Method for producing aqueous dispersion of low molecular weight polytetrafluoroethylene

Abstract

Provided is a production method in which tetrafluoroethylene is polymerized in the presence of a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon-based chain transfer agent, and an aqueous medium, thereby preparing an aqueous dispersion containing low-molecular-weight polytetrafluoroethylene, after the aqueous dispersion is prepared, the aqueous dispersion is pretreated, and the low-molecular-weight polytetrafluoroethylene is produced by polymerizing tetrafluoroethylene in the presence of a fluorine-containing surfactant, a polymerization initiator, a hydrocarbon-based chain transfer agent, and an aqueous medium. A radical generator is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the radical generator is heat-treated, thereby obtaining an aqueous dispersion of low molecular weight polytetrafluoroethylene.

Description

Technical Field

[0001] The present invention relates to a method for producing a low-molecular-weight polytetrafluoroethylene aqueous dispersion. Background Art

[0002] Patent Document 1 describes a method for producing a fluoropolymer composition, which is a method for producing a fluoropolymer composition containing a fluoropolymer, wherein a fluoromonomer is polymerized in a reactor in the presence of a fluorosurfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing the fluoropolymer. After the aqueous dispersion is prepared, either the fluoromonomer remaining in the reactor is removed from the reactor or the aqueous dispersion in the reactor is recovered and stored in a container different from the reactor. A free radical generator is added to the aqueous dispersion, and the aqueous dispersion containing the free radical generator is heat-treated to obtain the fluoropolymer composition.

[0003] Patent Document 2 describes a method for producing a fluoropolymer composition containing a fluoropolymer, wherein a fluoromonomer is polymerized in a reactor in the presence of a fluorosurfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing the fluoropolymer, an inert gas is supplied to the reactor, and the aqueous dispersion in the reactor is heat-treated to obtain the fluoropolymer composition.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2022 / 163814

[0007] Patent Document 2: International Publication No. 2022 / 163815 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] An object of the present invention is to provide a method for producing an aqueous dispersion of low-molecular-weight polytetrafluoroethylene having a reduced content of a fluorine-containing compound having a hydrophilic group.

[0010] Means for solving problems

[0011] According to the present invention, a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene is provided, comprising polymerizing tetrafluoroethylene in the presence of a fluorinated surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium to prepare an aqueous dispersion containing low molecular weight polytetrafluoroethylene, pre-treating the obtained aqueous dispersion, adding a free radical generator to the pre-treated aqueous dispersion, and heat-treating the aqueous dispersion containing the free radical generator to obtain the aqueous dispersion of low molecular weight polytetrafluoroethylene.

[0012] Effects of the Invention

[0013] According to the present invention, there can be provided a method for producing an aqueous dispersion of low-molecular-weight polytetrafluoroethylene having a reduced content of a fluorine-containing compound having a hydrophilic group. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 These are first-order differential spectra obtained by analyzing the aqueous dispersions obtained in Examples 1, 9, 11, 15, and 16 using an electron spin resonance method. DETAILED DESCRIPTION

[0015] Before describing the present invention in detail, some terms used in the present invention are defined or described.

[0016] In the present invention, melt processability refers to the ability to melt and process the polymer using existing processing equipment such as extruders and injection molding machines. Therefore, melt-processable fluororesins generally have a melt flow rate of 0.01 g / 10 min to 500 g / 10 min as measured by the measurement method described below.

[0017] In the present invention, the polytetrafluoroethylene [PTFE] is preferably a fluorine-containing polymer having a tetrafluoroethylene unit content of 99 mol % or more based on all polymerized units.

[0018] In the present invention, the content of each monomer constituting the fluorinated polymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer.

[0019] In the present invention, an "organic group" refers to a group containing one or more carbon atoms, or a group formed by removing one hydrogen atom from an organic compound. The organic group is preferably an alkyl group which may have one or more substituents.

[0020] In the present invention, ranges represented by endpoints include all numerical values ​​included in the ranges (for example, 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0021] In the present invention, the term "at least 1" includes all numerical values ​​greater than or equal to 1 (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0022] Hereinafter, specific embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0023] Patent Documents 1 and 2 propose the above-mentioned production method as a method for producing a fluoropolymer composition having a reduced content of a fluorosurfactant used when polymerizing a fluoromonomer and a reduced content of a fluorochemical compound produced by polymerization of the fluoromonomer.

[0024] However, there is a demand for a method for reducing the content of a fluorine-containing compound having a hydrophilic group in an aqueous dispersion of low-molecular-weight polytetrafluoroethylene by a means different from the conventional production method.

[0025] In the production method of the present invention, tetrafluoroethylene is polymerized in the presence of a fluorinated surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium to prepare an aqueous dispersion containing low molecular weight polytetrafluoroethylene. After the aqueous dispersion is prepared, the aqueous dispersion is pretreated, a free radical generator is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the free radical generator is heat-treated to obtain an aqueous dispersion of low molecular weight polytetrafluoroethylene.

[0026] Each step and the materials used in each step are described in detail below.

[0027] (Polymerization of tetrafluoroethylene)

[0028] In the production method of the present invention, tetrafluoroethylene is first polymerized in the presence of a fluorinated surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium to prepare an aqueous dispersion containing low-molecular-weight polytetrafluoroethylene.

[0029] The polymerization of tetrafluoroethylene can be carried out in a reactor. The polymerization of tetrafluoroethylene can be carried out as follows: for example, tetrafluoroethylene, a fluorinated surfactant, a polymerization initiator, an aqueous medium, and other additives as needed are added to a reactor, the contents of the reactor are stirred, the reactor is then maintained at a specified polymerization temperature, and a specified amount of polymerization initiator is then added to initiate the polymerization reaction. After the polymerization reaction begins, tetrafluoroethylene, polymerization initiator, fluorinated surfactant, chain transfer agent, etc. can be added according to the purpose. The polymerization method of tetrafluoroethylene is not particularly limited, and an emulsion polymerization method is preferred.

[0030] (Fluorinated surfactant)

[0031] The fluorinated surfactant used in the polymerization of tetrafluoroethylene may be a fluorinated surfactant commonly used in the polymerization of tetrafluoroethylene. Typical fluorinated surfactants have a molecular weight of 1000 g / mol or less, preferably 800 g / mol or less.

[0032] The fluorinated surfactant is not particularly limited as long as it contains at least one fluorine atom, and a conventionally known fluorinated surfactant can be used.

[0033] Examples of the fluorinated surfactant include anionic fluorinated surfactants, etc. The anionic fluorinated surfactant may be, for example, a surfactant containing fluorine atoms and having a total carbon number of 20 or less in the moiety excluding the anionic group.

[0034] Furthermore, the fluorine-containing surfactant may be a surfactant containing fluorine whose anionic portion has a molecular weight of 1000 or less.

[0035] It should be noted that the above-mentioned "anionic part" refers to the part other than the cation of the above-mentioned fluorinated surfactant. For example, in the F(CF2) shown in the formula (I) described later n1 In the case of COOM, it is "F(CF2) n1 COO” part.

[0036] Examples of the fluorinated surfactant include those having a LogPOW of 3.5 or less. The LogPOW is the partition coefficient between 1-octanol and water and is represented by LogP [where P represents the ratio of the fluorinated surfactant concentration in octanol to the fluorinated surfactant concentration in water when a 1:1 octanol / water mixture containing the fluorinated surfactant undergoes phase separation].

[0037] The above LogPOW is calculated as follows: On column: TOSOH ODS-120T column ( HPLC was performed on standard substances with known octanol / water partition coefficients (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) under the following conditions: (a) a column having a 1:1 ratio of 1:1 and a column temperature of 40°C; (b) a column having a 1:1 ratio of 1:1 and a column temperature of 40°C; (c) a column having a 1:1 ratio of 1:1 and a column temperature of 40°C; (d) a column having a 1:1 ratio of 1:1 and a column temperature of 40°C; (e) a column having a 1:1 ratio of 1:1 and a column temperature of 40°C; (e) a column having a 1:1 ratio of 1:1 and a column temperature of 50°C; (f) a column having a 1:1 ratio of 1:1 and a column temperature of 50°C; (f) a column having a 1:1 ratio of 1:1 and a column temperature of 50°C; (g) a column having a 1:1 ratio of 1:1 and a column temperature of 50°C; (h ...

[0038] Specific examples of the fluorinated surfactants include U.S. Patent Application Publication No. 2007 / 0015864, U.S. Patent Application Publication No. 2007 / 0015865, U.S. Patent Application Publication No. 2007 / 0015866, U.S. Patent Application Publication No. 2007 / 0276103, U.S. Patent Application Publication No. 2007 / 0117914, U.S. Patent Application Publication No. 2007 / 142541, U.S. Patent Application Publication No. 2008 / 0015319, and U.S. Patent No. 3,250,808. 3271341, Japanese Patent Application Publication No. 2003-119204, International Publication No. 2005 / 042593, International Publication No. 2008 / 060461, International Publication No. 2007 / 046377, Japanese Patent Application Publication No. 2007-119526, International Publication No. 2007 / 046482, International Publication No. 2007 / 046345, U.S. Patent Application Publication No. 2014 / 0228531, International Publication No. 2013 / 189824, and International Publication No. 2013 / 189826.

[0039] Examples of the anionic fluorinated surfactant include the following general formula (N 0 ):

[0040] X n0 -Rf n0 -Y 0 (N 0 )

[0041] (Where, X n0 For H, Cl or and F. Rf n0 It is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H groups are replaced by F. The alkylene group may contain one or more ether bonds, and some of the H groups may be replaced by Cl. 0 is an anionic group).

[0042] Y 0 The anionic group may be -COOM, -SO2M or -SO3M, or may be -COOM or -SO3M.

[0043] M is H, metal atom, NR 7 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7 is H or an organic group.

[0044] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, and Li.

[0045] As R 7 , which can be H or C 1-10 The organic group can also be H or C 1-4 The organic group can also be H or C 1-4 of alkyl.

[0046] M can be H, metal atom or NR 7 4, can also be H, alkali metal (Group 1), alkaline earth metal (Group 2) or NR 7 4, can also be H, Na, K, Li or NH4.

[0047] The above Rf n0 In the present invention, more than 50% of the H can be replaced by fluorine.

[0048] As the above general formula (N 0 ) can be exemplified by:

[0049] The following general formula (N 1 ):

[0050] X n0 -(CF2) m1 -Y 0 (N 1 )

[0051] (Where, X n0 is H, Cl and F, m1 is an integer from 3 to 15, Y 0 The compound represented by the following general formula (N 2 ):

[0052] Rf n1 -O-(CF(CF3)CF2O) m2 CFX n1 -Y 0 (N 2 )

[0053] (Where Rf n1 is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, X n1 F or CF3, Y 0 The compound represented by the following general formula (N 3 ):

[0054] Rf n2 (CH2) m3 -(Rf n3 ) q -Y0 (N 3 )

[0055] (Where Rf n2 is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond and / or a chlorine atom, m3 is an integer of 1 to 3, Rf n3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y 0 The compound represented by the following general formula (N 4 ):

[0056] Rf n4 -O-(CY n1 Y n2 ) p CF2-Y 0 (N 4 )

[0057] (Where Rf n4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond, n1 and Y n2 The same or different, H or F, p is 0 or 1, Y 0 The compound represented by the above-defined substance); and the general formula (N 5 ):

[0058] [Chemistry 1]

[0059]

[0060] (Where, X n2 、X n3 and X n4 Rf may be the same or different and is H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond. n5 is a linear or branched partially or fully fluorinated alkylene group having 1 to 3 carbon atoms and which may contain an ether bond, L is a connecting group, Y 0 is the substance defined above. n2 、X n3 、X n4 and Rf n5 The total number of carbon atoms is 18 or less).

[0061] As the above general formula (N 0), more specifically, the compounds represented by the following general formula (I), perfluorocarboxylic acid (I) represented by the following general formula (II), perfluoroether carboxylic acid (III) represented by the following general formula (III), perfluoroalkylalkylene carboxylic acid (IV) represented by the following general formula (IV), perfluoroalkoxyfluorocarboxylic acid (V) represented by the following general formula (V), perfluoroalkylsulfonic acid (VI) represented by the following general formula (VI), ω-H perfluorosulfonic acid (VII) represented by the following general formula (VII), perfluoroalkylalkylenesulfonic acid (VIII) represented by the following general formula (VIII), alkylalkylene carboxylic acid (IX) represented by the following general formula (IX), fluorocarboxylic acid (X) represented by the following general formula (X), alkoxyfluorosulfonic acid (XI) represented by the following general formula (XI), compound (XII) represented by the following general formula (XII), compound (XIII) represented by the following general formula (XIII), etc.

[0062] The above-mentioned perfluorocarboxylic acid (I) is represented by the following general formula (I):

[0063] F(CF2) n1 COOM(I)

[0064] (where n1 is an integer from 3 to 13, M is H, metal atom, NR 7 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7 is H or an organic group).

[0065] The above-mentioned ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II):

[0066] H(CF2) n2 COOM(II)

[0067] (wherein n2 is an integer of 4 to 15, and M is the substance defined above).

[0068] The above-mentioned perfluoroether carboxylic acid (III) is represented by the following general formula (III):

[0069] Rf 1 -O-(CF(CF3)CF2O) n3 CF(CF3)COOM(III)

[0070] (Where Rf 1 is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is the substance defined above).

[0071] The above-mentioned perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV):

[0072] Rf2 (CH2) n4 Rf 3 COOM(IV)

[0073] (Where Rf 2 is a perfluoroalkyl group having 1 to 5 carbon atoms, Rf 3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is the substance defined above).

[0074] The above-mentioned alkoxy fluorocarboxylic acid (V) is represented by the following general formula (V):

[0075] Rf 4 -O-CY 1 Y 2 CF2-COOM(V)

[0076] (Where Rf 4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond and / or a chlorine atom, 1 and Y 2 are the same or different, are H or F, and M is the substance defined above).

[0077] The above-mentioned perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI):

[0078] F(CF2) n5 SO3M(VI)

[0079] (wherein n5 is an integer of 3 to 14, and M is the substance defined above).

[0080] The above-mentioned ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII):

[0081] H(CF2) n6 SO3M(VII)

[0082] (wherein n6 is an integer of 4 to 14, and M is the substance defined above).

[0083] The above-mentioned perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII):

[0084] Rf 5 (CH2) n7 SO3M(VIII)

[0085] (Where Rf 5 is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is the substance defined above).

[0086] The above-mentioned alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX):

[0087] Rf 6 (CH2) n8 COOM(IX)

[0088] (Where Rf 6 is a linear or branched partially or fully fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer of 1 to 3, and M is the substance defined above).

[0089] The above-mentioned fluorocarboxylic acid (X) is represented by the following general formula (X):

[0090] Rf 7 -O-Rf 8 -O-CF2-COOM(X)

[0091] (Where Rf 7 is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond and / or a chlorine atom, Rf 8 is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and M is defined as above).

[0092] The above-mentioned alkoxy fluorosulfonic acid (XI) is represented by the following general formula (XI):

[0093] Rf 9 -O-CY 1 Y 2 CF2-SO3M(XI)

[0094] (Where Rf 9 is a linear or branched, partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond and may contain chlorine, 1 and Y 2 are the same or different, are H or F, and M is the substance defined above).

[0095] The above compound (XII) is represented by the following general formula (XII):

[0096] [Chemistry 2]

[0097]

[0098] (Where X 1 、X 2 and X 3 Rf may be the same or different and is H, F and a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms which may contain an ether bond. 10is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a connecting group, Y 0 is an anionic group).

[0099] Y 0 It can be -COOM, -SO2M or -SO3M, or it can be -SO3M or COOM (wherein M is the substance defined above).

[0100] Examples of L include a single bond and a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may include an ether bond.

[0101] The above compound (XIII) is represented by the following general formula (XIII):

[0102] Rf 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM(XIII)

[0103] (Where Rf 11 is a fluorinated alkyl group having 1 to 5 carbon atoms and containing chlorine, n9 is an integer from 0 to 3, n10 is an integer from 0 to 3, and M is a substance as defined above). Examples of compound (XIII) include CF2ClO(CF2CF(CF3)O) n9 (CF2O) n10 CF2COONH4 (a mixture having an average molecular weight of 750, wherein n9 and n10 are the numbers defined above).

[0104] As described above, examples of the anionic fluorinated surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0105] The fluorinated surfactant may be a single type of fluorinated surfactant or a mixture of two or more types of fluorinated surfactants.

[0106] The fluorinated surfactant preferably does not have a methylene group (-CH2), more preferably does not have a CH bond. By using a fluorinated surfactant that does not have a methylene group (-CH2) or a CH bond in its molecule, polymerization of tetrafluoroethylene in the presence of an aqueous medium can be smoothly performed.

[0107] The number of H atoms possessed by the hydrophobic group of the fluorinated surfactant is preferably 0 or 1, more preferably 0. By using a fluorinated surfactant having a small number of H atoms bonded to the carbon atoms constituting the hydrophobic group, the polymerization of tetrafluoroethylene in the presence of an aqueous medium can be smoothly carried out. The number of carbon atoms in the hydrophobic group of the fluorinated surfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and further preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "part other than the anionic group" in the molecular structure of the fluorinated surfactant. As the hydrophilic group, Y 0 The fluorine-containing surfactant may be a saturated fluorinated surfactant in which all carbon atoms bonded to the hydrophobic group are substituted with fluorine atoms.

