U.S. patent application number 11/708903 was filed with the patent office on 2007-08-23 for co-extrusion process for preparing roofing membranes.
This patent application is currently assigned to BFS Diversified Products, LLC. Invention is credited to Bruce Douglas, Richard Peng, Greg Sharrun.
Application Number | 20070194482 11/708903 |
Document ID | / |
Family ID | 38291268 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070194482 |
Kind Code |
A1 |
Douglas; Bruce ; et
al. |
August 23, 2007 |
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.
Inventors: |
Douglas; Bruce; (Zionsville,
IN) ; Sharrun; Greg; (Greenville, SC) ; Peng;
Richard; (Fishers, IN) |
Correspondence
Address: |
Bridgestone Americas Holding, Inc.;Chief Intellectual Property Counsel
1200 Firestone Parkway
Akron
OH
44317-0001
US
|
Assignee: |
BFS Diversified Products,
LLC
|
Family ID: |
38291268 |
Appl. No.: |
11/708903 |
Filed: |
February 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60775128 |
Feb 21, 2006 |
|
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Current U.S.
Class: |
264/173.11 ;
264/173.14 |
Current CPC
Class: |
B32B 27/18 20130101;
B32B 2307/5825 20130101; B32B 3/04 20130101; B32B 27/32 20130101;
B32B 27/12 20130101; B32B 37/153 20130101; B32B 2307/712 20130101;
B32B 2274/00 20130101; B32B 2262/0253 20130101; E04D 5/10 20130101;
B32B 27/20 20130101; B32B 5/024 20130101; B32B 2270/00 20130101;
B32B 2307/71 20130101; B32B 2264/10 20130101; B32B 2307/3065
20130101; B32B 2419/06 20130101; B32B 2305/18 20130101; B32B 25/14
20130101; B32B 37/02 20130101; B32B 2262/0284 20130101; B32B 27/08
20130101; B32B 2307/31 20130101; B32B 27/322 20130101 |
Class at
Publication: |
264/173.11 ;
264/173.14 |
International
Class: |
B32B 27/00 20060101
B32B027/00 |
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; and d) 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; and f)
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; and g) bonding said sheets together.
Description
[0001] The present application claims priority to and the benefit
of the filing date of U.S. Provisional Patent Application No.
60/775,128, filed Feb. 21, 2006.
BACKGROUND
[0002] The present embodiments relate to a co-extrusion process for
preparing roofing or other structural membranes comprising at least
two polymeric sheets. More particularly, the present embodiments
relate to a co-extrusion process for preparing multilayer membranes
having a cap layer adhered to a one or more support layers.
[0003] Polymeric roof sheeting is used as single ply roofing
membrane for covering industrial and commercial flat roofs. Such
membranes are generally applied to the roof surface in vulcanized
or cured state.
[0004] Because of its outstanding weathering resistance and
flexibility, cured EPDM based roof sheeting has rapidly gained
acceptance. This material is often prepared by vulcanizing the
composition in the presence of sulfur or sulfur containing
compounds such as mercaptans or using radiation curing.
Notwithstanding the usefulness of radiation curing and sulfur
curing, a potential drawback of utilizing these elastomers is the
lack of adhesion of EPDM, especially cured EPDM, to itself. This is
a potential concern in that, in applying EPDM sheets to a roof, it
is usually necessary to splice the cured EPDM sheets together along
the seams. This splice or seam area is subjected to both short term
and long term stresses such as those caused by roof movement, heavy
winds, freeze-thaw cycling and thermal cycling. Under certain
conditions, such stresses may manifest themselves in shear forces
that can result in seam peel back under severe stress
conditions.
[0005] In view of the foregoing, it has been necessary to use an
adhesive to bond the cured EPDM sheets together. These adhesives
must not only provide sufficient strength to resist the short and
long term stresses described above, they must also be resistant to
oxidation, hydrolysis and chemical breakdown. Adhesives that meet
these requirements are difficult to produce and can be time
consuming to apply to the seams of EPDM sheets, thereby increasing
the overall cost of installing the waterproof membrane.
[0006] Therefore, other materials for use in roofing membrane have
been investigated. Within the last decade, thermoplastic polyolefin
(TPO) sheeting has come into use in the manufacture of waterproof
roofing membranes. TPO membrane provides good service life, good
chemical resistance and has the advantage of being recyclable. In
addition, TPO membrane can be sealed along its seams without the
use of an adhesive by heating the edges of the sheets to a
temperature above the melt temperature of the TPO and pressing the
sheets together. This technique of joining sheets of roofing
membrane, known as heat welding, provides a strong seal and results
in overall time and cost savings in the application of the roofing
membrane.
[0007] Nevertheless, TPO roofing membrane suffers from several
distinct disadvantages. First, TPO roofing generally requires scrim
reinforcement embedded within the sheets to improve the flame
resistance and allow manipulation of the sheets under hot air
welding. Scrim is a support structure typically comprising a mesh
of interwoven strands of thermoplastic. Without such scrim, the TPO
often becomes too "soupy" to laminate together and may not possess
sufficient mechanical properties. This scrim adds an additional
cost to the TPO membrane.
[0008] Second, such membranes exhibit relatively weak bond strength
with the roofing substrate. This, along with the typical ductile
behavior of most TPOs prevents such membranes from supporting high
wind uplift loads. In addition, present day TPO membranes are often
too stiff and lacking in compliability (as indicated by the high
secant modulus properties of TPO resins) due to the relatively high
crystallinity of many TPOs to be easily bent to conform to the
contours of a roof, and therefore are quite cumbersome to install
due to this non-pliable property.
[0009] Finally, TPO layers, especially top layers, which must be
loaded with various additives such as fire retardants, UV
stabilizers, anti-oxidants, funcides can be expensive to produce
due to the high cost of such additives.
