NL8403426A - POLYMER PREPARATION SUITABLE FOR INSULATING TELEPHONE WIRES. - Google Patents

Description

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Polymer preparation suitable for insulating telephone wires.

This invention relates to polymer compositions suitable for insulating metal conductors, especially telephone wires.

The person skilled in the art knows how to use polyethylene with a density below 0.935, obtained in the presence of free radical initiators, or else polyethylene with a density above 0.955, obtained by polymerizing ethylene in the presence of Ziegler catalysts, for insulating metal conductors.

The problem faced by this invention was the use of polyethylene compositions with interposed densities, for example, from 0.940 to 0.950, which for mechanical insulating electrical and telephone wires have mechanical and dielectric properties at least equivalent to those of the corresponding homopolymers. In order to solve that problem, the applicant has identified the need to select certain characteristics of those polymers very closely.

An object of this invention consists of a polymer composition with a density between 0.940 and 0.950 and a fluidity index below 2 dg / min, which consists of at least 50 to 60 wt% of at least one copolymer A of ethylene with α-olefins with 3 to 12 carbon atoms, and having a density between 0.932 and 0.940, and 40 to 50% by weight from at least one polymer B of ethylene with a density between 0.52 and 0.960, characterized in that a) the fluidity index of copolymer A is between 1.5 and 5 dg / min, and b) the fluidity index of polymer B is between 0.15 and 0.4 dg / min.

The fluidity indices are measured at 190 ° C

8403426 3> 5 - 2 - measured with a load of 2.16 kg, according to the regulation ASTM D 1238-73.

The composition of the invention may additionally contain 3 to 10 parts by weight of at least one polyethylene-5 wax with molecular weight below 6000 per 100 parts by weight of copolymer / polymer B mixture. The presence of the polyethylene wax with a fluidity index above about 100 permits molding of the composition of the invention by extrusion, and even at great speed.

For a foam insulation of telephone wires, the preparation according to the invention also contains up to 1.5 parts by weight of blowing agent per 100 parts by weight of the mixture of copolymer A with polymer B. That blowing agent is preferably chosen among the compounds of diazo group which decompose between 170 ° and 230 ° C, such as azodicarbonamide.

Advantageously, the content of the copolymer A in ct-olefin units is between 0.9 and 2.2 mol%. The copolymer A may contain 20 units derived from one or more α-olefins. Advantageously, at least one α-olefin of the copolymer A has at least 4 carbon atoms and is butene-1, hexene-1, octene-1 and / or 4-methylpen-toe-1. In that case it may be advantageous that the distribution of the α-olefin units over this copolymer is heterogeneous, that this copolymer has crystalline regions and amorphous regions, and that the content of α-olefin units varies within this copolymer. between 0.2 and 5 times their average content.

The polymer B is preferably obtained by homopolymerization of ethylene at low pressure (below 100 bar) and at moderate temperature (below 100 ° C) and in the presence of a Ziegler type catalytic system. The polymer B may also be a copolymer of ethylene with at least one alpha olefin having 3 to 12 carbon atoms, preferably obtained by copolymerization of ethylene and at least one alpha olefin under the conditions indicated above.

8403426 - 3 -

The preparation according to the invention is prepared in any known manner from copolymer A and polymer B and optionally the wax and / or the porogenic agent, for example by hot mixing and kneading, before being extruded.

The preparations according to the invention have a particularly interesting application in insulating metal conductors. They are used with the co-extrusion technique for insulating cables as described, for example, in the Encyclopedia of Chemical Technology of 10 Kirk-Othmer, 3 edition, vol. 18, pages 194-195. The compositions of the invention allow high extrusion rates, on the order of 2000 m / min. More particularly, the compositions containing at least one blowing agent are intended for foamed insulation of telephone wires. They have 15 small, closed cells that are regularly distributed over the whole. The insulation obtained has good mechanical properties (in particular it has good flattening resistance) and also good dielectric properties.

Furthermore, the compositions of the invention may contain the per se known antioxidants, stabilizers, dyes and other auxiliary substances.

The invention is further illustrated by the following examples.

