Reactive mixture for producing polyurethane layers with a heat-activatable catalyst system

Abstract

The present invention relates to a reactive mixture for producing polyurethane layers, comprising: an isocyanate component composed of at least one polyfunctional isocyanate, a polyfunctional isocyanate oligomer, or an isocyanate prepolymer; a polyol component composed of at least one polyol; and a catalyst system comprising a metal-based catalyst based on a salt or an organometallic compound and a diketone compound having a melting point of ≥15°C. This catalyst system has the unique characteristics of low toxicity and very low reactivity under processing conditions, but can be activated by increasing the temperature, resulting in a polyurethane that is fully reacted in a short period of time. The present invention further relates to a method for producing such polyurethane layers, polyurethane layers produced from these reactive mixtures, and composite structures comprising such polyurethane layers. Furthermore, the present invention relates to the use of the specified catalyst system for the reaction of polyols and polyisocyanates.

Description

Technical Field

[0001] The present invention relates to a reactive mixture for producing polyurethane layers, comprising: an isocyanate component composed of at least one polyfunctional isocyanate, an oligomer of a polyfunctional isocyanate, or an isocyanate prepolymer; a polyol component composed of at least one polyol; and a catalyst system comprising a metal-based catalyst based on a salt or an organometallic compound and a diketone compound having a melting point of ≥15°C. The present invention further relates to a method for producing such polyurethane layers, polyurethane layers produced from these reactive mixtures, and composite structures comprising such polyurethane layers. Furthermore, the present invention relates to the use of a specified catalyst system for the reaction of a polyol and a polyisocyanate. Background Art

[0002] Due to their high durability in artificial leather materials, polyurethane systems are used as cover or substrate materials to produce durable products with a thickness comparable to leather or thicker. While it is possible to coat artificial leather with a thin layer of a polyurethane solvent system or polyurethane dispersion system and select the textile thickness accordingly, this creates an artificial leather with a thickness comparable to leather. However, such structures, due to the typically thin coating, are not very robust in use. For this reason, polyurethane artificial leather is typically produced in such a way that at least one of the textile coatings consists of a relatively thick, low-solvent or solvent-free reactive polyurethane system.

[0003] As an alternative to polyurethane artificial leather, PVC-based artificial leather is also widely used due to its significantly lower price compared to leather and polyurethane artificial leather. However, the problem with these is that PVC requires plasticizers for processing. The use of plasticizers has been a subject of public debate for many years and has been increasingly criticized. As a result, the use of plasticizers has been increasingly restricted in recent years, for example, by the REACH regulation or the GADSL list for automotive manufacturers.

[0004] Another problem with plasticizers is that they are not firmly bound to the PVC matrix. Over time, the plasticizers can migrate out of the polymer matrix, leading to changes in the flexibility characteristics of PVC artificial leather. Furthermore, PVC artificial leather tends to experience undesirable discoloration, accompanied by a deterioration in mechanical stability, particularly when exposed to elevated temperatures for relatively long periods of time, such as when a car is left exposed to the sun for extended periods.

[0005] Therefore, polyurethane is often preferred as a coating system compared to other PVC plastisols, especially since textiles coated with polyurethane also have a feel similar to that produced by touching leather.

[0006] Coatings containing polyurethane can be produced by coagulating the polyurethane from a solution or producing the polyurethane directly on the substrate from isocyanate and polyol precursors. Direct production here offers many advantages over using polyurethane dissolved in a solvent or dispersed in water. For example, it can be difficult to produce defect-free parts or meshes using dissolved or dispersed polyurethane because, from an economic point of view, the solvent or water must be contained and evaporated as quickly as possible during the manufacturing process. Moreover, the evaporation process requires a large amount of energy. When using solvent-based polyurethane systems, solvent residues often remain in the polyurethane and can still be detected in the finished product and / or can adversely affect the odor of the finished product.

[0007] By contrast to the direct production of polyurethanes, in which the processor can tailor properties through appropriate selection of polyisocyanates or polyisocyanate prepolymers and polyols, dissolved or dispersed polyurethanes are typically only commercially available in designated polyurethane systems.

[0008] Since solvent-based polyurethane systems can hardly undergo rapid drying without bubbles and defects at thicknesses >100 μm, the use of reactive polyurethane systems offers advantages over dissolved or dispersed polyurethanes, especially for producing polyurethane layers of such thicknesses.

[0009] In the direct production of polyurethane layers, production speed is a key economic factor. This speed is increased by using additional catalysts. The required characteristics are that the reaction at room temperature is suppressed as much as possible to allow thorough mixing of the reactive components and any additional additives, and that the mixture is brought into the desired form before "curing," for example, by spreading the reactive mixture on a backing paper in a continuous process for producing artificial leather. On the other hand, however, the reaction between the isocyanate and the polyol should proceed as quickly as possible at the process temperature.

[0010] To meet these requirements, various solutions have been proposed in the past:

[0011] One established method is to use blocked polyisocyanate prepolymers, for example in a mixture with polyamines, which react to form polyurethane ureas. Blocked polyisocyanates have the advantage that the reactive mixture can be left at room temperature for extended periods, and processing does not require special mixing head systems, which require mixing the reactive components only shortly before processing.

[0012] Examples of blocking agents for reactive isocyanate groups are oximes or caprolactams, which cleave from the blocked polyisocyanate at elevated temperatures, thereby releasing the reactive isocyanate groups. However, in addition to the high temperatures sometimes required to cleave off the blocking agent, a disadvantage is that the cleaved groups are sometimes classified as toxic and – especially in thicker products – remain in the product to a certain extent, where they are visually and functionally problematic due to their odor or their undesirable tendency to migrate to the surface.

