EP0000348B1 - Polyuret polyisocyanates, preparation thereof and their use in the preparation of polyurethanes. - Google Patents

Description

The present invention relates to new organic polyisocyanates containing polyurethane groups, a novel process for their preparation and the use of the new compounds as an isocyanate component in the production of polyurethane plastics.

Polyisocyanates containing biuret groups are known and find practical use as raw materials for high-quality, lightfast coatings. You can, for example, from diisocyanates and water (DT-AS 1 101 394), hydrogen sulfide (DT-AS 1 165 580), formic acid (DT-AS 1 174760), tertiary alcohols (DT-AS 1 543 178, DT-AS 1 931 055, monoamines (DT-OS 2308015) or polyamines (DT-OS 2 261 065).

These prior art processes for the production of biuret polyisocyanates have a number of snap parts.

In most of the processes, some of the isocyanate groups initially form amino groups, which react further with excess diisocyanate via the corresponding diisocyanate ureas to form biuret polyisocyanates. The conversion of the isocyanate groups into amino groups is always accompanied by the formation of gaseous by-products such as carbon dioxide, carbon monoxide, carbon sulfoxide or olefins, the removal of which can lead to exhaust gas problems. In the heterogeneous reaction of diisocyanates with water, there is also the risk of the formation of insoluble polyureas which are difficult to separate. The reaction of diisocyanates with tertiary alcohols, which is used industrially for the production of biuret polyisocyanates, has the further disadvantage that relatively high temperatures are necessary for the urethane cleavage to convert the isocyanate groups into amino groups. Of particular disadvantage, however, is the fact that in these processes a part of the isocyanate groups of the diisocyanate used as the starting material must first be destroyed with the formation of amines.

According to DT-OS 2 261 065, the direct reaction of polyamines with diisocyanates leads to biuret polyisocyanates without elimination of volatile by-products and without conversion of isocyanate groups into amino groups. In this process, however, considerable practical difficulties arise, particularly when using technically easily accessible starting materials such as hexamethylene diamine and hexamethylene diisocyanate, since the tendency towards the formation of insoluble polyureas is very great because of the high reactivity of the amino groups with the isocyanate groups, and so in most cases To complete the implementation, uneconomically long reheating of the reaction mixture at high temperature is necessary, which leads to a severe impairment of the properties of the process products, in particular their inherent color.

In all of the prior art processes, the transition from diisocyanates to biuret polyisocyanates takes place under the disadvantages mentioned. The further reaction to polyurethane polyisocyanates is not observed.

It was therefore the object of the present invention to provide a new process which allows the preparation of high-quality modified polyisocyanates which combine the advantages of the biuret polyisocyanates in a simple manner without the process having the disadvantages of the processes of the prior art mentioned is affected by technology.

This object was surprisingly achieved by reacting certain organic monoamines, described in more detail below, with excess amounts of certain diisocyanates, described in more detail below, under certain reaction conditions described in more detail below.

in welcher

• R₁ und R₂ für gleiche oder verschiedene Reste stehen und aliphatische Kohlenwasserstoff- reste mit 1-4 Kohlenstoffatomen bedeuten, wobei R₁ und R₂ zusammen mit dem Stickstoffatom auch einen Piperidinrest bilden können,
• R₃ und R₄ für gleiche oder verschiedene Reste stehen und aliphatische, gegebenenfalls durch Estergruppen unterbrochene Kohlenwasserstoffreste mit 4-12 Kohlenstoffatomen oder cycloaliphatische Kohlenwasserstoffreste mit 4-15 Kohlenstoffatomen bedeuten und eine Zahl von 2-8 bedeutet.

