MXPA96005706A

MXPA96005706A - Process for preparing a polyuretanoflexi foam

Info

Publication number: MXPA96005706A
Application number: MXPA/A/1996/005706A
Authority: MX
Inventors: Berthine Albert De Witte Mireille
Original assignee: Imperial Chemical Industries Plc
Priority date: 1994-06-16
Filing date: 1995-05-31
Publication date: 1998-10-30

Abstract

The present invention relates to a process for preparing a flexible polyurethane foam by reacting I) an organic polyisocyanate with II) a polyol having a nominal average hydroxyl functionality of 2-3 and average molecular weight number from 1000 to 12000; and optionally with III) an isocyanate-reactive compound containing at least 2 hydrogen atoms reactive with isocyanate and having an average molecular weight number of 60 to 999, using IV) a blowing agent, and optionally V) a catalyst; and optionally VI) other auxiliaries and additives known per se, is characterized in that it comprises: a) the polyisocyanate is a polyisocyanate composition having an NCO value of 11-22% by weight, which is a mixture of a1. the polyisocyanate is a polyisocyanate composition having an NCO value of 11-22% by weight, which is a mixture of a1. 75-95 parts by weight of an isocyanate-terminated semi-prepolymer having an NCO value of 9-20% by weight, prepared by reacting an excessive amount of a polyisocyanate composition, which consists of 35-75% by weight of diisocyanate of diphenylmethane and 25-65% by weight of polymethylene-polyphenylene polyisocyanate, with a polyol having a nominal average hydroxyl functionality of 2-3 and an average number of molecular weight of 1000 to 12000, and a2. 5-25 parts by weight of a polymethylene-polyphenylene polyisocyanate, b) 25-120 parts by weight of polyol 2) are used per 100 parts by weight of the organic polyisocyanate, c) water is used as the blowing agent in an amount from 3-15 parts by weight per 100 parts by weight of polyol 2); and d) the reaction is carried out at a rate of 40-1

Description

PROCESS FOR PREPARING A FLEXIBLE POLYURETHANE FOAM DESCRIPTION OF THE INVENTION The present invention relates to a process for preparing flexible polyurethane foams and to a polyisocyanate composition for preparing such flexible foams. It is widely known to prepare flexible polyurethane foams by reacting an organic polyisocyanate and a high molecular weight isocyanate-reactive compound in the presence of a blowing agent. More particularly, it has been described in EP-111121 for preparing 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. This polyisocyanate is used either completely in the preparation of the semi-prepolymer or is added after the semi-prepolymer has been prepared. It has been found that the use of polymeric MDI as proposed in EP-111121 does not provide satisfactory stability combined with low viscosity, particularly for those polyisocyanate compositions having a relatively low NCO value, for example 11-22% by weight . In EP-392788 the flexible foams are prepared by reacting semi-prepolymers or prepolymers with an isocyanate-reactive composition containing a high amount of water. In EP-269445 the flexible foams are prepared by reacting polyisocyanates, polyols and water at a relatively low NCO index. Surprisingly, it has been found that when part of the polymethylene-polyphenylene polyisocyanate (polymeric MDI's) are used to prepare a semi-prepolymer and the other part of polymeric MDI is added to the semi-prepolymer thus formed, the polyisocyanate compositions according to present invention are stable, transparent liquids having low viscosity; consequently its processing in the preparation of the foams is also improved. When the polymeric MDI is used either completely in preparation of the semi-prepolymer or is added completely after the semi-prepolymer is prepared the stability and / or viscosity are adversely affected. In addition, it has been found that the polyisocyanate compositions can contain higher amounts of polymeric MDI, while the rest of the stable and therefore flexible foams have a lower density can be prepared; the lower density does not significantly affect the other physical properties of the foam in a negative way. Accordingly, the present invention relates to a process for preparing a flexible polyurethane foam by the reaction of: 1) an organic polyisocyanate with 2) a polyol having a nominal average hydroxyl functionality of 2-3 and a weight number molecular from 1000 to 12000; and optionally with 3) an isocyanate-reactive compound containing at least two hydrogen atoms reactive with isocyanate and having an average number of molecular weight of 60 to 999; using 4) a blowing agent; and optionally 5) a catalyst; and optionally 6) other auxiliaries and additives known per se, characterized in that a) the polyisocyanate is a polyisocyanate composition having an NCO value of 11-22, preferably 13-20% by weight and more preferably more than 15. to 20%, which is a mixture of al. 75-95 parts by weight of an end-isocyanate semi-prepolymer having an NCO value of 9-20, preferably 11-18 and more preferably 13-18% by weight, prepared by the reaction of an excess amount of the polyisocyanate composition, which consists of 35-75% by weight of diphenylmethane diisocyanate and 25-65% by weight of polymethylene-polyphenylene polyisocyanate, with a polyol having a nominal average of hydroxyl functionality of 2-3 and a number of average molecular weight from 1000 to 12000; and a2. 5-25 parts by weight of a polymethylene-polyphenylene polyisocyanate; b) 25-120 and preferably 35-100 parts by weight of the polyol 2) is used per 100 parts by weight of the organic polyisocyanate; c) Water is used as the blowing agent in an amount of 3-15, preferably 5-12 parts by weight and more preferably more than 8 to 12 parts by weight per 100 parts by weight of polyol 2); and d) the reaction is carried out at an index of 40-130 and preferably above 70 to 100. In addition, the present invention is related to a reaction system comprising the ingredients mentioned in the foregoing, with the proviso that that the polyisocyanate is kept in a separate container of the isocyanate-reactive compounds. Still further, the present invention is related to the polyisocyanate mentioned in the foregoing.

