EP2132249A1

EP2132249A1 - Method for the production of colorless polyisocyanates that have biuret groups and are stable in storage

Info

Publication number: EP2132249A1
Application number: EP08717448A
Authority: EP
Inventors: Andreas Wölfert; Klaus-Peter Metzner; Carl Jokisch; Harald Schäfer; Eckhard Stroefer
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2007-03-09
Filing date: 2008-03-06
Publication date: 2009-12-16
Also published as: WO2008110492A1

Abstract

The invention relates to a method for producing colorless polyisocyanates, which have biuret groups and are stable in storage, from di- or polyisocyanates with diamines in the absence of biuret-forming agents and the use thereof.

Description

Process for the preparation of colorless, storage-stable biuret polyisocyanates

description

The present invention relates to a process for the preparation of colorless, storage-stable biuret-containing polyisocyanates from di- or polyisocyanates with diamines in the absence of biuretizing agents and their use.

DE 196 33 404 describes the preparation of biuret-containing polyisocyanates using a high shear mixing element. The application mentions the use of acid catalysts in the simultaneous presence of water or tert-butanol. A disadvantage of the addition of water or dehydrating agents is the degradation of isocyanate groups to amine groups, wherein the isocyanates are technically produced from the corresponding amines, and the formation of carbon dioxide during the reaction, resulting in a gas-liquid reaction mixture. The explicit examples without water have been consistently carried out at a high temperature and result in slightly colored products.

EP-A1 716 080 also describes a process for the preparation of biuret-containing isocyanates from isocyanates and water or steam, wherein the water is introduced to control the reaction in finely dispersed Fom.

DE 10 2004 060739 describes a process for the preparation of biuret group-containing polyisocyanates with addition of e.g. Water as a biuretizer under high shear. This procedure shows the usual disadvantages of biuretization with the aid of a biuretizing agent.

As an alternative to the previously described methods with addition of biuretizing agents, the preparation of biuret-based polyisocyanates by reaction of two diisocyanate molecules and one diamine molecule was also investigated. The first advantage of these methods over the reaction of three diisocyanate molecules is that neither isobutene (from tert-butanol) nor carbon dioxide are formed as unwanted by-products.

The second advantage is that the starting material diisocanate is theoretically replaced by one third by the diamine, which is cheaper than the diisocyanate. Usually, the diisocyanate is prepared by complex phosgenation or on a phosgene-free path from the diamine. Processes based on the use of diisocyanates and diamines thus also have an economic advantage. The disadvantage is, first, that after the mixing of diamine and diisocyanate usually suspended solids are formed, the first in the course of further reaction continue to react to the desired, solids-free biuret-containing polyisocyanate.

DE 22 61 065 describes a process for the preparation of biuret-containing polyisocyanates from diisocyanate and amine. Disadvantages are the high residence times of the reaction mixture (see Example 16 of the application), which lead to unacceptable discoloration of the product.

DE 2609995 describes a process for the preparation of biuret polyvinyl lyisocyanaten by gaseous introducing diamines in diisocyanates at temperatures of 100 to 250 ⁰ C. The disadvantage is the low because of the participation of gases in the production process space-time yield.

According to this method is for color ENHANCE a 6 to 10-hour heat treatment at 120-195 ⁰ C, preferably 160-180 ⁰ C are required, whereby the space-time yield is deteriorated.

EP 3 505 describes the preparation of biurets based on diisocyanates and diamine in a smooth-jet nozzle mixing device in which the educts are mixed under high mixing power. A disadvantage of the method is the use of high reaction temperatures up to 250 ⁰ C. An estimate of the mixing work from the examples of EP 3505 gives values for the mixing work to about 11 kJ / kg of diamine. Disadvantageous is the poor relatively poor color of the product due to the thermal stress that is necessary during manufacture to obtain a clear product without solids at the end of the process. Typically, the higher the thermal load during manufacture, the higher the level of by-product uretdione formed from two diisocyanate groups, but this by-product is not stable and slowly degrades back to HDI, thereby increasing the shelf life of the biuret is reduced as a period between production and processing.

EP 12 973 describes a process for the preparation of polyisocyanates containing biuret groups using strong carbamic acid anhydride-forming acids mixed with isocyanates. An estimate of the mixing work from the examples of EP 12973 gives values for the mixing work below 5 kJ / kg of diamine.

Disadvantages are the high residence times of the reaction mixture to achieve a clear biuret-containing liquid, which lead to a non-acceptable coloration of the product.

EP 277 353 describes a process for the preparation of biuret Polyi- socyanaten, wherein the reactants are reacted at temperatures above 250 ^0C. The disadvantage is that the residence time at the high temperature must be very tightly limited, so that the product undergoes no unwanted yellowing by thermal stress. The smallest load fluctuations in the production plant, which can not be avoided in everyday operation, lead to an unacceptable product.

EP 1158013 describes the preparation of biurets of diisocyanates and diamines based at temperatures above 170 ⁰ C in the presence of an acidic substance as the catalyst. In the examples, the mixing of the components is described in a mixing chamber not specified with faster heating of the starting materials. A disadvantage of this process, as in EP 0277 353, is the higher color number compared to products prepared by the processes using biuretizing agents.

DE-C1 197 07 576 describes a process for the preparation of biuret-containing aromatic polyisocyanates from isocyanates and diamines in which diamine and isocyanate are reacted in a mixing chamber with each other and then reacted in a single-stage stirred tank or optionally also a multi-stage stirred tank cascade.

The object of the present invention was to develop a process for the preparation of biurets from isocyanates and diamines, with the colorless products than under comparable reaction conditions of the prior art, which comprises the biuretizing agent-free production of biurets, the storage stability according to at least to be maintained in the prior art.

