EP4330320A1

EP4330320A1 - Use of solid-based foaming aids in aqueous polyurethane dispersions

Info

Publication number: EP4330320A1
Application number: EP22726084.1A
Authority: EP
Inventors: Michael Klostermann; Kai-Oliver Feldmann; Marvin JANSEN
Original assignee: Evonik Operations GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2021-04-30
Filing date: 2022-04-28
Publication date: 2024-03-06
Also published as: KR20230170924A; US20240209233A1; JP2024516424A; CN117203270A; MX2023012733A; WO2022229311A1; BR112023021957A2

Abstract

Described is the use of solid-based foaming aids as additives in aqueous polymer dispersions for producing porous polymer coatings, preferably for producing porous polyurethane coatings.

Description

Use of solid-based foaming aids in aqueous polyurethane dispersions

The present invention is in the field of plastic coatings and artificial leather.

In particular, it relates to the production of porous polymer coatings, preferably porous polyurethane coatings, using solid-based foaming aids, which are preferably made hydrophobic.

Textiles coated with plastics, such as artificial leather, usually consist of a textile carrier onto which a porous polymer layer is laminated, which in turn is covered with a top layer or top coat.

The porous polymer layer preferably has pores in the micrometer range, is air-permeable and therefore breathable, i.e. permeable to water vapor but water-resistant. The porous polymer layer is often porous polyurethane. A process based on aqueous polyurethane dispersions, so-called PUDs, was developed some time ago for the environmentally friendly production of PU-based artificial leather. These usually consist of polyurethane microparticles dispersed in water, the solids content is usually in the range of 30 - 60% by weight. To produce a porous polyurethane layer, these PUDs are mechanically foamed, coated onto a carrier (layer thicknesses typically between 300-2000 μm) and then dried at elevated temperature. During this drying step, the water contained in the PUD system evaporates, causing the polyurethane particles to form a film. In order to further increase the mechanical strength of the film, certain hydrophilic isocyanates or carbodiimides can also be added to the PUD system during the manufacturing process lead to additional crosslinking of the polyurethane film.

Both the mechanical and the haptic properties of PUD coatings produced in this way are largely determined by the cell structure of the porous polyurethane film. Furthermore, the cell structure of the porous polyurethane film influences the air permeability and breathability of the material. Particularly good properties can be achieved with cells that are as fine and homogeneously distributed as possible. In order to influence the cell structure during the production process described above, it is customary to add foam stabilizers to the PUD system before or during mechanical foaming. On the one hand, appropriate stabilizers ensure that sufficient amounts of air can be introduced into the PUD system during the foaming process. On the other hand, the foam stabilizers have a direct influence on the morphology of the air bubbles generated. The stability of the air bubbles is also significantly influenced by the type of stabilizer. This is particularly important during the drying of foamed PUD coatings, as this prevents drying defects such as cell coarsening or drying cracks.

Various foam stabilizers have already been used in the past in the PUD process described above. In the documents US 2015/0284902 A1 or US 2006 0079635 A1, for example, the use of ammonium stearate-based foam stabilizers is described. However, the use of corresponding ammonium stearate-based stabilizers is associated with a number of disadvantages. A major disadvantage here is that ammonium stearate has a very high ability to migrate in the finished artificial leather. Over time, this means that surfactant molecules accumulate on the surface of the imitation leather, which can lead to white discolorations on the surface of the leather. Furthermore, this migration of surfactants can result in a smear film on the surface of the imitation leather that is perceived as unpleasant, especially when the corresponding materials come into contact with water.

Another disadvantage of ammonium stearate is that it forms insoluble lime soaps when it comes into contact with hard water. When synthetic leather made on the basis of ammonium stearate comes into contact with calcareous water, white bloating can occur on the synthetic leather surface, which is particularly undesirable in the case of dark-colored leather.

Another disadvantage of ammonium stearate-based foam stabilizers is that although they permit efficient foaming of aqueous polyurethane dispersions, they often lead to a very coarse and irregular foam structure. This can have a negative effect on the visual and tactile properties of the finished artificial leather.

Another disadvantage of ammonium stearate is that the PUD foams produced often have insufficient stability, which can lead to disadvantages in their processing, especially when drying the PUD foams at elevated temperatures. A consequence of this would be, for example, that corresponding foams have to be dried relatively gently and slowly, which in turn leads to longer process times in the production of artificial leather.

As an alternative to ammonium stearate-based foam stabilizers, polyol esters and polyol ethers have been identified as effective foam additives for aqueous polyurethane dispersions in the past. These structures are described, for example, in the documents EP 3487945 A1 and WO2019042696A1. Compared to ammonium stearate, polyol esters and polyol ethers have the significant advantage that they migrate only slightly or not at all in the finished artificial leather and therefore do not lead to undesirable surface discolorations. In addition, polyol esters and polyol ethers are not susceptible to hard water.