In the context of the present invention, the following terms have the following meaning: 1) isocyanate index or NCO index or index: the ratio of NCO groups on the isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage : [NCO] xl00 (%). [active hydrogen] In other words, the NCO index expresses the percentage of the isocyanate actually used in a formulation with respect to the amount of isocyanate theoretically required to react with the amount of isocyanate-reactive hydrogen used in a formulation. It should be noted that the isocyanate index as used herein is considered from the point of view of the actual foam formation process, which involves the isocyanate ingredient and the isocyanate-reactive ingredients. Any of the isocyanate groups consumed in a preliminary step to produce the semi-prepolymer or other modified polyisocyanates or any of the active hydrogens reactive with isocyanate, to produce the modified polyols or polyamines, are not counted in 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 step are taken into account. 2) The expression "hydrogen atoms reactive with the isocyanate" as used herein for the purpose of calculating the isocyanate index, refers to the total hydroxyl and amine hydrogen atoms present in the reactive compositions in the form of polyols, polyamines and / or water; this means that for the purpose of calculating the isocyanate index in the actual foaming process, a hydroxyl group is considered to consist of a reactive hydrogen and a water molecule is considered to consist of two active hydrogens. 3) Reaction System: a combination of the components, in which the polyisocyanate component is kept in a separate container from the isocyanate reactive components. 4) The term "polyurethane foam" as used herein, generally refers to cellular products as obtained by the reaction of polyisocyanates with hydrogen-containing compounds reactive with the isocyanate, using foaming agents and in particular including cellular products obtained with water as the reactive foaming agent (which involves a reaction of water with isocyanate groups that produce urea and carbon dioxide bonds and produce polyurea-urethane foams). 5) The term "nominal average hydroxyl functionality" is used herein to indicate the average number of functionality (number of hydroxyl groups per molecule) of the polyol composition on the assumption that this is the average number of the functionality (number of hydroxyl atoms per molecule) of the initiator or initiators used in its preparation, although in practice it will frequently be a little less due to some terminal unsaturation. 6) The "MDI functionality" is the average number of isocyanate functionality of all of the diphenylmethane diisocyanate and all of the polymethylene-polyphenylene polyisocyanate used in preparing the polyisocyanate composition according to the present invention, with the proviso that the NCO groups used in the preparation of the semi-prepolymer are also taken into account in determining this functionality. The diphenylmethane diisocyanate (MDI) used can be selected from 4,4 '- pure MDI and isomeric mixtures of 4,4' -MDI and 2, 4 '-MDI and less than 10% by weight of 2,2' - MDI and its modified variants containing carbodiimide, uretonimine, isocyanurate, urethane, allophanate, urea or biuret groups. Most preferred are 4.4 '- pure MDI, isomeric mixtures of 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 making reacting the excess of MDI and polyol (preferably having a molecular weight of at most 999) and having an NCO content of at least 25% by weight. The polymethylene polyphenylene polyisocyanates used in the preparation of the semi-prepolymer al) and used as the polyisocyanate a2) are known as such and are polyisocyanates comprising MDI and MDI homologs, which have isocyanate functionalities of 3 or more. These polyisocyanates are often referred to as "unpurified MDI" or "polymeric MDI" and are made by the phosgenation of a mixture of polyamines obtained by acid condensation of aniline and formaldehyde. The manufacture of both of the polyamine blends and the polyisocyanate blends is well known. The condensation of the aniline with formaldehyde in the presence of strong acids such as hydrochloric acid, gives a reaction product containing diaminophenylmethane together with polymethylene-polyphenylene polyamines of greater functionality, the precise composition depending on the ratio of aniline / formaldehyde in known manner. The polyisocyanates are prepared by phosgenation of the polyamine mixtures and the various proportions of diamines, triamines and higher polyamines which produce related proportions of diisocyanates, triisocyanates and higher polyisocyanates. The relative proportions of higher diisocyanate, triisocyanate and polyisocyanate in unpurified diphenylmethane diisocyanate compositions determine the average functionality of the compositions, ie the average number of isocyanate groups per molecule. By varying the proportions of the starting materials, the average functionality of the polyisocyanate compositions can be varied from a little more than 2 to 3 or even higher. In practice, however, the average number of isocyanate functionality is preferably in the range of 2.35-2.9. The NCO value of these polymeric MDI is at least 30% by weight. Such compositions contain from 30 to 65% by weight of diphenylmethane diisocyanate, the rest being polymethylene-polyphenylene polyisocyanates of greater than two functionality together with the by-products formed in the manufacture of such polyisocyanates by phosgenation. These products that are liquid are convenient for use in accordance with the present invention. The polyols having an average nominal hydroxyl functionality of 2-3 and an average number of molecular weight of 1000 to 12000 (polyol 2) and the polyol used in preparing the semi-prepolymer a) can be selected from polyester polyols, polyester amide polyols, polythioethers polyols, polycarbonate polyols, polyacetal polyols, polyolefin polyols, polysiloxane polyols and especially polyether polyols. The polyether polyols which may be used include products obtained by the polymerization of a cyclic oxide, for example ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran in the presence, where necessary, of polyfunctional initiators. Suitable initiator compounds contain a plurality of active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethanolamine, diethanolamine, triethlonamine, toluenediamine, diethyl toluene diamine, cyclohexanediamine, cyclohexanedimethanol, glycerol, trimethylolpropane 1, 2, 6 -hexantriol. Mixtures of initiators and / or cyclic oxides can be used. Especially useful polyether polyols include polyoxypropylene diols and triols and polyoxyethylene polyoxypropylene diols and triols obtained by the simultaneous or sequential addition of ethylene and di- or trifunctional di-propylene oxides as fully described in the prior art. The random copolymers having oxyethylene contents of 10-80%, block copolymers having oxyethylene contents of up to 50%, based on the total weight of oxyalkylene units can be mentioned, in particular those having at least part of the oxyethylene groups at the end of the polymer chain. Mixtures of the diols and triols may be particularly useful. Small amounts of polyoxyethylene diols and triols can also be used; the amount in general is less than 20% by weight of the amount of the polyol 2) used. The polyester polyols which may be used include the hydroxyl-terminated reaction products of polyhydric alcohols, such as ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cycloxandimethanol, glycerol, trimethylolpropane or polyether. polyols or mixtures of such polyhydric alcohols and polycarboxylic acids, especially dicarboxylic acids or their ester-forming derivatives, for example succinic, glutaric and adipic acids or their dimethyl esters, sebasic acid, phthalic anhydride, tetrachlorophthalic anhydride or dimethyl terephthalate or their mixtures. Polyesters obtained by the polymerization of lactones, for example caprolactone, together with a polyol, or hydrocarboxylic acids such as hydroxycaproic acid can also be used.

