Laminates, panels and methods for making them

Sandwich panels and methods of making them, i.e., laminates which comprise two metal sheets with a filled resin core between a bonded metal sheets, which are useful for structural and other uses wherein the laminates utilize combinations of metal skins, metal surface preparation, resins, fillers, and reinforcement bonded together in the sandwich structure to provide a laminate having a flexural modulus of at least 1.7 million psi, a rigidity index of at least about 2,000 and other unique properties which enable the laminates to be particularly useful for thin wall trailer body construction, as well as other structural and non-structural uses. A rigidity index property for sandwich structures and panels and a falling ball impact test are disclosed and used to characterize the properties of sandwich laminates. A laminate of plywood core or a reconstituted wood product core, such as hardboard, particleboard or flakeboard, bonded to prepared metal surfaces with the resin also has properties suitable for structural uses.

FIELD OF THE INVENTION 
This invention relates to the field of structural laminates, and in 
particular to sandwich laminates comprising two metal sheets and a resin 
core. This invention also relates to the field of trailer body 
construction. 
BACKGROUND OF THE INVENTION 
This invention relates to structural laminates which comprise two metal 
sheets or two metal skin layers with a polymer core disposed between and 
attached to each of the inside surfaces of the metal sheets. The laminates 
of this invention have improved structural strength compared to prior 
laminates of this type. The laminates of this invention are also useful in 
decorative and protective applications as well as structural applications. 
In the field of laminates, metal-resin-metal laminates are disclosed in 
U.S. Pat. No. 4,313,996 to Newman, et al. and U.S. Pat. No. 4,601,941 to 
Lutz, et al. Additional laminates are disclosed in U.S. Pat. No. 3,382,136 
to Bugel, et al., U.S. Pat. No. 3,392,045 to Holub, U.S. Pat. No. 
3,455,775 to Pohl, et al., U.S. Pat. No. 3,594,249 to Mueller-Tamm, et 
al., U.S. Pat. No. 3,623,943 to Altenpohl, et al., U.S. Pat. No. 3,655,504 
to Mueller-Tamm, et al., U.S. Pat. No. 3,952,136 to Yoshikawa, et al., 
U.S. Pat. No. 4,330,587 to Woodbrey, U.S. Pat. No. 4,369,222 to Hedrick et 
al., U.S. Pat. No. 4,416,949 to Gabellieri, et al., U.S. Pat. No. 
4,424,254 to Hedrick et al., U.S. Pat. No. 4,477,513 to Koga, and U.S. 
Pat. No. 4,594,292 to Nagai, et al. In these references, a property which 
is generally important is that the laminates be formable, particularly 
thermoformable. Other properties which have been important for 
metal-resin-metal laminates have been the resistance of the metal skin to 
heat, weather, chemicals and impact, as well as the metal skin's hardness, 
impermeability and strength. Multi-layer laminates have been made with 
multiple, alternating layers of resin and metal. Laminates in this field 
have been used also for heat insulation and vibration damping. 
In U.S. Pat. No. 3,499,819 to Lewis, the resin core is a polypropylene 
which contains a foaming agent additive to cause the polypropylene to form 
a foam between the metal layers. In U.S. Pat. No. 3,560,285 to Schroter, 
et al. a mixture of polyether polyols is reacted with polyisocyanate and a 
blowing agent to form foamed urethane cores between metal layers. U.S. 
Pat. No. 4,421,827 to Phillips discloses metal-clad articles which use a 
combination of thermosetting resins and particular adhesives to bond a 
resin layer to a metal facing. 
As disclosed by Vogelesang (Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 
492-496) aluminum laminates with high tensile strength and fatigue 
resistance have also been made with multiple core layers of aramid 
fiber-reinforced epoxy resins. These aluminum laminates, known as "ARALL" 
laminates, have been developed for use as aircraft skins. See also U.S. 
Pat. Nos. 4,489,123 and 4,500,589 to Schijve, et al. 
While metal-resin-metal laminates have been used in trailer bodies, such 
laminates have not been used for structural members. Examples of such 
non-structural laminates are sandwich structures which have been used for 
thermal insulation in trailer bodies, as shown in U.S. Pat. Nos. 3,363,231 
to Grosgebauer, et al., and 4,482,589 to Widman. In U.S. Pat. No. 
2,730,722 to Jones, a metal-resin-plywood laminate is disclosed that is 
both insulative and structural, but is over 2 inches (5 cm) thick. Thermal 
insulation panels usually have very low density cores, i.e., specific 
gravities in the range of 0.10 or less, and thus a low shear modulus and 
low impact resistance. 
For trucks operated on public highways, United States federal law now 
limits the exterior width of trailers to 102.38 inches (260 cm). 
Therefore, interior space can be increased if the thickness of the walls 
of the trailer body can be decreased. This is particularly important in 
industries transporting light, bulky loads, such as empty beverage cans, 
where the volume of the trailer is often more limiting than the weight of 
the load. Thus, emphasis in this field is on designing trailers for 
maximum interior usable width. Also, because of the dimensions of standard 
pallets, it is desirable that the interior width of the trailer be at 
least 101 inches (256.5 cm). The advantages of having thin walls and the 
additional interior space provided by thin-wall trailer construction are 
discussed by Pennington, Modern Metals, November, 1986, pp. 20-25. 
In order to achieve the desired interior width dimension of at least 101 
inches (256.5 cm), each sidewall of the trailer body, including rivet 
heads, can be no thicker than 0.69 inches (1.75 cm). Sheet and post 
trailers, the most common type, follow a truss design which generally uses 
about 0.045 inch (0.114 cm) or 0.050 inch (0.127 cm) aluminum sheet 
riveted to steel or aluminum frame and posts. The sheet and post trailer 
has an overall wall thickness of 1.4 inches (3.56 cm) to 1.7 inches (4.32 
cm) and a maximum interior width of 99.58 inches (252.9 cm) to 99 inches 
(251.4 cm). Conventional trailer bodies made with resin-fiberglass-plywood 
laminates use either 0.625 inch (1.6 cm) or 0.75 inch (1.9 cm) plywood as 
the core, resulting in an overall thickness of up to 0.86 inches (2.18 cm) 
even in a post-free design using that type of panel. 
In U.S. Pat. No. 4,212,405 to Schmidt there is disclosed a trailer having a 
"box" type of design using unitary aluminum alloy plates as the walls and 
supporting structure in a frameless trailer body. This structure is 
intended to provide an interior trailer dimension of at least 101.5 inches 
(257.8 cm). While this configuration provides the desired wall thickness 
of down to about 0.156 inch (0.4 cm), but usually about 0.25 inch (0.6 
cm), a trailer made of the aluminum alloy plate is much heavier than 
desired. There are other disadvantages, as well, in having a trailer wall 
made of a unitary aluminum alloy plate. Since these plates are typically a 
single 9 ft. (2.74 m) by 44 ft. (13.41 m) rigid plate, there are 
associated problems in manufacturing, shipping and handling of the plates, 
as well as in assembling and repairing the trailer. It is particularly 
difficult to repair these trailers without losing interior space and 
without either decreasing wall thickness or, if the damage is repaired by 
welding, without loss of strength. 
In order to overcome these disadvantages, Banerjea discloses an alternative 
trailer construction having a box type design in U.S. Pat. No. 4,685,721. 
This trailer body construction uses smaller sized individual plates 
spliced together with joining panels and stiffener panels designed to be 
riveted with the aluminum sheets to keep the wall thickness to a minimum. 
Since the additional splices add undesired weight, some of the panels or 
sheets are thinner in lower stress areas than in higher stress areas in 
order to partially compensate for the added weight from the splices and 
joining panels. The overall result, however, is a trailer that is still 
heavier and has more susceptibility to denting of the thinner side panels 
than desired, and the interior width of which is less than desired because 
of the splices and rivets. 
The disclosures of the above references are incorporated herein by 
reference. 
OBJECT OF THE INVENTION 
I have determined that it would be desirable to use sandwich panels as 
structural elements in trailer construction. This invention provides 
laminates which have improved structural and strength properties and which 
are useful as structural components in trailer body construction to 
accomplish the desired lighter weight, thinner wall construction. 
As used herein, the term "sandwich" is used to refer to metal-resin-metal 
laminate structures. 
I have also determined that it would be desirable to construct and use 
structural laminates which have a high rigidity index, which is the ratio 
of rigidity to the product of basis weight (weight per unit area) and 
thickness. The factors desired for a high rigidity index are thus high 
rigidity, low basis weight and low laminate thickness. 
It is an object of this invention to provide improved wall and structural 
panel materials, which is accomplished by the metal-resin-metal laminates 
of this invention having improved structural properties, in particular 
vertical and longitudinal stiffness. This invention provides such 
laminates which have reduced thickness and weight, while still providing 
desired load bearing capacity, improved resistance to buckling under load, 
improved impact resistance and improved resistance to delamination. 
Another object of this invention is to provide a wall panel having 
sufficient stiffness and other structural properties to enable the 
construction of trailer bodies having a wall thickness of about 0.6 inches 
(1.52 cm) or less, including rivet heads, to provide an interior width of 
the trailer of not less than about 101 inches (256.5 cm) without exceeding 
the maximum outside width of 102.38 inches (260 cm). The laminate of this 
invention is a wall panel which meets these requirements. 
It is another object of this invention to provide the above trailer 
construction which is lighter in weight than the unitary aluminum alloy 
plate trailer construction. It has been found that the structural laminate 
of this invention can provide side wall weight that is in the range of 20% 
to 30% less than typical monolithic aluminum plate construction. 
The above objects with respect to the structural laminates of this 
invention and particularly with respect to trailer construction using 
these laminates will be apparent to those skilled in the art from the 
following description and from the use of the laminates of this invention. 
Other uses and advantages of the laminates of this invention will also be 
apparent to those skilled in the art, such as in construction of freight 
container bodies, including intermodal (ocean, truck, rail) freight cargo 
containers, truck trailer bodies, trailer doors and freight containers for 
aircraft; residential trailers, mobile homes, recreational vehicles, 
collapsible and portable buildings, flooring for buses and other vehicles, 
exterior building and architectural panels, concrete pouring forms, 
including any of these or other uses where metal-covered plywood has been 
used. 
SUMMARY OF THE INVENTION 
In one aspect the laminate of this invention comprises two metal sheets and 
a resin core between and bonded to the metal sheets, wherein each metal 
sheet has a thickness between about 0.015 inch (0.038 cm) and about 0.1 
inch (0.25 cm), and the total thickness of the laminate is between about 
0.1 inch (0.25 cm) and about 2 inches (5 cm), wherein the laminate is 
characterized by having a flexural modulus, as described herein, of at 
least about 1.75.times.10.sup.6, preferably at least about 
2.5.times.10.sup.6 psi. 
In the above aspect and all other aspects of this invention the resin core 
comprises a reinforced thermoset resin core or comprises a thermoplastic 
resin core, preferably reinforced and/or filled. 
In another aspect the laminate of this invention comprises two metal sheets 
and a resin core between and bonded to the two metal sheets, wherein each 
metal sheet has a thickness between about 0.015 inch (0.038 cm) and about 
0.1 inch (0.25 cm), and the thickness of the laminate is between about 0.1 
inch (0.25 cm) and 2 inches (0.25 cm), wherein the laminate is 
characterized by having a rigidity index, described herein, of at least 
about 2000. 
In another aspect the laminate of this invention comprises two metal sheets 
and a resin core between and bonded to the two metal sheets, wherein each 
metal sheet has a thickness between about 0.015 inch (0.038 cm) and about 
0.1 inch (0.25 cm), and the thickness of the laminate is between about 0.1 
inch (0.25 cm) and 2 inches (0.25 cm), wherein the laminate is 
characterized by having an impact resistance sufficient to pass the 
falling ball impact test, as described herein. 
In another aspect the laminate of this invention comprises two metal sheets 
and a resin core between and bonded to the two metal sheets, wherein each 
metal sheet has a thickness between about 0.015 inch (0.038 cm) and about 
0.1 inch (0.25 cm) and a tensile (Young's) modulus of at least 
9.times.10.sup.6 psi, and the thickness of the laminate is between about 
0.1 inch (0.25 cm) and 2 inches (0.25 cm), wherein the laminate is 
characterized by the core having a shear modulus of at least about 20,000 
psi, preferably at least about 30,000 psi, more preferably at least about 
40,000 psi, determined as described herein, and wherein the resin from 
which the core is made exhibits a neat resin to metal bond having a lap 
shear strength of at least 1,000 psi. 
In another aspect the laminate of this invention comprises two metal sheets 
and a resin core between and bonded to the two metal sheets, wherein each 
metal sheet has a thickness between 0.015 inch (0.038 cm) and about 0.1 
inch (0.25 cm), the thickness of the laminate is between about 0.1 inch 
(0.25 cm) and about 2 inches (5 cm), and the resin core is a conventional 
or syntactic foam (containing microballoons) so that the weight of the 
laminate is less than about 3.5 lb./ft..sup.2 (17.1 kg/m.sup.2). 
In another aspect the laminate of this invention comprises two metal sheets 
and a resin core between and bonded to the two metal sheets, wherein the 
metal sheet has a thickness between about 0.015 inch (0.038 cm) and about 
0.10 inch (0.25 cm), and wherein the resin core comprises a thermoplastic 
resin and wherein the specific gravity of the resin core is between about 
0.7 and about 1.5. 
In another aspect the process of this invention comprises placing between 
two metal sheets having prepared surfaces, a resin composition comprising 
(a) thermoplastic resin capable of bonding to the prepared surfaces of the 
metal sheets upon heating and cooling to provide a lap shear strength of 
at least 500 psi, (b) optional reinforcing material present in an amount 
between about 3 and about 30 parts by weight based upon the weight of the 
resin, and (c) optional microballoons present in an amount sufficient to 
provide the resin composition a specific gravity less than about 1.5, and 
heating then cooling the resin composition while positioned between and in 
contact with the two metal sheets. 
In another aspect this invention comprises a trailer body comprising at 
least one panel in the structure thereof which is a structural laminate 
comprising two metal sheets and a thermoplastic resin core, preferably 
reinforced, between and bonded to the two metal sheets, wherein each metal 
sheet has a thickness between 0.015 inch (0.038 cm) and about 0.1 inch 
(0.25 cm), the thickness of the laminate is between about 0.15 inch (0.25 
cm) and about 2 inches (5 cm), and the resin core is such that the weight 
of the laminate is less than about 3 lb./ft..sup.2. 
