CA1094745A - Process for the manufacture of paste-extrudable polymers of tetrafluoroethylene - Google Patents

Abstract

Abstract of the Disclosure:
Modified tetrafluoroethylene dispersion polymers are prepared by poly-merizing tetrafluoroethylene in the presence of perfluorinated vinyl ethers of the formula I

Description

HOE 75/~ 918 10~745 Thi~ inuentlon relateq to a proce~s for the manufacture of modified tetrafluoroethylene dispersion polymers by polymerizing tetrafluoroethylene in the presence of catalyst3~ dispersion agents and modification agents, optionally also in the presence of an aqueous saed disper~ion.
It is known that polymers of tetrafluoroethylene can be obtained by two substantially different methods, i.e. by suspension polymerization coarse-grained polymsrs having an auerage particle size of about 20 to about 1000 microns are obtained~ which~ after drying and grinding or after a treatment to improve their flow properties~ can be u ed for mold sinter-1~ ing or ram extrusion,and by dispers~on polymerization ~L~ the u3e of suitabls emulQifiers stable aqueous polytetrafluoroethylene dispersions are obtained having a particles slze of ~rom about 0.05 to 0.6 micron which are e~pecially suitable for impregnation and coating purposes. ~y mechanical coagulation and subsequent drying of the precipitated disper-qion polymer flowable powders can be obtained. ~ut these polytetrafluoroethylsns pow-ders obtained by di~persion polymsrization are hardly suitable for the so-called paste extrusion techniqus according to which the polymer is first mada into a pasts by mixing with a liquid lubricant~ for example a high boiling hydrocarbon, and the paste is then extruded under pressure through a dia. The drawback resides in the fact that, owing to the lack of orien-tation of the material, the extruded article has a rough surface and knots are formed. In order to ensure a uniform extrusion and to avoid the afore-said disadvantages~ dispersions are wantad in which the particles ~ubst2n-t~ally have an almost spherical shape. Moreover, it i8 desirable to reduce the high extrusion pressur~ required for the extrusion of dispersion poly-mar~ in pa9t2 form by modification of the polymer during polymerization.
Processes have already been described the aim of which is to improva the paste extrusion propertie~ of di~parsion polymers of tetrafluoroethyl-ene. US.Patent Specification 3,088,941 proposes, for example, to carry out -- 2 _ or~

HOE 75/f 918 the diQpersion polymar$zation of tetrafluoroethylene with tha use of a saed disper~ion of the tetrafluoroethylene homopolymer. The dispersion particles obtained have, however~ a very broad particle size distribution, which iq not da~ired. To overcome thi-~ drawback US.Patant Specification 3,654,210 propose~ to polymerize in the presence of seed~ of dispersion copolymers of a pr~dominant proport$on of tetrafluoroethylene with fluoroolefins con-taining chlorine~ bromine~ iodine or hydrogen~ especially trifluorochloro-ethylene.
In the two aforesaid procas~es, in the main polymerization, carried out after the preparation of the seeds~ no modifying substances having a regulat$ng effect or chain intarrupting properties ara used. It come-~ tr w that thi~ is of advantaga for the poly~erization speed~ since modifying ad-ditive~ reduce tha space-time-yiQld becau~e of their regulating ef~ect.
But, on the other hand~ ths processes withour modification in the main polymer$zation have the disadvantages that the polymers obtained have a higher melt viscosity and the extruded article~ made therefrom~ for example pipes and flexibla tubss, have a reduced alternating bending strength, a poorer tran~parancy and a higher brittleness. Moreover~ product~ made from copolymer~ prepared in tha presenca of a seed disper3ion exhibit a hiqher shrinkage in transverse diraction on sintering, which detrimentally af-~ects~ for example~ the dimensional accuracy of pip8 linings.
US.Patent Speci~ication 3~142~665 provides a process tor the msnu-facture of pasts-extrudabls disparsion polymers in which, at leact in the la~t part of the polymerization of tatrafluoroethylene, so-called modifying agents are present, ~or example hydrogen, ~ethanol or a perfluoroalkena or perfluoroalkoxyalkene. The polymer~ obtained in this manner have good paste extrusion properties within a wide range of reduction ratios~ which is the ratio~ important in pasta sxtrusion, o~ the cross sectional area of the preform to the cross sectional area of the die opaning~ and a r&-HOE '75/F 918 duced melt visco~ity and the articles made therefrom have an improved trans-parency and a higher alternating bending strsngth~ but~ like ths products of the former processes~ they are distinguished by a series of drawbacks~
especially with respect to their properties as insulating material for electric conductors. In the case of wire3 provided with a thin coating a relativsly great 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 pa~te is extruded at a higher rsduc-tion rat~o. Due to the fact that ~uch defective section must be cut out of the insulatsd conductor, the faultless wirelength is shortened and a high percentage of waste i8 obtained. The number of puncture~ of the insu-lation is also increa~ed when the so-called draw-off rate i~ increased.
This meanq the quotisnt of the cross sectional area of the die opening ~inus the CrOSQ section of the metallic conductor) and the cross sectional area of the unsintered insulation. In practice it i8 desirable to shift this draw-off rate towards higher values, if po~sible, since in thi~ manner a coating can oe obtained which ha~ a much smoother surface and a higher gloqs. In the whole rangs of draw-off rates not only the numbers of punc-tures of insulation i~ increased to a noteworthy extent with the products 2D obtained according to the 3tate of the art, with a distinctly increasing tendency towards a higher draw-off rate, but also a relatively favoraole behauior in this respect is li~ited to a very narrow range of the draw-off rate. Hencs~ the manufacturer mu~t operate under substantially con-~tant conditions which is extremely difficult in practice.
Due to the diminished transparency of the products prspared with a seed dispersion the conductor insulation becomes turbid in many cases (the so-call~d chal~ing ~ffect)~ which results in a brightening which iQ rather embarrassing with colored insulationQ.
It is the object of ths pressnt invention to provida a tetrafluoro-109~745 ethylene dispersion polymer having good paste sxtruQion properties and especially an improved suitability as insulation material for electric conductors.
The present invention therefor~ provides a process for the manufacture S of modified tetra~luoroethylene di~persion polymers by polymerizing tetra-fluoroethylene in the presence of the usual catalysts~ dispersion agent~
and modifying agents and optionally anti-coagulants and optionally in the presence of an aqueous seed dispersion containing diRpersed particles of polytetrafluoroethylsne or of a copolymer consisting of at least 90 % by weight of tetrafluoroethylene units~ the balance being a fluoroolefinic compound~ with subsequent coagulation and drying of the polymer obta~aed~
which compriReR carrying out the po~ymerization of tatrafluoroethylene in the presence of from 0.0005 to 1.5 % by weight~ calculated on the tetra-fluoroethylena..used without consideration of a possible seed dispersion~ of a perfluorinated vlnyl ether of the formula ~ ~ ~ 3 F~ ~ ~

