Patent Description:
Preparations of polyisocyanates, isocyanurates for example, are already well established and are available in the form of numerous commercial products from a variety of manufacturers.

Since polyisocyanates frequently have a high viscosity or are even solid at room temperature, it is common to add a solvent to polyisocyanate preparations of this kind (see for instance <CIT>, <CIT> or <CIT>).

Widespread solvents include butyl acetate, ethyl acetate, methoxypropyl acetate, toluene, xylene, fluorinated aromatics, aliphatic and aromatic hydrocarbon mixtures and mixtures thereof. The latter are sold for example under the trade names Solvesso® from ExxonMobil, Hydrosol® from Kemetyl or Shellsol® from Shell, or under the designations solvent naphtha, Kristalloel, white spirit, heavy benzine, etc., in different and varying compositions.

The purpose of blending polyisocyanates with solvents is to dissolve high-viscosity or solid polyisocyanates and to provide polyisocyanate preparations in as low-viscosity a form as possible. The purpose of this is, for example, to improve miscibility and processibility, especially of solid polyisocyanates and those of relatively high viscosity, but also to enhance the surface quality of coatings.

It was an object of the present invention to provide polyisocyanate preparations which have a particularly low viscosity.

This object has been achieved by means of mixtures comprising.

It has been found that such mixtures exhibit a significantly lower viscosity than mixtures containing the same amount of (A) and solvents other than (B).

The mixtures of the invention comprising at least one polyisocyanate obtainable by reacting at least one monomeric isocyanate (A).

The monomeric isocyanates used may be aromatic, aliphatic, or cycloaliphatic, preferably aliphatic or cycloaliphatic, which is referred to for short in this text as (cyclo)aliphatic; aliphatic isocyanates are particularly preferred.

Aromatic isocyanates are those which comprise at least one aromatic ring system, in other words not only purely aromatic compounds but also araliphatic compounds.

Cycloaliphatic isocyanates are those which comprise at least one cycloaliphatic ring system.

Aliphatic isocyanates are those which comprise exclusively linear or branched chains, i.e., acyclic compounds.

The monomeric isocyanates are preferably diisocyanates, which carry precisely two isocyanate groups. They can, however, in principle also be monoisocyanates, having one isocyanate group.

In principle, higher isocyanates having on average more than <NUM> isocyanate groups are also possible. Suitability therefor is possessed for example by triisocyanates, such as triisocyanatononane, <NUM>'-isocyanatoethyl <NUM>,<NUM>-diisocyanatohexanoate, <NUM>,<NUM>,<NUM>-triisocyanatotoluene, triphenylmethane triisocyanate or <NUM>,<NUM>,<NUM>'-triisocyanatodiphenyl ether, or the mixtures of diisocyanates, triisocyanates, and higher polyisocyanates that are obtained, for example, by phosgenation of corresponding aniline/formaldehyde condensates and represent methylene-bridged polyphenyl polyisocyanates.

These monomeric isocyanates do not contain any substantial products of reaction of the isocyanate groups with themselves.

The monomeric isocyanates are preferably isocyanates having <NUM> to <NUM> C atoms. Examples of typical diisocyanates are aliphatic diisocyanates such as tetramethylene diisocyanate, pentamethylene-<NUM>,<NUM>-diisocyanate, hexamethylene diisocyanate (<NUM>,<NUM>-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysine diisocyanate (e.g., methyl <NUM>,<NUM>-diisocyanatohexanoate or ethyl <NUM>,<NUM>-diisocyanatohexanoate), trimethylhexane diisocyanate or tetramethylhexane diisocyanate, cycloaliphatic diisocyanates such as <NUM>,<NUM>-, <NUM>,<NUM>- or <NUM>,<NUM>-diisocyanatocyclohexane, <NUM>,<NUM>'- or <NUM>,<NUM>'-di(isocyanatocyclohexyl)methane, <NUM>-isocyanato-<NUM>,<NUM>,<NUM>-trimethyl-<NUM>-(isocyanatomethyl)cyclohexane (isophorone diisocyanate), <NUM>,<NUM>- or <NUM>,<NUM>-bis(isocyanatomethyl)cyclohexane or <NUM>,<NUM>-, or <NUM>,<NUM>-diisocyanato-<NUM>-methylcyclohexane, and also <NUM> (or <NUM>), <NUM> (or <NUM>)-bis(isocyanatomethyl)tricyclo-[<NUM>. <NUM><NUM>,<NUM>]decane isomer mixtures, and also aromatic diisocyanates such as tolylene <NUM>,<NUM>- or <NUM>,<NUM>-diisocyanate and the isomer mixtures thereof, m- or p-xylylene diisocyanate, <NUM>,<NUM>'- or <NUM>,<NUM>'-diisocyanatodiphenylmethane and the isomer mixtures thereof, phenylene <NUM>,<NUM>- or <NUM>,<NUM>-diisocyanate, <NUM>-chlorophenylene <NUM>,<NUM>-diisocyanate, naphthylene <NUM>,<NUM>-diisocyanate, diphenylene <NUM>,<NUM>'-diisocyanate, <NUM>,<NUM>'-diisocyanato-<NUM>,<NUM>'-dimethylbiphenyl, <NUM>-methyldiphenylmethane <NUM>,<NUM>'-diisocyanate, tetramethylxylylene diisocyanate, <NUM>,<NUM>-diisocyanatobenzene or diphenyl ether <NUM>,<NUM>'-diisocyanate.

Particular preference is given to hexamethylene-<NUM>,<NUM>-diisocyanate, <NUM>,<NUM>-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate, pentamethylene-<NUM>,<NUM>-diisocyanate and <NUM>,<NUM>'- or <NUM>,<NUM>'-di(isocyanatocyclohexyl)methane, very particular preference to isophorone diisocyanate and hexamethylene-<NUM>,<NUM>-diisocyanate, and especial preference to hexamethylene-<NUM>,<NUM>-diisocyanate.

Mixtures of said isocyanates may also be present.

Isophorone diisocyanate is usually in the form of a mixture, specifically a mixture of the cis and trans isomers, generally in a proportion of about <NUM>:<NUM> to <NUM>:<NUM> (w/w), preferably of <NUM>:<NUM>-<NUM>:<NUM>.

