CH627739A5 - Process for preparing polyisocyanates that contain biuret groups - Google Patents

Description

The present invention relates to an improved process for the preparation of polyisocyanates containing biuret groups by direct reaction of polyamines with polyisocyanates.

It is known, for example, polyisocyanates containing biuret groups from diisocyanates and water (DT-PS 1 101 394), hydrogen sulfide (DT-PS 1 165 580), formic acid (DT-PS 1 174 760) or tertiary alcohols (DT-PS 1 543 178). In this case, from some of the isocyanate groups of the diisocyanates used, amino groups initially form, which react further with excess diisocyanate via the corresponding urea diisocyanates to form the biuret groups-containing polyisocyanates. These prior art methods have a number of disadvantages. In the heterogeneous reaction of diisocyanates with water, there is a risk of the formation of insoluble polyureas, which are difficult to separate. Furthermore, gaseous by-products such as carbon dioxide, carbon monoxide, carbon sulfoxide or olefins are always formed in the aforementioned prior art processes. Finally, a particular disadvantage is the fact that, in these prior art processes, part of the isocyanate groups of the diisocyanate used as the starting material must first be destroyed with the formation of amines. There was therefore no lack of attempts to produce the polyisocyanates containing biuret groups by directly reacting polyamines with polyisocyanates without splitting off volatile by-products and without destroying isocyanate groups with amine formation. Because of the high reactivity of the amino groups with the isocyanate groups, however, these attempts encountered considerable practical difficulties, since the formation of insoluble polyureas and crosslinked products is very high. Only processes that made use of very special starting materials were therefore of some success. According to DT-PS 1 215 365, higher molecular weight diaminopolyethers must be used as the diamine component in order to eliminate the formation of the poorly soluble by-products mentioned. It goes without saying that the detour via the diaminopolyethers to be prepared beforehand using a complex process cannot be a technically fully satisfactory solution to the problem. The process of DT-OS 1 963 190 is in turn restricted to the use of diprimeric aromatic diamines with a reactivity reduced by steric or electronic effects.

The process of DT-OS 2 261 065 also does not yet provide a technically viable route for the production of polyisocyanates containing biuret groups by direct reaction of organic polyisocyanates with simple aliphatic and / or cycloaliphatic polyamines.

Thus, according to Example 16 of this publication, in the preparation of polyisocyanates based on hexamethylene diisocyanate and hexamethylene diamine which contain biuret groups, the reaction mixture has to be reheated to 180 ° C. for 12 hours in order to complete the reaction. This long post-heating at high temperature is not only uneconomical, but also leads to discoloration of the reaction product, especially under large-scale production conditions, so that its use in lightfast paints is subject to strict limits. As a reworking of Example 16 of DT-OS 2 261 065 also showed, it is not possible to obtain a biuret polyisocyanate free of monomeric starting diisocyanate which is completely free of insoluble gel-like by-products according to the procedure described therein.

As has now surprisingly been found, the direct reaction of simple aliphatic and / or cycloaliphatic polyamines with organic polyisocyanates to the corresponding biuret group-containing polyisocyanates succeeds if the biuret group-free polyisocyanate used as the starting material and the polyamine are reacted in vapor form. The polyisocyanate which is free of biuret groups is preferably introduced and the vaporous polyamine is introduced into it. In this case, the reaction mixture remains a bare solution even in the case of the reaction of hexamethylene diisocyanate with hexamethylene diamine and is completely reacted after the introduction of the diamine has ended, so that the disadvantageous reheating is not necessary.

The present invention thus relates to a process for the preparation of polyisocyanates containing biuret groups by reacting 2 aliphatic and / or cycloaliphatically bonded primary amino groups containing organic polyamines with biuret group-free organic polyisocyanates in a molar NH2 / NCO ratio of 1: 5 to 1 : 100, which is characterized in that the polyamines are reacted in vapor form with the polyisocyanates heated to a temperature of 100 ° C to 250 ° C.

