Catalysts for Producing Isocyanurates from Isocyanates

Abstract

The invention relates to a method for producing isocyanurates and isocyanurate-containing polyurethanes, comprising the step of reacting an isocyanate in the presence of a catalyst.

Claims

1. A process for producing isocyanurates and isocyanurate-containing polyurethanes comprising reacting an isocyanate in the presence of a catalyst, wherein: the catalyst comprises the product of the reaction of a thiol group containing carboxylic acid with an alkali metal, alkaline earth metal, scandium-group or lanthanoid base, wherein the reaction is performed in the absence of compounds comprising tin or lead, wherein the degree of deprotonation of the catalyst is ≧50% to ≦100% and the H atoms present in carboxyl groups as well as the carboxylate groups and the H atoms present in thiol groups as well as the thiolate groups are considered when calculating the degree of deprotonation.

2. The process as claimed in claim 1, wherein the thiol group containing carboxylic acid comprises a thiol group and a carboxyl group.

3. The process as claimed in claim 2, wherein the thiol group containing carboxylic acid is selected from the group consisting of 2-mercaptoacetic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, thiosalicylic acid, and combinations of any thereof.

4. The process as claimed in claim 1, wherein the degree of deprotonation of the catalyst is ≧70% to ≦100% and the H atoms present in carboxyl groups as well as the carboxylate groups and the H atoms present in thiol groups as well as the thiolate groups are considered when calculating the degree of deprotonation.

5. The process as claimed in claim 1, wherein the base for deprotonating the catalyst precursor is selected from the group consisting of an alkali metal, alkaline earth metal, scandium-group or lanthanoid hydride, an alkali metal, alkaline earth metal, scandium-group or lanthanoid alkoxide or an alkali metal, alkaline earth metal, and scandium-group or lanthanoid alkyl.

6. The process as claimed in claim 1, wherein the catalyst is present in the form of a solution or a suspension in a solvent before commencement of the reaction.

7. The process as claimed in claim 1, wherein the temperature at commencement of the reaction is ≧20° C. to ≦90° C.

8. The process as claimed in claim 1, wherein the isocyanate is a polyisocyanate.

9. The process as claimed in claim 8, wherein the reaction is further performed in the presence of a polyol.

10. The process as claimed in claim 9, wherein the reaction is further performed in the presence of a physical blowing agent and/or a chemical blowing agent.

11. The process as claimed in claim 10, wherein the reaction is performed at an NCO index of ≧200.

12. A polyurethane/polyisocyanurate foam produced by a process as claimed in claim 10.

13. The polyurethane/polyisocyanurate foam as claimed in claim 12, wherein the polyurethane/polyisocyanurate foam further has a combustibility index CI of 5 and a flame height of ≦135 mm, in each case determined in the BVD test.

14. A thermal insulation element comprising a polyurethane/polyisocyanurate foam as claimed in claim 12.

15. The process as claimed in claim 3, wherein the degree of deprotonation of the catalyst is ≧70% to ≦100% and the H atoms present in carboxyl groups as well as the carboxylate groups and the H atoms present in thiol groups as well as the thiolate groups are considered when calculating the degree of deprotonation.

16. The process as claimed in claim 15, wherein the base for deprotonating the catalyst precursor is selected from the group consisting of an alkali metal, alkaline earth metal, scandium-group or lanthanoid hydride, an alkali metal, alkaline earth metal, scandium-group or lanthanoid alkoxide or an alkali metal, alkaline earth metal, and scandium-group or lanthanoid alkyl.

17. The process as claimed in claim 16, wherein the catalyst is present in the form of a solution or a suspension in a solvent before commencement of the reaction.

18. The process as claimed in claim 17, wherein the temperature at commencement of the reaction is ≧20° C. to ≦90° C.

19. The process as claimed in claim 18, wherein the isocyanate is a polyisocyanate.

20. A thermal insulation element comprising a polyurethane/polyisocyanurate foam as claimed in claim 13.

Description

EXAMPLES

[0079] The present invention is elucidated in detail by the figures and examples which follow, but without being limited thereto.

