Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/32—Compounds containing nitrogen bound to oxygen

Definitions

• the present invention relates to aqueous fluoropolymer dispersion and more particularly relates to aqueous fluoropolymer dispersion comprising amine oxide surfactant and a process for making coagulated fluoropolymer resin from such dispersion.
• Fluoropolymer dispersions have a wide variety of end uses.
• coating compositions containing fluoropolymer dispersion are applied to any of a variety of substrates in order to confer release, chemical and heat resistance, corrosion protection, cleanability, low flammability, and weatherability.
• Fluoropolymer dispersions for coating use are usually in a concentrated form and typically are stabilized with a significant quantity of a nonionic surfactant such as an alkyl phenol ethoxylate or an aliphatic alcohols ethoxylate as taught in U.S. Patent 3,037,953 to Marks et al., U.S. 6,153,688 to Miura et al., and U.S. 2003/0130393 to Cavanaugh et al.
• a nonionic surfactant such as an alkyl phenol ethoxylate or an aliphatic alcohols ethoxylate as taught in U.S. Patent 3,037,953 to Marks et al
• raw dispersion also referred to as “unstabilized” dispersion
• fine powder coagulated fluoropolymer resin
• the aqueous fluoropolymer dispersion is mixed with other materials, often in dispersion or slurry form, such as particulate polymers, fillers, pigments, solid lubricants, etc. and then the fluoropolymer is co-coagulated together with the other material.
• Conventional nonionic surfactants such as alkyl phenol ethoxylates or aliphatic alcohol ethoxylates are not used in coagulation processes because they generally confer high stability to the dispersion preventing or making coagulation difficult. In some processes where coagulation does succeed, the result is an undesirable sticky or fibrillated product which is difficult to process into a finished article.
• anionic fluorosurfactant is typically used as a polymerization aid in the dispersion polymerization process, the anionic fluorosurfactant functioning as a non- telogenic dispersing agent.
• anionic fluorosurfactant functioning as a non- telogenic dispersing agent.
• fluoropolymer dispersions are generally stabilized with the same nonionic surfactants that are employed for coating end uses, i.e., alkyl phenol ethoxylates or aliphatic alcohol ethoxylates.
• aqueous fluoropolymer dispersions are desired which are especially suitable for end use applications which produce coagulated fluoropolymer resin from the dispersion.
• an aqueous fluoropolymer dispersion which comprises an aqueous medium, fluoropolymer particles, and an amine oxide surfactant of the formula:
• R 1 is radical of the formula:
• R 4 is a saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl, hydroxyalkyl, ether or hydroxyether radical having 1 to 20 carbon atoms
• X is an O, NH or NR 5
• n is 2-6
• R 2 and R 3 are independently selected from saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl, hydroxyalkyl, ether or hydroxyether radical having 1 to 10 carbon atoms optionally substituted with halogen;
• R 5 is selected from saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl, hydroxyalkyl, ether or hydroxyether radical having 1 to 10 carbon atoms optionally substituted with halogen or an N-oxylamino group; and wherein that R 2 and R 3 may be joined by a chemical bond to form a ring.
• the invention also provides a process for producing a coagulated fluoropolymer resin comprising providing an aqueous fluoropolymer dispersion comprising an aqueous medium, fluoropolymer particles, and an amine oxide surfactant.
• An acidic reagent is added to the dispersion in sufficient amount to coagulate the fluoropolymer particles to produce coagulated fluoropolymer resin.
• the coagulated fluoropolymer resin is then separated from the aqueous medium.
• process further comprises agitating the dispersion.
• the process further comprises drying said coagulated fluoropolymer resin.
• the process further comprises adding a particulate component such as a particulate polymer, filler, pigment, solid lubricant, etc., to the aqueous dispersion prior to adding the acidic reagent.
• a particulate component such as a particulate polymer, filler, pigment, solid lubricant, etc.
• the acidic reagent causes co-coagulation of the fluoropolymer particles and the particulate component.
• the particulate component is added to the dispersion as a dispersion or a slurry in an aqueous medium.
• the aqueous fluoropolymer dispersion in accordance with the present invention is made by dispersion polymerization (also known as emulsion polymerization).
• Fluoropolymer dispersions are comprised of particles of polymers made from monomers wherein at least one of the monomers contains fluorine, i.e., a fluorinated monomer, preferably an olefinic monomer with at least one fluorine or a perfluoroalkyl group attached to a doubly-bonded carbon.
