U.S. patent application number 10/233756 was filed with the patent office on 2003-03-27 for self-extinguishing cable and flame-retardant composition used therein.
Invention is credited to Albizzati, Enrico, Martinotto, Luca, Pelizzoni, Andrea, Peruzzotti, Franco, Tirelli, Diego.
Application Number | 20030059613 10/233756 |
Document ID | / |
Family ID | 27224225 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030059613 |
Kind Code |
A1 |
Tirelli, Diego ; et
al. |
March 27, 2003 |
Self-extinguishing cable and flame-retardant composition used
therein
Abstract
A self-extinguishing cable and the flame-retardant composition
used therein are disclosed. The cable comprises at least one
flame-retardant coating comprising a) at least one polymer
material; b) at least one inorganic hydrated flame-retardant
filler; and c) at least one silane substituted with at least one
C.sub.10-C.sub.40 hydrocarbon group and with at least one
hydrolysable group. The self-extinguishing cable shows improved
insulating properties in water or in the presence of a moist
environment without adversely affecting self-extinguishing
properties.
Inventors: |
Tirelli, Diego; (Sesto San
Giovanni, IT) ; Martinotto, Luca; (Legnano, IT)
; Pelizzoni, Andrea; (Seveso, IT) ; Peruzzotti,
Franco; (Legnano, IT) ; Albizzati, Enrico;
(Lesa, IT) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Family ID: |
27224225 |
Appl. No.: |
10/233756 |
Filed: |
September 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60317171 |
Sep 6, 2001 |
|
|
|
Current U.S.
Class: |
428/375 ;
428/921 |
Current CPC
Class: |
H01B 7/295 20130101;
C08K 3/016 20180101; Y10T 428/2933 20150115 |
Class at
Publication: |
428/375 ;
428/921 |
International
Class: |
D02G 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2001 |
EP |
01121137.2 |
Claims
1. Self-extinguishing cable comprising at least one conductor and
at least one flame-retardant coating, wherein the at least one
flame-retardant coating comprises: a) at least one polymer material
selected from: olefin homopolymers, olefin copolymers, copolymers
of at least one olefin with at least one ethylenically unsaturated
ester, polyesters, polyethers, polyether/polyester copolymers, and
mixtures thereof; b) at least one inorganic hydrated
flame-retardant filler; c) at least one silane substituted with at
least one C.sub.10-C.sub.40 hydrocarbon group and with at least one
hydrolysable group.
2. A cable according to claim 1, wherein the polymer material is
selected from: polyethylene; copolymers of ethylene with at least
one .alpha.-olefin containing from 3 to 12 carbon atoms, and
optionally with at least one diene containing from 4 to 20 carbon
atoms; polypropylene; thermoplastic copolymers of propylene with
ethylene and/or at least one .alpha.-olefin containing from 4 to 12
carbon atoms; copolymers of ethylene with at least one ester
selected from alkyl acrylates, alkyl methacrylates and vinyl
carboxylates, wherein the alkyl and the carboxylic groups comprised
therein are linear or branched, and wherein the linear or branched
alkyl group may contain from 1 to 8, preferably from 1 to 4, carbon
atoms, while the linear or branched carboxylic group may contain
from 2 to 8, preferably from 2 to 5, carbon atoms; and mixtures
thereof.
3. A cable according to claim 2, wherein the linear or branched
alkyl group may contain from 1 to 4 carbon atoms, while the linear
or branched carboxylic group may contain from 2 to 5 carbon
atoms.
4. A cable according to any of the previous claims, wherein the
polymer material is selected from copolymers of ethylene with at
least one .alpha.-olefin containing from 3 to 12 carbon atoms, and
optionally with at least one diene containing from 4 to 20 carbon
atoms, obtained by single-site catalysis.
5. A cable according to any of the previous claims, wherein the
inorganic hydrated flame-retardant filler is selected from: metal
hydroxides, hydrated metal oxides, metal salts having at least one
hydroxyl group, and hydrated metal salts.
6. A cable according to any of the previous claims, wherein the
inorganic hydrated flame-retardant filler is a calcium, aluminium,
magnesium or zinc hydroxide, hydrated oxide, salt having at least
one hydroxyl group or hydrated salt.
7. A cable according to any of the previous claims, wherein the
flame-retardant filler is selected from: magnesium hydroxide,
alumina trihydrate, hydrated magnesium carbonate, hydrated calcium,
magnesium carbonate, 4ZnO.B.sub.2O.sub.3.H.sub.2O,
2ZnO.3B.sub.2O.sub.3.3.5H.sub.2O- , or mixtures thereof.
8. A cable according to any of the previous claims, wherein the
flame-retardant filler is magnesium hydroxide.
9. A cable according to any of the previous claims, wherein the
C.sub.10-C.sub.40 hydrocarbon group contained in the silane is a
C.sub.10-C.sub.40 alkyl, alkenyl, aryl, alkylaryl, arylalkyl,
arylalkenyl, alkenylaryl group, whereas the hydrolysable group is a
C.sub.1-C.sub.16 alkoxy group, optionally substituted by at least
one C.sub.1-C.sub.16 alkoxy group.
10. A cable according to any of the previous claims, wherein the
C.sub.10-C.sub.40 hydrocarbon group contained in the silane is a
C.sub.12-C.sub.24 alkyl, alkenyl, aryl, alkylaryl, arylalkyl,
arylalkenyl, alkenylaryl group.
