CA2161065C - Production of rigid polyurethane foams having reduced thermal conductivity, and the use thereof - Google Patents

Abstract

The present invention relates to a process for the production of rigid polyurethane foams having a content of aromatic radicals of at least 32% by weight which are incorporated into formative components (a), (b) and/or (c) and reduce the thermal conductivity of the polyurethane matrix, by reacting a) modified or unmodified organic, preferably aromatic polyisocyanates with b) at least one relatively high-molecular-weight compound containing at least two reactive hydrogen atoms and preferably containing arylene units, and, if desired, c) low-molecular-weight chain extenders and/or crosslinking agents, in the presence of d) blowing agents, preferably cyclopentane and/or cyclohexane, in combination with water, e) catalysts, and, if desired, f) additives. The rigid polyurethane foams are preferably used as insulating materials in the refrigeration equipment industry and as insulating materials in heating and composite elements.

Description

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Production of rigid polyurethane foams having reduced thermal conductivity, and the use thereof The present invention relates to a process for the production of rigid polyurethane (abbreviated to PU below) foams containing at least 32% by weight of aromatic radicals and thus further reduced thermal conductivity by reacting a) organic, preferably aromatic polyisocyanates with b) relatively high-molecular-weight compounds containing at least two reactive hydrogen atoms and preferably containing bonded arylene units, and, if desired, c) low-molecular-weight chain extenders and/or crosslinking agerlts, in the preserice of d) blowing agents, preferably blowing agent combinations of cyclopentane and/or cyclohexane and water, e) catalysts and, if desired, f) additives, and to the use of these rigid PU foams for foam-filling cavities in refrigeration equipment or heating elements and as insulation materials for composite elements.

The production of composite or sandwich elements built up from a rigid PU foam and at least one outer layer of a rigid or elastic material, for example paper, plastic film, metal sheeting, glass nonwovens, chipboard, inter alia, is known.
Also known is the foam-filling of cavities in domesti-c appliances, such as refrigeration equipment, for example refrigerators or freezers, or of hot-water starage tanks, by means of rigid PU foam as insulating material. In order to prevent foam flaws, the foarnable PU reaction mixtur.e must be introduced into the cavity to be insulated wit.hin a short time.
Such articles are usually foam-filled using low-pressure or preferably high-pressure machines.

A review of the production of rigid PU foams and their use as the outer layer or preferably the core layer in composite elements and their use as the insulating layer in refrigeration or heating technology has been published, for example, in Polyurethane, Kunststoff-Handbuch, Volume 7, l-st Edition 1966, edited by Dr. R. Vieweg and Dr. A. Hdchtlen, and 2nd Edition 1983, edited by Dr. Giinter Oertel, Carl Hanser Verlag, Munich, Vienna.

Heat- and cold-insulating rigid PU foams which are su.itable for this purpose can, as is known, be produced by reactirig organic polyisocyanates with one or more relatively 216 106 5_ high-molecular-weight compounds containing at least two reactive hydrogen atoms, preferably polyester-- and/or polyether-polyols, usually in the presence of low-molecular-weight chain extenders and/or crosslinking agents, in the presence of blowing agents, catalysts and, if desired, auxiliaries and/or additives. A suitable choice of the formative components allows the prodtiction of rigid PU foams having a low thermal conductivity and good mechanical properties.
Blowing agents which have been used worldwide in large amounts for the productiori of heat- and cold-insulatirig rigid PU foams are chlorofluorocarborls (CFCs), preferably trichlorofluoromethane. The only disadvantage of these blowing gases is that they are suspected of causing erivironmental pollution by participating in degradation of the ozone layer in the stratosphere.

There has therefore been no lack of attempts to replace CFCs by blowing agents which cause little or preferably no environmental damage.

According to EP-A---351 614 (US.--A-4,972,002), the blowing agents can be fluorinated hydrocarbons, perfluorinated hydrocarbons, sulfur hexafluoride or mixtures of at least, two of these compounds. Since these fluorinated or perfluorinated blowing agents are only sparirigly soluble or insoluble in the formative components for the preparation of the polyisocyanate polyaddition products, they are emulsified in at least one organic and/or modified organic polyisocyanate, at least orie relatively high-molecular-weight compound containing at least two reactive hydrogen atoms or a mixture of at: least one relatively high-molecular-weight compound containing at least two reactive hydrogen atoms and a low-molecular-weight chain extender and/or crosslinking agent. This method gives cellular plastics having a uniform and fine cell structure. The only disadvantages of this process are the r.estri.cted cho:i-ce of suitable fluorinated or perfluorinated compourids having a boiling point in the requisite range arid the high price of these blowing agents. The production of cellulLar plastics having the cell structure desired by industry has to rely on a highly restricted range of mixtures of perfluoropentane and perfluorohexane.

The production of cellular plastics by the polyisocyanate polyaddition process is, according to DE-A-41 43 148, also highly successful usirig blowing agents (d), if desired in combination with water, which contain at least: one low-boiling, fluorinated or perfluorinated organic compounci which is sparingly soluble or insoluble in formative components (a), (b) and (c) and at least one isoalkane having 6 tc> 12 carbon atoms.
Rigid PU foams having low thermal conductivity are furthermore described in EP-A-O 421 269 (US-A-5,096,933). The blowing agents used, preferably in combination with water, are cyclopentane or mi.xtures, expediently having a boiling point of below 500C, containing:
cyclopentane and/or cyclohexane and at least one inert, low-boiling compound which is homogeneously miscible with cyclopentane and/or cyclohexane, preferably from the group consisting of alkanes, cycloalkanes having a niaximum of 4 carbon atoms, dialkyl ethers, cycloalkylene ethers and fluoroalkanes.
A suitable choice of blowing agent, which remains in the rigid PU foam for a considerable period as cell gas, since its diffusion rate is very low, in particular if the foam is provided on all sides with plastic or metal outer layers, allows a significant reduction in the thermal conductivity of the rigid PU foam.

Since heat transport from a warm to a cold point in ei foam can take place, for example, via the foam matrix, the cell gas or by radiation, there is still a need to minimize the thermal conductivity of rigid PU foam by suitable measures and thus to reduce the energy consumption, for example in refrigeration equipment, or the release of heat, for example by (remote) heating systems and hot--water storage tanks by means of insulation elements.

It is an object of the present invention further to reduce the thermal conductivity of the PU foams while substantially avoiding the use of toxic and/or environmentally damaging blowing agents. The polyol and polyisocyanate components (A) and (B) shoul.d have a long shelf life, and the reaction mixture for the production of the rigid PU foams shoul.d be very free-flowing and should cure without shrinkage. During foam-filling of casing parts, a strong bond between the outer layer and the rigid PU foam should be formed.

We have found that, surprisingly, this object is achieved by using organic polyisocyanates and/or relatively high-molecular-weight or low-molecular-weight compounds which are reactive with NCO groups and contain at least two reactive hydrogen atoms and bonded aromatic radicals.

The present invention accordingly provides a process for the production of rigid polyurethane foams having low thermal conductivity by reacting a) organic and/or modified organic polyisocyanates with b) at least one relatively high-molecular-weight compound containing at least two reactive hydrogen atoms and, optionally, c) low-molecular-weight chain extenders and/or crosslinking agents, in the presence of d) blowing agents, e) catalysts and, optionally, f) additives, wherein the process further comprises incorporating at least 32% by weight, preferably at least 33 to 50% by weight, or more preferably from 34 to 40% by weight, based on the rigid polyurethane foams, of aromatic radicals incorporated in formative components (a), (b) and/or, if used, (c) or in at lest two of the formative components (a), (b) and/or if used, (c).

