Process for producing a fluoropolymer dispersion

Abstract

The present invention relates to a process for producing stable fluoropolymer latexes using non-fluorinated surfactants with higher thermal stability. Polymerization is carried out at higher pressures than those typically used. The resulting polymers exhibit improved melt color stability compared to those produced under similar conditions at lower pressures.

Description

[Technical Field]

[0001] This invention relates to a process for forming a high-solids latex, fluoropolymer dispersion using a non-fluorinated surfactant having higher thermal stability (i.e., less yellowing). Polymerization is carried out at a higher pressure than typically used with an emulsifier containing segments of polyethylene glycol and / or polypropylene glycol and / or polytetramethylene glycol. This process can also be used with little to no surfactant. [Background technology]

[0002] Emulsion polymerization is a preferred method for forming fluoropolymers, producing fluoropolymer particles with an average particle size in the range of 20 nm to 1000 nm, and latex generally having a low viscosity of less than 10 cP. This range is stable in shear and storage and can be easily transported by pumps and other common liquid process technologies.

[0003] In the field of commercially available fluoropolymers, it is generally understood that stabilizing additives must be used to obtain stable dispersion of polymer particles in the liquid (aqueous) phase. Common additives known as surfactants or emulsifiers include ionic amphiphilic substances such as sodium lauryl sulfate (SLS) and hexadecyltrimethylammonium bromide (CTAB), and nonionic amphiphilic substances such as octaethylene glycol monododecyl ether and polyethylene glycol octylphenyl ether (TRITON X-100, etc.). These compounds act to stabilize the interface between (fluoro)polymer particles and the aqueous phase, reducing the strength of interparticle interactions and the overall strength, and suppressing premature solidification of the solid from the liquid phase. Emulsions made with these types of surfactants often exhibit improved stability against solidification by mechanical shear, and it is often possible to increase the solid concentration while maintaining very low viscosity. Both enable efficient and cost-effective commercial production of fluoropolymer resins, as well as direct use in applications requiring low-viscosity aqueous dispersions of solids, such as substrates for high-performance architectural coatings. [Overview of the project] [Problems that the invention aims to solve]

[0004] Conversely, while these surfactants improve desirable properties of fluoropolymer latexes, they have the undesirable effect of interfering with free radical polymerization reactions via chain transfer. This interference manifests as a decrease in polymerization rate, reduced production throughput, and the possibility of incorporating parts of the surfactant structure into the fluoro(co)polymer itself. This can lead to undesirable changes in the physical properties of the final material, such as giving it a yellow or brown color.

[0005] To address these issues, those skilled in the art have widely utilized (per)fluorinated surfactants for fluoromonomer polymerization that does not interfere with or involve the fluoromonomer polymerization reaction. While this approach is highly effective, serious concerns have arisen regarding the biological and environmental persistence of these fluorinated surfactants, as well as their toxicity. Therefore, it is highly desirable to discontinue their use. Recently, regulations have been implemented to eliminate the use of C8 and long-chain perfluorinated surfactants, and it is expected that short-chain (per)fluorinated surfactants will also be phased out in the near future.

[0006] Stable fluoropolymers that do not contain fluorosurfactants have been manufactured, for example, as described in U.S. Patents 8,080,621, 8,124,699, 8,158,734, 8,338,518, 8,765,890, and 9,068,071. While this solves the toxicity problem, fluoropolymers manufactured with non-fluorinated surfactants can oxidize under thermal aging, potentially causing undesirable yellowing of the fluoropolymer. [Means for solving the problem]

[0007] Surprisingly, it was found that stable, low-viscosity, high-solids aqueous fluoropolymer emulsions with improved thermal color stability could be produced when the polymerization pressure was greater than 800 psi and up to 13000 psi, preferably greater than 1000 psi and up to 3000 psi, more preferably between 1100 psi and 2000 psi. A surfactant comprising a non-fluorinated nonionic emulsifier containing at least one segment of polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), or a combination thereof was used, with repeating units of 2 to 200, preferably 3 to 100, more preferably 5 to 50, and the process was carried out at a solids level of at least 33.5% by weight, preferably greater than 34% by weight, preferably greater than 35% by weight, and more preferably at least 36%. Polymerization was found to be carried out at a solids level of at least 37% by weight, or at least 38% by weight. The surfactant can be added before and / or after the start of the polymerization reaction.

[0008] An advantage of the present invention is that the melt-treated plaques of the resulting fluoropolymer exhibit improved thermal color stability against the relevant control, which is a crucial factor for many fluoro(co)polymer applications that use melt processing techniques such as extrusion and injection molding to produce final parts and products.

[0009] In some embodiments of the present invention, lower levels of initiators and / or surfactants can be used compared to standard polymerization processes using equivalent solids content and run times. The presence of surfactants and / or initiators can adversely affect the color of the polymer. Reducing the amount of surfactants and / or initiators used in polymerization reduces the amount of surfactants and / or initiators in the final product, resulting in a whiter product (less yellowing).

