Production method of purified polytetrafluoroethylene powder and low molecular weight polytetrafluoroethylene powder

Abstract

To provide a production method of purified polytetrafluoroethylene powder, in which short chain fluorine compounds from low molecular weight polytetrafluoroethylene are reduced.SOLUTION: A production method of purified polytetrafluoroethylene powder includes a step to reduce short chain fluorine compounds from low molecular weight polytetrafluoroethylene powder obtained by radical polymerization. In the step, at least compounds represented by the general formula (1) are reduced to 179 ppb or less, and compounds represented by the general formula (2) are reduced to 6,900 ppb or less. General formula (1): (H-(CF2)m-COO)pM1 (in formula, m is 3-20, M1 is H, a metal atom, or NR54 (each R5 may be H or a 1-10C organic group identical to or different from each other) being an imidazolium, a pyridinium, or a phosphonium each of which may have a substituent, and p is 1 or 2). General formula (2): (H-(CF2)n-SO3)qM2 (in formula, n is 4-21, M2 is H, a metal atom, or NR54 (R5 is the same as written above) being the imidazolium, the pyridinium, or the phosphonium each of which may have a substituent, and q is 1 or 2).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for producing purified polytetrafluoroethylene powder and a low molecular weight polytetrafluoroethylene powder. [Background technology]

[0002] Low-molecular-weight polytetrafluoroethylene (also called "polytetrafluoroethylene wax" or "polytetrafluoroethylene micropowder"), which has a molecular weight ranging from several thousand to several hundred thousand, has excellent chemical stability, extremely low surface energy, and is not prone to fibrillation, and is therefore used as an additive to improve the slipperiness and texture of coating surfaces in the production of plastics, inks, cosmetics, paints, greases, and the like (see, for example, Patent Document 1).

[0003] Known methods for producing low-molecular-weight polytetrafluoroethylene include the polymerization method, the radiation decomposition method, the thermal decomposition method, and the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-147617 [Patent Document 2] International Publication No. 2020 / 218622 Summary of the Invention [Problem to be solved by the invention]

[0005] Since low-molecular-weight polytetrafluoroethylene is used as an additive in semiconductor applications, it is preferable that the amount of substances other than low-molecular-weight polytetrafluoroethylene is as small as possible. Patent Document 2,

[0407] , describes low-molecular-weight polytetrafluoroethylene, but does not describe in detail how to reduce short-chain fluorine compounds from low-molecular-weight polytetrafluoroethylene.

[0006] An object of the present disclosure is to provide a method for producing purified polytetrafluoroethylene powder that reduces short-chain fluorine compounds from low-molecular-weight polytetrafluoroethylene. Another object of the present disclosure is to provide a low-molecular-weight polytetrafluoroethylene powder having a low content of a specific fluorine compound. [Means for solving the problem]

[0007] This disclosure (1) The method includes a step of reducing short-chain fluorine compounds from a low-molecular-weight polytetrafluoroethylene powder obtained by radical polymerization, In the above steps, a method for producing a purified polytetrafluoroethylene powder is provided (hereinafter also referred to as the "production method of the present disclosure") that reduces at least the compound represented by the following general formula (1) to 179 ppb or less and the compound represented by the following general formula (2) to 6,900 ppb or less. General formula (1):(H-(CF2) m -COO) p M 1 (In the formula, m is 3 to 20, M 1 is H, metal atom, NR 5 4(R 5 may be the same or different and are H or an organic group having 1 to 10 carbon atoms), imidazolium which may have a substituent, pyridinium which may have a substituent, or phosphonium which may have a substituent. p is 1 or 2. General formula (2):(H-(CF2) n -SO3) q M 2 (In the formula, n is 4 to 21. 2 is H, metal atom, NR 5 4(R 5 is the same as above), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. q is 1 or 2.

[0008] This disclosure (2) The method for producing the purified polytetrafluoroethylene powder according to the present disclosure (1), wherein a fluorosurfactant other than perfluorooctanoic acid and its salts is used in the radical polymerization.

[0009] This disclosure (3) The method for producing the purified polytetrafluoroethylene powder according to the present disclosure (1), wherein a hydrocarbon chain transfer agent is used in the radical polymerization.

[0010] This disclosure (4) The method for producing a purified polytetrafluoroethylene powder according to the present disclosure (1) or (2), wherein the radical polymerization is emulsion polymerization.

[0011] This disclosure (5) The method for producing a purified polytetrafluoroethylene powder according to any one of the present disclosure (1) to (4), wherein the short-chain fluorine compounds are reduced by a heat treatment at 170° C. or higher.

[0012] This disclosure (6) The melt viscosity of the low-molecular-weight polytetrafluoroethylene powder at 380° C. is 1×10 2 ~7×10 5 A method for producing a purified polytetrafluoroethylene powder according to any one of the present disclosures (1) to (5), wherein Pa·s is 0.01 to 0.05.

[0013] This disclosure (7) The method for producing a purified polytetrafluoroethylene powder according to any one of (1) to (6) of the present disclosure, further comprising reducing perfluorocarboxylic acid and its salt to below the quantitation limit in the above step.

[0014] This disclosure (8) The method for producing a purified polytetrafluoroethylene powder according to the present disclosure (7), wherein the perfluorocarboxylic acid is a perfluorocarboxylic acid other than perfluorooctanoic acid.

[0015] This disclosure (9) The content of perfluorocarboxylic acid and its salt is below the quantification limit, the content of the compound represented by the following general formula (1) is 179 ppb or less, and the content of the compound represented by the following general formula (2) is 6900 ppb or less, In the first differential spectrum measured by electron spin resonance, the peak intensity at g=2.0218 is 0g -1 More than 7g -1 A low-molecular-weight polytetrafluoroethylene powder having the following structure (hereinafter also referred to as the "low-molecular-weight polytetrafluoroethylene powder of the present disclosure"). General formula (1):(H-(CF2) m -COO) p M 1 (In the formula, m is 3 to 20, M 1 is H, metal atom, NR 5 4(R 5 may be the same or different and are H or an organic group having 1 to 10 carbon atoms), imidazolium which may have a substituent, pyridinium which may have a substituent, or phosphonium which may have a substituent. p is 1 or 2. General formula (2):(H-(CF2) n -SO3) q M 2 (In the formula, n is 4 to 21. 2 is H, metal atom, NR 5 4(R 5 is the same as above), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. q is 1 or 2.

