Note: Descriptions are shown in the official language in which they were submitted.
2111510
41592-134
WOOD BASED COMPOSITE
This invention relates to a method of finishing a
wooden surface.
In any industry that involves the reduction in size
of non-uniform materials at high speed, particularly in
saw milling, the cutting action of the tool results in
very rough surfaces and variable dimensions of the cut
pieces. A saw mill cutting lumber to a nomi n~l thickness
of one inch will obtain actual thicknesses ranging from
0.5 to 1.25 inches. r~Am;nAting such pieces to produce
larger members for structural or decorative applications
requires that the pieces be planed to uniform thickness
with smooth surfaces. Failure to finish in this way will
prevent the application of an adhesive or the formation
of a durable bond. The cost of processing the wood to
obtain the requisite surfaces and the amount of waste
generated are both high. The processing of nominAl one
inch lumber to meet the adhesion requirements can result
in losses of wood fibre in the range 25 to 40 percent by
weight of the original wood.
The present invention seeks to provide a method of
avoiding the above processing and thus the consequent
waste.
The invention seeks to avoid the waste involved in
the above processing and is a method of finishing a
wooden surface, said method comprising applying to the
surface a composition comprising, (a) a thermosetting
adhesive; (b~ a mat comprising wood fibre, a
thermosetting resin and at least one other fibre having a
longer strand length than the wood fibre; and applying
heat and pressure sufficient to bond the components to
each other and to the wooden surface.
Although the present invention is useful in
finishing any wooden surface, its preferred application
-- 2
is in the finishing of a rough wooden surface, such as
would result from a saw cut.
The thermosetting resin is preferably phenol-
formaldehyde. However, other useful thermosetting
adhesives include phenol-resorcinol-formaldehyde resin,
resorcinol-formaldehyde resin, urea-formaldehyde resin,
melamine-urea-formaldehyde resin and melamine-
formaldehyde resin.
The wood fibre of the mat may be either mechanically
refined without delignification or chemically refined
with some degree of delignification. The wood fibre may
be derived from virgin or recycled, including post-
consumer, wood. In carrying out the manufacture of the
wood mat, the fibre is treated with the thermosetting
resin and dried. The dried, resinated wood fibre is
formed into a mat in an air-laid process. This mat is
intimately mixed with another mat composed of at least
one other fibre. That fibre may be a synthetic material
such as polyester or a polyolefin, or a natural material
such as hemp, flex jute or kenaf. The two mats are
blended together by passing them through a toothed
roller. A fine synthetic scrim is fed onto the bottom of
blended mat as a carrier and the entire mat-scrim
assembly is needled to produce a string fibre mat with
mechanically interlocked wood and synthetic fibre.
In practising the invention the combined fibre mat
is placed on top of lumber, for example nominal one inch
thick pieces of spruce - pine - fir (SPF) as commonly
produced in Western CAnA~A. A layer of the thermosetting
adhesive is applied between the two layers. The mat is
transferred to a heated platen press which bonds the
materials of the mat and bonds the mat to the lumber
substrate. In general the pressing conditions are chosen
such that compression of the lumber substrate is
~ _ 3 _ 2111510
minimized while the fibre layer is compressed to a
density of up to 1.2 g/cm2.
The following examples illustrate the invention. In
the drawings referred to in these examples:
5Figure 1 relates thickness of the composition to the
position on the wooden surface;
Figure 2 illustrates the mouldability of the
composition of the present invention;
Figure 3 shows density profiles achieved on an X-ray
density analyzer; and
Figure 4 relates the screw withdrawal resistance of
the composition of the present invention and other,
comparative materials.
General Procedure
15Rough, kiln-dried lumber with a moisture content in
the range 8 - 16%, based on the weight of dry wood, and
with nominal thickness and width or 25-50 mm and 75-300
mm respectively is planed to a thickness between 14 and
38 mm. A thermosetting adhesive layer, cont~ining
phenol-formaldehyde, phenol-resorcinol-formaldehyde,
resorcinol-formaldehyde, urea-formaldehyde, melamine-
urea-formaldehyde or melamine-formaldehyde resin but
preferably comprising a) a commercially available phenol-
formaldehyde resole resin, b) wood flour, c) wheat flour,
d) soda ash and e) water, is applied at a rate of about
0.244-0.489 kg/m2 to both faces of the lumber. On top of
the adhesive is placed a pre-formed mat consisting of a)
refined wood fibre (80-90%); b) phenol-formaldehyde or
urea-formaldehyde thermosetting resin (4-9%); and c)
polyester, thermoplastic or natural fibre (4-12~). The
combined five element construction, comprising from top
to bottom, fibre mat, adhesive, lumber, adhesive, fibre
mat is consolidated and cured in a flat platen hot press.