Organic 2 aliphatic or cycloaliphatic bound primary amino groups containing polyamines are used for the process according to the invention. Examples of this are diprimary diamines of the formula R (NH2) 2, in which R represents an aliphatic hydrocarbon radical having 2 to 12 carbon atoms, a cycloaliphatic hydrocarbon radical having 4 to 17 carbon atoms or an araliphatic hydrocarbon radical having 8 to 10 carbon atoms, such as e.g. Ethylenediamine, 1,2- and 1,3-propylenediamine, 1,4-diaminobutane, 2,2-dimethylpropandiamine- (1,3), 1,6-diaminohexane, 2,5-dimethylhexane-diamine- (2, 5), 2,2,4-trimethylhexanediamine- (1,6), 1,8-diamino-nooctane, 1,10-diaminodecane, 1,11-undecanediamine, 1,12-dodecanediamine, 1-methyl-4- ( aminoisopropyl) -cyclohexyl-amine-1,3-aminomethyl-3,5,5-trimethylcyclohexylamine- (l), l, 2-bis- (aminomethyl) -cyclobutane, p-xylylene-diamine, 1,4-bis-- (2-aminoethyl) benzene, 1,2- and 1,4-diaminocyclohexane, 1,2- and 1,4-, 1,5- and 1,8-diaminodecalin, l-methyl-4-aminosopropylcyclohexylamine- 1, 4,4'-diamino-dicyclohexyl, 4,4'-diamino-dicyclohexylmethane, 2,2 '- (bis-4-aminocyclo-hexyl) propane, 3,3'-dimethiyl-4,4' -diamino-dicyclohexyl-

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methane, 1,2-bis (4-aminocyclohexyl) ethane and 3,3'-, 5,5 '- tetramethyl-bis (4-aminocyclohexyl) methane and propane.

Polyamines which are furthermore suitable for the process according to the invention are, in particular, bis (aminoalkyl) amines preferably having a total of 4 to 12 carbon atoms, such as e.g. Bis (2-aminoethyl) amine, bis (3-aminopropyl) amine, bis (4-aminobutyl) amine, bis (6-aminohexyl) amine, and isomer mixtures of dipropylenetriamine and dibutylene-triamine.

Tetramethylene diamine, hexamethylene diamine or 1,2-bis (aminomethyl) cyclobutane are preferably used. Hexamethylene diamine is particularly preferred.

Polyisocyanates suitable for the process according to the invention are in particular diisocyanates of the formula Q (NCO) 2, in which Q is an aromatic hydrocarbon radical having 6 to 15 carbon atoms, an aliphatic hydrocarbon radical having 8 carbon atoms in particular, an aliphatic hydrocarbon radical having 4 to 12 carbon atoms or a cycloaliphatic hydrocarbon radical with 4 to 15 carbon atoms. Examples of this are tolylene-2,4- and 2,6-diisocyanate and their isomer mixtures, 4,4'- and 2,4'-diphenylmethane diisocyanate, xylylene diisocyanate. Aliphatic or cycloaliphatic diisocyanates such as 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 2,4,4-trimethylhexane-1,6-diisocyanate, 1,11-diisocyanatoundecane, 3-isocyanato-methyl- are particularly suitable. 3,5,5-trimethylcyclohexyl isocyanate-1, 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexyl methane diisocyanate or 1,2-bis (isocyanatomethyl) cyclobutane. Hexamethylene diisocyanate is particularly preferably used.

In the process according to the invention, particularly light-colored process products can be obtained if the starting diisocyanate is subjected to a heat pretreatment at 120-195 ° C., preferably 160-180 ° C. for several hours (approx. 6-10 hours) and then distilled.

The process according to the invention is preferably carried out in such a way that the diisocyanate is introduced in an excess of about 5 to 100, preferably 7 to 25, NCO groups onto a primary amino group at elevated temperature with vigorous stirring and the polyamine, if appropriate under reduced pressure and possibly together with an inert gas stream. In the case of reactions in which the polyamine used has a lower boiling point than the diisocyanate, a simple inlet tube which is immersed in the diisocyanate is usually sufficient to introduce the polyamine vapor. A suitable evaporator for the polyamine is generally connected to the inlet pipe. A pressure should then be maintained in the reactor at which the boiling point of the polyamine is about 10 to 80 ° C below the temperature of the initially introduced diisocyanate, since otherwise the polyamine partially condenses in the inlet tube and in liquid form with the diisocyanate in It comes into contact, which leads to the formation of solid polyureas and clogging of the inlet pipe. Is the liquid column above the exit point of the polyamine vapor - especially in the case of larger batches - so high that the hydrostatic pressure increases the boiling point of the polyamine to such an extent that it comes close to the temperature of the diisocyanate present one advantageously introduces a hollow stirrer (gassing stirrer) to introduce the polyamine vapor, which exerts an additional suction and ensures good distribution of the polyamine vapor in the diisocyanate.

