Single-component baking system

Abstract

The invention relates to a one-component baking system comprising A) a blocked polyisocyanate component comprising the reaction product of at least one of the following components: a) at least one polyisocyanate component having at least an isocyanurate and / or iminooxadiazindione structure, the amount of component b) is greater than 2% by weight, based on the total amount of components a) and b), and the amount of component c) corresponds to at least 95 mol% of the isocyanate groups that remain arithmetically present after the reaction of components a) and b), and at least one branched aliphatic diol and c) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents, the amount of component b) being greater than 2% by weight, based on the total amount of components a) and b), and the amount of component c) being equal to at least 95 mol% of the isocyanate groups that remain arithmetically present after the reaction of components a) and b). The present invention relates to a composition comprising A) at least one isocyanate-reactive group, B) at least one binder which is reactive to isocyanate groups and which has a statistical average of at least two isocyanate-reactive groups per molecule, C) optionally a catalyst, and D) optionally a solvent and / or optionally auxiliary agents and additives.

Description

[0001] Blocked polyisocyanates, which can be obtained by reacting isocyanate groups with suitable blocking agents, have long been known. They can be combined with polyols to produce blends that are storage-stable at room temperature, so-called one-component polyurethane baking varnishes (1K-PUR). At higher temperatures, the blocking agents cleave again, releasing the isocyanate groups for crosslinking with the polyol component.

[0002] Today, 1K-PUR lacquers are used, for example, for the initial painting of cars, for the painting of plastics, and for can and coil coating. The type of sealant used here is very important. For example, reactivity, thermal yellowing and other paint properties are largely determined by the sealant. (U. Meier-Westhues et al. "Polyurethanes: Coatings, Adhesives and Sealants", 2nd revised edition, Hanover: Vincentz Network, 2019).

[0003] Secondary monoamines are of particular interest as blocking agents because they allow particularly low baking temperatures. Polyisocyanates containing isocyanurate groups and based on linear aliphatic diisocyanates (e.g. 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI) and 1,5-diisocyanatopentane (pentamethylene diisocyanate, PDI) which are of great technical and economic importance offer the required high flexibility for coatings for coil and can coating applications, but have hitherto been of no practical significance in the form of blocking with secondary amines (e.g. diisopropylamine). The reason for this is the fact that solutions of such blocked polyisocyanates in conventional coating solvents are not storage-stable for a long time because they exhibit a very high tendency to solidify, for example due to crystallization of the contained blocked polyisocyanates (DA Wicks, ZW Wicks Jr, Progress in Organic Coatings 41 (2001) 1–83).

[0004] Polyisocyanates, in particular 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) and toluene diisocyanate (TDI), which are blocked only with secondary amines, optionally after chain extension with diols and / or triols, were first described in EP-A 0 096 210 as crosslinker components for solventborne 1K-PUR stoving varnishes. Sterically hindered secondary amines, such as diisopropylamine, dicyclohexylamine or 2,2,6,6-tetramethylpiperidine, are considered suitable blocking agents. Isocyanurate polyisocyanates are also very generally considered to be suitable starting diisocyanates. However, no examples of polyisocyanates containing isocyanurate groups using linear aliphatic diisocyanates were found in this publication, from which the storage stability of such products in organic solutions could be inferred.

[0005] EP-A 0125438 also describes 1K adhesives whose crosslinker component consists of the reaction product of polyisocyanates, optionally pre-extended with polyols, and exclusively secondary amines as blocking agents. These adhesives are used both in solventborne coatings, powder coatings and also in their protonated form for cathodic electrophoretic coating. However, no information is found in this publication about the storage stability of blocked polyisocyanate solutions.

[0006] From EP-A 0407829 it is known to use polyisocyanates blocked with secondary amines, in particular isocyanate-functional prepolymers, as crosslinker components for polyamines. HDI derivatives containing biuret or isocyanurate groups are also very generally considered to be suitable starting polyisocyanates for the production of blocked prepolymers, which may optionally be modified with substoichiometric amounts of low molecular weight polyhydroxy compounds before blocking. This publication does not allow for any conclusions to be drawn about the storage stability of polyisocyanates blocked with secondary amines or about their suitability as crosslinkers in 1K-PUR coatings.

[0007] EP-A 3643733 describes the use of special secondary monoamines which carry both branched alkyl radicals with 3 to 6 carbon atoms and hydrocarbon substituents with 1 or 2 ether groups as blocking agents for isocyanates. Preferred blocking agents of this type are N-(furan-2-ylmethyl)-2-methylpropane-2-amine, 2-methyl-N-((tetrahydrofuran-2-yl)methyl)propane-2-amine, N-(2-methoxyethyl)-2-methylpropane-2-amine and N-(tert-butyl)-1-methoxypropane-2-amine. The isocyanate groups blocked with these amines are released again at very low temperatures. The publication contains no information about the lack of crystallization stability of isocyanurate polyisocyanates blocked with secondary amines of linear aliphatic diisocyanurates, nor any suggestions on how to overcome this problem.

[0008] The high crystallization tendency of amine-blocked isocyanurate polyisocyanates of linear aliphatic diisocyanates can be reduced in various ways. For example, one concept is so-called mixed blocking, i.e. the simultaneous use of two or more different blocking agents.

[0009] The subject matter of EP-A 0600314 is a blocked polyisocyanate, at least 30 equivalent % and up to 70 equivalent % of the isocyanate groups of which are blocked with diisopropylamine and a total of 30 to 70 equivalent % are blocked with at least one CH-acidic ester and / or 1,2,4-triazole. This mixed blocking prevents the crystallization tendency of derivatives of, for example, HDI polyisocyanurate polyisocyanates. However, when such products are used in 1K-PUR coating systems, the different deblocking temperatures of the differently blocked isocyanate groups often lead to practical problems. In addition, the blocking agent mixtures released when baking such systems may also have a negative impact on the properties of the paint layer, so that mixed blocked polyisocyanates are not generally practical.

[0010] One possibility for producing crystallization-stable, exclusively amine-blocked polyisocyanate crosslinkers is to react specific mixtures of linear aliphatic and cycloaliphatic polyisocyanates with secondary amines, according to the teaching of EP-A 0 900 814. However, coating layers produced using such polyisocyanates have a significantly different property profile, in particular an elasticity that is lower than that required, for example, for many coil coating applications, and are likewise not generally practical.

[0011] According to EP-A 1524284, polyisocyanates blocked with secondary amines and containing a specific amount of biuret structures are crystal-stable. Suitable polyisocyanates are pure HDI biuret or HDI polyisocyanates with subsequent biuretization of isocyanurate and / or iminooxadiazinedione structures. These polyisocyanates can be optionally partially reacted with compounds reactive to isocyanate groups, such as low molecular weight or higher molecular weight difunctional or polyfunctional alcohols, amines or higher molecular weight polyhydroxy compounds based on polyesters, polyethers, polycarbonates or polyacrylates before blocking. In particular, diisopropylamine, N-tert-butylbenzylamine, dicyclohexylamine or mixtures thereof are used as blocking agents.

[0012] According to the teaching of WO 2004 / 104065, polyisocyanates based on linear aliphatic diisocyanates blocked with secondary amines, in which some of the urea groups formed during the blocking process are further converted into biuret structures, also exhibit similar crystal stability.

[0013] However, polyisocyanates containing biuret structures have in common that they have a much lower temperature resistance than isocyanurates. Due to equilibrium reactions which occur under conventional baking conditions, especially in the field of coil coating applications, and which can optionally lead to the release of monomeric diisocyanates, such products cannot be marketed.

