MXPA06003307A - Low surface energy polyisocyanates and their use in one- or two-component coating compositions - Google Patents

Abstract

The present invention is directed to a polyisocyanate mixture i) having an NCO content of 5 to 35%by weight and a monomeric diisocyanate content of less than 3%by weight, and prepared from a polyisocyanate adduct, ii) containing allophanate groups in an amount such that there are more equivalents of allophanate groups than urethane groups and such that the polyisocyanate mixture remains stable and homogeneous in storage for 1 month at 25 DEG C. and iii) containing siloxane groups (calculated as SiO, MW 44) in an amount of 0.002 to 50%by weight, wherein the preceding percentages are based on the solids content of the polyisocyanate mixture and wherein the siloxane groups are incorporated by reacting an isocyanate group with a compound containing one or more hydroxyl groups directly attached to a carbon atom and one or more siloxane groups. The present invention is also directed to a process for the production of this polyisocyanate mixture and to its use, optionally in blocked form, as an isocyanate component in one- or two-component coating compositions.

Description

POLYISOCIANATES OF LOW SURFACE ENERGY AND ITS USE IN COMPOSITIONS OF COATING OF ONE OR TWO COMPONENTS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention is directed to low surface energy polyisocyanates containing allophanate groups and siloxane groups, to a process for their preparation by allophanatization of the isocyanate groups of adducts of polyisocyanates in the presence of compounds containing hydroxyl groups and siloxane and its use in one or two component coating compositions.

DESCRIPTION OF THE PRIOR ART Polyurethane coating compositions containing a polyisocyanate component, in blocked or unblocked form, and an isocyanate-reactive component, generally a high molecular weight polyol, are well known. Although the coatings prepared from these compositions possess many valuable properties, one property, in particular, that needs to be improved is the surface quality. It may be difficult to formulate coating compositions to obtain a coating having a "smooth surface, as opposed to one containing surface defects, such as craters, etc. It is believed that these difficulties are related to the high surface tension of the coating compositions. Two components Another problem caused by high surface tension is the difficulty to clean the coatings, regardless of their application area, there is a high probability that the coatings are subjected to stress, graffiti, etc. The incorporation of fluoride or siloxane groups in polyisocyanates through allophanate groups to reduce the surface tension of the polyisocyanates and the surface energy of the resultant polyurethane coatings is described in U.S. Patents 5,541,281, 5,574,122, 5,576,411, 5,646. 227, 5,691,439 and 5,747,629 A drawback of the polyisocyanates described in these patents that is, they are prepared by reaction of an excess of monomeric diisocyanates with the compounds containing fluorine or siloxane groups. After the end of the reaction, monomeric diisocyanates that have not reacted by an expensive fine film distillation process have to be removed. Furthermore, it is important to avoid the use of any unnecessary apparatus, such as a distillation apparatus, in preparing the low surface energy polyisocyanates, since fluorine and si-loxane groups can contaminate the production apparatus, requiring a cleaning face before you can use the appliance to prepare other products. Accordingly, it is an object of the present invention to provide coating compositions which have a low surface tension and, therefore, are sule for the production of coatings having lower surface energies, better surfaces and better cleaning ability and that also possess the other valuable properties of known polyurethane coatings. It is a further object of the present invention to provide polyisocyanates which achieve the above objective and which can be prepared without the expensive face and difficult removal of the excess unreacted monomeric diisocyanates. Surprisingly, these objectives can be achieved with the polyisocyanate mixtures according to the present invention, which contain allophanate groups and siloxane groups, which are described a. continuation. These mixtures of polyisocyanates are prepared from polyisocyanate adducts instead of monomeric diisocyanates. Although the use of higher molecular weight polyisocyanate adducts and eventually higher functionality as starting materials would be expected to result in insoluble high viscosity or gel type products, this is not the case.

