MXPA99008220A - Process for preparing flexible polyurethane foam - Google Patents

Abstract

Process for making flexible polyurethane foams using MDI and TDI and a polyol composition comprising dispersed particulate material.

Description

PROCESS FOR PREPARING A FLEXIBLE POLYURETHANE FOAM The present invention relates to a process for preparing flexible polyurethane foams. The preparation of flexible polyurethane foams by the reaction of an organic polyisocyanate and a high molecular weight compound reactive to the isocyanate in the presence of a blowing agent is well known. Particularly, EP-111121 has disclosed the preparation of flexible polyurethane foams from a polyisocyanate composition comprising a semi-prepolymer. The polyisocyanate composition is prepared by reacting a diphenylmethane diisocyanate and a polyol; a polymethylene polyphenylene polyisocyanate (polymeric MDI) is also used. EP-392788 prepares flexible foams by reacting semi-prepolymers or prepolymers with a reactive composition to the isocyanate containing a large amount of water. In EP-296449 flexible foams are prepared by reacting polyisocyanates, polyols and water at a relatively low NCO index. Co-pending application PCT / EP95 / 02068 relates to a process for preparing flexible foams using a semi-prepolymer which has been obtained by reacting a portion of polymeric MDI with a polyol and adding the other part to the reaction product as well obtained. Although useful flexible foams based on MDI and polymeric MDI can be obtained, there is a possibility to improve them. In particular the foams prepared in a closed mold in which the foam is produced, which will be used as cushioning material in automotive seats could be improved in relation to foam resistance, elasticity particularly at low density of the foam. In the past some of these improvements have been obtained using tolylene diisocyanate (TDI) instead of MDI. Those foams in particular show a high elasticity, good foam resistance at low density. However, due to its vapor pressure and toxicity it is necessary to take special measures to manipulate TDI. Other foams based on TDI show a relatively poor hardness especially at low density and slow curing and a narrow process range (index of socianato). More recently, proposals have been made to avoid the disadvantages of both foams, those based on MDI and based on TDI using combinations of MDI and TDI. In EP-439792 the use of a polyisocyanate comprising 21-95% by weight of TDI has been proposed to improve the tensile strength; still the amount of TDI used is relatively high. In EP-679671 the use of a mixture of polymeric DI and TDI comprising 3-20% by weight of TDI has been proposed to prepare a low density foam having improved impact elasticity, improved compression deformation and an excellent reduction of the transmission of a vibration of 6 Hz. The polymeric MDI used has a high content of compound of three benzene rings in comparison with the compound content of four or more benzene rings of the less active ingredient. The use of polymer polyols has been proposed in very general terms. In EP-694570 the use of a polyisocyanate prepolymer comprising MDI, polymeric MDI and 5-15% by weight of TDI has been proposed.

