DUAL-CURING COATING COMPOSITIONS

The present invention relates to polymerizable compositions which contain components that can be crosslinked both via isocyanurate bonds and by a radical reaction mechanism. The invention further relates to methods by way of which polymers can be produced from said compositions.

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Description

The present invention relates to polymerizable compositions comprising components which can be crosslinked either via isocyanurate bonds or by a free-radical reaction mechanism. It further describes processes by which polymers can be prepared from these compositions.

WO 2015/155195 describes a composite material obtainable from a reinforcing material and a polyurethane composition consisting of at least one polyisocyanate (PIC), a PIC-reactive component consisting of at least one polyol and at least one methacrylate having OH groups, and a free-radical initiator. The addition reaction between PIC and OH groups takes place simultaneously with the free-radically initiated chain polymerization of the methacrylates. A disadvantage of the process used, in addition to the short pot lives/gel times of the polyurethane compositions, is the fact that, in the preparation of polyurethanes, the mixing ratio of the components, especially of the polyisocyanate and the polyol, is limited by the necessity of keeping the molar ratio of isocyanate and isocyanate-reactive groups close to 1:1.

WO 2016/087366 describes a free-radically polymerizable composition consisting of a polyurethane containing double bonds and a reactive diluent based on various methacrylates.

A disadvantage here is the two-stage reaction regime (the reaction of the hydroxymethacrylate with an isocyanate takes place in the first stage, and the reaction of the isocyanate-bonded (meth)acrylates to give polyacrylates takes place in the second stage, in order to obtain a crosslinked composition). A further disadvantage is the necessity of working under precise stoichiometric conditions in order to avoid free unconverted isocyanate.

U.S. Pat No. 6,133,397 and PCT/EP2017/073276 describe coating compositions that are cured primarily through the crosslinking of isocyanate groups with one another. This forms isocyanurate groups inter alia that impart advantageous properties to the coatings formed.

The low-monomer polyisocyanate compositions described as reactants in these applications have a relatively high viscosity which can be a hindrance in some applications.

The addition of monomeric polyisocyanates as reactive diluents is undesirable for reasons of occupational hygiene in many cases since these compounds are firstly volatile, and secondly act as irritants. Alternatively, conventional organic solvents can be used to reduce the viscosity. However, these are disadvantageous for reasons of environmental protection since they are released into the environment during or after the polymerization.

At the same time, it is desirable for coating applications when the viscosity of the coating composition even immediately before application can be increased to such an extent that running of the coating off an oblique surface is avoided. Since the crosslinking reaction of isocyanate groups, for example to give isocyanurate groups, generally takes at least a few minutes, the compositions described in U.S. Pat. No. 6,133,397 do not meet this requirement.

What are desirable, therefore, are compositions having a viscosity in the unprocessed state, without use of organic solvents, that can be adjusted with maximum freedom according to the demands of the respective application, and the viscosity of which can be increased with maximum speed after application to a surface. To the extent that such coatings are used for production of coatings, the coatings formed are also to have good optical properties, especially clarity.

This object is achieved by the embodiments of the invention disclosed in the claims and in the description below.

In a first embodiment, the present invention relates to a coating composition having a ratio of isocyanate groups to isocyanate-reactive groups of at least 2.0:1.0, comprising:

    • a) an isocyanate component A;
    • b) at least one trimerization catalyst C; and
    • c) at least one component selected from the group consisting of components B, D and E, where
    • component B has at least one ethylenic double bond but no isocyanate-reactive group;
    • component D has at least one isocyanate-reactive group and at least one ethylenic double bond in one molecule; and
    • component E has both at least one isocyanate group and at least one ethylenic double bond in one molecule.

The isocyanate component A enables the formation of a polymer that forms through the addition of isocyanate groups. This forms isocyanurate groups in particular. The crosslinking of the isocyanate groups present in the isocyanate component A endows the polymer with the majority of its mechanical and chemical stability. The crosslinking of the isocyanate groups is mediated by the trimerization catalyst C.

Components B, D and E are each characterized by the presence of an ethylenic double bond. This double bond is a prerequisite for a second crosslinking mechanism to be available in addition to the polyaddition of the isocyanate groups in the polymerizable composition. Each of these components enables crosslinking by free-radical polymerization. This is a crosslinking mechanism that enables the buildup of viscosity within a period of a few seconds. The use of these individual components or particular combinations of components has specific advantages here:

Component B lowers the viscosity of the polymerizable composition and can be rapidly crosslinked by free-radical polymerization and thus used for rapid buildup of viscosity. If there is just a component B present in the polymerizable composition without components D or E, the two different crosslinking mechanisms give rise to two different polymer networks. This can lead to turbidity in the finished product and under some circumstances to poorer mechanical properties.

In areas of application where this is to be avoided, component B is used in combination with a component D or E. It can also be used in combination with both components. Components D and E mediate the crosslinking of the network, formed by free-radical polymerization, of component B with the polymer of isocyanate component A formed through polyaddition of the isocyanate groups. They thus ensure that there are no two separate polymer networks of components A and B present in the polymer, but rather a single polymer network.

Even if they are used without an additional component B, components D and E enable the formation of a polymer network via free-radical polymerization. Similarly to the case of exclusive use of component B, rapid buildup of viscosity after application of the composition of the invention is enabled. However, unlike component B, components D and E are only of limited suitability as reactive diluents.

In a preferred embodiment of the present invention, the polymerizable composition contains at least one of the two components D and E, but no component B.

In another preferred embodiment, the composition of the invention contains a component B and at least one of the two components D and E. Particular preference is given to the combination of B and D.

In a preferred embodiment, the proportions of components B, D and E are adjusted such that the coating composition, after the free-radical polymerization of the ethylenic double bonds, does not run on a vertical surface within a period of at least 30 seconds, preferably at least 2 minutes and more preferably at least 10 minutes. A coating composition does not run if no difference in the coating thickness is visually perceptible between the upper end of the surface and the lower end thereof after the aforementioned time.

Whether a coating composition fulfils this criterion can be determined by simple preliminary tests. The composition is applied to a surface and treated with actinic radiation so as to initiate free-radical polymerization. Subsequently, the surface is stored vertically at 23° C. (room temperature) for the abovementioned period and then visually assessed.

Dimensional stability of a coating results from the interplay between coating thickness and viscosity. The higher the coating thickness, the higher the viscosity of the coating has to be.

In a particular embodiment of the invention, target coating thicknesses are at least 0.005 mm, preferably at least 0.02 mm and most preferably at least 0.04 mm, and at most 5 mm, preferably at most 0.5 mm and most preferably at most 0.1 mm.

In a further preferred embodiment, the proportion of components B, D and E in the composition of the invention is such that the viscosity of the coating is at least doubled, preferably quadrupled and more preferably dectupled after polymerization triggered by actinic radiation.

In a further preferred embodiment, the dynamic viscosity to EN ISO 2884-1:2006 measured in a cone-plate viscometer at room temperature after polymerization with actinic radiation is at least 200 mPas, preferably at least 500 mPas, more preferably at least 1000 mPas, even more preferably at least 10 000 mPas and even more preferably still at least 100 000 mPas.

In a preferred embodiment, the polymerizable composition of the invention comprises isocyanate component A and component B preferably in a quantitative ratio that lowers the viscosity of the undiluted isocyanate component to at most 75%, preferably at most 25%, more preferably at most 5% and most preferably to at most 1% of the viscosity of undiluted isocyanate component A. The presence of at least one of components D and E is particularly preferred in this embodiment.

In a preferred embodiment, the quantitative ratio of component A to the total amount of components B, D and E is such that the polymerizable composition before each crosslinking has a viscosity at room temperature of at most 100 000 mPas, more preferably of at most 10 000 mPas, even more preferably of at most 1000 mPas and most preferably at most 100 mPas.