In a preferred embodiment, the organic polyisocyanates (a), preferably aromatic polyisocyanates, and the relatively high-molecular-weight compounds (b) used in the novel process for the production of the rigid PU foams containing at least 32% by weight of aromatic radicals are preferably those containing arylene radicals, so that formative components (a) and (b) introduce aromatic radicals into the rigid PU foam 21s1 fi5 matrix. In other process variants, however, the content of at least 32% by weight of aromatic radicals in the rigid PU foam can result exclusively from the aromatic polyisocyanates (a) or exclusively from the relatively high-molecular-weight compounds (b) and/or low-molecular-weight chain extenders and/or crosslinking agents.

The novel process allows the thermal conductivity of the rigid PU foams to be reduced by at least 0.5 mW/mK, usually by from 1 to 2 mW/mK under otherwise identical conditior.is. However, the increase in the aromatic content in the rigid PU foam not only reduces the thermal conductivity, but also improves its mechanical properties in general, specifically the flame resistance and the aging behavior. It is f_urthermore advantageous that the compatibility and miscibility of formative components (a), (b), (e) and, if used, (c) and/or (f) with one another and with the blowing agents (d) preferably used, for example alkanes arid/or in particular cycloalkanes, is increased and the flowability of the reaction mixture is extended.

The rigid PU foams can be produced by the novel process using the formative components known per se, preference bei-ng given to those having a high content of aromatic groups in order to achieve a content of at least 32% by weight in the rigid PU
foam. However, it is also possible to use formative components (a) to (c) containing no aromatic groups as a mixture with the formative components preferably containing bor.ided aromatic groups or as the only starting material, with the proviso that the rigid PU foams formed contain at least 321; by weight of bonded aromatic radicals.

The following details apply to the formative componerits:

a) Suitable organic polyisocyanates are the aliphatic, cyclo-aliphatic, araliphatic and preferably aromatic polyiso-cyanates known per se.

The following may be mentioned as examples: alkylene diiso-cyanates having from 4 to 12 carbon atoms in the alkylene moiety, such as 1,12--dodecane diisocyanate, 2-ethyltetra-methylene 1,4-diisocyanate, 2-methylpentarnethylene 1,5-diisocyanate, 2-ethyl--2-butylpentamethylene 1,5-diiso-cyanate, tetramethylene 1,4-diisocyanate and preferably hexamethylene 1,6--diisocyanate; cycloaliplzatic diisocya-nates, such as cycl.ohexane 1,3- and 1,4-diisocyanate and any desired mixtures of these isomers, 1-.Lsocyana-to-3,3,5-trimethy:l- 5-isocyanatomethylcyc:lohexane (isopho-rone diisocyariate), 2,4-- and 2,6-hexahydrotolylene diisocy-anate, and the corresponding isomer mixtures, 4,4'-, 2,2'-and 2,4'-dicyclohexylmethane diisocyariate and the corre-sponding isomer mixtures, araliphatic diisocyanates, for example 1,4--xylylene diisocyanate and xylylene diisocyanate isomer mixtures, and preferably aromatic diisocyanates and polyisocyanates, eg. 2,4- and 2,6-tolylene diisocyanate and the corresponding isomer mixtures, 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate and the corresponding isomer mixtures, mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanates, po].yphenyl-polymethylene polyisocyanates, mixtures of 4,4'-, 2,4'- and 2,2'-dipheny]Lmethane diisocya-nates and polyphenyl-polymethylene polyisocyanates (crude MDI), and mixtures of crude MDI and tolylene diisocyanates.
The organic diisocyanates and polyisocyanates may be employed individually or in the form of mixtures.

The organic polyisocyanates can be prepared by known pro-cesses. They are preferably prepared by phosgenation of the corresponding polyamines with formation of polycarbamoyl chlorides, and thermolysis thereof to give the organic polyisocyanate anci hydrogen chloride, or by phosgene-free processes, for example by reacting the corresponding poly-amines with urea and alcohol to give polycarbamates, and thermolysis thereof to give the polyisocyanate and alcohol.
Frequently, modified polyisocyanates are also used, ie.
products which are obtained by chemical reaction of organic diisocyanates and/or polyisocyanates. Specific examples are ester-, urea-, biuret-, allophanate-, uretoneimine-, carbo-diimide-, isocyanurate-, uretdione- and/or urethane-containing diisocyanates and/or polyisocyanates. Individual examples are urethane-containing organic, preferably aro-matic, polyisocyariates containing from 33.6 to 15% by weight, preferably from 31 to 21% by weight, of NCO, based on the total weight, for example 4,4'-diphenylmethane diis-ocyanate, 4,4'- and 2,4'-dipheriy.lmethane diisocyanate mix-tures, or crude MDI or 2,4- or 2,6-to.lylerie diisocyanate, in each case modified by means of low-molecular-weight diols, triols, dialkylene glycols, trialkylene glycols or 216 106 5 _ polyoxyalkylen.e glycols having molecular weights of up to 6000, specific examples of di- and polyoxyalkylene glycols, which can be employed individually or as mixtures, being diethylene, dipropylene, polyoxyethylene, polyoxypropylene and polyoxypropylene--polyoxyethylene glycols, triols and/or tetrols. NCO-containing prepolymers containing from 25 to 3.5% by weight, preferably from 21 to 14% by weight, of NCO, based on the total weight, and prepared from the poly-ester- and/or preferably polyether-polyols described below and 4,4'-diphenylrnethane diisocyanate, mixtures of 2,4'-and 4,4'-diphenylrnethane diisocyanate, 2,4- and/or 2,6-to-lylene diisocyanates or crude MDI are also suitable. Fur-thermore, liquid polyisocyanates containing carbodiimide groups and/or isocyanurate rings and containing from 33.6 to 15% by weight, preferably from 31 to 2:1% by weight, of NCO, based on the total weight, eg. based on 4,4'-, 2,4'-and/or 2,2'-diphenylmethane diisocyanate and/or 2,4- and/or 2,6-tolylene diisocyanate, have also proven successful.

The modified polyisocyanates may be mixed with one another or with unmodified organic polyisocyanates, eg. 2,4'- or 4,4'-diphenylmethane diisocyanate, crude MDI or 2,4- and/or 2,6-tolylene diisocyanate.

Organic polyisocyanates which have proven particularly successful and are therefore preferred for the production of the rigid PU foams are: mixtures of modified organic polyisocyanates containing urethane groups, having an NCO
content of from 33.6 to 15% by weight, in particular those based on tolylene diisocyanates, 4,4'-diphenylmethane diis-ocyanate, diphenylmethane diisocyanate isomer mixtures or crude MDI, in part:icular 4,4'-, 2,4'-- and 2,2'-diphenylme-thane diisocyanate, polyphenyl-polymethyl(ane polyisocya-nates, 2,4- and 2,6-tolylene diisocyanate, crude MDI having a diphenylmethane diisocyanate isomer content of from 30 to 80% by weight, preferably from 35 to 45% by weight, and mixtures of at least two of the said polyisocyanates, for example crude MDI or mixtures of tolylene diisocyanates and crude MDI.
b) The relatively high-molecular-weight compounds (b) contain-ing at least two reactive hydrogen atoms are preferably polyhydroxyl compounds having a functionality of from 2 to 216 yo6 5 8, preferably 3 to 8, and a hydroxyl number of from 100 to 850, preferably from 120 to '770.

