Manufacturing of large particle fluororesin latex

Abstract

A shear-stable latex is disclosed that includes a fluororesin, a particle size modifier, and a surfactant, the latex having a solids content of at least 15% by weight and a particle size modifier to surfactant ratio of 2 or greater on a mole-to-mole basis.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This invention describes the preparation of large particle size fluororesin latexes. The large particle size fluororesin latexes can be prepared by emulsion polymerization using fluorine-containing monomers, surfactants, particle size modifiers, and initiators. These large particle size fluororesin latexes can be used to coat battery separators. [Background technology]

[0002] Background of the Invention Commercial grades of PVDF produced by emulsion polymerization have primary particle sizes between 100 and 400 nm. PVDF shear-stable latexes larger than 400 nm are not commercially available. There is a desire in the industry to improve the adhesion of battery separators to electrodes without reducing separator porosity, which reduces lithium ion mobility and limits the usefulness of the battery. Increasing the particle size of the PVDF binder may solve this problem.

[0003] As is well known in the art, latexes become more difficult to stabilize as the polymer concentration increases. Furthermore, many salts are known to destabilize latexes. It is also well known that large particle sizes tend to destabilize latexes and limit the ability to achieve high polymer concentrations. There is a need to provide shear-stable latexes using fluoropolymers with larger particle sizes. The fact that the present invention provides good latex stability was unexpected. Indeed, the particular effectiveness of the present invention is highlighted by the ability to produce shear-stable latexes with large particle sizes in the presence of a particle size modifier containing functionalized fluoropolymers at high solids contents (greater than 15% by weight, preferably greater than 20% by weight of the total reaction mixture) in the latex.

[0004] The present inventors have discovered that the use of certain particle size modifiers in the production of fluoropolymers can increase the primary particle size of the fluoropolymer to greater than 400 nm, compared to the same polymerization process without the use of particle size modifiers. The use of these particle size modifiers makes it possible to produce fluoropolymer shear-stable latexes containing high concentrations of dispersed polyvinylidene fluoride and having primary particle sizes of 400 nm or greater. This result is surprising because fluoropolymers produced by emulsion polymerization typically have particles smaller than 400 nm. Summary of the Invention [Means for solving the problem]

[0005] The present invention provides a shear-stable latex comprising a fluororesin, a particle size modifier, and a surfactant, wherein the shear-stable latex has a solids content of at least 15% by weight, the ratio of the particle size modifier to the surfactant is 2 or greater on a mole to mole basis, and the volume average particle size of the fluororesin in the shear-stable latex is greater than 400 nm and less than 3000 nm, preferably greater than 450 nm and less than 2000 nm, as measured by light scattering.

[0006] For a multimodal particle size latex, at least 20%, more preferably at least 30%, and most preferably at least 35% of the total number of fluororesin particles in the latex have a volume average primary particle size greater than 475 nm and less than 2000 nm, more preferably greater than 500 nm and less than 2000 nm.

[0007] The present invention provides a method for producing a fluororesin having a large particle size, the method comprising the steps of: (a) contacting an aqueous mixture containing a particle size modifier, a surfactant, and a radical initiator with a monomer feed containing one or more fluorine-containing monomers; (b) initiating polymerization of said one or more fluorine-containing monomers, thereby forming a fluororesin shear-stable latex. The surfactant comprises a non-fluorinated surfactant; and the fluororesin is thermoplastic and comprises at least 71% by weight of vinylidene fluoride.

[0008] Embodiments of the present invention include embodiment 1, which is an aqueous latex comprising a surfactant, a particle size modifier, and a fluororesin, wherein the surfactant comprises at least one alkane sulfonate selected from the group consisting of C7 to C20 1-alkane sulfonate, C7 to C20 2-alkane sulfonate, C7 to C20 1,2-alkane disulfonate, and mixtures thereof, and the particle size modifier comprises MX, where M is an alkali metal or NH4, preferably an alkali metal, and X is a halide, and the particle size modifier for the surfactant is the ratio of the agent to the fluororesin is 2 or greater on a mole to mole basis, the concentration of the fluororesin is at least 15% by weight, preferably at least 20% by weight, based on the total weight of the aqueous latex, the volume average particle size of the fluororesin in the aqueous latex is greater than 400 nm and less than 3000 nm, preferably greater than 450 nm and less than 2000 nm, as measured by light scattering, and the aqueous latex is shear stable as measured by the Latex Shear Stability Test, and has a viscosity of less than 100 cps after 30 minutes at 2500 rpm and 25°C.

[0009] Embodiment 2 is the aqueous latex of embodiment 1, wherein the volume average particle size of the fluororesin in the aqueous latex is greater than 500 nm and less than 1500 nm, as measured by a light scattering method.