The polyisocyanate prepolymer has better fluence, the foams made therefrom show better ILD, compression deformation and flammability characteristics. It has also been proposed to use a dispersion in a polyol of a grafted polymer. In the co-pending application PCT / EP96 / 04392 it has been proposed to use an MDI and TDI prepolymer to improve the elasticity and stability of the foam, comfort properties and mechanical strength. The amount of TDI can be 2-25% by weight of the polyisocyanate composition, which has an MDI + TDI functionality of 2.05-2.35. It has been proposed in general terms the use of a polymer polyol prepared by the in situ polymerization of styrene and / or acrylonitrile in polymeric polyols or by the in situ reaction between a polyisocyanate and triethanolamine in a polymeric polyol (polyol PIPA). The polymeric polyol can contain 5-50% by weight of dispersed polymer. Surprisingly it has been found that by using an MDI and TDI polyisocyanate composition which has a limited content of polyisocyanates having isocyanate functionality of 3 or more and limited TDI content and functionality., together with a polyol composition comprising a limited amount of a PIPA polyol, it is possible to obtain a low density molded flexible foam which exhibits a high elasticity, fast curing, short demolding times and good properties of resistance to loads, properties of tear strength, elongation, comfort and durability. Therefore the present invention relates to a process for preparing a flexible polyurethane foam by reaction at an NCO index of 70-120 of a) a polyisocyanate composition comprising every 100 parts by weight of composition 5 to 20 parts in weight of tolylene diisocyanate and 80-95 parts by weight of diphenylmethane diisocyanate and homologues thereof having an isocyanate functionality of 3 or more, the amount of diphenylmethane diisocyanate is from 70 to 95% by weight calculated on the amount of diphenylmethane diisocyanates and homologues, and the diphenylmethane diisocyanate comprises 8-45% by weight, calculated on the weight of this diphenylmethane diisocyanate, of diphenylmethane diisocyanate containing at least one NCO group in the ortho position, and in which preferably the weight ratio of homologs that have 3 NCO groups to homologs that has 4 or more NCO groups plus by-products is less than 1.0; and b) a polyol composition comprising 1) a polyoxyethylene polyoxypropylene polyol having an average nominal hydroxyl functionality of 2-6 and preferably 2-4 and most preferably 3 and an average equivalent weight of 1000-4000 and containing 5-25% by weight of oxyethylene groups which are preferably at the end of the polymer chains; 2) 2 to 7 parts by weight of water; 3) 2 to 10 parts by weight of a polyether polyol having an average nominal hydroxyl functionality of 2-6, an average equivalent weight of 200-1500 and containing at least 60% by weight of oxyethylene groups; 4) 1 to 15 parts by weight of particulate material which is the reaction product of a polyisocyanate and a compound having a plurality of hydroxyl-, primary amine and / or secondary amine groups and having an equivalent weight of up to 400 and which is dispersed in said polio composition; the amounts of b2) to b4) are calculated on 100 parts by weight of bi); and 5) optionally auxiliaries and additives known per se. Furthermore, the present invention relates to a reaction system comprising the polyisocyanate composition and the aforementioned polyol composition and said polyisocyanate and polyol composition. In the context of the present application the following terms have the following meaning: 1) isocyanate index or NCO index or index: the ratio of -NCO groups on isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage: GNCOI X OO (%) [active hydrogens] In other words, the -NCO index expresses the percentage of isocyanate actually used in the formulation with respect to the amount of isocyanate theoretically required to react with the amount of hydrogen reactive to the isocyanate used in the formulation . It should be noted that the isocyanate index as used herein is considered from the point of view of the actual foaming process which involves the isocyanate ingredient and the ingredients reactive to the isocyanate. Any of the isocyanate groups consumed in the preliminary step to produce the semi-polymer or other modified polyisocyanates or any of the active hydrogens that reacted with isocyanate to produce modified polyols or polyamines, are not taken into account for the calculation of the isocyanate index. Only the free isocyanate groups and the free isocyanate-reactive hydrogens (including those of the water) present in the actual foaming stage are taken into account. 