Note: Descriptions are shown in the official language in which they were submitted.
TITLE OF THE INVENTION
REINFORCING COMPOSITE FOR
ROOFING MEMBRANES AND PROCESS
FOR MAKING SUCH COMPOSITES
_UMMARY OF THE INVENTION
This invention relates to reinforcing composites for use
in bituminous roofing membranes. Specifically, this
invention relates to composites which utilize uniformly
heat-stabilized, mechanically-fastened networks of high
tenacity polyester yarn, either as the sole continuous
filament reinforcing element or in combination with
lightweight preformed mats, preferably polyester mats,
mechanically fastened (for example, by knitting or
stitching) to the open network of continuous filamen-t
polyester yarns. After heat-stabilization, thermosetting
resins may be added -to these composites. This invention
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also comprises processes for making such composites, heat
stabilization of such composites, resin treatment of such
composites, combinations of such composites with
fiber~lass scrim, and roofing membranes which incorporate
such composites as a reinforcement. These composites are
flexible, capable of being impregnated by bituminous
material, and have sufficient strength to be useful in
reinforcing roofing membranes.
DETAILED DESCRIPTION
1. Field of the Invention
In the manufacture of roofing membranes, a reinforcing
sheet is saturated with bituminous material by leading the
sheet through a tank or vat of biturninous material heated
to about 275 to 425~F (135 to 220C) using methods which
are known in the art. The resulting combination is then
rolled up for later installation, principally on flat
roofs using additional bituminous material and/or a torch
or other source of heat to seal the joints. The
bituminous material used in making these membranes is
often a "modified bitumen" such as asphalt combined with
about 20% by weight of atactic polypropylene or 5 to 15~
styrene butadiene rubber. This invention relates to a new
form of polyester composite sheet for use in reinforcing
such membranes.
2. Description of the Prior Art
Some of the various kinds of sheets used to reinforce
bituminous roofing membranes are described in applicant's
United States Patents No. 4,491,617 and 4,539,254.
Spun-bonded, continuous filament polyester mats, including
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mats of polyester combined with other materials such as
nylon, have been used as such reinforcements for many
years. ("Mat" as used herein refers to an entangled mass
of filaments.) In the prior art, these polyester mats
have been heat stabilized to improve dimensional in-tegrity
and impregnated with resins to increase stiffness, but
they have suffered from several disadvantages. These
prior art mats are relatively thick and dense, typically
having a weight of about 5 to 10.3 ounces per square yard
(170 to 350 grams per square meter), and are difficult to
saturate with bituminous material. Moreover, after
saturation they become easier to tear and subject to
stressing, stretching or other distortions which can lead
to unevenness and other defects in the final roofing
membrane. The filaments used in such mats are low
tenacity polyester, which has contributed to their
inability to withstand these stresses. In order to
overcome this weakness, they have been made heavier,
resulting in thicker, less porous composites, which are
more difficult to saturate. Non-woven, high tenacity
polyester networks, held together with thermoplastic
adhesives and having yarn spacings of 2 to 8 yarns per
inch, have somekimes been combined with polyester mats,
but such networks (and combinations which lnclude them)
have not been completely successful.
With the present invention better properties, especially
ease of saturation and improved finished tear strength,
can be obtained, a thinner roofing membrane can be
obtained, and lesser amounts of polyester may be used to
achieve comparable results than was previously possible.
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3. Descript on of the Invention
This invention comprises composites of heat-stabilized,
mechanically-fastened networks of high tenacity continuous
filament polyester yarns, either as the sole continuous
filament reinforcing element or in combination with a mat
and/or a fiberglass scrim. "Mechanically-fastened"
indicates that -the network is held together by mechanical
means (~g~, by warp-knit weft-insertion techniques)
rather than by forminy a non-woven network held together
by use of thermosetting or thermoplastic adhesives. It is
preferred to heat stabilize these composites before
application of any thermosetting resins which may be added
to improve stiffness or other properties of the composite,
but such resins may be added before heat-stabilization if
they are tack-free at heat-stabilization temperatures.