In another aspect the laminate of this invention comprises two metal sheets 
and a plywood, hardboard, particleboard or flakeboard core wherein the 
core is bonded to the metal sheets with a thermoset or thermoplastic resin 
and the metal sheet surface is prepared or activated by anodizing or 
etching.

DESCRIPTION OF THE INVENTION 
The high structural performance of the laminates of this invention is due 
to a rigid polymer core, i.e., one with a high shear modulus, and a strong 
bond of that core to the metal facings. Of almost equal importance for the 
preferred laminates of the present invention is the impact resistance of 
the core and the core-to-metal bond. These unique properties and 
characteristics of the laminates of this invention are described below. 
As an illustration of one embodiment of this invention, the following Table 
A is provided to show comparison of the laminate of the present invention 
to typical values for other materials in the construction of a typical 
trailer 48 ft. (14.6 m) in length. A unitary aluminum plate type trailer 
is disclosed in Schmidt U.S. Pat. No. 4,212,405 and the plate type trailer 
with external splices is disclosed in Banerjea U.S. Pat. No. 4,658,721. As 
shown in Table A, the laminates of this invention provide about the same 
interior width as the unitary plate but at considerably less weight. The 
laminates of this invention will provide an average trailer wall weight 
(including splices and posts) of about 2.6 lb/ft.sup.2 compared to 3.4 to 
3.6 lb/ft.sup.2 for the plate construction using; the lighter weight 
panels of this invention results in about 1,000 lb. less weight in the 
overall construction of a 48 ft. trailer. The laminates of this invention 
are lighter in weight than the 1/2 inch plywood generally used in trailers 
designed for heavy duty hauling and are at least as light weight as the 
5/8 inch plywood construction, but the laminates of this invention are 
stronger than both. Trailer designs based on the laminates of this 
invention provide more interior trailer width than plywood construction 
because of the thinner wall construction which results from the laminate 
of this invention. Additionally, the panels of this invention do not lose 
strength in high humidity conditions, as do the FRP plywood panels. In 
addition, the cost of the laminate of this invention in such trailer 
construction is considerably less than that of the metal plate in the 
unitary plate trailer. 
TABLE A 
__________________________________________________________________________ 
VAN TRAILER FEATURES 
(Values typical for 48-ft. length) 
Trailer type 
Unitary 
Aluminum 
Plate with 
Laminate of 
Post & sheet 
FRP Plate Splices 
This Invention 
__________________________________________________________________________ 
Design type Truss Box Box Box Box 
Support posts 
Yes No No No No 
Vertical splices 
No No No External 
Internal 
Panel size, ft. 
4 .times. 9 
9 .times. 48 
9 .times. 48 
4 .times. 9 
4 .times. 9 
2 .times. 9 2 .times. 9 
(2 .times. 9) 
Panel material 
Aluminum 
Fiberglass- 
Aluminum 
Aluminum 
Aluminum- 
reinforces faced 
resin-faced laminate 
plywood 
Panel thickness, in. 
0.050 0.65-0.80 
0.25 0.19-0.25 
0.31 
Interior scuff strip 
Plywood 
Plastic 
None None None 
Total wall thickness, in. 
1.7 0.78-1.02 
0.37 0.63-0.69 
0.56 
(incl. 0.13 or 0.25 in. 
for rivets) 
Max interior width, in. 
99.0 100.32-100.72 
101.62 
101.04-101.10 
101.24 
Ave. wall weight (incl. 
1.6.+-. 
2.5-2.9 
3.6 3.4 2.6 
posts & splices), lb./sq. ft. 
__________________________________________________________________________ 
The four basic elements present in the structural laminates of the present 
invention are (1) the metal sheets, (2) the resin or polymer core between 
the sheets and bonded to the inside surfaces of the sheets, (3) optional 
reinforcing material in the polymer or resin core which increases the 
strength properties of the resin core, and (4) optional filler in the 
polymer or resin core to lower the density of the core, which filler can 
be a gas to foam the resin or is preferably microballoons which are gas 
filled. In addition to these elements, other optional ingredients or 
optional resin properties can also be included in the polymer or resin 
core, such as flame retardants, viscosity modifiers, pigments, UV 
stabilizers, antioxidants, surfactants and other additives desired by one 
skilled in the art for the particular application in which the structural 
laminate of this invention is being used. 
PREATION OF THE LAMINATE 
The laminates of the present invention preferably are prepared by applying 
the resin core mixture containing all necessary fillers, reinforcements 
and other additives to the interior surface of one of the metal facings, 
applying the second metal facing, and curing or heating to form the 
resulting sandwich structure. The principal advantage of in situ curing of 
the liquid thermosetting resin mixture or heating the thermoplastic resin 
core over assembly of the laminate from a similar precured or preformed 
core material is simplicity and economy. When precured or preformed resin 
cores are used, their surfaces must be suitable for bonding to the 
prepared metal surfaces by applying and curing a thermosetting resin or by 
heating and cooling a thermoplastic resin at the resin-metal interface. 
The laminates can be produced batchwise, i.e. from metal facings pre-cut 
approximately or exactly to the desired final panel size before 
fabrication, or they can be produced continuously from coiled metal sheet. 
In both types of processes, the bottom facing is first laid on a flat 
surface, and a means of preventing the liquid resin mixture from flowing 
over the edges is provided. A preferred method involves the use of 
removable spacers which are pressed down along the edges. These spacers 
determine core thickness and prevent liquid resin from exuding from the 
panel prior to cure. 
The composition of the spacers can vary. If the spacers are to be re-used, 
and particularly if an edge with a recessed core is desired, a material 
that does not bond to the resin is used. An example of an effective 
reusable spacer of this type is a solid polypropylene bar, or a metal 
sheet covered with polypropylene. Other materials such as polyethylene 
(preferably of the linear type) or thermoplastic polyester such as 
Mylar(TM) sheet, or in some cases even metal coated with a release agent 
may also be employed. As an example of non-reusable spacers, smoothly 
sanded plywood strips are quite effective. These become bonded to the 
resin, and the edge portion containing them can be sawed off after curing. 
Combinations of both reusable and non-reusable spacers can also be 
employed. 
The key features of a continuous process are shown in FIGS. 1a and 1b. 
Metal sheet of the desired width from two coils 1 and 2 is passed through 
straightening rollers 3 and 4 to remove coil set. Sheet 5 for the bottom 
facing is then fed to a conveyor belt 6 or roller table, where it travels 
over supporting rollers 7. Spacers 8 are then applied to the two edges of 
sheet 5 and held down with moderate pressure using rollers 9. The spacers 
may consist of polypropylene-covered steel strips that are separate or 
linked together flexibly into a continuous loop. They are applied to the 
sheet and later removed after curing. 
The liquid resin, catalyst or curing agent, filler, fiber reinforcement and 
any other desired additives are applied to the inner surface of the facing 
sheet 5 with a spray gun 10 (also known as a chopper gun). With this 
common device, liquid resin containing the filler is pumped to a discharge 
nozzle. Liquid catalyst or curing agent is injected just before discharge. 
The mixture is then sprayed onto the inside surface of the metal facing. A 
cutting unit and a compressed air nozzle, both of which are attached to 
the spray gun, discharge cut fiberglass in the same direction as the 
resin. Commercial guns of this type allow the resin layer to be deposited 
to within 0.25 to 0.5 in. (6.3 to 12 mm) of the edge spacer with virtually 
no overspray. 
With the concentrations of microballoons and chopped fiber preferred for 
the laminates of this invention, the mixture 11 deposited on the metal 
sheet is quite viscous, and there is no significant flow of liquid resin 
between the edge spacer and the bottom facing sheet. Uniform deposition on 
the moving sheet is achieved by having the spray head traverse back and 
forth across the width of sheet 5 on an automatic reciprocator unit. In 
some cases two or more such units may be needed. Reciprocating spray gun 
assemblies are commercially used in the manufacture of fiberglass sheets 
and panels. As indicated in cross section A--A' in FIG. 1b, the initial 
thickness of the deposited core mixture 11 is slightly greater than that 
of the edge spacers to allow some spreading of the mixture after the top 
facing sheet 14 is applied. 
In tests with commercial medium-pressure spray equipment (200 to 700 psi at 
the pump discharge), the core mixture was deposited evenly and without any 
entrapped air. Any further compaction and smoothing of the deposited core 
layer with rollers was unnecessary. 
Following the spray station, the top facing sheet 14 then passe under one 
or more rollers 12 that guide the straightened metal sheet from the coil 1 
onto the resin mixture-covered bottom sheet. A series of rollers 13 exert 
moderate downward pressure across the width of the top sheet 14 so as to 
provide good contact of the top sheet 14 with the resin mixture 11 and 
with the spacers 8 at the edges. The deposited resin mixture 11 is spread 
out slightly under the applied pressure, filling the void at the edges 
left to avoid overspray. 
The uncured laminate next passes into a curing oven (not shown in the 
Figure), where the laminate is brought to the desired temperature while 
still constrained by rollers above and below. Heating can be accomplished 
with infrared heaters, with hot air or by other desired means. 
After the oven, the spacers, if removable, are separated from the cured 
laminate and returned to the front of the laminating unit. The laminate 
then enters the cutting station where, while still hot, it is cut to the 
desired length with a traversing saw or a high-pressure water jet. The hot 
panels may then be stacked in an insulated room to allow continuing the 
cure, or they may be stacked in the open and allowed to cool. 
If desired, a paint station may be inserted in the above-described 
laminating line. Partially cured panels, even though still hot, are 
sufficiently rigid to be supported by the spacers projecting out from the 
side of the continuous laminate, allowing it to be roll--or spray-coated 
from either or both sides. After cutting, the painted panels can, if 
desired, be placed in an infrared or hot air baking oven to conclude the 
cure of the painted surface as well as of the core. Phoshoric 
acid-anodized aluminum surfaces, even after some heating, show excellent 
adhesion to paints and yield painted surfaces with good durability. A 
primer may therefore not always be required before application of a 
topcoat. 
Line speed for a polyester-based laminate will typically range from about 4 
to 8 ft./min. (about 1.2 to 2.4 m/min.), but can be faster with 
appropriate equipment modifications and with the appropriate catalyst and 
curing temperature. 
The above resin cores can also be formed from thermoplastic resins in the 
form of powders, pellets, sheets, emulsions, slurries or other forms 
suitable for the desired manufacturing method or process. The form of 
resin selected should provide suitable mixing with any desired fiber 
reinforcing materials and any desired filler materials and should be 
adapted for appropriate heating to form the core and bond the core to the 
prepared metal surfaces and subsequent cooling. In many instances it will 
be desirable to provide for removal of air or other gasses from the core 
during processing. 
It was originally expected that thermoplastic resins would not form bonds 
with the prepared metal surfaces of sufficient strength for use in this 
invention due to the higher viscosity of the thermoplastic polymer melts. 
They were not expected to penetrate into the anodized or etched metal 
surface sufficiently to form a strong bond. However, contrary to such 
expectation I have found that the preformed thermoplastic resin core 
provides good resin-metal bond strength, as well as other forms of 
thermoplastic resin cores formed from powders, etc. 
The metal sheets used in the structural laminates of the present invention 
may be aluminum, steel, nickel, copper, titanium, magnesium, zinc, and the 
like, as well as various alloys thereof. Although it is generally 
preferred that the two metal sheets of a particular structural laminate 
according to the present invention be the same metal and in general the 
same thickness, structural laminates according to the present invention 
can be made with different metal sheets and with different thicknesses. 
When metal sheets of different thicknesses are used, it will in general be 
desirable to have one metal sheet no more than about five times the 
thickness of the other metal sheet. While the use of various combinations 
of the above metals and various thicknesses will be apparent to one 
skilled in the art for particular applications, the discussion herein 
describing examples and embodiments of the present invention is primarily 
in terms of aluminum sheets and in terms of a preferred structural 
laminate wherein the metal aluminum sheets have essentially the same 
thickness. In addition, while the laminates of the present invention are 
referred to herein as "structural" laminates, the laminates of the present 
invention can also be used for decorative or protective purposes as well. 
The structural laminates of the present invention in general have an 
overall thickness between about 0.1 inches and about 2 inches (about 0.25 
cm to about 5 cm). Preferably, the overall thickness of the structural 
laminate of the present invention will be between about 0.15 and about 1.0 
inches (about 0.38 cm and about 2.5 cm), and more preferably, between 
about 0.2 and about 0.75 inches (about 0.5 cm and about 1.9 cm). The metal 
sheets will in general have a thickness between about 0.015 inch (0.38 mm) 
and about 0.1 inch (2.5 mm), preferably between about 0.025 inch (0.63 mm) 
and about 0.075 inch (1.9 mm), and most preferably between about 0.035 
inch (0.9 mm) and about 0.065 inch (1.7 mm). The thickness of the polymer 
or resin core can be any thickness within the above parameters, however, 
it is in general preferred that the thickness of the resin or polymer core 
be equal to or greater than the thickness of the two metal sheets 
combined. 
The metal sheets can be any metal or alloy which preferably has a tensile 
strength of at least about 15,000 psi and a tensile (Young's) modulus of 
at least about 9.times.10.sup.6 psi. 
The surface properties as well as the surface condition and surface 
preparation of the metal sheets is frequently important in the structural 
laminates of the present invention because it is important that the 
polymer or resin core bond to the surfaces of the metal sheets with 
sufficient strength to provide the desired properties of the structural 
laminate. The surface properties of the metal sheets as well as the 
surface condition and the surface preparation will be apparent to one 
skilled in the art following the teachings of the present disclosure. The 
necessary or desirable properties of the metal surfaces will depend upon 
the type of polymer or resin core which is used, the type of curing 
mechanism and the like. The bonding of resins and polymer to metal 
surfaces is generally known to those skilled in the art, and selection 
and/or preparation of particular metal sheets having appropriate surface 
properties and conditions and selection of the particular resin or polymer 
formulation to obtain the laminate properties according to this invention 
will be apparent to one skilled in the art when following the criteria, 
guidelines and specifications disclosed in the description and examples 
set forth herein. 