[0016] This disclosure (10) The low molecular weight polytetrafluoroethylene powder according to the present disclosure (9), having an average particle size of 20 μm or less and an apparent density of 0.6 g / ml or less.

[0017] This disclosure (11) Melt viscosity at 380℃ is 1×10 2 ~7×10 5The low molecular weight polytetrafluoroethylene powder according to the present disclosure (9) or (10), wherein the Pa·s is 0.01 to 0.01. Effect of the Invention

[0018] According to the production method of the present disclosure, a purified polytetrafluoroethylene powder with reduced short-chain fluorine compounds can be obtained. The low molecular weight polytetrafluoroethylene powder of the present disclosure has a low content of a specific fluorine compound. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Manufacturing Method of the Present Disclosure) The manufacturing method of the present disclosure includes a step of reducing short-chain fluorine compounds from low-molecular-weight polytetrafluoroethylene (low-molecular-weight PTFE) powder obtained by radical polymerization.

[0020] In the manufacturing method of the present disclosure, a low molecular weight PTFE powder is obtained by radical polymerization. In the manufacturing method of the present disclosure, the polymerization of low molecular weight PTFE may be carried out by combining radical polymerization with other polymerizations, but it is preferable to carry out only radical polymerization. This can simplify the manufacturing procedure.

[0021] The radical polymerization may be, for example, emulsion polymerization, suspension polymerization, or bulk polymerization, with emulsion polymerization being preferred.

[0022] The emulsion polymerization is usually carried out by carrying out a polymerization reaction of tetrafluoroethylene in an aqueous medium in the presence of a fluorine-based surfactant and a chain transfer agent. The method and conditions of the polymerization reaction are not particularly limited, and the polymerization reaction can be carried out by a conventionally known method.

[0023] The fluorosurfactant is a compound that contains at least one fluorine atom in its molecular structure and exhibits surface activity. For practical purposes, the fluorosurfactant may be one that is composed of a hydrocarbon having 2 to 7 carbon atoms in which at least one hydrogen atom is replaced with a fluorine atom, and a hydrophilic group such as a carboxylic acid, a carboxylate, a sulfonic acid, or a sulfonic acid group. The fluorosurfactant is preferably one other than perfluorooctanoic acid and its salts.

[0024] The aqueous medium is preferably deionized water of high purity, and may contain an organic solvent such as alcohol, ether, ketone, or paraffin wax.

[0025] The chain transfer agent includes hydrogen, hydrocarbons, halogenated hydrocarbons, and the like. When a hydrocarbon chain transfer agent such as a hydrocarbon or a halogenated hydrocarbon is used, a short-chain fluorine compound is generated as described above. Since the manufacturing method of the present disclosure includes a step of reducing the amount of short-chain fluorine compounds, the amount of short-chain fluorine compounds in the low-molecular-weight PTFE can be reduced even when a hydrocarbon chain transfer agent is used.

[0026] Examples of the hydrocarbon chain transfer agent include hydrocarbons having 1 to 3 carbon atoms and halogenated hydrocarbons having 1 to 3 carbon atoms. Examples of the hydrocarbons having 1 to 3 carbon atoms include methane, ethane, and propane, and examples of the halogenated hydrocarbons having 1 to 3 carbon atoms include chloromethane and chloroethane. Among these, ethane and propane are preferred.

[0027] The amount of the chain transfer agent to be added cannot be generally specified because the appropriate range varies depending on the polymerization conditions, such as the chain transfer ability, reaction temperature, polymerization pressure, or the amount of polymerization initiator to be added. However, the amount is preferably 0.2 to 20 mol %, and more preferably 1.0 to 10 mol %, based on the TFE present in the reaction system.

[0028] The low molecular weight PTFE powder is generally a TFE polymer having a number average molecular weight of not more than 600,000. A high molecular weight PTFE powder having a number average molecular weight of more than 600,000 exhibits fibrillation properties specific to PTFE (see Patent Document 1), and therefore, when used as an additive, the PTFE particles tend to aggregate together, resulting in poor dispersibility in a matrix material.

[0029] The low molecular weight PTFE powder has a melt viscosity of 1×10 2 ~7×10 5 (Pa·s) is preferable. When the melt viscosity of the low-molecular-weight PTFE powder is within this range, the number average molecular weight is usually 600,000 or less (see Patent Document 1). The high molecular weight PTFE powder is generally non-melt processable, and is different from the low molecular weight PTFE powder in that the melt viscosity cannot be measured.

[0030] The melt viscosity is a value measured in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, with a 2g sample preheated at 380°C for 5 minutes and kept at the above temperature under a load of 0.7 MPa. The number average molecular weight is a value calculated from the melt viscosity measured by the above measurement method.

[0031] The PTFE constituting the low molecular weight PTFE powder may be tetrafluoroethylene homopolymer [TFE homopolymer] or modified polytetrafluoroethylene [modified PTFE].

[0032] The above TFE homopolymer is obtained by polymerizing only tetrafluoroethylene [TFE] as a monomer. The above-mentioned modified PTFE means a polymer obtained by copolymerizing TFE and a modifying monomer copolymerizable with TFE.

[0033] The modifying monomer in the modified PTFE is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene [HFP], chlorofluoroolefins such as chlorotrifluoroethylene [CTFE], hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF], perfluorovinyl ether, perfluorobutylethylene, ethylene, etc. The modifying monomer used may be one type or multiple types.

[0034] The perfluorovinyl ether is not particularly limited, and may be, for example, a perfluorovinyl ether represented by the following general formula (X): CF2=CF-ORf(X) (wherein Rf represents a perfluoro organic group). In this specification, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro organic group may have an ether oxygen.

