Note: Descriptions are shown in the official language in which they were submitted.
CA 02026470 1997-06-20
APPARATUS AND METHOD OF MANUFACTURING
SY~,n~ C BOARDS INCLUDING FIRE-RET~ T BOARDS
The present invention relates to an apparatus and
method of manufacturing synthetic boards and
fire-retardant synthetic boards from cellulosic or
lignocellulosic furnish materials using an organic binder.
The present invention also relates to a fire-retardant
synthetic board product comprising cellulosic or
lignocellulosic furnish materials, an organic binder and
fire-retardant chemicals.
Background of the Invention
Many synthetic board products are manufactured
using a thermosetting binder, heat and pressure to
reconsolidate refined cellulosic and/or lignocellulosic
furnish materials into a unitary finished board product.
Examples of board manufacturing processes are shown in
U.S. Patent No. 2,757,115 to Heritage and U.S. Patent
No. 4,407,771 to Betzner et al. Basically, furnish
material, such as wood, is reduced to fibers of the
desired size by a refiner, mixed with a binder and other
chemicals, such as release and sizing agents, partially
dewatered, formed into mats and compressed between heated
platens in a hot press to form a board product of the
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desired thickness and density. In many current processes,
the binder is applied to a rapidly moving stream of the
fibers of the fibers as it exits the refiner, in the
so-called "blowline" of the process equipment.
Alternatively, the binder may be added in the blender or
elsewhere downstream of the refiner.
A wide variety of binder systems have been
utilized in the production of synthetic boards, includiny
various thermosetting organic binders, such as
isocyanates, polyisocyanates, urea formaldehydes,
phenolics, melamines and various mixtures thereof.
Isocyanate and polyisocyanate binders have advantages over
urea formaldehyde binders in that boards with greatly
improved weather resistance can be produced. Processing
time can typically be substantially reduced using
isocyanate and polyisocyanate binders, rather than
standard phenolic binders. Although specially formulated
phenolic binders can decrease the processing time, the
cost of these ~pecialty binders makes their use less
attractive. Additionally, urea formaldehyde binders tend
to produce formaldehydes, and phenolic binders tend to
produce both formaldehydes and free phenols around the
press area, which can cause significant health problems.
Heretofore, successful application of isocyanate
binders in fiberboard manufacture has been limited due to
many factors. First, there is often difficulty in
achieving adequate distribution at low dosage rates.
Second, many systems require the use of an expensive
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release agent-containing binder or must utilize a caul
plate system which allows external release agent
application. These problems usually result in increased
production costs and/or inferior finished board product
quality.
Many of the binder systems used today in board
manufacture include an organic isocyanate binder which is
specially mixed with a variety of diluent/extender agents
to enhance binder distribution. These admixtures must
also have a relatively long pot life to avoid premature
curing, which can clog the binder delivery system.
Unfortunately, even quite stable admixtures tend to
deposit reaction products in process lines during use, and
especially when use is interrupted. Both problems usually
necessitate expensive machine downtime to unclog or
replace components of the binder delivery system.
In systems utilizing isocyanate binders, the
binder is typically formulated into an aqueous emulsion
long before application to the furnish. Since the binder
is highly reactive, the temperature during and after
emulsification must be kept relatively low to avoid
prereaction of the binder before it is applied to the
furnish materials. Water-cooled addition devices, such as
the nozzle described in U.S. Patent No. 4,402,896 to
Betzner et al., have been used, but require a constant
supply of cooling water and are still subject to clogging.
Another problem associated with specialty binders
and their mixing equipment is that if the binder is not
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completely removed from the binder delivery system at the
end of a production run, the binder will usually cure and
clog the system. Therefore, there is a need for a binder
delivery system which assures that all of the binder is
removed therefrom to avoid these problems.
Additionally, release agents are often added to
the binder system to avoid sticking of the board to
platens or caul plates during processing. However, these
specially formulated binders are typically proprietary to
a particular manufacture and are prohibitively expensive
for large-scale fiberboard manufacturing operations.
