Note: Descriptions are shown in the official language in which they were submitted.
CA 02345555 2002-06-11
SYSTEM AND METHOD FOR FORMING WOOD PRODUCTS
Field of the Invention
The present invention relates generally to wood processing methods, and more
particularly to systems and methods of bonding wood members together.
Background
In woodworking applications, it is often necessary to bond wood pieces
together to produce a wood product. For example, recent environmental
regulations
and depletion of old-growth timber supplies have made i~t increasingly
difficult and
expensive for manufacturers to obtain high-grade lumber to use in wood
products,
which may include furniture, cabinets and millwork. One way of addressing the
shortage and high cost of high quality lumber is the use of veneered stock.
Typically,
veneered wood products are created by laminating high quality veneer over a
lower
grade core material, such as medium density fiberboard (MDF), particle board,
plywood or finger jointed stock. Use of veneered wood members results in a
substantially more efficient utilization of high quality wood, and therefore
reduces raw
material costs. Other examples of wood products produced by joining wood
members
together include door and window jambs, plywood, laminated veneer lumber, and
other laminated wood products.
Wood used in construction varies significantly in moisture content. An
elevated
moisture content of wood members may add time and cost to a lamination
process.
Recently-harvested timber may have a moisture content of 50-60% or higher,
which
may be further increased by transport of the timber along a waterway, or
storage of
processed lumber in a wet environment. Prior lamination methods frequently
require a
kiln-drying step prior to bonding to remove excess water, even from green
dimensional lumber which typically has a moisture content of about 18%. After
kiln
drying, wood has a moisture content of about 12%, providing a relatively
reproducible
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CA 02345555 2002-06-11
surface environment for bonding. However, the drying step prior to lamination
introduces a significant additional cost and increases the processing time.
For most woodworking applications, a wood bond must be strong in order to
provide structural strength and stability. For example, it is often desirable
to form a
"high-strength wood bond" that has a shear-strength exceeding the shear-
strength of
the wood itself. Generally, high strength woad bonding procedures require
application
of an adhesive to a wood surface, and subsequent pressing of the wood surface
against
another wood surface or against a polymeric material such as PVC,
polyethylene,
polystyrene, polypropylene, phenolic paper and wood fiber composites with any
one of
the above-listed polymers.
One significant limitation with prior wood bonding techniques is that the
procedure required to produce a high-strength wood bond may take a long tinge,
for
example, several hours, to produce a cured product.
Other procedures can be performed more rapidly by using an adhesive that is
activated to some extent during the pressing process. For example, adhesives
may be
activated by applying heat. These adhesives are referred to as "thermoset
adhesives."
Presses may use heating platens or radio frequency mechanisms to activate and
speed
up significantly the cure time of a thermoset adhesive. Presses with heat
activation
mechanisms are somewhat complex, and expensive. These presses may also be
limited
in their ability to achieve uniform curing in some composite configurations.
Another way of activating an adhesive during pressing is to use a two-part
adhesive system in which the two parts are substantially separate and unmixed
until
the pressing step, sometimes referred to as a "honeymooning" process. For
example,
see U.S. Patents Nos. 5,944,938 and 5,626,705. However, a problem with this
approach is that the pressing step may not adequately or reproducibly mix the
two
adhesive parts, thereby creating an inferior or inconsistent bond, or causing
delays in
the curing process. Another problem with a honeymooning process is that it is
difficult
to control the actual ratio of mixed adhesive components due to variable
penetration or
dilution of the components into the wood prior to mixing, particularly where
the
moisture content of the wood is variable.
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There is a need for universal simplified wood bonding systems and procedures
that can produce a rapidly-curing, high-strength wood bond between different
types of
wood pieces having a wide range of possible moisture contents, and between
wood and
polymeric materials such as vinyl, without requiring complicated adhesive
activation
steps while the wood pieces are being pressed.
Summary of the Invention
The invention provides systems and methods of forming a composite wood
product by using a multi-component adhesive to bond wood pieces together
rapidly
without requiring a preparatory drying operation or a subsequent heating step
to cure the
adhesive.