[0010] In embodiments of the present invention, the present invention relates to a method for producing a thermally stable fluoropolymer emulsion composition comprising at least 33.5% by weight of a fluoropolymer, preferably more than 34% by weight of a fluoropolymer or more than 35% by weight of a fluoropolymer. Here, the polymerization process is carried out at a pressure exceeding 800 psi, preferably more than 1000 psi, more preferably at least 1100 psi, and preferably at least 1200 psi. In all cases, the process does not contain a fluorinated surfactant.

[0011] The level of fluoropolymer solids in the composition is 33.5 to 50% by weight, preferably more than 34 to 45% by weight, more preferably more than 35 to 45% by weight, and more preferably 36 to 45% by weight. The level of fluoropolymer solids in the latex may exceed 37% by weight.

[0012] In one embodiment, the resulting stable fluoropolymer composition or emulsion may contain little to no surfactants and have a high fluoropolymer solids content. The latex can be dried to a solid resin that contains little to no surfactants without the use of ion exchange, washing, or other additional unit operations.

[0013] The stable fluoropolymer emulsion composition of the present invention may be a homopolymer or copolymer having at least 70% by weight of vinylidene fluoride monomer units.

[0014] The stable fluoropolymer emulsion composition of the present invention may further contain one or more initiators in an amount of 100 ppm to 10,000 ppm. Preferably, the initiator contains at least one persulfate.

[0015] In another embodiment, the stable fluoropolymer emulsion composition has a level of zero surfactant.

[0016] One embodiment is a method for forming a stable fluoropolymer emulsion, comprising the following steps: a) The reaction mixture is filled into the reactor while stirring. The reaction mixture contains one or more fluoromonomers and a non-fluorinated surfactant. b) The reaction mixture is heated to a temperature of at least 25°C, preferably at least 50°C, or at least 80°C, but not exceeding 145°C, and one or more initiators are added. c) Pressurize the reactor to a pressure exceeding 800 psi, preferably exceeding 1000 psi, and more preferably at least 1100 psi. d) Supply additional monomers and initiators, and optionally surfactants, continuously or intermittently until polymerization is complete.

[0017] Another embodiment of the present invention relates to a fluoropolymer composition produced by the process of the present invention, which has improved thermal color stability.

[0018] The fluoropolymer composition may optionally contain dyes; colorants; impact modifiers; antioxidants; flame retardants; UV stabilizers; flow aids; conductive additives such as metals, carbon black, and carbon nanotubes; defoamers; crosslinking agents; waxes; solvents; plasticizers; and antistatic agents.

[0019] Embodiments of the present invention

[0020] Embodiment 1. A process for forming a stable fluoropolymer emulsion, comprising polymerizing one or more fluoromonomers in an aqueous medium containing an initiator and optionally a fluorine-free surfactant in a reactor at a pressure exceeding 800 psi, wherein the surfactant comprises a non-fluorinated nonionic emulsifier having 2 to 200, preferably 3 to 100, more preferably 5 to 50 repeating units, comprising at least one segment from polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), or a combination thereof.

[0021] Aspect 2. The process according to Aspect 1, wherein the pressure during the polymerization exceeds 1000 psi.

[0022] Aspect 3. The process according to Aspect 1 or 2, wherein the pressure during the polymerization is at least 1100 psi, preferably at least 1150 psi, more preferably at least 1200 psi.

[0023] Aspect 4. The process according to Aspect 1, wherein the pressure during the polymerization exceeds 1000 psi and is up to 2500 psi.

[0024] Aspect 5. The process according to Aspect 4, wherein the pressure during the polymerization is from 1100 psi to 2000 psi.

[0025] Aspect 6. The process according to any one of Aspects 1 to 5, wherein the surfactant comprises at least one surfactant selected from the group consisting of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEG-MA), dimethyl polyethylene glycol (DMPEG), polyethylene glycol butyl ether (PEGBE), polyethylene glycol (PEG), polyethylene glycol phenyl oxide (Triton X-100), polypropylene glycol acrylate (PPGA), polypropylene glycol (PPG), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPG-MA), and polytetramethylene glycol (PTMG).

[0026] Aspect 7. The process according to any one of Aspects 1 to 5, wherein the surfactant comprises an emulsifier of Formula 1. T1 - [(CH2 - CH2 - O - ) X m - [(CH2 - CH(CH3) - O - ) Y n - [(CH2 - CH2 - O - ) Z k - T2 (Formula 1) ​​​In the formula, X, Y, and Z are between 2 and 200, m, n, and k are between 0 and 5, at least one of m, n, and k is greater than 0, and T1 and T2 are terminal groups such as hydrogen, hydroxyl, carboxyl, ester, ether, and / or hydrocarbon.