11. A cable according to any of the previous claims, wherein the
silane has the following formula:Y.sub.4-(x+z)SiR.sub.xR'.sub.z
(I)wherein: x is 1, 2 or 3; z is zero, 1 or 2; with the proviso
that x+z is not higher than 3; Y, equal or different from each
other, are C.sub.1-C.sub.8 alkoxy groups, optionally substituted by
at least one C.sub.1-C.sub.8 alkoxy group; R, equal or different
from each other, are selected from: C.sub.10-C.sub.40 alkyl groups,
optionally substituted by at least one C.sub.6-C.sub.14 aryl group;
C.sub.10-C.sub.40 alkenyl groups, optionally substituted by at
least one C.sub.6-C.sub.14 aryl group; C.sub.6-C.sub.14 aryl
groups, optionally substituted by at least one C.sub.1-C.sub.30
alkyl group and/or by at least one C.sub.2-C.sub.30 alkenyl group;
with the proviso that each of R has from 10 to 40 carbon atoms; R',
equal or different from each other, are selected from: hydrogen;
C.sub.1-C.sub.20 alkyl groups, optionally substituted by at least
one C.sub.6-C.sub.14 aryl group; C.sub.2-C.sub.20 alkenyl groups,
optionally substituted by at least one C.sub.6-C.sub.14 aryl group;
C.sub.6-C.sub.14 aryl groups, optionally substituted by at least
one C.sub.1-C.sub.20 alkyl group and/or by at least one
C.sub.2-C.sub.20 alkenyl group.
12. A cable according to any of the previous claims, wherein the
silane has the following formula:Y.sub.4-(x+z)SiR.sub.xR'.sub.z
(I)wherein: x is 1, 2 or 3; z is zero, 1 or 2; with the proviso
that x+z is not higher than 3; Y, equal or different from each
other, are C.sub.1-C.sub.4 alkoxy groups, optionally substituted by
at least one C.sub.1-C.sub.4 alkoxy group; R, equal or different
from each other, are selected from: C.sub.12-C.sub.24 alkyl groups,
optionally substituted by at least one C.sub.6-C.sub.14 aryl group;
C.sub.12-C.sub.24 alkenyl groups, optionally substituted by at
least one C.sub.6-C.sub.14 aryl group; C.sub.6-C.sub.10 aryl
groups, optionally substituted by at least one C.sub.1-C.sub.30
alkyl group and/or by at least one C.sub.2-C.sub.30 alkenyl group;
with the proviso that each of R has from 10 to 40 carbon atoms; R',
equal or different from each other, are selected from: hydrogen;
C.sub.1-C.sub.16 alkyl groups, optionally substituted by at least
one C.sub.6-C.sub.14 aryl group; C.sub.2-C.sub.16 alkenyl groups,
optionally substituted by at least one C.sub.6-C.sub.14 aryl group;
C.sub.6-C.sub.10 aryl groups, optionally substituted by at least
one C.sub.1-C.sub.20 alkyl group and/or by at least one
C.sub.2-C.sub.20 alkenyl group.
13. A cable according to any of the previous claims, wherein the
silane has the following formula:Y.sub.4-(x+z)SiR.sub.xR'.sub.z
(I)wherein: x is 1, 2 or 3; z is zero, 1 or 2; with the proviso
that x+z is not higher than 3; Y, equal or different from each
other, are C.sub.1-C.sub.4 alkoxy groups, optionally substituted by
at least one C.sub.1-C.sub.4 alkoxy group; R, equal or different
from each other, are selected from: C.sub.14-C.sub.20 alkyl groups,
optionally substituted by at least one C.sub.6-C.sub.14 aryl group;
C.sub.14-C.sub.20 alkenyl groups, optionally substituted by at
least one C.sub.6-C.sub.14 aryl group; C.sub.6-C.sub.10 aryl
groups, optionally substituted by at least one C.sub.1-C.sub.30
alkyl group and/or by at least one C.sub.2-C.sub.30 alkenyl group;
with the proviso that each of R has from 10 to 40 carbon atoms; R',
equal or different from each other, are selected from: hydrogen;
C.sub.1-C.sub.12 alkyl groups, optionally substituted by at least
one C.sub.6-C.sub.14 aryl group; C.sub.2-C.sub.12 alkenyl groups,
optionally substituted by at least one C.sub.6-C.sub.14 aryl group;
C.sub.6-C.sub.10 aryl groups, optionally substituted by at least
one C.sub.1-C.sub.20 alkyl group and/or by at least one
C.sub.2-C.sub.20 alkenyl group.
14. A cable according to any of the claims 11-13, wherein, in
formula (I), x is 1; z is zero; Y, equal or different from each
other, are selected from C.sub.1-C.sub.4 alkoxy group, optionally
substituted by at least one C.sub.1-C.sub.4 alkoxy group; R is a
C.sub.14-C.sub.20 alkyl.
15. A cable according to any of the claims 11-14, wherein, in
formula (I), x is 1; z is zero; Y, equal or different from each
other, are selected from methoxy, ethoxy or methoxyethoxy group,
optionally substituted by at least one methoxy, ethoxy or
methoxyethoxy group and R is a hexadecyl or octadecyl group.
16. A cable according to any of the previous claims, wherein the
silane is in an amount from 0.1% to 10% with respect to the total
weight of the inorganic flame-retardant filler.
17. A cable according to any of the previous claims, wherein the
silane is in an amount from 0.5% to 5% by weight with respect to
the total weight of the inorganic flame-retardant filler.
18. Flame-retardant composition comprising: a) at least one polymer
material; b) at least one inorganic hydrated flame-retardant
filler; and c) at least one silane; a), b) and c) being defined
according to any of the previous claims.
Description
[0001] The present invention concerns a self-extinguishing cable
and the flame-retardant composition used therein. In particular,
the invention relates to a self-extinguishing cable having improved
insulating properties and to the flame-retardant composition used
therein.
[0002] Self-extinguishing cables are generally produced by
extruding over the core of the cable a flame-retardant coating
consisting of a polymer composition which has been given flame
retardant properties by the addition of a suitable additive.
Polyolefin-based compositions comprising, for example, polyethylene
or ethylene/vinyl acetate copolymers, containing an organic halide
combined with antimony trioxide as flame-retardant additive can,
for example, be used for this purpose. However, halogenated
flame-retardant additives have many drawbacks since they partially
decompose during processing of the polymer, giving rise to
halogenated gases which are toxic to workers and corrode the metal
parts of the polymer-processing equipment. In addition, when they
are placed directly in a flame, their combustion gives rise to very
large amounts of fumes containing toxic gases. Similar drawbacks
are encountered when polyvinyl chloride (PVC) with added antimony
trioxide is used as base polymer.
