Blocked polyisocyanates

Abstract

The invention relates to a method for producing a blocked polyisocyanate, having the steps of reacting A) at least one polyisocyanate component, which has at least isocyanurate and / or iminooxadiazindione structures, with B) at least one branched aliphatic diole and C) at least one secondary amine with aliphatic, cycloaliphatic, and / or araliphatic substituents. The invention is characterized in that the component B) is used in a quantity of more than 2 wt.% based on the total quantity of the components A) and B), the component C) is used in a quantity which corresponds to at least 95 mol.% of the isocyanate groups mathematically still present after the reaction of the components A) and B), and as the polyisocyanate component A), polyisocyanates are used which are produced by modifying simple linear aliphatic, cycloaliphatic, araliphatic, and / or aromatic diisocyanates and which have at least isocyanurate and / or iminooxadiazindione structures, wherein > 70 equiv.%, based on the NCO content, is used for the modification process. The invention also relates to said blocked polyisocyanates.

Description

[0001] Blocked polyisocyanates

[0002] 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 form mixtures that are stable at room temperature. At higher temperatures, the blocking agent is cleaved off, releasing the isocyanate group for crosslinking with the polyol component.

[0003] Such blocked polyisocyanates serve as crosslinking components for one-component polyurethane baking coatings (1K-PUR) and are used, for example, in automotive OEM coatings, plastic coatings, and coil coating. The type of blocking agent used is of considerable importance. Reactivity, thermal yellowing, and other coating properties are essentially determined by the blocking agent. (L.I. Meier-Westhues et al., "Polyurethanes: Coatings, Adhesives and Sealants," 2 nd Revised Edition, Hanover: Vincentz Network, 2019).

[0004] Secondary monoamines are of particular interest as blocking agents because they enable particularly low baking temperatures. In particular, the technically and economically important polyisocyanates containing isocyanurate groups and based on linear aliphatic diisocyanates, such as 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI) and 1,5-diisocyanatopentane (pentamethylene diisocyanate, PDI), have, to date, remained of no practical importance in a form blocked with secondary amines such as diisopropylamine. The reason for this is the fact that solutions of such blocked polyisocyanates in conventional paint solvents are not stable over long periods of time because they show a very high tendency to solidify, e.g. through crystallization of the blocked polyisocyanate they contain. (DA Wicks, ZW Wicks Jr, Progress in Organic Coatings 41 (2001) 1-83).

[0005] Polyisocyanates, in particular 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) and tolylene diisocyanate (TDI), which are blocked exclusively with secondary amines, if appropriate after chain extension with diols and / or triols, were first described in EP-A 0 096 210 as crosslinker components for solvent-borne 1-component polyurethane stoving enamels. Sterically hindered secondary amines, such as diisopropylamine, dicyclohexylamine, or 2,2,6,6-tetramethylpiperidine, are mentioned as suitable blocking agents. Isocyanurate polyisocyanates are also generally mentioned as suitable starting diisocyanates. However, this publication does not contain any examples using polyisocyanates containing isocyanurate groups or linear aliphatic diisocyanates, which would allow conclusions to be drawn about the storage stability of such products in organic solution.EP-A 0 125 438 also describes one-component binders whose crosslinking component consists of a reaction product of polyisocyanates, optionally pre-extended with polyols, with exclusively secondary amines as blocking agents. These binders are used for solvent-borne coatings, for powder coatings, and, in their untreated form, for cathodic electrocoating. However, this publication does not provide any information on the storage stability of solutions of the blocked polyisocyanates.

[0006] Polyisocyanates, especially isocyanate-functional prepolymers blocked with secondary amines, are known as crosslinking components for polyamines from EP-A 0 407 829. HDI derivatives containing biuret or isocyanurate groups are also generally mentioned as suitable starting polyisocyanates for the preparation of the blocked prepolymers. These derivatives can optionally be modified with a substoichiometric amount of a low-molecular-weight polyhydroxyl compound prior to blocking. The publication does not provide any information on the storage stability of polyisocyanates blocked with secondary amines.

[0007] EP-A 3 643 733 describes special secondary monoamines which bear both a branched alkyl group having 3 to 6 carbon atoms and a hydrocarbon substituent having 1 or 2 ether groups as blocking agents for isocyanates. Preferred blocking agents of this type are N-(furan-2-ylmethyl)-2-methylpropan-2-amine, 2-methyl-N-((tetrahydrofuran-2-yl)methyl)propan-2-amine, N-(2-methoxyethyl)-2-methylpropan-2-amine, and N-(tert-butyl)-1-methoxypropan-2-amine. The isocyanate groups blocked with these amines are released again at particularly low temperatures. The publication contains neither references to the lack of crystallization stability of isocyanurate polyisocyanates of linear aliphatic diisocyanates blocked with secondary amines, nor suggestions for how to overcome this.

[0008] The high crystallization tendency of amine-blocked isocyanurate polyisocyanates of linear aliphatic diisocyanates can be reduced in several ways. One approach, for example, is so-called mixed blocking, the simultaneous use of two or more different blocking agents.

[0009] Blocked polyisocyanates whose isocyanate groups are blocked to a minimum of 30 equivalent % and a maximum of 70 equivalent % with diisopropylamine, and to a total of 30 to 70 equivalent % with at least one CH-acidic ester and / or 1,2,4-triazole, are the subject of EP-A 0 600 314. This mixed blocking prevents the crystallization tendency of, for example, derivatives of HDI polyisocyanurate polyisocyanates. However, the different deblocking temperatures of the differently blocked isocyanate groups often lead to problems in practice when using such products in 1-component PU coating systems. In addition, the blocking agent mixtures released during the baking of such systems can also negatively influence the coating properties, which is why mixed-blocked polyisocyanates are not generally suitable for use.

[0010] According to the teaching of EP-A 0 900 814, one possibility for producing crystallization-stable, exclusively amine-blocked polyisocyanate crosslinkers is the reaction of defined mixtures of linear aliphatic and cycloaliphatic polyisocyanates with secondary amines. However, coatings produced using such polyisocyanates exhibit a significantly different property profile and are also not generally applicable.

[0011] According to EP-A 1 524 284, polyisocyanates blocked with secondary amines that contain a defined amount of biuret structures are crystallization-stable. Suitable polyisocyanates are pure HDI biurets or subsequently biuretized HDI polyisocyanates with isocyanurate and / or iminooxadiazinedione structures. These polyisocyanates can, if desired, be partially reacted with compounds reactive toward isocyanate groups, such as low- or high-molecular-weight di- or polyfunctional alcohols, amines, or high-molecular-weight polyhydroxyl compounds based on polyester, polyether, polycarbonate, or polyacrylate, prior to blocking. Blocking agents used include, in particular, diisopropylamine, N-tert-butylbenzylamine, dicyclohexylamine, or mixtures thereof.