[0027] Embodiment 8. The process according to any one of Embodiments 1 to 5, wherein the surfactant preferably comprises a triblock copolymer having a PEG central block and a PPG end block.

[0028] Embodiment 9. The process according to any one of Embodiments 1 to 8, wherein the non-fluorinated nonionic emulsifier is present in the process at an amount of 0 to 1%, preferably 100 ppm to 1%, relative to the weight of the fluoropolymer solids.

[0029] Embodiment 10. The process according to any one of Embodiments 1 to 5, wherein no surfactant is added during polymerization.

[0030] Embodiment 11. The process according to any one of Embodiments 1 to 10, wherein the fluoromonomer is one or more fluoromonomers selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, 1,1,1,3,3-pentafluoropropene, 3,3,3-trifluoro-1-(trifluoromethyl)prop-1-ene, 1,1,1,2-tetrafluoropropene, 1,1,1-trifluoropropene, 1,1,1,3-tetrafluoropropene, 1,1,1,2,3-pentafluoropropene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.

[0031] Embodiment 12. The process according to any one of Embodiments 1 to 11, wherein the fluoropolymer comprises at least 50 mol% vinylidene fluoride monomer units.

[0032] Embodiment 13. The process according to any one of Embodiments 1 to 12, wherein the fluoropolymer comprises 70 to 100 mol% vinylidene fluoride monomer units and the level of one or more other fluoromonomers is 0 to 30 mol%.

[0033] Aspect 14. The process according to any one of Aspects 1 to 13, further comprising one or more ionic or ionizable initiators in a concentration of 100 ppm to 10,000 ppm.

[0034] Embodiment 15. The process according to any one of Embodiments 1 to 14, wherein the initiator comprises at least one or more initiators selected from the group consisting of ammonium persulfate, alkali metal salts of persulfates, dialkyl persulfates, diacyl peroxide, peroxyesters, and peroxydicarbonates, preferably from the group consisting of ammonium or alkali metal salts of persulfates.

[0035] Embodiment 16. The process according to any one of Embodiments 1 to 15, wherein the solids content level in the stable emulsion produced is at least 33.5% by weight, preferably more than 34% by weight, preferably more than 35% by weight, preferably more than 36% by weight, and more preferably more than 37% by weight of fluoropolymer solids.

[0036] Embodiment 17. The process according to any one of Embodiments 1 to 16, wherein the solids content level in the stable emulsion produced is at least 33.5 to 50% by weight, or more than 34 to 45% by weight of solids, more preferably 35 to 45% by weight, more preferably 36 to 45% by weight, and more preferably 37 to 45% by weight of fluoropolymer solids.

[0037] Embodiment 18. The process according to any one of Embodiments 1 to 17, wherein the surfactant is not added before the start of the polymerization reaction.

[0038] Embodiment 19. The process according to any one of Embodiments 1 to 17, wherein at least a portion of the surfactant is added before the start of the polymerization reaction.

[0039] Embodiment 20. The process according to any one of Embodiments 1 to 19, wherein the YI of the polymer is 20 or less.

[0040] Embodiment 21. A polymer produced by the process described in any one of Embodiments 1 to 20.

[0041] Embodiment 22. The polymer according to Embodiment 21, further comprising at least one additive selected from the group consisting of dyes; colorants; impact modifiers; antioxidants; flame retardants; ultraviolet stabilizers; flow aids; conductive additives such as metals, carbon black, and carbon nanotubes; defoamers; crosslinking agents; waxes; solvents; plasticizers; and antistatic agents. [Modes for carrying out the invention]

[0042] All references cited herein are incorporated herein by reference. All percentages in the compositions are weight percent unless otherwise specified, and all molecular weights are given as weight-average molecular weights determined by GPC using PMMA as a standard, unless otherwise specified.

[0043] The term "polymer" is used to mean both homopolymers, copolymers, and terpolymers (three or more monomer units) unless otherwise specified. Any copolymer or terpolymer may be random, blocky, or gradient, and polymers may be linear, branched, star-shaped, comb-shaped, or any other form.

[0044] The term "stable" in relation to the fluoropolymer latex composition of the present invention means that the latex flowing out of the reactor can be injected and pumped without forming solids, which are defined as material that does not pass through a 100-mesh screen. Such solids include hard particles and clumps of wet material (also called "blobs"). The stable fluoropolymer latex of the present invention does not visually settle after 3 months of storage, or if some settling occurs, it can be redispersed by gentle stirring. If solids form during settling, the material is considered unstable. If more than 6% of solids are recovered, it is not sufficiently stable.