Examples which may be mentioned are polythioether-polyols, polyester-amides, hydroxyl-containing polyacetals and hydroxyl-containing aliphatic polycarbonates, and preferably polyester-polyols and polyether-polyols. Use is also made of mixtures of at least two of the said polyhydroxyl compourids and with polyhydroxyl compounds having hydroxyl numbers of less than 100, so long as the mixtures have a mean hydroxyl number in the above range.
Suitable polyester-polyols may be prepared, for example, from organic dicarboxyl.ic acids having from 2 to 12 carbon atoms, preferably aromatic dicarboxylic acids having from 8 to 12 carbon atoms and polyhydric alcohols, preferably diols, having from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms. Examples of suitable dicarboxylic acids are succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid and preferably phthalic acid, isophthalic acid, terephthalic acid and the isomeric naph-thalenedicarboxylic acids. The di.carboxylic acids may be used either individually or mixed with one another. The free dicarboxylic acids may also be replaced by the corre-sponding dicarboxylic acid derivatives, for example dicar-boxylic esters of alcohols having 1 to 4 carbon atoms or dicarboxylic anhydri.des. Preferetlce .i.s given to dicarboxyl-ic acid mixtures comprising succinic acid, glutaric acid and adipic acid in ratios of, for example, from 20 to 35 to 50 : 20 to 32 parts by weight, and adipic acid, and in particular mixtures of phthalic acid and/or phthalic anhydride and adipic acid, mixtures of phthalic acid or phthalic anhydride, isophthalic acid and adipic acid or dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid and mixtures of terephthalic acid and adipic acid or dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid. Examples of dihydric and polyhydric alcohols, in particular diols, are ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanedio:l, 1,6-hexanediol, 1,10-decanediol, glycerol, trimethylol.propane. Preference is given to ethanediol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol or mixtures of at least two 21fi1qfi5 of said diols, in particular mixtures of 1,4-butanedi_ol, 1,5-pentanediol and 1,6-hexanediol. Furthermore, polyester-polyols made from lactones, eg. e-caprolactone or hydroxy-carboxylic acids, e.g. w-hydroxycap.roic acid and. hydroxy-benzoic acids, may also be employed.

The polyester-polyols may be prepared by polycondensing the organic, eg. aliptiatic and preferably aromatic polycarbox-ylic acids and mixtures of aromatic and a:liphatic poly--carboxylic acids, and/or derivatives thereof, and polyhyd-ric alcohols without using a catalyst or preferably in the preserice of arz esterification catalyst, expediently in an inert gas atmosphere, eg. nitrogen, carbon monoxide, he-lium, argon, inter alia, in the melt at f_rom 150 to 250 C, preferably from 180 to 220 C, at atmospheric pressure or under reduced pressure until the desi.red acid number, which is advantageously less than 10, preferably less than 2, is reached. In a preferred embodiment, the esterification mix-ture is polyconderised at the abovementioned temperatures under atmospheric pressure and subsequently unde:r a pres-sure of less than 500 mbar, preferably from 50 to 150 mbar, until an acid number of from 80 to 30, preferably from 40 to 30, has been reached. Examples of suitable esterifica-tion catalysts are iron, cadmium, cobalt, lead, zinc, anti-mony, magnesium, t:itanium and tin catalysts in the form of metals, metal oxides or metal salts. However, the polycon-densation may also be carried out in the liquid phase in the presence of diluents and/or entrainers, eg. benzene, toluene, xylene or chlorobenzene, for removal of the water of condensation by azeotropic distillation.

The polyester-polyols are advantageously prepared by poly-condensing the organic polycarboxyli.c acids and/or deriva-tives thereof with polyhydric alcohols in a molar ratio of from 1:1 to 1.8, preferably from 1:1.05 to 1.2.

The polyester-polyols obtained preferably have a furictiona-lity of from 2 to 3 and a hydroxyl number of from 150 to 600, in particular from 200 to 400.
However, the polyhydroxyl compounds used are in particular polyether-polyols prepared by known processes, for example by anionic polymerization using alkali metal hydroxides such as sodium hydroxide or potassium hydroxide, or alkali metal alkoxides, such as sodium methoxide, sodium ethoxide, potassium ethoxide or potassium isopropoxide as catalysts and with addition of at least one initiator molecule con-taining from 2 to 8, preferably 3 to 8, reactive hydrogen atoms in bound form or by cationic polymerization using Lewis acids, such as aritimony pentachloride, boron fluoride etherate, inter alia, or bleaching earth as catalysts, from one or more alkylene oxides having from 2 to 4 carbon atoms in the alkylene moiety.
Examples of suitable alkylene oxides are tetrahydrofuran, 1,3-propylene oxicie, 1,2- and 2,3-butylene oxide, styrene oxide and preferably ethylene oxide and 1,.2-propylene ox-ide. The alkylene oxides may be used individually, alterna-tively one after the other or as mixtures. Examples of suitable initiator molecules are water, organic di.carboxyl-ic acids, such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, unsubsti-tuted or N-mono-, N,N- and N,N'-dialkyl-substituted dia-mines having from 1 to 4 carbon atoms in the alkyl moiety, such as unsubstituted or mono- or dialkyl--substituted ethy-lenediamine, diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- and 1,4-butyleriediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, aniline, phenylenediamines, 2,3-, 2,4--, 3,4- and 2,6-toly:lenediamine and 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethane.

Other suitable initiator molecules are alkanolamines, eg.
ethanolamine, N-methyl- and N-ethylethanolamine, dialkanol-amines, eg. diethanolamine, N-methyl- and N-ethyldiethanol-amine, and trialkanolamines, eg. triethanolamirie, and ammonia, and polyhydric alcohols, in particular dihydric and/or trihydric alcohols, such as ethanediol, 1,2- and 1,3-propanediol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpro-pane, pentaerythritol, sorbitol and sucrose, polyhydric phenols, for example 4,4'-dihydroxydiphenylmethane and 4,4'-dihydroxy-2,?,-diphenylpropane, resols, for example oligomeric products of the conderisation oi= phenol and formaldehyde, and Mannich condensates of phenols, formalde-hyde and dialkanolamines, and melamine.

_ The relatively high-molecular-weight compaunds (b) are ad-vantageously polyether-polyols having a functionality of from 2 to 8 and a hydroxyl number of from 100 to 850 pre-pared by anionic polyaddition of at least one alkylene oxide, preferably ethylene oxide or 1,2-propylene oxide or 1,2--propylene oxide and ethylene oxi.de, onto, as initiator molecule, at least: one aromatic compound containing at least two reactive hydrogen atoms and containing at least one hydroxyl, amirro and/or carboxyl group. Examples which may be rnentioned of such initiator molecules are aromatic polycarboxylic acids, for example hemimellitic acid, tri-mellitic acid, tri-mesic acid and preferably phthalic acid, isophthalic acid and terephthalic acid, oi.- mixtures of at :least two of said polycarboxylic acids, hydroxycarboxylic acids, for example salicylic acid, p- and m-hydroxybenzoic acid and gallic acid, aminocarboxylic acids, for example anthranilic acid, m- and p-aminobenzoic acid, polyphenols, for example resorcinol, and preferably dihydroxydiphenyl-methanes and dihyciroxy-2,2-diphenylpropanes, Mannich con-densates of pheno]-s, formaldehyde and dia]Lkanolamines, pre-ferably diethanolamine, and preferably aromatic polyamines, for example 1,2-, 1,3- and 1,4-phenylenedaamine and in par-ticular 2,3-, 2,4--, 3,4-- and 2,6-tolylenediamine, 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethane, polyphenyl-polyme-thylene-polyamines, mixtures of diaminodiphenylmethanes and polyphenyl-polymethylene-polyamines, as formed, for example, by conderisation of aniline with formaldehyde, and mixtures of at least two of said polyamines.

