MXPA97010053A - Polyisocianatos of low surface energy and its use in compositions of coating of one or two components - Google Patents

Abstract

The present invention relates to a polyisocyanate adduct containing allophanate groups, siloxane groups and optionally isocyanurate groups which is prepared by reacting a compound a) which i) is substantially free of hydroxyl groups and isocyanate groups, ii) has an average of at least two urethane groups per molecule and iii) contains from 0 to 50% by weight of siloxane groups (calculated as SiO, MW 44), based on the weight of the polyisocyanate adduct, with an excessive amount, based on the equivalents of urethane groups, of polyisocyanates b), optionally containing siloxane groups, to form a polyisocyanate adduct and optionally removing at least a portion of the unreacted excessive polyisocyanate b), provided that compound a) and polyisocyanate b) contain a total of at least 0.001% by weight of siloxane groups based on the weight of the polyisocyanate adduct

Description

POLYISOCIANATOS 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 relates to low surface energy polyisocyanates containing allophanate groups, siloxane groups and optionally isocyanurate groups, to a process for preparing said polyisocyanates, to mixtures of said polyisocyanates with other polyisocyanates which do not contain siloxane groups and the use of said polyisocyanates or polyisocyanate mixtures 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 known.

Although the coatings prepared from said compositions possess many valuable properties, one property, in particular, that has to be improved is the surface quality. It can be difficult to formulate coating compositions to obtain a coating with a smooth surface as opposed to another having surface defects, such as craters, etc. It is believed that these difficulties are related to the high surface tension of the two component coating compositions. Another problem caused by the high surface tension is the difficulty of cleaning the coatings. Regardless of its possible field of application, it is very likely that the coatings are subjected to stains, graffiti, etc. Accordingly, it is an object of the present invention to provide coating compositions having reduced surface tension and, therefore, are suitable for the production of coatings having lower surface energies and improved surfaces. A further object of the present invention is to provide coating compositions that have better cleanability. A final object of the present invention is to provide coating compositions that meet said requirements without substantially affecting the other valuable properties of known polyurethane coatings. Unexpectedly said objects can be achieved by formulating coating compositions with the polyisocyanates according to the present invention containing allophanate groups, siloxane groups and optionally isocyanurate groups described below. Polyisocyanates containing allophanate groups, siloxane groups and optionally isocyanurate groups are described in co-pending applications, US Serial Nos. 08 / 536,556 and 08 / 593,129. The polyisocyanates described in said co-pending applications are preferably prepared by reacting an excess of an initial diisocyanate material with a compound containing hydroxy groups and siloxane groups to initially form urethane groups, which are then converted to allophanate groups by reaction with the excessive diisocyanate. in the presence of an allophanatization catalyst and optionally trimerization (if isocyanurate groups are desired). One of the disadvantages of this preparation process is that it is difficult to avoid the presence of by-products containing monoisocyanate in the resulting polyisocyanate. The amount of said by-products can be reduced according to the present invention by initially forming compounds containing urethane groups which are essentially free of isocyanate groups and isocyanate reagents, and then reacting said compounds in the presence of excessive polyisocyanate to convert the urethane groups to allophanate groups and optionally introduce isocyanurate groups.

U.S. Patent 4,590,224 relates to the production of fully reacted polymers, primarily in the form of molded articles or foams, which are prepared by reacting a polyisocyanate with a polysiloxane polysiloxane in the presence of a trimerization catalyst. In addition to the oligomerization of the polyisocyanate to form isocyanurate groups, a portion of the isocyanate groups will react with the polyahl to form urethane or urea groups depending on the type of polyahl. This patent does not suggest the incorporation of allophanate groups to the polyisocyanate component and certainly does not recognize the importance of incorporating allophanate groups to maintain the clarity of the polyurethane coatings. Furthermore, this patent does not suggest the two-step process for preparing the polyisocyanates according to the present invention. COMPENDIUM OF THE INVENTION The present invention relates to polyisocyanate adducts containing allophanate groups, siloxane groups and optionally isocyanurate groups which are prepared by reacting compounds a) which i) are substantially free of hydroxyl groups and isocyanate groups, ii) have a average of at least two urethane groups per molecule and iii) contain from 0 to 50% by weight of siloxane groups (calculated as SiO, MW 44), based on the weight of the polyisocyanate adducts, with an excessive amount, based on the equivalents of urethane groups, of polyisocyanates b), optionally containing siloxane groups, to form polyisocyanate adducts and eliminating optionally at least a portion of the unreacted excessive polyisocyanates b), provided that the compounds a) and the polyisocyanates