[0012] According to the teaching of WO 2004 / 104065, polyisocyanates based on linear aliphatic diisocyanates blocked with secondary amines also behave in a similarly stable manner with regard to crystallization, in which some of the urea groups formed during blocking were further converted to biuret structures.

[0013] However, polyisocyanates containing biuret structures have in common their significantly lower temperature resistance compared to isocyanurates. Due to equilibration reactions, which can occur particularly under the baking conditions common in coil coating applications and potentially lead to the release of monomeric diisocyanates, such products have not been able to establish themselves on the market.

[0014] The problem of the lack of crystallization stability and high tendency to solidify in polyisocyanates based on linear aliphatic diisocyanates containing isocyanurate groups blocked with secondary monoamines has not yet been satisfactorily resolved. Despite the high interest in blocked polyisocyanate crosslinkers that crosslink at low baking temperatures, no amine-blocked HDI and / or PDI polyisocyanurate polyisocyanates are currently available to users.

[0015] As has now been surprisingly discovered, polyisocyanurate polyisocyanates based on linear aliphatic diisocyanates, such as HDI or PDI, which have been partially urethanized with branched alcohols, especially branched diols, can also be reacted with secondary amines, such as diisopropylamine, to form completely solidification-stable, non-crystallizing, blocked polyisocyanate crosslinkers. These new amine-blocked polyisocyanates are particularly suitable for coil coating applications.

[0016] The present invention relates to a process for the preparation of a blocked polyisocyanate comprising a reaction

[0017] A) at least one polyisocyanate component which has at least isocyanurate and / or iminooxadiazinedione structures, with

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

[0019] C) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents, 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), and component C) is used in an amount which corresponds to at least 95 mol% of the isocyanate groups still present after the reaction of components A) and B), and polyisocyanates which have at least isocyanurate and / or iminooxadiazinedione structures and which are prepared by modifying simple linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates are used as polyisocyanate component A), wherein > 70 equivalent%, based on the NCO content, of linear aliphatic diisocyanates were used for the modification.

[0020] According to the invention, the terms "comprising" or "containing" preferably mean "consisting essentially of," and particularly preferably "consisting of." The further embodiments mentioned in the claims and in the description can be combined in any desired way, unless the context clearly indicates otherwise.

[0021] "At least one," as used herein, refers to 1 or more, for example, 2, 3, 4, 5, 6, 7, 8, 9, or more. In the context of components of the compounds described herein, this statement does not refer to the absolute amount of molecules, but rather to the type of component. "At least one polyisocyanate component" therefore means, for example, that only one type of polyisocyanate component or several different types of polyisocyanate components may be present, without specifying the amount of the individual components.

[0022] Numerical values ​​stated herein without decimal places refer to the full specified value with one decimal place. For example, "99%" represents "99.0%." Numerical ranges stated in the format "in / from x to y" include the stated values. If multiple preferred numerical ranges are specified in this format, it is understood that all ranges resulting from the combination of the various endpoints are also included.

[0023] For the purposes of this document, the term "aliphatic" is defined as non-aromatic hydrocarbon groups that are saturated or unsaturated.

[0024] The term "linear aliphatic" refers to compounds that are completely free of cyclic structural elements, while the term "alicyclic" or "cycloaliphatic" is defined as optionally substituted, carbocyclic, or heterocyclic compounds or units that are not aromatic (such as cycloalkanes, cycloalkenes, or oxa-, thia-, aza-, or thiazacycloalkanes). Specific examples are cyclohexyl groups, cyclopentyl groups, and their N- or O-heterocyclic derivatives, such as pyrimidine, pyrazine, tetrahydropyran, or tetrahydrofuran.

[0025] For the purposes of this document, the term "araliphatic" is defined as hydrocarbon residues that consist of both an aromatic and a saturated or unsaturated hydrocarbon group directly bonded to the aromatic residue.

[0026] In the event that the groups or compounds are disclosed as "optionally substituted" or "substituted," suitable substituents are -F, -Cl, -Br, -I, -OH, -OCH3, -OCH2CH3, -O-isopropyl or -on-propyl, -OCF3, -CF3, -S-C1-6-alkyl, and / or (optionally via an attached heteroatom) a linear or branched, aliphatic and / or alicyclic structural unit having 1 to 12 carbon atoms, each acting as a replacement for a carbon-bonded hydrogen atom of the molecule in question. Preferred substituents are halogen (especially -F, -Cl), C1-6-alkoxy (especially methoxy and ethoxy), hydroxy, trifluoromethyl, and trifluoromethoxy, each acting as a replacement for a carbon-bonded hydrogen atom of the molecule in question.

[0027] The at least one polyisocyanate component A) which has at least isocyanurate and / or iminooxadiazinedione structures is also referred to in the context of the present invention as starting compound A) or as starting polyisocyanate A) or as polyisocyanate A) or as polyisocyanate A) having isocyanurate and / or iminooxadiazinedione structures.

[0028] Starting compounds A) for the process according to the invention are any polyisocyanates prepared by modifying linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates which have at least isocyanurate and / or iminooxadiazinedione structures. Suitable diisocyanates for preparing these polyisocyanates A) are any diisocyanates accessible in various ways, for example by phosgenation of the corresponding diamines in the liquid or gas phase or by a phosgene-free route, such as, for example, by thermal urethane cleavage, in particular those in the molecular weight range 140 to 400 with aliphatically, cycloaliphatically, araliphatically and / or aromatically bound isocyanate groups, such as, for example, B. 1,4-diisocyanatobutane, 1,5-diisocyanatopentane (pentamethylene diisocyanate, PDI), 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI), 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or2,4,4- Trimethyl-1,6-diisocyanatohexan, 1,8-Diisocyanatooctan, 1,9-Diisocyanatononan, 1 ,10- Diisocyanatodecan, 1,3- und 1,4-Diisocyanatocyclohexan, 1,4-Diisocyanato-3,3,5- trimethylcyclohexan, 1 ,3-Diisocyanato-2-methylcyclohexan, 1 ,3-Diisocyanato-4-methyl- cyclohexan, 1-lsocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexan (Isophorondiisocya- nat; IPDI), 1-lsocyanato-1-methyl-4(3)-isocyanatomethylcyclohexan, 2,4’- und 4,4'-Diiso- cyanatodicyclohexylmethan (H12-MDI), 1 ,3- und 1 ,4-Bis(isocyanatomethyl)cyclohexan, 4,4'- Diisocyanato-3,3'-dimethyldicyclohexylmethan, 4,4' Diisocyanato-3,3',5,5'-tetramethyldicyclo- hexylmethan, 4,4'-Diisocyanato-1 ,1'-bi(cyclohexyl), 4,4'-Diisocyanato-3,3'-dimethyl-1 ,T- bi(cyclohexyl), 4,4'-Diisocyanato-2,2',5,5'-tetra-methyl-1 ,1'-bi(cyclohexyl), 1 ,8-Diisocyanato-p- menthan, 1 ,3-Diisocyanatoadamantan, 1,3-Dimethyl-5,7-diisocyanatoadamantan, 1,3- und.

