Manufacturing method for recycled pellets

Abstract

To provide a manufacturing method for producing 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.

Description

[Technical Field]

[0001] This disclosure relates to a method for producing recycled pellets of fluoropolymers. [Background technology]

[0002] Patent Document 1 describes a method for recycling waste fluororesin molded products, characterized by washing the waste molded product made of fluororesin with a cleaning solution, drying it, and then melt-extruding it to obtain recycled fluororesin pellets. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-30074 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present disclosure aims to provide a manufacturing method for producing 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. [Means for solving the problem]

[0005] According to this disclosure, 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. [Effects of the Invention]

[0006] According to this disclosure, a manufacturing method is provided for producing 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. [Modes for carrying out the invention]

[0007] The following describes specific embodiments of this disclosure in detail, but this disclosure is not limited to the embodiments described below.

[0008] 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.

[0009] 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.

[0010] 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) with a hydrophilic coating containing silica on one side, which had been used for a long period as a covering material for agricultural greenhouses, as waste fluororesin. The copolymer forming this waste fluororesin does not contain fluorine-containing ether monomer units.

[0011] When pellets are regenerated using a molded article containing a fluoropolymer that contains 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, the recycled pellets contain the general formula: [C5F 11 COO - ]M + Compounds represented by the formula (wherein M + The symbol represents a cation. Fluorine-containing compounds with hydrophilic groups, such as ( ), may be included.

[0012] This is presumed to be because, during pelletization, heat and shear forces are applied to the fluoropolymer, making it easier for the CO bonds in the fluorine-containing ether monomer units to break. Therefore, it is presumed that fluoropolymers containing fluorine-containing ether monomer units are more likely to generate hydrophilic fluorine-containing compounds with hydrophilic groups due to the heat and shear forces required for melt molding during the production of recycled pellets, compared to fluoropolymers that do not contain fluorine-containing ether monomer units, such as copolymers of tetrafluoroethylene and ethylene.

[0013] In other words, the manufacturing method of the present 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 heat-treated at a temperature below the melting point of the fluoropolymer to produce recycled pellets.

[0014] Next, the manufacturing method of this disclosure will be described in more detail.

[0015] (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.

[0016] There are no particular limitations on the melt molding method, and conventionally known methods can be used. For example, a single-screw extruder, a twin-screw extruder, a tandem extruder, etc., 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.

[0017] When extruding a molded article containing a fluoropolymer by melt extrusion, heat is usually 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.

[0018] The extrusion temperature during melt extrusion needs to be adjusted depending on the melt viscosity of the copolymer and the manufacturing method, and is 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 method of cutting the melt extruded material, and conventionally known methods such as strand cutting, hot cutting, underwater cutting, and sheet cutting can be employed.

[0019] The shape of the pellets obtained by melt molding is not particularly limited and may be any shape that fluoropolymer pellets typically have. For example, the pellets may be disc-shaped or cylindrical with a diameter of 0.3 to 10.0 mm, preferably 0.5 to 7.0 mm, more preferably 1.0 to 5.0 mm, and a height (thickness) of 0.3 to 10.0 mm, preferably 0.5 to 7.0 mm, more preferably 1.0 to 5.0 mm.

[0020] In the manufacturing method of this disclosure, a molded article containing a fluoropolymer may be supplied to an extruder without pulverization and melt-molded to produce pellets, or the molded article containing the fluoropolymer may be pulverized before melt-molding, and the pulverized molded article may be melt-molded.

[0021] Crushing refers to the process of dividing raw materials using energy to reduce their size (volume). Examples of energy sources include compression, impact, collision, shear, and abrasion. Examples of crushing by compression include jaw crushers, gyrant rerry crushers, cone crushers, and roll crushers. Examples of crushing by collision include hammer mills, pin mills, and mill grinders. Examples of crushing by collision include jet mills and ball mills. Examples of crushing by shear include single-screw pusher crushers, granulators, plastic runner crushers, cutter mills, shredders, and guillotine cutters. Examples of crushing by abrasion include disc mills and millstones. Some of these processes involve not just one type of energy but a combination of multiple energies. Fluoropolymers are soft and tend to stretch thinly when subjected to friction under stress, so shear-type crushing is preferable as it minimizes this stretching. Among shear-type crushing machines, single-screw pusher crushers, granulators, and plastic runner crushers are preferred because they minimize friction while applying stress.