[0108] As the fluorinated surfactant, among the above-mentioned anionic fluorinated surfactants, there can be mentioned the general formula (N 1 ) represented by the compound of the general formula (N 2 ) represented by the compound of the general formula (N 4 ):

[0109] Rf n4 -O-(CY n1 F) p CF2-Y 0 (N 4 )

[0110] (Where Rf n4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms which may contain an ether bond (excluding alkyl groups having -CH2-), n1 is H or F, p is 0 or 1, Y 0 As defined above), and the compound represented by the general formula (N 5 ):

[0111] [Chemistry 3]

[0112]

[0113] (Where X n2 、X n3 and X n4 may be the same or different and are H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and which may contain an ether bond (excluding an alkyl group having -CH2-), wherein X n3 and X n4 Neither is H. Rf n5is a linear or branched partially or fully fluorinated alkylene group having 1 to 3 carbon atoms and which may contain an ether bond (excluding alkylene groups having -CH2-), L is a connecting group, and Y 0 As defined above. Where X n2 、X n3 、X n4 and Rf n5 The total number of carbon atoms is 18 or less).

[0114] As the fluorinated surfactant, among the above-mentioned anionic fluorinated surfactants, more preferably at least one selected from the group consisting of the following substances: a perfluorocarboxylic acid (I) represented by the general formula (I), an ω-H perfluorocarboxylic acid (II) represented by the general formula (II), a perfluoroether carboxylic acid (III) represented by the general formula (III), a perfluoroalkyl alkylene carboxylic acid (IV) represented by the general formula (IV), a perfluoroalkoxy fluorocarboxylic acid (V) represented by the general formula (V), a perfluoroalkylsulfonic acid (VI) represented by the general formula (VI), an ω-H perfluorosulfonic acid (VII) represented by the general formula (VII), a perfluoroalkyl alkylenesulfonic acid (VIII) represented by the general formula (VIII), and a general formula (X): Rf 7 -O-Rf 8 -O-CF2-COOM

[0115] (Where Rf 7 is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms (excluding an alkyl group having -CH2-), which may contain an ether bond and / or a chlorine atom, 8 is a fluorinated carboxylic acid (X) represented by a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms (excluding an alkyl group having -CH2-), M being as defined above), and the general formula (XI): Rf 9 -O-CY 1 FCF2-SO3M

[0116] (Where Rf 9 is a linear or branched, partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond and may contain chlorine (excluding an alkyl group having -CH2-), 1 is H or F, M is as defined above) represented by an alkoxy fluorosulfonic acid (XI), general formula (XII):

[0117] [Chemistry 4]

[0118]

[0119] (Where, X 1 、X 2 and X 3may be the same or different and are H, F and a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and which may contain an ether bond (excluding an alkyl group having -CH2-), wherein X 2 and X 3 Neither of them is H, Rf 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a connecting group, Y 0 is an anionic group), and the compound (XII) represented by the general formula (XIII):

[0120] Rf 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM

[0121] (Where Rf 11 Compound (XIII) is represented by a fluorinated alkyl group having 1 to 5 carbon atoms (excluding a fluorinated alkyl group having -CH2-) containing chlorine, n9 is an integer from 0 to 3, n10 is an integer from 0 to 3, and M is as defined above. By using these fluorinated surfactants, tetrafluoroethylene polymerization can be smoothly carried out in the presence of an aqueous medium.

[0122] Examples of the fluorinated surfactant include compounds represented by the following formula: The fluorinated surfactant may be a mixture of these compounds.

[0123] F(CF2)7COOM,

[0124] F(CF2)5COOM,

[0125] H(CF2)6COOM,

[0126] H(CF2)7COOM,

[0127] CF3O(CF2)3OCHFCF2COOM,

[0128] C3F7OCF(CF3)CF2OCF(CF3)COOM,

[0129] CF3CF2CF2OCF(CF3)COOM,

[0130] CF3CF2OCF2CF2OCF2COOM,

[0131] C2F5OCF(CF3)CF2OCF(CF3)COOM,

[0132] CF3OCF(CF3)CF2OCF(CF3)COOM,

[0133] CF2ClCF2CF2OCF(CF3)CF2OCF2COOM,

[0134] CF2ClCF2CF2OCF2CF(CF3)OCF2COOM,

[0135] CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM,

[0136] CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM,

[0137] [Chemistry 5]

[0138]

[0139] (In each formula, M is H, metal atom, NR 7 4. An imidazolium which may have a substituent group, a pyridinium which may have a substituent group, or a phosphonium which may have a substituent group. 7 is H or an organic group. )

[0140] The amount of the fluorinated surfactant added is preferably 10 to 10 mass ppm, more preferably 100 mass ppm or more, further preferably 300 mass ppm or more, more preferably 5 mass % or less, further preferably 1 mass % or less, relative to the aqueous medium.

[0141] (Polymerization initiator)

[0142] The polymerization initiator used in the polymerization of tetrafluoroethylene is not particularly limited as long as it can generate free radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent to initiate polymerization in a redox manner. The concentration of the above-mentioned polymerization initiator is appropriately determined based on the type of monomer, the molecular weight of the target low molecular weight polytetrafluoroethylene, and the reaction rate.

[0143] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0144] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, and for example, the following peroxides may be cited as representative substances: dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxyesters such as tert-butyl peroxyisobutyrate and tert-butyl peroxypivalate; dialkyl peroxides such as di-tert-butyl peroxide; and di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetrafluorooctanoyl) peroxide, di(ω-hydro-hexafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleranoyl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide. peroxide, bis(perfluorononanoyl) peroxide, bis(ω-chloro-hexafluorobutyryl) peroxide, bis(ω-chloro-decafluorohexanoyl) peroxide, bis(ω-chloro-tetrafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydro-dodecafluoroheptanoyl-perfluorobutyryl-peroxide, bis(dichloropentafluorobutyryl) peroxide, bis(trichlorooctafluorohexanoyl) peroxide, bis(tetrachloroundecanoyl) peroxide, bis(pentachlorotetrafluorodecanoyl) peroxide, bis(undecachlorotriadecanoyl) peroxide, etc.

[0145] The water-soluble free radical polymerization initiator may be a known water-soluble peroxide, for example, ammonium, potassium, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonic acid, organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide, t-butyl peroxymaleate, and t-butyl hydroperoxide. A reducing agent such as a sulfite may also be included, and its amount may be 0.1 to 20 times that of the peroxide.

[0146] For example, when the polymerization is carried out at a low temperature below 30°C, it is preferred to use a redox initiator composed of an oxidizing agent and a reducing agent as the polymerization initiator. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and ammonium cerium nitrate. Examples of the reducing agent include sulfites, bisulfites, bromates, diimides, and oxalic acid. Examples of the persulfates include ammonium persulfate and potassium persulfate. Examples of the sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferred to add copper salts and iron salts to the combination of the redox initiators. Examples of the copper salt include copper (II) sulfate, and examples of the iron salt include iron (II) sulfate.

[0147] Examples of the redox initiator include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / ferric sulfate, manganese triacetate / oxalic acid, ceric ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When a redox initiator is used, either the oxidizing agent or the reducing agent can be pre-charged into a polymerization vessel, followed by continuous or intermittent addition of the other to initiate polymerization. For example, when potassium permanganate / oxalic acid is used, oxalic acid is preferably added to the polymerization vessel and potassium permanganate is continuously added thereto.

[0148] The amount of polymerization initiator added is not particularly limited; it may be added all at once, sequentially, or continuously in the initial stage of polymerization in an amount sufficient to prevent a significant decrease in the polymerization rate (e.g., a concentration of several ppm relative to water). The upper limit is a range within which the heat of polymerization can be removed from the apparatus surface while simultaneously raising the reaction temperature. A more preferred upper limit is a range within which the heat of polymerization can be removed from the apparatus surface.

[0149] During the polymerization of tetrafluoroethylene, the free radical concentration in the polymerization can be adjusted by adding a decomposition agent. As decomposition agents, sulfites, bisulfites, bromates, diimides, oxalic acid, copper salts, iron salts, etc. can be mentioned. As sulfites, sodium sulfite and ammonium sulfite can be mentioned. As copper salts, copper (II) sulfate can be mentioned, and as iron salts, iron (II) sulfate can be mentioned. The amount of the decomposition agent added is in the range of 25% to 300% by mass relative to the amount of the oxidant combined as a polymerization initiator (redox initiator). As the amount of the decomposition agent added, it is preferably 25% to 150% by mass, and more preferably 50% to 100% by mass. In addition, it is preferred to add the decomposition agent after 5% by mass of all tetrafluoroethylene consumed in the polymerization reaction is polymerized, and more preferably after 10% by mass is polymerized. The amount of the decomposition agent added is preferably an amount equivalent to 0.1% to 20% by mass of the mass of the aqueous medium used, and more preferably an amount equivalent to 3% to 10% by mass.

[0150] (Chain transfer agent)

[0151] In the production method of the present invention, a hydrocarbon chain transfer agent is used as a chain transfer agent for the polymerization of tetrafluoroethylene. The hydrocarbon chain transfer agent is not particularly limited as long as it contains only carbon atoms and hydrogen atoms. However, an alkane having 1 to 5 carbon atoms is preferred, and at least one selected from the group consisting of isopentane, methane, ethane, and propane is more preferred.

[0152] The amount of chain transfer agent used is generally 1 to 50,000 ppm by mass, preferably 1 to 20,000 ppm by mass, relative to the total amount of tetrafluoroethylene supplied. The amount of chain transfer agent used is preferably an amount that is completely consumed during the polymerization of tetrafluoroethylene and does not remain in the aqueous dispersion containing low-molecular-weight polytetrafluoroethylene, thereby minimizing the reduction in the efficiency of removing fluorinated compounds having hydrophilic groups. Therefore, the amount of chain transfer agent used is more preferably 10,000 ppm by mass or less, further preferably 5,000 ppm by mass or less, even more preferably 1,000 ppm by mass or less, particularly preferably 500 ppm by mass or less, and most preferably 200 ppm by mass or less, relative to the total amount of tetrafluoroethylene supplied.

[0153] The chain transfer agent may be added to the reaction vessel all at once before the start of polymerization, may be added all at once after the start of polymerization, may be added in several portions during polymerization, or may be added continuously during polymerization.

[0154] (Aqueous medium)

[0155] The aqueous medium used in tetrafluoroethylene polymerization is a reaction medium that allows the polymerization to proceed, and is a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and a non-fluorinated organic solvent such as an alcohol, ether, or ketone, and / or a fluorinated organic solvent with a boiling point of 40°C or less.

[0156] As the aqueous medium, from the perspective of being able to smoothly carry out the polymerization of tetrafluoroethylene and also being able to suppress the reduction in the removal efficiency of the fluorinated compound having a hydrophilic group, an aqueous medium containing only water, or an aqueous medium containing only water and a non-fluorinated organic solvent is preferred, and an aqueous medium containing only water is more preferred.

[0157] From the perspective of being able to smoothly carry out the polymerization of tetrafluoroethylene and also being able to suppress the reduction in the removal efficiency of the fluorinated compound having a hydrophilic group, the water content in the aqueous medium is preferably 90% or more, more preferably 95% or more, further preferably 99.0% or more, further preferably 99.5% or more, particularly preferably 99.9% or more, and may also be 100% relative to the mass of the aqueous medium.

[0158] (Other additives)

[0159] In the polymerization of tetrafluoroethylene, additives such as buffers, pH regulators, stabilizing agents, and dispersion stabilizers may be used. Furthermore, free radical scavengers and decomposers may be added to adjust the polymerization rate and molecular weight. Furthermore, non-fluorinated anionic surfactants, non-fluorinated nonionic surfactants, and non-fluorinated cationic surfactants may also be used in the polymerization of tetrafluoroethylene.

[0160] Preferred stabilizing agents include paraffin wax, fluorinated oil, fluorinated solvent, and silicone oil. One stabilizing agent may be used alone or in combination of two or more. Paraffin wax is more preferred. Paraffin wax may be liquid, semisolid, or solid at room temperature, but is preferably a saturated hydrocarbon with 12 or more carbon atoms. The melting point of paraffin wax is generally preferably 40°C to 65°C, more preferably 50°C to 65°C.

[0161] The amount of the stabilizing agent used is preferably 0.1% to 12% by mass, more preferably 0.1% to 8% by mass, based on the mass of the aqueous medium used. The stabilizing agent is preferably sufficiently hydrophobic to be completely separated and removed from the aqueous dispersion after polymerization and not to become a contaminating component.

[0162] (Modified monomer)

[0163] The modified monomer can be polymerized with tetrafluoroethylene. As the modified monomer, there is no particular limitation as long as it can be copolymerized with tetrafluoroethylene (TFE), and fluorine-containing monomers and non-fluorine-containing monomers can be mentioned. In addition, the modified monomer used can be one or more.

[0164] The non-fluorine-containing monomer is not particularly limited, but examples thereof include the following:

[0165] CH2=CR Q1 -LR Q2

[0166] (Where R Q1 represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents the same Q2 The bonding position of R Q2 represents a hydrogen atom, an alkyl group or a nitrile group).

[0167] Examples of the non-fluorine-containing monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether. Among the non-fluorine-containing monomer, butyl methacrylate, vinyl acetate, and acrylic acid are preferred.

[0168] Examples of the fluorinated monomer include perfluoroolefins such as hexafluoropropylene [HFP]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ether; (perfluoroalkyl)ethylene; and perfluoroallyl ether.

[0169] The perfluorovinyl ether is not particularly limited, and examples thereof include those of the general formula (A):

[0170] CF2=CF-ORf(A)

[0171] (wherein Rf represents a perfluoroorganic group) and the like. In the present invention, the "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0172] Examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) [PAVE], wherein Rf in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

[0173] Examples of the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0174] Examples of the perfluorovinyl ether include monomers wherein Rf in the general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf is the following formula:

[0175] [Chemistry 6]

[0176]

[0177] (wherein m represents 0 or an integer of 1 to 4), and Rf is the following formula:

[0178] CF3CF2CF2-(O-CF(CF3)-CF2) n -

[0179] (wherein n represents an integer of 1 to 4) and the like.

[0180] Examples of hydrogen-containing fluoroolefins include CH2=CF2, CFH=CH2, CFH=CF2, CH2=CFCF3, CH2=CHCF3, CHF=CHCF3 (E-isomer), and CHF=CHCF3 (Z-isomer).

[0181] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0182] Examples of perfluoroallyl ethers include

[0183] General formula: CF2=CF-CF2-ORf

[0184] (wherein Rf represents a perfluoro organic group).

[0185] Rf in the above general formula is the same as Rf in general formula (A). As Rf, a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms is preferred. As the perfluoroallyl ether, at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9 is preferred, at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9 is more preferred, and CF2=CF-CF2-O-CF2CF2CF3 is further preferred.

[0186] Preferred examples of the modifying monomer include a modifying monomer (3) having a monomer reactivity ratio of 0.1 to 8. The presence of the modifying monomer (3) allows for the production of PTFE particles having a small particle size and an aqueous dispersion having high dispersion stability.

[0187] Here, the monomer reactivity ratio in copolymerization with TFE is calculated as follows: when the growth radical is smaller than the repeating unit based on TFE, the rate constant of the growth radical reaction with TFE is divided by the rate constant of the growth radical reaction with the modifying monomer. The lower this value, the higher the reactivity of the modifying monomer with TFE. The monomer reactivity ratio can be calculated by copolymerizing TFE and the modifying monomer, determining the composition of the resulting polymer immediately after the start of the copolymerization, and then calculating it using the Fineman-Ross equation.

[0188] The copolymerization was carried out in a stainless steel autoclave with an internal volume of 6.0 L using 3600 g of deionized and degassed water, 1000 ppm by mass of ammonium perfluorooctanoate relative to the water, and 100 g of paraffin wax at a pressure of 0.78 MPaG and a temperature of 70°C. 0.05 g, 0.1 g, 0.2 g, 0.5 g, and 1.0 g of the modified monomer were added to the reactor, 0.072 g of ammonium persulfate (20 ppm by mass relative to water), and TFE was continuously supplied to maintain a polymerization pressure of 0.78 MPaG. When the TFE charge reached 1000 g, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. After cooling, the paraffin wax was separated to obtain an aqueous dispersion containing the generated polymer. The aqueous dispersion was stirred to precipitate the generated polymer and dried at 150°C. The composition of the resulting polymer was calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of monomer.

[0189] The modified monomer (3) having a monomer reactivity ratio of 0.1 to 8 is preferably at least one selected from the group consisting of modified monomers represented by formulae (3a) to (3d).

[0190] CH2=CH-Rf 1 (3a)

[0191] (Where Rf 1 It is a perfluoroalkyl group having 1 to 10 carbon atoms.)

[0192] CF2=CF-O-Rf 2 (3b)

[0193] (Where Rf 2 It is a perfluoroalkyl group having 1 to 2 carbon atoms.

[0194] CF2=CF-O-(CF2) n CF=CF2(3c)

[0195] (Where n is 1 or 2.)

[0196] [Chemistry 7]

[0197]

[0198] (Where X 3 and X 4 is F, Cl or methoxy, and Y is of the formula Y1 or Y2.)

[0199] [Chemistry 8]

[0200] -CF=CF- (Y1)

[0201]

[0202] (In formula Y2, Z and Z' are F or a fluoroalkyl group having 1 to 3 carbon atoms.)

[0203] The content of the modified monomer (3) unit is preferably in the range of 0.00001% by mass to 1.0% by mass relative to the total polymerized units of PTFE. As the lower limit, it is more preferably 0.0001% by mass, more preferably 0.0005% by mass, further preferably 0.001% by mass, and even more preferably 0.005% by mass. As the upper limit, it is preferably 0.90% by mass, 0.50% by mass, 0.40% by mass, 0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08% by mass, 0.05% by mass, and 0.01% by mass.

