Polytetrafluoroethylene fine powder

Abstract

To provide a polytetrafluoroethylene fine powder which is reduced in the moisture content and impurities.SOLUTION: The present disclosure provides a polytetrafluoroethylene fine powder which does not substantially contain moisture and a fluorine-containing compound having a molecular weight of 1,000 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to polytetrafluoroethylene fine powder. [Background technology]

[0002] Polytetrafluoroethylene (PTFE) fine powder is used in insulating tape, covering materials for coaxial cables and oxygen sensors, and tubing for fuel and drinking water, due to its excellent electrical insulation, water resistance, chemical resistance, heat resistance, and cleanliness. These are manufactured by paste extrusion molding of PTFE fine powder. In recent years, there has been a trend toward weight reduction in various applications, and thinner covering materials, for example, are required.

[0003] Furthermore, tapes obtained by paste extrusion of PTFE fine powder can be processed into porous materials by highly stretching them, allowing for the production of water-resistant and breathable membranes and filter media, which are used in a wide range of applications such as clothing, separation membranes, and air filters.

[0004] PTFE fine powder is produced by emulsion polymerization of tetrafluoroethylene (TFE).

[0005] Patent Document 1 describes a method for reducing thermally induced discoloration of a fluoropolymer resin by exposing the fluoropolymer resin obtained by emulsion polymerization using a hydrocarbon surfactant to an oxidizing agent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2015-516029 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to provide a PTFE fine powder with reduced moisture and impurities. [Means for solving the problem]

[0008] The present disclosure (1) relates to a polytetrafluoroethylene fine powder that is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1,000 or less.

[0009] The present disclosure (2) is the polytetrafluoroethylene fine powder of the present disclosure (1), which is substantially free of any of the fluorine-containing compounds represented by the following formulas: F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1is H or an organic group.

[0010] The present disclosure (3) is the polytetrafluoroethylene fine powder of the present disclosure (1) or (2), in which the content of the fluorine-containing compound is less than 25 ppb by mass relative to the polytetrafluoroethylene fine powder.

[0011] The present disclosure (4) also relates to a polytetrafluoroethylene fine powder that is stretchable, has a standard specific gravity of 2.160 or less, and is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1,000 or less.

[0012] The present disclosure (5) also relates to a polytetrafluoroethylene fine powder that is stretchable, has a standard specific gravity of 2.160 or less, and is substantially free of both moisture and a fluorine-containing compound represented by the following formula: F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1 is H or an organic group.

[0013] The present disclosure (6) is the polytetrafluoroethylene fine powder of the present disclosure (4) or (5), which has a breaking strength of 25.0 N or more and 70.0 N or less, measured using an elongated bead obtained in an elongation test at a total elongation rate of 2400%.

[0014] The present disclosure (7) is the polytetrafluoroethylene fine powder of the present disclosure (4) or (5), which has a breaking strength of 10.0 N or more but less than 25.0 N as measured using an elongated bead obtained in an elongation test at a total elongation rate of 2400%.

[0015] The present disclosure (8) is the polytetrafluoroethylene fine powder of the present disclosure (4), (5), or (7), in which the extrusion pressure at a reduction ratio of 100 is 18 MPa or less.

[0016] The present disclosure (9) is a polytetrafluoroethylene fine powder in any combination with any of the present disclosures (4) to (8), in which the content of the fluorine-containing compound is less than 25 ppb by mass relative to the polytetrafluoroethylene fine powder.

[0017] The present disclosure (10) is a polytetrafluoroethylene fine powder in any combination with any of the present disclosures (4) to (9), which has a water content of 0.010% by mass or less relative to the polytetrafluoroethylene fine powder.

[0018] The present disclosure (11) is a polytetrafluoroethylene fine powder obtained by polymerization in the presence of a fluorine-containing surfactant, in any combination with any of the present disclosures (4) to (10).

[0019] The present disclosure (12) is a polytetrafluoroethylene fine powder in any combination with any of the present disclosures (4) to (11) which are stretched materials.

[0020] The present disclosure (13) also relates to an elongated body using the polytetrafluoroethylene fine powder in any combination with any of the present disclosures (4) to (12).

[0021] The present disclosure (14) is the stretched body of the present disclosure (13) which is a porous membrane, a biaxially stretched membrane, or a filter medium.

[0022] The present disclosure (15) also relates to a modified polytetrafluoroethylene fine powder that can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1,000 or less.

[0023] The present disclosure (16) also relates to a modified polytetrafluoroethylene fine powder that can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of both moisture and the fluorine-containing compound represented by the following formula: F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1 is H or an organic group.

[0024] The present disclosure (17) is the modified polytetrafluoroethylene fine powder of the present disclosure (15) or (16), in which the extrusion pressure at a reduction ratio of 1500 is 15 to 80 MPa.

[0025] The present disclosure (18) is a modified polytetrafluoroethylene fine powder in any combination with any of the present disclosures (15) to (17), in which the content of the fluorine-containing compound is less than 25 ppb by mass relative to the modified polytetrafluoroethylene fine powder.

[0026] The present disclosure (19) is a polytetrafluoroethylene fine powder in any combination with any of the present disclosures (15) to (18), which has a water content of 0.010% by mass or less relative to the modified polytetrafluoroethylene fine powder.

[0027] The present disclosure (20) is a modified polytetrafluoroethylene fine powder obtained by polymerization in the presence of a fluorine-containing surfactant in any combination with any of the present disclosures (15) to (19).

[0028] The present disclosure (21) also relates to a molded article using the modified polytetrafluoroethylene fine powder in any combination with any of the present disclosures (15) to (20).

[0029] The present disclosure (22) is a molded article of the present disclosure (21) that is an electric wire coating material or a tube.

[0030] The present disclosure (23) also provides a perfluorovinyl ether-modified polytetrafluoroethylene fine powder that can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of both moisture and the fluorine-containing compound represented by general formula (2). General formula (2):[C n-1 F 2n-1 COO - ]M + (wherein n is an integer of 9 to 14, M + represents a cation.)

[0031] The present disclosure (24) is the modified polytetrafluoroethylene fine powder of the present disclosure (23), in which the amount of modification with perfluorovinyl ether is 0.02 mass % or more and 0.30 mass % or less.

[0032] The present disclosure (25) is the modified polytetrafluoroethylene fine powder of the present disclosure (23) or (24), in which the extrusion pressure at a reduction ratio of 1500 is 15 to 80 MPa.

[0033] The present disclosure (26) is a modified polytetrafluoroethylene fine powder in any combination with any of the present disclosures (23) to (25), in which the total content of the fluorine-containing compounds is less than 25 ppb by mass relative to the modified polytetrafluoroethylene fine powder. [Effects of the Invention]

[0034] According to the present disclosure, it is possible to provide a PTFE fine powder with reduced moisture and impurities. DETAILED DESCRIPTION OF THE INVENTION

[0035] Moisture and impurities in PTFE fine powder can cause cracks and defects, making it difficult to obtain homogeneous molded products. In recent years, there has also been a demand to reduce emissions of low-molecular-weight fluorine-containing compounds, including PFOA, as part of sustainable chemical substance management. As a result of extensive research, it was discovered that PTFE fine powder with reduced moisture and specific impurities can be obtained by processing under extremely specific conditions.

[0036] The present disclosure will be specifically described below.

[0037] The present disclosure provides a PTFE fine powder that is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1,000 or less. The PTFE fine powder of the present disclosure is substantially free of moisture and fluorine-containing compounds with a molecular weight of 1000 or less, and is therefore less likely to suffer from problems caused by residual moisture or fluorine-containing compounds.

[0038] The PTFE fine powder of the present disclosure is substantially free of moisture. Substantially free of moisture means that the moisture content of the PTFE fine powder is 0.010% by mass or less. The water content is preferably 0.005% by mass or less, and more preferably 0.002% by mass or less. The water content is measured by the following method. The mass of the PTFE fine powder is measured before and after heating at 150°C for 2 hours, and calculated according to the following formula. Three samples are taken, and the values ​​are calculated for each, and the average value is calculated and used. Moisture content (mass%) = [(mass (g) of PTFE fine powder before heating) - (mass (g) of PTFE fine powder after heating)] / (mass (g) of PTFE fine powder before heating) x 100

[0039] The PTFE fine powder of the present disclosure is substantially free of fluorine-containing compounds having a molecular weight of not more than 1000. "Substantially free of fluorine-containing compounds having a molecular weight of not more than 1000" means that the amount of the fluorine-containing compounds is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0040] The amount of the fluorine-containing compound having a molecular weight of 1,000 or less is measured by the following method. Weigh out 1 g of sample, add 10 g (12.6 ml) of methanol, and ultrasonicate for 60 minutes to obtain an extract. The resulting extract is concentrated using an appropriate nitrogen purge, and the fluorine-containing compounds in the concentrated extract are measured by LC / MS / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate fluorine-containing compound is confirmed. Aqueous solutions with five or more levels of standard substance content are prepared, and LC / MS analysis is performed on each solution. The relationship between content and area relative to that content is plotted, and a calibration curve is drawn. Using the above calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing compounds in the extract is converted to the content of the fluorine-containing compounds. The lower detection limit for this measurement method is 10 ppb by mass.

[0041] The amount of the fluorine-containing compound having a molecular weight of 1,000 or less can also be measured by the following method. Weigh out 1 g of sample, add 10 g (12.6 ml) of methanol, and ultrasonicate at 60°C for 2 hours. Allow to stand at room temperature, then remove the solids to obtain an extract. The resulting extract is concentrated using an appropriate nitrogen purge, and the fluorine-containing compounds in the concentrated extract are measured by LC / MS / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate fluorine-containing compound is confirmed. Five levels of methanol standard solutions of known concentrations of fluorine-containing compounds are prepared, and measurements are performed using a liquid chromatograph mass spectrometer. A calibration curve is created using a first-order approximation from the methanol standard solution concentration and peak integral value for each concentration range. The content of fluorine-containing compounds in the extract is measured using the calibration curve, and the content of fluorine-containing compounds in the sample is converted. The detection limit for this measurement method is 1 ppb by mass.

[0042] Examples of the fluorine-containing compound having a molecular weight of 1000 or less include a fluorine-containing compound having a hydrophilic group and a molecular weight of 1000 g / mol or less. The molecular weight of the fluorine-containing compound is preferably 800 or less, and more preferably 500 or less. Polymer particles obtained by polymerization carried out in the presence of a fluorine-containing surfactant usually contain a fluorine-containing surfactant in addition to PTFE. In this specification, the fluorine-containing surfactant is one that is used during polymerization. The fluorine-containing compound having a molecular weight of 1,000 or less may be a compound that is not added during polymerization, for example, a compound that is produced as a by-product during polymerization. When the fluorine-containing compound having a molecular weight of 1000 or less contains an anionic moiety and a cationic moiety, the fluorine-containing compound has a molecular weight of 1000 or less in the anionic moiety. The fluorine-containing compound having a molecular weight of 1000 or less does not include PTFE.

[0043] The hydrophilic group may be, for example, -COOM, -SO2M, or -SO3M, where -COOM, -SO3M (in each formula, M is H, a metal atom, NR 14. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R 1 is H or an organic group.

[0044] As the fluorine-containing surfactant, a surfactant containing fluorine (anionic fluorine-containing surfactant) in which the molecular weight of the anionic part is 1000 or less can also be used. The "anionic part" means the part of the fluorine-containing surfactant excluding the cation. For example, F(CF2) n1 In the case of COOM, "F(CF2) n1 The "COO" part. The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N 0 ): X n0 -Rf n0 -Y 0 (N 0 ) (In the formula, X n0 is H, Cl or F. n0 is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. Y 0 is an anionic group. Y 0 The anionic group may be -COOM, -SO2M, or -SO3M, and may be -COOM or -SO3M. M is H, metal atom, NR 1 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R 1 is H or an organic group. The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li. R 1 As for H or C 1-10 may be an organic group of H or C1-4 may be an organic group of H or C 1-4 The alkyl group may be: M is H, a metal atom, or NR 1 4, and may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR 1 4, which may be H, Na, K, Li, or NH4. Above Rf n0 may be one in which 50% or more of H is substituted with fluorine.

[0045] The above fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0046] Examples of the fluorine-containing surfactant include compounds represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1 is H or an organic group. The PTFE fine powder of the present disclosure preferably does not substantially contain any of the fluorine-containing compounds represented by the above formulas.

[0047] In each of the above formulas, M is H, a metal atom, or NR 1 4, and may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR 1 4, which may be H, Na, K, Li, or NH4. R 1 is H or C 1-10 may be an organic group of H or C 1-4 may be an organic group of H or C 1-4 The alkyl group may be:

[0048] When the PTFE fine powder of the present disclosure is substantially free of any of the fluorine-containing compounds represented by the above formulas, it is possible to suppress the occurrence of problems caused by the remaining fluorine-containing compounds. "Substantially free of any of the fluorine-containing compounds represented by the above formulas" means that the amount of the fluorine-containing compounds is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 ppb by mass, more preferably 10 ppb by mass or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0049] Emulsion-polymerized particles obtained by polymerizing monomers such as TFE and modified monomers may contain, in addition to PTFE, fluorine-containing compounds formed by the polymerization of the monomers. The above-mentioned fluorine-containing compounds having a molecular weight of 1000 or less (or fluorine-containing compounds having a hydrophilic group having a molecular weight of 1000 g / mol or less) also include such fluorine-containing compounds formed by the polymerization of the monomers.

[0050] In one embodiment of the emulsion polymerized particles, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (1). General formula (1):[X-Rf 11 -A - ] i Y i+ (Wherein, X is H, Cl, Br, F or I, Rf 11 represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A - is the acid group, Y i+ represents a cation having a valence of i, where i is an integer of 1 to 3.

[0051] In one embodiment of the emulsion polymerized particles, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (2). General formula (2):[C n-1 F 2n-1 COO - ]M + (wherein n is an integer of 9 to 14, preferably an integer of 9 to 12; M + represents a cation.)

[0052] It is known that the compound represented by general formula (2) (perfluoroalkanoic acid) is formed during polymerization when perfluoroalkyl vinyl ether or the like is used as a modifying monomer (see WO 2019 / 161153).

[0053] In one embodiment of the emulsion polymerized particles, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (3). General formula (3):[R 31 -OL-CO2 - ]M + (In the formula, R 31represents a linear or branched partially or fully fluorinated aliphatic group, or a linear or branched partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M represents a + represents a cation.)

[0054] In one embodiment of the emulsion polymerized particles, the fluorine-containing compound having a hydrophilic group contains a compound represented by general formula (4). General formula (4):[H-(CF2) m CO2 - ]M + (wherein m is an integer of 3 to 19, M + represents a cation.)

[0055] M constituting the cation in the above formula may be the same as M described above.

[0056] The PTFE fine powder of the present disclosure preferably does not substantially contain the fluorine-containing compound represented by the above general formula (2), and more preferably does not substantially contain any of the fluorine-containing compounds represented by the above general formulas (1) to (4), thereby making it possible to suppress the occurrence of problems caused by the remaining fluorine-containing compounds. "Substantially free of the fluorine-containing compound represented by the above general formula" means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0057] It is also preferable that the PTFE fine powder of the present disclosure is substantially free of hydrocarbon surfactants. This can prevent problems caused by residual hydrocarbon surfactants. The hydrocarbon surfactant preferably does not contain fluorine atoms. The phrase "substantially free of hydrocarbon surfactants" means that the amount of the hydrocarbon surfactants is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the hydrocarbon surfactant is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0058] The amount of the hydrocarbon surfactant is measured by the following method. Weigh out 1 g of sample, add 10 g (12.6 ml) of methanol, and ultrasonicate for 60 minutes to obtain an extract. The resulting extract is concentrated using a nitrogen purge, and the hydrocarbon surfactant in the concentrated extract is measured by LC / MS / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate hydrocarbon surfactant is confirmed. Aqueous solutions with five or more levels of standard substance content are prepared, and LC / MS analysis is performed for each content. The relationship between content and area relative to that content is plotted, and a calibration curve is drawn. Using the above calibration curve, the area of ​​the LC / MS chromatogram of the hydrocarbon surfactant in the extract is converted to the hydrocarbon surfactant content. The lower detection limit for this measurement method is 10 ppb by mass.

[0059] The amount of the hydrocarbon surfactant can also be measured by the following method. Weigh out 1 g of sample, add 10 g (12.6 ml) of methanol, and ultrasonicate at 60°C for 2 hours. Allow to stand at room temperature, then remove the solids to obtain an extract. The resulting extract is concentrated using a nitrogen purge, and the hydrocarbon surfactant in the concentrated extract is measured by LC / MS / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate hydrocarbon surfactant is confirmed. Five methanol standard solutions of known concentrations of hydrocarbon surfactant are prepared and measured using a liquid chromatograph mass spectrometer. A calibration curve is created using a first-order approximation of the methanol standard solution concentration and the peak integral value for each concentration range. The content of hydrocarbon surfactant in the extract is measured using the calibration curve, and the content of hydrocarbon surfactant in the sample is converted. The detection limit for this measurement method is 1 ppb by mass.

[0060] The PTFE fine powder of the present disclosure preferably does not substantially contain a polymer (I) (excluding PTFE) containing a polymer unit (I) based on a monomer (I) represented by general formula (I). CX 1 X 3 =CX 2 R 11 (-CZ 1 Z 2 -A 0 ) m (I) (In the formula, X 1 and X 3 are each independently F, Cl, H, or CF; X 2 is H, F, an alkyl group or a fluorine-containing alkyl group; A 0 is an anionic group; R 11 is a linking group; Z 1 and Z 2 are each independently H, F, an alkyl group or a fluorine-containing alkyl group; and m is an integer of 1 or more. The polymer (I) contains two or more polymer units (I).

[0061] A 0The anionic group as the above includes functional groups that provide anionic groups such as an acid group like -COOH, an acid-base group like -COONH4, as well as anionic groups such as a sulfate group and a carboxylate group. The anionic group includes a sulfate group, a carboxylate group, a phosphate group, a phosphonate group, a sulfonate group, or a -C(CF3)2OM (wherein M is -H, a metal atom, -NR 1 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R 1 is H or an organic group.) is preferred, with a sulfate group, a carboxylate group, a phosphate group, a phosphonate group or a sulfonate group being more preferred.

[0062] The polymer (I) may contain only polymerized units (I) based on one type of monomer represented by general formula (I), or may contain polymerized units (I) based on two or more types of monomers represented by general formula (I).

[0063] R 11 is a linking group. The linking group is an (m+1)-valent linking group, and when m is 1, it is a divalent linking group. The linking group may be a single bond and preferably contains at least one carbon atom, and the number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. There is no upper limit, but it may be, for example, 100 or less, or 50 or less.

[0064] The linking group may be linear or branched, cyclic or acyclic in structure, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may optionally contain one or more functional groups selected from the group consisting of ester, amide, sulfonamide, carbonyl, carbonate, urethane, urea, and carbamate. The linking group may not contain carbon atoms but may be a catenary heteroatom such as oxygen, sulfur, or nitrogen.

[0065] The number average molecular weight of the polymer (I) is 0.1×10 4 or more, and 75.0 × 10 4 It may be the following:

[0066] The weight average molecular weight of the polymer (I) is 0.2×10 4 or more, and 150.0 × 10 4 It may be the following:

[0067] "Substantially free of polymer (I)" means that the amount of polymer (I) is 25 ppb by mass or less relative to the PTFE fine powder. The amount of polymer (I) is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0068] The amount of polymer (I) is measured by the following method. Weigh out 1 g of the sample, add 10 g (12.6 ml) of methanol, and ultrasonicate for 60 minutes to obtain an extract. The extract is then concentrated with a nitrogen purge, and the polymer (I) in the concentrated extract is measured by LC / MS / MS. The lower detection limit for this measurement method is 10 ppb by mass.

[0069] The amount of polymer (I) can also be measured by the following method. Weigh out 1 g of sample, add 10 g (12.6 ml) of methanol, and ultrasonicate at 60°C for 2 hours. Allow to stand at room temperature, then remove the solids to obtain an extract. The resulting extract is concentrated using an appropriate nitrogen purge, and the polymer (I) in the concentrated extract is measured by LC / MS / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate polymer (I) is confirmed. Five methanol standard solutions of polymer (I) with known concentrations are prepared and measured using a liquid chromatograph mass spectrometer. A calibration curve is created using a first-order approximation from the methanol standard solution concentration and peak integral value within each concentration range. The content of polymer (I) in the extract is measured using the calibration curve, and the content of polymer (I) in the sample is converted. The detection limit for this measurement method is 1 ppb by mass.