[0010] Embodiment 3 is the water-based latex of any one or more of the previous embodiments, wherein the fluororesin comprises at least 50% by weight vinylidene fluoride.

[0011] Embodiment 4 is the aqueous latex of any one or more of the previous embodiments, wherein the fluorine-containing monomer comprises hexafluoropropylene.

[0012] Embodiment 5 is the aqueous latex of any one or more of the previous embodiments, wherein M is an alkali metal.

[0013] Embodiment 6 is the aqueous latex of any one or more of the previous embodiments, wherein M is selected from the group consisting of Na, Cs, and Li.

[0014] Embodiment 7 is the aqueous latex of any one or more of the previous embodiments, wherein X is Cl or Br, preferably Cl.

[0015] Embodiment 8 is the aqueous latex of any one or more of embodiments 1-4, wherein the particle size control agent comprises at least one of NaCl, CsCl, LiCl, or NH4Cl.

[0016] Embodiment 9 is the aqueous latex of any one or more of embodiments 1-4, wherein M is lithium, sodium, cesium, or NH4, and X is Cl.

[0017] Embodiment 10 is the aqueous latex of any one or more of the previous embodiments, wherein the molar ratio of particle size control agent to surfactant is at least 3.

[0018] Embodiment 11 is the aqueous latex of any one or more of the preceding embodiments, wherein the molar ratio of particle size control agent to surfactant is at least 2 and at most 7.8, preferably at most 7.0.

[0019] Embodiment 12 is the aqueous latex of any one or more of embodiments 1-4, 7, 10, or 11, wherein when M is cesium, the fluororesin exhibits a monomodal particle size distribution.

[0020] Embodiment 13 is the aqueous latex of any one or more of embodiments 1-4, 7, 10, or 11, wherein when M is sodium or lithium, the fluororesin exhibits a multimodal particle size distribution.

[0021] Embodiment 14 is a method for increasing the volume average particle size of a fluororesin, comprising the steps of: (a) contacting an aqueous mixture containing a surfactant and a particle size modifier with a monomer feed containing one or more fluorine-containing monomers and a radical initiator feed; and (b) initiating polymerization of said one or more fluorine-containing monomers, thereby forming a fluororesin shear-stable latex. Including, The surfactant comprises an alkane sulfonate selected from C7 to C20 1-alkane sulfonates, C7 to C20 2-alkane sulfonates, C7 to C20 1,2-alkane disulfonates, and mixtures thereof; The grain size modifier comprises MX, where M is an alkali metal or NH4, and X is a halide; The ratio of particle size modifier to surfactant is 2 or greater on a mole-to-mole basis It is a method.

[0022] Embodiment 15 is the method of embodiment 14, wherein the fluorine-containing monomer comprises vinylidene fluoride.

[0023] Embodiment 16 is the method of any one or more of embodiments 14-15, wherein the fluorine-containing monomer comprises hexafluoropropylene.

[0024] Embodiment 17 is the method of any one or more of embodiments 14-16, wherein the alkanesulfonate is selected from C8 to C12 1-alkanesulfonates, C8 to C12 2-alkanesulfonates, C8 to C12 1,2-alkanedisulfonates, and mixtures thereof.

[0025] Embodiment 18 is the method of any one or more of embodiments 14-16, wherein the surfactant comprises an alkane sulfonate selected from 1-octane sulfonate, 2-octane sulfonate, 1,2-octane disulfonate, 1-decane sulfonate, 2-decane sulfonate, 1,2-decane disulfonate, 1-dodecane sulfonate, 2-dodecane sulfonate, 1,2-dodecane disulfonate, and combinations thereof.

[0026] Embodiment 19 is the method of any one or more of embodiments 14-16, wherein the alkanesulfonate comprises 1-octanesulfonate.

[0027] Embodiment 20 is the method of any one or more of embodiments 14-16, wherein the alkane sulfonate is sodium alkane sulfonate, potassium alkane sulfonate, or ammonium alkane sulfonate, or a mixture thereof.

[0028] Embodiment 21 is the method of any one or more of embodiments 14-20, wherein the grain size modifier is MX, where M is a metal or NH4, and X is a halide.

[0029] Embodiment 22 is the method of any one or more of embodiments 14-20, wherein M is an alkali metal or NH4.

[0030] Embodiment 23 is the method of any one or more of embodiments 14-20, wherein M is selected from the group consisting of Na, Cs, and Li.

[0031] Embodiment 24 is the method of any one or more of embodiments 14-23, wherein X is Cl or bromide, preferably Cl.

