EP4031589A1 - Low molecular weight polytetrafluoroethylene micropowder and process for preparing the same - Google Patents

Low molecular weight polytetrafluoroethylene micropowder and process for preparing the same

Info

Publication number
EP4031589A1
EP4031589A1 EP20866024.1A EP20866024A EP4031589A1 EP 4031589 A1 EP4031589 A1 EP 4031589A1 EP 20866024 A EP20866024 A EP 20866024A EP 4031589 A1 EP4031589 A1 EP 4031589A1
Authority
EP
European Patent Office
Prior art keywords
ptfe
molecular weight
low molecular
micropowder
polymerization
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20866024.1A
Other languages
German (de)
French (fr)
Other versions
EP4031589A4 (en
Inventor
Deepak Kapoor
Rajeev Chauhan
Sanjay BHAN
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Gujarat Fluorochemicals Ltd
Original Assignee
Gujarat Fluorochemicals Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gujarat Fluorochemicals Ltd filed Critical Gujarat Fluorochemicals Ltd
Publication of EP4031589A1 publication Critical patent/EP4031589A1/en
Publication of EP4031589A4 publication Critical patent/EP4031589A4/en
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F14/00—Homopolymers and 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
    • C08F14/18—Monomers containing fluorine
    • C08F14/26—Tetrafluoroethene
    • 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
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F114/00—Homopolymers 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
    • C08F114/18—Monomers containing fluorine
    • C08F114/26—Tetrafluoroethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/18—Suspension polymerisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/22—Emulsion polymerisation
    • C08F2/24—Emulsion polymerisation with the aid of emulsifying agents
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/22—Emulsion polymerisation
    • C08F2/24—Emulsion polymerisation with the aid of emulsifying agents
    • C08F2/28—Emulsion polymerisation with the aid of emulsifying agents cationic
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/38—Polymerisation using regulators, e.g. chain terminating agents, e.g. telomerisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F4/00—Polymerisation catalysts
    • C08F4/28—Oxygen or compounds releasing free oxygen
    • C08F4/32—Organic compounds
    • C08F4/34—Per-compounds with one peroxy-radical
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F6/00—Post-polymerisation treatments
    • C08F6/008—Treatment of solid polymer wetted by water or organic solvents, e.g. coagulum, filter cakes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F6/00—Post-polymerisation treatments
    • C08F6/14—Treatment of polymer emulsions
    • C08F6/18—Increasing the size of the dispersed particles
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F6/00—Post-polymerisation treatments
    • C08F6/14—Treatment of polymer emulsions
    • C08F6/22—Coagulation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F6/00—Post-polymerisation treatments
    • C08F6/24—Treatment of polymer suspensions
    • 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
    • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene

Definitions

  • the present invention pertains to a process for preparing a polymeric material. More particularly, the present invention relates to low molecular weight polytetrafluoroethylene. More particularly, the invention also relates to a process for preparing low molecular weight Polytetrafluoroethylene also known as “PTFE micropowders”. BACKGROUND OF THE INVENTION
  • PTFE micropowders are low molecular weight PTFE, mainly used as an additive in polymers, coatings, paints, rubbers, cosmetics, waxes, inks, adhesives, greases and lubricants.
  • PTFE Micropowders exhibit impressive array of following properties that make them the material of choice for various demanding applications:
  • low molecular weight PTFE powders have been produced typically from high molecular weight PTFE powders by degradation methods like irradiation with high energy electrons from either a gamma source or an electron beam, or high temperature treatment.
  • ECHA European Chemical Agency
  • EU 2020/784 EU 2019/1021, Annex -XVII to REACH, Entry 68
  • PFOA Perfluorooctanoic acid
  • US7176265B patent titled “Directly polymerized low molecular weight granular polytetrafluoroethylene” discloses direct polymerized low molecular weight PTFE.
  • Low molecular weight granular polytetrafluoroethylene or modified polytetrafluoroethylene having a melt viscosity of less than about lxlO 6 Pa-S powder is isolated directly from the reaction vessel.
  • the low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder in this patent has a melt viscosity of less than about lx 10 6 Pa-S, a specific surface area of less than about 8 m / g, an extractable fluoride level of about 3 ppm or less by weight, and a narrow molecular weight distribution as indicated by a polydispersity index of about 5 or less.
  • the particles of low molecular powder have a weight average particle size of about 2 to about 40 micrometers and the powder is substantially free of particles having a particle size of less than about 1 micrometer.
  • the low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder in this patent has a melt viscosity of less than about lxlO 6 Pa-S,
  • US8754176B2 patent titled “Low molecular weight polytetrafluoroethylene powder and preparation method therefore” discloses Low molecular weight polytetrafluoroethylene powder.
  • a low-molecular weight polytetrafluoroethylene powder has been disclosed.
  • the low molecular weight PTLE micropowder has been used as an additive in a coating material, etc., can form a coating with excellent texture and gliding properties, while also improving dispersibility and viscosity; and a production process therefor.
  • It discloses a process for producing a low-molecular weight polytetrafluoroethylene powder comprising: an emulsion polymerization step of polymerizing at least tetrafluoroethylene in the presence of a polymerization initiator and an aqueous medium to produce emulsified particles thereof; an agglomeration step of agglomerating the emulsified particles to form an agglomerated powder thereof; and a suspension polymerization step of polymerizing at least tetrafluoroethylene in the presence of the agglomerated powder, a polymerization initiator, and an aqueous medium.
  • the low-molecular weight polytetrafluoroethylene powder satisfies a melt viscosity of 700,000 Pa-s or less has been disclosed.
  • melt viscosity was only found ranging from 1.0x10 to 7.0xl0 5 Pa-s, at 380°C.
  • the present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances.
  • the main objective of this invention is to provide low molecular weight PTFE powder and a process of direct polymerization for preparing low molecular weight Polytetrafluoroethylene (PTFE) micropowder that overcomes limitations of the melt viscosities over prior art.
