Note: Descriptions are shown in the official language in which they were submitted.
HOE 85/H 022 J~
The present invention relates to a microencapsulated
flame-retardant agent stable to hydrolysis, based on free
flowing, pulverulent ammonium polyphosphate, and to a
process for making it!
It is generally accepted that ammonium polyphos-
phates can be used for imparting flame-retardant pro-
perties to plastics materials. German Speclfication
DE-AS 12 83 532, for example, discloses a process for
making flame-retardant polyurethanes from high molecular
weight polyhydroxyl compounds, polyisocyanates and cata-
lysts, containing, as a flame-retardant additive,an
ammonium polyphosphate of the general formula
~ l (n-m)~2(NH4)mPn3n~1
in which n stands for an integer having an averaye value
; 15 of more than 10, m stands for an integer of at most n~2
and the ratio of m/n is between about 0.7 and 1.1.
While ammonium polyphosphates of the above general
formula are known to impart good flame-retardant pro-
perties to polyurethanes, the fact remains that they are
not sufficiently water-insoluble and therefore liable
to be washed out from the plastics material in the course
-of time under outdoor conditions. As can be inferred
from the statements made in column 3 of DE-AS 12 83 532,
the ammonium polyphosphates said to be practically water-
insoluble really have a considerable solubility in water;
indeed up to 5 9 ammonium polyphosphate becomes dissolved
on suspending 10 9 ammonium polyphosphate in lûO ml water
at 25C; in other words, up to 50 % of the ammonium poly-
~5~
phosphate is water-soluble.
German Specifications DE-OS 29 49 537 and DE-OS
30 05 252 disclose processes for making pulverulent
ammonium polyphosphates stable to hydrolysis by
encapsulating the ammonium polyphosphate particles in a
melamine/formaldehyd~-resin or phenol formaldehyde-resin.
Ammonium polyphosphate less soluble in water than untreated
ammonium polyphosphate is obtained in the two cases.
The encapsulated material fails however to be an
ideal flame-retardant agent as it tends to liberate
formaldehyde.
A further process for making pulverulent ammonium
polyphosphates stable to hydrolysis by encapsulating them
with a hardened epoxide resin has been described in Ger-
man Speciflcation OE-OS 32 17 816. The epoxide resins do
however not reduce the water-soluble fractions as effec-
tively as melamine/formaldehyde-resins.
It is therefore highly desirable to have an agent
and process permitting the solubility of ammonium poly-
phosphate in water to be minimized and produce a flame-
retardant agent based on ammonium polyphosphate which is
substantially not liable to be washed out from plastics
materials, wood or paper under outdoor conditions. In
addition, it is highly desirable to have encapsulating
materials liberating no pollutants.
We have now unexpectedly found that polycarbodiimides
should advantageously be substituted for melamine and
phenol resins.
The present invention now provides a microencap-
sulated flame retardant agent stable to hydrolysis, based
on free flowing, pulverulent ammonium polyphosphate of
the general formula
H(n m)+2(NH4)mPnO3~in which n stands for an integer having an average value
of about 20 to 800 and the ratio of m/n is about 1,
consisting substantially of
a) about 75 to 99.5 mass % ammonium polyphosphate and
b) about 0.5 to 25 mass % of a reaction product of a
polyisocyanate and a carbodiimidization catalyst,
; 10 the polycarbodiimide encapsulating the individual ammonium
polyphosphate particles.
The agent of this invention generaly consists substan-
tially of particles having an average size of about 0.01
to 0.1 mm, and the degree of condensation n of the ammo-
nium polyphosphate preferably is an integer having anaverag0 value of 450 to 800 , determined by the terminal
group titration process described by "van Wazer, Griffiter
and McCullough" in Anal. Chem. 26, page 1755 (1954).
The agent of this invention shoud preferably contain
the polycarbodiimide in a proportion of 2 to about 15
; mass %.
The polycarbodiimide is a reaction product which is
obtained on subjecting a polyisocyanate to a catalyzed
polycondensation reaction. The term "polyisocyanate" as
used herein denotes all commercially available aromatic
and aliphatic diisocyanates and poly-isocyanates which are
customarily used for making polyurethane, polyisocyanurate
or polycarbodiimide foams, for example.
The process of this invention for making the micro-
encapsulated flame-retardant agent stable to hydrolysis
comprises:microencapsulating - in a polycarbodiimide - a
suspension consisting substantially of a diluent, a free-
flowing pulverulent ammonium polyphosphate of the general
formula
H(n m)+2(NH4)mpnû3n+l
in which n stands for an integer having an average value
of about 20 to 800 and the ratio of m/n is about 1, a
polyisocyanate and a carbodiimidization catalyst by
heating the suspension, while stirring, over a period
10 of 0.5 to 5 hours to a temperature between 30 and 200C
and -thereafter cooling, filtering and drying the ammonium
polyphosphate microencapsulated in the polycarbodiimide.
