PROCESS FOR PREPARING A POLYMERIC FOAM USING A PERFLUOROCHEMICAL COMPOUND DISSOLVED OR DISPERSED IN A HYDROFLUOROETHER

Abstract: The invention provides a method of making a polymeric foam comprising the step of vaporizing a blowing agent composition comprising perfluorochemical compound dissolved or dispersed in hydrofluoroether in the presence of at least one foamable polymer and a precursor composition thereof, said hydrofluoroether and perfluorochemical compounds being liquids at atmospheric pressure and about 20 DEG C. Also provided are blowing agent compositions and foamable compositions useful in such process.

Description: PROCESS FOR PREPARING A POLYMERIC FOAM USING A PERFLUOROCHEMICAL COMPOUND DISSOLVED OR DISPERSED IN A HYDROFLUOROETHER Field of the Invention The present invention relates to a process for making a polymeric foam using a perfluorochemical compound as a blowing agent. The invention further relates to a foamable composition and blowing agent composition comprising a perfluorochemical compound and hydrofiuoroether. Background of the Invention According to "Cellular Materials," Encyclopedia of Polymer Science and Engineering, vol. 3, pages 1-59, (2d ed. John Wiley & Sons, 1985), foamed plastic is defined as a plastic in which the apparent density decreases substantially with the presence of numerous cells disposed through its mass. The gas phase in a foamed plastic is generally distributed in cells. Blowing agents produce gas used to generate cells in foamable polymeric materials, for example, to make foamed insulation. Physical blowing agents form cells by a phase change, for example, a liquid may be volatilized or a gas dissolved in a polymer under high pressure. Low boiling liquids, particularly chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), are used throughout the world on a large scale to produce foamed plastics. However, CFCs and HCFCs are linked to the destruction of the earth's protective ozone layer. See Encyclopedia, vol. 2, page 437. Commercially important liquid blowing agents are aliphatic hydrocarbons and their chloro- and fluoro-derivatives. For example, isomers of pentane, hexane, and heptane are used mainly in the production of very low density polystyrene foam. These liquids tend to be inexpensive and low in toxicity but they are highly flammable. See Encyclopedia, vol. 2, page 434. Production of cellular plastic products, such as cellular polyurethane elastomers and flexible, semi-rigid or rigid polyurethane foams in the presence of catalysts, blowing agents, processing aids or additives is described in numerous patents and publications in the literature. A survey of methods of producing cellular polyurethane elastomers, polyurethane foams and polyisocyanurate foams, their mechanical properties and their use can be found, for example, High Polymers, Vol. 14, "Polyurethanes," Parts I and U by J. H. Saunders and K. C. Frisch (Interscience Publishers, New York 1962 and 1964), Plastics Handbook, Volume VII, "Polyurethanes," 1st ed. 1966, published by R. Vieweg and A. Hochtlen and 2d ed. 1983, published by G. Oertel (Carl Hanser Verlag, Munich), and "Integral Foams", published by H. Piechota and H. Rohr (Carl Hanser Verlag, Munich, 1975). Essentially two types of blowing agents are used to produce cellular polyurethanes: (1) low boiling inert liquids that evaporate under the influence of the exothermic polymerization process, for example, alkanes, such as butane, n-pentane or cyclopentane, halogenated hydrocarbons or halogenated fluorocarbons, such as methylene chloride, dichloromonofluoromethane, and trichlorofluoromethane; and (2) chemical compounds that form gaseous blowing agents by means of a chemical reaction or thermal decomposition, such as isocyanate groups reacted with water to produce carbon dioxide. U.S. Patent No. 4,972,002 describes producing cellular plastics by the polyisocyanate polyaddition process by reaction of (a) organic and/or modified organic polyisocyanates with (b) at least one high molecular compound with at least two reactive hydrogen atoms and, optionally, (c) low molecular weight chain extenders and/or cross- linking agents in the presence of (d) blowing agents, (e) catalysts, (f) additives and/or processing aids, wherein the blowing agents are low boiling fluorinated aliphatic and/or cycloaliphatic hydrocarbons that have 3 to 8 carbons. According to the teaching of this patent, the uniform fine celled structures are obtained by appropriate emulsification of the blowing agent that is insoluble or sparingly soluble in the reaction mixture. The cost of this type of blowing agent however presents a severe disadvantage. U.S. Patent No. 5,290,823 discloses a blowing agent mixture for use in the production of rigid polyurethane foams. The mixture comprises from 5 to 40% by weight of highly fluorinated or perfluorinated compound, from 30 to 95% by weight of cyclopentane and from 0 to 45% by weight of further