EP0000194B1 - Preparation of isocyanate-substituted allophanates and their use for the preparation of lacquers - Google Patents

Description

in der

• R' einen mono- oder polyvalenten organischen Rest einer mono- oder polyfunktionellen Hydroxylverbindung,
• n eine ganze Zahl von 1 bis 6 und
• R einen bifunktionellen organischen Rest bedeutet,

mit überschüssigen Diisocyanaten entweder rein thermisch oder in Gegenwart von Metallcarboxylaten, Metallchelaten oder tertiären Aminen als Katalysator zur Reaktion gebracht werden, bis der eintretende NCO-Abfall einer vollständigen Umsetzung der vorhandenen Urethangruppen mit Isocyanatgruppen entspricht. Die exakte Konstitution der Reaktionsprodukte kann gemäß der Lehre der britischen Patentschrift nicht mit Sicherheit angegeben werden. Aus den gemessenen NCO-Werten der Reaktionsgemische bzw. der daraus isolierten Endprodukte wird geschlossen, daß diese im wesentlichen Allophanatpolyisocyanate darstellen. Bei der genaueren analytischen Kontrolle der nach der Lehre der britischen Patentschrift erhaltenen Produkte durch IR-Spektroskopie und insbesondere gelchromatographische Untersuchung wird jedoch gefunden, daß ein beträchtlicher Teil aus Isocyanuratpolyisocyanaten und Uretdionpolyisocyanaten besteht, die durch als Nebenreaktionen ablaufende Dimerisierung und Trimerisierung der NCO-Gruppen entstehen. Wird nun die Reaktion nach Erreichen des für vollständige Allophanatisierung errechneten NCO-Gehaltes abgestoppt, so bleibt für jede durch Nebenreaktion abreagierte NCO-Gruppe eine Urethangruppe unumgesetzt im Reaktionsgemisch zurück.British Patent No. 994 890 describes a process for the production of organic polyisocyanates in which urethane isocyanates of the general formula

in the

• R 'is a mono- or polyvalent organic radical of a mono- or polyfunctional hydroxyl compound,
• n is an integer from 1 to 6 and
• R represents a bifunctional organic radical,

be reacted with excess diisocyanates either purely thermally or in the presence of metal carboxylates, metal chelates or tertiary amines as a catalyst until the NCO drop which occurs corresponds to a complete reaction of the urethane groups present with isocyanate groups. The exact constitution of the reaction products cannot be given with certainty according to the teaching of the British patent. From the measured NCO values of the reaction mixtures or the end products isolated therefrom, it is concluded that these are essentially allophanate polyisocyanates. However, on closer analytical control of the products obtained according to the teaching of the British patent specification by IR spectroscopy and in particular gel chromatographic analysis, it is found that a considerable part consists of isocyanurate polyisocyanates and uretdione polyisocyanates which result from dimerization and trimerization of the NCO groups which occur as side reactions. If the reaction is stopped after the NCO content calculated for complete allophanatization is reached, a urethane group remains unreacted in the reaction mixture for each NCO group which has been reacted by a side reaction.

The occurrence of trimerization and dimerization as side reactions in the reactions according to the teaching of British Patent 994 890 is not surprising, since in the absence of catalysts until the NCO content drops to the value calculated for complete conversion of the urethane groups, long reaction times at relatively high temperatures (eg 24 hours at 130 to 135 ° C in Example 1, page 3, lines 49 to 51) and the formation of isocyanurates from allophanates and isocyanates or dimers of these isocyanates is known from the literature (JC Kogon, Joum. Am. Chem. Soc., Vol. 78, 1956, pages 4911 to 4914).

Although the use of catalysts permits a sharp reduction in the reaction temperature (see 2, lines 92 to 95), it has long been known that the catalysts described (metal carboxylates, metal chelates, tertiary amines) are excellent dimerization and trimerization catalysts for isocyanates, so that the occurrence of such side reactions can be explained to a considerable extent in the reaction of urethane groups with isocyanates to allophanates.

The side reactions to dimeric or trimeric polyisocyanates which cannot be ruled out according to the process of GB-PS 994 890 lead to reaction mixtures which differ from the corresponding pure allophanate polyisocyanates, in particular due to their poorer compatibility with numerous polyhydroxyl compounds, in particular with polyhydroxy polyacrylates, as used in the production of Differentiate polyurethane plastics as reactants for the polyisocyanates.

The problem of producing pure allophanate polyisocyanates, i.e. Allophanate polyisocyanates which are not "contaminated" with dimeric and in particular trimeric polyisocyanates have already been mentioned in DT-ASs 2,009,179 and 2,040,645. The processes of these publications, however, involve the production of aromatic allophanate polyisocyanates containing bonded isocyanate groups which, according to the teaching of the aforementioned prior publications, can be obtained free of the by-products mentioned if the addition reaction leading to the allophanate polyisocyanate is carried out in the presence of alkylating substances (DT- AS 2 009 179), and optionally in the presence of certain metal compounds as catalysts (DT-AS 2 040 645). However, the processes of DT-AS's 2 009 179 and 2 040 645 are unsuitable for the production of allophanate polyisocyanates with aliphatic and / or cycloaliphatic isocyanate groups. For example, the isocyanate content of a reaction mixture of a urethane and an aliphatic polyisocyanate drops only insignificantly at 160-170 ° C. over 50 hours. In the case of simultaneous use of metal catalysts according to DT-AS 2 040 645, only a 66% conversion was observed at 110-120 ° C. over the course of 35 hours. The reaction mixture had changed color very strongly. According to the prior art, there is therefore no usable process for the preparation of pure, light-colored allophanate polyisocyanates with isocyanate groups bound by aliphatic or cycloaliphatic means.