The preparation of polyether-polyols usinq at least difunc-tional aromatic iriitiator molecules of thiLs type is known and is described, for example, in DD-A-290 201, DD-A-290 202, DE-A-34 12 082, DE-A--4 232 970 and GB-A-2,187,449.

The polyether-polyols preferably have a functionality of from 3 to 8, in particular from 3 to 6, and hydroxyl numbers of from 120 to 770, in particular from 240 to 570.

Other suitable pol.yether-polyols are melanline/po_lyether-polyol dispersions as described in EP-A--23 987 (US-A-4,293,657), polymer/polyether-polyol dispersions pre-pared from po].yepoxides and epoxy resin curing agents in the presence of polyether-polyols, as described in DE 29 43 689 (US 4,305,861), dispersions of aromatic poly-esters in polyhydroxyl compounds, as described in EP-A-62 204 (US-A-4,435,537) and DE-A 33 00 474, disper-sions of organic and/or inorganic fillers in polyhydroxyl compounds, as described in EP-A-11 751 (US 4,243,755), polyurea/polyether-polyol dispersions, as described in DE-A-31 25 402, tris(hydroxyalkyl) isocyanurate/polyether-polyol dispersions, as described in EP-A-136 571 (US 4,514,526), and crystallite suspensions, as described in DE-A-33 42 176 and DE-A-33 42 177 (US 4,560,708).

Like the polyester-polyols, the polyether-polyols can be used individually or in the form of mixtures. Furthermore, they may be mixed with the graft polyether-polyols or poly-ester-polyols and the hydroxyl-containing polyester-amides, polyacetals, polycarbonates and/or phenolic polyols.

Examples of suitable hydroxyl-containing polyacetals are the compounds which can be prepared from glycols, such as diethylene glycol, triethylene glycol, 4,4'-dihydroxyethox-ydiphenyldimethylmethane, hexanediol and formaldehyde.
Suitable polyacetals can also be prepared by polymerizing cyclic acetals.

Suitable hydroxyl-containing polycarbonates are those of a conventional type, which can be prepared, for example, by reacting diols, such as 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol, triethylene gly-col or tetraethylene glycol, with diaryl carbonates, eg.
diphenyl carbonate, or phosgene.

The polyester-amides include, for example, the predominant-ly linear condensates obtained from polybasic, saturated and/or unsaturated carboxylic acids or anhydrides thereof and polyhydric, saturated and/or unsaturated amino alco-hols, or mixtures of polyhydric alcohols and amino alcohols and/or polyamines.
Suitable relatively high-molecular-weight compounds (b) containing at least two reactive hydrogen atoms are furthermore phenolic and halogenated phenolic polyols, for example resol-polyols containing benzyl ether groups.

2 6~06 5-, Resol-polyols of t:his type can be prepared, for example, from phenol, formaldehyde, expedient.ly par_aformaldehyde, and polyhydric aliphatic alcohols and are described, for example, in EP-A-0 116 308 and EP-A-0 116 310.

The relatively high-molecular-weight compounds (b) are in particular mixtures of polyether-polyols c:ontain:ing at least one polyether-polyol based ori an aromatic, polyfunc-tional initiator nlolecule and at least one polyether-polyol based on a nonaromatic initiator molecule, preferably a trihydric to octahydric alcohol.

c) The rigid PU foams can be produced with or without the use of chain extenders and/or crosslinking agents. However, it may prove advantageous, in order to modify the mechanical properties, to add difunctional chain extenders, trifunc-tional or polyfunctional. crosslinking agerits or, if de--sired, mixtures thereof. Examples of chain extenders and/or crosslinking agents are alkanolamines, in particular diols and/or triols, having molecular weights of less than 400, preferably from 60 to 300. Examples are alkanolamines, for example ethanolamine and/or isopropanolami_ne, dialkanol-amines, for example diethanolamine, N-methyl and N-ethyl-diethanolamine, di.isopropanolamine, trialkanolamines, for example triethanolamine, and triisopropanolamine, and the products of the addition reaction of ethylene oxide or 1,2-propylene oxicie and alkylenediamines having 2 to 6 carbon atoms in the alkylene radical, for example N,N,N',N'-tetra (2--hydroxyethyl) ethyl.enediamine and N,N,N',N'-tetra(2--hydroxypropyl)ethylened:iamine, aliphatic, cycloaliphatic and/or araliphatic diols having from 2 to 14 carbon atoms, preferably from 4 to 10 carbon atorns, eg.
ethylene glycol, 1,3-propanediol., 1,10-decanediol, o-, m-and p-dihydroxycyclohexane, diethylene glycol, dipropylene glycol and preferably 1,4-butanediol, 1,6--hexanediol and bis(2-hydroxyethyl)hydroquinone, triols, such as 1,2,4-. and 1,3,5-trihydroxycyclohexane, glycerol and trimethylolpro-pane, and low-molecular-weight hydroxyl-containing polyal-kylene oxides based on ethylene oxide and/or 1,2-propylene oxide and aromatic diamines, for example tolylenediamines and/or diaminodiphenylmethanes, and the abovementioned alkanolamines, diols and/or triols as initiator rnolecules.

Any chain extenders, crosslinking agents or mixtures there-of used for the production of the rigid PU foams are ex-pediently used in an amount of from 0 to 20% by weight, preferably from 2 to 5% by weight, based on the weight of the polyhydroxyl compound.

d) The blowing agent for the production of the rigid PU foams is preferably cyclopentane (dl). However, good results have also been achieved usirig mixtures (d2) coritaining (d2i) cyclopentane, cyclohexane or a mixture of these cycloalkanes and (d2ii) at least orie low-boiling compourid, preferably having a boiling point of below 40'C, which is homogeneously miscible with cyclopentane and/or cyclohexane.