aliphatic and/or cycloaliphatic hydrocarbon compounds having 4 to 8 carbon atoms. Since substantial amounts of the fluorinated blowing agent are replaced by cyclopentane and other hydrocarbon blowing agents, the blowing agent is less expensive than the blowing agent mixture disclosed in U.S. Patent No. 4,972,002. Also in this patent the fact that the fluorinated blowing agent is sparingly soluble or insoluble in the reactive mixture is taught to be essential to obtain a fine cell structure. The poor solubility, although effective in producing desirable foams, also presents disadvantages in the production of the foam. For example, the foamable emulsion produced has a low stability requiring continuous and vigorous stirring to maintain the emulsion. Moreover, the fluorinated blowing agent cannot be readily dissolved in the cyclopentane blowing agent so that both blowing agents need to be stored separately prior to their use in the foaming process. U.S. Patent No. 4,981,879 describes a process for preparing cellular polymers having urethane groups, isocyanurate groups, or both. The cellular polymers are prepared by reacting an organic polyisocyanate with a polyol in the presence of a blowing agent, typically a hydrocarbon, hydrochlorofluorocarbon, or chlorofluorocarbons, a catalyst and a perfluorinated hydrocarbon or a mixture of perfluorinated hydrocarbons, such that the lower boiling perfluorinated hydrocarbons can function as a co-blowing agent. According to this U.S. patent, the perfluorochemical additive results in a size reduction and an improved initial k-factor relative to foams produced without the perfluorochemical additive. The use of unsaturated perfluorochemicals as blowing agent or co-blowing agent is described in U.S. Patent No. 5,539,008. The use of the unsaturated perfluorochemical as co-blowing agent is said to be preferred due to cost and availability considerations. Conventional blowing agents disclosed for use in combination with the unsaturated perfluorochemical blowing agent include hydrocarbons such as pentane and cyclopentane. U.S. Patent No. 5,210,106 discloses a blowing agent emulsion that comprises as a blowing agent a mixture of one or more low boiling hydrochlorofluorocarbon and/or one or more hydrofluorocarbon and one or more low boiling, chlorine-free perfluorinated compound; a fluorochemical surfactant and a continuous organic phase. U.S. Patent No. 5,162,384 discloses a blowing agent emulsion comprising at least one low boiling, perfluorinated, N-aliphatic, cyclic 1,3-, or 1 ,4-aminoether blowing agent for use in a foamable polymerizable reaction mixture to produce a foamed plastic. U.S. Patent No. 4,997,706 discloses the use of C 2-6 polyfluorocarbon compound containing no chlorine or bromine atoms as physical blowing agent in the preparation of rigid, closed-cell, polymer foams. It is disclosed that the loss of thermal insulation with time of polyurethane foams produced with such blowing agents can be substantially reduced. Summary of the Invention The invention provides a process for preparing polymeric foam comprising the step of vaporizing a blowing agent composition comprising perfluorochemical compound dissolved or dispersed in hydrofiuoroether in the presence of at least one foamable polymer or a precursor composition thereof. Said hydrofiuoroether and perfluorochemical compound are liquids at atmospheric pressure and about 20°C and mixtures of perfluorochemical compound and hydrofluoroethers may be employed in the invention. Preferably, the blowing agent composition also contains one or more co-blowing agents other than said perfluorochemical compound or hydrofluoroethers. One advantage of the invention is that the blowing agent composition is more stable (i.e., it does not phase separate) because hydrofiuoroether substantially increases the solubility of the perfluorochemical compound in the co-blowing agent. Also, the solubility of the blowing agent composition in the foamable polymer or precursor composition thereof is improved. Nevertheless, despite the improved solubility of the perfluorochemical compound, the foams prepared according to the invention (and particularly rigid polyurethane foams), show uniform fine cells and good thermal insulation. The invention also provides a homogeneous blowing agent composition comprising perfluorochemical compound, hydrofiuoroether and co-blowing agent other than said perfluorochemical compound wherein the hydrofiuoroether and perfluorochemical compound are liquids under atmospheric pressure at 20°C. Also, the invention provides a foamable composition comprising a foamable polymer or a precursor composition thereof and the blowing agent composition. Detailed Description of the Invention The blowing agent composition of the invention comprises a perfluorochemical compound dissolved or dispersed in a hydrofluoroether. In the invention, a polymeric foam is produced by vaporizing the perfluorochemical