[0010] As disclosed in published U.S. Patent Application
US2001/0003625 to Apgar et al., it is known to produce a heat
weldable roofing membrane comprised of a layer of TPE or TPO on a
vulcanized EPDM sheet. Such a membrane suffers from the fact that
the processing temperature of TPO and TPE and the curing
temperature of EPDM are too close, thus making it difficult to seal
the seam. In addition, physically bonded thermoplastic and
crosslinked rubber may reject each other in the long term,
resulting in delamination and compromising the effectiveness of the
membrane.
[0011] Therefore, a need exists for a heat-weldable roofing
membrane that retains the advantages of TPO top layers while being
more pliable, easier to install and less expensive.
BRIEF DESCRIPTION OF THE FIGURES
[0012] FIG. 1 is a cross-section of a prior art roofing
membrane.
[0013] FIG. 2 is a cross-section of a 3-layer roofing membrane made
in accordance with the present embodiments.
[0014] FIG. 3 is a cross-section of a 4-layer roofing membrane made
in accordance with the present embodiments.
[0015] FIG. 4A is a schematic diagram showing the set-up for
co-extruding a roofing membrane according to a present
embodiment.
[0016] FIG. 4B is a schematic diagram showing an alternate set-up
for co-extruding a roofing membrane according to a present
embodiment.
[0017] 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.
SUMMARY OF THE INVENTION
[0018] In a first aspect, there is provided 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 the top sheet, wherein said first
polymeric material forms the cap layer and said second polymeric
material forms the upper inner layer, and bonding the top sheet to
the bottom sheet.
[0019] In a second aspect, there is provided 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, the process including the steps
of co-extruding first and second polymeric materials through a
first die to form the top sheet, wherein said first polymeric
material forms the cap layer and said second polymeric material
forms the upper inner layer, co-extruding third and fourth
polymeric materials through a second die to form the bottom sheet,
wherein said third polymeric material forms the lower inner layer
and said fourth polymeric material forms the core layer,
positioning a scrim between the top and bottom sheets, and bonding
the top sheet to the bottom sheet with the scrim therebetween.
[0020] In a third aspect, there is provided a process for preparing
a co-extruded sheet suitable for use in structural membranes
comprising two or more layers, the process including the step of
co-extruding first and second polymeric materials through a common
die to form the sheet, wherein said first polymeric material forms
a cap layer and said second polymeric material forms an inner
layer.
[0021] In a fourth aspect, there is provided 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; and f) bonding said top
sheet to said bottom sheet.
[0022] In a fifth aspect, there is provided 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 orifice; b) providing third and fourth extruders
having outlets in fluid communication with a second die having a
die 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; and g) bonding said sheets together.
DETAILED DESCRIPTION
[0023] As used herein, the term co-extrusion refers to a
manufacturing process in which two or more polymeric compounds are
fed into a common extrusion die having a single discharge orifice
and form distinct yet intimately bonded layers in a finished
extruded sheet. This may be accomplished through a combination of
control of viscosity and flow rates of the different compounds as
well as the die geometry, which together maintain separate and
generally uniform layers in the extruded piece.
[0024] In the present embodiments, co-extrusion is used to both
reduce material costs as well as add unique properties to extruded
roofing membranes. Costs can be reduced by co-extruding lower cost
inner layer(s) and/or a bottom layer of material with a higher cost
top layer in lieu of a single extrusion of higher cost material.
Special properties such as color, fire retardancy, oil resistance,
and/or enhanced strength can be achieved by co-extruding a thin
layer of material with special properties on top of a layer of
standard base material.
[0025] The present embodiments find particular application with
respect to structural membranes for use in housing, construction,
aquatic applications, etc. The discussion and figures presented
herein relate particularly to roofing membranes useful on various
types of roofs, including flat or low-sloped roofs. However, other
structural membranes are contemplated and are intended to be
encompassed by the present claims and discussion. Particularly, geo
membranes such as pond liners, aquatic farm liners, etc. are
specifically covered. In addition, the present embodiments relate
to other membranes such as scaffold sheeting, tarpaulins, shelters,
and other damp proof or waterproof membranes.
[0026] With reference to FIG. 1, prior art TPO roofing membranes
have generally included an extruded top layer 2, an intermediate
scrim layer 4, and an extruded bottom layer 6. The top layer, which
is exposed to the elements, contains significant amounts of
additives such as fire retardants, antioxidants, and UV blockers in
order to assure satisfactory service life as well as meet industry
standards. Because the bottom layer is not exposed in normal
applications, the material for this layer requires fewer expensive
additives. In addition, the bottom layer can typically also contain
lower grades of polymer as well as re-processed material to further
reduce cost.
[0027] The present embodiments make use of the process of
co-extrusion to produce a three or more polymeric layer laminate. A
scrim layer, if present in the finished membrane, is not considered
a "layer" for purposes of the present discussion. That is, "layers"
refer only to the polymeric extruded material layers. Thus, with
reference to FIG. 2, a three layer laminate roofing membrane 10 is
shown in accordance with one embodiment of the present invention.
The roofing membrane 10 includes a cap layer 12, an upper inner
layer 14 and a core (or bottom) layer 18. The cap layer refers to
the layer of the membrane that will be laying face up when the
membrane is installed on a roof while the core layer is the layer
that will be facing the roof deck. All three layers may be made
from the same polymeric material, such as thermoplastic polyolefin
(TPO) or TPO blends, although this is not necessary. Specifically,
the upper inner layer 14 and core layer 18 may be made from a lower
cost polymeric material, such as linear low density polyethylene
(LLDPE) or other lower cost polymer material.
[0028] The cap layer 12 and upper inner layer 14 are co-extruded
through a common extrusion die to form an intimately bonded
bi-layer sheet. This sheet may be subsequently bonded together with
a core layer 18 and, optionally, an intermediate scrim 20 via known
means such as calendering rolls or lamination wheels to form the
final membrane 10.
