Process for producing a composite

Abstract

The present invention lies in the field of production of composites, especially of textile coatings and imitation leathers, and in the production of the aforementioned materials. It relates to a process for producing a composite, for example a carrier layer coated with a foam layer, to the use of said composite for production of an imitation leather article, to an imitation leather article obtained thereby, and to the use of such an imitation leather article for production of further articles.

Description

[0001] PROCESS FOR PRODUCING A COMPOSITE

[0002] The present invention lies in the field of production of composites, especially of textile coatings and imitation leathers, and in the production of the aforementioned materials. It relates to a process for producing a composite, for example a carrier layer coated with a foam layer, to the use of said composite for production of an imitation leather article, to an imitation leather article obtained thereby, and to the use of such an imitation leather article for production of further articles.

[0003] BACKGROUND OF THE INVENTION

[0004] Imitation leather generally consists of a textile carrier to which a porous polymer layer has been applied, and the latter has in turn been coated with a top layer or a topcoat.

[0005] The porous polymer layer in this context preferably has pores in the micrometre range and is air- permeable and hence breathable, i.e. permeable to water vapour, but water-resistant. The porous polymer layer often comprises porous polyurethane (PU). For environmentally friendly production of PU- based imitation leather, a method based on aqueous polyurethane dispersions, called PUDs, was developed some time ago. These generally consist of polyurethane microparticles dispersed in water. The solids content is usually in the range of 30-60% by weight. For production of a porous polyurethane layer, PUDs are mechanically foamed, the foam thus obtained is coated onto a carrier layer (layer thicknesses typically between 300-2000 pm), and then the composite thus produced is cured.

[0006] The foam layer can be cured either by thermal drying or by wet coagulation. In the case of thermal drying, the water present in the PUD system evaporates, which results in formation of a film of the polyurethane particles. In the case of wet coagulation, which is primarily employed in the case of anionically stabilized polyurethane dispersions, the coated carrier layer is first treated with a coagulation bath. This generally comprises aqueous solutions of salts or acids through which the coated carrier layer is pulled. The high electrolyte concentration in the coagulation bath greatly attenuates the electrostatic stabilization of the polyurethane dispersion, so as to result in filming of the polyurethane particles and hence to curing of the foam layer here too. After the wet coagulation, the coated carrier layer is often washed with water and finally dried, likewise at relatively high temperatures.

[0007] While the thermal drying of PUD-based foam layers is already long-established prior art, the wet coagulation method still has a number of technical shortcomings. For instance, in many cases, there is only inadequate wetting of the foam layer by the coagulation bath during the coagulation, which results in occurrence of unwanted surface defects during the coagulation, for example colour runs or corrugated surface patterns. Furthermore, inadequate wetting leads to only slow curing of the foam layer, which leads to long coagulation times and hence also one process times in the production.

[0008] OBJECT OF THE INVENTION

[0009] The object of the present invention was therefore to overcome the disadvantages of the wet coagulation method that were outlined at the outset. One object was therefore to provide a process by which carrier layers coated with a foam layer can be produced rapidly and in a defect-free manner by wet coagulation.

[0010] SUMMARY OF THE INVENTION

[0011] The objects underlying the invention are achieved by the process according to the invention for production of a composite comprising at least one carrier layer and at least one foam layer, comprising the following process steps:

[0012] (i) providing at least one carrier layer;

[0013] (ii) providing a mixture comprising at least one aqueous polymer dispersion and at least one foaming aid;

[0014] (iii) foaming the mixture by mechanical foaming;

[0015] (iv) coating the at least one carrier layer with the foamed mixture;

[0016] (v) treating the coated carrier layer with a coagulation bath;

[0017] (vi) optionally removing, preferably mechanically removing, excess coagulation liquid from the coated carrier layer;

[0018] (vii) optionally washing the coated carrier layer with water, optionally followed by removing water, preferably by mechanical removal; and

[0019] (viii) drying the coated carrier layer; so as to obtain the composite, characterized in that the coagulation bath in step (v) comprises at least one polyethersiloxane.

[0020] The process according to the invention permits the production of the composite without surface defects. For instance, during the wet coagulation, it is possible to avoid defects such as unwanted colour runs or corrugated surface patterns.

[0021] Moreover, the process according to the invention permits much faster production of a composite comprising at least one carrier layer and at least one foam layer. Thus, the foam layer cures much more quickly during wet coagulation, which can reduce process times, which offers process-related benefits both from an environmental and economic point of view.

