Note: Descriptions are shown in the official language in which they were submitted.
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"Self-extinguishing cable with low-level production of fumes,
and flame-retardant composition used therein"
******
The present invention relates to cables, in particular electrical cables
for low-voltage power transmission or for telecommunications, or
alternatively for data transmission, as well as mixed
power/telecommunications cables, which have self-extinguishing
properties and produce a low level of fumes, and to flame-retardant
compositions used therein.
Self-extinguishing cables are generally produced by extruding over
the core of the cable a flame-retardant coating consisting of a polymer
composition to which flame-retardant properties have been imparted by
the addition of a suitable flame-retardant filler of inorganic type,
generally a hydroxide, a hydrated oxide or a hydrated salt of a metal, in
particular of magnesium or aluminium. The polymer base generally
consists of copolymers of ethylene and ethylenically unsaturated
esters, in particular ethylene/vinyl acetate or ethylene/ethyl acrylate
copolymers, optionally mixed with polyolefins (see for example patents
US-4,673,620 and EP-530,940).
Patent application WO 96/23311 describes a low-voltage, high-
current cable in which the inner sheath, the insulating coating and the
outer sheath consist of the same black-coloured base material and the
insulating layer contains a longitudinal coloured stripe for identification
purposes. The use of this material for the various layers would not
require the separation of the various components in a recycling
process. The base material can, depending on the maximum working
temperature of the cable, be a polyethylene with a density of between
0.92 and 0.94 g/cm3 and a Shore D hardness _ 42, or a thermoplastic
elastomer based on polypropylene, for example polypropylene modified
with an ethylene/propylene copolymer or a polypropylene-based
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reactor mixture wherein the elastomeric phase content is greater than
25%. When flame-retardant properties are required, it is no longer
possible to use the same material for the various coating layers of the
cable, and as a polymer base for the layer containing the flame-
retardant filler, the use of ethylene/vinyl acetate copolymers or ultra-
low-density polyethylene (ULDPE) and, in particular, ethylene-based
copolymers obtained with metallocene catalysts is suggested.
On the basis of the Applicant's experience, in order to achieve
successful results in the flame-resistant tests commonly carried out on
self-extinguishing cables, the amount of flame-retardant filler required is
high, generally greater than 30% by weight, usually more than 50% by
weight, relative to the total weight of the flame-retardant coating. Such
a high level of inorganic filler leads to a deterioration in processability
and in mechanical properties of the flame-retardant composition, in
particular as regards elongation at break and stress at break. Then, the
Applicant has found that, in order to obtain a self-extinguishing cable
which satisfies the specifications required by the market, it is necessary
to have available a polymer base which is capable of incorporating
large amounts of flame-retardant filler and, at the same time, of
maintaining good mechanical properties, in particular as regards
elongation at break and stress at break.
The Applicant has now found that it is possible to produce self-
extinguishing cables with high flame resistance and excellent
mechanical properties by using as flame-retardant coating a mixture of
a flame-retardant inorganic filler and a polymer base comprising a
heterophase copolymer having an elastomeric phase based on
ethylene copolymerized with an a-olefin and a thermoplastic phase
based on propylene, wherein the elastomeric phase is at least 45% by
weight relative to the total weight of the heterophase copolymer and
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this copolymer is substantially devoid of crystallinity deriving from
polyethylene sequences.
In a first aspect, the present invention thus relates to a cable
comprising at least one conductor and at least one flame-retardant
coating layer based on a polymer material and a flame-retardant
inorganic filler, characterized in that the said polymer material
comprises a heterophase copolymer having an elastomeric phase
based on ethylene copolymerized with an a-olefin and a thermoplastic
phase based on propylene, the said elastomeric phase in the said
heterophase copolymer being at least 45% by weight relative to the
total weight of the heterophase copolymer, the said heterophase
copolymer being substantially devoid of crystallinity deriving from
polyethylene sequences.
According to a first embodiment, the cable has an electrically
insulating inner layer and the flame-retardant coating is placed outside
the said insulating inner layer.
According to another embodiment, the flame-retardant coating is
placed directly on the conductor.
In a second aspect, the present invention relates to a flame-retardant
composition based on a polymer material and a flame-retardant
inorganic filler, characterized in that the said polymer material
comprises a heterophase copolymer having an elastomeric phase
based on ethylene copolymerized with an a-olefin and a thermoplastic
phase based on propylene, the said elastomeric phase in the said
heterophase copolymer being at least 45% by weight relative to the
total weight of the heterophase copolymer, the said heterophase
copolymer being substantially devoid of crystallinity deriving from
polyethylene sequences.