[0204] As above-mentioned modified monomer, owing to the aqueous dispersion that the average primary particle diameter that can obtain primary particle is little, the aspect ratio of primary particle is little, the stability is excellent, thereby preferably selected from by hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, perfluor (alkyl vinyl ether), (perfluoroalkyl) ethylene, ethene and have at least one in the group that the modified monomer of functional group and hydrophilic group that can pass through free radical polymerization forms.By using above-mentioned modified monomer, the aqueous dispersion that can obtain the PTFE of average primary particle diameter is little, the aspect ratio of primary particle is little, the dispersion stability is excellent.In addition, the aqueous dispersion that can obtain not precipitating polymer is few.

[0205] From the viewpoint of reactivity with TFE, the modifying monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether) and (perfluoroalkyl)ethylene.

[0206] More preferably, it contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), (perfluorobutyl)ethylene, (perfluorohexyl)ethylene, and (perfluorooctyl)ethylene.

[0207] The total amount of the hexafluoropropylene unit, the perfluoro(alkyl vinyl ether) unit and the (perfluoroalkyl) ethylene unit is preferably in the range of 0.00001% by mass to 1% by mass relative to the total polymerized units of PTFE. As the lower limit of the above-mentioned total amount, it is more preferably 0.0001% by mass, more preferably 0.0005% by mass, further preferably 0.001% by mass, further preferably 0.005% by mass. As the upper limit, it is 0.80% by mass, 0.70% by mass, 0.50% by mass, 0.40% by mass, 0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08% by mass, 0.05% by mass, 0.01% by mass in the preferred order.

[0208] The above-mentioned modified monomer also preferably includes a modified monomer having a functional group capable of radical polymerization and a hydrophilic group (hereinafter referred to as "modified monomer (A)").

[0209] The presence of the modified monomer (A) can produce PTFE particles with a small primary particle size, thereby obtaining an aqueous dispersion with high dispersion stability. Furthermore, the amount of unprecipitated polymer can be reduced, thereby lowering the aspect ratio of the primary particles.

[0210] The amount of the modified monomer (A) is preferably an amount exceeding 0.1 mass ppm of the aqueous medium, more preferably an amount exceeding 0.5 mass ppm, further preferably an amount exceeding 1.0 mass ppm, and further more preferably 5 mass ppm or more, particularly preferably 10 mass ppm or more. If the amount of the modified monomer (A) is too small, the average primary particle size of the resulting PTFE may not be reduced.

[0211] The amount of the modified monomer (A) can be within the above range, for example, the upper limit can be 5000 mass ppm. In addition, in the above production method, in order to improve the stability of the aqueous dispersion during or after the reaction, the modified monomer (A) can be added to the system during the reaction.

[0212] The modified monomer (A) has high water solubility. Therefore, even if unreacted modified monomer (A) remains in the aqueous dispersion, it can be easily removed in the concentration step or the precipitation / washing step.

[0213] The modified monomer (A) is introduced into the resulting polymer during the polymerization process. However, since the concentration of the modified monomer (A) in the polymerization system is low and the amount introduced into the polymer is small, there is no problem of reduced heat resistance of PTFE or coloring after firing.

[0214] Examples of the hydrophilic group in the modified monomer (A) include -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, -COOM (wherein M is H, a metal atom, NR 7y 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7y (H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring). As the above-mentioned hydrophilic group, -SO3M or -COOM is preferred. 7y The organic group in is preferably an alkyl group. 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4 The organic group is preferably H or C 1-4 of alkyl.

[0215] Examples of the metal atom include monovalent and divalent metal atoms, such as alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred.

[0216] Examples of the "functional group capable of free radical polymerization" in the modified monomer (A) include groups having an ethylenically unsaturated bond, such as a vinyl group and an allyl group. The group having an ethylenically unsaturated bond can be represented by the following formula:

[0217] CX e X g =CX f R-

[0218] (Where, X e 、X f and X g Each independently represents F, Cl, H, CF3, CF2H, CFH2 or CH3; R is a linking group). As the linking group of R, there can be mentioned the following R a Preferred examples include groups having an unsaturated bond such as -CH=CH2, -CF=CH2, -CH=CF2, -CF=CF2, -CH2-CH=CH2, -CF2-CF=CH2, -CF2-CF=CF2, -(C=O)-CH=CH2, -(C=O)-CF=CH2, -(C=O)-CH=CF2, -(C=O)-CF=CF2, -(C=O)-C(CH3)=CH2, -(C=O)-C(CF3)=CH2, -(C=O)-C(CH3)=CF2, -(C=O)-C(CF3)=CF2, -O-CH2-CH=CH2, -O-CF2-CF=CH2, -O-CH2-CH=CF2, and -O-CF2-CF=CF2.

[0219] Since the modified monomer (A) has a functional group capable of free radical polymerization, it reacts with the fluorinated monomer in the early stages of the polymerization reaction. This is believed to result in the formation of highly stable particles due to the hydrophilic groups derived from the modified monomer (A). Therefore, when polymerization is carried out in the presence of the modified monomer (A), the number of particles is expected to increase.

[0220] In the polymerization, the modifying monomer (A) may be present alone or in combination of two or more.

[0221] In the above polymerization, a compound having an unsaturated bond can be used as the above-mentioned modifying monomer (A).

[0222] The modified monomer (A) is preferably of the general formula (4):

[0223] CX i X k =CX j R a -(CZ 1 Z 2 ) k -Y 3 (4)

[0224] (Where, X i 、Xj and X k are each independently F, Cl, H or CF3; Y 3 is a hydrophilic group; R a is a connecting group; Z 1 and Z 2 Each independently represents H, F or CF3, and k represents 0 or 1).

[0225] Examples of the hydrophilic group include -NH2, -PO3M, -OPO3M, -SO3M, -OSO3M, and -COOM (wherein M is H, a metal atom, NR 7y 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7y (H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring). As the above-mentioned hydrophilic group, -SO3M or -COOM is preferred. 7y The organic group in is preferably an alkyl group. 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4 The organic group is preferably H or C 1-4 Examples of the metal atom include monovalent and divalent metal atoms, such as alkali metals (Group 1) and alkaline earth metals (Group 2), and preferably Na, K or Li.

[0226] By using the modified monomer (A), an aqueous dispersion having a smaller average primary particle size and better stability can be obtained, and the aspect ratio of the primary particles can be further reduced.

[0227] The above R a is a linking group. In the present invention, a "linking group" refers to a divalent linking group. The linking group may be a single bond and preferably contains at least one carbon atom. The number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. The upper limit is not limited, for example, it may be 100 or less, or 50 or less.

[0228] The linking group may be linear or branched, cyclic or acyclic, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen. It may also optionally contain one or more functional groups selected from the group consisting of esters, amides, sulfonamides, carbonyls, carbonates, carbamates, ureas, and urethanes. The linking group does not contain carbon atoms and may contain chain heteroatoms such as oxygen, sulfur, or nitrogen.

[0229] The above Ra Preferred are, for example, chain heteroatoms such as oxygen, sulfur, and nitrogen, or divalent organic groups.

[0230] R a In the case of a divalent organic group, the hydrogen atom bonded to the carbon atom may be replaced by a halogen other than fluorine, such as chlorine, and may or may not contain a double bond. a It may be either linear or branched, or cyclic or acyclic. a Functional groups (eg, ester, ether, ketone, amine, halide, etc.) may be included.

[0231] In addition, R a It may be a non-fluorinated divalent organic group or a partially fluorinated or perfluorinated divalent organic group.

[0232] As R a , and can be, for example: a hydrocarbon group in which no fluorine atom is bonded to the carbon atom; a hydrocarbon group in which a part of the hydrogen atoms bonded to the carbon atom are substituted by fluorine atoms; a hydrocarbon group in which all the hydrogen atoms bonded to the carbon atom are substituted by fluorine atoms; a hydrocarbon group containing -(C=O)-, -(C=O)-O- or -(C=O)-, which may contain oxygen atoms, may contain double bonds, and may contain functional groups.

[0233] R a Preferred is a hydrocarbon group having 1 to 100 carbon atoms which may contain -(C=O)-, -(C=O)-O- or an ether bond and may contain a carbonyl group, wherein some or all of the hydrogen atoms bonded to carbon atoms in the hydrocarbon group may be substituted with fluorine.

[0234] As R a , preferably selected from -(CH2) a -、-(CF2) a -、-O-(CF2) a -、-(CF2) a -O-(CF2) b -、-O(CF2) a -O-(CF2) b -、-(CF2) a -[O-(CF2) b ] c -、-O(CF2) a -[O-(CF2) b ] c -、-[(CF2) a -O] b -[(CF2) c -O] d -、-O[(CF2) a -O] b-[(CF2) c -O] d -、-O-[CF2CF(CF3)O] a -(CF2) b -, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2) a -、-(C=O)-(CF2) a -、-(C=O)-O-(CH2) a -、-(C=O)-O-(CF2) a -、-(C=O)-[(CH2) a -O] b -、-(C=O)-[(CF2) a -O] b -、-(C=O)-O[(CH2) a -O] b -、-(C=O)-O[(CF2) a -O] b -、-(C=O)-O[(CH2) a -O] b -(CH2) c -、-(C=O)-O[(CF2) a -O] b -(CF2) c -、-(C=O)-(CH2) a -O-(CH2) b -、-(C=O)-(CF2) a -O-(CF2) b -、-(C=O)-O-(CH2) a -O-(CH2) b -、-(C=O)-O-(CF2) a -O-(CF2) b -, -(C=O)-O-C6H4-, and at least one of combinations thereof.

[0235] In the formula, a, b, c, and d are independently at least 1. a, b, c, and d can independently be 2 or more, 3 or more, 4 or more, 10 or more, or 20 or more. The upper limit of a, b, c, and d is, for example, 100.

[0236] As R aPreferred specific examples include -CF2-O-, -CF2-O-CF2-, -CF2-O-CH2-, -CF2-O-CH2CF2-, -CF2-O-CF2CF2-, -CF2-O-CF2CH2-, -CF2-O-CF2CF2CH2-, -CF2-O-CF(CF3)-, -CF2-O-CF(CF3)CF2-, -CF2-O-CF(CF3)CF2-, -CF2-O-CF(CF3)CF2-O-, -CF2-O-CF(CF3)CH2-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2)-, -(C=O)-(CF2)-, -(C=O)-O-(CH2)-, -(C=O)-O-(CF2)-, -(C=O)-[(CH2)2-O] n -、-(C=O)-[(CF2)2-O] n -、-(C=O)-O[(CH2)2-O] n -、-(C=O)-O[(CF2)2-O] n -、-(C=O)-O[(CH2)2-O] n -(CH2)-, -(C=O)-O[(CF2)2-O] n -(CF2)-, -(C=O)-(CH2)2-O-(CH2)-, -(C=O)-(CF2)2-O-(CF2)-, -(C=O)-O-(CH2)2-O-(CH2)-, -(C=O)-O-(CF2)2-O-(CF2)-, -(C=O)-O-C6H4-, etc. Specifically, the above R a Preferably -CF2-O-, -CF2-O-CF2-, -CF2-O-CF2CF2-, -CF2-O-CF(CF3)-, -CF2-O-CF(CF3)CF2-, -CF2-O- CF(CF3)CF2-O-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2)-, -(C=O)-O-(CH2)-, -(C=O)-O[(CH2)2-O] n -、-(C=O)-O[(CH2)2-O] n -(CH2)-, -(C=O)-(CH2)2-O-(CH2)-, or -(C=O)-O-C6H4-.

[0237] In the above formula, n is an integer of 1 to 10.

[0238] As -R in the general formula (4) a -(CZ 1 Z 2 ) k-, preferably -CF2-O-CF2-, -CF2-O-CF(CF3)-, -CF2-O-C(CF3)2-, -CF2-O-CF2-CF2-, -CF2-O-CF2-CF(CF3)-, -CF2-O-CF2-C(CF3)2-, -CF2-O-CF2CF2-CF2-, -CF2-O-CF2CF2-CF(CF3)-, -CF2-O-CF2CF2-C(CF3)2-, -CF2-O-CF(CF3)-CF2-, -CF2-O-CF(CF3)-CF(CF3)-, -CF2-O-CF(CF3)-C(CF3)2-, -CF2-O-CF(CF3)CF2-CF2-, -CF2-O-CF(CF3)CF2-CF(CF3)-, -CF2-O-CF(CF3)CF2-C(CF3)2-, -CF2-O-CF(CF3)CF2-O-CF2-, -CF2-O-CF(CF3)CF2-O-CF(CF3)-, -CF2-O-CF(CF3)CF2-O-C(CF3)2-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH2)-, -(C=O)-(CF2)-, -(C=O)-O-(CH2)-, -(C=O)-O-(CF2)-, -(C=O)-[(CH2)2-O] n -(CH2)-, -(C=O)-[(CF2)2-O] n -(CF2)-, -(C=O)-[(CH2)2-O] n -(CH2)-(CH2)-, -(C=O)-[(CF2)2-O] n -(CF2)-(CF2)-, -(C=O)-O[(CH2)2-O] n -(CF2)-, -(C=O)-O[(CH2)2-O] n -(CH2)-(CH2)-, -(C=O)-O[(CF2)2-O] n -(CF2)-, -(C=O)-O[(CF2)2-O] n-(CF2)-(CF2)-, -(C=O)-(CH2)2-O-(CH2)-(CH2)-, -(C=O)-(CF2)2-O-(CF2)-(CF2)-, -(C=O)-O-(CH2)2-O-(CH2)-(CH2)-, -(C= O)-O-(CF2)2-O-(CF2)-(CF2)-, -(C=O)-O-(CH2)2-O-(CH2)-C(CF3)2-, -(C=O)-O-(CF2)2-O-(CF2)-C(CF3)2-, or -(C=O)-O-C6H4 -C(CF3)2-, more preferably -CF2-O-CF(CF3)-, -CF2-O-CF2-CF(CF3)-, -CF2-O-CF2CF2-CF(CF3)-, -CF2-O-CF(CF3)-CF(CF3)-, -CF2-O-CF(CF 3)CF2-CF(CF3)-, -CF2-O-CF(CF3)CF2-O-CF(CF3)-, -(C=O)-, -(C=O)-O-(CH2)-, -(C=O)-O-(CH2)-(CH2)-, -(C=O)-O[(CH2)2-O] n -(CH2)-(CH2)-, -(C=O)-O-(CH2)2-O-(CH2)-C(CF3)2-, or -(C=O)-O-C6H4-C(CF3)2-.

[0239] In the above formula, n is an integer of 1 to 10.

[0240] Specific examples of the compound represented by the general formula (4) include:

[0241] [Chemistry 9]

[0242]

[0243] (Where X j and Y 3 Same as above. (n is an integer from 1 to 10) etc.

[0244] As R a , preferably general formula (r1):

[0245] -(C=O) h -(O) i -CF2-O-(CX 6 2) e -{O-CF(CF3)} f -(O) g -(r1)

[0246] (Where X 6Each independently represents H, F or CF3, e is an integer from 0 to 3, f is an integer from 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1), and the general formula (r2) is also preferred:

[0247] -(C=O) h -(O) i -CF2-O-(CX 7 2) e -(O) g -(r2)

[0248] (Where, X 7 Each independently represents H, F or CF3, e is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1).

[0249] As -R in the general formula (4) a -(CZ 1 Z 2 ) k -, the following formula (t1) is also preferred:

[0250] -(C=O) h -(O) i -CF2-O-(CX 6 2) e -{O-CF(CF3)} f -(O) g -CZ 1 Z 2 -(t1)

[0251] (Where, X 6 Each independently represents H, F or CF3, e represents an integer from 0 to 3, f represents an integer from 0 to 3, g represents 0 or 1, h represents 0 or 1, i represents 0 or 1, Z 1 and Z 2 Each independently represents a divalent group represented by F or CF3), in formula (t1), Z 1 and Z 2 More preferably, one is F and the other is CF3.

[0252] In the general formula (4), -R a -(CZ 1 Z 2 ) k -, the following formula (t2) is also preferred:

[0253] -(C=O) h -(O) i -CF2-O-(CX 7 2) e -(O) g -CZ1 Z 2 -(t2)

[0254] (Where X 7 Each independently represents H, F or CF3, e represents an integer from 0 to 3, g represents 0 or 1, h represents 0 or 1, i represents 0 or 1, Z 1 and Z 2 Each independently represents a divalent group represented by F or CF3), in formula (t2), Z 1 and Z 2 More preferably, one is F and the other is CF3.

[0255] The compound represented by the general formula (4) is also preferably 3 ) has a CF bond and does not have a CH bond. That is, in the general formula (4), it is preferred that X i 、X j and X k All F, R a The perfluoroalkylene group is a perfluoroalkylene group having 1 or more carbon atoms. The perfluoroalkylene group may be linear or branched, cyclic or acyclic, and may contain at least one linear heteroatom. The perfluoroalkylene group may have 2 to 20 carbon atoms, or 4 to 18 carbon atoms.

[0256] The compound represented by the general formula (4) may also be partially fluorinated. That is, the compound represented by the general formula (4) also preferably has a hydrophilic group (Y 3 ) has at least one hydrogen atom bonded to a carbon atom and at least one fluorine atom bonded to a carbon atom.

[0257] The compound represented by the general formula (4) is preferably a compound represented by the following formula (4a).

