PROCESS FOR RIGID POLYURETHANE FOAMS

Abstract: Process for preparing rigid polyurethane or urethane-modified polyisocyanurate foams by reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive component comprising more than 2 % by weight of water and from 5 to 50 % by weight of polyester polyols of average functionality below 3, especially crude polyester polyols.

Description: DESCRIPTION PROCESS FOR RIGID POLYURETHANE FOAMS This invention relates to processes for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, to foams prepared thereby, and to novel compositions useful in the process. Rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting the appropriate polyisocyanate and isocyanate- reactive compound (usually a polyol) in the presence of a blowing agent. One use of such foams is as a thermal insulation medium and filler as for example in the construction of water heaters. Recyclability of water heaters has become an important feature. The dismantling of the water heaters needs to be facilitated allowing an easy separation and recovery of all the different materials used to manufacture the water heaters. It is an object of the present invention to provide a rigid polyurethane foam that can be easily recovered from the cavity which is filled by the foam. These objects are met by using in the process of making rigid polyurethane or urethane-modified polyisocyanurate foams from polyisocyanates, isocyanate-reactive components and water as blowing agent, polyester polyols of average functionality below 3 in an amount of between 5 and 50 % by weight based on the total isocyanate-reactive components. The foam prepared according to the process of the present invention shows almost no adhesion to metal as is the cavity wall and thus can easily be recovered from the cavity in any recycling process. The term "polyester polyols" as used herein means products obtained by the condensation of appropriate proportions of glycols and higher functionality polyols with dicarboxylic or polycarboxylic acids; the term includes any minor amounts of unreacted polyol remaining after the preparation of the polyester polyol and/or unesterified polyol added after the preparation. The polyester polyols for use in the present invention advantageously have an average functionality of about 1.5 to 3, preferably about 1.7 to 2.5 and more preferably about 1.8 to 2.3. Their hydroxyl number values generally fall within a range of about 15 to 750, preferably about 30 to 550, more preferably 70 to 550 and most preferably about 200 to 550 mg KOH/g. The molecular weight of the polyester polyol generally falls within the range of about 400 to about 10000, preferably about 1000 to about 6000. Preferably the polyester polyols have an acid number between 0.1 and 20 mg KOH/g; in general the acid number can be as high as 90 mg KOH/g. The polyester polyol can advantageously include up to about 40 % by weight free glycol. Preferably the free glycol content is from 2 to 30, more preferably from 2 to 15 % by weight of the total polyester polyol component. These polyester polyols are preferably present m amounts ranging from 5 to 30 %, more preferably from 10 to 25 % and most preferably from 16 to 23 % by weight based on the total isocyanate-reactive components. The polyester polyols for use in the present invention can be prepared by known procedures from a polycarboxylic acid or acid derivative, such as an anhydride or ester of the polycarboxylic acid, and any polyhydric alcohol. The polyacid and/or polyol components may be used as mixtures of two or more compounds m the preparation of the polyester polyols. The polyols can be aliphatic, cycloaliphatic, aromatic and/or heterocyclic. Low molecular weight aliphatic polyhydric alcohols, such as aliphatic dihydric alcohols having no more than about 20 carbon atoms are highly satisfactory. The polyols optionally may include substituents which are inert in the reaction, for example, chlorine and bromine substituents, and/or may be unsaturated. Suitable ammo alcohols, such as, for example, monoethanolamme, diethanolamme, triethanolamme, or the like may also be used. A preferred polyol component is a glycol. The glycols may contain heteroatoms (e.g., thiodiglycol) or may be composed solely of carbon, hydrogen and oxygen. They are advantageously simple glycols of the general formula C n H 2n (OH) 2 or polyglycols distinguished by intervening ether linkages in the hydrocarbon chain, as represented by the general formula C n H 2n O > . (OH) 2 . Examples of suitable polyhydric alcohols include: ethylene glycol, propylene glycol -(1,2) and -(1,3), butylene glycol -(1,4) and -(2,3), hexanediol - (1,6), octanediol -(1,8), neopentyl glycol, 1, 4-bιshydroxymethyl cyclohexane, 2-methyl-l, 3-propane diol, glycerin, tnmethylolethane, hexanetriol -(1,2,6), butanetriol -(1,2,4), quinol, methyl glucoside, triethyleneglycol, tetraethylene glycol and higher polyethylene glycols, dipropylene glycol and higher polypropylene glycols, diethylene glycol, glycerol, pentaerythritol, trimethylolpropane, sorbitol, manmtol, dibutylene