[0070] In view of excellent extensibility, the PTFE fine powder of the present disclosure preferably has a standard specific gravity (SSG) of 2.200 or less, more preferably 2.180 or less, even more preferably 2.170 or less, even more preferably 2.160 or less, even more preferably 2.150 or less, especially preferably 2.145 or less, and particularly preferably 2.140 or less. The SSG is also preferably 2.130 or more. The SSG is measured by the water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D 4895.

[0071] The PTFE fine powder of the present disclosure preferably has an average primary particle diameter of 350 nm or less, more preferably 330 nm or less, even more preferably 320 nm or less, even more preferably 300 nm or less, especially preferably 280 nm or less, and particularly preferably 250 nm or less, and preferably 100 nm or more, more preferably 150 nm or more, even more preferably 170 nm or more, and particularly preferably 200 nm or more. The average primary particle size is measured by the following method. The PTFE aqueous dispersion is diluted with water to a solid content of 0.15% by mass, and the transmittance of the 550 nm incident light per unit length of the diluted latex obtained and the number-average particle diameter determined by measuring a specific direction in a transmission electron microscope photograph are measured to prepare a calibration curve. Using this calibration curve, the number-average particle diameter is determined from the measured transmittance of the 550 nm incident light of each sample, and this is taken as the average primary particle diameter.

[0072] The PTFE fine powder of the present disclosure may have an average secondary particle diameter of 350 μm or more, preferably 400 μm or more, more preferably 450 μm or more, even more preferably 500 μm or more, even more preferably 550 μm or more, and especially preferably 600 μm or more, and is preferably 1000 μm or less, more preferably 900 μm or less, even more preferably 800 μm or less, and even more preferably 700 μm or less. The average secondary particle diameter is measured in accordance with JIS K 6891.

[0073] The PTFE fine powder of the present disclosure may have an extrusion pressure at a reduction ratio (RR) of 100 of 5 MPa or more, preferably 10 MPa or more, more preferably 12 MPa or more, even more preferably 15 MPa or more, and even more preferably 17 MPa or more. In addition, the extrusion pressure in RR100 is preferably 50 MPa or less, more preferably 40 MPa or less, even more preferably 30 MPa or less, even more preferably 25 MPa or less, even more preferably 23 MPa or less, even more preferably 21 MPa or less, and particularly preferably 20 MPa or less, in terms of improving processability.

[0074] The PTFE fine powder of the present disclosure has an extrusion pressure of preferably 20 MPa or more, more preferably 25 MPa or more, and even more preferably 30 MPa or more, at RR1600. The extrusion pressure in RR1600 is preferably 60 MPa or less, more preferably 50 MPa or less, in terms of improving processability.

[0075] The extrusion pressure in RR100 is measured by the following method. 50 g of PTFE powder was mixed with 10.25 g of hydrocarbon oil (trade name: Isopar E, manufactured by Exxon Chemical Co.) as an extrusion aid in a polyethylene container for 3 minutes. The mixture was filled into the cylinder of an extruder at room temperature (25±2°C), and a load of 0.47 MPa was applied to the piston inserted into the cylinder and maintained for 1 minute. The mixture was then extruded through the orifice at a ram speed of 18 mm / min. The ratio of the cross-sectional area of ​​the cylinder to the cross-sectional area of ​​the orifice was 100. The extrusion pressure (MPa) was determined by dividing the load (N) by the cross-sectional area of ​​the cylinder when the pressure reached equilibrium in the latter half of the extrusion operation.

[0076] The extrusion pressure in RR1600 is measured by the following method. 50 g of PTFE powder was mixed with 10.25 g of hydrocarbon oil (trade name: Isopar G, manufactured by Exxon Chemical Co.) as an extrusion aid in a polyethylene container for 3 minutes. The mixture was filled into the cylinder of an extruder at room temperature (25±2°C), and a load of 1.2 MPa was applied to the piston inserted into the cylinder and maintained for 1 minute. The mixture was then extruded through the orifice at a ram speed of 18 mm / min. The ratio of the cross-sectional area of ​​the cylinder to the cross-sectional area of ​​the orifice was 1600. The extrusion pressure (MPa) was determined by dividing the load (N) by the cross-sectional area of ​​the cylinder when the pressure reached equilibrium in the latter half of the extrusion operation.

[0077] The PTFE fine powder of the present disclosure is preferably extensible. Being extensible means that an extensible body can be obtained in the following extensibility test. The bead obtained by paste extrusion using the RR100 is dried at 230°C for 30 minutes to remove the lubricant. The dried bead is cut to an appropriate length and placed in an oven heated to 300°C, where it is stretched at an extension rate of 100% / sec.

[0078] The PTFE fine powder of the present disclosure has excellent extensibility and is preferably extensible up to 25 times. Whether or not the film can be stretched 25 times can be confirmed by the following stretching test. The bead obtained by paste extrusion using the RR100 is dried at 230°C for 30 minutes to remove the lubricant. After drying, the bead is cut to an appropriate length and placed in an oven heated to 300°C. In the oven, it is stretched at an extension rate of 100% / second until it reaches 25 times its length before the extension test. If it does not break during extension, it is determined that it can be stretched to 25 times its original length.

[0079] The PTFE fine powder of the present disclosure preferably has a breaking strength of 20.0 N or more, more preferably 25.0 N or more, even more preferably 30.0 N or more, even more preferably 32.0 N or more, and even more preferably 35.0 N or more. The higher the breaking strength, the better, but it may be 100.0 N or less, 80.0 N or less, or 50.0 N or less. The breaking strength is a value determined by the following method. The stretched bead (produced by stretching the bead) obtained in the above 25-fold stretching test is clamped and fixed in a movable jaw with a gauge length of 5.0 cm, and a tensile test is carried out at 25°C and a speed of 300 mm / min, and the strength at the time of break is measured as the breaking strength.

[0080] The PTFE fine powder of the present disclosure preferably has a thermal instability index (TII) of less than 40, more preferably 15 or less, even more preferably 10 or less, and particularly preferably less than 5, in terms of lower extrusion pressure, higher breaking strength, and improved heat resistance. The thermal instability index is preferably −10 or more, and more preferably 0 or more. The heat instability index is measured in accordance with ASTM D 4895.

[0081] In view of excellent handleability, the PTFE fine powder of the present disclosure may have an average aspect ratio of 2.0 or less, preferably 1.8 or less, more preferably 1.7 or less, even more preferably 1.6 or less, even more preferably 1.5 or less, even more preferably 1.4 or less, especially preferably 1.3 or less, particularly preferably 1.2 or less, and most preferably 1.1 or less. The average aspect ratio may also be 1.0 or more. The average aspect ratio is determined by observing PTFE powder or an aqueous PTFE dispersion diluted to a solid content of approximately 1% by mass with a scanning electron microscope (SEM), processing the images of 200 or more randomly selected particles, and averaging the ratio of their major axis to their minor axis.

[0082] In terms of excellent handleability, the PTFE fine powder of the present disclosure preferably has an apparent density of 0.40 g / ml or more, more preferably 0.43 g / ml or more, even more preferably 0.45 g / ml or more, even more preferably 0.48 g / ml or more, and particularly preferably 0.50 g / ml or more. There is no particular upper limit, but it may be 0.70 g / ml. The apparent density is measured in accordance with JIS K 6892.

[0083] The PTFE fine powder of the present disclosure preferably has non-melt secondary processability. The non-melt secondary processability means that the melt flow rate cannot be measured at a temperature higher than the melting point in accordance with ASTM D-1238 and D-2116, in other words, the PTFE fine powder does not easily flow even in the melting temperature range.

[0084] The PTFE may be a homopolymer of tetrafluoroethylene (TFE), or may be a modified PTFE containing polymerized units based on TFE (TFE units) and polymerized units based on a modified monomer (hereinafter also referred to as "modified monomer units"). The modified PTFE may contain 99.0% by mass or more of TFE units and 1.0% by mass or less of modified monomer units. Alternatively, the modified PTFE may consist only of TFE units and modified monomer units. The PTFE is preferably the modified PTFE.

[0085] In order to improve stretchability, the modified PTFE preferably has a content of the modified monomer unit in the range of 0.00001 to 1.0% by mass relative to all polymerized units. The lower limit of the content of the modified monomer unit is more preferably 0.0001% by mass, even more preferably 0.001% by mass, even more preferably 0.005% by mass, and particularly preferably 0.010% by mass. The upper limit of the content of the modified monomer unit is preferably 0.90% by mass, more preferably 0.80% by mass, even more preferably 0.50% by mass, even more preferably 0.40% by mass, even more preferably 0.30% by mass, even more preferably 0.20% by mass, even more preferably 0.15% by mass, even more preferably 0.10% by mass, even more preferably 0.08% by mass, even more preferably 0.05% by mass, and most preferably 0.03% by mass. In this specification, the modified monomer unit means a part of the molecular structure of PTFE that is derived from the modified monomer.

[0086] The content of each of the above-mentioned polymerized units can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0087] The modifying monomer is not particularly limited as long as it is copolymerizable with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP), hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF), perhaloolefins such as chlorotrifluoroethylene, perfluorovinyl ethers, perfluoroallyl ethers, vinyl heterocycles such as perfluoro-2,2-dimethyl-1,3-dioxole (PDD), (perfluoroalkyl)ethylenes, ethylene, etc. The modifying monomer used may be one type or multiple types.

[0088] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A): CF2=CF-ORf (A) (wherein Rf represents a perfluoroorganic group). In this specification, the "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0089] An example of the perfluorovinyl ether is perfluoro(alkyl vinyl ether) [PAVE], where Rf in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0090] Examples of the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0091] The perfluorovinyl ether further includes those in which Rf in the general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those in which Rf ...

[0092] [ka]

[0093] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0094] [ka]

[0095] (wherein n represents an integer of 1 to 4).

[0096] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0097] Examples of perfluoroallyl ethers include those represented by the general formula (B): CF2=CF-CF2-ORf 1 (B) (In the formula, Rf 1 represents a perfluoroorganic group.

[0098] Above Rf 1 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The perfluoroallyl ether is preferably 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, more preferably 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, and even more preferably CF2=CF-CF2-O-CF2CF2CF3.

[0099] As the modifying monomer, at least one selected from the group consisting of PAVE and HFP is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE) and HFP is more preferred, in terms of improving stretchability.

[0100] The above-mentioned modified monomer is preferably at least one selected from the group consisting of VDF, HFP, CTFE and PAVE, and more preferably at least one selected from the group consisting of VDF, HFP and CTFE, in that it results in a lower extrusion pressure and a higher breaking strength. In addition, in terms of improving heat resistance, one preferred embodiment is that the PTFE contains TFE units, VDF units, and HFP units, and the total amount of VDF units and HFP units is 1.0 mass% or less based on the total polymerized units.

[0101] The PTFE may have a core-shell structure. Examples of PTFE having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0102] The above-mentioned PTFE preferably exhibits one or more endothermic peaks in the range of 333 to 347°C in a heat of fusion curve when heated at a rate of 10°C / min using a differential scanning calorimeter (DSC), and the heat of fusion between 290 and 350°C calculated from the heat of fusion curve is 62 mJ / mg or more.

[0103] The PTFE fine powder of the present disclosure is preferably substantially free of organic solvents. Substantially free of organic solvents means that the organic solvent content relative to the PTFE fine powder is 5% by mass or less. The organic solvent content is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

[0104] The PTFE fine powder of the present disclosure can be suitably produced by a production method including, for example, step (A) of preparing an aqueous dispersion of PTFE, step (B) of coagulating the aqueous dispersion to obtain a wet PTFE powder, and step (C) of placing the wet powder in a container whose bottom and / or sides are breathable and heat-treating it at a temperature of 130 to 300°C for 2 hours or more to obtain the PTFE fine powder. The present disclosure also provides a method for producing the above.

[0105] The aqueous dispersion in step (A) can be produced, for example, by emulsion polymerization.

[0106] The emulsion polymerization can be carried out by a known method. For example, an aqueous dispersion containing the PTFE particles (primary particles) can be obtained by emulsion polymerization of the monomers necessary for constituting the PTFE in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. In the emulsion polymerization, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, etc. may be used as needed.

[0107] The aqueous dispersion may contain at least one of the above-mentioned fluorine-containing compounds.

[0108] The above step (A) may be a step of emulsion polymerizing TFE and, if necessary, a modifying monomer.

[0109] The emulsion polymerization can be carried out, for example, in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. The emulsion polymerization can be carried out by charging an aqueous medium, the anionic fluorine-containing surfactant, monomers, and other additives as necessary into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to initiate the polymerization reaction. After the start of the polymerization reaction, monomers, polymerization initiator, chain transfer agent, the surfactant, etc. may be additionally added depending on the purpose.

[0110] The polymerization initiator is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, polymerization can also be initiated as a redox reaction in combination with a reducing agent, etc. The concentration of the polymerization initiator is determined appropriately depending on the type of monomer, the molecular weight of the target PTFE, and the reaction rate.

[0111] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0112] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. Also usable are di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0113] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perborate, perchloric acid, perphosphoric acid, or percarbonate, t-butyl permaleate, t-butyl hydroperoxide, or disuccinic acid peroxide. Among these, ammonium persulfate and disuccinic acid peroxide are preferred. A reducing agent such as sulfites or sulfites may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0114] The amount of the water-soluble radical polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously at the beginning of the polymerization in an amount (for example, several ppm relative to the water concentration) that does not significantly decrease the polymerization rate. The upper limit is a range in which the reaction temperature can be increased while removing heat from the equipment using the heat of polymerization reaction, and a more preferred upper limit is a range in which the heat of polymerization reaction can be removed from the equipment. In terms of easily obtaining the above-mentioned physical properties, the amount of the polymerization initiator added is preferably an amount corresponding to 0.1 ppm or more, more preferably an amount corresponding to 1.0 ppm or more, and is preferably an amount corresponding to 100 ppm or less, more preferably an amount corresponding to 10 ppm or less, relative to the aqueous medium.

[0115] For example, when polymerization is carried out at low temperatures below 30°C, it is preferable to use a redox initiator, which combines an oxidizing agent and a reducing agent, as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and bromates. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. To increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0116] As the redox initiator, it is preferred that the oxidizing agent is permanganic acid or a salt thereof, a persulfate, manganese triacetate, a cerium (IV) salt, or bromic acid or a salt thereof, and the reducing agent is a dicarboxylic acid or a salt thereof, or a diimine. More preferably, the oxidizing agent is permanganic acid or a salt thereof, persulfate, or bromic acid or a salt thereof, and the reducing agent is a dicarboxylic acid or a salt thereof.

[0117] Examples of the redox initiator include combinations of potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, manganese triacetate / oxalic acid, manganese triacetate / ammonium oxalate, cerium ammonium nitrate / oxalic acid, and cerium ammonium nitrate / ammonium oxalate. When a redox initiator is used, either the oxidizing agent or the reducing agent may be charged into a polymerization vessel in advance, and then the other may be added continuously or intermittently to initiate polymerization. For example, when potassium permanganate / ammonium oxalate is used, it is preferable to charge ammonium oxalate into a polymerization vessel and then continuously add potassium permanganate thereto. In this specification, when the redox initiator is described as "potassium permanganate / ammonium oxalate," it means a combination of potassium permanganate and ammonium oxalate. The same applies to other compounds.

[0118] The redox initiator is particularly preferably a combination of an oxidizing agent that is a salt and a reducing agent that is a salt. For example, the oxidizing agent that is the salt is more preferably at least one selected from the group consisting of persulfates, permanganates, cerium (IV) salts, and bromates, further preferably permanganates, and particularly preferably potassium permanganate. Furthermore, the reducing agent which is the salt is more preferably at least one selected from the group consisting of oxalate, malonate, succinate, glutarate and bromate, further preferably oxalate, and particularly preferably ammonium oxalate.

[0119] Specifically, the redox initiator is preferably at least one selected from the group consisting of potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, potassium bromate / ammonium sulfite, manganese triacetate / ammonium oxalate, and cerium ammonium nitrate / ammonium oxalate, more preferably at least one selected from the group consisting of potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, potassium bromate / ammonium sulfite, and cerium ammonium nitrate / ammonium oxalate, and even more preferably potassium permanganate / oxalic acid.

[0120] When a redox initiator is used, the oxidizing agent and the reducing agent may be added all at once at the beginning of the polymerization, or the reducing agent may be added all at once at the beginning of the polymerization and the oxidizing agent may be added continuously, or the oxidizing agent may be added all at once at the beginning of the polymerization and the reducing agent may be added continuously, or both the oxidizing agent and the reducing agent may be added continuously.

[0121] When one of the redox polymerization initiators is added at the beginning of the polymerization and the other is added continuously, the rate of addition is preferably gradually reduced in order to obtain PTFE with a low SSG, and it is further preferable to discontinue the addition midway through the polymerization, preferably before 20 to 40 mass % of the total TFE consumed in the polymerization reaction has been consumed.

[0122] When a redox initiator is used as a polymerization initiator, the amount of oxidizing agent added to the aqueous medium is preferably 0.1 ppm or more, more preferably 0.3 ppm or more, even more preferably 0.5 ppm or more, even more preferably 1 ppm or more, particularly preferably 5 ppm or more, particularly preferably 10 ppm or more, and preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 100 ppm or less, and even more preferably 10 ppm or less. The amount of reducing agent added is preferably 0.1 ppm or more, more preferably 1.0 ppm or more, even more preferably 3 ppm or more, even more preferably 5 ppm or more, particularly preferably 10 ppm or more, and preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 100 ppm or less, and even more preferably 10 ppm or less. When a redox initiator is used in the emulsion polymerization, the polymerization temperature is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower. The polymerization temperature is preferably 10° C. or higher, more preferably 20° C. or higher, and even more preferably 30° C. or higher.

[0123] As the polymerization initiator, a water-soluble radical polymerization initiator and a redox initiator are preferred, since the above-mentioned properties can be easily obtained.

[0124] The aqueous medium is a reaction medium for polymerization and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, ether, or ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or lower.

[0125] In the emulsion polymerization, a nucleating agent, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, a decomposing agent for the polymerization initiator, a dicarboxylic acid, etc. may be used, if necessary.

[0126] The emulsion polymerization is preferably carried out with the addition of a nucleating agent for the purpose of adjusting the particle size, and the nucleating agent is preferably added before the start of the polymerization reaction. As the nucleating agent, known agents can be used, and for example, at least one selected from the group consisting of fluoropolyethers, nonionic surfactants, and chain transfer agents is preferred, and a nonionic surfactant is more preferred.

[0127] The fluoropolyether may, for example, be a perfluoropolyether (PFPE) acid or a salt thereof. The perfluoropolyether (PFPE) acid or salt thereof may have any chain structure in which oxygen atoms in the main chain of the molecule are separated by saturated fluorocarbon groups having 1 to 3 carbon atoms. Two or more types of fluorocarbon groups may be present in the molecule. A typical structure has a repeating unit represented by the following formula: (-CFCF3-CF2-O-) n (-CF2-CF2-CF2-O-) n (-CF2-CF2-O-) n -(-CF2-O-) m (-CF2-CFCF3-O-) n -(-CF2-O-) m

[0128] These structures are described by Kasai in J. Appl. Polymer Sci. 57, 797 (1995). As disclosed therein, the PFPE acid or its salt may have a carboxylic acid group or a salt thereof at one or both ends. The PFPE acid or its salt may also have a sulfonic acid or phosphonic acid group or a salt thereof at one or both ends. The PFPE acid or its salt may also have a different group at each end. For monofunctional PFPEs, the other end of the molecule is usually perfluorinated but may contain a hydrogen or chlorine atom. The PFPE acid or its salt has at least two ether oxygens, preferably at least four ether oxygens, and even more preferably at least six ether oxygens. Preferably, at least one of the fluorocarbon groups separating the ether oxygens, more preferably at least two of such fluorocarbon groups, has 2 or 3 carbon atoms. Even more preferably, at least 50% of the fluorocarbon groups separating the ether oxygens have 2 or 3 carbon atoms. Also preferably, the PFPE acid or salt thereof has a total of at least 15 carbon atoms, for example, the preferred minimum value of n or n+m in the repeating unit structure above is at least 5. Two or more of the PFPE acids or salts thereof having acid groups at one or both termini can be used in the manufacturing method of the present disclosure. The PFPE acid or salt thereof preferably has a number average molecular weight of less than 6000 g / mol.

