# US 11,028,239 B2 · Manufacturing method for low molecular weight polytetrafluoroethylene, and powder

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- Number: US 11,028,239 B2
- Document ID: US11028239B2
- Status: Granted
- Kind: B2
- Application number: 16/967,875
- Filed: 2019-02-05
- Published: 2021-01-14
- Granted: 2021-06-08
- Earliest claimed: 2018-02-07
- Assignees: Daikin Industries, Ltd.
- Applicants: Daikin Industries, Ltd.
- Inventors: Masayuki Tsuji; Hirotoshi Yoshida
- Web page: https://patentgrep.com/patent/US11028239B2

## CPC

- C08J 3/28: Treatment by wave energy or particle radiation
- C08F 8/50: Partial depolymerisation
- C08F 114/26: Tetrafluoroethene
- C08J 3/12: Powdering or granulating
- C08J 2327/18: Homopolymers or copolymers of tetrafluoroethylene
- 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

Provided is a method for producing low molecular weight polytetrafluoroethylene less likely to generate C6-C14 perfluorocarboxylic acids and salts thereof. The method for producing low molecular weight polytetrafluoroethylene includes: (1) feeding into an airtight container: high molecular weight polytetrafluoroethylene: and a gas mixture containing an inert gas and oxygen and having an oxygen content relative to the total of the inert gas and oxygen of 1 to 10 vol %; and (2) irradiating the high molecular weight polytetrafluoroethylene to provide low molecular weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×102 to 7.0×105 Pa·s.

## Claims

### Claim 1

A method for producing low molecular weight polytetrafluoroethylene, comprising:
(1) feeding into an airtight container:
high molecular weight polytetrafluoroethylene: and
a gas mixture containing an inert gas and oxygen and having an oxygen content relative to the total of the inert gas and oxygen of 1 to 5 vol %; and
(2) irradiating the high molecular weight polytetrafluoroethylene to provide low molecular weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×102 to 7.0×105 Pa·s,
wherein the low molecular weight polytetrafluoroethylene contains perfluorooctanoic acid and salts thereof in a total amount by mass of not more than 20 ppb.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

The production method according to claim 1, further comprising:
(3) heating the high molecular weight polytetrafluoroethylene up to a temperature that is not lower than the primary melting point thereof to provide a molded article before the step (1),
the molded article having a specific gravity of 1.0 g/cm3 or higher.

### Claim 5

Powder comprising low molecular weight polytetrafluoroethylene,
the low molecular weight polytetrafluoroethylene having a melt viscosity at 380° C. of 1.0×102 to 7.0×105 Pa·s and containing 30 or more carboxyl groups at ends of the molecular chain per 106 carbon atoms in the main chain,
the powder containing perfluorooctanoic acid and salts thereof in a total amount of not less than 5 ppb but not more than 20 ppb.