[0013] Another disadvantage of such systems is that their availability is predetermined, which means that the desired product properties can only be influenced to a small extent by suitable selection of the raw materials. Finally, commercially available blocked polyisocyanate systems often contain high-boiling solvents (such as methoxypropyl acetate) to reduce viscosity, which remain as residues in the final product and must be removed in an energy-intensive manner.

[0014] Systems have also been proposed in which a reactive polyisocyanate prepolymer is reacted with a dihydrazide that is solid at room temperature, such as adipic acid dihydrazide or sebacic acid dihydrazide. The resulting mixture is relatively unreactive at room temperature, while a rapid reaction is achieved at higher temperatures by melting the dihydrazide. However, this system can also be adjusted by the user only within a narrow range in terms of the choice of raw materials, and if the stoichiometry is not accurately maintained, excess dihydrazide may migrate during subsequent use, leading to visible and functionally troublesome surface deposits.

[0015] EP 1 059 379 B1 has described the polyurethane system with longer pot life at room temperature, and it reacts very fast under elevated temperature.The starting raw materials of the polyurethane system described in EP 1 059 379 B1 and the final characteristics of the product can be selected from a wide range of suitable polyisocyanates and polyols. In EP 1 059 379 B1, the use of metal acetylacetonates is decisive for reactivity, and the metal catalyst employed is chelated by the acetylacetone ligand and thereby spatially shielded. Only under elevated temperature, acetylacetone will crack, and the catalytic metal core will be exposed. However, it has been found that some acetylacetones are left in the finished product as troublesome and poisonous solvents, and nickel acetylacetonate (especially effective as catalyst) is classified as carcinogenic.

[0016] A further disadvantage of this system is that the reaction at room temperature is not suppressed to such an extent that long pot lives (ie processing times) are possible, which means that the mixhead system generally still has to be used for processing.

[0017] EP 1 927 466 B1 describes a similar system in which a metal acetylacetonate, for example a tin-based catalyst, is used in combination with additional acetylacetone in the reaction mixture. This inhibits the reaction at room temperature, and the acetylacetone evaporates only at higher temperatures, thereby increasing the reactivity of the catalyst system. However, the disadvantages of using acetylacetone outlined in EP 1 059 379 B1 and its relatively short pot life also present a problem here.

[0018] WO 2013 / 087682 A1 describes bismuth-containing catalysts for polyurethane systems. In this process, a bismuth salt or complex is reacted with a 1,3-ketoamide in a preceding reaction. The resulting catalyst is oily / liquid but still results in relatively short processing times at room temperature, which translates into short skin formation times.

[0019] Against this background, there is a need for catalyst systems which, on the one hand, are not catalytically active at room temperature or at the "mixing temperature" of the polyurethane-forming mixture, but on the other hand are sufficiently active at process temperatures, in particular at temperatures above 80° C., to form very fully reacted polyurethanes within short reaction times. The present invention addresses this need.

[0020] There is also a need for the formulation of reactive polyurethane systems based on polyisocyanates or polyisocyanate prepolymers and polyols, with which decorative and flexible surfaces can be produced that can be used in all applications where artificial leather or leather is currently used. In such formulations, metal catalysts that are not classified as toxic should be used as much as possible, and the reactivity at room temperature should be suppressed to such an extent that processing does not require complex equipment such as mixing head systems.

[0021] These formulations and their use should allow the production of films having at least one polymer layer, which may also be foamed and which, as the sole film layer or one of a plurality of film layers, is a component of a decorative material such as a film or artificial leather. By allowing the production of layers having a specific thickness, the formulation should allow the production of decorative films that are pleasant to the touch and, due to the thickness of the applied layer, also prevent the textile structure from being noticeable on the surface.

[0022] The present invention addresses this need. Summary of the Invention

[0023] The present invention is based on the surprising discovery that these properties can be imparted by a catalyst system comprising a metal-based catalyst based on a salt or organometallic compound and a diketone compound having a melting point of ≥15° C. Mixtures of these catalyst systems with polyisocyanates and polyols exhibit relatively stable viscosities at room temperature and can be activated by increasing the temperature, with the result that, for example, at 150° C. within 120 seconds, a tacky polyurethane layer is no longer formed.

[0024] Therefore, in a first aspect, the present invention relates to a reactive mixture for producing a polyurethane layer, said mixture comprising

[0025] an isocyanate component consisting of at least one polyfunctional isocyanate, an oligomer of a polyfunctional isocyanate or an isocyanate prepolymer,

[0026] a polyol component consisting of at least one polyol, and

[0027] - a catalyst system comprising a metal-based catalyst based on a salt or an organometallic compound and a diketone compound having a melting point ≥ 15°C.

[0028] A "metal-based catalyst" in the reactive mixture is a substance that, when added to the mixture of polyisocyanate and polyol, is capable of accelerating the reaction to form polyurethane as compared to the reaction in the absence of the catalyst.

[0029] The "catalyst system" is conveniently produced by intimately mixing a metal-based catalyst with a diketone compound, optionally with the addition of a solvent. Instead of a solvent, short-chain esters of mono-, di-, and tricarboxylic acids that are liquid at room temperature and aliphatic monofunctional polyols with a molar mass of less than 1000 g / mol can also be used. The diketone compound is assumed to bind to the metal of the metal-based catalyst, potentially displacing the anion of the salt.

[0030] In the context of this specification, the terms "polyfunctional isocyanate" and "polyisocyanate" are used synonymously.

[0031] A particular advantage of the reactive mixtures described herein compared to the prior art outlined above is that the mixtures have a particularly long processing time (pot life) at room temperature without significantly affecting the activity of the catalyst at elevated processing / process temperatures.