When aluminum sheets are used with a polyester resin, it is important that 
the surface be cleaned properly to ensure that it is free of rolling oils 
and other contaminants. This can be accomplished by one or more of the 
cleaning methods used in industry. These include vapor degreasing, 
treatment with non-etching or etching alkaline cleaning solutions, and/or 
treatment with acidic cleaning solutions. After cleaning, the surface is 
rendered receptive to the core resin, i.e., it is modified so as to 
provide strong adhesion to the resin core. The two preferred process 
providing such a surface are anodizing with phosphoric acid and etching 
with chromic acid or dichromate-sulfuric acid. The former is preferred, 
since it is faster and does not present the toxicity and pollution hazards 
associated with chromium compounds. A preferred surface preparation 
consists of cleaning the aluminum by solvent or vapor degreasing or by 
acid or alkaline treatment, or both, followed by anodizing with 10% 
phosphoric acid for about 5 minutes at a temperature of about 113.degree. 
F. (45.degree. C.) followed by a water rinse and air drying. Conventional 
cleaning, sulfuric acid treatment and sandblasting alone without the above 
anodizing or etching are not sufficiently effective for use in this 
invention. 
I have found that a poorly prepared or contaminated surface cannot be 
modified to give significantly stronger adhesion to the resin core by use 
of a primer. However, primers can be applied to active phosphoric 
acid--anodized surfaces without reducing adhesion to the resin core if 
desired. 
The resins or polymers used to form the core between the metal sheets of 
the structural laminate of the present invention can be any desired type 
of thermoset resin having a desired curing mechanism or thermoplastic 
resin having a desired forming temperature which will provide the overall 
strength properties appropriate for use according to the present 
invention. The strength of the structural laminate of the present 
invention is provided in part by the strength properties of the resin used 
and in part by the bond strength between the resin and the surfaces of the 
metal sheets. The resin must be sufficiently tough (impact resistant) and 
rigid (high shear modulus) to provide adequate strength in the laminate. 
If the resin is too rigid, however, bonding to the metal surface is likely 
to be inadequate and the resin may be too brittle to provide good impact 
resistance. Therefore, the resin should have some flexibility to provide 
good bonding to the metal and good impact resistance. However, the resin 
should not be so flexible that it does not have sufficiently high shear 
modulus to provide the desired rigidity of the laminate. As is the case in 
formulating resins in many other uses, the desired properties are often 
competing and mutually exclusive and in order to achieve the desired 
overall characteristics of the laminate, a compromise or balance of 
particular properties is necessary. Following the examples and disclosure 
contained herein, one skilled in the art will be able to select, formulate 
and test the resin desired for a particular structural laminate to easily 
determine if a particular resin is useful for a particular application and 
will provide a laminate having characteristics according to this 
invention. In the event the desired characteristics for the laminate are 
not achieved initially with a particular resin, one skilled in the art, 
following the teaching of the disclosure herein, will be able to 
reformulate the resin to adjust the desired properties of the resin or 
change the surface preparation in order to provide the desired laminate 
having the characteristics of the laminates of this invention. 
The various properties to be considered in selection of a polymer or resin 
for the core include the following. A liquid thermoset resin before it is 
cured should have a low viscosity to enable rapid and efficient mixing 
with catalyst or curing agent, the reinforcing material, density-reducing 
filler and to allow easy application by spraying in the fabrication of the 
laminate. The resin should have sufficient work time and be compatible 
with the fillers to be used. During the curing of the resin, any exotherm, 
gas evolution, volume change, and the like should be minimal and not 
interfere with the structure or properties of the final laminate. A 
thermoplastic resin should have a melt or forming temperature in a desired 
working range and should have a sufficiently low viscosity at that 
temperature to intimately contact the prepared metal surfaces and form a 
good bond therewith upon cooling. Similarly, the thermoplastic resin 
should be in a form to enable sufficient mixing with other components 
present and to minimize air or gas entrapment. 
The reinforcing material added to the polymer or resin to increase the 
strength of the polymer resin core will in general be various conventional 
materials used to form reinforced resin compositions. Any resin 
reinforcing material such as fibers, flakes, ribbons, filaments and the 
like, which function in the laminate of this invention to provide the 
necessary tensile strength and shear modulus of the core without 
interfering with the bond of the resin core to the metal sheets, may be 
used. Fiber reforcing materials can be present either as chopped fibers or 
in the form of woven fabrics or in nonwoven or mat configurations. 
However, since the preferred method of fabricating the structural 
laminates of the present invention involve mixing the liquid resin and 
fillers and then casting or spraying the resin mixture on one of the metal 
sheets or injecting the liquid resin containing the fibers between the two 
metal sheets, it is generally preferred to use the fibers in a chopped 
form. The same is true for flakes, ribbons, filaments and the like which 
can be chopped. A preferred method involves chopping the reinforcing 
material at the point where the resin is sprayed up to form the laminate. 
Reinforcing fibers useful in the present invention include fiberglass, 
carbon fibers, graphite fibers, aramid fibers, metal fibers and other 
organic and inorganic fibers. The formulation and use of particular 
reinforcing fibers with particular resin systems are known in the art; see 
Handbook of Reinforcements for Plastics, Milewski, et al., Van Nostrand 
Reinhold, New York (1987). The selection of appropriate fibers for the 
desired properties and for compatibility with the resin system being used 
will be apparent to one skilled in the art following the teachings of this 
disclosure. 
The filler used in the resin core to lower the density of the core may be a 
foaming agent or blowing agent conventionally used to foam various resins, 
known by those skilled in the art. The desired specific gravity of the 
cured, reinforced, filled resin core in this invention should be in the 
range of about 0.8 to about 1.5, preferably about 0.85 to about 1.3. A 
preferred filler for providing this desired density of the resin core is 
glass microballoon filler or other expanded material which may have an 
average diameter up to about 1 millimeter, preferably between about 20 and 
about 300 microns, and more preferably in the range of about 30 microns to 
about 200 microns. Such microballoons fillers for resins are well known in 
the art as described in Handbook of Fillers for Plastics, Katz, et al., 
Van Nostrand Reinhold, New York (1987), pages 437-452. In some 
formulations the microballoons are preferred because they improve the 
impact resistance of the laminate of this invention and because they 
provide a more easily controlled manufacturing process and an easier to 
obtain uniformity than gaseous foaming agents. The microballoons used 
should preferably have a resin-compatible surface or coupling agents may 
be used to enhance the compatibility and the bonding of the resin to the 
surface of the microballoons. For example, when glass or ceramic 
microballoons are used in unsaturated polyesters or vinyl esters a silane 
coupling agent is desirable. This is similar to the use of coupling agents 
with fiberglass in reinforced resin systems. See Katz, et al., referred to 
above, pages 63-115. In some cases it may be desirable to include other 
additives such as wetting and suspending agents. Other fillers can also be 
used which increase the specific gravity of the core. But, for lower 
density cores and lighter weight laminates the microballoons and foaming 
agents are preferred. 
The selection of polymers for use in the present invention can be 
facilitated by selecting a polymer which provides the desired properties 
when cured or heated with the reinforcing fibers and the fillers present. 
The cured or hardened core is preferred to have a shear modulus, as 
defined herein, of at least about 40,000 psi for preferred structural 
laminates. Formulating a fiber reinforced, filled resin composition which 
will cure or melt and set to have the desired shear modulus is within the 
skill of the art. Resin core compositions producing cores having a lower 
shear modulus may be used when the strength requirements of the laminate 
are lower or when the laminate is intended for non-structural uses. In 
such cases the shear modulus of the core may be as low as about 20,000 or 
30,000 psi, but at least about 35,000 psi is usually preferred. The shear 
modulus of the cured reinforced filled resin core, without the metal 
sheets present is determined as described below. 
An additional criterion for selecting polymers or polymer systems for use 
in this invention is the requirement that the neat polymer bond 
sufficiently to the metal surface with a bond strength sufficient to 
provide an ASTM D1002-72 lap shear strength (using neat resin) of at least 
1000 psi. For non-structural uses the lap shear strength can be as low as 
about 500 psi but preferably is at least about 700 psi. This lap shear 
strength test using neat resin reliably predicts whether the filled and 
reinforced resin core in the laminate structure, including the metal 
sheets, will fail by delamination when stressed in bending or subjected to 
impact. The test could not be used to predict, however, whether a laminate 
will fail due to cracking of a core which is too brittle or due to a core 
which is too flexible. 
In accordance with the test methods and calculations set forth in the 
following section, the properties of the structural laminates and panels 
of this invention, which provide the improved performance in various 
applications, such as in trailer body construction, are the one or more of 
following: 
1. A tensile yield strength of at least about 2,000 lb. per in. width and 
preferably at least about 2,500 lb./in. 
2. A flexural modulus of at least about 1.75.times.10.sup.6 psi, or at 
least about 2.5.times.10.sup.6 psi for a 0.30 inch thick laminate, 
preferably at least about 3.times.10.sup.6 psi, and more preferably at 
least about 4.times.10.sup.6 psi. 
3. A shear modulus of the core of at least about 20 ksi, preferably at 
least about 33 ksi and more preferably at least about 40 ksi. 
4. A rigidity index of at least about 2000, preferably at least about 3000, 
more preferably at least about 4000 and most preferably at least about 
4500. 
5. Pass the falling ball impact test described herein with no delamination 
of the core and the metal sheets and no cracks in the core. 
6. Have moisture resistance whereby the laminate retains at least 70% of 
the dry flexural modulus and impact resistance after exposure of a 1 inch 
wide cut test specimen to liquid water for one month at 65.degree. F. to 
75.degree. F., and preferably a retention of at least 80% of dry flexural 
modulus and impact resistance after exposure of the test specimen to 
liquid water at 65.degree. F. to 75.degree. F. for two months. 
TEST METHODS AND CALCULATIONS 
With the exception of impact resistance, all of the panel properties 
mentioned in the Examples herein were determined by standard methods, as 
follows: 
Core Specific Gravity. This was calculated from the measured weight and 
dimensions of a panel sample and from the known weight of the metal 
facings for that sample. 
Tensile Strength. Laminates were tested according to ASTM method D 838-84 
(Type III), aluminum plate by ASTM B 209 and FRP plywood by ASTM D 
3500-76. 
Flexural Properties. Test specimens 1.times.6 in. in size were evaluated in 
a 3-point bending test essentially in accordance with ASTM method D 
790-84a, Method I using a 5.5-in. support span and a loading rate of 0.1 
in./min. Typically, stress-strain plots for aluminum-faced laminates such 
as those listed in Table I were linear up to a load of 250 lb., with a 
corresponding deflection of 0.060 in. Flexural modulus was calculated 
using equation 5. The test was terminated when the specimen deflection at 
midspan reached 0.275 in. (5% of the support span as recommended), or 
earlier if the sample failed before reaching 0.275 in. deflection. 
Flexural Modulus. This property was calculated using equation (5) in ASTM 
method D 790-84a, where it is called "tangent modulus of elasticity". 
##EQU1## 
where E(B)=flexural modulus, psi (1 ksi=1000 psi) 
L=support span, in. 
m=deflection force, lb./in., i.e. force required for 1 in. deflection in 
3-point bending stiffness test, lb./in. (=P / .DELTA. , with P and .DELTA. 
as defined below); 
b=test specimen width, in. 
d=specimen thickness, in. 
The flexural modulus is widely used as a measure of rigidity of plastics 
and of composites. It is useful for comparisons of gross material 
properties, but it provides no information on the relative contributions 
of the facings and of the core in sandwich laminates. Deductions from 
comparisons of the E(B) values of different laminates are difficult to 
draw if there is considerable variation in total laminate thickness d, as 
has been the case in the present work. Shear Modulus. To permit a more 
meaningful comparison of laminate properties, and in particular to assess 
the separate contributions of the facings and the core, the shear modulus 
of the core was calculated from the 3-point bending test results using the 
following relationship: 
##EQU2## 
where G(c)=shear modulus of core, psi (1 ksi=1000 psi) of the core 
K(s)=shear deflection constant=0.25 
P=load on specimen, lb. 
.DELTA.=deflection due to load at midspan in elastic regime, in. 
K(b)=bending deflection constant=0.02083 
D=specimen stiffness, lb.-in.= 
=E(f)t(f)h.sup.2 b / 2(1-.mu..sup.2) 
E(f)=tensile modulus of facing material, psi(10.1 million psi for the 
aluminum alloys used here) 
t(f)=facing thickness, in. 
t(c)=core thickness, in. 
h=centroid distance=t(c)+t(f) (if both facings are of the same thickness) 
b=width of the test specimen, in. 
.mu.=Poisson's ratio (=0.33 for aluminum) 
(1-.mu..sup.2)=0.89 for aluminum. 
The above relationship is based on derivations of relevant formulas for 
stress analysis published in several references. One of the more recent 
appeared in Engineered Materials Handbook, Vol.1, Composites, p.328, ASM 
International, Metals Park, Ohio, 1987. 
Rigidity Index. This composite measure of panel utility was calculated 
using the relationship 
##EQU3## 
where R. I.=rigidity index 
b=panel test specimen width, in. 
d=panel thickness, in. 
W=panel basis weight, lb./sq.ft. 
The rigidity index is a dimensionless value representing the rigidity of 
the panel--expressed as the calculated force needed for a deflection of 1 
in. at midspan in the 3-point bending test in the elastic regime--per unit 
panel thickness and per unit panel basis weight. The force m is identical 
with the factor m in equation 5 in ASTM test D 790. This force was 
calculated from measured deflections that were considerably less than 1 
in. Typically, they were less than 0.07 in. At higher deflections the 
stress-strain relationship began to depart from linearity. It should also 
be noted that R. I. values are only comparable if based on the same 
support span length (L above) in the 3-point bending test. In this 
disclosure, all R. I. values are based on measurements with a support span 
of L=5.5 in. 