[0029] 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

[0030] 1,4-Phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate, and any mixtures of these isomers, diphenylmethane 2,4'- and / or 4,4'-diisocyanate, and naphthylene 1,5-diisocyanate, as well as any mixtures of such diisocyanates. Other suitable diisocyanates can be found, for example, in Justus Liebig's Annalen der Chemie, Volume 562 (1949), pp. 75-136.

[0031] In a further preferred embodiment, polyisocyanates prepared by modifying linear aliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates which have at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component A), wherein > 80 equivalent%, particularly preferably > 90 equivalent%, in each case based on the NCO content, and very particularly preferably exclusively linear aliphatic diisocyanates were used for the modification.

[0032] In a further preferred embodiment, polyisocyanates prepared by modifying linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, which have at least isocyanurate and / or iminooxadiazinedione structures, are used as polyisocyanate component A). Preferred diisocyanates for preparing the polyisocyanates A) having isocyanurate and / or iminooxadiazinedione structures are those of the type mentioned with linear-aliphatic and / or cycloaliphatic bonded isocyanate groups, particularly preferably unbranched linear aliphatic diisocyanates, such as, 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.

[0033] Also preferred is a process for producing a blocked polyisocyanate comprising a reaction

[0034] A) at least one essentially linear aliphatic polyisocyanate component which has at least isocyanurate and / or iminooxadiazinedione structures, with

[0035] B) at least one branched aliphatic diol and

[0036] C) with at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents, characterized in that component B) is used in an amount of more than 2 wt.%, based on the total amount of components A) and B), and component C) is used in an amount which corresponds to at least 95 mol.% of the isocyanate groups still present after the reaction of components A) and B).

[0037] According to this preferred embodiment, the polyisocyanate component A) is at least one substantially linear aliphatic polyisocyanate component. "Substantially linear aliphatic" in this context means in particular that the diisocyanates used for modification are > 70 equivalent%, preferably > 80 equivalent%, particularly preferably > 90 equivalent%, based in each case on the NCO content, linear aliphatic diisocyanates, and very particularly preferably exclusively linear aliphatic diisocyanates.

[0038] The starting polyisocyanates A) containing at least isocyanurate and / or iminooxadiazinedione structures for 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, in DE-A 1 954 093, DE-A 2 414 413, DE-A 2 452 532, DE-A 2 641 380, DE-A 3 900 053 and DE-A 3928503 or in EP-A 0336205, EP-A 0339396 and EP-A 0798299. Depending on the modification process chosen, the polyisocyanates A) used in the process according to the invention may, in addition to isocyanurate and / or iminooxadiazinedione structures, optionally also have uretdione, allophanate, biuret, urethane and / or oxadiazinetrione structures.

[0039] In the preparation of the starting polyisocyanates A), the actual modification reaction is usually followed by a further process step to separate the unreacted excess monomeric diisocyanates. This monomer separation is carried out by conventional methods, preferably by thin-film distillation under vacuum or by extraction with suitable solvents inert toward isocyanate groups, for example, aliphatic or cycloaliphatic hydrocarbons such as pentane, hexane, heptane, cyclopentane, or cyclohexane.

[0040] In the process according to the invention, polyisocyanates of the type mentioned which have a monomeric diisocyanate content of less than 5 wt. %, preferably less than 0.5 wt. %, particularly preferably less than 0.3 wt. %, are preferably used as starting polyisocyanates A). The residual monomer contents are determined by gas chromatography using an internal standard in accordance with DIN EN ISO 10283:2007-11.

[0041] The polyisocyanates A) mentioned above as suitable, preferred, particularly preferred and very particularly preferred preferably contain isocyanurate structures and have an average NCO functionality of 2.3 to 5.0, preferably of 2.5 to 4.5, and a content of isocyanate groups of 6.0 to 26.0 wt.%, preferably of 8.0 to 25.0 wt.%, particularly preferably 10.0 to 24.0 wt.%.

[0042] In the process according to the invention, the polyisocyanate component A), which has at least isocyanurate and / or iminooxadiazinedione structures, is reacted with at least one branched aliphatic diol B).

[0043] These are any saturated or unsaturated aliphatic diols, which may be singly or multiply branched, may optionally contain heteroatoms, ester groups and / or carbonate groups in the chain and may optionally be further substituted.

[0044] In a further preferred embodiment, the at least one branched aliphatic diol has 3 to 36 carbon atoms. Examples mentioned are simple diols such as 1,2-propanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-dibutyl-1,3-propanediol, 2,2-dimethyl-1,3-butanediol, 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-propanediol, 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,as are obtainable in a manner known per se, for example by hydrogenation of dimeric fatty acids and / or their esters and are commercially available, for example, under the names Pripol® 2030, Pripol® 2033 (Croda International Plc, UK) and Sovermol 908 (BASF SE, DE), ether diols such as dipropylene glycol, tripropylene glycol and ethylhexylglycerin, ester diols such as 3-hydroxy-2,2-dimethylpropyl-3-hydroxy-2,2-dimethylpropionate (hydroxypivalyl hydroxypivalate, HPN), glycerol monocaprylate and glycerol monostearate, or any mixtures of such alcohols.

[0045] In a further preferred embodiment, the at least one branched aliphatic diol has 4 to 12 carbon atoms. 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 such alcohols.

[0046] The branched aliphatic diols B) are used in the process according to the invention in an amount of more than 2 wt. %, preferably from 3 to 20 wt. %, particularly preferably from 4 to 15 wt. %, and most preferably from 5 to 12 wt. %, based on the total amount of components A) and B). Amounts less than 2 wt. % are insufficient to permanently prevent the crystallization of the blocked polyisocyanate; the use of more than 20 wt. % can lead to products of very high viscosity, which are not economical in practical use due to their low isocyanate content.

