Method for producing fluoropolymer

Abstract

To provide a novel method for producing a fluoropolymer.SOLUTION: Provided is a method for producing a fluoropolymer by polymerizing a fluoromonomer in the presence of a surfactant and an aqueous medium, wherein the polymerization pressure is 1.5 MPaG or less, the surfactant is a carboxylic-acid-type hydrocarbon-based surfactant, the surfactant is added before or simultaneously with the initiation of polymerization, and the surfactant is further added after the initiation of polymerization.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to methods for making fluoropolymers. [Background technology]

[0002] Patent Document 1 describes a method for producing a fluoropolymer, which includes a polymerization step of obtaining a fluoropolymer by polymerizing a fluoromonomer in an aqueous medium in the presence of a surfactant, wherein the surfactant is a carboxylic acid-type hydrocarbon-containing surfactant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 172382 Summary of the Invention [Problem to be solved by the invention]

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

[0005] According to the present disclosure, there is provided a method for producing a fluoropolymer by polymerizing a fluoromonomer in the presence of a surfactant and an aqueous medium, wherein the polymerization pressure is 1.5 MPaG or less, the surfactant is a carboxylic acid type hydrocarbon surfactant, the surfactant is added before or simultaneously with the start of polymerization, and the surfactant is further added after the start of polymerization. [Effects of the Invention]

[0006] According to the present disclosure, a new method for producing a fluoropolymer can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0007] Before specifically describing the present disclosure, some terms used in the present disclosure will be defined or explained.

[0008] In the present disclosure, fluororesins are partially crystalline fluoropolymers, or fluoroplastics. Fluororesins have a melting point and are thermoplastic, but may be melt-processable or non-melt-processable.

[0009] In the present disclosure, melt-processable means that the polymer can be melted and processed using conventional processing equipment such as an extruder, an injection molding machine, etc. Therefore, melt-processable fluororesins usually have a melt flow rate of 0.01 to 500 g / 10 min, as measured by the measurement method described below.

[0010] In this disclosure, fluoroelastomer refers to an amorphous fluoropolymer. "Amorphous" means that the magnitude of the melting peak (ΔH) appearing in differential scanning calorimetry (DSC) (heating rate 10°C / min) or differential thermal analysis (DTA) (heating rate 10°C / min) of the fluoropolymer is 4.5 J / g or less. Fluoroelastomers exhibit elastomeric properties through crosslinking. Elastomeric properties refer to the ability of a polymer to be stretched and to retain its original length when the force required to stretch the polymer is no longer applied.

[0011] In the present disclosure, polytetrafluoroethylene [PTFE] is preferably a fluoropolymer having a content of tetrafluoroethylene units relative to all polymerized units of 99 mol % or more.

[0012] In the present disclosure, both the fluororesin (excluding polytetrafluoroethylene) and the fluororubber are preferably fluoropolymers having a tetrafluoroethylene content of less than 99 mol% relative to all polymerized units.

[0013] In the present disclosure, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0014] In the present disclosure, 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. The organic group is preferably an alkyl group which may have one or more substituents.

[0015] In this disclosure, ranges expressed by endpoints include all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0016] In this disclosure, the term "at least 1" includes all numbers 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.).

[0017] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0018] Patent Document 1 describes that the use of a carboxylic acid-type hydrocarbon-containing surfactant in the polymerization of a fluoromonomer in an aqueous medium results in a high yield of a fluoropolymer. However, further improvement in the physical properties of the resulting fluoropolymer is desired.

[0019] It has now been found that in the polymerization of a fluoromonomer in the presence of an aqueous medium, a carboxylic acid type hydrocarbon surfactant is used as a surfactant, the polymerization is initiated in the presence of the carboxylic acid type hydrocarbon surfactant in the aqueous medium, and further the carboxylic acid type hydrocarbon surfactant is added during the polymerization, and the fluoromonomer is polymerized at a low polymerization pressure, thereby making it possible to produce a fluoropolymer with excellent physical properties.

[0020] According to the production method of the present disclosure, high molecular weight polytetrafluoroethylene can be produced as a fluoropolymer, and moreover, high molecular weight polytetrafluoroethylene having high tensile strength at break and excellent extensibility can be produced.

[0021] When high-molecular-weight polytetrafluoroethylene is produced using conventional manufacturing methods that use hydrocarbon surfactants, problems arise, such as breakage of the bead (extruded product) during paste extrusion of the resulting high-molecular-weight polytetrafluoroethylene, or cracks or chips occurring in the resulting molded product when the resulting high-molecular-weight polytetrafluoroethylene is mixed with other materials such as carbon and processed into a molded product. The manufacturing method of the present disclosure uses a carboxylic acid-type hydrocarbon surfactant and, further, polymerizes the fluoromonomer at a low polymerization pressure, thereby solving these problems. The high-molecular-weight polytetrafluoroethylene obtained using the manufacturing method of the present disclosure exhibits a bead elongation of, for example, 180% or more.

[0022] The reason for this is not clear, but lowering the polymerization pressure slows down the reaction rate and lengthens the polymerization time. Also, the solubility of the monomer in the aqueous dispersion decreases, reducing initiator efficiency. These factors broaden the molecular weight distribution of the fluoropolymer. As a result, even if the average molecular weight is the same, the relatively higher content of high molecular weight components is thought to result in higher bead elongation.

[0023] Furthermore, according to the production method of the present disclosure, low-molecular-weight polytetrafluoroethylene can be produced as a fluoropolymer, and the resulting aqueous dispersion has high stability, making it possible to produce an aqueous dispersion containing a high content of low-molecular-weight polytetrafluoroethylene.

[0024] When low-molecular-weight polytetrafluoroethylene is produced using a conventional production method that uses a hydrocarbon surfactant, the resulting PTFE aqueous dispersion becomes colored, so it is necessary to reduce the amount of hydrocarbon surfactant used. However, if the amount of hydrocarbon surfactant used is reduced, the stability of the aqueous dispersion decreases, making it impossible to obtain a high yield.

[0025] The production method of the present disclosure is a production method for producing a fluoropolymer by polymerizing a fluoromonomer in the presence of a surfactant and an aqueous medium. The production method of the present disclosure will be described in detail below.

[0026] (surfactant) In the production method of the present disclosure, a carboxylic acid type hydrocarbon surfactant is used as the surfactant, and further, a surfactant is added before or simultaneously with the start of polymerization, and further surfactant is added during the period from the start of polymerization to the termination of polymerization, thereby enabling the production of a fluoropolymer with excellent physical properties.

[0027] Polymerization can be said to have begun when the gaseous fluoromonomer in the reactor becomes a fluoropolymer and a pressure drop occurs in the reactor.Punderson, U.S. Pat. No. 3,391,099, discloses the dispersion polymerization of tetrafluoroethylene in an aqueous medium, which comprises two distinct stages of the polymerization process: first, the formation of polymer nuclei as nucleation sites, and then, the growth stage, which includes the polymerization of the established particles.Note that polymerization usually begins when both the monomer to be polymerized and the polymerization initiator are charged into the reactor.

[0028] In the production method of the present disclosure, it is preferable to adjust the concentration of the carboxylic acid type hydrocarbon surfactant at the start of polymerization to less than 150 mass ppm relative to the aqueous medium by adding a surfactant before or simultaneously with the start of polymerization.The concentration of the carboxylic acid type hydrocarbon surfactant at the start of polymerization is preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, even more preferably 15 ppm by mass or more, still more preferably 20 ppm by mass or more, relative to the aqueous medium, from the viewpoint of increasing the number of fluoropolymer particles produced by polymerization.From the viewpoint of quickly starting polymerization, it is preferably 120 ppm by mass or less, more preferably 100 ppm by mass or less, even more preferably 80 ppm by mass or less, still more preferably 60 ppm by mass or less, particularly preferably 50 ppm by mass or less, and most preferably 40 ppm by mass or less.

[0029] In the production method of the present disclosure, the amount of carboxylic acid type hydrocarbon surfactant further added after polymerization initiation until polymerization termination is preferably 100 to 5000 ppm by mass relative to the amount of the finally obtained fluoropolymer, and from the viewpoint of improving the stability of the obtained aqueous fluoropolymer dispersion, is more preferably 300 ppm by mass or more, even more preferably 500 ppm by mass or more, still more preferably 1000 ppm by mass or more, and from the viewpoint of maintaining the polymerization rate, is preferably 3500 ppm by mass or less, more preferably 2000 ppm by mass or less, even more preferably 1500 ppm by mass or less. Furthermore, the amount of carboxylic acid type hydrocarbon surfactant further added after polymerization initiation until polymerization termination may be 5 ppm by mass or more, 10 ppm by mass or more, 15 ppm by mass or more, or 20 ppm by mass or more.