Is the boiling point of the polyamine used e.g.

Above that of the diisocyanate, the inlet connection for the polyamine vapor must be heatable to temperatures which are above that of the diisocyanate submitted. The inlet pipe is then expediently heat-insulated to the outside, so that excessive heat exchange with the diisocyanate is avoided.

When carrying out the process on an industrial scale, in addition to the hollow stirrer already mentioned, an optionally mechanically closable ring nozzle can be used instead of an inlet tube.

The rate of introduction of the polyamide vapor can be controlled in two ways, for example. In the first option, the total amount of polyamine is brought into the evaporator and the distillation rate is regulated by the supply of heat; in the second case, the polyamine is metered into the superheated evaporator.

It goes without saying that the method can also be carried out continuously. For this purpose e.g. an amount of diisocyanate suitable for metering the polyamine is fed into the reactor and the corresponding proportion of the reaction mixture is continuously removed, if appropriate by an overflow.

The temperature of the initially introduced diisocyanate is preferably selected so that the a, w-diisocyanato, bis- or tris-urea compounds primarily formed from polyamine and diisocyanate can react further rapidly with addition of NCO groups to the urea groups to form biuret compounds, so that there is no precipitation of the poorly soluble and mostly higher melting urea compounds. Experience has shown that temperatures above 100 ° C, better above 120 ° C, are necessary. The temperature is, as already mentioned, restricted by the tendency to discolouration and side reactions (max. 250 ° C). The temperature range from 130 ° C. to 200 ° C. is preferred. The range from 140 ° C. to 180 ° C. is particularly preferred.

According to a particular embodiment of the method according to the invention, which allows the production of particularly low-viscosity biuret polyisocyanates,

the vaporous polyamine is introduced into the initially introduced diisocyanate in a mixture with a gas which is inert to the reactants and the end products under the reaction conditions. A suitable carrier gas is nitrogen, for example. In this embodiment, the volume ratio / carrier gas: vaporous polyamine is generally between 2: 1 and 100: 1, preferably 40: 1 to 80: 1.

It goes without saying that the vaporous polyamine can be produced not only by evaporating a liquid polyamine, but also by sublimation of a solid polyamine or simply by passing an intensive inert gas stream through a liquid polyamine, in the latter case a mixture of vaporous polyamine and Polyamine aerosol is obtained.

When the process according to the invention is carried out under the specified temperature conditions, the reaction to the polyisocyanate having biuret groups takes place spontaneously, so that post-heating after the addition of polyamine has largely been dispensed with. At the same time, the reaction mixture is equilibrated to a complex mixture of mono-, bis-, trisbiure-ten and higher biurets, the molar distribution of which ultimately only depends on the selected NCO / NH2 ratio, due to the constant cleavage and new formation of biuret groups. As a result of these regrouping reactions, a large proportion of the polyamine used, which is dependent on the selected NCO excess, is converted into the corresponding polyisocyanate. A polyisocyanate mixture containing biuret groups, which was prepared by the process according to the invention, for example from hexamethylene diisocyanate and 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, contains

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Removal of the unreacted excess of hexamethylene diisocyanate has a content of the 3,3'-dimethyl-4,4'-diisocyanate dicyclohexylmethane corresponding to the starting diamine, which is dependent on the NCO / NH2 ratio.

If you use the biuretization of e.g. 1,6-diisocyanato-hexane, for example 1,4-diaminocyclohexane, 1,4-diisocyanatocyclohexane is contained in the reaction mixture.

Now exempt e.g. the biuret polyisocyanate from the excess diisocyanate, a distillate is obtained as a diisocyanate mixture which has to be reused in the technical process. A distillative separation is required for this. If the mixture is used as such, a longer start-up period (in the case of continuous production) or several batches (in the case of a batchwise procedure) are required until the product composition is constant. For these reasons, combinations of diisocyanates and diamines of the same constitution are preferred, or amines which give polyisocyanates with very low vapor pressure after conversion are preferably used for the biuretization of diisocyanates. Such amines are e.g. the bis (aminoalkyl) amines already mentioned, since these equilibrium reactions, as the most volatile polyisocyanate component, can give rise to these polyamines only as the triisocyanates corresponding to the polyamine, which are, for example, relatively volatile compared to hexamethylene diisocyanate and have a urea group.