2) The expression "isocyanate-reactive hydrogen atoms" as used herein for the purpose of calculating the isocyanate index refers to the total of hydrogen atoms of hydroxyls or amines present in the reaction composition in the form of polyols, polyamines and / or water; this means that for the purpose of calculating the socianate index in the actual foaming process, it is considered that a hydroxyl group comprises a reactive hydrogen and it is considered that a water molecule comprises two reactive hydrogens. 3) Reaction system: a combination of components in which the polyisocyanate component is kept in a container separate from the isocyanate-reactive components. 4) The term "polyurethane foam" as used herein generally refers to products of cellular structure which are obtained by reaction of polyisocyanates with compounds containing hydrogen reactive to the isocyanate, using foaming agents, and in particular includes cellular products obtained with water as a reactive foaming agent (involving a reaction of water with isocyanate groups to give urea and carbon dioxide bonds and producing polyurea-urethane foams). 5) The term "average nominal hydroxyl functionality" is used herein to indicate the average base number functionality (number of hydroxyl groups per molecule) of the polyol composition with the assumption that this is the average base number functionality (number of active hydrogen atoms per molecule) of the initiator (s) used in its preparation although in practice it will often be somewhat smaller due to some terminal unsaturation. The term "equivalent weight" refers to the molecular weight for each hydrogen atom reactive to the isocyanate in the molecule. 6) The word "average" refers to an average base number. The diphenylmethane diisocyanate ( used can be selected from mixtures of isomers of 4, 4'-MDI and 2,4'-MDI and less than 10% by weight of 2,2'-MDI and modified variants thereof containing carbodiimide, uretonimine, isocyanurate, urethane, allophanate, urea or biuret groups. Preferred are mixtures of isomers with 2,4'-MDI, and MDI modified with uretonimine and / or carbodiimide having an NCO content of at least 25% by weight and urethane-modified MDI obtained by reacting excess MDI and a polyol of molecular weight less than 1000 and having an NCO content of at least 25% by weight Most preferably it is a mixture of isomers comprising 5-45% by weight of 2,4'-MDI and less than 5% by weight. % by weight of 2,2'-MDI with the remaining 4,4'-MDI. Homologs having an isocyanate functionality of 3 or more are contained in the so-called crude or polymeric MDI. The crude or polymeric MDI comprises MDI and homologs having a socianate functionality of 3 or more and are well known in the art. They are prepared by the phosgenation of a mixture of polyamines obtained by the acid condensation of aniline and formaldehyde. The preparation of the polyamine mixtures and that of the polyisocyanate mixtures is well known. The condensation of aniline with formaldehyde in the presence of strong acids such as hydrochloric acid yields a reaction product containing diaminodiphenylmethane together with polyphenylene polyamines of higher functionality, the precise composition depends in a manner known per se from the aniline / formaldehyde ratio. The polyisocyanates are obtained by phosgenation of the polyamine mixtures and the various proportions of diamines, triamines and higher polyamines give rise to related proportions of isocyanates, triisocyanates and higher polyisocyanates. The relative proportions of diisocyanate, triisocyanate and higher polyisocyanates in such crude or polymeric MDI compositions determine the average functionality of the compositions, ie the average number of isocyanate groups per molecule. By varying the proportion of the starting materials, the average functionality of the polyisocyanate compositions can be varied from little more than 2 to 3 or greater. In practice, however, the average isocyanate functionality preferably ranges from 2.3 to 2.8. The NCO value of these crude or polymeric MDI is at least 30% by weight. The crude or polymeric MDI contains diphenylmethane diisocyanate, the remainder being polymethylene polyphenylene polyisocyanates of greater than two functionality together with by-products formed in the manufacture of such polyisocyanates by phosgenation. It should be noted that the crude or polymeric MDI may contain 2,4'-MDI and that the range of ortho-substituted