Note: Descriptions are shown in the official language in which they were submitted.
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FOAMED CORE COMPOSITE PLATE
FOR USE IN HER WALLS AND DOORS
B~~:~GROUND OF THE I1WENTION
This invention is generally directed to a novel composite plate for a trailer
wall
construction or a trailer door construction. More particularly, the invention
contemplates a novel composite plate that has a foamed thermal plastic core
which
provides a variety of advantages over prior art solid core composite plates.
Composite plates having solid plastic cores for use in forming trailer walls
or
doors are known in the art. Such composite plates are formed from a pair of
metal
skins, formed of aluminum or steel, having a solid plastic core member, formed
of
polyethylene or polypropylene, sandwiched therebetween. The use of a solid
plastic
core member in a composite plate has worked reliably in the prior art,
however,
several disadvantages have been found.
Solid core composite plates tend to have low peel strength. That is, the metal
skins peel away from the plastic core with small force. Furthermore, with the
prior art
solid core member, a high shear stress is obtained as the plastic core
material changes
temperature and if the shear stress gets too high, then the metal skins can
delaminate
from the solid plastic core member.
2 o The present invention provides a novel composite plate having a foamed
thermal plastic core member that is used in a trailer wall construction or a
trailer door
construction which overcomes the disadvantages of using a prior art solid
plastic core
member in a composite plate. Other features and advantages will become
apparent
upon a reading of the objects and description taken in combination with a
study of the
2 5 drawings.
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OBJECTS AND SUM11~IARY OF THE INVENTION
A general object of the present invention is to provide a novel composite
plate
having a foamed thermal plastic core member which forms a wall or a door of a
vehicle, such as a trailer.
An object of the present invention is to provide a novel composite plate for a
trailer wall or door construction having a foamed thermal plastic core member
which
reduces the weight of the plate versus prior art solid core composite plates.
Another object of the present invention is to provide a novel composite plate
for a trailer wall or door construction having a foamed thermal plastic core
member
which increases the peel strength of the plate versus prior art solid core
composite
plates.
A further object of the present invention is to provide a composite plate for
a
trailer wall or door construction which reduces the shear stress of the skin
to core
bond layer so as to reduce the potential of delamination of the metal skins
from the
thermal plastic core member under changing temperatures.
Briefly, and in accordance with the foregoing, the present invention discloses
a
novel composite plate which is used to form a wall or a door of a vehicle,
such as a
trailer or van. Each composite plate used in the trailer is formed from a pair
of metal
skins, such as aluminum or steel, having a foamed thermal plastic core member
2 0 sandwiched therebetween. The skins are bonded to the core member by a
known
flexible adhesive layer. The foamed thermal plastic core member is resilient
and may
be made from foamed high density thermal plastic, such as polyethylene or
polypropylene, or foamed low density thermal plastic, such as polyethylene or
polypropylene, or other foamed thermal plastic.
2 5 To make the foamed core member used in the present invention, foaming
beads or pellets are first mixed with thermal plastic resin beads or pellets
by means of
an auger in a mixing chamber. The foaming pellets have a gas therein. The
mixed
pellets are subjected to heat in a hot die chamber and the foaming pellets
burst and
produce carbon dioxide or nitrogen to foam the mixture. The mixture is
extruded into
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a layei by an extruder to form the foamed core member. Thereafter, a layer of
flexible
adhesive is preferably applied to the inner surface of the skins by suitable
means, the
layer of flexible adhesive can be applied to the opposite sides of the foamed
thermal
plastic core member by like suitable means, an adhesive film can be co-
extruded on
both sides of the core member and laminated to the core member immediately, or
the
surfaces of the core member can be treated to become the adhesive bonding
layer such
that the skins can be directly bonded thereto. Thereafter, the metal skins are
adhered
to the core member by means of the flexible adhesive layer under pressure.
This
process may be continuous. It is envisioned that other means of foaming the
core
l0 member may be provided such as by injecting nitrogen into a heating chamber
in
which the thermal plastic resin pellets are being heated and are in a molten
state and
thereafter extruding the foamed core material into a core member, or by using
both the
nitrogen producing beads or pellets and the direct injection of nitrogen gas
into a
heating chamber in which the thermal plastic resin pellets and the nitrogen
producing
pellets are being heated.
BRIEF DESCRIPTION OF THE DRAWINGS
The organization and manner of the structure and operation of the invention,
together with further objects and advantages thereof, may best be understood
by
reference to the following description, taken in connection with the
accompanying
2 0 drawings, wherein like reference numerals identify like elements in which:
FIGURE 1 is a perspective view of a trailer having a plurality of composite
plates which incorporate the features of the invention and which form the
walls and
the rear doors thereof;
FIGURE 2 is a cross-sectional view of one of the plates of FIGURE 1; and
2 5 FIGURE 3 is a schematic view of an apparatus for forming one of the plates
of
FIGURES 1 and 2.