[0003] Thus, in recent years, use has been made of halogen-free
compositions in the production of self-extinguishing cables, in
which a polymer base, generally of polyolefin type, is mixed with
inorganic flame-retardant fillers, generally hydroxides, hydrated
oxides or hydrated salts of metals, in particular of aluminium or
magnesium, such as magnesium hydroxide or alumina trihydrate, or
mixtures thereof (see, for example, patents U.S. Pat. No.
4,145,404, U.S. Pat. No. 4,673,620, EP-B-328,051 and
EP-B-530,940).
[0004] Inorganic flame-retardant fillers, generally hydroxides as
above noted, can be used as they are or coated with various
hydrophobic products since they are usually strongly hygroscopic
and this tendency to absorb water, even at the operating conditions
of the cable, can cause the loss of the electric insulating
characteristics of the coating material; therefore, to reduce
hygroscopicity, hydrophobic agents are advantageously used to coat
the flame-retardant filler.
[0005] Among hydrophobic agents, saturated or unsaturated fatty
acids or the salts thereof, in particular oleic, stearic or
isostearic acid and the corresponding oleates or stearates, etc.
with e.g. zinc, magnesium or aluminium, etc.; or organic silanes
such as short chain alkyl- and alkylalkoxy-silanes, or titanium,
aluminium and zirconium organic compounds, are known.
[0006] For example, WO 96/27885 describes a flame-retardant
composition for coating electrical cables, comprising polypropylene
as polymer matrix supplemented with 1-20% by weight of a
polyethylene wax and 100-200% by weight of magnesium hydroxide
coated with a hydrophobic product, for example an alkylsilane. This
coating is said to increase the compatibility between the filler
and the polymer matrix and at the same time to impart hydrophobic
properties to the flame-retardant coating, thus avoiding the
absorption of moisture which would reduce the efficiency of the
insulating properties of the material.
[0007] EP-A-0249010 describes thermoplastic mouldings compounds
having high impact strength and high elongation at break, with good
fire performance, which are based on polymer blends consisting of a
mixture of 1 to 40% by weight of propylene homo- and/or co-polymer,
from 0.5 to 5% by weight of ethylene-propylene-diene terpolymer
rubber and from 40 to 70% by weight of silane coated magnesium
hydroxide and, optionally, polyethylene, polyacrylic ester and
polyvinyl acetate homo- and co-polymer.
[0008] JP-5-17692 and JP-7-161230 disclose a flame retardant
composition endowed with either improved acid resistance or
suppressed hygroscopicity, respectively, comprising magnesium
hydroxide processed with a surface-treatment agent containing at
least one compound selected from fatty acids and the metal salts
thereof, silane and titanate coupling agents, the composition being
added to a plastic or rubber and being used as a coating material
on halogen-free self-extinguishing electric wires and cables.
[0009] EP-A-0568488 discloses particulate magnesium hydroxide
suitable for use as a flame-retardant additive for a polymer,
especially for wires and cables, having peculiar BET surface area
and average particle size. Optionally, the particulate magnesium
hydroxide may be coated with an agent selected from a fatty acid, a
carboxylated unsaturated polymer, an organosilane, e.g.
3-aminopropyltriethoxysilane or vinyl-tris(2-methoxy-ethoxy)silane,
an organotitanate or a salt thereof. The articles formed by mixing
particulate magnesium hydroxide with a polymer are said to exhibit
optimal properties including flame-retardant effectiveness, tensile
strength and percent elongation as well as the dispersability of
the particulate magnesium hydroxide in the polymer material.
[0010] WO 99/05688 discloses a low smoke, self-extinguishing cable
and a halogen-free flame retardant coating used therein wherein
natural magnesium hydroxide is used as flame-retardant filler. The
coating comprises (a) a crystalline propylene homopolymer or
copolymer; (b) a copolymer of ethylene with at least one
.alpha.-olefin, and optionally with a diene, having a Composition
Distribution Index (CDI) greater than 45%; (c) natural magnesium
hydroxide. To improve compatibility between magnesium hydroxide and
the polymer material, a coupling agent, such as saturated silane
compounds or silane compounds containing at least one ethylenic
unsaturation, epoxides containing an ethylenic unsaturation,
monocarboxylic acids or dicarboxylic acids having at least one
ethylenic unsaturation, or derivatives thereof, f.i. anhydrides or
esters, may be added to the coating composition. The cable thus
obtained exhibits enhanced flexibility, thermocompression
resistance and flame-retardant properties.
[0011] WO 00/39810 discloses a process for producing
self-extinguishing low smoke cables wherein the flame-retardant
coating layer is obtained by extruding a flame-retardant
composition comprising a polymer base, such as polyethylene,
polypropylene, copolymers of ethylene or propylene with
.alpha.-olefins, copolymers of ethylene with at least one ester
chosen from alkyl acrylates, alkyl methacrylates and vinyl
carboxylates, natural rubber, butyl rubber or mixtures thereof, an
inorganic flame-retardant filler such as hydroxides, hydrated
oxides, salts or hydrated salts of calcium, aluminium or magnesium
and a dehydrating agent, such as calcium oxide and zeolites. The
resulting flame-retardant layer is smooth and uniform and
substantially free of pores and succeeds in ameliorating the
mechanical properties of the coating. A coupling agent, capable of
increasing the interaction between the active groups of the
flame-retardant filler and the polymer chains, may be added in
order to enhance the compatibility between the filler and the
polymer base. This coupling agent can be, for example, a saturated
silane compound or a silane compound containing at least one
ethylenic insaturation, for instance
vinyltris(2-methoxyethoxy)silane.