[0030] When low-molecular-weight polytetrafluoroethylene is produced as the fluoropolymer, the amount of carboxylic acid-type hydrocarbon surfactant further added after the start of polymerization and before the termination of polymerization is, from the viewpoint of suppressing coloration, preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, even more preferably 600 ppm by mass or less, even more preferably 500 ppm by mass or less, even more preferably 400 ppm by mass or less, particularly preferably 300 ppm by mass or less, preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, even more preferably 15 ppm by mass or more, still more preferably 20 ppm by mass or more, and may be 100 ppm by mass or more.

[0031] The method for adding the carboxylic acid type hydrocarbon surfactant after the initiation of polymerization is not particularly limited, and a method of adding a desired amount all at once after the initiation of polymerization or a method of adding it continuously after the initiation of polymerization can be used. In particular, by continuously adding the carboxylic acid type hydrocarbon surfactant after the initiation of polymerization, the physical properties of the resulting fluoropolymer are further improved. In addition, it is easy to maintain the polymerization rate. Adding the carboxylic acid type hydrocarbon surfactant continuously means, for example, adding the carboxylic acid type hydrocarbon surfactant not all at once but over time, continuously or in portions.

[0032] When the carboxylic acid hydrocarbon surfactant is continuously added after the start of polymerization, it is preferable to start adding the carboxylic acid hydrocarbon surfactant when the concentration of the fluoropolymer formed in the aqueous medium is 2.0 mass% or more and 10.0 mass% or less. From the viewpoint of maintaining the polymerization rate, the timing to start adding the carboxylic acid hydrocarbon surfactant is when the fluoropolymer concentration is more preferably 3.0 mass% or more, even more preferably 3.5 mass% or more, still more preferably 4.0 mass% or more, and from the viewpoint of improving the stability of the aqueous fluoropolymer dispersion, it is more preferably when the fluoropolymer concentration is 9.0 mass% or less, even more preferably 8.0 mass% or more, still more preferably 7.0 mass% or less. The fluoropolymer concentration is the concentration of the fluoropolymer relative to the total of the aqueous medium and the fluoropolymer.

[0033] Carboxylic acid hydrocarbon surfactants are usually anionic surfactants having a hydrophilic portion of a carboxylate salt and a hydrophobic portion that is a long-chain hydrocarbon portion such as an alkyl. The carboxylic acid hydrocarbon surfactant may be an aliphatic carboxylic acid hydrocarbon surfactant, or may be a non-aliphatic carboxylic acid hydrocarbon surfactant. In this specification, "aliphatic carboxylic acid hydrocarbon surfactant" refers to a carboxylic acid hydrocarbon surfactant that does not contain a carbonyl group (excluding the carbonyl group in a carboxyl group or an ester group). The ester group refers to a group represented by -COO- or -OCO-.

[0034] Examples of the carboxylic acid type hydrocarbon surfactant include those represented by the following formula: R 10 -COOM (In the formula, R 10 is a monovalent organic group containing one or more carbon atoms. M is H, a metal atom, NR 11 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R 11 R is H or an organic group, and may be the same or different. 11 as H or C 1-10 is preferably an organic group represented by the formula: 1-4 The organic group is more preferred. From the viewpoint of surfactant activity, R 10 The number of carbon atoms in R is preferably 2 or more, and more preferably 3 or more. 10 The number of carbon atoms is preferably 29 or less, and more preferably 23 or less. The metal atom of M includes alkali metals (Group 1) and alkaline earth metals (Group 2), and is preferably Na, K, or Li. M may be H, a metal atom, or NR 11 4 is preferred, H, an alkali metal (Group 1), an alkaline earth metal (Group 2) or NR 114 is more preferred, H, Na, K, Li or NH4 is even more preferred, Na, K or NH4 is even more preferred, Na or NH4 is particularly preferred, and NH4 is most preferred.

[0035] The carboxylic acid type hydrocarbon surfactants include R 12 -COOM(in the formula, R 12 is a linear or branched alkyl group, alkenyl group, alkylene group or alkenylene group having 1 or more carbon atoms which may have a substituent, or a cyclic alkyl group, alkenyl group, alkylene group or alkenylene group having 3 or more carbon atoms which may have a substituent, and these may contain an ether bond. When the number of carbon atoms is 3 or more, it may contain a monovalent or divalent heterocycle or may form a ring. M is the same as above.) Specifically, CH3-(CH2) n -COOM (wherein n is an integer of 2 to 28, and M is the same as above).

[0036] From the viewpoint of emulsion stability, the carboxylic acid type hydrocarbon surfactant preferably does not contain a carbonyl group (excluding the carbonyl group in the carboxyl group). The surfactant used in the polymerization is preferably a carboxylic acid type hydrocarbon surfactant that does not contain a carbonyl group. Examples of the carboxylic acid type hydrocarbon surfactant not containing a carbonyl group include those represented by the following formula (α): R-COO-M (α) (In the formula, R is an alkyl group, an alkenyl group, an alkylene group, or an alkenylene group, which may contain an ether bond. M is H, a metal atom, NR 11 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 11 are the same or different and are H or an organic group having 1 to 10 carbon atoms. In the above formula (α), R is preferably an alkyl group or an alkenyl group (which may contain an ether group). The alkyl group or alkenyl group in R may be linear or branched. The number of carbon atoms in R is not limited, but is, for example, 2 to 29. The alkyl group or alkenyl group in R preferably does not contain a carbonyl group (excluding the carbonyl group in an ester group).

[0037] When the alkyl group is linear, the carbon number of R is preferably 3 to 29, and more preferably 5 to 23. When the alkyl group is branched, the carbon number of R is preferably 5 to 35, and more preferably 11 to 23. When the alkenyl group is linear, the number of carbon atoms in R is preferably 2 to 29, more preferably 9 to 23. When the alkenyl group is branched, the number of carbon atoms in R is preferably 2 to 29, more preferably 3 to 29, and even more preferably 9 to 23.

[0038] Examples of the alkyl group and alkenyl group include a methyl group, an ethyl group, an isobutyl group, a t-butyl group, and a vinyl group.

[0039] Examples of the carboxylic acid type hydrocarbon surfactants include butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, (9,12,15)-linolenic acid, (6,9,12)linolenic acid, eleostearic acid, arachidic acid, 8,11-eicosadienoic acid, mead acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, cerotic acid, montanic acid, melissic acid, crotonic acid, milian acid, malianthic ... Examples of the fatty acids include stearic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, nervonic acid, linoleic acid, eicosadienoic acid, docosadienoic acid, linolenic acid, pinolenic acid, α-eleostearic acid, β-eleostearic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, adrenic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, sardine acid, tetracosapentaenoic acid, docosahexaenoic acid, herring acid, and salts thereof. In particular, at least one selected from the group consisting of lauric acid, capric acid, myristic acid, pentadecylic acid, palmitic acid, and salts thereof is preferred, lauric acid and salts thereof are more preferred, salts of lauric acid are particularly preferred, and sodium laurate or ammonium laurate is most preferred. The salts include those in which the hydrogen of the carboxyl group is replaced by a metal atom of the formula M, NR 11 4. Examples include, but are not limited to, imidazolium which may have a substituent, pyridinium which may have a substituent, or phosphonium which may have a substituent.

[0040] In the production method of the present disclosure, the polymerization may further include a step of adjusting the pH of the aqueous medium containing the carboxylic acid-type hydrocarbon surfactant to a basic pH. The basic pH is preferably 7.1 or higher, more preferably 7.5 or higher, even more preferably 8.0 or higher, particularly preferably 8.5 or higher, and even more preferably 9.0 or higher. Adjusting the pH to a basic pH can enhance the surface activity. The pH adjustment step may be performed before or after the step of radical treatment or oxidation treatment of the carboxylic acid-type hydrocarbon surfactant, but is preferably performed after. The method for adjusting the pH is not particularly limited, but examples include adding a pH adjuster to the aqueous medium. Examples of the pH adjuster that can be used include ammonia, NaOH, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, sodium phosphate, potassium phosphate, sodium citrate, potassium citrate, ammonium citrate, sodium gluconate, potassium gluconate, and ammonium gluconate. The pH can be measured using a pH / ION meter manufactured by HORIBA.

[0041] In the production method of the present disclosure, the polymerization may be carried out using at least one carboxylic acid type hydrocarbon surfactant. In addition, in the production method of the present disclosure, two or more of the carboxylic acid type hydrocarbon surfactants may be used simultaneously as the surfactant, or a surfactant other than the carboxylic acid type hydrocarbon surfactant may be used simultaneously as long as it is volatile or may remain in a molded product made of a fluoropolymer.