[0032] Embodiment 25 is the method of any one or more of embodiments 14-20, wherein the particle size control agent comprises at least one of NaCl, CsCl, LiCl, or NH 4 Cl.

[0033] Embodiment 26 is the method of any one or more of embodiments 14-25, wherein the fluororesin comprises a copolymer including vinylidene fluoride and hexafluoropropylene monomer units.

[0034] Embodiment 27 is the method of any one or more of embodiments 14-26, wherein the fluororesin comprises at least 75% by weight vinylidene fluoride units.

[0035] Embodiment 28 is the method of any one or more of embodiments 14-27, wherein the radical initiator comprises a persulfate.

[0036] Embodiment 29 is the method of any one or more of embodiments 14-28, wherein the weight percent of the functionalized fluororesin in the latex after step (b) comprises at least 15 weight percent of the latex, preferably at least 20 weight percent.

[0037] Embodiment 30 is the method of any one or more of embodiments 14-21, 24, 26-29, wherein when M is cesium, the fluororesin exhibits a unimodal particle size distribution.

[0038] Embodiment 31 is the method of any one of embodiments 14-21, 24, 26-29, wherein when M is sodium or lithium, the fluororesin exhibits a multimodal particle size distribution.

[0039] Embodiment 32 is a method of making a multimodal fluororesin dispersion, comprising the steps of: (a) contacting an aqueous mixture containing a surfactant, a particle size modifier, a monomer feed containing one or more fluorine-containing monomers, and a radical initiator; and (b) applying heat and pressure sufficient to polymerize said one or more fluorine-containing monomers, thereby forming a fluororesin dispersion; Includes; the surfactant comprises at least one alkane sulfonate selected from the group consisting of C7 to C20 linear 1-alkane sulfonates, C7 to C20 linear 2-alkane sulfonates, C7 to C20 linear 1,2-alkane disulfonates, and mixtures thereof; and at least 50% by weight of vinylidene fluoride; The method wherein the particle size modifier comprises MX, where M is lithium, sodium, or NH4, and X is Cl, and the ratio of particle size modifier to surfactant is greater than 2 on a mole-to-mole basis.

[0040] Embodiment 33 is the use of the aqueous latex of any one or more of embodiments 1-13 in a lithium ion battery application, preferably as a separator coating or electrode binder. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a graph showing the effect of the molar ratio of particle size modifier / surfactant on the particle size of the latex. DETAILED DESCRIPTION OF THE INVENTION

[0042] Detailed Description of the Invention The present invention provides a shear-stable fluororesin latex having a solids content of at least 20% and a volume average primary particle size of 400 nm or more, preferably 450 nm or more, and most preferably 500 nm or more. The present invention also provides a method for producing a shear-stable fluororesin latex having a volume average primary particle size of 400 nm or more, preferably 450 nm or more, and most preferably greater than 500 nm, wherein the fluororesin of the present invention is thermoplastic. Shear stability is measured using the Latex Shear Stability Test Method described herein.

[0043] Fluoroplastics are produced as aqueous dispersion polymerization reaction mixtures (typically called emulsions or latexes) containing one or more surfactants and using one or more radical initiators.

[0044] Optionally, the polymerization to produce the fluororesin may be carried out in the presence of a chain transfer agent to control molecular weight, a buffer to maintain a desired pH range during polymerization, and an antifouling agent to reduce or eliminate adhesion of the polymer to the interior surfaces of the polymerization vessel.

[0045] As used for purposes of the present invention, the term "fluoroplastic" means a polymeric material containing at least 71% by weight of fluorinated monomer units. Suitable fluorinated monomers are described below. The remainder of these units may be one or more of fluorinated monomers, ethene, propene, (meth)acrylates, (meth)acrylic acid, or other monomers known to copolymerize with fluorinated monomers.

[0046] In a preferred embodiment, the fluororesin of the present invention comprises vinylidene fluoride and may be a vinylidene fluoride homopolymer or copolymer, preferably in which at least 71% by weight of the fluorinated monomer units are vinylidene fluoride.

[0047] Fluoroplastics may be homopolymers, copolymers, terpolymers, or polymers derived from more than two monomers. As used herein, the term copolymer includes polymers containing two or more different monomer units. These are typically thermoplastic, where "thermoplastic" means capable of being formed into shapes by the application of heat and (typically) pressure, as occurs in molding and extrusion processes. Exemplary polymers produced by the methods of the present invention include polyvinylidene fluoride homopolymers; copolymers, terpolymers, and higher polymers having a vinylidene fluoride content of at least 71% by weight, typically at least 75% by weight. VDF monomer unit levels of up to about 99% by weight may be found in some exemplary embodiments of the present invention. Specific preferred fluoroplastics according to the present invention include, for example, copolymers of vinylidene fluoride with hexafluoropropylene, tetrafluoroethylene, or trifluoroethylene, and terpolymers of vinylidene fluoride with tetrafluoroethylene and hexafluoropropylene, or tetrafluoroethylene and trifluoroethylene. Other copolymers and terpolymers may contain other fluorine-containing monomers in combination with vinylidene fluoride, suitable examples of such other fluorine-containing monomers for use in accordance with the present invention are described in further detail below.

