POLYURETHANE COMPOSITION HAVING POLYMERIC PLASTICIZER AND A LOW CONTENT OF MONOMERIC DIISOCYANATES

Abstract

A moisture-curing polyurethane composition having a content of monomeric diisocyanates of at most 0.1 wt %, containing: at least one isocyanate-group-containing polyurethane polymer having a content of monomeric diisocyanates of at most 0.5 wt %, obtained from reaction of at least one monomeric diisocyanate with at least one polyether polyol at a NCO/OH ratio of at least 3/1 and subsequent removal of a large part of monomeric diisocyanates by way of a suitable separating method; and at least one polyether having blocked hydroxyl groups and free of isocyanate groups, as a plasticizer. Moisture-curing polyurethane composition is highly storage-stable when moisture is excluded, can be safely handled without special safety precautions, can be sold without hazard label, can be well processed, has long open time and has fast curing to form elastic material of high strength and extensibility, high cold flexibility, good adhesion properties and high stability with respect to heat and moisture.

Claims

1. A moisture-curing polyurethane composition having a monomeric diisocyanate content of not more than 0.1% by weight, comprising at least one polyetherurethane polymer containing isocyanate groups and having a monomeric diisocyanate content of not more than 0.5% by weight, obtained from the reaction of at least one monomeric diisocyanate with at least one polyether polyol in an NCO/OH ratio of at least 3/1, and subsequent removal of a majority of the monomeric diisocyanates by means of a suitable separation method, and at least one polyether having blocked hydroxyl groups, which is free of isocyanate groups, as plasticizer.

2. The polyurethane composition as claimed in claim 1, wherein the polyetherurethane polymer has an NCO content in the range from 0.5% to 6.0% by weight.

3. The polyurethane composition as claimed in claim 1, wherein the polyetherurethane polymer has 80% to 100% by weight of 1,2-propyleneoxy groups and 0% to 20% by weight of 1,2-ethyleneoxy groups in the polyether segment.

4. The polyurethane composition as claimed in claim 1, wherein the monomeric diisocyanate used for the reaction is diphenylmethane 4,4′-diisocyanate, tolylene 2,4-diisocyanate or mixtures thereof with tolylene 2,6-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane or hexane 1,6-diisocyanate.

5. The polyurethane composition as claimed in claim 1, wherein the NCO content of the polyetherurethane polymer is at least 80% of the theoretical NCO content which is calculated from the addition of one mole of monomeric diisocyanate per mole of OH groups of the polyether polyol.

6. The polyurethane composition as claimed in claim 1, wherein the blocked hydroxyl groups are selected from ester, aceto ester, carbonate, acetal and urethane groups.

7. The polyurethane composition as claimed in claim 1, wherein the blocked hydroxyl groups are acetate groups.

8. The polyurethane composition as claimed in claim 1, wherein the polyether having blocked hydroxyl groups is derived from a hydroxy-functional polyether having an average OH functionality in the range from 1 to 3.

9. The polyurethane composition as claimed in claim 1, wherein the polyether having blocked hydroxyl groups has an average molecular weight M.sub.n in the range from 600 to 15,000 g/mol, determined by means of gel permeation chromatography (GPC) versus polystyrene standard with tetrahydrofuran as mobile phase, refractive index detector and evaluation from 200 g/mol.

10. The polyurethane composition as claimed in claim 1, wherein it contains 5% to 40% by weight of polyether having blocked hydroxyl groups.

11. The polyurethane composition as claimed in claim 1, wherein it additionally comprises at least one further constituent selected from oligomeric isocyanates, catalysts and fillers.

12. The polyurethane composition as claimed in claim 1, wherein it contains 20% to 60% by weight of polyetherurethane polymer containing isocyanate groups and having a monomeric diisocyanate content of not more than 0.5% by weight, 5% to 35% by weight of polyether having blocked hydroxyl groups, 20% to 60% by weight of fillers, and optionally further constituents.