Another advantage of polyol esters and polyol ethers compared to ammonium stearate-based foam stabilizers is that they often lead to a significantly finer and more homogeneous foam structure, which has an advantageous effect on the properties of these substances manufactured leatherette materials. Polyol esters and polyol ethers also often lead to significantly more stable PUD foams, which in turn brings process advantages in the manufacture of artificial leather. Despite these advantages, polyol esters and polyol ethers are also not entirely free of potential disadvantages. A potential disadvantage here is that the foam-stabilizing effect of these classes of compounds can under certain circumstances be impaired by the presence of other co-surfactants contained in the PUD system. However, the use of co-surfactants is not unusual, particularly in the production of aqueous polyurethane dispersions. In this context, co-surfactants are used to improve the dispersion of polyurethane prepolymers in water and generally remain in the final product. During the mechanical foaming of aqueous polyurethane dispersions which contain polyol esters or polyol ethers as foam additives, the corresponding co-surfactants can under certain circumstances have a negative effect on the foaming behavior of the system. As a result, under certain circumstances, little or no air can be blown into the system; the resulting foam structure could then suffer. Co-surfactants can also have a negative effect on the stability of the foams produced, which can lead to foam aging during processing of the foamed PUD system, which in turn leads to voids and defects in the foam coatings produced. Another potential disadvantage is that PUD systems that contain polyol esters or polyol ethers as foam additives often require very high shear energies for efficient foaming. This, in turn, can sometimes result in limitations and disadvantages in terms of process technology. The object of the present invention was therefore to provide additives for the production of PUD-based foam systems and foam coatings which allow PUD systems to be foamed efficiently and do not have the disadvantages listed in the prior art. Surprisingly, it has been found that solids-based foaming aids make it possible to achieve the stated object.

The present invention therefore relates to the use of solids-based foaming aids as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, for producing porous polymer coatings, preferably for producing porous polyurethane coatings.

The porous polymer layer to be produced according to the invention (ie the porous polymer coating; these terms are used synonymously) preferably has pores in the micrometer range, with the mean cell size preferably being less than 350 μm, preferably less than 200 μm, particularly preferably less than 150 μm, very particularly preferably smaller 100 pm is. The preferred layer thickness is in the range from 10 to 10000 μm, preferably from 50 to 5000 μm, more preferably from 75 to 3000 pm, in particular from 100 to 2500 mhΊ. The mean cell size can preferably be determined microscopically, preferably by electron microscopy, as explained further below.

The use according to the invention of solids-based foaming aids surprisingly has a wide range of advantages.

One advantage is that solid-based foaming aids enable particularly efficient foaming of aqueous PUD systems. The foams produced in this way are characterized by an extraordinarily fine pore structure with a particularly homogeneous cell distribution, which in turn has a very advantageous effect on the mechanical and haptic properties of the porous polymer coating, which are produced on the basis of these foams. Furthermore, this can improve the air permeability or breathability of the coating.

Another advantage is that solid-based foaming aids enable efficient foaming of PUD systems even at relatively low shear rates, which leads to fewer limitations and broader processability during synthetic leather production.

Another advantage is that solid-based foaming aids enable the production of particularly stable foams. On the one hand, this has an advantageous effect on their processability. On the other hand, the increased foam stability has the advantage that drying defects such as cell coarsening or drying cracks can be avoided during the drying of corresponding foams. In addition, the improved foam stability allows the foams to dry more quickly, which offers process engineering advantages from both an ecological and economic point of view.

Another advantage is that the effectiveness of solid-based foaming aids is hardly or not at all impaired by the co-surfactants optionally present in the PUD system. Thus, the solids-based foaming aids according to the invention enable efficient foaming of the system, even in the case of co-surfactant-containing PUD systems, and the formation of fine and homogeneous and at the same time extremely stable foams.

Another advantage is that the solids-based foaming aids according to the invention are not capable of migrating in the finished synthetic leather and thus do not lead to unwanted surface discoloration or bloating. Furthermore, the surfactants according to the invention are not or hardly susceptible to hard water.

For the purposes of the present invention as a whole, the term solids-based foaming aid comprises, in particular, foaming aids which consist of particles which are insoluble in the aqueous polymer dispersion, preference being given to both organic and inorganic particles. It is synonymous with the term particulate foam aid. The term particle includes both rigid, non-swellable particles and deformable, swellable particles, with the particles in both cases can be charged or uncharged. In this context, insoluble means that less than 5% by weight, preferably less than 2.5% by weight, more preferably less than 1% by weight, of the Dissolve particles in the polymer dispersion. In the context of the present invention, preference is given in particular to particles whose surface has been made hydrophobic or partially hydrophobic. This corresponds to a very particularly preferred embodiment of the invention.

The term hydrophobing is known per se to those skilled in the art. This is understood to mean, also within the meaning of this invention, the treatment of substances with so-called hydrophobing agents in order to reduce their wettability with water. Appropriate water repellents can accumulate on the surface of the substances to be treated. In the case of completely hydrophobic fabrics, the entire surface is covered with hydrophobic agents, whereas in the case of partially hydrophobic fabrics, only part of their surface is modified with hydrophobic agents. For the purposes of this invention, the term hydrophobing also includes partial hydrophobing. So when “hydrophobing” or “hydrophobicized” is mentioned below, this also includes “partially hydrophobicizing” or “partially hydrophobicized”, even if it is not explicitly mentioned.

In the context of this invention, hydrophobing can preferably be effected by (reversible) adsorption and/or by (permanent) covalent attachment of suitable hydrophobing agents to the particle surface. Preference is given here in particular to hydrophobic particles whose surface is uniformly hydrophobic and which are not Janus particles. The term Janus particle is known to those skilled in the art. For the purposes of the present invention as a whole, the term co-surfactant encompasses surfactants which can optionally be present in the polymer dispersion in addition to the solid-based foaming aids according to the invention. In particular, this includes surfactants that can be used during the preparation of the polymer dispersion. For example, polyurethane dispersions are often produced by synthesizing a PU prepolymer, which is dispersed in water in a second step and then reacted with a chain extender. Co-surfactants can be used here to improve the dispersion of the prepolymer in water. In the context of the present invention, co-surfactants are preferably anionic co-surfactants.