[0129] The emulsion polymerization is preferably carried out with the addition of a radical scavenger or a decomposer for the polymerization initiator, since this allows the PTFE to have a higher molecular weight and improves the stretchability. The radical scavenger or decomposer for the polymerization initiator is preferably added after the start of the polymerization reaction, preferably before 10% by mass or more, preferably 20% by mass or more of the total TFE consumed in the polymerization reaction is polymerized, and preferably before 50% by mass or less, preferably 40% by mass or less is polymerized. When depressurization and repressurization are performed as described below, it is preferable to add it after that.

[0130] The radical scavenger is a compound that does not have the ability to restart after addition or chain transfer to a free radical in the polymerization system. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a propagating radical to generate a stable radical that does not subsequently react with the monomer, or a compound that easily undergoes an addition reaction with a primary radical or a propagating radical to generate a stable radical, is used. Generally, the activity of what is called a chain transfer agent is characterized by the chain transfer constant and the reinitiation efficiency, but among chain transfer agents, those with a reinitiation efficiency of almost 0% are called radical scavengers. The radical scavenger can also be described as a compound whose chain transfer constant with TFE at the polymerization temperature is greater than the polymerization rate constant and whose reinitiation efficiency is substantially zero percent. "Reinitiation efficiency is substantially zero percent" means that the generated radicals turn the radical scavenger into stable radicals. Preferably, the compound has a chain transfer constant (Cs) with TFE at the polymerization temperature (=chain transfer rate constant (kc) / polymerization rate constant (kp)) of more than 0.1, and the compound has a chain transfer constant (Cs) of more preferably 0.5 or more, even more preferably 1.0 or more, even more preferably 5.0 or more, and particularly preferably 10 or more.

[0131] The radical scavenger is preferably at least one selected from the group consisting of, for example, aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl). Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, p-nitrosophenol, etc. Examples of the polyhydric phenol include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, naphthresorcinol, etc. Examples of aromatic amines include o-, m-, or p-phenylenediamine, benzidine, and the like. Examples of the quinone compound include o-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN). Of the above radical scavengers, aromatic hydroxy compounds are preferred, unsubstituted phenols or polyhydric phenols are more preferred, and hydroquinone is even more preferred.

[0132] The amount of the radical scavenger added is preferably an amount equivalent to 3 to 500% (molar basis) of the polymerization initiator concentration, from the viewpoint of appropriately reducing the standard specific gravity. A more preferred lower limit is 10% (molar basis), and even more preferred is 15% (molar basis). A more preferred upper limit is 400% (molar basis), and even more preferred is 300% (molar basis).

[0133] The polymerization initiator decomposer may be any compound capable of decomposing the polymerization initiator used, and is preferably at least one selected from the group consisting of sulfites, bisulfites, bromates, diimines, diimine salts, oxalic acid, oxalates, copper salts, and iron salts. Examples of sulfites include sodium sulfite and ammonium sulfite. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. The amount of the decomposing agent added is preferably an amount equivalent to 3 to 500% (molar basis) of the initiator concentration, from the viewpoint of appropriately reducing the standard specific gravity. A more preferred lower limit is 10% (molar basis), and even more preferred is 15% (molar basis). A more preferred upper limit is 400% (molar basis), and even more preferred is 300% (molar basis).

[0134] The emulsion polymerization may be carried out in the presence of 5 to 500 ppm of dicarboxylic acid relative to the aqueous medium, preferably 10 to 200 ppm, in order to reduce the amount of coagulation produced during polymerization. If the amount of dicarboxylic acid relative to the aqueous medium is too small, sufficient effects may not be obtained, while if the amount is too large, a chain transfer reaction may occur, resulting in a low molecular weight polymer. The amount of dicarboxylic acid is more preferably 150 ppm or less. The dicarboxylic acid may be added before the start of the polymerization reaction or during the polymerization.

[0135] The dicarboxylic acid is preferably, for example, one represented by the general formula: HOOCRCOOH (wherein R represents an alkylene group having 1 to 5 carbon atoms), more preferably succinic acid, malonic acid, glutaric acid, adipic acid, or pimelic acid, and even more preferably succinic acid.

[0136] In the emulsion polymerization, the polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer used, the molecular weight of the target PTFE, and the reaction rate. Usually, the polymerization temperature is 5 to 150°C, preferably 10°C or higher, more preferably 30°C or higher, and even more preferably 50°C or higher. Also, the polymerization temperature is more preferably 120°C or lower, and even more preferably 100°C or lower. The polymerization pressure is 0.05 to 10 MPaG. The polymerization pressure is more preferably 0.3 MPaG or more, and even more preferably 0.5 MPaG or more. The polymerization pressure is more preferably 5.0 MPaG or less, and even more preferably 3.0 MPaG or less.

[0137] When VDF is used as the modifying monomer, the VDF concentration in the gas in the reactor at the start of polymerization (when the initiator is added) is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, in order to easily obtain the above-mentioned physical properties in the emulsion polymerization. The concentration may also be 15 mol% or less, preferably 6.0 mol% or less, more preferably 5.0 mol% or less, even more preferably 3.0 mol% or less, and particularly preferably 1.0 mol% or less. The VDF concentration may be maintained until the end of the polymerization reaction, or pressure may be released during the reaction. VDF is preferably charged all at once before the start of polymerization, but a portion may be added continuously or intermittently after the start of polymerization.

[0138] When VDF is used as the modifying monomer, it is preferable not to release the pressure in the emulsion polymerization after VDF is charged into the polymerization vessel until the polymerization is completed, which allows VDF to remain in the system until the end of the polymerization, thereby further increasing the breaking strength of the resulting PTFE.

[0139] When HFP is used as the modifying monomer, the HFP concentration in the gas in the reactor at the start of polymerization (when the initiator is added) is preferably 0.01 to 3.0 mol % in the emulsion polymerization, since this facilitates the attainment of the above-mentioned physical properties. Furthermore, the HFP concentration in the gas in the reactor at the time when 40 mass % of the total TFE consumed in the polymerization reaction has been polymerized is preferably greater than 0 mol % and 0.2 mol % or less. The above HFP concentration is preferably maintained thereafter until the end of the polymerization reaction. HFP may be charged all at once before the start of polymerization, or a portion may be charged before the start of polymerization and then added continuously or intermittently after the start of polymerization. By allowing HFP to remain until the end of the polymerization reaction, the extrusion pressure is reduced, despite the high breaking strength of the resulting PTFE.

[0140] When HFP is used as the modifying monomer, in the above emulsion polymerization, it is preferable to release the pressure before 5 to 40 mass % of the total TFE consumed in the polymerization reaction is polymerized, and then re-increase the pressure using only TFE, in order to further improve the breaking strength of the resulting PTFE. The pressure reduction is preferably carried out so that the pressure inside the reactor becomes 0.2 MPaG or less, more preferably 0.1 MPaG or less, and even more preferably 0.05 MPaG or less, and is preferably carried out so that the pressure inside the reactor becomes 0.0 MPaG or more. The depressurization and re-increase in pressure may be repeated several times. The depressurization may be carried out until the pressure is reduced using a vacuum pump.

[0141] When CTFE is used as the modifying monomer, in the emulsion polymerization, the CTFE concentration in the gas in the reactor at the start of polymerization (when the initiator is added) is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, since this facilitates the attainment of the above-mentioned physical properties. The concentration is also preferably 3.0 mol% or less, more preferably 1.0 mol% or less. The CTFE concentration may be maintained until the end of the polymerization reaction, or pressure may be released during the reaction. CTFE is preferably charged all at once before the start of polymerization, but a portion may be added continuously or intermittently after the start of polymerization.

[0142] When CTFE is used as the modifying monomer, it is preferable not to release the pressure in the emulsion polymerization after the CTFE is charged into the polymerization vessel until the polymerization is completed, which allows the CTFE to remain in the system until the end of the polymerization, thereby further increasing the breaking strength of the resulting PTFE.

[0143] The coagulation in step (B) can be carried out by a known method.

[0144] In step (C), the wet powder obtained in step (B) is placed in a container whose bottom and / or sides are air permeable, and is heat-treated for 2 hours or more at a temperature of 130 to 300° C. By carrying out the heat treatment under such extremely specific conditions, the fluorine-containing compound having a molecular weight of 1,000 or less can be efficiently removed together with water, and the contents of the fluorine-containing compound and water can be kept within the above-mentioned ranges.

[0145] The temperature of the heat treatment in step (C) is preferably 140°C or higher, more preferably 150°C or higher, even more preferably 160°C or higher, even more preferably 180°C or higher, still more preferably 200°C or higher, particularly preferably 220°C or higher, and is preferably 280°C or lower, more preferably 250°C or lower, in order to more efficiently remove moisture and fluorine-containing compounds.

[0146] The time for the heat treatment in step (C) is preferably 5 hours or more, more preferably 10 hours or more, and even more preferably 15 hours or more, from the viewpoint of more efficiently removing moisture and fluorine-containing compounds. The upper limit is not particularly limited, but is, for example, preferably 100 hours, more preferably 50 hours, and even more preferably 30 hours.

[0147] The air velocity in step (C) is preferably 0.01 m / s or more, more preferably 0.03 m / s or more, even more preferably 0.05 m / s or more, and even more preferably 0.1 m / s or more, from the viewpoint of more efficiently removing moisture and fluorine-containing compounds, and is preferably 50 m / s or less, more preferably 30 m / s or less, and even more preferably 10 m / s or less, from the viewpoint of suppressing scattering of powder.

[0148] The heat treatment in step (C) can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a radiant conveyor-type electric furnace, a fluidized-bed electric furnace, a vacuum electric furnace, a stirring-type electric furnace, an airflow-type electric furnace, or a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by replacing the electric furnace in the apparatus name of each electric furnace with steam furnace). In terms of being able to remove moisture and fluorine-containing compounds more efficiently, a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a fluidized-bed electric furnace, a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by replacing the electric furnace in the apparatus name of each electric furnace with steam furnace) is preferred.

[0149] The heat treatment in step (C) is carried out by placing the wet powder in a container whose bottom and / or sides are breathable. The container whose bottom and / or sides are breathable may be any container that can withstand the heat treatment temperature, but is preferably made of a metal such as stainless steel. The container having breathable bottom and / or sides is preferably a tray (bat) having breathable bottom and / or sides, and more preferably a tray having a mesh bottom and / or sides (mesh tray). The mesh is preferably either a woven mesh or a punched metal. The mesh size is preferably 2000 μm or less (ASTM standard 10 mesh or more), more preferably 595 μm or less (30 mesh or more), even more preferably 297 μm or less (50 mesh or more), even more preferably 177 μm or less (80 mesh or more), particularly preferably 149 μm or less (100 mesh or more), and particularly preferably 74 μm or less (200 mesh or more). Also, 25 μm or more (500 mesh or less) is preferred. When the mesh is a woven net, the weaving method may be, for example, plain weave, twill weave, plain tatami weave, or twill tatami weave. When the mesh is a punched metal, the porosity is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more, and is preferably 95% or less.

[0150] In step (C), the amount of the wet powder to be placed is preferably 10 g / cm 3 in order to more efficiently remove moisture and fluorine-containing compounds. 2 Preferably, it is 8 g / cm or less. 2 More preferably, it is 5 g / cm or less. 2 More preferably, it is 3 g / cm or less. 2 It is particularly preferable that the density is 0.01 g / cm or less. 2 It is preferable that the concentration is 0.05 g / cm or more. 2 More preferably, it is 0.1 g / cm or more. 2 More preferably, it is equal to or greater than this.

[0151] The moisture content of the moist powder to be heat-treated in step (C) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to the moist powder, in order to more efficiently remove moisture and fluorine-containing compounds, and is preferably 150% by mass or less, and more preferably 100% by mass or less.

[0152] The PTFE fine powder of the present disclosure has excellent physical properties that are in no way inferior to those of conventionally known PTFE fine powders, and can be used in the same manner and for the same applications as conventionally known PTFE fine powders.

[0153] The PTFE fine powder of the present disclosure is particularly useful as a raw material for an elongated body. An elongated body using the PTFE fine powder of the present disclosure is also a suitable embodiment of the present disclosure.

[0154] The above-mentioned stretched body can be obtained by stretching the PTFE fine powder of the present disclosure.

[0155] The stretched body is preferably in the form of a film, a tube, a fiber, or a rod.

[0156] When the stretched body is a membrane (stretched membrane or porous membrane), it can be stretched by a known PTFE stretching method. Preferably, a sheet-like or rod-like paste extrudate is roll-stretched in the extrusion direction to obtain a uniaxially stretched film. Furthermore, a biaxially stretched film can also be obtained by stretching the film in the width direction using a tenter or the like. It is also preferable to carry out a semi-baking treatment before stretching.

[0157] The stretched body can be made into a porous body having a high porosity, and can be suitably used as a filter material for various precision filters such as air filters and chemical filters, a support material for polymer electrolyte membranes, and the like. It is also useful as a material for products used in the fields of textiles, medicine, electrochemicals, sealing materials, air filtration, ventilation / internal pressure adjustment, liquid filtration, and general consumer goods. Specific examples of applications are given below.

[0158] Electrochemical field Dielectric material prepreg, EMI shielding material, heat transfer material, etc. More specifically, printed wiring boards, electromagnetic shielding materials, insulating heat transfer materials, insulating materials, etc. Sealing materials field Gaskets, packing, pump diaphragms, pump tubes, aircraft sealing materials, etc.

[0159] Air Filtration ULPA filters (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical cartridge filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN filters (for industrial use), catalytic filters (for exhaust gas treatment), adsorbent filters (for HDD integration), adsorbent vent filters (for HDD integration), vent filters (for HDD integration and others), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt material, GT cartridge filters (for GT compatible products), cooling filters (for electronic equipment housings), etc.

[0160] Ventilation / internal pressure regulation field Freeze-drying materials such as freeze-drying containers, automotive ventilation materials for electronic circuits and lamps, container applications such as container caps, protective ventilation applications for electronic devices including small terminals such as tablet devices and mobile phones, medical ventilation applications, etc.

[0161] Liquid Filtration Semiconductor liquid filtration filters (for semiconductor manufacturing), hydrophilic PTFE filters (for semiconductor manufacturing), chemical filters (for chemical liquid treatment), filters for pure water production lines (for pure water production), backwash type liquid filtration filters (for industrial wastewater treatment), etc.

[0162] General consumer goods Clothing, cable guides (movable wires for motorcycles), motorcycle clothing, cast liners (medical supporters), vacuum cleaner filters, bagpipes (musical instruments), cables (guitar signal cables, etc.), strings (for stringed instruments), etc.

[0163] Textile field PTFE fiber (textile material), sewing thread (textile), weaving thread (textile), rope, etc.

[0164] Medical field Implants (extended products), artificial blood vessels, catheters, general surgery (tissue reinforcement materials), head and neck products (dura mater replacement), oral health (tissue regenerative medicine), orthopedics (bandages), etc.

[0165] The PTFE fine powder of the present disclosure can also be suitably used as various additives such as dust-proof additives, anti-drip agents, and binders for batteries, in coating applications, and in glass cloth impregnation processing applications. Furthermore, the aqueous dispersion containing the PTFE fine powder of the present disclosure can be used in a variety of applications, for example, as a surface coating agent for cooking utensils, or to impregnate glass fiber, carbon fiber, Kevlar fiber, etc. to produce impregnated bodies such as roofing materials, and can also be used to form films by applying the dispersion to an object to be coated and baking it in applications such as high-frequency printed circuit boards, conveyor belts, and packing.

[0166] The present disclosure also provides a PTFE fine powder (hereinafter also referred to as "PTFE fine powder (1a)") that is stretchable, has a standard specific gravity of 2.160 or less, and is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1,000 or less. Because the PTFE fine powder (1a) is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1,000 or less, it is less likely to cause problems due to residual moisture or the fluorine-containing compounds.

[0167] The present disclosure also provides a PTFE fine powder (hereinafter also referred to as "PTFE fine powder (1b)") that is stretchable, has a standard specific gravity of 2.160 or less, and is substantially free of both moisture and the fluorine-containing compound represented by the following formula (hereinafter "PTFE fine powder (1a)" and "PTFE fine powder (1b)" are collectively referred to as "PTFE fine powder (1)"). Because the PTFE fine powder (1b) is substantially free of both moisture and the fluorine-containing compound represented by the following formula, it is less likely to cause problems due to residual moisture or the fluorine-containing compound. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1 is H or an organic group.

[0168] The PTFE fine powder (1) is substantially free of moisture, and therefore can be used to produce uniaxially stretched bodies with stable extrusion pressure and stretching strength, and biaxially stretched membranes with high membrane homogeneity, good appearance, and stable membrane performance such as pressure loss and collection efficiency.

[0169] The PTFE fine powder (1) is extensible. The fact that the PTFE fine powder (1) is stretchable means that an elongated body can be obtained in the following stretching test. The bead obtained by the paste extrusion described below was heated at 230°C for 30 minutes to remove the lubricant from the bead. The bead (extrudate) was then cut to an appropriate length, clamped at each end with a 2.0 inch (51 mm) clamp spacing, and heated to 300°C in an air-circulating oven. The clamps were then separated at a desired speed (stretch rate) until a separation distance corresponding to the desired stretch rate (total stretch rate) was reached, and a stretching test was performed. This stretching method essentially follows the method disclosed in U.S. Pat. No. 4,576,869, except for the extrusion speed (51 cm / min instead of 84 cm / min). "Stretch rate" refers to the increase in length due to stretching, usually expressed relative to the original length. In this production method, the stretch rate was 100% / sec, and the total stretch rate was 2400%.

[0170] The paste extrusion is carried out in the following manner. 21.7 g of lubricant (trade name: Isopar H®, Exxon) was added to 100 g of PTFE powder and mixed for 3 minutes at room temperature to obtain a PTFE fine powder mixture. The resulting PTFE fine powder mixture was then left at room temperature (25°C) for at least 1 hour before extrusion, and then paste-extruded through an orifice (2.5 mm diameter, 11 mm land length, 30° entry angle) at room temperature with a reduction ratio of 100:1 (ratio of the cross-sectional area of ​​the die inlet to the cross-sectional area of ​​the outlet) to obtain a uniform bead (extrusion molded product). The extrusion speed, i.e., ram speed, was 20 in / min (51 cm / min).

[0171] The PTFE fine powder (1) has a standard specific gravity (SSG) of 2.160 or less. The SSG is preferably 2.150 or less, more preferably 2.145 or less, and even more preferably 2.140 or less. The SSG is also preferably 2.130 or more.

[0172] The PTFE fine powder (1) is substantially free of moisture. Substantially free of moisture means that the moisture content of the PTFE fine powder is 0.010% by mass or less. The water content is preferably 0.008% by mass or less, more preferably 0.005% by mass or less, and even more preferably 0.002% by mass or less.

[0173] The PTFE fine powder (1a) is substantially free of fluorine-containing compounds having a molecular weight of not more than 1000. "Substantially free of fluorine-containing compounds having a molecular weight of not more than 1000" means that the amount of the fluorine-containing compounds is not more than 25 ppb by mass relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0174] Examples of the fluorine-containing compound having a molecular weight of 1000 or less include those mentioned above. The PTFE fine powder (1) is preferably obtained by polymerization carried out in the presence of a fluorine-containing surfactant.

[0175] The fluorine-containing surfactant may also be any of those mentioned above, and in particular, may be a compound represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is the same as above.) The PTFE fine powder (1a) preferably does not substantially contain any of the fluorine-containing compounds represented by the above formulas. The PTFE fine powder (1b) preferably does not substantially contain any of the fluorine-containing compounds represented by the above formulas.