The object was achieved by a process for the preparation of biuret-containing polyisocyanates

a) at least one (cyclo) aliphatic di- and / or polyisocyanate, b) at least one (cyclo) aliphatic diamine having two primary amino groups, c) at least one acid and d) optionally at least one solvent, comprising i) mixing the components a) , b) and c) and, if appropriate, d) in a mixing device with a mixing work of at least 1.2 x 10 ⁴ J / kg diamine mixture and ii) passing the reaction mixture obtained from i) into at least one reactor, in which the reaction mixture in a Temperature below 170 ⁰ C and thermally treated in the absence of water or dehydrating compounds.

The term "absence of water or dehydrating compounds" is understood in the context of this application that in the starting materials few than 0.5 mol% of water, based on the isocyanate groups in the freshly fed isocyanate (a), are contained or cleaved off in the course of the reaction under the reaction conditions, preferably less than 0.4 mol%, particularly preferably less than 0.3 mol%, very particularly preferably less than 0.2 mol% and in particular less than 0.1 mol%.

The advantage of the present invention is that the products thus obtained have a lower color than the products obtained from the prior art and have at least comparable or even better storage stability.

Suitable di- and polyisocyanates a) for the process according to the invention are (cyclo) aliphatic isocyanates, ie those compounds which have at least 2, preferably 2 to 6, more preferably 2 to 4, very preferably 2 to 3 and in particular exactly 2 Have isocyanate groups attached to carbon atoms that are part of an aliphatic and / or cyclic system.

Suitable diisocyanates are preferably diisocyanates having 4 to 20 C atoms.

Cycloaliphatic isocyanates are those containing at least one cycloaliphatic ring system.

Aliphatic isocyanates are those which contain exclusively straight or branched chains, ie acyclic compounds.

The terms "aliphatic" and "cycloaliphatic" are summarized in this document as (cyclo) aliphatic.

Particularly preferred aliphatic diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate (1,6-diisocyanatohexane), octamethylene diisocyanate, deca methylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysine diisocyanate, tetramethylxylylene diisocyanate, 2,4,4- and / or 2,2,4-trimethylhexane diisocyanate or Tetramethylhexandiisocyanat, and as cycloaliphatic diisocyanates 1, 4, 1, 3 or 1, 2-diisocyanatocyclohexane, 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, 1 -lsocyanato-3,3,5-trimethyl -5- (isocyanatomethyl) cyclohexane (isophorone diisocyanate), 1,3- or 1,4-bis (isocyanatomethyl) cyclohexane or 2,4- or 2,6-diisocyanato-1-methylcyclohexane and also 3 (or 4), 8 (or 9) - Bis (isocyanatomethyl) tricyclo [5.2.1.0 ²⁶ ] decane isomer mixtures. The aliphatic or cycloaliphatic isocyanates are preferably hexamethylene diisocyanate or isophorone diisocyanate, more preferably hexamethylene diisocyanate. There may also be mixtures of said diisocyanates. 2,2,4- and 2,4,4-trimethyl-1,6-hexamethylene diisocyanate fall production-related mostly as a mixture of isomers in the ratio of 1, 5: 1 to 1: 1, 5, preferably 1, 2: 1 - 1: 1 , 2, more preferably 1, 1: 1 - 1: 1, 1 and most preferably 1: 1 at.

Diisocyanates may be industrially e.g. by phosgenation of diamines according to the processes described in DE-PS 20 05 309 and DE-OS 2 404 773 or by a phosgene-free process (cleavage of biurethanes) as described in EP-B-

0 126 299 (US Pat. No. 4,596,678), EP-B-0 126 300 (US Pat. No. 4,596,679), EP-AO 355 443 (US Pat. No. 5,087,739) and EP-A-0 568 782 be prepared described. According to the invention, it does not matter whether the isocyanate used has been obtained after a phosgene-free or a phosgene-containing preparation route.

Diisocyanates from both production processes are equally preferred.

Isocyanates derived from a phosgenation process often have a total chlorine content of 100-400 mg / kg, whereas the phosgene-free isocyanates have a total chlorine content of less than 80 mg / kg, preferably less than 60, more preferably less than 40, all more preferably less than 20 and especially less than 10 mg / kg.

The total bromine content is usually less than 15 mg / kg, preferably less than 10 mg / kg and especially less than 5 mg / kg.

It is also possible to distinguish between hydrolyzable and non-hydrolyzable halogen content, the hydrolyzable fraction generally being about 0.5-80%, preferably

1 to 50%, and more preferably 2 to 30% of the total halogen content.

The content of hydrolyzable chlorine is determined according to ASTM D4663-98 and is preferably less than 40 ppm, more preferably less than 30 ppm and most preferably less than 20 ppm by weight.

The biuret polyisocyanates are reacted by mixing with at least one, preferably exactly one diamine b).

Typical organic diamines having exclusively aliphatic and / or cycloaliphatic bonded primary amino groups have a molecular weight below 300. Examples are 1, 2-diaminoethane, 1, 2-diaminopropane, 1, 3-diaminopropane, 1, 4-diaminobutane, 1, 6-diaminohexane , 1, 6-diamino-2,2,4-trimethylhexane and / or 1, 6-diamino-2,4,4-trimethylhexane, 1, 4 and / or 1, 5-diaminohexane, 2,4- and / or or 2, 6-diamino-1-methylcyclohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 1, 3 and / or 1, 4-bis (aminomethyl) cyclohexane or 4,4'-diaminodicyclohexylmethane , Any mixtures of such diamines can also be used. 1, 6-diaminohexane is particularly preferred.

In carrying out the process according to the invention, said isocyanates a) and diamines b) are reacted in proportions which correspond to an equivalent ratio of isocyanate groups to amino groups of at least 4: 1, preferably from 4: 1 to 50: 1 and in particular from 5: 1 to 40: 1, wherein the primary amino groups are included as monofunctional groups in the calculation.

The reaction is carried out in the presence of at least one catalyst c).