The compounds of said type which are suitable as blowing agent can be selected from the group consi_sting of alkanes, cycloalkanes having a maximum of 4 carbon atoms, dialkyl ethers, cycloalkylene ethers and fluoroalkanes. :[t is also possible to use mixtures of at least two compounds of said groups of compound. Specific examples which may be men-tioned are: alkanes, for example propane, n-butane, iso-butane, n- and isopentane and technical-grade pentane mix-tures, cycloalkanes, for example cyclobutane, dialkyl ethers, for example dimethyl ether, methyl ethyl ether, methyl butyl. ether and diethyl ether, cycloalkylene ethers, for example furan, and fluoroalkanes which are broken down in the troposphere and therefore do not damage the ozone layer, for example t.rifluoromethane, difluoromethane, difluoroethane, tetrafluoroethane and heptafluoropropane.
The preferred blowing agents can be used alone or prefer-ably in combination with water, the following cornbinations having proven highly successful and are therefore pre-ferred: water and cyclopentane, water and cyclopentane or cyclohexane or a niixture of these cycloalkanes and at least one compound from the group consisting of n-butane, iso-butane, n- and isopentane, technical-grade peritane mix-tures, cyclobutane, rnethyl butyl ether, diethyl ether, furan, trifluoromethane, difluoromethane, difluoroethane, tetrafluoroethane and heptaf].uoropropane. The amount of low-boiling compounds which are homogeneously miscible with 216 10,65 cyclopentane and/or cyclohexane used in combination with cyclohexane and iri particular with cyclopentane is such that the resultant: mixture advantageously has a boiling point of below 50"C, preferably from 30 to 0'C. The requi-site amount depencls on the course of the boiling--point curve of the mixture and can be determined experimentally by known methods. Rigid PU foams having low conductivity are obtained, in particular, if the blowirig agent (d) used is, per 100 parts by weight of forrnative component (b):
dl) from 3 to 22 parts by weight, prefera:bly from 5 to 18 parts by weight, in particular from 8 to 14 parts by weight, of cyclopentane and from 0 to 7 parts by weight, preferably from 1.0 to 5.0 parts by weight, in particular from 2.2 to 4.5 parts by weight, of water or d2i) from 2 to 22 parts by weight, preferalbly from 5 to 19 parts by weight, in particular from 9 to 19 parts by weight, of cyclopentane and/or cyclohexane, d2ii) from 0.1 to 18 parts by weight, preferably from 0.5 to 10 parts by weight, in particular froin 1.0 to 6.0 parts by weight, of at least one compound having a boiling point of below 400C which is homogeneously miscible witti cyclopentane and/o.r cyclohexane, selected from the group consisting of alkanes, cycloalkanes having a maximum of. 4 carbon atoms, dialkyl ethers, cycloalkylene ethers and preferably fluoroalkanes, and from 0 to 7 parts by weight, preferably from 1.0 to 5.0 parts by weight, in particular from 2.2 to 4.5 parts by weight, of water.

In order to produce the rigid PU foams, the cyclopentane (dl) or the blowirig agent mixture (d2), preferably in com-bination with water, is introduced by knovm methods into at least one formative component (a) to (c) f:or the production of the rigid P[J foam, if desired under pressure, or introduced directly into the reaction mixture, expediently by means of a suitable mixing device.

Blowing agents of said type are described, for example, in EP-A-O 421 269 (US-A-5,096,933).

Other suitable blowing agents are blowing-agent-containing emulsions with a long shelf life which contain at least one low-boiling, fluorinated or perfluorinated hydrocarbon hav-ing 3 to 8 carbon atoms which is sparingly soluble or in-soluble in formative components (a) to (c), sulfur hexa-fluoride or mixtures thereof, and at least one formative component (a), (b) or (c) as described in EP-A-O 351 614 or emulsions of mixtures of the abovementioned low-boiling, fluorinated or perfluorinated hydrocarbon having 3 to 8 carbon atoms which is sparingly soluble or insoluble in the formative components (a) to (c), and at least one isoalkane having 6 to 12 carbon atoms or cycloalkane having 4 to 6 carbon atoms and at least one formative component (a), (b) or (c), for example as described in DE-A-41 43 148.

e) The catalysts (e) used are, in particular, compounds which greatly accelerate the reaction of the hydroxyl-containing compounds of components (b) and, if used, (c) with the polyisocyanates. Suitable compounds are organometallic com-pounds, preferably organotin compounds, such as tin(II) salts of organic carboxylic acids, eg. tin(II) diacetate, tin(II) dioctanoate, tin(II) diethylhexanoate and tin(II) dilaurate, and dialkyltin(IV) salts of organic carboxylic acids, eg. dibutyltin diacetate, dibutyltin dilaurate, di-butyltin maleate and dioctyltin diacetate. The organometal-lic compounds can be employed alone or preferably in com-bination with highly basic amines. Examples which may be mentioned are amidines, such as 1,8-diazabicyclo[5.4.0]un-dec-7-ene, 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, ter-tiary amines, such as triethylamine, tributylamine, dime-thylbenzylamine, N-methyl-, N-ethyl-, N-cyclohexylmorpho-line, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine or -hexanediamine, pentamethyl-diethylenetriamine, tetramethyldiaminoethyl ether, bis(di-methylaminopropyl)urea, dimethylpiperazine, 1,2-dimethyli-midazole, 1-azabicyclo[3.3.0]octane, and, preferably, 1,4-diazabicyclo[2.2.2]octane and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine.

Other suitable catalysts are: tris(dialkylaminoa.lkyl)-s-hexahydrotriazines, in particular 1,3,5--tris(N,N-di-methylaminopropyl)-s-hexahydrotriazi.ne, tetraalkylammonium hydroxides, such as tetramethylammonium hydroxide, alkali metal hydroxides, such as sodium hydroxide, and alkali metal alkoxides, such as sodium methoxide and potassium isopropoxide, and alkali metal salts of long-chain fatty acids having 10 tc> 20 carbon atoms and possibly pendant OH
groups. Preference is given to 0.001 to 5% by weight, in particular from 0.05 to 2.5% by weight, of_ catalyst or catalyst combination, based on the weight of component (b).
f) The reaction mixture for the production of the rigid PU
foams may also be adrnixed with additives (f) conventional in polyurethane chemistry. Additives which may be mentioned are surfactants, foam stabilizers, cell regulators, fillers, dyes, pigments, flameproofing agents, antistatics, hydrolysis-protection agents, and fungistatic and bacterio-static substances.
Suitable surfactants are, for example, conipounds which support homogenization of the starting materials and may also be suitable f:or regulating the cell structure. Exam-ples which may be mentioned are emulsifiers, such as the sodium salts of castor oil sulfates, or of' fatty acids and salts of fatty acids with amines, for example diethylamine oleate, diethariolamine stearate, diethanolamine ricino-leate, salts of sulfonic acids, for example alkali metal or ammonium salts of dodecylbenzene- or dinaphthylmethanedi-sulfonic acid and ricinoleic acid; foam st:abilizers, such as siloxane-oxyalkylene copolymers and other organopolysi-loxanes, oxyethylated alkylpherlols, oxyethylated fatty alcohols, paraffiri oils, castor oil esters, ricinoleic acid esters, Turkey reci oil and groundnut oil and cell regula-tors, such as paraffins, fatty alcohols and dimethyl poly-siloxanes. Suitable compounds for impr_ovirig the emulsi-fication action, the cell structure arid/or stabi:Lizing the rigid foam are furthermore oligomeric polyacrylates con-taining polyoxyalkylene and fluoroalkane radicals as side groups. The surfactants are usually used in amounts of from 0.01 to 5 parts by weight, based on 100 parts by weight of component (b).

For the purposes of the present invention, fillers, in particular reinforcing fillers, are conventional organic and inorganic fillers, reiriforcing agerits and weighting agents. Specific examples are inorgariic fillers, such as silicate minerals, for example phyllosilicates, such as antigorite, serpentine, hornbl.ende, amphiboles, chrysotile, talc; metal oxides, such as kaolin, aluminum oxides, aluminum silicate, titanium oxide and iron oxides, metal salts, such as chalk, barytes and inorganic pigments, such 1.0 as cadmium sulfide, zinc sulfide and glass. Examples of suitable organic fillers are: carbori black, melamine, colophony, cyclopentadienyl resins and graft polymers.