  • Another objective of this invention is to provide a low molecular weight PTFE powder and a process for preparing low molecular weight Polytetrafluoroethylene (PTFE) micropowder that may be devoid of the step of exposure to high temperature or ionizing radiations.
  • Still another objective of this invention is to provide a low molecular weight PTFE micropowder and a process for producing the same employing direct polymerization.
  • the present invention relates to low molecular weight PTFE powder and a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder.
  • PTFE polytetrafluoroethylene
  • the present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances.
  • the low molecular weight PTFE micropowder may be produced by direct polymerization technology and it may be devoid of the degradation steps like irradiation or high temperature treatment.
  • the low molecular weight PTFE micropowder may have particle size is in the range from 2 pm to 600 pm.
  • the low molecular weight PTFE micropowder may have specific surface area (SSA) ranging from 3.0 to 20.0 m /g.
  • the low molecular weight PTFE micropowder may have standard gravity ranges from 2.145-2.212.
  • the low molecular weight PTFE micropowder may have molecular weight less than or equal to 6,00,000.
  • a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder having melt viscosity of range melt viscosity of 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load is disclosed.
  • the process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder may comprises the steps of:
  • TFE Tetrafluoroethylene
  • the step of polymerizing TFE may comprises:
  • the aqueous emulsion may comprise an initiator for initiating the polymerization process, selected from the group consisting of Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS), Potassium Persulphate (KPS) and combinations thereof.
  • an initiator for initiating the polymerization process selected from the group consisting of Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS), Potassium Persulphate (KPS) and combinations thereof.
  • the aqueous emulsion may comprise chain transfer agents selected from the group consisting of alcohols, hydrocarbons and combinations thereof.
  • the step of polymerizing TFE may comprise suspension polymerisation.
  • the process for polymerizing TFE may be carried out at a temperature of 20 to 1201C, pressure of 8 to 25 Bar, and for a polymerization reaction period of 60 to 400 minutes.
  • the step of coagulation is induced by adding organic acids or inorganic acids.
  • the organic acids comprises of group consisting of phosphoric acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid and combination thereof
  • wet PTFE micropowder After washing the coagulated particles with water and steam, the drying of wet PTFE micropowder may be carried out.
  • a low molecular weight PTFE micropowder produced by direct polymerization and devoid of any degradation steps like irradiation or high temperature treatment.
  • the particle size of PTFE micropowder may varies from a range of 2 pm to 600 pm, the melt viscosity may ranges from 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load.
  • Figure 1 Flowchart for the process for preparing a low molecular weight Polytetrafluoroethylene micropowder.
  • the present invention relates to low molecular weight PTFE powder and a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder.
  • the present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances
  • the melt viscosity may be also measured according to ASTM D 1238 using a flow tester(make: Dynisco) die diameter of 2.095 and is a value measured by preheating 3 g of test sample for 5 min at 380°C. and measuring the same with a load of 21.6 kg while maintaining that temperature
  • the low molecular weight PTFE micropowder may have particle size is in the range from 2 pm to 600 pm.
  • the particle size may be measured by Dynamic light scattering system.
  • the particle size may be measured by D50 analysis.
  • the particle size analysis may be done by laser diffraction method as per ASTM D4894.
  • the low molecular weight PTFE micropowder may have specific surface area (SSA) ranging from 3.0 to 20.0 m /g,
  • the specific surface area may be measured by BET using a surface analyzer with a mixed gas of 30% nitrogen and 70% helium as the carrier gas and liquid nitrogen. Standard Gravity
  • the low molecular weight PTFE micropowder may have standard gravity ranges from 2.145-2.212.
  • the melt viscosity may be measured at 380°C at 21.6 Kg load.
  • the temperature may be measured by using ASTM D 4591 by using differential scanning calorimeter.
  • approximately 3 mg of the low-molecular weight PTFE powder may be placed in an aluminum pan (crimped container) and the temperature is raised 10°C./min in the 240 to 380°C at 21.6 Kg load under a 50 mF/min air flow.
  • the melting point may be defined as the minimum point of required melting heat within the above range.
  • the low molecular weight PTFE micropowder may have extractable fluoride level which may range from 1 ppm or less by weight .
  • low molecular weight PTFE micropowder is made by direct polymerization process that is devoid of any further degradation step like irradiation or high temperature treatment.
  • a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder having melt viscosity of range melt viscosity of 1,000,000- 999,999,999 Pascal at 380°C at 21.6 Kg load is disclosed.
  • Figure 1 illustrates process for producing low molecular weight polytetrafluoroethylene micropowder from high molecular weight PTFE composition.
  • a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder comprising the steps of: (a) polymerizing Tetrafluoroethylene (TFE);
  • fluoromonomers may comprises of Tetrafluoroethylene. It may be in gas form and condensed at high pressure into liquid form. The monomer may be stored in metering tank for further adding it for further process in to required quantity.
  • the fluoromonomer may be passed through silica gel absorber to remove moisture prior to feeding it into polymerization reactor.
  • the reactor may be made free from any oxygen content. DI water may be further added to reactor as media at specified RPM to control reaction rate.
  • reaction additives added into reactor may comprise of following: a. Inorganic sulphates as initiator, used as a positive catalyst for initiation of monomer during reaction b. Ammonia to maintain basic pH c. Surfactant system which reduces surface tension between media and monomer by micelles formation required for growth of polymer to make stable dispersion d. Organic Chain transfer agents(CTA) which helps in required size chain formation
  • polymerization step is step 1 where fluoromonomers are polymerized into various process conditions
  • the temperature for polymerization may range from 20-120 deg C.
  • Pressure The pressure during polymerization may range from 8-25 bar
  • Reaction Time The total reaction time varies from 60-400 mins After consumption of defined quantity of fluoromonomers and down polymerization to certain pressure gets completed, pressure eventually may be released to atmosphere and polymer may be formed in latex form (solid and liquid mixture). All solid particles present in primary particles may ranges from 50-200 nm.
