NL2030817B1

NL2030817B1 - Process for preparing a multi-layered composite suitable for making polyurethane synthetic leather

Info

Publication number: NL2030817B1
Application number: NL2030817A
Authority: NL
Inventors: Cormelis Maria Timmermans Henricus; Cappozzo Roberto
Original assignee: Stahl Int B V
Priority date: 2022-02-03
Filing date: 2022-02-03
Publication date: 2023-08-11
Also published as: WO2023149799A1

Abstract

A process for producing a multi-layered composite comprising at least a support layer provided With at least one microporous layer based on polyurethane comprising the following steps: (i) providing a polyurethane formulation containing aqueous polyurethane dispersion and optional additives; (ii) foaming said polyurethane formulation; (iii) providing a support layer; (iv) treating the support layer With an aqueous coagulation solution and optionally removing excess coagulation liquid; (v) coating the foamed polyurethane formulation obtained in step (ii) onto a surface of the treated support layer obtained in step (iv); (vi) treating the coated support layer obtained in step (v) With an aqueous coagulation bath; (vii) optionally removing, preferably mechanically removing, excess coagulation liquid, for example, by squeezing the coagulated foamed polyurethane layer obtained in step (vi); (viii) drying the coagulated foamed polyurethane layer; (viiii) optionally washing the dried composite obtained in step (viii) With water and drying again.

Description

P131801NL00

Title: Process for preparing a multi-layered composite suitable for making polyurethane synthetic leather

This invention relates to a method for preparing a multi-layered composite comprising at least one microporous polyurethane layer, to the multi-layered composite thus obtained and the use thereof to make polyurethane synthetic leather.

Artificial leather also called imitation leather or synthetic leather, or leatherette or PU leather is used as a substitute for leather in fields such as upholstery, clothing, footwear and other uses where a leather-like appearance and performance is required but the actual material is cost- prohibitive or unsuitable. Artificial leather is a flexible composite material that typically consists of several layers, with the top layer being a polymer layer to protect against abrasion and impact and that determines the visual appearance and with a support layer typically being a textile or a non-woven type fabric, usually coated with (multiple layers of) a material like PVC, polyolefin or polyurethane and that provides the mechanical strength to the artificial leather. Artificial leather provides an economic and multi- functional way to replace natural leather.

Artificial leather comprising a polyurethane layer on a substrate such as a woven fabric or non-woven fabric has been used widely for many years. Such artificial leather is required to be qualified in stain resistance, water resistance, flexibility, abrasion resistance and non-tackiness, and it is also often required to have a low coefficient of surface friction.

The production of coated textile fabrics such as e.g. synthetic leather has been known for a long time. In the production of high quality coated textile fabrics, flexibility, tensile strength and softness play a decisive role in terms of desired comfort, among other things, since stiff fabrics lack comfort.

In the manufacture of artificial leather fabrics coated and/or impregnated with a microporous polyurethane coating are a popular choice as the basis. They are still mostly being produced by the so-called bath coagulation process (also called wet process or DMF coagulation). In the process of bath coagulation, which is the preferred process used today, textiles are coated or impregnated with polyurethanes dissolved in organic solvents (e.g. dimethylformamide (DMF), dimethylacetamide, dimethylsulfoxide, tetrahydrofuran). The coagulation takes place immediately thereafter by immersion in a water bath. Disadvantages of this process are in particular the complex measures that are necessary for the safe handling, the working-up and the recycling of the very large amounts of solvent and water.

For many years, especially in the field of coatings, the trend had increasingly been moving away from solvent-based systems towards solvent- free high solids systems and, in particular aqueous systems because of the ecological advantages thereof.

Water based (WB) coagulation also called salt, acid or electrolyte coagulation takes place by immersing the coated substrate in a concentrated salt solution or in acidified water or similar, the binder coagulating as a result of the high electrolyte content.

Coagulation of aqueous polyurethane dispersions is known in the art and the salt, acid or electrolyte coagulation is carried out by immersing the wet-coated substrate in a concentrated saline solution or in water with mineral or organic acids as coagulation bath so that the binder coagulates due to the high electrolyte content. Preferred electrolytes are mineral acids like hydrochloric acid or sulfuric acid or organic acids, such as acetic acid or citric acid. Particularly preferred is the use of citric acid because it is of biobased origin and results in less polluted waste water, even though coagulation occurs slower upon using citric acid compared to using mineral acids like hydrochloric acid. For a typical coagulation bath, the concentration of mineral acid in water is in the range of between 0.5 mole/L to 2 mole/L in case of hydrochloric acid and in the range of 10 gram to 50 gram of organic acid in 1 liter of water, in case of citric acid.

The object of the present invention consists in providing a novel process for producing a multi-layered composite provided with at least one polyurethane microporous layer obtained by aqueous coagulation which enables products of high quality to be achieved in a simple process. In particular the obtained multi-layered composites are highly porous, highly breathable, open, highly resilient, elastic and flexible structures that makes them very suitable as base material for artificial leather. Another important advantage of this water-based coagulation procedure is the absence of DMF traces in the final article.

The present invention provides a process for producing a multi- layered composite comprising at least a support layer provided with at least one microporous layer based on polyurethane comprising the following steps: (1) providing a polyurethane formulation containing one or more aqueous polyurethane dispersion and optional additives; (1) foaming said polyurethane formulation; (111) providing a support layer; (iv) treating the support layer with an aqueous coagulation solution and optionally removing excess coagulation Liquid; (v) coating the foamed polyurethane formulation obtained in step (11) onto a surface of the treated support layer obtained in step (iv); (vi) treating the coated support layer obtained in step (v) in an aqueous coagulation bath; (vi) optionally removing, preferably mechanically removing, excess coagulation liquid, for example, by squeezing the coagulated foamed polyurethane layer obtained in step (vi); (vii) drying the coagulated foamed polyurethane layer;

(vim) optionally washing the dried composite obtained in step (viii) with water and drying again.

The process of the present invention provides a multi-layer composite having a foamed coagulated polyurethane layer. Using the combination of foaming the polyurethane dispersion and coagulation allows to obtain the same physical properties obtained by the known DMF coagulation route while offering a completely DMF-free (so environmentally friendly) process. Due to the foaming of the polyurethane dispersion a super open structure, more flexible and more breathable compared to regular water-based coagulation not including the foaming step, is created.