Accordingly, the present invention provides a method for joining wood members
together, the method comprising selecting a resorcinol based adhesive system
including
components A and B, components A and B being formulated to cure rapidly upon
mixing, providing resorcinol based adhesive components A and B in separate
containers
1 S near an adhesive application station along a conveyor path, the adhesive
components
being formulated to have a gel time of less than about two minutes,
positioning an
applicator device along the conveyor path, the applicator device having a
mixing
chamber connected to a tip member having an orifice, the tip member being
configured
to spray or splatter mixed adhesive onto a contact surface on a first wood
member being
transported on a conveyor past the adhesive application station, pumping
metered
proportions of adhesive components A and B from the respective containers,
through an
adhesive intersection, through the mixing chamber where the adhesive
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components are thoroughly mixed into a fully activated adhesive mixture,
channeling the
adhesive from the mixture intersection out of the applicator device onto the
first wood
member, contacting a contact surface of a second wood member with the contact
surface
of the first wood member, and cold-pressing the contact surfaces together
until the
S adhesive mixture is cured.
The present invention also provides a method for joining wood members
together, the method comprising selecting a resorcinol-based adhesive system
including
components A and B, components A and B being formulated to cure in less than
about
ten minutes after mixing, providing adhesive components A and B in separate
containers
near an adhesive application station along a conveyor path, positioning an
applicator
device along the conveyor path, the applicator device having a mixing chamber
connecting to a tip member having an orifice, the tip member being configured
to spray
or splatter mixed adhesive onto a contact surface on a first wood member being
transported on a conveyor past the adhesive application station, pumping
metered
proportions of adhesive components A and B from the respective containers,
through an
intersection, through the mixing chamber where the adhesive components are
thoroughly
mixed into a fully activated adhesive mixture, dispensing substantially all of
the adhesive
from the mixture intersection through a single aperture provided in the
applicator device,
onto the first wood member, contacting a contact surface of a second wood
member with
the contact surface of the first wood member, and cold-pressing the contact
surfaces
together until the adhesive mixture is cured.
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Many other features of the present invention will be realized by those versed
in
the art upon reading the detailed description which follows and the
accompanying sheets
of drawings in which preferred embodiments incorporating the principles of
this
invention are disclosed as illustrative examples.
Brief Description of the Fi ures
Fig. 1 is a partial isometric view of a wood product constructed according to
the
present invention.
Fig. 2 is a cross-sectional view of another wood product made according to the
present invention.
Fig. 3 is a cross-sectional view of another wood product made according to the
present invention.
Fig 4 is a cross-sectional view of another wood product made according to the
present invention.
Fig. 5 is a cross-sectional view of another wood product made according to the
present invention.
Fig. 6 is a timeline showing various events in a preferred method of
embodiment
of the invention
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Fig. 7 is a schematic view of a system for producing the wood products shown
in Figs. 1-5.
Fig. 8 is an enlarged detail of another embodiment of the applicator of Fig.
6.
Fig. 9 is a cross-sectional view of another embodiment of the invention for
applying adhesive to a wood surface.
Fig. 10 is a side view of a press including opposing platens for bonding wood
pieces together.
Fig. 11 is a partial side view of a press including a roller assembly.
Fig. 12 is a side view of another press designed for use in accordance with
the
invention.
Detailed Description
A wood product constructed according to the present invention is shown in
Fig. 1 and indicated generally at 10. Product 10 includes wood members 12 and
14,
which are adhered together by an adhesive 16. As used herein, the term "wood"
1 S includes all known wood-based and cellulosic materials, including lumber,
processed
wood products, particle board, fiberboard, finger jointed stock, cellulosic
materials,
and paper.
In Fig. 1, members 12 and 14 generally represent any wood member falling
within the scope of the above definition. Each member 12 and 14 includes a
contact
surface 18 and 20, respectively, that face each other in a generally opposed
relationship and define a region of overlap, which is generally indicated at
22. It is
within the scope of the present invention that wood members 12 and 14 may vary
in
composition, size and shape, and may include, for example, components of
window
and door frames, layers of wood, processed wood, unfinished wood, finished
wood,
etc. For example, in Fig. 2, adhesive 16 extends between the opposed contact
surfaces
in the region of overlap to secure together wood members 24 and 26 to form
wood
product 28, which in Fig. 2 is a door frame. In Fig. 3, wood member 30 is a
core, and
wood member 32 is veneer, which is secured to core 30 by adhesive 16 to form a
veneered product 34.