Accordingly, there is a need for a process and apparatus
which can utilize basic nonproprietar~ isocyanate and
other binder compounds and release agents.
Summary of the Invention
It is, therefore, an object o~ the present
invention to provide a method of producing a synthetic
board from cellulosic or lignocellulosic materials wherein
standard, nonproprietary, inexpensive and readily
available isocyanate, polyisocyanate and similar binders
can be utilized, thus obviating the need for expensive
specialty chemical formulations.
It is also an object of the present invention to
provide an apparatus for producing a synthetic board
wherein standard binders and release agents can be
utilized.
It is a further object of the present invention
to provide a method and apparatus for forming a binder
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emulsion immediately upstream from the point of
application to the wood fibers, thus allowing the use of
isocyanates or polyisocyanates which do not form emulsions
having extended stabilities or pot life.
It is also an object of the present invention to
provide a method and apparatus for binder application
wherein the emulsion is cooled by the diluent.
It is an object of the present invention to
provide a method and apparatus for applying the binder
which would avoid periodic plugging of the process
equipment and the binder system.
It is also an object of the present invention to
provide a method and apparatus for flushing the binder
from the nozzle at the end of a production run so that the
binder does not cure within the nozzle and clog the same.
Another object of the invention is to provide a
method and apparatus as aforesaid which includes a new and
improved method and apparatus for producing a fi.berboard
that is fire-retardant.
Still another object of the invention is to
provide a method and apparatus as aforesaid which produces
a fire-retardant fiberboard having size, strength,
water-resistance and other characteristics comparable to
those of standard fiberboard.
Another object is to provide a method and
apparatus as aforesaid capable of producing an exterior
grade fiberboard that is fire-retardant.
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Another object is to provide a cellulosic or
lignocelluslosi.c Eiberboard product that is fire-retardant
and yet has size, strength, water-resistance and other
characteristics comparable to those of standard
fiberboard.
According to one aspect of the present invention,
there is provided an apparatus adapted for mixing a binder
stream and a diluent stream and applying the product
stream to the fibers in the production of synthetic boards
from cellulosic fibers, the apparatus comprising:
binder inlet means for receiving a first stream
containing a binder;
diluent inlet means for receiving a second steam
containing a diluent;
mixing means fluidly connected to the binder
inlet means and the diluent inlet means for mixing the
first stream and the second stream to produce a fourth
stream containing a product stream containing the binder
and the diluent; and
outlet means positioned proximate the mixing
means and fluidly connected to the mixing means for
immediately applying the product stream to the fibers.
According to another aspect of the present
invention, there is provided an apparatus for producing
synthetic boards from a cellulosic material, comprising:
refining means for extracting fibers from a
cellulosic material;
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conduit means connected to the refiner means for
conveying the fibers along the fiber flow path;
binder application means for mixing a binder and
a diluent to form a binder/diluent mi~ture and immediately
mixing the binder/diluent mixture with the fibers in the
fiber flow path;
dryer means for partially dewatering the
fiber/binder mixture;
forming means for creating a mat of the dewatered
fiber/binder mixture; and
heated pressing means for compressing the fibers
and curing the binder in the mat for forming a
consolidated board product.
According to yet another aspect of the present
invention, there is provided a method of blending a binder
with cellulosic fibers in the manufacture of synthetic
boards from cellulosic fibers, the method comprising:
conveying cellulosic fibers in a first stream;
conveying a binder in a second stream;
conveying a diluent in a third stream;
merging the second stream and the third stream to
produce a fourth stream; and
immediately thereafter merging the fourth stream
and the first stream to apply the binder and the diluent
to the fibers.