20 CFF3~0/~--~ CF --- CF2--O~F=CF2 in which n stands for zero to 4~ or of a mixture of any.two or mors of -Ruch per~luorinated vinyl ethers as modifying agent.
The invention further provides a modified tstrafluoroethylena disper-sion polymer which has been prepared in accordance with the invention in the presence of ~rom O.Oû05 to 1.5 % by weight, calculated on the tetra-fluoroethylene used without consideration of a possible seed dispersion~
of a perfluorinat~d vinyl ether of formula I in which n i-~ zero to 4~ or of a mixture of such perfluorinated vinyl ethsrs as modifying agent.
The perfluorinated vinyl etherR cf formula I to be used as modifying HO~ 75lF 91 P, agent in ths process of the invsntion are prspared by reacting hexafluoro-_ p_opene epoxide with_a phosphoric acid tris-dialkylamids of the ~ormula o (R)2N - P - N(R)2 (II) S N(R)2 preferably phosphoric acid tris-dimethylamida~ to obtain an acid fluoride of ths formula F ~ CFF3 (II~) CF3 ~ ~ ~

Th~ acid fluorides o~ ~ormula III ars thsn hydrolyzed to tha corrssponding i1uorocarboxylic acids which ars neutralizsd w~th alkali. The carboxylic acid;salts obtained are heatsd to a temperature abovs 150 C~ whersby they are trans~ormed by pyrolyris into the corrssponding vinyl ethers ot rormu-la I. Synthsses o~ the atore~aid perfluorinated vinyl athers of ~ormula I
are dsscrib~d in ~erman C~enlsgungsschri~ten 2~434,992 and 2~517~57. It is likswise possibls to use mixturss of ths~afor~said perfluorinatsd vinyl ethers ot ~ormula ~ in which n has dif~erent valuss. Prs~srred modifying agsnts are psrfluorinatsd vinyl ethers of formula I in whlch n is zero or 1 or mixtures of the two compounds.
In ths courss of polymsrization the modi~ying agsnt -~hould bs pressnt in an a00unt of ~rom 0.0005 to 1.5 % by wsight, preferably 0.01 to 1.0 %
by wsight, calculatsd on the tetrafluoroethylene used without considera-tion Q~ a possible seed dispersion~ whether or not the dispersion poly-~erization i9 carried out in the presence of a qeed disper~ion. The modi-fying agent is prs~srably introduced into the reaction ~essel prior to the bzginning of polymerization, but it can be added as well in dosed quanti-HDE 75/F 91 a 10947~5 tie~ during the course of polymerization at any moment before a conversionof 70 %~ preferably 40 %, is reached. Alternatively~ part of the modifying agsnt can be first introduced into the polymerization vsssel and the balance is then mstered in during polymerization. Another po-~sibility is to add the modi~ying agent from the beginning of polymerization~eithsr continuous-ly or in portion~until 70 ~ and preferably 40 % of the tetrafluoroethylQne hsve reacted.
The dispersion polymerization is carried out under ths usual prssa-ures of ~rom 5 to 30~ pre~erably 6 to 16 atmospheres gauge and at tempera-turas of from 10 to 70 C~ prsfsrably 20 to 40 C~ in the pre~ence of the usual catalyst-~ preferably redox sy~tems, i.8. combinationq 0~ a per-oxid~c compound, for example an organic or anorganic peroxida~ a peracid~
a persulfats~ perborate, or percarbonate, with a reducing component, for example a bisulfite, thioQulfite~ dithionite~ hydrogan sulfite, sulfinata~
or a compound yielding diimine~ such as azodiearboxylic acid and the salts thereof~ or azodicarbonamids. There are prsferred combination~ of alkali metal or ammonium persulfate with alkali metal bisulfite~. In all cases it i~ absolutely indispen~ible that the catalyst ussd is~ soluble in water, especially in th~ alkalins range.