[0022] DESCRIPTION OF THE INVENTION

[0023] The invention is described further and by way of example hereinafter, without any intention that the invention be restricted to these illustrative embodiments. Where ranges, general formulae or classes of compounds are specified hereinafter, these are intended to encompass not only the corresponding ranges or groups of compounds that are explicitly mentioned but also all subranges and subgroups of compounds that can be obtained by removing individual values (ranges) or compounds. Where documents are cited in the context of the present description, the entire content thereof, particularly with regard to the subject matter that forms the context in which the document has been cited, is intended to form part of the disclosure content of the present invention.

[0024] Percentages in the description and in the claims are percentages by weight (abbreviated as % by weight), unless otherwise specified. Concentrations in the description and in the claims refer to the total mass or the total volume of the solutions or dispersions or compositions concerned, unless otherwise specified.

[0025] The various details and embodiments described hereinbelow can be combined with one another where this is technically possible and nothing to the contrary is specified.

[0026] The term “aliphatic” encompasses for the purposes of the present invention cyclic and acyclic (non- cyclic), saturated and unsaturated carbon compounds, with express exclusion of aromatic compounds from this term (cf. Compendium of Technical Terminology, Gold Book, International Union of Pure and Applied Chemistry, 2014, version 2.3.3, p. 57).

[0027] The term “alkyl” for the purposes of the present invention encompasses branched and unbranched alkyl groups including cyclic and / or acyclic structural elements, where cyclic structural elements by definition comprise at least three carbon atoms. C1-CX alkyl in the description and in the claims refers to alkyl groups comprising 1 to X carbon atoms (X is a natural number). For example, C1 -C8 alkyl includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, tert-pentyl, neopentyl, hexyl, heptyl and octyl.

[0028] Where more than one radical needs to be selected for a compound named in the claims or in the description - no matter whether from one or more lists - said radicals are selected independently of one another unless stated otherwise. If envisaged in the lists, they may thus be the same or different.

[0029] Where the expression “at least one” is included in the description and in the claims, this means that one or more than one, for example two or three, of the named elements may be selected. The same applies to higher numbers such as two or three.

[0030] Where parameters that have been determined by measurement are given hereinbelow, the measurements were carried out at a temperature of 25°C and a pressure of 101 325 Pa, unless stated otherwise.

[0031] Where chemical (empirical) formulas are used in the present invention, the stated indices may represent either absolute numbers or average values. In the case of polymeric compounds, the indices preferably represent average values. Structural and empirical formulae presented in the present invention are representative of all isomers that are conceivable via different arrangement of the repeating units. The processes described hereinafter comprise the process steps mentioned and optionally the optional process steps that are identified as such or other optional steps that are not detailed herein, which can be performed before, between or after the process steps mentioned. The processes described hereinafter comprise the process steps mentioned preferably in the sequence mentioned.

[0032] The process according to the invention for producing a composite comprising at least one carrier layer and at least one foam layer, comprising the following process steps:

[0033] (i) providing at least one carrier layer;

[0034] (ii) providing a mixture comprising at least one aqueous polymer dispersion and at least one foaming aid;

[0035] (iii) foaming the mixture by mechanical foaming;

[0036] (iv) coating the at least one carrier layer with the foamed mixture;

[0037] (v) treating the coated carrier layer with a coagulation bath;

[0038] (vi) optionally removing, preferably mechanically removing, excess coagulation liquid from the coated carrier layer;

[0039] (vii) optionally washing the coated carrier layer with water, optionally followed by removing water, preferably by mechanical removal; and

[0040] (viii) drying the coated carrier layer; so as to obtain the composite, is characterized in that the coagulation bath in step (v) comprises at least one polyethersiloxane.

[0041] The at least one polyethersiloxane is preferably selected from the group consisting of pendent polyethersiloxanes and linear terminally modified polyethersiloxanes. In the context of the present invention, it is preferable in this context when corresponding polyethersiloxanes can be prepared by reaction of at least one siloxane bearing Si-H groups with at least one polyether having at least one double bond reactive toward Si-H groups, preferably in the form of an allyl group. The chemical reactions forming the basis of this preparation are known in the technical literature and are described extensively therein (see, for example, Silicones - Chemistry and Technology, Vulkan-Verlag Essen, 1989). The reaction of the siloxane bearing Si-H groups with at least one polyether preferably takes place in the presence of at least one catalyst, with particular preference here for platinum catalysts, especially platinum(O) catalysts. Such catalysts are known to the person skilled in the art; see, for example, Lewis et al., “Platinum Catalysts used in Silicones Industry”, Platinum Metal Review, 1997, 44(23), 66-74.

