Note: Descriptions are shown in the official language in which they were submitted.
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FLAT ORIENTED STRAND BOARD-FIBERBOARD COMPOSITE
STRUCTURE AND METHOD OF MAKING THE SAME
CROSS REFERENCE TO RELATED APPLICATION
This application is related to Canadian Patent
File No. 2,039,559, filed April 2, 1991.
FIELD OF THE INVENTION
The present invention is directed to oriented
strand board (OSB) and, more particularly, to an
improved OSB-fiberboard composite structure having a
fiberboard surface which will resist weathering, OSB-
fiberboard delamination and is properly balanced in
multiple layer thicknesses to prevent warping,
particularly cupping. The surface of the fiberboard
upper layer may be readily embossed with relatively
deep patterns, can maintain sharp outside embossed
corners in board or panel construction, and may be
finished with paint or the like so that the product can
be used as a visible siding or panelling. The
fiberboard outer (top) layer is bonded to an OSB
baseboard including at least three layers of OSB
wherFin the oriented strand board outer (bottom) layer
is about 25% to about 35% thicker than the fiberboard
overlay-contacting OSB layer; and a central OSB core
layer comprises about 25% to about 35% of the total
thickness of the three OSB layers, to prevent warping
of the product.
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BACRG~tOUND OF THE INVENTION
OSB is made from flakes that are created from
debarked round logs by placing the edge of a cutting
knife parallel to a length of the log and the slicing
thin flakes from the log. The thickness of the flake
is approximately 0.010 to 0.030 inch. The cut flakes
are subjected to forces that break the flakes into
strands having a length parallel to the grain of the
wood several times the width of the strand. The
strands can be oriented on the board forming machine
with the strands predominantly oriented in a single,
e.g., cross-machine direction in one, e.g., core layer
and predominantly oriented in the generally
perpendicular (machine) direction in adjacent layers,
The various layers are bonded together by natural or
synthetic resins) under heat and pressure to make the
finished OSB product.
The common grade of OSB is used for sheathing
walls and decking roofs and floors where strength,
light weight, ease of nailing, and dimensional
stax~ility under varying moisture conditions are the
most important attributes. In these applications, the
appearance and/or weathering of the rough surfaces are
not of concern since the product will be covered with
roofing, siding, or flooring. Because of the
unfinished attributes of utility grade OSB, it commands
a relatively low price in the marketplace and is sold
at a discount to structural grades of softwaod plywood.
The light weight, ease of nailing, and
dimensional stability of OSB are attributes much
desired in siding products but, due to the irregular
surface, OSB has required surface modification before
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being used as siding or otherwise where aesthetics is
important to the consumer. If the material could be
imparted with the surface smoothness, coatability, and
weatherability of hardboard while retaining its other
desirable structural properties, it would be
significantly improved in comparison to the commodity
structural grade. Others have pursued this objective
along different lines with partial success.
One attempt to prevent "telegraphing" is
described in Greten U.S. Patent No. 3,098,781. The
Greten '781 patent discloses a particleboard product
made from materials, such as flakes, wherein the flakes
are graduated in size from the center or core to the
outer surfaces, with the coarsest flakes at the core
and the finer flakes, together with fines, at one or
both outer surfaces. The Greten produced particleboard
is disclosed to have the advantage of accepting an
overlay of veneer, paper or plastic sheets without
"telegraphing" the relatively irregular surface of the
underlying particleboard.
Similar OSB siding products are commercially
sold. that include a resin-bonded overlay of paper
laminated to one surface. The paper can accept a
limited degree of embossing but it cannot stretch to
accept deep embossing. When embossed beyond a certain
depth, the paper ruptures from the tensile strain and
reveals the underlying flakes. Furthermore, exposure
to the weather causes irreversible swelling of the
flakes in thickness which telegraphs the structure of
the underlying baseboard (OSB) through the thin overlay
and creates a bumpy, irregular exposed surface. The
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result is an unsightly appearance of the front surface,
especially of product that is unembossed or only
slightly embossed.
Another example is described in Wentworth
U.S. Patent No. 4,364,984 where wood fines are
distributed on the surface of the flake baseboard (OSB)
graduated with the coarsest wood fines adjacent to the
flakes and the finest on the visible surface. Since
the fines are bundles of wood fibers which retain the
stiffness of wood, they do not consolidate into a tight
surface, but rather, retain susceptibility to the ready
entry of water and do not holdout paint to a
satisfactory degree.
Similarly, Ufermann, et al. U.S. Patent No.
4,068,991 discloses a particleboard, e.g., chipboard
product that includes a continuous particle size
gradient between a coarser particle core and a finer
particle surface layer wherein the particle size
gradient transition from one particle size to another
can be continuous or step-wise.
Others have disclosed the manufacture of
laminates of plywood or particleboard with a
wet-process fiberboard surface, e.g., Birmingham U.S.
Patent No. 2,343,740; Bryant 3,308,013 and Shaner,
et al. U.S. Patent No. 4,361,612 discloses forming an
oriented strand board (OSB), that may be in three or
more layers, formed from a mixture of hardwood species
and then laminating the OSB to a veneer, wet-process
hardboard or plywood face panel.
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One of the problems associated with the
application of an overlay onto an OSB baseboard is that
of achieving a strong bond at the interface between the
OSB and the overlay capable of resisting weathering.
The above-described Wentworth U.S. Patent No. 4,364,984
suggests that a strong bond can be achieved at the
interface between an OSB product and a fine particle
overlay by manufacturing the OSB with the largest OSB
flakes at the interface, and applying the overlay fine
particles such that the longest fines are disposed at
the interface. Similarly, the Shaver, et al. U.S.
Patent No. 4,361,612 discloses that shorter fibers in
the surface of an OSB product will degrade the bending
strength of an OSB product. Further, the Shaver '612
patent teaches that a laminated wood product including
a flakeboard core laminated to a wood veneer, a
wet-process hardboard or a wet-process fiberboard
overlay, as in typical plywood practice, may need a
core finishing operation on a drum sander to achieve a
core surface capable of good bonding to the overlay.