2U The d~spersion polymsrization of tstrafluoroethylen~ is also carrisd out in the pre~encs of ths usual emul~ifisrs~ as de~cribad, ~or example, in US.Patent Spscification 2~559~752. Thsre are msntioned by way of ex-ampls the alkali metal and ammonium salts of long chain psrfluorocarb-oxylic acids, w-hydroperfluorocarboxylic acid~, chlorofluorocarboxylic acidst perfluorodicarboxylic acid~ as well as psrfluorosulfonic acids and p~rfluorophosphonic acids. Preferrsd smulsi~iers in the proce~ af ths invsntion ar2 ths ammonium salts of psr~luoro-octanoic acid and of w-hydroparfluoro-octanoic acid. If possible, the Pmulsifi~r usQd should not have telogenic properties. Optionally, the di~per~ion polymsr~zation HOE 75/f 918 lV9~7~S
can al90 be carried out in the presenca of ~mall amounts (0.0001 to 0.01 prefsrably 0.0005 to 0.01 % by weight~ calculated on ths weight of ths aqueous mixture) of compounds having a regulating effsct, which ars used in addition to the aforssaid modifying agent~ such as hydrogsn~ propsne~
chloroform~ carbon tetrachlDride or methanol. further auxiliaries which may be prasent during polymer$zation are anticoagulants or dispersion sta-bilizers, for exampla long chain paraffin hydrDcarbons, paraffin waxes~ or so-called white oils which should be liquid under thH polymerization con-titions. As dispersicn stabilizers thsre may also be uqed cyclic ethsrs~
such as dioxane or tetrahydrofurane~ polyoxalkylation productQ or ths eQters thsreof~ for example alkylphenol polyglycol ether~ such as nonyl-phenyl polyglycol ether or triisobutylphenyl polyglycol ethsr, as wsll as polyglycol ester~ of fatty acids or polyoxalkylation products of fatty aminss. Stabilizing agsnts of this type are de~cribed~ for example~ in US.Patent Specification 2~612,~84 and in German Patsnt 1,720~738. Further suitable dispersion stabilizers ar~ polyalkylene glycols~ for exampls di-ethylene, triethylene, dipropylene, tripropylene ~lycol or higher analog~
ther~of as well as mixed glycols of ethylene and propylene oxide. Poly-msrization 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 aboYa in the prssencQ of the modifying agent according to the invention can bs carried out without the use of a sead dispHrsion. In a preferred mod- of operation, however~ the reactor is firqt charged with a seed diQ-Z5 persion of polyfluorotetraethylene or, ~ore pr8ferably, a seed dispersion o~
a copolymer of tetrafluoroethylene with a fluoroolefinic compound contain-ing at least 90 % by waight of tetrafluorosthylene units.
The sesd dispersion can be prepared according to the usual methods oF di per-qion polymerization as de~cribed above from fluoroolefinq with 10947~5 the aforesaid catalysts~ emulsifiers and at the ~pecified pressures and tempsratures, howe~er, without the uss of the modifying agent. A seed dis-persion of polytetrafluoroethylene must be stabilized by one of the afore-said stabilizers, while a seed dispersion of ons of ths said copolymers may contain such a stabilizsr. In principls, a copolymer seed is preparsd as describsd abov~ with the US8 of the following comonomers:
a~ fluoroalksnes of the formula R R
C = C

in which one of ths radicals R reprssents fluorine~
ons or two of the radicals R are hydrogen, bromine, chlorine or iodine, and the remaining radical(s) R i~ fluorine, a perfluoro-alkyl group or a perfluoroalkoxy group, the alkyl or alkoxy group~ hzving from 1 to 4, preferably 1 to 2 carbon atoms in a branched or preferably straight chain~ in the case of 2 radicals R
standing for perfluoroalkyl or perfluoroalkoxy groups same may be identical or different;
b) perfluoroalkenas o~ the formula

2- \ , R'f-CF=C-Rf or \ C-CFR

R'f R'f in which Ff and R'f which may be identical or different, each represent a perflu~orinated alkyl radical having frGm 1 to 4 and preferably from 1 to 2 carbon atoms, which is preferably linear or may be branched, preferably CF3;
c) psrfluorQ-(alkylvinyl) ether~ of the formula CF2 = CF - ORf in which R~ represents a preferably linear or a branched perfluorinated alkyl radical hauin~ from 1 to 5 carbon atoms, preferably 1 to 3 B g ` ~094745 caroon atoms;
d) perfluorinated vinyl ethers of ths aforesaid formula I;

