Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes

Definitions

• Such flame retardant compositions are described, for example, in document FR-2 678 942. They have proven their advantage in terms of resistance to flame propagation, the most important characteristic of flame retardant compositions.
• Document EP-0 393 959 relates to flame retardant compositions based on specific polymers containing at least 40% of certain specific copolymers.
• the basic constituents of these compositions are a silicone and a filler in the form of any compound of a metal from group IIA of the periodic table of the elements.
• This filler can be covered with an organometallic salt used to promote the dispersion of the filler in the mixture and intimately bonded to the latter within the flame retardant material.
• These compositions have good fire behavior only if they contain the specific copolymers mentioned, and this in very high quantities. important. If they contain common polymers, their Oxygen Limit Index (ILO) is only around 25%.
• ILO Oxygen Limit Index
• US Patent 4,273,691 also describes flame retardant compositions based on polyolefins, which contain a silicone as well as a salt of a metal from group IIA of the periodic table of the elements, such as magnesium stearate, and which are also provided for cable insulation.
• a silicone as well as a salt of a metal from group IIA of the periodic table of the elements, such as magnesium stearate, and which are also provided for cable insulation.
• silica or clay can be incorporated as fillers in the flame retardant composition, but this in very small quantity (less than 5 parts by weight per 100 parts of base material).
• compositions described in US Pat. No. 4,273,691 have a much less good fire behavior than those of document FR-2,678,942: the ILO is of the order of 26.5% at most according to the document US -4,273,691 while it is around 35% at least for the compositions of document FR-2,678,942.
• the aim of the present invention is therefore, in addition to developing new compositions with high resistance to fire propagation, to improve the fire resistance, even after long ignition times, of the compositions of the prior art , in particular those of the type described in document FR-2 678 942.
• the object of the present invention is to meet the requirements mentioned above by developing a solution to guarantee resistance to the propagation of the flame and prevention of drip flow, for example by fire, insulation materials used in industry cables, in particular power cables, but also telecommunications, optical or other cables.
• the metal salt is dissociated from the filler, that is to say that no preliminary treatment of the filler with the salt is carried out, so that a on the one hand, the filler is not coated with the metal salt, and on the other hand, the metal salt and the filler are distributed in the base material without necessarily being bound to it.
• the combination of the filler, the silicone and the metal salt according to the invention not only meets the current requirements applied to compositions with high resistance to the propagation of fire, in particular for the use as coating and / or insulation of cables, but increases also considerably the ILO for ignition times greater than 10 seconds.
• the drip flow of the insulating material forming, for example, a cable sheath does not occur with a composition according to the invention in the event of fire.
• the composition according to the invention offers, in relation to the polymers used as base materials, good properties, both mechanical and electrical. Due to the choice of the constituents of the composition, the mixture can be manufactured at an attractive price, transformed on current and known equipment, and the unused materials can also without problem be recycled.
• the metal salts according to the invention make it possible in particular to use the filler / silicone system in any polymer (homopolymer, thermoplastic elastomer, copolymer, etc.), which makes it possible to produce inexpensive compositions, by choosing the least expensive polymers.
• the preferred salts which give the best results in terms of ILO, are those based on calcium and magnesium. These are for example stearates, palmitates or oleates of these metals.
• the salts of the specific metals of the present invention are preferably chosen so that their mechanical and electrical properties remain compatible with use within the insulation of a cable, and have good thermal stability at processing temperatures.
• the metal salt has a melting point lower than the temperature at which the base material begins to decompose.
• compositions according to the invention may contain more than one of the preceding specific metal salts.
• the filler is chosen from calcium carbonate, magnesium carbonate and talc.
• the essential role of the filler can be explained by the fact that, at high temperature, it aggregates and creates a structure with capillary properties which absorbs any underlying fluid material, and in particular silicone and metal salt, which allows these to migrate to the surface of the base material to form the mineral barrier.
• the filler will preferably be present in the compositions according to the invention in a relatively large amount, typically between 30 and 160 parts by weight per 100 parts of base material.
• an additive with a laminated structure is added to the load.
• This additive is advantageously chosen from mica, talc, kaolin, graphite, molybdenum sulfide and vermicullite.
• Such an additive further improves fire resistance.
• the use of an additive is particularly advantageous for the manufacture of cable plies, these may require, depending on the configuration of the ply ( number of cables, distance between cables, etc.) of compositions having a fire resistance greater than that which would be necessary for a monofilament cable.
• the silicone in the form of an oil or a gum, can be chosen from polydimethylsiloxanes, preferably comprising unsaturated groups to promote crosslinking, polymethylphenylsiloxanes, polymethylalkylsiloxanes, polydiphenylsiloxanes, polysiloxanes terminated by reactive functional groups such as amine, acetoxy or alkoxy groups.
• the silicone will preferably be present in the compositions according to the invention in a large amount, typically between 2 and 20 parts by weight per 100 parts of base material.
• the basic materials which can be used in the compositions of the present invention may be, in a first embodiment, homopolymers such as for example high or low density polyolefins, in particular high density, low density, very low density polyethylene and ultra low density, polypropylene, polybutylene terephthalate, polyamides, polycarbonates.
