Thermoplastic elastomer compositions rheology-modified using peroxides and free radical coagents

Abstract

Rheology-modified thermoplastic elastomer compositions comprising a melt blend of an ethylene / a-olefin polymer and a high melting polymer such as polypropylene or a propylene / a-olefin copolymer wherein the rheology modification is induced by a combination of a peroxide and a free radical coagent. The resulting compositions have an elastomeric phase, a non-elastomeric phase and certain physical properties that exceed those of a like composition that is rheology-modified by peroxide alone. The compositions can be used to make a variety of articles of manufacture, such as automotive instrument panel skins, via calendaring and thermoforming procedures.

Description

FIELD OF THE INVENTION This invention relates generally to rheology-modified thermoplastic elastomer (TPE) compositions that comprise an elastomeric ethylene / alpha (α)-olefin (EAO) polymer or EAO polymer blend and a high melting propylene polymer, wherein both components are peroxide-modified and to the preparation of the compositions, use of such compositions in processes such as calendaring and thermoforming to make articles of manufacture and the resulting articles of manufacture. This invention particularly relates to such compositions wherein the rheology modification is induced by a combination comprising an organic peroxide and a free radical coagent, methods for preparing the compositions, such as by modifying a physical blend of the components, and use of such compositions in calendaring operations and thermoforming applications. BACKGROUND OF THE INVENTION Heck et al. describe rheology modified TPE compositions in WO 98 / 32795. The rheology modification can be induced by ...

AI Technical Summary

Benefits of technology

Applicant has found that rheology modification by addition of at least one peroxide and at least one free radical coagent has a signicant effect on the melt toughness and high temperature tensile properties of blends of at least one elastomeric EAO polymer or EAO polymer blend and a polyolefin such as PP. The rheology modified compositions of this invention have melt toughness and high temperature tensile properties that are higher than corresponding compositions rheology modified by the addition of peroxides alone. As such, one aspect of this invention is a rheology-modified, substantially gel-free thermoplastic elastomer (TPE) composition comprising an EAO polymer or EAO polymer blend and a high melting polymer selected from the group consisting of polypropylene homopolymers and propylene / ethylene copolymers, wherein the composition is rheology modified by at least one peroxide and at least one free radical coagent and the rheology modified composition has a melt toughness of at least 600 centinewton millimeters per second (cNmm / s), a true ultimate tensile strength at 140° C. of at least 3 mega-Pascals (MPa) and an elongation to break at 140° C. of at least 400%. The TPE compositions may be compounded with conventional additives or process aids including, for example, fillers, stabilizers, dispersants, pigments and process oils. Compounds prepared from the rheology modified polymers of this invention retain their processing advantages over compounds prepared from the same polymers, but rheology modified by peroxide alone.

A third aspect of this invention is an article of manufacture having at least one component thereof fabricated from the TPE composition of the first aspect of the invention. The TPE compositions suitably include at least one additive selected from the group consisting of process oils, fillers and blowing agents. The compositions readily allow formation of articles of manufacture using apparatus for calendaring and / or thermoforming. In a related aspect, the TPE compositions of the first aspect may be blended with another polymer, preferably one of the polymers used to make the TPE composition, prior to fabrication of an article of manufacture. Such blending may occur by any of a variety of conventional techniques, one of which is dry blending of pellets of the TPE composition with pellets of another polymer.

Problems solved by technology

If the elongation is too low, the sheeting will tear when thermoformed.

However, lower peroxide levels result in lower melt strength and less tensile strength.