IE42432B1 - Polythylene foam/polyurethane composites - Google Patents

Abstract

1503542 Polyethylene foam/polyurethane composites BAYER AG 1 May 1975 [24 July 1974 6 May 1974] 18196/75 Heading B2E A composite material comprises a layer of cross-linked polyethylene foam joined in the absence of an adhesion promotor to a layer of unfoamed polyurethane. Several alternate layers of each material may be present. The polyethylene foam is preferably crosslinked by electron beam, Co90 rays, or by peroxides. An exhaustive list of suitable polyurethanes is given. The polyurethane may be applied as a dispersion, solution, suspension or powder and heated, or by applying a mixture of isocyanate/reactive hydrogen precursors e.g. as a melt and allowing them to harden. Powder coatings may be calendered after being heated. In Examples: (1 to 3) polyurethane powders are applied to the surface of polyethylene foams which have a closed-cell surface or open-cell surface formed by slicing off the closed-cell surface; (4, 6) a reaction mixture is sprayed onto polyethylene foam surfaces; and (5) a hot reaction mixture is poured onto polyethylene foam.

Description

This invention relates to polyethylene foam/polyurethane composites.

Various types of composites are known. For example, German Offenlegungsschrift No. 1,704»647 describes composite \ foams consisting of thermoplastic, foamed plastics materials in the form of strands, tapes, films or mixtures thereof and foamed duroplastic, i.e. thermosetting, plastics materials, the proportion of thermoplastic foams being from 10 to 90$, by weight, preferably from 50 to 75$, by weight, of the com10 posite foam mass. Polyethylene, for example, may be used as the thermoplastic foamed plastics material, whilst polyurethane, for example, may be used as the foamed, duroplastic plastics material.

The composite foams known from the prior art are produced by introducing the thermoplastic foam strands or tapes into a suitable vessel or container in a totally random arrangement to form a tangled ball of strands or tapes. This is followed by the addition of the hardenablc and foamable duroplastic masses and by the known foaming process.

The composite foams produced in this way do not consist of a combination of various layers, instead the thermoplastic foam, for example the polyethylene foam, is contained in the duroplastic foam in a random arrangement in the form of strands, tapes or films without any appreciable adhesion.

Attempts have been made to combine polyethylene in compact form, for example, in the form of polyethylene film, with polyurethane foam. It has been found that there is hardly any adhesion between the two plastics, so that polyethylene film may even be successfully used as a release film in the in-mould foaming of polyurethanes (cf. US Patent No. 187,069).

If it is desired to unite the polyethylene film with the polyurethane foam, it is necessary to take additional measures, for example to add adhesion promoters, such as adhesives, in order to obtain enough adhesion in the composite. The use of adhesion promoters is, expensive because it involves additional operations. Additionally adhesion promoters are often expensive so that, in each case, economic disadvantages are incurred by the use of adhesion promoters. Moreover, the use of adhesion promoters gives rise to the formation of an intermediate layer in the composite material which influences the physical properties of the composite. Accordingly, it is desirable to produce composites without the use of adhesion promoters.

Composite systems have now surprisingly been found which contain at least one combination of a layer of a polyethylene foam and a layer of a polyurethane without any adhesion-promoting intermediate layer.

Accordingly, the invention provides a composite material comprising at least one combination of a layer of a cross-linked polyethylene foam other than a polyethylene foam which has been cross-linked by radiation or by means of a periodic cross-linking agent and a layer of a polyurethane, the said layers being joined in the absence of an adhesion promoter.

The composites according to the present invention may be produced using any polyethylene foams which have been produced using known chemical blowing agents and crosslinked by treatment with peroxides.

Processes for the production of polyethylene foam are known (cf. German Offenlegungsschrift No. 1,694,130 = US Patent specification No. 3,651,183 and US Patent specification No. 3,098,831). „ ~i 42432 In these processes, organic peroxides and blowing agents are added to polyethylene, the mixture extruded into a sheet under such conditions that no appreciable cross-linking nor blowing agent decomposition takes place. This sheet may then be heated in a hot-air oven initially to such an extent that the cross-linking reaction begins anti, as the temperature is further increased, the blowing agent decomposes and the cross-linked polyethylene is foamed by the gas liberated.

Polyethylenes suitable for producing the foam are low-pres10 sure polyethylenes (density ^0.94 - 0.97 g/cc) and high-pressure polyethylenes (density -v0.91 to 0.94 g/cc), preferably highpressure polyethylenes.

Suitable peroxides for the cross-linking reaction are orga- . nic peroxides, such as dicumylperoxide, 2,5-dimethyl-2,5-di-(tert.15 butylperoxy)-hexane, 2,5-dimethyl-2,5-di-(tert.-butylperoxy)hexyne, tert.-butyl hydroperoxide, cumyl-tert.-butylperoxide, di-tert.-butylperoxide and bis-(tert.-butylperoxy isopropylbenzene, preferably dicumylperoxide.

The peroxides are used in quantities of from 0.3 to 1.5Ji, by weight, based on the total mixture.

The polyethylenes are preferably mixed with the cross-linking and blowing agents or their concentrates in an extruder, followed by moulding at temperatures below the decomposition point of the-peroxide. The average residence time in the extruder is about 5 minutes, so that the mixtures to be foamed do not undergo any appreciable cross-linking at this stage.

The actual cross-linking reaction takes place at temperatures upwards of l60°C, whilst the foaming reactions take place at temperatures of from 190 to 250°C.

Accordingly, in a preferred embodiment, the present invention4 relates to composite materials produced using a peroxide-cross-linked polyethylene foam, preferably from 25 to 80% cross-linked polyethylene foam.

Polyethylene foams having a unit weight of from 20 to 200 kg/m are preferred.

Composite materials preferred in accordance with the present invention are also those which have been obtained using cold-hardening, flexible or semi-flexible, as well as hard, polyurethanes.