The polymer obtainable by polymerizing the coating composition of the invention receives its advantageous properties very substantially through crosslinking of the isocyanate groups with one another. Consequently, it is essential to the invention that the ratio of isocyanate groups to the total amount of the isocyanate-reactive groups in the polymerizable composition is restricted such that there is a distinct molar excess of isocyanate groups. The molar ratio of isocyanate groups of the isocyanate component to isocyanate-reactive groups in the reactive resin is consequently at least 2.0:1.0, preferably at least 3.0:1.0, more preferably at least 4.0:1.0 and even more preferably at least 8.0:1,0. “Isocyanate-reactive groups” in the context of the present application are hydroxyl, thiol, carboxyl and amino groups, amides, urethanes, acid anhydrides and epoxides. The isocyanate groups present in the polymerizable composition are present in components A and—if present—E. The isocyanate-reactive groups may in principle be present in all other components except for component B.

By comparison with the polyurethane resins known from WO 2015/155195 with additional radiative curing, the use of the polymerizable composition of the invention enables greater flexibility in the selection of the proportions of the individual components. If a polyurethane or a polyurea is to be obtained, the molar ratio of isocyanate groups to isocyanate-reactive groups must if possible be close to 1:1. According to the present invention, however, there is a distinct excess of isocyanate groups that is consequently not just acceptable but actually desired because the polymer formed owes its advantageous properties very substantially to the reaction of isocyanate groups with other isocyanate groups. The structures thus formed, especially the isocyanurate groups, lead to polymers with exceptional hardness and exceptional stability to chemicals.

Isocyanate Component A

“Isocyanate component A” in the context of the invention refers to the isocyanate component in the starting reaction mixture. In other words, this is the sum total of all the compounds in the starting reaction mixture that have isocyanate groups, except for component E. The isocyanate component A is thus used as reactant in the process of the invention. When reference is made here to “isocyanate component A”, especially to “providing the isocyanate component A”, this means that the isocyanate component A exists and is used as reactant. The isocyanate component A preferably contains at least one polyisocyanate.

The term “polyisocyanate” as used here is a collective term for compounds containing two or more isocyanate groups in the molecule (this is understood by the person skilled in the art to mean free isocyanate groups of the general structure —N═C═O). The simplest and most important representatives of these polyisocyanates are the diisocyanates. These have the general structure O═C═N—R—N═C═O where R typically represents aliphatic, alicyclic and/or aromatic radicals.

Because of the polyfunctionality (≥2 isocyanate groups), it is possible to use polyisocyanates to produce a multitude of polymers (e.g. polyurethanes, polyureas and polyisocyanurates) and low molecular weight compounds (for example those having uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure).

The term “polyisocyanates” in this application refers equally to monomeric and/or oligomeric polyisocyanates. For the understanding of many aspects of the invention, however, it is important to distinguish between monomeric diisocyanates and oligomeric polyisocyanates. Where reference is made in this application to “oligomeric polyisocyanates”, this means polyisocyanates formed from at least two monomeric diisocyanate molecules, i.e. compounds that constitute or contain a reaction product formed from at least two monomeric diisocyanate molecules.

The preparation of oligomeric polyisocyanates from monomeric diisocyanates is also referred to here as modification of monomeric diisocyanates. This “modification” as used here means the reaction of monomeric diisocyanates to give oligomeric polyisocyanates having uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure.

For example, hexamethylene diisocyanate (HDI) is a “monomeric diisocyanate” since it contains two isocyanate groups and is not a reaction product of at least two polyisocyanate molecules:

Reaction products which are formed from at least two HDI molecules and still have at least two isocyanate groups, by contrast, are “oligomeric polyisocyanates” within the context of the invention. Representatives of such “oligomeric polyisocyanates” are, proceeding from monomeric HDI, for example, HDI isocyanurate and HDI biuret, each of which is formed from three monomeric HDI units:

According to the invention, the proportion by weight of isocyanate groups based on the total amount of the isocyanate component A is at least 15% by weight.

In principle, monomeric and oligomeric polyisocyanates are equally suitable for use in the isocyanate component A of the invention. Consequently, the isocyanate component A may consist essentially of monomeric polyisocyanates or essentially of oligomeric polyisocyanates. It may alternatively comprise oligomeric and monomeric polyisocyanates in any desired mixing ratios.

In a preferred embodiment of the invention, the isocyanate component A used as reactant in the trimerization has a low level of monomers (i.e. a low level of monomeric diisocyanates) and already contains oligomeric polyisocyanates. The expressions “having a low level of monomers” and “having a low level of monomeric diisocyanates” are used here synonymously in relation to the isocyanate component A.

Results of particular practical relevance are established when the isocyanate component A has a proportion of monomeric diisocyanates in the isocyanate component A of not more than 20% by weight, especially not more than 15% by weight or not more than 10% by weight, based in each case on the weight of the isocyanate component A. Preferably, the isocyanate component A has a content of monomeric diisocyanates of not more than 5% by weight, preferably not more than 2.0% by weight, more preferably not more than 1.0% by weight, based in each case on the weight of the isocyanate component A. Particularly good results are established when the isocyanate component A is essentially free of monomeric diisocyanates. “Essentially free” here means that the content of monomeric diisocyanates is not more than 0.5% by weight, based on the weight of the isocyanate component A.

In a particularly preferred embodiment of the invention, the isocyanate component A consists entirely or to an extent of at least 80%, 85%, 90%, 95%, 98%, 99% or 99.5% by weight, based in each case on the weight of the isocyanate component A, of oligomeric polyisocyanates. Preference is given here to a content of oligomeric polyisocyanates of at least 99% by weight. This content of oligomeric polyisocyanates relates to the isocyanate component A as provided. In other words, the oligomeric polyisocyanates are not formed as intermediate during the process of the invention, but are already present in the isocyanate component A used as reactant on commencement of the reaction.

Polyisocyanate compositions which have a low level of monomers or are essentially free of monomeric isocyanates can be obtained by conducting, after the actual modification reaction, in each case, at least one further process step for removal of the unconverted excess monomeric diisocyanates. This removal of monomers can be effected in a particularly practical manner by processes known per se, preferably by thin-film distillation under high vacuum or by extraction with suitable solvents that are inert toward isocyanate groups, for example aliphatic or cycloaliphatic hydrocarbons such as pentane, hexane, heptane, cyclopentane or cyclohexane.

In a preferred embodiment of the invention, the isocyanate component A of the invention is obtained by modifying monomeric diisocyanates with subsequent removal of unconverted monomers.

In a particular embodiment of the invention, an isocyanate component A having a low level of monomers, however, contains an extra monomeric diisocyanate. In this context, “extra monomeric diisocyanate” means that it differs from the monomeric diisocyanates which have been used for preparation of the oligomeric polyisocyanates present in the isocyanate component A.

An addition of extra monomeric diisocyanate may be advantageous for achievement of special technical effects, for example an exceptional hardness. Results of particular practical relevance are established when the isocyanate component A has a proportion of extra monomeric diisocyanate in the isocyanate component A of not more than 20% by weight, especially not more than 15% by weight or not more than 10% by weight, based in each case on the weight of the isocyanate component A. Preferably, the isocyanate component A has a content of extra monomeric diisocyanate of not more than 5% by weight, especially not more than 2.0% by weight, more preferably not more than 1.0% by weight, based in each case on the weight of the isocyanate component A.

