Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/12—Powdering or granulating
  • C08J3/16—Powdering or granulating by coagulating dispersions
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/12—Powdering or granulating
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms

Definitions

• This invention is in the field of finishing processes for melt-fabricable fiuoropolymer resins, particularly for making beads from aqueous dispersions of such fluoropolymers.
• VF 2 vinylidene fluoride
• TFE tetrafiuoroethylene
• CTFE chlorotrifluoroethylene
• HFP hexafluoropropylene
• PAVE perfluoro(alkyl vinyl ether)
• Such cubes are not suitable for all uses, and other physical forms of melt-fabricable fiuoropolymer such as powders and aqueous dispersions are also supplied.
• One use for which extrusion cubes are not suitable is rotational casting (rotocasting), which encompasses rotational molding (rotomolding) and rotational lining (rotolining).
• Rotocasting requires a combination of good solid-state flow of the fiuoropolymer particles to facilitate uniform distribution of resin in the final article, and a spherical shape and small particle size, in the range of 0.1-0.5 mm, to promote a smooth profile on the free surface of the article.
• the free surface is that surface not in contact with the surface of the mold or with the surface of the article to be lined.
• a convenient product form for this purpose is a bead or granule such as that disclosed by Buckmaster et al. in Canadian Patent 1,248,292.
• Such beads can be prepared, as therein disclosed, by agitation of aqueous dispersion of fiuoropolymer particles in the presence of electrolyte and water- immiscible organic liquid, a process known as solvent-aided coagulation or as solvent-aided pelletization (SAP).
• solvent-aided coagulation or as solvent-aided pelletization (SAP).
• SAP solvent-aided pelletization
• the resultant beads can be subjected to treatments to harden them and/or to stabilize any unstable end groups present on the fiuoropolymer.
• Water-immiscible organic liquids that can be used in SAP processes include the aliphatic hydrocarbons such as hexane, heptane, gasoline and kerosene, aromatic hydrocarbons such as benzene, toluene and xylene, halogenated derivatives such as carbon tetrachloride, monochlorobenzene, the trichlorotrifluoroethanes, difluorotetrachloroethanes, and liquid oligomers of chlorotrifluoroethylene as disclosed in Canadian Patent 1248292, in which 1,1,2- trichloro-l,2,2-trifluoroethane (CFC-113) is used in the examples.
• aliphatic hydrocarbons such as hexane, heptane, gasoline and kerosene
• aromatic hydrocarbons such as benzene, toluene and xylene
• halogenated derivatives such as carbon tetrachloride, monoch
• Hydrocarbons are hazardous because of their flammability, while chlorocarbons and CFCs present environmental problems.
• Alternative water-immiscible liquids for use in SAP processes include the hydrofluorocarbons (HFC) disclosed by Takakura and Funagi in Japanese Patent Application Publication (Kokai) H07-278314. While such HFCs have low ozone depletion potential (ODP), they do have global warming potential (GWP). For example, one isomer of C 5 H 2 F 10 (HFC 43-10) has GWP of about 1300.
• HFCs can be sensitive to alkaline gelation agents, which restricts their application to acidic gelation processes. Additional environmentally friendly solvents are needed for SAP.
• the SAP process is complicated in the sense that many variables are involved. Any change, e.g., a new solvent, may require adjustment of other variables. A process for preparing beads that has a broader operating window, i.e., is less sensitive to the variables, is desired.
• This invention provides a process comprising forming beads of melt- fabricable fiuoropolymer resin by solvent-aided pelletization of aqueous dispersion of particles of said resin, wherein said solvent-aided pelletization is carried out using fluorinated solvent containing oxygen in which the oxygen is present only as ether oxygen.
• Fluorinated solvents containing ether oxygen include (a) perfluorinated cyclic amines of formula (I) hereafter, (b) hydrofluoroethers having the formula R-O-R f , wherein R is alkyl having 1-3 carbon atoms and R f is linear or branched fiuoroalkyl having 2-7 carbon atoms and containing no halogen other than fluorine and at most one terminal hydrogen atom, and (c) hydrofluoroether having the formula R 4 -O-R 5 , wherein R 4 is a fiuoroalkyl having 1-6 carbon atoms and at least one hydrogen atom and R 5 is linear or branched fiuoroalkyl containing no halogen other than fluorine and having 1 -7 carbon atoms and optionally containing ether oxygen.
• Preferred solvents include hydrofluoroethers.
• the process of the invention has environmental advantages, and also yields small well-formed beads over a broad range of solvent-to-polymer ratio, extending to low solvent-to-polymer ratios.
