High melt viscosity fluoropolymer process aid

Processing aid composition for a difficultly melt-processible polymer that contains an abrasive inorganic filler, said composition consisting essentially of:

• (a) at least 90 wt. % of a polymer that is compatible with the difficultly melt-processible polymer and
• (b) up to 10 wt. % of, with the parts totaling 100 %:
• (1) 5-95 parts by weight of a fluorocarbon copolymer which has an apparent viscosity at 200.degree. C of at least about 400 Pa.s measured at an apparent shear stress of 360 KPa and which at the melt-processing temperature of the difficultly melt-processible polymer is either in a melted form if crystalline or is above its glass transition temperature if amorphous;
• and
• (2) 95-5 parts by weight of a tetrafluoroethylene homopolymer or copolymer of tetrafluoroethylene and a monomer which is copolymerizable therewith, wherein the mole ratio of fluorine to hydrogen is at least 1:1, and which is solid at the melt-processing temperature of the difficultly melt-processible polymer.

Improved extrusion process comprising melt extruding a difficultly melt-processible polymer having incorporated therein an effective amount, to improve processibility, of a processing aid consisting essentially of, with the parts totaling 100 parts:

• (a) 5-95 parts by weight of a fluorocarbon copolymer which at the melt-processing temperature of the difficultly melt-processible polymer is either in a melted form if crystalline or is above its glass transition temperature if amorphous;
• and
• (b) 95-5 parts by weight of a tetrafluoroethylene homopolymer or copolymer of tetrafluoroethylene and a monomer which is copolymerizable therewith, wherein the mole ratio of fluorine to hydrogen is at least 1:1, and which is solid at the melt-processing temperature of the difficultly melt-processible polymer,
• said difficultly melt-processible polymer also having incorporated therein an abrasive inorganic filler that retards its processibility in the presence of (a) and (b), the improvement consisting of minimizing the retarding effect of the inorganic filler by employing (a) having an apparent viscosity at 200.C of at least about 400 Pa s measured at an apparent shear stress of 360 KPa.