Coagulation also creates a porous film but it has shown to be difficult to approach the same flexibility by WB coagulation as by DMF coagulation of polyurethane.

In the context of the present invention, the term polyurethane is meant to include next to polyurethane, also polyurea, polyisocyanurate, isocyanurate-modified polyurethane and other derivates such as polyurethanes modified by carbodiimide, allophonate, biuret, uretonimine, etc.

The one or more aqueous polyurethane dispersions in the polyurethane formulation for use in the present invention can be any aqueous polyurethane dispersion. The category of polyurethane is selected that allows an aqueous dispersion according to the physical characteristics of resilience, elasticity, rigidity, flexibility, transparency, colour and elongation at break. The aqueous polyurethane dispersions are preferably solvent-free, but may also contain some solvent or solvents. The solids level of the aqueous polyurethane dispersions is generally between 25% and 65%, preferably between 40% and 60%, most preferably between 50 and 60% by weight. The aqueous polyurethane dispersions may further comprise fillers, colorants, pigments, silicones, matting agents, flow agents, plasticizers, viscosity modifiers, levelling agents, adhesion promoters, rheology modifiers, ultra-violet (UV) absorbers, hindered amine light stabilizers (HALS), biocides.

Preferably the aqueous polyurethane dispersion 1s selected so that the obtained dried polyurethane is resilient. A polyurethane is thought to be 5 resilient when the shape and size of the dried polyurethane returns to its original size and dimensions after being physically distorted. Such resilience is needed to obtain a flexible foam layer. In the context of the present invention, it has been found beneficial to use polyurethanes that are elastic and soft, which can be described as their dried polyurethane sheets having a tensile strength of less than 4 MPa at 100% stretch, preferably having a tensile strength of less than 3 MPa at 100% stretch, and a maximum elongation at break of more than 300%, and preferably a maximum elongation at break of more than 400%. Tensile strength and maximum elongation at break are meant as measured according to ISO 527.

Preferred polyurethane dispersion for use in the present invention include RU-92-213 (an aqueous polyurethane dispersion with 60% non-volatile content, and which gives upon drying a resilient polyurethane; obtainable from

Stahl Europe BV), RU-92-103 (an aqueous polyurethane dispersion with 50% non- volatile content, and which gives upon drying a resilient polyurethane; obtainable from Stahl Europe BV) and RU-92-299 (an aqueous polyurethane dispersion with 50% non-volatile content, and which gives upon drying a resilient polyurethane; obtainable from Stahl Europe BV) .

An overview of properties and synthesis methods of aqueous polyurethane dispersions can be found in Chapter 14 “Waterborne

Polyurethanes” in textbook ‘Szycher’s Handbook of Polyurethanes’, edited by

M Szycher, published 1999 by CRC Press, ISBN 0-8493-0602-7.

Polyurethane dispersions are generally made by dispersing a polyurethane prepolymer into water. Suitable prepolymers may be made by reacting isocyanate components with polyols.

Preferred prepolymers may be made with aliphatic di-isocyanates, aromatic di-isocyanates, or a mixture of aromatic and aliphatic di- isocyanates, such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate and mixtures thereof, diphenylmethane-4,4-diisocyanate, 1,4- phenylenediisocyanate, dicyclohexyl-methane-4,4'-dusocyanate, 3- isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate, 1,6-hexyldi- isocyanate, 1,5-pentyldiisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 2,2 4-trimethyl-1,6-diisocyanatohexane (2,2,4-1somer, 2,4,4-1somer, or mixture thereof), 1,4-cyclohexyldiisocyanate, norbonyldiisocyanate, p- xylylene diisocyanate, 2,4'-diphenylmethane diisocyanate, and/or 1,5- naphthylene diisocyanate. Mixtures of polyisocyanates can be used and also polyisocyanates which have been modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues. Particularly preferred polyisocyanates are aliphatic polyisocyanates including 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, hexamethylene diisocyanate and dicyclohexyl-methane-4,4’- diisocyanate.

Polymeric polyols having molecular weights in the range of 500 to 6000 Dalton which may be used in the preparation of the prepolymer particularly include diols and triols and mixtures thereof but higher functionality polyols may be used as well, for example as minor components in admixture with diols. The polyols may be members of any of the chemical classes of polymeric polyols used or proposed to be used in polyurethane formulations. Preferred polyols are selected from the group of polyester polyols, polyesteramide polyols, polyether polyols, polythioether polyols, polycarbonate polyols, polyacetal polyols, polyolefin polyols or polysiloxane polyols or mixtures thereof. Preferred polyol molecular weights are from 700 to 4500 Dalton or even more preferred from 1000 to 2500 Dalton. Polyols having molecular weights below 500 which may optionally be used in the preparation of the prepolymer particularly include diols and triols and mixtures thereof but higher functionality polyols may be used. Examples of such lower molecular weight polyols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, bis (hydroxyethyl) terephthalate, neopentylglycol, trimethylol propane, cyclohexane dimethanol, furan dimethanol, glycerol and the reaction products, up to molecular weight 499 Dalton, of such polyols with propylene oxide and/or ethylene oxide.

Dispersibility of the polyurethane prepolymers in water can be achieved by incorporating hydrophilic groups into the prepolymer. For this reason other polyols may be present during the prepolymer formation such as a polyethoxy diol, a poly(ethoxy/propoxy) diol, a diol containing a pendant ethoxy or (ethoxy/propoxy) chain, a diol containing a carboxylic acid, a diol containing a sulfonic group, a diol containing a phosphate group, a polyethoxy mono-ol, a poly(ethoxy/propoxy) mono-ol, a mono-ol containing a pendant ethoxy or (ethoxy/propoxy) chain, a mono-ol containing a carboxylic acid or a sulfonic acid or salt, or mixtures thereof. A diol containing a carboxylic acid include carboxyl group containing diols and triols, for example dihydroxy alkanoic acids of the formula: R-C-(CH:-0H)2-COOH wherein R is hydrogen or alkyl. Examples of such carboxyl containing diols are 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid. Other useful acid group containing compounds include amino carboxylic acids, for example lysine, cysteine and 3,5-diaminobenzoic acid and sulfonic acids, for example 4,6-diaminobenzene-1,3-disulfonic acid.

