WO1995029943A1 - Suspension polymerization of tfe - Google Patents
Suspension polymerization of tfe Download PDFInfo
- Publication number
- WO1995029943A1 WO1995029943A1 PCT/US1995/005297 US9505297W WO9529943A1 WO 1995029943 A1 WO1995029943 A1 WO 1995029943A1 US 9505297 W US9505297 W US 9505297W WO 9529943 A1 WO9529943 A1 WO 9529943A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- temperature
- polymerization
- tfe
- autoclave
- ptfe
- Prior art date
Links
Classifications
-
- 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
Definitions
- This invention is in the field of suspension processes to make polytetrafluoroethylene.
- TFE tetrafluoroethylene
- PTFE polytetrafluoroethylene
- the emulsion (dispersion) process for polymerizing TFE yields an aqueous dispersion of PTFE particles having typical average diameter of about 0.2 ⁇ m.
- PTFE dispersion particles ordinarily have a characteristic property of fibrillating under shear stress.
- the dispersion product of polymerization may be concentrated and/or stabilized and used as an aqueous dispersion, or may be coagulated and dried to obtain a PTFE resin that is variously called coagulated dispersion resin or fine powder.
- Articles are usually fabricated from fine powder by a lubricated extrusion (paste extrusion) process at temperature near room temperature, utilizing the fibrillatable character of the dispersion particle, followed by removal of the lubricant and then by fusing (sintering) of the PTFE.
- the suspension process for polymerizing TFE usually involving vigorous agitation of the aqueous medium, yields non-fibrillatable solid particles that typically are irregular, fibrous, and coarse.
- the raw PTFE resin is commonly subjected to various finishing operations such as cutting, or cutting and pelletizing, to obtain resins with desired processing characteristics.
- PTFE resins derived from suspension polymerization of TFE are typically fabricated into finished articles by compacting at room temperature and then sintering, optionally followed by machining, i.e., by techniques adapted from powder metallurgy.
- the temperature increase may be step-wise, with resultant pressure increasing above the starting pressure, or gradual to maintain constant pressure in the autoclave.
- the temperature raising time is stated, in general, to be the time at which the polymerization yield reaches a value of 80-95% of the total monomer charge. This time, signaled by a pressure drop in the autoclave, probably corresponds to depletion of the monomer liquid phase.
- the initial polymerization temperature was 25°C though a much lower temperature was used during the step of charging TFE to the autoclave.
- pressure began to drop after 10 hr temperature was raised to 45°C, apparently step-wise. From the data given, the space-time yield is calculated to be 0.19 g/l-min.
- the present invention solves the problem of being able to obtain the properties of PTFE yielded by the low-temperature suspension process only with sacrifice in production rate by providing a process that gives both the properties of low-temperature polymerization and high space-time yield.
- This invention provides an improved process for suspension polymerization of tetrafluoroethylene using an aqueous medium and in the presence of polymerization initiator to form non-fibrillatable polytetrafluoroethylene, the improvement comprising
- FIG. 1 Plot of shrinkage vs. nominal reaction temperature for suspension polymerization of TFE as conducted in Comparative Examples A-C.
- PTFE can be made by a suspension process in which the temperature starts at a low value and increases to higher value as polymerization progresses, but which surprisingly yields PTFE having properties similar to those of polymer made at constant temperature equal to the low starting temperature, even though a substantial fraction of the PTFE is formed at higher temperature.
- PTFE made by the process of this invention has the general non-fibrillatable character of PTFE made by previously-known suspension polymerization processes.
- Such product after any appropriate finishing operations such as cutting, or cutting and pelletizing, is also known as granular resin, or as molding resin, and may be used as ram extrusion rein.
- Suspension-polymerized PTFE is usually of such high molecular weight that the polymer is considered to be non-melt-fabricable.
- Such molecular weight ordinarily corresponds to standard specific gravity (SSG) of less than 2.25, and more commonly to SSG of less than 2.20, SSG being a parameter that decreases with increasing molecular weight.
- SSG standard specific gravity
- the general relationship between SSG and number average molecular weight is well known. See, for example, Sperati & Starkweather, Fortschr. Hochpolym-Forsch. 2, 465 (1961).
- comonomers are illustrated by, for example, perfluorobutyl ethylene and perfluoro(alkyl vinyl ether) such as perfluoro(propyl vinyl ether).
- concentration of optional comonomer is sufficiently low that the polymer is still non-melt-fabricable.
- Optional comonomer concentration in the polymer will generally be less than 0.2 mol%, usually much less.
- TFE polymer containing such low concentrations of comonomer is often called modified PTFE.
- modified PTFE is intended to cover modified PTFE as well as true PTFE homopolymer.
