Use of surfactant formulations comprising long-chain alcohols in aqueous polyurethane dispersions

Abstract

The present invention discloses the use of surfactant formulations comprising long-chain alcohols as additives in aqueous polymer dispersions for the preparation of porous polymer coatings, preferably for the preparation of porous polyurethane coatings.

Description

[0001] The invention belongs to the field of plastic coatings and imitation leathers.

[0002] The present invention more particularly relates to the use of surfactant formulations comprising long chain alcohols as additives for preparing porous polymer coatings, preferably porous polyurethane coatings.

[0003] Plastic-coated textiles, such as artificial leather, usually consist of a textile carrier to which is laminated a porous polymer layer which in turn is coated with a topcoat.

[0004] In this context, the porous polymer layer preferably has pores in the micrometer range and is air-permeable and therefore breathable, i.e. permeable to water vapor, but waterproof. The porous polymer layer generally comprises porous polyurethane. For the environmentally friendly production of PU-based artificial leather, a method based on aqueous polyurethane dispersions (called PUDs) has recently been developed. These generally consist of polyurethane microparticles dispersed in water; the solid content is generally in the range of 30-60% by weight. In order to produce the porous polyurethane layer, these PUDs are mechanically foamed, coated on a carrier (the layer thickness is generally between 300-2000 μm), and then dried at elevated temperatures. In this drying step, the water present in the PUD system evaporates, which leads to the formation of a polyurethane particle film. In order to further increase the mechanical strength of the film, hydrophilic (poly)isocyanates can also be added to the PUD system during the production process, which can react with the free OH groups present on the surface of the polyurethane particles during the drying step, thereby leading to additional crosslinking of the polyurethane film.

[0005] The mechanical and tactile properties of the PUD coating prepared in this way depend to a large extent on the pore structure of the porous polyurethane membrane. In addition, the pore structure of the porous polyurethane membrane affects the permeability and air permeability of the material. Particularly good properties can be achieved here using very fine, homogeneously distributed pores. A common method for influencing the pore structure in the above-mentioned production process is to add a foam stabilizer to the PUD system before or during mechanical foaming. The first function of a suitable stabilizer is that a sufficient amount of air can be pumped into the PUD system during the foaming operation. Secondly, the foam stabilizer has a direct impact on the morphology of the bubbles produced. The stability of the bubbles is largely affected by the type of stabilizer. This is especially important during the drying of the foamed PUD coating, because it can prevent drying defects such as pore coarsening or drying cracks in this way.

[0006] In the past, various foam stabilizers have been used in the above-mentioned PUD methods. For example, the documents US 2015 / 0284902A1 or US 2006 0079635 A1 describe the use of foam stabilizers based on ammonium stearate. However, the use of corresponding stabilizers based on ammonium stearate is accompanied by many disadvantages. A significant disadvantage here is that ammonium stearate has a very high migration ability in the finished artificial leather. The effect of this is that the surfactant molecules gather on the surface of the artificial leather over time, causing the leather surface to whiten. In addition, this surfactant migration can lead to an uncomfortable greasy film on the surface of the artificial leather, especially when the corresponding material is in contact with water.

[0007] Another disadvantage of ammonium stearate is that it forms insoluble lime soap when in contact with hard water. In the case of artificial leather produced on the basis of ammonium stearate coming into contact with hard water, white bloom is thus generated at the surface of the artificial leather, which is undesirable especially in the case of dark leathers.

[0008] A further disadvantage of foam stabilizers based on ammonium stearate is that they do allow efficient foaming of aqueous polyurethane dispersions, but generally result in a rather coarse and irregular foam structure. This can have an adverse effect on the optical and tactile properties of the finished artificial leather.

[0009] A further disadvantage of ammonium stearate is that the PUD foams produced generally have insufficient stability, which leads to defects during their processing, in particular when the PUD foams are dried at elevated temperatures. As a result, for example, the corresponding foams must be dried relatively gently and slowly, which in turn leads to longer processing times in the production of artificial leather.

[0010] As an alternative to ammonium stearate-based foam stabilizers, polyol esters and polyol ethers have been considered to be effective foam additives for aqueous polyurethane dispersions in the past. These structures are described in, for example, documents EP 3487945 A1 and WO2019042696A1. Compared with ammonium stearate, the main advantage of polyol esters and polyol ethers is that they only migrate slightly (if at all) in the finished artificial leather, so they do not cause undesirable surface discoloration. In addition, polyol esters and polyol ethers are not sensitive to hard water.

[0011] In addition, another advantage of polyol esters and polyol ethers over foam stabilizers based on ammonium stearate is that they generally lead to a significantly finer and more homogeneous foam structure, which has a favorable effect on the properties of artificial leather materials produced with these substances. Polyol esters and polyol ethers generally also lead to more stable PUD foams, which in turn brings process-related advantages in artificial leather production.

[0012] Despite these advantages, polyol esters and polyol ethers are not completely without disadvantages. One potential disadvantage is that, in some cases, the presence of other cosurfactants present in the PUD system can weaken the foam stabilizing effect of these classes of compounds. However, the use of cosurfactants is not uncommon, especially in the production of aqueous polyurethane dispersions. Cosurfactants are used in this case to improve the dispersion of the polyurethane prepolymer in water and usually remain in the final product. During the mechanical foaming of aqueous polyurethane dispersions containing polyol esters or polyol ethers as foam additives, the corresponding cosurfactants can, in some cases, have an adverse effect on the foaming characteristics of the system. As a result, in some cases, usually only little air, if any, can be driven into the system; the resulting foam structure is relatively coarse and the leather quality is reduced. Cosurfactants also have an adverse effect on the stability of the foam produced, which can lead to foam aging during the processing of the foamed PUD system and thus to faults and defects in the foam coating produced.