• the fluorinated monomer used in the process of this invention is preferably selected from the group consisting of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkyl ethylene, fluorovinyl ethers, vinyl fluoride (VF), vinylidene fluoride (VF2), perfluoro-2,2-dimethyl-1 ,3-dioxole (PDD) and perfluoro-2- methylene-4-methyl-1 ,3-dioxolane (PMD).
• TFE tetrafluoroethylene
• HFP hexafluoropropylene
• CTFE chlorotrifluoroethylene
• TFE hexafluoroisobutylene
• perfluoroalkyl ethylene perfluoroalkyl ethylene
• fluorovinyl ethers vinyl
• a preferred perfluoroalkyl ethylene monomer is perfluorobutyl ethylene (PFBE).
• Preferred fluorovinyl ethers include perfluoro(alkyl vinyl ether) monomers (PAVE) such as perfluoro (propyl vinyl ether) (PPVE), perfluoro (ethyl vinyl ether) (PEVE), and perfluoro (methyl vinyl ether) (PMVE).
• PAVE perfluoro(alkyl vinyl ether) monomers
• PPVE perfluoro (propyl vinyl ether)
• PEVE perfluoro (ethyl vinyl ether)
• PMVE perfluoro (methyl vinyl ether)
• Non-fluorinated olefinic comonomers such as ethylene and propylene can be copolymerized with fluorinated monomers.
• a preferred class of fluoropolymers are homopolymers and copolymers of tetrafluoroethylene (TFE).
• Preferred fluoropolymer particles in the dispersion employed in this invention are non-melt-processible particles of polytetrafluoroethylene (PTFE) including modified PTFE which is not melt-processible.
• PTFE polytetrafluoroethylene
• Modified PTFE refers to copolymers of TFE with such small concentrations of comonomer that the melting point of the resultant polymer is not substantially reduced below that of PTFE.
• the concentration of such comonomer is preferably less than about 1 wt%, more preferably less than about 0.5 wt%.
• the modified PTFE preferably contains a comonomer modifier which improves film forming capability during baking (fusing), such as perfluoroolefin, notably hexafluoropropylene (HFP) or perfluoro(alkyl vinyl) ether (PAVE), where the alkyl group contains 1 to 5 carbon atoms, with perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE) being preferred.
• a comonomer modifier which improves film forming capability during baking (fusing), such as perfluoroolefin, notably hexafluoropropylene (HFP) or perfluoro(alkyl vinyl) ether (PAVE), where the alkyl group contains 1 to 5 carbon atoms, with perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE) being preferred.
• the PTFE or modified PTFE typically has a melt creep viscosity of at least 1 x 10 8 Pa «s.
• the resins in the dispersion used in this form of the invention when coagulated and dried are thus non-melt-processible.
• non-melt-processible it is meant that no melt flow is detected when tested by the standard melt viscosity determining procedure for melt- processible polymers.
• This test is according to ASTM D-1238-00 modified as follows: The cylinder, orifice and piston tip are made of corrosion resistant alloy, Haynes Stellite 19, made by Haynes Stellite Co. The 5.0 g sample is charged to the 9.53 mm (0.375 inch) inside diameter cylinder which is maintained at 372°C. Five minutes after the sample is charged to the cylinder, it is extruded through a 2.10 mm (0.0825 inch diameter), 8.00 mm (0.315 inch) long square-edge orifice under a load (piston plus weight) of 5000 grams.
• the fluoropolymer particles are of high molecular weight polytetrafluoroethylene (PTFE) or modified polytetrafluoroethylene which, in fine powder form, are useful for the manufacture of paste extruded shapes that can be stretched rapidly in the unsintered state to form a high tensile strength PTFE fiber or expanded PTFE sheets or membranes.
• PTFE polytetrafluoroethylene
• Processes for making dispersions containing PTFE or modified PTFE of this type are disclosed in Malhotra, U.S. Patent 4,576,869, and Jones, U.S. Patent 6,177,533 Bl
• the preferred non-melt-processible PTFE or modified PTFE have a standard specific gravity (SSG) of about 2.13 to about 2.50.
• SSG standard specific gravity
• the SSG is less than about 2.40, more preferably less than about 2.30, and most preferably less than about 2.25.
• the SSG is generally inversely proportional to the molecular weight of PTFE or modified PTFE.