[0042] In the production method of the present disclosure, it is preferable to carry out polymerization of fluoromonomers substantially in the absence of a fluorine-containing surfactant. In the present disclosure, "substantially in the absence of a surfactant" means that the amount of fluorine-containing surfactant relative to the aqueous medium is 10 mass ppm or less. The amount of fluorine-containing surfactant relative to the aqueous medium is preferably 1 mass ppm or less, more preferably 100 mass ppb or less, even more preferably 50 mass ppb or less, still more preferably 25 mass ppb or less, particularly preferably 10 mass ppb or less, and most preferably 1 mass ppb or less.

[0043] Specific examples of the fluorine-containing surfactant include compounds represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds. F(CF2)7COOM, F(CF2)5COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and [ka] (In each formula, M is H, metal atom, NR 1 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent.1 is H or an organic group.

[0044] (polymerization) In the production method of the present disclosure, the polymerization of fluoromonomers is carried out at low pressure, which allows the production of fluoropolymers with excellent physical properties.

[0045] In the production method of the present disclosure, the polymerization pressure is 1.5 MPaG or less, preferably 1.3 MPaG or less, more preferably 1.1 MPaG or less, even more preferably 1.0 MPaG or less, still more preferably 0.9 MPaG or less, preferably 0.05 MPaG or more, more preferably 0.3 MPaG or more, and even more preferably 0.5 MPaG or more.

[0046] In the production method of the present disclosure, the polymerization temperature is preferably 10 to 150°C, more preferably 30°C or higher, even more preferably 50°C or higher, more preferably 120°C or lower, even more preferably 100°C or lower.

[0047] The polymerization in the above production method can be carried out by charging an aqueous medium, a carboxylic acid type hydrocarbon surfactant, a monomer, and other additives as necessary into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to initiate the polymerization reaction. After the initiation of polymerization, additional monomers, polymerization initiators, chain transfer agents, the surfactants, etc. may be added depending on the purpose. The hydrocarbon surfactant may also be added after the initiation of the polymerization reaction.

[0048] (Polymerization initiator) As the polymerization initiator, at least one selected from the group consisting of a water-soluble radical polymerization initiator and a redox initiator can be suitably used. As the polymerization initiator, at least one selected from the group consisting of a persulfate and a redox initiator using a persulfate or a permanganate as an oxidizing agent is preferred, since this allows the polymerization reaction to proceed more smoothly.

[0049] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium, potassium, or sodium salts of persulfuric acid, perborate, perchloric acid, perphosphoric acid, or percarbonate; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; or t-butyl hydroperoxide. A reducing agent such as a sulfite may also be included, and the amount used may be 0.1 to 20 times the amount of the peroxide. Furthermore, during polymerization, a radical scavenger such as hydroquinone or catechol, or a peroxide decomposer such as ammonium sulfite, may be added to adjust the radical concentration in the system.

[0050] It is also preferable to use a redox initiator, which combines an oxidizing agent and a reducing agent, as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. To increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0051] Examples of the redox initiator include potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, ammonium persulfate / bisulfite / iron sulfate, ammonium persulfate / ammonium sulfite, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite. Potassium permanganate / oxalic acid and ammonium persulfate / bisulfite / iron sulfate are preferred. When using a redox initiator, either an oxidizing agent or a reducing agent may be charged into a polymerization vessel in advance, followed by continuous or intermittent addition of the other agent to initiate polymerization. For example, when using potassium permanganate / oxalic acid, it is preferred to charge oxalic acid into a polymerization vessel and then continuously add potassium permanganate thereto.

[0052] (chain transfer agent) Examples of chain transfer agents include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0053] Among them, the chain transfer agent is preferably a non-halogenated alkane having 2 to 4 carbon atoms. Specifically, at least one selected from the group consisting of methane, ethane, propane, butane, and isobutane is more preferred, and at least one selected from the group consisting of ethane and propane is even more preferred.

[0054] The amount of the chain transfer agent used is usually 1 to 50,000 ppm by mass, and preferably 1 to 20,000 ppm by mass, based on the total amount of fluoromonomers supplied.

[0055] The chain transfer agent may be added all at once to the reaction vessel before the initiation of polymerization, may be added all at once after the initiation of polymerization, may be added in multiple divided portions during the polymerization, or may be added continuously during the polymerization.

[0056] (aqueous medium) The aqueous medium is a reaction medium for polymerization and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an ether or a ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or lower.

[0057] As the aqueous medium, an aqueous medium containing only water or an aqueous medium containing only water and a fluorine-free organic solvent is preferred, as it allows the polymerization to proceed smoothly, and an aqueous medium containing only water is more preferred.

[0058] The content of water in the aqueous medium is preferably 90% or more, more preferably 95% or more, even more preferably 99.0% or more, still more preferably 99.5% or more, particularly preferably 99.9% or more, and may be 100%, based on the mass of the aqueous medium, in order to allow the polymerization to proceed smoothly.

[0059] (additives) In the polymerization, additives can be used, such as buffers, pH adjusters, stabilizing aids, and dispersion stabilizers.

[0060] The stabilizing aid is preferably paraffin wax, fluorine-based oil, fluorine-based solvent, silicone oil, etc. The stabilizing aid may be used alone or in combination of two or more. The stabilizing aid is more preferably paraffin wax. The paraffin wax may be liquid, semi-solid, or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms. The melting point of the paraffin wax is usually preferably 40 to 65°C, more preferably 50 to 65°C.

[0061] The amount of the stabilizing aid used is preferably 0.1 to 12 mass % based on the mass of the aqueous medium used, and more preferably 0.1 to 8 mass %. It is desirable that the stabilizing aid is sufficiently hydrophobic so that it is completely separated from the aqueous dispersion after polymerization and does not become a contaminating component.

[0062] (Fluoromonomer) The fluoromonomer preferably has at least one double bond. Examples of the fluoromonomer include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), vinyl fluoride, vinylidene fluoride (VDF), trifluoroethylene, fluoroalkyl vinyl ether, fluoroalkyl ethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, and fluoroalkyl ethers represented by the general formula (100): CHX 101 =CX102 Rf 101 (In the formula, X 101 and X 102 is H on one side and F on the other side, and Rf 101 is preferably at least one selected from the group consisting of a fluoromonomer represented by (a linear or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluorinated vinyl heterocyclic compound, and a monomer that provides a crosslinking site.

[0063] Examples of the fluoroalkyl vinyl ether include: General formula (110): CF2=CF-ORf 111 (In the formula, Rf 111 represents a perfluoroorganic group; General formula (120): CF2=CF-OCH2-Rf 121 (In the formula, Rf 121 is a perfluoroalkyl group having 1 to 5 carbon atoms), General formula (130): CF2=CFOCF2ORf 131 (In the formula, Rf 131 is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms, General formula (140): CF2=CFO(CF2CF(Y 141 )O) m (CF2) n F (In the formula, Y 141 represents a fluorine atom or a trifluoromethyl group, m is an integer of 1 to 4, and n is an integer of 1 to 4. General formula (150): CF2=CF-O-(CF2CFY 151 -O) n -(CFY 152 ) m -A 151 (In the formula, Y 151represents a fluorine atom, a chlorine atom, a -SO2F group, or a perfluoroalkyl group. The perfluoroalkyl group may contain an etheric oxygen and a -SO2F group. n represents an integer of 0 to 3. n Y 151 may be the same or different. 152 represents a fluorine atom, a chlorine atom, or a -SO2F group. m represents an integer of 1 to 5. m Y 152 may be the same or different. 151 -SO2X 151 , -COZ 151 or -POZ 152 Z 153 represents X 151 are F, Cl, Br, I, -OR 151 or -NR 152 R 153 represents Z. 151 , Z 152 and Z 153 are the same or different and are -NR 154 R 155 -OR 156 Represents R 151 , R 152 , R 153 , R 154 , R 155 and R 156 are the same or different and represent H, ammonium, an alkali metal, an alkyl group which may contain a fluorine atom, an aryl group, or a sulfonyl-containing group. It is preferable that the material is at least one selected from the group consisting of:

[0064] In the present disclosure, the term "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen atom.

[0065] The fluoromonomer represented by the general formula (110) is Rf 111 is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0066] Examples of the perfluoroorganic group in the general formula (110) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. The fluoromonomer represented by the general formula (110) further includes a fluoromonomer represented by the general formula (110) in which Rf 111 is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf 111 is the following formula:

[0067] [ka]

[0068] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0069] CF3CF2CF2-(O-CF(CF3)-CF2) n - (wherein n represents an integer of 1 to 4).

[0070] Among the fluoromonomers represented by the general formula (110), General formula (160): CF2=CF-ORf 161 (In the formula, Rf 161 Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms. Fluoromonomers represented by 161 is preferably a perfluoroalkyl group having 1 to 5 carbon atoms.

[0071] The fluoroalkyl vinyl ether is preferably at least one selected from the group consisting of fluoromonomers represented by the general formulas (160), (130) and (140).