It was an object of the present invention to provide such a method.

Surprisingly, this object was achieved by carrying out the reaction between aliphatic or cycloaliphatic polyisocyanates and compounds containing urethane groups in the presence of certain acids, which are described in more detail below.

The present invention relates to a process for the preparation of allophanates containing aliphatic and / or cycloaliphatic isocyanate groups by reacting organic compounds containing urethane groups with organic polyisocyanates with aliphatic and / or cycloaliphatic isocyanate groups, characterized in that the reaction in the presence of strong, performs a mixed carbamic acid anhydride with aliphatic or cycloaliphatic isocyanates.

The present invention also relates to the use of the allophanates containing isocyanate groups obtained by this process in combination with hydroxyl-functional higher molecular weight compounds for the production of coatings.

in welcher

• A für einen Rest steht, wie er durch Entfernung der Hydroxylgruppen aus einer n-wertigen organischen Hydroxylgruppen aufweisenden Verbindung erhalten wird, welcher von den Hydroxylgruppen abgesehen gegenüber Isocyanatgruppen inert ist,
• R₁ für einen Rest steht, wie er durch Entfernung der Isocyanatgruppen aus einem Diisocyanat mit aliphatisch und/oder cycloaliphatisch gebundenen Isocyanatgruppen erhalten wird und
• ⁿ für eine ganze Zahl von 1 bis 4 steht.

In the process according to the invention, any starting urethane groups and optionally aliphatic or cycloaliphatically bound isocyanate groups which are otherwise inert under the reaction conditions are used as starting materials. These compounds are generally obtained by reacting isocyanates with compounds containing alcoholic or phenolic hydroxyl groups. However, it is also. possible to use in the process according to the invention those urethanes which have been obtained, for example, by reacting chloroformates with amines having primary amino groups or in any other way. According to a particular embodiment of the process according to the invention, urethanes prepared in situ from phenols or alcohols and excess amounts of aliphatic or cycloaliphatic polyisocyanates are used as starting materials. The reaction mixture obtained in this reaction then already contains the second main component of the process according to the invention, the aliphatic or cycloaliphatic polyisocyanate, which was used in excess in the production of urethane. The preferred compounds containing urethane groups to be used as starting materials in the process according to the invention include those of the general formula

in which

• A represents a radical as obtained by removing the hydroxyl groups from a compound having n-valent organic hydroxyl groups which, apart from the hydroxyl groups, is inert to isocyanate groups,
• R _{1 represents} a radical as it is obtained by removing the isocyanate groups from a diisocyanate with aliphatic and / or cycloaliphatic isocyanate groups and
• ^{n represents} an integer from 1 to 4.

mit Diisocyanaten der Formel

erhalten, wobei pro Mol der Hydroxylgruppen aufweisenden Verbindung vorzugsweise mindestens n Mol des Diisocyanats zum Einsatz gelangen. Es ist jedoch auch möglich, bei dieser, zu den Urethangruppen aufweisenden Ausgangsmaterialien des erfindungsgemäßen Verfahrens führenden Umsetzung pro Mol der Hydroxylgruppen aufweisenden Verbindung A(OH)_n weniger als n Mole eines Diisocyanats einzusetzen, d.h. die Menge des Diisocyanats so zu bemessen, daß sie im Bereich zwischen 0,5 n und 1 n Mol pro Mol der Hydroxylgruppen aufweisenden Verbindung liegt. In diesem Falle würden wegen der eintretenden Kettenverlängerungsreaktion über Urethangruppen mehr als n Urethangruppen aufweisende Ausgangsmaterialien entstehen. Ebenfalls möglich wäre der Einsatz von Urethangruppen aufweisenden Verbindungen, die durch Umsetzung von Hydroxylgruppen aufweisenden Verbindungen A(OH)_n mit Monoisocyanaten und/oder höher als difunktionellen Polyisocyanaten gegebenenfalls im Gemisch mit Diisocyanaten erhalten worden sind, und welche gegebenenfalls keine freien Isocyanatgruppen aufweisen.In accordance with these statements, the urethanes of the general formula mentioned which are preferably to be used in the process according to the invention and which have isocyanate groups are preferably reacted with compounds of the formula having hydroxyl groups

with diisocyanates of the formula

obtained, preferably at least n mol of the diisocyanate being used per mole of the compound containing hydroxyl groups. However, it is also possible to use less than n moles of a diisocyanate per mole of the hydroxyl group-containing compound A (OH) _n in this reaction leading to the starting materials of the process according to the invention containing urethane groups, ie the amount of the diisocyanate is such that it is in the Range is between 0.5 n and 1 n mol per mol of the compound having hydroxyl groups. In this case, more than n starting materials containing n urethane groups would be formed due to the chain extension reaction occurring via urethane groups. It would also be possible to use compounds containing urethane groups which were obtained by reacting compounds A (OH) _n containing hydroxyl groups with monoisocyanates and / or higher than difunctional polyisocyanates, if appropriate in a mixture with diisocyanates, and which may have no free isocyanate groups.

The starting materials containing urethane groups for the process according to the invention are prepared by the well-known methods of polyurethane chemistry, i.e. in particular by simply heating the starting materials to 40 to 150 °, preferably 50 to 100 ° C.

Both polyols such as phenol, α-naphthol, cresol, resorcinol or tris-hydroxybenzenes and organic compounds containing alcoholic hydroxyl groups can be used as polyhydroxyl compounds A (OH) _n . Such alcoholic compounds containing hydroxyl groups are preferred over the phenols mentioned by way of example.