[0014] The lack of crystallization stability and high solidification tendency of polyisocyanates containing isocyanurate groups and based on linear aliphatic diisocyanates blocked with secondary monoamines have not been satisfactorily solved. Despite the great interest in blocked polyisocyanate crosslinkers which crosslink and cure at low baking temperatures to form elastomeric coatings, no amine-blocked HDI and / or PDI polyisocyanurate polyisocyanates are currently available to users.

[0015] Surprisingly, it has now been found that polyisocyanurate polyisocyanates based on linear aliphatic diisocyanates (e.g. HDI or PDI) which have been partially urethanized with branched alcohols (in particular branched diols) can also be reacted with secondary amines (e.g. diisopropylamine) to give completely solidification-stable, non-crystalline blocked polyisocyanate crosslinkers. These novel amine-blocked polyisocyanates can be formulated with polyols to give 1K-PUR baking lacquers which are crystallization-stable and storage-stable at room temperature, which are particularly suitable for coil coating applications.

[0016] The subject of the present invention is a one-component baking system comprising

[0017] A) a blocked polyisocyanate component comprising the reaction product of at least one of the following components

[0018] a) at least one polyisocyanate component having at least an isocyanurate and / or an iminooxadiazinedione structure, and

[0019] b) at least one branched aliphatic diol and

[0020] c) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents,

[0021] wherein the amount of component b) is greater than 2% by weight, based on the total amount of components a) and b), and the amount of component c) corresponds to at least 95 mol % of the isocyanate groups which are still present after the reaction of components a) and b),

[0022] B) at least one binder reactive toward isocyanate groups having a statistical average of at least two isocyanate-reactive groups per molecule,

[0023] C) optionally a catalyst, and

[0024] D) Optional solvents and / or optional auxiliaries and additives.

[0025] According to the present invention, the term "comprising" or "containing" preferably means "consisting essentially of", more preferably means "consisting of...." Further embodiments described in the claims and the description may be combined in any manner, as long as the context does not clearly indicate otherwise.

[0026] As used herein, "at least one" refers to one or more, such as 2, 3, 4, 5, 6, 7, 8, 9 or more. For the components of the compounds described herein, the data do not refer to the absolute number of molecules, but to the type of component. Thus, "at least one polyisocyanate component" means, for example, that only one polyisocyanate component or a plurality of different types of polyisocyanate components may be included, rather than specifying the amount of various compounds.

[0027] Numerical values ​​without decimal places shown herein refer in each case to the full shown value with one decimal place, for example, "99%" means "99.0%".

[0028] Numerical ranges expressed in the format "from x to y" include the values ​​recited. If multiple preferred numerical ranges are expressed in this format, of course all ranges resulting from combinations of the individual endpoints are also contemplated.

[0029] The term "aliphatic" is defined herein as a saturated or unsaturated non-aromatic hydrocarbon group.

[0030] The term "straight-chain aliphatic" refers to compounds that are completely free of cyclic structural units, while the term "cycloaliphatic" or "alicyclic" is defined as non-aromatic, optionally substituted carbocyclic or heterocyclic compounds or units (e.g. cycloalkanes, cycloalkenes or oxa-, thia-, aza- or thiacycloalkanes). Particular examples are cyclohexyl, cyclopentyl and their N- or O-heterocyclic derivatives, such as pyrimidine, pyrazine, tetrahydropyran or tetrahydrofuran.

[0031] The term "araliphatic" is defined herein as a hydrocarbon group consisting of an aromatic hydrocarbon group and a saturated or unsaturated hydrocarbon group directly bonded to the aromatic group.

[0032] If a group or compound is disclosed as "optionally substituted" or "substituted", suitable substituents are -F, -Cl, -Br, -I, -OH, -OCH3, -OCH2CH3, -O-isopropyl or -O-n-propyl, -OCF3, -CF3, -SC 1-6 Alkyl and / or (optionally via pendant heteroatoms) straight-chain or branched aliphatic and / or alicyclic structural units having 1 to 12 carbon atoms, which in each case act as replacement groups for carbon-bonded hydrogen atoms of the molecule in question. Preferred substituents are halogen (especially -F, -Cl), C 1-6 Alkoxy (especially methoxy and ethoxy), hydroxy, trifluoromethyl and trifluoromethoxy, which in each case act as replacement groups for carbon-bonded hydrogen atoms of the molecule in question.

[0033] The at least one polyisocyanate component a) having at least isocyanurate and / or iminooxadiazinedione structures is also referred to in the present invention as starting compound a) or starting polyisocyanate a) or polyisocyanate a) or polyisocyanate a) having isocyanurate and / or iminooxadiazinedione structures.

[0034] Starting compounds a) for the process according to the invention are any polyisocyanates which are obtained by modification of linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates and have at least isocyanurate and / or iminooxadiazinedione structures.

[0035] Suitable diisocyanates for the preparation of these polyisocyanates a) are any diisocyanates which can be obtained in various ways, for example by phosgenation of the corresponding diamines in the liquid or gas phase or by a phosgene-free route, for example by thermal urethane cleavage, in particular those diisocyanates having a molecular weight in the range from 140 to 400 and having aliphatically, cycloaliphatically, araliphatically and / or aromatically bonded isocyanate groups, for example 1,4-diisocyanatobutane, 1,5-diisocyanatopentane (pentyl diisocyanate, PDI), 1,6-diisocyanatohexane (hexyl diisocyanate, HDI), 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethylolpropane. -1,6-diisocyanatohexane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3- and 1,4-diisocyanatocyclohexane, 1,4-diisocyanato-3,3,5-trimethylcyclohexane, 1,3-diisocyanato-2-methylcyclohexane, 1,3-diisocyanato-4-methylcyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate; IPDI), 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, 2,4'- and 4,4'-diisocyanatodicyclohexylmethane (H 12 -MDI), 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, 4,4'-diisocyanato-3,3'-dimethyldicyclohexylmethane, 4,4'-diisocyanato-3,3',5,5'-tetramethyldicyclohexylmethane, 4,4'-diisocyanato-1,1'-bis(cyclohexyl), 4,4'-diisocyanato-3,3'-dimethyl-1,1'-bis(cyclohexyl), 4,4'-diisocyanato-2,2',5,5'-tetramethyl-1,1'-bis(cyclohexyl), 1,8-diisocyanato-p-menthane, 1,3-diisocyanatoadamantane, 1,3 -dimethyl-5,7-diisocyanatoadamantane, 1,3- and 1,4-bis-(isocyanatomethyl)benzene (xylylene diisocyanate, XDI), 1,3- and 1,4-bis(1-isocyanato-1-methylethyl)benzene (TMXDI), bis(4-(1-isocyanato-1-methylethyl)phenyl)carbonate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-toluene diisocyanate and any mixtures of these isomers, diphenylmethane 2,4'- and / or 4,4'-diisocyanate and naphthalene 1,5'-diisocyanate and any mixtures of these diisocyanates. Other diisocyanates that are also suitable can be found, for example, in Justus Liebigs Annalen der Chemie 562 (1949) pp. 75-136.

[0036] In a further preferred embodiment, polyisocyanates which have been prepared by modification of linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates and have at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component a), with >70 equivalents, preferably >80 equivalents, particularly preferably >90 equivalents, and very particularly preferably exclusively linear aliphatic diisocyanates being used for the modification, based in each case on the NCO content.

[0037] In a further preferred embodiment, polyisocyanates having at least isocyanurate and / or iminooxadiazinedione structures which are prepared by modification of linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, are used as polyisocyanate component a).

