Reinforcing sheet for the reinforcement of panel and method of reinforcing panel

A reinforcing sheet adaptable to the reinforcement of a panel formed of metal, plastic or sheet molding compound, which reinforcing sheet contains a moisture impermeable barrier embedded in a thermosetting adhesive layer and a reinforcement adhered to the surface of the adhesive layer opposite the surface to be applied to the panel to be reinforced. The reinforcing sheet with improved resistance to the adverse effects of moisture is advantageously used to reinforce cold rolled steel, such as an automobile panel.

FIELD OF THE INVENTION 
The present invention relates to a reinforcing sheet for the reinforcement 
of a panel formed of metal, plastic or sheet molding compound and to a 
method for reinforcing a panel formed of metal, plastic or sheet molding 
compound with the reinforcing sheet. 
More specifically, this invention relates to a reinforcing sheet with 
improved resistance to the adverse effects of moisture and to a method for 
reinforcing a cold rolled steel panel, such as an automobile panel, using 
such a reinforcing sheet. 
BACKGROUND OF THE INVENTION 
From the standpoint of resource and energy savings, for example in the 
automotive industry, it is desirable to reduce vehicle body weight. 
However, attempts to reduce weight by reducing the thickness of materials 
result in deterioration in strength. For example, in the case of quarter 
panels for automobiles, such attempts have created problems such as low 
strength at various points (particularly flexural strength). 
Insufficiently rigid outer panels cause buckling and bending with minimum 
applied stress. 
In order to solve such problems, it is necessary to develop a suitable way 
to reinforce such structures. Reinforcement with a heavy metal panel is 
contradictory to the purpose of vehicle weight reduction. Hence, it has 
been proposed to reinforce the outer panels entirely or partly with 
lightweight resin materials. 
Reinforcement comprised of thermosetting adhesive layers and a reinforcing 
material has been applied to steel panels for use in the production of the 
body of automobiles. Such reinforcement provides increased strength 
against force applied to the outside surfaces of the automobile body. Such 
reinforcement further serves to decrease vibration and corrosion of the 
metal panels. 
For example, U.S. Pat. No. 4,369,608 describes a door for an automobile 
wherein a main reinforcing member made of a thermosetting resin is bonded 
to the inner side of an outer metal panel of the door to improve the 
strength and rigidity of the door. A multilayer sheet-like auxiliary 
reinforcing member, preferably made of a glass fabric, is bonded to the 
main reinforcing member. A wave-like or bead-like projection is provided 
on the main reinforcing member, which projection functions as a rib of the 
metal panel to be reinforced and serves to increase the reinforcement 
effects of the reinforcing sheet. 
Typically, the reinforcing sheet is adhered under pressure, for example to 
the back surface of the metal panel to be reinforced, and thereafter cured 
by usual heating methods, e.g. in a hot air circulation type heating 
furnace, an infrared ray heating furnace or a radio frequency induction 
heating furnace. This heat curing treatment can be carried out 
simultaneously at a stage in a vehicle assembly line at which painted 
metal panels, having a reinforcing sheet thereon, are baked to cure the 
paint. 
The reinforcing sheet may be premolded to conform its shape with that of 
the metal panel to be reinforced. Preferably, the reinforcing sheet has 
sufficient flexibility so as to conform to the shape of the metal panel 
upon its application to the metal panel without premolding. In either 
case, in order for the reinforcing sheet to decrease vibration and 
corrosion of the metal panel and to provide enhanced strength and rigidity 
to the panel, it is necessary that the reinforcing sheet maintain good 
contact with the panel to be reinforced both before, during and after 
curing of the thermosetting adhesive layer. 
U.S. Pat. No. 4,444,818 describes a reinforcing sheet containing a first 
thermosetting adhesive layer, a second thermosetting adhesive layer with a 
reinforcing material embedded therein, and a protective film covering the 
entire reinforcing sheet. This sheet is used to secure a flattened tubular 
material to the metal panel to be reinforced. Upon heating the sheet to 
cure the thermosetting adhesive layers, the flattened tubular material 
recovers its original tubular form to provide a wave-like or ribbed 
construction for the reinforcing sheet. 