In a further particular embodiment of the process of the invention, the isocyanate component A contains monomeric monoisocyanates or monomeric isocyanates having an isocyanate functionality greater than two, i.e. having more than two isocyanate groups per molecule. The addition of monomeric monoisocyanates or monomeric isocyanates having an isocyanate functionality greater than two has been found to be advantageous in order to influence the network density of the coating. Results of particular practical relevance are established when the isocyanate component A has a proportion of monomeric monoisocyanates or monomeric isocyanates having an isocyanate functionality greater than two in the isocyanate component A of not more than 20% by weight, especially not more than 15% by weight or not more than 10% by weight, based in each case on the weight of the isocyanate component A. Preferably, the isocyanate component A has a content of monomeric monoisocyanates or monomeric isocyanates having an isocyanate functionality greater than two of not more than 5% by weight, preferably not more than 2.0% by weight, more preferably not more than 1.0% by weight, based in each case on the weight of the isocyanate component A. Preferably, no monomeric monoisocyanate or monomeric isocyanate having an isocyanate functionality greater than two is used in the trimerization reaction of the invention.

The oligomeric polyisocyanates may, in accordance with the invention, especially have uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure. In one embodiment of the invention, the oligomeric polyisocyanates have at least one of the following oligomeric structure types or mixtures thereof:

In a preferred embodiment of the invention, an isocyanate component A is used, wherein the isocyanurate structure component is at least 50 mol %, preferably at least 60 mol %, more preferably at least 70 mol %, even more preferably at least 80 mol %, even more preferably still at least 90 mol % and especially preferably at least 95 mol %, based on the sum total of the oligomeric structures from the group consisting of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and oxadiazinetrione structure present in the isocyanate component A, is used.

In a further preferred embodiment of the invention, in the process of the invention, an isocyanate component A containing, as well as the isocyanurate structure, at least one further oligomeric polyisocyanate having uretdione, biuret, allophanate, iminooxadiazinedione and oxadiazinetrione structure and mixtures thereof is used.

The proportions of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure in the isocyanate component A can be determined, for example, by NMR spectroscopy. It is possible here with preference to use 13C NMR spectroscopy, preferably in proton-decoupled form, since the oligomeric structures mentioned give characteristic signals.

Irrespective of the underlying oligomeric structure (uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure), an oligomeric isocyanate component A for use in the process of the invention and/or the oligomeric polyisocyanates present therein preferably have/has an (average) NCO functionality of 2.0 to 5.0, preferably of 2.3 to 4.5.

Results of particular practical relevance are established when the isocyanate component A to be used in accordance with the invention has a content of isocyanate groups of 8.0% to 28.0% by weight, preferably of 14.0% to 25.0% by weight, based in each case on the weight of the isocyanate component A.

Preparation processes for the oligomeric polyisocyanates having uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure that are to be used in accordance with the invention in the isocyanate component A are described, for example, in J. Prakt. Chem. 336 (1994) 185-200, in DE-A 1 670 666, DE-A 1 954 093, DE-A 2 414 413, DE-A 2 452 532, DE-A 2 641 380, DE-A 3 700 209, DE-A 3 900 053 and DE-A 3 928 503 or in EP-A 0 336 205, EP-A 0 339 396 and EP-A 0 798 299.

In an additional or alternative embodiment of the invention, the isocyanate component A of the invention is defined in that it contains oligomeric polyisocyanates which have been obtained from monomeric diisocyanates, irrespective of the nature of the modification reaction used, with observation of an oligomerization level of 5% to 45%, preferably 10% to 40%, more preferably 15% to 30%. “Oligomerization level” is understood here to mean the percentage of isocyanate groups originally present in the starting mixture which are consumed during the preparation process to form uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structures.

Suitable polyisocyanates for production of the isocyanate component A for use in the process of the invention and the monomeric and/or oligomeric polyisocyanates present therein are any desired polyisocyanates obtainable in various ways, for example by phosgenation in the liquid or gas phase or by a phosgene-free route, for example by thermal urethane cleavage. Particularly good results are established when the polyisocyanates are monomeric diisocyanates. Preferred monomeric diisocyanates are those having a molecular weight in the range from 140 to 400 g/mol, having aliphatically, cycloaliphaticaily, araliphatically and/or aromatically bonded isocyanate groups, for example 1,4-diisocyanatobutane (BDI), 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), 2-methyl-1,5-diisocyanatopentane, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3- and 1,4-diisocyanatocyclohexane, 1,4-diisocyanato-3,3,5-trimethylcyclohexane, 1,3-diisocyanato-2-methylcyclohexane, 1,3-diisocyanato-4-methylcyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate; IPDI), 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, 2,4′- and 4,4′-diisocyanatodicyclohexylmethane (H12MDI), 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, bis(isocyanatomethyl)norbornane (NBDI), 4,4′-diisocyanato-3,3′-dimethyldicyclohexyl methane, 4,4′-diisocyanato-3,3′,5,5′-tetramethyldicyclohexylmethane, 4,4′-diisocyanato-1,1′-bi(cyclohexyl), 4,4′-diisocyanato-3,3′-dimethyl-1,1′-bi(cyclohexyl), 4,4′-diisocyanato-2,2′,5,5′-tetramethyl-1,1′-bi(cyclohexyl), 1,8-diisocyanato-p-menthane, 1,3-diisocyanatoadamantane, 1,3-dimethyl-5,7-diisocyanatoadamantane, 1,3- and 1,4-bis(isocyanatomethyl)benzene (xylylene diisocyanate; XDI), 1,3- and 1,4-bis(1-isocyanato-1-methylethyl)benzene (TMXDI) and bis(4-(1-isocyanato-1-methylethyl)phenyl) carbonate, 2,4- and 2,6-diisocyanatotoluene (TDI), 2,4′- and 4,4′-diisocyanatodiphenylmethane (MDI), 1,5-diisocyanatonaphthalene and any desired mixtures of such diisocyanates. Further diisocyanates that are likewise suitable can additionally be found, for example, in Justus Liebigs Annalen der Chemie, volume 562 (1949) p. 75-136.

Suitable monomeric monoisocyanates which can optionally be used in the isocyanate component A are, for example, n-butyl isocyanate, n-amyl isocyanate, n-hexyl isocyanate, n-heptyl isocyanate, n-octyl isocyanate, undecyl isocyanate, dodecyl isocyanate, tetradecyl isocyanate, cetyl isocyanate, stearyl isocyanate, cyclopentyl isocyanate, cyclohexyl isocyanate, 3- or 4-methylcyclohexyl isocyanate or any desired mixtures of such monoisocyanates. An example of a monomeric isocyanate having an isocyanate functionality greater than two which can optionally be added to the isocyanate component A is 4-isocyanatomethyloctane 1,8-diisocyanate (triisocyanatononane; TIN).

In one embodiment of the invention, the isocyanate component A contains not more than 30% by weight, especially not more than 20% by weight, not more than 15% by weight, not more than 10% by weight, not more than 5% by weight or not more than 1% by weight, based in each case on the weight of the isocyanate component A, of aromatic polyisocyanates. As used here, “aromatic polyisocyanate” means a polyisocyanate having at least one aromatically bonded isocyanate group.

Aromatically bonded isocyanate groups are understood to mean isocyanate groups bonded to an aromatic hydrocarbyl radical.

In a preferred embodiment of the process of the invention, an isocyanate component A having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups is used.

Aliphatically and cycloaliphatically bonded isocyanate groups are understood to mean isocyanate groups bonded, respectively, to an aliphatic and cycloaliphatic hydrocarbyl radical.

In another preferred embodiment of the process of the invention, an isocyanate component A consisting of or comprising one or more oligomeric polyisocyanates is used, where the one or more oligomeric polyisocyanates has/have exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

In a further embodiment of the invention, the isocyanate component A consists to an extent of at least 70%, 80%, 85%, 90%, 95%, 98% or 99% by weight, based in each case on the weight of the isocyanate component A, of polyisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups. Practical experiments have shown that particularly good results can be achieved with isocyanate component A in which the oligomeric polyisocyanates present therein have exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

In a particularly preferred embodiment of the process of the invention, a polyisocyanate composition A is used which consists of or comprises one or more oligomeric polyisocyanates, where the one or more oligomeric polyisocyanates is/are based on 1,4-diisocyanatobutane (BDI), 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), isophorone diisocyanate (IPDI) or 4,4′-diisocyanatodicyclohexylmethane (H12MDI) or mixtures thereof.

