DE19903657A1 - Tetrafluoroethylene/hexafluoropropylene copolymers useful in production of wires and cables and as structural materials for halls have increased drawability and avoid difficulty in controlling metal impurity levels - Google Patents

Abstract

A melt granulated copolymer comprising monomer units consisting of tetrafluoroethylene, hexafluoropropene, and fluorinated monomers which can be polymerized with a mixture of tetrafluoroethylene and hexafluoropropene, the copolymer having an Mw/Mn molecular weight ratio of less than 2 and less than 80 unstable end groups per 1.10<6> C atoms obtained by aqueous emulsion polymerization is new. A melt granulated copolymer comprising monomer units consisting of 78-95 wt.% tetrafluoroethylene, 5-22 wt.% hexafluoropropene, and 3 mole% fluorinated monomers which can be polymerized with a mixture of tetrafluoroethylene and hexafluoropropene, the copolymer having an Mw/Mn molecular weight ratio of less than 2 and less than 80 unstable end groups per 1.10<6> C atoms obtained by aqueous emulsion polymerization is new. An Independent claim is also included for preparation of the copolymer as above by aqueous emulsion polymerization with mechanical coagulation of the copolymer, agglomeration of the coagulated copolymer, by bringing it into contact with an organic liquid immiscible with water, isolation of the agglomerate, and drying of this to a free flowing product without partial sintering.

Description

Field of the invention

The present invention relates to melt granules of copolymers that can be processed from the melt Tetrafluoroethylene (TFE) and Hexafluoropropylene (HFP) with improved processability for wire and Cable applications and a method of use this polymer for coating wire and Cable ladders.

background

Processable copolymers with TFE and HFP are best known under the name FEP. As perfluorinated thermoplastics have such copolymers unique end-use properties such as Chemical resistance, weather resistance, Flame resistance, thermal stability and excellent electrical properties. Like others FEP can be easily thermoplastic coated wires, hoses, pipes, foils and Shaping films.  

Because of its excellent thermal stability and because it is practically non-flammable, FEP often as construction material for halls and Meeting rooms used to the severe fire to meet protective requirements. FEP is recommended because of its excellent dielectric properties too very for use in data transmission cables (EP 0 423 995 A1).

For the extrusion coating of wires and cables high processing speeds are required. Such high extrusion rates are common to many Thermoplastics set limits due to melt fractures. Melt fractures lead to rough surfaces and / or uneven wall thicknesses. Therefore, it is believed that one to increase the extrusion speed Very broad molecular weight distribution copolymer should use, for example, the FEPs according to US A-4 552 925.

To significantly increase the molecular weight distribution widen, is usually a mixture of at least two FEPs with very different molecular weights used. The molecular weights are mostly based on of melt viscosity or melt flow index (MFI value) characterized. The desired blends will be often obtained by having the components manufactures separately by polymerization and they then in the form of latices, pearls or fluffy Products mixed before melting granulation. The Manufacturing these mixtures is therefore tedious and expensive.

Other FEP mixtures are described in DE 26 13 642 and DE 26 13 795.  

These mixtures are said to be advantageous for suppressing the foaming that occurs during the stabilization process of FEP. The resin is treated at high temperatures (up to 400 ° C), preferably with steam. With the help of this method, thermally unstable end groups (mostly COOH and CONH ₂ groups) are eliminated. These end groups can easily be detected by means of IR spectroscopy.

These mixtures have a very wide range Molecular weight distribution based on what is more general Experts consider extrudability improved.

For processing FEP, especially for wire sheathing, must have thermally unstable end groups be removed. The decomposition reaction of the unstable End groups described in "Modern Fluoropolymers", ed. John Scheirs, Wiley & Sons 1997, page 228 leads to bubbles and holes in the end products. The melt granulation of unstabilized Polymer resins lead to corrosion damage to the used equipment and metal contamination of the melt granulate produced. The in DE 26 13 642 and DE 26 13 795 described stabilization methods are difficult to perform because of the Use of water vapor corrosion problems on the throw up used equipment.

