Blocked polyisocyanates

Abstract

The invention relates to a method for producing blocked polyisocyanates, comprising the reaction of A) a polyisocyanate component with B) at least one branched aliphatic diol and C) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents, characterized in that component A) comprises at least one linear aliphatic polyisocyanate A1), component A) having at least one cycloaliphatic polyisocyanate A) having at least an isocyanurate and / or iminooxadiazindione structure, and at least one cycloaliphatic polyisocyanate A2), in which A1) and A2) are present in an equivalence ratio of 2.0: 1.0 to 5.9: 1.0 relative to each other, and component B) is used in an amount greater than 2% by weight, based on the total amount of components A) and B), and component C) is used in an amount corresponding to at least 95 mol% of the isocyanate groups that are arithmetically still present after the reaction of components A) and B), and a blocked polyisocyanate.

Description

Technical Field

[0001] The present invention relates to a blocked polyisocyanate. Background Art

[0002] Such 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 blends that are storage-stable at room temperature. At higher temperatures, the blocking agents cleave again and release isocyanate groups that crosslink with the polyol component.

[0003] Such blocked polyisocyanates are used as crosslinker components of one-component polyurethane (1K-PU) stoving varnishes, for example for automotive OEM finishing, plastics painting and coil coatings. The type of blocking agent used here is quite important. Reactivity, thermal yellowing and other coating properties are largely determined by the blocking agent. (U. Meier Westhues et al., "Polyurethanes: Coatings, Adhesives and Sealants", 2nd revised edition, Hanover: Vincentz Network, 2019).

[0004] Secondary monoamines are of particular interest as blocking agents because they allow particularly low baking temperatures. In particular, technically and economically important polyisocyanates having isocyanurate groups and based on linear aliphatic diisocyanates such as 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI) and 1,5-diisocyanatopentane (pentamethylene diisocyanate, PDI) have not been of practical interest so far in the form of blocking with secondary amines such as diisopropylamine. The reason for this is that solutions of such blocked polyisocyanates in conventional paint solvents are not storage-stable for long periods of time because they show a very high tendency to solidify, for example by crystallization of the blocked polyisocyanates present. (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 toluene diisocyanate (TDI), which, optionally after chain extension with diols and / or triols, are terminated only with secondary amines, were first described as crosslinker components for solventborne 1K-PU stoving lacquers in EP-A 0 096 210. Sterically hindered secondary amines, such as diisopropylamine, dicyclohexylamine or 2,2,6,6-tetramethylpiperidine, were identified as suitable blocking agents.

[0006] EP-A 0125438 also describes 1K adhesives in which the crosslinking component consists of reaction products of polyisocyanates, optionally pre-extended with polyols, with secondary amines used exclusively as blocking agents. These adhesives are used for solventborne coating materials, powder coatings and, in their protonated form, also for cathodic electrodeposition coatings. However, no information is found in this publication about the storage stability of solutions of blocked polyisocyanates.

[0007] Polyisocyanates blocked with secondary amines, in particular isocyanate-functional prepolymers, are known polyamine crosslinker components from EP-A 0 407 829. HDI derivatives containing biuret or isocyanurate groups are also very generally identified as suitable starting polyisocyanates for producing blocked prepolymers and can optionally be modified with substoichiometric amounts of low molecular weight polyhydroxy compounds before blocking. This publication does not allow any conclusions to be drawn about the storage stability of secondary amine-blocked polyisocyanates.

[0008] EP-A 3643733 describes special secondary monoamines which carry branched alkyl groups 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 particularly low temperatures. The publication contains neither any information about the lack of crystallization stability of isocyanurate polyisocyanates based on linear aliphatic diisocyanates blocked with secondary amines nor any suggestions about how to overcome this problem.

[0009] The high crystallization tendency of amine-terminated isocyanurate polyisocyanates based on linear aliphatic diisocyanates can be reduced in various ways. For example, one concept is so-called mixed blocking, ie the simultaneous use of two or more different blocking agents.

[0010] The subject of EP-A 0600314 is a blocked polyisocyanate, wherein the isocyanate groups are blocked with diisopropylamine to at least 30 equiv. % and up to 70 equiv. %, and with at least one C 6H 4 ester and / or 1,2,4-triazole to a total of 30 to 70 equiv. %. This mixed blocking prevents the crystallization tendency of, for example, HDI polyisocyanurate polyisocyanate derivatives. However, when such products are used in 1K-PU coating systems, different deblocking temperatures (deblockingtemperatures) of different blocked isocyanate groups usually cause problems in practice. In addition, the blocking agent mixture released during the baking of such systems may also have a negative impact on the coating properties, which is why polyisocyanates with mixed blocking do not enjoy widespread use.

[0011] One possibility for producing crystallization-stable, exclusively amine-terminated polyisocyanate crosslinkers is the reaction of defined mixtures of linear aliphatic and cycloaliphatic polyisocyanates with secondary amines, according to the teaching of EP-A 0 900 814. However, the coating films produced using such polyisocyanates have a significantly different property profile and likewise do not demonstrate their long-term storage stability.

[0012] According to EP-A 1524284, polyisocyanates terminated with secondary amines and containing a defined amount of biuret structures are crystallization-stable. Suitable polyisocyanates are pure HDI biuret or retrospectively biuretized HDI polyisocyanates having isocyanurate and / or iminooxadiazinedione structures. Prior to termination, these polyisocyanates can optionally be partially reacted with compounds reactive toward isocyanate groups, such as low-molecular-weight or high-molecular-weight difunctional or polyfunctional alcohols, amines or high-molecular-weight polyhydroxy compounds based on polyesters, polyethers, polycarbonates or polyacrylates. In particular, diisopropylamine, N-tert-butylbenzylamine, dicyclohexylamine or mixtures thereof are used as termination agents.

[0013] According to the teaching of WO 2004 / 104065, polyisocyanates based on linear aliphatic diisocyanates and blocked with secondary amines also behave similarly in terms of crystallization stability when some of the urea groups formed during the blocking process are further converted into biuret structures.

[0014] However, polyisocyanates containing biuret structures are overall much less temperature resistant than isocyanurates. Due to equilibrium reactions, especially under conventional baking conditions in coil coating applications, and the possible release of monomeric diisocyanates, such products cannot be marketed.

