Note: Descriptions are shown in the official language in which they were submitted.
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MULTI-DIMENSIONAL TAILORED LAMINATE
TECHNICAL FIELD
The present invention relates to laminate structural panels
and, more specifically, to light-weight laminates having desirable
structural characteristics.
BACKGROUND OF THE INVENTION
Vehicle bodies commonly include metal panels which are
selected for properties such as strength and stiffness, formability,
corrosion resistance, weldability, impact resistance, and the Pike,
according to the intended location of the panel on a vehicle. Where
the application requires a mixture of properties, the selected metal
panel may be a specialized alloy, have had custom heat treatments
and may have to be joined, for example by welding or with fasteners
to other metals in order to provide the desired properties in selected
zones. More than any other material, steel is used extensively in
motor vehicles to form panels and other structures. It will be
appreciated by those skilled in the art that the required structural
characteristics, such as stiffness, vary depending upon the specific
application. When higher stiffness values are required for steel, the
thickness is typically increased. Increasing steel thickness, however,
produces a panel or part which is not only heavier, but is also more
expensive. In Unified States Patent 5,985,457, STRUCTURAL PANEL
WITH KRAFT PAPER CORE BETWEEN METAL SKINS, the entire
disclosure of which is incorporated herein by reference, the inventor
of the present invention discloses structural panels which are laminate
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s~r~;ct~,~res_ hashing _.m..etals skins separated by and bonded to an
intervening fibrous core. The laminates described therein have very
high specific stiffness and are comparatively light weight. As
described therein, however, the placement of the fibrous core is
continuous with the metal skins. In some applications, the presence
of the core may interfere with fasteners, welds or clearance openings
and their methods of formation. It would be desirable to provide a
light weight structural laminate which could be customized to
accommodate specific fastening, welding and clearance opening
operations. The present invention meets these and other desirable
goals.
SUMMARY OF THE INVENTION
In one aspect, a structural laminate is provided having a
profile which varies compositionally along the laminate body. The
laminate has first and second skins of sheet metal. A fibrous paper
core layer is provided between the sheet metal skins and is bonded to
the skins. In one aspect, the fibrous paper core layer is impregnated
with an adhesive resin which bonds the core layerdirectlyto the skins.
In another aspect layers of adhesive are placed between the core
material and the skins to bond the core to the skins. Along the edge
of the laminates there is a gap or space between the two metal skins;
that is, the paper core does not extend completely to the edges of the
steel skins in at least some spots. The core is non-uniform in cross-
section, having a profile which is "tailored" for a desired application.
For example, this non-uniform profile may allow fasteners or fixtures
to pass through the laminate or facilitate the placement of clearance
holes. The resulting tailored laminate structure is ext remely
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Iightv,~Pight rnmp_a_red toa singlesteel sheet of comparable thickness
and strength.
In still another aspect of the invention, a method of forming
a tailored structural laminate is provided. The method includes the
steps of placing a fibrous core of paper material between two metal
skins, the fibrous core covering less than the entire adjacent skin
surfaces, i.e., along the edge of the laminates there is a gap or space
between the two metal skins as described in the preceding paragraph.
Pressure is applied to the tailored laminate to promote bonding
between the core and the metal skins. In one aspect a number of
laminates are prepared which are then stacked one upon another and
are then pressed to simultaneously bond the individual layers.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-section of the laminate of the present
invention.
Figure 2 is a plan view of the laminate of Figure 1.
Figure 3 is the laminate of the invention in another
configuration.
Figure 4 is a diagram depicting a die press forming the
laminate of the invention.
Figure 5 illustrates a door panel.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
Referring now to Figure 1 of the drawings, non-uniform or
tailored laminate panel 20 is shown having metal skins 22 and
intervening region 23 in which fibrous core 24 is seen. As best shown
in Figure 2, fibrous core 24, in this embodiment, is recessed from each
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Adge 25 nfpanel. 20.Thus an .unfilled gap or space 27 exists
between portions of opposed metal skins 22. In this embodiment, the
space is in the shape of a channel extending completely around the
perimeter of panel 20. In plan view, the area of space 27 may vary
widely, but will typically be at least 1 square inch. It will be seen
that the composition of panel 20 varies along axis 21 as indicated by
arrows A and B. In other words, along the path of arrow A panel 20
is metal-space-metal; at arrow B panel 20 is metal-paper-metal. It is to
be understood that the placement of gap 27 in panel 20 will vary
depending on the intended application for the laminate panel or part;
gap 27 may occur at one or more edges of panel 20, may be located
solely in the interior regions of panel 20 (i.e., as a hole cut in the
center of core 24 or may have an irregular shape to accommodate a
specific application. Core 24 may be discontinous, for example
forming separate strips or the like.
