Note: Descriptions are shown in the official language in which they were submitted.
HOE 35/H 027 JK
The present invention relates to a microencapsulated
flarne-retardant agent stable to hydrolysis, based on free
flowing, pulverulent arnmonium 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 Specification
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
H(n m)~2(NH4)mPn3n~1
in which n stands for an integer having an average value
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 ammoniurn 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 ~he plastics material in tha 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 po].yphosphate becomes dissolved
on suspending 10 9 ammonium polyphosphate in 100 ml water
at 25C; in other words, up to 50 % of the ammonium poly-
,~r,
~S~
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 encap-
sulating the ammonium polyphosphate particles in a mela-
mine/formaldehyde-resin or phenol-formaldehyde-resin.
Ammonium polyphosphate less soluble in water than Ull-
treated 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
German Specification DE-OS 32 17 816. The epoxide resins
do however not reduce the water-soluble fractions as
effectively as melamine/formaldehyde-resin.
It is therefore highly desirable to have an agent
and process permitting the solubility of ammonium poly-
phosphate in water to be minimized, and to produce a
flame-retardant agent based on ammonium polyphospha-te
which is substantially not liable to be washed out From
plastics materials, wood or paper under outdoor condi-
tions. In addition, it is highly desirable to have
encapsulating materials liberating no pollutants.
We have now unexpectedly found that polyureas should
advantageously be substituted for melamine and phenol
resins.
The present invention now provides a microencapsu-
--2--
L~
lated flame-retardant ayent stable to hydrolysis, based
on free flowing pulverulent ammonium polyphosphate of the
general formula
H(n m)+2(NH4)mpno3n+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,
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 water, the resulting polyurea
encapsulating the individual ammonium polyphosphate
particles.
The agent of this invention general consists sub-
stantially of particles having an average size of about
0.01 to 0.1 mm, and the degree of condensation n of the
ammonium polyphosphate preferably is an integer having an
average 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 should preferably con-
tain the polyurea in a proportion of 2 to about 15 mass %.
The polyurea is a reaction product which is obtained
by subjecting a polyisocyanate to a polyaddition reaction
with the polyamine resulting from the reaction of the
polyisocyanate with water, during which carbon dioxide
is split off. The form "polyisocyanate" as used herein
denotes all commercially available aromatic and aliphatic
diisocyanates and poly-isocyanates as well as prepolymers
based on polyisocyanates modified with a polyurethane,
-3-
polyisocyanurate or polycarbodiimide, which are prepared
from commercially available arornatic or aliphatic diiso-
cyanates ancl polyisocyanates by subjec-t:ing these latter
to partial reaction with a polyhydroxy compound, or to a
partial carbodiimidization reaction or to a partial
trimerization reaction, and which are used, e.g. for the
manufacture of polyurethane, polyisocyanurate or poly-
carbodiimide foams.
The process of this invention for making the micro-
encapsulated flame-retardant agent stable to hydrolysis
comprises: microencapsulating - in a polyurea - a suspen-
sion consisting substantially of a diluent, a free-flowing
pulverulent ammonium polyphosphate of the general formula
H(n m)~2(NH4)mPn3n~1
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 water by heating the suspension, while
stirring, over a period of 0.5 to 5 hours to a tempera-
ture between 30 and 200C and thereafter cooling, filtering
and drying the ammonium polyphosphate microencapsulated
in the polyurea.
Further preferred and optional eaturas of the pre-
sent process provide:
a) for the suspension of diluent and ammonium polyphos-
phate to be gradually admixed with a solution of the
polyisocyanate and with the water, 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 80û;
--4--
c) for the diluent to be selected from proton-inactive
solvents miscible with water- or solvent mixtures
such as aliphatic, aromatic and rnixed aliphatic/
aromatic ketones, preferably acetone;
d) for the polyisocyanate to be selected from commer-
cially available aromatic or aliphatic di- and poly-
isocyanates as well as from prepolymers based on a
a polyisocyanate modified with a polyurethane or
polycarbodiimide or polyisocyanurate, the prepoly-
mers being made from commercially available aromatic
or aliphatic di- and polyisocyanates by subjecting
these latter to partial reaction with a polyhydroxy
compound, to a partial carbodiimidization reaction
or partial ,trimerization reaction;
e) for the polyisocyanate to be s.elected from poly-
isocyanates modified with a polycarbodiimide in a
partial carbodiimidization reaction, preferably
to be 4,4'-diphenylmethanediisocyanate modified
with a polycarbodiimids;
f) for the reactant selected for the polyisocyanates to
be water;
g) for an ammonium polyphosphate/diluent/polyisocyanate/
water-ratio of 1 : 1.5-2.5 : 0.05-0.25 : 0.005-0.1
more preferably 1 : 2 : 0.1 : 0.02 to be established
in the suspension;
h) for'the heating to be effecte,d over a period of 1
to 2 hours to a temperature of 50 - 100C;
i) 'for the drying to be effected at a temperature bet-
ween 80 and 150C under inert gas, preferably under
nitrogen;
~2tDl~
k) for the flame-retardant microencapsulated ammonium
polyphosphate to consis-t substantially of particles
having an average size between 0.01 and 0.1 mm,
more preferably between 0.03 and 0.06 mm;
l) for the flame-retardant agent to contain the polyurea
in a proportion of 2 to about 15 mass %.
