COPPER CONDUCTORS IN CONTACT WITH A POLYETHYLENE COMPOSITION

CONDUCTEURS EN CUIVRE EN CONTACT AVEC UN COMPOSE DE POLYETHYLENE

English Abstract

ABSTRACT OF THE DISCLOSURE
Copper conductors in contact with polyethylene
insulation containing between 0.2 to 0.8% by weight of an
antioxidant such as 2:2'-methylene bis 6(.alpha.-methyl cyclohexyl)-
4-methyl phenol or similar dihydroxy phenols.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A copper conductor in contact with a polyethylene
composition wherein the polyethylene composition comprises
between 0.2 to 0.8% by weight of an antioxidant which is a di-
hydroxy phenol or a normal or basic salt of a member selected
from the group consisting of aluminium barium, calcium, magne-
sium, strontium and zinc, the dihydroxy phenol having the
general formula
<IMG>
in which R1 and R4 are alkyl radicals, preferably primary alkyl
radical s containing from 1 to 3 carbon atoms, R2 and R3 are
alkyl, cycloalkyl or alkyl substituted cycloalkyl radicals
and R5 is an alkylene radical which may contain side-chain
alkyl groups.
2. A copper conductor in contact with a polyethylene
composition as claimed in Claim 1 wherein the antioxidant in
the polyethylene composition is 2:2'-methylene bis[6-(.alpha.-methyl
cyclohexyl)-4-methyl phenol].
3. A copper conductor in contact with a polyethylene
composition as claimed in Claim 1 wherein the polyethylene
composition comprises from 0.3 to 0.5% by weight of the anti-
oxidant.
4. A copper conductor in contact with a polyethylene
composition as claimed in Claim 1 wherein the polyethylene
composition is foamed.

Description

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This invention relates to copper conductors
in contact with a polyethylene compo~ition.
~ver since the di~co~ery of polyethyle~e, it
has been u~ed as insulation for copper conductors
used in telephone cable~ and rad~r installati~ns.
Polyethylene u~ed as insulation normally contains
small amounts of an antioxidant co~pound which le3sens
the degradative effects o~ oxygen on the polyethyle~e
and polyethylene insulation which is in contact with
copper frequently co~tains a ~o-called copper stabiliser
such as N,N'diacetyl(adipoyl dihydrazide) or nickel
bis-(3:5-ditertiarybutyl-4-hydroxy be~zyl phosphonic
acid monoethylate) which lessen~ the embrittlement
which occurs in the presence of copper~ ~hese
so-called copper ~tabilisers tend to be expensive
materials.
Antioxidants such as 2:2'-methylene bis[6-(a~methyl
cyclohexyl)-4-methyl phenoll and the similar compounds
described in British patent specification 744 875
have been commercially available ~or over fifteen
years and have been used in non-irradiated polyethylene
insulation in amounts of up to 0.1% though as much as
1%~by weight of the antioxidants have been proposed ~or
use in thermoplastic rubbers where the loss of
antioxidant by "blooming" (i.e. exuding of the
- ~ . .: .. .. .: - . . . . : .. . . . . : .

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antioxidant from the thermopla~tic) i8 a le~s serious
problem and where it i~ believed the ~ntioxidant~
al~o retard the onset of copper catalysed oxidation
of rubber.
It has now been discovered that the presence of
certain ~pecified amounts of 2:2'-methylene
bi~[6-(a-methyl cyclohexyl)-4-methyl phenol] and
similar antioxidants in polyethylene which is in
contact with copper does not lead to excessive
amounts of bloomi~g and it reduces the embrittlement
of the polyethylene by the copper.
Accordingly by thi~ invention we provide a copper
conductor in contact with a polyeth~lene composition
wherein the polyethylene composition comprises
between 0.2 to 0.8% by weight of an antioxidant which
is a dihydroxy phenol or a normal or basic aluminium,
barium, calcium, magnesium, strontium or zinc salt
thereof, the dihydroxy phenol having the general
formula
R2 OH OH R3
~< ~ :
~ _ ~5_ y ~
1 4

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in which R1 and R~ are alkyl radisals, preferably
primary alkyl radicals containing from 1 to 3 carbo~
atoms, ~ and R3 are alkyl, cycloalkyl or alkyl
substituted cycloalk~l radicals and R5 is an alkylene
radical which may contai~ side-chain alkyl groups.
The radicals R1 and R4 may be the same or different
but are pre~erably both m~th~l groups. Tha radicals
~ and R3 may also be the same or differe~t. ~5,may
be ~or example a methylene, ethylene, isoprop~lene or
4-methyl pent~lene radical. A preferred a~tioxidant ~-
i~ 2:2'-methylene bi~6-(a-methyl c~clohex~ 4-methyl
phenol].
Preferably the polyethylene compositio~ comprises
from 0~3 to 0.5% by weight of the antioxidant.
It is particularly preferred tha~ the polyethylene
composition be foamed. The polyethylene composition
may be foamed by means of blowing agents such as
a~odicarbonamide or diphenyl oxide-4,4'-disulphohydrazide.
Other blowing agents are described in an article by
Dr A H Scheurlen in ~unststoffe Volume 47 No. 8 of
1957 pages 446 to 455.
~he invention is illustrated by the following -
example.
:E~AMPIæ
A polyethylene composition having a melt flow

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index of 0.3 (when mea~ured according to Briti~h
Standard 2782: Part 1/105C/1970 using a 2.16 Kg load)
and a density of 0.932 Kg/cm2 (when measured according
to British Standard ~412 of 1966) and containing
0.3~ by weight o~ 2,2'-methylene bi~t6(~-methyl
cyclohexyl)-4-methyl phenol] and 0.~/o by weight of
azodicarbonamide was extrusion coated onto copper :~
wire 90 as to produce a foamed polyethylene covering
which wac 0.1 mm thick. Samples of the covered
conductor were then suspended in an oven maintained ~: .
at 105C for 1,000 hours. ~he sample~ were then
removed and it was found that they could all be bent
through 360 without crack~ forming. Hence it wa~
concluded that no serious embrittlement of the
polyethylene had occurred.
~.