[0032] The diketone compounds preferably used in the reactive mixture are diketone compounds having a melting point of ≥25° C. and more preferably ≥30° C. Particular preference is given to diketone compounds in the form of 1,3-diketone compounds. The carbon atom located between the two CO groups may be substituted or unsubstituted (in which case the carbon atom is present in the form of a CH 2 group). Very particular preference is given to diketone compounds of the structure R 1-CO-CH2-CO-R 2 , where R 1 and R 2 Preferably, it is independently selected from aliphatic and aromatic groups, which may optionally be substituted. In this context, preferred aliphatic groups are alkyl or alkenyl groups, which may be straight-chain, branched or cyclic. Preferred aromatic groups are aryl groups and especially phenyl groups, or heteroaryl groups, especially pyridyl groups.

[0033] Suitable substituents that may be present in the corresponding groups are, in particular, halogens that are non-reactive toward the metal center in the catalyst, in particular in the form of fluorine atoms, and non-polar substituents such as methoxy groups, aryl groups (when the main group is an aliphatic group) or alkyl or alkenyl groups (when the main group is an aromatic group). However, other substituents are also conceivable.

[0034] Examples of possible substituents of diketone compounds are, for example, the group R in the formula shown above. 1 and R 2 , are alkyl and alkenyl groups, cycloalkyl, cycloalkenyl and cycloalkylalkylene groups having 1 to 18 carbon atoms, and alkylcycloalkyl groups having 5 to 18 carbon atoms, and non-fused aryl groups (including aralkyl and alkylaryl groups) having 6 to 18 carbon atoms, such as methyl, ethyl, propyl, isopropyl, isobutyl, n-butyl, sec-butyl, tert-butyl, 1-pentyl, 3-pentyl, 1-hexyl, 1-heptyl, 3-heptyl, 1-octyl, 2,4,4-trimethylpentyl, tert-octyl, nonyl, decyl, tridecyl, pentadecyl, heptadecan-1-yl, n-octadecyl, allyl, methylallyl, 2-hexenyl, 1-methylcyclopentyl, cyclohexyl, cyclohexanepropyl, phenyl, m-tolyl, p-ethylphenyl, tert-butylphenyl, benzyl, phenylpropyl, and nonylbenzyl.

[0035] One of the keto functional groups of the diketone compound may be present in a ring, such as in 2-acetyl-1-tetralone, 1-palmitoyl-2-tetralone, 2-stearoyl-1-tetralone, 2-benzoyl-1-tetralone, 2-acetyl-cyclohexanone, and 2-benzoylcyclohexanone. In one embodiment, the diketone compound comprises one of these substances.

[0036] Examples of preferred diketone compounds in which both keto functional groups are present outside the ring include benzoyl-p-chlorobenzoylmethane, bis(4-methylbenzoyl)methane, bis(2-hydroxybenzoyl)methane, benzoylacetylmethane, tribenzoylmethane, diacetylbenzoylmethane, stearoylbenzoylmethane, palmitoylbenzoylmethane, lauroylbenzoylmethane, dibenzoylmethane, 4-methoxybenzoylbenzoylmethane, bis(4-methoxybenzoyl)methane, bis(4-chlorobenzoyl)methane, bis(3,4-methylenedioxybenzoyl)methane, benzoyl-p-chlorobenzoylmethane, bis(4-methoxybenzoyl)methane, bis(4-chlorobenzoyl)methane, bis(3,4-methylenedioxybenzoyl)methane, benzoyl-p-chlorobenzoylmethane, bis(4-methoxybenzoyl)methane, bis(4-chlorobenzoyl)methane, bis(3,4-methylenedioxybenzoyl)methane, benzoyl-p-chlorobenzoylmethane, bis(4-methoxybenzoyl)methane, bis(4-chlorobenzoyl)methane, bis(4-hydroxy ... The diketone compound can also be included in the catalyst system in the form of a mixture of two or more of the above-mentioned diketone compounds.

[0037] The diketone compound preferably contains 5 to 30 carbon atoms.

[0038] Very particularly preferred diketone compounds for the reactive mixture according to the invention are stearoylbenzoylmethane (Tm 56-59° C.), palmitoylbenzoylmethane, 1-phenylbutane-1,3-dione (Tm 54-56° C.), dibenzoylmethane (Tm 77-79° C.), 1,3-bis(4-methoxyphenyl)propane-1,3-dione (Tm 108-115° C.), 1,3-di-(2-pyridyl)-propane-1,3-dione (Tm 104-109° C.), 5,5′-dimethylcyclohexane-1,3-dione (Tm 146-148° C.), cyclohexane-1,3-dione (101-105° C.) or mixtures of the diketone compounds, in particular in the form of a mixture of stearoylbenzoylmethane and palmitoylbenzoylmethane (Tm 55° C.) (available as Rhodiastab 55P from Solvay).

[0039] Other diketone compounds that can be used are listed in US Pat. No. 8,859,654 B2, column 2, lines 16-34 (hereby incorporated by reference into the present application), provided that they have a melting point of ≧15°C.

[0040] The metal present in the metal-based catalyst is a metal that is capable and suitable for catalyzing the reaction of isocyanates and alcohols. In most cases, the catalysis occurs by attachment of the metal to the oxygen atom of the isocyanate, thereby reducing the electron density at the carbon atom of the isocyanate. Metals that facilitate this activation and are therefore preferred as metals for metal-based catalysts are selected from the group consisting of tin, zinc, bismuth, potassium, cobalt, manganese, titanium, iron, zirconium, and nickel. Very particularly preferred metals are zinc and / or bismuth (fully active and non-toxic metals), with bismuth being particularly preferred.