• 1. Niedermolekulare, gegebenenfalls Ätherbrücken aufweisende 1-4-wertige aliphatische Alkohole des Molekulargewichtsbereichs 32-250 wie z.B. Methanol, Äthanol, Propanol, Isopropanol, isomere Butanole, Allylalkohol, Pentanole, Hexanole und Heptanole, 2-Äthylhexanol, Fettalkohole mit 10-20 Kohlenstoffatomen, Äthandiol, Propandiol-1,2 und -1,3, Butandiol-1,2, -1,3 und -1,4, Pentandiol-1,5, Neopentylglykol, Hexandiol-1,6 und -2,5, 3-Methylpentandiol-1,5, 2-Methyl-2-propyl- propandiol-1,3, 2,2-Diäthyl-propandiol-1,3, 2- Äthylhexandiol-1,3, 2,2,4-Trimethylpentandiol-1,3, Trimethylhexandiol-1,6, Decandiol-1,10, Dodecandiol-1,12, 2-Butandiol-1,4, 2-Methylenpropandiol-1,3, Glyzerin, Butantriol, 2-Hydroxymethyl-2-methylpropandiol-1,3, 1,2,6-Hexantriol, Trimethylol-äthan, Trimethylolpropan, Pentaerythrit, Äthylenglykol-monoalkyl- oder -aryläther, Propylenglykol-monoalkyläther, Diäthylenglykol, Triäthylenglykol, Tetraäthylenglykol.
• 2. Cycloaliphatische 1-4-wertige Alkohole des Molekulargewichtsbereichs 88-250, wie z.B. Cyclopentanol, Cyclohexanol, Methylcyclohexanol, Trimethylcyclohexanol, 4-tert.-Butyl- cyclohexanol, Menthol, Borneol und Isoborneol, 2-Hydroxydecalin, 1,2-, 1,3- und 1,4-Cyclohexandiol, 2,4-Dihydroxy-1,1,3,3-tetramethyl- cyclobutan, 1,4-Bis-hydroxymethylcyclohexan, Bis-(4-hydroxycyclohexyl)-methan, 2,2-Bis(4-hydroxycyclohexyl)-propan, 2-Methyl-2,4-bis-(4-hydroxycyclohexyl)-pentan, Furfuryl- und Tetrahydrofurfurylalkohol, Bis-hydroxymethylnorbornan, Dihydroxymethyl-tricyclodecan.
• 3. Araliphatische 1-4-wertige Alkohole des Molekulargewichtsbereichs 103-300, wie z.B. Benzylalkohol, Phenyläthylalkohol, 3-Phenylpropanol oder 4,4'-Di-(2-hydroxyäthyl)-diphenylmethan oder.
• 4. 1-4 Hydroxylgruppen aufweisende. Polythioäther, Polyacetale, Polycarbonate oder insbesondere Polyester bzw. Polyäther der in der Polyurethanchemie an sich bekannten Art mit mittleren Molekulargewichten von 250 bis 5000, vorzugsweise 300 bis 2000. Die in Frage kommenden Hydroxylgruppen aufweisenden Polyester sind z.B. Umsetzungsprodukte von mehrwertigen, vorzugsweise zweiwertigen und gegebenenfalls zusätzlich dreiwertigen Alkoholen mit mehrwertigen, vorzugsweise zweiwertigen, Carbonsäuren. Anstelle der freien Polycarbonsäuren können auch die entsprechenden Polycarbonsäureanhydride oder entsprechende Polycarbonsäureester von niedrigen Alkoholen oder deren Gemische zur Herstellung der Polyester verwendet werden. Die Polycarbonsäuren können aliphatischer, cycloaliphatischer, aromatischer und/oder heterocyclischer Natur sein und gegebenenfalls, z.B. durch Halogenatome, substituiert und/oder ungesättigt sein. Als Beispiele hierfür seien genannt:
  • Bernsteinsäure, Adipinsäure, Korksäure, Azelainsäure, Sebacinsäure, Phthalsäure, Isophthalsäure, Trimellitsäure, Phthalsäureanhydrid, Tetrahydrophthalsäureanhydrid, Hexahydrophthalsäureanhydrid, Tetrachlorphthalsäureanhydrid, Endomethylentetrahydrophthalsäureanhydrid, Glutarsäureanhydrid, Maleinsäure, Maleinsäureanhydrid, Fumarsäure, dimere und trimere Fettsäuren wie Ölsäure, gegebenenfalls in Mischung mit monomeren Fettsäuren, Terephthalsäuredimethylester, Terephthalsäure-bis-glykolester. Als mehrwertige Alkohole kommen z.B. Äthylenglykol, Propylenglykol-(1,2) und -(1,3), Butylenglykol-(1,4) und -(2,3), Hexandiol-(1,6), Octandiol-(1,8), Neopentylglykol, Cyclohexandimethanoi(1,4 - bis - hydroxymethylcyclohexan), 2-Methyl-1,3-propandiol, Glycerin, Trimethylolpropan, Hexantriol-(1,2,6), Butantriol-(1,2,4), Trimethyloläthan, Pentaerythrit, Chinit, Mannit und Sorbit, Methylglykosid, ferner Diäthylenglykol, Triäthylenglykol, Tetraäthylenglykol, Polyäthylenglykole, Dipropylenglykol, Polypropylenglykole, Dibutylenglykol und Polybutylenglykole in Frage. Auch Polyester aus Lactonen, z.B. _E-Caprolacton oder Hydroxycarbonsäuren, z.B. w-Hydroxycapronsäure, sind einsetzbar.