[0012] WO 00/19452 discloses a low smoke, self-extinguishing
electrical cable coated with a flame-retardant composition,
comprising (a) an ethylene homopolymer or copolymer with an
.alpha.-olefin or with an ethylenically unsaturated ester, having a
density of from 0.905 to 0.970 g/cm.sup.3; (b) a copolymer of
ethylene with at least one .alpha.-olefin, and optionally with a
diene, having a density of from 0.860 to 0.904 g/cm.sup.3 and a
Composition Distribution Index (CDI) greater than 45%; and (c)
natural magnesium hydroxide in an amount such as to impart
flame-retardant properties; wherein at least one of the polymeric
components (a) and (b) contains hydrolyzable organic silane groups
grafted onto the polymer chain in order to effectively
compatibilize said components with the magnesium hydroxide. The
resulting cable shows good tensile properties with excellent
flexibility.
[0013] Self-extinguishing cables as those described above are
usually tested and used in alternating current. Quality control
tests in alternating current include measuring the variation of the
insulating constant (Ki) after having subjected the cable to an
ageing treatment in water at the working temperature.
[0014] Unexpectedly, the Applicant has found that common flame
retardant coatings which show positive results in ageing tests in
water performed in alternating current do not give equally good
performances when subjected to analogous ageing tests in water
carried out in direct current.
[0015] The Applicant has realised that the use of conventional
hydrophobic agents, such as fatty acids or short chain silanes, in
halogen-free flame retardant compositions gives unsatisfactory
results when it is requested to produce self-extinguishing cables
able to pass ageing tests in water, particularly in salt containing
water, performed in direct current. Such tests are of outstanding
importance for some applications where the cables are operated in
direct current, such as in the railway field.
[0016] Therefore, the Applicant has faced the technical problem of
how to produce cables with a flame-retardant, halogen-free coating
showing enhanced insulating properties in water or in the presence
of a moist environment, not only in alternating current but also in
direct current, without adversely affecting self-extinguishing
properties.
[0017] The Applicant has now found that it is possible to solve the
above problem by adding a peculiar organosilane to a
flame-retardant composition comprising a polymer base and an
inorganic flame-retardant filler as described hereinunder.
[0018] In a first aspect, the present invention thus relates to a
self-extinguishing cable comprising at least one conductor and at
least one flame-retardant coating, wherein the at least one
flame-retardant coating comprises:
[0019] a) at least one polymer material selected from: olefin
homopolymers, olefin copolymers, copolymers of at least one olefin
with at least one ethylenically unsaturated ester, polyesters,
polyethers, polyether/polyester copolymers, and mixtures
thereof;
[0020] b) at least one inorganic hydrated flame-retardant
filler;
[0021] c) at least one silane substituted with at least one
C.sub.10-C.sub.40 hydrocarbon group and with at least one
hydrolysable group.
[0022] Preferably, the polymer material in the flame-retardant
coating of the self-extinguishing cable of the invention is
selected from: polyethylene; copolymers of ethylene with at least
one .alpha.-olefin containing from 3 to 12 carbon atoms, and
optionally with at least one diene containing from 4 to 20 carbon
atoms; polypropylene; thermoplastic copolymers of propylene with
ethylene and/or at least one .alpha.-olefin containing from 4 to 12
carbon atoms; copolymers of ethylene with at least one ester
selected from alkyl acrylates, alkyl methacrylates and vinyl
carboxylates, wherein the alkyl and the carboxylic groups comprised
therein are linear or branched, and wherein the linear or branched
alkyl group may contain from 1 to 8, preferably from 1 to 4, carbon
atoms, while the linear or branched carboxylic group may contain
from 2 to 8, preferably from 2 to 5, carbon atoms; and mixtures
thereof.
[0023] With ".alpha.-olefin" it is generally meant an olefin of
formula CH.sub.2.dbd.CH--R, wherein R is a linear or branched alkyl
having from 1 to 10 carbon atoms. The .alpha.-olefin can be
selected, for example, from propylene, 1-butene, 1-pentene,
4-methyl-1-pentene, 1-hexene, 1-octene, 1-dodecene and the like.
Among them, propylene, 1-butene, 1-hexene and 1-octene are
particularly preferred.
[0024] With "diene" it is generally meant:
[0025] a linear, conjugated or non-conjugated diolefin having from
4 to 20 carbon atoms, for example 1,3-butadiene, 1,4-hexadiene or
1,6-octadiene;
[0026] a monocyclic or polycyclic diene having from 4 to 20 carbon
atoms, for example 1,4-cyclohexadiene, 5-ethylidene-2-norbornene,
5-methylene-2-norbornene, 5-vinyl-2-norbornene.
[0027] More preferably, the polymer material is selected from
copolymers of ethylene with at least one (.alpha.-olefin containing
from 3 to 12 carbon atoms, and optionally with at least one diene
containing from 4 to 20 carbon atoms, obtained by single-site
catalysis.
[0028] Preferably, the inorganic hydrated flame-retardant filler is
selected from: metal hydroxides, hydrated metal oxides, metal salts
having at least one hydroxyl group, and hydrated metal salts;
particularly, the flame-retardant filler is a calcium, aluminium,
magnesium or zinc hydroxide, hydrated oxide, salt having at least
one hydroxyl group or hydrated salt.
[0029] In the flame-retardant coating of the self-extinguishing
cable of the invention, the C.sub.10-C.sub.40 hydrocarbon group
contained in the silane is preferably a C.sub.10-C.sub.40, more
preferably C.sub.12-C.sub.24, alkyl, alkenyl, aryl, alkylaryl,
arylalkyl, arylalkenyl, alkenylaryl group, whereas the hydrolysable
group is preferably a C.sub.1-C.sub.16 alkoxy group, optionally
substituted by at least one C.sub.1-C.sub.16 alkoxy group.