[0029] As detailed above, the cap layer may comprise the same or
different base polymeric material as the upper inner layer and/or
the core layer. However, since the cap layer will be facing up and
exposed to the elements, it typically will contain a number of
additives in order for the membrane to meet various building codes
and roofing membrane standards.
[0030] That is, when made from the same base polymeric material,
the primary difference between the layers is the inclusion of
different additives to each layer. By using a co-extrusion process,
specialty additives necessary for the membrane to meet such codes
and standards (e.g. fire retardants, anti-oxidants, UV stabilizers,
weatherability and chemical resistance enhancers, etc.) can be
confined to the relatively thin cap layer, reducing the amount of
such fillers needed and the resulting cost. In addition, other
fillers that improve the physical properties of the membrane can be
added to the inner and core layers.
[0031] Thus, the resulting membrane can be made more cheaply by
restricting expensive fillers to the cap layer only, while also
improving the physical properties of the membrane as a whole by
limiting the amount of such specialty fillers (which often tend to
negatively impact the mechanical properties of a material) as well
as allowing for the possibility of incorporating other,
mechanically favorable fillers in the other layers.
[0032] In another embodiment, a four layer laminate is produced
having co-extruded bi-layer top and bottom sheets. Again, an
intermediate scrim layer may be included between the co-extruded
sheets.
[0033] Thus, with reference to FIG. 3, a four layer laminate
roofing membrane 110 is shown in accordance with one embodiment of
the present invention. The roofing membrane 110 includes upper and
lower inner plies or layers 112, 114 a cap layer 116, and a core
layer 118. Again, all four layers may be made from thermoplastic
polyolefin (TPO) or TPO blends or other polymeric materials.
Specifically, the two inner plies 112, 114 may be made from linear
low density polyethylene (LLDPE) or other lower cost polymer
material.
[0034] A scrim reinforcement layer 120 may be provided between the
two inner layers for added support.
[0035] As indicated above, the layers of the membrane may
independently be formed from TPO or other polymeric material.
Preferably, at least the cap layer contains a TPO component. The
TPO layer used in the various embodiments of the present invention
may be any commercialized TPO conventionally used in roofing
membrane applications. TPOs are a class of uncrosslinked
thermoplastic elastomers (TPEs) based predominantly or wholly on
olefin polymers.
[0036] Thermoplastic elastomers (TPEs) are an important class of
polymeric compositions that are particularly useful in producing
durable components through conventional extrusion, calendaring or
injection molding processes. Typically a TPE is a blend of
thermoplastic polymer and an elastomer rubber. TPEs possess
properties similar to a cured elastomer but TPEs have the
advantage, compared to a rubber, that they undergo plastic flow
above the melting point of the thermoplastic polymer component of
the blend. This permits TPEs to be used in component fabrication
through common polymer processing techniques, such as injection
molding techniques to produce finished articles having resilient
rubber-like properties without the need for a vulcanizing cure of
the finished article. This provides TPEs with an advantage compared
to conventional curable elastomers because conventional curable
elastomers are tacky, do not undergo plastic flow at elevated
temperatures and therefore cannot be fabricated into finished
article forms by an extrusion or injection molding technique.
[0037] A typical TPO is a melt blend or reactor blend of a
polyolefin plastic, typically a propylene polymer, with a
non-crosslinked olefin copolymer elastomer (OCE), typically an
ethylene-propylene rubber (EPM) or an ethylene-propylene-diene
rubber (EPDM). In those TPOs made from EPDM, the diene monomer
utilized in forming the EPDM terpolymer is preferably a
non-conjugated diene. Illustrative examples of non-conjugated
dienes which may be employed are dicyclopentadiene,
alkyldicyclopentadiene, 1,4-pentadiene, 1,4-hexadiene,
1,5-hexadiene, 1,4-heptadiene, 2-methyl-1,5-hexadiene,
cyclooctadiene, 1,4-octadiene, 1,7-octadiene,
5-ethylidene-2-norbornene, 5-n-propylidene-2-norbornene,
5-(2-methyl-2-butenyl)-2-norbornene and the like. Conventional
EPDM's utilized in TPOs for roofing membranes include various
grades of VISTALON, available from the Exxon Chemical Co., and
ROYALENE, available from Uniroyal Chemical Co.
[0038] The polyolefin plastic imparts to the TPO the temperature
resistance and rigidity typical of that thermoplastic resin while
the olefin copolymer elastomer imparts flexibility, resilience and
toughness to the TPO. As stated, any conventional TPO used in the
roofing membrane industry is suitable for use in the present
invention. Preferred TPOs are those made by blending
ethylene-propylene elastomers with polypropylene.
[0039] The ethylene-propylene elastomers may be blended with the
polypropylene by conventional mixing techniques. An example of a
suitable group of TPOs for use in the present invention are medium
flow TPOs manufactured under the trade name ADFLEX, available from
Basell. TPO blends are also useful in the present embodiments.
[0040] In another embodiment, at least one of the layers in the
laminate comprises a blend of a plastomer, a low density
polyethylene, and a propylene-based polymer, as described in
commonly owned co-pending PCT application no. Pct/US2006/033522,
filed on Aug. 29, 2006, the disclosure of which is incorporated
herein by reference in its entirety.
[0041] More specifically, in one or more of these embodiments
utilizing such a blend, the plastomer may include an
ethylene-.alpha.-olefin copolymer. The plastomer employed in one or
more embodiments of this invention may include those described in
U.S. Pat. Nos. 6,207,754, 6,506,842, 5,226,392, and 5,747,592,
which are incorporated herein by reference. This copolymer may
include from about 1.0 to about 15 mole percent, in other
embodiments from about 2 to about 12, in other embodiments from
about 3 to about 9 mole percent, and in other embodiments from
about 3.5 to about 8 mole percent mer units deriving from
.alpha.-olefins, with the balance including mer units deriving from
ethylene. The .alpha.-olefin employed in preparing the plastomer of
one or more embodiments of this invention may include butene-1,
pentene-1, hexene-1, octene-1, or 4-methyl-pentene-1.