[0038] Preferred diisocyanates for preparing polyisocyanates a) having isocyanurate and / or iminooxadiazinedione structures are diisocyanates of the type described having linear aliphatic and / or cycloaliphatic isocyanate groups, particularly preferably unbranched linear aliphatic diisocyanates, for example 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane and 1,10-diisocyanatodecane. Very particularly preferred diisocyanates are HDI and / or PDI.

[0039] In the preparation of the blocked polyisocyanate component A), at least one substantially linear aliphatic polyisocyanate component having at least isocyanurate and / or iminooxadiazinedione structures is used as polyisocyanate component a).

[0040] In this context, “substantially linear aliphatic” means in particular that >70 equivalents, preferably >80 equivalents, particularly preferably >90 equivalents (in each case based on the NCO content) of the diisocyanates used for modification are linear aliphatic diisocyanates, very particularly preferably exclusively linear aliphatic diisocyanates.

[0041] The preparation of the starting polyisocyanates a) having at least isocyanurate and / or iminooxadiazinedione structures is carried out in a manner known per se by modification, in particular catalytic trimerization, of the aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates. Suitable processes are described by way of example in J. Prakt. Chem. 336 (1994) 185–200, DE-A 1954093, DE-A 2414413, DE-A 2452532, DE-A 2641380, DE-A 3900053 and DE-A 3928503 or EP-A 0336205, EP-A 0339396 and EP-A 0798299. Depending on the modification method chosen, the polyisocyanates a) used in the process according to the invention may optionally have uretdione, allophanate, biuret, urethane and / or oxadiazinetrione structures in addition to isocyanurate and / or iminooxadiazinedione structures.

[0042] In the preparation of the starting polyisocyanates a), the actual modification reaction is usually followed by a further process step for separating off the unreacted excess monomeric diisocyanate. This monomer separation is carried out according to methods known per se, preferably by vacuum thin-film distillation or by extraction with suitable solvents inert toward isocyanate groups, for example aliphatic or cycloaliphatic hydrocarbons, such as pentane, hexane, heptane, cyclopentane or cyclohexane.

[0043] In the process of the invention, the starting polyisocyanate a) used preferably comprises a polyisocyanate of the type mentioned having a monomeric diisocyanate content of less than 5% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.3% by weight. The residual monomer content is determined by gas chromatography using an internal standard in accordance with DIN EN ISO 10283:2007-11.

[0044] The abovementioned suitable, preferred, particularly preferred and very particularly preferred polyisocyanates a) preferably contain isocyanurate structures, have an average NCO functionality of 2.3 to 5.0, preferably 2.5 to 4.5, and an isocyanate group content of 6.0 to 26.0% by weight, preferably 8.0 to 25.0% by weight, particularly preferably 10.0 to 24.0% by weight.

[0045] In the preparation of the blocked polyisocyanate component A) of the blocked one-component baking system of the invention, the polyisocyanate component a) having at least an isocyanurate and / or iminooxadiazinedione structure is reacted with at least one branched aliphatic diol b).

[0046] These are any saturated or unsaturated aliphatic diols which may be mono- or polybranched, optionally have heteroatoms, ester groups and / or carbonate groups in the chain and may optionally be further substituted.

[0047] Preferably, the branched aliphatic diols b) are those having 3 to 36 carbon atoms. Examples include simple diols such as 1,2-propylene glycol, 1,3-butylene glycol, 2-methyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol (neopentyl glycol), 2,2-dibutyl-1,3-propylene glycol, 2,2-dimethyl-1,3-butylene glycol, 1,2-hexanediol, 2-methyl-2,4-pentanediol, 3-methyl-2,4-pentanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propylene glycol, 2,2-dimethyl-1,3-hexanediol, 2-ethyl-1,3-hexanediol, 1,2- Octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,2,4-trimethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2,4- and / or 2,4,4-trimethylhexanediol, 2,2-dibutyl-1,3-propanediol, 1,2-decanediol, 2-(2-methyl)butyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2-propylheptane-1,3-diol and 9-octadecene-1,12-diol, dimer diols which are obtainable in a manner known per se, for example by hydrogenation of dimerized fatty acids and / or their esters and which are marketed, for example, under the names 2030, 2033 (Croda International Plc, UK) and Sovermol 908 (BASF SE, DE) are commercially available, as well as ether diols, such as dipropylene glycol, tripropylene glycol and ethylhexylglycerol, ester diols, such as 3-hydroxy-2,2-dimethylpropyl 3-hydroxy-2,2-dimethylpropionate (hydroxyneopentyl hydroxypivalate, HPN), glyceryl monocaprylate and glyceryl monostearate, or any mixtures of these alcohols.

[0048] Particularly preferably, the branched aliphatic diol has 4 to 12 carbon atoms. Very particular preference is given to 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol (BEPD), 2,2-dibutyl-1,3-propanediol, 2,2,4-trimethyl-1,5-pentanediol and 2,2,4- and / or 2,4,4-trimethylhexanediol or any mixtures of these alcohols.

[0049] The amount of branched aliphatic diol b) used in the preparation of the polyisocyanate component A) is greater than 2% by weight, preferably 3% to 20% by weight, particularly preferably 4% to 15% by weight, and very particularly preferably 5% to 12% by weight, based on the total amount of components a) and b). An amount of less than 2% by weight is insufficient to permanently prevent crystallization of the blocked polyisocyanate A); the use of more than 20% by weight leads to a very high product viscosity, which is uneconomical in practical use due to the low isocyanate content.

[0050] In addition to the branched aliphatic diols mentioned, component b) may optionally contain small amounts of other alcohol compounds.

[0051] These are, for example, monohydric alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomeric pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecyl alcohol, cyclohexanol, the isomeric methylcyclohexanols, hydroxymethylcyclohexane, 3-methyl-3-hydroxymethyloxetane, benzyl alcohol, phenol, the isomeric cresols, octylphenol, nonylphenol and naphthol, furfuryl alcohol and tetrahydrofurfuryl alcohol, unbranched aliphatic diols, such as 1,2-ethanediol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol , 1,6-hexanediol, 1,7-heptanediol and 1,8-octanediol, cycloaliphatic diols, for example 1,2- and 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4′-(1-methylethylidene)bicyclohexanol, triols, for example 1,2,3-propanetriol, 1,1,1-trimethylolethane, 1,2,6-hexanediol, 1,1,1-trimethylolpropane and 1,3,5-tris(2-hydroxyethyl)isocyanurate, tetrafunctional alcohols, for example 2,2-bis(hydroxymethyl)-1,3-propanediol or any mixtures of these alcohols.

[0052] If present, these further alcohol compounds are used in the process according to the invention in an amount of maximum 25% by weight, preferably maximum 20% by weight and particularly preferably 15% by weight, based on the amount of branched aliphatic diol used.

[0053] This means that the average OH functionality of component b) is preferably from 1.6 to 2.4, particularly preferably from 1.8 to 2.2, very particularly preferably from 1.9 to 2.1 and in particular 2.0.

[0054] In the preparation of the blocked polyisocyanate component A) of the blocked one-component baking system of the invention, at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents is used as blocking agent c).

[0055] These are in particular secondary amines of the general formula (I)

[0056]

[0057] wherein R and R' are independently identical or different radicals which denote saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic or araliphatic organic radicals having 1 to 18 carbon atoms, which are substituted or unsubstituted and / or have oxygen atoms in the chain, wherein R and R' can also form, in combination with one another, together with the nitrogen atom and optionally with further oxygen atoms, a heterocyclic ring having 5 to 8 ring members, which can optionally be further substituted.

