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, and c) in the presence of one or more catalysts C is oligomerized with formation of dimer, trimer and/or allophanate structures and optionally urethane structures (I), the reaction is thermally and/or chemically interrupted (II) and optionally the polyisocyanate obtained is freed from excess isocyanate of the component A down to <1% by weight (III), characterized in that a first portion of the isocyanate component A is initially introduced into a reactor (A.sub.1) and the second portion of the isocyanate component A is added to the reactor (A.sub.2) in at least one metering after the beginning of the addition of catalyst, however before ≤50% of the isocyanate groups available from component A.sub.1 are oligomerized, and that the isocyanate component A.sub.1, in comparison with the isocyanate component A.sub.2, differs with regard to i) the temperature, viewed at the moment of the beginning of the addition of catalyst, and/or ii) the oligomerization activity.

2: Process according to claim 1, in which the second portion of the isocyanate component A is added to the reactor (A.sub.2) in at least one metering after the beginning of the addition of catalyst, however before ≥5% to ≤50% of the NCO groups available from component A.sub.1 are oligomerized.

3: Process according to claim 1, in which the second portion of the isocyanate component A is added to the reactor (A.sub.2) in at least one metering after the beginning of the addition of catalyst, however before ≥5% to ≤40% of the NCO groups available from component A.sub.1 are oligomerized.

4: Process according claim 1, in which the temperature difference between the isocyanate component initially introduced A.sub.1 and the isocyanate component to be metered in A.sub.2, viewed at the moment of the beginning of the addition of catalyst, is ≥25° C.

5: Process according to claim 1, in which, at the moment of the beginning of the addition of catalyst, the temperature of the isocyanate component initially introduced A.sub.1 is higher than that of the isocyanate component to be metered in A.sub.2.

6: Process according to claim 1, in which the difference in the oligomerization activity is determined as follows (activity test): 60 g of isocyanate A.sub.1 are initially introduced into a 100 ml 2-necked flask with a magnetic stirrer, thermometer and vacuum connection, heated up with an oil bath to 60° C. and evacuated for 15 minutes. Subsequently, the vacuum is broken with nitrogen and a dropping funnel with a pressure equalizer and a drying tube and which is filled with catalyst C is installed. Immediately afterwards, the dropwise metering of the catalyst is begun. The consumption of the catalyst (in g) is measured up to the moment at which the temperature of the reaction mixture begins to climb. The experiment is carried out analogously with isocyanate component A.sub.2, in which the catalyst C is added with an identical metering rate. The isocyanate component with the higher or lower oligomerization activity is determined from the comparison of the amounts of the catalyst C consumed in the two experiments. The activity is higher as the amount of catalyst consumed becomes lower; and in the activity test described above, the amount of catalyst consumed with the less active isocyanate component is approximately ≥5% higher than with the more active isocyanate component.

7: Process according to claim 6, in which isocyanate component A.sub.2 is the less active and isocyanate component A.sub.1 is the more active isocyanate component.

8: Process according to claim 1, in which isocyanate recovered from process stage III is initially introduced (component A.sub.1) and fresh isocyanate is metered in (component A.sub.2).

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

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

11: Process according to claim 1, in which different isocyanates from component A.sub.2 are used in component A.sub.1.

12: Process according to claim 10, in which the diisocyanates are chosen from HDI, IPDI and PDI.

13: Process according claim 1, in which the same diisocyanate is used in component A.sub.1 and A.sub.2.

14: Process according to claim 13, in which HDI, IPDI or PDI is used.

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

Description

EXAMPLES

[0130] All percentages are based on weight, unless stated otherwise.

[0131] The following compounds were used:

[0132] Desmodur® H: hexamethylene diisocyanate (HDI) from Covestro AG, Leverkusen, Germany

[0133] Triton® B: benzyltrimethylammonium hydroxide from Merck KGaA, Darmstadt, Germany

[0134] 2-ethylhexanol: Sigma-Aldrich Chemie GmbH, Taufkirchen, GER

[0135] dibutyl phosphate: Sigma-Aldrich Chemie GmbH, Taufkirchen, GER

Determination Methods

[0136] The NCO contents were determined by titrimetric means according to DIN EN ISO 11909 (2007-05).

[0137] The residual monomer contents were measured according to DIN EN ISO 10283 (2007-11) by gas chromatography with an internal standard.

[0138] 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.

[0139] 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).

Comparative Example (Following WO 2015/124504)

[0140] 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.

[0141] 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.

[0142] 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).

[0143] A faintly yellow clear polyisocyanate with a monomer content of 0.25% residual HDI was obtained.

[0144] Further characteristics: NCO content: 21.7%, viscosity: 3120 mPa.Math.s (23° C.)

[0145] The HDI distillate recovered exhibited an HDI content (GC) of 98.4%. The AC content was 2 ppm.

Example According to the Invention

[0146] 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).

[0147] 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.

[0148] 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).

[0149] A largely colourless clear polyisocyanate with a monomer content of 0.28% residual HDI was obtained.

[0150] Further characteristics: NCO content: 21.8%, viscosity: 3030 mPa.Math.s (23° C.)

[0151] The HDI distillate recovered exhibited an HDI content (GC) of 98.7%. The AC content was 2 ppm.

[0152] 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.