CA1096085A - Melt processible tetrafluoroethylene copolymers containing organo polysiloxanes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Compositions which when coated onto wire as insulation have good resistance to deterioration under low voltage AC
stress in hot water are provided which comprise a melt-processible copolymer consisting essentially of units of tetrafluoroethylene and at least one comonomer that is a selected ethylenically unsaturated fluorinated monomer, and an organo-polysiloxane that is substantially stable the copolymer used is substantially incompatible with the copolymer, and is dispersed in the copolymer. The compositions are prepared by employing techniques which provide sufficient transporting pressure to transport the components into a mixing zone, and which provide shearing action sufficient to cause the organo-polysiloxane to disperse.

Description

_IELD OF THE INVENTION
This invention relates to melt-processible tetrafluoroethylene copolymers, and more specifically to such copolymers which contain an organo-polysiloxane additive.
BACKGROUND OF THE INVENTION

-1. Electrical Wire Insulation The deterioration and breakdown of electrical insulation under stress of applied voltage has been studied, and some aspects of insulation failure are well understood.
For example, it is well known that application of very high voltages (e.g., 2000-3000 volts or more) to electrical apparatus of certain configurations gives rise to the pheno-menon of corona discharge and that such corona can cause progressive deterioration and failure of insulation.
The corona discharge can occur under :influence of both direct current (DC) and alternating current (AC) potential and can occur in both wet and dry env:ironments. It is further well known that insulation fa:ilure due to corona discharge can be greatly reduced or eliminated by proper design of apparatus and by selection of insulation recog-nized as being resistant to corona attack.
However, there have been reports of unexpected failures in certain wire insulations even though the voltage - .
to which the insulated wire was subjected was too low for corona to occur. Thus, in testing insulated wires for use in wet locations, it has been observed that the application of AC potentials in the range of only 600 volts can cause insulation failure within a few days. This unusual pheno-menon has been observed for a number of semi-crystalline -.. . -.: - ",,:, : .

: , - ,~ , :,, B~

polymer insulation materials such as high density polyethylene (C. A. Liddicoat and B. F. Brown, Wire and Wire Products, 38, 1874 (1963) and W. D. Paist, Wire and Wire Products, 39, 1587 (1964~) and polypropylene (M. Okada, Polymer Letters, 3, 407 (1965)).
Tests have also shown that wire insulations of the fluoro~ ~ -carbon resins, polytetrafluoroethylene (PTFE), fluorinated-ethylenepropylene (FEP), and perfluoroalkoxy (PFA) fluorocarbon, are subject to failure at the same low voltage AC under wet conditions.
These relatively low voltage deteriorations of insulating ability have been called "AC wet service failure" to distinguish from the type of deterioration due to corona discharge. The "AC wet service failure"
deterioration is measured by an "Insulation Resistance Test" described below.

2. The Use of Fluorocarbon Resin as Electrical Insulation.
Despite deterioration at low voltages under wet conditions, fluorocarbon resins such as tetrafluoro-ethylene homopolymer and copolymers are recognized as having excellent electrical properties which make them useful as electrical insulations. The commercial pro-cessing of these resins into suitable form for use as ~` insulation for electrical wire is carried out by one of two distinctly different fabrication technologies: namely, a. Paste Extrusion And Sintering b. Melt Extrusion The first of these two fluorocarbon resin fab-rication technologies used for the production of wire _ 3 _ ~ :' - ~ - , ;, ,:

insulation is called "paste extrusion and sintering".
The fabrication of wire insulation by the "paste extrusion and sintering" technology involves, first, forming or shaping the resin mass by a specific low temperature fibrillation process known as "paste extrusion" and subsequently "sintering" the resin mass at a temperature above 327C.
The "paste extrusion and sintering" type of wire insulating fabrication is carried out with non-melt-processible tetrafluoroethylene polymers. These are polymers that cannot be melt-processed with usual melt-processing equipment because of their extremely high viscosities. Such polymers include the homopolymers of tetrafluoroethylene and copolymers of it and small amounts of comonomer, which amounts are too small to impart melt-processibility to the polymer. These polymers are prepared by tlle coagulat:ion of aqueous dispersions of dispersion polymerized monomers, such as those described in Cardinal et al. U.S. 3 142 665.
In the "paste extrusion and sintering" process, the resin can be used to form a coating around an electrical conductor directly, or it can be used to form an unsintered tape, which can subsequently be wrapped around the conductor and sintered to form the insulated wire. Regardless of whether the insulation is formed directly or by way of unsintered tape, it is essential that the resin be fibrillatible in order that it can be fibrillated and sub-sequently sintered in thicknessesofabout O.lmm or more without application of pressure and without formation of cracks in the coatings. The use of the sintering .. .. .
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s technology for commercial wire coating thus inherently requires selection of a resin composition capable of undergoing this specific fibrillation phenomenon. The non-melt-processible tetrafluoroethylene resins described above undergo the phenomenon. The unique crystal structure necessary for fibrillation in paste extrusion arises in the polymerization and is adversely affected by melting. Any tetrafluoroethylene polymer or copolymer previously heated above its crystalline melting point is not suitable for fabrication by paste extrusion and sintering.
It should be mentioned that "sintering" is a term having a specific meaning in the field of fluorocarbon resin processing and concerns the no-flow phenomenon characteris-tic of the sintering used in the fields of ceramics and powder metallurgy. Thus, although fluorocarbon resin sint-ering entails heating above the crystalline melting point, as measured by differential thermal analysis, the tetra-fluoroethylene polymers applicable to this fabrication technology have such high molecular weights that they are practically form-stable, i.e., non-flowing, at usual sintering temperatures in the range of 327 to about 400C.
Therefore, sintering of non-melt processible resins is not the same as melt-processing (i.e., melt extrusion) of melt-processible resins. The sinterable, i.e., non-melt pro-cessible, resins do not sag or drip off wire during transit in making wire coating through the hot zone of -the sintering oven because their melt viscosities, measurable only by tensile creep, are in the range of 101 to 1012 poise. This range is too "viscous" for processing by conventional melt fabrication methods. The term "sintering"
'~