[0176] When the PTFE fine powder (1) is substantially free of any of the fluorine-containing compounds represented by the above formulas, it is possible to prevent problems caused by the remaining fluorine-containing compounds. "Substantially free of any of the fluorine-containing compounds represented by the above formulas" means that the amount of the fluorine-containing compounds is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0177] The PTFE fine powder (1) preferably does not substantially contain the fluorine-containing compound represented by the general formula (2) above, and more preferably does not substantially contain any of the fluorine-containing compounds represented by the general formulas (1) to (4) above, thereby making it possible to prevent problems caused by the remaining fluorine-containing compounds. "Substantially free of the fluorine-containing compound represented by the above general formula" means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0178] It is also preferable that the PTFE fine powder (1) is substantially free of hydrocarbon surfactants. This can prevent problems caused by residual hydrocarbon surfactants. The hydrocarbon surfactant preferably does not contain fluorine atoms. The phrase "substantially free of hydrocarbon surfactants" means that the amount of the hydrocarbon surfactants is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the hydrocarbon surfactant is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0179] It is preferable that the PTFE fine powder (1) does not substantially contain the above-mentioned polymer (I) (excluding PTFE).

[0180] "Substantially free of polymer (I)" means that the amount of polymer (I) is 25 ppb by mass or less relative to the PTFE fine powder. The amount of polymer (I) is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0181] The PTFE fine powder (1) may have a breaking strength of 25.0 N or more and 70.0 N or less, measured using an expanded bead obtained in an expansion test at a total expansion rate of 2400% (hereinafter also referred to as "PTFE fine powder (1-1)"). The PTFE fine powder (1-1) preferably has a breaking strength of 28.0 N or more, more preferably 30.0 N or more, and preferably 60.0 N or less, more preferably 50.0 N or less. The breaking strength is a value determined by the following method. The stretched bead (produced by stretching the bead) obtained in the following stretching test is clamped and fixed between movable jaws with a gauge length of 5.0 cm, and a tensile test is carried out at 25°C and a speed of 300 mm / min, and the strength at the time of break is measured as the breaking strength.

[0182] The stretching test is carried out by the following method. The bead obtained by the paste extrusion described below was heated at 230°C for 30 minutes to remove the lubricant from the bead. The bead (extrudate) was then cut to an appropriate length, clamped at each end with a 2.0 inch (51 mm) clamp spacing, and heated to 300°C in an air-circulating oven. The clamps were then separated at a desired speed (stretch rate) until a separation distance corresponding to the desired stretch rate (total stretch rate) was reached, and a stretching test was performed. This stretching method essentially follows the method disclosed in U.S. Pat. No. 4,576,869, except for the extrusion speed (51 cm / min instead of 84 cm / min). "Stretch rate" refers to the increase in length due to stretching, usually expressed relative to the original length. In this production method, the stretch rate was 100% / sec, and the total stretch rate was 2400%.

[0183] The paste extrusion is carried out in the following manner. 21.7 g of lubricant (trade name: Isopar H®, Exxon) was added to 100 g of PTFE powder and mixed for 3 minutes at room temperature to obtain a PTFE fine powder mixture. The resulting PTFE fine powder mixture was then left at room temperature (25°C) for at least 1 hour before extrusion, and then paste-extruded through an orifice (2.5 mm diameter, 11 mm land length, 30° entry angle) at room temperature with a reduction ratio of 100:1 (ratio of the cross-sectional area of ​​the die inlet to the cross-sectional area of ​​the outlet) to obtain a uniform bead (extrusion molded product). The extrusion speed, i.e., ram speed, was 20 in / min (51 cm / min).

[0184] The PTFE fine powder (1-1) may have an extrusion pressure of 5 MPa or more at a reduction ratio (RR) of 100, preferably 10 MPa or more, more preferably 12 MPa or more, even more preferably 15 MPa or more, and even more preferably 17 MPa or more. In addition, the extrusion pressure in RR100 is preferably 50 MPa or less, more preferably 40 MPa or less, even more preferably 30 MPa or less, even more preferably 25 MPa or less, even more preferably 23 MPa or less, even more preferably 21 MPa or less, and particularly preferably 20 MPa or less, in terms of improving processability.

[0185] The PTFE fine powder (1) may also have a breaking strength of 10.0 N or more and less than 25.0 N, as measured using an expanded bead obtained in an expansion test at a total expansion rate of 2400% (hereinafter also referred to as "PTFE fine powder (1-2)"). The PTFE fine powder (1-2) preferably has a breaking strength of 12.0 N or more, more preferably 15.0 N or more, and preferably 23.0 N or less, more preferably 20.0 N or less.

[0186] The PTFE fine powder (1-2) preferably has an extrusion pressure of 18 MPa or less in RR100, more preferably 17 MPa or less, even more preferably 16 MPa or less, and even more preferably 15 MPa or less, and preferably 8 MPa or more, and more preferably 10 MPa or more.

[0187] The strength ratio of the PTFE fine powder (1), expressed as breaking strength (N) / extrusion pressure (MPa), is preferably 1.85 N / MPa or more, more preferably 1.90 N / MPa or more, even more preferably more than 1.90 N / MPa, even more preferably 1.95 N / MPa or more, even more preferably 2.00 N / MPa or more, even more preferably 2.05 N / MPa or more, even more preferably 2.10 N / MPa or more, even more preferably 2.20 N / MPa or more, and particularly preferably 2.25 N / MPa or more. The higher the strength ratio, the better, but it may be 5.00 N / MPa or less, or may be 4.00 N / MPa or less. A higher strength ratio means a higher breaking strength and a lower extrusion pressure. The breaking strength and extrusion pressure are values ​​determined by the above-mentioned methods.

[0188] In order to further improve the heat resistance, the PTFE fine powder (1) preferably has a stress relaxation time of 450 seconds or more, more preferably 500 seconds or more, even more preferably 550 seconds or more, and particularly preferably 600 seconds or more. The longer the stress relaxation time, the better, but it may be 2000 seconds or less, or may be 1000 seconds or less. The stress relaxation time is a value determined by the following method. Both ends of the stretched bead obtained in the same manner as in the above stretch evaluation test, except that the clamp distance was 1.5 inches (38 mm) and the stretching rate was 1000% / second, were connected to fixtures to create a taut bead sample with a total length of 8 inches (20 cm). The oven was maintained at 390°C, and the fixture was inserted into the oven through a (covered) slit in the side of the oven. The time required from the time of insertion into the oven until the bead sample broke was measured as the stress relaxation time.

[0189] Other properties of the PTFE fine powder (1) may be similar to those of the PTFE fine powder of the present disclosure described above.

[0190] The PTFE fine powder (1) preferably contains substantially no organic solvents. "Containing substantially no organic solvents" means that the content of organic solvents relative to the PTFE fine powder is 5% by mass or less. The organic solvent content is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

[0191] The PTFE fine powder (1) (PTFE fine powders (1-1) and (1-2)) can be suitably produced by a production method including, for example, a step (A1) of preparing an aqueous dispersion of PTFE, a step (B1) of coagulating the aqueous dispersion to obtain a wet PTFE powder, and a step (C1) of placing the wet powder in a container whose bottom and / or sides are breathable and heat-treating it at a temperature of 130 to 300°C for 2 hours or more to obtain a PTFE fine powder.

[0192] Step (A1) can be carried out in the same manner as step (A) described above. From the viewpoint of easily obtaining the PTFE fine powder (1-2), when a water-soluble radical polymerization initiator is used as the polymerization initiator, the amount added is preferably an amount corresponding to 0.1 ppm or more relative to the aqueous medium, more preferably an amount corresponding to 1.0 ppm or more, even more preferably an amount corresponding to 5.0 ppm or more, still more preferably an amount corresponding to 10.0 ppm or more, and preferably an amount corresponding to 500 ppm or less, more preferably an amount corresponding to 200 ppm or less, even more preferably an amount corresponding to 100 ppm or less, still more preferably an amount corresponding to 50 ppm or less.

[0193] Step (B1) can be carried out in the same manner as step (B) described above.

[0194] Step (C1) can be carried out in the same manner as step (C) described above. From the viewpoint of easily obtaining the PTFE fine powder (1-1), the temperature of the heat treatment in step (C1) is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 180°C or higher, and even more preferably 200°C or higher. From the viewpoint of easily obtaining the PTFE fine powder (1-2), the temperature of the heat treatment in step (C1) is preferably 200°C or less, more preferably 180°C or less, even more preferably 160°C or less, and even more preferably 150°C or less.

[0195] The PTFE fine powder (1) has excellent physical properties that are in no way inferior to those of conventionally known PTFE fine powders, and can be used in the same manner and for the same applications as conventionally known PTFE fine powders.

[0196] The PTFE fine powder (1) can be suitably used for the same applications as the PTFE fine powder of the present disclosure described above, but is particularly useful as an elongated material. An elongated body using the PTFE fine powder (1) as an elongated material is also a suitable embodiment of the present disclosure.

[0197] The stretched body can be obtained by stretching the PTFE fine powder (1).

[0198] The stretched body is preferably in the form of a film, a tube, a fiber, or a rod.

[0199] When the stretched body is a membrane (stretched membrane or porous membrane), it can be stretched by a known PTFE stretching method. Preferably, the sheet- or rod-shaped paste extrudate is rolled in the extrusion direction, dried to obtain an unsintered film, which is then roll-stretched to obtain a uniaxially stretched film. Furthermore, a biaxially stretched film can also be obtained by stretching the film in the width direction using a tenter or the like. It is also preferable to carry out a semi-baking treatment before stretching.

[0200] The stretched body can be made into a porous body having a high porosity, and can be suitably used as a filter material for various precision filters such as air filters and chemical filters, a support material for polymer electrolyte membranes, and the like. It is also useful as a material for products used in the fields of textiles, medicine, electrochemicals, sealing materials, air filtration, ventilation / internal pressure adjustment, liquid filtration, and general consumer goods. Specific examples of applications are given below.

[0201] Electrochemical field Dielectric material prepreg, EMI shielding material, heat transfer material, etc. More specifically, printed wiring boards, electromagnetic shielding materials, insulating heat transfer materials, insulating materials, etc. Sealing materials field Gaskets, packing, pump diaphragms, pump tubes, aircraft sealing materials, etc.

[0202] Air Filtration ULPA filters (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical cartridge filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN filters (for industrial use), catalytic filters (for exhaust gas treatment), adsorbent filters (for HDD integration), adsorbent vent filters (for HDD integration), vent filters (for HDD integration and others), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt material, GT cartridge filters (for GT compatible products), cooling filters (for electronic equipment housings), etc.

[0203] Ventilation / internal pressure regulation field Freeze-drying materials such as freeze-drying containers, automotive ventilation materials for electronic circuits and lamps, container applications such as container caps, protective ventilation applications for electronic devices including small terminals such as tablet devices and mobile phones, medical ventilation applications, etc.

[0204] Liquid Filtration Semiconductor liquid filtration filters (for semiconductor manufacturing), hydrophilic PTFE filters (for semiconductor manufacturing), chemical filters (for chemical liquid treatment), filters for pure water production lines (for pure water production), backwash type liquid filtration filters (for industrial wastewater treatment), etc.

[0205] General consumer goods Clothing, cable guides (movable wires for motorcycles), motorcycle clothing, cast liners (medical supporters), vacuum cleaner filters, bagpipes (musical instruments), cables (guitar signal cables, etc.), strings (for stringed instruments), etc.

[0206] Textile field PTFE fiber (textile material), sewing thread (textile), weaving thread (textile), rope, etc.

[0207] Medical field Implants (extended products), artificial blood vessels, catheters, general surgery (tissue reinforcement materials), head and neck products (dura mater replacement), oral health (tissue regenerative medicine), orthopedics (bandages), etc.

[0208] The stretched body using the PTFE fine powder (1-1) is suitably used as a porous membrane, a biaxially stretched membrane, or a filter medium. The stretched product using the PTFE fine powder (1-2) is useful as a material for products used in the air filtration field, and is particularly suitable for use as a HEPA filter.

[0209] The PTFE fine powder (1) can be suitably used as a dustproof additive, an anti-drip agent, a binder for batteries, and various other additives, as well as for coating applications and glass cloth impregnation processing applications. The aqueous dispersion containing the PTFE fine powder (1) can be used in a variety of applications, for example, as a surface coating agent for cooking utensils, or for impregnating glass fiber, carbon fiber, Kevlar fiber, etc. to produce impregnated articles such as roofing materials, and can also be used to form films by applying the dispersion to an object to be coated and baking it in applications such as high-frequency printed circuit boards, conveyor belts, and packing.

[0210] The present disclosure also provides a modified PTFE fine powder (hereinafter also referred to as "PTFE fine powder (2a)") that can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1000 or less. Since the PTFE fine powder (2a) is substantially free of moisture and fluorine-containing compounds having a molecular weight of 1000 or less, it is less likely to cause problems due to residual moisture or the fluorine-containing compounds.

[0211] The present disclosure also provides a modified PTFE fine powder (hereinafter also referred to as "PTFE fine powder (2b)") that can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of both moisture and the fluorine-containing compound represented by the following formula (hereinafter "PTFE fine powder (2a)" and "PTFE fine powder (2b)" are collectively referred to as "PTFE fine powder (2)"). Because the PTFE fine powder (2b) is substantially free of both moisture and the fluorine-containing compound represented by the following formula, it is less likely to cause problems due to residual moisture or the fluorine-containing compound. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1 is H or an organic group.

[0212] Since the PTFE fine powder (2) contains substantially no moisture, the extrusion pressure is stable, the wire diameter fluctuation is small, and no sparks or cracks occur, making it possible to produce molded articles with good appearance.

[0213] The PTFE fine powder (2) can be paste-extruded. If the RR1500 extrusion pressure exceeds 150 MPa during measurement, it is determined that the paste cannot be extruded. Furthermore, if a rod-shaped material obtained by RR1500 extrusion is subjected to tensile testing and breaks at an elongation of 5% or less, it is determined that the paste cannot be extruded. Here, tensile testing refers to pulling the rod-shaped material at a tensile speed of 200 mm / min at room temperature. If the extrusion pressure does not reach a balanced state, it is determined that the extrusion is not possible. The phrase "paste extrudable" refers to a state other than that in which paste extrusion is not possible or that is determined to be unextrudable, and refers to a state in which a uniform extrudate (rod-shaped product) can be obtained.

[0214] The extrusion pressure in RR1500 is measured by the following method. 50 g of PTFE powder and 10.25 g of hydrocarbon oil (product name: Isopar G, manufactured by ExxonMobil Corporation) serving as an extrusion aid were mixed in a glass bottle and aged for 1 hour at room temperature (25±2°C). The mixture was then loaded into an extrusion die (with a 30° aperture angle and an orifice at the bottom (orifice diameter: 0.65 mm, orifice length: 2 mm)) equipped with a cylinder (inner diameter: 25.4 mm). A load of 1.2 MPa was applied to the piston inserted into the cylinder and held for 1 minute. The mixture was then immediately extruded through the orifice at room temperature at a ram speed of 20 mm / min to obtain a rod-shaped product. The extrusion pressure was calculated by dividing the pressure at which the pressure reached equilibrium in the latter half of the extrusion by the cross-sectional area of ​​the cylinder.

[0215] The PTFE fine powder (2) is substantially free of moisture. Substantially free of moisture means that the moisture content of the PTFE fine powder is 0.010% by mass or less. The water content is preferably 0.008% by mass or less, more preferably 0.005% by mass or less, and even more preferably 0.002% by mass or less.

[0216] The PTFE fine powder (2a) is substantially free of fluorine-containing compounds having a molecular weight of not more than 1000. "Substantially free of fluorine-containing compounds having a molecular weight of not more than 1000" means that the amount of the fluorine-containing compounds is not more than 25 ppb by mass relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0217] Examples of the fluorine-containing compound having a molecular weight of 1000 or less include those mentioned above. The PTFE fine powder (2) is preferably obtained by polymerization carried out in the presence of a fluorine-containing surfactant.

[0218] The fluorine-containing surfactant may also be any of those mentioned above, and in particular, may be a compound represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is the same as above.) The PTFE fine powder (2a) preferably does not substantially contain any of the fluorine-containing compounds represented by the above formulas. The PTFE fine powder (2b) preferably does not substantially contain any of the fluorine-containing compounds represented by the above formulas.

[0219] When the PTFE fine powder (2) is substantially free of any of the fluorine-containing compounds represented by the above formulas, it is possible to prevent problems caused by the remaining fluorine-containing compounds. "Substantially free of any of the fluorine-containing compounds represented by the above formulas" means that the amount of the fluorine-containing compounds is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0220] The PTFE fine powder (2) preferably does not substantially contain the fluorine-containing compound represented by the general formula (2) above, and more preferably does not substantially contain any of the fluorine-containing compounds represented by the general formulas (1) to (4) above, thereby making it possible to prevent problems caused by the remaining fluorine-containing compounds. "Substantially free of the fluorine-containing compound represented by the above general formula" means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0221] It is also preferable that the PTFE fine powder (2) is substantially free of hydrocarbon surfactants. This can prevent problems caused by residual hydrocarbon surfactants. The hydrocarbon surfactant preferably does not contain fluorine atoms. The phrase "substantially free of hydrocarbon surfactants" means that the amount of the hydrocarbon surfactants is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the hydrocarbon surfactant is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0222] It is preferable that the PTFE fine powder (2) does not substantially contain the above-mentioned polymer (I) (excluding PTFE).

[0223] "Substantially free of polymer (I)" means that the amount of polymer (I) is 25 ppb by mass or less relative to the PTFE fine powder. The amount of polymer (I) is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0224] The PTFE fine powder (2) has a standard specific gravity (SSG) of 2.135 to 2.200. The SSG is preferably 2.190 or less, more preferably 2.185 or less, even more preferably 2.180 or less, still more preferably 2.175 or less, and is preferably 2.145 or more, more preferably 2.155 or more, even more preferably 2.160 or more, still more preferably 2.165 or more.

[0225] The PTFE fine powder (2) is preferably extruded at a pressure of 15 to 80 MPa in RR1500. The extrusion pressure in RR1500 is more preferably 70 MPa or less, even more preferably 60 MPa or less, and even more preferably 55 MPa or less, and is more preferably 20 MPa or more, and even more preferably 25 MPa or more.

[0226] The extrusion pressure in RR1500 is measured by the following method. 50 g of PTFE powder and 10.25 g of hydrocarbon oil (product name: Isopar G, manufactured by ExxonMobil Corporation) serving as an extrusion aid were mixed in a glass bottle and aged for 1 hour at room temperature (25±2°C). The mixture was then loaded into an extrusion die (with a 30° aperture angle and an orifice at the bottom (orifice diameter: 0.65 mm, orifice length: 2 mm)) equipped with a cylinder (inner diameter: 25.4 mm). A load of 1.2 MPa was applied to the piston inserted into the cylinder and held for 1 minute. The mixture was then immediately extruded through the orifice at room temperature at a ram speed of 20 mm / min to obtain a rod-shaped product. The extrusion pressure was calculated by dividing the pressure at which the pressure reached equilibrium in the latter half of the extrusion by the cross-sectional area of ​​the cylinder.

[0227] The PTFE fine powder (2) is a modified PTFE fine powder. That is, the PTFE constituting the PTFE fine powder (2) is a modified PTFE containing polymerized units (TFE units) based on tetrafluoroethylene (TFE) and polymerized units based on a modified monomer (hereinafter also referred to as "modified monomer units"). The modified PTFE may contain 99.0% by mass or more of TFE units and 1.0% by mass or less of modified monomer units. Alternatively, the modified PTFE may consist only of TFE units and modified monomer units.

[0228] The modified PTFE preferably has a content of the modified monomer unit in the range of 0.00001 to 1.0% by mass relative to the total polymerized units. The lower limit of the content of the modified monomer unit is more preferably 0.0001% by mass, even more preferably 0.001% by mass, even more preferably 0.005% by mass, and particularly preferably 0.010% by mass. The upper limit of the content of the modified monomer unit is preferably 0.90% by mass, more preferably 0.80% by mass, even more preferably 0.50% by mass, even more preferably 0.40% by mass, even more preferably 0.30% by mass, even more preferably 0.20% by mass, even more preferably 0.15% by mass, even more preferably 0.10% by mass, even more preferably 0.08% by mass, even more preferably 0.05% by mass, and most preferably 0.03% by mass.

