POLYURETHANE COMPOSITION WITH IMPROVED ADHESION ON PAINTED SURFACES

Abstract

A moisture-curing, one-component polyurethane composition, containing at least one isocyanate group-containing polyether urethane polymer obtained by reacting at least one polyisocyanate with at least one polyether polyol; at least one isocyanurate-containing trimer of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane or 1,6-hexane diisocyanate in a quantity of between 1 and 4 percent by weight in the composition; at least one polyether with blocked hydroxyl groups, which is free of isocyanate groups, as a plasticiser, in a quantity of more than 5 percent by weight in the composition. Where moisture is excluded, the moisture-curing polyurethane composition has good storage stability, good processability and good thermal stability, and surprisingly good adhesive effect on highly scratch-resistant, hydrophobic automotive paints, and no pretreatment with adhesion promoters, primers or activators is needed. It is especially suitable for use as an elastic adhesive in the production of means of transport.

Claims

1. A moisture-curing one-component polyurethane composition comprising at least one polyether urethane polymer containing isocyanate groups that has been obtained from the reaction of at least one polyisocyanate with at least one polyether polyol; at least one isocyanurate-containing trimer I of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane or hexane 1,6-diisocyanate in an amount present in the composition of between 1% and 4% by weight; at least one polyether having blocked hydroxyl groups which is free of isocyanate groups as plasticizer, in an amount present in the composition of more than 5% by weight.

2. The polyurethane composition as claimed in claim 1, wherein the polyether urethane 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 at least one polyether urethane polymer containing isocyanate groups has a monomeric diisocyanate content of not more than 0.5% by weight and has been prepared 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 process, and the polyurethane composition has a monomeric diisocyanate content of not more than 0.1% by weight.

4. The polyurethane composition as claimed in claim 1, wherein the polyisocyanate used for the reaction is a monomeric diisocyanate selected from 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 not more than 3.5% by weight of isocyanurate-containing trimer I is present in the composition.

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 composition contains between 15% and 30% by weight of carbon black, based on the overall composition.

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 as 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 6% to 25% by weight of polyether having blocked hydroxyl groups.

11. The polyurethane composition as claimed in claim 1, wherein it additionally contains at least one further plasticizer.

12. The polyurethane composition as claimed in claim 1, wherein it contains 35% to 60% by weight of polyether urethane polymer containing isocyanate groups; 6% to 25% by weight of polyether having blocked hydroxyl groups; 0% to 15% by weight of further plasticizers; 1% to 3.5% by weight of isocyanurate-containing trimer I; 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. The method as claimed in claim 13, wherein one of the substrates is a surface that has been painted with automotive paint and no pretreatment has been conducted on this substrate apart from optional cleaning prior to the application of the polyurethane composition.

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

Description

EXAMPLES

[0193] Working examples are adduced hereinafter, which are intended to further elucidate the invention described. The invention is of course not limited to these described working examples.

[0194] “Standard climatic conditions” (“SCC”) refer to a temperature of 23±1° C. and a relative air humidity of 50±5%.

[0195] Unless stated otherwise, the chemicals used were from Sigma-Aldrich.

Preparation of Polyethers Having Blocked Hydroxyl Groups

[0196] Viscosity was measured using 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).

[0197] 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. Absorption bands are reported in wavenumbers (cm.sup.−1).

[0198] .sup.1H NMR spectra were measured on a spectrometer of the Bruker Ascend 400 type at 400.14 MHz; the chemical shifts 6 are reported in ppm relative to tetramethylsilane (TMS). No distinction was made between true coupling and pseudo-coupling patterns.

[0199] Polymeric Plasticizer PL1:

[0200] Butanol-started acetylated PPG monool with average molecular weight M.sub.n about 790 g/mol

[0201] 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 acid 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. FT-IR: 2970, 2931, 2867, 1738, 1454, 1372, 1345, 1296, 1241, 1098, 1014, 959, 925, 866, 827.

[0202] .sup.1H NMR (CDCl.sub.3): 5.02 (hept., 1 H, CH.sub.2(CH.sub.3)CH—OAc), 3.75-3.34 (2×m, ca. 39 H, 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., 2 H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2O), 1.36 (sext., 2 H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2O), 1.22 (d, 3H, CH.sub.2(CH.sub.3)CH—OAc), 1.17-1.10 (m, ca. 36 H, OCH.sub.2CH(CH.sub.3)O), 0.91 (t, 3H, CH.sub.3CH.sub.2CH.sub.2CH.sub.2O).