Dicyclohexylmethane <NUM>,<NUM>'-diisocyanate may likewise be in the form of a mixture of the different cis and trans isomers.

For the present invention it is possible to use not only those diisocyanates obtained by phosgenating the corresponding amines but also those prepared without the use of phosgene, i.e., by phosgene-free processes. According to <CIT> (<CIT>), <CIT> (<CIT>), and <CIT> (<CIT>), for example, (cyclo)aliphatic diisocyanates, such as hexamethylene <NUM>,<NUM>-diisocyanate (HDI), isomeric aliphatic diisocyanates having <NUM> carbon atoms in the alkylene radical, <NUM>,<NUM>'- or <NUM>,<NUM>'-di(isocyanatocyclohexyl)methane, and <NUM>-isocyanato-<NUM>-isocyanatomethyl-<NUM>,<NUM>,<NUM>-trimethylcyclohexane (isophorone diisocyanate or IPDI) can be prepared by reacting the (cyclo)aliphatic diamines with, for example, urea and alcohols to give (cyclo)aliphatic biscarbamic esters and subjecting said esters to thermal cleavage into the corresponding diisocyanates and alcohols. The synthesis takes place usually continuously in a circulation process and optionally in the presence of N-unsubstituted carbamic esters, dialkyl carbonates, and other by-products recycled from the reaction process. Diisocyanates obtained in this way generally contain only a very low or even unmeasurable fraction of chlorinated compounds, which is advantageous, for example, in applications in the electronics industry.

In one embodiment of the present invention the isocyanates used have a hydrolyzable chlorine content of less than <NUM> ppm, preferably of less than <NUM> ppm, in particular less than <NUM> ppm, and especially less than <NUM> ppm. This can be measured by means, for example, of ASTM specification D4663-<NUM>. The total chlorine contents are, for example below <NUM> ppm, preferably below <NUM> ppm, and more preferably below <NUM> ppm (determined by argentometric titration after hydrolysis).

It will be appreciated that it is also possible to employ mixtures of those monomeric isocyanates which have been obtained by reacting the (cyclo)aliphatic diamines with, for example, urea and alcohols and cleaving the resulting (cyclo)aliphatic biscarbamic esters, with those diisocyanates which have been obtained by phosgenating the corresponding amines.

The polyisocyanates (A) which can be formed by oligomerizing the monomeric isocyanates are generally characterized as follows:
The average NCO functionality of such compounds is in general at least <NUM> and can be up to <NUM>, preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>.

The isocyanate group content after oligomerization, calculated as NCO = <NUM>/mol, is generally from <NUM>% to <NUM>% by weight unless otherwise specified.

The polyisocyanates (A) are preferably compounds as follows:.

The diisocyanates or polyisocyanates recited above may also be present at least partly in blocked form.

Classes of compounds used for blocking are described in <NPL>), <NPL>), and also <NPL>).

Examples of classes of compounds used for blocking are phenols, imidazoles, triazoles, pyrazoles, oximes, N-hydroxyimides, hydroxybenzoic esters, secondary amines, lactams, CH-acidic cyclic ketones, malonic esters or alkyl acetoacetates.

In one preferred embodiment of the present invention the polyisocyanate is selected from the group consisting of isocyanurates, biurets and asymmetric isocyanurates, more preferably biurets and asymmetric isocyanurates.

In one particularly preferred embodiment the polyisocyanate encompasses polyisocyanates comprising isocyanurates, biuret and/or asymmetric isocyanurate groups, more preferably biurets and asymmetric isocyanurates and obtained from hexamethylene <NUM>,<NUM>-diisocyanate.

In one further preferred embodiment the polyisocyanate encompasses a mixture of polyisocyanates comprising biuret and/or asymmetric isocyanurate groups and obtained very preferably from hexamethylene <NUM>,<NUM>-diisocyanate and from isophorone diisocyanate.

In this specification, unless noted otherwise, the viscosity is reported at <NUM> in accordance with DIN EN ISO <NUM>/A. <NUM> in a cone/plate system with a shear rate of <NUM>-<NUM>.

The process for preparing the polyisocyanates may take place as described in <CIT>, especially from page <NUM> line <NUM> to page <NUM> line <NUM> therein, which is hereby made part of the present specification by reference.

The reaction can be discontinued, for example, as described therein from page <NUM> line <NUM> to page <NUM> line <NUM>, and working up may take place as described therein from page <NUM> line <NUM> to page <NUM> line <NUM>, which in each case is hereby made part of the present specification by reference.

The reaction can alternatively and preferably be affected as described in <CIT> for ammonium alpha-hydroxycarboxylate catalysts. Express reference is hereby made to the ammonium α-hydroxycarboxylates described in <CIT> at page <NUM> line <NUM> to page <NUM> line <NUM>.

Particular preference is given to ammonium cations of tetraoctylammonium, tetramethylammonium, tetraethylammonium, tetra-n-butylammonium, trimethylbenzylammonium, triethylbenzylammonium, tri-n-butylbenzylammonium, trimethylethylammonium, tri-n-butylethylammonium, triethylmethylammonium, tri-n-butylmethylammonium, diisopropyldiethylammonium, diisopropylethylmethylammonium, diisopropylethylbenzylammonium, N,N-dimethylpiperidinium, N,N-dimethylmorpholinium, N,N-dimethylpiperazinium or N-methyldiazabicyclo[<NUM>. <NUM>]octane. Preferred alkyl ammonium ions are tetraoctylammonium, tetramethylammonium, tetraethylammonium, and tetra-n-butylammonium, more preferably tetramethylammonium and tetraethylammonium, and very preferably tetramethylammonium and benzyltrimethylammonium.

Particular preference is given to α-hydroxycarboxylates of glycolic acid (hydroxyacetic acid), lactic acid, citric acid, <NUM>-methyllactic acid (α-hydroxyisobutyric acid), <NUM>-hydroxy-<NUM>-methylbutyric acid, <NUM>-hydroxy-<NUM>-ethylbutyric acid, <NUM>-hydroxy-<NUM>-methylbutyric acid, <NUM>-hydroxycaproic acid, maleic acid, tartaric acid, glucuronic acid, gluconic acid, citramalic acid, saccharic acid, ribonic acid, benzylic acid, china acid, mandelic acid, hexahydromandelic acid, <NUM>-hydroxycaproic acid or <NUM>-phenyllactic acid. Preferred α-hydroxycarboxylates are lactic acid, <NUM>-methyllactic acid, (α-hydroxyisobutyric acid), <NUM>-hydroxy-<NUM>-methylbutyric acid, and <NUM>-hydroxycaproic acid, more preferably lactic acid, <NUM>-methyllactic acid (α-hydroxyisobutyric acid), and <NUM>-hydroxycaproic acid, and very preferably α-hydroxyisobutyric acid and lactic acid.