b) contain a total of at least 0.001% by weight of siloxane groups based on the weight of the polyisocyanate adducts. The present invention also relates to a process for preparing said polyisocyanate adducts by reacting compounds which i) are substantially free of hydroxyl groups and isocyanate groups, ii) have an average of at least two urethane groups per molecule and iii) contain 0 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adducts, with an excessive amount, based on the urethane groups, of polyisocyanates, optionally containing siloxane groups, to form the polyisocyanate adducts and optionally removing at least one portion of the unreacted excessive polyisocyanates, provided that such compounds or such polyisocyanates contain at least 0.001% by weight of siloxane groups based on the weight of the polyisocyanate adducts. Finally, the present invention also relates to mixtures of said polyisocyanates with other polyisocyanates that do not contain siloxane groups and to the use of said polyisocyanates or polyisocyanate mixtures, optionally in blocked form, in one or two component coating compositions. DETAILED DESCRIPTION OF THE INVENTION The starting materials for the process according to the invention are compounds a) containing urethane groups and optionally siloxane groups and polyisocyanates b), preferably diisocyanates, optionally containing siloxane groups, provided that at least one of said components contain siloxane groups. The two initial components are reacted together to form polyisocyanates containing allophanate groups, siloxane groups and optionally isocyanurate groups. Compounds a) have an average of at least two urethane groups per molecule and a number average molecular weight, which can be calculated from the stoichiometry of the starting materials, of less than 10,000, preferably less than 5,000 and more preferably less of 3,000. The compounds are substantially free of isocyanate groups and hydroxyl groups, ie the NCO content of compounds a) is less than 2% by weight, preferably less than 0.5% by weight and more preferably less than 0.2% by weight , and the content of hydroxyl groups is less than 1% by weight, preferably less than 0.3% by weight and more preferably less than 0.1% by weight. This objective can be achieved during the preparation of said compounds by reacting the initial components at an NCO / OH equivalent ratio of 1.2: 1 to 1: 1.2, preferably 1.1: 1 to 1: 1.1 and more preferably 1: 1. The reaction to form urethane groups is generally carried out at a temperature of 20 to 130 ° C, preferably 50 to 90 ° C. The reaction is preferably carried out in the melt, although suitable organic solvents can be used. Compounds a) can be prepared by reacting a polyol, preferably a diol, with a monoisocyanate containing siloxane groups, optionally in admixture with other monoisocyanates; reacting a polyol containing siloxane groups, preferably a diol, optionally in admixture with other polyols, with a monoisocyanate; reacting a polyisocyanate containing siloxane groups, preferably a diisocyanate, optionally in admixture with other polyisocyanates, with a monohydroxy compound; or reacting a polyisocyanate, preferably a diisocyanate, with a monohydroxy compound containing siloxane groups, optionally in admixture with other monohydroxy compounds. In another embodiment of the present invention, both compounds used to prepare compounds a) may contain siloxane groups. In addition, any of the foregoing monofunctional compounds can be mixed with higher functional compounds, provided that the resulting urethane compounds are substantially free of isocyanate and hydroxy groups. The presence of said higher functional compounds gives rise to chain extension, which introduces more urethane groups. If said urethane groups are then converted to allophanate groups, the resulting products will have a higher isocyanate functionality. Most preferably, compounds a) are diurethanes prepared by reacting a diisocyanate with a monohydroxy compound containing siloxane groups. The isocyanates used for the production of compounds a) containing urethane groups are selected from mono-, di- and / or aromatic or linear (branched) aliphatic polyisocyanates having a molecular weight of 99 to 1,000, preferably from 99 to 400, and more preferably from 140 to 300, and an NCO content of 10 to 60% by weight, preferably 18 to 60% by weight and more preferably 30 to 50% by weight. The average NCO functionality of said isocyanates is from 1 to 4, preferably from 1 to 2 and more preferably 2. Examples of monoisocyanates, which may be used alone or in admixture with di- or polyisocyanates to prepare the compounds containing urethane groups, include aromatic monoisocyanates, such as phenyl isocyanate; (cyclo) aliphatic monoisocyanates having from 4 to 18 carbon atoms, such as n-butyl isocyanate, n-hexyl isocyanate, cyclohexyl isocyanate, n-stearyl isocyanate; and aromatic or (cyclo) aliphatic monoisocyanates containing siloxane groups, such as triethoxy- (3-isocyanopropyl) -silane. Examples of suitable organic diisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,2-dodecamethylene diisocyanate, cyclohexane-1, 3- and -1,4-diisocyanate, l-isocyanato-2-isocyanatomethyl cyclopentane, l-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), 4,4 'and / or 2, 4 '-diisocyanato-dicyclohexylmethane diisocyanate, 1,3- and 1, -bis- (isocyanatomethyl) -cyclohexane, bis- (4-isocyanato-3-methyl-cyclohexyl) -methane, xylylene diisocyanate, a, a , a '-, a'-tetramethyl-1, 3- and / or -1, -xylylene diisocyanate, 1-isocyanato-l-methyl-4 (3) -isocyanatomethyl cyclohexane, 2,4- and / or 2, 6 hexahydrotoluylene diisocyanate, 2,4- and / or 2,6-toluene diisocyanate, 2,4- and / or 4,4'-diphenylmethane