The polyester amides can be obtained by the inclusion of aminoalcohols such as ethanolamine in polyesterification mixtures. The polyester polyols which may be used include the products obtained by the condensation of thiodiglycol either alone or with other glycols, alkylene oxides, dicarboxylic acids, formaldehyde, amino alcohols or aminocarboxylic acids. The polycarbonate polyols which may be used include the products obtained by the reaction of diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol or tetraethylene glycol with diaryl carbonates for example diphenyl carbonate or with phosgene. The polyacetal polyols which may be used include those prepared by reacting glycols such as diethylene glycol, triethylene glycol or hexanediol with formaldehyde. Suitable polyacetals can also be prepared by the polymerization of cyclic acetals. Suitable polyolefin polyols include homo- and copolymers of butadiene terminated in hydroxy and suitable polysiloxane polyols include polydimethylsiloxane diols and triols. Other polyols which can be used as the polyol 2) and / or in the preparation of the semi-prepolymer a) comprise dispersions or solutions of polymers of addition or condensation in polyols of the types described in the above. Such modified polyols, often mentioned, as "polyol polymer" have been fully described in the prior art and include the products obtained by the in situ polymerization of one or more vinyl monomers, for example styrene and / or acrylonitrile, in polyols polymeric, for example, polyether polyols, or by the in situ reaction between a polyisocyanate and an amino- and / or hydroxy-functional compound such as triethanolamine in a polymeric polyol. Polyoxyalkylene polyols containing from 5 to 50% by weight of the dispersed polymer are particularly useful. Particle sizes of dispersed polymers of less than 50 microns are preferred. The average number of molecular weight of the polyols 2) and the polyols used in the preparation of the semi-prepolymer a) is preferably 1000-8000 and more preferably 1500-7000; the hydroxyl value is preferably in the range of 15-200 and more preferably 20-100. Most preferred are polyoxyethylene-polyoxypropylene polyols having an average molecular weight number and 2000-7000, an average nominal functionality of 2-3 and an oxyethylene content of 10-25% by weight, preferably having the groups oxyethylene at the end of the polymer chain. During the past few years, various methods have been described for preparing polyether polyols that have a low level of unsaturation. These developments have made it possible to use polyether polyols at the upper end of the molecular weight range, since many polyols can now be prepared with an acceptably low level of unsaturation. In accordance with the present invention, polyols having a low level of unsaturation can also be used. In particular, such high molecular weight polyols having a low level of unsaturation, can be used to prepare flexible foams having a high bounce of ball. The semipolymer al. Isocyanate-terminated is prepared by first mixing the diphenylmethane diisocyanate and the polymethylene-polyphenylene polyisocyanate. Subsequently, the polyol is added and the mixture is allowed to react. Such a reaction is carried out at 60-100 ° C and in general the use of the catalyst is not necessary. The relative amount of polyisocyanate and polyol depends on the desired NCO value of the semi-prepolymer, the NCO value of the polyisocyanate used and the OH value of the polyol and can be easily calculated by those skilled in the art. After the above reaction is completed, the polymethylene-polyphenylene a2 polyisocyanate. it is added and mixed. The "MDI functionality" of the polyisocyanate composition according to the present invention, is 2.15-2.35 and preferably 2.20-2.30. The chain crosslinking and extension agents, which can optionally be used (compound 3) reactive with isocyanate) can be selected from amines and polyols containing 2-8 and preferably 2-4 amine and / or hydroxy groups such as ethanolamine, diethanolamine, triethanolamine, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, sucrose, polyethylene glycol having a molecular weight of at most 999, toluenediamine, diethyl toluene diamine, cyclohexanediamine, phenyldiamine, diphenylmethanediamine, alkylated diphenylmethanediamine and ethylenediamine. The amount of chain crosslinking and extension agents is, if applicable, up to 25, preferably up to 10 parts by weight per 100 parts by weight of polyol 2). The auxiliaries and additives which among others can be used are the formation of urea and urethane increasing catalysts such as tertiary amines and tin compounds, surfactants as stabilizers, and pyro-retardants, fillers and anti-oxidants.

