Process for preparing low-monomer-content TDI trimers
View Patent ↗The invention relates to a novel process for preparing low-monomer-content trimers based on 2,4- and/or 2,6-diisocyanatotoluene (TDI). A catalytic trimerization is carried out in a mixture of from 20 to 80% by weight of a diisocyanate component containing at least 80% by weight of 2,4- and/or 2,6-diisocyanatotoluene, from 20 to 80% by weight of solvent, and 0–20% by weight of an alcohol component, and also phenolic catalysts containing dialkylamino-methyl groups. In the course of ongoing trimerization, in one or more steps, additional monomeric 2,v4-diisocyanatotoluene is metered in.
1. Process for preparing solvent-containing polyisocyanates based, at least in part, on 2,4- and/or 2,6-diisocyanatotoluene which contain isocyanurate groups comprising
a) reacting, at a temperature from 20° C. to 120° C., a mixture of
A) from 20 to 80% by weight, based on the mixture, of a diisocyanate component containing at least 80% by weight, based on all diisocyanates, of 2,4- and/or 2,6-diisocyanatotoluene,
B) from 20 to 80% by weight, based on the mixture, of solvent and
C) 0–20% by weight, based on the mixture, of an alcohol component, and also
D) phenolic catalysts containing dialkylaminomethyl groups;
b) metering in, in one or more steps, in the course of ongoing trimerization additionally 0.1–25% by weight, based on the amount of diisocyanates employed, of monomeric 2,4-diisocyanatotoluene, wherein at least a portion of the 2,4-diisocyanatotoluene is added after the NCO content in the mixture of a) as been reduced due to the reaction of A); and
c) ending the reaction by adding catalyst poisons; wherein the reacted mixture contains <0.1% by weight, based on the mixture, of monomeric diisocyanate.
2. Process according to claim 1 , wherein the amount of the monomeric 2,4-diisocyanatotoluene metered in additionally in the course of ongoing trimerization is from 10 to 20% by weight.
3. Process according to claim 1 , wherein the amount of the monomeric 2,4-diisocyanatotoluene metered in additionally in the course of ongoing trimerization is from 1–10% by weight.
4. Process according to claim 1 , wherein catalysts are employed which contain in one molecule both dialkylaminomethyl groups (alkyl =C1 to C3 chain) and phenolic OH groups.
5. Process according to claim 4 , wherein catalysts are used which contain Mannich bases which are obtained from phenol, p-isononylphenol or bisphenol A by reaction with dimethylamine and formaldehyde.
6. Process according to claim 1 , wherein the trimerization is conducted at a temperature from 50 to 80° C.
7. Process according to claim 1 , wherein a mixture of 2,4- and 2,6-diisocyanatotoluene (TDI) in a weight ratio of from 3:2 to 9:1 2,4-TDI:2,6-TDI is used as starting diisocyanate.