[0035] An example of the perfluorovinyl ether is perfluoro(alkyl vinyl ether) [PAVE], where Rf in the general formula (X) represents a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0036] Examples of the perfluoroalkyl group in the above PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. Preferred is purpuro(propyl vinyl ether) [PPVE], in which the perfluoroalkyl group is a perfluoropropyl group.

[0037] The perfluorovinyl ether further includes those represented by the above general formula (X), in which Rf is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those represented by the following formula: [ka] (wherein a represents 0 or an integer of 1 to 4), Rf is a group represented by the following formula: [ka] (wherein b represents an integer of 1 to 4) and the like.

[0038] The perfluoroalkylethylene is not particularly limited, and examples thereof include perfluorobutylethylene (PFBE), perfluorohexylethylene (PFHE), and perfluorooctylethylene (PFOE).

[0039] The modifying monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PMVE, PPVE, PFBE, PFHE, CNVE and ethylene.

[0040] The modified PTFE preferably contains modified monomer units in the range of 0.0001 to 2 mol %, more preferably 0.0001 to less than 1 mol %, further preferably 0.0001 to 0.5 mol %, and particularly preferably 0.001 to 0.2 mol %.

[0041] In the above steps of the manufacturing method of the present disclosure, at least the compound represented by the following general formula (1) is reduced to 179 ppb or less (preferably 120 ppb or less, more preferably 70 ppb or less, even more preferably 40 ppb or less, and particularly preferably below the quantification limit), and the compound represented by the following general formula (2) is reduced to 6900 ppb or less (preferably 2500 ppb or less, more preferably 2000 ppb or less, and even more preferably below the quantification limit). Note that all of these amounts are based on mass. General formula (1):(H-(CF2) m -COO) p M 1 (In the formula, m is 3 to 20, M1 is H, metal atom, NR 5 4(R 5 may be the same or different and are H or an organic group having 1 to 10 carbon atoms), imidazolium which may have a substituent, pyridinium which may have a substituent, or phosphonium which may have a substituent. p is 1 or 2. General formula (2):(H-(CF2) n -SO3) q M 2 (In the formula, n is 4 to 21. 2 is H, metal atom, NR 5 4(R 5 is the same as above), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. q is 1 or 2. As a method for reducing short-chain fluorine compounds such as the compound represented by the general formula (1) and the compound represented by the general formula (2), a method of heat-treating the above-mentioned low-molecular-weight PTFE powder can be mentioned.

[0042] The method of the heat treatment is not particularly limited, and can be performed using a box dryer, band dryer, tunnel dryer, jet flow dryer, moving bed dryer, rotary dryer, fluidized bed dryer, flash dryer, box dryer, disk dryer, cylindrical stirring dryer, inverted cone stirring dryer, microwave device, vacuum heat treatment device, box type electric furnace, hot air circulation device, flash dryer, vibration dryer, belt dryer, extrusion dryer, spray dryer, etc.

[0043] The heat treatment may be carried out on the wet PTFE powder containing water obtained from the PTFE dispersion after polymerization, or on the PTFE powder after drying.

[0044] In the above heat treatment, the heating temperature is preferably 170°C or higher from the viewpoint of the efficiency of reducing short-chain fluorine compounds. A more preferable lower limit is 175°C, and an even more preferable lower limit is 180°C. The upper limit is preferably lower than the melting point of the low-molecular-weight PTFE powder. The melting point of the low-molecular-weight PTFE powder is usually 327°C. A more preferable upper limit is 300°C, and an even more preferable upper limit is 240°C.

[0045] In the heat treatment, the heating time is preferably 5 to 30 hours from the viewpoint of the efficiency of reducing short-chain fluorine compounds, etc. A more preferable lower limit is 7 hours, and an even more preferable lower limit is 10 hours. Also, a more preferable upper limit is 25 hours, and an even more preferable upper limit is 22 hours. In addition, in the case where the above-mentioned heat treatment is carried out when drying the wet PTFE powder and on the PTFE powder after drying, the above-mentioned heating time is the total time of these treatments.

[0046] By the heat treatment, the compounds represented by the general formula (1) and the compounds represented by the general formula (2), which are short-chain fluorine compounds, are reduced from the low-molecular-weight PTFE powder. The short-chain fluorine compound may be a perfluorocarboxylic acid and a salt thereof in addition to the compound represented by the general formula (1) and the compound represented by the general formula (2). That is, in the production method of the present disclosure, it is preferable to further reduce the amount of perfluorocarboxylic acid and a salt thereof to the quantification limit or less in the above step.

[0047] The perfluorocarboxylic acid preferably has 4 to 14 carbon atoms. The perfluorocarboxylic acid may be perfluorooctanoic acid or a perfluorocarboxylic acid other than perfluorooctanoic acid, but is preferably perfluorooctanoic acid.

[0048] In the above general formulas (1) and (2), the metal atom may be a monovalent or divalent metal atom, more specifically, an alkali metal (Group 1) or an alkaline earth metal (Group 2). Specific examples include Na, K, and Li.

[0049] In the above general formulas (1) and (2), the four R 5 may be the same or different. 5 is preferably H or an organic group having 1 to 10 carbon atoms, more preferably H or an organic group having 1 to 4 carbon atoms. Also, it is preferably an alkyl group having 1 to 10 carbon atoms, and further preferably an alkyl group having 1 to 4 carbon atoms. 5 The above provisions are applicable.

[0050] In the above general formula (1), m may be 5-11.

[0051] In the above general formula (2), n may be 6-12.

