US2007100012A1PendingUtilityA1

Production of high porosity open-cell membranes

Assignee: POROUS POWER TECHNOLOGIES LLCPriority: Jan 20, 2004Filed: Dec 6, 2006Published: May 3, 2007

Est. expiryJan 20, 2024(expired)· nominal 20-yr term from priority

H01M 50/497H01M 50/494H01M 50/426H01M 50/491H01M 50/489B01D 2323/082B01D 71/301B01D 67/00091C08J 5/18B01D 39/1692B01D 2325/20B01D 71/34B01D 2325/26B01D 69/02C08J 2327/16Y10T428/249979Y10T442/2033Y10T428/249921Y02E60/10

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References

Claims

Abstract

The present invention is directed to methods of producing a symmetric, strong, highly porous, microporous polymer film by (a) forming a layer of a polymer solution on a substrate, the solution comprising two miscible liquids and a polymer material dissolved therein, and wherein the first liquid has a surface tension lower than the surface energy of the polymer and the second liquid has a surface tension greater than the surface energy of the polymer; (b) producing a film of gelled polymer from the layer of polymer solution; and (c) rapidly removing the liquid from the film of gelled polymer by unidirectional mass transfer without dissolving the gelled polymer.

Claims

exact text as granted — not AI-modified

1 . A method of producing a symmetric, strong, highly porous, microporous polymer film comprising:
(a) forming a layer of a polymer solution on a substrate, wherein the polymer solution comprises two miscible liquids and a polymer material dissolved therein, and wherein the two miscible liquids comprise (i) a principal liquid that has a surface tension at least 5% lower than the surface energy of the polymer and (ii) a second liquid that has a surface tension at least 5% greater than the surface energy of the polymer; (b) producing a film of gelled polymer from the layer of polymer solution under conditions sufficient to provide a non-wetting, high surface tension solution within the layer of polymer solution; and (c) rapidly removing the liquid from the film of gelled polymer by unidirectional mass transfer without dissolving the gelled polymer to produce the strong, highly porous, microporous polymer film.

2 . The method of claim 1 , wherein the principal liquid has a normal boiling point of less than about 125° C.

3 . The method of claim 2 , wherein the second liquid has a normal boiling point of less than about 160° C.

4 . The method of claim 3 , wherein the principal and second liquids are removed in less than about 5 minutes.

5 . The method of claim 1 , wherein the principal and second liquids are removed at a temperature no higher than the temperature at which the polymer solution was formed.

6 . The method of claim 1 , wherein the polymer is semi-crystalline.

7 . The method of claim 1 , wherein the polymer is a blend of amorphous and crystalline polymers.

8 . The method of claim 1 , wherein the polymer is selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoro-propylene copolymer, polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, polymethyl methacrylate, and mixtures thereof.

9 . The method of claim 8 , wherein the polymer is a mixture of polyvinylidene fluoride polymers and a polyvinylidene fluoride-hexafluoro-propylene copolymer.

10 . The method of claim 1 , wherein the principal liquid is selected from the group consisting of:

Normal Boiling
Surface Energy,

Principal Liquid
Point, ° C.
dynes/cm

methyl formate
31.7
24.4

acetone (2-propanone)
56
23.5

methyl acetate
56.9
24.7

tetrahydrofuran
66
26.4

ethyl acetate
77
23.4

methyl ethyl ketone (2-butanone)
80
24

acetonitrile
81
29

Dimethyl carbonate
90
31.9

1,2-dioxane
100
32

Toluene
110
28.4

methyl isobutyl ketone
116
23.4

11 . The method of claim 1 , wherein the second liquid is selected from the group consisting of:

Normal boiling
Surface Energy,

Second Liquid
point, ° C.
dynes/cm

nitromethane
101
37

bromobenzene
156
37

formic acid
100
38

pyridine
114
38

ethylene bromide
131
38

3-furaldehyde
144
40

bromine
59
42

tribromomethane
150
42

quinoline
24
43

nitric acid (69%)
86
43

water
100
72.5

12 . The method of claim 1 , wherein the principal liquid comprises acetone and the second liquid comprises water.

13 . The method of claim 1 , wherein the polymer membrane is less than 50 microns thick.

