NZ210343A - Cable insulating polymeric compositions - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £10343 210343 Plic: WE COT NO DRAWIi ■ Dau>;.: Cotrpidte Spac:.'--!iJ.l cijsk . GCft.CSb./ .1.0. . H.Qv6.2>|.<t£iH.Qi.61 /.l,8.... , .v;; ;* ..'.3D. 3 .< ■ I— SL-jSTiiunnji OF Appuasr UNDER StCMf. 24 CTAfJDA'N"' TE t + £Vy KMiTtD- NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "CABLE INSOUXZNG OOMPOUTC- !/ WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: r\ 210343 This invention relates to a silane cross-linkable polymer mixture for the sheathing of electric and/or optical cables and wires, containing copolymers of ethylene-vinyl acetate and ethylene-butyl acrylate, organosilane grafted thereon for the cross-linking, a cross-linking catalyst, as well as a flame-retardant filling material.

Polymer mixtures of the aforementioned type for the sheathing of cables and wires are commercially available. Upon adding the catalyst, they are chiefly processed by way of extrusion in the course of which, owing to the effects of humidity from the ambient atmosphere and on account of the grafted silane, there occurs a silane cross-linking or vulcanizing. As a catalyst there is used, for example, dibutyl-tin dilaurate in the form of a 10-% batch based on ethylene-vinyl acetate (EVA). The silane cross-linking can be accelerated by immersing the extruded product in hot water or by exposing it to water vapour. The cross-linked product shows to have an elongation at break of about 130% and an oxygen index of 29%. With regard to some purposes of practical application, the material is not sufficiently flame-retardant, with this being indicated by the relatively low oxygen index. With this material it is not possible to increase the flame-retardant properties by adding a further aluminium hydroxide. Moreover, with regard to some practical applications, the material is of insufficient flexibility.

It is an object of the present Invention to modify the aforementioned polymer mixture in such a way that the cross-linked product shows to have a substantially improved flame-retardant property as well as a higher flexibility.

Accordingly there is provided a silane cross-linkable polymer mixture for the sheathing of electric and/or optical cables and wires, containing copolymers of ethylene-vinyl acetate and ethylene-butyl acrylate, an organosilane grafted thereon for the cross-linking, a cross-linking catalyst, and a flame-retardant filling material, wherein the mixture additionally contains 3 to 15/1 by weight of the total amount of the mixture of ethylene-vinyl acetate having a vinyl-acetate content of 50%, and 21 to 32% by weight of the total amount of the mixture of aluminum hydroxide.

By combining the aforementioned polymer mixture with an ethylene-vinyl acetate copolymer having a vinyl-acetate content of 50% It is achieved, that the mixture can take up a considerable amount of aluminum hydroxide, thus considerably improving the flame-retardant properties of the final product. At the same time, the final product shows to have a substantially higher flexibllltty than the aforementioned polymer mixture. In spite of this modification, the mixture can be cross-linked Just like the conventional types of silane cross-linkable polymer mixtures. The final product shows to have an elongation at break at 150%, and thus complies better with the requirements of German Military Specification VDE 0207, Pt. 27, than the starting mixture. The oxygen index amounts to about 40%, which means to imply that the flame-retardant properties were able to be inp roved considerably, 2103 43 Therefore, also with thin cables, it is possible to comply with the flame test according to VDE 0472, Pt.804 Method C. In spite of the higher filling degree, the modified material is considerably more flexible than the aforementioned silane cross-linked material.

The cross-linkable polymer mixture according to the invention has a composition within the ranges specified below, with ethylene-vinyl acetate being referred to as EVA, and with vinyl-acetate being referred to as VA: grafted, flame-retardant polymer 53 to 75% by weight EVA copolymer (50%VA) 3 to 15% by weight aluminum hydroxide 21 to 32% by weight The preferred composition consists of the following components: grafted, flame-retardant polymer 146 parts by weight + catalyst EVA copolymer (50% VA) 40 parts by weight aluminum hydroxide 85 parts by weight The cross-linked insulating compound has the following properties: tensile strength approx. 9 N/mma elongation at break approx. 150% Shore-A hardness approx. 88 oxygen index approx. 40% The cross-link time for 1mm thick stampings amounts to

Claims (3)

2103 about three hours in the hot-water bath at 70°C, by adding the usual catalyst of 3% as a batch. - 5 - 210^43 What we claim is:

1. A silane cross-linkable polymer mixture for the sheathing of electric and/or optical cables and wires, containing copolymers of ethylene-vinyl acetate and ethylene-butyl acrylate, an organosilane grafted thereon for the cross-linking, a cross-linking catalyst, and a flame-retardant filling material, wherein the mixture additionally contains 3 to 15% by weight of the total amount of the mixture of ethylene-vinyl acetate having a vinyl-acetate content of 50%, and 21 to 32% by weight of the total amount of the mixture of aluminum hydroxide.

2. A polymer mixture as claimed In claim 1, wherein the content of organosllane-grafted copolymers of ethylene-vinyl acetate and ethylene-butyl acrylate and the cross-linking catalyst amounts from 53 to 75% by weight of the total amount of the mixture.

3. A polymer mixture as claimed in claim 1 or 2, comprising the following composition: 145 parts by weight of flame-retardant, grafted copolymer of ethylene vinyl acetate and ethylene-butyl acrylate and catalyst, 40 parts by weight of ethylene-vinyl acetate copolymer with 50% of vinyl acetate, and 85 parts by weight of aluminum hydroxide. STANDARD TELEPHONES AND CABLES PTY. LIMITED C.H. Matthews Secretary "9 SEPI987 *