MDI with NCO in the diphenylmethane diisocyanate in the polyisocyanate composition a) is the total of 2,2'- and 2, 4'-MDI in the MDI and in the raw or polymeric MDI. The ratio of the homologs having 3 NCO groups to the homologues having 4 or more NCO groups plus the by-products is preferably less than 1.0. The crude or polymeric MDI having such a relationship are commercially available; for example, Suprasec DNR from Imperial Chemical Industries PLC. The tolylene diisocyanate used is known as such and can be selected from all isomers or mixtures thereof and in particular from 2,4- and 2,6-tolylene diisocyanate and mixtures thereof, such as those sold commercially as TDI 80/20 and TDI 65/35. The total amount of crude or polymeric MDI used to prepare the polyisocyanate composition should be such that the amount of diphenylmethane diisocyanate and the amount of ortho substituted diisocyanate remain within the ranges given above. Those skilled in the art will be able to easily calculate the amount, which will depend on the chosen MDI and the crude or polymeric MDI, certainly in the light of the examples. The polyisocyanate composition a) is prepared by simple mixing of the MDI, the TDI and the crude or polymeric MDI in any order. The polyether polyols b1) which can be used include the products obtained by the polymerization of ethylene oxide and propylene oxide in the presence, where necessary, of polyfunctional initiators. Suitable initiator compounds contain a plurality of active hydrogen atoms and include water, butane diol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethanolamine, diethanolamine, triethanolamine, toluene diamine, diethyl toluene diamine, cydohexane diamine. , cyclohexane dimethanol, glycerol, trimethylolpropane, and 1, 2,6-hexanetriol. Mixtures of initiators and / or cyclic oxides can be used. The polyoxyethylene polyoxypropylene polyols are obtained by the simultaneous or sequential addition of ethylene and propylene oxide to the initiators as fully described in the prior art. Random copolymers, block copolymers and combinations thereof having the indicated amount of oxyethylene groups in particular those having at least part and preferably all the oxyethylene groups at the end of the polymer chain (crowned or tip). Mixtures of such polyols can be particularly useful. Most preferred are polyoxyethylene polyoxypropylene polyols having an average nominal functionality of 2-4 and most preferably 3 and an oxyethylene content of 5-25% by weight, and preferably having the oxyethylene groups at the end of the chains. polymer. During the last few years, various methods for preparing polyether polyols having a low level of unsaturation have been described. These developments have made possible the use of polyether polyols that are at the upper end of the molecular weight range since many polyols can now be prepared with acceptably low levels of unsaturation. Polyols having a low level of unsaturation can also be used according to the present invention. In particular, such high molecular weight and low unsaturation polyols can be used to prepare flexible foams having a high ball bounce. The polyols b3) used in the polyol composition b) can be selected from the aforementioned polyether-polyol for b1) with the proviso that the equivalent weight is 200-1500 and the oxyethylene content is at least 60% in weigh. The most preferred polyols are 1) polyoxyethylene polyoxypropylene polyols with an oxyethylene content of 60-95% by weight in which the oxyethylene groups are randomly distributed in the polymer chains, an average equivalent weight of 1000-1500 and a functionality average nominal hydroxyl of 2-4 and 2) polyoxyethylene polyols having an equivalent weight of 200-500. The particulate material b4) which is the reaction product of a compound having a plurality of hydroxyl, primary and / or secondary amine groups and having an equivalent weight of up to 400 and preferably up to 200 (hereinafter referred to as co-reactive) and a polyisocyanate and which is dispersed in a polyol, is generally known as such in the art, as for example, a PIPA polyol. Such PIPA polyols have been described extensively in the prior art: see for example, GB2072204, US4452923, EP-418039 and WO94 / 12533. Such PIPA polyols are commercially available: for example, Daltocel ™ XF 417 from Imperial Chemical Industries PLC. The particulate material which is the reaction product of a polyisocyanate and The co-reactant can be prepared in the ways described in the prior art mentioned above. Usually the particulate material is prepared in the polyol