8) perfluoro-(2-methylene-4-methyl-1,3-dioxolanc~, or f) perfluoropropene aesides the compounds listed sub d) and e) the following comonomers of groups a)~ b) and c) are mantioned hy 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, trifluorobrom~-ethylene~ trifluoroiodoethylene~ 1-chloro-~ 1-bromo- and 1-iodo-2~2-difluoroethylene, 1-chloro-, 1-bromo- and 1-iodo-1,2-difluoroethylens, lH-pentafluoropropene(1)~ ZH-pentafluoropropene(1), 1,1H- and 1~2~-tetra~luoropropene(1), 1- and 2-chloropentafluoropropene(1~, 1- and 2-bromopentafluoropropene(1), 1-iodopentafluoropropene(1), 1,1- and 1,2-chloro- or bromotetrafluoropropene(1), 1H- and 2H-heptafTuorobutens(1)~ --1,1H- and 1,2~-hexafluorobutene(1)~ 2~-heptafluorobutene(2)~ ,H-hepta-fluoroisobutPne(1), 1- and 2-chloroheptafluorobutene(1)~ 1-chlorohapta-fluoroi~obutene(1), 1ff- and 1-chlorononafluoropentene(1), trifluoro-methyl- and pentafluoroethyl-1-~luoro-2~2-dichlorovinyl ethers, 1-tri-fluoromethyl- and 1-tetrafluoroethyl-(2~2-difluorovinyl3 ethers~ per-2û fluorobutene(1) and -t2)~ perfluoroisobutene, perfluorop2nt2ne(1) and -(2), parfluoro-¦ -me~hylbutene(1)7, - ~-methyl-butane(2 )7 and -~ -methyl-butene(3)7, perfluoro-(msthylvinyl), perfluoro-(athylvinyl), psrfluoro-(butylvinyl), perfluoro-(isopropylvinyl) and perfluoro-(isobutylvinyl) ethers.
8esides perfluoro-(2-methylene-4-methyl-1,3-dioxolane) mentioned above the following compounds ar~ preferred as comonomers:
trifluoroethylene, vinylidene fluoride, perfluoroprooene, perfluoro-(propyl-vinyl) ether and especially tri~luorochloroethylene. According to a pre-ferred embodiment the perfluorinated vinyl ethers of formula I, especially HOE 75/F` 918 10~i~74S
those in ~hich n stands for zero or 1 or mixturss thereof~ which are ussd as modification agant in tha main polymerization, ars ussd as comonomer for the preparation of the seed copolymer in an amount of up to 10 % by weight.
The proportion of the fluoroolefinic compound a~ comonomar in ths copolymer seedt calrulated on the copolymer as solid~ should be in the range of from 0.1 to 10 % by weight~ preferably 0.3 to 5 % by weight~ ths balanca up to 100 % cnnRiRting of tetrafluoroathylsna units. It is lik~-wise posqible to uss as comonomers two or more of the aforasaid fluoro-olefinic compound~ in ths form of a mixturs. The amount of tetrafluors-ethylene used in the ~eed polymerization is chosen in such ~manner that tho seed diQpersion obtained has a solids content of from 3 to 15~ prefer-ably S to 12 % by weight.
The transition point of the crystalline phase of the Qolid copolymar seed is in the range of from 290 to 322 C, preferably 300 to 317 C. Ths saed d$-Qpersion prsdomina~tly contains ~phsrical particl~s of uniform siza having an a~eraQs diamster of from 0.01 to D.2~ perfsrably 0.03 to O.lS
micron.
In the main polymerization according to the invention the ssed dis-pers~on described above is first introduced inta the polymarization vsssel ~n an amount such that the final ~olid dispersion polymar contains the solid se~ds in an amount of from û.5 to 15~ prsperab}y 4 to 12 ~ by weight.
The aqu20us ssed dispersion can be first introduced into the reaction - vessel to~ether with the aquaous solution of the catalyst and the other auxiliaries required for the main polymerization. The mod~fication agent can ba added either prior to poly~erization or it can be metered in in the manner describad abo~e~ and then the required amount of gaseous tstra-fluoroethylene i8 for~ed in. Alternatively, the amount of catalyst neces-sary for the main polymerization and the other auxiliaries can ba added HOE '15/F 91 B
~0~'~7~S

to the ssed polymerizatiQn; when the disperqion polymerization of tha seed i3 terminated the preQsure of the reaction vessel i9 thsn raleaqed for a short period of time whereupon polymerization is continued with the addi-tion of tetrafluoroethylene and the modifying agsnt.
The di~persion polymerization of tha sesds as well as ths main poly-merization are praferrably carried out in an alkaline medium, i.e. at a pH
of from about 5 to 8, prefsrably 5 to 7. for thi-~ purpose alkaline agents are added to ths polym~rization mixture, for example sodium or potasQium hydroxids solution, preferably aquaous ammonia.
The modifisd polytetrafluoroethylena dispar~ions obtained by the pro-ces~ of the invention can be coagulatsd according to ths usual and known methods, for example mechanically with ths 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 o~ from about 3~ to 200 C, prefsrably 50 to 180 C in a stationary drying cabinet or a drying cabinst with air circulation. A low extrusion pressure of the pa~te i8 favorsd when the d~qpersion is drisd at low temperature of from about 40 to 80 C
according to ths so-called fluidized bed technique.
Ths product~ obtainsd hy the procs~e of the inuention havs a seris~
of -qurprisingly improved properties. Tabls I reveals that they ars di-etinctly superior at low and high reduction ratio with ragard to the numbsr of punctures of the insulation (d~sruptivs discharge~ psr 1000 meters of insulated conductor) and with regard to tha transparsncy of ths insula-tion. It should be mentioned that the comparative products ars practically useleQs at th~ high reduction ratio o~ 2,400 : 1. Tabls II shows that the processing range with rsspect to ths draw-off rat~ is considerably im-provsd. Whileths product prspared in accordancc with US.Patent 3,142,665 yields satiqfactory rssults practically only within a ~ery small rangs ("Window") of tha draw-off rate, the number of puncturss of insulation of HOE 75/F 91~
105~745 the product of the invention is reduced to the optimum within the whole rangs. At higher draw-off rates the quality of tran~parency is altered to a s~allsr extent. Quits ganerally, by increase of the draw-off rate the gloss and the smoothness of the surface are improved.
S T A B L E
NumbQr of disruptive dischargQQ and transparency of coated con-ductors at different reduction ratios product reduct~on draw-off extrusion punctures/ transparency ratio I) rats ~+) pre9~ure 1000 m of insulation atm.