In a further embodiment of the invention, in the process of the invention, isocyanate components A having a viscosity greater than 500 mPas and less than 200 000 mPas, preferably greater than 1000 mPas and less than 100 000 mPas, more preferably greater than 1000 mPas and less than 50 000 mPas and even more preferably greater than 1000 mPas and less than 25 000 mPas, measured according to DIN EN ISO 3219 at 21° C., are used.

Component B

Suitable components B are all compounds containing at least one ethylenic double bond. This ethylenic double bond is crosslinkable with other ethylenic double bonds by a free-radical reaction mechanism. This condition is met by preferably activated double bonds between the α carbon atom and the β carbon atom alongside an activating group. The activating group is preferably a carboxyl or carbonyl group. Most preferably, component B is an acrylate, a methacrylate, the ester of an acrylate or the ester of a methacrylate. Preferably, component B does not contain any of the isocyanate-reactive groups as defined further up in this application or any isocyanate group either.

Preferred components B are components B1 with one, component B2 with two and component B3 with three of the above-described ethylenic double bonds. Particular preference is given to B1 and/or B2.

In a preferred embodiment, component B used is a mixture of at least one component B1 and at least one component B2.

In a further preferred embodiment, component B used is a mixture of at least one component B1 and at least one component B3.

In yet a further preferred embodiment, component B used is a mixture of at least one component B2 and at least one component B3.

In yet a further preferred embodiment, component B used is a mixture of at least one component B1, at least one component B2 and at least one component B3. Preference is given to using a mixture of at least one component B1 with at least one component B2. The mass ratio of components B1 and B2 here is preferably between 30:1 and 1:30, more preferably between 20:1 and 1:20, even more preferably between 1:10 and 10:1 and most preferably between 2:1 and 1:2.

Preferred components B1 are methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, octadecyl (meth)acrylate, dodecyl (meth)acrylate, tetradecyl (meth)acrylate, oleyl (meth)acrylate, 4-methylphenyl (meth)acrylate, benzyl (meth)acrylate, furfuryl (meth)acrylate, cetyl (meth)acrylate, 2-phenylethyl (meth)acrylate, isobornyl (meth)acrylate, neopentyl (meth)acrylate, methacrylamide and n-isopropylmethacrylamide.

Preferred components B2 are vinyl (meth)acrylate, tetraethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, hexane-1,6-diol di(meth)acrylate, neopentyl glycol propoxylate di(meth)acrylate, tripropylene glycol di(meth)acrylate, bisphenol A ethoxylated di (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hexamethylene glycol di(meth)acrylate, bisphenol A di(meth)acrylate and 4,4′-bis(2-(meth)acryloyloxyethoxy)diphenylpropane.

Preferred components B3 are ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated glycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane ethoxytri(meth)acrylate, trimethylolpropane tri(meth)acrylate, alkoxylated tri(meth)acrylate and tris(2-(meth)acryloylethyl) isocyanurate.

Trimerization Catalyst C

The trimerization catalyst C may be mixed from one catalyst type or different catalyst types, but contains at least one catalyst that brings about the trimerization of isocyanate groups to isocyanurates or iminooxadiazinediones.

Suitable catalysts for the process of the invention are, for example, simple tertiary amines, for example triethylamine, tributylamine, N,N-dimethylaniline, N-ethylpiperidine or N,N′-dimethylpiperazine. Suitable catalysts are also the tertiary hydroxyalkylamines described in GB 2 221 465, for example triethanolamine, N-methyldiethanolamine, dimethylethanolamine, N-isopropyldiethanolamine and 1-(2-hydroxyethyl)pyrrolidine, or the catalyst systems known from GB 2 222 161 that consist of mixtures of tertiary bicyclic amines, for example DBU, with simple aliphatic alcohols of low molecular weight.

Likewise suitable as trimerization catalysts for the process of the invention are a multitude of different metal compounds. Suitable examples are the octoates and naphthenates of manganese, iron, cobalt, nickel, copper, zinc, zirconium, cerium or lead or mixtures thereof with acetates of lithium, sodium, potassium, calcium or barium that are described as catalysts in DE-A 3 240 613, the sodium and potassium salts of linear or branched alkanecarboxylic acids having up to 10 carbon atoms that are known from DE-A 3 219 608, for example of propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid and undecylenoic acid, the alkali metal or alkaline earth metal salts of aliphatic, cycloaliphatic or aromatic mono- and polycarboxylic acids having 2 to 20 carbon atoms that are known from EP-A 0 100 129, for example sodium or potassium benzoate, the alkali metal phenoxides known from GB-A 1 391 066 and GB-A 1 386 399, for example sodium or potassium phenoxide, the alkali metal and alkaline earth metal oxides, hydroxides, carbonates, alkoxides and phenoxides known from GB 809 809, alkali metal salts of enolizable compounds and metal salts of weak aliphatic or cycloaliphatic carboxylic acids, for example sodium methoxide, sodium acetate, potassium acetate, sodium acetoacetate, lead 2-ethylhexanoate and lead naphthenate, the basic alkali metal compounds complexed with crown ethers or polyether alcohols that are known from EP-A 0 056 158 and EP-A 0 056 159, for example complexed sodium or potassium carboxylates, the pyrrolidinone-potassium salt known from EP-A 0 033 581, the mono- or polynuclear complex of titanium, zirconium and/or hafnium known from application EP 13196508.9, for example zirconium tetra-n-butoxide, zirconium tetra-2-ethylhexanoate and zirconium tetra-2-ethylhexoxide, and tin compounds of the type described in European Polymer Journal, vol. 16, 147-148 (1979), for example dibutyltin dichloride, diphenyltin dichloride, triphenylstannanol, tributyltin acetate, tributyltin oxide, tin dioctoate, dibutyl(dimethoxy)stannane and tributyltin imidazolate.

Further trimerization catalysts suitable for the process of the invention are, for example, the quaternary ammonium hydroxides known from DE-A 1 667 309, EP-A 0 013 880 and EP-A 0 047 452, for example tetraethylammonium hydroxide, trimethylbenzylammonium hydroxide, N,N-dimethyl-N-dodecyl-N-(2-hydroxyethyl)ammonium hydroxide, N-(2-hydroxyethyl)-N,N-dimethyl-N-(2,2′-dihydroxymethylbutyl)ammonium hydroxide and 1-(2-hydroxyethyl)-1,4-diazabicyclo[2.2.2]octane hydroxide (monoadduct of ethylene oxide and water with 1,4-diazabicyclo[2.2.2]octane), the quaternary hydroxyalkylammonium hydroxides known from EP-A 37 65 or EP-A 10 589, for example N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium hydroxide, the trialkylhydroxylalkylammonium carboxylates that are known from DE-A 2631733, EP-A 0 671 426, EP-A 1 599 526 and U.S. Pat. No. 4,789,705, for example N,N,N-trimethyl-N-2-hydroxypropylammonium p-tert-butylbenzoate and N,N,N-trimethyl-N-2-hydroxypropylammonium 2-ethylhexanoate, the quaternary benzylammonium carboxylates known from EP-A 1 229 016, such as N-benzyl-N,N-dimethyl-N-ethylammonium pivalate, N-benzyl-N,N-dimethyl-N-ethylammonium 2-ethylhexanoate, N-benzyl-N,N,N-tributylammonium 2-ethylhexanoate, N,N-dimethyl-N-ethyl-N-(4-methoxybenzyl)ammonium 2-ethylhexanoate or N,N,N-tributyl-N-(4-methoxybenzyl)ammonium pivalate, the tetrasubstituted ammonium α-hydroxycarboxylates known from WO 2005/087828, for example tetramethylammonium lactate, the quaternary ammonium or phosphonium fluorides known from EP-A 0 339 396, EP-A 0 379 914 and EP-A 0 443 167, for example N-methyl-N,N,N-trialkylammonium fluorides with C8-C10-alkyl radicals, N,N,N,N-tetra-n-butylammonium fluoride, N,N,N-trimethyl-N-benzylammonium fluoride, tetramethylphosphonium fluoride, tetraethylphosphonium fluoride or tetra-n-butylphosphonium fluoride, the quaternary ammonium and phosphonium polyfluorides known from EP-A 0 798 299, EP-A 0 896 009 and EP-A 0 962 455, for example benzyltrimethylammonium hydrogen polyfluoride, the tetraalkylammonium alkylcarbonates which are known from EP-A 0 668 271 and are obtainable by reaction of tertiary amines with dialkyl carbonates, or betaine-structured quaternary ammonioalkyl carbonates, the quaternary ammonium hydrogencarbonates known from WO 1999/023128, such as choline bicarbonate, the quaternary ammonium salts which are known from EP 0 102 482 and are obtainable from tertiary amines and alkylating esters of phosphorus acids, examples of such salts being reaction products of triethylamine, DABCO or N-methylmorpholine with dimethyl methanephosphonate, or the tetrasubstituted ammonium salts of lactams that are known from WO 2013/167404, for example trioctylammonium caprolactamate or dodecyltrimethylammonium caprolactamate.