- the process of this invention is similar to TFE suspension polymerizations known in the art, except for temperature control.
- a typical suspension polymerization process involves the steps of precharging a liquid medium to a stirred autoclave, precharging small amounts of other ingredients, deoxygenating, pressuring with TFE to predetermined level, agitating, bringing the system to desired temperature, introducing initiator, adding more TFE according to predetermined basis, and regulating temperature.
- the suspension process for polymerization of TFE is typically conducted in aqueous medium. Water is convenient, liquid over a broad temperature range, essentially non-telogenic when impurities are reduced to low level, inexpensive, and safe.
- the process of this invention uses an aqueous medium. In prior-art suspension polymerization processes, recipe and operating parameters not fixed by the equipment are commonly selected in order that temperature is maintained approximately constant througout the polymerization.
- any workable pressure can be used in the process of this invention.
- High pressure offers an advantage over low pressure in increased reaction rate.
- the polymerization of TFE is highly exothermic, so high reaction rate increases the heat that must be removed or accommodated as temperature increases.
- Pressures that can be used are also determined by equipment design and by safety concerns in the handling of TFE. Generally, pressures in the range of about 0.3-7 MPa are known for suspension polymerization of TFE, and pressures in the range 0.7-3.5 MPa are common. While it is common to maintain constant TFE pressure, pressure can be varied.
- Initiators that can be used in the practice of this invention include any free radical initiator for TFE polymerization that is effective over the temperature range to be employed.
- the initiator should generate radicals at adequate rate at low temperature.
- Preferred initiators include, for example, potassium permanganate systems, and various other redox systems such as ammonium persulfate/bisulfite/iron sulfate or bromate bisulfite.
- ingredients can be used in recipes for TFE polymerization by the process of this invention.
- Such other ingredients include, for example, surfactants, additives to minimize formation of autoclave adhesions, color inhibitors, and the like as known to one skilled in the art.
- Such other ingredients are usually, but not necessarily, introduced into the autoclave as part of the precharge. If the recipe is to yield modified PTFE, comonomer is commonly included in the precharge, but comonomer properties such as reactivity and volatility would influence time and method of addition.
- the process of this invention is characterized by starting TFE polymerization at low temperature, permitting temperature to increase to higher temperature as polymerization progresses, and substantially completing polymerization at higher temperature.
- Polymerization starting temperature is considered to be the measured temperature at the time polymerization starts (kick-off), as kick-off is normally determined. Commonly, kick-off is sensed by a decrease in pressure, indicating that reaction is consuming TFE. Since an aqueous medium is used, polymerization starting temperature must be high enough that the water is in the liqu'd state, considering the effect of dissolved ingredients and operating pressure on freezing point. Desirably, starting temperature is up to about 20°C. Preferably, starting temperature is in the approximate range 0°-20°C.
- the temperature reaches at least about 30°C, preferably at least 35°C, and most preferably at least 40°C. Temperature may increase continuously throughout the batch, but highest temperature is not necessarily realized at the end of the batch. For example, one might reduce pressure to slow the reaction or employ a react-down procedure to consume residual monomer in the polymerization vessel, accompanied by decrease in temperature. It is contemplated that the reaction is substantially completed at higher temperature reached during polymerization as recited above, recognizing the possibilities of various temperature profiles, also as discussed above. To achieve substantial benefit from the process of this invention, it is desired that at least about 35% of PTFE formed during the batch is formed at temperature above 20°C, preferably at least 45%, and most preferably at least 55%.
- Substantially completed at higher temperature is to be interpreted to mean that the fraction of total PTFE formed during the batch that is formed at temperature above 20°C is as recited in the previous sentence. Even more preferably, these fractions of total PTFE formed are formed at about 30°C or above. If heat transfer capability is adequate, one can control the temperature profile by regulating the heat transfer system to raise the temperature as desired. However, a particular advantage of the process of this invention is realized in exceeding the heat transfer capability of polymerization equipment in any given configuration, thereby achieving reaction rates in excess of that corresponding to the heat transfer limit.
- a preferred mode of operation is to set heat transfer at a high level consistent with equipment design and operating economics, and then control temperature through selection of recipe variables, such as amount of initiator or use of surfactant, and of operating parameters such as TFE pressure. While TFE pressure is maintained constant in the following examples of the invention, except for a react-down procedure at the end of the batch, pressure can be varied to influence reaction rate and thereby heat generated and consequently temperature. Thus, in the practice of this invention, one can cause temperature to increase by regulation of heat transfer, by choice of recipe, by control of operating parameters, and the like. The phrase "permitting temperature to increase" is intended to encompass all such modes of temperature regulation. Normally, polymerization continues as temperature increases above the starting temperature.