b1) by adding the co-reactant to the poly b1) followed by the addition of the polyisocyanate. The amount of co-reactant and polyisocyanate depends on the desired amount of particulate material dispersed in the polyol. If desired, charges of dispersed material greater than those specified hereinafter can be obtained followed by a dilution with polyol b1) to the desired amount. When desired, special addition schemes of the co-reactant and the polyisocyanate can be employed as disclosed in EP-418039 and W094 / 125333. The relative amounts of co-reactant and polyisocyanate are -! ' they generally choose such that the number of hydrogen atoms in the co-reactant capable of reacting with the polyisocyanate exceeds the number of isocyanate groups. The polyisocyanate used in the preparation of the particulate material is any organic compound having at least two, preferably 2 to 4, isocyanate groups per molecule. The polyisocyanate can be aliphatic, aromatic or cycloaiiphatic, although those of the aromatic type are preferred due to its desirable reactivity properties. Representative of these diisocyanate types are m- and p-phenyl diisocyanate, toluene-2,4-diisocyanate, toluene-2, 6-isocyanate, hexamethylene-1,6-diisocyanate, tetramethylene-1,4-diisocyanate, cyclohexane. -1,4-diisocyanate, hexahydrotoluene diisocyanate (and isomers), naphthylene-1,5-diisocyanate, 1-methylphenyl-2,4-phenyldiisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate , 4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, and 3,3'-dimethyldiphenylpropane-4,4'-diisocyanate; triisocyanates such as toluene-2,4,6-triisocyanate and tetraisocyanates such as 2,4,4'-dimethyl diphenylmethane 2, 2 ', 5,5'-tetraisocyanate, and other polyisocyanates such as the various polymethylene polyphenyl polyisocyanates (crude or polymeric MDI) ). The co-reactive is a material having a plurality of -OH groups, > NH and / or -NH2 and an equivalent weight per active hydrogen atom of up to 400, preferably up to 200. Because the co-reactant reacts with the polyisocyanate in situ in the polyol, it is also preferred that the co-reactant be more reactive with the polyisocyanate than the polyol. Preferred co-reactants are alkanolamines, polyether-polyols initiated by low-weight equivalent amine, alkylene oxide, acrylonitrile, or acrylic ester-type adducts of amines, primary amines, secondary amines, hydrazines, dihydrazides, urea, ammonia, Mannich-type condensates, low-weight hydroxyl-terminated compounds such as ethylene glycol, glycerin, glycol ethers, pentaerythritol, aminobenzenes, or mixtures thereof. Of these, the alkanolamines are the most preferred. Suitable alkanolamines include mono-di- and trialkanolamines, particularly those in which the alkanol groups have from 2 to 6, preferably from 2 to 3, carbon atoms. The mono- and dialkanolamines may also have a unique N-alkyl substituent, preferably consisting of 2 to 6 carbon atoms. Preferred among these are monoethanolamine, diethanolamine, triethanolamine, N-methylethanoiamine, N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine, diisopropapolamine, triisopropanolamine, N-methylisopropanolamine, N-ethyl isopropanolamine, and N-propylisopropanolamine. Suitable primary and / or secondary amines include the polyhydric aliphatic amines, arylaliphatic, cycloaliphatic and aromatic including, for example, ethylenediamine, 1,2- and 1,3-propylene diamine, tetramethylene diamine, hexamethylene diamine, dodecamethylene diamine, trimethyldiaminohexane, N, N'-dimethylethylenediamine, higher homologs of ethylene diamine such as diethylene triamine, triethylene tetramine and tetraethylene pentamine, homologs of propylene diamine, 4-aminobenzylamine, 4-aminophenylethylamine, piperazine, N, N'-bisaminoethyldipropylene triamine, and 1-amino-3,3,5-trimethyl-5 -aminomethylcyclohexane. Suitable hydrazines include hydrazine itself and N.N'-disubstituted or monosubstituted hydrazines having substituent groups such as C 1 -C alkyl, cyclohexyl or phenyl groups. Among these, hydrazine itself is preferred. Suitable hydrazides include the hydrazides of multifunctional carboxylic acids such as carbonic acid, oxalic acid, malonic acid, succinic acid, adipic acid, sebacic acid, azeiacic acid, maleic acid, fumaric acid, phthalic acid, soft acid, and terephthalic acid , and the esters of a monocarboxylic hydrazine acid with dihydric or polyhydric alcohols and phenols. These hydrazides preferably have a molecular weight of 90 to 1000. The reactants are mixed advantageously at any temperature at which the mixture is a liquid and at which the reagents do not