CA2006697A1

CA2006697A1 - Process for the preparation of flame resistant, elastic polyurethane flexible foams and low viscosity melamine polyether polyol dispersions therefor

Info

Publication number: CA2006697A1
Application number: CA002006697A
Authority: CA
Inventors: Heinz-Dieter Lutter; Gerhard Ramlow; Erhard Reich; Manfred Genz; Reinhard Leppkes
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1988-12-28
Filing date: 1989-12-27
Publication date: 1990-06-28
Also published as: DE3844049A1; EP0377891A3; EP0377891A2

Abstract

PROCESS FOR THE PREPARATION OF FLAME RESISTANT
ELASTIC POLYURETHANE FLEXIBLE FOAMS AND LOW
VISCOSITY MELAMINE POLYETHER POLYOL DISPERSIONS THEREFOR
ABSTRACT OF DISCLOSURE
The present invention deals with a process for the preparation of flame resistant, elastic polyurethane flexible foams, comprising reacting:

a) organic and/or modified organic polyisocyanate; with b) higher molecular weight polyols; and c) 1,6-hexanediol and/or trimethylolpropane;

in the presence of d) melamine or mixtures of melamine and other flame retardants;

e) at least one blowing agent; and f) at least one catalyst; and optionally g) auxiliaries and/or additives.

In addition the present invention deals with suitable low viscosity melamine and polyetherpolyol dispersions for the process of the present invention comprising melamine, 1,6-hexanediol and/or trimethylolpropane and at least one polyetherpolyol.

Description

~ 6~9'7 PROCESS FOR THE PREPARATION OF FLAME RESISTANT
ELASTIC POLYURETHANE FLEXIBLE FOAMS AND LOW
VISCOSITY MELAMINE POLYETHER POLYOL DISPERSIONS THEREFOR

BACKGROUND OF THE INVENTION

The preparation of elastic polyurethane flexible foams is disclosed in numerous patent and literature pu~lications. Typical examples are: I~he Plastics Handbook, volume VII, PolYurethane , Carl-Hanser Publishers, Munich, 1st edition, 1966, edited by Dr. R. Vieweg and Dr. A.
Hochtlen, and the 2nd edition 1983, edited by Dr. G. Oertel; and the monograph, Integral Skin Foams, by Dr. H. Piechota and Dr. ~. Rohr~ 1975, Carl-~anser Publisher6.
Normally, in the preparation of polyurethane flexible foams commercially available toluene diisoeyanates are used as polyi~ocyanates; polyoxyalkylene polyols based on 1,2-propylene oxide and/or ethylene oxide, as well as mixtures of polyoxyalkylene polyol~ and graft polyoxyalkylene polyols are used as the polyfunctional higher molecul~r weight compounds; and alkane disls or hydroxyl group containing and/or amino group containing .: : ' ~q306~

compounds having a functionality greater than 2, such as, for example, glycerin or alkanolamines are used as the chain extending agents.
The aforesaid polyurethane flexible foams are not flame resistant and a disadvantage is particularly their high flammability. To overcome this disadvantage, flarne retardant, preferably halogen- and/or phosphorous-containing compound~ are incorporated into the foamable polyurethane mixture. ~owever, adding these products often has a negative impact on the mechanical properties of the resulting polyurethane foams. Numerous experiments were aimed at developing novel flame retardants and at replacing the halogen- and/or phosphorous-containing compounds completely or at least partially by these in polyurethane foams.
A typical compound, for example, i5 ~he polyfunctional melamine having a melting point of 354C.
According to DE-A-23 48 83B, melamine i suspended in the polyol and/or the polyisocyanate component and then the resulting suspension is immediately proces~ed into isocyanurate ~rGup containing, flame resistant polyurethane plastic~ United States patent 4,221,875 ~DE-A-28 09 084) discloses flame resistant polyurethane rigid foams prepared by reacting organic polyisocyanates and polyoxyalkylene polyols in the presence of blowing agents and silicones as surfactants and from 20 to 100 parts by weight of melamine as a flame retardant per 100 parts by weight of polyoxyalkylene polyol.
EP~A-0 004 618 (US Patent 4,258,141) discloses a process for the preparation of low flame resistant polyurethane Elexible foams while using a mixture of diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates (polymeric MDI) ha~ing a content of diphenylmethane diisocyanate isomers of from 40 to 90 weight percent based on the total weight as the polyisocyana~e; and cyanic a~id derivatives, preferably melamine as flame retardants.
Although according to this process the flame resistance of the polyurethane foams is significantly improved, the strong sedimentation of the melamine in the polyol which occurs after a hort period of storage is regarded as a disad~antage. EP-B-023 ~87 (US patent 4,293,657) discloses stable melamine polyol dispersions in which the melamine is reduced in size to a particle size less than 10 microns in situ in the polyol in the presence of at least one ~tabilizer ~mploying a local energy density s~

~f from 10 to 3000 kW/m3. This additional processing step requires additional equipment and is more costly.
Attempts were also made to improve processi-ng of polyurethane formulations containing melamine by adding suitable additives but without reducing the flame retardancy of the resulting foams. According to DE-A-35 30 519 (GB-A-21 63 762A) a mixture of melamine and an addition product of an alkanolamine and an isocyanate are used as a flame retardant additive which is dispersed in the polyol. GB-A-21 77 405A and GB-A-21 77 406A disclose mixtures of melamine and styrene acrylonitrile graft polyoxypropylene polyoxyethylene pslyols dispersed in conventional polyoxypropylene polyoxyethylene polyols as well as optionally phosphorous-and/or halogen-containing compounds as flame retardant additives. Foams prepared according to this process indeed demonstrate good flame retardancy, however, their mechanical properties often do not satisfy specific requirements. ~nother disadvantage is that the formulations must be processed using multiple component mixing equipment since the components containing melamine have an inadequate storage stability.
The objeot of the present invention was to prepare flame resistant elastic polyurethane foams, preferably molded foams, having good mechanical properties, while using melamine as a flame retardant preferably according ~o the 2 component process.
Moreover, the mechanical properties of the resulting products should at least be improved, and the processing steps required simplified. $houg~ suitable measures, particularly the viscosity of the melamine-containing system components should be reduceable.
This object was surprisingly met by using selected chain extending agents and/or crosslinking agents in conjunction with melamine or melamine containing mixtures as flame retardants.
6UMMARY OF THE INVEN~ION

Accordingly, the subject of the invention is a process for the preparation of flame resistant elastic polyurethane flexible foams, comprising reacting:

a) organic polyisocyanates and/or modified organic polyisocyanates; with b) higher molecular weight polyols; and c) chain extending agents and/or crosslinking agents;

., , , . _. . .. . . .. . .