[0042] The plastomer of one or more embodiments of this invention
can be characterized by a density of from about 0.865 g/cc to about
0.900 g/cc, in other embodiments from about 0.870 to about 0.890
g/cc, and in other embodiments from about 0.875 to about 0.880 g/cc
per ASTM D-792. In these or other embodiments, the density of the
plastomers may be less than 0.900 g/cc, in other embodiments less
than 0.890 g/cc, in other embodiments less than 0.880 g/cc, and in
other embodiments less than 0.875 g/cc.
[0043] In one or more embodiments, the plastomer may be
characterized by a weight average molecular weight of from about
7.times.10.sup.4 to 13.times.10.sup.4 g/mole, in other embodiments
from about 8.times.10.sup.4 to about 12.times.10.sup.4 g/mole, and
in other embodiments from about 9.times.10.sup.4 to about
11.times.10.sup.4 g/mole as measured by using GPC with polystyrene
standards. In these or other embodiments, the plastomer may be
characterized by a weight average molecular weight in excess of
5.times.10.sup.4 g/mole, in other embodiments in excess of
6.times.10.sup.4 g/mole, in other embodiments in excess of
7.times.10.sup.4 g/mole, and in other embodiments in excess of
9.times.10.sup.4 g/mole. In these or other embodiments, the
plastomer may be characterized by a molecular weight distribution
(M.sub.w/M.sub.n) that is from about 1.5 to 2.8, in other
embodiments 1.7 to 2.4, and in other embodiments 2 to 2.3.
[0044] In these or other embodiments, the plastomer may be
characterized by a melt index of from about 0.1 to about 8, in
other embodiments from about 0.3 to about 7, and in other
embodiments from about 0.5 to about 5 per ASTM D-1238 at
190.degree. C. and 2.16 kg load.
[0045] The plastomer of one or more embodiments of this invention
may be prepared by using a single-site coordination catalyst
including metallocene catalyst, which are conventionally known in
the art. Useful plastomers include those that are commercially
available. For example, plastomer can be obtained under the
tradename EXXACT.TM. 8201 (ExxonMobil); or under the tradename
ENGAGE.TM. 8180 (Dow DuPont).
[0046] Similarly, in one or more these embodiments, the low density
polyethylene may include an ethylene-.alpha.-olefin copolymer. In
one or more embodiments, the low density polyethylene includes
linear low density polyethylene. The linear low density
polyethylene employed in one or more embodiments of this invention
may be similar to that described in U.S. Pat. No. 5,266,392, which
is incorporated herein by reference. This copolymer may include
from about 2.5 to about 13 mole percent, and in other embodiments
from about 3.5 to about 10 mole percent, mer units deriving from
.alpha.-olefins, with the balance including mer units deriving from
ethylene. The .alpha.-olefin included in the linear low density
polyethylene of one or more embodiments of this invention may
include butene-1, pentene-1, hexene-1, octene-1, or
4-methyl-pentene-1. In one or more embodiments, the linear low
density polyethylene is devoid or substantially devoid of propylene
mer units (i.e., units deriving from propylene). Substantially
devoid refers to that amount or less of propylene mer units that
would otherwise have an appreciable impact on the copolymer or the
compositions of this invention if present.
[0047] The linear low density polyethylene of one or more
embodiments of this invention can be characterized by a density of
from about 0.885 g/cc to about 0.930 g/cc, in other embodiments
from about 0.900 g/cc to about 0.920 g/cc, and in other embodiments
from about 0.900 g/cc to about 0.910 g/cc per ASTM D-792.
[0048] In one or more embodiments, the linear low density
polyethylene may be characterized by a weight average molecular
weight of from about 1.times.10.sup.5 to about 5.times.10.sup.5
g/mole, in other embodiments 2.times.10.sup.5 to about
10.times.10.sup.5 g/mole, in other embodiments from about
5.times.10.sup.5 to about 8.times.10.sup.5 g/mole, and in other
embodiments from about 6.times.10.sup.5 to about 7.times.10.sup.5
g/mole as measured by GPC with polystyrene standards. In these or
other embodiments, the linear low density polyethylene may be
characterized by a molecular weight distribution (M.sub.w/M.sub.n)
of from about 2.5 to about 25, in other embodiments from about 3 to
about 20, and in other embodiments from about 3.5 to about 10. In
these or other embodiments, the linear low density polyethylene may
be characterized by a melt flow rate of from about 0.2 to about 10
dg/min, in other embodiments from about 0.4 to about 5 dg/min, and
in other embodiments from about 0.6 to about 2 dg/min per ASTM
D-1238 at 230.degree. C. and 2.16 kg load.
[0049] The linear low density polyethylene of one or more
embodiments of this invention may be prepared by using a convention
Ziegler Natta coordination catalyst system. Useful linear low
density polyethylene includes those that are commercially
available. For example, linear low density polyethylene can be
obtained under the tradename Dowlex.TM. 2267G (Dow); or under the
tradename DFDA-1010 NT7 (Dow).
[0050] In one or more embodiments, the propylene-based polymer of
the blend may include polypropylene homopolymer or copolymers of
propylene and a comonomer, where the copolymer includes, on a mole
basis, a majority of mer units deriving from propylene. In one or
more embodiments, the propylene-based copolymers may include from
about 2 to about 6 mole percent, and in other embodiments from
about 3 to about 5 mole percent mer units deriving from the
comonomer with the remainder including mer units deriving from
propylene. In one or more embodiments, the comonomer includes at
least one of ethylene and an .alpha.-olefin. The .alpha.-olefins
may include butene-1, pentene-1, hexene-1, oxtene-1, or
4-methyl-pentene-1. In one or more embodiments, the copolymers of
propylene and a comonomer may include random copolymers. Random
copolymers may include those propylene-based copolymers where the
comonomer is randomly distributed across the polymer backbone.