14 . The method of claim 1 , wherein the polymer membrane is less than 35 microns thick.

15 . The method of claim 1 , wherein the polymer is about 3 to 10% by weight of the solution, the void volume of the polymer membrane is at least 75%, and less than 5% of the surface voids are occluded.

16 . The method of claim 1 , wherein the polymer solution is formed by heating the mixture with agitation to about the normal boiling point of the principal liquid in a sealed, pressurized container.

17 . The method of claim 1 , where the polymer solution is applied to the high surface energy substrate prior to gelation of the polymer.

18 . The method of claim 17 , wherein the polymer solution is applied to the high energy substrate within about 5 hours of being mixed and cooled.

19 . The method of claim 1 , wherein the high surface energy substrate comprises a metal.

20 . The method of claim 19 , wherein the high surface energy substrate is a metalized polymeric film.

21 . The method of claim 20 , wherein the metalized polymeric film is selected from the group consisting of aluminized polyethylene and aluminized polypropylene.

22 . The method of claim 1 wherein the polymer membrane has an average pore diameter of less than 1 micron as determined by mercury porosimitry.

23 . The method of claim 1 wherein the polymer membrane has an average pore diameter of less than 0.5 microns as determined by mercury porosimitry.

24 . The method of claim 1 wherein the polymer membrane has a permeability greater than 500 centimeter micron centipoise/minute Torr.

25 . The method of claim 1 wherein the polymer membrane has a tensile strength greater than 300 psi in both machine and transverse directions.

26 . The method of claim 1 , wherein the polymer membrane has a tensile modulus greater than 10,000 psi in the machine direction.

27 . The method of claim 1 , wherein the polymer membrane has a MacMullin number between 1.01 and 3.

28 . The method of claim 1 , wherein the polymer membrane has a MacMullin number between 1.01 and 2.

29 . The method of claim 1 , wherein the principal liquid has a surface tension at least 10% lower than the surface energy of the polymer.

30 . The method of claim 1 , wherein the second liquid has a surface tension at least 10% higher than the surface energy of the polymers

31 . A process of preparing highly porous, strong, thin, polymer membranes with symmetric open cells of a relatively uniform size throughout the thickness of each membrane comprising:
(a) preparing a solution of one or more polymers in a mixture of a principal liquid which is a solvent for the polymer and a second liquid which is miscible with the principal liquid, wherein (i) the principal liquid has a surface tension at least 5% lower than the surface energy of the polymer, (ii) the second liquid has a surface tension at least 5% higher than the surface energy of the polymer, (iii) the normal boiling point of the principal liquid is less than 125° C. and the normal boiling point of the second liquid is less than about 160° C., (iv) the polymer has a lower solubility in the second liquid than in the principal liquid, and (v) the solution is prepared at a temperature less than about 20° C. above the normal boiling point of the principal liquid and while precluding any substantial evaporation of the principal liquid; (b) reducing the temperature of the solution by at least 5° C. to between the normal boiling point of the principal liquid and the temperature of the substrate upon the solution is to be cast; (c) casting the polymer solution onto a high surface energy substrate to form a liquid coating thereon, said substrate having a surface energy greater than the surface energy of the polymer; and (d) removing the principal liquid and the second liquid from the coating by unidirectional mass transfer without use of an extraction bath, (ii) without re-dissolving the polymer, and (iii) at a maximum air temperature of less than about 100° C. in a period of about 5 minutes, to form the strong, highly porous, thin, symmetric polymer membrane.

32 . The process of claim 31 , wherein the polymer is semi-crystalline.

33 . The process of claim 31 , wherein the polymer is a blend of amorphous and crystalline polymers.

34 . The process of claim 31 , wherein the polymer is selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexa-fluoropropylene copolymer, polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, polymethyl methacrylate, and mixtures thereof.

35 . The process of claim 34 , wherein the polymer comprises a mixture of a polyvinylidene fluoride polymer and a polyvinylidene fluoride-hexafluoropropylene copolymer.