[0052] In this specification, unless otherwise specified, the term "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. Examples of the "organic group" are: an alkyl group which may have one or more substituents; an alkenyl group optionally having one or more substituents; an alkynyl group optionally having one or more substituents; a cycloalkyl group optionally having one or more substituents, a cycloalkenyl group optionally having one or more substituents, a cycloalkadienyl group optionally having one or more substituents, an aryl group which may have one or more substituents; an aralkyl group optionally having one or more substituents; a non-aromatic heterocyclic group optionally having one or more substituents, a heteroaryl group optionally having one or more substituents, Cyano group, Formyl group, RaO-, RaCO-, RaSO2-, RaCOO-, RaNRaCO-, RaCONRa-, RaOCO-, and RaOSO2- (In these formulas, Ra is independently an alkyl group which may have one or more substituents; an alkenyl group optionally having one or more substituents; an alkynyl group optionally having one or more substituents; a cycloalkyl group optionally having one or more substituents, a cycloalkenyl group optionally having one or more substituents, a cycloalkadienyl group optionally having one or more substituents, an aryl group which may have one or more substituents; an aralkyl group optionally having one or more substituents; a non-aromatic heterocyclic group optionally having one or more substituents, or is a heteroaryl group which may have one or more substituents. Includes:

[0053] The organic group is preferably an alkyl group which may have one or more substituents. The organic group also includes those exemplified as the substituents below.

[0054] In this specification, unless otherwise specified, the term "substituent" refers to a substitutable group. Examples of the "substituent" include an aliphatic group, an aromatic group, a heterocyclic group, an acyl group, an acyloxy group, an acylamino group, an aliphatic oxy group, an aromatic oxy group, a heterocyclic oxy group, an aliphatic oxycarbonyl group, an aromatic oxycarbonyl group, a heterocyclic oxycarbonyl group, a carbamoyl group, an aliphatic sulfonyl group, an aromatic sulfonyl group, a heterocyclic sulfonyl group, an aliphatic sulfonyloxy group, an aromatic sulfonyloxy group, a heterocyclic sulfonyloxy group, a sulfamoyl group, an aliphatic sulfonamide group, an aromatic sulfonamide group, a heterocyclic sulfonamide group, an amino group, an aliphatic aryl group, an aromatic ... Examples of such groups include an amino group, an aromatic amino group, a heterocyclic amino group, an aliphatic oxycarbonylamino group, an aromatic oxycarbonylamino group, a heterocyclic oxycarbonylamino group, an aliphatic sulfinyl group, an aromatic sulfinyl group, an aliphatic thio group, an aromatic thio group, a hydroxy group, a cyano group, a sulfo group, a carboxy group, an aliphatic oxyamino group, an aromatic oxyamino group, a carbamoylamino group, a sulfamoylamino group, a halogen atom, a sulfamoylcarbamoyl group, a carbamoylsulfamoyl group, a dialiphatic oxyphosphinyl group, and a diaromatic oxyphosphinyl group.

[0055] The aliphatic group may be saturated or unsaturated, and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, or the like. Examples of the aliphatic group include alkyl groups having a total of 1 to 8 carbon atoms (preferably 1 to 4 carbon atoms). Specific examples thereof include a methyl group, an ethyl group, a vinyl group, a cyclohexyl group, a carbamoylmethyl group, or the like.

[0056] The aromatic group may have, for example, a nitro group, a halogen atom, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic group include an aryl group having a total of 6 to 12 carbon atoms (preferably 6 to 10). Specific examples thereof include a phenyl group, a 4-nitrophenyl group, a 4-acetylaminophenyl group, and a 4-methanesulfonylphenyl group.

[0057] The heterocyclic group may have a halogen atom, a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the heterocyclic group include 5- or 6-membered heterocycles having a total of 2 to 12 (preferably 2 to 10) carbon atoms. Specific examples thereof include a 2-tetrahydrofuryl group, a 2-pyrimidyl group, etc.

[0058] The acyl group may have an aliphatic carbonyl group, an arylcarbonyl group, a heterocyclic carbonyl group, a hydroxy group, a halogen atom, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the acyl group include acyl groups having a total of 2 to 8 carbon atoms (preferably 2 to 4). Specific examples thereof include an acetyl group, a propanoyl group, a benzoyl group, and a 3-pyridinecarbonyl group.

[0059] The acylamino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc., and more specifically, may have an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include an acylamino group having a total of 2 to 12 carbon atoms (preferably 2 to 8), and an alkylcarbonylamino group having a total of 2 to 8 carbon atoms, etc. Specific examples thereof include an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

[0060] The aliphatic oxycarbonyl group may be saturated or unsaturated, and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, or the like. The aliphatic oxycarbonyl group may be an alkoxycarbonyl group having a total of 2 to 8 carbon atoms (preferably 2 to 4). Specific examples thereof include methoxycarbonyl, ethoxycarbonyl, and (t)-butoxycarbonyl groups.

[0061] The carbamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the carbamoyl group include an unsubstituted carbamoyl group, an alkylcarbamoyl group having a total of 2 to 9 carbon atoms, etc., and an unsubstituted carbamoyl group, an alkylcarbamoyl group having a total of 2 to 5 carbon atoms is preferable. Specific examples of the alkylcarbamoyl group include an N-methylcarbamoyl group, an N,N-dimethylcarbamoyl group, and an N-phenylcarbamoyl group.

[0062] The aliphatic sulfonyl group may be saturated or unsaturated, and may have a hydroxy group, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, or the like. Examples of the aliphatic sulfonyl group include alkylsulfonyl groups having a total of 1 to 6 carbon atoms (preferably 1 to 4). Specific examples thereof include methanesulfonyl, etc.

[0063] The aromatic sulfonyl group may have a hydroxy group, an aliphatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic sulfonyl group include arylsulfonyl groups having a total of 6 to 10 carbon atoms. Specific examples thereof include benzenesulfonyl, etc.

[0064] The amino group may have an aliphatic group, an aromatic group, a heterocyclic group, or the like.

[0065] The acylamino group may have, for example, an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include an acylamino group having a total of 2 to 12 carbon atoms (preferably 2 to 8). The acylamino group is preferably an alkylcarbonylamino group having a total of 2 to 8 carbon atoms. Specific examples thereof include an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

[0066] The aliphatic sulfonamide group, aromatic sulfonamide group, and heterocyclic sulfonamide group may be, for example, a methanesulfonamide group, a benzenesulfonamide group, or a 2-pyridinesulfonamide group.