[0080] FIG. 1 shows a measurement of foam height from example 2-1* (Ac) and 2-2 (3-MP) as a function of time in the foaming apparatus from Format which is fitted with the “Advanced Test Cylinder” (ATC). The ATC and the instrument bottom had been temperature-controlled to 50° C.

[0081] FIG. 2 shows a time-resolved ATR mid-infrared spectrum of the Ac- and 3-MP-catalyzed foam systems from FIG. 1. The development of the carbamate-specific peak area with time (amide III between 1170 and 1250 cm.sup.−1) is shown.

[0082] FIG. 3 shows a time-resolved ATR mid-infrared spectrum of the Ac- and 3-MP-catalyzed foam systems from FIG. 1. The development of the trimer-specific peak area with time (isocyanurate ring vibration between 1380 and 1450 cm.sup.−1) is shown.

METHODS

[0083] In-situ infrared spectroscopy: The composition of the reaction mixture as a function of time was monitored with a Bruker MATRIX-MX spectrometer. The infrared (IR) spectrometer was fitted with a high-pressure ATR (attenuated total reflectance) IR fiber optic probe (diameter 3.17 mm). The ATR-IR fiber optic probe (90° diamond prism with 1×2 mm basal area and 1 mm height as ATR element, 2×45° reflection of the IR beam, IR-beam-coupled fiber optics) was introduced into the reactor used in the reaction such that the diamond at the end of the probe was completely immersed in the reaction mixture. The IR spectra (20 scans per measurement) were acquired in a time-resolved manner at a scan rate of 266.7 scans per minute in the range of 400-4000 cm.sup.−1 at a resolution of 4 cm.sup.−1 at 4.5 second time intervals. An argon background spectrum (100 scans) was acquired at the beginning of each experiment. OPUS 7.0 software was used for recording the spectra.

[0084] Quantitative evaluation of the measured IR spectra was by means of PEAXACT 3.5.0 Software for Quantitative Spectroscopy from S•PACT GmbH using the Integrated Hard Model (IHM) method. The Hard Model for the product mixture was generated from the characteristic IR absorption bands of the individual components isocyanate, isocyanurate and carbamate. To achieve quantitative determination of the concentration of the individual components in the reaction mixture a calibration with known concentrations of the individual components at the respective reaction temperature was effected.

[0085] The time-resolved measurements in the reacting foam system (cf. FIGS. 2 and 3) were effected in a Bruker Tensor 27—spectrometer on a ZnSe ATR crystal of 1×5 cm.sup.2 in size embedded in a heated metal plate at a constant controlled temperature of 40° C., 70° C. or 120° C. The reaction sequences in the approx. 1-μm-thick contact zone of the foam material with the ATR crystal at the established temperature are monitored therewith (spectral resolution 4 cm.sup.−1; average over 8 scans).

[0086] The BVD test as per the Swiss Basic Test for Determination of Combustibility of Building Materials from the Vereinigung kantonaler Feuerversicherungen [Association of Cantonal Fire Insurers] in the edition of 1988, with the supplements of 1990, 1994, 1995 and 2005 (available from Vereinigung kantonaler Feuerversicherungen, Bundesstr. 20, 3011 Bern, Switzerland) was used as a basis for describing fire behavior. In this small burner test a combustibility index (CI) and a flame height (in mm) is determined for the foam.