Further pre~erred and optional features of the pre-
sent process provide:
a) for the suspension of diluent and ammonium poly-
phosphate to be gradually admixed with a solution
of the polyisocyanate and a solution of the carbo-
diimidization catalyst in the diluent, in the
sequential order indicated;
b) for n in the above general formula of the ammonium
polyphosphate to stand for an integer having an
average value of 450 to 800;
c) for the diluent to be selected from solvents based
on aromatic, aliphatic or cycloaliphatic hydrocar-
bons or in aliphatic, aromatic and mixed aliphaticl
aromatic ketones, preferably acetone;
d) for the polyisocyanate to be selected from commer-
cially available aromatic or aliphatic diisocyanates
and polyisocyanates, preferably commercial 4,4'-di-
phenylmethanediisocyanate (MDI);
~5~
e) or the carbodiimidization catalyst to be selected
from organophosphorus, preferably from cyclic organo-
phosphorus compounds, especially to be l-methyl-l-
o~o-phospholene;
f3 for an ammonium polyphosphate/diluent/polyisocyanate/
carbodiimidization catalyst-ratio of 1 : 1.5-2.5 :
0.05-û.25 : 0.00025-O.û125, more preferably 1 :
2 : 0.1 : 0.002 to be established in the suspension;
g) for the heating to be effected over a period of 1
to 2 hours to a temperature of 50 - 100C;
h) for the drying to be effected at a tempera-ture bet-
ween 80 and 15ûC under inert gas, preferably under
nitrogen;
i) for the flame-retardant microencapsulated ammonium
polyphosphate to consist substantially of particles
having an average size between 0.01 and 0.1 mm, more
preferably between 0.03 and 0.06 mm;
k) for the flame-retardant agent to contain the polycar-
bodiimide in a proportion of 2 to about 15 mass%.
The invention finally relates to a process using the
present agent for imparting flame-retardant properties
to polyurethanes and polyurethane foams, the polyurethane
foams containing the agent in a proportion of about 5 to
25 mass%, based on the quantity of the polyol component
of the polyurethane.
The polycarbodiimide should conveniently be applied
to the ammonium polyphosphate particles in a solvent based
on an aromatic, aliphatic or cycloaliphatic hydrocarbon or
in an aliphatic, aromatic or mixed alipha-tic/aromatic
ketone; more particularly, the polycarbodiimide is applied
whi].e stirring to an ammonium polyphosphate/polyisocya-
nate-suspension, the catalyzed polycondensation reaction
being carried out while heating.
By encapsulating the ammonium polyphosphate particlRs
with a polycarbodiimide in accordance with this inven~ion,
the solubility of ammonium polyphosphate in water is
considerably reduced; this beneficially influeneces ths
encapsulated ammonium polyphosphate for use as a flame-
retardant agent in polyurethane foams, for example.
As an encapsulating material for ammonium polyphos-
phates, the polycarbodiimides compare favorably with
standar,d phenol/formaldehyde resins and epoxide resins;
they permit the water-solubility to be more effectively
reduced but unlike those resins do not liberate formal-
dehyde.
In addition, material encapsulated in a polycarbo-
di.mide has a greater thermal stability than material
encapsulated in a melamine/formaldehyde-resin; this is
of particular interest for incorporation into thermo-
plastic materials which are processed at high temperatures.
The agents of this invention, the process for makingthem and their advantages are described in the following
Examples. The experiments described in the Examples were
carried out with the use of commercially available ammo-
nium polyphosphates and various commercially available
polyisocyanates and carbodiimidization catalysts. More
particularly, the followiny products were used:
1. EXOLIT 422 (this is a registered Trade Mark of Hoechst
Aktiengesellschaft, Frankfurt/Main). It is a fine
particulate dlfficultly water-soluble ammonium
polypho~phate with a degree of condensation n of
about 700.
2. CARADATE 30 (this is a registered Trade Mark of
Deutsche Shell Chemie GmbH, Frankfurt/Main). It is
a blend of various aromatic diisocyanates and tri-
isocyanates with 4,4'-diphenylmethanediisocyanate
as its principal component. The product is a liquid,
deep brown to black. Its isocyanate content liss
at 30.2 % NCû. It has a density (at 23C) of 1.22-1.24
g/ml and a viscosity (at 25C) of 160-240 mPa.s.