[0022] The crushing process may be performed once, or it may be repeated until a molded body of the desired shape can be produced. The crushed molded body may also be classified by known methods such as airflow classification.

[0023] The shape of the crushed molded body is not particularly limited and may be particulate, granular, or other shapes. The maximum length of a single piece of the crushed molded body is not particularly limited as long as it can be fed into the extruder, but may be, for example, 0.1 to 50 mm or 1 to 15 mm.

[0024] The pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group. The hydrophilic group of the fluorine-containing compound is preferably anionic, such as an acidic group, for example, -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, and -COOM (where M represents a cation in each formula). Among these hydrophilic groups, -SO3M or -COOM are preferred, with -COOM being more preferred. As for the cation, H +, examples include ammonium ions, alkali metal ions, alkaline earth metal ions, etc.

[0025] In one embodiment, the pellets obtained by melt molding contain, as a fluorine-containing compound having a hydrophilic group, a compound represented by the following general formula (H1). General formula (H1): [X-Rf-A - i M i+ (where X is H, Cl, Br, F or I, Rf is a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, A - is an acid group, M i+ is a cation having a valence i, and i represents an integer from 1 to 3)

[0026] In one embodiment, the pellets obtained by melt molding contain, as a fluorine-containing compound having a hydrophilic group, a compound represented by the following general formula (H2). General formula (H2): [C n-1 F 2n-1 COO - M + (where n is an integer from 4 to 14, and M + represents a cation.)

[0027] In one embodiment, the pellets obtained by melt molding contain, as a fluorine-containing compound having a hydrophilic group, a compound represented by the following general formula (H3). General formula (H3): [R 1 -O-L-CO2 - M + (where R 1 is a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, L is a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group, M +(This represents a cation.)

[0028] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, represented by the general formula (H4). General formula (H4):H-Rf n0 -Y 0 (In the formula, Rf n0 This is an alkylene group having 3 to 20 carbon atoms, being linear, branched, or cyclic, in which some or all of the hydrogen atoms are substituted with fluorine, and the alkylene group may contain one or more ether bonds, and some of the hydrogen atoms may be substituted with chlorine. 0 (This is an anionic group.)

[0029] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, represented by the following general formula (H5). General formula (H5):[A - -Rf h0 -A - ] i M k+ M l+ (In the formula, Rf h0 This refers to a partially fluorinated or fully fluorinated aliphatic group of a linear or branched chain, or a partially fluorinated or fully fluorinated aliphatic group of a linear or branched chain interrupted by at least one oxygen atom, A - is an acid group, M k+ M is a cation having a valency k. l+ (where i is a cation with a valency of l, i is an integer between 1 and 3, and k and l are integers between 0 and 3, never both being 0, and representing integers such that k + l = i.)

[0030] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, which is represented by the following general formula (H6). General formula (H6):[ - OCOC n-1 F 2n-2 COO - ]M1 + M2+ (In the formula, n is an integer between 4 and 14, M1 + M2 + (This represents a cation.)

[0031] The content of the hydrophilic fluorine-containing compound in the pellets obtained by melt molding may be 5 ppb or more by mass, 15 ppb or more by mass, 25 ppb or more by mass, 30 ppb or more by mass, 35 ppb or more by mass, 40 ppb or more by mass, 45 ppb or more by mass, or 50 ppb or more by mass, and may be 1000 ppb or less by mass, or 500 ppb or less by mass.

[0032] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, which is represented by the following general formula. General formula: [C5F 11 COO - ]M + (In the formula, M + (This represents a cation.)

[0033] General formula in pellets obtained by melt molding: [C5F 11 COO - ]M + The content of the compound represented by may be 5 ppb by mass or more, 15 ppb by mass or more, 25 ppb by mass or more, 30 ppb by mass or more, 35 ppb by mass or more, 40 ppb by mass or more, 45 ppb by mass or more, or 50 ppb by mass or more, and may be 1000 ppb by mass or less, or 500 ppb by mass or less.

[0034] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, which is represented by the following general formula. General formula: [C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer between 8 and 14, M + (This represents a cation.)

[0035] The general formula in pellets obtained by melt molding is: [C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer between 8 and 14, M + ' represents a cation.' The content of the compound represented by ') may be 1 ppb by mass or more, 2 ppb by mass or more, 3 ppb by mass or more, 4 ppb by mass or more, or 5 ppb by mass or more, and may be 1000 ppb by mass or less, or 500 ppb by mass or less.

