Note: Descriptions are shown in the official language in which they were submitted.
C06-12-03~9
10fà7~3~
BACKGROUND OF THE INVENTION
Urea-formaldehyde resins are widely used in the wood
products industry as adhesives for plywoods and binder resins
for hardboard, chipboard, particle board and the like.
Recently, due to considerations of safety and fire prevention,
there has developed a demand for fire-retardant or fire-
resistant plywoods and particle board or chipboard. Therefore,
the prior art has sought methods for the incorporation of fire-
retardant salts, and specifically such salts as ammonium
phosphates and polyphosphates, into plywoods and particle
board.
The prior art methods of incorporation of ammonium
; ~ phosphates into particle boards have required mixing in the dry
phosphate salt or spraying a solution thereof onto the particle
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board wood furnish and drying such furnish before adding resin
,
binder thereto. Alternatively, it has been suggested to
- incorporate the powdered dry salt into a binder resin, but such
; dry powdered sal~s are very difficult to disperse and maintain
evenly dispersed in such resin solutions. Attempts to blend
aqueous solutions of monoammonium phosphate, diammonium phos-
phate or ammonium polyphosphates with aqueous syrups or urea-
formaldehyde or melamine-urea-formaldehyde resins have been
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successful only in very low concentrations of the phosphates,
since higher concentrations of phosphates cause the resins to
; 25 cloud and precipitate. These low concentrations are generally
`~ not sufficient to confer an acceptable level of flame retard-
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`ir ancy on the final particle board product. Consequently, it has
been desired to incorporate aqueous solutions of phosphate
-~ salts into such urea-formaldehyde and melamine-urea-formaldehyde
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resins at cOncentrations higher than 10% by weight in order to
simplify the process of production of fire-retardant particle
boards.
It has now been found that certain aminoplast reslns
will remaln stable to aqueous solutions of the above ammonium
phosphates for adequate periods making possible a fire-
retardant binder resin solution quite suitable for use in the
general commercial process for the productiOn of particle
board. The avallability of such blnder resin solutions makes
possible the production of fire-retardant particle board pro-
duced as rapidly with the same number of steps as are required
for the present production of non-fire-retardant particle
boards. These novel fire-retardant blnder resin solutions can
be used in the same manner and with the same facility as
ordinary aminoplast binder resln solutions but contai~ much
hlgher concentrations of ammonium phosphates than are compati-
ble with ~uch normal resin solutions. Thus, industry is
enabled to produce fire-retardant particle board by the ~ame
process and at the same rate of production as the non-fire-
retardant particle boards. A further advantage is the factthat the novel blnder resin solutions can be produced at high
- percent solids, and do not require dilution with increased
amOunts of water which would, in turn, require a separate
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drying step for the wood furnish in order to eliminate same.
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As a consequence, these novel binder resln solutions and
~ process ~or their productiOn represent a decided lmprovement
; ln both economics and safety.
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SUMMARY OF THE I~ENTION
The present invention is directed to the pro&e~s fOr
the production Or a resin binder solution and the resin binder
solution product comprising an aqueous solution o~ predomln-
antly a urea-formaldehyde resin having a formaldehyde to urea
ratiO of less than 2.0, and preferably about 1.2 to 1.8, pre-
ferably a minor proportion of a methylolated melamine-formalde-
hyde resin, rrom about 12 to 30% by weight dissolved diammonium
pho!~phate or a mixture of diammonium phosphate and ammonium
polyphosphate acidified with phosphoric acid and not more than
50% by weight water.
The process for production of the novel binder resln
solution comprises mixing with a substantially neutral aqueous
solUtlon o~ a low molecular weight urea-formaldehyde resin of
a mol ratio of from about 3.0 to 3.5 formaldehyde/urea, said
solution having a viscosity of from 60 to lOO~cps and a percent
~olids Or at least about 70 percent, sufricient urea to reduce
the formaldeh~yde/urea ratio to from about 1.2 to 2.0 and suf-
ficient of a stable concentrated aqueous solution of diammonium
~.
phosphate or diammonium phosphate, ammonium polyphosphate and
phosphorlc acid havlng a percent solids Or at least 40 percent
to produce a concentratlon of dissolved diammonium phosphate
and ammonium polyphosphate of about 12 to 30 percent in the
resulting stable binder resin solution. Preferably, from about
~5 15 to ~5 percent by weight of a methylolated melamlne-
rormaldehyde resin in aqueOus solution of at least about 50
percent solids, and pre~erably more than 60 p~rcent solids, is
added to the neutral aqueousurea-formaldehyde solutlon prior
to mixing therewith the urea and ammonium phosphate solutlon
detalled above.