SUMMARY OF THE INVENTION The present invention is directed to a mixture of polyisocyanates which i) has an NCO content of 5 to 35% by weight and a monomeric diisocyanate content of less than 3% by weight and prepared from an adduct of polyisocyanate; ii) contains allophanate groups in an amount such that there are more equivalents of allophanate groups than of urethane groups and such that the mixture of polyisocyanates remains stable and homogeneous in storage for 1 month at 25 ° C, and iii) contains siloxane groups (calculated as Sio, MW 44) in an amount of 0.002 to 50% by weight, where the above percentages are based on the solids content of the polyisocyanate mixture and where the siloxane groups are incorporated by reaction of an isocyanate group with a compound containing one or more hydroxyl groups di-straightly attached to a carbon atom and one or more siloxane groups. The present invention is also directed to a process for the production of a polyisocyanate mixture which i) has an NCO content of 5 to 35% by weight and a monomeric diisocyanate content of less than 3% by weight and prepared from a polyisocyanate adduct; ii) contains allophanate groups in an amount such that there are more equivalents of allophanate groups than of urethane groups and such that the mixture of polyisocyanates remains stable and homogeneous in storage for 1 month at 25 ° C, and iii) contains siloxane groups (calculated as SiO, MW 44) in an amount of 0.002 to 50% by weight, where the above percentages are based on the solids content of the polyisocyanate mixture, by a) reaction of a portion of the isocyanate groups of a polyisocyanate adduct with 0.01 to 500 millimoles per mole of polyisocyanate adduct of a compound containing one or more hydroxyl groups directly attached to a carbon atom and one or more siloxane groups to form urethane; b) addition of a allophanatization catalyst before, during or after step a); c) conversion of a sufficient amount of the urethane groups formed in step a) into allophanate groups to satisfy the requirements of ii), and d) ending the allophanatization reaction to the desired NCO content by adding a catalyst poison and / or thermally deactivating the catalyst and recovering the polyisocyanate mixture without removing the monomeric diisocyanates. The present invention also relates to the use of the mixture of polyisocyanates, optionally in blocked form, as an isocyanate component in one or two component coating compositions.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the term "(cyclic) aliphatically bound isocyanate groups" means isocyanate groups attached aliphatically and / or cycloaliphatically. According to the present invention, the polyisocyanate mixtures are prepared from polyisocyanate adducts prepared from monomeric polyisocyanates and contain isocyanurate, uretdione, biuret, urethane, allophanate, iminooxadiazinedione, carbodiimide, acylurea and / or oxadiazinetrione groups. The polyisocyanate adducts, which preferably have an NCO content of 5 to 30% by weight, include: 1) Polyisocyanates containing isocyanurate groups, which can be prepared as set forth in DE-PS 2,616,416, EP-OS 3,765, EP-OS 10,589, EP-OS 47,452, US-PS 4,288,586 and US-PS 4,324,879. The isocyanato isocyanurates generally have an average NCO functionality of 3 to 4.5, and an NCO content of 5 to 30%, preferably 10 to 25% and, more preferably, 15 to 25% by weight. 2) uretdione diisocyanates, which can be prepared by oligomerization of a portion of the isocyanate groups of a diisocyanate in the presence of a suitable catalyst, for example, of a trialkyl phosphine catalyst, and which can be used in admixture with other aliphatic polyisocyanates and / or cycloaliphatics, particularly the polyisocyanates containing isocyanurate groups indicated above in (1). 3) Polyisocyanates containing biuret groups, which can be prepared according to the procedures described in US Pat. 3,124,605, 3,358,010, 3,644,490, 3,862,973, 3,906,126, 3,903,127, 4,051,165, 4,147,714 or 4,220,749 using co-reactants such as water, tertiary alcohols, primary and secondary monoamines and primary and / or secondary diamines. These polyisocyanates preferably have an NCO content of 18 to 22% by weight. 4) Polyisocyanates containing iminooxadiazinedione groups and optionally isocyanurate, which can be prepared in the presence of special fluorine-containing catalysts, as described in DE-A 19611849. These polyisocyanates generally have an average NCO functionality of 3 to 3, 5 and a NCO content of 5 to 30%, preferably 10 to 25% and more preferably 15 to 25% by weight. 5) Polyisocyanates containing carbodiimide groups, which can be prepared by oligomerization of di- or polyisocyanates in the presence of known carbodiimidation catalysts, as described in DE-PS 1,092,007, US-PS 3,152,162 and DE-OS 2,504 .400, 2,537,685 and 2,552,350. 6) Polyisocyanates containing oxadiazinetrione groups and containing the reaction product of two moles of a diisocyanate and one mole of carbon dioxide. Preferred polyisocyanate adducts are polyisocyanates containing isocyanurate, uretdione, biuret and / or iminooxadiazinedione groups, especially polyisocyanates containing isocyanurate groups and optionally uretdione or iminooxadiazinedione groups. Suitable monomeric diisocyanates for preparing the polyisocyanate adducts are those represented by the formula R (NC0) 2 where R represents an organic group obtained by removing isocyanate groups from an organic diisocyanate having a molecular weight of about 140 to 400 Preferred diisocyanates are those in which R represents a divalent aliphatic hydrocarbon group having from 4 to 40, preferably from 4 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon group of 5 to 15 carbon atoms, a hydrocarbon group divalent araliphatic of 7 to 15 carbon atoms or a divalent aromatic hydrocarbon group of 6 to 15 carbon atoms. Examples of suitable