Bryant U.S. Patent No. 3,308,013 suggests
that a water-laid fiber sheet containing resin and
havi~.Zg a basis weight of dry fiber from 30 to 750
pounds per thousand square feet can be employed to mask
defects in plywood, particleboard, and the like. These
heavy papers have been used to produce medium density
overlain plywood that has found application in road
signs where the smooth surface accepts lettering and
reflective laminates. High cost, limited
embossability, poor weathering, and poor adhesion of
coatings preclude the use of this product in siding
applications.
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It has heretofore been generally accepted by
those skilled in the art that an OSB baseboard and a
fiberboard overlay will not form a good bond at their
interface and that the differential in dimensional and
elastic properties of the fiberboard and OSB materials
will result in delamination because of moisture cycling
due to weather conditions. This conventional wisdom
also advised against using dried board trim waste as a
raw feed to the fiber pulping operation because of
residual bonded and consolidated resin. While this
theory has been verified for OSB wet-process fiberboard
composite structures, surprisingly and unexpectedly,
excellent bonding and resistance to weathering is
achieved in accordance with one embodiment of the
present invention by applying a fiberboard overlay by
the dry process to an OSB baseboard. Additional
advantages are achieved in the preferred embodiment by
forming the OSB such that the smallest flakes of the
OSB are disposed at the fiberboard interface, as will
be described in more detail hereinafter.
In the prior art manufacture of OSB, a
warping problem was encountered when the OSB was formed
from three OSB layers using a screen within the platen
press for final consolidation of the three strand
layers into a unitary OSB structure. It was theorized
that the screen marks on the one OSB surface layer
increased the amount of effective surface area on that
OSB surface layer, thereby causing the warping problem.
In order to compensate for warpage, it was found in the
prior art that warping could be prevented by increasing
the thickness of the screen-marked (higher surface
area) OSB surface layer, in comparison to the thickness
of the OSB surface layer without screen marks, an
amount such that the screen-marked OSB surface layer
~~~~'~~ aj:..~
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had a thickness 15% higher than one-half the total
thickness of the OSB surface layers surrounding the OSB
core layer. Typically, warping was prevented in prior
art OSB manufacture, wherein one of the surface layers
of the OSB included screen indentations, by providing a
three-layer OSB product such that the top (non screen-
marked) OSB layer comprised 31.6% - 33.4% of the total
OSB thickness; the center OSB layer comprised 42% - 45%
of the total OSB thickness; and the lower (screen-
indented) OSB layer comprised 23.4% - 24.6% of the
total OSB thickness. Thus, the top OSB layer (not
screen-indented) having the smaller surface area was
made 15% thicker than 1/2 the sum of top and bottom OSB
layer thicknesses to prevent warping, with the central
OSB layer, oriented perpendicularly to the machine
direction, comprising 42%-45% of the total board
thickness.
It has been found, in accordance with one
embodiment of the present invention, that to achieve
excellent embossing fidelity (the capability of
achieving a sharp, accurate and permanent transference
of an embossing plate design from an embossing plate to
a board surface) in an OSB fiberboard overlay, the
fiberboard overlay should be air-laid (formed by the
dry process). If the fiberboard overlay applied over
an OSB surface is water-laid (formed by the wet
process), as suggested in the prior art, the sharp
corners and other embossing precision necessary for
high quality transference of an embossing plate design
is not possible.
Unexpectedly, it has been found that the
application of a dry layer of a mixture of defibrated
fiber and resin binder over an OSB surface enables
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exact and precise transference of embossing plate
details into the surface of the fiberboard overlay.
Further, the bonding achieved at the interface between
the OSB and the dry process fiberboard overlay, and the
resistance to weathering of the fiberboard overlay are
unexpectedly better when the fiberboard overlay is
formed into a loose, but handleable mat formed by the
dry process (the fibers are laid onto a support surface
by gravity from a mixture with air, or mechanically,
and are contacted with a binder resin during the fall
of fibers onto the support surface, and generally
contain less than about 15% water) and the fiberboard
overlay and OSB layers are consolidated in a hot press
simultaneously. As set forth in more detail
hereinafter, the bonding is unexpectedly higher and the
boil swell values substantially lower for the OSB-
fiberboard composite products of the present invention
than for a similar product that includes a fiberboard
overlay applied by the typical wet process.
Furthermore, those skilled in the art have
anticipated warping of the product if the overlay were
applied only to one surface but, in accordance with
another embodiment of the present invention, it has
been found that the expected warping does not occur
even in full size panels, e.g., 4' x 8', when the
fiberboard overlay is applied to only one major
surface, and the thicknesses of the underlying OSB
layers are carefully selected, as described in more
detail to follow.
The mufti-layer OSB-fiberboard composite
structure of the present invention, having one
fiberboard surface layer and the other surface layer
formed from an OSB layer without screen indentations,
°
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and having at least two OSB layers therebetween, has
substantially different characteristics and physical
properties from an OSB without the overlay and,
therefore, was completely different in terms of
possible warp or cupping during manufacture.
Initial experimental trials in the
manufacture of the OSB-fiberboard composite of the
present invention on a commercial scale, having three
OSB layers pf equal thickness, and a surface layer of
fiberboard over one of the outer OSB layers resulted in
a board that cupped or warped substantially, even with
light weight overlays, e.g., 150 pounds per thousand
square feet, leading to the present invention.
In accordance with another embodiment of the
present invention, warping or cupping of OSB-fiberboard
composite structures can be eliminated with careful
selection of OSB layer thicknesses, regardless of
whether the fiberboard layer is applied by the wet or
dry process, as described in more detail hereinafter.