Impact Resistance. The only non-standard procedure used in the present work 
was the falling ball impact test. It was conducted as follows. The test 
specimen was a 1.times.6 in. section of the laminate or panel being 
investigated (laminate, FRP plywood, or 0.25 in. aluminum plate), 
identical in size with that used in the 3-point bending test. As shown in 
FIG. 2, the specimen 21 was placed with its long dimension A across the 
gap B between two 1 in. wide and 4 in. long pieces 22 of 0.2 in. thick 
aluminum plate fastened 2.0 in. apart to a flat base plate 23, also made 
of 0.25 aluminum. The base plate was 4.times.9 in. in size, and rested on 
a smooth, level concrete floor. A 2.75-in. steel sphere 24, weighing 3.0 
lb. and held by an eyelet 26, was dropped through a 3 in. inner diameter 
plastic guide pipe 25 onto the center of the test specimen from a height C 
of 18 in. The specimen tested was inspected for signs of delamination 
between the facings and the core (or in the case of plywood, between 
plies) and of cracking of the core. Ratings were assigned to both 
properties ranging from 0 for severe failure to 5 for no visible effect. 
In addition, the maximum permanent deflection of the test strip was 
recorded. For the 0.25 aluminum plate, only the deflection was measured, 
of course. 
Lap Shear Strength. This property was determined in accordance with ASTM 
method D1002-72 using catalyzed neat resins (without filler or 
reinforcement) on 1.times.6 in. strips of metal sheet, with an overlap of 
0.5 in. Assembled specimens were cured under low pressure (3-5 psi) for 2 
hours at 212.degree. F. Tests were carried out with an Instron tester at a 
crosshead speed of 0.05 in./min. 
Having disclosed this invention in the above disclosure, I include the 
following examples and embodiments of the invention to illustrate how this 
invention is practiced by one skilled in the art following the teachings 
herein. 
EXAMPLE I 
Small-Scale Preparation of Laminate 
Frame. Single 12.times.18 in. (305.times.457 mm) panels were assembled in a 
specially designed frame with reusable edge inserts. The frame consisted 
of a 12.times.20 in. (305.times.508 mm) base plate made of 0.25 in. (6.3 
mm) thick aluminum with a 1-in. (25 mm) wide, 0.5 in. (13 mm) thick 
polypropylene bar bolted to one of the 12-in. edges. The principal purpose 
of the reusable edge inserts, which were equal in thickness to the desired 
core thickness, was to ensure separation of the face sheets at the proper 
distance, and to prevent liquid resin from exuding prior to gelation. 
Another function of the long inserts was to provide panels with a recessed 
core at the edges, allowing insertion of a solid metal splice for 
subsequent joining of two panels. 
A cross section of the frame for fabricating 12.times.18 in. laminates is 
shown in FIG. 3a. The 18-in. inserts consisted of steel strips 3 covered 
with 0.03 or 0.06 in. (0.76 or 1.52 mm) thick polypropylene sheet 4, with 
an overall thickness equal to the desired core thickness. The inserts were 
attached to other metal strips 5 so that the whole insert assembly would 
firmly fit over the edge of the bottom facing 1 and the base plate 2. The 
18-in. inserts were 1.5 in. (38 mm) wide. Inserts for the 12-in. edges 
(about 9 in. long) were of the same thickness but were inserted loosely. 
They were constrained within the sandwich panel by the bolted-on 
polypropylene bar on one side, and by small C-clamps on the other. After 
assembly as described below, the top facing 7 was finally secured with a 
0.25-in. (6.3 mm) thick aluminum cover plate 8 to the spacers and the base 
plate with clamps at the pressure points 9, and the panel was allowed to 
cure. 
For some of the tests, panels were prepared in smaller sizes, generally 
6.times.12 in. (152.times.305 mm). The procedure was similar, with the 
exception that removable inserts were placed loosely only along the 
shorter (6 in.) edges, while solid 1.times.0.5 in. polypropylene bars 
bolted to the base plate on the outside of the longer (12 in. edges) acted 
as barriers to keep the viscous, uncured core mixture confined within the 
sandwich panel. In cases where less viscous resins tended to exude from 
the core before curing (especially under pressure after the top sheet was 
clamped down), 1-in. wide masking tape was used to seal the long edges. 
The removable inserts were made of aluminum loosely covered with 
polypropylene sheet, or of solid polypropylene. 
Facings. These were typically 0.047 to 0.051 in. (1.19 to 1.29 mm) thick, 
12.times.18 in. (305.times.457 mm) or 6 x 12 in. sheets of 5052-H32 or 
5052-H34 aluminum alloy. After evaluation of various possible surface 
treatments, a standard procedure was adopted for preparing the surface for 
tests of other variables. The aluminum was cleaned by vapor degreasing 
with trichloroethylene at atmospheric pressure for 5 min., followed by 
immersion in a commercial mild alkaline cleaner (a dilute sodium carbonate 
solution with an added surfactant) for 30 sec. at 50.degree. C., and then 
anodized in 10%w phosphoric acid at 10 volts and a current density of 10 
amperes/sq. ft. (108 A/sq. meter) for 5 min. at 113.degree. F. (45.degree. 
C.). Rectified 3-phase current with less than 5% ripple was used. A lead 
sheet served as the cathode. Anodized sheets were rinsed and dried with 
air heated to 120.degree. F. (50.degree. C.). 
Resin Mixture B. To a blend of 275 g Koppers 1063-5 orthophthalic polyester 
resin (now sold as "Reichhold Polylite 51-020" Koppers Co.) and of 275 g 
Derakane 8084 vinyl ester resin (Dow Chemical Co.) was added with mixing, 
in the sequence listed, 0.137 g (0.025 parts per hundred parts of resin 
(phr)) N,N-dimethylaniline (DMA); 1.10 g cobalt naphthenate (0.20 phr) 
with a cobalt content of 6%; 8.80 g (1.60 phr) methyl ethyl ketone 
peroxide (MEKP) solution with a nominal active oxygen content of 9%; 27.5 
g (5 phr) Dicaperl HP 210 glass microballoons (Grefco) and 55 g (10 phr) 
CR 352 fiberglass roving (Owens Corning Fiberglas), cut to 0.50-in. 
length. The resulting mixture had the consistency of a putty, with a gel 
time of about 25 min. at 68.degree. F. (20.degree. C.). 
Resin Mixture D. To 550 g Derakane 8084 vinyl ester resin was similarly 
added with mixing 0.275 g (0.05 phr) DMA; 2.25 g (0.4 phr) cobalt 
napthenate, 9.60 g (1.75 phr) MEKP solution; 22 g (4 phr) Dicaperl HP 210 
microballoons and 55 g (10 phr) CR 352 fiberglass roving, 0.5 in. long. 
This mixture had a similar consistency, with a gel time of about 40 min. 
at 68.degree. F. 
Fabrication. An anodized sheet serving as the bottom facing was placed on 
the assembly frame and fastened to the base plate with the two 18 in. 
(45.72 cm) long inserts. The short inserts were placed along the narrower 
edges of the sheet. They had been cut to a length about 0.16 in. (4 mm) 
shorter than the distance between the long inserts, providing for a gap 
through which air and a small amount of liquid resin could escape during 
assembly of the panel. The freshly catalyzed resin mixture, prepared as 
described above, was then evenly spread on the bottom facing between the 
inserts, making certain that the top surfaces of the inserts remained 
clean and dry. The second facing sheet and the cover plate were then 
placed on top and secured to the frame with clamps. 
Cure. The whole assembly was allowed to stand at ambient temperature for 
about 1 hour and then placed in an oven for 2 hours at 100.degree. C. 
After cooling, the panel was separated from the frame and, after removal 
of the inserts, was used for testing. Panels prepared with the removable 
inserts had a recessed core along at least two edges as shown in FIG. 3b. 
This edge design allowed panels to be fastened together with internal 
metal joining strips as described in a later Example. 
Laminate Properties. Test specimens were cut from the cured panels with a 
saw. All rough edges were filed smooth. The cores contained very few 
visible air bubbles trapped during mixing and assembly. The glass fibers 
appeared moderately well dispersed. All water exposures were carried out 
with specimens cut to the proper dimensions for the various tests. 
The results of the tests of two representative laminates are summarized in 
Table I. Also listed for comparison are test results for two other 
structural panel materials used commercially in truck trailers, namely 
nominal 1/4-in. aluminum plate as well as FRP (fiberglass-reinforced 
plastic-faced) plywood of two thicknesses--3/4 and 5/8 in. - widely used 
in trailer manufacture. These thicknesses refer to the nominal thickness 
of the plywood core. The performance properties shown in Table I include 
tensile strength, elongation at break during the tensile test, rigidity, 
flexural modulus, and impact resistance. The rigidity index is a 
calculated composite property. The test procedures and methods of 
calculation are described more fully in an earlier section. The rigidity 
index is a measure of the utility of a structural laminate in applications 
such as truck trailers where the most desirable properties include high 
rigidity, low thickness and low weight. 
The results show that the structural laminates of this invention were equal 
or superior in rigidity (in its most direct measure, the deflection force 
m) to both of the above types of commercial panel materials, but were 
lower in basis weight (weight per unit area) than the aluminum plate and 
the 3/4-in. FRP plywood, and in the same range as 5/8 in. FRP. The 
flexural modulus of the laminates of this invention exceeded that of other 
composite laminates of similar thickness reported in the literature. It 
was considerably higher than that of FRP plywood, and more than 50% of 
that of the solid aluminum plate. The tensile yield strength of the 
laminates of this invention was in a similar range as that of FRP plywood 
(that of solid aluminum plate is unnecessarily high). 
After exposure to water, my laminates were clearly superior to FRP plywood, 
which had lost nearly half of its rigidity and one-quarter to one-third of 
its tensile strength. Examination of samples of the laminates of this 
invention after forced mechanical separation of the facings showed no 
evidence that the bond-metal interface had been weakened by water. As 
indicated above, the laminate and plywood specimens exposed to water prior 
to rigidity and impact testing were 1.times.6 in. in size. Since the cores 
were exposed at the edges, the maximum distance over which water had to 
diffuse was only 0.5 in. for wetting of the resin or of the resin-metal 
bond. Other than a slight reduction in rigidity due to the effect of 
moisture, there was no loss in the laminates of this invention in 
important properties of the magnitude encountered with FRP plywood. 
The laminates of this invention matched 1/4-in. aluminum plate in the 
falling ball impact test, displaying similar permanent deflection without 
core failure or delamination. Both types of FRP plywood, on the other 
hand, failed the impact test when dry. Considering that my laminate is 
significantly thinner than FRP plywood, closely approaching the low 
thickness of the heavier 1/4-in. aluminum plate, its advantages in 
applications such as truck trailer panels are evident. This is also 
reflected in the rigidity index values of the laminates of this invention, 
which are significantly higher than those of the other two types of panel 
materials. 
TABLE I 
__________________________________________________________________________ 
Properties of Panels 
__________________________________________________________________________ 
Panel Elonga- 
Panel 
basis 
Tensile strength 
tion 
thickness 
weight 
lb./in. width 
at break 
Sample 
Panel composition (a, b) 
in. lb./sq. ft. 
Yield 
Ultimate 
% 
__________________________________________________________________________ 
New laminated with reinforced, filled resin core 
0.051 in. aluminum facings, 5052-H34 alloy, resin mixture B 
I-1 At 50% rel. humidity 
0.322 
2.56 3350 
4330 5 
I-2 At 50% rel. humidity 
0.320 
2.58 
I-2 After 2 months in water 
0.322 
2.59 
0.050 in. aluminum facings, 5052-H32 alloy, resin mixture D 
I-3 At 50% rel. humidity 
0.319 
2.45 2845 
3590 
I-3 After 3 months in water 
0.321 
2.45 2820 
3525 
Aluminum plate; properties in rolling direction 
I-4 5052-H32 alloy; properties 
0.26 3.70 6315 
9516 13 
FRP plywood; nominal 3/4 in. core, with 0.044 in. (ave.) inside and 
outside FRP 
facings properties parallel to face grain 
I-5 At 50% rel. humidity 
0.786 
2.92 4320 
4790 4 
I-5 After 12 days in water 
0.827 
4.55 2900 
3550 5 
FRP plywood; nominal 5/8 in. core, with 0.038 in. inside and 0.047 in 
(ave.) outside 
FRP facings properties parallel to face grain 
I-6 At 50% rel. humidity 
0.645 
2.44 2700 
3960 2 
I-6 After 12 days in water 
0.679 
3.73 2150 
2800 
__________________________________________________________________________ 
3-Point bending test 
Deflection 
Maximum 
Core shear 
Flexural Impact resistance 
force m 
deflection 
modulus 
modulus 
Rigidity Deflection 
Sample 
lb./in. 
in. ksi ksi index 
Rating 
in. 
__________________________________________________________________________ 
New laminated with reinforced, filled resin core 
0.051 in. aluminum facings, 5052-H34 alloy, resin mixture B 
I-1 -- -- -- -- -- 
I-2 4350 &gt;0.275 
79 5469 5215 5 0.06 
I-2 3845 &gt;0.275 
70 4790 4610 5 0.08 
0.050 in. aluminum facings, 5052-H32 alloy, resin mixture D 
I-3 4000 &gt;0.275 
64 5126 5120 5 0.06 
I-3 3570 &gt;0.275 
55 4489 4540 5 0.09 
Aluminum plate; properties in rolling direction 
I-4 3690 &gt;0.275 
-- 8728 3875 5 0.06 
FRP plywood; nominal 3/4 in. core, with 0.044 in. (ave.) inside and 
outside FRP 
facings properties parallel to face grain 
I-5 4354 0.110 
.sup. 18 (b) 
353 1895 3 0 
I-5 2390 0.270 261 635 5 0 
FRP plywood; nominal 5/8 in. core, with 0.038 in. inside and 0.047 in 
(ave.) outside 
FRP facings properties parallel to face grain 
I-6 2900 0.180 
.sup. 18 (b) 
450 1840 4 0 
I-6 1835 &gt;0.275 244 725 5 0 
__________________________________________________________________________ 
(a) Details in Example 1. 
(b) Calculated from tests of aluminumfaced laminates with 0.25 in. plywoo 
core 
EXAMPLE 11 
Effect of Facing Material 
Although the preferred facing material is aluminum, other metals can also 
be used to advantage. In this example, the laminates of this invention are 
illustrated by panels which were prepared from 0.018 in. cold-rolled steel 
sheet (A.I.S.I. alloy 1015) that had been glass bead-blasted and then 
vapor-degreased with trichloroethylene. The core material was based on a 
polyamide-cured epoxy resin as indicated in Table II. Panels 6.times.12 
in. (152.times.305 mm) in size were prepared by a method similar to that 
described in Example I, and cured at 212.degree. F. (100.degree. C.) for 2 
hours. An aluminum-faced (5052-H32 alloy) panel was similarly prepared 
using the same resin system for the core. 