[0048] (surfactant) The surfactant used in the polymerization comprises at least one alkane sulfonate. As used herein, the terms "alkane sulfonate" and terms ending in "sulfonate" refer to alkali metal, ammonium, or monoalkyl-, dialkyl-, trialkyl-, or tetraalkyl-substituted ammonium salts of alkane sulfonic acids or alkane disulfonic acids. Sodium alkane sulfonate, potassium alkane sulfonate, ammonium alkane sulfonate, or mixtures thereof are typically used.

[0049] Preferably, the surfactant used in the polymerization comprises at least one alkane sulfonate selected from the group consisting of C7-C20 1-alkane sulfonates, C7-C20 2-alkane sulfonates, C7-C20 1,2-alkane disulfonates, and mixtures thereof; more preferably, the alkane sulfonate is selected from C8-C12 1-alkane sulfonates, C8-C12 2-alkane sulfonates, C8-C12 1,2-alkane disulfonates, and mixtures thereof. Preferably, the alkane sulfonate is sodium alkane sulfonate, potassium alkane sulfonate, ammonium alkane sulfonate, or a mixture thereof. Preferably, the alkane sulfonate is linear. One or more types of alkane sulfonates can be used in the present invention.

[0050] Examples of alkanesulfonates include, but are not limited to, 1-octane sulfonate, 2-octane sulfonate, 1,2-octane disulfonate, 1-decane sulfonate, 2-decane sulfonate, 1,2-decane disulfonate, 1-dodecane sulfonate, 2-dodecane sulfonate, 1,2-dodecane disulfonate, and the like.

[0051] 1-octanesulfonate is the preferred surfactant.

[0052] (Fluorine-containing monomer) As used in accordance with the present invention, the term "fluorine-containing monomer" refers to a fluorinated olefinically unsaturated monomer capable of participating in a free radical polymerization reaction. The fluorine-containing monomer used in accordance with the present invention may consist solely of vinylidene fluoride, or may include any of a wide variety of other fluorine-containing monomers known in the art. The fluorine-containing monomer suitable for use in accordance with the present invention contains at least one fluorine atom, and can incorporate, for example, a fluoroalkyl group, a fluoroalkoxy group, or a vinylic fluorine atom.

[0053] Exemplary fluorine-containing monomers suitable for use in accordance with the present invention include vinylidene fluoride (VDF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, 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 ethers (PBVE), long-chain perfluorovinyl ethers, one or more partially or fully fluorinated α-olefins such as 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 such as perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), C4 or higher partially or perfluorinated α-olefins, C3 or higher partially or perfluorinated cyclic alkenes, partially fluorinated allyls, or fluorinated allyl monomers, and combinations thereof.

[0054] In a preferred embodiment, VDF is used in combination with at least one fluorine-containing monomer selected from the group consisting of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), and hexafluoropropene (HFP).

[0055] (Particle size adjuster) The grain size modifier comprises MX, where M is an alkali metal or NH4, preferably an alkali metal, and X is a halide. Preferably, M is an alkali metal. Preferably, X is Cl or Br, preferably Cl.

[0056] Examples of M include Na, Cs, and Li.

[0057] Examples of particle size adjusters include NaCl, CsCl, LiCl, or NH4Cl.

[0058] Preferably, M is lithium, sodium, cesium or NH4 and X is Cl.

[0059] The molar ratio of particle size control agent to surfactant is greater than 2, preferably 3 or greater, on a mole to mole basis.

[0060] In some embodiments, the molar ratio of particle size control agent to surfactant is at least 2 and at most 7.8, preferably 2-7.

[0061] In one embodiment, when M is cesium, the fluoroplastic exhibits a monomodal particle size distribution.

[0062] In another embodiment, when M is sodium or lithium, the fluororesin exhibits a multimodal particle size distribution.