The biuret polyisocyanates produced by the process according to the invention, in particular from aliphatic starting compounds, are valuable raw materials for the production of high-quality, weatherproof, light-stable paints. For use in this sector, the reaction mixtures for obtaining a polyisocyanate with low vapor pressure are usually freed from the excess of diisocyanate. This can be done by extraction or by distillation. In the second case, thin-film evaporators are expediently used.

example 1

4620 g (27.5 mol) of 1,6-diisocyanatohexane are placed at 160 ° C. with stirring in a 6 1 four-necked flask with a reflux condenser, contact thermometer and stirrer. A glass tube is placed on the remaining flask neck and immersed approximately 8 cm in the liquid. At the lower end it is bent sideways in the direction of rotation of the stirrer and extended to a tip of about 2 mm in diameter. At the upper end there is a ground sleeve into which the bridge of a 500 ml distillation apparatus opens. The bridge is heated to 200 ° C. The distillation apparatus is charged with 290 g (2.5 mol) of 1,6-diaminohexane at 60 ° C, in which a boiling capillary is immersed. A vacuum of 50 torr is now set via the reflux condenser of the four-necked flask. A weak stream of nitrogen is passed through the capillary. The distillation flask is then immersed in an oil bath at 180 ° C. The diamine begins to distill at an internal temperature of 125 to 135 ° C. The vapors overheated in the bridge are immediately absorbed in the diisocyanate. The immersion depth of the distillation flask in the oil bath regulates the distillation rate so that the reaction is completed in about 2 hours. The clear reaction mixture is subjected to thin-film distillation at 175 ° C. and 1 torr. 2150 g of a pale yellow biuret polyisocyanate with an NCO content of 22.3% and a viscosity of 12000 cP at 25 ° C. are obtained. The gel chromatographic analysis shows approximately the following composition:

1,6-diisocyanatohexane

Monobiuret

Bis-biuret

Tris-biuret

Tetra-biuret

Penta-biuret unidentified or higher molecular weight components

Example 2

15 In the same apparatus as in Example 1, 2856 g (17 mol) of 1,6-diisocyanatohexane are placed in a 41-flask at 180 ° C. and 232 g (2 mol) of 1,6-diaminohexane are evaporated at 80 torr within 60 minutes . The almost completely clear reaction mixture is freed of a few solid particles by pressure filtration and excess diisocyanate by thin-layer distillation. A viscous, pale yellow biuret polyisocyanate with an NCO content of 20.4% and a viscosity of 73400 cP at 25 ° C. is obtained.

25 Example 3

1288 g mol) of 1,6-diisocyanatohexane are placed in a 21-reaction flask at 160 ° C. and 50 torr. The distillation apparatus described in Example 1 is completely immersed in an oil bath at 220 ° C; the distillation bridge is also heated to 220 ° C. From a dropping funnel, 38.7 g of Q4 mol) of 1,6-diaminohexane at 80 ° C. are added dropwise to the distillation flask over the course of 30 minutes, where it passes into the gas form as a bath. After thin-film distillation of the clear reaction mixture, 305 g of a low-viscosity biuret polyisocyanate with an NCO content of 23.8% and a viscosity of 2240 cP / 25 ° C. are obtained.

Comparative Example I 408 g (11 mol) of 1,6-diisocyanatohexane are initially introduced at 70 ° C. in a nitrogen atmosphere. 116 g (1 mol) of 1,6-diaminohexane are added dropwise from a heated dropping funnel over the course of about 60 minutes with thorough stirring. A mushy reaction mixture is formed which is heated to 180 ° C. After stirring at this temperature for twelve hours, the brown-colored reaction mixture still contains considerable amounts of gel-like solids which are difficult to separate by filtration.

see example 4

1512 g (9 mol) of 1,6-diisocyanatohexane at 12 mm are placed in a 21 four-necked flask and heated to weak reflux (at 135 ° C.). 127.5 g (0.75 mol) of 3-aminomethyl-3,5,5-trimethyl-cyclohexylamine-1 (from the distillation apparatus described in Example 1 (oil bath and bridge heated to 55 220 ° C.) "Isophoronediamine") in vapor form through the inlet pipe into the diisocyanate, where it immediately reacts to a clear reaction product. After thin-film distillation 60, 650 g of a light-colored biuret polyisocyanate with an NCO content of 23.4% and a viscosity of 18450 cP / 25 ° C. are obtained. According to the gas chromatogram, the distillate (990 g) contains 0.69% by weight of 3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl-isocyanate-1.

