. % PTFE, 3.1 wt. % Newcol 1308 FA(90) and 188 ppm of APFO (292 ppm of APFO based on the weight of PTFE). [0090] 7. The supernatant was drained into a separate container for future recycling. [0091] 8. The reduction of APFO (1117 to 292 ppm on PTFE) was 74%. [0092] 9. The concentrated latex was used for metal coating application.

Example 3

[0093] An aqueous dispersion of PTFE with trace commoner PPVE containing 20.5 wt. % by weight of modified PTFE, 66 ppm of APFO (322 ppm of APFO based on the weight of PTFE), and having a pH of 3.5 was processed as follows: [0094] 1. The raw latex was stabilized with 18 wt. % of Triton X-100. 0.25 ml of NH4OH (30 wt. % aqueous solution) was added to adjust the pH. [0095] 2. It was then transferred into a lab Thermal Concentrator, which was connected to a circulating temperature control bath with maximum temperature set at 80° C. [0096] 3. The dispersion was slowly heated up from room temperature with no agitation. [0097] 4. Heating continued until temperature reached about 72° C. [0098] 5. The temperature was maintained between 70 and 75° C. until phase separation was complete. [0099] 6. The concentrated latex contained 71.8 wt. % PTFE, 4 wt. % Triton X-100 and 108 ppm of APFO (150 ppm of APFO by weight of PTFE). [0100] 7. The supematant was drained into a separate container for future recycling. [0101] 8. The reduction of APFO (322 to 150 ppm on PTFE) was 53%. [0102] 9. The concentrated latex was used for metal coating application.