The present invention relates to compounds of the formula

in which

• R ₁ and R ₂ stand for identical or different radicals and mean aliphatic hydrocarbon radicals with 1-4 carbon atoms, where R ₁ and R ₂ together with the nitrogen atom can also form a piperidine radical,
• R ₃ and R _{4 represent} identical or different radicals and are aliphatic hydrocarbon radicals with 4-12 carbon atoms, optionally interrupted by ester groups, or cycloaliphatic hydrocarbon radicals with 4-15 carbon atoms and represent a number from 2-8.

in welcher R_1' R₂, R₃, R₄ und n die genannte Bedeutung haben, dadurch gekennzeichnet, daß man

• a) aliphatische sekundäre Monoamine, deren aliphatische Kohlenwasserstoff-reste 1-4 Kohlenstoffatome aufweisen oder Piperidin oder
• b) Harnstoff- und/oder Biuretgruppen, sowie den bezüglich der Umsetzung indifferenten Rest der Amine aufweisende Umsetzungsprodukte der unter a) genannten Monoamine mit aliphatischen Diisocyanaten, deren aliphatischer Kohlenwasserstoffrest 4-12 Kohlenstoffatome aufweist und durch Estergruppen unterbrochen sein kann oder mit cycloaliphatischen Diisocyanaten, deren cycloaliphatischer Kohlenwasserstoffrest 4-15 Kohlenstoffatome aufweist

mit Diisocyanaten der unter b) genannten Art bei 0­140°C in Gegenwart von starken, mit Isocyanaten ein gemischtes Carbamidsäureanhydrid bildenden Säuren umsetzt, wobei man die Menge der eingesetzten Diisocyanate so wählt, daß insgesamt ein NCO/NH-Molverhältnis, bezogen auf Diisocyanate und Monoamine von 5,5:1 bis 100:1 vorliegt.The present invention also relates to a process for the preparation of compounds of the formula

in which R _{1 '} R ₂ , R ₃ , R ₄ and n have the meaning given, characterized in that

• a) aliphatic secondary monoamines whose aliphatic hydrocarbon radicals have 1-4 carbon atoms or piperidine or
• b) urea and / or biuret groups, and the reaction products of the monoamines mentioned under a) with aliphatic diisocyanates whose aliphatic hydrocarbon radical has 4-12 carbon atoms and which may be interrupted by ester groups or with cycloaliphatic diisocyanates, the reaction products of the amines mentioned under a) cycloaliphatic hydrocarbon radical has 4-15 carbon atoms

with diisocyanates of the type mentioned under b) at 0140 ° C in the presence of strong acids forming a mixed carbamic acid anhydride with isocyanates, the amount of diisocyanates used being chosen so that a total NCO / NH molar ratio, based on diisocyanates and monoamines from 5.5: 1 to 100: 1.

Finally, the present invention also relates to the use of the new compounds as an isocyanate component in the production of polyurethane plastics by the isocyanate polyaddition process.

in welcher

• R₁ und R₂ die bereits oben angegebene Bedeutung haben.

Starting materials for the process according to the invention are monoamines of the formula

in which

• R ₁ and R _{2 have} the meaning already given above.

Any mixtures of the amines mentioned can also be used. Specific examples of suitable monoamines are: dimethylamine, diethylamine, dipropylamine, dibutylamine or piperidine.

When carrying out the process according to the invention, modified polyisocyanates containing triuret or higher polyuret groups are formed from the monoamines mentioned above and the diisocyanates mentioned below by way of example, in which the rest of the amine which is indifferent to the reaction is incorporated. This reaction takes place via the intermediate stages of the compounds having urea groups which form from the amines and the diisocyanates or the compounds which have urea groups and compounds having further diurayate-forming biuret groups. Intermediate stages are therefore the monourea monoisocyanates formed by the addition of one mole of amine and one mole of diisocyanate or also of bisheas formed from two moles of amine and one mole of diisocyanate, or the biuret polyisocyanates formed from these and further diisocyanate. A logical consequence of this fact is, of course, that as a starting material according to a modification of the process according to the invention, these can also be used, for example, in a separate operation from the intermediates prepared in the example of monoamines and the isocyanates mentioned below as examples. Of course, the type of manufacture of these intermediates is of no importance here. It would of course also be conceivable to use as the starting material in the process according to the invention the reaction product containing urea groups from one mole of hexamethylene-bis-carbamic acid chloride and 2 moles of a monoamine which corresponds to the reaction product containing urea groups from one mole of hexamethylene diisocyanate and 2 moles of the same monoamine.

