Blocked polyisocyanates

Abstract

The invention relates to a method for producing blocked polyisocyanates, comprising reacting A) at least one polyisocyanate component having at least an isocyanurate and / or iminooxadiazindione structure with B) at least one branched aliphatic diol and with C) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents, the invention is characterized in that the amount of component B) is greater than 2% by weight, based on the total amount of components A) and B), and that 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 using, as the polyisocyanate component A), a polyisocyanate which is produced by simple modification of linear aliphatic, alicyclic, araliphatic and / or aromatic diisocyanates and has at least an isocyanurate and / or iminooxadiazindione structure, wherein gt; gt; gt; gt; gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt, gt; 70 equivalents% for modification, and to blocked polyisocyanates.

Description

[0001] Blocked polyisocyanates, which can be obtained by reacting isocyanate groups with so-called blocking agents, have long been known. They can be combined with polyols to produce storage-stable mixtures at room temperature. At higher temperatures, the blocking agents cleave again, releasing the isocyanate groups for crosslinking with the polyol component.

[0002] Such blocked polyisocyanates are used as crosslinker components for one-component polyurethane stoving varnishes (1K-PUR) and are used, for example, for automotive first coating, plastic coating and coil coating. The type of sealant used here is very important. For example, reactivity, thermal yellowing and other paint properties are mainly 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 particularly interesting as blocking agents because they achieve particularly low baking temperatures. However, 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 important both technically and economically have not been practical so far 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 show 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 insufficient amounts of low molecular weight polyhydroxy compounds before blocking. This publication does not allow any conclusions to be drawn about the storage stability of polyisocyanates blocked with secondary amines.

[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 diisocyanates, nor any suggestions about 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 its isocyanate groups 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 crystal-stable, exclusively amine-blocked polyisocyanate crosslinkers is to react a specific mixture of linear aliphatic and cycloaliphatic polyisocyanates with secondary amines, according to the teaching of EP-A 0 900 814. However, the coatings produced using such polyisocyanates have a significantly different property profile and are likewise not generally applicable.

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

[0015] It has now surprisingly 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 produce completely set-stable, non-crystalline blocked polyisocyanate crosslinkers. These novel amine-blocked polyisocyanates are particularly suitable for coil coating applications.

[0016] The subject of the present invention is a process for producing blocked polyisocyanates, which comprises reacting the following components:

[0017] A) at least one polyisocyanate component having at least an isocyanurate and / or an iminooxadiazinedione structure, and

[0018] B) at least one branched aliphatic diol and

[0019] C) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents,

[0020] Characterized in that the amount of component B) used is greater than 2% by weight, based on the total amount of components A) and B), the amount of component C) used corresponds to at least 95 mol % of the isocyanate groups still present after the reaction of components A) and B), and that polyisocyanates prepared by simple modification of linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates and having at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component A), with >70 equivalent % of linear aliphatic diisocyanates, based on the NCO content, being used for the modification.

[0021] 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.

[0022] 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.

[0023] Numerical values ​​shown herein without decimal places refer in each case to the full indicated value with one decimal place. For example, "99%" stands for "99.0%". Numerical ranges shown in the format "x to y" include the values. If multiple preferred numerical ranges are shown in this format, of course all ranges resulting from combinations of the individual endpoints are also covered.

[0024] The term "aliphatic" is defined herein as a saturated or unsaturated non-aromatic hydrocarbon group.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The starting compounds A) used in the process according to the invention are any 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.

[0030] 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) pages 75-136.

[0031] 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 >80 equivalents, particularly preferably >90 equivalents, in each case based on the NCO content, and very particularly preferably exclusively linear aliphatic diisocyanates being used for the modification.

[0032] In a further preferred embodiment, polyisocyanates prepared by modification of linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, and having at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component A).

[0033] 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.

[0034] Also preferred is a process for producing a blocked polyisocyanate comprising reacting:

[0035] A) at least one substantially linear aliphatic polyisocyanate component having at least an isocyanurate and / or an iminooxadiazinedione structure, and

[0036] B) at least one branched aliphatic diol and

[0037] C) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents,

[0038] The invention is characterized in that 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 still present after the reaction of components A) and B).

[0039] According to this preferred embodiment, the polyisocyanate component A) is at least one substantially linear aliphatic polyisocyanate component. 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.

[0040] The starting polyisocyanates A) having at least an isocyanurate and / or an iminooxadiazinedione structure used in the process according to the invention are prepared in a manner known per se by modification, in particular catalytic trimerization, of the aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates mentioned. 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.

