GB1558976A - Process for the manufacture of paste-extrudable polymers of tetrafluorethylene - Google Patents

Description

PATENT SPECIFICATION (" 1) 1558 976

CD ( 21) Application No 40614/76 ( 22) Filed 30 Sept 1976 ( 19) ( 31) Convention Application No 2 544 040 4, ( 32) Filed 2 Oct 1975 in t MI ( 33) Fed Rep of Germany (DE) U: ( 44) Complete Specification published 9 Jan 1980 _ ( 51) INT CL 3 CO 8 F 14/26, 2/40 ( 52) Index at acceptance C 3 P 412 506 510 540 HG ( 54) PROCESS FOR THE MANUFACTURE OF PASTE-EXTRUDABLE POLYMERS OF TETRAFLUOROETHYLENE ( 71) We, HOECHST AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following 5 statement:-

This invention relates to a process for the manufacture of modified tetrafluoroethylene dispersion polymers.

It is known that polymers of tetrafluoroethylene can be obtained by two substantially different methods, i e by suspension polymerization to obtain coarse-grained 10 polymers having an average particle size of 20 to 1000 microns which, after drying and grinding or after treatment to improve their flow properties, can be used for mold sintering or ram extrusion, and by dispersion polymerization with the use of suitable emulsifiers to obtain stable aqueous dispersions of polytetrafluoroethylene having a particles size of from 0 05 to 0 6 micron which are especially suitable for impregna 15 tion and coating purposes By mechanical coagulation and subsequent drying of the precipitated dispersion polymer flowable powders can be obtained However, these polytetrafluoroethylene powders obtained by dispersion polymerization are hardly suitable for the so-called paste extrusion technique according to which the polymer is first made into a paste by mixing with a liquid lubricant, for example a high boiling 20 hydrocarbon, and the paste is then extruded under pressure through a die The drawback resides in the fact that, owing to the lack of orientation of the material, the extruded article has a rough surface and knots are formed In order to ensure uniform extrusion and to avoid the aforesaid disadvantages, there are required dispersions in which substantially all the particles have an almost spherical shape Moreover, it is 25 desirable to reduce the high extrusion pressure required for the extrusion of dispersion polymers in paste form by modification of the polymer during polymerization.

Processes have already been described the aim of which is to improve the paste extrusion properties of dispersion polymers of tetrafluoroethylene US Patent Specification 3,088,941 proposes, for example, to carry out the dispersion polymerization 30 of tetrafluoroethylene with the use of a seed dispersion of the tetrafluoroethylene homopolymer The dispersion particles obtained have, however, a very broad particle size distribution, which is not desired To overcome this drawback US Patent Specification 3,654,210 proposes to polymerize in the presence of seeds of dispersion copolymers of a predominant proportion of tetrafluoroethylene with fluoroolefins contain 35 ing chlorine, bromine, iodine or hydrogen, especially trifluorochloroethylene.

In the two aforesaid processes, in the main polymerization, carried out after the preparation of the seeds, there are used no modifying substances having a regulating effect or chain interrupting properties It is true that this is of advantage for the polymerization speed, since modifying additives reduce the space-timeyield because 40 of their regulating effect But, on the other hand, the processes without modification in the main polymerization have the disadvantages that the polymers obtained have a higher melt viscosity and the extruded articles made therefrom, for example pipes and flexible tubes, have a reduced alternating bending strength, a poorer transparency and a higher brittleness Moreover, products made from copolymers prepared in the 45 presence of a seed dispersion exhibit a higher shrinkage in the transverse direction on sintering, which detrimentally affects, for example, the dimensional accuracy of pipe linings.

US Patent Specification 3,142,665 provides a process for the manufacture of paste-extrudable dispersion polymers in which, at least in the last part of the polymerization of tetrafluoroethylene, so-called modifying agents are present, for example hydrogen, methanol or a perfluoroalkene or perfluoroalkoxyalkene The polymers obtained in this manner have good paste extrusion properties within a wide range of reduction ratios (which is the ratio, important in paste extrusion, of the crosssectional area of the preform to the cross-sectional area of the die opening), and a reduced melt viscosity and the articles made therefrom have an improved transparency and a higher alternating bending strength, but, like the products of the former processes, they are distinguished by a series of drawbacks, especially with respect to their 1 properties as an insulating material for electric conductors In the case of wires provided with a thin coating a relatively large number of punctures of the insulation indicate defects in the insulation, for example cracks This number is multiplied or permanent disruptive discharges occur when the paste is extruded at a higher reduction ratio Due to the fact that such defective section must be cut out of the 1 insulated conductor, the length of faultless wire is shortened and a high percentage of waste is obtained The number of punctures of the insulation is also increased when the so-called draw-off rate is increased This means the quotient of the crosssectional area of the die opening (minus the cross-section of the metallic conductor) and the cross-sectional area of the unsintered insulation In practice it is desirable to 2 shift this draw-off rate towards higher values, if possible, since in this manner a coating can be obtained which has a much smoother surface and a higher gloss In the whole range of draw-off rates, not only is the number of punctures of the insulation increased to a noteworthy extent with the products obtained according to the state of the art, with a distinctly increasing tendency towards a higher draw-off rate, 2 but also a relatively favorable behavior in this respect is limited to a very narrow range of draw-off rates Hence, the manufacturer must operate under substantially constant conditions which is extremely difficult in practice.