[0072] The fluoromonomer represented by general formula (160) is preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether), and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether).

[0073] The fluoromonomer represented by the general formula (130) is preferably at least one selected from the group consisting of CF2=CFOCF2OCF3, CF2=CFOCF2OCF2CF3, and CF2=CFOCF2OCF2CF2OCF3.

[0074] The fluoromonomer represented by general formula (140) is preferably at least one selected from the group consisting of CF2=CFOCF2CF(CF3)O(CF2)3F, CF2=CFO(CF2CF(CF3)O)2(CF2)3F, and CF2=CFO(CF2CF(CF3)O)2(CF2)2F.

[0075] The fluoromonomer represented by general formula (150) is preferably at least one selected from the group consisting of CF2=CFOCF2CF2SO2F, CF2=CFOCF2CF(CF3)OCF2CF2SO2F, CF2=CFOCF2CF(CF2CF2SO2F)OCF2CF2SO2F and CF2=CFOCF2CF(SO2F)2.

[0076] The fluoromonomer represented by the general formula (100) is Rf 101 is a linear fluoroalkyl group, and Rf 101 More preferred is a fluoromonomer in which Rf is a linear perfluoroalkyl group. 101The number of carbon atoms in the formula (100) is preferably 1 to 6. Examples of the fluoromonomer represented by the formula (100) include CH2=CFCF3, CH2=CFCF2CF3, CH2=CFCF2CF2CF3, CH2=CFCF2CF2CF2H, CH2=CFCF2CF2CF2CF3, CHF=CHCF3 (E-isomer), and CHF=CHCF3 (Z-isomer), and among these, 2,3,3,3-tetrafluoropropylene represented by CH2=CFCF3 is preferred.

[0077] Fluoroalkylethylenes include: General formula (170): CH2=CH-(CF2) n -X 171 (In the formula, X 171 is H or F, and n is an integer of 3 to 10.) is preferred, and fluoroalkylethylenes represented by CH2=CH-C4F9 and CH2=CH-C6F 13 It is more preferable that the material is at least one selected from the group consisting of:

[0078] Examples of the fluoroalkyl allyl ether include: General formula (180): CF2=CF-CF2-ORf 111 (In the formula, Rf 111 represents a perfluoroorganic group.

[0079] Rf of general formula (180) 111 is Rf in general formula (110) 111 is the same as Rf 111is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The fluoroalkyl allyl ether represented by general formula (180) is preferably at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and even more preferably CF2=CF-CF2-O-CF2CF2CF3.

[0080] The fluorinated vinyl heterocycle includes a compound represented by the general formula (230): [ka] (In the formula, X 231 and X 232 are independently F, Cl, a methoxy group, or a fluorinated methoxy group; Y 231 is the formula Y 232 or formula Y 233 is.

[0081] [ka] (In the formula, Z 231 and Z 232 are independently F or a fluorinated alkyl group having 1 to 3 carbon atoms.

[0082] Monomers that provide crosslinking sites include CF2=CFOCF2CF(CF3)OCF2CF2CN, CF2=CFOCF2CF(CF3)OCF2CF2COOH, CF2=CFOCF2CF(CF3)OCF2CF2CH2I, CF2=CFOCF2CF2CH2I, CH2=CFCF2OCF(CF3)CF2OCF(CF3)CN, CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOH, CH2=CFCF2OCF( It is preferably at least one selected from the group consisting of CF3)CF2OCF(CF3)CH2OH, CH2=CHCF2CF2I, CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)6CH=CH2, and CF2=CFO(CF2)5CN, and more preferably at least one selected from the group consisting of CF2=CFOCF2CF(CF3)OCF2CF2CN and CF2=CFOCF2CF2CH2I.

[0083] In the polymerization, the fluoromonomer may be polymerized with a non-fluorine-containing monomer, such as a hydrocarbon-based monomer reactive with the fluoromonomer.

[0084] Examples of the hydrocarbon monomer include alkenes such as ethylene, propylene, butylene, and isobutylene; and (meth)acrylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, and vinyl methacrylate.

[0085] The fluorine-free monomer may also be a functional group-containing hydrocarbon monomer (excluding the monomer that provides a crosslinking site). Examples of the functional group-containing hydrocarbon monomer include hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether, and hydroxycyclohexyl vinyl ether; fluorine-free monomers having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, succinic acid, succinic anhydride, fumaric acid, fumaric anhydride, crotonic acid, maleic acid, maleic anhydride, and perfluorobutenoic acid; fluorine-free monomers having a sulfo group such as vinyl sulfonic acid; fluorine-free monomers having a glycidyl group such as glycidyl vinyl ether and glycidyl allyl ether; fluorine-free monomers having an amino group such as aminoalkyl vinyl ether and aminoalkyl allyl ether; fluorine-free monomers having an amide group such as (meth)acrylamide and methylolacrylamide; fluorine-free monomers having a nitrile group such as acrylonitrile and methacrylonitrile.

[0086] In the manufacturing method of the present disclosure, it is preferable to use at least TFE as the fluoromonomer.In one embodiment, as the fluoromonomer, only TFE or a combination of TFE and a fluoromonomer other than TFE is used.As the fluoromonomer other than TFE, among the above-mentioned fluoromonomers, fluoromonomers other than TFE can be mentioned, and for example, at least one selected from the group consisting of HFP, CTFE, fluoroalkyl vinyl ether, fluoroalkyl ethylene and fluoroalkyl allyl ether can be suitably used.

[0087] In the above polymerization, the desired fluoropolymer can be obtained by polymerizing one or more of the above fluoromonomers.

[0088] (fluoropolymer) The polymerization can produce an aqueous dispersion containing a fluoropolymer. The fluoropolymer usually has a concentration of 8 to 50 mass% in the aqueous dispersion obtained by the polymerization. In the aqueous dispersion, the lower limit of the fluoropolymer concentration is preferably 10 mass%, more preferably 15 mass%, and the upper limit is preferably 40 mass%, more preferably 35 mass%.

[0089] The fluoropolymer content in the aqueous dispersion is a value obtained by drying 1 g of the aqueous dispersion in a blower dryer at 150°C for 60 minutes, measuring the mass of the heating residue, and calculating the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion as a percentage.

[0090] In one embodiment of the production method, polytetrafluoroethylene (PTFE) is produced using at least TFE as the fluoromonomer. When the polymerization of TFE is completed, a polymer dispersion having a solid content of 10 to 50 mass % and an average primary particle size of 50 to 500 nm can be obtained. The lower limit of the solid content is preferably 12% by mass, more preferably 15% by mass, and even more preferably 20% by mass or less. The upper limit is not particularly limited, but may be 40% by mass or 35% by mass. The lower limit of the average primary particle size is preferably 100 nm, more preferably 150 nm, and the upper limit is preferably 400 nm, more preferably 350 nm.

[0091] Alternatively, a fluoropolymer powder can be obtained by coagulating the fluoropolymer in the aqueous dispersion and drying the coagulated product. The coagulated product may be washed before being dried.

[0092] After obtaining a fluoropolymer by polymerizing a fluoromonomer, the obtained fluoropolymer may be dried. The drying temperature is preferably 155°C or higher, more preferably 160°C or higher, preferably 170°C or higher, and particularly preferably 180°C or higher. The upper limit of the drying temperature is not particularly limited as long as it is a temperature at which the fluoropolymer does not deteriorate, but may be, for example, 300°C or lower. The drying temperature is preferably 280°C or lower, more preferably 260°C or lower, even more preferably 240°C or lower, particularly preferably 225°C or lower, and particularly preferably 210°C or lower. When the fluoropolymer is high-molecular-weight PTFE, a higher drying temperature increases the strength of the paste-extruded extrusion molded body (bead) but reduces elongation, so it is necessary to select an appropriate drying temperature depending on the purpose.

[0093] The manufacturing method of the present disclosure can provide a fluoropolymer, such as a TFE polymer in which the monomer having the largest molar fraction in the polymer (hereinafter referred to as the "most abundant monomer") is TFE, a VDF polymer in which the most abundant monomer is VDF, or a CTFE polymer in which the most abundant monomer is CTFE.

[0094] The fluoropolymers preferably have an ion exchange ratio (IXR) greater than 53. Preferred fluoropolymers have no ionic groups or a limited number of ionic groups resulting in an ion exchange ratio greater than about 100. Preferred fluoropolymers preferably have an ion exchange ratio of 1000 or greater, more preferably 2000 or greater, and even more preferably 5000 or greater.

[0095] The TFE polymer may suitably be a TFE homopolymer or a copolymer comprising (1) TFE, (2) one or more fluorine-containing monomers other than TFE having 2 to 8 carbon atoms, particularly VDF, HFP, or CTFE, and (3) other monomers. Examples of the (3) other monomers include fluoro(alkyl vinyl ethers) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; fluorodioxole; perfluoroalkylethylene; and ω-hydroperfluoroolefin.