Ge for the inventive process _- suitable diisocyanates are those having aliphatically and / or cycloaliphatically attached isocyanate groups, in particular those in which the two isocyanate groups are connected via aliphatic hydrocarbon radicals having 4-12 carbon atoms or cycloaliphatic hydrocarbon radicals having 4-15 carbon atoms, wherein the aliphatic or Cycloaliphatic hydrocarbon chains can be interrupted or substituted by ester groups, such as: 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 2,4,4-trimethyl-1,6-di-isocyanatohexane, 1,11-diisocyanatoundecane, 3-isocyanatomethyl -3,5,5-trimethylcydohexyl isocyanate, 4,4'-cydohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,2-bis (isocyanatomethyl) cyclobutane or 6-isocyanato-caproic acid 2-isocyanatoethyl ester. Hexamethylene diisocyanate is preferably used.

Of course, diisocyanate mixtures can also be used, e.g. a urea or a biuret are first produced from a diisocyanate with a monofunctional amine, which then form polyurets with another diisocyanate.

While the reaction of amines with diisocyanates to the corresponding ureas or biurets belongs to the prior art, no technically usable process has been known to date, which would continue the addition reaction between amine and isocyanate beyond the intermediate stage of the corresponding biurets allowed. This is due to the inertia of the biurets with organic diisocyanates, which can only be overcome by using suitable catalysts. According to the invention the further reaction of monoamines with excess diisocyanate beyond the urea and biuret stage to give polyurets in the presence of catalysts is now also carried out.

The catalysts to be used in accordance with the invention are proton-releasing strong acids which react with isocyanates, in particular with aliphatic or cycloaliphatic isocyanates, to form a mixed acid anhydride, the carbamic acid corresponding to the isocyanate and the proton-releasing acid being the acids of the mixed acid anhydride. Such acids HX (X = acid residue after proton cleavage) suitable for the process according to the invention react with isocyanates Y-NCO to form adducts of the formula Y-NH-CO-X, which as a mixed anhydride of the carbamic acid Y-NH-COOH and Acid HX can be seen.

Examples of suitable acids are hydrogen halides such as e.g. Hydrogen fluoride, hydrogen chloride, hydrogen bromide or hydrogen iodine, chlorosulfonic acid, fluorosulfonic acid, sulfuric acid, alkanesulfonic acids such as e.g. Methanesulfonic acid or perhalogenated alkanesulfonic acids such as e.g. Trifluoromethanesulfonic acid. Hydrogen chloride is the preferred acid to be used in the process according to the invention. Instead of the acids, the ammonium salts corresponding to the acids with the amines used as starting material or the mixed carbamic acid anhydrides corresponding to the acids, in particular carbamic acid chlorides, the diisocyanates used as starting material or any other isocyanate can of course be used in the process according to the invention. In general, the catalysts are used in amounts of 0.001-10, preferably 0.01-1.0% by weight, based on the total weight of the reactants.

The process according to the invention can be carried out, in particular, using the acids mentioned as examples as catalysts at relatively low temperatures in the range from about 0-140 ° C., the reaction leading to triuret and polyuret groups having reaction products going beyond the stage of the biuret polyisocyanates in general Range between 90 and 140 ° C expires. The catalysis according to the invention with the acids mentioned by way of example thus permits, under mild reaction conditions, the preparation of isocyanate addition products containing polyurethane groups from organic diisocyanates and organic monoamines or urea groups or compounds having biuret groups formed from monoamines and diisocyanates. When the process according to the invention is carried out using monoamines as starting materials, no volatile by-products arise due to the mild reaction conditions. The remainder of the monoamines, which are indifferent to the implementation of the invention, thus always forms part of the process products of the invention.

When carrying out the process according to the invention using monoamines as starting materials, these and the diisocyanates are generally used in proportions which have an NCO / NH molar ratio of 5.5: 1 to 100: 1, preferably 6: 1 to 30: 1, correspond. When using starting materials containing urea groups, i.e. Corresponding quantitative ratios of monourea monoisocyanates or bis-ureas formed from monoamines and diisocyanates are used, taking into account that monoamines and diisocyanates in a molar ratio of 1: 1 or 2: 1 are already present in the starting materials containing urea groups. These monoamines and diisocyanates, which are present in the form of the starting materials containing urea groups, are included in the calculation of the amine: diisocyanate ratio. The same statements apply mutatis mutandis when starting materials containing biuret groups are used, as they result from the reaction of the intermediate products containing urea groups with further diisocyanate.