65 Comparative Example II

1512 g (9 mol) of 1,6-diisocyanatohexane are placed at 25 ° C. 127.5 g (0.75 mol) of 3-aminomethyl-3,5,5-trimethyl-cyclohexylamine-1 are added dropwise in the course of 20 minutes

0.3% by weight 38.5% by weight 19.5% by weight 12.0% by weight 7.8% by weight 5.0% by weight 16.9% by weight

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a. A mushy, easily stirrable reaction mixture is formed. Now the resulting polyureas are heated for the purpose of further reaction. At around 140 ° C, the solid components clump together to form a rubber-like chunk, so that the batch can no longer be stirred. The mixture is heated to 170 ° C. for a further 8 hours without stirring. Then the reaction mixture is reasonably homogeneous. During this time the reaction mixture turns strongly yellow.

Example 5

1680 g (10 mol) of 1,6-diisocyanatohexane are placed at 160 ° C. under a slight vacuum (600-650 torr). 74 g (1 mol) of 1,2-propylenediamine are introduced in vapor form together with a gentle stream of nitrogen over 90 minutes through a gassing stirrer with stirring at a temperature of 200.degree. A clear reaction product is obtained which is subjected to thin-film distillation.

Yield: 830 g of a pale yellow biuret polyisocyanate with an NCO content of 21.7% and a viscosity of 4800 cP / 25 ° C.

Example 6

1512 g (9 mol) of 1,6-diisocyanatohexane are placed at 160 ° C and 80 torr. As described in Example 3, 43 g (0.377 mol) of 1,4-diaminocyclohexane are then introduced in vapor form over the course of 30 minutes. The crude product is freed of very little solid particles by filtration and subjected to thin-film distillation. This gives 380 g of a thin, almost colorless biuret polyisocyanate with an NCO content of 24.3% and a viscosity of 2400 cP / 25 ° C.

Example 7

1512 g (9 mol) of 1,6-diisocyanatohexane are placed at 140 ° C. and 50 torr. With stirring, 158 g (1 mol) of 2,2,4-trimethylhexanamine-1,6 are introduced through a heatable inlet tube as steam superheated to 200.degree. After the thin-layer treatment of the clear reaction mixture, 870 g of a pale yellow biuret polyisocyanate with an NCO content of 21.1% and a viscosity of 21700 cP are obtained.

Example 8

1554 g (7 mol) of 3-isocyanatomethyl-3,5,5-trimethyl-cyclo-hexyl isocyanate-1 are placed at 160 ° C. and 12 mm. As described in Example 1, 170 g (1 mol) of 3-aminomethyl-3,5,5-trimethylcyclo-hexylamine-1 are introduced in the course of 2 hours as steam superheated to 200.degree. The clear biuret polyisocyanate solution has an NCO content of 27.6% and a viscosity of 7300 cP / 25 ° C.

Example 9

1512 g (9 mol) of 1,6-diisocyanatohexane are placed at 160 ° C and 50 Torr. Analogously to Example 1, 61.8 g (0.6 mol) of bis (2-aminoethyl) amine are introduced in vapor form over the course of 40 minutes. After thin-film treatment of the clear reaction mixture, 620 g of a light yellow biuret polyisocyanate with an NCO content of 28.0% and a viscosity of 10300 cP / 25 ° C. are obtained.

Example 10

Analogously to Example 9, 1580 (9 mol) of 1,6-diisocyanatohexane and 984 g (0.75 mol) of di- (1,2-propylene) -triamine (mixture of isomers) after thin-layer treatment of the clear reaction mixture give 680 g of a light yellow Biuret polyisocyanate with an NCO content of 20.1% and one. Viscosity of 23000 cP / 25 ° C.

Example 11

From 2520 g (15 mol) of 1,6-diisocyanatohexane and 131 g (1 mol) of bis (3-aminopropyl) amine, analogous to Example 9, a pale yellow biuret polyisocyanate freed from excess diisocyanate with an NCO content of 22% and a viscosity of Obtained 12500 cP / 25 ° C.

