Note: Descriptions are shown in the official language in which they were submitted.
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1 FLAME RETARDANT AND SMOKE SUPPRESSED POLY~ERIC
COM.POSITION AND ELECTRIC WIRE, AND OPTICAL COMPOSITE . . _
CABLE HAVING SHEATH MADE FROM SUCH COMPOSITION
BACKGROUND OF ~HE INVENTIC3N
.
S The present invention relates to a flame retardant
and smoke suppressed polymeric composition which is flame
retardant and, even upon flaming, smoke suppressed and
productive of no aggressive gases The in~ention also
relates to an electric wire having a sheath made Erom such a.
composition. The invention further relates to an optical
composite cable having an outer sheath made from such a
composition.
Recently, requirements for the flame retardancy of
wirings for buildings and wirings in electrical instruments
are getting more and more severe. Insulating materials for
such wirings are required to be not only flame retardant but
also, even upon flaming, smoke suppressed and productive of
no harmful gases that would exert adverse effects upon.human
body and the instruments. Resins containing-halogen atoms
in the molecular structure, such as polyvinyl chloride
resins, cannot be used for this purpose, since they evolve
aggressive, harmful gases upon flaming. Halogen free resins
such as polyolefins which have generally incorporated
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1 therein a flame retarding amount of a halogen compound as a
flame retardant additive are also productive of halogen
cJases upon flaming.- Thus, attempts to-impart the flame - -
retardancy to a halogen free resin by adding thereto a
halogen free flame retardant have been proposed. Among
others, hydroxides and carbonates of certain metalsl such as
aluminum hydroxide, magnesium hydroxide and magnesium
carbonate, as well as zinc borate are known in the art as a
suitable halogen free flame retardant (see K.C. Hecker et
al., Paper No. 17l ACS Division of Rubber Chem., April,
1~72; I. Sobelev et al~, SPE 31st. Ann. Tech. Conf.
~ontreal, 1973, Preprints, p. 709; and D.F. Lawson et al.
Paper No. 13, ASC Division of Rubber Chem. October, 1974).
The flame retardancy of a polymeric material may
be estimated by the oxygen index which may be determined,
for example, by the procedure prescribed in JIS-K-7201. In
order that a polymeric material can be rated as being flame
retardant upon vertical burning tests it should have an
oxygen index as high as 27 to 30 or higher. The amount of
smoke upon flaming o~ a polymeric material may be estimated
in terms of the maximum smoke density upon flaming of the
material, which may be determined using a suitable equipment
known as an NBS smoke density chamber. It is generally
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1 desired to reduce the maximum smoke density of the material
to a level of 100 or below.
It has been ~requently experienced that when a
halogen free flame retardant filler such as magnesium
carbonate, magnesium hydroxide, aluminum hydroxide or zinc
borate is added to a halogen free polymeric material such as
a polyolefin to provide a halogen free polymeric composition
which is satisfactorily flame retardant (e.g. having an
oxygen index of 30 or higher) and simultaneously satis-
factorily smoke suppressed (e.g. having a maximum smoke
density, upon flaming, of loo or below), the addition of an
undesirably large amount of the filler, which adversely
affects mechanical properties and processability of the
resultant polymeric composition~ is normally required.
I~ is therefore desired to provide a halogen free
flame retardant and smoke suppressed polymeric composition
with a reduced amount of a halogen free flame retardant
filler, which composition is particularly suitable for use
in producing sheaths of electric and optical wires and
cablesO
On the other hand, electronic instruments such as
computers and facsimiles have come into wide use. As the
amount of information to be transmitted increases, the use
. , . , . , . . . ... , ~ ...... ... . .
1 of composite optical cables in which normal insulated
electric wires of a metallic conductor and optical trans-
mission lines of an optical fiber excellenl- in transmission
efficienc~, is growing. Wirings for the instruments are
made in buildings and offices, and thus required to be flame
retardant and smoke suppressed upon flaming from a view
point of prevention of calamities. Insulating materials for
such wires and cables should desirably be highly flame
retardant and smoke suppressed. Fluorine resins are
generally used for this purpose.
Nith a cable of normal insulated electric wires
enveloped within an outermost sheath of a fluorine resin, no
problems are posed. It has been found, however, that the
fluorine resin, when used as an outermost sheath of an
optical composite cable haviny insulated electric wires and
optical transmission lines enveloped within the outer-most
sheath, undesirably increases the transmission loss of the
optical transmission lines. A particular problem re-lating
to such optical transmission lines concerns the transmission
loss, which is usually within the range between about 2 and
3 dB/Km. However, with the optical composite cables having
an outermost sheath of a fluorine resin, the transmission
loss of the line amounts to 1.5 to 2 times that of the
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1 optical transmission line alone. This means a reduction of
the effective cable length by 1/2 to 2/3 and is a serious
problem in the cable system connecting instruments.