[0041] In addition, the use of metal or metal compounds of lead or mercury is possible, but the high toxicity of these metals means that their use in the reactive mixture according to the present invention should be avoided. Therefore, in the context of the invention described herein, preference is given to reactive mixtures that do not contain added lead or mercury.

[0042] The metals listed can be included in the catalyst system in the form of metal salts or organometallic compounds, preferably metal salts, because they are generally more stable. Preferred metal salts for the catalyst system according to the present invention are organic metal salts selected from the group comprising metal acetylacetonates, metal ethylhexanoates, metal octoates, metal naphthenates, metal acetates, metal neodecanoates, metal malonates, and metal carboxylates, and inorganic metal salts selected from the group comprising metal nitrates, metal pyrophosphates, and metal halides. Due to their very good reactivity at elevated temperatures and because they are not classified as toxic, in the reactive mixture according to the present invention, very particularly preferred are bismuth carboxylates or bismuth neodecanoate.

[0043] The amount of catalyst system is not subject to any relevant restrictions and can generally be adjusted by a person skilled in the art so that, on the one hand, the desired reactivity is established, but on the other hand the amount of catalyst system is as low as possible. Preference is given to a catalyst system content in the reaction mixture of 0.01% to 1% by weight, and preferably 0.02% to 0.5% by weight. Any solvent added to form the catalyst system or the added low molecular weight carboxylic acid ester, which is liquid at room temperature, need not be taken into account, since such solvents themselves are not active in the catalysis of polyurethane formation.

[0044] The ratio of the metal-based catalyst to the diketone compound is preferably in the range of from about 1:2 to 1:20, and more preferably in the range of from about 1:4 to 1:15.

[0045] The isocyanate component is not subject to any relevant restrictions in the reactive mixture according to the present invention, provided that the combination of isocyanate and polyol in the reactive mixture is not so reactive that a significant reaction occurs even under ambient conditions (room temperature) in the absence of a catalyst. The polyfunctional isocyanates that can be used in the isocyanate component are, in particular, aliphatic or aromatic polyisocyanates selected from the group consisting of 2,2'-, 2,4'- and 4,4'-methylenediphenylisocyanate (MDI), toluene 2,4- and 2,6-diisocyanates (TDI), naphthylene-1,5-diisocyanate, hexamethylene-1,6-diisocyanate (HMDI), isophorone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate, bis(isocyanatomethyl)cyclohexane and dicyclohexylmethane-4,4'-diisocyanate, oligomers or polymers of such polyfunctional isocyanates, isocyanate prepolymers obtained by reacting such polyfunctional isocyanates with polyols, or mixtures thereof.

[0046] Oligomers of polyfunctional isocyanates include, for example, isocyanurates, uretdiones, and biuret. An example of a polyisocyanate polymer that can be used is poly-MDI.

[0047] It is preferred to use isocyanate prepolymers at least partially as the isocyanate component. Isocyanate prepolymers are understood here to mean the reaction products of polyisocyanates and polyols, the polyisocyanates preferably being used in a ratio with the polyols such that the NCO / OH ratio is at least 2. This means that in such isocyanate prepolymers, all OH groups will generally be converted into -O-CO-NH-R-NCO groups (wherein "R" indicates the structure of the polyisocyanate without isocyanate groups). It is also preferred that the polyols used to produce the isocyanate prepolymers are polyols having an average functionality in the range of from 1.85 to 2.5, in particular from 1.9 to 2.2, and very particularly preferably about 2.0.

[0048] The isocyanate prepolymers also preferably have a content of isocyanate groups (determined as a proportion by weight) of between about 2% and 20%, and in particular between about 4% and 13%. In addition to urethane groups, these isocyanate prepolymers may also contain other functional groups such as ether, thioether, ester and carbonate groups (which may be incorporated into the isocyanate prepolymer via polyols), or urea groups.

[0049] For the purposes of the present invention, it is also possible, but not preferred, to use isocyanate-containing compounds in which the isocyanate groups are temporarily chemically blocked and can be reactivated again by heating and cleaving off the blocking groups. Examples of blocking agents used here are ketoximes such as butanone oxime or acetone oxime, or caprolactam. Mixtures of the above-mentioned components of the isocyanate component can also be used.

[0050] The polyol component in the reactive mixture according to the invention is also not subject to any relevant restrictions, but it must also be ensured that the polyol does not form a mixture with the isocyanate that would react significantly even under ambient conditions (room temperature) without a catalyst. Suitable polyols for the reactive mixture according to the invention have a molecular weight in the range of from 62 to 20,000, in particular from 250 to 10,000 g / mol, and more preferably in the range of from 2000 to 8000 g / mol. In the case of polymeric polyols, the molecular weight is the average molecular weight Mw and is determined by GPC including suitable standards (e.g., polystyrene).

[0051] In the reactive mixture according to the present invention, particularly preferred are aliphatic polyols, which are preferably difunctional or higher functional. The term "aliphatic" is understood herein to mean that the polyol does not contain any aromatic components, while functional groups such as ether, ester, carbonate and urea groups may be present in the polyol. Therefore, taking into account the specified preferred molecular weight, preferred are polymer-based polyols and in particular polyols selected from the group consisting of polyester polyols, polyether polyols, polythioether polyols, polycarbonate polyols, polyols having multiple functional groups present in the above-mentioned polymers, aliphatic polyacetals containing hydroxyl groups, and aliphatic polycarbonates containing hydroxyl groups. Very particularly preferably, the polyol component comprises at least one polyether polyol, and most preferably, the polyol component comprises only polyether polyols.