In Examples 9, 10 and 11, the 1,6-diisocyanatohexane obtained as a distillate from thin-film distillation contains no further isocyanate component.

Example 12

1740 g (10 mol) of an isomer mixture of 80% 2,4- and 20% 2,6-tolylene diisocyanate are placed at 150 ° C and 80 Torr. Analogously to Example 7, 158 g (1 mol) of 2,2,4-trimethylhexanediamine-1,6 are introduced as steam superheated to 220 ° C. through a heatable tube. A clear yellow biuret-modified polyisocyanate solution with an NCO content of 35.7% and a viscosity of 200 cP / 25 ° C. is obtained.

Comparative Example III The following comparative example is carried out in 3 variants a), b) and c), with which it is to be shown that the preparation of polyisocyanates containing biuret groups according to the procedure of Example 16 of DT-OS 2 261 065 is a technically hardly usable method, since the disadvantageous side effects known from DT-PS 1 770 927 are also observed when working according to this example. In particular, in the case of larger batches, considerable difficulties arise because the formation of insoluble polyureas and crosslinked products is very high, which can be broken down again at temperatures around 200.degree. C., but as a result of the high thermal stress on the reaction mixture, the formation of undesirable and strongly colored ones By-products is favored.

Embodiment a)

(corresponding to Example 16 of DT-OS 2 261 065) To 168 parts (1 mol) of 1,6-hexamethylene diisocyanate, 14.5 parts (0.125 mol) are added at 70 ° with stirring in a nitrogen atmosphere at about 25 ° C. in 20 minutes C heated hexamethylenediamine. The spontaneous precipitation of completely insoluble, high molecular weight, mush-like a, w-di-isocyanatopolyureas starts immediately. A uniform dissolution of the polyureas cannot be observed. For extremely slow biuretization, the reaction mixture has to be stirred at 180 ° C for 12 hours, the solution becoming reddish yellow. The mixture (= yield approx. 182 parts by weight) consists of a reaction mixture containing powdery parts and gel particles, which contains approx. 20% by weight monomeric hexamethylene diisocyanate. The reaction mixture contains a total of 3.5 parts by weight of higher molecular weight components which can only be broken down very slowly at 200 ° C. When this solution is filtered, filters are blocked by gel particles. After isolation of the solution by centrifugation and subsequent removal of monomers by thin-layer distillation, a polyisocyanate mixture containing biuret groups is obtained which is reddish-yellow-brown. The product has an NCO content of 17.1% and a viscosity of 143000 cP / 25 ° C. It is unsuitable for the production of moisture-crosslinked, lightfast, high-gloss paint films.

Embodiment b)

The procedure is exactly the same as under a), but the 10-fold approach is carried out. The dropping time is 20 minutes. A uniform dissolution of the mushy poly urine

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No substances can be observed. Otherwise the procedure is as under a). The reddish-yellow-brown end product can no longer be filtered because of a significantly increased powdery and gel portion compared to experiment a) (approx. 45 parts by weight). In order to obtain a gel-free mixture, the reaction mixture must be centrifuged and then freed of the gel portion by decanting. After the monomer has been liberated by thin-layer distillation, the reaction product is colored deep brown.

% NCO: 16.9 ïj25oC:> 152000 cP 7) 75 = c = 29800 cP

Embodiment c)

The procedure is as under b), but the metering rate of the hexamethylenediamine is slowed down by a factor of 10. The hexamethylenediamine is added dropwise over the course of 200 minutes. Otherwise the procedure is the same as for a) and b). In the case of c), extremely long reaction times of at least 12 hours are required. The same filtration difficulties result as in experiment b). The final product cleaned by thin-film distillation is unsuitable for the production of lightfast, high-gloss two-component paints by reaction with hydroxyl polyesters. 7j75,, c = 29100 cP.

Example 13

This example describes the process variants a) and b) according to the invention, according to which superheated hexamethylenediamine vapors are heated in an upper tube (= to the immersion depth) to 190 ° C. in a hexamethylene diisocyanate heated to 165 ° C. (- 1008% by weight). Parts = 6 mol) are sucked in under a vacuum of approx. 60 torr as superheated steam (= approx. 190 ° C). To generate the superheated steam, 58 parts by weight of hexamethylenediamine (= 0.5 mol) are evaporated in a small flask at approx. 115-120 ° C (N2 capillary). The vapors are overheated to approx. 190 ° C in a 20 cm long tube which is heated to approx. 210 ° C. The reaction is carried out in a ground glass beaker with a well-cooled reflux condenser and vacuum connection.