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DETAILED EMBODIMENTS
The starting material to produce the desired resin
binder solutions of the present invention is a low molecular
weight urea-rormaldehyde resin Or from about 3.0 to 3.5
formaldehyde/urea ratio in substantially neutral aqueous solu-
tlon. Such high F~U ratio, low or lightly bodied resin can be
obtained by the method described in British Patent :~
Number 1, 486, 342 .
initial reaction under alkaline conditions
at a temperature of at least 75C., cooling and ad~usting to
an acid pH Or ~rom about 1.7 to 2.1 and reacting at a temper-
ature Or from 30 to 55C. to body the resin to the desired
viscosity, neutralizing the solution and coollng to amblent
temperature. The desired low molecular weight or lightly
bodled resin will have a viscosity Or about 60 to 100 cps at
21C. which can be obtained with only about 3 to 10 minutes
of bodying reactiOn at the acid pH specified and 30 to 55C.
Thereafter the neutralized aqueous solution i8 conveniently
sub~ected to distillat~on of a portion Or the water present
to concentrate the UF resin solution to a high solids content
Or from about 70 to 95 percent, preferably 80 to 90 percent
solids. Such early concentratiOn will avoid the necessity for
later concentration Or the finished binder resln or the added
st~p of drying the particle board furnlsh to acceptable moisture
limlts for hot pressing.
A preferred base resin comprlses such high F ~ ratlo,
low molecular weight urea-formaldehyde resin above described
further mixed with a methylolated melamine-formaldehyde resin
ln aqueOus solution Or a solids content Or at least 50 percent,
and prererably at least 60 percent, in an amount of rrOm about
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15 to 25 percent by welght o~ the starting UF re~in. Such
mlxed re~ln solution ls hereafter re~erred to as melamine-urea
rormaldehyde re~in solutlon or MUF resln base. It ha~ been
~ound that the presence o~ ammonium phosphates in UF binder
resln Rolutions tends to lead to decompositlon o~ the UF resin
under hlgh temperature hot pressing conditions, but that forti-
ricatlon t~ereof with the lndlcated amount of methylolated
melamlne-~ormaldehyde re~ln~ overcomes thls tendency and renders
the mlxed res~n base relatively stable ln the presence of
ammonlum phosphates under high temperatures. De~irably the
resln base wlll constltute ~rom about 30 to about 55 percent by
wei~ht Or the total binder solution compositlon.
- - A dlstillation proces can be used to concentrate the -
sollds content o~ the MUF ba~e resln to at least 70 percent,
and preferably ~o about 80 to 90 percent, if required. If
deslred, the concentratlon can be per~ormed after addltlon of
the melamine-formaldehyde resin solutlon, rather than Or the
startlng urea-~ormaldehyde resln as dl3cussed above.
There 1~ added to the concentrated urea-formaldehyde
base resin or MUF resin base, sufficlent urea to ad~ust the FjU
ratlo Or the resultlng mixture to less than 2Ø Preferably,
, - surrlcient urea is added to produce an F ~ ratlo of rrom 1.2 to
1.8. The urea can be added dry or ~ a concentrated aqueOu~
solutlon as deslred.
In order to produce a ~ire-retardant resin blnder
solutlon and a partlcle board produced therewith of the highest
~ire-retardant ratin~s, it ls desirable to lnclude in the resin
binder solution the hlghest concentration of ammonlum phosphates
which is compatible with stability of the mixed resin solution
3 produced. However, care must be taken that the ammonlum
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1067638
phosphate content Or the binder solutlon 1~ not 80 great as to
lnterfere wlth the spraylng and mixing o~ the blnder solutlon
wlth the wood particle furni~h for the manufacture of partlcle
boards. The amounts of ammonlum phosphate ~olutions speclfied
hereln have been found to produce hlgh flre-retardant ratlngs
in partlcle board pr~duct~ and to be easlly and ef~iclently
applied and mlxed ln typlcal commerclal partlcle board produc-
tlon processes.