[0229] Examples of the modifying monomer include those exemplified for the PTFE fine powder of the present disclosure. As the above-mentioned modified monomer, fluoro(alkyl vinyl ethers) such as perfluoro(alkyl vinyl ether) [PAVE]; vinyl heterocycles such as perfluoro-2,2-dimethyl-1,3-dioxole [PDD]; fluoroolefins such as hexafluoropropylene [HFP] and chlorotrifluoroethylene [CTFE] are preferred, in that the above-mentioned physical properties can be easily obtained, and one or more of these can be used. Among them, at least one selected from the group consisting of fluoro(alkyl vinyl ether) and fluoroolefin is preferred, and at least one selected from the group consisting of PAVE, HFP, and CTFE is more preferred. It is also preferred to use PAVE and HFP in combination. As PAVE, perfluoro(propyl vinyl ether) [PPVE] is preferred.

[0230] In order to further improve paste extrudability, the modified PTFE constituting the PTFE fine powder (2) preferably has a core-shell structure. In the core-shell structure, the core and the shell do not necessarily have to have a clear boundary therebetween, and the modified PTFE constituting the core and the modified PTFE constituting the shell may be mixed near the boundary between the core and the shell.

[0231] The core in the core-shell structure is preferably a modified PTFE having polymerized units based on a modified monomer. The modifying monomer in the core is preferably at least one selected from the group consisting of fluoro(alkyl vinyl ether), vinyl heterocycle, and fluoroolefin, more preferably at least one selected from the group consisting of fluoro(alkyl vinyl ether) and fluoroolefin, and even more preferably at least one selected from the group consisting of PAVE, HFP, and CTFE.

[0232] The shell in the core-shell structure is preferably a modified PTFE having polymerized units based on a modifying monomer and / or a modified PTFE obtained by polymerization using a chain transfer agent. The modifying monomer in the shell is preferably at least one selected from the group consisting of fluoro(alkyl vinyl ether)s and fluoroolefins, more preferably at least one selected from the group consisting of PAVE, HFP, and CTFE, and even more preferably at least one selected from the group consisting of HFP and CTFE.

[0233] The chain transfer agent is not particularly limited as long as it reduces the molecular weight of the modified PTFE that constitutes the shell, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons and fluorinated hydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide [DSP], and persulfates such as ammonium persulfate [APS] and potassium persulfate [KPS]. The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0234] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, HFC-134a, HFC-32, DSP, APS, and KPS, still more preferably methanol and / or isobutane, and particularly preferably methanol.

[0235] Other properties of the PTFE fine powder (2) may be similar to those of the PTFE fine powder of the present disclosure described above.

[0236] The PTFE fine powder (2) preferably contains substantially no organic solvents. "Containing substantially no organic solvents" means that the organic solvent content relative to the PTFE fine powder is 5% by mass or less. The organic solvent content is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

[0237] The PTFE fine powder (2) can be suitably produced by a production method including, for example, a step (A2) of preparing an aqueous dispersion of modified PTFE, a step (B2) of coagulating the aqueous dispersion to obtain a wet powder of modified PTFE, and a step (C2) of placing the wet powder in a container whose bottom and / or sides are breathable and heat-treating it at a temperature of 130 to 300°C for 2 hours or more to obtain a PTFE fine powder.

[0238] The above step (A2) is preferably a step of emulsion polymerizing TFE and a modifying monomer. Step (A2) preferably includes step (1) of feeding a modified monomer into a reaction system at the initial stage of the polymerization reaction and carrying out the polymerization reaction, and step (2) of introducing a chain transfer agent and / or a modified monomer into the reaction system after step (1).

[0239] Examples of the modifying monomer in step (1) include fluoro(alkyl vinyl ethers) such as perfluoro(alkyl vinyl ether) [PAVE]; vinyl heterocycles such as perfluoro-2,2-dimethyl-1,3-dioxole [PDD]; and fluoroolefins such as hexafluoropropylene [HFP] and chlorotrifluoroethylene [CTFE]. One or more of these may be used. Among these, at least one selected from the group consisting of fluoro(alkyl vinyl ether)s and fluoroolefins is preferred, and at least one selected from the group consisting of PAVE, HFP, and CTFE is more preferred. It is also preferable to use PAVE and HFP in combination as the modifying monomers in step (1). The PAVE is preferably perfluoro(propyl vinyl ether) [PPVE].

[0240] The chain transfer agent used in step (2) is not particularly limited as long as it reduces the molecular weight of the modified PTFE that constitutes the shell of the core-shell structure, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons and fluorinated hydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide [DSP], and persulfates such as ammonium persulfate [APS] and potassium persulfate [KPS]. The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0241] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, HFC-134a, HFC-32, DSP, APS, and KPS, still more preferably methanol and / or isobutane, and particularly preferably methanol.

[0242] The modifying monomer in step (2) is preferably at least one selected from the group consisting of the above-mentioned fluoro(alkyl vinyl ether) and fluoroolefin, more preferably at least one selected from the group consisting of PAVE, HFP, and CTFE, and even more preferably at least one selected from the group consisting of HFP and CTFE.

[0243] In step (2), it is also preferable to use the chain transfer agent and the modifying monomer in combination.

[0244] When CTFE is used as the modifying monomer in step (1), it is preferable to use CTFE as the modifying monomer in step (2). When PAVE (and HFP) is used as the modifying monomer in step (1), it is preferable to use methanol (and HFP as the modifying monomer) as the chain transfer agent in step (2).

[0245] In the above step (1), it is preferable to carry out the polymerization reaction until the conversion rate of TFE used in the entire emulsion polymerization process including steps (1) and (2) reaches 80% or more, preferably 80 to 97%, and more preferably 85 to 95%. In this specification, the above-mentioned "conversion rate" refers to the proportion of the amount of TFE consumed in the polymerization from the start of polymerization to a certain point during the polymerization, relative to the amount of TFE corresponding to the target amount of TFE units.

[0246] In the above steps (1) and (2), the reaction conditions can be appropriately set depending on the type of modifying agent used, the desired composition and yield of the modified PTFE, and the like.

[0247] The emulsion polymerization can be carried out in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. If necessary, a dispersion stabilizer or the like may be used. The anionic fluorine-containing surfactant can be present in an amount of 0.02 to 0.3% by mass of the aqueous medium.

[0248] Examples of the polymerization initiator include persulfates such as ammonium persulfate (APS), and water-soluble organic peroxides such as disuccinic acid peroxide (DSP). These polymerization initiators can be used alone or in combination of two or more. Among them, APS, DSP, etc. are preferred because they also act as chain transfer agents. The emulsion polymerization is preferably carried out in an amount of 0.0001 to 0.02 parts by mass of the polymerization initiator per 100 parts by mass of the aqueous medium.

[0249] As the aqueous medium, the same one as in the above-mentioned step (A) can be used.

[0250] The emulsion polymerization can be carried out at a polymerization temperature of 10 to 95°C, but is preferably carried out at a temperature of 60 to 90°C when a persulfate or a water-soluble organic peroxide is used as the polymerization initiator. The emulsion polymerization can be carried out usually at a pressure of 0.5 to 3.9 MPaG, preferably 0.6 to 3 MPaG. The emulsion polymerization can also be carried out by carrying out the reaction at a pressure of 0.5 MPaG or less at the initial stage of the polymerization, particularly until the TFE conversion rate reaches 15% or less of the total, and then maintaining the pressure at a level exceeding 0.5 MPaG; alternatively, the reaction pressure can be reduced, for example, to 0.1 MPaG or less during the formation of the core, and TFE is again supplied to carry out the reaction at a predetermined pressure.

[0251] Step (B2) can be carried out in the same manner as step (B) described above.

[0252] Step (C2) can be carried out in the same manner as step (C) described above. In order to obtain a PTFE fine powder having even better paste extrudability, the temperature of the heat treatment in step (C2) is preferably 200°C or less, more preferably 170°C or less, and even more preferably 150°C or less.

[0253] The PTFE fine powder (2) has excellent physical properties that are in no way inferior to those of conventionally known PTFE fine powders, and can be used in the same manner and for the same applications as conventionally known PTFE fine powders.

[0254] The PTFE fine powder (2) is particularly useful as a raw material for a molded article. A molded article using the PTFE fine powder (2) is also a preferred embodiment of the present disclosure.

[0255] The above molded body can be obtained by molding the PTFE fine powder (2).

[0256] The molding is not particularly limited, but is usually carried out by paste extrusion. The paste extrusion can be carried out under conditions appropriately set according to the desired shape and application of the molded body. For example, the paste can be extruded by mixing an extrusion aid, aging for about 1 to 24 hours, preforming at a pressure of 0.5 to 5.0 MPa, extruding at an extrusion pressure of 2 to 100 MPa, and firing at 360 to 460°C.

[0257] The molded article can be suitably used as a printed circuit board, wire coating, tube, etc. that require heat resistance and chemical resistance in, for example, aircraft, automobiles, medical equipment, precision machinery, etc., and is particularly preferably used as a wire coating material that requires core wire adhesion strength, or as a tube such as a medical tube.

[0258] The present disclosure also provides a perfluorovinyl ether-modified polytetrafluoroethylene fine powder (hereinafter also referred to as "PTFE fine powder (3)") that is paste-extrudable, has a standard specific gravity of 2.135 to 2.200, and is substantially free of both moisture and the fluorine-containing compound represented by general formula (2). General formula (2):[C n-1 F 2n-1 COO - ]M + (wherein n is an integer of 9 to 14, M + represents a cation.)

[0259] Since the PTFE fine powder (3) contains substantially no moisture, the extrusion pressure is stable, the wire diameter fluctuation is small, and no sparks or cracks occur, making it possible to produce molded articles with good appearance.

[0260] The PTFE fine powder (3) can be paste-extruded. If the RR1500 extrusion pressure exceeds 150 MPa during measurement, it is determined that the paste cannot be extruded. Furthermore, if a rod-shaped material obtained by RR1500 extrusion is subjected to tensile testing and breaks at an elongation of 5% or less, it is determined that the paste cannot be extruded. Here, tensile testing refers to pulling the rod-shaped material at a tensile speed of 200 mm / min at room temperature. If the extrusion pressure does not reach a balanced state, it is determined that the extrusion is not possible. The phrase "paste extrudable" refers to a state other than that in which paste extrusion is not possible or that is determined to be unextrudable, and refers to a state in which a uniform extrudate (rod-shaped product) can be obtained.

[0261] The extrusion pressure in RR1500 is measured by the following method. 50 g of PTFE powder and 10.25 g of hydrocarbon oil (product name: Isopar G, manufactured by ExxonMobil Corporation) serving as an extrusion aid were mixed in a glass bottle and aged for 1 hour at room temperature (25±2°C). The mixture was then loaded into an extrusion die (with a 30° aperture angle and an orifice at the bottom (orifice diameter: 0.65 mm, orifice length: 2 mm)) equipped with a cylinder (inner diameter: 25.4 mm). A load of 1.2 MPa was applied to the piston inserted into the cylinder and held for 1 minute. The mixture was then immediately extruded through the orifice at room temperature at a ram speed of 20 mm / min to obtain a rod-shaped product. The extrusion pressure was calculated by dividing the pressure at which the pressure reached equilibrium in the latter half of the extrusion by the cross-sectional area of ​​the cylinder.

[0262] The PTFE fine powder (3) is substantially free of moisture, which means that the moisture content of the PTFE fine powder is 0.010% by mass or less. The water content is preferably 0.008% by mass or less, more preferably 0.005% by mass or less, and even more preferably 0.002% by mass or less.

[0263] The PTFE fine powder (3) does not substantially contain a fluorine-containing compound represented by the following general formula (2). General formula (2):[C n-1F 2n-1 COO - ]M + (wherein n is an integer of 9 to 14, M + represents a cation.) This can prevent problems caused by the fluorine-containing compound remaining. "Substantially free of the fluorine-containing compound represented by the general formula (2)" means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0264] Examples of the fluorine-containing compound represented by general formula (2) include those mentioned above.

[0265] It is more preferable that the PTFE fine powder (3) is substantially free of any of the fluorine-containing compounds represented by the above general formulas (1), (3), and (4), thereby preventing problems caused by the remaining fluorine-containing compounds. "Substantially free of the fluorine-containing compound represented by the above general formula" means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0266] The PTFE fine powder (3) preferably does not substantially contain fluorine-containing compounds having a molecular weight of not more than 1000. "Substantially not containing fluorine-containing compounds having a molecular weight of not more than 1000" means that the amount of the fluorine-containing compounds is not more than 25 ppb by mass relative to the PTFE fine powder. The amount of the fluorine-containing compound is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0267] Examples of the fluorine-containing compound having a molecular weight of 1,000 or less include those mentioned above. The PTFE fine powder (3) is preferably obtained by polymerization carried out in the presence of a fluorine-containing surfactant. Examples of the fluorine-containing surfactant include those mentioned above.

[0268] It is also preferable that the PTFE fine powder (3) is substantially free of hydrocarbon surfactants. This can prevent problems caused by residual hydrocarbon surfactants. The hydrocarbon surfactant preferably does not contain fluorine atoms. The phrase "substantially free of hydrocarbon surfactants" means that the amount of the hydrocarbon surfactants is 25 ppb by mass or less relative to the PTFE fine powder. The amount of the hydrocarbon surfactant is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0269] It is preferable that the PTFE fine powder (3) does not substantially contain the above-mentioned polymer (I) (excluding PTFE).

[0270] "Substantially free of polymer (I)" means that the amount of polymer (I) is 25 ppb by mass or less relative to the PTFE fine powder. The amount of polymer (I) is preferably less than 25 mass ppb, more preferably 10 mass ppb or less, even more preferably 5 mass ppb or less, particularly preferably 3 mass ppb or less, and even more preferably 1 mass ppb or less. The lower limit is not particularly limited, and may be an amount below the detection limit.

[0271] The PTFE fine powder (3) has a standard specific gravity (SSG) of 2.135 to 2.200. The SSG is preferably 2.190 or less, more preferably 2.185 or less, even more preferably 2.180 or less, even more preferably 2.175 or less, and is preferably 2.145 or more, more preferably 2.155 or more, even more preferably 2.160 or more, even more preferably 2.165 or more.

[0272] The PTFE fine powder (3) is preferably extruded at a pressure of 15 to 80 MPa in RR1500. The extrusion pressure in RR1500 is more preferably 70 MPa or less, even more preferably 60 MPa or less, and even more preferably 55 MPa or less, and is more preferably 20 MPa or more, and even more preferably 25 MPa or more.

[0273] The extrusion pressure in RR1500 is measured by the following method. 50 g of PTFE powder and 10.25 g of hydrocarbon oil (product name: Isopar G, manufactured by ExxonMobil Corporation) serving as an extrusion aid were mixed in a glass bottle and aged for 1 hour at room temperature (25±2°C). The mixture was then loaded into an extrusion die (with a 30° aperture angle and an orifice at the bottom (orifice diameter: 0.65 mm, orifice length: 2 mm)) equipped with a cylinder (inner diameter: 25.4 mm). A load of 1.2 MPa was applied to the piston inserted into the cylinder and held for 1 minute. The mixture was then immediately extruded through the orifice at room temperature at a ram speed of 20 mm / min to obtain a rod-shaped product. The extrusion pressure was calculated by dividing the pressure at which the pressure reached equilibrium in the latter half of the extrusion by the cross-sectional area of ​​the cylinder.

[0274] The PTFE fine powder (3) is a modified PTFE fine powder modified with perfluorovinyl ether. That is, the PTFE constituting the PTFE fine powder (3) is a modified PTFE containing polymerization units (TFE units) based on tetrafluoroethylene (TFE) and polymerization units based on perfluorovinyl ether (hereinafter also referred to as "perfluorovinyl ether units"). The modified PTFE may contain 99.0 mass% or more of TFE units and 1.0 mass% or less of perfluorovinyl ether units. Alternatively, the modified PTFE may consist only of TFE units and perfluorovinyl ether units.

[0275] The modified PTFE preferably has a perfluorovinyl ether unit content of 0.02% by mass or more and 0.30% by mass or less based on the total polymerized units. The lower limit of the perfluorovinyl ether unit content is more preferably 0.03% by mass, even more preferably 0.05% by mass, and even more preferably 0.10% by mass. The upper limit of the perfluorovinyl ether unit content is preferably 0.27% by mass, more preferably 0.25% by mass.

[0276] Examples of the perfluorovinyl ether include those exemplified for the PTFE fine powder of the present disclosure. As the perfluorovinyl ether, PAVE is preferred. As the PAVE, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoro(propyl vinyl ether) [PPVE] are preferred, and PPVE is more preferred.

[0277] The PTFE fine powder (3) may contain polymerized units based on other modified monomers other than perfluorovinyl ether (hereinafter also referred to as "other modified monomer units"). When other modified monomer units are contained, the total amount of the perfluorovinyl ether units and the other modified monomer units is preferably 1.0 wt % or less based on the total polymerized units.

[0278] Examples of the other modifying monomers include those exemplified for the PTFE fine powder of the present disclosure. As the other modifying monomer, vinyl heterocycles such as perfluoro-2,2-dimethyl-1,3-dioxole [PDD]; fluoroolefins such as hexafluoropropylene [HFP] and chlorotrifluoroethylene [CTFE] are preferred, in that the above-mentioned properties can be easily obtained, and one or more of these can be used. Among these, at least one selected from the group consisting of fluoroolefins is preferred, at least one selected from the group consisting of HFP and CTFE is more preferred, and HFP is even more preferred.

[0279] In order to further improve paste extrudability, the modified PTFE constituting the PTFE fine powder (3) preferably has a core-shell structure. In the core-shell structure, the core and the shell do not necessarily have to have a clear boundary therebetween, and the modified PTFE constituting the core and the modified PTFE constituting the shell may be mixed near the boundary between the core and the shell.

[0280] The core in the core-shell structure is preferably a modified PTFE having polymerized units based on perfluorovinyl ether, or a modified PTFE having polymerized units based on perfluorovinyl ether and polymerized units based on other modifying monomers. The other modifying monomer in the core is preferably at least one selected from the group consisting of vinyl heterocycles and fluoroolefins, more preferably at least one selected from the group consisting of fluoroolefins, even more preferably at least one selected from the group consisting of HFP and CTFE, and even more preferably HFP.

[0281] The shell in the core-shell structure is preferably a modified PTFE having polymerized units based on another modifying monomer and / or a modified PTFE obtained by polymerization using a chain transfer agent. The other modifying monomer in the shell is preferably at least one selected from the group consisting of fluoroolefins, more preferably at least one selected from the group consisting of HFP and CTFE, and even more preferably HFP.

[0282] The chain transfer agent is not particularly limited as long as it reduces the molecular weight of the modified PTFE that constitutes the shell, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons and fluorinated hydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide [DSP], and persulfates such as ammonium persulfate [APS] and potassium persulfate [KPS]. The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0283] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, HFC-134a, HFC-32, DSP, APS, and KPS, still more preferably methanol and / or isobutane, and particularly preferably methanol.

[0284] Other properties of the PTFE fine powder (3) may be similar to those of the PTFE fine powder of the present disclosure described above.

[0285] The PTFE fine powder (3) preferably contains substantially no organic solvents. "Substantially no organic solvents" means that the organic solvent content relative to the PTFE fine powder is 5% by mass or less. The organic solvent content is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

[0286] The PTFE fine powder (3) can be suitably produced by a production method including, for example, a step (A3) of preparing an aqueous dispersion of modified PTFE, a step (B3) of coagulating the aqueous dispersion to obtain a wet powder of modified PTFE, and a step (C3) of placing the wet powder in a container whose bottom and / or sides are breathable and heat-treating it at a temperature of 130 to 300°C for 2 hours or more to obtain a PTFE fine powder.

[0287] The above step (A3) is preferably a step of emulsion polymerizing TFE and a perfluorovinyl ether. Step (A3) preferably includes step (3) of feeding a perfluorovinyl ether into the reaction system at the beginning of the polymerization reaction to carry out the polymerization reaction, and step (4) of introducing a chain transfer agent and / or a perfluorovinyl ether into the reaction system after step (3). In steps (3) and (4), in addition to the perfluorovinyl ether, a modifying monomer other than the perfluorovinyl ether may be added.

