Note: Descriptions are shown in the official language in which they were submitted.
3 2~6~
67~.01û URETHANE BONDING METHOD AND LAMINATE
Field of the Invention
_
A method of bonding, particularly of porous or fibrous materials,
utilizing polyurethane foam as the bond;ng medium and the resultant ~minated
structures.
Description of the Prior Art
Industrial applications often require bonding to relatively porous or
fibrous materia}s. Por example, molded fiberglass shells are used QS a substrate
for automotive headliners, however, the fiberglass shell must be covered. In the
preferred application, the shell is covered with a reticulated polyester foam
backed vinyl fabric. Contact cement is used to glue the foam cover sheet to the
contoured fiberglass panel, however, because of the small surface contact areas
available for bonding in this application, the adhesion is often lost, resulting in a
very substantial percentage of scr~p. This adhesion proble m is compounded
where the molded contoured fiberglass panel includes deep draws, pl~cing the
foam backed vinyl sheet under tensisn. Contact cement works best when the
surfaces to be bonded are clean, smooth and relatively derLse.
Another difficult application is bonding carpet to various substrates,
including foam pads or backing. Carpet generally includes a flexible nonresilient
~crim bucking to which the carpet loops are knotted, resulting in a relfltively
porous structure. Carpet pads include various polymer foams and pressed foflm
scraps. A liquid polyurethane foam may be applied directly to the carpet scrim
backing, however, this is a rel~tively expensive application which is not widely
used. The need therefore remains for a bonding method which may be used in
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676.010 commercial applications to bond relatively porous materials, including contoured
substrates. As used herein, "porous" refers to any surface having a reLstively
small contact area available for bonding, including, for example, fibrous
materia]s such as fiberglass panels, carpet, foam, woven and unwoven fabrics,
etc.
Another potential app]ication for the urethane bonding method of this
invention is gluing structural plywood because of the very substantial energy
savings available. At present, the veneer outer plywood layers must be dried in
large commercial dryers from a moisture content of 60 to 12096 for green veneer
to no greater ~an 7% for softwoods and 8% for hardwoods. The veneer is rotary
lathe peeled from the log, which requires soaking the log to prevent splitting of
the veneer. The formaldehyde resins used to bond the plies will not properly cure
at greater moisture contents. Softwoods are glued with phenol-formaldehyde
resin adhesives and hardwoods are glued with urea-formaldehyde resin adhesives.
The form~ldehyde adhesives are applied to the softwood plies by sprQy and
curtain coater applicators and to hardwood plies by roll coater applicators. Theplies are then stacked in a large press having plates heated to about 300CP for
phenol-formaldehyde resin bonded softwoods and a50oF for urea-formaldehyde
bonded hardwoods. The presses are closed under pressure of 150 to 200 pounds
per square inch, requiring 20 to 40 minutes to complete the curing of the
formaldehyde Qdhesives, resulting in very substantial energy consumption.
Formulating an adhesive to attain acceptable bond qualities for plywood
is ~s much an art as a science because each wood ply represents a different
combination of avaiLqble capill~ries and surfaces of avail~ble wettability. The
nature of the adhesive to wood bonds has been variously described as physical,
chemical and secondary chemical bonding. It is apparent, however, thQt the
present formaldehyde bonding adhesives and method of gluing structural plywood
are not energy efficient because of the severe drying requirements, resulting
from the use of formaldehyde adhesives, and the substantial energy used in the
hot presses required to bwld the plies. The urethHne bonding method of this
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676.010 invention, which does not use a water soluble adhesive and which does not require
the substantial pressures and temperatures required by the form~ldehyde
adhesives, will result in a substantisl energy savings.
Summary of the Invention
As described, the urethane bonding method of this invention is
particularly suitable for adhering two substrates together, one or both of whichmay be relatively porous. The method may be performed rapidly with a minimum
amount of process heat and pressure, resulting in a unique laminate. The method
of this invention includes spraying a fine mist of a two component foamable
liquid polyurethane on one of the substrate surfaces under pressure forming
dispersed discrete liquid droplets of liquid foamable polyurethane on the surface.
The polyurethane droplets are then allowed to rise and at least partially gel,
preferably in discrete foam pods. The urethane only partially reacts, slowly,
because the separation of the droplets and the consequent loss of the heat of
reaction, becoming tacky and vic~cous. The second substrate is then brought intocontact with the urethene coated substrate, while the urethane remains between
20 and 60% of full cure, preferably about 30 to 50% of full cure. Then, usually
with the addition of heat and slight pressure, the urethene foam reaction is
011owed to go to completion, resulting in a very strong permanent bond.