One material for use in forming fibrous core 24 is fully
described in the aforementioned United States Patent No. 5,985,457,
the entire disclosure of which is incorporated herein by reference.
The individual layers shown in Figure 1 will now be
described in more detail. As stated, metal skins 22 generally will be
flat having planar surfaces on each side. Metals which may be utilized
to form skins 22 are preferably selected from the group consisting of
steel, aluminum, copper alloys and various combinations thereof.
Metals which provide adequate structural and (if required) corrosion
resistance properties in the specific environment in which panel 20 is
used, at the lowest cost, are most desirable.
In one preferred construction, skins 22 are most preferably
formed of zinc coated steel, with each layer 22 having a thickness of
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abou .005 inchor greater, preferably from between about .005 inch
and about .030 inch and more preferably from about .005 inch to
about 0.012 inch in thickness. In one embodiment intervening fibrous
layer 24 preferably has a thickness of from about .01 inch and greater
and preferably from about .01 inch to about .05 inch. Thus, the
overall thickness of panel 20 in one embodiment wi(I typically be
between about 0.020 inch and about 0.110 inch. A panel having the
dimensions set forth above in the description of Figure 1 of the
d rawi ngs and havi ng the preferred I aver th i cknesses j ust descri bed wi
I I
typically have weight that is about 40 - 70% of the weight of a single
sheet of steel of comparable dimensions and stiffness.
As wi I I be appreciated by those ski I led i n the art, steel comes
in a number of grades based on the amount of carbon and other
elements which it contains. Broadly these grades can be described as
low carbon steel, medium steel and high carbon steel. Preferred for
use herein are low carbon steel and low carbon micro-alloyed high-
strength steel (HSLA). The most preferred metal skins for use in the
present invention are cold rolled steel, galvanized steel, tin coated
steel, and stainless steel. It may be desirable to utilize single sided
galvanized sheet with a galvanized surface comprising the outer
surface of skins 22 with the inner surfaces of the skins being bare
metal for adhesion purposes. In one embodiment differential zinc
coating is preferred, i.e. a light zinc coating on the inside surface and
a heavier zinc coating on the outer surface. In one embodiment, zinc
coated steel is cold rolled with zinc on the surface to the final
th ickness.
As stated, layer 24 is a fibrous material. As used herein, the
term "fibrous," without limiting its scope in the context of the
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inventie~_n_;is. intended to mean a generally homogeneous collection of
fibers, either natural or synthetic, which can be formed into a sheet
product. The most preferred fibrous material for use herein as layer
24, a material which is believed to be unique among fibrous sheets,
is paper. As will be appreciated by those skilled in the art, paper is
essentially a matted or felted structure of fibrous material formed into
a relatively thin sheet through the medium of a dilute suspension of
pulp and water. It is composed essentially of cellulose fibers. Pulp for
paper making can be prepared by grinding wood or other plant matter
mechanically, by chemical processing (sulfite, kraft, or soda) and also
by chemically treating cotton, linen and hemp rags, waste, straw, and
the like.
In the present invention, paper formed using the kraft process
is most preferred. It will be appreciated by those skilled in the art that
the kraft process (which may also be referred to as sulphate pulping or
alkaline process) results in papers of high physical strength and bulk.
One preferred paper is sold as saturating kraft paper, by Westvaco, of
Charleston, S.C.
Also, as will be appreciated by those skilled in the art, the
average alignment of cellulose fibers in paper is controlled somewhat
by the "machine direction" during production of the paper. It is
believed that in the present invention the orientation of the paper in
the laminates is a factor which may affect the stiffness and strength of
the laminate. Most preferred are laminates where the machine
direction of the kraft paper is a line parallel to a neutral axis of bending
of the laminate. Another class of fibrous materials for use herein is
plastic-fiber paper.
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Inonepreferredembodiment of the invention, layer 24 is
provided as a resin-impregnated fibrous material. Where layer 24 is
kraft paper, the paper is saturated with a resin which is then dried.
