Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This inven-tion rela-tes to polymeric composi-tions
comprising bromine~containiny flame :retardants, and to
their use, especially for insulating electrical components,
particularly wire and cable.
It is known to provide electrical wire and cable with
an electrically insulating covering by coating the wire or
cable with a polymeric composition which contains a
chlorinated flame retardant, and an unsaturated compound
which promotes cross-linking (a "co-agent"), and then cross-
linking the coating by heat. While brominated flame
retardants are also known, they have not been used in
compositions which are cross-linked by peroxides, because
the resulting cross-linked compositions have absorbed water
too rapidly (i.n particular they have IPCEA water absorptions
of greater than 3%) and therefore have unsatisfactory
electrical characteristics.
I'his invention is based on the surprising discovery
that by increasing the amount of co-agent and reducing the
amount of peroxide in cross-linkable polymeric compositions
containing bromine-containing organic flame retardants, a
very significant reduction in the water absorption of the
resulting cross-Iinked compositions is obtained, and in
particular that compositions meeting the accepted industry
stanlards can Feadily be obtained.
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In its first aspect, the i.nvent.ion provides a
composlt:ion which can be cross-linked by hea-tiny and
which comprises:
(a) a polymer which can be cross-linked with the
aid of an organic peroxide,
(b) an organic peroxide,
(c) a compound which contains carbon-carbon
unsaturation and which co-operates with said
peroxide, when the composition is heated, to
promote cross-linking of said polymer;
and
(d) a bromine-containing organic flame retardant,
the ratlo by weight o~ the unsaturated compound (c) to the
peroxide (b) being at least 1.2:1.
In its second aspect, -the invention provides a process
for the production o-f a shaped article o-f a cross-linked
polymer composition, which process comprises
(1) melt-shaping a composition which comp:rises
(a) a polymer which can be cross-linked with
~o the aid of an organic peroxide1
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(b) an organic peroxide;
(c) a compound which contai.ns carbon-carbon
unsaturation, which cooperates with said
peroxide, when the composition is heated,
to promote cross-linking of said polymer;
and
(d) a bromine~containing flame retardant.
said melt~shaping being carried out under conditions such
that cross-linkiny of said composition is substantially
prevented, and
(2) heating said melt-shaped composition to
effect cross-linking of the polymer, the
absolute and relative amounts of said per-
oxide (b) and said compound (c) being such
that the shaped articIe has an Mloo value
of at least 40 and a change in capacitance
over 14 days in the IPCEA Test No. S-66-524,
NEMA WC 7, paragraph 6.6, of less than 3%.
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;~ In its third aspect the invention provides an
: article having a~coating thereon comprising (i) a polymer
;: which has been cross-linked with the aid of an organic
peroxide and a compound ~ch contai~s carbon-carbon
~25 unsaturation, and (ii) a bromine-containing organic flame
retardant, said coating having a change in capac.itance over:
14 days in the IPCEA Test No. S-66-524, NEMA WC 7, paragraph
: 6.6, of less than 3%~
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The polymers which can be used ln the present
inven-tion include polymers of one or more olefins
polymers of one or more olefins with one or more
copolymerisable ethylenically unsaturated monomers
containing fun~tional groups, such polymers preferably
containing at least 50%, especially at least 80%, by
weight of units derived from one or more olefins, and
polymers of one or more ethylenically unsaturated
monomers containing functional groups, and blends o~ one
or more such polymers, such blends preferably containiny
at least 50%, especially at least 80%, by weight, of
units derived from one or more olefins. Particularly
suitable olefins are -mono-olefins, especially
ethylene, Functional groups which may be present on
ethylenically unsaturated monomers include acid groups
e.g., carboxyl groups and carboxylate salt groups, ester
groups, e.g., alkoxy carbonyl groups, alkyl carbonyloxy
groups, and halogen atoms, The choice of polymer will,
of course, depend upon the end use of the composition.
When the composition is used to produce insulation on
; electrical wire or cable by extrusion coating, preferred
~ compositions comprise a blend of a low density
-~ polyethylene and an ethylene/vinyl acetate copolymer,
;~ preferably containing 10 to 30% by weight of units
derived from vinyl acetate, in a ratio by weight of
polyethylene to copolymer of at least 30:70~ e.g., 40:60
to 60:40. Particularly good results are obtained using a
blend of about equal parts of a low density polyethylene.