[0058] Preferably, the radicals R and R′ are saturated straight-chain or branched aliphatic radicals having 1 to 18, particularly preferably 1 to 6, carbon atoms, or cycloaliphatic hydrocarbon radicals having 6 to 13, particularly preferably 6 to 9, carbon atoms, wherein R and R′ can also optionally form, in combination with one another, together with the nitrogen atom and optionally with a further oxygen atom, a heterocyclic ring having 5 to 6 ring members, which can optionally be further substituted.

[0059] Suitable secondary amines c) for preparing the polyisocyanate component A) are, for example, dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, diisobutylamine, di-n-pentylamine, di-n-hexylamine, N-methyl-n-propylamine, N-methyl-n-hexylamine, N-methylstearylamine, N-ethyl-n-propylamine, N-ethylcyclohexylamine, N-isopropyl-tert-butylamine, N-isopropylcyclohexylamine, dicyclohexylamine, di(3,5,5-trimethylcyclohexyl)amine, N-tert-butylbenzylamine, dibenzylamine, piperidine, 2,6-dimethylpiperidine, 2,2,6,6-tetramethylpiperidine, 2,2,4,6-tetramethylpiperidine, hexahydroazacycloheptatriene, pyrrolidine, 2,5-dimethylpyrrolidine or morpholine.

[0060] Likewise suitable, although less preferred, secondary amines c) are those which, in addition to the secondary amino group, carry further groups reactive toward isocyanate groups, but these groups, such as hydroxyl groups, are less reactive toward isocyanate groups than the secondary amino groups. Examples of such secondary amines are amino alcohols, such as diethanolamine and diisopropanolamine.

[0061] The secondary amine c) is preferably diisopropylamine, dicyclohexylamine, N-tert-butylbenzylamine or any mixtures of these amines. Particular preference is given to diisopropylamine.

[0062] In the preparation of the blocked polyisocyanate component A), the secondary amine c) is used in an amount corresponding to at least 95 mol %, preferably at least 96 mol %, particularly preferably at least 98 mol % and very particularly preferably at least 100 mol % of the isocyanate groups arithmetically still present after the reaction of components a) and b).

[0063] When preparing the blocked polyisocyanate component A), it is also possible to use at the same time a suitable solvent which is inert toward isocyanate groups. Suitable solvents are, for example, customary coating solvents known per se, such as ethyl acetate, butyl acetate, ethylene glycol monomethyl ether or monoethyl ether acetate, 1-methoxyprop-2-yl acetate (MPA), 3-methoxy-n-butyl acetate, acetone, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, chlorobenzene, solvent naphtha, higher-substituted aromatic compounds, for example known under the names solvent naphtha, (Deutsche EXXON CHEMICALGmbH, DE) and (Deutsche Shell Chemie GmbH, Eschborn, DE), and solvents such as propylene glycol diacetate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol ethyl and butyl ether acetate, N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone and N-methylcaprolactam, or any mixtures of these solvents.

[0064] To prepare the blocked polyisocyanate component A), the polyisocyanate component a) is reacted with the diol component b) and the amine component c) optionally under an inert gas (for example nitrogen) and optionally in the presence of a suitable solvent of the type mentioned at a temperature of 0 to 120° C., preferably 20 to 100° C., particularly preferably 40 to 80° C., in any order and in the quantitative ratios mentioned above.

[0065] In the process according to the invention, the progress of the reaction can be followed, for example by titrating the NCO content, preferably in accordance with DIN EN ISO 11909:2007-05.

[0066] In the preparation of the blocked polyisocyanate component A), the reaction of the polyisocyanate component a) with the diol component b) and the amine component c) can be carried out without catalysis, but in order to accelerate the reaction, a conventional urethanization catalyst known in polyurethane chemistry can also be used simultaneously, for example, a tertiary amine such as triethylamine, pyridine, picoline, benzyldimethylamine, N,N-endoethylenepiperazine, N-methylpiperidine, pentamethyldiethylenetriamine, N,N-dimethylaminocyclohexane, N,N'-dimethylpiperazine or Metal salts such as iron(III) chloride, zinc chloride, zinc octoate, zinc 2-ethylhexanoate, zinc acetylacetonate, tin(II) octoate, tin(II) ethylhexanoate, tin(II) palmitate, dibutyltin(IV) dilaurate, zirconium(IV) 2-ethyl-1-hexanoate, zirconium(IV) neodecanoate, zirconium(IV) naphthenate, zirconium(IV) acetylacetonate, aluminum tris(ethyl acetoacetate), bismuth(III) 2-ethylhexanoate, bismuth(III) octoate, bismuth(III) neodecanoate, and molybdenum glycolate.

[0067] These catalysts are optionally used in amounts of 0.001% to 2.0% by weight, preferably 0.01% to 0.2% by weight, based on the total amount of starting components a), b) and c) used.

[0068] If a catalyst is used simultaneously to accelerate the reaction, the catalyst used can optionally be deactivated after the desired NCO content has been reached, preferably by chemical methods. Suitable catalyst poisons for this are, for example, mineral acids, such as hydrochloric acid, phosphorous acid or phosphoric acid, acid chlorides, such as acetyl chloride, benzoyl chloride or isophthaloyl chloride, sulfonic acids and sulfonic esters, such as methanesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, perfluorobutanesulfonic acid, methyl and ethyl p-toluenesulfonate, monoalkyl and dialkyl phosphates, such as monotridecyl phosphate, dibutyl phosphate and dioctyl phosphate, and silylated acids, such as trimethylsilyl methanesulfonate, trimethylsilyl trifluoromethanesulfonate, tris(trimethylsilyl) phosphate and diethyltrimethylsilyl phosphate.

[0069] The amount of catalyst poison optionally required for deactivation depends on the amount of catalyst used. If used, 0.1 to 2.0, preferably 0.4 to 1.6, particularly preferably 0.8 to 1.2, very particularly preferably 1 equivalent of inhibitor is used, based on the amount of catalyst used.

[0070] After the reaction of the polyisocyanate component a) with the diol component b) and the amine component c), the blocked polyisocyanate A) can optionally be further diluted with a solvent, for example to reduce the viscosity, preferably if the content of free isocyanate groups is less than 1.0% by weight, preferably less than 0.8% by weight, particularly preferably less than 0.3% by weight. In addition to the abovementioned solvents, alcoholic solvents such as n-butanol or isobutanol can also be used here, since the isocyanate groups have then reacted substantially, preferably completely, with the blocking agent.

[0071] When preparing the blocked polyisocyanate component A), other auxiliaries and additives, such as antioxidants or light stabilizers, may also be used at the same time. These auxiliaries and additives may already be mixed into one or more of the reactants a), b) and c) before the actual reaction begins. However, they may also be added to the reaction mixture at any point in time during the reaction or added to the blocked polyisocyanate according to the invention after the reaction.

[0072] Suitable antioxidants are, for example, phenols, in particular sterically hindered phenols, such as 2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 2,6-di-tert-butyl-4-methylphenol, 2,4-dimethyl-6-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-hydroxyphenyl Esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with aliphatic branched C7 to C9 alcohols, for example 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid isoheptyl ester, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid isooctyl ester or 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid isononyl ester, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid isononyl ester, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid Isotridecyl propionate, diethylthiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide, 1,2-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)hydrazide, 4'-hydroxy-3',5'-di-tert-butylbenzoic acid 2,4-di-tert-butylphenyl ester, (3,5-di-tert-butyl-4- Esters of 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate or 2,5-di-tert-amylhydroquinone.

[0073] Suitable antioxidants are also thioethers, for example didodecyl 3,3'-thiodipropionate or distearyl 3,3'-thiodipropionate, which are preferably used in combination with phenolic antioxidants of the type described.