These may be, for example, OH-acidic compounds, as known from DE-A1 44 43 885. These have the advantage that they are low volatility and therefore, optionally as salts, can be filtered off from the product mixture or as non-interfering compounds remain in the final product and also do not form interfering decomposition or by-products during the reaction. Another advantage is the good catalytic activity of the acids.

Suitable OH-acidic compounds are, in particular, protic acids for the process according to the invention. Preference is given to using and have proven particularly useful: phosphoric acids and / or their mono- and / or dialkyl esters or aryl sulfates and / or. Use is preferably made of mono- and / or dialkyl esters or aryl esters of phosphoric acid whose aliphatic, branched aliphatic, araliphatic or aromatic radicals have 1 to 30, preferably 4 to 20, carbon atoms. Di-iso-propyl phosphate, di- (2-ethylhexyl) phosphate, di (n-butyl) phosphate and di-hexadecyl phosphate are preferably used.

The latter are particularly preferred acids for the process according to the invention.

Hydrogen sulfates, in particular Tetralkylammoniumhydrogensulfate whose aliphatic, branched aliphatic or araliphatic radicals 1 to 30, preferably 4 to 20, carbon atoms have, for example, further suitable proton acids.

Also conceivable are anhydrous mineral acids such as hydrogen chloride gas, sulfuric acid or oleum.

Further examples are sulfonic acids, such as, for example, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2- or 4-toluenesulfonic acid, benzenesulfonic acid, cyclododecanesulfonic acid, camphorsulfonic acid or naphthalene-1 or 2-sulfonic acid, or else mono- and dicarboxylic acids, such as, for example, formic acid, Acetic acid, propionic acid, butter acid, pivalic acid, stearic acid, cyclohexanecarboxylic acid, oxalic acid, malonic acid, succinic acid, adipic acid, benzoic acid or phthalic acid.

Among these, the dicarboxylic acids mentioned are less preferred, as far as they are significant under the reaction conditions, for example more than 10 mol% with respect to the amount used, preferably more than 8 mol%, more preferably more than 5 mol% and very particularly preferably More than 3 mol%, release water, as can be released from these by anhydride water as a biuretizing agent.

The (ar) aliphatic carboxylic acids described, for example, in EP-A-259,233 are found to be less effective.

Suitable catalysts in the process according to the invention are any acids, preferably protic acids, having a pKa value <10, more preferably <9 and very particularly preferably <8.

These acids are used in the process according to the invention in amounts of from 0.01 to 1.0% by weight, preferably from 0.02 to 0.5% by weight and very particularly preferably from 0.05 to 0.5% by weight. , based on the total amount of diisocyanates used. The acids may be added dissolved or dispersed in a suitable solvent. Preferably, the acids are added in substance.

The abovementioned OH-acidic compounds have the advantage that they are often difficult to volatilize and therefore, if appropriate as salts, can be filtered off from the product mixture or remain as non-interfering compounds in the end product or likewise form non-interfering decomposition or by-products during the reaction , Another advantage is the good catalytic activity of the acids.

As a catalyst, for example, strong inorganic Lewis or

Branstedt acids, such as boron trifluoride, aluminum trichloride, sulfuric acid, phosphorous acid, hydrochloric acid and / or salts of nitrogenous bases and inorganic and / or organic acids, as described in DE-A-19 31 055, page 3, last paragraph bis Page 6, first full paragraph, which hereby by reference would be the subject of the present disclosure, are used.

If desired, it is additionally possible to add a small amount of a stabilizer e) selected from the group consisting of urea, ammonia, biuret, urea derivatives or carboxamides as described in WO 96/25444, preferably urea, N-methylurea, N-ethylurea, N, N-dimethylurea, N ₁ N ¹ -

Dimethylurea, N, N-diethylurea, N, N'-diethylurea, ethyleneurea or phenylurea, especially preferred is urea. Such stabilizers are used in amounts of 0.01-2.0, preferably 0.05-1 mol%, based on the isocyanate groups in (a).

In a preferred embodiment, these stabilizers are dissolved or dispersed in at least one solvent d), as listed below.

In order to suppress the formation of insoluble polyureas even better, solvents d) may optionally additionally be used as solubilizers. For example, dioxane, tetrahydrofuran, alkoxyalkyl carboxylates, e.g. Triethylene glycol diacetate, butyl acetate, ethyl acetate, 1-methoxypropyl-2-acetate, propylene glycol diacetate, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, hexane, toluene, xylene, benzene, chlorobenzene, o-dichlorobenzene, hydrocarbon mixtures, methylene chloride and or trialkyl phosphates. Also preferred are N-methylpyrrolidone and other N- (cyclo) alkylpyrrolidones, such as N-ethylpyrrolidone, N-n-butylpyrrolidone and N-cyclohexylpyrrolidone.

Examples of hydrocarbons as solvents are aromatic and / or (cyclo) aliphatic hydrocarbons and mixtures thereof, halogenated hydrocarbons, esters and ethers.

Also conceivable are mono- or polyalkylated benzenes and naphthalenes and mixtures thereof.

Suitable aromatic hydrocarbon mixtures are those which comprise predominantly aromatic C7 to C30 hydrocarbons and may have a boiling range of from 10 to 300 ^° C., examples of which are toluene, o-, m- or p-xylene, trimethylbenzene isomers, tetramethylbenzene isomers, ethylbenzene , Cumene, tetrahydronaphthalene and mixtures containing such.

Examples include the Solvesso® brands of ExxonMobil Chemical, especially Solvesso® 100 (CAS No. 64742-95-6, predominantly C ₉ and Cio-aromatics, boiling range about 154-178 ⁰ C), 150 (boiling range about 182 - 207 ⁰ C) and 200 (CAS No. 64742-94-5), as well as the Shellsol® brands of Shell. Hydrocarbon mixtures of paraffins, cycloparaffins and aromatics are also known under the names of crystal oil (for example, crystal oil 30, boiling range about 158-198 ⁰ C or crystal oil 60: CAS No. 64742-82-1), white spirit (for example, also CAS no. 64742-82-1) or solvent naphtha (light: boiling range about 155-180 ⁰ C, heavy: boiling range about 225-300 ⁰ C) commercially available. The aromatic content of such hydrocarbon mixtures is generally more than 90% by weight, preferably more than 95, more preferably more than 98, and very particularly preferably more than 99% by weight. It may be useful to use hydrocarbon mixtures with a particularly reduced content of naphthalene.