When a relatively high viscosity bituminous material is to
be used in making the roofing membrane -- i.e., a
bituminous material sufficiently thick that the material
fills the openings in the network -- the heat-stabilized
ne-twork may be impregnated with a thermosetting resin and
used as the sole reinforcing element.
When a relatively low viscosity bituminous material is to
be used, the composite may include a mat which enables the
bituminous material to form a continuous sheet on the
composite by providing coverage in the openings, or
"windows", between the yarns of the open network. The mat
of this invention preferably consists essentially of
polyester filaments, though other synthetic mats such as
mats of nylon or combinations of polyester and nylon, may
be used. The ma-t is preformed, preferably spun-bonded,
and relatively lightweight. By "lightweight" is meant a
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mat weighing about 0.3 to 4 ounces per square yard (lO to
140 grams per square meter), most preferably about 0.5 to
l.0 ounces per square yard (17 to 35 grams per square
meter). By "preformed" is meant a mat which has been
fabricated into the mat form before it is combined with
the open network. In this invention the mat may be
mechanically fastened to the open network at the time the
open network is made, the network being an open grid
having yarns which cross each o-ther in substantially
perpendicular directions and preferably being non-woven.
For example, this invention comprises compo~ites made of
lightweight polyester mat knitted into a warp-knit,
weft-inserted polyester structure, such as may be made
using a LIBA Copcentra or Malimo warp knitting machine
with full wid-th weft insertion. Alternatively, the mat
may be stitched to the open ne-twork.
With some bituminous materials the heat-stabilized
network, without later impregnation with a thermosettir,g
resin, may (a) be led with a fiberglass mat, as two
separate components, through a va-t of bituminous material
to create a single roofing membrane sheet, or (b) may be
laminated to a fiberglass scrim and led through a vat of
bituminous material to make a roofing membrane.
The continuous filament polyester yarn open network
structure preferably consists of high tenacity polyester
warp and weft yarns of abou-t 220 to 2000 denier, and most
preferably about 1000 denier, knitted together at about 3
to 18 yarns per inch (l to 7 yarns per centimeter),
preferably at 6 to 9 yarns per inch (2 to 3.5 yarns per
centimeter), with a knit, or sewing, yarn of about 40 to
500 denier (preferably of about 70 denier re~ular
tenacity) polyester yarn. The knit, or stitch, may be
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tricot, chain or other stitch, but preferably chain
stitch. The weight of the entire composite (mat
mechanically fastened to the open network) may range from
about l.0 ounces per square yard (34 grams per square
meter) to about 6.0 ounces per square yard (205 grams per
square meter), preferably about 2 to ~ ounces per square
yard (68 to 140 grams per square meter).
This composite of continuous filament polyester open
network alone, or of network mechanically fastened to a
mat, results in a reinforcement which has dimensional
integrity with uniform coverage of interstices in the
structure. The composite can be readily and thoroughly
saturated with modified asphalts or other bituminous
material on roll roofing manufacturing lines and has
several other advantages. For example, approximately
equal tensile strengths can be achieved at one-half the
weight of polyester and one-half the thickness, because
the continuous filament polyester yarn has more than twice
the tenacity of polyester filaments in a spun-bonded mat.
This results in a thinner and more porous reinforcing
composite, which is important for several reason's. Such a
reinforcing composite can be saturated with bituminous
material more easily than a thick, dense one, and less
bituminous material is required. Saturation of the mat
(that is to say, thoroughly impregnating the mat and
coating individual fibers so that fibers are isolated from
adjacent fibers) is highly important in the manufacture of
roofing membranes. To insure thorough saturation, some
manufacturers have first saturated prior art mats with a
low viscosity bituminous mixture, followed by a second
application of a high viscosity bituminous mixture, but
that two-step procedure is not necessary with the
composite of this invention.
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With the reinforcing composite of this invention, there is
also less danger -that par-t of the reinforcement will be
near the surface of the membrane and be burnt, or
"torched," while the membrane is being installed on a
roof. Also, the reinforcing composite of this invention
can be more readily heat stabilized at high temperatures
without adversely affecting its properties.