o~

in the presence of d~ at least one flame retardant;
e) at least one blowing agent;
f) at least one catalyst;
and optionally g) auxiliaries and/or additives, wherein 1,6-hexanediol, trimethylolpropane or mixtures thereof are used as the chain extending a9ent(s) and/or crosslinking agent(s) ~c); and melamine or mixtures of melamine and other flame retardants are used as the flame retardant (d).
The subject of the present invention is also a process for the preparation of flame resistant, flexible polyurethane molded foams, preferably airplane seats having a density of from 35 to 100 grams per liter using high pressure technology in an essentially closed mold from, above-mentioned starting components ta) through (f) as well as optionally ~9) according to claim 2 and/or the subject of the present invention according ~o claims 2 in conjunction with 16 is al80 low viscosity melamine polyether polyol dispersions, comprising:

1 to 150 parts by weightl more preferably 70 to 130 parts by weight of melamine having an average particle size of 20 to 40 microns and having a bulk density in a range of from 500 to 650 grams per liter; 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight of 1,6-hexanediol, tri~ethylolpropane or mixtures thereof: and 100 parts by weight of at least one polyether polyol, a polymer modified polyether polyol or mixtures thereof whereby the polyether polyols, polymer modified polyether polyols or the mixture thereof has an average functionality of froln 1.8 to 3.0 and an average molecul~r weight of from 3600 to 6500 according to claim 17.

Dependent claims 3 ~hrough 15 illustrate special embodiments of the process of invention.
~ y using 1,6-hexanediol, trimethylolpropane or mixtures thereof as said chain extending agent and/or said crosslinking agent in conjunction with melamine or melamine containing flame retardant mixtures and higher molecular weight polyols, preferably polyether polyols, surprisingly obtained were system component~ which processed well on high pressure machines and compared to conventional 8y5tems, the system components' visc05ity was reduced by 10 to 25 percent. The polyurethane molded foams prepared according to the present invention have good flame resistan~e and in spite of the relatively high melamine content have a good mechanical property level. Also noteworthy are the following: increased flexibility, increased tear propagation strength and improved compression permanent sets.
The following should be noted with respect to the starting components used according to the process of the present invention:
a) conventional organic, for example, aliphatic, cycloaliphatic, araliphatic, cycloaliphatic-aromatic and preferably aromatic di- and/or polyisocyanates are suitable in the preparation of the flame resistant, elastic polyurethane flexible foams, preferably polyurethane molded flexible foams. Individual examples of aromatic polyisocyanates are mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanates (MDI); mixtures of MDI isomers and polyphenyl polymethylene polyisocyanatest so-called polymeric MDI having an MDI isomeric content of at least 50 weight percent, more preferably 60 to 90 weight percent and more i69~

based on the total weight of the mixture; 2,4- and 2,6-toluene diisocyanate as well as the corresponding commercially available isomeric mixtures; mixtures of toluene diisocyanates and MDI
and/or polymeric MDI, for example, those having a MDI content of 30 to 90 weight percent, more preferably 40 to 80 weight percent based on the total weight of the polymeric MDI's.

Also suitable are the so-called modified multivalent isocyanates, i.e. products which are obtained by the chemical reaction of organic di-and/or polyisocyanates. Individual examples are ester, urea, biuret, allophonate, isocyanurate and preferably carbodiimide, uretonimine and/or urethane group containing di- and/or polyisocyanate~. Individual examples are urethane group containing prepolymers having an NCO content of 14 to 2.8 weight percent, more preferably 12 to 3.5 weight percent or quasi-prepolymers having an NCO content of 35 to 14 weight percent, more preferably 34 to 22 weight percent whereby polyisocyanates of toluene dii~ocyanates modified _g_ .... .. ....

: '~' ' ' . . .

... .

. .

, .

with urethane groups preferably have an NCO content of 34 to 28 weight percent and those of 4,4'-MDI, 4,4'- and 2,4'-MDI isomeric mixtures or polymeric MDI preferably have an NCO content of 28 to 22 weight percent based on the total weight; and are prepared by reacting diols, oxalkylene glycols and/or polyoxyalkylene glycols having molecular weights of 62 to 6000, preferably 134.18 to 4200 with toluene diisocyanates, 4,4'-MDI, MDI isomeric mixtures and/or polymeric MDI, for example, at temperatures of from 20 to 110C, more preferably 50 to 90C, whereby the following can be used individually or as mixtures thereof as the oxalkylen2 glycols and polyoxyalkylene glycols:
diethylene glycol, dipropylene glycol, polyoxyethylene, polyoxypropylene glycol and polyoxypropylene-polyoxyethylene glycol;
carbodiimide group and/or isocyanurate group containing polyisocyanates, for example, based on MDI isomers and/or toluene diisocyanate.

~owever, the ollowing have proven particularly useful and thus are preferably used: 2,4~toluene ,. . . ..

. ; , ': - ,: ' , diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate and urethane group containing polyisocyanates having a NCO
content of 34 to 28 weight percent, more preferably ~4 to 30 weight percent prepared from 2,4- and 2,6-toluene diisocyanate mixtures efficaciously in a weight ratio of 80:20; and polyoxypropylene-polyo~yethylene glycols having a molecular weight of 2~00 to 4200.

b~ Preferred higher molecular weight polyols ~b) include those with an average functionality of 1.8 to 4, more preferably 1.8 to 3 and nlost preferably 2 to 2.4, and an average molecular weight of 2200 to 8000, preferably 3600 to 6500, selected from the group consistin~ of polyether polyols, polyester polyol~, polythioether polyols, polyester amides, aliphatic polycarbonates containing hydroxyl groups, and mixtures of at least two of the aforementioned polyols. Polyester polyols and/or polyether polyols are preferred. Polyols are also suitable having molecular weights below 2,200, e.g., from 250 to 2,200. ~owever, only small ... ,. , . . . , . . . .. . _, . .
,, , ,. : ' - ': ' ' , ' ~ '. ' . :

. , ' amounts of these polyols can be used and mixed with higher molecular weight polyols so that one obtains polyol mixtures having average molecular weights of at least 2,200.

Suitable polyester polyols can be produced, for example, from organic dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic acids with 4 to 6 carbonst and multivalent alcohols, preferably diols, with 2 to 12 carbons, preferably 2 to 6 carbons. Examples of dicarboxylic acids include ~uccinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids can be used individually or in mixtures. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives may also be used such a~
dicarboxylic acid ester6 of alcohols with 1 to 4 carbons or dicarboxylic acid anhydride~.
Dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid in a quantity ratio .. . .. . . . . . .
-~ ,, - - : .

,, ' .

.

,. ~, .

6~7 of 20-35:35-50;20-32 parts by weight are preferred, especially adipic acid. Examples of divalent and multivalent alcohols, especially diols, include ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, l,10-decanediol, glycerine and trimethylolpropane. Ethanediol, diethylene glycol, 1,4-butanediol, 1,5-pen~anediol, 1,6-hexanediol, or mixtures of at least two of these diols are preferred, especially mixtures of 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol. Furthermore, polyester polyols of lactones, e.g., E-caprolactone or hydroxycarboxylic acids, e.g., ~-hydroxycaproic acid, may also be used.

