# US 10,870,735 B2 · Method for producing low molecular weight polytetrafluoroethylene, low molecular weight polytetrafluoroethylene, and powder

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- Number: US 10,870,735 B2
- Document ID: US10870735B2
- Status: Granted
- Kind: B2
- Application number: 16/069,735
- Filed: 2017-08-04
- Published: 2019-01-24
- Granted: 2020-12-22
- Earliest claimed: 2016-08-04
- Assignees: Daikin Industries, Ltd.
- Applicants: Daikin Industries, Ltd.
- Inventors: Ken Yoshida; Hirotoshi Yoshida; Keisuke Hagi; Masayuki Tsuji; Taketo Kato; Yuuji Tanaka; Taku Yamanaka; Kazuya Kawahara; Masamichi Sukegawa; Kazutaka Hosokawa
- Web page: https://patentgrep.com/patent/US10870735B2

## CPC

- C08J 3/12: Powdering or granulating
- C08F 8/06: Oxidation
- C08F 8/50: Partial depolymerisation
- C08F 14/26: Tetrafluoroethene
- C08J 3/28: Treatment by wave energy or particle radiation
- C08F 2500/07: High density, i.e. > 0.95 g/cm3
- C08F 2500/17: Viscosity
- C08F 2800/20: as weight or mass percentages
- C08F 2810/40: taking place solely at one end or both ends of the polymer backbone, i.e. not in the side or lateral chains
- C08J 2327/18: Homopolymers or copolymers of tetrafluoroethylene
- C08J 2327/22: modified by chemical after-treatment
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS

## Abstract

The invention provides a production method for producing low molecular weight polytetrafluoroethylene enabling easy removal of most of C8-C14 perfluorocarboxylic acids and salts thereof, which are unfortunately generated by irradiation, from the low molecular weight polytetrafluoroethylene. The method for producing low molecular weight polytetrafluoroethylene includes: (1) irradiating polytetrafluoroethylene to provide low molecular weight polytetrafluoroethylene having a melt viscosity of 1×102 to 7×105 Pa·s at 380° C.; (2) pulverizing the low molecular weight polytetrafluoroethylene; and (3) heating the low molecular weight polytetrafluoroethylene pulverized in the step (2).

## Claims

### Claim 1

A method for producing low molecular weight polytetrafluoroethylene, comprising:
(1) irradiating polytetrafluoroethylene at a dose of 10-750 kGy to provide low molecular weight polytetrafluoroethylene having a melt viscosity of 1×102 to 7×105 Pa·s at 380° C.;
(2) pulverizing the low molecular weight polytetrafluoroethylene;
(3) heating the low molecular weight polytetrafluoroethylene pulverized in the step (2), wherein the heating is performed at a temperature of 100° C. to 300° C. for 10 minutes to 5 hours; and
(4) heating the polytetrafluoroethylene up to a temperature that is not lower than the primary melting point thereof to provide a molded article before the step (1), wherein the molded article has a specific gravity of 1.0 g/cm3 or higher, and the molded article is used as the polytetrafluoroethylene in the step (1).

### Claim 2 (depends on 1)

The production method according to claim 1,
wherein the heating is performed at a temperature of 100° C. to 200° C.

### Claim 3 (depends on 1)

The production method according to claim 1,
wherein the polytetrafluoroethylene has a standard specific gravity of 2.130 to 2.230.

### Claim 4 (depends on 1)

The production method according to claim 1,
wherein both the polytetrafluoroethylene and the low molecular weight polytetrafluoroethylene are in the form of powder.