Peroxide cured fluorocarbon elastomer compositions

Abstract

A process involves adding a peroxide masterbatch to a molten blend of a fluorocarbon elastomer and a thermoplastic material. The peroxide masterbatch contains greater than or equal to 5% weight percent organic peroxide, further contains a fluorocarbon elastomer, and typically also contains a crosslinker containing at least two sites of olefinic unsaturation. The fluorocarbon elastomer in the molten blend and in the peroxide masterbatch may be the same or different. After the peroxide masterbatch is added to the molten blend, the combination is mixed at a temperature and for a time sufficient to effect cure of the fluorocarbon elastomers. By using a masterbatch, a faster and more uniform dispersion of peroxide curative is possible due to pre-dispersion of peroxide in the elastomer phase, which leads to shaped articles having improved mechanical properties.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10 / 771,693 filed on Feb. 4, 2004, the disclosure of which is incorporated herein by reference.INTRODUCTION [0002] The present invention relates to dynamic vulcanization of fluorocarbon elastomers in thermoplastics. More particularly, it relates to the use of organic peroxides as curing agents for the elastomers. [0003] Cured elastomers or rubbers have a variety of physical properties useful for applications in molded articles. Among the properties are a high degree of flexibility, elasticity, and resistance to compression set. As such they find use in a variety of applications, such as seals and gaskets. Uncured elastomers or rubbers are in the form of a resin or gum. To obtain a molded article with suitable elastomeric properties, the uncured resins are crosslinked or cured with a variety of crosslinking agents. [0004] For conventional elastomers, cure is generally ca...

AI Technical Summary

Benefits of technology

[0003] Cured elastomers or rubbers have a variety of physical properties useful for applications in molded articles. Among the properties are a high degree of flexibility, elasticity, and resistance to compression set. As such they find use in a variety of applications, such as seals and gaskets. Uncured elastomers or rubbers are in the form of a resin or gum. To obtain a molded article with suitable elastomeric properties, the uncured resins are crosslinked or cured with a variety of crosslinking agents.

[0007] In one aspect, the problem of post curing can be minimized by using fast reacting crosslinkers such as organic peroxides, preferably in combination with organic crosslinking molecules having two or more sites of olefinic unsaturation. Because the peroxide initiated cure is rapid, the cure tends to be nearly completed by the time the molding is finished, or in the case of dynamic vulcanization, by the time the dynamic blending is finished. In this way, peroxide initiated curing provides faster turnaround time and molded articles with desirable physical properties.

[0010] In one embodiment, a high temperature peroxide is added to a molten blend of fluorocarbon elastomer and thermoplastic material to make a thermoplastic vulcanizate (TPV) by a process of dynamic vulcanization. The peroxide is subject to a lower level of volatilization and degradation due to its high temperature stability, which leads to improved physical properties of shaped articles made from the TPV's.

Problems solved by technology

The heat generated can lead to volatilization of various components of the composition during the post cure phase.

Physical properties such as tensile strength may be adversely affected.

Because it is added to a hot molten mixture of an elastomer and thermoplastic, the peroxide may splash or bump upon addition.