[0036] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, which is represented by the following general formula. General formula: [C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer between 11 and 14, M + (This represents a cation.)

[0037] The general formula in pellets obtained by melt molding is: [C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer between 11 and 14, M + ' represents a cation.' The content of the compound represented by ') may be 1 ppb by mass or more, 2 ppb by mass or more, 3 ppb by mass or more, 4 ppb by mass or more, or 5 ppb by mass or more, and may be 1000 ppb by mass or less, or 500 ppb by mass or less.

[0038] The content of hydrophilic fluorine-containing compounds in pellets can be quantified by known methods. For example, it can be quantified by LC / MS analysis. First, the pellets are freeze-milled to prepare a powder. Methanol is added to the resulting powder, and extraction is performed. The resulting extract is then analyzed by LC / MS. To further improve the extraction efficiency, treatments such as Soxhlet extraction and sonication may be performed. The resulting extract is concentrated by nitrogen purging as appropriate, and the fluorine-containing compounds in the concentrated extract are measured by LC / MS. From the obtained LC / MS spectrum, molecular weight information is extracted and its agreement with the structural formula of a candidate fluorine-containing compound having a hydrophilic group is confirmed. Subsequently, aqueous solutions containing five or more levels of the identified hydrophilic fluorine-containing compound were prepared. LC / MS analysis was performed on each aqueous solution with its respective content, and the relationship between the content and the area of ​​the solution was plotted to create a calibration curve. Furthermore, using a calibration curve, the area of ​​the LC / MS chromatogram of the hydrophilic fluorine-containing compound in the extract can be converted to the content of the hydrophilic fluorine-containing compound. Furthermore, since the obtained extract can be concentrated by purging it with nitrogen, the lower limit of quantification in the measurement method can be lowered.

[0039] (Heat treatment) In the manufacturing method of this disclosure, recycled pellets are produced by heat-treating the pellets at a temperature below the melting point of the fluoropolymer.

[0040] The heat treatment temperature is below the melting point of the fluoropolymer. By performing heat treatment at a temperature below the melting point of the fluoropolymer, the content of fluorine-containing compounds with hydrophilic groups can be reduced while maintaining the pellet shape.

[0041] The heat treatment temperature is preferably below the melting point of the fluoropolymer -10°C, more preferably below the melting point of the fluoropolymer -50°C, even more preferably below the melting point of the fluoropolymer -100°C, preferably above 50°C, more preferably above 100°C, even more preferably above 150°C, and still more preferably above 180°C. In one embodiment, the heat treatment temperature may be 300°C or less, 260°C or less, or less than 230°C.

[0042] The heat treatment time is not particularly limited as long as it is longer than the time it takes for the center of the pellet to reach that temperature, but is preferably 10 minutes to 48 hours, more preferably 1 hour or more, even more preferably 3 hours or more, even more preferably 6 hours or more, and more preferably 24 hours or less. The heat treatment time may also be 20 minutes or more, 30 minutes or more, 40 minutes or more, or 50 minutes or more.

[0043] The heat treatment can be carried out in air or an inert gas. In one embodiment, the pellets can be heat-treated by bringing them into contact with hot air. In one embodiment, the pellets can be heat-treated by leaving them in a heat treatment apparatus. In one embodiment, the pellets can be heat-treated while leaving them in a heat treatment apparatus and circulating hot air through them. As the heat treatment apparatus, an electric furnace, a constant temperature bath, a dryer, a heat treatment furnace, etc., can be used. In one embodiment, the pellets can be continuously supplied to and discharged from the heat treatment apparatus while hot air is supplied into the apparatus, and the pellets can be left in the apparatus for a certain period of time to perform the heat treatment. In one embodiment, the pellets can be heat-treated by irradiating them with microwaves. In one embodiment, the pellets can be heat-treated by airflow drying supplied with hot air.

[0044] (Recycled material) In the manufacturing method of this disclosure, a molded article 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 used as the recycled material.

[0045] In the manufacturing method of this disclosure, the fluoropolymer used as the recycled material is melt-processable and is typically a melt-processable fluororesin. Melt-processability means that the polymer can be melted and processed using conventional processing equipment such as extruders and injection molding machines.

[0046] The perfluorovinyl ether unit is a monomer unit based on perfluorovinyl ether. Examples of perfluorovinyl ether include: General formula (1): CF2=CF-ORf 1 (In the formula, Rf 1 ) represents a perfluoroorganic group. Examples include fluoromonomers represented by ).

