Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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- 3 - MP0831
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
- 4 - MP0831
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
::
, ,
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- 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
1 1 1
--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-
11 11
O O
.
I
- 10 - MP0831
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.,
0 0
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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- 12 - POW
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
- 13 - MP0831
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.
* I
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