In accordance with the present invention, the use of a heterophase
copolymer as described above as a base polymer material makes it
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possible to obtain self-extinguishing cables which have a flame-
retardant coating with an elongation at break (E.B.) value, measured
according to CEI standard 20-34 5.1, of at least 100%, preferably of
at least 150%, and a stress at break (S.B.) value, measured according
to CEI standard 20-34 5.1, of at least 6 MPa, preferably of at least 9
MPa.
For the purposes of the present description and of the claims which
follow, the expression "heterophase copolymer having an elastomeric
phase based on ethylene copolymerized with an a-olefin and a
thermoplastic phase based on propylene" means a thermoplastic
elastomer obtained by sequential copolymerization of: (a) propylene,
optionally containing small amounts of at least one olefin comonomer
selected from ethylene and a-olefins other than propylene; and then of:
(b) a mixture of ethylene with an a-olefin, in particular propylene and,
optionally, with small amounts of a diene. This class of products is also
commonly referred to as "thermoplastic reactor elastomers".
For the purposes of the present description and of the claims, the
expression "heterophase copolymer substantially devoid of crystallinity
deriving from polyethylene sequences" means that the heterophase
copolymer, subjected to differential scanning calorimetry (DSC)
analysis, shows no appreciable melting peaks attributable to a
crystalline polyethylene phase, i.e. to (CH2), sequences of the
crystalline type. In quantitative terms, this means that the heat of fusion
of peaks present below 130 C and attributable to polyethylene
sequences is generally less than 3 J/g; preferably substantially zero.
Alternatively, the substantial absence of crystallinity due to
polyethylene sequences can be ascertained by extracting the
elastomeric (amorphous) phase using suitable organic solvents (for
example refluxing xylene at 135 C for 20 min.) and analysing the
residue formed by the crystalline phase, for example by X-ray
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defractometry. The substantial absence of the typical reflection of
crystalline polyethylene at the angle 20 = 21.5 (with copper radiation)
indicates that the heterophase copolymer is substantially devoid of
crystalline polyethylene sequences.
The amount of elastomeric phase present in the heterophase
copolymer can be determined according to known techniques, for
example by extracting the elastomeric (amorphous) phase with a
suitable organic solvent (in particular refluxing xylene at 135 C for 20
min.): the amount of elastomeric phase is calculated as the difference
between the initial weight of the sample and the weight of the dried
residue.
The term "a-olefin" means an olefin of formula CH2=CH-R, wherein R
is a linear or branched alkyl containing from 1 to 10 carbon atoms. The
a-olefin can be selected, for example, from: propylene, 1-butene,
1-pentene, 1-hexene, 1-octene, 1-dodecene and the like.
The preparation of the heterophase copolymers according to the
present invention is usually carried out by copolymerization of the
corresponding monomers in the presence of Ziegler-Natta catalysts
based on halogenated titanium compounds supported on magnesium
chloride. Details regarding the preparation of these copolymers are
given, for example, in EP-A-0,400,333, EP-A-0,373,660 and US-A-
5,286,564.
The thermoplastic phase of the heterophase copolymer, mainly
produced during the above mentioned step (a) of the process, consists
of a propylene homopolymer or a crystalline copolymer of propylene
with an olefin comonomer selected from ethylene and a-olefins other
than propylene. The olefin comonomer is preferably ethylene. The
amount of olefin comonomer is preferably less than 10 mol% relative to
the total number of moles of the thermoplastic phase.
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As mentioned above, the elastomeric phase of the heterophase
copolymer, mainly produced during the above mentioned step (b) of the
process, is at least 45% by weight, preferably at least 55% by weight,
and even more preferably at least 60% by weight, relative to the total
weight of the heterophase copolymer, and consists of an elastomeric
copolymer of ethylene with an a-olefin, and optionally with a diene. The
said a-olefin is preferably propylene. The diene optionally present as
comonomer generally contains from 4 to 20 carbon atoms and is
preferably selected from: linear, conjugated or non-conjugated
diolefins, for example 1,3-butadiene, 1,4-hexadiene, 1,6-octadiene and
the like; monocyclic or polycyclic dienes, for example
1,4-cyclohexadiene, 5-ethylidene-2-norbornene, 5-methylene-2-
norbornene and the like. The composition of the elastomeric phase is
generally as follows: from 15 to 85 mol% of ethylene, from 15 to 85
mol% of a-olefin, from 0 to 5 mol% of a diene.