[0013] One potential disadvantage is that PUD systems containing polyol esters or polyol ethers as foam additives usually require very high shear energies for effective foaming. This in turn leads to limitations and process-related disadvantages in certain cases. It limits the choice of machines for foam generation in the industry.

[0014] The problem addressed by the present invention is therefore to provide additives for producing foam systems and foam coatings based on PUDs which enable efficient foaming of the PUD systems and do not have the disadvantages detailed in the prior art. It has surprisingly been found that surfactant formulations comprising long-chain alcohols are able to solve the problems described.

[0015] The present invention therefore provides the use of a surfactant formulation comprising a long-chain alcohol as an additive in aqueous polymer dispersions, preferably aqueous polyurethane dispersions, preferably as a foam additive, for producing porous polymer coatings, preferably for producing porous polyurethane coatings.

[0016] The inventive use of surfactant formulations comprising long-chain alcohols surprisingly has multiple advantages here. These advantages are all the more surprising since long-chain alcohols used as the only additive in aqueous polymer dispersions have negligible foam stabilizing properties (if any) and can even have a defoaming effect.

[0017] One advantage is that the surfactant formulations according to the invention comprising long-chain alcohols are particularly effective in foaming aqueous PUD systems. The foams produced in this way are notable for a particularly fine pore structure with a particularly homogeneous pore distribution, which in turn has a very favorable effect on the mechanical and haptic properties of porous polymer coatings produced on the basis of these foams. In addition, the permeability or gas permeability of the coating can be improved in this way.

[0018] A further advantage is that the surfactant formulations of the present invention comprising long-chain alcohols enable efficient foaming of PUD systems even at relatively low shear rates, which results in fewer restrictions and broader processability during artificial leather production.

[0019] A further advantage is that the surfactant formulations according to the invention comprising long-chain alcohols enable the production of particularly stable foams. This firstly has a favourable effect on their processability. Secondly, the advantage of the increased foam stability is that during the drying of the corresponding foam, drying defects such as pore coarsening or drying cracks can be avoided. Furthermore, the improved foam stability enables the foam to dry faster, which offers processing advantages from an environmental point of view, since it saves energy, and from an economic point of view.

[0020] Yet another advantage is that the efficacy of the surfactant formulations of the present invention comprising long-chain alcohols is hardly impaired by the presence of co-surfactants (if any) in the PUD system. Thus, the surfactant formulations according to the present invention, even in the case of PUD systems containing co-surfactants, enable the system to foam efficiently and form fine and homogeneous foams that are extremely stable at the same time.

[0021] Yet another advantage is that the surfactant formulations according to the invention comprising long-chain alcohols have little, if any, migration capability in the finished artificial leather and thus do not cause undesirable surface discoloration or efflorescence. Furthermore, the surfactant formulations according to the invention are little, if any, sensitive to hard water.

[0022] The term "surfactant formulation" throughout the present invention encompasses formulations comprising at least one interface-active foam stabilizer (or interface-active foaming assistant) and at least one long-chain alcohol and optionally further surfactants or interface-active substances (co-surfactants).

[0023] In this context "long-chain" means that the alcohol has at least 12, preferably at least 14, more preferably at least 16 carbon atoms. Preference is given here to branched and straight-chain alcohols. It should be clear that the use of surfactant formulations in the aqueous polymer dispersion according to the invention includes the following options: foam stabilizer, long-chain alcohol and any additional surfactants can be added to the aqueous polymer dispersion in the form of a preformulated 1-component mixture or individual components or in the form of a plurality of formulations containing the respective individual components, which each corresponds to a particularly preferred embodiment of the present invention.

[0024] The term "co-surfactant" throughout the present invention includes further surfactants which may be present in the polymer dispersion together with the surfactant formulations of the invention comprising long-chain alcohols. These include in particular surfactants which are used during the production of the polymer dispersion. For example, polyurethane dispersions are usually produced by synthesizing a PU prepolymer which is dispersed in water in a second step and then reacted with a chain extender. In order to improve the dispersion of the prepolymer in water, co-surfactants can be used here. In the context of the present invention, co-surfactants are preferably anionic co-surfactants.

[0025] The present invention is further described below by way of example, but it is not intended to limit the present invention to these illustrative embodiments. In the case of specifying a range, general formula or compound class below, these are intended to include not only the corresponding range or group of the compounds explicitly mentioned, but also all sub-ranges and sub-groups of the compounds that can be obtained by removing a single value (range) or compound. When a document is cited in the context of this specification, its entire contents, especially the entire contents of the subject matter forming the context of the document, are intended to form a part of the disclosure of the present invention. Unless otherwise stated, percentages are all weight percentages. In the case of parameters determined by measurement given below, unless otherwise stated, the measurement is carried out at a temperature of 25° C. and a pressure of 101 325Pa. In the case of using a chemical (empirical) formula in the present invention, the specified index can be not only an absolute number, but also an average value. For polymeric compounds, the index preferably represents an average value. The structural formula and empirical formula given in the present invention represent all isomers that may be produced by different arrangements of repeating units.

[0026] In the context of the present invention, it is preferred that the long-chain alcohols present in the surfactant formulations according to the invention correspond to the general formula (I)

[0027] R 1 -OH Formula (I)

[0028] Where R 1It is a monovalent aliphatic or aromatic, saturated or unsaturated, linear or branched hydrocarbon group having 12 to 40 carbon atoms, preferably 14 to 30 carbon atoms, and more preferably 16 to 24 carbon atoms.

