CA2062727C

CA2062727C - Fluoropolymer blends

Info

Publication number: CA2062727C
Application number: CA002062727A
Authority: CA
Inventors: Leonard Barrett
Original assignee: Tyco Electronics Corp
Current assignee: TE Connectivity Corp
Priority date: 1989-08-17
Filing date: 1990-08-02
Publication date: 2002-03-19
Anticipated expiration: 2010-08-02
Also published as: JP3365768B2; ATE129271T1; JPH04507430A; EP0487559B1; CA2062727A1; US5057345A; EP0487559A1; DE69023142T2; WO1991002770A1; DE69023142D1

Abstract

A polymer blend comprises (A) a fluorinated ethylenepropylene copolymer and (B) a fluoroelastomer. The fluoroelastomer comprises a block copolymer comprising at least one elastomeric segment comprising tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene repeat units in a mole ratio 45-90:5-50:0-35 and at least one nonelastomeric segment comprising tetrafluoroethylene and ethylene repeat units. The weight per cent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) is between about 70 and about 97%
or between about 3 and about 30%.

Description

This invention relates to blends of a fluoroplastic and a fluoro-elastomer, methods therefor, and articles made therefrom.
to Fluoroplastics are unique among polymers, o~'ering performance characteristics unobtainable with most other polymers. Commercially available fluoropolymers include polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoro-ethylene copolymer (ECTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), and polyvanylfluoride (PVF).
Some fluoroplastics such as PTFE are completely fluorinated, while others such as ETFE or PVDF are only partially fluorinated.
Fluoroplastics generally are thermoplastics, prosessable by conventional thermoforming techniques such as extrusion and molding, thereby facilitating their fabrication into shaped articles. Typically, they are characterized by high melting points and low glass transition temperatures, enabling them to be advantageo~xsly used over a wide 2s temperature range, such as from well below 0 °C to -X260 °C.
Other desirable properties of fluoro plastics include their excellent solvent resistance, electrical insulative properties, low coeil~aent of friction, low flammability; low gas permeability,, and high inertness and stability. _ i However, a limitatioaa pf many fluoroplastics is their susceptibility to so stress-cracking.
Thermoplastic elasto~ers are materials which combine the properties of a thermoplastic and an elastomer. They can be melt processed like a thermoplastic, but, up~n cooling, exhibit rubbery 35 properties, without the need for covalent crosslinking. The development of these rubbery properties may be achieved by several methods. On~ method is to blend a crystalline polymer and an elastomex. Another method is to block-copolymerize an elastomer with a crystalline thermoplastic, to form.
a block copolymer having elastomeric and crystalline domains. The copolymer may be configured such that the ends are crystalline blocks with the middle being elastomeric, or the blocks can be alternating, with s many blocks per molecule.
Thermoplastic fluoroelastomers are fluorinated thermoplastic elastomers, possessing the melt processability of other fluoroplastics, along with the aforementioned desirable solvent resistance, thermal io stability, electrical, and other characteristics of fluoroplastics.
However, unless crosslinked, they tend to have inferior or moderate mechanical strength relative to fluoroplastics. In some instances it is possible to improve mechanical properties by blending them with a fluoroplastic;
however, more often the resulting blend has inferior properties relative to ~s the predicted properties based on the weight average of the two components - that is, there is negative synergism.
Blending of two or more polymers is a common practice for producing a product composition having improved mechanical;
2o rheological, and/or degradative properties compared to those of the individual polymers. It can be a very efl'ective way to customize a composition, providing highly specific properties which may not be available in any singh known polymer or which would require the tiny~-consuming and expensive development of a hitherto unknown new 2s polymer.
Although virtually an infinite number of different polymer blends is possible, not all polymer blends result in compositions with desirable properties. If the component polymers are incompatible, the resultant so blend often will have inferior properties, particularly in the case of blends involving fluoropoly~ers. l~lormally, incompatibility is the rule, and compatibility is the exception. A rigorous and technically precise definition of a compatible blend is a blend in which the constituents are capable of forming a single phase mixture, at least in the amorphous 35 phase, if not the crystalline phase as well. However, at a practical level a compatible blend is often defined as one which displays useful properties.
In this application, this latter definition of compatibility will be used.

