Claims
- 1. A process of manufacturing a microporous sheet comprising: plasticating a blend comprising a polyolefin selected from the group consisting of homopolymers and copolymers of ethylene, propylene and buylene, and mixtures thereof; finely divided silica; and a substantially water-insoluble plasticizer selected from the group consisting of dialkyl phthalates and dialkyl adipates having between about two to eleven carbon atoms in the oxo-alcohol moiety; forming a sheet from the plasticated blend; and contacting the sheet with water for a period of time sufficient to remove an amount of the plasticizer from the sheet sufficient to render the sheet microporous.
- 2. The process of claim 1 wherein the polyolefin is selected from the group consisting of high-density polyethylene and substantially isotactic polypropylene.
- 3. The process of claim 2 wherein the polyolefin is high-density polyethylene having a standard load melt index of substantially 0.
- 4. The process of claim 1 where the polyolefin comprises between about 4% and about 20% by weight of the blend, the silica comprises between about 15% and about 50% by weight of the blend, and the plasticizer comprises between about 30% and about 80% by weight of the blend.
- 5. The process of claim 1 wherein the polyolefin component is a mixture of high-density polyethylene having a standard load melt index of substantially 0 and a high-density polyethylene having a standard load melt index greater than about 10 g. per 10 min.
- 6. The process of claim 5 wherein the polyethylene having a substantially 0 melt index comprises between about 30% and about 60% by weight of the polyolefin component.
- 7. The process of claim 1 wherein the plasticizer has a solubility in water of less than about 0.1% by weight at 30.degree. C.
- 8. The process of claim 1 wherein the finely divided silica is hydrophilic, has a specific surface area greater than about 100 m.sup.2 /g, as measured by nitrogen absorption, and a particle size between about 0.001 and about 0.1 micron.
- 9. The process of claim 1 wherein the plasticizer has between about 7 and about 11 carbon atoms in the oxo-alcohol moiety.
- 10. The process of claim 1 wherein the sheet, after contact with the water, is subjected to a surface treatment to remove any film of plasticizer adhering thereto.
- 11. The process of claim 1 wherein the temperature of the water is between about 20.degree. C. and about 100.degree. C.
- 12. The process of claim 1 wherein the plasticizer has a density sufficiently different from water to permit separation from water by decantation.
- 13. The process of claim 12 wherein the plasticizer is removed from the water by decantation.
- 14. The process of forming a microporous battery separator comprising: plasticating a blend comprising a polyolefin selected from the group consisting of homopolymers and copolymers of ethylene, propylene and buylene, and mixtures thereof; finely divided silica; and a substantially water-insoluble plasticizer selected from the group consisting of dialkyl phthalates and dialkyl adipates having between about 2 and about 11 carbon atoms in the oxo-alcohol moiety; forming a sheet from the plasticated blend; contacting the sheet with water for a period of time sufficient to remove an amount of the plasticizer from the sheet sufficient to render the sheet microporous; drying the sheet; and cutting the sheet into a size suitable for separating the plates in a battery.
Parent Case Info
This is a continuation of application Ser. No. 865,413, filed Dec. 29, 1977 now abandoned.
US Referenced Citations (5)
Foreign Referenced Citations (2)
Number |
Date |
Country |
1044028 |
Sep 1966 |
GBX |
1044502 |
Oct 1966 |
GBX |
Continuations (1)
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Number |
Date |
Country |
Parent |
865413 |
Dec 1977 |
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