POLYISOCYANATE COMPOSITION FOR COATINGS

Abstract

The present invention relates to a polyisocyanate composition, comprising a mixture of ≥60 wt. %, relative to the total weight of the mixture, of at least one polyisocyanate based on pentamethylene diisocyanate and ≤40 wt. %, relative to the total weight of the mixture, of at least one polyisocyanate based on a cycloaliphatic diisocyanate and and/or of at least one polyisocyanate based on pentamethylene diisocyanate and at least one cycloaliphatic diisocyanate, the polyisocyanate composition having a residual monomer content of monomer diisocyanates below 0.5 wt. %, relative to the total weight of the polyisocyanate composition.

Claims

1. A polyisocyanate composition comprising a mixture of ≥60 wt %, based on the total weight of the mixture, of at least one polyisocyanate based on pentamethylene diisocyanate and ≤40 wt %, based on the total weight of the mixture, of at least one polyisocyanate based on a cycloaliphatic diisocyanate or of at least one polyisocyanate based on pentamethylene diisocyanate and at least one cycloaliphatic diisocyanate, wherein the polyisocyanate composition has a residual monomer content of monomeric diisocyanates of below 0.5 wt %, based on the total weight of the polyisocyanate composition.

2. The polyisocyanate composition as claimed in claim 1, wherein the mixture comprises ≥70 wt %, based on the total weight of the mixture, of the at least one polyisocyanate based on pentamethylene diisocyanate, and fractions making up the balance to 100 wt % consist of the at least one polyisocyanate based on a cycloaliphatic diisocyanate or of the at least one polyisocyanate based on pentamethylene diisocyanate and at least one cycloaliphatic diisocyanate.

3. The polyisocyanate composition as claimed in claim 1, wherein the mixture of the polyisocyanate composition comprises ≥2 wt %, based on the total weight of the mixture, of the at least one polyisocyanate based on a cycloaliphatic diisocyanate or of the at least one polyisocyanate based on pentamethylene diisocyanate and at least one cycloaliphatic diisocyanate.

4. The polyisocyanate composition as claimed in claim 1, wherein the polyisocyanate based on pentamethylene diisocyanate and at least one cycloaliphatic diisocyanate comprises to an extent of ≥50 wt %, of at least one cycloaliphatic diisocyanate.

5. The polyisocyanate composition as claimed in claim 4, wherein the cycloaliphatic diisocyanate is selected from the group consisting of 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, 2,4--diisocyanato-1-methylcyclohexane, 2,6-diisocyanato-1-methylcyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, 4,4′-diisocyanatodicyclohexylmethane, 2,4′-diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, and bis(isocyanatomethyl)norbornane.

6. The polyisocyanate composition as claimed in claim 1, wherein the polyisocyanate composition consists comprises to an extent of ≥70 wt %, of the mixture.

7. A process for producing a polyisocyanate composition as claimed in claim 1, wherein the at least one polyisocyanate based on pentamethylene diisocyanate is mixed with the at least one polyisocyanate based on a cycloaliphatic diisocyanate or at least one polyisocyanate based on pentamethylene diisocyanate and at least one cycloaliphatic diisocyanate and one or more selected from the group consisting of auxiliaries and additives.

8. A coating composition including the polyisocyanate as claimed in claim 1 as a crosslinking agent.

9. In a process for increasing the chemical resistance of a coating, the improvement comprising including a pentamethylene diisocyanate in a polyisocyanate composition as claimed in claim 1.

10. A two-component system comprising: component A) comprising at least one polyisocyanate composition as claimed in claim 1; and component B) comprising at least one binder reactive toward isocyanate groups, wherein at least one of component A) and/or component B) optionally further comprises at least one selected from the group consisting of flow control assistant and auxiliaries and additives.

11. A process for producing a coating on a substrate, wherein the two-component system as claimed in claim 10 is applied to the substrate and is cured at a temperature >25° C.

12. The coating produced by the process as claimed in claim 11.

13. A composite comprising the coating as claimed in claim 12 and a substrate having a surface selected from the group consisting of metal and plastic.

Description

EXAMPLES

[0049] All reported percentages are based on weight unless otherwise noted.

[0050] The NCO contents are determined by titrimetric means to DIN EN ISO 11909:2007 (Binders for coating materials—Isocyanate resins—General test methods).

[0051] All viscosity measurements were made with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) to DIN EN ISO 3219:1994 (Plastics—Polymers/resins in the liquid state or as emulsions or dispersions—Determination of viscosity using a rotational viscometer with defined shear rate).