The present invention also relates to a process for the preparation of such composite materials which comprises·either (a) applying to a layer of a polyethylene foam a reactive mixture comprising at least one polyisocyanate and at least one compound containing at least two isocyanate-reactive hydrogen atans and alleging the reactive mixture to harden or (b) applying to a layer of polyethylene foam a polyurethane dispersion, solution suspension or powder and heating the applied polyurethane.

Starting components suitable for use in polyurethane production in accordance with the present invention include aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates of the type described, for example, by W. Siefgen in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136, for example ethylene di-isocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diiocyanate, 1,12dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3 and 1,4-diisocyanate, also mixtures of these isomers, l-isocyanate-3,3,5-trimethyl-5-isoeyanato methyl cyclohexane (DAS No. 1,202,785),2,4- and 2,6-hexahydrotolylene diiocyanate, also mixtures of these isomers, hexahydro-1,3- and/or1,4-phenylene diisocyanate, perhydro-2,4’- and/or -4,4’-diphenyl methane diisocyanate, 1,3 - and 1,4-phenylene diisoeyanate, - 5 42432 2.4- and 2,6-tolylene diisocyanate, also mixtures of these isomers, diphenyl methane-2,4·- and/or -4,4'-diisocyanate, naphthylene1.5- diisocyanate, triphenyl methane-4,4'4-triisocyanate, polyphenyl-polymethylene polyisocyanates, of the type obtained by condensing aniline with formaldehyde, followed by phosgenation and described, for example in British Patent Specification Nos. 874,450 and 848,671, perchlorinated aryl polyisocyanates of the type described, for example, in German Auslegeechrift No. 1,157,601, polyisocyanates containing carbodiimide groups of the type described in German Patent Specification No. 1,092,007, diisocyanates of the type described in U.S. Patent Specification No. 5,492,550, polyisocyanates containing allophanate groups of the type described?for example, in British Patent Specification No. 994,890,Belgian Patent Specification No. 761,626 and published Dutch Patent Application No.^102,524, polyisocyanates containing isocyanurate groups of the type described, for example, in German Patent Specification Nos. 1,022,789; 1,222,067 and 1,027,594 and in German Offenlegungsschrift Nos. 1,929,034 and 2,004,048, polyisocyanates containing urethane groups of the type described?for example?in Belgian Patent Specification No. 752,261 or in U.S. Patent Specification No. 3,394,164, polyiBocyanates containing acylated urea groups according to German Patent Specification No, 1,230,778, polyisocyanates containing biuret groups of the type described, for example, in German Patent Specification No. 1,101,394, in British Patent Specification No. 889,050 and in French Patent Specification No, 7,017,514, polyisocyanates obtained by telomerisation reactions of the type described, for example, in Belgian Patent Specification No. 723,640, polyisocyanates containing ester groups of the type described, for example, in British Patent Specifi- 6 42433 cation Noe. 965,474 and 1,072,956, in U.S. Patent Specification No. 3,567,763 and in German Patent Specification No 1,231,688 and reaction products of the aforementioned isocyanates with acetals according to German Patent Specification No. 1,072,385.

It is also possible to use the isocyanate group-containing distillation residues accumulating in the production of isocyanates on an industrial scale, optionally in solution in one or more of the aforementioned polyisocyanates. It is also possible to use mixtures of the aforementioned polyisocyanates.

In general, it is particularly preferred to use the commercially readily available polyisocyanates, for example 2,4- and 2,6-tolylene diisocyanate, also mixtures of these isomers (TDI), polyphenyl-polymethylene polyisocyanates of the type obtained by condensing aniline with formaldehyde, followed by phosgenation (crude MDI) and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups (modified polyisocyanates).

Other suitable starting components suitable for polyurethane production in accordance with the present invention are compounds with at leaet two isocyanate-reactive hydrogen atoms and generally having molecular weights of from 400 to 10,000- In addition to compounds containing amino groups, thiol groups or carboxyl groups, compounds of this type are preferably polyhydroxyl compounds, especially compounds containing from 2 to 8 hydroxyl groups, especially those with a molecular weight of from 800 to 10,000, preferably from 1000 to 6000, for example polyesters, polyethers, polythioethers, polyacetals, polycarbonates, polyester amides containing at least two, generally - 7 48432 to 8, but preferably from 2 to 4 hydroxyl groups, of the type known for the production Of cellular and non-cellular polyurethanes.

Suitable hydroxyl-group-containing polyesters are, for 5 example, reaction products of polyhydric, preferably dihydric and, optionally, also trihydric, alcohols with polybasic, preferably dibasic carboxylic acids. Instead of using the free polycarboxylic acids, it is also possible to use the corresponding polycarboxylic acid anhydrides or corresponding -]q polycarboxylic acid esters of lower alcohols or mixtures thereof for producing the polyesters. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally be substituted by, for example, halogen atoms, and/or may be unsaturated. Examples of reactants of this type are succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic acid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride, endomethylene tetrahydrophthalic acid anhydride, glutaric acid anhydride, maleic acid, maleic acid anhydride, fumaric acid, dibasic andtpibasic fatty acids, such as oleic acid, optionally in admixture with monobasic fatty acids, terephthalic acid dimethyl ester, terephthalic acid-bis-glycol ester. Examples of suitable polyhydric alcohols include: ethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,6-hexane diol, 1,8-octane diol, neopentyl glycol, cyclohexane dimethanol (1,4-bis-hydroxy methyl cyclohexahe), 2-methyl-l,3-propane diol, glycerol, trimethylol propane, 1,2,6-hexane triol, 1,2,4-butane triol, 3q trimethylol ethane, pentaerythritol, quinitol, mannitol , - 8 48433 sorbitol, methyl glycoside, also diethylene glycol, triethylene glycol, tetraethylene glycol, higher polyethylene glycols, dipropylene glycol, higher polypropylene glycols, dibutylene glycol and high polybutylene glycols. The polyesters may also contain some terminal carboxyl groups. It is also possible to use polyesters of lactones, for example i-caprolactone, or hydroxy carboxylic acids, for exampleiU-hydroxy caproic acid. The aforementioned polyhjrdric glycols (molecular weight 62 to 400) may also be additionally used as cross-linkers.