The reaction may be discontinued for example as described therein from page <NUM> line <NUM> to page <NUM> line <NUM>, hereby made part of the present specification by reference.

The reaction may alternatively take place as described in <CIT> or <CIT>.

In the case of thermally labile catalysts it is also possible, furthermore, to terminate the reaction by heating of the reaction mixture to a temperature above at least <NUM>, preferably at least <NUM>, more preferably at least <NUM>.

In the case both of thermally non-labile catalysts and of thermally labile catalysts, the possibility exists of terminating the reaction at relatively low temperatures by addition of deactivators. Deactivators can also be added stoichiometrically in deficit to the catalyst, if the catalyst is at least partly thermally destroyed or the product is stable in viscosity on subsequent storage (e.g., undergoes no more than a threefold increase in viscosity on storage of the <NUM>% form over <NUM> weeks at <NUM> under nitrogen). Examples of suitable deactivators are hydrogen chloride, phosphoric acid, organic phosphates, such as dibutyl phosphate or diethylhexyl phosphate, phosphonates such as dioctyl phosphonate, and carbamates such as hydroxyalkyl carbamate. Dibutyl or diethylhexyl phosphate is preferred.

These compounds are added neat or diluted in a suitable concentration as necessary to discontinue the reaction. Examples of suitable solvents are the monomer, alcohols such as ethylhexanol or methyl glycol, or polar, aprotic solvents such as propylene carbonate.

The amount of the isocyanate component (A) in the mixture of the invention can be in general up to <NUM>% by weight, based on the sum of polyisocyanate and solvent, preferably up to <NUM>%, more preferably up to <NUM>%.

The amount of the isocyanate component (A) in the mixture of the invention is in general <NUM>% by weight or more, based on the sum of polyisocyanate and solvent, preferably <NUM>% by weight or more, more preferably <NUM>% by weight or more, and very preferably <NUM>% by weight or more.

Solvent used for the isocyanate preparations of the invention is p-cymene.

The amount of p-cymene in the mixture of the invention can be in general up to <NUM>% by weight, based on the sum of polyisocyanate and solvent, preferably up to <NUM>%, more preferably up to <NUM>%, even more preferably up to <NUM>%.

The amount of p-cymene in the mixture of the invention is in general <NUM>% by weight or more, based on the sum of polyisocyanate and solvent, preferably <NUM>% by weight or more and more preferably <NUM>% by weight or more.

The present invention further provides p-cymene with a <NUM>C : <NUM>C isotope ratio of from <NUM> × <NUM>-<NUM> to <NUM> × <NUM>-<NUM>, preferably from <NUM> × <NUM>-<NUM> to <NUM> × <NUM>-<NUM> and more preferably from <NUM> × <NUM>-<NUM> to <NUM> × <NUM>-<NUM>. Such p-cymene is obtainable when synthesis is performed proceeding from biological material.

The advantage of such p-cymene is that it has a <NUM>C isotope content which corresponds to natural material, whereas p-cymene which is prepared on a petrochemical basis has an unnatural content, which is generally below <NUM> × <NUM>-<NUM>, usually below <NUM> × <NUM>-<NUM> and usually below <NUM> × <NUM>-<NUM>. Owing to its isotope content, this inventive p-cymene can then be used to synthesize compounds for use as probes for, for example, <NUM>C studies.

A further, optional constituent of the mixtures of the invention is at least one further solvent other than (B).

Solvents which can be used for the polyisocyanate component, and also for the binder and any other components, are those which contain no groups that are reactive toward isocyanate groups or blocked isocyanate groups, and in which the polyisocyanates are soluble to an extent of at least <NUM>%, preferably at least <NUM>%, more preferably at least <NUM>%, very preferably at least <NUM>%, more particularly at least <NUM>%, and especially at least <NUM>% by weight.

Examples of solvents of this kind are aromatic hydrocarbons (including alkylated benzenes and naphthalenes) and/or (cyclo)aliphatic hydrocarbons and mixtures thereof, chlorinated hydrocarbons, ketones, esters, alkoxylated alkyl alkanoates, ethers, and mixtures of the solvents.

Preferred aromatic hydrocarbon mixtures are those which comprise predominantly aromatic C<NUM> to C<NUM> hydrocarbons and may encompass a boiling range from <NUM> to <NUM>; particular preference is given to toluene, o-, m- or p-xylene, trimethylbenzene isomers, tetramethylbenzene isomers, ethylbenzene, cumene, tetrahydronaphthalene, and mixtures comprising them.

Examples thereof are the Solvesso® products from ExxonMobil Chemical, especially Solvesso® <NUM> (<NPL>, predominantly C<NUM> and C<NUM> aromatics, boiling range about <NUM> - <NUM>), <NUM> (boiling range about <NUM> - <NUM>), and <NUM> (<NPL>), and also the Shellsol® products from Shell, Caromax® (e.g., Caromax® <NUM>) from Petrochem Carless, and Hydrosol from DHC (e.g., as Hydrosol® A <NUM>). Hydrocarbon mixtures comprising paraffins, cycloparaffins, and aromatics are also available commercially under the names Kristalloel (for example, Kristalloel <NUM>, boiling range about <NUM> - <NUM> or Kristalloel <NUM>: <NPL>), white spirit (for example likewise <NPL>) or solvent naphtha (light: boiling range about <NUM> - <NUM>, heavy: boiling range about <NUM> - <NUM>). The aromatics content of such hydrocarbon mixtures is generally more than <NUM>%, preferably more than <NUM>%, more preferably more than <NUM>%, and very preferably more than <NUM>% by weight. It may be advisable to use hydrocarbon mixtures having a particularly reduced naphthalene content.

Examples of (cyclo)aliphatic hydrocarbons include decalin, alkylated decalin, and isomer mixtures of linear or branched alkanes and/or cycloalkanes.