According to a further aspect of the present
invention, there is provided a method of producing
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synthetic boards from a cellulosic material, comprising
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extracting hot and wet fibers from a cellulosic
material;
transporting the hot and wet fibers in a first
stream;
transporting separate second and third streams
comprising a binder and a diluent, respectively, generally
toward the first stream;
merging the second and third stream to form a
fourth stream;
emulsifying the binder and the diluent in the
fourth stream;
immediately after emulsifying, applying the
binder/diluent emulsion in the fourth stream to the hot
and wet fibers in the first stream;
partially dewatering the hot and wet fibers;
forming the partially dewatered fibers into a
mat; and
compressing the mat in a heated press to cure the
binder to form a consolidated board product.
The present invention further relates to an
apparatus and method for the production of fire-retardant
fiberboard. Such boards have traditionally been
manufactured by a post-production impregnation treatment
of the boards with a suitable fire-retardant chemical. In
order to achieve a board which conforms to the British
Standard Class 1 (as set out in BS476: Part 7: 1987) by
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this method, it is necessary to vacuum/pressure impregnate
the boards. Fire-retardant boards produced by such
post-production treatments suffer from the disad~antage
that since the treatments are aqueous, thickness swell of
the boards of up to 10% is common. Furthermore,
substantial reduction in internal bond strength results
from these processes. Thus, the boards produced by
post-manufacturing treatments are of inferior ~uality, as
compared to an otherwise compa:rable, but nonfire-retardant
board.
U.S. Patent No. 3,874,990 to Surdyk discloses a
method for producing a flame retardant particle-board or
chip-board in which the flame ratardant chemicals are
added during production of the particle board, prior to
mat-forming, and comprise alkaline borate chemicals and
flame retardant phosphoric acid-dicyandiamide-formaldehyde
resin. The alkaline borate chemicals are added to the
wood chips as a dry powder. Such a method does not lend
itself to applications in the field of fiberboard
production as it wou].d be extremely difficult to achieve a
good dispersion of a powder with the fine fiber used.
Therefore, there is a need for an apparatus and method for
producing a fire-retardant fiberboard in which the
fire-retardant compound is incorporated into the board
during its production and the product board has the
desirable physical characteristics of standard fiberboard,
as well as excellent fire-retardant characteristics.
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According to a further aspect, there is provided
an apparatus for producing synthetic fire-retardant boards
from a cellulosic material comprising:
refining means for extracting fibers from a
cellulosic material;
conduit means connected to the refiner means for
conveying the fibers along the fiber flow path;
binder application means for mixing a binder and
a diluent to form a binder/diluent mixture and immediately
mixing the binder/diluent mixture with the fibers in the
fiber flow path;
dryer means for partially dewatering the
fiber/binder mixture;
forming means for creating a mat of the dewatered
fiber/binder mixture;
liquid fire-retardant application means for
introducing fire-retardant liquid onto the cellulosic
material located upstream of the forming means; and
heated pressing means for compressing the fibers
and curing the binder in the mat for forming a
consolidated fire-retardant board product.
According to yet a further aspect, there is
provided a method of producing fire-retardant synthetic
boards from a cellulosic material, comprising the steps
of:
extracting hot and wet fibers from a cellulosic
material;
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transporting the hot and wet fibers in a first
stream;
transporting separa-te second and third streams
comprising a binder and a diluent, respectively, generally
toward the first stream;
merging the second and third streams to form a
fourth stream;
emulsifying the binde:r and the diluent in the
fourth stream;
immediately after emulsifying, applying the
binder/diluent emulsion in the fourth stream to the hot
and wet fibers in the first stream;
partially dewatering the hot and wet fibers;
introducing fire-retardant liquid onto the
cellulosic material;
forming the partially dewatered fibers into a
mat; and
compressing the mat in a heated press -to cure the
binder to form a consolidated board product.
