CA1214528A

CA1214528A - Electrical insulation with improved flexibility and preferably with low smoke evolution characteristics

Info

Publication number: CA1214528A
Application number: CA000436688A
Authority: CA
Inventors: Stephen L. Tondre; Hans E. Lunk
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1982-09-15
Filing date: 1983-09-14
Publication date: 1986-11-25
Also published as: GB8324662D0; ATE21462T1; EP0103487A2; EP0103487B1; GB2127210A; JPS5973807A; EP0103487A3; JPH0517642B2; DE3365309D1; GB2127210B

Abstract

ABSTRACT

Electrical insulation comprises (1) an inner layer of a cross-linked polymer, e.g. an ethylene/tetra-fluoroethylene copolymer, an ethylene/chlorotri-fluoroethylene polymer or a vinylidene fluoride poly-mer, and (2) an outer layer of an aromatic polymer having a glass transition temperature of at least 100°C, e.g. a polyether ether ketone, a polyether ketone or a polyether sulfone. Such insulation com-bines excellent properties under normal service con-ditions with low smoke evolution on burning, and is therefore particularly useful for aircraft wire and cable.

Description

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- 2 - MP0831 This invention relates to insulation for elect tribal articles.

Electrical insulation must meet a variety of electrical and physical requirements under normal service conditions. In addition, for many purposes the insulation must meet test requirements which are intended to ensure that if the insulation is exposed to very high temperatures, e.g. in a fire, it will not evolve excessive amounts of toxic products or smoke.
These requirements are particularly severe for elect tribal cable which is to be used in aircraft and similar equipment. The term "cable" is used herein to include a single electrically insulated elongate conductor often referred to in the art as 'Ire an article comprising a plurality of separate elongate conductors each of which is separately insulated, and an article comprising a plurality of elongate conduct ions which are physically joined together but elect tribally insulated from each other by insulating material, e.g. ribbon cable.

Fluorocarbon polymer, especially ethylene/tetra-fluoroethylene (ETFE) copolymers such as Tefzel, are used extensively for electrical insulation, in par-titular for aircraft wire. Particularly when cross-linked, such polymers can exhibit an excellent come bination of physical and electrical properties under normal service conditions. In this connection, rev-erroneous may be made to US. Patents Nos. 3,5B0,829,

3,738,923, 3,763,222, 3,840,619, 3,894,118, 3,911,192, 3~,947,525, 3,970,770, 3,985,716, 3,995,091, 4,031,167,

4,155,823, 4,121,001, and 4,176,027. Other polymers ad ' . ' ` , ~2~S2g31 which have been used for electrical insulation include other Lenin polymers (both homopolymers and Capella-mews) and various high-melting aromatic polymers.

We have discovered that insulation which has improved properties and which can be efficiently manufactured comprises an inner layer of a cros~-linked melt-extruded olefin polymer covered by a layer of a melt extruded aromatic polymer having a glass trueness it ion temperature of at least 100C. Accordingly, the present invention provides an insulated electrical article, especially an insulated electrical wire or cable comprising:

(a) a conductor;

(b) a melt-shaped, preferably melt-extruded, inner insulating layer which preferably contacts the con doctor and comprises a first organic polymer component which is a cross-linked olefin polymer, particularly an ETFE copolymer, and (c) a melt-shaped, preferably melt extruded, outer insulating layer which contacts the inner ins-feting layer and which comprises a second organic polymer component which is a substantially linear aromatic polymer having a glass transition temperature of at least 100C, preferably at least 130C.

The olefin polymer forming the inner layer prefer-ably has a tensile (Youngls) modulus of at least 138 Ma (20,000 pi especially at least 207 Ma (30,000 so pi and particularly at least 276 Ma t40,000 pi in order to minimize wrinkling of the outer layer when the article, e.g. in the form of a wire, is bent.