The polyethers containing at least two, generally from two to eight, preferably two or three hydroxyl groups suitable for use in accordance with the present invention are also known and are obtained, for example, by the polymerisation of epoxides, such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorhydrin on their own, for example in the presence of BF^, or by the chemical addition of these epoxides, optionally in admixture or successively, to starter components containing reactive hydrogen atoms, such as water, alcohols or amines, for example, ethylene glycol, 1,3- or 1,2-propylene glycol, trimethylol propane, 4,4·dihydroxy diphenyl propane, aniline, ammonia, ethanol amine, and ethylene diamine. Sucrose polyethers of the type described, for example in German Auslegeschrift Nos. 1,176,358 and 1,064,938 may also be used in accordance with the present invention. Xn many cases, it is preferred to use polyethers of the type predominantly containing primary OH-groups (up to 90)t, by weight, based on all the OH-groups present in the polyether). Polyethers modified by vinyl polymers of the type formed, for example, by polymerising styrene, acrylonitrile in the presence of polyethers ( U.S. Patent Specification Nos. 3,383,351; - 9 2432 3,304,273; 3,523,093 and 3,110,695 and German Patent Specification No, 1,152,536) are also suitable, as are polybutadienes containing OH-groups.

Among the polythio ethers, particular reference is made to the condensation products of thio diglycol with itself and/ or with other glycols, dicarboxylic acids, formaldehyde, amino carboxylic acids or amino alcohols. The products in question are polythio mixed ethers, polythio ether esters, polythio ether ester amides, depending upon the co-components.

Examples of suitable polyacetals are the compounds which may be obtained from the reaction of glycols,such as diethylene glycoi triethylene glycol, 4,4'-dioxethoxy diphenyl dimethyl methane, hexane diol,with formaldehyde. Polyacetals suitable for use in accordance with the present invention may also be obtained by polymerising cyclic acetals.

Suitable known polycarbonates containing hydroxyl groups are those which may be obtained, for example, by reacting diols, such as 1,3-propane diol, 1,4-butane diol and/or 1,6-hexane diol diethylene glycol, triethylene glycol and tetraethylene glycol, with diaryl carbonates, for example diphenyl carbonate or phosgene.

Polyester amides and polyamides include, for example, the predominantly linear condensates obtained from polybasic saturated and unsaturated carboxylic acids or their anhydrides and polyfunctional, saturated and unsaturated amino alcohols, diamines, polyamines and mixtures thereof.

Polyhydroxyl compounds already containing urethane or urea groups, and optionally modified natural polyols, such as castor oil, carbohydrates and starch, may also be ueed. Addition products of alkylene oxides with phenol-formaldehyde resins - 10 42432 or even with urea-formaldehyde resins may also be used in accordance with the invention.

Examples of these compounds suitable for use in accordance with the present invention are described, for example, in High Polymers, Vol. XVI, Polyurethanes, Chemistry and Technology, by Saunders-Frisch, Interscience Publishers, New York, London, Vol, I, 1962, pages 32 to 42 and pages 44 to 54, and Vol. 11, 1964, pages 5 to 6 and 198 to 199, and also in Kunststoff-Handbuch, Vol. VII, Vieweg-ilochtlen, Carl-Hanser-Verlag, Munich, 1966, for example on pages 45 to 71.

In many cases, catalysts are also used in accordance with the present invention. Suitable known catalysts are, for example, tertiary amines, such as triethyl amine, tri butyl amine, N-methyl morpholine, N-ethyl morpholine, N-cocomorphoiine, Ν,Ν,Ν’,N'-tetramethyl ethylene diamine, l,4-diuzabicyclo-(2,2,2)-octane, N-methyl-Ν'-dimethyl amino ethyl piperazine, Ν,Ν-dimethyl benzyl amine, bis-(N,Ndiethyl amino ethyl)-adipate, Ν,Ν-diethyl benzyl amine, pentamethyl diethylene trlamine, Ν,Ν-dimethyl cyclohexyl amine, Ν,Ν,Ν',N'-tetramethyl-l,3-butane diamine, N,N-dimethyl-pphenyl ethyl amine, 1,2-dimethyl imidazole and 2-methyl imidazole.

Tertiary amines containing isocyanate-reactive hydrogen atoms are, for example, triethanolamine, trllsopropanolamine, N-methyl-diethanolamine, N-ethyl diethanolamine, Ν,Ν-dimethyl ethanolamine, also their reaction products with alkylene oxides, such as propylene oxide and/or ethylene oxide.

Other suitable catalysts include silaamines having carbon silicon bonds of the type described, for example, in German Patent Specification No. 1,229,290« for example 2,2,4-trimethyl11 1424 32 2-silamorpholene and 1,3-diethylaminomethyl tetramethyl disiloxane.

Other suitable catalysts include nitrogen-containing bases, such as tetraalkyl ammonium hydroxides, also alkali metal hydroxides, such as sodium hydroxide, alkali metal phenolates, such as sodium phenolate or alkali metal alcoholates, such as sodium methylate. Hexahydrotriazines may also be used as catalysts.

Organo metallic compounds, especially organo-tin compounds, may also be used as catalysts in accordance with the present invention. Preferred organo—tin compounds are tin(II)salts of carboxylic acids, such as tin(ll)acetate, txn(ll)octoate, tin(ll)ethyl hexoate and tin(Il)laurate, and the dialkyl tin salts of carboxylic acids, such as dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin maleate or dioctyl tin diacetate.

Further examples of catalysts suitable for use in accordance with the present invention and details on the way in which the catalysts work may be found in Kunststoff-Handbuch, Vol. VII, published by Vieweg and Hoohtlen, Carl-Hanser-Verlag, Munich, 1966, for example on pages 9b to 102.