The heatable inlet pipe has an immersion depth of approx. 6 cm. During the entire time of the hexamethylene diamine vapor metering, which is completed in about 90 minutes (= variant a), no formation of poorly soluble a, w-diisocyanatopolyureas can be observed in the reaction vessel. The a, w-diisocyanatoureas or a, ü) -diisocyanatopolyureas that are formed in extremely small concentrations are converted practically in statu nascendi at the selected temperature of 165 ° C. to biuret polyisocyanates with the course of equilibration reactions. The completely gel-free reaction mixture can be immediately freed from monomeric hexamethylene diisocyanate by thin-layer distillation without cooling at 170 ° C. and 1 Torr. Yield: 415 parts by weight,% NCO = 21.9, ïj25o0 = 11200 cP; yellow COLOUR. In this experiment, the molar ratio of hexamethylene diamine / hexamethylene diisocyanate = 12: 1.

The process product is excellently suitable both for the production of light-fast, moisture-crosslinked one-component lacquers and for the production of two-component lacquers with hydroxyl polyesters, elastic, high-gloss films being obtained.

In variant b), the procedure is exactly as described under a), but the metering of the superheated hexamethylenediamine vapor is slowed down by about a factor of 2 (= 3 hours). After working up the batch, the viscosity of the biuret polyisocyanate mixture at 25 ° C. is about 8500 cP. With decreasing dosing speed of the superheated hexamethylenediamine vapors and doubled

Response time, the viscosity of the process products can therefore be reduced without any appreciable impairment of the color properties.

Example 14

This example describes two interesting process variants, according to which it is possible to produce light yellow to colorless biuret polyisocyanates of very different viscosities even under normal pressure, by diluting the superheated hexa-methylenediamine vapors with inflowing nitrogen as propellant so that 40-80 parts by volume nitrogen per Part by volume of hexamethylenediamine vapor are metered into the hexamethylene diisocyanate which has been preheated to 158 ° C. The small amounts of hexamethylene diisocyanate vapors leaving the reflux condenser are condensed in a cold trap.

Option A)

Molar ratio of hexamethylene diisocyanate / hexamethylene diamine = 18: 1.

1512 parts by weight of hexamethylene diisocyanate (= 9 mol) are heated to 158 ° C. and 58 parts by weight (= 0.5 mol) of superheated hexamethylenediamine vapors together with nitrogen are passed into the reaction vessel of example 13 via an inlet pipe heated to 190 ° C. a. Nitrogen is introduced into the hexamethylene diamine evaporator, which is heated to about 115 ° C. The amount of nitrogen is adjusted via a gas meter so that the N2 / hexamethylenediamine volume ratio in the superheated feed pipe is approximately 40: 1. The work-up of the biuret polyisocyanate solution can be carried out without problems after 2 hours, as in Example 13.

Yield: 408 parts by weight,% NCO = 21.9.

y) 25oC - 5800 cP.

15 parts by weight of hexamethylene diisocyanate were condensed in a cold trap downstream of the reflux condenser.

Variant b)

Molar ratio of hexamethylene diisocyanate / hexamethylene diamine used = 18: 1.

The procedure is exactly the same as in variant a) of this example, but the nitrogen-hexamethylene diamine volume ratio is set to about 80: 1.

After a reaction time of 2 hours, a light yellow solution is obtained which is subjected to thin-film distillation. Yield: 407 parts by weight,% NCO: 22.3.

The viscosity of this biuret polyisocyanate mixture is only 4500 cP at 25 ° C. Therefore, by diluting the superheated steam mixture, a process product is obtained with a viscosity reduced by approximately 22% compared to variant a).

Variant c)

Molar ratio of hexamethylene diisocyanate / hexamethylene diamine = 24: 1.

N2 / hexamethylene diamine volume ratio = 80: 1.

The reaction is carried out with 2016 parts by weight of hexamethylene diisocyanate and 58 parts by weight (= 0.5 mol) of vaporous, superheated hexamethylene diamine in a 3 liter stirred beaker with a heated inlet tube (cf. Example 13).