[0047] The perfluoroorganic group is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, preferably a perfluoroalkyl group having 1 to 6 carbon atoms, and preferably a perfluoroalkyl group having 1 to 3 carbon atoms. Examples of perfluoroorganic groups include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group.

[0048] As the perfluorovinyl ether, at least one selected from the group consisting of perfluoro(methyl vinyl ether) (CF2=CF-O-CF3), perfluoro(ethyl vinyl ether) (CF2=CF-O-C2F5), and perfluoro(propyl vinyl ether) (CF2=CF-O-C3F7) is preferred, and at least one selected from the group consisting of perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether) is more preferred.

[0049] The perfluoroallyl ether unit is a monomer unit based on perfluoroallyl ether. Perfluoroallyl ethers include: General formula (2): CF2=CF-CF2-ORf 2 (In the formula, Rf 2 ) represents a perfluoroorganic group. Examples include fluoromonomers represented by ).

[0050] Rf of general formula (2) 2 Rf of general formula (1) 1It is the same as above. As the perfluoroallyl ether, at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7 and CF2=CF-CF2-O-C4F9 is preferred, at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7 and CF2=CF-CF2-O-C4F9 is more preferred, and CF2=CF-CF2-O-CF2CF2CF3 is even more preferred.

[0051] As the fluoropolymer containing fluorine-containing ether monomer units, at least one selected from the group consisting of tetrafluoroethylene / fluorine-containing ether monomer copolymers and tetrafluoroethylene / hexafluoropropylene / fluorine-containing ether monomer copolymers is preferred.

[0052] The content of fluorine-containing ether monomer units in the fluoropolymer is preferably 0.1 to 12.0% by mass, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, still more preferably 1.5% by mass or more, particularly preferably 2.0% by mass or more, more preferably 10.0% by mass or less, and still more preferably 8.0% by mass or less, relative to the total monomer units of the fluoropolymer.

[0053] The content of fluorine-containing ether monomer units in the tetrafluoroethylene / fluorine-containing ether monomer copolymer is preferably 1.0 to 12.0% by mass, more preferably 1.5% by mass or more, even more preferably 2.0% by mass or more, still more preferably 2.5% by mass or more, more preferably 10.0% by mass or less, and still more preferably 8.0% by mass or less, relative to the total monomer units of the polymer.

[0054] The content of tetrafluoroethylene units in the tetrafluoroethylene / fluorine-containing ether monomer copolymer is preferably 88.0 to 99.0% by mass, more preferably 90.0% by mass or more, even more preferably 92.0% by mass or more, preferably 98.5% by mass or less, more preferably 98.0% by mass or less, and even more preferably 97.5% by mass or less, relative to the total monomer units of the polymer.

[0055] In one embodiment, the tetrafluoroethylene / fluorine-containing ether monomer copolymer does not contain hexafluoropropylene units, or contains less than 0.1% by mass of hexafluoropropylene units relative to the total monomer units of the polymer. In another embodiment, the tetrafluoroethylene / fluorine-containing ether monomer copolymer contains only tetrafluoroethylene units and fluorine-containing ether monomer units.

[0056] The content of fluorine-containing ether monomer units in the tetrafluoroethylene / hexafluoropropylene / fluorine-containing ether monomer copolymer is preferably 0.1 to 20.0% by mass, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, even more preferably 10.0% by mass or less, and even more preferably 3.0% by mass or less, relative to the total monomer units of the polymer.

[0057] The content of tetrafluoroethylene units in the tetrafluoroethylene / hexafluoropropylene / fluorine-containing ether monomer copolymer is preferably 70.0 to 99.8% by mass, more preferably 75.0% by mass or more, even more preferably 80.0% by mass or more, more preferably 98.0% by mass or less, and even more preferably 97.0% by mass or less, relative to the total monomer units of the polymer.

[0058] The content of hexafluoropropylene units in the tetrafluoroethylene / hexafluoropropylene / fluorine-containing ether monomer copolymer is preferably 0.1 to 25.0% by mass, more preferably 1.0% by mass or more, even more preferably 2.0% by mass or more, even more preferably 20.0% by mass or less, and even more preferably 15.0% by mass or less, relative to the total monomer units of the polymer.