[0288] The perfluorovinyl ether in step (3) is preferably PAVE. Preferred PAVEs include perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and PPVE, and more preferred is PPVE.

[0289] Other modifying monomers in step (3) include vinyl heterocycles such as perfluoro-2,2-dimethyl-1,3-dioxole (PDD); fluoroolefins such as hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE); and the like, and one or more of these may be used. Among these, at least one selected from the group consisting of fluoroolefins is preferred, at least one selected from the group consisting of HFP and CTFE is more preferred, and HFP is even more preferred.

[0290] The chain transfer agent used in step (4) is not particularly limited as long as it reduces the molecular weight of the modified PTFE that constitutes the shell of the core-shell structure, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons and fluorinated hydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide [DSP], and persulfates such as ammonium persulfate [APS] and potassium persulfate [KPS]. The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0291] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, HFC-134a, HFC-32, DSP, APS, and KPS, still more preferably methanol and / or isobutane, and particularly preferably methanol.

[0292] The other modifying monomer in step (4) is preferably at least one selected from the group consisting of the above-mentioned fluoroolefins, more preferably at least one selected from the group consisting of HFP and CTFE, and even more preferably HFP.

[0293] In the step (4), it is also preferable to use the chain transfer agent in combination with the other modifying monomer.

[0294] When CTFE is used as the other modifying monomer in step (3), it is preferable to use CTFE as the other modifying monomer in step (4). When HFP is used as the other modifying monomer in step (3), it is preferable to use methanol (and HFP as the other modifying monomer) as a chain transfer agent in step (4).

[0295] In the above step (3), the polymerization reaction is preferably carried out until the conversion rate of TFE used in the entire emulsion polymerization process including steps (3) and (4) reaches 80% or more, preferably 80 to 97%, and more preferably 85 to 95%. In this specification, the above-mentioned "conversion rate" refers to the proportion of the amount of TFE consumed in the polymerization from the start of polymerization to a certain point during the polymerization, relative to the amount of TFE corresponding to the target amount of TFE units.

[0296] In the above steps (3) and (4), the reaction conditions can be appropriately set depending on the type of modifying agent used, the desired composition and yield of the modified PTFE, and the like.

[0297] The emulsion polymerization can be carried out in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. If necessary, a dispersion stabilizer or the like may be used. The anionic fluorine-containing surfactant can be present in an amount of 0.02 to 0.3% by mass of the aqueous medium.

[0298] Examples of the polymerization initiator include persulfates such as ammonium persulfate (APS), and water-soluble organic peroxides such as disuccinic acid peroxide (DSP). These polymerization initiators can be used alone or in combination of two or more. Among them, APS, DSP, etc. are preferred because they also act as chain transfer agents. The emulsion polymerization is preferably carried out in an amount of 0.0001 to 0.02 parts by mass of the polymerization initiator per 100 parts by mass of the aqueous medium.

[0299] As the aqueous medium, the same one as in the above-mentioned step (A) can be used.

[0300] The emulsion polymerization can be carried out at a polymerization temperature of 10 to 95°C, but is preferably carried out at a temperature of 60 to 90°C when a persulfate or a water-soluble organic peroxide is used as the polymerization initiator. The emulsion polymerization can be carried out usually at a pressure of 0.5 to 3.9 MPaG, preferably 0.6 to 3 MPaG. The emulsion polymerization can also be carried out by carrying out the reaction at a pressure of 0.5 MPaG or less at the initial stage of the polymerization, particularly until the TFE conversion rate reaches 15% or less of the total, and then maintaining the pressure at a level exceeding 0.5 MPaG; alternatively, the reaction pressure can be reduced, for example, to 0.1 MPaG or less during the formation of the core, and TFE is again supplied to carry out the reaction at a predetermined pressure.

[0301] Step (B3) can be carried out in the same manner as step (B) described above.

[0302] Step (C3) can be carried out in the same manner as step (C) described above. In order to obtain a PTFE fine powder having even better paste extrudability, the temperature of the heat treatment in step (C3) is preferably 200°C or less, more preferably 170°C or less, and even more preferably 150°C or less.

[0303] The PTFE fine powder (3) has excellent physical properties that are in no way inferior to those of conventionally known PTFE fine powders, and can be used in the same manner and for the same applications as conventionally known PTFE fine powders.

[0304] The PTFE fine powder (3) is particularly useful as a raw material for a molded article. A molded article using the PTFE fine powder (3) is also a preferred embodiment of the present disclosure.

[0305] The above molded body can be obtained by molding the PTFE fine powder (3).

[0306] The molding is not particularly limited, but is usually carried out by paste extrusion. The paste extrusion can be carried out under conditions appropriately set according to the desired shape and application of the molded body. For example, the paste can be extruded by mixing an extrusion aid, aging for about 1 to 24 hours, preforming at a pressure of 0.5 to 5.0 MPa, extruding at an extrusion pressure of 2 to 100 MPa, and firing at 360 to 460°C.

[0307] The molded article can be suitably used as a printed circuit board, wire coating, tube, etc. that require heat resistance and chemical resistance in, for example, aircraft, automobiles, medical equipment, precision machinery, etc., and is particularly preferably used as a wire coating material that requires core wire adhesion strength, or as a tube such as a medical tube. [Example]

[0308] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0309] Various physical properties were measured by the following methods.

[0310] Average primary particle size The PTFE aqueous dispersion is diluted with water to a solid content of 0.15% by mass, and the transmittance of the 550 nm incident light per unit length of the diluted latex obtained and the number-average particle diameter determined by measuring a specific direction in a transmission electron microscope photograph are measured to prepare a calibration curve. Using this calibration curve, the number-average particle diameter is determined from the measured transmittance of the 550 nm incident light of each sample, and this is taken as the average primary particle diameter.

[0311] apparent density Measurement was carried out in accordance with JIS K6892.

[0312] Average secondary particle size Measurement was carried out in accordance with JIS K6891.

[0313] Standard specific gravity (SSG) The sample was prepared in accordance with ASTM D 4895 and measured by the water displacement method in accordance with ASTM D 792.

[0314] Modified Monomer Content The PMVE content was determined by dissolving PTFE powder at 370°C. 19 F-NMR measurement was carried out, and the signal derived from the functional group was used to calculate the value based on the following formula. PMVE content (mass%)=(664B / (300A+364B))×100 (A: Total integral of the CF2 signal appearing around -120 ppm and the CF signal appearing around -136 ppm, B: Integrated value of the PMVE-derived CF3 signal appearing around -54 ppm) The chemical shift value was determined by setting the peak top of the CF2 signal derived from the polymer main chain at -120 ppm. The VDF content was determined by the following method. 19 F-NMR was measured. In addition, a thin film disk was produced by pressing the PTFE powder, and the infrared absorbance measured by FT-IR was found to be 1429 cm -1 / 2360cm -1 The absorbance ratio was calculated. 19 A calibration curve was created from the F-NMR measurements and the above absorbance ratio, and the VDF content was calculated from this calibration curve. The HFP content was determined by press-molding PTFE powder to create a thin film disk, and measuring the infrared absorbance of the thin film disk by FT-IR. -1 Absorbance at / 935cm -1 The absorbance ratio was calculated by multiplying the absorbance ratio by 0.3. The CTFE content was determined by press-molding PTFE powder to create a thin film disk, measuring the infrared absorbance of the thin film disk by FT-IR, and determining the CTFE content at 957 cm -1 absorbance / 2360cm -1 The absorbance ratio was multiplied by 0.58.

[0315] moisture content Approximately 20 g of PTFE powder was heated at 150°C for 2 hours, and the mass was measured before and after, and calculated according to the following formula. Three samples were taken, and the values ​​were calculated respectively, and the average value was calculated and used. Moisture content (mass%) = [(mass (g) of PTFE powder before heating) - (mass (g) of PTFE powder after heating)] / (mass (g) of PTFE powder before heating) × 100

[0316] Fluorine-containing compound content (1) Weigh 1 g of PTFE powder each, add 10 g (12.6 ml) of methanol, perform ultrasonic treatment for 60 minutes to obtain an extract. The obtained extract was measured by LC / MS / MS. For the fluorine-containing compounds in the extract, measurement was carried out using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). The measurement instrument configuration and LC-MS measurement conditions are shown in Table 1. An aqueous solution of a fluorine-containing compound with a known concentration was used to prepare aqueous solutions with a content of 5 levels or more, and LC / MS analysis was performed on each aqueous solution with a different content. The relationship between the content and the area of the peak was plotted to draw a calibration curve. Using the above calibration curve, the area of the peak in the LC / MS chromatogram of the fluorine-containing compounds in the extract was converted to the content of the fluorine-containing compounds. Note that the detection limit in this measurement method is 10 mass ppb.

[0317]

Table 1

[0318] Fluorine-containing compound content (2) The content of the fluorine-containing compounds contained in the PTFE powder was determined as the content of the fluorine-containing compounds extracted from the powder.

[0319] <Extraction of fluorine-containing compounds from PTFE powder> Add 10 g (12.6 mL) of methanol to 1 g of PTFE powder, and perform ultrasonic treatment at 60 °C for 2 hours. After standing at room temperature, the solid content was removed to obtain an extract.

[0320] <Measurement of perfluoroether carboxylic acids A and C> 1. Calibration curve of perfluoroether carboxylic acids A and C Prepare 5 levels of methanol standard solutions of perfluoroether carboxylic acids A and C with known concentrations, and perform measurement using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). In each concentration range, a calibration curve was created using linear approximation from the methanol standard solution concentration and the integral value of the peak.

[0321] Measurement equipment configuration and LC-MS measurement conditions [Table 2]

[0322] MRM measurement parameters [Table 3]

[0323] 2. Contents of perfluoroether carboxylic acids A and C in PTFE powder The contents of perfluoroethercarboxylic acids A and C contained in the extract were measured from a calibration curve using a liquid chromatograph mass spectrometer. The content of perfluoroethercarboxylic acid A contained in the PTFE powder was calculated using the following relational formula (1). Y A =X A ×12.6 (1) Y A : Content of perfluoroethercarboxylic acid A in powder (mass ppb) X A : Perfluorocarboxylic acid A content in the extract (ng / mL) The content of perfluoroether carboxylic acid C contained in the PTFE powder was determined by the following relational formula (2). Y C =X C ×12.6 (2) Y C : Content of perfluoroether carboxylic acid C contained in powder (mass ppb) X C : Perfluorocarboxylic acid C content in the extract (ng / mL) The lower limit of determination for the content of perfluoroethercarboxylic acids A and C contained in the PTFE powder is 1 ppb by mass.

[0324] <Content of compound represented by general formula (2)> The content of the compound represented by the general formula (2) was determined using a calibration curve of a linear perfluorocarboxylic acid having the same number of carbon atoms.

[0325] 1. Calibration curve of perfluorocarboxylic acid Five methanol standard solutions of known concentrations of perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, and perfluorotetradecanoic acid were prepared and measured using a liquid chromatograph mass spectrometer (Agilent, Ultivo Triple Quadrupole LC-MS). A calibration curve was created for each concentration range using a first-order approximation based on the concentration of the methanol standard solution and the peak integral value.

[0326] Measurement equipment configuration and LC-MS measurement conditions [Table 4]

[0327] MRM measurement parameters [Table 5]

[0328] 2. Content of the compound represented by general formula (2) contained in the powder Using a liquid chromatograph mass spectrometer, the content of the compound represented by general formula (2) with carbon number n contained in the extract was measured from a calibration curve. The content of the compound represented by general formula (2) with carbon number n contained in the powder was calculated using the following relational expression (3). Yn=Xn×12.6 (3) Yn: Content (mass ppb) of the compound represented by general formula (2) with carbon number n contained in the powder Xn: Content of the compound represented by general formula (2) with carbon number n contained in the extract (ng / mL) The lower limit of determination for the content of the compound represented by general formula (2) having a carbon number n contained in the powder is 1 ppb by mass.

[0329] MRM measurement parameters [Table 6]

[0330] Extrusion pressure at reduction ratio 100 (RR100 extrusion pressure) 21.7 g of lubricant (trade name: Isopar H (registered trademark), manufactured by Exxon Chemical) was added to 100 g of PTFE powder and mixed at room temperature for 3 minutes to obtain a PTFE fine powder mixture. The resulting PTFE fine powder mixture was then left at room temperature (25°C) for at least 1 hour before extrusion, and then paste-extruded through an orifice (diameter 2.5 mm, land length 11 mm, entrance angle 30°) at room temperature at a reduction ratio of 100:1 (ratio of the cross-sectional area of ​​the die inlet to the cross-sectional area of ​​the outlet) to obtain a uniform bead (extrusion molded product). The extrusion speed, i.e., ram speed, was 20 in / min (51 cm / min). The extrusion pressure was determined by measuring the load when the extrusion load reached equilibrium during paste extrusion and dividing it by the cross-sectional area of ​​the cylinder used for paste extrusion.

[0331] Extrusion pressure at reduction ratio 1500 (RR1500 extrusion pressure) 50 g of PTFE powder and 10.25 g of hydrocarbon oil (product name: Isopar G, manufactured by ExxonMobil Corporation) serving as an extrusion aid were mixed in a glass bottle and aged for 1 hour at room temperature (25±2°C). The mixture was then loaded into an extrusion die (with a 30° aperture angle and an orifice at the bottom (orifice diameter: 0.65 mm, orifice length: 2 mm)) equipped with a cylinder (inner diameter: 25.4 mm). A load of 1.2 MPa was applied to the piston inserted into the cylinder and held for 1 minute. The mixture was then immediately extruded through the orifice at room temperature at a ram speed of 20 mm / min to obtain a rod-shaped product. The extrusion pressure was determined by dividing the pressure at which the pressure reached equilibrium in the latter half of the extrusion by the cross-sectional area of ​​the cylinder. If the pressure did not reach equilibrium, extrusion was deemed impossible.

[0332] Coefficient of variation of extrusion pressure In the measurement of the extrusion pressure, the load when the extrusion load of the paste extrusion reached a balanced state was measured, and the coefficient of variation of the extrusion pressure was calculated from the average value and standard deviation of the load at the balanced state. (Variation coefficient of extrusion pressure) = (Standard deviation of load) / (Average value of load)

[0333] Extension test The bead obtained by the above paste extrusion was heated at 230°C for 30 minutes to remove the lubricant from the bead. The bead (extrudate) was then cut to an appropriate length, clamped at each end with a clamp spacing of 2.0 inches (51 mm), and heated to 300°C in an air-circulating oven. The clamps were then separated at a desired speed (stretching rate) until a separation distance corresponding to the desired stretching rate (total stretching rate) was reached, and a stretching test was performed. This stretching method essentially follows the method disclosed in U.S. Pat. No. 4,576,869, except for the extrusion speed (51 cm / min instead of 84 cm / min). "Stretching rate" refers to the increase in length due to stretching, and is usually expressed relative to the original length. In the above manufacturing method, the stretching rate was 100% / sec, and the total stretching rate was 2400%.

[0334] Breaking strength (measured using a stretched bead obtained in a stretching test with a total stretch rate of 2400%) The stretched bead (produced by stretching the bead) obtained in the above stretching test was clamped and fixed between movable jaws with a gauge length of 5.0 cm, and a tensile test was performed at 25°C and a speed of 300 mm / min, and the strength at the time of break was measured as the breaking strength.

[0335] Stretched film evaluation (Preparation of biaxially stretched membrane and filter medium) 100 parts by mass of PTFE powder was mixed with 28 parts by mass of hydrocarbon oil (IP Solvent 2028 manufactured by Idemitsu Kosan Co., Ltd.) as an extrusion aid. This mixture was placed in a paste extrusion device equipped with a sheet die having a rectangular extrusion opening measuring 2 mm in width and 150 mm in length at the tip of the paste extrusion device, and a sheet-shaped molded product was obtained by paste extrusion. This sheet-shaped molded product was then formed into a film using a calendar roll heated to 70°C, resulting in an unsintered film containing the aid. Next, the unsintered film containing this extrusion aid was passed through a hot air drying oven at 250°C to evaporate and remove the extrusion aid, resulting in an unsintered film with an average thickness of 200 μm. This unsintered film was stretched in the longitudinal direction at a stretch ratio of 10 times to obtain a uniaxially stretched film. The stretching temperature was 250°C. Next, the obtained uniaxially stretched film (longitudinal stretched film) was stretched in the width direction at a stretch ratio of 43 times using a tenter capable of continuous clipping to obtain a biaxially stretched film. The obtained biaxially stretched film was heat-set to obtain a PTFE porous film. The stretching temperature was 290°C, the heat-setting temperature was 345°C, and the stretching speed was 330% / sec. Next, a spunbond nonwoven fabric ("Elves T0303WDO" manufactured by Unitika Ltd.) consisting of fibers with a core / sheath structure, with PET as the core and PE as the sheath, was used as the breathable support material, and the nonwoven fabric was laminated by heat fusion using a laminating device so as to sandwich the obtained multilayer porous membrane, thereby obtaining a three-layer filter medium.

[0336] (Extrusion pressure during molding) The extrusion pressure was measured using a paste extrusion device during paste extrusion in the production of the biaxially stretched film. The extrusion pressure was determined by measuring the load when the extrusion load reached equilibrium during paste extrusion and dividing the load by the cross-sectional area of ​​the cylinder used for paste extrusion.

[0337] (Appearance of unbaked film) Unbaked films with tears or holes were rated as "Bad," while homogeneous films were rated as "Good." Furthermore, even if the film was homogeneous, unbaked films containing additives before drying were rated as "No Good" if they had devitrification (a phenomenon where the concentration of additives was uneven) in one location per 10 meters.

[0338] (Appearance of PTFE porous membrane) The appearance of the PTFE porous membrane obtained by the above biaxially stretched membrane production was visually observed. PTFE porous membranes with one or more thin layers of 100 x 100 mm or more per 100 m were rated as "No Good," membranes with one or more membrane breaks or one or more through holes per 100 m were rated as "Bad," and homogeneous membranes were rated as "Good."

[0339] (film thickness) Using a film thickness meter (1D-110MH model, manufactured by Mitutoyo Corporation), five porous membranes were stacked and the total film thickness was measured, and the value was divided by 5 to obtain the film thickness of one porous membrane. This film thickness is the film thickness (average film thickness) of one entire porous membrane.

[0340] Filter media evaluation (pressure loss) A section of about 5 m including the tip was pulled out from a long filter material wound into a roll, and the filter material was divided into 25 sections every 200 mm in the longitudinal direction and into 4 sections every 130 mm in the width direction excluding both ends, and the pressure loss was measured at 100 lattice-shaped locations.The pressure loss measurement here was carried out by using a measuring device equipped with 5 or more filter holders in the width direction of the filter material, and moving the filter material in the longitudinal direction to measure continuously at multiple lattice-shaped locations. The obtained measurement sample of the filter medium was set in a filter holder with a diameter of 100 mm, the inlet side was pressurized with a compressor, the air flow rate was adjusted to 5.3 cm / sec with a flow meter, and the pressure loss at this time was measured with a manometer.

[0341] (coefficient of variation of pressure loss) The standard deviation was calculated from the pressure loss distribution consisting of the pressure losses measured above, and the coefficient of variation was calculated by dividing the calculated standard deviation by the average value of the pressure losses at all the measured points. (Coefficient of variation of pressure loss) = (Standard deviation of pressure loss) / (Average pressure loss) x 100 (%)

[0342] (Collection efficiency) According to the method described in JIS B9928 Appendix 5 (Regulations) NaCl aerosol generation method (pressure spray method), NaCl particles generated by an atomizer were classified to a particle size of 0.1 μm using an electrostatic classifier (TSI). After neutralizing the particle charge using americium-241, the permeating flow rate was adjusted to 5.3 cm / sec. A particle counter (TSI, CNC) was used to determine the number of particles before and after the filter material (measurement sample), and the collection efficiency was calculated using the following formula. Collection efficiency (%) = (CO / CI) x 100 CO = Number of 0.1 μm particles of NaCl collected by the measurement sample CI = Number of 0.1 μm particles of NaCl supplied to the measurement sample

[0343] Insulated Wire Evaluation (Production of coated wire) (i) Preforming 2 kg of the obtained PTFE powder was mixed with 17% by mass (410 g) of an extrusion aid (Isopar H), and the mixture was aged at room temperature for 12 hours. After that, the mixture was passed through a 10-mesh SUS wire mesh in a preforming machine (manufactured by Tabata Machinery Industry Co., Ltd.) at a ram speed of 100 mm / min, under a pressure of 3 MPa, and at room temperature for 30 minutes to obtain a preformed body. (ii) Paste Extrusion The obtained preform was extruded using a φ50 mm electric wire forming machine (manufactured by Tabata Machinery Industry Co., Ltd.) at a ram speed of 33 mm / min and a core wire speed of 23 m / min, using an AWG18 nickel-plated copper wire with an outer diameter of 1.024 mm as the core wire. (iii) Drying and calcination The resulting extrudate was passed through a cabstan set at 160°C, and then passed through a drying furnace set at temperatures in stages of 200°C, 220°C, and 250°C for drying. The extrudate was then passed through a baking furnace set at temperatures in stages from 250°C to 460°C at a speed of 23 m / min for baking, and then cooled to obtain a coated electric wire with a coating layer thickness of 0.36 mm.