.
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is not used in connection with melt-processible fluoro-carbon resins.
The second type of fabrication technique used for the production of fluorocarbon resin wire insulations is the technique of melt extrusion. In this technique conventional melt processing procedures used for other thermoplastic polymers are employed. However, only certain tetrafluoroethylene resins can be melt-processed.
For example, M. I. Bro and B. W. Sandt, U.S. 2 946 763, describe a narrow range of melt-processible copolymers of tetrafluoroethylene and hexafluoropropylene having useful properties; and J. F. Harris, Jr., and D. I. McCane, U.S. 3 132 123, describe closely related melt processible copolymers of tetrafluoroethylene and perfluoroalkyl perfluorovinyl ethers.
These melt processible tetrafluoroethylene copolymers generally have melt viscos:ities in the range of 103 to 107 poise at their processing temperature.
; The melt extrusion coating of wire with some of these resins, using conventional single screw extruders, is described by D.I. McCane (Encyclopedia of Polymer Science and Technology, ~lol. 13, pages 663-664, John Wiley & Sons, Inc., 1970).
The tetrafluoroethylene polymers useful in one ^
of these two types of fabrication techniques cannot be used in the other type because any tetrafluoroethylene polymer useful for sintering fabrication technology for production of wire insulations must, of necessity, be a polymer having a molecular weight, crystal structure, and monomer content capable of fibrillation in paste extrusion , : :. , , -, . , . . . ~, , ,~. ... . .

to form the unsintered tape or unsintered wire coveringand must then provide form stability and absence of cracking in the sintering step which follows. On the other hand, a tetrafluoroethylene copolymer useful in the melt processing technique must, of necessity, have a molecular weight and comonomer content to give the desired lower melt viscosity for melt processing, to- ;
gether with useful mechanical properties in the finished ~`
insulation. Thus, any fluorocarbon resin composition having the properties required for successful fabrication by paste extrusion and sintering is inherently unsuited for melt processing into wire insulation in the usual melt processing manner of operation. Its melt viscosity is much too high. Conversely, any fluorocarbon resin having the properties required for successful fabrication into wire insulation by melt processing in a conventional single screw extruder is inherently incapable of fibrilla-tion as required for fabrication by paste extrusion and sintering.

3. Failure of Fluorocarbon Insulation at Low `~
Voltage Insulated electrical wire has commonly been made by both fabrication techniques described above using each respective type of fluorocarbon polymer. All such insulated wires exhibit insulation failure in wet locations when subjected to AC potentials in the range of about 600 volts. Specifically, they fail to pass an Insulation Resistance Test, described further below, in which they ;
` are subjected to 75C. water for 12 weeks with 600 volts AC stress applied across the insulation (i.e. r between wire `'' ' . ~:

conductor and the surrounding water).
The prior art, e.g., U.S. 3 150 207 to W. L. Gore, teaches use of tetrafluoroethylene polymers to make insulated wire by the technique using a fibrillatable polymer and teaches that if a dielectric fluid, e.g., a silicone, is mixed with and incorporated in the polymer, the resulting insulation is resistant to corona as measured by sub]ecting the insulated wire to 3000-6000 volts in water containing a wetting agent. However, when such insulated wires are sub-jected to the Insulation Resistance Test discussed in thepreceding paragraph, deterioration occurred under wet conditions, i.e., they undergo "AC wet service failure".
Accordingly, fibrillatable tetrafluoroethylene polymer compositions having good corona resistance do not provide a means of achieving acceptable resistance to AC wet service failure; apparently the failure mechanism of wet service at low voltage (e.g., 600 volts) is different from that of corona attack at high voltage (e.g., 3000-6000 volts).
SUMMARY OF THE INVENTION
A composition which when coated onto wire has good resistance to deterioration under low voltage AC stress in hot water is provided by this invention. The composition comprises -a) a melt-processible copolymer consisting essentially of units of tetrafluoroethylene and at least one comonomer represented by the formula (1) Rl \

C = CF2 R2~

,~ ,;; . ..... ~., ., , : :
~: : . ,. :; : .

3~i wherein R i~ F, H, or Cl;
and when Rl is F, H or Cl, R2 may be -RFg -ORF, -R'FX or -OR'FX in which RF is a linear per~luoroalk~l radical of 1-5 carbon atoms~ R'F is a linear per~luoroalkylene diradical of 1-5 carbon atoms in which the valences are at each end of the linear chain, and X is H or Cl;
and when Rl is F, R2 may be yo ~ CF - C~2 ~ ~n ~3 . ~`
wherein n is 1 or 2; and Y i~ perfluoroaIkyl of 1-9 ~arbon atom~y or may be ~ 0 ~ ' F2l fF~CF3 CF3-FC CF - 0 ~ CF - CF2 - 0 ~z wherein .,.
Z is 0, 1 or 2;
with the proviso that R1 and R2 taken together may be O\ /0 ;'~
CF2- CF(CF3) or the formula (2)C = CH

4 ~:
wherein R3 and R4 independentl~ are -CF3 or -CF2Cl, and b) an organo~polysiloxane that i~ substantially stable and nonvolatile at the temperature of melt-processing _ g ;, , ; , , -, : . : , .. ..

for the copolymer used and is substantially incompati~le with the copolymer, said organo-polysiloxane being pr~sent in the composition in an amount of between about 0.2 and