[0015] The problem of the lack of crystallization stability and the high curing tendency of polyisocyanates based on linear aliphatic diisocyanates and containing isocyanurate groups blocked with secondary monoamines has not yet been solved satisfactorily. The object of the present invention is to provide blocked polyisocyanates derived from linear aliphatic polyisocyanates which are storage-stable over a period of at least 6 months.

[0016] As has now been found, surprisingly, polyisocyanates based on defined mixtures of linear aliphatic diisocyanates (such as HDI or PDI) and cycloaliphatic polyisocyanates, as well as polyisocyanurate polyisocyanates which have been partially urethanized with branched alcohols (especially branched diols), can be reacted with secondary amines (such as diisopropylamine) to give fully cured stable, non-crystalline blocked polyisocyanate crosslinkers. These novel blocked polyisocyanates are particularly suitable for coil coating applications. Summary of the invention

[0017] The subject of the present invention is therefore a process for preparing blocked polyisocyanates, which comprises the following reactions:

[0018] A) polyisocyanate component and

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

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

[0021] Characterized in that component A) comprises at least one linear aliphatic polyisocyanate A1) having at least an isocyanurate and / or an iminooxadiazinedione structure, and at least one alicyclic polyisocyanate A2), wherein A1) and A2) are present in an equivalent ratio of 2.0:1.0 to 5.9:1.0 to one another, and component B) is used in an amount of more than 2% by weight, based on the total amount of components A and B), and component C) is used in an amount corresponding to at least 95 mol % of the isocyanate groups arithmetically still present after the reaction of components A) and B).

[0022] According to the present invention, the term "comprising" or "containing" preferably means "consisting essentially of", and more preferably means "consisting of...." The further embodiments recited in the claims and the description may be combined as desired, provided that the context does not clearly indicate otherwise.

[0023] As used herein, "at least one" means 1 or more, such as 2, 3, 4, 5, 6, 7, 8, 9 or more. With respect to the components of the compounds described herein, the number does not refer to the absolute number of molecules, but rather to the nature of the component. Thus, "at least one branched aliphatic diol" means, for example, that only one branched aliphatic diol or two or more different types of branched aliphatic diols are present, without specifying the amount of a single compound.

[0024] Numerical values ​​without decimal points specified herein refer to the complete value to one decimal place in each case. For example, "99%" means "99.0%".

[0025] Numerical ranges given in the format "from x to y" are inclusive of the stated values. If two or more preferred numerical ranges are given in this format, it is understood that all ranges resulting from combinations of the various limits are encompassed.

[0026] The term "aliphatic" is presently defined as a saturated or unsaturated non-aromatic hydrocarbon group.

[0027] The term "straight-chain 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 non-aromatic units (e.g. cycloalkanes, cycloalkenes or oxacycloalkanes, thiacycloalkanes, azacycloalkanes or thiazaazacycloalkanes). Specific examples are cyclohexyl, cyclopentyl and their N-heterocyclic derivatives or O-heterocyclic derivatives, such as pyrimidine, pyrazine, tetrahydropyran or tetrahydrofuran.

[0028] The term "araliphatic" is presently defined to mean a hydrocarbyl group consisting of an aromatic hydrocarbyl group and a saturated or unsaturated hydrocarbyl group directly bonded to the aromatic group.

[0029] If a group or compound is disclosed as "optionally substituted" or "substituted", suitable substituents are -F, -Cl, -Br, -I, -OH, -OCH 3 、-OCH 2 CH 3 , -O-isopropyl or -O-n-propyl, -OCF 3 , -CF 3 , -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 serve as substituents for carbon-bonded hydrogen atoms of the corresponding molecule. Preferred substituents are halogen (especially -F, -Cl), C 1-6 Alkoxy (especially methoxy and ethoxy), hydroxy, trifluoromethyl and trifluoromethoxy, in each case as substituents of carbon-bonded hydrogen atoms of the corresponding molecules.

[0030] In a preferred embodiment, the polyisocyanate A1) and the polyisocyanate A2) are present in an equivalent ratio of 2.5:1.0 to 5.5:1, preferably 3.0:1 to 5.0:1 and particularly preferably 3.5:1 to 4.5:1 to one another.

[0031] The at least one linear aliphatic polyisocyanate A1) having at least an isocyanurate and / or iminooxadiazinedione structure is also referred to in the present invention as starting compound A1) or starting polyisocyanate A1) or polyisocyanate A1) having an isocyanurate and / or iminooxadiazinedione structure.

[0032] Starting compounds A1) for the process according to the invention are any desired polyisocyanates which have been prepared by modifying linear aliphatic and optionally araliphatic and / or aromatic diisocyanates and have at least isocyanurate and / or iminooxadiazinedione structures.

[0033] Suitable diisocyanates for the preparation of these polyisocyanates A1) are any desired 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, more particularly diisocyanates with aliphatic, araliphatic and / or aromatically bonded isocyanate groups in the molecular weight range from 140 to 400, for example 1,4-diisocyanatobutane, 1,5-diisocyanatopentane (pentamethylene diisocyanate, PDI), 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI), 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3- and 1,4-bis(isocyanatomethyl)benzene (xylylene diisocyanate, XDI), 1,3- and 1,4-bis(1-isocyanato-1-methylethyl)benzene (TMXDI), 1,3- and 1,4-phenylene diisocyanate, toluene 2,4- and 2,6-diisocyanate and any mixtures of these isomers, diphenylmethane 2,4'- and / or 4,4'-diisocyanate and naphthalene-1,5-diisocyanate and any mixtures of such diisocyanates. Other diisocyanates which are likewise suitable can be found, for example, in Justus Liebigs Annalen der Chemie, volume 562 (1949), pages 75-136.

[0034] In a further preferred embodiment, polyisocyanates which have been prepared by modifying linear aliphatic, araliphatic and / or aromatic diisocyanates and have at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component A1), in each case >80 equivalent %, particularly preferably >90 equivalent %, based on the NCO content, and particularly preferably exclusively linear aliphatic diisocyanates are used for the modification.

[0035] In a further preferred embodiment, polyisocyanates which are prepared by modifying linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, and have at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanate component A1).

