Convective leaching of polybenzazole films
AssigneeThe Dow Chemical Company
InventorsLalitha Reddy, Willie E. Rochefort, Ming-Biann Liu, Peter E. Pierini
Life of this patent
Estimating the term…
Abstract
Films made from polybenzazole dopes can quickly be leached to remove polyphosphoric acid and other residual solvents by passing a leaching fluid such as steam through pores in the wet, never dried film. The process can reach acceptable residual phosphorous levels (1500-2000 ppm) in as little as about 2 or 3 minutes.
Claims19
A process to leach residual solvent from a polybenzazole film that has two faces, comprising the step of contacting one face of the wet, never-dried polybenzazole film with a fluid, that is capable of removing residual solvent from the film, at a pressure higher than the pressure on the other face of the film such that the fluid passes through the film from one face to the other, whereby a polybenzazole film containing no more than about 2000 ppm phosphorus is formed.
A process to coagulate and leach a dope film that has two faces and contains polybenzazole polymer dissolved in polyphosphoric acid, said process comprising the steps of:
- (1) contacting the dope film with a coagulant fluid;
- and
- (2) contacting one face of the wet, never dried polybenzazole film with a leaching fluid, that is capable of removing residual solvent from the film, at a pressure higher than the pressure on the other face of the film such that the fluid passes through the film from one face to the other,
- whereby a polybenzazole film containing no more than about 2000 ppm phosphorus is formed.
The process of claim 16 wherein the steam has a temperature of at least about 150.degree. C.
A process to coagulate and leach a dope film that has two faces and contains polybenzazole polymer dissolved in polyphosphoric acid, said process comprising the steps of:
- (1) contacting the dope film with an aqueous solution that contains 10-50 weight percent phosphoric acid for no more than about 5 minutes:
- and
- (2) contacting one face of the wet, never dried polybenzazole film with steam at a pressure higher than the pressure on the other face of the film, such that the steam passes through the film from one face to the other, for no more than about 15 minutes,
- whereby a polybenzazole film containing no more than about 2000 ppm phosphorus is formed.
Dependencies are inferred from the claim text.