The flexible polyurethane foams are prepared by combining and mixing the ingredients l) -6) and allowing the mixture to form a foam. Preferably the ingredients 2) -6) are premixed and subsequently combined with the polyisocyanate. The relative amounts of polyisocyanate on the one hand and ingredients 2) -6) on the other hand depend on the desired index and can be easily calculated by those skilled in the art. The process can be used to manufacture a supply of flexible molded boards or foams. The foams in general have a density of 15-80 kg / m ^ and can be used as cushioning material in furniture, car seats and mattresses. The present invention is illustrated by the following Examples Example A semi-prepolymer is prepared by 1) mixing 29. 6 parts by weight of a diphenylmethane diisocyanate containing 85% by weight of 4,4'-diphenylmethane diisocyanate and 15% by weight of 2,4'-diphenylmethane diisocyanate and 15 parts by weight of a polymethylene-polyphenylene polyisocyanate having an NCO value of 30.7% by weight and an average isocyanate functionality of 2.7, 2) adding 45.4 parts by weight of a polyoxyethylene-polypropylene polyol having a nominal functionality of 3, an average molecular weight number of 6000 and an oxyethylene content of 15% by weight (all at the end) followed by mixing and 3) allowing this mixture to react at 85 ° C for 4 hours. To the semi-prepolymer thus obtained, which has an NCO value of 15.1% by weight, 10 parts by weight of the above polyisocyanate are added. The composition obtained was an isocyanate composition according to the present invention; tube an NCO value of 16.7% by weight and a viscosity of 1095 mPa. at 25 ° C; the composition was transparent and stable for more than two weeks at 0 ° C and at room temperature (stability was determined visually, when solids and turbidity were visually absent, the composition was considered stable) and had an "MDI functionality" of 2.25. A flexible foam was prepared by mixing in a container 100 parts of the above isocyanate composition according to the invention and an isocyanate-reactive composition (index 77) comprising 50 parts by weight (ppp) of the above polyol, 4.3 ppi of water, 4.3 ppp of a polyoxyethylene polyol having a nominal functionality of 3 and an average number of molecular weight of 1200, 1.45 ppp of surfactant SH210, 0.85 ppp of 1,2-dimethyl imidazole as a catalyst and 0.03 ppp of Niax Al as a catalyst. The mixture is allowed to react and foam under free rise conditions. The foam obtained was a flexible foam having a free increase density of 32 kg / m3.