[0036] Preferred diisocyanates for preparing polyisocyanates A1) having isocyanurate and / or iminooxadiazinedione structures are diisocyanates of the type described having linear aliphatically bonded isocyanate groups, particularly preferably unbranched linear aliphatic diisocyanates such as 1,4-diisocyanatobutane, 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), 1,8-diisocyanatooctane, 1,9-diisocyanatononane and 1,10-diisocyanatodecane. Particularly preferred diisocyanates are HDI and / or PDI.

[0037] In the context of the present invention, the at least one cycloaliphatic polyisocyanate A2) is also referred to as starting compound A2) or starting polyisocyanate A2) or polyisocyanate A2) having an isocyanurate and / or urethane structure.

[0038] Starting compounds A2) for the process according to the invention are any desired polyisocyanates which have been prepared by modifying cycloaliphatic diisocyanates and which preferably have at least an isocyanurate and / or urethane structure.

[0039] Suitable diisocyanates for the preparation of these polyisocyanates A2) are any desired diisocyanates which are obtainable 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, such as more particularly those with cycloaliphatic bonded isocyanate groups in the molecular weight range from 140 to 400, for example with 1,3- and 1,4-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, 1-isocyanato-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-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), 1,3-diisocyanatoadamantane, 1,3-dimethyl-5,7-diisocyanatoadamantane.

[0040] In a preferred embodiment, the cycloaliphatic diisocyanates are prepared by modifying 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 (HDI). 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, As polyisocyanates A2) are used 1'-bis(cyclohexyl), 1,8-diisocyanato-p-menthane, 1,3-diisocyanatoadamantane, 1,3-dimethyl-5,7-diisocyanatoadamantane or mixtures thereof, and particularly preferably polyisocyanates prepared by modifying 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane and / or 1,3- and 1,4-diisocyanatocyclohexane and having at least an isocyanurate and / or urethane structure.

[0041] Also preferred is a process for preparing blocked polyisocyanates comprising the following reactions:

[0042] A) polyisocyanate component and

[0043] B) at least one branched aliphatic diol and

[0044] C) at least one secondary amine having aliphatic, cycloaliphatic and / or araliphatic substituents,

[0045] The invention is characterized in that component A) comprises at least one linear aliphatic polyisocyanate A1) based on 1,5-diisocyanatopentane (pentamethylene diisocyanate; PDI) and / or 1,6-diisocyanatohexane (hexamethylene diisocyanate; HDI), which has at least an isocyanurate and / or an iminooxadiazinedione structure, and at least one aliphatic polyisocyanate A1) based on 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate; IPDI). Cyclic polyisocyanates A2), wherein A1) and A2) are present in an equivalent ratio of 2.0:1.0 to 5.9:1.0, preferably 2.5:1.0 to 5.5:1, preferably 3.0:1 to 5.0:1 and particularly preferably 3.5:1 to 4.5:1 to one another, and component B) is used in an amount of more than 2% by weight, based on the total amount of components A) and B), and component C) is used in an amount corresponding to at least 95 mol % of the isocyanate groups arithmetically still present after the reaction of components A) and B).

[0046] The polyisocyanates A1) and A2) and the polyisocyanate component A) 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. Suitable processes are described, for example, in J. Prakt. Chem. 336 (1994) 185-200, in DE-A 1954093, DE-A 2414413, DE-A 2452532, DE-A 2641380, DE-A 3900053 and DE-A 3928503 or in EP-A 0336205, EP-A 0339396 and EP-A 0798299. Depending on the modification process selected, the polyisocyanates A) used in the process according to the invention may, in the case of polyisocyanates A1), in addition to isocyanurate and / or iminooxadiazinedione structures, and in the case of polyisocyanates A2), in addition to isocyanurate and / or urethane structures, optionally also have iminooxadiazinedione, semicarbazidedione, allophanate, biuret, urethane and / or oxadiazinedione structures.

[0047] In the production of the starting polyisocyanates A1) and A2), 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 thin-film distillation under reduced pressure or by extraction with suitable solvents inert toward isocyanate groups, for example aliphatic or cycloaliphatic hydrocarbons, such as pentane, hexane, heptane, cyclopentane or cyclohexane.

[0048] In the process according to the invention, polyisocyanates A1) and A2) of said type with 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, are preferably used as starting polyisocyanates. The residual monomer content is determined by gas chromatography using an internal standard in accordance with DIN EN ISO 10283:2007-11.

[0049] The above-mentioned suitable, preferred, particularly preferred and very particularly preferred polyisocyanates A1) contain an isocyanurate structure and have an average NCO functionality of 2.3 to 5.0, preferably 2.5 to 4.5, and an isocyanate group content of 6.0 to 26.0% by weight, preferably 8.0 to 25.0% by weight, particularly preferably 10.0 to 24.0% by weight.

[0050] In the process according to the invention, the polyisocyanate component A) is reacted with at least one branched aliphatic diol B).

[0051] These are any saturated or unsaturated aliphatic diols, which can be mono-branched or multi-branched, can optionally have heteroatoms, ester groups and / or carbonate groups in the chain, and can optionally be further substituted.

[0052] In another preferred embodiment, at least one branched aliphatic diol has 3 to 36 carbon atoms. Examples 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, which can be obtained in a manner known per se, for example by hydrogenation of dimer fatty acids and / or their esters, and are named for example (Croda International Plc, UK) and Sovermol 908 (BASFSE, DE), as well as ether glycols, such as dipropylene glycol, tripropylene glycol and ethylhexylglycerol, ester glycols, such as 3-hydroxy-2,2-dimethylpropyl 3-hydroxy-2,-2-dimethylpropionate (hydroxypivaloyl hydroxyneopentyl ester, HPN), glyceryl monocaprylate and glyceryl monostearate, or any mixtures of such alcohols.

[0053] In another preferred embodiment, 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 such alcohols.

[0054] The branched aliphatic diol B) in the process according to the invention is used in an amount of more than 2% by weight, preferably 3% to 20% by weight, particularly preferably 4% to 15% by weight and especially 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 the blocked polyisocyanate from crystallizing; the use of an amount of more than 20% by weight leads to a very high product viscosity, which is uneconomical in practical use due to the low isocyanate content.

