CA2097373C

CA2097373C - Polyisocyanates containing allophanate and isocyanurate groups, a process for their production and their use in two-component coating compositions

Info

Publication number: CA2097373C
Application number: CA002097373A
Authority: CA
Inventors: Terry A. Potter; William E. Slack
Original assignee: Bayer Corp
Current assignee: Bayer Corp
Priority date: 1991-10-02
Filing date: 1993-05-31
Publication date: 2003-11-11
Anticipated expiration: 2013-05-31
Also published as: ES2087386T3; EP0535483B1; US5444146A; EP0535483A2; EP0535483A3; CA2097373A1

Abstract

The present invention is directed to a polyisocyanate mixture having an NCO content of 10 to 47% by weight and a viscosity of less than 10,000 mPa.s and containing isocyanurate and allophanate groups in a molar ratio of monoisocyanurates to monoallophanates of 10:1 to 1:5, wherein the allophanate groups are formed from urethane groups which are based on the reaction product of an organic diisocyanate having (cyclo)aliphatic bound isocyanate groups and an aromatic monoalcohol containing 6 to 9 carbon atoms.
The present invention is also directed to a process for the production of a polyisocyanate mixture having an NCO
content of 10 to 47% by weight, having a viscosity of less than 10,000 mPa.s and containing isocyanurate and allophanate groups in a molar ratio of monoisocyanurates to monoallophanates of 10:1 to 1:5 by a) catalytically trimerizing a portion of the isocyanate groups of an organic diisocyanate having (cyclo)aliphatically bound isocyanate groups b) adding 0.01 to 0.5 moles, per mole of organic diisocyanate, of an aromatic monoalcohol containing 6 to 9 carbon atoms to the organic diisocyanate prior to or during the trimerization reaction of step a) and c) terminating the trimerization reaction at the desired degree of trimerization by adding a catalyst poison and/or by thermally deactivating the catalyst.
Finally, the present invention is directed to the use of these polyisocyanate mixtures, optionally in blocked form, as an isocyanate component in the two-component coating compositions.