[0096] The TFE polymer may also be a copolymer of TFE and one or more fluorine-free monomers. Examples of the fluorine-free monomers include alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers. The TFE polymer may also be a copolymer of TFE and one or more fluorine-containing monomers having 2 to 8 carbon atoms and one or more fluorine-free monomers.

[0097] The fluoropolymers may be glassy, ​​plastic or elastomeric. They may be amorphous or partially crystalline and may be subject to compression-sintering, melt-processing or non-melt-processing.

[0098] In the production method of the present disclosure, for example, (I) as a non-melt-processable fluororesin, tetrafluoroethylene polymer [TFE polymer (PTFE)] can be suitably produced; (II) as a melt-processable fluororesin, ethylene / TFE copolymer [ETFE], TFE / HFP copolymer [FEP], TFE / perfluoro(alkyl vinyl ether) copolymer [PFA, MFA, etc.], TFE / perfluoroallyl ether copolymer, TFE / VDF copolymer, and electrolyte polymer precursor can be suitably produced; and (III) as a fluororubber, TFE / propylene copolymer, TFE / propylene / third monomer copolymer (the third monomer is VDF, HFP, CTFE, fluoroalkyl vinyl ethers, etc.), copolymers composed of TFE and fluoroalkyl vinyl ethers; HFP / ethylene copolymer, HFP / ethylene / TFE copolymer; VDF / HFP copolymer, HFP / ethylene copolymer, VDF / TFE / HFP copolymer; and the fluorine-containing segmented polymer described in Japanese Patent Publication No. 61-49327 can be suitably produced.

[0099] The fluorine substitution rate of the fluoropolymer calculated by the following formula is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, still more preferably 75% or more, and particularly preferably 80% or more. The fluorine substitution rate of the fluoropolymer is most preferably 90 to 100%.

[0100] The fluoropolymer is preferably a fluororesin, and particularly, a fluororesin having a fluorine substitution rate of 50% or more as calculated by the following formula is more preferred, a fluororesin having a fluorine substitution rate of more than 50% is even more preferred, a fluororesin having a fluorine substitution rate of 55% or more is even more preferred, a fluororesin having a fluorine substitution rate of 60% or more is even more preferred, a fluororesin having a fluorine substitution rate of 75% or more is even more preferred, a fluororesin having a fluorine substitution rate of 80% or more is particularly preferred, and a fluororesin having a fluorine substitution rate of 90 to 100%, i.e., a perfluororesin, is most preferred.

[0101] (formula) Fluorine substitution rate (%) = (number of fluorine atoms bonded to carbon atoms constituting the fluoropolymer) / ((number of hydrogen atoms bonded to carbon atoms constituting the fluoropolymer) + (number of fluorine atoms and chlorine atoms bonded to carbon atoms constituting the fluoropolymer)) × 100

[0102] The perfluororesin is more preferably a fluororesin having a fluorine substitution rate of 95 to 100%, further preferably PTFE, FEP or PFA, still more preferably PTFE, and particularly preferably high molecular weight PTFE.

[0103] The fluoropolymer may have a core-shell structure. Examples of the fluoropolymer having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0104] The core-shell structure may have the following structure. Core: TFE homopolymer Shell: TFE homopolymer Core: Modified PTFE Shell: TFE homopolymer Core: Modified PTFE Shell: Modified PTFE Core: TFE homopolymer Shell: Modified PTFE Core: Low molecular weight PTFE Shell: High molecular weight PTFE Core: High molecular weight PTFE Shell: Low molecular weight PTFE

[0105] In the fluoropolymer having the core-shell structure, the lower limit of the core ratio is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the core ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0106] In the fluoropolymer having the core-shell structure, the lower limit of the shell ratio is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the shell ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0107] PTFE can be produced by polymerizing at least TFE as a fluoromonomer. In the production of PTFE, various known modified monomers can also be used in combination. In the present disclosure, PTFE is a concept that includes not only TFE homopolymer but also a copolymer of TFE and a modified monomer (hereinafter referred to as "modified PTFE").

[0108] The modifying monomer is not particularly limited as long as it is copolymerizable with TFE, and examples thereof include fluoromonomers and non-fluoromonomers. The modifying monomer used may be one type or multiple types.

[0109] The non-fluoromonomer is not particularly limited and may be selected from the group consisting of monomers having the general formula: CH2=CR Q1 -LR Q2 (In the formula, R Q1represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents R Q2 R represents the bond position with Q2 represents a hydrogen atom, an alkyl group or a nitrile group.

[0110] Examples of non-fluoromonomers 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, cyclohexyl vinyl ether, etc. Of these, butyl methacrylate, vinyl acetate, and acrylic acid are preferred as non-fluoromonomers.

[0111] Examples of fluoromonomers include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers; (perfluoroalkyl)ethylenes; and perfluoroallyl ethers.

[0112] 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. 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.

[0113] In the production of the TFE polymer, a saturated hydrocarbon having 12 or more carbon atoms that is substantially inert to the reaction and becomes liquid under the reaction conditions can also be used as a dispersion stabilizer for the reaction system in an amount of 2 to 10 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, ammonium carbonate, ammonium phosphate, or the like can be added as a buffer to adjust the pH during the reaction.

[0114] Fine powders can be produced by coagulating aqueous dispersions of TFE polymers. The aqueous dispersions of TFE polymers can be used for various applications as fine powders after coagulation, washing, and drying. When coagulating the aqueous dispersions of TFE polymers, the aqueous dispersion obtained by polymerization of a polymer latex or the like is typically diluted with water to a polymer concentration of 5 to 20% by mass. In some cases, the pH is adjusted to neutral or alkaline, and the mixture is stirred in a vessel equipped with a stirrer with more vigor than during the reaction. The coagulation may be performed while stirring, using a coagulant such as a water-soluble organic compound (e.g., methanol or acetone), an inorganic salt (e.g., potassium nitrate or ammonium carbonate), or an inorganic acid (e.g., hydrochloric acid, sulfuric acid, or nitric acid). The coagulation may also be performed continuously using an in-line mixer or the like.

[0115] The concentration of the unaggregated TFE polymer in the wastewater resulting from the aggregation is preferably low from the viewpoint of productivity, more preferably less than 0.4% by mass, and particularly preferably less than 0.3% by mass.

[0116] According to the production method of the present disclosure, it is also possible to produce low-molecular-weight PTFE as PTFE.

[0117] Low-molecular-weight PTFE (also called PTFE micropowder) having a molecular weight of 600,000 or less has excellent chemical stability, extremely low surface energy, and is resistant to fibrillation. Therefore, it is suitable as an additive for improving the slipperiness and texture of coating surfaces in the production of plastics, inks, cosmetics, paints, greases, office automation equipment components, toners, etc. (see, for example, JP-A-10-147617).

[0118] When the low-molecular-weight PTFE obtained by the above polymerization is used as a powder, the aqueous dispersion can be coagulated to form powder particles.

[0119] According to the production method of the present disclosure, high molecular weight PTFE can also be produced as PTFE. In this disclosure, high molecular weight PTFE refers to non-melt-processible and fibrillating PTFE, while low molecular weight PTFE refers to melt-processible and non-fibrillating PTFE.

[0120] The term "non-melt processable" means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D 1238 and D 2116.

[0121] The presence or absence of fibrillating properties can be determined by "paste extrusion," a typical method for molding "high molecular weight PTFE powder," a powder made from a TFE polymer. Paste extrusion is usually possible because high molecular weight PTFE has fibrillating properties. If the unsintered molded product obtained by paste extrusion has no substantial strength or elongation, for example, if it breaks when pulled at 0% elongation, it can be considered to have no fibrillating properties.

[0122] The high-molecular-weight PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.280. The standard specific gravity is measured by a water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D4895-89. In the present disclosure, "high molecular weight" means that the standard specific gravity is within the above range.

[0123] The above low molecular weight PTFE has a melt viscosity of 1×10 at 380°C. 2 ~7×10 5The molecular weight is Pa·s. In the present disclosure, "low molecular weight" means that the melt viscosity is within the above range. The melt viscosity is 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 to 380°C for 5 minutes, and maintained at the above temperature under a load of 0.7 MPa.

[0124] The high-molecular-weight PTFE has a melt viscosity significantly higher than that of the low-molecular-weight PTFE, making it difficult to measure its melt viscosity accurately. On the other hand, while the melt viscosity of the low-molecular-weight PTFE can be measured, it is difficult to obtain a molded article from the low-molecular-weight PTFE that can be used to measure its standard gravity, making it difficult to measure its standard gravity accurately. Therefore, in this disclosure, standard gravity is used as an indicator of the molecular weight of the high-molecular-weight PTFE, and melt viscosity is used as an indicator of the molecular weight of the low-molecular-weight PTFE. There are no known methods for directly determining the molecular weight of either the high-molecular-weight PTFE or the low-molecular-weight PTFE.