• the fluoropolymer particles in the dispersion used in this invention have a number average particle size of about 10 nm to about 400 nm, preferably, about 100 nm to about 350 nm.
• melt-processible it is meant that the polymer can be processed in the molten state (i.e., fabricated from the melt into shaped articles such as films, fibers, and tubes etc. that exhibit sufficient strength and toughness to be useful for their intended purpose).
• melt-processible fluoropolymers include homopolymers such as polychlorotrifluoroethylene or copolymers of tetrafluoroethylene (TFE) and at least one fluorinated copolymerizable monomer (comonomer) present in the polymer usually in sufficient amount to reduce the melting point of the copolymer substantially below that of TFE homopolymer, polytetrafluoroethylene, e.g., to a melting temperature no greater than 315°C.
• TFE tetrafluoroethylene
• a melt-processible TFE copolymer typically incorporates an amount of comonomer into the copolymer in order to provide a copolymer which has a melt flow rate (MFR) of about 1-100 g/10 min as measured according to ASTM D-1238 at the temperature which is standard for the specific copolymer.
• MFR melt flow rate
• the melt viscosity is at least about 10 2 Pa s, more preferably, will range from about 10 2 Pa # s to about 10 6 Pa » s, most preferably about 10 3 to about 10 5 Pa*s measured at 372 0 C by the method of ASTM D-1238 modified as described in U.S. Patent 4,380,618.
• melt-processible fluoropolymers are the copolymers of ethylene or propylene with TFE or CTFE, notably ETFE, ECTFE and PCTFE.
• a preferred melt-processible copolymer for use in the practice of the present invention comprises at least about 40-98 mol% tetrafluoroethylene units and about 2-60 mol% of at least one other monomer.
• the other monomer is a perfluorinated monomer.
• Preferred comonomers with TFE are perfluoroolefin having 3 to 8 carbon atoms, such as hexafluoropropylene (HFP), and/or perfluoro(alkyl vinyl ether) (PAVE) in which the linear or branched alkyl group contains 1 to 5 carbon atoms.
• Preferred PAVE monomers are those in which the alkyl group contains 1 , 2, 3 or 4 carbon atoms, and the copolymer can be made using several PAVE monomers.
• TFE copolymers include FEP (TFE/HFP copolymer), PFA (TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE 1 MFA (TFE/PMVE/PAVE wherein the alkyl group of PAVE has at least two carbon atoms) and THV (TFE/HFP/VF2).
• a typical process for the aqueous dispersion polymerization of preferred PTFE polymer is a process wherein TFE vapor is fed to a heated reactor containing fluorosurfactants, paraffin wax and deionized water.
• a chain transfer agent may also be added if it is desired to reduce the molecular weight of the PTFE.
• a free-radical initiator solution is added and, as the polymerization proceeds, additional TFE is added to maintain the pressure. The exothermic heat of reaction is removed by circulating cooling water through the reactor jacket. After several hours, the feeds are stopped, the reactor is vented and purged with nitrogen, and the raw dispersion in the vessel is transferred to a cooling vessel. Paraffin wax is removed and the dispersion is isolated and stabilized with dispersing agent.
• the fluorosurfactant used in the manufacture of the dispersion is a non-telogenic, anionic dispersing agent, soluble in water and comprising an anionic hydrophilic group and a hydrophobic portion.
• the hydrophobic portion is an aliphatic fluoroalkyl group containing at least four carbon atoms and bearing fluorine atoms and having no more than two carbon atoms not bearing fluorine atoms adjacent to the hydrophilic group.
• the fluorosurfactant is a perfluorinated carboxylic or sulfonic acid having 6-10 carbon atoms and is typically used in salt form.
• Suitable fluorosurfactants are ammonium perfluorocarboxylates, e.g., ammonium perfluorocaprylate or ammonium perfluorooctanoate.
• the fluorosurfactants are usually present in the amount of 0.02 to 1 wt % with respect to the amount of polymer formed.
• the fluorinated surfactant is used to aid the polymerization process but the amount remaining in the dispersion is significantly reduced as will be explained below.
• the initiators preferably used to make dispersion of this invention are free radical initiators.
• persulfates e.g., ammonium persulfate or potassium persulfate.
• persulfate initiators reducing agents such as ammonium bisulfite or sodium metabisulfite, with or without metal catalysis salts such as Fe (III), can be used.
