Flame retardant plenum cable
View Patent ↗The present invention is a flame retardant cable having an insulated conductor and at least two insulation layers. The cable demonstrates a composite dielectric constant less than or equal to about 2.6 and a composite dissipation factor less than or equal to 0.005 even though one of the insulation layers has a dielectric constant greater than 2.6 or a dissipation factor greater than 0.005. The presently invented cable is achieved with a non-halogenated polyolefin as an insulation layer polymer, where the polyolefin having relatively poor dielectric/dissipative properties and the insulation layer composition being substantially free of halogenated or antimony trioxide flame retardant additives.
1. A flame retardant cable comprising:
an insulated conductor which comprises
(a) a conductor;
(b) an inner insulation layer surrounding the conductor; and
(c) an outer insulation layer surrounding the inner insulation layer,
wherein the insulated conductor having a composite dielectric constant less than or equal to 2.6 and a composite dissipation factor of less than or equal to 0.005, and wherein the inner insulation layer or the outer insulation layer has a dielectric constant greater than 2.6 or a dissipation factor greater than 0.005.
2. The cable as recited in claim 1 where the inner insulation layer, the outer insulation layer, or both insulation layers are foamed.
3. The cable as recited in claim 1 , comprising four twisted pairs of the insulated conductor and a plenum-rated jacket material.
4. A flame retardant cable comprising:
an insulated conductor which comprises
(a) a conductor;
(b) an inner insulation layer surrounding the conductor; and
(c) an outer insulation layer surrounding the inner insulation layer,
wherein the insulated conductor having a composite dielectric constant less than or equal to about 2.6 and a composite dissipation factor of less than or equal to 0.005, and wherein a first polymeric composition for preparing the inner insulation layer comprises a first non-halogenated polymer and being substantially-free of halogenated flame retardant additives or antimony oxide and a second polymeric composition for preparing the outer insulation layer comprises a second non-halogenated polymer and being substantially-free of halogenated flame retardant additives or antimony oxide.
5. The cable as recited in claim 4 , wherein the first polymeric composition further comprises non-halogenated flame retardant additives in an amount no more than 30 parts per hundred parts of the first non-halogenated polymer by weight and the second polymeric composition further comprises non-halogenated flame retardant additives in an amount between 100 to 300 parts per hundred parts by weight of the second non-halogenated polymer by weight.
6. The cable as recited in claim 5 , wherein the non-halogenated flame retardant additives are selected from the group consisting of ethylene diamine phosphate, melamine, melamine pyrophosphate, melamine phosphate, ammonium polyphosphate, melamine polyphosphate, calcium carbonate, talc, clay, organo-modified clay, calcium hexaborate, alumina, titanium oxides, carbon nanotubes, zinc borate, wollastonite, mica, silicone polymers, phosphate esters, hindered amine stabilizers, melamine octomolybdate, ammonium octomolybdate, expandable graphite, frit, hollow glass beads, and mixtures thereof.
7. The cable as recited in claim 6 , wherein the insulated conductor has two layers which have a composite dielectric constant (∈ t ) and a composite dissipation factor (tan δ t ) defined by the following
ɛ
t
=
ɛ
1
ɛ
2
1
n
(
r
2
r
0
)
ɛ
2
1
n
(
r
1
r
0
)
+
ɛ
1
1
n
(
r
2
r
1
)
and
tan
δ
t
=
tan
δ
1
ɛ
1
1
n
(
r
1
r
0
)
[
tan
δ
1
2
+
1
]
+
tan
δ
2
ɛ
2
1
n
(
r
2
r
1
)
[
tan
δ
2
2
+
1
]
1
ɛ
1
1
n
(
r
1
r
0
)
[
tan
δ
1
2
+
1
]
+
1
ɛ
2
1
n
(
r
2
r
1
)
[
tan
δ
2
2
+
1
]
where ∈ 1 and ∈ 2 are the dielectric constants of the inner and outer insulation layers, respectively, and r 0 is the radius of the conductor; r 1 is the sum of r 0 and the thickness of the inner insulation layer; and r 2 is the sum of r 1 plus the thickness of the outer insulation layer; and where tan δ 1 and tan δ 2 are the dissipation factors of the inner and outer insulation layers, respectively.