[0047] If necessary, component B) may contain, in addition to the branched aliphatic diols mentioned, other alcoholic compounds in minor amounts.

[0048] These include, for example, monoalcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomeric pentanoyl, hexanoyl, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols, hydroxymethylcyclohexane, 3-methyl-3-hydroxymethyloxetane, benzyl alcohol, phenol, the isomeric cresols, octylphenols, nonylphenols and naphthols, furfuryl alcohol and tetrahydrofurfuryl alcohol, unbranched aliphatic diols such as. B. 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol and 1,8-octanediol, cycloaliphatic diols, such as B. 1,2- and 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4'-(1-methylethylidene)-biscyclohexanol, triols such as B. 1,2,3-propanetriol, 1,1,1-trimethylolethane, 1,2,6-hexanetriol, 1,1,1-trimethylolpropane, and 1,3,5-tris(2-hydroxyethyl)isocyanurate, tetrafunctional alcohols, such as B.B. 2,2-bis(hydroxymethyl)-1,3-propanediol or any mixtures of such alcohols.

[0049] If at all, these further alcoholic compounds are used in the process according to the invention in amounts of not more than 25% by weight, preferably not more than 20% by weight, particularly preferably 15% by weight, based on the amount of branched aliphatic diols used.

[0050] 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.

[0051] 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).

[0052] These are in particular secondary amines of the general formula (I)

[0053] R 'N' R '

[0054] H (I) in which R and R' independently of one another represent identical or different radicals which are 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, where R and R' can also form heterocyclic rings having 5 to 8 ring members in combination with one another together with the nitrogen atom and optionally with further oxygen atoms, which can optionally be further substituted.

[0055] The radicals R and R' are preferably saturated linear 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, where R and R' can optionally also in combination with one another together with the nitrogen atom and optionally with a further oxygen atom form heterocyclic rings having 5 to 6 ring members, which can optionally be further substituted.

[0056] Suitable secondary amines C) 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, hexahydroazepine, pyrrolidine, 2,5-Dimethylpyrrolidine or morpholine.

[0057] Also suitable, although less preferred, secondary amines C) are those that, in addition to a secondary amino group, carry other groups reactive toward isocyanate groups, but which, such as hydroxyl groups, have a lower reactivity toward isocyanate groups than secondary amino groups. Examples of such secondary amines are amino alcohols, such as diethanolamine and diisopropanolamine.

[0058] Preferred secondary amines C) are diisopropylamine, dicyclohexylamine, N-tert-butylbenzylamine, or any mixtures of these amines. Diisopropylamine is particularly preferred.

[0059] The secondary amines C) are used in the process according to the invention in an amount which corresponds 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 still present after the reaction of components A) and B).

[0060] The process according to the invention can optionally be used in suitable solvents that are resistant to isocyanate groups. Suitable solvents include, for example, the conventional paint solvents known per se, such as, for example, ethylenediamine dimethyl ether (E40). B. Ethyl acetate, butyl acetate, ethylene glycol monomethyl or ethyl ether acetate, 1-methoxypropyl-2-acetate (MPA), 3-methoxy-n-butyl acetate, acetone, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, chlorobenzene, white spirit, higher substituted aromatics, such as those sold under the names Solventnaphtha, Solvesso®, Isopar®, Nappar® (Deutsche EXXON CHEMICAL GmbH, Cologne, DE) and Shellsol® (Deutsche Shell Chemie GmbH, Eschborn, DE), but also 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 such solvents.

[0061] 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) optionally under an inert gas, such as nitrogen, and optionally in the presence of a suitable solvent of the type mentioned, at a temperature between 0 and 120°C, preferably 20 to 100°C, particularly preferably 40 to 80°C, in any desired sequence in the above-mentioned proportions. The course of the reaction in the process according to the invention can be monitored, for example, by titrimetric determination of the NCO content, preferably according to DIN EN ISO 11909:2007-05.

[0062] The reaction of the polyisocyanate component A) with the diol component B) and the amine component C) can be carried out uncatalyzed in the process according to the invention, but the usual urethanization catalysts known from polyurethane chemistry can also be used to accelerate the reaction, for example tert. Amines such as triethylamine, pyridine, methylpyridine, 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-ethylcaproate, Zinc acetylacetonate, tin(II) octoate, tin(II) ethyl caproate, tin(II) palmitate, dibutyltin(IV) dilaurate, zirconium (IV) 2-ethyl-1-hexanoate, zirconium (IV) neodecanoate, zirconium (IV) naphthenate, zirconium (IV) acetylacetonate, Aluminum tri(ethyl acetoacetate), bismuth(III)-2-ethylhexanoate, Bismuth(III) octoate, bismuth(III) neodecanoate and molybdenum glycolate.

[0063] These catalysts are optionally used in amounts of 0.001 to 2.0 wt. %, preferably 0.01 to 0.2 wt. %, based on the total amount of the starting components A), B) and C) used.

[0064] If catalysts are used to accelerate the reaction, they can be deactivated, preferably chemically, once the desired NCO content has been reached. Suitable catalyst poisons include, for example, inorganic acids such as hydrochloric acid, phosphorous acid, or phosphoric acid; acid chlorides such as acetyl chloride, benzoyl chloride, or isophthaloyl dichloride; sulfonic acids and sulfonic acid esters such as methanesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, perfluorobutanesulfonic acid, methyl and ethyl p-toluenesulfonate; mono- and dialkyl phosphates such as monotridecyl phosphate, dibutyl phosphate, and dioctyl phosphate; and also silylated acids such as trimethylsilyl methanesulfonate, trimethylsilyl trifluoromethanesulfonate, tris-(trimethylsilyl) phosphoric acid, and trimethylsilyl phosphoric acid diethyl phosphate.

[0065] The amount of catalyst poison required for deactivation, if any, depends on the amount of catalyst used. If used at all, 0.1 to 2.0, preferably 0.4 to 1.6, particularly preferably 0.8 to 1.2 equivalents, and most preferably an equivalent amount of the terminator, based on the amount of catalyst used, are used.

[0066] Following the reaction of the polyisocyanate component A) with the diol component B) and the amine component C), preferably when the content of free isocyanate groups is less than 1.0 wt. %, preferably less than 0.8 wt. %, particularly preferably less than 0.3 wt. %, the blocked polyisocyanates can optionally be further diluted with solvent, for example to reduce the viscosity. In addition to the solvents mentioned above, alcoholic solvents such as n-butanol or isobutyl alcohol can also be used, since the isocyanate groups have then reacted largely, preferably completely, with the blocking agent.

