PROCESS FOR PRODUCING POLYTETRAFLUOROETHYLENE FINE POWDER

• US 20140343239A1
• Filed: 08/01/2014
• Published: 11/20/2014
• Est. Priority Date: 02/02/2012
• Status: Abandoned Application

• Current Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Inventors: HIGUCHI, Shinya, Kobayashi, Shigeki, Nagai, Hiroki
• Application Number:
  US14/449,436
• Publication Number:
  US 20140343239A1
• Time in Patent Office: Days
• US Class Current: 526/255
• CPC Class Codes: C08F 114/26 Tetrafluoroethene
• CPC Class Codes: C08F 2/24 with the aid of emulsifying agents
• CPC Class Codes: C08F 6/18 Increasing the size of the dispersed particles
• CPC Class Codes: C08F 6/22 Coagulation
• CPC Class Codes: C08J 3/16 by coagulating dispersions C08J3/122 takes precedence
• CPC Class Codes: C08L 27/18 Homopolymers or copolymers or tetrafluoroethene

Abstract

To provide a process for producing a PTFE fine powder having a high bulk density, whereby the concentration of non-coagulated PTFE in coagulation wastewater is low.

Tetrafluoroethylene is emulsion-polymerized in the presence of an aqueous medium, at least one fluorinated emulsifier selected from the group consisting of a C_4-7 fluorinated carboxylic acid having from 1 to 4 etheric oxygen atoms in its main chain, and its salts, and a radical polymerization initiator, to produce a polytetrafluoroethylene emulsion; the obtained polytetrafluoroethylene emulsion is adjusted to a polytetrafluoroethylene concentration of from 10 to 25 mass %, followed by coagulation and stirring at a coagulation temperature of from 5 to 18° C. to separate a wet-state polytetrafluoroethylene fine powder; and the obtained wet-state polytetrafluoroethylene fine powder is dried to produce a polytetrafluoroethylene fine powder.

Claims

1. A process for producing a polytetrafluoroethylene fine powder, which comprises

emulsion-polymerizing tetrafluoroethylene in the presence of an aqueous medium, at least one fluorinated emulsifier selected from the group consisting of a C_4-7 fluorinated carboxylic acid having from 1 to 4 etheric oxygen atoms in its main chain, and its salts, and a radical polymerization initiator, to produce a polytetrafluoroethylene emulsion,

adjusting the obtained polytetrafluoroethylene emulsion to a polytetrafluoroethylene concentration of from 10 to 25 mass %, followed by coagulation and stirring at a coagulation temperature of from 5 to 18°

C. to separate a wet-state polytetrafluoroethylene fine powder, and

drying the obtained wet-state polytetrafluoroethylene fine powder to produce a polytetrafluoroethylene fine powder.

2. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the coagulation and stirring of the polytetrafluoroethylene emulsion is carried out without using a coagulant.

3. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the bulk density of the polytetrafluoroethylene fine powder is at least 500 g/L.

4. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the standard specific gravity of the polytetrafluoroethylene fine powder is from 2.135 to 2.220.

5. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the emulsion polymerization of tetrafluoroethylene is conducted under emulsion polymerization conditions of a polymerization temperature of from 10 to 95°

C., a polymerization pressure of from 0.5 to 4.0 MPa and a polymerization time of from 90 to 520 min., to produce the polytetrafluoroethylene emulsion.

6. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the concentration of non-coagulated polytetrafluoroethylene in coagulation wastewater having the wet-state polytetrafluoroethylene fine powder separated by the coagulation and stirring, is less than 0.4 mass %.

7. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the fluorinated emulsifier is CF₃O(CF₂)₃OCHFCF₂COONH₄, CF₃OCF(CF₃)CF₂OCF(CF₃)COONH₄, C₃F₇OCF(CF₃)COONH₄ or C₂F₅OCF₂CF₂OCF₂ COONH₄.

8. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the amount of the fluorinated emulsifier used, is from 1,500 to 20,000 ppm to the yield of polytetrafluoroethylene.

9. The process for producing a polytetrafluoroethylene fine powder according to claim 1, wherein the drying of the wet-state polytetrafluoroethylene fine powder is carried out in an atmosphere containing ammonia.