Method for producing fluorinated polymer particles

1. A method for producing fluorinated polymer particles comprising the following (i) and (ii), being a method for producing particles of a fluorinated polymer (A) which has either one or both of structural units (u1) derived from tetrafluoroethylene and structural units (u2) having no sulfonic acid type functional group and having a cyclic structure and fluorine atoms, and which has structural units (u3) having a sulfonic acid type functional group, wherein the proportion of the structural units (u1) is from 0 to 82 mol % in all structural units (100 mol %) in the fluorinated polymer (A),

the method comprising:

(i) preparing a solution or dispersion of the fluorinated polymer (A) having the above fluorinated polymer (A) dissolved or dispersed in a solvent (B), wherein the following conditions (i-1) and (i-2) are satisfied:

(i-1) the solvent (B) comprises a solvent (B2) wherein the solubility of the fluorinated polymer (A) is at least 30%, and

(i-2) even when the above solution or dispersion of the fluorinated polymer (A) is passed through a filter of 200 mesh made of stainless steel, no residue remains on the filter; and

(ii) mixing the solution or dispersion of the fluorinated polymer (A) and a solvent (C) to aggregate the fluorinated polymer (A) to form particles of the fluorinated polymer (A), wherein the following conditions (ii-1) to (ii-3) are satisfied:

(ii-1) the solvent (C) comprises a solvent (C1) whereby the degree of swelling of the fluorinated polymer (A) is at most 100%,

(ii-2) the degree of swelling of the fluorinated polymer (A) by a mixed solvent (BC) of the solvent (B) and the solvent (C) is from 70 to 250%, and

(ii-3) the ratio (W C /W B ) of the mass (W C ) of the solvent (C) to the mass (W B ) of the solvent (B) is from 1 to 5.

2. The method for producing fluorinated polymer particles according to claim 1 , wherein the degree of swelling of the fluorinated polymer (A) by the solvent (BC) is from 80 to 250%.

3. The method for producing fluorinated polymer particles according to claim 1 , wherein the degree of swelling of the fluorinated polymer (A) by the solvent (BC) is from 105 to 250%.

4. The method for producing fluorinated polymer particles according to claim 1 , wherein the solvent (B2) is a hydrofluorocarbon.

5. The method for producing fluorinated polymer particles according to claim 1 , wherein the solvent (B2) is either one or both of C 6 F 13 H and CF 3 CFHCFHCF 2 CF 3 .

6. The method for producing fluorinated polymer particles according to claim 1 , wherein the solvent (C1) is at least one selected from the group consisting of hydrofluoroethers, hydrofluorocarbons, non-fluorinated alcohols, hydrocarbons and fluorinated alcohols.

7. The method for producing fluorinated polymer particles according to claim 1 , wherein the solvent (C1) is at least one selected from the group consisting of CF 3 CH 2 OCF 2 CF 2 H, CHF 2 CH 2 CF 3 , CF 3 CH 2 CF 2 CH 3 , methanol, hexane, CF 3 CF 2 CH 2 OH,CF 3 CH 2 OH and H(CF 2 ) 4 CH 2 OH.

8. The method for producing fluorinated polymer particles according to claim 1 , wherein the solvent (C1) is at least two selected from the group consisting of hydrofluoroethers, hydrofluorocarbons, non-fluorinated alcohols, hydrocarbons and fluorinated alcohols.

9. The method for producing fluorinated polymer particles according to claim 1 , wherein the degree of swelling of the fluorinated polymer (A) by the solvent (BC), is adjusted by the mixing ratio of at least two of the solvent (C1).

10. The method for producing fluorinated polymer particles according to claim 1 , wherein the degree of swelling of the fluorinated polymer (A) by the solvent (BC), is adjusted by the temperature of the solvent (C) immediately before mixing it with the solution or dispersion of the fluorinated polymer (A) in the (ii) mixing.

11. The method for producing fluorinated polymer particles according to claim 1 , wherein the temperature of the solvent (C) immediately before mixing it with the solution or dispersion of the fluorinated polymer (A) in the (ii) mixing is within a range of from −15 to 30° C.

12. The method for producing fluorinated polymer particles according to claim 1 , wherein in all structural units (100 mol %) in the fluorinated polymer (A), the proportion of the structural units (u1) is from 35 to 82 mol %, the proportion of the structural units (u2) is at least 0 mol % and less than 30 mol %, and the proportion of the structural units (u3) is from 18 to 35 mol %.

13. The method for producing fluorinated polymer particles according to claim 12 , wherein the degree of swelling of the fluorinated polymer (A) by the solvent (BC) is from 70 to 200%.

14. The method for producing fluorinated polymer particles according to claim 1 , wherein in all structural units (100 mol %) in the fluorinated polymer (A), the proportion of the structural units (u1) is from 0 to 60 mol %, the proportion of the structural units (u2) is from 20 to 85 mol %, and the proportion of the structural units (u3) is from 10 to 35 mol %.

15. The method for producing fluorinated polymer particles according to claim 14 , wherein the degree of swelling of the fluorinated polymer (A) by the solvent (BC) is from 105 to 250%.

16. The method for producing fluorinated polymer particles according to claim 1 , wherein following the (i) preparing and (ii) mixing, the fluorinated polymer (A) is separated and recovered.

17. The method for producing fluorinated polymer particles according to claim 1 , wherein the ion-exchange capacity of a polymer having the sulfonic acid type functional groups of the fluorinated polymer (A) converted to ion exchange groups, is from 0.9 to 2.5 meq/g dry resin.