According to U.S. Pat. No. 4,444,818, the reinforcing material is embedded 
in the second thermosetting adhesive layer and provides increased 
reinforcing effect to the metal panel. Reinforcing materials include 
cloths of inorganic fibers, such as of glass or asbestos fabric; cloths of 
organic fibers, such as of flax, cotton, nylon, polyester or polypropylene 
fiber; plastic films such as of polyester or nylon film; paper such as 
kraft paper; nonwoven fabrics such as of polyester fiber or polypropylene 
fiber; and metal foils such as of aluminum, iron, copper or zinc foil. 
U.S. Pat. No. 4,444,818 further describes the use of a protective film on 
the side of the reinforcing sheet opposite that of the metal panel to be 
reinforced. According to the patent, the protective film facilitates 
separation of the reinforcing sheet when stored in the form of a rolled 
tape, participates in the reinforcement of the metal panel to be 
reinforced, and improves the moisture resistant characteristics of the 
fabric reinforced resin layer. Various films, such as polyester, 
polyethylene, nylon, polyvinyl chloride, and polypropylene films, are 
described. 
However, the use of conventional reinforcing adhesive sheets containing 
thermosetting resins for reinforcing a metal panel, including those 
adhesive sheets containing a protective film as described in U.S. Pat. No. 
4,444,818, has drawbacks. 
Thus, reinforcing adhesive sheets containing thermosetting resins have a 
tendency readily to absorb moisture, including moisture that is naturally 
present, for example in the atmosphere. The absorbed moisture adversely 
affects the thermosetting adhesive layer of the reinforcing sheet and, 
therefore, the adhesion of the reinforcing sheet to the metal panel upon 
curing of the thermosetting adhesive layer. Such adverse effects are 
particularly pronounced when the metal panel, with attached reinforcing 
sheet, is stored for a number of months, especially under humid 
conditions, before curing of the adhesive layer. It is believed that such 
adverse effects stem from decomposition of the curing agents in the 
thermosetting adhesive layer such that gas forms and is trapped in the 
thermosetting adhesive layer during curing. Due to the trapped gas, the 
adhesive layer is not as cohesive and the reinforcing sheet tends to fall 
from the metal panel. 
Even the protective film described in U.S. Pat. No. 4,444,818 does not 
adequately prevent or solve the problems caused by the absorption of 
moisture by the reinforcing sheet before curing. One skilled in the art 
can readily appreciate that the thin polyester, polyethylene, nylon, 
polyvinyl chloride or polypropylene films described in U.S. Pat. No. 
4,444,818 cannot maintain complete impermeability to atmospheric moisture 
over an extended period of time due to their relatively poor humidity 
barrier properties. 
Moreover, the location of the protective film, presumably positioned to 
protect the entire reinforcing sheet including the expandable core, 
necessarily involves drawbacks. The location of the protective layer as 
the outside layer of the reinforcing sheet subjects the protective layer 
to wear and tear during handling and storage of the reinforcing sheet. In 
addition, the adverse consequences resulting from any damage to the 
protective layer, such as a worn spot, tear or hole, would be aggravated 
by its placement on top of the absorptive woven or nonwoven reinforcing 
material. Capillary action of the reinforcing material magnifies the 
amount of moisture absorbed by the thermosetting adhesive layer such that 
the area affected by any damage to the protective layer would be 
proportionately larger than the area of the damage itself. Furthermore, 
capillary action from the unprotected sides of the reinforcing material 
when the protective layer is placed on top of the absorptive reinforcing 
material is sufficiently strong adversely to affect the entire adhesive 
layer. As a result of the absorption of moisture by the adhesive layer, 
the reinforcing sheet would tend to fall from the metal panel during 
curing of the adhesive layer. 
To replace the polyester protective layer of U.S. Pat. No. 4,444,818 with a 
material that has greater impermeability to moisture and greater 
resistance to damage, such as a metal film, would be expected to induce 
additional drawbacks. Such metal foil would necessarily be more inflexible 
than the polyester layer and would tend to buckle and separate from the 
underlying reinforcing material during handling and upon conforming the 
shape of the reinforcing sheet to the shape of the panel to be reinforced. 
Such buckling and separation of the metal protective layer from the 
underlying reinforcing material would create tunnels which would allow 
moisture to be even more readily absorbed by the reinforcing sheet. 