Methoxypropyl acetate, trimethyl phosphate, tri-n-butyl phosphate and triethyl phosphate or any desired mixtures of these compounds are preferably used according to the invention.

If a solvent is used, the diamine is preferably dissolved in this and this diamine solution is fed into the reaction. In this case, the concentration of the diamine in the solvent is from 2 to 100% by weight (solvent-free), preferably from 5 to 30% by weight, more preferably from 10 to 25% by weight, and most preferably from 15 to 20% by weight.

In a preferred embodiment of the present invention, a solvent is present.

The reaction mixture may also contain additional inert gas streams, e.g. contain a liquid or gaseous inert stream. The inert stream is preferably added in gaseous form. Suitable inert medium are all gases which are not essential, i. at the reaction conditions less than 5 mol%, preferably less than 2 mol%, more preferably less than 1 mol%, react with the isocyanate stream, the amine-containing stream and / or the catalyst. Examples are CO, N2, He, Ar, hydrocarbons, such as methane, etc., and mixtures thereof. Preference is given to using argon and / or nitrogen. Nitrogen is particularly preferably used.

Also conceivable are nitrogen-oxygen or, preferably, nitrogen-air mixtures having an oxygen content of less than 10% by volume, preferably less than 8% by volume and more preferably of about 6% by volume.

The addition of inert gases is less preferred.

The process according to the invention is carried out in the absence of water or compounds which release significantly water under the reaction conditions according to the invention. In addition to water or steam, these may also be dicarboxylic acids which can release water by anhydride formation, or compounds containing water of crystallization.

In the absence of water, in the context of the present invention a water content of less than 1% by weight, preferably less than 0.8% by weight, particularly preferably less than 0.6, very particularly preferably less than 0.5, in particular less than 0, 3 and especially less than 0.1% by weight, based on the total reactant regardless of whether the water is added, is in one of the starting compounds and / or released under the reaction conditions onsgemisch.

Static or agitated mixing devices may be used as the mixing device in step i).

Examples of static mixers are packs such as Sulzer SMX / SMV, nozzle or orifice mixers, examples of agitated mixers are pumps, mixing pumps or gassing stirrers, as well as combinations thereof. Preferably, nozzle mixing devices are used.

Mixing usually takes place at temperatures of at least 30 ⁰ C, preferably at least 50 ⁰ C, more preferably at least 80 and most preferably at least 100 ⁰ C instead.

The upper limit of the temperature of the reaction mixture during mixing i) is less than 170 ⁰ C, preferably not more than 165 ⁰ C, especially not more than 160 ⁰ C, most preferably not more than 155 ⁰ C and in particular - Not more than 150 ⁰ C.

The mixing time in the mixing device is preferably not more than one tenth of the total average residence time, ie the mean time between starting and stopping the reaction, more preferably not more than one twentieth, very particularly preferably not more than one thirtieth and in particular not more than one hundredth.

The mixing time in this mixing device i) is usually from 0.002 s to 5 s, preferably from 0.005 to 1 s, particularly preferably from 0.01 to 0.5 s, very particularly preferably from 0.01 to 0.2 s and in particular of 0.01 to 0.1 s. The mixing time is understood to be the time which elapses from the start of the mixing operation until 97.5% of the fluid elements of the resulting mixture have a mixing fraction less, based on the value of the theoretical final value of the mixture fracture of the resulting mixture upon reaching the state of perfect mixing than 2.5% deviate from this final value of the mixture break, (for the concept of mixture fracture, see, for example, J. Warnatz, U. Maas, RW Dibble: Verbrennungs, Springer Verlag, Berlin Heidelberg New York, 1997, 2nd edition, p. 134. )

The absolute pressure at the outlet of the mixing device is in the range of 0.3 bar to 10 bar, preferably from 0.6 bar to 7 bar, more preferably from 0.8 bar to 5 bar. If a static mixing device is used, the admission pressure on the isocyanate supply side to the mixing device is 10 to 140 bar, preferably 30 to 120 bar, particularly preferably 40 to 100 bar, higher than the pressure on the outlet side of the mixing device.

When using a static mixing device, the pre-pressure on the diamine feed side to the mixing device is 10 to 140 bar, preferably 30 to 120 bar, particularly preferably 40 to 100 bar higher than the pressure on the outlet side of the mixing device.

According to the invention, a mixing work of at least 1.2 × 10 ⁴ J, preferably of at least 1.3 × 10 ⁴ J, particularly preferably of at least 1.4 × 10 ⁴ J, is very particularly preferred, depending on the type of mixing device per kg of diamine mixture of at least 1. 5 × 10 ⁴ J, in particular of at least 1. 8 × 10 ⁴ J and especially of at least 2.0 × 10 ⁴ J, in order to obtain the components a), b) and c) and, if appropriate, d) and / or e) to mix.

As a rule, a mixing work is sufficient up to 20 × 10 ⁶ , preferably up to 10 × 10 ⁶ , very particularly preferably up to 7 × 10 ⁶ Joule sufficient.

The mixing work is defined as the sum of the dissipation work performed during the injection of amine mixture and diisocyanate stream into the mixing device.

The mixing work is in this case based on the diamine b) used, which may optionally be dissolved as stream in the reaction in at least one solvent d), which is expressed by the term "diamine mixture".

In the mixing device, the educts a) and b) and the catalyst c) are mixed with or without solvent and with or without inert gas.