Description

Mo-3678 POLYISOCYANATES CONTAINING ALLOPHANATE AND ISOCYANURATE
GROUPS, A PROCESS FOR THEIR PRODUCTION AND THEIR USE
IN TWO-COMPONENT COATING COMPOSITIONS
BACKGROUND OF THE INDENTION
Field of the Invention The present invention is directed to polyisocyanates which contain allophanate groups and isocyanurate groups and have a low viscosity and improved compatibility with polar and slightly polar solvents and isocyanate-reactive components.
to The present invention is also directed to a process for the production of these polyisocyanates and their use in two-component coating compositions.
Description of the Prior Art Polyisocyanates containing isocyanurate groups are 15 known and disclosed in U.S. Patents 3,487,080, 3,996,223, 4,324,879 and 4,412,073. While these polyisocyanates possess many outstanding properties, they do require improvement in two areas. First, the viscosity of commercially available polyisocyanates containing isocyanurate groups needs to be 2o reduced in order to reduce the amount of solvent which is necessary to obtain a suitable processing viscosity.
Presently, there are an increasing number of government regulations which limit the amount of volatile solvents which may be present in coating systems. Therefore, isocyanurate 2s group-containing polyisocyanates may be precluded from certain applications b~acause it is not possible to reduce the viscosity of these polyi ocyanates to a suitable processing viscosity without using high amounts of solvent. Second, the isocyanurate group-containing polyisocyanates do not possess 3o sufficient compatibility with highly branched polyester co-reactants as evidenced by the gloss and distinctness of -2- ~~~~~ 1 J
image readings, obtained from coatings prepared from these reactants.
It has been proposed in U.S. Patent 4,801,663 to reduce the viscosity of isocyanurate group-containing polyisocyanates prepared from 1,6-hexamethylene diisocyanate (HDI). By terminating the reaction at a very low degree of trimerization higher contents of the monoisocyanurate of HDI
are obtained and the quantity of polyisocyanates containing more than one isocyanurate ring is reduced. Because these to latter polyisocyanates have a much higher viscosity than the monoisocyanurate, the resulting polyisocyanates have a reduced viscosity. However, a significant disadvantage of this system is that because the reaction is terminated at a very low degree of trimerization, the overall yield is very low and the amount 15 of HDI which must be separated from the product is substantially increased. In other words the small reduction in viscosity is offset by a significant increase in the production cost of the product. Further, the resulting product does not possess optimum compatibility with highly branched polyester 2o resins.
Accordingly, it is an object of the present invention to provide polyisocyanates which have a reduced viscosity and improved compatibility with crosslinked polyester co-reactants, while possessing the desirable properties of known 2s polyisocyanates containing isocyanurate groups. It is an additional object of the present invention to provide polyisocyanates which may be produced at reasonable production costs and which are obtained in high yields. Surprisingly, these objectives may be achieved in accordance with the present invention as described hereinafter by the incorporation of 3o specific monoalcohols before or during the trimerization process in order to produce a polyisocyanate containing isocyanurate and allophanate groups.
U.S. Patents 4,582,888, 4,604,418, 4,647,623, 4,789,705 are directed the incorporation of various diols in Mo3649 -order to imprcwe the compatibility of the resulting polyisocyanates with certain solvents and co-reactants. While the use of dials may improve the compatibility of the polyisocyanates, the diols do not reduce the viscosity of the polyisocyanurates for a given yield.
Many of these references as well as those previously set forth disclose the use of monoalcohols or glycols as co-catalysts for the trimerization reaction. However, none of these references suggest the incorporation of allophanate to groups to reduce the viscosity of polyisocyanates containing isocyanurate groups. Further, these references teach that the use of these cocatalysts should be kept to a minimum since the resulting urethane groups reduce the drying time of coatings prepared from the polyisocyanates. In particular, U.S. Patent 15 4,582,888 cautions against the use of any amount of monoalcohol which is in excess of that needed to dissolve the catalyst.
Japanese Publication 61-151179 discloses the use of aliphatic monoalcohols containing 6 to 9 carbon atoms as co-catalysts for trimerization catalysts which do not trimerize 2o HDI in the absence of a co-catalyst.
SUMMARY OF THE INDENTION
The present invention is directed to a polyisocyanate mixture having an NCO content of 10 to 47% by weight and a viscosity of less than 10,000 mPa.s and containing isocyanurate 2s and allophanate groups in a molar ratio of monoisocyanurates to monoallophanates of 10:1 to 1:5, wherein the allophanate groups are formed from urethane groups which are based on the reaction product of an organic diisocyanate having (cyclo)aliphatically bound isocyanate groups and an aromatic monoalcohol containing 6 to 9 carbon atoms.
3o The present invention is also directed to a process for the production of a polyisocyanate mixture having an NCO
content of 10 to 47% by weight, having a viscosity of less than 10,000 mPa.s and containing isocyanurate and allophanate groups Mo3649 -4- 2 ~ ~'~ ~ rl a in a molar ratio of monoisocyanurates to monoallophanates of 10:1 to 1:5 by a) catalytically trimerizing a portion of the isocyanate groups of an organic diisocyanate having {cyclo)aliphatically bound isocyanate groups b) adding 0.01 to 0.5 moles, per mole of organic diisocyanate, of an aromatic monoalcohol containing 6 to 9 carbon atoms to the organic diisocyanate prior to or during the trimerization reaction of step a) and to c) terminating the trimerization reaction at the desired degree of trimerization by adding a catalyst poison and/or by thermally deactivating the catalyst.