Preparation of Polymers Containing Isocyanate Groups

[0203] Viscosity was measured using a thermostated (20° C., unless stated otherwise) 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) (or, if so stated, 50 s.sup.−1).

[0204] 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.

[0205] Polymer P1:

[0206] 6950 g of polyoxypropylenepolyoxyethylene triol (Caradol® MD34-02, Shell Chemicals Ltd., UK; OH number 35.0 mg KOH/g), 1145 g of 4,4′-methylene diphenyl diisocyanate (4,4′-MDI; Desmodur® 44 MC L, Bayer MaterialScience AG), and 203 g of diisodecyl phthalate (DIDP; Palatinol® Z, BASF SE, Germany) were reacted at 80° C. by a known method to give an NCO-terminated polyurethane polymer having an isocyanate group content of 2.38% by weight. Viscosity was 50-60 Pa.Math.s at 20° C. and 50 s.sup.−1.

[0207] Polymer P2:

[0208] 400 g of polyoxypropylene diol (Acclaim® 4200, from Covestro AG; OH value 28.5 mg KOH/g) and 52 g of diphenylmethane 4,4′-diisocyanate (Desmodur® 44 MC L, from Covestro AG) were reacted by a known procedure at 80° C. to give an NCO-terminated polyurethane polymer that is liquid at room temperature and has an isocyanate group content of 1.85% by weight. Viscosity was 30-40 Pa.Math.s at 20° C. and 50 s.sup.−1.

[0209] Polymer P3:

[0210] 682.9 g of Voranol® CP 4755 polyether triol and 317.0 g of diphenylmethane 4,4′-diisocyanate (Desmodur® 44 MC L, from Covestro) were reacted by a known method at 80° C. to give a polyetherurethane polymer having an NCO content of 8.8% by weight, a viscosity of 5.1 Pas at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of about 25% by weight. 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 2.0% by weight, a viscosity of 16.8 Pas at 20° C., a monomeric diphenylmethane 4,4′-diisocyanate content of 0.05% by weight and an average molecular weight of about 5700 g/mol.

[0211] Polymer P4:

[0212] 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 Pas at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of about 18% by weight.

[0213] 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 polyether urethane polymer thus obtained had an NCO content of 1.8% by weight, a viscosity of 15.2 Pas at 20° C. and a monomeric diphenylmethane 4,4′-diisocyanate content of 0.08% by weight.

[0214] Moisture-Curing Polyurethane Compositions:

[0215] Compositions Z1 to Z14:

[0216] For each composition, the ingredients specified in tables 1 to 3 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:

[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 the 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 E modulus at 0.5-5% or elongation in accordance with DIN EN 53504 at a strain rate of 200 mm/min. These results are given the addition “7 d SCC”. In addition, further punched-out dumbbells were stored in an air circulation oven at 90° C. for 7 days, cooled down under standard climatic conditions and tested in the manner already described for tensile strength, elongation at break, and modulus of elasticity. These results are given the addition “7 d 90° C.”.

[0218] G modulus (shear modulus) was determined by measuring the samples at 23° C. and 50% relative air humidity to DIN 54 451 after storage at room temperature and 50% relative air humidity for 7 days. The aluminum substrates used for this purpose were pretreated prior to bonding with Sika® Primer 204N, available from Sika Schweiz AG.

[0219] The results from the abovementioned test methods are reported in table 4.

[0220] Adhesion was determined by cleaning various automotive paint substrates by means of a heptane-soaked cellulose cloth (Tele, Tela-Kimberly Switzerland GmbH). Within 10 minutes, a triangular bead (height 12 mm, width 8 mm) of the composition to be tested was then applied by means of an extrusion cartridge and nozzle and pressed together with a polypropylene film to a thickness of 4-5 mm.