SUb~~lARY OF Z'HE INVENTION
The present invention combines the desirable
attributes of OSB baseboard with the embossability,
ease of finishing, bonding strength, and weatherability
of a fiberboard, e.g., hardboard overlay. An OSB
baseboard mat is overlain with a preformed dry fiber
sheet and the two structures are consolidated and
bonded in a single hot pressing. Because of the
unconsolidated condition of the fiber overlay before
hot pressing, and, unexpectedly, due to the fiberboard
~~'4.a~~;,~r": r '
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overlay being formed by the dry process, deep embossing
of architectural profiles are passible without fracture
of the overlay while achieving unexpectedly precise
embossing fidelity. The dry-process fiberboard overlay
mat can be consolidated into a hardboard-like layer
which has the smoothness, resistance to water
penetration, weatherability, resistance to boil swell,
and paint holdout of conventionally made hardboard used
for siding. In accordance with one embodiment of the
present invention, when the OSB baseboard is
manufactured such that the smallest flakes are disposed
at the OSB-fiberboard interface, the overlay masks
flake telegraphing of even smooth-surfaced, unembossed
product having a relatively thin fiberboard overlay,
e.g., less than about 1/8 inch thick, e.g., about 3/32
inch thick.
To achieve the full advantage of the present
invention, in accordance with one embodiment, sized
board trim OSB waste can be used as feed for pulping
for the dry process manufacture of the fiberboard
overlay so that defiberized fiber from the OSB
baseboard trim can be refined to form the dry-process
fiberboard overlay that is consolidated under heat and
pressure to yield a product that has the stability,
ease of working, and light weight of OSB and the
architectural aesthetics, coatability, and
weatherability of hardboard. The OSB-fiberboard
composite structure shows no tendency to delaminate
after severe moisture cycling between boiling water and
hot oven conditions and remains free of warping over a
wide range of moisture environments.
CA 02097275 2000-OS-10
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Accardinc~ly, one aspect of the present invention is
to provide an oriented strand board-fiberboard composite
structure that has new and unexpected resistance to
delamination of the' fiberboard overlay, unexpected
weatherability and unexpected resistance to warping.
Another aspect of the present invention is to
provide an oriented strand board-fiberboard composite
structure that inc:Ludes the surface deformability and
aesthetics of fiberboard as well as the structural strength of
oriented strand board without separation of the fiberboard
from the oriented strand board, wherein the fiberboard is
felted by the dry process.
A furthe~~ aspect of the present invention is
to provide an oriented strand board-fiberboard composite
structure, wherein the oriented strand board is formed with
the smallest flake: at the fiberboard interface to prevent
telegraphing of thE~ flakes through the fiberboard surface.
Still another aspect of the present invention
is to provide an oriented strand board-fiberboard composite
structure that doe; not warp, cup or bow upwardly at its edges
upon removal from ~~ hot press by the judicious selection of
thicknesses of the OSB layers, whether the fiberboard overlay
is formed by the wet process, e.g., water-laid, or by the dry
process, e.g., air-laid.
More particularly, the invention in one aspect
provides a non-war~~ing oriented strand board-fiberboard
composite structure comprising a multi-layer oriented strand
baseboard having a plurality of wood strand layers, including
a central layer foamed from wood strands oriented generally in
a random or cross-machine direction sandwiched between two
CA 02097275 2000-OS-10
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adjacent layers formed from wood strands oriented in a
direction generall~r perpendicular to the central layer; and a
wood fiber overlay layer bonded to one of the strand board
layers. After con:~olidation, the thickness of the central
strand board layer comprises about 25% to about 35% of the
total thickness of the central and adjacent strand board
layers and the strand board layer adjacent to the central
layer that is not :in cantact with the fiberboard overlay is
about 25% to about 35% thicker than the strand board layer in
contact with the fiberboard overlay.
Another parti~~ular aspect of the invention comprehends a
method of manufacturing a non-warping oriented strand board-
fiberboard composit=e structure comprising forming a baseboard
having a top layer of oriented wood strands, a central core
layer of wood strands oriented perpendicularly to the top
layer of wood strands or oriented randomly, and a bottom layer
of wood strands oriented in the same direction as the top
layer of wood strands, such that the bottom layer of wood
strands, after consolidation, is about 25% to about 35%
thicker than the top layer of wood strands, and the core layer
comprises about 25'~ to about 35% of the thickness of the
baseboard, disposing a preformed fiberboard mat over the top
layer of the baseboard, and consolidating the fiberboard mat
and the baseboard :layers simultaneously in a heated press.
The above and other aspects and advantages of the
present invention ~~aill become apparent from the following
detailed descripti~~n of the preferred embodiments taken in
conj unction with t:he drawings .
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure la is a cut-away perspective view of
an OSB-fiberboard composite structure of the present
invention;
Figure 1b is a side view of the OSB-
fiberboard composite structure of Figure 1a;
Figure 2a is a profile view of the top flake
layer of a conventional OSB product;
Figure 2b is a profile view of the top flake
layer of the preferred OSB-fiberboard composite
structure of Figure la;
Figure 3a is a cut-away perspective view of a
conventional OSB product in board form utilizing
strands in the top flake layer and exhibiting a
telegraphed flake in the surface of a thin paper
overlay;
Figure 3b is a profile view of the
conventional OSB product of Figure 3a;
Figure 4a is a perspective view of an OSB-
fiberboard composite structure of the present invention
having an embossed surface.
Figure 4b is a profile view of the OSB-
fiberboard composite structure of Figure 4a;
Figure 5a is a perspective view of a molded
OSB-fiberboard composite structure of the present
invention; and
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Figure 5b is a profile view of the molded
OSB-fiberboard composite structure of Figure 5a.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Low density woods, such as aspen, have been
preferred for making hot pressed oriented strand boards
because the higher pressure needed to develop the board
densities improves consolidation. The ratio of pressed
board density to wood density is referred to as the
compaction ratio. The compaction ratio of a product
may be obtained by dividing the specific gravity of the
product by the specific gravity of the wood. For
example, a compaction ratio of about 1.23 is obtained
for a product having a specific gravity of 0.665 which
is made from Southern Yellow Pine having a specific
gravity of 0.54. The specific gravity of the. strands
usually is in the range of about 0.45 to about 0.60.