glycol and higher polybutylene glycols. Especially suitable polyols are alkylene glycols and oxyalkylene glycols, such as ethylene glycol, diethylene glycol, dipropylene glycol, tnethylene glycol, tripropylene glycol, tetraethylene glycol, tetrapropylene glycol, trimethylene glycol, tetra ethylene glycol and 1, 4-cyclohexanedιmethanol (1, 4-bιs-hydroxymethylcyclohexane) . The polycarboxylic acid component may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally be substituted, for example, by halogen atoms and/or may be unsaturateα. Examples of suitable carboxylic acids and derivatives thereof for the preparation of the polyester polyols include: oxalic acid, malonic acid, adipic acid, glutaric acid, succinic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, phthalic acid anhydride, terephthalic anhydride, isophthalic acid, terephthalic acid, tπmellitic acid, tetrahydrophthalic acid anhydride, pyromellitic dianhydride, hexahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride, endomethylene tetrahydrophthalic anhydride, glutaric acid anhydride, maleic acid, aleic acid anhydride, terephthalic acid dimethylester, terephthalic acid-bis glycol ester, fumaric acid, dibasic and tπbasic unsaturated fatty acids optionally mixed with monobasic unsaturated fatty acids, such as oleic acids. While the polyester polyols can be prepared from substantially pure reactant materials, more complex ingredients can be used, such as the side-stream, waste or scrap residues from the manufacture of phthalic acid, terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, and the like. These compositions can be converted by reaction with polyols to polyester polyols through conventional transesterification or esterification procedures . Aliphatic and/or aromatic polyester polyols can be used according to the present invention. Mixtures of two or more different polyester polyols can be used. Preferably the polyester polyols for use according to the present invention are crude polyester polyols. By the term "crude polyester polyols" as employed herein is meant any polyester polyol obtained from crude reaction residues or scrap polyester resins . Generally speaking, they consist of mixtures of a number of low and high molecular weight hydroxyl containing components with their overall or average molecular weights and average functionalities falling within a range of from about 255 to about 5000 and from about 2 to about 6, respectively. Preferably, the average molecular weight falls within a range of about 250 to about 1500 with corresponding average functionalities of about 2 to about 4. A most preferred class of crude polyester polyol has an average molecular weight from about 250 to about 1000 and average functionality from about 1.5 to about 3. Those crude polyester polyols obtained from crude reaction residues include a number of sources. One such source comprises the polyester polyols deπveo from phthalic anhydride bottoms as disclosed m US 4521611. A preferred source is best exemplified by the mixtures derived from the so- called DMT (dimethyl terephthalate) process residues by transesterification with low molecular weight aliphatic glycols. Typical DMT polyester polyols, for example, are disclosed in US 3647759 wherein the residue derived from DMT production via air oxidation of p-xylene is utilised. The oxidate residue contains a complex mixture of polycarbomethoxy substituted diphenyls, polyphenyls, and benzylesters of the toluate family. This residue is transesteπfled with an aliphatic diol such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and the like to produce a variety of low cost, predominately hydroxyl-functional polyester polyols with a wide variety of physical properties. Such DMT derived polyester polyols are produced under the name TERATE resins supplied by Hoechst Celanese. Those crude polyester polyols obtained from scrap polyester resins are best exemplified by the mixtures obtained by digesting scrap polyethylene terephthalate (PET) with low molecular weight aliphatic glycols. Typical are the aromatic ester based polyols derived from digesting polyalkylene terephthalate with organic diols and tπols having a molecular weight from 62 to 500 as disclosed in US 4048104; the aromatic polyester polyols obtained from the reaction of polyethylene terephthalate residue with alkylene oxides in the presence of a basic catalyst as disclosed in US 4439549; the aromatic polyester polyols derived from recycled polyethylene terephthalate waste streams, alkylene glycols, and dibasic acid waste streams as disclosed in US 4439550 and US 4444918; the aromatic polyester polycarbonate polyols derived from polyethylene terephthalate residues and alkylene carbonates as disclosed in US 4465793; the liquid terephthalic ester polyols derived from recycled or scrap polyethylene terephthalate and diethylene glycol and one or more oxyalkylene glycols as disclosed m US 4469824; the polyester polyols made by first reacting recycled polyethylene terephthalate scrap with an alkylene glycol followed