Claims
- 1. A method of forming a polymeric film having differing degrees of microporosity including the steps of:providing a film of a microporous formable polymer composition; and interdigitally stretching the film throughout its depth along a plurality of lines to form a microporous area in the film adjacent a film boundary area while controlling said film in a substantially unstretched condition in said boundary area adjacent said microporous area to reduce pinhole formation in the film.
- 2. The method of claim 1 wherein controlling the film in an unstretched condition is performed by creating slack areas along the length of the film prior to interdigital stretching.
- 3. The method of claim 2 wherein the slack is created by passing a preselected area of the film between opposed rollers.
- 4. The method of claim 2 wherein the step of creating the slack areas is selected from the group consisting of folding, corrugating and overlapping a preselected area of the sheet.
- 5. The method of claim 1 wherein the interdigital stretching forms micropores in the film along the plurality of interdigitally stretched lines.
- 6. The method of claim 1 wherein said polymer composition comprises a polyolefin and a pore initiator.
- 7. The method of claim 6 wherein said polyolefin is a polyethylene.
- 8. The method of claim 7 wherein said polyethylene is a linear low density polyethylene.
- 9. The method of claim 1 including the further step of laminating said film before stretching to at least one non-woven strip having opposite edges to form a laminate having a laminated area and unlaminated film areas along the opposite edges and interdigitally stretching the laminate throughout its depth and along the plurality of lines while controlling the film in a substantially unstretched condition adjacent to the lines so as to reduce pin-hole formation in the film.
- 10. The method of claim 9 wherein said polymer composition comprises a polyolefin and a pore initiator.
- 11. The method of claim 10 wherein said polyolefin is a polyethylene.
- 12. The method of claim 11 wherein said pore initiator is a particulate filler and wherein inditerdigital stretching forms micropores in the film along the plurality of interdigitally stretched lines.
- 13. The method of claim 9 wherein the non-woven strip comprises fibers selected from the group consisting of polyethylene, polypropylene, polyesters, rayon, cellulose, nylon, and blends of such fibers.
Parent Case Info
This is a divisional of application Ser. No. 09/124,583, filed Jul. 29, 1998, now U.S. Pat. No. 6,265,045.
US Referenced Citations (33)
Foreign Referenced Citations (1)
Number |
Date |
Country |
141592 |
May 1985 |
EP |
Non-Patent Literature Citations (1)
Entry |
Schwarz, Eckhard C. A., New Fibrillated Film Structures, Manufacture and Uses, Pap, Synth. Conf. (TAPPI), 1976, pp. 33-39. |