[0087] Compounds Used:

[0088] Unless otherwise stated the catalysts employed were produced as follows from the corresponding catalyst precursor (thiol group containing carboxylic acid: 3-mercaptopropionic acid, 2-mercaptoacetic acid, 4-mercaptobutyric acid, o-thiosalicylic acid, S-methylthiosalicylic acid):

[0089] Production of the Catalyst as Solid

[0090] Under an argon atmosphere a solution of the catalyst precursor (0.01 mol) in anhydrous methanol (15 mL) was initially charged and at 25° C. a 25% solution of potassium methoxide in methanol (0.745 g, corresponding to 2.66 mmol, for forming the disalts and 0.372 g, corresponding to 1.33 mmol, for forming the monosalt) was added dropwise. The obtained reaction mixture was stirred at 25° C. for 30 minutes. This was followed by addition of anhydrous diithyl ether (10 mL) to precipitate-out a colorless solid. The supernatant solution was filtered off via a filter cannula and the solid filtration residue was washed three times with 10 mL respectively of a 1:5 mixture of anhydrous methanol and anhydrous diethyl ether. The thus obtained solid was dried for 16 h at 60° C. under vacuum (2.0×10.sup.−2 mbar).

[0091] Production of the Catalyst Solution in Diethylene Glycol Monomethyl Ether (DEME)

[0092] An 11.2 percent solution of the solid-form catalysts in diethylene glycol monomethyl ether (DEME) was produced.

Examples 1-1 to 1-10

Production of Isocyanurates from p-tolyl Isocyanate in the Presence of Diethylene Glycol Monomethyl Ether

[0093] All reactions explicated in examples 1-1 to 1-10 were performed according to the following general procedure:

[0094] Into an autoclave made of stainless steel having an internal volume of 160 mL was initially charged a mixture of para-tolyl isocyanate (11 mL; 11.62 g; 0.087 mol) and propylene carbonate (47.40 mL; 57.05 g; 0.559 mol). Once the autoclave was sealed a low argon stream (20 L/min) was passed through the reactor and the reaction mixture heated to reaction temperature with stirring. Once a constant reaction temperature had been observed over a period of 5 minutes the in-situ IR measurement was initiated. The catalyst solution was subsequently injected into the reaction mixture in the reported amounts. The thus obtained reaction mixture was stirred at the relevant reaction temperature at a stirring speed of 500 rpm. If the intensity of the in-situ IR signal of the isocyanate group had fallen below the detection limits in a period of less than 40 minutes the reaction was terminated after a further 20 minutes by cooling the reactor to 25° C. and stopping the stirrer. Otherwise the reaction was terminated in the same way after one hour. The results are reported in Table 1.

[0095] Examples marked with an * are comparative examples.

TABLE-US-00001 TABLE 1 Activity: Activity: Selectivity Selectivity Selectivity Selectivity Time Time for trimer for trimer for trimer for trimer Degree until until formation formation formation formation of conver- conver- at an iso- at an iso- at an iso- at an iso- Mol depro- sion of sion of cyanate cyanate cyanate cyanate K ton- 20% of 50% of conver- conver- conver- conver- per ation Catalyst isocyan- isocyan- sion of sion of sion of sion of Catalyst mol in mol %/ ate ate 20% in 50% in 90% in 99% in Example precursor cat. % wt % in s in s % % % % 1-1* acetate 1 50 0.1/0.07 19.09 82.29 17.16 41.92 59.00 68.40 1-2* 3- 1 50 0.1/0.11 32.40 134.19 0.0 34.94 57.27 65.99 mercapto- propionate 1-3 3- 1.5 75 0.1/0.12 11.53 28.00 25.78 43.96 61.08 70.74 mercapto- propionate 1-4 3- 1.7 83.6 0.1/0.13 7.15 17.06 27.28 48.34 61.03 72.57 mercapto- propionate 1-5 3- 2 100 0.1/0.14 5.70 16.18 25.64 43.65 59.92 70.97 mercapto- propionate 1-6 4-mercapto- 2 100 0.1/0.15 4.73 15.09 7.40 31.55 53.23 62.16 butyrate 1-7 thiosalicylate 2 100 0.1/0.17 6.59 22.48 4.57 24.25 50.03 60.06 1-8* S- 1 100 0.2/0.3  28.09 139.46 0.0 27.78 62.29 70.07 methyl- thiosalicylate 1-9* 3-mercapto- 1 50 0.1/0.15 58.21 279.30 0.0 13.14 50.05 59.82 propionate + DBTL 9:1 molar ratio 1-10* 3-mercapto- 2 100 0.1/0.17 9.44 33.32 17.36 25.22 50.06 65.28 propionate + DBTL 9:1 molar ratio

