Co-extrusion process for preparing roofing membranes

Abstract

A process for preparing a multi-layer roofing or structural membrane is provided including a top sheet including co-extruding a cap and inner layer and bonding the top sheet to a bottom sheet. The use of the co-extrusion process allows for multi-layer sheets that reduce the need for expensive fillers in all but a cap layer of the membrane. A scrim reinforcement layer is optionally embedded in the membrane. When installed on a roof substrate, the membrane can be sealed by heat welding the seams of the membrane sheets or by other means.

Description

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-section of a prior art roofing membrane.

FIG. 2 is a cross-section of a 3-layer roofing membrane made in accordance with the present embodiments.

FIG. 3 is a cross-section of a 4-layer roofing membrane made in accordance with the present embodiments.

FIG. 4A is a schematic diagram showing the set-up for co-extruding a roofing membrane according to a present embodiment.

FIG. 4B is a schematic diagram showing an alternate set-up for co-extruding a roofing membrane according to a present embodiment.

FIGS. 5A, 5B, and 5C show a cross-sections of an edge of a roofing membrane according to various present embodiments where the scrim is encapsulated by one or more of the polymeric layers of the membrane.

Claims

1. A process for preparing a structural membrane comprising a top sheet including a cap layer and an upper inner layer, and a bottom sheet, the process including the steps of co-extruding first and second polymeric materials through a common die to form said top sheet, wherein said first polymeric material forms said cap layer and said second polymeric material forms said upper inner layer, and bonding said top sheet to said bottom sheet, wherein said bottom sheet comprises a third polymeric material.

2. The process of claim 1, further comprising the step of positioning an intermediate scrim between said top and bottom sheets prior to bonding said sheets.

3. The process of claim 1, further comprising forming said bottom sheet by co-extruding a lower inner layer and a core layer through a second die.

4. The process of claim 3, wherein at least one of said first, second, and third polymeric materials comprise a thermoplastic olefin.

5. The process of claim 1, wherein said first polymeric material comprises a fire retardant and a UV stabilizer.

6. The process of claim 5, wherein at least one of said second and third polymeric materials is at least substantially free of said fire retardant and UV stabilizer.

7. The process of claim 1, wherein said common die is a dual or multi-cavity die.

8. The process of claim 1, wherein at least one of said second and third polymeric materials comprise a reinforcing filler that functions to improve the mechanical properties of said membrane.

9. The process of claim 8, wherein said first polymeric material is substantially free of said reinforcing filler.

10. The process of claim 8, where said reinforcing filler comprises wollastonite.

11. The process of claim 1, wherein at least one of said first, second and third polymeric materials comprise a nano-mineral or nano-clay.

12. The process of claim 1, wherein said membrane has superior tongue tear, puncture resistance, and bond strength as compared to a two layer TPO roofing membrane.

13. The process of claim 1, wherein at least one of said second and third polymeric materials comprises linear low density polyethylene (LLDPE).

14. The process of claim 13, wherein said at least one of second and third polymeric materials comprises a LLDPE/PP blend.

15. The process of claim 1, wherein said first polymeric material comprises a pigment and wherein said second polymeric material is substantially free of pigment.

16. The process of claim 1, further comprising extruding an adhesive to form an adhesive strip on at least one edge of said bottom sheet.

17. The process of claim 1, wherein said first polymeric material comprises at least one of liquid crystal polymer, a fluoropolymer, or nano-mineral oxide/hydroxide.

18. The process of claim 3, wherein the co-extrusion through said first and second dies is performed such that each of said cap layer, upper inner layer, lower inner layer and core layer has a thickness of from 5-23 mils (0.13-0.58 mm).

19. The process of claim 18, where the co-extrusion through said first and second dies is performed such that said cap layer has a thickness of about 21 mils (0.53 mm), said upper inner layer has a thickness of about 6 mils (0.15 mm), said lower inner layer has a thickness of about 6 mils (0.15 mm), and said core layer has a thickness of about 21 mils (0.53 mm).

20. The process of claim 2, wherein said scrim comprises polypropylene, polyethylene terephthalate, and/or polyester.

21. The process of claim 1, wherein at least one of said first, second and third polymeric materials comprise a blend of a plastomer, low density polyethylene, and a propylene based polymer.

22. The process of claim 21, where said plastomer includes an ethylene-a-olefin copolymer characterized by a density of from about 0.865 g/cc to about 0.900 g/cc.

23. The process of claim 21, where the low-density polyethylene includes linear low density polyethylene.

24. The process of claim 23, where the linear low density polyethylene includes an ethylene-a-olefin copolymer including from about 2.5 to about 13 mole percent mer units deriving from a-olefins.