The insulation of the article to the invention provides a valuable combination of physical and elect tribal properties. The outer layer provides excellent resistance to physical abuse. The inner layer is more flexible than the outer layer and thus provides ins-lotion which is more flexible, for a particular dip electric strength, than insulation which is composed only of the aromatic polymer. Furthermore, the art-matte polymers often have poor resistance to stress-cracking which can seriously reduce their dielectric strength, the olefin polymers do not suffer from this disadvantage, and the inner jacket will therefore provide continuous insulation even in environments which cause stress-cracking of the outer jacket.

The term "olefin polymer" as used herein is defined as being a polymer of one or more unsubstituted and/or substituted olefins. Where the polymer includes substituted olefins as monomers or comonomers they are preferably polar monomers and especially fluorine-con-twining monomers, e.g. tetrafluorethylene, or a carboxylic ester, in particular an alkyd acrylate, e.g.
methyl or ethyl acrylate, or a vinyl ester, e.g. vinyl acetate. The olefin is preferably a fluorocarbon polymer as explained below.

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5 - MP0831 Particularly useful properties are obtained when the inner layer is composed of a cross-linked flyer-carbon layer. We have discovered that the combination of an inner layer of a cross-linked fluorocarbon polymer and an outer layer of an aromatic polymer results in a completely unexpected reduction in the smoke evolved under standard test convictions.
Thus it is possible, through use of the present in-mention to manufacture electrical wire which, when 10 tested for smoke evolution by ASTM E 662-79 (flaming mode), has a Do value of less than 50, preferably less than 35, where Do is the maximum specific optical density.

The term "fluorocarbon polymer" is used herein to denote a polymer or mixture of polymers which contains more than 10%, preferably more than 25%, by weight of Lorraine. Thus the fluorocarbon polymer may be a single fluorine-containing polymer, a mixture of two or more fluorine-containing polymers, or a mixture of one of more fluorine-containing polymers with one or more polymers which do not contain fluorine. In one preferred class, the fluorocarbon polymer comprises at least 50%, particularly at least 75% especially at least 85~, by weight of one or more thermoplastic crystalline polymers each containing at least 25% by weight of fluorine, a single such crystalline polymer being preferred. Such a fluorocarbon polymer may contain, for example, a fluorine containing elastomers and/or a polyolefin, preferably a crystalline polyole-fin, in addition to the crystalline fluorine-containing ,,, ~2~æ8

6 - MP0831 polymer or polymers. The fluorine-containing polymers are generally home- or copolymers of one or more fluorine-containing olefinically unsaturated monomers, or copolymers of one or more such monomers with one or more olefins. The fluorocarbon polymer usually has a melting point of at least 150C, and will often have a melting point of at least 250C, e.g. up to 350C, the melting point being defined for crystalline polymers as the temperature above which no crystallinity exists in the polymer (or when a mixture of crystalline polymers is used, in the major crystalline component in the mixture). Preferably the polymeric composition, prior to cross-linking, has a viscosity of less than 105 poise at a temperature not more than 60C above its melting point. A preferred fluorocarbon polymer is a copolymer of ethylene and tetrafluoroethylene and optionally one or more other comonomers (known as ETFE
polymers), especially a copolymer comprising 35 to 60 mole percent of ethylene, 35 to 60 mole percent of tetrafluoro-ethylene and up to 10 mole percent of one or more other comonomers. Other specific polymers which can be used include copolymers of ethylene and chlorotrifluoroethylene; polyvinylidene fluoride;
copolymers of vinylidene fluoride with one or both of hexafluoropropylene and tetrafluoroethylene, or with hexafluoroisobutylene; and copolymers of tetrafluoro-ethylene and hexafluoropropylene.

Either or both of the inner and outer insulating layers can optionally contain suitable additives such as pigments, antioxidant, thermal stabilizers, acid acceptors and processing aids.