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and an ethylene~vinyl acetate copolymer~ The compo~ition~
of the invention will generally contain at lea~t ~%,
preferably a-k lea~t 5~/0, especially 50 to 80~o~ e.g. about 6~/~,
by weight of thc polymer.
The bromine~containing organic fire retardants used
in thi~ invention are preferabl~f aromatic buk may be ali,phatic.
The ~ire retardant should, of course, be one w~i.ch will be e~ec-
~îve even after the composition has been sha,ped and cro~.~ llnked
by hea~ing. Particularly good results have been obtained u~ing
~acabromo-diphenylethe.r. r~hi~ and other brominated compound~
are known in the art as flame retardant~. The ~lame retardant
may be one which becomes at lea~t in part chemically bonded ~,
to the polymer duriny khe cross linking~ Especially when the
bromine~containing organic fire retardant i~ the sole fir,e
retardant, the amount thereo~ will generally b~ at least 1~ol
pre~erably at lea~t 15%, particularly at least 2~%, by weight
o~ the composition~ Si~ce exces~ive amounts of the fire
retardant can cause poor physical propertie~, amount~ in
excess o~ 35~/0 are generally avoided 7
The composition3 may contai~ other ~lame-retardant~, '
for example, inorganic fire retardant~, which may ~a present in
~ub~tantial amount, e.~. up to 20~o~ preferably 5 to 15%o
weight of the compo~ition. Especially u~e~uI are ~lame
~ xetardant~ which are known to demon~trate a synergi3tic ef~ec~
wit'n halogenated flame retardants, e~g. antimony compound~,
e9pecially Sb203. Chlorinated fire re~ardant~ may al50 be
present, but the brominated fire retarda~lt pr~ferably provi.de~
50 to 100% Ps~?ecially 80 ~o l OO%, of ~he total wei~ht o~ organic
`-` fire retard~nts in tl~e compo~;ition and i~ usually present in an
30 amount at lea~3t 5% ;~y weight of the compo~i~ion~.
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The composltions may also con-tain other inyredients
such as fillers, processing aids and stabilisers, for
example acid scavengers such as lead fumerate and free
radical scavengers such as aromatic secondary arnines
The amount of such other ingredients will generally not
exceed 10%, preferably 5%, by weight o~ compositions to
be used for extrusion-coating as insulation on-to wire or
cable.
The organic peroxides used in this invention are
those conventionally used in the art, the choice of proxide
being dependent inter alia on the temperature at which the
composition is to be shaped (at which decomposition of the
pe~roxide should be sufficiently slow not to interfere with
the shaping operation) and the temperature (and, especially
in a continuous process, the time) of the subsequent cr~ss-
linking step, during which rapid decomposition of the
peroxide is desirable. The peroxides which can be used -
include dicumyl peroxide and 2,5-dimethyl-2,5-di-t-butyl-
peroxyhexane.
The compounds (c) which contain carbon-carbon
unsaturation and which cooperate with the peroxides to
promote cross-linking are referred to herein as co-agents.
The co-agents which can be used are the compounds which
; have been widely used to promote cross-lin~ng in
; 25 irradiation cross-linking procedures. Generally they contain
at least two ethylenic double bonds. Examples of suitable
compounds are triallyl isocyanurate, pentaerythritol
triacrylate and pentaerythritol tetraacrylate~ ~
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The hlgher the ratio of the co-ayent to -the peroxide,
-the les.s the water absorp-tion of the croa,s-lin~d composition.
The ra-tio by weight is preferably ak least 1.2:1, parti-
cularly at least 1.5:1, especially at least 2.5:1. This
ratio is preferably not more than 10:1 especially not more
than 7.5:1, in order to ensure an adequate amount of peroxide.
The total amount of peroxide and co-agent preferably
employed is dependent on the cross~linking conditions and the
degree of cross-linking required. This amount is generally 1
to 8%, preferably 2 to 5%, by weight of the composition.
