Method for producing recycled pellets

Abstract

Provided is a method for producing recycled pellets that include a fluoropolymer including at least one kind of fluorinated ether monomer units selected from the group consisting of perfluorinated vinyl ether units and perfluorinated allyl ether units, the method comprising melt-molding a molded body comprising the fluoropolymer at a temperature not lower than the melting point of the fluoropolymer to produce pellets and heat-treating the pellets at a temperature lower than the melting point of the fluoropolymer to produce recycled pellets.

Description

Manufacturing method for recycled pellets

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

[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.

[0003] Japanese Patent Application Publication No. 11-30074

[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.

[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.

[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.

[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) 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.

[0011] 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 as a recycled material, the recycled pellets contain the following: General formula: [C ５ F １１ COO － ] M ＋ A compound represented by the formula (wherein M ＋ The symbol represents a cation. Fluorine-containing compounds with hydrophilic groups, such as ( ), may be included.

[0012] The reason for this is presumed to be that when the fluoropolymer is molded into pellets, heat and shear forces are applied to it, making the C-O bonds in the fluorine-containing ether monomer units easily cleaved. Therefore, it is presumed that fluoropolymers containing fluorine-containing ether monomer units are more likely to generate fluorine-containing compounds with hydrophilic groups due to the heat and shear forces of melt molding required when producing 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] (Preparation of pellets) In the manufacturing method of the present disclosure, pellets are produced by melt-molding a molded body 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 product, 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 reducing the size (volume) of raw materials by dividing them with energy. Examples of energy include compression, impact, collision, shear, and abrasion. Crushers using compression include jaw crushers, gyratory crushers, cone crushers, roll crushers, etc. Crushers using collision include hammer mills, pin mills, and mill saws. Crushers using impact include jet mills, ball mills, etc. Crushers using shear include single-axis pusher crushers, granulators, plastic runner crushers, cutter mills, shredder types, guillotine cutters, etc. Crushers using abrasion include disk mills, mortar types, etc. Some of these involve not only a single type of energy but also the combined action of multiple types of energy. Fluoropolymers have the characteristic of stretching thinly when rubbed in a soft and stressed state, so a shear type that is less likely to generate them is preferred. Among shear types, single-axis pusher crushers, granulators, and plastic runner crushers, which are less likely to generate friction while under stress, are preferred.

[0022] Crushing may be carried out once, or may be repeated until a molded body of the desired shape can be produced. Also, the crushed molded body may be classified by a known method such as air classification.

[0023] The shape of the crushed molded body is not particularly limited and may be in the form of particles, granules, etc. The maximum length of one piece of the crushed molded body is not particularly limited as long as it can be supplied to an extruder, and 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. As the hydrophilic group possessed by the fluorine-containing compound, an anionic group such as an acid group is preferred. For example, -NH ２ 、-PO ３ M、-OPO ３ M、-SO ３ M、-OSO ３ M、-COOM (in each formula, M represents a cation). Among the above hydrophilic groups, in particular, -SO ３M or -COOM is preferred, and -COOM is more preferred. As for the cation, H ＋ Examples include ammonium ions, alkali metal ions, and alkaline earth metal ions.

[0025] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, represented by the following general formula (H1): General formula (H1): [X-Rf-A － ] ｉ M ｉ＋ (wherein X is H, Cl, Br, F or I, Rf is 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 ｉ＋ (where i is a cation with a valency i, and i is an integer from 1 to 3)

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

[0027] In one embodiment, the pellets obtained by melt molding contain a fluorine-containing compound having a hydrophilic group, represented by the following general formula (H3): General formula (H3): [R １ -O-L-CO ２ － ] M ＋ (In the formula, R １ L is 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, L is a non-fluorinated, partially fluorinated or fully fluorinated alkylene group of a linear or branched chain, 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 (wherein, 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. 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＋ (wherein, Rf ｈ０ A is 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 from 1 to 3, and k and l are integers from 0 to 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, represented by the following general formula (H6). General formula (H6): [ － OCOC ｎ－１ F ２ｎ－２ COO － ] M １ ＋ M ２ ＋ (In the formula, n is an integer from 4 to 14, M １ ＋ M ２ ＋ (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, represented by the following general formula: General formula: [C ５ F １１ COO － ] M ＋ (In the formula, M ＋ (This represents a cation.)

