FLEXIBLE ELECTRIC CABLES

CABLES ELECTRIQUES SOUPLES

English Abstract

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ABSTRACT OF THE DISCLOSURE
A low voltage cable comprises a plurality of
insulated conductors which are contained within an
insulating bedding layer of circular cross-section,
the bedding layer comprising a thermoplastic polymer
and at least 50% by weight of one or more inorganic
fillers, and an outer sheath of a cross-linked
polyvinyl chloride-based insulation composition.

Claims

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THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A low voltage electric cable which comprises a plur-
ality of insulated conductors which are contained within an
insulating bedding layer comprising a thermoplastic polymer and
at least 50% by weight of one or more inorganic fillers, and an
outer sheath of a cross-linked polyvinyl chloride-based insula-
tion composition, the sheath being of substantially uniform
cross-sectional thickness and being free of longitudinally extend-
ing ribs.
2. A cable as set forth in claim 1, wherein said thermo-
plastic polymer of the bedding layer is selected from the group
consisting of polyvinyl chloride, ethylene-vinyl acetate copoly-
mer, ethylene-propylene copolymer, and ethylene-propylene-diene
monomer copolymer.
3. A cable as set forth in claim 1, wherein said bedding
layer comprises 60 to 80% by weight of at least one inorganic
filler.
4. A cable as set forth in claim 1, wherein the inorganic
filler of said bedding layer is chalk or whiting.
5. A cable as set forth in claim 1, wherein the composi-
tion of said bedding layer comprises:
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6. A cable as set forth in claim 1, wherein the
composition of said outer sheath comprises:
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Description

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FLEXIBLE ELECTRIC CABLES
BACKGROIJND OF THE INVENTION
This invention is concerned with flexible electric
cables which are primarily intended for use as the power
leads of domestic and industrial tools and appliances,
which are likely to be subjected to heat hazards and/or
mechanical abuse in use.
The power leads of such appliances as domestic
irons, soldering irons and other heated appliances, and
power tools, such as drills, are liable to be subjected
to heat hazards from accidental contact with hot objects
and/or mechanical abuse by repeated rubbing against hard
surfaces, by contact with abrasive materials or sharp
edges and the like. Some such tools and appliances
are conventionally provided with flexible leads which
are covered with braided textiles or vulcanised rubber
or polyvinyl chloride (PVC)- based sheaths, but each
of these materiaIs is subject to one or more of the
following disadvantages; it is insufficiently
resistant to thermal and~or mechanical abuse, it is
relatively expensive, it cannot be produced in a wide
range of colours, or it is not suitable for the formation
of moulded terminations.
More re~cently flexible leads for this purpose
have been mad~e by surrounding the insulated conductors
(usually thre~) with PVC-based insulation which is
cross-linked~ normally by irradiation with ionising
radiation. Cross-linked PVC insulation compositions
have good heat, abra.sion and wcar resistance. However
the non-c;ircular cro~ss-section provided by thrce
twisted insulated conductors means that the cross-linked
3 PVC coating is of non-uni~orm thickness in section and

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is provided, in effect, with internal longitudinally extending
ribs. This variation in the thickness of the PVC coating substan-
tially increases the stiffness of the cable and the latter tends
to have insufficient flexibility for the intended uses.
SUMMARY OF THE INVENTION
An object of the invention is to provide a cable con-
struction which provides a combination of properties which are
desirable for the purpose indicated, that is good heat, wear and
abrasion resistance and good flexibility.
In accordance with the present invention, there is pro-
vided a low voltage electric cable which comprises a plurality of
insulated conductors which are contained within an insulating bed-
ding layer comprising a thermoplastic polymer and at least 50% by
weight of one or more inorganic fillers, and an outer sheath of a
cross-linked polyvinyl chloride-based insulation composition, the
sheath being of substantially uniform cross-sectional thickness
and being free of longitudinally extending ribs.
DESCRIPTION OF THE INVENTION
In order that the invention may be more fully understood,
a preferred embodiment of cable will now be described, by way of
example, with reference to the single Figure of the accompanying
drawing, which is a cross-section of the embodiment.
Referring to the drawing, the cable 10 comprises three
conductors 11, each provided with its own insulation 12 (the core
insulation). The insula-ted conductors 11/12 are embedded in an
insulating bedding layer 13 which has a circular cross-section.

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The bedding layer 13 is, in turn, contained within an outer
sheath 14 of a cross-linked PVC-based sheathing composition.
The elements of the cable, and preferred features
thereof, will now be described in greater detail.

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The conductors and the core insulation thereof may
be entirely conventional and as are generally used in
power supply cables for tools and appliances of the
kind.s referred to abo~e. Suitable conduct.ors and core
j insulation for this purpose h~ill be well knoh~n to those
skilled in the art and these element,s of the cable will
not be furt.her described.
The beddinc layeT comprises, as already .stated~
a thermoplast.ic polymer and at. least 50~0 by wei~ht
of one or more inorcanic filler~s. Generall,v, it is
preferred to use P~'C as the bedding layer polymer, but,
other suitable pol mers are, for example~ ethylene-
vinyl acetat.e copol~mer tE~'A.~ et,hylene-propylene
copolymer ~EPR), and ethylene-propylene-diene monomer
Ij copolymer (~P~). The beddin~ layer is preferably
highly filled, that is it is preferred that it should
contain 60 to 80~ by wei~ht of filler. Any of the
inorganic fillers which are conventionally used in
insulating compositions can~ in principle~ be used in
2~ the bedding layer~ It is preferred~ for economic
reasons, to use cheap and readil~ a~ailable fillers~
such as chal~ or whiting. The principal function of
the beddin~ layer is to pro~ide circularit~-~ but it
also ha~s the subsidiar~ funct,ion of providin~ a layer
of low t,hermal conductivity betheen the outer sheath
and t.he insulat,ed conductor.s and the components of
the beddinc layer are preferabl~ chosen wit.h this end
n vlew.
A preferred beddinc~ layer composit.ion i.s, for
example! as follow.s (all pa-t~s by hei~ht):
PV~ 100 part.s
pht.halat.e plasticisel- 125 part.s
~ par~t~i
stabiliser 2 parts
l~lL)r-icclllt]~ part,s
~he o~ter cheath c~f' cro~-lin~ed ~\'0-ba,~ed

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insulation material may be of convent.ional composition,
such sheath materials ha~ing been used for cables, as
previously ment.ioned; as compared with the jackets of
this type of material pre~iously used, the sheath of
the present in-ention is of sub.st,antially uniform thick-
ness around the cable so that, the latter has ~ood
flexibility.
The det,ailed formulat,ion of such sheath materials
including suitable cross-linking agents therefor-e and
suitable radiation dosages to obt.ain the de.sired le~el
of cross-linking~ will be known to t,hose skilled in
the art.
A preferred sheath composition is, for example,
as follows (all parts by weight):
P~'C 100 parts
phthalate plasticiser 60 parts
clay 20 parts
antimony based flame
retardant. ~ parts
st.abiliser 7 parts
lubricant 1 part
sensitiser ~ parts