Due to the diminished transparency of the products prepared with a seed dispersion, the conductor insulation becomes turbid in many cases (the socalled a chalking effect), which results m a brightening which is rather embarrassing with colored insulation.

The present invention seeks to provide a tetrafluoroethylene dispersion polymer having good paste extrusion properties and especially an improved suitability as an insulation material for electric conductors.

The present invention therefore provides a process for the manufacture of a modified tetrafluoroethylene dispersion polymer which comprises polymerizing tetrafluoroethylene in the presence of a catalyst, a dispersion agent and optionally an aqueous seed dispersion containing dispersed particles of polytetrafluoroethylene or of a copolymer consisting of at least 90 % by weight of tetrafluoroethylene units and the balance of fluoroolefin units, and in the presence of, as modifying agent from 0.0005 to 1 5 % by weight, calculated on the tetrafluoroethylene excluding any seed polymer, of a perfluorinated vinyl ether of the formula F O o C Fx F O ' CF -CF 2-C C CF CF 3 o O IF 'Iz + C I l:C: (I) in which N is zero or an integer from 1 to 4, or of a mixture of any two or more of such perfluorinated vinyl ethers, and coagulating and drying the polymer obtained.

The perfluorinated vinyl ethers of the formula I used as modifying agents in the process of the invention are prepared by reacting hexafluoropropene epoxide with a phosphoric acid tris-dialkylamide of the formula 1,558,976 (II) 3 1,558,976 preferably hexamethylphosphoramide to obtain an acid fluoride of the formula 1 = O CF 5 N F CF CF 2 C CF 3 O F 4 OTCF-C o II XF (III) CF 3 CF 5 N F The acid fluorides of the formula III are then hydrolyzed to the corresponding fluorocarboxylic acids which are neutralized with alkali The carboxylic acid salts obtained are heated to a temperature above 150 C, whereby they are transformed by pyrolysis 5 into the corresponding vinyl ethers of the formula I Syntheses of the aforesaid perfluorinated vinyl ethers of the formula I are described in German Offenlegungsschriften 2,434,992 and 2,517,357 It is likewise possible to use mixtures of the aforesaid perfluorinated vinyl ethers of the formula I in which N has different values PreD ferred modifying agents are perfluorinated vinyl ethers of the formula I in which N 10 is zero or 1 or mixtures of the two compounds.

In the course of polymerization, the modifying agent should be present in an amount of from 0 0005 to 1 5 % by weight, preferably 0 01 to 1 0 % by weight, calculated on the tetrafluoroethylene used (but excluding any seeddispersion) The modifying agent is preferably introduced into the reaction vessel prior to the beginning 15 of polymerization, but it can be added in dosed quantities during the course of polymerization at any moment before a conversion of 70 %, preferably 40 %/, is reached.

Alternatively, part of the modifying agent can be first introduced into the polymerization vessel and the balance metered in during polymerization Another possibility is to 0 add the modifying agent from the beginning of polymerization, either continuously 20 or in portions, until 70 % and preferably 40 % of the tetrafluoroethylene have reacted.

The dispersion polymerization is carried out under the usual pressures of from to 30, preferably 8 to 16 atmospheres gauge and at temperatures of from 10 to 70 C, preferably 20 to 40 C, in the presence of the usual catalysts, preferably redox systems, i e combinations of a peroxidic compound, for example an organic or in 25 organic peroxide, a peracid, a persulfate, perborate, or percarbonate, with a reducing component, for example a bisulfite, thiosulfite, dithionite, hydrogen sulfite, sulfinate, or a compound yielding diimine, such as azodicarboxylic acid and the salts thereof, or azodicarbonamide There are preferred combinations of alkali metal or ammonium persulfate with alkali metal bisulfites In all cases it is absolutely essential that the 30 catalyst is soluble in water, especially in the alkaline range.