[0067] The sulfamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the sulfamoyl group include a sulfamoyl group, an alkylsulfamoyl group having a total of 1 to 9 carbon atoms, a dialkylsulfamoyl group having a total of 2 to 10 carbon atoms, an arylsulfamoyl group having a total of 7 to 13 carbon atoms, and a heterocyclic sulfamoyl group having a total of 2 to 12 carbon atoms, etc., and the sulfamoyl group, an alkylsulfamoyl group having a total of 1 to 7 carbon atoms, a dialkylsulfamoyl group having a total of 3 to 6 carbon atoms, an arylsulfamoyl group having a total of 6 to 11 carbon atoms, and a heterocyclic sulfamoyl group having a total of 2 to 10 carbon atoms are preferred. Specific examples of these include a sulfamoyl group, a methylsulfamoyl group, an N,N-dimethylsulfamoyl group, a phenylsulfamoyl group, and a 4-pyridine sulfamoyl group.

[0068] The aliphatic oxy group may be saturated or unsaturated, and may have a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, a methoxyethoxy group, etc. Examples of the aliphatic oxy group include an alkoxy group having a total of 1 to 8 carbon atoms (preferably 1 to 6). Specific examples thereof include a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, a methoxyethoxy group, etc.

[0069] The aromatic amino group and heterocyclic amino group may have an aliphatic group, an aliphatic oxy group, a halogen atom, a carbamoyl group, a heterocyclic group condensed with an aryl group, an aliphatic oxycarbonyl group, or the like, and preferably has an aliphatic group having 1 to 4 carbon atoms in total, an aliphatic oxy group having 1 to 4 carbon atoms in total, a halogen atom, a carbamoyl group having 1 to 4 carbon atoms in total, a nitro group, or an aliphatic oxycarbonyl group having 2 to 4 carbon atoms in total.

[0070] The aliphatic thio group may be saturated or unsaturated, and may be an alkylthio group having a total of 1 to 8 carbon atoms (preferably 1 to 6), etc. Specific examples thereof include a methylthio group, an ethylthio group, a carbamoylmethylthio group, a t-butylthio group, etc.

[0071] The carbamoylamino group may have an aliphatic group, an aryl group, a heterocyclic group, etc. Examples of the carbamoylamino group include a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 9 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 10 carbon atoms, an arylcarbamoylamino group having a total of 7 to 13 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 12 carbon atoms, etc., and are preferably a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 7 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 6 carbon atoms, an arylcarbamoylamino group having a total of 7 to 11 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 10 carbon atoms. Specific examples of these include a carbamoylamino group, a methylcarbamoylamino group, an N,N-dimethylcarbamoylamino group, a phenylcarbamoylamino group, and a 4-pyridinecarbamoylamino group.

[0072] One form of the purified PTFE powder obtained by the production method of the present disclosure is the low-molecular-weight PTFE powder of the present disclosure.

[0073] (Low molecular weight PTFE powder of the present disclosure) The low-molecular-weight PTFE powder of the present disclosure has a perfluorocarboxylic acid and its salt content below the quantification limit, a compound represented by the above general formula (1) of 179 ppb or less, and a compound represented by the above general formula (2) of 6900 ppb or less. In a first differential spectrum obtained by measurement using an electron spin resonance method, the peak intensity at g=2.0218 is less than 0g -1 More than 7g -1 The following is the result.

[0074] In the low molecular weight PTFE powder of the present disclosure, the content of perfluorocarboxylic acid and its salt is below the quantification limit on a mass basis. In other words, the low molecular weight PTFE powder of the present disclosure does not substantially contain perfluorocarboxylic acid and its salt. The quantification limit of perfluorocarboxylic acids and their salts is 1 ng / mL when measured by the method described in the Examples below.

[0075] In the low molecular weight PTFE powder of the present disclosure, the content of the compound represented by the above general formula (1) is 179 ppb or less by mass. The lower limit is not particularly limited, but is preferably 120 ppb or less, more preferably 70 ppb or less, and even more preferably 40 ppb or less, and may be an amount below the quantification limit. In other words, the low molecular weight PTFE powder of the present disclosure may be substantially free of the compound represented by the above general formula (1). The quantification limit of the content of the compound represented by the above general formula (1) is 1 ng / mL when measured by the method in the Examples described later.

[0076] In the low molecular weight PTFE powder of the present disclosure, the content of the compound represented by the above general formula (2) is 6900 ppb or less by mass. The lower limit is not particularly limited, but is preferably 2500 ppb or less, more preferably 2000 ppb or less, and may be an amount below the quantification limit. In other words, the low molecular weight PTFE powder of the present disclosure may be substantially free of the compound represented by the above general formula (2). The quantification limit of the content of the compound represented by the above general formula (2) is 1 ng / mL when measured by the method in the Examples described later.

[0077] The perfluorocarboxylic acid may be perfluorooctanoic acid or a perfluorocarboxylic acid other than perfluorooctanoic acid, but is preferably perfluorooctanoic acid.

[0078] The contents of the perfluorocarboxylic acid and its salt, the compound represented by the general formula (1), and the compound represented by the general formula (2) can be measured by liquid chromatography.

[0079] The low-molecular-weight PTFE powder of the present disclosure has a peak intensity at g=2.0218 in a first differential spectrum (hereinafter also referred to as an ESR spectrum) obtained by measurement using an electron spin resonance (ESR) method. -1 More than 7g -1 The following is the result.