These preferred alcoholic hydroxyl compounds include A (OH) _n

• 1. Low molecular weight, optionally ether-bridged 1-4-valent aliphatic alcohols of the molecular weight range 32-250 such as methanol, ethanol, propanol, isopropanol, isomeric butanols, allyl alcohol, pentanols, hexanols and heptanols, 2-ethylhexanol, fatty alcohols with 10-20 carbon atoms , Ethanediol, 1,2-and 1,3-propanediol, 1,2-butanediol, 1,3 and 1,4, pentanediol-1,5, neopentylglycol, 1,6-hexanediol and 2,5,3 -Methylpentanediol-1,5,2-methyl-2-propyl-propanediol-1,3,2,2-diethyl-propanediol-1,3,2-ethylhexanediol-1,3,2,2,4-trimethylpentanediol-1 , 3, trimethylhexanediol-1,6, decanediol-1,10, dodecanediol-1,12, 2-butanediol-1,4, 2-methylene-propanediol-1,3, glycerol, butanetriol, 2-hydroxymethyl-2-methylpropanediol-1 , 3, 1,2,6-hexanetriol, trimethylol-ethane, trimethylolpropane, pentaerythritol, ethylene glycol monoalkyl or aryl ether, propylene glycol monoalkyl ether, diethylene glycol, triethylene glycol, tetraethylene glycol.
• 2. Cycloaliphatic 1-4-valent alcohols in the molecular weight range 88-250, such as cyclopentanol, cyclohexanol, methylcyclohexanol, trimethylcyclohexanol, 4-tert-butylcyclohexanol, menthol, borneol and isoborneol, 2-hydroxydecalin, 1,2-, 1 , 3- and 1,4-cyclohexanediol, 2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane, 1,4-bis-hydroxymethylcyclohexane, bis- (4-hydroxycyclohexyl) methane, 2,2- Bis (4-hydroxycyclohexyl) propane, 2-methyl-2,4-bis (4-hydroxycyclohexyl) pentane, furfuryl and tetrahydrofurfuryl alcohol, bis-hydroxymethylnorbornane, dihydroxymethyltricyclodecane.
• 3. Araliphatic 1-4-valent alcohols in the molecular weight range 103-300, such as, for example, benzyl alcohol, phenylethyl alcohol, 3-phenylpropanol or 4,4'-di- (2-hydroxyethyl) diphenylmethane or.
• 4. 1-4 hydroxyl groups. Polythioethers, polyacetals, polycarbonates or, in particular, polyesters or polyethers of the type known per se in polyurethane chemistry with average molecular weights of 250 to 5000, preferably 300 to 2000. The polyesters in question containing hydroxyl groups are, for example, reaction products of polyvalent, preferably divalent and optionally additionally trihydric alcohols with polyhydric, preferably dihydric, carboxylic acids. Instead of the free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof can also be used to produce the polyesters. The polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic and / or heterocyclic in nature and optionally substituted, for example by halogen atoms, and / or unsaturated. Examples include:
  • Succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimeric and trimeric fatty acids such as oleic acid, optionally mixed with monomeric fatty acids, terephthalic acid dimethyl ester, Terephthalic acid bis-glycol ester. Polyhydric alcohols include, for example, ethylene glycol, propylene glycol (1,2) and - (1,3), butylene glycol (1,4) and - (2,3), hexanediol (1,6), octanediol (1, 8), neopentyl glycol, cyclohexanedimethanoi (1,4 - bis - hydroxymethylcyclohexane), 2-methyl-1,3-propanediol, glycerin, trimethylolpropane, hexanetriol (1,2,6), butanetriol (1,2,4), Trimethylolethane, pentaerythritol, quinite, mannitol and sorbitol, methylglycoside, also diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycols, dipropylene glycol, polypropylene glycols, dibutylene glycol and polybutylene glycols in question. Polyesters of lactones, for example _E- caprolactone or hydroxycarboxylic acids, for example w-hydroxycaproic acid, can also be used.

The polyethers which have one to four hydroxyl groups and which are suitable according to the invention are also those of the At known per se and are obtained, for example, by polymerizing epoxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with themselves, for example in the presence of BF ₃ , or by adding these epoxides, optionally in a mixture or in succession, to starting components with reactive hydrogen atoms such as alcohols or phenols, for example water, ethylene glycol, propylene glycol (1,3) or - (1,2), trimethylolpropane, 4,4'-dihydroxydiphenylpropane .

Among the polythioethers, the condensation products of thiodiglycol with itself and / or with other glycols, dicarboxylic acids or formaldehyde should be mentioned in particular. Depending on the co-components, the products are polythio ether, polythioether ester or polythioether-polyacetal.

As polyacetals e.g. the compounds which can be prepared from glycols, such as diethylene glycol, triethylene glycol, 4,4'-dioxethoxy-diphenyldimethylmethane, hexanediol and formaldehyde. Polyacetals suitable according to the invention can also be prepared by polymerizing cyclic acetals.

Suitable polycarbonates containing hydroxyl groups are those of the type known per se, which can be obtained, for example, by reacting diols such as propanediol (1,3), butanediol (1,4) and / or hexanediol (1,6), diethylene glycol, tri ethylene glycol, tetraethylene glycol with diaryl carbonates, for example diphenyl carbonate or phosgene, can be prepared.

The simple aliphatic alcohols mentioned under 1. and the polyester or polyether polyols mentioned under 4. are preferably used in the process according to the invention.