Further trimerization catalysts C suitable for the process of the invention can be found, for example, in J. H. Saunders and K. C. Frisch, Polyurethanes Chemistry and Technology, p. 94 ff. (1962) and the literature cited therein.

Particular preference is given to carboxylates and phenoxides with metal or ammonium ions as counterion. Suitable carboxylates are the anions of all aliphatic or cycloaliphatic carboxylic acids, preferably those with mono- or polycarboxylic acids having 1 to 20 carbon atoms. Suitable metal ions are derived from alkali metals or alkaline earth metals, manganese, iron, cobalt, nickel, copper, zinc, zirconium, cerium, tin, titanium, hafnium or lead. Preferred alkali metals are lithium, sodium and potassium, more preferably sodium and potassium. Preferred alkaline earth metals are magnesium, calcium, strontium and barium.

Very particular preference is given to the octoate and naphthenate catalysts described in DE-A 3 240 613, these being octoates and naphthenates of manganese, iron, cobalt, nickel, copper, zinc, zirconium, cerium or lead, or mixtures thereof with acetates of lithium, sodium, potassium, calcium or barium.

Very particular preference is likewise given to sodium benzoate or potassium benzoate, to the alkali metal phenoxides known from GB-A 1 391 066 and GB-A 1 386 399, for example sodium phenoxide or potassium phenoxide, and to the alkali metal and alkaline earth metal oxides, hydroxides, carbonates, alkoxides and phenoxides that are known from GB 809 809.

The trimerization catalyst C preferably contains a polyether. This is especially preferred when the catalyst contains metal ions. Preferred polyethers are selected from the group consisting of crown ethers, diethylene glycol, polyethylene glycols and polypropylene glycols. It has been found to be of particular practical relevance in the process of the invention to use a trimerization catalyst B containing, as polyether, a polyethylene glycol or a crown ether, more preferably 18-crown-6 or 15-crown-5. Preferably, the trimerization catalyst B comprises a polyethylene glycol having a number-average molecular weight of 100 to 1000 g/mol, preferably 300 g/mol to 500 g/mol and especially 350 g/mol to 450 g/mol.

Very particular preference is given to the combination of the above-described carboxylates and phenoxides of alkali metals or alkaline earth metals with a polyether.

Component D

Component D is a compound having at least one isocyanate-reactive group as defined further up in this application and at least one ethylenic double bond in one molecule. The isocyanate-reactive group of component D may also be a uretdione group. Ethylenic double bonds are preferably those that are crosslinkable with other ethylenic double bonds by a free-radical reaction mechanism. Corresponding activated double bonds are defined in detail further up in this application for component B.

Preferred components D are alkoxyalkyl (meth)acrylates having 2 to 12 carbon atoms in the hydroxyalkyl radical. Particular preference is given to 2-hydroxyethyl acrylate, the isomer mixture formed on addition of propylene oxide onto acrylic acid, or 4-hydroxybutyl acrylate.

Component E

Component E is a compound having both at least one isocyanate group and at least one ethylenic double bond in one molecule. It can advantageously be obtained by crosslinking a component D described in the preceding paragraph with a monomeric or oligomeric polyisocyanate as described further up in this application. This crosslinking is effected by the reaction of the isocyanate-reactive groups, in this case especially a hydroxyl, amino or thiol group, and an isocyanate group of the polyisocyanate. This is preferably catalyzed by a component G, which is described further down in this application. But any other suitable catalyst known to those skilled in the art is also conceivable. It is also possible to dispense with a catalyst entirely.

The isocyanate group of component E may also be in reversibly blocked form. The reversible blocking of isocyanate groups is preferably effected with blocking agents that are free of elimination products.

In a further preferred embodiment, the free-radically crosslinkable structural material contains blocked or unblocked NCO groups. When the NCO groups are blocked, the process of the invention further includes the step of deblocking these NCO groups. After they have been deblocked, they are thus available for further reactions.

The blocking agent is chosen such that, on heating in the process of the invention, the NCO groups are at least partly deblocked. Examples of blocking agents are alcohols, lactams, oximes, malonic esters, alkyl acetoacetates, triazoles, phenols, imidazoles, pyrazoles and amines, for example butanone oxime, diisopropylamine, 1,2,4-triazole, dimethyl-1,2,4-triazole, imidazole, diethyl malonate, ethyl acetoacetate, acetone oxime, 3,5-dimethylpyrazole, ε-caprolactam, N-methyl-, N-ethyl-, N-(iso)propyl-, N-n-butyl-, N-isobutyl-, N-tert-butylbenzylamine or 1,1-dimethylbenzylamine, N-alkyl-N-1,1-dimethylmethylphenylamine, adducts of benzylamine onto compounds having activated double bonds, such as malonic esters, N,N-dimethylaminopropylbenzylamine and other optionally substituted benzylamines containing tertiary amino groups and or dibenzylamine or any desired mixtures of these blocking agents.

Particular preference is given to combinations in which a hexamethylene diisocyanate- or pentamethylene diisocyanate-based oligomeric polyisocyanate is combined with a component D selected from the group consisting of 2-hydroxyethyl acrylate, the isomer mixture formed on addition of propylene oxide onto acrylic acid, and 4-hydroxybutyl acrylate.

Further preferred components E are 2-isocyanatoethyl (meth)acrylate, tris(2-hydroxyethyl) isocyanate tri(meth)acrylate, vinyl isocyanates, allyl isocyanates and 3-isopropenyl-α,α-dimethylbenzyl isocyanate.

Component F

In principle, free-radical polymerization of the ethylenically unsaturated compounds present in the reaction mixture can be brought about by actinic radiation with a sufficient energy content. This is especially UV-VIS radiation in the wavelength range between 200 and 500 nm. In this case, the polymerizable composition of the invention need not contain any component F.

But if the use of corresponding radiation is to be dispensed with, the presence of at least one component F suitable as an initiator for a free-radical polymerization of the ethylenic double bonds present in the polymerizable composition of the invention is required. This component F is preferably a radiation-activated initiator.