The invantion fina.lly 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 polyurea should conveniently be applied to the
ammonium polyphosphate particles in a proton-inactive
solvent miscible with water, or in a solvent mixture e.y.
in an aliphatic, aromatic or mixed aliphatic/aromatic
ketone; more particularly, the polyurea is applied while
stirring to an ammonium polyphosphate/polyisocyanate/
water-suspension, the polyaddition reaction being carried
20 out while heating.
By encapsulating the ammonium polyphosphate particles
in a polyurea in accordance with this invention, the
solubility of ammonium polyphosphate in water is conside-
rably reduced; this beneficially influences the encapsu-
25 lated arnmonium polyphosphate for use as a flame-retardant
agent in polyurethane foams, for example.
As an encapsulating material for ammonium poly-
phosphates, the polyureas compare favorably with standard
phenol/formaldehyde resins and epoxide resins; they
30 permit tha water-solubility to be more effectively re-
duced but unlike melamine/formaldehyde resins andphenol/formaldehyde resins do not liberate formaldehyde.
The agents of this invention, the process for
making them and their advantages are described in the
following Examples. The experiments described in the
Examples were carried out with the use of commercially
available ammonium polyphosphates and various commer-
cially available polyisocyanates. More particularly,
the following products were used:
1. EXOLIT 422 (this is a registered Trade Mark of
Hoechst Aktiengesellschaft, Frankfurt/Main). It is
a fine particulate difficultly water-soluble ammo-
nium polyphosphate~ (NH4P03)n, 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
lies at 30.2 % NCO.
It has a density (at 23C) of 1.22-1.24 g/ml and a
viscosity (at 25C) of 160-240 mPa~s.
3. SUPRASEC 1042 (this is a registered Trade Mark of
Deutsche ICI GmbH, Frankfurt/Main). It is a dark
liquid free from solvent which has a density (at
25C) of 1,24 g/ml and a viscosity (at 25C) of
235 mPa.s.. Its isocyanate content lies at 28.8-
30.2 % NCO.
4. DESMODUR T 80 (this is a registered Trade Mark of
-7-
- , ., ,-.,
~s~
Bayer Aktiengesellschaft, Leverkusen). It is an
isomer mlxture of an arornatic ~iisocyanate with 80
mass % 2,4-diisocyanatotoluene and 20 mass % 2,~~
diisocyanatotoluene. The product is a colorless
liquid whose isocyanate content lies at about 48 %.
Its densi.ty (at 25C) is about 1.2 g/ml.
5. Isophoronediisocyanate (3-isocyanatomethyl-3,5,5-
trimethylcyclohexyl isocyanate) (a product of Che-
mische Werke Huls Aktiengesellschaft, Marl).
It is a liquid, colorless product whose isocyanate
content lies at 37.5-37.8 % NCO. Its density (at
20C) is 1.058-1.064 g/ml and its viscosity (at
20C) is 15 mPa.s.
Example 1
250 9 EXOLIT 422 was suspended in 1000 ml acetone
(water cont0nt less than 0.3 ~) in a stirring apparatus
of gIass; next, a solution of 15 9 CARADATE 30 in 100 ml
acetone was added dropwise. The suspension was then heated
to gentle boiling and admixed dropwise with a solution of
5 9 water in 50 ml acetone. The whole was stirred for a
period of 2 hours, then cooled to room temperature and
filtered. The filter cake was dried at 110C under nitro-
90n. 253 9 encapsulated ammonium polyphosphate containing
4.5 mass % polyurea was obtained.