diisocyanate, 1,5-di-naphthalene naphthalene and mixtures thereof. Polyisocyanates containing 3 or more isocyanate groups, such as 4-isocyanatomethyl-1, 8-octamethylene diisocyanate and aromatic polyisocyanates, such as 4,4 ', 4', 4"-triphenylmethane triisocyanate and polymethylene polyphenyl polyisocyanates obtained by phosphiding condensates of aniline / formaldehyde. Also suitable are polyisocyanates containing siloxane groups. For example, those described in U.S. Patent 4,942,164, incorporated herein by reference. Derivatives of the above isocyanates containing biuret groups, uretdione groups, isocyanurate groups, carbodiimide and especially urethane groups are also suitable for preparing compounds a), but are less preferred. Suitable alcohols for preparing the compounds containing urethane groups are selected from monohydric to hexahydric alcohols having a molecular weight of from 32 to 900, preferably from 74 to 300, and mixtures of said alcohols. Examples of suitable monohydric alcohols include saturated monohydric alcohols, such as methanol, ethanol, n-propanol, isopropanol, methoxypropanol and the isomeric butanols, pentanols, hexanols, octanols, decanoles, dodecanols and octadecanols. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, butanediol-1,4, hexanediol-1,6, neopentyl glycol, 2-methyl-propanediol-1, 3, 2,2,4-tri-methyl-entanediol-1. , 3, dimer fatty alcohols, trimeric fatty alcohols, glycerol, trimethylolpropane, trimethylolethane, the isomeric hexanetriols, pentaerythritol and sorbitol. Also suitable are unsaturated alcohols such as allyl alcohol, diallyl ether of trimethylolpropane, butene-diol and monofunctional alcohols which are derived from corresponding acids or acid mixtures of unsaturated natural and synthetic fatty acids. Also suitable for preparing compounds are a) alkoxylation products containing ether groups of the monohydric and polyhydric alcohols previously discussed and / or transesterification products containing hydroxyl groups of fats or oils with polyhydric alcohols, in particular glycerol, trimethylolpropane or pentaerythritol. Suitable compounds containing isocyanate reactive groups and siloxane groups, which are suitable for preparing compounds a), are those containing one or more (preferably one or two and more preferably one) isocyanate reactive groups (preferably hydroxyl groups) directly attached to carbon atoms, and one or more siloxane groups, preferably in the form of dimethyl siloxane groups, -Si (CH3) 20-, Examples of said compounds are those corresponding to the formula: Y-R'-X- [Si (R2) 20-] n- [Si (R2) sX ^ -R'-Y 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), R2 represents hydrogen or an optionally substituted lower alkyl inert form, phenyl or benzyl group, preferably ethyl or methyl, more preferably methyl, X represents a bond between a group R1 and a Si atom, for example, a covalent bond, -O- or -COO-, Y represents hydrogen or an isocyanate reactive group, preferably h anhydrogen, a hydroxyl group or a primary or secondary amino group, more preferably a hydrogen or a hydroxy group, 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 the allophanate and / or the trimerization reaction of the isocyanate groups. Examples include halogen atoms, such as fluorine. Examples of compounds containing an isocyanate reactive group in which R1 represents an oxyalkylene group, are compounds corresponding to the formula: Y- (CHR3-CH20) 0- (R4) m- [Si (R2) 20-] n- [Si (R2) 2-X '] m-R4-H and examples of compounds containing more than one isocyanate reactive group in which R1 represents an oxyalkylene group are compounds corresponding to the formula: Y- (CHR3-CH20-) or- (R) m- [Si (R2) 20-] n- (CH2-CHR3-0-) p-CH2-CHR3-Y where R2, Y, m and n are those defined above , R3 is hydrogen or an alkyl group having 1 to 12 carbon atoms, preferably hydrogen or methyl, R4 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 a Si atom, for example, a covalent bond -0- or -COO-, or is an integer from 1 to 200, preferably from 2 to 50 and more preferably from 4 to 25, and p is an integer from 0 to 200, preferably from 2 to 50 and more preferably from 4 to 25. Said siloxane compounds are prepared by reacting the appropriate siloxane with an amount of an alkylene oxide (preferably ethylene or propylene oxide) sufficient to prepare a compound having the desired siloxane content. Amine or amino alkylene groups are introduced by aminating in a known manner the resulting hydroxyl-terminated compound. Other suitable siloxane-containing compounds can be linear, branched or cyclic and have a molecular weight (number of average molecular weight determined by gel permeation chromatography using polystyrene as a rule) 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 have in general OH number greater than 5, preferably greater than 25 and more preferably greater than 35. Compounds of this type are described in "Silicon Compounds", fifth edition, which can be obtained from Hüls America, Inc. Most preferably, compounds a) are prepared from monomeric diisocyanates and monohydroxy compounds containing siloxane groups. The molecular weight of compound a) containing urethane groups is adjusted by the appropriate selection of the isocyanate and alcohol components and, in particular, by their average functionality. At least 20 mol% of the isocyanate or alcohol component is formed by monofunctional components to produce chain termination during the reaction to form urethane groups. This means that the average functionality of the isocyanate and alcohol components is preferably less than 2. It is also possible according to the present invention to use compounds containing urethane groups prepared by other methods such as the known "phosgene-free