[0029] It is particularly preferred here that the alcohol present in the surfactant formulations according to the invention is lauryl alcohol (1-dodecanol), myristyl alcohol (1-tetradecanol), cetyl alcohol (1-hexadecanol), margaryl alcohol (1-heptadecanol), stearyl alcohol (1-octadecyl alcohol), arachidyl alcohol (1-eicosanol), behenyl alcohol (1-docosanol), lignocerol (1-tetracosanol), ceryl alcohol (1-hexacosanol), montanyl alcohol (1-octacosanol), myristyl alcohol (1-triacontanol), palmitoleyl alcohol (cis-9-hexadecen-1-ol), oleyl alcohol (cis-9-octadecen-1-ol), anti-oleyl alcohol (trans-9-octadecen-1-ol), and / or the corresponding structural isomers of the same empirical formula, and mixtures of these substances, particularly preferably cetyl alcohol, stearyl alcohol and / or behenyl alcohol and mixtures of these two substances.

[0030] The source of the above long-chain alcohols can be vegetable or animal fats, oils or waxes. For example, it is possible to use: lard, beef tallow, goose fat, duck fat, chicken fat, horse fat, whale oil, fish oil, palm oil, olive oil, avocado oil, seed kernel oil, coconut oil, palm kernel oil, cocoa butter, cottonseed oil, pumpkin seed oil, corn kernel oil, sunflower oil, wheat germ oil, grape seed oil, sesame oil, linseed oil, soybean oil, peanut oil, lupine oil, rapeseed oil, mustard oil, castor oil, jatropha oil, walnut oil, jojoba oil, lecithin (e.g. based on soybean, rapeseed or sunflower), bone oil, neatsfoot oil, borage oil, lanolin, emu oil, deer fat, woodchuck oil, mink oil, safflower oil, hemp oil, pumpkin oil, evening primrose oil, tall oil, as well as carnauba wax, beeswax, candelilla wax, cocoa bean wax, sugar cane wax, retamo wax, palm wax, raffia wax, esparto wax wax), alfalfa wax, bamboo wax, hemp wax, douglas fir wax, cork wax, sisal wax, flax wax, cotton wax, dammar wax, tea wax, coffee wax, rice wax, oleander wax or wool wax.

[0031] It is further preferred that the alcohol present in the surfactant formulation according to the invention is a long-chain branched primary or secondary alcohol. Guerbet alcohols, ie branched alcohols formed by Guerbet condensation, and branched secondary alcohols formed by oxidation of paraffin by the Bashkirov process are particularly preferred here.

[0032] In the context of the present invention, it is preferred that the interface-active foam stabilizers (or interface-active foaming aids) used in combination with the long-chain alcohols are selected from amphoteric surfactants or betaines, such as amidopropyl betaine, amphoacetates; anionic surfactants, such as alkyl or alkylarylsulfosuccinates, sulfosuccinamates, sulfates, sulfonates, phosphates and citrates, carboxylates; nonionic surfactants, such as polyol ethers, polyol esters, and mixtures of these substances, particularly preferably polyol ethers, polyol esters, alkyl phosphates and alkyl citrates, and mixtures of these substances.

[0033] If the foam stabilizer used in combination with a long-chain alcohol is a polyol ether, polyglycerol ethers, sorbitan ethers and mixtures of these substances are particularly preferred here, and polyglycerol ethers are particularly preferred. In this regard, polyglycerol ethers having an average of at least 2, preferably at least 3 polyglycerol units are particularly preferred. Even more preferred at this point are polyglycerol hexadecyl ethers, polyglycerol stearyl ethers, polyglycerol hydroxyhexadecyl ethers, especially polyglycerol 1-hydroxyhexadecyl ethers, polyglycerol 2-hydroxyhexadecyl ethers and / or polyglycerol hydroxyhexadecyl ethers, especially polyglycerol 1-hydroxyhexadecyl ethers and / or polyglycerol 2-hydroxyhexadecyl ethers, and mixtures of these substances. In the case of preferred polyol ethers in the context of the present invention, reference is also made in full to document WO2019042696A1.

[0034] If the foam stabilizer used in combination with the long-chain alcohol is a polyol ester, particular preference is given here to polyglycerol esters, sorbitan esters and mixtures of these substances, particularly preferably polyglycerol esters. In this regard, particular preference is given to polyglycerol esters having an average of at least 2, preferably at least 3, polyglycerol units. Even more preferred in this regard are polyglycerol palmitate and polyglycerol stearate, and mixtures of these substances. In the case of the polyol ether esters preferred in the context of the present invention, reference is also made in its entirety to document EP 3487945 A1.

[0035] If the foam stabilizer used in combination with the long-chain alcohol is an alkyl sulfosuccinamate, particular preference is given here to hexadecyl sulfosuccinamate, dihexadecyl sulfosuccinamate, octadecyl sulfosuccinamate, dioctadecyl sulfosuccinamate and mixtures of these substances.

[0036] If the foam stabilizer used in combination with the long-chain alcohol is an alkyl phosphate, particular preference is given here to phosphates with long-chain alcohols having at least 12, preferably at least 14, even more preferably 16 carbon atoms. The degree of esterification of these phosphates is preferably in the range from 1 to 2.5, preferably from 1.3 to 2.4, more preferably from 1.4 to 2.3, even more preferably from 1.5 to 2, wherein the degree of esterification is defined as the molar ratio of alcohol to phosphorus atoms. In this context, very particular preference is given to hexadecyl phosphate, octadecyl phosphate and mixtures of these substances.