[0055] Besides the branched aliphatic diols mentioned, component B) may optionally also contain minor amounts of other alcohol compounds.

[0056] These are, for example, monohydric alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, pentanol, hexanol, isomers of octanol and nonanol, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, isomers of methylcyclohexanol, hydroxymethylcyclohexane, 3-methyl-3-hydroxymethyloxetane, benzyl alcohol, phenol, cresol, octylphenol, isomers of 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, such as 1,2- and 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4'-(1-methylene)bicyclohexanol; triols, such as 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, such as 2,2-bis(hydroxymethyl)-1,3-propanediol or any mixtures of such alcohols.

[0057] If present, these further alcohol compounds are used in the process according to the invention in an amount of not more than 25% by weight, preferably not more than 20% by weight and particularly preferably 15% by weight, based on the amount of branched aliphatic diol used.

[0058] 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, especially preferably from 1.9 to 2.1 and in particular 2.0.

[0059] 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).

[0060] These are in particular secondary amines of the general formula (I)

[0061]

[0062] Where R and R' are independent of each other

[0063] are identical or different radicals and 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' may also be combined with one another to form, together with the nitrogen atom and optionally further oxygen atoms, a heterocycle having 5 to 8 ring members, which may optionally be further substituted.

[0064] Preferably, the radicals R and R' are saturated, straight-chain or branched aliphatic radicals having 1 to 18 carbon atoms, particularly preferably 1 to 6 carbon atoms, or alicyclic hydrocarbon radicals having 6 to 13 carbon atoms, particularly preferably 6 to 9 carbon atoms, wherein R and R' can optionally also be combined with one another, with the nitrogen atom and optionally further oxygen atoms, to form a heterocycle having 5 to 6 ring members, which can optionally be further substituted.

[0065] 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, (hexahydroazepine), pyrrolidine, 2,5-dimethylpyrrolidine or morpholine.

[0066] Also suitable, although less preferred, are secondary amines C) which, in addition to the secondary amino group, carry further groups which are reactive toward isocyanate groups but, like the 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.

[0067] As secondary amine C), preference is given to diisopropylamine, dicyclohexylamine, N-tert-butylbenzylamine or any mixtures of these amines. Diisopropylamine is particularly preferred.

[0068] The secondary amines C) are used in the process of the invention in an amount corresponding to at least 95 mol %, preferably at least 96 mol %, particularly preferably at least 98 mol % and especially preferably at least 100 mol % of the isocyanate groups arithmetically still present after the reaction of components A) and B).

[0069] The process according to the invention can optionally also be carried out in a suitable solvent which is inert toward isocyanate groups. Suitable solvents are, for example, customary lacquer solvents known per se, such as ethyl acetate, ethyl butyrate, 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, white spirit, higher substituted aromatics, such as those known under the names solvent naphtha, (Deutsche EXXON CHEMICAL GmbH, Cologne, DE) and (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-ethylpyrrolidone, N-butylpyrrolidone and N-methylcaprolactam, or any mixtures of such solvents.

[0070] 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 described, at a temperature of 0 to 120° C., preferably 20 to 100° C., particularly preferably 40 to 80° C., in any order of the ratios mentioned above.

[0071] 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.

[0072] The reaction of the polyisocyanate component A) with the diol component B) and the amine component C) can be carried out in the process according to the invention without catalysis, but in order to accelerate the reaction it is also possible to 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(ethylacetoacetate), bismuth(III) 2-ethylhexanoate, bismuth(III) octoate, bismuth(III) neodecanoate and molybdenum glycolate.

[0073] 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.

[0074] If a catalyst is also used to accelerate the reaction, it can optionally be deactivated, preferably chemically, after the desired NCO content has been reached. Catalyst poisons suitable for this purpose 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 p-toluenesulfonate 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 trimethylsilyl diethyl phosphate.

[0075] Optionally, the amount of catalyst poison used for deactivation depends on the amount of catalyst used. If used, based on the amount of catalyst used, 0.1 to 2.0 equivalents, preferably 0.4 to 1.6 equivalents, particularly preferably 0.8 to 1.2 equivalents, especially preferably an equivalent amount of stopper is used.

[0076] After the reaction of the polyisocyanate component A) with the diol component B) and the amine component C), 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, the blocked polyisocyanate can optionally be further diluted with a solvent, for example to reduce the viscosity. In addition to the abovementioned solvents, alcoholic solvents such as n-butanol or isobutanol can also be used here, since the isocyanate groups are already largely consumed, preferably completely consumed, during the reaction with the blocking agent.

[0077] In the process according to the invention, other auxiliaries and adjuvants, such as antioxidants or light stabilizers, may optionally also be used. On the one hand, these auxiliaries and adjuvants may be mixed with one or more of the reaction components A), B) and C) before the actual reaction begins. However, they may also be added to the reaction mixture at any time during the reaction or added to the blocked polyisocyanate according to the invention after the reaction.

[0078] 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, tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and aliphatic branched C7 to C9 alcohols, such as 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, Isotridecyl ester, bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] diethylthioate, N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyphenyl) propionamide, 1,2-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hydrazine, 2,4-di-tert-butylphenyl 4'-hydroxy-3',5'-di-tert-butylbenzoate, (3,5-di-tert-butyl-4- esters of 1,2-di-(2-hydroxyphenyl)methylthioacetic acid and aliphatic branched C10 to C14 alcohols, 2,2'-thiobis(4-methyl-6-tert-butylphenol), 2-methyl-4,6-bis(octylthiomethyl)phenol, 1,3,5-trimethyl-2,4,6-tri(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate or 2,5-di-tert-amylhydroquinone.

[0079] Suitable antioxidants are also thioethers, such as didodecyl 3,3'-thiodipropionate or distearyl 3,3'-thiodipropionate, which are preferably used in combination with phenolic antioxidants of the type mentioned.

[0080] 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, phenyl neopentyl glycol phosphite, 2,4,6-tri-tert-butylphenyl 2-butyl 2-ethyl-1,3-propanediol phosphite, diisodecyl pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite or tetraphenyl dipropylene glycol diphosphite.

