CA1240092A - Flame retardant and smoke suppressed polymeric composition and electric wire, and optical composite cable having sheath from such composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A flame retardant and smoke suppressed polymeric composition comprising a radiation curable copolymer of ethylene and vinyl acetate containing 50-85% by weight of vinyl acetate having intimately admixed therewith a flame retarding and smoke suppressing amount of a finely divided filler mixture consisting essentially of a first filler selected from hydroxides and carbonate of di- and tri-valent metals and a second filler which is zinc borate. The composition may be shaped into a desired article, such as a sheath of an electric wire or a optical composite cable, which may be radiation cured.

Description

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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 ~ ,~, ,, ,, n.~b .. ~ s~

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 ~2~

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 _ ~ _ ~2~

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 ~, ~Lt~

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 .j 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 ~ 11 -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.

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 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 g~

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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Claims (30)

WHAT IS CLAIMED IS:

1. 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 to 0.75.

2. The composition according to Claim 1 wherein said first filler is aluminum hydroxide.

3. The composition according to Claim 1 wherein said first filler is magnesium hydroxide.

4. The composition according to Claim 1 wherein said first filler is calcium hydroxide.

5. The composition according to Claim 1 wherein said first filler is barium hydroxide.

6. The composition according to Claim 1 wherein said first filler is magnesium carbonate.

7. The composition according to Claim 1 wherein said first filler is magnesium calcium carbonate.

8. The composition according to Claim 1 wherein said first filler is calcium carbonate.

9. The composition according to Claim 1 wherein said first filler is zinc carbonate.

10. The composition according to Claim 1 wherein said first filler is barium carbonate.

11. An electric wire comprising a core conductor and a flame retardant and smoke suppressed insulating sheath wherein said 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 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 to 0.75.

12. The electric wire according to Claim 11 wherein said first filler is aluminum hydroxide.

13. The electric wire according to Claim 11 wherein said first filler is magnesium hydroxide.

14. The electric wire according to Claim 11 wherein said first filler is calcium hydroxide.

15. The electric wire according to Claim 11 wherein said first filler is barium hydroxide.

16. The electric wire according to Claim 11 wherein said first filler is magnesium carbonate.

17. The electric wire according to Claim 11 wherein said first filler is magnesium calcium carbonate.

18. The electric wire according to Claim 11 wherein said first filler is calcium carbonate.

19. The composition according to Claim 11 wherein said first filler is zinc carbonate.

20. The electric wire according to Claim 11 wherein said first filler is barium carbonate.

21. 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 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.

22. The optical composite cable according to Claim 21 wherein said first filler is aluminum hydroxide.

23. The optical composite cable according to Claim 21 wherein said first filler is magnesium hydroxide.

24. The optical composite cable according to Claim 21 wherein said first filler is calcium hydroxide.

25. The optical composite cable according to Claim 21 wherein said first filler is barium hydroxide.

26. The optical composite cable according to Claim 21 wherein said first filler is magnesium carbonate.

27. The optical composite cable according to Claim 21 wherein said first filler is magnesium calcium carbonate.

28. The optical composite cable according to Claim 21 wherein said first filler is calcium carbonate.

29. The optical composite cable according to Claim 21 wherein said first filler is zinc carbonate.

30. The optical composite cable according to Claim 21 wherein said first filler is barium carbonate.