[0059] Fluoropolymers may contain monomers other than fluorine-containing ether monomer units, tetrafluoroethylene units, and hexafluoropropylene units. Other monomers include vinyl fluoride, vinylidene fluoride, chlorotrifluoroethylene, and CZ. 1 Z 2 =CZ 3 (CF2) n Z 4 (In the formula, Z 1 , Z 2 and Z 3 These represent H or F, and Z, which are the same or different. 4 represents H, F, or Cl, and n represents an integer from 2 to 10. However, Z 1 ~Z 4 It is not possible for both to be F at the same time. ) The vinyl monomer represented by CF2 = CF-OCH2-Rf 3 (In the formula, Rf 3 represents a perfluoroalkyl group having 1 to 5 carbon atoms. Examples include alkyl perfluorovinyl ether derivatives represented by ), ethylene, and propylene. The content of other monomers is preferably 0 to 0.5% by mass, more preferably 0.05 to 0.3% by mass, and even more preferably 0.1 to 0.2% by mass, relative to the total monomer units of the polymer.

[0060] In this disclosure, the content of each monomer unit in the fluoropolymer is: 19 Measurement is performed using the 1F-NMR method.

[0061] The melt flow rate (MFR) of the fluoropolymer is preferably 0.1 g / 10 min or more, more preferably 0.5 g / 10 min or more, even more preferably 1.0 g / 10 min or more, preferably 100 g / 10 min or less, more preferably 90 g / 10 min or less, and even more preferably 80 g / 10 min or less.

[0062] In this disclosure, MFR is a value obtained in accordance with ASTM D1238 as the mass (g / 10 min) of polymer flowing out of a nozzle with an inner diameter of 2.1 mm and a length of 8 mm per 10 minutes using a melt indexer at 372°C and a load of 5 kg.

[0063] The melting point of the fluoropolymer is preferably 200°C or higher, more preferably 210°C or higher, even more preferably 220°C or higher, preferably 320°C or lower, and more preferably 315°C or lower.

[0064] The melting point of the tetrafluoroethylene / fluorine-containing ether monomer copolymer is preferably 280°C or higher, more preferably 285°C or higher, even more preferably 290°C or higher, preferably 320°C or lower, and more preferably 315°C or lower.

[0065] The melting point of the tetrafluoroethylene / hexafluoropropylene / fluorine-containing ether monomer copolymer is preferably 200°C or higher, more preferably 210°C or higher, even more preferably 220°C or higher, preferably 300°C or lower, more preferably 285°C or lower, and even more preferably 270°C or lower.

[0066] In this disclosure, the melting point can be measured using a differential scanning calorimetry (DSC).

[0067] In this disclosure, recycled material means "material that would otherwise be disposed of as waste or used for energy recovery purposes, but is instead collected and recovered [recycled] as a substitute for new raw materials for recycling or manufacturing processes" (JIS Q14021:2000, 7.8 Recycled material content 7.8.1 Usage of terms).

[0068] The shape of the molded fluoropolymer article (recycled material) used in the manufacturing method of this disclosure is not particularly limited and may be any shape. However, if the molded fluoropolymer article is too large or otherwise difficult to put into a molding machine or melt, it is preferable to crush it using the method described above and then melt-mold it.

[0069] Examples of fluoropolymer molded articles used in the manufacturing method of this disclosure include scraps and waste materials generated during the production of fluoropolymer molded articles, and used fluoropolymer molded articles. Examples of scraps and waste materials include: defective products resulting from molding fluoropolymers; sprues and runners generated during injection molding of fluoropolymers; waste materials generated from edge trimming and punching of fluoropolymer molded products; and waste materials generated from the start of molding until the shape of the extruded product stabilizes when manufacturing molded products such as sheets, tubes, and electric wires by extrusion molding of fluoropolymers. Examples of used fluoropolymer molded products include sheets, tubes, fittings, sealants, films, bottles, and wafer carriers. These may have been used in high-temperature environments, in contact with water or chemicals, or outdoors. If the used molded products are contaminated, they may be cleaned with a cleaning solution, dried, and reused as recycled materials. The molded body may be a molded body (excluding pellets). The maximum length of the molded body may be, for example, 0.1 mm to 100 cm, or 1 mm to 50 cm. Molded bodies that are too large can be crushed and then melt-molded.