Disclosures of blends in which a component is a fluorinated elastomer include published European application EP 304,487 (1989), which discloses a blend of ETFE or PVDF with a thermoplastic fluoroelastomer. Also, published Japanese patent application 52-086,442 (1977) by Daikin Kogyo KK discloses a composition comprising (a) tetrafluoroethylene/hexafluoropropene copolymer and (b) a fluorinated elastomer such as hexafluoropropene/vinylidene fluoride copolymer, tetrafluoroethylene/ vinylidene fluoridelhexafluoropropene copolymer, io and tetrafluoroethylene/propylene copolymer.
It has now been discovered that certain blends of a fluoroplastic and a fluoroelastomer are characterized by unexpected and useful properties such as high tensile strength or elongation, low modulus, increased i5 flexibility, improved stress-crack resistance, stress-induced crystal-lization, and/or optical clarity. These blends are useful as wire and cable jacketing or insulation, dimensionally heat-recoverable articles, conductive polymeric compositions (when filled with conductive particles), and chemically resistant hoses.
This invention provides a polymer blend comprising:
(A) a fluorinated ethylene-propylene copolymer; and (B) a block copolymeric fluoroelastomer comprising at least one elastomeric segment comprising tetrafluoroethylene and vinylidene fluoride, and optionally heaafluoropropylene, in repeat units having a relative weight ratio 45-90:5-50:0-35, and at least one nonelastomeric segment comprising tetrafluoroethytene and 3o ethylene repeat units;
the weight per cent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) being 70-97% or 3-30%.
The fluorinated ethylene-propylene copolymer (or FEP) used in the blends of this invention is a copolymer having tetrafluoroethylene (TFE) -~2-~2-and hexafluoropropylene (HFP) ~3 -CF2_CF-repeat units. Preferably, the FEP is predominantly random and has a relatively low HFP content, between about 1 and about 15 weight % based io on the total weight of TFE and HFP. Preferably the molecular weight is between about 100,000 and about 600,000. A preferred FEP is available from E.I. du Pont de Nemours & Co., under the trade name Teflon FEP.
In accordance with this invention, FEP is blended with a block i5, copolymeric fluoroelastomer, having elastomE~ric and non-elastomeric segments (or blocks). The eIastomeric segment comprises tetrafluoro-ethylene, vinylidene fluoride, and hexafluoropropylene repeat units ~3 -CF2-CF2- +
with preferred relative weight ratios of about 20-40:40-60:10-30, respectively. The nonelastomeric segment comprises substantially alternating tetrafluoroethylene and ethylene repeat units -CF2-CF2- +
A preferred weight ratio of elastomeric to nonE:lastomeric segments of between about 70-95:30-5. Such a thermoplastic fluoroelastomer is available from Daikin Inc. (Japan) under the tirade name Dai-el T530 Other preferred fluoroelastomers, which may contain iodine, are disclosed in Tatemoto et aL, U.S. Pat. 4,158,678 (1979).

