RIGID POLYURETHANE FOAMS

Abstract: Process for the preparation of open celled rigid polyurethane foams comprising the step of reacting an organic polyisocyanate with an isocyanate-reactive material in the presence of a blowing promoter which is an isocyanate-reactive cyclic carbonate or cyclic urea, and in the presence of an insoluble fluorinated organic liquid and a metal salt catalyst wherein the insoluble fluorinated organic liquid is a perfluorinated acyclic unsaturated organic compound.

Description: DESCRIPTION RIGID POLYURETHANE FOAMS This invention relates to rigid polyurethane foams and especially to open celled rigid polyurethane foams, to methods for their preparation and to their use in evacuated insulation panels. The production of foamed materials based on polyurethane and other polymer systems derived from organic polyisocyanates is well established. Depending upon the formulations used in their manufacture, the products can vary in te;:ture from the soft flexible foams used as cushioning materials to the rigid foams used as insulating or structural materials. Rigid polyurethane foams can be of the closed cell type or of the open cell type. An important application of open celled rigid polyurethane foam is as filler material in evacuated insulation panels as described in European Patent Publications Nos 188806 and 498628. In European Patent Publication No. 498628 (incorporated herein by reference) a process for preparing open celled rigid polyurethane foam is described, said process comprising the step of reacting an organic polyisocyanate with an isocyanate- reactive material in the presence of a blowing promotor being an isocyanate-reactive cyclic compound of formula: (CR ) CR wherein Y is 0 or NR 1 wherein each R 1 independently is a lower alkyl radical of C C; or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C : -C € or (CH 2 ) m -X wherein X is an isocyanate-reactive group which is OH or NH : and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R 1 or R is or comprises an isocyanate-reactive group; and in the presence of an inert insoluble organic liquid which is present as the dispersed phase of an emulsion or a microemulsion and in the presence of a metal salt catalyst. Preferred compounds to be used as inert insoluble organic liquid are described in EP-A-498628 as highly fluorinated or perfluorinated compounds including fluorinated hydrocarbons such as fluorinated (cyclo) alkanes, fluorinated ethers, fluorinated amines, fluorinated hydro:-:yl amines, fluorinated amino-ethers and fluorinated sulfones. A disadvantage of the fluorinated compounds listed in EP-A-498628 is their global warming potential due to their relatively long atmospheric lifetime. Therefore it is an object of the present invention to improve said process for preparing open celled rigid polyurethane foam in respect of the type of fluorinated compound used, in particular in respect of its global warming potential. Accordingly the present invention provides a process for the preparation of open celled rigid polyurethane foams comprising the step of reacting an organic polyisocyanate with an isocyanate-reactive material in the presence of a blowing promotor being an isocyanate-reactive cyclic compound of formula: (C wherein Y is 0 or NR 1 wherein each R 1 independently is a lower alkyl radical of C 1 -C € or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C 2 -C 6 or (CH 2 )-,-X wherein X is an isocyanate-reactive group which is OH or NH- and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R : or R is or comprises an isocyanate-reactive group; and in the presence of an insoluble fluorinated organic liquid which is present as the dispersed phase of an emulsion or a microemulsion and in the presence of a metal salt catalyst, characterised in that said insoluble fluorinated organic liquid comprises a perfluorinated acyclic unsaturated organic compound. The perf luorinated acyclic unsaturated organic compound to be used in the process of the present invention has a shorter atmospheric lifetime than the fluorinated compounds described in EP-A-498628, and thus a lower global warming potential. Further their use does not lead to inferior end products . Thus the present invention provides a more environmentally friendly process for preparing open celled rigid polyurethane foam. The perf luorinated acyclic unsaturated organic compounds to be used in the present process are normally liquid perf luoroolef in compounds. These compounds may contain some residual carbon-bonded hydrogen (generally less than about 0.4 mg/g and preferably less than about 0.1 mg/g) but are preferably completely fluorinated. The perf luoroolef in compound can contain one or more catenary heteroatoms, e.g., nitrogen or o.