[0258] CF2=CF-O-Rf 0 -Y 3 (4a)

[0259] (Where Y 3 is a hydrophilic group, Rf 0 It is perfluorinated and may be linear or branched, cyclic or acyclic, saturated or unsaturated, substituted or unsubstituted, and is a perfluorinated divalent linking group that optionally contains one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen.

[0260] The compound represented by the general formula (4) is also preferably a compound represented by the following formula (4b).

[0261] CH2=CH-O-Rf 0 -Y 3 (4b)

[0262] (Where Y 3 is a hydrophilic group, Rf 0 is a perfluorinated divalent linking group defined by formula (4a).

[0263] In the general formula (4), Y 3 -OSO3M is one of the preferred methods. 3 In the case of -OSO3M, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2CH2OSO3M), CF2=CF(O(CF2)4CH2OSO3M), CF2=CF(OCF2CF(CF3)CH2OSO3M), CF2=CF(OCF2CF(CF3)OCF2CF2CH2OSO3M), CH2=CH((CF2)4CH2OSO3M), CF2=CF(OCF2CF2SO2N(CH3)CH2CH2OSO3M), CH2=CH(CF2CF2CH2OSO3M), and CF2=CF(OCF2CF2CF2CF2SO2N(CH3)CH2CH2OSO3M). In the above formula, M is the same as above.

[0264] In the general formula (4), Y 3 -SO3M is also one of the preferred methods. 3 In the case of -SO3M, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2SO3M), CF2=CF(O(CF2)4SO3M), CF2=CF(OCF2CF(CF3)SO3M), CF2=CF(OCF2CF(CF3)OCF2CF2SO3M), CH2=CH(CF2CF2SO3M), CF2=CF(OCF2CF(CF3)OCF2CF2CF2CF2SO3M), CH2=CH((CF2)4SO3M), and CH2=CH((CF2)3SO3M). In the above formula, M is the same as above.

[0265] In the general formula (4), Y 3 -COOM is also one of the preferred methods. 3 In the case of -COOM, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2COOM), CF2=CF(OCF2CF2CF2COOM), CF2=CF(O(CF2)5COOM), CF2=CF(OCF2CF(CF3)COOM), CF2=CF(OCF2CF(CF3)O(CF2) nCOOM) (n is greater than 1), CH2=CH(CF2CF2COOM), CH2=CH((CF2)4COOM), CH2=CH((CF2)3COOM), CF2=CF(OCF2CF2SO2NR'CH2COOM), CF2=CF(O(CF2)4SO2NR'CH2COOM), CF2=CF(OCF2CF(CF3)SO2NR'CH2COOM), CF2=CF(OCF2CF(CF3)OCF2CF2SO2NR'CH2COOM), CH2=CH(CF2CF2SO2NR'CH2COOM), CF2=CF(OCF2CF(CF3)OCF2CF2CF2SO2NR'CH2COOM), CH2=CH((CF2)4SO2NR'CH2COOM), CH2=CH((CF2)3SO2NR'CH2COOM), etc. In the above formula, R' is H or C 1-4 The alkyl group and M are the same as those described above.

[0266] In the general formula (4), Y 3 -OPO3M or -OP(O)(OM)2 is also one of the preferred forms. 3 In the case of -OPO3M or -OP(O)(OM)2, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2CH2OP(O)(OM)2), CF2=CF(O(CF2)4CH2OP(O)(OM)2), CF2=CF(OCF2CF(CF3)CH2OP(O)(OM)2), CF2=CF(OCF2CF(CF3)OCF2CF2CH2OP(O)(OM)2), CF2=C F(OCF2CF2SO2N(CH3)CH2CH2OP(O)(OM)2), CF2=CF(OCF2CF2CF2CF2SO2N(CH3)CH2CH2OP(O)(OM)2), CH2=CH(CF2CF2CH2OP(O)(OM)2, CH2=CH((CF2)4CH2OP(O)(OM)2), CH2=CH((CF2)3CH2OP(O)(OM)2), etc. In the above formula, M is the same as above.

[0267] In the general formula (4), Y 3 -PO3M or -P(O)(OM)2 is also one of the preferred forms. 3In the case of -PO3M or -P(O)(OM)2, examples of the compound represented by the general formula (4) include CF2=CF(OCF2CF2P(O)(OM)2), CF2=CF(O(CF2)4P(O)(OM)2), CF2=CF(OCF2CF(CF3)P(O)(OM)2), CF2=CF(OCF2CF(CF3)OCF2CF2P(O)(OM)2), CH2=CH(CF2CF2P(O)(OM)2), CH2=CH((CF2)4P(O)(OM)2), CH2=CH((CF2)3P(O)(OM)2), etc., wherein M is the same as above.

[0268] The compound represented by the general formula (4) is preferably at least one selected from the group consisting of the following compounds, wherein the compound is represented by the general formula (5):

[0269] CX2=CY(-CZ2-O-Rf-Y 3 ) (5)

[0270] (wherein, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorinated alkyl group, and Z is the same or different and is -H, -F, an alkyl group or a fluorinated alkyl group. Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having 2 to 100 carbon atoms and having an ether bond. Y 3 Same as above) and the compound represented by the general formula (6):

[0271] CX2=CY(-O-Rf-Y 3 ) (6)

[0272] (wherein, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorinated alkyl group, and Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having an ether bond and having 2 to 100 carbon atoms. Y 3 Same as above); and the compound represented by general formula (7):

[0273] CX2=CY(-Rf-Y 3 ) (7)

[0274] (wherein, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorinated alkyl group, and Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having an ether bond and having 2 to 100 carbon atoms. Y 3 Same as above).

[0275] The fluorine-containing alkylene group having an ether bond and having 2 to 100 carbon atoms is an alkylene group having no terminal oxygen atom and having an ether bond between carbon atoms.

[0276] In the general formula (5), X is -H or -F. Both Xs may be -F, or at least one of them may be -H. For example, one may be -F and the other may be -H, or both may be -H.

[0277] In the general formula (5), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group.

[0278] The alkyl group is an alkyl group that does not contain fluorine atoms and has at least 1 carbon atom. The alkyl group preferably has 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0279] The fluorinated alkyl group is an alkyl group containing at least one fluorine atom and may have at least 1 carbon atom. The fluorinated alkyl group preferably has 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0280] As the above-mentioned Y, -H, -F or -CF3 is preferred, and -F is more preferred.

[0281] In the general formula (5), Z is the same or different and is -H, -F, alkyl or fluoroalkyl.

[0282] The alkyl group is an alkyl group that does not contain fluorine atoms and has at least 1 carbon atom. The alkyl group preferably has 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0283] The fluorinated alkyl group is an alkyl group containing at least one fluorine atom and may have at least 1 carbon atom. The fluorinated alkyl group preferably has 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0284] As the above-mentioned Z, -H, -F or -CF3 is preferred, and -F is more preferred.

[0285] In the general formula (5), at least one of X, Y, and Z preferably contains a fluorine atom. For example, X may be -H, and Y and Z may be -F.

[0286] In the general formula (5), Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having 2 to 100 carbon atoms and having an ether bond.

[0287] The number of carbon atoms in the fluorinated alkylene group is preferably 2 or more. In addition, it is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Examples of the fluorinated alkylene group include -CF2-, -CH2CF2-, -CF2CF2-, -CF2CH2-, -CF2CF2CH2-, -CF(CF3)-, -CF(CF3)CF2-, and -CF(CF3)CH2-. The fluorinated alkylene group is preferably a perfluoroalkylene group.

[0288] The number of carbon atoms in the fluorinated alkylene group having an ether bond is preferably 3 or more. The number of carbon atoms in the fluorinated alkylene group having an ether bond is preferably 60 or less, more preferably 30 or less, and even more preferably 12 or less.

[0289] As the fluorine-containing alkylene group having an ether bond, for example, the following formula is also preferred:

[0290] [Chemistry 10]

[0291]

[0292] (Where Z 1 F or CF3; Z 2 and Z 3 H or F; Z 4 is a divalent group represented by H, F or CF3; p1+q1+r1 is an integer of 1 to 10; s1 is 0 or 1; t1 is an integer of 0 to 5).

[0293] Specific examples of the fluorine-containing alkylene group having an ether bond include -CF(CF3)CF2-O-CF(CF3)-, -(CF(CF3)CF2-O) n -CF(CF3)- (wherein n is an integer from 1 to 10), -CF(CF3)CF2-O-CF(CF3)CH2-, -(CF(CF3)CF2-O) n -CF(CF3)CH2- (wherein n is an integer of 1 to 10), -CH2CF2CF2O-CH2CF2CH2-, -CF2CF2CF2O-CF2CF2-, -CF2CF2CF2O-CF2CF2CH2-, -CF2CF2O-CF2-, -CF2CF2O-CF2CH2-, etc. The fluorine-containing alkylene group having an ether bond is preferably a perfluoroalkylene group.

[0294] In the general formula (5), Y 3 Preferably -COOM, -SO3M or -OSO3M (M is H, metal atom, NR 7y 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7y (H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring).

[0295] As R 7y The organic group in is preferably an alkyl group.

[0296] As R 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4The organic group is preferably H or C 1-4 of alkyl.

[0297] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred.

[0298] As M, -H, a metal atom or NR 7 4, more preferably -H, alkali metal (Group 1), alkaline earth metal (Group 2) or NR 7 4, further preferably -H, -Na, -K, -Li or NH4, further more preferably -H, -Na, -K or NH4, particularly preferably -H, -Na or NH4, most preferably -H or -NH4.

[0299] As the above Y 3 , preferably -COOM or -SO3M, more preferably -COOM.

[0300] The compound represented by the general formula (5) is preferably a compound (5a) represented by the general formula (5a).

[0301] CH2=CF(-CF2-O-Rf-Y 3 )(5a)

[0302] (Where Rf and Y 3 Same as above.)

[0303] Specific examples of the compound represented by general formula (5a) include the following:

[0304] [Chemistry 11]

[0305]

[0306] (Where Z 1 F or CF3; Z 2 and Z 3 H or F; Z 4 is H, F or CF3; p1+q1+r1 is an integer from 0 to 10; s1 is 0 or 1; t1 is an integer from 0 to 5, Y 3 Same as above. Where Z 3 and Z 4 When all are H, p1+q1+r1+s1 is not 0). More specifically, preferably,

[0307] [Chemistry 12]

[0308]

[0309] etc., among which the preferred

[0310] [Chemistry 13]

[0311]

[0312] As the compound represented by the general formula (5a), Y in the formula (5a) is preferably 3 It is -COOM, and is particularly preferably at least one selected from the group consisting of CH2=CFCF2OCF(CF3)COOM and CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOM (wherein M has the same definition as above), and more preferably CH2=CFCF2OCF(CF3)COOM.

[0313] The compound represented by the general formula (5) is preferably a compound (5b) represented by the general formula (5b).

[0314] CX 2 2=CFCF2-O-(CF(CF3)CF2O) n5 -CF(CF3)-Y 3 (5b)

[0315] (Where, each X 2 The same, represents F or H. n5 represents 0 or an integer from 1 to 10, Y 3 Same as the above definition.)

[0316] In the above formula (5b), from the perspective of the stability of the obtained aqueous dispersion, the above n5 is preferably 0 or an integer of 1 to 5, more preferably 0, 1 or 2, and even more preferably 0 or 1. From the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 -COOM is preferred. From the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the obtained molded article, the above-mentioned M is preferably H or NH 4 .

[0317] Examples of the compound represented by the formula (5b) include CH2=CFCF2OCF(CF3)COOM and CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOM (wherein M has the same meaning as above).

[0318] In addition, examples of the compound represented by the general formula (5) include compounds represented by the general formula (5c).

[0319] CF2=CFCF2-O-Rf-Y 3 (5c)

[0320] (Where Rf and Y 3 Same as above.)

[0321] More specifically, we can cite

[0322] [Chemistry 14]

[0323] wait.

[0324] In the general formula (6), X is -H or -F. Both Xs may be -F, or at least one may be -H. For example, one may be -F and the other may be -H, or both may be -H.

[0325] In the general formula (6), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group.

[0326] The alkyl group is an alkyl group that does not contain fluorine atoms and has at least 1 carbon atom. The alkyl group preferably has 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0327] The fluorinated alkyl group is an alkyl group containing at least one fluorine atom and may have at least 1 carbon atom. The fluorinated alkyl group preferably has 6 or less carbon atoms, more preferably 4 or less carbon atoms, and even more preferably 3 or less carbon atoms.

[0328] As the above-mentioned Y, -H, -F or -CF3 is preferred, and -F is more preferred.

[0329] In the general formula (6), at least one of X and Y preferably contains a fluorine atom. For example, X may be -H, and Y and Z may be -F.

[0330] In the general formula (6), Rf is a fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having 2 to 100 carbon atoms and having an ether bond.

[0331] The number of carbon atoms in the fluorinated alkylene group is preferably 2 or more. In addition, the number of carbon atoms in the fluorinated alkylene group is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Examples of the fluorinated alkylene group include -CF2-, -CH2CF2-, -CF2CF2-, -CF2CH2-, -CF2CF2CH2-, -CF(CF3)-, -CF(CF3)CF2-, and -CF(CF3)CH2-. The fluorinated alkylene group is preferably a perfluoroalkylene group.

[0332] In the above general formula (6), Y 3 Preferably -COOM, -SO3M or -OSO3M (M is H, metal atom, NR 7y 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7y (H or an organic group, which may be the same or different. Any two of them may be bonded to each other to form a ring).

[0333] As R 7yAs an organic group, preferably an alkyl group. 7y , preferably H or C 1-10 An organic group, more preferably H or C 1-4 The organic group is preferably H or C 1-4 of alkyl.

[0334] Examples of the metal atom include alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred.

[0335] As M, -H, a metal atom or NR 7 4, more preferably -H, alkali metal (Group 1), alkaline earth metal (Group 2) or NR 7 4, further preferably -H, -Na, -K, -Li or NH4, further more preferably -H, -Na, -K or NH4, particularly preferably -H, -Na or NH4, most preferably -H or -NH4.

[0336] As the above Y 3 , preferably -COOM or -SO3M, more preferably -COOM.

[0337] The compound represented by the general formula (6) is preferably at least one selected from the group consisting of compounds represented by the general formulae (6a), (6b), (6c), (6d), and (6e).

[0338] CF2=CF-O-(CF2) n1 -Y 3 (6a)

[0339] (where n1 represents an integer from 1 to 10, Y 3 Same as the above definition.)

[0340] CF2=CF-O-(CF2C(CF3)F) n2 -Y 3 (6b)

[0341] (where n2 represents an integer from 1 to 5, Y 3 Same as the above definition.)

[0342] CF2=CF-O-(CFX 1 ) n3 -Y 3 (6c)

[0343] (Where, X 1 represents F or CF3, n3 represents an integer from 1 to 10, Y 3 Same as the above definition.)

[0344] CF2=CF-O-(CF2CFX 1 O)n4 -(CF2) n6 -Y 3 (6d)

[0345] (wherein, n4 represents an integer of 1 to 10, n6 represents an integer of 1 to 3, and Y 3 and X 1 Same as the above definition.)

[0346] CF2=CF-O-(CF2CF2CFX 1 O) n5 -CF2CF2CF2-Y 3 (6e)

[0347] (where n5 represents an integer from 0 to 10, Y 3 and X 1 Same as the above definition.)

[0348] In the above formula (6a), the above n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. From the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M. M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0349] As the compound represented by the above formula (6a), for example, CF2=CF-O-CF2COOM, CF2=CF(OCF2CF2COOM), CF2=CF(OCF2CF2CF2COOM), CF2=CF-O-CF2SO3M, CF2=CF(OCF2CF2SO3M), CF2=CF(OCF2CF2CF2SO3M) (wherein, M has the same definition as above).

[0350] In the above formula (6b), from the perspective of the stability of the obtained aqueous dispersion, the above n2 is preferably an integer of 3 or less, and from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, Y 3 It is preferably -COOM or -SO3M. M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0351] In the above formula (6c), from the perspective of water solubility, the above n3 is preferably an integer of 5 or less, and from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M. From the viewpoint of improving dispersion stability, the above-mentioned M is preferably H or NH4.

[0352] In the above formula (6d), from the perspective of the stability of the aqueous dispersion, the above X 1 Preferably -CF3, from the perspective of water solubility, the above n4 is preferably an integer of 5 or less, from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M, and the above-mentioned M is preferably H or NH4.

[0353] As the compound represented by the above formula (6d), for example, CF2=CFOCF2CF(CF3)OCF2CF2COOM, CF2=CFOCF2CF(CF3)OCF2COOM, CF2=CFOCF2CF(CF3)OCF2CF2CF2COOM, CF2=CFOCF2CF(CF3)OCF2CF2SO3M, CF2=CFOCF2CF(CF3)OCF2SO3M, CF2=CFOCF2CF(CF3)OCF2CF2CF2SO3M (wherein, M represents H, NH4 or alkali metal).

[0354] In the general formula (6e), from the perspective of water solubility, the above n5 is preferably an integer of 5 or less, and from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M, and the above-mentioned M is preferably H or NH4.

[0355] Examples of the compound represented by the general formula (6e) include CF2=CFOCF2CF2CF2COOM and CF2=CFOCF2CF2CF2SO3M (wherein M represents H, NH4 or an alkali metal).

[0356] In the general formula (7), Rf is preferably a fluorine-containing alkylene group having 1 to 40 carbon atoms. In the general formula (7), at least one of X and Y preferably contains a fluorine atom.

[0357] The compound represented by general formula (7) is preferably selected from general formula (7a):

[0358] CF2=CF-(CF2) n1 -Y 3 (7a)

[0359] (where n1 represents an integer from 1 to 10, Y 3 Same as the above definition) and the compound represented by the general formula (7b):

[0360] CF2=CF-(CF2C(CF3)F) n2 -Y 3 (7b)

[0361] (where n2 represents an integer from 1 to 5, Y 3 At least one member selected from the group consisting of compounds represented by (same as defined above).