Preferred radiation-activated initiators F are compounds of the unimolecular type (I) and of the bimolecular type (II). Suitable type (I) systems are aromatic ketone compounds, for example benzophenones in combination with tertiary amines, alkylbenzophenones, 4,4′-bis(dimethylamino)benzophenone (Michler's ketone), anthrone and halogenated benzophenones or mixtures of the recited types. Also suitable are type (II) initiators such as benzoin and derivatives thereof, benzil ketals, acylphosphine oxides, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylphosphine oxides, phenylglyoxylic esters, camphorquinone, α-aminoalkylphenones, α,α-dialkoxyacetophenones and α-hydroxyalkylphenones. Specific examples are Irgacure®500 (a mixture of benzophenone and 1-hydroxycyclohexyl phenyl ketone, from Ciba, Lampertheim, Del.), Irgacure®819 DW (phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, from Ciba, Lampertheim, Del.) or Esacure® KIP EM (oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanones], from Lamberti, Aldizzate, Italy) and bis(4-methoxybenzoyl)diethylgermanium. Mixtures of these compounds may also be employed.

It should be ensured that the photoinitiators have a sufficient reactivity toward the radiation source used. A multitude of photoinitiators is known on the market. Commercially available photoinitiators cover the wavelength range of the entire UV-VIS spectrum.

Component G

Component G is a catalyst that catalyzes the crosslinking of an isocyanate group with an isocyanate-reactive group. This preferably gives rise to a urethane group, a thiourethane group or a urea group.

The polymerizable composition preferably contains a component G when a component D having at least one isocyanate-reactive group is present. However, the use of a component G is not obligatory in this case either, since the crosslinking of isocyanate groups with isocyanate-reactive groups can also be accelerated by the trimerization catalysts C used and also proceeds at sufficient speed even entirely without catalysis when the reaction temperature is high enough. It is possible to dispense with the addition of a component G especially when the crosslinking of the isocyanate groups present in the isocyanate component A is conducted at a temperature of at least 60° C., preferably at least 120° C.

Preferred components G are the typical urethanization catalysts as specified, for example, in Becker/Braun, Kunststoffhandbuch [Plastics Handbook] volume 7, Polyurethane [Polyurethanes], section 3.4. The catalyst used may especially be a compound selected from the group of the tertiary amines, tertiary amine salts, metal salts and metal organyls, preferably from the group of the tin salts, tin organyls and bismuth organyls.

Component H

According to the invention, the viscosity of the polymerizable composition is preferably adjusted by the use of a component B in suitable concentration. These act as reactive diluents and basically make it possible to dispense with the use of additional solvents to lower the viscosity of the isocyanate component A.

In particular embodiments, however, it may be desirable to additionally add a solvent suitable for isocyanates to the polymerizable composition of the invention. This may be desirable, for example, when the proportion of component B in the polymerizable composition is to be limited and the aim is a lowering of viscosity unachievable with this limited proportion of component B. In this case, the polymerizable composition of the invention may contain all solvents suitable for the dilution of isocyanates that are known to the person skilled in the art. These are preferably hexane, toluene, xylene, chlorobenzene, ethyl acetate, butyl acetate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monomethyl or monoethyl ether acetate, diethylene glycol ethyl and butyl ether acetate, propylene glycol monomethyl ether acetate, 1-methoxyprop-2-yl acetate, 3-methoxy-n-butyl acetate, propylene glycol diacetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, lactones such as β-propiolactone, γ-butyrolactone, ε-caprolactone and ε-methylcaprolactone, but also solvents such as N-methylpyrrolidone and N-methylcaprolactam, 1,2-propylene carbonate, methylene chloride, dimethyl sulfoxide, triethyl phosphate or any desired mixtures of such solvents.

Component I

In a preferred embodiment, the polymerizable composition of the invention additionally comprises at least one additive I selected from the group consisting of UV stabilizers, antioxidants, mold release agents, water scavengers, slip additives, defoamers, leveling agents, rheology additives, flame retardants and pigments. These auxiliaries and additives, except for the flame retardants, are typically present in an amount of not more than 20% by weight, preferably not more than 10% by weight and more preferably not more than 3% by weight, based on the polymerizable composition of the invention. According to the end use, flame retardants may be present in higher amounts of up to a maximum of 40% by weight.

Component J

In a particularly preferred embodiment of the present invention, the polymerizable composition comprises at least one organic filler and/or at least one inorganic filler. Said fillers may be present in any shape and size known to the person skilled in the art.

Preferred organic fillers are dyes and organic nanoparticles, for example those based on carbon.

Preferred inorganic fillers are pigments AlOH3, CaCO3, silicon dioxide, magnesium carbonate, TiO2, ZnS, minerals containing silicates, sulfates, carbonates and the like, such as magnesite, baryte, mica, dolomite, kaolin, talc, clay minerals, and carbon black, graphite, boron nitride, glass, basalt, boron, ceramic and silica.

The coating composition of the invention more preferably contains at least one organic or inorganic pigment.

Use

In a further embodiment, the present invention relates to the use of at least one component selected from the group consisting of components B, D and E for production of a coating composition having a ratio of isocyanate groups to isocyanate-reactive groups of at least 2.0:1.0, which contains an isocyanate component A and is polymerizable either by free-radical polymerization or by crosslinking of isocyanate groups with one another.

Preferably, at least one component B as defined above in this application is additionally used.

All definitions given further up in this application for the coating composition are also applicable to this embodiment. This is especially true of the quantitative ratios of components A, B, D and E and the ratio of isocyanate groups to the total amount of the isocyanate-reactive groups in the polymerizable composition.

Process

In a further embodiment, the present invention relates to a process for preparing a coating, comprising the steps of

    • a) providing a coating composition as described further up in this application;
    • b) applying the coating composition to a surface;
    • c) crosslinking at least some of the ethylenic double bonds present in said polymerizable composition; and
    • d) crosslinking the isocyanate groups present in said polymerizable composition;

wherein process step b) is conducted first, then process step c) and finally process step d).

All other definitions given above with regard to the polymerizable composition of the invention are also applicable to the process of the invention, unless stated otherwise hereinafter.

When the polymerizable composition contains at least one component D, it is preferable that the process of the invention includes a further reaction step e) in which the isocyanate-reactive group of component D is crosslinked with an isocyanate group of the isocyanate component A or of a reaction product of the isocyanate component A. Said process step e) is preferably conducted after process step c). In most cases, however, it will be effected in parallel to process step e) since both the crosslinking of isocyanate groups with one another and the reaction of isocyanate groups with isocyanate-reactive groups proceed at similar temperatures.

Processes for producing an adhesive bond comprising the steps of

    • a) providing a coating composition as defined further up in this application;
    • b) applying the coating composition to a surface;
    • c) polymerizing at least some of the ethylenic double bonds present in said polymerizable composition;
    • d) compressing the at least one coated surface together with a further surface; and
    • e) crosslinking the reactive isocyanate groups present in said polymerizable composition and the ethylenic double bonds as yet unconverted in process step c);
    • wherein process steps c), d) and e) are conducted in any sequence after process step b).

It is preferable that process step c) is conducted prior to process steps d) and e).

If not all ethylenic double bonds have yet been polymerized in process step c), the unconverted double bonds are converted in process step e).

Applying to a Surface

The composition of the invention can be applied by different methods known per se. These are preferably spraying, painting, dipping, pouring, flow-coating or coating with the aid of brushes, rolls, nozzles or coating bars. Particular preference is given to printing technologies, especially screen-printing, valvejet, bubblejet and piezo printing. The surface to be coated has to be adequately wetted by the composition of the invention. Adequate wettability of a surface is preferably defined in that the contact angle of the liquid on the surface is not more than 100°, the contact angle measurement preferably being conducted by means of a tensiometer by the Wilhelmy method.