The test properties of both laminates are summarized in Table II. Since 
both laminates exhibited slight cracking of the core but no delamination 
in the impact test, another aluminum-faced panel was prepared in which a 
slightly more flexible epoxy resin mixture was used for the core. Its 
composition and the properties of the resulting laminate are also listed 
in Table II. This second aluminum panel passed the impact test with no 
sign of delamination or core cracking. This improvement was primarily due 
to the improved toughness of the resin which, however, also resulted in a 
lower shear modulus. Other tests have shown that the contribution of the 
slightly higher core thickness to the impact resistance of this panel was 
minor. 
TABLE II 
__________________________________________________________________________ 
Properties of Laminates 
3-Point bending test Impact 
Core resistance 
Panel 
Basis 
Core 
Deflection 
Maximum 
shear 
Flexural Deflec- 
Laminate composition 
thickness 
weight 
specific 
force m 
deflection 
modulus 
modulus tion 
Sample 
Facings 
Core (a) 
in. lb./sq. ft. 
gravity 
lb./in. 
in. ksi ksi Rating 
in. 
__________________________________________________________________________ 
II-1 
0.018 in. steel, 
Epoxy 0.260 
2.57 0.825 
3360 &gt;0.275 
61 7181 4 0.10 
bead-blasted 
formulation E 
II-2 
0.050 in. 
Epoxy 0.327 
2.42 0.831 
4000 &gt;0.275 
56 4759 4 0.07 
aluminum, 
formulation E 
phosphoric 
acid-anodized 
II-3 
0.050 in. 
Epoxy 0.346 
2.51 0.833 
4050 &gt;0.275 
44 4069 5 0.09 
aluminum, 
formulation E 
phosphoric 
acid-anodized 
__________________________________________________________________________ 
(a) Resin mixtures consisted of epoxy resin, 50 phr Ancamide 400 curing 
agent (Pacific Anchor), 4 phr HP 210 glass microballoons (Grefco), and 10 
phr chopped 0.5 in. CR 352 fiberglass (OwensCorning Fiberglas). Resin E 
was Epotuf 37139 (100%, Reichhold). Resin F was a blend of Eoptuf 37139 
(75% w) and DER 732 (25%, Dow). 
EXAMPLE III 
Effect of Aluminum Surface Treatment 
Panels were prepared from aluminum sheets that had been subjected to the 
most common treatments used in preparing the surface for coating, 
laminating or adhesive bonding. These included glass bead blasting, 
etching with caustic, treatment with a commercial aqueous alkaline 
formulation (Alodine 401), anodizing with sulfuric acid, treatment with 
sulfuric acid-dichromate solution (known as the Forest Products Laboratory 
or FPL etch), and anodizing with phosphoric acid. 
Three unsaturated polyester resin--vinyl ester resin blends were used for 
the cores as indicated in Table III. One blend, designated as Al in Table 
III, gave better results with phosphoric acid-anodized aluminum than with 
three other commercial surface treatments. Cores made with this blend were 
somewhat brittle, however, and impact resistance was limited. A somewhat 
different blend of the same two resins, designated A2, gave acceptable 
impact resistance but also resulted in a lower shear modulus and lower 
panel rigidity. 
Fully acceptable performance was obtained with resin Blend B, but here 
again only when the aluminum had been anodized with phosphoric acid or 
treated with the FPL etch. Not only did the laminates pass the impact test 
but they also displayed very good rigidity, due to a high shear modulus of 
the core, but without excessive brittleness. 
The results in Table III also illustrate the fact that to prevent 
delamination during the bending or impact tests, there must be a strong 
bond between the core and the facing. Bond strength can be estimated from 
lap shear strength tests with neat, catalyzed resin. These and other 
results of my work indicate a lap shear strength of at least 1000 psi is 
required. Even with an effectively bonding resin system such as blend B, 
only phosphoric acid anodizing or the FPL etch was capable of providing a 
sufficiently active aluminum surface to meet this requirement. 
TABLE III 
__________________________________________________________________________ 
Effect of Aluminum Surface Treatment 
__________________________________________________________________________ 
Panel composition 
Facing Panel 
Basis 
Sample 
Thickness thickness 
weight 
no. in. Alloy 
Surface treatment (a) 
Core (b) 
in. lb./sq. ft 
__________________________________________________________________________ 
III-1 
0.050 5052-H32 
Anodized w/H2SO4 Resin blend A1 
0.329 
2.44 
III-2 
" " Anodized w/H2SO4, sealed 
" 0.344 
2.48 
III-3 
" " Treated w/Alodine 401 
" 0.350 
2.49 
III-4 
" " Anodized w/H3PO4 " 0.312 
2.43 
III-5 
" " Anodized w/H3PO4 Resin blend A2 
0.292 
2.56 
III-6 
0.047 5052-H34 
Degreased & cleaned 
Resin blend B 
0.311 
2.41 
III-7 
" " Bead-blasted " 0.325 
2.52 
III-8 
" " Etched with caustic 
" 0.305 
2.31 
III-9 
" " Anodized w/H2SO4 " 0.313 
2.36 
III-10 
" " Treated w/Alodine 401 
" 0.315 
2.48 
III-11 
" " Anodized w/H3PO4 " 0.315 
2.51 
III-12 
0.050 5052-H32 
Etched w/H2SO4 + Na2CrO7 (FPL) 
" 0.329 
2.49 
__________________________________________________________________________ 
3-pt. bending test Neat resin 
Deflection 
Maximum 
Core shear 
Impact resistance 
lap shear 
Sample force m 
deflection 
modulus Deflection 
strength 
no. lb./in. 
in. ksi Rating 
in. psi 
__________________________________________________________________________ 
III-1 5370 &gt;0.276 
67 3 0.09 605 
III-2 5620 &gt;0.275 
70 3 0.05 570 
III-3 5110 0.121 52 1 0.11 400 
III-4 5160 &gt;0.275 
77 4 0.08 1620 
III-5 2880 0.187 41 5 0.09 1620 
III-6 (c) 0.045 (c) 0 (c) &lt;400 
III-7 (c) 0.012 (c) 1 0.25 540 
III-8 (c) (c) (c) 0 (c) 930 
III-9 (c) 0.020 (c) 1 0.20 700 
III-10 (c) 0.010 (c) 1 0.33 410 
III-11 5050 &gt;0.275 
76 5 0.07 2020 
III-12 5140 &gt;0.275 
59 5 0.05 1990 
__________________________________________________________________________ 
(a) Details in Example III. 
(b) Core compositions: 
A1 Blend of 6246 isopthalic polyester resin (67% w, Koppers) and Derakan 
8084 vinyl ester (33%, Dow) with 0.015 phr DMA, 0.15 phr cobalt 
naphthenate, 1.6 phr MEK peroxide, 8 phr HP 210 microballoons and 10 phr 
CR 352 0.5 in. chopped fiberglass. 
A2 Similar to A1 but with 4 phr instead of 8 phr HP 210 microballoons. 
B Blend of 10635 orthophthalic polyester (50% w, Koppers) and Derakane 
8084 (50%), with 5 phr HP 210 microballoons and 10 phr CR 352 chopped 0.5 
in. fiberglass. Initiator system as described in Example I. 
(c) Delamination prevented accurate measurement. 
EXAMPLE IV 
Effect of Microballoons and Foaming Agents 
Laminates were prepared from 6.times.12 in. (152.times.305 mm) sheets of 
phosphoric acid-anodized aluminum by a similar procedure as described in 
Example I. Several different grades of microballoons were added to 
determine their effects on specific gravity of the core and on key 
laminate properties. Two chemical blowing agents were similarly evaluated. 
All resin mixtures contained chopped fiberglass reinforcement and were 
catalyzed with methyl ethyl ketone peroxide. The laminates were cured 2 
hr. at 212.degree. F. (100.degree. C.). Additional data on laminate 
compositions are listed in Table IVa. The microballoons and chemical 
blowing agents are described in Table IVb. To show the relationships 
between microballoon concentration and laminate properties more clearly, 
relevant data have been plotted in FIGS. 4 and 5. 
The results led to the following conclusions: 
1. All of the microballoon grades and blowing agents tested were effective 
in reducing the specific gravity of the core significantly. In a number of 
cases, core density reductions of 30% were readily achieved without loss 
in important laminate properties. The corresponding reduction of specific 
laminate weight, ranging around 15%, represents important savings in 
materials weight and cost, and in vehicles such as trailers can 
additionally improve fuel economy. 
2. Microballoons can contribute to rigidity. FIGS. 4 and 5 show that over 
certain concentration ranges, glass microballoons as well as polymeric 
microspheres can increase core shear modulus up to a point. With higher 
add-ons, the volume ratio occupied by glass-reinforced resin declines to a 
point where both rigidity as well as impact resistance suffer. Core 
compositions can thus be designed to have the best desired balance of 
weight and performance properties. 
3. Chemical blowing agents appear to be less effective in retaining impact 
resistance as core density is reduced. The production process is also more 
difficult to control, since concentrations of the blowing agent and of the 
MEK peroxide as well as curing schedules must be closely controlled so as 
to properly synchronize gas production and foaming with polymerization and 
gelling of the resin. Furthermore, it is also generally more difficult to 
achieve uniform distribution of the reinforcing fibers in the foamed core. 
In other tests some of the compositions listed in Table IVa were applied 
with a commercial airless spray gun ("chopper" gun) at nozzle pressures in 
the 400-700 psi range. At these pressures, some of the microballoon grades 
listed in the Table appeared to be crushed, with the result that cured 
resin mixtures displayed higher than expected densities. Other grades, 
such as Q-CEL 2106 and the Expancel products, were relatively unaffected. 
Measured densities of the cured cores were in close agreement with values 
calculated from the known densities of cured, glass-reinforced resins and 
from the true densities of the dry microballoons. Low-pressure spray gun 
designs are available than can dispense resin mixtures containing some of 
the more fragile microballoon grades without crushing or breaking them. 
TABLE IVa 
__________________________________________________________________________ 
Effect of Microballoons and Foaming Agents 
__________________________________________________________________________ 
Panel composition 
Core (a) 
Facing Low-density 
Panel Basis 
Thickness additive thickness 
weight 
Sample 
in. Alloy 
Resin Grade phr 
in. lb./sq. ft. 
__________________________________________________________________________ 
IV-1 
0.050 5052-H32 
Blend B 
None 0 0.290 2.65 
IV-2 
" " " HP 210 5.0 
0.292 2.60 
IV-3 
" " " " 8.0 
0.314 2.57 
IV-4 
" " " " 12.0 
0.325 2.46 
IV-5 
" " " HP 510 8.0 
0.322 2.46 
IV-6 
0.047 5052-H34 
" HP 210 5.0 
0.319 2.66 
IV-7 
" " " HP 220 5.0 
0.330 2.48 
IV-8 
" " " HP 520 8.0 
0.327 2.51 
IV-9 
0.050 5052-H32 
" Q-CEL 200 
8.0 
0.318 2.41 
IV-10 
" " " Q-CEL 600 
8.0 
0.321 2.49 
IV-11 
0.051 5052-H34 
" Q-CEL 2106 
9.0 
0.342 2.60 
IV-12 
0.047 " " EX 461 DE 
2.0 
0.334 2.42 
IV-13 
0.051 " " EX 551 DE 
0.7 
0.309 2.55 
IV-14 
" " " " 0.9 
0.319 2.57 
IV-15 
" " " " 1.0 
0.306 2.42 
IV-16 
" " " " 1.3 
0.312 2.41 
IV-17 
" " " Cel. XP100 
1.7 
0.351 2.57 
IV-18 
" " B608-64 (b) 
Luperfoam 
1.0 
0.295 2.37 
__________________________________________________________________________ 
3-Point bending test 
Core Deflection 
Maximum 
Core shear Impact resistance 
specific 
force m 
deflection 
modulus 
Rigidity Deflection 
Sample 
gravity 
lb./in. 
in. ksi index 
Rating 
in. 
__________________________________________________________________________ 
IV-1 
1.223 
3450 &gt;0.275 
76 4490 5 0.11 
IV-2 
1.157 
3705 &gt;0.275 
95 4880 5 0.09 
IV-3 
1.010 
4350 &gt;0.275 
98 5400 5 0.08 
IV-4 
0.872 
4340 &gt;0.275 
75 5430 3 0.04 
IV-5 
0.886 
3850 &gt;0.275 
54 4850 5 0.09 
IV-6 
1.115 
4350 &gt;0.275 
97 5130 5 0.07 
IV-7 
0.905 
4150 &gt;0.275 
60 5030 4 0.05 
IV-8 
0.950 
4310 0.252 
76 5250 4 0.04 
IV-9 
0.851 
4000 &gt;0.275 
66 5230 5 0.07 
IV-10 
0.913 
3580 &gt;0.275 
45 4470 5 0.07 
IV-11 
0.903 
4675 &gt;0.275 
67 5270 5 0.04 
IV-12 
0.813 
4260 &gt;0.275 
53 5110 5 0.06 
IV-13 
1.007 
3710 &gt;0.275 
61 4700 5 0.10 
IV-14 
0.970 
4000 &gt;0.275 
63 4890 5 0.09 
IV-15 
0.892 
3760 &gt;0.275 
68 5090 5 0.08 
IV-16 
0.857 
4000 &gt;0.275 
73 5330 5 0.06 
IV-17 
0.905 
5245 &gt;0.275 
92 5830 4 0.06 
IV-18 
0.896 
3333 &gt;0.275 
58 4770 3 0.07 
__________________________________________________________________________ 
(a) Blend B consisted of 10635 polyester (50% w) and Derakane 8084 vinyl 
ester (50%). The initiator system was as described in Example I. Resin 
mixtures contained 10 phr CR 352 fiberglass (0.5 in.), except nos. IV13 
through 17, where 10 phr chopped 0.75 in. CL 392 fiberglass (Certainteed 
Corp.) was used. Lowdensity additives are listed in Table IVb. 
(b) Supplied by Koppers Co., for use with Luperfoam 329 system (Pennwalt 
Corp.). No DMA or cobalt was added; MEK peroxide addon was 2.0 phr. 