[0052] To impart adequate resistance to external stresses, the reactive mixture according to the present invention preferably contains a certain proportion of higher-functional polyols, and in particular trifunctional polyols. Even more preferably, the reactive mixture does not contain any polyols with a higher functionality than trifunctional. When the reactive mixture contains or is formed from trifunctional and difunctional polyols in the polyol component, it is preferred that the trifunctional polyols account for at least 50% by weight of the polyol component, and more preferably, a proportion in the range of 65% to 90% by weight. Polyether polyols are very particularly preferably used as trifunctional and difunctional polyols.

[0053] The polyisocyanate component and the polyol component are expediently used in a ratio in which the isocyanate groups are present in excess compared to the OH groups, especially when the polyol component comprises polyols with a functionality > 2. The excess of isocyanate groups means that the reaction of all OH groups in the reactive mixture is then largely complete; excess NCO groups remain, but these can subsequently react with atmospheric moisture and thus decompose into -NH2 groups.

[0054] In addition to polyols, other compounds that react with isocyanates and contain reactive hydrogen atoms can be used in the reactive mixture according to the invention to replace a certain proportion of the polyol in order to modify the properties of the reacted system. Such compounds contain two or more reactive groups, for example in the form of OH groups, SH groups, NH groups, NH2 groups or acidic CH groups, for example in β-diketone compounds.

[0055] In addition to the above-mentioned components, the reactive mixture according to the invention may also comprise one or more additives conventionally used for producing polyurethane layers and polyurethane artificial leathers, for example in order to optimize specific properties or to increase the reactivity even further.

[0056] Examples of additives that increase reactivity are cocatalysts, for example in the form of bases that stabilize the protons provided by the polyols or other compounds with acidic H atoms during polyurethane formation. Examples of suitable bases are 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), dimethylaminoethanol, and the like. Liquid additives that delay the reactivity of the metal catalyst, such as acetylacetone or 2-ethylhexanoic acid, can also be added, but this is not necessary for the purposes of the present invention. Such liquid additives are preferably not present in the reactive mixture according to the present invention, as reactive mixtures containing acetylacetone have a pungent odor after conversion to polyurethane, and 2-ethylhexanoic acid is classified as teratogenic and, due to its boiling point of 228°C, remains in the product during polyurethane formation.

[0057] Additives used in polyurethane layers and polyurethane artificial leathers are, in particular, anti-aging agents, flame retardants, fillers (preferably in the form of chalk (CaCO 3 ) or cellulose derivatives), pigments, leveling agents, degassing agents, processing aids, rheological agents, leveling agents, foaming agents, solvents, carboxylates, and crosslinkers. Therefore, the reactive mixture according to the invention preferably contains one or more of these additives.

[0058] Suitable flame retardants are, for example, aluminum trihydrate or organic phosphites such as aluminum diethylphosphite. Suitable leveling agents are, for example, silicone oils.

[0059] In the reactive mixtures according to the invention, the solvent content should be as low as possible, and if they contain solvents, solvents which can be easily evaporated during subsequent processing should be used as far as possible. This allows the production of end products with very low VOC (volatile organic compound) contents.

[0060] For processing, the reactive mixture according to the invention is preferably adjusted to a suitable viscosity, preferably in the range of from 1 Pa·s to 120 Pa·s, in particular from 5 Pa·s to 15 Pa·s; according to ISO 2555:2018, this viscosity can be determined, for example, in the mixture before the coating rod gap (via which the mixture is applied to the substrate).

[0061] In another aspect, the present invention relates to a polyurethane layer that can be obtained by applying the reactive mixture described above to a substrate and reacting the isocyanate component with the polyol component to form a polyurethane. Since the catalyst system used for the reaction contains a high-boiling diketone compound, these compounds are present in the polyurethane layer after the reaction and can be detected by extraction and detection, for example, by GC or HPLC-MS.

[0062] With the reactive mixtures according to the invention, thick layers can also be produced in particular, for example in artificial leather or film composites, so that it is preferred that the polyurethane layer has a thickness of at least 100 μm, in particular in the range from 150 to 800 μm and more preferably in the range from 200 to 350 μm.

[0063] For example, in order to give the polyurethane layer the appearance that a normal user associates with leather, it is advantageous if the polyurethane layer has a visually recognizable structure on one side. A structure in the form of an embossing that simulates the surface side of leather is preferred.

[0064] In some cases, it is particularly advantageous to provide the polyurethane layer with a lacquer layer. For example, the purpose of this lacquer layer is to improve the surface properties, in particular the abrasion resistance. Furthermore, the lacquer layer provides a means of controlling the optical properties of the surface, such as the desired gloss. The lacquer layer is applied to the surface of the polyurethane layer in a manner known in the art, while being freely accessible from above.

[0065] In one embodiment, the polyurethane layer is compact and has no cavities. In another embodiment, the cover layer is foamed and has isolated cavities. In another embodiment, the cover layer is foamed and has interconnected cavities.

[0066] The polyurethane layer may be flat / planar or in the form of an object onto or into which it is applied or incorporated, for example by spraying, casting, pouring into a mold, pouring onto a mold, dipping, printing or spraying.

[0067] In another aspect, the present invention relates to a method for producing a polyurethane layer as described above, wherein

[0068] - applying the reactive mixture as described above to a substrate,

[0069] - heating the reactive mixture to react the isocyanate component and the polyol component to form the polyurethane layer, preferably to a temperature above the melting temperature of the diketone compound present in the reactive mixture,

[0070] - and then optionally removing the substrate from the polyurethane layer.