5% by weight based on weight of the composition and being dispersed in the copolymer.
In addition, the process of the invention comprise~
(1) coating a melt-processible copolymer resin def~ned as above with between about 0.2 and 5~ by weight based on weight of the composition of an organo-poly-siloxane, (2) transporting the coated resin into a zone of pressure sufficient to cause the coated resin to pass through the remainder of the steps of the process, (3) melting the coated resln, either prior to or simultaneou~ly with said transporting or immediately sub-sequent thereto, and after carrying out steps (2) ~nd (3), (4) subjecting the melted coated resin to ~ -a shear force suf~icient to disperse the organo-poly-; 20 siloxane within the copolymer.
; One embodiment o~ the process also comprises (1) sub~ecting a melt-processible copolymer resin, defined as above, to pressur~ suf~icient to cause the resin to pass through the zones in which the remainder of the steps o~ the process occur, " - 10 -(2) melting said resin elther prior to or æub~equently to or simultaneou~lg with said pre~uring, and after carrylng out ~teps (1) and (2), (3) adding to ~he melted resin between about 0.2 and 5~ by weight ba~ed on weight o~ composition o~
an organo-poly3iloxane, and (4) subjecting the mixture o~ step (3) to a shear force su~iclent to disperse the organopoly~ ane within the copolymer~ ;
10 ~ao~ 01 The melt-proces~ible tetra~luoroethylene copoly-mers employed herein are copolymers made from ~etra-rluoroethylene and at least one comonomer selected ~rom ~ .
the ones described above. Pre~erably the comonomers are perfluoro talkyl ~inyl etheræ) containin 3-7 carbon atom3 and per~luoro (terminally unsàturated ole~in~) containing 3-7 carbon atom3. Repre~entative comonomers lnclude ; he~a~luoropropylenel perfluorohexene-l, perfluorononene-l~
per~luoro(methyl ~inyl ether), per~luoro(n-propylv~nyl : 20 ether), per~luoro(n-hep~yl vinyl ether) and the li~e.
~ y the term "melt-processlble" i~ meant that the copolymer can be proce~æed (l.e~, fabri~ated into ~haped articl~s such a~ ~ilm~, ~ibers, tubes, ~ire coat~ng~ and the like) b~ conventional melt extrudi~g meansO Such re~uires tha~ the melt ~iscosity at the proc2ssing temperature be no m~re than 107 pol~e. Pre~erably i~ i~ ln the range o~

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103 to 107 poi e, and most pre~erably 104 to 10 poise.
Thus, the amount of comonomer present in the melt-prQcessible tetra~luoroethylene copolymers will be an amount su~icient to impart melt-processibility to the co-polymer. Generally, ~or the per~luoro (alkyl vinyl ethers), this amount will be at least 0.5~ by weight based on weight of copolymer, and can be up to about 20%. Preferablg the amount will be about 3-5% and the alkgl group will be n-C3F7. Generally, ~or the per~luoro (terminally unsaturated olefin), the amount will be at least about 10% by weight based on weight o~ copolymer, and can be up to about 25~.
Preferably the ~mount will be about 15-17~ and the ole~in will be C3F6 The copolymer~ are substantially non-elastomeric~
In other words the copolymers are partially cry~talline and, a~ter extru~ion, do not e~hibit a ra]?id retraction to sub-s-tantially the orig:Lnallength ~rom a stretched conditlon of 2X at room temperature. me copolymer will become elastomerlc i~ too much comonomer is present. Exactly how much depends on 20 th~ molecular weight of the comonomer. The smaller the co-monomer the more may be present without having the copolymer becoming elastomeric.
The melt vi3cosity is ~easured according to ASTM D-1238-52T modi~ied by 1) using a cglinder, orif~ce and plston tip made of a corrosion-resistant allo~, Haynes Stellite 19, 2) charging a 5,0g sample to the 9.53mm inside diameter cylinder which is maintained at 372C. + 1C.

- lla -- ~ .
. : , ~ , ., 3) extruding the sample 5 minutes after charging through a 2.10mm diameter, 8.00 mm long square-edged orifice under a load (piston plus weight) of 5000g (this corresponds to a shear stress of 0.457 kg/cm2). The melt viscosity in poise is calculated as 53150 divided by the observable extrusion rate in grams per minute.
The organo-polysiloxane can be liquid or gum and is substantially stable (i.e., nondecomposible) and sub-stantially nonvolatile at the processing temperature of the copolymer employed (i.e., some decomposition or volatiliza-tion can be tolerated). The polysiloxane is substantially incompatible with the melt-processible copolymer. By the term "incompatible" is meant that the materials are lacking in mutual solubility. The amount of polysiloxane present in the copolymer/polysiloxane composition will be between about 0.2 and 5% based on weight of the composition and preferably between about 0.5 and 3%.
Preferably, the organo-polysiloxane will have the structure ~ R' R3Sio- -Si O- - SiR3 R~ n wherein R' and R" are each independently a hydrocarbyl group of 1-20 carbon atoms and one of R' and R" can be hydrogen, n is an integer of between about 5 to 5000, preferably between lO and 2000, and most preferably between lO and lO0 and R is lower (i.e., 1-4 carbon atoms) alkyl or phenyl, and wherein the polysiloxane can be a homopolymer or a copolymer with another polysiloxane having different ;~