• Man legt das Diisocyanat in einem geeigneten Reaktionsgefäß vor und gibt das Amin bei Temperaturen von 0-100°C zu. Dabei beträgt das NCO/NH-Molverhältnis im allgemeinen 6:1 bis 30:1. Feste Amine werden über einen beheitzten und flüssige Amine über einen normalen Tropftrichter dosiert. Gasförmige Amine werden eventuell zusammen mit einem Inertgasstrom in das Diisocyanat eingeleitet. Es bilden sich spontan die entsprechenden Hamstoffe. Bei Einsatz von sekundären Aminen bliebt die Reaktion bei Abwesenheit des Katalysators auf der Stufe der zumeist in überschüssigem Diisocyanat nicht vollständig löslichen Harnstoffe stehen. Die Katalysatorzugabe kann zu jedem Zeitpunkt der Reaktion erfolgen. Man kann ihn z.B. mit dem Diisocyanat vorlegen, ihn als Ammoniumsalz mit den Aminen eindosieren oder ihn erst nach Beendigung der Vorreaktion zu Harnstoff- oder Biuretisocyanaten zugeben. Danach wird das Reaktionsgemisch auf 90­140°C erhitzt und der Reaktionsverlauf durch Kontrolle der NCO-Gehaltsabnahme verfolgt. Bei Verwendung von flüchtigen Katalysatoren, z.B. Chlorwasserstoff, kann zur Vermeidung von bei höheren Temperaturen möglichen Katalysatorverlusten unter Druck gearbeitet werden.

The procedure for carrying out the process according to the invention is generally as follows:

• The diisocyanate is placed in a suitable reaction vessel and the amine is added at temperatures of 0-100 ° C. The NCO / NH molar ratio is generally 6: 1 to 30: 1. Solid amines are dosed via a heated and liquid amine via a normal dropping funnel. Gaseous amines may be introduced into the diisocyanate together with an inert gas stream. The corresponding ureas form spontaneously. When secondary amines are used, the reaction remains in the absence of the catalyst at the stage of the ureas, which are usually not completely soluble in excess diisocyanate. The catalyst can be added at any time during the reaction. It can be introduced, for example, with the diisocyanate, metered in as the ammonium salt with the amines, or added to urea or biuret isocyanates only after the preliminary reaction has ended. The reaction mixture is then heated to 90140 ° C. and the course of the reaction is monitored by checking the decrease in NCO content. When using volatile catalysts, for example hydrogen chloride, it is possible to work under pressure to avoid possible catalyst losses at higher temperatures.

If the NCO decrease corresponds to the desired "degree of polyurethaneization": i.e., if the desired amount of NCO groups has been reacted per amino group, the reaction is terminated. This is done simply by cooling the reaction mixture to 20-50 ° C. The reaction times required depend on the type of starting products, on the temperature and in particular on the type and amount of the catalyst used. They are generally 1-20, preferably 2-8, hours. After the reaction has ended, clear, colorless to slightly yellowish reaction solutions are obtained.

The reactions are usually ended at a point in time when on average about 3 NCO groups have been consumed per amino group. The products then have an average functionality of 3.5, taking into account the polymer homologue. However, it is possible to achieve a higher "degree of polyuretization", i.e. implement 4 and more NCO groups per amino group. However, the viscosities of the products then increase quickly.

The catalyst is generally removed by distilling the reaction mixture in vacuo. If hydrogen halides are used as catalysts, the removal, in particular in the case of smaller amounts of catalyst, can also be carried out by adding equimolar amounts of propylene oxide. It is also possible to remove the catalyst by e.g. Remove thin film evaporation if the crude isocyanate is freed from excess diisocyanate. The distillate from the thin-film distillation, which then contains the catalyst in addition to the diisocyanate, can be reused as the starting material.

If the removal of excess diisocyanate is provided, it is usually done by thin-layer evaporation; however, it can also be extracted by extraction of the reaction mixture with suitable solvents, e.g. Hexane, heptane etc. can be achieved.

The crude isocyanates can be used as such. In most cases, however, they are preferably freed from monomeric isocyanate fractions by thin-layer evaporation or extraction. The monomer-free products are light yellow oils or solid resins; the NCO content is 10-22%.