compound in the presence of a foamable polymer or precursor composition thereof. Typically, the perfluorochemical compound is used in an amount of about 0.05 to about 2.5 % by weight of the total foamable composition. The amount of hydrofluoroether will generally be sufficient to dissolve or disperse all of the perfluorochemical compound into the hydrofluoroether mixtures of perfluorochemical compounds and hydrofluoroethers. The perfluorochemical compounds for use in the present invention are preferably free of other halogens such as chlorine or bromine and include a perfluorinated saturated or unsaturated hydrocarbon compound and in particular they include perfluoroaliphatic compounds, perfluorocycloaliphatic compounds, perfluoroolefin compounds, perfluorocycloolefin compounds and perfluoroaliphatic, perfluorocycloaliphatic, perfluoroolefin or perfluorocycloolefin compounds containing heteroatoms such as divalent oxygen, trivalent nitrogen and polyvalent sulfur. Preferably, the perfluorochemical compound contains about 4 to about 12 carbon atoms. Specific examples include perfluoroalkanes, such as perfluorobutane, perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane; perfluorocycloalkanes, such as perfluorocyclobutane, perfluorodimethylcyclobutane, perfluoromethylcyclopentane; perfluoroethers, such as perfluoro-2-butyl-tetrahydrofuran; formals, such as perfluoro-3,5- dioxaheptane; perfluoroamines, such as perfluorotriethylamine, perfluorotripropylamine, perfluorotributylamine, perfluoro-N-methyl pyrrolidine; perfluoroaminoethers, such as perfluoro-N-methyl morpholine; and perfluorinated sulfur compounds. Still further suitable perfluorochemical compounds include the perfluorinated heterocyclic compounds disclosed in U.S. Patent No. 5,162,384. Examples of perfluoroolefin compounds and perfluorocycloolefin compounds include hexafluoropropene dimers, e.g., perfluoro(4- methylpent-2-ene) and perfluoro(2-methylpent-2-ene); hexafluoropropene trimers, e.g., perfluoro(4-methyl-3-isopropylpent-2-ene) and perfluoro(2,4-dimethyl-3-ethylpent-2-ene); tetrafluoroethylene oligomers, e.g., perfluoro(3-methylpent-2-ene), perfluoro(3,4- dimethylhex-3-ene), and perfluoro(2,4-dimethyl-4-ethylhex-2-ene); perfluoro(l-pentene); perfluoro(2-pentene); perfluoro(l-hexene); perfluoro(2 -hexene); perfluoro(3-hexene); perfluoro(l-heptene); perfluoro(2-heptene); perfluoro(3-heptene); hexafluorobenzene; octafluorotoluene; decafluoro-o-xylene; decafluoro-m-xylene; decafluoro-p-xylene; perfluorocyclopentene; isomers of C 6 Fιo, e.g., perfluorocyclohexene, perfluoro(l- methylcyclopentene), perfluoro(3-methylcyclopentene), and perfluoro(4- methylcyclopentene); perfluoro( 1-methylcyclohexene); perfluoro(3-methylcyclohexene); perfluoro(4-methylcyclohexene); perfluoro(oxaalkenes), e.g., perfluoro(3-oxahex-l-ene), perfluoro(3-oxahept-l-ene), and perfluoro(3-oxa-4-methylpent-l-ene); and perfluoro(3- ethyl-3-azapent- 1 -ene). Still further suitable perfluorinated compounds for use in this invention include perfluorinated ketones. Preferably the perfluorinated ketone is normally liquid, i.e., liquid at 20°C and atmospheric pressure, and examples of such ketones include perfluorinated aliphatic ketones having at least about 4 carbon atoms. Preferably, the boiling point of the perfluorinated ketone is between about 20°C to about 120°C. A highly preferred perfluorinated ketone for use in this invention corresponds to the following formula (I): O O ι I I I I 2 Rr— C— (Q-C) n -R f 2 wherein R f 1 and R f 2 each independently represents a luorinated aliphatic group, Q represents a fluorinated alkylene group or a bond and n represents 0 or 1. Preferably at least one of R f 1 , R f 2 , and Q are perfluorinated, most preferably all three are perfluorinated. Particular examples of perfluorinated ketones useful in this invention include: C 2 F 5 COCF(CF 3 ) 2 C 2 F 5 COCF 3 (CF 3 ) 2 CFCOCF(CF 3 ) 2 CF 3 COCF 2 COCF 3 Preferably the hydrofluoroether, i.e., a partially fluorinated ether, comprises a perfluorinated aliphatic group bonded to a hydrocarbon group by an oxygen atom. The perfluoroaliphatic group may contain one or more catenary heteroatoms such as oxygen, nitrogen or sulfur, although oxygen and nitrogen are preferred, if present. More preferably, the perfluoroaliphatic moiety comprises two to about ten carbon atoms and may optionally contain either oxygen and/or nitrogen catenary heteroatoms, and the alkyl moieties comprise one to about four carbon atoms. Particularly preferred fluorinated ethers correspond to the following formula: (R h -O) x -R f (IT) wherein: x is 1 or 2; Rh represents an alkyl group having 1 to about 4 carbon atoms; R f represents a perfluorinated aliphatic group comprising at least two carbon atoms, preferably between 2 and about 9 carbon atoms, and optional catenary heteroatoms such as oxygen, nitrogen and sulfur atoms. When x is 1, R f preferably is selected from the group