It can thus be readily appreciated that provision of a reinforcing sheet 
which is resistant to moisture and the tendency to absorb atmospheric 
humidity and eliminates the previously discussed problems would be a 
highly desirable advance over the current state of panel reinforcement 
technology. 
OBJECTS OF THE INVENTION 
It is an object of this invention to provide a reinforcing sheet for the 
reinforcement of a panel formed of metal, plastic or sheet molding 
compound, which reinforcing sheet resists the tendency to absorb 
atmospheric humidity. 
It is a second object of this invention to provide a reinforcing sheet 
which contains a moisture impermeable barrier positioned within the sheet 
such that the likelihood of damage to the barrier is greatly reduced, and 
such that the effect of any such damage is minimized. 
It is an additional object of this invention to provide such a moisture 
resistant reinforcing sheet for the reinforcement of a panel, which sheet 
is sufficiently flexible to conform to the shape of the panel to be 
reinforced without risking contact with atmospheric moisture. 
It is also an object of the invention to provide a reinforcing sheet which 
adheres to the panel before, during and after curing of the adhesive layer 
even after storage of the panel with applied uncured reinforcing sheet 
under humid conditions. 
It is a further object of the invention to provide a method for reinforcing 
a panel formed of metal, plastic or sheet molding compound by using a 
reinforcing sheet which is resistant to the adverse effects of atmospheric 
humidity. 
It is yet another object of the invention to provide a reinforced panel 
which exhibits improved resistance to corrosion and vibration compared to 
an unreinforced panel. 
These and other objects and advantages of the present invention will become 
more readily apparent after consideration of the following. 
STATEMENT OF THE INVENTION 
In one aspect the present invention is directed to a reinforcing sheet for 
the reinforcement of a panel formed of metal, plastic or sheet molding 
compound, which reinforcing sheet comprises a moisture impermeable barrier 
embedded in a thermosetting adhesive layer and a reinforcement adhered to 
the surface of the thermosetting adhesive layer opposite the surface to be 
applied to the panel to be reinforced. 
In a further aspect the present invention relates to a method for 
reinforcing a panel formed of metal, plastic or sheet molding compound, 
which method comprises applying to the panel a reinforcing sheet 
containing a moisture impermeable barrier embedded in a thermosetting 
adhesive layer and a reinforcement adhered to the surface of the 
thermosetting adhesive layer opposite the surface to be applied to the 
panel to be reinforced, and then heating the reinforcing sheet with the 
embedded moisture impermeable barrier to the curing temperature of the 
thermosetting adhesive to harden the reinforcing sheet.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS 
With reference now to FIG. 1, reinforcing sheet 10 for the reinforcement of 
panel 11, shown as formed of metal but which may also be plastic or sheet 
molding compound, includes moisture impermeable barrier 12 embedded within 
thermosetting adhesive layer 13, 13'. 
In a preferred embodiment, thermosetting adhesive layer 13, 13' is formed 
of an epoxy resin and a curing agent. Advantageously, a mixture of 
cycloaliphatic epoxides, epoxidized novolac resins, epoxidized bisphenol A 
or bisphenol F resins, butanediol diglycidyl ether, neopentyl glycol 
diglycidyl ether or flexibilizing epoxy resins can be used. These resins 
can be reacted with carboxy terminated butadiene acrylonitrile to produce 
rubber modified epoxy resins. The diglycidyl ether of bisphenol A and the 
diglycidyl ether of bisphenol A reacted with carboxy terminated butadiene 
acrylonitrile to produce a crosslinkable resin with improved peel strength 
and impact resistance are preferably used as the epoxy resin. 
Advantageously, Lewis acids, substituted imidazoles or amine salts can be 
used as curing agents. Preferably, dicyandiamide is used as the curing 
agent. 
Thermosetting adhesive layer 13, 13' can include a plasticizer for impact 
and thermal shock resistance improvement. Advantageously, benzoates, 
adipates and phthalates can be used as the plasticizer. A phthalate, for 
example dibutyl phthalate, is preferred. 
In addition, this thermosetting adhesive layer can further contain a flame 
retardant, such as a halogenated epoxy, hydrated alumina or antimony 
oxide; a flow control agent, such as clay or fumed silica; or a filler, 
such as glass, phenolic or aluminum oxide bubbles, preferably glass 
bubbles. Such fillers further serve as a low density reinforcing agent. 