[0037] If the foam stabilizer used in combination with the long-chain alcohol is an alkyl citrate, particular preference is given here to citric acid esters with long-chain alcohols having at least 12, preferably at least 14 and even more preferably 16 carbon atoms. The degree of esterification of these citric acid esters is preferably in the range from 1 to 2.6, preferably from 1.3 to 2.4, more preferably from 1.4 to 2.3 and even more preferably from 1.5 to 2.2, wherein the degree of esterification is defined as the molar ratio of alcohol to citric acid units. In this context, very particular preference is given to hexadecyl citrate, octadecyl citrate and mixtures of these substances.

[0038] In the context of the present invention, it is preferred that the concentration of the long-chain alcohol according to the invention in the surfactant formulation according to the invention is in the range from 0.1% to 60% by weight, preferably between 0.5% and 50% by weight, more preferably between 1% and 40% by weight, even more preferably between 2% and 30% by weight, based on the total mixture of foam stabilizer and long-chain alcohol.

[0039] As already discussed, the present invention contemplates the use of surfactant formulations containing long-chain alcohols as described above as additives in aqueous polymer dispersions, preferably aqueous polyurethane dispersions. The polymer dispersions here are preferably selected from aqueous polystyrene dispersions, polybutadiene dispersions, poly(meth)acrylate dispersions, polyvinyl ester dispersions and polyurethane dispersions. The solids content of these dispersions is preferably in the range of 20-70% by weight, more preferably in the range of 25-65% by weight. According to the present invention, it is particularly preferred to use surfactant formulations containing long-chain alcohols as additives in aqueous polyurethane dispersions. Particularly preferred here are polyurethane dispersions based on polyester polyols, polyesteramide polyols, polycarbonate polyols, polyacetal polyols and polyether polyols.

[0040] When a surfactant formulation comprising a long-chain alcohol is used in an aqueous polymer dispersion, it is preferred that the final concentration of the foam stabilizer comprising a long-chain alcohol in the aqueous polymer dispersion is in the range of 0.2-20 wt. %, more preferably in the range of 0.4-15 wt. %, particularly preferably in the range of 0.5-10 wt. %.

[0041] The surfactant formulations according to the invention which contain long-chain alcohols in aqueous polymer dispersions are preferably used as foaming aids or foam stabilizers for foaming the dispersions. In addition, they can also be used as drying aids, leveling additives, wetting agents and rheology additives.

[0042] Besides the surfactant formulations according to the invention comprising long-chain alcohols, the aqueous polymer dispersions may also comprise further additives / formulation components, for example colour pigments, fillers, matting agents, stabilizers such as hydrolysis or UV stabilizers, antioxidants, bactericides, absorbers, crosslinkers, levelling additives, thickeners and further co-surfactants.

[0043] It is clear that the use of surfactant formulations containing long-chain alcohols as additives in aqueous polymer dispersions includes the possibility of adding foam stabilizers, long-chain alcohols and optionally other surfactants (co-surfactants) to aqueous polymer dispersions in the form of a pre-formulated mixture or in the form of individual components or in the form of a plurality of formulations containing the respective individual components. In addition, all components or individual components can also be blended in a solvent in advance. In this regard, preferred 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, very particularly preferably aqueous diluents or blends. In this regard, it is very particularly preferred that foam stabilizers, long-chain alcohols and optionally other surfactants are blended to form an aqueous 1-component formulation. It is particularly preferred if these formulations contain a total of 10 to 80% by weight, more preferably 15 to 70% by weight, even more preferably 20 to 60% by weight, of foam stabilizer and long-chain alcohol.

[0044] In addition, in the case of aqueous 1-component formulations consisting of foam stabilizers, long-chain alcohols and optionally other surfactants, it may be advantageous when the formulation properties (viscosity, homogeneity, etc.) of the formulation are improved by adding hydrotropic compounds. Hydrophilic compounds here are water-soluble organic compounds consisting of a hydrophilic part and a hydrophobic part, but the molecular weight is too low to have surfactant properties. They lead to an improvement in the solubility or solubility properties of organic substances, especially hydrophobic organic substances, in aqueous formulations. The term "hydrotropic compound" is known to those skilled in the art. Preferred "hydrotropic compounds" in the context of the present invention are alkali metal and ammonium toluenesulfonates, alkali metal and ammonium xylenesulfonates, alkali metal and ammonium naphthalenesulfonates, alkali metal and ammonium isopropylbenzenesulfonates, and phenol alkoxylates, especially phenol ethoxylates, which have up to 6 alkoxylate units.

[0045] As already described, the surfactant formulations comprising long-chain alcohols of the present invention may optionally include other surfactants (i.e. co-surfactants). For example, these can be used to improve system compatibility, or in the case of a pre-formulated 1-component formulation, to improve formulation properties. In this context, preferred co-surfactants according to the present invention are fatty acid amides, ethylene oxide-propylene oxide block copolymers, amine oxides, quaternary ammonium surfactants, amphoteric acetates, ammonium salts and / or alkali metal salts of fatty acids, and mixtures of these materials. In addition, other surfactants may include silicone-based surfactants, such as trisiloxane surfactants or polyether siloxanes. In the case of ammonium salts and / or alkali metal salts of fatty acids, it is preferred that they contain stearates lower than 25% by weight, particularly without stearates.