As mixing nozzles non-axisymmetric or preferably axially symmetrical mixing nozzles can be used. When using axially symmetrical mixing nozzles usually one of the educt streams is injected via a coaxial inlet pipe or more coaxially arranged inlet pipes in a mixing tube. The second reactant stream is injected via the annular gap between the coaxial inlet tube and the mixing tube. The diameter ratio of the coaxial inlet tube to the mixing tube is usually 0.05 to 0.95, preferably 0.2 to 0.8. The amine-containing stream can be injected centrally via the internal coaxial introduction or through the annular gap. Preferably, the amine stream b) is introduced via the internal coaxial injection. The length of the mixing tube after the nozzle is usually 2 to 20 times the mixing tube diameter, preferably 4 to 10 times the mixing tube diameter.

The speeds in the mixing tube are usually 1 to 50 m / s, preferably 5 to 25 m / s.

When using non-axisymmetric mixing nozzle devices mixing chamber constructions can be used in which countercurrent the E- educt streams are introduced into a mixing chamber and the mixture flow is removed from the mixing chamber. Further possible non-axisymmetric mixing nozzle devices are T or Y mixers.

Diamine or diisocyanate streams may be fed through the die at rates of at least 20 m / s, preferably at least 40 m / s and more preferably at least 60 m / s. As a rule, a speed of up to 160 m / s, preferably up to 100 m / s and particularly preferably up to 80 m / s is sufficient.

Preferably, the rate of flow of isocyanate a) and amine b) differ by at least 20 m / s, preferably at least 35 m / s and more preferably at least 50 m / s.

In a preferred embodiment, in the case of corresponding nozzles, for example coaxial mixing nozzles, the diamine or the diamine solution is metered in on the inside and the diisocyanate on the outside.

As reaction apparatus for stage ii), it is possible to use all customary volume-containing reactors, such as stirred tanks, jet loop reactors, bubble columns, tubular reactors, vessels, columns. Combinations or multiple uses of the types of apparatus are also possible. For example, a stirred tank can be combined with a tubular reactor. The process can also be carried out in a cascade of stirred tanks.

Advantageously, the flow in the reaction apparatus is at least partially, preferably completely turbulent.

If the reaction apparatus is one or more stirred tanks, the flow state is preferably set so that the Newton number characterizing the power input does not depend inversely proportionally on the Reynolds number formed with the stirrer diameter with variation of the rotational speed. Particularly preferably, the flow state is adjusted so that the Newton number does not depend on the Reynolds number with variation of the speed. If it is a tube reactor without internals, the Reynolds number is preferably at least 2300, more preferably at least 2700, more preferably at least 3000, in particular at least 4000, at least 7000 or especially at least 10000.

Preferably, at least one longitudinally flow-through stirred tank with a diameter to length ratio of 1 to 1.2 to 1 to 10, preferably from 1 to 1.5 to 1 to 6 is used. In a further particularly preferred embodiment, this stirring element is cascaded by internals. As internals perforated plates, sieves, slotted bottoms, concentric discs are possible, as described in DE-A1 195 25 474. By the internals of the stirred tank is divided into preferably 2 to 10 segments, more preferably in 3 to 6 segments of others are separated by the said internals. Of course, these can also be separate stirred tanks.

The volume-specific power input in this stirred tank should be at least 0.1 watt / l, preferably at least 0.3, particularly preferably at least 0.5 watt / l. In general, up to 20 watts / l, preferably up to 6 watts / l and more preferably up to 2 watts / l is sufficient.

The performance can be entered via all types of stirrers, such as angled blades, anchors, discs, turbines, bar stirrers. Disc and turbine stirrers are preferably used.

There may also be several stirrers installed on the shaft. Preferably, a stirrer is used on the shaft per segment of the cascade. The diameter of the stirring elements is 0.1 to 0.9 times the Rührkesseldurchmessers, preferably 0.2 to 0.6 times the Rührkesseldurchmessers.

The stirred tank or cascaded stirred tank can be operated with or without baffles. Preferably, the operation is carried out with baffles. The operation is usually carried out with 1 to 10 baffles, preferably with 2 to 4 baffles per segment.

The reaction mixture is fed after leaving the mixing stage i) the reactor. If an inert gas is present, it may be a preferred embodiment that the reactor is a predominantly vertically arranged apparatus (for example, a vertical tubular reactor, column or slender stirred tank). In this case, the supply of the reaction mixture from below (direct current of the liquid phase with the inert gas) or from above (countercurrent to the inert gas), preferably from below. The removal of the optionally added inert gas can be carried out at any point in the system. Preferably, the removal takes place only after complete reaction of the reaction mixture.

The residence time in the reactor ii) is in the range from 0.5 to 5 hours, preferably from 0.75 to 3 hours and more preferably 1 to 2 hours. The reaction time is favorably chosen so that at the end of the theoretical NCO value is reached. The theoretical NCO value is the NCO value that the reaction mixture has when the total amount of amine used has formed the theoretically expected amount of biuret groups.

The temperature is in the range of the reaction distance ii) in the range of 30 to less than 170 ⁰ C, preferably from 100 to 165 ⁰ C, more preferably in the range of 120 to 160 ⁰ C, most preferably 125 to 155 ⁰ C and in particular 130 to 150 ⁰ C.

It may be useful to change the temperature from segment to segment, for example, the temperature may rise, fall or remain the same in the course of the reactor, preferably it rises or stays the same.

The absolute pressure in the reactor is in the range from 0.3 to 10 bar, preferably from 0.6 to 4 bar, more preferably from 0.8 to 2 bar.

The catalyst c) is added to the reaction mixture in the mixing stage i). The mixing of the catalyst stream may also instead or additionally be carried out separately in the reactor or else at several points or else to one of the streams which are fed to the mixing nozzle. Preferably, the catalyst is mixed into one of the streams, which are passed to the mixing nozzle. Particularly preferably, the catalyst stream is fed to the isocyanate group-containing stream which passes into the mixing device.

