Diffusion film, electrode having the diffusion film, and process for producing diffusion film
A diffusion membrane contains uncalcined polytetrafluoroethylene (PTFE), calcined PTFE and a conductive substance. An electrode has the diffusion layer (membrane) and a catalyst layer disposed thereon. A process for producing diffusion membranes comprises dispersing uncalcined PTFE, calcined PTFE and a conductive substance in a dispersion medium, removing the dispersion medium, adding a liquid lubricant followed by kneading, compressing the resultant kneaded product (preferably a rod-shaped preform) to expand the same into a membrane, and removing the liquid lubricant. The diffusion membrane preferably contains 1 to 30 wt % of the uncalcined PTFE and 5 to 30 wt % of the calcined PTFE. The conductive substance is desirably a combination of graphite and carbon black. The diffusion membrane is free from local variation in properties, has suitable mass producibility and can be produced inexpensively.
1. A diffusion layer membrane comprising 1 to 30 wt. % uncalcined polytetrafluoroethylene fibers, 5 to 30 wt. % calcined polytetrafluoroethylene powder having a mean particle diameter of 5 to 100 μm and a conductive substance.
2. The diffusion layer membrane as claimed in claim 1 wherein the conductive substance is a combination of graphite and carbon black.
3. The diffusion layer membrane as claimed in claim 2 , which contains the conductive substance in an amount of 50 to 90 wt %.
4. The diffusion layer membrane of claim 1 , wherein the diffusion layer membrane is obtained by dispersing uncalcined polytetrafluoroethylene, calcined polytetrafluoroethylene and a conductive substance in a dispersion medium, removing the dispersion medium, adding a liquid lubricant followed by kneading, compressing the resultant kneaded product to extend the same into a membrane, and removing the liquid lubricant.
5. The diffusion layer membrane as claimed in claim 1 which contains the conductive substance in an amount of 50 to 90 wt %.
6. An electrode comprising:
a diffusion layer membrane comprising 1 to 30 wt. % uncalcined polytetrafluoroethylene fibers, 5 to 30 wt. % calcined polytetrafluoroethylene powder having a mean particle diameter of 5 to 100 μm and a conductive substance; and
a catalyst layer disposed on the diffusion layer.
7. The electrode of claim 5 , wherein the diffusion layer membrane contains a conductive substance in an amount of 50 to 90 wt %.