• homopolymers such as for example high or low density polyolefins, in particular high density, low density, very low density polyethylene and ultra low density, polypropylene, polybutylene terephthalate, polyamides, polycarbonates.
• compositions of the present invention are based on one or more homopolymers, ILOs are observed greater than 30% after an ignition time greater than 10 seconds, and of the order of 34% when the salt used is magnesium stearate.
• This additional material serves to improve the compatibility of the base material with the other constituents of the composition, which makes it possible to further improve the fire resistance of the latter.
• the additional material is preferably added in small amounts to the base material, with 1 to 20 parts per 100 parts of base material.
• the base materials which can be used in the compositions of the present invention may also be, in a second embodiment of the invention, copolymers, such as those described for example in the document EP-0 393 959 mentioned above.
• copolymers capable of reacting with the charge, causing carbon to form on their surface in the event of a fire (coal).
• These copolymers are, for example, the following: ethylene alkyl acrylate copolymers or ethylene vinyl acetate copolymer.
• the additional material plays the same role as in the first embodiment, and its preferred concentration is similar to that of the first embodiment.
• the base material can also be a thermoplastic elastomer which may or may not include additional materials such as those mentioned above. It may for example be a mixture of crosslinked polypropylene and ethylene propylene diene monomer (EPDM).
• EPDM ethylene propylene diene monomer
• the three constituents are essential to form on the surface of the burning material a barrier which reduces the exchanges between the oxygen of the air and the combustible materials.
• thermoplastic elastomer or a polyolefin elastomer.
• the filler is calcium carbonate and the metal salt is a magnesium stearate.
• Magnesium stearate makes it possible in particular to use the calcium carbonate / silicone system in any polymer (homopolymer, thermoplastic elastomer, copolymer, etc.).
• compositions according to the invention can be used as insulating materials, sheath materials, and also filling materials inside the cables.
• compositions according to the invention can be non-crosslinkable or crosslinkable.
• compositions are crosslinkable, it is preferable to carry out a crosslinking by irradiation rather than a peroxidic crosslinking, which risks causing a cross-crosslinking of the silicone with the base material, which would prevent the silicone from migrating to the surface. in the event of a fire, and to play its essential role in the fireproofing of the composition according to the invention.
• compositions according to the invention also contain conventional agents used in flame retardant compositions in particular to facilitate the manufacture of the mixture, prevent aging and oxidation, etc. These agents are well known to those skilled in the art. art and therefore will not be described here in detail.
• Examples I, II and V to VIII relate more particularly to compositions which can serve as insulation and / or protection for cables, while Examples III and IV relate more particularly to materials which can serve as sheath or insulator for flexible pipes.
• This mixture can be produced without problem and at an attractive price because of its good thermomechanical properties, and is recyclable.
• composition also meets the requirements which are the basis of the invention.
• this composition is particularly advantageous if it is used for flexible pipes.
• the polyethylene grafted with maleic anhydride used in the examples cited contributes to increasing the resistance to flame propagation.
• compositions can be used as sheath and / or insulating material for electrical or optical cables, in particular for the products among which preference has hitherto been given to polyvinyl chloride as insulating material.
• materials such as mica, talc, kaolin, graphite, molybdenum sulfide and vermicullite can be used as an additive.
• the size of the particles with a laminated structure is preferably chosen between 0.5 and 20 ⁇ m, and in particular of the order of 10 ⁇ m.
• the proportion of additive is for example from 0.5 to 20 parts by weight per 100 parts of the base material, that is to say of the polymer, and preferably from 1 to 10 parts by weight per 100 parts of the material basic.
• composition C1 is presented for comparison; composition It is a composition according to the invention, the charge of which does not include an additive with a laminated structure; and the compositions 12 and 13 are compositions according to the invention, the charge of calcium carbonate of which has been supplemented with graphite in laminated form in proportion of 1.25 and 3.5 parts by weight per 100 parts of polyethylene.
• composition C1 I1 I2 I3 polyethylene 100 100 100 100 100 calcium carbonate 40 40 40 40 graphite * 1.25 3.5 magnesium stearate 6 6 6 polydimethylsiloxane 10 10 10 10 antioxidant 0.5 0.5 0.5 0.5 ILO ** 22% 31% 35% 41% *: laminated structure - 10 ⁇ m particles **: ILO after an ignition time of 30 seconds
• Graphite is the material currently preferred as a filler additive in the context of the present invention.
• Other materials such as mica, kaolin, talc, molybdenum sulfide and vermicullite, already mentioned, also provide a significant increase in the ILO when incorporated into the filler as an additive under puff form.
• Table 2 shows that a composition 14 according to the invention and devoid of additive has an ILO much higher than that of a composition C2 containing no metal salt according to the invention, and that compositions 15 and 16 in accordance with the invention and containing a filler additive, respectively 3.5 parts of graphite and 5 parts of mica by weight for 100 parts of polyethylene, have a higher ILO than composition 14 without additive.
• the preparation of the mixtures according to the invention can be carried out on standard installations, for example Buss Ko kneaders or twin screw extruders, and the extrusion in the form of an outer sheath, insulator, or inner sheath is for example possible by means of a classic PVC extrusion line.
• the three essential constituents according to the invention and, where appropriate, the filler additive can be added directly to the base material during production, but it can sometimes also be advantageous to mix these (three) constituents already under the form of a mixture with the base material.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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Cited By (11)

Citations (7)

• 1996
  • 1996-11-07 EP EP96402368A patent/EP0774488A1/de not_active Withdrawn

Patent Citations (7)

Non-Patent Citations (1)

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