13. A method of bonding or sealing, comprising the steps of (i) applying the polyurethane composition as claimed in claim 1 to a first substrate and contacting the composition with a second substrate within the open time of the composition, or to a first and to a second substrate and joining the two substrates within the open time of the composition, or between two substrates, (ii) curing the composition by contact with moisture.

14. A method of coating or sealing, comprising the steps of (i) applying the polyurethane composition as claimed in claim 1 to a substrate, (ii) curing the composition by contact with moisture.

15. An article obtained from the method as claimed in claim 13.

Description

EXAMPLES

[0181] Working examples are adduced hereinafter, which are intended to elucidate the invention described. The invention is of course not limited to these described working examples.

[0182] “Standard climatic conditions” (“SCC”) refer to a temperature of 23±1° C. and a relative air humidity of 50±5%.

[0183] Unless stated otherwise, the chemicals used were from Sigma-Aldrich.

[0184] Preparation of Polyethers Having Blocked Hydroxyl Groups:

[0185] Viscosity was measured with a thermostated Rheotec RC30 cone-plate viscometer (cone diameter 25 mm, cone angle 1°, cone tip-plate distance 0.05 mm, shear rate 10 s.sup.−1).

[0186] Infrared spectra (FT-IR) were measured as undiluted films on a Nicolet iS5 FT-IR instrument from Thermo Scientific equipped with a horizontal ATR measurement unit with a diamond crystal. The absorption bands are reported in wavenumbers (cm.sup.−1).

[0187] .sup.1H NMR spectra were measured on a spectrometer of the Bruker Ascend 400 type at 400.14 MHz; the chemical shifts 5 are reported in ppm relative to tetramethylsilane (TMS). No distinction was made between true coupling and pseudo-coupling patterns.

[0188] Compound V-1: Butanol-started acetylated PPG monool with average molecular weight M.sub.n about 790 g/mol

[0189] 120.00 g of butanol-started polyoxypropylene monool (Synalox® 100-20B, average molecular weight M.sub.n about 750 g/mol; from Dow) and 18.74 g of acetic anhydride were initially charged in a round-bottom flask with distillation attachment under a nitrogen atmosphere. Then the reaction mixture was stirred under a gentle nitrogen stream at 130° C., with collection of acetic acid as distillate. Subsequently, the volatile constituents were removed from the reaction mixture at 80° C. and a reduced pressure of 10 mbar. A clear, colorless liquid having a viscosity of 74 mPa.Math.s at 20° C. was obtained.

[0190] FT-IR: 2970, 2931, 2867, 1738, 1454, 1372, 1345, 1296, 1241, 1098, 1014, 959,925,866,827.

[0191] .sup.1H NMR (CDCl.sub.3): 5.02 (hept., 1H, CH.sub.2(CH.sub.3)CH—OAc), 3.75-3.34 (2×m, ca. 39H, OCH.sub.2CH(CH.sub.3)O), 3.33-3.28 (m, 2H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2O), 2.04 (s, 3H, O(CO)CH.sub.3), 1.55 (quint., 2H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2O), 1.36 (sext., 2H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2), 1.22 (d, 3H, CH.sub.2(CH.sub.3)CH—OAc), 1.17-1.10 (m, ca. 36H, OCH.sub.2CH(CH.sub.3)O), 0.91 (t, 3H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2O).

[0192] Compound V-2: Diacetylated PPG diol with average molecular weight M.sub.n about 1′080 g/mol

[0193] 80.00 g of polyoxypropylene diol (Voranol® P 1010, OH number 110 mg KOH/g; from Dow) and 18.74 g of acetic anhydride were converted as described for compound V-1. A clear, colorless liquid having a viscosity of 145 mPa.Math.s at 20° C. was obtained.

[0194] Compound V-3: Diacetylated PPG diol with average molecular weight M.sub.n about 4′080 g/mol

[0195] 600.0 g of polyoxypropylene diol (Acclaim® 4200, OH number 28 mg KOH/g; from Covestro) and 33.7 g of acetic anhydride were converted as described for compound V-1. A clear, colorless liquid having a viscosity of 1′174 mPa.Math.s at 20° C. was obtained.