Accordingly, it is also desired in the art to
provide a halogen free flame retardant and smoke suppressed
polymeric composition which does not suEfer from a substan-
tial increase in the transmission loss of optical trans-
mission lines, when used as a material for the outer sheath
of the optical composite cable.
SUMMARY OF T~E INVENTION
It is an object of the invention to provide a
halogen free polymeric composition which is satisfactorily
flame retardant and, even upon flaming, smoke suppressed and
producive of no aggressive gases, with a reduced amount of a
halogen free flame retardant filler.
Another object of the invention is to provide an
electric wire having a sheath of acceptable mechanical
properties which is flame retardant and, even upon flaming,
smoke suppressed and productive o~ no aggressive gases.
A still further object of the invention is to
provide an optical composite cable having an outermost
sheath, which is satisfactorily flame retardant and smoke
suppressed and which does not substantially increase the
1 transmission loss of optical transmission l.ines enveloped
therein.
In one aspect of the invention there is provided a -
flame retardant and smoke suppressed polymeric composition,
which comprises:
a radiation curable copolymer of ethylene and
vinyl acetate containing 50 to 85~ by weight of polymerized
units derived from vinyl acetate and
a flame retarding and smoke suppressing amount of
a finely divided filler mixture intimately admixed with said
copolymer, said filler mixture consisting essentially of a
first filler selected from the group consisting of
hydroxides and carbonates of di- and tri-valent metals and a
second filler which is zinc borate~ the ratio by weight of
said second filler to the filler mixture being within the
range between 0.25 and 0~75.
In another aspect of the invention there is pro-
vided an electric wire comprising a core conductor and a
flame retardant and smoke suppressed insulating sheath, said
sheath comprises: .
a radiat1on cured copolymer of ethylene and vinyl
acetate containing 50 to 85~ by weight of polymerized units
deri~ed from vinyl acetate and
1 a flame retarding and smoke suppressing amount of
a finely divided Eiller mixture intimately admixed with said
copolymer, said filler mixture consisting essentially OL a
first filler selected from the group consisting of
hydroxides and carbonates of di- and tri-valent metals and a
second filler which is zinc borate, the ratio by weight of
said second filler to the filler mixture being within the
range between 0.25 and 0.75.
In a still further aspect of the invention there
is provided an optical composite cable comprising ~1) at
least one insulated electric wire which comprises a core of
a metallic conductor and an insulating coating of a fluorine
resin, (2) at least one optical transmission line which
comprises a buffered core of an optical fiber and a coating
of a fluorine resin and (3) an outer sheath which envelops
aLl the eLectric wire and optical transmission line, wherein
said outer sheath comprises:
a radiation cured copolymer of ethylene and vinyl
: acetate containing 50 to 85~ by weight of polymerized units
derived from vinyl acetate; and
a flame retarding and smoke suppressing amount of
a finely divided filler mixture intimately admixed with said
copolymer, said filler mixture consisting essentially of a
1 f irst filler selected from the group consisting of
hydroxides and carbonates of di- and tri-valent metals and a
second Eiller ~hich is zinc borate, the ratio by weight of
said second filler to the f iller mixture ~eing within the
range between 0.25 to 0.75.
BRIEF EXPLANATION OF THE DRAWINGS
FigO 1 is a view schematically showing a cross-
section of an optical composite cable in accordance with one
embodiment of the invention;
DETAI~ED DESCRIPTION OF THE INVENTION
Examples of the fluorine resin include, e.g.,
polymers and copolymers of perfluoroalkylenes such as
polytetrafluoroethylene, polyhexafluoropropylene and
copolymers o~ tetrafluoroethylene and hexa~luoropropylene as
well as polymer~ of vinyl fluoride such as polyvinyl
fluoride.
Examples of the first filler include, ~or example,
aluminum hydroxide, magnesium hydroxide, calcium hydroxide,
barium hydroxide~ magnesium carbonate, magnesium calcium
carbonate, calcium carbonate, zinc carbonate and barium
carbonate.
By the term "an optical composite cable" used
herein is meant an op~ical cable wherein at least one
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l optical transmission line is enveloped with an outer sheath
together with at least one insulated electric wire.