[0046] If the surfactant formulation according to the invention comprises further surfactants (co-surfactants) as described above in addition to foam stabilizers and long-chain alcohols, it is particularly preferred that these combinations comprise between 1% and 50% by weight, preferably between 2% and 50% by weight, more preferably between 3% and 40% by weight, even more preferably between 5% and 30% by weight, based on the total composition consisting of foam stabilizer, long-chain alcohol and further surfactants, of additional surfactants.

[0047] Since, as described above, the use of surfactant formulations comprising long-chain alcohols according to the invention leads to a significant improvement in porous polymer coatings produced from aqueous polymer dispersions, the present invention likewise provides aqueous polymer dispersions comprising the surfactant formulations according to the invention, as described in detail above.

[0048] The present invention still further provides a porous polymer layer prepared from an aqueous polymer dispersion, which is obtained by the inventive use of a surfactant formulation comprising a long-chain alcohol as described in detail above.

[0049] Preferably, the porous polymer coating according to the present invention can be prepared by a method comprising the following steps:

[0050] a) providing a mixture comprising at least one aqueous polymer dispersion, at least one surfactant formulation according to the invention and optionally further formulation components,

[0051] b) frothing the mixture to obtain a foam,

[0052] c) optionally adding at least one thickener to adjust the viscosity of the wet foam,

[0053] d) applying a coating of the foamed polymer dispersion to a suitable support,

[0054] e) Drying / curing the coating.

[0055] The porous polymer coating has pores preferably in the micrometer range, preferably with an average pore size of less than 350 μm, more preferably less than 200 μm, particularly preferably less than 150 μm, very particularly preferably less than 100 μm. The average pore size can preferably be determined by microscopy, preferably by electron microscopy. For this purpose, a cross section of the porous polymer coating is observed by means of a microscope with sufficient magnification and the size of at least 25 pores is determined. The average pore size is then determined as the arithmetic mean of the observed pores or pore sizes.

[0056] With regard to preferred configurations, in particular with regard to surfactant formulations and polymer dispersions which can preferably be used in the process, reference is made to the preceding description as well as to the preceding preferred embodiments, especially as detailed in the claims.

[0057] It is clear that the method steps of the above method according to the present invention are not limited to any fixed order in time. For example, method step c) can be performed simultaneously with method step a) at an early stage.

[0058] A preferred embodiment of the present invention is that in process step b), the aqueous polymer dispersion is foamed by applying high shear forces. The foaming can be carried out with the aid of shear units familiar to the person skilled in the art, such as a Dispermat, a dissolver, a Hansa mixer or an Oakes mixer.

[0059] Furthermore, it is preferred that the wet foam produced at the end of process step c) has a viscosity of at least 5 Pa·s, preferably at least 10 Pa·s, more preferably at least 15 Pa·s and even more preferably at least 20 Pa·s, but not more than 500 Pa·s, preferably not more than 300 Pa·s, more preferably not more than 200 Pa·s and even more preferably not more than 100 Pa·s. The viscosity of the foam can be determined here, for example, with the aid of a Brookfield viscometer (LVTD type) equipped with a LV-4 spindle. Corresponding test methods for determining the viscosity of wet foams are known to the person skilled in the art.

[0060] In a preferred embodiment of the invention, in process step b), the foam has maximum homogeneity and pore fineness. If necessary, the person skilled in the art can verify this in a customary manner based on their typical experience by simple direct visual inspection with the naked eye or using optical aids such as a magnifying glass or a microscope. "Pore fineness" relates to the pore size. The smaller the average pore size, the finer the foam. If necessary, the pore content can be determined using, for example, an optical microscope or a scanning electron microscope. "Homogeneous" refers to the pore size distribution. A homogeneous foam has a very narrow pore size distribution, so that all pores have approximately the same size. This can in turn be quantified using an optical microscope or a scanning electron microscope.

[0061] As mentioned above, additional thickeners can be added to the system to adjust the wet foam viscosity. Thickeners that can be advantageously used in the context of the present invention are selected from the category of associative thickeners. Associative thickeners here are substances that produce a thickening effect by associating at the surface of the particles present in the polymer dispersion. This 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. In addition, it is preferred in the context of the present invention that the concentration of the thickener is in the range of 0.01-10% by weight, more preferably in the range of 0.05-5% by weight, and most preferably in the range of 0.1-3% by weight, based on the total composition of the dispersion.

[0062] In the context of the present invention, it is further preferred that in process step d), a coating of the foamed polymer dispersion is produced with a layer thickness of 10 to 10 000 μm, preferably 50 to 5000 μm, more preferably 75 to 3000 μm, even more preferably 100 to 2500 μm. The coating of the foamed polymer dispersion can be produced by methods familiar to the person skilled in the art, for example knife coating. Direct or indirect coating methods (known as transfer coating) can be used here.

[0063] In the context of the present invention, it is also preferred that in process step e) the drying of the foamed and coated polymer dispersion is carried out at elevated temperature. According to the invention, it is preferred here that the drying temperature is at least 50° C., preferably 60° C., more preferably at least 70° C. In addition, the foamed and coated polymer dispersion can be dried in a plurality of stages at different temperatures in order to avoid the occurrence of drying defects. Corresponding drying techniques which take into account the temperature, ventilation and relative humidity of the atmosphere are widely used in industry and are known to the person skilled in the art.

[0064] As already described, process steps c) to e) can be carried out with the aid of widely practiced methods known to the person skilled in the art. An overview of these is given, for example, in "Coated and laminated Textiles" (Walter Fung, CR-Press, 2002).

