CA2000019C - Process for the preparation of molded articles having a compressed peripheral zone and a cellular core, preferably shoe soles - Google Patents

Abstract

The invention deals with a process for the preparation of molded articles having a compressed peripheral zone and a cellular core, such as for example, flexible elastic shoe soles having a density of from 0.4 to 1.0 g/cm3, comprising reacting;
a) organic and/or modified organic polyisocyanates with;
b) at least one higher molecular weight compound having at least reactive hydrogen atoms and with or without;
c) lower molecular weight chain extending agents and/or crosslinking agents;
in the presence of d) low boiling point aliphatic and/or cycloaliphatic hydrocarbons having 4-8 carbon atoms in the molecule preferably pentanes as blowing agents;
e) catalysts; and with or without;
f) auxiliaries and/or additives.

Description

2Q~ 9 PROCESS FOR THE PREPARATION OF MOLDED ARTICLES=-HAVING A COMPRESSED PERIPHERAL ZONE AND A
CELLULAR CORE, PREFERABLY SHOE SOLES

Background of the Invention I. Field of the Invention The present invention relates to a process for the preparation of urethane group-containing molded articles, most preferably shoe soles, having a compressed peripheral zone and a cellular core, the so-called integral skin foams, from conventional starting materials, but using low boiling point aliphatic and/or cycloaliphatic hydrocarbons having 4 to 8 carbon atoms in the molecule as a blowing agent.
II. Description of the Related Art The preparation of molded articles having a cellular core and a compressed peripheral zone has been known for some time and, for example, is disclosed in Federal Republic of Germany, 16 94 138 (Great Britain 1 209 243), Federal Republic of Germany 19 55 891 (Great Britain 1 321 679) and Federal Republic of Germany 17 69 886 (United States Patent 3 824 199). Such products are generally prepared by reacting organic polyisocyanates, higher molecular weight compounds having at least two reactive hydrogen atoms and optionally chain sxtend-ing agents in the presence of blowing agents, more preferably 20~ 019 physically active blowing agents, catalysts, auxiliaries and/or additives in a closed, optionally heated, mold using compres-sion.
Also known is the preparation and use of urethane group-containing shoe soles prepared by the polyisocyanate addition polymerization process in the shoe industry. Direct shoe soling and the preparation of polyurethane finished soles are primary areas of application for polyurethanes in the shoe industry. Such polyurethane shoe soles can be manufactured using low pressure or high pressure technology (RIM) (Schuh-Technik + abc, 10/1980, pages 822 ff).
A comprehensive overview of polyurethane integral skin foams has been published, for example, in Integral Skin Foams by H. Piechota and H. Rohr, Carl-Hanser Publishers, Munich, Vienna, 1975, and in the Plastics Handbook, Volume 7, Polyurethanes, by G. Oertel, Carl-Hanser Publishers, Munich, Vienna, 2nd Ed., 1983, pages 333 ff. The latter reference describes (pages 362-366) using integral skin foams in the shoe industry.
Essentially two types of blowing agents are used in the preparation of cellular plastics employing the polyisocya-nate addition polymerization process:
Low boiling point inert liquids which evaporate under the influence of the exothermic addition polymerization 2C~ 019 reaction; for example, alkanes, like butane, pentane, etc. or preferably halogenated hydrocarbons, like methylene chloride, di-chloromonofluoromethane, trichlorofluoromethane, etc.; and chemical compounds which form propellants through a chemical reaction or by thermal decomposition. Examples of the latter are the reaction of water with isocyanates to form amines and carbon dioxide which occurs in synchronization with poly-urethane formation, and the cleavage of thermally labile compounds, such as, for example, azoisobutyric acid nitrile which along with nitrogen as a cleavage product forms the toxic tetramethylsuccinic acid dinitrile, or azodicarbonamide whose use as a component in a blowing agent combination is disclosed in European Patent Application 0 092 740 (Canadian Patent 1 208 912). While the latter method in which thermally labile compounds, such as azo-compounds, hydrazides, semicarbazides, N-nitroso compounds, benzoxazines, etc. (Kunstsoffe 66 (1976), 10, pages 698-701) are generally incorporated into a prefabri-cated polymer, or rolled into plastic granules following which the compound is foamed by extrusion has remained of little industrial importance, the physically active low boiling point liquids, particularly chlorofluoroalkanes (CFC), are used through~ut the world on a large scale to produce polyurethane foams and polyisocyanurate foams.

ZO(~Ol9 A disadvantage of propellants is the problem-~f environmental pollution. When propellants are formed by th~rmal cleavage or a chemical reaction, cleavage products and/or reactive byproducts are formed and become incorporated into the addition polymerization product or are chemically bound and thus can lead to an unwanted change in the mechanical properties of the plastic. In the case of formation of carbon dioxide from water and diisocyanate, urea groups are formed in the addition polymerization product and, depending on their quantity, can lead to either an improvement in compressive strength or to embrittlement of the polyurethane.
Although aliphatic hydrocarbons such as pentane, hexane and heptane are inexpensive and non-hazardous to health, in the prior art they are only used for foaming thermo-plastics. Pentane and its isomers are, for example, used in the preparation of expanded polystyrene (Kunststoffe 62 (1972), pages 206-208) and also in phenolic resin foams (Kunststoffe, 60 (1970), pages 548-549).
Federal Republic of Germany 1 155 234 (Great Britain 904 003) discloses the preparation of polyurethane foams from an isocyanate group containing prepolymer while using a blowing agent mixture comprising water and a soluble insert gas which is-liquid under pressure. Cited as typical inert gases, are, for example, gaseous hydrocarbons, halogenated hydrocarbons, z~n~ols ethylene oxide, nitric oxides, sulfur dioxide and more ~refer-ably, carbon dioxide. According to Great Britain 876 977, sat-urated or unsaturated hydrocarbons, saturated or unsaturated dialkylethers and fluorine containing halogenated hydrocarbons can be used, for example, as blowing agents in the preparation of polyurethane rigid foams.
The high flamability, and accordingly the expensive safety measures required to use gaseous alkanes in production, is why alkanes have not been used in the prior art as blowing agents for foaming polyisocyanate addition polymerization products. Heretofore, there have been no teachings dealing with using alkanes for the preparation of integral skin foams. The object of the present invention was to completely, or at least partially, replace the conventional CFC's used as blowing agents in the preparation of polyurethane integral skin foams by other environmentally compatible blowing agents.
This object was suprisingly met by using aliphatic or cycloaliphatic hydrocarbons as blowing agents.
Accordingly, the subject of the invention is a process for the preparation of molded articles having a compressed peripheral zone and a cellular core, comprising reacting:
a) organic and/or modified organic polyisocyanates with:

2(~ 9 b) at-least one higher molecular weight compound having at least two reactive hydrogen atoms; and with or without c) lower molecular weight chain extending agents and/or crosslinking agents;
in the presence of d) blowing agents;
e) catalysts; and with or without f) auxiliaries and/or additives;
in a closed, optionally heated mold under compres-sion, wherein low boiling point aliphatic or cycloaliphatic alkanes having 4 to 8 carbon atoms in the molecule or mixtures thereof are used as the blowing agent (d).
The process is particularly suited for the prepara-tion of flexible elastic shoe soles, having a total density of from 0.4 to 1.0 g/cm3, yet the starting components are effi-caciously reacted using a one shot process with the help of high pressure technology (RIM).
Description of the Preferred Embodiments It was unexpectedly found that the alkanes used as blowing agents provided polyurethane integral skin foams having good mechanical properties which are comparable at least with products prepared while using trichlorofluoromethane. Since the gas yields, i.e. the foam volume obtained per mole of 2~(30~9 blowing agent, with the (cyclo)aliphatic alkanes are suhstan-tially greater then those of the previously used CFC's having a comparable boiling point, the lower molecular weight allows a substantial reduction in the required quantity of blowing agent. Thus, with alkane contents of from 35 to 40 weight percent based on the required CFC quantity, polyurethane integral skin foams having the same total density were obtained. In spite of the reduced blowing agent quantity, the compressed peripheral zone on the surface is smooth and essentially pore-free. Because of the low required amount of blowing agent which for the most part, following curing of the integral skin foam, dissolves in the peripheral zone or remains in the cells of the core, the amount of alkane released during foaming is also low and thus no serious safety problems occur when processing.
The following should be noted with respect to typical starting components (a) through (f) for the preparation of molded articles such as shoe soles, more preferably urethane, or urethane and urea group-containing cellular elastomer molded articles and most preferably integral skin foams:
The organic polyisocyanates (a) may include all essentially known aliphatic, cycloaliphatic, araliphatic and preferably aromatic multivalent isocyanates.

2C~ 0~9 Specific examples include: alkylene diisocyanates with 4 to 12 carbons in the alkylene radical such as 1,12-dodecane diisocyanate, 2-ethyl-1,4-tetramethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, 1,4-tetramethylene diisocyanate, and preferably 1,6-hexamethylene diisocyanate;
cycloaliphatic diisocyanates such as 1,3- and 1,4-cyclohexane diisocyanate as well as any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), 2,4- and 2,6-hexahydrotoluene diisocyanate as well as the corresponding isomeric mixtures, 4,4'-, 2,2'-, and 2,4'-dicyclohexylmethane diisocyanate as well as the corresponding isomeric mixtures; and preferably aromatic diisocyanates and polyisocyanates such as 2,4- and 2,6-toluene diisocyanate and the corresponding isomeric mixtures, 4,4'-, 2,4'-, and 2,2'-diphenylmethane diisocyanate and the cor-responding isomeric mixtures, mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates (polymeric MDI~ as well as mixtures of poly-meric MDI and toluene diisocyanates. The organic di- and polyisocyanates can be used individually or in the form of mixtures.
Frequently, so-called modified multivalent iso-cyanates, i.e., products obtained by chemical reaction of organic diisocyanates and/or polyisocyanates, are used.

2C~ 019 Examples-include diisocyanates and/or polyisocyanates cQntain-ing ester groups, urea groups, biuret groups, allophanate groups, carbodiimide groups, isocyanurate groups, uretdione groups and/or urethane groups. Specific examples include organic, preferably aromatic, polyisocyanates containing urethane groups and having an NCO content of 33.6 to 15 weight percent, preferably 31 to 21 weight percent, based on the total weight, e.g., with low molecular weight diols, triols, dialkylene glycols, trialkylene glycols or polyoxyalkylene glycols with a molecular weight of up to 800: modified 4,4'-diphenylmethane diisocyanate or 2,4- and 2,6-toluene diisocya-nate, where examples of di- and polyoxyalkylene glycols that may be used individually or as mixtures include diethylene glycol, dipropylene glycol, polyoxyethylene glycol, polyoxy-propylene glycol and polyoxypropylene polyoxyethylene glycol.
Prepolymers containing NCO groups with an NCO content of 25 to 3.5 weight percent, preferably 21 to 14 weight percent, based on the total weight and produced from polyester polyols and/or preferably the polyether polyols described below; 4,4'-diphenylmethane diisocyanate, mixtures of 2,4'- and 4,4'-diphenylmethane diisocyanate, 2,4- and/or 2,6-toluene diiso-cyanates or polymeric MDI are also suitable. Furthermore, liquid polyisocyanates containing carbodiimide groups and/or isocyanurate rings and having an NCO content of 33.6 to 15 weight percent, preferably 31 to 21 weight percent, bas~d on the total weight, have also proved suitable, e.g., based on .

4,4'- and 2,4'- and/or 2,2'-diphenylmethane diisocyanate and/or 2,4- and/or 2,6-toluene diisocyanate.
The modified polyisocyanates may optionally be mixed together or mixed with unmodified organic polyisocyanates such as 2,4'- and 4,4'-diphenylmethane diisocyanate, polymeric MDI, 2,4- and/or 2,6-toluene diisocyanate.
The following have proven especially successful as organic polyisocyanates and are preferred for use in the preparation of cellular elastomers: prepolymers containing NCO
groups and having an NCO content of 25 to 9 weight percent, especially those based on polyether polyols or polyester polyols and one or more diphenylmethane diisocyanate isomers, preferably 4,4'-diphenylmethane diisocyanate; and/or modified organic polyisocyanates containing urethane groups and having an NCO content of 33.6 to 15 weight percent, especially those based on 4,4'-diphenylmethane diisocyanate or diphenylmethane diisocyanate isomeric mixtures; for preparation of flexible polyurethane foams: mixtures of 2,4- and 2,6-toluene diiso-cyanates, mixtures of toluene diisocyanates and polymeric MDI
or especially mixtures of the aforementioned prepolymers based on diphenylmethane diisocyanate isomers and polymeric MDI; and for the preparation of polyurethane rigid foams or poly-urethane-polyisocyanurate rigid foams, polymeric MDI.

