Microporous material from ethylene-chlorotrifluoroethylene copolymer and method for making same
Microporous material having a spherulitic matrix made from ethylene chlorotrifluoroethylene copolymer has a plurality of pores having an average pore size greater than about 0.01 micrometer. The material is made by thermally induced phase separation (TIPS) process that includes melt mixing ethylene chlorotrifluoroethylene copolymer, diluent and nucleating agent to provide a melt mixed composition; shaping the melt mixed composition; cooling the shaped melt mixed composition to induce phase separation of the ethylene chlorotrifluoroethylene copolymer to provide a phase separated material; and stretching the phase separated material to provide the microporous material. The microporous material may be incorporated into articles and the articles may include one, two or more layers of microporous material.
1. A microporous material, comprising:
a first layer comprised of a first layer spherulitic matrix comprising a plurality of individual polymer domains of a first layer ethylene chlorotrifluoroethylene copolymer connected to one another by radiating fibrils and a plurality of first layer pores extending through the first layer spherulitic matrix and having an average pore size greater than about 0.01 micrometer;
a first layer polymer crystallization nucleating agent uniformly dispersed within the first layer ethylene chlorotrifluoroethylene copolymer in an amount between 0.05 wt % and 1.0 wt %;
a second layer comprised of a second layer spherulitic matrix comprising a plurality of individual polymer domains of a second layer ethylene chlorotrifluoroethylene copolymer connected to one another by radiating fibrils and a plurality of second layer pores extending through the second layer spherulitic matrix and having an average pore size greater than about 0.01 micrometer;
a second layer polymer crystallization nucleating agent uniformly dispersed within the second layer ethylene chlorotrifluoroethylene copolymer; and
wherein, the average pore size of the first layer spherulitic matrix and the average pore size of the second layer spherulitic matrix are different.
2. The microporous material according to claim 1 wherein the microporous material is strong enough to withstand being flexed, folded, or pleated without breaking.
3. The microporous material according to claim 1 further comprising a third layer affixed to the second layer, the third layer comprised of a third layer spherulitic matrix comprising a plurality of individual polymer domains of a third layer ethylene chlorotrifluoroethylene copolymer connected to one another by radiating fibrils and a plurality of third layer pores having an average pore size greater than about 0.01 micrometer and extending through the third layer spherulitic matrix; and
a third layer polymer crystallization nucleating agent uniformly dispersed within the third layer ethylene chlorotrifluoroethylene copolymer.
4. The microporous material according to claim 3 further comprising a fourth layer affixed to the third layer, the fourth layer comprised of a fourth layer spherulitic matrix comprising a plurality of individual polymer domains of a fourth layer ethylene chlorotrifluoroethylene copolymer connected to one another by radiating fibrils and a plurality of fourth layer pores having an average pore size greater than about 0.01 micrometer and extending through the fourth layer spherulitic matrix; and
a fourth layer polymer crystallization nucleating agent uniformly dispersed within the fourth layer ethylene chlorotrifluoroethylene copolymer.
5. The microporous material according to claim 1 wherein the polymer crystallization nucleating agent is a fluoropolymer having a crystallization temperature higher than the crystallization temperature of the ethylene chlorotrifluoroethylene copolymer.
6. The microporous material according to claim 1 wherein the polymer crystallization nucleating agent is a copolymer of tetrafluoroethylene and ethylene (ETFE), a copolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV), a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), or combinations thereof.
7. The microporous material according to claim 1 wherein the polymer crystallization nucleating agent is a particulate dispersed in a thermoplastic polymer.
8. The microporous material according to claim 7 wherein the thermoplastic polymer comprises a polypropylene homopolymer, a polyethylene homopolymer, or a polypropylene polyethylene copolymer.
9. The microporous material according to claim 1 wherein the first layer is a stretched layer comprising a stretch ratio ranging from 1×1 (machine direction×transverse direction) to 3×3.
10. The microporous material according to claim 1 wherein the first layer is a stretched layer comprising an elongation of 10% to 300% in the machine direction, the transverse direction, or both.