• short half-life initiators such as potassium permanganate/oxalic acid can be used.
• DSP disuccinic acid peroxide
• the dispersion polymerization of melt-processible copolymers is similar except that comonomer in significant quantity is added to the batch initially and/or introduced during polymerization.
• Chain transfer agents are typically used in significant amounts to decrease molecular weight to increase melt flow rate.
• Amine oxide surfactants are employed in accordance with the invention to provide stabilization for the aqueous fluoropolymer dispersions and to be selectively destabilized by the addition of an acidic reagent.
• amine oxide surfactants of the formula are employed:
• R 1 is radical of the formula:
• R 4 is a saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl, hydroxyalkyl, ether or hydroxyether radical having 1 to 20 carbon atoms
• X is an O, NH or NR 5
• n is 2-6
• R 2 and R 3 are independently selected from saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl, hydroxyalkyl, ether or hydroxyether radical having 1 to 10 carbon atoms optionally substituted with halogen;
• R 5 is selected from saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl, hydroxyalkyl, ether or hydroxyether radical having 1 to 10 carbon atoms optionally substituted with halogen or an N-oxylamino group; and wherein that R 2 and R 3 may be joined by a chemical bond to form a ring.
• R 2 , R 3 R 4 and R 5 have halogen substitutions, preferably halogen substitutions are limited such that no more than about 70% of the atoms attached to carbon atoms of the radical are halogen atoms, more preferably no more than about 50% are halogen atoms. Most preferably, R 2 , R 3 R 4 and R 5 are not halogen substituted. If R 5 is substituted with N-oxylamino, groups bonded to the nitrogen atom preferably have 1 to 10 carbon atoms.
• R1 is a radical of the formula
• R1 is a radical of the formula:
• R 4 comprises alkyl having 5-20 carbon atoms
• X is NH
• n is 3.
• R 2 and R 3 in the formula above are independently selected from saturated or unsaturated, branched or unbranched, cyclic or acyclic, alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms.
• R 2 and R 3 in the formula above are each independently selected from alkyl or hydroxyalkyl radicals having 1 to 2 carbon atoms.
• Preferred surfactants useful for the practice of the present invention are cocoamidopropyl dimethyl amine oxide, 2-ethylhexylamidopropyl dimethyl amine oxide, and octylamidopropyl dimethyl amine oxide.
• amine oxide surfactant as described above is added in sufficient quantity to the dispersion after polymerization to stabilize the dispersion for the intended processing.
• the stability provided enables the dispersion to be treated to reduce fluorosurfactant content such as by anion exchange as discussed hereinafter.
• the amount and type of amine oxide surfactant is selected to enable the dispersion to be coagulated by addition of an acidic reagent.
• the amine oxide surfactant can be added to the dispersion anytime after polymerization but prior to fluorosurfactant reduction as discussed in more detail hereinafter. Usually, the amine oxide surfactant is added prior to concentration if concentration is to be performed. Concentration is discussed in more below.
• the aqueous dispersions in accordance with the invention preferably range in fluoropolymer solids content from about 10 to about 70 wt%, more preferably 25 to about 70 wt%.
• the amount of amine oxide surfactant is preferably selected based on the amount of fluoropolymer solids.
• the aqueous fluoropolymer dispersions in accordance with the invention preferably contain amine oxide surfactant in an amount of about 0.05 to about 15 wt% based on the weight of fluoropolymer solids.
• the aqueous fluoropolymer dispersion is present in an amount of about 0.1 to about 10 wt%, most preferably 0.5 to about 5 wt%, based on the weight of fluoropolymer solids.
• the exact amount of amine oxide surfactant in a particular dispersion should be selected to provide stability during processing but permit coagulation when desired.
• the amount of amine oxide surfactant may need to be adjusted for end uses in which particulate component is to be co-coagulated together with the fluoropolymer.
• the size of the fluoropolymer particles in the aqueous fluoropolymer dispersion is determined by the polymerization procedure used to make the dispersion.
• Preferred dispersions have a number average particle size of about 10 to about 400 nm.
• the dispersions in accordance with the invention preferably have reduced anionic fluorosurfactant content, preferably at a level no greater than about 300 ppm, more preferably no greater than about 100 ppm, most preferably no greater than about 50 ppm.