The dispersion polymerization of tetrafluoroethylene is also carried out in the presence of the usual emulsifiers, as described, for example, in US Patent Specification 2,559,752 There are mentioned by way of example the alkali metal and ammonium salts of long chain perfluorocarboxylic acids, whydroperfluorocarboxylic 35 acids, chlorofluorocarboxylic acids, perfluorodicarboxylic acids, as well as perfluorosulfonic acids and perfluorophosphonic acids Preferred emulsifiers in the process of the invention are the ammonium salts of perfluoro-octanoic acid and of whydroperfluoro-octanoic acid If possible, the emulsifier used should not have telogenic prot O perties Optionally, the dispersion polymerization can also be carried out in the pre 40 sence of small amounts ( 0 0001 to 0 01, preferably 0 0005 to 0 01 % by weight, calculated on the weight of the aqueous mixture) of compounds having a regulating effect, which are used in addition to the aforesaid modifying agent, such as hydrogen, propene, chloroform, carbon tetrachloride or methanol Further auxiliaries which may be present during polymerization are anticoagulants or dispersion stabilizers, for example 45 long chain paraffin hydrocarbons, paraffin waxes, or so-called white oils which should be liquid under the polymerization conditions As dispersion stabilizers there may also be used cyclic ethers, such as dioxane or tetrahydrofuran, polyoxyalkylation products or the esters thereof, for example alkylphenol polyglycol ethers such as nonylphenyl polyglycol ether or triisobutylphenyl polyglycol ether, as well as polyglycol so 50 esters of fatty acids or polyoxalkylation products of fatty amines Stabilizing agents of this type are described, for example, in US Patent Specification 2,612, 484 and in

German Patent 1,720,738 Further suitable dispersion stabilizers are polyalkylene glycols, for example diethylene, triethylene, dipropylene and tripropylene glycols and higher analogs thereof as well as mixed glycols of ethylene and propylene oxides 55 Polymerization is continued until the dispersion has a solids content of 10 to 40 % by weight, preferably 15 to 30 % by weight.

The dispersion polymerization of tetrafluoroethylene as described above in the presence of the modifying agent can be carried out without the use of a seed dispersion.

In a preferred process, however, the reactor is first charged with a seed dispersion of polyfluorotetraethylene or, more preferably, a seed dispersion of a copolymer of tetrafluoroethylene and a fluoroolefin containing at least 90 % by weight of tetrafluoroethylene units.

The seed dispersion can be prepared according to the usual methods of dispersion polymerization as described above from fluoroolefins with the above catalysts and emulsifiers and at the specified pressures and tempertures, but without the use or the modifying agent A seed dispersion of polytetrafluoroethylene must be stabilized by one of the above stabilizers, while a seed dispersion of a copolymer need not contain such a stabilizer In principle, a copolymer seed is prepared as described above with the use of one or more of the following comonomers:

(a) a fluoroalkene of the formula R R >C=C< R R in which one of the radicals R is fluorine, one or two of the radicals R is or are hydrogen, bromine, chlorine or iodine, and the remaining radical(s) R is (are) fluorine, a perfluoroalkyl group or a perfluoroalkoxy group, the alkyl or alkoxy groups having from 1 to 4, preferably 1 or 2 carbon atoms ill a branched or preferably straight chain, and when two radicals R are perfluoroalkyl or perfluoroalkoxy groups, such groups may be identical or different; (b) a perfluoroalkene of the formula R R', CF 2 =C< R' CF=CF-R, or >C=CFR, R't R', in which each of Rf and R'f, which may be identical or different, is a perfluoroalkyl radical having from 1 to 4 and preferably 1 or 2 carbon atoms, which is preferably linear or may be branched, preferably CF,; (c) a perfluoro-(alkylvinyl) ether of the formula CF 2 =CF-O Rf in which Rf is a perfluoroalkyl radical having from 1 to 5 carbon atoms, which is preferably linear or may be branched; (d) a perfluorinated vinyl ether of the formula I; (e) perfluoro-( 2-methylene-4-methyl-1,3-dioxolane); or (f) perfluoropropene.

Besides the compounds (d) and (e) the following comonomers (a), (b) and (c) are mentioned by way of example:

1,2 difluoroethylene, 1,1 and 1,2 dichlorodifluoroethylene, 1,1 and 1,2 dibromodifluoroethylene, 1,1 and 1,2 diiododifluoroethylene, 1 chloro 1 bromodifluoroethylene, 1 chloro 2 bromodifluoroethylene, trifluorobromoethylene, trifluoroiodoethylene, 1 chloro-, 1 bromo and 1 iodo 2,2 difluoroethylene, 1 chioro-, 1 bromo and 1 iodo 1,2 difluoroethylene, 1 H pentafluoropropene( 11), 2 Hpentafluoropropene( 1), l,1 H and 1,2 H tetrafluoropropene( 1), 1 and 2 chloropentafluoropropene( 11), 1 and 2 bromopentafluoropropene( 1), 1 iodopentafluoropropene(l), 1,1 and 1,2 chloro or bromotetrafluoropropene( 1), 1 H and 2 Hheptafluorobutene( 1), 1,l H and 1,2 H hexafluorobutene( 11), 2 H heptafluorobutene( 2), 1 H heptafluoroisobutene( 11), 1 and 2 chloroheptafluorobutene( 1), 1 chloroheptafluoroisobutene( 11), 1 H and 1 chlorononafluoropentene( 11), trifluoromethyland pentafluoroethyl 1 fluoro 2,2 dichlorovinyl ethers, 1 trifluoromethyl and 1 tetrafluoroethyl ( 2,2 difluorovinyl) ethers, perfluorobutene( 11) and ( 2), perfluoroisobutene, perfluoropentene( 1) and -( 2), perfluoro l 2 methylbutene( 1)l, -l 2 methyl butene( 2)l and -l 2 methylbutene( 3)l, perfluoro (methylvinyl), perfluoro (ethylvinyl), perfluoro(butylvinyl), perfluoro (isopropylvinyl) and perfluoro (isobutylvinyl) ethers.

Besides perfluoro ( 2 methylene 4 methyl 1,3 dioxolane) mentioned above the following compounds are preferred as comonomers: trifluoroethylene, vinylidene fluoride, perfluoropropane, perfluoro (propylvinyl) ether and especially tri1,558,976 fluorochloroethylene According to a preferred feature of the invention the perfluorinated vinyl ethers of the formula I, especially those in which N is zero or 1, or mixtures thereof, which are used as modification agent in the main polymerization, are used as comonomer for the preparation of the seed copolymer in an amount of up to 10 % by weight 5 The proportion of the fluoroolefin comonomer units in the seed copolymer, calculated on the copolymer as a solid, should be in the range of from 0 1 to 10 % by weight, preferably 0 3 to 5 % by weight, the balance up to 100 % consisting of tetrafluoroethylene units It is possible to use two or more of the aforesaid fluoroolefin compounds in the form of a mixture The amount of tetrafluoroethylene in the seed 10 polymer is chosen in such a manner that the seed dispersion has a solids content of from 3 to 15, preferably 5 to 12 % by weight.

The transition point of the crystalline phase of the solid seed copolymer is in the range of from 290 to 322 C, preferably 300 to 3170 C The seed dispersion contains predominantly spherical particles of uniform size having an average diameter of from 15 0.01 to 0 2, preferably 003 to 0 15 micron.

In the main polymerization according to the invention, the seed dispersion described above is first introduced into the polymerization vessel in an amount such that the final solid dispersion polymer contains the solid seeds in an amount of from 0 5 to 15, preferably 4 to 12 % by weight The aqueous seed dispersion can be first intro 20 duced into the reaction vessel together with the aqueous solution of the catalyst and the other auxiliaries required for the main polymerization The modification agent can be added either prior to polymerization or it can be metered in in the manner described above, and then the required amount of gaseous tetrafluoroethylene is forced in Alternatively, the amount of catalyst necessary for the main polymerization and 25 the other auxiliaries can be added to the seed polymerization; when the dispersion polymerization of the seed is terminated, the pressure of the reaction vessel is then released for a short period of time whereupon polymerization is continued with the addition of tetrafluoroethylene and the modifying agent.

The dispersion polymerization of the seeds as well as the main polymerization 30 are preferably carried out in an alkaline medium, i e at a p H of from 5 to 8, preferably 5 to 7 For this purpose alkaline agents are added to the polymerization mixture, for example sodium or potassium hydroxide solution, preferably aqueous ammonia.

The modified polytetrafluoroethylene dispersions obtained by the process of the 35 invention can be coagulated according to the usual known methods, for example mechanically with the aid of a rapid stirrer, by spraying under pressure, or by the addition of acids or electrolytes The moist powders obtained are dried at a temperature of from 30 to 200 C, preferably 50 to 180 C in a stationary drying cabinet or a drying cabinet with air circulation A low extrusion pressure of the paste is 40 favored when the dispersion is dried at a temperature of from 40 to 80 C according to the so-called fluidized bed technique.