The invention is described further below and by way of example, without the invention being restricted to these exemplary embodiments. If ranges, general formulas or compound classes are specified below, these should not only include the corresponding ranges or groups of compounds that are explicitly mentioned, but also all sub-ranges and sub-groups of compounds that are obtained by removing individual values (ranges) or compounds can become. If documents are cited in the context of the present description, their content, in particular with regard to the facts, should be in its Context the document was cited, fully belong to the disclosure of the present invention. Unless otherwise stated, percentages are percentages by weight. If parameters are given below that were determined by measurement, the measurements were carried out at a temperature of 25° C. and a pressure of 101325 Pa, unless otherwise stated. If chemical (sum) formulas are used in the present invention, the indices given can represent both absolute numbers and mean values. In the case of polymeric compounds, the indices preferably represent mean values. The structure and molecular formulas shown in the present invention represent all isomers that are conceivable due to different arrangements of the repeating units.

In the context of the present invention, both organic and inorganic particles can be used as solid-based foaming aids, and mixtures of two or more particles can also be used. The particles used as foam aids can be of natural or synthetic origin. Preferred organic particles here are cellulose, cellulose derivatives, cellulose, lignin, polysaccharides, wood fibers, wood flour, ground plastics, textile fibers and/or synthetic polymer particles, such as latex or polyurethane particles. Preferred inorganic particles are selected from the group of (mixed) oxides/hydroxides, such as silicon oxide, aluminum oxide, zirconium oxide, silicon aluminum oxide, silicic acid, aluminum/magnesium hydroxide or quartz powder, and the group of carbonates, such as calcium carbonate or chalk , the group of phosphates, the group of sulfates, such as calcium sulfate or barium sulfate, the group of silicates, such as talc, mica or kaolin and/or the group of silicone-based particles, in particular silicone resin or MQ resin-based particles , Oxides based on silicon oxide and/or aluminum oxide and silicates, in particular kaolin, being particularly preferred. In the context of the present invention, preference is given to using particles as solid-based foaming aids that have an average volume-weighted primary particle size in the range from 0.01-100 μm, preferably in the range from 0.05-50 μm, more preferably in the range from 0.1 - exhibit 35 pm. The term primary particle size describes the size of individual, non-aggregated or agglomerated particles. The term is known to those skilled in the art. The mean primary particle size can be determined here by methods familiar to the person skilled in the art. Preferred methods here are laser diffraction or dynamic light scattering. Measurements using laser diffraction can be carried out, for example, with a MasterSizer 3000 from Malvern, measurements using dynamic light scattering can be carried out, for example, with a ZetaSizer Nano ZSP, also from Malvern.

As described above, it is very particularly preferred in the context of the present invention if the particles used as foaming aids are hydrophobicized or partially hydrophobicized, with (partial) hydrophobicization being able to take place by (reversible) adsorption and/or by (permanent) covalent attachment of suitable hydrophobicizing agents . Choosing a suitable one Hydrophobing agent depends in particular on the surface properties of the particles to be hydrophobic.

If the particles have negative (partial) charges on the surface, preference is given in particular to water repellents which carry cationic or partially cationic anchor groups. If the particles have positive (partial) charges on the surface, preference is given in particular to water repellents which carry anionic or partially anionic anchor groups.

The surface charge of the particles can be determined, for example, by determining the zeta potential. Corresponding measurements are known to the person skilled in the art and are possible, for example, with a ZetaSizer Nano ZSP from Malvern. In addition to electrostatic interactions, suitable water repellents can also be attached by means of hydrogen bonds, dipole-dipole interactions, van der Waals interactions and coordinate or covalent bonds.

Depending on the surface quality of the particles to be hydrophobic, preferred hydrophobing agents are selected from the group of cationic polymers, the group of amines, preferably the group of alkylamines or their cations, the group of quaternary ammonium compounds, with both organic and silicone-based amines - and ammonium compounds are preferred, the group of carboxylates, alkyl sulfates, alkyl sulfonates, alkyl phosphates, alkyl phosphonates, alkyl and dialkyl sulfosuccinates, and in each case the corresponding free acids, the group of silicones, the group of silanes, the group of epoxides and/or isocyanates.

Particles which have reactive OH, NH or NH2 groups on the surface can preferably be modified with hydrophobizing agents which are reactive towards these groups, such as preferably silanes, silazanes, epoxides, isocyanates, carboxylic acid anhydrides or chlorides and/or alkyl chlorides, in which Connection in particular silanes and / or silazanes are preferred.

In a particularly preferred embodiment of the invention, silicon oxide, aluminum oxide and/or silicates, preferably sheet silicates, in particular kaolin, are used as solid-based foaming aids and amines or their cations, quaternary ammonium compounds, such as palmitamidopropyltrimonium chloride, alkyl sulfates or silanes are used as hydrophobing agents, with the solids-based foaming aid can be rendered hydrophobic beforehand or in situ, as explained below. The use of previously hydrophobic solid-based foaming aids is very particularly preferred. The use of in-situ hydrophobic solids-based foaming aids is also particularly preferred.

The optional, preferably mandatory, hydrophobing of the particles used as foaming aids can be carried out separately, ie before the addition of the foaming aids used Particles for aqueous polymer dispersion, as well as in-situ, ie directly in the aqueous polymer dispersion. In the case of separate water repellency, particles and water repellents are formulated into a one-component system before addition to the polymer dispersion, which is then added to the polymer dispersion. This can be done either neat or in a suitable solvent or dispersant, with water being particularly preferred as the solvent or dispersant. In the case of in-situ hydrophobing, particles and hydrophobing agents are added to the polymer dispersion as individual components. Here, too, particles and hydrophobing agents can each be added to the polymer dispersion in pure form or in each case as a solution or dispersion, preference being given in particular to aqueous solutions and dispersions.