The polyester polyols can be prepared by polycondensation of organic polycarboxylic acids, e.g., aromatic or preferably aliphatic polycarboxylic acids and/or derivatives thereof and multivalent alcohols in the absence of catalysts or preferably in the presencP ~f e~terification catalysts, preferably in an atmosphere of inert ,. , ~ ,. . .

: .

gases, e.g., nitrogen, carbon monoxide, helium, argon, ~tc., in the melt at temperatures of 150 to 250C, preferably 180 to 220C, optionally under reduced pressure, up to the desired acid value, which is preferably less than 10, especially less than 2. In a preferred embodiment, the esterification mixture is subjected to polycondensation at the temperatures mentioned above up to an acid value of 80 ~o 30, preferably 40 to 30, under normal pressure, and then under a pressure less than 500 mbar, preferably 50 to 150 mbar. Examples of ~uitable esterification catalysts include iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the ~orm of ~etals, metal oxides or metal salts. However, the polycondensation may also be performed in liguid phase in the presence of ~olvents and/or entraining agents such as benzene, toluene, xylene or chlorobenzene for azeotropic distillation of the water of condensation.

To produce the polyester polyols, the organic polycarboxylic acids and/or derivatives thereof and multivalent alcohols are preferably polycondensed in a mole ratio of 1:1-1.8, preferably 1:1.05-1.2.

~he resulting polyester polyols preferably have a functionality of 2 to 4, especially 2 to 3, and a molecular weight of 1200 to 3000, more preferably 2200 to 3000 and most preferably 2200 to 2500.

However, polyether polyols, which can be obtained by known methods, are especially preferred for use as the polyols. For example, polyether polyols can be produced by anionic polymerization with alkali hydroxides ~uch as sodium hydroxide or potassium hydroxide or alkali alcoholates, such as sodium methylate, sodium ethylate or potassium ethylate or potassium isopropyla~e as catalysts and with the addition of at least one initiator molecule containing 2 to 4, preferably 2 to 3, reactive hydrogens or by cationic polymeri2ation with Lewis acid such as antimony pentachloride, boron triFluoride etherate, etc., or bleaching earth as .

, . .. .

.

catalysts from one or more alkylene oxides with 2 to 4 carbons in the alkylene group.

Suitable alkylene oxidPs include, for example, tetrahydrofuran, 1,3-propylene oxide, 1,2- and 2,3-butylene oxide, styrene oxide and preferably ethylene oxide and 1,2-propylene oxide. The alkylene oxides may be used individually, in alternation, one after the other or as a mixture.
Examples of suitable initiator molecules include water, organic dicarboxylic acids such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optisnally N-mono-, N,N-, and N,N'-di~lkyl substituted diamines with 1 to 4 carbons in the alkyl group such as optionally mono- and dialkyl-substituted ethylenediamine, diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- and 1,4-butylene diamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, phenylenediamines, 2,3-, 2,4-and 2,6-toluenediamine and 4~4'-, 2,4'- and 2,2'-diaminodiphenylmethane.

- , -~, , , , ' ' '.: ', " ,: , , ' :

, . :
' : , 6~;~37 Suitable initiator molecules also include alkanolamines such as ethanolamine, diethanolamine, N-methyl- and N-ethylethanolamine, N-methyl- and N-ethyldiethanolamine and triethanolamine plus ammonia. Multivalent alcohols, especially divalent and/or trivalent alcohols are preferred such as ethanediol, 1,2-propanediol and 1,3-propanediol, diethylene glycol, dipropylene glycol, 1,~-butanediol, 1,6-hexanediol glycerine, trimethylolpropane and pentaerythritol.

The polyether polyols, preferably polyoxypropylene polyols and polyoxypropylene-polyoxyethylene polyols have a functionality of 1.8 to 4, more preferably 1.8 to 3.0 and most preferably 2 to 2.4;
and molecular weigh~s of 2200 to 8000, more preferably 3600 to 6500 and most preferably 3900 to 6000; and suitable polyoxytetramethylene glycols have a molecular weight of about 3500, more preferably 250 to 2200. Most preferably used are polyoxypropylene~polyoxyethylene polyols having more than 50~, ~ore preferably more than 70%, of terminal primarily hydroxyl groups.

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Suitable polyether polyols also include polymer modified polyether polyols, preferably graft polyether polyols. These are prepared by in situ polymerization of olefinic unsaturated monomers or mixtures thereof, such as, e.g., styrene, acrylonitrile or preferably mixtures of styrene and acrylonitrile in polyoxyalkylene polyols, for example, from the above described polyoxyalkylene polyols analogous to the teaching of Federal Republic of Germany patents 11 11 394, 12 22 669 ~US patents 3,304,~73; 2,383,351; 5,523,093), 11 52 536 (Great Britain 1 040 452) and 11 52 527 (Great Britain 987 618); or by dispersing graft polymers obtained previously by the radical polymerization in ~olvents; in polyoxyalkylene polyols analogous to the teaohings of US patents 3,391,092; 4,014,846 and 4,093,573. For the preparation of the graft polyoxyalkylene polyols both the above-mentioned saturated polyoxyalkylene polyols are suitable which acGording to US reissue patent 28,715 are es~entially free of ethylenically unsaturated unit~; and also olePinic unsaturated . ' ,............. : . :
. . . . . . .. .

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, ' ' ' ~0~iÇi97 , .

polyoxyalkylene polyols as disclosed, for example, in ~S patent 3,652,659 and in US reissue patent 29,014. Also suitable as polymer modified polyoxyalkylene polyols are polyurea, polyhydrazide or tertiary amino group containing polyurethane polyoxyalkylene polyol dispersions as disclosed in, for example, EP-B-0 011 752 (US 4,304,708), US
4,374,209 a~d DE-A-32 31 497. The polymer modified polyoxyalkylene polyols which efficaciously possess 2 to 35 weight percent, more preferably 3 to 25 weight percent based on the total weight of polymer particles, just as the polyoxyalkylene polyols, can be used individually or in the form of mixtures.

Preferred polyol mixtures lb) comprise:

bl) higher molecular weight polyether polyols having an average functionality of 1.8 to 3; and b2~ higher molecular weight polymer modified polyether polyols having an average functionality of 1.8 to 3 selected from the group consisting o graft polyether polyol~, and polyurethane polyurea ~19--. ~

, fi,~37 polyol dispersions containing in bonded form polyurea, polyhydrazide and/or tertiary amino g roups .