The process is ideal for continuous implementation. In these cases, several reaction vessels are cascaded together. In the first reaction vessel, the starting products diisocyanate and amine are mixed at approx. 60 ° C. The catalyst is added at about 80 ° C. in the second reaction vessel. In the third and optionally further reaction vessels, the further reaction to the polyisocyanate takes place at approx. 90-140 ° C., the desired degree of “polyurethaneisation” being set by controlling the temperature and the residence time.

Excess diisocyanate and the catalyst are e.g. removed via a coiled tube evaporator combined with a downstream thin film evaporator. The distillates consisting of diisocyanate and catalyst are combined and returned to the process. The polyisocyanate is obtained as the residue of thin-film distillation.

Extraction of the process product according to the invention with suitable solvents such as e.g. n-Hexane is not necessary since the elimination of monoisocyanate when carrying out the process according to the invention, which would have to be removed by extraction, is impossible.

When carrying out the process according to the invention, the properties of the modified polyisocyanates obtained, in particular their NCO functionality, NCO content, and the viscosity can be adjusted not only by selecting the suitable starting materials but also particularly simply by adjusting the "degree of polyuretization", i.e. the number of NCO groups converted per amino group can be controlled.

When secondary monoamines with aliphatically or cycloaliphatically bound amino groups and aliphatic or cycloaliphatic diisocyanates are used, the process products of the formula given at the outset are obtained. In the particularly preferred use of dialkyl amines with C _l- C ₄₇ A1kylresten or piperidine, and hexamethylene diisocyanate as starting materials in carrying out the process according to the invention are formed, the most preferred products of the process according to the invention of the above general. my formula in which the radicals R ₁ and R _{2 have} the meaning already mentioned, R ₃ and R _{4 are} hexamethylene radicals and n is a number from 2 to 8.

The process products according to the invention can be used in particular as an isocyanate component in the production of polyurethane plastics by the isocyanate polyaddition process. They are both suitable for the production of poly. urethane foams, as well as for the production of elastomers, coatings or bonds. In particular when using the process products according to the invention for the first-mentioned area of application, it is often unnecessary to distill off the excess diisocyanate after the reaction according to the invention has ended. The monomer-free process products according to the invention are excellent raw materials for producing high-quality, weatherproof and lightfast coatings.

Regarding the use of the process products according to the invention as "Lackiso _- cyanates" is to be emphasized with commercially available polyhydroxy polyacrylates particular their excellent compatibility. A Another advantage of the process products according to the invention over known biuret polyisocyanates is that they are stable against monomer cleavage, ie that the monomer content of the polyisocyanates according to the invention does not increase even during storage at elevated temperature (50 ° C.).

EXAMPLE 1

135 g (3 mol) of dimethylamine were introduced into 3024 g (18 mol) of 1,6-diisocyanatohexane under nitrogen blanket in a 4 l four-necked flask equipped with a stirrer, reflux condenser and contact thermometer, the temperature in the reaction vessel rising to approx. 60 ° C. The corresponding urea was formed, which, apart from small residual amounts, was dissolved after the amine addition had ended. 7 g (0.19 mol) of hydrogen chloride in 100 g of 1,6-diisocyanatohexane were then added to the reaction mixture and the temperature was raised to 100.degree. The NCO content of the now clear reaction solution was 44% (corresponding to a consumption of 1 NCO group per amino group). After 2 hours the NCO content was 40% (corresponding to a consumption of 2 NCO groups per amino group) and after 4 hours to 35% (corresponding to a consumption of 3.3 NCO groups per amino group, corresponding to n = 2.3 ) decreased. The reaction solution was cooled to 50 ° C. and 11 g (0.19 mol) of propylene oxide were added to bind the hydrolyzable chlorine. The subsequent thin-film distillation gave 1600 g of 1,6-diisocyanatohexane as the distillate and 1540 g of polyurethane polyisocyanate as the residue (NCO content = 19.5%; viscosity at 25 ° C = 5000 mPa.s; residual content of monomeric 1,6-diisocyanatohexane = 0 , 60%).

By checking the monomer content of product samples that were stored at 50 ° C. for a prolonged period, it was found that the polyisocyanate is stable against monomer cleavage.