[0080] The measurement conditions for the above ESR and the definitions of related terms will be explained below. The measurement conditions are as follows. Equipment: JEOL JES-FR30EX Measurement temperature: 23±3℃ Microwave frequency: 9.42GHz Microwave power: 0.4mW Center magnetic field: 347.548mT Sweep width: ±25mT Sweep time: 60s Time constant: 0.03s Magnetic field modulation width: 0.32mT Number of scans: 1 Modulation frequency: 100kHz Marker: Mn 2+

[0081] In the above ESR spectrum, the vertical axis represents the corrected signal intensity and the horizontal axis represents the g value. The corrected signal intensity is calculated using the following formula: Corrected signal strength (g -1 )=Int.[PTFE] / Int.[Mn 2+ ] / sample mass (g) (Where, Int.[PTFE] is the uncorrected signal intensity of the sample, Int.[Mn 2+ ] is defined as the signal intensity of the marker. In this specification, unless otherwise specified, when the intensity of a signal in the ESR spectrum of PTFE is simply mentioned, it refers to the above-mentioned corrected signal intensity. The g value of the ESR signal was determined by the Mn 2+ The g-value of the 4th peak from the low magnetic field side of the 6 peaks is corrected based on the known g-value of 1.981, and the following formula is used: g=g std -{(BB std ) / B std}×g std (In the formula, g std is the g value of the marker, B is the magnetic field strength at which a signal is obtained, and B stdis defined as the magnetic field strength of the marker). In the above ESR spectrum, a positive signal refers to a signal that appears in the positive region of the spectrum (above the baseline), and a negative signal refers to a signal that appears in the negative region of the spectrum (below the baseline).

[0082] The linear radical (radical 1) has the formula: [ka] (The wavy line in the formula represents the polymer chain of PTFE. The same applies below.) and the side chain type radical (radical 2) is represented by the following formula: [ka] As shown in the figure. When irradiated with radiation, the following formula: [ka] and a radical 3 of the formula: [ka] It is believed that radical 4, represented by the formula: is generated, and when this comes into contact with air, radical 1 and radical 2 are generated. Since the negative signal (peak) at g = 2.0218 is believed to be a signal based on radical 2, the amount of radical 2 can be estimated from the peak intensity at g = 2.0218.

[0083] The low molecular weight PTFE powder of the present disclosure has a peak intensity of 0g at g=2.0218 in the ESR spectrum. -1 More than 7g -1 Within this range, it is estimated that the amount of side chain radicals is significantly small. In other words, the low molecular weight PTFE powder of the present disclosure may be substantially free of side chain radicals. On the other hand, the low molecular weight PTFE powder obtained by irradiating the high molecular weight PTFE powder with radiation usually has a peak intensity at g=2.0218 outside the above range, which suggests that a large amount of side chain type radicals are present.

[0084] The low molecular weight PTFE powder of the present disclosure has an average particle size of 20 μm or less. The lower limit of the average particle size is preferably 1 μm, more preferably 2 μm, and the upper limit is preferably 11 μm, more preferably 10 μm, and even more preferably 9 μm.

[0085] The above average particle size is measured using a laser diffraction particle size distribution analyzer (HELOS&RODOS) manufactured by JEOL Ltd. without using a cascade and at a dispersion pressure of 3.0 bar, and is equal to the particle size corresponding to 50% of the integrated particle size distribution.

[0086] The low molecular weight PTFE powder of the present disclosure has an apparent density of 0.6 g / ml or less. The lower limit of the apparent density is preferably 0.1 g / ml, more preferably 0.2 g / ml, and the upper limit is preferably 0.5 g / ml.

[0087] The apparent density can be measured in accordance with JIS K 6891.

[0088] The low molecular weight PTFE powder of the present disclosure can be produced, for example, by the production method of the present disclosure. Also, the low molecular weight PTFE powder of the present disclosure is preferably obtained by emulsion polymerization using a fluorine-based surfactant other than perfluorooctanoic acid and its salt.

[0089] The purified PTFE powder obtained by the manufacturing method of the present disclosure and the low molecular weight PTFE powder of the present disclosure can be suitably used as a molding material, ink, cosmetics, paint, grease, office automation equipment parts, additives for modifying toner, additives for plating solutions, etc. A particularly suitable application of the additive is as a thickening agent for grease.

[0090] Specific examples of the molding material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide.

[0091] When the purified PTFE powder obtained by the manufacturing method of the present disclosure and the low-molecular-weight PTFE powder of the present disclosure are used as additives to the above-mentioned molding materials, they can be used in applications such as improving the non-stickiness and sliding properties of copy rolls, improving the texture of engineering plastic molded products such as surface sheets for furniture, automobile dashboards, and covers for home appliances, and improving the slipperiness and wear resistance of machine parts that generate mechanical friction, such as light-load bearings, gears, cams, push-button phone buttons, projectors, camera parts, and sliding materials.

[0092] The purified PTFE powder obtained by the manufacturing method of the present disclosure and the low molecular weight PTFE powder of the present disclosure can be used as a paint additive for the purpose of improving the slip properties of varnish or paint.

[0093] The purified PTFE powder obtained by the manufacturing method of the present disclosure and the low molecular weight PTFE powder of the present disclosure can be used as an additive in cosmetics for the purpose of improving the slipperiness of cosmetics such as foundation.

[0094] The purified PTFE powder obtained by the production method of the present disclosure and the low-molecular-weight PTFE powder of the present disclosure are further suitable for applications in which the oil repellency or water repellency of wax or the like is improved, and for applications in which the slipperiness of grease or toner is improved.

[0095] The purified PTFE powder obtained by the manufacturing method of the present disclosure and the low molecular weight PTFE powder of the present disclosure can also be used as an electrode binder for secondary batteries and fuel cells, a hardness adjuster for electrode binders, a water repellent treatment agent for electrode surfaces, and the like.

[0096] The purified PTFE powder obtained by the manufacturing method of the present disclosure and the low molecular weight PTFE powder of the present disclosure can also be mixed with a lubricating oil to prepare a grease. The grease contains the purified PTFE powder or the low molecular weight PTFE powder and a lubricating oil, and thus the purified PTFE powder or the low molecular weight PTFE powder is uniformly and stably dispersed in the lubricating oil, and has excellent properties such as load resistance, electrical insulation, and low moisture absorption.