[0041] 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.

[0042] In the process of the invention, the starting polyisocyanate A) used preferably comprises polyisocyanates 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.

[0043] 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.

[0044] In the process of the invention, a polyisocyanate component A) having at least an isocyanurate and / or iminooxadiazinedione structure is reacted with at least one branched aliphatic diol B).

[0045] 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.

[0046] In another preferred embodiment, the at least one branched aliphatic diol has 3 to 36 carbon atoms. Examples include simple diols such as 1,2-propylene glycol, 1,3-butanediol, 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.

[0047] In another preferred embodiment, the at least one branched aliphatic diol has 4 to 12 carbon atoms. Particularly preferred are 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.

[0048] The amount of branched aliphatic diol B) used in the process of the invention is greater than 2% by weight, preferably 3% to 20% by weight, particularly preferably 4% to 15% by weight, 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 blocked polyisocyanates; the use of more than 20% by weight leads to very high product viscosities, which are uneconomical in practical use due to the low isocyanate content.

[0049] Besides the branched aliphatic diols mentioned, component B) may optionally contain small amounts of other alcohol compounds.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In the process according to the invention, at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents is used as blocking agent C).

[0054] These are in particular secondary amines of the general formula (I)

[0055]

[0056] 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.

[0057] 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 optionally also 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.

[0058] Secondary amines C) suitable for the process according to the invention 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.

[0059] 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.

[0060] The secondary amine C) is preferably diisopropylamine, dicyclohexylamine, N-tert-butylbenzylamine or any mixtures of these amines. Particular preference is given to diisopropylamine.

[0061] In the process of the invention, 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).

[0062] The process according to the invention can also optionally be used simultaneously with suitable solvents for isocyanate groups. Suitable solvents are, for example, customary paint 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 those known under the names solvent naphtha, (Deutsche EXXON CHEMICAL GmbH, 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-methylpyrrolidone, N-butylpyrrolidone and N-methylcaprolactam, or any mixtures of these solvents.

[0063] To carry out the process according to the invention, the polyisocyanate component A) is reacted with the diol component B) and the amine component C) in any order and in the quantitative ratios mentioned above, 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.

[0064] 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.

[0065] In the process of the present invention, 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, it is also possible to simultaneously use customary urethanization catalysts known in polyurethane chemistry, for example tertiary amines 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] After the reaction of the polyisocyanate component A) with the diol component B) and the amine component C), the blocked polyisocyanate 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.

[0070] In the process according to the invention, 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] Further auxiliaries and additives which may optionally be used concomitantly in the process according to the invention 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.

[0076] The auxiliaries and additives mentioned can optionally be used in the process according to the invention alone or in any combination with one another 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 starting polyisocyanate A).

[0077] Irrespective of the nature of the process mode, the process according to the invention provides completely clear and transparent polyisocyanates containing isocyanurate groups blocked with secondary monoamines, or organic solutions of such polyisocyanates which, in contrast to similar polyisocyanates prepared using the same starting components but with partial urethanization without the use of branched alcohols, have no tendency to crystallize, even when stored at low temperatures for extended periods of time, for example at 15 to 25° C. for a period of 12 weeks.

[0078] A further subject of the present invention is therefore a blocked polyisocyanate component obtainable or obtainable by the process according to the invention.

[0079] The invention further provides for the use of more than 2% by weight, based on the total amount of components A) and B), of at least one branched aliphatic diol B) for stabilizing aliphatic polyisocyanates blocked with at least one secondary amine C).

[0080] The blocked polyisocyanates of the invention are valuable starting materials for the production of polyurethane plastics by the isocyanate polyaddition process. They are very suitable as crosslinker components for one-component heat-curing solvent-borne or water-borne coating systems, which are used 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.

[0081] Therefore, another subject of the present invention is a one-component baking system comprising

[0082] a) at least one blocked polyisocyanate according to the invention,

[0083] b) at least one binder which is reactive toward isocyanate groups and has a statistical average of at least two isocyanate-reactive groups per molecule,

[0084] c) optionally a catalyst, and

[0085] d) optional solvents and / or optional auxiliaries and additives.

[0086] 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 matter of the present invention.