The amount of aliphatic hydrocarbons is generally less than <NUM>%, preferably less than <NUM>%, and more preferably less than <NUM>% by weight.

Esters are, for example, n-butyl acetate, ethyl acetate, <NUM>-methoxyprop-<NUM>-yl acetate, and <NUM>-methoxyethyl acetate.

Ethers are, for example, THF, dioxane, and also the dimethyl, diethyl or di-n-butyl ethers of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol or tripropylene glycol.

Ketones are, for example, acetone, diethyl ketone, ethyl methyl ketone, isobutyl methyl ketone, methyl amyl ketone and tert-butyl methyl ketone.

Preferred solvents are n-butyl acetate, ethyl acetate, <NUM>-methoxyprop-<NUM>-yl acetate, <NUM>-methoxyethyl acetate, and also mixtures thereof, more particularly with the aromatic hydrocarbon mixtures recited above, especially xylene and Solvesso® <NUM>.

Such mixtures of (B) with (C) can be present in the volume ratio of <NUM>:<NUM> to <NUM>:<NUM>, preferably in a volume ratio of <NUM>:<NUM> to <NUM>:<NUM>, more preferably in a volume ratio of <NUM>:<NUM> to <NUM>:<NUM> and very preferably in a volume ratio of <NUM>:<NUM> to <NUM>:<NUM>.

If a solvent (C) is present then preference is given to inventive mixtures of (B) with n-butyl acetate or of (B) with <NUM>-methoxy-<NUM>-propyl acetate or of (B) with methyl amyl ketone or of (B) with xylene or of (B) with Solvesso® <NUM>.

The amount of solvent (C) in the mixture of the invention can be in general up to <NUM>% by weight, based on the sum of polyisocyanate and solvent, preferably up to <NUM>%, more preferably up to <NUM>%.

The amount of solvent (C) in the mixture of the invention is preferably <NUM>% by weight, based on the sum of polyisocyanate and solvent.

Examples of suitable Lewis-acidic organometallic compounds (D) are tin compounds, such as tin(II) salts of organic carboxylic acids, e.g., tin(ll) diacetate, tin(ll) dioctoate, tin(II) bis(ethylhexanoate), and tin(II) dilaurate, and the dialkyltin(IV) salts of organic carboxylic acids, e.g., dimethyltin diacetate, dibutyltin diacetate, dibutyltin dibutyrate, dibutyltin bis(<NUM>-ethylhexanoate), dibutyltin dilaurate, dibutyltin maleate, dioctyltin dilaurate, and dioctyltin diacetate.

Other preferred Lewis-acidic organometallic compounds are zinc salts, example being zinc(II) diacetate and zinc(II) dioctoate.

Tin-free and zinc-free alternatives used include organometallic salts of bismuth, zirconium, titanium, aluminum, iron, manganese, nickel, and cobalt.

These are, for example, zirconium tetraacetylacetonate (e.g., K-KAT® <NUM> from King Industries); zirconium dionates (e.g., K-KAT® XC-<NUM>; XC-A <NUM> and XC-<NUM> from King Industries); bismuth compounds, especially tricarboxylates (e.g., K-KAT® <NUM>, XC-B221; XC-C227, XC <NUM> from King Industries); aluminum dionate (e.g., K-KAT® <NUM> from King Industries). Tin-free and zinc-free catalysts are otherwise also offered, for example, under the trade name Borchi® Kat from Borchers, TK from Goldschmidt or BICAT® from Shepherd, Lausanne.

Bismuth catalysts and cobalt catalysts as well, cerium salts such as cerium octoates, and cesium salts can be used as catalysts.

Bismuth catalysts are more particularly bismuth carboxylates, especially bismuth octoates, ethylhexanoates, neodecanoates, or pivalates; examples are K-KAT <NUM> and XK-<NUM> from King Industries, TIB KAT <NUM>, 716LA, 716XLA, <NUM>, <NUM>, <NUM> from TIB Chemicals, and those from Shepherd Lausanne, and also catalyst mixtures of, for example, bismuth organyls and zinc organyls.

Further metal catalysts are described by <NPL>.

These catalysts are suitable for solvent-based, water-based and/or blocked systems.

Molybdenum, tungsten, and vanadium catalysts are described more particularly for the reaction of blocked polyisocyanates in <CIT> and <CIT>. Cesium salts as well can be used as catalysts. Suitable cesium salts are those compounds in which the following anions are employed: F-, Cl-, ClO-, ClO<NUM>-, ClO<NUM>-, Br-, I-, IO<NUM>-, CN-, OCN-, NO<NUM>-, NO<NUM>-, HCO<NUM>-, CO<NUM><NUM>-, S<NUM>-, SH-, HSO<NUM>-, SO<NUM><NUM>-, HSO<NUM>-, SO<NUM><NUM>-, S<NUM>O<NUM><NUM>-, S<NUM>O<NUM><NUM>-, S<NUM>O<NUM><NUM>-, S<NUM>O<NUM><NUM>-, S<NUM>O<NUM><NUM>-, S<NUM>O<NUM><NUM>-, H<NUM>PO<NUM>-, H<NUM>PO<NUM>-, HPO<NUM><NUM>-, PO<NUM><NUM>-, P<NUM>O<NUM><NUM>-, (OCnH2n+<NUM>)-, (CnH2n-<NUM>O<NUM>)-, (CnH2n-<NUM>O<NUM>)-, and also (Cn+<NUM>H2n-<NUM>O<NUM>)<NUM>-, where n stands for the numbers <NUM> to <NUM>. Preferred here are cesium carboxylates in which the anion conforms to the formulae (CnH2n-<NUM>O<NUM>)- and also (Cn+<NUM>H2n-<NUM>O<NUM>)<NUM>-, with n being <NUM> to <NUM>. Particularly preferred cesium salts contain monocarboxylate anions of the general formula (CnH2n-<NUM>O<NUM>)-, with n standing for the numbers <NUM> to <NUM>. Particular preference in this context is given to formate, acetate, propionate, hexanoate, and <NUM>-ethylhexanoate.

Preferred Lewis-acidic organometallic compounds are dimethyltin diacetate, dibutyltin dibutyrate, dibutyltin bis(<NUM>-ethylhexanoate), dibutyltin dilaurate, dioctyltin dilaurate, zinc(II) diacetate, zinc(II) dioctoate, zirconium acetylacetonate, and zirconium <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>,<NUM>-heptanedionate, and bismuth compounds.

