Shear-stable aqueous fluororesin dispersion

Abstract

The present invention relates to an aqueous fluororesin suspension having shear stability of a fluororesin having a particle size of less than 120 nm, a solid content of more than 25% by weight, a melt viscosity of more than 20 kP, and shear stability of more than 20 minutes at 1500 rpm, preferably polyvinylidene fluoride (PVDF), and a method for producing the fluororesin suspension.

Description

[Technical Field]

[0001] Description of research or development supported by the federal government. This application was made with government support under DE-EE0009106, granted by the U.S. Department of Energy. The government has certain rights to this invention.

[0002] Field of Invention The present invention relates to an aqueous fluororesin dispersion having shear stability and a method for producing the dispersion. [Background technology]

[0003] Fluorocarbon polymers have been used extensively in recent years. For example, polyvinylidene fluoride (PVDF) polymers, as homopolymers, copolymers, or alloys, are melt-processable resins that can be formed into polymer structures through various processes such as extrusion molding, injection molding, fiber spinning, extrusion blow molding, and blown film formation. Due to their low surface energy and phase behavior, fluorocarbon polymers are also used as polymer processing aids. Most fluorocarbon polymers are produced by emulsion polymerization followed by energy-intensive separation processes, resulting in high carbon dioxide emissions.

[0004] Fluorocarbon polymers, particularly PVDF, are gaining increasing importance in the renewable energy sector as binders for lithium-ion battery electrodes due to their excellent electrochemical resistance, outstanding adhesion, and flexibility. PVDF has been found to be a useful binder for forming electrodes used in non-aqueous electrolytic devices. U.S. Patents 5,776,637, 6,200,703, and 9,434,797 (as incorporated herein by reference) describe PVDF binder solutions in organic solvents, along with powdered electrode materials used in forming electrodes for non-aqueous batteries. Conventional solvent casting processes use large amounts of N-methyl-2-pyrrolidone (NMP) solvent as the dispersion medium. There is a need for environmentally and safety-conscious methods to produce superior electrodes without using large amounts of organic solvents.

[0005] On the other hand, fluoropolymers are gaining importance as exterior coatings because they possess not only excellent resistance to UV-A and UV-B rays, but also resistance to many corrosive chemicals. PVDF-based coatings are generally applied using high levels of organic solvents necessary to dissolve the acrylic and disperse the PVDF. These organic solvents are typically hazardous in terms of safety, health, and the environment, and are often regulated. Organic solvents are generally toxic and flammable, requiring special manufacturing controls to mitigate risks and reduce environmental pollution from organic solvents. In addition, the use of solvent-based coatings is undesirable from an environmental perspective due to the large amount of carbon dioxide emissions involved.

[0006] The polymerization rate of fluorinated monomers is substantially different from that of non-fluorinated monomers. Therefore, fluorinated emulsifiers have traditionally been used in fluorinated emulsion processes. Fluorinated emulsifiers are often referred to as "eternal chemicals" due to their environmental persistence and the fact that they are banned in many jurisdictions. Non-fluorinated emulsifiers are known to be used in the polymerization of fluororesins. However, these do not provide dispersions with the shear stability offered by the present invention.

[0007] Aqueous dispersions of fluororesins are highly unstable, tending to solidify when sheared and settling violently during storage. The main difference between fluororesins and acrylic dispersions is that fluororesins have a higher specific gravity, which varies depending on the degree of crystallinity. For example, the specific gravity of PVDF is 1.74-2.00 g / cm³. 3 The specific gravity of PTFE is 2.00-2.35 g / cm³. 3 It fluctuates within this range. As a result, fluororesin dispersions tend to settle quickly due to their specific gravity. Furthermore, the amorphous phase of fluororesins has a low glass transition temperature (Tg); for example, the Tg of PVDF is -40°C and the Tg of PTFE is -73°C. Consequently, when fluororesin particles in aqueous dispersions collide with each other due to Brownian motion and shear mixing, the particles tend to aggregate, and eventually the dispersion solidifies and becomes unusable. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 5,776,637 [Patent Document 2] U.S. Patent No. 6,200,703 [Patent Document 3] U.S. Patent No. 9,434,797 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] There is a need for more environmentally friendly and sustainable aqueous dispersions of fluoropolymers that can be used or formulated for the manufacture of coatings and films from aqueous formulations, while maintaining higher shear stability and matching the excellent properties of solution casting. Therefore, there is a demand to improve the storage stability and shear stability of aqueous fluoropolymer dispersions so that they can be used effectively in aqueous applications. [Means for solving the problem]

[0010] Summary of the Invention The present invention relates to an aqueous fluororesin dispersion, a. Fluororesin has an average particle size of less than 120 nm. b. Solids content exceeding 25% by weight, c. Melt viscosity exceeding 20kP, and d. Shear stability exceeding 20 minutes at 1500 rpm This relates to an aqueous fluororesin dispersion containing the following:

[0011] The present invention also relates to an emulsification process for producing fluororesin dispersions. The use of emulsifiers, stabilizers, and polymerization initiators in the polymerization process are important for producing stable fluororesin dispersions. The present invention provides stable fluororesin dispersions, and also provides a method for synthesizing a stable fluororesin in an aqueous reaction medium, comprising: (a) forming an aqueous emulsion containing at least two nonionic emulsifiers and at least one fluorine-containing monomer; (b) initiating polymerization of the fluorine-containing monomer using a desired initiator; and (c) continuously supplying at least one stabilizer after polymerization has started, during the reaction, or after polymerization has finished. This method uses at least two emulsifiers, namely an acrylic glycol ester and a nonionic block copolymer containing at least two blocks selected from polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Stabilizers are also used to produce the aqueous fluororesin dispersions of the present invention.

[0012] Aqueous fluoropolymer dispersions can be used directly in sustainable processes without the need for isolation. Articles manufactured with aqueous fluoropolymers are more environmentally friendly and sustainable than similar organic solvent-based processes, i.e., the manufacture of electrodes used in non-aqueous electrochemical devices such as batteries and electric double-layer capacitors or coatings for various substrates.

[0013] The fluororesin dispersion of the present invention does not contain fluorinated surfactants, which are often referred to as "eternal chemical substances."