The foamable liquid urethane is preferably sprayed on the first
substrate under a pressure of between about lS00 and 2000 pounds per square
inoh The size ~nd shape of the nozzle opening will depend upon the application,
as described herein, however ~ high pressure nozzle is used to spray a relatively
fine mist, such that ~e liqu;d urethane is dispersed on ~e substrate in discretedroplets. When the urethane e~pands and sets up, the foam preferably remeins in
discrete pods separated by a ~in, such ~at the foam does not expand
substentielly perpendicuL~r to the plane of the substrate, separating the layers of
the laminate. This substantially reduces ~e pressure required ~o form the
l~minate and the curing time. Another important feature of the method of this
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676.010 invention is the timing of the application of the second substrate. If the second
subs~rate is applied immediately after application of the liquid polyurethane, the
foam will blow through both lamina. If the foam is substantially completely
cured and set up, the second lamina will not sdhere to the first lamina. In a
typical application, the viscosity of the foam actually decreases at about 20% of
full cure, as the system exothermically reacts and polymerization begins. The
viscosity then increases exponentially. There is, therefore, a relatively small
window when the second substrate should be applied to the first substrate.
As described, the method of this invention is particularly suitable for
adhering a flexible element to a contoured substrate which may include deep
contoured draws. Where a flexible sheet, such as a reticulated polyester foam
backed vinyl fabric is attached to a self supporting substrate, such as a die
formed fiberglass panel, the polyurethane foam is prefer~bly applied to the selfsupporting element because of the ease of application. The method then includes
forming a substrate into a contoured shape in a die press. The two component
foamable liquid polyurethane is then sprayed on the contoured substrate in a fine
mist forming dispersed discrete liquid droplets of polyurethane, as described
~bove. The polyurethane droplets are then permitted to foam and expand in
discrete foam pods and the flexible finish sheet is applied over the substrate,
preferably while the foam pods are between 30 and 50% of full cure. Where the
substrate is formed in a die press, the press may be closed under light to
moderate pressure to complete the curing of the polyurethane.
l~e method of gluing structural plywood is substantially as described
above. The method includes spraying a fine mist of the two component liquid
foamable polyurethane under pressure on one surface of the fibrous panels to be
joined in ~e plywood, wherein ~e spray forms gener~ly dispersed discrete
droplets of foamuble liquid polyurethane on one surface of ~e panels to be
joined. The polyurethane is then allowed to rise ~nd gel to less ~n 60% of full
cure. The panels are ~en stacked in fae~t~faee contact and the curing of the
polyurethane foam is completed in seconds, rather than minutes, under moderate
pressure sufficient to sssure that the panels are flat.
632
676.010 It is believed that the resultant Lqminates are also unique because the
polyurethal1e pods which form the bonding medium preferably react and skin
prior to contacting the adjacent pods. Thus, the laminate includes the contacting
or substantial1y contacting substrates and a plurality of discrete polyurethane
foam pods each having end portions permanently joined to the opposed substrates
and a mid portion which is at lesst partially discrete and skinned.
Other advantages and meritorious features of the present invention will
be more fully understood from the following description of the preferred
embodiments, the appended claims, and the drawings, a brief description of
which follows.
BREF DESCRIPTION OF THE DRAWINGS
Figure l is an elevated side view of one method of applying the
polyurethane foam bonding medium;
Figure 2 is A top view of a panel after application of the
polyurethane foam bonding medium;
Figure 3 is a side cross-sectional view of ~ contoured laminate
bonded by the method of this invention;
Figure 4 is an enlarged side cross-sectional view of Figure 3; and
Figure 5 is a side elevation of a fiber board or plywood laminate
formed by the method of this invention.
s~
676.010 DESCRIPTION OF THE PREFERRED EMBODIMENTS
AND METHOI) OF THIS INVENTION
_
As described above, the method of bonding of this invention is
pQrticularly suitable for porous and fiberous materials. The prior methods of
bonding these materWs generally include the Qpplication of a contact cement or
adhesive which mfly result in delamination, p~rticuLqrly where one or both of the
surfaces to be bonded are relatively porous. For example, an automotive
head]iner may include a polyester foam covering which is difficult to bond to the
substrate, particularly where the substrate hAs a contoured surf~ce.