In a preferred embodiment, the elastomeric phase consists of an
elastomeric copolymer of ethylene and propylene which is rich in
propylene units, in particular having the following composition: from 15
to 50% by weight, more preferably from 20 to 40% by weight, of
ethylene, and from 50 to 85% by weight, more preferably from 60 to
80% by weight, of propylene, relative to the weight of the elastomeric
phase.
The amount of propylene units in the elastomeric phase can be
determined by extracting the elastomeric (amorphous) phase using a
suitable organic solvent (for example refluxing xylene at 135 C for
20 min.), followed by analysing the dried extract according to known
techniques, for example by infrared (IR) spectroscopy.
Heterophase copolymers with structural properties and related
physicochemical properties according to the present invention can be
found on the market among the large class of so-called "polypropylene
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reactor mixtures" sold, for example, by Montell under the brand name
Hifax .
Flame-retardant inorganic fillers which can generally be used are
hydroxides, hydrated oxides, salts or hydrated salts of metals, in
particular of calcium, aluminium or magnesium, such as, for example:
magnesium hydroxide, aluminium hydroxide, alumina trihydrate,
magnesium carbonate hydrate, magnesium carbonate, magnesium
calcium carbonate hydrate, magnesium calcium carbonate, or mixtures
thereof. Magnesium hydroxide, aluminium hydroxide and alumina
trihydrate (AI203-3H20) and mixtures thereof are particularly preferred.
Minor amounts, generally less than 25% by weight, of one or more
inorganic oxides or salts such as CoO, Ti021 Sb2031 ZnO, Fe203,
CaCO3 or mixtures thereof, can advantageously be added to these
compounds. The above mentioned metal hydroxides, in particular the
magnesium and aluminium hydroxides, are preferably used in the form
of particles with sizes which can range between 0.1 and 100 m,
preferably between 0.5 and 10 m.
One inorganic filler which is particularly preferred according to the
present invention is natural magnesium hydroxide. For the purposes of
the present invention, the expression "natural magnesium hydroxide"
indicates the magnesium hydroxide obtained by milling minerals based
on magnesium hydroxide, such as brucite and the like. Brucite is found
in nature as such, or, more frequently, in combination with other
minerals, such as calcite, aragonite, talc or magnesite, usually in
stratified form between silicate deposits, such as, for example, in
serpentine, in chlorite or in schists.
Brucite can be milled, according to known techniques, under wet or
dry conditions, preferably in the presence of milling coadjuvants, such
as polyglycols or the like. The specific surface area of the milled
product generally ranges from 5 to 20 m2/g, preferably from 6 to
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15 m2/g. The magnesium hydroxide thus obtained can subsequently be
classified, for example by sieving, in order to obtain an average particle
diameter ranging from 1 to 15 m, preferably from 1. 5 to 5 m, and a
particle size distribution such that the particles with a diameter of less
than 1.5 m form not more than 10% of the total, and the particles with
a diameter of greater than 20 m form not more than 10% of the total.
Natural magnesium hydroxide generally contains various impurities
deriving from salts, oxides and/or hydroxides of other metals, such as
Fe, Mn, Ca, Si, V, etc. The amount and nature of the impurities present
can vary as a function of the origin of the starting material. The degree
of purity is generally between 80 and 98% by weight. The content of
impurities of water-soluble ionic type can be determined indirectly by
measuring the electrical conductivity of the aqueous extract obtained by
placing the magnesium hydroxide in contact with a suitable amount of
water for a predetermined time and at a predetermined temperature
according to ISO method 787. According to this method, the electrical
conductivity of the aqueous extract obtained from natural magnesium
hydroxide is generally between 100 and 500 pS/cm, preferably
between 120 and 350 S/cm.
The amount of flame-retardant inorganic filler to be used in the
compositions of the present invention is predetermined so as to obtain
a cable which is capable of passing the usual flame resistance tests, for
example those according to IEC standard 332-1 and IEC 332.3 A, B
and C. This amount is generally between 10 and 90% by weight,
preferably between 30 and 80% by weight, and even more preferably
between 50 and 70% by weight, relative to the total weight of the flame-
retardant composition.