[0221] The adhesive was tested after a curing time of 7 days (‘7d RT’) or 14 days (‘14d RT’) under standard climatic conditions (23° C., 50% rel. humidity), and after subsequent storage at 40° C. (‘7d 40° C., 100% r.h.’) and 100% rel. humidity for 7 days, and with the same storage after 14 days (‘14d 40° C., 100% r.h.’) and 21 days (‘21d 40° C., 100% r.h.’).

[0222] The adhesion of the adhesive was tested in each case using the ‘bead test’. This involves cutting into the cured adhesive layer at its end just above the adhesive bonding surface. The cut end of the layer is held with round-nose pliers and pulled away from the substrate. This is done by carefully rolling up the adhesive layer onto the tip of the pliers, and making a cut at right angles to the pulling direction down to the bare substrate. The pulling speed should be chosen such that a cut has to be made about every 3 seconds. The test distance must correspond to at least 8 cm. What is assessed is the adhesive remaining on the substrate after the adhesive layer has been pulled away (cohesion fracture). The adhesion properties are assessed by visual determination of the cohesive proportion of the bonding area.

[0223] The higher the proportion of cohesive failure the better the adhesive bonding. Test results with proportions of cohesive failure of less than 60%, in particular less than 50%, are typically considered inadequate.

[0224] The substrates used were steel sheets painted with automotive paints. The adhesives were applied directly to the paint surface. The paint substrates used were: [0225] iGloss® HAPS (BASF, Germany) [0226] iGloss® (BASF, Germany) [0227] Axalta® Lumeera (Axalta Coating Systems, USA)

[0228] All substrates were cleaned immediately prior to the application of the adhesion promoter composition by wiping by means of a cellulose cloth (Tela®, Tela-Kimberly Switzerland GmbH) that had been soaked with heptane, and vented for at least 5 minutes prior to the application of the adhesion promoter composition and subsequently wiped dry with a cellulose cloth (“wipe on/wipe off”). The results are reported in Tables 5 and 6.

[0229] Compositions Z2, Z3, Z5 and Z6 are inventive examples. Compositions Z1, Z4 and Z7 to Z14 are comparative examples and are given the addition “(Ref.)”. Comparative examples Z1 and Z7 to Z10 and Z12 to Z14 do not contain any polyether with blocked hydroxyl groups (plasticizer PL1), and comparative example Z4 contains too little isocyanurate I.Z11 contains too little plasticizer PL1.

TABLE-US-00001 TABLE 1 Composition (in parts by weight) of Z1 to Z3 Composition Z1 (ref.) Z2 Z3 Polymer P1 14 14 14 Polymer P2 31 31 31 DIDP 15 5 — Plasticizer PL1 — 10 15 Isocyanurate I1 2 2 2 Desiccant .sup.4 0.1 0.1 0.1 Carbon black .sup.1 20 20 20 Kaolin .sup.2 17 17 17 Catalyst .sup.3 0.8 0.8 0.8 .sup.1 Monarch 570 (from Cabot) .sup.2 White Tex (from BASF) .sup.3 2,2′-dimorpholinodiethyl ether and dibutyltin dilaurate (10:1 weight ratio as a mixture to 10% by weight in DIDP) .sup.4 p-toluenesulfonyl isocyanate

TABLE-US-00002 TABLE 2 Composition (in parts by weight) of Z4 to Z9 Z4 Z7 Z8 Z9 Composition (ref.) Z5 Z6 (ref.) (ref.) (ref.) Polymer P3 14 14 14 14 16 18 Polymer P4 31 31 31 31 34 37 DIDP — — — 15 10 5 Plasticizer PL1 15 15 15 — — — Isocyanurate I1 0.9 3.5 2 2 2 2 Desiccant .sup.4 0.1 0.1 0.1 0.1 0.1 0.1 Carbon black .sup.1 20 20 20 20 20 20 Kaolin .sup.2 17 17 17 17 17 17 Catalyst .sup.3 0.8 0.8 0.8 0.8 0.8 0.8 .sup.1 Monarch 570 (from Cabot) .sup.2 White Tex (from BASF) .sup.3 2,2′-dimorpholinodiethyl ether and dibutyltin dilaurate (10:1 weight ratio as a mixture to 10% by weight in DIDP) .sup.4 p-toluenesulfonyl isocyanate