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In Figs. 1-3, one surface of each member is adhesively joined to a
corresponding contact surface of another member, however, a single wood member
may have multiple wood members secured to one or more of its surfaces by
adhesive
16. For example, in Fig. 4 a central core 36 is adhesively secured to four
wood
members 38, 40, 42, and 44 by adhesive 16. Core 36 includes plural contact
surfaces
48, 50, 52 and 54, which are each adhesively secured to a corresponding
contact
surface 56, 58, 60 and 62 on wood members 38, 40, 42, and 44, respectively.
Typically, core 36 is a lower grade wood material, such as MDF, finger jointed
wood
or low-grade lumber, and wood members 38, 40, 42, and 44 are veneer. As shown,
product 46 is shaped to be a window sill, although the particular shape and
configuration of core 36 and its contact surfaces may vary. Alternatively, one
wood
member may be wrapped around one or more contact surfaces of another wood
member, such as disclosed in U.S. Patent No. 6,214,148 issued April 10, 2001,
which is entitled "System for Applying a Wood Veneer Across a Corner of an
Elongate Core'
In Fig. 5, a wood product 62, also referred to as a wood assembly, is shown
with a multiplicity of wood members 64, 66, 68, 70, 72 and 74 forming multiple
overlapping layers that are adhesively secured together by plural layers of
adhesive 16
to form a composite that generally resembles plywood. In Fig. 5, six wood
members
are shown, although the number and compositions of the wood members may vary
and
still be within the scope of the present invention.
It should be understood that the examples of wood products discussed above
and illustrated in Figs. 1-5 are intended to provide illustrative, non-
limiting examples
of wood products that are within the scope of the present invention and which
may be
produced by the invented system and method. Also, the thickness of adhesive 16
has
been exaggerated in the Figures for purposes of illustration.
.
Unlike thermoset adhesives that require a heating step to fully activate the
adhesive during the curing period, adhesive 16 is formulated to cure rapidly
upon
mixing of two or more adhesive components without being heated. Two adhesive
components, hereafter referred to generically as component A and component B,
have
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CA 02345555 2002-06-11
a much longer pot-life, typically more than one hour, when maintained
separately,
prior to mixing. In contrast, when components A and B are mixed they gel
rapidly at
room temperature to a polymerized state, for example, in less than about five
minutes.
In some embodiments of the invention, component A may comprise an
empirically-determined mixture of two commercially available components,
referred
to hereafter as Al and A2. Components A1 and A2 each are separately capable of
producing an activated adhesive when mixed with component B, based on
substantially similar polymerization chemistries, but with distinct gel times.
For
example, an adhesive produced in accordance with the invention may comprise a
mixture of components A1, A2, and B that produces a gel time distinct from,
and
typically intermediate between, adhesives from mixtures of Al and B, or A2 and
B.
An adhesive produced by mixture of components A and B according to the
invention can be described as having a gel time and a cure time. The gel time
of an
adhesive is defined as the period of time in which the A+B mixture, in a
vessel,
achieves a breakable, semi-solid state at 21°C. Some activated
adhesives (A + B),
such as the resorcinol adhesives described in Example 1 below, frequently
exhibit
exothermic behavior upon mixing. Therefore, to test their gel time they are
cooled to
below 21 °C before mixing to eliminate the effect of heat released upon
mixing.
In contrast to the laboratory environment of the gel time measurement, the
cure
time is measured as a function of the wood bonding method of the invention.
The cure
time is the elapsed time between 1) adhesive mixing and 2) the point at which
the
bond between wood members is strong enough to allow handling of the wood
assembly without detectable separation of wood members.
The gel time described above is distinct from the cure time measured for
joined
pieces of wood. Specifically, other factors such as the temperature of the
wood
member surfaces to be bonded, the temperature of the activated adhesive
solution, and
the moisture content of the wood members may contribute to the overall rate of
curing.
Therefore, the cure time is a reflection of the ambient and conditions present
at the
time of forming the wood assembly. The cure time may be optimized by adjusting
the
ratio of A1 and A2 components to achieve minimal processing time and maximal
bond
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strength. Generally, the cure time may be, for example, about five-fold longer
than
the gel time, although this difference may range from less than 2-fold to
greater than
25-fold depending on the conditions.
