CA1116797A

CA1116797A - Coating composition for flame retardant cable jacket

Info

Publication number: CA1116797A
Application number: CA000348257A
Authority: CA
Inventors: John F. Porter; Dennis G. Hayashi
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1980-03-24
Filing date: 1980-03-24
Publication date: 1982-01-19

Abstract

COATING COMPOSITION FOR FLAME
RETARDANT CABLE JACKET

ABSTRACT OF THE DISCLOSURE

A composition, for use in the continuous coating of a jacketed cable to form an outer layer thereon, comprising:
at least one polymer resin, at least one filler and at least one stabilizer, proportioned whereby, on heating, the coating forms a flame retardant char.

Description

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FIELD OF THE INVENTION

This invention relates to the jacketing of cables such as electric cables and more particularly to flame retardant cable jackets.

~ACKGROUND OF THE INVENTION

Electric cables having a core of stranded conductors or the like are coated with one or more layers forming a jacket to protect the conductors from damage. One problem associated wi-th cable jackets presently in use is their combustibility. To overcome this problem flame retardants have been included in the jacketing ma-terial bu-t they serve to create another problem under exposure to flame or intense heat, namely the emission of .smoke and toxic gases (especially carbon monoxide and halogen or phosphorous containing gases). To avoid the hazard of high temperature smoke and gas emission there are presently available flame retardant sprays, pastes and wrap around tapes applicable to cables in situ for form coatings or coverings on the cable jackets. However~ these coatings or coverings reduce the flexibility of the cable twhich must be flexible to instal) especially at low temperatures and they also require additional labour to apply. me use of tapes additionally makes the cable bulky and difficult to pull through ducts and they also have a tendency to unravel.

It is an object of the present invention to provide a composition for use in the continuous coating of a jacketed cable to give flame retardancy while inhibiting the emission of smoke and toxic gases at high temperatures and retaining adequate flexibility at low temperatures.

'7~ f It is a further object of the invention to provide an improved flame retardant cable jacket having reduced emission of smoke and toxic gases at high temperatures and adequate flex-ibility at low temperatures.

STATEXENT OF THE INVENTION
-In its broadest aspect the invention consists of a composition for use in the continuous coating of a jacketed cable to fonn an outer layer thereon, comprising a polymer resin, a filler and a stabilizer, proportioned whereby on heating the coating forms a flame retardant char.
In another aspect the invention consists of a cable CQmprising a core and a jacket, the jacket campris.ing an inner layer and an outer layer comprising at least one polymer based resin, at least one filler and at least one stabilizer, propo~tioned whereby, on heating, the coating forms a flame retardant char.

DESCRIPTION OF THE DRAWINGS
.
An example embodiment of the invention is shown in the accompanying drawings in which:
Figu~e 1 is a side view, partly broken away, showing a cable jacketed according to the invention; and Figure 2 is a segmental cross-sectional view taken along line 2-2 of Figure 1.

DETAITT-~ DESCRIPTION

The example embodiment shown in the drawings consists of a cable 10 comprising (1) a core 12 which has a plurality of insulated conductors 14 bound by a core wrap 16, and (2) a jacket 18 having an inner layer 20 and an outer layer 22.

7' Inner layer 20 of jacket 18 consists of a flexible polymer based material such as polyvinylchloride (PVC). Other materials suitable for the purpose are polyolefin, polyamide or rubber, all well known in the trade and normally extruded continuously onto core 16. Outer layer 22 of ~acket 18 is also a polymer based resin with the addition of a filler and a stabilizer. The resin of the outer coating is preferably applied as a latex emulsion which also carries a surfactant although this latter ingredient is substantially lost by evaporation in the drying process. Additionally a plasticizer may be included to improve the flexibility of outer layer 22 and an anti-foam agent may be required to control the foam producing capacity of the plasticizer or the filler.
The purpose of outer layer 22 is to present a char forming outer surface of cable ~acket 18 where the flame retardant components are concentrated, thus interfering minimally with the strength a~d the cold temperature flexibility of the jacket. The generation of foam in the char formir~ outer surface under heat further enhances its effectlveness. The filler, and the plasticizer if present, are employed to generate foam. If a plasticizer is added to improve the flexibility of outer layer 22 is must be included in controlled amounts because it reduces the ultimate strength of the outer layer.
Too much foam, however, is not tolerable and for this reason it may be necessary to include an anti-foam agent in the composition used to form outer layer 22.
The ingredients of the emulsion applied to form outer layer 22 are present in the following range of proportions:

Ingredient Parts by dry wei~ht Polymer resin (as latex emulsion) 100 Plasticizer (liquid additive) 0 - 50 Ingredient Parts by dry wei~ht Fillers (flame retardant) 50 - 200 Stabilizers 0.5 - 10 Surfactants 0.5 - 2 Anti-foam agents 0 - 2.0 If a flame retardant plasticizer is not present the polymer resin is halogenated to provide flame retardancy.
The following are two specific examples of latex emulsion mixtures for applying to cable 10 to form outer layer 22:

Example I

Ingredient Parts by weight Vinyledene chloride-butadiene latex (resin) 230 parts (100 parts dry) Al~minum trihydroxide (filler) 133 Antimony oxide (filler) 7 Mono-ammonium phosphate (filler) 4.5 Organo lead liquid (stabilizer) 4.5 Starch (filler, surfactant) 2 L2ad stearate (stabilizer, antifoamer) Phenolic antioxidant (stabilizer) 0.5 Octyl alcohol~ (antifoamer) 0.5 Mixed linear alcohols* (surfactant) 0.1 Poly(dimethyl-siloxane) (antifoamer) 0.05 ~ater* (carrier) 45 *No longer present after hea~ drying of the formulation~

Example II

Ingredient Parts by we_~ht Vinyledene chloride-butadiene latex (resin) 183 (100 parts dry weight) Chlorinated paraffin (flame retardant plasticizer) 28 Activated azodicarbonamide (filler) 26 Pentaerythritol ~filler) 18 Monoammonium phosphate (filler) 39 Diammonium phosphate (filler) 56 Aluminum trihydroxide (filler) 21 Antimony oxide (filler) 10.5 Organo lead liquid (stabilizer) 6.5 Phenolic antioxidant (stabilizer) 1.3 Octyl alcohol* (antifoamer) 0.7 Mixed llnear alcohols* (surfactant) 0.3 Diethylene ~lycol monoether acetate*
(liquid additive O helps disperse solid fillers) 4,0 Polydimethyl-slloxane (antifoamer) 0.07 *No longer present after heat drying of the formulation Outer jacket 22 is thinner than inner Jacket 20.
The preferred thicknesses of the two jackets are in the following ranges:
outer jacket 0.05 to 0.5 millirneters inner jacket 0.2 to 3.0 millimeters Notwithstanding these two thickness ranges the preferred ratio between outer J'acket 22 and inner jacket 20 is in the range of 0.02 to 0.5.