• the dispersion preferably has a Gel Time of at least 100 seconds as determined by the Gel Time test described in the Test Methods of this application.
• Gel Time is a measurement of resistance of the dispersion to coagulation under high shear conditions and thus is an indicator of the stability of the dispersion during processing which subjects the dispersion to shear.
• a Gel Time of at least 100 indicates that the amine oxide surfactant is functioning to stabilize the polymer sufficiently for normal handling and processing, e.g., is sufficiently stabilized for fluorosurfactant removal in an anion exchange column.
• the Gel Time is at least about 300 seconds, even more preferably at least about 500 seconds, even more preferably at least about 1000 seconds, and most preferably at least about 1500 seconds.
• a preferred range of Gel Time provided by the present invention is about 100 seconds to about 2000 seconds.
• the dispersion contains less that about 300 ppm fluorosurfactant based on the weight of the dispersion and has the Gel Times as indicated above.
• the Gel Times described above are observed when the fluorosurfactant content is less that about 100 ppm, most preferably less that about 50 ppm.
• the preferred dispersions in accordance with the invention also have long storage stability and can be stored at least about 2 weeks without any significant coagulation or degradation. More preferably, the dispersions are stable for storage at least about 2 months.
• the anionic fluorosurfactant content of the aqueous fluoropolymer dispersion is preferable for the anionic fluorosurfactant content of the aqueous fluoropolymer dispersion to be reduced to a predetermined level, preferably a level no greater than about 300 ppm, more preferably no greater than about 100 ppm, most preferably no greater than about 50 ppm.
• the fluorosurfactant content can be reduced by any of a variety of procedures as known in the art. With stabilization being provided by amine oxide surfactant, the fluorosurfactant can be advantageously removed by adsorption onto an anion exchange resin without coagulation of the dispersion occuring. Any of a variety of techniques which bring the dispersion in contact with the anion exchange resin can be used to carry out the ion exchange of the process. For example, the process can be carried out by addition of ion exchange resin bead to the dispersion in a stirred tank, in which a slurry of the dispersion and resin is formed, followed by separation of dispersion from the anion exchange resin beads by filtration. Another suitable method is to pass the dispersion through a fixed bed of anion exchange resin instead of using a stirred tank. Flow can be upward or downward through the bed and no separate separation step is needed since the resin remains in the fixed bed.
• the contacting of the dispersion is performed at a temperature which is sufficiently high to facilitate the rate of ion exchange and to reduce the viscosity of the dispersion but being below a temperature at which the resin degrades at a detrimentally high rate or a viscosity increase in observed.
• Upper treatment temperature will vary with the type of polymer and amine oxide surfactant employed. Typically, temperatures will be between 2O 0 C and 8O 0 C.
• the fluorosurfactant can be recovered from the anion exchange resin if desired or the resin with the fluorosurfactant can be disposed of in an environmentally acceptable method, e.g., by incineration. If it is desired to recover the fluorosurfactant, the fluorosurfactant may be removed from resin by elution. Elution of fluorosurfactant adsorbed on the anion exchange resin is readily achieved by use of ammonia solution as demonstrated by Seki in U.S. Patent 3,882,153, by a mixture of dilute mineral acid with organic solvent (e.g., HCI/ethanol) as demonstrated by Kuhls in U.S.
• organic solvent e.g., HCI/ethanol
• Patent 4,282,162 or by strong mineral acids such as sulfuric acid and nitric, transferring the adsorbed fluorinated carboxylic acid to the eluent.
• the fluorosurfactant in the eluent in high concentration can easily be recovered in the form of a pure acid or in the form of salts by common methods such as acid-deposition, salting out, and other methods of concentration, etc.
• the ion exchange resins for use in accordance with reducing the fluorosurfactant content of the aqueous dispersion used in the present invention include anionic resins but can also include other resin types such as cationic resins, e.g., in a mixed bed.
• the anionic resins employed can be either strongly basic or weakly basic. Suitable weakly basic anion exchange resins contain primary, secondary amine, or tertiary amine groups. Suitable strongly basic anion exchange resin contain quaternary ammonium groups. Although weakly basic resins are useful because they can be regenerated more easily, strongly basis resins are preferred when it is desired to reduce fluorosurfactant to very low levels and for high utilization of the resin.
