Perfluorocarbon copolymer films
AssigneeE. I. Du Pont de Nemours and Company
InventorStanley B. Levy
Life of this patent
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Abstract
A perfluorocarbon copolymer film which, upon heat shrinking, does not expand in the direction perpendicular to stretching.
Claims39
A film of a melt fabricable perfluorocarbon copolymer, having a shrinkage of 0 to 10 percent in a first direction in the plane of the film, and a shrinkage of at least 20 percent in a second direction in the same plane as the first and which is perpendicular to the first direction when heated for two minutes at about 50.degree. C. below the crystalline melting point of the polymer.
A film of a melt-fabricable perfluorocarbon copolymer, having transverse shrinkage of 0 to 10 percent, and longitudinal shrinkage of at least 20 percent, when heated for two minutes at about 50.degree. C. below the crystalline melting point of the polymer.
A process for uniaxially stretching a substantially unstretched film of a melt-fabricable perfluorocarbon copolymer comprising:
- (a) providing a pair of adjacent and parallel rolls, one roll having peripheral drive speed slower than that of the other;
- (b) contacting said substantially unstretched film under pressure against the slower driven roll and heating said film so that, in a stretch zone between said pair of rolls the film is at a temperature at least about 40.degree. C. above, and no greater than about 80.degree. C. above, the second order transition temperature of the polymer;
- the pair of rolls being positioned so that the ratio of film width to stretch zone length is at least about 3,
- (c) feeding said film from said slow roll into contact with and under pressure against the faster driven roll, the difference in peripheral drive speeds between the two rolls being such that the film is stretched between the rolls to between about 2.5 times the length of the unstretched film and the break point of the film;
- and then
- (d) holding the film under tension while cooling the film to below the second order transition temperature of the polymer.
A cooking surface having a melt-fabricable perfluorocarbon copolymer film covering the surface, wherein the film has a transverse shrinkage of 0 to 10 percent, and a longitudinal shrinkage of at least 20 percent, when heated for two minutes at about 50.degree. C. below the crystalline melting point of the polymer.
Dependencies are inferred from the claim text.