-iygen atoms. Representative ei-iamples of suitable perf luorinated acyclic unsaturated compounds include h e :-: a f l u o r op r op e n e d ime r s , e . g . , perf luoro (4-methylpent-2-ene) and perfluoro (2- methylpent-2-ene) ; hei-iaf luoropropene trimers, e.g., perfluoro (4-methyl-3-isopropyl-2-ene) and perfluoro ( 2 , 4-dιmethyl-3-ethylpent-2-ene) ; tetraf luoroethylene oligomers, e.g., perfluoro (3- methylpent-2-ene) , perfluoro (3, 4-dimethylhe:-:-3-ene) , and perfluoro (2, 4-di me thyl-4-ethylhe:-:-2-ene perfluoro (1-pentene) ; perfluoro (2-pentene perfluoro (l-he:-:ene) ; perfluoro (1-heptene perfluoro (2-heρtene) ; perfluoro (3-heptene) ; perfluoro (oxaalkenes) , e.g., perfluoro (3-o:-:ahe:-:-l- ene) , perfluoro (3-o:-:ahept-l-ene) , andperfluoro (3-o:-.a- 4-methylpent-l-ene) ; perfluoro (3-ethyl-3-azapent-l- ene) ; and mixtures thereof. Perfluoro (4-methylpent-2- ene) is most preferred. For use in the process of the invention, the perfluorinated acyclic unsaturated compounds preferably have boiling points greater than or equal to about 20°C. More preferably, the compounds have boiling points in the range of from about 45°C to about 125°C. Perfluoroolefin compounds (as well as catenary heteroatom-containing perfluoroolefin compounds) can be prepared by methods such as the decarbo:-:ylation of salts of fluorocarboMylic acids (see, e.g., A.M. Lovelace, D.A. Rausch, and W. Postelnek, "Aliphatic Fluorine Compounds", Chapter III, Reinhold Publishing Corporation, New York (1958)) and the coupling of two or more perfluoroolefins (as described, e.g., in US-P-5, 220, 082, the description of which is incorporated herein by reference) . Her-.afluoropropene oligomers can be prepared by various gas-phase and liquid-phase methods such as those described in, e.g., US-P-5, 25 , 77 , the descriptions of which are incorporated herein by reference. He:-:afluoropropene trimers are also commercially available (e.g., from Fluorochem Limited) . Tetrafluoroethylene oligomers can be prepared by methods such as those described in, e.g., US-P-3, 758, 618 and 4,016,217, the descriptions of which are incorporated herein by reference. In the process of the present invention one or more of said perfluorinated acyclic unsaturated compounds can be used. Further the perfluorinated acyclic unsaturated compound (s) can also be used in combination with other fluorinated compounds. Representative examples of such other fluorinated compounds are given m EP-A-498628. The total amount of insoluble fluorinated organic compounds to be used m the process of the present invention, including the perfluorinated acyclic unsaturated compound (s) ranges from 0.05 to 5 % by weight based on the total reaction system. The insolubility of the fluorinated organic liquid in the reaction mixture usually arises from the fact that it is insoluble in one or more of the major ingredients of the foam formulation, especially the isocyanate-reactive material and/or the polyisocyanate. Solubility m these materials can be determined by conventional techniques. The insoluble fluorinated organic compound (s) will usually be incorporated m the foam-forming reaction mixture in the form of an emulsion or preferably a microemulsion in one of the ma or components, that is to say in the isocyanate-reactive component and/or the polyisocyanate component. Such emulsions or microemulsions may be prepared using conventional techniques and suitable emulsifying agents. Emulsifying agents suitable for preparing stable emulsions or microemulsions of fluorinated liquid compounds in organic polyisocyanates and/or isocyanate-reactive compounds include surfactants chosen from the group of nonionic, ionic (anionic or cationic) and amphoteric surfactants. Preferred surfactants for emulsifying the fluorinated liquid compound in the isocyanate-reactive composition are silicone surfactants, fluoro surfactants and/or alkoxylated alkanes. Particular examples of fluoro surfactants include fluorinated alkyl polyoxyethylene ethanols, fluorinated alkyl alkoxylates and fluorinated alkyl esters. Preferred surfactants for emulsifying the fluorinated liquid compound in the polyisocyanate composition are non-isocyanate-reactive silicone surfactants such as Tegostab B 8407 available from Goldschmidt and SR 234 available from Union Carbide. A preferred compound of formula (I) to be used in the process of