Mixtures of the above-mentioned hydroxyl compounds can of course also be used. This is even a preferred embodiment of the process according to the invention, since the functionality of the polyisocyanate containing allophanate groups can be varied as desired by using a mixture of hydroxyl compounds of different functionality.

zum Einsatz, wobei

• R₂ für einen aliphatischen Kohlenwasserstoffrest mit 2 bis 20, vorzugsweise 6 bis 10, Kohlenstoffatomen, einen cycloaliphatischen Kohlenwasserstoffrest mit 4 bis 20, vorzugs-_' weise 6 bis 15 Kohlenstoffatomen oder einen Xylylenrest steht.

According to the invention, diisocyanates of the formula are preferably used to prepare the compounds containing urethane groups as starting materials for the process according to the invention and as reactants for these compounds

used, whereby

• R ₂ is an aliphatic hydrocarbon radical having from 2 to 20, preferably 6 to 10 carbon atoms, a cycloaliphatic hydrocarbon radical having 4 to 20, preferential _'is, from 6 to 15 carbon atoms or a xylylene.

Examples of such isocyanates are ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, undecamethylene diisocyanate, 2,4,4-trimethyl-1,6-diisocyanatohexane, 3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl isocyanate, 1,3-diisocyanato- ^q yclobutane, 1 , 4 - diisocyanatocydohexane, 4,4 '- diisocyanato - dicyclohexylmethane, 1,2 - bis - (isocyanatomethyl) - cyclobutane, trimethylhexane - 1,6 - diisocyanate, 1,11 - diisocyanatoundecane, 3 - isocyanatomethyl - 3,5, 5-trimethyl-cyclohexyl isocyanate, 4,4 '- cyclohexane diisocyanate, 4,4' - dicyclohexyl methane diisocyanate, 1,2 - bis - (isocyanatomethyl) cyclobutane, bis - isocyanatomethyl norbornane (mixture of isomers), 3 (4), 8 (9) - Diisocyanatomethyltricyclo - (5.2.1.0 ^2.6 ) -decane or p-xylylene diisocyanate. Such diisocyanates are used both in the preparation of the compounds containing urethane groups to be used according to the invention and as their reactants. Hexamethylene diisocyanate is particularly preferred.

In the preparation of the compounds containing urethane groups serving as starting materials, but not as their reactants in the process according to the invention, monoisocyanates such as e.g. n-Hexyl isocyanate or cyclohexyl isocyanate may be used, although this is less preferred.

Higher than difunctional aliphatic or cycloaliphatic polyisocyanates can be used or used both in the production of the compounds containing urethane groups as starting materials and as their reactants. Examples of such polyisocyanates are the isocyanurate group-containing trimerization products of hexamethylene diisocyanate or 3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl isocyanate.

Any mixtures of the isocyanates mentioned can be used both in the preparation of the starting materials containing urethane and groups, as well as their reactants, with the restriction that it is advisable not to use monoisocyanates as reactants for the compounds containing urethane groups, since in these If used, the NCO functionality of the process products according to the invention would be reduced. The functionality of the process products according to the invention can be varied by selecting certain mixing ratios of the isocyanate component and by choosing the mixing ratio of different hydroxyl compounds.

Essential to the invention is the use of acids in the reaction of the compounds containing urethane groups with the isocyanate component to form the corresponding allophanates containing isocyanate groups. These acids are proton-releasing strong acids which react 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 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, 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.

The acids are used in the process according to the invention in amounts of 0.001-10.0, preferably 0.01-1.0% by weight, based on the total weight of the reactants.

The acids can the reaction mixture can be incorporated by any method. For example, it is possible to mix the acid already in the compound containing hydroxyl groups before producing the compound containing urethane groups, a variant which is a convenient embodiment of the process, in particular when using hydrogen chloride, since hydrogen chloride is readily soluble in many compounds containing hydroxyl groups and thus can dispense with introducing small amounts of gaseous hydrogen chloride. However, it is also possible to mix in the acid together with the isocyanate component either already during the formation of the compounds containing urethane groups or, if the two-stage process is used, when producing the compounds containing allophanate groups from a compound having a separately prepared urethane group and a polyisocyanate component . Of course, the carbamic acid chloride which is derived from the one used or from another isocyanate can also be used as the catalyst. Additional catalysis may be dispensed with if crude distillates are used as the diisocyanate, which still contain a residual hydrolyzable chlorine content of more than 0.001% by weight, predominantly in the form of the carbamic acid chloride.

To carry out the process according to the invention, the reactants are generally used in amounts such that 2 to 50, preferably 3 to 12, isocyanate groups of the polyisocyanate component, preferably the diisocyanate, are present in each urethane group of the compound containing urethane groups. If the compound containing urethane groups is prepared in situ, a corresponding excess of the isocyanate component, preferably the diisocyanate component, is accordingly used.

The reaction according to the invention is generally carried out in the temperature range between 90 and 140 ° C. The course of the reaction according to the invention can be followed by determining the NCO content of the reaction mixture. The reaction can be stopped at any time, for example by cooling to room temperature or by removing the catalytically active acid, for example by applying a vacuum. This latter method is particularly possible when using gaseous acids. Deactivation of the acid catalyst by adding compounds which react with the acids to form an adduct (for example propylene oxide or an active unsaturated compound such as styrene is also possible.

• Das vorzugsweise als Isocyanat-Komponente eingesetzte Diisocyanat wird bei 50-80°C vorgelegt und die Hydroxyl-Komponente in flüssiger Form unter gutem Rühren eingetropft. Soll für die Urethanbildung und die Allophanatbildung das gleiche Isocyanat bzw. Isocyanatgemisch verwendet werden, so setzt man es am einfachsten von Anfang an in einem solchen Überschuß ein, daß das NCO/OH-Verhältnis etwa zwischen 3:1 und 12:1 liegt.