The catalysts are generally used in a quantity of from 20 0.001 to 10 %, by Weight, based on the quantity of compounds containing at least two isocyanate—reactive hydrogen atoms with a molecular weight of from 400 to 10,000.

According to the present invention, it is also possible to use reaction retarders, for example acid-reacting substances, such as hydrochloric acid or organic acid halides, also pigments or dyes and known flameproofing agents, for example trischloroethyl phosphate or ammonium phosphate and polyphosphate, also stabilisers against ageing and weathering, plasticisers, fungistatic and bacteriostatic compounds and fillers, such as barium sulphate, kieselguhr, carbon black or whiting.

Other examples of reaction retarders, stabilisers, flameproofing agents, plasticisers, dyes, fillers and fungistatic and bacteriostatic compounds optionally used in accordance with the present invention, and also details on the way additives of this type are used and the way in which they work, may be found in Kunststoff-Handbueh, Vol. Vi, published by Vieweg und Uochtlen, (.arl-Uanser-Verlag, Munich, 1906, for example on pages 103 to 113.

The reaction components may be; reacted by the known one-stage process, by the prepolymer process or by the semi—prepolymer process, in many cases Using machines, for example those of the type described in U.S.

Patent Specification No. 2,764,565. Particulars of processing machines which may also be used in accordance with the present invention may be found in Kunststoff-Handbuch, Vol. VI, published by Vieweg und Hochtlen, Carl-Hanser-Verlag, Munich, 1966, for example on pages 121 to 205.

Polyurethane dispersions may be applied to the polyethylene foam. Suitable dispersions are dispersions both of cationic and of anionic polyurethanes.

Cationic polyurethanes suitable for use in accordance with the present invention are obtained, for example in accordance with HAS No. 1,270,276 in cases where at least one component with one or more basic tertiary nitrogen atoms is used in the synthesis of the polyurethane and the basic tertiary nitrogen atoms in the polyurethane are reacted with alkylating agents or organic or inorganic acids. In principle, the basic nitrogen atoms may be situated anywhere in the polyurethane macromolecule.

It is also possible to react polyurethanes containing reactive halogen atoms capable of quarternisation ^43433 with tertiary amines. Cationic polyurethanes may also be obtained by chain-extending quarternisation, for example, by producing dihalogen urethanes from optionally relatively high molecular weight diols and isocyanates containing reactive halogen atoms or diisocyanates and halogen alcohols and reacting the dihalogen urethanes thus produced with ditertiary amines. Conversely, diamino urethanes may be produced from compounds containing two isocyanate groups and tertiary amino alcohols, and subsequently reacted with reactive dihalogen compounds.

The cationic polyurethane mass may, of course, also be produced from a cationic salt-like starting component, for example a quarternised basic polyether or an isocyanate containing quarternary nitrogen. These production methods are described, for example, in German Auslegeechrift No. 1,184,946; 1K178,586 and 1,179,363, in ttS. Patent Specification No. 3,686,108 and in Belgian Patent Specification Nos. 653,223; 658,026 and 636,799. The starting materials suitable for synthesising the salt-like polyurethanes are also mentioned in these publications.

A suitable cationic dispersion in a mixture of dimethyl formamide and water may be prepared for example as follows: A polyester with terminal hydroxyl groups is reacted with a diisocyanate to form a prepolymer, diluted with dimethyl formamide and then further reacted with N-methyl diethanol amine. This is followed by quarternisation with dichlorodurol(l,4-bis25 (chloromethyl)-benzene) and by the addition of phosphoric acid and a mixture of equal quantities of dimethyl formamide and water.

Anionic polyurethane(urea)dispersions may be prepared by known processes. Suitable anionic polyurethanes are described, for example, in DAS No. 1,237,306, in DOS Nos. 1,570,556; 1,720,- H 42432 039 and 1,493,«47. In addition to the conventional glycols and diamines, compounds containing either anionic groups or groups which may subsequently be converted into anionic groups, are used, as in the production of cationic dispersions. Compounds of this type are, for example, hydroxy and mercapto acids, such as glyceric acid, citric acid or uric acid, amino acids, such as diaraino naphthoic acid, hydroxy and carboxy sulphonic acids, such as 2-hydroxy ethane sulphonic acid or £-suiphobenzoic acid, also amino sulphonic acids, such as hydrazine disulphonic acid, 2,4-diamino toluene-5-sulphonic acid or amino ethyl amino ethane sulphonic acid, derivatives of phosphinic acid, nhosphonous acids, phosphonic acids and phosphoric acids, esters of phosphorous and phosphoric acid and the thioanalogues thereof, for example phosphoric acid-bis-propylene glycol ester, also hydrazine dicarboxylic acids and diamino-amidocarboxyllc acids nr salts thereof, such as sodium phthalate-bis-N,N~(f-aminopropyl)amide.

The anionic dispersions may also be prepared from polyurethanes containing free hydroxyl and/or amino groups hy reacting them with aliphatic and/or aromatic aldehydes Phd, simultaneously or subsequently, with a metal sulphite, metal hydrogen sulphite, metal amino carboxylate or metal amino sulphate. Also, another possibility is to react polyurethanes containing free hydroxyl and/or amino groups with cyclic compounds containing from three to seven ring members and salt-like groups or groups capable of salt formation after ring opening (cf. DAS No. 1,237,306). Compounds of this type are, in particular, sultones, such as 1,3-propane sultone, 1,4-butane sultone or 1,8-naphth sultone, and lactones, such as β-propiolectone or y-butyrolacton?, also dicarboxylic acid - 15 v 42432 anhydrides, for example succinic acid anhydride.

Cationic or anionic polyurethanes suitable for use in the process according to the present invention may also be synthesised by formaldehyde polycondensation in accordance with DOS No. 1,770,068. In this process, relatively high molecular weight polyisocyanates are reacted with an excess of compounds containing terminal methylol groups (for example, amine-formaldehyde resins or phenol-formaldehyde resins), the reaction product containing methylol groups is dispersed in water and, finally, the -)0 resulting dispersion cross-linked by heat treatment to form methylene bridges.

