Note: Descriptions are shown in the official language in which they were submitted.
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1 FIELD OF THE INVENTION
2 The present invention relates to an overlaid corrugated
3 wafer board panel and to the process for making it.
4 BACKGROUND OF THE INVENTION
Typicallyl a wafer board panel comprises layers of wood
6 flakes or wafers formed into a composite structure using a
7 resinous binder. The preparation of wafer board panels is
8 complex, but broadly consists of two principal stages. The first
g stage comprises the preparation of the wafers and the admixing
thereof to form a loose layer or mat. The second stage involves
11 subsequent compression and heating of the mat to cure the resin
12 and form the consolidated panel.
13 Until recently, wafer board was manufactured in the
14 form of planar or flat sheets. However, as disclosed in U.S.
Patent 4,616,991, the present applicant has developed an
16 apparatus and process for the manufacture of panels having a
17 wave-like or corrugated configuration. Such wave-board panels
18 have improved structural strength properties, relative to planar
19 panels.
This prior patented apparatus involved a pair of
21 opposed, spaced-apart, upper and lower platens. Each platen was
22 formed of adjacent lengths of chain-like links. When the lengths
23 were moved laterally inwardly, they would shift from a planar to
24 an undulating corrugated form.
The process steps involved:
26 distributing a mat of loose wood wafers together
27 with a binder between the upper and lower platen
28 surfaces while they were maintained in the planar
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1 configuration;
2 - biasing the platens together to pre-compress the
3 mat, and thereby substantially fixing the wafers
4 together to limit their further relative movement;
- converting the two platen surfaces, still in
6 pressing association with the mat, from the planar
7 to the corrugated configuration; and
8 - applying additional pressure and heat for a
g sufficient time to cure the binder and produce a
corrugated wave-board panel.
11 The main advantage inherent in the patented process was
12 that the panel product so formed was characterized by having a
13 substantially uniform density. This was achieved because the
14 wafers were fixed by the pre-compression step and because the mat
was not significantly stretched or elongated during the
16 conversion from the planar to the corrugated configuration.
17 It would be an advantage if one could provide an
18 overlaid corrugated panel. By overlaid is meant with veneer, or
19 the like on at least one face thereof. Such veneer-clad product
would be useful for high structural strength purposes. By veneer
21 is meant 1-6 mm thick rotary cut wood sheets of substantial size.
22 The manufacture of a corrugated, veneered plywood has
23 been attempted in the prior art has been unsuccessful. This is
24 due to the structural failure of the veneer layer probably
because of the particular orientation of the grains lying in a
26 direction perpendicular to the direction of the wavetop of the
27 plywood panel.
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SUMMARY OF THE INVENTION
In accordance with the present invention, it has been
3 found that an overlaid corrugated wave-board panel may be
4 manufactured in a single stage. The process involves the concept
of:
6 _ utilizing corrugated platens like those described
7 in the '991 patent i.e. platens which are
8 mechanically convertible between a planar and a
g corrugated configuration;
~ placing the overlay to be used namely the sheet of
11 veneer or the like, on the lower press platen;
12 _ distributing the mat of loose wood wafers in
13 admixture with a binder onto the overlay sheet;
14 optionally placing a second sheet of overlay over
the mat;
16 biasing the platens together to pre-compress the
17 mat substantially fixing the wafers so as to limit
18 their relative movement and bringing the overlay
19 into contact therewith;
- converting the two platen surfaces, still in
21 pressing association with the mat and the overlay,
22 from the planar to the corrugated configuration so
23 as to translate both the overlay and mat in
24 combination in a single stage from the planar to
the corrugated overlaid form; and
26 - applying additional pressure (and optionally heat~
27 so as to cure the binder and adhere the overlay to
28 the mat core to thereby provide a cohesive
29 overlaid corrugated wave-board panel.
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1 The process relies on the concepts of converting the
2 overlay and mat in combination, in a single stage from the planar
3 to the corrugated form.
4 Nore ~pecifically, it has been determined that in order
to manufacture a veneer overlaid corrugated waferboard (wherein
6 the veneer layer is more than l mm thick) the wood veneer grains
7 must be orientated in a direction substantially parallel to the
8 direction of the wave tops. Furthermore, it is preferred that
g the moisture content of the core be in the range of between about
5% to about 15~.
11 An advantage of the panels of the present invention and
12 the process thereof resides in the improved strength properties
13 of the panels as will be demonstrated hereinafter.
14 In a first broad aspect, the invention is a corrugated
veneer overlaid panel which comprises: a binder-coated wafer
16 core which has been subjected to binder curing and compression
17 and a veneer overlay bonded to one face of said core which
18 overlay has been subjected to compression and densification.
19 In a second broad aspect, the invention is a process
for making a corrugated panel having an overlay thereon which
21 comprises: placing the overlay sheet onto the press platen;
22 distributing a mat of loose binder-coated wood wafers between the
23 overlay and the upper press platen or optionally between two
24 overlay sheets, said platens being adapted to be mechanically
actuated to move the surfaces together and when further required
26 to be converted from the planar configuration to a wave-like
27 configuration; biasing the platens together vertically to
28 precompress the mat between the planar surfaces to substantially
29 fix the wafers together to limit their further relative movement;
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converting the two platens and their platen surfaces still in
2 pressing association with the mat and overlay, from the planar to
3 the corrugated configuration; and applying heat and additional
4 pressure using the platen surfaces to the mat and overlay for a
sufficient time to cure the binder and adhere the overlay to the
6 mat and produce a corrugated wafer board panel having an overlay
7 thereover.