organic diisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,2-dodecamethylene diisocyanate. , cyclohexane-1,3- and -1,4-diisocyanate, l-isocyanato-2-isocyanatomethylcyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate or? IP-DI "), bis (4-isocyanatocyclohexyl) methane, 2,4'-dicyclohexylmethane diisocyanate, 1,3 - and 1,4-bis- (isocyanatomethyl) cyclohexane, bis (4-isocyanato-3-methylcyclohexyl) methane, a, a, a ',' -tetramethyl-1,3- and / or -1-diisocyanate, -xylylene, l-isocyanato-l-methyl-4 (3) -isocyanatomethylcyclohexane, 2,4- and / or 2,6-hexa-hydrotoluylene diisocyanate, 1,3- and / or 1,4-diisocyanate phenylene, 2,4- and / or 2,6-toluylene diisocyanate, 2,4- and / or 4,4'-diphenylmethane, 1,5-diisocyanato-naphthalene diisocyanate and mixtures thereof Polyisocyanates can also be used. have 3 or more isocyanate groups, such as 4-isocyanatomethyl-1, 8-octamethylene diisocyanate, and aromatic polyisocyanates such as 4,4 ', 4"-triphenylmethane triisocyanate and polyphenylene polymethylene polyisocyanates obtained by phosgenation of condensates of aniline / formaldehyde. Preferred organic diisocyanates include 1,6-hexamethylene diisocyanate, l-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate or IPDI), bis (4-isocyanatocyclohexyl) methane, diisocyanate, , a ',' -tetramethyl-1, 3- and / or -1, 4-xylylene, 2,4- and / or 2,6-toluylene diisocyanate and 2,4-and / or 4-diisocyanate, 4'-diphenylmethane. Suitable compounds are those containing hydroxyl groups and siloxane groups, which are suitable for preparing the polyisocyanate mixtures according to the invention, those containing one or more (preferably one or two and more preferably one) hydroxyl groups directly attached to carbon atoms and one or more siloxane groups, preferably in the form of dimethylsiloxane groups, -Si (CH3) 20-. Examples of these compounds are those corresponding to the formula HO-Ra ~ X- [Si (R2) 20-] n- [Si (R2) 2-X] -Y - and where R1 represents a divalent hydrocarbon radical optionally substituted inert form, preferably an alkylene radical (such as methylene, ethylene, propylene or butylene) or a polyoxyalkylene group (such as a polyoxyethylene or polyoxypropylene group); R 2 represents hydrogen or a phenyl or benzyl lower alkyl group optionally substituted inert form, preferably methyl or ethyl and more preferably methyl. X represents a bond between a group R1 and an atom of Si, e.g. , a covalent bond, -O- or -COO-; Y represents hydrogen or OH; m is 0 or 1, and n is an integer from 1 to 1,000, preferably from 2 to 100 and more preferably from 4 to 15. Inert substituents are those which do not interfere with the reaction of the siloxane compound with the polyisocyanate or with the reaction of allophanatization of the isocyanate groups. As examples, halogen atoms, such as fluorine, are included. Examples of compounds which contain an isocyanate-reactive group in which R1 represents an oxyalkylene group are the compounds corresponding to the formula H0- (CHR3-CH20-) or- (R) m- [Si (R2) 20-] n- [Si (R2) 2-X '] m-R4-H and are examples of compounds containing more than one isocyanate-reactive group wherein R1 represents an oxyalkylene group the compounds corresponding to the formula HO- (CHR3-CH20-) or- (R4) m- [Si (R2) 20-] n- (CH2-CHR3-0-) p-CH2-CHR3-OH where R2, m and n are as defined above; R3 represents hydrogen or an alkyl group of 1 to 12 carbon atoms, preferably hydrogen or methyl; R 4 represents a divalent hydrocarbon radical optionally substituted inertly, preferably - an alkylene radical (such as methylene, ethylene, propylene or butylene); X 'represents a bond between a group R4 and an atom of Si, e.g., a covalent bond, -O- or -C00-; or is an integer from 1 to 200, preferably from 2 to 50 and more preferably from 4 to 25; p is an integer from 0 to 200, preferably from 2 to 50 and more preferably from 4 to 25; These siloxane compounds are prepared by reaction of the appropriate siloxane with an amount of an alkylene oxide (preferably, ethylene or propylene oxide) sufficient to prepare a compound having the desired content of siloxane. Other suitable siloxane containing compounds can be linear, branched or cyclic and have a molecular weight (number average molecular weight determined by gel permeation chromatography using polystyrene as a standard) of up to 50,000, preferably up to 10,000, more preferably up to 6,000 and more preferably up to 2,000. These compounds generally have OH numbers greater than 5, preferably greater than 25 and more preferably greater than 35. Compounds of this type are described in "Silicon Compounds", 5th Edition, by Hüls America, Inc. To prepare the polyisocyanate mixtures, according to the invention, the minimum ratio of siloxane containing compounds to polyisocyanate adduct is about 0.01 millimole, preferably about 0.1 millimole and more preferably about 1 millimole of siloxane-containing compounds per each mole of Polyisocyanate adduct. The maximum amount of compounds containing siloxane with respect to polyisocyanate adduct is about 500 millimoles, preferably about 100 millimoles and more preferably about 20 millimoles of siloxane-containing compounds per mole of polyisocyanate adduct. The amount of siloxane is selected such that the resulting polyisocyanate mixture contains a minimum of 0.002% by weight, preferably 0.02% by weight and more preferably 0.2% by weight of siloxane groups (calculated as SiO, PM 44), based on solids, and a maximum of 50% by weight, preferably 10% by weight, more preferably 7% by weight and more preferably 3% by weight of siloxane groups, based on solids . Suitable methods are known for preparing the polyisocyanate mixtures containing allophanate groups and are described in US Pat. 3,769,318, 4,160,080 and 4,177,342 and 4,738,991, the descriptions of which are incorporated herein by reference. The allophanatization reaction can be conducted at a temperature of 50 to 