In the simplest embodiment, the invention consists of the combination mixing device i) and reactor ii). Here, the isocyanate stream and catalyst c) is then mixed with the amine-containing stream b) and then introduced into the reactor ii). In this case, the mixing device i) and the reactor ii) must not be separated in terms of apparatus, but the reactor can also be connected directly to the mixing device.

In the mixing device i), the reaction may already start immediately after mixing of the components, so that the reaction is not necessarily limited to the reactor.

The process according to the invention can be operated continuously and semicontinuously. In the semi-continuous mode, isocyanate and catalyst are used. lays and heats up. Subsequently, the mixture of amine and solvent is mixed in continuously. The implementation takes a total of about 3 to 4 hours.

In the continuous procedure, diisocyanate and catalyst are continuously metered into the mixing element and, in parallel, the mixture of amine and optionally solvent is introduced. The crude product of biuret oligomers and excess monomer is discharged continuously. The crude product is then worked up by distillation.

In general, in order to obtain products which do not release dangerous amounts of isocyanates during processing, it will be necessary to separate most of the unreacted isocyanates (a) from the biuret group-containing polyisocyanates formed. In most cases, products are desired whose content of the monomeric isocyanates (a) is less than 1% by weight, preferably less than 0.75% by weight, more preferably less than 0.5% by weight and most preferably less than 0, 3% by weight, based on the biuret polyisocyanates. The separation of the isocyanates (a) is advantageously carried out at reduced pressure at temperatures which are between 50 ^° C. and the reaction temperature chosen during the reaction, for example by distilling off them.

The apparatuses used for this purpose are flash, falling film, thin film or short path evaporators, to which optionally a short column can be placed.

The distillation is generally carried out at a pressure between 0.1 and 300 hPa, preferably below 200 hPa and particularly preferably below 100 hPa.

The thus separated and recovered, unreacted diisocyanate a) can advantageously be used again in the reaction.

If a solvent has been used in the reaction, this is likewise preferably removed by distillation from the reaction mixture. The distillation conditions and apparatuses are about the same as described in the separation of the excess diisocyanate.

Another object of the present invention is a process for the preparation of biuret polyisocyanates by reacting a diisocyanate with a diamine in the presence of at least one acid and optionally a solvent in which diisocyanate stream 1 and diamine stream 2 and a stream 9 of recycled optionally present solvent and recycled Excess diisocyanate 13 in the presence of at least one catalyst in a mixing device (I) mixed together, then the mixture of diamine and diisocyanate thus obtained in at least one reactor (II) leads to the biuret-containing Polyisocyanate reacted, then optionally existing solvent, excess excess diisocyanate and biuretgruppenhaltiges polyisocyanate separated by distillation and any solvent present and the excess diisocyanate in the mixing device (I) recycles.

In a preferred embodiment, the process according to the invention can be carried out in the presence of a solvent, as shown in FIG. 1:

The process comprises a mixing device (I), at least one reactor (II), two distillation apparatuses (III) and (IV) and optionally a further mixing device (V) and optionally a further distillation unit (VI).

Diisocyanate stream 1 and diamine stream 2 and a stream 9 of recycled solvent and recycled excess diisocyanate 13, which has been treated with catalyst 15, in the mixing device (I), preferably a mixing nozzle, mixed together.

Preferably, the diamine is mixed as stream 8 instead of the stream 2 already in an upstream mixing unit (V) with recycled solvent 7 and this mixture is passed as stream 9 into the mixing unit (I).

The mixture of diamine and diisocyanate obtained in the mixing unit (I) is then passed into at least one reactor (II) and converted to the biuret-containing polyisocyanate.

The reaction mixture 4 thus obtained is then passed into the first distillation unit (III), in which excess diisocyanate and solvent in the mixture are removed as stream 5 as low boilers.

The distillation unit (III) may have one or more theoretical plates, preferably a multi-stage, preferably at least two-stage, more preferably at least three-stage, most preferably at least four-stage cascade of falling film evaporator, thin film evaporator and / or short path evaporator.

The course 6 from the distillation unit (III) is the biuret group-containing polyisocyanate as desired product, which can generally be further processed without further purification.

The excess diisocyanate and solvent-containing vapors of the distillation unit (III) is then passed into a further distillation unit (IV), in which the preferably easier than diisocyanate boiling solvent is separated as a low boiler stream 7 as vapors from the excess diisocyanate as bottom effluent 10.

The distillation unit (IV) is, for example, a distillation unit having 5 to 40, preferably 10 to 30 theoretical plates.

In order to remove higher molecular weight impurities contained in the excess diisocyanate from the bottoms effluent, it is optionally possible to subject this stream to a preferably one-stage evaporation (VI), for example in a falling-film evaporator. The purified overhead withdrawn diisocyanate 13 is then mixed with catalyst 15 and fed into the mixing unit (I), the bottom outlet 14 is discarded.

In a preferred embodiment, when the distillation unit (VI) is present, the freshly used diisocyanate is not passed through the stream 1 directly into the mixing unit, but as stream 1 1 is added to the stream 10 and this mixture 12 is then distilled. By this distillation of the freshly added diisocyanate, the quality, in particular the color quality of the product is generally improved again.

The catalyst is usually fed directly into the mixing unit (I) (not shown in the figure.

A further preferred embodiment is shown in FIG. 2 and differs from that shown in FIG. 1 by the interconnection of the distillation units (III) and (IV):

Therein, from the reaction mixture 4 obtained from the reactor (II), first in a distillation unit (IV) which preferably has 5 to 40, particularly preferably 10 to 30 theoretical plates, the solvent 7 is separated off as low boilers and the excess diisocyanate and biuret group-containing polyisocyanate are contained - Tende stream 15 withdrawn in the bottom and in the preferred distillation unit (III), which is a multi-stage, preferably at least two stages, more preferably at least three stages, most preferably at least four stages cascade of falling film evaporator, thin film evaporator and / or short path evaporator.