2Q(~019 If molded articles having a lightfast surfacet such as for example, automobile steering wheels or instrument panels, are required for specific applications, then in their preparation one preferably uses aliphatic or cycloaliphatic polyisocyanates, most preferably, modified polyisocyanates based on 1,6-hexamethylene diisocyanate or isophorone diiso-cyanate or mixtures of the above-mentioned diisocyanates optionally with diphenylmethane diisocyanate and/or toluene diisocyanate isomers.
Preferred higher molecular weight compounds (b) having at least two reactive hydrogens include those with a functionality of 2 to 8, preferably 2 to 4, and a molecular weight of 400 to 8000, preferably 1200 to 6000. For example, polyether polyamines and/or preferably polyols selected from the group consisting of polyether polyols, polyester polyols, polythioether polyols, polyester amides, polyacetals containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl groups, and mixtures of at least two of the aforementioned polyols have proven suitable. Polyester polyols and/or polyether polyols are preferred.
Suitable polyester polyols can be produced, for example, from organic dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic acids with 4 to 6 carbons, and multivalent alcohols, preferably diols, with 2 to 12 2Q(3(~ L9 carbons, preferably 2 to 6 carbons. Examples of dicarb~xylic acids include succinic acid, glutaric acid, adipic aci-d, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids can be used individually or in mixtures. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives may also be used such as dicarboxylic acid esters of alcohols with 1 to 4 carbons or dicarboxylic acid anhydrides. Dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid in quantity ratios of 20-35:35-50:20-32 parts by weight are preferred, especially adipic acid. Examples of divalent and multivalent alcohols, especially diols, include ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, glycerol and trimethylolpropane. Ethanediol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or mixtures of at least two of these diols are preferred, especially mixtures of 1,4-butanediol, 1,5-pentane-diol and 1,6-hexanediol. Furthermore, polyester polyols of lactones, e.g., ~-caprolactone or hydroxycarboxylic acids, e.g., ~-hydroxycaproic acid, may also be used.
The polyester polyols can be produced by polyconden-sation of organic polycarboxylic acids, e.g., aromatic or 2Q~(~0~9 preferably aliphatic polycarboxylic acids and/or deriva~ives thereof and multivalent alcohols in the absence of catalysts or preferably in the presence of esterification catalysts, preferably in an atmosphere of inert gases, e.g., nitrogen, carbon monoxide, helium, argon, etc., in the melt at tempera-tures of 150 to 250~C, preferably 180 to 220~C, optionally under reduced pressure, up to the desired acid value, which is preferably less than 10, especially less than 2. In a prefer-red embodiment, the esterification mixture is subjected to polycondensation at the temperatures mentioned above up to an acid value of 80 to 30, preferably 40 to 30, under normal pressure and then under a pressure of less than 500 mbar, preferably 50 to 150 mbar. Examples of suitable esterification catalysts include iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the form of metals, metal oxides or metal salts. However, polycondensation may also be performed in liquid phase in the presence of solvents and/or entraining agents such as benzene, toluene, xylene or chlorobenzene for azeotropic distillation of the water of condensation.
To produce the polyester polyols, the organic polycarboxylic acids and/or derivatives thereof and multivalènt alcohols are preferably polycondensed in a mole ratio o~ 1:1-1.8, preferably 1:1.05-1.2. The resulting polyester polyols 2C~(~G0~9 preferably have a functionality of 2 to 4, especially 2-to 3, an~ a molecular weight of 480 to 3000, preferably 1200 to 30P0 and especially 18~0 to 2500.
However, polyether polyols, which can be obtained by known methods, are especially preferred for use as the polyols. For example, polyether polyols can be produced by anionic polymerization with alkali hydroxides such as sodium hydroxide or potassium hydroxide or alkali alcoholates, such as sodium methylate, sodium ethylate or potassium ethylate or potassium isopropylate as catalysts and with the addition of at least one initiator molecule containing 2 to 8, preferably 2 to 4, reactive hydrogens or by cationic polymerization with Lewis acids such as antimony pentachloride, boron trifluoride etherate, etc., or bleaching earth as catalysts from one or more alkylene oxides with 2 to 4 carbons in the alkylene group.
Suitable alkylene oxides include, for example, tetrahydrofuran, 1,3-propylene oxide, 1,2- and 2,3-butylene oxide, styrene oxide and preferably ethylene oxide and 1,2-propylene oxide. The alkylene oxides may be used individually, in alternation, one after the other or as a mixture. Examples of suitable initiator molecules include water, organic dicarbo-xylic acids such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optionally N-mono- N,N-, and N,N'-dialkyl substituted diamines with 1 to 4 2~ )19 carbons in the alkyl group such as optionally mono- and dialkyl-substituted ethylenediamine, diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- and 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylene-diamine, phenylenediamines, 2,3-, 2,4- and 2,6-toluenediamine and 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethane.
Suitable initiator molecules also include alkanol-amines such as ethanolamine, diethanolamine, N-methyl- and N-ethylethanolamine, N-methyl- and N-ethyldiethanolamine and triethanolamine plus ammonia. Multivalent alcohols, especially divalent and/or trivalent alcohols are preferred such as ethanediol, 1,2-propanediol and 1,3-propanediol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, pentaerythritol, sorbitol and sucrose.
The polyether polyols, preferably polyoxypropylene polyols and polyoxypropylene-polyoxyethylene-polyols have a functionality of preferably 2 to 6 and especially 2 to 4 and have a molecular weight of 400 to 8000, preferably 1200 to 6000 and especially 1800 to 4000. Suitable polyoxytetramethylene glycols have a molecular weight up to about 3500, more prefer-ably 400 to 2200.
Suitable polyether polyols also include polymer modified polyether polyols, preferably graft polyether polyols, 2~ 019 especially those based on styrene and/or acrylonitrile, which are produced by in situ polymerization of acrylonitrile, styrene or preferably mixtures of styrene and acrylonitrile, e.g., in a weight ratio of 90:10 to 10:90, preferably 70:30 to 30:70, preferably in the aforementioned polyether polyols according to the procedures described in Federal Republic of Germany Patents 1,111,394, 1,222,669 (U.S. Patents 3,304,273, 3,383,351, 3,523,093~, 1,152,536 (British Patent 1,040,452) and 1,152,537 (British Patent 987,618), as well as polyether polyol dispersions containing as the disperse phase, usually in the amount of 1 to 50 weight percent, preferably 2 to 25 weight percent: e.g., polyureas, polyhydrazides, polyurethanes containing tertiary amino groups and/or melamine, which are described, for example, in European Patent 11,752 (U.S. Patent 4,304,708), U.S. Patent 4,374,209 and Federal Republic of Germany Patent 3,231,497.
Like the polyester polyols, the polyether polyols may be used either individually or in the form of mixtures.
Furthermore, they can be mixed with the graft polyether polyols or polyester polyols as well as the polyester amides containing hydroxyl groups, the polyacetals, polycarbonates and/or polyether polyamines.
Examples of hydroxyl group-containing polyacetals that can be used include, for example, the compounds that can 2(~ 0~9 be produced from glycols such as diethylene glycol, triethylene glycol, 4,4'-dihydroxyethoxydiphenyldimethylmethane, hexanediol and formaldehyde. Suitable polyacetals can also be produced by polymerization of cyclic acetals.
Suitable hydroxyl group-containing polycarbonates include those of the known type such as those obtained by reaction of diols, e.g., 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol and diaryl carbonates, e.g., diphenyl carbonate, or phosgene.
The polyester amides include the mainly linear condensates obtained from multivalent saturated and/or unsatu-rated carboxylic acids and their anhydrides and multivalent saturated and/or unsaturated amino alcohols or mixtures of multivalent alcohols and amino alcohols and/or polyamines.
Suitable polyether polyamines can be produced from the polyether polyols mentioned above by known methods.
Examples include cyanoalkylation of polyoxyalkylene polyols and subsequent hydrogenation of the nitrile thus formed (U.S.
Patent 3,267,050) or partial or complete amination of polyoxy-alkylene polyols with amines or ammonia in the presence of hydrogen and catalysts (Federal Republic of Germany Patent 1,215,373).