The ingredients of the composition are thoroughly
mixed together by any convenien-t me-thod, taking care not to
activate the peroxide. The composition is then shaped prior
to being cross-linked. Shaping is preferably effected by melt
extrusion or other melt-shaping method at a temperature at
which decomposition of the peroxide is sufficiently slow that
any cross-linking that takes place does not interfere with
the shaping operation. Cross-linking is then effected, gener-
ally by raising the temperature. The temperatures employed
in these steps will depend upon the polymer and the peroxide.
In a preferred procedure, the composition is continuously
melt-extruded through a cross-head die onto a wire, and is
continuously cross-linked by passing the coated wire through
an oven. Generally, the wire size is 1000 MCM to 20 AWG,
preferably 2/0 to 16 AW~, and the coating has a thickness of
15-75 mils, preferably 20-50 mils. Especially for such use,
the cross-linking should be effective to increase the M1oo
modulus (measured as described below) of the composition to at
least 30, generally at least 50, preferably at least 70,
especially at least 80. On the other hand, the M1oo modulus
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will generally not exceed 20, since this can result in
undesirably low elongations.
The invention is illustrated in the following
Examples, in which parts are by weight.
EXAMPLE 1
In each of the Examples, the ingredients shown
in the Tabla below were thoroughl~ mixed together by
blending all the ingredients except the peroxide (B) and
the co-agent (C) in an internal batch mixer with two
counter-rotating rotors at 290F (143 C). In Examples
1-6 the peroxide (B) and the co-agent (C) were thoroughly
mixed together with the other previously blended
ingredients on a 3 inch two roller mill at 250F (120C).
In Examples 7-10 the peroxide (B) and the co~agent (C)
were thoroughly mixed together with the other previously
blended ingredients in a Banbury mixer at 250F (120C).
In Examples 1-6, the mixture was pressed into a
slab at 250F (120C), and the slab heated at 390F (200C)
for 1 minute. The M1oo value of the cured slab material
was measured using a ~ inch (0.3cm) wide strip cut from the
slab. The water absorption of the cured slab material was
also measured, using a disc cut from the slab. The results
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are shown in the Table.
~; In Examples 7-10, the mixture was extruded over a
wire and then cured at 390F (200C) for 1 minute. The
water absorption, capacitance change, stability factor and
M1oo value of the coated wire was measured, and the results
are shown in the Table.
In the Table, the Examples marked with an asterisk ~;*) -
are comparative Examples, and the various ingredients are
as identified below g
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A(:L) i.s a low dens:i-ty polyethylerle
A(2) is an ethylene/v.inylacetat:e (~ %) copolymer
B(1) is ducumyl per?xide suppor-ted on CaCO3
(40% peroxide)
B(2) is 2,5-dimethyl-2,5-di-t-butylperoxyhexane
(50% peroxide)
(C) is triallylisocyanurate (~IC)
(D) is decabrornodiphenylether
(E) is Sb203
(F) is lead f~ne~ate
(G) is an aromatic secondary amine
"Ratio" is the ratio of (C) to the peroxide
content of (s).
The various properties given in the Table for the
cured compositions were measured as follows:
100
The test specimen is suspended in a chamber
maintained at 120C + 2C and after it has equilibrated
load is applied incrementally until the specimen has
elongated 100%. The static modulus, M1oo is the slope of
a plot of load vs. elongation a-t 100% elongation and is
;~ expressed in psi.
Abs(1)
Discs cut from the cured slabs of Examples 1-6
were weighed dry. They were then immersed in water at 70C
for 65 hours, wiped dry and weighed again. The percent
weight change was calculated and is reported as Abs(1).
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The weight increase of samples of the coated wires
prepared in Examples 7-10 on exposure to water for seven
days was measured by the procedure of IPCEA Publication No.
8-19-81 NEMA WC3, paragraph 6.9.3 and is reported as Abs(2)
in mg/sq. inch.
Cap 1-14, cap 7-14 and ,Stab
The change in capacitance on exposure to water of
samples of the wlres prepared in Examples 7-10 was measured
in accordance with the procedure of IPCEA Publi.cation No.
S-66-524, NEMA WC7, paragraph 6.6. The percent change after
14 days, based on the capacitance after one day, is reported
as Cap 1-14, and the percent change between the seventh and
fourteh~nth days, based on the capacitance after seven days,
is reported as Cap 7-14. The stability factor was also
calculated and i~ reporeed as St~.
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