8 DESCRIPTION OF THE PREFERRED EMBODIMENT
9 The overlaid corrugated wafer board panels having a
10 wave-like configuration were prepared using the process and
11 platen system described in U.S. Patent 4,616,991. As stated
12 earlier, the platen system involved a pair of opposed, spaced-
13 apart upper and lower platens. Each platen was formed of
14 adjacent lengths of chain-like links. Upon application of a
lateral force thereto, the link assembly would move from a planar
16 to a corrugated form. The final outside dimensions of the
17 prepared panels were 24" x 36", the core plus overlay thickness
18 was approximately 11.3 mm (7/16"), and the panel depth wave peak
19 to bottom was 63.5 mm (2-1/2"). Additionally, it can be
appreciated that the final panel size can be scaled up to 1220 x
21 4880 mm (4' x 16'). Overlaid boards having panel core plus faces
22 densities approximately 750 kg/m3 were prepared.
23 ~he process for preparing the overlaid corrugated wafer
24 board comprised the following steps.
The furnish could be prepared using various wood
26 species or other fibrous lignocellotic materials e.g. flax or
27 sugarcane. Aspen logs approximately 8' in length and 6" - 14" in
28 diameter were used. The logs were cleaned, debarked, waferized
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1 and screened. The strand or wafer length averaged 76 mm (3 ) and
2 the thickness was about 0.76 mm (O.03"), however other strand or
3 wafer geometrics can be used.
4 The moisture content of the furnish was reduced from
the green state to about 5% to 10% using commercial dryers. The
6 wafer was screened following drying.
7 At 5~ moisture content, the furnish was blended with 2%
8 by weight of isocyanate resin and 1~ by weight wax in a
g laboratory drum blender.
Resin was utilized as a binder for the wafers and to
11 adhere the veneer or metal overlay to the wafer board core.
12 The wax and wax/resin in admixture were arranged
13 loosely by hand onto the overlay sheet which had been positioned
14 on the lower platen. The quantity of wafers and resin used were
sufficient to produce a board having the requisite density.
16 The overlay sheet could comprise veneers such as
17 Douglas fir, Spruce or Pine. The thickness of the sheet would
18 preferably range from between about 1 mm to about 6 mm. The wood
19 grains making up the veneer would be orientated substantially in
one direction.
21 In the press, the mat and overlay sheet were subjected
22 simultaneously to high temperature, which set the binder, and to
23 high pressure which compressed the mat to specified thickness,
24 and into adhesive engagement with the overlay sheet. The overlay
sheet would be positioned in the press so that the wood grains
26 thereof would be orientated in a direction generally parallel to
27 that of the wave tops. More particularly, the corrugated platen
28 temperature was maintained at 205C. The platen was heated by
29 electrically heated rods extending within the press platens.
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1 The open or fully extended surface area of the platens
2 was 920 x 920 mm.
3 To obtain pre-compression and corrugation the press was
4 operated in a manual control mode. Once the mat and overlay
sheet were in place on the platens, a vertical pre-compression
6 force of less than 3.4 x 106 Newtons were applied. Application
7 of this force brought the top and bottom platens towards one
8 another. At this displacement, the platens were, following pre-
g compression, actuated into the corrugated configuration by
application of a horizontal side force of less than 0.52 x 106
11 Newtons thereto.
12 It is to be noted that the application of this pressure
13 (of the order of about 450 p.s.i.) imparts a desirable degree of
14 densification to the veneer, thus improving the strength
properties thereof in unit volume of same.
16 A final compression was applied by bringing the press
17 platens closer together, until the latter reached their stops.
18 The panel was retained between the press platens for several
19 minutes to allow the resin to set.
Prior to removal of the finished wafer board panel from
21 the press, the pressure was released slowly to avoid steam
22 release damage.
23 The panels were then cooled.
24 EXPERIMENTAL
Table I herebelow is included to illustrate
26 the improved structural properties imparted by providing a veneer
27 face to a corrugated wafer board in comparison to a corrugated
28 wafer board and a flat waferboard.
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1 Table I
2 Wafer-core + Wafer Flat
3 Veneer faces of only Waferboard
4 Sample corrugated panel corrugated panel
Hoop PineSlash Pine All Wafer All Wafer
6 2.4 mm 2.4 mm No Veneer No Veneer
7 Panel Density 742 752 647 661
8 (kg/mm3)
9 Panel Mass 9.3 9.4 8.6 7.3
( kg/mm2 )
11 Wave Length 188 188 188 ---
12 (mm)
13 Panel Depth 65 65 65 ___
14 (mm)
Skin* Thickness 10.4 10.4 11.2 11.1
16 (mm)
17 "Strength" 5430 5350 4000 630
18 Unit Max.
19 Bending Noment
(N.mm/mm)
21 "Stiffness~ 29.9-106 29.2-106 20.4-106 0.7_106
2232 Unit EI
24 (N-mm/mm)
2 Moisture 5.1% 4.9% 4.1% 2.9%
265 Content
27 * Core + Faces.
28 The corrugated wafer board having no veneer, and having
29 random wafer orientation was used as the control.