It is also possible in the process according to the present invention to use dispersions of the type described in German Offenlegungsschrift Nos. 1,953,3^5; 1,953,348 and 1, 953,349. -,5 The dispersions in question are aqueous dispersions of ionic emulsion polymers obtained by the radical emulsion polymerisation of olefinically unSaturated monomers in the presence of cationic or anionic oligo urethanes or polyurethanes.

Dispersions of cationic and anionic polyurethanes which actually show chemical cross links when they are used, are also suitable.

It is also possible to apply polyurethane suspensions to the polyethylene foam. Cross-linked polyurethane particles in suspension may be produced by a variety of different methods known in principle to one skilled in the art. In general, cross-linked polyurethane particles may be prepared both in the form of a suspension in suitable organic solvents or even in water or even in the absence of a liquid medium and subsequently suspended. In addition, it is possible in any of these processes directly to obtain crosslinked particles by suitably selecting the reaction - 16 42432 components, or initially to prepare predominantly linear thermoplastic particles which are subsequently cross-linked» There are a number of processes for producing finely divided polyurethanes in aqueous media. For example, a solution of a polyurethane in a water-immiscible solvent may be dispersed in water using an emulsifier and the organic solvent removed by distillation, in one particularly preferred method, ionically-and/or hydrophilically-modified polyurethanes are mixed with water in the presence or absence of a solvent, polyurethane suspensions being formed in dependence both upon the constitution and upon the conditions. In one particularly preferred modification of this process, polyurethane prepolymers with terminal isocyanate or methylol groups are used. This may be carried out in highly concentrated solutions or even in the complete absence of solvents. The coarse emulsions initially formed are converted by reaction of the isocyanate groups with water or diamines or higher polyamines dissolved in the aqueous phase into high molecular weight polyurethane urea suspensions, accompanied by chain extension and cross-linking. The chain extension of prepolymers containing methylol groups may be obtained, for example, by heating or by reducing the pH.

Suitable suspensions may also be prepared by spraying high molecular weight polyurethanes or reactive precursors into water or organic non-solvents.

In principle, any of the methods which have been proposed for the production of polyurethane dispersions or latices may also be used for preparing polyurethane suspensions, providing measures are taken to ensure that these suspensions do not coalesce through sedimentation or under the effect of shear - 17 42432 forces. This means that a primary suspension which is not yet of adequately high molecular weight has to be kept in motion until the dispersed particles have become tack-free.

To crosslink the dispersed particles, it is possible either to start with more than bifunctional starting materials, i.e. to use, for example, branched polyesters or polyethers, triisocyanates or triols in the synthesis of the polyurethane, or to react an initially linear NCO-prepolymer, i.e. an NCOprepolymer prepared from bifunctional components, with higher functional amines to form a crosslinked polyurethane urea. However, crosslinked particles may also be synthesised from purely bifunctional components by working under conditions which promote branching, for example, by adding catalysts which promote isocyanate trimerisation or the formation of allophanate or biuret structures, in the presence of water and/or diamines, the use of more than equivalent quantities of isocyanate relative to the hydroxyl or amine compounds present is sufficient to produce crosslinking. Linear high molecular weight polyurethanes may also be subsequently crosslinked in the form of a suspension in a liquid medium or even in powder form, for example by treatment with polyisocyanates or formaldehyde or formaldehyde donors. Products containing basic groups may be crosslinked? for example, with polyfunctiottal quarternising agents or acids, whilst products containing acid groups may be crosslinked using metal oxides or polyamines. Polyurethanes containing unsaturated double bonds may be crosslinked, for example, with known radical formers, or sulphur, polymercaptans and other, at least bifunctional, agents capable of reacting with double bonds.

The production of crosslinked polyurethane particles in - 18 43432 the absence of solvents may be carried out, for example, by pulverising polyurethane elastomers, for example in an impact pulveriser, it is particularly favourable to pulverise the elastomer immediately after it has been produced when, although tack-free, it has not yet completely reacted so that dispersion may be obtained without excessive energy consumption.

A detailed description of the production of crosslinked ionic polyurethane suspensions may be found, for example, in German Auslegeschrift Nos. 1,495,745 (US Patent No. 3,479,310), 1,282,962 (Canadiun Patent No. 857,174) and 1,694,129 (British Patent Specification No. 1,158,0-88), and in German Offenlegungsschrift Nos. 1,595,687 (US Patent No. 3,714,095), 1,694,148 (US Patent No. 3,022,527), 1,729.201 (British Patent Specification No. 1,175,339) and l,77O,Ob8 (US Patent No. 3,756,992).

The composite systems according to the present invention may be produced by applying polyurethane powder. Polyurethane powders having melting points or ranges of from 110 to 250°C, preferably from 110 to 190°C, are particularly suitable for coating the polyethylene foams. In addition, the intrinsic melt index curves should preferably resemble the upwardly sloping arm of a parabola so that the IMI-value preferably changes from 2 g per 10 minutes to 50 g per 10 minutes within a temperature range of from 5 to 50°C, preferably from 10 to 40°C.

In addition, polyurethane(ureas)suitable for coating should have an ionic group content of 1 to 15 milliequivalents per 100 g, and a resistance of 10^θ to 10^ ohm.cm.

According to the present invention, the powder-form polyurethane (ureas) which generally have: 1. a smooth, spherical surface; 2. an average diameter of from 5 to 200p; .^4.8432 Λ 3. an ionic group content of from i to 15 milliequivalents per 100 g; and 4. a resistance of from ΙΟ^θ to lO^ ohm.cmj and in which: . the trend of the respective IMI-curves at temperatures of from 110 to 250°C represents the upwardly sloping arm of a parabola, the IMI-value changing from 2 g per 10 minutes to 50 g per 10 minutes within a temperature range from 5 to 50°C; (see Patent Specification No.39941 ) -,θ are applied dry to the polyethylene foam, subsequently sintered and/or melted by the action of heat, optionally followed by calendering.

