Method for forming microporous fluorocarbon polymer sheet and product
First Claim
1. In a method for forming a microporous fluorocarbon sheet membrane, the steps of:
- (a) mixing an aqueous dispersion of fluorocarbon polymer with a pore-forming agent comprising a watersoluble crystallizable metallic organic salt, the crystal of said salt being stable at the sintering point of said fluorocarbon polymer,(b) forming a wet sheet from said aqueous dispersion,(c) concentrating the aqueous dispersion to grow crystals of said dissolved organic salt dispersed through said sheet,(d) drying said crystal-containing sheet,(e) sintering the dry sheet, and(f) leaching the salt crystals from the sheet in an aqueous medium and removing the formed aqueous solution from the sheet.
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Abstract
A method for forming a microporous sheet of fluorocarbon polymer (e.g., polytetrafluoroethylene). An aqueous dispersion of polytetrafluoroethylene which includes a dissolved water-soluble, crystallizable metallic organic salt, preferably sodium benzoate, is formed into a sheet. Water is evaporated from an exposed surface of the sheet to grow crystals of the organic salt dispersed throughout the sheet. Then, the sheet is sintered. After cooling, the salt crystals are leached from the sheet by dissolution in water to leave a porous structure suitable for such uses as a filtration membrane or as a separation barrier in batteries or electrolytic cells.
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Citations
27 Claims
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1. In a method for forming a microporous fluorocarbon sheet membrane, the steps of:
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(a) mixing an aqueous dispersion of fluorocarbon polymer with a pore-forming agent comprising a watersoluble crystallizable metallic organic salt, the crystal of said salt being stable at the sintering point of said fluorocarbon polymer, (b) forming a wet sheet from said aqueous dispersion, (c) concentrating the aqueous dispersion to grow crystals of said dissolved organic salt dispersed through said sheet, (d) drying said crystal-containing sheet, (e) sintering the dry sheet, and (f) leaching the salt crystals from the sheet in an aqueous medium and removing the formed aqueous solution from the sheet. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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- 17. A microporous continuous sheet consisting essentially of fluorocarbon polymer and including pores dispersed throughout said sheet, said pores being interlaced in a void space network of intersecting shafts forming a matte surface in a sponge-like configuration on at least one side of said sheet, said sheet forming the negative image of said pores.
- 26. An electrolytic cell comprising an anolytic compartment, a catholyte compartment and a membrane therebetween, said membrane comprising a microporous continuous sheet consisting essentially of fluorocarbon polymer and including pores dispersed throughout said sheet, said pores being interlaced in a void space network of intersecting shafts forming a matte surface in a sponge-like configuration on at least one side of said sheet, said sheet forming the negative image of said pores.
Specification