[0081] Suitable light stabilizers are, for example, UV absorbers of the 2-hydroxyphenylbenzotriazole type, light stabilizers of the HALS compound type which are substituted or unsubstituted on the nitrogen atom, such as or DF (BASF SE, Ludwigshafen, DE), or as in ""Lichtschutzmittel Lacke" (A. Valet, Vincentz Verlag, Hanover, 1996) and those described in "Stabilization of Polymer Materials" (H. Zweifel, Springer Verlag, Berlin, 1997, Appendix 3, pages 181-213).

[0082] In the process according to the invention it is also possible to use further auxiliaries and adjuvants, for example the hydrazide- and / or hydroxyl-functional stabilizers described in EP-A 0 829 500, for example addition products of hydrazine and propylene carbonate.

[0083] The auxiliary agents and adjuvants 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, based in each case on the total amount of the starting polyisocyanate A).

[0084] Irrespective of the nature of the process variant, the process according to the invention provides completely clear and transparent polyisocyanates terminated with secondary monoamines and containing isocyanurate groups, or organic solutions of such polyisocyanates, which, in contrast to similar polyisocyanates prepared using the same starting components but without partial urethanization with branched alcohols, have no tendency to crystallize even after storage at low temperatures for relatively long periods of time, for example at 15 to 25° C. for 12 weeks.

[0085] A further subject of the present invention is therefore the blocked polyisocyanates obtainable or obtainable by the process according to the invention.

[0086] Another subject of the present invention is 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).

[0087] The blocked polyisocyanates according to the invention are valuable raw 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 particularly suitable for plastic painting, automotive OEM coating or coil coating applications. They provide coatings that have very good resistance to yellowing even under overbaking conditions.

[0088] Another subject of the present invention is therefore a one-component baking system comprising

[0089] a) at least one blocked polyisocyanate according to the invention,

[0090] b) at least one binder which is reactive toward isocyanate groups and has an average of at least two isocyanate-reactive groups per molecule,

[0091] c) optionally a catalyst, and

[0092] d) optional solvents and / or optional auxiliaries and adjuvants.

[0093] Finally, a substrate at least partially coated with at least one curing one-component baking system according to the invention is also a further subject of the present invention.

[0094] To prepare the one-component baking systems according to the invention (1K baking varnishes), the blocked polyisocyanates according to the invention a) are mixed with coating binders b) known per se from coating technology, optionally with the simultaneous use of catalysts c) to accelerate the crosslinking reaction, and optionally with the use of solvents and / or optionally with auxiliaries and adjuvants d). This mixing must take place below the 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 baking systems according to the invention is carried out at temperatures of 15 to 100° C.

[0095] 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 an average of at least two isocyanate-reactive groups per molecule, for example hydroxyl, mercapto, amino or carboxylic acid groups.

[0096] Preferably, these binders b) are customary dihydroxy and / or polyhydroxy compounds known from polyurethane chemistry, for example polyester polyols, polyether polyols, polycarbonate polyols and / or polyacrylate polyols, or any blends of such polyols.

[0097] 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 blends of such polyols.

[0098] 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, of the type which can be produced in a manner known per se by reaction of polyols with insufficient amounts of polycarboxylic acids, the corresponding carboxylic anhydrides, the corresponding polycarboxylic esters of lower alcohols or by reaction with lactones.

[0099] Suitable polyols for producing the polyester polyols b) are, for example, 1,2-ethanediol, 1,2- and 1,3-propylene glycol, butanediol, pentanediol, hexanediol, isomers of 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, 1,1,1,1-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)sorbitol-4-oxaheptane-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.

[0100] Suitable carboxylic acids and carboxylic acid derivatives for producing the polyester polyols b) in the one-component baking systems of 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, 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, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic anhydride, dimethyl terephthalate and diol terephthalate, and also dimer and trimer fatty acids, which can be used alone or in any desired mixtures with one another.

[0101] Monocarboxylic acids, such as benzoic acid, acetic acid, propionic acid, butyric acid or 2-ethylhexanoic acid, can optionally also be used in minor amounts for producing the polyester polyols b).

[0102] Suitable polyester polyols b) for the one-component baking systems of the invention are also those which can be produced in a manner known per se from lactones and polyols such as those listed above by way of example as ring-opening starter molecules. Suitable lactones for the production 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.

[0103] The production 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 synthesis components for the production of these polyester polyols b) are, for example, the polyols, polycarboxylic acids and derivatives thereof mentioned above as being suitable for the production of the polyester polyols b), which can also be used in the form of any desired mixtures.

[0104] The production of polyester polyols b) can be carried out according to methods known per se, such as the methods described in detail by E. Gubbels et al. in Polyesters. Included 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, a catalytic amount of a standard esterification catalyst, such as an acid, a base or a transition metal compound, such as tetrabutoxytitanium, can be used. The esterification reaction is generally 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.

[0105] 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 manner known per se by alkoxylation of suitable starter molecules. As mentioned above, any desired polyols suitable for the production of polyester polyols b) can be used as starter molecules for the production of these polyether polyols.

[0106] Suitable alkylene oxides for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be used in any sequence or in a mixture.

[0107] Suitable polycarbonate polyols b) are in particular the reaction products of diols known per se (e.g. those illustrated above in the list of polyols) with diaryl carbonates (e.g. diphenyl carbonate, dimethyl carbonate or phosgene). Suitable polycarbonate polyols b) are also those which contain ester groups in addition to the carbonate structure. These are in particular polyester carbonate diols known per se, obtained, for example, according to the teaching of DE-B 1770245, by reaction of diols with lactones (e.g. in particular ε-caprolactone) and subsequent reaction of the resulting polyester diols with diphenyl carbonate or dimethyl carbonate. Likewise suitable polycarbonate polyols b) are those which contain additional ether groups in addition to the carbonate structure. These are in particular polyether carbonate polyols known per se, obtained, for example, by the process of EP-A 2046861, by catalytic reaction of alkylene oxides (epoxides) and carbon dioxide in the presence of H-functional starter substances.

[0108] 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 average molecular weight can be calculated from the functionality and the hydroxyl number or can be determined by gel permeation chromatography (GPC), and a hydroxyl content of 0.1 to 12% by weight, preferably 1 to 10% by weight. Such polyols are prepared in a customary manner by copolymerization of hydroxyl-containing ethylenically unsaturated monomers with hydroxyl-free ethylenic monomers.