[0063] (radical initiator) Radical initiators suitable for use in accordance with the present invention are compounds or combinations of compounds that can provide a source of free radicals, either spontaneously or upon exposure to heat or light. The radical initiator is added to the reaction mixture in an amount sufficient to initiate and maintain the polymerization reaction at the desired reaction rate. Suitable non-limiting classes of initiators include persulfates, peroxides, percarbonates, azo compounds, and redox systems, all of which are well known in the art. As used herein, the term "ionic initiator" refers to a radical initiator that includes at least one salt containing a metal cation and / or an ammonium or substituted ammonium cation. The terms "radical" and "free radical" refer to a chemical species that includes at least one unpaired electron.

[0064] Preferred radical initiators include persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate, etc. The amount of persulfate added to the reaction mixture (based on the total weight of the monomers added to the reaction mixture) is typically about 0.005 to about 1.0 wt %, based on the total weight of the monomers used in the reaction.

[0065] The radical initiator can include organic peroxides, such as alkyl, dialkyl, or diacyl peroxides, peroxydicarbonates, and peroxyesters, or mixtures thereof. A preferred dialkyl peroxide is di-t-butyl peroxide (DTBP), which can be added to the reaction mixture in an amount of about 0.01 to about 5% by weight based on the total monomers, preferably about 0.05 to about 2.5% by weight based on the total weight of the monomers used in the reaction. Preferred peroxydicarbonate initiators are di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate, which can be added to the reaction mixture in an amount of about 0.5 to about 2.5% by weight based on the total monomers. Peroxyester initiators include t-amyl peroxypivalate, t-butyl peroxypivalate, and succinic acid peroxide.

[0066] The radical initiator may include an azo-based initiator such as 2,2'-azobis(2-methyl-propionamidine) dihydrochloride.

[0067] The radical initiator may include a redox system. The term "redox system" refers to a system containing an oxidizing agent, a reducing agent, and, optionally, a promoter as an electron transfer medium. Examples of oxidizing agents include persulfates; peroxides such as hydrogen peroxide; hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide; 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. The promoter is a component of the redox system that reacts with both the oxidizing agent and the reducing agent at different oxidation states, thereby accelerating the overall reaction. Examples of promoters include transition metal salts such as ferrous sulfate. In a redox system, the oxidizing agent and reducing agent are used in an amount of about 0.01 to about 0.5 wt % based on the total weight of the monomers used in the reaction. The optional accelerator may be used in an amount of about 0.005 to about 0.025% by weight, based on the total weight of the monomers used in the reaction. Redox systems are described in G.S. Misra and U.D.N. Bajpai, Prog. Polym. Sci., 1982, 8(1-2), pp. 61-131.

[0068] (chain transfer agent) Chain transfer agents can also be added to the polymerization mixture to control the molecular weight of the product. These can be added all at once at the beginning of the reaction, or in stages or continuously throughout the reaction. The amount and manner of addition of chain transfer agent, if any, depends on the activity of the particular agent employed and the desired molecular weight of the polymer product. The amount of chain transfer agent added to the polymerization reaction is typically about 0.05 to about 5 weight percent, more typically about 0.1 to about 2 weight percent, based on the total weight of monomers used in the reaction.

[0069] Oxygen-containing compounds such as alcohols, carbonates, ketones, esters, and ethers function as chain transfer agents. Examples of oxygen-containing compounds useful as chain transfer agents include isopropyl alcohol, ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propylaldehyde, and ethyl propionate. Other classes of compounds that can function as chain transfer agents in the polymerization of halogen-containing monomers include halocarbons, hydrohalocarbons, and chlorocarbons such as carbon tetrachloride. Simple or branched alkanes such as ethane, propane, or 2-ethylhexane also function as chain transfer agents.

[0070] (buffering agent) The polymerization reaction mixture may optionally contain a buffer to maintain a controlled pH throughout the polymerization reaction. The pH is typically controlled in the range of about 3 to about 8 to minimize undesirable color development in the product.

[0071] The buffer may comprise an organic or inorganic acid or an alkali metal salt thereof, or a base or salt of such an organic or inorganic acid, having at least one pKa and / or pKb value in the range of about 4 to about 10, usually about 4.5 to about 9.5. Exemplary buffers suitable for use in accordance with the present invention include phosphate buffers and acetate buffers, which are well known in the art.

[0072] Buffers are particularly useful when persulfates (e.g., potassium persulfate) are used as the radical initiator. A preferred buffer in this situation is sodium acetate. A preferred amount of sodium acetate buffer is about 50% to about 150% by weight, based on the weight of initiator added to the reaction. In one exemplary embodiment, the initiator feed comprises approximately equal weights of potassium persulfate and sodium acetate in aqueous solution.

