Microporous material resistant to capillary collapse

• US 6,461,724 B1
• Filed: 08/30/1999
• Issued: 10/08/2002
• Est. Priority Date: 08/30/1999
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Thomas, Scott D., Radovanovic, Philip D., Perez, Mario A.
• Primary Examiner(s): Copenheaver, Blaine
• Assistant Examiner(s): ROCHE, LEANNA M
• Application Number:
  US09/385,265
• Time in Patent Office: 1,135 Days
• Field of Search: 428/315.5, 428/315.9, 428/316.6, 264/45.1, 429/254
• US Class Current: 428/315.5
• CPC Class Codes: B01D 2325/34 Molecular weight or degree of polymerisation
• CPC Class Codes: B01D 67/0027 by stretching
• CPC Class Codes: B01D 67/003 by selective elimination of components, e.g. by leaching
• CPC Class Codes: B01D 71/26 Polyalkenes
• CPC Class Codes: B01D 71/262 Polypropylene
• CPC Class Codes: B32B 2305/026 Porous
• CPC Class Codes: B32B 2323/10 Polypropylene
• CPC Class Codes: B32B 2457/10 Batteries
• CPC Class Codes: B32B 27/00 Layered products comprising a layer of synthetic resin fibrous or filamentary layer made of a synthetic resin B32B5/02; particulate layer made of a synthetic resin B32B5/16; foamed layer made of a synthetic resin B32B5/18
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/32 comprising polyolefins comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30
• CPC Class Codes: C08J 2201/0462 using organic solvents
• CPC Class Codes: C08J 2323/10 Homopolymers or copolymers of propene
• CPC Class Codes: C08J 2323/12 Polypropene
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: C08J 9/26 by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
• CPC Class Codes: C08L 23/0823 Copolymers of ethene with aliphatic cyclic olefins
• CPC Class Codes: C08L 23/10 Homopolymers or copolymers of propene
• CPC Class Codes: C08L 2666/04 Macromolecular compounds according to groups C08L7/00 - C08L49/00, or C08L55/00 - C08L57/00; Derivatives thereof
• CPC Class Codes: H01M 50/417 Polyolefins
• CPC Class Codes: H01M 50/457 : comprising three or more layers
• CPC Class Codes: H01M 50/489 : Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• CPC Class Codes: H01M 50/491 : Porosity
• CPC Class Codes: H01M 50/497 : Ionic conductivity
• CPC Class Codes: Y02E 60/10 : Energy storage using batteries
• CPC Class Codes: Y10T 428/249978 : Voids specified as micro
• CPC Class Codes: Y10T 428/24998 : Composite has more than two layers
• CPC Class Codes: Y10T 428/249981 : Plural void-containing components

Abstract

Microporous material comprising a polypropylene polymer having at least 20 percent crystallinity; and a compatible, amorphous, glassy polymer, wherein said polymers are miscible in a compound when heated above the melting temperature of the polypropylene polymer and wherein a polypropylene polymer phase separates from the compound when cooled below the crystallization temperature of the polypropylene polymer. Microporous material is made by a thermally induced phase separation process using a compound such as mineral oil to form one phase containing both polymers. The pores of the microporous material resist collapse during processing. Membranes made of this material are useful as battery separators having a good combination of strength, porosity, and ionic resistance when imbibed with an electrolyte.

Claims

1. A microporous material comprising

a polypropylene polymer having at least 20 percent crystallinity;

and

a compatible, amorphous, glassy polymer,

wherein said polymers are miscible in a compound when heated above the melting temperature of the polypropylene polymer and wherein the polymers phase separate from the compound when cooled below the crystallization temperature of the polypropylene polymer and wherein the microporous material has a microstructure comprising spherulites connected by fibrils.

2. The microporous material of claim 1 having a puncture resistance of at least 350 g/25 μ

m.

3. The microporous material of claim 1 in which the compatible, amorphous, glassy polymer is an ethylene norbomene copolymer having a Tg above 80°

C., and it comprises greater than 0 to 30 weight percent of the microporous material.

4. A battery separator comprising the microporous material of claim 1.

5. The microporous material of claim 1 having a porosity between about 30 to 70 percent and a Gurley number below 600 seconds per 64.5 mm².

6. The microporous material of claim 1 which is a sheet material comprising two layers.

7. The microporous material of claim 6 wherein the two layers have two different compositions.

8. A three layer film wherein the outer two layers comprise the microporous material of claim 1.

9. A method of making the microporous material of claim 1, comprising:

(a) melt blending to form a mixture comprising about 15 to 80 parts by weight of a polypropylene polymer having at least 20 percent crystallinity, greater than 0 to 30 parts by weight of a compatible, amorphous, glassy polymer, and about 20 to 85 parts by weight based on a total mixture content, of a compound, the compound being miscible with the polypropylene and glassy polymers at a temperature above the melting temperature of the polypropylene polymer;

(b) shaping the melt blended material;

(c) cooling the shaped material to a temperature at which phase separation occurs between the compound and the polymers through crystallization of the polypropylene polymer to form a network of polymer domains; and

(d) creating porosity by (1) orienting said material at least in one direction to separate adjacent crystallized polymer domains from one another to provide an interconnected porous network therebetween, followed by (2) removing at least a part of the compound.

10. A method of making the microporous material of claim 1, comprising:

(a) melt blending to form a mixture comprising about 15 to 80 parts by weight of a polypropylene polymer, greater than 0 to 30 parts by weight of a compatible, amorphous, glassy polymer, and about 20 to 85 parts by weight, based on a total mixture content, of a compound, the compound being miscible with the polypropylene and glassy polymers at a temperature above the melting temperature of the polypropylene polymer;

(b) shaping the melt blended material;

(c) cooling the shaped material to a temperature at which phase separation occurs between the compound and the polymers through crystallization of the polypropylene polymer to form a network of polymer domains;

(d) stretching the shaped material in at least one direction to provide a network of interconnected regions comprising the compound, and then

(e) removing the compound to provide a microporous material.

11. The method of claim 10 wherein the stretching step provides an area expansion ratio of greater than nine.

12. A microporous material comprising

a polypropylene polymer having at least 20 percent crystallinity;

and

a compatible, amnorphous, glassy ethylene norbornene copolymer,

wherein said polymers are miscible in a compound when heated above the melting temperature of the polypropylene polymer and

wherein the polymers phase separate from the compound when cooled below the crystallization temperature of the polypropylene polymer and

wherein the microporous material has a microstructure comprising an interconnected porous network of crystallized polymer spherulites connected by amorphous polymer fibrils.

13. A The microporous material of claim 12 having a puncture resistance of at least 350 g/25 μ

m.

14. The microporous material of claim 12 in which the ethylene norbornene copolymer has a Tg above 80°

C., and comprises greater than 0 to 30 weight percent of the microporous material.

15. A battery separator comprising the microporous material of claim 14.

16. The microporous material of claim 14 having a porosity between about 30 to 70 percent and a Gurley number below 600 seconds per 64.5 mm².

17. The microporous material of claim 12 which is a sheet material comprising two layers.

18. The microporous material of claim 17 wherein the two layers have two different compositions.

19. A three layer film wherein the outer two layers comprise the microporous material of claim 12.