Preferably, the surface to be coated consists of a material selected from the group consisting of minerals, metal, rigid plastics, flexible plastics, textiles, leather, wood, wood derivatives and paper. Minerals are preferably selected from the group consisting of glass, stone, ceramic materials and concrete. In a particularly preferred embodiment, these materials are already in the form of surfaces modified with customary organic or inorganic or hybrid lacquers, primers or waxes.

Crosslinking of the Ethylenic Double Bonds

The ethylenic double bonds present in the polymerizable composition of the invention are crosslinked by a free-radical polymerization. This polymerization reaction is initiated in accordance with the invention by the use of radiation suitable for activation of the radiation-activated initiator F. In principle, however—irrespective of the presence of an initiator—the use of sufficiently high-energy radiation as defined further up in this application is also sufficient to initiate the free-radical polymerization in process step c).

It is preferable that process step c) is conducted not more than 120 seconds, more preferably not more than 30 seconds, after process step b).

Crosslinking of the Isocyanate Groups

The “crosslinking” of the isocyanate component A in process step d) is a process in which the isocyanate groups present therein react with one another or with urethane groups already present to form at least one structure selected from the group consisting of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and oxadiazinetrione structures. In this reaction, the isocyanate groups originally present in the isocyanate component A are consumed. The formation of the aforementioned groups results in combination of the monomeric and oligomeric polyisocyanates present in the isocyanate composition A to form a polymer network.

Since there is a distinct molar excess of isocyanate groups over isocyanate-reactive groups in the polymerizable composition of the invention, the result of the crosslinking reaction is that at most 20%, preferably at most 10%, more preferably at most 5%, even more preferably at most 2% and especially at most 1% of the total nitrogen content of the isocyanate component A is present in urethane and/or allophanate groups.

In a particularly preferred embodiment of the invention, the cured isocyanate component A, however, is not entirely free of urethane and allophanate groups. Consequently, taking account of the upper limits defined in the preceding paragraph, it preferably contains at least 0.1% urethane and/or allophanate groups based on the total nitrogen content.

It is preferable that the crosslinking of the isocyanate groups present in the polymerizable composition of the invention proceeds predominantly via cyclotrimerization of at least 50%, preferably at least 60%, more preferably at least 70%, especially at least 80% and most preferably 90% of the free isocyanate groups present in the isocyanate component A to give isocyanurate structural units, Thus, in the finished material, corresponding proportions of the nitrogen originally present in the isocyanate component A are bound within isocyanurate structures. However, side reactions, especially those to give uretdione, allophanate and/or iminooxadiazinedione structures, typically occur and can even be used in a controlled manner in order to advantageously affect, for example, the glass transition temperature (Tg) of the polyisocyanurate plastic obtained. However, the above-defined content of urethane and/or allophanate groups is preferably present in this embodiment too.

The crosslinking of the isocyanate groups is preferably effected at temperatures between 50° C. and 220° C., more preferably between 80° C. and 200° C. and even more preferably between 100° C. and 200° C.

The abovementioned temperatures are maintained in process step d) until at least 50%, preferably at least 75% and even more preferably at least 90% of the free isocyanate groups present in the isocyanate component A at the start of process step b) have been consumed. The percentage of isocyanate groups still present can be determined by a comparison of the content of isocyanate groups in % by weight in the isocyanate component A present at the start of process step b) with the content of isocyanate groups in % by weight in the reaction product, for example by the aforementioned comparison of the intensity of the isocyanate band at about 2270 cm−1 by means of IR spectroscopy.

The exact duration of process step d) naturally depends on the geometry of the workpiece to be created, especially the ratio of surface area and volume, since the required temperature has to be attained for the minimum time required even in the core of the workpiece being formed. The person skilled in the art is able to determine these parameters by simple preliminary tests.

In principle, crosslinking of the above mentioned proportions of free isocyanate groups is achieved when the abovementioned temperatures are maintained for 1 minute to 4 hours. Particular preference is given to a duration between 1 minute and 15 minutes at temperatures between 180° C. and 220° C. or a duration of 5 minutes to 120 minutes at a temperature of 120° C.

Polymer

In yet a further embodiment, the present invention relates to a coating obtainable by the process described above.

A “coating” is preferably characterized in that it has been applied to a substrate. This substrate is preferably selected from the group consisting of wood, plastic, metal, natural rock, concrete, paper and glass. In this respect, the present invention also relates to a substrate coated with the polymer of the invention. The coating is more preferably characterized in that the layer thickness is at least 0.005 mm and at most 5 mm and preferably has a measurement in at least one of the two other dimensions of at least a factor of 10, more preferably 100, of the layer thickness. Preferably in both the aforementioned factors are attained in both further dimensions.

In a further embodiment, the present invention relates to at least one coating which is compressed between two substrates having been applied to at least one substrate and is then polymerized and crosslinked and hence acts as an adhesive.

In a particular embodiment, prior to the compression, the at least one coating between the two substrates, at least one of which has been coated in accordance with the invention, is prepolymerized by use of actinic radiation and/or heat with the aim of obtaining a dimensionally stable adhesive coating according to the invention prior to the compression.

The examples which follow serve only to illustrate the invention. They are not intended to limit the scope of protection of the patent claims in any manner.

EXAMPLES

General Details:

All percentages, unless stated otherwise, are based on percent by weight (% by weight).

The ambient temperature of 23° C. at the time of conduct of the experiments is referred to as RT (room temperature).

The methods detailed hereinafter for determination of the appropriate parameters were employed for conduction and evaluation of the examples and are also the methods for determination of the parameters of relevance in accordance with the invention in general.

Starting Compounds

Polyisocyanate A: HDI trimer (NCO functionality >3) with an NCO content of 23.0% by weight from Covestro AG. The viscosity is about 1200 mPa·s at 23° C. (DIN EN ISO 3219/A.3).

Acrylate 1: hexanediol diacrylate (HDDA) was sourced with a purity of 99% by weight from abcr GmbH or with a purity of <=100% by weight from Sigma-Aldrich.

Acrylate 2: hydroxypropyl methacrylate (HPMA) was sourced with a purity of 98% by weight from abcr GmbH.

Potassium acetate was sourced with a purity of >99% by weight from ACROS.

Lucirin TPO-L is an ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate from BASF.

Polyethylene glycol (PEG) 400 was sourced with a purity of >99% by weight from ACROS.

All raw materials except for the catalyst and HPMA were degassed under reduced pressure prior to use.

Preparation of the Catalysts:

Potassium acetate (5.0 g) was stirred in the PEG 400 (95.0 g) at RT until all of it had dissolved. In this way, a 5% by weight solution of potassium acetate in PEG 400 was obtained and was used as catalyst without further treatment.

Preparation of the Reaction Mixture

Unless stated otherwise, the reaction mixture was prepared by mixing polyisocyanate (A1-A2) and the acrylate(s) with an appropriate amount of catalyst, initiator and optionally additive at 23° C. in a Speedmixer DAC 150.1 FVZ from Hauschild at 2750 min−1.

This was then knife-coated onto a glass plate (tin-free side, 250 μm).

In a first crosslinking step, the layer applied was treated by means of UV curing with a gallium-doped mercury vapor lamp and an undoped mercury vapor lamp, both operated at 80 W/cm and with a belt speed of 5 m/min. The dose obtained under these conditions is 1400 mJ/cm2.

After the first crosslinking step, the plate was placed on its edge and it was observed whether the UV light-treated coating runs or not.

Subsequently, the coating was cured completely. For this purpose, it was introduced into an air circulation oven at 180° C. for 15 min.

Test Methods

Run-Off

The coated plate was placed onto a paper towel on its edge for 10 min, and a visual assessment was made as to whether the coating runs. If there is a perceptible change in the coating as a result of the upright position (for example formation of a bulge at the lower edge), the coating is classified as “runs off”.