urethane synthesis" described, for example, in EP-A-0.027.940, EP-A-0.027.952, EP-A-0.027.953, EP-A-0.323.514 and EP-A-0.355.443. After the preparation of the compounds containing urethane groups, they are reacted with the component p-oliisocyanate b), which is selected from the organic polyisocyanates previously exposed for use in the preparation of compound a), with the exception of monoisocyanates. Preferably, the organic polyisocyanates are those which can be removed by distillation after the formation of the allophanate groups. The monoisocyanates should be used, if used, only in minor amounts because, when they react with urethane groups, they give rise to non-functional allophanate groups, i.e., groups which do not contain isocyanate groups. The average functionality of component b) is from 2 to 4, preferably 2. The reaction of the compound containing a urethane group a) with polyisocyanate component b) is carried out at an NCO / urethane equivalent ratio of 3: 1 to 100: 1, preferably 6: 1 to 60: 1 and more preferably 8: 1 to 30: 1, and at a temperature of 50 ° C to 250 ° C, preferably 60 ° C to 150 ° C and more preferably 70 ° C to 120 ° C. Suitable methods for preparing polyisocyanates containing an allophanate group are known and are described in U.S. Patents 3,769,318, 4,160,080 and 4,177,342 and 4,738,991, the disclosures of which are incorporated herein by reference. The allophanatization of the compounds a) in the presence of polyisocyanates b) can be carried out in the absence or in the presence of solvents which are inert to the isocyanate groups. Depending on the area of application of the products according to the invention, low to medium boiling solvents or high boilers 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 trichloro-ethylene; ethers such as diisopropyl ether; and alkanes such as cyclohexane, petroleum ether or ligroin. Instead of using catalysts that promote the formation of allophanate groups, it is also possible according to the present invention to use catalysts that promote the formation of allophanate groups and isocyanurate groups. Suitable methods and catalysts for the preparation of polyisocyanates containing isocyanurate groups and allophanate groups are known and described in U.S. Patents 5,124,427, 5,208,334, 5,235,018, 5,290,902 and 5,444,146, whose descriptions they are incorporated herein by reference. The trimerization of the initial diisocyanate mixture can be carried out in the absence or in the presence of solvents which are inert to isocyanate groups, such as those described above. Examples of suitable catalysts include tetraalkylammonium hydroxides or arylalkylammonium hydroxides; salts of metals such as iron (III) chloride or potassium octoate; zinc compounds, such as zinc stearate, zinc octoate, zinc naphthenate or zinc acetylacetonate; tin compounds such as tin (II) octoate, tin (II) 2-ethylhexanoate, tin (II) laurate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate or dioctyltin diacetate; tri (ethyl acetoacetate) of aluminum; and manganese, cobalt or nickel compounds and mineral acids such as trifluoroacetic acid, sulfuric acid, hydrogen chloride, hydrogen bromide, phosphoric acid or perchloric acid. The catalysts are preferably added before the allophanatization reaction. Although they can be added before the formation of urethane, this is less preferred because of the possibility of forming allophanate groups, which would affect the stoichiometry of the urethane-forming reaction. The catalysts are used in concentrations of 0.001 to 5% by weight, preferably 0.005 to 1% by weight. At a temperature of about 50 ° C and in the presence of the necessary catalyst or catalyst solution, the allophanatization reaction begins and is indicated by an exothermic reaction. When catalysts are present for the formation of allophanate groups and isocyanurate groups, it is possible to control the rate of formation of these two groups. As the reaction temperature increases, the conversion rate of urethane groups to allophanate groups increases more rapidly than the formation of isocyanurate groups. Therefore, by varying the reaction temperature, it is possible to obtain different ratios of allophanate groups to isocyanurate groups. The progress of the reaction is still determined by the NCO content with a suitable method such as titration, refractive index or IR analysis. Thus, the reaction can be allowed to continue until it is finished or can be finished to the desired degree of allophanatization. The allophanatization reaction is terminated after 50 to 100%, preferably 80 to 100% by weight, more preferably 90 to 100% by weight and most preferably 95 to 100% by weight of the urethane groups have been converted to allophanate groups. The polyisocyanate adducts should contain sufficient allophanate groups to ensure that the adducts remain stable and homogeneous in storage for 3 months at 25 ° C. If the polyisocyanate adducts contain an insufficient number of allophanate groups, the product may be cloudy and a gradual sedimentation of insoluble constituents may occur during storage. The termination of the allophanatization reactions and optionally trimerization can take place, for example, by the addition of a catalyst poison, such as those described in literature references explained above. For example, when basic catalysts are used, the reaction is terminated by the addition of an amount, which is at least equivalent to the amount of catalyst, of an acid chloride such as benzoyl chloride. When thermolabile catalysts are used, for example, some quaternary ammonium hydroxides, the poisoning of the catalyst can be dispensed with by adding a catalyst-poison, since these catalysts decompose during the course of the