degrade, but are preferably mixed at 0 to 170 ° C, greater preference of 15 to 70 ° C. The socianate and the co-reactant are mixed with advantage with stirring, to promote the formation of a plurality of small particles. Usually, rapid agitation is desired to optimize the particle size and minimize the viscosity of the resulting dispersion. The process may be carried out continuously or discontinuously, as described in U.S. Patent No. 4,374,209. Often the reaction between the polyisocyanate and the co-reactant is exothermic, and it occurs rapidly, and is completed essentially in most cases in a period of 1 minute to 3 hours, preferably 1 to 30 minutes, although this depends on some mode of the choice of polyisocyanate and co-reactant, the size of the batch and the initial temperature. The stirring is preferably carried out throughout the reaction period. If desired, a catalyst of the reaction between the polyisocyanate and the co-reactant can be used to accelerate the reaction. Suitable catalysts include those described below with respect to the use of this dispersion to prepare polyurethanes, with the organotin catalyst being preferred. The amount of catalyst is advantageously up to 1% by weight based on the polyol, preferably up to 0.1% by weight and more preferably up to 0.05% by weight. However, the catalyst may not be necessary in particular with the most reactive co-reactants. Once the polyol was prepared with the dispersed particulate material the polyol composition b) is prepared by adding water and polyol b3) and mixing. To this polyol composition b) additives and auxiliaries known per se can be added, such as catalysts which improve the formation of urethane and urea bonds (for example, tertiary amine and organotin catalysts), chain extenders and crosslinking agents having an equivalent weight of 31 to less than 200 and having 2-8 hydrogen atoms reactive to the isocyanate (eg, ethanolamine, diethanolamine, triethanolamine, glycol, triethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol, trimethylolpropane) , pentaerythritol, sorbitol, sucrose, polyethylene glycol with molecular weight less than 400, toluene diamine, diethyl thioiden diamine, cyclohexane diamine, phenylene diamine, diphenylmethane diamine, alkylated diphenylmethane diamine and ethylene diamine), surfactants, stabilizers, flame retardants, fillers, antioxidants, antimicrobial agents, dyes and other blowing agents other than water (for example, Liquid or gaseous CO2 supplied under pressure via polyisocyanate or polyol composition).

The foams are prepared by combining and blending the polyisocyanate and polyol compositions a) and b) and allowing the mixture to react. The relative amounts will depend on the desired index which can vary from 70-120 and can be easily calculated by those skilled in the art from a selected polyisocyanate and polyol composition. A further advantage of the use of the polyisocyanate composition a) and the polyol composition b) is that to operate at an index of 70-120 the relative amounts of the compositions do not differ much, allowing for easy dosing and mixing of the compositions The process can be used to make flexible sheet foams in continuous or discontinuous form, flexible foam molded in an open or closed mold including the applications called foam-in-cloth and poured-in-situ. Flexible foams prepared in accordance with the present invention can have a free lift density of 20-60 kg / m3 (ISO 845) and can be used in mattresses, cushions, seat furniture and automotive seats. The process according to the present invention can be carried out according to the one-step process, the prepolymer process or the semi-or quasi-prepolymer process. In the prepolymer and semi-or quasi-prepolymer processes all or part of the polyols used in the polyol composition are pre-reacted with an excess amount of the polyisocyanate before the reaction of the polyisocyanate and the water takes place, i.e. , the foaming. If the prepolymer or semi- or quasi-prepolymer process is used, preferably all or only part of the polyol b1) is pre-reacted. It should be noted that any previously reacted polyol is not taken into consideration for calculating the amount of the ingredients in the polyisocyanate composition and must be taken into account in calculating the amounts of the ingredients in the polyol composition. The present invention is also related to such prepolymer and semi-prepolymer compositions. Preferably such compositions have a free NCO content of 8-38 and preferably 12-26% by weight, they contain the polyisocyanate composition a) described