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

Abstract

The invention relates to a process for the preparation of polyisocyanates with dimer, trimer and/or allophanate and optionally urethane structure.

Claims

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.sub.1 is initially introduced into a reactor and a second portion of the isocyanate component A.sub.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.sub.1 are oligomerized, and that the first portion of the isocyanate component A.sub.1, in comparison with the second portion of the isocyanate component A.sub.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.sub.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.sub.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.sub.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.sub.1 are oligomerized.

3. Process according to claim 1, in which the second portion of the isocyanate component A.sub.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.sub.1 are oligomerized.

4. Process according to claim 1, in which the temperature difference between the first portion of the isocyanate component A.sub.1 initially introduced and the second isocyanate component A.sub.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.sub.1 initially introduced is higher than the temperature of the second portion of the isocyanate component A.sub.2 to be metered in.

6. Process according to claim 1, in which the second portion of the isocyanate component A.sub.2 is the less active and the first portion of the isocyanate component A.sub.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.sub.1 and fresh isocyanate is metered in as the second portion of the isocyanate component A.sub.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.sub.2 are used in the first portion of the isocyanate component A.sub.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.sub.1 and the second portion of the isocyanate component A.sub.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.

Description

EXAMPLES

(1) All percentages are based on weight, unless stated otherwise.

(2) The following compounds were used:

(3) Desmodur® H: hexamethylene diisocyanate (HDI) from Covestro AG, Leverkusen, Germany

(4) Triton® B: benzyltrimethylammonium hydroxide from Merck KGaA, Darmstadt, Germany

(5) 2-ethylhexanol: Sigma-Aldrich Chemie GmbH, Taufkirchen, GER

(6) dibutyl phosphate: Sigma-Aldrich Chemie GmbH, Taufkirchen, GER

(7) Determination Methods:

(8) The NCO contents were determined by titrimetric means according to DIN EN ISO 11909 (2007-05).

(9) The residual monomer contents were measured according to DIN EN ISO 10283 (2007-11) by gas chromatography with an internal standard.

(10) The dynamic viscosities were determined at 23° C. using the VT 550 viscometer from Haake. By measurements at different shear rates, it was ensured that the flow behaviour of the polyisocyanate mixtures described according to the invention and also that of the comparative products corresponds to that of ideal Newtonian fluids. The indication of the shear rate can therefore be omitted.

(11) Activity test on the ability of the isocyanate component to oligomerize: according to embodiments in the descriptive part. Catalyst: 1% benzyltrimethylammonium hydroxide solution in 2-ethylhexanol (benzyltrimethylammonium hydroxide from Aldrich).

(12) Comparative Example (Following WO 2015/124504):

(13) 700 g of fresh hexamethylene diisocyanate (HDI, content: 99.7% (GC)) are mixed with 980 g of recycled HDI distillate (from a preceding identical batch in which exclusively fresh HDI was used, content: 98.2% according to GC) in a dry 2-1 four-necked flask with a stirrer, dropping funnel, vacuum connection and drying tube, heated to 60° C. and briefly evacuated twice. After the respective breaking of the vacuum and the inerting with nitrogen, catalyst (0.5% benzyltrimethylammonium hydroxide in 2-ethylhexanol) was slowly added dropwise via a dropping funnel. After approximately 30 minutes, 10 g of catalyst were consumed. The incipient trimerization led to a marked exothermicity. In spite of interrupting the addition of catalyst, the temperature quickly rose further to over 72° C. The metering remained interrupted and the reaction vessel was additionally cooled with a water bath (18° C.). After the reaction temperature had fallen to 62° C., the catalysis was continued markedly slowed down in 0.7-0.8 g portions. The further development of heat could be brought under control using water bath cooling. Thus, the temperature could be maintained between 60 and 68° C.

(14) The reaction was monitored through sampling and NCO content measurement. After 3.5 hours, the reaction was terminated at an NCO content of 39.5% by addition of dibutyl phosphate (50 equimolar % with regard to the total amount of catalyst used of 16 g) and the reaction mixture was stirred at 60° C. for a further 1 h.

(15) The crude product thus obtained was worked up in a glass molecular evaporator with an upstream pre-evaporator (pre-evaporation: 145° C., main evaporation: 135° C., 0.2 mbar).

(16) A faintly yellow clear polyisocyanate with a monomer content of 0.25% residual HDI was obtained.

(17) Further characteristics: NCO content: 21.7%, viscosity: 3120 mPa.Math.s (23° C.)

(18) The HDI distillate recovered exhibited an HDI content (GC) of 98.4%. The AC content was 2 ppm.

(19) Example According to the Invention:

(20) 980 g of recycled HDI distillate (from a preceding identical batch in which exclusively fresh HDI was used, content: 98.4% according to GC) initially introduced into a dry 2-1 four-necked flask with a stirrer, dropping funnel, vacuum connection and drying tube, and heated to 60° C. The inerting is carried out by briefly evacuating twice. After the respective breaking of the vacuum and the inerting with nitrogen, the catalyst (0.5% benzyltrimethylammonium hydroxide in 2-ethylhexanol) was slowly added dropwise via a dropping funnel. After approximately 5 minutes, 3 g of catalyst were consumed. The incipient trimerization led to a marked exothermicity. The metering of the catalyst was kept up. The temperature could be maintained at approximately 64° C. by continuous addition of 700 g of cold (AT) fresh HDI (according to activity test approximately half as active as the recycled HDI distillate). Surprisingly, however, the reaction does not come to a standstill through the addition. After 40 min, the stock of fresh HDI was consumed. The further metering of catalyst and the trimerization reaction associated therewith could be maintained by water bath cooling within a range of 60 to 65° C. After each noticeable decline in reaction, the catalysis was continued through respective addition of catalyst (in portions of 0.7-0.8 ml).

(21) The reaction was monitored through sampling and NCO content measurement. After 2.75 hours, the reaction was terminated at an NCO content of 39.7% by addition of dibutyl phosphate (50 equimolar % with regard to the total amount of catalyst used of 12 g) and the reaction mixture was stirred at 60° C. for a further 1 h.

(22) The crude product thus obtained was worked up in a glass molecular evaporator with an upstream pre-evaporator (pre-evaporation: 145° C., main evaporation: 135° C., 0.2 mbar).

(23) A largely colourless clear polyisocyanate with a monomer content of 0.28% residual HDI was obtained.

(24) Further characteristics: NCO content: 21.8%, viscosity: 3030 mPa.Math.s (23° C.)

(25) The HDI distillate recovered exhibited an HDI content (GC) of 98.7%. The AC content was 2 ppm.

(26) The advantages of the new process are obvious, through the initially moderate exothermicity behaviour (saving of cooling energy through use of the low temperature of the fresh HDI), the clearly reduced incubation time combined with a lower total reaction time and the altogether lower amount of initiator and accordingly of stopper.