TABLE IVb 
__________________________________________________________________________ 
Microballoons and Foaming Agents 
Bulk density 
Particle 
Grade Supplier 
Composition g/cm.sup.- 3 
size, .mu.m 
Comments 
__________________________________________________________________________ 
Dicaperl HP 210 
Grefco, Inc. 
Glass microballoons 
0.08 110 Ave. 
Surface-modified 
Dicaperl HP 510 
" " 0.11 70 Ave. 
" 
Dicaperl HP 220 
" " 0.08 110 Ave. 
Surface modifier different 
Dicaperl HP 520 
" " 0.11 70 Ave. 
from the on HP 210 and 520 
Q-CEL 200 
PQ Corp. 
" 0.40 20-200 
Surface-modified 
Q-CED 600 
" " 0.20 62 Ave. 
" 
Q-CEL 2106 
" " 0.20 60 Ave. 
" 
Expancel 561 DE 
Nobel Expanded copolymer 
0.05 40-60 
Industries AB 
microspheres 
Expancel 551 DE 
Nobel Expanded copolymer 
0.036 40-60 
Industries AB 
microspheres 
Celogen XP100 
Uniroyal, Inc. 
Sulfonylhadrazide 
-- -- Reacts with peroxide to form 
nitrogen gas 
blowing agent 
Luperfoam 329 
Pennwalt Corp. 
Alkyl hydrazinium chloride 
-- Reacts with peroxide to form 
nitrogen gas 
and ferric chloride 
__________________________________________________________________________ 
EXAMPLE V 
Effect of Fiber Reinforcement 
Laminates were prepared from 6.times.12-in. (152.times.305 mm) sheets of 
phosphoric acid-anodized aluminum by a procedure similar to that in 
Example I. The core mixtures were based on a vinyl ester and an 
orthophthalic polyester resin as indicated in Table V. In one series, 
chopped fiberglass was incorporated in concentrations from zero to 20 phr 
in a resin mixture containing 10 phr Dicaperl HP 510 glass microballoons. 
The results are listed in Table V and plotted in FIG. 6. It can be seen 
that in the absence of any fiber reinforcement, laminate rigidity was low, 
and the core failed the falling ball impact test. With increasing levels 
of reinforcement, rigidity and impact resistance rose noticeably. Core 
density also rose with increasing fiberglass concentration, of course. 
In another series with a somewhat different resin and microballoon grade, 
10 phr fiberglass was compared with 5 phr cut Aramid fiber and 5 phr cut 
graphite fiber. As the results in Table V show, both of the latter fibers 
yielded acceptable, albeit somewhat less rigid laminates than the higher 
concentrations of glass. 
TABLE V 
__________________________________________________________________________ 
Effect of Fiber Reinforcement of Laminate Properties 
__________________________________________________________________________ 
Panel composition 
Facing Core (a) Panel Basis 
Thickness Fiber reinforcement 
Filler thickness 
weight 
Sample 
in. Alloy 
Resin 
Type (b) 
phr 
Grade 
phr 
in. lb./sq. ft 
__________________________________________________________________________ 
V-1 0.050 5052-H32 
D8084 
Glass CR352 
10 HP 210 
5 0.336 2.62 
V-2 " " " Graphite 
5 " 0.348 2.72 
V-3 " " " Aramid 5 " 0.343 2.57 
V-4 0.047 5052-H34 
Blend B 
Glass CL292 
0 HP 510 
10 0.268 2.17 
V-5 " " " " 5 " " 0.345 2.53 
V-6 " " " " 10 " " 0.340 2.54 
V-7 " " " " 15 " " 0.325 2.52 
V-8 " " " " 20 " " 0.345 2.68 
__________________________________________________________________________ 
3-Point bending test 
Core Deflection 
Maximum 
Core shear 
Flexural Impact resistance 
specific 
force m 
deflection 
modulus 
modulus 
Rigidity Deflection 
Sample 
gravity 
lb./in. 
in. ksi ksi index 
Rating 
in. 
__________________________________________________________________________ 
V-1 0.959 4340 &gt;0.275 
61 4768 4940 5.0 0.05 
V-2 0.994 5000 &gt;0.275 
76 4935 5720 5.0 0.08 
V-3 0.893 4765 &gt;0.275 
71 4909 5400 5.0 0.10 
V-4 0.820 2500 &gt;0.275 
45 5403 4300 1.5 0.20 
V-5 0.853 4400 &gt;0.275 
54 4457 5050 4.5 0.11 
V-6 0.879 4425 &gt;0.275 
60 4681 5120 4.5 0.09 
V-7 0.924 4095 &gt;0.275 
62 4964 5000 5.0 0.10 
V-8 0.969 4800 &gt;0.275 
70 4863 5200 5.0 0.10 
__________________________________________________________________________ 
(a) Resins were Derakane 8084 and Blend B, with the composition given in 
Table IVa. 
(b) Fiber reinforcements: Graphite from Hexcel 716 hybrid fabric, cut to 
0.5 in. length. Aramid from Hexcel 281 Kevlar (TM) 49 Fabric, cut to 0.5 
in. length. Glass OwensCorning Fiberglas CR 352211 roving cut to 0.5 in. 
and Certainteed CL 292207 roving cut to 0.75 in. length. 
EXAMPLE VI 
Effect of Resin Selection on Laminate Properties 
With respect to the selection of resins for structural laminates, I have 
used primarily unsaturated polyesters and vinyl esters for the above 
Examples. Although a number of different resin types are effective for the 
cores of the present invention structural laminates, unsaturated 
polyesters and vinyl esters are of special interest because of their 
relatively low viscosity, good compatibility with fillers and reinforcing 
agents, controllable cure over a wide range of temperatures, and low to 
moderate cost. Additional resin types also investigated included epoxies, 
polyester-polyurethane hybrids, polyurethanes and others. 
Following procedures similar to that described in Example I, the resins in 
this Example were mixed with initiator/curing agent, Dicaperl HP 210 
microballoons and fiberglass as indicated in Table VIa, and used for the 
preparation of metal-faced laminates. The metal facings were phosphoric 
acid-anodized aluminum. The laminates were generally cured for 2 hours at 
212.degree. F. Representative panel compositions and performance test 
results are summarized in Table VIa. Resin suppliers and curing agents or 
catalysts are listed in Table VIb. 
As can be seen from the results, only some of the many tested polyester and 
vinyl ester resins were effective for high performance structural panels, 
but could be used in less demanding applications. The majority of resins 
gave panels that either delaminated or cracked in the falling ball impact 
test or 3-point bending stiffness test, or that were not sufficiently 
rigid in the latter test. In other words, such resins displayed 
insufficient bonding to the anodized metal and/or were too brittle. Some 
resins bonded well but were too soft. 
The difficulty in selecting suitable resins for particular uses of the 
laminates of this invention reflects primarily the conflicting 
requirements for strong adhesion to metal and impact resistance, which is 
generally enhanced by resin toughness and some degree of flexibility, and 
for rigidity, which is usually also accompanied by brittleness. These 
competing and conflicting requirements for resin performance and 
properties are not unlike those encountered in formulating resin systems 
for other uses, such as protective and decorative resin coatings, resin 
castings, etc. It has not been possible to predict the performance in the 
laminates of this invention of a given resin from published resin data, 
which are generally limited to tensile strength, tensile modulus, 
elongation at yield and flexural strength and modulus of the neat cured 
resin or of resin reinforced with one or two levels of a specific fiber. 
The limited data that have been published for the resins evaluated here 
are listed in Table VIa. 
In some cases, brittleness and poor bonding (as with Koppers 1063-5 
orthophthalic polyester) could be overcome by blending with a more 
flexible, tougher resin such as Dow Derakane 8084 vinyl ester. In most 
other cases, however, blending of a brittle resin with a more flexible 
resin did not yield an acceptable high performance structural laminate 
product, nor did addition of isoprene, a flexibilizing comonomer, under 
the same relatively mild curing conditions. When the cure time at 
100.degree. C. was increased to 5 hours, however, the laminate did show 
acceptable rigidity as well as impact resistance. 
Several tests, not shown in the Tables, confirmed that resin systems such 
as blend B used with MEKP catalyst gave nearly as good laminate properties 
after ambient-temperature cure (64.degree.-69.degree. F.) for a week than 
after the usual 2-hour cure at 212.degree. F. 
The epoxy resins that were evaluated were based on Reichhold Epotuf 37-139, 
a purified form of the most basic epoxy resin, the diglycidyl ether of 
Bisphenol-A. As the results in Table VIa indicate, the resin failed the 
impact test when cured with tetraethylene triamine. It performed only 
slightly better when cured with a type of polyamide commonly used in 
adhesive applications. But, when blended with Dow DER 732, a more flexible 
epoxy resin, the laminate displayed good impact resistance. As the results 
show, however, the improvement in toughness was accompanied by some 
reduction in core shear modulus and rigidity. 
Another interesting resin type was Dow SpectrimTM 354, a polyurethane used 
commercially for reaction injection molding. This system consisted of MM 
354 A isocyanate and MM 383 B polyol. The catalyst was 0.05 phr Dabco 33 
triethylenediamine, which gave a gel time of 20 minutes for the filled, 
reinforced mixture at 55.degree. F. Although this system appeared to have 
cured significantly in 1 hour at 70.degree. F., the assembled laminate was 
subjected to a similar 2-hour post-cure at 212.degree. F. as all the other 
resins. Due to absorption of some atmospheric moisture during hand mixing 
in an open vessel, some carbon dioxide was produced. The foam that was 
produced made it necessary to reduce the add-on of HP 210 glass 
microballoons to 3 phr. Also, to maintain core shear modulus, the 
fiberglass add-on had to be raised from 10 to 15 phr. With these changes, 
the resulting laminate performed acceptably. 
Another group of resins offering some of the processing and performance 
characteristics of unsaturated polyesters as well as of polyurethanes are 
the so-called polyester-urethane hybrids. Two Amoco Xycon (TM) 
two-component systems were tested and found to perform quite well. The 
systems consisted of a polyisocyanate (A component) and a solution of an 
unsaturated polyester polyol in styrene (B component). The A and B 
components, which already contained a proprietary catalyst, were mixed in 
the weight ratios recommended by the manufacturer. Microballoons and 
fiberglass were subsequently mixed in as in the other preparations herein. 
The final resin mixtures had gel times of 15-25 min. at 60.degree. F. Most 
of the assembled laminates were cured for two hours at 212.degree. F. One 
laminate was allowed to cure at ambient temperature (64.degree.-68.degree. 
F.) for one week. The resulting laminates generally performed well. Data 
for a laminate cured at 212.degree. F. are shown in Table VIa. The 
laminate possessed good rigidity and did not crack or delaminate in the 
falling ball impact test. 
Although aluminum-faced laminates are not considered to present any 
significant flammability hazard, enhanced flame retardance of the core may 
be desirable in some applications. A laminate was therefore prepared from 
a commercial brominated vinyl ester (Hetron FR 992) to which 3 phr 
antimony oxide had been added as recommended by the supplier. As the 
results in Table VIa indicate, the laminate did not pass the impact test 
but displayed adequate rigidity. Flammability was compared using 1.times.6 
in. (25.times.152 mm) strips of laminate in horizontal and vertical burn 
tests similar to UL 94 (Underwriters Laboratories). A non-flame-retarded 
laminate (sample VI-8, based on resin Blend B) barely supported combustion 
after about 60 seconds' exposure to the burner flame, but 
self-extinguished immediately after the ignition source was removed. The 
flame-retarded laminate (sample VI-24), on the other hand, did not even 
appear to support combustion. The relatively high thermal conductivity of 
the aluminum facings clearly kept temperatures in the combustion zone 
below the level required to sustain the combustion even of the 
non-flame-retarded laminate. 
The performance of particular resins in the laminates of this invention is 
somewhat unpredictable, as indicated above. As in other applications 
requiring materials with complex combinations of properties, the 
effectivess of candidate resins will have to be determined experimentally, 
that is, by preparing laminates and subjecting them to the above-mentioned 
and other appropriate performance tests to determine which resin or resin 
system gives the desired performance characteristics and properties 
according to this invention. However, the lap shear test described herein 
provides a predictable method of predicting resin performance in the resin 
to metal bond property, without having to construct and test the entire 
laminate. 