[0014] Embodiments of the Invention Aspect 1 of the present invention provides an aqueous fluororesin dispersion containing a fluororesin, where the fluororesin has an average particle diameter of less than 120 nm, 230 °C and 100 seconds -1 and has a melt viscosity of at least 20 kP or more, the above dispersion has a solid content of at least 25% by weight, and has a Brookfield viscosity of less than 1000 cP after shearing for at least 20 minutes at 1500 rpm.

[0015] Embodiment 2 is the aqueous fluororesin dispersion of Embodiment 1, wherein the fluororesin contains at least 60% by weight of VDF monomer units, preferably at least 70% by weight of VDF monomer units.

[0016] Embodiment 3 is the aqueous fluororesin dispersion of Embodiment 1 or 2, wherein the fluororesin contains at least comonomer units selected from the group consisting of monomer units of HFP, CTFE, PMVE, PPVE, TFE, 2,3,3,3 - tetrafluoropropene, preferably containing HFP.

[0017] Embodiment 4 is the aqueous fluororesin dispersion according to any one of Embodiments 1 to 3, having an average particle diameter of less than 100 nm.

[0018] Embodiment 5 is the aqueous fluororesin dispersion according to any one of Embodiments 1 to 4, containing (1) an acrylic glycol ester, preferably at least one selected from polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), or polypropylene glycol methacrylate (PPGMA); (2) a non - ionic block copolymer emulsifier containing at least two blocks of polyethylene glycol, polypropylene glycol and / or polytetramethylene glycol; and (3) a stabilizer.

[0019] Embodiment 6 is an aqueous fluororesin dispersion of Embodiment 5, wherein the fluororesin comprises polyvinylidene fluoride having at least 60% by weight of VDF monomer units, the acrylic glycol ester is selected from polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), and polypropylene glycol methacrylate (PPGMA), and the nonionic block copolymer emulsifier comprises at least one block of polyethylene glycol and at least one block of polypropylene glycol.

[0020] Embodiment 7 is an aqueous fluororesin dispersion according to any one of Embodiments 1 to 6, wherein the fluororesin comprises at least one non-fluorinated monomer having at least one reactive double bond and an ionic moiety.

[0021] Embodiment 8 is an aqueous fluororesin dispersion according to any one of Embodiments 5 to 7, further comprising a stabilizer, the stabilizer comprising a non-fluorinated oligomer containing at least one ionic moiety, preferably an acidic moiety.

[0022] Embodiment 9 is an aqueous fluororesin dispersion according to any one of Embodiments 5 to 8, further comprising a stabilizer, the stabilizer comprising at least one alkyl sulfate or alkyl sulfonate, wherein the alkyl group is a C6-C18 alkyl group.

[0023] Embodiment 10 is a method for producing a shear-stable aqueous fluororesin dispersion having a particle size of less than 120 nm, comprising the following steps: (a) Prepare in a reaction vessel an aqueous reaction medium, at least one fluorine-containing monomer, at least one acrylic glycol ester, and at least one nonionic emulsifier selected from polyethylene glycol, polypropylene glycol and / or polytetramethylene glycol, having at least two blocks with 2 to 200 repeating units per block, (b) The fluorine-containing monomer of (a) is polymerized in the presence of at least one initiator, wherein the amount of initiator added to the polymerization is at least 1500 ppm based on the weight of the fluorine-containing monomer added to the polymerization, and (c) Adding at least one stabilizer to the fluororesin dispersion during or after polymerization. This provides a method that includes [something].

[0024] Embodiment 11 is the method of Embodiment 10, wherein the fluorine-containing monomer includes a vinylidene fluoride monomer.

[0025] Embodiment 12 is the method of Embodiment 10 or 11, wherein the glycol-based acrylic emulsifier comprises at least one of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), or polypropylene glycol methacrylate (PPGMA).

[0026] Embodiment 13 is the method according to any one of Embodiments 10 to 12, wherein the amount of glycol-based acrylic emulsifier added to the polymerization is 0.05 to 5% by weight, preferably 0.1 to 2% by weight, based on the total fluorine monomers added to the polymerization.

[0027] Embodiment 14 is the method according to any one of Embodiments 10 to 13, wherein the stabilizer comprises at least one alkyl sulfate or alkyl sulfonate.

[0028] Embodiment 15 is the method according to any one of Embodiments 10 to 13, wherein the stabilizer is selected from the group consisting of C6-C18 alkyl sulfonates, C6-C18 alkyl sulfates, C6-C18 alkyl disulfonates, C6-C18 alkyl disulfates, and mixtures thereof.

[0029] Embodiment 16 is the method of Embodiment 14, wherein a stabilizer containing at least one alkyl sulfate or alkyl sulfonate is added after polymerization is complete, or after at least 50% by weight of the fluorinated monomer has been supplied to the reactor, preferably after at least 75% by weight of the fluorinated monomer has been supplied to the reactor.

[0030] Embodiment 17 is the method of Embodiment 14, wherein a stabilizer containing at least one alkyl sulfate or alkyl sulfonate is added in an amount of 0.1 to about 5% by weight based on the total weight of fluorine-containing monomers added to the polymerization.

[0031] Embodiment 18 is the method according to any one of Embodiments 10 to 13, wherein the stabilizer comprises an oligomer containing an ionic monomer unit having an acid group, preferably a carboxylic acid group.

[0032] Embodiment 19 is the method according to any one of Embodiments 10 to 13, wherein the stabilizer is selected from the group consisting of polyacrylic acid oligomers, poly(meth)acrylic acid oligomers, oligomers containing maleic acid monomer units, and any of the aforementioned co-oligomers and combinations thereof.

[0033] Embodiment 20 is the method of Embodiment 18, wherein the stabilizer is added after at least 30% by weight of the fluorinated monomer has been supplied to the reactor, preferably after at least 50% by weight of the fluorinated monomer has been supplied to the reactor.

[0034] Embodiment 21 is the method of Embodiment 18, wherein a stabilizer containing an oligomer having an acidic group-containing ionic monomer unit is added in an amount of 0.1 to about 2.5% by weight, based on the total fluorine-containing monomers added to the polymerization.

[0035] Embodiment 22 is the method according to any one of Embodiments 10 to 13, wherein the stabilizer comprises a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety, preferably the ionic moiety being an acidic moiety or a salt thereof.

