CA1110789A

CA1110789A - Flame-resistant hydrocarbon polymer compounds, and insulated electrical products thereof

Info

Publication number: CA1110789A
Application number: CA305,583A
Authority: CA
Inventors: Joseph E. Betts; Fred F. Holub
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1977-07-18
Filing date: 1978-06-15
Publication date: 1981-10-13
Also published as: ES471841A1; FR2398371B1; DE2821807A1; SE7807904L; YU171078A; FR2398371A1; JPS5421449A; DK321878A

Abstract

ABSTRACT OF THE DISCLOSURE
Halogen-free, flame-resistant hydrocarbon polymer compounds comprising an organopolysiloxane gum, and a lead compound, and electrical conductors insulated therewith.

Description

-~~ 21 WC lg46 The significantly increased use of organic hydrocarbon based polymeric compositions, such as polyolefins, in many and diverse applications or products, and the relatively high combustibility of such hydrocarbon based polymeric ma-terials, and their propensity to spread ~ ;;
or propagate burning due to flow and dr.ipping at high temperatures has greatly stimulated the investigation of flame-proofing measures for such organic polymeric compositions. Moreover, the high costs of fire damage in lives and property, and the current trend of the imposition of increasingly stringent safety requirements, have substantially intensified the pursuit of more effective and practical means of controlling or inhibiting combustion and its spread or propagation in many products and materials comprising organic polymers.
Notwithstanding prior developments of a great number of flame-proofing measures or additives :
resulting from this expanding effort, there remains !;
a continuing need for improvements to meet current or new requirements in this area. The magnitude and urgency of this need for even greater improvements in this area ~.
and the proliferati.on of efforts and developments in this field are best evidenced by the ever increasing number of publications produced dealing with this subject. -This invention comprises the discovery that effective resistance to flame or combustion, its spread or propagation due to loss of physical integrity and extensive volatilization, and other advantages, in hydro-gen based polymers, such as polyolefins, can be attained by the incorporation therein of the combination of a polysiloxane gum and lead compound, without the presence .
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of a halogen. The invention thus relates to flame-resistant hydrocarbon based polymer compounds, such as polyolefin polymers, and i-t has particular application or utility in flame-proofing electrical insulations such as or wire and cable comprising dielectric ethylene-containing polymer compounds, such as polyethylene, which have been crosslink cured to a substantially thermoset condition.
It is a primary object of this invention to provide hydrocarbon based polymer compounds having effective resistance to flame and combustion which do ~ ;
not require a halogen, and thereby avoid the disadvantages and problems attributable to halogens.
It is also an object of this invention to provide hydrocarbon based polymer compound, such as polyolefins, having effective electrical and physical properties, and chemical properties such as resistance to heat aging as well, as a high degree of resistance to flame and combustion and the spread or propagation of ire due to loss of physical integrity and extensive volatilization.
It is a further object of this invention to provide flame resistant hydrocarbon based polymer compounds such as polyolefins which are very flexible, and which effectively and extensively char at flame or com~ustion conditions and thereby resist loss of physical integrity and excessive volatilization.
It is a still further object of this invention to provide a new and improved electrical conductor comprising a metallic conductive element having a dielectric insulation thereabout of a crosslink cured polyolefin polymer compound which is resistant to flame

- 2 ~

$~ 21 WC 1946 and combustion, chars and minimiæes volatilization and loss of physical in-tegrity at flame temperatures, and has superior electrical and physical properties.
In accordance with this inventiorl, hydrocarbon based polymer compounds having an effective level of resistance to flame and combustion, a high level of physical integrity at high temperatures, among other advantages and improved attributes, are provided by a combination of such a hydrocarbon based polymer composition with effective amounts of an organopolysiloxane gum or -~
elastomer and a lead compound, without the presence of a halogen.
The hydrocarbon based polymeric materials of this invention comprise polyolefins such as ethylene-~efhy~e~
containing polymers, for example pollTe~ e~, both high and low densi-ty, copolymers of ethylene and other ; polymerizable materials, and blends of such polymers including copolymers. Typical copolymers o~ ethylene i include, for example, ethylene-propylene copolymers and ethylene copolymers and ethylene-propylene-dience ~
terpolymers, ethylene-vinyl acetate, ethylene-e-thyl ~-acrylate and ethylene-methyl acrylate. Other hydrocarbon based polymers within the scope of this invention includes ;;
polypropylene, ethylene butene copolymer, polybutylene, polypentene, polystryrene, styrene maleic anhydride copolymer, styrene acrylonitrile copolymer, acrylonitrile butadiene styrene copolymer, methacrylate butadiene styrene copolymer, polycarbonates, polyesters, and the like. - ~r The flame-resistant, hydrocarbon based polymers, or compounds thereofl of this invention can additionally comprise fillers, for example extendin~ or reinforcing