[0045] Fluoropolymer

[0046] The fluoropolymers of the present invention include, but are not limited to, polymers containing at least 50% by weight of one or more fluoromonomers. As used in the present invention, the term "fluoromonomer" means fluorinated and olefin unsaturated monomers capable of undergoing free radical polymerization. Exemplary fluoromonomers suitable for use according to the present invention include, but are not limited to, the following: vinylidene fluoride (VDF); tetrafluoroethylene (TFE); trifluoroethylene (TrFE); chlorotrifluoroethylene (CTFE); hexafluoropropene (HFP); vinyl fluoride (VF); 3,3,3-trifluoro-1-(trifluoromethyl)prop-1-ene (HFIB); perfluorobutylethylene (PFBE); pentafluoropropene; 3,3,3-trifluoro-1-propene; 2-trifluoromethyl-3,3,3-trifluoropropene; 1,1-dichloro-1,1-difluoroethylene; 1,2-dichloro 1,2-difluoroethylene; 1,1,1-trifluoropropene; 1,3,3,3-tetrafluoropropene; 2,3,3,3-tetrafluoropropene; 1-chloro-3,3,3-trifluoropropene; fluorinated or perfluorovinyl ethers including perfluoromethyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), perfluoropropyl vinyl ether (PPVE), perfluorobutyl vinyl ether (PBVE), and long-chain perfluorovinyl ethers; fluorinated dioxole; partially or perfluorinated alphaolefins of C4 or higher; partially or perfluorinated cyclic alkenes of C3 or higher; and combinations thereof. Fluoropolymers produced in the embodiment of the present invention include homopolymers produced by polymerization products of the above fluoromonomers, such as polyvinylidene fluoride (VDF), by polymerization of the VDF itself.

[0047] Fluoro-terpolymers are also conceivable, including terpolymers having tetrafluoroethylene, hexafluoropropene, and vinylidene fluoride monomer units. Most preferably, the fluoropolymer is polyvinylidene fluoride (PVDF). While the present invention is exemplified with respect to PVDF, those skilled in the art will recognize that other fluoropolymers, including those containing four or more fluoromonomers, may also be represented when the term PVDF is used as an example.

[0048] The polyvinylidene fluoride (PVDF) of the present invention is a PVDF homopolymer, copolymer, or polymer alloy. The polyvinylidene fluoride polymer of the present invention includes homopolymers, copolymers, terpolymers, and higher polymers of vinylidene fluoride produced by polymerizing vinylidene fluoride (VDF), wherein the vinylidene fluoride units exceed 51% by weight of the total weight of all monomer units in the polymer, preferably exceeding 70% by weight, and more preferably exceeding 75% by weight of the total weight of monomer units. Copolymers, terpolymers, and higher polymers of vinylidene fluoride (generally referred to herein as “copolymers”) can be prepared by reacting vinylidene fluoride with one or more monomers from the group consisting of: vinyl fluoride; trifluoroethene; tetrafluoroethene; one or more partially or completely fluorinated monomers such as 3,3,3-trifluoro-1-propene, 1,2,3,3,3-pentafluoropropene, 3,3,3,4,4-pentafluoro-1-butene, and 3,3,3-trifluoro-1-(trifluoromethyl)prop-1-ene. Modified alpha-olefins; perfluorovinyl ethers such as perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl vinyl ether, and perfluoro-2-propoxypropyl vinyl ether; fluorinated dioxoles such as perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole); allyls; partially fluorinated allyls; or fluorinated allyl monomers such as 2-hydroxyethyl allyl ether or 3-allyloxypropanediol; and ethenes or propenes. Preferred copolymers or terpolymers are formed from vinyl fluoride, trifluoroethene, tetrafluoroethene (TFE), and hexafluoropropene (HFP).

[0049] Preferred copolymers include those containing about 55 to about 99% by weight of VDF and correspondingly about 1 to about 45% by weight of HFP, preferably 2 to 30% by weight of HFP; copolymers of VDF and CTFE; terpolymers of VDF / HFP / TFE; copolymers of VDF and TFE; and copolymers of VDF and 1,1,1,2-tetrafluoropropene.

[0050] In one embodiment of the present invention, it is preferable that all monomer units are fluoromonomers, but copolymers of fluoromonomers and non-fluoromonomers are also envisioned by the present invention. In the case of copolymers containing non-fluoromonomers, at least 60% by weight of the monomer units are fluoromonomers, preferably at least 70% by weight, more preferably at least 80% by weight, and most preferably at least 90% by weight are fluoromonomers. Useful comonomers include, but are not limited to, ethylene, propylene, styrene, acrylate, methacrylate, vinyl ester, vinyl ether, non-fluorine-containing halogenated ethylene, vinylpyridine, and N-vinyl linear and cyclic amides.

[0051] surfactant

[0052] The emulsifiers (surfactants) suitable for use in the present invention are non-fluorinated non-ionic emulsifiers containing segments of polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), or combinations thereof, with repeating units of 2 to 200, preferably 3 to 100, more preferably 5 to 50. The glycol-based emulsifiers used in the present invention include, but are not limited to, polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEG-MA), dimethyl polyethylene glycol (DMPEG), polyethylene glycol butyl ether (PEGBE), polyethylene glycol (PEG), polyethylene glycol phenoxide (Triton X-100), polypropylene glycol acrylate (PPGA), polypropylene glycol (PPG), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPG-MA), and polytetramethylene glycol (PTMG).