[0067] In the process according to the invention, other auxiliaries and additives, such as antioxidants or light stabilizers, may optionally be used. These can be added either to one or more of the reactants A), B), and C) before the actual reaction begins. However, they can also be added to the reaction mixture at any time during the reaction or to the blocked polyisocyanates according to the invention after the reaction.

[0068] 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,

[0069] Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with aliphatic branched C7 to C9 alcohols, such asisoheptyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or isononyl-3-(3,5-di-tert-butyl-4-hydroxyphenylpropionate, Isotridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethyl bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylene-bis(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid amide, 1 ,2-Bis(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)hydrazide, 2,4-di-tert-butylphenyl-4'-hydroxy-3',5'-di-tert- butyl benzoate, esters of (3,5-di-tert-butyl-4-hydroxyphenyl)methylthioacetic acid with aliphatic branched C10 to C14 alcohols, 2,2'-thio-bis(4-methyl-6-tert-butylphenol), 2-methyl-4,6-bis(octylthiomethyl)phenol, 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.

[0070] Suitable antioxidants are also thioethers, such as didodecyl-3,3'-thiodipropionate or dioctadecyl-3,3'-thiodipropionate, which are preferably used in combination with phenolic antioxidants of the type mentioned.

[0071] Other suitable antioxidants are phosphites, for example di- or preferably trisubstituted phosphites, such as: B. dibutyl phosphite, dibenzyl phosphite, triethyl phosphite, tributyl phosphite, triisodecyl phosphite, trilauryl phosphite, tris (tridecyl) phosphite, triphenyl phosphite, tris (2,4-di-tert-butylphenyl) phosphite, tris (nonylphenyl) phosphite, diphenyl isooctyl phosphite, Diphenyl isodecyl phosphite, diisodecyl phenyl phosphite, diisooctyl-octyl phenyl phosphite, phenyl neopentyl glycol phosphite, 2,4,6-T ri-tert-butylphenyl-(2-butyl-2-ethyl-1,3-propanediol) phosphite, Diisodecyl pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, Bis(2,4-di-tert-butylphenyl)-pen-taerythritol diphosphite or tetraphenyl-dipropylene glycol diphosphite.

[0072] Suitable light stabilizers include, for example, UV absorbers of the 2-hydroxyphenylbenzotriazole type, those of the nitrogen-substituted or unsubstituted HALS compound type, such as Tinuvin® 292 or Tinuvin® 770 DF (BASF SE, Ludwigshafen, Germany), or those described, for example, in "Lichtschutzmittel für Lacke" (A. Valet, Vincentz Verlag, Hanover, 1996) and "Stabilization of Polymeric Materials" (H. Zweifel, Springer Verlag, Berlin, 1997, Appendix 3, pp. 181-213).

[0073] Further auxiliaries and additives which may optionally be used in the process according to the invention are also the hydrazide group-containing and / or hydroxy-functional stabilizers described in EP-A 0 829 500, such as, for example, the addition product of hydrazine and propylene carbonate.

[0074] The auxiliaries and additives mentioned can optionally be used in the process according to the invention individually or in any desired combinations with one another in amounts of from 0.001 to 3.0% by weight, preferably from 0.002 to 2.0% by weight, particularly preferably from 0.005 to 1.0% by weight, in each case based on the total amount of starting polyisocyanate A).

[0075] Regardless of the type of process, 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 comparable polyisocyanates prepared using the same starting components but without partial urethanization with branched alcohols, do not show any tendency to crystallize even after prolonged storage at low temperatures, for example over a period of 12 weeks at 15 to 25°C.

[0076] The invention therefore also relates to the blocked polyisocyanate obtainable or obtained by the process according to the invention.

[0077] The invention also relates to the use of more than 2 wt. % of at least one branched aliphatic diol B), based on the total amount of components A) and B), for stabilizing aliphatic polyisocyanates blocked with at least one secondary amine C).

[0078] The blocked polyisocyanates of the invention represent valuable starting materials for the production of polyurethane plastics by the isocyanate polyaddition process. They are excellently suited as crosslinker components for one-component, thermosetting, solvent-based or water-based coating systems, which are used particularly in plastics coating, automotive OEM coating, or coil coating applications. They provide coatings that exhibit very good yellowing resistance even under overbaking conditions.

[0079] A further subject of the invention therefore are one-component baking systems comprising a) at least one blocked polyisocyanate according to the invention, b) at least one binder which is reactive towards isocyanate groups and has on average at least two isocyanate-reactive groups per molecule, c) optionally catalysts and d) optionally solvents and / or optionally auxiliaries and additives.

[0080] Finally, substrates at least partially coated with at least one cured one-component baking system according to the invention are also a further subject of the invention.

[0081] To produce the one-component stoving systems (1K stoving lacquers) according to the invention, the blocked polyisocyanates according to the invention are mixed a) with lacquer binders b) known per se from lacquer technology, optionally with the use of catalysts c) that accelerate the crosslinking reaction, and optionally with solvents and / or optionally with auxiliaries and additives d). Mixing must take place below the temperature at which the blocking agent is split off, since the release of the isocyanate groups would lead to premature crosslinking of the lacquer system. The one-component stoving systems according to the invention are preferably produced at temperatures between 15 and 100°C.

[0082] As binder component b), the one-component stoving systems according to the invention contain at least one binder which is reactive towards isocyanate groups and has on average at least two isocyanate-reactive groups, such as hydroxyl, mercapto, amino or carboxylic acid groups, per molecule.

[0083] These binders b) are preferably the usual di- and / or polyhydroxyl compounds known from polyurethane chemistry, such as polyester polyols, polyether polyols, polycarbonate polyols and / or polyacrylate polyols, or any mixtures of such polyols.

[0084] Suitable polyols b) are, for example, the usual di- and / or polyhydroxyl compounds known from polyurethane chemistry, such as polyester polyols, polyether polyols, polycarbonate polyols and / or polyacrylate polyols, or any mixtures of such polyols.

[0085] Suitable polyester polyols b) are, for example, those having a number-average molecular weight, calculable from functionality and hydroxyl number, of 500 to 10,000 g / mol, preferably 800 to 5,000 g / mol, particularly preferably 1,000 to 3,000 g / mol, with a hydroxyl group content of 1 to 21% by weight, preferably 2 to 18% by weight, as can be prepared in a manner known per se by reacting polyhydric alcohols with sub-stoichiometric amounts of polybasic carboxylic acids, corresponding carboxylic anhydrides, corresponding polycarboxylic acid esters of lower alcohols or by reacting with lactones.