[0042] The polyethers used for production of the polyethersiloxanes according to the invention are preferably polyoxyalkylenes, preferably based on ethylene oxide and propylene oxide. If the polyethers here have more than one alkylene oxide species, the polyethers may be in random distribution (random polymer), in ordered form (block polymer) or in the form of a gradient distribution.

[0043] The polyethers used for production of the polyethersiloxanes according to the invention may be either OH-functional or terminated. What is meant by “terminated” in this connection is that the polyethers have a -O-R' radical or a carboxyl radical of the -O-C(O)-R" form, where R' and R" represent a monovalent aliphatic, saturated or unsaturated hydrocarbon radical having 1 to 20, preferably having 1 to 10, carbon atoms, most preferably a methyl radical.

[0044] Pendent polyethersiloxanes in the context of the present invention are especially preferably those that conform to the general formula 1 : where x represents an integer in the interval of 1 to 50, preferably in the interval of 2 to 25, more preferably in the interval of 2 to 15; y represents an integer in the interval of 0 to 250, preferably in the interval of 5 to 150, more preferably in the interval of 5 to 100; each R1independently represents a monovalent aliphatic or monovalent aromatic hydrocarbon radical having 1 to 20 carbon atoms, preferably having 1 to 10 carbon atoms, most preferably a methyl radical, each R2independently represents an OH-functional or terminated polyether radical, and each R3independently corresponds to R1or R2.

[0045] Linear terminally modified polyethersiloxanes in the context of the present invention are especially preferably those that conform to the general formula 2: where z represents an integer in the interval of 1 to 100, preferably in the interval of 2 to 50, more preferably in the interval of 3 to 30; each R4independently represents a monovalent aliphatic or monovalent aromatic hydrocarbon radical having 1 to 20 carbon atoms, preferably having 1 to 10 carbon atoms, most preferably a methyl radical, and each R5independently represents an OH-functional or terminated polyether radical.

[0046] The carrier layer provided in process step (i) is preferably a flexible carrier layer, more preferably a textile carrier layer. In the case of textile carrier layers, these are preferably woven, nonwoven or knitted materials based on natural or synthetic fibres and mixtures thereof, for example cotton, polyester, polyester-cotton mixtures, wool, silk, flax, jute, bamboo, nylon, viscose, spandex, aramid or acrylic fibres. The carrier layer may additionally have been pretreated, for example with dyes, pigments, UV absorbers, plasticizers, antioxidants, polymer dispersions or flame retardants.

[0047] The aqueous polymer dispersion used in process step (ii) is preferably selected from the group of aqueous polystyrene dispersions, aqueous polybutadiene dispersions, aqueous poly(meth)acrylate dispersions, aqueous polyvinylester dispersions and aqueous polyurethane dispersions. The solids content of these dispersions is preferably in the range of 20-70% by weight, more preferably in the range of 35-65% by weight, based on the total weight of the dispersion. Particular preference is given in accordance with the invention to aqueous polyurethane dispersions based in particular on polyester polyols, polyesteramide polyols, polycarbonate polyols, polyacetal polyols and polyether polyols. The polymer dispersions are preferably aqueous, meaning that the dispersion medium used is essentially water (i.e. at least 90% by weight, preferably at least 95% by weight).

[0048] In particular, it is preferable when the polymer dispersion used in process step (ii) is anionically stabilized, meaning that the polymer particles in the dispersion have anionically charged groups. Most preferred in this connection are neutralized and partly neutralized acid groups, in particular neutralized and partly neutralized carboxylic acid and sulfonic acid groups.

[0049] In principle, it is possible in process step (ii) to use any foaming aids capable of stabilizing a foam based on at least one polymer dispersion. The function of the at least one foaming aid here is to enable efficient foaming of the mixture provided in process step (iii). Furthermore, the at least one foaming aid should stabilize the foam produced in process step (iii) as well as possible during the further process steps, so as to minimize ageing effects, such as foam drainage or cell coarsening. Preferably, the at least one foaming aid is used in process step (ii) in a concentration of 0.2-15% by weight, more preferably in the range of 0.4-10% by weight, especially preferably in the range of 0.5-7.5% by weight, based on the total weight of the mixture provided in process step (ii).

[0050] Most preferably, the at least one foaming aid used in process step (ii) is selected from the group of the polyglycerol esters, especially those obtainable by the esterification of at least one polyglycerol with at least one carboxylic acid.