[0033] The general formula for pellets obtained by melt molding is: [C ５ F 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, represented by the following general formula: General formula: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 8 to 14, M ＋ (This represents a cation.)

[0035] The general formula for pellets obtained by melt molding is: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 8 to 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, represented by the following general formula: General formula: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 11 to 14, M ＋ (This represents a cation.)

[0037] The general formula for pellets obtained by melt molding is: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 11 to 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-ground to prepare a powder. Methanol is added to the obtained powder, and extraction is performed. The obtained extract is then analyzed by LC / MS. To further improve the extraction efficiency, treatment by Soxhlet extraction, sonication, etc., may be performed. The obtained extract is concentrated by nitrogen purging as appropriate, and the fluorine-containing compounds in the concentrated extract are measured by LC / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and its agreement with the structural formula of candidate hydrophilic fluorine-containing compounds is confirmed. Subsequently, aqueous solutions with five or more levels of content of the confirmed hydrophilic fluorine-containing compounds are prepared, and LC / MS analysis is performed on each aqueous solution. The relationship between the content and the area area corresponding to that content is plotted, and a calibration curve is drawn. Then, using the calibration curve, the area area of ​​the LC / MS chromatogram of the hydrophilic fluorine-containing compounds in the extract can be converted to the content of the hydrophilic fluorine-containing compounds. Furthermore, since the obtained extract can be concentrated by purging with nitrogen, the lower limit of quantification in the measurement method can be lowered.

[0039] (Heat treatment) In the manufacturing method of the present 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 the present 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. Perfluorovinyl ether is represented by the general formula (1): CF ２ =CF - ORf１ (wherein, Rf １ represents a perfluoro organic group). Examples of the fluoromonomer include those represented by the following formula.

[0047] As the perfluoro organic group, a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms is preferable, a perfluoroalkyl group having 1 to 6 carbon atoms is more preferable, and a perfluoroalkyl group having 1 to 3 carbon atoms is further preferable. Examples of the perfluoro organic group include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, and the like.

[0048] Examples of the perfluorovinyl ether include perfluoro(methyl vinyl ether) (CF ２ =CF - O - CF ３ ), perfluoro(ethyl vinyl ether) (CF ２ =CF - O - C ２ F ５ ), and perfluoro(propyl vinyl ether) (CF ２ =CF - O - C ３ F ７ ). At least one selected from the group consisting of them is preferable, and at least one selected from the group consisting of perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether) is more preferable.

[0049] The perfluoroallyl ether unit is a monomer unit based on a perfluoroallyl ether. Examples of the perfluoroallyl ether include those represented by the general formula (2): CF ２ =CF - CF ２ - ORf ２ (wherein, Rf ２ represents a perfluoro organic group).

[0050] Rf in the general formula (2) ２ is the same as Rf in the general formula (1). Examples of the perfluoroallyl ether include CF １ =CF - CF ２ - O - CF ２ - ３CF ２ = CF - CF ２ -O-C ２ F ５ CF ２ = CF - CF ２ -O-C ３ F ７ and CF ２ = CF - CF ２ -O-C ４ F ９ Preferably, at least one selected from the group consisting of CF ２ = CF - CF ２ -O-C ２ F ５ CF ２ = CF - CF ２ -O-C ３ F ７ and CF ２ = CF - CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ = CF - CF ２ -O-CF ２ CF ２ CF ３ That is even more preferable.