The inorganic and organic fillers may be used individually or as mixtures and are advantageously introduced into the reaction mixture in amounts of from 0.5 to 50 % by weight, preferably from 1 to 40% by weight, based on the weight of components (a) to (c).

20 Examples of suitable flameproofing agents are tricresyl phosphate, tris(2--chloroethyl) phosphate, tris(2-chloro-propyl) phosphate, tris(1,3--dichl.oropropyl) phosphate, tris(2,3-dibromopropyl) phosphate and tetrakis(2-chloro-ethyl)ethylene diphosphate.

In addition to the abovementioned halogen--substituted phos-phates, it is also possible to use inorganic flameproofing agents, such as red phosphorus, preparations containing red phosphorus, aluminum oxide hydrate, antimony trioxide, 30 arsenic oxide, ammonium polyphosphate and calcium sulfate, or cyanuric acid derivatives, eg. melamine, or mixtures of two or more flameproofing agents, eg. ammonium polyphos-phates and melamine, and also, if desired, starch, in order to flameproof the rigid PU foams produced by the novel pro-cess. In general, it has proven expedient to use from 5 to 50 parts by weight, preferably from 5 to :25 parts by weight, of said f.lamep.roofing agents or mixtures per 100 parts by weight of components (a) to (c).

40 Further details on the other conventional auxiliaries and additives mentioned above can be obtained from the special-ist literature, for example from the monograph by J.H. Saunders and K.C. Frisch in High Polymers, Volume XVI, Polyurethanes, Parts 1 and 2, Interscience Publishers 1962 and 1964 respectively, or Kunststoff--Handbuch, Polyure-thane, Volume VII, Carl-Hanser--Verlag, Munich, Vienna, lst and 2nd Editioris, 1966 and 1.98:3.

In order to produce the rigid PU foams, the organic, modified or unmodified polyisocyariates (a), the relatively high-molecu-lar-weight compounds containing at least two reactive hydrogen atoms (b) and, if used, chain extenders arid/or crosslinking agents (c) are reacted in such amounts that the ratio between the number of equivalents of NCO groups iri the pol.yisocyanates (a) and the total number of reactive hydrogen atoms in compo-nents (b) and, if used, (c) is from 0.85 to 1.80:1, preferably from 0.95 to 1.35:1, in particular from about 1.0 to 1.15:1. If the foams containing urethane groups have beer.i modified by the formation of isocyanurate groups, for example in order to in-crease the flame retardarrcy, the ratio bet-weer.t the NC:O groups in the polyisocyanates (a) and the total number of reactive hydrogen atoms in component (b) and, if used, (c) is usually from 1.8 to 10:1, preferably from 2.0 to 6:1.
The rigid PU foams can be produced batchwise or continuously by the prepolymer process or preferably by the one-shot process with the aid of known mixing equipmerit.

It has proven particularly advantageous to use the two-compo-nent process and to combine formative components (b), (d), (e) and, if used, (c) and (f) in componerrt (A) and to use the organic polyisocyanates or modified polyisocyanates (a) or mix-tures of said polyisocyanates and, if desired, blowing agents (d) as component (B).

The starting components are mixed at from 15 to 90 C, preferably from 20 to 35 C, and introduced into an open, unheated or temperature-controlled mold, in which the reaction mixture is allowed to expand essentially without pressure in order to avoid a compacted peripheral zone. In order to form composite elements, the reverse of arr outer layer is expediently coated, for example by pouring or spraying, with the foamable reaction inixture, which is allowed to expand and cure to give the rigid Pt1 foam.

The rigid PU foams containing at least 32% by weight, preferably at least 33% by weight, of aromatic radicals and produced by the novel process preferably have densities of from 2i6106~

20 to 50 g/1 and usually have a thermal conductivity of less than 0.020 W/m=K, for example from 0.020 to 0.017 W/ni=K or less.

The rigid PU foams are preferably used as heat-insulating interlayers in composite elements and for foam-filling cavities in housings for refrigeration equipment, in particular for refrigerators and freezers, and as the jacket of hot-water storage tanks. The products are also suitable for the 10 insulation of warmed materials, as engine covers and as pipe shells.

Examples Production of rigid PU foams Comparative Example I

Component A: a mixture comprising 63.5 parts by weight of a polyether-polyol having a hydroxyl number of 440, prepared by ariionic polyaddition of 1,2-propylene oxide onto sucrose, 15.0 parts by weight of a polyether-polyol having a hydroxyl number of 400, prepared by anionic polyaddition of 1,2-propylene oxide onto sorbitol, 10.0 parts by weight of a polyether-polyol having a hydroxyl number of 120, prepared by anionic polyaddition of 1,2-propylene oxide onto N-(3-dimethylaminopropyl)ethylenediaminE_, followed by anionic polyaddition of ethylene oxide onto the resultant N-(3-dimethy.laminopropyl)ethylenediaminE=_/1,2-propylene oxide adduct, 5.0 parts by weight of polyoxypropylene glycol having a hydroxyl number of 250, 1.5 parts by weight of a silicone-based foarn stabilizer (Tegostab'vt' B 8462 from Goldschmi_dt AG, Essen), 2.2 parts by weight of N,N-dimethylcyclohexylamine, 0.5 part by weight of a 47% strength by weiqht solution of potassium acetat:e in ethylene glycol, 2.0 parts by weight of water and 11.0 parts by weight of cyclopentarie.

Component B:

A mixture of diphenylmethane diisocyanat.es and polyphenyl-polymethylerie polyisocyanates (crude MDI) having an NCO content of 31.5% by weight and a content of aromatic radicals of about 56% by weight.

100 parts by weight of component A and 125 parts by weight of component B were mixed in a high-pressure Puromat'j~ PU 15 unit, and the reaction mixture was injected into a Bosch lance., A uniform rigid PU foam having a density of about 38 g/]L and a thermal conductivity of 20.5 mW/mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative comporrents (a) to (c) was 31% by weight.
Example 1 Component A: a mixture comprising 63.5 parts by weight of a polyether-polyo]. having a hydroxyl number of 440, prepared by anionic polyaddition of 1,2-propylene oxide onto sucrose, 15.0 parts by weight of a polyether-polyol having a hydroxyl number of 550 and a content of aromatic radicals of about 11% by weight, prepared by ariionic polyaddition of 1,2-propylene oxide onto, as initiator molecule, a Mannich condensate obtai.nable from 4,4'-dihydroxy-2,2-diphenylpropane, forrnaldehyde and diethanolamine, 10.0 parts by weight of a polyether-polyol having a hydroxyl number of 120, prepared by anionic polyaddition of 1,2-propylene oxide onto N-(3-dimethylaminopropyl)ethylenediamine, followed by anionic polyaddition of ethylene oxide onto the resultant N-(3-dimethylaminopropyl.)ethylenediamine/1,2-propylene oxide adduct, 5.0 parts by weight of polyoxypropylene glycol having a hydroxyl number of 250, 1.5 parts by weight of a silicone-based foarn stabilizer (Tegostab'J~ B 8462 from Goldschmidt. AG, Essen), 2.2 parts by weight of N,N-dimethylcyclohexylamine, 0.5 part by weight of a 47% strength by weight solution of potassium acetate in ethylene glycol, 2.0 parts by weight of water and 11.0 parts by weight of cyclopentane.
Component B:

A mixture of diphenylmethane diisocyanates and polyphenyl-polymethylene polyisocyanates (crudle MDI) having an NCO content of 31.5% by weight and a conterit of aromatic radicals of about 56% by weight.
100 parts by weight of component A and 130 parts by weight of component. B were mixed in a high-pressure Puromat'"' PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 38 g/l and a thermal conductivity of 19.7 mW/mK, measured at 230C, was obtained. The content of aromatic radicals in the formative comporients (a) to (c) was 32.4% by weight.