[0109] Examples of monomers suitable for producing 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, methacrylic acid 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-butyl methacrylate, norbornyl methacrylate or isobornyl methacrylate, diesters of fumaric acid, itaconic acid or maleic acid having 4 to 8 carbon atoms, acrylamide, methacrylamide, vinyl esters of alkanemonocarboxylic acids having 2 to 5 carbon atoms, such as 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, trimethylolpropane monoacrylate or pentaerythritol monoacrylate or methacrylate, and any mixtures of such monomers as exemplarily mentioned.

[0110] The one-component baking system according to the invention may optionally contain catalysts c). These catalysts are in particular the urethanization catalysts customary in isocyanate chemistry, which have already been specified above as being 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 baking system according to the invention as individual substances or in any mixture with one another in an amount of 0.005% by weight to 5% by weight, preferably 0.005% by weight to 2% by weight, particularly preferably 0.005% by weight 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).

[0111] The one-component baking system according to the invention may also optionally contain further auxiliaries and adjuvants d). In addition to the above-mentioned antioxidants and light stabilizers for optional use in the process according to the invention, these are, for example, customary plasticizers, leveling agents, rheological additives, slip additives, defoamers, fillers and / or pigments familiar to the person skilled in the art, if any, used in customary coating technology amounts. A comprehensive overview of such suitable auxiliaries and adjuvants can be found, for example, in "Additive kompakt" by Bodo Müller, Vincentz Network GmbH & Co KG (2009).

[0112] In the production of the one-component baking system according to the invention, the polyisocyanate component a) and the binder component b) are preferably used in such amounts that the equivalent ratio of the sum of blocked and unblocked isocyanate groups from a) to the isocyanate-reactive groups from b) is from 0.5:1 to 1.5:1, more preferably from 0.7:1 to 1.3:1, particularly preferably from 0.8:1 to 1.2:1.

[0113] The one-component baking system according to the invention may optionally contain other compounds reactive toward isocyanate-reactive groups as additional crosslinker components. These are, for example, compounds containing epoxy groups and / or amino resins. Amino resins are condensation products of melamine and formaldehyde or urea and formaldehyde known in coating technology.

[0114] All conventional melamine-formaldehyde condensates which are unetherified or have been etherified with saturated monoalcohols having 1 to 4 carbon atoms are suitable. In the case of simultaneous use of further crosslinking components, the amount of binder having isocyanate-reactive groups must be adjusted accordingly.

[0115] The one-component baking systems according to the invention thus obtained can be applied by methods known per se, for example by spraying, brushing, dipping, flooding or by means of a roller or doctor blade in one or more coats.

[0116] Candidate substrates are any substrates, such as metal, wood, glass, stone, ceramic materials, composite materials or any kind of plastic, which before coating may optionally also be provided with generally known primer systems, topcoat systems, basecoat systems and / or clearcoat systems.

[0117] Curing of the dried film is carried out by baking at a temperature of 90 to 160° C., preferably 110 to 140° C. For example, the dry film coating thickness here may be 10 to 120 μm.

[0118] The one-component baking system according to 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 coating thicknesses of, for example, 3 to 40 μm can be achieved.

[0119] The features specified as being preferred for the method according to the invention are also preferred for the further subject matter of the invention.

[0120] The following examples are used to illustrate the present invention, but should not be construed as any limitation to the scope of protection. DETAILED DESCRIPTION

[0121] Example

[0122] Unless otherwise indicated, all percentages are by weight.

[0123] The NCO content was determined titrimetrically according to DIN EN ISO 11909:2007-05. The progress of the blocking reaction and the NCO freedom of the blocked polyisocyanate were determined by the isocyanate band (approx. 2270 cm -1 ) decreases or disappears to track.

[0124] 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 250 s -1 carried out at a shear rate of .

[0125] The residual monomer content is measured by gas chromatography using an internal standard in accordance with DIN EN ISO 10283:2007-11.

[0126] 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.

[0127] The contents (mol %) of isocyanurate and / or iminooxadiazinedione structures present in the polyisocyanate A1) and of isocyanurate and / or urethane structures present in the polyisocyanate A2) and of structures present in the polyisocyanate component A) are calculated from the integration of the proton decoupled 13C-NMR spectrum (recorded on a Bruker DPX-400 instrument) and are in each case based on the sum of the isocyanurate and / or iminooxadiazinedione and / or urethane structures and optionally present uretdione, allophanate, biuret and / or oxadiazinetriaone structures. 3In the case of , 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; carbamate: 156.3; oxadiazinedione: 147.8 and 143.9.

[0128] Starting compound

[0129] Polyisocyanate A)

[0130] Starting polyisocyanate A1)

[0131] Polyisocyanate prepared by catalytic trimerization of HDI based on Example 11 of EP-A 330966, except that the reaction was terminated by adding dibutyl phosphate having an NCO content of 40% in the crude mixture. Subsequently, unconverted HDI was removed 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:

[0132]

[0133] Starting polyisocyanate A2)

[0134] Polyisocyanates containing isocyanurate groups based on IPDI prepared according to EP-A-0003765:

[0135] 1332 g (6 mol) of IPDI was charged into a reactor equipped with a stirrer, a reflux condenser, and N 2 In a four-necked flask with a purge tube and an internal thermometer, degassing is performed three times at room temperature by applying a reduced pressure of about 50 mbar and covered with nitrogen. 10 ml of catalyst solution, i.e. 6% (2-hydroxyethyl) trimethylammonium hydroxide solution in 2-ethylhexanol / methanol 4:1 v / v, is added dropwise. Heat release (maximum 75 ° C) begins within 30 minutes. The reaction mixture is then heated to 80 ° C and subsequently stirred until the NCO content of the solution reaches 31.1% (about 30 minutes). Excess IPDI is removed by thin film distillation, and the obtained resin is dissolved in solvent naphtha (SN 100) with 70%. This obtains almost colorless polyisocyanurate polyisocyanates, which have the following characteristics:

[0136]

[0137] Example 1 (Comparative Example)

[0138] At a temperature of 70° C., 770 g (4.00 equivalents) of the starting polyisocyanate A1) containing an isocyanurate structure were introduced under stirring and dry nitrogen, mixed within 15 minutes with 58 g (0.73 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD), an amount corresponding to 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 within 4 hours. In order to reduce the viscosity which increased significantly during the blocking reaction, a total of 250 g of 1-methoxyprop-2-yl acetate (MPA) was added in several 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 (IR check). The product was then diluted with a further 250 g of isobutanol. This gives a colorless, clear solution of the amine-terminated HDI polyisocyanurate polyisocyanate according to the invention, which has the following characteristics:

[0139]

[0140]

[0141] After 12 weeks of storage at room temperature, the solution remained completely clear. After a total storage time of 14 weeks, a slight turbidity was observed, and after 16 weeks, the sample was completely crystallized.