3. l-methyl-l-oxo-phospholene (a product of Hoechst
Aktiengesellschaft, Frankfurt/Main)
It is an isomer mixture of the following two products
and ~
0 ~ CH3 0~ \CH3
having a purity of at least 98 %. The product is a
yellow-brownish liquid; it has a density ~at 20C)
of 1.12 g/ml and it boils at a temperature of
150-155C/33 mbars.
4. 2-methyl-2-oxo-1,2-oxaphospholane (a product of
Hoechst Aktiengesellschaft, Frankfurt/Main)
It is a compound of the following formula
~ 'I
~p,~O
0 ~ \ CH
having a purity of at least 95 %. The product is a
~:258~
colorless liquid having a density cf 1.19 g/ml. It
has a boiling temperature of 89C/1.5 millib.ar.
5. 2-methyl-2,5-dioxo-1-oxa-2-phospholane (a product of
Hoechst Aktiengesellschaft, Frankfurt/Main). It is
a compound of the following formula
I--I = û
~ p /
~\
O CH3
having a purity of 95 - 98 %. The product (colorl.ess
crystals) has a melting point of 102-104C.
Example 1
250 g EXOLIT-422 was suspended in 1000 ml xylene in
a stirring apparatus of glass; next, a solution of 15 g
CARADATE 30 in 100 ml xylene was added dropwise. The
suspension was then heated to gentle boiling and admixed
dropwise with a solution of 0.06 9 of a carbodiimidiza-
tion catalyst (e.g. an isomer mixture of l-methyl-l-oxo-
phospholene; this is a product of Hoechst Aktiengesell-
schaft, Frankfurt/Main) in 50 ml xylene. The whole was
stirred for a period of 2 hours, then cooled to room
temperature and flltered. The filter cake was dried at
130C under nitrogen. 258 g encapsulated ammonium poly-
phosphate containing 3.9 mass % polycarbodiimide was ob-
tained.
To determine the water-soluble fraction, 10 g of the
product so made was suspended in 100 ml water and the
~2~
suspension was stirred for 20 minutes at 25C. Next, the
product fraction undissolved in the water was caused to
deposit within 40 minutes by centrifugation. 5.0 ml of the
supernatant solution was pipetted in a previously weighed
aluminium dish and evaporated at 120C in a drying cabinet.
The water-soluble fraction was calcula-ted from the
quantity of evaporation residue. The result obtained is
indicated in Table 1 hereinafter.
Example 2
The procedure was as in Example 1 but a solution of
30 9 CARADATE 30 in 100 ml xylene and a solution of 0.12 9
l-methyl-l-oxo-phospholene (isomer mixture) in 50 ml
xylene were used. 27û g encapsulated ammonium polyphos-
phate which contained 8.8 mass % polycarbodiimide was
obtained. The values determined for the water-soluble
fractions are indicated in Table 1.
Example 3
The procedure was as in Example 1 but a solution of
45 g CARADATE 30 in 100 ml xylene and a solution of 0.18 g
l-methyl-l-oxo-phospholene (isomer mixture) in 50 ml
xylene were used. 275 9 encapsulated ammonium polyphos-
phate which contained 12.1 mass % polycarbodiimide was
obtained. The values determined for the water-soluble
fractions are indicated in Table 1.
; 25 Example 4
The procedure was as in Example 1 but a solution of
60 9 CARADATE 30 in 100 ml xylene and a solution of 0.24 g
l-methyl-l-oxo-phospholene (isomer mixture) in 50 ml
xylene were used.
288 g encapsulated ammonium polyphosphate which con-
~:25~
tained 15.2 mass % polycarbodiimide was obtained. The
values determined for the water-soluble fractions are
indicated in Table 1.
Example 5
250 9 EXOLIT 422 was suspended in 400 ml acetone in
a stirring apparatus of glass, next, a solution of 30 9
CARADATE 30 in 100 ml acetone and a solution of 0.03 9
l-methyl-l-oxo-phospholene (isomer mixture) in SO ml
acetone were added. The suspension was then heated to
gentle boiling. The whole was stirred for a period of 1
hour, cooled to room temperature and filtered. The filter
cake obtained was dried at 100C in a stream of nitrogen.
255 9 encapsulated ammonium polyphosphate which contained
5.6 mass % polycarbodiimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 2.
Example 6
The procedure was as in Example 5 but a solution of
0.15 9 l-methyl-l-o~o-phospholene (isomer mixture) in 50 ml
acetone was used. 260 9 encapsulated ammonium polyphosphate
which contained 6.9 mass % polycarbodiimide was obtained.
The values determined for the water-soluble frac-
tions are indicated in Table 2.