[0125] The high-molecular-weight PTFE preferably has a peak temperature of 333 to 347°C, more preferably 335 to 345°C. The low-molecular-weight PTFE preferably has a peak temperature of 322 to 333°C, more preferably 324 to 332°C. The peak temperature can be identified as the temperature corresponding to the maximum value that appears on a differential thermal analysis (DTA) curve obtained by using a TG / DTA (thermogravimetric / differential thermal analyzer) to raise the temperature of PTFE that has no history of being heated to a temperature of 300°C or higher at a rate of 10°C / min.

[0126] The peak temperature of the PTFE may be 322 to 347°C. When the PTFE is a high molecular weight PTFE, the upper limit of the peak temperature of the PTFE may be 347°C or less, 346°C or less, 345°C or less, 344°C or less, 343°C or less, 342°C or less, 341°C or less, or 340°C or less. When the PTFE is a high-molecular-weight PTFE, the lower limit of the peak temperature of the PTFE may be 333°C or higher, or 335°C or higher. When the PTFE is a low-molecular-weight PTFE, the upper limit of the peak temperature of the PTFE may be 333°C or less, or 332°C or less. When the PTFE is a low-molecular-weight PTFE, the lower limit of the peak temperature of the PTFE may be 322°C or higher, or 324°C or higher.

[0127] The average primary particle size of the primary particles of the low-molecular-weight PTFE is preferably 10 to 350 nm, more preferably 100 nm or more, even more preferably 150 nm or more, more preferably 400 nm or less, and even more preferably 350 nm or less.

[0128] The high-molecular-weight PTFE preferably exhibits at least one endothermic peak in the range of 333 to 347°C in a heat of fusion curve when PTFE that has not been heated to a temperature of 300°C or higher is heated at a rate of 10°C / min using a differential scanning calorimeter (DSC), and the heat of fusion between 290 and 350°C calculated from the heat of fusion curve is 52 mJ / mg or more. The heat of fusion of PTFE is more preferably 55 mJ / mg or more, and even more preferably 58 mJ / mg or more.

[0129] The manufacturing method of the present disclosure can also be used to produce TFE / HFP copolymer (FEP). The monomer composition (mass %) of FEP is preferably TFE:HFP=(60-95):(5-40), more preferably (85-92):(8-15).

[0130] In addition to TFE and HFP, other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, HFP, and other monomers as FEP. Examples of the other monomers include the above-mentioned fluorine-containing monomers (excluding TFE and HFP) and non-fluorine-containing monomers. One or more types of other monomers may be used. Perfluoro(alkyl vinyl ether) is preferred as the other monomer. The content of the other monomer units in FEP may be 0.1 to 2% by mass based on the total monomer units.

[0131] The manufacturing method of the present disclosure can also be used to produce TFE / perfluoro(alkyl vinyl ether) copolymers (PFA). The preferred monomer composition (mol %) of the TFE / perfluoro(alkyl vinyl ether) copolymer is TFE:perfluoro(alkyl vinyl ether)=(90-99.7):(0.3-10), more preferably (97-99):(1-3). The perfluoro(alkyl vinyl ether) is represented by the formula: CF2=CFORf 4 (In the formula, Rf 4 It is preferable to use one represented by a perfluoroalkyl group having 1 to 6 carbon atoms.

[0132] In addition to TFE and perfluoro(alkyl vinyl ether), other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, perfluoro(alkyl vinyl ether), and other monomers as a TFE / perfluoro(alkyl vinyl ether) copolymer. Examples of the other monomers include the above-mentioned fluorine-containing monomers (excluding TFE and perfluoro(alkyl vinyl ether)) and fluorine-free monomers. One or more types of other monomers may be used. The content of the other monomer units in the TFE / perfluoro(alkyl vinyl ether) copolymer may be 0.1 to 2% by mass based on the total monomer units.

[0133] (High molecular weight PTFE) According to the manufacturing method of the present disclosure, PTFE can be manufactured, and in particular, high-molecular-weight PTFE having high breaking strength can be manufactured.

[0134] In one embodiment, the PTFE obtained by the manufacturing method of the present disclosure has a standard specific gravity of 2.196 or less. The standard specific gravity may be 2.130 or more. The standard specific gravity is measured by the water displacement method according to ASTM D 792 using samples molded according to ASTM D 4895-89.

[0135] In one embodiment, the PTFE obtained by the manufacturing method of the present disclosure has a breaking strength of 15 N or more.

[0136] The breaking strength is measured by the following method. 21.7 g of lubricant (trade name: Isopar H®, Exxon) was added to 100 g of PTFE and mixed for 3 minutes in a glass bottle at room temperature. The glass bottle was then left at room temperature (25°C) for at least 1 hour before extrusion to obtain a lubricated resin. The lubricated resin was paste-extruded through an orifice (2.5 mm diameter, 11 mm land length, 30° entry angle) at room temperature at a reduction ratio of 100:1 to obtain a uniform bead. The extrusion speed was 20 inches / min. The lubricated PTFE extrusion bead obtained by the paste extrusion is dried at 230°C for 30 minutes, and the lubricant is removed from the bead to obtain a dried PTFE extrusion bead. The dried PTFE extrusion bead is then cut to an appropriate length, and each end is fixed to a clamp with a clamp spacing of 1.5 inches, and heated to 300°C in an air-circulating oven. The clamps are then separated at 1000% / second until a separation distance equivalent to 2400% is reached, and a stretch test is performed to obtain an expanded bead. The stretched bead is clamped between movable jaws having a gauge length of 5.0 cm and subjected to a tensile test at 25° C. and a rate of 300 mm / min. The strength at which the bead breaks is taken as the breaking strength.

[0137] In one embodiment, the PTFE obtained by the manufacturing method of the present disclosure has a bead elongation of 180% or more. The larger the bead elongation, the more preferable it is, with 200% or more being more preferable, 240% or more being even more preferable, 280% or more being even more preferable, and 320% or more being particularly preferable. The greater the bead elongation, the less likely the molded article will be cut or cracked during extrusion molding or molding into a composite membrane with other materials, allowing for more productive production and improving the handleability of the composite membrane.

[0138] The elongation is measured by the following method. 13.2 g of lubricant (trade name: Isopar E®, manufactured by Exxon) was added to 60 g of PTFE and mixed for 3 minutes in a glass bottle at room temperature. The glass bottle was then left at room temperature (25°C) for at least 1 hour before extrusion to obtain a lubricated resin. The lubricated resin was paste-extruded through an orifice at room temperature at a reduction ratio of 300:1 to obtain a uniform bead (extrusion product). The extrusion speed was 15 mm / min. The lubricant-containing extruded PTFE beads obtained by the paste extrusion described above are dried at 230° C. for 30 minutes to remove the lubricant from the beads, thereby obtaining dried extruded PTFE beads. The PTFE extrusion bead is set in a tensile tester with a chuck distance of 50 mm, and a tensile test is performed at 25°C and a speed of 300 mm / min. The elongation at the time when the bead breaks is taken as the bead elongation. The bead strength is calculated by dividing the maximum stress in the tensile test by the cross-sectional area of ​​the bead.

[0139] (Low molecular weight PTFE) The production method of the present disclosure makes it possible to produce PTFE, and in particular to produce an aqueous dispersion containing low-molecular-weight PTFE at a high concentration.

[0140] In one embodiment, the aqueous dispersion of low-molecular-weight PTFE obtained by the production method of the present disclosure contains 10% by mass or more of low-molecular-weight PTFE relative to the aqueous dispersion. The content of low-molecular-weight PTFE in the aqueous dispersion is preferably 13% by mass or more, more preferably 15% by mass or more, and may be 50% by mass or less.