hydrocarbyl R' and R" substituents. More preferably R' and R" are each independently alkyl of 1-10 carbon atoms, aryl of 6-10 carbon atoms, alkaryl of 7-11 carbon atoms, or aralkyl of 7-11 carbon atoms.
Representative organo-siloxanes include phenyl methyl siloxane, dimethyl siloxane, monophenyl siloxane, propyl-modified phenyl siloxane, and a copolymer of phenyl methyl siloxane and dimethyl siloxane.
The organo-polysiloxane is dispersed in the co-polymer as a result of the mechanical mixing of the resinand the polysiloxane. The polysiloxane is generally dispersed in a random heterogenous fashion which can, however, appear to be uniformly dispersed to the unaided human eye. The siloxane is dispersed predominantly in irregularly shaped nonspherical, finely divided orm.
Conventional melt blending procedures for blending melt-processible polymers and additives are, in general, not applicable or olendi.ng the melt-processible tetrafluoroethylene polymers and the organo-siloxane, for several reasons.
Firstly, the melt viscosities of the melt proces-sible tetrafluoroethylene copolymer resins at their melt ~ -processing temperatures are 10 to 100 times greater than the usual melt viscosities of other thermoplastic polymers;
and conventional apparatus commonly used for blending ther-moplastic polymers with other materials is generally not adaptable to blend them with such viscous materials.
Secondly, the high temperature necessary for melt processing of melt-processible tetrafluoroethylene copolymer resins results in a considerable thinning of the liquid or :, ,, . :

gum; and conventional melt processing techniques are not adaptable to blending a polymer phase of unusually high vis-cosity with a liquid or gum phase of lower ~iscosity.
Thirdly, the polysiloxane liquids and gums are substantially incompatible with the melt-processible tetra-fluoroethylene copolymer resins; whereas the blending of a plasticizing fluid into a conventional thermoplastic resin is ordinarily aided by the compatibility of the components.
Thus, attempts to blend an organo-polysiloxane - 10 with a melt-processible perfluorinated copolymer on a con-ventional electrically-heated differential speed roll mill ;
and in a conventional single screw extruder were unsuccess- ~-ful, resulting in poor dispersion of the siloxane. Generally, the siloxane remained segregated (usually as large drops) and did not disperse throughout the copolymer~
In addition, melt-processible tetrafluoro-ethylene copolymer resins are not normally available in a convenient porous state for impregnation as are the fibrillatable coagulated dispersion powders or unsintered tapes made from the fibrillatable extrudable resins.
Instead, such melt-processible resins are available commer-cially as previously melted solid material obtained from extruding linear strands and cutting them into cylindrical pellets (e.g., about 2.5mm in diameter and length). These ; solid pieces have very low surface area, and addition of a small amount (e.g., about 1%) of a gum or an oily liquid, such as a polysiloxane, results in a liquid-coated mass of particles which is so slippery that it is difficult or im-possible to transmit sufficient shear energy into the par-ticles to effect a blending action in the usual plastics : ~. .
'' :

f ' melt processing equipment.
Accordingly, the compositions of this invention are prepared by employing a means which overcomes the difficulties described above. This can be accomplished by separating the transporting function and the melt mixing function into two separate zones. For example, a solids metering screw and barrel can be used as a transporting zone, while melting and mixing can be carried out in a sub-sequent zone containing an independently driven mixing shaft operated at a speed sufficient to develop shear which causes the siloxane to disperse. In another embodiment, a co-rotating, self-wiping twin screw extruder can be employed as the transporting zone, while a set of kneading blocks in a zone subsequent to the screw zone operates to develop the necessary shear.
In the transporting zone, the copolymer can first be melted and subjected to pressure sufficient to move the melted mass into the mixing zone, where it is combined and mixed with the siloxane. Alternatively, in the transporting zone, the siloxane can be coated on the solid copolymer and then the polymer melted (as in a twin screw extruder) before mixing the two in a mixing zone which develops the necessary shear force.
It is important in the transporting zone to develop ~
pressure on the material in the zone sufficient to cause ;-the material to enter into the mixing zone.
; Various additives, such as pigments (e.g., titanium dioxide or carbon black), fillers (e.g., glass particles or graphite), and reinforcing agents (e.g., fibrous materials such as asbestos or glass fibers) can be present in the compositions of this invention. When high pigment or filler loadings are used, some of the polysiloxane is ab-sorbed onthe solid surfaces of the pigment or filler, and it is often desirable to increase the polysiloxane level accordingly to achieve the desired processing behavior or product properties. With loadings of several percent or more of electrically conductive fillers, such as carbon or graphite, it may be observed that electrical properties are altered in a manner less favorable for use as wire coatings but more favorable for use as electrically semiconductive or thermally conductive components or coatings.
The melt-processible tetrafluoroethylene copolymer compositions of the present invention are useful as wire insulations for use in wet locations for AC power wiring ;
at voltages below the corona inception level. Such wet locations are often encountered in industrial plants, particularly in connection with pumps and scrubbers for pollution ahatement and in the operation of down-hole, submersible pumps used for oil recovery in deep wells.
Moreover, it has been found that improved dispersion of pigments and other solid fillers in the tetra-fluoroethylene copolymers is obtained when the organo-polysiloxane is present and higher loadings of such pigments and fillers can be extruded successfully. It has also been found that the presence of the organo-polysiloxane in the copolymers facilitates melt extrusion of their resins by providing reduced back pressure in extrusion, reduced power consumption in extrusion equipment, extrusion at lower temperatures, and production of smooth-surfaced extrudates at up to 50% higher rates than are .:

i - 16 - ~ ~

,. .

possible in the absence of polysiloxane. The benefits described in this paragraph are obtained whether one uses the tetrafluoroethylene copolymers described herein or other melt-processible tetrafluoroethylene copolymers such as ethylene/tetrafluoroethylene copolymers or terpoly-mers with the poly-siloxane.
In the Examples which follow, the "Insulation Resistance Test" employed is described generally in Under-writers Laboratory Subject 44 publication. Specially, electrical wire coated with insulation material is formed into a coil 15.25 meters in length with both ends protruding and connected together. The coil is suspended by its lead wires into a vessel of water at 75C., the vessel being made of either stainless steel or glass with a stainless steel screen liner. A potential of 600 volts alternating current (root-mean-square) 60 hertz is applied ` between the protruding lead wires and the stainless steel vessel or screen, as the case may be, contacting the water.
From time to time, the 600 volt AC connections are removed briefly and the insulation resistance between the wire ends ;
; and the metal vessel or the metal screen liner is measured using a 500 volt DC power supply in series with an electro-meter capable of reading currents as low as 10 12 ampere.
Current readings are taken one minute after application of DC voltage. Current for 15.25 meters of wire is mul-; tiplied by a factor of 20 in order that results will be converted to the basis of 305 meters of the insulated wire. Insulation resistance is then calculated using Ohm's Law. The alternating 600 volt potential is applied at all times except while DC readings are being taken.

