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1. WO2020020768 - PROCESS FOR PREPARING POLYISOCYANATES CONTAINING URETHANE GROUPS

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[ EN ]

Claims:

1. A process for preparing polyisocyanates containing urethane groups by reacting an excess of diisocyanate with a composition comprising at least one polyhydroxy compound, characterized in that the reaction is operated continuously in a reaction system which consists of at least two residence apparatuses.

2. The process according to Claim 1, characterized in that the diisocyanate is 2,4-toluene diisocyanate or a mixture of 2,4 tolylene diisocyanate with up to 35 wt% of 2,6-toluene diisocyanate, based on the total weight of the mixture.

3. The process according to Claim 1 or 2, characterized in that the polyhydroxy compound is selected from the group consisting of di- to tetrahydric alcohols having a molecular weight of 62 to 146 g/mol and polyether polyols prepared from them by addition reaction of ethylene oxide and/or propylene oxide and having a molecular weight, calculable from hydroxy group content and hydroxyl functionality, of 106 to 600 g/mol.

4. The process according to any of the preceding claims, characterized in that the polyhydroxy compound is trimethylolpropane and/or diethylene glycol.

5. The process according to any of the preceding claims, characterized in that the composition consists of only trimethylolpropane and / or diethylene glycol.

6. The process according to any of the preceding claims, characterized in that the reaction system comprises or consists of a stirred tank cascade having 2 to 10 stirred tanks.

7. The process according to any of the preceding claims, characterized in that the reaction system comprises or consists of at least one stirred tank and a tubular reactor connected downstream to this at least one stirred tank.

8. The process according to any of the preceding claims, characterized in that the reaction system is charged with diisocyanate and heated at 50 to 120°C, preferably at 60 to 110°C and more preferably at 70 to 100°C, before the continuous reaction started by introducing continuous feed streams of the diisocyanate and the composition comprising at least one polyhydroxy compound into the reaction system.

9. The process according to any of the preceding claims, characterized in that during the continuous operation, the diisocyanate, before being added to the reaction system, has a temperature < 40°C, preferably < 30°C and more preferably < 22°C.

10. The process according to any of the preceding claims, characterized in that the composition comprising at least one polyhydroxy compound, before being added to the reaction system, has a temperature < 65°C, preferably < 50°C.

11. The process according to any of the preceding claims, characterized in that the diisocyanate and the composition comprising at least one polyhydroxy compound are passed into the first residence apparatus in an NCO:OH equivalent ratio of between 2.5: 1 and 20: 1, preferably between 3: 1 and 10: 1 and more preferably between 3.2: 1 and 8: 1.

12. The process according to any of the preceding claims, characterized in that a first substream of the composition comprising at least one polyhydroxy compound is metered into the first residence apparatus and a further substream of the composition is metered into at least one further residence apparatus.

13. The process according to any of the preceding claims, characterized in that the reaction system consists of n residence apparatuses and the composition comprising at least one polyhydroxy compound is metered only into the first n-1 residence apparatuses.

14. A polyisocyanate containing urethane groups, obtainable or obtained by a process according to any of the preceding claims.