  • Coagulation leads to an increase in the particle size distribution of the polymer from nanometer range to micrometers.
  • the wet powder may be subjected to drying systems.
  • powder may be dried with help of hot air to moisture level less than 0.1%.
  • Maximum air temperature may be 450°C.
  • powder coming may be free flowing low molecular weight PTFE in form of final product.
  • the process for polymerizing TFE may comprises the steps of:
  • the aqueous emulsion formed in the present invention may comprise of surfactant system, fluoromonomers, initiators and chain transfer agents.
  • the step of polymerizing TFE may comprise suspension polymerisation.
  • the process of the present invention is preferably carried so that the contents of the reaction vessel are essentially free of surfactant, i.e., the amount of surfactant is less than 0.010% based on the amount of water present.
  • surfactant means a type of molecule which has both hydrophobic and hydrophilic, portions, which allows it to stabilize and disperse hydrophobic molecules and aggregates of hydrophobic molecules in aqueous systems.
  • a preferred group of surfactant system for fluoropolymer synthesis according to the embodiments of the present invention include fluorinated surfactants, non- fluorinated surfactant and a combination of these.
  • surfactants for the present invention may include Ammonium or potassium or sodium salts of perfluoro alkyl ether carboxylic acids.
  • fluoromonomer or the expression “fluorinated monomer” means a polymerizable alkene which contains at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group attached to the double bond of the alkene that undergoes polymerization.
  • fluoropolymer means a polymer formed by the polymerization of at least one fluoromonomer, and it is inclusive of homopolymers, copolymers, terpolymers and higher polymers.
  • the fluoromonomer is tetrafluoroethylene (TFE) and the fluoropolymer is polytetrafluoroethylene (PTFE).
  • the aqueous emulsion may further comprise an initiator for initiating the polymerization process.
  • Initiators for initiating the polymerization process.
  • initiator and the expressions “radical initiator” and “free radical initiator” refer to a chemical that is capable of providing a source of free radicals, either induced spontaneously, or by exposure to heat or light.
  • suitable initiators include peroxides, peroxydicarbonates and azo compounds. Initiators may also include reduction-oxidation systems which provide a source of free radicals.
  • radical and the expression “free radical” refer to a chemical species that contains at least one unpaired electron.
  • the radical initiator is added to the reaction mixture in an amount sufficient to initiate and maintain the polymerization reaction rate. Preferably, the addition of the initiator into the reaction vessel or reactor is carried out in one shot.
  • the radical initiator may comprise a persulfate salt, such as sodium persulfate, potassium persulfate, or ammonium persulfate and combinations thereof .
  • the radical initiator may comprise a redox system.
  • Redox system is understood by a person skilled in the art to mean a system comprising an oxidizing agent, a reducing agent and optionally, a promoter as an electron transfer medium.
  • the radical initiator is selected from the group consisting of Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS) and combinations thereof.
  • DSAP Disuccinic Acid Peroxide
  • APS Ammonium Persulphate
  • the initiator may be used from 50-3000 ppm. Chain transfer agents
  • Chain transfer agents also referred to as modifiers or regulators, comprises of at least one chemically weak bond.
  • a chain transfer agent reacts with the free -radical site of a growing polymer chain and halts an increase in chain length. Chain transfer agents are often added during polymerization to regulate chain length of a polymer to achieve the desired properties in the polymer.
  • chain transfer implies the stopping of growth of one polymer chain and the initiation of growth of another such that the number of growing polymer radicals remains similar and the polymerization proceeds at a similar rate without the introduction of more initiator.
  • the new radical formed by the reaction of the growing polymer chain with a CTA does not always initiate a new polymer chain.
  • chain transfer agents examples include, but not limited to, halogen compounds, hydrocarbons in general, aromatic hydrocarbons, thiols (mercaptans), alcohols and so forth; each of which can be used individually or in combination.
  • the chain transfer agent may varies from 50-3,000 ppm.
  • the temperature used for polymerization may vary, for example, from 20 to 120 °C, depending on the initiator system chosen and the reactivity of the fluoromonomer(s) selected. In a preferred embodiment, the polymerization is carried out at a temperature in the range of 50 to 85 °C.
  • the pressure used for polymerization may vary from 2-200 bar, depending on the reaction equipment, the initiator system, and the monomer selection. In preferred embodiment the reaction is carried out at a pressure in the range of 8 to 25 bar.
  • the polymerization occurs under stirring or agitation.
  • the stirring may be constant, or may be varied to optimize process conditions during the course of the polymerization. In one embodiment, both multiple stirring speeds and multiple temperatures are used for controlling the reaction.
  • a pressurized polymerization reactor equipped with a stirrer and heat control means is charged with water, preferably deionized water, surfactant system in accordance with the invention, chain transfer agents and at least one fluoromonomer.
  • the surfactant is added in an amount in the range from 2000 to 7000 ppm, more preferably from 2500 to 5000 ppm, based on the weight of fluoropolymer dispersion.
  • the surfactant is added in one shot into the reaction vessel.
  • the reaction mixture comprises chain transfer agents in an amount in the range from 50 to 3000 ppm.
  • the mixture may optionally contain paraffin wax.
  • the reactor is then heated up to the reaction temperature and pressure. Thereafter initiators are added into the reaction vessel to initiate the polymerization reaction.
  • the initiator is introduced into the reaction vessel in one shot.
  • the initiator is added in an amount in the range from 50 to 3000 ppm, based on the weight of de-ionized water.
  • air is removed from the reactor in order to obtain an oxygen-free environment for the polymerization reaction.
  • the oxygen is removed from the reaction vessel until its concentration is less than 10 ppm.
  • the reactor may also be purged with a neutral gas such as, for example, nitrogen.
  • the reactor Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure.
  • the aqueous reaction medium containing the fluoropolymer is then recovered from the reaction vessel.
  • the latex content ranges from 10 to 30%, and the particle size of the fluoropolymer particles ranges from 50 to 200 nm.
