Porous polytetrafluoroethylene and preparation
AssigneeE. I. Du Pont de Nemours and Company
InventorsEdward George Howard, Jr., Arthur Zenker Moss
Life of this patent
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Abstract
This invention relates to porous polyfluoroethylene (PTFE), shaped articles prepared therefrom, and to methods of preparing said articles.
Claims30
A porous polytetrafluoro-ethylene PTFE/polymer composition prepared by a process comprising:
- (a) contacting PTFE with a fluid which penetrates and swells but does not significantly dissolve the polymer or eliminate viscoelastic memory therefrom, at a temperature in the range of about 250.degree.-400.degree. C.;
- (b) cooling and separating the penetrated polymer from unabsorbed fluid, said polymer containing up to about 80% by weight of absorbed fluid;
- and
- (c) removing the absorbed fluid, to form a porous product having a single DSC melting endotherm, the melting point being in the range of about 315.degree. to 333.degree. C. with an associated heat of fusion of at least 35 J/g.
A non-draining polytetrafluoroethylene (PTFE) polymer composition prepared by a process comprising:
- (a) contacting PTFE, characterized by a melting point in the range of 315.degree. to 333.degree. C. and a heat of fusion of less than about 35 J/g which melting point and heat of fusion is determined by Differential Scanning Calorimetry from a specimen which has, prior to said determination, been heated at least 20.degree. C. above its melting point and recrystallized from the melt at a cooling rate of 1.degree. C./min from 20.degree. C. above its melting point to about 250.degree. C. or lower, in an inert atmosphere, with a fluid which penetrates but does not significantly dissolve the PTFE or eliminate viscoelastic memory therefrom, at a temperature in the range of about 250.degree.-400.degree. C.;
- and
- (b) cooling and separating the penetrated PTFE/fluid composition from unabsorbed fluid, said composition containing up to about 80% by weight of absorbed fluid, the PTFE moiety of said composition having a single DSC melting endotherm, the melting point being in the range of about 315.degree. C. to 333.degree. with an associated heat of fusion of a least 35 J/g.
A composite comprising PTFE and up to about 50% by weight of one or more polymers other than PTFE, prepared according to a process comprising:
- (a) contacting PTFE, characterized by a melting point in the range of 315.degree. to 333.degree. C. and a heat of fusion of less than about 35 J/g which melting point and heat of fusion is determined by Differential Scanning Calorimetry from a specimen which has, prior to said determination, been heated at least 20.degree. C. above its melting point and recrystallized from the melt at a cooling rate of 1.degree. C./min from 20.degree. C. above its melting point to about 250.degree. C. or lower, in an inert atmosphere, with a fluid which penetrates and swells but does not significantly dissolve the PTFE or eliminate viscoelastic memory therefrom, at a temperature in the range of about 250.degree.-400.degree. C.;
- (b) cooling and separating the penetrated, swollen PTFE from unabsorbed fluid;
- (c) removing the absorbed fluid to form a porous product having a single DSC melting endotherm, the melting point being in the range of about 315.degree. C. to 333.degree. C. with an associated heat of fusion of at least 35 J/g;
- (d) infusing one or more polymerizable monomers and appropriate initiators into the porous product from step (c);
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- (e) polymerizing the one or more monomers to form the said composite.
An unstretched, porous PTFE containing up to 81% voids, and having a single crystalline melting point, said melting point being in the range of 315.degree. to 333.degree. C. with an associated heat of fusion of at least 35 J/g.
A porous, shrink-resistant polytetrafluoro-ethylene (PTFE) shaped article having a mean pore size of less than about 10 .mu.m, a porosity of at least 40%, a DSC melting point in the range of 315.degree. to 333.degree. C. with an associated heat of fusion of at least 35 J/g, and having no DSC melting endotherm at temperatures above 370.degree. C.
Porous PTFE product made by a process for preparing a porous shaped solid PTFE article comprising:
- (a) forming a shaped solid article of PTFE, characterized by a melting point in the range of 315.degree. to 333.degree. C. and a heat of fusion of less than about 35 J/g which melting point and heat of fusion is determined by Differential Scanning Calorimetry from a specimen which has, prior to said determination, been heated at least 20.degree. C. above its melting point and recrystallized from the melt at a cooling rate of 1.degree. C./min from 20.degree. C. above its melting point to about 250.degree. C. or lower;
- (b) contacting the shaped article, at a temperature in the range of about 250.degree. C. to 450.degree. C., with fluid which penetrates and swells the shaped article, the shaped article thereby substantially retaining its shape;
- (c) removing the fluid from the shaped article to form said porous PTFE article which has a single DSC melting endotherm, the melting point being in the range of about 315.degree. C. to 333.degree. C. with an associated heat of fusion of at least 35 J/;
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- (d) stretching said article to increase its porosity.
Dependencies are inferred from the claim text.