[0052] Polyisocyanate 1 (Based on m-PDI)

[0053] An initial charge of 100 g (0.59 mol) of 2-methylpentamethylene 1,5-diisocyanate (m-PDI) in a four-neck flask equipped with stirrer, reflux condenser, N.sub.2 passage tube and internal thermometer was degassed three times at room temperature by applying a vacuum of about 50 mbar and vented with nitrogen. Subsequently, the mixture was heated to 60° C. and the catalyst solution (0.5% N,N,N-trimethyl-N-benzylammonium hydroxide solution in a 1:1 mixture of 2-ethyl-l-hexanol and 2-ethyl-1,3-hexanediol) was metered in at a rate such that the temperature of the reaction mixture, in spite of the exothermically ensuing trimerization reaction, increased to a maximum of 74° C. On attainment of an NCO content of 40.2 wt %, dibutyl phosphate (80 mol % based on trimethylbenzylammonium hydroxide used) was used to stop the reaction, and the unreacted monomeric PDI was removed at a temperature of 140° C. and a pressure of 0.5 mbar on a thin-film evaporator. This gave a virtually colorless, high-viscosity polyisocyanurate polyisocyanate which, as a 90% solution in butyl acetate, had the following characteristic data:

[0054] NCO content: 18.4%

[0055] Viscosity (23° C.): 1800 mPa.s

[0056] Solids content (butyl acetate): 90%

[0057] Polyisocyanate 2 (Based on PDI)

[0058] An initial charge of 1000 g (6.49 mol) of pentamethylene 1,5-diisocyanate (PDI) in a four-neck flask equipped with stirrer, reflux condenser, N2 passage tube and internal thermometer was degassed three times at room temperature and vented with nitrogen. Subsequently, the mixture was heated to 60° C. and 9.0 ml of the catalyst solution (1.5% N,N,N-trimethyl-N-benzylammonium hydroxide solution in methanol and 2-ethylhexanol) were metered in such that the exothermic trimerization was held at a temperature of 60-80° C. On attainment of an NCO content of 36.7 wt %, dibutyl phosphate (equimolar amount based on trimethylbenzylammonium hydroxide used) was used to stop the reaction, and the excess PDI was removed at 140° C. and a pressure of 0.5-0.6 mbar via thin-film distillation. The resultant resin had the following characteristics:

[0059] NCO content: 21.5%

[0060] Solids content: 100%

[0061] Polyisocyanate 3 (Based on HDI) Desmodur® N 3390 BA

[0062] NCO content: 19.6%

[0063] Solids content (butyl acetate): 90%

[0064] Polyisocyanate 4 (Based on IPDI) Desmodur® Z 4470

[0065] NCO content: 11.9%

[0066] Solids content (butyl acetate): 70%

[0067] To ascertain the general mechanical data of the cured 2K PU coatings, clearcoats with the following composition were applied by spraying to substrates in accordance with stated property analyses, and cured at 130° C. for 30 min.

TABLE-US-00001 TABLE 1 Composition of the 2K PU clearcoats Formulation Solids A B C D E F content (comp.) (inv.) (comp.) (comp.) (comp.) (comp.) Component A (binder) Macrynal SM 60% 49.58 50.37 51.34 48.75 49.43 49.80 510n/60XMPAC (OH content: 2.7) Tinuvin 1130, 8% in xylene  8% 2.92 2.93 2.98 2.92 2.93 2.94 Tinuvin 292, 8% in xylene  8% 2.92 2.93 2.98 2.92 2.93 2.94 Octa-Soligen Calcium 4, basic - 20% 0.84 0.85 0.86 0.84 0.84 0.85 as supplied (as supplied) Addocat 201 (DBTL) 1% in  1% 0.47 0.47 0.48 0.47 0.47 0.47 BA 3M Novec Fluorosurfactant 10% 2.11 2.11 2.15 2.10 2.11 2.11 FC-4430 with DPM, 10% in BA Component B (curing agent) Polyisocyanate 1 in butyl 90% 13.25 9.66 acetate Polyisocyanate 2 100%  11.70 8.57 Polyisocyanate 3 in butyl 90% 13.09 9.51 acetate Polyisocyanate 4 in butyl 70% 7.30 7.17 7.21 12.40 12.24 12.24 acetate Weight ratio of aliphatic/cycloaliphatic 7:3 7:3 7:3 1:1 1:1 1:1 polyisocyanates (solid resins) Butyl acetate/xylene/DBE (41.4:41.0:17.6) 20.61 21.47 18.91 19.94 20.48 19.14 Total 100.0 100.0 100.0 100.0 100.0 100.0 NCO/OH ratio 1.0 1.0 1.0 1.0 1.0 1.0 comp. = comparative example; inv. = example according to the invention