Particular preference is given to dibutyltin dilaurate.

Further, typical coatings additives (E) used may be the following, for example: antioxidants, UV stabilizers such as UV absorbers and suitable free-radical scavengers (especially HALS compounds, hindered amine light stabilizers), activators (accelerators), drying agents, fillers, pigments, dyes, antistatic agents, flame retardants, thickeners, thixotropic agents, surface-active agents, viscosity modifiers, plasticizers or chelating agents. UV stabilizers are preferred.

The secondary antioxidants are preferably selected from the group consisting of phosphites, phosphonites, phosphonates, and thioethers.

Phosphites are compounds of the type P(ORa)(ORb) (ORc) with Ra, Rb, and Rc being identical or different, aliphatic or aromatic radicals (which may also form cyclic or spiro structures).

Preferred phosphonites are described in <CIT>, particularly from page <NUM> line <NUM> to page <NUM> line <NUM> therein, hereby made part of the present disclosure content by reference.

Preferred phosphonates are described in <CIT>, particularly from page <NUM> line <NUM> to page <NUM> line <NUM> therein, hereby made part of the present disclosure content by reference.

These are more particularly dialkyl phosphonates and dialkyl diphosphonates.

Examples thereof are mono- and di-C<NUM> to C<NUM> alkyl phosphonates and mixtures thereof, preferably the dialkyl phosphonates, more preferably those having C<NUM> to C<NUM> alkyl groups, very preferably having C<NUM> to C<NUM> alkyl groups, and more particularly those having C<NUM>, C<NUM>, C<NUM> or C<NUM> alkyl groups.

The alkyl groups in dialkyl phosphonates may be identical or different and are preferably identical.

Examples of C<NUM> to C<NUM> alkyl groups are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, <NUM>-ethylhexyl, and <NUM>-propylheptyl, more particularly di-n-octyl phosphonate Irgafos® OPH (see image above), and di-(<NUM>-ethylhexyl) phosphonate.

Preferred thioethers described in <CIT>, particularly from page <NUM> line <NUM> to page <NUM> line <NUM> therein, hereby made part of the present disclosure content by reference.

Sterically hindered phenols may be present and have the function of a primary antioxidant. This is a term commonly used by the skilled person to refer to compounds which scavenge free radicals.

Sterically hindered phenols of this kind are described in <CIT>, for example, preference being given to the compounds described therein at page <NUM> line <NUM> to page <NUM> line <NUM>, hereby made part of the present disclosure content by reference.

The phenols in question are preferably those which have exactly one phenolic hydroxyl group on the aromatic ring, and more preferably those which have a substituent, preferably an alkyl group, in the ortho-positions, very preferably in ortho-positions and para-position, to the phenolic hydroxyl group, preferably contain an alkyl group, and more particularly are alkyl <NUM>-(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl)propionates, or substituted alkyl derivatives of such compounds.

Phenols of this kind may also be constituents of a polyphenolic system having a plurality of phenol groups: pentaerythritol tetrakis(<NUM>-(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl)propionate (e.g., Irganox® <NUM>); ethylenebis(oxyethylene) bis(<NUM>-(<NUM>-tert-butyl-<NUM>-hydroxy-m-tolyl)propionate) (e.g., Irganox <NUM>); <NUM>,<NUM>',<NUM>",<NUM>,<NUM>',<NUM>"-hexa-tert-butyl-a,a',a"-(mesitylene-<NUM>,<NUM>,<NUM>-triyl)tri-p-cresol (e.g., Irganox® <NUM>); <NUM>,<NUM>,<NUM>-tris(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxybenzyl)-<NUM>,<NUM>,<NUM>-triazine-<NUM>,<NUM>,<NUM>(<NUM>,<NUM>,<NUM>)-trione (e.g., Irganox® <NUM>), in each case products of Ciba Spezialitätenchemie, now BASF SE.

Corresponding products are available, for example, under the trade names Irganox® (BASF SE), Sumilizer® from Sumitomo, Lowinox® from Great Lakes, and Cyanox® from Cytec.

Also possible are, for example, thiodiethylenebis[<NUM>-[<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl]propionate] (Irganox® <NUM>) and <NUM>,<NUM>'-di-tert-butyl-<NUM>,<NUM>'-thiodi-p-cresol (e.g., Irganox® <NUM>), each products of BASF SE.

Preference is given to <NUM>,<NUM>-di-tert-butyl-<NUM>-methylphenol (BHT); isooctyl <NUM>-(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl)propionate (Irganox® <NUM>, <NPL>), octadecyl <NUM>-(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl)propionate (Irganox® <NUM>, <NPL>), and pentaerythritol tetrakis(<NUM>-(<NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxyphenyl)propionate (<NPL>; e.g., Irganox® <NUM>).

Other primary antioxidants are, for example, secondary arylamines.

Suitable UV absorbers comprise oxanilides, triazines and benzotriazole (the latter available, for example, as Tinuvin® products from BASF SE) and benzophenones (e.g., Chimassorb® <NUM> from BASF SE). Preference is given, for example, to <NUM>% benzenepropanoic acid, <NUM>-(<NUM>-benzotriazol-<NUM>-yl)-<NUM>-(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxy-, C7-<NUM>-branched and linear alkyl esters; <NUM>% <NUM>-methoxy-<NUM>-propyl acetate (e.g., Tinuvin® <NUM>) and α-[<NUM>-[<NUM>-(<NUM>-benzotriazol-<NUM>-yl)-<NUM>-(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxyphenyl]-<NUM>-oxopropyl]-ω-hydroxypoly(oxo-<NUM>,<NUM>-ethanediyl) (e.g., Tinuvin® <NUM>), in each case products, for example, of BASF SE. DL-alpha-Tocopherol, tocopherol, cinnamic acid derivatives, and cyanoacrylates can likewise be used for this purpose.