[0362] The above Y 3 Preferably -SO3M or -COOM, M is preferably H, metal atom, NR 7y 4. Imidazolium with or without substituents, pyridinium with or without substituents, or phosphonium with or without substituents. 7y represents H or an organic group.

[0363] In the above formula (7a), the above n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. From the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, the above Y 3 It is preferably -COOM or -SO3M. M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0364] Examples of the compound represented by the above formula (7a) include CF2=CFCF2COOM and CF2=CFCF2SO3M (wherein M has the same meaning as above).

[0365] In the above formula (7b), from the perspective of the stability of the obtained aqueous dispersion, the above n2 is preferably an integer of 3 or less, and from the perspective of obtaining appropriate water solubility and stability of the aqueous dispersion, Y 3 It is preferably -COOM or -SO3M. M is preferably H or NH4 because it is less likely to remain as an impurity and the heat resistance of the obtained molded body is improved.

[0366] The above-mentioned modified monomer preferably includes a modified monomer (A), preferably includes at least one selected from the group consisting of compounds represented by general formula (5a), general formula (5c), general formula (6a), general formula (6b), general formula (6c) and general formula (6d), and more preferably includes a compound represented by general formula (5a) or general formula (5c).

[0367] When using modified monomer (A) as modified monomer, the content of modified monomer (A) unit is preferably in the range of 0.00001 mass % to 1.0 mass % relative to the total polymerized units of above-mentioned TFE polymer (PTFE). As the lower limit, it is more preferably 0.0001 mass %, more preferably 0.0005 mass %, further preferably 0.001 mass %, and then more preferably 0.005 mass %. As the upper limit, it is 0.90 mass %, 0.50 mass %, 0.40 mass %, 0.30 mass %, 0.20 mass %, 0.15 mass %, 0.10 mass %, 0.08 mass %, 0.05 mass %, 0.01 mass %.

[0368] (Polymerization Conditions)

[0369] Polymerization of tetrafluoroethylene can be carried out under normal pressure and temperature. Typically, the polymerization temperature is 5°C to 120°C, and the polymerization pressure is 0.05 MPaG to 10 MPaG. The polymerization temperature and pressure are appropriately determined based on the type of monomer, the molecular weight of the desired low-molecular-weight polytetrafluoroethylene, the reaction rate, and other factors.

[0370] After the aqueous dispersion is prepared, the stirring of the contents of the reactor may be stopped as needed, and the reactor may be vented until the pressure inside reaches normal pressure, thereby stopping the polymerization of tetrafluoroethylene.

[0371] In order to stop the polymerization reaction of tetrafluoroethylene, a polymerization inhibitor (radical scavenger) may be added.

[0372] As polymerization inhibitors, compounds that add to free radicals in the polymerization system or do not have the ability to reinitiate after chain transfer are used. Specifically, compounds with the following functions are used: they easily undergo chain transfer reactions with primary free radicals or growing free radicals, and then generate stable free radicals that do not react with monomers, or they easily undergo addition reactions with primary free radicals or growing free radicals to generate stable free radicals. The activity of substances generally referred to as chain transfer agents is characterized by the chain transfer constant and reinitiation efficiency. Among chain transfer agents, substances with a reinitiation efficiency of basically 0% are called polymerization inhibitors. As polymerization inhibitors, it is preferred that at least one of the group consisting of aromatic hydroxyl compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates and copper chloride (CuCl2) is selected. As aromatic hydroxyl compounds, unsubstituted phenols, polyphenols, salicylic acid, m-salicylic acid or p-salicylic acid, gallic acid, naphthol, etc. can be mentioned. Examples of the above-mentioned unsubstituted phenols include o-nitrophenol, m-nitrophenol or p-nitrophenol, o-aminophenol, m-aminophenol or p-aminophenol, and p-nitrosophenol. Examples of the polyphenols include catechol, resorcinol, hydroquinone, pyrogallol, pyrogallol, and naphthol resorcinol. Examples of the aromatic amines include o-phenylenediamine, m-phenylenediamine or p-phenylenediamine, and benzidine. Examples of the above-mentioned quinone compounds include hydroquinone, o-benzoquinone, m-benzoquinone or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN). Among the above-mentioned polymerization inhibitors, quinone compounds are preferred, and hydroquinone is more preferred.

[0373] (Aqueous dispersion obtained by polymerization)

[0374] The polymerization of tetrafluoroethylene produces an aqueous dispersion of primary particles containing low-molecular-weight polytetrafluoroethylene. The content of the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion after polymerization is generally 8% to 50% by mass relative to the aqueous dispersion.

[0375] Aqueous dispersions obtained by polymerizing tetrafluoroethylene may contain, in addition to low-molecular-weight polytetrafluoroethylene, fluorinated compounds having hydrophilic groups generated by the polymerization of monomers. In particular, when tetrafluoroethylene is polymerized using a hydrocarbon chain transfer agent, fluorinated compounds having hydrophilic groups tend to be generated.

[0376] The fluorinated compound having a hydrophilic group in the aqueous dispersion obtained by polymerization is typically a fluorinated compound having a hydrophilic group having a molecular weight of 1000 g / mol or less. The production method of the present invention ultimately produces an aqueous dispersion in which the content of the fluorinated compound having a hydrophilic group having a molecular weight of 1000 g / mol or less is reduced.

[0377] In one embodiment of the aqueous dispersion obtained by polymerization, a fluorinated surfactant added during polymerization is contained as a fluorinated compound having a hydrophilic group. The fluorinated surfactant added during polymerization is as described above as the fluorinated surfactant used in the polymerization of tetrafluoroethylene.

[0378] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, or may be 10% by mass or less, or 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0379] The content of the fluorinated surfactant used when polymerizing tetrafluoroethylene in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, and may be 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0380] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound (I) represented by the following general formula (I).

[0381] General formula (I): F(CF2) n1 COOM(I)

[0382] (where n1 is an integer from 3 to 13, M is H, metal atom, NR 7 4. an imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent, R 7 is H or an organic group. )

[0383] When the aqueous dispersion obtained by polymerization contains at least the compound (I) represented by the general formula (I) as the fluorine-containing compound having a hydrophilic group, the content of the compound (I) in the aqueous dispersion obtained by polymerization may be 200 ppb by mass or more, 300 ppb by mass or more, or 400 ppb by mass or more, and may be 10% by mass or less, 1% by mass or less, or 0.5% by mass or less, relative to the aqueous dispersion.

[0384] In one embodiment of the aqueous dispersion obtained by polymerization, the compound represented by the following general formula (H1) is contained as the fluorine-containing compound having a hydrophilic group.

[0385] General formula (H1): [X-Rf-A - ] i Mi+

[0386] (wherein, X represents H, Cl, Br, F or I, Rf represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, A - Represents acid group, M i+ represents a cation having a valence number i, where i represents an integer from 1 to 3)

[0387] In one embodiment of the aqueous dispersion obtained by polymerization, the compound represented by the following general formula (H2) is contained as the fluorine-containing compound having a hydrophilic group.

[0388] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0389] (where n represents an integer from 9 to 14, M + represents a cation.)

[0390] It is known that when perfluoro(alkyl vinyl ether) or the like is used as a monomer, a compound represented by general formula (H2) (perfluoroalkanoic acid) is formed during polymerization (see International Publication No. 2019 / 161153).

[0391] In one embodiment of the aqueous dispersion obtained by polymerization, the compound represented by the following general formula (H3) is contained as the fluorine-containing compound having a hydrophilic group.

[0392] General formula (H3): [R 1 -OL-CO2 - ]M +

[0393] (Where R 1 represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group, M + represents a cation.)

[0394] In one embodiment of the aqueous dispersion obtained by polymerization, the compound represented by the general formula (H4) is contained as the fluorine-containing compound having a hydrophilic group.

[0395] General formula (H4): H-Rf n0 -Y 0

[0396] (Where Rf n0It is an alkylene group having 3 to 20 carbon atoms, which is linear, branched or cyclic, in which some or all of the H groups are substituted with F, and the alkylene group may or may not contain one or more ether bonds, and some of the H groups may or may not be substituted with Cl. 0 is an anionic group.)

[0397] Examples of the compound represented by the general formula (H4) include compounds represented by any of the following general formulae.

[0398] General formula (H4-1): [H-(CF2) m1 CO2 - ]M +

[0399] (wherein, m1 represents an integer from 3 to 19, M + represents a cation.)

[0400] General formula (H4-2): [H-(CF2) m2 -(CF(CF3)) m3 -CO2 - ]M +

[0401] (wherein, m2 represents an integer of 1 to 17, m3 represents an integer of 1 to 9, and M + represents a cation. Here, m2 and m3 are selected so as to satisfy 3≤(m2+2×m3)≤19, and the order of the repeating units in the formula is arbitrary.

[0402] (Preprocessing)

[0403] In the production method of the present invention, tetrafluoroethylene is polymerized to prepare an aqueous dispersion containing low molecular weight polytetrafluoroethylene, and then the aqueous dispersion is pretreated before adding a radical generator to the aqueous dispersion.

[0404] As a pretreatment method, any of the following methods (1) to (4) is preferred. These methods can be carried out alone or in combination.

[0405] (1) A method of contacting an aqueous dispersion with a gas containing oxygen.

[0406] (2) A method of contacting an aqueous dispersion with an oxidizing agent.

[0407] (3) A method of contacting an aqueous dispersion with alcohol.

[0408] (4) A method of adjusting the pH of the aqueous dispersion to 4.0 or higher.

[0409] As method (1), for example, the following can be mentioned:

[0410] A method of polymerizing tetrafluoroethylene and then supplying a gas containing oxygen into a reactor to contact the aqueous dispersion with the gas containing oxygen;

[0411] A method of recovering the aqueous dispersion in the reactor after polymerizing tetrafluoroethylene and placing it in a container separate from the reactor, and contacting the aqueous dispersion with an oxygen-containing gas (air);

[0412] A method in which a gas containing oxygen is blown into an aqueous dispersion to generate bubbles, thereby contacting the aqueous dispersion with the oxygen-containing gas (bubbling method);

[0413] Methods for stirring in the atmosphere; etc.

[0414] As method (1), a method of blowing an oxygen-containing gas into the aqueous dispersion to generate bubbles and bring the aqueous dispersion into contact with the oxygen-containing gas (bubbling method) is preferred, or a method of stirring the aqueous dispersion in the atmosphere. The flow rate of the oxygen-containing gas when blowing the aqueous dispersion is, for example, 1 L / min to 30 L / min. The aqueous dispersion may be stirred while blowing the oxygen-containing gas into the aqueous dispersion (ventilation stirring).

[0415] Examples of the oxygen-containing gas include oxygen gas and air. The oxygen content of the oxygen-containing gas may be 20% to 100% by volume.

[0416] The temperature when the aqueous dispersion is brought into contact with the oxygen-containing gas is preferably 5°C to 99°C, more preferably 15°C or higher, and even more preferably lower than 35°C.

[0417] The pressure when the aqueous dispersion is brought into contact with the oxygen-containing gas may be normal pressure.

[0418] The time for which the aqueous dispersion is in contact with the oxygen-containing gas is preferably 1 minute or longer, more preferably 5 minutes or longer, even more preferably 10 minutes or longer, particularly preferably 30 minutes or longer, preferably 48 hours or shorter, more preferably 24 hours or shorter, and even more preferably 12 hours or shorter. The time for which the aqueous dispersion is in contact with the oxygen-containing gas may be the time for which the bubbling method is performed. Alternatively, the time for which the aqueous dispersion is in contact with the oxygen-containing gas may be the stirring time for stirring in the atmosphere.

[0419] In one embodiment of the production method of the present invention, the aqueous dispersion is preferably pretreated using method (1) to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more. By sufficiently increasing the dissolved oxygen content of the aqueous dispersion before adding the free radical generator to the aqueous dispersion, the content of the fluorinated compound in the aqueous dispersion can be more efficiently reduced. The oxygen saturation of the aqueous dispersion is preferably 60.0% or more, more preferably 70.0% or more, and even more preferably 80.0% or more. The oxygen saturation of the aqueous dispersion may be 99% or less.

[0420] In addition, one embodiment of the production method of the present invention is to pretreat the aqueous dispersion using method (1) to increase the oxygen saturation of the aqueous dispersion to 50.0% to 70.0%, and then use any one of methods (1) to (4) to increase the oxygen saturation of the aqueous dispersion to 80.0% or more.

[0421] In the present invention, oxygen saturation refers to the ratio of the actual dissolved oxygen content to the saturated dissolved oxygen content of water at 1 atmosphere. The oxygen saturation can be measured using an optical dissolved oxygen meter.

[0422] In one embodiment of the production method of the present invention, it is preferred to pre-treat the aqueous dispersion using method (1) to obtain a polymerization radical content of 0 g represented by the general formula (1). -1 The content of the oxidative radical represented by the following general formula (2) is 0.1 g -1 The above aqueous dispersion. The content of oxidative free radicals can be 9.0g -1 The following. In tetrafluoroethylene or an aqueous dispersion obtained by polymerizing tetrafluoroethylene and a modified monomer, a polymerization radical represented by the general formula (1) is contained. Before adding a radical generator to the aqueous dispersion, the polymerization radical in the aqueous dispersion is converted into an oxidative radical, thereby more efficiently reducing the content of the fluorine-containing compound in the aqueous dispersion. The content of the polymerization radical is theoretically not less than 0g -1 , but sometimes get below 0g -1 The measured value of .

[0423] General formula (1): R-(CF2-CF2) n (In the formula, R represents a monovalent group, n represents an integer greater than or equal to 1, and represents an unpaired electron.)

[0424] General formula (2): R-(CF2-CF2) n OO·(wherein, R represents a monovalent group, n represents an integer greater than or equal to 1, and · represents an unpaired electron.)

[0425] In the general formulae (1) and (2), R is a monovalent group. R is preferably COOH, OH, SO3H, CF3, CH3 or R 11 -R 12 -(where R 11 Represents COOH, OH, SO3H, CF3 or CH3, R 12 represents a chain formed by polymerization of tetrafluoroethylene and a modifying monomer).

[0426] As method (2), for example, there can be mentioned a method in which an oxidizing agent is added to an aqueous dispersion to bring the aqueous dispersion into contact with the oxidizing agent.

[0427] Examples of the oxidizing agent include: gaseous oxidizing agents such as ozone, fluorine, chlorine, bromine, and iodine; inorganic acids and inorganic acid salts such as nitric acid, nitric acid, sulfurous acid, sulfuric acid, persulfuric acid, hydrochloric acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, hydrofluoric acid, bromic acid, iodic acid, phosphoric acid, boric acid, chromic acid, dichromic acid, and permanganic acid; and peroxides such as hydrogen peroxide. Among these, hydrogen peroxide is preferred as the oxidizing agent.

[0428] The amount of the oxidizing agent brought into contact with the aqueous dispersion is preferably 1 to 500 mass ppm, more preferably 3 mass ppm or more, and even more preferably 200 mass ppm or less, relative to the mass of the aqueous dispersion.

[0429] The temperature when the aqueous dispersion is brought into contact with the oxidizing agent is preferably 5°C to 99°C, more preferably 15°C or higher, and even more preferably lower than 35°C.

[0430] The pressure when the aqueous dispersion is brought into contact with the oxidizing agent may be normal pressure.

[0431] The time for contacting the aqueous dispersion with the oxidant is preferably 1 minute or longer, more preferably 5 minutes or longer, further preferably 10 minutes or longer, particularly preferably 30 minutes or longer, and preferably 48 hours or shorter, more preferably 24 hours or shorter, further preferably 12 hours or shorter.

[0432] In one embodiment of the production method of the present invention, the aqueous dispersion is preferably pretreated using method (2) to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more. By sufficiently increasing the dissolved oxygen content of the aqueous dispersion before adding the free radical generator to the aqueous dispersion, the content of the fluorinated compound in the aqueous dispersion can be more efficiently reduced. The oxygen saturation of the aqueous dispersion is preferably 60.0% or more, more preferably 70.0% or more, and even more preferably 80.0% or more. The oxygen saturation of the aqueous dispersion may be 99% or less.

[0433] In one embodiment of the production method of the present invention, it is preferred to pre-treat the aqueous dispersion using method (2) to obtain a polymerization radical content of 0 g represented by the general formula (1). -1 The content of the oxidative radical represented by the following general formula (2) is 0.1 g -1 The above aqueous dispersion. The content of oxidative free radicals can be 9.0g -1 The following is an aqueous dispersion of tetrafluoroethylene or tetrafluoroethylene obtained by polymerizing a modified monomer, wherein the polymerization radicals represented by the general formula (1) are contained. Before adding a radical generator to the aqueous dispersion, the polymerization radicals in the aqueous dispersion are converted into oxidation radicals, thereby more efficiently reducing the content of the fluorinated compound in the aqueous dispersion. The polymerization radicals and oxidation radicals are as described above.

[0434] As method (3), for example, a method in which an aqueous dispersion is brought into contact with alcohol by adding alcohol to the aqueous dispersion can be cited. In tetrafluoroethylene or an aqueous dispersion obtained by polymerizing tetrafluoroethylene and a modified monomer, a polymerization radical represented by the general formula (1) is contained. If the aqueous dispersion is brought into contact with alcohol, the polymerization radical contained in the aqueous dispersion removes H from the C-H bond of the alcohol, and the polymerization radical is deactivated. By deactivating the polymerization radical in the aqueous dispersion before adding a radical generator to the aqueous dispersion, the content of the fluorinated compound in the aqueous dispersion can be more efficiently reduced.