[0086] Suitable polyhydric alcohols for the preparation of polyester polyols b) are, for example, 1,2-ethanediol, 1,2- and 1,3-propanediol, the isomeric butanediols, pentanediols, hexanediols, heptanediols and octanediols, 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-trimethylolethane, 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, di-trimethylolpropane, 2,2-bis(hydroxymethyl)-1,3-propanediol (pentaerythritol), 2,2,6,6-tetrakis(hydroxymethyl)-4-oxa-heptane-1,7-diol (dipentaerythritol), mannitol or sorbitol, low molecular weight ether alcohols, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol or dibutylene glycol or low molecular weight ester alcohols, such as neopentyl glycol hydroxypivalate, or mixtures of at least two such alcohols.

[0087] Suitable carboxylic acids or carboxylic acid derivatives for producing the polyester polyols b) to be used in the one-component stoving systems according to the invention are polybasic carboxylic acids, their carboxylic anhydrides, and polycarboxylic esters of lower alcohols. These are any aromatic, aliphatic, or cycloaliphatic, saturated or unsaturated di- and tricarboxylic acids or their anhydrides, in particular those having 4 to 18 carbon atoms, preferably 4 to 10 carbon atoms, such as 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,

[0088] Phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic anhydride, terephthalic acid dimethyl ester and terephthalic acid bis-glycol ester but also dimeric and trimeric fatty acids, which can be used individually or in the form of any mixtures with each other.

[0089] If necessary, monocarboxylic acids such as benzoic acid, acetic acid, propionic acid, butyric acid or 2-ethylhexanoic acid can also be used in minor amounts to produce the polyester polyols b).

[0090] Suitable polyester polyols b) for the one-component baking systems according to the invention also include those that can be prepared in a conventional manner from lactones and polyhydric alcohols, such as those exemplified above, as starter molecules by ring opening. Suitable lactones for the preparation of 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 such lactones.

[0091] These lactone polyesters are generally prepared in the presence of catalysts such as Lewis or Brönstedt acids, organic tin or titanium compounds at temperatures of 20 to 200°C, preferably 50 to 160°C. Suitable synthesis components for the preparation of these polyester polyols b) are, for example, the polyhydric alcohols, polybasic carboxylic acids and their derivatives mentioned above as suitable for the preparation of the polyester polyols b), which can also be used in the form of any desired mixtures.

[0092] The polyester polyols b) can be prepared by methods known per se, as described in detail, for example, in E. Gubbels et al., Polyesters. In: Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KgaA; 2018. URL: https: / / doi.org / 10.1002 / 14356007. a21_227.pub2. If necessary, catalytic amounts of conventional esterification catalysts, such as acids, bases, or transition metal compounds such as titanium tetrabutylate, can be used. The esterification reaction is generally carried out in a temperature range of approximately 80 to 260°C, preferably from 100 to 230°C, until the desired values ​​for the hydroxyl and acid number are reached.

[0093] Suitable polyether polyols b) are, for example, those with an average molecular weight, calculated from functionality and hydroxyl number, of 200 to 6000, preferably 250 to 4000, with a hydroxyl group content of 0.6 to 34 wt. %, preferably 1 to 27 wt. %, as are obtainable in a conventional manner by alkoxylation of suitable starter molecules. To prepare these polyether polyols, any polyhydric alcohols, as described above as suitable for preparing the polyester polyols b), can be used as starter molecules. Alkylene oxides suitable for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be used in any order or as a mixture in the alkoxylation reaction.

[0094] Suitable polycarbonate polyols b) are, in particular, the known reaction products of dihydric alcohols, for example those exemplified above in the list of polyhydric alcohols, with diaryl carbonates, such as, for example, diphenyl carbonate, dimethyl carbonate, or phosgene. Suitable polycarbonate polyols b) are also those which, in addition to carbonate structures, also contain ester groups. These are, in particular, the known polyester carbonate diols, as can be obtained, for example, according to the teaching of DE-AS 1 770245 by reacting dihydric alcohols with lactones, such as, in particular, s-caprolactone, and subsequently reacting the resulting polyester diol with diphenyl or dimethyl carbonate. Likewise suitable polycarbonate polyols b) are those which, in addition to carbonate structures, also contain ether groups.These are in particular the polyether carbonate polyols known per se, such as those obtainable, for example, by the process of EP-A 2 046 861 by catalytic conversion of alkylene oxides (epoxides) and carbon dioxide in the presence of H-functional starter substances.

[0095] Suitable polyacrylate polyols b) are, for example, those having an average molecular weight of 800 to 50,000, preferably 1,000 to 20,000, which can be calculated from functionality and hydroxyl number or determined by gel permeation chromatography (GPC), and having a hydroxyl group content of 0.1 to 12% by weight, preferably 1 to 10, as can be prepared in a manner known per se by copolymerizing olefinically unsaturated monomers containing hydroxyl groups with hydroxyl-free olefinic monomers.

[0096] Examples of suitable monomers for producing the polyacrylate polyols b) are vinyl or vinylidene monomers such as styrene, a-methylstyrene, o- or p-chlorostyrene, o-, m- or p-methylstyrene, p-tert-butylstyrene, acrylic acid, acrylonitrile, methacrylonitrile, acrylic and methacrylic acid esters of alcohols with 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.-Butycyclohexyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl 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, such as. B. vinyl acetate or vinyl propionate, hydroxyalkyl esters of acrylic acid or methacrylic acid with 2 to 5 carbon atoms in the hydroxyalkyl radical, such as2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 3-hydroxybutyl, 4-hydroxybutyl, trimethylolpropane mono- or pentaerythritol monoacrylate or methacrylate, as well as any mixtures of such monomers mentioned as examples.

[0097] The one-component baking systems according to the invention can optionally contain catalysts c). These are, in particular, the urethanization catalysts already mentioned above as suitable for accelerating the reaction of the polyisocyanate component A) with the diol component B) and the amine component C) and are customary in isocyanate chemistry. These catalysts c) are used in the one-component baking systems according to the invention as individual substances or in the form of any desired mixtures with one another in amounts of from 0.005 wt.% to 5 wt.%, preferably from 0.005 wt.% to 2 wt.%, particularly preferably from 0.005 wt.% to 1 wt.%, 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).