[0074] Further suitable antioxidants are phosphites, for example disubstituted or preferably trisubstituted phosphites, such as dibutyl phosphite, dibenzyl phosphite, triethyl phosphite, tributyl phosphite, triisodecyl phosphite, trilauryl phosphite, tritridecyl phosphite, triphenyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, tris(nonylphenyl) phosphite, diphenyl isooctyl phosphite, diphenyl isodecyl phosphite, diisodecylphenyl phosphite, diisooctyl-octylphenyl phosphite, neopentyl glycol phenyl phosphite, 2,4,6-tri-tert-butylphenyl(2-butyl-2-ethyl-1,3-propanediol)phosphite, pentaerythritol diisodecyl diphosphite, pentaerythritol distearyl diphosphite, pentaerythritol dibis(2,4-di-tert-butylphenyl) phosphite or dipropylene glycol tetraphenyl diphosphite.

[0075] Suitable light stabilizers are, for example, UV absorbers of the 2-hydroxyphenylbenzotriazole type, UV absorbers of the HALS compound type which are substituted or unsubstituted on the nitrogen atom, for example 292 or 770DF (BASF SE, Ludwigshafen, Germany), or those described, for example, in "Lichtschutzmittel für Lacke" (A. Valet, Vincentz Verlag, Hannover, 1996) and "Stabilization of Polymer Materials" (H. Zweifel, Springer Verlag, Berlin, 1997, Appendix 3, pages 181-213).

[0076] Further auxiliaries and additives which may optionally be used concomitantly in the preparation of the blocked polyisocyanate component A) are also the stabilizers containing hydrazide groups and / or hydroxyl functions described in EP-A 0 829 500, for example addition products of hydrazine and propylene carbonate.

[0077] The auxiliaries and additives mentioned can optionally be used alone or in any combination with one another for the preparation of the blocked polyisocyanate component A) in amounts of 0.001 to 3.0% by weight, preferably 0.002 to 2.0% by weight, particularly preferably 0.005 to 1.0% by weight, in each case based on the total amount of the starting polyisocyanate a).

[0078] Regardless of the nature of its preparation, the blocked polyisocyanate component A) is a completely clear and transparent polyisocyanate containing isocyanurate groups blocked with secondary monoamines, or an organic solution of such a polyisocyanate which, in contrast to a similar polyisocyanate prepared with the same starting components but without the use of branched alcohols b), has no tendency to crystallize, even when stored at low temperatures for relatively long periods of time, for example for a period of 12 weeks at 15 to 25° C.

[0079] In the one-component baking system of the invention, a blocked polyisocyanate component A) is combined with at least one isocyanate-reactive binder B) having a statistical average of at least two isocyanate-reactive groups per molecule, such as hydroxyl, mercapto, amino or carboxylic acid groups.

[0080] Suitable polyols B) are, for example, the customary dihydroxy and / or polyhydroxy compounds known from polyurethane chemistry, such as polyester polyols, polyether polyols, polycarbonate polyols and / or polyacrylate polyols, or any desired mixtures of these polyols.

[0081] Suitable polyester polyols B) are, for example, those having a number-average molecular weight (calculated from functionality and hydroxyl number) of 500 to 10 000 g / mol, preferably 800 to 5000 g / mol, particularly preferably 1000 to 3000 g / mol, having a hydroxyl content of 1 to 21% by weight, preferably 2 to 18% by weight, which can be prepared in a manner known per se by reaction of polyols with insufficient amounts of polycarboxylic acids, the corresponding carboxylic anhydrides, the corresponding lower alcohol polycarboxylic esters or by reaction with lactones.

[0082] Suitable polyols for preparing the polyester polyols B) are, for example, 1,2-ethanediol, 1,2- and 1,3-propylene glycol, isomeric butanediols, pentanediol, hexanediol, heptanediol and octanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,10-decanediol, 1,12-dodecanediol, 2,2,4,4-tetramethylcyclobutane-1,3-diol (TMCD), 1,2- and 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bis(2-hydroxyethoxy)benzene, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxycyclohexyl)propane (perhydrobisphenol), 1,2,3-propanetriol, 1,2,4-butanetriol, 1,1,1-trimethylol ethane, 1,2,6-hexanetriol, 1,1,1-trimethylolpropane (TMP), bis(2-hydroxyethyl)hydroquinone, 1,2,4- and 1,3,5-trihydroxycyclohexane, 1,3,5-tris(2-hydroxyethyl)isocyanurate, 3(4),8(9)-bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane, ditrimethylolpropane, 2,2-bis(hydroxymethyl)-1,3-propanediol (pentaerythritol), 2,2,6,6-tetra(hydroxymethyl)-4-oxaheptane-1,7-diol (dipentaerythritol), mannitol or sorbitol, low molecular weight ether alcohols, for example diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol or dibutylene glycol, or low molecular weight ester alcohols, for example neopentyl glycol hydroxypivalate, or mixtures of at least two such alcohols.

[0083] Suitable carboxylic acids or carboxylic acid derivatives for preparing the polyester polyols B) used in the one-component baking systems according to the invention are polycarboxylic acids, their carboxylic anhydrides and polycarboxylic acid esters of lower alcohols. These are any aromatic, aliphatic or cycloaliphatic, saturated or unsaturated dicarboxylic and tricarboxylic acids or their anhydrides, in particular those having 4 to 18 carbon atoms, preferably 4 to 10 carbon atoms, for example succinic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, tetrahydrophthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic anhydride, dimethyl terephthalate and diethylene glycol terephthalate, and also dimerized and trimerized fatty acids, which can be used both individually and in any desired mixtures with one another.

[0084] It is also possible, if appropriate, to concomitantly use small amounts of monocarboxylic acids, such as benzoic acid, acetic acid, propionic acid, butyric acid or 2-ethylhexanoic acid, for the preparation of the polyester polyols B).

[0085] The polyester polyols B) suitable for the one-component baking systems of the invention are also those which can be prepared in a manner known per se from lactones and polyols (such as those listed above by way of example) as starter molecules under ring opening. Suitable lactones for preparing these polyester polyols B) are, for example, β-propiolactone, γ-butyrolactone, γ- and δ-valerolactone, ε-caprolactone, 3,5,5- and 3,3,5-trimethylcaprolactone or any mixtures of these lactones.

[0086] The preparation of these lactone polyesters is generally carried out in the presence of catalysts, such as Lewis acids or Bronsted acids, organotin or titanium compounds, at temperatures of 20 to 200° C., preferably 50 to 160° C. Suitable building blocks for the preparation of these polyester polyols B) are, for example, the polyols, polycarboxylic acids and derivatives thereof which are described above as being suitable for the preparation of the polyester polyols B), which can also be used in the form of any desired mixtures.

[0087] The preparation of polyester polyol B) can be carried out according to methods known per se, for example as described in detail in E. Gubbels et al., Polyesters., Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA; 2018. URL: https: / / doi.org / 10.1002 / 14356007.a21_227.pub2. Optionally, a catalytic amount of a conventional esterification catalyst, such as an acid, a base or a transition metal compound, such as titanium tetrabutoxide, can be used. The esterification reaction is usually carried out in a temperature range of about 80 to 260° C., preferably 100 to 230° C., until the desired hydroxyl value and acid value are reached.

[0088] Suitable polyether polyols B) are, for example, those having an average molecular weight (calculated based on functionality and hydroxyl number) of 200 to 6000, preferably 250 to 4000, and a hydroxyl content of 0.6 to 34% by weight, preferably 1 to 27% by weight, which are obtainable in a known manner by alkoxylation of suitable starter molecules. For the preparation of these polyether polyols, any polyols (as described above as being suitable for the production of the polyester polyols B)) can be used as starter molecules.