the present invention, wherein Y is 0 is an isocyanate-reactive cyclic carbonate which is glycerol carbonate. Preferred compounds of formula (I) wherein Y is NR- are isocyanate-reactive cyclic ureas of formula: and 0 II H-C - C-H I i OH OH The isocyanate-reactive cyclic blowing promotor is used in amounts ranging from 1 to 99 %, preferably from 1 to 60 % by weight based on the total isocyanate-reactive material. Suitable further blowing agents may be used in the method of the present invention such as water or inert low boiling compounds having a boiling point of above -50°C at 1 bar. The amount of water used as blowing agent may be selected in known manner to provide foams of the desired density, typical amounts being in the range from 0.05 to 5 parts by weight per 100 parts by weight of reactive ingredients, although it may be a particular embodiment of the present invention to incorporate up to 10 % by weight or even up to 20 % by- weight of water. Suitable inert blowing agents include, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaliphatic hydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons and fluorine-containing ethers. Suitable hydrocarbon blowing agents include lower aliphatic or cyclic hydrocarbons such as n-pentane, isopentane, cyclopentane, neopentane, hexane and cyclohexane. Preferred metal salt catalysts for use in the present invention are those selected among group la and group Ila metal salts, more preferably among group la and group Ila metal carboxylates. Particularly suitable catalysts for use in the present invention are potassium acetate and potassium ethylhexoate. The metal salt catalyst is used in the process of the present invention in amounts ranging from 0.01 to 3 % by weight based on the total reaction system. Organic polyisocyanates which may be used in the method of the present invention include aliphatic, cycloaliphatic, araliphatic and aromatic polyisocyanates but especially the polyisocyanates proposed in literature for use in the production of foams. Of particular importance are aromatic diisocyanates such as tolylene and diphenylmethane diisocyanate in the well known pure, modified or crude forms. Special mention may be made of the so-called MDI variants (diphenylmethane diisocyanate modified by the introduction of uret ane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues) and the mixtures of diphenylmethane diisocyanate (s) and oligomers thereof known in the art as "crude" or "polymeric" MDI (polymethylene polyphenylene polyisocyanates) . In performing the method of the invention the polyisocyanate may be reacted with the isocyanate- reactive cyclic carbonate or isocyanate-reactive cyclic urea in the absence or presence of other isocyanate-reactive materials. It is preferred, however, to perform the method of the invention in the presence of other isocyanate-reactive materials. Suitable isocyanate-reactive materials generally include polyols, amines, imines and enamines and mixtures thereof. For the preparation of rigid polyurethane foams, suitable isocyanate-reactive compounds, especially polyols, in general have a molecular weight of 62 to 1500 and a functionality of 2 to 8, especially 3 to 8. Polymeric polyols have been fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, with initiators containing from 2 to 8 active hydrogen atoms per molecule. Suitable initiators include polyols, for example, glycerol, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol and sucrose, and polyamines, for example ethylenediamine, tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylene polyamines, and aminoalcohols, for example, ethanolamine, diethanolamine and triethanolamine, and mixtures of such initiators. Other suitable polyols for use in the process of the present invention include polyesters obtained by the condensation of appropriate proportions of glycols and higher functionality polyols with dicarboxylic acids. Still further suitable polyols include hydroxyl terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes. In addition to the ingredients already mentioned the foam-forming mixture may contain one or more other auxiliaries or additives conventional to isocyanate- based foam formulations. Such optional additives include further conventional catalysts, fire retardants, smoke suppressants, organic or inorganic fillers, thixotropic agents, dyes, pigments, mould release agents, surfactants, foam stabilisers and the like. Isocyanate indices of from 70 to 140 will typically be used in operating the method of the present invention but lower