Metal contamination is difficult to control and can be used to degrade and decompose the copolymer lead at high processing temperatures. This Decomposition leads to discoloration and degradation as well Laying on nozzles. This is Accumulations of molecular fractions of the polymer on the Surface of the nozzle outlet that the Be  negatively impact the stratification process. You can also so-called "cone breaks" also occur. At the Coating a wire becomes the molten one Polymer extruded in the form of a tube or jacket and drawn onto the wire by means of vacuum. Cone breaks are interruptions or breaks in this process occur. Every time such a cone break occurs, you have to start the coating process again and wait for the system to rebalance is coming. This makes it difficult for a long time To achieve operating times. It also decreases productivity.

Furthermore, the extrusion temperatures must be like this to be kept as low as possible Decomposition reactions and the resulting Counteract the release of toxic gases, their Speed significantly with increasing temperature increases. On the other hand, low extrusion effects temperatures and thus higher melt viscosities earlier occurrence of melt fractures. A Lowering the melt limit viscosity by Decrease in molecular weight leads to poorer mechanical properties.

It follows that the material is not only through Elimination of the thermally unstable end groups, but also by avoiding Metal impurities and against shear and / or thermal degradation of more susceptible Mw fractions should be made more thermally stable.

Another way to eliminate unstable End groups is post-fluorination, for example according to GB 1 210 794, US 4 743 658 and EP 0 457 225 B1. This method is generally used  Elemental fluorine diluted with nitrogen and works at elevated temperatures up to Melting range of the polymer. The polymer can in the form of melt granules, agglomerates or fluffy products are fluorinated. Here too are excessive contamination with metals avoid.

In EP 0 222 945 B1 the fluorination of hardened Agglomerates described there as granules be designated.

The fluorination leads to perfluorinated end groups, whereas the treatment described above with moist heat does not mechanistically form a fluorinated polymer resin can lead. It is to assume that in this case in the main chain of the Polymer-inserted double bonds are present, that cause inherent thermal instability. These bonds may do that Discoloration caused by long-term exposure to high Temperatures.

US 4,626,587 describes another FEP degradation reaction described. Here the reaction should begin with that initially at temperatures above the Split the melting point of HFP diads in the middle of the chain become. Such diads form in the radical Polymerization by recombination of the corresponding Polymer radicals as a termination step. The destruction of the Diades under the processing conditions leads to halving the molecular weight of this polymer chain what the mechanical properties of the polymer negatively influenced, and also to the formation of more unstable end groups. According to US 4,626,587 such diads by exposure to very high shear rates  on the material at a temperature that is clear above the melting point, destroyed. This method is also very expensive.

Another method of reducing the Main chain instability is described in EP 0 789 038 A1 disclosed. The termination of Polymer radicals through the use of relatively large ones Amounts of a chain transfer agent suppressed.

Summary of the invention

The present invention provides a material for Wire and cable coatings ready, that at higher Speeds and higher temperatures processed and longer machine run times are possible. The invention continues Manufacturing process ready, the more economical and more controllable in terms of consistent quality is. The invention also provides a method for Reduction of nozzle transfers and frequency of cone breaks in the extrusion coating of Wires or cables ready.

Detailed description

The polymer according to the invention is a copolymer of TFE and HFP. It has an HFP Content in the range from 5 to 22% by weight, preferably 10 up to 18% by weight, a TFE content of 95 to 78% by weight, preferably 90 to 82 wt .-%, and contains optionally up to 3 mol% of a fluorinated Monomer that is copolymerizable with HFP and TFE. The comonomer, if present, is involved  is preferably a perfluoroalkyl vinyl ether according to EP 0 789 038 and DE 27 10 501 C2. The Monomer content can be determined by IR spectroscopy as described in US 4,552,925. The Polymers according to the invention generally have one Melting point from 240 to 275 ° C, preferably 245 to 265 ° C.