[0071] In order to produce a structured surface in the polyurethane layer, the substrate can have a structure that corresponds to the negative structure of the structure to be produced on the polyurethane layer. This method is also known in the prior art as reverse coating.

[0072] A thick polyurethane layer which forms the cover layer of the artificial leather (i.e. the layer which forms the visible side, which can optionally in turn be coated with a lacquer layer) is particularly advantageous in the production of artificial leather, since the high layer thickness means that the textile structure of the back layer is not pressed onto the surface and the overall composite material has a pleasant feel / tactile pleasure.

[0073] Therefore, in another aspect, the present invention relates to a composite structure comprising: a polyurethane layer as described above; a backing layer, in particular a textile backing layer or a backing layer made of PVC, polyolefin, thermoplastic polyurethane or polyurethane foam; and optionally an adhesive layer arranged between the layers and / or a lacquer layer applied to the side of the polyurethane layer opposite to the backing layer.

[0074] In a preferred embodiment, the polyurethane layer in the composite structure consists essentially (i.e., to an extent of at least 98% by weight, preferably at least 99% by weight, and even more preferably at least 99.5% by weight) of aliphatic polyols and polyisocyanates. Such polyurethanes have the advantage of high resistance to yellowing and aging.

[0075] In another preferred embodiment, the polyurethane layer in the composite structure is dark or black, or the polyurethane layer does not form the uppermost layer of the composite structure (the paint layer is not counted as the uppermost layer in this case). In this case, it is preferred to additionally use or even only use aromatic polyisocyanates to form the polyurethane layer.

[0076] In another aspect, the present invention relates to the use of a mixture of a metal-based catalyst based on a salt or an organometallic compound and a diketone compound having a melting point ≥ 15° C. (preferably as described above) as catalyst system for the reaction of polyols and polyisocyanates.

[0077] For the specified polyurethane layers, methods, composite structures and uses, features described as preferred with respect to the reactive mixture are also considered disclosed and preferred, provided they are not explicitly inconsistent with one another.

[0078] When processed in the production of artificial leather or films having a surface that simulates the appearance of leather, the reactive mixture according to the invention achieves the following additional advantages, which should additionally be mentioned in this context:

[0079] Composite structures comprising at least one polyurethane layer obtained from the reactive mixture according to the invention can be produced in the same thickness as leather already used to date (for example in automotive interiors). To produce the necessary thickness, one or more layers can optionally be used.

[0080] Polyurethane layers formed from the reactive mixture according to the invention or composite structures comprising such layers can also be produced in a continuous process, such as a continuous coating process (direct coating or transfer coating).

[0081] By selecting the right polyols, polyisocyanates, and other components of the reactive mixture, the discoloration of the polyurethane layers produced therefrom after prolonged exposure to heat or UV radiation can be kept so low that even light-colored artificial leathers based on the invention can be used without problems in vehicle dashboards. Furthermore, the resulting products remain dimensionally stable even after prolonged exposure to heat (e.g., 26 weeks of climatic storage at temperatures of up to 105°C).

[0082] In particular embodiments, the polyurethane layer according to the invention may also be wear-resistant and flexible to a sufficient extent to allow use in customary seating applications in the furniture and automotive industries and to pass the qualification tests necessary for this purpose (robot test, in-and-out test).

[0083] The polyurethane layer according to the invention may also be flexible within a wide temperature range (from -20°C), thereby minimizing the risk of cracking of the artificial leather due to brittleness when the seat is cold.

[0084] The present invention is described in more detail below with reference to several examples, which however should not be construed as limiting the scope of protection of the present application in any way. DETAILED DESCRIPTION

[0085] Examples:

[0086] Production of catalyst mixtures:

[0087] To produce the catalyst system according to the present invention, the mixture of metal salt and diketone used in Table 1 was prepared as follows: To a mixture including Rhodiastab 55P (a mixture of stearoylbenzoylmethane and palmitoylbenzoylmethane, Tm = 56°C), the specified amount of toluene was added to dissolve the mixture and the mixture was stirred at room temperature until a homogeneous solution was formed. No solvent was added to the mixture containing acetylacetonate. The metal salt catalyst was used as is without the diketone additive.

[0088] The following substances were used as metal salts:

[0089] Nickel acetylacetonate (Sigma-Aldrich), bismuth neodecanoate (Borchikat 315EU, Borchers), zinc neodecanoate (Reaxis C616, Reaxis), bismuth carboxylate (Reaxis C716, Reaxis), dioctylbis(2,4-pentanedionato-KO2-KO4)tin (Reaxis C2013, Reaxis), bismuth / zinc neodecanoate mixture (Bicat 8, Shepherd), zinc salt of C12-C14 fatty acid (Kosmos 54, Evonik)

[0090] Acetylacetone (Sigma-Aldrich) and Rhodiastab 55P (Rhodia / Sowell) were used as diketone additives.

[0091] Table 1:

[0092]

[0093]

[0094] Use of catalysts in the production of polyurethane:

[0095] The catalyst system thus obtained was used to produce a homogeneous mixture with polyisocyanate prepolymer and polyol according to the following recipe:

[0096] 770 g trifunctional polyether polyol (OH value 20.2; viscosity about 5000 mPa·s)

[0097] 140 g difunctional polyether polyol (OH value 28; viscosity about 1000 mPa·s)

[0098] 281 g of diisocyanate prepolymer based on MDI and polyether (isocyanate content 6.8%, viscosity about 5500 mPa·s)

[0099] 7g leveling agent (Levacast Fluid SN, Lanxess)

[0100] 235g aluminum trihydrate powder (flame retardant, average particle size = 13-20 μm)

[0101] 45g organic phosphite (flame retardant, average particle size = 10 μm)

[0102] 295 g chalk powder (filler, average particle size = 2 μm)

[0103] The amount of catalyst used corresponds to the sum of the values ​​in the corresponding rows in Table 1. The isocyanate component was used in excess (NCO / OH ratio 1.29).