[0141] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0142] <1> According to a first aspect of the present disclosure, A method for producing a fluoropolymer by polymerizing a fluoromonomer in the presence of a surfactant and an aqueous medium, comprising: The polymerization pressure is 1.5 MPaG or less, the surfactant is a carboxylic acid-type hydrocarbon surfactant, The surfactant is added before or simultaneously with the start of polymerization, and the surfactant is further added after the start of polymerization. A method of manufacture is provided. <2> According to a second aspect of the present disclosure, There is provided a production method according to a first aspect, wherein the concentration of the surfactant at the start of polymerization is less than 150 ppm by mass relative to the aqueous medium. <3> According to a third aspect of the present disclosure, There is provided a production method according to the first or second aspect, wherein the amount of the surfactant added after the initiation of polymerization is 100 to 5000 ppm by mass relative to the amount of the finally obtained fluoropolymer. <4> According to a fourth aspect of the present disclosure, There is provided a production method according to any one of the first to third aspects, wherein the fluoromonomer is tetrafluoroethylene. <5> According to a fifth aspect of the present disclosure, There is provided a production method according to any one of the first to fourth aspects, wherein the fluoropolymer is polytetrafluoroethylene. <6> According to a sixth aspect of the present disclosure, There is provided a production method according to any one of the first to fourth aspects, wherein the fluoropolymer is polytetrafluoroethylene, and the standard specific gravity of the polytetrafluoroethylene is 2.196 or less. <7> According to a seventh aspect of the present disclosure, In a sixth aspect, there is provided a method for producing the polytetrafluoroethylene, wherein the polytetrafluoroethylene has a breaking strength of 15 N or more. <8> According to an eighth aspect of the present disclosure, The sixth or seventh aspect of the present invention provides a production method in which the polytetrafluoroethylene has a bead elongation of 180% or more. <9> According to a ninth aspect of the present disclosure, The method according to any one of the first to fourth aspects is provided, wherein the fluoropolymer is low-molecular-weight polytetrafluoroethylene. <10> According to a tenth aspect of the present disclosure, A method for producing an aqueous dispersion containing the low-molecular-weight polytetrafluoroethylene as the fluoropolymer, comprising the steps of: A ninth aspect of the present invention provides a production method in which the content of the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion is 10% by mass or more. <11> According to an eleventh aspect of the present disclosure, The polymerization pressure is 1.0 MPaG or less, The surfactant is R-COO-M (α) (In the formula, R is a linear alkyl group having 5 to 23 carbon atoms which may contain an ether bond, or a branched alkyl group having 5 to 35 carbon atoms which may contain an ether bond, M is H, metal atom, NR 11 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, R 11 are the same or different and are H or an organic group having 1 to 10 carbon atoms. is a compound represented by the concentration of the surfactant at the start of polymerization is 5 ppm by mass or more and less than 150 ppm by mass with respect to the aqueous medium; the amount of the surfactant added after the initiation of polymerization is 20 to 5000 mass ppm relative to the amount of the finally obtained fluoropolymer, The fluoromonomer is tetrafluoroethylene or a fluoromonomer other than tetrafluoroethylene and tetrafluoroethylene, The fluoropolymer is polytetrafluoroethylene. According to any one of the first to fourth aspects, there is provided a manufacturing method. [Example]

[0143] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0144] The values ​​in the examples were measured by the following methods.

[0145] pH value The pH value was measured at 25°C using a HORIBA pH / ION METER F-72.

[0146] Average primary particle size Measurements were made using dynamic light scattering. Using the obtained PTFE powder, an aqueous dispersion of PTFE powder with a solids concentration of approximately 1.0% by mass was prepared, and measurements were made using an ELSZ-1000S (Otsuka Electronics Co., Ltd.) at 25°C, accumulating 70 times. The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPa·s.

[0147] Solids concentration of PTFE aqueous dispersion (fluoropolymer aqueous dispersion) 1 g of the PTFE aqueous dispersion (fluoropolymer aqueous dispersion) was dried in a blower dryer at 150°C for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion was expressed as a percentage and used as the value.

[0148] Standard specific gravity (SSG) Using samples molded in accordance with ASTM D 4895-89, measurements were made by the water displacement method in accordance with ASTM D 792.

[0149] HFP content The HFP content was determined by measuring the infrared absorbance of a thin film disk prepared by press molding the PTFE powder. -1 Absorbance at / 935cm -1 The absorbance ratio was calculated by multiplying the absorbance ratio by 0.3.

[0150] Peak Temperature A heat of fusion curve was drawn for the obtained PTFE powder using a TG / DTA (thermogravimetric / differential thermal analyzer) at a temperature rise rate of 10°C / min, and the temperature corresponding to the maximum value of the endothermic peak appearing on the heat of fusion curve was determined.

[0151] Extrusion pressure (A) 21.7 g of lubricant (trade name: Isopar H (registered trademark), manufactured by Exxon Chemical) was added to 100 g of the resulting PTFE powder and mixed in a glass bottle at room temperature for 3 minutes. The glass bottle was then left at room temperature (25°C) for at least 1 hour before extrusion to obtain a lubricated resin. The lubricated resin was paste-extruded through an orifice (diameter 2.5 mm, land length 11 mm, entrance angle 30°) at a reduction ratio of 100:1 at room temperature to obtain a uniform bead (extrusion molded product). The extrusion speed, i.e., ram speed, was 20 in / min (51 cm / min). The extrusion pressure was determined by measuring the load when the extrusion load reached equilibrium during paste extrusion and dividing the load by the cross-sectional area of ​​the cylinder used for paste extrusion.

[0152] Extension test The bead obtained by the above paste extrusion is heated at 230°C for 30 minutes to remove the lubricant from the bead. The bead (extrudate) is then cut to an appropriate length, clamped at each end with a clamp distance of 1.5 inches (38 mm), and heated to 300°C in an air-circulating oven. The clamps are then separated at a desired speed (stretch rate) until a separation distance corresponding to the desired stretch (total stretch) is reached, and a stretch test is performed. This stretching method essentially follows the method disclosed in U.S. Pat. No. 4,576,869, except for the extrusion speed (51 cm / min instead of 84 cm / min). "Stretch" refers to the increase in length due to stretching, usually expressed as a percentage of the original length. In this production method, the stretch rate is 1000% / sec, and the total stretch is 2400%. Stretched beads are thus obtained.

[0153] Breaking Strength The stretched beads (produced by stretching the beads) obtained in the above stretching test were subjected to a tensile test at 25°C and a speed of 300 mm / min, and the strength at break was measured as the breaking strength.

[0154] Extrusion pressure (B) 13.2 g of lubricant (trade name: Isopar E (registered trademark), manufactured by Exxon Chemical) was added to 60 g of the obtained PTFE and mixed in a glass bottle at room temperature for 3 minutes. The glass bottle was then left at room temperature (25°C) for at least 1 hour before extrusion to obtain a lubricated resin. The lubricated resin was paste-extruded through an orifice at room temperature at a reduction ratio of 300:1 to obtain a uniform bead (extrusion molded product). The extrusion speed was 15 mm / min. The extrusion pressure (B) was determined by measuring the load when the extrusion load reached equilibrium during paste extrusion and dividing it by the cross-sectional area of ​​the cylinder used for paste extrusion.

[0155] Bead elongation, bead strength The lubricant-containing PTFE extrusion bead obtained by the paste extrusion is dried at 230°C for 30 minutes, and the lubricant is removed from the bead to obtain a dried PTFE extrusion bead. The PTFE extrusion bead is set in a tensile tester with a chuck distance of 50 mm, and a tensile test is performed at 25°C and a speed of 300 mm / min. The elongation at the time the bead breaks is defined as the bead elongation. The bead strength is defined as the maximum stress in the tensile test divided by the cross-sectional area of ​​the bead.

[0156] Melt Viscosity According to ASTM D 1238, a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die were used, and a 2g sample preheated at 380°C for 5 minutes was measured under a load of 0.7 MPa while maintaining the temperature.

[0157] Preparation Example 1 9.9 g of lauric acid was added to 90.1 g of deionized water, and 12.0 g of a 10.0% aqueous solution of ammonia was gradually added thereto while stirring, to obtain an aqueous solution A.

[0158] Example 1: A 6-L stainless steel reactor was charged with 3560 g of deionized water, 180 g of paraffin wax, and 1.2 g of aqueous solution A obtained in Preparation Example 1. A 10.0% aqueous ammonia solution was then added to adjust the pH of the aqueous medium to 8.7. The reactor was sealed and heated to 65°C while stirring. The system was then purged with nitrogen to remove oxygen. The reactor was heated to 85°C, 2.0 g of HFP was added, and the pressure was increased to 0.78 MPaG with TFE. An aqueous polymerization initiator solution containing 0.61 g of ammonium persulfate (APS) dissolved in 20 g of deionized water was charged to the reactor. TFE was added to maintain a constant reaction pressure of 0.78 MPaG. When 143 g of TFE had been charged, stirring was stopped and the reactor was depressurized to atmospheric pressure. The reactor was immediately filled with TFE, and the reaction pressure was adjusted to 0.78 MPaG. Stirring was resumed to continue the reaction. Aqueous solution A was immediately and continuously charged into the reactor. Thereafter, an aqueous solution prepared by dissolving 0.22 g of ammonium persulfate (APS) in 10 g of deionized water at the time of charging 176 g of TFE, and an aqueous solution prepared by dissolving 36 mg of hydroquinone in 10 g of deionized water at the time of charging 437 g of TFE, were charged into the reactor.