ZQ~ )19 The molded articles having a compressed peripheral zone and a cellular core and preferably urethane or urethane and urea group-containing molded articles can be prepared with or without using chain extending agents and/or crosslinking agents. To modify the mechanical properties, e.g., hardness, however, it has proven advantageous to add (c) chain extenders, crosslinking agents or mixtures thereof. Suitable chain extenders and/or crosslinking agents include diols and/or triols with molecular weights of less than 400, preferably 60 to 300. Examples include aliphatic, cycloaliphatic and/or araliphatic diols with 2 to 14 carbons, preferably 4 to 10 carbons, such as ethylene glycol, 1,3-propanediol, 1,10-decanediol, 1,2-, 1,3-, and 1,4-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 trimethylolpropane and low molecular weight hydroxyl group-containing polyalkylene oxides based on ethylene oxide and/or 1,2-propylene oxide and the aforementioned diols and/or triols as initiator molecules.
In addition to the aforementioned diols and/or triols, or in admixture with them as chain extenders or -crosslinking agents to prepare the cellular elastomer molded articles and integral skin foams, most preferably shoe soles 20~3~0~9 according to this invention, it is also possible to use-secondary aromatic diamines, primary aromatic diamines, 3,3' di- and/or 3,3'-, 5,5'-tetraalkyl-substituted diaminodiphenyl-methanes.
Examples of secondary aromatic diamines include N,N'-dialkyl-substituted aromatic diamines, which may optionally be substituted on the aromatic ring by alkyl groups, where there are 1 to 20, preferably 1 to 4 carbons in the N-alkyl group such as N,N'-diethyl-, N,N'-di-sec-pentyl-, N,N'-di-sec-hexyl-, N,N'-di-sec-decyl-, N,N'-dicyclohexyl-p- or -m-phenylene-diamine; N,N'-dimethyl-, N,N'-diethyl-, N,N'-diisopropyl-, N,N'-di-sec-butyl-, N,N'-dicyclohexyl-4,4',-diaminodiphenyl-methane and N,N'-di-sec-butylbenzidine.
The preferred aromatic diamines are those having at least one alkyl substituent in ortho position to the amino groups and they are liquid at room temperature and are miscible with component (b), especially the polyether polyols. Further-more, alkyl-substituted meta-phenylenediamines of the following formulas have also proven successful:

2 ~ R and/or ~ R

2~ 019 where R3 and R2 may be the same or different and denote a methyl group, a propyl group, and an isopropyl group, and Rl is a linear or branched alkyl group with 1 to 10 carbons, preferably 4 to 6 carbons.
Alkyl groups Rl in which the branching site is on the cl carbon are especially suitable. Examples of Rl groups include methyl, ethyl, isopropyl, l-methyloctyl, 2-ethyloctyl, l-methylhexyl, l,l-dimethylpentyl, 1,3,3-trimethylhexyl, 1-ethylpentyl, 2-ethylpentyl and preferably cyclohexyl, l-methyl-n-propyl, tert.-butyl, l-ethyl-n-propyl, l-methyl-n-butyl, and l,l-dimethyl-n-propyl.
Examples of alkyl-substituted m-phenylenediamines include especially: 2,4-dimethyl-6-cyclohexyl-1,3-phenylene-diamine, 2-cyclohexyl-4,5-diethyl-1,3-phenylenediamine, 2-cyclohexyl-2,6-isopropyl-1,3-phenylenediamine, 2,4-dimethyl-6-(l-ethyl-n-propyl)-1,3-phenylenediamine, 2,4-dimethyl-6-(1,1,-dimethyl-n-propyl)-1,3-phenylenediamine and 2-(1-methyl-n-butyl)-4,6-dimethyl-1,3-phenylenediamine. Preferred examples include l-methyl-3,5-diethyl-2,4- and 2,6-phenylenediamines, 2,4-dimethyl-6-tert-butyl-1,3-phenylenediamine, 2,4-dimethyl-6-isooctyl-1,3-phenylenediamine and 2,4-dimethyl-6-cyclohexyl-1,3-phenylenediamine.