[0051] Most preferably, the polyglycerol esters used in process step (ii) are selected from the group consisting of polyglycerol palmitate and polyglycerol stearate. In respect of the polyglycerol esters usable as foaming aids in the context the present invention, reference is made in full, but without restriction, to EP 3487945 B1 (paragraphs 18-34). More preferably, the polyglycerol ester used in process step (ii) is one conforming to the general formula 3:

[0052] MaDbTc Formula 3 where

[0053] M = [C3H5(OR6)2OI / 2]

[0054] D = [C3H5(OR6)IO2 / 2]

[0055] T = [C3H5O3 / 2] a = 1 to 10, preferably 2 to 3, especially preferably 2, b = 0 to 10, preferably greater than 0 to 5, especially preferably 1 to 4, c = 0 to 3, preferably 0, where the R6radicals are independently radicals of the R7-C(O)- form or H, where R7is a monovalent aliphatic saturated or unsaturated hydrocarbon radical having 3 to 39 carbon atoms, preferably 7 to 21 and more preferably 9 to 17 carbon atoms, where at least one R6radical corresponds to a radical of the R7-C(O)- form.

[0056] As well as the at least one polymer dispersion and the at least one foaming aid, the mixtures provided in process step (ii) may optionally also contain further additions, for example fillers, organic and inorganic pigments, flatting agents, stabilizers, such as hydrolysis stabilizers or UV stabilizers, antioxidants, absorbers, crosslinkers, levelling additives, thickeners or surfactants.

[0057] Preferred fillers used in process step (ii) are selected from the group of the silicates, for example talc, mica or kaolin, of the carbonates, for example calcium carbonate or chalk, of the oxides / hydroxides, for example ground quartz, silica, aluminium / magnesium hydroxide, magnesium oxide or zinc oxide, and of the organic fillers, for example chemical pulp, cellulose and cellulose derivatives, lignin, wood fibres / wood flour, ground plastics or textile fibres. It is further preferable when fillers are used in process step (ii) in a concentration of 5-50% by weight, more preferably of 10-45% by weight, even more preferably of 15-40% by weight, based on the total weight of the mixture provided in process step (ii).

[0058] Preferred thickeners used in process step (ii) are selected from the class of the associative thickeners. Associative thickeners here are substances which lead to a thickening effect through association at the surfaces of the particles present in the polymer dispersions. The term is known to those skilled in the art. Preferred associative thickeners are selected here from polyurethane thickeners, polyacrylate thickeners, polyether thickeners and hydrophobically modified cellulose ethers. Very particular preference is given to polyurethane thickeners. In addition, it is preferable in the context of the present invention when the concentration of the thickeners based on the total weight of the mixture provided in process step (ii) is in the range of 0.01 -10% by weight, more preferably in the range of 0.05-5% by weight, most preferably in the range of 0.1-3% by weight. In process step (iii), the mixture is foamed, so as to obtain a foamed mixture. The foaming can be effected here with the aid of shear units familiar to the person skilled in the art, for example Dispermats, dissolvers, Hansa mixers, Oakes mixers or mixers made by Gemata. It is preferable in the context of the present invention when the mixture is foamed in process step (iii) to a density in the range of 200-850 g / l, more preferably in the range of 300-800 g / l, even more preferably in the range of 400-750 g / l.

[0059] In process step (iv), the carrier layer is coated with the foamed mixture, so as to form a coated carrier layer. Coatings of the foamed mixture can be produced by methods familiar to the person skilled in the art, for example knife coating. It is preferable in the context of the present invention when the foamed mixture is coated on to the carrier layer in process step (iv) in a layer thickness of 100-2000 pm, preferably in the range of 150-1500 pm, even more preferably in the range of 200-1000 pm. In addition, it is preferable in the context of the present invention when the foamed mixture is coated on to the carrier layer in process step (iv) so as to obtain a coat weight in the range of 20-1000 g / m2, more preferably in the range of 75-750 g / m2, even more preferably in the range of 100-500 g / m2.

[0060] In process step (v), the coated carrier layer is treated with a coagulation bath, which results in coagulation and curing of the carrier layer coated with the foamed mixture. The coagulation bath here contains at least one coagulation agent which is preferably selected from the group consisting of acids and salts. Salts that are particularly preferred in the context of the present invention are selected from the group consisting of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride and calcium nitrite. Acids that are particularly preferred in the context of the present invention are selected from the group consisting of mineral acids, for example hydrochloric acid, and organic acids, where organic acids are especially preferred. Most preferably, the organic acid is citric acid or lactic acid, and mixtures of these substances. In addition, it is preferable when the coagulation agent is present in the coagulation bath in a concentration in the range of 0.5-25% by weight, more preferably in the range of 1- 20% by weight, even more preferably in the range of 2-15% by weight, based on the total amount of the coagulation bath.

[0061] In the context of the present invention, it is preferable when the coated carrier layer is treated with the coagulation bath in process step (v) for a period of 0.2-15 minutes, preferably of 0.5-12 minutes, more preferably of 1 -10 minutes.