[0096] The degree of deprotonation is to be understood as meaning the percentage of Zerewittinoff-active protons removed from the acid upon which the catalyst molecule is based. Zerewittinoff-active protons are those that react with the Grignard reagent methylmagnesium iodide to form one molecule of methane per active proton.

[0097] Comparison of example 1-1 with examples 1-5 to 1-7 shows that the dipotassium salts of the mercaptoacids are superior to the potassium acetate (prior art) in terms of activity since the time for achieving a reported conversion is always lower.

[0098] Examples 1-2 and 1-8 compared to examples 1-5 to 1-7 show that it is advantageous when not only the carboxyl group but also the mercapto group is deprotonated.

[0099] A comparison of example 1-2 with example 1-9 and a comparison of example 1-5 with example 1-10 show that addition of DBTL (prior art) reduces activity, i.e. sole use of the deprotonated mercapto acid is advantageous over the prior art. The formation of trimers is desirable since they are advantageous for flame retardancy and heat resistance.

[0100] Example 1-5 shows that the dipotassium salt of 3-mercaptopropionic acid shows the greatest selectivity for trimer formation for all isocyanate conversions investigated. The comparisons of example 1-2 with example 1-9 and of example 1-5 with example 1-10 show that an addition of DBTL (dibutyltin dilaurate) has a disadvantageous effect on selectivity for trimer formation.

[0101] Examples 1-3 to 1-5 show that even at degrees of deprotonation of the catalyst in the range from ≧70% to ≦100% (examples 1-3 to 1-5) or from ≧80% to ≦100% (examples 1-4 to 1-5) a high selectivity for trimer formation is obtained for all isocyanate conversions investigated.

Example Group 2

Production of Polyurethane/Polyisocyanurate Foams

[0102] In the production of rigid foams the following compounds were employed:

TABLE-US-00002 Polyesterpolyol obtained from phthalic anhydride, adipic acid, P1 Monoethylene glycol and diethylene glycol, OH number 240 mg KOH/g TCPP tris(1-chloro-2-propyl)phosphate from Lanxess GmbH, Germany. TEP triethylphosphate from Lanxess GmbH, Germany. Stabiliser B8443 polyether-polysiloxane copolymer from Evonik. Desmophen ® polyetherpolyol based on trimethylolpropane and V 657 ethylene oxide having an OH number of 255 mg KOH/g according to DIN 53240 from Bayer MaterialScience AG, Leverkusen, Germany. Additive 1132 Polyesterpolyol from phthalic anhydride and diethylene glycol, OH-number 795 mg KOH/g from Bayer MaterialScience AG, Leverkusen, Germany. Desmodur ® polymeric polyisocyanate based on 4,4-diphenyl- 44V70L methane diisocyanate having an NCO content of about 31.5 wt % from Bayer MaterialScience AG, Leverkusen, Germany. 3-MP solution of 3-mercaptopropionic acid dipotassium salt (3-MP) (17.3 wt %) in DEG

[0103] To produce the rigid foams the raw materials listed in table 2 except the polyisocyanate component were weighed into a paper cup, temperature-controlled to 23° C. and mixed using a Pendraulik laboratory mixer (e.g. Type LM-34 from Pendraulik) and volatilized blowing agent (n-pentane) was optionally supplemented. The polyisocyanate component (likewise temperature-controlled to 23° C.) was then added to the polyol mixture with stirring and the resultant reaction mixture was mixed for 8 s at 4200 rpm.

[0104] Examples marked with an * are comparative examples.

