JP-2026075087-A - Manufacturing method for recycled pellets

Abstract

[Problem] To provide a manufacturing method that can produce recycled pellets in which the content of hydrophilic fluorine-containing compounds is reduced, using a fluoropolymer containing at least one fluorine-containing ether monomer unit selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units as a recycled material. [Solution] A method for producing recycled pellets containing a fluoropolymer containing at least one fluorine-containing ether monomer unit selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units is provided, wherein a molded body containing the fluoropolymer is melt-molded at a temperature above the melting point of the fluoropolymer to produce pellets, and the pellets are heat-treated at a temperature below the melting point of the fluoropolymer to produce recycled pellets. [Selection Diagram] None

Inventors

• 山本 有香里
• 村上 眞司
• 加藤 丈人
• 藤澤 学

Assignees

• ダイキン工業株式会社

Dates

Publication Date

20260507

Application Date

20251021

Priority Date

20241021

Claims (11)

1. A method for producing recycled pellets containing a fluoropolymer containing at least one fluorine-containing ether monomer unit selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units, A pellet is produced by melt-molding a molded body containing the fluoropolymer at a temperature above the melting point of the fluoropolymer. A method for producing recycled pellets by heat-treating the pellets at a temperature below the melting point of the fluoropolymer.
2. The manufacturing method according to claim 1, wherein the molded body is crushed and the crushed molded body is melt-molded to produce the pellets.
3. The manufacturing method according to claim 1 or 2, wherein the molded body is a molten molded body.
4. The manufacturing method according to claim 1 or 2, wherein the molded article is at least one selected from the group consisting of an extruded article, an injection-molded article, a blow-molded article, and a transfer-molded article.
5. The manufacturing method according to claim 1 or 2, wherein the molded body is a molten molded body, and the pellets are produced by crushing the molten molded body and then molten-molding the crushed molded body.
6. The manufacturing method according to claim 1 or 2, wherein the temperature of the heat treatment is 150°C or higher.
7. The manufacturing method according to claim 1 or 2, wherein the heat treatment time is 10 minutes to 48 hours.
8. The manufacturing method according to claim 1 or 2, wherein the content of the fluorine-containing ether monomer units is 1.0 to 12.0% by mass.
9. The manufacturing method according to claim 1 or 2, wherein the fluoropolymer is at least one selected from the group consisting of tetrafluoroethylene/fluorine-containing ether monomer copolymers and tetrafluoroethylene/hexafluoropropylene/fluorine-containing ether monomer copolymers.
10. The manufacturing method according to claim 1 or 2, wherein the pellet obtained by melt molding contains, with respect to the mass of the pellet, 5 ppb by mass or more of a fluorine-containing compound having a hydrophilic group represented by the general formula: [C 5 F 11 COO - ] M + (wherein M + represents a cation).
11. The manufacturing method according to claim 1 or 2, wherein the recycled pellet contains a fluorine-containing compound having a hydrophilic group represented by the general formula: [C 5 F 11 COO - ] M + (wherein M + represents a cation) in an amount of less than 5 ppb by mass with respect to the mass of the recycled pellet.

Description

This disclosure relates to a method for producing recycled pellets of fluoropolymers. Patent Document 1 describes a method for recycling waste fluororesin molded products, characterized by washing the waste fluororesin molded product with a cleaning solution, drying it, and then melt-extruding it to obtain recycled fluororesin pellets. Japanese Patent Application Publication No. 11-30074 The following describes specific embodiments of this disclosure in detail, but this disclosure is not limited to the embodiments described below. This disclosure relates to a method for producing recycled pellets of fluoropolymers, and more particularly to a method for producing recycled pellets of fluoropolymers containing at least one fluorine-containing ether monomer unit selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units. Technologies for recycling scraps generated during the manufacturing of fluoropolymer molded products, as well as used fluoropolymer molded products, into pellets, are needed from the perspective of efficient resource utilization and reduction of waste volume. Patent Document 1 describes the production of pellets using a fluororesin film (a copolymer of tetrafluoroethylene and ethylene copolymerized in a 53/47 molar ratio, 30 μm thick) that had been used for a long period as a covering material for agricultural greenhouses and had a hydrophilic coating containing silica on one side, as waste fluororesin. The copolymer forming this waste fluororesin does not contain fluorine-containing ether monomer units. When pellets are regenerated using a molded article containing a fluoropolymer that includes at least one fluorine-containing ether monomer unit selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units, the regenerated pellets may contain fluorine-containing compounds having hydrophilic groups, such as compounds represented by the general formula: [C 5 F 11 COO - ] M + (wherein M + represents a cation). This is presumed to be because, during pelletization, heat and shear forces are applied to the fluoropolymer, making the C-O bonds in the fluorine-containing ether monomer units more susceptible to cleavage. Therefore, it is presumed that fluoropolymers containing fluorine-containing ether monomer units are more likely to generate hydrophilic fluorine-containing compounds under the heat and shear forces of melt molding required for the production of recycled pellets, compared to fluoropolymers that do not contain fluorine-containing ether monomer units, such as copolymers of tetrafluoroethylene and ethylene. In other words, the manufacturing method of this disclosure is a method for producing recycled pellets containing a fluoropolymer containing at least one fluorine-containing ether monomer unit selected from the group consisting of perfluorovinyl ether units and perfluoroallyl ether units, wherein a molded body containing the fluoropolymer is melt-molded at a temperature above the melting point of the fluoropolymer to produce pellets, and the pellets are then heat-treated at a temperature below the melting point of the fluoropolymer to produce the recycled pellets. Next, the manufacturing method of this disclosure will be described in more detail. (Pellet preparation) In the manufacturing method of this disclosure, pellets are produced by melt-molding a molded article containing a fluoropolymer at a temperature above the melting point of the fluoropolymer. There are no particular limitations on the melt molding method, and conventionally known methods can be used. For example, a single-screw extruder, twin-screw extruder, or tandem extruder can be used for melt molding. In one embodiment, a molded body containing a fluoropolymer is melted using an extruder, extruded, and cut to a predetermined length to produce pellets. When extruding a molded article containing a fluoropolymer by melt extrusion, heat is typically applied to the molded article to melt it, and then shear force is applied to the molten fluoropolymer. According to the manufacturing method of this disclosure, even when pellets are produced by applying heat and shear force to a fluoropolymer containing fluorine-containing ether monomer units, the content of fluorine-containing compounds having hydrophilic groups can be reduced by subsequent heat treatment. The extrusion temperature during melt extrusion needs to be adjusted depending on the melt viscosity of the copolymer and the manufacturing method, preferably between the melting point of the fluoropolymer + 20°C and the melting point of the fluoropolymer + 140°C. There are no particular limitations on the cutting method of the melt extruded material; conventionally known methods such as strand cutting, hot cutting, underwater cutting, and sheet cutting can be employed. The shape of the pellets obtained by melt molding is not particularly limited and may be any shape typically found in fluoropolymer pel