In the preferred variant of the process according to the invention in which the starting compound containing urethane groups is prepared in situ, the procedure is generally as follows:

• The diisocyanate, which is preferably used as the isocyanate component, is initially introduced at 50-80 ° C. and the hydroxyl component is added dropwise in liquid form with thorough stirring. If the same isocyanate or isocyanate mixture is to be used for urethane formation and allophanate formation, it is easiest to use it in such an excess from the start that the NCO / OH ratio is approximately between 3: 1 and 12: 1.

After the urethane reaction 'controlled by determining the NCO content - the catalyst (generally hydrogen chloride) is added. The temperature is increased to 90 to 140 ⁰ C and stirred so long, has fallen to the calculated for complete allophanatization value until the NCO content.

At temperatures above 130 ° C, it is advisable to keep the apparatus under mild overpressure so that the hydrogen chloride does not escape. However, the catalyst can also be initially introduced together with the isocyanate, or metered in together with the hydroxyl compound.

After the reaction has ended, the catalyst can easily be removed by distillation in vacuo or added by adding equivalent amounts of propylene oxide or an active unsaturated compound. If the polyisocyanate containing allophanate groups is to be freed from excess diisocyanate, this is done either by thin-layer distillation or by fractional extraction, for example using n-hexane or cyclohexane as the extractant. In the first case, the hydrogen chloride can be left in the crude product because it is distilled off together with the diisocyanate and is subsequently contained in the distillate. This can then be used for a new approach.

When carrying out the process according to the invention, the nature and proportions of the starting materials are generally chosen so that at least two allophanates containing isocyanate groups, i.e. Allophanate polyisocyanates are produced as process products. Process products of this type are distinguished by excellent stability during thin-film treatment even at temperatures of 180 ° C. and more. The side and equilibration reactions observed in polyisocyanates with a biuret structure do not occur, which lead to annoying caking and an increase in viscosity.

The method according to the invention is suitable for continuous implementation. In this case, several reactors are advantageously connected in series in the form of a cascade. In the first reactor Diisocyanate, hydroxyl compound and catalyst are metered in continuously. By adjusting the temperature and throughput it is achieved that the reaction is complete when leaving the last reactor. The raw product then passes through a thin film evaporator, where it is freed from excess diisocyanate. This is returned to the first reactor.

The allophanate polyisocyanates which can be prepared according to the invention can, if appropriate after removal of excess diisocyanate, be used to produce polyurethane foams, elastomers, duromers, coatings and adhesives.

They are particularly suitable as raw materials for high-quality, light-stable, weatherproof coatings, possibly in combination with hydroxyl-functional high-molecular compounds. Compared to polyisocyanates with urethane, biuret or isocyanurate structure, the allophanate polyisocyanates are characterized by their good compatibility with commercially available polyacrylates.

A further advantage of the inventive method is ichkeiten in the varied variation poss ⁼ particular with regard to type and quantity ratio of inexpensive starting materials (hydroxyl groups) to be seen. For example, the NCO functionality of the process products according to the invention can be controlled within wide limits depending on the choice of the hydroxyl compound. The use of fatty alcohols results in products with good petrol solubility. The use of cycloaliphatic or aromatic hydroxyl compounds achieves an excellent hardness of the coatings.

In particular, the excellent storage stability of the allophanate polyisocyanates according to the invention, freed from excess starting isocyanate, should be emphasized. The products of the process according to the invention show no tendency to split off monomeric starting isocyanate and, in this point in particular, advantageously differ from the known polyisocyanates containing biurethane groups.

The invention is explained in more detail by the following examples:

example 1

In a 3 l three-necked flask, 150 g (1 mol) of triethylene glycol were added dropwise to 2016 g (12 mol) of hexamethylene diisocyanate at 70 ° C. in the course of 30 minutes. After a further 30 minutes at 70 ° C., the NCO content of the reaction mixture was 42.65%, which corresponds to the complete conversion of the OH groups to urethane groups. 7 g of hydrogen chloride were then introduced and the temperature was raised to 100.degree. After 8.5 hours, the NCO content of the reaction mixture corresponded to a complete conversion of the urethane groups to allophanate groups with 38.8%. The crude product was subjected to thin film distillation. 900 g of a pale yellow product with a viscosity of 1200 cP / 25 ° C. and an NCO content of 19.3% were obtained. The composition of the preparation was examined by gel chromatography (Table 1).

Comparative examples analogous to GB-PS 994 890 A) (without catalyst as in Example 1 of the British patent)

As in Example 1 above, a solution of the bisurethane in excess hexamethylene diisocyanate was first prepared. A further decrease in the NCO content up to the value of 38.8% calculated for complete allophanatization could only be achieved after 48 hours at 135-145 ° C. The mixture had changed color strongly during this time. The product was worked up and analyzed as in Example 1 (Table 1).

Viscosity: 1330 cP / 25 ° C;

NCO content: 19.5%.

B) (zinc naphthenate as catalyst as in Example 5 of the GB-PS)

As in Example 1 above, the urethane solution was prepared and then 2.3 g of zinc naphthenate was added. Over the course of 8 hours at 50 ° C., the NCO content dropped to 38.8%. After working up: (Analysis Table 1)

Viscosity: 1350 cP / 25 ° C;

NCO content: 20.4%;

Color: brown-yellow.

C) (Tertiary amine as catalyst as in Example 4 of GB-PS)

After adding 2.3 g of diazabicyclooctane to the urethane solution, the mixture was first heated to 70 ° C. for 24 hours. The theoretical NCO drop was only reached after a further 16 hours at 120 ° C. After working up, a deep yellow oil with a viscosity of 1050 cP / 25 ° C. and an NCO content of 20.2% was obtained (analysis in Table 1).