[0073] (Anti-fouling agent) The optional addition of an antifouling agent, such as paraffin wax or hydrocarbon oil, to the reaction mixture is typically done to minimize or prevent fouling of the fluororesin to reactor parts. Any long-chain saturated hydrocarbon wax or oil can serve this function. The oil or wax is added to the reactor prior to formation of the fluororesin in an amount sufficient to minimize the formation of polymer fouling on the reactor parts.

[0074] (Polymerization process) The general procedure is as follows: deionized water, surfactant, and particle size modifier are added to a reactor, followed by deoxidation (removal of oxygen). The reactor may be a pressurized polymerization reactor equipped with an agitator and heat control means. Agitation may be constant or may be used to optimize process conditions during stabilizer production. After the reactor reaches the desired temperature, predetermined amounts of fluorine-containing monomer and optional comonomer are added to the reactor. The ratio of monomer to comonomer may be constant throughout the polymerization or may vary throughout the polymerization process. An initiator solution is fed to the reactor at a flow rate appropriate to maintain the desired reaction rate. After the desired monomer amount is reached, the monomer feed can be stopped. Unreacted monomer is vented, and the produced latex can be recovered through a drain port or other recovery means. The latex can be retained in an aqueous medium for subsequent application or use.

[0075] The production of the fluororesin of the present invention is typically carried out in a pressurized reactor equipped with an efficient stirring system using equipment known in the art. The pressure used for polymerization can be selected from a wide range of about 280 to about 20,000 kPa, depending on the volume of the reactor, the initiator system selected, and the monomer composition used. The polymerization pressure is typically about 2,000 to about 11,000 kPa, most typically about 2,750 to about 6,900 kPa. The polymerization temperature can vary from 20°C to about 160°C, typically about 35°C to about 130°C, and most typically about 65°C to about 95°C, depending on the initiator system selected.

[0076] (Latex Characterization) The present invention provides fluororesin latexes that are shear stable as measured by the Latex Shear Stability Test Method, in which the latex is stirred at 2500 rpm for 30 minutes as described in the Test Methods section (below). If the latex maintains a viscosity of 100 cps or less under these test conditions, it is a shear stable latex.

[0077] The volume average particle size of the latex of the present invention is greater than 400 nm, preferably greater than 450 nm, and most preferably greater than 500 nm. The volume average particle size of the latex of the present invention is 3 microns or less.

[0078] For a latex having a multimodal particle size distribution, at least 20%, more preferably at least 30%, and most preferably at least 35% of the total number of fluororesin particles in the latex have a volume average primary particle diameter greater than 475 nm and less than 2000 nm, more preferably greater than 500 nm and less than 2000 nm, or greater than 525 nm and less than 2000 nm.

[0079] The shear-stable latex may have a solids content of greater than 20% by weight, preferably greater than 22% by weight.

[0080] Fluoroplastics can have melt viscosities of 50 kpoise or greater using the method of the present invention.

[0081] The following examples are provided to illustrate the practice of the present invention and should not be construed as limiting the scope of the claims. Deionized water and ACS reagent grade ingredients were used in the examples unless otherwise noted. [Example]

[0082] (Test Method) Light scattering test method for latex particle size: Measure the particle size of the latex particles using a Nicomp CW380 particle size analyzer (light scattering method). Use the volume average particle size.

[0083] (Latex shear stability test method) (a) Filter 450.0 grams of latex sample through a 125 micron pore size screen. Add 0.5 grams of antifoam agent (TEGO® Foamex 840, manufactured by Evonik) to the latex sample. (b) Pour the sample into a 500 mL container. Stir the sample (2500 rpm) at room temperature using a Caframo Universal Overhead Stirrer (Model BDC3030). Monitor the latex while stirring, noting any change in consistency. Run the stirrer for 30 minutes, or until the latex stops moving or coagulates. (c) After 30 minutes of stirring, the latex is filtered through a 125 micron pore size screen. The coagulum (if any) collected on the screen is weighed. The Brookfield viscosity of the filtered latex is measured at 25°C using a Brookfield viscometer (Model DV-II+Pro, spindle #34, 35 rpm). (d) A latex sample is considered shear stable if the collected coagulum (wet coagulum) is less than 1.0% by weight (4.5 g) of the total latex and the Brookfield viscosity after 30 minutes of stirring is less than 100 cps.

[0084] Melt viscosity (MV): ASTM method D3835-16 (capillary rheometry). Measured at 232°C for 100 seconds. -1 Report values ​​in kilopoise (kP).

[0085] Solids content: Weigh a sample of latex. Dry the sample at 100°C for 24 hours and weigh the dry sample. Solids content (%) = dry weight / total weight.

[0086] Four sets of examples were prepared, and the synthesis parameters and latex properties are summarized in the table below.