The products obtained by the process of the invention have a series of surprisingly improved properties Table I reveals that they are distinctly superior at low and high reduction ratios with regard to the number of punctures of the insulation (disruptive 45 discharges per 1000 meters of insulated conductor) and with regard to the transparency of the insulation It should be mentioned that the comparative products are practically useless at the high reduction ratio of 2,400:1 Table II shows that the processing range with respect to the draw-off rate is considerably improved While s O the product prepared in accordance with US Patent 3,142,665 yields satisfactory S O results practically only within a very small range (" Window ") of the draw-off rate, the number of punctures of insulation of the product of the invention is reduced to the optimum within the whole range At higher draw-off rates the quality of transparency is altered to a smaller extent Quite generally, by increase of the draw-off rate the gloss and the smoothness of the surface are improved 55 1.558976 TABLE I

Number of disruptive discharges and transparency of coated conductors at different reduction ratios extrusion reduction draw-off pressure punctures/ transparency product ratio +) rate ++) atm 1000 m of insulation Example 16 1450: 1 1 27 550 0 1 (invention) 2400: 1 1 275 770 3 1US Patent 1450: 1 1 27 650 52 4 3,088,041 permanent Ex 8 2400: 1 1 275 720 discharge 4-5 US Patent 1450: 1 1 27 650 8 3 3,654,210 permanent Ex 27 2400: 1 1 275 800 discharge 4-5 US Patent 1450: 1 1 27 560 10 1 3,142,665 Ex 17 2400: 1 1 275 770 62 1-2 +) with the reduction ratio of 1450 1 the die opening had a diameter of 1 47 mm and with the reduction ratio of 2400: 1 the diameter was 1 244 mm The reduction ratio in the extrusion of coated electric conductors means the ratio of cross-sectional area of preform cross-sectional area of die orifice cross-sectional area of conductor ++) the draw-off rate is the quotient of the cross sectional areas of the die orifice and the non-sintered insulation When calculating the area of the die orifice the cross sectional area of the conductor is deducted.

The extrusion of electric conductors was carried out with a Jennings wire extruder of the type CEB 233-05 using a cable of 7 silver-coated copper wires (silver coating 2 microns) according to American Wire Gauge Standards 22 having a total conductor diameter of 0 76 mm As lubricant, gasoline boiling in the range of from 5 to 125 C was used in a proportion of 18 % by weight, calculated on the total mixture with the modified polytetrafluoroethylene dispersion polymer The preform consisting of polymer and lubricant, which had been densified under a pressure of 100 bars, was inserted into the pressure cylinder of the wire extruder and the conductor was passed through the perforated mandrel, the wire guide and the die The wire was 10 then passed through a drying zone having a length of 4 meters to suctionoff the lubricant and through a sintering zone having a length of 6 meters and a temperature increasing from about 280 to 4500 C The coated wire was withdrawn by a drawoff device with varying draw-off rate To increase the draw-off ratio the extrusion rate of the polymer was reduced by diminishing the advance of the piston (cf Table 15 II) with the wire speed of 15 n/min being constant The increase in the draw-off rate results in a reduction of the thickness of the insulating layer and a diminution of the cable diameter The value of the draw-off rate is obtained from the quotient of the cross-sectional area of the die orifice (minus the conductor crosssection) and the unsintered insulation After having passed the draw-off means, the insulated con 20 ductor runs through the fault tracer and then to the wind-off device As electrical fault tracer a disruptive discharge tester of Messrs Richter (Debring near Bamberg, Federal Republic of Germany) of the type HT 1 was used The test was carried out at 3 5 kilovolt according to VED Measuring Prescription 0472 and a frequency of 100 cycles per second The number of punctures of the insulation per 100 meters 25 of coated conductor was recorded With the draw-off ratio chosen in Table I the sintered insulation had a thickness of 250 microns, corresponding to a diameter of the sintered insulated conductor of 1 26 mm.

1,558,976 1,558,976 TABLE II disruptive draw-off discharges ratio per 1000 meters 1.0 1.08 1.12 1.27 1.30 1.33 1.35 1.38 1.42 1.43 1.1 1.15 1.17 1.19 1.22 1.25 1.27 1.30 1.32 1.33 1.36 1.42 permanent di srupture permanent di srupture transparency of insulation 1-2 -2 -2 1-2 2-3 In all cases the reduction ratio was 1450:1 (diameter of die orifice 1 47 mm) and the wire rate 15 meters per minute.

The quality of the transparency of the insulations obtained was evaluated in Tables I, II, IV optically according to the following scale:

1) insulation absolutely clear, original color of metallic conductor shining through; 2) insulation slightly turbid, original color of metallic conductor no longer visible; 3) partly covered areas in insulation, metallic conductor still visible; generally increased turbidity; product according to Example 16 of invention US Patent 3,142,665 Example 17

4) over 50 % of insulation in covered state, metallic conductor only partly visible; 5) insulation almost entirely covered, metallic conductor no longer visible.

The products obtained by the process of the invention can be processed with the use of a lubricant according to the paste extrusion process also intoother types of profiles, for example tubes, pipe linings, flexible tubes and the like After removal 5 of the lubricant by suction filtration the profiles are sintered in the usual manner.