According to a preferred embodiment polyol mixture (b) comprises:

bl~ at least 70 weight percent, more preferably 75 to 99.9 weight percent, based on the weight of mixture ~b), of at least one polyether polyol having an average functionality of 1.8 to 3, more preferably 2 to 2.4 and having an average molecular weight of 3600 to ~500, more preferably 3900 to 6000; and b2~ less than 30 weight percent, more preferably 25 to 0.1 weight percent, based on the weight of mixture tb), of at least one polymer modified polyether polyol having an average Punctionality of 1.8 to 3, more preferably 2 to 2.~ and having an average molecular weight of 3600 to 6500, more pref~rably 3900 to 6000 selected from the group conRisting of polyurethane polyether polyol ' : ' ' ~ . -'' , ', ' , ' . ', , 6~

dispersi~ns containing in bonded form polyurea, polyhydrazide and tertiary amino groups, graft polyether polyols and mixtures thereof.

Examples of hydroxyl group-containing polyacetals that can be used include, for example, the compounds that can be produced from, glycols such as diethylene glycol, triethylene glycol, 4,4'-dihydroxyethoxydiphenyldimethylethane, hexanediol and formaldehyde. Suitable polyacetals can also be produced by polymerization of cyclic acetals.

Suitable hydroxyl group-containing polycarbonates include those of the known type such as those obtained by reaction of diols, ~.g., 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol and diaryl carbonates, e.g., diphenyl carbonate, or phosgene.

The polyester amides include the mainly linear conden~ates obtained from multivalent unsaturated and/or unsaturated carboxylic acids and their .,., : .

anhydrides and multivalent saturated and/or unsaturated amino alc~hols or mixtures of multivalent alcohols and amino alcohols and/or polyamines.

c) According to the present invention, l,~-hexanediol, trimethylolpropane or mixtures of both are used as said chain extending agent and/or crosslinking agent (c) in the preparation of said flame resistant, elastistic polyurethane flexible foams or flexible, elastic polyurethane molded foams.
The 1,6-hexanediol and/or trimethylolpropane is commonly used so th2t per 100 parts by weight of higher molecular weight polyols lb) from 0.1 to 5 parts by weight, more preferably n ~ 5 to 3 parts by weight of said chain extending agent and/or crosslinking agent Ic) is present in the reaction mixture .

d~ According to the present invention, melamine is used 2S flame retardant ~d) in conjunction with 1,6-he~anediol and/or trimethylolpropane.
commercial form of melamine can be used and .... . . . , . . . .; , , ,,, .
. ' ' : -normally it has an average particle size of from 5 to 50 microns and possesses the following particle size distribution:

10 weight percent of the particles are greater than 30 microns;
30 weight percent of the particles are greater than 24 mlcrons;
50 weight percent of the particles are greater than 20 microns;
70 weight percent of the particles are greater than 16 microns;
90 weight percent of the particles are greater than 11 microns.

Melamine which has proven most useful and therefore preferably used has an average particle size of from 20 to 50 micr~ns, more preferably 20 to 40 microns and a bulk density of from 300 to 800 grams per liter, more preferably S00 to 650 grams per liter. The melamine is best used in a quanti~y of fro~ 5 to 150 parts by weight, more preferably 50 to 130 parts by weight, and most preferably 70 to -~3~

X~6~7 ,, 100 parts by weight per 100 parts by weight of higher molecular polyols (b).

Efficaciously, melamine is exclusively used as said flame retardant. However, it can also be advantageous in achievin~ special effects, for example, homogenation and stabilization of the starting component mixture, reducing smoke development in a fire, specific improvement of mechanical properties of the polyurethane foams prepared, etc., to combine the melamine with other organic or inorganic flame retardants so that the melamine can be used in a reduced quantity.
Mixtures of flame retardants (d) which have provPn most suitable in improving flame retardance comprise:

dl) 70 to 100 parts by weight of melamine;

d2~ 0 to 30 parts by weight, more preferably 3 to 15 parts by weight of starch, preferably selected from the group consisting o~ corn starch, rice starch, potato starch, wheat ~tarch, mixtures thereof and :

.
' ~7 optionally chemically modified starch derivatives;
and d3) 0 to 30 parts by weight, more preferably 3 to 15 parts by weight of at least one additional flame retardant selected from the group consisting of tricresyl phosphate, tris-~2-chloroethyll-phosphate, tris(2-chloropropyl)phosphate, tris(l,3- -dichloropropyl)-phosphate, tris(2,3-dibromopropyl)phosphate, tetrakis-(2-chloroethyl)ethylene diphosphate, aluminum hydroxide, ammonium sulfa~e, ammonium, phosphate, and preferably ammonium polyphosphate;

whereby the parts by weight are each based on 100 parts by weight of higher molecular weight polyols (b)-Also effective are mi~tures of flame retardants(d), comprising:

dl) 7D to 100 parts by weight of melamine; and ~ 2~6~7 d2) 3 to 30 parts by weight of at least one of the above mentioned starches or the corresponding starch derivatives; or d3) 1 to 30 parts by weight of ammonium polyphosphate;

whereby the parts by weight are each based on 100 parts by wei~ht of higher molecular weight polyols lb) .

Most preferred as ammonium polyphosphate is the finely divided, diffioultly soluble, modified form having the following general formula H~n_m)+2tNH4)ll~Pno3n+l in which n i~ a number having an average value of from 20 to 800, more preferably about 700 and the ratio of m to n is about 1 and the modified ammonium polyphosphate comprises about 80 to 99.5 mass percent of ammonium polyphosphate and about 0.5 to 20 mass percent of a hardened epoxy resin having an epoxy equivalent weight of about 170 to .
', ' ~ ' ' ' ' 6fi~7 about 220 which envelops the individual ammonium polyphosphate particles. Such ammonium polyphosphate, for example, can be purchased from Hoechst AG as Exolit~.

e) Water i5 among the blowing agents (e) which can be used in the preparation of polyurethane flexible foams which reacts with the isocyanate groups to form carbon dioxide. The amount of water which is efficaciously used is from 0.1 to 6 parts by weight, more preferably 1.0 to 3.5 parts by weight and most preferably 2.5 to 3.0 parts by weight based on 100 parts by weight of higher molecular weight polyols (b~.

In addition, physically active blowing agents can be used mixed with water. Suitable liquids are those which are inert to the organic optionally modified polyisocyanates (a) and which have boiling points below 100C, more preferably below 50C, and most preEerably between -50 and 30~C at atmospheric pressure 80 that they evaporate under the influence of the exothermic polymerization reaction.

.. . . . . . . . . . . ... .. .. ...

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Examples of such preferably used liquids are hgdrocarbons such as pentane, n- and isobutane, and propane; ethers such as dimethylether and diethylether; ketones such as acetone and methylethyl ketone, ethylacetate and preferably halogenated hydrocarbons, such as methylene chloride, trifluorochloromethane, dichlorodifluoromethane, dichloromonofluoromethane, dichlorotetrafluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane and noble gases, such as krypton.
In addition, mixtures of these low boiling point liquids can be used with one another or with other sub6tituted or unsubstituted hydrocarbons.