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Insulatlon resi~tance readings are taken at least once per week ~or a period o~ at least 12 weeks.
In~ulation re~istance (or logarithm o~ insulation resis-tance) iB plotted graphically as a function o~ time. An insulation i~ con~ider~d to have failed thi~ test i~ the in~ulation resi~tance drops below 10 megohm~ (305 meter basis) during 12 week~ o~ exposure. An insulation i8 ~ons~dered to have pas~ed if the insulation resi~tance at the end of 12 weeks i3 10 megohms or greater (305 meter basi~) and there 1~ no sub~tantial decrea~e ln insulation reslstance during the last 3 weeks of the 12 week period. Some variation in individual data points i8 considered acc~ptable as long as the predomlnant trend o~
~he insulation re~istance plot i~ clearly evident. All in~ulation resl~tance ~alues reported hereinbelow are calculated on the 305 meter basis as described above.
The Examples which ~ollow ~llu~trate the lnvention, while the Comparisons ~hich ~ollow compare the product~
of the E~a~pl~ with products not with1n the inYention~
~0 EXA~E 1 ' A m~lt proces~ible copolymer of recurring units o~ tetrafluoroethylene and a~out 16~ by weight o~
uni~ o~ hexa*luoropropylene (re~erred to hereinaftsr as ~EP) and ha~ing a melt ~lscosity o~ about 8 x 104 poise when mèasured at a temperat~xe of 37~C. (comm~r¢lally ~ailable a~ TEFI~N~ 100 FEP M uorocarbon resin) was used as starting ma~erial. A 2300g portion o~ thi~ reæln in it~ original form (~olid cylindr~cal pellets of about 0.25cm leng~h and dlame~er) was added to a Banbury mixer whi~h had 30 been preheat~d ~o about 165C. ThQ mixer wa~ run at 230 `~
~.

~s rpm causlng the FEP re~in to melt and the temperature to rise to 300C. A separate 325g Q~ FEP r~sln wa~ grownd to a ~inely di~ded powder~ greatly increasing its ~ ace area, and to thi~ powder ~a~ added 75g o~ a copolym~r o~
methylphenyl-~iloxane and dimethyl siloxane (Dow-Corning 550* ~luid). The ~wo materials were intimatsly mixed ~n a ~ortar. The m~xture o~ FEP powder and ~iloxane wa~
divided into ~our portions and added, on~-~ourth at a time, to the melted ~EP in the mixer. A~ter each addi~ion, the m~xer wa~ run ~r several mlnutes to blend the ~aterials and bring the temperature back up to the range o~ 290-300C.
: In this way, the fluid was gradually blended into the polymer and dispersed without causin~, a sudden excessive : lubrication Or the mixing element~, which would caus~
; slippage of materials and a 10~8 o~ ~hear energy tran~er ~rom the mixing elements to the poly~ler ma~s. A~ter the : la~t addition, ~he mixin~ was continued ~or 3 minute3 at . 290~C., the mixer wa~ stopped and cooled to 180C~, and the polymer blend was di~hargedO Af`ter f`urther coolin~g 20 th~ product wa~ ground to obtaln particles that pas~ed throu~;h a 0095cm mesh ~creenO
~ he ground particles were then melt extruded through a 3.8~m diameter plastics proce~slng extruder havin~ a constant pitch, rapid compression~ meterin~ type :~
. æcrewJ and an ele~trically heated barrel. me mel~ed com-posltion was extruded at a temperature of about 360C.
me me~ pa~sed through a 0.63¢m diameter die and the melt strand wa8 drawn down to about 0.32cm diameter3 cooled in water, and chopped lnto cyllndrical pellets abou~ 0.32cm in length.
* denotes trad~ mark : ~ .
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The pell~t~ contalned 2.8% silicone oil, They were then processed in a 3.8cm diameter melt extruder~
eguipped wi~h a wire coating cro~shead and a tube~type di~) ~uch that the polymer melt at 350~C. was extruded ~rom an annular op~ning o~ 1.26cm OD and 0~76cm ID. me mel~
wa~ drawn down onto a copper wire conductor (AWG 22, f ~trands) to produce a tight coating o~ 0.25 m~llimeters wall th~cknes~.
The coated wira pas~ed the In~ulation Resistance Test, giving an insulation resistance value of 4.9 x 104 megohms a~ter 12 w~ek~ in 75C. water at 600 volt~ AC
stress with no substantial decrease in resls~ance during the last three week8. The ~Bt was continued, but no decrease in insulat~on re8i~tance Na~ observed a~ter 101 week~' total expo~ure. mi~ good re~ult i~ much bekter ~han the re~ults obtained when no siloxane is present, a~
~een in the ~ollowing Compari~on.
~0~
For comparison purpo~es, five 15.25 meter coils o~ ~ire were pxepared ~or ~he In~ulation Re~istance Test, as in Example 1~ m~ polymer compositions employed were all TEFLO~ 100 FEP fl~orocarbon resins that did not cont~in any ~iloxane. m~e repre8ented three di~ferent resin lo~s and three wire coating extru~ion run~O
All ~ive o~ the~e coil~ ~ailed the Insulation Resi~tance Te~t within 3 to 12 day~. Xhe a~erage time o~
failure (by insulation resi~tance droppin~ below 10 mego~ms~ was ~.6 d~ys.