Heat stabilization of the composite may be accomplished by
subjecting the composite to heat treatment, for example by
passing the composite through an oven while conditions
such as temperature, tension, and dwell-time at high
temperature are controlled to achieve minimal shrinkage in
the machine and cross-machine directions at temperatures
used in satura-ting with bituminous material. It is
preferred to use temperatures up to about 460F (238C)
and preferably to control the tension and dwell-time to
result in shrinkage during the heat stabiliza-tion step of
5~ to 10%, with the resulting composite having a free
shrinkage (i.e., residual shrinkage) of less than 2% and
preferably less than 1% in both machine and cross-machine
directions as a result of the combination of heat setting
and heat relaxation which occurs under these conditions.
In rnaking the measurement of free shrinkage, it is
preferred to cut ten strips of fabric ten inches long b~
one inch wide. Five are cut in the machine direction and
five in the cross-machine direction at positions selected
from across the width of the structure. These strips are
placed vertically in an oven under light tension just
sufficient to keep them straight. The shrinkage of each
set of five samples is measured after five minutes at
~00F (222C) and the results are averaged. If the
average shrinkage is too great (greater than two percent
or preferably one percent) in either direction, the
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composite is run through the heat stabilization treatment
again at higher -temperature, or slower speed, or less
tension, until the desired level of free shrinkage is
reached. We have found that composites of high tenacity
polyester yarns hea-t-stabilized as described retain their
desirable proper-ties, such as strength, and also re-tain
their shape in bituminous impregnated roofing membranes.
The mechanically fastened knit or sewn structure of this
invention may be laminated to a fiberglass scrim
preferably of 37 1/0 to 150 1/0 yarns, or more preferably
75 1/0 to 150 1/0, with about 2 yarns per inch (0.8 yarns
per centimeter) held -together with an adhesive. Scrims
made of yarns as heavy as about 18 1/0 may be used and the
number of yarns per inch may range from about 1 to 10 (0.4
to 4 yarns per centimeter). Fiberglass scrim may provide
additional strength, higher modulus and other desirable
properties, particularly during manufacture of the roofing
membrane when the heat of processing causes the polyester
to lose strength.
This lamination of fiberglass scrims to polyester
composite may be accomplished by one of the following
exemplary methods:
(a) using a fiberglass scrim bonded with a thermosetting
adhesive (such as 5 to 1~% by weight of polyvinyl alcohol
or 5 to 75% by weight of cross-linking acrylic or
styrene-butadiene latex) and laminating it to the
polyester composite by dipping the polyester composite in
a cross-linking acrylic latex, marrying the fiberglass
scrim to the wet polyester composite, and drying and
curing in contact with heated steel drums,
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(b) using a fiberglass scrim bonded with a thermosetting
adhesive (such as 5 to 10% by weight of polyvinyl alcohol
or 5 to 75% by weight of cross-linking acrylic or
styrene-butadiene latex), carrying this scrim together
~ith the polyester composite through a saturating bath of
cross-linkirlg acrylic latex, and taking 'hem over heated
steel drums to dry and cure,
(c) by using a fiberglass scrim bonded with a
thermosetting adhesive (such as 5 to 75% by weight of
cross-linking acrylic or styrene-butadiene latex) and
laminating it to a resin-impregnated, heat-stabilized
composite made from a network of adhesive-free, high
tenacity continuous filament polyester yarns as follows:
(i) the fiberglass scrim is dipped in polyvinyl alcohol,
(ii) the wet fiberglass scrim is married to the polyester
network, and (iii) -the resulting combination is dried in
contact with heated steel drums, or
(d) by reactivating a thermoplastic adhesive (such as 50%
by weight of polyvinyl chloride late~ or similar
thermoplastic adhesive) on the fiberglass scrim and
heat-sealing or hot-nipping the scrim to the composite by
means of a steel-on-rubber roll nip.