The amount of physically effective blowing agent required in addition to the water depends on the desired foam density and can be simply determined. The amount is from about O to 25 parts by weight, more preferably O to 8 parts by weight pex 100 parts by weight of higher molecular weight polyols lb). It ca~ be efficacious to mix the physically effective blowing agent with the optionally modified polyisocyanates ~a) and thereby decrease the viscosi~y.

.. . . . . . . .

f~ To accelerate the reaction between the higher molecular weight polyols (b), 1,6-hexanediol and/or trimethylolpropane ~c) and water as blowing agent (e), conventional polyurethane catalysts are added to the reaction mixture to accelerate the reaction with the organic polyisocyanates and/or msdified polyisocyanates (a). Preferably basic polyurethane catalysts are used, for example, tertiary amines, such as dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N,N,N',N'-teramethyldiamino-diethylether, bis(dimethylaminopropyl)urea, N-methyl- and /or N-ethylmorpholine, dimethylpiperazine, N-dimethylaminoethylpiperidine, 1,2-dimethylimidazole, l-azabicyclol2.2.0loctane, dimethylaminoethanol, 2-~N,N-dimethylaminoethoxy)ethanol~ N,N',N"-tris-(dialkylaminoalkyl)-hexahydrotria~ine, e.g.., N,N',N"-tris-(dimethylaminopropyl)-s-hexahydrotriazine and most preferably triethylenediamine. ~owever, also suitable are metal salts ~uch as iron~II)chloride, zinc -2~-q~ 9~
.

chloride, lead octoate and preferably tin salts, such as, tin dioctoate, tin diethylhexoate, ~nd dibutyltin dilaurate as well as preferably, mixtures of tertiary amines and organic tin salts. A most preferred catalyst combination comprises triethylene diamine, bis(dimethylaminoethyl)ether, 2-~dimethylaminoethoxyJethanol, dibutyltin dilaurate and dibutyldilauryltin mercaptide, each present in the following quantity ratios: 0.2-1.5 to 0.1-0.2 to 0.1-0.25 to Ool-0~3 to 0.05-0.15~

Commonly used is from 0.1 to 10 weight percent, more preferably 0.3 to 3 weight percent of catalyst based on the tertiary amine and/or 0.01 to 0.5 weight percent, more preferably 0.03 to 0.25 weight percent of metal alt or 0.1 to 5 weight percent, : more preferably 0.3 to 3.5 weight percent of the previously mentioned satalyst combination based on the weight of higher molecular weight polyols (bj.

g) Auxiliaries and/or additives ~g) can al30 be added to the reaction mixture. Typical examples are : -30 . ' ' ' ' ~urfactants, stabilizers, agents to protect against hydrolysis, cell regulators; fungistatic and bacteriostatic substances, dyes, pigments and fillers.

Typical ~urfactants are those which serve to support the homogenation of the starting materials and which also possibly regulate the cell structure of the foam. Typical examples are siloxane-o~yalkylene mixed polymers and other organopolysiloxanes, oxethylated alkylphenols, oxethyl~ted fatty al~ohol , paraffin oil, castor oil and/or ricinoleic acid esters and Turkey red oil used in quantities of from 0.05 to S parts by weight, more preferably 0.1 to 2 parts by weight per 100 parts by weight of higher molecular weight polyols lb3.

Additional information concerning other above-mentioned additives and auxiliaries can be found in the technical literature, for example, the monograph of J.~.
8aunders and K.C. Frisch, igh Polymers, volume XVI, Polyurethanest partR 1 and 2, Interscience Publishers, 1962 6~3~

and/or 1964, or in the Plastics Handbook, Polyurethanes, volume VII, Carl-Hanser Publishers, Munich, Vienna, 1st and 2nd editions, 1966 and 1983.

When preparing the polyurethane flexible ~oams, the organic optionally modified polyisocyanates ~a), the higher molecular polyols ~b), chain extendir.g agents and/or crosslinking agents (c) are reacted in the presence of flame retardant (d), blowing agents (e), catalysts (f) and optionally auxiliaries and/or additives (g) at temperatures of ~rom 0 to lOO~C, more preferably 15 to 80C in such quantity ratios so that p~r NCO group from 0.5 to 2, more preferably 0.8 to 1.3 and most preferably about 1 reactive hydrogen atom(s) is/are present in bonded form from starting components (b) and optionally (c).

The polyurethane flexible foams are efficaciously prepared according to the one ~hot process by mixing two components namely, (A) and (B). Here starting components lb)~ (d), le), (f~ and optionally (g) are added to the so-called (A) component, and (a) optionally mixed with (d), (g) and inert, physically active blowing agents are used as starting component (B). Since the (A) componen~ is storage Z~ 6~

stable for at least 6 months, the (A) and (~) components need only to be mixed intensively before the preparation of the polyurethane flexible foams. The reaction mixture can be foamed in open or closed molds and is also suitable for the preparation of slab stoclc foams.

As previously stated, the process of the present invention is preferably used for the preparation of polyurethane flexible foams. The reaction mixture is normally introduced into a preferably heated metal mold at a temperature of from 15 to 80~C, more preferably 30 to 65C. The mold temperature generally is from 20 to 90C, more preferably 35 to 70C. The reaction mixture can cure under compression, for example, with a degree of compression of from 1.1 to 8, more preferably 2 to 6, in a closed mold.

The polyurethane flexible foams prepared according to the present invention have densities of from 35 to 100 9/1, preferably 40 to 80 y/l~ ~hey possess good flame resistance, pass the kerosene burner test (FAR 25.853C) ~nd have a good mechanical property level. ~he molded foams are preferably u~ed as cushioning elements, for example, as seat cushions~ arm rest~, head rests, sun visors and safety ~)0~6~7 coverings in the interior of motor vehicles, preferably automobiles and airplanes! whereby most preferably airplane seats are prepared having densities of from 35 to 100 g/l.

The low viscosity melamine polyether polyol dispersions are used in the preparation of noncellular or cellular polyisocyanate addition polymerization products, for example, in the preparation of urethane, isocyanurate or urethane and isocyanurate group-containing flexible, semi-xigid or rigid foams; noncellular or cellular elastomers;
and preferably flexible elastic, flame resistant polyurethane foams.

The parts in the examples refer to parts by weight.

Example 1 A Component: a mixture compri6ing:

75 parts by weight of a polyoxypropylene (86 weight percent3 polyoxyethylen~ (14 weight percent) polyol initi ted with glycerin having an average molecular weight of 6000;

-fi97 ..