[0051] The propylene-based polymers employed in one or more
embodiments of these embodiments may be characterized by a melt
flow rate of from about 0.5 to about 15 dg/min, in other
embodiments from about 0.7 to about 12 dg/min, in 10 other
embodiments from about 1 to about 10 dg/min, and in other
embodiments from about 1.5 to about 3 dg/min per ASTM D-1238 at
230.degree. C. and 2.16 kg load. In these or other embodiments, the
propylene-based polymers may have a weight average molecular weight
(M.sub.w) of from about 1.times.10.sup.5 to about 5.times.10.sup.5
g/mole, in other embodiments from about 2.times.10.sup.5 to about
4.times.10.sup.5 g/mole, and in other embodiments from about
3.times.10.sup.5 to about 4.times.10.sup.5 g/mole, as measured by
GPC with polystyrene standards. The molecular weight distribution
of these propylene-based copolymer may be from about 2.5 to about
4, in other embodiments from about 2.7 to about 3.5, and in other
embodiments from about 2.8 to about 3.2.
[0052] In one or more embodiments, propylene-based polymers may be
characterized by a melt temperature (T.sub.m) that is from about
165.degree. C. to about 130.degree. C., in other embodiments from
about 160 to about 140.degree. C., and in other embodiments from
about 155.degree. C. to about 140.degree. C. In one or more
embodiments, particularly where the propylene-based polymer is a
copolymer of propylene and a comonomer, the melt temperature may be
below 160.degree. C., in other embodiments 25 below 155.degree. C.,
in other embodiments below 150.degree. C., and in other embodiments
below 145.degree. C. In one or more embodiments, they may have a
crystallization temperature (T.sub.c) of about at least 90.degree.
C., in other embodiments at least about 95.degree. C., and in other
embodiments at least 100.degree. C., with one embodiment ranging
from 105.degree. to 115.degree. C.
[0053] Also, these propylene-based polymers may be characterized by
having a heat of fusion of at least 25 J/g, in other embodiments in
excess of 50 J/g, in other embodiments in excess of 100 J/g, and in
other embodiments in excess of 140 J/g.
[0054] Useful propylene-based polymers include those that are
commercially available. For example, propylene-based polymers can
be obtained under the tradename PP7620Z.TM. (Fina), PP33BF01.TM.
(Equistar), or under the tradename TR3020.TM. (Sunoco).
[0055] In addition to the polymeric component, various fillers and
processing materials as well as other components may be added to
one or more of the layers in the membrane of the present
embodiments. Suitable fillers may include reinforcing and
non-reinforcing materials such as those customarily added to
roofing membranes. Non-limiting examples of such fillers include
carbon black, calcium carbonate, clay, silica, and the like. With
respect to processing materials, various processing oils, waxes and
the like intended to improve the processing of the material may be
included in any concentration that does not significantly detract
from the properties of the membrane.
[0056] The polymer may also be formulated with stabilizers,
pigments and antioxidants to obtain the appropriate weathering
properties. In addition, flame retardant fillers such as alumina
trihydrate (ATH), magnesium trioxide, calcium carbonate, mica,
talc, or glass may be added. Adding ATH to the inner layer(s)
and/or core layer has great advantage since LLDPE can be processed
below the decomposition temperature of ATH. Filler levels can range
from 0 to about 80% by weight.
[0057] In this respect, flame retardants may include any compound
that will increase the burn resistivity of the membranes of the
present invention or at least one layer thereof. In one or more
embodiments, the flame retardant may include halogenated flame
retardants, non-halogenated flame retardants, or mixtures thereof.
Examples of halogenated flame retardants may include halogenated
organic species or hydrocarbons such as hexabromocyclododecane or
N,N'-ethylene-bis(tetrabromophthalimide). Exemplary non-halogenated
flame retardants include magnesium hydroxide, alumina trihydrate,
zinc borate, ammonium polyphosphate, melamine polyphosphate, and
antimony oxide.
[0058] Magnesium hydroxide (Mg(OH).sub.2) is commercially available
under the tradename Vertex.TM., ammonium polyphosphate is
commercially available under the tradename Exolite.TM. (Clarian),
which is sold together as a polyol masterbatch, melamine
polyphosphate is available under the tradename Budit.TM. 3141
(Budenheim), and antimony oxide (Sb.sub.2CO.sub.3) is commercially
available under the tradename Fireshield.TM..
[0059] In one or more embodiments, treated or functionalized
magnesium hydroxide may be employed. For example, magnesium oxide
treated with or reacted with a carboxylic acid may be employed. In
one embodiment, the magnesium hydroxide may be treated or reacted
with stearic acid. In other embodiments, the magnesium hydroxide
may be treated with or reacted with certain silicon-containing
compounds. The silicon-containing compounds may include silanes,
polysiloxanes including silane reactive groups. Treated magnesium
hydroxide is commercially available.
[0060] Other additives can include additional various stabilizers.
Stabilizers may include one or more of a UV stabilizer, an
antioxidant, and an antiozonant. UV stabilizers may include
Tinuvin.TM. 622. Antioxidants can include Irganox.TM. 1010.
[0061] Other materials that could be used in forming the layers
include various thermoplastics such as nylon as well as
thermoplastic vulcanizates (TPV's). TPV's are polyolefinic
matrices, preferably crystalline, through which thermoset
elastomers are generally uniformly distributed. Examples of
thermoplastic vulcanizates include EPM and EPDM thermoset materials
distributed in a crystalline polypropylene matrix. One example of a
commercial TPV is SANTOPRENE thermoplastic rubber, which is
manufactured by Advanced Elastomer Systems and is a mixture of
crosslinked EPDM particles in a crystalline polypropylene matrix.