The flame-retardant fillers can be used advantageously in the form of
coated particles. Coating materials preferably used are saturated or
unsaturated fatty acids containing from 8 to 24 carbon atoms, and
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metal salts thereof, such as, for example: oleic acid, palmitic acid,
stearic acid, isostearic acid, lauric acid; magnesium or zinc stearate or
oleate; and the like.
A coupling agent selected, for example, from: saturated silane
compounds or silane compounds containing at least one ethylenic
unsaturation; epoxides containing an ethylenic unsaturation; organic
titanates; mono- or dicarboxylic acids containing at least one ethylenic
unsaturation, or derivatives thereof such as, for example, anhydrides or
esters, can be added to the mixture in order to enhance the
compatibility between the inorganic filler and the polymer material.
Examples of suitable silane compounds are: y-methacryloxy-
propyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane,
allylmethyidimethoxysilane, allylmethyldiethoxysilane, methyltri-
ethoxysilane, methyltris(2-methoxyethoxy)silane, dimethyl-
diethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltrimethoxysilane,
vinylmethyldimethoxysilane, vinyltriethoxysilane, octyltriethoxysilane,
isobutyltriethoxysilane, isobutyltrimethoxysilane and the like, or
mixtures thereof.
Examples of suitable epoxides containing an ethylenic unsaturation
are: glycidyl acrylate, glycidyl methacrylate, itaconic acid monoglycidyl
ester, maleic acid glycidyl ester, vinyl glycidyl ether, allyl glycidyl ether
and the like, or mixtures thereof.
An example of a suitable organic titanate is tetra-n-butyl titanate.
Mono- or dicarboxylic acids containing at least one ethylenic
unsaturation, or derivatives thereof, which can be used as coupling
agents are, for example: maleic acid, maleic anhydride, fumaric acid,
citraconic acid, itaconic acid, acrylic acid, methacrylic acid and the like,
and the anhydrides or esters derived therefrom, or mixtures thereof.
Maleic anhydride is particularly preferred.
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The coupling agents can be used as such or pregrafted onto a
polyolefin, for example polyethylene or copolymers of ethylene with an
a-olefin, by means of a radical reaction (see, for example, patent
EP-0,530,940). The amount of grafted coupling agent is generally
between 0.05 and 5 parts by weight, preferably from 0.1 to 2 parts by
weight, relative to 100 parts by weight of polyolefin. Polyolefins grafted
with maleic anhydride are available as commercial products identified,
for example, by the brand names Fusabond , (Du Pont), Orevac (Elf
Atochem), Exxelor (Exxon Chemical), Yparex (DSM), etc.
Alternatively, the coupling agents of carboxylic or epoxy type
mentioned above (for example maleic anhydride) or silanes containing
an ethylenic unsaturation (for example vinyltrimethoxysilane) can be
added to the mixture in combination with a radical initiator so as to graft
the compatibilizing agent directly onto the polymer material. Initiators
which can be used are, for example, organic peroxides such as tert-
butyl perbenzoate, dicumyl peroxide, benzoyl peroxide, di-tert-butyl
peroxide and the like. This technique is described, for example, in
patent US-4,317,765 and in Japanese patent application JP/62-58774.
The amount of coupling agent to be added to the mixture can vary
mainly as a function of the type of coupling agent used and the amount
of flame-retardant filler added, and is generally between 0.01 and 10%,
preferably between 0.02 and 5%, and even more preferably between
0.05 and 2%, by weight relative to the total weight of the base polymer
mixture.
Other conventional components, such as antioxidants, processing
coadjuvants, lubricants, pigments, other fillers and the like, can be
added to the flame-retardant compositions according to the present
invention.
Examples of suitable antioxidants are: polymerized trimethyldihydro-
quinoline, 4,4'-thiobis(3-methyl-6-tert-butyl)phenol; pentaerythrityl-
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tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,2'-
thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and
the like, or mixtures thereof.
Processing coadjuvants usually added to the polymer material are,
for example, calcium stearate, zinc stearate, stearic acid, paraffin wax,
silicone rubbers and the like, or mixtures thereof.
Other fillers which can be used are, for example: glass particles,
glass fibres, calcined kaolin, talc and the like, or mixtures thereof.
The flame-retardant compositions according to the present invention
are preferably used in non-crosslinked form, in order to obtain a coating
with thermoplastic and thus recyclable properties.