A detailed description of these procedures is set forth in
applicant's patents identified above. The words
"thermosetting adhesiva" are used herein to mean a
thermosetting adhesive which maintains its bonding ability
up to about 425F, that is to say, a thermosetting
adhesive which is not tacky at about 425~F. In accordance
with this definition, it will be understood that some
thermosetting adhesives, if partially cured, may act as
thermoplastic adhesives.
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The weight of the fiberglass scrim is preferably a small
fraction of the weight of the polyester composite
structure, and the laminating procedure must be carefully
controlled with respect to tension in order to avoid
placing tensile stresses on the polyester structure. As
already mentioned, polyester has a relatively low modulus
at high temperatures, and stresses can be induced easily
which may result in dimensional distortion and
consequential defects in the final roofing membrane.
Resins, by which is meant chemicals that increase
stiffness, provide water resistance, or otherwise improve
properties of the polyester composite or the properties of
the final roofing membrane, may be added to the network,
the composite of mat and open network, or the combination
of -those structures with fiberglass scrim. Some resins
can also serve the functions of adhesives described
above. Resins are added by thoroughly saturating the
composite at an add-on rate of about 5 to 100 parts of
resin per 100 parts by weight of composite but preferably
with about 10 to 20 parts of resin.
The resin is typically a cross-linked acrylic resin but
may be any resinous material which is unaffected by water
and retains its bonding properties up to ~emperatures used
in making roofing membranes. For finished roofing
membranes containing a polyester composite or a polyester/
fiberglass combination as a reinforcement, both the amount
of resin added and the stiffness of the resin may be
adjusted to achieve desired properties. For example, when
the final roofing membrane is to be thick, stiffer
reinforcements may be required to help processing through
the production line. Also, a stiffer reinforcement is
required for low modulus asphalt membranes to facilitate
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har~ l.in~ d~lri.nq ins-tallation on the roof, and also to
improve ro~ teclrity and minimize damage in transi-t.
The ~ollowi~ e~amples will illustrate the invention.
Examele l
UsiLIg a L:~BA Copcentrc~ machine, a spun-bonded polyester
mat wei~hing 0.5 oz/sq yd was knitted into a polyester
knit structure having 9 yarns per inch in the machine
di.rection and 9 yarns per inch in the weft direction of
LOOO denier h:igh tenacity polyester yarn. The knitting
yarll usecl was 7n de!lieL regulaL tenacity polyester yarn.
A chain stitch was used with the 70 denier yarn spaced at
9 st:itclles/incll over each lOOO denier warp yarrl and
torming ~ l1 sti-tch between each 1000 denier weft yarn.
This polyester structure weiqhed 3.25 oz/sq yd.
The polyesteL str~lcture was heat stabilized by unrolling
it ~Ind feedlng over a series of preheated rolls at ~50F,
then thro~lqh a heated nip at 450F, under tension which
was con~rolled to result in an overfeed into the heating
seotion of S`?S. Dwell-time was adjusted u}ltil the finished
fabric had 1'~ or less of free shrinkage, in both the
machilla and cross machine direction when tested at 400F
~or ive min~ltes ~s set forth above.
The heat st~bilized polyester structure was in turn
sattlrated with 20 parts (per 100 parts by weight of
comp~site~ of ca black-tinted cross-linkin~ acrylic latex
L~Sin satur~:nt consistin~ of Rohm ~ Haas Rhoplex HA16 (92
parts L1Y weight per 100 parts of the solids contellt of the
sattaral~t), Cymel 303 cross-linkinq agent (~.~ parts~
blac~ pigmellt ~2.8 parts) and ammonium nitrate as a
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catalys-t (0.8 parts) in water (in the proportion of 28% by
weight of solids to 72~ by weight of water), and the
composite was dri.ed and cured. Conditions of tension,
speed, solids content of the saturant, and pressure used
to squeeze off excess saturant were adjusted such that -the
acrylic latex resin penetrated the polyester fiber bundles
and the finished surface remained porous, i.e. the acrylic
latex resin did not form a surface film on the structure
or yarns. The resulting structure was suitable for use as
a reinforcing composite for roofing membranes.