[0065] In the context of the present invention, particularly preferred are those porous polymer coatings that contain surfactant formulations according to the present invention and have an average pore size of less than 350 μm, preferably less than 200 μm, particularly preferably less than 150 μm, most preferably less than 100 μm. The average pore size can preferably be determined by microscopy, preferably by electron microscopy. For this purpose, the cross section of the porous polymer coating is observed through a microscope with sufficient magnification and the size of at least 25 holes is determined. In order to obtain sufficient statistical data for the evaluation method, the magnification of the selected microscope should preferably be such that at least 10×10 holes are present in the observation field. The average pore size is then calculated in the form of the arithmetic mean of the observed pores or pore sizes. This determination of pore size by microscopy is familiar to those skilled in the art.

[0066] The porous polymer layer (or polymer coating) according to the invention comprising at least one surfactant formulation according to the invention and optionally further additives can be used, for example, in the textile industry (for example for artificial leather materials), in the construction industry, the electronics industry, the sports industry or the automotive industry. For example, based on the porous polymer coating according to the invention, everyday items such as shoes, insoles, bags, suitcases, small boxes, clothes, automotive parts, preferably seat covers, door parts, dashboard parts, steering wheels and / or handle covers, and gearshift gaiters, fitout articles such as table mats, cushions or seats, gap fillers in electronic devices, cushioning and damping materials in medical applications, or adhesive tapes can be produced. Example

[0067] substance:

[0068] YS:3000: Polyurethane dispersion based on MDI (methyl diphenyl diisocyanate) from DOW. As a result of its preparation process, this product contains 1-3% by weight of the anionic co-surfactant sodium dodecylbenzenesulfonate (CAS: 25155-30-0).

[0069] DLU: Aliphatic polycarbonate ester-polyether-polyurethane dispersion from Covestro.

[0070] WX 151: Aqueous polyurethane dispersion from Cromogenia.

[0071] PC 287 PRG: Aqueous polyurethane dispersion from Cromogenia

[0072] STA: ammonium stearate from Bozetto (about 30% in H2O).

[0073] SR: sodium sulfosuccinamate based on beef tallow from Bozetto (about 35% in H2O).

[0074] Sodium dodecylbenzene sulfonate (LAS; CAS: 25155-30-0) was from Sigma Aldrich. This is a standard co-surfactant used in the production of waterborne polyurethane dispersions.

[0075] ECO Pigment Black: Aqueous pigment dispersion (black) from Cromogenia.

[0076] 250: Leveling additive based on polyether siloxane from Evonik Industries AG.

[0077] PV 301: Polyurethane-based associative thickener from Evonik Industries AG.

[0078] TH 27: Isocyanate-based leveling additive from Cromogenia.

[0079] Polyglycerol-3 stearate: prepared by reacting 103.3 g of polyglycerol (OHN=1124 mg KOH / g, Mw=240 g / mol) with 155.0 g of technical grade stearic acid.

[0080] Stearyl citrate: a foaming aid prepared by reacting stearyl alcohol (≥95%, 275.2 g, 1.02 mol, 2.1 eq.) with citric acid (anhydrous, 93.10 g, 0.485 mol, 1.0 eq.).

[0081] Stearyl phosphate: foaming aid, made of stearyl alcohol (≥95%, 178.7g, 0,661mol) and P4O 10 (21.31 g, 0.0751 mol) was prepared by reaction.

[0082] Viscosity measurement:

[0083] All viscosity measurements were performed using a Brookfield Viscometer LVTD equipped with a LV-4 spindle at a constant rotation speed of 12 rpm. For the viscosity measurement, the sample was transferred to a 100 ml wide-mouth bottle and the measuring spindle was immersed in it to a defined depth. A constant viscometer measurement value was always displayed.

[0084] Example 1: Blending of surfactant formulations according to the present invention:

[0085] For the foaming experiments, the surfactant formulations described in Table 1 were used. All surfactant formulations were homogenized at 80°C. Surfactant formulations (1, 2, 4 and 5) containing stearyl phosphate and stearyl citrate were neutralized to pH = 7 with KOH after blending. Surfactant formulations 1-3 are formulations of the present invention containing long chain alcohols, while surfactant formulations 4-6 are used for comparative purposes.

[0086] Table 1: Composition of the surfactant blend used below:

[0087]

[0088] Example 2: Foaming test:

[0089] In order to test the efficacy of the additive combination according to the invention, a series of foaming experiments were carried out. For this purpose, in a first step, a foaming agent from Covestro was used. DLU polyurethane dispersion. The foam stabilizers used were the surfactant formulations 1-3 according to the invention (see Table 1) and a combination of two surfactants Stokal STA (ammonium stearate) and Stokal SR (sodium sulfosuccinamate) as comparison. Table 2 gives an overview of the compositions of the individual experiments.

[0090] All foaming experiments were performed manually. For this reason, the polyurethane dispersion and surfactant were first placed in a 500 ml plastic cup and homogenized at 1000 rpm for 3 minutes using a dissolver equipped with a dispersing disc (diameter = 6 cm). In order to foam the mixture, the shear rate was then increased to 2000 rpm, ensuring that the dissolving disc was always immersed in the dispersion to a degree sufficient to form a suitable vortex. At this speed, the mixture was foamed to a volume of about 425 ml. The mixture was then sheared at 1000 rpm for another 15 minutes. In this step, the dissolving disc was fully immersed in the mixture so that no air entered the system, but the entire volume was still in motion.

[0091] Table 2: Overview of foam formulations:

[0092]

[0093] In all cases, a fine, homogeneous foam is obtained at the end of this foaming operation. It is noteworthy that the foams prepared with the surfactants 1 and 2 according to the invention have a higher viscosity (see Table 2). The foams are applied to siliconized polyester films (coating thickness = 800 μm) with the aid of a film applicator (AB3220 from TQC) equipped with an applicator frame and then dried at 60° C. for 5 minutes and at 120° C. for a further 5 minutes.