Example 7
The procedure was as in Example 5 but a solution of
0.30 9 l-methyl-l-oxo-phospholene (isomer mixture) in 50 ml
acetone was used. 263 9 encapsulated ammonium polyphos-
phate which contained 7.8 mass % polycarbodiimide was
obtained.
The values determined for the water-soluole frac-
-10-
~258~
tions are indicated in Table 2.
Example 8
The procedure was as in Example 5 but a solution of
0.60 9 l-methyl-l-oxo-phospholene (isomer mixture) in
50 ml acetone was used. 272 9 encapsulated ammonium poly-
phosphate which contained 8.4 mass % polycarbodiimide was
obtained.
The values determined for -the water-soluble fractions
are indicated in Table 2.
Example 9
The procedure was as in Example 7 but the reac-tion
period was prolonged to 2 hours. 275 9 encapsulated ammo-
nium polyphosphate which contained 8.1 mass % polycarbo-
diimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 3.
Example 10
The procedure was as in Example 7 but the reaction
period was prolonged to 5 hours. 276 9 encapsulated ammo-
nium polyphosphate which contained 8.3 mass % polycarbo-
diimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 3.
Example 11
2500 9 EXOLIT 422 was suspended in 4000 ml acetone in
a heated enamelled pressure raactor (capacity = 16 1);
next, a solution of 300 9 CARAûATE 30 in 1000 ml acetone
and a solution of 3.0 9 l-methyl-l-oxo-phospholene (i.so-
mer mixture) in 500 ml acetone were added. The tempera-
ture was then increased to 80C and a pressure of 2.7 bars
-11-
~25~
was found to have established. The whole was then heated
for 1 hour, cooled to room temperature and fil-tered. The
filter cake obtained was dried at 100C in a stream of
nitrogen. 2850 9 encapsulated ammonium polyphosphate
which contained 8.5 mass % polycarbodiimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 3.
Example 12
The procedure was as in Example 11 but the reaction
period was prolonged to 2 hours. 2800 9 encapsulated
ammonium polyphosphate which contained 8.3 mass % poly-
carbodilmide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 3.
Example 13
The procedure was as in Example 11 but the reaction
temperature was increased to 100C; a pressure of 3.8 bars
was found to have established. 2820 9 encapsulated ammo-
nium polyphosphate which contained 8.0 mass % polycarbo-
diimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 3.
Example 14
The procedure was as in Example 5 but a solution of
1.20 9 2-methyl-2-oxo-1,2-oxaphospholane in 50 ml acetone
was used. The reaction period was prolonged to 4 hours.
265 9 encapsulated ammonium polyphospha-te which contained
8.2 mass % polycarbodiimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 4.
Example 15
The procedure was as in Example 5 but a solution of
2.40 9 2-methyl-2-oxo-1,2-oxaphospholane in 50 ml acetone
was used. The reaction period was prolonged to 4 hours.
270 9 encapsulated ammonium polyphosphate which contained
8.3 mass % polycarbodiimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 4.
Example 16
The procedure was as in Example 5 but a solution of
1.2û g 2-methyl-2,5-dioxo-l-oxa-2-phospholane in 50 ml
acetone was used. The reaction period was prolonged to
4 hours. 250 g encapsulsted ammonium polyphosphate which
contained 8.3 mass % polycarbodiimide was obtained.
The values determined for the water-soluble fractions
are indicated in Table 4.
Example 17
60 kg EXûLIT 422 was suspended in 100 l acetone in a
heatable enamelled reactor (capacity = 300 l) provided
with a stirrer. Next, a solution of 7.2 kg CARADATE 30
in 18 l acetone and solution of 144 9 l-methyl-l-oxo-
phospholene (isomer mixture) (2 %, based on CARADATE 30)
in 2 l acetone were added. The suspension was then heated
to boiling and maintained at boiling temperature over a
period of 3 hours. The whole was cooled to room tempera-
ture and filtered, and the filter cake was dried at 100C
in a stream of nitrogen. 64.5 kg encapsulated ammonium
polyphosphat~ which contained 8.8 mass % polycarbodiimide
was obtained. 0.1 % was water-soluble at 25C and 0.6 %
was wa-ter-soluble at 60C~ This meant a 99 % reduction of
-13-
~25~
the water-soluble fractions in each case, compared with
uncoated EXOLIT 422.
The values determined by thermogravimetrical analy-
sis are indioated in Table 5.
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-19-
~58~
The values indicated in Tables 1 through 4 indicate
that the modifying agents of this invention permit the
content of water-soluble matter to be considerably re-
duced (up to 99 % at 25C and also up to 99 % at 60C).
The values indicated in Table 5 show that modified
ammonium polyphosphate, i.e. encapsulated in a polycar-
bodiimide, has a distinctly improved thermal stability.
-20-