[0089] Alkylene oxides suitable for the alkoxylation are, in particular, ethylene oxide and propylene oxide, which can be used in any sequence or in a mixture.

[0090] Suitable polycarbonate polyols B) are in particular the reaction products of diols known per se (e.g. those mentioned by way of example in the above polyol list) with diaryl carbonates (e.g. diphenyl carbonate, dimethyl carbonate or phosgene). Suitable polycarbonate polyols B) are also those which contain ester groups in addition to the carbonate structure. These are in particular polyester carbonate diols known per se, which can be obtained, for example, according to the teaching of DE-AS 1770245, by reaction of diols with lactones (e.g. in particular ε-caprolactone) and subsequent reaction of the resulting polyester diols with diphenyl carbonate or dimethyl carbonate. Likewise suitable polycarbonate polyols B) are those which contain ether groups in addition to the carbonate structure. These are in particular polyether carbonate polyols known per se, which can be obtained, for example, by the method of EP-A 2046861 by catalytic reaction of alkylene oxides (epoxides) and carbon dioxide in the presence of H-functional starter substances.

[0091] Suitable polyacrylate polyols B) are, for example, those having an average molecular weight (calculated from functionality and hydroxyl number or determinable by gel permeation chromatography (GPC)) of 800 to 50 000, preferably 1 000 to 20 000, and a hydroxyl content of 0.1 to 12% by weight, preferably 1 to 10% by weight, which can be prepared in a manner known per se by copolymerizing hydroxyl-containing ethylenically unsaturated monomers with hydroxyl-free ethylenic monomers.

[0092] Examples of suitable monomers for preparing the polyacrylate polyols B) are vinyl or vinylidene monomers, for example styrene, α-methylstyrene, o- or p-chlorostyrene, o-, m- or p-methylstyrene, p-tert-butylstyrene, acrylic acid, acrylonitrile, methacrylonitrile, acrylic and methacrylic esters of alcohols having up to 18 carbon atoms, for example methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, 3,3,5-trimethylhexyl acrylate, stearyl acrylate, lauryl acrylate, cyclopentyl acrylate, cyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, methyl methacrylate, amyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, 3,3,5-trimethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, 4-tert-butylcyclohexyl methacrylate, norbornyl methacrylate or isobornyl methacrylate, diesters of fumaric acid, itaconic acid or maleic acid with alcohols having 4 to 8 carbon atoms, acrylamide, methacrylamide, vinyl esters of alkanemonocarboxylic acids having 2 to 5 carbon atoms, for example vinyl acetate or vinyl propionate, hydroxyalkyl esters of acrylic acid or methacrylic acid having 2 to 5 carbon atoms in the hydroxyalkyl group; for example 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 3-hydroxybutyl, 4-hydroxybutyl acrylic acid or methacrylate, trimethylolpropane mono- or pentaerythritol mono-acrylate or methacrylate, and any mixtures of these monomers mentioned by way of example.

[0093] Preferred adhesive components B) are polyester polyols and polyacrylate polyols of the type mentioned. Very particular preference is given to the polyester polyols mentioned.

[0094] In the preparation of the one-component baking system of the invention, the polyisocyanate component A) and the binder component B) are preferably used in such an amount that the equivalent ratio of the sum of blocked and unblocked isocyanate groups from A) to the isocyanate-reactive groups from B) is from 0.5:1 to 1.5:1, particularly preferably from 0.7:1 to 1.3:1, very particularly preferably from 0.8:1 to 1.2:1.

[0095] The one-component stoving system according to the invention may optionally contain catalysts C). These catalysts are in particular the urethanization catalysts customary in isocyanate chemistry which have been described above as suitable for accelerating the reaction of the polyisocyanate component a) with the diol component c) and the amine component c). These catalysts C) are used in the one-component stoving system according to the invention as individual substances or in any mixture with one another in an amount of 0.005% to 5% by weight, preferably 0.005% to 2% by weight, particularly preferably 0.005% to 1% by weight, calculated as the sum of all catalysts C) used and based on the total amount of solvent-free blocked polyisocyanate A) and solvent-free binder component B).

[0096] The one-component baking systems according to the invention may also optionally contain further auxiliaries and additives D). In addition to the above-mentioned antioxidants and light stabilizers which are optionally used simultaneously in the process according to the invention, they also include, for example, customary plasticizers, leveling agents, rheological additives, slip additives, defoamers, fillers and / or pigments known to the person skilled in the art and, if used, in the amounts customary in coating technology. A comprehensive overview of these suitable auxiliaries and additives can be found, for example, in Bodo Müller, "Additive kompakt", Vincentz Network GmbH & Co KG (2009).

[0097] The one-component baking system of the invention may optionally contain other compounds reactive toward isocyanate-reactive groups as additional crosslinker components. These compounds are, for example, compounds containing epoxy groups and / or aminoplast resins. Aminoplast resins are condensation products of melamine and formaldehyde or urea and formaldehyde known in coating technology.

[0098] All customary melamine-formaldehyde condensates which are not etherified or which have been etherified with saturated monohydric alcohols having 1 to 4 carbon atoms are suitable. In the case of simultaneous use of further crosslinker components, the amount of binder having isocyanate-reactive groups must be adjusted accordingly.

[0099] The present invention further provides a process for preparing the one-component stoving system of the invention by mixing a blocked polyisocyanate component A) with a binder component B), optionally with the simultaneous use of a catalyst C) which accelerates the crosslinking reaction, and optionally a solvent and / or optionally auxiliaries and additives D).

[0100] The mixing of components A) to D) must be carried out at a temperature that cleaves the blocking agent, since the release of isocyanate groups can lead to premature crosslinking of the coating system. Preferably, the preparation of the one-component baking system of the invention is carried out at a temperature of 15 to 100°C.

[0101] The one-component baking systems of the invention are valuable starting materials for the preparation of polyurethane plastics according to the isocyanate polyaddition process. They are very suitable for heat-curing solvent-borne or water-borne paint systems, in particular for plastics painting, automotive first painting or coil coating applications. They provide coatings that have very good yellowing resistance even under overbaking conditions.

[0102] A further subject matter of the present invention is therefore the use of the one-component baking system according to the invention for coating substrates.

[0103] Finally, a substrate at least partially coated with at least one cured one-component baking system according to the invention is also a further subject of the present invention.

[0104] The one-component stoving systems of the invention can be applied by methods known per se, for example by spraying, brushing, dipping, flow coating or by means of a roller or doctor blade in one or more layers.

[0105] Substrates are any substrates, for example metal, wood, glass, stone, ceramic materials, composite materials of all types or plastics, which before coating may optionally also be provided with conventionally known primers, surfacers, basecoats and / or clearcoats.

[0106] Curing of the dry film is carried out by baking at a temperature range of 90 to 160° C., preferably 110 to 140° C. The layer thickness of the dry film here can be, for example, 10 to 120 μm.

[0107] The one-component stoving systems of the invention can also be used for continuous strip coating (coil coating), wherein maximum stoving temperatures (known to those skilled in the art as peak metal temperatures) of 130 to 300° C., preferably 190 to 260° C. and dry film thicknesses of, for example, 3 to 40 μm can be achieved.

[0108] The features specified as being preferred for the method according to the invention are also preferred for the further subject matter of the invention.

[0109] The following examples are used to illustrate the present invention, but should not be construed as any limitation to the scope of protection. Example

[0110] Unless stated otherwise, all percentage data refer to weight.