These can be employed alone or together with suitable free-radical scavengers, examples being sterically hindered amines (often also identified as HALS or HAS compounds; hindered amine (light) stabilizers) such as <NUM>,<NUM>,<NUM>,<NUM>-tetramethylpiperidine, <NUM>,<NUM>-di-tert-butylpiperidine or derivatives thereof, e.g., bis(<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-piperidyl) sebacate. They are obtainable, for example, as Tinuvin® products and Chimassorb® products from BASF SE. Preference in joint use with Lewis acids, however, is given to those hindered amines which are N-alkylated, examples being bis(<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentamethyl-<NUM>-piperidinyl) [[<NUM>,<NUM>-bis(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxyphenyl]methyl]butylmalonate (e.g., Tinuvin® <NUM> from BASF SE); a mixture of bis(<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentamethyl-<NUM>-piperidinyl)sebacate and methyl(<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentamethyl-<NUM>-piperidinyl) sebacate (e.g., Tinuvin® <NUM> from BASF SE); or which are N-(O-alkylated), such as, for example, decanedioic acid bis(<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-(octyloxy)-<NUM>-piperidinyl) ester, reaction products with <NUM>,<NUM>-dimethylethyl hydroperoxide and octane (e.g., Tinuvin® <NUM> from BASF SE) and especially the HALS triazine "<NUM>-aminoethanol, reaction products with cyclohexane and peroxidized N-butyl-<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-piperidinamine-<NUM>,<NUM>,<NUM>-trichloro-<NUM>,<NUM>,<NUM>-triazine reaction product" (e.g., Tinuvin® <NUM> from BASF SE).

UV stabilizers are used typically in amounts of <NUM>% to <NUM>% by weight, based on the solid components present in the preparation.

Suitable thickeners include, in addition to free-radically (co)polymerized (co)polymers, typical organic and inorganic thickeners such as hydroxymethylcellulose or bentonite.

Chelating agents which can be used include, for example, ethylenediamineacetic acid and salts thereof and also β-diketones.

As component (F) in addition it is possible for fillers, dyes and/or pigments to be present.

Pigments in the true sense are, according to<NPL>, with reference to DIN <NUM>, particulate "colorants that are organic or inorganic, chromatic or achromatic and are virtually insoluble in the application medium".

Virtually insoluble here means a solubility at <NUM> below <NUM>/<NUM> application medium, preferably below <NUM>, more preferably below <NUM>, very particularly preferably below <NUM>, and in particular below <NUM>/<NUM> application medium.

Examples of pigments in the true sense comprise any desired systems of absorption pigments and/or effect pigments, preferably absorption pigments. There are no restrictions whatsoever on the number and selection of the pigment components. They may be adapted as desired to the particular requirements, such as the desired perceived color, for example, as described in step a), for example. It is possible for example for the basis to be all the pigment components of a standardized mixer system.

Effect pigments are all pigments which exhibit a platelet-shaped construction and give a surface coating specific decorative color effects. The effect pigments are, for example, all of the pigments which impart effect and can be used typically in vehicle finishing and industrial coatings. Examples of such effect pigments are pure metallic pigments, such as aluminum, iron or copper pigments; interference pigments, such as titanium dioxide-coated mica, iron oxide-coated mica, mixed oxide-coated mica (e.g., with titanium dioxide and Fe<NUM>O<NUM> or titanium dioxide and Cr<NUM>O<NUM>), metal oxide-coated aluminum; or liquid-crystal pigments, for example.

The coloring absorption pigments are, for example, typical organic or inorganic absorption pigments that can be used in the coatings industry. Examples of organic absorption pigments are azo pigments, phthalocyanine pigments, quinacridone pigments, and pyrrolopyrrole pigments. Examples of inorganic absorption pigments are iron oxide pigments, titanium dioxide, and carbon black.

Dyes are likewise colorants and differ from the pigments in their solubility in the application medium; i.e., they have a solubility at <NUM> of more than <NUM>/<NUM> in the application medium.

Examples of dyes are azo, azine, anthraquinone, acridine, cyanine, oxazine, polymethine, thiazine, and triarylmethane dyes. These dyes may find application as basic or cationic dyes, mordant dyes, direct dyes, disperse dyes, development dyes, vat dyes, metal complex dyes, reactive dyes, acid dyes, sulfur dyes, coupling dyes or substantive dyes.

Coloristically inert fillers are all substances/compounds which on the one hand are coloristically inactive, i.e., exhibit a low intrinsic absorption and have a refractive index similar to that of the coating medium, and which on the other hand are capable of influencing the orientation (parallel alignment) of the effect pigments in the surface coating, i.e., in the applied coating film, and also properties of the coating or of the coating compositions, such as hardness or rheology, for example. Inert substances/compounds which can be used are given by way of example below, but without restricting the concept of coloristically inert, topology-influencing fillers to these examples. Suitable inert fillers meeting the definition may be, for example, transparent or semi-transparent fillers or pigments, such as silica gels, blanc fixe, kieselguhr, talc, calcium carbonates, kaolin, barium sulfate, magnesium silicate, aluminum silicate, crystalline silicon dioxide, amorphous silica, aluminum oxide, microspheres or hollow microspheres made, for example, of glass, ceramic or polymers, with sizes of <NUM>-<NUM>, for example. Additionally, as inert fillers it is possible to employ any desired solid inert organic particles, such as urea-formaldehyde condensates, micronized polyolefin wax and micronized amide wax, for example. The inert fillers can in each case also be used in a mixture. It is preferred, however, to use only one filler in each case.

Preferred fillers comprise silicates, examples being silicates obtainable by hydrolysis of silicon tetrachloride, such as Aerosil® from Degussa, siliceous earth, talc, aluminum silicates, magnesium silicates, calcium carbonates, etc..

The constitution of the polyisocyanate compositions of the invention is for example as follows:.

Preferably the sum always makes <NUM>% by weight.

The mixtures of the invention are generally prepared by simply mixing the isocyanate component (A) with the solvent (B) and, if appropriate, (C). Particularly in the case of viscous or solid isocyanate components (A), simple mixing may present difficulties since the commixing of the two phases may in that case be hindered.

In one preferred embodiment, therefore, isocyanate component (A) and solvent (B) and also, if appropriate, (C) are mixed with one another at a temperature of at least <NUM> under a pressure above atmospheric pressure.

The temperature in this case can amount to preferably at least <NUM>, more preferably at least <NUM>, very preferably at least <NUM>, in particular between <NUM> and <NUM>.

The stated temperature refers to at least one of the solvents and isocyanate component (A) to be mixed, preferably at least to the isocyanate component (A), and more preferably to both.