10 parts by weight of a graft polyoxypropylene (84 weight percent) polyoxyethylene (16 weight percent) polyol initiated with trimethylolpropane having an average molecular weight of about 6000 and a graft polymer content of 20 weight percent based on the total weight prepared while using an acrylonitrile styrene mixture in grafting;

20 parts by weight of a polyoxypropylene (81 weight percent) polyoxyethylene ~19 weight percent3 glycol having an average molecular weight of about 3900 prepared while using dipropylene glycol as an initiator molecule;

1.2 parts by weight of a silicone stabilizer (~ilicone DC 5043 from Dow Corning Corporation);

2.4 parts by weight of water;

10.0 parts by weight of trichlorofluoromethane;

0.42 parts by weight of a 33 weight perc~nt olution of triethylene diamine in dipropylene glycol;

Z~3~6~;~7 0.2 parts by weight of 2-dimethylaminoethyloxy)ethanol;

0.12 parts by weight of bi~(dimethylaminoethyl)ether;

1.0 parts by weight of trimethylolpropane; and 100.0 parts by weight of melamine.

B Component:

95 parts by weight of a urethane group containing quasi-prepolymer having a NC0 content of 31 weight percent and a viscosity of 52 moPas at 25C prepared from a 2,4- and 2,6-toluene diisocyanate isomeric mixture in a weight ratio of 20:20 and from a polyoxypropylene-polyoxyethylene glycol having a molccular weight of 3900 and 5 parts by weight of trichloroethylphosphate.

100 parts by weight of A component and 22 parts by weight of the B component corresponding to a NC~ index of 100 were intensively mixed together then the reaction - . , - ,, _, = .. .. .. .

..

.

., , fi~3~7 ,, .

mixture at a temperature of 23C was introduced into the hollow cavity of an airplane seat mold in such a quantity so that in the closed mold there was a degree of compression of 1.2.

The moled part was demolded after 12 minutes and stored 24 hours at room temperature.

The flame resistant moled article had the following mechanical properties:

Density 19/1]: 80 Tensile strength according to DIN 53 571 lKPa]: 70 Elongation according to DIN 53 571 1%]: 52 Tear propagation strength according to DIN 53 575 [N/mm]: 0.42 ' ' ~

Example 2 A Component:

Analogous to example 1, but in place of the melamine as a flame retardant a mixture comprising the following was u~ed:

B5 parts by weight of melaminei 10 parts by weight of wheat starch; and 5 parts by weight of ammonium polyphosphate (Exolit~
422 from Hoechst AG).

B Component:

A ureth~ne group containing quasi-prepolymer having a NCO content of 31 weight percent, a viscosity of 52 m~Pas at 25DC
prepared fro~ a 2,4- and 2,6~toluene diisocyanate isomeric mixture (weight ratio 80:20) and a polyoxypropylene-polyoxyehtylene glycol initiated with dipr~pylene glycol, having a mol~cular weight of 3900.

' - ~. ~ ' -, ' :

, ' Z~ifi~37 100 parts by weight of the A component and 21 parts by weight of the B component were reacted analogous to the disclosure in example 1 to form a flexible polyurethane molded foam.

The mechanical properties of the resulting flexible, flame resistant polyurethane molded foam corresponded essentially to those of the product obtained acc~rding to example 1.

' ~, , ' ' Example 3 A Component:

Analogous to example 1, however, in place of the melamine as a flame retardant a mixture of the following was used:

75 parts by weight of melamine and 25 parts be weight of ammonium polyphosphate (Exolit0 422 from Hoechst AG).

B Component:

A urethane group containing quasi-prepolymer having a NCO content of 31 weight percent prepared from a 2,4- and 2,6-toluene diisocyanate isomeric mixture ~weight ratio 80:20 and a polyoxypropylene-polyoxyethylene polyol initiated with trimethylolpropane having a moleoular weight of 62D0.

100 part~ by weight of the A component and 21 parts by weight of the B component were reacted analogous to the teachings of examples 1 into a flexible polyurethane molded foam.

--~0--. ~ .
-' ', '. ' ~ ~-, . ' :.
, The flame resistant moled article obtained had the following mechanical properties:

Density 19/1]: 75 Tensile strength according to DIN 53 571[KPal: 80 Elongation according to DIN 53 571 ¦~]: 160 Tear propagation strength according to DIN 53 575 [N/mm]: 0.73 Compression permanent set according to DIN 53 572 1~]: 21 j ~0~3Ç~

Example 4 A Component:

Analogous to example 1, however in place of the melamine is a flame retardant a mixture of the following was used:

85 parts by weight of melamine; and 15 parts by weight of potato starch.

B Component:

A mixture of 2,4- and 2,6-toluene diisocyanate in a weight ratio of 80:20.

100 parts by weight of the A component and lS parts by weight of the B compon~nt were reacted analogous to the teachings of example 1 into a flexible polyure~hane molded foam.

The flame resistant molded article obtained had the following mechanical prop~rtie :

-4~-' ~ .. ' -.. . :
. . - .

.~7 Density lg/l]: 75 Tensile strength according to DIN 53 571[KPa~: 80 Elongation according to DIN 53 571 [~]: 71 Tear propagation strength according to DIN 53 575 [N/mm]; 0.16 Compression permanent set according to DIN 53 572 1~]: 9.9 i97 Example 5 A Component:

85 parts by weight of a polyoxypropylene (86 weight percent) polyoxyethylene 114 weight percent) polyol initiated with glycerin having an average molecular weight of 6000;

20 parts by weight of a polyoxypropylene (81 weight percent) polyoxyethylene (19 weight percent) glycol having an average molecular weight of about 3900 prepared while using dipropylene glycol as an initiator molecule;

102 parts by weight of a silicon stabilizer (silicon DC
5043 from Dow Corning Company~;

2.4 parts by weight of water;

10 partR by weight of trichlorofluoromethane;

Q.42 part~ by weight of triethylenediamine (Dabco~ X
540 from Air Products C~mpany);

- , ' ' ." ' .

, 369~

0.2 parts by weight of 2-(dimethylaminoethoxy3ethanol;

0.15 parts by weight of bis-(dimethylaminoethyl)ether;

1.0 parts by weight of dibutyltin dilaurate;

0.05 parts by weight of dibutyldilauryltin mercaptide;

2.00 parts by weight of 1,6-hexanediol;

0.35 parts by weight of green paste 9650; and 100 parts by weight of melamine having a bulk density of 600 grams per liter.

B Component:

A urethane group containing quasi-prepslymer having a NCO content of 31 weight percent and a viscosity of 52 m-Pas at 25C prepared from a 2,4-, 2,6-toluene diisocyanate i~omeric ~ixture in a weight ratio of 80:20 and a polyoxypropylene-p~lyoxyethylene glycol having a molecular weight of 3900.

.' '. ~ .
.

~ 7 100 parts by weight of the A component and 22.5 to 27 parts hy weight of the B component, corresponding to a NCO index of 100 to 120, were intensively mixed together and then the reaction mixture at a temperature of 23C was introduced into the hollow cavity of an airplane seat mold in such a quantity so that in the closed mold there was a degree of compression of 1.2.

The part was demolded after 12 minutes and stored at room temperature for 24 hours.

