Oriented porous polypropylene films

Claim 2

An oriented polymeric porous film with polygonal cells having average diameters of about 5 to about 30 microns and interconnecting pores between the cells having average diameters of about 0.2 to about 20 microns prepared from a polypropylene-based resin having at least 40% crystallinity by a process comprising the steps of: (a) dispersing in said polypropylene-based resin a nucleating agent capable of producing beta-spherulites; (b) extruding the nucleating agent-containing polypropylene-based resin into a film; (c) cooling said film below the crystallization temperature of said polypropylene-based resin to form at least 20 weight percent of beta-spherulites in the film; (d) extracting selectively said beta-spherulites in an amount corresponding to at least 15 weight percent of the polypropylene-based resin from the cooled film with an extraction solvent to form a porous film; and (e) orienting the porous film by heating the porous film at a temperature of about 115° to about 135° C. for a time period of about 2 to about 20 seconds and stretching the heated porous film in at least one direction at a stretch ratio of about 1.5 to about 7.5 to form said oriented polymeric porous film.

Claim 3

The oriented polymeric porous film of claim 1 wherein said nucleating agent has the structural formula: ##STR2##

Claim 4

The oriented polymeric porous film of claim 2 wherein said nucleating agent is dispersed in the polypropylene-based resin at a level of about 0.1 to about 10 ppm based on the weight of said resin.

Claim 5

The oriented polymeric porous film of claim 1 wherein said extracting solvent is selected from the group consisting of toluene, carbon tetrachloride or xylene.

Claim 6

The oriented polymeric porous film of claim 1 wherein said polypropylene-based resin contains about 5 to about 15 weight percent cornstarch based on the weight of said resin.

Claim 7

The oriented polymeric porous film of claim 1 wherein said step of extracting selectively said beta-spherulites from the cooled film is at a temperature of about 85° to about 95° C. for a time period of 10 minutes or less.

Claim 8

The oriented polymeric porous film of claim 5 wherein said step of extracting selectively said beta-spherulites from the cooled film is at a temperature of about 85° to about 90° C. for a time period of 10 minutes or less.

Claim 9

A process for preparing an oriented polymeric porous film with polygonal cells having average diameters of about 5 to about 30 microns and interconnecting pores between the cells having average diameters of about 0.2 to about 20 microns from a polypropylene-based resin having at least 40% crystallinity comprising the steps of: (a) dispersing in said polypropylene-based resin a nucleating agent capable of producing beta-spherulites; (b) extruding the nucleating agent-containing polypropylene-based resin into a film; (c) cooling said film below the crystallization temperature of said polypropylene-based resin to form at least 20 weight percent of beta-spherulites in the film; (d) extracting selectively said beta-spherulites in an amount corresponding to at least 15 weight percent of the polypropylene-based resin from the cooled film with an extraction solvent to form a porous film; and (e) orienting the porous film by heating the porous film at a temperature of about 115° to about 135° C. for a time period of about 2 to about 20 seconds and stretching the heated porous film in at least one direction at a stretch ratio of about 1.5 to about 7.5 to form said oriented polymeric porous film.

Claim 10

A process for preparing an oriented polymeric porous film with polygonal cells having average diameters of about 5 to about 30 microns and interconnecting pores between the cells having average diameters of about 0.2 to about 20 microns from a polypropylene-based resin having at least 40% crystallinity comprising the steps of: (a) dispersing in said polypropylene-based resin a nucleating agent capable of producing beta-spherulites; (b) extruding the nucleating agent-containing polypropylene-based resin into a film; (c) cooling said film below the crystallization temperature of said polypropylene-based resin to form at least 20 weight percent of beta-spherulites in the film; (d) extracting selectively said beta-spherulites in an amount corresponding to at least 15 weight percent of the polypropylene-based resin from the cooled film with an extraction solvent to form a porous film; and (e) orienting the porous film by heating the porous film at a temperature of about 115° to about 135° C. for a time period of about 2 to about 20 seconds and stretching the heated porous film in at least one direction at a stretch ratio of about 1.5 to about 7.5 to form said oriented polymeric porous film.