The temperature of the mixture during the mixing operation ought normally to be at least <NUM> below the boiling temperature or below the lower limit of the boiling range, in accordance with ASTM D850, of the solvent or solvent mixture used, under the applied pressure, preferably at least <NUM>, and more preferably less than <NUM>.

The pressure under which the mixing operation can be carried out ought preferably to be at least <NUM> bar (<NUM><NUM> Pa) above the ambient pressure, more preferably at least <NUM> bar (<NUM><NUM> Pa), very preferably at least <NUM> bar (<NUM><NUM> Pa), in particular at least <NUM> bar (<NUM><NUM> Pa), and especially at surrounding pressure.

It is normally sufficient to carry out commixing under a superatmospheric pressure of not more than <NUM> bar (<NUM><NUM> Pa), preferably not more than <NUM> bar (<NUM><NUM> Pa), and more preferably not more than <NUM> bar (<NUM><NUM> Pa).

Advantages of a process of this kind are, firstly, that under mixing conditions of this kind, as a result of the elevated temperature, the viscosity of the isocyanate component (A) is lowered and it is therefore more readily miscible with the solvent, and, secondly, that under mixing conditions of this kind the elevated pressure hinders evaporation of the solvent.

In one preferred embodiment the isocyanate component (A) with the stated minimum temperature is introduced into the at least one solvent for the purpose of mixing. In this context it may be advantageous for the temperature of said at least one solvent to differ by not more than <NUM>, preferably not more than <NUM>, more preferably not more than <NUM>, and very preferably not more than <NUM> from the temperature of the at least one polyisocyanate.

In one particularly preferred embodiment the isocyanate component (A) is introduced in the form of a distillation bottom product into said at least one solvent. Since the polyisocyanates are prepared by conventional partial oligomerization from diisocyanates, it is necessary to separate off unreacted diisocyanate from the reaction mixture in order to obtain a monomer content of less than <NUM>% by weight, preferably of less than <NUM>%, more preferably of less than <NUM>%, and very preferably of less than <NUM>% by weight, and very preferably of less than <NUM>% by weight. This generally takes place by distillation in conventional manner, such as by thin-film distillation, at a temperature from <NUM> to <NUM>, advantageously under reduced pressure, and additionally, if appropriate, with an inert stripping gas passed through the system.

Apparatus employed for this purpose includes flash evaporators, falling-film evaporators, thin-film evaporators and/or short-path evaporators, surmounted if appropriate by a short column.

The distillation takes place in general under a pressure of between <NUM> and <NUM> hPa, preferably below <NUM> hPa, and more preferably below <NUM> hPa.

The distillation discharge can then be mixed advantageously directly with said at least one solvent. This has the advantage, moreover, that the hot, concentrated reaction mixture is diluted by its introduction into the solvent and is therefore cooled directly, which makes it possible to reduce follow-on reactions, such as further polymeric molecular enlargement, in the reaction mixture.

For the purpose of generating the mixtures an energy input into the mixing means of generally <NUM> W/kg or more is sufficient, preferably <NUM> or more W/kg, more preferably <NUM> or more, very preferably <NUM> or more, in particular <NUM> or more, and especially <NUM> W/kg or more. Generally speaking, an energy input of more than <NUM> W/kg affords no advantages. The specific energy input indicated should be interpreted here as the work put in per unit amount of polyisocyanate and solvent in the mixing chamber volume of the mixing means.

Within the process the mixing of the streams takes place in a suitable mixing means distinguished by very complete mixing.

The mixing means used is preferably a mixing circuit, a stirred tank, a static mixer or a pump. Static mixers which can be used include all typical static mixers (e.g., Sulzer SMX/SMV) or else nozzle or baffle mixing means, examples being coaxial mixing nozzles, Y-mixers or T-mixers.

By a mixing circuit is meant in this context a pumped circulation which comprises at least one pump and also, if appropriate, at least one heat exchanger and into which at least one of the components to be mixed, preferably the polyisocyanate, more preferably polyisocyanate and solvent, is/are metered in, preferably upstream of the pump. The pumped circulation may further comprise additional static mixers and/or mixing elements.

When a mixing circuit is used as the mixing means, one component is introduced at high velocity through nozzles. The velocities of the streams immediately prior to mixing are typically between <NUM> and <NUM>/s, preferably between <NUM> and <NUM>/s, more preferably between <NUM> and <NUM>/s.

The mixing time in this mixing means is typically from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, very preferably from <NUM> to <NUM>, and in particular from <NUM> to <NUM>. The mixing time is understood as the time which elapses from the beginning of the mixing operation until <NUM>% of the fluid elements of the resulting mixture have a mixing fraction which, based on the theoretical final value of the mixing fraction of the resulting mixture when a state of perfect mixing has been attained, deviates by less than <NUM>% from this final mixing fraction value (regarding the concept of the mixing fraction see, for example,<NPL>).

If mixing is carried out in one or more stirred tanks, such as in <NUM> to <NUM>, preferably <NUM> - <NUM>, more preferably <NUM> - <NUM>, and very preferably one stirred tank, or tube reactor, then the average total residence time in all stirred tanks together can be up to <NUM> hours, preferably up to <NUM> hours. The lower limit for the average total residence time in stirred tanks is taken in general to be <NUM> minutes, preferably <NUM> minutes. In tube reactors the residence time may for example be up to <NUM> minutes, preferably up to <NUM> minutes, more preferably up to <NUM> minutes, very preferably up to <NUM> minutes, and in particular up to <NUM> minutes. A longer residence time, though possible, does not in general afford any advantages.

The work in the case of stirred tanks may be put in via all possible types of stirrer, such as propeller, inclined-blade, anchor, disk, turbine or bar stirrers. Preference is given to using disk stirrers and turbine stirrers.

In a further possible embodiment, however, the commixing and the energy input in the stirred tank may also take place by means of at least one pumped circulation, which if appropriate may be thermally conditioned by means of at least one heat exchanger mounted in said pumped circulation.

The reactor may be, for example, a reactor with double-wall heating, welded-on tubes or half-tubes, and/or internal heating coils. Also possible is a reactor with an external heat exchanger with natural circulation, in which the circulation flow is brought about without mechanical auxiliary means, or forced circulation (using a pump), forced circulation being particularly preferred.