36 . The process of claim 31 , wherein the principal liquid is selected from the group consisting of

Normal Boiling
Surface Energy,

Principal Liquid
Point, ° C.
dynes/cm

methyl formate
31.7
24.4

acetone (2-propanone)
56
23.5

methyl acetate
56.9
24.7

tetrahydrofuran
66
26.4

ethyl acetate
77
23.4

methyl ethyl ketone (2-butanone)
80
24

acetonitrile
81
29

dimethyl carbonate
90
31.9

1,2-dioxane
100
32

Toluene
110
28.4

methyl isobutyl ketone
116
23.4

37 . The process of claim 31 , wherein the second liquid is selected from the group consisting of

Normal boiling
Surface Energy,

Second Liquid
point, ° C.
dynes/cm

nitromethane
101
37

bromobenzene
156
37

formic acid
100
38

pyridine
114
38

ethylene bromide
131
38

3-furaldehyde
144
40

bromine
59
42

tribromomethane
150
42

quinoline
24
43

nitric acid (69%)
86
43

water
100
72.5

38 . The process of claim 31 , wherein the principal liquid comprises acetone and the second liquid comprises water.

39 . The process of claim 31 , wherein the polymer membrane is less than 50 microns thick.

40 . The process of claim 31 , wherein the polymer membrane is less than 35 microns thick.

41 . The process of claim 31 , wherein the polymers are about 3 to 10% by weight of the solution, the void volume of the polymer membrane is at least 75%, and less than 5% of the surface voids are occluded.

42 . The process of claim 31 , wherein the polymer solution is formed by heating the mixture to about the normal boiling point of the principal liquid in a sealed, pressurized container.

43 . The process of claim 42 , where the cooled polymer solution is applied to the high surface energy substrate prior to gelation of the polymer.

44 . The process of claim 42 , wherein the cooled polymer solution is applied to the high energy substrate within about 5 hours of being cooled.

45 . The process of claim 31 , wherein the high surface energy substrate comprises a metal.

46 . The process of claim 45 , wherein the high surface energy substrate is a metalized polymeric film.

47 . The process of claim 46 , wherein the metalized polymeric film is selected from the group consisting of aluminized polyethylene and aluminized polypropylene.

48 . The process of claim 31 , wherein the second liquid is a solvent for the polymer.

49 . The process of claim 31 , wherein the second liquid is a non-solvent for the polymer.

50 . The process of claim 31 wherein the polymer membrane has an average pore diameter is less than 1 micron as determined by mercury porosimitry.

51 . The process of claim 31 wherein the polymer membrane has an average pore diameter less than 0.5 microns as determined by mercury porosimitry.

52 . The process of claim 31 wherein the polymer membrane has a permeability greater than 500 centimeter micron centipoise/minute Torr.

53 . The process of claim 31 wherein the polymer membrane has a tensile strength greater than 300 psi in both machine and transverse directions.

54 . The process of Claim 31 , wherein the polymer membrane has a tensile modulus greater than 10,000 psi in the machine direction.

55 . The process of claim 31 , wherein the polymer membrane has a McMullin number between about 1.01 and about 5.

56 . The process of claim 55 , wherein the McMullin Number is between about 1.01 and about 2.

57 . The process of claim 31 , wherein the principal liquid has a surface tension at least 10% lower than the surface energy of the polymers.

58 . The process of claim 31 , wherein the second liquid has a surface tension at least 10% higher than the surface energy of the polymers.

59 . A method of preparing a strong, thin, symmetric microporous polymer membrane which comprises the steps of:
(a) dissolving about 3 to 20% by weight of a polymer in a heated multiple liquid system comprising (a) a principal liquid which is a solvent for the polymer and (b) a second liquid to form a polymer solution, wherein (i) the principal liquid has a surface tension at least 5% lower than the surface energy of the polymer, (ii) the second liquid has a surface tension at least 5% greater than the surface energy of the polymer; and (iii) the polymer has a lower solubility in the second liquid than it has in the principal solvent liquid; (b) reducing the temperature of the solution by at least 5° C. to between the normal boiling point of the principal liquid and the temperature of the substrate upon which it will be cast; (c) casting a film of the fully dissolved solution onto a substrate which has a higher surface energy than the surface energy of the polymer; (d) precipitating the polymer to form a continuous gel phase while maintaining at least 70% of the total liquid content of the initial polymer solution, said precipitation caused by a means- selected from the group consisting of cooling, extended dwell time, solvent evaporation, vibration, or ultrasonics; and (e) removing the residual liquids without causing dissolution of the continuous gel phase by unidirectional mass transfer without any extraction bath, at a maximum film temperature which is less than the normal boiling point of the lowest boiling liquid, and within a period of about 5 minutes, to form a strong, highly porous, thin, symmetric polymer membrane.