[0087] (General manufacturing procedure for large particle size shear stable fluororesin latex) A 2-gallon autoclave was charged with 4500 g of deionized water, surfactant, and particle size modifier. The autoclave was stirred at 72 rpm, heated to 83°C, and pressurized to 650 psi (4481 kPa) with HFP and vinylidene fluoride. A 2.0 wt. % aqueous KPS feed was started at 180 mL / h. When a pressure drop began, indicating the onset of polymerization, the KPS feed rate was reduced to 25 mL / h, and the pressure was maintained by additional VDF and HFP feeds. Feeds continued in this manner until the desired VDF and HFP levels were reached. The reaction temperature was maintained at 83°C for an additional 30 minutes. The pressure was then allowed to spontaneously decrease over 10 minutes, at which point the reactor was vented to atmospheric pressure and cooled to room temperature. The product was discharged from the reactor.

[0088] All examples were prepared according to the procedure described above, and the monomers, surfactants, and particle size modifiers used in each example are listed in the table.

[0089] (Effect of particle size adjuster level) The effect of particle size modifier level on the production of large particle size "LPS" shear-stable latex was investigated using two particle size modifiers: NaCl and CsCl. As shown in Tables 1A and 1B, an LPS shear-stable latex (PS > 400 nm) was obtained when the particle size modifier / surfactant ratio was 5.3. The reaction mixture coagulated when the particle size modifier / surfactant ratio reached 7.9. As shown in Figure 1, the particle size increased linearly with increasing particle size modifier / surfactant ratio. This trend was also observed in the case of using CsCl and SOS. A CsCl / SOS ratio of 4.9 resulted in LPS shear-stable latex (>400 nm). The reaction coagulated when the CsCl / SOS ratio reached 7.2.

[0090] [Table 1A]

[0091] [Table 1B]

[0092] Figure 1 shows the particle size as a function of the particle size modifier / surfactant ratio. As the ratio increases, the volume average particle size also increases.

[0093] Effect of different particle size modifiers: Tables 2A and 2B show that certain halide salts can be used to increase the particle size of fluororesin latex. CaCl2 coagulated the batch at this ratio, and FeSO4 failed to achieve the particle size of the present invention.

[0094] [Table 2A]

[0095] [Table 2B]

[0096] (Effect of different surfactants) Tables 3A and 3B show that surfactants other than SOS, such as the triblock polyether glycols manufactured by BASF, cannot be used to prepare LPS shear-stable latexes.

[0097] [Table 3A]

[0098] [Table 3B]

[0099] LPS shear-stable latexes made with different particle size modifiers can have different particle size distributions. LPS shear-stable latexes made with NaCl, LiCl, or NH4Cl have a multimodal distribution. LPS shear-stable latexes made with CsCl have a unimodal distribution.

Claims

1. An aqueous latex comprising a surfactant, a particle size modifier, and a fluororesin, the surfactant comprises at least one alkane sulfonate selected from the group consisting of C7 to C20 1-alkane sulfonates, C7 to C20 2-alkane sulfonates, C7 to C20 1,2-alkane disulfonates, and mixtures thereof; The grain size modifier comprises MX, where M is an alkali metal or NH 4 and preferably an alkali metal, and X is a halide; the ratio of particle size control agent to surfactant is 2 or greater on a mole-to-mole basis; the concentration of the fluororesin is at least 15% by weight, preferably at least 20% by weight, based on the total weight of the aqueous latex; the volume average particle diameter of the fluororesin in the aqueous latex is more than 400 nm and less than 3000 nm, preferably more than 450 nm and less than 2000 nm, when measured by a light scattering method; The aqueous latex is shear stable as measured by the Latex Shear Stability Test, and has a viscosity of less than 100 cps after 30 minutes at 2500 rpm and 25°C.

2. 2. The aqueous latex according to claim 1, wherein the volume average particle diameter of the fluororesin in the aqueous latex is greater than 500 nm and less than 1500 nm, as measured by a light scattering method.

3. 2. The aqueous latex of claim 1, wherein the fluororesin comprises at least 50% by weight of vinylidene fluoride.

4. 2. The aqueous latex according to claim 1, wherein the fluorine-containing monomer comprises hexafluoropropylene.

5. 10. The aqueous latex of claim 1, wherein M is an alkali metal.

6. 2. The aqueous latex of claim 1, wherein M is selected from the group consisting of Na, Cs, and Li.

7. 2. The aqueous latex of claim 1, wherein X is Cl or Br, preferably Cl.

8. The particle size adjuster is NaCl, CsCl, LiCl or NH 4 10. The aqueous latex of claim 1, comprising at least one of:

9. M is lithium, sodium, cesium or NH 4 and X is Cl.

10. 10. The aqueous latex of claim 1, wherein the molar ratio of particle size modifier to surfactant is at least 3.