[0036] Embodiment 23 is the method according to any one of Embodiments 10 to 13, wherein the stabilizer is selected from the group consisting of acrylic acid, methacrylic acid, salts of styrene sulfonic acid, alkyl methacrylate phosphate, 2-acrylamido-2-methylpropanesulfonic acid, β-carboxyethyl acrylate, and combinations thereof.

[0037] Embodiment 24 is the method of Embodiment 22, wherein a stabilizer containing a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety is added during polymerization, preferably after at least 15% by weight of fluorinated monomers have been supplied to the reactor, and more preferably after at least 30% by weight of fluorinated monomers have been supplied to the reactor.

[0038] Embodiment 25 is the method of Embodiment 22, wherein a stabilizer containing a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety is added in an amount of 0.1 to about 1.5% by weight based on the total monomers added to the polymerization.

[0039] In embodiments of the method, the stabilizer may include one or more of the following: an alkyl sulfate or alkyl sulfonate, an oligomer containing an ionic monomer unit having an acid group, a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety, or a combination thereof.

[0040] Another embodiment of the present invention is an aqueous fluororesin dispersion comprising: (1) a vinylidene fluoride polymer having at least 60% by weight of vinylidene fluoride monomer units; (2) an acrylic glycol ester, preferably comprising at least one of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), or polypropylene glycol methacrylate (PPGMA); (3) a nonionic block copolymer emulsifier comprising at least two blocks of polyethylene glycol, polypropylene glycol, and / or polytetramethylene glycol; and (4) a stabilizer, wherein the fluororesin has an average particle size of less than 120 nm, and is conditioned at 230°C and 100 seconds. -1 It has a melt viscosity of at least 20 kP, The above dispersion is an aqueous fluororesin dispersion having a solid content of at least 25% by weight and a Brookfield viscosity of less than 1000 cP after shearing at 1500 rpm for at least 20 minutes. The stabilizer comprises a non-fluorinated oligomer containing at least one ionic moiety, preferably an acidic moiety, or the stabilizer comprises at least one alkyl sulfate or alkyl sulfonate, wherein the alkyl group is a C6-C18 alkyl group. The fluororesin may contain at least one non-fluorinated monomer having at least one reactive double bond and an ionic moiety. [Modes for carrying out the invention]

[0041] The documents cited herein are incorporated herein by reference.

[0042] In this specification, percentages are weight percentages (W%) unless otherwise specified, and molecular weights are weight-average molecular weights (Mw) unless otherwise specified. Amounts expressed as "ppm" are weight-based amounts. Molecular weight is measured by gel permeation chromatography (GPC) using PMMA (polymethyl methacrylate) reference material.

[0043] The melt viscosity was determined according to ASTM D3835 at 230°C and a shear rate of 100 seconds. -1 and 4 seconds -1 It is measured by capillary rheometry.

[0044] The term "fluororesin" refers to polymers and copolymers (including polymers having two or more different monomers, such as ternary copolymers) that contain at least 50 mol% of fluorine-containing monomer units. Copolymers may be homogeneous, heterogeneous, or random, and the distribution of comonomer units may have a gradient.

[0045] The term "copolymer" is used to mean a polymer having two or more distinct monomer units, including ternary copolymers and higher-order polymers. The term "polymer" is used to mean both homopolymers and copolymers.

[0046] "PVDF" stands for polyvinylidene fluoride, and unless otherwise specified, includes both homopolymers and copolymers. "VDF" stands for vinylidene fluoride.

[0047] A dispersion refers to a dispersion or suspension of polymer particles in water. No oil phase or other organic phases are present.

[0048] Solids refer to the substance remaining after the dispersion has been dried. The solids content of the aqueous dispersion was measured by gravimetric analysis using a Mettler Toledo HG63 moisture meter.

[0049] The present invention provides a fluororesin dispersion having shear stability, a particle size of less than 120 nm, a solids content of more than 25%, and a melt viscosity of more than 20 kP. The aqueous fluororesin dispersion of the present invention is suitable for direct use in applications such as coating various substrates or casting aqueous electrodes for lithium-ion batteries, without the use of fluorinated surfactants. Therefore, the fluororesin dispersion of the present invention is manufactured using a combination of particle size, a suitable emulsifier, and a stabilizer (detailed below).

[0050] The present invention also provides a method for producing the fluororesin dispersion of the present invention. A general process for synthesizing the stable fluororesin of the present invention includes (a) forming an aqueous emulsion comprising at least one nonionic glycol-based acrylic emulsifier, at least one nonionic emulsifier, and at least one fluorine-containing monomer; (b) initiating polymerization of the fluorine-containing monomer using a persulfate initiator; and (c) after polymerization has been initiated, simultaneously supplying at least one stabilizer during the reaction or adding a stabilizer after polymerization has been completed.

[0051] Polymerization process The polymerization reaction according to the present invention can be carried out by adding water (preferably deionized water), at least one nonionic glycol-based acrylic emulsifier, at least one nonionic emulsifier (different from the glycol-based acrylic emulsifier), at least one fluorine-containing monomer, and optionally a chain transfer agent and / or antifouling agent to a reactor. Air may be purged from the reactor before introducing the fluorine-containing monomer. Water is generally added before heating the reactor to the desired starting temperature, but other materials can be added before or after the reactor reaches that temperature. At least one persulfate radical initiator is added to start and maintain polymerization. Additional monomers may be optionally added to replenish consumed monomers, and other materials may also be optionally added during the polymerization process for the purpose of maintaining the reaction and controlling the properties of the final product. Stabilizers are generally added during or after polymerization.

[0052] Fluorine-containing monomers Fluorine-containing monomers are used to obtain the fluororesin of the present invention. In the present invention, "fluorine-containing monomer" means a fluorinated monomer having an unsaturated carbon-carbon double bond that can undergo free radical polymerization.

[0053] Preferably, the fluororesin of the present invention comprises a vinylidene fluoride polymer having at least 60% by weight of VDF units, preferably 70% by weight of VDF units.