The carboxylic acid functions are generally neutralized with a neutralizing agent, such as a mineral base or a non-volatile tertiary amine, before or during dispersion of the polyurethane prepolymer into water. Both the polyurethane prepolymer and the tertiary amine functional urethane prepolymer or oligomer or dispersion thereof may contain additional functional groups with the objective to improve the waterdispersibility, to improve adhesion to substrates during application, for performance reasons,

or as potential sites for crosslinking. Suitable functions are polyalkoxy functions with a large concentration of ethoxy functions, tertiary amine or quaternary amine functions, perfluoro functions, incorporated silicon functions, hydrazide functions or hydrazone functions, ketone, acetoacetate, or aldehyde functions, or mixtures thereof.

The conversion of any acid groups present in the prepolymer to anionic groups may be effected by neutralising the said acidic groups before, after or simultaneously with formation of the aqueous dispersion. Suitable neutralising agents include sodium hydroxide, potassium hydroxide, lithium hydroxide or tertiary amines such as N-butyldiethanolamine, N‚N-bis[3- (dimethylamino)propyl]-N',N'-dimethylpropane-1,3-diamine.

Polyurethane prepolymers useful in the practice of the present invention may be prepared in conventional manner by reacting a stoichiometric excess of the organic polyisocyanate with the polymeric polyol having a molecular weight in the range 500 to 6000 and the other required 1socyanate-reactive compounds under substantially anhydrous conditions at a temperature between about 30°C and about 130°C until reaction between the isocyanate groups and the hydroxyl groups is substantially complete.

The polyisocyanate and the active hydrogen containing components are suitably reacted in such proportions that the ratio of number of isocyanate groups to the number of hydroxyl groups is in the range from about 1.1:1 to about 6:1, preferably within the range of from 1.5:1 to 3:1. If desired, catalysts, such as bismuth carboxylate, zinc carboxylate, dibutyltin dilaurate, aluminium chelate, zirconium chelate, stannous octoate or triethylenediamine, may be used to assist prepolymer formation.

Prepolymers useful in the practice of the present invention should be substantially liquid under the conditions of the dispersing step, which means that these prepolymers should have a viscosity below 100,000 mPa.s at a temperature of 90°C, measured using a Brookfield LVF Viscometer.

The polyurethane dispersions used in the present invention include generally an extension agent, which is used to build the molecular weight of the polyurethane prepolymer by reacting the extension agent with the isocyanates functionality of the polyurethane prepolymer. The active hydrogen containing extension agent which is reacted with the prepolymer is suitably a polyol, an amino alcohol, ammonia, a primary or secondary aliphatic, alicyclic, aromatic, araliphatic or heterocyclic amine especially a diamine, hydrazine or a substituted hydrazine. Water-soluble extension agents are preferred, and water itself may be effective. Examples of suitable extension agents useful herein include ethylene diamine, diethylene triamine, triethylene tetramine, propylene diamine, butylene diamine, hexamethylene diamine, cyclohexylene diamine, piperazine, 2-methyl piperazine, phenylene diamine, bis(3-aminopropylamine), sodium 2-[(2- aminoethyl)amino]ethane-sulfonate, tolylene diamine, xylylene diamine, tris (2-aminoethyl) amine, 3,3'-dimitrobenzidine, 4,4'methylenebis (2- chloraniline), 3,3'-dichloro-4,4'bi-phenyl diamine, 2,6-diaminopyridine, 4,4'- diaminodiphenylmethane, menthane diamine, m-xylene diamine, 5-amino- 1,3,3-trimethyl-cyclohexanemethyl-amine, amine terminated polyethers such as, for example, Jeffamine D-230 from Huntsman Chemical Company, and adducts of diethylene triamine with acrylate or its hydrolyzed products.

Also suitable are materials such as hydrazine, azines such as acetone azine, substituted hydrazines such as, for example, dimethyl hydrazine, 1,6- hexamethylene-bis-hydrazine, carbodihydrazine, hydrazides of dicarboxylic acids and sulfonic acids, adipic acid mono- or dihydrazide, oxalic acid dihydrazide, 1isophthalic acid dihydrazide, tartaric acid dihydrazide, 1,3- phenylene disulfonic acid dihydrazide, omega-amino-caproic acid dihydrazide, hydrazides made by reacting lactones with hydrazine such as gamma-hydroxylbutyric hydrazide, bis-semi-carbazide, bis-hydrazide carbonic esters of glycols such as any of the glycols mentioned above. The amount of extension agent employed should be approximately equivalent to the free-NCO groups in the prepolymer, the ratio of active hydrogens in the chain extender to NCO groups in the prepolymer preferably being in the range from 0.7:1 to 2.0:1. Of course when water is employed as the extension agent, these ratios will not be applicable since the water, functioning both as extension agent and dispersing medium, will be present in a gross excess relative to the free-NCO groups.

The viscosity of the aqueous polyurethane dispersion is generally lower than 1000 mPa.s, preferably lower than 750, more preferably lower than 500, and most preferably lower than 250 mPa.s, as measured at 25°C using a Brookfield LVF Viscometer.

Optionally the polyurethane formulation for use in the present invention comprises also additives which may be selected, amongst others, from the group consisting of one or more foaming agents, one or more foam stabilizers, one or more foam boosters, one or more drying retardants, one or more fillers, one or more crosslinkers, one or more thickeners, or any mixture of two or more of the aforementioned. The polyurethane formulation generally contains between 50 and 90 parts, preferably between 60 and 85 parts, of aqueous polyurethane dispersion, between 0.5 part and 10 parts, preferably between 2 and 5 parts, of one or more foam stabilizers, between 0.1 part and 5 parts, preferably between 0.2 and 2 parts, of one or more foaming agents, between 0.1 part and 5 parts, preferably between 0.5 and 3 parts, of one or more foam boosters, between 0.1 part and 3 parts, preferably between 0.2 and 1 parts, of one or more drying retardants, between 0 and 40 parts of fillers, between 0 and 30 parts of additional water, and between 0 and 10 parts of one or more crosslinkers, the parts expressed based on the total polyurethane formulation.

The one or more foam stabilizers in the polyurethane formulation for use in the present invention can be any foam stabilizer that is capable of stabilizing foam made from polyurethane dispersions. The main function of the foam stabilizer is to slow down the dissipation of the foam and stabilize the foam. The amount of foam stabilizer in the formulation mixture for use in the present invention can be an amount between 0.5 and 10% by weight of the polyurethane formulation. Foam stabilizers can include, for example, sulphates, succinamates, sulphosuccinamates and stearate salts. Any foam stabilizer known to be useful by those of ordinary skill in the art of preparing polyurethane foams can be used in the present invention.