250 ° C, preferably 60 to 150 ° C and more preferably 70 to 120 ° C. The reaction can be terminated by reducing the reaction temperature, removing the catalyst, e.g. by vacuum application, or by addition of a catalyst poison. After completion of the reaction, there is no need to remove monomeric diisocyanates that have not reacted, e.g., by thin film evaporation, since polyisocyanate adducts having low contents of monomeric diisocyanates are used as starting material. The allophanatization reaction can be carried out in the absence or in the presence of solvents inert to the isocyanate groups, preferably in the absence of solvents, especially when using liquid starting materials. Depending on the area of application of the products according to the invention, medium-boiling solvents or high-boiling solvents can be used. Suitable solvents include esters, such as ethyl acetate or butyl acetate; ketones, such as acetone or butanone; aromatic compounds, such as toluene or xylene; halogenated hydrocarbons, such as methylene chloride and trichloroethylene; ethers, such as diisopropyl ether, and alkanes, such as cyclohexane, petroleum ether or ligroin. The process according to the invention can take place batchwise or continuously, for example, as described below. The starting polyisocyanate adduct is introduced with the exclusion of moisture and optionally with an inert gas in a suitable stirred vessel or tube and optionally mixed with a solvent inert to the isocyanate groups, such as toluene, butyl acetate, diisopropyl ether or cyclohexane. The previously described compounds containing hydroxyl and siloxane groups can be introduced into the reaction vessel according to various embodiments. They can pre-react with the starting polyisocyanate adduct to form urethane and, before introducing the polyisocyanate adducts into the reaction vessel, they can be mixed with the polyisocyanate adducts and introduced into the reaction vessel; they can be added separately to the reaction vessel sooner or later, preferably afterwards, of adding the polyisocyanate adducts; or the catalyst can be dissolved in these compounds before introducing the solution into the reaction vessel. The progress of the reaction is monitored by determining the NCO content by a suitable method, such as titration, refractive index or IR analysis. Thus, the reaction may end to the desired degree of allophanatization. The completion of the allophanatization reaction can take place, for example, after the NCO content has fallen by 5 to 80% by weight, preferably by 10 to 60% by weight and more preferably by 20% by weight. 50% by weight, based on the initial isocyanate group content of the polyisocyanate adduct starting material. The polyisocyanate mixtures obtained according to the present invention have an average functionality of about 2 to 7, preferably 2 to 4; an NCO content of 10 to 35% by weight, preferably 10 to 30% by weight and more preferably 15 to 30% by weight, and a monomeric diisocyanate content of less than 3% by weight, preferably less than 2% by weight; % by weight and more preferably less than 1% by weight. The polyisocyanate mixtures have a content of allophanate groups (calculated as N2, C2, H, 03, PM 101) of preferably at least 0.001% by weight, more preferably at least 0.01% by weight and more preferably at least 0.5% by weight. The upper limit for the content of allophanate groups is preferably 20%, preferably 10% by weight and more preferably 5% by weight. The above percentages are based on the solids content of the polyisocyanate mixtures. The products according to the present invention are mixtures of polyisocyanates containing allophanate groups and siloxane groups. The products may also contain residual urethane groups which do not convert to allophanate groups depending on the temperature maintained during the reaction and the degree of consumption of isocyanate groups. Although it is preferred to convert at least 50%, more preferably at least 70% and more preferably at least 90% of the urethane groups formed from the hydroxyl compounds containing siloxane into allophanate groups, it is not necessary that the number of equivalents of allophanate groups exceeds the number of equivalents of urethane groups and provided that the mixture of polyisocyanates contains sufficient allophanate groups to ensure that the polyisocyanate mixture remains stable and homogeneous in storage for 1 month at 25 ° C. If the polyisocyanate mixture contains an insufficient number of allophanate groups, the mixture may be cloudy and a gradual settling of insoluble constituents may take place during storage. The products according to the invention are valuable starting materials for the production of polyisocyanate polyaddition products by reaction with compounds containing at least two isocyanate-reactive groups. The products according to the invention can also be cured by moisture to form coatings. Preferred products are one or two component coating compositions, more preferably polyurethane coating compositions. When the polyisocyanates are not blocked, two-component compositions are obtained. On the contrary, when the polyisocyanates are blocked, one-component compositions are obtained. Prior to their use in coating compositions, the polyisocyanate mixtures according to the invention can be mixed with other known polyisocyanates, e.g. , polyisocyanate adducts containing biuret, isocyanurate, allophanate, urethane, urea, carbodiimide and / or uretdione group. The amount of polyisocyanate mixtures according to the invention which can be mixed with these other polyisocyanates depends on the siloxane content of the polyisocyanate mixtures according to the invention, the intended application of the resulting coating compositions and the amount of properties of the polyisocyanates. Low surface energy desired for this application. To obtain low surface energy