[0030] According to a preferred embodiment, the silane may have the
following formula:
Y.sub.4-(x+z)SiR.sub.xR'.sub.z (I)
[0031] wherein:
[0032] x is 1, 2 or 3; z is zero, 1 or 2; with the proviso that x+z
is not higher than 3;
[0033] Y, equal or different from each other, are C.sub.1-C.sub.8,
preferably C.sub.1-C.sub.4, alkoxy groups, optionally substituted
by at least one C.sub.1-C.sub.8, preferably C.sub.1-C.sub.4, alkoxy
group;
[0034] R, equal or different from each other, are selected
from:
[0035] C.sub.10-C.sub.40, preferably C.sub.12-C.sub.24, more
preferably C.sub.14-C.sub.20 alkyl groups, optionally substituted
by at least one C.sub.6-C.sub.14 aryl group;
[0036] C.sub.10-C.sub.40, preferably C.sub.12-C.sub.24, more
preferably C.sub.14-C.sub.20 alkenyl groups, optionally substituted
by at least one C.sub.6-C.sub.14 aryl group;
[0037] C.sub.6-C.sub.14, preferably C.sub.6-C.sub.10, aryl groups,
optionally substituted by at least one C.sub.1-C.sub.30 alkyl group
and/or by at least one C.sub.2-C.sub.30 alkenyl group;
[0038] with the proviso that each of R has from 10 to 40 carbon
atoms;
[0039] R', equal or different from each other, are selected
from:
[0040] hydrogen;
[0041] C.sub.1-C.sub.20, preferably C.sub.1-C.sub.16, more
preferably C.sub.1-C.sub.12 alkyl groups, optionally substituted by
at least one C.sub.6-C.sub.14 aryl group;
[0042] C.sub.2-C.sub.20, preferably C.sub.2-C.sub.16, more
preferably C.sub.2-C.sub.12 alkenyl groups, optionally substituted
by at least one C.sub.6-C.sub.14 aryl group;
[0043] C.sub.6-C.sub.14 aryl groups, optionally substituted by at
least one C.sub.1-C.sub.20 alkyl group and/or by at least one
C.sub.2-C.sub.20 alkenyl group.
[0044] According to a particularly preferred embodiment, in formula
(I) x is 1; z is zero; Y, equal or different from each other, are
selected from C.sub.1-C.sub.4 alkoxy group, optionally substituted
by at least one C.sub.1-C.sub.4 alkoxy group, f.i. methoxy, ethoxy
or methoxyethoxy group; R is a C.sub.14-C.sub.20 alkyl, f.i.
hexadecyl or octadecyl group.
[0045] In a second aspect, the present invention concerns a
flame-retardant composition comprising:
[0046] a) at least one polymer material selected from: olefin
homopolymers, olefin copolymers, copolymers of at least one olefin
with at least one ethylenically unsaturated ester, polyesters,
polyethers, polyether/polyester copolymers, and mixtures
thereof;
[0047] b) at least one inorganic hydrated flame-retardant
filler;
[0048] c) at least one silane substituted with at least one
C.sub.10-C.sub.40 hydrocarbon group and with at least one
hydrolysable group.
[0049] Examples of polymer materials that may be used in the
self-extinguishing cables and flame-retardant compositions of the
invention are: high-density polyethylene (HDPE) (d=0.940-0.970
g/cm.sup.3), medium-density polyethylene (MDPE) (d=0.926-0.940
g/cm.sup.3), low-density polyethylene (LDPE) (d=0.910-0.926
g/cm.sup.3); linear low-density polyethylene (LLDPE) and
ultra-low-density polyethylene (ULDPE) (d=0.860-0.910 g/cm.sup.3) ;
polypropylene (PP); thermoplastic copolymers of propylene with
ethylene; ethylene/vinyl acetate (EVA) copolymers; ethylene/ethyl
acrylate (EEA) copolymers, ethylene/butyl acrylate (EBA)
copolymers; ethylene/.alpha.-olefin rubbers, in particular
ethylene/propylene rubbers (EPR), ethylene/propylene/diene rubbers
(EPDM); and mixtures thereof.
[0050] Copolymers which are particularly preferred are those which
can be obtained by copolymerization of ethylene with at least one
.alpha.-olefin containing from 3 to 12 carbon atoms, and optionally
with at least one diene, in the presence of a single-site catalyst,
in particular a metallocene catalyst or a constrained geometry
catalyst. These copolymers are characterized by a density of
between 0.860 and 0.904 g/cm.sup.3, preferably from 0.865 to 0.902
g/cm.sup.3, and by a Composition Distribution Index (CDI) greater
than 45%, said index being defined as the percentage by weight of
the copolymer molecules having an .alpha.-olefin content of up to
50% of the total average molar content of .alpha.-olefin. These
copolymers preferably have the following monomer composition: 75-97
mol %, preferably 90-95 mol %, of ethylene; 3-25 mol %, preferably
5-10 mol %, of .alpha.-olefin; 0-5 mol %, preferably 0-2 mol %, of
a diene. The .alpha.-olefin is preferably selected from propylene,
1-butene, 1-hexene, 1-octene and the like. Products of this type
are commercially available under the tradenames Engage.RTM. from Du
Pont-Dow Elastomers and Exact.RTM. from Exxon Chemical.
[0051] The ethylene copolymers obtained by single-site catalysis
are preferably used as a mixture with a crystalline propylene
homopolymer or copolymer, as described, for example, in the above
mentioned WO 99/05688, or with an ethylene homopolymer or copolymer
which has a density of between 0.905 and 0.970 g/cm.sup.3,
preferably between 0.910 and 0.940 g/cm.sup.3, as described, for
example, in WO 00/19452 or, alternatively, in U.S. Pat. No.
5,707,732. In particular, the polymer material preferably comprises
from 5 to 60% by weight, more preferably from 10 to 45% by weight,
of a propylene or ethylene homopolymer or copolymer as defined
above, and from 40 to 95% by weight, more preferably from 55 to 90%
by weight, of an ethylene copolymer obtained by single-site
catalysis as defined above, the percentages being relative to the
total weight of the polymeric components.