25. The process of claim 24, where the linear low density polyethylene is characterized by a density of from about 0.885 g/cc to about 0.930 g/cc per ASTM D-792.

26. The process of claim 21, where the propylene-based polymer comprises a propylene homopolymer or copolymer comprising propylene and a comonomer, and where the copolymer includes, on a mole basis, a majority of mer units derived from propylene.

27. The process of claim 26, where the propylene-based copolymers include from about 2 to about 6 mole percent mer units deriving from comonomer, with the balance including mer units deriving from propylene.

28. The process of claim 21, within said at least one of said first, second and third polymeric materials further comprises a flame retardant selected from the group consisting of halogenated flame retardants, non-halogenated flame retardants, and mixtures thereof.

29. The process of claim 28, where the halogenated flame retardants are selected from halogenated hydrocarbons, where the halogenated hydrocarbons are selected from hexabromocyclododecane, N,N′-ethylene-bis-(tetrabromophthalimide), and mixtures thereof, and where the non-halogenated flame retardants are selected from magnesium hydroxide, aluminum trihydrate, zinc borate, ammonium polyphosphate, melamine polyphosphate, and mixtures thereof.

30. The process of claim 29, where the magnesium hydroxide includes a treated magnesium hydroxide or a functionalized magnesium hydroxide.

31. The process of claim 30, where the magnesium hydroxide includes magnesium oxide treated with or reacted with a carboxylic acid, or where the magnesium hydroxide is treated or reacted with stearic acid, or where the magnesium hydroxide is treated or reacted with silicon-containing compounds selected from the group including silanes, and polysiloxanes, or where the magnesium hydroxide includes magnesium hydroxide treated with titanates.

32. The process of claim 21, where the at least one polymeric material comprises i) from about 5 to about 50% by weight plastomer, ii) from about 10 to about 90% by weight low density polyethylene, and iii) from about 5 to about 50% by weight propylene-based polymer based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer, and also includes iv) from about 10 to about 50% by weight magnesium hydroxide, based upon the total weight of the at least one polymeric material.

33. The process of claim 32, where the at least one polymeric material includes i) from about 10 to about 45% by weight plastomer, ii) from about 15 to about 85% by weight low density polyethylene, and iii) from about 10 to about 45% by weight propylene-based polymer based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer, and also includes iv) from about 15 to about 45% by weight magnesium hydroxide, based upon the total weight of the at least one polymeric material.

34. The process of claim 1, where said roofing membrane is characterized by a flexural modulus of from 10,000 to 30,000 psi (69-207 MPa).

35. The process of claim 21, where the at least one polymeric material includes at least 31% by weight low density polyethylene based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer.

36. The process of claim 35, where the at least one polymeric material includes at least 35% by weight low density polyethylene.

37. The process of claim 1, wherein said top sheet is bonded to said bottom sheet by passing said sheets through a pair of lamination wheels or calendering rolls.

38. The process of claim 2, wherein one of said top or bottom sheet is bonded to said scrim via a first bonding process to form a laminate and the other of said top or bottom sheet is subsequently bonded to said laminate via a second bonding process to form said membrane.

39. The process of claim 38, wherein the thicknesses of said top and bottom sheets can be independently varied.

40. The process of claim 38, wherein each of said first and second bonding processes is performed using a pair of lamination wheels or calendering rolls.

41. The process of claim 1, wherein at least one of said top and bottom sheets comprises at least three distinct layers.

42. The process of claim 1, wherein said membrane comprises a roofing membrane.

43. The process of claim 1, wherein said membrane comprises a geo membrane.

44. A process for preparing a structural membrane comprising a top sheet including a cap layer and an upper inner layer, and a bottom sheet including a lower inner layer and a core layer, said process including the steps of: a) co-extruding first and second polymeric materials through a first die to form said top sheet, wherein said first polymeric material forms said cap layer and said second polymeric material forms said upper inner layer;b) co-extruding third and fourth polymeric materials through a second die to form said bottom sheet, wherein said third polymeric material forms said lower inner layer and said fourth polymeric material forms said core layer;c) positioning a scrim between said top and bottom sheets; andd) bonding said top sheet to said bottom sheet with said scrim therebetween.

45. The process of claim 44, wherein at one of said cap layer and upper inner layer of said first sheet and at least one of said lower inner layer and core layer of said second sheet is extruded to a greater width than a width of said scrim, such that when step d) is performed, the scrim is completely surrounded by said layers on the sides of the membrane.

