Process for the preparation of polyisocyanates with dimer, trimer and/or allophanate and optionally urethane structure

1. Process for the preparation of polyisocyanates with dimer, trimer and/or allophanate and optionally urethane structure, in which

a) an isocyanate component A, consisting of

≥70% by weight to ≤100% by weight of one or more diisocyanates with aliphatically, cycloaliphatically, araliphatically and/or aromatically bonded isocyanate groups and of

≥0% by weight to ≤30% by weight of one or more monoisocyanates with aliphatically, cycloaliphatically, araliphatically and/or aromatically bonded isocyanate groups and/or one or more isocyanates with aliphatically, cycloaliphatically, araliphatically and/or aromatically bonded isocyanate groups and with a functionality of isocyanate groups >2

b) optionally with an isocyanate-reactive component B,

is oligomerized in the presence of one or more catalysts C with formation of dimer, trimer and/or allophanate structures and optionally urethane structures (process stage I), the oligomerization reaction is thermally and/or chemically interrupted (process stage II) and optionally the polyisocyanate obtained is freed from excess isocyanate of the component A down to <1% by weight (process stage III), characterized in that

a first portion of the isocyanate component A 1 is initially introduced into a reactor and a second portion of the isocyanate component A 2 is added to the reactor in at least one metering after beginning of the addition of one or more catalysts C, however before ≤50% of the isocyanate groups available from component A 1 are oligomerized,

and that the first portion of the isocyanate component A 1 , in comparison with the second portion of the isocyanate component A 2 , differs with regard to

i) the temperature, viewed at the beginning of the addition of the one or more catalysts C, and/or

ii) the oligomerization activity,

wherein a difference in oligomerization activity is determined according to an activity test comprising the steps of:

(1) introducing 60 g of the first portion of the isocyanate component A 1 into a 100 ml 2-necked flask with a magnetic stirrer, thermometer and vacuum connection,

(2) heating the 2-necked flask with an oil bath to 60° C.,

(3) evacuating the 2-necked flask for 15 minutes to form a vacuum,

(4) breaking the vacuum formed in (3) with nitrogen,

(5) installing a dropping funnel with a pressure equalizer and a drying tube which is filled with one or more catalysts C,

(6) beginning dropwise metering of the one or more catalysts C to produce a reaction mixture,

(7) measuring consumption of the one or more catalysts C (in g) until the temperature of the reaction mixture begins to climb,

(8) repeating the activity test with the second portion of the isocyanate component A 2 , in which the one or more catalysts C is added at an identical metering rate,

determining a higher or lower oligomerization activity from a comparison of the amounts of the one or more catalysts C consumed in the two activity tests in which the activity is higher as the amount of catalyst consumed becomes lower, and in the activity test, the amount of catalyst consumed with the less active isocyanate component is approximately ≥5% higher than with the more active isocyanate component.

2. Process according to claim 1 , in which the second portion of the isocyanate component A 2 is added to the reactor in at least one metering after beginning the addition of the one or more catalysts C, before ≥5% to ≤50% of the NCO groups available from the first portion of the isocyanate component A 1 are oligomerized.

3. Process according to claim 1 , in which the second portion of the isocyanate component A 2 is added to the reactor in at least one metering after the beginning the addition of the one or more catalysts C, before ≥5% to ≤40% of the NCO groups available from the first portion of the isocyanate component A 1 are oligomerized.

4. Process according to claim 1 , in which the temperature difference between the first portion of the isocyanate component A 1 initially introduced and the second isocyanate component A 2 to be metered in, measured at the beginning of the addition of the one or more catalysts C, is ≥25° C.

5. Process according to claim 1 , in which, at the beginning of the addition of the one or more catalysts C, the temperature of the first portion of the isocyanate component A 1 initially introduced is higher than the temperature of the second portion of the isocyanate component A 2 to be metered in.

6. Process according to claim 1 , in which the second portion of the isocyanate component A 2 is the less active and the first portion of the isocyanate component A 1 is the more active.

7. Process according to claim 1 , in which isocyanate recovered from process stage III is introduced in a subsequent process as the first portion of the isocyanate component A 1 and fresh isocyanate is metered in as the second portion of the isocyanate component A 2 .

8. Process according to claim 1 , in which diisocyanates with aliphatically and/or cycloaliphatically bonded isocyanate groups are used in component A.

9. Process according to claim 1 , in which exclusively diisocyanates are used in component A.

10. Process according to claim 1 , in which different isocyanates from the second portion of the isocyanate component A 2 are used in the first portion of the isocyanate component A 1 .

11. Process according to claim 9 , in which the diisocyanates are chosen from 1,6-diisocyanatohexane (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI) and 1,5-diisocyanatopentane (PDI).

12. Process according to claim 1 , in which the same diisocyanate is used in the first portion of the isocyanate component A 1 and the second portion of the isocyanate component A 2 .

13. Process according to claim 12 , in which 1,6-diisocyanatohexane (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI) or 1,5-diisocyanatopentane (PDI) is used.

14. Process according to claim 1 , in which an isocyanate-reactive component B is used.