Other fillers such as talcs, carbonates, silicates and aluminum oxide 
powder can be used to modify impact, reinforcement and adhesion 
characteristics. Still other fillers such as ferrites can be used to 
impart magnetic properties to the adhesive sheet. 
The thermosetting adhesive is advantageously formed of 100 parts by weight 
of epoxy resin, 3 to 15 parts by weight of curing agent, 0 to 30 parts by 
weight of plasticizer, 0 to 15 parts by weight of clay filler and 0 to 60 
parts by weight of glass bubbles. 
The thermosetting adhesive suitably cures at about 160.degree. to 
220.degree. C. The thermosetting adhesive composition may also include a 
catalyst compatible with the curing agent for curing the composition at 
lower temperatures. An appropriate catalyst is a substituted urea 
catalyst, preferably phenyl dimethyl urea. With such a catalyst, the 
adhesive cures at about 120.degree. to 180.degree. C. 
Reinforcement 14, suitably in the form of a layer, is adhered to the 
surface of thermosetting adhesive layer 13' opposite the surface of 
thermosetting adhesive layer 13 to be applied to panel 11 to be 
reinforced. Preferably, the reinforcement is a woven glass fabric. The 
woven glass fabric reinforcement provides increased strength for the 
reinforcing sheet. 
With reference now to FIGS. 1 through 5, the reinforcing sheet may take 
various forms while still maintaining the necessary flexibility to conform 
to the shape of the panel to be reinforced. The reinforcing sheet may be 
flat such as reinforcing sheet 10 in FIG. 1 and reinforcing sheet 20 in 
FIG. 2. As shown in FIG. 2, woven glass fabric 14 may have reinforcing 
constructions 21 woven into it, such as by weaving carbon fiber into the 
woven glass fabric or by changing the weave of the woven glass fabric. The 
reinforcing sheet may have a ribbed configuration such as reinforcing 
sheet 30 in FIG. 3, reinforcing sheet 40 in FIG. 4 and reinforcing sheet 
50 in FIG. 5. As shown in FIG. 3, the rib may be formed of additional 
material 31 of the same composition as thermosetting adhesive layer 13' 
under the unexposed surface of woven glass fabric 14. As shown in FIG. 4, 
resin impregnated roving 41, such as a slightly twisted strand of textile 
fibers coated with resin, may be placed on the exposed surface of woven 
glass fabric 14 to form a rib. As shown in FIG. 5, the rib may be formed 
of flexible expandable material 51 which expands during curing to form a 
bead-like projection. 
In accordance with the present invention, moisture impermeable barrier 12 
is embedded between thermosetting adhesive layers 13 and 13'. Moisture 
impermeable barrier 12 acts to prevent moisture from adversely affecting 
protected thermosetting adhesive layer 13 after reinforcing sheet 10 is 
applied to panel 11 to be reinforced. For example, upon storage of panel 
11 with applied adhesive reinforcing sheet 10, especially under humid 
conditions, moisture may be absorbed by woven glass fabric 14 and 
unprotected thermosetting adhesive layer 13'. However, migration of the 
moisture to protected thermosetting adhesive layer 13 is prevented by 
moisture impermeable barrier 12. In this manner, decomposition of the 
curing agents in protected thermosetting adhesive layer 13 and gassing of 
protected thermosetting adhesive layer 13 upon curing is prevented (except 
for possibly an inconsequential amount around the edges of the reinforcing 
sheet itself). Thus, the density of protected thermosetting adhesive layer 
13 is not reduced by trapped gas. Accordingly, the corrosion and vibration 
resistance imparted by reinforcing sheet 10 to panel 11 is maintained. 
Moreover, good adhesion between reinforcing sheet 10 and panel 11 is 
likewise maintained to provide advantageous reinforcement and rigidity. 
Any material that is moisture impermeable, remains stable up to the curing 
temperature, and exhibits sufficient adhesion to the thermosetting 
adhesive layer and sufficient flexibility to conform to the shape of the 
panel to be reinforced can be used as moisture impermeable barrier 12. A 
metal foil, such as aluminum, tin, copper, zinc, brass, steel or iron 
foil, can be advantageously used as moisture impermeable barrier 12. 