6' t The elastomeric segment preferably hays a molecular weight of from about 10,000 to about 10,000,000. The nonelastomeric segment preferably has a molecular weight of from about 1,000 to about 1,000,000, more preferably from about 5,000 to about 500,000.
The weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) is preferably between about 70 and 97010 or between about 3 and 30%, more preferably between about 80 and about 95% or between about 5 and 20%.
io The blends of this invention can be prepared by melt blending the components in a twin screw extruder; Banbwry mixer, Brabender Plasticorder torque rheometer, Buss kneader, or other plastics processing equipment at temperatures above the melting temperatures of the is copolymer (A) and fluoroelastomer (B).
Various additives can be added to the polymeric composition. Such additives include, for example, antioxidants such as alkylated phenols, e.g. those commercially available as Goodrite 3125, Irganox 1010, Irganox 20 1035, Irganox 1076, Irganox 1093, Vulkanox BKF; organic phosphite or phosphates, e:g. dilauryl phosphite, Mark 117.8, alkylidene polyphenols, e.g. Ethanox 330, thio-bis alkylated phenol, e.~;. Santonox R', dilauryl thio-dipropionate, a : Carstab DLTDP;~dim yristyl thiodipropionate, e.g.
Carstab DMTDP, distearyl thiodipropionate, e~.g. Cyanox STDP, amines, 25 e.g. Wingstay 29=, etc.; tJV stabilizers such as [2,2'-thio-bis(4-t-octylphenol-ato)] n-butylamine nickel; Cyasorb UV 1084; '3,5-ditertiarybutyl-p-hydroxy-benzoic acid, UV Chek AM-240; flame retardants such as decabromodi-phenyl ether, perchloropentacyclodecane, 1,2-lbis(tetrabromophthalimido)-ethylene; pigments such as titanium dioxide, antimony trioxide, zinc so oxide, iron oxide, and the like. Mixtures of such additives can be used.
The composition of this invention has numerous uses. In general, the composition has good electrical insulating characteristics. The compositions can be formed into shaped articles, coatings, and the like by a5 melt processing or other suitable techniques. A, preferred use of the composition of this invention is as an insulation for an elongate electrical ~P~a~a-PC-r s conductor, such as a wire, or as a jacket for a cable, such as a signal, power, or heating cable.
Another preferred use is in the preparation of heat recoverable articles, particularly articles for use as wire and cable harnessing. A heat recoverable article is one whose dimensional configuration may be made to change when subjected to an appropriate treatment. Usually these articles recover, on heating, towards an original shape from which they previously have been deformed but the term "heat-recoverable," as usEd io herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
In their most common form, heat-recoverable articles comprise a heat-shrinfrable sleeve made from a polymeric material exhibiting the i5 property of elastic or plastic memory as described, for example, in U.S.
Pat. 2,027,9s2; 3,036,242; and 3,59?,372. As is nnade clear in, for example, U.S. Pat. 2,02?,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, while hot, to a dimensionally heat-unstable 2o form but, in other applications, a preformed dimensionally heat stable article is deformed to a dimensionally heat unstable form in a separate stage.
Jn the production of )heat recoverable articles, the polymeric as material may be crosslinked (as discussed more fully below) at any stage in tho production of the article that will enhance the desired dimensional recoverability. one manner of producing a heat-recoverable article comprises shaping the polymeric article into the desired heat-unstable Form, subsequently crosslankang the polymeric material, heating the so article to a temperature above the crystalline melting point of the polymer, deforming the article, and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat unstable, application of the heat will cause the article to assume its original heat-stable shape.
In another embodiment of the invention, the composition is rendered conductive by dispersing conductive fillers such as carbon black, metal powder, metal flakes, graphite fiber, metal coated particles or fibers, or the like therein. The amount of conductive particles added depends on the desired resi.stivity of the composition. In general, about 0.5 to about 50, preferably about 5 to about 40 and most preferably about 5 to s about 25 weight %, based o:n the weight of copolymer (A) and fluoroelastomer (B) are added. The conductivity of the conductive polymeric composition varies depending on the use of the composition. In a preferred embodiment, th.e resistivity is below about 100,000 ohm-cm, more preferably below about 2,000 ohm-cm. The resisitivity is also io preferably greater than about 0.01, more preferably 0.1 ohm-cm.
Conductive compositions of this invention are particularly useful as conductive jackets for electrical cables. For example, the composition can be applied as a conductive jacket on a high frequency attenuative cable as is discussed in U.S. Pat. 4,347,48?. The conductive compositions can also be used to prepare electric devices such as heaters, sensors, circuit protectors, such as those disclosed in U.S. Pat. 3,861,029; 4,177,376;
4,188,276; 4,318,881; 4,388,607; 4,413,301; 4,426,339; 4,237,441; 4,238,812;
4,286,376; 4,352,083; and 4,591,700.
The compositions of this invention may optionally be crosalinked.
Crosslinking can be achieved for example by use of a suitable cross-linlang agent, such as a peroxide or amine, or by irradiation. In a preferred embodiment, the composition is crosslinked by irradiation. The dosage employed in the irradiation step is generally below about 50 Mrads to ensure that the polymer is not degraded by excess irradiation, although in certain applications a higher dosage may be desirable or even necessary. The dosage preferably employed depends upon the extent of so croaslinking desired, balan~xd against the tendency of the polymer to be degraded by high doses of irradiation. Suitable dosages generally are in the range of 2 to 4 Mrads, for example 2 to 30 Mrads, preferably 3 to 20 Mrads, especially 4 to 25 M:rads, particularly 4 to 15 Mrads. The ionizing radiation can for example tie in the form of accelerated electrons or ss gamma rays. Irradiation is generally carried out at about room temperature, but higher temperatures can also be used.