Preferably one or more foam stabilizers is a carboxylic acid salt. Such carboxylic acid salt can be represented by the general formula, RCO>X?*, wherein R represents a Cs-Cgo linear or branched alkyl, which can contain an aromatic, a cycloaliphatic, or heterocycle; and X is a counter ion.

Generally X 1s Na, K, or an amine, such as NH", morpholine, ethanolamine, triethanolamine, etc. Preferably R is from 10 to 18 carbon atoms. More preferably R contains from 12-18 carbon atoms. The carboxylic acid salt can contain a plurality of different R species, such as a mixture of Cs-C>0 alkyl salts of fatty acids. Preferably X is an amine. More preferably the carboxylic acid salt 1s an ammonium salt, such as ammonium stearate.

The one or more foaming agents is a material that facilitates the formation of foam and a surfactant fulfills these requirements. A surfactant, when present in small amounts, reduces surface tension of a liquid or increases its colloidal stability by inhibiting coalescence of bubbles.

Surfactants that can be used as foaming agent in the present invention may comprise cationic surfactants, anionic surfactants, amphoteric surfactants or non-ionic surfactants. Examples of anionic surfactants include sulfonates, carboxylates, and phosphates. Examples of cationic surfactants include quaternary amines. Examples of non-ionic surfactants include silicone surfactants and block copolymers containing ethylene oxide. Examples of amphoteric surfactants are sultaines, betaines and tertiary amine oxides.

The one or more foam boosters is generally a Cs-Cis alkanoic acid mono- or di-ethanolamide. This component is widely recognized as a foam booster and suitable alkanoic acid ethanolamides include lauric mono-

ethanolamide, myristic mono-ethanolamide, lauric diethanolamide, myristic diethanolamide and coconut (Cs-Cis) alkanoic acid mono-ethanolamide and diethanolamide. Preferred alkanoic acid ethanolamides contain 12 to 14 carbons in the fatty acyl group and a particularly preferred compound is cocamido propyl dimethylamine oxide. It is thought that the foam booster helps to obtain a uniform cellular foam structure, which is advantageous, as a large variation in foam cells would have a weakening effect on the obtained foam coagulate.

The one or more drying retardants is a material that slows down the drying of the foam between step (v) and (vi) by slowing down the surface evaporation of water or other liquids. This has the advantage that it prevents the drying or collapsing of the foam or the forming of a skin on the outer surface of the foam prior to the immersion in the coagulation bath.

Examples of suitable drying retardants are glycols, humectants, which absorb or hold water, or agents that form a barrier to prevent evaporation of water or other liquids. Particularly preferred are agents that form a barrier to prevent evaporation of water such as RO(CH2CH:20),H wherein n is number of moles of ethylene oxide and R 1s a hydrocarbon chain, and in which n ranges from 3 to 9 and the hydrocarbon chain is an —(CH2), CH with m larger than 7, for example ethoxylated isotridecanol.

The optional one or more crosslinker in the polyurethane formulation for use in the present invention can be any crosslinker suitable for crosslinking polyurethane dispersions, such as epoxide crosslinker, polycarbodiimide crosslinker, isocyanate crosslinker, aziridine crosslinker or polyurea crosslinker, of which an epoxide crosslinker, such as MA-2919 (obtainable from Stahl Europe BV) is a preferred type of crosslinker. Of the polycarbodiimide crosslinkers, an aqueous polycarbodiimide crosslinker, such as XR-5577 or XR-5508 (both obtainable from Stahl Europe BV), is a preferred type of polycarbodiimide crosslinkers. When such a crosslinker is used in the present invention good mechanical properties, including improved hydrolysis resistance, are obtained by drying only at modest temperatures of between 20°C and 100°C without the need for subsequent curing at higher temperatures. This is advantageous when textiles are used as substrate, as many textiles may deteriorate upon exposure to high temperature.

The optional one or more thickeners in the polyurethane formulation for use in the present invention can be any thickener that can increase the viscosity of the polyurethane formulation to the desired viscosity range. Particularly suitable thickeners belong to the group of associative polyurethane thickeners with pseudoplastic character, such as

Permutex RM-2956 or Permutex RM-22-294 (obtainable from Stahl Europe

BV.

The polyurethane formulation for use in the present invention can also contain additives that are generally used for the application, such as fillers (e.g. alumina trihydrate, silica, talc, calcium carbonate, clay, and the like), colorants, pigments, silicones, matting agents, flow agents, plasticizers, viscosity modifiers, levelling agents, adhesion promoters, rheology modifiers, ultra-violet (UV) absorbers, hindered amine light stabilizers (HALS), biocides.

The preparation of the polyurethane formulation is carried out by homogeneously mixing all the components in any desired sequence by methods known in the art.

The polyurethane formulation for use in the present invention generally has a viscosity of between 2000 and 25000 cps, preferably between 5000 and 10000 cps measured as Brookfield viscosity (RVT) at room temperature.

In step (11) of the claimed invention the polyurethane formulation is foamed. This can be done by mechanical stirring at high speed (mechanically foaming), i.e. with the introduction of high shear forces or alternatively by expansion of a blowing gas, such as, for example, by blowing in of compressed air. The mechanical foaming can be carried out using any desired mechanical stirring, mixing and dispersing techniques.

Air is generally introduced thereby, but nitrogen and other gases can also be used. The foam obtained has a density that is lower than the density of the polyurethane formulation because the foam is filled with air or other gasses, which have a lower density. The density of the unfoamed polyurethane formulation of step (i) of the claimed process is generally between 900 g/L and 1100 g/L, depending on the type of components. The density of the obtained foam of step (i1) of the claimed process is generally between 300 g/L and 850 g/L, preferably between 500 g/L and 850 g/L and most preferably between 600 g/L and 850 g/L.

The foamed polyurethane formulation is applied onto a suitable support layer using various application techniques. Preferred support layers are substrates that are non-rigid and more preferred are textile fabrics such as woven textiles, non-woven textiles or knits, that can be made of synthetic or natural fibers or mixtures thereof, preferably built up from fibres of cotton, polyester/cotton blends, wool, silk, flax, jute, bamboo, polyester, nylon, rayon, viscose, ramie, spandex, aramid, acrylic, thermoplastic polyurethane (TPU), thermoplastic olefins (TPO) or the like. The substrate can be treated with dyes, colorants, pigments, UV absorbers, plasticizers, lubricants, antioxidants, flame inhibitors and the like, either before coating or thereafter, but there is a preference for such treatments prior to coating with the foamed polyurethane.