reaction. The use of suspended catalysts is also possible. These catalysts are removed after achieving the desired degree of trimerization by filtering the reaction mixture. The operation of the reaction mixture, optionally after the previous separation of insoluble catalyst constituents, can take place in various ways depending on how the reaction was carried out and the area of application for the isocyanates. The solvent used during the reaction and any unreacted monomer present in the polyisocyanate product can be optionally removed, for example, by distillation, in a known manner. The product obtained after the distillation generally contains a total of less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight and most preferably less than 0.2. % by weight, based on the solids content of the polyisocyanate adduct, of the free polyisocyanate component (unreacted) b). The products according to the invention are polyisocyanate adducts containing allophanate groups, siloxane groups and optionally isocyanurate groups, having an NCO content of 2 to 30% by weight, preferably 5 to 28% by weight; an average functionality of 2 to 4, preferably 2 to 3 and more preferably 2 to 2.5; and a minimum content of siloxane groups (calculated as SiO, MW 44) of 0.001% by weight, preferably 0.01% by weight and more preferably 0.1% by weight, based on solids, and a maximum content of groups siloxane 50% by weight, preferably 10% by weight, more preferably 7% and most preferably 3% by weight, based on the solids. The products according to the invention range from low viscosity liquids having a viscosity of 200 mPa.s to high viscosity liquids to solids. The low viscosity products are generally obtained from aliphatic diisocyanate starting materials, such as 1,6-hexamethylene diisocyanate, and have a viscosity of less than 5000, preferably less than 2000 and more preferably less than 1300 mPa.s . High viscosity products can also be obtained from these diisocyanates if the oligomerization reaction is terminated at a considerably lower NCO content. The high viscosity products have a minimum viscosity of 5,000, preferably 12,000 and more preferably 15,000 to 70,000 mPa.s and a maximum viscosity of 100,000, preferably 90,000 and more preferably 70,000 mPa.s. The viscosities are determined at 25 ° C from the products, which do not contain solvents (100% solids) and are substantially free of unreacted excessive monomer. In general, highly viscous solids are obtained from cyclic diisocyanates, such as isophorone diisocyanate, bis- (4-isocyanatocyclohexyl) -methane or the aromatic diisocyanates described above. The polyisocyanate adducts have a content of allophanate groups (calculated as N2, C2, H, 03, MW 101) of at least 5%, preferably at least 10% by weight. The upper limit of the content of allophanate groups is 35%, preferably 30% by weight. The polyisocyanate adducts have a content of isocyanurate groups (calculated as N3, C3,? 3, MW 126) of up to 25% by weight, preferably up to 20% by weight. When allophanatization / tri-merization catalysts are used, the polyisocyanate adducts will generally have a content of isocyanurate groups of at least 5%, preferably at least 10% by weight. Even when highly selective allophanatization catalysts are used, smaller amounts of isocyanurate groups are formed. Depending on the viscosity of the products according to the invention, it may be useful to dilute them with inert solvents.

Suitable solvents include those previously exposed for the production of the compounds containing allophanate groups and optionally isocyanurate. The products according to the invention are valuable in-icial 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 wet cured to form coatings. However, they are preferably used in combination with an isocyanate reactive component in one or two component coating compositions, more preferably polyurethane coating compositions. When the polyisocyanate adducts are not blocked, two-component compositions are obtained. On the contrary, when the polyisocyanate adducts are blocked, one component compositions are obtained. Before use in coating compositions, the polyisocyanate adducts according to the invention can be mixed with other known polyisocyanates, for example, polyisocyanate adducts containing biuret, isocyanurate, allophanate, urethane, urea, carbodiimide, and / or uretdione groups. The amount of the polyisocyanate adducts according to the invention to be mixed with these other polyisocyanates depends on the content of siloxane groups of the polyisocyanates according to the invention, the intended application of the resulting coating compositions and the amount of low energy properties. surface that are desired for said application. To obtain low surface energy properties, the resulting polyisocyanate blends should contain a minimum of 0.001% by weight, preferably 0.01% by weight and more preferably 0.1% by weight, of siloxane groups (MW 44), based on to 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 the solids. Knowing the siloxane content of the polyisocyanate mixtures according to the invention and the desired siloxane content of the resulting polyisocyanate mixtures, the relative amounts of the polyisocyanate adducts according to the invention and the other polyisocyanates can be easily determined. The mixtures preferably have an isocyanate content of 10 to 35%, more preferably 12 to 25% by weight, based on solids. Any of the polyisocyanate adducts according to the invention can be mixed with other polyisocyanates. However, the polyisocyanate adducts to be mixed preferably have a minimum siloxane content of 5% by weight, more preferably 10% by weight and most preferably 20% by weight, and preferably have a maximum siloxane