[0054] Examples of vinylidene fluoride copolymers include those containing at least 60% by weight of vinylidene fluoride copolymerized with at least one copolymer. Fluorinated monomers include tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), perfluorobutylethylene (PFBE), hexafluoropropene (HFP), vinyl fluoride (VF), pentafluoropropene, 2,3,3,3-tetrafluoropropene, trifluoropropene, fluorinated (alkyl) vinyl ethers, such as perfluoroethyl vinyl ether (PEVE) and perfluoro-2-propoxypropyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutyl vinyl ether (PBVE), and long-chain perfluorinated vinyl ethers. The following can be selected: one or more partially fluorinated or fully fluorinated α-olefins, for example, 3,3,3-trifluoro-1-propene, 2-trifluoromethyl-3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 3,3,3,4,4-pentafluoro-1-butene, hexafluoroisobutylene (HFIB), fluorinated dioxoles, for example, perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), partially fluorinated or perfluorinated α-olefins of C4 or higher, partially fluorinated or perfluorinated cyclic alkenes of C3 or higher, partially fluorinated allyls, or fluorinated allyl monomers, and combinations thereof.

[0055] Other monomer units in these polymers may include any monomer containing a polymerizable C=C double bond that copolymerizes with the VDF monomer. Possible additional monomers include 2-hydroxyethyl allyl ether, 3-allyloxypropanediol, allyl monomers, ethane, propene, acrylic acid, and methacrylic acid.

[0056] Preferred fluorinated copolymers are tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, 2,3,3,3-tetrafluoropropylene, vinyl fluoride, pentafluoropropene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether. The most preferred is hexafluoropropene.

[0057] emulsifier This invention uses an emulsifier.

[0058] Examples of emulsifiers used in the present invention include, but are not limited to, nonionic block copolymers comprising at least two blocks selected from polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, with 2 to 200 repeating units, preferably 5 to 100, per block. These emulsifiers do not have carbon double bonds that can undergo free radical polymerization. These emulsifiers do not have acrylate groups or methacrylate groups. The terminal groups of these block copolymers are preferably selected from hydrogen, hydroxyl groups, carboxyl groups, ester groups, ether groups, and / or hydrocarbon groups. Examples of block copolymers include polyethylene oxide (PEO) and polypropylene oxide (PPO) arranged in an AB (2-block) or ABA (3-block) structure, with 2 to 200 repeating units, preferably 5 to 100, per block. Particularly preferred emulsifiers within this group include PEG and PPG blocks, such as polypropylene glycol-block-polyethylene glycol PPO-PEO, polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol "PPO-PEO-PPO", or block-polyethylene glycol-block-polypropylene glycol-block-polyethylene glycol "PEO-PPO-PEO". These nonionic block emulsifiers do not contain reactive double bonds and therefore cannot undergo free radical polymerization.

[0059] A second group of non-fluorinated nonionic emulsifiers useful in the present invention includes, but is not limited to, acrylic glycol esters having an unsaturated carbon-carbon double bond capable of undergoing radical polymerization, preferably an acrylate group or a methacrylate group, and containing segments of polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), or combinations thereof, preferably containing 3 to 100 repeating units, more preferably 3 to 50 repeating units. Examples of acrylic glycol esters used in the present invention include, but is not limited to, polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEG-MA), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPGMA), and the like.

[0060] The chemical structure of the nonionic acrylic glycol ester emulsifier of the present invention preferably has properties such as water solubility, and it is preferable that a fluororesin dispersion with a particle size of less than 120 nm can be obtained.

[0061] The total amount of emulsifier used is at a level of 100 ppm to 5% by weight, preferably 100 ppm to 3% by weight, and more preferably 1000 ppm to 1% by weight, based on the total fluorine-containing monomers added to the polymerization.

[0062] In the polymerization process, the nonionic emulsifier of the present invention may be added in its entirety all at once before polymerization, continuously supplied during polymerization, or partially supplied before polymerization and then supplied during polymerization.

[0063] Initiator The terms "initiator," "radical initiator," and "free radical initiator" refer to chemical substances that can spontaneously generate free radicals or become a source of free radicals through exposure to heat or light. The amount of initiator added to the reaction mixture (expressed in ppm based on the total weight of fluorine-containing monomers added to polymerization) can be 1500 ppm to 1.0 wt%, preferably 2000 ppm to 1.0 wt%. Preferred radical initiators may include persulfates such as sodium persulfate, potassium persulfate, potassium persulfate, or ammonium persulfate. The amount of persulfate added to the reaction mixture (based on the total weight of fluorine-containing monomers added to polymerization) can be, for example, about 1500 ppm to about 1.0 wt%, preferably 2000 ppm to 1.0 wt%. The terms "radical" and "free radical" refer to chemical species containing at least one unpaired electron. The radical initiator is added to the reaction mixture in an amount sufficient to initiate the polymerization reaction and maintain the polymerization reaction rate. The order of addition can be modified depending on the desired process and the characteristics of the dispersed emulsion. In some embodiments of the present invention, the initiation system does not contain a reducing agent, and most preferably does not use a reducing agent.

[0064] Radical initiators may include a redox system. A "redox system," as understood by those skilled in the art, means a system comprising an oxidizing agent, a reducing agent, and optionally an accelerator as an electron transport medium. Examples of oxidizing agents include persulfates, peroxides, and oxidizing metal salts such as ferric sulfate. Examples of reducing agents include sodium formaldehyde sulfoxylate, sodium sulfite and potassium sulfite, ascorbic acid, bisulfite, metabisulfite, and reducing metal salts. Accelerators are components of the redox system and, depending on their oxidation state, can react with both the oxidizing and reducing agents to accelerate the overall reaction. Examples of accelerators include transition metal salts such as ferrous sulfate. In the redox system, the oxidizing and reducing agents can be used in amounts of about 0.01 to about 0.5% by weight, based on the total fluorine monomers added to the polymerization. Optional accelerators can be used in amounts of about 0.005 to about 0.025% by weight, based on the total fluorine monomers. Redox systems are described, for example, in GSMisra and UDNBajpai, Prog.Polym.Sci., 1982, 8(1-2), pp.61-131.