The polymer according to the invention is essentially free of thermally unstable end groups, their removal by subsequent fluorination of the agglomerates. Under "Essentially devoid of end groups" are less than 80 end groups per million carbon atoms, preferred less than 40 end groups and particularly preferred less than 30 end groups per million carbon atoms to understand. The substance points in relation to metals a high degree of purity, that is, the Total iron, chromium and nickel content below 200 ppb (= parts per billion), preferably below 100 ppb, lies.

That for coating wire and cable conductors polymer used according to the invention has a very narrow molecular weight distribution, i.e. H. an Mw / Mn Ratio less than 2 (Mw = weight average, Mn = Number average molecular weight). The minimum value for this ratio is 1.5. This stands in contrast to those for wire coatings with high Extrusion rates recommended FEP grades for which a broad molecular weight distribution is advised. The breadth of the molecular weight distribution is reduced the method of W.H. Tuminello, Polym. Closely. Sci. 26, 1339 (1986). For the High speed wire extrusion is the MFI value of the Polymers ≧ 15. Lower MFI values are for others usable such. B. foamed coaxial cable.  

This polymer is preferably essentially free of unstable end groups. Very particularly preferred it is the polymer of the invention.

A melt-granulated copolymer according to the invention with an MFI of 24 and 15 wt% HFP can be as below described. This polymer can with a wire coating extruder, for example 390 ° C (735 ° F) at a speed of 1500 Feet / min over a machine run time of 6 hours operated, without discoloration, without Occurrence of significant nozzle transfers and with less Cone breaks than with standard FEP qualities. The causes of the surprisingly good performance are not entirely clear.

Despite the narrow molecular weight distribution, achieve high processing rates. As above has been carried out, it is assumed in the professional world that to achieve such high processing rates a broad molecular weight distribution is required is. It has now been found that a close Molecular weight distribution is better, creating a prevailing prejudice is overcome.

In addition, none occurs during processing Discoloration on. This is an indication that none Decomposition reaction takes place. The MFI value of the extruded material is practically unchanged. The Number of end groups detectable by IR increases not to. It can be concluded from these two findings that there is no significant chain degradation. This Observation suggests that in the material no weak main chain bonds, such as as HFP diads (US 4,626,587) are present.  

Like the absence of discoloration as well as the almost unchanged MFI value and the almost unchanged number prove by end groups occurs even at higher ones Processing temperatures no significant decomposition on. It is believed that this is too diminished Nozzle placement and the sharp decrease in frequency of cone breaks. So that's what distinguishes it copolymer according to the invention by a surprisingly high thermal stability even under shear stress. The polymer according to the invention can therefore also be used for others Applications are used with advantage.

Evidence of the absence of decomposition reactions is surprising and not yet fully understood. It will assumed that metal contaminants, in particular Heavy metals like iron, nickel and chrome, one Could induce decomposition reaction. As a matter of fact the neutron activation analysis showed that the material used less than 50 ppb iron, Contained nickel and chromium ions. The invention Copolymer can therefore be classified as high purity.

The polymer of the invention can be according to the following described methods are produced.

The polymerization can be carried out as a free-radical aqueous emulsion polymerization, as is known in the prior art (see US Pat. No. 2,946,763). Ammonium or potassium peroxodisulfate is used as initiators. Standard emulsifiers, such as the ammonium salt of perfluorooctanoic acid, are used as emulsifiers. Buffer substances such as NH ₃ , (NH ₄ ) ₂ CO ₃ or NaHCO ₃ can be added to the formulation. Usual chain transfer agents such as H ₂ , lower alkanes, methylene fluoride or methylene chloride are used. Chain transfer agents containing chlorine and bromine should be avoided. These components can cause severe corrosion damage during fluorination. The polymerization temperature can be 40 to 120 ° C and preferably 50 to 80 ° C; the polymerization pressure can be 8 to 25 bar, preferably 10 to 20 bar. HFP is introduced and metered into the reactor according to the rules of copolymerization (see, for example, "Modern Fluoropolymers", ed. John Scheirs, Wiley & Sons (1997), page 241). The preferred polymerization formulation is free of alkali metal salts.