46. The process of claim 45, wherein each of said cap layer, upper inner layer, lower inner layer, and core layer are all extruded to a greater width than a width of said scrim.

47. The process of claim 45, wherein only said cap layer and said core layer are extruded to a greater width than a width of said scrim.

48. The process of claim 45, wherein only said upper and lower inner layers are extruded to a greater width than a width of said scrim.

49. The process of claim 44, wherein at least one of said first, second, third, and fourth polymeric materials comprise a thermoplastic olefin.

50. The process of claim 44, wherein said first polymeric material comprises a fire retardant and a UV stabilizer.

51. The process of claim 50, wherein at least one of said second, third, and fourth polymeric materials is at least substantially free of said fire retardant and UV stabilizer.

52. The process of claim 44, wherein at least one of said first and second dies is a dual or multi-cavity die.

53. The process of claim 44, wherein at least one of said first and second dies is a single cavity die having a splitting feedblock attached thereto.

54. The process of claim 44, wherein at least one of said second, third and fourth polymeric materials comprises a reinforcing filler that functions to improve the mechanical properties of said membrane.

55. The process of claim 54, wherein said first polymeric material is substantially free of said reinforcing filler.

56. The process of claim 54, where said reinforcing filler comprises wollastonite.

57. The process of claim 44, wherein at least one of said first, second, third, and fourth polymeric materials comprises a nano-mineral or nano-clay.

58. The process of claim 44, wherein said membrane has superior tongue tear, puncture resistance, and bond strength as compared to a two layer TPO roofing membrane.

59. The process of claim 44, wherein at least one of said second and third polymeric materials comprises linear low density polyethylene (LLDPE).

60. The process of claim 59, wherein said at least one of second and third polymeric materials comprises a LLDPE/PP blend.

61. The process of claim 44, wherein said first polymeric material comprises a pigment and wherein at least one of said second, third and fourth polymeric materials is substantially free of pigment.

62. The process of claim 44, further comprising extruding an adhesive to form an adhesive strip on at least one edge of said bottom sheet.

63. The process of claim 44, wherein said first polymeric material comprises at least one of liquid crystal polymer, a fluoropolymer, or nano-mineral oxide/hydroxide.

64. The process of claim 44, wherein the co-extrusion through said first and second dies is performed such that each of said cap layer, upper inner layer, lower inner layer and core layer has a thickness of from 5-23 mils (0.13-0.58 mm).

65. The process of claim 44, wherein said scrim comprises polypropylene, polyethylene terephthalate, and/or polyester.

66. The process of claim 44, wherein at least one of said first, second, third, and fourth polymeric materials comprise a blend of a plastomer, low density polyethylene, and a propylene based polymer.

67. The process of claim 44, wherein said top sheet is bonded to said bottom sheet by passing said sheets through a pair of lamination wheels or calendering rolls.

68. The process of claim 41, wherein one of said top or bottom sheet is bonded to said scrim via a first bonding process to form a laminate and the other of said top or bottom sheet is subsequently bonded to said laminate via a second bonding process to form said membrane.

69. The process of claim 68, wherein thicknesses of said top and bottom sheets can be independently varied.

70. The process of claim 68, wherein each of said first and second bonding processes is performed using a pair of lamination wheels or calendering rolls.

71. A process for preparing a co-extruded sheet comprising two or more layers and suitable for use in a structural membrane, the process including the step of co-extruding first and second polymeric materials through a common die to form said sheet, wherein said first polymeric material forms a cap layer and said second polymeric material forms an inner layer.

72. A process for preparing a structural membrane comprising a top sheet including a cap layer and an upper inner layer, and a bottom sheet, the process including the steps of: a) extruding a first polymeric material to form said cap layer;b) extruding a second polymeric material to form said upper inner layer;c) adhering said cap layer to said upper inner layer to form said top sheet;d) extruding a third polymeric material to form said bottom sheet;e) positioning a scrim between said top and bottom sheets; andf) bonding said top sheet to said bottom sheet.

73. A process for producing a structural membrane comprising: a) providing first and second extruders having outlets in fluid communication with a first die having a die outlet orifice;b) providing third and fourth extruders having outlets in fluid communication with a second die having a die outlet orifice;c) extruding first and second polymeric materials through said first and second extruders, respectively, into said first die;d) extruding third and fourth polymeric materials through said third and fourth extruders, respectively, into said second die;e) discharging a first sheet from said orifice of said first die, said sheet comprising distinct layers of said first and second material;f) discharging a second sheet from said orifice of said second die, said sheet comprising distinct layers of said third and fourth material; andg) bonding said sheets together.