It may be necessary to pretreat the surface of the particles before the optional hydrophobic treatment in order to achieve sufficient interaction between the particle and the hydrophobing agent. For example, in the case of aqueous particle dispersions, the surface charge of the particles can be adjusted by varying the pH. In the case of a permanent, covalent modification of the particles, it may also be necessary to accelerate the reaction between the particle and the hydrophobing agent by choosing suitable reaction parameters, e.g. by heating, by distilling off volatile reaction by-products or by using suitable catalysts, in order to achieve sufficient hydrophobicization of the particles get.

In the case of hydrophobicized or partially hydrophobicized particles, it is preferred within the scope of the present invention if the hydrophobicizing agent is present in a concentration of 0.01-50% by weight, preferably 0.02-25% by weight, more preferably in the range of 0.03-20% by weight. -%, even more preferably in the range of 0.04-15% by weight, even more preferably in the range of 0.05-10% by weight, based on the total amount of particles and hydrophobing agent.

As already described, the present invention provides for the use of solids-based foaming aids, as described above, in aqueous polymer dispersions, preferably in aqueous polyurethane dispersions. The polymer dispersions are preferably selected from the group of aqueous polystyrene dispersions, polybutadiene dispersions, poly(meth)acrylate dispersions, polyvinyl ester dispersions and/or polyurethane dispersions and also dispersions from combinations of said polymers or mixed dispersions. The solids content of these dispersions is preferably in the range from 20-70% by weight, more preferably in the range from 25-65% by weight, based on the dispersion as a whole. According to the invention, the use of solids-based foaming assistants in aqueous polyurethane dispersions is particularly preferred. Particular preference is given here to polyurethane dispersions based on polyester, polyesteramide, polycarbonate, polyacetal and/or polyether polyols.

In the context of the present invention, it is preferred if the concentration of the solid-based foaming aids based on the total weight of the aqueous polymer dispersion in In the range from 0.1 to 50% by weight, particularly preferably in the range from 0.5 to 40% by weight, particularly preferably in the range from 1.0 to 35% by weight.

As previously described, the present invention provides for the use of solid-based foaming aids in aqueous polymer dispersions. Here, the solid-based foaming aids can on the one hand enable efficient foaming of the polymer dispersion and on the other hand enable the formation of a stable and at the same time fine-celled and homogeneous foam. The solid-based foaming aids can thus act as foaming agents or foam stabilizers. These terms can be used synonymously for the term foam aid. The fine cells of the foam can be checked by a person skilled in the art in the usual way by means of a simple direct visual inspection with the naked eye or with optical aids such as magnifying glasses or microscopes based on his usual experience. "Fine" refers to the cell size. The smaller the average cell size, the finer the foam. If necessary, the fine cell content can be determined, for example, using a light microscope or using a scanning electron microscope. "Homogeneous" means the cell size distribution. A homogeneous foam has the narrowest possible cell size distribution, so that all cells are approximately the same size. This could in turn be quantified with a light microscope or with a scanning electron microscope. The less the fine cells and homogeneity of the foam change over time, especially when the foam is dried at elevated temperatures, the more stable the foam is. In addition to this purpose, the solids-based foaming aids can also serve as drying aids, rheology additives, or fillers, which also corresponds to preferred embodiments of the present invention. A use of fillers in dispersions for the production of porous polymer coatings is known. The solid-based foaming aids according to the invention differ from mere fillers in that they are more hydrophobic or are made more hydrophobic, if necessary in situ, and thus enable an improvement in the foam quality in terms of the parameters mentioned above and are very positive for the foamability of the contribute to the system.

In addition to the solid-based foaming aids according to the invention, the aqueous polymer dispersions can also contain other additives/formulation components such as color pigments, other fillers, matting agents, stabilizers such as hydrolysis or UV stabilizers, antioxidants, absorbers, crosslinkers, leveling additives, thickeners or other surface-active substances . It corresponds to a particularly preferred embodiment of the present invention if the aqueous polymer dispersions, in addition to the solids-based foaming aids according to the invention, contain less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, even more preferably less than 0.1 wt. As already mentioned, the solids-based foaming aids and any water repellents used can be added to the aqueous polymer dispersion either in pure form or predispersed or predissolved in a suitable dispersing medium or solvent. In the case of an in situ modification of the particles used as foaming aids, it is also possible to disperse or dissolve one of the two components in a suitable dispersing medium or solvent and to add the other component in pure form to the aqueous polymer dispersion. In this context, preferred dispersing media or solvents are selected from water, propylene glycol, dipropylene glycol, polypropylene glycol, butyl diglycol, butyl triglycol, ethylene glycol, diethylene glycol, polyethylene glycol, polyalkylene glycols based on EO, PO, BO and/or SO, alcohol alkoxylates based on EO, PO, BO and/or SO and mixtures of these substances, with aqueous dispersions and solutions being very particularly preferred.

In the event that the solids-based foaming aids according to the invention are not added in pure form but as a dispersion to the aqueous polymer dispersion, it can also be advantageous if the corresponding dispersions contain other formulation aids such as dispersing or rheological additives. This also corresponds to a preferred embodiment of the present invention.

Since, as described above, the use of solids-based foaming aids according to the invention leads to a significant improvement in porous polymer coatings produced from aqueous polymer dispersions, aqueous polymer dispersions containing at least one of the solids-based foaming aids according to the invention, as described in detail above, are also the subject of the present invention .

Another subject of the present invention are porous polymer layers produced from aqueous polymer dispersions, obtained using the inventive use of solid-based foaming aids, as described in detail above, the solids content of these dispersions preferably being in the range of 20-70% by weight, more preferably in the range of 25-65% by weight, based on the total dispersion, and the concentration of the solid-based foaming aids, based on the total weight of the aqueous polymer dispersion, preferably in the range of 0.1-50% by weight, particularly preferably in the range of 0.5-40% by weight, particularly preferably in the range of 1.0-35% by weight.