Because of its ready accessibility, inexpensive cost and high flexibility, 
aluminum foil is most preferred. 
Moisture impermeable barrier 12, and in particular the aluminum foil used 
as the moisture impermeable barrier, must have sufficient thickness to 
maintain its integrity in order to prevent moisture from migrating to 
protected thermosetting adhesive layer 13. However, moisture impermeable 
barrier 12 must not have so great a thickness that its flexibility and 
capacity to conform to the shape of panel 11 to be reinforced are 
sacrificed. If aluminum foil is used as the moisture impermeable barrier, 
it suitably has a thickness of 0.0005 inch to 0.003 inch, more preferably 
0.0008 inch to 0.002 inch, most preferably 0.001 inch. 
Preferably, moisture impermeable barrier 12 is embedded approximately 
midway between the surface of the thermosetting adhesive layer 13 which 
comes in contact with panel 11 to be reinforced and the surface of 
thermosetting adhesive layer 13' which binds to reinforcement 14. Each of 
adhesive layers 13 and 13' has a thickness sufficient to bond the 
reinforcing sheet to the panel and to adhere the woven glass fabric 
reinforcement to the surface opposite the surface to be applied to the 
panel, respectively. Preferably, the combined adhesive layer has a 
thickness of 0.02 inch to 0.20 inch, preferably 0.03 inch to 0.10 inch, 
and at least 0.01 inch of the adhesive is provided on each side of the 
moisture impermeable barrier. 
As shown in FIG. 3, the surface of protected thermosetting adhesive layer 
13 away from moisture impermeable barrier 12 is advantageously covered 
with release sheet 32, preferably release paper, to facilitate handling of 
reinforcing sheet 30 and to prevent unintentional adhesion of the 
reinforcing sheet prior to its application to the panel to be reinforced. 
The release sheet can be removed just prior to applying the reinforcing 
sheet to the panel. 
The reinforcing sheet advantageously is prepared by spreading a 
thermosetting adhesive layer onto release paper with a coating knife to a 
uniform thickness suitably of 0.01 inch to 0.10 inch, preferably 0.02 inch 
to 0.05 inch. The moisture impermeable barrier is then placed on the 
thermosetting adhesive layer and pressed with a pressure roll. A second 
thermosetting adhesive layer is pumped onto the moisture impermeable 
barrier and spread with a coating knife again to form a layer of uniform 
thickness suitably of 0.01 inch to 0.10 inch, preferably 0.02 inch to 0.05 
inch. The reinforcement, such as the woven glass fabric, is adhered to the 
top of the second thermosetting adhesive layer, the surface of the 
adhesive layer opposite the surface to be applied to the panel to be 
reinforced. The woven glass fiber preferably has a thickness of 0.005 inch 
to 0.050 inch. The entire reinforcing sheet is then pressed with a roller 
to provide a sheet with total thickness suitably of 0.03 inch to 0.30 
inch, preferably 0.04 inch to 0.10 inch. 
To apply the reinforcing sheet to the panel to be reinforced, the release 
paper is removed from the reinforcing sheet and the reinforcing sheet is 
brought in contact with the panel. The reinforcing sheet has sufficient 
flexibility and thickness to conform to the shape of the panel to be 
reinforced. Because of the moisture impermeable barrier in the reinforcing 
sheet, the panel with the reinforcing sheet applied on it can be stored 
for long periods of time, for example three to six months, with minimal 
adverse effects due to the absorption of moisture, even under humid 
conditions. 
Because the moisture impermeable barrier is embedded within the 
thermosetting adhesive layer, it is protected from damage during handling 
and storage of the reinforcing sheet. Furthermore, the position of the 
moisture impermeable barrier embedded within the uncured thermosetting 
adhesive layer serves to prevent buckling and separation of the barrier 
from the laminated reinforcing sheet, even when conforming the reinforcing 
sheet to the shape of the panel to be reinforced. 