[0065] Stabilizer The term "stabilizer" refers to a molecule or oligomer (a low molecular weight water-soluble polymer with a molecular weight of less than 10,000 g / mol) that provides stability to fluororesin particles such as PVDF in an aqueous medium and protects them from aggregation or floc formation during shearing or vigorous mixing. Surprisingly, the inventors have found that introducing the stabilizer according to the present invention into a fluororesin dispersion significantly improves the shear stability of the dispersion. The stabilizer of the present invention is described below.

[0066] The stabilizer may be used in the form of an aqueous solution or other form to facilitate handling.

[0067] The first category of stabilizers consists of molecules that have both hydrophobic and hydrophilic parts, which can stabilize and disperse hydrophilic molecules and aggregate hydrophobic molecules in aqueous media. Examples of stabilizers include those in which an alkyl or aryl group is bonded to a sulfonic acid group, sulfate group, phosphonic acid group, phosphate group, or carboxylic acid group. These acidic groups generally exist in salt form.

[0068] A first category of preferred stabilizers for the fluororesin dispersion of the present invention includes alkyl sulfate and alkyl sulfonate stabilizers. "Alkyl sulfate stabilizer" or "alkyl sulfonate stabilizer" means a stabilizer having an alkyl hydrocarbon group, preferably a C6-C18 alkyl hydrocarbon group, as the hydrophobic portion, and an alkyl sulfate group or alkyl sulfonate group as the hydrophilic portion. The hydrocarbon group does not contain fluorine. Preferred stabilizers in the first category are in salt form, with a counterion of an alkali metal (i.e., lithium, sodium, or potassium), an ammonium ion, or an alkyl-substituted ammonium ion.

[0069] Examples of alkyl sulfate stabilizers used in the present invention include, but are not limited to, ammonium salts, lithium salts, sodium salts, or potassium salts of alkyl sulfates. Examples of alkyl sulfate stabilizers include, but are not limited to, salts of C6-C18 alkyl sulfates such as lauryl sulfate and octyl sulfate. Examples include, but are not limited to, sodium lauryl sulfate (SLS), potassium lauryl sulfate (KLS), ammonium lauryl sulfate, lithium lauryl sulfate (ALS), sodium laureth sulfate, sodium octyl sulfate, potassium octyl sulfate, ammonium octyl sulfate, lithium octyl sulfate, and mixtures thereof.

[0070] Examples of alkyl sulfonate surfactants include, but are not limited to, C6-C18 alkyl sulfonates, C6-C18 alkyl disulfonates, and mixtures thereof. Typical counterions of alkyl sulfonate surfactants include, but are not limited to, sodium, potassium, lithium, ammonium, or alkyl-substituted ammonium. For example, salts of C8-C12 alkyl sulfonic acids such as octyl sulfonate, octyl disulfonate, decyl sulfate, decyl disulfate, dodecyl sulfonate, dodecyl disulfonate, and combinations thereof can be used. For example, sodium octyl sulfonate, potassium octyl sulfonate, ammonium octyl sulfonate, alkyl-substituted ammonium octyl sulfonate, and lithium octyl sulfonate can be used. As an example, sodium octyl sulfonate (SOS) is a stabilizer used in the present invention.

[0071] Alkyl sulfate or alkyl sulfonate stabilizers are used in an amount of about 0.01 to about 10% by weight based on the total fluorine-containing monomers added to the polymerization. Preferably, they are used in an amount of about 0.1 to about 5% by weight, more preferably about 0.1 to 2.5% by weight based on the total fluorine-containing monomers. These stabilizers are added after polymerization is complete, or after at least 50% by weight of the fluorinated monomers has been supplied to the reactor, preferably after at least 75% by weight of the fluorinated monomers has been supplied to the reactor.

[0072] A second category of stabilizers is oligomers comprising at least one repeating unit having at least one ionic moiety, preferably an acidic moiety. The oligomers are produced similarly to polymers using monomer units, but with a very short chain length (less than 200). As a result, they exhibit higher water solubility than similar polymers and readily adsorb to the surface of fluororesin particles. The oligomers of the present invention have a chain length of monomer repeating units of less than 200. Examples of stabilizers in this group include, but are not limited to, oligomers of polyacrylic acid, oligomers of polymethacrylic acid, oligomers of maleic acid, and copolymers thereof. The second category of stabilizers is used in an amount of about 0.1 to about 5% by weight based on the total monomers. Preferably, it is used in an amount of about 0.2 to about 2% by weight based on the total fluorinated monomers added to the polymerization. The second category of stabilizers is preferably added after at least 30% by weight of fluorinated monomers have been supplied to the reactor, and more preferably after at least 50% by weight has been supplied.

[0073] The third category of stabilizers is a type of non-fluorinated ionic copolymer that can be optionally co-added with VDF during polymerization after the start of polymerization. These stabilizers have at least one unsaturated carbon-carbon double bond capable of undergoing free radical polymerization and contain an ionic moiety. The ionic moiety on the copolymer can be a carboxyl group, a phosphate group, a phosphonic acid group, a sulfonic acid group, or an -OH group.

[0074] Examples of stabilizers in this group include, but are not limited to, acrylic acid, methacrylic acid, sodium styrene sulfonate, sodium 1-allyloxy-2-hydroxypropanesulfonate, alkyl methacrylate phosphate, alkyl acrylate phosphate, ammonium allyl ether phosphate, 2-acrylamido-2-methylpropanesulfonic acid, β-carboxyethyl acrylate, and ethyl methacrylate phosphate. The third category of stabilizers is used in amounts of about 0.05 to about 5% by weight based on the total fluorine-containing monomers added to the polymerization. Preferably, it is used in amounts of about 0.1 to about 2% by weight based on the weight of the total fluorine-containing monomers added to the polymerization. The third category of stabilizers is added during polymerization, preferably after at least 15% by weight of fluorinated monomers have been supplied to the reactor, and more preferably after at least 30% by weight has been supplied to the reactor. It can be added continuously or intermittently while the VDF is polymerized in the presence of a polymerization initiator.

[0075] Adding the stabilizer of the present invention during polymerization may slow down the polymerization reaction rate, depending on how quickly and what type of stabilizer is added to the polymerization medium. This can be compensated for by adding a polymerization initiator to maintain the reaction rate.

[0076] The resulting polymer dispersion The fluororesin obtained by the process of the present invention conforms to ASTM D3835 and with a shear rate of 100 seconds at 230°C. -1 The reported melt viscosity exceeds 20 kpoise, and the solid content of the dispersion exceeds 25% by weight.

