Note: Descriptions are shown in the official language in which they were submitted.
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The present invention is broadly concerned with a fire retardant
particleboard and with its special process of manufacture. In accordance
with an aspect of the present invention wood particles are treated with
boron compounds such as, for example, ~oric acid or alkali metal borates
in combination with sulfur acids, such as, for example, sulfuric acid,
prior to their consolidation into a particleboard panel.
It is well known in the art to produce wood particleboard panels
by various processes and techniques. In general, particles such as, for
example, wood particles of various sizes and geometrical configurations, are
consolidated using various glue or binder mixes such as urea formaldehyde,
phenol formaldehyde, melamine formaldehyde, acid phenol resins, etc., under
heat and pressure. Typical processes are described in U.S. Patent 2,642,371
issued June 23, 1953, inventor, Fahrni, entitled "Composite Wooden Board",
and in U.S. Patent 2,686,143, issued August 10, 1954, inventor, Fahrni,
entitled "Process for Manufacturing a Composite Wooden Board".
It is also known in the art to use, with the chips~ added chemicals
designed to reduce the fire hazard of these products. Many compounds have
been suggested and used in order to meet various fire underwirters tests
such as, for example, the 25 foot tunnel flame spread rating. Smoke rating
tests must also be met in many installations for these products. Typical
patents covering developments in this field are U.S. Patent No. 3,383,274,
issued May 14, 1968, inventor: Craig, entltled "Flame Proofing of Construc-
tion Material~", and U.S. Patent No. 3,360,822, issued December 28, 1971,
inventor: Carmellini, entitled "Acoustical and Fire Resistant Particle-
board". These patents are assigned to the applicant of the present invention.
It is also known in the art to use borates to produce so-called
"Borate Fire Retardant Systems", by various processes. One method used is
to treat the green chips with Polybor (Registered Trade Mark of U.S. Borax
& Chem. Corp. Los Angeles, Calif.~ sodium borate, (Na2B8O13.4H2O~, e;ther
in solution or as a dry powder. It is then conventional to add powdered
boric acid, (H3B03), into the resin mix prior to using the resin mix to
consolidate the treated wood chips. The addition of the boric acid to the
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glue mix is required since all sodium borates such as, for example,
Na2B8O13.4H2O have a relatively high pH such as, for example,
about 7 which retards the cure cycle particularly when using a
urea-formaldehyde resin. Thls retarding effect is compensated to
some extent by the addition of a strongly buffered catalyst such
as, for example, boric acid to the glue mix. Boric acid in the
glue mix tends to alter the wood-resin interface pH and thus
allow the normal cure cycle~
Certain troublesome problems are, however, encountered
when the boric acid is added to the glue mix. One limiting factor
as to the amount of boric acid which can be added to the glue
mix is dictated by the viscoslty of the resin which can be handled
by the resin spray system. Also great difficulty is encountered
in securing a uniform distribution of the boric acid throughout
the resin system particularly a urea-formaldehyde system. High
speed expensive mixing equipment is required to secure a satisfactory
dispersion of the powdered boric acid. Also, since the solubility
of the boric acid in this system is slight, the greater amount
of the boric acid will remain in suspenslon, thus causing difficulty
in spraying~ and plug-ups in the spray system~ Furthermore, when
using boric acid in the resin mix, it is necessary to increase
the resin content of the finished board to compensate for the
poor resin distribution due to the larger nozzles needed to
spray the boric acid suspension.
The present invention in one of its aspects provides
a high quality fire retardant particleboard using boron compounds
in con~unction with sulfuric acid, in the direct treatment of the
green chips.
Thus, by one broad aspect of this invention a process
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is provided for the manufacture of an improved fire resistant wood part
particleboard which comprises: spraying wood particles with an
aqueous solution of a boron compound and sulfuric acid, said boron
compound selected from the group, borax decahydrate (Na2B407. 10H20),
borax dehydrated (Na2B407), borax pe~tahydrate (Na2B407.5H20), polybor
(Na2B8013.4H20)~ salts of meta or ortho boric acids and boric acid
in conjunction with the borate and sulfuric acid to give the proper
Na20 to B203 ratio for maximum solubility of the final mixture;
said sulfuric acid being of 90% to 98% concentration which is
present in a weight ratio of from 1.5 to 4.0 boron compound to 1
of sulfuric acid; with the aqueous solution having a pH in the range
of 4.5 to 6.0, and wherein the amount sprayed intO the particles is
in the range of 10% to 40% by weight based on the weight of the
dry wood particles, the solution is heated to temperatures of
150F. to 225F. before use; thereafter conditioning and drying
the wood particles to moisture content of 3% to 7%; applying a
resin glue system of urea formaldehyde, and wherein the amount
used is in the range of 2% to 12% by weight based on the wood
particles; and consolidating the particles under heat at a
temperature in the range of 275F. to 360F. and pressure in the
range of 200 psi to 300 p9i for a time period in the range of
5 minutes to 20 minutes.