above, part of said polyisocyanate composition is present in the urethane-containing adduct form with the polyol b1), the amount of this adduct is preferably 30-60% by weight of the polyisocyanate composition. Such a prepolymer or semi-prepolymer composition according to the present invention is preferably prepared by reacting an excess amount of diphenylmethane diisocyanate (MDI) and optionally crude or polymeric MDI (which comprises MDI and homologues thereof having a functionality of isocyanate of 3 or more) with the polyol and adding to this reaction product tolylene diisocyanate (TDI) and optionally MDI and / or crude or polymeric MDI. The crude or polymeric MDI can be added to the MDI which must be used for the reaction with the polyol, the crude or polymeric MDI can be added to the reaction product of the MDf and the polyol or part of the crude or polymeric MDI can be added to the MDI. which must be used for the reaction with the polyol while the other part is added to the reaction products thus obtained. The reaction for preparing the prepolymer, between the MDI (and optionally the crude or polymeric MDI) and the polyol is carried out in a known manner by mixing the ingredients and allowing them to react. Preferably the reaction is carried out at 60-100 ° C until no changes in the NCO value are observed. Usually the reaction will be completed in 1-4 hours. A catalyst that improves the formation of urethane groups may be used, if desired, but is not necessary. Sometimes the used polyols still contain small amounts of catalysts, or residues thereof, which have been used in the preparation of such polyols; the presence of these catalysts or residues could have a negative effect on the reaction of the MDI and the polyol; to avoid this, an acid or an acid halide can be added to the ingredients, such as benzoyl chloride, toluenesulfonyl chloride or thionyl chloride, in a low proportion (generally less than 1000 ppm). After completing the reaction the reaction product is mixed with TDI and optionally with additional MDI, polymeric MDI and / or crude MDI. Examples 1 and 2 A prepolymer was prepared as follows: 1) by mixing 43.0 parts by weight of diphenylmethane diisocyanate containing 78.6% by weight of 4,4'-diphenylmethane diisocyanate and 21.4% by weight of 2.4 '-diphenylmethane diisocyanate and 11 parts by weight of a polymethylene polyphenylene polyisocyanate having an NCO value of 30.7% by weight and an average isocyanate functionality base number of 2.7 (Suprasec 2185, Suprasec is a registered trademark of ICI ), 2) by adding to said mixture 38.0 parts by weight of a polyoxyethylene polyoxypropylene polyol having a nominal functionality of 3, a number average molecular weight of 6000 and an oxyethylene content of 15% by weight (all pointed) then mixing and 3) allowing the mixture to react for 4 hours at 85 ° C. After the reaction the prepolymer is mixed with 8 parts of the polymethylene polyphenylene polyisocyanate mentioned above. Isocyanate A is prepared by mixing 90.1 parts of this prepolymer mixture with 9.9 parts of TDI for 15 minutes. The socianate B is prepared by mixing 86.6 parts of this prepolymer mixture with 13.4 parts of TDI for 15 minutes. An isocyanate-reactive composition was prepared by mixing polyols, water, catalysts and surfactants in the amounts in parts by weight given in the table. A flexible foam molded by reaction in a mold of the isocyanates A and B with the isocyanate-reactive composition was prepared (mold temperature 65 ° C and size 21,4 I, machine: Krauss Maffei Komet 40/20).

The recalculation of these mixtures gives: Example 1 Example 2 Polyisocyanate composition: TDI (parts by weight) 15 20 Mixing MDI (parts by weight) (without polioi) 85 80 Diisocyanate in the MDI mixture (% w / w) 80.9 Orthocyanide in the MDI diisocyanate (% w / w) 15.5 4,4'-MDI in the MDI mixture (% w / w) 65.4 Triisocyanate in the mixture MDI mixture (% w / w) 8.2 Higher oligomers in the MDI mixture 10.9 (% W / W) Ratio f = 3 / f = 4 (% w / w) 0.75 Polymer adduct on the polyisocyanate 38, 6 37.1 total (% w / w) NCO value of the composition of 22.3 23.4 polyisocyanate (% w / w) Polio composition! parts by weight (pep) of water per 4.5 4.5 100 pbw polyol b1 pep of polyether polyol b3 per 100 5.9 pbw polyol b1 pbw of particulate material per 7.8 7 , 5 100 pb of polyol b1 Polyol A: a polyoxyethylene / polyoxypropylene triol of molecular weight 6000 with 15% by weight of EO in tip; OH number = 28 mg KOH / g. Polyol B: a PIPA polyol; Daltocel XF 417 ex ICI; it contains 20% by weight of dispersed particulate material.