[0142] Example 2 (Comparative Example)

[0143] According to EP0900814 B, Example 1.

[0144] At a temperature of 50° C., 140 g (0.70 equivalent) of the starting polyisocyanate A1 containing an isocyanurate structure and 105 g (0.30 equivalent) of the starting polyisocyanate A2 containing an isocyanurate structure were introduced under stirring and dry nitrogen, and mixed with 106.0 g (1.00 equivalent) of diisopropylamine over 2 hours. After the addition of the amine was completed, the reaction mixture was diluted with 70.0 g of 1-methoxypropan-2-yl acetate (MPA) and 70.0 g of isobutanol and stirred at 50° C. for another hour until the isocyanate groups were completely reacted (IR examination, at 2270 cm -1 There are colorless solutions of amine-terminated HDI and IPDI polyisocyanurate polyisocyanates with the following characteristics:

[0145]

[0146] After cooling to room temperature, the solution became turbid after 6 weeks and completely crystallized after 12 weeks.

[0147] Example 3 (Comparative Example)

[0148] At a temperature of 50° C., 458 g (2.38 equivalents) of the starting polyisocyanate A1 containing an isocyanurate structure and 210 g (0.59 equivalents) of the starting polyisocyanate A2 containing an isocyanate structure were introduced under stirring and dry nitrogen and mixed with 301 g (2.98 equivalents) of diisopropylamine over a period of 2 hours. After the addition of the amine was complete, the reaction mixture was diluted with 542 g of solvent naphtha (SN 100) and stirred at 50° C. for a further hour until the isocyanate groups had reacted completely (IR examination, 1.0 % IR at 2270 cm -1 There are colorless solutions of amine-terminated HDI and IPDI polyisocyanurate polyisocyanates with the following characteristics:

[0149]

[0150] After cooling to room temperature, the solution became cloudy after 2 days and completely crystallized after 7 days.

[0151] Example 4 (The present invention)

[0152] At a temperature of 50° C., 362 g (1.88 equivalents) of the starting polyisocyanate A1) containing an isocyanurate structure and 223 g (0.63 equivalents) of the starting polyisocyanate A2 containing an isocyanurate structure were introduced under stirring and dry nitrogen, mixed over 15 minutes with 37 g (0.47 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD), an amount corresponding to 6.0% by weight based on the total amount of polyisocyanate and branched diols, and stirring was continued until an NCO content of 13.75% corresponding to complete urethanization was reached. The reaction mixture was cooled to 50° C. and 206 g (2.04 equivalents) of diisopropylamine were added over 4 hours. In order to reduce the viscosity which increased significantly during the blocking reaction, a total of 441 g of solvent naphtha (SN 100) were added in portions over the entire metering time. After the end of the amine addition, the reaction mixture was stirred at 50° C. for a further hour until the isocyanate groups had reacted completely (IR check). This gave a colorless solution of amine-terminated HDI and IPDI polyisocyanurate polyisocyanates having the following characteristics:

[0153] NCO content (end-capping): 6.7%

[0154] NCO content (free): 0.0%

[0155] Solid content: 60% by weight

[0156] Viscosity (23°C): 9002mPas

[0157] After 6 months of storage at room temperature, the solution remained completely clear. No turbidity, solid precipitation or crystallization was observed.

[0158] After cooling to room temperature, the solution became cloudy after 2 days and completely crystallized after 7 days.

[0159] Example 5 (The present invention)

[0160] At a temperature of 50° C., 458 g (2.38 equivalents) of the starting polyisocyanate A1 containing an isocyanurate structure and 210 g (0.59 equivalents) of the starting polyisocyanate A2 containing an isocyanurate structure were introduced under stirring and dry nitrogen, mixed over 15 minutes with 42 g (0.53 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD), an amount corresponding to 6.0% by weight based on the total amount of polyisocyanate and branched diols, and stirring was continued until an NCO content of 14.4% corresponding to complete urethanization was reached. The reaction mixture was cooled to 50° C. and 248 g (2.45 equivalents) of diisopropylamine were added over 4 hours. In order to reduce the viscosity which increased significantly during the blocking reaction, a total of 534 g of solvent naphtha (SN 100) were added in 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 (IR check). This gave colorless solutions of amine-terminated HDI and IPDI polyisocyanurate polyisocyanates having the following characteristics:

[0161] NCO content (end-capping): 6.9%

[0162] NCO content (free): 0.0%

[0163] Solid content: 60% by weight

[0164] Viscosity (23°C): 7770mPas

[0165] After 6 months of storage at room temperature, the solution remained completely clear. No turbidity, solid precipitation or crystallization was observed.

[0166] Example 6 (The present invention)

[0167] At a temperature of 50 °C, 458 g (2.38 equivalents) of the starting polyisocyanate A1 containing an isocyanurate structure and 169 g (0.48 equivalents) of the starting polyisocyanate A2 containing an isocyanurate structure were introduced under stirring and dry nitrogen and mixed within 15 minutes with 40 g (0.50 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD) in an amount corresponding to 6.0% by weight based on the total amount of polyisocyanate and branched diol, and stirring was continued until an NCO content of 14.9% corresponding to complete urethanization was reached. The reaction mixture was cooled to 50 °C and 238 g (2.36 equivalents) of diisopropylamine were added within 4 hours. To reduce the viscosity which increases significantly during the blocking reaction, a total of 519 g of solvent naphtha (SN 100) were added in portions over the entire metering time. After the amine addition was complete, the reaction mixture was stirred at 50 °C for one more hour until the isocyanate groups had completely reacted (IR check). This gave a colorless solution of amine-blocked HDI and IPDI polyisocyanurate polyisocyanate with the following characteristics:

[0168] NCO content (blocked): 6.95%

[0169] NCO content (free): 0.0%

[0170] Solid content: 60% by weight

[0171] Viscosity (23 °C): 7150 mPas

[0172] After storage at room temperature for 6 months, the solution remained completely clear. No turbidity, solid precipitation or crystallization was observed.