1G Example 16 1450 ~ 27 550 0 t invention) 2400 : 1 1.2?5 770 3 1-US.patent 1450 : 11.27 650 52 4

3,088,C41 240û : 11.275 720 p r~anwnt 4_5 US.Patent 1450 : 11.27 650 B 3 3~654~210 2400 : 11.275 800 discharge US.Patsnt 1450 : 11.27 560 10 3~142,665 240~ : 11.275 770 62 1-2 ~) with the reduction ratio of 1450 : 1 the die opening had a diametar of 1.47 m~ and with the reduction ratio of 2400 : 1 the diameter was 2~ 1.244 mm. The reduction ratio in the sxtrusion of coated electric conductor~ means the ratio of cross qectional araa of die crifice - croas sectional srea of conductor ~+) the draw-off rata i9 tha quotient of the cross sectional area 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 wa~ carried out wit~ a ~ennings wirs axtruder of the type CEB 233-OS using a cable of 7 sil~er coated cop-per wiras (silver coating 2 microns) according to American Wire Gaugs _ 13 ~

10947~5 Standards 22 having a total conductor diameter of 0.76 mm. As lubricant Shell special gasolins boiling in the range of from 100 to 125 C wa~ used in a proportion of 10 % by weight~ calculatsd 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 pres~ura cyllndar of the wire extruder and the conductor was passed throug~ the perforated mandrel, the wir~ guide and ths die. The wire wa~ thsn pas~ed through a drying zone having a length of 4 meters to suction oft the lubricant and through a sintering zone hav-ing a length of 6 meters and a temperatura increasing from about 280 to450 C. The coated wire was withdrawn by a draw-off device with varying draw-off rate. To increase the draw-off rstio the extrusion rate of the polymer was rsducad by diminishing tha advance of the piston (c~. Table II) with the wire ~peed of 15 m/min being con~tant. The increa~e in the draw-off rate results in a reduction of the thickness of the insulating layerand a diminution of the cable diameter. The value of the draw-of~ rats is obtained fro0 the quotient of the cross sectional arsa of the die orifice tminus the conductor cross section) and the unsintered insulation. After having paYsed the draw-off means, the insulatad conductor runs through the fault tracer and then to the wind-off device. AQ electrical fault tracer a disruptive discharge tester of Messrs. Richter (Debrinq near Bamberg, Federal Republic of Germany) of the typa HT 1 was used. The test wa~ car-risd out at 3.S kilovolt according to VED Measuring Prescription 0472 and - a frequency of 100 cycles psr second, The number~ of punctures of the insulation per 100~ meters of coated conductor was recorded. With the draw-off ratio chosen in Table I the ~intered insulation had a thickne~s of 2S0 microns~ corresponding to a diameter of the sintered insulatad con-ductor of 1.26 mm.

_ 14 -HûE 75/F 918 109~'7~5 T A B L E II
product draw-offdisruptivs transparency of according to ratio discharges insulation per 1000 meters Example 16 1.0 0 of invention S l.oa 1.12 o 1.27 0 1.3~ 0 . 1.33 0 1.35 1 1 - 2 1.38 0 _ 2 1.42 0 - 2 1.43 1 2 US.Patent 1.1 3 3,142,665 Example 17 1.15 5 1.17 6 1.19 1.22 4 1.25 2 1 -1.27 15 1 -1.30 12 1 - 2 1.32 16 - 2 1.33 17 2 1.36 permanent 2 - 3 disrupture 1.42 permanent 3 dlsrupture In all casss the reduction ratio was 1450 : 1 ~diameter of di~ ori-fice 1.47 mm) and the wire rate 15 meters per minute.
The quality of the transparency of the insulations obtainad was e~a-- luated in Tables I, II, IV optically according to the following scale:

1~)94745 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 incrsassd turbidity;