For aspen, the ratio is generally in the range of 1.6
to 1.8 using oven dry weights and green volumes.
In accordance with a preferred embodiment of
the present invention, wood species of intermediate to
high density axe used to form the OSB flakes to achieve
flakes that are relatively stiff and have a relatively
high resistance to compression. When hot pressed, the
stiff flakes in the OSB baseboard force the overlaying
dry-process fiberboard mat to undergo most of the
resulting compaction, thereby developing maximum
density in the overlay. In practicing this invention,
wood species having an approximate specific gravity in
the range of about 0.45 to about 0.60 are preferred.
Wood flakes having a specific gravity in the range of
about 0.45 to about 0.60 generally offer compaction
~('~'~~°~
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ratios of 1.2 to 1.5. It is preferred that the final
OSB-fiberboard product has an overall specific gravity
of about 0.60 to about 0.80.
The preparation of flakes is accomplished in
the usual manner so as to yield strands having aspect
ratios (ratio of length to width) of about 5 to about
30, and moisture contents of about 15 percent or less,
preferably about 1 to about 15 percent, based on the
dry fiber weight. Generally, green logs having a
moisture content of about 40% to about 60%, green basis
weight, are sliced, and dried to, for example, about
3o by weight moisture, before being screened and
contacted with resin. The strands are screened to
separate out slivers, which are particles with a width
of approximately 3/8 inch or less. To achieve the full
advantage of the present invention in the forming of
the OSB baseboard, the conventional practice of placing
slivers in the core and larger strands on the faces is
reversed. For siding, the core is made up of strands
deposited in a random pattern or in the direction
perpendicular to the machine direction, followed by
larger strands adjacent to the core aligned parallel to
the machine direction, followed by slivers arranged
parallel to the machine direction. The purpose of the
layer of slivers is to aid in masking the large strands
that lay beneath and to provide a stiff layer to force
the compression of the fiber overlay. This
orientation, with the smallest strands at the
fiberboard overlay interface, achieves the best results
for smooth-surfaced (non-embossed) product,
particularly where the fiberboard overlay is in a layer
of about 200 pounds of fiber, dry weight basis, per
thousand square feet or less, to prevent telegraphing
of flakes through the fiberboard overlay. For product
..a ~ a.6'
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containing thicker fiberboard overlays, or for product
that is embossed on the fiberboard overlay, the
distribution of flakes in the OSB layer is less
important.
In accordance with a preferred embodiment of
the present invention, fiber for the overlay can be
liberated, defiberized and refined from the rough trim
cut from the ends and edges of the OSB layer, from the
OSB-fiberboard composite structure. Such trim is
consolidated board with cured resin and wax sizing with
the layered structure typical of waferboards and strand
boards. The trim strips are chipped, e.g., in a drum
chipper and steamed at pressures of about 25 to about
300 psig saturated steam pressure for a period of about
2 minutes to about 10 minutes, and refined under
pressure in a pressurized refiner similar in operation
to those used for producing fiber from chips. Because
of the layered structure of OSB chips, steam readily
penetrates the chip, permeates to the middle lamella
(interfiber layer), softens the interfiber layer, and
permits separation of the individual fibers into a pulp
finer than that obtainable by refining log chips. The
ready pulpability of the consolidated board trim, in
accordance with the present invention, was unexpected
to those skilled in the art, and the uniform fiber that
results is very compliant and readily densifies into a
hardboard layer under heat and pressure with
unexpectedly precise embossing fidelity when applied by
the dry process. Furthermore, the dried trim produces
fiber having a moisture content of 15 percent by weight
or less, based on the dry weight of the fiber, that
does not require drying prior to hot pressing. An
elevated moisture, up to about 15 percent by weight of
- 16 -
dry fiber, contributes to the development of
consolidation but is not a requirement for
consolidation.
The strands preferably are blended with a
hydrocarbon size (typically paraffinic or
microcrystalline wax) in an amount of about 0.5% to
about 4.0%, preferably about 2.5% based on the dry
weight of the strands; and, a binder resin, such as
phenol formaldehyde resin or a polydiphenylmethyl
diisocyanate (PMDI) resin, and delivered to the forming
machine. The slivers are blended in a similar fashion
with the same binder and size and delivered to a
forming machine. The overlay fibers are blended with
wax and resin, dry-formed and laid onto a support
surface, e.g., forming belt, separately by means of
forced air or mechanical means, prepressed and
transferred to the top major surface of the OSB
baseboard mat.
The OSB baseboard is formed preferably in
three layers, the first and third using air or
mechanical classification to classify the particles so
that, preferably, the finest particles are the first
down on the forming belt and the last down on the mat.
The first layer is laid with the strands oriented in
the machine direction. The core, or central OSB layer,
is formed with randomly oriented strands or with the
strands oriented in the cross-machine direction. The
third (fiberboard adjacent) layer is laid with the
strands oriented in the machine direction and
preferably with graduation from coarse strands to
slivers so that the smallest strands are disposed
against the fiberboard overlay. Once the three-layered
mat is formed, the preformed dry-process overlay is
~f'~3'~~' ~',~~
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deposited upon it and the total mat (OSB-fiberboard
composite structure) is prepressed prior to cutting
into lengths for loading into the platen press for
final consolidation.
The formulation of the furnish and the basis
weight of the OSB baseboard mat and the overlay can be
varied widely without going beyond the scope of the
present invention. It is preferred that a phenol
formaldehyde resin or isocyante resin binder be used
with microcrystalline or paraffinic waxes for sizing.