[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, even 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 (CF ２ ) ｎ Z ４ (In the formula, Z １ Z ２ and Z ３ These represent H or F, and Z, either identical 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.) Vinyl monomer, CF ２ = CF - OCH ２ -Rf ３ (wherein, 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 F-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 manufacture of fluoropolymer molded articles, and used fluoropolymer molded articles. Examples of scraps and waste materials include defective products generated when molding fluoropolymers; sprues and runners generated when injection molding fluoropolymers; waste materials generated from edge trimming and punching of fluoropolymer molded articles; and waste materials generated from the start of molding until the shape of the extruded product stabilizes when extruding fluoropolymers to manufacture molded articles such as sheets, tubes, and electric wires. Examples of used fluoropolymer molded articles include sheets, tubes, fittings, sealants, films, bottles, and wafer carriers. These may be used in high-temperature environments, in contact with water or chemicals, or outdoors. If used molded articles are dirty, they may be washed with a cleaning solution, dried, and used as recycled materials. The molded articles may be molded articles (except 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 fluoropolymer contains components other than fluoropolymer (hereinafter sometimes referred to as "other components"). In one embodiment, the molded article (recycled material) of fluoropolymer substantially does not contain other components. In one embodiment, the molded article (recycled material) of fluoropolymer either does not contain any other components at all, or contains only trace amounts of other components (for example, less than 0.1% by mass or less than 0.01% by mass) relative to the mass of the molded article.

[0073] 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, and hydrofluoricating agents.

[0074] (Recycled Pellets) According to the manufacturing method of the present disclosure, recycled pellets can be produced in which the content of fluorine-containing compounds having hydrophilic groups is reduced. The fluorine-containing compounds having hydrophilic groups are as described above.

[0075] In one embodiment, the general formula in recycled pellets is: [C ５ F １１ COO － ] M ＋ (In the formula, 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.

[0076] In one embodiment, the general formula in recycled pellets is: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 8 to 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.

[0077] In one embodiment, the general formula in recycled pellets is: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 11 to 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 － ] M １ ＋ M ２ ＋ (In the formula, n is an integer from 8 to 14, M １ ＋ M ２ ＋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 is provided, wherein the method for producing recycled pellets is provided by melt-molding a molded body containing the fluoropolymer at a temperature above the melting point of the fluoropolymer, and then heat-treating the pellets at a temperature below the melting point of the fluoropolymer. <2> According to the second aspect of this disclosure, a method for producing pellets according to the first aspect is provided, wherein the molded body is crushed and the crushed molded body is melt-molded. <3> According to the third aspect of this disclosure, a method for producing pellets according to the first or second aspect is provided, wherein the molded body is a molten-molded body. <4> According to the fourth aspect of this disclosure, a method for producing pellets according to any one of the first to third aspects is provided, wherein the molded body is at least one selected from the group consisting of an extruded body, an injection-molded body, a blow-molded body, and a transfer-molded body. <5> According to a fifth aspect of this disclosure, a manufacturing method according to any of the first to fourth aspects is provided, wherein the molded article is a molten molded article, and the pellets are produced by crushing the molten molded article and melt-molding the crushed molded article. <6> According to a sixth aspect of this disclosure, a manufacturing method according to any of the first to fifth aspects is provided, wherein the temperature of the heat treatment is 150°C or higher. <7> According to a seventh aspect of this disclosure, a manufacturing method according to any of the first to sixth aspects is provided, wherein the time of the heat treatment is 10 minutes to 48 hours. <8> According to an eighth aspect of this disclosure, a manufacturing method according to any of the first to seventh aspects is provided, wherein the content of the fluorine-containing ether monomer units is 1.0 to 12.0% by mass. <9> According to a ninth aspect of this disclosure, a manufacturing method according to any 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 copolymer and tetrafluoroethylene / hexafluoropropylene / fluorine-containing ether monomer copolymer.<10> According to the tenth aspect of this disclosure, 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 ＋ A method for producing a fluorine-containing compound having a hydrophilic group represented by the general formula: [C] is provided, where is represents a cation. <11> According to the 11th aspect of this disclosure, the recycled pellet contains less than 5 ppb by mass of the recycled pellet, with respect to the mass of the recycled pellet. ５ F 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 tenth aspects.