The present invention is a method and apparatus
for producing a synthetic board from cellulosic or
lignocellulosic fibers, preferably wood fibers, wherein a
standard thermosetting binder, preferably an isocyanate or
polyisocyanate binder, is emulsified and immediately
applied to the fibers before consolidation of the fibers
into a mat or finished board product. The apparatus
includes a binder emulsification and application nozzle
comprising a diluent inlet, a binder inlet, a mixing
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section for emulsifying the diluent and the binder, and a
spray nozzle ~or applying the binder/diluent emulsion to
the fibers in a fiber stream upstream of the forming mat
in the board forming process. The method includes
supplying a binder stream, supplying a diluent stream,
merging the two streams, emulsifying the binder with the
diluent and immediately thereaEter applying the emulsion
to the fiber stream. The method further includes flushing
the nozzle with the diluent stream at the end of a
production run to remove the binder from the nozzle to
prevent curing of the binder emulsion and clogging of the
nozzle. In the apparatus of the present invention, the
nozzle can be used to apply the emulsi~ied binder to the
fiber stream either in the refiner, the blowline or
downstream of the blowline, such as in the blender, of the
board forming apparatus.
The method may also include introducing a
fire-retardant liquid into the fiber stream as part of the
board forming process. The apparatus may also include
means for applying a fire-retardant liquid to the fiber
stream.
Description of Drawinqs
The invention will now be described more
particularly with reference to the accompanying drawings.
In the drawings:
FIG. 1 is a schematic diagram showing the process
and apparatus in accordance with the present invention.
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FIG. 2 is a side view of a nozzle in accordance
with the present invention mounted on a blowline of a
fiberboard manufacturing process.
FIG. 3 is a schematic view of the nozzle in
accordance with the present invention.
FIG. 4 is a schematic drawing showing the
positions of entry of binder, diluent, and other agents to
the fiber flow path.
DETAILED DESCRIPTION OF PREFERRED EMBODI~ENTS
Embodiments Producinq Boards Having
Optimum Water Resistance
The present invention is intended for use in the
production of reconstituted products made from cellulosic
or lignocellulosic materials, and in particular, the
production of fiberboard from wood fibers. The invention
is also intended for use in the production of fiberboard
having ~ire-retardant characteristics.
As shown in FIG. 1, pieces of wood, such as
chips, are fed into a plug feeder 10 for delivery to a
digester 12, where they are subjected to steam and high
pressure to soften the chips and break down the lignin
therein. The cooked chips are transferred to a refiner 14
where they are separated into their constituent fibers,
such as between uni- or bi-directional rotating discs.
The hot and wet fibers exit refiner 14 with steam
in a rapidly moving continuous stream which is transported
through a so-called "blowline" 16, where the binder and
other desired compounds, such as rel~ase and sizing
agents, are typically added. The binder is preferably a
material selected from the group consisting of monomeric
isocyanates, oligomeric isocyanates t and mixtures thereof
having a functionality of at least 2. In addition, other
conventional thermosetting binders may be used.
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Aqueous emulsions of the, binder and other
additives are well-suited to blowline injection for
several reasons. First, a large portion of the heat
energy available in the blowline is absorbed in raising
the temperature of the applied emulsions since the
specific heat of water is higher than many of the other
substances being added. Second, the water-to-water
solvent compatibility between the wood fibers and the
additive emulsion is excellent and helps assure good flow
and distribution of the binder. Third, deposits of the
additive emulsion on the wall of the blowline are
minimized due to the presence of a continuous ~ilm of
water condensate, with which the additive emulsions are
also compatible. Fourth, the great turbulence within the
blowline results in a scouring action which tends to keep
the blowline wall clean, providing those adhering
substances are also water compatible. Lastly, the
residence time in the blowline is so short that most
chemical reactions, such as curing of the binder, have
insufficient time and energy to move very far toward
reaction products.
A binder emulsion and application nozzle assembly
18 in accordance with the present invention is connected
to blowline 16 for emulsifying the isocyanate binder with
a diluent and applying the resulting emulsion to the
fibers as they pass through blowline 16. Conventional
nozzles 20 and 22 are also plumbed to blowline 16 for
applying release and sizing agents to the fibers.
Alternatively, the isocyanate binder, release agent and
siziny agents may be added at other locations in the
process, as will be described below.