These materials have found utility in many applications which
previously used vulcanized rubber, e.g. hose, gaskets, and the
like. TPV's are noted for their processability as thermoplastics
while retaining the excellent resilience and compression set
properties of vulcanized rubbers.
[0062] Commercial TPV's are typically based on vulcanized rubbers
in which a phenolic resin, sulfur or peroxide cure system is used
to vulcanize, that is crosslink, a diene (or more generally, a
polyene) copolymer rubber by way of dynamic vulcanization, which is
a process in which the rubber is crosslinked while mixing
(typically vigorously), in a thermoplastic matrix. Sulfur or a
phenolic resin is typically preferred over peroxide free radical
cure systems because peroxide may degrade and/or crosslink the
polypropylene or polyethylene thermoplastic as well as the rubber
and this is in turn limits the extent of rubber crosslinking that
can occur before the entire mixture degrades or crosslinks and is
no longer thermoplastic.
[0063] A preferred method of preparing a thermoplastic vulcanizate
known by those skilled in the art is to form an admixture of
non-crosslinked elastomeric polymer and polyolefin resin and curing
agent. The admixture is then masticated at a vulcanization
temperature. Preferably the non-crosslinked polymer and polyolefin
are intimately mixed before a curing agent is added. When prepared
in a conventional mixing apparatus such as a multiple-roll mill,
Banbury or Brabender mixer or mixing extruder, this is known as a
"two-pass" cycle. Additional additives may added, including, but
not limited to those fillers, fire retardants, stabilizers,
pigments and antioxidants described above with respect to the TPO
layer.
[0064] Any conventional TPV having the desired weatherability,
flexibility and strength may be used in the present embodiments. An
exemplary TPV includes a copolymer of ethylene and a carbonyl
containing monomer such as vinyl acetate, acrylic acid,
(alk)acrylic acid, methacrylate and unsaturated polycarboxylic
acid. A particular TPV is a dynamically cured blend of metallocene
polyethylene (m-PE), ethylene/vinyl acetate or
ethylene/methacrylate copolymer, and optionally, a polypropylene
polymer. As used herein, polypropylene polymer is meant to include
both homopolymers as well as copolymers of polypropylene and
another olefinic polymer. A suitable propylene polymer is
ethylene-propylene random copolymer. A peroxide may be used as the
curing agent. The metallocene polyethylene may be a homopolymer or
a copolymer of ethylene and a small amount of olefinic monomer. A
suitable ethylene copolymer is an ethylene/vinyl acetate copolymer
marketed under the name EVANTANE, available from AtoFina. The
various ingredients may be mixed and dynamically cured using
standard techniques known in the industry. For example, the
compounding ingredients can be admixed, utilizing an internal mixer
(such as a Banbury or Brabender mixer or other mixers suitable for
forming a viscous relatively uniform admixture.
[0065] As noted, a scrim reinforcement layer 120 may be used in any
of the embodiments. A suitable scrim reinforcement layer may
comprise a mesh of interwoven strands of thermoplastic or metal
having a tensile strength sufficient to resist tearing when exposed
to typical tensile loads experienced by roofing membranes from
various directions. A preferred scrim reinforcement layer is one
comprised of polypropylene or polyethylene terephthalate (PET),
although of course other materials may be used.
[0066] The membrane of the present invention may be formed by
co-extruding the cap and upper inner layer 16, 12 through a single
extrusion die to form a single sheet of material in which the two
materials are intimately bonded, but nevertheless retain a
relatively distinct dividing line between the two. This is
accomplished through a combination of control of viscosity and flow
rates of the different compounds as well as the die geometry, which
together maintain separate and uniform layers in the extruded
piece. The relative thicknesses of each of the layers may be
varied, but for cost saving purposes, the thickness of the top
layer 16 is preferably as thin as possible without degrading the
properties of the resultant membrane.
[0067] When the bottom sheet comprises only a single bottom core
layer, for example as in the embodiment of FIG. 2, the core layer
may be provided through conventional means, such as by extrusion
through a conventional extrusion die. The two sheets may then be
run through a lamination wheel with an intermediate scrim layer
(when present) to form the final membrane.
[0068] When the bottom sheet comprises two or more layers, such as
shown in the embodiment of FIG. 3, these two or more layers can
likewise be extruded through a single extrusion die to form a
co-extruded sheet in which the two materials are intimately bonded,
but nevertheless retain a relatively distinct dividing line between
the two. The two sheets may then be run through a lamination wheel
with an intermediate scrim layer to form the final membrane.
[0069] With more detail and with reference to FIG. 4A, an exemplary
process for forming a four layer membrane is shown. Twin screw
extruders may be set up for each individual layer material. Thus,
for a four ply membrane as discussed above, four extruders 130 and
132 are set up in parallel arrangement. The extruders may process
pre-compounded material in pellet form, for example, or the
material for the individual layers may be compounded in the
extruders themselves. The cap layer 116 and upper inner layer 112
are then extruded through a multi-manifold die 140 or a single
manifold die with a multi-component capable feedblock to form an
upper co-extruded top sheet 141. Likewise the bottom inner layer
114 and core layer 118 are extruded through a similar die 142 to
form a lower co-extruded sheet 144. Such dies and feedblocks are
available commercially from various manufacturers, such as
Extrusion Dies Industries, LLC (Chippewa Falls, Wis.). Suitable
dies include those described in U.S. Pat. No. 5,494,429, the
disclosure of which is incorporated herein by reference. The upper
and lower sheets are bonded together with an intermediate scrim 146
via known means such as a pair of calendering rolls 148 or
lamination wheels to form the final membrane 150.