TABLE-US-00003 TABLE 3 Composition (in parts by weight) of Z10 to Z14 Z10 Z11 Z12 Z13 Z14 Composition (ref.) (ref.) (ref.) (ref.) (ref.) Polymer P3 20 15 14 14 14 Polymer P4 40 40 31 41 36 DIDP — — 15 — — Plasticizer PL1 — 5 — — — Diol 12200 — — — 5 10 Isocyanurate I1 2 2 2 2 2 Desiccant .sup.4 0.1 0.1 0.1 0.1 0.1 Carbon black .sup.1 20 20 20 20 20 Kaolin .sup.2 17 17 17 17 17 Catalyst .sup.3 0.8 0.8 0.8 0.8 0.8 .sup.1 Monarch 570 (from Cabot) .sup.2 White Tex (from BASF) .sup.3 2,2′-dimorpholinodiethyl ether and dibutyltin dilaurate (10:1 weight ratio as a mixture to 10% by weight in DIDP) .sup.4 p-toluenesulfonyl isocyanate

TABLE-US-00004 TABLE 4 Measurement results with mechanical data. Z4 Z7 Z3 Composition (ref.) Z5 Z6 (ref.) Z1 (ref.) Tensile strength 7 d SCC 10.3 10.2 11 11.2 10.1 10 [MPa] Tensile strength 7 d 90° C. 10.9 10.3 10.9 10.4 9 8.8 [MPa] E modulus 7 d SCC [MPa] 6.7 9.4 7.4 7.8 8.2 8.3 E modulus 7 d 90° C. [MPa] 6 8.6 6.7 7.1 7.4 7.5 Elongation at break 7 d SCC 494 308 454 476 447 454 [%] Elongation at break 7 d 90° C. 528 329 458 435 408 412 [%] G modulus 7 d SCC [MPa] 2.2 3.1 2.4 2.5 3 3.1

[0230] It is to be seen from table 4 that the inventive compositions Z1, Z5 and Z6 have excellent mechanical values that persist even after heated storage, which suggests excellent heat stability. Comparative experiments with conventional plasticizers are at most equivalent in mechanical terms. Comparative experiment Z4 has values for E modulus and G modulus that are too low.

TABLE-US-00005 TABLE 5 Results of the adhesion test (values in % cohesive fracture). “n/m” means that the value was not measured. 7 d 14 d 21 d 7 d 40° C. .sup.1, 2 40° C. .sup.1, 2 40° C. .sup.1, 2 Composition RT .sup.1, 2 100% r.h. 100% r.h. 100% r.h. Z4 (ref.) 30 0 0 0 Z5 100 100 100 100  Z6 100 100 100 n/m Z7 (ref.) 25 0 0 0 Z8 (ref.) 25 0 0 n/m Z9 (ref.) 0 0 0 n/m Z10 (ref.) 0 0 0 n/m Z11 (ref.) 0 0 0 n/m Z12 (ref.) 20 15 5 n/m Z13 (ref.) 5 0 0 n/m Z14 (ref.) 15 0 0 n/m .sup.1 Substrate (paint): iGloss ® HAPS (BASF) Pretreatment: heptane (wipe on/wipe off) .sup.2 Open time: 5 min

TABLE-US-00006 TABLE 6 Results of the adhesion test (values in % cohesive fracture). 7 d 14 d 21 d 40° C. 40° C. 40° C. Substrate 7 d 14 d 100% 100% 100% Composition (paint).sup.1, 2 RT RT r.h. r.h. r.h. Z1 (ref.) Axalta ® 75 20 20 90 70 Z2 Lumeera 100 100 80 100 95 Z3 overbaked 90 100 100 100 100 (Axalta) Z1 (ref.) iGloss ® 85 60 70 70 70 Z2 overbaked 100 95 70 85 85 Z3 (BASF) 100 100 95 95 95 Z1 (ref.) iGloss ® 100 100 80 75 65 Z2 HAPS 100 100 100 100 100 Z3 overbaked 100 100 100 100 100 (BASF) .sup.1 Pretreatment: heptane (wipe on/wipe off) .sup.2 Open time: 2 min

[0231] The data in tables 5 and 6 show that only the compositions of the invention have sufficient adhesion to the automotive paints of high scratch resistance that are difficult to bond. At the same time, they do not lose adhesion even after hot storage.