  • coagulation is one of the vital processes that determines the particle size distribution of a product made by emulsion polymerization. Coagulation leads to an increase in the particle size distribution of the polymer from nanometer range to micrometers. Preferably coagulation is carried out till the particle size distribution of the fluoropolymer particles is in the range of 2 to 600pm.
  • the coagulation of polymer particles is achieved by using inorganic or organic acids. Examples of acids that can be used in the present invention include, but not limited to phosphoric acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid and so forth, each of which can be used alone or in combination.
  • the polymer particles having micrometer sized particle distribution are separated from the mother liquor, and washed with hot and cold water with high speed stirring to remove remaining surfactant, unreacted substances and byproducts.
  • the resulting powder is further subjected to steam treatment to remove volatile impurities to afford wet low molecular weight PTFE micropowder.
  • the wet low molecular weight PTFE micropowder is dried in an oven to afford low molecular weight PTFE micropowder.
  • drying of the wet low molecular weight PTFE micropowder is carried out at a temperature of less than or equal to 450 C.
  • the polymerization process was carried out in a 150 L reactor with 100 L of de-ionized water. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant(s), 3200 ppm, was added in one shot into the reactor. Further, chain transfer agent, 60 ppm (aqueous based), was added into the reactor. Thereafter, the addition of Tetrafluoroethylene (TFE) caused an increase in the pressure to 15 bar and the temperature was increased to 65°C. After attaining the operating pressure and temperature a solution comprising an initiator Ammonium Persulphate (APS) was added into the reactor in one shot for initiating the polymerization process.
  • TFE Tetrafluoroethylene
  • APS Ammonium Persulphate
  • the PTFE particles were coagulated, using nitric acid.
  • the coagulated particles were separated from the mother liquor and washed with hot and cold water, steam treated and dried at a temperature of 240°C to get low molecular weight PTFE micropowder.
  • the advantages of the present invention are as following: a) The invention discloses a low molecular weight PTFE powder by direct polymerization overcoming melt viscosity limitation over prior art. b) The present invention discloses a process for producing low molecular weight PTFE micropowder that complies with various regulations on restriction of PFOA, its salts and related compounds in substances. c) The present invention discloses a process for producing low molecular weight Polytetrafluoroethylene (PTFE) micropowder by using methods which may be devoid of the step of irradiating or other degradation methods.
  • PTFE Polytetrafluoroethylene
  • Low molecular weight polytetrafluoroethylene can be advantageously used as an additive in other materials for improving sliding properties, increasing release, improving wear resistance, conferring increased stain and mar resistance, enhancing flame retardancy, and increasing water repellency.
  • These low molecular weight powders are advantageously added to thermoplastics, paints, coatings, lacquers, greases, oils, lubricants, thermoset resins, and elastomers.

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  • Medicinal Chemistry (AREA)
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  • Health & Medical Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
  • Polymerisation Methods In General (AREA)
  • Polymerization Catalysts (AREA)
  • Processes Of Treating Macromolecular Substances (AREA)

Abstract

The present invention relates to low molecular weight polytetrafluoroethylene (PTFE) micropowder, The present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances. The present invention relates to a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder, comprising the steps of:(a) polymerizing Tetrafluoroethylene (TFE); (b) coagulating the particles of PTFE to increase particle size; (c) washing the particles of PTFE to remove impurities; and (d) drying the wet PTFE micropowder to remove moisture and volatiles.

Description

LOW MOLECULAR WEIGHT POLYTETRAFLUOROETHYLENE MICROPOWDER AND PROCESS FOR PREPARING THE SAME
FIELD OF THE INVENTION
The present invention pertains to a process for preparing a polymeric material. More particularly, the present invention relates to low molecular weight polytetrafluoroethylene. More particularly, the invention also relates to a process for preparing low molecular weight Polytetrafluoroethylene also known as “PTFE micropowders”. BACKGROUND OF THE INVENTION
PTFE micropowders are low molecular weight PTFE, mainly used as an additive in polymers, coatings, paints, rubbers, cosmetics, waxes, inks, adhesives, greases and lubricants.
PTFE Micropowders exhibit impressive array of following properties that make them the material of choice for various demanding applications:
1. Low coefficient of friction
2. Improved wear characteristics in engineering polymers
3. Increased rub resistance in inks and coatings
4. Corrosion resistance
5. Excellent chemical and temperature resistance
6. Improvement in non-stick and release properties
7. Anti-drip
The excellent properties of PTFE notwithstanding, high molecular weight PTFE is rarely used as a modifier of other materials by dispersion or blend. The reason these powders are not suitable for dispersion or blend is that the powders are fibrillated due to shear generated during dispersing or blending. Consequently, viscosity of the mixture increases significantly and no uniform mixing of the composition or blend is possible. Accordingly, for dispersing in or blending with the molding resin material, paints, printing inks, coatings and industrial finishes, oil and grease compositions, the fine particles or powder of low molecular weight PTFE are suitable. Hence; the demand for low molecular weight PTFE is ever increasing.
In prior arts, low molecular weight PTFE powders have been produced typically from high molecular weight PTFE powders by degradation methods like irradiation with high energy electrons from either a gamma source or an electron beam, or high temperature treatment.
Such degradation processes of high molecular weight PTFE to produce low molecular weight PTFE also generates hazardous byproducts like PFOA and HF. Hence, there was an urgent need to develop an alternate method to produce low molecular weight PTFE without the use of irradiation process and that complies with regulations on control of PFOA, its salts and related compounds as suggested by various regulatory bodies globally.
European Chemical Agency (ECHA) through various regulations (EU 2020/784, EU 2019/1021, Annex -XVII to REACH, Entry 68), places restrictions on the manufacture, placing on the market and use of certain dangerous substances, mixtures and articles containing Perfluorooctanoic acid (PFOA), its salts and related compounds.