[0435] The alcohol is preferably an alcohol having 1 to 10 carbon atoms, more preferably at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol, and even more preferably at least one selected from the group consisting of methanol and ethanol.

[0436] The amount of the alcohol brought into contact with the aqueous dispersion is preferably 1 to 500 mass ppm, more preferably 3 mass ppm or more, and even more preferably 200 mass ppm or less, relative to the mass of the aqueous dispersion.

[0437] The temperature when the aqueous dispersion is brought into contact with the alcohol is preferably 5°C to 99°C, more preferably 15°C or higher, and even more preferably lower than 35°C.

[0438] The pressure when the aqueous dispersion is brought into contact with the alcohol may be normal pressure.

[0439] The time for contacting the aqueous dispersion with the alcohol is preferably 1 minute or longer, more preferably 5 minutes or longer, further preferably 10 minutes or longer, particularly preferably 30 minutes or longer, and preferably 48 hours or shorter, more preferably 24 hours or shorter, further preferably 12 hours or shorter.

[0440] In one embodiment of the production method of the present invention, the aqueous dispersion is preferably pretreated using method (3) to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more. By sufficiently increasing the dissolved oxygen content of the aqueous dispersion before adding the free radical generator to the aqueous dispersion, the content of the fluorinated compound in the aqueous dispersion can be more efficiently reduced. The oxygen saturation of the aqueous dispersion is preferably 60.0% or more, more preferably 70.0% or more, and even more preferably 80.0% or more. The oxygen saturation of the aqueous dispersion may be 99% or less.

[0441] As method (4), a method of adjusting the pH of the aqueous dispersion to 4.0 or more by adding a base such as ammonia to the aqueous dispersion can be cited. In tetrafluoroethylene or an aqueous dispersion obtained by polymerizing tetrafluoroethylene and a modified monomer, a polymerization radical represented by the general formula (1) is contained. If the pH of the aqueous dispersion is adjusted to 4.0 or more, the reactivity of the polymerization radicals contained in the aqueous dispersion is improved, and free radicals are easily generated from the free radical generator during heat treatment. As a result, by adjusting the pH of the aqueous dispersion to 4.0 or more before adding the free radical generator to the aqueous dispersion, the content of the fluorinated compound in the aqueous dispersion can be more efficiently reduced.

[0442] The pH of the aqueous dispersion obtained by polymerization is usually less than 4.0. Therefore, in method (4), the pH of the aqueous dispersion is usually increased by adding a base.

[0443] In the method (4), the pH of the aqueous dispersion can be adjusted to preferably 5.0 or higher, more preferably 6.0 or higher, and even more preferably 7.0 or higher.

[0444] (Free radical generator)

[0445] In the production method of the present invention, a radical generator is added to the aqueous dispersion after pre-treatment of the aqueous dispersion and before heat treatment of the aqueous dispersion.

[0446] The radical generator is not particularly limited as long as it is a compound that can decompose at the temperature during heat treatment to generate radicals. As the radical generator, a water-soluble radical generator is preferred because it can easily diffuse the radicals into the aqueous dispersion.

[0447] Examples of the free radical generator include organic peroxides, inorganic peroxides, organic azo compounds, and combinations of oxidizing agents and reducing agents. Preferably, the free radical generator is at least one selected from the group consisting of inorganic peroxides, organic peroxides, and combinations of oxidizing agents and reducing agents, and more preferably, an inorganic peroxide.

[0448] As the inorganic peroxide, a water-soluble inorganic peroxide is preferred. Examples of the inorganic peroxide include hydrogen peroxide, perchlorates, perborates, perphosphates, percarbonates, and persulfates, with persulfates being preferred. As the persulfate, at least one selected from the group consisting of ammonium persulfate, sodium persulfate, and potassium persulfate is preferred, with ammonium persulfate being more preferred.

[0449] As the organic peroxide, a water-soluble organic peroxide is preferred. Examples of the organic peroxide include peroxydicarbonates such as disuccinic acid peroxide and diglutaric acid peroxide.

[0450] As the free radical generator, an oxidizing agent and a reducing agent may be used in combination. By using the oxidizing agent and the reducing agent in combination, free radicals can be generated from the free radical generator by a redox reaction between the oxidizing agent and the reducing agent, thereby lowering the temperature during the heat treatment.

[0451] Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimides, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the oxidizing agent, it is also preferable to add copper salts or iron salts. Examples of copper salts include copper (II) sulfate, and examples of iron salts include iron (II) sulfate.

[0452] Examples of combinations of oxidizing agents and reducing agents include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / ferric sulfate, manganese triacetate / oxalic acid, ceric ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When using a combination of an oxidizing agent and a reducing agent, either the oxidizing agent or the reducing agent may be pre-added to the aqueous dispersion, followed by the addition of the other agent continuously or intermittently.

[0453] From the perspective of improving the removal efficiency of fluorinated compounds having hydrophilic groups, the amount of the radical generator added is preferably 0.0001 mole times or more, more preferably 0.001 mole times or more, further preferably 0.01 mole times or more, preferably 1000 mole times or less, more preferably 500 mole times or less, and further preferably 100 mole times or less, relative to the molar number of the fluorinated surfactant in the aqueous dispersion.

[0454] In the case where the addition amount of the free radical generator is relatively large, by heat treatment, a part or all of the fluoropolymer in the aqueous dispersion is sometimes precipitated. Therefore, in order to obtain a low molecular weight polytetrafluoroethylene aqueous dispersion in which the primary particles of the low molecular weight polytetrafluoroethylene are stably dispersed in an aqueous medium, the upper limit of the addition amount of the free radical generator is preferably selected. From the aspect of being able to suppress the precipitation of the low molecular weight polytetrafluoroethylene when the removal efficiency of the fluorochemical with a hydrophilic group is not damaged, the addition amount of the free radical generator is preferably less than 50 mole times relative to the mole number of the fluorosurfactant in the aqueous dispersion, more preferably less than 25 mole times, further preferably less than 10 mole times, and particularly preferably less than 5 mole times.

[0455] The method for adding the free radical generator is not particularly limited. The free radical generator may be added directly to the aqueous dispersion, or a solution containing the free radical generator may be prepared and added to the aqueous dispersion. Furthermore, the free radical generator may be added while stirring the aqueous dispersion, or the aqueous dispersion may be stirred after the free radical generator is added.

[0456] The temperature of the aqueous dispersion to which the radical generator is added is not particularly limited. The aqueous dispersion may be heated for heat treatment after the radical generator is added, or the aqueous dispersion may be heated to a temperature suitable for heat treatment before the radical generator is added.

[0457] The heat treatment may be performed while stirring the aqueous dispersion.

[0458] (Heat Treatment)

[0459] A radical generator is added to an aqueous dispersion to prepare an aqueous dispersion containing the radical generator, and then the aqueous dispersion containing the radical generator is heat-treated.

[0460] The temperature of the heat treatment is not particularly limited as long as it is above the temperature at which the free radical generator decomposes to generate free radicals (decomposition temperature), but is preferably above 35°C, more preferably above 40°C, further preferably above 45°C, particularly preferably above 50°C, preferably below 120°C, more preferably below 110°C, further preferably below 100°C, and particularly preferably below 90°C.

[0461] When the heat treatment temperature is relatively high, some or all of the fluoropolymer in the aqueous dispersion may precipitate during the heat treatment. Therefore, in order to obtain a low molecular weight polytetrafluoroethylene aqueous dispersion in which primary particles of low molecular weight polytetrafluoroethylene are stably dispersed in the aqueous medium, it is preferable to select an upper limit for the heat treatment temperature. To suppress the precipitation of low molecular weight polytetrafluoroethylene without compromising the removal efficiency of the fluorinated compound having a hydrophilic group, the heat treatment temperature is preferably 95°C or lower, more preferably 90°C or lower, and even more preferably 85°C or lower.

[0462] During the heat treatment of an aqueous dispersion, the aqueous dispersion does not necessarily need to be heated, as long as the aqueous dispersion can be maintained at a desired temperature or above. However, the aqueous dispersion may be heated while being heat treated. The heating method for heat treating the aqueous dispersion while being heated is not particularly limited. For example, the container containing the aqueous dispersion may be placed in a thermostatic bath for heating, or the aqueous dispersion may be placed in a container equipped with a heater and heated using the heater.

[0463] The heat treatment pressure is not particularly limited and may be normal pressure. For example, when the heat treatment temperature is relatively high and boiling of the aqueous dispersion needs to be suppressed, the heat treatment pressure may be higher than normal pressure.

[0464] The heat treatment time is not particularly limited as long as the generated free radicals sufficiently act on the components contained in the aqueous dispersion, but is preferably 15 minutes or longer, more preferably 30 minutes or longer, and even more preferably 60 minutes or longer, and is preferably 1200 minutes or shorter, more preferably 900 minutes or shorter, and even more preferably 600 minutes or shorter.

[0465] The aqueous dispersion may also be heat-treated while being stirred. Free radicals are generated by decomposing a free radical generator by heat treatment. However, when an oxidizing agent and a reducing agent are used in combination as free radical generators, free radicals are generated by thermal decomposition of the free radical generator and also by redox reactions.

[0466] (Low molecular weight polytetrafluoroethylene aqueous dispersion)

[0467] The production method of the present invention can produce an aqueous dispersion of low molecular weight polytetrafluoroethylene. The low molecular weight polytetrafluoroethylene can be a TFE homopolymer containing only tetrafluoroethylene units or a modified polytetrafluoroethylene containing TFE units and modifying monomer units.

[0468] The low molecular weight polytetrafluoroethylene contained in the aqueous dispersion is polytetrafluoroethylene that has melt processability but does not fibrillate. On the other hand, the high molecular weight polytetrafluoroethylene is polytetrafluoroethylene that does not have melt processability and does not fibrillate.

[0469] Non-melt processability refers to the property that the melt flow rate cannot be measured at a temperature above the crystallization melting point according to ASTM D 1238 and D 2116.

[0470] The presence of fibrillation can be determined by paste extrusion, a typical method for molding a powder made from a tetrafluoroethylene polymer, known as "high molecular weight polytetrafluoroethylene powder." Paste extrusion is generally possible because high molecular weight polytetrafluoroethylene exhibits fibrillation. If the unfired molded article obtained by paste extrusion lacks substantial strength or elongation, for example, if it breaks when stretched at 0% elongation, it is considered non-fibrillation.

[0471] The melt viscosity of low molecular weight polytetrafluoroethylene at 380°C is preferably 1×10 2 ~7×10 5 Pa·s. In the present invention, "low molecular weight" means that the melt viscosity is within the above range. High molecular weight polytetrafluoroethylene has a much higher melt viscosity than low molecular weight polytetrafluoroethylene, and it is difficult to measure its exact melt viscosity. The melt viscosity is the following value: according to ASTM D1238, using a flow tester (manufactured by Shimadzu Corporation) and A 2 g sample preheated at 380° C. for 5 minutes was held at the above temperature using a mold and a load of 0.7 MPa, and the obtained value was measured as the above melt viscosity.

[0472] The peak temperature of the low molecular weight polytetrafluoroethylene is preferably 322° C. to 333° C., more preferably 323° C. or higher, further preferably 324° C. or higher, and more preferably 332° C. or lower.

[0473] The peak temperature can be determined as follows: using a differential scanning calorimeter (DSC), low molecular weight polytetrafluoroethylene that has not been heated to a temperature of 300°C or higher is heated at a rate of 10°C / minute to plot a DSC curve, and the temperature corresponding to the minimum point of the heat of fusion in the temperature range of 250°C to 380°C of the DSC curve is determined, thereby determining the peak temperature.

[0474] In one embodiment of the aqueous dispersion obtained by the production method of the present invention, the fluorinated compound having a hydrophilic group is contained in an amount of preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, further preferably 5 ppb by mass or less, further preferably less than 1 ppb by mass, and preferably greater than 0 ppb by mass, relative to the mass of the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion.

[0475] In one embodiment of the aqueous dispersion obtained by the production method of the present invention, the compound represented by the following general formula (H1) is contained as the fluorine-containing compound having a hydrophilic group.

[0476] General formula (H1): [X-Rf-A - ] i M i+

[0477] (wherein, X represents H, Cl, Br, F or I, Rf represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, A - Represents acid group, M i+ represents a cation having a valence number i, where i represents an integer from 1 to 3)

[0478] In one embodiment of the aqueous dispersion obtained by the production method of the present invention, the aqueous dispersion contains a compound represented by the following general formula (H2) as the fluorine-containing compound having a hydrophilic group.

[0479] General formula (H2): [C n-1 F 2n-1 COO - ]M +

[0480] (where n represents an integer from 9 to 14, M + represents a cation.)

[0481] It is known that when perfluoro(alkyl vinyl ether) or the like is used as a monomer, a compound represented by general formula (H2) (perfluoroalkanoic acid) is formed during polymerization (see International Publication No. 2019 / 161153).

[0482] In one embodiment of the aqueous dispersion obtained by the production method of the present invention, the aqueous dispersion contains a compound represented by the following general formula (H3) as the fluorine-containing compound having a hydrophilic group.

[0483] General formula (H3): [R 1 -OL-CO2 - ]M +

[0484] (Where R1 represents a linear or branched partially fluorinated or fully fluorinated aliphatic group, or a linear or branched partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom, L represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group, M + represents a cation.)

[0485] In one embodiment of the aqueous dispersion obtained by the production method of the present invention, the compound represented by the general formula (H4) is contained as the fluorine-containing compound having a hydrophilic group.

[0486] General formula (H4): H-Rf n0 -Y 0

[0487] (Where Rf n0 It is an alkylene group having 3 to 20 carbon atoms, which is linear, branched or cyclic, in which some or all of the H groups are substituted with F, and the alkylene group may or may not contain one or more ether bonds, and some of the H groups may or may not be substituted with Cl. 0 is an anionic group.)

[0488] Examples of the compound represented by the general formula (H4) include compounds represented by any of the following general formulae.

[0489] General formula (H4-1): [H-(CF2) m1 CO2 - ]M +

[0490] (where m1 represents an integer from 3 to 20, M + represents a cation.)

[0491] General formula (H4-2): [H-(CF2) m2 -(CF(CF3)) m3 -CO2 - ]M +

[0492] (wherein, m2 represents an integer of 1 to 17, m3 represents an integer of 1 to 9, and M + represents a cation. Here, m2 and m3 are selected so as to satisfy 3≤(m2+2×m3)≤19, and the order of the repeating units in the formula is arbitrary.

[0493] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion or powder can be quantified by a known method, for example, by LC / MS analysis.

[0494] First, methanol is added to the aqueous dispersion or powder for extraction, and the resulting extract is analyzed by LC / MS. To further improve extraction efficiency, Soxhlet extraction, ultrasonic treatment, or other methods can be used. The resulting extract is then concentrated using a nitrogen purge, and the fluorinated compounds in the concentrated extract are analyzed by LC / MS.

[0495] Molecular weight information was extracted from the obtained LC / MS spectrum, and it was confirmed that the molecular weight matched the structural formula of a candidate fluorine-containing compound having a hydrophilic group.

[0496] Then, aqueous solutions of the confirmed fluorinated compound having a hydrophilic group at five or more levels were prepared, and the aqueous solutions at each level were analyzed by LC / MS. The relationship between the content and the area relative to the content was plotted to create a calibration curve.

[0497] Then, using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing compound having a hydrophilic group in the extract can be converted into the content of the fluorine-containing compound having a hydrophilic group.

[0498] Note that the obtained extract can be concentrated by purging with nitrogen, thereby lowering the lower limit of quantification of the measurement method.

[0499] (Preparation and drying of wet powder)

[0500] In the production method of the present invention, after obtaining the low molecular weight polytetrafluoroethylene aqueous dispersion by the above-mentioned production method, the low molecular weight polytetrafluoroethylene in the aqueous dispersion is precipitated to produce a wet powder containing particles of the low molecular weight polytetrafluoroethylene, and the wet powder is dried to produce a powder.

[0501] The precipitation method of low molecular weight polytetrafluoroethylene is not particularly limited. For example, the aqueous dispersion is diluted with water to a polymer concentration of 5% to 20% by mass, and the pH is adjusted to neutral or alkaline depending on the situation. Then, stirring is carried out in a container with a stirrer more vigorously than the stirring in the polymerization of tetrafluoroethylene. Water-soluble organic compounds such as methanol and acetone; inorganic salts such as potassium nitrate and ammonium carbonate; inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid can also be added to the aqueous dispersion as a precipitating agent and stirred to precipitate the low molecular weight polytetrafluoroethylene. After the low molecular weight polytetrafluoroethylene is precipitated, a wet powder containing particles of the low molecular weight polytetrafluoroethylene can be recovered.

[0502] The wet powder may be washed before drying. The wet powder may be washed with water or an organic solvent. Washing may be performed once or multiple times. Examples of organic solvents used for washing include ethers, halogenated hydrocarbons, aromatic hydrocarbons, pyridine, nitriles, nitrogen-containing polar organic compounds, dimethyl sulfoxide, and alcohols.

[0503] The production method of the present invention allows the wet powder to be dried at a relatively low temperature. By drying the wet powder at a relatively low temperature, a powder having a small particle size and excellent microdispersibility in other materials can be obtained.

[0504] The drying temperature of the wet powder is preferably 70° C. or lower than the peak temperature of the low molecular weight polytetrafluoroethylene, more preferably 100° C. or lower than the peak temperature of the low molecular weight polytetrafluoroethylene.