Whereas aluminum foil laminated to the woven glass reinforcement of the 
reinforcing sheet does not significantly improve the sheet's resistance to 
humidity absorption, a moisture impermeable barrier embedded within the 
thermosetting adhesive layer does provide resistance to humidity 
absorption. Moreover, the disadvantageous effects of any flaw in the 
moisture impermeable barrier which otherwise would allow aggravated damage 
to the thermosetting adhesive layer due to absorption of moisture if the 
barrier were located at the surface of the reinforcing sheet, particularly 
at the reinforcement adhered to the thermosetting adhesive layer, are 
minimized due to the location of the barrier embedded in the thermosetting 
adhesive layer. 
A panel with a reinforcing sheet having an embedded moisture impermeable 
barrier applied to the panel can be heated to the curing temperature of 
the thermosetting adhesive layer, preferably to a temperature of 
120.degree. to 220.degree. C., to harden the reinforcing sheet without 
adverse effects, even after storage for a number of months under humid 
conditions. 
Further objects of this invention, together with additional features 
contributing thereto and advantages accruing therefrom, will be apparent 
from the following examples of the invention. 
EXAMPLE 1 
A flat reinforcing sheet containing a 0.001 inch aluminum foil moisture 
impermeable barrier was constructed according to the invention. The 
aluminum foil was embedded midway within a thermosetting adhesive layer 
formed of 30 parts by weight of the diglycidyl ether of bisphenol A, 70 
parts by weight of the diglycidyl ether of bisphenol A reacted in a 3:2 
ratio with carboxy terminated butadiene acrylonitrile, 7 parts by weight 
of a phthalate plasticizer, 6 parts by weight of dicyandiamide curing 
agent, 7 parts by weight of clay, 15 parts by weight of glass bubbles, and 
1.5 parts by weight of phenyl dimethyl urea catalyst for dicyandiamide 
curing. The reinforcing sheet contained a woven glass fabric adhered to 
the surface of the thermosetting adhesive layer opposite the surface to be 
applied to the panel to be reinforced. 
A comparative sample was prepared in an identical manner to the sample 
according to the invention except omitting the moisture impermeable 
barrier. 
A 1 inch wide by 6 inch long piece of the reinforcing sheet according to 
the invention was applied to a first cold rolled steel metal panel of 
dimensions 1 inch wide by 6 inch long by 0.030 inch thick. Similarly, a 1 
inch wide by 6 inch long sample of the comparison reinforcing sheet 
without the moisture impermeable barrier was applied to an identical 
second cold rolled steel metal panel of dimensions 1 inch wide by 6 inch 
long by 0.030 inch thick. 
Both metal panels with uncured reinforcing sheet were stored at 100.degree. 
F. and 100% relative humidity for 48 hours. 
The two samples were then heated at 150.degree. C. for 0.5 hour to cure and 
harden the thermosetting adhesive. 
The following test results compare the flexural reinforcement properties of 
an unreinforced metal panel, the metal panel reinforced by the reinforcing 
sheet according to the invention and the metal panel reinforced by a 
reinforcing sheet without a moisture impermeable barrier, measured at 
74.degree. F. at a load rate of 0.2 inch per minute on a support span of 4 
inch. 
TABLE I 
______________________________________ 
Flexural Properties of Cold Rolled Steel Panel 
Unrein- 
With Without 
forced Barrier Barrier 
______________________________________ 
Post cure thickness, inches 
0.087 0.090 
Load at 0.1 in. deflection, lbs. 
7 41 43 
Ultimate load, lbs. 
11 69 72 
Ultimate deflection, in. 
&gt;0.5 0.20 0.23 
______________________________________ 
Thus, the presence of the moisture impermeable barrier does not affect the 
reinforcement capability of the reinforcing sheet. 
In addition, the adhesive layers of the two reinforcing adhesive sheets 
were visually compared. In the reinforcing sheet without the moisture 
impermeable barrier, the thermosetting adhesive layer was gassed through 
the entire sheet. Presumably, this gassing was caused by decomposition of 
the curing agent in the presence of moisture absorbed by the thermosetting 
adhesive layer. The trapped gas reduced the cohesiveness and density of 
the thermosetting adhesive layer during and after curing. Loss of cohesion 
of the adhesive layer resulted in the reinforcing sheet peeling away from 
the cold rolled steel during curing. 