- 3 -~ Y~ ~ 21 WC 1946 components such as silica, clay or fibers, pigments, curing coagents, and other conventiona:L addltives including preservatives, such as antioxidants, modifying agents such as plasticizers, processing aids, mold rel.ease ingredients or lubricants, and the like which are commonly compounded with molding or insulating polymers, or typical products formed therefrom such as, for example, electrical insulations. Moreover, the polymer compounds of this invention can also include auxiliary flame retarding ingredients such as conventional flame retarding agents, for example, phosphates, halogens, borates, antimony oxides, and the like coImmon flame retardants.
This invention also specifically applies to and includes any of the above-reference hydrocarbon polymers which can be crosslink cured and thermoset, when effected by means of high energy irradiation such as by electrons or chemical means such as a heat-ac~ivatable organic peroxide crosslinking agent such as disclosed in U.S. patents 2,888,424 - issued May 26, 1959; 3,079,360 - issued February 26, 1963; 3,086,966 issued April 23, 1963 and 3,214,422 issued October 26, 1965.
Suitable peroxide crosslink curing agents comprise organic tertiary peroxides characterized by at least one unit of -the structure:
:` Ic f C _ C--O--O--C _ ~
C C
which decompose at a temperature above about 1~6C

(295F) and thereby provides free radicals. Preferred ,~
. peroxides for curing polyolefins are a di~ cumyl peroxide, and other apt peroxides comprising the ter~iary

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diperoxides such as 2,5-dimethyl-2,4-di(t-butyl peroxy) hexane, and 2,5-dimethyl-2,4-di(t-butyl peroxy) hexyne-3, and the like diperoxy and polyperoxide compounds.
The organopolysiloxane gum or elastomer of this invention, for use incombination with a lead compound, among o-ther preferred or optional ingredients, and the hydrocarbon polymer, comprises gums or organo-polysiloxanes which have been condensed to a high molecular weight polymer of a gummy elastic, substantially semi-solid state. For example a typical silicone elastomer for use in the composition of this invention ~.
is a class of dimethylpolysiloxanes having the following repeating units:

- r ~ o-- ~
~H ;,:~
: : L 3 ....
Other classes of silicone elastomers for :~
use in this invention are the methyl-phenyl polysiloxanes, dimethyl-diphenyl copolymers, and all such silicones containing minor amounts of vinyl groups. Further examples of the type of silicone elas~omer gums usable in obtaining the compositions of this invention --comprise the organopolysiloxanes referred to in U~S.
patents 2,888,424 and 2,888,419 issued May 26, 1959, and .
identified in detail in U. S. patents 2,448,556 issued September 7, 1948; 2,448,756 - issued September 7, 1948;