[0077] The solid content of the dispersion of the present invention is 25-60% by weight.

[0078] The fluororesin particles in the dispersion have a particle size in the range of 20 to 120 nm, preferably 50 to 120 nm, and more preferably 50 to 100 nm. [Examples]

[0079] melt viscosity The melt viscosity measurement is carried out after drying the fluororesin of the present invention overnight in a convection oven at 110 °C. The measurement is performed at 230 °C in accordance with ASTM D3835 and reported at shear rates of 4 seconds -1 and 100 seconds. -1

[0080] shear stability The shear stability of the aqueous fluororesin dispersion was measured at room temperature using a 48 mm dispersion blade model A164 (manufactured by Caframo Lab Solution). 750 ml of the dispersion was placed in a 1-liter wide-mouth jar, the dispersion blade was lowered from the bottom of the jar to about 1 / 3 of the dispersion height, and the speed was set to 1500 rpm. The stability time is recorded when the fluidity of the dispersion decreases and gelation occurs (at room temperature (22 °C) and the Brookfield viscosity at spindle LV-4 rises above 1000 cp). When the Brookfield viscosity exceeds 1000 cp, the dispersion loses its fluidity and behaves like a gel. In order to pass the shear stability test, the sample can be sheared for 20 minutes. If the Brookfield viscosity is less than 1000 cP after 20 minutes at 1500 rpm, the sample is considered to have shear stability. The Brookfield viscosity is measured at room temperature (22 °C) using spindle LV-4.

[0081] Particle size SEM images were acquired using a Hitachi SU8010 SEM, and the particle size was measured directly from the SEM images by averaging 50 or more particle sizes.

[0082] The PPGMA used in the examples is polypropylene glycol methacrylate with a number average molecular weight (Mn) of 300 to 500. (Sartomer® SR604 manufactured by Arkema). The particle size, melt viscosity, solid content, and shear stability of the examples and comparative examples were measured and reported in Table 1.

[0083] Comparative Example 1: Homopolymer ​4000 g of water and a predetermined amount of nonionic emulsifier Pluronic® 31Rl (BASF) were added to a 7.5 liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C for steam-off. The reactor was sealed and the temperature was set to the desired reaction temperature while stirring continued. Vinylidene fluoride (VDF) was added to the reactor to a pressure of 650 psig; an initiator aqueous solution consisting of 1% by weight in potassium persulfate and 1% by weight in sodium acetate was added at a rate of 360 g / hour to start the reaction. The rate of the initiator solution was set to approximately 20 g / hour to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After a total of 2000 g of VDF was added to the reactor, the monomer supply was stopped. Stirring continued for 10 minutes to maintain the temperature. Stirring and heating were stopped. After cooling to room temperature, excess gas was discharged, and the dispersion was removed from the reactor through a stainless steel mesh.

[0084] No acrylic glycol ester emulsifier was used. This comparative example shows that the particle size is large and the stability is low.

[0085] Comparative Example 2: Homopolymer The following comparative examples are based on the descriptions in U.S. Patent Nos. 8,338,518 and 8,765,890.

[0086] 4200 g of water, a predetermined amount of nonionic emulsifier Pluronic 31Rl (BASF), and PPGMA were added to a 7.5-liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C for steam-off. The reactor was sealed and the temperature was set to the desired reaction temperature while stirring continued. Vinylidene fluoride was added to the reactor to a pressure of 650 psig; an initiator aqueous solution consisting of 2 wt% potassium persulfate and 2 wt% sodium acetate was added at a rate of 500 g / hour to start the reaction. The rate of the initiator solution was set to approximately 60 g / hour to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After adding a total of 1700 g of VDF to the reactor, the monomer supply was stopped. Stirring continued for 10 minutes to maintain the temperature. Stirring and heating were stopped. After cooling to room temperature, excess gas was discharged, and the dispersion was removed from the reactor through a stainless steel mesh.

[0087] This comparative example demonstrates poor stability because, although a predetermined particle size is used, no stabilizer is employed.

[0088] Comparative Example 3: Copolymer (Pilot Plant) In an 80-gallon stainless steel reactor, 400 pounds of deionized water, 270 g of PLURONIC 31R1 (BASF non-fluorinated nonionic emulsifier), and 0.42 pounds of ethyl acetate were added. After evacuating, stirring was started at 23 rpm and the reactor was heated. After the reactor temperature reached the desired set point of 100°C, VDF and HFP monomers were introduced into the reactor at a ratio of 13.8% by weight of HFP relative to the total monomers. Subsequently, the reactor pressure was increased to 650 psi by adding approximately 30 pounds of monomers to the reactor. 4.0 pounds of an initiator solution consisting of 1.0% by weight of potassium persulfate and 1.0% by weight of sodium acetate was added to the reactor to initiate polymerization. At the start, the ratio of HFP to VDF was adjusted so that HFP reached 4.3% of the total monomers in the feed. The rate of addition of the initiator solution was also adjusted to obtain a polymerization rate of approximately 70 pounds per hour. Copolymerization of VDF and HPF was continued until approximately 150 pounds of monomers were introduced into the reaction mass. The supply of HFP was stopped, but the supply of VDF continued until approximately 172 pounds of monomers were supplied to the reactor. The supply of VDF was stopped, and the batch was allowed to react at the reaction temperature and consume the residual monomers under reduced pressure. After 40 minutes, the supply of initiator and stirring were stopped, the reactor was cooled, evacuated, and the dispersion was recovered. The initiator concentration was approximately 555 ppm relative to the total monomers. To the resulting dispersion, a 10 wt% aqueous solution of SLS (stabilizer) was added so that the SLS concentration reached 2500 ppm based on the total weight of fluorine-containing monomers added to the polymerization. SLS = sodium lauryl sulfate.

[0089] Comparative Example 3 used a nonionic emulsifier with a large particle size and at least two blocks (PLURONIC), but did not use an acrylic glycol ester. As a result, stability was poor despite the presence of 2500 ppm of stabilizer.