[0196] Preparation of Polymers Containing Isocyanate Groups:

[0197] Viscosity was measured with a thermostated Rheotec RC30 cone-plate viscometer (cone diameter 50 mm, cone angle 1°, cone tip-plate distance 0.05 mm, shear rate 10 s.sup.−1).

[0198] Monomeric diisocyanate content was determined by means of HPLC (detection via photodiode array; 0.04 M sodium acetate/acetonitrile as mobile phase) after prior derivation by means of N-propyl-4-nitrobenzylamine.

[0199] Polymer P1:

[0200] 725.0 g of Desmophen® 5031 BT (glycerol-started ethylene oxide-terminated polyoxypropylene triol, OH number 28.0 mg KOH/g, OH functionality about 2.3; from Covestro) and 275 g of diphenylmethane 4,4′-diisocyanate (Desmodur® 44 MC L, from Covestro) were converted by a known method at 80° C. to a polyetherurethane polymer having an NCO content of 7.6% by weight, a viscosity of 6.5 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of about 20% by weight.

[0201] Subsequently, the volatile constituents, especially a majority of the monomeric diphenylmethane 4,4′-diisocyanate, were removed by distillation in a short-path evaporator (jacket temperature 180° C., pressure 0.1 to 0.005 mbar, condensation temperature 47° C.). The polyetherurethane polymer thus obtained had an NCO content of 1.7% by weight, a viscosity of 19 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of 0.04% by weight.

[0202] Polymer P2:

[0203] 727.0 g of Acclaim® 4200 (polyoxypropylene diol, OH number 28.0 mg KOH/g; from Covestro) and 273.0 g of diphenylmethane 4,4′-diisocyanate (Desmodur® 44 MC L, from Covestro) were converted by a known method at 80° C. to a polyetherurethane polymer having an NCO content of 7.6% by weight, a viscosity of 5.2 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of about 18% by weight.

[0204] Subsequently, the volatile constituents, especially a majority of the monomeric diphenylmethane 4,4′-diisocyanate, were removed by distillation in a short-path evaporator (jacket temperature 180° C., pressure 0.1 to 0.005 mbar, condensation temperature 47° C.). The polyetherurethane polymer thus obtained had an NCO content of 1.8% by weight, a viscosity of 15.2 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of 0.08% by weight.

[0205] Polymer P3:

[0206] 300.0 g of Desmophen® 5031 BT (glycerol-started ethylene oxide-terminated polyoxypropylene triol, OH number 28.0 mg KOH/g, from Covestro), 300.0 g of Acclaim® 4200 (polyoxypropylene diol, OH number 28.0 mg KOH/g, from Covestro), 75.5 g of compound V-1 and 78.8 g of diphenylmethane 4,4′-diisocyanate (Desmodur® 44 MC L, from Covestro) were converted by the known method at 80° C. The polyetherurethane polymer thus obtained had an NCO content of 1.65% by weight, a viscosity of 67.1 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of 2.1% by weight.

[0207] Polymer P4:

[0208] The polymer P4 was prepared as described for polymer P3, except using the same amount of compound V-2 rather than compound V-1. The polyetherurethane polymer thus obtained had an NCO content of 1.68% by weight, a viscosity of 56.8 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of 2.0% by weight.

[0209] Polymer P5:

[0210] The polymer P5 was prepared as described for polymer P3, except using the same amount of compound V-3 rather than compound V-1. The polyetherurethane polymer thus obtained had an NCO content of 1.68% by weight, a viscosity of 67.8 Pa.Math.s at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of 2.0% by weight.

[0211] Moisture-Curing Polyurethane Compositions:

[0212] Compositions Z1 to Z7:

[0213] For each composition, the ingredients specified in table 1 were mixed in the amounts specified (in parts by weight) by means of a centrifugal mixer (SpeedMixer™ DAC 150, FlackTek Inc.) with exclusion of moisture at 3000 rpm for one minute and stored with exclusion of moisture. Each composition was tested as follows:

[0214] A measure determined for storage stability was the viscosity of the composition after storage, in that one closed cartridge in each case was stored at room temperature for 1 day or in an air circulation oven at 60° C. for 7 days, and then the viscosity was measured with a thermostated Rheotec RC30 cone-plate viscometer (cone diameter 25 mm, cone angle 1°, cone tip-plate distance 0.05 mm, shear rate 10 s.sup.−1). The results are given the addition “1d RT” or “7d 60° C.”.