[0052] Examples of inorganic hydrated flame-retardant fillers which
may be used in the self-extinguishing cables and flame-retardant
compositions of the invention are: magnesium hydroxide, alumina
trihydrate, hydrated magnesium carbonate, hydrated calcium,
magnesium carbonate, 4ZnO.B.sub.2O.sub.3.H.sub.2O,
2ZnO.3B.sub.2O.sub.3.3.5H.sub.2O , or mixtures thereof. Magnesium
hydroxide is particularly preferred, since it is characterized by a
decomposition temperature of about 340.degree. C. and thus allows
high extrusion temperatures to be used. It is more particularly
preferred to use magnesium hydroxide of natural origin, obtained by
grinding minerals based on magnesium hydroxide, such as brucite or
the like, as described in WO 99/05688.
[0053] The flame-retardant filler is generally used in the form of
particles which are untreated or surface-treated with saturated or
unsaturated fatty acids containing from 8 to 24 carbon atoms, or
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. In order to increase the
compatibility with the polymer material, the flame-retardant filler
can likewise be surface-treated with suitable coupling agents, for
example short chain organic silanes or titanates such as
vinyltriethoxysilane, vinyltriacetylsilane, tetraisopropyl
titanate, tetra-n-butyl titanate and the like.
[0054] The amount of flame-retardant filler to be added is
predetermined so as to obtain a cable which is capable of passing
flame/fire-propagation tests, particularly those according to
standard IEC 332-1 or IEC 332-3 A,B,C. In general, this amount is
between 10 and 90% by weight, preferably between 30 and 80% by
weight, relative to the total weight of the flame-retardant
composition.
[0055] The silanes above defined as component c) of the
flame-retardant coating of the cable of the invention are
preferably in an amount from 0.1% to 10%, preferably 0.5% to 5% by
weight with respect to the total weight of the inorganic
flame-retardant filler. Examples of silanes which are suitable for
the cable and composition of the invention are:
hexadecyltrimethoxysilane, hexadecyltriethoxysilane,
octadecyltrimethoxysilane and octadecyltriethoxysilane.
[0056] A coupling agent capable of increasing the interaction
between the active hydroxyl groups of the flame-retardant filler
and the polymer chains may be added to the mixture in order to
enhance the compatibility between the flame-retardant filler and
the polymer material. This coupling agent can be selected from
those known in the art, for example: short chain saturated silane
compounds or silane compounds containing at least one ethylenic
unsaturation; epoxides containing an ethylenic unsaturation;
monocarboxylic acids or, preferably, dicarboxylic acids having at
least one ethylenic unsaturation, or derivatives thereof, in
particular anhydrides or esters.
[0057] Examples of short chain silane compounds which are suitable
for this purpose are: .gamma.-methacryloxypropyltrimethoxysilane,
allyltrimethoxysilane, allyltriethoxysilane,
allylmethyldimethoxysilane, allylmethyldiethoxysilane,
methyltriethoxysilane, methyltris (2-methoxyethoxy)silane,
dimethyldiethoxysilane, vinyltris (2-methoxyethoxy)silane,
vinyltrimethoxysilane, vinyl methyldimethoxysilane,
vinyltriethoxysilane, octyl triethoxysilane,
isobutyltriethoxysilane, isobutyl trimethoxysilane and the like, or
mixtures thereof.
[0058] Examples of epoxides containing an ethylenic unsaturation
are: glycidyl acrylate, glycidyl methacrylate, monoglycidyl ester
of itaconic acid, glycidyl ester of maleic acid, vinyl glycidyl
ether, allyl glycidyl ether and the like, or mixtures thereof.
[0059] Monocarboxylic or dicarboxylic acids, having 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 anhydrides or esters derived
from these, or mixtures thereof. Maleic anhydride is particularly
preferred.
[0060] The coupling agents can be used as they are or pre-grafted
onto a polyolefin, for example polyethylene or copolymers of
ethylene with an .alpha.-olefin, by means of a radical reaction
(see for example EP-A-530,940). The amount of pre-grafted coupling
agent is generally between 0.05 and 5 parts by weight, preferably
between 0.1 and 2 parts by weight, relative to 100 parts by weight
of polyolefin. Polyolefins pre-grafted with maleic anhydride are
available as commercial products known, for example, under the
brand names Fusabond.RTM. (Du Pont), Orevac.RTM. (Elf Atochem),
Exxelor.RTM. (Exxon Chemical), Yparex.RTM. (DSM), etc.
[0061] Alternatively, the coupling agents of carboxylic or epoxide
type mentioned above (for example maleic anhydride) or the short
chain silanes with 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. An organic peroxide such as
tert-butyl perbenzoate, dicumyl peroxide, benzoyl peroxide,
di-tert-butyl peroxide and the like, can, for example, be used as
initiator. This method is described, for example, in patent U.S.
Pat. No. 4,317,765, in Japanese patent application JP-62-58774 or
alternatively in the above mentioned WO 99/05688 and WO
00/19452.
[0062] The amount of coupling agent to be added to the mixture can
vary mainly depending on the type of coupling agent used and on the
amount of flame-retardant filler added, and is generally between
0.01 and 5%, preferably between 0.05 and 2%, by weight relative to
the total weight of the polymer material mixture.
[0063] Conventional antioxidants which are suitable for this
purpose are, for example:
[0064] polymerized trimethyldihydroquinoline, 4,4'-thiobis
(3-methyl-6-tert-butyl)phenol; pentaerythryl
tetra-[3-(3,5-di-tert-butyl-- 4-hydroxyphenyl)propionate],
2,2'-thiodiethylene bis[3-(3,5-di-tert-butyl--
4-hydroxy-phenyl)propionate] and the like, or mixtures thereof.