[0097] The lubricating oil (base oil) may be a mineral oil or a synthetic oil. Examples of the lubricating oil (base oil) include paraffinic or naphthenic mineral oils, synthetic hydrocarbon oils, ester oils, fluorine oils, and synthetic oils such as silicone oils. From the viewpoint of heat resistance, fluorine oils are preferred. Examples of the fluorine oils include perfluoropolyether oils and low polymers of trifluorochloroethylene. The low polymers of trifluorochloroethylene may have a weight average molecular weight of 500 to 1200.

[0098] The grease may further contain a thickener. Examples of the thickener include metal soaps, composite metal soaps, bentonite, phthalocyanine, silica gel, urea compounds, urea-urethane compounds, urethane compounds, and imide compounds. Examples of the metal soaps 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, diurethane compounds, and mixtures thereof.

[0099] In the grease, the total content of the purified PTFE powder and the low molecular weight PTFE powder is preferably 0.1 to 50% by mass. The lower limit is more preferably 0.5% by mass, and the upper limit is more preferably 30% by mass. If the amount of the purified PTFE powder and the low molecular weight PTFE powder is too large, the grease may become too hard and may not exhibit sufficient lubrication, and if the amount of the purified PTFE powder and the low molecular weight PTFE powder is too small, the grease may not exhibit sufficient sealing properties.

[0100] The grease may also contain solid lubricants, extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, viscosity index improvers, detergents and dispersants, and the like. EXAMPLES

[0101] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0102] The values ​​in the examples were measured by the following methods.

[0103] <Average particle size> Measurements were performed using a laser diffraction particle size distribution analyzer (HELOS&RODOS) manufactured by JEOL Ltd. without using a cascade and at a dispersion pressure of 1.0 bar. The particle size corresponding to 50% of the integrated particle size distribution was taken as the average particle size.

[0104] <apparent density> The apparent density was measured according to JIS K 6891.

[0105] <Melt viscosity> According to ASTM D 1238, using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, the melt viscosity was measured for a 2g sample that had been preheated at 380°C for 5 minutes under a load of 0.7 MPa while maintaining the above temperature.

[0106] <Fluorine compound content> The content of fluorine compounds was measured using liquid chromatography mass spectrometry under the following conditions.

[0107] Extraction from powder 10 g (12.6 mL) of methanol was added to 1 g of the powder, and ultrasonic treatment was performed at 60°C for 120 minutes to extract the supernatant containing the fluorine compounds.

[0108] Perfluorooctanoic acid calibration curve Five levels of methanol standard solutions of perfluorooctanoic acid with known concentrations ranging from 1 ng / mL to 100 ng / mL were prepared and measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). Using a first-order approximation from each sample concentration and peak integral value, a and b were calculated using the following relational formula (1). A = a × X + b (1) A: Peak area of ​​perfluorooctanoic acid X: Perfluorooctanoic acid concentration (ng / mL)

[0109] Measurement equipment configuration and LC-MS measurement conditions [Table 1]

[0110] MRM measurement parameters [Table 2]

[0111] The content of the compound represented by the general formula (1) having 4 to 20 carbon atoms contained in the extract A liquid chromatograph mass spectrometer was used to measure the compounds represented by general formula (1) having a carbon number of 4 to 20. The peak areas of the compounds represented by general formula (1) having each carbon number were determined for the extracted liquid phase using the MRM method.

[0112] Perfluorocarboxylic acid calibration curve Five standard solutions of perfluorocarboxylic acids with known concentrations ranging from 1 ng / mL to 100 ng / mL were prepared in methanol and measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). Using a first-order approximation from the concentration of each sample and the integral value of the peak, a and b were calculated using the following equation. A=a×X+b A: Peak area of ​​perfluorocarboxylic acid X: concentration of perfluorocarboxylic acid (ng / mL)

[0113] Measurement equipment configuration and LC-MS measurement conditions [Table 3]

[0114] MRM measurement parameters [Table 4]

[0115] Perfluorocarboxylic acid and its salt content The content of perfluorocarboxylic acids and their salts was measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). The extracted liquid phase was measured using the MRM (Multiple Reaction Monitoring) method. The limit of quantification for this assay is 1 ng / mL. In this example, the contents of perfluorocarboxylic acids having 4 to 14 carbon atoms and salts thereof were calculated to determine the total amount.

[0116] Content of the compound represented by formula (1) The content of the compound represented by the general formula (1) and having the carbon number (m+1) in the extract was calculated using the following formula. In the formula, a and b were calculated from the relational formula explained in the calibration curve of perfluorocarboxylic acid. In this example, the content of the compound having 4 to 21 carbon atoms was calculated, and the total amount was calculated. XCm=((ACm-b) / a)×((50×m+45) / 413) XCm: Content (ng / mL) of the compound represented by general formula (1) with carbon number (m+1) in the extract solution ACm: Peak area of ​​the compound represented by general formula (1) with carbon number (m+1) in the extract solution The limit of quantification for this assay is 1 ng / mL.

[0117] Measurement of the content of the compound represented by general formula (1) in the extract The content of the compound represented by the general formula (1) in the extract was calculated as perfluorooctanoic acid.

[0118] Perfluorooctanoic acid calibration curve The value was determined from the calibration curve of the perfluorocarboxylic acid.

[0119] Content of compounds represented by general formula (1) having 4 to 21 carbon atoms contained in the extract A liquid chromatograph mass spectrometer was used to measure the compounds represented by general formula (1) having 4 to 21 carbon atoms. The peak areas of the compounds represented by general formula (1) having each carbon number were determined for the extracted liquid phase using the MRM method.