The porous polymer coatings according to the invention can preferably be produced using, preferably hydrophobicized or partially hydrophobicized, solid-based foaming aids as additives in aqueous polymer dispersions, preferably as described above, by a method comprising the steps: a) providing a mixture containing at least one aqueous polymer dispersion, at least one solid-based foaming aid, and optionally further additives, b) foaming the mixture to form a foam, c) optionally adding at least one thickener to adjust the viscosity of the wet foam, d) applying a coating of the foamed polymer dispersion on a suitable carrier, e) drying the coating.

This method for producing a porous polymer coating, preferably porous polyurethane coating using, preferably hydrophobic or partially hydrophobic, solid-based foaming aids as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, preferably as described above, is another subject of the invention. The solids-based foaming aid used in step a) is preferably made hydrophobic or partially hydrophobic, it being possible for the solids-based foaming aid to be made hydrophobic beforehand or in situ, as described above.

With regard to preferred configurations, in particular with regard to the solids-based foaming aids and polymer dispersions that can preferably be used in the process, reference is made to the preceding description and also to the aforementioned preferred embodiments, in particular as presented in the claims.

It is made clear that the method steps of the method according to the invention, as presented above, are not subject to a fixed time sequence. For example, method step c) can already be carried out at the same time as method step a).

It corresponds to a preferred embodiment of the present invention if, in process step b), the aqueous polymer dispersion is foamed by applying high shear forces. The foaming can be carried out here with the aid of shearing units familiar to the person skilled in the art, such as Dispermats, dissolvers, Hansa mixers or Oakes mixers. The aim in step b) is preferably to obtain foams which are as finely celled and as homogeneous as possible.

It is also preferred if the wet foam produced at the end of process step c) has a viscosity of at least 5, preferably at least 10, more preferably at least 15, even more preferably at least 20 Pa s, but at most 500 Pa s, preferably at most 300 Pas, more preferably not more than 200 Pas, even more preferably not more than 100 Pas. The viscosity of the foam can preferably be determined with the aid of a Brookfield viscometer, model LVTD, equipped with an LV-4 spindle. Corresponding measuring methods for determining the wet foam viscosity are known to the person skilled in the art. As already described above, additional thickeners can optionally be added to the system to adjust the wet foam viscosity. The optional thickeners which can advantageously be used within the scope of the invention are preferably selected from the class of associative thickeners. Associative thickeners are substances which lead to a thickening effect through association on the surfaces of the particles contained in the polymer dispersions or through association to form networks. The term is known to those skilled in the art. Preferred associative thickeners are selected from polyurethane thickeners, hydrophobically modified polyacrylate thickeners, hydrophobically modified polyether thickeners and hydrophobically modified cellulose ethers. Polyurethane thickeners are very particularly preferred. Furthermore, it is preferred within the scope of the present invention if the concentration of the optionally usable thickeners, based on the total composition of the dispersion, is in the range from 0.01-10% by weight, more preferably in the range from 0.05-5% by weight. , very particularly preferably in the range from 0.1 to 3% by weight.

In the context of the present invention, it is also preferred if, in process step d), the foamed polymer dispersion is coated with a layer thickness of 10-10000 μm, preferably 50-5000 μm, more preferably 75-3000 μm, even more preferably 100-2500 μm getting produced. Coatings of the foamed polymer dispersion can be produced by methods familiar to those skilled in the art, such as knife coating. Both direct and indirect coating processes (so-called transfer coating) can be used here.

In addition, it is preferred for the purposes of the present invention if, in process step e), the foamed and coated polymer dispersion is dried at elevated temperatures. Drying temperatures of at least 50° C., preferably 60° C., more preferably at least 70° C., are preferred according to the invention. It is also possible to dry the foamed and coated polymer dispersions in several stages at different temperatures in order to avoid the occurrence of drying defects. Corresponding drying techniques are widespread in the industry and known to the person skilled in the art.

As already described, process steps c)-e) can be carried out with the aid of common methods known to those skilled in the art. An overview of this is given, for example, in "Coated and Laminated Textiles" (Walter Fung, CR-Press, 2002).

In the context of the present invention, particular preference is given to porous polymer coatings containing solids-based foaming aids which have an average cell size of less than 350 μm, preferably less than 200 μm, particularly preferably less than 150 μm, very particularly preferably less than 100 μm. The mean cell size can preferably be determined microscopically, preferably by electron microscopy. For this purpose, a cross section of the porous Polymer coating viewed using a microscope with sufficient magnification and the size of at least 25 cells determined. In order to obtain sufficient statistics from this evaluation method, the magnification of the microscope should preferably be chosen so that at least 10x10 cells are in the observation field. The mean cell size is then obtained as the arithmetic mean of the cells or cell sizes considered. The person skilled in the art is familiar with this cell size determination by means of microscopy.

Another subject of the invention is therefore a porous polymer coating, preferably porous polyurethane coating, obtainable by using preferably hydrophobic or partially hydrophobic, solid-based foaming aids as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, in the production of such polymer coatings, preferably obtainable by a method as previously described.

The porous polymer layers (or polymer coatings) according to the invention containing at least one of the preferably hydrophobic solid-based foaming aids according to the invention and optionally other additives can be used, for example, in the textile industry, e.g. for artificial leather materials, in the construction industry, in the electronics industry, in the sports industry or used in the automotive industry. Thus, articles of daily use, such as shoes, can be produced on the basis of the porous polymer coatings according to the invention.