By another aspect of this inventlon, a process is
provided for the manufacture of an improved fire resistant wood
particleboard and for improving the cure cycle of the resin glue
system which comprises: Spraying wood particles with an aqueous
solution of borax (Na2B407) and sulfuric acid of 96% concentration,
said solution containing, by weight, 35% borax, and wherein the
weight ratio of borax to sulfuric acid is 52 to 21; said aqueous
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solution having a pH in the range of 4.5 to 6.0, and wherein
the amount of aqueous solution sprayed onto the particles is in
the range of 15% to 35% by weight based on the weight of the
dry wood particles, and said aqueous solution is sprayed at a
temperature in the range of 150F. to 225F. and wherein said
particles, after spraying, are allowed to stand before being dried
for a time period of ten minutes; apply a urea formaldehyde resin
glue system to said wood particles wherein the amount of said
resin glye system used is in the range of 2% to 12% by weight
based on the wood particles; and then consolidating said wood
particles under heat and pressure into a fire resistant particle-
board.
By still another aspect of this invention a process is
provided for the manufacture of an improved fire resistant wood
particleboard and for improving the cure cycle of the resin glue
system which comprises: spraying wood particles with an aqueous
solution of borax (Na2B407.XH20) wherein X has a value of from 0 to
10~ and sulfuric acid, said solution containing 35% by weight of
borax, wherein the weight ratio of borax to sulfuric acid is 1.5
to 4.0 borax to 1 of acld~ wherein the amount of solution sprsyed
is 25% by weight based on the dry particles, the solution being
sprayed at a temperature of 170F and having a pH in the range
of 4.5 to 6.0; thereafter conditioning the sprayed particles for
lO to 20 minutes; then drying the particles and applying 2% to
12% by weight of a urea formaldehyde glue system to said particles,
followed by consolidating said particles into a particleboard at
a pressure of 200 psi to 300 psi, at a temperature in the range
of 275F to 360 F for a time period of 10 to 20 minutes.
As seen above, the resin mix, especially a urea
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formaldehyde resin mix, is not diluted with boric acid and thereby
is more stable and more effective permitting the use of less resin,
all other factors being equal. Also, the expensive step heretofore
required of adding boric acid to the resin mix to secure a borate
system fire retardant particleboard is eliminated.
The present inVentiOn in one of its aspects may be
more fully understood by reference to the drawing which diagramatical-
ly illustrates one embodiment of the same. Referring to the
drawing~ raw wood finish is intro- -
. , . , , . _ , . . , _, . . .. .. . . .
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duced into grinder or flaker 2 as illustrated by line 1. The flakes orchips are then passed through a blower 3 into a section of a blow pipe 8.
The chips may be of any size and configuration as those known in
the art for the manufacture of particle boards. They may, for example,
have lengths of 5 to 50 mm,, widths of 5 to 10 mm., and thicknesses of from
1 to 5 mm. It is preferred that the chips have a moisture content above
100%, such as, for example, 125% to 150%, as for example, of 135% based on
the dry wood.
In blow pipe apparatus 8 the flakes are sprayed with fire retar-
dant solution from spray nozzles 9 or equivalent applicators. The fire
retardant solution comprises a borate, preferably a mixture of borates
introduced into storage tank 4 by means of line 5 and sulfuric acid intro-
duced by means of line 6. The fire retardant solution is passed to nozzles
9 by means of pump 7.
As mentioned above, the fire retardant solution comprises a boron
compound, or a borate, or a mixture of borates and sulfuric acid. Boric
acid is not satisfactory for application to the green chips since the chips
carry no more than 5% boric acid. Above this quantity the excess boric acid
falls away from the chips surfaces. The preferred acid is sulfuric acid,
preferably 90% - 98%, such as, for example, 96% concentration.