[0087] To produce the one-component stoving systems (1K stoving varnishes) of the invention, the blocked polyisocyanates a) of the invention are mixed with the coating binders b) known per se from coating technology, optionally with the simultaneous use of catalysts c) which accelerate the crosslinking reaction, and optionally solvents and / or optional auxiliaries and additives d). This mixing must be carried out at a temperature at which the blocking agent breaks down, since the release of isocyanate groups would lead to premature crosslinking of the coating system. Preferably, the production of the one-component stoving systems of the invention is carried out at temperatures of 15 to 100° C.

[0088] As binder component b), the one-component baking system according to the invention contains at least one binder which is reactive toward isocyanate groups and has a statistical average of at least two isocyanate-reactive groups per molecule, for example hydroxyl, mercapto, amino or carboxylic acid groups.

[0089] Preferably, these binders b) are the customary dihydroxy and / or polyhydroxy compounds known from polyurethane chemistry, for example polyester polyols, polyether polyols, polycarbonate polyols and / or polyacrylate polyols, or any desired mixtures of these polyols.

[0090] 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.

[0091] 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.

[0092] 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 A), 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.

[0093] 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.

[0094] 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).

[0095] 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.

[0096] 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 mentioned above for the preparation of the polyester polyols b), which can also be used in the form of any desired mixtures.

[0097] 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.

[0098] 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 polyester polyols b)) can be used as starter molecules.

[0099] 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.

[0100] Suitable polycarbonate polyols b) are especially 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 especially polyester carbonate diols known per se, which can be obtained, for example, according to the teaching of DE-AS 1770245, by the reaction of diols with lactones (e.g., in particular ε-caprolactone) and the 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 especially 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.

[0101] 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.

[0102] Examples of monomers suitable for preparing the polyacrylate polyols b) are vinyl or vinylidene monomers, such as 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, such as 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.

[0103] 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 B) 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).

[0104] 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 may 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 such suitable auxiliaries and additives can be found, for example, in Bodo Müller, "Additive kompakt", Vincentz Network GmbH & Co KG (2009).

[0105] When producing the one-component baking system of the present invention, the amount of polyisocyanate component a) and adhesive component b) used is preferably such that the equivalent ratio of the sum of blocked and unblocked isocyanate groups from a) to the isocyanate-reactive groups from b) is 0.5:1 to 1.5:1, more preferably 0.7:1 to 1.3:1, and particularly preferably 0.8:1 to 1.2:1.

[0106] 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.

[0107] 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.

[0108] The one-component stoving systems of the invention thus obtained 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.

[0109] 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.

[0110] 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.

[0111] The one-component baking system of the invention can also be used for continuous strip coating, wherein maximum baking 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.

[0112] The features specified as being preferred for the method according to the invention are also preferred for the further subject matter of the invention.

[0113] The following examples are used to illustrate the present invention, but should not be construed as any limitation to the scope of protection. Example

[0114] Unless stated otherwise, all percentage data refer to weight.

[0115] 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

[0116] 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.

[0117] The residual monomer content is measured according to DIN EN ISO 10283:2007-11 using gas chromatography with internal standard.

[0118] 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.

[0119] 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 (recorded on a Bruker DPX-400 instrument) and is in each case based on the sum of the uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and / or oxadiazinedione 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.

[0120] Starting compound

[0121] Polyisocyanate A)

[0122] Starting polyisocyanate A1)

[0123] 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.

[0124] The product has the following characteristic values ​​and composition:

[0125]

[0126] Starting polyisocyanate A2)

[0127] Polyisocyanates prepared by trimerization of HDI according to Example 2a of WO 2018 / 153801, using a 20% solution of 5-azonia-spiro[4.5]decane hydrodifluoride in 2-ethylhexanol as catalyst, the reaction being terminated at an NCO content of the crude mixture of 44.8% by adding a 70% solution of dodecylbenzenesulfonic acid in isopropanol in an amount equivalent to the amount of the catalyst, and unconverted HDI being separated off by thin-film distillation at a temperature of 130° C. and a pressure of 0.2 mbar.

[0128] The product has the following characteristic values ​​and composition:

[0129]

[0130] Starting polyisocyanate A3)

[0131] PDI polyisocyanate containing isocyanurate groups, prepared by catalytic trimerization of PDI by the method described in WO 2016 / 146579 for the polyisocyanate component A2). At an NCO content of 36.7% of the crude mixture, the reaction was deactivated by adding an equimolar amount of dibutyl phosphate (based on the amount of catalyst used) and stirring for a further 30 minutes at 80°C. Subsequently, the unconverted PDI was separated off by thin film distillation at a temperature of 140°C and a pressure of 0.5 mbar.