[0070] The recycled material described above is typically a molten body obtained by melt-molding a fluoropolymer. It has now been found that when pellets are produced using a molten body containing a fluoropolymer with fluorine-containing ether monomer units as the recycled material, the resulting pellets contain a larger amount of fluorine-containing compounds with hydrophilic groups compared to the molten body. By using the manufacturing method of this disclosure, recycled pellets can be produced with a reduced content of fluorine-containing compounds with hydrophilic groups, even when a molten body is used as the recycled material.

[0071] Molding methods for producing molten articles include extrusion molding, injection molding, compression molding, blow molding, transfer molding, roto molding, and roto lining molding. In extrusion molding, injection molding, blow molding, and transfer molding, not only heat but also shear force is applied to the fluoropolymer, so the resulting molded article may contain a small amount of fluorine-containing compound having hydrophilic groups. In particular, injection molding tends to apply a large shear force to the fluoropolymer because it is necessary to fill every corner of the mold with fluoropolymer through a narrow gate before the resin cools and solidifies. According to the manufacturing method of this disclosure, even when an extruded article obtained by extruding a fluoropolymer, an injection-molded article obtained by injection molding a fluoropolymer, a blow-molded article obtained by blow molding a fluoropolymer, or a transfer-molded article obtained by transfer molding a fluoropolymer is used as a recycled material, recycled pellets with a reduced content of fluorine-containing compound having hydrophilic groups can be produced. These molten articles may also be crushed, and the crushed articles may be used as recycled materials.

[0072] In one embodiment, the molded article (recycled material) of the fluoropolymer contains components other than the fluoropolymer (hereinafter sometimes referred to as "other components"). In one embodiment, the molded article (recycled material) of the fluoropolymer substantially does not contain other components. In one embodiment, the molded article (recycled material) of the fluoropolymer contains no other components or contains only a trace amount (for example, less than 0.1% by mass or less than 0.01% by mass) of other components with respect to the mass of the molded article.

[0073] Examples of the other components include fillers, plasticizers, processing aids, mold release agents, pigments, flame retardants, lubricants, light stabilizers, weather stabilizers, conductive agents, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, fragrances, oils, softeners, dehydrofluorinating agents, and the like.

[0074] (Recycled pellets) According to the production method of the present disclosure, recycled pellets with a reduced content of the fluorine-containing compound having a hydrophilic group can be produced. The fluorine-containing compound having a hydrophilic group is as described above.

[0075] In one embodiment, the content of the compound represented by the general formula: [C5F 11 COO - M <​​​​​​​​​​​​​​​​​​​​​​F 2n-1 COO - ]M + (In the formula, n is an integer between 11 and 14, M + represents a cation. The content of the compound represented by ) is less than 5 ppb by mass, less than 4 ppb by mass, less than 3 ppb by mass, less than 2 ppb by mass, or less than 1 ppb by mass.

[0078] In one embodiment, the general formula in recycled pellets is: [ - OCOC n-1 F 2n-2 COO - ]M1 + M2 + (In the formula, n is an integer between 8 and 14, M1 + M2 + represents a cation. The content of the compound represented by ) is less than 5 ppb by mass, less than 4 ppb by mass, less than 3 ppb by mass, less than 2 ppb by mass, or less than 1 ppb by mass.

[0079] In the manufacturing method of this disclosure, since the heat treatment is performed under the conditions described above, the heat treatment can be performed without significantly changing the shape of the pellets. Therefore, the shape of the recycled pellets produced by the manufacturing method of this disclosure is the same as or substantially the same as the shape of the pellets subjected to heat treatment. The shape of the recycled pellets is not particularly limited and may be any shape that fluoropolymer pellets normally have. For example, they may be disc-shaped or cylindrical pellets with a diameter of 0.3 to 10.0 mm, preferably 0.5 to 7.0 mm, more preferably 1.0 to 5.0 mm, and a height (thickness) of 0.3 to 10.0 mm, preferably 0.5 to 7.0 mm, more preferably 1.0 to 5.0 mm.

[0080] Recycled pellets obtained by the manufacturing method of this disclosure can be used in the same manner as non-recycled pellets of fluoropolymers. A mixture may be prepared by mixing recycled pellets and non-recycled pellets and used.

[0081] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims.