[0070] Alternately, and with respect to FIG. 4B, two pairs of
calendering rolls or lamination wheels, 148A and 148B, can be used
to sequentially bond the upper sheet 141 to a scrim layer 146 and
then subsequently bonding the lower sheet 144 to the upper
sheet/scrim laminate 151 to form the final membrane 152. Although
such a process requires the use of additional calendering rolls or
lamination wheels, it allows one to more easily and independently
control the thicknesses of both the upper and lower sheets by
controlling the gap distance between the rolls or wheels. This
allows one to optimize the thickness of the relatively more
expensive cap layer in relation to the other layers in the final
membrane.
[0071] As detailed above, the co-extrusion process can be performed
using a dual or multi-cavity die or a single cavity die with a
multi-component or "splitting" feedblock. With regard to a single
manifold die with a multi-component capable feedblock, precise
control of the layer sequence arrangements can be preset upstream
of the combining point in the feedblock by installing a customized
selector spool, without the need to remove the feedblock from the
line. Layers pass through the sculptured manifolds that are housed
in split-body combining spools. Fine adjusters allow these
combining spools to be rotated to vary both the height and width of
the tapered exit geometry for each layer, providing on-line control
of layer uniformity in the final product. Such single cavity dies
with multi-component feedblocks are commercially available and
potentially work best when the two or more polymeric materials
introduced into the die for forming distinct layers of the sheet
have similar viscosities.
[0072] Dual or multi-cavity dies on the other hand have distinct
flowpaths for the polymeric materials in each cavity. Depending on
the exact design of the die, these flowpaths meet at some point
within the die prior to exiting the output orifice of the die.
While more expensive that single cavity dies, dual or multi-cavity
dies are more flexible and allow for more control over co-extrusion
of a wider range of materials having different viscosities and
other properties. The line speed can be any conventional rate
typically used for roofing membranes. Roofing membranes are
typically sheeted in 10 foot (3.05 m) widths.
[0073] As shown in FIGS. 5A, 5B and 5C, in one embodiment, the
individual layers 212, 214, 216, 218 of the membrane may overcoat
the sides of the scrim 246 such that the scrim is completely
surrounded by the layers on the sides of the membrane, producing
what is known as a "gum edge". That is, the scrim does not extend
to the edge of two or more of the membrane layers, but instead at
least one of the cap layer 216 and upper inner layer 212 and at
least one of the bottom inner layer 214 and core layer 218 are
bonded to each other at the edges to encapsulate the scrim. FIG. 5A
shows an embodiment wherein all four layers encapsulate the scrim.
FIG. 5B shows an alternate embodiment wherein only the cap and core
layers encapsulate the scrim. FIG. 5C shows still another alternate
embodiment wherein only the upper and lower inner layers
encapsulate the scrim. Similar arrangements are possible with
membranes having a different number of layers.
[0074] The use of co-extrusion allows for the use of less expensive
materials in all but the top layer and a reduction in the amount of
fillers normally needed for a roofing membrane while still allowing
the membrane to meet industry standards. Co-extrusion shows better
results than a comparable membrane that might be produced using
multiple single material extruders because the bond between the
layers is more intimate and secure and reduces the chances of
de-lamination. In addition, it reduces the need for additional
lamination wheels or other bonding mechanisms.
[0075] The above embodiment describes three and four ply membranes
with an intermediate scrim. Of course, additional layer membrane
can also be produced by extruding additional materials through the
dies to form additional layers. Thus, a six layer membrane could be
produced by co-extruding three layers through both first and second
dies, or a 4-layer membrane with three layers co-extruded through a
first die and a single layer extruded through a second die. Other
arrangements are likewise contemplated and can be produced by
simply adding additional extruders to feed each of the dies. In
this way, customized membranes with any properties can be
produced.
[0076] Generally, the thickness of each of the plies may preferably
range between from about 2-25 mils (0.051-0.64 mm), in one
embodiment between 5 and 23 mils (0.13-0.58 mm), and in another
embodiment between 6 and 21 mils (0.15-0.53 mm), although greater
or less thicknesses may be employed and thus, are not precluded.
The total thickness of the membrane is typically from about 30 to
about 100 mils (0.76-2.54 mm), in one embodiment from 35 to 65 mils
(0.89-1.65 mm) preferably at least 39 mils (1.0 mm), or the minimum
thickness specified in standards set by the Roofing Council of the
Rubber Manufacturers Association for non-reinforced rubber sheets
for use in roofing applications.
[0077] The multi-layer co-extruded sheets may be adhered to each
other along with an intermediate scrim. This can be accomplished
using conventional techniques known in the industry. For example,
the co-extruded sheets may be melt-bonded to each other under
elevated temperature and pressure or laminated using a lamination
roll.
[0078] The above described membranes can be installed on a roof
deck. During installation on a roof deck, sheets of the roofing
membrane of the present invention may be bonded to each other
without the use of adhesives using heat welding. Such techniques
are well-known in the industry. Generally, sheets of the roofing
membrane are laid on the roof such that each sheet overlaps an
adjacent sheet. Next, heat and pressure are applied to the
overlapping edges of the two roofing membrane sheets to form a
seam. The amount of overlap and the corresponding width of the seam
can vary depending on the requirements of the application. At the
location of the seam, heat is applied to the membrane to raise its
temperature above the melt temperature of the TPO layer(s). The TPO
layer(s) will flow along the seam, forming a weatherproof seal.
Alternately, adhesives may be used to adhere the sheets to each
other and/or the roof deck. Such adhesives may include solvent
based adhesives or hot melt adhesives applied either at the factory
or on the job site.
[0079] In this respect, the above described co-extrusion process
can be modified such that an extruded adhesive or other polymeric
material can be co-extruded on only the edges of one or more of the
membrane layers during the process. This can be accomplished by the
use of internal baffles and/or modified feedblocks to ensure that
the adhesive or polymeric material is confined to only the edges of
the membrane. The polymeric material may comprise a different
polymer having higher strength than other parts of the membrane to
improve hold down strength of the membrane on the roof deck.