[0053] Emulsifiers containing blocks and having the following Formula 1 are preferred for producing light-colored polymers that are resistant to discoloration at room temperature for extrusion or other manufacturing techniques. T1 - [(CH2-CH2-O-) X m - [(CH2-CH(CH3)-O-) Y n - [(CH2-CH2-O-) Z k - T2 (Formula 1) In the formula, X, Y, and Z are 2 to 200, and m, n, k are 0 to 5. T1 and T2 are end groups such as hydrogen, hydroxyl, carboxyl, ester, ether, and / or hydrocarbon.

[0054] ​​​One preferred block copolymer of the present invention is a triblock copolymer of Formula 1 comprising PEG and PPG blocks. These triblock polymers have a central block of either PEG or PPG, and the end blocks may differ from those of the central block. In one embodiment, the PEG block constitutes less than 30% by weight, preferably less than 20% by weight, and most preferably less than 10% by weight of the triblock. One particularly preferred triblock copolymer is a triblock having a PEG central block and PPG end blocks.

[0055] Emulsifiers may contain the same or different end groups at each end, such as hydroxyl, carboxylate, benzoate, sulfonate, phosphonic acid, acrylate, methacrylate, ether, hydrocarbon, phenol, functionalized phenol, ester, and fatty ester. End groups may include halogen atoms such as Cl, Br, and I, as well as other groups or functionalities such as amines, amides, and cyclic hydrocarbons. For example, polyethylene glycol acrylate with approximately 375 Mn, polyethylene glycol with approximately 570 Mn, polyethylene glycol methacrylate with approximately 526 Mn, dimethylethylene glycol with approximately 250 Mn, polyethylene glycol butyl ether with approximately 206 Mn, polyethylene glycol with approximately 300 Mn, polypropylene glycol acrylate with approximately 475 Mn, polypropylene glycol with approximately 400 Mn, polypropylene glycol methacrylate (PPG-MA) with approximately 375 Mn, polytetramethylene glycol with approximately 250 Mn, and polyethylene glycol having phenol oxide end groups. More specifically, PPG-b-PEG-b-PPG (BASF's Pluronic 31R1 and 25R2), PEG-b-PPG-b-PEG (BASF's Pluronic L101 and L-92), PPG (Pluronic P-4000), and PEG (Pluronic The stable fluoropolymer dispersions of the present invention can be produced using single, di, and triblock PEGs, PPGs, PTMGs, and many other examples, such as E-2000.

[0056] A preferred embodiment of the present invention uses an emulsifier comprising a segment of polyethylene glycol and / or polypropylene glycol and / or polytetramethylene glycol.

[0057] Emulsifiers are generally used at levels of 2 ppm to 2.5%, 100 ppm to 1% (10,000 ppm), and 100 ppm to 0.5% (5,000 ppm) relative to the total polymer solids of the fluoropolymer formed in the dispersion. In other embodiments of the present invention, very low levels of surfactants, less than 0.01% by weight, preferably less than 0.004% by weight, relative to the total monomers, can be used. In yet another embodiment of the present invention, no surfactant is used throughout the polymerization process. In all cases, the reaction pressure is greater than 800, preferably greater than 1000 psi, more preferably at least 1100 psi, and more preferably at least 1200 psi. The pressure can be greater than 1000 psi and up to about 2500 psi, preferably 1100 to 2000 psi.

[0058] This process does not include fluorinated or partially fluorinated emulsifiers.

[0059] In the polymerization process, the emulsifier of the present invention can be added entirely before polymerization, continuously supplied during polymerization, partially supplied before and after polymerization, or supplied after polymerization has started and progressed for a while.

[0060] If the emulsifier of the present invention is not supplied after the start of polymerization, it may be supplied after the fluoromonomer conversion rate has reached at least 0.5%, more preferably at least 1% (the conversion rate is defined as [(mass of polymer formed) / mass of total polymer at completion) × 100]. Preferably, the addition of the emulsifier is started before the conversion rate of the fluoropolymer reaches 15%, more preferably before it reaches 10%.

[0061] Chain transfer agent

[0062] Chain transfer agents are added to polymerization as needed to adjust the molecular weight of the product. They may be added all at once at the start of the reaction, or intermittently or continuously throughout the reaction. The amount and method of adding the chain transfer agent depend on the activity of the specific chain transfer agent used and the desired molecular weight of the polymer product. The amount of chain transfer agent added to the polymerization reaction is preferably about 0.05 to about 5% by weight, more preferably about 0.1 to about 2% by weight, relative to the total weight of the monomers added to the reaction mixture.