The latex emulsion is preferably sprayed onto inner ~acket 20 to form cable 10.
The cable of the invention exhibits (under conditions of high heat flux) a low rate of flame spread and a lengthy time to ignition, low cumulative evolution and low rate of evolution of carbon monoxide and gases containing halogen or phosphorus~ and a low rate of smoke output, while under low temperatures, for example -30C, flexibility of the cable is retained.
A test of a cable of the invention was carried out using as a sample an outer layer having the composition of ExampleI
and using a standard single layer jacketed cable for comparison. A
chamber wlth radiant heat panel and pilot flames (commonly called the Ohio State University Release Rate Apparatus) was used. Such a chamber is equipped with a window, a sealable entrance and a 15 cm x 15 cm vertical plate to hold cable samples exposed to the radiant panel. A thermocouple, a photo-electric detector, and a gas sampling tube are included. Thirty minute exposures were performed at a set incident heat flux from the radiant panel. The cable models were stacked horizontally on the vertical plate. The samples were about 30 cm from the panel. A pilot flame at the bottom of the sam~le array was used to help lnduce combustion. Heat, smoke, and carbon monoxide outputs were continuously monitored. Six inch cable core lengths were wrapped with jacketing material of the desired thickness. Several lengths were stacked and tied to the support.
The following results were produced by testing the two samples:
Sample 1 Sample 2 Core: 50 pr FVC insulated 50 pr PVC insulated 24 A~G copper 24 AWG copper Inner Jacket: 0.76 mm PVC 0.76 mm PVC
Outer Jacket: - 0.10 mm Flame retardant outer jacket (Example I) ~ASUR~ PARAMEr~
@ 30 kW/m2 HEAT FLUX Sample 1 Sample 2 Ignition time (sec)* 21 123 (~ Time to onset of net heat release from sample) Cumulative Smoke Output after 300 sec. (smoke units)1.60 0.80 Cumulative Carbon Monoxide 0utput at-ter 300 sec.
(mL/Meter length) 4463 323 It will be appreciated that mor~ than one resin, filler or stabilizer may be used in the composition of the invention.

Claims

WE CLAIM:

1. A composition, for use in the continuous coating of a jacketed cable to form an outer layer thereon, comprising: at least one polymer resin, at least one filler and at least one stabilizer, proportioned whereby, on heating, the coating forms a flame retardant char.

2. A composition as claimed in claim 1 in which the resin is in latex form and the composition includes a surfactant.

3. A composition as claimed in claim 2 in which the ingredi-ents are present in approximately the following proportions by dry weight: 100 parts polymer resin, 50 to 200 parts filler, 0.5 to 10 parts stabilizer, and 0.05 to 2 parts surfactant.

4. A composition as claimed in claim 2 including a plasticizer.

5. A composition as claimed in claim 3 including a plasticizier in an amount up to 50 parts by dry weight.

6. A composition as claimed in claim 4 in which the plasticizer is flame retardant.

7. A composition as claimed in claim 2 including an anti-foam agent.

8. A composition as claimed in claim 3 including an anti-foam agent in an amount up to 2 parts by dry weight.

9. A composition as claimed in claim 2 including a plasticizer and an anti-foam agent.

10. A composition as claimed in claim 3 including a plasticizer in an amount up to 50 parts by dry weigt and an anti-foam agent in an amount up to 2 parts by dry weight.

11. A composition as claimed in claim 8 in which: the polymer resin is vinyledene chloride-butadiene latex; the filler is a mixture of aluminum tribydroxide, antimony oxide and mona-ammonium phosphate;
the stabilizer is a mixture of organo lead liquid and phenolic antioxidant; the surfactant is a mixture of linear alcohol and starch, and the anti-foam agent is a mixture of lead stearate and poly-dimethyl-silixane; and including water as a carrier.

12. A composition as claimed in claim 10 in which: the polymer resin is vinyledene chloride-butadiene latex; the plasticizer is chlorinated paraffin; the filler is a mixture of activated axodi-carbonamide, pentaerythritol, mono-ammonium phosphate, diammonium phosphate, aluminum tribydroxide, and antimony oxide; the stabilizer is a mixture of organo lead liquid and phenol antioxidant; the surfact-ant is lenear alcohol, and the anti-foam agent is a mixture of octyl alcohol and polydimethyl-silicone.

13. A cable comprising a core and a jacket having an inner layer and an outer layer, the outer layer of the jacket comprising:
at least one polymer resin, at least one filler and at least one stabilizer, proportioned whereby, on heating, the coating forms a f lame retardant char.

14. A cable as claimed in claim 13 in which the ingredients are present in approximately the following proportions by dry weight:
100 parts polymer resin, 50 to 200 parts filler, 0.5 to 10 parts stabilizer, and 0.05 to 2 parts surfactant.