Furthermore, the copolymerization is preferably so carried out that in contrast to EP 0 789 038 A1 no Chain transfer agent is used. Chain transfer agents automatically lead to one Broadening the molecular weight distribution. The Plotting the rate of polymerization against the Time is supposed to be the form of in "Modern Fluoropolymers", Ed. John Scheirs, Wiley & Sons, 1997, page 226, have the curve described. As published in this is specified, the Mw / Mn ratio easily against the plots of speed the time in the absence of a chain transfer agent can be calculated using equation (6), page 230, assuming that the termination is exclusive done by recombination. The recombination leads at low sales to an Mw / Mn ratio of 1.5. One mainly through chain transfer termination leads to an Mw / Mn ratio of 2nd

The radical polymerization can also be carried out in one non-aqueous medium, for example R 113 as described in US 3,528,954. This  however, non-aqueous process is not preferred because it is believed that due to the in this "Suspension polymerization" occurring gel effect also lower proportions of high molecular weight products delivers. It is more likely that the weak Main chain bonds (HFP diads) through the gel effect arise. The appearance of a gel effect in the aqueous emulsion polymerization is complete unlikely due to chain growth and termination the surface of the latex particles take place.

The dispersion resulting from the polymerization becomes mechanically coagulated with a homogenizer (see EP 0 591 888 B1) and with an immiscible with water organic liquid, for example gasoline, agglomerates as is well known in the art (see "Modern Fluoropolymers", ed. John Scheirs, Wiley & Sons, 1997, page 227). In the agglomerates are free-flowing pearls with a Diameter from 0.5 to 2 mm. The free flow is with regard to the technically safe implementation of the following processing steps preferred. The The agglomerate is dried by rinsing with Nitrogen and then under moderate vacuum Temperatures up to 180 ° C.

A chemical coagulation of the agglomerate is also possible. However, this is used in the general acids. This is not preferred as it is too very high levels of metal contamination in all subsequent processing steps leads.

The agglomerate can then at temperatures from 60 to 150 ° C, preferably at 100 to 140 ° C, with a Mixture of fluorine to be fluorinated in nitrogen. The Mixture generally contains 10% by weight of fluorine. The Fluorination continues until 90 to 95%  the end groups of the original agglomerate have been eliminated. Higher fluorination temperatures can cause a difficult change to control MFI value, which can be up to 30%. This can widen the Molecular weight distribution lead and the Negatively affect performance. Consequently reproducibility is not achieved, so that Quality and uniformity of wires and Cables coated with the polymer are negative being affected. Because the response times are higher Temperatures have not been significantly reduced higher fluorination temperatures are not advantageous classified. In addition, high temperatures can cause the agglomerate to pre-sinter or even sinters and the material on the apparatus wall sticks. The fluorination is in one Tumble dryer carried out the material in Movement keeps going. This will make them more homogeneous Reaction conditions achieved. The free flowing Agglomerate should preferably not contain any fines and be mechanically so stable that the Post-treatment essentially no fines form. Fine fractions can increase the reliability of the Adversely affect process management. On a Hardening of the agglomerate, as described in EP 0 222 945 B1 can be omitted here.

Fluorination of the agglomerate has two advantages. she is not diffusion controlled because the End groups on the surface of the latex particles are located. The response times are therefore relative short. In addition, uncured agglomerate is so soft that no metal contamination from the wall of the Tumble dryer scraped off. That way the content of metal impurities decreased. Both  does not meet the fluorination of melt granules to. In this case, higher temperatures are required for the fluorination temperatures and significantly longer response times required to take account of the fact that the reaction takes place under diffusion control. In addition, the hard and sharp enamel granules scratch a considerable amount of metal from the wall of the Tumble dryer. An extension of the response time leads to increased contamination with metals. These contaminants are difficult to remove. The Order of magnitude of metal contamination increased when using the granulate process by two Powers of ten.