60 . The process of claim 59 , wherein the polymer is semi-crystalline.

61 . The process of claim 59 , wherein the polymer is a blend of amorphous and crystalline polymers.

62 . The process of claim 59 , wherein the polymer is selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, polymethyl methacrylate, and mixtures thereof.

63 . The process of claim 62 , wherein the polymer comprises a mixture of a polyvinylidene fluoride polymer and a polyvinylidene fluoride-hexafluoro-propylene copolymer.

64 . The process of claim 59 , wherein the polymer is about 3 to 10% by weight of the solution and the membrane has a porosity greater than 75%.

65 . The process of claim 59 , wherein the polymer is about 10 to 20% by weight of the solution and the membrane has a porosity of about 60 to 70%.

66 . The process of claim 1 , wherein the principal liquid is selected from the group consisting of

Normal Boiling
Surface Energy,

Principal Liquid
Point, ° C.
dynes/cm

methyl formate
31.7
24.4

acetone (2-propanone)
56
23.5

methyl acetate
56.9
24.7

tetrahydrofuran
66
26.4

ethyl acetate
77
23.4

methyl ethyl ketone (2-butanone)
80
24

acetonitrile
81
29

Dimethyl carbonate
90
31.9

1,2-dioxane
100
32

Toluene
110
28.4

methyl isobutyl ketone
116
23.9

67 . The process of claim 59 , wherein the second liquid is selected from the group consisting of

Normal boiling
Surface Energy,

Second Liquid
point, ° C.
dynes/cm

nitromethane
101
37

bromobenzene
156
37

formic acid
100
38

pyridine
114
38

ethylene bromide
131
38

3-furaldehyde
144
40

bromine
59
42

tribromomethane
150
42

quinoline
24
43

nitric acid (69%)
86
43

water
100
72.5

68 . The process of claim 59 , wherein the principal liquid comprises acetone and the second liquid comprises water.

69 . The process of claim 59 , wherein the polymer membrane is less than 50 microns thick.

70 . The process of claim 59 , wherein the polymer membrane is less than 35 microns thick.

71 . The process of claim 59 , wherein the polymer solution is formed by heating the mixture to about the normal boiling point of the principal liquid in a sealed, pressurized container.

72 . The process of claim 71 , where the cooled polymer solution is applied to the high surface energy substrate prior to gelation of the polymer.

73 . The process of claim 71 , wherein the cooled polymer solution is applied to the high energy substrate within about 5 hours of being cooled.

74 . The process of claim 59 , wherein the high surface energy substrate comprises a metal.

75 . The process of claim 74 , wherein the high surface energy substrate is a metalized polymeric film.

76 . The process of claim 75 , wherein the metalized polymeric film is selected from the group consisting of aluminized polyethylene and aluminized polypropylene.

77 . The process of claim 59 , wherein the second liquid is a non-solvent for the polymer.

78 . The process of claim 59 , wherein the polymer membrane has an average pore diameter of less than 1 micron as determined by mercury porosimitry.

79 . The process of claim 59 wherein the polymer membrane has an average pore diameter is less than 0.5 microns as determined by mercury porosimitry.

80 . The process of claim 59 wherein the polymer membrane has a permeability greater than 500 centimeter micron centipoise/minute Torr.

81 . The process of claim 59 wherein the polymer membrane has a tensile strength greater than 300 psi in both machine and transverse directions.

82 . The process of claim 59 , wherein the polymer membrane has a tensile modulus greater than 10,000 psi in the machine direction.

83 . The process of claim 59 , wherein the polymer membrane has a McMullin number between about 1.01 and about 3.

84 . The process of claim 83 , wherein the McMullin Number is between about 1.01 and about 2.

85 . The process of claim 59 , wherein the principal liquid has a surface tension at least 10% lower than the surface energy of the polymer.

86 . The process of claim 59 , wherein the second liquid has a surface tension at least 10% higher than the surface energy of the polymer.

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