content of 50% by weight, more preferably 45% by weight. These so-called "concentrates" can then be mixed with other polyisocyanates to form polyisocyanate mixtures that can be used to prepare coatings with low surface energy characteristics. The concentrates preferably have an isocyanate content of 2 to 15%, preferably 2 to 10% by weight, based on the solids. Preferred reaction partners of the products according to the invention are polyhydroxy polyesters, polyhydroxy polyethers, polyhydroxy polyacrylates, polyhydroxy polylactones, polyhydroxy polyurethanes, polyhydroxy polyepoxides and optionally low molecular weight polyhydric alcohols known from the technology of polyurethane coatings. The polyamides, in particular 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 (succinates) 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 are selected to obtain equivalent ratios of isocyanate groups (whether present in blocked or unblocked form) to isocyanate reactive groups of about 0., 8 to 3, preferably about 0.9 to 1.5. To accelerate hardening, the coating compositions may contain known polyurethane catalysts, for example, tertiary amines such as triethylamine, pyridine, methyl pyridine, benzyl dimethylamine, N, N-dimethylamino cyclohexane, N-methyl-piperidine, pentamethyl diethylene triamine , 1,4-diazabicyclo [2, 2, 2] -octane and N, N'-dimethyl piperazine; or salts of metals 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, in which the isocyanate groups are used in blocked form by known blocking agents. The blocking reaction is carried out in a known manner by reacting the isocyanate groups with suitable blocking agents, preferably at elevated temperature (for example, about 40 to 160 ° C), and optionally in the presence of a suitable catalyst, for example, the amines previously described tertials or metal salts. Suitable blocking agents include monophenols such as phenol, cresols, trimethylphenols and tertiary butyl phenols; tertiary alcohols such as tertiary butanol, tertiary amyl alcohol and dimethylphenyl carbinol; compounds which easily form enols such as acetoacetic ester, acetyl acetone and malonic acid derivatives, for example malonic acid diethyl ester; secondary aromatic amines such as N-methyl aniline, N-methyl toluidine, N-phenyl toluidine and N-phenyl xylidine; imides as succinimide; lactams such as e-caprolactam and d-valerolactam; pyrazoles such as 3,5-dimethyl pyrazole; oximes such as butanone oxime, methyl amyl ketoxime and cyclohexanone oxime; mercaptans such as methyl mercaptan, ethyl mercaptan, butyl mercaptan, 2-mercapto-benzthiazole, α-naphthyl mercaptan and dodecyl mercaptan; and triazoles such as 1H-1, 2,4-triazole. The polyisocyanate adducts according to the invention can also be used as the polyisocyanate component in two component floating coating compositions. To be useful in these compositions the polyisocyanate adducts must be made hydrophilic by mixing with external emulsifiers or by reaction with compounds containing cationic, anionic or nonionic groups. Methods for making the polyisocyanates hydrophilic are described in co-pending application, U.S. Patents 5,194,487 and 5,200,489, the disclosures of which are incorporated herein by reference. The reduced surface tension of the modified polyisocyanate mixtures improves the pigment dispersion and wetting of the substrate. The coating compositions may also contain additives such as wetting agents, flow control agents, leveling agents, scale inhibitors, antifoaming agents, fillers (such as silica, aluminum silicate and high boiling waxes), substances for viscosity control. , pigments, dyes, UV absorbers and thermal and oxidative stabilizers. 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, spraying, dipping or flow coating. Suitable substrates include wood, plastic, leather, paper, textiles, glass, ceramics, plaster, masonry, metals and concrete. The coating compositions containing the polyisocyanate adducts according to the invention provide coatings which have good drying times, adhere well to a metal base, and are especially resistant to light, stable in the presence of heat and highly resistant to heat. abrasion. In addition, they are characterized by great hardness, elasticity, very good resistance to chemicals, high gloss, good resistance to weathering, good resistance to environmental attack and good pigmentation qualities. First of all, the coating compositions have an excellent surface appearance and excellent cleanability. The invention is better illustrated, although not intended to be limited, with the following examples in which all parts and percentages are by weight unless otherwise specified. The content of siloxane groups is based on SiO, PM 44. EXAMPLES Polyisocyanate 1 - Comparison A polyisocyanate containing a biuret group prepared from 1,6-hexamethylene diisocyanate and having an isocyanate content of approximately 23%, a diisocyanate content monomeric of <0.7% and a viscosity at 25 ° C of 1300-2200 mPa.s (obtainable from Bayer Corporation as Desmodur N 3200). Polyisocyanates 2 and 3 - According to the invention HDI and a butyl initiated polydimethylsiloxane alcohol, finished with cabinol (which can be obtained from Chisso Copr., As Silaplane FM-0411, PM 1000) were added at an equivalent NCO / OH ratio from 1: 1 to a three-neck flask equipped with a gas bubbler, mechanical stirrer, thermometer and condenser. Dry nitrogen was bubbled through the stirred reaction mixture while heating to 90 ° C. After 4 hours at 90 ° C, there were no free NCO groups measured by IR. 10 equivalents, based on the equivalents of urethane groups present in the diurethane, of HDI or IPDI, were added to the diurethane, the resulting mixture was heated to 120 ° C and stannous octoate