consisting of linear or branched perfluoroalkyl groups, perfluorocycloalkyl groups containing a perfluoroalkyl group, perfluorocycloalkyl groups, linear or branched perfluoroalkyl groups having one or more catenary heteroatoms, perfluorocycloalkyl groups containing a perfluoroalkyl group having one or more catenary heteroatoms and perfluorocycloalkyl groups having one or more catenary heteroatoms. Particularly preferred catenary heteroatoms include oxygen or nitrogen atoms. When x is 2, R is preferably selected from the group consisting of linear or branched perfluoroalkylene groups, perfluorocycloalkyl groups containing a perfluoroalkylene group, perfluorocycloalkylene groups, linear or branched perfluoroalkylene groups having one or more catenary heteroatoms, perfluorocycloalkyl groups containing a perfluoroalkylene group having one or more catenary heteroatoms and perfluorocycloalkylene groups having one or more catenary heteroatoms. Particularly preferred heteroatoms include oxygen and nitrogen atoms. Most preferably, x is 1 , and the hydrofluoroether is normally liquid, R f is selected from the group consisting of linear or branched perfluoroalkyl groups having from 3 to about 9 carbon atoms, perfluorocycloalkyl-containing perfluoroalkyl groups having from 5 to about 7 carbon atoms, and perfluorocycloalkyl groups having from 5 to about 6 carbon atoms; R h is a methyl or ethyl group; Rf can contain one or more catenary heteroatoms; and the sum of the number of carbon atoms in Rf and the number of carbon atoms in Rh is greater than or equal to about 4. Representative examples of hydrofluoroethers suitable for use in the processes and composition of the invention include the following compounds : n-GtFoOCHs, n-C 4 F 9 OCK 2 CU i , CF 3 CF(CF 3 )CF 2 OCH 3 , CF 3 CF(CF 3 )CF 2 OC 2 H 5 , C 8 F 17 OCH 3 , CH 3 O-(CF 2 ) 4 -OCH 3 , CsFnOC^s, C 3 F 7 OCH 3 , CF 3 OC 2 F 4 OC 2 H 5 , C 3 F 7 OCF(CF 3 )CF 2 OCH 3 , (CF 3 ) 2 CFOCH 3 , (CF 3 )COCH 3 , C4F9OC2F4OC 2 F4OC2H 5 , C 4 F 9 O(CF 2 ) 3 OCH 3 , Q r F ~ \ N(CF 2 ) 3 OCH 3 CH 3 OCF 2 - -CF2OCH3 O r F ~ \ NCF 2 CF 2 OCH 3 and 1 , 1 -dimethoxyperfluorocyclohexane. In a particularly preferred embodiment of this invention, the blowing agent composition further comprises a co-blowing agent other than the perfluorochemical compound. Although the perfluorochemical compounds are effective blowing agents, they can be expensive and incorporating another less expensive blowing agent in the blowing agent composition can be advantageous. Such compositions can be optimized in terms of cost and performance. In this preferred embodiment, the hydrofluoroether can increase the compatibility of the perfluorochemical compound and co-blowing agent. Examples of useful co-blowing agents can include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), hydrochlorocarbons (HCCs), iodofluoro carbons (IFCs), and hydrocarbons. The co-blowing agent for use in this invention should have a boiling point of from about -45°C to about 100°C at atmospheric pressure. Preferably at atmospheric pressure the co-blowing agent has a boiling point of at least about 20°C, more preferably between about 20°C and about 100°C, and most preferably between about 30°C and about 65°C. Examples of co-blowing agents that can be used in the invention include aliphatic and cycloaliphatic hydrocarbons having about 5 to about 7 carbon atoms, such as n- pentane and cyclopentane, CFCs such as CFC1 3 (CFC-11) and CC1 2 FCC1F 2 (CFC-113), HFCs such as CF 3 CF 2 CHFCHFCF 3 , CF 3 CH 2 CF 2 H, CF 3 CH 2 CF 2 CH 3 , CF 3 CF 2 H, CH 3 CF 2 H (HFC- 152a), CF 3 CH 2 CH 2 CF 3 , and CHF 2 CF 2 CH 2 F, HCFCs such as CH 3 CC1 2 F, CF 3 CHC1 2 , and CF 2 HC1, HCCs such as 2-chloropropane, and IFCs such as CF 3 I. A preferred blowing agent composition of this invention comprises (in parts by weight) between about 5 and about 50 parts of the co-blowing agent, between about 0.5 and about 10 parts of the perfluorochemical compound and between about 0.1 and about 5 parts of the hydrofluoroether. Foamable polymers suitable for use in the foamable compositions of the invention include polyolefins, e.g., polystyrene, poly( vinyl chloride), and polyethylene. Foams can be prepared from styrene polymers using conventional extrusion methods. The blowing agent composition can be injected into a heat-plastified styrene polymer stream within an extruder and admixed therewith prior to extrusion to form foam. Representative examples of suitable styrene polymers include the solid homopolymers of styrene, α-methylstyrene, ring-alkylated styrenes, and ring-halogenated styrenes, as well as copolymers of these monomers with minor amounts of other readily copolymerizable olefinic monomers, e.g., methyl methacrylate, acrylonitrile, maleic anhydride, citraconic anhydride, itaconic anhydride, acrylic acid, N-vinylcarbazole, butadiene, and divinylbenzene. Suitable vinyl chloride polymers include vinyl chloride homopolymer