It has been found that the ammonium phosphate content
can be ~upplled by a variety Or compatlble aqueous solutions
thereo~. Suitable sources are concentrated aqueous-~olutions
from about 30 to 40 and more percent dlammonlum phosphate
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and as nearly saturated as can be practlcally handled and
stored without precipitation. A convenlent commercially avall-
- 15 able solution i~ a 40 percent diammonium phosphate aqueOus
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801ution. Such 40 percent DAP solutlon can be used to the
extent Or from about 30 to 50 parts per hundréd parts o~ base
.. . .
- re~ln and urea, l.e., sufflcient to produce resin solutions
- ~ containing ~rom 12 to 20 percent DAP, but ~mo~lts of up to 40 -~
parts supplying from 12 to 16 percent DAP are preferred for
reasOn~ of ~ta~illty Or the binder~solutions.-~ Such 801utlon~
w~ll supply from about 2.4 to 6.5 percent by welght of the
phosphate when applled at 20 to 40 parts per hundred parts or
wo~d rurnlsh.
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Even more preferred sources o~ ammonIum phosphates are
aqueous solutlons of ammonlum polyphosphates slnce such ~olu-
tion~ can contaln greater amounts Or the ~ho~phates prlor to
8aturatlon. Such solutions are generally commercially avail-
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:~ able from the fertlllzer lndustry and are complex gro~s mlx-
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~ 30 tures o~ varlou~ condensed and polyphosphates as the ammonium
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8alt~ produced by ammonlating a phospholeum of rrOm 95 to 12
percent total phosphate content, which phospholeums are com-
merically available condensed phosphoric arld solutlons. Typl-
cal ammonium polyphosphate solutions expressed by plant food
content analysis are the 10-34-0 ammOnium polyphosphate avail-
~ able as a 60 percent solutlon rrOm fertllizer producers and
~1-37-0 ammonium polyphosphate avallable as a 66 percent solu-
- tlon from the TVA and other~. Such ammonlum polyphosphate
solutlons enable one to produce blnder solutions containlng
higher phosphate content~ with llttle increase in the dlluting
water present.
- However, such condensed ammonium phosphate and poly-
-~ phosphates cannot practically be used ln blnder resins wlthout
-other addltl~es because they are very strOng bu~ers in which
the ammonium ion demonstrates no latency so that such polyphos-
phate salts severely retard the cure of the binder resln at
board presslng temperatures. Diammonium phosphate on the other
hand dlsplays a latent ammonlum lon er~ect and serves-as a
- latent curlng catalyst. Hence, when ammonlum polyphosphates
are employed lt has been found advantageous to use DAP there-
with to supply a part Or the desired phosphate content and
curlng catalytic ef~ect. Furthermore, it has been ~ound that
-~ the strong buffering effect Or ammonlum polyphosphate keep3
the pH Or a resin solution-contalning same too alkallne to
prQmOte an acceptable curlng rate. Consequently, it has been
~ound essential to include an acid to lower the pH and phos-
phorlc acld has been round most useful as a thlrd souroe Or
phosphate lon. However, solutlon~ Or both ammonium polyphos-
phates and dlamMonium phosphate are nOt stable ln the pre~ence
3 Or relatlvely small percentages Or phosphoric acid; as llttle
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as 6 to 15 percent o~ a 75 percent phosphoric acid wlll cause
precipitatlon Or the 10-34-0 and 11-37-O ammonium polyphosph~te
solutlons described above.
It has been ~ound that mixed solutlons of ammonium
polyphosphate3 and diammonium phosphate are stable in the
presence of much greater quantltle~ o~ phosphoric acid. There-
~Ore, to produce the mixed ammonium phosphate solutlon use~ul
ln a binder resin solution lt has been ~ound necessary to
lnclude an amount of concentrated phosphoric acld of ~rOm about
10 to 20 perc~nt Or the total of the ammonium phosphates on a
welght basis. Thls ls sur~iclent to reduce the pH o~ the phos-
phate solutions to a range o~ rrOm about 4.4 to 5.4.