Acetone Resistance

A small piece of cotton wool is soaked with acetone and placed onto the coating surface. Every minute, the piece of cotton wool was soaked again with acetone in order to compensate for the evaporation. For this purpose, the acetone was added by means of a wash bottle in order that the piece of cotton wool is not moved during the contact operation. After 1 min and 5 min, the acetone-soaked piece of cotton wool is removed, the affected site is dried off and an inspection is made immediately in order to anticipate any regeneration. The test area is inspected for changes visually and by touching by hand. Subsequently, an assessment is made as to whether and what changes have occurred in the test area.

An assessment is made of softening or discoloration of the coating surface.

    • 0 no changes detectable
    • 1 swelling ring, hard surface, merely visible alteration/trace of a change in hue
    • 2 swelling ring, slight softening/slight change in hue
    • 3 distinct softening (possible slight blistering)/moderate change in hue
    • 4 significant softening (possibly significant blistering), can be scratched through down to the substrate/significant change in hue
    • 5 coating completely destroyed without outside action/very significant change in hue

Hardness

Hardness is the mechanical resistance of a body to the penetration of another body. It is the quotient of measured indentation force and the contact area of the indentation body on penetration into the surface. The contact area is calculated with the known geometry of the penetration body and the measured indentation depth.

In the case of the instrumented indentation test (Martens hardness), indentation force and indentation depth are measured during the deformation, taking account of the elastic and plastic deformation. A pyramidal indentation body (Vickers tip) presses into the coating with rising test force.

Indentation force, indentation depth and indentation body geometry are used to calculate a Martens hardness value (HM).

Hardness was determined by means of a Fischerscope H100C in accordance with DIN EN ISO 14577-1.

The samples are conditioned under standard climatic conditions at 23° C. and 50% rel. humidity for at least 16 h and then analyzed. Choice of maximum indentation force either the same for all samples within the test series or individual assessment and adjustment for each sample. The adjustment criterion here is the Buckle rule, according to which the maximum indentation force is adjusted such that the penetration depth attained is not more than 10% of the coating thickness.

The measurement result reported in table 1 is the Martens hardness HM (F) in N/mm2 as an average from 5 measurements.

Visual Assessment

After complete curing, the film was visually assessed and briefly described.

Working Examples:

The amounts of polyisocyanate, acrylate, catalyst solution specified in table 1 were treated according to the abovementioned production method for reaction mixtures.

The reaction mixture was coated with a coating bar in a thickness of 250 μm onto the tin-free side of a glass plate and then UV-treated with a gallium-doped mercury vapor lamp and an undoped mercury vapor lamp. Subsequently, the samples were cured in an air circulation oven at 180° C. for 15 min.

TABLE 1 Compositions and material properties of working examples 1-10 Results Catalyst + initiator Martens Resin composition Amount of hardness HM (F) Acetone resistance Amount of Amount of Amount of Amount of Lucirin [N/mm2] 1 min/5 min Visual observation Isocyanate A Acrylate 1 Acrylate 2 Cat. K1 TPOL-L After After After Runoff Appearance Ex. [g] [g] [g] [g] [g] curing exposure curing after exposure after curing B1 50.0 0.5 9.5 2.0 0.3 133 3/3 0/0 no homogeneous layer B2 50.0 0.375 7.125 2.0 0.3 126 4/4 0/0 no homogeneous layer B3 50.0 0.25 4.75 2.0 0.3 133 5/5 0/0 no homogeneous layer B4 50.0 0.375 9.5 2.0 0.3 130 3-4/4  0/0 no homogeneous layer B5 50.0 0.25 9.5 2.0 0.3 134 3-4/4   0/0-1 no homogeneous layer B6 50.0 0.0 0 2.0 0.3 135 5/5 0/0 obvious homogeneous layer

All examples where the number is preceded by a B are inventive. All examples where the number is preceded by a V are comparative examples and noninventive. Comparative example 1 is prophetic.

All examples show a high Martens hardness HM (F) after complete curing.

Examples B1 to B5 show that runoff-free films are obtained after radiative curing and homogeneous clear hard films after complete curing.

Comparative example V1 shows that the straight isocyanate after radiative curing does not form a runoff-free layer.

Claims

1.-15. (canceled)

16. A coating composition having a ratio of isocyanate groups to isocyanate-reactive groups of at least 2.0:1.0, comprising the following components:

a) an isocyanate component A;
b) at least one trimerization catalyst C; and
c) at least one component selected from the group consisting of components B, D and E, where
component B has at least one ethylenic double bond but no isocyanate-reactive group;
component D has at least one isocyanate-reactive group and at least one ethylenic double bond in one molecule; and
component E has both at least one isocyanate group and at least one ethylenic double bond in one molecule.

17. The composition as claimed in claim 16, containing at least one component D or E.

18. The composition as claimed in claim 16, containing at least one component B.

19. The composition as claimed in claim 16, wherein the molar ratio of isocyanate groups to isocyanate-reactive groups in the polymerizable composition is at least 4.0:1.0.

20. The composition as claimed in claim 16, additionally containing a component F suitable as a radiation-activated initiator for a free-radical polymerization of the ethylenic double bonds present in the polymerizable composition of the invention.

21. The composition as claimed in claim 16, wherein the proportion of components B, D and E is chosen such that the coating, after free-radical polymerization of the ethylenic double bonds present therein, does not run on a vertical surface.

22. The use of at least one component selected from the group consisting of components B, D and E for production of a coating composition having a ratio of isocyanate groups to isocyanate-reactive groups of at least 2.0:1.0, which contains an isocyanate component A and is polymerizable either by free-radical polymerization or by crosslinking of isocyanate groups with one another.

23. A process for producing a coating, comprising the steps of

a) providing a coating composition as defined in claim 16;
b) applying the coating composition to a surface;
c) crosslinking at least some of the ethylenic double bonds present in said polymerizable composition; and
d) crosslinking the isocyanate groups present in said polymerizable composition;
wherein process step b) is conducted first, then process step c) and finally process step d).

24. The process as claimed in claim 23, wherein the polymerizable composition comprises at least one component D and the process comprises a further process step d) in which the isocyanate-reactive group of component D is crosslinked with an isocyanate group of the isocyanate component A or of a reaction product of the isocyanate component A.

25. The process as claimed in claim 23, wherein, in process step d), at least 50% of the free isocyanate groups present in isocyanate component A are converted to isocyanurate structural units.

26. The process as claimed in claim 23, wherein process steps b) and c) are conducted within an interval of not more than 120 seconds.

27. A coating obtainable by the process as claimed in claim 23.

28. A process for producing an adhesive bond, comprising the steps of

a) providing a coating composition as defined in claim 16;
b) applying the coating composition to a surface;
c) polymerizing at least some of the ethylenic double bonds present in said polymerizable composition;
d) compressing the at least one coated surface together with a further surface; and
e) crosslinking the reactive isocyanate groups present in said polymerizable composition and the ethylenic double bonds as yet unconverted in process step c);
wherein process steps c), d) and e) are conducted in any sequence after process step b).

29. A coated product obtainable by the process as claimed in claim 23.

30. A bonded product obtainable by the process as claimed in claim 28.

Patent History
Publication number: 20190367666
Type: Application
Filed: Nov 14, 2017
Publication Date: Dec 5, 2019
Inventors: Jörg TILLACK (Solingen), Dirk ACHTEN (Leverkusen), Paul HEINZ (Leverkusen), Richard MEISENHEIMER (Köln), Thomas BÜSGEN (Leverkusen), Michael LUDEWIG (Odenthal), Christoph TOMCZYK (Leverkusen), Roland WAGNER (Leverkusen)
Application Number: 16/349,373
Classifications
International Classification: C08G 18/73 (20060101); C09D 175/14 (20060101); C09J 175/14 (20060101); C09J 5/00 (20060101); C08J 3/24 (20060101); C08G 18/67 (20060101); C08G 18/22 (20060101);