Prior to irradiation it is preferred to incorporate a crosslinking agent into the composition. Preferred radiation crosslinking agents contain carbon-carbon unsaturated groups in a molar percentage greater than 15, especially greater than 20, particularly greater than 25, based on the total molar amount of copolymer (A) and fluoroelastomer (B). In many cases the crosslinking agent contains at least two ethylenic double bonds, which may be present, for example, in allyl, methallyl, propargyl, or vinyl groups. We have obtained excellent results with crosslinking agents containing at least two allyl groups, especially three or four allyl groups.
io Particularly preferred crosslinking agents are triallyl cyanurate (TAC) and triallyl isocyanurate I;TAIC); other specific crosslinking agents include triallyl trimellitatf~, triallyl trimesate, tetraallyl pyromellitate, the diallyl ester of 1,1,3-trimethyl-5-carboxy-3-(p-carboxyphenylhndane. Other crosslinking agents which. are known for incorporation into fluorocarbon i5 polymers prior to shaping" for example those disclosed in U.S. Pat.
3,763,222; 3,840,619; 3,894,:118; 3,911,192; 3,970,770; 3,985,716; 3,995,091;
4,031,167; 4,155,823; and 4,353,961. Mixtures of crosslinking agents can be used.
2o In a preferred embodiment, the compositions of this invention consist essentially of copolymer (A), fluoroelastomer (B), and non-polymeric additives such as stabilizers, conductive particles, crosslinking agents, and the like, and are substantially free of polymeric components other than (A) and (B).
The practice of this invention can be further understood by reference to the following example, which is provided by way of illustration and not of limitation.
~~7CSIriDl~ E 1 A fluorinated ethylene-propylene copolymer (Teflon FEP 140 from du Pont) was melt blended with a thermoplastic block copolymeric fluoroelastomer (Dai-el T530 from Daikin, Inc. (Japan)), using a Brabender PlasticordeT torque rheometer equipped with a forty cubic centimeter miung chamber. The lower melting constituent (T530, melting point about 220 °(:) was added first to the mixing chamber and allowed to melt. The higher melting Teflon FEP (melting point about 260 °C) was then added. Affer completion of addition of the constituent polymers, the composition was blended for 5 min at 300 °C. The blend was then removed, and allowed to cool.
Using this method, blends containing 10, 20, 35, 50, 65, 80 and 90 %
by volume of Teflon FEP were prepared. Additionally, to provide control samples of Teflon FEP and Daiel T530 with the same heat and shear history as the blend sample, samples of 10090 Teflon FEP and 100°!0 Daiel io T530 were processed in the Brabender in like manner.
About 15 x 15 x 0.08 cm (6 x 6 x 0.03 inch) slabs of the blends (and controls) were molded at 285 °C under 25,000 psi using a hydraulic hot press, for 3 min. Dumbbell shaped tensile specimens, about 3.8 cm ( 1.5 ~5 in.) long overall (testing region about 2.3 cm (0.9 in) long) were cut from the slabs. Stresa-strain curves were obtained using an Instrori mechanical tester, with at least seven specimens tested for each blend or control. The mechanical properties of the blends and control samples are provided in Table I below, TABLE I

Tensile Strength ~ Young's Modulus ~ _ 96 FEP (psi) ~St. dev. ( si) St. dev.

100 2,467 133 18,597 694 90 3,187 344 15,860 350 80 3,2.88 322 13,810 410 66 1,941 116 9,9?0 550 50 1,613 84 3,880 170 36 1,749 113 1,593 196 2,016 195 929 61 10 1,838 181 ?00 255 0 1,048 56 483 17 - It can be seen that in each instance the modulus is higher than for the T530 alone, and that most blends also have a higher tensile strength.
Further, at FEP contents of 80-909, the tensile strength of the blends are higher than even for FEP alone, a most surprising result considering that s the FEP has been blended with a polymer of lesser mechanical strength.
n These results indicate that; FEP and Dai-el T530 TPFE are unexpectedly highly mechanically compatible. Additionally, the blends are quite clear, a characteristic which may suggest compatibility.
io The effect of aging at 232 °C for 1000 hr on mechanical properties was also evaluated, with results provided in Table II below:
TABLE II

Ultimate Tensile 96 FEP I Strength (psi) I Elon~ati Unaeed I Aced * ( Unaeed I Aged 100 4,114 2,951 644 231 96 4,745 3,005 7T9 342 92.5 3,436 3,580 ~4 381 90 4,088 3,182 ?08 35A

86 3,988 3,001 756 343 80 3,772 2,764 ?62_- 351 * Aged 1000 hr at 232 °C
is These results show that there is significant improvement in the retention of elongation after aging, compared to 10096 FEP.