The polyurethane(urea)-powders used in accordance with the present invention may be obtained by reacting NCO prepolymers containing ionic groups with primary and/or secondary diamines (containing aliphatic amino groups) and/or dicarboxylic aoidbis-hydrazides in the presence of water. The active NH:NCO molar-ratio in the chain-extending reaction is preferably from 0,1 to 0.95 and, particularly from 0.25 to 0.85. The ionic group 2Q content of the NCO prepolymers should generally be such that the endproducts show the preferred ionic group content of from 1 to 15 milliequivalents, preferably from 2 to 10 milliequivalents, per 100 ®· It is preferred initially to prepare a solution of the prepolymer containing both isocyanate groups and also ionic groups in organic solvents, to combine this solution with an aqueous solution of the chain extender and finally to remove the organic solvent, preferably by distillation. In this way, the powders used in accordance with the present invention are obtained 3° in the form of a sedimenting, aqueous dispersion. 2432 One particular advantage of this embodiment is that it is not essential to use high-speed stirrers, instead the NGOprepolymer may be combined with the chain extender simply by stirring the two components together at low speeds, The aforementioned prepolymers containing both free isocyanate groups and also ionic groups, are known compounds in the production of einulsif ier-free polyurethane dispersions. It is preferred to use NGO-prepolymers of the type which have an average molecular weight of from 300 to 25,000, more especially from 800 to 15,000 and particularly from 2000 to 7000.

The properties of the polyurethane foam powders obtained in this way may be specifically varied within wide limits by suitable measures. This applies above all to the hardness and size of the particles.

The first possibility of influencing the property spectrum lies in the synthesis of the isocyanate-group-containing ionic preadduct. Synthesis is curried out hy known methods (eg. Belgian Potent Specification Nos. 653,223 and 730,543) using the starting materials mentioned therein. In addition to the compounds mentioned therein, however, it is also possible to use as relatively high molecular weight substances containing reactive hydrogen atoms compounds containing amino groups of the type described in French Patent Specification Nos. 1,361,810 and 1,300,981, in German Auslegeschrift No. 1,122, 254 and US Patent Specification No. 2,888,439.

The size of the particles is essentially determined by the ionic groups content of the preadduct, whilst the hardness thereof is predominantly determined by the chemical nature of the polyisocyanates and compounds containing reactive hydrogen κ 42432 atoms used in the production of the NCO-prepolymers. if these compounds are confined to those having low molecular weights of up to about 500, relatively hard polyurethanes obtained, whereas in cases where compounds having relatively high molecular weights of up to about 10,000 are used, softer products are obtained.

Any mixing ratios between these two extremes are possible, Since preadduct formation is carried out using relatively large excesses of isocyanate (the molar ratio of the NCO-groups to the reactive hydrogen atoms is best between 4 and 1.1, preferably between 2 and 1.4), in other words the molecular weights of the prepolymers do not become very high, there is no need for strict linearity in the structure of the chain. However, the powders are preferably prepared from linear NCO-prepolymers having two terminal aliphatic isocyanate groups.

To this end, a solution of the prepolymer is preferably reacted with an aqueous solution or dispersion of the chain extender. In exceptional cases, the chain extender may also be added during dispersion in solution in an organic solvent. Basically, the polyurethane powders used in accordance with the present invention may be produced, by the process described in Belgian Patent Specification Nos, 653,223 and 730,543 for producing emulsifier-free polyurethane dispersions.

Suitable chain extenders are, in particular, primary and/or secondary diamines containing aliphatic amino groups, also dicarboxylic acid-bis-hydrazides. (So far as chain extenders of the second kind are concerned, it may be assumed that the amino groups in the 3-position to the carbonyl groups react primarily with the NCU-prepolymer so that the dicarboxylic acid-bis-hydrazides may be regarded, in broad terms, as hi functional chain extenders). Suitable diamines are, in particular, those having a molecular weight below 250, such as ethylene diamine, 1,2-propylene diamine, N-methyl propylene diamine, butylene diamine, hexamethylene diamine, piperizine, 2-methyl piperizine, dimethyl piperizines, Ν,Ν'-dimethyl ethylene diamine, N,N'-diethyl diethylene diamine, Ν,Ν'-diisopropyi-1,2-propylene diamine, N,N'-bis-hydroxy ethylethylene diamine, N-hydroxy ethyl ethylene diamine, N-hydroxy propyl ethylene diamine, N,N'-uis-(hydroxy propyl)-ethylene diamine, Ν,Ν'-dimethyl hexamethylene diamine, 1,3-propylene diamine, f,f'-bis-amino propyl sulphide, f,f'-bis-amino propyl methyl amine, N,N-bis-(y-amino propyl)-aniline, N,N-bis(y-amino propyl)-m-tolidine. other suitable chain extenders include ether diamines and ester diamines, also diamines of the type formed during the hydrogenation of cyanoethylated diols and bifunctional dihydroxy polyesters or dihydroxy polyethers.

The diamines may be used in the form of their salts, for example carbonates or acetates. Salt formation need only be partial, for example to improve solubility. Salt formation on the primary amino group results in a reduction in reactivity.

Examples of suitable dicarboxylic acid-bis-hydrazides include bis-hydrazides of low molecular weight dicarboxylic acids having a molecular weight below 250, such as carbonic acidbis-hydrazide, oxalic acid-bis-hydrazide, succinic acid-bishydrazide, adipic acid-bis-hydrazide, phthalic acid-bishydrazide, terephthalic acid-bis-hydrazide, tetrahydrophthalic acid-bis-hydrazide, Bifunctional polyesters having terminal carboxylic acid hydrazide groups may also be used.

Solvents suitable for use in the production of the products employed in accordance with the present invention are, in particular water-miscible compounds having a boiling point below 100°C, such as acetone, methyl ethyl ketone, tetrahydrofuran or acetic acid ethyl ester. Water-immiscible solvents may also be used providing the reactants are intensively admixed by appropriate stirring. Solvents of this type are, for example, benzene or toluene. Solvents with a boiling point above 100°C, such as toluene, to which reference has just been made, or even chlorobenzene, dimethyl formamide or dimethyl sulphoxide, may also be used, although their removal thereof from the products generally involves more expense.