TABLE VIa 
__________________________________________________________________________ 
Performance of Resins in Laminates (a) 
__________________________________________________________________________ 
Curing 
Neat cured resin properties 
Filler 
agent 
Measured 
Published in 
Resin (b) or lap shear 
Tensile 
Elongation 
Flex. mod. 
core 
Sample 
Grade Type catalyst 
psi ksi % ksi phr 
__________________________________________________________________________ 
Preferred resins for structure laminates 
VI-1 
D8084 VE MEKP 2540 10 10 550 5 
VI-2 
" " 4 
VI-3 
Spectrim 354A-383B 
PU TEDA 2240 NA NA NA 2 
VI-4 
R37-139/DER732 75:25 w 
Epoxy 
PA 2200 NA NA NA 4 
VI-5 
Xycon HX21107 Hybrid 
Peroxide 
2110 NA NA NA 12 
VI-6 
" 5 
VI-7 
R37-139/DER732 83:17 w 
Epoxy 
TETA 2020 NA NA NA 4 
VI-8 
D8084/K1063-5 50:50 w 
VE/OP 
MEKP 1940 NA NA NA 5 
VI-9 
" " 5 
VI-10 
K6908 IP " 1680 NA 2 NA 4 
VI-11 
K6641T IP " 1610 10 2 540 5 
Less effective resins for structural laminates (c) 
VI-12 
RE37-139 Epoxy 
PA 1990 NA NA NA 4 
VI-13 
TAP Isophthalic 
IP MEKP 1750 NA NA NA 3 
VI-14 
K7000A BPA " 1650 8.5 
4 420 8 
VI-15 
D411-45 VE " 1615 11 5 450 5 
VI-16 
R33-072/K87-186 75:25 
OP/IP 
" 1490 NA NA NA 8 
VI-17 
K87-186/K1063-5 25:75 
IP/OP 
" 1480 NA NA NA 5 
VI-18 
K6631T IP " 1450 9 2 520 5 
VI-19 
K1211-5 OP " 1310 2 55 NA 8 
VI-20 
K3102-5 OP " 1310 5 7 200 8 
VI-21 
K87-186 IP " 1270 NA 50 NA 5 
VI-22 
HET 700 BPA " 1100 NA 2 NA 5 
VI-23 
K1063-5 + 10 phr isoprene 
OP " 1085 NA NA NA 5 
VI-24 
HET FR992 VE " 1060 12 5 540 5 
VI-25 
K6246 IP " 1045 11 4 460 4 
VI-26 
K1063-5 OP " 1020 9 2 640 3 
VI-27 
R33-072 OP " 940 5.3 
1 600 8 
__________________________________________________________________________ 
Laminate properties 
Facing 
Panel 
Basis 
Core Deflection 
Maximum 
Core shear 
Flexural Impact 
thickness 
thickness 
weight 
specific 
force m 
deflection 
modulus 
modulus 
Rigidity 
resistance 
Sample 
in. in. lb./sq. ft 
gravity 
lb./in. 
in. ksi ksi index 
rating 
__________________________________________________________________________ 
Preferred resins for structure laminates 
VI-1 
0.047 
0.303 
2.31 0.874 
3428 &gt;0.275 
58 5127 4908 5 
VI-2 
0.050 
0.319 
2.45 0.884 
4000 &gt;0.275 
64 5126 5120 5 
VI-3 
0.051 
0.343 
2.46 0.793 
4083 &gt;0.275 
45 4209 4830 5 
VI-4 
0.050 
0.346 
2.51 0.833 
4051 &gt;0.275 
43 4069 4671 5 
VI-5 
0.047 
0.351 
2.46 0.830 
4500 &gt;0.275 
56 4329 5202 5 
VI-6 
0.050 
0.340 
2.68 0.989 
4166 &gt;0.275 
50 4410 4579 5 
VI-7 
0.050 
0.308 
2.53 1.009 
3484 &gt;0.275 
52 4962 4466 5 
VI-8 
0.047 
0.315 
2.39 0.896 
4000 &gt;0.275 
76 5324 5324 5 
VI-9 
0.051 
0.320 
2.58 0.980 
4308 &gt;0.275 
78 5469 5215 5 
VI-10 
0.050 
0.325 
2.68 1.055 
4000 &gt;0.275 
57 4847 4598 5 
VI-11 
0.050 
0.329 
2.50 0.890 
4166 &gt;0.275 
60 4867 5062 5 
Less effective resins for structural laminates (c) 
VI-12 
0.050 
0.327 
2.42 0.831 
4000 &gt;0.275 
55 4759 5050 4 
VI-13 
0.050 
0.315 
2.73 1.156 
1960 &gt;0.275 
15 2610 2276 5 
VI-14 
0.050 
0.303 
2.14 0.663 
3218 &gt;0.275 
46 4813 4960 1 
VI-15 
0.047 
0.322 
2.51 0.971 
4354 &gt;0.275 
89 5426 5394 4 
VI-16 
0.050 
0.307 
2.42 0.906 
4000 0.231 
84 5751 5391 0 
VI-17 
0.050 
0.303 
2.48 0.984 
3703 &gt;0.275 
70 5539 4928 2 
VI-18 
0.050 
0.320 
2.46 0.894 
3571 &gt;0.275 
45 4534 4528 2 
VI-19 
0.050 
0.317 
2.32 0.775 
1545 &gt;0.275 
10 2018 2104 5 
VI-20 
0.050 
0.325 
2.29 0.730 
3454 0.071 
39 4186 4631 2 
VI-21 
0.050 
0.310 
2.45 0.927 
3030 &gt;0.275 
35 4231 3984 5 
VI-22 
0.047 
0.307 
2.41 0.949 
3790 0.260 
76 5446 5128 2 
VI-23 
0.051 
0.336 
2.74 1.043 
2143 &gt;0.275 
15 2350 2327 5 
VI-24 
0.051 
0.315 
2.51 0.936 
4032 &gt;0.275 
70 5367 5106 4 
VI-25 
0.050 
0.298 
2.46 0.993 
3400 &gt;0.275 
59 5344 4629 0 
VI-26 
0.051 
0.303 
2.64 1.118 
3850 &gt;0.275 
106 6188 5174 3 
VI-27 
0.050 
0.313 
2.48 0.933 
4036 &gt;0.275 
75 5476 5310 0 
__________________________________________________________________________ 
(a) Details in Example VI. All core compositions were reinforced with 10 
phr CR 352 or CL 292 chopped fiberglass, except sample VI3, which 
contained 15 phr. 
(b) Resin sources and initiator systems are listed in Table VIb. 
(c) When used in similar formulations as preferred resins. 
TABLE VIb 
__________________________________________________________________________ 
Resins Used in Laminate Cores (a) 
Curing agent 
Cobalt (c) 
Dimethyl 
Resin Resin or catalyst 
6% sol'n. 
aniline 
Sample 
Grade Type supplier Type (b) 
phr 
phr (DMA), 
__________________________________________________________________________ 
phr 
VI-1 
Derakane (TM) 8084 
VE Dow Chemical Co. 
MEKP 1.75 
0.4 0.05 
VI-3 
Spectrim (TM) 354A/383B 
PU " TEDA 0.05 
-- -- 
VI-4 
R37-139/DER732 75:25 w 
Epoxy 
See VI-12 & VI-28 
PA 50 -- -- 
VI-5 
Xycon HX21107 
Hybrid 
Amoco Chemical Co. 
Peroxide 
(e) 
-- -- 
VI-7 
R37-139/DER732 83:17 w 
Epoxy 
See VI-12 & VI-29 
TETA 14 -- -- 
VI-8 
D8084/K1063-5 50:50 w 
VE/OP 
See VI-1 & VI-18 
MEKP 1.60 
0.2 0.02 
VI-10 
Polyester resin 6908 
IP Koppers Co. " 1.25 
-- -- 
VI-11 
Polyester resin 6641T 
IP " " 1.50 
-- -- 
VI-12 
RE37-139 Epoxy 
Reichhold Chemicals, Inc. 
PA 50 -- -- 
VI-13 
TAP Isophthalic 
IP TAP Plastics, Inc. 
MEKP 1.50 
-- -- 
VI-14 
K7000A BPA Koppers Co. " 1.50 
-- -- 
VI-15 
D411-45 VE Dow Chemical Co. 
" 1.70 
0.4 0.05 
VI-16 
R33-072/K87-186 75:25 
OP/IP 
See VI-27 & VI-21 
" 1.50 
-- -- 
VI-17 
K87-186/K1063-5 25:75 
IP/OP 
See VI-21 & VI-26 
" 1.50 
-- -- 
VI-18 
Polyester resin 6631T 
OP Koppers Co. " 1.50 
-- -- 
VI-19 
Polyester resin 1211-5 
IP " " 1.50 
-- -- 
VI-20 
Polyester resin 3102-5 
OP " " 1.50 
-- -- 
VI-21 
Polyester resin 87-186 
OP " " 1.50 
0.3 -- 
VI-22 
Hetron (TM) 700 
IP Ashland Chemical CO. 
" 1.50 
-- -- 
VI-23 
K1063-5 + 10 phr isoprene 
OP See VI-26 " 1.50 
-- -- 
VI-24 
Hetron FR 992 
BPA Ashland Chemical Co. 
" 1.50 
0.4 -- 
VI-25 
Polyester resin 6246 
VE Koppers Co. " 1.50 
0.3 0.05 
VI-26 
Polyester resin 1063-5 
IP Koppers Co. " 1.50 
0.4 -- 
VI-27 
Polylite (TM) 33-072 
OP Reichhold Chemicals, Inc. 
" 1.50 
0.3 0.05 
VI-28 
Polyester resin B 608-84 
OP Koppers Co. " 1.50 
-- -- 
VI-29 
D.E.R. 732 Epoxy 
Dow Chemical Co. 
-- -- -- -- 
__________________________________________________________________________ 
(a) Core mixtures consisted of resin, curing agent/catalyst, cobalt and 
DMA as indicated in Tables VIa and Vib. 
(b) MEKP = methyl ethyl ketone peroxide (9% active oxygen); TEDA = 
triethylene diamine (Air Products Dabco 33LV) TETA = triethylene tetramin 
(Pacific Anchor Teta); PA = polyamide (Pacific Anchor Ancamide 400). 
(c) Cobalt naphthenate solution. 
(d) With 3% antimony oxide added to core mixture for increased fire 
retardance 
(e) Proprietary peroxide incorporated in resin by supplier; none added in 
present work. 
EXAMPLE VII 
Laminate from Pre-Formed Cores 
Although it is more convenient and more economical to prepare the present 
laminates from liquid core resins that are cured in situ, the laminates of 
this invention can also be fabricated by bonding active metal facings to 
preformed cores with an adhesive. 
Thus 1.times.6 in. strips of the cured core from a panel that had 
delaminated (sample III-8, listed in Table III above) were sanded, wiped 
with trichloroethylene and bonded to phosphoric acid-anodized aluminum 
facings with an epoxy resin blend known to give an acceptable structural 
laminate. The assembled laminate was cured for 2 hours at 212.degree. F. 
under moderate pressure. As indicated in Table VII, the laminate had good 
impact resistance and displayed excellent rigidity. 
Also tested were laminates in which the preformed core was plywood and 
nylon 66 thermoplastic resin. In the case of the plywood, the bonding 
resin was a vinyl ester. The cured 6.times.12-in. laminate displayed good 
metal-core bonding but failed in the impact as well as in the 3-point 
bending stiffness test due to interply delamination within the plywood. 
The core shear modulus obtained from the 3-point bending stiffness test 
was low, in the range expected from data previously published for plywood 
(cf. R. C. Mitzner, P. W. Post and G. A. Ziegler, "Plywood Overlaid With 
Metal", Publication C235, American Plywood Association, Tacoma, WA 
(1979)). A plywood core laminate can also be formed using a thermoplastic 
resin to bond the plywood to the prepared aluminum surfaces. For example, 
an over dry plywood (3-5% moisture) can be used with an emulsion or slurry 
of thermoplastic resin. After heating to bond the plywood to the metal 
with the resin, the plywood will have a normal moisture content (5-10%). 
Other core materials useful in the laminates of this invention include 
reconstituted wood products, such as hardboard (sometimes referred to as 
"Masonite panels"), particleboard and flakeboard, which materials can be 
bonded to the prepared or activated metal surface with thermoset or 
thermoplastic resin. Other thermoplastic resins useful herein include a 
latex type resin (an example of which is commercially available as 
"Elmers" adhesive), such as an emulsion polymer based on vinyl acrylate 
copolymers. 
The nylon-cored laminate was prepared by placing a trichloroethylene-wiped 
1.times.6 in. strip of nylon 66 between two strips of phosphoric 
acid-anodized aluminum, wrapping the assembly with aluminum foil to 
prevent the softened nylon from deforming excessively, and heating the 
assembly under light pressure to incipient melting at 520.degree. F. After 
cooling and conditioning at 68.degree. F. and 50% relative humidity for 2 
days (which was probably too short for the sample to come to equilibrium), 
the laminate was tested. As shown in Table VII, bending stiffness was 
fair; the calculated core shear modulus was slightly below the minimum 
value acceptable for structural use in trailer panels. Since water is 
known to be a plasticizer for nylon, it is expected that with longer 
conditioning at this humidity the shear modulus would have been lower. At 
higher humidities, even lower stiffness would be likely. Thus, this 
laminate normally would be suitable only for less demanding structural 
uses or other uses, such as non-structural, and for use where humidity 
would not present a problem. Because of the higher density of nylon, the 
very high processing temperatures required (even if the laminate were 
prepared from freshly extruded, molding-grade nylon pellets), and the 
relatively high cost of the resin, nylon 66 is less preferred for the 
present laminates than the liquid thermosetting resins mentioned earlier. 
TABLE VII 
__________________________________________________________________________ 
Properties of Laminates from Pre-Formed Cores 
__________________________________________________________________________ 
Panel composition Resin used 
Facing to bond 
Panel 
Thickness Pre-formed core facings 
thickness 
Weight 
Sample 
& alloy 
Material (a) 
Fiberglass 
Filler to core (b) 
in. lb./sq. ft 
__________________________________________________________________________ 
VII-1 
0.050 in. 
Plywood (c) 
None None D8084 0.343 2.23 
5052-H32 
(APA grade A-A) 
VII-2 
0.047 in. 
Resin blend B 
10 phr CR 352 
10 phr HP210 
Epoxy C 
0.303 2.49 
5052-H34 
(from III-8) 
VII-3 
0.047 in. 
Nylon 66 sheet 
None None None (d) 
0.341 2.84 
5052-H34 
(d) 
__________________________________________________________________________ 
3-Point bending test 
Core Deflection 
Maximum 
Core shear 
Flexural Impact resistance 
specific 
force m 
deflection 
modulus 
modulus 
Rigidity Deflection 
Sample gravity 
lb./in. 
in. ksi ksi index 
Rating 
in. 
__________________________________________________________________________ 
VII-1 0.625 
2430 0.150 
18 2514 3185 3 0.10 
VII-2 1.045 
3835 &gt;0.275 
89 5732 5080 5 0.05 
VII-3 1.152 
3670 &gt;0.275 
39 3847 3790 5 0.13 
__________________________________________________________________________ 
(a) Blend B with composition listed in Table IVa. 
(b) D8084: Derakane 8084 vinyl ester. Epoxy C: Blend of Epotuf 370139 
(Reichhold) and DER 732 (Dow) epoxy resins in 75:25 weight ratio, with 50 
phr Ancamide 400 polyamide as curing agent. 
(c) Plywood APA Grade AA, 0.25 in. thick, bonded to facings with resin 
free of fillers or reinforcements. 
(d) Bonded by heating assembled sandwich to 520 F. for 6 min., until nylo 
began to melt. 
EXAMPLE VIIl 
Effect of Aluminum Surface Preparation and Resin Reinforcement on 
Thermoplastic Core Laminate Properties 
Materials. The facings for all the laminates prepared for this Example were 
0.051 in. thick 5052-H34 aluminum sheet. Unanodized aluminum sheets were 
first degreasd with hot trichloroethylene and then cleaned further by 
treatment with Oakite 164, a commerical alkaline cleaner, at a 
concentration of 5 oz./gal. for 5 minutes at 170.degree. F., and then 
rinsed and dried. In the preparation of anodized sheets, the metal was 
first degreased by treatment with 5% phosphoric acid containing 1% of a 
nonionic surfactant (Van Waters & Rogers 681-C) for 1 min. at 150.degree. 