Z0(~(~019 Suitable 3,3'-di- and 3,3',5,5'-tetra-n-alkyl-substituted 4,4'-diaminodiphenylmethanes include, for examplç, 3,3'-dimethyl-3,3',5,5'-tetramethyl, 3,3'-diethyl-, 3,3',5,5'-tetraethyl-, 3,3'-di-n-propyl and 3,3',5,5'-tetra-n-propyl-4,4'-diaminodiphenylmethane.
Diaminodiphenylmethanes of the following formula are preferred:

H2N~ CH2--~NH2 where R4, R5, R6 and R7 may be the same or different and denote a methyl group, an ethyl group, a propyl group, an isopropyl group, a sec-butyl group and a tert.-butyl group, but at least one of the groups must be an isopropyl group or a sec-butyl group. The 4,4'-diaminodiphenylmethanes may also be used in mixture with isomers of the formulas 2~G0~9 R4~H2 ~NH2 and/or R4--~--CH ~R6 where R4, R5, R6 and R7 have the meanings given above.
The preferred diaminodiphenylmethanes are 3,5-dimethyl-3',5'-diisopropyl-4,4'-diaminodiphenylmethane and 3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane. The diaminodiphenylmethanes may be used individually or in the form of mixtures.
These chain extenders and/or crosslinking agents (c) may be used individually or as mixtures of the same or dif-ferent types of compounds.
If chain extenders, crosslinking agents or mixtures thereof are used, they are preferably used in amounts of 2 to 60 weight percent preferably 8 to 50 weight percent and especially 10 to 40 weight percent, based on the weight of components (b) and (c).
In the preparation of the flexible elastic shoe soles, one preferably uses as said higher molecular weight compounds (b), polyester polyols or polyether polyols having a functionality of from 2 to 4, more preferably 2 and a molecular zoo~o~9 weight of 1200 to 6000 and as said chain extending agent or cross linking agent (c), primary aromatic diamines which in the ortho position relative to each amino group have at least one alkyl radical having 1 to 3 carbon atoms in bonded form, or mixtures of such aromatic alkyl substituted diamines, and diols and/or triols.
Blowing agents (d) that can be used according to this invention include low boiling point cycloalkanes having 4 to 8 carbon atoms, more preferably 5 to 6 carbon atoms in the molecule and most preferably linear or branched alkanes having 4 to 8 carbon atoms, more preferably 5 to 7 carbon atoms in the molecule. Typical cycloaliphatic hydrocarbons are, for example: cyclobutane, cyclopentane, cycloheptane, cyclooctane, and more preferably cyclohexane. Most preferably used are aliphatic hydrocarbons, such as for example: butane, n- and isopentane, n- and isohexane, n- and isoheptane, and n- and isooctane. Having been successfully proven and therefore most preferably used are isopentane, more particularly n-pentane and mixtures of pentanes.
The (cyclo)aliphatic alkanes used in the present invention are employed individually or in the form of mixtures of two or more blowing agents. Efficaciously, the (cyclo)ali-phatic alkanes are used in a quantity of from 0.5 to 10 weight percent, more preferably 1 to 7 weight percent based on the 2QQ~019 weight of components (a), (b) and optionally (c), whereby in the preparation of cellular elastomers quantities of from 1 to 4 weight percent based on (a) through (c) result in products having satisfactory mechanical properties.
In addition to the blowing agents (d) used according to the invention, water is also suitable as a blowing agent which reacts with the organic, optionally modified, polyiso-cyanates (a) to form carbon dioxide and urea groups and accordingly the compressive strength of the finished products are influenced. Since the water normally contained in poly-ester and polyether polyols as a byproduct is generally sufficient, often no additional water is necessary. However, if additional water must be incorporated into the polyurethane formulation, then conventionally one uses from 0.05 to 2 weight percent, more preferably 0.1 to 1 weight percent based on the total of starting components (a) through (c).
Suitable catalysts (e) for producing the molded articles having a compressed peripheral zone and a cellular core include especially compounds that greatly accelerate the reaction of the hydroxyl group containing compounds of com-ponent (b) and optionally (c) with the organic optionally modified polyisocyanates (a). Examples include organic metal compounds, preferably organic tin compounds such as tin(II) salts of organic carboxylic acids, e.g., tin(II) acetate, ZQ~(~Ol9 tin(II) dioctoate, tin(II) ethylhexoate and tin(II) laurate, as well as the dialkyltin(IV) salts of organic carboxylic acids e.g., dibutyltin diacetate. The organic metal compounds are used alone or preferably in combination with strong basic amines. Examples include amines such as 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methylmorpholine, N-ethylmorpholine, N-cyclohexylmorpholine, N,N,N',N'-tetra-methylethylenediamine, N,N,N',N'-tetramethylbutanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ester, bis~dimethylaminopropyl) urea, dimethylpiperazine, 1,2-di-methylimidazole, l-aza-bicyclo-[3.3.0]octane and preferably 1,4-diaza-bicyclo[2.2.2]octane and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine.
Suitable catalysts when using a large polyisocyanate excess also include tris(dialkylamino)-s-hexahydrotriazines, especially tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, alkali hydroxides such as sodium hydroxide and alkali alcoholates such as sodium methylate and potassium isopropylate as well as alkali salts of long-chain fatty acids with 10 to 20 carbons and optionally OH pendent groups. 0.001 to 5 weight percent, especially 0.05 to 2 weight percent, of - - -o~9 catalyst or catalyst combination based on the weight of component (b) is preferred.
Optionally other additives and/or auxiliaries (f) may be incorporated into the reaction mixture to produce the molded articles. Examples include surface active substances, foam stabilizers, cell regulators, fillers, dyes, pigments, flame retardants, hydrolysis preventing agents, fungistatic and bacteriostatic agents.
Examples of surface active substances include compounds that support the homogenization of the starting materials and are optionally also suitable for regulating cell structure. Examples include emulsifiers such as the sodium salts of castor oil sulfates or of fatty acids as well as salts of fatty acids with amines, e.g., diethanolamine oleate, diethanolamine stearate, diethanolamine ricinoleate, salts of sulfonic acids, e.g., alkali or ammonium salts of dodecyl-benzenesulfonic acid or dinaphthylmethanedisulfonic acid and ricinoleic acid; foam stabilizers such as siloxane-oxyalkylene copolymers and other organopolysiloxanes, ethoxylated alkyl-phenols, ethoxylated fatty alcohols, paraffin oils, castor oil and ricinoleic acid esters, Turkey red oil and peanut oil as well as cell regulators such as paraffins, fatty alcohols and dimethyl-polysiloxanes. Furthermor-e, the oligomeric acrylates with polyoxyalkylene and fluoroalkane side groups are also 2 ~

