Claims
- 1. A method for preparing a microporous polymeric shaped article which comprises the steps of
- a) melt blending thermoplastic polymer with a solubilizing amount of a compatible liquid to form a homogeneous solution;
- b) forming a shaped article from the solution;
- c) cooling said shaped article at a rate and to a temperature sufficient to initiate thermodynamic, non-equilibrium liquid-liquid phase separation and then to solidify the thermoplastic polymer;
- (d) stretching the article in a first direction sufficient to permanently attenuate the article and effect orientation of the polymer; and
- e) removing at least a substantial portion of the compatible liquid before or after said stretching step to form an oriented microporous shaped article.
- 2. The method of claim 1 wherein said homogeneous solution contains about 10 to 75 weight percent of said thermoplastic polymer in said compatible liquid.
- 3. The method of claim 1 wherein said thermoplastic polymer is polypropylene and said compatible liquid is tallowamine.
- 4. The method of claim 1 wherein said thermoplastic polymer is polyethylene and said compatible liquid is dioctyl phthalate.
- 5. The method of claim 1 wherein said solidified thermoplastic polymer is stretched at least 10 percent in at least one direction.
- 6. The method of claim 1 wherein said compatible liquid is removed by extraction or volatilization.
- 7. The method of claim 1 wherein said stretched article is further heated to a stabilizing temperature under restraint.
- 8. The method of claim 1 wherein said article is further stretched in a direction transverse to said first direction.
- 9. The method of claim 1 wherein said cooling comprises immersing said shaped article into a liquid cooling medium.
- 10. The method of claim 1 wherein said cooling comprises casting said shaped article onto a casting wheel.
- 11. The method according to claim 1 wherein said microporous polymeric shaped article has a thickness of more than zero and less than 1000 micrometers.
- 12. The method according to claim 1 wherein said microporous polymeric shaped articles has a matrix tensile strength at break in the oriented direction which is increased at least 10% over an unoriented article.
- 13. The method according to claim 1 wherein said article is stretched in the range of about 10 to 1000 percent to provide uniform, controlled porosity.
- 14. A method for preparing a microporous polymeric shaped article having a gradient porosity therethrough which comprises the steps of
- a) melt blending thermoplastic polymer with a solubilizing amount of a compatible liquid to form a homogeneous solution;
- b) forming a shaped article from the solution;
- c) rapidly cooling said shaped article from one surface thereof at a rate and to a temperature sufficient to initiate thermodynamic, non-equilibrium liquid-liquid phase separation and then to solidify the thermoplastic polymer;
- d) stretching the article in a first direction sufficient to permanently attenuate the article and effect orientation of the polymer; and
- e) removing at least substantial portion of the compatible liquid before or after said stretching step to form an oriented microporous shaped article having a gradient porosity therethrough.
Parent Case Info
This is a continuation of application Ser. No. 07/374,488 filed Jun. 29, 1989, now abandoned, which is a division of application Ser. No. 07/098,601, filed Sep. 14, 1987, now U.S. Pat. No. 4,867,881.
US Referenced Citations (7)
Divisions (1)
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Number |
Date |
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Parent |
98601 |
Sep 1987 |
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Continuations (1)
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Number |
Date |
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Parent |
374488 |
Jun 1989 |
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