was added dropwise as a catalyst. When the NCO content reached the desired value, the reaction was stopped by adding 1.0 equivalent (based on the catalyst) of di (2-ethylhexyl) phosphate. The excess diisocyanate monomer was removed from the resulting crude reaction mixture by thin film evaporation to obtain the final product. The diisocyanate reacted with the diurethane, amount of catalyst, NCO content to completion, and the properties of the final product are shown in Table 1. The final products had 100% solids contents. TABLE 1 Polyisocyanate 4 - According to the invention 2.47 parts of triethoxy (3-isocyanopropyl) silane and 0.96 parts of tripropylene glycol were added to a reactor equipped with a gas sparger, stirrer and thermometer. The reaction mixture was heated to 70 ° C and maintained until the NCO peak disappeared on the IR scan. 100 parts of HDI were added to the diurethane. and the resulting mixture was heated to 90 ° C. Then 0.83 parts of a 0.5% solution of trimethylbenzyl ammonium hydroxide catalyst in ethyl acetate was added to said mixture with stirring. The catalyst solution was added at a rate such that the reaction mixture was maintained at about 90 ° C. After the catalyst addition was complete, the reaction mixture was maintained at 90 ° C for a further 15 minutes, after which 0.01 part of di (2-ethylhexyl) phosphate was added. The resulting reaction mixture had an NCO content of 39.4%. Excessive HDI monomer was removed from the reaction mixture by evaporation of cleaned thin film, and the resulting product was filtered (1 miera). A liquid polyisocyanate modified by dialphoanate having a viscosity at 25 ° C of 6615 mPa.s, an NCO content of 19.4%, an HDI monomer content of 3.7%, a content of siloxane groups of 0 , 90% and liquid surface tension of 34.3 dynes / cm. Polyisocyanate 5 - According to the invention 0.35 parts of HDI and 5.65 parts of a butyl initiated polydimethylsiloxane alcohol, finished with carbinol (which can be obtained from Chisso Corp., as Silaplane FM-0411, PM 1000) were added. to a reactor equipped with a gas bubbler, stirrer and thermometer. The reaction mixture was heated to 80 ° C and maintained until the NCO peak disappeared on the IR scan. 300 parts of HDI were added to the diurethane and the resulting mixture was heated to 90 ° C. Then 2.5 parts of a solution of 0.5% trimethylbenzyl ammonium hydroxide catalyst in ethyl acetate was added to said mixture with stirring. The catalyst solution was added at a rate such that the reaction mixture was maintained at about 90 ° C. After the catalyst addition was complete, the reaction mixture was maintained at 90 ° C for a further 15 minutes, after which 0.01 part of di (2-ethylhexyl) phosphate was added. A dark solution having an NCO content of 42.3% was obtained. The excess HDI monomer was removed from the reaction mixture by evaporation of cleaned thin film and the resulting product was filtered (1 miera). A dialisolated modified polyisocyanate having a viscosity at 25 ° C of 920 mPa.s, an NCO content of 20.8%, a content of HDI monomer of 2.0% and a content of siloxane groups of 0 was obtained. , 13%. Preparation of Component I Ingredients 1-7 were mixed at low speed using the amounts set forth in Table 2. The rate was then increased and grinding was continued until a Hegmann Grind Grinding > 7. This system was then mixed with the amounts of ingredients 8-11 set forth in Table 2. After mixing, the composition was filtered with gauze and stored in a wrong container. Table 2 - Ingredients 1. 24.7 parts of a polyester polyol (obtainable as Desmofen 631A-75 from Bayer Corporation) 2. 39.1 parts of titanium dioxide (obtainable as Ti-Pure R- 960 from Dupont) 3. 0.3 parts of a grinding aid (which can be obtained as Anti-Terra U from Byk Chemie) 4. 3.1 parts of a cellulose acetate butyrate (obtainable as CAB 551 -0.01 by Eastman) 5. 1.0 part of an anti-settling agent (which can be obtained as MPA-2000X from Rheox) 6. 0.4 parts of a 0.4% solution of dibutyltin dilaurate (obtainable as Metacure T-12 from Air Products and Chemicals) 7. 8.4 parts of a polyester polyol (which can be obtained as Desmophen 670A-80 from Bayer Corporation) 8. 0.2 parts of a tertiary amine catalyst (which can be obtained as Desmorapid PP from Bayer AG) 9. 1.4 parts of 2,4-pentanedione 10. 18.8 parts of methyl n-amyl ketone 11. 2.6 parts of diisobutyl ketone a Film preparation Component I was mixed with the amounts of the components listed in Table 3 (equivalent ratio of NCO / OH 1.24: 1; content of 0.06% siloxane groups, based on the weight of the dry film). After mixing the composition, it was sprayed to a wet film thickness of 3 mils. The films were allowed to cure for two weeks at a constant temperature and humidity of 70 ° C and 55%. The surface energies of the resulting films are shown in Table 3.

TABLE 3 Measurements of surface energy All the referred energies of the surface of the liquid (resin) (in dynes / cm) were obtained with the method of the ring or Du Noüy. In this static method, the force applied to a thin platinum ring was measured with a tensiometer. All the referred energies of the solid surface (coating) (in dynes / cm) were obtained with the Owens-Wendt procedure. The contact angle of two solvents (water and methylene iodide) was measured with a goniometer. Several readings were taken, which were averaged. The averages were then used to calculate the solid surface energy of the coating, taking into account the contributions of the polar and dispersive forces. 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 such purpose and that those skilled in the art can make variations without departing from the spirit and scope of the invention, with the exception of of what is limited by the claims.