Most preferred for use herein is phenolic resin-impregnated kraft
paper. Polyester resin impregnation may also be suitable in some
applications. Methods of impregnating paper with resin will be
well-known to those skilled in the art. In essence, the preferred
resin-impregnated paper is formed by immersing a substrate paper
web in liquid phenolic resin. Typically, layers of saturated
impregnated paper are layered together to form a single layer of
semi-cured impregnated paper. Although it may be suitable or
desirable in specific applications to go beyond the ranges set forth
hereinafter with respect to the resin content layer 24, in a preferred
embodiment of the present invention resin constitutes from about 15%
to about 45% by weight of resin-impregnated layer 24.
In most instances thermosetting resins are preferred for use
in impregnating paper layer 24, although in some applications
thermoplastic resins may be acceptable. In the case of thermosetting
resins, as stated the resin will generally be cured to B-stage prior to
forming panel 20, but it may be possible to fully cure the impregnated
paper prior to the laminate pressing operation (controlled heat and
pressure) described below. In the case of a phenolic resin, the resin
is cured to B-stage prior to lamination. It is then fully cured as skins
22 and impregnated paper core 24 are laminated together using the
press. It may be suitable in some applications to include a number of
standard additives in the resin such as curing agents, fillers and the
i ke.
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With or_without resinimpregnation of fibrous layer 24, it
may be desirable or required to use a layer of adhesive to bond skins
22 to fibrous core 24. A number of adhesives may be suitable in
specific applications, including epoxies, phenolics, isocyanates,
polyurethanes, and hot-melts. A particularly preferred adhesive for
this purpose is a nitrite phenolic sold as "Arofene 1166" from Ashland
Chemical. The adhesive may be applied directly to layer 24 or to
metal skins 22 or both by any number of methods. It is preferred to
pretreat the steel with a conversion coating such as a complex oxide
or zinc phosphate to improve bond integrity and corrosion resistance.
In another embodiment, as shown in Figure 3 edge strips 28
are provided which are of a different material than that of fibrous core
24. Various materials may be used for edge strips 28, such as a
thermoplastic or an adhesive. Strips 28 may constitute a single strip
aroundthe outer perimeter of panel 20.
In another embodiment, fibrous layer24mayhaveaplurality
of holes (not shown) extendingtherethrough; these holes may provide
adhesive "bridges" as more fully described in the aforereferenced U.S.
Patent No. 5,985,457.
Referring now to Figure 4 of the drawings, one method of
assembling skins 22 and layer 24 is shown using press 30. Press 30
includes platens 32 which move towards one another in the customary
manner using hydraulics or the like. Platens 32 are preferably
heatable so both heat and pressure can be applied to the laminates to
cure the resin and bond the adhesive as more fully described in
copending United States Patent Application Serial No. 09/373,298
filed August 12, 1999, entitled, "IMPROVED STRUCTURAL PANEL
AND METHOD OF MANUFACTURE", the entire disclosure of which
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is_in~~rporatedherein by_reference.
Several metal/fiber/metal laminates may be stacked and
pressed as described in the immediately preceding U.S. Patent
Application Serial No. 373,298. After the pressed stack has cooled, it
is removed from the press, individual panels are then separated.
In some applications, the laminate panels of the present
invention may substitute for a metal section which is not a flat sheet.
Therefore, as described in the immediately preceding U.S. Patent
Application Serial No. 373,298, parts having non-planar geometries
my benefit from the tailored laminate approach of the present
invention.
Such a multi-dimensional laminate 20 may find application
for use as a door panel 34 shown in Figure 4. The body of the door
panel 34 designated by numeral 36 may comprise a stiff, lightweight
composite material comprising outer metal skins made of steel and an
inner core made of paper of the kind described herein. The door
panel 34 has forward and rear edge portions designated 38, 40 which
comprise outer skins of steel and an inner core made of high strength
steel suitable for welding. Adjacent to an opening 42 formed in the
door panel 34 to create a window, there is an area designated by
reference numeral 44 which will be deformed to create a recess
associated with a door handle (not shown) and comprises outer skins
of steel and an inner core made of thermoplastic material which may
sustain strains of up to 30%.
While particular embodiments of this invention are shown
and described herein, it will be understood, of course, that the
invention is not to be limited thereto since many modifications may be
made, particularlybythoseskilled in this art, in light of this disclosure.
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~t is rnntemnlated; therefore; by_the appendedclaims,tocover any
such modifications as fall within the true spirit and scope of this
invention.
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