The polyurethane powders used in accordance with the present invention are preferably prepared as follows: The ionic NCO-prepolymers are synthesised from known dihydroxyl compounds with a molecular weight of from 500 to 5000, diisocyanates and, optionally, chain extenders, using such an excess of diisocyanate that the adduct contains from 1 to 4$, by weight, of free NCO-groups. The NCO-prepolymer also contains from 1 to 15 milliequivalents per 100 g of quaternary nitrogen or carboxylate or sulphonate groups.

From 30 to 90$, by weight, solutions of the ionic NCOprepolymer in acetone (viscosity at 50°C; from 30 to 8000 oP) are mixed with aqueous solutions of aliphatic diamines containing primary and/or secondary amino groups. The acetone is then distilled off, and the polyurethane urea powder is obtained in the form of an aqueous sedimenting dispersion.

The product may be obtained, in pure form by straightforward filtration. Although it may be redispersed in water at any later stage, the dry powder is preferably applied by the dry knife or screen process.

During the chain-extending reaction, the aqueous solution may be added to the acetone solution or the acetone solution - 24' 42433 added to the aqueous solution, in both cases with stirring. Mixing is preferably carried out continuously in suitable apparatus by introducing the two solutions into a mixing vessel, for example by means of pumps. In the most simple case, the mixing vessel is equipped with a stirrer and an overflow through which the aqueous-acetone dispersion flows into a distillation apparatus. The dispersion temperature is from 20 to bo°C, preferably from 35 to 55C. The quantity of water required for dispersion, in which the diamine is dissolved, is from 0.8 to 3 times, preferably from 1 to 2 times the quantity of the ionic NCO-prepolymer.

For continuous high-throughput mixing, it is preferred to use high-speed stirrers or even mixers of the type which enable high shear forces to be applied. Suitable machines, such as screw machines, more especially multiple-shaft screws, internal mixers, high-pressure or low-pressure mixing chambers with countercurrent mixing or ultrasonic dispersers, are known to those skilled in the art. With apparatus of this type, it is preferred to use 70 to 90# solutions, although it is even possible to work in the complete absence of solvents given adequately free-flowing prepolymers.

The properties of the polyurea powders initially accumulating in the form of suspensions may be specifically influenced not only by the chemical composition of the polyisocyanate preadduct, but also by the dispersion conditions.

The most important factors are; the type and quantity of chain extender, the quantity of water, the type and quantity of organic solvent, the pH-value and the reaction temperatures which may be varied from q°c up to t,oil±ng point of the organic solvent, the reaction optionally being carried - 25 42432 out under pressure.

Another important factor is the way in whioh the aqueous and organic phases are mixed, i.e. whether this mixing is carried out substantially simultaneously, for example in a continuous mixer, or whether the organic phase is added to the aqueous phase'or the aqueous phase to the organic phase.

However, it is emphasised once again that, even with eimple means, it is possible to obtain useful products, for example by allowing the aqueous phase to flow into the organic phase with stirring using a normal stirrer. The organic solvent .. is removed by distillation after or during mixing. The powder is obtained by filtration from the aqueous polyurethane dispersion formed.

The polyurethane powder is applied to the polyethylene foam by conventional coating techniques, i.e. by means of fixed coating systems, such as air-knife coaters, rubber blanket coaters and, above all, doctor roll coaters, and by means of roll or reverse-roll coaters.

The coating may be coloured or pigmented in different ways. The polyurethane powders are preferably mixed before application with powder-form pigments or fillers, such as carbon black, titanium dioxide, aluminium bronze, iron or cadmium pigments.

The composite materials according to the present invention are eminently suitable for the production of travel goods, leather substitutes, floor coverings and are also used, for example, in the clothing industry or, for example, in lacquered form and deep-drawn in the car industry as crashpads.

Application cf the polyurethane reaction mixture to the polyethylene foam, which may be used, for example, in the form of a sheet of foam, is by no means critical and may be carried out in any way. It is, of course, even possible to use machines for this purpose.

The composite systems according to the present invention con5 tain at least one combination of a layer of s polyethylene foam and a layer of a polyurethane. The present invention also encompasses composite systems containing several such combinations. In this connection, it is essential that the layer of polyethylene foam and the layer of polyurethane should always be joined together in the absence of adhesion promoters.

The following Examples illustrate the present invention. (in the Examples, the references to a sliced surface mean that a thin layer has been removed using a knife so that a surface having an open-cell structure results. The unsliced samples have a closed-cell surface).

EXAMPLE 1 After its preparation, a polyurethane polymer (I) consisting of: 100 parts, by weight, of butane diol adipate 9-5 parts, by weight, of 1,4-butane diol 37,5 parts, by weighty of 4,4'-diphenyl methane diisocyanate is co-extruded with 1 % of SiO^, pelletised and subsequently ground^ under nitrogen, into a powder. Particles less than 200/u in size are separated off from the powder. They are sifted or even scattered through a sieve onto a dicumyl-poroxidecross-linked, azodicgrboimide blown, continuously produced polyethylene foam (unit weight 35 kg/m^) with (a) a sliced surface and (b) an unsliced surface, and sintered together in an IR-field at temperatures some 25 to 30°C above the sintering temperature of fe polyurethane polymer (145°C +(25- 30°C)), to form coherent films. This procedure may be repeated several times and it is recommenp ded to apply no less than 50 g/m per article. The upper weight limit is imposed by the heat capacity of the IR-field.

Bonding was tested in accordance with DIN 53 357. Material breakout occurred in the polyethylene foam.