[0104] For the mixture thus produced, the viscosity was determined at t = 0 and t = 30 and 60 min using a Brookfield viscometer in accordance with ISO 2555: 2018. During this time, the mixture was stored at room temperature (25°C).

[0105] To determine the reactivity of the catalyst, the mixture was applied to the coated paper using a doctor blade and a gap distance of 300 μm and then heated to 150° C. for 120 seconds, thereby providing a film having a particle size of approximately 300 g / m 2 The weight of the film per unit area was determined. The curing of the film was then evaluated as "tacky" or "dry". The results of the viscosity determination and curing are shown in Table 2 below:

[0106] Table 2

[0107]

[0108]

[0109] Comparative mixtures 1-6, 13, 19, and 25 show that (except for the zinc-based catalyst V3, whose catalytic activity was insufficient) dry films can be produced from the reactive mixtures using the catalysts tested. However, in all cases, the possible processing time is very short, because the viscosity increases so much within 30 minutes that it is no longer possible to process the reactive mixture. Only when the toxicologically questionable catalyst V1 (Example 1) is used does the mixture still have a processable viscosity after 30 minutes, but here too, there is a very large increase compared to the initial viscosity. In all cases, the mixtures are barely processable without the use of a technically complex mixing head system.

[0110] Comparative mixtures 7 to 12 show that the processing time can be significantly extended by combining the liquid 1,3-diketone compound acetylacetone with the reactive catalyst bismuth neodecanoate. This is due to the acetylacetone complexing with the metal catalyst and only being completely released by evaporation to be available again for catalysis. The application of this principle is also described, for example, in EP 1 927 466 B1.

[0111] However, comparative mixtures 7 to 12 also show a relatively significant increase in viscosity, especially when the amount of catalyst is increased, which means that processing without a mixing head system is also difficult here. In addition, in order to achieve a useful effect, it is necessary to use relatively large amounts of acetylacetone. Due to the high boiling point of acetylacetone (140° C.), some of this highly odorous substance (which is classified as toxic) at 150° C. remains in the final product.

[0112] By way of example, mixtures 14 to 18, 20 to 24, and 26 to 30 demonstrate the effectiveness of a solid diketone compound (in this case, a mixture of stearoylbenzoylmethane and palmitoylbenzoylmethane) in a mixture with bismuth neodecanoate as a catalyst. The diketone compound employed did not adversely affect the reactivity of the mixture at any of the amounts used, and in all cases, dried films could be produced at 150° C. within 2 minutes.

[0113] Furthermore, the addition of an appropriate amount of diketone significantly increased the proportion of catalyst without thereby increasing the viscosity or pot life of the mixture (see mixtures 16, 22, and 28). This shows that the amount of catalyst can be easily increased for faster processing without adversely affecting the processing time / pot life during production and storage of the mixture.

[0114] It is also clear from Examples 14 to 30 that there is an optimal amount of 1,3-diketone compound to be used for the longest possible processing time, and that further increasing this amount relative to the catalyst used does not bring any further benefits. Thus, the viscosity of reactive mixtures 17 and 18 after 60 minutes is not lower than that of mixture 16, which has a lower content of diketone compound.

[0115] The good effectiveness of 1,3-diketone compounds, which are solid at room temperature, is presumably due to the fact that the 1,3-diketone compounds are very stable complexes to the catalyst metal core: first, because they cannot evaporate at room temperature, and second, because they form stable micelle-like structures that effectively shield the metal atoms, with the nonpolar aliphatic ends pointing outward. This also explains the particularly good interaction shown here between the aliphatic groups in bismuth neodecanoate and the long aliphatic chains in stearoylbenzoylmethane or palmitoylbenzoylmethane. Only at higher temperatures does this interaction disappear and the metal core is "released."

[0116] It is clear from mixtures 31 to 34 that even when using other metal catalysts containing diketone compounds that are solid at room temperature, long processing times are achieved at room temperature, and the viscosity of the mixture is still low even after 60 minutes. With the exception of the two mixtures 31 and 33 containing zinc catalysts, which have insufficient reactivity even without the addition of diketone compounds, dry films were also produced in 2 minutes at 150°C.

Claims

1. A reactive mixture for producing a polyurethane layer, comprising an isocyanate component consisting of at least one polyfunctional isocyanate, an oligomer of a polyfunctional isocyanate or an isocyanate prepolymer, a polyol component consisting of at least one polyol, and - a catalyst system comprising a metal-based catalyst based on a salt or an organometallic compound and a diketone compound having a melting point of ≥ 15° C., wherein The diketone compound is selected from stearoylbenzoylmethane, palmitoylbenzoylmethane, 1-phenylbutane-1,3-dione, dibenzoylmethane, 1,3-bis(4-methoxyphenyl)propane-1,3-dione, 1,3-di-(2-pyridyl)-propane-1,3-dione, 5,5'-dimethylcyclohexane-1-3-dione, cyclohexane-1,3-dione or a mixture of the diketone compounds, and the ratio of the metal-based catalyst to the diketone compound is in the range of 1:2 to 1:

20.

2. The reactive mixture according to claim 1, wherein The diketone compound has a melting point ≥ 25°C.

3. The reactive mixture according to claim 1, wherein The diketone compound has a melting point of ≥30°C.

4. The reactive mixture according to claim 1, wherein The metal-based catalyst is a metal selected from the group comprising tin, zinc, bismuth, potassium, cobalt, manganese, titanium, iron, zirconium and nickel.