. .,

- 7 - MP0831 The aromatic polymers which are used in this invention are will known to those skilled in the art, and reference may be made for example to US. Patents Nos. 3,025,605, 3,354,129, 3,441,538, 3,442,538, 53,446,~54, 3,65~938, 3,838,097, 3,847,867, 3,953,400, 3,956,240, 4,107,147, 4,108,837, 4,111,908, 4,175,175, 4,293,670, 4,320,224, and 3,446,554 and British Patents Nos. 971,227, 1,369,210 and 1,599,106. Such polymers include polyketones, polyether kittens, polyether ether kittens and polyether sulfones, polyether kitten/
cellophane copolymers and polyether immediacy. Blends of different polymers can be used. Preferred aromatic polymers are crystalline polymers with a melting point of at least 250C, particularly at least 300C. In one class of such polymers the polymer comer isles, and preferably consists essentially of, units of the formula -AR-Q-the units being the same or different, An being a diva lent aromatic radical and Q being -O-, -S-, -SO-!
-CO-, -NH-CO- or -COO-, or An being a polyvalent radical and Q being OKAY--N
KIWI-the Q radical preferably being directly bonded to aromatic carbon atoms in the An radical.

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- 8 - MP0831 In another class of aromatic polymers the aromatic polymer is a crystalline polyarylene ether comprising recurring units of the formula OWE'-where E is the residue of a dihydric phenol and E' is the residue of an aromatic compound having an electron withdrawing group in at least one of the positions orate and En to the valence bonds, the E and E' radicals being linked to the -O- radicals through aromatic carbon atoms. In one preferred subclass E
is a radical of the formula I

v (Y I

wherein R is a diva lent radical; x is 0 or 1; Y is a radical selected from halogen atoms, alkyd radicals containing 1 to 4 carbon atoms and alkoxy radicals containing 1 to 4 carbon atoms; y is n, 1, 2, 3 or 4;
Y' is a radical selected from halogen atoms, alkyd fad-teals containing 1 to 4 carbon atoms and alkoxy fad-teals containing 1 to 4 carbon atoms; z is 3, 1, 2, 3 or 4, and E' is a radical of the formula R

::

, , so - g - MP0831 wherein R' is a cellophane, carbonyl, vinyl, sulfoxide, ago, saturated fluorocarbon, organic phosphine oxide or ethylidene radical. In his class preferred polyp sulfones are those in which y and z are 0, x is 1, R' is a cellophane radical and R is a radical of the formula --C--I

I

wherein each of R'' and R''' is independently selected from the group consisting of hydrogen; alkyd radicals containing 1 to 4 carbon atoms; halogen-substituted alkyd radical containing 1 to 4 carbon atoms; aureole, alkaryl and aralkyl radicals containing 6 to 10 carbon atoms; and halogen-substituted aureole alkaryl and aralkyl radicals containing 6 to 10 carbon atoms.

In another class of aromatic polymers, the polymer is a polyether imide or polysulfone imîde which comprises recurring units of the formula O O
If 11 -Q-Z NUN / / Z-Q-R-O O

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where Q is -O- or -S02, Z is a trivalent aromatic radical, R is a diva lent aromatic radical and R' is a diva lent organic radical.

Preferred aromatic polymers consist essentially of repeating units having one of the following formulae ( 1 ) I okay-(2) O O CO-(3) O CO-~O~/CO~ol~CO~O~CO~

wherein each of x, m and n is O or 1, with n being O
when x is 1, p is an integer from 1 to 4, with m being 1 and x being O when p is greater than 1, e.g., If 11 e3~O~c~c_ .
(5) 52-, . :

~2~5~2~

(6) SHEA
o I So I

(7) o SHEA 0 / I SHELLEY ~\~/
O O

The insulated articles of the present invention can be produced by conventional techniques; the inner layer usually con teats the conductor, and the inner and outer layers generally constitute the total insulation of the article; however, other insulating layers can be present. The olefin polymer is preferab-lye cross-linked by radiation, and cross-linking can be effected before or after the aromatic polymer (which is generally not cross-linked by radiation) is applied. For electrical cable, the inner layer will usually be of annular cross-section of thickness for example 76.2 to 381 micrometers (3 to 15 miss), preferably 101.6 to 177.8 micrometers (4 to 7 miss). The outer layer may also be annular cross-section of thickness for example 3 to 15 miss. Alternatively, the cable can comprise a plurality of con-doctors, each of which has an inner insulating layer around it, with the conductors being joined together and further insulated by the outer insulating layer.