[0111] The NCO content was determined titrimetrically according to DIN EN ISO 11909:2007-05. The progress of the blocking reaction and the NCO freeness of the blocked polyisocyanate were determined by the isocyanate band (approx. 2270 cm -1 ) to track the reduction or disappearance of

[0112] The residual monomer content is measured according to DIN EN ISO 10283:2007-11 using gas chromatography with internal standard.

[0113] All viscosity measurements were performed using a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) according to DIN EN ISO 3219:1994-10 at a shear rate of 250 s -1 Next proceed.

[0114] The platinum-cobalt color values ​​were measured spectrophotometrically using a LICO 400 spectrophotometer from Lange, Germany, according to DIN EN ISO 6271-2:2005-03.

[0115] The pendulum damping is determined according to DIN EN ISO 1522:2007-04.

[0116] The T-bend test was performed according to NEN-EN 13523-7:2014.

[0117] Pencil hardness is measured according to NEN-EN 13523-4:2014.

[0118] Gloss measurement was performed according to NEN-EN 13523-2:2014, ISO 2813.

[0119] The MEK double rub test was conducted according to ASTM-D 7835. The visually evaluated paint film damage after 100 double rubs was shown as 100 / 1 (substrate visible, paint film severely damaged) to 100 / 5 (paint film without damage).

[0120] The measurement of the baking yellowing Δb is carried out as a color measurement in accordance with NEN-EN 13523-3:2021.

[0121] The content (mol %) of uretdione, optionally isocyanurate and / or iminooxadiazinedione structures present in the polyisocyanate a) is calculated from the integration of the proton decoupled 13C-NMR spectrum (carried out on a Bruker DPX-400 instrument) and refers in each case to the sum of the uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and / or oxadiazinetriaone structures present. For the HDI polyisocyanate dissolved in CDCl3, the individual structural units exhibit the following chemical shifts (in ppm): uretdione: 157.1; isocyanurate: 148.4; iminooxadiazinedione: 147.8, 144.3 and 135.3; allophanate: 155.7 and 153.8, biuret: 155.5; urethane: 156.3; oxadiazinedione: 147.8 and 143.9.

[0122] Chemicals and starting compounds

[0123] Uralac SN844 S2G3-60ND, saturated polyester polyol, OH value: 30-35 mg KOH / g (DSM coating resin)

[0124] 1-Methoxypropyl-2-acetate (MPA) (Azelis Deutschland GmbH)

[0125] Isobutanol (abcr GmbH)

[0126] Diisopropylamine (Sigma Aldrich, Germany)

[0127] Diethyl Malonate (Acros Organics)

[0128] 2-Butyl-2-ethyl-1,3-propanediol (BEPD) (Sigma Aldrich, Germany)

[0129] Sodium methoxide solution (Acros Organics)

[0130] Solvent Naphtha 150ND(S150ND)(DHC Solvent Chemie GmbH)

[0131] Butyl glycol (Brenntag GmbH)

[0132] Kronos 2360(titanium dioxide)(Kronos International Inc.)

[0133] Dibutyltin dilaurate (DBTL)(DB Becker Co Inc.)

[0134] Urad dd27 ND; acrylate-based surface additive (Synres BV)

[0135] Polyisocyanatea)

[0136] Starting polyisocyanate A1)

[0137] Polyisocyanate prepared by catalytic trimerization of HDI according to Example 11 of EP-A 330966, except that the reaction was terminated by adding dibutyl phosphate at an NCO content of 40% of the crude mixture. Subsequently, unconverted HDI was separated off by thin-film distillation at a temperature of 130° C. and a pressure of 0.2 mbar.

[0138] The product has the following characteristic values ​​and composition:

[0139]

[0140] Example 1 (Comparative Example)

[0141] 289 g (1.50 equivalents) of the starting polyisocyanate A1 containing isocyanurate structures were pre-charged at a temperature of 50° C. under stirring and dry nitrogen, and 151.8 g (1.50 equivalents) of diisopropylamine were added over a period of 2 hours. After the amine addition was complete, the reaction mixture was diluted with 188.9 g of 1-methoxyprop-2-yl acetate (MPA) and stirred at 50° C. for a further hour until the isocyanate groups had reacted completely (infrared examination, at about 2270 cm -1 There is a colorless solution of amine-blocked HDI polyisocyanurate polyisocyanate with the following characteristic values:

[0142]

[0143]

[0144] After cooling to room temperature, the solution became turbid after one day and completely crystallized after five days.

[0145] Example 2 (Comparative Example)

[0146] 250.5 g (1.30 equivalents) of the starting polyisocyanate A1) containing an isocyanurate structure and 52 g (0.325 equivalents) of diethyl malonate were pre-loaded at a temperature of 50 ° C. Subsequently, a mixture of 52 g (0.325 equivalents) of diethyl malonate and 1.3 g of a 0.2 wt % sodium methoxide solution was added dropwise over a period of 15 minutes, the temperature was raised to 70 ° C and stirring was continued until the NCO content reached 7.7%. In order to reduce the increasing viscosity, 180.6 g of MPA was added as a solvent and the mixture was cooled to 40 ° C. Subsequently, 65.7 g (0.65 equivalents) of diisopropylamine were added dropwise over a period of 25 minutes. After the amine addition was completed, the reaction mixture was stirred at 50 ° C for another 2 hours until the isocyanate groups were completely reacted. A colorless, transparent solution with the following characteristic values ​​was present:

[0147]

[0148] After 12 weeks of storage at room temperature, the solution remained completely clear. No turbidity, solid precipitation or crystallization was observed.

[0149] Example 3 (The present invention)

[0150] 770 g (4.00 equivalents) of the starting polyisocyanate A1) containing isocyanurate structures were pre-charged at a temperature of 70° C. under stirring and dry nitrogen, 49 g (0.62 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD) were added over 15 minutes, corresponding to an amount of 6.0% by weight based on the total amount of polyisocyanate and branched diols, and stirring was continued until an NCO content of 17.3% corresponding to complete urethanization was reached. The reaction mixture was cooled to 50° C. and 344 g (3.41 equivalents) of diisopropylamine were added dropwise over a period of 4 hours. In order to reduce the viscosity that increased significantly during the blocking reaction, a total of 242 g of MPA were added in several separate portions over the entire metering time. After the amine addition was complete, the reaction mixture was stirred at 50° C. for a further hour until the isocyanate groups had reacted completely (infrared check). The product was then diluted with a further 242 g of isobutanol. There is a colorless, transparent solution of the amine-blocked HDI polyisocyanurate polyisocyanate of the invention having the following characteristic values:

[0151]

[0152] After 12 weeks of storage at room temperature, the solution remained completely clear. No turbidity, solid precipitation or crystallization was observed.

[0153] Example 4 (The present invention)

[0154] 770 g (4.00 equivalents) of the starting polyisocyanate A1 containing an isocyanurate structure were pre-loaded at a temperature of 70 ° C under stirring and dry nitrogen, 58 g (0.73 equivalents) of BEPD were added within 15 minutes, corresponding to an amount of 7.0% by weight based on the total amount of polyisocyanate and branched diols, and stirring was continued until an NCO content of 16.9% corresponding to complete urethanization was reached. The reaction mixture was cooled to 50 ° C and 337 g (3.34 equivalents) of diisopropylamine were added dropwise over a period of 4 hours. In order to reduce the viscosity that increased significantly during the blocking reaction, a total of 250 g of MPA was added in multiple separate portions over the entire metering time. After the amine addition was completed, the reaction mixture was stirred at 50 ° C for another hour until the isocyanate groups were completely reacted (infrared inspection). The product was then diluted with another 250 g of isobutanol. There was a colorless, transparent solution of the amine-blocked HDI polyisocyanurate polyisocyanate of the present invention having the following characteristic values:

[0155]

[0156] After 12 weeks of storage at room temperature, the solution remained completely clear. No turbidity, solid precipitation or crystallization was observed.