[0065] Other fillers which may be used in the present invention
include, for example, glass particles, glass fibres, calcined
kaolin, talc and the like, or mixtures thereof. Processing
co-adjuvants 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. Another
component that may be added to the flame-retardant composition and
cables according to the present invention is at least one
dehydrating agent, such as calcium oxide or a zeolite, generally in
an amount of from 0.5 to 15% by weight with respect to the weight
of the flame retardant filler, as described in the above-mentioned
patent application WO 00/39810.
[0066] The flame-retardant compositions according to the present
invention are preferably used in non-crosslinked form, in order to
obtain a coating with thermoplastic properties which is thus
recyclable.
[0067] The flame-retardant compositions according to the present
invention can be prepared by mixing the components a), b) and c) as
above defined together with the other additives which may be
present according to techniques known in the art, for example using
an internal mixer of the type containing tangential rotors
(Banbury) or interpenetrating rotors, or in continuous mixers of
the Ko-Kneader (Buss) type or of the co-rotating or
counter-rotating twin-screw type.
[0068] As an alternative, the flame-retardant compositions of the
invention can be prepared by treating component b) with component
c) as above defined and then mixing the resulting mixture with
component a) as above defined.
[0069] As a further alternative, rather than adding the component
c) as above defined during the phase of preparation of the
flame-retardant composition, it can be added during the deposition
by extrusion of the flame-retardant coating to produce the cable,
for example via the extruder hopper or by injection into the
extruder cylinder.
[0070] The component c) as above defined may be added to the
flame-retardant composition as such (usually in the form of a
liquid), or supported on a solid inert carrier, or also
predispersed in a polymer material, such as one of those described
above as component a).
[0071] During the extrusion phase, the flame-retardant compositions
thus obtained can be used to coat the conductor directly, or to
make an outer sheath on the conductor which has been precoated with
an insulating layer. When two layers are present, the extrusion can
take place in two separate phases, the inner layer being extruded
on the conductor in a first passage and the outer layer being
extruded on the inner layer in a second passage. Advantageously,
the coating process can take place in a single passage, for example
by means of the "tandem" technique, in which two separate extruders
arranged in series are used, or alternatively by co-extrusion with
a single extrusion head.
[0072] The temperature at which the flame-retardant composition is
extruded can vary within a wide range and is predetermined as a
function of the extrusion rate to be obtained. The extrusion rate
in fact depends on the viscosity of the composition in the molten
state and thus on its temperature. In turn, the viscosity depends
mainly on the type of polymer material and on the type and amount
of flame-retardant filler used. The minimum extrusion temperature
for the composition is generally not less than the plasticization
temperature of the polymer material, while the maximum extrusion
temperature is predetermined so as to avoid degradation or
decomposition of the polymer material and/or of the flame-retardant
filler. Thus, on the basis of the abovementioned criteria, in the
case of flame-retardant compositions based on a mixture of
polypropylene and ethylene/.alpha.-olefin copolymers as described
above, in which magnesium hydroxide is used as flame-retardant
filler, the temperature at which the flame-retardant composition is
extruded is generally between 160.degree. C. and 320.degree. C.,
preferably between 200.degree. C. and 280.degree. C.
[0073] Some examples of embodiments will now be reported for the
purpose of illustrating the present invention more clearly, with
particular reference to the accompanying drawings, in which:
[0074] FIG. 1 is a cross-section of a low voltage cable of the
unipolar type according to the invention;
[0075] FIG. 2 is a cross-section of another low voltage cable of
the unipolar type according to the invention;
[0076] FIG. 3 is a cross-section of a low voltage cable of the
tripolar type according to the invention.
[0077] "Low voltage" generally means a voltage lower than 5 kV,
preferably lower than 2 kV, more preferably lower than 1 kV.
[0078] With reference to FIG. 1, a self-extinguishing cable (1) of
the unipolar type, in particular for low voltage electric energy
distribution, comprises: a conductor (2), an inner layer having
electric insulating function (3) and an outer layer (4) having the
function of a protective sheath with flame retardant properties
consisting of the composition according to the present
invention.
[0079] The inner layer (3) can be made of a polymer material,
either cross-linked or non cross-linked, preferably halogen-free,
having electric insulation properties. The polymer material can be
selected, for instance, from: polyolefins, (omopolymers or
copolymers of different olefins), copolymers ethylene/unsaturated
esters, polyesters, polyethers, copolymers polyethers/polyesters,
and mixtures thereof. Examples of such polymers are: polyethylene
(PE), particularly linear low density PE (LLDPE); polypropylene
(PP); thermoplastic copolymers propylene/ethylene; elastomeric
copolymers ethylene-propylene (EPR) or ethylene-propylene-diene
(EPDM); copolymers ethylene/vinylacetate (EVA); copolymers
ethylene/methylacrylate (EMA); copolymers ethylene/ethylacrylate
(EEA); copolymers ethylene/butylacrylate (EBA); copolymers
ethylene/alpha-olefin, and the like. The inner layer (3) may also
be a flame-retardant coating obtained e.g. from a flame-retardant
composition according to the present invention.
[0080] Alternatively, referring to FIG. 2, a self-extinguishing
cable (1) of the unipolar type, particularly for the distribution
of low voltage electric energy, can be made of a conductor (2)
directly coated with the flame-retardant composition above
described so as to form an outer layer (4) having flame retardant
properties, without interposing other insulating layers. In this
way, the outer layer (4) works also as electric insulation
layer.
[0081] A thin polymer layer (not shown in the figures) having an
antiabrasive function may also be externally applied.
[0082] A pigment may be added to the material forming the outer
layer (4) or the antiabrasive layer in order to provide the cable
with a specific colouring for identification purposes.
Alternatively, the cable can be identified by a thin coloured strip
which may be applied externally.