Example 2 Component A: a mixture comprising 48.5 parts by weight of a polyether-pol.yol having a hydroxyl number of 440, prepared by anioriic polyaddition of 1,2-propylene oxide onto sucrose, 30.0 parts by weight of a polyether-pol.yol having a hydroxyl number of 550 and a content of aromatic radicals of about 11% by weight, prepared by anionic polyaddition of 1,2-propylene oxide onto, as initiator rnolecule, a Mannich condensate obtainable from 4,4'-dihydroxy-?,2-diphenylpropane, formaldehyde and diethano.lamine, 10.0 parts by weight of a polyether-polyol having a hydroxyl number of 120, prepared by anionic polyaddition of 1,2-propylene oxide onto N-(3-dimethylam:inopropyl)ethylenediamine, followed by anionic polyaddition of ethylene oxide onto the resultant N-(3-dimethylam:inopropyl)ethylenediamine/1,2-propylene oxide adduct, 5.0 parts by weight of polyoxypropylene glycol having a hydroxyl number of 250, 1.5 parts by weight of a silicone-based foam stabilizer (Tegostab"~' B 8462 from Goldschmidt AG, Essen), 2.2 parts by weight of N,N-dimethylcyclohexylamine, 0.5 part by weight of a 47% str_ength by weight solution of potassium acetate in ethylene glycol, 2.0 parts by weight of water and 11.0 parts by weight of cyclopentane.
Component B: analogou=_: to Example 1.

100 parts by weight of component A and 133 parts by weight of component B were mixed in a high-pressure Puromat.o PLI 15 uriit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 38.7 g/1 and a thermal conductivity of 19.0 mW/mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative components (a) to (c) was 33.4% by weight.
Example 3 Component A: a mixture comprising 55.9 parts by weight of a polyether-polyol having a hydroxyl number of 370 and a content of aromatic radicals of 19.3%
by weight, prepared by anionic polycondensation of 1,2-propylene oxide onto a mixture of diaminodiphenylinethane isomers and polyphenyl-po.lymethylene-polyamines, 37.0 parts by weight of a polyether-polyol having a hydroxyl number of 340, prepared by anionic: polyaddition of 1,2-propylene oxide onto sorbitol, 3.0 parts by weight of a silicone-based foain stabilizer (Tegostab'"' B 8465 from Goldschmidt AG, Essen), 1.3 parts by weight of N,N-dimethyl.cyclohexylamine, 0.7 part by weight of N, N, N' , N" , N"---pentamethyl-diethylenetriamine, 0.3 part by weight of dipotassium hydrogenplhosphate, 1.8 parts by weight of water and 13.0 parts by weight of cyclopentane.

'2i b1,065 Component B: analogous to Example 1.

100 parts by weight of component A and 110 parts by weight of component B were mixed in a high-pressure Puromat'~ PU 1.5 uriit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about :36 g/l and a thermal conductivity of 20.0 mW/mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative components (a) to (c) was 34.5% by weight.
Example 4 Component A: analogous to Example 3.
Component B: analogous to Example 1.

100 parts by weight of component A and 130 parts by weight of component B were mixed in a high-pressure Puromat(R) PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 38 g/l and a thermal conductivity of 19.2 mW/mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative components (a) to (c) was 36.5% by weight.
Example 5 Component A: a mixture comprising 30.0 parts by weight of a polyether-polyol having a hydroxyl number of 350 and a content of aromatic radicals of 11.4%
by weight, prepared by block copolyaddition of 1,2-propylene oxide (50% by weight) and ethylene oxide (50% by weight) onto a tolylenediamine isomer mixture as initiator molecules, 23.7 parts by weight of a polyether-polyol having a hydroxyl number of 440, prepared by anionic polyaddition of 1,2-propylene oxide onto sucrose, 20.0 parts by weight of a polyether-polyol having a hydroxyl number of 550 and a content of aromatic radicals of about 11% by weight, prepared by anionic polyaddition of 1,2-propylene oxide onto, as initiator molecule, a Mannich condensate obtainable from 4,4'-dihydroxy-2,2--diphernylpropane, formaldehyde and diethanolamine, 20.0 parts by weight of a polyether-po].yol having a hydroxyl number of 120, prepared by anionic polyadditio:n of 1,2-propylene oxide onto N-(3-dimethylam:inopropyl)ethylenediamine, followed by anionic polyadd_ltion of ethylene oxide onto the resultant N-(3-dimethylaminopropyl)ethylenediamine/1,2-propylene 10 oxide adduct, 3.0 parts by weight of a silicone-based foam stabilizer (Tegostab B 8465 from Goldschmicit AG, Essen), 1.0 parts by weight of N,N-dimethylcyclohexylamine, 0.5 part by weight of N,N,N',N ",N " -pentamethyldiethylenetriamine, 1.8 parts by weight of water and 13.0 parts by weight of cyclopentane.
Component B: analogous to Example 1.
100 parts by weight of component A and 123 parts by weight of component B were mixed in a high-pressure Puromat''V PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 35 g/1 and a thermal conductivity of 19.5 mW/mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative comporients (a) to (c) was 33.4% by weight.

Example 6 Component A: analogous to Example 5 Component B: analogous to Example 1.

100 parts by weight of component A and 145 parts by weight of component B were mixed in a high-pressure Ptzromat'a' PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 37 g/l and a thermal conductivity of 18.8 mW/mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative components (a) to (c) was 35.4% by weight.

216 1 fi5 Example 7 Component A: a mixture comprising 20.0 parts by weight of a polyester-polyol having a hydroxyl number of 240 and a content of aromatic radicals of about 25% by weight, prepared by polycondensation of phthalic anhydride, ethylene glycol and diethylene glycol in a weight ratio of 43:5:52, 43.6 parts by weight of a polyether-polyol having a hydroxyl number of 490, prepared by anionic polyaddition of 1,2-propylene oxide onto sucrose, 20.0 parts by weight of a polyether-polyol having a hydroxyl number of 570 and a content of aromatic radicals of about 11.4% by weight, prepared by anionic polyaddition of 1,2-propylene oxide onto, as initiator rnolecule, a Mannich condensate obtainable froni 4,4'-dihydroxy-2,2-diphenyl.pr.opane, forrnaldehyde and diethanolamine, 10.0 parts by weight of a polyether-polyol having a hydroxyl number of 770, prepared by anionic polyaddition of 1,2-propylene oxide onto ethylenediamine as initiator molecule, 2.5 parts by weight of a silicone-based foarn stabilizer (Tegostab0 B 8465 from Goldschmi(it AG, Essen), 1.4 parts by weight of N,N-dimethylcyclohexyl.amine, 0.7 part by weight of 2,2'-bis(dimethylamino)diethyl ether, 1.8 parts by weight of water and 13.0 parts by weight of cyclopentane.
Component B: analogous to Example 1.