- Reported space-time yields were based on the volume of the empty autoclave and on two different times, both measured from the start of polymerization (kickoff), at which point the feed valve was opened to add TFE continuously.
- the end point for the first time was the closing of the TFE feed valve.
- the end point for the second time was the venting of the autoclave.
- the autoclave was charged with 21.3 1 of demineralized water, 1 g of oxalic acid and 0.2 g of potassium meta-bisulfite. Oxygen was then removed from the autoclave by alternately pressuring with 1540 g of TFE and evacuating. The autoclave was pressured to 2.17 MPa with TFE, cooled to 15°C, and agitated at 700 rpm. A solution of potassium permanganate (0.008 g/1) was continuously injected at 25 ml/min into the autoclave for the duration of the batch.
- Comparative Example B The autoclave was charged with 21.8 1 of demineralized water, 0.7 g of ammonium perfluorooctanoate (C-8), and 0.0023 g of an ocytlphenol polyethoxyethanol surfactant (Triton ® X-100, Rohm & Haas), as 10 ml of 0.023 g/1 solution, and purged of oxygen as before.
- the autoclave was pressured to 1.83 MPa with 1090 g of TFE, heated to 35°C and agitated at 700 rpm.
- the autoclave was charged with demineralized water, C-8, and "Triton" X-100 as in Comparative Example B, and purged of oxygen as before.
- the autoclave was pressured to 1.83 MPa with 820 g of TFE monomer, heated to 65°C, and agitated at 600 rpm.
- the reaction was initiated by injecting 0.3 g of APS as 300 ml of 1 g/1 solution at 50 ml/min for 6 min.
- the feed valve was then opened and TFE was fed continuously to maintain pressure at 1.83 MPa.
- the maximum temperature observed in the vapor space was 80°C.
- 8720 g of TFE had been fed to maintain pressure, and the feed valve was closed.
- Comparative Examples A-C were run at nominally constant temperature. Taken together, they show that shrinkage increases with reaction temperature. This is illustrated graphically in Figure 1 in which measured shrinkage is plotted against nominal polymerization temperature, i.e., the starting temperature. The fact that slight temperature increases were observed indicates that they were run at or near rates corresponding to the heat removal capability of the equipment and cooling fluid at the reaction temperatures chosen. The space-time yield values indicate the sacrifice in productivity incurred to realize PTFE properties attainable at low polymerization temperature.
- Example 1 The autoclave was charged with 21.3 1 of demineralized water, 1 g of oxalic acid, 0.1 g of potassium meta-bisulfite, 0.7 g of C-8 and 0.0023 g of Triton ® X-100 as in Comparative Example B, and 0.1 g of potassium phosphate. The agitator was turned on at 800 rpm. The autoclave was pressured to 2.17 MPa with approximately 1450 g of TFE and cooled to 15°C. To initiate polymerization, an aqueous solution of potassium permanganate (0.01 g/1) was continuously injected into the autoclave at 25 ml/min for the duration of the reaction.
- the pressure was observed to fall to 0.16 MPa in 3 min, during which time essentially all of the TFE remaining in the autoclave was reacted for a total of about 7260 g of TFE reacted including the precharge.
- the autoclave was vented and the polymer was recovered, cut to 17 ⁇ m average particle size, and dried.
- the SSG was 2.168 and the shrinkage was 2.8%.
- about 76% of the monomer including precharge was converted into polymer at 20°C or higher, about 61% at 26°C or higher, and about 37% at 36°C or higher, assuming that temperature did not drop below 36°C by the end of the short react-down interval.
- the autoclave was charged with the same recipe as in Example 1, except that 0.5 g of ammonium perfluorodecanoate was used instead of C-8 and Triton ® X-100, and that the autoclave was pressured to 2.17 MPa with approximately 1630 g of TFE .
- the batch proceeded in a manner similar to Example 1, but at faster average polymerization rate, as summarized in Table 2.
- the recovered polymer was cut to 20 ⁇ m average particle size and dried as before.