[0080] As described above, one embodiment of a roofing membrane as
described herein comprises top and bottom TPO layers, each
co-extruded with a separate TPO layer. While the top and bottom TPO
layers are loaded with anti-oxidants, pigments and flame
retardants, the inner layers may be loaded with a reinforcing
filler such as wollastonite (calcium silicate) or glass fiber
filler to increase the crystallinity, which decreases the strain
(creep) relaxation of the membrane. Thus, the membrane provides the
advantages of heat weldability, strong mechanical performance and
excellent chemical resistance, while still allowing the membrane to
be pliable, allowing for easier handling and installation of the
membrane.
[0081] Although not intended to be limiting, a roofing membrane
according to the present embodiments may have a flexural modulus,
which may also be referred to as a 1% secant modulus of from 10,000
to 30,000 psi (69-207 MPa), as measured according to ASTM D-790, in
one embodiment from 12,000 to 25,000 (83-172 MPa).
[0082] Likewise, the roofing membrane preferably meets or exceeds
all standards for TPO roofing membrane as outlined in ASTM D6878
(the current active standard is D6878-06a). Thus, the membrane
preferably meets or exceeds the standards in table 1 below, as well
as other standards outlined in ASTM D6878, such as weather
resistance, properties after heat aging, etc.
TABLE-US-00001 TABLE 1 Thickness 1.0 mm Breaking strength 976 N
Tearing strength 245 N Brittleness point (max) -40.degree. C.
[0083] As detailed above, depending on the application and the
desired properties of the final membrane, no reinforcing scrim may
be necessary. The bottom layer of the membrane typically
contributes to producing a secure seam during the heat welding of
the membrane. The roofing membranes produced according to the
present embodiments advantageously cost less to produce than a pure
TPV membrane and are 100% recyclable.
EXAMPLE
[0084] A sample 4-layer membrane made in accordance with the
teachings of the present embodiments comprising ADFLEX TPO
laminated onto a scrim reinforcement in accordance with the
formulation set out in Table 2 was produced. The numbers are the
weight percent of each component in the layers. The mechanical
properties of this membrane were better than a conventional 2-ply
TPO membrane known by those skilled in the art having the same
grade of ADFLEX on both sides of a standard polypropylene
scrim.
TABLE-US-00002 TABLE 2 Upper Inner Bottom Component Cap Layer Layer
Inner Layer Core Layer TPO Resin 51.50 85.00 85.00 85.50 Phenolic
0.15 0.10 Antioxidant Phosphate 0.40 0.30 Antioxidant HALS 1 0.15
HALS 2 0.15 Struktol TR-016 0.15 0.20 Vertex HST 38.50 12.50 Kronos
2160 5.00 1.00 Firebrake ZB 4.00 Wollastonite 15.00 15.00 Carbon
Black 0.40 TOTAL: 100.00% 100.00% 100.00% 100.00% HALS1 (hindered
amine short term UV light stabilizer): Tinuvin 770 from Ciba
Specialty Chem. HALS2 (long term UV stabilizer): Tinuvin 622 from
Ciba Specialty Chem. TR-016 (calcium based fatty acid metal soap
lubricant): from Struktol Co. External Lubricant Vertex HST:
magnesium hydroxide (flame retardant) treated with stearic acid
from JM Huber Kronos 2160: titanium oxide white pigment from Kronos
Firebrake ZB: Zinc borate flame retardant from Borax Wollastonite:
Nyglos 8 (a white reinforcing filler) from Nycon Minerals Co.
[0085] The scrim used was a 9.times.9 weft insertion, 1000 denier
polyester. The thickness of the layers in the membrane was: cap
layer (21 mil-0.53 mm), upper inner layer (6 mil-0.15 mm), lower
inner layer (6 mil-0.15 mm), and core layer (21 mil-0.53 mm) for a
total membrane thickness of 60 mils (1.52 mm). This membrane passed
Class A UL burn on 4'' ISO95+GL. The membrane was tested on a FSBP
wind simulator and had a rating of 120 lbs/sf (5.75 kPa). It was
found that the tongue tear, puncture resistance and bond strength
(regardless of substrate) are superior for the present 4-ply
membrane compared to conventionally extruded 2-ply TPO membranes,
thus giving overall improved membrane performance.
[0086] It is also possible that, in certain applications, just the
co-extruded top-sheet may be used as a roofing membrane, without a
scrim layer, or core layer.
[0087] Specific design features for the membranes can be controlled
by varying the composition of one or more the membrane layers,
including both identity of the base polymeric material as well as
the identity and amount of additives to each layer. Although not
limiting, examples of various desired membrane characteristics and
potential strategies to improves such characteristics include:
[0088] (A) for better oil/gasoline resistance--use a thin cap layer
comprising high crystalline HDPE or Fluoro-polymer.
[0089] (B) for steep slope flame resistance--incorporate a thin
surface layer of liquid crystalline polymers (LCP) or
fluoropolymers or nano-mineral oxide/hydroxide as flame
retardant.
[0090] (C) for improved mechanical properties--use LLDPE based
PE/PP blend as the inner plies to enhance the puncture
resistance.
[0091] (D) for better UV, thermal stability and long term
reflectivity--use nano-mineral (zinc, copper, tin, magnesium) oxide
or hydroxide, some of which can also can function also as a fire
retardant.
[0092] (E) for desired colors--add pigment concentrate to the cap
layer compound, the color of the inner ply also can be adjusted to
enhance the color on the surface.
[0093] (F) for cost reduction--load all the functional additives in
the cap layer only. All the inner plies are made of cheaper
polymers with only high puncture resistance/mechanical strength
required.
[0094] The invention has been described with reference to the
preferred embodiments. Obviously, modifications and alterations
will occur to others upon a reading and understanding of this
specification. The invention is intended to include all such
modifications and alterations in so far as they come within the
scope of the appended claims and the equivalents thereof.
* * * * *