Method for producing TDI-trimerisates with high purity
The invention relates to a novel method for producing polyisocyanurates comprising isocyanate groups, based on 2,4- and 2,6-toluylene diisocyanate (TDI) and to the use thereof in coating compositions.
1. A method for producing polyisocyanates comprising solvent or diluent and isocyanurate groups, based on 2,4- and/or 2,6-toluylene diisocyanate, having a content of monomeric diisocyanate of <0.5 wt. %, based on polyisocyanate plus solvent, comprising trimerising
A) from 20 to 80 wt. % of a mixture comprising 2,4-toluylene diisocyanate and 2,6-toluylene diisocyanate comprising from 65 to 95 wt. % 2,4-toluylene diisocyanate and from 5 to 35 wt. % 2,6-toluylene diisocyanate in the presence of
B) from 20 to 80 wt. % of solvents or diluents and
C) a phenolic catalyst comprising dialkylaminomethyl groups at a temperature of from 40 to 120° C. to almost complete conversion, and then deactivating the catalyst by addition of an acid-reacting substance or by reaction with an alkylating agent, wherein the toluylene diisocyanate has a content of 2-chloro-6-isocyanato-methylcyclohexadienes (CIMCH) of <5 wt.ppm and wherein the polyisocyanates comprising solvent or diluent and isocyanurate groups have APHA colour indices <100 Hazen.
2. The method according to claim 1 , wherein the toluylene diisocyanate is produced by gas phase phosgenation.
3. The method according to claim 1 , wherein the toluylene diisocyanate has a content of 2-chloro-6-isocyanato-methylcyclohexadienes below the detection limit of 1 wt.ppm.
4. The method according to claim 1 , wherein the catalysts is obtained as Mannich base based on phenol or bisphenol A by reaction with dimethylamine and formaldehyde.
5. The method according to claim 1 , wherein the catalyst is deactivated by dibutyl phosphate or p-toluenesulfonic acid methyl ester.
6. The polyisocyanates produced by the method according to claim 1 comprising solvent or diluent and isocyanurate groups.
7. A method comprising utilizing the polyisocyanate produced according to the method of claim 6 as the polyisocyanate component in polyurethane coatings.
8. The method according to claim 7 wherein the polyisocyanates comprise a crosslinker in two-component polyurethane coatings.
9. A polyurethane adhesive comprising the polyisocyanates produced according to the method of claim 6 .