Another mode of processing is the extrusion of profiles which are rolled to unsintered ribbons, for example with the aid of calender rolls To obtain ribbons of reduced density they can be stretched and then freed from the lubricant by extraction, for example in a chlorohydrocarbon Ribbons of this kind can be used as sealing material in 10 armatures or for wound cable insulation By sintering such products in the fixed state highly porous membranes can be produced.

To improve the mechanical properties of the modified tetrafluoroethylene polymers according to the invention or to reduce their friction resistance, they can be blended with the usual fillers The fillers can be incorporated either into the dispersion or into 15 the coagulated powders They can be added in an amount up to 50 % by weight, calculated on the total mixture, an amount of from 5 to 30 % by weight being preferred.

Suitable fillers are all types of non-metallic and metallic, granular and fibrous, fillers for example, glass fibers, asbestos, mica, graphite, carbon black, silicon dioxide, or pulverulent metals such as copper, aluminum, silver or alloys, for example bronze or 20 brass The products of the invention can also be mixed with other auxiliaries, for example inorganic or organic pigments or dyestuffs, optical brighteners and the like, provided these auxiliaries are stable at the sintering temperture or the final products are to be used in the non-sintered state.

The filler-containing products can also be used for making profiles such as tubes, 25 flexible tubes, ribbons and the like, and for Bowden wires Fillers, such as bismuth oxide, improve the contrast in radiography, for example in the case of catheter tubes.

In the form of their aqueous dispersions, optionally after concentration, the modified polytetrafluoroethylene polymers can likewise be used for coating metallic surfaces or for impregnating porous articles, for example glass fiber or textile mats 30 The Examples listed in Table III (nos 1 to 27) illustrate the manufacture of the products according to the invention In Tables IV and V further properties of extruded tubes such as punctures of insulation and transparency are summarized.

The products listed in Table III were polymerized under the following conditions:

1) Polymerization of seed polymer 35 An autoclave having a capacity of 400 liters with an enamel inner coating and an anchor stirrer was charged with a mixture consisting of 120 liters of desalted water, 5.3 cc of 2 % by weight cupric sulfate solution and the amounts of emulsifier (NH 4 salt of perfluorooctanoic acid) and ammonia solution ( 18 % by weight in water) as specified in column 2 of Table III, the autoclave was repeatedly flushed with nitrogen 40 and, against a weak current of tetrafluoroethylene, the amounts of comonomer speci-fied in column 2 of the Table (except Examples 26 and 27, in which pure polytetrafluoroethylene seed was used) were metered in gaseous form By adding tetrafluoroethylene the pressure was then increased to 14 atmospheres gauge and polymerization was started by adding 8 grams of sodium hydrogen sulfite and 7 7 45 grams of ammonium persulfate in the form of aqueous solutions and while stirring The polymerization was performed at a temperature of 350 C until a solids content of % by weight had been reached.

2) Main polymerization.

A 400 liter autoclave was charged with a mixture of 210 liters of desalted water, 50 184 g of the ammonium salt of perfluorooctanoic acid, 252 cc of ammonia ( 18 % by weight in water), 5 3 cc of cupric sulfate solution ( 2 % by weight) and the additives specified in column 3 of Table III As seed dispersion the respective dispersion according to column 2 having a solids content of 10 % by weight was used.

After having flushed the vessel several times with nitrogen, the pressure was 55 increased to 14 atmospheres gauge by adding tetrafluoroethylene and simultaneously the amount of perfluorinated vinyl ether of formula I as indicated in column 3 of Table III was metered in The mixture was heated to 2800 C and polymerization was started by adding 9 5 g of sodium hydrogen sulfite and 14 7 grams of ammonium persulfate in the form of aqueous solutions and while stirring 60 1,558,976 1,558,976 3) Processing.

In an enameled vessel provided with a MIG stirrer and baffles the dispersion obtained was diluted to a solids content of 10 % by weight and coagulated by stirring at a temperature of 200 C After having washed the solids three times, each time with 150 liters of desalted water, the powder obtained was dried for 20 hours at 1100 C 5 1,558,976 TABLE III

Example

No.