Prior to the coating the support layer is treated with an aqueous coagulation solution in step (iv). Treatment of the support layer with an aqueous coagulation solution is preferably done by immersing the support layer into a bath containing the aqueous coagulation solution. A preferred method for immersing uses a set-up with a conveyor belt to immerse the support layer in the bath containing the aqueous coagulation solution. The treatment or immersion is done for a short period of time to allow the support layer to be completely covered or saturated with the aqueous coagulation solution, which generally takes about 5 to 60 seconds, preferably between 10 and 30 seconds. Said aqueous coagulation solution contains as coagulating agent an acid or salt in case the aqueous polyurethane dispersion is anionically stabilised. Any coagulation acid or salt can be used.

Examples of suitable acids include mineral acids such as hydrochloric acid or organic acids such as citric acid, tartaric acid, lactic acid and acetic acid.

Citric acid is specifically preferred as it is relatively easy available, easy to handle in operational environment, a natural source and leaves no smell. If the aqueous polyurethane formulation is instead cationically stabilised then the coagulating agent is a base. Any coagulation base can be used. Examples of suitable bases include solutions of metal hydroxides, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, or organic bases such as amines, for example triethylamine, ethanolamine, tripropylamine, dimethyl butyl amine, dimethyl ethanol amine, diethyl ethanol amine, 2-amino-2- methyl-1-propanol and N-ethylmorpholine or non-volatile tertiary amines such as N-butyldiethanolamine or N,N-bis[3-(dimethylamino)propyl]-N',N'- dimethylpropane-1,3-diamine. The concentration of the coagulation agent (acid or base) in the aqueous coagulation solution is generally between 0.1 and 10 wt%, preferably between 1 and 5 wt%.

An aqueous polyurethane dispersion that is anionically stabilised comprises a polyurethane chain in which a negative group, an anionic group, is present, that is neutralized with a positive counterion. An aqueous polyurethane dispersion that 1s cationically stabilised comprises a polyurethane chain in which a positive group, a cationic group, 1s present, that 1s neutralized with a negative counterion. An aqueous polyurethane dispersion that is nonionically stabilised comprises a polyurethane chain in which only neutral groups are present, which thus are not neutralized with either a positive counterion or a negative counterion.

Applying in step (v) the polyurethane foam onto the thus treated support layer obtained in step (iv) of the claimed process may be effected by various means such as roll coater, knife coating, spraying, doctor blading or pouring from a container. Preferably the polyurethane foam is applied by direct knife coating.

In general no extra drying step is carried out between step (iv) and (v) and the treated support layer, optionally being squeezed to remove excess coagulation agent, which is then still wet, 1s immediately coated with the foamed polyurethane formulation. Omitting such drying leads to energy savings, offering a cost and simplicity advantage.

The foamed polyurethane is suitably applied onto the support layer with a wet thickness of the foam layer generally between 100 micron and 800 micron, preferably between 100 micron and 500 micron. Since the support layer has first been treated with the aqueous coagulation bath, there will be limited penetration of this foam layer into the support layer and thus most of this foam layer will be remaining on top of the support layer. The thickness of the foam layer of the present invention is after coagulation in step (vi) and drying in step (viii) generally about 50% to 100% of the thickness that was originally applied onto the support layer.

The coating amount of the foamed polyurethane formulation in step (v) is generally in the range 20 to 600 g/m?, preferably 100 to 400 g/m?2.

Due to the pre-treatment of the support layer (step 1v) the layer of foamed polyurethane coated onto the support layer, directly in contact with the support layer is coagulating which prevents deep penetration.

The coated support layer, which 1s still wet, is subsequently treated with an aqueous coagulation bath to coagulate the foamed polyurethane layer. A preferred method for treating uses a set-up with rollers, as described above with respect to step (iv) to immerse the coated support fabric in the bath containing the coagulation solution. The immersion is done for a short period of time, which generally takes about 5 to 60 seconds, preferably between 10 and 30 seconds. Said coagulation bath contains an acid or base coagulation agent in case of respectively an anionically stabilised polyurethane dispersion or a cationically stabilised polyurethane dispersion, as explained above. Preferably, but not necessarily the coagulation agent used in step (vi) is the same as used in step (iv). The concentration ranges of the coagulation agent are also the same as described above.

After said coagulation step (step vi), the coagulated foamed layer may be slightly squeezed to (mechanically) remove excess of coagulation liquid (water) but this is not essential; even without the extra squeeze (which makes it easier to dry) the wet coagulated layer may go directly into the drying oven. Due to the squeezing some layer thickness may be lost; alternatively vacuum may be applied.

Drying with concurrent curing of the support layer provided with coagulated foamed polyurethane from step (vi) is preferably affected in step (vii) by subjecting to an elevated temperature. It is generally desirable to select a drying/curing temperature at which the foam will cure to a tack-free state within about 30 minutes, preferably between about 1 minute and about 5 minutes. A preferred temperature range is between 60°C and 170°C, especially between 80°C and 150°C, and a most preferred drying/curing step is by first subjecting to a modest elevated temperature, for example between 10°C and 100°C, preferably between 60 and 100°C, followed by subjecting to a somewhat higher temperature, for example between 100°C and 140°C.

Drying with concurrent curing is conveniently performed by passing the support layer provided with coagulated foamed polyurethane through an oven at a rate that provides the desired time at the specific elevated drying temperature. The oven, through which the support layer coated with coagulated foamed polyurethane passes, can conveniently have a gradient in temperature, so that there is first a passing through a temperature zone of modest temperature, followed by a temperature zone of higher temperature.

Any other suitable drying apparatus can be used, such as (air-circulating) drying cabinets, hot air or IR radiators. Drying by passing over heated surfaces, for example rollers, is also possible.

The thus obtained dried multi-layered composite may go through a subsequent washing to remove unnecessary coagulant. The washing step may be performed by immersing the composite in a washing tank containing water, which can be conveniently at ambient temperature.