The borate may be selected from the class consisting of borax
decahydrate (Na2B407.10H20), borax dehydrated (Na2B407), borax pentahydrate
(Na2B407.5H20), and Polybor (Na2B8013.4H20), or salts of meta or ortho boric
acids. Also under certain conditions boric acid may be used in conjunction
with the borate and sulfuric acid to give the proper Na20 to B203 ratio for
maximum solubility of the final mixture. Thus, a preferred fire retardant
spraying solution is a borax Na2B407.XH20 where X can be any value from 0 to
10, but preferably can be 0, 5, or 10 and 96% sulfuric acid present in the
weight ratio of from 1.5 to 4,0 borax to 1 of sulfuric acid, preferably a
weight ratio of 2-1/2 to 1,
A desirable ratio is 52 parts by weight if anhydrous borax (or
equivalent parts of borax penta or borax deca hydrate~ to 15 to 25 parts of
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96% sulfuric acid. A much preferred ratio is 52 parts of anhydrous borax
to 21 parts of 96% sulfuric acid. The p~ of the fire retardant solution
is in the range of 4.5 to 6.0, preferably 5.0 to 5.5, such as, for example,
5.25. The solution is adjusted to 30 - 50% solids, such as, for example,
40% by weight with water and heated to a temperature in the range of 150F
to 225F, such as, for example, 170F when sprayed on the chips.
The treated chips then continue through the blowpipe to a cyclone
10 and then to a wet storage bin 11. After some stand time (i.e.~ over ten
minutes), in the bin or silo, the wet chips or particles are fed into a
dryer 13 by means of either a blowpipe-cyclone setup (not shown) or a
conveyor 12. The wet storage or conditioning bin 11 permits the chips to
become thoroughly impregnated and saturated with the fire retardant solution.
After drying to a moisture content of 3% to 7%, such as, for example, 5%, the
chips are taken through a blow pipe 14 to a cyclone 15 and then into a dry
storage silo 16. From here the chips are conveyed by blowpipe or conveyor
belt 17 to a screen 18 where the fines 20 are separated from the oversize
particles 19; the fines are sent to a fine storage silo 22~ then through a
glue applicator 24 and spread as face layers 27 and 29. The oversized are
stored in 21, glued in a glue applicator 23, and used as a core layer 28.
Urea resin 25 and 26 is fed into the flue applicator. The resulting mat is
pressed in a hot press 30 and sent through a board cooler 31 to glve a
finished panel.
As pointed out, the resin glue mix, preferably a urea formaldehyde
glue mix, is added to the chips by applicators 23 and 24. The amount of
resin glue mix used is 2% to 12%, such as, for example, 8% by weight based
on the weight of the dry chips. Core chips impregnated as described are
introduced onto a caul at positions 27, 28 and 29.
The board is then hotpressed at position 30. The pressing condi-
tionS will vary somewhat depending UpOn operating factors. If the board be,
for example, a 0.7g/cc density 3/4" panel, the temperature would be 275F to
360F, such as, for example, 340F. The pressure is 200 to 300 psi, such as,
for example, 250 psi for a time period of 5 to 20 minutes, such as, for
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example, 10 minutes~ The board is then dry cooled in zone 31 and then
remoyed as a finished product,
The boron compound and sulfuric acld are preferably mixed with
water to give a 20% to 50%, such as, for example, a 35% by weight solution.
The amount of boron compound used as compared to the sulfuric acid used is
to give a weight ratio in the range of 52 parts of anhydrous borax to 15 to
25 parts, preferably 21 parts of 96% acid. As mentioned, it is important
that the pH of the solution be ~elow 6.5 in the range of 4.0 to 6.0, such
as, for example, 5.25.
The amount of boron compound-sulfuric acid solution used based by
weight on the dry flakes is in the range of 10% to 40%, preferably 15% to
35%, such as, for example, 25%.
In order further to illustrate an aspect of this invention, the
following example is given.
EXAMPLE:
A 1:1 mixture of white fir and Douglas fir planer shavings were
sprayed with a 30% solids solution of fire retardant consisting of 100 parts
of sodium tetraborate decahydrate and 21 parts of 96% H2S04 in 122 parts of
water. The solution was heated to 170F before spraying, to insure solution
of the materials and to aid penetration into the wood. A total of 25 parts
of fire retardant solids per 100 parts of dry wood was obtained. The treated
wood particlt-s were then dried to a ~noisture content oP from 3 to 7% and
sprayed with a commercial particleboard resin consisting of urea formalde-
hyde condensates and ammonium sulfate catalyst. The level of resin used was
8% based on total resin solids to dry, treated wood.
The glued material was then spread to form a mat and pressed at
340F for ten minutes to give a particleboard having a density of .70 g/cc
and a thickness of 3/4~'. This board was then cut into three sections
21" x 96" and tested in accordance with ASTM E84-68 25~ tunnel test. Test
results gave a flame spread rating of 20 with a smoke rating of 0; this is a
Class I rating.
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