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Description  |
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BACKGROUND OF THE INVENTION
The increased use of polymeric compositions, such as polylefins, in many
and diverse applications or products, and the combustibility of such
polymeric materials, has greatly stimulated the investigation of
flame-proofing measures for polymeric compositions. Moreover, the high
costs of fire damage in lives and property, and the imposition of
increasingly stringent safety regulations, have recently significantly
intensified the pursuit of more effective or practical means of
controlling or inhibiting combustion and the propagation thereof in many
products and materials.
Notwithstanding prior developments of a great number of flameproofing
measures or additives resulting from this expanding effort, there remains
a continuing need for improvements to meet current or new requirements in
this area.
SUMMARY OF THE INVENTION
This invention comprises the discovery of the improved resistance to flame
or combustion, and the propagation thereof, and other advantages
attributable to the combination of decabromodiphenyl ether, silicone gum
and dibasic lead phthlate with cross-liked polyolefins, such as
polyethylene, and other ingredients. The invention thus relates to
flame-resistant polyolefin compounds, and it has particular utility in
flame-proofing electrical insulations comprising ethylenecontaining
polymer compounds which have been cross-link cured.
OBJECTS OF THE INVENTION
It is a primary object of this invention to provide polyolefin compounds of
improved resistance to flame and combustion, and deformation and flow at
high or flame temperatures.
It is also an object of this invention to provide polyolefin compounds
having improved electrical and physical properties, as well as resistance
to flame and combustion.
It is a further object of this invention to provide an electrical conductor
comprising a metallic conductive element having an insulation thereabout
of a cross-linked polyolefin compound which is highly resistant to flame
and combustion and has superior electrical and physical properties.
BRIEF DESCRIPTION OF THE DRAWING
The Figure comprises a perspective view of an insulated conductor
comprising a metallic element having a cross-linked polyolefin insulation
thereabout.
DESCRIPTION OF A PREFERRED EMBODIMENT
In accordance with this invention, a cured polymeric compound having a high
level of resistance to flame and combustion, and deformation and flow at
high or flame temperatures, among other improved and advantageous
attributes, is provided with a polyolefin composition comprising
cross-linked ethylene-containing polymers by combining therewith
decabromodiphenyl ether, silicon gum and dibasic lead phthlate.
The polyolefin compositions of this invention comprise ethylene-containing
polymers such as polyethylene, copolymers of ethylene and other
polymerizable materials, and blends of such polymers including copolymers.
Typical copolymers of ethylene and other polymerizable materials include,
for example, ethylene-propylene copolymers and ethylene-propylene diene
terpolymers, ethylene-vinyl acetate, ethylene alkylacrylate copolymers,
and ethylene-butene copolymers.
The flame-resistant, cross-link cured polyolefin compound products of this
invention can comprise fillers, pigments, curing coagents, and other
conventional additives including preservatives such as antioxidants,
modifying agents, mold release ingredients, processing aids or lubricants
such as lead or zinc stearates in minuscule amounts of about 1 to 5 parts
by weight, and the like which are commonly compounded with polyolefins, in
addition to the essential ingredients or basic components thereof set
forth hereinafter, such as the decabromodiphenyl ether, silicone gum and
dibasic lead phthlate.
The invention applies to and includes all of the above-referred polyolefins
when cross-link cured and thermoset by a heat-activated peroxide
cross-linking agent such as disclosed in U.S. Pat. Nos. 2,888,424;
3,079,370; 3,086,966 and 3,214,422, or by irradiation. Suitable peroxide
cross-link curing agents comprise organic tertiary peroxides characterized
by at least one unit of the structure:
##STR1##
which decomposes at a temperature above about 295.degree. F. and thereby
provide free radicals. Peroxide curing agents can be used in amounts of
about 2 to 8 parts by weight per 100 parts of the polymer. A preferred
peroxide is a di-.alpha.-cumyl peroxide, and other apt peroxides comprise
the tertiary diperoxides such as 2,5-dimethyl-2,5-di (t-butyl peroxy)
hexane and 2,5-dimethyl-2,5-di(t-butyl peroxy) hexyne-3, and the like
diperoxy and polyperoxide compounds. Also a curing coagent such as
triallyl cyanurate is preferably employed in amounts of up to about 5
parts by weight per 100 parts of the polymer. Radiation cross-link curing
can be produced by high energy electrons, X-ray and the like sources of
irradiation.
The organopolysiloxane gum or eleastomer of this invention, for use in
combination with the polyolefin, decabromobiphenyl ether, and lead
compound, among other ingredients, comprises gums or organopolysiloxanes
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 chemical structure:
##STR2##
Another class of silicone elastomers for use in this invention is the
methyl-phenyl polysiloxanes. Further examples of the type of silicone
elastomer gums usable in obtaining the compositions of this invention
comprise the organopolysiloxanes referred to in U.S. Pat. Nos. 2,888,424
and 2,888,419, and identified in detail in U.S. Pat. Nos. 2,448,556;
2,448,756; 2,457,688; 2,484,595; 2,490,357; 2,521,528; 2,541,137;
3,098,836; and 3,341,489. Such high molecular weight siloxane polymers
normally have Brookfield viscosities of in excess of about 100,000
centipoise at 25.degree. C.
The lead component comprises dibasic lead phthlate, or equivalent lead
compounds.
The fumed silica comprises a form of silica described in U.S. Pat. No.
2,888,424, and a type which is sold under the trade designation of Cabosil
MS7 of Godfrey L. Cabot, Inc., of Boston, Massachusetts.