• organic liquids having oxygen present only as ether oxygen can be used in SAP processes for agglomeration of melt- fabricable fiuoropolymer particles in aqueous dispersion.
• the organic liquids Preferably, the organic liquids have one ether oxygen per molecule.
• Organic liquids that can be used to form beads of melt-fabricable fiuoropolymer resin by the SAP process of the present invention include perfluorinated cyclic amines having a nitrogen atom in the ring and having an ether oxygen in the ring. These compounds have no ODP.
• perfluorinated cyclic amines useful in this invention are those having the general formula
• R is a linear or branched saturated perfluorocarbon group having 1-4 carbon atoms
• R 2 and R 3 are linear or branched saturated perfluorocarbon groups having, independently, 1-5 carbon atoms, and the total number of carbon atoms in the molecule of formula (I) is 3-10.
• Examples of compounds of formula (I) include perfluoro-N- methylmorpholine (PFNMM) and perfluoro-N-isopropylmorpholine.
• Preferred compounds of formula (I) are those in which the total number of carbon atoms is 4-8 and the number of atoms bonded in the ring is 5-6.
• Especially preferred compounds are those in which R 2 and R 3 are -CF 2 CF 2 -, and R, has 1-3 carbon atoms.
• PFNMM and perfluoro-N-isopropylmorpholine are available commercially (Fluorinert ® PF-5052 and FC-6003, respectively, 3M Company). PFNMM is most preferred.
• Organic liquids that can be used also include hydrofluoroethers (HFE) having the formula R-O-R f , wherein R is alkyl having 1-3 carbon atoms, preferably 1-2 carbon atoms, and R f is linear or branched fiuoroalkyl, preferably linear, containing no halogen other than fluorine and having 2-7 carbon atoms, preferably 4-5 carbon atoms, and at most one terminal hydrogen atom.
• HFE hydrofluoroethers
• R f is perfluorinated.
• HFE perfluorobutyl methyl ether
• C 2 H 5 -O-C 4 F 9 perfluorobutyl ethyl ether
• HFE-7100 and HFE-7200 are commercially available as HFE-7100 and HFE-7200 respectively, from 3M Company, St. Paul Minnesota USA.
• R 4 -O-R 5 Other suitable HFE have the formula R 4 -O-R 5 , wherein R 4 is a fiuoroalkyl having 1-6 carbon atoms, preferably 1-3 carbon atoms, and at least one hydrogen atom, preferably on the carbon adjacent to the oxygen atom, and R 5 is linear or branched fiuoroalkyl, preferably linear, containing no halogen other than fluorine and having 1-7 carbon atoms, preferably 2-4 carbon atoms and optionally containing ether oxygen.
• R 5 is perfluorinated.
• Examples include CF 3 -CHF-O-CF 2 -CF 2 -CF 3 and CF 3 -CHF-O-CF 2 -CF(CF3)-O-CF 2 -CF 2 -CF 3 , the preparation of which is described in Preparation, properties, and industrial applications of organofluorine compounds, by R. E. Banks, John Wiley and Sons, NY, 1982, page 100.
• the process of this invention may employ any of the techniques known to use a water-immiscible organic liquid (solvent) to pelletize particles of fiuoropolymer initially present in an aqueous medium.
• a vessel equipped with baffles is charged with a quantity of aqueous dispersion of fiuoropolymer particles.
• the aqueous dispersion is agitated with an impeller rotating at a chosen speed, and, with agitation continuing, an electrolyte (sometimes called a gelation agent) is added.
• a quantity of solvent is added, either simultaneously with electrolyte addition or sequentially, and agitation is continued for several minutes, optionally at different speed.
• the resultant product is filtered to drain away the liquid, and the beads are dried, usually at elevated temperature and optionally under vacuum.
• elevated temperature usually at elevated temperature and optionally under vacuum.
• the temperature of the mixture can be increased toward the end of the process to boil off the solvent before screening the beads from the liquid. This alternative can facilitate solvent recovery.
• the resultant beads can be subjected to various treatments.
• the beads can be heat hardened by baking them for several hours, e.g., 3-24 hr, either under nitrogen or in air, at a temperature near but below the melting point of the fiuoropolymer as determined by differential scanning calorimetry (DSC), e.g., within 30°C of the melting point. Drying and heat hardening can be combined if drying is carried out at high temperature.
• the beads can be treated with elemental fluorine to reduce the concentration of unstable end groups as disclosed by
• the fiuoropolymer particles are produced by dispersion polymerization as known in the art.