The various consecutive steps of treating the support layer in a coagulation bath (step iv), optionally squeezing the treated support layer, applying the foamed polyurethane formulation (step v), treating the coated support layer with a coagulation bath (step vi), optionally squeezing of the immersed coated substrate (step vii), drying (step vii) and optional washing (step viii) of the complete layered structure, is preferably done using a dip & foulard squeezing set-up, as is widely used in the industry. Such a dip & foulard squeezing set-up is usually conveniently equipped with rollers, which facilitates the various consecutive steps. The speed of the entire process is conveniently selected such that the various periods for each individual step are sufficiently long, which can be helped by adjusting the dip depth and the length of the oven or the temperature or the temperature gradient in the oven.

After coagulation and drying, the coagulated foamed polyurethane has a microporous structure having a large number of medium-sized (generally 20 to 70 um) pores, and in general a porosity of at least 20%, preferably at least 25%. The density of the dried foam 1s generally between 650 and 800 g/L.

The multi-layered composite obtained according to the process of the invention forms a coagulated supported foam and is elastic as well as resistant to pressure, which means that upon applying pressure on the coagulated supported foam the foam layer regains almost all of its original thickness when said pressure is removed, hence having a resilience close to

100 %, or at least 95% or even 97%. Said resilience can be measured as follows. A specified force is being applied on a specimen. The thickness of the specimen before applying the force is measured and compared with the thickness after applying the force on the specimen. The ratio is expressed in a percentage, where 100% resilience means that the thickness of the specimen is the same after applying the force as before applying the force on the specimen.

The obtained multi-layer composite is flexible, and has similar flexibility as a traditional coagulated foam obtained via the DMF coagulation process. Such flexibility can be assessed by Bally Flex test method, according to ISO 32100. Ballyflex resistance is important for surfaces that should be flexible, such as car seats and shoes. Ballyflex resistance is less important for surfaces that do not have to be flexible, such as automobile dashboards.

The obtained multi-layer composite has a good breathability, and has similar breathability as a traditional coagulated foam obtained via the

DMF coagulation process The breathability can be measured according to

ASTM E96, via which the water vapour transmission (WVT) of materials is tested. A higher value means that more water vapour has gone through the material, which means a higher breathability. The water vapour transmission is expressed in gram per surface per time.

The obtained multi-layer composite has a good resistance to deterioration by accelerated ageing. Deterioration by accelerated ageing can be measured according to ISO 1419:2019, method C, also known as the

Tropical Test, commonly referred to as the Jungle Test. In the Jungle Test a sample of the material is placed in a controlled air-oven & humidity apparatus. The material is subjected to relative humidity of 95% and a temperature of 70°C. The material is ‘aged’ for several weeks and compared to the control sample for degradation and various physical properties.

The multi-layer composite of the present invention can be used like a conventional coagulated base, such as a coagulated base made via the traditional DMF coagulation method, for applying additional coating layers on top of the coagulated base. A common method to apply such an additional coating is by the process of transfer coating. The transfer coating method comprises the steps of a) coating a carrier, such as release paper, with a coating layer, followed by heat curing the coating layer; b) coating an adhesive, which can be a polyurethane dispersion, on the dried coating layer and then adhering the coagulated base thereon, followed by drying at elevated temperature; c) peeling off the carrier; and d) optionally applying a lacquer layer on top of the coating layer and then drying.

After the multi-layer composite of the present invention has been transfer coated, the transfer coated material can be used as artificial leather. Alternatively, one or more other coating layers can be applied on the composite of the present invention to obtain a layered material composite that can be used as artificial leather.

The multi-layer composite of the present invention provides flexibility, elasticity and breathability to the artificial leather.

The present invention will be further elaborated by the following non-limiting working examples, executed according to procedures known in the art. It goes without saying that many other embodiments are possible, all within the protective scope of the invention.

EXAMPLES

Example 1: coagulated base

A polyester knitted fabric, with an area density of 200 g/m?, was pre-treated by immersing the fabric in a coagulation liquid, consisting of 1 molar hydrochloric acid in water, during about 15 seconds, by using a dip & foulard squeezing set-up. In the laboratory set-up the conveying speed was set to 1 m/second to have an immersion time of about 15 seconds. Next, the pre-treated fabric was squeezed, using the foulard squeezing set-up, and not dried, so that the fabric remains wet. The squeezing pressure was set to about 2 bar and the maximum thickness was set to 400 micron. In a separate vessel, the polyurethane formulation, consisting of 81 parts of RU- 92-213 (an aqueous polyurethane dispersion with 60% non-volatile content, and which gives upon drying a resilient polyurethane; obtainable from Stahl

Europe BV), 0.3 parts of 2-amino-2-methylpropanol as volatile base, 3 parts of a 30% aqueous solution of ammonium stearate as foam stabilizer, 0.4 parts of Nonax 118 (an aqueous solution of 50% of an amphoteric linear alkenyl amido betaine; obtainable from Pulcra Chemicals GmbH) as foaming agent, 1.4 parts of Empigen OS/A (an aqueous solution of 30% of cocamido propyl dimethylamine oxide, usable as a foam booster; obtainable from Huntsman Performance Products) as foam booster, 6.4 parts of china clay and 2 parts of silicon dioxide as fillers, 0.5 parts of a 40% aqueous solution of ethoxylated isotridecanol as drying retardant, 3 parts of water and 3 parts of MA-2919 (an epoxide crosslinker; obtainable from Stahl

Europe BV), was mechanically foamed by mixing at high speed with a stirrer to a density of 600 g/L. Then by direct knife coating the foamed polyurethane formulation was applied onto the pre-treated textile, with a wet layer thickness of 600 micron. Due to the pre-treatment the layer directly in contact with the textile was coagulating, which prevents a deep penetration. The same dip & foulard squeezing set-up was used for this step. Next, the wet coated substrate is fully submersed in a second coagulation bath, consisting of 1 molar hydrochloric acid in water, during about 15 seconds, to coagulate the full layer of foamed polyurethane. Next, the substrate with the coagulated foam layer was squeezed, using the foulard squeezing set-up, with a squeezing pressure that was set to about 2 bar, in order to remove access of coagulation liquid. In a next step, the coagulated foam layer is dried by passing through an oven, with three consecutive temperature zones of 90°C, 110°C and 140°C during in total 9 minutes at a passing speed of 1 m/minute. The resulting dried coagulated foam was not washed.

The dry article that was made can be used as a typical coagulated base, like the conventional DMF based coagulate, in a transfer coating process of making synthetic articles.