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While the invention may be susceptible to embodiment in different forms,
there is shown in the drawings, and herein will be described in detail, a
specific
embodiment with the understanding that the present disclosure is to be
considered an
exemplification of the principles of the invention, and is not intended to
limit the
invention to that as illustrated and described herein.
The present invention discloses a novel composite plate 20 for use in a wall
or
door construction of a vehicle, such as a trailer 22, as shown in FIGURE 1,
van or the
like. The trailer 22 is generally comprised of a floor 24, a roof 26, a front
wall 28, a
pair of opposite side walls 30 (only one of which is shown), rear cargo doors
32, a
landing gear 34, and an undercarriage assembly 36. As shown in FIGURE 1, the
trailer 22 is connected to a tractor 38 by conventional means, such as a fifth
wheel.
Each side wall 30 and the front wall 28 of the trailer 22 is formed from a
plurality of the novel composite plates 20 of the present invention which are
fastened
together by suitable means such as by riveting. Preferably, each composite
plate 20 is
rectangular having a height greater than its width. The composite plates 20
can be
relatively equal in size or the width and thickness of each plate 20 may vary.
When
composite plates 20 are used in the construction of the side walls 30 and the
front wall
28, each composite plate 20 is connected to the floor 24 and extends upwardly
2 0 therefrom and is attached to upper and lower rails of the trailer 20 by
suitable joining
members, such as bolts or rivets. When composite plates 20 are used in the
construction of the rear doors 32, outer composite plates 20 are connected to
the
respective side walls 30 of the trailer 22 by hinges. When closed the doors 32
extend
upwardly from the floor 24. Alternatively, each side wall 30 and the front
wall 28 of
2 5 the trailer 22 may be formed from one such continuous plate 20.
Attention is directed to FIGURE 2 which shows a cross-section of one of the
novel composite plates 20 used in the construction of the trailer walls 28, 30
and/or
doors 32. The composite plate 20 includes a pair of metal sheets or skins 40,
42
which are bonded to a foamed thermal plastic core member 44, described more
fully
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herein, which is sandwiched therebetween by a thin adhesive layer 46 (such
thickness
of the adhesive layer has been exaggerated in the drawings for clarity in
understanding
the invention). The skins 40, 42 are bonded to the foamed thermal plastic core
member 44 by means of a known flexible adhesive bonding film 46. Skin 40 forms
an inner surface of the trailer 22 and skin 42 forms an outer surface of the
trailer 22.
The metal skins 40, 42 used in the composite plate 20 of the present invention
are preferably formed of aluminum or full hard, high strength, high tension,
galvanized steel. Preferably, the each of the skins 40, 42 are formed from
galvanized
steel and preferably, the inner skin 40 is over nineteen thousandths of an
inch in
thickness and the outer skin 42 is over nineteen thousandths of an inch in
thickness.
The core member 44 is formed from a foamed thermal plastic, preferably
foamed high density polyethylene (HDPE) or high density polypropylene, which
makes the core member 44 resilient. That is, the core member 44 can flex
without
breaking. As shown in FIGURE 2, the core member 44 includes a plurality of air
bubbles 48 interspersed with the thermal plastic material 50. It has been
found that
molecular integrity of the core member 44 is not lost by the foaming of the
core
member 44 and peel strength is increased versus prior art composite plates
which use
a solid core member. That is, it_ takes a greater force to peel the metal
skins 40, 42
from the foamed thermal plastic core member 44 than in prior art solid core
composite
2 0 plates. This is described more fully herein. The foaming of the core
member 44
lowers the density of the thermal plastic and improves the strength to weight
ratio
thereof. Alternatively, the core member 44 may be made from foamed low density
thermal plastic, such as foamed low density polyethylene or low density
polypropylene. Low density thermal plastic will foam and produce a resilient
core
2 5 member, however, the resulting composite plate is not as stiff as when
foamed high
density thermal plastic is used in the composite plate. When foamed high
density
thermal plastic is used as the core member in the composite plate, the
composite plate
is approximately twice as stiff as when a foamed low density thermal plastic
is used as
the core member in the composite plate.
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The core member 44 preferably has a thickness of one half of an inch or less.
The core member 44 used in the present invention is thinner than prior art
solid cores
which are mush thicker, typically three quarters of an inch to four inches.