There, the excess diisocyanate is withdrawn as vapors 10 and recycled as described above and the biuret polyisocyanate 6 removed as a bottom outlet.

By virtue of the fact that, in the embodiment illustrated in FIG. 1, the biuret-containing polyisocyanate is less thermally stressed and consequently has a better quality, especially color quality, the embodiment shown in Figure 1 is preferred.

With the method described according to the invention products are generally obtained which have a color number of less than 20 APHA according to DIN ISO 6271 and / or a viscosity of 1000 to 10,000 mPas at 23 ⁰ C according to DIN 53019 Part 1 (rotary onsviskosimeter).

In the paint industry, especially biuret-containing polyisocyanates having a viscosity of 2,000 to 15,000, preferably from 2,500 to 10,000 mPas (based on a solids content of 100% measured at a temperature of 23 ° C and a shear rate of 100 S ^"1 ), If desired, such polyisocyanates can be diluted with solvents, for example those mentioned above, preferably butyl acetate, xylene or methoxypropyl acetate.

In addition to biuret group-containing polyisocyanates, uretdione- and / or allophanate-group-containing polyisocyanates may also be present to a lesser extent. The proportion of such polyisocyanates is in each case less than 5% by weight, more preferably less than 3, very preferably less than 2, in particular less than 1 and especially less than 0.5% by weight.

Since the process of the invention is carried out in the absence of water or water-releasing compounds, no carbon dioxide (CO2) is released by the process according to the invention, which partially dissolves in the reaction mixture and / or partially form a gas phase next to the reaction mixture.

Due to the absence of the carbon dioxide in the reaction mixture, no oxadiazinetrione-containing polyisocyanates are formed. As a rule, the proportion of oxadiazinetrione group-containing polyisocyanates in the reaction mixture according to the invention is less than 1% by weight, preferably 0.75% by weight, more preferably less than 0.5% by weight, very preferably less than 0.3% by weight and especially less as 0.1% by weight.

The products produced according to the invention are distinguished by an improved color number with at least comparable storage stability, which means that during a storage lasting several weeks, a smaller proportion of monomers split back from the biuret-containing polyisocyanate than is known from the prior art.

The biuret-containing polyisocyanates obtained by the process according to the invention are generally used in the coatings industry and can be used, for example, in coating compositions for 1K or 2K polyurethane coatings, for example for primers, fillers, basecoats, unpigmented topcoats, pig- mated topcoats and clearcoats in the field of industrial, in particular aircraft or large vehicle painting, wood, automotive, in particular OEM or automotive refinish tion, or decor painting can be used. The coating compositions are particularly suitable for applications in which particularly high application safety, outdoor weathering resistance, appearance, solvent resistance and / or chemical resistance are required. The curing of these coating compositions is not essential according to the invention. In the automotive industry, in particular, multilayer curing, for example of clearcoat and basecoat, (so-called two-in-one), or of filler, clearcoat and basecoat (so-called three-in-one) are increasingly being carried out.

Examples

example 1

An isocyanate-containing stream of 1000 ml / h, which is 99.2% by volume from 1, 6

Hexamethylene diisocyanate (HDI) and 0.8% by volume phosphoric acid bis (2-ethylhexyl ester) catalyst was used with an amine-containing stream of 200 ml / h and 10% by weight of 1, 6-diaminohexane (HDA) and to 90 wt .-% of the solvent N-methyl-2-pyrrolidone (NMP) was mixed. The mixing took place in a mixing pump into which the two streams were continuously conveyed.

The isocyanate-containing stream had on introduction into the mixing pump, a temperature of 120 ⁰ C. The amine-containing stream had a temperature of 100 ⁰ C on introduction into the mixing pump.

From the current consumption of the pump it could be deduced that the power consumption of the mixing pump was 96 W. This corresponds to a dissipation work of 2 ^* 10 ⁶ J / kg amine mixture.

The discharge of the pump was then passed through a heated to 140 ⁰ C residence time, which consisted of three over jacketed heated residence time tubes, with a total residence time of 60 minutes. At the end of the residence time section, a clear discharge of biuret group-containing polyisocyanate was obtained. The discharge was colorless and could be used after distilling off the solvent NMP and the unreacted 1, 6-hexamethylene diisocyanate in a wiper blade evaporator as a component in polyurethane coatings.

Example 2 (comparison)

As in Example 1, an isocyanate-containing stream of 1000 ml / hr, containing 99.2% by volume of 1,6-hexamethylene diisocyanate (HDI) and 0.8% by volume of the catalyst phosphoric acid-bis- (n-butyl ester), with an amine-containing stream of 100 ml / hr, which consisted of 10% by weight of 1,6-diaminohexane (HDA) and 90% by weight of the solvent N-methyl-2-pyrrolidone (NMP). The mixing took place in a mixing pump into which the two streams were continuously conveyed.

The isocyanate-containing stream had on introduction into the mixing pump, a temperature of 150 ⁰ C. The amine-containing stream had a temperature of 150 ⁰ C on introduction into the mixing pump.

The discharge of the pump was then passed through a heated to 190 ⁰ C residence time, which consisted of three over jacketed heated residence time tubes, with a total residence time of 65 minutes. At the end of the residence time section, a clear biuret-containing discharge occurred. In comparison to the discharge in Example 1, it was significantly more yellowish and thus did not meet the requirements for the colorlessness of polyurethane coatings.

Example 3 (comparison)

As in Example 2, an isocyanate-containing stream of 1000 ml / hr, containing 99.2% by volume of 1,6-hexamethylene diisocyanate (HDI) and 0.8% by vol. From the catalyst phosphoric acid bis- (n-butyl) consisted, with an amine-containing stream of 100 ml / hr, the 10 wt .-% of 1, 6-diaminohexane (HDA) and to 90 wt .-% of the solvent N-methyl-2-pyrrolidone (NMP) was mixed. The mixing took place in a mixing pump into which the two streams are continuously conveyed. The isocyanate-containing stream had on introduction into the mixing pump, a temperature of 140 ⁰ C. The amine-containing stream had a temperature of 140 ⁰ C on introduction into the mixing pump.