• the dispersion thus produced is referred to as "raw dispersion".
• the raw dispersion may be used directly or after addition of water to adjust the solids concentration.
• Average fiuoropolymer raw dispersion particle size (RDPS) is generally in the range of 50-350 nm, preferably in the range of 100-300 nm, more preferably in the range of 150-250 nm.
• the concentration of polymer solids in water is usually in the range of about 10-30 wt%, preferably 14-25 wt%, based on combined weight of polymer particles and water.
• the temperature at which the agglomeration bead-forming process is carried out can be any convenient temperature between the freezing point of water and the boiling point of the solvent used. Room temperature is convenient and preferred for this reason, but higher temperature favors formation of smaller beads.
• the amount of electrolyte used will vary with the strength of the electrolyte, and is sufficient to cause formation of a gel, hence the term "gelation agent". Generally, the amount of electrolyte is in the range of about 0.4-10 wt%, preferably 0.5-5 wt%, based on the dry weight of polymer solids.
• the amount of solvent used is generally such that the solvent-to-polymer (S/P) ratio on a weight basis is in the range of about 0.4-1.4, preferably 0.5-1.0.
• the duration of agitation before electrolyte addition, the duration of agitation after gelation, and the duration of agitation after addition of the solvent can be selected independently. For efficiency reasons, it is desirable that the process be as short as possible.
• the three recited times are usually of the order of minutes.
• the agitation profile is usually chosen to ensure that the structure of the gel is maintained, that is, that the gel is not broken into separate phases before the solvent is added. Thus, the agitation time is relatively short and the agitation speed is relatively low in the intervals before solvent addition.
• the absolute agitation speed used will vary with the scale of the equipment.
• the duration of agitation after solvent addition is relatively long to enhance the uniformity of the resultant beads.
• Agitation speed after solvent addition influences the size of the beads, and may be faster than in earlier intervals, faster agitation generally resulting in smaller beads.
• the preliminary agitation period is in the range of about 0-5 min
• the agitation period after electrolyte addition is in the range of about 0-20 min
• the agitation period after solvent addition is in the range of about 1-10 min.
• Melt-fabricable fluoropolymers that can be used in the process of the present invention are made from at least one fluorine-containing monomer, but may incorporate monomer(s) which contain no fluorine or other halogen, and preferably contain at least 35 wt% fluorine.
• melt-fabricable fluoropolymers include copolymers of TFE with one or more copolymerizable comonomers chosen from perfluoroolefins having 3-8 carbon atoms and perfluoro(alkyl vinyl ethers) (PAVE) in which the linear or branched alkyl group contains 1 -5 carbon atoms, with comonomer(s) in the copolymer present in amount(s) sufficient to reduce the melting point of the copolymer substantially below that of TFE homopolymer, e.g., to a melting point no greater than 315°C.
• PAVE perfluoro(alkyl vinyl ethers)
• Preferred perfluoropolymers include copolymers of TFE with at least one of hexafluoropropylene (HFP) and PAVE. TFE/PAVE copolymers are especially preferred. Preferred comonomers include PAVE in which the alkyl group contains 1-3 carbon atoms, especially 2-3 carbon atoms, i.e., perfluoro(ethyl vinyl ether) (PEVE) and perfluoro(propyl vinyl ether) (PPVE). Additional fluoropolymers that can be used include copolymers of ethylene with TFE (ETFE), optionally including minor amounts of one or more modifying comonomer such as perfluorobutyl ethylene (PFBE).
• melt-fabricable resins have melt viscosity (MV) in the range of 0.5-50 x 10 3 Pa-s though viscosities outside this range can be used. MV is measured according to ASTM D-1238 at the temperature appropriate for the particular fiuoropolymer. Preferably, MV is in the range of 1-35 x 10 3 Pa-s.
• fluoropolymers can be produced by aqueous dispersion polymerization as known in the art.
• Beads produced by the process of the present invention can have a wide range of dimensions, such as D 50 of 100-3000 ⁇ m measured as described below. D 50 of 200-1000 ⁇ m is preferred.
• the laboratory-scale apparatus for the following examples is a 2-L glass beaker equipped with a cylindrical stainless steel insert, whose outer diameter is only slightly smaller than the inner diameter of the beaker, and an agitator.
• the beaker is 7 inch (17.8 cm) high and 5.125 inch (13 cm) in diameter.
• Four vertical baffles equally-spaced around the stainless steel insert are 5.6 inch (14.2 cm) tall, starting at the bottom of the cylinder, are 0.47 inch (1.2 cm) wide, and extend 0.6 inch (1.5 cm) radially from the cylinder into the beaker.