seed polymerization 1 750 g CF 2 CFCI 152 g CF, (CF 2)6 COONH 4 96 cm' NH 3 solution 2 750 g CF 2 = CFCI 152 g CF, (CF 2)6 COONH 4 96 cm' NH 3 solution 3 750 g CF 2 = CFC 1 152 g CF 3 (CF,)6 COONH 4 96 cm' NH 3 solution 4 750 g CF 2 CFC 1 152 g CF (CF 2)6 COONH 4 96 cm' NIH 3 I solution 750 g CF 2 = CFC 1 152 g CF 3 (CF 2)6 COONH 4 96 cm 3 NH 3 solution 6 750 g CF 2 = CFCI 152 g CF, (CF 2)6 COONH 4 96 cm 3 NH, solution 7 750 g CF 2 = CF Cl 152 g CF, (CF 2)6 COONH 4 96 cm 3 NH, solution 8 750 g CF 2 = CFCI 152 g CF 3 (CF 2),COONH 4 96 cm 3 NHI solution 9 750 g CF 2 CFC 1 152 g CF 3 (CF 2)6 COONH 4 96 cm 3 Ni H 3 solution 750 g C Fi CFC 1 152 g CF (CF 2)6 COONH, 96 cm' NHA, solution 11 750 g CF, CFC 1 152 g CF 3 (CF,)6 COONH 4, 96 cm' NH 3 solution 12 750 g CF 2 = CFC 1 152 g CF, (CF 2)6 COONH 4 96 cm' NH 3 solution 13 750 g CF 2 = CFCI 152 g CF, (CF)6 COONH 4 96 cm 3 NH, solution 14 750 g CF 2 = CFCI 152 g CF 3 -(CF 2)6 COONH 4 96 cm' NH, solution 750 g CF 2 = CFCI 152 g CF, (CF 2)6 COONH 4 96 cm 3 NH, solution main polymerization 31.5 kg seed dispersion 6.68 g comp I (n = 0) 4.2 g diethyleneglycol 31.5 kg seed dispersion 27.8 g comp I(n= 0) 4.2 g diethyleneglycol 47.3 kg seed dispersion 77.5 gcomp I(n = 0) 4.2 g diethyleneglycol 44.0 kg seed dispersion 83.4 g comp I(n= 0) 4.2 g diethyleneglycol 37.8 kg seed dispersion 139 g comp I (n = 0) 4.2 g diethyleneglycol 47.3 kg seed dispersion g comp I (n 0) 4.2 g diethyleneglycol 37.8 kg seed dispersion 166 8 g comp I (n = 0) 0.42 g diethyleneglycol 18.85 kg seed dispersion 166 8 g comp I (n 0) 0.42 g diethyleneglycol 37.8 kg seed dispersion 166 g comp 1 (n 0) 37.8 kg seed dispersion 278 g comp I (n = 0) 4.2 g diethyleneglycol 37.8 kg seed dispersion 556 g comp I (n = 0) 4.2 g diethyleneglycol 37.8 kg seed dispersion 77.8 gcomp I(n= 0) 4.2 g diethyleneglycol 44.1 kg seed dispersion 77.8 g comp I(n = 0) 4.2 g diethyleneglycol 44.1 kg seed dispersion g comp I (n 0) 4.2 g diethyleneglycol 44.1 kg seed dispersion g comp I (n = 0) 4.2 g diethyleneglycol TABLE III (cont) TABLE Ill (cont) Example

No.

seed polymerization 16 232 g CF 2 = CFCI 184 g CF 3 (CF 2)6 COONH 4 116 cm 3 NH 3 solution 17 150 g CF 2 = CFCI 184 g CF 3 (CF 2),COONH 4 116 cm 3 N Ha solution 18 150 g CF 2 = CFCI 184 g CF 3 (CF 2)COONH 4 116 cm 3 NH 3 solution 19 150 g CF 2 = CFC 1 184 g CF, (CF 2)6 COONH 4 116 cm 3 NH 3 solution 150 g CF 2 = CFCI 184 g CF 3 (CF 2)6 COONH 4 116 cm 3 NH 3 solution 21 150 g CF 2 = CFC 1 184 g CF 3 (CF 2)6 COONH 4 116 cm 3 NH 3 solution 22 150 g CF 2 = CFCI 184 g CF 3 (CF 2)6 COONH 4 116 cm' NH 3 solution 23 450 g CF 3 (CF 2)2 OCF=CF 2 184 g CF 3 (CF 2)6 COONH 4 116 cm 3 NH% solution 24 350 g comp I (n = 0) 184 g CF 3 (CF 2)6 COONH 3 116 cm' NH 3 solution 150 g CF 2 CH 2 184 g CF 3 (CF 2)6 COONH 4 116 cm 3 NH 3 solution 26 184 g CF 3 (CF 2)6 COONH 4 116 cm 3 NH 3 solution 4.2 g dioxane 27 184 g CF 3 (CF)6 COONH 4 116 cm 3 NH 3 solution 4.2 g dioxane main polymerization 44.1 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 44.1 kg seed dispersion g comp I (n = 0) 1.05 g diethyleneglycol 44.1 kg seed dispersion g comp I (n 0) 44.1 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 44.1 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 37.8 kg seed dispersion g comp I (n 0) 1.05 g diethyleneglycol 44.1 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 44.1 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 37.8 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 31.5 kg seed dispersion g comp I (n 0) 2.1 g diethyleneglycol 44.1 kg seed dispersion g comp I (n = 0) 2.1 g diethyleneglycol 37.8 kg seed dispersion g comp I (n = 0) 2.1 g diethyleneglycol 1,558,976 TABLE IV

