Reactively Processed, High Heat Resistant Composition of Polypropylene and an Olefinic Interpolymer

Abstract

A propylene polymer is coupled with an olefinic interpolymer by a process comprising contacting under reactive processing conditions at least: A. 10 wt % of at least one propylene polymer; B. 10 wt % of at least one olefinic interpolymer; C. 35 wt % of at least one metal hydrate; and D. A coupling amount of a coupling agent, each weight percent based on the combined weight of the propylene polymer, olefinic interpolymer and metal hydrate. Wire and cable insulation sheaths made from compositions comprising the coupled polymer exhibit desirable heat resistance.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]The present application claims priority to U.S. patent application Ser. No. 61 / 059,356, filed on Jun. 6, 2008, the entire content of which is incorporated by reference herein.FIELD OF THE INVENTION[0002]This invention relates to compositions comprising a polypropylene polymer and an olefinic interpolymer. In one aspect, the invention relates to compositions comprising polypropylene and an olefinic interpolymer that have been reactively processed and which display characteristics of high heat resistance suitable for wire and cable coatings. In another aspect, the invention relates to power cables comprising an insulation layer while in still another aspect, the invention relates to a power cable in which the insulation layer comprises a composition comprising polypropylene and an olefinic interpolymer that have been reactively processed.BACKGROUND OF THE INVENTION[0003]Polymeric compositions are used extensively as primary insulation materi...

AI Technical Summary

Benefits of technology

"The invention relates to a composition made of a polypropylene polymer that has been modified with an olefinic interpolymer and a metal hydrate. This composition has improved resistance to heat, ignition, and flame spread, as well as good flexibility. The process for making this composition involves contacting the polypropylene polymer, olefinic interpolymer, metal hydrate, and a coupling agent under reactive processing conditions. The resulting composition can be used to make cables with improved insulation."

Problems solved by technology

When using silane-peroxide blends for polymer crosslinking, a compromise must be made between grafting efficiency and process efficiency, such as extrusion rate and run times. The formation of a crosslinkable material by this means is difficult to carry out since it requires critical control of the process.

If the process is conducted at too high a temperature, for example, the polymer may partially cross-link in the processing apparatus, e.g., an extruder, with consequent difficulties in achieving a consistently good quality product.

Moreover gel formation, screw-build up and scorching may result when using highly reactive silane-peroxide blends.

This is particularly significant for processes using conditions and processing equipment that impose severe melting and mixing conditions leading to high shear stresses in the polyolefin.

These problems generally arise due to early, and eventually complete, activation of the peroxide during the initial melting and homogenization process.

Traditionally, this problem has been dealt with by using less reactive silane blends, but this approach can diminish the grafting efficiency of the crosslinking reaction.

Radiation crosslinking requires complex equipment and is thus relatively costly to perform.

Furthermore, radiation can cause polymer degradation by oxidation and / or chain scission thus requiring special stabilization.

Furthermore, the sizes of cable that can be handled by commercial radiation equipment are limited, both in terms of jacket thickness and overall diameter of the cable.

This limitation is typically manifested as non-uniform crosslinking of the jacket and a resultant variation in physical properties around the circumference of the cable or within the material wall of the jacket.

Alternative materials, such as, polyurethane and fluorinated ethylene propylene elastomers, are expensive, and the materials are sensitive to water.

In addition, halogens often are required in order to make the materials flame resistant, and this reduces the attractiveness of these compounds.