• D) Aus 1008 g (6 Mol) Hexamethylendiisocyanat und 106 g (1 Mol) Diäthylenglykol wurde zunächst bei 70°C eine Urethanlösung bereitet (NCO-Gehalt: 36,85%). Nach Zugabe von 0,7 g p-Toluolsulfonsäuremethylester wurde unter Uberleiten von trockenem Stickstoff die Temperatur auf 160°C gesteigert. Nach 50 Stunden war der NCO-Gehalt auf 33,5% gefallen (berechnet für vollständige Allophanatisierung 30,1%). Da das Reaktionsgemisch sehr stark verfärbt war, wurde der Ansatz zu diesem Zeitpunkt abgebrochen. Eine IR-spektroskopische Analyse ergab einen deutlichen Gehalt an Uretdion- und Isocyanuratgruppen.
• E) Aus 1008 g (6 Mol) Hexamethylendiisocyanat und 57 g (0,75 Mol) 1,2-Propylenglykol wurde bei 70°C eine Urethanlösung bereitet (NCO-Gehalt: 41,4%). Nach Zugabe von 1 g p-Toluolsulfonsäuremethylester und 0,2 g Zinkacetylacetonat wurde die Temperatur allmählich auf 110-120°C gesteigert. Im Verlauf von 36 Stunden fiel der NCO-Gehalt der Reaktionsmischung auf 38,1% ab (ber.: für vollständige Allophanatisierung 35,45%). Der Ansatz war gelbbraun verfärbt; ein IR-Spektrum zeigte eine starke Isocyanurat-Bande.

Comparative examples analogous to DAS 2 009 178 and 2 040 645, in which the preparation of aromatic allophanate polyisocyanates is described.

• D) From 1008 g (6 mol) of hexamethylene diisocyanate and 106 g (1 mol) of diethylene glycol, a urethane solution was first prepared at 70 ° C. (NCO content: 36.85%). After addition of 0.7 g of methyl p-toluenesulfonate, the temperature was raised to 160 ° C. while passing dry nitrogen. After 50 hours the NCO content had dropped to 33.5% (calculated for complete allophanatization 30.1%). Since the reaction mixture was very strongly discolored, the batch was stopped at this point. An IR spectroscopic analysis showed a clear content of uretdione and isocyanurate groups.
• E) A urethane solution was prepared at 70 ° C. from 1008 g (6 mol) of hexamethylene diisocyanate and 57 g (0.75 mol) of 1,2-propylene glycol (NCO content: 41.4%). After adding 1 g of methyl p-toluenesulfonate and 0.2 g of zinc acetylacetonate, the temperature was gradually increased to 110-120 ° C. The NCO content of the reaction mixture dropped to 38.1% over the course of 36 hours (calculated: 35.45% for complete allophanatization). The approach was colored yellow-brown; an IR spectrum showed a strong isocyanurate band.

When attempting to complete the NCO decrease at 150-160 ° C, the reaction mixture suddenly became completely swollen with exothermic reaction and gas evolution.

Example 2

1512 g (9 mol) of hexamethylene diisocyanate were mixed with 120 g (0.5 mol) of melted 2,2-bis (4-hydroxycyclohexyl) propane at 100 ° C. A solution of 4 g of hydrogen chloride in 16 g (0.5 mol) of methanol was then added dropwise at 100 ° C. After a further 9 hours under nitrogen at 100 ° C., the NCO content was 38.27% (calculated for complete allophanate formation 38.4%). The mixture was then stirred with 8 g of propylene oxide at 50 ° C. for 15 minutes. Thereafter, no more hydrolyzable chlorine was found. After degassing in vacuo, the crude product was subjected to thin film distillation at 170 ° C / 0.5 mm. 630 g of a colorless oil with a viscosity of 11,600 cP / 25 ° C. and an NCO content of 17.4% were obtained. The residual hexamethylene diisocyanate content was 0.48%.

Example 3

4 g of hydrogen chloride were introduced into 3024 g (18 mol) of hexamethylene diisocyanate at 90 ° C. Then 180 g (2 Mol) of 1 A-butanediol. After a further hour the temperature was raised to 100 ° C. After 8 hours under nitrogen the NCO content of the mixture had dropped to the value of 36.8% calculated for complete allophanate formation. After stirring with 10 g of propylene oxide at 50 ° C, the product was degassed in vacuo and subjected to distillation in a thin film evaporator. 1415 g of a pale yellow liquid were obtained. (Distillate: 1750 g hexamethylene diisocyanate).

Viscosity: 6500 cP / 25 ° C;

NCO content: 18.6%;

Residual content of diisocyanate: 0.65%.

The IR spectrum showed traces of uretdione and no isocyanurate groups. A sample of the product was stored at 50 ° C for 50 days. The residual hexamethylene diisocyanate content was then determined to be 0.66%.

Example 4

Analogously to Example 1, 3080 g (18 mol) of hexamethylene diisocyanate, 201 g (1.5 mol) of trimethylolpropane and 8 g of hydrogen bromide as catalyst were used to prepare 1480 g of a highly viscous, highly functional allophanate polyisocyanate which was 80% pure in xylene / ethyl glycol acetate (1: 1) dissolved had a viscosity of 2800 cP / 25 ° C and an NCO content of 18.2%.