[0215] A measure determined for the processing time (open time) was the skin time (“ST”). For this purpose, a few grams of the composition were applied to cardboard in a layer thickness of about 2 mm and, under standard climatic conditions, the first period of time after which no residues remained any longer on an LDPE pipette used to gently tap the surface of the composition was determined.

[0216] A measure determined for the curing rate was curing after 24 h under standard climatic conditions. For this purpose, the composition was applied as a free-standing cone of diameter 3 cm, left to stand under standard climatic conditions and cut open with a crosscut after 24 h, and the layer thickness of the cured polymer ring formed was measured.

[0217] As a measure of mechanical properties and stability to heat and hydrolysis, each composition was pressed between two wax-coated transfer printing papers to give a film of thickness 2 mm and stored under standard climatic conditions for 7 days. After the wax papers had been removed, a few dumbbells having a length of 75 mm and a bar length of 30 mm and a bar width of 4 mm were punched out of the film. These were used to determine tensile strength, elongation at break and modulus of elasticity at 0.5-5% elongation or 0.5-50% elongation in accordance with DIN EN 53504 at a strain rate of 200 mm/min. These results are given the addition “7d SCC”. In addition, further punched-out dumbbells were stored in an air circulation oven at 100° C. for 7 days or at 70° C./100% relative humidity for 7 days, cooled down under standard climatic conditions and tested in the manner already described for tensile strength, elongation at break, and 5% and 50% modulus of elasticity. These results are given the addition “7d 100° C.” or “7d 70/100”.

[0218] To determine the strength of an adhesive bond, lap shear strength (“LSS”) was determined on glass. For this purpose, composite specimens were produced by bonding two glass plates that had been degreased with isopropanol and pretreated with Sika® Primer 207 (from Sika Schweiz) in such a way that the overlapping adhesive bond had dimensions of 12×25 mm and a thickness of 4 mm and the glass plates protruded at the top ends. After the composite specimens had been stored under standard climatic conditions for 7 d, lap shear strength was tested to DIN EN 1465 at a strain rate of 20 mm/min.

[0219] Shore A hardness was determined according to DIN 53505 on test specimens cured under standard climatic conditions for 7 d.

[0220] Complex modulus of elasticity M* was determined by means of DMTA measurement on strip samples (height 2-3 mm, width 2-3 mm, length 8.5 mm) which had been stored/cured under standard climatic conditions for 7 days, with a Mettler DMA/SDTA 861e instrument. The measurement conditions were: measurement in tensile mode, excitation frequency 10 Hz and heating rate 5 K/min. The samples were cooled down to −70° C. and heated to 100° C. with determination of M*. Table 1 reports M* at −20° C., −10° C., 0° C., 10° C. and 20° C. A low value for the M*(−20° C.)/M*(20° C.) ratio is a measure of good temperature independence of the modulus of elasticity, and high cold flexibility.

[0221] The results are reported in table 2.

[0222] Compositions Z2, Z3 and Z4 are inventive examples. Compositions Z1 and Z5 to Z7 are comparative examples and are given the addition “(Ref.)”.

[0223] Comparative example Z1 contains a conventional prior art plasticizer, and comparative examples Z5 to Z7 each contain a conventionally prepared polymer containing isocyanate groups and having a high monomeric diisocyanate content.