The flame resistant molded article obtained had the following mechanical properties:

De~sity [9/1]: 70- 80 Tensile strength according to DIN 53 571~KPa]: 100-110 Elongation according to DIN 53 571[%]: 100-120 Tear propagation strength according to DIN 53 575 [N/mm]: 0.5 Compression permanent set according to DIN 53 572 [%]: 7-8 .

6~7 Example 6 A Component:

Analogous to example 5, but in place of the melamine as a flame retardant a mixture of the following was used:

85 parts by weight of melamine;

10 parts by weight of wheat starch; and 5 parts by weight of ammonium polyphosphate (Exolit~
422 from Hoechst AG).

B Component: analogous to example 2.

100 p~rt by weight o~ the A component and 22.5 to 27 parts by weight of the B component, correspsnding to a NCO index of 100 to 120, analogou~ to the teachings of e~ample 5 were reacted to form flexible polyurethane molded foam.

`
.

Flame resistant polyurethane flexible foam was obtained whose mechanical properties were in the ranges cited in example -48- .

~-- 2~ i9~

Example 7 A Component:

Analogous to example 5, however in place of the melamine as a fire retardant a mixture comprising the following was used:

75 parts by weight of melamine; and 25 parts by weight of ammonium polyphosphate (Exolit~ 422 from Hoechst AG).

B Component, analogous to example 3.

100 parts by weight of the A component and 21 part~ by weight of the B component were reacted analogous to the teachings of example 5 into flexible polyurethane foam.

~ he resulting flame resistant molded article had the following mechanical properties:

Den~ity 19/1]: 70 .
"' ' '',, ~ ' ' ' ' ''' ' ,:. , . . '' ~

;~0669~7 Tensile ~trength according to DIN 53 571 lKPa]: 98 Elongation according to DIN 53 571 [%~: 110 Tear propagation strength according to DIN 53 575 lN/mm]: 0.45 Compression permanent set according to DIN 53 572 ¦%]: 7.2 Example 8 A Component:

Analogous to example S, but in place of the melamine as a flame retardant a mixture ~f the following was used:

85 parts by weight melamine; and 15 parts by weight of pokato starch.

B Component:

A mixture of 2,9- and 2,6- toluene diisocyanate and a weight ratio of 80:20.

100 parts by weight of the A component and 25 part~ by weight o the B component were reacted analogous to the teachings of example 5 into flexible flame resistant polyurethane molded foam.
-5~-The molded articles prepared according to examples 1 through 8 passed the kerosene burner test (FAR 25.823) with less than 10~ weight loss and accordingly fulfill the current atrictest fire requirements for polyurethane flexible foams.

By using the other flame retardants suitable according to the process of the present invention, the melamine content was able to be reduced and smoke gas densities were also reduced.

.
' ' i6~7 Examples 9-14 Measuring the viscosity of the A component in the absence of trichlorofluoromethane and as a function of the melamine and chain extending agent or crosslinking agent used.

A mixture of: ~

75 parts by weight of a polyoxypropylene (86 weight percent) polyoxyethylene (14 weight percent) polyol initiated with glycerin having an average molecular weight of 6~00;

10 parts by weight of a graft polyoxypropylene ~84 weight percent) polyoxyethylene ~16 weight percent) polyol initiated with trimethylolpropane having an a~erage molecular weight of about 6000 and a graft polymer content of 20 weight percent based on the total weight prepared while u6ing an acrylonitrile styrene mixture for grafting;

20 parts by weight of a polyoxypropylene (81 weight percent) polyoxyethylene (19 wei~ht percent) glycol having an ~verage molecular weight oF about 3900 prepared while using dipropylene glycol aq an initiator molecule;

i69~

1.2 parts by weight of a silicon stabilizer ~Silicon DC
5043 from Dow Corning Company);

2.4 parts by weight of water;

0.42 parts by weight of triethylenediamine (Dabco~ X
540 from Air Products Corporation);

0.2 parts by weight of 2-ldimethylaminoethyoxy)ethanol;

0.15 parts by weight of bis-(dimethylaminoethyl)ether;

0.1 parts by weight of dibutyltin dilaurate;

0.05 parts by weight of dibutyldilauryltin mercaptide;

0.35 parts by weight of green paste 9650; and 100 parts by weight of melamine.

The followin~ amounts of ohain extending agent or crosslinking ag~nt cited in the table were added to the above -53- .

'' " ~ ' " ~ ' ,fi~

described mixture and then the viscosity of the resulting mixture was measured at 25C.

ExampleMelamine Chain Extending Agent Viscosity or Crosslinking Agent at 25C
Bulk Density Type Quantity [9/1] lparts] [m-Pas]
. ~
9 (comparison) 440 ~U 28) diethanolamine 1 12,550 440 (") trimethylolpropane 1 10,900 11 440 ~") 1,6-hexanediol 2 10,560 12 (comparison) 600 (U 24) diethanolamine 1 12,210 13 600 (") trimethylolpropane 1 8,230 14 600 (") 1,6-hexanediol 2 7,600 Examples 9-14 show that the viscosity of the melamine containing A component i8 reduced by using the chain extending agent and/or crosslinking agent of the present invention, and as a result the flowability of the reaction mixture was improved.
Such formulations insure excellent filling of molds having spaces which are difficult to fill, for example, molds for airplane seat~.

5~-i9~

Examples 15-17 A Component:

The mixture of examples 12-14, but additionally 10.2 parts by weight of trichlorofluoromethane was added as a blowing agent.

~ Component:

A urethane group containing quasi-prepolymer having a NCO content of 31 weight percent and a viscosity of 52 m.Pas at 25C prepared from a 2,4- and 2,6 toluene diisocyanate isomeric mixture in a weight ratio of 80:20, and from a polyoxypropylene-polyoxyethylene glycol having a molecular weight of 3900.

100 parts by weight of ~he A componen~ and 22.5 to 27 parts by weight of the B component were reacted analogous to the teachings of example 5 into flexible flame resistant polyurethane molded foam.

The Pollowing mechanical properties were measured on the molded article obtained:

, , ': ' "~ ' ' `

~ti~37 Examples 15-1?

A Component:

The mixture of examples 12-14, but additionally 10.2 parts by weight of trichlorofluoromethane was added as a blowing agent.

B Component:

A urethane group containing quasi-prepolymer having a NCO content of 31 weight percent and a vi~c08ity of 52 m~Pas at 25-C prepared ~rom a 2,4- and 2,6-toluene dii~ocyanate isomeric mixture in a weight ratio of 80:20, and from a polyoxypropyl~ne-polyoxyethylene glycol having a molecular weight of 3900.

100 parts by weight of the A component and 22.5 to 27 parts by weight of the B component were reacted analogous to the teachings of example 5 into flexible flame re~istant polyurethane molded fsam.

