Isocyanato-isocyanurates and a process for their preparation

The present invention relates to isocyanato-isocyanurates of the formula<chemistry id="chem0001" num="0001"><img file="EP0082987B1_D0001.tif" /></chemistry>in which the individual radicals R are the same or different and hydrocarbon radicals of the formulas<chemistry id="chem0002" num="0002"><img file="EP0082987B1_D0002.tif" /></chemistry>mean and n is an integer or fractional number from 1-5.

The present invention also relates to a process for the preparation of new compounds by partial trimerization of aliphatic diisocyanates, characterized in that the aliphatic diisocyanates are essentially those of a diisocyanate of the formula<chemistry id="chem0003" num="0003"><img file="EP0082987B1_D0003.tif" /></chemistry>and optionally a diisocyanate of the formula<chemistry id="chem0004" num="0004"><img file="EP0082987B1_D0004.tif" /></chemistry>existing diisocyanate or diisocyanate mixture used, the minimum content of 2-ethyl-1,4-diisocyanatobutane being 1% by weight and the amount of catalyst being 0.2-0.02% by weight and the temperature range being 40- 140 ° C.

The trimerization of hexamethylene diisocyanate (HDI) has been known for a long time and is described in a large number of patents with various catalysts (see, for example, DE-ASsen 10 13 869, 12 03 792, 22 26 191; DE-OS 26 16415; GB-PSsen 952,931, 966,338; U.S. Patents 3,211,703, 3,330,828).

None of the processes described allows the problem-free production of practically colorless, low-viscosity, solvent-free isocyanurate-containing polyisocyanates based on HDI in a technically simple manner.

Only in DE-OS 28 39 133 is the technical production of the isocyanato-isocyanurate based on HDI shown. The products obtained by this process have a viscosity below 10,000 mPas at 25 ° C and an NCO content of 18 - 24, in particular 20 - 23% by weight, and represent valuable starting materials for the production of lightfast polyurethane coatings.

However, they have the disadvantage that they are only compatible to a limited extent with the polyhydroxyl compounds generally used in PUR coatings and, in particular, are only of limited solubility in the nonpolar solvents which are often used, such as white spirit. Another disadvantage of these HDI isocyanato isocyanurates is their only moderate resistance to heat and oxidation, which is particularly evident when the paint films made from these compounds are overburned.

Furthermore, isocyanato-isocyanurates according to EP-PS 13 880 based on 5-methyl-1,9-diisocyanato-nonane and 2,4-dimethyl-1,8-diisocyanato-octane are known.

It was therefore the object of the present invention to provide new polyisocyanato-isocyanurates which combine the known advantages of this class of compounds, such as high NCO content, low vapor pressure, good light fastness, processable without solvents, without the disadvantages of the compounds mentioned of the prior art (DE-OS 28 39 133) to be afflicted.

This problem was solved by providing the new isocyanato-isocyanurates mentioned at the outset or by the process according to the invention for their preparation.

Starting materials for the process according to the invention are diisocyanate mixtures, which essentially consist of a diisocyanate of the formula<chemistry id="chem0005" num="0005"><img file="EP0082987B1_D0005.tif" /></chemistry>and a diisocyanate of the formula<chemistry id="chem0006" num="0006"><img file="EP0082987B1_D0006.tif" /></chemistry>consist. In general, the diisocyanate mixtures used in the process according to the invention have the following compositions:<ul id="ul0001" list-style="none"><li>88 99% by weight of 2-methyl 1,5-diisocyanatopentane (MPDI)</li><li>12th 1% by weight of 2-ethyl-1,4-diisocyanatobutane (EBDI)</li></ul>

Pure diisocyanate of the first-mentioned formula can also be used instead of the mixtures.

The preferred starting material is a corresponding diisocyanate mixture of approximately 88-95% by weight of 2-methyl-1,5-diisocyanatopentane and 12-5% by weight of 2-ethyl-1,4-diisocyanatobutane.

The diisocyanates or diisocyanate mixtures are prepared in a manner known per se by phosgenation of the corresponding diamines (cf., for example, US Pat. No. 3,631,198). These are obtained by catalytic hydrogenation of corresponding dinitriles, which are obtained, for example, as a by-product in the production of adiponitrile by reacting butadiene with HCN or in the dimerization of acrylonitrile.

In principle, all known trimerization catalysts can be used as catalysts for the process according to the invention. For example, the diisocyanates just mentioned can be readily trimerized with Na benzoate in dimethylformamide (DMF) (Chem. Abstr. 60, 8332 (1963)) or with Na phenolates in n-butyl acetate (GB-PS 1 386 399). however, the catalysts just mentioned must be separated from the reaction product. This disadvantage is overcome in DE-OS 28 21 109 by using a Mg or Ca salt of monohydroxyethylphthalic acid as a catalyst, which is incorporated into the reaction product. Particularly suitable for the production of the isocyanato-isocyanurates according to the invention are those catalysts which, after the trimerization has ended, can either be easily removed or are already completely deactivated during the reaction. Examples of such trimerization catalysts are aziridine (derivatives) in combination with a tertiary amine (DE-AS 12 03 792, DE-OS 23 25 826); further the combination of alkylene oxide and N, N'-endoethylene piperazine (DE-OS 25 44 684) and quaternary ammonium hydroxides (GB-PS 837 120).