Typical use~ul ammonium pho~phate solutions for
blending with the urea-formaldehyde or melamlne-urea-formaldehyde
- 15 re31n bases are those o~ the following compositlons:
~ .
Ingredient As Solution Conc. Parts - % Phosphate
10-34-0 APP 60% 5 - 72 30-43.2
or 10-37-0 APP 66% 50 - 72 33-47.5
DAP 40% 10 - 40 4-16
Phosphoric Acid 75~ - 10 - 18 7.5-13.5
Thus, on a 100 percent basis, such solutions can contain ~rOm
56 to 73% ammonium polyphosphate~ from 6 to 30% diammonlum
phosphate and from 14 to 21~ phosphorlc acld. Such solutlons
will supply ~rom about 18 to 30 percent phosphate ln the blended
blnder resln; the resln wlll thus supply from about 3.6 to 10.5
percent total phosphate to the flnlshed boards when applied to
20 to 35 parts per hundred parts wood furnish.
The most prererred solutions are those contalning the
~' greater amount3 of ammonlum polyphosphates since they wlll pro-
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~ 3 duce the hlghest phosphate concentratiOns ln the blended blnder
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iO~7638
resln solution~. A qùite useful and stable ammonium phosphate
solution has been found to be one of the following compositlon:
65.2 parts 10-34-0 APP - 60% solutlon
21.8 parts DAP - 40% solution
13.0 parts Phosphoric Acid - 75~ solution
on a 100% basis the above solution contains 61.5~ ammonium
polyphosphate, 23.2~ diammonium phosphate and 15.3% phosphor~c
acid.
When referred to hereln as condensed ammonium phos-
pr.atesor ammonium polyphosphates any Or the condensed ammonium
phosphates can be employedl includlng the ammOnium polyphos-
pnates from orthophosphoric ac~d, the ammonium metaphosphates
and the ammonium ultraphosphates. Any o~ such as aqueous solu-
tions can be used as a source of ammOnium phosphate in the new
rire-retardant binder resin
The fire-retardant particle boards produced with the
ne~ blnder re~ins are made by the usual industrial prOcesses
fcr such boards. These prOcesses invOlve spraying the desired
a-ount of resin solution, generally from about 20 to about 40
pcrts per hundred parts o~ furnlsh, onto a dried wood particle
f~-nish, thorough blending thereofJ deposit of the furnish and
r~sin onto supporting cauls and pressing the wood particle
~rnish to stops at from about 20 to 30 ~ækm2 at temperatures of
f~om about 135 to 177C ~Or periods of from about 3 to 8
m~utes to produce the finished particle boards.
The sample particle boards described in the examples
~clow were tested for fire-retardancy rating by the well-known
S~;~lyter Burning Test described in "Fire-Test Methods", Forest
F~oducts Laboratory Report No. 1443, U.S.D.A. Forest Service
3 (:9~9). When modified by the use of propane as the fuel rather
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than the standard methane or natural ga~ such ~uel i8 noted
- below. Ratlngs from the test are given in terms of rlame
spread in 5 minutes as a percentage of the flame spread in the
same period On standard untreated red oak lumber One inch thick.
Type I or Class I fire-retardancy is represented by flame
spread ratings Or 25 or less, l.e., 25 percent Or standard,
while Type II Or Class II rire-retardancy is represented by
ratings of from 25 to 75, i.e. percent, based On red oak lumber
as standard.
The examples below will serve to ~urther illustrate
the fire-retardant prOperties of particle boards prepared with
the novel binder resin solutions of the present invention.