The moisture content of the wood to which the adhesive is applied may play an
important role in the rate of curing and the strength of the wood assembly
bonds that
are achieved. Not only does the moisture content sometimes affect the rate of
curing,
but it may determine the relationship between the bond strength and the curing
time.
Specifically, the wood moisture content may help determine the amount of
adhesive
that cures at the set line at the interface between the joined wood members
versus the
amount that is absorbed into the wood. Wet wood has the ability to rapidly
absorb
adhesive, thus a shorter cure time may provide a stronger bond between wood
members. It will be appreciated that the range of gel times provided by the
invention
are suitable to compensate for changes in adhesive absorption. Furthermore,
the range
of gel times provided by the invention and the ability to adjust the adhesive
gel time,
allow a fairly constant cure time to be achieved under a variety of wood
moisture
contents, inherent wood characteristics, and environmental conditions.
The adhesive compositions used according to the invention are considered
"fast-gelling" and "fast-curing." A fast-gelling adhesive typically has a gel
time of
less than about two minutes. A fast-curing adhesive is characterized typically
by a cure
time of less than about ten minutes, and preferably in less than about five
minutes.
After adhesive application, wood members are pressed together, either
manually or preferably using a pressing device. Whatever the pressing method
used,
the wood assembly is cold-pressed as the adhesive cures. In cold-pressing, no
heat is
applied to the wood or adhesive through an external source after the adhesive
is
applied, such as by heating the wood members through conduction or radio
frequency
heating. Instead, a cold-pressed wood assembly produced by the present
invention
relies on fast-gelling, fast-curing adhesives.
Because the mixed, activated adhesive 16 used according to the invention is
fast-curing when cold-pressed, the components of adhesive 16 are maintained
separate from each other until just prior to application on a wood member.
Typically,
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CA 02345555 2002-06-11
this involves mixing the components just prior to applying them onto the wood
surface. This application technique is shown in Fig. 6. Suitable two-component
applicators in which the reactants are not mixed until just prior to
application are
manufactured by the Gusmer Corp. of Lakewood, New Jersey.
Instead of mixing the components of adhesive 16 just prior to application,
another alternative is to spray the components onto the desired contact
surface so that
mixing does not occur until after the components are dispensed from the
applicator.
The spray streams may be oriented to mix in the air, or to create generally
parallel
streams that are mixed on the contact surface. An illustrative example of this
application technique is shown in Fig. 7 and will be discussed in more detail
below.
It should be understood that other methods for applying the components of
adhesive 16 exist and are within the scope of the present invention. When a
spray
applicator is used, the applicator may be manually positioned, or it may be
mounted in
a defined position on an automated apparatus for producing wood products. In
such
an automated apparatus, wood members typically are moved on conveyors past one
or
more applicators. Whatever the application method used, it is important to
efficiently
and thoroughly mix adhesive components A and B to activate the adhesive before
joining the surfaces of the wood members and pressing them together.
Because the activated adhesive systems of the present invention are fast-
curing,
care also must be taken that the adhesive does not gel or cure substantially
before a
second wood member is pressed against the applied adhesive to adhesively bond
the
contact surfaces together. This may be done either manually, or the process
may be
automated with an apparatus that includes conveyors and other assemblies for
positioning and contacting wood members together. It is also important to
align the
wood members properly before substantial curing of the adhesive occurs.
People in the woodworking field may not have expected the feasibility of using
a rapid curing, pre-activated adhesive in a cold-press procedure due to
stringent timing
and precision handling requirements that are inherent to such a system. The
present
invention preferably uses highly automated precision handling apparatus to
coordinate
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CA 02345555 2002-06-11
mixing of an appropriate adhesive system, application of the mixture, assembly
of the
wood pieces, transport, and pressing in a smooth rapid operation.
After placing the wood members together, the members should be compressed
to retain the members in a selected position until the adhesive cures. This
compression
step also spreads the adhesive between the contact surfaces and removes any
air
trapped between the contact surfaces. Although the wood members may be
compressed manually, this step is preferably performed with a press, which may
include platens or rollers, such as has been used in the past with thermoset
adhesives
that required heating during the pressing step. Unlike these known compression
systems, however, the invented system cold-presses the wood assembly during
adhesive curing. No heat is required to cure the adhesive. Therefore, the
pressing and
curing time interval can be reduced compared to prior methods.