The platens are heated to a temperature in the range 150-
211l510
-- 4
250C. The platens are closed at a rate of 20-40 mm/sec
to a separation of 140-240% of the final thickness of the
product and at a rate of 1-10 mm/sec until the r-~;mum
pressure is obtained. The final position is chosen so as
to allow fibre layer thicknesses of 2-6 mm. The maximum
pressure exerted on the board is in the range 20-30
kg/cm2. The total press time, daylight to daylight,
ranges from 2-3.5 minutes and includes from 0-4 breathing
cycles of 5 to 15 seconds, which prevents steam pressure
from causing inter- or intra-l~m; n~r rupturing of the
elements and are achieved by opening and re-closing the
press. At the end of the pressing cycle, the platens are
separated to allow the finished boards to be removed from
the press. The boards are subsequently stacked together
so as to cool slowly to room temperature and allow
complete curing of the adhesive.
The following examples illustrate the invention more
specifically.
Example 1
New Composite Products
Four 16 inch lengths of clear kiln-dried SPF lumber
with a moisture content in the range 8-16% and with
nominal thickness and width of 1 inch and 4 inches
respectively were planed to a thickness of 14 mm. A
layer of thermosetting adhesive as described in Table 1
was applied at a rate of 0.244 kg/m2 to both faces of each
piece of lumber at room temperature. On top of each
glued face was placed a similarly sized section of pre-
formed fibre mat from Canadian Forest Products Ltd.'s
Panel and Fibre Division. The basis weight of the fibre
mat was 2.4 kg/m2 and the thickness was 25.4 mm. The four
sets of combined elements were placed in a hot press with
16 x 18" platens heated to 205C. The platens were
closed at a rate of 27 mm/sec to a separation of 45 mm
and then at a rate of 3 mm/sec to a pressure of 24 kg/cm2.
21Il~lU
-- 5
The minimum separation of the platens was governed by a
pair of aluminum bars of 19.0 mm thickness on the sides
of the bottom platen. Once the pressure reached the
maximum value, a timer was started. The pressure was
maintained to an elapsed time of 60 seconds before the
platen separation was increased to allow venting of the
steam pressure. This opening and the subsequent closing
was completed at an elapsed time of 65 seconds. The
pressure was maintained again at 24 kg/cm2 until an
elapsed time of 90 seconds when the pressure was again
removed and reapplied. This was completed at an elapsed
time of 95 seconds. The maximum pressure was then
maintained until an elapsed time of 120 seconds when the
platen separation was increased and returned to 19.0 mm
by an elapsed time of 125 seconds. At an elapsed time of
150 seconds, the platens were separated to allow removal
of the pressed boards. The boards were stacked on top on
one another to retain heat and complete the cure of the
adhesive.
The difference between the lumber thickness and the
thickness of the product is accounted for by the pressed
fibre, neglecting any compression of the lumber
substrate. In this example the target thickness of the
fibre layer in the finished product was 2.5 mm. This
corresponds to a density of that layer of ca. 1.0 g/cm3.
This example demonstrates the feasibility of using
fibre mats for overlaying solid wood substrates.
_ - 6 - 2~ 9
Table 1
Phenol-Formaldehyde Thermosetting Adhesive
Liquid Resole Resin 43.70
Water 14.31
-Wood Flour 7.31
Wheat Flour 5.91
Soda Ash 1.97
Mix for 20 minutes
Liquid Resole Resin 19.81
Water 6.99
Mix for 5 minutes
Total 100.00
211151~
-- 7
Example 2
SPF Lumber with Various Thickness Profiles
Example 1 described the preparation of the new
composite using smooth, planed lumber as the substrate.
One of the main advantages of this invention is the
ability of the fibre mat to mould to the shape of the
lumber substrate and effectively mask any thickness
variations or extreme roughness. It is a desirable
feature of the invention that large variations in the
thickness of the substrate can be tolerated without
impairing the bonding at the solid wood/fibre interface.
To illustrate this point, some samples of the
composite were prepared from lumber that had been
analyzed with a custom built laser-based thickness
scanner. The system consisted of a conveyor, laser heads
and sensors mounted above and below the conveyor, data
acquisition card, encoder and personal computer. The
lumber thicknesses were determined by subtracting the sum
of the distance from the bottom laser head to the bottom
of the board and the distance from the top laser head to
the top of the board from the total distance between the
laser heads. This technique allowed non-contact
measurement unaffected by any vertical board movement.
In this manner, the data depicted in Figure 1 were
collected from 4 pieces of lumber. Board 1 was a sample
of rough, unplaned lx4 SPF with an average thickness of
approximately 28.5 mm from a C~nA~;an Forest Products
sawmill in northern British Columbia. Board 2,3,4, were
from the same source but had been planed in the
laboratory to average thickness of ca. 27.4, 25.1, 22.1
mm respectively.