Claims (18)

1. CLAIMS 1. A polyisocyanate adduct containing allophanate groups, siloxane groups and optionally isocyanurate groups which is prepared by reacting a compound a) which i) is substantially free of hydroxyl groups and isocyanate groups, ii) has an average of at least two urethane groups per molecule and iii) contains from 0 to 50% by weight of siloxane groups (calculated as SiO, MW 44), based on the weight of the polyisocyanate adduct, with an excessive amount, based on urethane group equivalents, of polyisocyanates b ), optionally containing siloxane groups, to form a polyisocyanate adduct and optionally removing at least a portion of the unreacted excessive polyisocyanate b), provided that compound a) and polyisocyanate b) contain a total of at least 0.001% by weight of siloxane groups based on the weight of the polyisocyanate adduct.
2. 2. The polyisocyanate adduct of claim 1, wherein compound a) contains from 0.01 to 50% by weight of siloxane groups.
3. 3. The polyisocyanate adduct of claim 2, wherein the compound a) is prepared by reacting an aliphatic diisocyanate with a compound containing siloxane groups containing a hydroxy group.
4. 4. The polyisocyanate adduct of claim 2, wherein the compound a) is prepared by reacting a monoisocyanate with a compound containing two hydroxy groups.
5. 5. The polyisocyanate adduct of claim 3, wherein said aliphatic diisocyanate includes 1,6-hexamethylene diisocyanate.
6. 6. The polyisocyanate adduct of claim 1, wherein the compound a) contains from 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct.
7. The polyisocyanate adduct of claim 2, wherein the compound a) contains from 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct.
8. The polyisocyanate adduct of claim 3, wherein the compound a) contains from 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct.
9. The polyisocyanate adduct of claim 4, wherein the compound a) contains from 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct.
10. The polyisocyanate adduct of claim 5, wherein the compound a) contains from 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct.
11. 11. A polyisocyanate composition comprising A) a polyisocyanate adduct containing allophanate groups, siloxane groups and optionally isocyanurate groups which is prepared by reacting a compound a) which i) is substantially free of hydroxyl groups and isocyanate groups, ii) has an average of at least two urethane groups per molecule and iii) contains from 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct, with an excessive amount, based on the equivalents of urethane groups, of a polyisocyanate b ) to form a polyisocyanate adduct and optionally removing at least a portion of the unreacted excessive polyisocyanate b), and B) a polyisocyanate adduct containing biuret, isocyanurate, allophanate, urethane, urea, carbodiimide and / or uretdione groups, where the components A) and B) are present in amounts such that said polyisocyanate composition has a content of siloxane groups, based on solids, of 0.001 to 10% by weight.
12. The polyisocyanate composition of claim 11, wherein compound a) contains from 0.01 to 50% by weight of siloxane groups.
13. 13. The polyisocyanate composition of claim 12, wherein compound a) is prepared by reacting an aliphatic diisocyanate with a compound containing siloxane groups containing a hydroxy group.
14. The polyisocyanate composition of claim 12, wherein the compound a) is prepared by reacting a monoisocyanate with a compound containing two hydroxy groups.
15. 15. The polyisocyanate composition of claim 13, wherein said aliphatic diisocyanate includes 1,6-hexamethylene diisocyanate.
16. 16. A process for the preparation of a polyisocyanate adduct containing allophanate groups, siloxane groups and optionally isocyanurate groups which includes reacting a compound a) which i) is substantially free of hydroxyl groups and isocyanate groups, ii) has an average of at least two urethane groups per molecule and iii) contains from 0 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct, with an excessive amount, based on the equivalents of urethane groups, of a polyisocyanate b), which optionally contains siloxane groups, to form an adduct of p-oliisocyanate and optionally removing at least a portion of the unreacted excessive polyisocyanate b), provided that the compound a) and the polyisocyanate b) contain a total of at least 0.001% in weight, of siloxane groups, based on the weight of the polyisocyanate adduct.
17. 17. A two component coating composition containing the polyisocyanate adduct of claim 1 and a compound containing at least two isocyanate reactive groups.
18. 18. A one component coating composition containing the polyisocyanate adduct of claim 1, wherein the isocyanate groups are blocked, and a compound containing at least two isocyanate reactive groups. SUMMARY OF THE INVENTION The present invention relates to polyisocyanate adducts containing allophanate groups, siloxane groups and optionally isocyanurate groups which are prepared by reacting compounds a) which i) are substantially free of hydroxyl groups and isocyanate groups, ii) have an average of at least two urethane groups per molecule and iii) contain from 0 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adducts, with an excessive amount, based on the urethane group equivalents, of polyisocyanates b), containing optionally siloxane groups, to form polyisocyanate adducts and optionally removing at least a portion of the unreacted excessive polyisocyanates b), provided that the compounds a) and the polyisocyanates b) contain a total of at least 0.001% by weight of siloxane groups based on the weight of the polyisocyanate adducts. The present invention also relates to a process for preparing said polyisocyanate adducts, to blends of the polyisocyanates with other polyisocyanates containing no siloxane groups and to the use of the polyisocyanate adducts or polyisocyanate mixtures, optionally in blocked form, in compositions of coating of one or two components.