Upon entering blowline 16, the steam and the
fibers undergo a rapid drop in pressure and temperature,
but travel therethrough in less than about 1 second. The
velocity of the fibers through a typical blowline has been
reported to be approximately 325 feet per second. There
is extreme turbulence in blowline 16, which provides
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excellent mixing of additives, such as the binder, with
the fibers.
After exiting blowline 16, the fibers enter a
dryer 24 where they are partially dewatered. A first
cyclone 26 and an air lock 28 are provided to separate the
fiber from the dryer airstream. The fibers next pass to a
blender 30 wherein the isocyanate binder, siziny, release
agents or other desired materials can be mixed with the
fibers, if desired. If all desired compounds have already
been added, the fibers can be directed through a bypass
chute 32 and go directly to a second cyclone 34 with an
air lock 36 and then into a fiber storage bin 38. ~iber
storage bin 38 provides fibers to one or more forming head
apparatuses 40 which are used to dispense a forming mat of
15 fibers 41 onto a forming belt 42. Forming mat 41 is
deaerated by one or more prepressees 44 and then
compressed to the final pressed thickness by a hot
press 46 wherein the binder is cured to form the desired
board product.
In general, the binder can be added to the fibers
in any suitable location in the board forming apparakus
upstream of forming mat 41. Alternative locations where
the binder can be added to the fibers are designated by
dashed arrows 17a-d in FIG. 1. For example, the binder
may be added using the nozzle assembly of the present
invention in any of the following locations: refiner 14;
blender 30; bypass chute 32 or forming head
apparatuses 40. Similarly, the sizing and release agents
can be added, separately or together, in the various
locations in the board forming apparatuses, including:
plug feeder 10, digester 12, refiner 14, blowline 16,
blender 30 or bypass chute 32.
Referring to FIGS. 2 and 3, nozzle assembly 13
comprises a diluent inlet 52, a binder inlet 54, a mix
section 56 for emulsifying diluent and binder and a spray
nozzle 58 adapted for connection to a blowline 16 for
spraying the emulsion on the fibers. A stream of water or
other diluent is introduced through diluent inlet 52, and
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a stream of a binder, which can be isocyanate,
polyisocyanate or other suitable thermosetting binder, is
introduced through binder inlet 54.
Diluent inlet 52 includes a coupling 62, such as
a quick disconnect coupling shown, for connection to a
diluent supply line 64 with an appropriate coupling 66
through which water or other suitable diluent is delivered
to nozzle assembly 18. A pressure relief check valve 68
for diluent inlet 52 is operated by a control spring 70
and is threadedly connected to coupling 62. Diluent check
valve 68 prevents backflow from mix section 56 into
diluent supply line 64. In addition, diluent check
valve 68 will only open to allow diluent into mix
section 56 when the pressure of the water stream is above
a certain minimum pressure, for example, 15 psi. This
assures that there will be no admixing of water and binder
until the water stream has achieved proper operating
pressure, such as by the use of an appropriate metering
pump (not shown). It also assures that the flow of
diluent into nozzle assembly 18 will stop ;mr~-~;ately upon
stopping the flow of the diluent stream or upon a drop in
the pressure of the stream. Suitabls check valves are
available from the NuPro Company of Willoughby, Ohio.
Although alternative diluents, such as propylene
carbonate or furfural, can be used under various
conditions, water has long been used to reduce the
viscosity of binders and thus improve distribution. The
water also serves as a thermal buffer of the binder. This
is particularly significant for those applications
utilizing blowline addition of isocyanates. Since there
is a constant flow of relatively cool (less than ambient
temperature) diluent water through nozzle assembly 18, the
temperature to which the binder is subjected during
emulsification is also less than ambient, which prevents
precuring. No additional cooling of the emulsion, such as
provided by a cooling water jacket, is required.