These boards were overlaid with wood/polyester fibre
mat using the conditions described in Example 1. Inter-
laminar adhesion of the pressed composite were evaluated
using a modification of ASTM D 2338-82, St~n~rd Test
2111~10
-- 8
Method for Strength Properties of Adhesives in Two-Ply
Wood Construction in Shear by Tension Testing in which
the samples were sliced so that the lumber r~m~;n;ng was
the same thickness as the pressed fibre layer. In this
way, each glueline could be evaluated as two-ply
construction. The results of the shear testing are shown
in Table 2 and reveal that the strength of the inter-
lAm;nAr bond does not depend on the average thickness or
the thickness profile. At the end of the test, the
broken samples were inspected and the reason for the
breakage was determined by visual inspection and ascribed
to solid wood failure, fibre mat failure, glueline
failure or a combination thereof. The amount of glueline
failure during the test is very small in all cases.
This example demonstrates that lumber thickness and
surface roughness are not key determinants of the
integrity of the present invention and that smooth lumber
surfaces, usually of vital importance to the bond quality
of laminated wood composites, is not required in the
invention.
21~
Ll
Ll
a) u
u
,1 Ll ~ O
a~ _I o ~ U~
_I ~
~'
C
Ll,
¢-,1
U~
~d t~ ~N tY ~ C`~l Ul
tU-- ~d
u~ ~ 3
a,
L -- n
r tJ~ D o x
~ U~
~ ~ ~ ~ a
U, -- Ll
m -
u~
~q u
a a)
u~ ~ _
O
Q. U
e ,l-- . n
o~ ~ ~ o 1- u a
u~
u~ ~
U~ ~ Ll
~ ~ O
Ll ~:-- Co oo Co
O O O O ~ Ll
-1 U ~ . .
E~ O
o $
U~ ~ 3
Ll
ao o q)
er
u k n~
~ '
::1 h
u~ a~
~1
O ~ t~
h
O ~1 ~1 ~1 ~ ~
O lI ~ ~ ~ ~ ,1
.,
a
u a,
E~ h
a) - a)
_I 'J~ -
Z
2111510
-- 10 --
Example 3
Density Profile Measurements
Lumber thickness variations such as those described
in Example 2 are compensated for in this invention by the
mouldability of the fibre mat which allows the fibre to
fill depressions and voids in the lumber surface. As a
result, the density of the fibre layer is lower in
density in such areas.
To demonstrate this property, some composite
0 samples, as shown in Figure 1, were prepared from lumber
10, machined to create some exaggerated thickness changes
as shown at 12, and mat 14. In the samples prepared
distance D was 1.5, 3.0, 4.5 or 6mm. Finished height H
was 36mm. These samples were analyzed on a Recon Model
8900/DA X-Ray Density Analyzer and the resultant density
profiles are shown in Figure 2. The sample with the
shallowest depression (40X) clearly shows 3 distinct
density ranges. In the middle, the density is constant
at approximately 0.40 g/cm3 which corresponds to the
density of the lumber substrate. On each face, there is
a high density region resulting from the pressed fibre
mat. In each of these fibre areas there is also some
density variation as the density in the middle of the
region is lower than the density either at the lumber
interface or the surface that would have been next to the
platen during pressing. The density profile of the fibre
layers changes as the depth of the depressions becomes
greater (Samples 50x, 60x and 70x). In these cases, the
average density of the fibre regions lowers considerably
on the side cont~;n;ng the depression. In fact in the
extreme cases, the density of the fibre layer is lower
than that of the lumber. However, there are also some
noticeable changes in the fibre layer on the side
opposite to the depression. In this case there is also a
lowering in average density and the density profile
across the fibre layer becomes more pronounced.
2111Sl~
Therefore, the conclusion is that both fibre layers
assist in masking a defect on one of the faces.
Another advantage of this invention is that the
average density is considerably lower than other wood-
based composites such as particleboard or medium densityfibreboard. This is advantageous from the point in view
of the user (e.g. better machinability and lower shipping
costs) and the producer (e.g. increased fibre
utilization). However, the composite does have a high
surface density of up to 1.0 g/cm3. In fact, it is
possible, by changing the fibre layer thickness, to alter
the surface density to produce a desired surface
property. This is important since the surface qualities
(e.g. bending strength - see Table 4 - abrasion
resistance and paintability) depend on surface density.
The above example demonstrates why the strength to
weight ratios of the present invention are superior to
other wood based composites such as particleboard or
medium density fibreboard. In simple terms, the product
can be described as being "strong and light".
