Continuous oligomerization of isocyanates

1. A method for oligomerization of isocyanates comprising a step for continuous conversion of an isocyanate monomer into a polyisocyanate containing carbamate and/or allophanate groups in the presence of a catalyst, wherein the conversion step is carried out in a plate exchange reactor and at a specific heat exchange coefficient of greater than or equal to about 200 kW/m 3 /° C.

2. The method as defined by claim 1 , wherein the catalyst is selected from quaternary ammonium hydroxides of the following formula (I):

wherein:

R 1 is an alkyl group, either saturated or not, comprising from 1 to 20 carbon atoms, an aryl group comprising from 6 to 12 carbon atoms, a cycloalkyl group comprising from 5 to 12 carbon atoms or a heterocyclic system with 5 or 6 chain links including a nitrogen atom, an oxygen atom or a sulfur atom,

R 2 , R 3 and R 4 represent independently of each other an alkyl group, either saturated or not, comprising from 1 to 20 carbon atoms, an aryl group comprising from 6 to 12 carbon atoms, said groups R 2 , R 3 and R 4 may optionally be substituted with at least one hydroxyl group or one thiol group.

3. The method as defined by claim 1 , wherein the conversion step is carried out during a dwelling time in the reactor of less than one hour.

4. The method as defined by claim 1 , wherein the isocyanate monomer and the catalyst are added into the reactor simultaneously.

5. The method as defined by claim 1 , wherein the isocyanate monomer is selected from the group consisting of aliphatic, cycloaliphatic and aromatic isocyanates.

6. The method as defined by claim 1 , wherein the isocyanate monomer is selected from the group consisting of 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3and/or 1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, isocyanatomethyloctylene-diisocyanates, dicyclohexyl-methane-4,4′-diisocyanate, toluene diisocyanate, methylene bis-phenylisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 2,4- and/or 2,6-hexahydrotoluylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, hexahydro-1,3 and/or 1,4-phenylene diisocyanate, 2-methyl -pentamethylene diisocyanate, 1,3- and/or 1,4-phenylene diisocyanate, tetramethylxylylene diisocyanates, triphenylmethane-4,4′,4″-triisocyanate, lysine diisocyanate, esters of lysine di- or tri-isocyanate, diphenylmethane-2,4′ and/or 4,4′-diisocyanate, perhydro 2,4′- and/or 4,4′-diphenylmethane diisocyanate, and generally aromatic amino precursors or perhydrogenated carbamates, bis-isocyanatomethylcyclo-hexanes, bis-isocyanato-methyl-norbornanes and oligomers of methylene bis-phenylisocyanate or toluene diisocyanate.

7. The method as defined by claim 1 , wherein the catalyst is selected from the group consisting of tetrabutylammonium hydroxide and N,N, N-trimethyl-N-(2-hydroxyethyl) ammonium hydroxide.

8. The method as defined by claim 1 , wherein the amount of catalyst used is from about 0.01% to about 0.5% by weight relatively to the monomer weight.

9. The method as defined by claim 1 , for preparing a hexamethylene diisocyanate trimer comprising a step for converting 1,6-hexamethylene diisocyanate in the presence of N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium.

10. The method as defined by claim 1 , for preparing a hexamethylene diisocyanate trimer comprising a step for converting 1,6-hexamethylene diisocyanate in the presence of tetrabutylammonium hydroxide.

11. The method as defined by claim 1 , wherein the isocyanate monomer contains more than 30 ppm of hydrolyzable chlorine.

12. The method as defined by claim 6 , wherein the bis-isocyanatomethylcyclo-hexanes comprise 1,3-bis-isocyanatomethylcyclo-hexane and 1,4-bis-isocyanatomethylcyclo -hexane.