An important objective of the invention is to match the cure time of the
adhesive system to the processing and handling time required to properly
transport,
combine, and press the wood pieces together. The cure time must allow
sufficient
time to handle the wood prior to pressing, with minimal extra time so that the
entire
manufacturing process can be performed as rapidly as possible.
A timeline is shown in Figure 6 illustrating an unsealed temporal sequence of
adhesive application, wood handling, pressing, and curing steps. Adhesive
components A and B are mixed at tl. The adhesive mixture is applied to the
wood
surface at t2. Wood pieces are combined at t3. The combined wood pieces are
positioned precisely together in press at t4. High pressure is exerted on the
composite
continuously from is to t6.
The cure time in the process shown in Figure 6 spans from tl to t~. The
adhesive system continues to polymerize and set-up during the entire interval
from tl
to t~. Initially after mixing and application, the adhesive is generally
fluid, and not
particularly tacky or sticky. During this phase the adhesive is "smearable" ,
i.e., may
be pushed around by touching the wood surface. It is important that the
adhesive
remain substantially smearable at least until t4 when the pieces of wood are
being
precisely positioned relative to each other before applying high pressure.
Accordingly,
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CA 02345555 2002-06-11
the adhesive system should be optimized along with the wood handling and
pressing
equipment so that the cure time of the adhesive, tl to tb, is minimal while
allowing the
adhesive mixture to be smearable at least until t4.
In Fig. 7, a system for producing wood products according to the present
invention is schematically illustrated and generally indicated at 76. System
76
includes supplies 78 and 80, which respectively contain components 82 and 84,
which
correspond to component A and component B of adhesive 16. Each supply 78 and
80
is in communication with a pump 86 and 88, respectively., which is adapted to
deliver
feeds 90 and 92 of the components under pressure to a proportioner 94.
Proportioner
94 controls, or meters, the flowrate and ratio of each feed 86 and 88, and may
also
control the temperature and pressure of the feeds. In place of the separate
pumps
shown in Fig. 7, a dual-head pump may be used to deliver and control the mix
ratio of
the feeds.
From proportioner 94, feeds 90 and 92 are delivered to an applicator 96. The
component feeds are delivered to applicator 96 at an elevated pressure.
Optionally,
one or both components may be heated somewhat to regulate the viscosity and
thus
flow properties of components. With the fast-gelling adhesives used in
accordance
with the invention, heating of the adhesive prior to application is generally
not used to
accelerate the reaction rate. Instead, the rate of curing is substantially
determined by
the temperature and moisture conditions at the bonding interface. When
temperature
control of the components prior to application is elected, the feeds are
insulated with a
jacket 98 that is heated by a heater 100 to maintain the feeds at a desired
temperature.
If proportioner 94 also heats the feeds, then the heater 100 may be omitted
from the
system. Jacket 98 may be retained, however, to prevent heat loss as the feeds
are
delivered to applicator 96.
In Fig. 7 it can be seen that feeds 90 and 92 are prevented from mixing until
they are delivered to applicator 96. Depending upon the particular applicator
selected,
the feeds may be either mixed within the applicator shortly before being
applied, or the
feeds may be applied sequentially and thereby mixed by the application
process. In
Fig. 7, applicator 96 mixes the component streams and dispenses a stream 102
of
CA 02345555 2002-06-11
activated adhesive through outlet 104 and onto contact surface 108 of a wood
member
110. Examples of suitable applicators are manufactured by the Gusmer
Corporation of
Lakewood, New Jersey and are known as two-component impingement sprayers.
An alternative embodiment of the applicator of Fig. 7 (not shown)
accommodates three-components. Such an applicator is quite similar to the two-
component applicator of Fig. 7, except that a third supply and pump are
included, and
a proportioner is configured to proportion three components. In this
embodiment two
of the supplies represent distinct A-type components, Al and A2, and the third
is
component B. A proportioner is used to regulate the ratios of components A1,
A2, and
B. This system would allow the operator to easily modify the gel time of the
activated
adhesive by changing the relative amounts of A1 and A2 to adapt to changing
conditions, such as the moisture content of the wood members or ambient wood
temperatures.