The procedure of Exàmple 1 wa~ ~ollowed to ~.~

:,: '" ":~

s ma~e a wire insulated wi~h TEFL0~ 100 FEP ~luorocarbon resin ~ontaining 1.0% o~ a copolymer o~ methylph~nyl~iloxane and dimethyl ~lloxane (DC 550) ~luid. This wire pas~ed the Insulation Resistance Test, gi~ing an ln~ulation re~istance value o~ 8.1 x 104 megohm~ a~ter 12 weeks~ expo~ure to 6Qo ~olts A~ in 75C~ water with no substantial decrea~e in resi~tance during the la~t 3 weeks.
EX~MPLE 3 A compositlon o~ ~he present inventlon was made by a continuou~ proces~ which in~ol~ed u~ing the ~pecialized apparatu~ described by Go B. Dunnington and R. T. Fieldæ in U.S. 3,325,865. A key element of thi~ apparatus i8 a separation of ~unction~ into zones, one zone being a solids ~eterlng ~eed æcrew and barrel (described in Example 1 o~
said U.S. 3,325,~65) capable o~ transportin~ slippery, un-melted p~rticulate materials and generating pre~ure to ~orce the materi~1 through the appara~u~, and a second zone being a 50 ~m diameter melting and mixlng barrel haYing an independently dri~en mixlng element capable of rotation at hi~her ~peed than th~ solids met~ring screw.
The ~eed material was a mixture o~ TEF0N~ 100 ~EP re~in with 1~ by weighk o~ polymeth~lphenylsll~xane (Dow-Corning 710* ~lu~d) coated over the particles. Prior to coating the FEP resin~ the s~r~ace area o~ the re~in wa~ increased by crushin~ ~he origlnal cylindri~al particl~s in an unheated Banbur~ mill and u8ing only the portion pas~in~ through 0.282cm screen openings prior to mi~ture with th~ ~luld~
The sollds metering ~eed screw w~s operated at 13 rpm, while the mixing eleme~t wa~ operated at 120 rpm. me temperatur~
in the m~xing ~ection wa~ about 320C., and the blended * denotes trade mark ~.- ', product was extruded at a rate of 19.8 kg/hr through a strand dle. The extrudate was water-$uenched and cut into c~lindrical pellets. In~rared analy$is indicated about 1%
o~ DC 710 fluid in the pelIet~. The pellets were then re-extruded in a conventional wire coating extruder, ~
in Example 1, to ~orm in~ulation o~ 0.25mm thickness on AWG 22 stranded conductor. Two coils of the coated wire were sub~ected to the Insulation Re~stance Test, both pa~sed, gi~ing in~ulation re istance values at the end o~ 12 wee~' exposure of 1.56 x 106 and 6.6 x 105 megohm~
with no ~ubstantial decrease in resistance dur~ng the la~t 3 we~ks.
EX~MP~E 4 The procedure and apparatus o~ Example 3 w~re employed using TEFION~ 100 FEP resin and 0.28% b~ ~elght . .
of Do~ Corning 710 ~luid. Insulation resistance values o~ duplicate coll~ a~ter 12 weeks~ exposure ln the In~ulation Resistance Test were 5,3 x 105 and 8.9 x 105 megohm~ and the coated wires showed no substan~ial decrea~e in re~
tance ~uring the la~t 3 weeks.
COMPARISON WITH E~MPLE 4 me procedure and apparatus of Example 3 were emplo~ed u~ing TEFION~ 100 FEP resin and 0.17~ by weight o~ Dow-Corning 710 ~luid. Duplicate ~oils did not re~ain insulation re~istance in the Insulation ResistanGe Teæt ~u~icient to pass the 12 week te~t, The apparatu~ of Example 3 wa~ modified by additi~n o~ a 1~.8cm long barrel section bet~een the solid~ ;
metering section and original m~lter-m~xer b~rrel. The ~j ,, inner wall o~ the new barrel æection w~s contoured wi~h eight smooth-surfaced lor~itudinal ridges. Turning with~n ~he ne~ barrel ~ectlon was an added mix~ng eiement having the cros~-section o~ a regular hexagon and driven by ~ttachment at one end of the mixing element of the original melter-mixer.
TEF10~ 100 ~EP ~luorocarbon re~in in cylindrical pellet form was dry blended by tumbllng wi~h 0.2% by weight o~ titanium dioxide pigm~nt and the resln-pigment blend ~ed direc~ly to the solids metering screw tuxning at 10 rpm. me material passed through the ~olids meter-ing section~ the two melting and mixing sections at about 320C.~ and exlted through a single strand dieO Mixing sp~ed wa~ about 100 rpm and throughput; ~ate 29.25 kg/hr.
Polymethypher~lsiloxane tDow-Corning DC 710 rluid) waæ
pumped into the extruder through a port in the wail near ~he entrance end o~ the new 1~.8cm long barrel section at a rate ~alculated to provide 1% by wei45ht o~ the siloxane rlul~ ln the product. Micro~copic examination o~ the 20 produ~t showed the pigment dlspersion to be exeellent and con~iderabl~ ~ore uniform ~han normall~r obt~Lned in re~in-pig~ nt blendæ made ~y melt proce~sing in the absence o~
~he Muid additive. m~ product wa~ used to make 810 : :
meters of wire i~ula~ed wlth 0~38mm ~all thlckrles~ an~
810 meters ~ith 0051mm w~ll thick~ess on AWG 14 solld copper conductor u~ s ordinary melt proc~sæin~ method~
in a ~;.35~`11Q diameter single screw exl;ruder. Five 15.25 meter spec~mens ~rom the 0.38mm irlsulated ~irè were subje¢ted to the In ulat~on P~sistan~e Test modi~ied by 30 making conditions more se~srë than the standard test b~ raising ~!
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the water temperature to 90C. All specimens retained insulation resistance higher than 10 megohms for a period of 12 weeks with no substantial decrease in resistance during the last 3 weeks. Six 15.25 meter specimens from the 0.51mm insulated wire were tested with similar results.
Exposure of the 11 coils of wire to 600 volts AC in 90~C.
water was continued to 125 weeks (over 10 times the normal time requirement) with substantially no deterioration of insulation resistance.