Binder inlet 54 similarly includes a coupling 72
for connection to a bindsr supply line 74 with a
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coupling 76 through which binder is de:Livered to nozz]e
assembly 18. In the preferred embodiment, the binder is
standard technical grade isocyanate or polyisocyanate. A
pressure relief check valve 78 for binder inlet 54
includes a control spring 80 and is threadedly connected
to coupling 72. Binder check valve 78 operates as above
to prevent backflow from mix section 56 into binder supply
line 74. Binder check valve 78 also prevents the admixing
of water and binder before the binder stream has achieved
its proper operating pressure, or if the flow of the
binder stream has been stopped or if the pressure of the
binder stream drops below a proper operating pressure.
Additional compounds, such as release agents,
sizing agents, etc., may be applied to the fibers, if
desired. Referring to FIG. 4, release agents and sizing
agents may be added, separately or together, to diluent
stream 81a, binder stream 81b, combined binder/diluent
stream 81c or directly to fiber stream 81d, as shown by
dashed lines 82a - 82d, respectively. If the additional
compounds are to be added to combined binder/diluent
stream 81c, a third inlet 83 (shown by dashed lines in
FIG. 2) can be plumbed to mix section 56 of nozzle
assembly 18 for introducing such compounds into mix
section 56. In this way, the additional compounds will be
merged with the binder/diluent immediately before
application to the fibers.
Mix section 56 includes an intersection tee 84
which is threadedly attached to the outlets of diluent
check valve 68 and hinder check valve 78 for receiving the
binder stream and the ~iluent stream. Tee 84 is also
threadedly connected to an in-line mix section 85 equipped
with a plurality of interior baffles 86 which cause mixing
and emulsion of the binder with the diluent. The exact
number and configuration of baffles 86 has not been found
to be critical, as long as sufficient mixing results.
plastic baffled-style motionless mixer insert sized for
insertion into in-line mix section 85 and sold by TAH
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Industries of Imalyston, New Jersey, under the name
Kinetic Mixer, has been found to give good results.
Spray nozzle 58 is threadedly attached to in-line
mix section 85 for applying the diluent/binder emulsion to
the fibers passing through blowline 16. Spray nozzle 58
is provided with external threads 90 for attachment to
mating internal threads 92 in wall 94 of blowline 16.
Spray nozzle 58 is mounted so that only a small tip
portion 96 of the nozzle 90 extends into blowline 16 and
is subjected to the abrasive atmosphere therein. Due to
the abrasive atmosphere of blowline 16 and to avoid any
possible interaction with the emulsion, it has been
determined that spray nozzle 58 should be constructed out
of stainless steel or other suitable material.
It has also been determined that a spray nozzle
obtained from Spraying Systems Company of Wheaton,
Illinois, and sold under the trademark FULLJET gives good
results. This nozzle tip includes an integral interior
spiral vane mixer which produces a full cone spray pattern
for good distribution of the emulsion on the fibers. It
has also been determined that a nozzle I.D. of 0.245
inches is preferred to maintain proper backpressure in
nozzle assembly 18. Nozzle assembly 18 is typically
operated at an emulsion flow rate of approximately
5 gallons per minute and a pressure of between 80 and
125 psi, although some applications may require other
application rates and parameters.
In a working embodiment, blowline 16 has an
interior diameter of about 6 inches. Thus, the distance
between the point of emulsification of the binder and the
point of application to the fibers in blowline 16 is very
small, approximately 4 inches. This relatively short
distances helps assure that tha binder emulsion does not
cure before application to the fibers.
In accordance with the present invention, a
method of and means for flushing binder and emulsion out
of nozzle assembly 18 is also provided. This flushing is
necessary to avoid leaving the emulsion in mix section 56
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or spray nozzle 58 where it could quickly cure and plug
nozzle assembly 18. To flush nozzle assembly 18 at the
end of a production run, the binder pump should be turned
off to stop the flow of binder. This causes binder check
valve 78 to close. The water stream is allowed to
continue to flow for a few seconds (3-5 seconds) to flush
out any residual emulsion. Pr,eferably, the binder stream
should be shut off before fiber stream flow past spray
nozzle 58 has ended to avoid buildup of binder in
blowline 16.