and copolymers of vinyl chloride with other vinyl monomers. Ethylene homopolymers and copolymers of ethylene with, e.g., 2-butene, acrylic acid, propylene, or butadiene are also useful. Mixtures of different types of polymers can be employed. Precursors of foamable polymers suitable for use in the foamable compositions of the invention include precursors of phenolic polymers, silicone polymers, and isocyanate- based polymers, e.g., polyurethane, polyisocyanurate, polyurea, polycarbodiimide, and polyimide. Precursors of isocyanate-based polymers are preferred, as the blowing agent compositions of the invention are especially useful for preparing polyurethane or polyisocyanurate foams. Thus, preferred foamable compositions of the invention comprise: (a) perfluorochemical compound dissolved or dispersed in hydrofluoroether; (b) at least one organic polyisocyanate; and (c) at least one compound containing at least two reactive hydrogen atoms. Most preferably, the foamable composition further comprises at least one co-blowing agent. Polyisocyanates suitable for use in the preferred compositions of the invention include aliphatic, alicyclic, arylaliphatic, aromatic, or heterocyclic polyisocyanates, or combinations thereof. Any polyisocyanate which is suitable for use in the production of polymeric foams can be utilized. Of particular importance are aromatic diisocyanates such as toluene and diphenylmethane diisocyanates in pure, modified, or crude form. MDI variants (diphenylmethane diisocyanate modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine, or isocyanurate residues) and the mixtures of diphenylmethane diisocyanates and oligomers thereof known in the art as crude or polymeric MDI (polymethylene polyphenylene polyisocyanates) are especially useful. Representative examples of suitable polyisocyanates include ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1 ,6-hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate, 1 , 12-dodecane diisocyanate, cyclobutane- 1 ,3-diisocyanate, cyclohexane- 1,3- and -1,4-diisocyanate (and mixtures of these isomers), diisocyanato-3,3,5-trimethyl-5- isocyanatomethyl cyclohexane, 2,4- and 2,6-toluene diisocyanate (and mixtures of these isomers), diphenylmethane-2,4- and/or -4,4 -diisocyanate, naphthalene- 1,5-diisocyanate, the reaction products of four equivalents of the aforementioned isocyanate-containing compounds with compounds containing two isocyanate-reactive groups, triphenyl methane-4,4',4"-triisocyanate, polymethylene polyphenylene polyisocyanates, m- and p- isocyanatophenyl sulfonyl isocyanates, perchlorinated aryl polyisocyanates, polyisocyanates containing carbodiimide groups, norbornane diisocyanates, polyisocyanates containing allophanate groups, polyisocyanates containing isocyanurate groups, polyisocyanates containing urethane groups, polyisocyanates containing acrylated urea groups, polyisocyanates containing biuret groups, polyisocyanates produced by telomerization reactions, polyisocyanates containing ester groups, reaction products of the above-mentioned diisocyanates with acetals, polyisocyanates containing polymeric fatty acid esters, and mixtures thereof. Distillation residues (obtained in the commercial production of isocyanates) having isocyanate groups can also be used alone or in solution in one or more of the above-mentioned polyisocyanates. Reactive hydrogen-containing compounds suitable for use in the preferred foamable compositions of the invention are those having at least two isocyanate-reactive hydrogen atoms, preferably in the form of hydroxyl, primary or secondary amine, carboxylic acid, or thiol groups, or a combination thereof. Polyols, i.e., compounds having at least two hydroxyl groups per molecule, are especially preferred due to their desirable reactivity with polyisocyanates. Preferred polyols are those having from 2 to about 50, preferably from 2 to about 8, more preferably from 2 to about 4, hydroxyl groups. Such polyols can be, e.g., polyesters, polyethers, polythioethers, polyacetals, polycarbonates, polymethacrylates, polyester amides, or hydroxyl-containing prepolymers of these compounds and a less than stoichiometric amount of polyisocyanate. Generally, the reactive hydrogen-containing compounds utilized in the preferred foamable compositions of the invention have a weight average molecular weight of from about 50 to about 50,000, preferably from about 500 to about 25,000. Representative examples of suitable reactive hydrogen-containing compounds have been described, e.g., by J. H. Saunders and K. C. Frisch in High Polymers, Volume XVI, "Polyurethanes," Part I, pages 32-54 and 65-88, Interscience, New York (1962). Mixtures of such compounds are also useful, and, in some cases, it is particularly advantageous to combine low-melting and high-melting polyhydroxyl-containing compounds with one another, as described in DE 2,706,297 (Bayer AG). Useful polyols include ethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,5-pentane diol, 1,6-hexane diol, 1,8-octane diol, neopentyl glycol, l,4-bis(hydroxymethyl)cyclohexane, 2 -methyl- 1,3- propane diol, dibromobutene diol, glycerol, trimethylolpropane, 1,2,6-hexanetriol, trimethylolethane, pentaerythritol, quinitol, mannitol, sorbitol, diethylene glycol, triethylene glycol, tetraethylene glycol, higher polyethylene glycols, dipropylene glycol, higher polypropylene glycols, dibutylene glycol, higher polybutylene glycols, 4,4 - dihydroxydiphenyl propane, and dihydroxymethyl hydroquinone. Other suitable polyols include the condensation products of polybasic acids and polyols such as polyethylene adipate and polycaprolactone-based polyols, as well as the mixtures of hydroxy aldehydes and hydroxy ketones ("formose") and the polyhydric alcohols obtained therefrom by reduction ("formitol") that are formed in the autocondensation of formaldehyde hydrate in the presence of metal compounds as catalysts and compounds capable of enediol formation as co-catalysts (see, e.g., U.S. Patent No. 4,341,909 (Schneider et al.), U.S. Patent No. 4,247,653 (Wagner), U.S. Patent No. 4,221,876 (Wagner), U.S. Patent No. 4,326,086 (Mohring et al.), and U.S. Patent No. 4,205,138 (Muller et al.), as well as CA 1,088,523 (Bayer AG)). Solutions of polyisocyanate polyaddition products, particularly solutions of polyurethane ureas containing ionic groups and/or solutions of polyhydrazodicarbonamides, in low molecular weight polyhydric alcohols can also be used (see DE 2,638,759). Many other compounds containing isocyanate-reactive hydrogen atoms are useful in the preferred foamable compositions of the invention, as will be apparent to those skilled in the art of polyurethane science and technology. Preferred polymeric foams can be prepared using the preferred foamable compositions of the invention by vaporizing (e.g., by utilizing the heat of precursor reaction) at least one normally liquid, blowing agent in the presence of a perfluorochemical compound dissolved in a hydrofluoroether, at least one organic polyisocyanate and at least one compound containing at least two reactive hydrogen atoms. Preferably, from 1 to 10 parts by weight of perfluorochemical compound and 0.1 to 2 parts by weight of hydrofluoroether is used in combination with from about 100 to about 300 parts by weight of polyisocyanate(s) and from about 100 to about 150 parts by weight of reactive hydrogen-containing compound(s). Most preferably, a co-blowing agent is also used in an amount from 5 to 50 parts by weight. In making a polyisocyanate-based foam, the polyisocyanate, reactive hydrogen-containing compound, and blowing agent composition can generally be combined, thoroughly mixed (using, e.g., any of the various known types of mixing head and spray apparatus), and permitted to expand and cure into a cellular polymer. It is often convenient, but not necessary, to preblend certain of the components of the foamable composition prior to reaction of the polyisocyanate and the reactive hydrogen-containing compound. For example, it is often useful to first blend the reactive hydrogen-containing compound, blowing agent composition, and any other components (e.g., surfactant) except the polyisocyanate, and to then combine the resulting mixture with the polyisocyanate. Alternatively, all components of the foamable composition can be introduced separately. It is also possible to pre-react all or a portion of the reactive hydrogen-containing compound with the polyisocyanate to form a prepolymer. Other conventional components of foam formulations can optionally be present in the foamable compositions of the invention. For example, cross-linking or chain-extending agents, foam-stabilizing agents or surfactants, catalysts and fire-retardants can be utilized. Other possible components include cell regulators, fillers (e.g., carbon black), colorants, fungicides, bactericides, antioxidants, reinforcing agents, antistatic agents, and other additives or processing aids known to those skilled in the art. Preferably, the foamable compositions of the invention include at least one surfactant. Suitable surfactants include fluorochemical surfactants, organosilicone surfactants, polyethylene glycol ethers of long chain alcohols, tertiary amine or alkanolamine salts of long chain alkyl acid sulfate esters, alkyl sulfonate esters, alkyl arylsulfonic acids, fatty acid alkoxylates, and mixtures thereof. Surfactant is generally employed in amounts sufficient to stabilize the foaming reaction mixture against collapse and the formation of large, uneven cells. Typically, from about 0.1 to about 5 percent by weight of surfactant is sufficient for this purpose. Organosilicone surfactants and fluorochemical surfactants are preferred. Catalysts suitable for use in the preferred foamable compositions of the invention include compounds which greatly accelerate the reaction of the reactive hydrogen- containing