[0157] Examples 5 to 7 (The present invention and comparative example)

[0158] A white basecoat was formulated using the commercial polyester polyol Uralac SN844 S2G3-60ND and the amine-blocked HDI polyisocyanurate polyisocyanates according to the invention of Examples 3 and 4 and the mixed blocked HDI polyisocyanurate polyisocyanate of Comparative Example 2 in an NCO:OH equivalent ratio of 1:1, which was applied to an aluminum substrate by means of a doctor blade and baked at a peak metal temperature of 216° C. or 241° C. The layer thickness was 22 μm in all cases.

[0159] Table 1 below shows the composition by weight of the paint formulation; Tables 2 and 3 show the paint layer technical properties of the coatings obtained under different baking conditions.

[0160] Table 1 :Composition of paint formula

[0161]

[0162] Table 2 :Paint performance at peak metal temperature 216℃ and furnace temperature 330℃

[0163]

[0164]

[0165] Table 3:Paint performance at peak metal temperature 241°C and furnace temperature 330°C

[0166]

[0167] The examples show that the coatings obtained by using the coatings of the invention (Examples 5 and 6), in particular the coating of Example 5 based on the blocked polyisocyanate of Example 3, exhibit improved properties in terms of thermal stability and physical properties compared to the coating of Example 7. In particular, the use of the coating compositions of Examples 5 and 6 can significantly reduce the yellowing tendency.

Claims

1. Single component baking system, which includes A) a blocked polyisocyanate component comprising the reaction product of at least one of the following components a) at least one polyisocyanate component having at least an isocyanurate and / or an iminooxadiazinedione structure, and b) at least one branched aliphatic diol and c) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents, wherein component b) is used in an amount of more than 2% by weight, based on the total amount of components a) and b), and component c) is used in an amount corresponding to at least 95 mol % of the isocyanate groups still present after the reaction of components a) and b), B) at least one binder reactive toward isocyanate groups having a statistical average of at least two isocyanate-reactive groups per molecule, C) optionally a catalyst, and D) Optional solvents and / or optional auxiliaries and additives.

2. The one-component baking system according to claim 1, characterized in that: As polyisocyanate component a), polyisocyanates which have been prepared by simple modification of linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates and have at least isocyanurate and / or iminooxadiazinedione structures are used to prepare blocked polyisocyanate component A), wherein in each case >70 equivalents, preferably >80 equivalents, particularly preferably >90 equivalents and very particularly preferably exclusively linear aliphatic diisocyanates are used for the modification, based on the NCO content.

3. The one-component baking system according to any one of claims 1 and 2, characterized in that To prepare the blocked polyisocyanate component A), polyisocyanates which are prepared by modification of linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, and which have at least isocyanurate and / or iminooxadiazinedione structures and have an average NCO functionality of 2.3 to 5.0, preferably 2.5 to 4.5, and an isocyanate group content of 6.0 to 26.0% by weight, preferably 8.0 to 25.0% by weight, particularly preferably 10.0 to 24.0% by weight, are used as polyisocyanate component a).

4. The one-component baking system according to any one of claims 1 to 3, characterized in that: To prepare the blocked polyisocyanate component A), at least one branched aliphatic diol having 3 to 36, preferably 4 to 12, carbon atoms is used as diol component b) in an amount of 3 to 20% by weight, preferably 4 to 15% by weight, particularly preferably 5 to 12% by weight, based on the total amount of components a) and b).

5. The one-component baking system according to any one of claims 1 to 4, characterized in that: As diol component b), 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-dibutyl-1,3-propanediol, 2,2,4-trimethyl-1,5-pentanediol and 2,2,4- and / or 2,4,4-trimethylhexanediol or any mixtures of these alcohols are used to prepare the blocked polyisocyanate component A).

6. The one-component baking system according to any one of claims 1 to 5, characterized in that: Use of at least one secondary amine of the general formula (I) as blocking agent c) for the preparation of a blocked polyisocyanate component A) wherein R and R' are independently identical or different radicals, and denote a saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic or araliphatic organic radical having 1 to 18 carbon atoms, which is substituted or unsubstituted and / or has oxygen atoms in the chain, wherein R and R' can also form, in combination with one another, together with a nitrogen atom and optionally with further oxygen atoms, a heterocyclic ring having 5 to 8 ring members, which can optionally be further substituted, and preferably denote identical or different, saturated, linear or branched aliphatic radicals having 1 to 18, particularly preferably 1 to 6, carbon atoms, or alicyclic hydrocarbon radicals having 6 to 13, particularly preferably 6 to 9 carbon atoms, wherein R and R' can optionally also form, in combination with one another, together with a nitrogen atom and optionally with further oxygen atoms, a heterocyclic ring having 5 to 6 ring members, which can optionally be further substituted.

7. The one-component baking system according to any one of claims 1 to 6, characterized in that: Diisopropylamine, dicyclohexylamine, N-tert-butylbenzylamine or any mixtures of these amines are used as blocking agents c) for preparing the blocked polyisocyanate component A).

8. The one-component baking system according to any one of claims 1 to 7, characterized in that: To prepare the blocked polyisocyanate component A), at least one secondary amine is used as blocking agent c) in an amount corresponding to at least 96 mol %, preferably at least 98 mol %, particularly preferably at least 100 mol % of the isocyanate groups still present after the reaction of components a) and b).

9. The one-component baking system according to any one of claims 1 to 8, characterized in that: To prepare the blocked polyisocyanate component A), the polyisocyanate component a) is reacted with the diol component b) and the amine component c) in any order, optionally in the presence of a suitable solvent, at temperatures of 0 to 120° C., preferably 20 to 100° C., particularly preferably 40 to 80° C.

10. The one-component baking system according to any one of claims 1 to 9, characterized in that: As binder component B), polyester polyols, polyether polyols, polycarbonate polyols and / or polyacrylate polyols or any mixtures of these polyols, preferably polyester polyols and / or polyacrylate polyols, particularly preferably polyester polyols are used in such an amount that the equivalent ratio of the sum of blocked and unblocked isocyanate groups of the polyisocyanate component A) to the isocyanate-reactive groups of the binder component B) is from 0.5:1 to 1.5:1, particularly preferably from 0.7:1 to 1.3:1, very particularly preferably from 0.8:1 to 1.2:

1.

11. Method for producing a one-component baking system according to any one of claims 1 to 10, characterized in that The blocked polyisocyanate component A) is mixed with the adhesive component B), optionally with the use of a catalyst C) which accelerates the crosslinking reaction, and optionally a solvent and / or optionally auxiliaries and additives D), at a temperature below the deblocking temperature of component A), preferably at a temperature of 15 to 100° C.

12. Use of the one-component baking system according to any one of claims 1 to 10 as a heat-curing solvent-borne or water-borne coating system.

13. Use of the one-component baking system according to any one of claims 1 to 10, characterized in that The curing by baking is performed at a temperature ranging from 90 to 160°C, preferably from 110 to 140°C.

14. Use of a one-component stoving system according to any one of claims 1 to 10 in coil coating applications with a peak metal temperature of 130 to 300°C, preferably 190 to 260°C.

15. A substrate at least partially coated with at least one cured one-component baking system according to any one of claims 1 to 10.

Images