The method of this invention includes spraying a foamable liquid
polyurethane onto one of the surfQces to be bonded using a reLatively high
pressure spray apparatus and forming discrete droplets of ]iquid urethane on thesurface sprayed. As shown in ~igure 1, a conventional high pressure urethane
foam spray apparatus 22 may be utilized to spray the surface of the panel 20.
The spray gun 22 may be a conventional high pressure spray gun as presently
utilized to sprny two component liquid foamable polymers, such as polyurethane.
A suitable spray gun is manufactured by Gusmer Corpor&tion, model "ARn. As
will be understood, urethanes are polymers which ~re generally formed by
reQcting two monomers, one of which is an isocyanate, such as toluene
diisocyanate or polymeric isocyanate and the other monomer having molecules
containing active hydroxyl groups or molecules reactive with isocyanates,
including themselves. The technology is well developed whereby the two
reactive components described are blended with appropriate catalysts, blowing
agents, surfactants &nd flame inhibitors. The components are simultaneously
pumped in two æparate streams at high pressure to the spray gun, where the
components are mixed and sprayed through the high pressure nozzle 24. A
blowing agent is used to alter the density of the resultant polymer, ranging ~rom
about 70 lbs. per cubic foot with no blowing agent to as low as 0.4 lbs. per cubic
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676.010 foot, with a blowin~ agent. Water, which reacts with isocyanate to form carbon
dioxide gas, or chlorofluorocarbon gases are normally used as the blowing agents.
With ~e addition of the blowing agent, the reacting polymer may expand to more
than 50 times its liquid volume after being sprayed. As the polymer is reacting,it goes from a mixed liquid to a viscous and very tacky substance and finally to a
dry, fully cured polymer. The final polymer may be hard or flexible, depending
upon the starting materials.
The process of this invention utilizes a two component foamable
liquid polyurethane as the bonding medium which is applied in a finely dispersedmist of droplets 26. In a typical application, a foamable liquid polyurethane,
which is preferably catalyzed, B sprayed on one of the surfaces to be bonded
with a relatively high pressure nozzle 24. Por example9 ;n a manual application
as shown in Figure 1, a cone~haped nozzle opening may be preferred. A cone-
shaped nozzle opening sprays a greater density at the axis of the cone,
permitting overlap to assure complete coverage. Where the nozzle is directed
mechanically, 8 fan-shaped nozzle opening may be preferred, wherein the density
of the spray is substantially uniform. In the examples described hereinbelow, a
1500 psi hydraulic pressure cone-shaped nozzle available from Gusmer
Corporation was utilized. In actual testing, it was found that a hydraulic
pressure of less than 1000 psi was insufficient to form the finely dispersed mist
of droplets preferred. Further testing established that R nozzle pressure of
between about 1500 psi ~nd 2000 psi was preferred. This pres ure in a nozzle of
the type disclosed created a finely dispersed mist a6 ~d disbursed droplets 28 on
the surface sprayed, as shown in Figure 1.
Figure 2 illustrates a panel 30 having dispersed discrete droplets
32 of polyurethane foam 3a which have been sprayed on the surface of the panel
30 by the method described above in regard to Pigure 1 and permitted to foam
and expand. As descril~ed, the tiguid fo~mable pol~urethane is sprayed on at
least one surfa~e to l~e bonded in a relatively ~ine mist, such that the liquid
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676.010 urethane is dispersed on the surface in discrete droplets 32. When the urethane
expands and sets up, the foam preferably remains in discrete pods separated by askin, such that the foam does not expand primarily perpendicular to the plane ofthe surface, separating the lsyers of the final laminate. This method
substantially reduces the pressure required to form the laminate and reduces thecuring time. The droplets 32 shown in ~igure 2 have substantially completely
expsnded, but remain in discrete droplets. As will be understood, a small
percentage of the droplets may contact, but remain separated by the skin formed
on the droplets as they cure. Preferably, however, the droplets remsin spaced
and discrete, allowing for lateral expansion when the laminate is foPmed.
The laminste shown in Figures 3 and 4 illustrates some of the
sdvsntages of the method of this invention. The disclosed lsminate includes a
fiberglass panel 38, a reticulated polyester foam layer 40 and a vinyl finish layer
42. The polyester foam layer 40 must be bonded to the fiberglass panel 38. This
laminate is used for automotive headliners wherein the fiberglass panel 38 is
received against the automotive roof panel and the vinyl surface layer 42
provides the finish surface within the automotive compartment. The foam lsyer
40 provides the preferred "soft hand" texture for the headliner and the fiberglass
layer assists in sound attenustion. In this application, the fiberglass panel 38 is
formed in a conventional die press into a contoured shape conforming to the
interior surface of the automotive roof and the panel must include relatively
deep draws for this application. It has been found very difficult, however, to
bond the rel~tively porous foam layer 40 to the contoured surface of ~e
fiberglass panel 38. Attempts have been made to bond these surfaces using
contact cement, which has resulted in substanti~l serap because ~e panels
del~minate. The method of this invention solves this problem in ~ very simple
and reLatively inexpensive process.