[0505] The drying temperature of the wet powder is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 220°C or lower.

[0506] The drying temperature of the wet powder is preferably 100° C. or higher, more preferably 120° C. or higher, further preferably 140° C. or higher, and further preferably 160° C. or higher. If the drying temperature is too low, drying takes time and productivity may decrease.

[0507] The resulting powder can be classified or granulated. Furthermore, the resulting powder can be formed into pellets. In the production method of the present invention, since a powder with excellent microdispersibility in other materials can be directly obtained after drying, it is also preferred not to perform any post-treatment on the dried powder.

[0508] (use)

[0509] The aqueous dispersion and powder obtained by the production method of the present invention can be suitably used as molding materials, inks, cosmetics, coatings, greases, components for office automation equipment, additives for modifying toners, and additives for plating solutions. Examples of such molding materials include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide. The powder is particularly suitable as a thickener for grease.

[0510] Aqueous dispersions and powders can be used as additives to molding materials, for example, to improve the non-stickiness and sliding properties of copy rollers, enhance the texture of engineering plastic molded products such as furniture surface sheets, automobile dashboards, and home appliance covers; and improve the sliding properties and wear resistance of mechanical parts that generate mechanical friction, such as light-load bearings, gears, cams, push-button telephone buttons, projector and camera parts, and sliding materials.

[0511] Aqueous dispersions and powders can be used as additives in coatings to improve the slip of varnishes and paints. Aqueous dispersions and powders can be used as additives in cosmetics to improve the slip of foundations and other cosmetics.

[0512] The powder is also suitable for improving the oil repellency or water repellency of waxes and the like, and for improving the slip properties of greases and toners.

[0513] The aqueous dispersion and powder can also be used as an electrode binder for secondary batteries or fuel cells, a hardness adjuster for electrode binders, a water-repellent treatment agent for electrode surfaces, and the like.

[0514] Grease can also be prepared using powder and lubricating oil. The grease described above is characterized by containing powder and lubricating oil, so the powder is uniformly and stably dispersed in the lubricating oil, resulting in excellent properties such as load bearing, electrical insulation, and low moisture absorption.

[0515] The lubricating oil (base oil) may be a mineral oil or a synthetic oil. Examples of the lubricating oil (base oil) include paraffinic and cycloparaffinic mineral oils, synthetic hydrocarbon oils, ester oils, fluorinated oils, and synthetic oils such as silicone oils. Fluorinated oils are preferred due to their heat resistance. Examples of the fluorinated oil include perfluoropolyether oils and oligomers of trifluoroethylene chloride. The weight average molecular weight of oligomers of trifluoroethylene chloride may be 500 to 1200.

[0516] The grease may further contain a thickener. Examples of the thickener include metal soaps, complex metal soaps, bentonite, phthalocyanine, silica gel, urea compounds, urea-urethane compounds, urethane compounds, and imide compounds. Examples of the metal soap include sodium soaps, calcium soaps, aluminum soaps, and lithium soaps. Examples of the urea compounds, urea-urethane compounds, and urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, urea-urethane compounds, diurea compounds, and mixtures thereof.

[0517] The grease preferably contains 0.1% to 50% by mass of the powder, more preferably 0.5% or more by mass, and even more preferably 30% or less by mass. If the amount of powder is too high, the grease becomes too hard and may not exhibit sufficient lubricity. If the amount of powder is too low, the grease may not exhibit sufficient sealing properties.

[0518] The above-mentioned grease may also contain a solid lubricant, an extreme pressure agent, an antioxidant, an oiliness agent, a rust inhibitor, a viscosity index improver, a detergent dispersant, and the like.

[0519] While the embodiments have been described above, it will be understood that various changes can be made to the aspects and details without departing from the spirit and scope of the claims.

[0520] <1> According to a first aspect of the present invention, there is provided a method for producing an aqueous dispersion of low molecular weight polytetrafluoroethylene, wherein:

[0521] In the presence of a fluorinated surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium, tetrafluoroethylene is polymerized to prepare an aqueous dispersion containing low molecular weight polytetrafluoroethylene.

[0522] The obtained aqueous dispersion is pretreated.

[0523] A free radical generator is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the free radical generator is heat-treated to obtain a low molecular weight polytetrafluoroethylene aqueous dispersion.

[0524] <2> According to a second aspect of the present invention, there is provided the production method according to the first aspect, wherein the aqueous dispersion is pretreated by at least one of the following methods.

[0525] (1) A method of contacting the aqueous dispersion with a gas containing oxygen.

[0526] (2) A method of contacting the aqueous dispersion with an oxidizing agent.

[0527] (3) A method of contacting the aqueous dispersion with alcohol.

[0528] (4) A method of adjusting the pH of the aqueous dispersion to 4.0 or higher.

[0529] <3> According to a third aspect of the present invention, there is provided the production method according to the first aspect or the second aspect, wherein the aqueous dispersion is pretreated by contacting the aqueous dispersion with a gas containing oxygen to obtain an aqueous dispersion having an oxygen saturation of 50.0% or higher.

[0530] <4> According to a fourth aspect of the present invention, there is provided a production method based on any one of the first to third aspects, wherein the aqueous dispersion is pretreated by blowing a gas containing oxygen into the aqueous dispersion or by stirring the aqueous dispersion in the atmosphere to bring the aqueous dispersion into contact with the oxygen-containing gas.

[0531] <5> According to a fifth aspect of the present invention, there is provided a production method based on any one of the first to fourth aspects, wherein the aqueous dispersion is pretreated by contacting the aqueous dispersion with a gas containing oxygen to obtain a polymerization radical content of 0 g represented by the general formula (1). -1 The content of the oxidative radical represented by the following general formula (2) is 0.1 g -1 The above aqueous dispersion.

[0532] General formula (1): R-(CF2-CF2) n (In the formula, R represents a monovalent group, n represents an integer greater than or equal to 1, and represents an unpaired electron.)

[0533] General formula (2): R-(CF2-CF2) n OO·(wherein, R represents a monovalent group, n represents an integer greater than or equal to 1, and · represents an unpaired electron.)

[0534] <6> According to a sixth aspect of the present invention, there is provided the production method according to the first aspect or the second aspect, wherein the aqueous dispersion is pretreated by contacting the aqueous dispersion with an oxidizing agent to obtain an aqueous dispersion having an oxygen saturation of 50.0% or higher.

[0535] <7> According to a seventh aspect of the present invention, there is provided the production method according to the second aspect or the sixth aspect, wherein the oxidizing agent is hydrogen peroxide.

[0536] <8> According to an eighth aspect of the present invention, there is provided a production method according to the first aspect, the second aspect, the sixth aspect or the seventh aspect, wherein the aqueous dispersion is pretreated by contacting the aqueous dispersion with an oxidizing agent to obtain a polymerization radical content of 0 g represented by the general formula (1). -1 The content of the oxidative radical represented by the following general formula (2) is 0.1 g -1 The above aqueous dispersion.

[0537] General formula (1): R-(CF2-CF2) n (In the formula, R represents a monovalent group, n represents an integer greater than or equal to 1, and represents an unpaired electron.)

[0538] General formula (2): R-(CF2-CF2) n OO·(wherein, R represents a monovalent group, n represents an integer greater than or equal to 1, and · represents an unpaired electron.)

[0539] <9> According to a ninth aspect of the present invention, there is provided the production method according to the first or second aspect, wherein the aqueous dispersion is pretreated by contacting the aqueous dispersion with alcohol to obtain an aqueous dispersion having an oxygen saturation of 50.0% or higher.

[0540] <10> According to a tenth aspect of the present invention, there is provided the production method according to the second aspect or the ninth aspect, wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol.

[0541] <11> According to an eleventh aspect of the present invention, there is provided the production method according to any one of the first to tenth aspects, wherein the polymerization initiator is a water-soluble radical polymerization initiator.

[0542] <12> According to a twelfth aspect of the present invention, there is provided the production method according to any one of the first to eleventh aspects, wherein the temperature of the heat treatment is equal to or higher than the decomposition temperature of the radical generator.

[0543] <13> According to a 13th aspect of the present invention, there is provided the production method according to any one of the 1st to 12th aspects, wherein the radical generator is an inorganic peroxide.

[0544] <14> According to a fourteenth aspect of the present invention, there is provided the production method according to any one of the first to thirteenth aspects, wherein the peak temperature of the low molecular weight polytetrafluoroethylene is 322°C to 333°C.

[0545] <15> According to a fifteenth aspect of the present invention, there is provided a production method based on any one of the first to fourteenth aspects, wherein the low molecular weight polytetrafluoroethylene has a melt viscosity at 380° C. of 1×10 2 Pa·s~7×10 5 Pa·s.

[0546] <16> According to a 16th aspect of the present invention, there is provided a production method based on any one of the 1st to 15th aspects, wherein the polymerization initiator is a persulfate, the hydrocarbon chain transfer agent is an alkane having 1 to 5 carbon atoms, and the aqueous dispersion is pretreated by (1) contacting the aqueous dispersion with an oxygen-containing gas to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more.

[0547] <17> According to a seventeenth aspect of the present invention, there is provided a production method according to any one of the first to sixteenth aspects, wherein:

[0548] The polymerization initiator is a persulfate, and the hydrocarbon chain transfer agent is an alkane having 1 to 5 carbon atoms.

[0549] After preparing the aqueous dispersion containing the low molecular weight polytetrafluoroethylene,

[0550] (1-1-1) recovering the aqueous dispersion in the reactor and placing it in a container separate from the reactor, thereby contacting the aqueous dispersion with a gas containing oxygen to obtain an aqueous dispersion having an oxygen saturation of 50.0% to 70.0%,

[0551] then,

[0552] (1-1-2) blowing a gas containing 20% ​​to 100% by volume of oxygen into the aqueous dispersion at a flow rate of 1 L / min to 30 L / min to generate bubbles, and allowing the aqueous dispersion and the oxygen-containing gas to contact at 5° C. to 99° C. for 5 minutes or longer; or

[0553] (2-1) contacting the aqueous dispersion with hydrogen peroxide in an amount corresponding to 1 to 500 ppm by mass relative to the mass of the aqueous dispersion at 5° C. to 99° C. for 1 minute or longer; or

[0554] (3-1) contacting the aqueous dispersion with an alcohol having 1 to 10 carbon atoms in an amount corresponding to 1 to 500 ppm by mass relative to the mass of the aqueous dispersion at 5° C. to 99° C. for 1 minute or longer; or

[0555] (4-1) adding a base to the aqueous dispersion to adjust the pH of the aqueous dispersion to 4.0 or higher,

[0556] Thus, the aqueous dispersion is pretreated to obtain an aqueous dispersion having an oxygen saturation of 80% or more.

[0557] A persulfate in an amount of 0.01 to 5 molar times the molar number of the fluorinated surfactant in the aqueous dispersion is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the persulfate is heat-treated at 35° C. to 95° C. for 15 minutes or longer to obtain a low molecular weight polytetrafluoroethylene aqueous dispersion.

[0558] <18> According to an eighteenth aspect of the present invention, there is provided a method for producing a powder of low molecular weight polytetrafluoroethylene, wherein:

[0559] After obtaining a low molecular weight polytetrafluoroethylene aqueous dispersion by the production method according to any one of the first to seventeenth aspects,

[0560] The low molecular weight polytetrafluoroethylene in the aqueous dispersion is precipitated to prepare a wet powder containing particles of the low molecular weight polytetrafluoroethylene.

[0561] The wet powder is dried to produce the powder.

[0562] Example

[0563] Next, embodiments of the present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0564] Each numerical value in the examples was measured by the following method.

[0565] <Amount of Free Radicals in Aqueous Dispersion>

[0566] The contents of polymerization radicals and oxidation radicals in the aqueous dispersion were determined using an electron spin resonance method (ESR method).

[0567] Polymerization radical: HOOC-(CF2-CF2)n (In the formula, n represents an integer greater than or equal to 1, and represents an unpaired electron.)

[0568] Oxidative free radical: HOOC-(CF2-CF2) n OO·(wherein, n represents an integer greater than or equal to 1, and · represents an unpaired electron.)

[0569] The content of polymerization radicals was determined from the intensity of the peak at g = 2.0056, which appeared in the first-order differential spectrum obtained by analyzing the aqueous dispersion using electron spin resonance. The content of oxidation radicals was determined from the intensity of the peak at g = 2.0218, which appeared in the first-order differential spectrum obtained by analyzing the aqueous dispersion using electron spin resonance.

[0570] Analysis conditions

[0571] Device: JEOL Ltd. (JEOL), JES-FR30EX

[0572] Measurement temperature: 23±3℃

[0573] Microwave frequency: 9.42 GHz

[0574] Microwave output power: 0.4mW

[0575] Central magnetic field: 347.548mT

[0576] Scan width: ±25mT

[0577] Scan time: 60s

[0578] Time constant: 0.03s

[0579] Magnetic field modulation width: 0.32mT

[0580] Scan times: 1

[0581] Modulation frequency: 100kHz

[0582] Mark:Mn 2+

[0583] <Oxygen saturation>

[0584] The measurement was performed using an optical dissolved oxygen meter FDO380.

[0585] <Solid Content Concentration of Aqueous Dispersion>

[0586] 1 g of the aqueous dispersion was dried in a forced air dryer at 150° C. for 60 minutes, and the ratio of the mass of the heating residue to the mass of the aqueous dispersion (1 g) was expressed as a percentage.

[0587] <Melt viscosity>

[0588] According to ASTM D 1238, using an overhead flow tester (manufactured by Shimadzu Corporation) and a die of 2Φ - 8L, 2 g of the sample pre-heated at 380 °C for 5 minutes was held at the above temperature under a load of 0.7 Mpa for measurement.

[0589] <Peak temperature>

[0590] Approximately 10 mg of PTFE powder that has not been heated to a temperature above 300 °C was accurately weighed, placed in a dedicated aluminum dish, and measured using TG / DTA (simultaneous differential thermal and thermogravimetric analyzer). Regarding the peak temperature, in an atmospheric atmosphere, in the temperature range of 25 °C to 600 °C, the aluminum dish was heated at a rate of 10 °C / min to obtain a differential thermal (DTA) curve, and the temperature corresponding to the maximum value in the obtained differential thermal (DTA) curve was taken as the peak temperature.

[0591] <Content of the compound represented by the general formula (H4 - 1) in the PTFE aqueous dispersion and PTFE powder>

[0592] The content of the fluorine-containing compound contained in the powder and the dispersion was determined in the form of the content of the fluorine-containing compound extracted from the powder and the dispersion.

[0593] 0 - 1. Extracting fluorine-containing compound from the powder

[0594] To 1 g of the powder, 10 g (12.6 mL) of methanol was added, and ultrasonic treatment was performed at 60 °C for 2 hours. After standing at room temperature, the solid component was removed to obtain an extract.

[0595] 0 - 2. Extracting fluorine-containing compound from the dispersion

[0596] The dispersion and methanol were mixed at a weight ratio of 1:1, and shaken to precipitate the powder. The supernatant was passed through a membrane filter to remove the solid component, thereby obtaining an extract.

[0597] The content of the compound represented by the general formula (H4 - 1) was determined by conversion to perfluorooctanoic acid.

[0598] 1. Preparation of calibration curve

[0599] Five levels of methanol standard solutions of perfluorooctanoic acid with known concentrations were prepared respectively, and measured using a liquid chromatography - mass spectrometer (Waters, LC - MS ACQUITY UPLC / TQD). In each concentration range, a and b were respectively obtained by using linear approximation from the methanol standard solution concentration and the peak integral value through the following relationship.

[0600] A = a×X + b

[0601] A: Peak area of ​​perfluorocarboxylic acid (perfluorooctanoic acid)

[0602] X: Concentration of perfluorocarboxylic acid (PFOA) (ng / mL)

[0603] Measurement equipment structure and LC-MS measurement conditions

[0604]

[0605] MRM assay parameters

[0606] [Table 2]

[0607] Table 2 MRM assay parameters

[0608]

[0609] 2. Determination of content

[0610] The content of the compound represented by the general formula (H4-1) having the carbon number (m1+1) contained in the extract was measured using a liquid chromatography-mass spectrometer based on a calibration curve.

[0611] The content of the compound represented by the general formula (H4-1) with the carbon number (m1+1) contained in the powder was determined from the following relational formula (1).

[0612] Ym=Xm×12.6 (1)

[0613] Ym: The content of the compound represented by the general formula (H4-1) with the number of carbon atoms (m1+1) contained in the powder (mass ppb / resin)

[0614] Xm: The content of the compound represented by the general formula (H4-1) with the number of carbon atoms (m1+1) contained in the extract (ng / mL)

[0615] The content of the compound represented by the general formula (H4-1) having the carbon number (m1+1) contained in the aqueous dispersion was determined from the following relational expression (2).

[0616] Ym=Xm×(1.26+(100-P) / 100) / (P / 100) (1)

[0617] Ym: The content of the compound represented by the general formula (H4-1) with the carbon number (m1+1) contained in the aqueous dispersion (mass ppb / resin)

[0618] Xm: The content of the compound represented by the general formula (H4-1) with the number of carbon atoms (m1+1) contained in the extract (ng / mL)

[0619] P: solid content concentration of aqueous dispersion (mass %)

[0620] The lower limit of quantification of the content of the compound represented by the general formula (H4-1) having a carbon number (m1+1) contained in the aqueous dispersion is 1.26+(100-P) / 100) / (P / 100) mass ppb / resin.

[0621] The content of the compound represented by the general formula (H4-1) having a carbon number (m1+1) contained in the powder had a quantitative lower limit of 13 mass ppb / resin.