Another way to control or adjust the cure time of a wood bonding process is to
add a predetermined amount of water to one or both of the wood surfaces before
applying the adhesive. For some applications, adding water to the wood surface
may
favorably increase or decrease the cure time, and may also help to strengthen
the
resulting bond by increasing the depth of adhesive penetration into the wood
prior to
curing.
In Fig. 8, applicator 96 is shown with an outlet 112 that includes plural
orifices
114 and 116, each of which receives a respective one of feeds 90 and 92 and
applies
the feed to at least one wood member without mixing the feeds until after
being
dispensed from the outlet. As shown, the orifices cooperate to deliver
generally
parallel streams 118 and 120 of components 82 and 84. As shown, the streams
are
applied to a contact surface 108 of wood member 110 as the wood member and
outlet
are moved with respect to each other. Where the applied streams overlap,
components
82 and 84 mix to form fully activated adhesive 122.
Figure 9 shows an alternative applicator system for mixing and depositing a
two-part rapid curing adhesive. The applicator shown in Figure 9 is
particularly
advantageous for depositing higher viscosity adhesives such as polyurethane.
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Polyurethane adhesives may be preferred, for example, to bond wood to other
materials such as plastics. Splatter applicator 130 sprays adhesive components
132a
and 132b into a first mixing chamber 134. The adhesive mixture then moves into
post-
mixing chamber 136 and exits spray tip 138. The adhesive then enters another
chamber 140 which has an upper port or valve 142 for receiving compressed air.
Compressed air entering port 142 adds adhesive down through chamber 140,
through
spray tip 144. Spray tip 144 is secured to chamber 140 by lock nut 146.
Applicator 130
is particularly useful for depositing higher viscosity adhesive such as
polyurethane
which would be preferable for rapidly bonding wood to plastic materials.
Adhesive
applicator 130 may be used to deposit rapid curing adhesives that are more
viscous
than adhesives deposited by the spray system shown in Figure 7. For example,
an
applicator system may be used to splatter applicate adhesives having a
viscosity up to
at least about 20,000 CPS. Applicator 130 may also be used to apply adhesives
having
viscosities substantially less than 20,000 CPS.
After the application step shown in Figs. 7-9, one or more wood members are
bonded to wood member 110 by aligning their respective contact surfaces in a
generally opposed relationship with contact surface 108. The contact surfaces
of the
respective members face each other and define a region of overlap in which
adhesive
16 is sandwiched between the contact surfaces. After the contact surfaces are
both in
engagement with activated adhesive, the wood members are compressed to urge
the
members toward each other. As discussed, the two-component adhesive system of
the
invention is fast-curing when the wood assembly is cold-pressed, so this
pressing step
may be significantly shorter than the similar step that is required when
external heat
must be applied to cure the adhesive .
The compression step may be performed manually, or it may be automated, in
conjunction with a press. In Fig. 10, an example of a suitable press is
generally
indicated at 160 and includes a pair of platens 162 and 164 that are driven
toward each
other to compress a wood product 166. The platens are configured to move
toward
each other to a minimum spacing, which corresponds to the thickness of the
finished
wood product. It should be understood that wood product 166 may have a shape
and
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configuration of any of the wood products described herein, and that the size
and
shape of the platens should be selected to correspond with the shape of the
wood
product to be compressed. The platens may also be larger than the wood
products so
that multiple wood products may be compressed at one time. Also, the minimum
distance between the platens is typically adjustable to accommodate wood
products of
differing sizes.
Another example of a press is shown in Fig. 11 and is generally indicated at
170. Press 170 includes upper and lower roller assemblies 172 and 174 that not
only
compress wood product 176, but also convey wood product 176 along a feed path
while being compressed. This form of press enables wood products to be
produced in
a continuous process.
It should be understood that presses 160 and 170 would typically be mounted
on a frame of an apparatus for producing wood products. For example, a system
of
conveyors may be used to receive wood products and convey them to an
applicator,
such as applicator 96, then position other wood members upon the applied
adhesive to
form a wood product, such as wood product 166. After joining the wood members
together, the conveyors then transport the product to a press, such as presses
160 or
170.
Figure 12 shows a system for bonding wet lumber pieces using a friction press,
and an impingement spray system. Friction press 210 includes support rail 220
which
may be an I-beam structure. Support rail 220 is secured and supported in a
diagonal
orientation by posts 222a and 222b. On the other side of Friction press 210,
support
beams 224a and 224b support steel tube 230. Steel tube 230 supports air hose
232
creating an inner passage 233 for receiving and pressing wet lumber pieces.