The combination of decabromodiphenyl ether, silicone gum and dibasic lead
phthlate and other ingredients of this invention can be mixed and combined
with a polyolefin component by means of any conventional compounds method
or apparatus, such as working in a Banbury mixer or on a two roll rubber
mill. Preferably the ingredients of the compound formulation, except those
which are sensitive to the relative moderate mixing temperatures of about
300.degree. F. to about 400.degree. F., such as a heat decomposable
peroxide curing agent, are combined and initially admixed together or
substantially uniformly dispersed with each other at a temperature
sufficient to soften and plasticize the particular polyolefin ingredient.
Following the attainment of substantial uniformity of the admixed
ingredients, the temperature of the admixed batch is reduced below the
decomposition level of the particular peroxide curing agent, or other heat
sensitive ingredient, and the curing agent or any other sensitive
ingredient is then introduced and dispersed preferably uniformly in the
mix.
The proportions of the flame-proofing combination of decabromodiphenyl
ether, silicone gum, dibasic lead phthalate and the like ingredients
admixed with the polyolefin compounds depend, of course, upon the desired
or required degree of resistance to flame and combustion, and the content
of polymeric or other combustible materials in the overall compound.
Suitable amounts for effective flame resistance in polyolefins comprise
about 15 to about 50 parts by weight of the decabromodiphenyl ether, about
3 to about 10 parts by weight of the silicone gum, and about 3 to about 10
parts by weight of the dibasic lead phthlate, per 100 parts by weight of
the organic polymer content of the compound. However, greater or smaller
quantities can suffice for particular applications.
In accordance with this invention, the level of resistance to flame and
deformation or flow at high or flame temperatures provided by the
combination of decabromodiphenyl ether, silicone gum and lead, and other
ingredients of this invention within a polyolefin compound can be enhanced
by the inclusion of an oxide of antimony, such as antimony trioxide, in
the compound. Suitable amounts of such oxides of antimony include about 5
to about 25 parts by weight per 100 parts by weight of the polyolefin
polymer.
Typical formulations for the practice of this invention comprise, in
approximate relative parts by weight, the following combinations of
essential and preferred ingredients.
______________________________________
Ingredient Parts by Weight
______________________________________
Polyolefin 100
Decabromodiphenyl ether
15-50
Silicone gum 3-10
Dibasic lead phthalate
3-10
Antimony oxide 5-25
Fumed silica 3-10
Clay 0-25
Antioxidants 1-10
Processing aid or molding lubricant
0-5
Curing coagent 0-3
Organic peroxide curing agent
2-5
______________________________________
The following comprise examples of the novel and improved flame resistant
polyolefin composition of this invention, with the ingredients given in
relative parts by weight.
The test specimens for each example were compounded in a typical manner,
comprising combining all ingredients, except the peroxide curing agent, at
a temperature of about 100.degree. C. + 5.degree. C. for about 5 minutes,
then adding and blending in the peroxide for another 5 minutes at the same
temperature, and curing the sample specimens thereof at 177.degree. C. for
30 minutes in a press. The composition of the specific formulation given
in the above mentioned example exhibited the properties set forth below:
______________________________________
INGREDIENTS EXAMPLES
Parts By Weight I II
______________________________________
Polyethylene 100 100
Decabromodiphenyl ether 40 25
Silicone gum 6.25 5
Dibasic lead phthalate 5 5
Antimony oxide 14 10
Fumed silica 5 5
Clay -- 15
Antioxidants
Polymerized trimethyl dihydroquinoline,
1.5 --
Agerite MA
4,4'-thiobis-(6-tert-butyl-m-
0.25 --
cresol), Santowhite Crystals
0.25 --
Thioester bis hindered-phenol, Irganox 1035
3
Thio dipropionate polyester, Poly TDP 2000
3
Processing aid
Lead stearate -- 1
Vinyl silane -- 1.25
Curing coagent-triallyl cyanurate
1 1
Peroxide curing agent-dicumy peroxide
2.5 2.5
______________________________________
PROPERTIES EXAMPLES
I II
______________________________________
Oxygen Index Value 28.4 27.2
UL-44 FR-1 Flame Test passed passed
Original Tensile Strength, psi
2460 2233
Original Elongation, percent
400 376
Heat Treated 7 Day at 150.degree. C
Percent Retention - Tensile, psi
88 99
Percent Retention - Elongation
91 90
Heat Treated 30 Days at 136.degree. C
Percent Retention - Tensile, psi
89 92
Percent Retention - Elongation
88 80
Heat Treated 60 Days at 136.degree. C
Percent Retention - Tensile, psi
89 99
Percent Retention - Elongation
82 82
Heat Treated 90 Days at 136.degree. C
Percent Retention - Tensile, psi
55 60
Percent Retention - Elongation
34 19
______________________________________
The flame resisting properties of the examples of the compositions of this
invention were all identically evaluated by the Oxygen Index Test (ASTM
D-2863-7-) which 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 combustion and flame.
Referring to the drawing, there is shown a typical construction for an
insulated electrical wire or cable product 10*, comprising a metallic
conductive element 12* and an overlying body of cured polymeric insulation
14* extending thereabout or covering the conductor. In the drawing, the
product 10* is illustrated as a short section with the insulation 14*
removed from the end portion of the conductor 12*. According to one
embodiment of this invention, the novel flame-resistant polyolefin thereof
can be used to provide or form the insulation 14* on conductive element
12* of wire or cable product 10*. It is to be understood from the
foregoing, however, that the insulation can comprise a coating on any
portion of a conductive element and that the insulation need not
completely enclose the element where such is not necessary for a desired
insulative effect.
Although the invention has been described with reference to certain
specific embodiments thereof, numerous modifications are possible and it
is desired to cover all modifications falling within the spirit and scope
of the invention.
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