TABLE-US-00003 TABLE 2 Example No. 2-1* 2-2 2-3* 2-4 2-5* 2-6 Polyesterpolyol P1 (parts by weight) 63.8 63.8 63.8 63.8 63.8 63.8 TCPP (parts by weight) 20.0 20.0 20.0 20.0 20.0 20.0 TEP (parts by weight) 5.0 5.0 5.0 5.0 5.0 5.0 Desmophen ® V 657 (parts by weight) 5.0 5.0 5.0 5.0 5.0 5.0 Additive 1132 (parts by weight) 2.2 2.2 2.2 2.2 2.2 2.2 Stabiliser B8843 (parts by weight) 4.0 4.0 4.0 4.0 4.0 4.0 Potassium acetate, 10.0 wt % in DEG 6.64 — 6.66 7.18 (parts by weight) 3-MP, 17.3 wt % in DEG (parts by — 7.20 7.20 7.80 weight) n-Pentane (parts by weight) 17.1 17.5 17.1 17.5 18.1 18.5 Desmodur ® 44V70L (parts by weight) 196 201 196 201 214 221 Index 340 340 340 340 364 364 Fibre time (s) 105 40 100 39 Core apparent density (kg/m.sup.3) 37 39 37 40 Mol % of catalyst based on employed 0.5 0.5 0.5 0.5 0.5 0.5 NCO groups BVD test, CI 5, CI 5, CI 5, CI 5, Flame height 150 120-130 140-150 130 mm mm mm mm

[0105] Characterization of Reactivity of Catalyst 3-MP

[0106] FIG. 1 shows a plot of the rise height of the PUR/PIR foam versus time, measured for the foam recipe from example 2-2, where potassium acetate has been replaced by 3-MP as catalyst (K/S=2). In both cases the catalyst concentration was 0.5 mol% based on the employed isocyanate groups.

[0107] It was observed that the foam obtained using 3-MP achieved a greater rise height in a shorter time than the foam obtained using the comparative catalyst potassium acetate (Ac).

[0108] The inventive catalyst accordingly shows a higher activity. Furthermore, when using potassium acetate (example 2-1*) a reduced rate of increase in rise height (PIR kink) which is typically associated with onset of the trimerization reaction (isocyanurate formation) was observed after a time of >100 s.

[0109] Without wishing to be bound to a particular scientific theory the absence of the PIR kink when using 3-MP as catalyst is attributed to the trimerization reaction undergoing earlier onset and progressing simultaneously to the urethane formation in this case. The catalyst derived from 3-mercaptopropionic acid thus exhibits an increased relative reactivity for the formation of isocyanurate units compared to the comparative catalyst, potassium acetate.

[0110] FIG. 2 also confirms the increased activity of 3-MP for trimer formation through IR spectroscopic investigations. FIG. 2 shows a corresponding analysis of the reaction processes in the edge zone of the reacting foams in contact with a substrate at constant temperature (40, 70 and 120° C.). The experiments reflect the reaction behavior that the foam systems would show for example in contact with appropriately temperature-controlled covering layers in the production of metal panels.

[0111] Carbamate formation is activated virtually identically by both catalysts (FIG. 2).

[0112] FIG. 3 confirms temperature-dependent differences in the formation of trimer: at 40° C. and 70° C. 3-MP catalyses trimer formation markedly earlier and more strongly than Ac. At 120° C. a difference over time is still apparent but the final level achieved is comparable.

[0113] Characterization of Fire Behavior of Foams Produced with the Catalyst 3-MP

[0114] Identical catalyst concentrations of 0.5 mol% based on isocyanate groups employed and similar apparent densities were established for all foams. It is apparent that the foams activated with potassium acetate (examples 2-3* and 2-5*) have markedly longer fibre times, thus illustrating the lower activity compared to 3-MP (examples 2-4 and 2-6). Also, while all foams achieve the same combustibility of 5, the foams produced with the inventive catalyst 3-MP exhibit markedly lower flame heights.