The use of quaternary ammonium salts of organic acids according to DE-OS 29 16 201 has proven very suitable:<chemistry id="chem0007" num="0007"><img file="EP0082987B1_D0007.tif" /></chemistry>in which X is the same or different aliphatic, cycloaliphatic, araliphatic or heterocyclic hydrocarbon radicals of a quaternary ammonium nitrogen or 2 X form a ring with the quaternary nitrogen optionally containing one or more heteroatoms or 3 X form a ring with the quaternary nitrogen via a common heteroatom , R is an alkyl, cycloalkyl or aralkyl radical, and R and R "together are a C_l-C₁₂-Alkylene radical and R 'is hydrogen, a hydroxyl group and an optionally hydroxyl-containing C₁-C₁₂-Alkylrest and R "- R or hydrogen can mean.

The catalyst must be added to the trimerizing diisocyanate mixtures in amounts of 0.2-0.02% by weight, preferably 0.08-0.04% by weight; the trimerization is carried out in a temperature range of 40-140 ° C., preferably 60-90 ° C. The trimerization is complete within 1 - 60 minutes at these temperatures.

In batch trimerization of the diisocyanate mixture (MPDI ₊ EBDI) by the process according to the invention, the diisocyanate mixture and 0.02-0.2 part by weight of the catalyst described were stirred well in a closed reaction vessel at 40-60 ° C., but not above 140 ° C., preferably at 70-90 ° C, heated. The course of the reaction was determined with the aid of the refractive index, which is a direct measure of the degree of conversion of the diisocyanate mixture or, if appropriate, of the pure diisocyanate. With sales of approx. 30th - 45%, based on the diisocyanate mixture used, the reaction was stopped by cooling the reaction mixture to room temperature. Such diisocyanate / isocyanurate mixtures were stable in storage at room temperature. To separate the unreacted, ie the monomeric diisocyanate or diisocyanate mixture and the catalyst, the reaction mixture was then fed to thin-film evaporation (150 ° C./0.1 Torr). The isocyanurates according to the invention thus produced had an NCO content of 19-24, preferably 20.5-22.5,% by weight, a monomer content &lt;0.7% by weight and a viscosity below 12,000 mPas at 25 ° C.

The isocyanate isocyanurates according to the invention have; a number of advantageous properties which make it an isocyanate hardener for coating systems according to the; Make isocyanate polyaddition processes extremely suitable. Due to their low viscosity, which varies depending on the degree of oligomerization, but is generally below 12,000 mPas (at 25 ° C), no or only small amounts of solvents are required for their use.

The main advantage over polyisocyanates according to the prior art lies in the better compatibility of the compounds according to the invention with nonpolar solvents, which considerably increases the range of use of these compounds compared to conventional products. In addition, the surprisingly good thermal and oxidation resistance of the compounds according to the invention should be emphasized.

A. Preparation of the ammonium salts used as catalysts

Example A1

232 g of dipropylene glycol (DPG) and 90 g of glacial acetic acid were placed in a 1 liter three-necked flask equipped with a stirrer, reflux condenser and dropping funnel. This mixture was then introduced up to a weight gain of 87 g trimethylamine. 87 g of propylene oxide (PO) were then slowly added at 25 ° C. with vigorous stirring. After the PO addition had ended, the mixture was stirred at room temperature overnight, then the unreacted volatile materials were stripped off in vacuo at 45 ° C. within 6 h. A residue with a weight of 484 g remained.

Using the procedure described above, further compounds were prepared, the composition of which is summarized in Table 1- below (Example A2-A6).<tables id="tabl0001" num="0001"><img file="EP0082987B1_D0008.tif" /></tables>

Example A7

500 Parts by weight of triethylenediamine were refluxed with 500 parts by weight of propylene oxide for 8 hours. The reaction mixture became darker with increasing reaction time. After the reaction had ended, the conductivity of this mixture no longer changed.

Example A8

500 Parts by weight of triethylenediamine were dissolved in 500 parts by weight of dimethylformamide. 500 parts by weight of propylene oxide were then added to this solution at room temperature, and this solution was then heated at 40 ° C. for 18 h. The reaction was then over. The conductivity of this solution changed only marginally in the warehouse.

B. Preparation of the Isocyanatoisocyanurates According to the Invention

Example B1

500 Parts by weight of MPDI (approx. 6% EBDI) and 0.2 parts by weight of the catalyst of Example A6 were mixed with one another at 80 ° C. with vigorous stirring. In the course of this, an instantaneous heat development occurred, the temperature of the reaction mixture rising to approximately 95 ° C. At this temperature, the reaction mixture was heated for a further 20 minutes. During this time the NCO content fell to 35.4% by weight. To remove the unreacted MPDI, the reaction mixture was distilled at 160 ° C./0.1 torr in a thin-film evaporator. The reaction product (residue from thin-film evaporation) had an NCO content of 20.5% by weight and a monomer content of &lt;0.7% by weight. The viscosity at 25 ° C was 11,500 mPas.

Example B2

According to the process described in Example B1, 1,000 parts by weight of MPDI and 0.1 part by weight of the catalyst described in Example A7 were reacted at 80 ° C. After the partial trimerization had ended, the reaction mixture had an NCO content of 38.2% by weight. The isocyanato-isocyanurate isolated by thin-film distillation had an NCO content of 21.3% by weight and a monomer content of 0.6% by weight. The viscosity of this isocyanato-isocyanurate was 10,900 mPas at 25 ° C.

Example B3

Analogously to example B1, 1,000 parts by weight of MPDI and 0.15 parts by weight of the catalyst described in A1 were reacted at 80 ° C. After partial trimerization had ended, the reaction mixture had an NCO content of 41.1% by weight. The isocyanato-isocyanurate isolated by thin-film distillation had an NCO content of 25.7% by weight and a monomer content of 0.7% by weight. The viscosity of this isocyanato-isocyanurate was 10,500 mPas at 25 ° C.