[0098] The one-component stoving systems according to the invention may optionally also contain further auxiliaries and additives d). In addition to the above-mentioned antioxidants and light stabilizers that may be used in the process according to the invention, these include, for example, the conventional plasticizers, flow control agents, rheology additives, slip additives, defoamers, fillers, and / or pigments known to those skilled in the art, which, if used at all, are used in the usual amounts in coating technology. A detailed overview of such suitable auxiliaries and additives can be found, for example, in Bodo Müller, "Additive kompakt," Vincentz Network GmbH & Co KG (2009).

[0099] In the preparation of the one-component baking systems according to the invention, the polyisocyanate component a) and the binder component b) are preferably used in amounts such that the equivalent ratio of the sum of blocked and unblocked isocyanate groups from a) to 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.

[0100] The one-component stoving systems according to the invention may optionally contain other compounds reactive toward isocyanate-reactive groups as additional crosslinking components. These include, for example, compounds containing epoxy groups and / or aminoplast resins. The condensation products of melamine and formaldehyde, or urea and formaldehyde, known in coatings technology, are considered aminoplast resins.

[0101] All conventional melamine-formaldehyde condensates that are not etherified or etherified with saturated monoalcohols containing 1 to 4 carbon atoms are suitable. If additional crosslinking components are used, the amount of binder with isocyanate-reactive groups must be adjusted accordingly.

[0102] The application of the thus obtained one-component baking systems according to the invention can be carried out by methods known per se, for example by spraying, brushing, dipping, flow coating or by means of rollers or doctor blades in one or more layers.

[0103] Any substrate can be considered, such as metal, wood, glass, stone, ceramic materials, composite materials or plastics of all kinds, which can also be provided with conventional, well-known primers, filler coats, base coats and / or clear coats before coating.

[0104] The dried films are cured by baking at temperatures ranging from 90 to 160°C, preferably 110 to 140°C. The dry film thickness can be, for example, 10 to 120 pm.

[0105] The one-component baking systems according to the invention can also be used for continuous coil coating, whereby maximum baking temperatures, known to the person skilled in the art as peak metal temperatures, between 130 and 300°C, preferably 190 to 260°C, and dry film thicknesses of, for example, 3 to 40 pm can be achieved.

[0106] The features identified as preferred for the method according to the invention are also preferred for the other subject matters of the invention.

[0107] The following examples serve to illustrate the present invention, but should in no way be understood as a limitation of the scope of protection.

[0108] Examples

[0109] Unless otherwise stated, all percentages are based on weight.

[0110] The NCO content was determined titrimetrically according to DIN EN ISO 11909:2007-05. The course of the blocking reaction and the NCO-free nature of the blocked polyisocyanates were determined by the decrease or absence of the isocyanate band (approx. 2270 cm -1 ) in the IR spectrum.

[0111] 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.

[0112] The residual monomer contents were measured by gas chromatography with an internal standard according to DIN EN ISO 10283:2007-11.

[0113] The platinum-cobalt color number was measured spectrophotometrically according to DIN EN ISO 6271-2:2005-03 using a LICO 400 spectrophotometer from Lange, Germany.

[0114] The contents (mol%) of the uretdione, optionally isocyanurate, and / or iminooxadiazinedione structures present in the polyisocyanates A) were calculated from the integrals of proton-decoupled 13C NMR spectra (recorded on a Bruker DPX-400 instrument) and refer to the sum of the uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione, and / or oxadiazinetrione structures present. In the case of HDI polyisocyanates dissolved in CDCl3, the individual structural elements 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; oxadiazinetrione: 147.8 and 143.9.

[0115] Output connections

[0116] Polyisocyanates A)

[0117] Starting polyisocyanate A1)

[0118] Polyisocyanate prepared by catalytic trimerization of HDI based on Example 11 of EP-A 330 966, except that the reaction was stopped at an NCO content of the raw mixture of 40% by adding dibutyl phosphate. Unreacted HDI was then separated by thin-film distillation at a temperature of 130°C and a pressure of 0.2 mbar. The product had the following characteristics and composition:

[0119] NCO content: 21.8% monomeric HDI: 0.06%

[0120] Viscosity (23°C): 3020 mPas

[0121] Color number (Hazen): 8

[0122] Uretdione structures: 0.8 mol%

[0123] Isocyanurate structures: 90.2 mol%

[0124] Iminooxadazinedione structures: 3.8 mol%

[0125] Allophanate structures: 5.2 mol%

[0126] Starting polyisocyanate A2)

[0127] Polyisocyanate, prepared according to comparative example 2a of WO 2018 / 153801, by trimerization of HDI using a 20% solution of 5-azoniaspiro[4.5]decanium hydrogen difluoride in 2-ethylhexanol as catalyst, stopping the reaction at an NCO content of the crude mixture of 44.8% by adding an amount of a 70% solution of dodecylbenzenesulfonic acid in isopropanol equivalent to the amount of catalyst and subsequent separation of the unreacted HDI by thin-film distillation at a temperature of 130°C and a pressure of 0.2 mbar.

[0128] The product had the following characteristics and composition:

[0129] NCO content: 23.5% monomeric HDI: 0.11%

[0130] Viscosity (23°C): 720 mPas

[0131] Color number (Hazen): 49

[0132] Uretdione structures: 4.9 mol%

[0133] I socy anu rat structures: 46.7 mol%

[0134] Iminooxadazinedione structures: 48.4 mol%

[0135] Starting polyisocyanate A3)

[0136] PDI polyisocyanate containing isocyanurate groups, prepared by catalytic trimerization of PDI according to the process described in WO 2016 / 146579 for polyisocyanate component A2). The reaction was deactivated at an NCO content of the crude mixture of 36.7% by adding an equimolar amount of dibutyl phosphate, based on the amount of catalyst used, and stirring for 30 minutes at 80°C. Unreacted PDI was then removed by thin-film distillation at a temperature of 140°C and a pressure of 0.5 mbar.

[0137] NCO content: 21.8% monomeric PDI: 0.09%

[0138] Viscosity (23 °C): 9850 mPas

[0139] Color number (Hazen): 34

[0140] Uretdione structures: 4.9 mol%

[0141] I socy anu rat structures: 46.7 mol%

[0142] Iminooxadazinedione structures: 48.4 mol%

[0143] Example 1 (Compare I ei ch)

[0144] 289 g (1.50 eq) of the starting polyisocyanate A1) containing isocyanurate structures were placed at a temperature of 50 °C under stirring and dry nitrogen, and 151.8 g (1.50 eq) 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-methoxypropyl-2-acetate (MPA) and stirred for a further hour at 50 °C until the isocyanate groups were completely converted (IR control, absence of the isocyanate band at approximately 2270 cm -1 ) was stirred. A colorless solution of an amine-blocked HDI polyisocyanurate polyisocyanate with the following characteristics was obtained:

[0145] NCO content (blocked): 10.0%

[0146] NCO content (free): 0.0%

[0147] Solids content: 70 wt.%

[0148] Viscosity (23°C): 8050 mPas

[0149] After cooling to room temperature, the solution became cloudy after one day and was completely crystallized after five days.