EX~PLE I
Thls example illustrates the use of a fire-retardant
binder resin solution prepared from a sOlution o~ diammonium
phosphate. A urea-formaldehyde resin was prepared by reacting
100 parts of a 5 ~ aqueous formalin solution with 31.8 parts of
urea at a pH of about 9.0 for 5 minutes at 80C., cooling the
mixture to 60 C., distilling Orr 10~ of the water present to a
temperature of about 40C. Thereafter the resln solution was
ad~usted to a pH of 1.8 with sulfuric acid and the resin bodied
~or 5 minutes and neutralized. The resin solution was dis-
tllled to a solids content of 89 percent, cooled, and mixed
with 2 ~ by weight on the basis of the UF resin of a 65 percent
aqueous solution of a methylolated melamine-formaldehyde resin
(Resimene 841*). This 5:1 mixture formed the melamine-urea-
` formaldehyde base resin.
There were then mixed with 48 parts of the above MUFbase resin 14 parts of urea and 38 parts of a 40 percent aque-
ous solution of diammonium phosphate to produce a clear aqueous
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blnder resln syrup of 80 cp~ viscosity. This binder resin
solution Or only 19 percent water wa~ an excellent particle
board binder stable for at least four hours to clouding or
precipitation.
Particle boards were prepared in the usual manner
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rrom dried wood particle furnish sprayed with 20 percent and
30 percent o~ the above solution based on the weight of the
dry wood rurnlsh~ su~ficient solution to supply 3.04% and
4.56~, respectively, of ammonium phosphate ln the rinished
particle boards. The board~ were 1.9 cm thick with a density
- of about 753 Kg/m3 produced by pressing ror 7-1/2
minutes at 163C to thickness stops under an lnltial pressure
;~ of 25 Kg~cm~ ~hese sample particle boards and a control board
were sub~ected to testing by the Schlyter test described above
using the indicated fuel with the fire-retardant results set
out in Table 1 below. The board used as a control was prepared
from a similar melamine-urea-formaldehyde base resin with no
added ammonium phosphates.
TABLE 1
Flame
Board~ DAP Fuel Rating FR Type
Control 0Methane 125 --
1 3.04Propane 40 II
" "Methane 32-34 II
2 4.56Propane 25
Methane 23-25
~hus, Type I ~lame retardancy can be achieved by use Or the
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binder resin solution containing DAP ln normal productlon pro-
cesses and at reasonable application rates. All the boards
3 displayed good strengths, internal bonding and color.
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EXAMPLE II
In thls example the blnder resin is prepared from a
801ution 0~ ammonlum polyphosphate, dlammonium phosphate and
pho~phoric acld. The mixed ammonlum pho~phate solution is pre-
pared by mixing 65.2 parts o~ 10-34-0 ammonium polyphosphate
60 percent solution and 21.8 parts of a diammonil~ phosphate
40 percent solution and 13.0 parts o~ concentrated phosphoric
acid 75 percent ~olution. This mixed solution was stable and
dld not precipitate ror a period of longer than 10 days.
There was prepared a binder resin solutlon from the
same MUF base resin described in Example I. To 12 parts of
the MUF base resin there was added 3.7 part~ of urea and 13.8
parts of the above described mixed ammonium polyphosphate,
diammonlum phosphate and phosphoric acid solution. The binder
resin solutlon was clear, stable for at lease 4 hours and had
a viscosity of about 280 cps.
Particle boards were prepared in the usual way by
spraying 30 parts Or the binder resin solution onto 100 parts
of dry wood particle furnish and blending ~ame before deposit-
lng the furnl~h and pre3slng the board3 under the same condi-
tlons a~ in Example I above. There was thus supplied a totalof 7.95~ total phosphate in the pressed particle board~. The
rl~ished and cooled boards were treated in the about outlined
Schlyter test using methane fuel and the result~ are set out
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ln Table 2 below.
;, 25 TABLE 2
;~ Board% Total PhosphateFlame Rating FR Ty~
1 7.95 24
2 " 25
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All the boards tested displayed a Type I fire~
retardant rating, good strength, internal bonding and color and
represented good quality commercial particle boards.
It is clear from the above examples that fire-
retardant particle boards are produced when the ammonium phos-
phates are applied and coprecipitated from solution with the
resin binder in amounts of from about 2.4 to 10.5 percent by
weight. It is preferred that the ammonium salts be pre~ent in
amOunts of from about 2.8 to 10 percent by weight.
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