Finally, the present invention is directed to the use of these polyisocyanate mixtures, optionally in blocked form, as an isocyanate component in two-component coating compositions.
DETAILED DESCRIPTION OF THE INDENTION
In accordance with the present invention the term "monoisocyanurate" means a polyisocyanate containing one 2o isocyanurate group and formed from three diisocyanate molecules, and the term "polyisocyanurate" means a polyisocyanate containing more than one isocyanurate group.
The term "monoallophanate" means a polyisocyanate containing one allophanate group and formed from two diisocyanate 25 molecules and 1 monoalcohol molecule, and the term "polyallophanate" means a polyisocyanate containing more than one allophanat~e group. The term "(cyclo)aliphatically bound isocyanate groups" means aliphatically and/or cyclo-aliphatically 'bound isocyanate groups.
Examples of suitable diisocyanates to be used as 3o starting materials for preparing the polyisocyanates according to the present invention are organic diisocyanates represented by the formula R(NCO)2 Mo3649 wherein R represents an organic group obtained by removing the isocyanate groups from an organic diisocyanate having (cyclo)aliphatically bound isocyanate groups and a molecular weight of 112 to 1,000, preferably 140 to 400. Preferred diisocyanates for the process according to the invention are those represented by the above formula wherein R represents a divalent aliphatic hydrocarbon group having from 4 to 18 carbon atoms, a divalent cyc.loaliphatic hydrocarbon group having from 5 to 15 carbon atoms or a divalent araliphatic hydrocarbon group having from 7 to 15 carbon atoms. Examples of the to organic diisocyanates which are particularly suitable for the process include 1,4-tetramethylene diisocyanate, 1,6-hexa-methylene diisocyanate, 2,2,4-trimethyl-l, 6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis-(4-iso-cyanatocyclohexyl)-methane, 1,3- and 1,4-bis(isocyanato-methyl)-cyclohexane, bis-(4-isocyanato-3-methyl-cyclohexyl)-methane, a,a,a',a'-tetramethyl-1,3- and/or -1,4-xylylene 2o diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, and 2,4- and/or 2,6-hexahydrotoluylene diisocyanate. Mixtures of diisocyanates may also be used.
Preferred diisocyanates are 1,6-hexamethylene diisocyanate, isophorone diisocyanate and bis-(4-isocyanatocyclohexyl)-methane. 1,6-hexamethylene diisocyanate (HDI) is especially preferred.
It is also possible in accordance with the present invention to use blends of the previously mentioned diisocyanates with monoisocyanates or polyisocyanates having 3 or more isocyanate groups, provided that the isocyanate groups 3o are (cyclo)aliphatically bound.
In accordance with the present invention it is preferred to treat the starting diisocyanates by bubbling an inert gas such as nitrogen through the starting diisocyanate in Mo3649 order to reduce thf: content of carbon dioxide. This process is discussed in German Offenlegungsschrift 3,806,276.
Trimerization catalysts which are suitable for the process according to the invention include those previously known such as alkali phenolates of the type described in GB-PS 1,391,066 or GB-PS 1,386,399; aziridine derivatives in combination with tertiary amines of the type described in U.S. Patent 3,919,218; quaternary ammonium carboxylates of the type described in U.S. F'atenia 4,454,317 and 4,801,663; quaternary ammonium phenolates with a zwitterionic structure of the type described in U.S. Patent 4,335,219; ammonium phosphonates and phosphates of the type described in U.S. Patent 4,499,253; alkali carboxylates of the type described in DE-OS 3,2'19,608; basic alkali metal salts complexed with acyclic organic cornpounds as described in U.S. Patent 4,379,905 such as potassium acetate complexed with a polyethylene glycol which contains an average of 5 to 8 ethylene oxide units; basic alkali metal salts complexed with crown ethers <~s described in U.S. Patent 4,487,928; aminosilyl group-containing compo~~nds such as aminosilanes, diaminosilanes, silylureas and silazanes as described in U.S. Patent 4,412,073; and mixtures of alkali metal fluoridE~s and quaternary ammonium or phosphonium salts as described in U.S. Patent 4,992,548. The trimerization catalysts should also catalyze the formation of allophanate groups from urethane groups.
Phosphines, such as those described in DE-OS 1,935,763, are not suitable for preparing thE: products of the present invention. The phosphines, in addition to promoting the trimerization reaction, also promote the dimerization of diisocyanates. Also not suitable are Mannich bases, for examplE~, those based on nonylphenol, formaldehyde and dimethylamine of the type described in U.S. Patents 3,996,223 and 4,115,373.
f;, -7- ~0~"~3'~3 Particularly suitable as catalysts for the process according to the invention are quaternary ammonium hydroxides corresponding to the formula R3(+) R2 N - R4 OH ( ) 1o as described in U.S. Patent 4,324,879 and German Offenlegungsschriften 2,806,731 and 2,901,479. Preferred quaternary ammonium hydroxides are those wherein the radicals R1 to R4 represent identical or different alkyl groups having from 1 to 20, preferably from 1 to 4 carbon atoms, which may optionally be substituted by hydroxyl groups. Two of the radicals R1 to R4 may form a heterocyclic ring having from 3 to 5 carbon atoms together with the nitrogen atom and optionally with a further nitrogen or oxygen atom. Also the radicals R1 to R3 in each case may represent ethylene radicals which form a 2o bicyclic triethylene diamine structure together with the quaternary nitrogen atom and a further tertiary nitrogen atom, provided that the radical R4 then represents a hydroxyalkyl group having from 2 to 4 carbon atoms in which the hydroxyl group is preferably arranged in a 2-position to the quaternary nitrogen atom. The hydroxyl-substituted radical or the hydroxy l-substituted radicals may also contain other substituents, particularly C1 to C4-alkoxy substituents.
The production of these quaternary ammonium catalysts takes place in known manner by reacting a tertiary amine with an alkylene oxide in an aqueous-alcoholic medium (c.f. US-P