.
The procedure of Example 5 was used to make a composition of FEP fluorocarbon resin containing 0.2% by weight of carbon black and 1% by weight of polymethylphenyl-siloxane fluid. The composition was used to coat 3km of AWG 14 solid conductor having 0.38mm insulation and 2.07 km of the conductor having 0.51mm insulation. Six coils each of the 0.38 and 0.51mm insulated wire were placed on test.
All 12 specimens passed the Insulation Resistance Test through the 12 weeks' exposure to 600 volts alternating current at 90C. and retained high insulation resistance in continued exposure to a total of 125 weeks.

A twin screw extruder manufactured by the Werner & Pfleiderer Corporation, type ZSK 83, having barrel diameters of 83mm and barrel length of 2520mm, was set up with a series of screw bushings and kneading blocks appropriately selected to accomplish mixing of resin and siloxane. The screw bushing elements of the two screws were co~rotating, intermeshing, and self-wiping, 30 a mechanical configuration which has been found to be -~

-capable o~ transporking slippe~y material~ at uniform rate. Various ~cre~ bu~hings were placed on the screw shafts to pxovlde five ~eparate screw zones on each screw ~ha~t. Kneading block elements ~ere also placed on each sh~rt to provide ~our kneading zone~ between the five æcrew zones. The Punctlonæ within the e~truder were thus separated into zone~ mat~rial transport being accomplished by the screw zones and dispersal o~ the low viscoslty rluld into the high ~scosity polymer melt belng accompli~hed by intense shear action wlthin the kneading zones.
TEF10N~ 100 FEP re~in pellets were ~ed to a hopper over th~ ~ir~t screw section at a metered rate of about 65.25 kg/hr. S~mu~taneously, ~ow-Corning ~10 ~luid was pumped into the same hopper at a rate of 0.6525 kg/hr.
me twln ~crew~ ware rotated at 33 rpm, and the material wa~ tran~ported smoothly through the heated barrels. The melt blend compositlon exited at a temperature o~ 305C.
throu~h an 8 hole strand die. StrRndæ were water-quenched and cut into 0.25cm pellets.
In order to make ~olorea wire coatings~ 10 p~rt~
by waiæht of the above pellets were dry blended wlth 1 part o~ commerciall~ available T~FION~ 100 FEP red ~ig- -mented color concentrate pellets~ The color con~entrate did not contain s~licone ~luid. The dry blend ~as fed to a con~entional 5.1cm ~crew extruder æet up to apply 0.38mm o~ inæulation to an ~7G 1~ ætranded ~re b~ usual melt processlng methods.
me coated wire had a uniform red appearance, and its performance cap~bllities were demons~rated ~y ` ' first hea~ aging the wire in an oven for 1 week at 180C.
and then using two 15~25 meter coils of the coated wire in the In~ulation Re~iætance Test. In~ulation resi~tance value~ a~ter 12 weeks were 2.1 x 105 and 2.3 x 105 me~ohms ~ith no su~sta~tial decrea~e during the la~t 3 week~
Continued exposure to a total of 105 wee~s showed substan-tially no lo~s o~ insulation resistance.

Th~ twin screw extrusion apparatus of Example 7 was used in the procedurc o~ Example 7~ In place o~ th~
TEFION~ 100 FEP pellets, a melt processibie copo~ner of tetra~luoroethylene and about 4 w~.~ psrfluoro-n-propyl p~r~luorovinyl ether having a melt ~scosity o~ about 4 x 104 poise at 372C. ~as usad. Dow Corning 710 silicone ~luid was metered in to provide 1% by weight o~ it ln the ~eed. me twin screw extruder temperature ~ras ad~usted to gi~e a melt temperature o~ about 330C. ~or the blending operation wlth the re~ln. The extruded product waæ used ~or wire coating usin~ the same single screw ~Q e~trudex as ln E~ample 7, but in thi~ case~ no color concentrate was u~ed.
Two 1~.25 m~ter coil8 0~ AWG 14 stranded ~nre, ~n~ulated with 0~38mm o~ this composition~ ga~e insulat~on resiætance values in the Insulation Re~istance Test o~
8.9 x 10 and 9.6 x 104 me~ohms after 12 weekæ' test exposure with no 6ubstantial decrease in reæl~tance durlng the la~t 3 weeksO
COMPARISON ~IT~ EXAMPLE 8 .. . ..
FQr comparison purpose~3 ~our 15.25 meter coils o~
AWG 14 stranded wire insulated with 0.3$mm Q* the same.

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resin but without the silicone fluid additive were tested in the Insulation Resistance Test. All four failed within 8 days' exposure to 600 volts in 75C. water, one having an insulation resistance of 1.25 megohms and the other three being short circuited.