properties, the resulting polyisocyanate mixtures should contain a minimum of 0.002% by weight, preferably 0.02% by weight and more preferably 0.2% by weight of siloxane groups (MW 44). based on solids and a maximum of 10% by weight, preferably 7% by weight and more preferably 3% by weight of siloxane groups (MW 44) based on solids. Although contents in siloxane groups of greater than 10% by weight are also suitable for obtaining low surface energy coatings, further refinements are not to be obtained by using higher amounts. Knowing the siloxane content of the polyisocyanate mixtures according to the invention and the desired siloxane content of the resultant polyisocyanate mixtures, the relative amounts of the polyisocyanate mixtures and the other polyisocyanates can be easily determined. According to the present invention, any of the polyisocyanate mixtures according to the invention can be mixed with other polyisocyanates, provided that the resulting mixtures have the minimum content of siloxane required for the polyisocyanate mixtures of the present invention. However, the polyisocyanate mixtures to be mixed preferably have a minimum siloxane content of 5% by weight, more preferably 10% by weight, and preferably have a maximum siloxane content of 50% by weight, more preferably 40% by weight and more preferably 30% by weight. These so-called "concentrates" can then be mixed with other polyisocyanates to form mixtures of polyisocyanates that can be used to prepare coatings having low surface energy characteristics. Several advantages are obtained by preparing concentrates with high siloxane contents and then mixing them with polyisocyanates that do not contain siloxane. Initially, it is possible to convert many products into low surface energy polyisocyanates producing only one concentrate. By forming said low surface energy polyisocyanates by mixing commercial polyisocyanates with concentrates, it is not necessary to separately prepare each of the products in both a siloxane-containing and a non-siloxane-containing form. A possible drawback of the higher contents in siloxane is that all the isocyanate groups of a small portion of the starting polyisocyanate adducts can react. These molecules that do not contain isocyanate groups can not react in the resulting coating and, therefore, can adversely affect the properties of the final coating. Preferred reaction partners for the products according to the invention are polyhydroxypolyesters, polyhydroxypolyethers, polyhydroxypoly acrylates, polyhydroxy-lilactones, polyhydroxy polyurethanes, polyhydroxypoliepoxides and optionally low molecular weight polyhydric alcohols known from the technology of polyurethane coatings. The polyamines, particularly in blocked form, for example as polyketimines, oxazolidines or polyaldimines, are also suitable reaction partners for the products according to the invention. Also suitable are polyaspartic acid derivatives (aspartates) containing secondary amino groups, which also function as reactive diluents. To prepare the coating compositions, the amount of the polyisocyanate component and the isocyanate-reactive component is selected to obtain equivalent ratios of isocyanate groups (whether present in blocked or unblocked form) with respect to isocyanate-reactive groups of t 0, 8 to 3, preferably from 0.9 to 1.5. The coating compositions can be cured at room temperature or at elevated temperature. To accelerate the hardening, the coating compositions can contain known polyurethane catalysts, eg tertiary amines, such as triethylamine, pyridine, methylpyridine, benzyldimethylamine, N, N-dimethylaminocicloehxane, N-methylpiperidine, pentamethyldiethylentriamine, 1, 4 -diazabicyclo [2, 2, 2] octane and N, N'- dimethylpiperazine; or metal salts, such as iron (III) chloride, zinc chloride, zinc-2-ethyl caproate, tin (II) ethyl caproate, dibutyltin dilaurate (IV) and molybdenum glycolate. The products according to the invention are also valuable starting materials for one-component coating compositions, preferably polyurethane coating compositions, wherein the isocyanate groups are used in blocked form by known blocking agents. The blocking reaction is carried out in a known manner by reaction of the isocyanate groups with suitable blocking agents, preferably at a high temperature (eg, about 40 to 160 ° C) and optionally in the presence of a suitable catalyst, for example tertiary amines or metal salts previously described. Suitable blocking agents include monophenols, such as phenol, cresols, trimethylphene and tert-butylphenols; tertiary alcohols, such as tert-butanol, tere-amyl alcohol and dimethylphenylcarbonol; compounds that readily form enols, such as acetoacetic ester, acetylacetone and malonic acid derivatives, e.g., malonic acid diethyl ester; secondary aromatic amines, such as N-methylaniline, N-methyl toluidine, N-phenyl toluidine and N-phenylxidine; imides, such as succinimide; lactams, such as e-caprolactam and d-valerolactam; pyrazoles, such as 3,5-dimethylpyrazole; oxi-mas, such as butanone oxime, methylamylketoxime and cyclohexanone oxime; mercaptans, such as methyl mercaptan, ethyl mercaptan, butyl mercaptan, 2-mercaptobenzthiazole, naphthyl mercaptan and dodecyl mercaptan, and triazoles, such as lH-1, 2,4-triazole. The polyisocyanate mixtures according to the invention can also be used as the polyisocyanate component in two-component waterborne coating compositions. To be useful in these compositions, the polyisocyanate mixtures can be converted to hydrophilic by mixing with external emulsifiers or by reaction with compounds containing cationic, anionic or nonionic groups. The reaction with the hydrophilic compound can be carried out before or after the allophanatization reaction to incorporate the siloxane-containing compound. Methods for making the polyisocyanates hydrophilic are described in the co-pending application and US