Claims

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

1. A polymer blend comprising:

(A) a copolymer of tetrafluoroethylene and hexafluoropropylene; and (B) a block copolymeric fluoroelastomer comprising at least one elastomeric segment comprising tetrafluoroethylene and vinylidene fluoride, and optionally hexafluoropropylene, in repeat units having a mole ratio of 45-90:5-50:0-35, and at least one nonelastomeric segment comprising tetrafluoroethylene and ethylene repeat units;
the weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) being 70-97%.

2. A polymer blend comprising:
(A) a copolymer of tetrafluoroethylene and hexafluoropropylene; and (B) a block copolymeric fluoroelastomer comprising at least one elastomeric segment comprising tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene, in repeat units having a relative weight ratio of 20-40:40-60:10-30, and at least one nonelastomeric segment comprising tetrafluoroethylene and ethylene repeat units;
the weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) being 70-97%.

3. A blend according to claim 1 or 2, wherein the weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) is 80-95%.

4. A blend according to claim 1, 2 or 3, further comprising a crosslinking agent, selected from the group consisting of triallyl isocyanurate, triallyl cyanurate, triallyl mellitate, triallyl mesate, tetraallyl pyromellitate, and the diallyl ester of 1,1,3-trimethyl-5-carboxy-3-(p-carboxyphenyl)indane.

5. A blend according to any one of claims 1 to 4, which has been crosslinked.

6. A blend according to claim 5, which has been crosslinked by irradiation.

7. A heat recoverable article made from a blend according to any one of claims 1 to 6.

8. An elongate electrical conductor coated with a blend according to any one of claims 1 to 6.

9. A cable having a jacket of a blend according to any one of claims 1 to 6.

10. A cable according to claim 9, which is a heating cable.

11. A conductive composition comprising a blend according to any one of claims 1 to 6, and a conductive filler dispersed therein.

12. A cable having a jacket of a composition according to claim 11.

13. A polymer blend comprising:
(A) a copolymer of tetrafluoroethylene and hexafluoropropylene; and (B) a block copolymeric fluoroelastomer comprising at least one elastomeric segment comprising tetrafluoroethylene and vinylidene fluoride, and optionally hexafluoropropylene, in repeat units having a mole ratio 45-90:5-50:0-35, and at least one nonelastomeric segment comprising tetrafluoroethylene and ethylene repeat units;
the weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) being 3-30%.

14. A polymer blend comprising:
(A) a copolymer of tetrafluoroethylene and hexafluoropropylene; and (B) a block copolymeric fluoroelastomer comprising at least one elastomeric segment comprising tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene, in repeat units having a relative weight ratio 20-40:40-60:10-30, and at least one nonelastomeric segment comprising tetrafluoroethylene and ethylene repeat units;
the weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) being 3-30%.

15. A blend according to claim 13 or 14, wherein the weight percent of copolymer (A) relative to the combined weights of copolymer (A) and fluoroelastomer (B) is 5-20%.

16. A blend according to claim 13, 14 or 15, further comprising a crosslinking agent selected from the group consisting of triallyl isocyanurate, triallyl cyanurate, triallyl mellitate, triallyl mesate, tetraallyl pyromellitate, and the diallyl ester of 1,1, 3-trimethyl-5-carboxy-3-(p-carboxyphenyl)indane.

17. A blend according to any one of claims 13 to 16, which has been crosslinked.

18. A blend according to claim 17, which has been crosslinked by irradiation.

19. A heat recoverable article made from a blend according to any one of claims 13 to 18.

20. An elongate electrical conductor coated with a blend according to any one of claims 13 to 18.

21. A cable having a jacket of a blend according to any one of claims 13 to 18.

22. A cable according to claim 21, which is a heating cable:

23. A conductive composition comprising a blend according to any one of claims 13 to 18, and a conductive filler dispersed therein.

24. A cable having a jacket of a composition according to claim 23.