100 parts by weight of component A and 130 parts by weight of component B were mixed in a high-pressure Puromat(1' PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 37 g/l and a thermal conductivity of 18.9 mW%mK, measured at 23 C, was obtained. The content of aromatic radicals in the formative comporients (a) to (c) was 34.8% by weight.

276 'i~6 5 Comparative Example II

Component A: a mixture comprising 43.15 parts by weight of a polyether-polyol having a hydroxyl number of 440, prepared by ariionic polyaddition of 1,2-propylene oxide onto sucrose, 20.0 parts by weight of a polyether-polyol having a hydroxyl number of 490, prepared by anionic polyaddition of 1,2-propylene oxide onto sucrose, 12.0 parts by weight of polyoxypropylene glycol having a hydroxyl number of 105, 1.2 parts by weight of a silicone-based foarn stabilizer (Tegostabo" B 8409 from Goldschmidt AG, Lssen), 0.9 part by weight of 1,6-bis(dimethylamino)hexane, 0.4 part by weight of 1,3,5-tris(3-dimethylaminopropyl)hexahydro-s-triazine, 0.4 part by weight of N,N-dimethylcyclohexylamine, 0.3 part by weight of a 75% strength by weight solution of 2,2'-bis(dimethylamino)diethyl ether in dipropylene glycol, 1.65 parts by weight of water and 20.0 parts by weight of 1,1-dichloro-l--fluoroethane (Rl4lb).
Component B: analogous to Example 1 100 parts by weight of component A and 116 parts by weight of component B were mixed in a high-pressure Puromat'A) PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 38 g/l and a thermal conductivity of 19 mW/mK, measured at 2:3 C, was obtained.
The content of aromatic radicals in the formative comporients (a) to (c) was 30.096 by weight.

Example 8 Component A: a mixture comprising 30.0 parts by weight of a polyether-pol.yol having a hydroxyl number of 400 and a content of aromatic radicals of 13.4%
by weight, prepared by block copolyaddition of 1,2-propylene oxide (70% by weight) and ethylene oxide (30% by weight) onto a tolylenediamine isomer mixture as initiator molecules, 22.5 parts by weight of a polyether--polyol having a hydroxyl number of 490, prepared by ariionic polyaddition of 1,2-propylene oxide onto sucrose, 20.0 parts by weight of a polyether-polyol having a hydroxyl number of 550 and a content of aromatic radicals of about 11% by weight, prepared by ariionic polyaddition of 1,2-propylene oxide onto, as initiator molecule, a Mannich condensate obtainable from 4,4'-dihydroxy-2,2--diphenylpropane, formaldehyde and diethanolamine, 15.0 parts by weight of a polyether-polyol having a hydroxyl number of 120, prepared by ariionic polyaddition of 1,2-propylene oxide onto N-(3-dimethylaminopropyl)ethylenedi.amine, followed by anionic polyaddition of ethylene oxide onto the resultant N-(3-dimethylami_nopropyl)ethylenediamine/1,2-p:ropylene oxide adduct, 5.0 parts by weight of polyoxypropylene glyc:ol having a hydroxyl number of 250, 3.0 parts by weight of a silicone-based foam stabilizer (Tegostab B 8465 Goldschmidt AG, Essen), 0.7 part by weight of N,N,N',N ",N " -pentamethyldiethylenetriamine, 0.5 part by weight of N,N-dimethylcyclohexy]Lamine, 0.5 part by weight of a 42% strength by weiqht solution of a salt of a trimet.hylamine/1,2-propylene oxide adduct and formic acid in clipropylene glycol, 2.5 parts by weight of water and 20.0 parts by weight of 1,1-dichloro-l--fluoroethane (R141b).
Component B: analogous to Example 1.

100 parts by weight of component A and 140 parts by weight of component B were mixed in a high-pressure Puromat(N' PU 15 unit, and the reaction mixture was injected into a Bosch lance. A uniform rigid PU foam having a density of about 38 g/1 and a thermal conductivity of 17.5 mW/mK, measured at 23'C, was obtained. The content of aromatic radicals in the formative components (a) to (c) was 34.8% by weight.

Claims (11)

1. A process for the production of rigid polyurethane foams by reacting:

a) organic and/or modified organic polyisocyanates with b) at least one relatively high-molecular-weight compound containing at least two reactive hydrogen atoms and, optionally, c) low-molecular-weight chain extenders and/or crosslinking agents, in the presence of d) blowing agents, e) catalysts and, optionally, f) additives, wherein the process further comprises incorporating at least 32% by weight, based on the rigid polyurethane foams, of aromatic radicals incorporated in formative components (a), (b) and/or, if used, (c).

2. A process as claimed in claim 1, wherein the organic polyisocyanates (a) are aromatic polyisocyanates selected from the group consisting of 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate, polyphenyl-polymethylene polyisocyanates, 2,4- and 2,6-tolylene diisocyanate and mixtures of at least two of said polyisocyanates

3. A process as claimed in claim 1, wherein the organic polyisocyanates (a) are mixtures of diphenylmethane diisocyanates and polyphenyl-polymethylene polyisocyanates having a diphenylmethane diisocyanate isomer content of from 30 to 80% by weight.

4. A process as claimed in any one of claims 1 to 3, wherein the relatively high-molecular-weight compounds (b) are polyhydroxyl compounds having a functionality of from 2 to 8 and a hydroxyl number of from 100 to 850.

5. A process as claimed in any one of claims 1 to 4, wherein the relatively high-molecular-weight compounds (b) are polyether-polyols having a functionality of from 2 to 8 and a hydroxyl number of from 100 to 850 prepared by anionic polyaddition of at least one alkylene oxide onto, as initiator molecule, at least one aromatic compound containing at least 2 reactive hydrogen atoms and at least one hydroxyl, amino and/or carboxyl group.

6. A process as claimed in any one of claims 1 to 5, wherein the relatively high-molecular-weight compounds (b) are polyether-polyols having a functionality of from 2 to 8 and a hydroxyl number of from 100 to 850 prepared by anionic polyaddition of at least one alkylene oxide onto at least one aromatic initiator molecule from the group consisting of aromatic polycarboxylic acids, aromatic hydroxycarboxylic acids and aromatic aminocarboxylic acids, aromatic mono- and polyamines, polyphenols and Mannich condensates of phenols, formaldehyde and dialkanolamines.

7. A process as claimed in claim 6, wherein the initiator molecules are aromatic polyamines from the group consisting of 1,2-, 1,3- and 1,4-phenylenediamines, 2,3-, 2,4-, 3,4- and 2,6-tolylenediamines, 4,4'-, 2,4'- and 2,2-diaminodiphenylmethane, polyphenyl-polymethylene-polyamines, and mixtures of at least two of said polyamines.

8. A process as claimed in any one of claims 5 to 7, wherein the alkylene oxides are 1,2-propylene oxide and/or ethylene oxide.

9. A process as claimed in any one of claims 1 to 8, wherein the blowing agent (d) is cyclopentane (d1) in combination with water.

10. A process as claimed in any one of claims 1 to 8, wherein the blowing agents (d) are (d2) mixtures comprising (d2i) cyclopentane, cyclohexane or a mixture of these cycloalkane and (d2ii) low-boiling compounds which are homogeneously miscible with cyclopentane and/or cyclohexane, in combination with water.

11. The use of rigid polyurethane foams produced by a process as claimed in any one of claims 1 to 10 as an interlayer for composite elements and for foam-filling cavities in refrigeration equipment or heating elements.