Pat. 5,194,487 and 5,200,489, the descriptions of which are incorporated herein by reference. The reduced surface tensions of the modified polyisocyanate mixtures increase the dispersion of the pigment and the wetting of the substrate. The coating compositions may also contain other additives, such as pigments, dyes, fillers, leveling agents and solvents. The coating compositions can be applied to the substrate to be coated in solution or from the melt by conventional methods, such as painting, rolling, pouring or pulsing. The coating compositions containing the polyisocyanate mixtures according to the invention provide coatings having good drying times, which adhere surprisingly well to a metal base and which are particularly stable to light, color stable in the presence of heat and very resistant to abrasion. They are also characterized by high hardness, elasticity, very good resistance to chemical agents, high gloss, good resistance to weathering, good resistance to environmental corrosion and good pigmentation qualities. Above all, the coating compositions have an excellent surface appearance and excellent cleaning ability. The invention is further illustrated, but without intending to limit it, by the following examples, in which all parts and percentages are by weight, unless otherwise specified. EXAMPLES In the examples, the contents in allophanate groups are based in the theoretical content assuming a conversion of 100% of the urethane groups into allophanate groups. Siloxane Alcohol 0411 A polydimethylsiloxane alcohol initiated with butyl and finished with carbinol having a molecular weight of about 1,000 (available from Chisso Corp. as Sila-plane FM-0411). 4411 Siloxane Alcohol A polydimethylsiloxanediol finished in carbinol having a molecular weight of about 1,000 (available from Chisso Corp. as Silaplane FM-4411). Polyisocyanate 3400 A polyisocyanate containing uretdione and isocyanurate groups prepared from diisocyanate of 1, 6-hexamethylene and having an isocyanate content of 21.5%, a monomeric diisocyanate content of <0.50%, a viscosity at 25 ° C of 200 mPa.s and a surface tension of 40 dynes / cm2 (available from Bayer Material Science as Desmodur N 3400). Polyisocyanate 3600 A polyisocyanate containing isocyanurate groups prepared from 1,6-hexamethylene diisocyanate and having an isocyanate content of 22.8%, a monomeric diisocyanate content of < 0.25%, a viscosity at 25 ° C of 1145 mPa.s and a surface tension of 45 dynes / cm2 (available from Bayer Material Science as Desmodur N 3600). Polyisocyanate 2410 A polyisocyanate containing isocyanurate and iminooxadiazinedione groups prepared from 1,6-hexamethylene diisocyanate and having an isocyanate content of 23.6%, a monomeric diisocyanate content of < 0.30%, a viscosity at 25 ° C of 640 mPa.s and a surface tension of 40 dynes / cm2 (available from Bayer Material Science as Desmodur XP 2410). Polyisocyanate 4470 A polyisocyanate containing isocyanurate groups prepared from isophorone diisocyanate and having an isocyanate content of 11.9%, a monomeric diisocyanate content of < 0.50%, a viscosity at 25 ° C of 670 mPa.s and a surface tension of 40 dynes / cm2 as a 70% solution in n-butyl acetate (available from Bayer Material Science as Desmodur Z 4470 BA). Polyisocyanate 3200 A polyisocyanate containing pre-stopped biuret groups from 1,6-hexamethylene diisocyanate and having an isocyanate content of 23%, a monomeric diisocyanate content of < 0.70%, a viscosity at 25 ° C of 1,750 mPa.s and a surface tension of 47 dynes / cm2 (available from Bayer Material Science as Desmodur N 3200). Surface tension of liquid samples The Wilhelmy plate technique (flamed glass slides) was used to determine surface tension. The samples were analyzed with a Cahn DCA 312 dynamic contact angle analyzer. All samples were shaken before analysis. Surface tension of film samples Water and methylene iodide advance angles, polar and non-polar solvents, respectively, were measured using a Rame-Hart goniometer. The surface energies of the total solids, including the polar and dispersive components, were calculated using the advance angles according to the Owens Wendt procedure. Example 1 - Preparation of the mixture of polyisocyanates 1 693 g (3.76 eq., Based on the actual titrated value) of Polyisocyanate 3600 and 7 g (0.007 eq.) Of Siloxane Alcohol 0411 were charged in a bottom flask. round 1 liter and 3-neck equipped with mechanical agitation, a cold water condenser, heating mantle and N2 inlet. While stirring the reaction and heating to 110 ° C, a total of 0.10 g of stannous octoate was charged into the mixture. After heating for 5 hours at 110 ° C, the NCO content reached the theoretical value of 22.46%; the heat was removed and a cold water / ice bath was applied. The viscosity was 1,320 mPa.s @ 25 ° C and the surface energy of the liquid was 22.6 dynes / cm2. Examples 2 to 10 - Preparation of the polyisocyanate mixtures 2-10 Other polyisocyanate mixtures were prepared in a similar manner to Example 1 using different polyisocyanates and different types and amounts of siloxanes. Isobutanol was used in a comparative example to show that siloxane alcohols are necessary to obtain a low surface energy. Comparative Examples 4 and 5 use the same alcohol equivalents as Examples 1 and 2, respectively. The details of Examples 1-10 are set forth in Table 1. TABLE 1 Examples 11-14 - Preparation of moisture curable coatings Moisture curable coatings were prepared by diluting the polyisocyanate mixtures set forth in Table 2 with ethyl acetate to obtain a viscosity of about 200 mPa.s and then adding 1 percent to Weight of dibutyltin dilaurate, based on solids. The coatings were deposited on standard panels of thermoplastic polyolefin ("TPO") using a 2 mil bar. The coatings were cured overnight on the laboratory bench at ambient conditions. The details of Examples 11-14 are set forth in Table 2.