A further object of the invention are therefore commodities containing a porous polymer coating, as described above, these preferably being shoes, insoles, bags, suitcases, cases, clothing, automobile parts, preferably seat covers, coverings for door parts, dashboard parts, steering wheels and/or or handles and shift bags, furnishings such as writing pads, cushions or seating furniture, gap fillers in electronic devices, padding and damping materials in medical applications and/or adhesive tapes.

Examples:

Substances:

IMPRANIL® DLU: aqueous aliphatic polycarbonate ester polyether polyurethane dispersion from Covestro,

REGEL® WX 151: aqueous polyurethane dispersion from Cromogenia,

CROMELASTIC® PC 287 PRG: aqueous polyurethane dispersion from Cromogenia, CROMELASTIC® PS 075: aqueous aliphatic polyester-polyol polyurethane dispersion from Cromogenia,

KT 736: aqueous aliphatic polyurethane dispersion from Scisky,

KT 650: aqueous aliphatic polyurethane dispersion from Scisky,

Kaolin: Powdered kaolin with a particle size in the range of 1-20 pm (measured with a Mastersizer 3000 from Malvern), purchased from Sigma Aldrich,

VARIFSOFT® PATC: palmitamidopropyltrimonium chloride from Evonik Industries AG, STOKAL® STA: ammonium stearate (approx. 30% in H2O) from Bozetto,

STOKAL® SR: Talc fat-based sodium sulfosuccinamate (approx. 35% in H2O) from Bozetto,

ECO Pigment Black: Aqueous pigment dispersion (black) from Cromogenia, TEGOWET® 250: Polyether-siloxane-based leveling additive from Evonik Industries AG, ORTEGOL® PV 301: Polyurethane-based associative thickener from Evonik Industries AG, REGEL® TH 27: Isocyanate-based crosslinking additive from Cromogenia.

LUDOX® HS 40: Colloidal dispersion of unmodified silica particles (mean particle size=12 nm; solids content=40% by weight) from Grace.

AEROSIL® R 812 S: Pyrogenic silica, surface-modified with hexamethyldisilazane (CAS: 68909-20-6) from Evonik.

Viscosity measurements: All viscosity measurements were carried out using a Brookfield LVTD viscometer equipped with an LV-4 spindle at a constant rotational speed of 12 rpm. For the viscosity measurements, the samples were filled into a 100 ml glass, into which the measuring spindle was immersed. We always waited until the viscometer showed a constant reading.

Example 1: Foaming tests with hydrophobic kaolin:

In this series of tests, kaolin hydrophobicized with palmitamidopropyltrimonium chloride was used as the solid-based foaming aid. The hydrophobing took place in situ, i.e. kaolin and palmitamidopropyltrimonium chloride (VARISOFT® PATC) were added as separate components to the aqueous polyurethane dispersion.

A series of foaming experiments were carried out to test the effectiveness of this solid-based foaming aid. For this purpose, the polyurethane dispersion IMPRANIL® DLU from Covestro was used in a first step. This was foamed using kaolin hydrophobicized with palmitamidopropyltrimonium chloride (run #3). In addition, two comparative tests were carried out, in each of which only one of the two individual components was used, i.e. only palmitamidopropyltrimonium chloride (test #1) or kaolin (test #2). In addition, two comparative tests were carried out using ammonium stearate-based foaming aids, once in a kaolin-free (test #4) and in a kaolin-containing polyurethane dispersion. These tests demonstrate the improved effectiveness of the solids-based foaming aids according to the invention compared to the prior art. Table 1 gives an overview of the compositions of the respective experiments.

All foaming experiments were carried out in manual tests. For this purpose, all components, with the exception of the rheology additive ORTEGOL® PV 301, were initially placed in a 500 ml plastic beaker and homogenized for 3 minutes at 1000 rpm using a dissolver equipped with a dispersing disc (diameter = 6 cm). To foam the mixtures, the stirring speed was then increased to 2000 rpm, care being taken to ensure that the dispersing disk was always immersed in the dispersion to such an extent that a proper vortex formed. At this rate the mixtures were foamed to a volume of ca. 425 ml. Then the ORTEGOL® PV 301 was added to the mixture with a syringe and it was stirred for a further 15 minutes at 1000 rpm. In this step, the dispersing disk was immersed deep enough into the mixture that no further air was introduced into the system, but the entire volume was still in motion.

Table 1 :

Overview foam formulations:

When the mixtures were foamed, it was noticeable that the polyurethane dispersion, which contained only kaolin (experiment #1), could hardly be foamed. The target volume of 425 ml was not reached. Although the dispersion containing only palmitamidopropyltrimonium chloride (experiment #2) foamed well, a coarse, irregular and low-viscosity foam was obtained at the end of the foaming process. In the case of the polyurethane dispersion which contained the kaolin according to the invention hydrophobicized with palmitamidopropyltrimonium chloride (test #3), a very fine and homogeneous foam with high viscosity was obtained at the end of the foaming process. Compared to the two foams that contained ammonium stearate as a foaming aid (trials #4 and #5), this foam was significantly finer and more homogeneous.

All foams were then applied to a siliconized polyester film using a film applicator (type AB3220 from TQC) equipped with a doctor blade (squeegee thickness = 800 μm) and the coating was applied for 5 minutes at 60° C. and for a further 5 minutes at 120° C dried.

In the case of the system containing only kaolin (run #1), a compact coating containing only a few large air pockets was obtained after drying. As a result, the coating conveyed a very rigid, not very flexible haptic impression. After coating and drying, the system containing only palmitamidopropyltrimonium chloride (experiment #2) produced a coarse-celled, inhomogeneous foam, which also exhibited significant drying cracks. The haptic impression of this sample was inferior. In contrast, in Experiment #3 according to the invention, an optically homogeneous, fine-celled foam coating was obtained which was free of defects. The coating had an extremely velvety, supple feel on. Compared to the two comparison samples #4 and #5, which contained ammonium stearate as the foaming aid, the coating #3 according to the invention had a more homogeneous appearance, and its haptic impression was also better. In electron microscopic investigations, when all samples were compared, it was also found that sample #3 according to the invention had the finest pore structure.