The preferred furnish formulas are generally about 2 to
about 10 percent by weight resin and about 0.5 to about
2.5 percent by weight wax based on the dry weight of
the fiber. OSB baseboard basis weight can be varied
between about 900 and about 2,000 pounds/thousand
square feet with about 1,100 to about 1,500, eg., 1,200
pounds/thousand square feet being preferred. The
dry-process fiberboard overlay basis weight can range
between about 75 and about 400 pounds/thousand square
feet with about 200 to about 350 pounds/thousand square
feet preferred.
Final pressing of the OSB-fiberboard
prepressed composite mat to fully consolidate the
composite board preferably should be limited to prevent
over compaction of the board which increases thickness
swelling potential. Although the pressed board will
typically be between about 0.25 and about 1.0 inch
thick, the preferred product is about 0.400 to about
0.500 inch thick with an overall density in the range
of about 38 to about 47 pounds per cubic foot (specific
gravity in the range of about 0.60 to about 0.75 oven
dry weight and air dry volume basis). This leads to a
compaction ratio of approximately 1.3 for a species
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such as southern yellow pine. Under these conditions,
the dry-process fiberboard overlay will average about
50 to about 55 pounds per cubic foot, which is typical
for hardboard siding. At a given overall product
density, the density of the hardboard overlay can be
increased by using fiber moisture contents of
approximately 15 percent or less, e.g., 12 percent by
weight of dry fiber, and flake moisture contents of
about 8 percent or less, e.g., 6 percent by weight of
dry flakes. This leads to compliant fiber arid
relatively stiff flakes which foster tighter overlay
surfaces having properties of excellent embossing
fidelity, bonding to the OSB baseboard, and
weatherability.
In those instances of embossing deep enough
to cause overdensification of the baseboard along
deepest embossing contours, the hot press can be
outfitted with a backer plate that is roughly contoured
to complement the contours of the top embossing plate.
In this manner, the top and bottom embossing plates
become a die set which molds the OSB baseboard to a
shape that permits deep embossing of the top fiberboard
overlay surface while creating sharp outside corners in
the overlay fibers and near uniform density in the
baseboard, with a contoured OSB baseboard, instead of
overdensification of fiberboard along lines of deepest
embossing. The molded (contoured) profile of the OSB
baseboard can be sanded on the back surface, if
necessary, to restore a flat surface that facilitates
installation against a flat suX:port surface, e.g., as
siding.
2~'~3"7;~ ::
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A further benefit of molding the product in a
die set to contour both major outer surfaces of the
OSB-fiberboard composite structure is the opportunity
to densify specific regions of the product that will
subsequently be cut or shaped by cutters to facilitate
proper installation. Densification improves
machinability and the quality of resulting cut surfaces
and also enhances the resistance of any cut surfaces to
the entry of water.
Turning now to the drawings, and initially to
Figure la, a portion of an OSB-fiberboard composite
structure 100 is cut away to show several details of
its construction. Bottom flake layer 101 is comprised
of wood strands and slivers oriented generally in the
machine direction, with a strand fraction 103 on its
uppermost surface, nearest middle flake or core layer
105. Middle flake or core layer 105 is comprised of
wood strands oriented generally in the cross-machine
direction. Top flake layer 107 is disposed above
middle flake layer 105 and is comprised of wood strands
and slivers, oriented generally in the machine
direction preferably with a strand fraction nearest the
middle flake layer 105 and a sliver fraction 109
disposed on the uppermost surface of flake layer 105.
Construction of the OSB-fiberboard composite structure
100 is completed with the addition of a dry-process
fiberboard overlay 111 upon the top surface of the top
flake layer 107.
As shown in Figure 1b, the OSB-fiberboard
composite structure 100 is comprised of bottom flake
layer 101, middle flake or core layer 105, top flake
layer 107 and dry-process fiberboard overlay layer 111,
wherein sliver fractions 109 and 109a are seen at the
2(?~'7~'~'::;
- 20 -
upper surface of top flake layer 107 and the lower
portion of the bottom flake layer 101, respectively.
Strand fractions 103 and 103a are seen at the lower
portion of top flake layer 107 and the upper portion of
bottom flake layer 101, respectively.
Figure 2a depicts a profile of a conventional
top flake layer 200 having its strand fraction 201
oriented near the top surface and its sliver fraction
203 oriented near its bottom surface.
Figure 2b depicts a profile of top flake
layer 107 from the board shown in Figure 1a, having a
sliver fraction 109 oriented near the fiberboard
interface and a strand fraction 103a oriented near the
bottom portion of the flake layer 107.
Figures 3a and 3b show a conventional OSB
product 300 in cut-away perspective and profile,
respectively. The conventional product 300 is
comprised of bottom flake layer 301, middle flake or
core layer 303, top flake layer 305 and a thin paper
overlay 313. Wood strands 307 and 311 are oriented
generally in the machine direction while strands 309
are oriented generally in the cross-machine direction.
Telegraphed flake 315 is an unsightly blemish in the
thin paper overlay 313 and is one of the disadvantages
seen in the use of conventional OSB product 300 in
applications where appearance is important.
Figures 4a and 4b depict in perspective and
profile view, respectively, an embossed OSB-fiberboard
composite structure 400 of the present invention. The
OSB-fiberboard composite structure 400 includes a
bottom flake layer 401, a middle flake or core layer
~1r1t?I'~';~~~t~ .
~.r~, v :..~ d ,.a
- 21 -
403, a top flake layer 405 and a dry-process fiberboard
overlay layer 407 capable of receiving a suitable
embossing impression, thereby exhibiting embossed
surface 409.
Figures 5a and 5b, respectively, depict a
perspective and profile view of a molded dry process
lain OSB-fiberboard composite structure, having a
dry-process fiberboard overlay surface over a three
layer flake construction OSB.