The fluorinated agglomerate will then melt granulated.

With drying and fluorination it will Agglomerate crushed to a certain extent. This creates Fine particles that allow the free flow of the material hinder. It is advantageous to use the fluorinated Agglomerate before melting granulation to compact. This way it becomes a more reliable constant Dosage rate reached.

Melt granulation of fluorinated agglomerates offers compared to the melt granulation of non-fluorinated agglomerates have many advantages. The Melt granulation is practically without decomposition. The MFI value remains almost unchanged. This finding suggests that essentially none weak main chain bonds are present. The corrosion the equipment used is significantly reduced. Therefore, metal contamination is only minimal tender amount added. The emission of gaseous Decomposition products at the nozzle outlet become essential  reduced (e.g. by four powers of ten). The entire This makes the process much safer. The Occurrence of nozzle laying becomes essential reduced. Therefore, the procedure is easier too monitor. The melting granules differ to melt granules from non-fluorinated agglomerates, which often colored the extruder in a typical coffee brown leave no discoloration on.

The MFI value according to the procedure described above Melt granulate produced increases compared to copolymer obtained during the polymerization only slightly, namely by about 10%. So you can achieve consistent quality more easily.

The melt granulate is, as in DE 195 47 909 A1 described for the removal of volatile components and COF groups subjected to an aqueous treatment. There hardly any gaseous decomposition products and acidic End groups are present, too, the corrosion of the stainless steel Water treatment tank significantly reduced. In addition, the further contamination with Heavy metals reduced. Beyond that water-soluble from the manufacturing process Salts removed. The amount of extractable fluoride is reduced to less than 1 ppm.

Test methods

The MFI value is according to ASTM D 1238 (DIN 53735) 372 ° C measured with a load of 5 kg. The MFI value can in the value of the melt viscosity in 0.1 Pas (Poise) can be converted by dividing 53150 by the Divided MFI value (g / min).  

The HFP content can be determined by FTIR spectroscopy in accordance with US Pat. No. 4,552,925. The absorption at the wave numbers 980 cm ^-1 or 2350 cm ^-1 is determined on a film with a thickness of 0.05 ± 0.01 mm, which is produced at 350 ° C. and measured with an FTIR-Nicolet Magna 560 FTIR spectrometer becomes. The HFP content is determined according to the following equation:

HFP content (% by weight) = A ₉₈₀ / A ₂₃₅₀ × 3.2.

The end groups (-COOH, -COF, -CONH ₂ ) are determined by means of FTIR spectroscopy, as is described in EP 226 668 B1 and US 3,085,083. A film produced at 350 ° C. with a thickness of 0.1 mm and a reference film made of a material that does not contain any of the end groups to be analyzed are used. A Nicolet Magna 560 FTIR spectrometer with software in interactive subtraction mode was used. When the number of end groups is stated, the sum of the isolated and associated COOH, CONH ₂ and COF groups is meant.

The melting points of the copolymers were determined by DSC ASTM D 4591-87 with a heating rate of 10 K / min. certainly. The melting temperature given here is the Peak temperature of the endotherm during the second melting.

The breadth of the molecular weight distribution by the Mw / Mn ratio was characterized by rheological spectroscopy with an "Advanced Rheometer Expansion System "(ARES) from Rheometric Scientific determined. The measurements were taken at 372 ° C carried out and according to the method of W. H. Tuminello, Polym. Closely. Sci. 26, 1339 (1989).  

To determine the metal contents, the samples were extracted at room temperature for 72 hours with 3% HNO ₃ and the extracts were analyzed by means of atomic absorption spectroscopy.