Example 2
Using a LIBA Copcentra machine, a network of
adhesive--free, 1000 denier high tenacity continuous
filament polyester yarn of the ~ind used in making tires
was knit into a structure having 9 yarns per inch in the
machine direction and 9 yarns per inch in the weft
direction. The knitting yarn used was 70 denier regular
tenacity yarn. A chain stitch was used with the 70 denier
yarn spaced at 9 stitches/inch over each lOOO denier warp
yarn and forming a full stitch between each lOOO denier
weft yarn to create a structure weighing 3.25 oz/sq. yd.
This structure was heat stabilized following the procedure
of Example 1 and then impregnated with the acrylic latex
composition of Example l, again following the procedure of
Example l. The resulting composite was suitable for use
as a reinforcing composite for roofing membranes.
Example 3
Using a LI~A Copcentra machine, a spun-bonded polyester
mat weighing 0.5 oz/sq yd was knitted into a polyester
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knit s-tructure having 6 yarns per inch in the machine
direction and 6 yarns per inch in the weft direction of
lO00 denier high tenacity polyester yarn. The knitting
yarn used was 70 denier regular tenacity polyester yarn.
A chain stitch was used to combine the structure with 7G
denier yarn spaced at 6 stitches/inch over each 1000
denier warp yarn and forming a full stitch between each
lO00 denier weft yarn. This polyester structure weighed
2.35 oz/sq yd.
The polyester structure was heat stabilized by unrolling
it and feeding over a series of preheated rolls at 450~F,
then through a heated nip at 450F, under tension which
was controlled to result in an overfeed into the heating
section of 5%. Conditions were adjusted until the
finished fabric had 1% or less of free shrinkage in both
the machine and cross machine directions when tested at
400F for five minutes as set forth above.
The heat stabilized polyester structure was then combined
with a fiberglass scrim having 2 yarns per inch in both
the machine and cross machine directions of 75 1/0
fiberglass yarns coated with 50 parts of PVC latex (per
100 parts of fiberglass yarn). This combination was
achieved by unwinding both the polyester structure and the
fiberglass scrim, feeding them together over a preheat
roll at 350F, then through a heated nip 380F at 150
pounds per linear inch (PLI).
This structure was in turn saturated with 20 parts (per
lO0 parts by weight of composite) of the black-tinted
cross-linking acrylic latex resin used in Example l and
the composite was dried and cured. Conditions of tension,
speed, solids content of the saturant, and pressure used
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to squeeze off excess saturant were adjusted such that the
acrylic latex penetra-ted the polyester fiber bundles and
the finished surface remained porous, i.e. the acrylic
latex did not form a surface film. The resulting
structure was suitable for use as a reinforcing composite
for roofing membranes.
Example 4
A spun-bonded polyester mat weighing 1 oz/sq yd may be
knitted into a polyester structure using a Malimo machine
having 7 yarns per inch in the machine direction and 7
yarns per inch essentially perpendicular to the machine
direction of 1000 denier high tenacity polyester yarn.
The knitting yarn used may be 70 denier regular tenacity
polyester yarn. A chain stitch may be used to combine the
structure with 70 denier yarn spaced at 7 stitches/inch
over each 1000 denier machine direction yarn and forming a
full stitch at each lO00 denier cross direction yarn.
This polyester structure weighs 3.15 oz/sq yd.
The structure is in turn coated with 20 parts (per 100
parts by weight of composite) of a black-tinted cross-
linking acrylic latex resin and the composite is dried and
cured. Conditions of tension, speed, solids content of
the saturant, and pressure used to squeeze off e~cess
saturant are adjusted such that the acrylic latex
penetrates the polyester fiber bundles, and the finished
surface remains porous, i.e. that the acrylic latex does
not form a surface film.
The above resin treated polyester structure is then heat
stabilized by unrolling it and feeding over a series of
preheated rolls at 450~F, then through a heated nip at
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450F under controlled tension. Conditions are adjusted
as described above until the finished fabric has 1% or
less of free shrinkage in both the machine and
cross-machine directions, when tested at 400F for five
minutes. The resulting structure is sui-table for use as a
reinforcing composite for roofing membranes.
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