By the term "a base polymeric material" used -
herein is meant a polymeric material, of which the flame
retardant and smoke suppressed polymeric composition is
prepared by intimately admi~ing therewith the specified
filler mixture~ Preferably, the base polymeric material
essentially consists of a radiation curable copolymer of
ethylene and vinyl acetate containing 60 to 85% by weight of
polymeri~ed units derived from vinyl acetate. However,
depending upon the desired properties of the final products
the base polymeric material may be a blend of such a
copolymer ahd up to about 50~ by weight, based on the blend
of one or more other polymers. Examples of such other
polymers include, for example, polyethylene, polypropylene,
a copolymer of ethylene and vinyl acetate containing less
th~an 50~ by weight of vinyl acetate, a copolymer of ethylene
and ethyl acrylate, a copolymer of ethylene and ~-olefin, EP
rubber, butyl rubber, polybutadiene and polyurethane
By the term "a flame retarding and smo~e
suppressing amount of a filler mixture" used herein is meant
an amount of the filler mixture required to achieve a
desired level of flame retardancy and at the same time a
1 desired level of suppressed smoking. More particularly, it
means an amount of the filler mixture admixed with a base
polymeric material to provide a polymeric composition having
concurrently a desired level of flame retardancy and a
desired level of suppressed smoking. GeneralLy at least Ioo
parts by weight of the filler mixture based on 100 parts by
weight of the base polymeric material is required to obtain
satisfactory resl-lts. A desirable polymeric composition
both before and after radiation curing has an oxygen index
iO of 3Q or higher and a maximum smoke density of 100 or below.
The upper limit of the filleL mixture admixed with the base
polymeric material is not strictly critical. But it should
be noted that addition of an excessive amount of the filler
mixture adversely affect mechanical properties and
processability of the composition, and therefore addition of
the filler mixture in excess of about 300 parts by weight
based on 100 parts by weight of the base polymeric material
should be normally avoided. In this connection, a base
polymeric material consisting essentially of a copolymer of
ethylene and vinyl acetate containing 50-85~ by weight of
polymerized units derived from vinyl acetate is advantageous
in that it can be heavily loaded with the filler mixture, if
desired, without its mechanical properties aEter curing and
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1 processability intolerably deteriorated.
Mechanical properties of the base polymeric
material which have been reduced by the addition o the
filler mixture can be improved by subjecting the composition
to radiation curing normally after shaping. For example, a
copolymer o~ ethylene and vinyl acetate containing about 60%
by weight of vinyl acetate and having a molecular weight of
about 200,000, as admixed with the same weight of a finely
divided inorganic filler (aluminum hydroxide), has a tensile
strength as low as 0.1 kg/mm2 and is of no practical use.
However, when such a composition is irradiated with 20 M rad
of beams, the tensile strength reaches 0.6 kg/mm2, the level
normally possessed by vulcaniæed rubbers, rendering the
product practically useful.
It should al50 be pointed out that radiation
curing ensures effective shaping and crosslinking of the
-material. This is not the case with chemical curing by
mèans of an organic peroxide. Because of a high torque in
the filled material being shaped, a temperature of the
material being shaped necessarily reaches about 200C, which
exceeds the decomposition temperature (normally 120to
180C) of organic peroxides. Accordingly, when the material
contains an organic peroxide, crosslinking takes place
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1 within the shaping machine, so that the material may not be
suitably shaped~
The filler micture consists essentially of a first
filler selected from the group consisting of hydroxides and
carbonates of di- and tri-valent metals and a second filler
which is zinc borate. For ~he purpose of the invention, the
ratio by weight of the second filler to the filler mixture
must be within the. range between 0.25 and 0.75. I~ this
ratio is substantially higher than 0.75, an intolerably
large amount of khe filler mixture is required to achieve a
desirably high oxygen index. Likewise, if this ratio is
substantially lower than 0.25, an unacceptably large amount
of ~he filler mixture is required to achieve a desirably low
maximum smoke density.
Optionally, the polymeric composikion may contain
other additives~, including, for example~ antioxidants,
lubricants, slipping agents, pigments and halogen contain-
ing flame retardants, in an amount of up to abouk 10 parts
by weight based on 100 parts by weight of the base poly-
meric material.
While the flame retardant and smoke suppressed
polymeric composition disclosed herein is particularly
useful for formin~ a sheath or coatiny of a wire or cable,
1 it is also use~ul for the production of other shaped
articles. The composition is shaped into a desired article,
which may be radiation cured. For example, an electric wire --
of the invention may be prepared by extrusion-coating a core
of a metallic c~nductor with the polymeric omposition
diselosed herein and radiation curing the resultant coated
conductor.
With reference to Fig. 1, an optical composite
cable according to the invention comprises at least one
optical transmission line comprising a core of an optical
fiber 1 buffered with a bufferiny material 2, such as a
silieone oil and a coating 3 of a ~luorine resini at least
one insulated electric wire comprising a core of a metallie
eonductor 4 and an insulating coating 5 of a fluorine resin;
and an outer sheath 6 enveloping all the wire and line.
Such a structure of the optical composite cable in itself is
well-known in the art. The optical composite eable
according to the invention may be prepared by extruding the
polymerie composition diselosed herein so as to form a
sheath around a bundle of the insulated eleetrie wires and
optical transmission lines, and radiation curing the so
formed sheath.