3,995,997, col. 2, lines 19-44). Examples of suitable tertiary amines include trimethylamine, tributylamine, 2-dimethylamino-ethanol, triethanolamine, dodecyldimethylamine, N,N-dimethyl-Mo3649 -$- ~~9'~3'~3 cyclohexylamine, N-methylpyrrolidine, N-methylmorpholine and 1,4-diazabicyc:lo-[x'.,2,2]-octane. Examples of suitable alkylene oxides include ethylene oxide, propylene oxide, 1,2-butylene oxide, styrene oxide and methoxy, ethoxy or phenoxy propylene oxide. The most preferred catalysts from this group are N,N,N-trimethyl-N-(2-~hydroxyethyl)-ammonium hydroxide and N,N,N-trimethYl-N-(2-~hydroxypropyl)ammonium hydroxide. Another most preferred catalyst is N,N,N-trimethyl-N-benzyl-ammonium hydroxide.
1o The trimerization of the starting diisocyanates may be carried out in the absence or in the presence of solvents which are inert to isocyanate groups. Depending on the area of application of the products according to the invention, low to medium-boiling solvents or high-boiling solvents can be used.
15 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 diisopropylether; and alkanes such as cyclohexane, petroleum 2o ether or ligroin.
The trimerization catalysts are generally used in quantities of about 0.0005 to 5% by weight, preferably about 0.002 to 2% by weight, based on the diisocyanate used. If, for example, a preferred catalyst such as N,N,N-trimethyl-N-25 (2-hydroxypropyl)-ammonium hydroxide is used, then quantities of about 0.0005 to 1% by weight, preferably about 0.001 to 0.02 by weight, based on starting diisocyanate, are generally sufficient. The catalysts may be used in pure form or in solution. The previously named solvents which are inert to isocyanate groups are suitable as solvents, depending on the 3o type of catalysts. Dimethyl formamide or dimethyl sulphoxide may also be used as solvents for the catalysts.
The simultaneous use of co-catalysts is possible in the process according to the invention, but not necessary. All substances from which a polymerizing effect on isocyanates is Mo3649 known are suitable as co-catalysts such as those described in DE-OS
2,806,731. The co-catalysts are optionally used in a lesser amount on a weight basis in relation to the amount of the trimerization catalyst.
In accordance with the present invention urethane groups and subsequently allophanai:e groups are incorporated into the polyiso-cyanates by the us;e of an aromatic monoalcohol containing 6 to 9 carbon atoms. The molar ratio of monoalcohol to diisocyanate is about 0.01 to 0.5, preferably about O.G4 to 0.2. Examples of suitable monoalcohols include phenol, them cresols, the xylenols and the trimethylphenols.
It is also po:,sible in accordance with the present invention to use mixtures of the previously described aromatic monoalcohols with up to 70% by weight, based on the total weight of the alcohol mixture, of monoalcohols having a molecular weight of less than 2500, preferably monoalcohols coni:aininq 1 to 5 carbon atoms, as disclosed in U.S. Patent 5,124,427.
The reaction temperature for isocyanurate and allophanate formation in accordance with the present invention is about 10 to 160°C, preferably about 50 to 150°C and more preferably about 90 to 120°C.
The process according to the invention may take place either batchwise or continuously, for example, as described below. The starting diisocyanate is introduced with the exclusion of moisture and optionally with an inert gas into a suitable stirred vessel or tube and optionally mixed with a solvent which is inert to isocyanate groups such as toluene, butyl acetate, diisopropylether or cyclohexane. The previously described monoalcohol may he introduced into the reaction vessel in accordance with several embodiments. The monoalcohol may be prereacted with the diisocyanate to form urethane groups ~f:

-1°- 2 Q ~'~ 3'~ ~
prior to introducing the diisocyanate into the reaction vessel;
the monoalcohol may be mixed with the diisocyanate and introduced into the reaction vessel; the monoalcohol may be separately added to the reaction vessel either before or after, preferably after, t:he diisocyanate is added; or the catalyst may be dissolved in the monoalcohol prior to introducing the solution into the reaction vessel.
The polyisocyanates according to the invention may also be prepared by blending polyisocyanates containing to isocyanurate groups with monoallophonates.
At a temperature of about 60°C and in the presence of the required catalyst. or catalyst solution the trimerization begins and is indicated by an exothermic reaction. As the reaction temperature increases the conversion rate of urethane groups to allophanate groups increases faster than the formation of isocyanurate groups. At temperatures above 85°C
when the desired degree of trimerization is achieved, the urethane groups are generally completely converted to allophanate groups and the product, after removal of unreacted 2o monomer and any solvent present has a low viscosity relative to the yield which is obtained. At temperatures below 85°C at the same degree of isocyanate group consumption, some urethane groups remain unconverted and the product has a slightly higher, but still low viscosity relative to the yield which is obtained. The progress of the reaction is followed by determining the NCO content by a suitable method such as titration, refractive index or IR analysis. Thus, the reaction may be terminated at the desired degree of trimerization. The termination of the trimerization reaction can take place, for example, at an NCO content of about 15% to 47%, preferably 3o about 20 to 40~%.
The termination of the trimerization reaction can take place, for example, by the addition of a catalyst-poison of the type named b,y way of example in the above-mentioned literature references. For example, when using basic catalysts Mo3649 -II- 2 0 0'~ 3'~ 3 the reaction is terminated by the addition of a quantity, which is at least equivalent to the catalyst quantity, of an acid chloride such as benzoyl chloride. When using heat-labile catalysts, for example, the previously described quaternary ammonium hydroxides, poisoning of the catalyst by the addition of a catalyst-poison may be dispensed with, since these catalysts decompose in the course of the reaction. When using such catalysts, the catalyst quantity and the reaction temperature are preferably selected such that the catalyst to which continuously decomposes is totally decomposed when the desired degree of trimerization is reached. The quantity of catalyst or reaction temperature which is necessary to achieve this decomposition can be determined by a preliminary experiment. It is .also possible initially to use a lesser quantity of a heat sensitive catalyst than is necessary to achieve the desired degree of trimerization and to subsequently catalyze the reaction by a further incremental addition of catalyst, whereby the quantity of catalyst added later is calculated such that when the desired degree of trimerization 2o is achieved, the total quantity of catalyst is spent. The use of suspended c;3talysts is also possible. These catalysts are removed after ;achieving the desired degree of trimerization by filtering the reaction mixture.
The working-up of the reaction mixture, optionally after previous separation of insoluble catalyst constituents, may take place in various ways depending upon how the reaction was conducted ~~nd the area of application for the isocyanates.
It is possible to use the polyisocyanates according to the invention which have been produced in solution directly as a lacquer raw maiterial, without a purification stage, if it is 3o not necessary i~o reduce the free monomer content. Any solvent used during tr~imerization reaction and any unreacted monomer present in the polyisocyanate product can also be removed by distillation in known manner. The product generally contains a total of less i:han .?, preferably less than 1% of free Mo3649 (unreacted) monomeric diisocyanates. The products according to the invention have a viscosity of less than 10,000 mPa.s, preferably less than 2000 mPa.s and more preferably less than 1300 mPa.s.
The products according to the present invention are polyisocyanates containing isocyanurate groups and allophanate groups. The products may also contain residual urethane groups which have not been converted to allophanate groups depending upon the temperature maintained during the reaction and the to degree of isocyanate group consumption. The ratio of monoisocyanurate groups to monoallophanate groups present in the polyisocyanates according to the invention is about 10:1 to 1:5, preferably about 5:1 to 1:2.
The products according to the invention are valuable 15 starting materials for the production of polyisocyanate polyaddition products by reaction with compounds containing at least two isocyanate reactive groups. Preferred products are most preferably one or two-component polyurethane coatings.
Preferred reaction partners for the products 2o according to the invention, which may optionally be present in blocked form, are the polyhydroxy polyesters, polyhydroxy polyethers, polyhydroxy polyacrylates and optionally low molecular weight, polyhydric alcohols known from polyurethane coatings technology. Polyamines, particularly in blocked form, 25 for example as polyketimines or oxazolidines are also suitable reaction partners for the products according to the invention.
The amounts of the polyisocyanates according to the invention and their reaction partners are selected to provide equivalent ratio of isocyanate groups (whether present in blocked or unblocked form) to isocyanate-reactive groups of about 0.8 to 30 3, preferably about 0.9 to 1.1.
To accelerate hardening, the coating compositions may contain known polyurethane catalysts, e.g., tertiary amines such as trieth,ylamine, pyridine, methyl pyridine, benzyl dimethylamine, N,N-dimethylamino cyclohexane, N-methyl-Mo3649 -13- ~ 0 9'~ 3'~ 3 piperidine, pentamethyl diethylene triamine, 1,4-diaza-bicyclo[2,2,2]-octane and N,N'-dimethyl piperazine; or metal salts such as iron(III)-chloride, zinc chloride, zinc-2-ethyl caproate, tin(II)-ethyl caproate, dibutyltin(IU)-dilaurate and molybdenum glycolate.
The products according to the invention are also valuable starting materials for two-component polyurethane stoving enamels in which the isocyanate groups are used in a form blocked by known blocking agents. The blocking reaction a o is carried out in known manner by reacting the isocyanate groups with suitable blocking agents, preferably at an elevated temperature (e.g. about 40 to 160°C), and optionally in the presence of a suitable catalyst, for example, the previously described tertiary amines or metal salts.
Suitable blocking agents include monophenols such as phenol, the cresols, the trimethylphenols and the tert. butyl phenols; tertiary alcohols such as tert. butanol, tert. amyl alcohol and dimethylphenyl carbinol; compounds which easily form enols such as acetoacetic ester, acetyl acetone and 2o malonic acid derivatives, e.g. malonic acid diethylester;
secondary aromatic amines such as N-methyl aniline, the N-methyl tolui~dine, N-phenyl toluidine and N-phenyl xylidine;
imides such as succinimide; lactams such as E-caprolactam and b-valerolactam; oximes such as butanone oxime and cyclohexanone oxime mercaptans such as methyl mercaptan, ethyl mercaptan, butyl mercaptan, 2-mercaptobenzthiazole, a-naphthyl mercaptan and dodecyl mercaptan; and triazoles such as 1H-1,2,4-triazole.
The bloating compositions may also contain other additives such as pigments, dyes, fillers, levelling agents and solvents. The coating compositions may be applied to the 3o substrate to bye coated in solution or from the melt by conventional methods such as painting, rolling, pouring or spraying.
The bloating compositions containing the polyisocyanates according to the invention provide coatings Mo3649 -14- ~p9~3'~3 which adhere surprisingly well to a metallic base, and are particularly light-fast, color-stable in the presence of heat and very resistant to abrasion. Furthermore, they are characterized by high hardness, elasticity, very good resistance to chemicals, high gloss, excellent weather resistance and good pigmenting qualities. The polyisocyanates according to the invention also possess good compatibility with highly branched polyester resins.
The invention is further illustrated, but is not to intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES

To a 500 ml 3-neck flask equipped with a gas bubbler, 15 mechanical stirrer, thermometer and condenser were added 334 grams of hexamethylene diisocyanate and 18.7 grams of phenol.
Dry nitrogen was bubbled through the stirred reaction mixture while it was heated at 60°C. When the urethane reaction was complete (about 1 hour), the temperature was raised to 90°C.
2o To the reaction mixture at 90°C were added 0.24 grams of a 4.4%
solution of trimeth,ylbenzylammonium hydroxide dissolved in 1-butanol. The reaction temperature was maintained at 90 to 100°C. When tike reaction mixture reached NCO contents of 40.1%
and 37.0%, an .additional 0.12 grams of the catalyst solution 25 was added. When the reaction mixture reached an NCO content of 34.8%, the rea~~tion was stopped by adding 0.4 grams of di-(2-ethylhex;yl) phosphate. The excess monomer was removed by thin film evap~~ration to provide an almost colorless, clear liquid having .a viscosity of 1210 mPa.s (25°C), an NCO content of 18.8%, and .a free monomer (HDI) content of 0.1%. The yield 3o was 45.2%. Th~a yield was calculated by determining the percentage of Free hexamethylene diisocyanate in the product prior to dist illation.
Mo3649 -15_ 20~~3'~3 Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
to Mo3649

