Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-09-22
2003-04-29
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C524S127000, C524S145000, C524S425000, C524S427000, C524S436000, C174S11000P, C174S1210AR
Reexamination Certificate
active
06555605
ABSTRACT:
The present invention refers to a halogen-free additive composition, for polymer compounds with a halogen-free polymer base, that confers flame-retardant properties to the polymer to which it is added.
The present invention also concerns polymer products containing said flame-retardant composition; a preferred embodiment concerns the use of said polymer products containing the flame-retardant composition of the invention as a coating for telecommunication and low-voltage power transmission cables. The aforesaid cables coated with the polymer product containing the flame-retardant composition in question are also included within the framework of this invention.
Among the possible ways of making a polymer compound flame-retarded, one solution may be to add a halogenated substance to the base polymer. As an alternative, it is possible to use halogenated polymers (such as polyvinyl chloride) which reduce the inflammability of the compound. Nevertheless, these solutions present the drawback that the halogenated products of decomposition are toxic, so the use of these materials is inadvisable, at least for use in closed environments.
One halogen-free flame-retardant additive that endows polymer compounds with resistance to flame propagation is magnesium hydroxide (see, for example, patent GB 2 163 167). This substance is particularly appreciated for the fact that it does not begin to decompose until it reaches 220° C. and is thus able to withstand the various processing phases of the base polymer compound without degrading. However, to endow the polymer with these flame-retardant properties, a rather large quantity of magnesium hydroxide must be added. This may alter the mechanical properties of the polymer, particularly reducing drastically the extensibility of the polymer products so prepared. Other inorganic extenders, also capable of lending flame-retardant properties to the polymer to which they are added, have a weaker flame-retardant action than magnesium hydroxide.(e.g. the basic hydrated carbonates of aluminum and magnesium or sodium), which requires the use of greater quantities, with the result of markedly worsening the mechanical properties of the product. Other inorganic flame-retardant additives, such as the compounds of boron or aluminum hydroxide, since their decomposition temperature is below 200° C., are unsuitable as additives to the compound before the processing phases, typically effected, at higher temperatures, such as some types of polymer extrusion. Other inorganic substances (such as fiberglass, calcined kaolin, calcium carbonate,), unlike the substances cited earlier, at normal combustion temperatures undergo no decomposition reactions to give products capable of actively interfering with the combustion process (calcium carbonate, for example, decomposes at about 825° C.). Nonetheless, these substances are used as inert extenders to produce a “dilution effect” in plastics (see, for example, the volume “Compounding Materials for the Polymer Industry”, J. S. Dick 1987, Noyes publ., particularly pages 63 and 144). The result is that the combustibility of the compound is reduced as a consequence of the fact that there is less polymer material per unit of volume that can burn.
Another group of additives that can explicate a flame-retardant effect are the phosphorus-based flame-retardants (see, for example, the reference book
The Chemistry and Uses of Fire Retardants,
Chap. 2, J. W. Lyons, Wiley-Interscience Ed., 1970).Typical compounds containing phosphorus suitable for use as flame-retardant additives may be salts of phosphorous or phosphoric acid (phosphites, phosphates and polyphosphates), organic esters or polyesters of phosphoric acid (mono-, di- or tri-alkyl or -aryl phosphates or polyphosphates), phosphites (mono-, di- or tri-alkyl or -aryl phosphites), phosphonates or polyphosphonates (mono or dialkyl or -aryl phosphonates or polyphosphonates). Some phosphate compounds usable as flame-retardant additives also possess plasticizing properties and may thus modify the mechanical properties of the polymer, reducing the rigidity of the finished material. On the other hand, this characteristic limits the use of these additives in the polymer compound, since large quantities may cause a decrease in the mechanical resistance of the polymer. The alternative use of red phosphorus, when the quantities used are sufficient to provide the desired flame-retardant effect, may also have a negative impact on the electrical properties of the final compound, in addition to lending the compound a red coloration. Therefore, the need to add small quantities of these phosphorus compounds consequently limits the capacity to endow the base polymer with sufficient flame-retardant properties.
Besides just phosphorus compounds, it is also possible to use blends of phosphorus and nitrogen compounds as flame-retardant additives for polymers. These flame-retardant are, also indicated as “P-N blends (or additives)” (see
The Chemistry and Uses of Fire Retardants,
Chap. 2, J. W. Lyons, Wiley-Interscience Ed., 1970, page 20 and chap. 2).
Said nitrogen compounds may be inorganic salts such as ammonium salts, or organic compounds and their organic salts, such as guanidine, melamine and their derivatives (e.g. melamine cyanide or guanidilurea and their salts). Compounds containing both phosphorus and nitrogen may also be used, such as phosphates or polyphosphates of ammonium, guanidine or melamine, phosphoramides, phosphorylamides, phosphonated starch and phosphazene compounds.
Nevertheless, the use of these blends, in addition to the problems already mentioned for the use of phosphorus compounds, presents additional drawbacks associated with the possible toxicity of the products of decomposition of the nitrogen compounds. Nitrogen-based can therefore be added only in limited quantities, which reduces their flame-retardant capacity.
Patent GB 2 163 167 describes a flame-retardant composition for olefin polymers and copolymers containing magnesium hydroxide, red phosphorus and carbon black. Besides the aforesaid disadvantages to the use of red phosphorus, however, it was also observed that the use of carbon black also presents some practical drawbacks, such as a black color to the compound and a reduction of its electrical properties.
It has been found now that a composition according to the invention, containing magnesium hydroxide, calcium carbonate and a small quantity of P-N blend satisfies the need to lend the desired flame-retardant properties to the polymer compound to which it is added while maintaining the mechanical properties of the compound within limits acceptable for the use of the end product. This polymer compound may therefore be advantageously used for coating a conductor, e.g. of copper or aluminum, thus obtaining a cable with flame-retardant coating according to the present invention.
A surprising aspect of the invention (as observed in tables 2 and 3 of the examples) is the fact that a composition containing only magnesium hydroxide and a P-N compound does not ensure the necessary flame-retardation requisites in the final compound. A similar behavior can also be observed in a composition containing only calcium carbonate and the P-N compound. A composition containing magnesium hydroxide, calcium carbonate and a P-N compound, on the contrary, provides the desired flame-retardant properties in the final compound.
The desired flame-retardant characteristics are provided by adding a predetermined quantity of a composition containing magnesium hydroxide, calcium carbonate, at least a phosphorus compound and at least a nitrogen compound to the base compound.
The term “predetermined quantity” is used to mean a quantity of said composition, containing each of the aforesaid components in a determined ratio, capable of imparting the desired flame-retardant properties to the polymer compound, such as to maintain the mechanical properties of the compound within acceptable values. As illustrated here below, both the ratio of total flame-retardant composition to base polymer and th
Finnegan Henderson Farabow Garrett & Dunner LLP
Pirelli Cavi E Sistemi S.p.A.
Szekely Peter
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