• Strongly basic ion exchange resins also have the advantage of less sensitivity to the pH of the media. Strong base anion exchange resins have an associated counter ion and are typically available in chloride or hydroxide form but are readily converted to other forms if desired. Anion exchange resins with hydroxide, chloride, sulfate, and nitrate can be used for the removal of the fluorosurfactant but anion exchange resins in the form of hydroxide are preferred to prevent the introduction of additional anions and to increase pH during anion exchange because a high pH, i.e., greater than 9, is desirable in the product prior to shipping to inhibit bacterial growth.
• Suitable commercially-available strong base anion exchange resins with quaternary ammonium groups with a trimethylamine moiety include DOWEX® 550A, US Filter A464-OH, SYBRON M-500-OH, SYBRON ASB1-OH, PUROLITE A-500-OH, ltochu TSA 1200, AMBERLITE® IR 402.
• Ion exchange resin used to reduce fluorosurfactant for use in the process of the present invention is preferably monodisperse.
• the ion exchange resin beads have a number average size distribution in which 95% of the beads have a diameter within plus or minus 100 ⁇ m of the number average bead diameter.
• concentration of the dispersions of this invention any of a variety of known methods can be used. If an amine oxide surfactant is employed which has a cloud point in a practical temperature range for concentration, i.e., about 3O 0 C and about 9O 0 C, concentration can be performed as taught in Marks et al., U.S. Patent 3,037,953. Other known methods can be practiced if desired and can be used when the amine oxide surfactant does not have a suitable cloud point. Ultrafiltration as as taught in Kuhls, U.S. Patent 4,369,266, can be used. Another suitable method is concentration using acrylic polymers of high acid content as described in U.S. Patent 5,272,186 to Jones.
• the process of the invention produces coagulated fluoropolymer resin from aqueous fluoropolymer dispersions containing amine oxide surfactant.
• An acidic reagent preferably a mineral acid or strong organic acid, is added to the dispersion in sufficient amount to coagulate the fluoropolymer particles to produce coagulated fluoropolymer resin.
• the coagulated fluoropolymer resin is then separated from the aqueous medium.
• process further comprises agitating the dispersion.
• the process further comprises drying said coagulated fluoropolymer resin.
• Coagulation of fluoropolymer dispersion in accordance with the invention preferably is accomplished by introducing the dispersion into a vessel equipped with an agitator suitable for providing suitable shear to the dispersion for mixing and assisting with coagulation.
• Turbine agitators are suitable for this purpose and may have pitched blades with the vertical displacement given to the dispersion being either up or down. If air entrainment is be minimized, vertical displacement upwards is generally desirable.
• amine oxide surfactants and particularly with the preferred amine oxide surfactants, the stability of the dispersion deceases with decreasing pH. It is preferably for the pH to be decreased together with suitable agitation for mixing.
• the acid is added over time to allow good dispersal of the acid and it is usually desirable for the pH of the dispersion is gradually dropped.
• the pH is adjusted to be acidic, i.e., a pH in the range of about 7 to about 0.
• the pH is adjust to less than about 7, more preferably less than about 5, most preferably less than about 3.
• the agitation rate can be increased to effect the coagulation of the dispersion, optionally with the addition of more acid either continuously or by aliquots. Usually upon coagulation, the dispersion will separate into a floating polymer layer and a relatively clear water layer.
• the aqueous medium can be drained off, siphoned off, or otherwise separated from the polymer. Additional acidified water or fluoropolymer surface wetting solvents such as the lower alcohols can be contacted with the polymer one or more times to remove more of the adsorbed amine oxide surfactant if desired. Once a suitable amount of the amine oxide surfactant is removed, the polymer is separated from the bulk of water and or solvent, and the polymer is dried and can be used as desired.
• the process further comprises adding a particulate component such as a particulate polymer, filler, pigment, solid lubricant, etc., to the aqueous dispersion prior to adding the acidic reagent.
• the acidic reagent causes co-coagulation of the fluoropolymer particles and the particulate component.
• This form of the invention is advantageously used when it is desired to have an intimate mixture of the fluoropolymer and the particulate component.
• the particulate component is preferably uniformly distributed in the coagulated fluoropolymer resin such that the mixture is homogeneous.
• Preferred co-coagulated materials made in this process can be processed in, for example, paste extrusion processes similar to fine powder resin without additives.