suitable for improving the emulsifying effect, the cell structure and/or for stabilizing the foam. These surface-active substances are generally used in amounts of 0.01 to 5 parts by weight based on 100 parts by weight of component (b).
Typical release agents are for example: reaction products of fatty acid esters with polyisocyanates, salts from amino group containing polysiloxanes and fatty acids, salts of unsaturated or saturated ~cyclo)aliphatic carboxylic acids having at least 8 carbon atoms and tertiary amines as well as most preferably internal release agents, such as for example, carboxylic acid esters and/or amides prepared by the esterifi-cation or amination of a mixture of montanic acid and at least one aliphatic carboxylic acid having at least 10 carbon atoms with at least difunctional alkanolamines, polyols and/or polyamines having molecular weights of from 60 to 400 (European Patent 153 639), or mixtures of organic amines, metal salts of a steric acid and organic mono- and/or dicarboxylic acids or their anhydrides (Federal Republic of Germany 36 07 447).
Fillers, especially reinforcing fillers, are under-stood to refer to the known conventional organic and inorganic fillers, reinforcing agents, weighting agents, agents to improve abrasion properties in paints, coatings agents, etc.
Specific examples include inorganic fillers, such as silicate minerals, such as layer silicates; e.g. antigorite, serpentine, 2¢;~019 hornblendes, amphiboles, chrysotile, talc; metal oxides such as kaolin, aluminum oxides, aluminum silicate, titanium oxides and iron oxides, metal salts such as chalk, heavy spar; and inorganic pigments such as cadmium sulfide, zinc sulfide as well as glass, etc. Examples of organic fillers include carbon black, melamine, colophony, cyclopentadienyl resins and graft polymers.
The organic and inorganic fillers may be used individually or as mixtures and are advantageously incorporated into the reaction mixture in amounts of 0.5 to 50 weight percent, preferably 1 to 40 weight percent, based on the weight of components (a) to (c).
Suitable flame retardants include, for example, tricresyl phosphate, tris-2-chloroethyl phosphate, tris-chloropropyl phosphate, tris-2,3-dibromopropyl phosphate, tris(l,3-dichloropropyl)phosphate and tetrakis-(2-chloroethyl)-ethylene diphosphate.
In addition to the aforementioned halogen substituted phosphates, inorganic flame retardants may also be used such as red phosphorus, aluminum oxide hydrate, antimony trioxide, arsenic oxide, aluminum polyphosphate and calcium sulfate.or cyanuric acid derivatives such as melamine or mixtures of at least two flame retardants, such as for example, ammonium polyphosphates and melamine, plus optionally cornstarch for 2Q~C~0~9 making the polymerization polyaddition products flame resist-ant. In general, it has proven expedient to use 5 to 50 parts by weight, preferably 5 to 25 parts by weight, of the afore-mentioned flame retardants for each 100 parts by weight of components (a~ through (c).
Details regarding the aforementioned other conven-tional additives and auxiliaries can be obtained from the technical literature, e.g., the monograph by J.D. Sauders and K.C. Frisch "High Polymers," volume XVI, Polyurethanes, parts 1 and 2, Interscience Publishers, 1962 and 1964, or Plastics Handbook, Polyurethanes, volume VII, Carl Hanser Publishers, Munich, Vienna, 1st and 2nd editions, 1966 and 1983.
To produce the molded articles the organic poly-isocyanates (a), higher molecular weight compounds with at least two reactive hydrogens (b) and optional chain extenders and/or crosslinking agents (c) are reacted in amounts such that the equivalent ratio of NCO groups of polyisocyanates la) to the total reactive hydrogens of component (b) and optionally (c) amounts to 1:0.85-1.25, preferably 1:0.95-1.15. If the molded articles contain at least some isocyanurate groups in bonded form then conventionally a ratio of NCO groups of polyisocyanates (a) to the total reactive hydrogens of com-ponent (b) and optionally (c) will be from 1.5-60:1, preferably 1.5-8:1.

2C(~G019 Molded articles, especially flexible elastic integral skin foams and cellular elastomer molded articles are prepared employing a prepolymer process or preferably a one shot process with the help of low pressure technology or more preferably high pressure reaction injection molding technology in closed, efficaciously heated molds, for example, metal molds made from aluminum, cast iron or steel, or molds made of fiber reinforced polyester compositions or epoxied compositions. Examples of these process variations are described by Piechota and Rohr in Integral Skin Foams, Carl-Hanser Publishers, Munich, Vienna, 1975; D.J. Prepelka and J.L. Wharton in Journal of Cellular Plastics, March/April, 1975, pages 87-98; U. Knipp in Journal of Cellular Plastics, March/April, 1973, pages 76-84; and in the Plastics Handbook, volume 7, Polyurethanes, 2nd ed., 1983, pages 333 ff.
It is proven to be most beneficial to work according to a two component process and to incorporate starting com-ponents (b), (d), (e) and optionally (c) and (f) into component (A) and to use organic polyisocyanates, modified polyiso-cyanates (a) or mixtures of the aforesaid polyisocyanates as the ~B) component optionally including blowing agent (d).
The starting components are mixed together at a temperature of from 15 to 90~C, more preferably 20 to 35~C and injected into the closed mold optionally under increased z~ 9 pressure. Mixing can be done mechanically using a stirrer or using a stirrer screw or even under an elevated pressure in a so-called countercurrent injection process. The mold tempera-ture is normally 20 to 90~C, more preferably 30 to 60~C and most preferably 45 to 50~C.
The preparation of the out-, mid-, or comfort shoe soles, for example, employs a one shot process with the help of high pressure technology. The preparation of dual density shoe soles is described for example, in Schuh-Technik + abc 10 (1980), pages 822 ff. In the preparation of the aforesaid, first the reaction mixture is injected into the mold to form the urethane and urea group containing out-soles. Following a mold residency time of from 10 to 120 seconds, more preferably 20 to 90 seconds the out-sole can be demolded, or when using a shoe mold having a swiveling double last stand adapter this may be rotated by 180~ to prepare the mid- or comfort sole follow-ing which the mold is reclosed. The reaction mixture for preparing the mid- or comfort sole is then injected while the out-sole has sufficient green strength but before it is completely cured. Generally, the injection is done at 20 to 100 seconds, more preferably 30 to 90 seconds after completion of the injection process for forming the out-sole. Normally one can dispense with the additional use of adhesives for bonding the out-, mid-, or comfort soles.