The extractable fluoride ion content in the Melt granulate was produced according to the method described in EP 0 220 910 B1 specified method determined. The extraction was but only done with water.

example 1

In a 1500 liter stainless steel reactor 1000 l of deionized water with 3 kg of Ammonium salt of perfluorooctanoic acid presented. The Air was evacuated and flushed with Nitrogen removed. The reactor was at 70 ° C heated and kept at this temperature. After that 2 kg of a 25% aqueous ammonia solution admitted.

The reactor was brought to a total pressure of 17 bar with TFE and HFP, the HFP partial pressure being 12.5 bar. The polymerization was started within 10 min by adding 1600 g of ammonium persulfate as a solution in 5 l of deionized water. The pressure was kept constant by feeding a gas mixture of TFE / HFP into the reactor. The TFE / HFP weight ratio was 0.14. After 6 hours the reaction was stopped by interrupting the monomer feed. The monomers were released by venting the reactor. The reactor was discharged after cooling to room temperature. The solids content of the polymer dispersion was 29%. The dispersion was practically free of coagulum. The MFI was 20 g / min. The HFP content of the copolymer was 13% by weight. The melting point was 255 ° C. The copolymer had 660 COOH end groups per 10 ⁶ carbon atoms. The measured Mw / Mn ratio was 1.7, whereas the Mw / Mn ratio calculated from the rate of polymerization versus time was 1.6.

The dispersion was coagulated with a homogenizer and agglomerated with gasoline. The agglomerate was washed three times with deionized water and 6 Dried at 180 ° C in a tumble dryer, first flushed with nitrogen and then in Vacuum was finally dried.

The agglomerate obtained was divided into two parts divided. A part was then melt granulated, washed with water and dried, whereby a coffee brown color revealed. After fluorination and repeated treatment with water to remove the remaining COF end groups disappeared. This sample is called A0. The material pointed 43 end groups per million carbon atoms. The other part of the agglomerate was first fluorinated, then melt granulated, treated with water and dried. This sample labeled A1 just pointed 18 end groups per million carbon atoms.

In each process step, the iron content, Nickel and chrome after the extraction process determined. The results are together with the amount at end groups listed in Table 1.  

Table 1

Metal contamination of samples A0 and A1 according to various processing steps. The agglomerate had 660 end groups.

Sample A0

Fluorination of the melt granulate (comparison)

Sample A1

Fluorination of the Agglomerate (Invention)

The fluorination was carried out in a 300 liter tumble dryer made of stainless steel with a mixture of 10% fluorine in nitrogen at 140 ° C. (sample A0) or at 100-140 ° C. (sample A1). Details are given in Table 2. The fluorine mixture had to be replaced several times (refill). At the end of the fluorination, excess fluorine was displaced from the reactor by purging with air. The excess fluorine was absorbed by passing the air stream through a bed of Al ₂ O ₃ granules and through a washer containing an aqueous CaCO ₃ slurry.

Table 2

Fluorination conditions for samples A0 and A1

The aqueous treatment of the melt granules (see DE 195 47 909 A1) was produced in a 1000 l reactor stainless steel. 200 kg of Melting granules and 400 l of deionized water with 1 l a 25% ammonia solution were in the reactor submitted. The reactor was heated to 100 ° C and 4 hours in the case of non-fluorinated melt granules and 1 hour in the case of fluorinated melt granules kept at this temperature. This response time is needed to determine the level of COF end groups decrease less than 5 ppm. The reactor was cooled by changing the water twice. The The product was dried by blowing in Hot air in the reactor. The melt granules had one Extractable fluoride ion content of 0.1 ppm.

Example 2

Sample A11 was combined with a commercially available Product labeled C1 under two different ones  Setting conditions about one Wire coating extruder sent. Sample A11 was made Made like A1, but had an MFI of 24 g / min. Regarding polymerization and processing for A11 proceed as for A1. A11 has 28 end groups and an iron content of 18 ppb. The measured Mw / Mn ratio was 1.6. The calculated value was 1.7. The extractable fluoride ion content was 0.2 ppm.