[0062] As described at the outset, the process according to the invention is characterized in that the coagulation bath used in process step (v) comprises at least one polyethersiloxane. It is preferable here when the polyethersiloxane is present in the coagulation bath in a concentration of 0.05-5% by weight, more preferably in the range of 0.1-3% by weight, even more preferably in the range of 0.2-2.5% by weight, based on the total amount of the coagulation bath.

[0063] After process step (v), excess coagulation liquid can be removed from the coated carrier layer in an optional process step (vi). This is preferably done mechanically, for example by squeezing the coated carrier layer with a drum or a padder. Corresponding techniques are known to those skilled in the art. In addition, the coated carrier layer may be washed with water in an additional optional process step (vii), in order to remove further residues of excess coagulation liquid from the coated carrier layer. It is optionally possible to remove residues of the wash water from the coated carrier layer after this washing operation. This is preferably also done mechanically, for example by squeezing the washed coated carrier layer with a drum or a padder.

[0064] In process step (viii), the coated carrier layer is dried, so as to obtain the composite comprising at least one carrier layer and at least one foam layer. Preferably in accordance with the invention, this drying is effected at temperatures in the range of 60-170°C, preferably in the range of 70-160°C, more preferably in the range of 80-150°C. In addition, it is possible to dry the coated carrier layer in multiple stages at different temperatures, in order to avoid occurrence of drying defects. Corresponding drying techniques are widespread in industry and are known to those skilled in the art.

[0065] The invention further provides a composite comprising at least one carrier layer and at least one foam layer, obtained by the process according to the invention. Preferably, the at least one foam layer of the composite here has an average cell size of up to 250 pm, preferably of up to 150 pm, especially preferably of up to 100 pm, most preferably of less than 75 pm. Average cell size can preferably be determined by microscopy, preferably by electron microscopy. For this purpose, a cross section of the porous polymer coating is viewed by means of a microscope with sufficient magnification and the size of at least 25 cells is ascertained. In order to obtain sufficient statistics for this evaluation method, the magnification of the microscope chosen should preferably be such that at least 10 x 10 cells are present in the observation field. The average cell size is then calculated as the arithmetic average of the cells or cell sizes viewed. This determination of cell size by means of microscopy is familiar to those skilled in the art.

[0066] In addition, it is preferable when the foam layer of the composite of the invention has a layer thickness in the range of 100-2000 pm, preferably in the range of 150-1500 pm, even more preferably in the range of 200-1000 pm. It should be made clear that process steps (v)-(viii) may result in a decrease in the thickness of the foam layer coated on to the carrier layer in process step (iv), for example via loss of water or via mechanical compression. The layer thickness of the foam layer of the composite of the invention therefore need not necessarily be identical to the layer thickness of the foam layer coated in process step (iv).

[0067] The present invention additionally relates to the use of the composite according to the invention for production of an imitation leather article. According to the invention, an imitation leather article is considered to mean an article comprising or consisting of imitation leather. Such an imitation leather article can preferably be produced by a process comprising the following process steps:

[0068] M1) initially charging at least one composite according to the invention;

[0069] M2) providing at least one aqueous polymer dispersion; M3) coating the at least one composite according to the invention with the at least one aqueous polymer dispersion;

[0070] M4) drying the coated composite;

[0071] M5) optionally applying one or more further layers of the at least one aqueous polymer dispersion and then drying the repeatedly coated composite;

[0072] M6) optionally embossing the coated composite; so as to obtain the imitation leather article.

[0073] The polymer dispersion used in process step M2) is preferably selected from the group of aqueous polystyrene dispersions, aqueous polybutadiene dispersions, aqueous poly(meth)acrylate dispersions, aqueous polyvinylester dispersions and aqueous polyurethane dispersions. The solids content of these dispersions is preferably in the range of 20-70% by weight, more preferably in the range of 35-65% by weight. Particular preference is given in accordance with the invention to aqueous polyurethane dispersions, especially those based on polyester polyols, polyesteramide polyols, polycarbonate polyols, polyacetal polyols and polyether polyols.

[0074] In addition, the polymer dispersions used in process step M2) may optionally also contain further additions, for example fillers, organic and inorganic pigments, flatting agents, stabilizers, such as hydrolysis stabilizers or UV stabilizers, antioxidants, absorbers, crosslinkers, levelling additives, thickeners or surfactants. Reference is made here to the observations above.