[0090] Comparative Example 4 3000 g of water and a specified amount of PPGMA were added to a 7.5 liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C for steam-off. The reactor was sealed while stirring continued, and the reactor temperature was set to the desired reaction temperature. Vinylidene fluoride was added to the reactor to a pressure of 650 psig; an initiator aqueous solution consisting of 2 wt% potassium persulfate and 2 wt% sodium acetate was added at a rate of 500 g / hour to start the reaction. The rate of the initiator solution was set to approximately 60 g / hour to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After adding a total of 1700 g of VDF to the reactor, the monomer supply was stopped. Stirring continued for 20 minutes to maintain the temperature. Stirring and heating were stopped. After cooling to room temperature, excess gas was discharged, and the dispersion was removed from the reactor through a stainless steel mesh.

[0091] Examples 1-4 4200 g of water, a predetermined amount of the nonionic emulsifier Pluronic® 31Rl (BASF), and PPGMA were added to a 7.5-liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C for steam-off. The reactor was sealed and the temperature was set to the desired reaction temperature while stirring continued. Vinylidene fluoride was added to the reactor to a pressure of 650 psig; an initiator aqueous solution consisting of 2 wt% potassium persulfate and 2 wt% sodium acetate was added at a rate of 500 g / hour to start the reaction. The rate of the initiator solution was set to approximately 60 g / hour to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After adding a total of 1500 g of VDF to the reactor, the monomer supply was stopped. Stirring continued for 10 minutes to maintain the temperature. Stirring and heating were stopped. After cooling to room temperature, excess gas was discharged, and the dispersion was removed from the reactor through a stainless steel mesh. To the obtained dispersion, a 10% by weight aqueous solution of SLS was added so that the SLS concentration reached 2000 ppm, based on the weight of the fluorine-containing monomers added to the polymerization.

[0092] Example 5 4200 g of water, a predetermined amount of the nonionic emulsifier Pluronic® 31Rl (BASF), and PPGMA were added to a 7.5-liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C to steam off. The reactor was sealed and the temperature was set to the desired reaction temperature while stirring continued. Vinylidene fluoride was added to the reactor to a pressure of 650 psig; the reaction was started by adding an initiator aqueous solution consisting of 2 wt% potassium persulfate and 2 wt% sodium acetate at a rate of 500 g / hour. The rate of introduction of the initiator solution was set to approximately 60 g / h to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After adding a total of 1500g of VDF to the reactor, the supply of VDF was stopped, and 273g of HFP monomer was added to the reactor, followed by the addition of VDF to bring the total to 1500g. Stirring was continued for 10 minutes to maintain the temperature. Stirring and heating were then stopped. After cooling to room temperature, excess gas was discharged, and the dispersion was removed from the reactor through a stainless steel mesh. Subsequently, a 10 wt% aqueous solution of SLS was added to the dispersion so that the SLS concentration reached 2000 ppm based on the fluorine-containing monomers added to the polymerization.

[0093] Example 6 3000 g of water, a predetermined amount of nonionic emulsifier Pluronic 31Rl (BASF), and PPGMA were added to a 7.5-liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C to steam off. The reactor was sealed and the temperature was set to the desired reaction temperature while stirring continued. Vinylidene fluoride was added to the reactor to a pressure of 650 psig; an initiator aqueous solution consisting of 2 wt% potassium persulfate and 2 wt% sodium acetate was added at a rate of 500 g / hour to start the reaction. The rate of the initiator solution was set to approximately 60 g / hour to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After adding a total of 800g of VDF to the reactor, a 10% aqueous solution of polyacrylic acid (a second type of stabilizer) with a weight-average molecular weight of approximately 4000 was supplied to the reactor at a rate of 200 ml / hour while continuing to supply VDF. The addition of VDF and polyacrylic acid solution was stopped when the total amount of VDF supplied reached 1700g. Stirring was continued for 10 minutes to maintain the temperature. Stirring and heating were stopped. After cooling to room temperature, excess gas was discharged and the dispersion was removed from the reactor through a stainless steel mesh. Mv stands for melt viscosity.

[0094] Example 7 3000 g of water, a predetermined amount of nonionic emulsifier Pluronic 31Rl (BASF), and PPGMA were added to a 7.5-liter stainless steel reactor. The mixture was purged with nitrogen and stirred for 0.5 hours. The reactor temperature was raised to 105°C to steam off. The reactor was sealed and the temperature was set to the desired reaction temperature while stirring continued. Vinylidene fluoride was added to the reactor to a pressure of 650 psig; an initiator aqueous solution consisting of 2 wt% potassium persulfate and 2 wt% sodium acetate was added at a rate of 500 g / hr to start the reaction. The rate of introduction of the initiator solution was set to approximately 60 g / h to maintain a good reaction rate throughout the remainder of the reaction. The reaction pressure was maintained at 650 psig by adding vinylidene fluoride as needed. After adding a total of 800g of VDF to the reactor, a 1% wt / wt aqueous solution of a third-category stabilizer, such as alkyl methacrylate phosphate (Sipomer® PAM4000, Solvay), was supplied to the reactor at a rate of 100ml / hour while continuing to supply VDF. The addition of VDF and PAM4000 solution was stopped when the total amount of VDF supplied reached 1700g. Stirring was continued for 10 minutes to maintain the temperature. Stirring and heating were then stopped. After cooling to room temperature, excess gas was discharged, and the dispersion was removed from the reactor through a stainless steel mesh.

[0095] [Table 1] *Based on total fluorine monomers (VDF + HFP)

Claims

1. A water-based fluororesin dispersion containing a fluororesin, The fluororesin has an average particle size of less than 120 nm and is heated at 230°C for 100 seconds. -1 An aqueous fluororesin dispersion having a melt viscosity of at least 20 kP, wherein the aqueous fluororesin dispersion has a solid content of at least 25% by weight and a Brookfield viscosity of less than 1000 cP after shearing at 1500 rpm for at least 20 minutes.

2. The aqueous fluororesin dispersion according to claim 1, wherein the fluororesin contains at least 60% by weight of VDF monomer units.

3. The aqueous fluororesin dispersion according to claim 1, wherein the fluororesin comprises at least a copolymer unit selected from the group consisting of HFP, CTFE, PMVE, PPVE, TFE, and 2,3,3,3-tetrafluoropropene.