2,457,688 - issued December 26, 1948; 2,484,595 -issued Oc~ober 11, 1949; 2,490,357 - issued December 6, 1949; 2,521,528 - issued September 5, 1950;
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2,541,137 - issued February 13, 1951; 3,098,836 -issued July 23, 1963 and 3,341,489 - issued September 12, 1967. Such high molecular weight sllicone polymers normally have Brookfield viscosities of in excess of about 100,000 centipoise at 25C.
The lead compound comprises dibasic lead phthalate, lead stearate, lead sebacate, tribasic lead maleate, basic lead silicate sulfate, and comperable lead compounds. -It is highly preferred that the compositions of this invention also include effective amounts of conven-tional antioxidants, such as polymerized 1,2-dihydro-2,2,4 tri-methylquinoline, which in combination with the other essential ingredients, provides a high degree of resistance in the compound to flow or dripping when exposed to flame or combustion temperatures.
Fumed silica fillers also comprise a pre-ferred ingredient which enhances the overall resistance to flame and other desired attributes in some embodiments of the hydrocarbon polymer compounds of this invention.
Also fumed silica can be employed as an aid to improve disperson of the silicone gum with the other ingredients.
Fumed silica comprises a form of silica described in U. S. Patent 2,888,~24 and a type which is sold under the trade designation of Carbosil MS7 o~ Godfrey L.
Cabot, Inc., of Boston, MassachusettsO
The essential combination of organopolysiloxane `! gum, with the lead compound, and preferred ingredients such as an antioxidant and fumed silica, can be mixed and combined w.ith a hydrocarbon based polymer material or compound thereo~, by means of any conventional compounding method or apparatus, such as working in a Banbury mixer or on a two roll rubber mill~
I the polymer compound is to be cured with a heat activatable curing agen-ts such as an organic peroxide, it .is preferred that all ingredients of the compound Eormulation, except the heat decomposable organic peroxide curing agent or any o-ther ingredients which are sensitive to the relatively moderate mixing temperatures of about 150C (300F) to about 205C
(400F), are combined and initially admixed together at a temperature sufficient to sof-ten and plasticize the particular polyolefin polymer ingredients.
Following the attainment of substantial uniformi.ty of l:
the initially admlxed ingredients, the tempe~ature of the a~nixed batch is reduced below the decomposition :
level of the particular peroxide curing agent used, or other heat sensitive ingredients to be added, and the curing agent or other heat sensi-tive ingredients are then introduced and dispersed preferably uniformly throughout the mix.
The proportions of the essential ingredients of the combination of this invention, as well as the :
optional ingredien-ts and/or conventional additives or : compounding agents can be varied and depend primarily upon the level or degree of resistance to flame and combus-tion, or charring, of the polymer, or compound thereof, and the relative flammability or combustibility of the polymer or compound ingredients and their ratios.
~; ~Ioweverl effective resistance to flame or combustion, ~:~ and effective charring, in many typical polym~ric compounds can be achieved with ratios of the respective ingredients in the following approximate relative parts ;~ by weight of:

Hydrocarbon based polymer 100 Organopolysiloxane gum 2 - 20 Lead compound 2 - 15 Fumed silica 0 - 10 Antioxidant 0 - 10 Filler 0 - 50 Organic peroxide curing agent 0 - 10 In a preferred embodiment of this invention for a highly effective electrical insulation hav.ing a high degree of resistance to flame and combustion, and substantial charring at flame temperature, -the ingre-dients and their proportions comprise the following in the approximate relative parts by weight of: :
Polyolefin 100 Organopolysiloxane 3 - 10 Dibasic lead phthalate l - 5 : Fumed silica 2 - 6 Antioxidant l - 6 Antimony oxide 0 - 15 ~ 20 Filler 0 - 30 ; Curing coagent 0O5 - 2 ~; Organic tertiary peroxide curing agent l - 5 The following examples of the compositions of this invention and data derived therefrom demonstrate the resistance to flame or combustion, and charring, as well as other beneficial and improved attributes, of ~;; the halogen-fr~e, novel compositions of the inven~ion, with respec-t to similar compositions for standards of comparison. The pol~mer composition formulations of the examples of this i.nvention and also of the standards are all given in parts by weight, and the compositions ~
of the examples of this invention and o their respective . ~ :
standards were each prepared, crosslink cured where `;
indicated, and tested or evaluated under identical ~ :
.. . :
condikions..
The relative degress of resistance to flame and combustion of the various compositions of the examples of this invention and of the standards were `.
all determined in accordance with the Oxygen Index :
: 10 Test procedure prescribed in ASTM Test Method D-2863-70, and as described in U. S. patents 3,755,214 issued August 28, 1973 and 2,787,356 issued April 2, 1957 As is known, this test designates the fraction of ~.
oxygen by volume in nitrogen required to just maintain ;:
flaming of the material of the test sample. Thus, the higher the oxygen index for a composition, the better its resistance to flame and combustion.