[0173] Example 7 (Comparative example)

[0174] At a temperature of 50 °C, 487 g (2.53 equivalents) of the starting polyisocyanate A1 containing an isocyanurate structure and 142 g (0.40 equivalents) of the starting polyisocyanate A2 containing an isocyanurate structure were introduced under stirring and dry nitrogen and mixed within 15 minutes with 40 g (0.5 equivalents) of 2-butyl-2-ethyl-1,3-propanediol (BEPD) in an amount corresponding to... based on the total amount of polyisocyanate and branched...

[0175]

[0176] 6.0 wt % of the total amount of chain diols, and continued stirring until a 15.2% NCO content corresponding to complete urethanization was reached. The reaction mixture was cooled to 50°C and 245 g (2.42 equivalents) of diisopropylamine were added within 4 hours. In order to reduce the viscosity that increased significantly during the blocking reaction, a total of 609 g of solvent naphtha (SN 100) was added in several portions over the entire metering time. After the amine addition was completed, the reaction mixture was stirred at 50°C for another hour until the isocyanate groups were completely reacted (IR inspection). This gave a colorless solution of amine-terminated HDI and IPDI polyisocyanurate polyisocyanates, which had the following characteristics:

[0177]

[0178] After 12 weeks of storage at room temperature, the solution remained completely clear. After a total of 14 weeks of storage, a slight turbidity was observed; after 16 weeks the sample was completely crystallized.

[0179] Table 1: Storage stability survey results

[0180] Comparative Example 1 shows that a polyisocyanurate based solely on HDI and partially urethanized with a branched diol such as BEPD initially produces a stable DIPA-terminated system, but slowly starts to crystallize after 16 weeks.

[0181] Comparative Example 2, prepared according to EP0900814 B, shows that mixed HDI / IPDI capping in an equivalent ratio of 2.3 (HDI):1 (IPDI) likewise leads to an initially stable DIPA-capped product; however, complete crystallization is also observed here after 12 weeks.

[0182] Furthermore, Comparative Example 3 shows that a mixed HDI / IPDI end-capped system (4 / 1 equivalent ratio) that was not partially urethanized with a branched diol began to crystallize after only 2 days.

[0183] Examples 4 to 6 demonstrate the synergistic effect of partial urethanization with branched aliphatic diols and a specific equivalent ratio of aliphatic to cycloaliphatic polyisocyanates, i.e. long-term stability of >6 months, according to the present invention.

[0184] Furthermore, by comparison with Example 7, it is clear that above an equivalent ratio of 6:1 (HDI:IPDI), there is no longer any long-term crystallization stability.

Claims

1. A method for preparing a blocked polyisocyanate, comprising the following reactions: A) polyisocyanate component 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 A) comprises at least one linear aliphatic polyisocyanate A1) having at least an isocyanurate and / or an iminooxadiazinedione structure, and at least one alicyclic polyisocyanate A2), wherein A1) and A2) are present in an equivalent ratio of 2.0:1.0 to 5.9:1.0 relative to one another, and component B) is used in an amount of more than 2% by weight, based on the total amount of components A) and B), and component C) is used in an amount corresponding to at least 95 mol % of the isocyanate groups arithmetically still present after the reaction of components A) and B).

2. The method according to claim 1, characterized in that By modifying alicyclic diisocyanates, preferably by modifying 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 (HDI) 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- As polyisocyanates A2) are used 1,1′-bis(cyclohexyl), 1,8-diisocyanato-p-menthane, 1,3-diisocyanatoadamantane, 1,3-dimethyl-5,7-diisocyanatoadamantane or mixtures thereof, and particularly preferably polyisocyanates which are prepared by modifying 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane and / or 1,3- and 1,4-diisocyanatocyclohexane and have at least an isocyanurate and / or urethane structure.

3. The method according to any one of claims 1 or 2, characterized in that Polyisocyanates which are prepared by modifying linear aliphatic diisocyanates, preferably 1,6-diisocyanatohexane and / or 1,5-diisocyanatopentane, and have at least isocyanurate and / or iminooxadiazinedione structures are used as polyisocyanates A1).

4. The method according to any one of claims 1 to 3, characterized in that Polyisocyanates having an isocyanurate structure and having an average NCO functionality of 2.3 to 5.0, preferably 2.5 to 4.5, and an isocyanate group content of 6.0 to 26.0% by weight, preferably 8.0 to 25.0% by weight, particularly preferably 10.0 to 24.0% by weight, are used as polyisocyanates A1).

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 and is particularly preferably 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 mixture of such alcohols.

6. The method according to any one of claims 1 to 5, characterized in that The polyisocyanate A1) and the polyisocyanate A2) are present in an equivalent ratio of 2.5:1.0 to 5.5:1, preferably 3.0:1 to 5.0:1 and particularly preferably 3.5:1 to 4.5:1 to one another.

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 and 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' may also be combined with one another and, together with the nitrogen atom and optionally further oxygen atoms, may form a heterocycle having 5 to 8 ring members, which may 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 carbon atoms, particularly preferably 1 to 6 carbon atoms, or alicyclic hydrocarbon radicals having 6 to 13 carbon atoms, particularly preferably 6 to 9 carbon atoms, wherein R and R' can optionally also be combined with one another to form, together with the nitrogen atom and optionally further oxygen atoms, a heterocycle having 5 to 6 ring members, which can 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 mixture 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 a temperature of 0 to 120° C., preferably 20 to 100° C., particularly preferably 40 to 80° C.

13. A blocked polyisocyanate obtainable by the process according to any one of claims 1 to 12 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 as claimed in claim 13, b) at least one binder which is reactive toward isocyanate groups and has an average of at least two isocyanate-reactive groups per molecule, c) optionally a catalyst, and d) optional solvents and / or optional auxiliaries and adjuvants.

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

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