Polyol C: a polyoxyethylene / polyoxypropylene triol of molecular weight 4000 with 75 % by weight of EO randomly distributed; OH number = 42 mg KOH / g. Polyol D: a polyoxyethylene / polyoxypropylene triol of molecular weight 4700 with 14.2 % by weight of EO in tip; OH number = 36 mg KOH / g. Dabco 331 Iv: amine type catalyst supplied by Air Products. Niax A1: amine type catalyst supplied by Osi Specialties. B4113: a silicone surfactant supplied by Th. Goldschmidt AG. After unmolding (5 min.) A foam with properties as described in the table below was obtained.

Claims (8)

1. CLAIMS 1. A process for preparing a flexible polyurethane foam at an NCO index of 70-120 CHARACTERIZED BECAUSE it comprises causing the reaction of a) a polyisocyanate composition comprising every 100 parts by weight of composition 5 to 20 parts by weight of tolylene diisocyanate and 80-95 parts by weight of diphenylmethane diisocyanate and homologues thereof having an isocyanate functionality of 3 or more, the amount of diphenylethane diisocyanate is from 70 to 95% by weight calculated on the amount of diphenylmethane diisocyanates and homologs, and the diphenylmethane diisocyanate comprises 8-45% by weight, calculated on the weight of this diphenylmethane diisocyanate, of diphenylmethane diisocyanate containing at least one NCO group in the ortho position, b) a polyol composition comprising 1) a polyoxyethylene polyoxypropylene polyol, having an average nominal hydroxyl functionality of 2-6, an average equivalent weight of 1000-4000 and containing 5-25% by weight d and oxyethylene groups; 2) 2 to 7 parts by weight of water; 3) 2 to 10 parts by weight of a polyether polyol having an average nominal hydroxyl functionality of 2-6, an average equivalent weight of 200-1500 and containing at least 60% by weight of oxyethylene groups; 4) 1 to 15 parts by weight of particulate material which is the reaction product of a polyisocyanate and a compound having a plurality of hydroxyl-, primary amine and / or secondary amine groups and having an equivalent weight of up to 400 and which is dispersed in said polyol composition; the quantities of b2) to b4) are calculated per 100 parts by weight of b1); and 5) optionally auxiliaries and additives known per se.
2. 2. A process according to claim 1, CHARACTERIZED BECAUSE the weight ratio of homologs having 3 NCO groups to homologs having 4 or more NCO groups plus by-products is less than 1.0.
3. 3. A process according to claim 1-2, CHARACTERIZED BECAUSE the particulate material is the reaction product of triethanolamine and diphenylmethane diisocyanate which optionally comprises homologs thereof having a socianate functionality of 3 or more.
4. 4. CHARACTERIZED foams BECAUSE they are manufactured according to claim 1-3.
5. 5. A reaction system characterized in that it comprises the polyisocyanate and polyoi compositions described in claims 1-3.
6. 6. A prepolymer or semi- or quasi-prepolymer composition having a content of 8-38% by weight of free NCO, containing the polyisocyanate composition described in claims 1-2, CHARACTERIZED BECAUSE part of said polyisocyanate composition is present in the form of an adduct containing urethane with the polyol b1) described in claim 1.
7. 7. A prepolymer or semi- or quasi-prepolymer composition according to claim 6 CHARACTERIZED BECAUSE it comprises a content of 12-26% by weight of free NCO.
8. 8. A prepolymer or semi- or quasi-prepolymer composition according to claims 6-7 CHARACTERIZED BECAUSE the adduct amount is 30-60% by weight of the composition.