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I''~'Y`ZD~9 ~ i7~ 21 WC 1946 EXAMPLE V
INGREDIENTS PARTS PERCENT
Polyethylene 100 82.82 Polysiloxane gum* 5 4.14 Dibasic lead phthalate 4 3.31 (25% polybutene) Octamethylcyclotetra siloxane 3 2.48 Antioxidants Flectol-H 1.5 1.24 Santowhi-te Crystals 0.25 0.21 Pigment - titanium dioxide 2 1.66 triallyl cyanurate 1.5 1.24 Dicumyl peroxide 3.5 2.90 * Vinyl containing polysiloxane, containing minor amounts .
of siloxane treated fumed silica and diatomaceous earth ..
Flectol-H is a Monsanto Co. trademark for polymerized :
1,2-dihydro-2,2,4-trimethylquinoli.ne, a rubber antioxidant.
When crosslink cured at 182C (360F) for 45 minutes, the polymer compound of Example 3 exhibited the following prop~rties~
Toluene extraction: 10% based on polymer Tensile strength: 2779 psi -~
Elongation: 318%
; After heat aging 7 days at 121C ~ ~:
Tensile strength: 2832 psi (102~ ret.) Elongation: 336 (106% ret.) Oxygen Index~ percent: 30.2 Char (UL - 94 - NB?: Yes Drip: Slightly The composition of Example V ex-truded on #14 copper wire in a wall thickness of each 0.Q30 inch and 0.045 inch passed the UL - 44 - XHHW and RHH - RHW Horizontal Flame -~3 21 WC 19~6 Test and did not drip, while comperable crosslink cured, unfilled polyethylene compositions without the flame retardant system of this invention both failed thls test and dripped.

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Claims

The embodiments of the invention in which an exlu-sive property or privilege is claimed are defined as follows:

1. A flame-resistant, hydrocarbon based polymer compound comprising the following, in the approximate relative parts by weight of Hydrocarbon polymer 100 Organopolysiloxane gum 2 - 20 Lead compound 2 - 15

2. The product of the hydrocarbon based polymer compound of claim 1, wherein the hydrocarbon based polymer is a polyolefin.

3. The flame-resistant hydrocarbon based polymer compound of claim 2, wherein the polyolefin comprises at least one ethylene-containing polymer selected from the group consisting of polyethylene, copolymers of ethylene and other polymerizable materials, and blends of such polymers.

4. The product of the ethylene-containing polymer of claim 3, which has been crosslink cured.

5. A flame-resistant, hydrocarbon based polymer compound as defined in claim 1 wherein said organopolysiloxane gum comprises 3 to 10 parts, said lead compound comprises 1 to 6 parts, and further comprising 1 to 10 parts fumed silica, 1 - 6 parts antioxidant and 0 - 50 parts filler, based on 100 parts of said hydrocarbon polymer all said parts being on a wight basis.

6. The product of the hydrocarbon based polymer compound of claim 5, wherein the hydrocarbon based polymer is a polyolefin.

7. The flame-resistant hydrocarbon based polymer compound of Claim 6, wherein the polyolefin comprises at least one ethylene-containing polymer selected from the group consisting of polyethylene, copolymers of ethylene and other polymerizable materials, and blends of such polymers.

8. The cured product of the ethylene-containing polymer of claim 7, which has been crosslink cured with an organic peroxide curing agent.

9. The cured product of the ethylene-containing polymers of claim 7, wherein the organopolysiloxane gum is poly-dimethyl siloxane, and the lead compound is dibasic lead phthalate.

10. The cured product of the ethylene-containing of claim 7, wherein the antioxidant is polymerized 1,2-dihydro-2,2,4-trimethylquinoline.

11. A flame-resistant, crosslink cured polyethylene compound comprising the cured product of the following, in the approximate relative parts by weight of:
Polyethylene 100 Organopolysiloxane gum 3 - 10 Dibasic lead phthalate 2 - 6 Fumed silica 1 - 5 Antioxidant 0 - 6 Antimony oxide 0 - 15 Organic peroxide curing agent 1 - 5.

12. An electrical conductor comprising a metallic conductive element having as an insulation thereabout any of the compositions of claim 1, 2 or 11.