Suitable circulatory evaporators are known to the skilled worker and are described for example in<NPL>. Examples of circulatory evaporators are tube-bundle heat exchangers, plate-type heat exchangers, etc..

It is of course also possible for there to be two or more heat exchangers present in the circulation.

In a tube reactor it is possible, for the purpose of improved commixing, for perforated plates, slotted plates, packings or static mixers to be installed. The Bodenstein number of a tube reactor of this kind ought for example to be <NUM> or more, preferably at least <NUM>, more preferably at least <NUM>, very preferably at least <NUM>, and in particular at least <NUM>.

During the commixing operation the mixture may also be further heated, so that the temperature during mixing operation may be increased by up to <NUM>, preferably by up to <NUM>, more preferably by up to <NUM>.

After the mixing operation the mixed discharge can be cooled again to ambient temperature. The discharge can be rationally used to preheat at least one of the streams which is run into the mixing stage, or for the purpose of further heating during the mixing stage.

In any streams in which an isocyanate-containing stream is conveyed, pumps used in the process are preferably forced-delivery pumps, examples being gear pumps, peristaltic pumps, screw pumps, eccentric-screw pumps, spindle pumps or piston pumps, or centrifugal pumps.

Forced-delivery pumps are used in the process preferably for conveying streams which have a viscosity of <NUM> mPas or more, more preferably <NUM> mPas or more, very preferably <NUM> mPas or more, and more particularly <NUM> mPas or more. Centrifugal pumps are employed preferably for conveying streams having a viscosity of up to <NUM> mPas, more preferably up to <NUM> mPas, and very preferably up to <NUM> mPas.

With very particular preference the polyisocyanate-containing stream, following removal of monomeric isocyanate, is conveyed using forced-delivery pumps, and in particular a stream of this kind is metered into the solvent.

Mixing may be practiced continuously, discontinuously or semicontinuously. This means that isocyanate component (A) and solvent are mixed with one another continuously and simultaneously in the desired proportion, or are mixed discontinuously in a separate container, or else one component, preferably the solvent, is introduced first and the other, preferably the polyisocyanate, is metered in. With particular preference the solvent is preheated - to the temperatures indicated above, for example.

The mixtures of polyisocyanates in solvents that are obtainable by the process described are stable on storage.

The obtainable mixtures of isocyanate component (A) in the solvents (B) and also, if appropriate, (C) are generally used in the coatings industry. The mixtures of the invention can be used, for example, in coating materials for <NUM> [one-component] or <NUM> [two-component] polyurethane coating materials, such as for primers, surfacers, basecoats, unpigmented topcoat materials, pigmented topcoat materials and clearcoat materials, for example, in the sectors of industrial coating, more particularly aircraft coating or large-vehicle coating, wood coating, automobile coating, more particularly automotive OEM or refinish, or decorative coating. The coating materials are especially suitable for applications requiring particularly high application reliability, outdoor weathering stability, optical qualities, solvent resistance and/or chemical resistance. In accordance with the invention, the curing of these coating materials is not important. More particularly in the automobile industry, multicoat curing regimes are on the increase, such as the curing of clearcoat and basecoat (referred to as two in one), or of surfacer, clearcoat, and basecoat (referred to as three in one).

The mixtures prepared with the process are generally in the form of solutions, but in exceptional cases may also take the form of dispersions.

ppm and percentage figures used in this specification are ppm by weight and percentages by weight, unless specified otherwise.

In this specification, unless noted otherwise, the viscosity is specified at <NUM> in accordance with DIN EN ISO <NUM>/A. <NUM> in a cone/plate system with a shear rate of <NUM>-<NUM>.

Polyisocyanate prepared by trimerizing some of the isocyanate groups of <NUM>,<NUM> diisocyanatohexane (HDI), and containing isocyanurate groups, and distilling of the monomer, said polyisocyanate being composed substantially of tris(<NUM>-isocyanatohexyl) isocyanurate and its higher homologs, with an NCO content of <NUM>% and a viscosity at <NUM> of <NUM> mPa*s.

Polyisocyanate prepared by trimerizing and urethanizing / allophanatizing some of the isocyanate groups of <NUM>,<NUM>-diisocyanatohexane (HDI) in presence of an alcohol [<NUM>-ethyl-<NUM>-hexanol], distilling of the monomer, and containing both isocyanurate and allophanate groups, with an NCO content of <NUM>% and a viscosity at <NUM> of <NUM> mPa*s.

Polyisocyanate prepared by trimerizing some of the isocyanate groups of <NUM>,<NUM> diisocyanatohexane (HDI), distilling of the monomer, and containing basically both isocyanurate and iminooxadiazinedione groups, with an NCO content of <NUM>% and a viscosity at <NUM> of <NUM> mPa*s (commercially available as Basonat HI® <NUM> at BASF SE, Ludwigshafen, Germany).

Polyisocyanate prepared by oligomerizing some of the isocyanate groups of <NUM>,<NUM>-diisocyanato-hexane (HDI), distilling of the monomer, and containing basically both isocyanurate and uretdione groups, with an NCO content of <NUM>% and a viscosity at <NUM> of <NUM> mPa*s.

Polyisocyanate prepared by biuretizing some of the isocyanate groups of <NUM>,<NUM> diisocyanatohexane (HDI), distilling of the monomer, and said polyisocyanate containing biuret groups, with an NCO content of <NUM>% and a viscosity at <NUM> of <NUM> mPa*s.

Waterdispersible polyisocyanate prepared by modification of an HDI-Isocyanurate with an NCO content of <NUM>% and a viscosity at <NUM> of <NUM> mPa*s.

All the polyisocyanate were diluted in the aromatic solvents to obtain 90wt% solutions and mixed overnight at room temperature using a tumbling mixer The viscosities were measured at <NUM> according to the DIN EN ISO <NUM> using a using a rotational viscometer equipped with cone-plate geometry and a shear rate of <NUM>-<NUM> :.

Claim 1:
A mixture comprising
- (A) at least one polyisocyanate obtainable by reacting at least one monomeric isocyanate,
- (B) p-cymene,
- (C) optionally at least one further solvent other than (B),
- (D) optionally at least one Lewis-acidic organic metal compound capable of accelerating the reaction of isocyanate groups with isocyanate-reactive groups and
- (E) optionally other coatings additives