Example 2: transfer coating of coagulated base

A transfer coating was applied on the coagulated base from

Example 1, and separately on an industry standard coagulated base, which had been made via traditional DMF coagulation process, using the following steps: a) applying a mixture of 100 parts of the polyurethane dispersion

Permutex RU-48-867 (an aliphatic polyurethane dispersion with 35% non- volatile content; obtainable from Stahl Europe BV), 10 parts of PP-39-611 (a black pigment paste, obtainable from Stahl Europe bv), 5 parts of XR-48-920 (an isocyanate crosslinker, obtainable from Stahl Europe bv), 1 part of LA- 91-120 (a levelling agent, obtainable from Stahl Europe bv), 1 part of RM- 22-294 (a thickener, obtainable from Stahl Europe bv) and 0.5 part of DF- 13-613 (a defoamer, obtainable from Stahl Europe bv) on release paper (Sappi UltraCast) with a thickness of about 10 micron to form a pre-skin layer upon drying for 1 minute in an oven at 80°C and next 2 minutes at 120°C; b) applying a mixture of 100 parts of the polyurethane dispersion

Permutex RU-92-213 (an aliphatic polyurethane dispersion with 60% non- volatile content; obtainable from Stahl Europe BV), 10 parts of PP-39-611, 5 parts of XR-48-920, 1 part of LA-91-120, 2 parts of RM-22-294 and 0.5 part of DF-13-673 on the pre-skin of step a), with a thickness of about 100 micron to form a skin layer upon drying for 1 minute in an oven at 80°C and next 2 minutes at 120°C;

c) applying an adhesive, which is a mixture of 100 parts of polyurethane dispersion Permutex RU-43-016 (an aliphatic polyurethane dispersion with 40% non-volatile content; obtainable from Stahl Europe BV) and 5 parts of XR-48-920, on the skin layer to a thickness of 150 micron, and then laminating the coagulated base onto the applied adhesive layer, followed by drying for 1 minute in an oven at 80°C and next 2 minutes at 120°C; d) peeling off the release paper.

Example 3: comparative, without coagulation

A polyester knitted fabric, with an area density of 200 g/m? was used. In a separate vessel, the polyurethane formulation, consisting of 81 parts of RU-92-213 (a polyurethane dispersion with 60% non-volatile content, and which gives upon drying a resilient polyurethane; obtainable from Stahl Europe BV), 0.3 parts of 2-amino-2-methylpropanol as volatile base, 3 parts of a 30% aqueous solution of ammonium stearate as foam stabilizer, 0.4 parts of Nonax 118 (an amphoteric foaming agent; obtainable from Pulcra Chemicals GmbH) as foaming agent, 1.4 parts of Empigen OS/A (an aqueous solution of 30% of cocamido propyl dimethylamine oxide, usable as a foam booster; obtainable from Huntsman Performance Products) as foam booster, 6.4 parts of china clay and 2 parts of silicon dioxide as fillers, 0.5 parts of a 40% aqueous solution of ethoxylated isotridecanol as drying retardant, 3 parts of water and 3 parts of MA-2919 (an epoxide crosslinker; obtainable from Stahl Europe BV), was mechanically foamed by mixing at high speed with a stirrer to a density of 600 g/L. Then by direct knife coating the foamed polyurethane composition was applied onto the textile, with a wet layer thickness of 600 micron. In a next step, the foam layer was dried by passing through an oven, with three consecutive temperature zones of 90°C, 110°C and 140°C during in total 9 minutes at a passing speed of 1 m/minute.

Example 4: testing of foamed coagulates

The Ballyflex resistance was measured according to ISO 32100, at room temperature for 100000 flexes, where the lowest score is the best, going from 5 to 0. Ballyflex resistance is important for surfaces that should be flexible, such as car seats and gaiters. Ballyflex resistance is not important for surfaces that do not have to be flexible, such as automobile dashboards. In this Example the Bally Flex resistance is reported as a number of flexes that could be done without getting surface damage at the bending point of the material. At certain intervals the Bally Flex specimens are inspected and the Bally Flex is stopped when either surface damage was noticed or when the maximum of 300.000 flexes was achieved. In the shoe industry a Bally Flex resistance of minimum 150.000 is required. The results are collected in Table 1.

The breathability was measured according to ASTM E96, via which the water vapour transmission (WVT) of materials is tested. The water method within ASTM E96 was used. A higher value means that more water vapour has gone through the material, which means a higher breathability. The water vapour transmission is expressed In gram per surface per time, or g/m2.d, wherein d represents a full day of 24 hours. The results are collected in Table 1.

The samples were subjected to a method of assessing the resistance of coated fabrics to deterioration by accelerated ageing according to ISO 1419:2019, method C, also known as the Tropical Test, commonly referred to as the Jungle Test. In the Jungle Test a sample of the material is placed in a controlled air-oven & humidity apparatus. The material 1s subjected to relative humidity of 95% and a temperature of 70°C. The material is ‘aged’ for several weeks and compared to the control sample for degradation and various physical properties. After exposure of 21 days to the Jungle Test conditions, the Ballyflex resistance was again measured on the exposed specimens. The results are collected in Table 1.

The average pore size was measured by visual assessment using a light microscope. The specimens were cut and the diameter of the bubbles in the foam layer of the intersection were digitally measured in the digital photo of said intersection. The average pore size is given as a range, and the upper and lower value given reflect the sizes of the largest and smallest bubbles that were observed. The results are collected in Table 1.

The resilience of the specimens was evaluated by applying a specified force on a specimen. An embossing cylinder set-up was used with flat cylinders, with a set pressure of 6 bar, operated at ambient temperature and the specimens were led through the cylinder set-up at a speed of 0.5 m per minute. The thickness before applying the force was measured and compared with the thickness after applying the force on the specimen. The ratio is expressed in a percentage, where 100% resilience means that the thickness of the specimen is the same as before applying the force on the specimen. A higher percentage of resilience is advantageous. The results are collected in Table 1.

The weight and thickness of the specimens were measured, as well as the thickness and weight of the substrate and thickness of the foamed layer on the substrate. From these data, the density of the foamed layer was calculated. The density of such a layer is about 1000 g/L if the layer would not have been foamed, and hence the porosity can be calculated from the density data. Porosity is the fraction of the volume occupied by voids, in this case the foam cells, in a material and is expressed in percentage. Because the unfoamed density is about 1000 g/L, the porosity is calculated as: 100% * ([density unfoamed layer] — [density foamed layer]/ ([density unfoamed layer]). The data are collected in Table 2.