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 o~ the invention can be process-ed with the use of a lubricant according to the paste extrusion prOcesQ
also into other types of profiles~ ~or example tubes, pipe lining~, tlex-ible tubes and the like. After re~oval ot the lubricant by suction ~iltra-tion the profiles are sintared in usual mannsr. Another mode of proce-~sing is ths extrusion of profiles which are rolled to unsintered ribbons~ for example with the aid ot calander rolls. To obtain ribbon~ of reduced den-sity they can be stretched and then freed from the lubricant by extraction~
for example in a chlorohydrocarbon. Ribbon~ of this kind can be used as 2û sealing material in armstures or for wound cable insulation. 5y sintering such products in the ~ixed state highly porous membranes can be produced.
To improve the mechanical properties of the modified tetrafluoro-ethylsne polyme~s according to the inuention or to reduca their friction resistance~ they can be blended with the usual fillors. The fillers can be incorporated either into the diepersion or into the coagulated powders.
They can be added in an amount up to 50 % by weight~ calculated on the total mixture, an amcunt of from S ta 30 ~ by weight being preferred.
Suitable ~illers are all tyoes of non ~etallic and metallic~ granular and fibrous, fillerc such as, for example, glaes fibers, asbestos~ nica~

HOE 75/f 918 graphite, carbon dioxide, silicium dioxide, or pulvsrulent mstals such as copper, aluminum~ silver or alloy~, for example bronze or brass. The prD-ducts of the invention can al~o be mixed with other auxiliaries, for ex-ample inorganic or organic pigments or dyeetuffs, optical brightaners and ths like~ provided the~e auxiliaries are otable at the sintering tempera-ture or the final product3 are to be u_ed in the non sintered state.
The filler containing products can alQo be used for making profile~
such as tubH-~, flexibl3 tube~ ribbons and the like, and for ~owdan wires.
Fillers~ such as bismuth oxide~ improvs the contrast in radiography, for example in the caoe of catheter tubeq. In the form of their aqueous dis-perQions, optionally aftar concentration,the modifisd polytetrafluoro-ethylsne polymers can likewise be used for coating metallic _urface3 or for impregnating porous articlss, for example glaQQ fiber or tèxtile mat3.
The examplee listed in Table III (nOQ 1 to 27) are intendsn to illu8-trate ths manufacture o~ the product~ according to the invention. In Tables IU and V further properties of extrudad tubes ~uch as punctures of insulation and transparency are summarized.
Ths products listed in Table III were polymerized under the following conditions:
1) Polvmerization of ~eed polvmsr An autcclava ha~ing a capacity of 400 liters with enamel inn~r coat-ing and anchor stirrer was chargad with a mixture consisting of 120 liter~
of desaltsd water, 5.3 cc of 2 % by wei~ht cupric sul~at~ ~olution and the amounts of emulsi~ier ~NH4 salt of perfluorooctano~c acid) and ammonia solution (18 % by weight in watsr) as specified in column 2 of Table III, the autoclava was repeatadly flu~hed with nitrogen and, against a w~sk current of tatrafluoroethylen2~ the amounts of comonomsr spacified in column 2 of the table (except Exa~ples 26 end 27, in which pure polytetra-fluoroethylene seed was ussd) were metered in in gaseous form. By adding 109~745 tetrafluoroethylene the pressure wa3 then increa~ed to 1~ atmospheres gauge and polymerization was started by adding 8 grams of Qodium hydrogen sulfite and 7.7 grams of ammonium persulfate in the form of aqueous solution~ and while stirring. The polymerization was performed at a temperature of 35 C
S until a solid~ content of 1D %i~y wsight had been reached.
2) ain oolymerization A 400 liter autoclavs was charged with a mixture of 210 liters of dssalted water~ 134 9 Or the ammonium salt Or perfluorooctarliC acid~
252 cc of ammonia (1~ % by wQiqht in watsr), 5.3 co of cupric ~ulfate 10 solution (2 % by wsight) and the additive~ ~pecifiad in column 3 of Table II~. As seed di~persion the re~pective dispersion according to column 2 having a Rolids content of 10 % by weight was used.
After having flushed several time~ with nitrogen, the pressure wa~
incrsased to 14 atmospheres gauge by adding tetrafluoroethylene and simul-15 tansously the amount of perfluorinated vinyl sther of forn~ula I a~ indicat-ed in column 3 of Table III was meterad in, The mixturs was hcated to 28û C and polymerization wa~ 3tarted by adding 9,S g of sod~um hydrogen ~ulf$ts and 14.7 grams o~ ammonium persulfate in the form of aqueous solu-tions and while 3tirring.
3) Pr-oce3cinq In an enamsl3d ve~l provided with ~IG ~tirrer and barfles the di~--per~ion obtained wa~ dilut~d to a solid~ contcnt of 10 % by ~eight and coagulatsd by ~tirring at a temperaturs of 2~ G. After having washQd thrse times~ each time with 15~ liters o1' d~salted watsr, the powdsr ob-25 tained was dried for 2D hours at 11û C.

HCE 75/~ 918 Example seed polymerization main polymerization No.