Claims

1. A process for the production of a polyisocyanate mixture which comprises a) catalytically trimerizing and allophanatizing a portion of the isocyanate groups of an organic diisocyanate having (cyclo)-aliphatically bound isocyanate groups in the presence of 0.01 to 0.5 moles, per mole of said organic diisocyanate, of an aromatic monoalcohol containing 6 to 9 carbon atoms at a temperature which is sufficient to provide a molar ratio of monoisocyanurates to monoallophanates of 10:1 to 1:5, b) terminating the trimerization and allophanatization reaction at an NCO content of 10 to 47% by weight by adding a catalyst poison and/or by thermally deactivating the catalyst and c) removing unreacted organic diisocyanate to obtain a product which contains less than 2% of unreacted organic diiso-cyanate and has a viscosity of less than 10,000 mPa.s.

2. The process of Claim 1 wherein said organic diisocyanate comprises 1,6-hexamethylene diisocyanate.

3. The process of Claim 1 wherein said aromatic monoalcohol comprises phenol.

4. The process of Claim 2 wherein said aromatic monoalcohol comprises phenol.

5. A process for the production of a polyisocyanate mixture which comprises a) catalytically trimerizing and allophanatizing a portion of the isocyanate groups of an organic diisocyanate having (cyclo)aliphatically bound isocyanate groups in the presence of 0.04 to 0.2 moles, per mole of said organic diisocyanate, of an aromatic monoalcohol containing 6 to 9 carbon atoms at a temperature which is sufficient to provide a molar ratio of monoisocyanurates to monoallophanates of 10:1 to 1:5, b) terminating the trimerization and allophanatization reaction at an NCO content of 10 to 47% by weight by adding a catalyst poison and/or by thermally deactivating the catalyst and c) removing unreacted organic diisocyanate to obtain a product which contains less than 2% of unreacted organic diiso-cyanate and has a viscosity of less than 10,000 mPa.s.

6. The process of Claim 5 wherein said organic diisocyanate comprises 1,6-hexamethylene diisocyanate.

7. The process of Claim 5 wherein said aromatic monoalcohol comprises phenol.

8. The process of Claim 6 wherein said aromatic monoalcohol comprises phenol.

9. A polyisocyanate mixture having an NCO content of 10 to 47% by weight and a viscosity of less than 10,000 mPa.s and containing isocyanurate and allophanate groups in a molar ratio of monoisocyan-urates to monoallophanates of 10:1 to 1:5, wherein said allophanate groups are formed from urethane groups which comprise the reaction product of an organic diisocyanate having (cyclo)aliphatic bound isocyanate groups and an aromatic monoalcohol containing 6 to 9 carbon atoms.

10. The polyisocyanate mixture of Claim 9 wherein said organic diisocyanate comprises 1,6-hexamethylene diisocyanate.

11. The polyisocyanate mixture of Claim 9 wherein said aromatic monoalcohol comprises phenol.

12. The polyisocyanate mixture of Claim 10 wherein said aromatic monoalcohol comprises phenol.

13. The polyisocyanate mixture of Claim 9 which has a viscosity of less than 2000 mPa.s.

14. The polyisocyanate mixture of Claim 9 which has a viscosity of less than 1300 mPa.s.

15. A two-component coating composition comprising the polyisocyanate of Claim 9 and a compound containing isocyanate-reactive groups.