[0075] In process step M3), the polymer dispersion is coated onto the composite according to the invention, so as to form a coated composite. Coatings of the polymer dispersion can be produced by methods familiar to the person skilled in the art, for example knife coating. It is preferable in the context of the present invention when the polymer dispersion is coated onto the composite in process step M3) in a layer thickness of 25-500 pm, preferably in the range of 50-300 pm, even more preferably in the range of 75- 250 pm.

[0076] In process step M4), the coated composite is dried. Preferably in accordance with the invention, this drying is effected at temperatures in the range of 60-170°C, preferably in the range of 70-160°C, more preferably in the range of 80-150°C. In addition, it is possible to dry the coated composite in multiple stages at different temperatures, in order to avoid occurrence of drying defects. Corresponding drying techniques are widespread in industry and are known to those skilled in the art.

[0077] Optionally, the coated composite, after being dried, and optionally after application of further top layers in an optional process step M5), may be embossed in a process step M6). By the embossment, it is possible to apply a surface structure to the coated composite, for example in the form of a typical leather grain. The coated composite is preferably embossed in process step M6) at elevated temperatures and pressures, for example by the use of heated plates or rolls that have a negative impression of the desired surface structure. Corresponding embossing techniques are known to those skilled in the art. In addition, it is preferable in the context of the present invention when the imitation leather article contain at least one composite according to the invention can be produced by an alternative process comprising the following process steps:

[0078] N1) providing at least one release paper;

[0079] N2) providing at least one aqueous polymer dispersion;

[0080] N3) providing at least one composite according to the invention;

[0081] N4) coating the at least one release paper with the at least one polymer dispersion;

[0082] N5) optionally drying the coated release paper, followed by the application of a further layer of aqueous polymer dispersion to the coated release paper;

[0083] N6) laminating the at least one composite according to the invention onto the coated release paper;

[0084] N7) drying the composite laminated onto the coated release paper, which affords the imitation leather article laminated onto the release paper;

[0085] N8) detaching the imitation leather article from the release paper, so as to obtain the imitation leather article.

[0086] The release paper provided in process step N1) is selected such that an aqueous polymer dispersion can be coated onto it in a defect-free manner and has good detachability in the dried state. Especially preferred here are wax- or silicone-coated release papers. Moreover, it may be advantageous when the release paper is structured since it is thus possible to create a surface structure in the production of the imitation leather article, for example in the form of a typical leather grain. Corresponding release papers are known to those skilled in the art.

[0087] The aqueous polymer dispersion used in process step N2) is preferably selected from the group of aqueous polystyrene dispersions, aqueous polybutadiene dispersions, aqueous poly(meth)acrylate dispersions, aqueous polyvinylester dispersions and aqueous polyurethane dispersions. The solids content of these dispersions is preferably in the range of 20-70% by weight, more preferably in the range of 35-65% by weight. Particular preference is given in accordance with the invention to aqueous polyurethane dispersions, especially those based on polyester polyols, polyesteramide polyols, polycarbonate polyols, polyacetal polyols and polyether polyols.

[0088] In addition, the polymer dispersions used in process step N2) may optionally also contain further additions, for example fillers, organic and inorganic pigments, flatting agents, stabilizers, such as hydrolysis stabilizers or UV stabilizers, antioxidants, absorbers, crosslinkers, levelling additives, thickeners or surfactants.

[0089] In process step N4), the polymer dispersion is coated onto the release paper, so as to form a coated release paper. Coatings of the polymer dispersion can be produced by methods familiar to the person skilled in the art, for example knife coating. It is preferable within the context of the present invention when the polymer dispersion in process step N4) is applied to the composite in a layer thickness of 25- 500 pm, preferably in the range of 50-300 pm, even more preferably in the range of 75-250 pm.

[0090] In optional process step N5), the coated release paper is dried. Preferably in accordance with the invention, this drying is effected at temperatures in the range of 60-170°C, preferably in the range of 70- 160°C, more preferably in the range of 80-150°C. In addition, it is possible to dry the coated release paper in multiple stages at different temperatures, in order to avoid occurrence of drying defects. Corresponding drying techniques are widespread in industry and are known to those skilled in the art.

[0091] If, in optional process step N5), a further layer of polymer dispersion is applied to the already coated release paper, the same constraints as already described for process step N2) are applicable to the polymer dispersion. Either identical or different polymer dispersions may be used for process steps N2) and N5). The same constraints as already described for process step N4) are likewise applicable to the coating of the polymer dispersion in process step N5).

[0092] In process step N7), the composite laminated onto the coated release paper is dried to obtain the imitation leather article. The same constraints as for process step N5) are applicable to the temperature provisions in this step. The imitation leather article obtained in this process step is finally detached from the release paper in a process step N8).