by reaction with an alkylene oxide as disclosed in US 4485196; the copolyester polyols comprising the reaction products of an aromatic component selected from phthalic derivatives, polyethylene terephthalate, or dimethyl terephthalate with dibasic acid compounds, at least one primary hydroxyl glycol, and at least small amounts of a secondary hydroxyl glycol as taught in US 4559370; and the like. Preferred crude polyester polyols for use in the present invention include Terate 2541 and Terate 2031, which are DMT based polyester polyols, both avaιlab_e from Hoechst Celanese and Isoexter 3471, which is a scrap PET polyester, available from COIM. Two or more different crude polyester polyols can be used in the process of the present invention. Other types of polyester polyols generally used in the production of rigid polyurethane foam can be used addition to the crude polyester polyols; but preferably the total amount of polyester polyols does not exceed 70 % of the total isocyanate-reactive components. Other suitable isocyanate-reactive compounds to be used in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams. Of particular importance for the preparation of rigid foams are polyols and polyol mixtures having average hydroxyl numbers of from 300 to 1000, especially from 300 to 700 mg KOH/g, and hydroxyl functionalities of from 2 to 8, especially from 3 to 8. Suitable 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, tπmethylolpropane, triethanolamme, pentaerythritol, sorbitol and sucrose; polyammes, for example ethylene diamme, tolylene diamine (TDA) , diammodiphenylmethane (DADPM) and polymethylene polyphenylene polyammes; and ammoalcohols, for example ethanolamme and diethanolamme; and mixtures of such initiators. Still further suitable polymeric polyols include hydroxyl terminated polythioethers, polyaimdes, polyesteramides, polycarbonates, polyacetals, polyolef s and polysiloxanes . Preferred polyethers include those initiated with sorbitol or sucrose and/or glycerol. Preferably the polyether polyols are made using propylene oxide as the sole alkylene oxide. Suitable organic polyisocyanates for use in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, and in particular the aromatic polyisocyanates such as diphenylmethane diisocyanate in the form of its 2,4'-, 2,2'- and 4,4' -isomers and mixtures thereof, the mixtures of diphenylmethane diisocyanates (MDI) and oligo ers thereof known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanates) having an isocyanate functionality of greater than 2, toluene diisocyanate in the form of its 2,4- and 2,6-ιsomers and mixtures thereof, 1, 5-naphthalene diisocyanate and 1, -dιιsocyanatobenzene. Other organic polyisocyanates which may be mentioned include the aliphatic diisocyanates such as isophorone diisocyanate, 1, 6-dιιsocyanatohexane and 4,4' -d ^ isocyanatodicyclohexylmethane . The quantities of the polyisocyanate compositions and the polyfunctional isocyanate-reactive compositions to be reacted will depend upon the nature of the rigid polyurethane or urethane-modified polyisocyanurate foam to be produced and will be readily determined by those skilled in the art. Water is used as blowing agent, optionally together with less than 15 % by weight on total blowing agent of physical blowing agents. When water is used as mam blowing agent the amount of water is generally between 2 and 10 % by weight based on isocyanate-reactive components, preferably between 4 and 6 % by weight. As additional blowing agent any of the blowing agents known n the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams can be used in the process of the present invention. Such blowing agents include other carbon dioxide-evolvmg compounds, or inert low boiling compounds having a boiling point of above -70°C at atmospheric pressure. Suitable inert blowing agents include those well known and described in the art, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaliphatic hydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons, hydrochlorocarbons and fluorine-containing ethers. The blowing agents are employed m an amount sufficient to give the resultant foam the desired bulk density which is generally in the range 15 to 70 kg/m 1 , preferably 20 to 50 kg/m 3 , most preferably 25 to 40 kg/m 3 . Typical amounts of blowing agents are in the range 2 to 25 % by weight based on the total reaction system. In addition to the polyisocyanate and polyfunctional isocyanate-reactive compositions and the blowing agent (mixture), the foam-forming reaction mixture will commonly contain one or more other auxiliaries or additives conventional to formulations for the production of rigid polyurethane and urethane-modified polyisocyanurate foams. Such optional additives include crossl kmg agents, for examples low molecular weight polyols such as triethanolamme, foam-stabilismg agents or surfactants, for example siloxane-oxyalkylene copolymers, urethane catalysts, for example tin compounds or tertiary amines, isocyanurate catalysts, fire retardants, for example halogenated alkyl phosphates