compounds (or the cross-linking or chain-extending agents) with the polyisocyanates. When used, catalysts are generally present in amounts sufficient to be catalytically effective. Suitable catalysts include organic metal compounds (preferably, organic tin compounds), which can be used alone or, preferably, in combination with strongly basic amines. Representative examples of these and other types of suitable catalysts are described in U.S. Patent No. 4,972,002 (Volkert). Foams prepared from the foamable compositions of the invention can vary in texture from very soft types useful in upholstery applications to rigid foams useful as structural or insulating materials. The foams can be used, for example, in the automobile, shipbuilding, aircraft, furniture, and athletic equipment industries, and are especially useful as insulation materials in the construction and refrigeration industries. The following examples are intended to further illustrate the invention without however the intention to limit the invention thereto. In the examples, all percentage and parts are by weight unless indicated otherwise. EXAMPLES In the following examples and comparative examples, the thermal conductivity (lambda) values of the foams were measured on a 200x200x25 cm 3 test sample, perpendicular to the foam rise direction. The thermal conductivity was measured at a temperature of 23°C, initially and after heat aging at 50°C for 3 weeks, using a Hesto Lambda Control A-50 thermal conductivity analyzer with a reproducibility of + 0.1. Abbreviations The following abbreviations were used in the examples : Isocyanate™ 44 V-20 : polymeric di-isocyanate having an isocyanate content of 31.5 % by weight and a viscosity of 200 + 40 cps at 25°C, commercially available from Bayer AG HFP dimer : hexafluoropropene dimer (C 6 Fι 2 ), available from Hoechst AG HFP trimer : hexafluoropropene trimer (C 9 Fj 8 ), available from Hoechst AG TFE-oligomer : mixture of tetrafluoroethylene oligomers (C 2 H 4 ) n , with n = 4,5 and 6, available from ICI Polyol 1832A/2 : polyether polyol having a hydroxy equivalent weight of 520 mg KOH/g, a water content of 1.9 parts, a catalyst content of 3.7 parts N,N- dimethylcyclohexylamine and a viscosity of about 4000 cps at 25°C, commercially available from Bayer AG under the trade name Baytherm™ VP-PU 1832 A/2 Silicone surfactant B-8423 : available from T.H. Goldschmidt HFE-1 : perfluoropropyl methyl ether, (C 3 F 7 OCH 3 ) can be prepared as described in U.S. Patent No. 5,925,611 (Flynn et al.) at column 20 HFE-2 : perfluorobutyl methyl ether, (C^OCHs), NOVEC™ HFE-7100 Specialty Fluid available from 3M rpm : revolutions per minute pbw: parts by weight Ex: Example FC-10 : FLUORAD™ FC-10 fluorochemical alcohol (N- ethylperfluorooctylsulfonamidoethanol), commercially available from 3M Example 1 In Example 1 , mixtures of perfluorochemical compound, hydrocarbon blowing agents and hydrofluoroether were prepared, in different ratios and at various temperatures. It was observed that clear solutions were obtained when mixtures were prepared comprising n-pentane or cyclopentane / HFP dimer or HFP trimer / HFE-1 or HFE-2 in a ratio between 50/35/15 and 90/8/2 and in a temperature range between about -20°C to 20°C. Examples 2 and 3 and Comparative Examples C-l and C-2 In Example 2, three parts HFP dimer were emulsified in 0.5 parts HFE-1, 15 parts cyclopentane and 122 parts Polyol 1832A/2, using 3.5 parts silicone surfactant B-8423 and a Pendraulic LD-50 high shear mixer at 6000 rpm. 199 parts Desmodur™ V-20 were added to the emulsion while stirring at 6000 rpm for 15 seconds. The resulting mixture was poured in a 350 cm x 350 cm x 60 cm aluminum mold, which was preheated to 50°C. Example 3 and Comparative Examples C- 1 and C-2 were made essentially according to the same procedure as described for Example 2, but using the components and amounts listed in Table 1. The density and thermal conductivity data of the resulting foams (initially and after heat aging) are shown in Table 1. Table 1 As can be seen from the results given in Table 1, the thermal insulation properties of the foams made in Examples 2 and 3 and Comparative Example C-1 were about the same. The polyol blend of Examples 2 and 3 were stable for about 3 days (no phase split observed), whereas the polyol blend of Comparative Example C-1 was only stable for a few hours. The polyol blend of Comparative Example C-1 is therefore less commercially attractive due to its instability. The presence of HFE-1 renders the blend more stable without significantly affecting the thermal insulation properties of the foam. The thermal conductivity data of the Comparative Example C-2 foam prepared with only hydrofluoroether and no perfluorochemical compound, had inferior thermal conductivity properties compared to the foams prepared using perfluorochemical compound. Examples 4 to 9 In Examples 4 to 9, polyurethane foams were prepared essentially