Claims

1. A process for preparing a flexible polyurethane foam by reacting I) an organic polyisocyanate with II) a polyol having a nominal average hydroxyl functionality of 2-3 and average molecular weight number from 1000 to 12000; and optionally with III) an isocyanate-reactive compound containing at least 2 hydrogen atoms reactive with isocyanate and having an average number of molecular weight of 60 to 999; using IV) a blowing agent; and optionally V) a catalyst; and optionally VI) other auxiliaries and additives known per se, is characterized in that it comprises: a) the polyisocyanate is a polyisocyanate composition having an NCO value of 11-22% by weight, which is a mixture of al. 75-95 parts by weight of an isocyanate-terminated semi-prepolymer having an NCO value of 9-20% by weight, prepared by reacting an excessive amount of a polyisocyanate composition, consisting of 35-75% by weight of diisocyanate of diphenylmethane and 25-65% by weight of polymethylene-polyphenylene polyisocyanate, with a polyol having a nominal average hydroxyl functionality of 2-3 and an average number of molecular weight of 1000 to 12,000; and a2. 5-25 parts by weight of a polymethylene-polyphenylene polyisocyanate; b) 25-120 parts by weight of polyol 2) are used per 100 parts by weight of the organic polyisocyanate; c) Water is used as the blowing agent in an amount of 3-15 parts by weight per 100 parts by weight of polyol 2); and d) the reaction is carried out at an index of 40-130.

