CA1258009A - Flame retardant agents stable to hydrolysis, based on ammonium polyphosphate - Google Patents

Abstract

FLAME-RETARDANT AGENTS STABLE TO HYDROLYSIS, BASED ON
AMMONIUM POLYPHOSPHATE
ABSTRACT OF THE DISCLOSURE
A flame-retardant agent based on free flowing, pulverulent ammonium polyphosphate of the general formula H(n-m)+2(NH4)mpn03n+1 in which n stands for an integer with an average value of about 20 to 800 and the ratio of m/n is about 1, consists 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 polyisocynate and a carbodiimidization catalyst, the polycarbodiimide encapsulating the individual ammonium poly-phosphate particles.

Description

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 /
~\

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-~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 ~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 ~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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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.

Claims (23)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flame-retardant agent based on free flowing pulverulent ammonium polyphosphate of the general formula H(n-m)+2(NH4)mPn03n+1 in which n stands for an integer having an average value of about 20 to 800 and the ratio 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, the polycarbodiimide encapsulating the individual ammonium polyphosphate particles.

2. Agent as claimed in claim 1 consisting substantially of particles having an average size of about 0.01 to 0.1 mm.

3. Agent as claimed in claim 1, wherein n stands for a whole number having an average value of 450 to 800.

4. Agent as claimed in claim 1 containing the polycarbodiimide in a proportion of 2 to 15 mass %.

5. Agent as claimed in claim 1, wherein the polycarbodiimide is a reaction product obtained by subjecting a polyisocyanate to a catalyzed polycondensation reaction.

6. A process for making a flame-retardant agent as claimed in claim 1 which comprises: microencapsulating, in a polycarbodiimide, a suspension consisting substantially of a diluent, a free flowing pulverulent ammonium polyphosphate of the general formula - 21a -H(n-m)+2(NH4)mPn03n+1 in which n stands for an integer having an average value of about 20 to 800 and the ratio m/n is about 1, a polyisocyanate and a carbodiimidization catalyst by heating the suspension, while stirring, over a period of 0.5 to 5 hours to a temperature between 30 and 200°C
and thereafter cooling, filtering and drying the ammo-nium polyphosphate microencapsulated in the polycar-bodiimide.

7. Process as claimed in claim 6, wherein a suspension of diluent and ammonium polyphosphate is gradually admixed with a solution of the polyisocyanate and with a solu-tion of the carbodiimidization catalyst in the diluent in the sequential order indicated.

8. Process as claimed in claim 6, wherein n stands for an integer having an average value of 450 to 800, in the general formula indicated for the ammonium polyphos-phate.

9. Process as claimed in claim 6, wherein the diluent is a solvent based on an aromatic, aliphatic or cycloali-phatic hydrocarbon or an aliphatic, aromatic or mixed aliphatic/aromatic ketone.

10. Process as claimed in claim 9, wherein the diluent is acetone.

11. Process as claimed in claim 6, wherein the polyiso-cyanate is a commercially available aromatic or ali-phatic di- or polyisocyanate.

12. Process as claimed in claim 11, wherein the polyiso-cyanate is commercial 4,4'-diphenylmethanediisocyanate (MDI).

13. Process as claimed in claim 6, wherein the carbodiimi-dization catalyst is an organophosphorus or cyclic organophoephorus compound.

14. Process as claimed in claim 13, wherein the carbodiimi-dization catalyst is 1-methyl-1-oxo-phospholene.

15. Process as claimed in claim 6, wherein an ammonium polyphosphate/diluent/polyisocyanate/carbodiimidization catalyst-ratio of 1 : 1.5-2.5 : 0.05-0.25 : 0.00025-0.0125 is maintained in the suspension.

16. Process as claimed in claim 15, wherein an ammonium polyphosphate/diluent/polyisocyanate/carbodiimidization catalyst-ratio of 1 : 2 : 0.1 : 0.002 is maintained in the suspension.

17. Process as claimed in claim 6, wherein the suspension is heated to temperatures between 50 and 100°C over a period of 1 to 2 hours.

18. Process as claimed in claim 6, wherein the drying is effected at temperatures between 80 and 150°C under inert gas.

19. Process as claimed in claim 18, wherein the drying is effected under nitrogen.

20. Process as claimed in claim 6, wherein the flame-re-tardant microencapsulated ammonium polyphosphate substantially consists of particles having an average size between 0.01 and 0.1 mm.

21. Process as claimed in claim 20, wherein the flame-re-tardant microencapsulated ammonium polyphosphate substantially consists of particles having an average particle size between 0.03 and 0.06 mm.

22. Process as claimed in claim 6, wherein the flame-re-tardant agent contains the polycarbodiimide in a pro-portion of 2 to about 15 mass %.

23. Polyurethanes and polyurethane foams having flame-retardant properties, containing - in the polyurethane foam - from about 5 to 25 mass %, based on the polyol component of the polyurethane, of a flame-retardant agent based on a free flowing, pulverulent ammonium polyphosphate of the general formula H(n-m)+2(NH4)mPn03n+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, the flame-retardant agent consisting substan-tially of a) about 75 to 99.5 mass % of an ammonium polyphosphate and b) about 0.5 to 25 mass % of a reaction product of a polyisocyanate and a carbodiimidization catalyst, the polycarbodiimide encapsulating the individual ammo-nium polyphosphate particles.