[0150] Example 2 (according to the invention)

[0151] 770 g (4.00 eq) of the starting polyisocyanate A1) containing isocyanurate structures were initially charged at 70°C with stirring under dry nitrogen. 58 g (0.73 eq) of 2-butyl-2-ethyl-1,3-propanediol (BEPD), corresponding to an amount of 7.0 wt.% based on the total amount of polyisocyanate and branched diol, were added over 15 min, and stirring was continued until the NCO content of 16.9%, corresponding to complete urethanization, was reached. The reaction mixture was cooled to 50°C, and 337 g (3.34 eq) of diisopropylamine were added dropwise over a period of 4 hours. To reduce the viscosity, which increased significantly during the blocking reaction, a total of 250 g of 1-methoxypropyl-2-acetate (MPA) was added in several individual portions over the entire metering time. After the amine addition was complete, the reaction mixture was stirred for another hour at 50°C until the isocyanate groups were completely converted (IR control).The product was then diluted with another 250 g of isobutanol. This yielded a colorless, clear solution of an inventive amine-blocked HDI polyisocyanurate polyisocyanate with the following characteristics:

[0152] NCO content (blocked): 8.3%

[0153] NCO content (free): 0.0%

[0154] Solids content: 70 wt.%

[0155] Viscosity (23°C): 13700 mPas

[0156] After 12 weeks of storage at room temperature, the solution remained completely clear.

[0157] No turbidity, solid precipitation or crystallization were observed.

[0158] Examples 3 to 11 (inventive and comparison)

[0159] According to the process described in Example 2, blocked polyisocyanates were prepared starting from different polyisocyanates by urethanization with different branched diols and diisopropylamine, whereby the entire amount of solvent was already introduced together with the polyisocyanate component before the start of the reaction.

[0160] The following table shows the compositions in wt.%, characteristics and storage stability of the resulting products after 4 weeks of storage at room temperature.

[0161] 2021PF30291 - Abroad

[0162] -25-

[0163] Examples 2, 3, 4, 6, 7, 9 and 11 according to the invention show that polyisocyanates containing isocyanurate and iminooxadiazinedione structures, 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 give clear blocked polyisocyanate crosslinkers which can be crosslinked over a period of 4

[0164] weeks and show no tendency to crystallize.

[0165] In contrast, the blocked polyisocyanates of Comparative Examples 1, 5, 8 and 10, which were prepared without or using only 2 wt.% of a branched diol, become cloudy after a short time at room temperature and are completely crystallized after 4 weeks.

Claims

Patent claims 1. Process for the production of a blocked polyisocyanate comprising a reaction A) at least one polyisocyanate component having at least isocyanurate and / or iminooxadiazinde ion structures, with B) at least one branched aliphatic diol and with C) at least one secondary amine with aliphatic, cycloaliphatic and / or araliphatic substituents, characterized in that component B) is used in an amount of more than 2 wt. %, 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 remaining after the reaction of components A) and B), and polyisocyanate component A) is produced by modifying simple linearaliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates, which have at least isocyanurate and / or iminooxadiazindeione structures, wherein > 70 equivalent %, based on the NCO content, of linearaliphatic diisocyanates were used for the modification.

2. Method according to claim 1, characterized in that polyisocyanates produced by modification of simple linearaliphatic, cycloaliphatic, araliphatic and / or aromatic diisocyanates, which have at least isocyanurate and / or iminooxadiazindeione structures, are used as the polyisocyanate component A), wherein > 80 equivalent %, particularly preferably > 90 equivalent %, in each case based on the NCO content, and most preferably exclusively linearaliphatic diisocyanates were used for the modification.

3. Method according to one of claims 1 characterized in that the polyisocyanate component A) is a polyisocyanate produced by modification of linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, which has at least isocyanurate and / or iminooxadiazinde ione structures.

4. A method according to any one of claims 1 to 3, characterized in that the polyisocyanate component A) comprises polyisocyanates having isocyanurate structures with A medium 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 wt.%, preferably 8.0 to 25.0 wt.%, particularly preferably 10.0 to 24.0 wt.%, are used. A process 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. A process 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 such alcohols. A process according to any one of claims 1 to 6, characterized in that the at least one branched aliphatic diol is present in an amount of 3 to 20 wt.%, preferably 4 to 15 wt.%.-% and particularly preferably 5 to 12 wt.%, based on the total amount of components A) and B). 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). comprising, in which R and R' independently represent identical or different residues, which are saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, or araliphatic organic residues with 1 to 18 carbon atoms, which are substituted or unsubstituted, and / or have oxygen atoms in the chain, wherein R and R' can also combine with each other, together with the nitrogen atom and optionally with further oxygen atoms, to form heterocyclic rings with 5 to 8 ring members, which may optionally be further substituted. A process according to any one of claims 1 to 8, characterized in that the at least one secondary amine C) has the general formula (I) comprising, in which R and R' independently represent identical or different saturated linear or branched aliphatic residues with 1 to 18, particularly preferably 1 to 6 carbon atoms, or cycloaliphatic hydrocarbon residues with 6 to 13, particularly preferably 6 to 9 carbon atoms, wherein R and R' may optionally also form heterocyclic rings with 5 to 6 ring members in combination with each other together with the nitrogen atom and optionally with a further oxygen atom, which may optionally be further substituted.

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

11. Method according to claims 1 to 10, characterized in that the at least one secondary amine C) is used in such an amount that corresponds 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).

12. A 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), optionally in the presence of suitable solvents, at a temperature between 0 and 120°C, preferably 20 to 100°C, particularly preferably 40 to 80°C, in any order.

13. Blocked polyisocyanate, obtainable or directly obtained by a method according to any one of claims 1 to 12.

14. One-component baking system comprising a) at least one blocked polyisocyanate according to claim 13, b) at least one binder reactive towards isocyanate groups with at least two isocyanate-reactive groups per molecule on average, c) optionally catalysts and d) optionally solvents and / or optionally auxiliary and additives.

15. Substrates, at least partially coated with at least one hardened single-component curing system according to claim 14.

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