[0344] (Extrusion pressure when forming wire) The extrusion pressure was determined by measuring the load when the extrusion load reached equilibrium in the extrusion (ii) and dividing the load by the cross-sectional area of ​​the cylinder used in forming the electric wire.

[0345] (Wire diameter deviation) In the extrusion of (ii), when the extrusion load reached a balanced state, the coated electric wire was passed through an outer diameter measuring instrument (manufactured by Keyence Corporation), and the wire diameter deviation was calculated from the average value and standard deviation of the obtained outer diameter measurements using the following formula. Wire diameter deviation = (standard deviation of outer diameter / average outer diameter) x 100 (%)

[0346] (Spark test) (iii) After drying and baking, the coated wire was passed through a high frequency spark tester (manufactured by Clinton) to count the number of sparks under the condition of an applied voltage of 5 kV.

[0347] (Self-wound heat resistant) A self-winding heat resistance test was carried out in accordance with the self-winding heat resistance test described in International Publication No. 2006-054612. Cracks occurring in the wound portion of the covered electric wire were visually observed. Those in which cracks occurred were rated as "Bad," and those in which no cracks occurred were rated as "Good."

[0348] The following fluorine-containing surfactants with molecular weights of 1,000 or less were prepared. Perfluoroether carboxylic acid A ammonium salt: Fujifilm Wako Pure Chemical Industries, Ltd., Ammonium perfluoro(2-methyl-3-oxahexanoate), structural formula: CF3CF2CF2OCF(CF3)COONH4 Perfluoroether carboxylic acid B ammonium salt: Perfluoroether carboxylic acid B was purchased from Apollo Scientific Ltd. and converted into the ammonium salt. Ammonium perfluoro-3,6-dioxaoctanoate, structural formula: CF3CF2OCF2CF2OCF2COONH4 Perfluoroether carboxylic acid C ammonium salt: Ammonium 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy]-propionate, structural formula: CF3OCF(CF3)CF2OCF(CF3)COONH4

[0349] The following hydrophilic monomers were prepared: Hydrophilic Monomer D: Ammonium 2,3,3,3-tetrafluoro-2-[(1,1,2-trifluoro-2-propenyl)oxy]- Propanoate, structural formula: CH2=CFCF2OCF(CF3)COONH4

[0350] Manufacturing Example 1 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3480 g of deionized water, 100 g of paraffin wax, 15.75 g of ammonium salt of perfluoroethercarboxylic acid A, and 35 mg of hydrophilic monomer D. The autoclave was heated to 70 °C and the atmosphere was purged with nitrogen gas to remove oxygen. TFE was introduced to adjust the system pressure to 0.78 MPaG, and the system temperature was maintained at 70 °C while stirring. Next, an aqueous solution containing 14.0 mg of ammonium persulfate dissolved in 20 g of water was introduced with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70 °C and the system pressure at 0.78 MPaG. When 433 g of TFE had been consumed since the start of polymerization, an aqueous solution of 17.0 mg of hydroquinone as a radical scavenger dissolved in 20 g of water was injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached 1,273 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to return to normal pressure, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain PTFE aqueous dispersion A. The resulting PTFE aqueous dispersion A had an average primary particle size of 295 nm and a solids concentration of 26.5 mass%.

[0351] Comparative Example 1 The PTFE aqueous dispersion A obtained in Production Example 1 was diluted to a solids concentration of 13% by mass, and the PTFE was coagulated in a container while stirring, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet PTFE powder was placed on a stainless steel flat tray (a tray with no air permeability at the bottom and sides; the same applies below) (amount placed: 2.0 g / cm 2 The flat tray was heat-treated in a hot air circulating electric furnace at 180° C. After 5 hours, the flat tray was removed and air-cooled to obtain a PTFE powder.

[0352] Comparative Example 2 A PTFE powder was obtained in the same manner as in Comparative Example 1, except that the heat treatment was changed from 5 hours to 20 hours.

[0353] Comparative Example 3 A PTFE powder was obtained in the same manner as in Comparative Example 1, except that the heat treatment temperature was changed from 180°C to 250°C.

[0354] Manufacturing Example 2 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-controlling jacket was charged with 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of the ammonium salt of perfluoroethercarboxylic acid B, 0.108 g of succinic acid, and 0.0252 g of oxalic acid, and the polymerization vessel was heated to 70°C while the atmosphere inside was purged with nitrogen gas to remove oxygen. After maintaining the temperature inside the vessel at 70°C while stirring, TFE gas was introduced to set the pressure to 2.7 MPaG. While stirring the contents, deionized water containing 3.5 mg of potassium permanganate was continuously added at a constant rate, and TFE was continuously supplied to maintain a constant pressure of 2.7 MPaG within the polymerization vessel. When 184 g of TFE was consumed, 3.8 g of the ammonium salt of perfluoroethercarboxylic acid B was added. When 900 g of TFE was consumed, the entire amount of deionized water containing 3.5 mg of potassium permanganate was added. When 1543 g of TFE was consumed, stirring and TFE supply were stopped, and the TFE within the polymerization vessel was purged to terminate the polymerization reaction. The aqueous dispersion was removed, cooled, and the paraffin wax was separated to obtain PTFE aqueous dispersion B. The resulting PTFE aqueous dispersion B had an average primary particle size of 310 nm and a solids concentration of 30.6% by mass.

[0355] Comparative Example 4 The PTFE aqueous dispersion B obtained in Production Example 2 was diluted to a solids concentration of 13% by mass, and nitric acid was added as a coagulant while stirring in a container to coagulate the PTFE, and the water was then filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet PTFE powder was placed on a stainless steel flat tray (amount placed: 2.0 g / cm 2 The flat tray was heat-treated in a hot air circulating electric furnace at 210° C. After 18 hours, the flat tray was removed and air-cooled to obtain a PTFE powder.

[0356] Manufacturing Example 3 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3560 g of deionized water, 104 g of paraffin wax, 5.4 g of the ammonium salt of perfluoroether carboxylic acid C, and 35 mg of hydrophilic monomer D. The autoclave was heated to 70 °C and the atmosphere was purged with nitrogen gas to remove oxygen. TFE was introduced to adjust the system pressure to 0.60 MPaG, and the system temperature was maintained at 70 °C while stirring. Next, 0.60 g of perfluoro(methyl vinyl ether) (PMVE) was introduced using TFE. Next, an aqueous solution containing 15 mg of ammonium persulfate dissolved in 20 g of deionized water was introduced using TFE to adjust the system pressure to 0.78 MPaG, initiating the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but TFE was added to maintain the system temperature at 70 °C and the system pressure at 0.78 MPaG. When 429 g of TFE had been consumed since the start of polymerization, an aqueous solution of 14 mg of hydroquinone as a radical scavenger dissolved in 20 g of deionized water was injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached 1,225 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to return to normal pressure, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain PTFE aqueous dispersion C. The resulting PTFE aqueous dispersion C had an average primary particle size of 234 nm and a solids concentration of 25.4 mass%.

[0357] Comparative Example 5 The PTFE aqueous dispersion C obtained in Production Example 3 was diluted to a solids concentration of 13% by mass, and nitric acid was added as a coagulant while stirring in a container to coagulate the PTFE, and the water was then filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet PTFE powder was placed on a stainless steel flat tray (amount placed: 2.0 g / cm 2 The flat tray was heat-treated in a hot air circulating electric furnace at 210° C. After 18 hours, the flat tray was removed and air-cooled to obtain a PTFE powder.

[0358] Comparative Example 6 A PTFE powder was obtained in the same manner as in Comparative Example 1, except that the stainless steel flat tray was replaced with a stainless steel mesh tray and the heat treatment at 200°C for 1 hour was changed from 180°C for 5 hours.

[0359] Example 1 A PTFE powder was obtained in the same manner as in Comparative Example 1, except that the stainless steel flat tray was replaced with a stainless steel mesh tray. The SSG of the obtained PTFE powder was 2.158.

[0360] Example 2 A PTFE powder was obtained in the same manner as in Example 1, except that the heat treatment was changed from 5 hours to 20 hours.

[0361] Example 3 A PTFE powder was obtained in the same manner as in Comparative Example 4, except that the stainless steel flat tray was replaced with a stainless steel mesh tray and the heat treatment at 210°C for 18 hours was changed to a heat treatment at 180°C for 5 hours. The SSG of the obtained PTFE powder was 2.153.

[0362] Example 4 A PTFE powder was obtained in the same manner as in Comparative Example 5, except that the stainless steel flat tray was replaced with a stainless steel mesh tray and the heat treatment at 210°C for 18 hours was changed to a heat treatment at 180°C for 20 hours. The PMVE content of the obtained PTFE powder was 0.046 mass %, and the SSG was 2.145.

[0363] The physical properties of each of the PTFE powders (PTFE fine powders) obtained above were measured by the methods described above. The results are shown in Tables 7 to 11.

[0364] [Table 7] [Table 8]

[0365] The results shown in Tables 7 and 8 show that when flat trays are used, the moisture content exceeds 0.010% by mass. Also, even when mesh trays are used, the moisture content is high when the heat treatment time is short, at 1 hour. On the other hand, when a mesh tray is used, the moisture content is low at 0.005% by mass or less even when the heat treatment time is the same as when using a flat tray.

[0366] [Table 9] [Table 10] [Table 11] When molding was carried out using the PTFE powder obtained in Comparative Example 1, holes were generated in the unsintered film, and therefore, neither a uniaxially stretched film nor a biaxially stretched film could be obtained.

[0367] Furthermore, in the PTFE powders obtained in Examples 1 to 4, the fluorine-containing compound represented by the following formula was not detected, or the content was 10 ppb by mass or less. F(CF2)7COOH, F(CF2)5COOH, H(CF2)6COOH, H(CF2)7COOH, CF3O(CF2)3OCHFCF2COOH, C3F7OCF(CF3)CF2OCF(CF3)COOH, CF3CF2CF2OCF(CF3)COOH (perfluoroether carboxylic acid A), CF3CF2OCF2CF2OCF2COOH (perfluoroether carboxylic acid B), C2F5OCF(CF3)CF2OCF(CF3)COOH, CF3OCF(CF3)CF2OCF(CF3)COOH (perfluoroether carboxylic acid C), CF2ClCF2CF2OCF(CF3)CF2OCF2COOH, CF2ClCF2CF2OCF2CF(CF3)OCF2COOH, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOH, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOH, and [ka] (wherein M is H).

[0368] Production Example 4 A 6-L stainless steel reactor equipped with a stirrer was charged with 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of the ammonium salt of perfluoroether carboxylic acid C, and 26.5 mg of oxalic acid. The reactor contents were then heated to 70°C while being aspirated and simultaneously purged with tetrafluoroethylene (TFE) to remove oxygen from the reactor, and the contents were stirred. 2.60 g of chlorotrifluoroethylene (CTFE) was added to the reactor under pressure using TFE, followed by the addition of TFE to bring the pressure to 2.70 MPaG. An aqueous solution of potassium permanganate (3.4 mg of potassium permanganate dissolved in deionized water) was continuously added to the reactor as an initiator. After the initiator injection, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 2.70 MPaG. When the amount of TFE charged reached 430 g, the addition of the aqueous potassium permanganate solution was stopped. When the amount of TFE charged reached 1660 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. The reactor was then evacuated until the pressure inside reached normal pressure, and the inside was replaced with nitrogen. The contents were then removed from the reactor and cooled. The paraffin wax was removed, yielding an aqueous PTFE dispersion. The solids concentration of the resulting aqueous PTFE dispersion was 31.4% by mass, and the average primary particle diameter was 248 nm.

[0369] Example 5 The PTFE aqueous dispersion obtained in Production Example 4 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 210°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. The obtained PTFE powder had an SSG of 2.150 and a CTFE content of 0.100% by mass. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 12.

[0370] Manufacturing Example 5 Polymerization was carried out under the same conditions as in Production Example 4, except that the amount of CTFE charged was changed to 1.28 g, the amount of potassium permanganate charged was changed to 3.87 mg, and the final amount of TFE was changed to 1790 g, to obtain a PTFE aqueous dispersion. The solids concentration of the obtained PTFE aqueous dispersion was 33.0 mass%, and the average primary particle diameter was 263 nm.

[0371] Example 6 Using the PTFE aqueous dispersion obtained in Production Example 5, a wet powder was obtained in the same manner as in Example 5. The moisture content of the wet powder was about 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 ) and a PTFE powder was obtained in the same manner as in Example 5. The obtained PTFE powder had an SSG of 2.150 and a CTFE content of 0.050 mass%. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 12.

[0372] Manufacturing Example 6 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3580 g of deionized water, 100 g of paraffin wax, and 5.4 g of the ammonium salt of perfluoroether carboxylic acid C. The autoclave was heated to 70 °C and the atmosphere was purged with nitrogen gas to remove oxygen. 0.50 g of HFP was then added using TFE, followed by TFE injection to adjust the system pressure to 0.78 MPaG. The system temperature was maintained at 70 °C while stirring. Next, an aqueous solution containing 15.4 mg of ammonium persulfate dissolved in 20 g of water was added using TFE injection to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70 °C and the system pressure at 0.78 MPaG. When 430 g of TFE had been consumed since the start of polymerization, an aqueous solution of 18.0 mg of hydroquinone as a radical scavenger dissolved in 20 g of water was injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached 1,540 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to normal pressure, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The solids concentration of the resulting aqueous PTFE dispersion was 29.6 mass% and the average primary particle size was 246 nm.

[0373] Example 7 The PTFE aqueous dispersion obtained in Production Example 6 was diluted to a solid concentration of 13% by mass, stirred in a container equipped with a stirrer to solidify, and then filtered to separate the water, yielding a wet powder having a water content of approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180° C. After 18 hours, the mesh tray was taken out and cooled in air to obtain a PTFE powder. The resulting PTFE powder had an SSG of 2.146 and an HFP content of 0.019% by mass. Various physical properties of the resulting PTFE powder were measured. The results are shown in Table 12.

[0374] Manufacturing Example 7 Except for changing the amount of HFP charged to 0.06 g, an aqueous PTFE dispersion was obtained in the same manner as in Production Example 6. The solids concentration of the obtained aqueous PTFE dispersion was 29.2 mass %, and the average primary particle diameter was 274 nm.

[0375] Example 8 Using the PTFE aqueous dispersion obtained in Production Example 7, a wet powder was obtained in the same manner as in Example 7. The moisture content of the wet powder was about 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 ) and the heat treatment temperature was changed to 160°C, and the same procedure as in Example 7 was carried out to obtain a PTFE powder. The resulting PTFE powder had an SSG of 2.154 and an HFP content of 0.002% by mass. Various physical properties of the resulting PTFE powder were measured. The results are shown in Table 12.

[0376] Manufacturing Example 8 A 6-L stainless steel reactor equipped with a stirrer was charged with 3600 g of deionized water, 180 g of paraffin wax, and 5.4 g of the ammonium salt of perfluoroether carboxylic acid C. The contents of the reactor were then heated to 80°C while evacuating and simultaneously purging with tetrafluoroethylene (TFE) to remove oxygen from the reactor, and the contents were stirred. 3.1 g of vinylidene fluoride (VDF) was added to the reactor under pressure using TFE, followed by the addition of TFE to bring the pressure to 2.70 MPaG. An initiator solution containing 7.2 mg of ammonium persulfate (APS) dissolved in deionized water was added to the reactor. After the initiator injection, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 2.70 MPaG. When the amount of TFE charged reached 430 g, an aqueous solution containing 18.2 mg of hydroquinone dissolved in deionized water was added. When the amount of TFE charged reached 1580 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. The reactor was then evacuated until the pressure inside reached normal pressure, and the inside was replaced with nitrogen. The contents were then removed from the reactor and cooled. The paraffin wax was removed, yielding an aqueous PTFE dispersion. The solids concentration of the resulting aqueous PTFE dispersion was 30.3% by mass, and the average primary particle size was 223 nm.

[0377] Example 9 The PTFE aqueous dispersion obtained in Production Example 8 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 210°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. The obtained PTFE powder had an SSG of 2.221 and a VDF content of 0.025% by mass. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 12.

[0378] Manufacturing Example 9 A 6-L stainless steel reactor equipped with a stirrer was charged with 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of the ammonium salt of perfluoroether carboxylic acid C, and 0.0265 g of oxalic acid. The contents of the reactor were then heated to 70°C while evacuating and simultaneously purging with tetrafluoroethylene (TFE) to remove oxygen from the reactor, and the contents were stirred. 1.70 g of vinylidene fluoride (VDF) was added to the reactor under pressure using TFE, followed by the addition of TFE to bring the pressure to 2.70 MPaG. An aqueous solution of potassium permanganate (3.4 mg of potassium permanganate dissolved in deionized water) was continuously added to the reactor as an initiator. After the initiator injection, a pressure drop occurred and the initiation of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 2.70 MPaG. When the amount of TFE charged reached 430 g, the addition of the aqueous potassium permanganate solution was stopped. When the amount of TFE charged reached 1815 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated. The reactor was then evacuated until the pressure inside reached normal pressure, and the contents were replaced with nitrogen. The contents were then removed from the reactor and cooled. The paraffin wax was removed, yielding an aqueous PTFE dispersion. The solids concentration of the resulting aqueous PTFE dispersion was 33.3% by mass, and the average primary particle size was 251 nm.

[0379] Example 10 The PTFE aqueous dispersion obtained in Production Example 9 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 210°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. The obtained PTFE powder had an SSG of 2.206 and a VDF content of 0.011% by mass. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 12.

[0380] [Table 12]

[0381] Furthermore, in the PTFE powders obtained in Examples 5 to 10, the fluorine-containing compound represented by the following formula was not detected, or the content was less than 10 ppb by mass. F(CF2)7COOH, F(CF2)5COOH, H(CF2)6COOH, H(CF2)7COOH, CF3O(CF2)3OCHFCF2COOH, C3F7OCF(CF3)CF2OCF(CF3)COOH, CF3CF2CF2OCF(CF3)COOH (perfluoroether carboxylic acid A), CF3CF2OCF2CF2OCF2COOH (perfluoroether carboxylic acid B), C2F5OCF(CF3)CF2OCF(CF3)COOH, CF3OCF(CF3)CF2OCF(CF3)COOH (perfluoroether carboxylic acid C), CF2ClCF2CF2OCF(CF3)CF2OCF2COOH, CF2ClCF2CF2OCF2CF(CF3)OCF2COOH, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOH, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOH, and [ka] (wherein M is H).

[0382] Example 11 A PTFE powder was obtained in the same manner as in Example 1, except that the heat treatment at 180°C for 5 hours was changed to a heat treatment at 210°C for 18 hours. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 13 and 14.

[0383] Example 12 A PTFE powder was obtained in the same manner as in Example 1, except that the heat treatment at 210°C for 5 hours was performed instead of at 180°C for 5 hours. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 13 and 14.

[0384] Comparative Example 7 A PTFE powder was obtained in the same manner as in Comparative Example 1, except that the heat treatment at 180°C for 5 hours was changed to a heat treatment at 210°C for 18 hours. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 13 and 14.

[0385] Example 13 A PTFE powder was obtained in the same manner as in Example 4, except that the heat treatment at 210°C for 18 hours was performed instead of at 180°C for 20 hours. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 13 and 14.