such as tris chloropropyl phosphate, and fillers such as carbon black. Preferably auxiliaries are used which do not promote adhesion to metal. The process is generally caned out at an isocyanate index of between 0.8 and 2.5, preferably between 1.0 and 1.5. In operating the process for making rigid foams according to the invention, the known one-shot, prepolymer or semi-prepolymer techniques may be used together with conventional mixing methods and the rigid foam may be produced in the form of slabstock, mouldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metal. A preferred application of the foam prepared according to the claimed process is as cavity filler for water heaters. It is convenient in many applications to provide the components for polyurethane production in pre-blended formulations based on each of the primary polyisocyanate and isocyanate-reactive components. In particular, many reaction systems employ a polyisocyanate-reactive composition which contains the ma] or additives such as the blowing agent in addition to the polyisocyanate-reactive component or components. The various aspects of the present invention are illustrated, but not limited by the following examples in which the following ingredients were used: Polyol 1: a polyether polyol of OH number 540 mg KOH/g initiated with glycerol . Polyol 2: a polyether polyol of OH number 460 mg KOH/g initiated with sorbitol . Polyol 3: a polyether polyol of OH number 380 mg KOH/g initiated with sorbitol . Polyol 4: a polyether polyol of OH number 280 mg KOH/g. Fire retardant: a halogenated fire retardant. Terate 2541: a DMT polyester polyol of OH number 240 mg KOH/g and functionality 2, available from Hoechst Celanese. Isoexter 3471: a scrap PET polyester of OH number 350 mg KOH/g and functionality 2 to 2.5, available from COIM. Arconate 1000: ethylene carbonate available from Arco. Surfactant: a silicone surfactant. Catalyst: a tertiary amine catalyst package. Isocyanate: a polymeric MDI Example 1 Rigid polyurethane foams were made from the ingredients listed below m Table 1. Reaction profile was followed terms of cream time and string time. Free rise density of the foam was measured according to standard ISO 845. Adhesion of the foam was measured according to standard ASTM D162. An adhesion of zero means that the foams ]ust falls off. The results are presented in Table 1. Table 1

Claims: CLAIMS 1. Process for preparing rigid polyurethane or urethane-modified polyisocyanurate foams comprising the step of reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive component characterised in that the polyfunctional isocyanate-reactive component comprises more than 2 % by weight of water and from 5 to 50 % by weight of polyester polyols of average functionality below 3. 2. Process according to claim 1 wherein the average functionality of the polyester polyols is between 1.7 and 2.5. 3. Process according to claim 1 or 2 wherein the polyester polyols are crude polyester polyols. . Process according to claim 3 wherein the crude polyester polyols are selected from the group consisting of DMT polyester polyols and scrap PET polyester polyols. 5. Process according to any one of the preceding claims wherein the polyester polyols are present in amounts ranging from 5 to 30 % by weight based on the total isocyanate-reactive components. 6. Process according to claim 5 wherein the polyester polyols are present m amounts ranging from 10 to 25 % by weight based on the total isocyanate-reactive components. 7. Process according to any one of the preceding claims wherein the polyfunctional isocyanate-reactive component further comprises polyether polyols. 8. Process according to claim 7 wherein said polyether polyols are made by reacting propylene oxide with initiators containing from 2 to 8 active hydrogen atoms per molecule. 9. Process according to claim 8 wherein said initiators are selected from the group consisting of glycerol, sorbitol, sucrose, tolylene diamme, diammodiphenyl ethane and polymethylene polyphenylene polyammes . 10. Process according to any one of the preceding claims wherein the amount of water is between 2 and 6 % by weight based on total isocyanate-reactive components. 11. Rigid polyurethane or urethane-modified polyisocyanurate foam obtainable by the process as defined in any one of tne preceding claims . 12. Cavity filled with a rigid polyurethane or urethane-modified polyisocyanurate foam as defined in claim 11. 13. Cavity according to claim 12 wherein the cavity is part of a water heater. 14. Isocyanate-reactive composition comprising from 5 to 50 % by weight of polyester polyols of average functionality below 3 and more than 2 % by weight of water. 15. Isocyanate-reactive composition according to claim 14 wherein the polyester polyols are crude polyester polyols.

Inventors: DE VOS RIK, GABRIELI FRANCO, DE VOS, RIK, GABRIELI, FRANCO
Applicants: GABRIELI FRANCO, HUNTSMAN ICI CHEM LLC, VOS RIK DE, DE VOS, RIK, GABRIELI, FRANCO, HUNTSMAN ICI CHEMICALS LLC
Application year: 1999
Main classification: C08G18
IPC codes: C08G18