Example 5

2150 g (1 mol) of a polyether consisting of 80 mol% of ethylene oxide and 20 mol% of propylene oxide started on n-butanol were mixed with 1008 g (6 mol) of hexamethylene diisocyanate and 4 g of hydrogen chloride. After 12 hours at 110 ° C the allophanate reaction was complete. After thin-film treatment, 2300 g of a pale yellow oil with a viscosity of 1200 cP / 25 ° C. and an NCO content of 3.2% were obtained, which solidified like a waxy after some time.

Example 6

Analogously to Example 1, 3024 g (18 mol) of hexamethylene diisocyanate, 261 g (4.5 mol) of allyl alcohol and 7 g of hydrogen chloride as catalyst became a bifunctional allophanate with a viscosity of 200 cP / 25 ° C. and an NCO content of 17.8 % produced.

Example 7

228 g (1 mol) of 2,2-bis (4-hydroxyphenyl) propane were melted and added dropwise to 100 g of 2016 g (12 mol) of hexamethylene diisocyanate from a heated dropping funnel. 5 g of hydrogen chloride were then introduced and the mixture was stirred at 110 ° C. under nitrogen for 5 hours. The allophanate reaction was then complete (NCO content: 37.5%). After two thin-layer distillation, 730 g of a viscous oil (viscosity: 124,000 cP / 25 ° C) were obtained, which solidified after standing for a while (softening point: 45-4.7 ° C). The NCO content was 16.03%. The free hexamethylene diisocyanate content of 0.8% did not increase after 30 days of storage at 50 ° C (0.78%).

Example 8

1332 g (6 mol) of 3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl isocyanate-1 were mixed at 100 ° C. with a mixture of 59 g (0.5 mol) of 1,6-hexanediol and 37 g of n-butanol . After one hour, 18 g of hydrogen chloride were introduced and the temperature was raised to 120 ° C. The allophanate reaction was complete after 18 hours (NCO content 27.6%). After thin-layer distillation at 190 ° C. and 0.4 mm, a light-colored resin was obtained which had 80% strength in ethyl glycol acetate, a viscosity of 890 cP at 25 ° C. and an NCO content of 10.2%.

Example 9

By reaction of 630 g (3 mol) of 2,4,4-trimethyl-1,6-diisocyanate with 30 g (0.3 mol) of 1,4-butanediol and 1.5 g of hydrogen chloride for 6 hours at 110 ° C. and subsequent thin-layer distillation, 360 g of a highly viscous colorless oil were obtained.

Viscosity: 150,000 cP / 25 ° C;

NCO content: 15.3%.

Example 10

From 678 g (3 mol) of 6-isocyanatohexanoic acid-2-isocyanatoethyl ester, 39 g of 1,6-hexanediol (0.3 mol) and 1.5 g of hydrogen chloride, a crude product was produced in 5 hours at 110 ° C., which after thin-film distillation light oil of viscosity 28,000 cP / 25 ° C (NCO content: 14.7%).

Example 11

A urethane solution in excess diisocyanate was prepared from 3024 g (18 mol) of hexamethylene diisocyanate and 152 g (2 mol) of 1,2-propanediol at 70 ° C. 380 g of the mixture were heated with various catalysts until the NCO content calculated for complete allophanatization was reached. was. The results are shown in the following table:

The products obtained showed no isocyanurate or uretdione edges in the IR spectrum.

Example 12 (Usage example)

154 g of a 65% solution of a polyester of 6 moles of phthalic anhydride and 7 moles of 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 as leveling agent diluted with 230 g of a solvent mixture of methyl ethyl ketone, butyl acetate, ethyl glycol acetate and toluene (4: 1: 4: 1). For this purpose 152 g of a 75% solution of the polyisocyanate from Example 2 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 hardened 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 properties: layer thickness approx. 50 μ Erichsen cupping (DIN 53 156) after 6 days 8.7 mm after 9 days 8.6 mm pendulum hardness (DIN 53 157) after 6 days 238 seconds after 8 days 220 seconds after 14 days 227 seconds

Example 13 (Usage example)

• Schichtdicke ca. 50 µ Erichsentiefung (DIN 53 156) nach 6 Tagen 8,1 mm nach 9 Tagen 8,0 mm Pendelhärte (DIN 53 157) nach 6 Tagen 193 Sekunden nach 9 Tagen 187 Sekunden nach 14 Tagen 192 Sekunden

154 g of the polyester solution described in Example 12 were processed with 100 g of titanium dioxide (rutile type) to form a paste. In addition to the catalyst and leveling agent, 140 g of the solvent mixture already described were added to this paste. The mixture thus obtained was mixed with 152 g of a 75% solution of the polyisocyanate from Example 12 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:

• Layer thickness approx. 50 µ Erichsen depth (DIN 53 156) after 6 days 8.1 mm after 9 days 8.0 mm pendulum hardness (DIN 53 157) after 6 days 193 seconds after 9 days 187 seconds after 14 days 192 seconds

Claims (4)

1. Process for the preparation of allophanates containing aliphatically and/or cycloaliphatically bound isocyanate groups by the reaction of organic compounds which contain urethane groups with organic polyisocyanates containing aliphatically and/or cycloaliphatically bound isocyanate groups, characterised in that the reaction is carried out in the presence of strong acids which form a mixed carbamic acid anhydride with aliphatic or cycloaliphatic isocyanates.

2. Process according to claim 1, characterised in that the acids are used in a quantity of from 0.001 to 10% by weight, based on the polyisocyanate.

3. Process according to claims 1 and 2, characterised in that the acid used is a hydrogen halide.

4. Use of the allophanates containing isocyanate groups, obtained according to claim 1, in combination with hydroxyl functional higher molecular weight compounds, for the production of lacquers.