[0094] The dried inventive samples #1-#3 had a more homogeneous macroscopic appearance and a softer feel than sample #4. In addition, in electron microscopy studies, a finer pore structure could be determined.

[0095] Example 3: Improved co-surfactant compatibility:

[0096] In order to test the co-surfactant compatibility of the surfactant formulations according to the invention, a series of foaming experiments were additionally performed. For this purpose, in a first step, YS:3000 polyurethane dispersion. This contained 1-3 wt% of the anionic co-surfactant sodium dodecylbenzene sulfonate (CAS: 25155-30-0). The surfactants used in these experiments were surfactant formulations 1 and 2, and 4 and 5 listed in Table 1. Table 3 gives an overview of the composition of the foam formulations.

[0097] Table 3: Summary of foam formulations:

[0098]

[0099] On the basis of these formulations, foam coatings were prepared by the method described in Example 2. It is noteworthy here that samples #7 and #8 prepared using comparative surfactants 4 and 5 have a rougher and more inhomogeneous foam structure. After the foam coatings have dried, clear cracks in the foam structure can also be observed, which is an indication of insufficient foam stability. In contrast, samples #5 and #6 prepared with the surfactant formulations of the present invention again show very fine pores and a homogeneous foam structure. They also have no drying cracks.

[0100] In addition, another series of foaming experiments were performed in which virtually no co-surfactant was present. The DLU system intentionally contains sodium dodecylbenzene sulfonate, a common co-surfactant for PUD stabilization, as described above. Also used in these experiments are surfactant formulations 1 and 2, as well as 4 and 5 listed in Table 1. Table 4 gives an overview of the composition of the foam formulations.

[0101] Table 4: Summary of foam formulations:

[0102]

[0103]

[0104] Here, too, the foam coatings were prepared by the above method. It is noteworthy here again that samples #11 and #12 prepared using comparative surfactants 4 and 5 have drying cracks and a coarser pore structure, while samples #9 and #10 of the present invention again show a fine and homogeneous pore structure and no defects. There is almost no difference observed here with similar samples #1 and #2 without co-surfactants (see Example 2). Therefore, these experiments demonstrate a clear improvement in the co-surfactant compatibility of the surfactant formulations according to the present invention.

[0105] Example 4: Migration test:

[0106] In order to evaluate the surface migration of the surfactant according to the present invention, an artificial leather material is prepared by the following method. First, a topcoat is applied to a siliconized polyester film (layer thickness 100 μm). It is then dried at 100 ℃ for 3 minutes. Subsequently, a foam layer is applied to the dry topcoat layer (layer thickness 800 μm) and dried at 60 ℃ for 5 minutes and at 120 ℃ for 5 minutes. In the last step, an aqueous adhesive layer (layer thickness 100 μm) is applied to the dry foam layer, and then a fabric carrier is laminated to the still wet adhesive layer. The finished laminate is dried at 120 ℃ for 5 minutes again and then separated from the polyester film.

[0107] All coating and drying operations were performed with a Labcoater LTE-S from Mathis AG. The topcoat and adhesive layers were formulated according to the compositions listed in Table 5; the foam layer used was the foam formulation listed in Table 2, which was foamed by the method described in Example 2.

[0108] To evaluate the migration of the surfactant, the prepared artificial leather samples were placed in water at 100° C. for 30 minutes and then dried at room temperature overnight. After this treatment, the comparative sample prepared with Stokal STA / SR surfactant (foam formulation #4, Table 2) had clearly visible white spots on the artificial leather surface, while no such surface discoloration was observed in the case of the samples prepared with the surfactant according to the invention (foam formulations #1, #2 and #3, Table 2).

[0109] Table 5: Topcoat and adhesive formulations for preparing artificial leather materials:

[0110]

[0111] Example 5: Improved Foaming Rate

[0112] A final series of foaming experiments was carried out to evaluate the foaming rate using Impranil DLU (a PU dispersion). For this purpose, two surfactant mixtures 3 and 6 (Table 1) were used. Table 6 gives an overview of the composition of the foam formulations.

[0113] Table 6: Summary of foam formulations:

[0114]

[0115] The foam formulation was foamed by the method described in Example 2, except that the foaming operation was carried out at a reduced speed of 1200 rpm. It was observed that the foam formulation (experiment #13) comprising the surfactant blend 3 of the present invention reached the target volume of 425 ml faster than the comparative sample #14 comprising the surfactant 6 of the present invention. In both cases, fine-cell foam was obtained at the end of the foaming operation. In the last step after the method described in Example 2, these were applied to release paper and dried. In both cases, a homogeneous foam coating with no drying defects after drying can be obtained. Therefore, the reduction in the foaming time achieved by the surfactant blend according to the present invention has no adverse effect on the quality of the resulting foam.

Claims

1. The use of a surfactant formulation comprising at least one interface-active foam stabilizer and at least one long-chain alcohol having at least 12 carbon atoms as an additive in aqueous polymer dispersions for foaming the aqueous polymer dispersions and producing stable foams, The interfacial active foam stabilizer in the surfactant formulation is selected from polyol esters, alkyl phosphates and alkyl citrates, and mixtures of these substances, If the foam stabilizer used in combination with the long-chain alcohol is an alkyl phosphate, a phosphate ester of a long-chain alcohol is used, the degree of esterification of these phosphates is in the range of 1.3-2.5, the degree of esterification being defined as the molar ratio of alcohol to phosphorus atoms, The surfactant formulation contains a total of 15 to 70 wt. % of a foam stabilizer and a long-chain alcohol, The aqueous polymer dispersion is an aqueous polyurethane dispersion.