• the selected particulate component For co-coagulation of the dispersion with another particulate component such as a particulate polymer, filler, pigment, solid lubricant, etc., it is usually desirable for the selected particulate component to be provided as a dispersion or as a slurry with water, preferably water containing surfactant. Solvents may also be present also is desired. Particulate components often have large and adsorptive surface areas that can absorb a surfactant and destabilize the dispersion causing premature co-coagulation, i.e., before intimate mixing is achieved.
• the particulate component may be desirable to treat the particulate component to prevent premature co-coagulation such as by contacting the particulate component with the same or different surfactant as is contained in the fluoropolymer dispersion, i.e., amine oxide.
• One way to achieve this is to provide an particulate component slurry or dispersion having the nearly the same or lower surface tension than that of the fluoropolymer dispersion.
• co- coagulation together the particulate component with can be achieved, in accordance with the invention, by addition of an acidic reagent.
• the manner of addition of the acidic reagent and the pH range employed is the same as discussed above for the coagulation of the fluoropolymer resin alone.
• agitation is also employed as discussed above.
• the co-coagulated mixture is dried or otherwise used as desired.
• Solids content of raw (as polymerized) fluoropolymer dispersion are determined gravimetrically by evaporating a weighed aliquot of dispersion to dryness, and weighing the dried solids. Solids content is stated in weight % based on combined weights of PTFE and water. Alternately solids content can be determined by using a hydrometer to determine the specific gravity of the dispersion and then by reference to a table relating specific gravity to solids content. (The table is constructed from an algebraic expression derived from the density of water and density of as polymerized PTFE.) Number average dispersion particle size on raw dispersion is measured by photon correlation spectroscopy.
• Standard specific gravity (SSG) of PTFE resin is measured by the method of ASTM D-4895. If a surfactant is present, it can be removed by the extraction procedure in ASTM-D-4441 prior to determining SSG by ASTM D-4895.
• Surfactant Content is calculated based on the amount of amine oxide surfactant added to the dispersion and is reported as wt% based on fluoropolymer solids.
• Fluorosurfactant Content is measured by a GC technique in which the fluorosurfactant is esterified with acidic methanol. Perfluoroheptanoic acid is used as an internal standard. Upon addition of electrolyte and hexane the ester is extracted into the upper hexane layer. The hexane layer is analyzed by injection onto a glass GC column of 20 ft. x 2mm I. D. packed with 10% OV-210 on 70/80 mesh Chromosorb W.AW.DMCS. held at 120 C. The detector is ECD and the carrier gas of 95% argon/5% methane has a flow rate of 20 to 30 ml/min.
• Fluorosurfactant content is reported as wt% based on dispersion weight.
• Gel time is measured as the time it takes a dispersion to completely gel in a blender. 200 ml of dispersion is placed in a Waring commercial explosion resistant blender (Model 707SB, one quart size, run at high speed, air requirements - 10 scfm @ 10 psi, available from Waring of New Hartford, Connecticut). This blender has a capacity of 1 liter and has an air purge for the motor. The dispersion is stirred at the highest speed until the dispersion gels. The Gel Time is recorded is seconds. If the dispersion does not gel in Vi hour (1800 seconds), the test is terminated to avoid damage to the blender. The blender is then completely disassembled and cleaned after each determination.
• This example illustrates a dispersion stabilized with cocoamidopropyl dimethyl amine oxide and reduction of fluorosurfactant from the dispersion using an anion exchange procedure.
• a 2 liter glass resin kettle with cover having an internal diameter of 5 inches (12.5 cm) is added 540 ml of a PTFE dispersion of a high molecular weight resin of 40 wt% fluoropolymer solids having a fluorosurfactant content of 1328 ppm and a particle size of 270 nm.
• a PTFE dispersion of a high molecular weight resin of 40 wt% fluoropolymer solids having a fluorosurfactant content of 1328 ppm and a particle size of 270 nm are also added to the kettle.
• 1420 ml of water 20 ml of concentrated ammonium hydroxide (30 wt% as NH 3 ) and 6 g of cocoamidopropyl dimethyl amine oxide supplied by Jeen International as Jeechem 1770 having about 30 wt% active ingredient.
• the content of amine oxide surfactant is 0.83 wt% based on fluoropolymer solids
• Example 2 This example illustrates a dispersion stabilized with
• 2-ethylhexylamidopropyl dimethyl amine oxide and reduction of fluorosurfactant from the dispersion using an anion exchange procedure.