[0093] The present invention further provides for the use of at least one imitation leather article according to the invention for production of an article, where the article is preferably selected from the group consisting of shoes, insoles, bags, suitcases, small cases, textiles, clothing, automobile parts, especially seat covers, coverings of door parts, dashboard parts, steering wheels and / or handles, and gearshift gaiters, fitout articles such as desk pads, cushions and seating furniture, and cushioning and damping materials in medical applications.

[0094] EXAMPLE

[0095] Commercial products are used as per the technical information sheets available at the time of filing of this application, unless stipulated otherwise.

[0096] Materials

[0097] HYDROTECH® MT 480 is an aliphatic polyether-based polymer dispersion from ERCA;

[0098] ORTEGOL® P 2 is a foaming aid for aqueous polymer dispersions from EVONIK;

[0099] ORTEGOL® PD 152 is a dispersing additive from Evonik.

[0100] ORTEGOL® PV 301 : polyurethane-based associative thickener from Evonik Industries AG; kaolin was sourced from SIGMA ALDRICH as mineral filler; ECO PIGMENT® BLACK is a water-based black colour paste from Cromogenia

[0101] Lactic acid in technical grade quality was sourced from Sigma-Aldrich

[0102] Polyethersiloxane 1 is a pendent polyethersiloxane of formula 1 with x = 8, y = 4, R1= R3= CH3 and where R2is an OH-functional polyoxyethylene radical having 13 repeat units (molar mass about 600 g / mol)

[0103] Polyethersiloxane 2 is a terminally modified polyethersiloxane with z = 18, R4= CH3 and where R5is a methylene end-capped polyoxyethylene-polyoxypropylene radical having 15 repeat units of ethylene oxide and 4 repeat units of propylene oxide (molar mass about 900 g / mol).

[0104] Coagulation experiments

[0105] The efficacy of the process according to the invention was tested by conducting a number of coagulation experiments with foam-coated textiles. The textile carrier layer used for these experiments was a woven polyester-cotton blend textile, onto which a foamed polyurethane dispersion had been coated. In a first step, for this purpose, the mixtures described in Table 1 were provided and foamed mechanically.

[0106] Table 1 : Composition of the foam formulation

[0107] Weight

[0108] HYDROTECH® MT 480 128.0 g

[0109] Kaolin 15.0 g

[0110] ORTEGOL® P 2 6.0 g

[0111] ORTEGOL PD® 152 0.5 g

[0112] ECO PIGMENT Black 1 g

[0113] ORTEGOL® PV 301 0.5 g

[0114] This mixture was foamed by first homogenizing an initial charge of all raw materials apart from the ORTEGOL® PV 301 in a 500 ml plastic beaker at 1000 rpm for 3 min with a dissolver equipped with a dispersing disk (diameter = 6 cm). The mixture was then foamed by increasing the shear rate to 2000 rpm, ensuring that the dissolver disk was always immersed into the mixture to such an extent as to form a proper vortex. At this speed, the mixture was foamed to a volume of about 325 ml. Subsequently, the ORTEGOL® PV 301 was added to the mixtures and the mixture was sheared at 1000 rpm for a further 15 minutes. In this step, the dissolver disk was immersed sufficiently deeply into the mixture that no further air was introduced into the system, but the complete volume was still in motion.

[0115] In a next step, the mixture thus foamed was coated onto the abovementioned textile carrier layer. This was done with the aid of the Labcoater LTE-S coating apparatus from Mathis AG. The layer thickness of the foam layer was 800 pm. Directly thereafter, the coated textile carrier layers were treated with different coagulation baths. The composition of the coagulation baths is compiled in Table 2. Table 2: Summary of the composition of the coagulation baths used

[0116] Bath #1 Bath #2Bath #3

[0117] Comparative .. ..

[0118] . . inventive inventive experiment

[0119] Water 90% by weight 89% by weight 89% by weight

[0120] Lactic acid 10% by weight 10% by weight 10% by weight

[0121] Polyethersiloxane 1 1% by weight

[0122] Polyethersiloxane 2 1% weight

[0123] For the treatment with the coagulation baths, the coated textile carrier layers were weighted down and immersed into the respective bath. A laboratory spatula was used to determine the extent to which the foam coating had cured in a time interval of 30 seconds. It was possible here to observe that the curing times were distinctly different depending on the bath. Coated carrier layers which had been treated with bath #1 cured after about 9 minutes, whereas samples which had been treated with bath #2 and bath #3 had already cured completely after 6 and 4 minutes respectively. The cured samples were then treated with a laboratory padder in order to remove excess coagulation liquid and then washed 4 times with water. After each washing operation, the samples were treated again with a laboratory padder in order to remove excess wash water. The washed samples were dried in an air circulation drying cabinet at 120°C for 10 minutes. In the case of the dried samples, it was noticeable that samples that had been treated with bath #1 had an irregular surface. It was thus possible to observe distinct colour shadows. Moreover, these samples showed a corrugated surface pattern. Samples which, by contrast, had been treated with the baths #2 and #3 had a completely homogeneous, defect-free surface. These experiments thus impressively demonstrate the benefits of the process according to the invention.