The flame-retardant compositions according to the present invention
can be prepared by mixing the polymer component, the filler and the
additives according to techniques known in the art. The mixing can be
carried out, for example, using an internal mixer of the type with
tangential rotors (Banbury) or with interpenetrating rotors, or
alternatively in continuous mixers such as Ko-Kneader (Buss) or co-
rotating or counter-rotating twin-screw mixers.
The flame-retardant composition can thus be used to coat the
conductor directly, or to produce an outer self-extinguishing sheath on
the conductor which has been precoated with an insulating layer. The
coating step is generally carried out by means of extrusion. When two
layers are present, the extrusion can be carried out in two separate
steps, extruding the inner layer onto the conductor in a first run and the
outer layer onto this inner layer in a second run. The coating process
can advantageously be carried out in a single run, for example by
means of a "tandem" method, wherein two separate extruders arranged
in series are used, or alternatively by co-extrusion using a single
extrusion head.
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Further details will be illustrated hereinbelow with reference to the
attached figures, wherein:
Fig. 1 is a cross-section of a low-voltage electrical cable of unipolar
type according to a first embodiment of the present invention;
Fig. 2 is a cross-section of a low-voltage electrical cable of unipolar
type according to a second embodiment of the present invention;
Figs. 3 and 4 are the DSC curves of two heterophase copolymers
according to the present invention (Cop. 1 and 2, respectively);
Figs. 5 and 6 are the DSC curves of two comparative heterophase
copolymers (Cop. 3 and 4, respectively).
The term "low voltage" generally means a voltage of less than 5 kV,
preferably less than 2 kV and even more preferably less than 1 kV.
The cable in Figure 1 comprises a metal conductor (1), and inner
layer (2) which acts as an electrical insulator, and an outer layer (3)
which acts as a protective sheath with flame-retardant properties
according to the present invention.
The inner layer (2) can consist of a crosslinked or non-crosslinked
polymer composition, preferably devoid of halogens, with electrical
insulating properties, which is known in the art, selected, for example,
from: polyolefins (homopolymers or copolymers of different olefins),
olefin/ethylenically unsaturated ester copolymers, polyesters,
polyethers, polyether/polyester copolymers and mixtures thereof.
Examples of such polymers are: polyethylene (PE), in particular linear
low-density PE (LLDPE); polypropylene (PP); propylene/ethylene
thermoplastic copolymers; ethylene-propylene rubbers (EPR) or
ethylene-propylene-diene rubbers (EPDM); natural rubbers; butyl
rubbers; ethylene/vinyl acetate (EVA) copolymers; ethylene/methyl
acrylate (EMA) copolymers; ethylene/ethyl acrylate (EEA) copolymers;
ethylene/butyl acrylate (EBA) copolymers; ethylene/a-olefin copolymers
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and the like. It is also possible to use the same polymer material for the
inner layer (2) as for the outer layer (3).
The cable in Fig. 2 comprises a conductor (1) coated directly with a
flame-retardant sheath (3) according to the present invention, without
interposing the insulating layer (2). In this case, if the conductor (1) is
metallic, the self-extinguishing coating (3) also acts as electrical
insulation.
A thin polymer layer having an anti-abrasive function, to which a
suitable pigment is optionally added in order to produce a coloration for
identification purposes, can then be added externally.
Figs. 1 and 2 show only two possible types of cable according to the
present invention. It is clear that suitable modifications known in the art
can be made to these embodiments, without thereby departing from the
scope of the present invention. In particular, telecommunications cables
or data transmission cables, or alternatively mixed power/tele-
communications cables, can be produced using the flame-retardant
compositions according to the present invention. In addition, although
the present description is mainly directed to self-extinguishing cables,
the flame-retardant compositions according to the invention can be
used to impart self-extinguishing properties to other articles, in
particular electrical junction or termination devices.
Table 1 gives a number of properties of some heterophase
copolymers used according to the present invention (Cop.1 and Cop. 2)
and for comparative purposes (Cop. 3 and Cop. 4).
The melt flow index (MFI) was measured at 230 C and 21.6 N
according to ASTM standard D 1238/L.
The heat of fusion deriving from polypropylene sequences (PP
enthalpy) and the heat of fusion deriving from polyethylene sequences
(PE enthalpy) was measured using DSC instrumentation from Mettler
(second melting value) with a scanning speed of 10 C/min. (instrument
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head: DSC 30 type; microprocessor: PC 11 type; software: Mettler
Graphware TA72AT.1). The DSC curves of the four heterophase
copolymers in Table 1 are given in Figures 3-6.