A two component polyurethane is preferab~y sprayed on the
contoured surface 44 of the ~iberglass panel 38 because the fiberglass panel is
self-supporting. As will be understood, however, the polyurethane fo~m may be
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676.010 applied to either surface. As described, the liquid foamable polyurethane is
sprayed on the surface 44 in a finely dispersed mist, forming discre~e droplets 46
on the surface 44 of the fibergLqss panel. Because the surfaces of the fiberglass
panel 38 and the reticulQted polyester foam are reLatively porous, the disperseddroplets 46 may expand L~terally and into the porous surfaces, as shown in Figure
4. Several polyurethane systems may be used in the method of this invention,
including rel~tively low functionality (2.2) ~lexible polyurethane foams and
medium functionality (3.5) relatively rigid foams. The most preferred
polyurethane system for bonding very porous surfaces, such as the laminate
shown in Figures 3 and 4, is a relatively unreactive rigid medium functionality
polyurethane foam having less than five functionality, Qnd preferably about 3.5
functionality. The "A" component of the polyurethane foam is preferably a
polymeric MDI (methylene diphenyl diisocyonate) which is less toxic ~an TDI
(toluene diisocyanate) systems. The more flexible, lower functionality
polyurethane foams may also be used~ as described herein, particularly in
applications which are subject to shear.
An important feature of the method of this invention is the
sequence and timing of the application of the second lamina to the fir~st laminawhich has received the urethane bonding medium. If the æcond laminais applied
immediately, the foam wi~l blow through both lamina where the lamina are very
porous, as shown in Figures 3 and 4. Alternatively, if the lamina are less porous,
the expanding urethane will separate the lamina. If the foam is substantially
fully cured and set-up, the second lamina will not adhere to the first lamina. In a
typical application5 the viscosity of polyurethane foam actually decreases at
about 2096 of full cure, as the ~stem exothermically reacts and polymerization
begins. The viscosity then increases exponentially. There is, therefore, Q
"window~ when ~e second Layer or lamina should be applied to the first ~amina.
Relatively unreactive foams are therefore preferred to provide sufficient
working time to form the laminate. In the most preferred method of this
invention~ the æcond lamina is ~pplied to the first lamina at ~bout 30 to 509b of
_g_
~29~63~
676.010 full cure, however, it is possible to apply the second L~mina to the first lamina in
the range of about 20 to 60% of full cure. A relatively light pressure may then
be applied to rnaintain the preferred dimensions of the laminate and the laminate
may be heated in some applications. As described above, the bonding system of
this invention is ~erefore energy efficient, particularly when compared to other
systems which require relatively high pressure and greater heat. The pressure
may be ~pplied by conventional means, including a die, rollers and clamps. In a
die application, the pressure may be sufficient to just close the die.
In ~e ~pplication shown in Figures 3 and 4, where a reticulated
polyester foam 40 is bonded to a contoured fiberglass panel 38, a medium
functionality slow rise rigid polyurethane foam having a density of about 2 lbs.
per cubic foot may be utilized. The following is Q suitable formulation for the
"B" or polyol component of the urethane, wherein the percentages of the
constituents is given in weight percent:
Wt. % Constituent
46 Multranol 4034
12 Multranol 4050
Terate 203
31 ~reon 11
L 5420
.03 Ul-24
0 5 DMEA
The "Mutranol" 4034 and 4050 are polyols available from Mobay
Chemical Corp. and "Terate" 203 is a polyol available from Hercules
Incorporated. "Freon 11" is a blowing agent available i~rom E.I. DuPont, "L 5420"
is a surfactant svQihble from Union Carbide Corporation and "UL-24" is an
organic tin eatalyst available from Witco Corporation. The described polyol
blend in the resin has a functionality of about 4Ø The described nB" resin
constituent was then mixed with a polymeric MDI in a 1:1 ratio by volume and
the liquid foamable urethane was sprayed at a temperature of about 85F. under
1500 to 2000 psi hydraulic pressure. The preferred spr~y nozzle is ~ cone-shaped
nozzle having an ~rifice diameter of 0.070 inches. As descri~ed, this nozzle
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676.010 sprays the urethane in a finely dispersed mist of droplets, wherein the droplets
cover substantially less than 50% of the total surface area. The fiberglass panel
38 was previously formed in a die press having opposed die plattens, which
formed a deep drawn dish-shaped panel utilized as an automotive headliner. The
reticulated polyester foam 40 includes a polyester skin layer 42, wherein the
foam surface was applied to the fiberglass panel, after forming. The foam layer
40 may be applied to the fiberglass panel after approximately 20 seconds or
about 30% of full cure of the polyurethane foam droplets 46. Where the
fiberglass panel 38 is formed in a die, the foam layer 40 may be applied over the
contoured fiberglass panel 38 in the die, wherein the die member is then closed,forming the finished laminate as shown in Figures 3 and 4.