Inner
passage 233 is lined from the air hose side by stainless steel band 234 which
is held
under tension by supports 236. Air caps 240 are provided on the ends of steel
tube
230.
An impingement spray device 242 is mounted in a position to deposit adhesive
on surfaces of wet lumber pieces prior to entering Friction press 210. In a
preferred
embodiment, a rapid curing two-part adhesive system such as resorcinol is
processed
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through impingement spray device 242. Two tanks 244 and 246 are provided to
contain the two parts of the adhesive system prior to mixing. A conduit system
248
connects tanks 244 and 246 to impingement spray device 242 to provide mixing
and
delivery of activated adhesive.
Conveyor 250 is positioned to carry wood pieces 252 to the adhesive
application station and then to the entrance of inner passage 233 of friction
press 210.
Hydraulic ram 260 operates to push lumber into friction press 210. In the
embodiment
shown in Figure 12, adhesive is applied on every other piece of lumber 252
conveyed
by conveyor 250. This results in final composite products having two pieces of
lumber
bonded together per product. For example, two pieces of 1x4 lumber can be
bonded to
produce one piece of 2x4 lumber, as shown exiting from friction press 210.
A second hydraulic ram 264 is provided at the output end of friction press 210
to urge bonded products to separate from the pressed stack 262, and proceed
down
slide 266.
One part of the invention may be thought of as a method for joining wood
members together by providing first and second wood members, each having a
contact
surface, and then applying a mixed two-component, fast-curing adhesive to at
least
one of the contact surfaces. Applying the adhesive includes applying
components that
when combined create the adhesive. As described further below, the adhesive
may be
any suitable two-component resin that is fast-curing when a wood assembly is
cold-
pressed. Examples presented below include a resorcinol-based adhesive, a
polyurethane-based adhesive, or a polyurea-based adhe live. The cure rate of
the
adhesive may be modified by adding substances to or eliminating them from the
adhesive. For example the amount of a reaction catalyst or inhibitor may be
adjusted
to accelerate or slow down the reaction. This may be earned out using a
mixture of
components A I and A2 as described above. The contact surfaces are then
positioned
so that they generally face each other and define a region of overlap, wherein
the
adhesive contacts the contact surfaces in the region of overlap and binds the
members
together. In this method, the adhesive may be applied by impingement spraying,
or by
splattering according to methods described above.
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CA 02345555 2002-06-11
The following examples describe the use of fast-curing adhesive compositions
in cold-press procedures. These adhesive compositions are intended to be
illustrative
and to exemplify specific compositions suitable for use with the invention.
Example 1
Resorcinol-based adhesives have been demonstrated to be effective for bonding
wood products together. A line of commercially available two-component
resorcinol
adhesives is offered by Borden Chemical, Inc. of Springfield, Oregon. These
two-
component resorcinol-based adhesive compositions are formulated to produce a
range
of gel times, based on the specific composition selected.
Component A in these compositions is referred to as a CASCOPHEN reagent.
Borden Chemical offers distinct CASCOPHEN reagents, that is, related
components
A, with different gel times when mixed at a ratio of 2:1 (volume:volume} with
CASCOSET FM-6310L catalyst, hereafter referred to as CASCOSET. For example,
Borden Chemical provides an ultra fast-gel CASCOPHEN that gels in about 1
second
when activated with CASCOSE'T catalyst. Fast-gel CASCOPHEN, product number
WS-662-64, gels in about S-10 seconds when activated with CASCOSET. In
contrast,
moderate-gel CASCOPHEN, product number WS-662-55, gels in about one minute
when mixed with CASCOSET. According to the invention, ultra fast-gel, fast-
gel,
and moderate-gel CASCOPHEN products may be mixed in the desired ratio, while
maintaining the overall 2:1 ratio of CASCOPHEN product to CASCOSET, to achieve
a gel time intermediate between that achieved with single, activated CASCOPHEN
reagents.
The ratios of CASCOPHEN reagents described above that are useful in
providing a fast cure time according to the invention are as follows:
moderate:fast,
ratios of 10:0 through 0:10; and fast:ultra-fast, 10:0 through 0:10.