The following mechanical properties were measur~d on the molded article obt~ined:

o~
-oc~oo~
~ o~

~D _ O ~ O O a~
~_ ~ _ ~ c ~ 7 ~
u) ~ '~I la ~ '" '~' 3 o~ 6 .......... ~, ' ~, o .~
_ _ U~
U~ U~ ~ V
~) ~ L ~I) - O~ Q U
~ ~ :1 =- ~ C Q~

~ n ~a ~:
o bO ~ ~ S
c Q' o ~ X ~ Q) ~ ~ ~ q 3 C~ ~ ~ ~ O

~ -I lO o 8 ~ ~ ~
a ~ ~ :~. 8> ~ ~ g7 a. ~ G .~ _I ~ Q~ 11) ~ ~ ~a~

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.
.
.

.

Claims

1. A process for the preparation of flame resistant, elastic polyurethane flexible foams, comprising reacting:

a) organic and/or modified organic polyisocyanates with:

b) higher molecular weight polyols; and c) chain extending agents and/or crosslinking agents;

in the presence of:

d) at least one flame retardant;

e) at least one blowing agent;

f) at least one catalyst, as well as optionally;

g) auxiliaries and/or additives;

wherein 1,6-hexanediol, trimethylolpropane or mixtures thereof are used as said chain extending agents and/or cross-linking agents (c) and melamine or mixtures of melamine and other flame retardants are used as said flame retardant (d).

2. A process for the preparation of flame resistant, elastic flexible polyurethane molded foams according to high pressure foam technology in an essentially closed mold, comprising reacting:

a) organic and/or modified organic polyisocyanates with:

b) higher molecular weight polyols; and c) chain extending agents and/or crosslinking agents;
in the presence of:

d) at least one flame retardant;

e) at least one blowing agent;

f) at least one catalyst, as well as optionally;

g) auxiliaries and/or additives;

wherein 1,6-hexanediol, trimethylolpropane or mixtures thereof are used as said chain extending agents and/or cross-linking agents (c) and melamine or mixtures of melamine and other flame retardants are used as said flame retardant (d).

3. The process of claim 1 wherein 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4- toluene diisocyanate and 2,6-toluene diisocyanate and urethane group containing polyisocyanate mixtures having a NCO content of from 34 to 28 weight percent based on the previously mentioned toluene diisocyanate isomers are used as said organic and/or modified organic polyisocyanates (a).

4. The process of claim 1 wherein said higher molecular weight polyols (b) are polyether polyols having an average functionality of from 1.8 to 3 and having an average molecular weight of from 3,600 to 6,500.

5. The process of claim 1 wherein mixtures of the following are used as said higher molecular weight polyols (b):

b1) higher molecular weight polyether polyols having an average functionality of 1.8 to 3; and b2) higher molecular weight polymer modified polyether polyols having an average functionality of 1.8 to 3 selected from the groups consisting of graft polyether polyols, and polyurethane polyether polyol dispersions containing polyurea-, polyhydrazide- and/or tertiary amino groups in bonded form and mixtures thereof.

6. The process of claim 1 wherein mixtures of the following are used as said higher molecular weight polyols (b):

b1) at least 70 weight percent, based on the weight of mixture (b), of at least one polyether polyol having an average functionality of 1.8 to 3 and having an average molecular weight of 3,600 to 6,500; and b2) less than 30 weight percent, based on the weight of the mixture (b), of at least one polymer modified polyether polyol having an average functionality of from 1.8 to 3 and an average molecular weight of 3,600 to 6,500 selected from the group consisting of graft polyether polyols, polyurea-, polyhydrazide-, and tertiary amino group in bonded form containing polyurethane polyether polyol dispersions and mixtures thereof and mixtures thereof.

7. The process of claim 1 wherein melamine having an average particle size of from 20 to 40 microns and having a bulk density in a range of from 500 to 650 g/l is used as said fire retardant (d).

8. The process of claim 7 wherein the melamine is used in an amount of from 50 to 130 parts by weight per 100 parts by weight of the higher molecular weight polyols (b).

9. The process of claim 1 wherein mixtures of the following are used as said fire retardant (d):

d1) 70 to 100 parts by weight of melamine;

d2) 0 to 30 parts by weight of starch; and d3) 0 to 30 parts by weight of ammonium polyphosphate;

wherein the parts by weight are each based on 100 parts by weight of higher molecular weight polyols (b).

10. The process of claim 1 wherein mixtures of the following are used as said fire retardant (d):

d1) 70 to 100 parts by weight of melamine;

d2) 3 to 15 parts by weight of starch; and/or d3) 3 to 15 parts by weight of ammonium polyphosphate;
wherein the parts by weight are based on 100 parts by weight of the higher molecular weight polyols (b).

11. The process of claim 1 wherein mixtures of the following are used as said fire retardant (d):

d1) 70 to 100 parts by weight of melamine; and d3) 1 to 30 parts by weight of ammonium polyphosphate;

wherein the parts by weight are based on 100 parts by weight of higher molecular weight polyols (b).

12. The process of claim 1 wherein mixtures of the following are used as said fire retardant (d):

d1) melamine; and d3) modified ammonium polyphosphate;

wherein the ammonium polyphosphate has the general formula H(n-m)+2 (NH4)mPnO3n+1 in which n is a whole number having an average value of about from 20 to 800 and the ratio of m to n is about 1, and the modified ammonium polyphosphate comprises:

about 80 to 99.5 mass percent ammonium polyphosphate; and about 0.5 to 20 mass percent of a cured epoxy resin having an epoxy equivalent weight of about from 170 to about 220 which envelopes the individual ammonium polyphosphate particles.

13. The process of claim 1 wherein mixtures of the following are used as said fire retardant (d):
d1) 70 to 100 parts by weight of melamine;

d2) 3 to 30 parts by weight of at least one starch selected from the group consisting of corn starch, rice starch, potato starch and wheat starch;

wherein the parts by weight are based on 100 parts by weight of higher molecular weight polyols (b).

14. The process of claim 1 wherein a catalyst combination which comprises the following components: triethylenediamine, bis(dimethylaminoethyl) ether, 2-(dimethylaminoethoxy) ethanol, dibutyltin dilaurate and dibutyldilauryltin mercaptide are used as said catalyst (f).

15. The process of claim 2 wherein the reaction is carried out in a closed mold under compression employing a degree of compression of from 1.1 to 8.

16. A process for the preparation of airplane seats from the flame resistant, elastic flexible polyurethane molded foams of claim 2 wherein said seats have a density of from 35 to 100 9/1.

17. Low viscosity melamine polyether polyol dispersions, comprising:

1 to 150 parts by weight of melamine having an average particle size of from 20 to 40 microns and a bulk density in a range of from 500 to 650 g/l;

0.1 to 5 parts by weight of 1,6 hexanediol, trimethylol-propane or mixtures thereof; and 100 parts by weight of at least one polyether polyol, a polymer modified polyether polyol or mixtures thereof having a functionality of 1.8 to 3 and having a molecular weight of from 3,600 to 6,500.