2. The process according to claim 1, characterized in that the organic polyisocyanate has an MDI functionality of 2.15-2.35.

3. A process according to claims 1-2, characterized in that the organic polyisocyanate has an NCO value of 13-20% by weight, the semi-prepolymer has an NCO value of 11-18% by weight, the amount of the polyol 2) is 35-100 parts by weight per 100 parts by weight of the organic polyisocyanate, the amount of water is 5-12 parts by weight per 100 parts by weight of polyol 2) and the index is above 70 to 100.

4. The reaction system comprising: I). an organic polyisocyanate; II). a polyol having a nominal average hydroxyl functionality of 2-3 and an average number of molecular weight of 1000 to 12,000; and optionally III). an isocyanate reactive compound containing at least two isocyanate reactive hydrogen atoms and having an average molecular weight number of 60 to 999; IV). a blowing agent; and optionally V). a catalyst; and optionally VI). other auxiliaries and additives known per se, the system is characterized in that it comprises a) the polyisocyanate is a polyisocyanate composition having an NCO value of 11-22% by weight, which is a mixture of al. 75-95 parts by weight of an isocyanate-terminated semi-prepolymer having an NCO value of 9-20% by weight, prepared by reacting an excessive amount of polyisocyanate composition, which consists of 35-75% by weight of diisocyanate of diphenylmethane and 25-65% by weight of polymethylene-polyphenylene polyisocyanate, with a polyol having a nominal average hydroxyl functionality of 2-3 and an average number of molecular weight of 1000 to 12,000; and a2. 5-25 parts by weight of a polymethylene-polyphenylene polyisocyanate; b) 25-120 parts by weight of polyol 2) is used per 100 parts by weight of the organic polyisocyanate; c) the water is used as the blowing agent in an amount of 3-15 parts by weight per 100 parts by weight of polyol 2); and d) the relative amount of the polyisocyanate 1) with respect to the other ingredients is such that when the index is combined it is 40-130; with the proviso that the polyisocyanate is kept in a separate container of the isocyanate-reactive compounds.

5. The reaction system according to claim 4, characterized in that the organic polyisocyanate has an MDI functionality of 2.15-2.35.

6. The reaction system according to claims 4-5, characterized in that the organic polyisocyanate has an NCO value of 13-20% by weight, the semi-prepolymer has an NCO value of 11-18% by weight, the amount of the polyol 2) is 35-100 parts by weight per 100 parts by weight of the organic polyisocyanate, the amount of water is 5-12 parts by weight per 100 parts by weight of polyol 2) and the index is above 70 to 100

7. The organic polyisocyanate composition, characterized in that the composition has an NCO value of 11-22% by weight and is a mixture of al. 75-95 parts by weight of an isocyanate-terminated semi-prepolymer having an NCO value of 9-20% by weight, prepared by reacting an excess amount of a polyisocyanate composition, consisting of 35-75% by weight of diphenylmethane diisocyanate and 25-65% by weight of polymethylene-polyphenylene polyisocyanate, with a polyol having a nominal average hydroxyl functionality of 2-3 and an average number of molecular weight of 1000 to 12,000; and a2. 5-25 parts by weight of a polymethylene-polyphenylene polyisocyanate.

8. The composition according to claim 7, characterized in that the MDI functionality of the composition is 2.15-2.35.

9. The composition according to claims 7-8, characterized in that the composition has an NCO value of 13-20% by weight and the semi-prepolymer has an NCO value of 11-18% by weight.

10. The composition according to claims 7-9, characterized in that the composition has an NCO value of more than 15 to 20% by weight and the semi-prepolymer has an NCO value of 13 to 18% by weight.