Claims

Claims:1 . A process for producing a composite comprising at least one carrier layer and at least one foam layer, comprising the following process steps:(i) providing at least one carrier layer;(ii) provi I I Iding a mixture comprising at least one aqueous polymer dispersion and at least oneO foaming aid; « 7J 7J - -(iii) foaming the mix“ I l Jtu _ _ re by mechanical foaming;(iv) coating the at least one carrier layer with the foamed mixture;(v) treating the coated carrier layer with a coagulation bath;(vi) optionally removing, preferably mechanically removing, excess coagulation liquid from the coated carrier layer;(vii) optionally washing the coated carrier layer with water, optionally followed by removing water, preferably by mechanical removal; and(viii) drying the coated carrier layer; so as to obtain the composite, characterized in that the coagulation bath in step (v) comprises at least one polyethersiloxane.

2. The process according to Claim 1 , characterized in that the at least one polyethersiloxane is selected from the group consisting of pendent polyethersiloxanes and linear terminally modified polyethersiloxanes.

3. The process according to Claim 2, characterized in that the pendent polyethersiloxanes conforms to the general formula 1 :R1R1" R1R ,3- S Ii — O - S Ii—-O R3Formula 1R I1R I1_ R1X y where x represents an integer in the interval of 1 to 50, preferably in the interval of 2 to 25, more preferably in the interval of 2 to 15; y represents an integer in the interval of 0 to 250, preferably in the interval of 5 to 150, more preferably in the interval of 5 to 100;each R1independently represents a monovalent aliphatic or monovalent aromatic hydrocarbon radical having 1 to 20 carbon atoms, preferably having 1 to 10 carbon atoms, most preferably a methyl radical, each R2independently represents an OH-functional or terminated polyether radical, and each R3independently corresponds to R1or R2.

4. The process according to Claim 2, characterized in that the linear terminally modified polyethersiloxanes conform to the general formula 2:where z represents an integer in the interval of 1 to 100, preferably in the interval of 2 to 50, more preferably in the interval of 3 to 30; each R4independently represents a monovalent aliphatic or monovalent aromatic hydrocarbon radical having 1 to 20 carbon atoms, preferably having 1 to 10 carbon atoms, most preferably a methyl radical, and each R5independently represents an OH-functional or terminated polyether radical.

5. The process according to at least one of Claims 1 to 4, characterized in that the at least one aqueous polymer dispersion has a solids content in the range of 20-70% by weight, preferably in the range of 35-65% by weight, based on the total weight of the aqueous polymer dispersion.

6. The process according to at least one of Claims 1 to 5, characterized in that the at least one aqueous polymer dispersion is selected from the group of polyurethane dispersions, more preferably polyester-, polyesteramide-, polycarbonate-, polyacetal- and polyether-based polyurethane dispersions.

7. The process according to at least one of Claims 1 to 6, characterized in that the at least one polyurethane dispersion is anionically stabilized.

8. The process according to at least one of Claims 1 to 7, characterized in that the coagulation bath contains at least one coagulation agent selected from the group consisting of salts and acids, more preferably citric acid and lactic acid in particular.

9. The process according to at least one of Claims 1 to 8, characterized in that the at least one foaming aid is selected from the group of the polyglycerol esters.

10. The process according to at least one of Claims 1 to 9, characterized in that the foamed polymer dispersion obtained in process step (iii) has a wet foam density in the range of 200- 850 g / l, preferably in the range of 300-800 g / l.

11. A composite consisting of at least one carrier layer and at least one foam layer, obtainable by a process according to at least one of Claims 1 to 10.

12. The use of the composite according to Claim 11 for production of an imitation leather article.

13. An imitation leather article comprising at least one composite according to Claim 11 .

14. The use of the imitation leather article according to Claim 13 for production of an article, where the article is preferably selected from the group consisting of shoes, insoles, bags, suitcases, small cases, textiles, clothing, automobile parts, especially seat covers, coverings of door parts, dashboard parts, steering wheels and / or handles, and gearshift gaiters, fitout articles such as desk pads, cushions and seating furniture, and cushioning and damping materials in medical applications.

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