[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> After freeze-grinding the sample (pellet) in a ball mill, 0.3 g of the collected powder was mixed with 10 mL (12.6 mL) of methanol and sonicated 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, all of which have known concentrations. Measurements were performed using a liquid chromatograph-mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). For each concentration range, a calibration curve was created using a first-order approximation based on the methanol standard solution concentration and the integrated peak value.

[0087]

[0088]

[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 from 6 to 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 relationship (2): Yn = Xn × 12.6 (2) Yn: Content of the compound represented by the general formula (I) for the number of carbon atoms (n) in the powder (mass ppb / powder) Xn: Content of the compound represented by the general formula (I) for the number of carbon atoms (n) in the extract (ng / mL) The limit of quantification for the content of the compound represented by the general formula (I) for the number of carbon atoms (n) in the powder is 1 mass ppb / powder.

[0091]

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

[0093] <Melt Flow Rate> In accordance with ASTM D1238, the mass of polymer flowing out per 10 minutes (g / 10 min) from a nozzle with an inner diameter of 2.1 mm and a length of 8 mm was determined using a melt indexer G-01 (manufactured by Toyo Seiki Seisakusho Co., Ltd.) at 372°C and 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 for the first time, then cooled from 350°C to 200°C at a cooling rate of 10°C / min, and then heated again from 200°C to 350°C at a heating rate of 10°C / min for the second time. The melting point was determined from the peak of the melting curve that occurred 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°C Melt flow rate: 30.0 g / 10 min

[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 molding scraps. The obtained injection molding scraps were pulverized using a HARMO GRANCUTTER SPCII-C200 to obtain pulverized material. The obtained pulverized material was extruded using an IMC-9513 manufactured by Imoto Seisakusho Co., Ltd. at 380°C (20 rpm, residence time in the extruder of 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 using 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 using 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 using a hot air circulating electric furnace, ESPEC Corporation's STPH-202M high-temperature constant temperature oven, to obtain regenerated pellets.

[0101] In Example 5 and Comparative Example 2, the following materials were used: PFA: Tetrafluoroethylene / perfluoropropyl vinyl ether copolymer Perfluoropropyl vinyl ether content: 4.0% by mass Melting point: 305°C Melt flow rate: 14.0 g / 10 min

[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 molding scraps. The obtained injection molding scraps were pulverized using a HARMO GRANCUTTER SPCII-C200 to obtain pulverized material. The obtained pulverized material was extruded using an IMC-9513 manufactured by Imoto Seisakusho Co., Ltd. at 380°C (20 rpm, residence time in the extruder of 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 using 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.

[0105] In Table 4, n=9 to 14 are the general formula in the pellet: [C ｎ－１ F ２ｎ－１ COO － ] M ＋ (In the formula, n is an integer from 9 to 14, M ＋ represents a cation. ) represents the total content (mass ppb) of the compound represented. 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, comprising: producing pellets by melt-molding a molded body containing the fluoropolymer at a temperature above the melting point of the fluoropolymer; and 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 any one of claims 1 to 3, 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 any one of claims 1 to 4, 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 any one of claims 1 to 5, wherein the temperature of the heat treatment is 150°C or higher.

7. The manufacturing method according to any one of claims 1 to 6, wherein the time of the heat treatment is 10 minutes to 48 hours.

8. The manufacturing method according to any one of claims 1 to 7, wherein the content of the fluorine-containing ether monomer units is 1.0 to 12.0% by mass.

9. The manufacturing method according to any one of claims 1 to 8, 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 a concentration of 5 mass ppb or more relative to the mass of the pellet, according to the general formula: [C ５ F １１ COO － ] M ＋ (In the formula, M ＋ A method for producing a product according to any one of claims 1 to 9, comprising a fluorine-containing compound having a hydrophilic group represented by ).

11. The recycled pellet contains a fluorine-containing compound having a hydrophilic group represented by the general formula: [C ５ F １１ COO － M ＋ (where 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 any one of claims 1 to 10.

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