Figure 5 illustrates a plywood panel 50 wherein the lamina 52 are
joined by the method of this invention. In the preferred method of forming a
plywood panel, one surface of each lamina is sprayed with a finely dispersed mist
of a two component liquid foamable urethane which preferably forms a relatively
nexible foam because of the shear stresses applied to structural plywood. As
described, the liquid droplets 54 are dispersed over the surface of the lamina,
using a high pressure spray gun assembly. The sl~ray gun is preferably
mechanically operated using a fan-shaped nozzle providing a substantiaJly
uniform spray pattern of discrete droplets 54. A suitable formulation for the two
component polyurethane system is as follows. The nB" or polyol component OI
the urethane may comprise the following, in weight percent:
W~ % Component
69.4 R650g
29 4 ~reon 11
0.6 LR221
Q3 DMEA
0.3 Catalyst
"R650~" is a polyol available from Texaco Corp~ration. "~reon
11" is a blowing agent available from E.I. DuPont. "LK221" is a ~urfactant
available from Air Products. DMEA is dimethyl et2 anolamine and ~e catalyst
~2~6~2
676.010 used was 24% lead octoate. The "B" component was mixed in the spray gun in a
1:1 ratio by volume with a polymeric isocyanate, such as ~Mondur MR~, available
from Mobay Chemical Corp. The above described formulation for ~he two
component liquid polyurethane will set up completely within about two minutes.
As described, however, the lamina should preferably be bonded within 30 seconds
to one minute after application of the foam. The polyol blend of the "B"
component has a functionality of about 3.7, which is mixed in ~e nozzle with thepolymeric MDI having a functionality of about 2.7. The liquid urethane foam was
sprayed under a pressure of about 2000 psi at a temperature of about 85~. The
pressure necessary to maintain the dimensional relation of the lamina is about 50
to 100 psi, which is sufficient to natten the lamina, which is maintained for
about one minute. This should be compared to the present method of forming
plywood panels which requires a temperature of 250F. and a pressure of 250 psi
for 5 to 6 minutes, as described above.
The method of this invention may also be utilized to form a
laminate of relatively porous fiber board, wherein the preferred urethane
composition may be similar to the composition described above in forming
plywood panels. Further, the method of this invention may be utilized to bond a
foam backing material to a carpet, wherein the urethane formulation may be
similar to the formulation described above in regard to the laminate shown in
Figures 3 and 4.
The method of this imention therefore includes spraying n fine
mist 26 of ~ two component foamable liquid polyurethane on one surface of the
elements to be pined, forming discrete dispersed droplets of liquid foamable
polyurethan0, such as shown at 28 in Figure 1, 32 in Figure 2, 46 in Figure 4 and
54 in Figure 5 The polyurethQne droplets are then permitted to foam and expand
in discrete foam pods to between 20 and 60% of full cure. Fin~ly, the surface ofthe second element may be applied to ff~e sprayed 6urface and ~e polyurethane
foam droplets are-then permitted to completely cure, permanently bonding the
surfaces together. As described, ~e components of the laminate may be formed
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676.010 in a die press, wherein one of the elements includes a contoured surface and the
liquid foamable polyurethane is sprayed onto the contoured surface, as shown in
Figure 3, forming dispersed discrete liqui.d droplets of polyurethane 46, as shown
in Figure 4. The 1qminate formed by the method of this invention is al~o unique
because the polyurethane foam bond comprises a plurality of discrete
polyurethane foam pods, 46 in Figure 4 and 54 in Figure 5, each having end
portions permanently joined to the opposed surfaces and the foam pods include a
mid portion at least partiaUy discrete and skinned.
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