On the other hand, the reinforcing sheet according to the invention with 
the moisture impermeable barrier exhibited gassing of the thermosetting 
adhesive layer only between the aluminum foil and the woven glass fabric 
but no gassing of the thermosetting adhesive between the aluminum foil and 
the cold rolled steel metal panel. Thus, the thermosetting adhesive layer 
in contact with the steel panel maintained its integrity, including its 
adhesion to the metal panel, despite the fact that the reinforcing sheet 
was subjected to moisture from atmospheric humidity. The reinforcing sheet 
containing the moisture impermeable barrier remained adhered to the metal 
panel during curing. The corrosion and vibration protection of the 
reinforced metal panel was maintained. 
EXAMPLE 2 
A flat reinforcing sheet having a 0.001 inch aluminum foil moisture 
impermeable barrier was constructed according to the invention. The 
aluminum foil was embedded midway within a thermosetting adhesive layer 
formed of 30 parts by weight of the diglycidyl ether of bisphenol A, 70 
parts by weight of the diglycidyl ether of bisphenol A reacted in a 3:2 
ratio with carboxy terminated butadiene acrylonitrile, 7 parts by weight 
of a phthalate plasticizer, 6 parts by weight of dicyandiamide curing 
agent, 7 parts by weight of clay, and 20 parts by weight of glass bubbles. 
The reinforcing sheet contained a woven glass fabric adhered to the 
surface of the thermosetting adhesive layer opposite the surface to be 
applied to the panel to be reinforced. 
A comparative sample was prepared in an identical manner to the sample 
according to the invention except omitting the moisture impermeable 
barrier. 
A 1 inch wide by 6 inch long piece of the reinforcing sheet according to 
the invention was applied to a first cold rolled steel metal panel of 
dimensions 1 inch wide by 6 inch long by 0.030 inch thick. Similarly, a 1 
inch wide by 6 inch long sample of the comparison reinforcing sheet 
without the moisture impermeable barrier was applied to an identical 
second cold rolled steel metal panel of dimensions 1 inch wide by 6 inch 
long by 0.030 inch thick. 
Both metal panels with uncured reinforcing sheet were stored at 100.degree. 
F. and 100% relative humidity for 48 hours. 
The two samples were then heated at 200.degree. C. for 0.5 hour to cure and 
harden the thermosetting adhesive. 
The following test results compare the flexural reinforcement properties of 
an unreinforced metal panel, the metal panel reinforced by the reinforcing 
sheet according to the invention and the metal panel reinforced by a 
reinforcing sheet without a moisture impermeable barrier, measured at 
74.degree. F. at a load rate of 0.2 inch per minute on a support span of 4 
inch. 
TABLE II 
______________________________________ 
Flexural Properties of Cold Rolled Steel Panel 
Unrein- 
With Without 
forced Barrier Barrier 
______________________________________ 
Post cure thickness, inches 
0.090 0.081 
Load at 0.1 in. deflection, lbs. 
7 39 32 
Ultimate load, lbs. 
11 70 64 
Ultimate deflection, in. 
&gt;0.5 0.24 0.31 
______________________________________ 
Thus, the presence of the moisture impermeable barrier does not affect the 
reinforcement capability of the reinforcing sheet. 
In addition, the adhesive layers of the two reinforcing adhesive sheets 
were visually compared. In the reinforcing sheet without the moisture 
impermeable barrier, the thermosetting adhesive layer was gassed through 
the entire sheet. Presumably, this gassing was caused by decomposition of 
the curing agent in the presence of moisture absorbed by the thermosetting 
adhesive layer. The trapped gas reduced the cohesiveness and density of 
the thermosetting adhesive layer during and after curing. Loss of cohesion 
of the adhesive layer resulted in the reinforcing sheet peeling away from 
the cold rolled steel during curing. 
On the other hand, the reinforcing sheet according to the invention with 
the moisture impermeable barrier exhibited gassing of the thermosetting 
adhesive layer only between the aluminum foil and the woven glass fabric 
but no gassing of the thermosetting adhesive between the aluminum foil and 
the cold rolled steel metal panel. Thus, the thermosetting adhesive layer 
in contact with the steel panel maintained its integrity, including its 
adhesion to the metal panel, despite the fact that the reinforcing sheet 
was subjected to moisture from atmospheric humidity. The reinforcing sheet 
containing the moisture impermeable barrier remained adhered to the metal 
panel during curing. The corrosion and vibration protection of the 
reinforced metal panel was maintained.