[0159] When 1123 g of TFE was charged, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. By the end of the reaction, 54.7 g of aqueous solution A had been charged. The resulting aqueous dispersion was removed from the reactor and cooled, after which the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 203 nm, and the solids concentration was 23.7 mass%.

[0160] The resulting PTFE aqueous dispersion was coagulated under high-speed stirring conditions, and the water was separated. The coagulated wet powder was dried at 160°C for 18 hours. The resulting PTFE powder had an SSG of 2.196, an HFP modification amount of 0.06% by mass, and a peak temperature of 340°C. The physical properties of the resulting PTFE powder are shown in Table 1 below.

[0161] Example 2: A 6-L stainless steel reactor was charged with 3560 g of deionized water, 180 g of paraffin wax, and 2.0 g of aqueous solution A obtained in Preparation Example 1. A 10.0% aqueous solution of ammonia was then added to adjust the pH of the aqueous medium to 8.7. The reactor was sealed and heated to 65°C while stirring. The system was then purged with nitrogen to remove oxygen. The reactor was heated to 85°C, 2.0 g of HFP was added, and the pressure was increased to 0.78 MPaG with TFE. An aqueous polymerization initiator solution containing 0.61 g of ammonium persulfate (APS) dissolved in 20 g of deionized water was charged to the reactor to initiate polymerization. TFE was then added to maintain a constant reaction pressure of 0.78 MPaG. When 143 g of TFE had been charged, stirring was stopped and the pressure was reduced to atmospheric pressure. The reactor was immediately filled with TFE, and the reaction pressure was adjusted to 0.78 MPaG. Stirring was resumed to continue the reaction. Aqueous solution A was immediately and continuously charged into the reactor. After that, when 437 g of TFE was charged, an aqueous solution of 36 mg of hydroquinone dissolved in 10 g of deionized water was charged into the reactor.

[0162] When 1212 g of TFE was charged, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. By the end of the reaction, 54.7 g of aqueous solution A had been charged. The resulting aqueous dispersion was removed from the reactor and cooled, after which the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the resulting aqueous PTFE dispersion was 229 nm, and the solids concentration was 25.1 mass%.

[0163] The resulting PTFE aqueous dispersion was coagulated under high-speed stirring conditions, and the water was separated. The coagulated wet powder was dried at 160°C for 18 hours. The resulting PTFE powder had an SSG of 2.189, an HFP modification amount of 0.04% by mass, and a peak temperature of 342°C. The physical properties of the resulting PTFE powder are shown in Table 1 below.

[0164] Comparative Example 1 A 6-L stainless steel reactor was charged with 3560 g of deionized water, 180 g of paraffin wax, and 6.1 g of aqueous solution A obtained in Preparation Example 1. A 10.0% aqueous ammonia solution was then added to adjust the pH of the aqueous medium to 8.7. The reactor was sealed and heated to 65°C while stirring. The system was then purged with nitrogen to remove oxygen. The reactor was heated to 85°C, 7.1 g of HFP was added, and the pressure was increased to 2.70 MPaG with TFE. 20 g of an aqueous polymerization initiator solution containing 0.61 g of ammonium persulfate (APS) dissolved in 20 g of purified water was charged to the reactor. TFE was added to maintain a constant reaction pressure of 2.70 MPaG. When 143 g of TFE had been charged, stirring was stopped and the reactor was depressurized to atmospheric pressure. The reactor was immediately filled with TFE, and the reaction pressure was adjusted to 2.70 MPaG. After 20 g of an aqueous solution containing 0.144 g of disuccinic acid peroxide was added to the reactor, stirring was resumed to continue the reaction, and at the same time, aqueous solution A was immediately and continuously added to the reactor.

[0165] When 1687 g of TFE was charged, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. By the end of the reaction, 66.7 g of aqueous solution A had been charged. The resulting aqueous dispersion was removed from the reactor and cooled, after which the paraffin wax was separated to obtain an aqueous PTFE dispersion. The resulting aqueous PTFE dispersion had an average primary particle size of 195 nm and a solids concentration of 31.7 mass%.

[0166] The resulting PTFE aqueous dispersion was coagulated under high-speed stirring conditions, and the water was separated. The coagulated wet powder was dried at 160°C for 18 hours. The resulting PTFE powder had an SSG of 2.176, an HFP modification amount of 0.03% by mass, and a peak temperature of 342°C. The physical properties of the resulting PTFE powder are shown in Table 1 below.

[0167] Comparative Example 2 The solidified wet powder obtained in Comparative Example 1 was dried for 18 hours at 240° C. The physical properties of the obtained PTFE powder are shown in Table 1 below.

[0168] Example 3: 3280 g of deionized water and 1.9 g of aqueous solution A obtained in Preparation Example 1 were added to a 6 L stainless steel autoclave. A 10.0% aqueous ammonia solution was then added to adjust the pH of the aqueous medium to 8.7. The reactor was sealed and heated to 65°C with stirring. The system was then purged with nitrogen to remove oxygen. The reactor was heated to 70°C and pressurized with TFE to 0.78 MPaG. 0.17 g of propane was added, and an aqueous polymerization initiator solution containing 1.65 g of ammonium persulfate (APS) dissolved in 20 g of deionized water was added to the reactor to initiate polymerization. TFE was added to maintain a constant internal pressure of 0.78 MPaG during the reaction.

[0169] When 100 g of TFE was charged, 1.9 g of aqueous solution A was charged, when 200 g of TFE was charged, 1.9 g of aqueous solution A was charged, and when 330 g of TFE was charged, 3.7 g of aqueous solution A was charged.

[0170] When 660 g of TFE had been charged, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. The resulting aqueous dispersion was removed from the reactor, yielding a PTFE aqueous dispersion. Only traces of polymer adhered to the reactor were observed. The resulting PTFE aqueous dispersion had an average primary particle size of 206 nm and a solids concentration of 16.4 mass%. The resulting PTFE aqueous dispersion was coagulated under high-speed stirring conditions, and the water was separated. The coagulated wet powder was dried at 100°C for 18 hours. The resulting PTFE powder had a peak temperature of 326°C and a melt viscosity of 299,000 Pa·s.

[0171] The results of measuring the physical properties of the powders obtained in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0172] [Table 1]

Claims

1. A method for producing a fluoropolymer by polymerizing a fluoromonomer in the presence of a surfactant and an aqueous medium, comprising: The polymerization pressure is 1.5 MPaG or less, the surfactant is a carboxylic acid-type hydrocarbon surfactant, The surfactant is added before or simultaneously with the start of polymerization, and the surfactant is further added after the start of polymerization. Manufacturing method.

2. 2. The production method according to claim 1, wherein the concentration of the surfactant at the start of polymerization is less than 150 ppm by mass relative to the aqueous medium.

3. 3. The production method according to claim 1, wherein the amount of the surfactant added after the initiation of polymerization is 100 to 5,000 ppm by mass based on the amount of the finally obtained fluoropolymer.

4. 3. The method according to claim 1, wherein the fluoromonomer is tetrafluoroethylene.

5. 3. The method according to claim 1, wherein the fluoropolymer is polytetrafluoroethylene.

6. 3. The method according to claim 1, wherein the fluoropolymer is polytetrafluoroethylene, and the standard specific gravity of the polytetrafluoroethylene is 2.196 or less.

7. The method according to claim 6, wherein the polytetrafluoroethylene has a breaking strength of 15 N or more.

8. 7. The method according to claim 6, wherein the polytetrafluoroethylene has a bead elongation of 180% or more.

9. 3. The method according to claim 1, wherein the fluoropolymer is a low molecular weight polytetrafluoroethylene.

10. A method for producing an aqueous dispersion containing the low-molecular-weight polytetrafluoroethylene as the fluoropolymer, comprising the steps of: The method according to claim 9, wherein the content of the low-molecular-weight polytetrafluoroethylene in the aqueous dispersion is 10% by mass or more.

11. The polymerization pressure is 1.0 MPaG or less, The surfactant is R-COO-M (α) (In the formula, R is a linear alkyl group having 5 to 23 carbon atoms which may contain an ether bond, or a branched alkyl group having 5 to 35 carbon atoms which may contain an ether bond, M is H, a metal atom, or NR １１ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, R １１ are the same or different and are H or an organic group having 1 to 10 carbon atoms. is a compound represented by the concentration of the surfactant at the start of polymerization is 5 ppm by mass or more and less than 150 ppm by mass with respect to the aqueous medium; the amount of the surfactant added after the initiation of polymerization is 20 to 5000 mass ppm relative to the amount of the finally obtained fluoropolymer, The fluoromonomer is tetrafluoroethylene or a fluoromonomer other than tetrafluoroethylene and tetrafluoroethylene, The fluoropolymer is polytetrafluoroethylene. The method according to claim 1 or 2.

Images