This Example and its Comparison demonstrate that the composition of the invention described hereinbelow exhibited substantially no enhancement in resistance to corona. A composition prepared as described in Example 3 was subjected to the corona resistance test described in ASTM D 2275-68 titled "Voltage Endurance Under Corona Attack of Solid Electrical Insulating Materials". A test specimen was 11.4 x 43.2cm in size and 305 microns in thickness. It was placed on a conducti.ve metal base and contacted from above at 10 positions by cylindrical ; electrodes 1.27cm in diameter with edges rounded to 0.15cm ; radius. A voltage of 2400 AC (root-mean-square) at 360 hertz was applied, and the time of failure by corona attack ; 20 at each electrode was recorded. Corona endurance was taken as the time required for failure at 5 of the 10 test elec- ;~ ;
trodes. The composition possessed a corona endurance time of 26.4 hours. Another test specimen prepared from the same starting polymer but containing no organopolysi-loxane possessed a corona endurance time of 23.9 hours. ;
The difference between these values is only about 10%. This lack of substantial difference is sùrprising when viewed in the light of the orders of ma~nitude greater increase in corona resistance obtained when fibrillatable PTFE
containing silicone oil is compared with a fibrillatable .- ~
.

polytetra~luoroethylene that does not contain silicone oil using the corona endurance test descriaed in U~S~ 3,150,207 at column 2, lines 2~41 ~ 28 ::
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Claims (18)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A composition comprising a) a melt-processible copolymer consisting essen-tially of units of tetrafluoroethylene and at least one comonomer represented by the formula (1) wherein R1 is F, H, or Cl;
and when R1 is F, H or C1, R2 may be -RF, -ORF, -R1FX or -OR1FX in which RF is a linear perfluoroalkyl radical of 1-5 carbon atoms, R1F is a linear perfluoroalkylene diradical of 1-5 carbon atoms in which the valences are at each end of the linear chain, and X is H or C1;
and when R1 is F, R2 may be wherein n is 1 or 2; and Y is perfluoroalkyl of 1-9 carbon atoms, or may be wherein Z is 0, 1 or 2;
with the proviso that R1 and R2 taken together may be ;
or the formula (2) wherein R3 and R4 independently are -CF3 or -CF2Cl, and b) an organo-polysiloxane that is substantially stable and nonvolatile at the temperature of melt-processing for the copolymer used and is substantially incompatible with the copolymer, said organo-polysiloxane being present in the composition in an amount of between about 0.2 and 5% by weight based on weight of the composition and being dispersed in the copolymer.

2. The composition of Claim 1 wherein the comonomer is a perfluoro (terminally unsaturated olefin) containing 3-7 carbon atoms and is present in the copolymer in an amount of between about 10 and 25% by weight of copolymer.

3. The composition of Claim 2 wherein the comonomer is hexafluoropropylene.

4. me composition of Claim 3 wherein the comonomer is present in the copolymer in an amount of between about 15 and 17% by weight of the copolymer.

5. The composition of Claim 1 wherein the comonomer is a perfluoro(alkyl vinyl ether) containing 3-7 carbon atoms and is present in an amount of between about 0.5 and 20% by weight of copolymer.

6. me composition of Claim 5 wherein the comonomer is perfluoro(propyl vinyl ether).

7. me composition of Claim 6 where the comonomer is present in an amount of between about 3% and 5% by weight of copolymer.

8. The composition of Claim 1 wherein the organo-polysiloxane is represented by the recurring structure wherein R' and R" are each independently a hydrocarbyl radical of 1 to 20 carbon atoms and one of R' and R" can be hydrogen, n is an integer of between about 5 and 5000, and R is lower alkyl or phenyl and wherein the polysiloxane can be a homopolymer or a copolymer with another polysiloxane having different hydrocarbyl R' and R" substituents.

9. The composition of Claim 8 where R' and R" are each independently alkyl of 1-10 carbon atoms, aryl of 6-10 carbon atoms, alkaryl of 7-11 carbon atoms or aralkyl of 7-11 carbon atoms, and one of R' and R" can be hydrogen; R is lower alkyl and n is an integer between about 10 and 100.

10. The composition of Claim 9 wherein the comono-mer is hexafluoropropylene.

11. The composition of Claim 10 wherein the organo-polysiloxane is polymethylphenyl siloxane.

12. The composition of Claim 11 wherein the hexafluoropropylene is present in an amount of 15-17 weight per cent.

13. The composition of Claim 9 wherein the comonomer is perfluoro(propyl vinyl ether).

14. The composition of Claim 13 wherein the organo-polysiloxane is polymethylphenyl siloxane.

15. The composition of Claim 14 wherein the perfluoro(propyl vinyl ether) is present in an amount of 3-5 weight per cent.

16. The composition of Claim 1 which contains a filler.

17. The composition of Claim 16 wherein the filler is graphite or carbon black.

18. A process for preparing the compositions of Claim 1 which comprises the steps of transporting and melt-mixing components of said compositions in two separate zones, wherein said steps are selected from sequence A and sequence B as follows:
A (1) coating a melt-processible copolymer resin defined as in Claim 1 with between about 0.2 and 5% by weight based on weight of the composition of an organo-polysiloxane defined as in Claim 1, (2) transporting the coated resin into a zone of pressure sufficient to cause the coated resin to pass through the zones in which the remainder of the steps of the process occur, (3) melting the coated resin, either prior to or simultaneously with said transporting or immediately subsequent thereto, and after carrying out steps (2) and (3), and (4) subjecting the melted coated resin to a shear force sufficient to disperse the organo-polysiloxane within the copolymer, or B (1) subjecting a melt-processible copolymer resin defined as in Claim 1 to pressure sufficient to cause the resin to pass through the zones in which the remainder of the steps of the process occur, (2) melting said resin either prior to or subsequently to or simultaneously with said pressuring, and after carrying out steps (1) and (2), (3) adding to the melted resin between about 0.2 and 5% by weight based on weight of composition of an organo-polysiloxane, and (4) subjecting the mixture of step (3) to a shear force sufficient to disperse the organo-polysiloxane within the copolymer.