• the same conditions as example 1 are employed except that 40 ml of concentrated ammonium hydroxide (30 wt% as NH 3 ) is added and 15 g of 2-ethylhexylamidopropyl dimethyl amine oxide supplied by lsotet Chemical, LLC is used as the surfactant having 42.6 wt % active ingredient.
• the content of amine oxide surfactant is 2.95 wt% based on fluoropolymer solids. After 31 hours the dispersion is found to contain 40.5 ppm fluorosurfactant content and essentially no coagulum.
• This example illustrates a dispersion stabilized with octylamidopropyl dimethyl amine oxide and reduction of fluorosurfactant from the dispersion using an anion exchange procedure.
• the same conditions as example 2 are employed except 15 g of octylamidopropyl dimethyl amine oxide supplied by lsotet Chemical, LLC having 44.3 wt % active ingredient is used as the surfactant (3.1 wt% based on fluoropolymer solids) and the temperature is held at 60 degrees
• Example 4 This example illustrates a dispersion stabilized with
• the apparatus consists of a 2 liter glass resin kettle of internal diameter of 13 cm, equipped with lid, baffles, a 4-bladed turbine agitator attached to a shaft, and a motor that rotates the shaft that passes through the lid.
• the baffles are a unit having an outer diameter of 12.7 cm, which slips into the kettle.
• the unit is comprised of 4 baffle blades of height 12.7 cm and 1.25 cm in width arranged equidistantly around on a wire ring.
• the agitator has a diameter of 7.5 cm and the blades are 1.4 cm wide.
• the blades have a pitch of 45 degrees and the shaft is rotated such that the agitator pumps upward.
• the agitator speed is set to 250 rpm and 3 ml of concentrated sulfuric acid is added to reduce the pH to less than about 3 and the dispersion begins to coagulate.
• the agitator speed is raised to 750 rpm to finish the coagulation.
• the liquid is decanted and the coagulated polymer is transferred to a large buchner funnel with fast filtering paper and the polymer is rinsed with water acidified with sulfuric acid.
• the polymer is removed and triturated in 2-propanol, the mixture again transferred to the buchner funnel to remove the solvent. This is repeated.
• the polymer is air dried and then dried at a temperature of 15O 0 C. SSG testing yields a dark colored chip and measured SSG of 2.1605.
• This example illustrates a dispersion stabilized with 2-ethylhexylamidopropyl dimethyl amine oxide and coagulation of PTFE resin from the dispersion with nitric and phosphoric acid.
• the dispersion prepared as in Example 2 (after fluorosurfactant reduction) is coagulated by the same technique as Example 4 except that 7 ml of nitric acid is used instead of sulfuric acid.
• the addition of the nitric acid yields a pH of 1-2 measured using pH indicating strips.
• the SSG chip still has some color but less than Example 4 and SSG measured 2.1612.
• Example 2 Using the dispersion of Example 2 (after fluorosurfactant reduction) but acidifying to a pH of 1-2 by use of 5 ml of phosphoric acid yields polymer with an SSG of 2.1581.
• This example illustrates on a larger scale a dispersion stabilized with cocoamidopropyl dimethyl amine oxide and reduction of fluorosurfactant from the dispersion using an anion exchange procedure.
• a dispersion stabilized with cocoamidopropyl dimethyl amine oxide and reduction of fluorosurfactant from the dispersion using an anion exchange procedure To a 50 gallon stainless steel tank with steam heated jacket with lid is added 212.7 kg of a 23.5 wt% dispersion of high molecular weight resin, 1 L of concentrated ammonium hydroxide (30 wt% as NH 3 ), 1.5 kg of Jeechem 1770 (cocoamidopropyl dimethyl amine oxide, 30wt%) and 2 kg of water.
• the content of amine oxide surfactant is 0.9 wt% based on fluoropolymer solids.
• Affixed to the agitator is 28 nylon mesh bags containing a total of 4400 g of A-244 ion exchange resin.
• the agitator was turned at 10 rpm and the tank was held at 50 C for 2 days.
• the dispersion is discharged from the tank by siphoning.
• the resulting dispersion has a fluorosurfactant content of 50 ppm.
• This example illustrates a dispersion stabilized with cocoamidopropyl dimethyl amine oxide and coagulation of PTFE resin from the dispersion with nitric acid at various amine oxide surfactant levels.
• Table 1 below shows the preparation of the dispersion and coagulation conditions.

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