Application of the aqueous emulsions o~ standard
isocyanate and polyisocyanate through nozzle assembly 18
into blowline 16 results in a practical and economical
means of producing a superior fiberboard product,
especially a medium density, water-resistant fiberboard
suitable for exterior use. The ready availability of the
binders are of great significance to a commercial
fiberboard production facility.
Embodiments Producinq Boards Havinq
OPtimum Fire Retardance
Fire-retardant fiberboard is advantageously
produced by the above-described method and apparatus, with
the introduction of an additional step whereby a
fire-retardant chemical in aqueous solution is added to
the wood or other cellulosic or lignocellulosic material.
Ammonium polyphosphate has been found to be a suitable
compound for this purpose when used with an isocyanate
binder. Ammonium polyphosphate is known as a
fire-retardant for the treatment by spraying, dipping,
etc. of fabrics. However, it has not, to Applicants'
knowledge, been used successfully as a fire-retardant in
fiberboard. Attempts have been made by the Applicants to
produce a fire-retardant fiberboard using urea
formaldehyde as the binder system, together with ammonium
polyphosphate as the fire-retardant compound. The product
was found to have poor internal bonding, probably due to
chemical reaction between the binder and fire-retardant,
resulting in inferior fire-retardancy, water resistance,
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strength and other characteristics. Applicants have now
found, surprisingly, that use of the same fire-retardant
chemical with an isocyanate binder system gives a product
board having superior physical characteristics and with
water resistance and strength similar to comparable
nonfire-retardant boards. It has been found that the
fire-retardant compound may be added in the range of
7 - 15% solid ammonium polyphosphate to oven dry weight of
wood where an isocyanate is used as the binder. Addition
of higher amounts of the fire-retardant compound, when
used with an isocyanate binder, has been found to result
in a finished fiberboard whose tensile strength is
unacceptably lowered. The preferred range is 7 - 10%
solid ammonium polyphosphate to oven dry weight of wood.
The fire-retardant chemical may be added to the
wood chips or fibers at any suitable location in the board
forming apparatus upstream of forming mat 41 (FIG. 1).
Suitable points are: plug feeder 10; digester 12;
refiner 14, blowline 16 or blender 30. Introduction of
the chemical is via a standard spray nozzle, for example,
a 1 inch FULLJET (trademark) nozzle. The fire-retardant
liquid may be added to the fiber stream either before or
after addition of the isocyanate binder emulsion to the
fiber stream. If desired, one of auxiliary nozzles 20, 22
may be used for this purpose. Alternatively, a stream of
the fire-retardant liquid may be merged with the stream of
emulsified isocyanate binder in nozzle assembly 18, for
example, by using inlet 83 to nozzle mix section 85. The
fire-retardant liquid may also be added to either the
diluent in inlet passage 64 or the binder in inlet
passage 74 to the nozzle assembly 18.
The fire-retardant fiberboard meets the same
technical specifications, including size, strength,
density and water-resistance characteristics, as the
nonfire-retardant fiberboard produced by the method and
apparatus according to the invention. With respect to its
fire-retardant properties, the fire-retardant fiberboard
described herein is certified to Class 1 surface spread of
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flame in accordance with the class definitions given in
British Skandard 476: Part 7: 1987. The test assesses
ignition characteristics and the extent to which the
product surface spreads flames laterally. Materials are
classified according to performance as Classes 1 to 4 in
descending order of performance. The fire-retardant
fiberboard is suitable for use, but is not limited to use,
in any of the following applications: ceilings, wall
linings, partitioning in build:ing and shopfitting, display
panels for the shopfitting and exhibitions industry,
shipbuilding applications, general purpose building panels
where greater fire integrity is specified or required
whilst still retaining a surface suitable for finishing.
Although preferred embodiments of the present
invention have been shown, it is obvious that many
modifications and variations of the present invention are
possible in the light of the above teachings. It is,
therefore, to be understood that the present invention
may be practiced otherwise than as specifically described.