The examples outlined below describe the
manufacture of the OSB-fiberboard composite structure
of one embodiment of the present invention using batch
equipment, but non-embossed product also may be made
using continuous equipment and continuous presses. In
a continuous process, the surface layers are not
separately screened to provide fine and coarse
fractions but the distribution of the strands with
standard distribution equipment will cause a transition
area between the wider chips and the slivers. The
examples are not intended to limit the scope of the
invention.
Example No. 1
In this example, green southern yellow pine
roundwood bolts were flaked in a pilot plant disk
flaker to a thickness of 0.020 inch. The resulting
strands had a length less than about 3 inches and a
width less than about 1 inch, with the average being
about 1/2 inch in width. These strands were dried in
an oven to 3 percent moisture content and screened into
two fractions, one with a width of over 3/8 inch
(strands) and one with a width less than 3/8 inch
CA 02097275 2002-07-02
- 22 -
(slivers}. These two fractions were handled separately
thereafter. A screen analysis of th~~ sliver fraction
using a Ro-TapTManalyzer yielded the weight fractions
shown below:
Screen Opening Percent Retained
0. 371" 0.0
0. 185" '7.2
0. 131" 27.3
0. 093" 19.4
0. 046" 3:1.2
< 0. 046" 14.9
Total 100.0
The wider fraction of strands was blended
with about 6% phenol formaldehyde resin and about
2% paraffinic wax applied as an aqueous emulsion.
The sliver fraction, which comprised about
1/3 of the surface flake furnish, was blended with
about 6% phenol formaldehyde resole resin formulated
for OSB bonding and with about 2% emulsified paraffinic
wax, both based on the dry wood weight. The use of
phenolic resin in the sliver fraction prevents contact
between the back of the board and the press platen
which could lead to sticking in the press if isocyanate
resin were used.
~ Fiber for the dry-felted fp_ber mat was
produced from oSB board trim waste that had been
chipped by a commercial drum chipper, steamed in
saturated steam for about 5 minutes ai: 125 prig, and
refined in a commercial single disk pressurized refiner
coupled to a digester. The fiber exited the refiner at
12o moisture content and 2.5o by weight, dry fiber
basis, molten paraffinic wax was added. The fiber then
I~~A~~~ ~t:_i
- 23 -
was dried to about 5% moisture content in order to
avoid blistering when deeply embossed. Once dry, the
fiber was blended with about 4% neat PMDT.
The OSB was produced from the foregoing
materials, first by laying down slivers having a basis
weight of about 130 to about 170 pounds/thousand square
feet by dropping them onto an orienting device
comprised of metal strips on edge and arranged in
parallel to form a series of slots through which the
slivers would fall. This oriented the slivers in a
direction generally parallel to the direction of the
slots. The first layer of slivers was oriented in the
machine direction. On top of the sliver layer was
deposited a layer of larger strands oriented in the
machine direction. This second, strand layer had a
basis weight of about 275 to about 355 pounds/thousand
square feet. A core layer was deposited next by
changing the orientation to the cross-machine
direction. The core layer had a basis weight of about
350 to about 430 pounds/thousand square feet. On top
of the core layer was deposited a layer of wide strands
oriented in the machine direction. This fourth layer
had a basis weight of about 275 to about 335
pounds/thousand square feet. The fifth layer was
deposited as slivers oriented in the machine direction.
This fifth, sliver layer had a basis weight of about
130 to about 170 pounds/thousand square feet.
The dry-felted fiber overlay mat was formed
by dropping fiber through a coarse screen onto a fine
screen and thereafter prepressing the mat to reduce its
thickness about in half. The basis weight of the
dry-process fiber mat was 100 pounds/thousand square
feet. The dry-formed mat was transferred to the top
24 -
surface of the OSB baseboard mat and loaded into a hot
press for final consolidation to provide a composite
board having an overall basis weight of 1,500
pounds/thousand square feet.
The press cycle used a hydraulic press with
heated platens at 750 psig pressure on the mat and at
417°F for 5 minutes in order to consolidate all layers
of the composite board. The 5 minutes press cycle
duration included a decompression cycle of 20 seconds
to permit releasing the board from the press without
delamination or blistering. The density of the product
was 41.5 pounds per cubic foot at an overall thickness
of 0.440 inch. The press plate was smooth and treated
with a release agent for PMDI before pressing.
Exsm~Dle PTo. 2
A board was made according to the procedures
in Example No. 1 except that the basis weight of the
dry-felted fiber mat was 150 pounds/thousand square
feet. The basis weight of the OSB core for this
Example, as well as Examples 3-6, was decreased in an
amount sufficient to provide a consistent overall basis
weight of 1,500 pounds/thousand square feet.
Example No. 3
A board was made according to the procedures
in Example No. 1 except that the basis weight of the
dry-felted fiber mat was 200 pounds/thousand square
feet.
2f'~'~~: ~ :~
- 25 -
ExamQle No. 4
A board was made according to the procedures
in Example No. 1 except that the basis weight of the
dry-felted fiber mat was 250 pounds/thousand square
feet.
Example No. 5
A board was made according to the procedures
in Example No. 1 except that the basis weight of the
dry-felted fiber mat was 300 pounds/thousand square
feet.
Example No. 6
A board was made according to the procedures
in Example No. 1 except that the basis weight of the
dry-felted fiber mat was 350 pounds/thousand square
feet.
The six boards described above were coated
with a conventional hardboard thermosetting acrylic
primer and entered into an accelerated aging chamber
specifically designed to cause swelling of wood
composite siding products that are vulnerable to
swelling. In this chamber, vertically oriented
specimens are subjected to 12 hours of water spray on
the front face followed by heat of 135°F for 12 hours.
The chamber remains humid during the early stages of
the dry cycle which increases the swelling capacity of
water that has entered the specimen. The cycling
procedure can be adjusted to repeat the wet and dry
cycles for as many periods as may be required to test
and compare the composite oriented strand board
' ~yt ~' ip"~'yt
~: ~ ('..: t a...