4. The aqueous fluororesin dispersion according to claim 1, wherein the average particle size is less than 100 nm.

5. An aqueous fluororesin dispersion according to any one of claims 1 to 4, comprising: (1) an acrylic glycol ester containing at least one of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), or polypropylene glycol methacrylate (PPGMA); (2) a nonionic block copolymer emulsifier containing at least two blocks selected from polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; and (3) a stabilizer.

6. The aqueous fluororesin dispersion according to claim 5, wherein the fluororesin comprises polyvinylidene fluoride having at least 60% by weight of VDF monomer units, the acrylic glycol ester is selected from polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), and polypropylene glycol methacrylate (PPGMA), and the nonionic block copolymer emulsifier comprises at least one block of polyethylene glycol and at least one block of polypropylene glycol.

7. The aqueous fluororesin dispersion according to claim 5, wherein the fluororesin comprises at least one non-fluorinated monomer having at least one reactive double bond and an ionic moiety.

8. The aqueous fluororesin dispersion according to claim 5, wherein the stabilizer comprises a non-fluorinated oligomer containing at least one ionic moiety.

9. The aqueous fluororesin dispersion according to claim 5, wherein the stabilizer comprises at least one alkyl sulfate or alkyl sulfonate, and the alkyl group is a C6 to C18 alkyl group.

10. A method for producing a shear-stable aqueous fluororesin dispersion having a particle size of less than 120 nm, comprising the following steps: (a) Prepare in a reaction vessel an aqueous reaction medium, at least one fluorine-containing monomer, at least one acrylic glycol ester, and at least one nonionic emulsifier having at least two blocks selected from polyethylene glycol, polypropylene glycol and / or polytetramethylene glycol, with 2 to 200 repeating units per block. (b) The fluorine-containing monomer of (a) is polymerized in the presence of at least one initiator, wherein the amount of initiator added to the polymerization is at least 1500 ppm based on the weight of the fluorine-containing monomer added to the polymerization, and (c) Adding at least one stabilizer to the fluororesin dispersion during or after polymerization. A method that includes this.

11. The method according to claim 10, wherein the fluorine-containing monomer comprises a vinylidene fluoride monomer.

12. The method according to claim 10, wherein the glycol-based acrylic emulsifier comprises at least one of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), or polypropylene glycol methacrylate (PPGMA).

13. The method according to claim 10, wherein the amount of glycol-based acrylic emulsifier added to the polymerization is 0.05 to 5% by weight based on the total fluorine-containing monomers added to the polymerization.

14. The method according to any one of claims 10 to 13, wherein the stabilizer comprises at least one alkyl sulfate or alkyl sulfonate.

15. The method according to any one of claims 10 to 13, wherein the stabilizer is selected from the group consisting of C6-C18 alkyl sulfonates, C6-C18 alkyl sulfates, C6-C18 alkyl disulfonates, C6-C18 alkyl disulfates, and mixtures thereof.

16. The method according to any one of claims 10 to 13, wherein a stabilizer comprising at least one alkyl sulfate or alkyl sulfonate is added after polymerization is completed or after at least 50% by weight of the fluorinated monomer has been supplied to the reactor.

17. The method according to any one of claims 10 to 13, wherein a stabilizer comprising at least one alkyl sulfate or alkyl sulfonate is added in an amount of 0.1 to about 5% by weight based on the total weight of fluorine-containing monomers added to the polymerization.

18. The method according to any one of claims 10 to 13, wherein the stabilizer comprises an oligomer containing an ionic monomer unit having an acid group.

19. The method according to any one of claims 10 to 13, wherein the stabilizer is selected from the group consisting of polyacrylic acid oligomers, poly(meth)acrylic acid oligomers, oligomers containing maleic acid monomer units, and any of the aforementioned co-oligomers and combinations thereof.

20. The method according to any one of claims 10 to 13, wherein the stabilizer is added after at least 30% by weight of the fluorinated monomer has been supplied to the reactor.

21. The method according to any one of claims 10 to 13, wherein a stabilizer containing an oligomer having an acidic group ionic monomer unit is added in an amount of 0.1 to about 2.5% by weight based on the total fluorine-containing monomers added to the polymerization.

22. The method according to any one of claims 10 to 13, wherein the stabilizer is added during polymerization, and the stabilizer comprises a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety.

23. The method according to any one of claims 10 to 13, wherein the stabilizer is added during polymerization, and the stabilizer is selected from the group consisting of acrylic acid, methacrylic acid, a salt of styrene sulfonic acid, alkyl methacrylate phosphate, 2-acrylamido-2-methylpropanesulfonic acid, β-carboxyethyl acrylate, and combinations thereof.

24. The method according to claim 22, wherein a stabilizer comprising a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety is added during polymerization.

25. The method according to claim 22, wherein a stabilizer comprising a non-fluorinated monomer having at least one reactive carbon-carbon double bond and an ionic moiety is added in an amount of 0.1 to about 1.5% by weight based on the total monomers added to the polymerization.

26. An aqueous fluororesin dispersion comprising: (1) a vinylidene fluoride polymer having at least 60% by weight of vinylidene fluoride monomer units; (2) an acrylic glycol ester containing at least one of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), or polypropylene glycol methacrylate (PPGMA); (3) a nonionic block copolymer emulsifier containing at least two blocks of polyethylene glycol, polypropylene glycol, and / or polytetramethylene glycol; and (4) a stabilizer, wherein the fluororesin has an average particle size of less than 120 nm and is conditioned at 230°C for 100 seconds. -1 An aqueous fluororesin dispersion having a melt viscosity of at least 20 kP, wherein the aqueous fluororesin dispersion has a solid content of at least 25% by weight and a Brookfield viscosity of less than 1000 cP after shearing at 1500 rpm for at least 20 minutes.

27. The aqueous fluororesin dispersion according to claim 26, wherein the stabilizer comprises a non-fluorinated oligomer containing at least one ionic moiety.

28. The aqueous fluororesin dispersion according to claim 26, wherein the stabilizer comprises at least one alkyl sulfate or alkyl sulfonate, and the alkyl group is a C6 to C18 alkyl group.

29. The aqueous fluororesin dispersion according to claim 26, wherein the fluororesin comprises at least one non-fluorinated monomer having at least one reactive double bond and an ionic moiety.