• the variable-speed agitator is on a vertical shaft having 4 rectangular blades at the bottom end of the shaft, which is mounted about 0.5 inch (1.3 cm) above the bottom of the beaker.
• the blades are 1.4 cm wide, approximately 3 mm thick, and approximately 1.5 inch (3.8 cm) long so that the circle defined by the tips of the rotating blades is 7.5 cm in diameter.
• the plane of each blade is inclined at an angle of approximately 35° from horizontal so as to pump upward when the agitator is rotated.
• the amount, solids content, and temperature of the fiuoropolymer dispersion, the agitation after gelation, and the agitation after addition of the solvent are fixed.
• the parameters that are varied are the preliminary agitation time and speed, the type and amount of gelation agent, the solvent type, and the amount of solvent and thus the solvent-to-polymer ratio (S/P).
• the general procedure is as follows.
• the beaker is charged with 590 g of fiuoropolymer dispersion at room temperature and 20 wt% solids, achieved by diluting the raw (as-polymerized) dispersion with demineralized water.
• the dispersion is agitated at 1000 rpm and after 1 min, with agitation continuing, the gelation agent is added quickly, the time for gelation is noted, and the gel is agitated for an additional minute.
• the solvent is added quickly and the agitation speed is simultaneously increased to 2250 rpm. Agitation at this speed is continued for 5 min and then stopped.
• the resultant product is poured into cheese cloth to drain away the liquid and the solids are dried for 3 hr in a vacuum oven at 150°C and then baked under nitrogen for 8 hr at 280°C.
• Average particle size (D 50 ) of beads is measured by dry sieve analysis generally following the procedure of ASTM D-4895-94 (10.3) using 3-inch
• the gelation agent is diethylamine and the amount is 3 mL (i .8 wt% based on polymer solids). Solvents and the amounts used, expressed as S/P ratio, are shown in Table 2. Values for D 50 in Table 2 show that HFE-7100, particularly, and PFNMM are effective solvents for pelletization under these conditions. Furthermore, they yield smaller well-formed beads than does CFC-113, and over a broader S/P range extending to lower S/P ratios. Use of less solvent (lower S/P) is environmentally desirable.
• the term "clumps" characterizes clusters or agglomerations of dispersion particles having the general appearance of popcorn. Clumps, powder, and irregular, that is, non- spherical beads, are undesirable in rotocasting applications.
• the dispersion has RDPS of 188 nm and the fluoropolymer resin contains 6.7 wt% of PEVE and has MV of 18.3 x 10 3 Pa-s.
• the dispersion has RDPS of 192 nm and the fluoropolymer resin contains 7.1 wt% of PEVE and has MV of 21.3 x 10 3 Pa-s.
• the gelation agent is 70% nitric acid and the amount is 1 mL (0.84 wt% of HNO 3 based on polymer solids).
• Solvents and the amounts used, expressed as S/P ratio, are shown in Table 6. Values for D 50 in Table 6 show that HFE-7100 and PFNMM are effective solvents for pelletization under these conditions. Furthermore, they yield smaller beads under these conditions than does CFC-113.
• TFE/HFP copolymer prepared generally according to the procedure of Carlson in U.S. Patent 4,029,868.
• the dispersion has RDPS of 262 nm and the fluoropolymer resin contains 6.5 wt% of HFP and 1.5 wt% PEVE, based on the calculation of 3.2 x HFPI, and has MV of 14.4 x 10 3 Pa-s.
• the gelation agent is 70% nitric acid and the amount is 1 mL (0.84 wt% of HNO 3 based on polymer solids). Solvents and the amounts used, expressed as S/P ratio, are shown in Table 7. Values for D 50 in Table 7 show that HFE-7100 is an effective solvent for pelletization under these conditions. Furthermore, it forms beads under a wider range of conditions than does CFC-113.
• ether oxygen-containing fluorinated solvents in solvent-aided pelletization processes is advantageous, as compared to conventional solvents used in such processes, in that for similar concentrations of the ether oxygen-containing fluorinated solvents and conventional solvents, the ether oxygen-containing fluorinated solvents result in smaller particle sizes for the fluoropolymer resin pellets formed. Additionally, the use of ether oxygen-containing fluorinated solvents according to the present invention is more environmentally friendly than for many conventional solvents for solvent-aided pelletization, and in many cases lower concentrations of ether oxygen-containing fluorinated solvents may be used to effect pelletization resulting in lower overall solvent consumption.

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