TABLE-US-00001 TABLE 1 Composition (in parts by weight) of Z1 to Z7. Z1 Z5 Z6 Z7 Composition (Ref.) Z2 Z3 Z4 (Ref.) (Ref.) (Ref.) Polymer P1 P1 P1 P1 P3 P4 P5 17.5 17.5 17.5 17.5 38.9 38.9 38.9 P2 P2 P2 P2 17.5 17.5 17.5 17.5 Plasticizer DINP V-1 V-2 V-3 V-1 V-2 V-3 20.4 20.4 20.4 20.4 16.5 16.5 16.5 Carbon black 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Chalk.sup.1 32.0 32.0 32.0 32.0 32.0 32.0 32.0 Silica.sup.2  2.0  2.0  2.0  2.0  2.0  2.0  2.0 DMDEE.sup.3  0.2  0.2  0.2  0.2  0.2  0.2  0.2 pTSI.sup.4  0.4  0.4  0.4  0.4  0.4  0.4  0.4 .sup.1Omyacarb ® 5 GU (from Omya) .sup.2Aerosil ® R 972 (from Evonik) .sup.32,2′-dimorpholinodiethyl ether .sup.4p-toluenesulfonyl isocyanate

TABLE-US-00002 TABLE 2 Properties of Z1 to Z7. Z1 Z5 Z6 Z7 Composition (Ref.) Z2 Z3 Z4 (Ref.) (Ref.) (Ref.) Viscosity 1 d RT 61 46 69 97 146 157 240 [Pa .Math. s] 7 d 60° C. 134 106 217 267 285 361 472 ST [min] 40 40 40 40 40 40 40 Curing after 24 h [mm] 4.0 5.3 4.7 4.6 4.3 4.5 4.1 7 d SCC: Tensile strength 3.81 5.19 5.52 5.76 4.89 4.12 5.40 [MPa] Elongation at break 772 831 856 816 833 745 835 [%] Modulus of elasticity 1.57 1.59 1.56 1.74 1.76 1.77 1.59 [MPa] 5% 50% 0.83 0.90 0.86 1.01 1.04 0.97 0.99 7 d 100° C.: Tensile strength 5.62 5.40 5.51 5.14 4.77 3.66 4.61 [MPa] Elongation at break 688 649 712 674 614 539 646 [%] Modulus of elasticity 1.77 1.62 1.46 1.47 2.00 1.76 1.68 [MPa] 5% 50% 1.05 1.01 0.87 0.95 1.32 1.13 1.21 7 d 70/100: Tensile strength 4.58 4.85 4.89 5.03 4.55 4.50 4.87 [MPa] Elongation at break 659 654 699 662 626 661 662 [%] Modulus of elasticity 1.34 1.25 1.20 1.36 1.58 1.57 1.44 [MPa] 5% 50% 0.75 0.76 0.71 0.85 0.90 0.84 0.88 LSS (glass) [MPa] 2.41 2.71 2.13 2.74 2.53 2.26 2.74 Shore A 38 39 38 39 41 39 38 M* (DMTA) −20° C. 10.2 7.4 8.5 10.3 n.d. n.d. n.d. [MPa] −10° C. 7.1 5.2 6.1 6.9 0° C. 5.4 4.1 4.8 5.2 10° C. 4.3 3.4 4.0 4.2 20° C. 3.6 3.0 3.4 3.6 M*(−20° C.)/M*(20° C.) 2.83 2.47 2.50 2.86 “n.d.” stands for “not determined”

[0224] It is apparent from table 2 that the inventive compositions Z2, Z3 and Z4, given the same open time (skin time), cure more quickly (thicker cured skin after 24 h), both by comparison with reference composition Z1 comprising a typical plasticizer from the prior art and having a low monomeric diisocyanate content and by comparison with the reference compositions Z5, Z6 and Z7 having a high monomeric diisocyanate content.

[0225] It is also apparent that the inventive compositions Z2, Z3 and Z4 have a distinctly higher tensile strength than the respective reference compositions, with uniformly high to slightly higher elongation at break and similar properties in relation to Shore hardness, adhesion and resistance to dry and moist heat.

[0226] Finally, the inventive compositions Z2 and Z3 show a distinct improvement in cold flexibility compared to reference composition Z1, whereas inventive composition Z4 comprising the polyether of very high molecular weight that has blocked hydroxyl groups shows similar cold flexibility.