Example 4
Other Processing Parameters
The procedure of Example 1 was repeated several
times with the following changes being made: 1) the total
time in the hot press was varied from 1.75 to 2.75
minutes and 2) the open assembly time (i.e. the amount of
time from the application of the adhesive to the lumber
substrate and the mating of the fibre mat to that layer)
was varied from 0 to 20 minutes. The pressed samples
were tested for inter-laminar adhesion using ASTM D 2339-
82, Standard Test Method for Strength Properties of
Adhesives in Two-Ply Wood Construction in Shear by
Tension Testing. The samples were tested for shear
values and position of failure (either glueline, wood or
211 1~10
- 12 -
fibre). The results, as shown in Table 3, show that 2.50
- minutes press time appears to be the optimum condition
for this combination of materials as the shear values are
near the maximum and the glueline failure is near the
min;~nm for all assembly times. However, the product
will tolerate other processing parameters required by
available species, materials, equipment or ambient
conditions.
- 13 - 2111~
Table 3
Inter-Laminar Adhesion of Fibre Mat Overlaid SPF
Open Press Stress Glueline
SampleTime Time Average Failure
(min) (min)(psi) (%)
A 0 1.75 136 94
198 48
171 50
197 50
189 25
B 0 2.00 148 75
92 68
238 06
202 06
223 12
C 0 2.25 164 50
89 63
217 00
237 00
220 00
D 0 2.50 237 01
233 00
229 00
214 00
225 00
E 0 2.75 239 00
207 00
245 00
236 00
216 01
2 llI510
- 14 -
Example 5
Incorporation of Other Natural Fibres
The above examples describe the use of fibre mats
composed of a mixture of natural wood and synthetic
(polyester) fibres. However, it is possible to replace
the synthetic fibre with other, natural materials such as
flax. In a typical experiment, resinated hemlock fibre
used in production of Woodmat at C~n~ n Forest Products
Ltd.'s Panel and Fibre Division (90%) was combined with
0 flax fibre (10%) cut to approximately 7.5 cm in length.
The flax (237.84g, 11.9% moisture) and hemlock (2156.88g,
11.9% moisture) fibre were blended in a static Littleford
mixer for 10 minutes. A portion (89.23g) of the blended
fibre was formed into a mat on each side of a 16" section
of SPF lx4 that had previously been coated with the
adhesive described in Example. 1. The resulting billet
was pressed under the same conditions as those used for
the polyester cont~;n;ng mats. The flexural (Modulus of
Rupture = 9400 psi, Modulus of Elasticity = 1066000 psi)
and lap shear properties (Stress = 200 psi) were in the
same range as those obtained for polyester-cont~;n;ng
samples.
The above example demonstrates that fibres, other
than polyester, that possess a length to width ratio and
good tensile strength can be used to prepare the
composite.
Example 6
Strength Properties
Test methods were taken from ASTM D1037-87, St~n~rd
Methods of Evaluating the Properties of Wood-Base Fibre
and Particle Panel Materials and ASTM D143-83, Standard
Methods of Testing Small Clear Specimens of Timber. The
Screw Withdrawal test was adapted for use with 19 mm
material by prorating the lead hole and screw insertion
depths to 12.75 mm. The material prepared as described
- - 15 - 2111~10
in Example 1 was compared with other wood composite
materials such as a) hardwood plywood bO a composite
comprised of a softwood veneer crossband laminate over a
particleboard core c) particleboard, and d) medium
density fibreboard. These samples were obtained from
commercial supplies and are believed to be representative
of products generally used in the marketplace. The
results are shown in Table 4 and demonstrate the
superiority of the present invention over currently
lo available wood base composites as it is up to 2-3 times
stronger than some other composites.
- 16 -
Table 4
Physical Properties of Wood Based Composites
Edge
Type ModulusModulus of Screw
Density of RuptureElasticityRetention
(g/cm^3) (psi) (psi) (lb)
Hardwood Plywood 0.523 6430 580800 140
Particleboard/Veneer Composite 0.585 4160 306300 90
Paticleboard 0.720 1700 327800 80
Medium Density Fibreboard 0.746 4990 455600 130
Oriented Standboard 0.649 2420 325600 150
Present Invention 0.538 7690 685300 200
2111~1~
-
- 17 -
Example 7
Retention of Screw Withdrawal Resistance
As an extension of the Screw Withdrawal results
described in Example 2, the ability of the materials to
retain withdrawal resistance after multiple failures was
investigated. The test consisted of applying load to the
screw until failure, reinserting the screw to the initial
depth and retesting the sample. This was repeated up to
5 reinsertions. The results are graphically displayed in
Figure 4 and show that even after 5 reinsertions this
invention offers withdrawal resistance superior to the
initial resistance of any of the other composites. Since
fastener retention is an important property of materials
used in the manufacture of furniture, casegoods and
cabinets, this invention should find applications in
those areas.
Although the forgoing invention has been described
in some detail by way of illustration and example for
purposes of clarity of underst~n~;ng, it will be readily
apparent to those of ordinary skill in the art in light
of the teachings of this invention that certain changes
and modifications may be made thereto without departing
from the spirit or scope of the appended claims.