US7176265B patent titled “Directly polymerized low molecular weight granular polytetrafluoroethylene” discloses direct polymerized low molecular weight PTFE. A process for producing low molecular weight, granular polytetrafluoroethylene or modified polytetrafluoroethylene by suspension polymerization of pressurized tetrafluoroethylene in an agitated reaction vessel. The polymerization is conducted in aqueous medium in the presence of a free radical initiator, and a telogen. The reaction vessel is agitated during polymerization sufficiently to coagulate the polytetrafluoroethylene or modified polytetrafluoroethylene. Low molecular weight granular polytetrafluoroethylene or modified polytetrafluoroethylene having a melt viscosity of less than about lxlO6 Pa-S powder is isolated directly from the reaction vessel. The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder in this patent has a melt viscosity of less than about lx 106 Pa-S, a specific surface area of less than about 8 m / g, an extractable fluoride level of about 3 ppm or less by weight, and a narrow molecular weight distribution as indicated by a polydispersity index of about 5 or less. The particles of low molecular powder have a weight average particle size of about 2 to about 40 micrometers and the powder is substantially free of particles having a particle size of less than about 1 micrometer. The low molecular weight material so produced suitable for use as additives to other materials such as inks, coatings, greases, lubricants, and plastics. The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder in this patent has a melt viscosity of less than about lxlO6 Pa-S,
US8754176B2 patent titled “Low molecular weight polytetrafluoroethylene powder and preparation method therefore” discloses Low molecular weight polytetrafluoroethylene powder. In this prior art, a low-molecular weight polytetrafluoroethylene powder has been disclosed. The low molecular weight PTLE micropowder has been used as an additive in a coating material, etc., can form a coating with excellent texture and gliding properties, while also improving dispersibility and viscosity; and a production process therefor. It discloses a process for producing a low-molecular weight polytetrafluoroethylene powder, the process comprising: an emulsion polymerization step of polymerizing at least tetrafluoroethylene in the presence of a polymerization initiator and an aqueous medium to produce emulsified particles thereof; an agglomeration step of agglomerating the emulsified particles to form an agglomerated powder thereof; and a suspension polymerization step of polymerizing at least tetrafluoroethylene in the presence of the agglomerated powder, a polymerization initiator, and an aqueous medium. In this patent, the low-molecular weight polytetrafluoroethylene powder satisfies a melt viscosity of 700,000 Pa-s or less has been disclosed.
In the prior arts, the melt viscosity was only found ranging from 1.0x10 to 7.0xl05 Pa-s, at 380°C.
The present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances.
OBJECTIVES OF THE INVENTION
The main objective of this invention is to provide low molecular weight PTFE powder and a process of direct polymerization for preparing low molecular weight Polytetrafluoroethylene (PTFE) micropowder that overcomes limitations of the melt viscosities over prior art. Another objective of this invention is to provide a low molecular weight PTFE powder and a process for preparing low molecular weight Polytetrafluoroethylene (PTFE) micropowder that may be devoid of the step of exposure to high temperature or ionizing radiations.
Still another objective of this invention is to provide a low molecular weight PTFE micropowder and a process for producing the same employing direct polymerization.
SUMMARY OF THE INVENTION
The present invention relates to low molecular weight PTFE powder and a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder.
The present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances.
In accordance with an aspect of the invention, there a low molecular weight PTFE powder having melt viscosity of range melt viscosity of 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load has been disclosed. In an embodiment, the low molecular weight PTFE micropowder may be produced by direct polymerization technology and it may be devoid of the degradation steps like irradiation or high temperature treatment.
In an embodiment, the low molecular weight PTFE micropowder may have particle size is in the range from 2 pm to 600 pm.
In an embodiument, The low molecular weight PTFE micropowder may have specific surface area (SSA) ranging from 3.0 to 20.0 m /g.
In an embodiument, The low molecular weight PTFE micropowder may have standard gravity ranges from 2.145-2.212.
In an embodiment, the low molecular weight PTFE micropowder may have molecular weight less than or equal to 6,00,000.
In another embodiment, a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder having melt viscosity of range melt viscosity of 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load is disclosed.
The process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder may comprises the steps of:
(a) polymerizing Tetrafluoroethylene (TFE);
(b) coagulating the particles of PTFE to increase particle size;
(c) washing the particles of PTFE to remove impurities; and
(d) drying the wet PTFE micropowder to remove moisture and volatiles.
In accordance with an embodiment, the step of polymerizing TFE may comprises:
(a) forming an aqueous emulsion comprising a surfactant system and a fluoromonomer; and
(e) initiating polymerization of said fluoromonomer. Further, the aqueous emulsion may comprise an initiator for initiating the polymerization process, selected from the group consisting of Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS), Potassium Persulphate (KPS) and combinations thereof.
In another embodiment, the aqueous emulsion may comprise chain transfer agents selected from the group consisting of alcohols, hydrocarbons and combinations thereof.
In alternate embodiment of the invention, the step of polymerizing TFE may comprise suspension polymerisation.
In accordance with an embodiment of the invention, the process for polymerizing TFE may be carried out at a temperature of 20 to 1201C, pressure of 8 to 25 Bar, and for a polymerization reaction period of 60 to 400 minutes.
In yet another embodiment, the step of coagulation is induced by adding organic acids or inorganic acids.
The organic acids comprises of group consisting of phosphoric acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid and combination thereof
Finally, after washing the coagulated particles with water and steam, the drying of wet PTFE micropowder may be carried out.
In accordance with another aspect of the invention, there is provided a low molecular weight PTFE micropowder produced by direct polymerization and devoid of any degradation steps like irradiation or high temperature treatment. The particle size of PTFE micropowder may varies from a range of 2 pm to 600 pm, the melt viscosity may ranges from 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load.
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description and accompanying drawings.
Figure 1. Flowchart for the process for preparing a low molecular weight Polytetrafluoroethylene micropowder.
DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting and understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
Discussed below are some representative embodiments of the present invention. The invention in its broader aspects is not limited to the specific details and representative methods. Illustrative examples are described in this section in connection with the embodiments and methods provided.