Example I

Kneaded together at 240 ° C - 50 parts by weight of copolymer A of ethylene with butene-1, with a density of 0.938 and a fluidity index (measured according to the ASTM D 1238-73 regulation) of 4 dg / min, which 1.2 mol.% Consisted of butene-1 and is marketed by the Société 30 Chimique des Charbonnages under the name Lotrex RG 0305,

- and 50 parts of polyethylene with a density of 0.955 and a fluidity index (according to the ASTM regulation

D 1238-73) of 0.2 dg / min which is marketed by Nafthachimie 35 under the name Natene 55010 AG.

The resulting mixture had a fluidity 84 3 4 2 6 & c -4 index of 1.2 dg / min and was extruded from an extruder at a speed of 2000 m / min to insulate metal wires with it. The surface of the obtained insulation looked smooth.

Example II

At 240 ° C, 95 parts by weight of the composition obtained in Example 1 and 5 parts by weight of polyethylene wax were mixed with a molecular weight (numbered and determined by penetration chromatography) of 3000.

The obtained preparation had a density of 0.947 and a fluidity index of 1.3 dg / min. It was extruded under the same conditions as in Example I. The surface of the insulation obtained was smooth. "

Example III

Kneaded together at 240 ° C - 50 parts by weight of copolymer of ethylene with butene with a density of 0.935 and a fluidity index of 1.5 dg / min. - 40 parts by weight of polyethylene with a density of 0.953 and a fluidity index of 0.25 dg / min, which had the designation "Wacker 5551", and - 10 parts by weight of the polyethylene also used in Example II. 25 was ethylene.

The resulting preparation had a density of 0.943 and a fluidity index of 1.1 dg / min; With this, insulation with a beautiful surface could be obtained by extrusion.

Example IV

To 100 parts of the preparation obtained in Example I was added 0.9 parts of azodicarbonamide (supplied by Olin under the designation "Kempore 125 MC"). The resulting mixture was extruded from an extrusion press such that foamed insulation of telephone wires was obtained - the insulation had a good surface 8403426 - 5 - and its resistance to crushing (determined according to regulation CM 25 of the Center National d'Etudes des Télécommunications) was 1880 N over 50 mm .

Example V

To 100 parts by weight of Example II

0.8 ml of azodicarbonamide obtained, which was marketed under the name "Genitron EPD", was obtained.

The resulting mixture was extruded from an extrusion press to provide foamed telephone wire insulation. The appearance of this insulation was good.

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Claims (6)

A polymeric composition having a density between 0.940 and 0.950 and a fluidity index below 52 dg / min, which consists of 50 to 60 wt% of at least one copolymer A of ethylene with α-olefins having 3 to 12 carbon atoms having a density between 0.932 and 0.940, and 40 to 50 wt% of an ethylene polymer B with a density between 0.952 and 0.960, characterized in that a) the fluidity index of the copolymer A is between 1.5 and 5 dg / min and b) the fluidity index of polymer B is between 0.15 and 0.4 dg / min. Preparation according to claim 1, characterized in that per 100 parts by weight of copolymer A with polymer B additionally contains 3 to 10 parts by weight of at least one polyethylene wax with a molecular weight below 6000. Preparation according to claim 1 or 2, which additionally contains 1.5 parts by weight of blowing agent per 100 parts by weight of the mixture of copolymer A with polymer B, characterized in that the blowing agent is one or more compounds with diazo group. Preparation according to any one of the preceding claims, characterized in that the copolymer A contains units derived from at least one α-olefin with at least 4 carbon atoms and in that the distribution of the C 1 -olefin units over copolymer A is heterogeneous such that the copolymer has crystalline regions and amorphous regions, and that the content of the copolymer in α-olefin units varies between 0.2 and 5 times their average content. 5. A composition according to any one of the preceding claims, characterized in that the polymer B is a copolymer of ethylene with at least one α-olefin with 3 to 12 carbon atoms. 8403426 V '--- - · * * - / - Insulated conductors, the insulation of which is obtained from a preparation according to any one of the preceding claims. 8403426