In other embodiments of resorcinol resins used in accordance with the
invention, the CASCOPHEN reagent or a related composition from another
supplier,
may be defined as component B and distinct formulations of the catalyst may
function
as components A 1 and A2.
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CA 02345555 2005-07-22
Example 2
Fast-curing polyurethane adhesiv es were used to bond wood to polymeric
materials, for example, PV'C. Polyurethane adhesives suitable for use
according to the
invention are available commercially. These polyurethane adhesives can be
rapidly
cured in cold-pressed wood assemblies.
Vantico Inc., of East Lansing, Michigan, produces a commercially available
polyurethane adhesive that is fast-curing when cold-pressed. Component A is
LSA
708-93 resin, and component B is LSA 708-95 hardener. They may be used at a
ratio
of 100:83, which provides a gel time of 30 seconds and a cure time in the
range of
about 2 to 3 minutes
Franklin Adhesives also offers a fast-curing adhesive useful in carrying out
the
invention. The REACTITE 82032 system may be mixed in a ratio of 4:1,
resin:hardener, providing a gel time of about 30 seconds, and a cure time of
about 2-3
minutes.
Example 3
Some embodiments of the invention use a two-component adhesive that rapidly
produces a polyurea resin upon mixing. In these embodiments, polyurea resin is
formed by mixing two 100% solids components, namely an isocyanate and an amine-
terminated polyether resin, under elevated pressure. The isocyanate component
is
typically a polyisocyanate, and may be either aromatic- or aliphatic-based.
The
polyether resin is an amine-terminated polyether resin, such as JEFFAMINE~
polyoxyalkylene diamines and triamines and m-TMXDI~ amine from the Huntsman
Corporation of Salt Lake City, Utah. The resin component may also include
various
additives, such as pigments, chain extenders and fire retardants. Examples of
polyurea
resins, the components for making polyurea resins, and preparation and
application
techniques and equipment are disclosed in L;.S. Patent Vos. 4,028,310,
4,663,201,
4,798,862, 4,983,643, 5,013,813, 5,104,930, 5,124,426, 5,225,118, 5,317,076,
5,442,034, 5,496,911, 5,504,181, 5,580,945, 5,731,397 and 5,759,695.
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CA 02345555 2002-06-11
A two-component polyurea resin composition that has proven effective for use
with the present invention is sold under the trade name PERMAX 700 produced by
the
Resin Technology Co. of Ontario, California. Components A1 and A2 of a
polyurea
adhesive may be Permax 700HP (high performance) and Permax 700-Slow. Mixtures
of Permax 700HP:700-Slow, may be mixed at a ratio between 10:0 to 0:10. The
HP:Slow mixture is combined with component B in a 1:1 ratio to activate the
adhesive.
One advantage of using polyurea resin as an adhesive is that it is formed in a
solvent-free system that is at least substantially, if not completely, free
from volatile
organic compounds.
Example 4
A two-part polyurethane adhesive was used to bond wood to vinyl. The
polyurethane adhesive system was obtained from Vantico Inc. of East Lansing,
Michigan, and included an isocyanate known as ARATHANE AW 8680 as the resin
component, and polyol, known as LSA 729-08, as the adhesive hardener. The
adhesive
was combined and applied through an applicator system such as applicator 130,
as
shown in Figure 8.
Example 5
Another polyurethane adhesive system was successfully used to bond wood to
wood. The two-part adhesive was obtained from Vantico Inc. of East Lansing,
Michigan. The adhesive system includes resin and hardener components under the
name RP 6450. RP 6450 polyurethane adhesive has a relatively low viscosity so
it can
be applied by spraying, as shown in Figure 7, or by splattering, as shown in
Figure 9.
While the invention has been disclosed in its preferred form, the specific
embodiments thereof as disclosed and illustrated herein are not to be
considered in a
limiting sense as numerous variations are possible. Applicant regards the
subject
matter of the invention to include all novel and non-obvious combinations and
subcombinations of the various elements, features, functions and/or properties
disclosed herein. The following claims define certain combinations and
subcombinations which are regarded as novel and non-obvious. Other
combinations
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CA 02345555 2002-06-11
and subcombinations of features, functions, elements and/or properties may be
claimed through amendment of the present claims or presentation of new claims
in this
or a related application.
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