EXAMPLE 2 A polyurethane polymer (II) of: parts, by weight, of ethylene-butylene-glycol adipate 50 parts, by weight, of hexanediol polycarbonate 13 parts, by weight, of 1,4-butane diol parts, by weight, of 4,4'-diphenyl urethane diisocyanate is dissolved to form a 25 % solution in a mixture of 3 parts, by weight, of dimethyl formamide and 2 parts, by weightyof methyl ethyl ketone. The solution is pigmented and coated in a thickness of 60 g/m onto a separation layer, - 28 42432 followed by drying in a conventional way. The polyurethane polymer I from Example 1 is sifted onto this film in a layer thickness of 100 g/m and sintered in the same way as described above. A dicumyl-peroxide-cross-linked, azodi5 carbonamide foamed, continuously-manufactured polyethylene foam (unit weight 35 kg/m3) having (a) a sliced surface and (b) an unsliced surface, is placed on the plastic surface of the sintered polyurethane polymer (I) gentle pressure applied and, after cooling the combination of polyurethane polymer (II) polyurethane polymer(l) polyethylene foam, mechanically lifted off the separation layer.

Bonding is tested in accordance with DIN 53 357. Material breakout occurs in the polyethylene foam.

EXAMPLE 3 A polyurethane polymer III in powder form, consisting of; 4«2.5 g of hexane polycarbonate g of 1,6-diisocyanato hexane 596.5 g of acetone 4 g of N-methyl diethanol amine 3.1 ml of dimethyl sulphate is coated in dry form onto a dicumyl-peroxide-cross-linked, with azodicarbonamide blown, continuously-produced polyethylene foam (unit weight 35 kg/m3) with (a) a sliced surface and - 29 42432 (_b) an unsliced surface, and sintered in a hot air oven at from 25 to 30“C above the sintering temperature of the polyurethane polymer to form a homogeneous film in a coating thickness of at least 50 g/m^. it is surprising that, in this Example, the oven temperature was approximately 200“C and the residence time approximately 10 minutes.

Bonding is tested in accordance with DIN 53 357· Material breakout occurs in the polyethylene foam.

EXAMPLE 4 4040 g of butane diol polyadipate (0H-number 64) are reacted with 114 g of 4,4'-diphenyl methane diisocyanate in 5180 g of perehlorethylene. A prepolymer with an NCO-content of 1.85$ is formed. 40 g of 4,4'-diamino diphenyl methane dissolved in 150 g of dioxane are introduced into 896 g of this prepolymer by means of a gear pump. After intensive mixing in a suitable mixing head, the reaction mixture is sprayed onto a chemically-blown, peroxide-cross-linked polyethylene foam. Spraying may be carried out, for example, with a Transpol 2.0 (Trade Mark) 201-Pistole.

After coating, the whole is left to react for 30 minutes at 80°C in a drying cabinet.

Bonding was tested in accordance with DIN 53 357.

Material breakout occurred in the polyethylene foam, EXAMPLE 5 100 parts, by weight, of an ethane diol polyadipate (0H-number 56.2, acid number 0.7) were dehydrated in vacuo at 135°c and then stirred at 100°C with 18 parts naphthylene diisocyanate. After a few minutes, the temperature reaches 126°C, the reaction mixture was degassed by brief evacuation - 30 42432 and then intensively mixed with 2 parts, by weight, of 1,4-butane diol. The hot reaction mixture (125UO) was poured, in a layer thickness of 3mm, onto a peroxide-cross-linked, chemically-blown, continuously-produced polyethylene foam, and the composite formed subsequently tempered for 13 hours at 110°C. After cooling, the composite material shows high strength nnd firm bonding which was tested in accordance with DIN 53 357.

Material breakout, occurred in the polyethylene foam.

EXAMPLE b A reactive mixture of; 455 parts of fatty-acid-based polyester mixed with ketone resin parts of a molecular sieve (zeolite) 395 parts of barium sulphate 32 parts of hydrogenated castor oil bOO parts of diacetone alcohol parts of pigment (for example, mixture of titanium dioxide, iron oxide and chromium oxide) and from 185-220 parts of diphenyl methane diisocyanate is applied by means of a standard compressed air spray gun to a dicumyl-peroxide-cross-linked, azodicarbonamide blown, continuously-produced polyethylene foam. Elasticity may be influenced by varying the isocyanate component. The reactive mixture takes about 12 hours to harden.

Bonding was tested in accordance with DIN 53 357. Material breakout occurred in the polyethylene foam.

Claims (12)

1. CLAIMS:1. A composite material comprising at least one combination of a layer of a cross-linked polyethylene foam other than a polyethylene foam which has been cross-linked by radiation Or by means of a periodic cross-linking agent and a layer of a polyurethane, the said layers being joined in the absence of an adhesion promoter.

2. A material as claimed in claim 1 in which the polyethylene is a high-pressure polyethylene.

3. A material as claimed in claim 1 or claim 2 in which the polyethylene foam has a unit weight of from 20 to 200 kg/m 3 .

4. A material as claimed in any of claims 1 to 3, in which the polyurethane layer comprises a cold-hardening, flexible, semi-flexible or hard polyurethane.

5. A material as claimed in claim substantially as herein described.

6. A material as claimed in claim 1 substantially as herein described with reference to any one of the Examples.

7. A process for the preparation of a composite material as claimed, in claim 1 which comprises either (a) applying to a layer of a polyethylene foam a reactive mixture comprising at least one polyisooyanate and at least one compound containing at least two isocyanate-reactive hydrogen atoms and allowing the reactive mixture to harden or (b) applying to a layer of a polyethylene foam a polyurethane dispersion, solution, suspension or powder and heating the applied polyurethane.

8. A prooess as claimed in claim 7 in which the polyethylene is a high-pressure polyethylene. 424 32

9. A process as claimed in claim 7 or claim 8 in which the polyethylene foam has a unit weight of from 20 to 200 kg/m J

10. A process as claimed in claim 7 substantially as herein described. 5

11. A process as claimed in claim 7 substantially as herein described with reference to any one of the Examples.

12. A composite material when prepared by a process as claimed in any of claims 7 to 11.