5. The reactive mixture according to claim 4, wherein The metal-based catalyst is chosen from zinc and / or bismuth.

6. The reactive mixture according to any one of claims 1 to 5, characterized in that The catalyst system comprises: an organic metal salt selected from the group comprising metal acetylacetonates, metal ethylhexanoates, metal octoates, metal naphthenates, metal acetates, metal neodecanoates, metal malonates, and metal carboxylates, and / or an inorganic metal salt selected from the group comprising metal nitrates, metal pyrophosphates, and metal halides.

7. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture comprises the catalyst system in an amount of from 0.01% to 1% by weight.

8. The reactive mixture according to claim 7, wherein The reactive mixture comprises the catalyst system in an amount of from 0.02% to 0.5% by weight.

9. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture comprises as the isocyanate component an aliphatic or aromatic polyisocyanate selected from the group comprising 2,2′-, 2,4′-, and 4,4′-methylene diphenyl isocyanate, toluene 2,4- and 2,6-diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene 1,6-diisocyanate, isophorone diisocyanate, cyclohexane 1,4-diisocyanate, bis(isocyanatomethyl)cyclohexane and dicyclohexylmethane 4,4′-diisocyanate, an oligomer or polymer of such a polyfunctional isocyanate, an isocyanate prepolymer obtained by reaction of such a polyfunctional isocyanate with a polyol, or a mixture thereof.

10. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture comprises as the polyol component a polyol having a molecular weight Mw of from 62 to 20 000 g / mol.

11. The reactive mixture according to claim 10, wherein The reactive mixture comprises, as the polyol component, a polyol having a molecular weight Mw in the range from 250 to 10 000 g / mol.

12. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture comprises a polyol as the polyol component which is selected from the group consisting of polyester polyols, polyether polyols, polythioether polyols, polycarbonate polyols, and aliphatic polyacetals containing hydroxyl groups.

13. The reactive mixture according to claim 12, wherein The reactive mixture comprises a polyether polyol as the polyol component.

14. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture comprises a mixture of trifunctional and difunctional polyols as the polyol component.

15. The reactive mixture according to claim 14, wherein The trifunctional polyol comprises a proportion of at least 50% by weight of the polyol component.

16. The reactive mixture of claim 14, wherein The trifunctional polyol accounts for a proportion ranging from 65% to 90% by weight of the polyol component.

17. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture contains NCO functional groups from the isocyanate component and OH functional groups from the polyol component in a ratio of 1.0 to 1.

5.

18. The reactive mixture of claim 17, wherein The reactive mixture contains NCO functional groups from the isocyanate component and OH functional groups from the polyol component in a ratio of 1.1 to 1.

45.

19. The reactive mixture of claim 17, wherein The reactive mixture contains NCO functional groups from the isocyanate component and OH functional groups from the polyol component in a ratio of 1.2 to 1.

35.

20. The reactive mixture according to any one of claims 1 to 5, characterized in that The reactive mixture additionally comprises one or more additives selected from anti-aging agents, flame retardants, fillers, pigments, leveling agents, degassing agents, rheology agents, foaming agents, solvents, and crosslinking agents.

21. The reactive mixture of claim 20, wherein The filler is in the form of chalk or a cellulose derivative.

22. A polyurethane layer obtainable by applying the reactive mixture of any one of claims 1 to 21 to a substrate and reacting the isocyanate component with the polyol component to form polyurethane.

23. The polyurethane layer according to claim 22, wherein The polyurethane layer has a thickness of at least 100 μm.

24. The polyurethane layer according to claim 23, wherein The polyurethane layer has a thickness in the range from 150 to 800 μm.

25. The polyurethane layer according to claim 23, wherein The polyurethane layer has a thickness in the range from 200 to 350 μm.

26. The polyurethane layer according to any one of claims 22 to 25, characterized in that The polyurethane layer has a visually recognizable structure on one side.

27. The polyurethane layer according to claim 26, wherein The structure is in the form of an embossing that simulates the surface side of leather.

28. A method for producing a polyurethane layer as claimed in any one of claims 22 to 27, characterized in that - applying the reactive mixture as claimed in any one of claims 1 to 21 to a substrate, - heating the reactive mixture to react the isocyanate component and the polyol component to form the polyurethane layer.

29. The method of claim 28, wherein The reactive mixture is heated to a temperature above the melting temperature of the diketone compound present in the reactive mixture.

30. The method of claim 28, wherein After heating, the substrate is removed from the polyurethane layer.

31. A composite structure comprising: The polyurethane layer according to any one of claims 22 to 27; Textile backing or backing made of PVC, polyolefin, thermoplastic polyurethane or polyurethane foam.

32. The composite structure of claim 31 , comprising: An adhesive layer arranged between the layers and / or a lacquer layer applied to the side of the polyurethane layer opposite the back layer.

33. Use of a mixture of a metal-based catalyst based on a salt or an organometallic compound and a diketone compound having a melting point of ≥15° C. as a catalyst system for the reaction of polyols and polyisocyanates, wherein: The diketone compound is selected from stearoylbenzoylmethane, palmitoylbenzoylmethane, 1-phenylbutane-1,3-dione, dibenzoylmethane, 1,3-bis(4-methoxyphenyl)propane-1,3-dione, 1,3-di-(2-pyridyl)-propane-1,3-dione, 5,5'-dimethylcyclohexane-1-3-dione, cyclohexane-1,3-dione or a mixture of the diketone compounds, and the ratio of the metal-based catalyst to the diketone compound is in the range of 1:2 to 1:20.

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