indices may be used if desired. Higher indices, for example 150 to 500 or even up to 3000, may be used in conjunction with trimerisation catalysts to make foams containing isocyanurate linkages. To reduce the number of component streams delivered to the final mixing apparatus, the cyclic isocyanate- reactive blowing promotor, the catalyst, the insoluble fluorinated organic compound (s) and 5 optionally other additives may be premixed with one of the major components of the foam formulation, in general with the isocyanate-reactive component. Therefore the present invention also provides an ID isocyanate-reactive composition comprising a blowing promotor being an isocyanate-reactive cyclic compound of formula: 0 II 15 .C. Y Y (I) (CR 2 CR? 20 wherein Y is 0 or NR : wherein each R 1 independently is a lower alkyl radical of C : -C e or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl 25 radical of C : -C 6 or (CH 2 ) [r -X wherein X is an isocyanate-reactive group which is OH or NH 2 and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R- or R is or 30 comprises an isocyanate-reactive group; an insoluble fluorinated organic liquid which is present as the dispersed phase of an emulsion or a microemulsion and a metal salt catalyst, characterised in that said insoluble fluorinated organic liquid comprises a perfluorinated acyclic unsaturated organic compound. The method of the present invention may be put into practice making use of conventional techniques. Thus known mixing methods may be used and the foams may be produced in the form of slabstock, mouldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, paper, plastics or metal. The rigid polyurethane foams prepared in accordance with the method of the invention are of particular use for evacuated insulation panel applications. Evacuated insulation panels generally comprise a low thermal conductivity filler material (such as open celled polyurethane foam) and a vessel formed of a gastight film enveloping said filler, the whole being evacuated to an internal pressure of about 5 mbar or less and then hermetically sealed. General descriptions of the construction of evacuated insulation panels and their use in thermal devices can be found in US Patents Nos 5,066,437, 5,032,439 and 5,076,984 and European Patent Publications Nos 434266, 434225 and 181778, all incorporated herein by reference as well as the references mentioned therein. The invention is illustrated but not limited by the following example. Example The following ingredients were used: Polyol A being a polyether polyol composition of average hydroxyl value 365 mg KOH/g and average functionality 2.9; Tegostab B 8406 being a silicone surfactant available from Goldschmidt; Catalyst LB being a metal salt catalyst available from Imperial Chemical Industries PLC; Fixapret NF being a cyclic urea available from BASF; perfluorohexane (PFH) ; perfluoro (4-methylpent-2-ene) (PFO) available from 3M under the tradename L 12596; SUPRASEC 2185 being a polymeric MDI available from Imperial Chemical Industries PLC. SUPRASEC is a trademark of Imperial Chemical Industries. Rigid foams were prepared on a commercial laminator at 30kg/min application rate using the formulations (amounts are given in parts by weight) as listed in Table 1. Some foam properties are also given in Table 1: isocyanate index, density expressed in kg/πr, closed cell content (CCC) given in % and cell size given in microns. Density (core density) was measured according to DIN 53420 standard. Closed cell content was measured according to BS 4370 Method 10 standard and represents volume % of closed cells. Cell size was measured according to the method described by A. Cunningham in "Proceedings of Conference on Heat and Mass Transfer in Cryoengineering and Refrigeration", September 1986, page 32-49. Blocks of foams were heat treated for 10 minutes at 150°C, pumped down to 0.05 mbar pressure and heat sealed in a metalised film. The initial thermal conductivity (lambda value expressed in mW/mK) was measured according to standard ISO 2581. Results are also given in Table 1. Table 1 Comparative foam Foam ace.to invention Formulation Polyol A 100.3 100.3 Catalyst LB 0.1 0.1 B 8406 4 4 Fixapret NF 1.6 1.6 SUPRASEC 2185 154 154 water 0.25 0.25 PFH 4 - PFO - 4 Foam properties Isocyanate Index 140 140 Density 58.1 58.7 Closed cell 0.6 0.7 content Cell size 170 170 Lambda initial 7.5 7.0 These results show that by using a more environmentally friendly perfluorinated acyclic unsaturated compound the foam properties are not detrimentally influenced.