- the SSG was 2.164 and the shrinkage was 2.9%.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE69507608T DE69507608T2 (en) | 1994-05-02 | 1995-04-28 | SUSPENSION POLYMERIZATION OF TETRAFLUORETHYLENE |
EP95918871A EP0758345B1 (en) | 1994-05-02 | 1995-04-28 | Suspension polymerization of tfe |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/236,852 | 1994-05-02 | ||
US08/236,852 US5405923A (en) | 1994-05-02 | 1994-05-02 | Suspension polymerization of TFE |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1995029943A1 true WO1995029943A1 (en) | 1995-11-09 |
Family
ID=22891249
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1995/005297 WO1995029943A1 (en) | 1994-05-02 | 1995-04-28 | Suspension polymerization of tfe |
Country Status (5)
Country | Link |
---|---|
US (1) | US5405923A (en) |
EP (1) | EP0758345B1 (en) |
CN (1) | CN1087309C (en) |
DE (1) | DE69507608T2 (en) |
WO (1) | WO1995029943A1 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6177533B1 (en) | 1998-11-13 | 2001-01-23 | E. I. Du Pont De Nemours And Company | Polytetrafluoroethylene resin |
US6136933A (en) * | 1998-11-13 | 2000-10-24 | E. I. Du Pont De Nemours And Company | Process for polymerizing tetrafluoroethylene |
US7176265B2 (en) * | 2002-11-22 | 2007-02-13 | E. I. Du Pont De Nemours And Company | Directly polymerized low molecular weight granular polytetrafluoroethylene |
US7247690B2 (en) * | 2003-04-17 | 2007-07-24 | E. I. Du Pont De Nemours And Company | Melt-fabricable tetrafluoroethylene/fluorinated vinyl ether copolymer prepared by suspension polymerization |
US8015998B2 (en) * | 2004-08-12 | 2011-09-13 | Harris Mud & Chemical, Inc. | Method for patching or sealing leaks in fluid systems |
KR101261110B1 (en) * | 2008-10-27 | 2013-05-06 | 다이호 고교 가부시키가이샤 | Ptfe series sliding material, bearing, and ptfe series sliding material manufacturing method |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE1770405A1 (en) * | 1967-05-15 | 1972-08-03 | Kureha Chemical Ind Co Ltd | Process for polymerizing fluoroethylenes |
DE2711455A1 (en) * | 1976-03-18 | 1977-10-13 | Daikin Ind Ltd | PROCESS FOR THE PROCESSING OF POLYTETRAFLUORAETHYLENE |
DE2244279B2 (en) * | 1971-09-13 | 1978-03-09 | Pechiney Ugine Kuhlmann, Paris | Process for the polymerization of tetrafluoroethylene in aqueous suspension and use of the process product for direct extrusion and for automatic loading of the compression molds |
US4481343A (en) * | 1979-12-21 | 1984-11-06 | Produits Chimiques Ugine Kuhlmann | Process for the polymerization of tetrafluoroethylene in aqueous dispersion |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2393967A (en) * | 1942-12-24 | 1946-02-05 | Du Pont | Process for polymerizing tetrafluoroethylene |
JPS4928026B1 (en) * | 1965-01-12 | 1974-07-23 | ||
US4189551A (en) * | 1978-06-19 | 1980-02-19 | E. I. Du Pont De Nemours And Company | Process for reducing adhesions during suspension polymerization |
DE4022405A1 (en) * | 1990-07-13 | 1992-01-16 | Hoechst Ag | METHOD FOR PRODUCING TETRAFLUORETHYLENE POLYMERISATE IN AQUEOUS SUSPENSION |
-
1994
- 1994-05-02 US US08/236,852 patent/US5405923A/en not_active Expired - Lifetime
-
1995
- 1995-04-28 CN CN95192915.1A patent/CN1087309C/en not_active Expired - Fee Related
- 1995-04-28 EP EP95918871A patent/EP0758345B1/en not_active Expired - Lifetime
- 1995-04-28 DE DE69507608T patent/DE69507608T2/en not_active Expired - Fee Related
- 1995-04-28 WO PCT/US1995/005297 patent/WO1995029943A1/en active IP Right Grant
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE1770405A1 (en) * | 1967-05-15 | 1972-08-03 | Kureha Chemical Ind Co Ltd | Process for polymerizing fluoroethylenes |
DE2244279B2 (en) * | 1971-09-13 | 1978-03-09 | Pechiney Ugine Kuhlmann, Paris | Process for the polymerization of tetrafluoroethylene in aqueous suspension and use of the process product for direct extrusion and for automatic loading of the compression molds |
DE2711455A1 (en) * | 1976-03-18 | 1977-10-13 | Daikin Ind Ltd | PROCESS FOR THE PROCESSING OF POLYTETRAFLUORAETHYLENE |
US4481343A (en) * | 1979-12-21 | 1984-11-06 | Produits Chimiques Ugine Kuhlmann | Process for the polymerization of tetrafluoroethylene in aqueous dispersion |
Also Published As
Publication number | Publication date |
---|---|
CN1087309C (en) | 2002-07-10 |
CN1147262A (en) | 1997-04-09 |
DE69507608D1 (en) | 1999-03-11 |
EP0758345A1 (en) | 1997-02-19 |
DE69507608T2 (en) | 1999-09-09 |
US5405923A (en) | 1995-04-11 |
EP0758345B1 (en) | 1999-01-27 |
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