[0083] With reference to FIG. 3, a self-extinguishing cable (1) of
the tripolar type, in particular for the distribution of low
voltage electric energy, comprises three conductors (2), each one
coated with an insulating layer (3), two of which being the phase
conductors, one being the neutral conductor. The insulating layers
(3) may consist of an insulating polymer material selected from the
ones above indicated. Alternatively, the insulating layers (3) may
consist of a common flame retardant composition, or even of a flame
retardant composition according to the present invention. The so
insulated three conductors (2) are stranded together and the
interstices among one conductor and the other are filled with a
material (5), preferably having flame retardant properties as well,
so as to form a continuous structure having a substantially
cylindrical form. An external sheath (6) comprising the flame
retardant composition according to the invention is then applied on
such a structure.
[0084] FIGS. 1-3 show only some possible embodiments of a cable
according to the invention. It is evident that suitable
modifications known in the art can be made in those embodiments,
but without departing from the scope of the invention. In
particular, the flame retardant composition of the invention can
also be advantageously used for coating telecommunications or data
transmission cables, , including optical fibre cables, or even
mixed energy/telecommunications cables.
[0085] The following examples are given to illustrate the invention
without limiting it.
EXAMPLE 1
[0086] Some accelerated ageing tests in water containing dissolved
NaCl were carried out on cable specimens as described
hereinbelow.
[0087] The following flame-retardant composition was used as a
reference (hereinafter: the reference mixture):
[0088] 85 phr Engage.RTM. 8003--ethylene-octene copolymer obtained
by single-site catalysis (Du Pont-Dow Elastomers);
[0089] 210 phr Hydrofy.RTM. G 1.5--natural magnesium hydroxide,
obtained by grinding brucite, not surface-treated (NUOVA SIMA);
[0090] 0.40 phr Luperox.RTM. DC40--peroxidic initiator: dicumyl
peroxide (Atofina);
[0091] 2.10 phr Silquest.RTM. A-172--coupling agent:
vinyltris(2-methoxyethoxy)silane (VTMOEO) (Witco);
[0092] 15 phr Moplen.RTM. EP1X35F--random crystalline
propylene-ethylene copolymer: d=0.900 g/cm.sup.3; MFI=9.0 g/10';
T.sub.2m=154.degree. C.; .DELTA.H.sub.2m=90.6 J/g (Basell);
[0093] 0.8 phr Irganox.RTM. 1010--antioxidant: pentaerythryl
tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]
(Ciba-Geigy);
[0094] 0.3 phr Irganox.RTM. MD1024--metal deactivator:
1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine
(Ciba-Geigy);
[0095] 6.10 phr Kezadol.RTM. GR--calcium oxide predispersed in
semicrystalline EPR rubber (80% by weight of CaO), in the form of
granules with average diameter 6-7 .mu.m (Kettlitz).
[0096] The amounts of the various components are expressed as phr
(parts by weight per 100 parts by weight of polymer material).
[0097] The above reference mixture was supplemented with
hydrophobic additives as reported in Table 1 (the amounts of
additives are expressed as % by weight with respect to the weight
of flame retardant filler).
[0098] The above flame-retardant compositions were prepared by
using a Banbury mixer and then deposited by means of a Bandera 45
extruder onto a copper conductor having a 1.5 mm.sup.2 section, to
obtain a cable having a flame-retardant coating of 0.7 mm
thickness.
[0099] Two separate tests in direct current were carried out on the
so obtained cables according to the conditions illustrated
herebelow:
[0100] (1) cables immersed in a 10 g/l NaCl solution at 60.degree.
C.; negative pole connected to conductors, positive pole inside the
solution; 3 kV direct current, applied for 5 minutes with 2 h
intervals.
[0101] (2) cables immersed in a 10 g/l NaCl solution at 60.degree.
C.; negative pole connected to conductors, positive pole inside the
solution; 1 kV direct current, applied for 30 minutes with 12 h
intervals.
[0102] The time (in hours) after which the cables short-circuited
is reported in Table 1 [t.sub.1 for test (1) and t.sub.2 for test
(2)].
1TABLE 1 SAMPLE t.sub.1 (h) t.sub.2 (h) REF. MIX.* 72 20 1* 120 26
2 216 50 3* 120 28 * = comparative REF. MIX. = reference mixture; 1
= REF. MIX. + 2% by weight of stearic acid; 2 = REF. MIX. + 2% by
weight of Dynasylan .RTM. 9116 (esadecyltrimethoxy silane); 3 =
REF. MIX. + 2% by weight of KR TTS (isopropyltriisostearyl
titanate).
[0103] The results reported in Table 1 show that the time needed to
short-circuit the cable specimens changes by varying the test
conditions, the performance of cable 2 being remarkably better than
that of cables 1 and 3.
EXAMPLE 2
[0104] The test in direct current applying a voltage of 1 kV for 30
minutes every 12 hours, which is closer to the operation conditions
of a cable, was repeated using for the flame-retardant coating the
same reference mixture of Example 1, by changing either the amount
of added VTMOEO or by adding different hydrophobic additives as
reported in Table 2 (the amounts of VTMOEO and of hydophobic
additives being expressed as % by weight with respect to the filler
weight).
2TABLE 2 VTMOEO HYDROPHOBIC ADDITIVE t SPECIMEN (% weight) (%
weight) (h) REF. MIX.* 1.0 -- 72 1* 2.0 -- 96 2* 3.0 -- 120 3* 1.0
2.0 STEARIC ACID 120 4 1.0 2.0 DYNASYLAN .RTM. 9116 216 * =
comparative; REF. MIX. = Reference mixture; 1 = REF. MIX. + 2%
VTMOEO; 2 = REF. MIX. + 3% VTMOEO; 3 = REF. MIX. + 2% stearic acid;
4 = REF. MIX. + 2% Dynasylan .RTM. 9116; t = 1 kV for 30 min every
12 hours.
[0105] From the above results, it is apparent that the silanes
suitable for the cable of the invention, among the tested
additives, allow to obtain the best results in direct current;
further, it can be noted that such silanes are better than short
chain silanes currently used, the amounts thereof being equal.
* * * * *