The following specimens were tested

Entry 1 = Coagulated base from Example 1

Entry 2 = Coagulated base, traditional from DMF process

Entry 3 = Comparative Example 3 (without coagulation)

Entry 4 = Coagulated base from Example 1, with transfer coat, according to

Example 2

Entry 5 = Coagulated base, traditional from DMF process with transfer coat, according to Example 2

Entry 6 and 7 = Comparative commercial samples, which are representative for non-foamed waterbased coagulated polyurethane base materials

Entry 8 = Coagulated base similar as from Example 1, but then made without applying squeezing after the coagulation bath.

Comparing the breathability results, it can be concluded that the coagulated base of entry 1 gives a similar value as the traditional coagulated base in entry 2, but a much higher value than obtained with non- foamed coagulated base materials in entries 6 and 7. Also with a transfer coat applied, the values obtained are similar for the entries 4 and 5. The difference in breathability results between entry 1 and entries 3, 6 and 7 (comparative) demonstrate that the coagulation step combined with foaming has a major beneficial influence.

Comparing the Bally Flex results and the Bally Flex results after exposure of 21 days to Jungle Test conditions, it can be concluded that the coagulated base of entry 1 gives a better performance than the traditional coagulated base in entry 2. This same difference was found with a transfer coat applied: performance of entry 4 is better than performance of entry 5.

The pore size data in Table 1 demonstrate that the foam bubbles in the coagulated base of entry 1 are larger than in the traditional coagulated base of entry 2. The higher pore size in entry 3 demonstrates that the foam bubbles have expanded more when no coagulation had been used.

The resilience data in Table 1 demonstrate that the coagulated base of entry 1 has a resilience that is close to 100%, which is very high and which is similar as for the traditional coagulated base in entry 2.

The porosity values in Table 2 demonstrate that the density of the foamed layer is relatively low, which corresponds to a relatively high porosity. When the layered material has not been squeezed after the coagulation bath, then the coating density 1s lower and the porosity higher.

A relatively high porosity is advantageous as it reduces weight of the layer, which means that less material is needed to construct such a layered material, which means costs saving.

Evaluating all properties, it can be concluded that the inventive coagulated base of entry 1 has the best combination of properties: good resilience, good Bally Flex performance, good Bally Flex performance after exposure to 21 days of Jungle Test conditions, high breathability and relatively high porosity.

None of the other specimens has this combination of advantageous properties.

Claims

Conclusions

A method for producing a multilayer composite comprising at least one backing layer provided with at least one microporous polyurethane-based layer comprising the steps of: (1) providing a polyurethane formulation containing one or more aqueous polyurethane dispersions and optional additives ; (1) foaming said polyurethane formulation; (111) providing a backing layer; (iv) treating the support layer with an aqueous coagulating solution and optionally removing excess coagulating liquid; (v) coating the foamed polyurethane formulation obtained in step (i1) on a surface of the treated backing layer obtained in step (iv); (vi) treating the coated support layer obtained in step (v) with an aqueous coagulation bath; (vin) optionally removing, preferably mechanically removing, excess coagulant liquid, for example, by squeezing out the coagulated foamed polyurethane layer obtained in step (vi); (fin) drying the coagulated foamed polyurethane layer; (1x) optionally washing the dried composite obtained in step (vin) with water and drying again in which no additional drying step is performed between step (iv) and step (v).

A method according to claim 1 wherein the viscosity of the polyurethane formulation as provided in step (1) is between 2000 and 25000 cps, preferably between 5000 and 10000 cps measured as Brookfield viscosity (RVT) at room temperature (25°C).

A method according to any one of the preceding claims, wherein the aqueous polyurethane dispersion has a solids content of 25 to 65% by weight, preferably 40 to 60% by weight, most preferably 50 to 60% by weight.

A method according to any one of the preceding claims wherein the optional additives in the polyurethane formulation comprise a drying retarder, preferably in an amount of 0.1 to 3% by weight.

A method according to any one of the preceding claims wherein the optional additive comprises one or a mixture of a foaming agent, a foam booster, a foam stabilizer, a crosslinker, a filler and a thickener.

A method according to any one of the preceding claims, wherein the foaming in step (1) is by mechanical foaming.

A method according to any one of the preceding claims wherein the treatment steps (iv), (vi) and (vi) are carried out by dipping and squeezing.

A method according to any one of the preceding claims wherein the drying step (viii) is carried out at temperatures ranging from 80 to 150°C, preferably in several successively rising temperature zones.

A method according to any one of the preceding claims, wherein the density of the foamed polyurethane obtained in step (1) is 300 to 850 g/l, preferably 600 to 850 g/l.

A method according to any one of the preceding claims wherein the backing layer is a textile fabric, a woven, a non-woven or a microfiber fabric.

A method according to any one of the preceding claims wherein in step (v) the foamed polyurethane formulation is applied to the surface of the treated backing via a direct knife coating.

A method according to any one of the preceding claims wherein the coating amount of the foamed polyurethane formulation in step (v) is 20 to 600 g/m? is, preferably 100 to 400 g/m=.

A method according to any one of the preceding claims wherein the aqueous polyurethane dispersion is anionically stabilized and the aqueous coagulation solution in steps (iv) and (vi) contains an acid or salt, preferably citric acid.

A method according to any one of claims 1 to 13 wherein the aqueous polyurethane dispersion is cationically stabilized and the aqueous coagulation solution in steps (iv) and (vi) contains a base.

A method according to any one of the preceding claims wherein the concentration of the aqueous coagulation solution in steps (iv) and (vi) is between 0.1 and 10% by weight, preferably between 1 and 5% by weight.

A multi-layer composite comprising at least one backing layer provided with at least one polyurethane-based microporous layer obtainable by the method as defined in any one of the preceding claims.

The composite of claim 16 wherein the microporous polyurethane layer has a porosity of at least 20%.

A composite according to claim 16 or 17 which has a resilience of at least 95%.

Use of a multilayer composite as defined in any one of claims 16 to 18 as a coagulated base for making an artificial leather article.

An imitation leather article comprising a coagulated base optionally provided with further layers, wherein the coagulated base is a multilayer composite as defined in any one of claims 16 to 18.