TABLE 2 Examples 15-18 - Preparation of two-component coating compositions Two-component coating compositions were prepared by mixing the polyisocyanate mixtures set forth in Table 3 with a trifunctional polyester polyol (Desmophen 670A-80, from Bayer Material Science LLC) , at an NCO: OH equivalent ratio of 1.05: 1.00, and by adding 0.05 g of dibutyltin dilaurate per one hundred parts of polyisocyanate / polyol mixture. A 2-mil bar was used to deposit the liners on standard panels of thermoplastic polyolefin (TPO). The coatings were cured overnight on the laboratory bench at ambient conditions. The details of Examples 15-18 are set forth in Table 3.

TABLE 3 Examples 19-25 - Use of Mixtures of Polyisocyanates as Concentrates 1 g of the polyisocyanate mixtures of Examples 1, 2, 4, 5 and 10 were mixed by hand with 9 g of the unmodified polyisocyanates listed in Table 4. These mixtures of resulting polyisocyanates possessed a low surface tension value, indicating that the polyisocyanate mixtures according to the invention could be used as concentrates to dilute unmodified polyisocyanates. Table 4 details the details.

TABLE 4 These data show that the polyisocyanate mixtures of Examples 1, 2 and 10 can be diluted with unmodified polyisocyanates, which did not contain siloxane groups, and still provide a low surface tension. Dilution of the comparative polyisocyanates of Examples 4 and 5 with the same unmodified polyisocyanates did not change the high surface tension. Examples 26-31 - Preparation of moisture curable coatings Moisture curable coatings were prepared by diluting the polyisocyanate mixtures set forth in Table 5 with ethyl acetate to obtain a viscosity of about 200 mPa. s and then adding 1 weight percent dibutyltin dilaurate, based on the solids. The coatings were deposited on standard panels of thermoplastic polyolefin (TPO) using a 2 mi-lipid bar. The coatings were cured overnight on the laboratory bench at ambient conditions. In Table 5 the details of Examples 26-31 are set forth. TABLE 5 These data show that the moisture curable coatings made from the polyisocyanate blends, which were prepared from concentrates, had the same low surface energy as the coatings made from polyisocyanate blends, which were directly prepared. with the same amounts of siloxane groups. The coatings prepared from the comparative polyisocyanates had high surface energies. Examples 32-37 - Preparation of two-component coating compositions Two-component coating compositions were prepared by mixing the polyisocyanate mixtures set forth in Table 6 with trifunctional polyester polyol (Desmophen 670A-80, from Bayer Material Science LLC), at an equivalent ratio of NCO: OH of 1.05: 1.00 and by adding 0.05 g of dibutyltin dilaurate per hundred parts of polyisocyanate / polyol mixture. A 2-mil bar was used to deposit the liners on standard panels of thermoplastic polyolefin (TPO). The coatings were cured overnight on the laboratory bench at ambient conditions. The details of Examples 32-37 are set forth in Table 6. TABLE 6 These data show that coatings made from coating compositions of two components containing mixtures of polyisocyanates, which were prepared from concentrates, had the same low surface energy as coatings made from two coating compositions. components containing polyisocyanate mixtures, which were directly pre-stopped with the same amounts of siloxane groups. The coatings prepared from the comparative polyisocyanates had high surface energies.