- 26 -
products. After 19 cycles, telegraphing was noted on
the board having overlay basis weights of 100 and 150
pounds/thousand square feet. Telegraphing was minimal
on boards having dry-felted fiberboard overlay of 200
pounds/thousand square feet and no telegraphing was
noted on boards having a dry-felted fiberboard overlay
with basis weights greater than 200 pounds/thousand
square feet. In commercial size plant trails, cupping
(the composite board turning upwardly at the
longitudinal edges with the exposed OSB layer convex)
or bowing (the composite board turning upwardly at the
transverse edges with the exposed OSB surface convex)
was noted in all boards, with the cupping or bowing
more prominent in the boards having higher basis weight
overlays.
It is noted that smooth, unembossed OSB made
according to the invention with dry-felted fiber
overlays having basis weights of about 200 to about 300
pounds/thousand square feet will weather free of
telegraphing. The combination of low compaction ratio
(about 1.3) and thick overlay prevents the excessive
thickness swelling of the baseboard flakes. Embossed
composite OSB products of the present invention can
have a wider ranging basis weight for the dry-felted
fiber overlay, e.g., about 100 to about 300 pounds per
thousand square feet, and weather free of telegraphing
and warping.
Initial laboratory trials indicated that
warping would not be a problem, despite the unbalanced
construction caused by applying the fiberboard overlay
to the front surface without a corresponding overlay
applied to the back surface, so long as the basis
weight of the dry-felted overlay is limited to about
~~~tllr'~') ~~e e'
vJ i.:
- 27 -
300 pounds/thousand square feet or less. Particularly,
when the overlay exceeds about 300 pounds/thousand
square feet, fiberboard overlay hygroexpansion forces
are sufficient to prevent severe warping of the board.
Example No. 7
Experiments were conducted to compare wet-
and dry-formed fiberboard overlay layers for identical
oriented strand boards. It was found that dry-formed
overlay mats are unexpectedly better than wet-formed
overlay mats in terms of surface quality, including
embossing fidelity and paintability, and bonding
properties.
The following conditions were used in the
preparation of the OSB-fiberboard composite structures:
Moisture content of
dry-formed overlay fiber 6%
Moisture content of
wet--,formed overlay f fiber 6-10
Resin content of
dry-formed overlay fiber 5% PMDI
Resin content of 5% Phenol
wet-formed overlay fiber Formaldehyde
Moisture content of
flakes after blended
with resins 6.5-7.5%
Resin content of
surface flakes (fine 6% Borden LH96B
and large flakes) Resin
Resin content of
core flakes 4% Mobay PMDI
~~w~~~~(is.3
- 28 -
Wax content of
all flakes 1.5% paraffin
wax
Pre-press sealer emulsion
2g solids/ft2
R & H E-2761
Pressing temperature 420°F
Pressing time 5 min.
The same fiber prepared from OSB trim was
used for both forming processes. In the wet-forming
process, the fiber was mixed with tap water, and the
phenol formaldehyde (PFj resin was precipitated into
the slurry with acetic acid. The mats were oven dried
at 250°F for 45 minutes and left at room temperature
for 24 hours. Thicknesses of wet-formed mats after
drying and dry-formed mats were 3/4" and 1/2",
respectively. A "Triple Four Pine Textured" die set
was used for the moldability study. All boards were
pressed with a 20" X 20" laboratory press. For each
forming process, three boards were made.
The surface quality was evaluated by visual
examination. The paintability was evaluated by coating
specimens with a Rohm & Haas primer. The bonding
properties were tested by boiling 2" X 2" specimens for
one hour followed by oven-drying at 225°F for 12 hours.
While fiber mats formed by both processes can
be bound to the OSB substrate, the dry-formed overlay
mat was unexpectedly superior to the wet-formed mat in
surface quality. The tightness of the fiberboard
overlay surfaces from the dry-forming process is much
greater than that of wet-formed fiberboard overlay
surfaces. Therefore, the dry-formed overlay shows a
~~'.~"'s l ~: ~',.:
- 29 -
smoother surface, while the wet-formed overlay presents
a rougher surface. The difference is more distinct in
areas adjacent to deeply grooved or curved areas.
Paintabilitv:
OSB specimens overlaid with dry-formed
fiberboard mats exhibit better paint hold-out compared
to those overlaid with wet-formed mats. It is more
distinct in areas adjacent to the guide line groovings,
where the specific gravity is considerably lower,
Bonding Properties:
Skin layers, which could be easily peeled
off, were found on surfaces of wet-formed fiberboard
overlay mats. Also, the wet-formed fiberboard overlays
could be separated from OSB substrates. These are
indications of resin pre-cure. The high amount of heat
energy used to dry wet-formed mats could cause curing
of the resin in fiberboard surface layers of mats.
Table 1 shows differences in caliper swelling
after one hour boiling between the two mat forming
processes. The wet-formed OSB-fiberboard composite
structure swelled a full 0.1 inch more in the
fiberboard overlay than the dry-process fiberboard
overlay. The average caliper swelling of OSB overlaid
with dry-formed mats is significantly and unexpectedly
lower than that of OSB overlaid with wet-formed mats.
After boiling, complete separation of wet-formed
overlays from substrates was found, whereas, no
delamination occurred in the OSB dry-process fiberboard
composite structure.
~G."~~~~~~ er:.:o
- 30 -
TABhE I
Caliper Swelling Of Dry-Formed And Wet-Formed
Overlay Mats After One Hour Boiling
Average Caliper Swelling
Wet-Formed 49.667
Dry-Formed 31.556
Embossing Fidelity:
OSB specimens overlaid with dry-formed
fiberboard mats exhibited visually distinctly better
embossing fidelity than OSB/wet-process fiberboard
structures. Sharp, precise transference of the details
of the embossing plate, with transference of sharp
corners was achieved with the dry-process fiberboard
overlays~but not with wet-process fiberboard overlays.