To determine the water-soluble fractions, 10 9 of
the product so made was suspended in 100 ml water and
the suspension was stirred for 20 minutes at 25C and
60C, respectively. Next, the product fraction
undissolved in the water was caused to deposit within
--8--
40 minutes by centrifugation. 5.0 ml of the supernatant
solution was pipe-tted in a previously weiyhed aluminium
dish and evaporated at 120C in a drying cabinet. The
water-soluble fraction was calculated 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 rnl acetone was used. 267 9
encapsulated ammonium polyphosphate which contained
9.7 mass % polyurea 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
15 9 SUPRASEC 1042 in 100 ml acetone was used. 249 9
encapsulated ammonium polyphosphate which contained
5.1 mass / polyurea was obtained. The values determined
for the water-soluble fractions are indicated in Table 1.
Example 4
The procedure was as in Example 1 but a solution of
30 9 SUPRASEC 1042 in 100 ml acetone was used. 264 9
encapsulated ammonium polyphosphate which contained
10.2 mass % polyurea 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 15 9
DESMODUR T 80 in 100 ml acetone and a solution of 5 9
water in 50 ml acetone were added. The suspension was
30 then heated to gentle boiling. The whole was stirred
_g_
,
~s~
for a period of 2 hours, cooled to room temperature and
filtered. The filter cake ob-tained was dried at 100C
in a stream of nitrogen. 257 g encapsulated ammonium
polyphosphate which contained 4.3 mass % polyurea was
obtained.
The values determined for the water-soluble frac-
tions are indicated in Table 2.
Example 6
The procedure was as in Example 5 but a solution
10 of 30 9 DESMODUR T 80 in 100 ml acetone was used. 272 g
encapsulated ammonium polyphosphate which contained
7.5 mass % polyurea 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
15 g isophoronediisocyanate in 100 ml acetone was used.
252 9 encapsulated ammonium polyphosphate which con-
tained 5.2 mass % polyurea was obtained.
The values determined ~or the water-soluble frac-
tions are indicated in Table 2.
Example 8
The proce~ure was as in Example 5 but a solution of
30 g isophoronediisocyanate in 100 ml acetone was used.
266 g encapsulated ammonium polyphosphate which con-
tained 8.9 mass ~ polyurea was obtained.
The values determined for the water-soluble frac-
tions are indicated in Table 2.
Example 9
The procedure was as in Example 5 but a solution of
-10-
~s~
30 9 CARADATE 30 modified with 30 9 polycarbodiimide
(prepared by heating CA~ADATE 30 with 15 ppm of a carbo-
diimidization catalyst (e.g. l-methyl-l-oxo-phospholene,
a product of Hoechst Aktiengesellschaft, frankfurt/Main)
to 110C until establishment of an isocyanate content of
27.5 %) in 100 ml acetone was used.
272 9 encapsulated ammonium polyphosphate which con-
tained 8.7 mass % ,oolyurea was obtained.
The values determined for the water-soluble frac-
tions are indicated in Table 3.
Example 10
The procedure was as in Example 9 but CARADATE 30
modified with a polycarbodiimide and containing 25.4 %
isocyanate was used.
266 9 encapsulated ammonium polyphosphate which con-
tained 8.3 mass % polyurea was obtained.
The values determined for the water-solubl0 frac-
tions are indicated in Table 3.
Example 11
The procedure was as in Example 9 but CARADATE 30
modified with a polycarbodiimide and containing 22.7 %
isocyanate was used.
269 9 encapsulated ammonium polyphosphate which con-
tained 8.8 mass % polyurea was obtained.
The values determined for the water-soluble frac-
tions are indicated in Table 3.
Example 12
The procedure was as in Example 9 but CARADATE 30
modified with a polycarbodiimide and containing 19.8 %
isocyana~e was used.
-11-
~Z5~
279 9 encapsulated ammonium polyphosphate which
contained 9.1 mass % polyurea was obtained.
The values determined for the ~Jater-soluble frac-
tions are indicated in Table 3.
-~2-
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-14-
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-15-
, . .. .
The values indicated in Tables 1 through 3 show
that the modifying agents of this invention permit the
content of water-soluble fractions to be considerably
reduced (up to 90 % at 25C and up to 97 % at 60C).
-16-