according to the procedure of Example 2. The components and their amounts are given in Table 2. The density and thermal conductivity data for the resulting foams are given in Table 2. Table 2 * Oligomeric fluorochemical surfactant as described in Example 1 of U.S. Patent No. 3,787,351 (Olson). The results indicate that the polyurethane foams prepared using the blowing agent composition of the invention had good to very good thermal conductivity, both initially and after heat aging. Examples 10 and 11 In Examples 10 and 11, polyurethane foams were made using a fluorochemical modified isocyanate, prepared according to the following procedure : a 500 ml three necked flask, equipped with a stirrer, thermometer and condensor was charged with 197 g Desmodur™ 44 V-20 and 2 g fluorochemical alcohol FC-10. The mixture was heated to 75°C under nitrogen atmosphere during 4 hours, after which GLC indicated that all fluorochemical alcohol had reacted. Polyurethane foams were prepared essentially according to the procedure for Example 2. The components and their amounts are given in Table 3. The density and thermal conductivity data for the resulting foams are recorded in Table 3. Table 3 The data shows that polyurethane foams prepared according to the invention, and with fluorochemical modified isocyanate had very good thermal conductivity, both initially and after aging at 50°C.

Claims: CLAIMS 1. A process for preparing polymeric foam comprising the step of vaporizing a blowing agent composition comprising a perfluorochemical compound dissolved or dispersed in hydrofluoroether in the presence of at least one foamable polymer or a precursor composition thereof, said hydrofluoroether and perfluorochemical compounds being liquids at atmospheric pressure and about 20°C. 2. A process according to claim 1 wherein the blowing agent composition further comprises co-blowing agent other than said perfluorochemical compound or said hydrofluoroether. 3. A process according to claim 1 wherein said hydrofluoroether comprises a perfluorinated aliphatic group bonded to a hydrocarbon group by an oxygen atom. 4. A process according to claim 1 wherein said hydrofluoroether corresponds to the formula: (R h -O) x -Rf wherein: x is 1 or 2; R h represents an alkyl group having 1 to about 4 carbon atoms and R f represents a perfluorinated aliphatic group comprising at least about two carbon atoms. 5. A process according to claim 1 wherein said perfluorochemical compound is selected from the group consisting of perfluorinated saturated or unsaturated hydrocarbon compounds having at least about 4 carbon atoms. 6. A process according to claim 2 wherein said co-blowing agent is a hydrocarbon. 7. A process according to claim 1 wherein said foamable polymer or a precursor composition thereof comprises at least one organic polyisocyanate and at least one compound containing two reactive hydrogen atoms. 8. A homogeneous blowing agent composition comprising perfluorochemical compound, hydrofluoroether and co-blowing agent other than said perfluorochemical compound and said hydrofluoroether, wherein said perfluorochemical compound and said hydrofluoroether are liquids at atmospheric pressure and 20°C. 9. A homogeneous blowing agent composition according to claim 8 wherein said co-blowing agent is a hydrocarbon compound, said perfluorochemical compound is a perfluorinated saturated or unsaturated hydrocarbon having at least about 4 carbon atoms and said hydrofluoroether corresponds to the following formula: (R h -O) x -R f wherein: x is 1 or 2; R h represents an alkyl group having 1 to about 4 carbon atoms and R f represents a perfluorinated aliphatic group comprising at least about two carbon atoms. 10. A foamable composition comprising a foamable polymer or a precursor composition thereof and a blowing agent composition according to claim 1. 11. A foamable composition according to claim 10 wherein said blowing agent composition further comprises a co-blowing agent other than said perfluorochemical compound or hydrofluoroether. 12. A foamable composition according to claim 11 wherein said perfluorochemical compound is selected from the group consisting of perfluorinated saturated or unsaturated hydrocarbon compounds having at least about 4 carbon atoms and said hydrofluoroether corresponds to the following formula: (R h -O) x -R f wherein: x is 1 or 2; R h represents an alkyl group having 1 to about 4 carbon atoms and R f represents a perfluorinated aliphatic group comprising at least about two carbon atoms. 13. A foamable composition according to claim 11 wherein said foamable polymer or precursor composition thereof comprises at least one organic polyisocyanate and at least one compound containing two reactive hydrogen atoms.

Inventors: DAMS RUDOLF J, DAMS, RUDOLF, J.
Applicants: 3M INNOVATIVE PROPERTIES CO, 3M INNOVATIVE PROPERTIES COMPANY
Application year: 1999
Main classification: C08J9
IPC codes: C08G18, C08J9, C09K3