[0063] Examples of chain transfer agents useful in the present invention include, but are not limited to, oxygenated compounds such as alcohols, carbonates, ketones, esters, and ethers that can function as chain transfer agents; halocarbons and hydrohalocarbons such as chlorocarbons, hydrochlorocarbons, chlorofluorocarbons, and hydrochlorofluorocarbons; and ethane and propane.

[0064] Initiator

[0065] The reaction can be initiated and maintained by the addition of any suitable initiator known for the polymerization of fluorinated monomers, including inorganic peroxides, "redox" combinations of oxidizing and reducing agents, organic peroxides, and azo compounds. Typical examples of inorganic peroxides are ammonium or alkali metal salts of persulfates. "Redox" systems can operate at even lower temperatures, and examples of combinations include: oxidizing agents such as hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, or persulfates; reducing agents such as reduced metal salts, iron(II) salts, which are specific examples; and optionally combined with activators such as sodium formaldehyde sulfoxylate, sodium metabisulfite, or ascorbic acid. Among the organic peroxides that can be used for polymerization are the classes of alkyl peroxides, dialkyl peroxides, diacyl peroxides, peroxyesters, and peroxydicarbonates. Examples of dialkyl peroxides include di-t-butyl peroxide, examples of peroxyesters include t-butyl peroxypivalate and t-amyl peroxypivalate, and examples of peroxydicarbonates include di(n-propyl)peroxydicarbonate, diisopropyl peroxydicarbonate, di(sec-butyl)peroxydicarbonate, and di(2-ethylhexyl)peroxydicarbonate. Azo initiators include azobisisobutyronitrile (AIBN), 2,3-diethyl-2,3-dimethylsuccinonitrile, and 2,3-diethyl-2,3-dimethylbutanedinitrile.

[0066] Useful ionic initiators include, but are not limited to, persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, as well as perphosphates and permanganates. Other ionic initiators known in the art, including organic initiators having acid-terminated groups such as organic peroxides containing ionic groups, are also intended for use in the present invention, one example being succinic acid peroxide. Alternatively, hydroxyl radical-generating initiators such as hydrogen peroxide function similarly. As is commonly practiced in the art, these types of initiators can be used in combination with reducing agents in “redox” type initiator systems, in which a third catalytic component may also be added. Blends of ionizable inorganic peroxides with other inorganic or organic peroxides are also conceivable. Potassium persulfate is a particularly preferred initiator.

[0067] The amount of initiator required for polymerization depends on its activity and the temperature used for polymerization. The total amount of initiator used is generally 0.002% to 2.5% by weight relative to the total weight of the monomers used. These compounds are typically added at a level sufficient to maintain a sufficient polymerization rate, typically 100 ppm to 10,000 ppm, preferably 200 ppm to 2,000 ppm, and most preferably 200 ppm to 1,500 ppm relative to the total monomers. While initiators can be supplied entirely in the initial feed, they are generally supplied delayed during the reaction process.

[0068] Typically, a sufficient amount of initiator is added first to start the reaction, and then additional initiators may be optionally added to maintain polymerization at a favorable rate. Depending on the initiator selected, the initiator can be added as a single substance, a solution, a suspension, or an emulsion. As a specific example, peroxydicarbonates are preferably added in the form of an aqueous emulsion.

[0069] Reaction conditions

[0070] The polymerization of the fluoropolymer emulsion free of fluorosurfactants of the present invention is carried out under high pressure compared to standard polymerization techniques. The pressure is greater than 800 psi, preferably greater than 1000 psi, more preferably at least 1100 psi, and more preferably at least 1200 psi. The pressure may be 800 to about 13000 psi, preferably greater than 1000 psi and up to 2500 psi, and even more preferably 1100 to 2000 psi. The polymerization of the fluoropolymer emulsion free of fluorosurfactants of the present invention is carried out at the polymerization temperature of a typical fluoropolymer emulsion. In the polymerization of vinylidene fluoride polymers and copolymers, the reaction temperature is 25°C to 145°C, preferably greater than 50°C, and more preferably greater than 80°C. In a preferred embodiment, this reaction temperature is kept constant (+ / -1°C) throughout the polymerization process. The solids content level in the stable emulsion is at least 33.5% by weight, preferably greater than 34% by weight, preferably greater than 35% by weight, preferably greater than 36% by weight, and more preferably greater than 37% by weight.

[0071] Polymerization can be carried out in batch mode, or preferably, at least a portion of the monomer and initiator are added initially, and a portion of the monomer and / or initiator are added later during the polymerization process.

[0072] Other additives

[0073] The fluoropolymer compositions of the present invention may also contain, but are not limited to, typical additives including: dyes; colorants; impact modifiers; antioxidants; flame retardants; UV stabilizers; flow aids; conductive additives such as metals, carbon black, and carbon nanotubes; defoamers; crosslinking agents; waxes; solvents; plasticizers; and antistatic agents. Other additives that provide whitening (including, but not limited to, metal oxide fillers such as zinc oxide; phosphate or phosphate stabilizers; and phenol stabilizers) may also be added to the fluoropolymer compositions.