2. The use according to claim 1, characterized in that The long-chain alcohol meets the general formula (I): 1 -OH formula (I) Where R 1 It is a monovalent aliphatic or aromatic, saturated or unsaturated, straight-chain or branched hydrocarbon group having 12 to 40 carbon atoms.

3. The use according to claim 2, characterized in that: R 1 Having 14 to 30 carbon atoms.

4. The use according to claim 2, characterized in that: R 1 Having 16 to 24 carbon atoms.

5. The use according to any one of claims 1 to 4, characterized in that The long-chain alcohol is lauryl alcohol (1-dodecanol), myristyl alcohol (1-tetradecanol), cetyl alcohol (1-hexadecanol), pearl ester alcohol (1-heptadecanol), stearyl alcohol (1-octadecyl alcohol), arachidyl alcohol (1-eicosyl alcohol), behenyl alcohol (1-docosanol), xylanyl alcohol (1-tetracosyl alcohol), wax alcohol (1-hexacosyl alcohol), montanol (1-octacosyl alcohol), myristyl alcohol (1-triacontanol), palmitoleyl alcohol (cis-9-hexadecene-1-ol), oleyl alcohol (cis-9-octadecene-1-ol) and / or anti-oleyl alcohol (trans-9-octadecene-1-ol), and / or corresponding structural isomers having the same empirical formula, and mixtures of these substances.

6. The use according to claim 5, characterized in that The long-chain alcohol is selected from cetyl alcohol, stearyl alcohol and / or behenyl alcohol and mixtures thereof.

7. The use according to any one of claims 1 to 4, characterized in that The long chain alcohol is a branched primary alcohol or a secondary alcohol.

8. The use according to claim 7, characterized in that The long-chain alcohols mentioned are Guerbet alcohols and branched secondary alcohols formed by oxidation of paraffin waxes by the Bashkirov process.

9. The use according to any one of claims 1 to 4, characterized in that The at least one foam stabilizer and the at least one long-chain alcohol are preformulated and used.

10. The use according to any one of claims 1 to 4, characterized in that The surfactant formulation additionally comprises at least one further surfactant.

11. The use according to claim 10, characterized in that The other surfactant is selected from fatty acid amides, ethylene oxide-propylene oxide block copolymers, amine oxides, quaternary ammonium surfactants, amphoacetates, ammonium and / or alkali metal salts of fatty acids, silicone-based surfactants, and mixtures of these substances.

12. The use according to claim 11, characterized in that The silicone-based surfactant is a trisiloxane surfactant or a polyether siloxane.

13. The use according to any one of claims 1 to 4, characterized in that The solids content of the dispersion is in the range of 20 to 70% by weight, based on the total dispersion.

14. The use according to any one of claims 1 to 4, characterized in that The solids content of the dispersion is in the range of 25-65% by weight, based on the total dispersion.

15. The use according to any one of claims 1 to 4, characterized in that The total concentration of the foam stabilizer and the long-chain alcohol in the aqueous polymer dispersion is 0.2-20% by weight.

16. The use according to claim 15, characterized in that The total concentration of foam stabilizer and long-chain alcohol in the aqueous polymer dispersion is in the range of 0.4-15% by weight.

17. The use according to claim 15, characterized in that The total concentration of foam stabilizer and long-chain alcohol in the aqueous polymer dispersion is in the range of 0.5-10% by weight.

18. An aqueous polymer dispersion comprising at least one interface-active foam stabilizer as defined in any one of claims 1 to 17 and at least one long-chain alcohol, the aqueous polymer dispersion being an aqueous polyurethane dispersion.

19. A method for preparing a porous polymer coating using a surfactant formulation as defined in any one of claims 1 to 17 as an additive in an aqueous polymer dispersion, comprising the steps of: a) providing a mixture comprising at least one aqueous polymer dispersion, at least one interface-active foam stabilizer as defined in any one of claims 1 to 17 and at least one long-chain alcohol, and optionally further formulation components, b) frothing the mixture to obtain 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 to a suitable support, e) drying the coating, The aqueous polymer dispersion is an aqueous polyurethane dispersion.

20. The method of claim 19, wherein the porous polymer coating is a porous polyurethane coating.

21. The method of claim 19, wherein the polymer dispersion in step d) is a polyurethane dispersion.

22. A porous polymer coating obtainable by using at least one interface-active foam stabilizer as defined in any one of claims 1 to 17 and at least one long-chain alcohol as additives in an aqueous polymer dispersion in the preparation of such a polymer coating, wherein the aqueous polymer dispersion is an aqueous polyurethane dispersion.

23. The porous polymer coating of claim 22, wherein the porous polymer coating is a porous polyurethane coating.

24. The porous polymer coating according to claim 22, obtainable by a method according to any one of claims 19 to 21.

25. An everyday item comprising a porous polymer coating according to any one of claims 22 to 24, which is a shoe, an insole, a bag, a suitcase, a small box, clothing, an automobile part, an interior furnishing item, a gap filler in an electronic device, a cushioning and damping material in medical applications, or an adhesive tape.

26. The daily necessities according to claim 25, wherein the automobile component is selected from the group consisting of seat covers, door components, dashboard components, coverings for steering wheels and / or handles, and gear lever covers.

27. The daily necessities according to claim 25, wherein the interior furnishing items are selected from table mats, cushions and seats.

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