Fire-resistant thermoplastic composition
The present invention relates to a fire-resistant thermoplastic composition, comprising at least one ethylene polymer and/or a copolymer of ethylene and of another organic compound, an inorganic loading material capable of releasing oxhydryl ions, an alkoxysilane acting as a coupling agent between the polymer or copolymer and the inorganic load, and a plasticizer. 
     Published French patent application FR-A-2 141 918 has already proposed such a composition, in which the alkoxysilane is an alkyl lower-alkoxysilane, an alcenyl-alkoxysilane, or an alcyne-alkoxysilane, especially a vinylsilane. That document also proposed substituting an aminosilane for the alkoxysilane, However, these compositions do not give very good results unless the polymer or copolymer is reticulated and one uses vinylsilane as a coupling agent. 
     The object of the present invention is to obtain a fire-resistant thermoplastic composition which does not require reticulation of the polymer or copolymer, and which still has good mechanical properties after aging and in the presence of oil. 
     The composition according to the invention is characterized by its alkoxysilane being an aminoalkyl-alkoxysilane and by a nonreticulated polymer or copolymer. 
     Preferably it has at least one of the following characteristics: 
     the aminoalkyl-alkoxysilane is gamma-aminopropyl-triethoxysilane; 
     the proportion of amino alkyl-alkoxysilane is between 0.5% and 5% by weight of the polymer or copolymer; 
     the copolymer is a copolymer of ethylene and vinyl acetate; 
     the copolymer is a copolymer of ethylene and ethyl acrylate or butyl acrylate; 
     the copolymer of ethylene is grafted with carboxyl groups; 
     the inorganic loading material is aluminum trihydrate, kaolin, silica, calcium carbonate, or talc; 
     the proportion of inorganic loading material is between 50% and 20% by weight of the polymer or copolymer; and 
     the plasticizer is triphenylphosphate, in the amount of 1% to 10%, by weight, of the polymer or copolymer. 
    
    
     What follows describes, by way of example, two thermoplastic compositions according to the invention and their mechanical properties after and before aging, either in air or in the presence of oil. 
     EXAMPLE 1 
     The composition comprises by weight: 
     
         ______________________________________
Copolymer of ethylene or of
                         100    parts
vinyl acetate
Aluminum Trihydrate Al(OH).sub.3
                         190    parts
Gamma-aminopropyl-triethoxysilane
                         125    parts
Antioxidant              1      part
(1, 2-dihydro-2, 2, 4-trimethyl-
quinolene)
Triphenylphosphate       3      parts
______________________________________
 
    
     The mechanical properties of this composition, as well as of an identical composition without the gamma-aminopropyl-triethoxysilane, are the following before and after aging: 
     
         ______________________________________
              Without Silane
                          With Silane
______________________________________
Resistance to breaking
                83.2          131
Rr (in bars)
Lengthening after
                92            180
breakage Ar (%)
After 10 days of
                Rr -55%       +16%
aging at 100° C.
                Ar +82%       -7%
After 7 days    Rr            +8.5%
at 135%         Ar            -20%
After 4 hours at 70° C.
                Rr -25%       -25%
in the presence of oil
                Ar +215%      +14%
&#34;ASTM n° 2&#34;
Index of                      39
threshold oxygen
______________________________________
 
    
     EXAMPLE 2 
     The composition comprises by weight: 
     
         ______________________________________
Copolymer of ethylene and of
                         100    parts
vinyl acetate grafted with
carboxyl groups
Aluminum Trihydrate Al(OH).sub.3
                         170    parts
Silica                   30     parts
Gamma-aminopropyl-triethoxysilane
                         2.5    parts
Antioxidant              1      part
(1, 2-dihydro-2, 2, 4-trimethyl-
quinolene)
Triphenylphosphate       3      parts
______________________________________
 
    
     The mechanical properties, as well as those of an analogous composition, without the gamma-aminopropyl-triethoxysilane, are the following, before and after aging: 
     
         ______________________________________
              Without Silane
                        With Silane
______________________________________
Resistance to   83          130
breaking Rr (in bars)
Lengthening at  52          150
breakage Ar (%)
After aging 10 days
                Rr brittle  +23%
at 100° C.
                Ar unusable -13%
After 4 hours at 70° C.
                Rr          -22%
in the presence of oil
                Ar          +35%
&#34;ASTM n° 2&#34;
______________________________________
 
    
     The invention is especially relevant to the manufacture of casing for electrical cables, such as the cables for telephone exchange.