2QO(~9 The quantity of reaction mixture injected into the mold is measured so that the resulting integral skin foam molded article has a density of 0.08 to 1.2 g/cm3, whereby micro-cellular elastomer molded articles preferably have a density of 0.7 to 1.2 g/cm3, more preferably 0.8 to 1.0 g/cm3;
the rigid and semi-rigid integral skin molded articles prefer-ably have a density of 0.2 to 0.8 g/cm3, most preferably 0.35 to 0.8 g/cm3; the flexible elastic integral skin foam molded articles have a density of from 0.08 to 0.7 g/cm3, more preferably 0.12 to 0.6 g/cm3; and the shoe soles have a density of from 0.4 to 1.0 g/cm3, whereby the out-soles preferably have a density of 0.8 to 1.0 g/cm3, or higher; and the mid- or comfort soles most preferably have a density of from 0.45 to 0.65 g/cm3. The degree of compression in the preparation of molded articles having a compressed peripheral zone and a cellular core lies in a range of from 1.1 to 8.5, more prefer-ably 2 to 7 whereby for elastic flexible integral skin foams and mid, or comfort soles the degree of compression is from 2.4 to 4.5 and for rigid integral skin foams and out-soles the degree of compression is preferably from 3 to 7.
If the molded articles prepared according to the present invention are not used as shoe soles then the micro-cellular elastomer molded articles may be suited for use in the automobile industry, for example, as bumper coverings, impact 20~ 9 protection moldings and body parts such as, drip moldings, fenders, spoilers and wheel extensions, as well as engineering housing components and rollers. The integral skin foams are used for example, as arm rests, head rests, safety coverings in the interior of automobiles and as motorcycle and bicycle saddles and finally as coverings for composite foams.
The parts cited in the following examples refer to parts by weight.
Example 1 A Component:
A mixture comprising:

70 parts by weight of a polyoxypropylene (75 weight percent) polyoxyethylene (25 weight percent) glycol having a hydroxyl number of 23 prepared while using ethylene glycol as an initiator molecule;

18 parts by weight of a polyoxypropylene (75 weight percent) polyoxyethylene (25 weight percent) triol having a hydroxyl number of 35 prepared while using glycerin as an initiator molecule;
10.5 parts by weight of 1,4-butanediol;

1.0 parts by weight of a foam stabilizer based on a silicone (DC 193 from Dow Corning);
0.5 parts by weight of triethylene diamine;
0.02 parts by weight of dibutyltin dilaurate; and 1.95 parts by weight n-pentane.

~Q~3~0~9 B Component:
A urethane group-containing polyisocyanate mixture having a NCO content of 23 weight percent prepared by reacting 89 parts by weight of 4,4'-diphenylmethane diisocyanate with 11 parts by weight of dipropylene glycol.
100 parts by weight of the A component and 52 parts by weight of B component were intensively mixed together at 23~C and then the reaction mixture was placed in a plaque shaped aluminum mold heated to 50~C having the dimensions 20 cm x 20 cm x 1 cm in such a quantity so that following foaming and curing in the closed mold the integral skin foam plaque had a total density of 0.6 g/cm3.
Obtained was a molded plaque having a pronounced peripheral zone and a smooth surface which had the following mechanical properties:

Tensile strength according to DIN 53 504 lN/mm2]: 5.5 Percentage elongation at break according to DIN 53 504 [%]: 450 Hardness according to DIN 53 505 [Shore A~: 70 Abrasion according to DIN 53 516 [mg]: 140 Comparison Example I:
The same procedure ùsed in example 1 was followed, however, in place of the 1.95 parts by weight of n-pentane 5.5 parts by weight of trichlorofluoromethane was used.

20~(~0~9 The resulting molded plaque had a smooth surface and the following mechanical properties:

Tensile strength according to DIN 53 504 [N/mm21: 5.3 Percentage elongation at break according to DIN 53 504 [%~: 440 Hardness according to DIN 53 505 [Shore A]: 72 Abrasion according to DIN 53 516 [mg]: 135 Example 2 A component A mixture comprising:
42 parts by weight of a polyoxypropylene (75 weight percent) polyoxyethylene ~25 weight percent) glycol having a hydroxyl number of 23 prepared while using ethylene glycol as an initiator molecule;
40 parts by weight of a polyoxypropylene (75 weight percent) polyoxyethylene (25 weight percent) triol having a hydroxyl number of 35 prepared while using glycerin as an initiator molecule;

5 parts by weight of ethylene glycol;
0.3 parts by weight of triethylene diamine; and 7.0 parts by weight n-pentane.
B Component:
A urethane group-containing polyisocyanate mixture having an NCO content of 28 weight percent prepared by par-tially reacting a mixture of diphenylmethane diisocyanates and ;~Q(~(~Ol9 polyphenyl polymethylene polyisocyanates with dipropylene glycol.
100 parts by weight of the A component and 30 parts by weight of the B component were intensively mixed together at 23~C and then the reaction mixture was placed in an aluminum mold heated to 50~C having the shape of an automobile head rest in such a quantity so that after foaming and curing the reaction mixture in the closed mold the integral skin headrest had a total density of 0.3 g/cm3.

Comparison Example II
15 parts by weight of trichlorofluoromethane had to be used in place of 7 parts by weight of n-pentane to obtain a head rest having an equal density and essentially the same mechanical properties while utilizing the starting materials described in example 2.

Example 3 Two high pressure units of the type Desma PSA 74 were used to prepare dual density shoe soles. The shoe mold heated to 50~C was equipped with a swiveling double last stand adapter. The mold volume for the out-sole was 80 cm3 and that of the mid-sole was 200 cm3. Using the first Desma PSA 74 high pressure unit the first reaction mixture was injected to 2~ )19 prepare the out-sole. Following 60 and/or 90 seconds the mold was opened by grasping the double last stand adapter which was then rotated by 180~ so that the second last came to rest over the mold. The second last was then lowered onto the mold, and the mold was closed from above. The reaction mixture for preparing the mid-sole was injected in such a quantity so that its density was 0.45 g/cm3. The dual density shoe sole was demolded after a total of 2 minutes. After several days of storage at room temperature the bond strength of the shoe sole bond was determined by a tensile test. Here the boundary surface between the out-sole and mid-sole were cut and then both soles were torn apart from one another. An adhesion break occurred when separating the out-sole and mid-sole at their boundary surface. In the cohesion break cracking occurred in the polyurethane, polyurea-elastomer.