[0082] <1> According to the first aspect of this disclosure, 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. Recycled pellets are produced by heat-treating the pellets at a temperature below the melting point of the fluoropolymer. A manufacturing method is provided. <2> According to the second aspect of this disclosure, A first-viewpoint manufacturing method is provided, which involves crushing the molded body and melt-molding the crushed molded body to produce the pellets. <3> According to the third aspect of this disclosure, A manufacturing method is provided in which the molded article is a molten article, according to a first or second viewpoint. <4> According to the fourth aspect of this disclosure, A manufacturing method is provided according to any one of the first to third aspects, 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> According to the fifth aspect of this disclosure, A manufacturing method is provided according to any of the first to fourth viewpoints, wherein the molded body is a molten molded body, and the pellets are produced by crushing the molten molded body and melt-molding the crushed molded body. <6> According to the sixth aspect of this disclosure, A manufacturing method is provided according to any one of the first to fifth views, wherein the temperature of the heat treatment is 150°C or higher. <7> According to the seventh aspect of this disclosure, A manufacturing method is provided according to any of the first to sixth aspects, wherein the heat treatment time is 10 minutes to 48 hours. <8> According to the eighth aspect of this disclosure, A manufacturing method is provided according to any of the first to seventh aspects, wherein the content of the fluorine-containing ether monomer units is 1.0 to 12.0% by mass. <9> According to the ninth aspect of this disclosure, A method for producing the fluoropolymer according to any one of the first to eighth aspects is provided, 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> According to the tenth aspect of this disclosure, The pellet obtained by melt molding contains a concentration of 5 ppb or more by mass relative to the mass of the pellet, according to the general formula:[C5F 11 COO - ]M + (In the formula, M + A method for producing a fluorine-containing compound having a hydrophilic group represented by ) is provided according to any one of the first to ninth aspects. <11> According to the eleventh aspect of this disclosure, The recycled pellets have a concentration of less than 5 ppb by mass relative to the mass of the recycled pellets. General formula: [C5F 11 COO - ]M + (In the formula, M + A method for producing a fluorine-containing compound having a hydrophilic group represented by ) is provided according to any of the first to tenth aspects. [Examples]

[0083] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to such embodiments.

[0084] Each value in the examples was measured by the following method.

[0085] <Measurement of the content of perfluorocarboxylic acids and their derivatives with 6 to 14 carbon atoms> The sample (pellet) was freeze-milled using a ball mill. 0.3 g of the collected powder was then mixed with 10 mL (12.6 mL) of methanol and subjected to sonication at 60°C for 2 hours. After standing at room temperature, the solid components were removed to obtain the extract.

[0086] 1. Calibration curve for linear perfluorocarboxylic acids Five levels of methanol standard solutions were prepared for perfluorohexanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, and perfluorotetradecanoic acid, each at known concentrations. Measurements were performed using a liquid chromatograph-mass spectrometer (Agilent Ultivo triple quadrupole LC-MS). Calibration curves were created for each concentration range using a linear approximation based on the methanol standard solution concentration and the integrated peak value.

[0087] [Table 1]

[0088] [Table 2]

[0089] 2. Content of the compound represented by general formula (I) contained in the powder General formula (I):[C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer between 6 and 14, M + (This represents a cation.)

[0090] Using a liquid chromatograph-mass spectrometer, the content of the compound represented by the general formula (I) for the number of carbon atoms (n) in the extract was measured from the calibration curve. The content of the compound represented by the general formula (I) for the number of carbon atoms (n) in the powder was determined using the following relation (2). Yn = Xn × 12.6 (2) Yn: Content of the compound represented by the general formula (I) with the number of carbon atoms (n) in the powder (mass ppb / powder) Xn: Content (ng / mL) of the compound represented by the general formula (I) with the number of carbon atoms (n) in the extract. The limit of quantification for the content of a compound represented by the general formula (I) with a carbon number (n) in a powder is 1 mass ppb / powder.

[0091] [Table 3]

[0092] <Composition of fluoropolymer> The content of each monomer unit was measured using an NMR analyzer (for example, a Bruker BioSpin AVANCE300 high-temperature probe).

[0093] <Meltflow Rate> In accordance with ASTM D1238, the mass (g / 10 min) of polymer flowing out of a nozzle with an inner diameter of 2.1 mm and a length of 8 mm per 10 minutes was determined using a melt indexer G-01 (manufactured by Toyo Seiki Seisakusho Co., Ltd.) at 372°C under a 5 kg load.