Although the invention has been described in detail in the foregoing for purposes of illustration, it is to be understood that such detail has only those purposes and that those skilled in the art can make variations therein without departing from the spirit and scope of the invention, except in what may be limited by the claims.

Claims (17)

Claims

1. A mixture of polyisocyanates which i) has an NCO content of 5 to 35% by weight and a monomeric diisocyanate content of less than 3% by weight and prepared from a polyisocyanate adduct; ii) contains allophanate groups in an amount such that there are more equivalents of allophanate groups than of urethane groups and such that the mixture of polyisocyanates remains stable and homogeneous in storage for 1 month at 25 ° C, and iii) contains siloxane groups (calculated as SiO, MW 44) in an amount of 0.002 to 50% by weight, where the above percentages are based on the solids content of the polyisocyanate mixture and where the siloxane groups are incorporated by reaction of an isocyanate group with a compound containing one or more hydroxyl groups directly attached to a carbon atom and one or more siloxane groups.

2. The polyisocyanate mixture of Claim 1, wherein the siloxane groups are incorporated by reaction of an isocyanate group with a compound containing a hydroxyl group directly attached to a carbon atom and one or more siloxane groups.

3. The polyisocyanate mixture of Claim 1, wherein the polyisocyanate adduct consists of a polyisocyanate containing isocyanurate groups prepared from 1,6-hexamethylene diisocyanate or isophorone diisocyanate.

4. The polyisocyanate mixture of Claim 2, wherein said polyisocyanate adduct consists of a polyisocyanate containing isocyanurate groups prepared from 1,6-hexamethylene diisocyanate or isophorone diisocyanate.

5. The polyisocyanate mixture of Claim 1, wherein the polyisocyanate mixture contains from 0.2 to 10% by weight, based on the solids, of siloxane groups.

6. The polyisocyanate mixture of Claim 2, wherein the polyisocyanate mixture contains from 0.2 to 10% by weight, based on the solids of siloxane groups. The polyisocyanate mixture of Claim 3, wherein the polyisocyanate mixture contains from 0.2 to 10% by weight, based on the solids of siloxane groups. The polyisocyanate mixture of Claim 4, wherein the polyisocyanate mixture contains from 0.2 to 10% by weight, based on the solids of siloxane groups. 9. The polyisocyanate mixture of Claim 1, wherein the polyisocyanate mixture contains from 10 to 40% by weight, based on the solids of siloxane groups. The polyisocyanate mixture of Claim 2, wherein the polyisocyanate mixture contains from 10 to 40% by weight, based on the solids of siloxane groups. The polyisocyanate mixture of Claim 3, wherein the polyisocyanate mixture contains from 10 to 40% by weight, based on the solids of siloxane groups. The polyisocyanate mixture of Claim 4, wherein the polyisocyanate mixture contains from 10 to 40% by weight, based on the solids of siloxane groups. 13. A process for the production of a polyisocyanate mixture which i) has an NCO content of 5 to 35% by weight and a monomeric diisocyanate content of less than 3% by weight and prepared from a polyisocyanate adduct; ii) contains allophanate groups in an amount such that there are more equivalents of allophanate groups than of urethane groups and such that the mixture of polyisocyanates remains stable and homogeneous in storage for 1 month at 25 ° C, and iii) contains siloxane groups ( calculated as SiO, MW 44) in an amount of 0.002 to 50% by weight, where the above percentages are based on the solids content of the polyisocyanate mixture, by a) reaction of a portion of the isocyanate groups of an adduct of polyisocyanate with 0.01 to 500 millimoles per mole of polyisocyanate adduct of a compound containing one or more hydroxyl groups directly attached to a carbon atom and one or more siloxane groups to form urethane; b) addition of a allophanatization catalyst before, during or after step a); c) conversion of a sufficient amount of the urethane groups formed in step a) into allophanate groups to satisfy the requirements of ü), and d) ending the allophanatization reaction to the desired NCO content by adding a catalyst poison and / or thermally deactivating the catalyst and recovering the polyisocyanate mixture without removing the monomeric diisocyanates. The method of Claim 13, wherein the siloxane groups are incorporated by reaction of an isocyanate group with a compound containing a hydroxyl group directly attached to a carbon atom and one or more siloxane groups. The process of Claim 13, wherein said polyisocyanate adduct consists of a polyisocyanate containing isocyanurate groups prepared from 1,6-hexamethylene diisocyanate or isophorone diisocyanate. The process of Claim 14, wherein said polyisocyanate adduct consists of a polyisocyanate containing isocyanurate groups prepared from 1,6-hexamethylene diisocyanate or isophorone diisocyanate. 1

7. A one or two component coating composition containing the polyisocyanate mixture of the Claim 1, optionally blocked by blocking agents for isocyanate groups, and optionally a compound containing isocyanate-reactive groups.