[0120] MRM measurement parameters [Table 5]

[0121] The content of the compound represented by general formula (1) having the carbon number (m+1) contained in the powder was calculated by the following formula. YCm=XCm×12.6 YCm: Content of the compound represented by the general formula (1) with the carbon number (m+1) contained in the powder (ppb vs. PTFE)

[0122] Content of the compound represented by formula (2) The content of the compound represented by general formula (2) with carbon number n in the extract was calculated using the following formula, where a and b were determined from the relationship explained in the calibration curve for perfluorooctanoic acid. In this example, the contents of compounds having 4 to 21 carbon atoms were calculated, and the total amount was determined. XSn=((ASn-b) / a)×((50×n+81) / 499) XSn: Content of the compound represented by general formula (2) with carbon number n in the extract solution (ng / mL) ASn: Peak area of ​​the compound represented by general formula (2) with carbon number n in the extract solution The limit of quantification for this assay is 1 ng / mL.

[0123] Measurement of the content of the compound represented by general formula (2) in the extract The content of the compound represented by the general formula (2) in the extract was calculated as perfluorooctanesulfonic acid.

[0124] Perfluorooctanesulfonic acid calibration curve Five levels of methanol standard solutions of perfluorooctanesulfonic acid with known concentrations of 1ng / mL to 100ng / mL were prepared and measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). Using a first-order approximation from each sample concentration and peak integral value, a and b were calculated using the following relational formula (2). A = a × X + b (2) A: Peak area of ​​perfluorooctanesulfonic acid X: Perfluorooctanesulfonic acid concentration (ng / mL)

[0125] Measurement equipment configuration and LC-MS measurement conditions [Table 6]

[0126] MRM measurement parameters [Table 7]

[0127] Content of the compound represented by general formula (2) having 4 to 21 carbon atoms contained in the extract A liquid chromatograph mass spectrometer was used to measure the compounds represented by general formula (2) having 4 to 21 carbon atoms. The peak areas of the compounds represented by general formula (2) having each carbon number were determined for the extracted liquid phase using the MRM method.

[0128] MRM measurement parameters [Table 8]

[0129] The content of the compound represented by general formula (2) having the carbon number n contained in the powder was calculated by the following formula. YSn = XSn x 12.6 YSn: Content of the compound represented by general formula (2) with carbon number n contained in the powder (ppb vs. PTFE)

[0130] <Measurement by Electron Spin Resonance (ESR)> Measurement was performed under the following conditions, and the peak intensity at g=2.0218 was obtained from the obtained ESR spectrum. Equipment: JEOL JES-FR30EX Measurement temperature: 23±3℃ Microwave frequency: 9.42GHz Microwave power: 0.4mW Center magnetic field: 347.548mT Sweep width: ±25mT Sweep time: 60s Time constant: 0.03s Magnetic field modulation width: 0.32mT Number of scans: 1 Modulation frequency: 100kHz Marker: Mn 2+

[0131] Synthesis Example 1 (Synthesis of low molecular weight PTFE aqueous dispersion) According to Example 5 of Japanese Patent No. 5338667, a low molecular weight PTFE aqueous dispersion was obtained.

[0132] Comparative Example 1 14.7 g of nitric acid was added to 660 g of the low molecular weight PTFE aqueous dispersion, and coagulation was performed by applying strong mechanical shearing force. The obtained wet powder was filtered and washed with 750 g of pure water. After repeating this washing operation five times, the powder was dried for 18 hours in a hot air circulation dryer at 150°C to obtain a low molecular weight PTFE powder.

[0133] Comparative Example 2 A low-molecular-weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature (heating temperature) was 160°C.

[0134] Example 1 A low molecular weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature was 170°C.

[0135] Example 2 A low molecular weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature was 180°C.

[0136] Example 3 A low molecular weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature was 200°C.

[0137] Example 4 A low molecular weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature was 210°C.

[0138] Example 5 A low molecular weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature was 230°C.

[0139] Example 6 A low molecular weight PTFE powder was obtained in the same manner as in Comparative Example 1, except that the drying temperature was 240°C.

[0140] The obtained low molecular weight PTFE powder was evaluated by the above-mentioned method, and the results are shown in Table 9.

[0141] [Table 9]

Claims

1. The method includes a step of reducing short-chain fluorine compounds from a low-molecular-weight polytetrafluoroethylene powder obtained by radical polymerization, In the above step, at least the compound represented by the following general formula (1) is reduced to 179 ppb or less, and the compound represented by the following general formula (2) is reduced to 6,900 ppb or less: The low-molecular-weight polytetrafluoroethylene powder has an average particle size of 20 μm or less and an apparent density of 0.6 g / ml or less, The melt viscosity of the low-molecular-weight polytetrafluoroethylene powder at 380° C. is 1×10 2 to 7×10 5 Pa·s. Method for producing purified polytetrafluoroethylene powder. General formula (1): (H-(CF ２ ) ｍ -COO) ｐ M １ (In the formula, m is 3 to 20, M １ is H, a metal atom, NR ５ ４ (R ５ may be the same or different and are H or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. p is 1 or 2. General formula (2): (H-(CF ２ ) ｎ -SO ３ ) ｑ M ２ (wherein n is 4 to 21. M ２ is H, metal atom, NR ５ ４ (R ５ is the same as above), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. q is 1 or 2.

2. 2. The method for producing a purified polytetrafluoroethylene powder according to claim 1, wherein a fluorosurfactant other than perfluorooctanoic acid and its salts is used in the radical polymerization.

3. 2. The method for producing a purified polytetrafluoroethylene powder according to claim 1, wherein a hydrocarbon chain transfer agent is used in the radical polymerization.

4. 3. The method for producing a purified polytetrafluoroethylene powder according to claim 1, wherein the radical polymerization is emulsion polymerization.

5. 3. The method for producing a purified polytetrafluoroethylene powder according to claim 1, wherein the short-chain fluorine compounds are reduced by a heat treatment at 170° C. or higher.

6. 3. The method for producing a purified polytetrafluoroethylene powder according to claim 1, wherein in the step, the amount of perfluorocarboxylic acid and its salt is further reduced to below the quantitation limit.

7. 7. The method for producing a purified polytetrafluoroethylene powder according to claim 6, wherein the perfluorocarboxylic acid is a perfluorocarboxylic acid other than perfluorooctanoic acid.