- , .

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~2~L~5~

The invention is illustrated by the following Examples, Examples 1, 2, 3 and 8 of which are compare-live.

In each of the Examples, a 20 AWN stranded (19/32) conductor was extrusion-coated with an inner insulating layer having the composition and thickness shown in the Table. Except in Examples 1 and 2, the inner ins-feting layer was then extrusion-coated with an outer insulating layer having the composition and thickness shown in the Table. In some of the Examples, as design noted in the Table, the coated conductor was irradiated to a dosage of about 10 Megarads to cross-link the inner coating; in these Examples, the inner coating also contained, when it was irradiated, a suitable amount of a radiation cross-linking agent. The outer coating was substantially unaffected by this irradiation. The coated conductor was annealed at 180C for 1 hour. Samples of the resulting cable were tested in accordance with the procedure of ASTM Eye (flaming mode), and the Table shows the values obtained for the minimum transmittance, the transmittance after 10 minutes, the time taken to reach the point of minimum transmittance, and the maximum optical density Do The various polymers used in the Examples are further identified below I

Tefzel 280 it a copolymer of ethylene and tetrafluoro-.
ethylene available from duo Pont.

I, Huller is a copolymer of ethylene and chlorotri-fluoroethylene available from Allied Chemical.

Conner 450 is polyvinylidene fluoride available from Penlight.
*

PEEK is a polyether ether kitten available from ICY.

Lute_* is a polyetherimide available from General Electric.

Victrex 200P a polyethersulphone available from ICY.

PEEK, Ultem and PUS are substantially linear aromatic polymers.

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Claims

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

1. An insulated electrical article, comprising (a) a conductor;

(b) a melt-shaped inner insulating layer comprising a first organic polymer component which is a cross-linked olefin polymer, and (c) a melt-shaped outer insulating layer which contacts the inner insulating layer and which comprises a second organic polymer com-ponent which is a substantially linear aromatic polymer having a glass transition temperature of at least 100°C.

2. An article according to Claim 1 wherein the inner layer is in contact with the conductor.

3. An article according to Claim 1 wherein the inner layer is radiation cross-linked.

4. An article according to claim 1, wherein the olefin polymer is a fluorocarbon polymer.

5. An article according to claim 1, wherein the olefin polymer contains more than 25% weight of fluorine.

6. An article according to claim 1, wherein the olefin polymer comprises at least 75% by weight of a thermoplastic crystalline polymer containing at least 25% by weight of fluorine.

7. An article according to Claims 1 wherein the olefin polymer consists essentially of an ethy-lene/tetrafluoroethylene copolymer.

8. An article according to Claim 1 wherein the olefin polymer consists essentially of a polymer selected from the group consisting of ethylene/chloro-trifluorethylene copolymers and vinylidene fluoride polymers.

9. An article according to Claim 1 wherein the olefin polymer has a melting point of at least 250°C.

10. An article according to Claim 1, wherein the aromatic polymer has a glass transition temperature of at least 130°C.

11. An article according to Claim 10 wherein the aromatic polymer is a crystalline polymer having a melting point of at least 250°C.