Bonding Strength:
The OSB specimens overlaid with dry-formed
fiberboard mats had an internal bonding strength of
90 prig vs. 78 psig for OSB specimens overlaid with the
wet-process mats.
One of the problems encountered by Applicants
in applying a single fiberboard overlay over one major
surface of a balanced three layer oriented strand board
was that upon exiting the hot consolidation press, the
~t~!~'~J"'~~:.
- 31 -
product cupped, or turned up at its longitudinal edges.
In commercial trials, this cupping occurred even at 150
pounds per thousand square feet fiberboard overlay
basis weights. For example, a composite board having a
top fiberboard layer with a basis weight of 300 pounds
per thousand square feet (Lb/MSF) over a three layer
OSB:428 Lb/MSF - 367 Lb/MSF - 428 Lb/MSF, cupped
severely at its longitudinal sides upon removal from
the heated consolidation press after all layers were
consolidated simultaneously in the hot press. Attempts
to approximately balance the composite board by
providing substantially less strand thickness in the
OSB layer directly under the fiberboard overlay, e.g.,
100 Lb/MSF, so that closer to the same weight of
material is above and below the 367 Lb/MSF core, will
not provide a composite board free from warp or
cupping. Surprisingly, it was found for a 300 Lb/MSF
fiberboard overlay, best results were achieved when the
OSB layers forming the OSB baseboard have thicknesses
such that 30% of the OSB strands are provided in the
layer interfacing the fiberboard overlay; 31% of the
OSB strands are provided in the OSB core layer; and 39~
of the OSB strands are provided in the exposed OSB
(back) layer.
Similar, non-warping results can be achieved
with either wet process or dry-felted fiberboard mat
overlays, so long as the center OSB (core) layer 105,
having strands in a random or cross-machine direction,
comprises about 25% to about 35% of the total thickness
of the three OSB layers combined, and the exposed
(back) OSB layer 101 is about 25% to about 35% thicker
than the OSB layer 107 bonded to the fiberboard overlay
111 (after consolidation). These non-warp results
apply, for these thickness relatianships over the full
~~~~~ I ~.
- 32 -
range of 75 - 400 Lb/MSF fiberboard overlays.
Generally, the fiberboard overlay will have a thickness
about 50% to about 125% the thickness of the OSB core
layer. A minimum core thickness of about 1/16 inch
provides sufficient structural integrity to the
composite OSB structure of the present invention for
its use as a siding or panelling product. In a
preferred embodiment, the baseboard comprises three
layers - the OSB layer adjacent to the fiberboard
overlay comprising 27.7% to about 33.3% of the total
baseboard thickness; the OSB core layer comprising
about 25% to about 35% of the total baseboard
thickness; and the bottom OSB layer comprising about
36.1% to about 43.1% of the total baseboard thickness.
Examples of useful thicknesses to provide
non-warping composite-OSB products, wherein the
fiberboard mat overlay can be formed by a wet-laying
operation, or by dry-felting are as follows:
Example No. 8
Layer Thickness
Wet-laid fiberboard
overlay layer 111 0.070 inch
Machine direction
OSB layer 107 0.092 inch
Random or cross-machine 0.070 inch
direction core 105 (25% of OSB
layers)
Machine direction exposed 0.120 inch
back OSB layer 101 (30% thicker
than layer 107)
OSB Total 0.282
2('~"~~~a'~:
- 33 -
Example No, 9
Layer_ Thickness
Dry-felted fiberboard
overlay layer 111 0.110 inch
Machine direction
OSB layer 107 0.089 inch
Random or cross-machine 0.080 inch
direction core 105 (28% of OSB
layers)
Machine direction exposed 0.117 inch
back OSB layer 101 (30% thicker
than layer 107)
OSB Total 0.286
Example No. 10
Layer Thickness
Wet-laid fiberboard
overlay layer 111 0.080 inch
Machine direction
OSB layer 107 0.071 inch
Random or cross-machine 0.090 inch
direction core 105 (35% of OSB
layers)
Machine direction exposed 0.096 inch
back OSB layer 101 (35% thicker
than layer 107)
OSB Total 0.257
a~~'~i'~~"'~'; a
- 34
Example No. il
L_aYer Thickness
Dry-felted fiberboard
overlay layer 111 0.090 inch
Machine direction
OSB layer 107 0.097 inch
Random or cross-machine 0.100 inch
direction core 105 (31% of OSB
layers)
Machine direction exposed 0.126 inch
back OSB layer 101 (30p thicker
than layer 107)
OSB Total 0.323
Exam s~l a No . 12
Layer Thickness
Wet-laid fiberboard
overlay layer 111 0.100 inch
Machine direction
OSB layer 107 0.095 inch
Random or cross-machine 0.120 inch
direction core 105 (35% of OSB
layers)
Machine direction exposed 0.128 inch
back OSB layer 101 (35% thicker
than layer 107)
OSB Total 0.343
- 35 -
Exampl8 No. 13
LLayer Thi.akness
Dry-felted fiberboard
overlay layer 111 0.085 inch
Machine direction
OSB layer 107 0.137 inch
Random or cross-machine 0.130 inch
direction core 105 (29% of OSB
layers)
l0 Machine direction exposed 0.182 inch
back OSB layer 101 (33~ thicker
than layer 107)
OSB Total 0.449
Exampl8 No. 14
Layer Thickness
Dry-felted fiberboard
overlay layer 111 0.095 inch
Machine direction
OSB layer 107 0.121 inch
Random or cross-machine 0.135 inch
direction core 105 (33% of OSB
layers)
Machine direction exposed 0.153 inch
back OSB layer 101 (27% thicker
than layer 107)
OSB Total 0.409
~f':'~'~~ : ;.
- 36 -
It should be understood that the present
disclosure has been made only by way of the preferred
embodiments and that numerous changes in details of
construction, combination and arrangement of parts can
be resorted to without departing from the spirit and
scope of the invention as hereunder claimed.