EXAMPLE 2

Analogously to Example 1, 3024 g (18 mol) of 1,6-diisocyanatohexane were reacted with 225 g (5 mol) of dimethylamine with the addition of 7 g (0.19 mol) of hydrogen chloride. After 7 hours, the NCO content of the reaction mixture was 27.4% (corresponding to a consumption of 3 NCO groups per amino group (n = 2)). After the thin-layer evaporation, 2150 g of polyisocyanate were obtained in addition to 1000 g of 1,6-diisocyanatohexane (NCO content = 16.2%; viscosity at 25 ° C. = 30,000 mPa.s; residual monomer content = 0.3%).

EXAMPLE 3

Analogously to Example 1, 1008 g (6 mol) of 1,6-diisocyanatohexane were reacted with 45 g (1 mol) of dimethylamine with the addition of 3 g (0.08 mol) of hydrogen chloride. After 6 hours the NCO content of the reaction mixture had dropped to 28% (corresponding to a degree of conversion of 5 NCO groups per amino group (n = 4)). The viscosity of the crude isocyanate was 200 mPa.s / 25 ° C.

EXAMPLE 5 (Usage example)

154 g of a 65% solution of a highly branched polyester based on phthalic anhydride and trimethylolpropane (hydroxyl content 8%) in ethyl glycol acetate / xylene (1: 1) were added after adding 1 g of a tertiary amine as catalyst and 0.4 g of cellulose butyrate propionate diluted as a leveling agent with 220 g of a solvent mixture of methyl ethyl ketone, butyl acetate, ethyl glycol acetate and toluene (4: 1: 4: 1). 135 g of a 75% solution of the polyisocyanate from Example 1 in ethyl glycol acetate / xylene (1: 1) were added (NCO / OH molar ratio = 1: 1). The finished paint solution was then applied to steel sheets where the paint films cured at room temperature. The fully cured clear lacquer films were scratch-resistant, elastic and resistant to solvents such as toluene, ethyl glycol acetate, ethyl acetate or acetone. They also had the following characteristics:

EXAMPLE 6 (Usage example)

154 g of the polyester solution described in Example 5 were processed with 100 g of titanium dioxide (rutile type) to form a paste. In addition to the catalyst and leveling agent, 120 g of the solvent mixture already described were added to this paste. The mixture thus obtained was mixed with 135 g of a 75% solution of the polyisocyanate from Example 1 in ethyl glycol acetate / xylene (1: 1) and applied in a thin layer to steel sheets. The paint films containing pigment hardened completely at room temperature. They were characterized by scratch resistance and solvent resistance and had the following properties compared to the clear lacquer films:

Claims (4)

1. Compounds of the formula

in which

R₁ and R₂ represent identical or different radicals and denote aliphatic hydrocarbon radicals with 1-4 carbon atoms, R₁ and R₂, together with the nitrogen atom, also being able to form a piperidine radical,

R₃ and R₄ represent identical or different radicals and denote aliphatic hydrocarbon radicals with 4-12 carbon atoms, optionally interrupted by ester groups, or they denote cycloaliphatic hydrocarbon radicals with 4-15 carbon atoms and

n denotes an integer from 2 to 8.

2. Compounds of the formula according to Claim 1, R,, R₂ and n having the meaning mentioned in Claim 1 and R₃ and R₄ each representing hexamethylene radicals.

3. A process for the preparation of compounds of the formula

in which R₁, R₂, R₃, R₄ and n have the meaning mentioned in Claim 1, characterised in that

a) aliphatic secondary monoamines, the aliphatic hydrocarbon radicals of which have 1-4 carbon atoms, or piperidine or

b) reaction products containing urea and/or biuret groups and the amine radical inert to the reaction, from the reaction of the monoamines named under a) with aliphatic diisocyanates, the aliphatic hydrocarbon radical of which contains 4-12 carbon atoms and can be interrupted by ester groups, or with cycloaliphatic diisocyanates, the cycloaliphatic hydrocarbon radical of which contains 4-15 carbon atoms,

are reacted with diisocyanates of the kind mentioned under b), at 0­140°C in the presence of strong acids which form a mixed carbamic acid anhydride with isocyanates; the quantity of diisocyanates used is chosen so that there is altogether an NCO/NH molar ratio of 5.5 : 1 to 100 : 1, related to the diisocyanates and and monoamines.

4. The use of the compounds according to Claim 1 as isocyanate components in the production of polyurethane plastics according to the isocyanate polyaddition process.