11. 2. The aqueous latex of claim 1, wherein the molar ratio of particle size modifier to surfactant is at least 2 and at most 7.8, preferably at most 7.

0.

12. 2. The aqueous latex of claim 1, wherein the fluororesin exhibits a monomodal particle size distribution when M is cesium.

13. 2. The aqueous latex of claim 1, wherein when M is sodium or lithium, the fluororesin exhibits a multimodal particle size distribution.

14. A method for increasing the volume average particle size of a fluororesin, comprising the steps of: (a) contacting an aqueous mixture containing a surfactant and a particle size modifier with a monomer feed containing one or more fluorine-containing monomers and a radical initiator feed; and (b) initiating polymerization of said one or more fluorine-containing monomers, thereby forming a fluororesin shear-stable latex; the surfactant comprises an alkane sulfonate selected from C7 to C20 1-alkane sulfonates, C7 to C20 2-alkane sulfonates, C7 to C20 1,2-alkane disulfonates, and mixtures thereof; The particle size modifier comprises MX, where M is an alkali metal or NH 4 and X is a halide; A process wherein the ratio of particle size modifier to surfactant is 2 or greater on a mole to mole basis.

15. The method of claim 14, wherein the fluorine-containing monomer comprises vinylidene fluoride.

16. The method of claim 14, wherein the fluorine-containing monomer comprises hexafluoropropylene.

17. 15. The method of claim 14, wherein the alkanesulfonate is selected from C8 to C12 1-alkanesulfonates, C8 to C12 2-alkanesulfonates, C8 to C12 1,2-alkanedisulfonates, and mixtures thereof.

18. 15. The method of claim 14, wherein the surfactant comprises an alkane sulfonate selected from 1-octane sulfonate, 2-octane sulfonate, 1,2-octane disulfonate, 1-decane sulfonate, 2-decane sulfonate, 1,2-decane disulfonate, 1-dodecane sulfonate, 2-dodecane sulfonate, 1,2-dodecane disulfonate, and combinations thereof.

19. The method of claim 14, wherein the alkanesulfonate comprises 1-octanesulfonate.

20. 15. The method of claim 14, wherein the alkanesulfonate is sodium alkanesulfonate, potassium alkanesulfonate, or ammonium alkanesulfonate, or a mixture thereof.

21. The particle size modifier is MX, where M is a metal or NH 4 15. The method of claim 14, wherein X is a halide.

22. M is an alkali metal or NH 4 The method of claim 14, wherein

23. 15. The method of claim 14, wherein M is selected from the group consisting of Na, Cs, and Li.

24. 15. The method of claim 14, wherein X is Cl or bromide, preferably Cl.

25. The particle size adjuster is NaCl, CsCl, LiCl or NH 4 15. The method of claim 14, further comprising at least one of: Cl.

26. 15. The method of claim 14, wherein the fluoroplastic comprises a copolymer comprising vinylidene fluoride and hexafluoropropylene monomer units.

27. 15. The method of claim 14, wherein the fluororesin comprises at least 75% by weight of vinylidene fluoride units.

28. 15. The method of claim 14, wherein the radical initiator comprises a persulfate.

29. 15. The method of claim 14, wherein the weight percent of the functionalized fluororesin in the latex after step (b) comprises at least 15 weight percent of the latex, preferably at least 20 weight percent.

30. 15. The method of claim 14, wherein when M is cesium, the fluororesin exhibits a monomodal particle size distribution.

31. 15. The method of claim 14, wherein when M is sodium or lithium, the fluororesin exhibits a multimodal particle size distribution.

32. 1. A method for producing a multimodal fluororesin dispersion, comprising the steps of: (a) contacting an aqueous mixture containing a surfactant and a particle size modifier with a monomer feed containing one or more fluorine-containing monomers and a radical initiator; and (b) applying heat and pressure sufficient to polymerize said one or more fluorine-containing monomers, thereby forming a fluororesin dispersion; Including; the surfactant comprises at least one alkane sulfonate selected from the group consisting of C7 to C20 linear 1-alkane sulfonates, C7 to C20 linear 2-alkane sulfonates, C7 to C20 linear 1,2-alkane disulfonates, and mixtures thereof; and at least 50% by weight of vinylidene fluoride; The particle size modifier comprises MX, where M is lithium, sodium, or NH 4 and X is Cl, and the ratio of size modifier to surfactant is greater than 2 on a mole to mole basis.

33. 10. Use of the aqueous latex according to claim 1 in lithium ion battery applications, preferably as a separator coating or electrode binder.

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