[0622] MRM assay parameters

[0623] [Table 3]

[0624] Table 3 MRM assay parameters

[0625]

[0626] Comparative Example 1

[0627] TFE was polymerized according to the method of Example 7 of International Publication No. 2009 / 020187 to obtain PTFE aqueous dispersion 1. 4 kg of PTFE aqueous dispersion 1 was obtained. The oxygen saturation was 0%.

[0628] Comparative Example 2

[0629] PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. The oxygen saturation was 0%.

[0630] Then, without opening the autoclave, nitrogen was repeatedly injected and degassed several times to perform nitrogen purging. The temperature inside the tank was then raised with stirring. After the temperature reached 80° C., an aqueous solution containing 1.2 g of ammonium persulfate [APS] was injected with nitrogen to a pressure of 0.60 MPa. The mixture was stirred for 3 hours to perform heat treatment, thereby obtaining PTFE Aqueous Dispersion 2. 4 kg of PTFE Aqueous Dispersion 2 was obtained. The solids concentration was 15.4% by mass.

[0631] Example 1

[0632] PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. The pH of PTFE aqueous dispersion 1 was 3.4. 14 kg of the PTFE aqueous dispersion obtained by opening the autoclave was then transferred to another container. The oxygen saturation was 53.4%, and the amount of polymerization free radicals was 0 g. -1 , the amount of oxidative free radicals is 4.0g -1After removing oxygen from the system by repeatedly injecting nitrogen and degassing, the temperature in the tank was raised with stirring. After the temperature reached 80°C, an aqueous solution containing 1.2 g of ammonium persulfate [APS] was injected into the tank with nitrogen to a pressure of 0.60 MPa. The mixture was stirred for 3 hours, thereby performing a heat treatment to obtain PTFE aqueous dispersion 3. The solid content concentration was 15.9% by mass.

[0633] Example 2

[0634] The same procedure as in Example 1 was repeated except that the amount of ammonium persulfate (APS) added during the heat treatment was 11.7 g. The oxygen saturation of the aqueous dispersion after the container transfer was 53.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 4.0g -1 The PTFE contained in the aqueous dispersion after polymerization was partially coagulated by heat treatment, thereby obtaining a PTFE aqueous dispersion and a PTFE wet powder 1. The solid content concentration of the PTFE aqueous dispersion was 0.1% by mass.

[0635] Comparative Example 3

[0636] 85.8 g of a 10% by mass aqueous nitric acid solution was added to 4 kg of the above-mentioned PTFE aqueous dispersion 1, and precipitated by applying a severe mechanical shear force. Then, 12.6 g of a 24% by mass sodium hydroxide aqueous solution was added for neutralization. The obtained wet powder was then filtered and washed again with 4200 g of pure water. After repeating this washing operation 6 times, it was dried in a hot air circulation dryer at 100°C for 18 hours to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2×10 4 Pa·s, and the peak temperature was 329° C. This shows that the obtained PTFE powder is low-molecular-weight PTFE.

[0637] Comparative Example 4

[0638] PTFE powder was obtained in the same manner as in Comparative Example 3 except that the above PTFE aqueous dispersion was used. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2×10 4 Pa·s, and the peak temperature was 329° C. This shows that the obtained PTFE powder is low-molecular-weight PTFE.

[0639] Example 3

[0640] PTFE powder was obtained in the same manner as in Comparative Example 3 except that the PTFE aqueous dispersion 3 was used. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2×104 Pa·s, and the peak temperature was 329° C. This shows that the obtained PTFE powder is low-molecular-weight PTFE.

[0641] Example 4

[0642] The wet PTFE powder 1 was washed with 4200 g of pure water. This washing operation was repeated 6 times, and then dried in a hot air circulation dryer at 100°C for 18 hours to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The melt viscosity of the PTFE powder was 2.2×10 4 Pa·s, and the peak temperature was 329° C. This shows that the obtained PTFE powder is low-molecular-weight PTFE.

[0643] Example 5

[0644] The same procedure as in Example 1 was followed except that the heat treatment time was set to 1 hour to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after the container transfer was 53.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 4.0g -1 The solid content concentration was 14.7% by mass.

[0645] Example 6

[0646] The same procedure as in Example 1 was followed except that the heat treatment time was set to 0.5 hours to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after the container transfer was 53.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 4.0g -1 The solid content concentration was 15.5% by mass.

[0647] Example 7

[0648] The PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. 4 kg of the PTFE aqueous dispersion 1 obtained by opening the autoclave was transferred to another container and air was blown into it at a flow rate of 2 L / min for 1 hour to perform bubbling. The oxygen saturation of the aqueous dispersion was 97.3%, and the amount of polymerization free radicals was 0 g. -1 , the amount of oxidative free radicals is 7.0g -1 .

[0649] After repeated nitrogen injection and degassing multiple times to remove oxygen from the system, the temperature in the tank was raised with stirring. After the temperature reached 80°C, an aqueous solution containing 1.2 g of ammonium persulfate [APS] was introduced into the tank with nitrogen pressure to a pressure of 0.60 MPa. The mixture was stirred for 0.5 hours to perform a heat treatment, thereby obtaining an aqueous PTFE dispersion. The solids concentration was 15.8% by mass.

[0650] Example 8

[0651] The same procedure as in Example 7 was followed except that the heat treatment time was set to 1 hour to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after bubbling was 97.3%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 7.0g -1 The solid content concentration was 15.4% by mass.

[0652] Reference Example 5

[0653] The same procedure as in Example 7 was followed except that the bubbling gas was nitrogen and the flow rate was 5 L / min to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after bubbling was 87.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 6.4g -1 The solid content concentration was 15.4% by mass.

[0654] Example 9

[0655] The same procedure as in Example 7 was followed except that the air flow rate was set to 5 L / min, the bubbling time was set to 0.1 hour, and the heat treatment time was set to 0.5 hour to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after bubbling was 88.5%, and the amount of polymerization free radicals was 0 g. -1 , the amount of oxidative free radicals is 6.5g -1 The solid content concentration was 15.9% by mass.

[0656] Example 10

[0657] The same procedure as in Example 9 was followed except that the bubbling time was set to 0.5 hours to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after bubbling was 97.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 7.0g -1 The solid content concentration was 15.8% by mass.

[0658] Example 11

[0659] The same procedure as in Example 9 was followed except that the bubbling time was set to 1 hour to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after bubbling was 97.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 7.2g -1 The solid content concentration was 15.9% by mass.

[0660] Example 12

[0661] The same procedure as in Example 9 was followed except that the bubbling time was set to 2 hours to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after bubbling was 97.4%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 7.0g -1 The solid content concentration was 15.9% by mass.

[0662] Example 13

[0663] PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. 4 kg of PTFE aqueous dispersion 1 obtained by opening the autoclave was transferred to another container. The temperature in the container was raised under stirring. After the temperature in the container reached 80°C, an aqueous solution of 3.5 g of hydrogen peroxide [H2O2] dissolved in 10 ml of deionized water was added as an oxidant. The mixture was stirred in an air atmosphere for 10 minutes. The oxygen saturation of the aqueous dispersion was 90.0%, and the amount of polymerization free radicals was 0 g. -1 , the amount of oxidative free radicals is 7.0g -1 After repeated nitrogen injection and degassing to remove oxygen from the system, an aqueous solution containing 1.2 g of ammonium persulfate [APS] was introduced into the tank with nitrogen pressure to a pressure of 0.60 MPa. The mixture was stirred for 0.5 hours and heat treated to obtain an aqueous PTFE dispersion. The solids concentration was 15.0% by mass.

[0664] Example 14

[0665] The same procedure as in Example 13 was followed except that the amount of H2O2 added was 35.4 g to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after adding H2O2 and stirring was 93.0%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 7.2g -1 The solid content concentration was 14.7% by mass.

[0666] Example 15

[0667] A PTFE aqueous dispersion was obtained in the same manner as in Example 13 except that the aqueous solution of hydrogen peroxide was replaced with 1.7 g of methanol [MeOH]. The oxygen saturation of the aqueous dispersion after adding MeOH and stirring was 88.0%, and the amount of polymerization radicals was 0 g. -1 , the amount of oxidative free radicals is 3.9g -1 The solid content concentration was 15.4% by mass.

[0668] Example 16

[0669] The same procedure as in Example 15 was followed except that the amount of MeOH added was 16.8 g to obtain a PTFE aqueous dispersion. The oxygen saturation of the aqueous dispersion after adding MeOH and stirring was 88.0%, and the amount of polymerization radicals was 0 g. -1 , oxidative free radicals are 2.6g -1 The solid content concentration was 15.3% by mass.

[0670] Example 17

[0671] PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. 4 kg of PTFE aqueous dispersion 1, obtained by opening the autoclave, was then transferred to another container and a 0.2% aqueous solution of NaCO was added to adjust the pH to 5.6. The system was deoxygenated by repeatedly injecting nitrogen and degassing the solution several times. The temperature in the tank was then raised with stirring. After the temperature reached 80°C, an aqueous solution containing 1.2 g of ammonium persulfate [APS] was introduced with nitrogen to a pressure of 0.60 MPa. The solution was stirred for 0.5 hours, thereby heat-treating the solution to obtain an aqueous PTFE dispersion. The solids concentration was 14.6% by mass.

[0672] Example 18

[0673] A PTFE aqueous dispersion was obtained in the same manner as in Example 17 except that the pH was adjusted to 7.0. The solid content concentration was 14.5% by mass.

[0674] Example 19

[0675] A PTFE aqueous dispersion was obtained in the same manner as in Example 17 except that the pH was adjusted to 9.0. The solid content concentration was 14.4% by mass.

[0676] Example 20

[0677] The PTFE aqueous dispersion 1 was polymerized in the same manner as in Comparative Example 1. 4 kg of the PTFE aqueous dispersion 1 obtained by opening the autoclave was transferred to another container, and air was blown into it at a flow rate of 5 L / min for 1 hour for bubbling.

[0678] Next, a 0.2% aqueous solution of NaCO was added to adjust the pH to 5.6. After repeated nitrogen injection and degassing to remove oxygen from the system, the temperature in the tank was raised with stirring. Once the temperature reached 80°C, an aqueous solution containing 1.2 g of ammonium persulfate (APS) was introduced with nitrogen to a pressure of 0.60 MPa. The mixture was stirred for 0.5 hours to perform a heat treatment, yielding an aqueous PTFE dispersion. The solids concentration was 13.4% by mass.

[0679] The various physical properties of the PTFE aqueous dispersions or PTFE powders obtained in Examples and Comparative Examples were evaluated by the above-mentioned methods. The results are shown in Tables 4 to 8.

[0680] [Table 4]

[0681]

[0682]

[0683]

[0684]

[0685]

[0686] Figure 1 The first-order differential spectra of the aqueous dispersions obtained in Examples 1, 9, 11, 15, and 16 (horizontal axis: g value (-), vertical axis: Int.[PTFE] / Int.[Mn 2+ ] / sample weight (g -1 )).according to Figure 1 The results shown show that in the first-order differential spectrum of the aqueous dispersion obtained by the production method of the present invention, only two peaks were observed, not three. This result shows that there are no polymerization radicals in the aqueous dispersion, and only oxidation radicals are present.

Claims

1. A method for producing a low molecular weight polytetrafluoroethylene aqueous dispersion, wherein: In the presence of a fluorinated surfactant, a polymerization initiator, a hydrocarbon chain transfer agent, and an aqueous medium, tetrafluoroethylene is polymerized to prepare an aqueous dispersion containing low molecular weight polytetrafluoroethylene. The obtained aqueous dispersion is pretreated. A free radical generator is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the free radical generator is heat-treated to obtain a low molecular weight polytetrafluoroethylene aqueous dispersion.

2. The manufacturing method according to claim 1, wherein The aqueous dispersion is pretreated by at least one of the following methods: (1) a method of contacting the aqueous dispersion with a gas containing oxygen; (2) a method of contacting the aqueous dispersion with an oxidizing agent; (3) a method of contacting the aqueous dispersion with alcohol; (4) A method of adjusting the pH of the aqueous dispersion to 4.0 or higher.

3. The manufacturing method according to claim 1 or 2, wherein: The aqueous dispersion is pretreated by contacting the aqueous dispersion with a gas containing oxygen to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more.

4. The production method according to any one of claims 1 to 3, wherein The aqueous dispersion is pretreated by blowing a gas containing oxygen into the aqueous dispersion or stirring the aqueous dispersion in the atmosphere to bring the aqueous dispersion into contact with the gas containing oxygen.

5. The production method according to any one of claims 1 to 4, wherein The aqueous dispersion is pretreated by contacting the aqueous dispersion with a gas containing oxygen to obtain a polymerization radical content of 0 g represented by the general formula (1). -1 The content of the oxidative radical represented by the following general formula (2) is 0.1 g -1 The above aqueous dispersion, General formula (1): R-(CF2-CF2) n · In the general formula (1), R represents a monovalent group, n represents an integer greater than 1, and · represents an unpaired electron. General formula (2): R-(CF2-CF2) n OO· In the general formula (2), R represents a monovalent group, n represents an integer of 1 or greater, and · represents an unpaired electron.

6. The manufacturing method according to claim 1 or 2, wherein: The aqueous dispersion is pretreated by contacting the aqueous dispersion with an oxidizing agent to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more.

7. The manufacturing method according to claim 2 or 6, wherein: The oxidant is hydrogen peroxide.

8. The manufacturing method according to claim 1, 2, 6 or 7, wherein: The aqueous dispersion is pretreated by contacting the aqueous dispersion with an oxidant to obtain a polymerization radical having a content of 0 g of the general formula (1). -1 The content of the oxidative radical represented by the following general formula (2) is 0.1 g -1 The above aqueous dispersion, General formula (1): R-(CF2-CF2) n · In the general formula (1), R represents a monovalent group, n represents an integer greater than 1, and · represents an unpaired electron. General formula (2): R-(CF2-CF2) n OO· In the general formula (2), R represents a monovalent group, n represents an integer of 1 or greater, and · represents an unpaired electron.

9. The manufacturing method according to claim 1 or 2, wherein: The aqueous dispersion is pretreated by contacting the aqueous dispersion with alcohol to obtain an aqueous dispersion having an oxygen saturation of 50.0% or more.

10. The manufacturing method according to claim 2 or 9, wherein: The alcohol is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol.

11. The production method according to any one of claims 1 to 10, wherein The polymerization initiator is a water-soluble free radical polymerization initiator.

12. The production method according to any one of claims 1 to 11, wherein The temperature of the heat treatment is equal to or higher than the decomposition temperature of the radical generator.

13. The production method according to any one of claims 1 to 12, wherein The free radical generator is an inorganic peroxide.

14. The production method according to any one of claims 1 to 13, wherein The peak temperature of the low molecular weight polytetrafluoroethylene is 322° C. to 333° C.

15. The production method according to any one of claims 1 to 14, wherein The melt viscosity of the low molecular weight polytetrafluoroethylene at 380°C is 1×10 2 Pa·s~7×10 5 Pa·s.

16. The production method according to any one of claims 1 to 15, wherein The polymerization initiator is a persulfate, the hydrocarbon chain transfer agent is an alkane having 1 to 5 carbon atoms, and the aqueous dispersion is pretreated by (1) contacting the aqueous dispersion with an oxygen-containing gas to obtain an aqueous dispersion with an oxygen saturation of 50.0% or more.

17. The production method according to any one of claims 1 to 16, wherein The polymerization initiator is a persulfate, and the hydrocarbon chain transfer agent is an alkane having 1 to 5 carbon atoms. After preparing the aqueous dispersion containing the low molecular weight polytetrafluoroethylene, (1-1-1) recovering the aqueous dispersion in the reactor and placing it in a container separate from the reactor, thereby contacting the aqueous dispersion with a gas containing oxygen to obtain an aqueous dispersion having an oxygen saturation of 50.0% to 70.0%, then, (1-1-2) blowing a gas containing 20% ​​to 100% by volume of oxygen into the aqueous dispersion at a flow rate of 1 L / min to 30 L / min to generate bubbles, and allowing the aqueous dispersion and the oxygen-containing gas to contact at 5° C. to 99° C. for 5 minutes or longer; or (2-1) contacting the aqueous dispersion with hydrogen peroxide in an amount corresponding to 1 to 500 ppm by mass relative to the mass of the aqueous dispersion at 5° C. to 99° C. for 1 minute or longer; or (3-1) contacting the aqueous dispersion with an alcohol having 1 to 10 carbon atoms in an amount corresponding to 1 to 500 ppm by mass relative to the mass of the aqueous dispersion at 5° C. to 99° C. for 1 minute or longer; or (4-1) adding a base to the aqueous dispersion to adjust the pH of the aqueous dispersion to 4.0 or higher, Thus, the aqueous dispersion is pretreated to obtain an aqueous dispersion having an oxygen saturation of 80% or more. A persulfate in an amount of 0.01 to 5 molar times the molar number of the fluorinated surfactant in the aqueous dispersion is added to the pretreated aqueous dispersion, and the aqueous dispersion containing the persulfate is heat-treated at 35° C. to 95° C. for 15 minutes or longer to obtain a low molecular weight polytetrafluoroethylene aqueous dispersion.

18. A method for producing a powder, which is a method for producing a powder of low molecular weight polytetrafluoroethylene, wherein: After obtaining a low molecular weight polytetrafluoroethylene aqueous dispersion by the production method according to any one of claims 1 to 17, The low molecular weight polytetrafluoroethylene in the aqueous dispersion is precipitated to prepare a wet powder containing particles of the low molecular weight polytetrafluoroethylene. The wet powder is dried to produce the powder.

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