The foaming of the core member 44 reduces the weight of the composite plate
22 versus prior art solid core composite plates. Because the core member 44 is
foamed in the present invention and is not solid as in prior art composite
plates, the
amount of plastic resin used in formation of the core member 44 is reduced by
up to
50% versus prior art solid core composite plates.
As mentioned herein, the foaming of the thermal plastic core member 44 also
increases the peel strength of the resulting composite plate 20. When the
composite
plate 22 is subjected to peel forces, that is, the skins 40, 42 are grasped
opposite of
each other and the skins 40, 42 are peeled away from the core member 44, the
entire
core member 44 flexes because the foamed core material is resilient and the
peel force
is along the length of the core member 44. Because the core member 44 is
resilient
and flexes, this allows for more of the core member 44 to be loaded during
application
of peel forces. In the prior art, solid core members are provided in composite
plates
and therefore, the peel strength is low; especially compared to the present
invention
because the solid core composite plate are not as resilient. When a solid core
member
is used in a composite plate as is used in the prior art, to peel a skin from
the core
2 0 member, peel force only is applied at a narrow line of the skin to crack
the skin away
from the solid core member.
In the present invention, peel strength was measured by means of a peel test.
The metal skins 40, 42 were grasped opposite of each other and the force
required to
peel the skins 40, 42 from the core member 44 was measured. It was found that
an
2 5 increase in peel strength is obtained with the resilient foamed core
member 44 of the
present invention versus a solid core member as used in the prior art. This
means that
in the present invention, the skins 40, 42 are less likely to delaminate from
the
resilient core member 44 upon impact or because of abuse.
In prior art solid core composite plates, a high shear stress is obtained
between
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the metal skins and the solid plastic core member as the composite plate
temperature
changes. If shear stress gets too high, then the metal skins can delaminate
from the
core member. The plastic core member expands or contracts fastener than the
metal
skins, however, the metal skins will restrict this expansion when they are
bonded to
the core member, but high shear stresses result at the adhesive face. In the
present
invention, because the core material 44 is foamed, lower shear stresses of the
skin to
core bond layer result as temperature is changed because the foamed core
member can
be compressed or expanded because of the cell structure so as to reduce the
potential
of delamination of the metal skins 40; 42 from the thermal plastic core member
44.
Thus, the foamed thermal plastic core member 44 will still expand or contract
faster
than the metal skins 40, 42, however, the foamed thermal plastic core member
44
compresses or expands thereby neutralizing this faster expansion or
contraction such
that the foamed thermal plastic core member 44 expands or contracts at
approximately
the same rate as the metal skins 40, 42 and lower shear stresses result at the
adhesive
face.
To make the foamed core member 44 used in the present invention, as shown
in FIGURE 3, foaming beads or pellets 52 are first mixed with thermal plastic
resin
beads or pellets 54 by means of an auger 56 in a mixing chamber 58. The
foaming
pellets 52 have a gas therein. The mixed pellets 54, 56 are subjected to heat
in a hot
2 0 die chamber 60 and the foaming pellets 56 burst and produce carbon dioxide
or
nitrogen to foam the mixture. The mixture is extruded into a layer by an
extruder 62
to form the foamed core member 44. Thereafter, a layer of flexible adhesive 46
is
preferably applied to the inner surface of the skins 40, 42 by suitable means
64, as
shown, the layer of flexible adhesive 46 can be applied to the opposite sides
of the
2 5 foamed thermal plastic core member 44 by like suitable means, an adhesive
layer of
film 46 can be co-extruded on both sides of the core member 44 and laminated
to the
core member 44 immediately, or the outer surfaces of the core member 44 can be
treated to become the adhesive bonding layer 46 such that the skins 40, 42 can
be
directly bonded thereto. Thereafter, the metal skins 40, 42 are adhered to the
core
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member 44 by means of the flexible adhesive layer 46 under pressure. It is to
be
noted that the more gas that is used during the heating step, the more
reduction in core
material is ultimately achieved. This process may be continuous.
It is envisioned that other means of foaming the core member 44 may be
provided such as by injecting nitrogen into a heating chamber in which the
thermal
plastic resin pellets 54 are being heated and are in a molten state (without
the foaming
pellets 52 being mixed therewith) and thereafter extruding the foamed core
material
into a core member 44, or by using both the foaming pellets 52 and the direct
injection
of nitrogen gas into a heating chamber {shown via conduit 61 shown in phantom
lines
in FIG. 3) in which both the thermal plastic resin pellets 54 and the foaming
pellets 52
are being heated.
While a preferred embodiment of the present invention is shown and
described, it is envisioned that those skilled in the art may devise various
modifications of the present invention without departing from the spirit and
scope of
the appended claims.
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