Tetrafluoroethylene/hexafluoropropylene copolymers with higher drawability

Abstract

A tetrafluoroethylene / hexafluoropropylene copolymer with high drawability is provided. Also provided is a process employing the polymer and an article coated with the polymer.

Description

[0001]This application claims priority from U.S. Serial No. 60 / 117,780 filed Jan. 29, 1999.FIELD OF THE INVENTION[0002]The invention relates to melt-processable tetrafluoroethylene (TFE) / hexafluoropropylene (HFP) copolymer melt pellets having an improved processability for wire and cable application and to a method of using this polymer to cost wire and cable conductors.BACKGROUND[0003]Melt processable copolymers with TFE and HFP are-well know under the name FEP. As perfluorinated thermoplasts, such copolymers have unique end-use properties like chemical resistance, weather resistance, low flammability thermal stability and outstanding electrical properties. Like other thermoplasts, FEP is easily molded to coated wires, tubes, pipes, foils and films.[0004]Because it has excellent thermal stability and is practically non-flammable, FEP is frequently used for plenum constructions to meet fire resistance requirements. It is also the natural choice in data transmission cables due to its...

AI Technical Summary

Benefits of technology

[0019]The invention provides a material for wire and cable coatings which can be processed at higher speeds and at higher temperatures for longer run times of the equipment. The invention furthermore provides a manufacturing process which is more economical and better controlled as to quality consistency. Still further, the invention provides a process for reducing die drool and the frequency of cone breaks during wire or cable coating extrusion coating.

Problems solved by technology

Such high extrusion rates are limited by the occurrence of melt-fracture like with many thermoplasts.

Melt-fracture results in surface roughness and / or uneven wall thickness.

Thus the manufacturing of these mixtures is a cumbersome and costly process.

Melt pelletizing of unstabilized polymer resins results in corrosion of the equipment used in the process and in metal contamination of the melt pellets.

However, the stabilization process of DE 2,613,642 and DE 2,613,795 is very difficult to manage due to corrosion of the equipment because of the use of a water steam.

Metal contaminants are difficult to cope with.

Such metal contaminants may result in degradation and decomposition of the copolymer at high processing temperatures.

Decomposition generally leads to discoloration and degradation, and to a build up of die drools.

Die drools impair the coating processing.

Also, cone breaks can occur.

Thus long processing times are more difficult to achieve.

Furthermore, extrusion temperatures have to be kept as low as possible to counteract the decomposition reactions and resulting toxic off-gases, the rate of which substantially increases with elevated temperatures.

On the other hand, lower extrusion temperatures result in higher melt-viscosities and thus an earlier onset of the melt fracture.

Lowering the intrinsic melt viscosity by lowering the molecular weight results in poorer mechanical properties.

The fluorination leads to perfluorinated endgroups whereas the humid heat treatment as mentioned above, mechanistically cannot result in a fully fluorinated polymer resin.

It is believed that inserted double bonds are present in the backbone leading to an inherent thermal unstability.

These kinds of bonds may lead to a discoloration at long exposures to high temperatures.

The destruction of the diads at processing conditions leads to having the molecular weight of these polymer chains and hence to negatively affecting the mechanical properties, and to formation of more unstable endgroups.

This process also is very costly.