Claim 11

The process of claim 8 wherein said nucleating agent has the structural formula: ##STR3##

Claim 12

The process of claim 8 wherein said nucleating agent is dispersed in the polypropylene-based resin at a level of about 0.1 to about 10 ppm based on the weight of said resin.

Claim 13

The process of claim 8 wherein said extracting solvent is selected from the group consisting of toluene, carbon tetrachloride or xylene.

Claim 14

The process of claim 8 wherein said polypropylene-based resin contains about 5 to about 15 weight percent cornstarch based on the weight of said resin.

Claim 15

The process of claim 8 wherein said step of extracting selectively said beta-spherulites from the cooled film is at a temperature of about 85° to about 95° C. for a time period of 10 minutes or less.

Claim 16

The process of claim 8 wherein the porous film is oriented by stretching the porous film uniaxially with a stretch ratio of about 2.0 to about 6.0.

Claim 17

The process of claim 8 wherein the porous film is oriented by stretching the porous film biaxially with a stretch ratio of about 2.0 to about 5.0 said stretch ratio being the same in a machine direction and a transverse direction.

Claim 18

The process of claim 8 wherein said oriented film has a thickness of about 0.005 to about 0.2 millimeters.

Claim 19

An oriented polymeric porous film having a thickness of about 0.005 to about 0.2 millimeters, a moisture vapor transmission rate as determined according to ASTM E-96, procedure E, in the range of about 2,500 to about 7,500 grams per square meter per 24 hours prepared from a polypropylene-based resin having at least 40% crystallinity by a process comprising the steps of: (a) forming a homogeneous blend of a polypropylene-based resin, about 0.5 to about 10 ppm of a red quinacridone dye acting as a beta-spherulite nucleant and optionally a starch-containing material; (b) extruding the blend into a film having a thickness of about 0.01 to about 0.4 millimeters and at least 20 percent beta-spherulites on a cast film line having a chill roll temperature of about 90° to 130° C.; (c) extracting beta-spherulites corresponding to at least 15 weight percent of the blend from the cast film by immersing the cast film in a toluene bath at a temperature of about 85° to about 95° C. for a time period of 10 minutes or less to form a porous film; (d) drying the porous film at a temperature of about 15° to about 110° C. for 20 minutes or less; and (e) orienting the porous film by heating the porous film at a temperature of about 115° to about 135° C. for a time period of about 2 to about 20 seconds and stretching the heated porous film in at least one direction at a stretch ratio of about 1.5 to about 7.5 to form the oriented polymeric porous film.

Claim 20

An oriented polymeric porous film having a thickness of about 0.005 to about 0.2 millimeters, a moisture vapor transmission rate as determined according to ASTM E-96, procedure E, in the range of about 2,500 to about 7,500 grams per square meter per 24 hours prepared from a polypropylene-based resin having at least 40% crystallinity by a process comprising the steps of: (a) forming a homogeneous blend of a polypropylene-based resin, about 0.5 to about 10 ppm of a red quinacridone dye acting as a beta-spherulite nucleant and optionally a starch-containing material; (b) extruding the blend into a film having a thickness of about 0.01 to about 0.4 millimeters and at least 20 percent beta-spherulites on a cast film line having a chill roll temperature of about 90° to 130° C.; (c) extracting beta-spherulites corresponding to at least 15 weight percent of the blend from the cast film by immersing the cast film in a toluene bath at a temperature of about 85° to about 95° C. for a time period of 10 minutes or less to form a porous film; (d) drying the porous film at a temperature of about 15° to about 110° C. for 20 minutes or less; and (e) orienting the porous film by heating the porous film at a temperature of about 115° to about 135° C. for a time period of about 2 to about 20 seconds and stretching the heated porous film in at least one direction at a stretch ratio of about 1.5 to about 7.5 to form the oriented polymeric porous film.