Claims: CLAIMS Process for the preparation of rigid foams comprising the step of reacting an organic polyisocyanate with an isocyanate-reactive material in the presence of a blowing promotor being an isocyanate-reactive cyclic compound of formula: 0 II wherein Y is 0 or NR 1 wherein each R 1 independently is a lower alkyl radical of C.-C; or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of Cx-C £ or (CH 2 ) π .-X wherein X is an isocyanate-reactive group which is OH or NH : and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of X or R is or comprises an isocyanate-reactive group; and in the presence of an insoluble fluorinated organic liquid which is present as the dispersed phase of an emulsion or a microemulsion and in the presence of a metal salt catalyst, characterised in that said insoluble fluorinated organic liquid comprises a perfluorinated acyclic unsaturated organic compound. Process according to claim 1 wherein the perfluorinated acyclic unsaturated organic compound comprises perfluoro (4-methylpent-2-ene) . Process according to claim 1 or 2 wherein the total amount of insoluble fluorinated organic compounds is between 0.05 and 5 % by weight based on the total reaction system. Process according to any one of the preceding claims wherein the isocyanate-reactive cyclic blowing promotor is a cyclic urea of formula or 0 (I C CH-.-N N-CH: III H-C C-H OH OH 5. Process according to any one of the preceding claims wherein the isocyanate-reactive cyclic blowing promotor is used in amounts ranging from 1 to 99 % by weight based on the total isocyanate-reactive material. 6. Process according to any one of the preceding claims wherein the metal salt catalyst is a group la or group Ila metal carboxylate. 7. Process according to any one of the preceding claims wherein the metal salt catalyst is used in amounts ranging from 0.01 to 3 % by weight based on the total reaction system. 8. Isocyanate-reactive composition comprising a blowing promotor being an isocyanate-reactive cyclic compound of formula: 0 6 Y Y (CR..; ■ CR- wherein Y is 0 or NR 1 wherein each R : independently is a lower alkyl radical of C : -C £ or a lower alkyl radical substituted with an isocyanate-reactive group; each R independently is hydrogen, a lower alkyl radical of C 1 -C 6 or (CH 2 ) r -X wherein X is an isocyanate-reactive group which is OH or NH 2 and m is 0, 1 or 2; and n is 1 or 2; with the proviso that at least one of R 1 or R is 5 or comprises an isocyanate-reactive group; an insoluble fluorinated organic liquid which is present as the dispersed phase of an emulsion or a microemulsion and a metal salt catalyst, characterised in that said insoluble fluorinated ID organic liquid comprises a perfluorinated acyclic unsaturated organic compound. 9. Rigid open celled polyurethane foam obtainable by the process as defined in any one of claims 1 to 15 7. 10. Evacuated insulation panel comprising a filler material and a vessel formed of a gastight film enveloping said filler, characterised in that 20 said filler material comprises a rigid open celled polyurethane foam as defined in claim 9.

Inventors: DAMS RUDOLF J, DE VOS RIK, DAMS, RUDOLF, J., DE VOS, RIK
Applicants: ICI PLC, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1996
Main classification: C08J9
IPC codes: C08G18, C08G101, C08J9