Further test results of wire extrusion Example Extrusion pressure No (bar) 580 575 635 610 565 580 600 530 560 ' 550 transparency 1 11 2 disruptive discharges/ 1000 m reduction ratio 1450: 1, diameter of die orifice 1 47 mm, draw-off ratio 1 27 TABLE V

Test results of hose extrusion (hose dimensions outside diameter 14 6 mm; inside diameter: 13 3 mm reduction ratio: 90: 1) tensile strength +) elongation at break +) kp/cm 2 % Example

No longitudinal transverse longitudinal transverse 3 36 4 28 6 340 610 6 29 3 26 4 300 620 16 31 4 27 1 370 600 +) measured according to ASTM D 1457 69 T

Claims (11)

WHAT WE CLAIM IS:-

1 A process for the manufacture of a modified tetrafluoroethylene dispersion polymer which comprises polymerizing tetrafluoroethylene in the presence of a catalyst, a dispersion agent and optionally an aqueous seed dispersion containing dispersed particles of polytetrafluoroethylene or of a copolymer consisting of at least 90 % by weight of tetrafluoroethylene units and the balance of fluoroolefin units, and in the presence of, as modifying agent, from 0 0005 to 1 5 % by weight, calculated on the 1.558976 11.1 1,558,976 tetrafluoroethylene excluding any seed polymer, of a perfluorinated vinyl ether of the formula F ( f F O CF CF

2 ' C -C 2 C 3 0 F Ii C F=F in which N is zero or an integer from 1 to 4, or of a mixture of any two or more of such perfluorinated vinyl ethers, and coagulating and drying the polymer obtained 5 2 A process according to claim 1, wherein the modifying agent is added to the polymerization mixture at the beginning of polymerization, optionally with the seed dispersion.

3 A process according to claim 1, wherein the modifying agent is added to the polymerization mixture during the course of polymerization when at most 70 % of the 10 tetrafluoroethylene have been polymerized.

4 A process according to claim 3, wherein the modifying agent is added to the polymerization mixture continuously or in portions.

A process according to any one of claims 1 to 4, wherein the particles of the seed dispersion comprise a copolymer of from 90 to 99 9 % by weight of tetra 15 fluoroethylene units and from 0 1 to 10 % by weight of units of a fluoroolefin.

6 A process according to any one of claims 1 to 5, wherein the seed copolymer contains units of (a) a fluoroalkene of the formula R R >C=C< R R 20 in which one of the radicals R is fluorine, one or two of the radicals R is or are hydrogen, bromine, chlorine or iodine and the remaining radical(s) R is (are) fluorine, a perfluoroalkyl group or a perfluoroalkoxy group, the alkyl or alkoxy groups having from 1 to 4 carbon atoms; (b) a perfluoroalkene of the formula 25 R, R', CF 2 =C< R'r-CF=CF-R, or >C=CFR, R', R', in which each of Rf and R'f is a perfluoroalkyl radical having from 1 to 4 carbon atoms; (c) a perfluoro-(alkylvinyl) ether of the formula GF 2 =CF-OR, in which R is a perfluorinated alkyl radical having from 1 to 5 carbon atoms; 30 (d) a perfluorovinyl ether of the formula specified in claim 1; (e) perfluoro-( 2-methylene-4-methyl-1,3-dioxolane); or (f) perfluoropropene.

7 A process according to any one of claims 1 to 4, wherein the seed polymer.

comprises particles of pure polytetrafluoroethylene prepared in the presence of a 35 dispersion stabilizer.

8 A process according to any one of claims 1 to 7, wherein the seed dispersion has a solids content of from 3 to 15 % by weight.

9 A process according to any one of claims 1 to 8, wherein the seed dispersion is present in such an amount as to provide from 0 5 to 15 % by weight of solid seeds 40 in the final dispersion polymer.

A process according to claim 1 carried out substantially as described in any one of the Examples herein.

11 A modified tetrafluoroethylene dispersion polymer whenever prepared by a process according to any one of claims 1 to 10 45 12 A shaped article which has been manufactured from a polymer according to cloaimn 11.

14 1,558976 14 ABEL & IMRAY, Chartered Patent Agents, Northumberland House, 303-306 High Holbornm, London WC 1 V 7 LH.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980.

Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.