It is to be noted that, as used in the specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a mixture of two or more compounds. It should also be noted that the term "‘or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
The expression of various quantities in terms of “%” or “% w/w” means the percentage by weight of the total solution or composition unless otherwise specified.
All cited references are incorporated herein by reference in their entireties. Citation of any reference is not an admission regarding any determination as to its availability as prior art to the claimed invention.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
Embodiments of the present invention will be described below in detail with reference to the accompanying drawing. The present invention relates to low molecular weight PTFE powder and a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder. The present invention relates to production of low molecular weight PTFE micropowder by direct polymerization technology and overcomes limitation of the melt viscosities over prior art and that is devoid of the step of irradiation or thermal degradation and complies with regulations on PFOA restriction in substances
Melt Viscosity
In accordance with an aspect of the invention, there a low molecular weight PTFE powder having melt viscosity of range melt viscosity of 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load has been disclosed.
The melt viscosity may be also measured according to ASTM D 1238 using a flow tester(make: Dynisco) die diameter of 2.095 and is a value measured by preheating 3 g of test sample for 5 min at 380°C. and measuring the same with a load of 21.6 kg while maintaining that temperature
Particle size
In an embodiment, the low molecular weight PTFE micropowder may have particle size is in the range from 2 pm to 600 pm.
The particle size may be measured by Dynamic light scattering system. The particle size may be measured by D50 analysis. The particle size analysis may be done by laser diffraction method as per ASTM D4894.
Specific Surface area
In an embodiument, The low molecular weight PTFE micropowder may have specific surface area (SSA) ranging from 3.0 to 20.0 m /g,
The specific surface area may be measured by BET using a surface analyzer with a mixed gas of 30% nitrogen and 70% helium as the carrier gas and liquid nitrogen. Standard Gravity
In an embodiment, the low molecular weight PTFE micropowder may have standard gravity ranges from 2.145-2.212.
Melting point/Temperature measurement
In an embodiment, the melt viscosity may be measured at 380°C at 21.6 Kg load.
The temperature may be measured by using ASTM D 4591 by using differential scanning calorimeter. Here approximately 3 mg of the low-molecular weight PTFE powder may be placed in an aluminum pan (crimped container) and the temperature is raised 10°C./min in the 240 to 380°C at 21.6 Kg load under a 50 mF/min air flow. The melting point may be defined as the minimum point of required melting heat within the above range.
In an embodiment, the low molecular weight PTFE micropowder may have extractable fluoride level which may range from 1 ppm or less by weight .
In an embodiment, low molecular weight PTFE micropowder is made by direct polymerization process that is devoid of any further degradation step like irradiation or high temperature treatment.
In another embodiment, a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder having melt viscosity of range melt viscosity of 1,000,000- 999,999,999 Pascal at 380°C at 21.6 Kg load is disclosed.
Accordingly, Figure 1 illustrates process for producing low molecular weight polytetrafluoroethylene micropowder from high molecular weight PTFE composition.
The present invention, in all its aspects, is described in detail as follows:
Referring to Figure 1, a process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder is disclosed which, comprising the steps of: (a) polymerizing Tetrafluoroethylene (TFE);
(b) coagulating the particles of PTFE to increase particle size;
(c) washing the particles of PTFE to remove impurities; and
(d) drying the wet PTFE micropowder to remove moisture and volatiles.
In an embodiment, fluoromonomers may comprises of Tetrafluoroethylene. It may be in gas form and condensed at high pressure into liquid form. The monomer may be stored in metering tank for further adding it for further process in to required quantity.
The fluoromonomer may be passed through silica gel absorber to remove moisture prior to feeding it into polymerization reactor. The reactor may be made free from any oxygen content. DI water may be further added to reactor as media at specified RPM to control reaction rate.
Various reaction additives added into reactor may comprise of following: a. Inorganic sulphates as initiator, used as a positive catalyst for initiation of monomer during reaction b. Ammonia to maintain basic pH c. Surfactant system which reduces surface tension between media and monomer by micelles formation required for growth of polymer to make stable dispersion d. Organic Chain transfer agents(CTA) which helps in required size chain formation
Referring to fig.1 , polymerization step is step 1 where fluoromonomers are polymerized into various process conditions
Temperature: The temperature for polymerization may range from 20-120 deg C. Pressure: The pressure during polymerization may range from 8-25 bar
Reaction Time: The total reaction time varies from 60-400 mins After consumption of defined quantity of fluoromonomers and down polymerization to certain pressure gets completed, pressure eventually may be released to atmosphere and polymer may be formed in latex form (solid and liquid mixture). All solid particles present in primary particles may ranges from 50-200 nm.
Following to polymerization step, coagulation of PTFE particles may occur. Coagulation leads to an increase in the particle size distribution of the polymer from nanometer range to micrometers.
Following to washing step, the wet powder may be subjected to drying systems. In such systems powder may be dried with help of hot air to moisture level less than 0.1%. Maximum air temperature may be 450°C. After drying operation, powder coming may be free flowing low molecular weight PTFE in form of final product.
In an embodiment, the process for polymerizing TFE, may comprises the steps of:
(a) forming an aqueous emulsion comprising a surfactant system and fluoromonomer; and
(b) initiating polymerization of said fluoromonomer.
The aqueous emulsion formed in the present invention may comprise of surfactant system, fluoromonomers, initiators and chain transfer agents.
In alternate embodiment of the invention, the step of polymerizing TFE may comprise suspension polymerisation. The process of the present invention is preferably carried so that the contents of the reaction vessel are essentially free of surfactant, i.e., the amount of surfactant is less than 0.010% based on the amount of water present.
The use of fluorosurfactants adds expense and presents a disposal problem after polymerization. Further, the addition of surfactant to the reaction media tends to produce an undesired increase in the specific surface area of the polymer and leads to reduced amounts of coagulated polymer and increased polymer loss is conducted preferably with a single liquid phase, i.e., aqueous medium. Therefore In suspension polymerisation, surfactant is not used. Water is convenient, liquid over a broad temperature range, inexpensive and safe. The suspension polymerization process is conducted in the presence of low levels of chain transfer agent (CTA).