A component A mixture comprising:

~2.95 parts by weight of a polyoxypropylene-polyoxyethylene glycol having a hydroxyl number of 29 prepared by the addition polymerization of 1,2-propylene oxide and subsequently ethyleneoxide on propylene glycol;

6.0 parts by weight 2,4-dimethyl-6-t-butylphenylene-1,3-diamine;

1.0 parts by weight of a 33 weight percent solution of diazabicyclooctane in dipropylene glycol; and 2C~ 9 0.05 parts by weight of dibutyltin dilaurate; and B Component:
A urethane group-containing polyisocyanate mixture having an NCO content of 23 weight percent prepared by par-tially reacting 4,4'-diphenylmethane diisocyanate with dipro-pylene glycol.
100 parts by weight of the A component and 23.1 parts by weight of the B component (corresponding to an NCO index of 1.05) were reacted at 30~C employing a RIM process on a high pressure machine of the type Desma PSA 74 into a non-cellular out-sole having a density of 1.1 g/cm3.
After 60 seconds the out-sole was partially demolded by elevating the out-sole mold of the double last, swiveling the double last stand adapter by 180~ and then reclosing the mold with the mid-sole mold. After another 15 seconds the reaction mixture for preparing the mid-sole was injected. It (the A component) was a mixture comprising:

~3.55 parts by weight of the aforesaid polyoxypropylene-polyoxyethylene glycol having a hydroxyl number of 29 prepared by the addition polymerization 1,2-propylene oxide and subsequently ethylene oxide on propylene glycol;
~.0 parts by weight of 2,4-dimethyl-6-t-butyl-phenylene-1,3-diamine;

z~ 9 1.0 parts by weight of a 33 weight percent solution of diazabicyclooctane in dipropylene glycol;
U.05 parts by weight of dibutyltin dilaurate;
.1 part by weight of a silicone oil (DC 193 from Dow Corning);
0.3 parts by weight of water;

2.0 parts by weight of a mixture of n-pentane and isopen-tane in a weight ratio of 50:50; and 30.4 parts by weight of a urethane group-containing polymer-ization mixture having an NCO content of 23 weight percent (B component), prepared by partially reacting 4,4'-diphenylmethane with dipropylene glycol.
The reaction mixture (isocyanate index was 1.05) was injected at a temperature of 30~C into the mold in such a quantity so that the mid-sole had a density of 0.45 g/cm3. The dual density shoe sole prepared in this fashion was demolded after two minutes.
After several days of storage the adhesion of the bond was measured using 2 cm wide strips with the help of a tensile testing machine. In all of the samples the propagation of the tearing occurred in the polyurethane polyurea elastomer (cohesion break) and not at the surface of the out-sole and mid-sole. The maximum tear propagation strength values were at 5.4 N/mm.

2~Q019 Example 4 A Component A mixture comprising:

55 parts by weight of a polyoxypropylene triol initiated with trimethylolpropane having a hydroxyl number of 550;

5 parts by weight of a polyoxypropylenepolyol initiated with sucrose having a hydroxyl number of 400;

15 parts by weight of a polyoxypropylene (75 weight percent) polyoxyethylene (25 weight percent) triol having a hydroxyl number of 35 prepared while using glycerin as an initiator molecule;
9 parts by weight of glycerin;

~.8 parts by weight of a foam stabilizer based on a silicone (Tegostab~ T 8418 from Goldschmidt AG, Essen, Federal Republic of Germany);
2.0 parts by weight of N,N-dimethylcyclohexylamine;
0.25 parts by weight of water; and 5.5 parts by weight of tri-(2-chloromethyl)phosphate.
B Component:
A mixture of diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates having an NCO content of 31 weight percent.
3.2 parts by weight of n-pentane were first incorpo-rated into 93.5 parts by weight of the A component and then 130 parts by weight of the B component was intensively added to the resulting mixture.

2C~ )19 The reaction mixture was filled into an open mold and allowed to foam there. A polyurethane rigid foam was obtained having a density (free rise foam) of 110 9/1.
In addition the reaction mixture was placed in an aluminum mold heated to 50~C whose internal dimensions were 20 cm x 20 cm x 1 cm in such a quantity so that after foaming in the closed mold and curing a molded plaque resulted having a density of 600 9/l.
A molded plaque made of polyurethane rigid integral skin foam was obtained having a very well pronounced external skin.

Comparison III
The procedure of example 4 was followed, however, 6.5 parts by weight of trichlorofluoromethane were used as a blowing agent in place of the 3.2 parts by weight of n-pentane.
Here we obtained: a polyurethane rigid foam having a density (free rise foam) of 110 g/l and a polyurethane rigid integral skin foam molded plaque having a density of 600 9/1 which likewise had a very well defined external skin.

Claims (12)

1. In a process for the preparation of an molded article having a compressed peripheral zone and a cellular core, prepared by reacting:
a) an organic and/or modified organic polyisocyanate with:
b) at least one higher molecular compound having at least two reactive hydrogen atoms;
in the presence of:
d) at least one blowing agent;
e) at least one catalyst;
in a closed mold under compression, the improvement comprising: employing as a blowing agent (d), a low boiling point aliphatic or cycloaliphatic alkane having 4-8 carbon atoms in the molecule, or mixtures thereof.

2. The process of claim 1, wherein components a) and b) are reacted together with c) lower molecular weight chain extending agents and/or cross-linking agents.

3. The process of claim 1 or 2, wherein the reaction is carried out in the presence of f) auxiliaries and/or additives.

4/. The process of claim 1, 2 or 3, wherein the aliphatic and/or cycloaliphatic alkane is used in a quantity of from 0.5 to 10 weight percent based on the total weight of components (a) through (c).

5. The process of any one of claim 1 to 4, wherein n-pentane, isopentane, or their mixture is used as the blowing agent.

6. The process of any one of claims 1 to 5, wherein the molded articles from the polymerization addition polymerization products are flexible integral skin type articles.

7. In a process for the preparation of a flexible shoe sole having a compressed peripheral zone and a cellular core having a total density of from 0.4 to 1 gram per cm3, comprising reacting:
a) an organic and/or modified polyorganic isocyanate with:
b) at least one higher molecular weight compound having at least two reactive hydrogen atoms;
in the presence of:
d) at least one blowing agent;
e) at least one catalyst;
using the one shot process with the help of high pressure technology (RIM) in a closed mold under compression, the improvement comprising: employing as a blowing agent (d), a low boiling point aliphatic or cycloaliphatic alkane having 4 to 8 carbon atoms in the molecule, or mixtures thereof.

8. The process of claim 7, wherein components a) and b) are reacted together with c) lower molecular weight chain extending agents and/or cross-linking agents.

9. The process of claim 7 or 8 wherein the reaction is carried out in presence of f) auxiliaries and/or additives.

10. The process of any one of claim s 7, 8 or 9, wherein the aliphatic and/or cycloaliphatic alkane is used in a quantity of from 0.5 to 10 weight percent based on the total weight of components (a) through (c).

11. The process of any one of claim 7 to 10, wherein n-pentane, isopentane or their mixture is used as the blowing agent.

12. The process of any one of claim 7 to 11, wherein polyester or polyetherpolyols having a functionality of 2 to 4 in a molecular weight of 1200 to 600 are used as the higher molecular weight compound (b); and primary aromatic amines are used as the chain extending and/or cross-linking agents (c) which comprise at least one alkyl radical having 1 to 3 carbon atoms in bonded form in the ortho position relative to each amino group.