[0074] characteristics

[0075] The particle size of the resulting emulsion is approximately the same as, or only slightly larger than, the product produced at low pressure. The general range of observed particle sizes is less than 350 nm, preferably less than 300 nm. Generally, particle sizes exceed 100 nm.

[0076] The solids content level in the stable emulsion produced by the present invention is at least 33.5% by weight, preferably exceeding 34% by weight, preferably exceeding 35% by weight, preferably exceeding 36% by weight, and more preferably exceeding 37% by weight. Solids content exceeding 40% or more by weight is also conceivable. The preferred solids content range is 33.5 to 50% by weight, or solids exceeding 34% up to 45% by weight, more preferably 35 to 45% by weight, more preferably 36 to 45% by weight, and more preferably 37 to 45% by weight.

[0077] The latexes of this invention have excellent shelf life, maintaining their fluidity and original viscosity with minimal sedimentation and no observed solidification after storage for more than three months. Furthermore, the latex is stable against common fluid transfer techniques such as discharging into storage containers, injection, stirring, and mechanical pumping.

[0078] The latex viscosity is typically 1.0 cP to 50 cP, preferably 1.5 to 25 cP.

[0079] For the purposes of this invention, a YI of 20 or less is considered acceptable. A YI greater than 20 is unacceptable. A YI value of less than 15 is recommended.

[0080] Purpose

[0081] The fluoropolymer emulsion free of fluorosurfactants of the present invention is useful in any application where surfactant-containing fluoropolymer emulsions are useful. Due to the low level of surfactant, the fluoropolymer of the present invention is particularly useful in applications involving thermal aging. Because of the reduced amount of surfactant, there is less surfactant that oxidizes and produces discoloration compared to polymerization operations at low pressure, and there are applications where radiation is applied to the material to promote crosslinking. [Examples]

[0082] Description and example of the invention: High-pressure FSF Example 1: Latex Synthesis: 8717 g of deionized water, 6.54 g of PPO-PEO-PPO block copolymer (BASF Pluronic® 31R1), and 20.0 g of ethyl acetate were added to the reactor. The reactor was stirred, heated to 83°C, and pressurized to 1250 psi with vinylidene fluoride. A 2.0 wt% aqueous potassium persulfate solution ("KPS") containing 2.0 wt% sodium acetate trihydrate ("SAT") was started at 650 g / hr. At the start of the pressure drop, the KPS / SAT supply was reduced to 200 g / hr. Additional VDF was supplied as needed to maintain the reaction pressure of 1250 psi. This supply was continued to maintain VDF uptake in the range of 1000-3000 g / hr. All supplies were continued until a total of 6213 g of VDF, including that used for pressurization, had been supplied to the reactor. The monomer supply was stopped, the pressure was allowed to drop spontaneously for 10 minutes, at which point the reactor was evacuated to atmospheric pressure and cooled to room temperature. The latex was discharged from the reactor and dried overnight in a convection oven. 14328.0 g of latex with a solids content of 33.5% by weight was recovered.

[0083] Except for the changes listed in Table 1, the same general procedure was used for tests 2-12. Data for the additional tests are shown in Table 1. The tests were performed with the same reactor / stirrer setup as in Example 1, but with variations in reaction pressure and total target latex solids.

[0084] [Table 1]

[0085] Examples 2-5 represent low-pressure reaction control, while tests 9-12 demonstrate the present invention. Tests 6 and 7 show lower solid content.

[0086] Test Example 1 uses higher pressure but shows lower solids content (less than 34%). Control tests were performed at low pressure (650 psi) (Examples 3-5), and in tests performed up to solids exceeding 33%, a considerable amount of solidified material was observed, with total solidification occurring at ~36% solids. At higher pressures, the amount of solidified material remained low (less than 5% of the total product), even in latex with a maximum solids content of 39.0% (Examples 9-12). Above that concentration, the latex solidifies completely into a solid. Notably, as evidenced by the test times, all tests were within the range of "typical" rates. Of course, this time is influenced by several factors, including the total amount of initiator and supply schedule, and the total amount of latex solids being tested, but it is immediately apparent that using new process conditions does not increase test times and does not negatively impact productivity. A "typical" reaction time of approximately 1.5 to 3.5 hours was maintained.

[0087] The dried material produced from the synthesis tests in Table 1 was melted and pressed onto four discs, each approximately 2.5 inches in diameter and 1 / 8 inch thick, on the same press plate, all made of the same material. After heating at 230°C for 10 minutes, the discs were removed.

[0088] A Minolta colorimeter was used to measure the YI (Yellowness Index) for each disc (YI is a value calculated from the absorbance measured by the instrument). Typical values ​​range from -10 to approximately 30. Generally, values ​​above YI=30 are meaningless, as they represent "brown" and saturate the instrument's detector. A YI of less than 7 is considered very good and represents a "clean-looking" white. A lower YI value is most desirable. For the purposes of this invention, a YI of 20 or less is considered acceptable.