[0132]

[0133] Example 1 (Comparative Example)

[0134] 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:

[0135]

[0136] After cooling to room temperature, the solution became turbid after one day and completely crystallized after five days.

[0137] Example 2 (The present invention)

[0138] 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, 58 g (0.73 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD) were added over 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 1-methoxyprop-2-yl acetate (MPA) was 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 250 g of isobutanol. There is a colorless, transparent solution of the amine-blocked HDI polyisocyanurate polyisocyanate of the invention having the following characteristic values:

[0139]

[0140] After 12 weeks of storage at room temperature, the solution remained completely transparent. No turbidity, solid precipitation or crystallization was observed.

[0141] Examples 3 to 11 (The present invention and comparative example)

[0142] Blocked polyisocyanates were prepared according to the process described in Example 2 starting from different polyisocyanates by urethanization with different branched diols and diisopropylamine, wherein in each case the entire amount of solvent was precharged together with the polyisocyanate component before the start of the reaction.

[0143] The table below shows the composition (expressed in % by weight), characteristic values ​​and storage stability of the products obtained after storage at room temperature for 4 weeks.

[0144]

[0145] Examples 2, 3, 4, 6, 7, 9 and 11 of the invention show that polyisocyanates containing isocyanurate and iminooxadiazinedione structures and which have been partially urethanized with more than 2% by weight of branched aliphatic diols, based on the total amount of polyisocyanate and diol, can be reacted with secondary amines such as diisopropylamine to form transparent blocked polyisocyanate crosslinkers which are completely storage-stable over a period of 4 weeks and have no tendency to crystallize.

[0146] In contrast, the blocked polyisocyanates of Comparative Examples 1, 5, 8 and 10 produced without or with only 2% by weight of branched diols became cloudy already after a short time at room temperature and completely crystallized after 4 weeks.

Claims

1. A method for producing a blocked polyisocyanate, comprising reacting 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, It is characterized in that Component B) is used in an amount of more than 2% by weight, based on the total amount of components A) and B), component C) is used in an amount corresponding to at least 95 mol % of the isocyanate groups still present arithmetically after the reaction of components A) and B), and polyisocyanates prepared by simple modification of linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates and having at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component A), with >70 equivalent % of linear aliphatic diisocyanates, based on the NCO content, being used for the modification.

2. The method 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, with >80 equivalents, particularly preferably >90 equivalents, in each case based on the NCO content, and very particularly preferably exclusively linear aliphatic diisocyanates being used for the modification.

3. The method according to any one of claims 1, characterized in that As 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 are used.

4. The method according to any one of claims 1 to 3, characterized in that As polyisocyanate component A), polyisocyanates are used which have an isocyanurate structure and 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.

5. The method according to any one of claims 1 to 4, characterized in that The at least one branched aliphatic diol has 3 to 36, preferably 4 to 12 carbon atoms.

6. The method according to any one of claims 1 to 5, characterized in that The at least one branched aliphatic diol is 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.

7. The method according to any one of claims 1 to 6, characterized in that The at least one branched aliphatic diol is used 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).

8. The method according to any one of claims 1 to 7, characterized in that The at least one secondary amine C) has the general formula (I) wherein R and R' are independently identical or different radicals which represent 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.

9. The method according to any one of claims 1 to 8, characterized in that The at least one secondary amine C) has the general formula (I) wherein R and R' independently of one another represent identical or different saturated, straight-chain 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' optionally 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 6 ring members, which may optionally be further substituted.

10. The method according to any one of claims 1 to 9, characterized in that The at least one secondary amine C) is diisopropylamine, dicyclohexylamine, N-tert-butylbenzylamine or any mixtures of these amines.

11. The method according to any one of claims 1 to 10, characterized in that The at least one secondary amine C) is used in an amount corresponding to at least 96 mol %, preferably at least 98 mol %, particularly preferably at least 100 mol %, of the isocyanate groups arithmetically still present after the reaction of components A) and B).

12. The method according to any one of claims 1 to 11, characterized in that 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., with one another.

13. Blocked polyisocyanate obtainable or directly obtained by the process according to any one of claims 1 to 12.

14. A one-component baking system comprising a) at least one blocked polyisocyanate according to claim 13, b) at least one binder which is reactive toward isocyanate groups and has 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.

15. Substrate at least partially coated with at least one cured one-component baking system according to claim 14.

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