Surfactant system
The term “surfactant” means a type of molecule which has both hydrophobic and hydrophilic, portions, which allows it to stabilize and disperse hydrophobic molecules and aggregates of hydrophobic molecules in aqueous systems. A preferred group of surfactant system for fluoropolymer synthesis according to the embodiments of the present invention include fluorinated surfactants, non- fluorinated surfactant and a combination of these.
Examples of surfactants for the present invention may include Ammonium or potassium or sodium salts of perfluoro alkyl ether carboxylic acids. Fluoromonomers
The term “fluoromonomer” or the expression “fluorinated monomer” means a polymerizable alkene which contains at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group attached to the double bond of the alkene that undergoes polymerization. The term “fluoropolymer” means a polymer formed by the polymerization of at least one fluoromonomer, and it is inclusive of homopolymers, copolymers, terpolymers and higher polymers. Preferably, the fluoromonomer is tetrafluoroethylene (TFE) and the fluoropolymer is polytetrafluoroethylene (PTFE). Although, the embodiments of the present invention are described in terms of polymerization of TFE, the process described herein can be applied to any fluoromonomer.
The aqueous emulsion may further comprise an initiator for initiating the polymerization process. Initiators
The term “initiator” and the expressions “radical initiator” and “free radical initiator” refer to a chemical that is capable of providing a source of free radicals, either induced spontaneously, or by exposure to heat or light. Examples of suitable initiators include peroxides, peroxydicarbonates and azo compounds. Initiators may also include reduction-oxidation systems which provide a source of free radicals. The term “radical” and the expression “free radical” refer to a chemical species that contains at least one unpaired electron. The radical initiator is added to the reaction mixture in an amount sufficient to initiate and maintain the polymerization reaction rate. Preferably, the addition of the initiator into the reaction vessel or reactor is carried out in one shot. The radical initiator may comprise a persulfate salt, such as sodium persulfate, potassium persulfate, or ammonium persulfate and combinations thereof . Alternatively, the radical initiator may comprise a redox system. “Redox system” is understood by a person skilled in the art to mean a system comprising an oxidizing agent, a reducing agent and optionally, a promoter as an electron transfer medium. In a preferred embodiment, the radical initiator is selected from the group consisting of Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS) and combinations thereof. The initiator may be used from 50-3000 ppm. Chain transfer agents
Chain transfer agents, also referred to as modifiers or regulators, comprises of at least one chemically weak bond. A chain transfer agent reacts with the free -radical site of a growing polymer chain and halts an increase in chain length. Chain transfer agents are often added during polymerization to regulate chain length of a polymer to achieve the desired properties in the polymer.
The term chain transfer implies the stopping of growth of one polymer chain and the initiation of growth of another such that the number of growing polymer radicals remains similar and the polymerization proceeds at a similar rate without the introduction of more initiator. However, in actual practice, the new radical formed by the reaction of the growing polymer chain with a CTA does not always initiate a new polymer chain.
Examples of chain transfer agents that can be used in the present invention include, but not limited to, halogen compounds, hydrocarbons in general, aromatic hydrocarbons, thiols (mercaptans), alcohols and so forth; each of which can be used individually or in combination. The chain transfer agent may varies from 50-3,000 ppm.
Polymerization conditions The temperature used for polymerization may vary, for example, from 20 to 120 °C, depending on the initiator system chosen and the reactivity of the fluoromonomer(s) selected. In a preferred embodiment, the polymerization is carried out at a temperature in the range of 50 to 85 °C.
The pressure used for polymerization may vary from 2-200 bar, depending on the reaction equipment, the initiator system, and the monomer selection. In preferred embodiment the reaction is carried out at a pressure in the range of 8 to 25 bar.
The polymerization occurs under stirring or agitation. The stirring may be constant, or may be varied to optimize process conditions during the course of the polymerization. In one embodiment, both multiple stirring speeds and multiple temperatures are used for controlling the reaction. According to one embodiment of the process of the invention, a pressurized polymerization reactor equipped with a stirrer and heat control means is charged with water, preferably deionized water, surfactant system in accordance with the invention, chain transfer agents and at least one fluoromonomer. Preferably, the surfactant is added in an amount in the range from 2000 to 7000 ppm, more preferably from 2500 to 5000 ppm, based on the weight of fluoropolymer dispersion.
Preferably, the surfactant is added in one shot into the reaction vessel. Preferably, the reaction mixture comprises chain transfer agents in an amount in the range from 50 to 3000 ppm. The mixture may optionally contain paraffin wax. The reactor is then heated up to the reaction temperature and pressure. Thereafter initiators are added into the reaction vessel to initiate the polymerization reaction. Preferably the initiator is introduced into the reaction vessel in one shot. Preferably, the initiator is added in an amount in the range from 50 to 3000 ppm, based on the weight of de-ionized water. Prior to introduction of the surfactant and monomer or monomers into the reaction vessel, air is removed from the reactor in order to obtain an oxygen-free environment for the polymerization reaction. Preferably, the oxygen is removed from the reaction vessel until its concentration is less than 10 ppm. The reactor may also be purged with a neutral gas such as, for example, nitrogen.
Upon completion of the polymerization reaction, the reactor is brought to ambient temperature and the residual unreacted monomer is vented to atmospheric pressure. The aqueous reaction medium containing the fluoropolymer is then recovered from the reaction vessel. Preferably, the latex content ranges from 10 to 30%, and the particle size of the fluoropolymer particles ranges from 50 to 200 nm. Coagulation, washing and drying:
In addition to particle growth due to polymerization, coagulation is one of the vital processes that determines the particle size distribution of a product made by emulsion polymerization. Coagulation leads to an increase in the particle size distribution of the polymer from nanometer range to micrometers. Preferably coagulation is carried out till the particle size distribution of the fluoropolymer particles is in the range of 2 to 600pm. In an embodiment of the invention the coagulation of polymer particles is achieved by using inorganic or organic acids. Examples of acids that can be used in the present invention include, but not limited to phosphoric acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid and so forth, each of which can be used alone or in combination.
