US4138459A — Process for preparing a microporous polymer film

Claim 1

Independent Claim 216 words

In a process for the preparation of an improved open-celled microporous polymer film in which a non-porous, crystalline, elastic precursor polymer film, said precursor film having an elastic recovery at 0 recovery time when subjected to a standard strain of 50% at 25° C. and 65% relative humidity of at least 40% and a percent crystallinity of at least 20%, is uniaxially cold-stretched at a temperature in the range of between about -20° C. and a temperature 25° C. below the crystalline melting temperature of the polymer film followed by hot-stretching, in the same direction, said cold-stretched film at a temperature in the range of between about 25° C. below the crystalline melting temperature of the polymer film and 5° C. below the crystalline melting temperature of the polymer film to produce a microporous film, the improvement which comprises heat relaxing said hot-stretched film by exposing the film under tension to a temperature in the range of between about 40° C. below the crystalline melting temperature of the polymer film and 5° C. below the crystalline melting temperature of the film such that the maximum dimension, in the direction of stretch, of the hot-stretched microporous film is decreased by between about 15 and 20%, based on the length of said hot-stretched microporous film prior to relaxation.

Claim 2

Dependent Claim 216 words

In a process for the preparation of an improved open-celled microporous polymer film in which a non-porous, crystalline, elastic precursor polymer film, said precursor film having an elastic recovery at 0 recovery time when subjected to a standard strain of 50% at 25° C. and 65% relative humidity of at least 40% and a percent crystallinity of at least 20%, is uniaxially cold-stretched at a temperature in the range of between about -20° C. and a temperature 25° C. below the crystalline melting temperature of the polymer film followed by hot-stretching, in the same direction, said cold-stretched film at a temperature in the range of between about 25° C. below the crystalline melting temperature of the polymer film and 5° C. below the crystalline melting temperature of the polymer film to produce a microporous film, the improvement which comprises heat relaxing said hot-stretched film by exposing the film under tension to a temperature in the range of between about 40° C. below the crystalline melting temperature of the polymer film and 5° C. below the crystalline melting temperature of the film such that the maximum dimension, in the direction of stretch, of the hot-stretched microporous film is decreased by between about 15 and 20%, based on the length of said hot-stretched microporous film prior to relaxation.

Claim 3

Dependent Claim 43 words

An improved process in accordance with claim 1 wherein said heat relaxation temperature is in the range of between about 25° C. below the crystalline melting temperature of the polymer film and 10° C. below the crystalline melting temperature of the polymer film.

Claim 4

Dependent Claim 31 words

An improved process in accordance with claim 1 wherein said heat relaxation step comprises moving said cold and hot stretched microporous film under tension over at least one pair of rollers.

Claim 5

Dependent Claim 28 words

An improved process in accordance with claim 3 wherein said upstream roller rotates at a peripheral speed in excess of the peripheral speed of the adjacent downstream roller.

Claim 6

Dependent Claim 20 words

An improved process in accordance with claim 3 wherein said heat relaxation step occurs immediately following said hot stretching step.

Claim 7

Dependent Claim 31 words

An improved process in accordance with claim 1 wherein said non-porous, crystalline elastic polymer film is selected from the group consisting of polyolefins, polyacetals, polyamides, polyesters, polyalkylene sulfides and polyarylene oxides.

Claim 8

Dependent Claim 41 words

An improved process in accordance with claim 1 wherein the maximum dimension, in the direction of stretch, of the hot-stretched microporous film is decreased by about 17 percent based on the length of said hot stretched microporous film prior to relaxation.

Claim 9

Dependent Claim 166 words

In a process for the preparation of an open-celled microporous polypropylene film in which a non-porous, crystalline, elastic polypropylene film, said polypropylene film having an elastic recovery at 0 recovery time when subjected to a standard strain of 50% at 25° C. and 65% relative humidity of at least 40% and a percent crystallinity of at least 20%, is uniaxially cold-stretched at a temperature in the range of between about 0° C. and 120° C. followed by hot-stretching, in the same direction, of said cold-stretched film at a temperature in the range of between about 120° C. and 150° C., the improvement which comprises heat relaxing said hot-stretched film under tension by exposing said film to a temperature in the range of between about 120° C. and 155° C. such that the maximum dimension, in the direction of stretch, of the hot-stretched microporous polypropylene film is decreased by between about 15 and 20%, based on the length of said hot-stretched microporous polypropylene film prior to relaxation.

Claim 10

Dependent Claim 166 words

In a process for the preparation of an open-celled microporous polypropylene film in which a non-porous, crystalline, elastic polypropylene film, said polypropylene film having an elastic recovery at 0 recovery time when subjected to a standard strain of 50% at 25° C. and 65% relative humidity of at least 40% and a percent crystallinity of at least 20%, is uniaxially cold-stretched at a temperature in the range of between about 0° C. and 120° C. followed by hot-stretching, in the same direction, of said cold-stretched film at a temperature in the range of between about 120° C. and 150° C., the improvement which comprises heat relaxing said hot-stretched film under tension by exposing said film to a temperature in the range of between about 120° C. and 155° C. such that the maximum dimension, in the direction of stretch, of the hot-stretched microporous polypropylene film is decreased by between about 15 and 20%, based on the length of said hot-stretched microporous polypropylene film prior to relaxation.

Claim 11

Dependent Claim 25 words

An improved process in accordance with claim 8 wherein said heat relaxation temperature is in the range of between about 138° C. and 150° C.

Claim 12

Dependent Claim 25 words

An improved process in accordance with claim 9 wherein said heat relaxation temperature is in the range of between about 138° C. and 145° C.

Claim 13

Dependent Claim 37 words

An improved process in accordance with claim 8 wherein said heat relaxation step comprises passing said cold and hot stretched film over at least one pair of rollers in an environment maintained at the heat relaxation temperature.

Claim 14

Dependent Claim 29 words

An improved process in accordance with claim 11 wherein said upstream roller is rotated at a peripheral speed in excess of the peripheral speed of the adjacent downstream roller.

Claim 15

Dependent Claim 20 words

An improved process in accordance with claim 8 wherein said heat relaxation step occurs immediately following said hot stretching step.

Claim 16

Dependent Claim 17 words

An improved process in accordance with claim 8 wherein the dimension of stretching is the longitudinal direction.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1982-02-05	1982-08-07	1983-02-06	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1986-02-05	1986-08-07	1987-02-06	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1990-02-05	1990-08-07	1991-02-06	$7700.00	Window Closed / Lapsed

Process for preparing a microporous polymer film

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