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A finely divided ~iller mixture consisting
essentially of 100 parts by weight of aluminium hydroxide
and 100 parts by weight of zinc borate was prepared.
copolymer of ethylene and vinyl acetate having a molecular
weight of about 200, oon and containing about 60~ by weight
of vinyl acetate was intimately admixed with the filler
mixture in varied amounts îndicated in Table 1 to provide
various polymeric composition.
A copper wire having a diameter of 0.8 mm was
coated with each polymeric composition to provide a coated
wire having an outer diameter of 2.4 mm, which was then
irradiated with 20 M rad of electron beams. A sheath of
each electric wire so prepared was tested for its maximum
density upon flaming, oxygen index and tensile strenyth,
Results are shown in Table 1.
Table 1
Polvmeric ~osition Maximum Tensile
Copol~mer Filler Mixture Smoke Oxygen Strength
(Parts by wei~ht~ (Parts bY weight) Density Index (kg/mm
1 100 100 90 30 0.61
2 100 150 75 32 0.66
3 100 200 75 35 0.65
100 250 60 55 0.79
1 It is revealed from Table 1 -that when the filler
mixture (lol aluminum hydroxide and zinc borate~ is used, a
preferred composition and sheath having a maximum smoke
density of 100 or below and an oxygen index of 30 or hiqher
can be obtained with less than 250 parts by weight of the
filler per 100 parts by weigh~ of the copolymer.
A similar series of experiments, in which aluminum
hydroxide alone was use~ instead of the filler mixture,
showed that at least 250 parts by weight of the aluminum
hydroxide per 100 parts by weight of the copolymer was
reuired to simultaneously achieve a maximum smoke density of
100 or below and an oxygen index of 30 or higher Another
series of the experiments wherein æinc borate was used as a
sole flame retardant revealed that a maximum smoke density
of 100 or below and an oxygen index of 30 or higher could be
simultaneously achieved only when the zinc borate was used
in an amount of about 300 parts by weight or more based on
. 100 parts by weight of the copolymer.
Example 2
. 20 The preparation and test procedures of Example 1
were repeated except that a 1:1 (by weight) mixture of
magnesium carbonate and zinc borate was used lnstead of the
filler ixture of Example 1. Results are shown iA Table 2.
1 Table 2
Pol~meric G~sition Maximum T~nsile
Copolymer Filler Mixture Smoke ~h~gen Strenyth
~arts by wei~ (Parts by wei~ht) Density Index ~kg/mm2)
_
1 100 100 88 31 ~.59
2 100 150 73 34 0.63
3 loo 200 55 36 0.63
4 100 250 50 60 0.66
Table 2 reveals that when the filler mi~ture (1:1
magnesium carbonate and zinc borate) i5 used, a preferred
composition and sheath having a maximum density o~ 100 or
below and an oxygen index of 30 or higher can be obtained
with less than 250 parts by weight of the filler mixture per
100 parts by weight of the copolymer.
Example 3
Optical composite cables of a structure as shown
in Fig. 1 were prepared and tested for the transmission
loss. The optical transmission line comprised a core of
optical fiber 1 having a diameter of 125 ~ coated with a
buffer 2 and FEP 3, and had an outside diameter of 2.8 mm.
The transmission loss of this optical transmission line
alone was 3.1 dB/Km. The insulated electric wire comprised
a bundle o~ twisted tin-plated copper wires tAWG 22) 4 coted
with an FEP insuLation 5, and had an outside diameter of
1.9 mm. A bundle of two lengths o~ the optical transmission
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1 line and two lengths of the insulated electric wire was
extrusion coated with each of the compositions 3 indicated
in Tables 1 and 2 to prepare an optical composite cable ---
having an outer diameter of 7.2 mm, the thickness oE the
outer sheath being 0.8 mmO The composite cables so prepared
exhibited a transmission loss of 3.0 to 3.2 dB/Km which was
substantially the same as that of the op~ical transmission
line alone.
For a comparison purpose, a control composite
cable of the same structure was prepared except that the
outer sheath was forined from FEP, and determined for the
transmission Loss. The control product exhibited a
transmission loss of 4.2 dB/Km.
Thus, the optical composite cable in accordance
with the invention having an outer sheath formed from the
specified flame retardant and smoke suppressed polymeric
composition has proved to be unexpectedly advantageous over
the comparable known products having an outer sheath of
fluorine resins in that the product of the invention does
not suffer from any substantial increase of the transmission
loss of the optical transmission line.
While the invention has been described in detail
and with reference to specific embodiment thereof, it will
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1 be apparent to one skilled in the art that various changes
and modifications can be made therein without departing from
the spiri-t and scope thereof.
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