[0068] The test for resistance of the cured clearcoats to simulated environmental influences was conducted according to DIN EN ISO 2812-5:2007-05 Determination of resistance to liquids—Part 5. Temperature-gradient oven method (ISO 2812-5:2017). The respective formulations were applied uniformly to steel gradient test panels in a two-coat system (clearcoat 40 μm±10 μm over black basecoat 10-15pm (Spies Hecker, Permacron® basecoat 293 RAL 9005 jet black, predried at 80° C. for 10 min)) and dried at 130° C. for 30 min. Thus prepared, the test panels were provided as per the gradient oven method with the corresponding test liquids and then subjected to a linear temperature gradient of 36°-68° C. After these exposures the panels were washed down with clear water and assessed after 1 and 24 hours to estimate not only the direct damage but also any self-healing properties of the coatings. For this assessment, the areas of first recognizable clearcoat attack were employed.

[0069] The results of the investigation (table 2—Resistance of clearcoats to simulated environmental influences) show that the comparative example of formulation C (polyisocyanate 3 and 4 in a ratio of 7:3) shows the weakest resistance to tree resin and to sodium hydroxide solution.

[0070] The comparative example of formulation A (polyisocyanate 1 and 4 in a ratio of 7:3) shows a weak resistance to alkali solution in combination with only moderate resistance to tree resin. The example according to the invention of formulation B (polyisocyanate 2 and 4 in a ratio of 7:3) shows not only very good resistance to tree resin but also the best resistance to sodium hydroxide solution.

TABLE-US-00002 TABLE 2 Resistance of the clearcoats to simulated environmental influences A B C D E F Formulation Comp. Inv. Comp. Comp. Comp. Comp. Test substances Ex. Ex. Ex. Ex. Ex. Ex. (gradient oven) Assessment after 1 h/24 h Tree resin 54°/54° 60°/60° 44°/44° 56°/56° 58°/58° 58°/58° Pancreatin (1:1 36°/36° 36°/36° 36°/36° 36°/36° 36°/36° 36°/36° dilution in water) Deionized >68°/>68° >68°/>68° >68°/>68° >68°/>68° >68°/>68° >68°/>68° water Sodium hydroxide 60°/60° 64°/64° 58°/58° 53°/53° 67°/67° 67°/67° (1% in water) Sulfuric acid (1% in 50°/50° 51°/51° 50°/50° 50°/50° 51°/51° 52°/52° water)

[0071] When the cycloaliphatic polyisocyanate fraction in the formulations is increased to a ratio of 1:1, formulations D, E and F show an almost similar level in terms of tree resin resistance, but the comparative example of formulation D (polyisocyanate 1 and 4 in a ratio of 1:1) falls in resistance to alkali solution, which is undesirable.

[0072] According to the stated object, the desire is not only for high resistance to environmental influences but also for a scratch-resistant coating, as scratches detract massively from the gloss of the surface (similarly to the environmental influences).

[0073] To test the resistance to wet mechanical stress, black test coil coating panels (CS-300570; Zanders PBL, Solingen, Germany) were spray-coated with clearcoat at 40 μm±10 μm and exposed to a wet scratching cycle (10 movements) in the Amtec-Kistler laboratory carwash.

TABLE-US-00003 TABLE 3 Resistance of the clearcoats to wet-chemical stress Formulation A B C D E F Comp. Inv. Comp. Comp. Comp. Comp. Ex. Ex. Ex. Ex. Ex. Ex. Gloss 20° Starting gloss 88 88 88 88 87 88 Residual gloss 31 42 43 29 36 36 Relative residual gloss 35% 48% 49% 33% 41% 41% Gloss 20° Self-healing 33 44 44 29 37 37 after 2 h 60° C. Relative residual gloss 38% 50% 50% 33% 43% 43%

[0074] To evaluate the scratch resistance and self-healing properties of the clearcoat, the gloss was measured - before scratch exposure (initial gloss), after scratch exposure and after self-healing at 60° C. over a period of two hours. As is apparent from table 3, formulations A and D (polyisocyanate 1 and 4) show the least resistance to wet mechanical stress. Formulations B, E (polyisocyanates 2 and 4) and formulations C and F (polyisocyanate 3 and 4) show a relatively high level in resistance to wet scratch exposure.

[0075] The desirable optimum resistance to simulated environmental influences and mechanical stress was, surprisingly, achieved with the combination of polyisocyanate 2 and 4.