Yield after working up and thin-layer distillation: 414 parts by weight, yellow-colored biuret polyisocyanate, viscosity 3200 cP / 25 ° C.

This low-viscosity biuret polyisocyanate is extremely suitable for the production of solvent-free or low-solvent one- and two-component paints. The previous

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Process variants a) to c) mentioned can be carried out continuously in that the nitrogen leaving the apparatus is freed from small amounts of hexamethylene diisocyanate in a cooling tower and is fed again to the hexamethylene diamine evaporator as a propellant gas via a gas pressure pump.

Example 15

This example describes the preparation of an almost colorless biuret polyisocyanate from hexamethylene diisocyanate and hexamethylene diamine in a molar ratio of 8: 1, N2-hexamethylene diamine volume ratio of about 40: 1, exactly according to the procedure of Example 14, variant a). Here, a technical hexamethylene diamine is used, which has previously been subjected to an 8-hour heat treatment at 180 ° C, whereby unknown impurities and catalytically active compounds are destroyed. The hexamethylene diisocyanate is then purified by distillation. 672 parts by weight (= 4 mol) of diisocyanate and 58 parts by weight of hexamethylenediamine (0.5 mol) are used from the distillate. Otherwise, the procedure is exactly as described in Example 14, variant a). Reaction vessel: 1 liter glass beaker.

After the thin-layer distillation, an almost water-white biuret polyisocyanate mixture is obtained in a yield of 416 parts by weight,% NCO = 21.5. The process product has a viscosity of 24800 cP at 25 ° C.

Example 16

The procedure of Example 14 is followed, but the following compounds are used as diisocyanates and diamines and the reaction is carried out in a 500 cm3 stirred flask:

a) Tetramethylene diisocyanate (= 140 parts by weight, 1 mol) and 11 parts by weight (= 0.125 mol) of tetramethylene diamine, molar ratio of tetramethylene diisocyanate: tetramethylene diamine = 8: 1.

b) 1,2-diisocyanatomethylcyclobutane (= 166 parts by weight, 1 mol) and 14.2 parts by weight of 1,2-bisaminomethyl-cyclobutane (0.125 mol) in a molar ratio of diisocyanatomethylcyclobutane: diaminomethylcyclobutane = 8: 1 .

5 c) Cycloaliphatic diisocyanates consisting of an isomer mixture of about

ÇH3

10 70% [H J and 30 wt% OCNy ^ y NCO MCO

15

20th

(180 parts by weight = 1 mol) and 15.9 parts by weight (= 0.125 mol) of a cycloaliphatic diamine consisting of

NHa approx. 70% F T and 30 wt.

CHa

.-% HjNÀ,

0

NHa

Molar ratio used of the cycloaliphatic diiso-25 cyanate isomers to the cycloaliphatic diamine isomers = 8: 1.

With regard to the temperature control, the metering of the superheated diamine / nitrogen vapors and the reaction time, the procedure of Example 14, 30 variant a) is followed exactly.

Gel-body-free solutions of biuret polyisocyanates in excess monomeric diisocyanates are obtained in the following yields:

a) 150 parts by weight, NCO content of the gel-free biuret 35 polyisocyanate solution in the monomeric diisocyanate: 41.5%.

b) 179 parts by weight, NCO content of the gel-free biuret polyisocyanate solution in the monomeric diisocyanate: 36.6%.

c) 195 parts by weight, NCO content of the gel-free biuret polyisocyanate solution in the monomeric diisocyanate: 31.5%.

v

Claims (3)

627739 1. Process for the preparation of polyisocyanates containing biuret groups by reacting 2 organic polyamines containing primary amino groups and aliphatically and / or cycloaliphatically with organic polyisocyanates free of biuret groups in a molar NH2 / NCO ratio of 1: 5 to 1: 100, characterized in that the polyamines are reacted in vapor form with the polyisocyanates heated to a temperature of 100 ° C to 250 ° C. 2. The method according to claim 1, characterized in that a gas mixture consisting of a carrier gas inert to the reactants and the vaporous polyamine is introduced into the heated polyisocyanates, the volume ratio of carrier gas: polyamine being between 2: 1 and 100: 1. 2nd PATENT CLAIMS 3. The method according to claim 1 and 2, characterized in that the biuret group-free polyisocyanate used for cleaning is subjected to a heat pretreatment at 120-195 ° C for several hours and then distilled.