. .
750 g CF8 ~ CFCl 31 ~ 5 kg ,seed disoQrsi,on _ 152 g CF, (Cl?2 )ffC00~4 6.68 g come. I (~- 0~
96 cm~ ~ -ioIut`i--n4.2 g diethylene~l~col 2 750 g CF~ . CFCl 31. 5 kg seed dispers,ior~
152 g CF5 (CF ) COO~27.8 g c_mp. I ''~~n~ ~

6 s ~- 8l'ffti 4,2 g,d~ethyleneQlycol 3 750 g CF~ - CFCl 47 ~ 3 kg ,g _d_di ~ r~ion 152 g CF~(CF2)ACOOII~" 77,5 g comp, I ~n -~
9o cm3 ~ soIu~ion 4. 2 g- d _thylen~ Qlycol _ 4 750 g CF2 . CFCl 44,,0 kg ~ead d- ~ersion,,,;
152 g CF5 (CF ) COO~I" B3,,4 g comp. I _ (n ~ O) 96 cm5 ~_o u~'ron 4~2 g die hyl! ~ i 750 g CF8 - CFCl 37.B kg'~ë disp~3rsion 152 ~ CF5(CF2) COOl~I4 139 g comp., I (n _0 96 cm3 N~s--o-lu~ion-~ 4.? g diQthyleneglycol . __ __ _ _ 6 750 g CF8 , CFCl 47 . 3 kg s,esd dispar3ion 152 g CF5(CF8~c0o~4155 g,comp.=~I (n ~ o2 96 ¢m3 NE5s~;u~iori 4,2 g disthylenssll~col

7 750 g CF2 - CFCl 37,,8 ~g s,Qed_disoe,rsion,=
}52 g CF~CF2)~COO~166.,8 g CO~nD. I (n . O)_ 96 cm5 ~ ~oiution' o.42 g diathyien_glYCol

8 750 g CF2, CFCl 18,85 kg ReQd diRpërsion 152 g CFs (CF2 )ffC00~4 l66!8 g 'comp.~ I (n .1 `0~' 96 cm~ N~I5 solutiono.,42 g diethylQnsglycol

9 750 g CF2 CF~l 37. 8 kg sezd di~per~i;on~
152 g CFs(CF~)"COON~I4 166 g comp~ I (n - or 96 cm3 N~ solut-loh 750 g CF2 = CFCl 37.,8 kg~'ReQd dispersion~~~~
152 g CF3 (CFz )ffC00~4 278 g comp. I (n - ~) 96 cmJ ~5 soIu ~ on~.4.2 g die~hy~énèglycol 11 750 g CF2 = CFCl 37.8 kg3ee~dispersion 152 g CFs (CF ) COON~I4 556 g comp.~ I ~n ~ 0~
96 cm5 ~1~5 qo~u~o~n.4~2 gd~ethylsneglycol:
12 7 50 g CF2 = CFCl 37, 8 k~~aed dispersion 152 B CFs (CF2 ) C00~77,8 gcomp. I ~r~ = 0) 96 cm3 ~ ~olu~cion 412 gdietl7yI~nsglyco~~
13 750 g CF2 = CFCl 44,1 kg~eed dispsrsion 152 g C~5(CF2)~cOO~H477,6 gcomp.; I (n ,. 0) 96 cm5 ~ solution~ 4.2 g diothyi~neglycol ~ . . .

~09L~745 HOE 75/F 918 Table III (cont.) Example seed polymerizationmain polymerization No.
.
14 750 g CF2 = CFCl 44.1kg Qeed diqpersion 152 g CFs (CF2 )~COON~I, 100g comp. I ~n = O) 96 cmS N}~5 _solutlon 4.2g _ thyleneglycoI
750 g CF2 ~ CFCl 44.1kg qsed d-ispsrsion 152 g CF8(CF2)8COONH4 155 g comp.. I .rn ~ 0) 96 cm5 ~ solut:ion 4, 2g d~iethyleneglycol 16 232 B CF2 . CFCl 44~1kg- eed dis`psrs on 184 g CF5 (CF2 )~COONH4 155g comp. I (n ~ 0) 116 cm5 ~ solution 2.1 B ~ hyleneglycol 17 150 g CF2 - CFCl 44~1kg~~_eed~diqpersion 184 g CF5(CF8)8C00~4 110g comp~ I ~n = O) 116 cmS NHS solution 1,05g diethyleneglyc-o~
18 150 g CF2 ~ CFCl 44 t 1 kg 5ee _diQpersion~~~
184 g CF3 (CF2 )~COONH4 55 g comp~ I ~n 0 116 cm5 ~15 solution-.... _ _ . _ _ _ 19 150 B CF2 ~ CFCl 44-1 kg ~eed~dispersion 184 g C~5(CF2)~COO~I4 55 g co~p._ I_(n = 0 116 cm5 ~5 QoLution 2.1 g d~ethyleneg 150 g CF2 = CFCl 44,1kg-seed dispersion 184 g CF5(CF2)~COON~4 110g comp, I (n = O) 116 cm~ ~ qolution2,1 g diethyleneqlycol 21 150 g CF2 - CFCl 37, 8 kg sse~ diapersion 184 g CF5 (CF2 )aCOO~I4 55g comp. I (n - O) 116 cm5 ~I5 solution 1. 05 g diethyleneglycol 22 150 g CF2 ~ CFCl 44.1kg seed dispersion _ 184 g CF5(CF2)~CO0 ~4 155g comp., I (n ~ 0 116 cm5 ~s Qolution 2,1g diethylene~lyco~
23 45~ B CFS(CF2)20CF,CF2 44,1kg~seed dispersion 1~4 g CF5~CF2)~COONH4 155g con~p.~~. I (n, 0 116 cm5 NE~-so:Iu~lon2,1 g diëthylen~lycol 24 35 ~comp-, I (n = 0)37,8 kg eed_di-~persion 184 g CFS(CF;~)~COO~H4110 ~ comp. I (n a 0 116 cm~ ~E~ solu~ion2,1 g diethyleneglycol - 2~ -Table III (cont.) Example ssed polymerizationmain polymsrization No.