These tests thus impressively demonstrate the excellent effect of hydrophobic particles as solid-based foaming aids in aqueous polyurethane dispersions. In the case of the hydrophobic particles (test #3), a significantly better result was achieved than was possible with the two individual components (pure kaolin, pure hydrophobing agent). In addition, an improved effect compared to the prior art could be demonstrated.

Example 2: Migration attempts:

To evaluate the surface migration of the solid-based foaming aid, leatherette materials were prepared according to the following procedure. First, a topcoat was applied to a siliconized polyester film (layer thickness 100 μm). This was then dried at 100° C. for 3 minutes. A foam layer was then coated onto the dried topcoat layer (layer thickness 800 μm) and dried at 60° C. for 5 minutes and at 120° C. for 5 minutes. In a final step, an aqueous adhesive layer (layer thickness 100 μm) was applied to the dried foam layer and then a textile backing was laminated to the adhesive layer, which was still wet. The finished laminate was dried again at 120° C. for 5 minutes and then detached from the polyester film.

All coating and drying processes were carried out using a Labcoater LTE-S from Mathis AG. The topcoat and adhesive layer were formulated according to the compositions listed in Table 2, and the foam formulations #3, #4 and #5 listed in Table 1 were used as the foam layer, which were foamed by the method described in Example 2.

To evaluate the surface migration, the artificial leather samples were placed in hot water at 100 °C for 30 minutes after their production and then dried overnight at room temperature. After this treatment, the comparison sample made from the surfactants Stokal STA / SR (foam formulation #4 and #5, Table 1) had clearly visible white spots on the surface of the imitation leather, while these surface discolorations were found in the samples made with the solid-based foam aid according to the invention (Formulation #3, Table 1) were not observed. Table 2:

Top coat and adhesive formulation for the manufacture of artificial leather materials: Example 3 Foaming tests with hydrophobic pyrogenic silica particles

In another series of tests, AEROSIL® R 812 S (hydrophobic pyrogenic silica particles) was used as a solid-based foaming agent in various PUD systems. Table 3 provides an overview of the foam formulations used for this: Table 3:

Foam formulations containing AEROSIL® R 812 S as a solid-based foaming aid

These formulations were foamed to a volume of approx 800 μm) equipped with a film-drawing device (type AB3220 from TQC) onto a siliconized polyester film and the coating dried for 5 minutes at 60° C. and for a further 5 minutes at 120° C. In all of these tests, it was observed that the use of Aerosil® R 812 enabled rapid and efficient foaming of the formulations. After foaming, uniform, stable foams were obtained in all cases, which could then be dried to form a defect-free coating. These tests thus also demonstrate the good effect of hydrophobized particles as a foam stabilizer in aqueous polyurethane dispersions.

Example 4 Foaming tests with hydrophobic colloidal silica particles

In this series of tests, colloidal silica particles hydrophobicized with palmitamidopropyltrimonium chloride were used as the solid-based foaming aid. The hydrophobing took place in situ, i.e. silica particles and palmitamidopropyltrimonium chloride (VARISOFT® PATC) were added as separate components to the aqueous polyurethane dispersion. The silica dispersion LUDOX® HS 40 was used as the silica particle.

Table 4:

These formulations were foamed to a volume of about 300 ml using the method described in Example 1 and then applied to a siliconized polyester film using a film applicator (type AB3220 from TQC) equipped with a doctor blade (squeegee thickness=800 μm) and the coating dried for 5 minutes at 60 °C and for a further 5 minutes at 120 °C. It was also observed in these tests that efficient foaming of the PU dispersions was possible through the use of hydrophobic silica particles. In this test series, too, uniform, stable foams were obtained in this way, which could then be dried to form a defect-free coating. These results thus underscore the advantages of the present invention.

Claims

Patent Claims:

1 . Use of solid-based foaming aids as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, for producing porous polymer coatings, preferably for producing porous polyurethane coatings.

2. Use according to claim 1, characterized in that the solids-based foaming aids consist of particles which are insoluble in the aqueous polymer dispersion, preferably the aqueous polyurethane dispersion, organic and/or inorganic particles being preferred, and preferred organic particles being selected from cellulose, cellulose derivatives, cellulose, lignin, polysaccharides, wood fibers, wood flour, ground plastics, textile fibers and/or synthetic polymer particles, such as latex or polyurethane particles, and where preferred inorganic particles are selected from the group of (mixed) oxides/hydroxides , such as silicon oxide, aluminum oxide, zirconium oxide, silicon aluminum oxide, silicic acid, aluminum/magnesium hydroxide or quartz powder, the

The group of carbonates, such as calcium carbonate or chalk, the group of phosphates, the group of sulfates, such as calcium sulfate or barium sulfate, and the group of silicates, such as talc, mica or in particular kaolin, and / or the group of silicone-based Particles, in particular silicone resin or MQ resin-based particles, oxides based on silicon oxide and/or aluminum oxide and/or silicates, in particular kaolin, being very particularly preferred.

3. Use according to at least one of claims 1 and 2, characterized in that the particles used as solid-based foaming aids have an average primary particle size in the range of 0.01-100 μm, preferably in the range of 0.05-50 μm, more preferably in the range of 0.1 - 35 pm, determined via laser diffraction or dynamic light scattering.