Thereafter, the polymer particles having micrometer sized particle distribution are separated from the mother liquor, and washed with hot and cold water with high speed stirring to remove remaining surfactant, unreacted substances and byproducts. The resulting powder is further subjected to steam treatment to remove volatile impurities to afford wet low molecular weight PTFE micropowder.
Finally, the wet low molecular weight PTFE micropowder is dried in an oven to afford low molecular weight PTFE micropowder. Preferably drying of the wet low molecular weight PTFE micropowder is carried out at a temperature of less than or equal to 450 C.
The present invention is more particularly described in the following examples that are intended as illustration only, since numerous modifications and variations within the scope of the present invention will be apparent to those of skill in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples were obtained or are available from the chemical suppliers. The following examples illustrates the basic methodology and versatility of the present invention.
Experiment
The polymerization process was carried out in a 150 L reactor with 100 L of de-ionized water. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant(s), 3200 ppm, was added in one shot into the reactor. Further, chain transfer agent, 60 ppm (aqueous based), was added into the reactor. Thereafter, the addition of Tetrafluoroethylene (TFE) caused an increase in the pressure to 15 bar and the temperature was increased to 65°C. After attaining the operating pressure and temperature a solution comprising an initiator Ammonium Persulphate (APS) was added into the reactor in one shot for initiating the polymerization process. After completion of the polymerization process the PTFE particles were coagulated, using nitric acid. The coagulated particles were separated from the mother liquor and washed with hot and cold water, steam treated and dried at a temperature of 240°C to get low molecular weight PTFE micropowder.
Experiments
In addition to above experiment, various other plant trials have been conducted and the detailed property analysis has been clearly illustrated in Table 1 depicting Experiment 1 - Experiment 3.
Table 1
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.
The advantages of the present invention are as following: a) The invention discloses a low molecular weight PTFE powder by direct polymerization overcoming melt viscosity limitation over prior art. b) The present invention discloses a process for producing low molecular weight PTFE micropowder that complies with various regulations on restriction of PFOA, its salts and related compounds in substances. c) The present invention discloses a process for producing low molecular weight Polytetrafluoroethylene (PTFE) micropowder by using methods which may be devoid of the step of irradiating or other degradation methods. Use
Low molecular weight polytetrafluoroethylene (PTFE) can be advantageously used as an additive in other materials for improving sliding properties, increasing release, improving wear resistance, conferring increased stain and mar resistance, enhancing flame retardancy, and increasing water repellency. These low molecular weight powders are advantageously added to thermoplastics, paints, coatings, lacquers, greases, oils, lubricants, thermoset resins, and elastomers.
The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.
Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims

We Claim:
1. A low molecular weight Polytetrafluoroethylene (PTFE) micropowder; wherein the low molecular weight polytetrafluoroethylene (PTFE) micropowder is having melt viscosity of 1,000,001- 999,999,999 Pascal at 380° C at 21.6 Kg load.
2. The low molecular weight Polytetrafluoroethylene (PTFE) micropowder as claimed in claim 1; wherein the low molecular weight polytetrafluoroethylene (PTFE) micropowder is produced by direct polymerization process.
3. The low molecular weight Polytetrafluoroethylene (PTFE) micropowder as claimed in claim 1 is produced without irradiation or any other forms of degradation methods.
4. The low molecular weight PTFE micropowder as claimed in claim 1 wherein specific surface area (SSA) is 3.0 to 20.0 m2/g.
5. A process for preparing a low molecular weight polytetrafluoroethylene (PTFE) micropowder, comprising the steps of:
(a) polymerizing Tetrafluoroethylene (TFE);
(b) coagulating the particles of PTFE to increase particle size;
(c) washing the particles of PTFE to remove impurities; and
(d) drying the wet PTFE micropowder to remove moisture and volatiles wherein the low molecular weight polytetrafluoroethylene (PTFE) micropowder is having melt viscosity of 1,000,001- 999,999,999 Pascal at 380°C at 21.6 Kg load
6. The process as claimed in claim 5, wherein the step of polymerizing TFE comprises:
(a) forming an aqueous emulsion comprising a surfactant system and a fluoromonomer; and
(b) initiating polymerization of said fluoromonomer Wherein in surfactant system comprises of fluorosurfactant or non fluoro-surfactant or a combination of these.
7. The process as claimed in any of the claims 5 to 6, wherein the aqueous emulsion comprises an initiator for initiating the polymerization process, selected from the group consisting of Disuccinic Acid Peroxide (DSAP), Ammonium Persulphate (APS), Potassium Persulphate (KPS) and combinations thereof and the aqueous emulsion comprises chain transfer agents selected from the group consisting of alcohols, hydrocarbons and combinations thereof.
8. The process as claimed in claim 5, wherein the step of polymerizing TFE comprises suspension polymerization or emulsion polymerization.
9. The process as claimed in claim 5, wherein the step of coagulation is induced by adding organic acids or inorganic acidswherein the organic acids comprises of group consisting of phosphoric acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid and combination thereof.
10. The process as claimed in claim 5, wherein the step of drying the wet PTFE micropowder is carried out at less than or equal to 450 °C and step of polymerizing TFE is carried out at a temperature of 20 to 120 °C, pressure of 8 to 25 Bar and for a period of 60 to 400 minutes.
EP20866024.1A 2019-09-17 2020-09-16 Low molecular weight polytetrafluoroethylene micropowder and process for preparing the same Pending EP4031589A4 (en)

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US8071198B2 (en) * 2006-11-17 2011-12-06 E.I. Du Pont De Nemours And Company Glass articles with adhesion and stain resistant non-stick coatings
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US9309335B2 (en) * 2010-09-30 2016-04-12 Daikin Industries, Ltd. Process for producing polytetrafluoroethylene fine powder
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KR20220065003A (en) 2022-05-19
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