It should be noted that the DSC curve for Cop. 2 shows a single
melting peak associated with the polypropylene phase centred at about
145 C, with a very pronounced "tail" which extends below 130 C and
which can be attributed to the presence of a polypropylene phase with
low crystallinity presumably consisting of short sequences of propylene
units interrupted by ethylene units.
The percentage of elastomeric phase was determined by extraction
with refluxing xylene at 135 C for 20 min., calculated as the difference
between the initial weight of the sample and the weight of the dried
residue.
The propylene content of the elastomeric phase was determined by
IR spectroscopic analysis of the polymer extracted as described above
and dried by evaporation of the solvent. The propylene content is
determined, by means of suitable calibration curves, as the ratio
between the intensity of the bands at 4377 and 4255 cm"'.
Table 1
Thermoplastic MFI PP PE Elastomeric Propylene in
elastomer (dg/min.) enthalpy enthalpy phase the
(J/g) (J/g) (% by weight) elastomeric
phase
(% by weight)
Cop.1 0.8 32.0 0 60 72
Cop.2 0.6 23.8 0 65 72
Cop. 3(') 0.9 35.4 7.3 55 41
Cop. 4(') 7.5 42.8 15.4 48 40
(') comparative
Cop. 1: Hifax KS080 from Montell;
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Cop. 2: Hifax CA10A from Montell;
Cop. 3: Hifax CA12A from Montell;
Cop. 4: Hifax CA43A from Montell.
The heterophase copolymers in Table 1 were used to prepare the
flame-retardant compositions reported in Table 2, using a 1.6 litre
Banbury mixer with a volumetric packing ratio of about 75%.
1 mm plates were prepared with the compositions thus obtained by
compression moulding at 190-195 C and 200 bar after preheating for
min. at the same temperature. Small cables were then prepared by
extruding identical compositions of Table 2 onto a single red copper
wire with a cross-section of 1.5 mm2, so as to obtain a 0.7 mm thick
flame-retardant layer. The extrusion line speed was 20 m/min, with
temperatures in the various zones of the extruder cylinder (diameter =
45 mm) of 160 - 170 - 190 - 200 C, the temperature of the extrusion
head was 200 C and that of the ring was 220 C.
The plates and small cables thus prepared were subjected to
mechanical tensile strength tests (E.B. and S.B.) according to CEI
standard 20-34, paragraph 5.1. The pulling speed of the jaws was
250 mm/min. The cables were also subjected to the flame resistance
test according to IEC standard 332-1, which consists in subjecting a
sample 60 cm long, placed vertically, to the direct action of a Bunsen
burner flame applied for 1 min at an inclination of 45 relative to the
sample. All the cable samples passed the test.
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Table 2
Example 1 2(*) 3 4 5(')
Cop.1 -- -- 90 -- --
Cop.2 100 -- -- 90 --
Cop.3 -- -- -- -- 90
Cop.4 -- 100 -- -- --
Orevac CA100 -- -- 10 10 10
Hydrofy GS 1.5 160 160 160 160 160
Rhodorsil MF175U 0.5 0.5 0.5 0.5 0.5
Irganox 1010 1.5 1.5 1.5 1,5 1.5
Mechanical properties on plates:
E.B. (%) 622 32 99 137 24
S.B. (MPa) 7.2 6.5 11.6 10.5 5.7
Mechanical properties on cables:
E.B. (%) 490 38 338 233 17
S.B. (MPa) 10.1 6.3 9.0 11.1 5.0
() comparative
Orevac CA100: polypropylene grafted with maleic anhydride (Elf
Atochem) (coupling agent);
Hydrofy GS1.5: natural Mg(OH)2 coated with stearic acid (Sima)
(average particle diameter 2 microns and specific
surface 11 m2/g);
Rhodorsil : MF175U: silicone rubber (Rhone Poulenc) (processing
coadjuvant/lubricant);
Irganox 1010: pentaerythrityltetrakis(3,5-di-tert-butyl-4-
hydroxyphenyl) propionate (Ciba-Geigy)
(antioxidant)
The data given in Table 2 show that the cables and compositions
according to the present invention have excellent mechanical
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properties, fully satisfying the specifications, despite the fact that they
have a high content (61 %) of inorganic filler.