F., rinsed, then treated with 10% sodium hydroxide for 2 min. at 
150.degree. F. The sheet was next anodized on both sides in 18% phosphoric 
acid for 8 min. at 100.degree. F., using a voltage of 23 V to obtain a 
current density of 10 amperes/sq.ft. total surface, and then was rinsed 
and dried. The anodized metal had been stored at ambient temperature for 
16 months before being used in the present tests. During this time its 
surface reactivity declined to some extent, as evidenced by a decrease in 
lap shear strength from about 2000 psi to about 1400 psi when metal 
specimens were bonded with a blend of unsaturated polyester resins as 
indicated in Table VIa of this application, samples VI-8 and VI-9. 
However, the surface reactivity remained sufficient for the tests of this 
Example. 
The resins used in this study were obtained from several suppliers (with 
designations as used in Table VIII): ICI Americas, Inc. (ICI), Amoco 
Chemical Co. (Am.), The BFGoodrich Co. (BFG), Alucobond Technologies, Inc. 
(Alucobond), and AIN Plastics, Inc. (AIN). Several of the resins were 
obtained as extruded pellets already compounded with 1/8 in. long 
fiberglasss reinforcement (samples 1, 2 and 12-15), one in thin sheet form 
(polypropylene, sample 9), and the remainder as powders. Although the 
commercial reinforced, pelleted PVC resin contained a heat stabilizer, the 
powdered PVC was not sufficiently stabilized as received. In two of the 
preparations (samples 16 and 17) the powdered PVC was therefore treated 
with 0.7% by weight of dibutyltin dilaurate. This stabilizer was added as 
a solution in xylene. After thorough blending, the material was heated to 
about 120.degree. F. (50.degree. C.) to allow the solvent to evaporate. 
Other thermoplastic resins can be selected from polyesters, 
polycarbonates, cellulosics, and other known thermoplastics using the 
criteria set forth herein for selection and properties. 
All of the reinforcements were fiberglass. The fiber length in the 
commercial pre-compounded pellets was 1/8 in. (samples 1, 2 and 12-15). In 
all other instances where the fibers were blended with powdered resins, 
the reinforcement was cut to length. Three grades were employed: 
Continuous type 352 roving from Owens-Corning Fiberglas Corp. (OCF) cut to 
1/4 in. length, type 3830 dry chopped 1/2 in. strand from PPG Industries, 
Inc., and type 457 wet chopped 1/4 in. strand, containing 12% moisture, 
also from OCF. 
The filler added to some of the formulations was Q-CEL 6263 inorganic 
microspheres from PQ Corp., with a reported true specific gravity of 0.26 
and an average particle size of 70 .mu.. 
Methods. All of the laminates were prepared from 6.times.6 in. sheets of 
aluminum, pretreated as shown in Table VIII, using molding frames, which 
were 10 in..times.10 in. aluminum sheets with cutouts slightly larger than 
6.times.6 in. The frames were 0.50 and 0.32 in. in thickness. After 
treatment with mold release, the frames were supported on a sheet of 0.25 
in. aluminum, and the bottom sheet of the laminate was placed into the 
cutout. A pre-weighed amount of core material was then added, and the top 
sheet applied. 
Core materials based on powdered polymers were mechanically blended in dry 
form, or in two instances (samples 4 and 5) were blended as aqueous 
slurries that were filtered through a 28 mesh screen (with 0.6 mm 
openings). The filtrates were recycled until they were substantially free 
of suspended solids. The resulting wet mats were dried for 6 hours at 
180.degree. F. (82.degree. C.) and then used for molding. 
Prior to molding, the frame assembly was covered with a polished steel 
sheet and then compressed in a preheated platen press. Platen temperatures 
were 450.degree.-460.degree. F. (232.degree.-238.degree. C.) for 
polypropylene, 405.degree.-410.degree. F. (207.degree.-210.degree. C.) for 
PVC, and 500.degree. F. (260.degree. C.) for ABS. Initially, powder 
mixtures were first partially molded in the 0.50 in. thick frame, and the 
hot laminates were transferred to the 0.32 in. frame for the final 
molding. Later the preliminary molding step was found to be unnecessary, 
and pellets as well as powder blends were all molded in the 0.32 in. 
frame. Platen pressures were 10,000 lb. for pellet-based laminates (277 
psi) and 5000 lb. for laminates made with powdered polymers (139 psi). 
Total molding times ranged from 5 to 8 min. About 1 min. before the end of 
a molding cycle, the press was briefly opened to allow escape of entrapped 
air and any other vapors. The pressure was then re-applied for the last 
minute of the molding cycle. The hot assembly was then removed and clamped 
between 0.25 in. aluminum sheets for cooling, which in most cases was 
accelerated by application of cold water. 
Testing. After cooling, the laminates were cut into 1 .times.6 in. test 
strips with a carbide-tipped radial saw and evaluated in the ASTM D 790 
3-point bending stiffness test and the falling ball impact tests as 
described previously. All tests were run at least in duplicate. 
Calculations of deflection force, shear modulus, flexural modulus and 
rigidity index were carried out as described previously. The results are 
summarized in Table VIII. 
Results. The most significant finding was that all of the laminates 
prepared with conventionally cleaned aluminum facings displayed poor 
interlaminar adhesion, and all delaminated either after molding or during 
sawing. Laminates prepared with phosphoric acid-anodized aluminum, on the 
other hand, showed significantly enhanced interlaminar adhesion, and in 
many cases displayed very good ridigity and impact resistance as well as 
light weight. 
Before discussing the results in more detail, it should be noted that in 
most laminates the measured core densities were lower than the theoretical 
values. This was primarily due to inadequate removal of entrapped air 
during the venting step in the molding cycle. In the case of PVC, the 
powder samples without added stabilizer (particularly sample 18) also 
showed signs of thermal decomposition. 
Of the polymer systems evaluated, glass-reinforced ABS and glass-reinforced 
PVC gave more rigid laminates than comparably reinforced polypropylene. As 
might be expected from the known toughness of the matrix polymer, unfilled 
ABS containing 20% glass fiber (25 phr based on the resin, sample 12) gave 
a more impact-resistant laminate than unfilled PVC with the same amount of 
reinforcement (sample 14). With a somewhat lower fiberglass content of 10 
phr and 10 phr added mmicrospheres, however, PVC gave a laminate of 
comparable rigidity (in terms of core shear modulus) and impact resistance 
(sample 18). As was observed in the tests with thermosetting resins 
described in earlier Examples, incorporation of microspheres not only 
reduced core density but also improved the impact resistance. The core 
shear modulus values of 68 ksi for these laminates approach those of the 
better glass-reinforced thermoset resins described in earlier Examples. 
Laminates from unreinforced PVC and anodized aluminum displayed good 
impact resistance, but with a core shear modulus of only 26 ksi, rigidity 
was not as high. 
Another advantageous feature of the laminates with PVC cores was their 
flame resistance. In experiments involving edgewise exposure of 1.times.6 
in. laminate strips to a flame, the polypropylene and ABS-containing cores 
readily supported combustion, while those based on PVC did not, and in 
fact were self-extinguishing. 
The data for polypropylene in Table VIII indicate that this polymer can 
yield laminates of acceptable impact resistance and moderate rigidity 
without reinforcement. With added fiberglass reinforcement, rigidity was 
improved, but not to the same high levels as with ABS or PVC. It should be 
noted that addition of microspheres enhanced rigidity in the dry-blended 
core material (sample 7 vs. 6) but not in the mat prepared from an aqueous 
slurry (sample 5 vs. 4). The reason was that exposure to water unfavorably 
affects the organophilic surface treatment applied by the producer to the 
microspheres, and compatibility with organic polymers is reduced. 
Conclusions. The results show that aluminum-faced sandwich laminates 
possessing high rigidity and impact resistance can be produced from 
thermoplastic core materials. Preferred laminates are produced when the 
aluminum facings have a strongly bonding surface, such as that obtained by 
anodizing with phosphoric acid, and the thermoplasic core material possess 
significant rigidity and impact resistance, both of which are enhanced by 
incorporation of fiber reinforcement as well as limited amounts of 
compatible microspheres. The microspheres offer the additional benefit of 
reducing weight. 
TABLE VIII 
__________________________________________________________________________ 
Effect of Aluminum Surface Preparation and Resin Reinforcement on 
Thermoplastic Core Laminate Properties 
__________________________________________________________________________ 
Aluminum 
facing (b) Core composition (c) Panel 
Panel 
surface Resin 
Fiberglass 
Filler 
integrity 
thickness 
Sample 
treatment 
Starting materials (resin supplier, grade) 
(c) Grade phr 
phr (d) in. 
__________________________________________________________________________ 
IX-1 
Anodized 
Resin/fiberglass pellets (ICI MF1004HS) 
PP N.A. 25 0 Good 0.288 
IX-2 
Cleaned only 
Resin/fiberglass pellets (ICI MF1004HS) 
PP N.A. 25 0 Delamin. 
0.29 
IX-3 
Anodized 
Resin powder (Am. 10-6400P) + fibers 
PP PPG 3830 
20 0 Good 0.306 
IX-4 
Anodized 
Resin powder (Am. 10 6400P) + fibers (e) 
PP OCF 457 
20 0 Good 0.32 
IX-5 
Anodized 
Resin powder (Am. 10-6400P) + fibers + filler 
PP) OCF 457 
20 10 Good 0.283 
IX-6 
Anodized 
Resin powder (Am. 10-7200P) + fibers 
PP OCF 352 
10 0 Good 0.300 
IX-7 
Anodized 
Resin powder (Am. 10-7200P) + fibers + filler 
PP OCF 352 
10 10 Good 0.285 
IX-8 
Cleaned only 
Resin powder (Am. 10-7200P) + fibers + filler 
PP OCF 352 
10 10 Delamin. 
0.28 
IX-9 
Anodized 
Polypropylene sheets 0.03 in. (AIN) 
PP 0 0 Good 0.305 
IX-10 
Anodized 
Resin powder (Am. 10-7200P) 
PP 0 0 Good 0.303 
IX-11 
Cleaned only 
Resin powder (Am. 10-7200P) 
PP 0 0 Delamin. 
0.29 
IX-12 
Anodized 
Resin/fiberglass pellets (ICI AF 1004) 
ABS N.A. 25 0 Good 0.311 
IX-13 
Cleaned only 
Resin/fiberglass pellets (ICI AF 1004) 
ABS N.A. 25 0 Delamin. 
0.31 
IX-14 
Anodized 
Resin/fiberglass pellets (BFG 802GR20) 
PVC N.A. 25 0 Good 0.397 
IX-15 
Cleaned only 
Resin/fiberglass pellets (BFG 802GR20) 
PVC N.A. 25 0 Delamin. 
0.40 
IX-16 
Anodized 
Resin powder (BFG 110X334) 
PVC PPG 3830 
20 0 Good 0.293 
IX-17 
Anodized 
Resin powder (BFG 110X334) 
PVC PPG 3830 
20 10 Good 0.295 
IX-18 
Anodized 
Resin powder (BFG 110X334) + fibers + filler 
PVC OCF 352 
10 10 Good 0.465 
IX-19 
Cleaned only 
Resin powder (BFG 110X334) + fibers + filler 
PVC OCF 352 
10 10 Delamin. 
0.45 
IX-20 
Anodized 
Resin powder (BFG 110X334) 
PVC 0 0 Good 0.287 
IX-21 
Cleaned only 
Resin powder (BFG 110X334) 
PVC 0 0 Delamin. 
0.45 
IX-22 
Unidentified 
Commercial laminate (Alucobond 6 mm) 
PE 0 0 Good 0.236 
IX-23 
Unidentified 
Commercial laminate (Alucobond 5 mm FR) 
CPVC 0 0 Good 0.200 
__________________________________________________________________________ 
3-Point bending test 
Basis 
Core Deflection 
Core shear 
Flexural Impact resistance 
weight 
specific 
force m 
modulus 
modulus 
Rigidity Deflection 
Sample 
lb./sq. ft 
gravity 
lb./in. 
ksi ksi index 
Rating 
in. 
__________________________________________________________________________ 
IX-1 
2.41 0.968 2881 44 5.016 
4157 2 0.47 
IX-2 
IX-3 
2.59 1.052 3263 44 4.739 
4124 3 0.46 
IX-4 
2.53 0.938 3361 39 4.267 
4146 5 0.08 
IX-5 
2.29 0.876 2429 32 4.457 
3739 2 0.27 
IX-6 
2.33 0.842 2700 31 4.160 
3851 5 0.12 
IX-7 
2.17 0.744 2627 37 4.720 
4231 4 0.12 
IX-8 
IX-9 
2.41 0.897 2775 31 4.069 
3781 5 0.15 
IX-10 
2.41 0.895 2558 27 3.826 
3509 2 0.51 
IX-11 
IX-12 
2.79 1.221 3917 69 5.417 
4500 5 0.08 
IX-13 
IX-14 
3.04 1.027 6260 68 4.162 
5174 3 0.20 
IX-15 
IX-16 
2.78 1.315 3214 54 5.316 
3950 5 0.11 
IX-17 
2.72 1.249 3507 68 5.684 
4364 5 0.07 
IX-18 
2.77 0.689 4533 22 1.876 
3517 4 0.04 
IX-19 
IX-20 
2.70 1.275 2299 26 4.045 
2969 5 0.12 
IX-21 
IX-22 
1.53 0.955 615 7 1.948 
1702 5 0.55 
IX-23 
1.29 0.878 727 20 3.782 
2823 5 0.45 
__________________________________________________________________________ 
(a) Laminates were prepared as described in Example VIII. 
(b) Facing thicknesses were 0.051 in. for samples 1 through 21, and 0.019 
in. for samples 22 and 23. 
(c) Details are given Example VIII. 
(d) Delamin. = Panel delaminated before or during sawing of test 
specimens. 
(e) Core materials formed as mat from aqueous slurry. 
Having described this invention in concept and general terms and having 
illustrated the invention with preferred embodiments and examples thereof, 
it is to be understood that these embodiments are capable of further 
variation and modification. Therefore, the present invention is not to be 
limited to any of the particular details of the embodiments set forth 
above, but is to be taken with such changes and variations as fall within 
the purview of the following claims.