[0094] <Melting point> Using a differential scanning calorimeter (product name: X-DSC7000, manufactured by Hitachi High-Tech Science Corporation), the temperature was increased from 200°C to 350°C at a heating rate of 10°C / min, followed by cooling from 350°C to 200°C at a cooling rate of 10°C / min. A second heating was then performed from 200°C to 350°C at a heating rate of 10°C / min, and the melting point was determined from the melting curve peak generated during the second heating process.

[0095] Examples 1-4 and Comparative Example 1 used the following materials. PFA: Tetrafluoroethylene / perfluoropropyl vinyl ether copolymer Perfluoropropyl vinyl ether content: 5.5% by mass Melting point: 302℃ Melt flow rate: 30.0g / 10 minutes

[0096] Comparative Example 1 PFA was injection molded using a Sumitomo Heavy Industries SE50EV-A injection molding machine with a cylinder temperature of 390°C, a mold temperature of 200°C, and an injection speed of 30 mm / s (residence time in the injection molding machine of approximately 2 minutes) to obtain injection-molded scraps. The obtained injection molding scraps were crushed using a HARMO GRANCUTTER SPCII-C200 to obtain pulverized products. The obtained pulverized material was extruded using an IMC-9513 extruder manufactured by Imoto Seisakusho Co., Ltd. at 380°C (20 rpm, residence time in the extruder approximately 4 minutes) to obtain pellets.

[0097] Example 1 The pellets obtained in Comparative Example 1 were heat-treated at 200°C for 12 hours in a hot air circulating electric furnace, ESPEC Corporation's STPH-202M high-temperature constant temperature oven, to obtain regenerated pellets.

[0098] Example 2 The pellets obtained in Comparative Example 1 were heat-treated at 200°C for 1 hour using a hot air circulating electric furnace, ESPEC Corporation's STPH-202M high-temperature constant temperature oven, to obtain regenerated pellets.

[0099] Example 3 The pellets obtained in Comparative Example 1 were heat-treated at 180°C for 12 hours in a hot air circulating electric furnace, ESPEC Corporation's STPH-202M high-temperature constant temperature oven, to obtain regenerated pellets.

[0100] Example 4 The pellets obtained in Comparative Example 1 were heat-treated at 220°C for 12 hours in a hot air circulating electric furnace, ESPEC Corporation's STPH-202M high-temperature constant temperature oven, to obtain regenerated pellets.

[0101] The following materials were used in Example 5 and Comparative Example 2. PFA: Tetrafluoroethylene / perfluoropropyl vinyl ether copolymer Perfluoropropyl vinyl ether content: 4.0% by mass Melting point: 305℃ Melt flow rate: 14.0g / 10 minutes

[0102] Comparative Example 2 PFA was injection molded using a Sumitomo Heavy Industries SE50EV-A injection molding machine with a cylinder temperature of 390°C, a mold temperature of 200°C, and an injection speed of 30 mm / s (residence time in the injection molding machine of approximately 2 minutes) to obtain injection-molded scraps. The obtained injection molding scraps were crushed using a HARMO GRANCUTTER SPCII-C200 to obtain pulverized products. The obtained pulverized material was extruded using an IMC-9513 extruder manufactured by Imoto Seisakusho Co., Ltd. at 380°C (20 rpm, residence time in the extruder approximately 4 minutes) to obtain pellets.

[0103] Example 5 The pellets obtained in Comparative Example 2 were heat-treated at 200°C for 12 hours in a hot air circulating electric furnace, ESPEC Corporation's STPH-202M high-temperature constant temperature oven, to obtain regenerated pellets.

[0104] The results are shown in Table 4. [Table 4]

[0105] In Table 4, n=9 to 14 is the general formula in the pellet: [C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer between 9 and 14, M + represents a cation. The table shows the total content (mass ppb) of the compounds represented by ). Additionally, the lower section of Table 4 shows the content of each compound corresponding to n=9 to n=14 (n=9, n=10, n=11-14).

Claims

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. Recycled pellets are produced by heat-treating the aforementioned pellets at a temperature below the melting point of the fluoropolymer. Manufacturing method.

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 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 method for producing a fluoropolymer 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 pellet obtained by melt molding contains 5 mass ppb or more of the general formula: [C ５ F １１ COO － ] M ＋ (In the formula, M ＋ The method for producing a product according to claim 1 or 2, which contains a fluorine-containing compound having a hydrophilic group represented by (where represents a cation).

11. 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 mass ppb based on the mass of the recycled pellet. The production method according to claim 1 or 2.

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