[0089] When high-pressure tests were conducted, YI showed a significant improvement compared to low-pressure tests.

Claims

1. A process for forming a stable fluoropolymer emulsion, The process involves polymerizing one or more fluoromonomers in an aqueous medium containing an initiator and a fluorine-free surfactant in a reactor, while maintaining a pressure exceeding 1000 psi (6.9 MPa). The fluoromonomer consists of vinylidene fluoride, or vinylidene fluoride and hexafluoropropene. The surfactant comprises a non-fluorinated nonionic emulsifier having 2 to 200 repeating units, preferably 3 to 100, more preferably 5 to 50, which includes at least one segment from polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), or a combination thereof. The non-fluorinated nonionic emulsifier is present during the process in an amount greater than 0 and less than or equal to 1%, preferably 100 ppm to 1%, relative to the weight of the fluoropolymer solids. The solids content level in the resulting stable emulsion is at least 33.5% by weight of fluoropolymer solids. process.

2. The process according to claim 1, wherein the pressure during polymerization is at least 1100 psi (7.6 MPa), preferably at least 1150 psi (7.9 MPa), and more preferably at least 1200 psi (8.3 MPa).

3. The process according to claim 1, wherein the pressure during polymerization is greater than 1000 psi (6.9 MPa) and less than 2500 psi (17.2 MPa).

4. The process according to claim 3, wherein the pressure during polymerization is 1100 psi (7.6 MPa) to 2000 psi (13.8 MPa).

5. The process according to any one of claims 1 to 4, wherein the surfactant comprises at least one surfactant selected from the group consisting of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEG-MA), dimethyl polyethylene glycol (DMPEG), polyethylene glycol butyl ether (PEGBE), polyethylene glycol (PEG), polyethylene glycol phenol oxide (Triton X-100), polypropylene glycol acrylate (PPGA), polypropylene glycol (PPG), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPG-MA), and polytetramethylene glycol (PTMG).

6. The process according to any one of claims 1 to 4, wherein the surfactant comprises an emulsifier of formula 1. T 1 -[((CH 2 -CH 2 -O-) X m -[((CH 2 -CH(CH 3 ))-O-) Y n -[((CH 2 -CH 2 -O-) Z k -T 2 (Formula 1)​​​ In the formula, X, Y, and Z are between 2 and 200, m, n, and k are between 0 and 5, and at least one of m, n, and k is greater than 0, T 1 and T 2 The terminal group is selected from hydrogen, hydroxyl, carboxyl, and hydrocarbons.

7. The process according to any one of claims 1 to 4, wherein the surfactant preferably comprises a triblock copolymer having a PEG central block and a PPG end block.

8. The process according to any one of claims 1 to 4, wherein no surfactant is added during polymerization.

9. The process according to any one of claims 1 to 8, wherein the fluoropolymer comprises at least 50 mol% vinylidene fluoride monomer units.

10. The process according to any one of claims 1 to 9, wherein the fluoropolymer comprises 70 to 100 mol% vinylidene fluoride monomer units and the hexafluoropropene level is 0 to 30 mol%.

11. The process according to any one of claims 1 to 10, wherein the initiator comprises at least one or more initiators selected from the group consisting of ammonium persulfate, alkali metal salts of persulfates, dialkyl persulfates, diacyl peroxide, peroxyesters, and peroxydicarbonates, preferably from the group consisting of ammonium or alkali metal salts of persulfates.

12. The process according to any one of claims 1 to 11, wherein the solids content level in the stable emulsion produced is more than 34% by weight, preferably more than 35% by weight, preferably more than 36% by weight, and more preferably more than 37% by weight of fluoropolymer solids.

13. The process according to any one of claims 1 to 12, wherein the solids content level in the stable emulsion produced is at least 33.5 to 50% by weight, or more than 34 to 45% by weight of solids, more preferably 35 to 45% by weight, more preferably 36 to 45% by weight, and more preferably 37 to 45% by weight of fluoropolymer solids.

14. The process according to any one of claims 1 to 4, wherein the surfactant is not added before the start of the polymerization reaction.

15. The process according to any one of claims 1 to 4, wherein at least a portion of the surfactant is added before the start of the polymerization reaction.

16. The process according to any one of claims 1 to 15, wherein the YI of the polymer is 20 or less.

17. The process according to any one of claims 1 to 16, wherein the fluoropolymer emulsion further comprises at least one additive selected from the group consisting of dyes; colorants; impact modifiers; antioxidants; flame retardants; ultraviolet stabilizers; flow aids; conductive additives such as metals, carbon black, and carbon nanotubes; defoamers; crosslinking agents; waxes; solvents; plasticizers; and antistatic agents.

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