150 g CF2 ' C~2~1.5 kg seed dispersion 184 g CF~(CF~)~COO~155 g comp~ I (n ~ O) 116 cmS NE~;~sdlution2,1 g diethylensgly=ol 26 184 g CF8(C~ COON~44~1 ~g ~e~d diseersion_' 116 cmS NEb solution155 g comp. I (n ~ O) 4,2 g dioxan~-~-~~~~-2~1 g di_thylsn glycol 27 1~4 g CFS(CF~)~COON~37t8 kg 5scd dispsrsion _ 116 cm~ N~s ~olutlon100 g comp. I (n - O) 4,2 g aloXa~o -2.1 g die hylenegiycol'~

_ 21 -HOE 75/F 91 E~
~ 094~745 O
, E rt ~ l o ~ O
~ o O

~ 5 ~ ~ e c ~ o ul ~n o n o o o o o ..
o tO co rr~ ~ O r~
b In U~ O
~ O o ~0~
O ~
E ~ C~ O O r~ ~ _ _ 1~ W

10~^1745 a o ~ O ~ O
r~

O ~. " OCl 000 m O E ^ ~ 3 N ~`J N O

~ ~-- C ~ _~
C ~ _~ O
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O E r~ ~~o _ .

Claims (15)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE AS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of a modified tetrafluoro-ethylene dispersion polymer in which tetrafluoroethylene is poly-merized in the presence of a catalyst, a dispersion agent and from 0.0005 to 1.5% by weight, calculated on the tetrafluoro-ethylene used, of at least one modifying agent selected from the group of perfluorinated vinyl ethers of the formula I

(I) wherein n represents zero to 4, and the resultant polymer is sub-sequently coagulated and dried.

2. A process as claimed in claim 1 in which an anti-coagu-lant is also present during polymerization.

3. A process as claimed in claim 1 in which the modified tetrafluoroethylene dispersion polymer is prepared in the presence of an aqueous seed dispersion containing dispersed particles of polytetrafluoroethylene or of a copolymer consisting of at least 90% by weight of tetrafluoroethylene units, the balance being a fluoroolefinic compound.

4. A process as claimed in claim 1 or claim 2 in which the modifiying agent is added at the beginning of polymerization

5. A process as claimed in claim 3 in which the modifying agent is added at the beginning of polymerization together with the seed dispersion.

6. A process as claimed in claim 1 or claim 2 in which the modifying agent is added during the course of polymerization when at most 70% of the tetrafluoroethylene have been converted.

7. A process as claimed in claim 1 or claim 2 in which the modifying agent is added continuously or in portions during the period from the beginning of polymerization to a tetrafluoroethy-lene conversion of at most 70%.

8. A process as claimed in claim 3 in which the particles of the seed dispersion consist of a copolymer of 90 to 99.9% by weight of tetrafluoroethylene units and 0.1 to 10% by weight of units of a fluoroolefinic compound.

9. A process as claimed in claim 3 in which the seed poly-mer contains as units of a fluoroolefinic compound units of a) fluoroalkenes of the formula wherein one of the radicals R represents fluorine, one or two of the radicals R are hydrogen, bromine, chlorine or iodine and the remaining radical(s) R are fluorine, a perfluoroalkyl group or a perfluoroalkoxy group, the alkyl or alkoxy groups having from 1 to 4 carbon atoms;
b) perfluoroalkenes of the formulae R'f-CF=CF-Rf or wherein Rf and R'f, which may be identical or different, each represent a perfluorinated alkyl radical having from 1 to 4 carbon atoms;
c) perfluoro-(alkylvinyl) ethers of the formula CF2=CF-ORf wherein Rf represents a perfluorinated alkyl radical having from 1 to 5 carbon atoms;
d) perfluorinated vinyl ethers of the formula I as defined in claim 1;
e) perfluoro-(2-methylene-4-methyl-1,3-dioxolane); or f) perfluoropropene

10. A process as claimed in claim 3 in which particles of pure polytetrafluoroethylene perpared in the presence of a dis-persion stabilizer are used as seed polymer.

11. A process as claimed in claim 3 in which the seed dis-persion has a solids content of from 3 to 15% by weight.

12. A process as claimed in claim 3 in which the seed dis-persion is used in an amount corresponding to 0.5 to 15% by weight of solid seeds in the final polymer.

13. A process as claimed in claim 1, claim 2 or claim 3 in which the polymerization is carried out at a pressure of from 5 to 30 atomospheres gauge and at a temperature of from 10 to 70°C.

14. A process as claimed in claim 1, claim 2 or claim 3 in which the catalyst is a redox system.

15. A modified polytetrafluoroethylene dispersion polymer, whenever obtained according to a process as claimed in claim 1, claim 2 or claim 3.