12. An article according to Claim 1 wherein the aromatic polymer comprises units of the general formula.

-Ar-Q-wherein Ar represents a polyvalent aromatic radical and Q represents a radical of the formula -O--S--CO--NH.CO--COO-or

13. An article according to Claim 12 wherein the aromatic polymer consists essentially of said units of formula -Ar-Q-.

14. An article according to Claim 12 wherein the Q
radial is bonded directly to aromatic carbon atoms.

15. An article according to claim 1, wherein the aromatic polymer is a crystalline polyarylene ether comprising recurring units of the general formula -O-E-O-E'-wherein E is the residue of a dihydric phenol and E' is the residue of an aromatic compound having an electron-withdrawing group in at least one of the positions ortho and para to the valence bonds ; the E and E' radicals being linked to the -O- radicals through aromatic carbon atoms.

16. An article according to claim 15, wherein E is a radical of the formula wherein R represents a divalent radical; x is O or 1; y is a radical selected from alkyl radicals containing 1 to 4 carbon atoms and alkoxy radicals containing 1 to 4 carbon atoms; y is O or an integer from 1 to 4; Y' is a radical selected from halogen atoms, alkyl radicals containing 1 to 4 carbon atoms and alkoxy radicals containg 1 to 4 carbon atoms; and z is O or an integer from 1 to 4, and E' is a radical of the formula wherein R' represents a radical selected from the group consisting of sulfone, carbonyl, vinyl, sulf-oxide, azo, saturated fluorocarbon, organic phosphine oxide or ethylidene radical.

17. An article according to claim 16, wherein y and z are O, x is 1, R' is a sulfone radical and R is a radical of the formula wherein each of R'' and R''' is independently selected from the group consisting of hydrogen; alkyl radicals containing 1 to 4 carbon atoms; halogen-substitutes alkyl radicals containing 1 to 4 carbon atoms; aryl, alkaryl and aralkyl radicals containing 6 to 10 carbon atoms; and halogen-substituted aryl, alkaryl and aralkyl radicals containing 6 to 10 carbon atoms.

18. An article according to Claim 1 wherein the aromatic polymer consists essentially of repeating units of the formula

19. An article according to Claim 1 wherein the aromatic polymer consists essentially of repeating units of the formula

20. An article according to Claim 1 wherein the aromatic polymer consists essentially of repeating units of the formula wherein each of x, m and n is O or 1, with n being O
when x is 1, p is an integer from 1 to 4, with m being 1 and x being O when p is greater than 1.

21. An article according to Claim 1 wherein the aromatic polymer consists essentially of repeating units of the formula

22. An article according to Claim 1 wherein the aromatic polymer consists essentially of repeating units of the formula

23. An article according to Claim 1 wherein the aromatic polymer consists essentially of repeating units of the formula

24. An article according to claim 1 which is in the form of an electrical wire or cable, the inner insu-lating layer being a melt-extruded layer which sur-rounds and contacts the conductor, and the outer insulating layer being a melt-extruded layer which surrounds and contacts the inner insulating layer.

25. An article according to Claim 24 wherein the inner layer is of annular cross-section with a wall thickness of 3 to 10 mils.

26. An article according to Claim 25 wherein the outer layer is of annular cross-section with a wall thickness of 3 to 15 mils.

27. An article according to Claim 26 wherein the wall thickness of the inner layer is 4 to 7 mils and the wall thickness of the outer layer is 4 to 7 mils.

28. An article according to Claim 24 which comprises a plurality of conductors, each of the conductors being surrounded by an inner layer which is of annular cross-section, and the conductors being joined together by the outer insulating layer.

29. An article according to claim 24 wherein the aromatic polymer is a crystalline polymer which has a melting point of at least 250°C and which consists essentially of units of the general wherein Ar represents a polyvalent aromatic radical and Q represents a radical of the formula -O--S--CO--NH.CO--COO-or

30. An article according to Claim 24 wherein the aromatic polymer is a polyether sulphone.

31. An article according to Claim 29 wherein the aromatic polymer is a polyether ether ketone.

32. An article according to Claim 29 wherein the aromatic polymer is a polyether ketone.