4. Use according to at least one of claims 1 to 3, characterized in that the particles used as solid-based foaming aids are hydrophobicized or partially hydrophobicized, this hydrophobicization preferably being effected by adsorption and/or by covalent attachment of suitable hydrophobing agents to the particle surface. 5. The use claimed in at least one of claims 1 to 4, characterized in that hydrophobing agents used to make the particles used as solid-based foaming aids hydrophobic are selected from the group of cationic polymers, the group of amines, preferably the group of alkylamines or their Cations, the group of quaternary ammonium compounds, both organic and silicone-based amine and ammonium compounds being preferred, the group of carboxylates, the

Alkyl sulfates, the alkyl sulfonates, the alkyl phosphates, the alkyl phosphonates, the alkyl and dialkyl sulfosuccinates, the respective corresponding free acids, the group of silicones, the group of silanes, the group of epoxides and/or isocyanates, with the choice of a suitable hydrophobing agent preferably based on the surface properties of the particles to be hydrophobic, wherein particles that have negative (partial) charges on the surface are preferably modified with hydrophobing agents that carry cationic or partially cationic anchor groups, and wherein particles that are positive on the surface Have (partial) charges, are preferably modified with those hydrophobing agents which carry anionic or partially anionic anchor groups, and wherein particles which have reactive OH, NH or NH2 groups on the surface preferably with hydrophobing agents reactive towards these groups, such as preferably These are silanes, silazanes, epoxides, isocyanates, carboxylic acid anhydrides or chlorides and/or alkyl chlorides, silanes and/or silazanes being particularly preferred in this context.

Use according to at least one of Claims 1 to 5, characterized in that the water repellents are present in a concentration of 0.01 - 50% by weight, preferably 0.02 - 25% by weight, preferably in the range of 0.03 - 20% by weight, even more preferably in the range from 0.04-15% by weight, even more preferably in the range from 0.05-10% by weight, based on the total amount of particles and hydrophobing agent.

Use according to at least one of Claims 4 to 6, characterized in that the solids-based foaming aids are made hydrophobic before they are added to the aqueous polymer dispersion and/or that the solids-based foaming aids are made hydrophobic in situ, i.e. only in the aqueous polymer dispersion takes place.

Use according to at least one of claims 1 to 7, characterized in that the aqueous polymer dispersions are selected from the group of aqueous polystyrene dispersions, polybutadiene dispersions, poly(meth)acrylate dispersions, polyvinyl ester dispersions and polyurethane dispersions, mixtures these dispersions or dispersions containing copolymers of the polymers mentioned, in particular polyurethane dispersions, and the solids content of these dispersions is preferably in the range from 20-70% by weight, more preferably in the range from 25-65% by weight, based on the total dispersion.

Use according to at least one of Claims 1 to 8, characterized in that the concentration of the solids-based foaming aids, based on the total weight of the aqueous polymer dispersion, is in the range from 0.1 to 50% by weight, particularly preferably in the range from 0.5 to 40 % by weight, particularly preferably in the range from 1.0-35% by weight.

10. The use as claimed in at least one of claims 1 to 8, characterized in that silicon oxide, aluminum oxide and/or silicates, preferably sheet silicates, in particular kaolin, are used as solid-based foaming aids, and amines or their cations, quaternary ammonium compounds, such as e.g. palmitamidopropyltrimonium chloride, alkyl sulfates or

Silanes used, the hydrophobing of the solid-based foaming aid can be done in advance or in situ.

11. Aqueous polymer dispersion, preferably aqueous polyurethane dispersion, containing solids-based foaming aids, preferably hydrophobicized or partially hydrophobicized solids-based foaming aids, the preferred hydrophobing of the solids-based foaming aids before they are added to the aqueous polymer dispersion and / or in situ, i.e. only in the aqueous polymer dispersion can take place in particular as described in claims 1 to 10, the solids content of these dispersions preferably being in the range of 20-70% by weight, more preferably in the range of 25-65% by weight, based based on the entire dispersion, and wherein the concentration of the solids-based foaming aids, based on the total weight of the aqueous polymer dispersion, is preferably in the range from 0.1-50% by weight, particularly preferably in the range from 0.5-40% by weight, particularly preferably in the range from 1.0 to 35% by weight.

12. A method for producing a porous polymer coating, preferably a porous polyurethane coating, using preferably hydrophobic or partially hydrophobic solid-based foaming aids as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, preferably as described in claims 1 to 10, comprising the steps a) providing a mixture containing at least one aqueous polymer dispersion, at least one solids-based foaming aid according to the invention, preferably hydrophobicized or partially hydrophobicized, and optionally further additives, b) foaming the mixture to form a foam, c) optionally adding at least one thickener for adjustment the viscosity of the wet foam, d) applying a coating of the foamed polymer dispersion, preferably polyurethane dispersion, to a suitable carrier, e) drying the coating.

13. The method according to claim 12, characterized in that the solids-based foaming aid used in step a) is made hydrophobic or partially hydrophobic, it being possible for the solids-based foaming aid to be made hydrophobic beforehand or in situ in the aqueous polymer dispersion.

14. Porous polymer coating, preferably porous polyurethane coating, obtainable through the use of preferably hydrophobic or partially hydrophobic solid-based foaming aids as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, in the production of such polymer coatings, preferably obtainable by a method according to claim 12 or 13.

15. commodities containing a porous polymer coating according to claim 14, which are preferably shoes, insoles, bags, suitcases, cases, clothing, automobile parts, preferably seat covers, coverings of door parts, dashboard parts, steering wheels and / or handles and shift bags, furnishings, how

writing pads, cushions or seating furniture, gap fillers in electronic devices, cushioning and damping materials in medical applications and/or adhesive tapes.