The coating conditions are in Table 3 listed.

Table 3

Coating behavior of the material according to the invention in comparison with the commercially available product C1 and sample A0

The temperature profiles that are not in the table were listed to maximize the Line output slightly adjusted, the Deviation from the insulation eccentricity between 0.0003 and 0.0007 inches was held.  

In runs 1 and 2 there were neither clear nozzle routings and cone breaks ascertain. In run 3 were the same duration considerable nozzle transfers and cone breaks ascertain. With aging C1 above the Melting temperature (i.e. 250 ° C) resulted in a noticeable brown discoloration.

Example 3

Samples A11, A12 and commercial products were through a slightly different wire coating sent extruder.

The coating conditions are in Table 4 listed.

Table 4

Coating behavior of the material according to the invention in comparison to two commercial products

The temperature profiles were used to maximize the Line output slightly adjusted, the Deviation from the insulation eccentricity between Held 0.0003 and 0.0007 inches (0.00076 and 0.0018 cm) has been.

Run # 1 was over a 29 hour period when extruding wires in the colors blue, green, orange, brown and white no clear Nozzle routing and only 2 cone breaks to be observed. In run number 2 there were 24 Hours of considerable nozzle transfers and an average of 6 to 8 cone fractures.

Claims (11)

1. melt-processible, melt-granulated copolymer consisting essentially of monomer units of 78 to 95 wt .-% tetrafluoethylene, 5 to 22 wt .-% hexafluoropropene and at most 3 mol% fluorinated monomers with a mixture of tetrafluoroethylene and hexafluoropropene are copolymerizable, has a weight average to number average molecular weight ratio of less than 2 and less than 80 unstable end groups per 1,10 ⁶ carbon atoms and is obtained by aqueous emulsion polymerization. 2. A copolymer according to claim 1 which is less than 200 ppb Contains heavy metals. 3. A copolymer according to claim 1 or 2, which has less than 40 unstable end groups per 1,10 ⁶ carbon atoms. 4. Copolymer according to claim 1 or 2, which in contains essentially no extractable fluoride. 5. A process for producing a copolymer which consists essentially of units of 78 to 95% by weight of tetrafluoethylene, 5 to 22% by weight of hexafluoropropene and at most 3 mol% of fluorinated monomers which are copolymerizable with a mixture of tetrafluoroethylene and hexafluoropropene , exists and a ratio of weight average to number average molecular weight of less than 2 and
has fewer than 80 unstable end groups per 1,10 ⁶ carbon atoms, in which one
the monomers are polymerized by aqueous emulsion polymerization in an aqueous medium,
the copolymer coagulates essentially by mechanical means,
the coagulated copolymer agglomerates by contacting it with an organic liquid which is essentially immiscible with water,
isolates the agglomerate,
the agglomerate dries to a free-flowing product without partial sintering,
bringing the free-flowing agglomerate into contact with an effective amount of fluorine at a temperature from 60 ° C. to the pre-sintering temperature for so long that unstable end groups are essentially converted into stable end groups,
the fluorinated agglomerate is melt-granulated and the melt granulate is brought into contact with water at a temperature of 60 to 130 ° C. 6. The method according to claim 5, wherein one aqueous polymerization medium used in essentially free of chain transfer agents is. 7. The method according to claim 5, wherein as Polymerization medium uses water. 8. The method according to claim 5, wherein one Polymerization medium used in is essentially free of alkali metal ions.   9. The method according to claim 5, wherein the Agglomeration of an organic liquid uses that is free of halogen atoms. 10. The method according to claim 5, wherein the Fluorination at a temperature of 60 to 150 ° C carries out. 11. The method according to claim 5, wherein the Melt granules with 0.01 to 1 wt .-% ammonia or a connection among the Contacting conditions releases ammonia, containing water in contact.