[0386] Comparative Example 8 A PTFE powder was obtained in the same manner as in Comparative Example 5, except that the heat treatment at 210°C for 5 hours was changed from 18 hours at 210°C. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 13 and 14.

[0387] Manufacturing Example 10 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3580 g of deionized water, 100 g of paraffin wax, and 5.4 g of ammonium salt of perfluoroether carboxylic acid C. The autoclave was heated to 70 °C and the atmosphere was purged with nitrogen gas to remove oxygen. 0.11 g of HFP was then injected using TFE, followed by TFE injection to adjust the system pressure to 0.78 MPaG. The system temperature was maintained at 70 °C while stirring. Next, an aqueous solution of 15.4 mg of ammonium persulfate dissolved in 20 g of water was injected using TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70 °C and the system pressure at 0.78 MPaG. When 430 g of TFE had been consumed since the start of polymerization, an aqueous solution of 18.0 mg of hydroquinone as a radical scavenger dissolved in 20 g of water was injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached 1,540 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to normal pressure, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The solids concentration of the resulting aqueous PTFE dispersion was 29.8 mass% and the average primary particle size was 312 nm.

[0388] Example 14 The PTFE aqueous dispersion obtained in Production Example 10 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. The obtained PTFE powder had an SSG of 2.153 and an HFP content of 0.005% by mass. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 13 and 14.

[0389] [Table 13]

[0390] [Table 14]

[0391] The results shown in Tables 11, 13, and 14 show that as the moisture content increases, the extrusion pressure decreases and the coefficient of variation of the extrusion pressure increases. In addition, the appearance of the unsintered film and the PTFE porous membrane deteriorates. When the moisture content was increased beyond 0.1%, holes were formed in the unbaked film. It can be seen that as the moisture content increases, the pressure drop of the filter medium decreases, the coefficient of variation of the pressure drop increases, and the pressure drop becomes non-uniform.

[0392] Example 15 A PTFE powder was obtained in the same manner as in Example 1, except that the heat treatment at 135°C for 18 hours was performed instead of at 180°C for 5 hours. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 15 and 16.

[0393] Comparative Example 9 A PTFE powder was obtained in the same manner as in Comparative Example 1, except that the heat treatment at 135°C for 18 hours was performed instead of at 180°C for 5 hours. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 15 and 16.

[0394] Manufacturing Example 11 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3600 g of deionized water, 180 g of paraffin wax, and 5.4 g of ammonium salt of perfluoroethercarboxylic acid C. The polymerization vessel was heated to 85°C and the atmosphere inside was purged with nitrogen gas to remove oxygen. After maintaining the temperature inside the vessel at 85°C while stirring, TFE gas was introduced to set the pressure to 2.4 MPaG. While stirring the contents, deionized water containing 468 mg of disuccinic acid peroxide was added to initiate polymerization. As the polymerization progressed, the pressure inside the polymerization vessel decreased, but TFE was continuously fed to maintain a constant pressure of 2.4 MPaG. When the TFE consumption reached 1,580 g, stirring and TFE supply were stopped, and the TFE in the polymerization vessel was purged to terminate the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 294 nm, and the solids concentration was 30.4 mass%.

[0395] Example 16 The PTFE aqueous dispersion obtained in Production Example 11 was diluted to a solids concentration of 13% by mass, vigorously stirred in a container equipped with a stirrer to solidify, and then filtered to separate the water, yielding a wet powder having a water content of approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 170°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. The SSG of the obtained PTFE powder was 2.160. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 15 and 16.

[0396] Manufacturing Example 12 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-controlling jacket was charged with 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of ammonium salt of perfluoroethercarboxylic acid C, and 0.0252 g of oxalic acid. The polymerization vessel was heated to 70°C and the atmosphere was purged with nitrogen gas to remove oxygen. After maintaining the temperature at 70°C with stirring, TFE gas was introduced to adjust the pressure to 2.7 MPaG. While stirring the contents, deionized water containing 7.5 mg of potassium permanganate was continuously added at a constant rate, and TFE was continuously supplied to maintain a constant pressure of 2.7 MPaG in the polymerization vessel. When the TFE consumption amount reached 1,730 g, stirring and the supply of TFE were stopped, and the TFE in the polymerization vessel was purged to terminate the polymerization reaction. The aqueous dispersion was taken out and cooled, and then the paraffin wax was separated to obtain an aqueous PTFE dispersion. The resulting PTFE aqueous dispersion had an average primary particle size of 296 nm and a solid content of 32.4 mass %.

[0397] Example 17 The PTFE aqueous dispersion obtained in Production Example 12 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. The SSG of the obtained PTFE powder was 2.156. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 15 and 16.

[0398] [Table 15]

[0399] [Table 16]

[0400] From Example 15 and Comparative Example 9 in Table 15, it can be seen that as the moisture content increases, the extrusion pressure decreases and the pressure loss decreases. Although it is suitable as a HEPA filter medium, as the moisture content increases, the extrusion pressure decreases and the coefficient of variation of the extrusion pressure worsens, as shown in Comparative Example 9. Furthermore, in the stretched membrane evaluation, the extrusion pressure decreases and the pressure loss of the filter medium worsens. In Examples 16 and 17, the SSG is larger than in Example 15, so the collection efficiency of the filter medium is lower, but the pressure loss is low and the coefficient of variation of the pressure loss is small, so they can be used as filter medium.

[0401] Manufacturing Example 13 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3580 g of deionized water, 100 g of paraffin wax, and 5.4 g of the ammonium salt of perfluoroether carboxylic acid C. The autoclave was heated to 80°C and the atmosphere was purged with nitrogen gas to remove oxygen. After adding 1.20 g of CTFE, TFE was further injected to bring the system pressure to 0.78 MPaG, and the system temperature was maintained at 80°C while stirring. Next, an aqueous solution of 360 mg of disuccinic acid peroxide in 20 g of water and an aqueous solution of 10 mg of ammonium persulfate in 20 g of water were injected with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 80°C and the system pressure at 0.78 MPaG. When 1530 g of TFE had been consumed since the start of polymerization (90% conversion), 4.2 g of PTFE was added under pressure. The polymerization continued, and when the amount of TFE polymerized reached 1700 g from the start of polymerization, stirring and the supply of TFE were stopped. The gas in the system was immediately released to normal pressure, and the polymerization reaction was terminated. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 241 nm, and the solids concentration was 32.0 mass%.

[0402] Example 18 The PTFE aqueous dispersion obtained in Production Example 13 was diluted to a solids concentration of 13% by mass, vigorously stirred in a container equipped with a stirrer to solidify, and then filtered to separate the water, yielding a wet powder. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 145°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.170, and the CTFE content was 0.23% by mass. The results are shown in Tables 17 to 19.

[0403] Example 19 A PTFE powder was obtained in the same manner as in Example 18, except that the heat treatment at 145°C for 5 hours was changed from 18 hours at 145°C. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 17 to 19.

[0404] Comparative Example 10 The PTFE aqueous dispersion obtained in Production Example 13 was diluted to a solids concentration of 13% by mass, and the PTFE was coagulated in a container while stirring, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet PTFE powder was placed on a stainless steel flat tray (amount placed: 2.0 g / cm 2 The flat tray was heat-treated in a hot air circulating electric furnace at 145°C. After 18 hours, the flat tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 17 to 19.

[0405] Comparative Example 11 A PTFE powder was obtained in the same manner as in Comparative Example 10, except that the heat treatment at 145°C for 5 hours was changed from 18 hours at 145°C. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 17 to 19.

[0406] Manufacturing Example 14 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3560 g of deionized water, 100 g of paraffin wax, and 0.9 g of ammonium salt of perfluoroether carboxylic acid C. The autoclave was heated to 70°C and the atmosphere was purged with nitrogen gas to remove oxygen. After adding 0.67 g of PPVE and 0.37 g of HFP, TFE was further injected to bring the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C while stirring. Next, an aqueous solution of 322 mg of disuccinic acid peroxide in 20 g of water and an aqueous solution of 13 mg of ammonium persulfate in 20 g of water were injected with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 160 g of TFE had been consumed since the start of polymerization, 4.5 g of ammonium salt of perfluoroethercarboxylic acid C was injected with TFE. When 1,440 g of TFE had been consumed since the start of polymerization (90% conversion), 1.57 g of HFP and 0.5 g of methanol were injected with TFE. The polymerization continued thereafter, and when the amount of TFE polymerized reached 1,600 g since the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to normal pressure, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 249 nm, and the solids concentration was 30.7 mass%.

[0407] Example 20 The PTFE aqueous dispersion obtained in Production Example 14 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2The mesh tray was heat-treated in a hot air circulating electric furnace at 145°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The obtained PTFE powder had an SSG of 2.176, a PPVE content of 0.03% by mass, and an HFP content of 0.05% by mass. The results are shown in Tables 17 to 19.

[0408] Comparative Example 12 The same procedure as in Example 20 was carried out except that the heat treatment in the mesh tray was changed to the heat treatment in the flat tray. A PTFE powder was obtained. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 17 to 19.

[0409] Manufacturing Example 15 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3560 g of deionized water, 100 g of paraffin wax, and 1.2 g of ammonium salt of perfluoroether carboxylic acid C. The autoclave was heated to 80°C and the atmosphere was purged with nitrogen gas to remove oxygen. After adding 2.6 g of PPVE and 0.67 g of HFP, TFE was further injected to bring the system pressure to 1.5 MPaG, and the system temperature was maintained at 80°C while stirring. Next, an aqueous solution of 285 mg of disuccinic acid peroxide in 20 g of water and an aqueous solution of 11 mg of ammonium persulfate in 20 g of water were injected with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 80°C and the system pressure at 1.5 MPaG. When 180 g of TFE had been consumed since the start of polymerization (10% conversion), the TFE supply and stirring were stopped. Gas was slowly released until the system pressure reached 0.1 MPaG. Then, TFE was supplied until the system pressure reached 1.5 MPaG, and stirring was resumed. At the same time, 4.5 g of ammonium salt of perfluoroethercarboxylic acid C was injected with TFE. When 1620 g of TFE had been consumed since the start of polymerization (90% conversion), 5.70 g of HFP and 0.17 g of methanol were injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached 1800 g since the start of polymerization, stirring and the TFE supply were stopped. The gas in the system was immediately released to return to normal pressure, and the polymerization reaction was terminated. The aqueous dispersion was removed, cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 252 nm, and the solids concentration was 33.2 wt%.

[0410] Example 21 The PTFE aqueous dispersion obtained in Production Example 15 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2The mesh tray was heat-treated in a hot air circulating electric furnace at 145°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The obtained PTFE powder had an SSG of 2.176, a PPVE content of 0.03% by mass, and an HFP content of 0.07% by mass. The results are shown in Tables 17 to 19.

[0411] Manufacturing Example 16 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3560 g of deionized water, 100 g of paraffin wax, and 1.45 g of the ammonium salt of perfluoroether carboxylic acid C. The autoclave was heated to 70°C and the atmosphere was purged with nitrogen gas to remove oxygen. After adding 3.0 g of PPVE, TFE was further injected to bring the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C while stirring. Next, an aqueous solution of 326 mg of disuccinic acid peroxide in 20 g of water and an aqueous solution of 12 mg of ammonium persulfate in 20 g of water were injected with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 170 g of TFE had been consumed since the start of polymerization, 2.2 g of ammonium salt of perfluoroethercarboxylic acid C was injected with TFE. When 1,530 g of TFE had been consumed since the start of polymerization (90% conversion), 0.28 g of methanol was injected with TFE. The polymerization continued thereafter, and when the amount of TFE polymerized reached 1,700 g since the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to return to normal pressure, thereby terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 243 nm, and the solids concentration was 31.6 mass%.

[0412] Example 22 The PTFE aqueous dispersion obtained in Production Example 16 was diluted to a solids concentration of 13% by mass, and the mixture was vigorously stirred in a container equipped with a stirrer to solidify, and then the water was filtered off to obtain a wet powder. The water content of the wet powder was approximately 40% by mass. The obtained wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 145°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.166, and the PPVE content was 0.13% by mass. The results are shown in Tables 17 to 19. Furthermore, the content of the compound having 9 to 14 carbon atoms and represented by general formula (2) in the obtained PTFE powder was below the lower limit of determination.

[0413] Comparative Example 13 A PTFE powder was obtained in the same manner as in Example 22, except that the heat treatment in a flat tray was used instead of the heat treatment in a mesh tray. Various physical properties of the obtained PTFE powder were measured. The results are shown in Tables 17 and 18. Furthermore, the content of the compound having 9 carbon atoms and represented by general formula (2) in the obtained PTFE powder was 2 ppb by mass, the content of the compound having 11 carbon atoms was 11 ppb by mass, the content of the compound having 13 carbon atoms was 18 ppb by mass, and the contents of the compounds having 10, 12, and 14 carbon atoms were below the lower limit of quantitation.

[0414] [Table 17]

[0415] [Table 18]

[0416] Table 17 shows that as the moisture content increases, the extrusion pressure decreases and the coefficient of variation of the extrusion pressure increases. When the moisture content exceeds 0.1%, the extrusion pressure becomes unstable and good beads cannot be obtained. In the evaluation of coated wires, it was found that as the moisture content increased, the wire diameter fluctuation increased, the number of sparks exceeded 10, and the self-winding heat resistance decreased.

[0417] [Table 19]

[0418] Furthermore, in the PTFE powders obtained in Examples 11 to 22, the fluorine-containing compound represented by the following formula was not detected, or the content was 10 ppb by mass or less. F(CF2)7COOH, F(CF2)5COOH, H(CF2)6COOH, H(CF2)7COOH, CF3O(CF2)3OCHFCF2COOH, C3F7OCF(CF3)CF2OCF(CF3)COOH, CF3CF2CF2OCF(CF3)COOH (perfluoroether carboxylic acid A), CF3CF2OCF2CF2OCF2COOH (perfluoroether carboxylic acid B), C2F5OCF(CF3)CF2OCF(CF3)COOH, CF3OCF(CF3)CF2OCF(CF3)COOH (perfluoroether carboxylic acid C), CF2ClCF2CF2OCF(CF3)CF2OCF2COOH, CF2ClCF2CF2OCF2CF(CF3)OCF2COOH, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOH, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOH, and [ka] (wherein M is H).

Claims

1. A fine powder of a homopolymer of tetrafluoroethylene or a modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on a modified monomer, A polytetrafluoroethylene fine powder that is substantially free of moisture and a fluorine-containing compound represented by CF 3 CF 2 OCF 2 CF 2 OCF 2 COONH 4 .

2. A fine powder of a homopolymer of tetrafluoroethylene or a modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on a modified monomer, A polytetrafluoroethylene fine powder that is substantially free of moisture and a fluorine-containing compound represented by CF 3 CF 2 CF 2 OCF(CF 3 )COONH 4 .

3. 3. The polytetrafluoroethylene fine powder according to claim 1, wherein the content of the fluorine-containing compound is less than 25 ppb by mass relative to the polytetrafluoroethylene fine powder.

4. A fine powder of a homopolymer of tetrafluoroethylene or a modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on a modified monomer, A stretchable polytetrafluoroethylene fine powder having a standard specific gravity of 2.160 or less and substantially free of water and a fluorine-containing compound represented by CF 3 CF 2 OCF 2 CF 2 OCF 2 COONH 4 .

5. A fine powder of a homopolymer of tetrafluoroethylene or a modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on a modified monomer, A polytetrafluoroethylene fine powder which is stretchable, has a standard specific gravity of 2.160 or less, and is substantially free of water and a fluorine-containing compound represented by CF 3 CF 2 CF 2 OCF(CF 3 )COONH 4 .

6. 6. The polytetrafluoroethylene fine powder according to claim 4, wherein the breaking strength measured using an elongated bead obtained in an elongation test at a total elongation rate of 2,400% is 25.0 N or more and 70.0 N or less.

7. 6. The polytetrafluoroethylene fine powder according to claim 4, wherein the breaking strength measured using an elongated bead obtained in an elongation test at a total elongation rate of 2,400% is 10.0 N or more and less than 25.0 N.

8. 6. The polytetrafluoroethylene fine powder according to claim 4, wherein the extrusion pressure at a reduction ratio of 100 is 18 MPa or less.

9. 6. The polytetrafluoroethylene fine powder according to claim 4, wherein the content of the fluorine-containing compound is less than 25 ppb by mass relative to the polytetrafluoroethylene fine powder.

10. 6. The polytetrafluoroethylene fine powder according to claim 4, wherein the water content is 0.010% by mass or less based on the polytetrafluoroethylene fine powder.

11. 6. The polytetrafluoroethylene fine powder according to claim 4, obtained by polymerization carried out in the presence of a fluorine-containing surfactant.

12. The polytetrafluoroethylene fine powder according to claim 4 or 5, which is an oriented material.

13. A stretched body using the polytetrafluoroethylene fine powder according to claim 4 or 5.

14. The stretched body according to claim 13, which is a porous membrane, a biaxially stretched membrane, or a filter medium.

15. A fine powder of modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on a modified monomer, A modified polytetrafluoroethylene fine powder which can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of moisture and a fluorine-containing compound represented by CF 3 CF 2 OCF 2 CF 2 OCF 2 COONH 4 .

16. A fine powder of modified polytetrafluoroethylene containing 99.0 mass% or more of polymerization units based on tetrafluoroethylene and 1.0 mass% or less of polymerization units based on a modified monomer, A modified polytetrafluoroethylene fine powder which can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of moisture and a fluorine-containing compound represented by CF 3 CF 2 CF 2 OCF(CF 3 )COONH 4 .

17. A modified polytetrafluoroethylene fine powder according to claim 15 or 16, wherein the standard specific gravity is 2.155 to 2.

190.

18. The modified polytetrafluoroethylene fine powder according to claim 15 or 16, wherein the extrusion pressure at a reduction ratio of 1500 is 15 to 80 MPa.

19. 17. The modified polytetrafluoroethylene fine powder according to claim 15, wherein the content of the fluorine-containing compound is less than 25 ppb by mass relative to the modified polytetrafluoroethylene fine powder.

20. 17. The modified polytetrafluoroethylene fine powder according to claim 15 or 16, having a water content of 0.010% by mass or less based on the modified polytetrafluoroethylene fine powder.

21. 17. The modified polytetrafluoroethylene fine powder according to claim 15 or 16, obtained by polymerization carried out in the presence of a fluorine-containing surfactant.

22. A molded article using the modified polytetrafluoroethylene fine powder according to claim 15 or 16.

23. The molded article according to claim 22, which is an electric wire coating material or a tube.

24. A fine powder of modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on perfluorovinyl ether, A modified polytetrafluoroethylene fine powder modified with perfluorovinyl ether, which can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of moisture and fluorine-containing compounds represented by general formula (2) and CF 3 CF 2 OCF 2 CF 2 OCF 2 COONH 4. General formula (2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.)

25. A fine powder of modified polytetrafluoroethylene containing 99.0% by mass or more of polymerization units based on tetrafluoroethylene and 1.0% by mass or less of polymerization units based on perfluorovinyl ether, A modified polytetrafluoroethylene fine powder modified with perfluorovinyl ether, which can be paste-extruded, has a standard specific gravity of 2.135 to 2.200, and is substantially free of moisture and fluorine-containing compounds represented by general formula (2) and CF 3 CF 2 CF 2 OCF(CF 3 )COONH 4 . General formula (2): [C n-1 F 2n-1 COO − ]M + (wherein n is an integer of 9 to 14, and M + represents a cation.)

26. A modified polytetrafluoroethylene fine powder according to claim 24 or 25, wherein the standard specific gravity is 2.155 to 2.

190.

27. 26. The modified polytetrafluoroethylene fine powder according to claim 24 or 25, wherein the amount of modification with perfluorovinyl ether is 0.02% by mass or more and 0.30% by mass or less.

28. The modified polytetrafluoroethylene fine powder according to claim 24 or 25, wherein the extrusion pressure at a reduction ratio of 1500 is 15 to 80 MPa.

29. 26. The modified polytetrafluoroethylene fine powder according to claim 24 or 25, wherein the total content of the fluorine-containing compounds is less than 25 ppb by mass with respect to the modified polytetrafluoroethylene fine powder.