The dissipation work was reduced to about 10 ⁴ J / kg amine mixture. This already resulted in the mixing pump, a solid, glassy mass.

Claims

claims

1) A process for the preparation of biuret-containing polyisocyanates from a) at least one (cyclo) aliphatic di- and / or polyisocyanate, b) at least one (cyclo) aliphatic diamine having two primary amino groups, c) at least one acid and d) optionally at least a solvent comprising i) mixing the components a), b) and c) and optionally d) in a mixing device with a mixing work of at least 1.2 x 10 ⁴ J / kg diamine mixture and ii) passing the reaction mixture obtained from i) into at least one reactor in which the reaction mixture is thermally treated at a temperature below 170 ⁰ C and in the absence of water or dehydrating compounds.

2) Process according to claim 1, characterized in that the (cyclo) aliphatic di- and / or polyisocyanate is selected from the group consisting of tetramethylene diisocyanate, hexamethylene diisocyanate (1, 6

Diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of the lysiisocyanate, tetramethylxylylene diisocyanate, 2,4,4- and / or 2,2,4-trimethylhexane diisocyanate, tetramethylhexane diisocyanate, 1, 4, 1, 3 or 1, 2-diisocyanatocyclohexane, 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl) cyclohexane (isophorone diisocyanate), 1, 3 - or 1,4-bis (isocyanatomethyl) cyclohexane and 2,4- or 2,6-diisocyanato-1-methylcyclohexane.

3) Method according to one of the preceding claims, characterized in that the (cyclo) aliphatic diamine is selected from the group consisting of 1, 2-diaminoethane, 1, 2-diaminopropane, 1, 3-diaminopropane, 1, 4-diaminobutane, 1, 6-diaminohexane, 1, 6-diamino-2,2,4-trimethylhexane and / or 1,6-diamino-2,4,4-trimethylhexane, 1, 4 and / or 1, 5-diaminohexane, 2 , 4- and / or 2,6-diamino-1-methylcyclohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 1, 3 and / or 1, 4-bis (aminomethyl) cyclohexane and 4 , 4'-diaminodicyclohexylmethane.

4) Method according to one of the preceding claims, characterized in that in the reaction, the equivalent ratio of isocyanate groups to Amino groups of at least 4: 1.

5) Method according to one of the preceding claims, characterized in that it is the acid c) is a protic acid having a pKa value <10.

6) Method according to one of the preceding claims, characterized in that the acid c) is di-iso-propyl phosphate, di (2-ethylhexyl) phosphate, di (n-butyl) phosphate or di-hexadecyl phosphate. delt.

7) Method according to one of the preceding claims, characterized in that the temperature during mixing i) is less than 170 ⁰ C.

8) Method according to one of the preceding claims, characterized in that the mixing time in the mixing device i) is from 0.002 s to 5 s.

9) Method according to one of the preceding claims, characterized marked, that the temperature in the region of the reaction path ii) from 100 to 165

⁰ C is.

10) Method according to one of the preceding claims, characterized in that the residence time in the reactor ii) is in the range of 0.5 to 5 hours.

1 1) Process according to one of the preceding claims, characterized in that at least one solvent d) is present.

12) Process according to claim 12, characterized in that the solvent d) is selected from the group consisting of dioxane, tetrahydrofuran, alkoxyalkylcarboxylates, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, hexane, toluene, xylene, benzene, Chlorobenzene, o-dichlorobenzene, hydrocarbon mixtures, methylene chloride, trialkyl phosphates and N- (cyclo) alkylpyrrolidone.

13) Process according to claim 12, characterized in that the solvent d) is N-methylpyrrolidone or N-ethylpyrrolidone.

14) Biuretgruppenhaltiges polyisocyanate, obtained according to any one of the preceding claims having a color number of less than 20 APHA according to DIN ISO

6,271th

15) Biuretgruppenhaltiges polyisocyanate according to claim 14 having a viscosity of 1000 to 10,000 mPas at 23 ⁰ C according to DIN 53019 Part 1 (Rotationsvisko- simeter).

16) Biuretgruppenhaltiges polyisocyanate according to claim 14 to 15 having a content of uretdione polyisocyanates of less than 5% by weight.

17) Biuretgruppenhaltiges polyisocyanate according to claim 14 to 16 having a content of allophanate-containing polyisocyanates of less than 5% by weight.

18) Biuretgruppenhaltiges polyisocyanate according to claim 14 to 17 having a content of oxadiazintriongruppenhaltigen polyisocyanates of less than 1

Wt%.

19) Use of biuret-containing polyisocyanates according to any one of claims 14 to 18 or obtained according to one of claims 1 to 13 in coating agents for 1 K or 2K polyurethane coatings, for primers, fillers, Basecoats, unpigmented topcoats, pigmented topcoats and clearcoats in Industrial, aircraft or large-vehicle painting, wood, automotive, OEM or car refinish, decoating filler, clearcoat and basecoat.

20) A process for the preparation of biuret polyisocyanates by reacting a diisocyanate with a diamine in the presence of at least one acid and optionally a solvent, characterized in that diisocyanate stream 1 and diamine stream 2 and a stream 9 of recycled optionally present solvent and recycled excess diisocyanate 13 and Catalyst in a mixing device (I) mixed with each other, then the resulting mixture of diamine and diisocyanate in at least one reactor (II) and reacts to biuret polyisocyanate, then optionally existing nes solvent, excess diisocyanate and biuretgruppenhaltiges

Separates polyisocyanate by distillation and the optionally present solvent and the excess diisocyanate in the mixing device (I) returns.